Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Kinetics of direct reduction of unagglomerated iron-ore with coal char Roman-Moguel, Guillermo Julio 1984

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1985_A1 R65.pdf [ 12.8MB ]
Metadata
JSON: 831-1.0096744.json
JSON-LD: 831-1.0096744-ld.json
RDF/XML (Pretty): 831-1.0096744-rdf.xml
RDF/JSON: 831-1.0096744-rdf.json
Turtle: 831-1.0096744-turtle.txt
N-Triples: 831-1.0096744-rdf-ntriples.txt
Original Record: 831-1.0096744-source.json
Full Text
831-1.0096744-fulltext.txt
Citation
831-1.0096744.ris

Full Text

KINETICS OF DIRECT REDUCTION OF UNAGGLOMERATED IRON-ORE WITH COAL CHAR by GUILLERMO JULIO ROMAN-MOGUEL B. Eng. ( M e t a l l u r g y ) I n s t i t u t o P o l i t e c n i c o N a c i o n a l , M e xico, 1977 M.Sc. ( M e t a l l u r g y ) I m p e r i a l C o l l e g e , London, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Department o f M e t a l l u r g i c a l E n g i n e e r i n g We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d c L THE UNIVERSITY OF BRITISH COLUMBIA December, 1984 © G u i l l e r m o J u l i o Roman-Moguel I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f >\e-TAtU)Q<^tc<SL. £Nc=>' M&EB. i M (L, The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date .iMsiUfray S-Hi \c\%S DE-6 (3/81) i i ABSTRACT The k i n e t i c s of d i r e c t reduction of a commercial unagglomerated iron ore, with low-rank coal chars, have been investigated in the temper-ature range of 800-950°C (1073-1223 K) using a laboratory-size rotary re-actor. The variables studied were temperature, coal type, p a r t i c l e s i z e of coal and ore, fixed carbon-to-iron r a t i o , rotational speed-and percent f i l l i n g . In addition the effects of a catalyst on the Boudouard r e a c t i o n and of i n e r t gas flushing on the reduction rate were determined. Mixing studies at room temperature and at reduction temperature yielded the best mixing conditions prior to the kinetics determinations. Agglomeration be-tween the reduced particles was also studied. The mixing experiments at room temperature yielded the following. The degree of mixing depends almost entirely on the coal-to-ore s i z e r a -t i o . Best mixing i s achieved with values of this r a t i o of 1 and smaller, for ore particles larger than 254 ym; for smaller s i z e s than t h i s , good mixing can be obtained at higher coal-to-ore size ratios. At reduction temperature, improvement in the reduction rate was not obtained e i t h e r by f u r t h e r increasing the fixed carbon-to-iron ra t i o from 0.32 to 0.64 or by varying the rotational speed from 7 to 20 r.p.m.. In the k i n e t i c s experiments, the o v e r a l l reduction process was found to be controlled up to 0.5 to 0.8 fractional reduction by the Bou-douard reaction, depending on the par t i c l e size and temperature; from then i i i on, the kinetics were controlled e s s e n t i a l l y by the reduction r e a c t i o n . The a c t i v a t i o n energies obtained were 224 kJ/mole for the Boudouard reac-t i o n , using sub-bituminous coal char, and 264 kJ/mole using l i g n i t e coal char; these values correspond to that of a catalyzed reaction. The cata-l y t i c effect of the coal ash on the Boudouard r e a c t i o n was found to be much l a r g e r than the respective effect of metallic iron. The presence of a diluent gas extended the fractional reduction over which Boudouard reac-tion control i s exerted. The activation energy obtained for the reduction of wustite by CO i s 116.4 kJ/mole. The analysis of the Poo/Pet^ r a t i o produced by the reaction proved to be a powerful tool i n e l u c i d a t i n g the rate controlling step. Smaller ore particles were found to agglomerate considerably more, in the non-catalyzed experiments; the addition of a catalyst f o r the Bou-douard r e a c t i o n also produced larger agglomerates. In neither case did agglomeration retard the reduction rate to a considerable extent. No ac-cretion growth was observed on the reactor wall. Estimative calculations showed that similar throughputs can be ob-tained by processing the unagglomerated concentrate, as compared to opera-tions which u t i l i z e indurated pellets under the same c o n d i t i o n s . An ad-vantage of a process using concentrates i s the lower temperature at which i t can be operated. i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i i LIST OF FIGURES x LIST OF SYMBOLS xvi ACKNOWLEDGEMENTS xix Chapter 1 INTRODUCTION 1 2 REVIEW OF PREVIOUS WORK 4 2.1 Introduction 4 2.2 Direct-reduction Rotary Kilns 10 2.2.1 Operation of reduction kilns 11 2.2.2 Accretion formation 15 2.3 Kinetics studies of iron-oxide reduction with s o l i d reductants 21 2.4 Laboratory scale studies in rotary reactors 31 3 SCOPE OF THE PRESENT WORK AND OBJECTIVES 41 4 EXPERIMENTAL 44 4.1 Introduction 44 4.2 Materials and their preparation 45 4.2.1 Iron-ore concentrate 45 4.2.2 Low rank coals 48 4.2.3 Catalyst 52 4.3 Reduction apparatus 52 4.3.1 Heating system 54 4.3.2 Sealing system 54 4.3.3 Building materials and dimensions 57 4.3.4 Rotating system 61 V 4.3.5 Feeding, sampling and emptying systems 61 4.3.6 Temperature monitoring and control 63 4.3.7 Gas flow measurement and analysis 64 4.4 Apparatus for Room-Temperature Mixing Experiments 65 4.5 Coal Charring Equipment 67 4.6 Experimental Design and Variables 69 4.6.1 Variables in room-temperature mixing experiments . 69 4.6.2 Variables in reduction experiments 71 4.6.3 Experimental design 72 4.7 Experimental Procedures 74 4.7.1 Room-temperature mixing experiments 74 4.7.2 Coal charring experiments 76 4.7.3 Reduction experiments 77 5 RESULTS OF ROOM-TEMPERATURE MIXING EXPERIMENTS 83 5.1 Effect of pa r t i c l e - s i z e r a t i o 87 5.2 Effect of rotational speed 88 5.3 Effect of fixed-carbon to iron r a t i o 90 5.4 Effect of percent loading 93 5.5 Preliminary discussion of results from room-temperature mixing experiments 93 6 RESULTS OF REDUCTION EXPERIMENTS 103 6.1 Results of coal d e v o l a t i l i z a t i o n experiments 103 6.1.1 Temperature measurement in the coal bed 105 6.1.2 Effect of soak time and par t i c l e size 105 6.1.3 Discussion of coal devolati1ization results 109 6.2 Calculation of fractional reduction I l l 6.3 Results of experiments to determine variables ranges ... 115 6.3.1 Effect of fixed-carbon-to-iron ra t i o 116 6.3.2 Effect of rotational speed 116 6.3.3 Effect of percent loading 116 6.3.4 Preliminary discussion of results from experi-ments to determine variables ranges 120 6.4 Results of main experimental block 122 6.4.1 Effect of temperature: the base case 122 v i 6.4.2 E f f e c t of Cp-j x/Fe s t o i c h i o m e t r i c r a t i o 126 6.4.3 Reduction of f i n e r p a r t i c l e s under well-mixed c o n d i t i o n s 126 6.4.4 Reduction under bed segregation c o n d i t i o n s 130 6.4.5 R e p r o d u c i b i l i t y t e s t s 130 6.4.6 Preliminary d i s c u s s i o n of r e s u l t s from the main experimental block 134 6.5 Results of comparative experiments 148 6.5.1 Reduction using a c a t a l y s t f o r Boudouard r e a c t i o n . 148 6.5.2 Reduction with l i g n i t e 151 6.5.3 Reduction with graphite 151 6.5.4 E f f e c t of i n e r t - g a s f l u s h i n g 151 6.5.5 Reduction of hematite p e l l e t s 155 6.5.6 Preliminary d i s c u s s i o n of r e s u l t s from the comparative experiments 157 7 STUDY OF PARTICLES AGGLOMERATION DURING REDUCTION 160 7.1 P a r t i c l e s i z e d i s t r i b u t i o n a f t e r reduction 160 7.2 Scanning e l e c t r o n microscope observations 166 7.3 Preliminary d i s c u s s i o n on p a r t i c l e s agglomera-t i o n during reduction 171 8 OVERALL DISCUSSION OF RESULTS AND PROPOSED MECHANISMS 175 8.1 Te s t i n g of a v a i l a b l e k i n e t i c s r e l a t i o n s h i p s f o r the reduction of iron-oxides with carbon 175 8.1.1 Boudouard r e a c t i o n as rate c o n t r o l l i n g mechanism . 177 8.1.2 Reduction r e a c t i o n as rate c o n t r o l l i n g mechanism . 191 8.2 Overall view of the reduction process 193 8.3 Estimative c a l c u l a t i o n s f o r the operation of an i n d u s t r i a l - s i z e rotary k i l n 199 9 SUMMARY AND CONCLUSIONS 203 LIST OF REFERENCES 207 APPENDICES A HEAT BALANCE CALCULATIONS TO DIMENSION ROTARY REACTOR .. 219 B CALIBRATION CURVES FOR FLOWMETERS ....' 224 C CONDITIONS FOR ROOM-TEMPERATURE MIXING EXPERIMENTS 229 v i i D LISTING OF PROGRAM TO PROCESS REDUCTION EXPERIMENTS DATA AND SAMPLE OUTPUT 230 E SUMMARY OF OVERALL MASS-BALANCES FOR REDUCTION EXPERIMENTS 243 F CALCULATIONS FOR THE OXIDATION OF SiC HEATING ELEMENT .. 244 vii i LIST OF TABLES Chapter 2 Page I Direct reduction of iron-bearing material with fluid reductants^'H'^ g II Direct reduction of iron-bearing materials with solid reductants9>ll>13 7 III Main operational features of rotary-kiln direct re-duction p lan t s 4 1 ' 4 6 13 IV Analysis of accretions formed in a pilot-plant size rotary k i l n 7 9 - 7 9 18 V Phases encountered in the accretions formed during direct reduction in a rotary k i ln 7 ^" 7 7 18 VI Studies on reduction kinetics of iron oxides with carbonaceous materials 26 VII Characteristics of laboratory-size rotary kiln ex-permiments for reduction of iron oxides 33 Chapter 4 VIII Chemical analysis of spiral iron-ore concentrate, full size range and two size fractions: -420 +300 and -106 +74 ym 47 IX Random loose and packed bulk densities of the iron-ore concentrate and the Forestburg coal, for different particle sizes 50 X Proximate and ultimate analyses of Forestburg coal and Saskatchewan lignite. Mean particle sizes: 718, 180 and 90 vm 51 XI Thermophysical properties of refractory materials used in the reactor 59 XII Summary of variables and levels tested in the mixing and reduction experiments using Forestburg coal . . 70 XIII Certified grade gas standard composition 79 i x XIV Gas chromatograph operating conditions 79 Chapter 5 XV Angle of repose for different coal p a r t i c l e sizes and ore/coal mixtures with 254 ym ore p a r t i c l e size ... 101 Chapter 6 XVI Temperatures at four locations in the coal bed, accord-ing to Figure 6.1, for pa r t i c l e sizes of -841 +600, -420 +300, -210 +149 and -106 +74 um 107 XVII Proximate and ultimate analyses of Forestburg coal and Saskatchewan l i g n i t e after 10 hours charring treat-ment. Mean p a r t i c l e sizes: 718, 180 and 90 \im 110 XVIII Ash composition of Forestburg coal and Saskatchewan l i g n i t e 110 XIX Retention times of the product gases at different sections of the reactor 137 XX Stoichiometric ratios for reduction of Fe203 with carbon under two types of reaction control: Boudouard and reduction 142 XXI Conditions and results for reduction of hematite pellets 156 Chapter 8 XXII Reaction rate constants for Stages I to III during reduction experiments 185 X LIST OF FIGURES Chapter 2 Page 2.1 Flowsheet for general direct reduction process (Modified from reference 15) 5 2.2 Main features of the SL/RN rotary k i l n process (Modified from reference 9) 9 2.3 Formation of accretions with 10% fines in three dimensional p l o t t i n g ' ^ 19 2.4 Qualitative progress of the formation of accretions as a function of reduction time and furnace l e n g t h ^ . 19 2.5 Sub-processes in the reduction of iron-oxide with carbon 23 2.6 Reactivities of different carbonaceous materials as a function of temperature-^! 37 Chapter 4 4.1 P a r t i c l e size d i s t r i b u t i o n of spiral iron-ore concentrate 46 4.2 SEM photograph of spiral iron-ore concentrate (lOOx) 49 4.3 Overall view of experimental set-up for reduction tests .. 53 4.4 Top view of rotary reactor showing sealing areas 55 4.5 (A) Side view of open rotary reactor 58 (B) Central cross-sections of rotary reactor 58 4.6 Sampling probe configuration 62 4.7 Equipment for room-temperature mixing experiments (A) Gen-eral view; (B) Detail view of a c r y l i c blade 66 4.8 Schematic view of coal devolati1ization equipment 68 4.9 Graph showing bed volume and depth as a function of per-cent loading for a reactor 14 cm in diameter 75 4.10 Reaction chamber temperature as a function of time 81 xi Chapter 5 5.1 Definition of boundaries of degree of mixing. Conditions: dp e = 358 m; CFj x / F e = 0.45; 15 r.p.m.; 20% loading; cf c / a ~ F e for (A), 4.464; (B), 2.000; (C), 1.285; (D), 1,000; (E), 0.714; and (F ) , 0.503. (A) and (B), segre-gated bed; (C) and (D), tr a n s i t i o n a l condition and (E) and (F ) , well-mixed bed 84 5.2 Efffect of d'c/cTpe size r a t i o on the degree of mixing for 90 m iron-ore p a r t i c l e s . Conditions: Cp-jx/Fe = 0.45; 15 r.p.m. and 20% loading 89 5.3 Effect of rotational speed on the degree_ of_ mixing for 180 m iron-ore p a r t i c l e s . Conditions: d c/dp e = 0.5; CFix/Fe = 0.45 and 20% loading 91 5.4 Effect of fixed-carbon to iron r a t i o on the degree of mix-ing for 358 m iron-ore p a r t i c l e s . Conditions: d c/dp e = 4; 20% loading and 15 r.p.m 92 5.5 Effect of percent loading on the degree of mi_xing for 358 ym iron-ore p a r t i c l e s . Conditions: d c/dp e = 4.0; CFi x / F e = 0.45 and 15 r.p.m 94 5.6 Predominance area diagram for the degree of mixing as a function of cTc/cIpe size ratio and iron-ore mean pa r t i c l e s i z e , ap e. Conditions: CF-j x/Fe = 0.45; 5 to 15 r.p.m. and 20% loading 95 5.7 Predominance area diagram for the type of bed motion as a function of cTc/dpe size ratio and iron-ore mean • pa r t i c l e s i z e , cTpe. Conditions: Cp-jx/Fe = 0.45; 5 and 15 r.p.m., and 20% loading 96 5.8 Void size between particles as a function of coal par-t i c l e size in a loose bed 99 Chapter 6 6.1 Temperature at four locations in the coal bed during d e v o l a t i l i z a t i o n treatment 106 6.2 Percent hydrogen remaining in char, after d e v o l a t i l -ization treatment at 900°C, for four coal p a r t i c l e sizes: 716, 358, 180 and 90 ym 108 6.3 Gas composition as a function of reaction time for a reduction experiment; conditions as shown 113 x i i 6.4 Plot of fractional reduction versus time showing the effect of Cp-jx/Fe r a t i o ; conditions as shown 117 6.5 Plot of fractional reduction versus time showing the effect of rotational speed at two C p i x/Fe r a t i o s ; conditions as shown 118 6.6 Plot of fractional reduction versus time showing the effect of percent f i l l at two Cf-\x/Fe r a t i o s ; conditions as shown 119 6.7 Variables in main experimental block 123 6.8 Plot of fractional reduction versus time showing the effect of temperature: the base case. Conditions as shown 124 6.9 Change in PQQ/PQQ r a t i o with fractional reduction during experiments of 2base case; conditions as shown 125 6.10 Plot of fractional redution versus time showing the effect of stoichiometric Cpix/Fe r a t i o ; conditions as shown 127 6.11 Change in PQQ/PQQ r a t i o with fractional reduction during experiments with stoichiometric Cpi x/Fe r a t i o ; con-ditions as shown 128 6.12 Plot of fractional reduction versus time showing the effect of f i n e r p a r t i c l e s ; conditions as shown 129 6.13 Change in Pco/pCOo r a t i o with fractional reduction during experiments with f i n e r p a r t i c l e s ; conditions as shown 131 6.14 Plot of fractional reduction versus time showing the effect of bed segregation; conditions as shown 132 6.15 Change in Pco / p COo r a t i o with fractional reduction during experiments with segregated bed; conditions as shown .. 133 6.16 Plot of fractional reduction versus time for experimental reproducibility t e s t s ; conditions as shown 135 6.17 Stoichiometric Cp-jx/Fe ra t i o as a function of temperature for the reduction of Fe203 with carbon 143 6.18 Fractional reduction rate as a function of fractional reduction for experiments of the base case 146 xi i i 6.19 Plot of fractional reduction versus time showing the effect of a catalyst of the Boudouard reaction; conditions as shown 149 6.20 Change in PQQ/PQ,Q0 r a t i o with fractional reduction during catalyzed and ^ - f l u s h i n g experiments; conditions as shown 150 6.21 Plot of fractional reduction'versus time for reduction with Saskatchewan l i g n i t e ; conditions as shown 152 6.22 Change in Pco/PcO? r a t i o with fractional reduction for experiments wixh l i g n i t e ; conditions as shown 153 6.23 Plot of fractional reduction versus time showing the ef-fects of N2~flushing on reduction with Forestburg coal and reduction with graphite; conditions as shown 154 Chapter 7 7.1 P a r t i c l e size d i s t r i b u t i o n after reduction of 90 pm particles 161 7.2 P a r t i c l e size d i s t r i b u t i o n after reduction, (a) base case; (b) catalyzed experiments 162 7.3 P a r t i c l e size d i s t r i b u t i o n after reduction, (a) segre-gated bed; (b) Stoichiometric Cpi x/Fe 163 7.4 P a r t i c l e size d i s t r i b u t i o n after reduction, (a) base case; (b) Lignite reductant 164 7.5 Agglomerates average size as a function of reduction temperature. Conditions of experiments as shown 167 7.6 Agglomeration r e l a t i v e to the original ore size as a function of temperature. Conditions of experiments as shown 168 7.7 Agglomerate formed during reduction of 90 vm iron-ore particles (lOOx) 169 7.8 Iron whiskers produced during reduction joining two reduced particles (800x) 169 7.9 S i l i c a t e p a r t i c l e between two reduced grains (800x) 170 7.10 Agglomerate formed during reduction under catalyzed conditions (lOOx) 170 X I V 7.11 Non-metallic particles between reduced iron grains during reduction under catalyzed conditions (200x) . . . 173 Chapter 8 8.1 Plot of In (1-fc) vs t for the base case experiments (Boudouard control) 179 8.2 Plot of In (1-fc) vs t for the stoichiometric Cpj x /Fe experiments (Boudouard control) 180 8.3 Plot of In (1 - fr) vs t for the finer particles experiments (Boudouard control) 181 8.4 Plot of ln (1 - fr) vs t for the segregated bed experiments iBoudouard control) 182 8.5 Plot of ln (1-fc) vs t for the catalyzed and N2~flushed experiments (Boudouard control) 183 8.6 Plot of ln (1 -fr) vs t for the l igni te reductant experiments (Boudouard control) 184 8.7 Arrhenius plots for base case, stoichiometric C p i x / F e , l igni te reductant and catalyzed experi-ments. Stage II (Boudouard control) 187 8.8 Arrhenius plots for base case, segregated bed and finer particles experiments. Stage II (Boudouard control) . 190 8.9 Arrhenius plots for base case, stoichiometric Cp-j x/Fe and segregated bed experiments. Stage I (Boudouard control) 192 8.10 Plot of 1 - ( l - fR) l /3 v s i f o r D a s e c a s e experiments. Stage III (Reduction control) 194 8.11 Plot of 1 - ( l - fR) l /3 vs t for segregated bed experi-ments. Stage III (Reduction control) 195 8.12 Plot of 1 - ( l - fR) l /3 v s t f o r catalyzed experiments. Stage III (Reduction control) 196 8.13 Arrhenius plots for base case, segregated bed and catalyzed experiments. Stage III (Reduction control) 197 XV Appendix A A . l Heat losses and surface temperature for different inner diameters and insulation thicknesses 223 Appendix B B . l Calibration curve for gas-standard flowrate in flow-meter Gilmont #1 225 B.2 Calibration curve for gas-standard flowrate in flow-meter Gilmont #2 226 B.3 Calibration curve for gas-standard flowrate in flow-meter Gilmont #3 227 B.4 Calibration curve for gas-standard flowrate in flow-meter Gilmont #4 228 XVI LIST OF SYMBOLS A Bed surface area [m^] C p i x Fixed carbon i n coal and char Cp-j x/Fe Fixed carbon-to-iron r a t i o by weight ( C ) t Amount of carbon reacted up to time t , [mole] d/\gg Average s i z e of agglomerate, [ym], i n Equations (7.1) and (7.2) d c Coal mean p a r t i c l e s i z e , [ym] d c/dp e Coal to ore s i z e r a t i o dp e Iron ore mean p a r t i c l e s i z e [ym] di Average s i z e of the openings between two s c r e e n s [ym], E q u a t i o n (7.2) E f f E f f i c i e n c y of s e a l i n g i n the reactor ( E f f ) - , E f f i c i e n c y o f s e a l i n g i n the rea c t o r at beginning o f experiment ( E f f ) f E f f i c i e n c y of s e a l i n g i n the rea c t o r at end of experiment fR F r a c t i o n a l reduction ll S p e c i f i c rate constant i n Equations (2.8) and (2.9) k Overall rate constant i n Equations (2.3) through (2.5), [cm^/s] kg Rate constant f o r Boudouard r e a c t i o n kp Rate constant f o r reduction r e a c t i o n Ki E q u i l i b r i u m constant i n Equation (6.11) K2 E q u i l i b r i u m constant i n Equation (6.12) K3 E q u i l i b r i u m constant i n Equation (6.13) 1 Average void s i z e , [ym] mc Molar flowrate of C, [mol/min], Equation (6.10) xvi i mco Molar f l o w r a t e o f CO, [mol/min], E q u a t i o n s ( 6 . 5 ) , ( 6 . 9 ) and (6.10) rfiQQ Molar f l o w r a t e o f CO2, [mol/min], E q u a t i o n s ( 6 . 6 ) , (6.9) and (6.10) ITIQ Molar flowrate of 0£, [mol/min], Equation (6.9) (Ox)t Moles of oxygen removed up to time t [mole], Equation (6.1) ( 0 x ) j o t T o t a l moles o f oxygen i n c o n c e n t r a t e and c o a l ash, E q u a t i o n (6.1) PQQ P a r t i a l pressure of CO PQQ P a r t i a l pressure of CO2 P H P a r t i a l pressure of H2 QQQ CO flowrate [£/min], Equations (6.3) and (6.5) QC0 2 c 0 2 flowrate [£/min], Equations (6.4) and (6.6) QR 0 T Gas flowrate measured by rotameter, [ V m i n ] , Equation (6.2) QTot Corrected gas flowrate [ V m i n ] , Equation (6.12) R K i l n radius RQ Overall rate constant [ m i n - 1 ] i n Equations (2.6) and (2.7) RQQ Rate of CO formation [mol/min] i n Equation (2.8) RQQ^  Rate of CO2 formation [mol/min] in Equation (2.9) r 0 I n i t i a l radius of oxide p a r t i c l e T Temperature t Reaction time V Bed volume [m 3] X-j Amount of material r e t a i n e d between two sieves Z Volume of product formed per u n i t volume of s o l i d consumed, i n Equation (2.5) xvi l i LIST OF SYMBOLS Greek 6 F r a c t i o n of CO u t i l i z e d i n reduc t i o n , Equations (2.8) and (2.9) <f> Mole f r a c t i o n o f CO i n e q u i l i b r i u m with FeO/Fe or CO/CO?, Equa-t i o n (6.16) p c o r r C o r r e c t i o n f a c t o r f o r d i f f e r e n c e i n d e n s i t i e s between standard and product gas a P r o p o r t i o n a l i t y constant, Equation (5.1) to Rotational speed T Retention time of gases i n reactor [ s ] $r,c Angle of repose of c o a l , [°] $r,mix Angle of repose of ore/coal mixture, [°] x i x ACKNOWLEDGEMENTS I wish to e x p r e s s my most sincere g r a t i t u d e to Dr. J.K. Brima-combe f o r h i s guidance and unswerving s u p p o r t t h r o u g h o u t the d i v e r s e d i f f i c u l t i e s t h i s research e n t a i l e d . To Dr. G.G. Richards I extend my warmest a p p r e c i a t i o n f o r useful d i s c u s s i o n s and f o r h i s help and support d u r i n g the l a s t , c r u c i a l s t a g e s o f t h i s work. To Mr. P. Wenman, my gra t i t u d e f o r a l l h i s i n t e r e s t and help throughout the du r a t i o n of t h i s task cannot be ove r s t a t e d . The f i n a n c i a l s u p p o r t o f CONACYT and IPN, Mexico, and NSERC, Canada, through the s c h o l a r s h i p s they p r o v i d e d me w i t h a t d i f f e r e n t stages of t h i s work, i s g r a t e f u l l y acknowledged. In t h i s regard, Mr. S. Martinez also deserves my very special thanks. The d i s c u s s i o n s and as s i s t a n c e of f e l l o w graduate students: Dr. A. Bustos ( f o r teaching me the " t r i a l and e r r o r " method), Mr. R. V a r v a l -hol , Mr. H. C a s t i l l e j o s and Mr. C. Schvezov are als o s i n c e r e l y acknowl-edged. Dr. G. Cabanas deserves my personal thanks f o r s t e e r i n g me i n t o graduate s t u d i e s . F i n a l l y , to my f a t h e r Vincente f o r everything he has given me, and to my wife Mayra f o r her patience and support, I g r a t e f u l l y dedicate t h i s work. XX How many roads must a man walk down Before you c a l l him a man? R. Zimnermann 1 CHAPTER 1 INTRODUCTION D i r e c t Reduction processes, that i s , f o r the r e d u c t i o n of i r o n o x i d e s i n the s o l i d s t a t e , p l a y an i n c r e a s i n g l y important part i n t o -day's ironmaking i n d u s t r y . The obvious advantages of c i r c u m v e n t i n g the s m e l t i n g o f the o x i d e s , w i t h the consequent lowering of the heat r e -quirements f o r the o v e r a l l process and ease i n handling of the p r o d u c t s are c l e a r . F u r t h e r m o r e , the c o m m e r c i a l l y proved c a p a b i l i t y of these processes to operate on a s m a l l e r s c a l e than the b l a s t f u r n a c e , even down to 40(10)3 tonnes per y e a r , and to use indigenous reductant r e -sources such as low-rank c o a l s or natural gas, makes them a t t r a c t i v e a t l e a s t i n r e g i o n s which do not have a st a b l e scrap supply. However i n d i r e c t reduction processes, which operate at 900 to 1150°C the reduction k i n e t i c s are slower and the t h r o u g h p u t per u n i t volume of rea c t o r i s consequently lower than i n the b l a s t furnace. Therefore the need to ac-c e l e r a t e the r e d u c t i o n rate and minimize inherent operational problems i s strong. Rotary k i l n D i r e c t Reduction processes, of which the SL/RN 1 type i s the most widely used, exemplify the foregoing c o n s i d e r a t i o n s . With p l a n t s ranging from a one u n i t , 30(10)^ ton/year, to nine u n i t s , 2(10)^ ton/year, i n c o u n t r i e s with such d i f f e r e n t r e d u c t a n t raw m a t e r i a l s as 2 India and A u s t r a l i a , the commercial c a p a b i l i t y of t h i s process i s demon-s t r a t e d . So f a r however, t h i s process has operated using mainly e i t h e r iron-ore p e l l e t s or lumps, with the notable exception of f i n e ores which contain r e l a t i v e l y high concentrations of refractory-metal o x i d e s , such as T i 0 2 or V2O5. The presence of these oxides hinders the formation of a c c r e t i o n s on the k i l n ' s inner wall i n s p i t e of the small p a r t i c l e s i z e . These a c c r e t i o n s , as w i l l be described i n Chapter 2, represent the main operational problem i n the rotary k i l n processes. The use o f p e l l e t s , on the o t h e r hand, diminishes the extent of t h i s problem but r e s u l t s i n a comparatively slower reduction rate and adds, with the p e l l e t i z a t i o n s t a g e , a f u r t h e r 30 p e r c e n t as a minimum to the cost2>3 0 f the D i r e c t Reduced Iron (DRI) product. T h i s work was thus aimed at the study of the reduction k i n e t i c s of an unagglomerated i r o n - o r e concentrate, using low rank c o a l s as r e -d u c t a n t i n a l a b o r a t o r y - s i z e rotary r e a c t o r . At the same time the pos-s i b l e formation of agglomerates against the r e a c t o r w a l l was examined, as a f i r s t step i n the development of a process of t h i s kind. This work also complements other k i l n research e f f o r t s i n t h i s department, namely: the motion c h a r a c t e r i s t i c s of the s o l i d s bed and the p a r t i c l e s segrega-t i o n , by H e n e i n , 4 the heat t r a n s f e r c h a r a c t e r i s t i c s of the process by GorogS and B a r r , 6 the o v e r a l l mathematical modelling of the SL/RN pro-c e s s by Venkateswaran, 7 and the reduction k i n e t i c s of t i t a n i f e r o u s ores by Sucre-Garcia.8 T h i s t h e s i s i s o r g a n i z e d a l o n g the f o l l o w i n g l i n e s . The most r e l e v a n t part of the extensive l i t e r a t u r e on the subject i s reviewed i n Chapter 2. This i n c l u d e s general papers on D i r e c t Reduction and rotary 3 k i l n o p e r a t i o n s , fundamental stu d i e s on iron-oxide reduction with s o l i d reductants and l a b o r a t o r y - s c a l e studies i n r o t a r y reactors i n c l u d i n g r e -d u c t i o n k i n e t i c s and the a c c r e t i o n formation. In Chapter 3, the objec-t i v e s of t h i s work are presented i n d e t a i l , and the e x p e r i m e n t a l t e c h -niques are l a i d out i n Chapter 4. The r e s u l t s of room-temperature mix-ing experiments, of the reduction experiments and the study o f p a r t i c l e a g g l o m e r a t i o n , with preliminary d i s c u s s i o n s i n each case, are presented i n Chapters 5, 6 and 7, r e s p e c t i v e l y . F i n a l l y , the o v e r a l l d i s c u s s i o n of the r e s u l t s and proposed mechanisms, are presented i n Chapter 8. 4 CHAPTER 2 REVIEW OF PREVIOUS WORK 2.1 Introduction The d i r e c t r e d u c t i o n of i r o n oxide, at the fundamental and i n -d u s t r i a l l e v e l s , i s a broad f i e l d of research and has been the s u b j e c t o f s e v e r a l s t u d i e s i n the l a s t t h i r t y y e a r s , owing to i t s i n c r e a s i n g economic s i g n i f i c a n c e . 9 - 1 4 A general flowsheet f o r the d i r e c t - r e d u c t i o n p r o c e s s e s i n commercial o p e r a t i o n i s shown i n Figure 2.1.15 The pro-cesses can be c l a s s i f i e d i n t o two groups: those which u t i l i z e f l u i d r e -a c t a n t s , i n sh a f t furnaces or f l u i d i s e d beds, and processes that employ s o l i d coal as reductant, u s u a l l y i n rotary k i l n r e a c t o r s . A summary o f d i r e c t - r e d u c t i o n p r o c e s s e s , according to t h i s c l a s s i f i c a t i o n , i s pre-sented i n Tables I and I I . P r o c e s s e s t h a t u t i l i z e f l u i d r e d u c t a n t s and s h a f t f u r n a c e s account f o r over 85 percent of the d i r e c t - r e d u c e d i r o n (DRI) produced t o d a y . 16 They can be described b r i e f l y as f o l l o w s : Iron ore lumps or p e l l e t s are charged to the top of the v e r t i c a l s h a f t and as they de-scend, c o n t a c t a r i s i n g stream o f r e d u c i n g gas. The i r o n oxide i s reduced i n the upper s e c t i o n of the r e a c t o r , while c a r b o n i z a t i o n and 5 Iron ore Pel letizer Iron ore pellets I I [_Fine_ concentrate I I (I) Sized coal i I 1 K2) CO a H2mixture I 1 i i Fuel pretreatment vessel 1 » Fossil fuel (1) Coal (2) Natural gas (3) Fuel oil Off-gas,dust, heat recovery >• Direct reduction reactor Oirect reduced iron 2.1 Flowsheet f o r general d i r e c t reduction process (Modified from reference 15) TABLE I: DIRECT REDUCTION OF IRON-BEARING MATERIALS WITH FLUID REDUCTANTS9.*1.!3 PROCESS REACTOR NAME Ld.xL Cn] FEED REDUCTANT T ENERGY CONMSMP. PROD. RATE [mm] (REDUCTION) Fuel Electric Ton DRI [°C] [GCal] [KWh] m3 Day COST* $ Ton DRI MET. PECULIARITIES AND [%] COMMENTS ARMCO Shaft 5 x 27.4 Pellets, Ore (5-20) Nat.Gas 760-800 2.83 37 1.77 136.66 92 Steam reformed natural gas. FIOR Fluid Bed Concentrate (<5) Nat.Gas 880 4.00 45 1200/Vol N.A. 93 3 Reactors In CC.series 10 Atm. Aux. Equipment HIB Fluid Bed Concentrate 6.7 x 52 (<2) Nat.Gas 870 40 0.30 N.A. 70 2 Reactors 1n series. 2 Atm. Product Briquetted HyL Fixed Bed Pellets, Ore (9-16) Nat.Gas 870-1030 2.40 45 0.85 132.56 92 Batch. 4 reactors In Cy-cle. Top inlet of Gas. MIDREX Shaft 4.9 x 28 Pellets, Ore (5-20) Nat.Gas 850-900 2.67 125 1.97 136.03 92 Countercurrent gas-solid. NSC Shaft 2.5 x ? Lump, Pellets Oil 1000 3.00 180 500/Vol N.A. Counterpressure: 5 Atm. Texaco Gasification process. PUROFER Sha ft 7 x ? Lump, Pellets Hydrocar- 950-1000 3.50 270 bons 960/Vol N.A. 92 Rectangular section. Product briquetted. * COST including capital cost in U.S. Oils in 1982. TABLE II. DIRECT REDUCTION OF IRON-BEARING MATERIALS UITHI SOLID REDUCTANTS9.11»13 PROCESS REACTOR NAME Ld.xL [•] FEED [mm] REDUCTANT (REDUCTION) [°C] ENERGY CONMSMP. Fuel Electric [GCal] [KWh] PROD. RATE fTon DRI( L«J|)jy J COST J Ton DRI MET. PECULIARITIES AND [i] COMMENTS KAWASAKI Rotary Kiln Waste dust/ Coke Breeze 5 x 50 sludge (10-15) 1100-1200 3.85 115 0.59 N.A. 95 Pelletl zed Dust. Grate-kiln plant. KINGLOR- Fixed Bed Lump ore or Coal/Char METOR 0.45x0.6x12 Pellets (6-25) 1050 3.80 80 1.16 N.A. 92 Preheatlng-Reductlon-Cool Ing KOHO Rotary K1ln Pellets with Char from 3.3 x 24 Carbon (5-16) BF Dust 1150 2.85 110 0.67 N.A. 74 GMndlng-PelletlzIng-Reduction Pellets from Dust. Bentonlte. KRUPP- Rotary Kiln Lump Ore CODIR 4.1 x 73.5 (5-25) Anthracite <10 mm 950-1150 3.90 55 0.42 124.78 93 Any reductant can be used. SDR Rotary K1ln 4.5 x 71 Pelletlzed waste Iron dust (>6) Coke fines (ground) 1150 3.69 700 0.41 N.A. 93 Product used as BF Feed. SL/RN Rotary K1ln 3.6 x 50 6 x 125 Lump (3-20) Pellets (8-10) Fines (0.04-3) Coal (<20) 900-1100 3.90 85 0.42 107.71 93 Simpler. Any solid re-ductant. Underbed air Injection. SPM Rotary Kiln Waste Sludge Anthracite 3.9 x 80 Fine 1200 2.10 220 0.54 N.A. 77 Reduction and Agglomera-tion simultaneously. M1x-F1lter-dry-feed. Scrapper bar. ACCAR Rotary Kiln Lump or Sinter Coal (20%) 2.5 x 45 Gas (80%) 1050-1100 3.00 35 0.45 116.23 93 Alternate Injection of gas (bottom) and air (top). * COST including capital cost in U.S. Dlls. in 1982. 8 c o o l i n g o f the p r o d u c t o c c u r i n the lower p a r t . 17,19 A v a r i a t i o n of t h i s process i s the r e t o r t system, which operates on a batch b a s i s w i t h the gas i n j e c t e d from above.18 Rotary k i l n processes,!'20 on the other hand, make use of a hor-i z o n t a l r o t a t i n g c y l i n d e r , as depicted i n Figure 2.2. This r e f r a c t o r y -l i n e d r e a c t o r , w i t h a diameter ranging from 4 to 6 meters and a length from 60 to 125 meters, i s f e d w i t h the i r o n - c o n t a i n i n g m a t e r i a l , the c a r b o n a c e o u s r e d u c t a n t and, i f necessary, a d e s u l p h u r i z i n g agent. The charge moves c o u n t e r c u r r e n t l y to the gas flowing through the f r e e b o a r d , e s s e n t i a l l y i n plug flow. A i r i s introduced i n t o the freeboard to burn the carbon monoxide e v o l v i n g from the bed, to provide heat f o r the p r o -c e s s , p a r t i c u l a r l y the endothermic Boudouard r e a c t i o n . Extra fuel i s i n j e c t e d from the discharge end d u r i n g s t a r t - u p of the k i l n . In the f i r s t s e c t i o n of the k i l n , the preheating zone, the charge i s heated up to operational temperature, most of the v o l a t i l e s from the coal a r e r e -l e a s e d and some r e d u c t i o n takes place. In the remaining length of the k i l n , the reduction zone, f u r t h e r reduction i s c a r r i e d out and m e t a l l i -z a t i o n i s achieved. The length of the zones i s determined, among other f a c t o r s , by the r e a c t i v i t y of the charge. A v a r i a t i o n to t h i s mode o f o p e r a t i o n i s found i n the ACCAR process21-22 where l i q u i d or gaseous f u e l s are i n j e c t e d beneath the bed near the p r o d u c t end of the k i l n . The t e m p e r a t u r e d i s t r i b u t i o n o f gas and s o l i d s and the reduction se-quence i n s i d e a reduction k i l n a l s o are presented i n Figure 2.2. Because the aim of t h i s work i s to study the reduction k i n e t i c s of f i n e i r o n - o r e under c o n d i t i o n s s i m i l a r to t h o s e found i n r o t a r y k i l n s , these c o n d i t i o n s are f i r s t reviewed in t h i s Chapter. This i s Main features of the SL/RN r o t a r y k i l n process (Modified from reference 9) 10 f o l l o w e d by an assessment of a common problem i n reduction k i l n s : the formation of a c c r e t i o n s on the i n s i d e w a l l . Then s t u d i e s o f the k i n e -t i c s o f i r o n - o x i d e r e d u c t i o n with s o l i d reductants, u t i l i z i n g thermo-balances, are summarized to provide an i n s i g h t i n t o the p o s s i b l e mechan-isms i n the complex r e a c t i o n system. F i n a l l y i n the l a s t s e c tion of the chapter, d i f f e r e n t studies i n v o l v i n g l a b o r a t o r y - s c a l e r o t a r y r e a c t o r s are c r i t i c a l l y examined. 2.2 D i r e c t - r e d u c t i o n Rotary K i l n s I n d u s t r i a l research r e l a t e d to r o t a r y - k i l n d i r e c t reduction can be c l a s s i f i e d , according to the i r o n - c o n t a i n i n g raw m a t e r i a l u t i l i z e d and the purpose of the product, i n t o three general areas: i ) Reduction o f p e l l e t and/or lump f e e d w i t h the p r o d u c t b e i n g charged to an e l e c t r i c furnace f o r steel making.23-47 i i ) Treatment of i r o n and steelmaking waste m a t e r i a l s such as fume, dusts and sludge, where the product obtained i s to be fed to the b l a s t furnace. 48-60 i i i ) Treatment o f f i n e m a t e r i a l s , e s p e c i a l l y ironsand concentrates, to produce a charge f o r the e l e c t r i c steelmaking furnace.61-71 In each case the achievement of a smooth operation r e q u i r e s c o n t r o l o f t e m p e r a t u r e , bulk d e n s i t i e s / s i z e of ore and coal f o r good bed mixing, coal r e a c t i v i t y , ore r e d u c i b i l i t y , r e s i d e n c e time o f m a t e r i a l s i n the k i l n , amount of f i n e s present, softening p o i n t of coal ash and a i r pro-f i l e . In a d d i t i o n pneumatic coal i n j e c t i o n at the discharge end of the 11 k i l n , a i r i n j e c t i o n under the bed of the feed end of the k i l n , e x i t gas v e l o c i t y , m ineralogical c h a r a c t e r i s t i c s of feed materials and waste-gas heat u t i l i z a t i o n are important f a c t o r s . 2.2.1 Operation of reduction k i l n s A summary41»46 0f ^ e pi ants p r e s e n t l y i n operation i s presented i n Table III and gives an idea of the range of composition of the i r o n -c o n t a i n i n g m a t e r i a l s t r e a t e d , as w e l l as of the d i f f e r e n t reductants used. I t i s important to emphasize that to date no plant has p r o c e s s e d f i n e i r o n - o r e concentrates s u c c e s s f u l l y . In the cases where f i n e mate-r i a l s have been processed, v i z . , at New Zealand Steel65 and Western T i -tanium L t d . , 6 6 the concentrate has a Ti02 content l a r g e r than 55 and of 8 percent, r e s p e c t i v e l y . This r e f r a c t o r y oxide a i d s i n the p r e v e n t i o n of a c c r e t i o n formation, even though the p a r t i c l e s i z e of -250 + 90 ym i s smal 1. Of the important aspects of k i l n operation mentioned above, heat t r a n s f e r i s one of the most c r i t i c a l f o r several reasons. F i r s t l y , both the g e n e r a t i o n of gaseous r e d u c t a n t , and oxide reduction have to take place i n s i d e the same v e s s e l , c f . , F i g u r e 2.1. The former p r o c e s s , c o n s i s t i n g e s s e n t i a l l y o f the Boudouard or S o l u t i o n - l o s s r e a c t i o n , i s strong l y endothermic whereas the oxide r e d u c t i o n r e a c t i o n i s s l i g h t l y exothermic as f o l l o w s : C + C0 2 = 2 CO A H° = 86232 J/mole CO (2.1) 2O3 + 3 CO = 2 Fe + 3 C0 2 A H° = -9355 J/mole CO....(2.2) 12 Secondly, the heat flow patterns i n the rotary k i l n are exceedingly com-p l e x . 5 F i n a l l y , the c y c l i c a l nature of the process renders temperature measurement d i f f i c u l t so t h a t c o n t r o l of t e m p e r a t u r e i s f r a u g h t w i t h problems. O p e r a t i o n of a r e d u c t i o n k i l n from a thermal standpoint i s a f -f e c t e d by the f o l l o w i n g parameters: i ) The c o a l r e a c t i v i t y : t h i s parameter has a strong i n f l u e n c e on the rate of g a s i f i c a t i o n and depends on the g e o l o g i c a l o r i g i n of the c o a l . More r e a c t i v e c o a l s permit lower temperature opera-t i o n . Moreover, the Boudouard r e a c t i o n has a s t r o n g i n f l u e n c e on the o v e r a l l reduction k i n e t i c s , i i ) The ore r e d u c i b i l i t y : t h i s parameter i s dependent on the mine-r a l o g i c a l c h a r a c t e r i s t i c s o f the raw m a t e r i a l s and on t h e i r treatment p r i o r to r e d u c t i o n , e.g., p e l l e t i z a t i o n . A g a i n a higher r e d u c i b i l i t y allows lower temperature operation, i i i ) The s o f t e n i n g point of the coal ash and i t s important e f f e c t on the a c c r e t i o n development: a lower s o f t e n i n g p o i n t f a c i l i t a t e s the formation of compounds with wustite with low m e l t i n g p o i n t . This t o p i c w i l l be discussed in more d e t a i l i n a subsequent sec-t i o n . Only l i m i t e d c o n t r o l can be exerted over the above mentioned aspects, as compared with the a i r p r o f i l e , which i s a very i m p o r t a n t p r o c e s s v a r i -a b l e . Meadowcroft and Brimacombe 7 3 have a s c e r t a i n e d that to achieve a TABLE III. OPERATIONAL FEATURES OF ROTARY-KILNS DIRECT REDUCTION PLANTS41.46 COMPANY START UP DATE Western Titanium 1969 Hlghveld I 1968/80 New Zealand Steel I 1969 Acos F1no* .Iratlnl 1973 Stelco** 1975 Nippon Kokan** 1974 Slderperu 1980 Unldo/SIIL 1980 Hlghveld II* 1983 Iscor* 1984 New Zealand Steel II* 1984 Dunswart-Krupp 1973 KILN SIZE [M] 2.4 x 30 4.0 x 60 4.0 x 75 3.6 x 50 6.0 x 125 6.0 x 70 2.9 x 62 3.0 x 40 4.0 x 60 4.6 x 80 4.6 x 65 4.6 x 73 KILN UNITS ORE 1 Ilmenlte concentrate 10 Lump ore 1 Pellets/lump ore 1 Pellets 1 Waste oxide pellets 3 Pellets 2 Lump ore 3 Lump ore 4 Lump Ore COAL Subbltumlnous Bituminous 1 Beach Sand concentrate Lignite Bituminous Subbltumlnous Bituminous Coke/Anthracite Bituminous Bituminous Bituminous 4 Beach Sand Concentrate Lignite 1 Lump ore Subbltumlnous CAPACITY (Ton/year DRI) 15000 2000000*** 175000 60000 360000 400000 120000 35000 600000*** 720000 900000 150000 * Under construction In operation as required *** Prereduction 14 smooth o p e r a t i o n t h i s v a r i a b l e must be c a r e f u l l y c o n t r o l l e d . A l s o , the bed composition, i . e . , f i x e d carbon-to-iron r a t i o ( C f - j x / F e ) , a f f e c t s the bed thermal c h a r a c t e r i s t i c s . For example, i n c r e a s i n g the Cp-j x/Fe r a t i o from 0.17 to 0.23 has been reported to d e c r e a s e 80°C the bed tempera-t u r e . 6 6 under t h e s e circumstances a s i g n i f i c a n t change i n k i l n opera-t i o n c o n d i t i o n s could be undetected, i f o n l y gas tempe r a t u r e i s b e i n g m o n i t o r e d . Consequently, thermocouples attached to the k i l n wall must have a quick response, i n order to record a c c u r a t e l y the temperature o f the s o l i d s and freeboard. M i x i n g o f the charge i n a r o t a r y k i l n must be o p t i m i z e d to achieve a good o p e r a t i o n . In t h i s regard, d e n s i t i e s and p a r t i c l e s i z e s of both ore and coal are of the utmost importance, and an optimum combi-nation which y i e l d s the best mixing c o n d i t i o n s must be sought. A neces-s a r y c o n d i t i o n f o r optimum mixing i s that the ore p a r t i c l e s should be l a r g e r than the coal.46 i t must be str e s s e d however that t h i s holds f o r r e l a t i v e l y l a r g e p a r t i c l e s , i . e . , iron-ore p e l l e t s o f about 12 mm, and may not be completely true f o r f i n e r s i z e s of both coal and ore. From the standpoint of r e a c t i o n k i n e t i c s alone the ore and c o a l p a r t i c l e s i z e should be as small as p o s s i b l e (at t h e i r optimum s i z e r a -t i o , d c / d p e , f o r m i x i n g ) . U t i l i z a t i o n o f f i n e i r o n concentrates has been r e s t r a i n e d though, because of inherent operational problems, name-l y : enhancement of a c c r e t i o n formation and high l e v e l s of dust c a r r y over i n the of f - g a s e s , a t present working temperatures. I t has been r e c o g n i z e d that the r o t a r y k i l n i s not very energy e f f i c i e n t ; 4 4 thus e f f o r t s have been d i r e c t e d at u t i l i z i n g as much of the heat a v a i l a b l e as p o s s i b l e . A i r i n j e c t i o n under the bed, a t the f e e d 15 end of the k i l n , has been implemented i n order to burn out most of the v o l a t i l e s e v o l v i n g from the coal at t h i s stage. In a d d i t i o n , the charge i s heated more r a p i d l y , which s h o r t e n s the preheating s e c t i o n of the k i l n , and brings about an i n c r e a s e i n the t h r o u g h p u t of the r e a c t o r . Moreover, waste-gas heat u t i l i z a t i o n has been optimized, to preheat the feed p r i o r to charging.71 In a n o t h e r area of p r o c e s s improvement, coal i n j e c t i o n at the discharge end of the k i l n has been employed to su s t a i n the reduction r e -a c t i o n , and to maintain h i g h l y reducing c o n d i t i o n s , which would minimize product r e o x i d a t i o n at t h i s l a s t stage. 2.2.2 A c c r e t i o n formation A c c r e t i o n s are s o l i d agglomerates which adhere to the r e f r a c t o r y wall i n s i d e the k i l n . The a c c r e t i o n i s formed i n i t i a l l y by s i n t e r i n g of f i n e c harge p a r t i c l e s a g a i n s t the r e f r a c t o r y s u r f a c e , and l a t e r by s i n -t e r i n g of the p a r t i c l e s themselves. An i n c r e a s i n g r a t e o f a c c r e t i o n growth can d i m i n i s h the k i l n c a p acity to the point where the operation has to be shut down and the a c c r e t i o n s removed. Temperature measure-ment, the importance of which was discussed i n the previous s e c t i o n , i s obviously impaired by a c c r e t i o n growth, which leads to s e r i o u s p r o c e s s c o n t r o l p r o b l e m s . The main mechanism i n the s i n t e r i n g process i s the p a r t i a l f u s i o n and d i s s o l u t i o n of the f i n e r p a r t i c l e s . 7 4 This process i s c o n t r o l l e d p r i m a r i l y by the l o c a l temperature and the chemical compo-s i t i o n of the f i n e s , where the l a t t e r determines t h e i r c a p a b i l i t y to form binary, ternary and even quaternary compounds. These phenomena can 16 o c c u r r e a d i l y i n the coal based processes, owing to the f o l l o w i n g f a c -t o r s : 7 5 " 8 5 i ) Poor c r y s t a l l i z a t i o n of the ore which causes i t to d i s i n t e g r a t e more e a s i l y to produce f i n e s . F o r example, h e m a t i t e i s more l i k e l y to i n c r e a s e a c c r e t i o n growth than magnetite, since the volume i n c r e a s e a s s o c i a t e d with the Fe203 to Fe304 transforma-t i o n and the r e s u l t i n g i n t e r n a l s t r e s s e s , enhances the f i n e s generation. i i ) C o m position of the f i n e s present, o r g i n a t i n g from the d i f f e r e n t components i n the bed, which determines the e q u i l i b r i u m s o f t e n -i n g and m e l t i n g t e m p e r a t u r e s . These components are coal ash, iron - o r e gangue, i r o n oxides and lime or dolomite, i i i ) L o c a l f u s i o n of these f i n e s caused by the thermal c o n d i t i o n s of the process. Among the important thermal c o n d i t i o n s are c y c l i c h e a t i n g and c o o l i n g due to the k i l n r o t a t i o n , the temperature d i f f e r e n c e between the wall and charge and p o s s i b l e hot s p o t s caused by the burner flame. i v ) The h i g h s u r f a c e t e n s i o n of the Ca0-Si02 and CaO-FeO-Si02 sys-tems which causes the p a r t i c l e s to c o a l e s c e more r e a d i l y and remain i n the l i q u i d phase, v) F a c t o r s o f a n c i l l a r y importance i n c l u d e the v i s c o s i t y of the softened phase, i n t e r f a c i a l tension between wall and p a r t i c l e s , c o m p r e s s i v e f o r c e s due to charge height, mechanical adhesion of the s o l i d p a r t i c l e s and dust s e d i m e n t a t i o n from the k i l n gas-exhaust system. 17 An i n s i g h t i n t o these f a c t o r s has been p r o v i d e d by L e i s t e r e t al .75-77 - j n a c h a r a c t e r i z a t i o n of the m a t e r i a l s used f o r d i r e c t reduc-t i o n i n r o t a r y k i l n s , where the importance o f the i n t e r a c t i o n between c o a l a s h , c a l c i n e d dolomite and hematite ores with respect to the s o f -tening point of the mix was assessed. This study a l s o i n c l u d e d an eva-l u a t i o n of the species present i n the a c c r e t i o n s from an i n d u s t r i a l s i z e r o t a r y k i l n . The ranges of composition observed were s i m i l a r t o t h o s e obtained from a study i n a p i l o t - p l a n t s c a l e o p e r a t i o n ? 8 - ^ and are pre-s e n t e d i n T a b l e IV. Gudenau et a l . , 8 2 and S c h l e b u s c h , 8 1 c a r r i e d out a study i n a d i r e c t l y - f i r e d r o t a r y drum, l a r g e enough (800 mm i.d.) to a l -low f o r the separation of the reducing atmosphere within the charge from the o x i d i s i n g gases i n the freeboard. They assessed the e f f e c t of time of r e d u c t i o n , charge t e m p e r a t u r e , and temperature d i f f e r e n c e between charge and wall on a c c r e t i o n growth, f o r d i f f e r e n t combinations o f p e l -l e t s , l i g n i t e and a n t h r a c i t e . A s i m i l a r study was performed, but on f i n e ores with the same reductants i n an i n d i r e c t l y heated r o t a r y r e a c -t o r , by Wenzel e t a l . 8 3 and Grosse-Daldrup. 8^ The most important f i n d i n g s from both studies can be summarized as f o l l o w s : i ) A c c r e t i o n formation increases s t r o n g l y with temperature and a l s o with the temperature g r a d i e n t between w a l l and c h a r g e , c f . , Figure 2.3. i i ) Two types of s i n t e r i n g "bridges" are p o s s i b l e according to the extent of r e d u c t i o n . 8 ^ 8 3 For a lower degree of r e d u c t i o n , the 18 TABLE IV. ANALYSIS OF ACCRETIONS FORMED IN A PILOT-PLANT SIZE ROTARY KILN78,79 P o s i t i o n Feedstock SiO? Al 0O3 CaO [%] FeO [%] Fe Layer c l o s e s t to ore charge (top) p e l l e t s 10-15 8-12 10-15 10-15 1 1-2 40-50 38-50 Middle l a y e r ore p e l l e t s 35-45 50-60 3 1 n i l 38-50 50-60 3-5 1 0.5 Layer c l o s e s t to k i l n l i n i n g ore (bottom) p e l l e t s 30-40 55-65 2-3 1 n i l 35-40 55-65 2-4 1 n i l TABLE V. PHASES ENCOUNTERED IN THE ACCRETIONS FORMED DURING DIRECT REDUCTION IN A ROTARY KILN 75-77 Phase Formula Melting Point [°C] Comments Wustite FeO 1369 Iron Fe 1565 S i l i c a S i 0 2 1723 F a y a l i te 2FeO-Si02 1205 Gehlenite 2CaO-Al203*Si02 1593 An o r t h i t e CaO-Al203«2Si02 1553 Hercynite FeO-Al2O3 1547 E u t e c t i c 1 FeO + 27% CaO 1070 in Fe presence E u t e c t i c 2 2FeO'Si02 + FeO 1175 E u t e c t i c 3 2FeO-Si02 + Si02 1180 S i 0 2 as t r i d i m i t e E u t e c t i c 4 CaO + S i02 + FeO 1105 O l i v i n e l i n e E u t e c t i c 5 FeO + AI2O3 + Si02 1070 F a y a l i t e / C o r d i e r i t e / H e r c y n i t e E u t e c t i c 6 CaO + AI2O3 + Si02 1165 Anorthite/Calcium S i l i c a t e 19 Accretion growth, d (mm) 120 40 Temperature difference wall/bed(°C) -7 Bed temperature (°C) 2.3 Formation of a c c r e t i o n s with 10% f i n e s i n three dimensional p l o t t i n g 7 4 Metallization Preheat FeO zone Oxidation zone zone zone o c o (J < Kiln length Reduction time 2.4 Q u a l i t a t i v e progress of the formation of a c c r e t i o n s as a fu n c t i o n of reduction time and furnace leng 20 le a d i n g phase i n the bridges j o i n i n g the agglomerates i s a s i l i -cate with a glassy s t r u c t u r e , w h i l e a t h i g h e r r e d u c t i o n s t h i s l e a d i n g phase becomes a network of m e t a l l i c i r o n grains formed a t the s t a r t of reduction.80-84 A q u a l i t a t i v e representation of t h i s sequence i n the k i l n i s p r e s e n t e d i n F i g u r e 2.4, where a maximum i s seen a t the preheating (low reduction) end ( s i l i c a t e b r i d g e ) , and a second maximum appears at higher reduction ( i r o n bridge) where some of the v i t r e o u s s t r u c t u r e i s s t i l l present, i i i ) A range of so f t e n i n g temperatures between 1020 and 1060°C was observed75-77,85 depending on the oxide phases present; a summa-ry of the phases most l i k e l y t o appear i s shown i n T a b l e V. G e h l e n i t e and a n o r t h i t e were found i n very small amounts i n the agglomerates, while h e r c y n i t e was found i n a few case s but i n r e l a t i v e l y l a r g e amounts. I t i s i n t e r e s t i n g to observe that m u l l i t e , which i s the product of the decomposition of k a o l i n i t e p r e s e n t i n a s h , i n v a r i a b l y o c c u r r e d c o u p l e d w i t h a n o r t h i t e . This suggests that the l a t t e r i s a product o f the r e a c t i o n be-tween the k a o l i n i t e and the CaO from the dolomite. At about 1120°C a n o n - c r y s t a l l i n e phase was observed to form, composed of FeO, S i 0 2 , Al2O3 and CaO, while at higher Si02 contents, a ten-dency to form c r y s t a l s was reported, i v ) With r e s p e c t to s i z e , the f i n e r f r a c t i o n s o f the r e l a t i v e l y l i g h t components, i . e . , coal ash and ore gangue, p r e f e r e n t i a l l y d e p o s i t e d on the w a l l ; the harder and l a r g e r components appa-r e n t l y f a l l o f f . 8 2 21 v) A c c r e t i o n s were produced by c o m b i n a t i o n s of f a c t o r s , such as high ash contents i n the coal p l u s h i g h t e m p e r a t u r e s , l i g n i t e ash plus f i n e ore at medium temperature; f i n e ore plus high tem-perature; and p e l l e t s and a n t h r a c i t e lumps c o a t e d w i t h f i n e s plus high temperatures of wall and c h a r g e . 8 2 v i ) F i n a l l y , the interweaving of the i r o n whiskers, produced d u r i n g the r e d u c t i o n , was proved to be the main component of the i r o n bridges during reduction of iron-sands concentrates with l i g n i t e and a n t h r a c i t e . 8 3 From the above s e c t i o n s , the degree of complexity of the o v e r a l l r o t a ry k i l n process i s c l e a r l y evident. I t i n v o l v e s at d i f f e r e n t stages of the p r o c e s s , d i f f e r e n t mechanisms of p a r t i c l e s mixing, heat t r a n s f e r and r e a c t i o n k i n e t i c s ; the l a t t e r i s the subject of the next s e c t i o n . 2.3 K i n e t i c s s t u d i e s of i r o n - o x i d e reduction with s o l i d reductants In order to improve the process k i n e t i c s of the r o t a r y k i l n , i n terms of the a s p e c t s d i s c u s s e d i n Section 2.2, the mechanism of i r o n -oxide reduction with carbon must be understood. This mechanism c o n s i s t s of chemical r e a c t i o n and mass-transfer processes and has been studied by numerous i n v e s t i g a t o r s . 8 6 - 1 0 4 j n e r e a c t i o n r a t e s , f o r s p e c i f i c iron-and carbon-containing m a t e r i a l s , have been obtained. In a d d i t i o n , d i f f e r e n t mathematical models, of isothermal non-moving systems, have been propos-ed w i t h d i f f e r e n t degrees of a p p l i c a b i l i t y . 1 0 5 - 1 1 0 T h e i r aim has been to assess the importance of each of the i n d i v i d u a l subprocesses i n v o l v e d i n the o v e r a l l r e d u c t i o n r e a c t i o n , i . e . , E q u a t i o n s (2.1) and (2.2) 22 c o u p l e d t o g e t h e r , i n order to obtain a f u n c t i o n a l r e l a t i o n s h i p between them and the o v e r a l l reduction r a t e . The o v e r a l l r e d u c t i o n r e a c t i o n has been recognized to proceed v i a the gaseous intermediates, CO and C O 2 . The i n d i v i d u a l subprocesses, schematically shown in Figure 2.5, are the f o l l o w i n g (numbers correspond to those i n f i g u r e ) : (1) D i f f u s i o n o f CO t h r o u gh the porous reduced i r o n - l a y e r , i n the p a r t i a l l y reduced iron-oxide p a r t i c l e . (2) Chemical r e a c t i o n at i r o n / i r o n - o x i d e i n t e r f a c e . ( 3 ) D i f f u s i o n outward of the gaseous reduction product, C O 2 , through the product l a y e r . ( 4 ) Transport of CO2 through the gas surrounding the p a r t i c l e s . (5) Boudouard r e a c t i o n . (6) Transport of CO through the gas surrounding the p a r t i c l e s . (7) D i r e c t s o l i d - s o l i d r e d u c t i o n . The most important f a c t o r s which may have an i n f l u e n c e on these subprocesses, are: (A) Temperature. (B) Stoichiometry. (C) Geometry and s t r u c t u r e of the p a r t i c l e s : e.g., p o r o s i t y , t o r -t u o s i t y , c r y s t a l l i n i t y . (D) S t r u c t u r e of the bed of p a r t i c l e s ; e.g., p a r t i c l e s i z e , void f r a c t i o n . Sub-processes in the reduction of iron-oxide with carbon 24 (E) Mixing of the r e a c t a n t s ; e.g., f i x e d bed, moving bed. (F) Presence of i m p u r i t i e s ; c a t a l y z e r s , x i n h i b i t e r s . (G) Gas p r o p e r t i e s . The i n f l u e n c e o f the above f a c t o r s on the o v e r a l l r e a c t i o n r a t e , has been the subject of many research e f f o r t s with varying degrees of success. E a r l i e r i n v e s t i g a t o r s , J a n d e r , 8 6 G i n s t l i n g , 8 6 a n d C a r t e r , 8 7 have obtained general r e l a t i o n s h i p s f o r d i f f u s i o n c o n t r o l l e d r e a c t i o n s i n p a r a l l e l , and they are, r e s p e c t i v e l y : 1 _ ( l - f R ) l / 3 = _ k _ t (2.3) o 1 - 2/3 f - (1 - f R ) 2 / 3 = J L t (2.4) ro Z - [1 + ( Z - l ) f R ] 2 / 3 . ( Z - l ) ( l - f R ) 2 / 3 HI^ > < 2- 5 ) These r e l a t i o n s h i p s were obtained with the f o l l o w i n g assumptions: i ) The r e a c t i n g p a r t i c l e s are s p h e r i c a l i n shape and remain so du-r i n g the r e a c t i o n , i i ) D i f f u s i o n obeys F i c k ' s law. i i i ) One o f the gaseous products d i f f u s e s i n t o the p a r t i c l e s of the s o l i d s with which i t r e a c t s . 25 i v ) The volume of the p a r t i c l e s remains constant, except i n the l a s t case, Equation (2.5), where the volume change i s considered. With r e s p e c t to the present iron-oxide/carbon r e a c t i o n system, the mechanisms e l u c i d a t i n g how the o v e r a l l r e a c t i o n d e v e l o p s under d i -verse c o n d i t i o n s have been p r o g r e s s i v e l y revealed. A summary of the ex-perimental c o n d i t i o n s of the most r e l e v a n t studies i s presented in Table V I . In an experimental study of Fe£03 reduction with pure carbon under vacuum, Y u n 8 e s t a b l i s h e d t h a t the most d i f f i c u l t stage of r e d u c t i o n , namely the step with the highest a c t i v a t i o n energy, i s the reduction of 'FeO' to Fe. This was l a t e r confirmed by R o s s 8 9 when studying the mech-anisms of oxygen migration, through the i r o n l a y e r , during the reduction o f c o a r s e l y c r y s t a l l i s e d ores. It was a l s o found that s o l i d - s t a t e d i f -f u s i o n of i r o n and oxygen through the s o l i d - p h a s e l a t t i c e becomes ex-t r e m e l y important in the f i n a l reduction stage, i . e . , above 80 percent. On the other hand, i n a study of Fe203 reduction with graphite, i n a n i -trogen atmosphere, Otsuka and K u n i i 9 0 showed that the r a t e - l i m i t i n g step i n the o v e r a l l reduction r e a c t i o n i s the Boudouard r e a c t i o n . On the basis of t h i s f i n d i n g , R a o 9 1 developed a model assuming that the g a s i f i -c a t i o n of carbon obeys f i r s t order k i n e t i c s , and formulated the f o l l o w -ing equation: dWr - = R W (2.6) dt In t h i s E q u a t i o n Wc i s the amount of carbon and R c i s an o v e r a l l rate constant. Thus f o r the o v e r a l l r e d u c t i o n , based on the stoichiometry of TABLE VI. STUDIES ON REDUCTION KINETICS OF IRON OXIDES WITHI CARBONACEOUS MATERIALS AUTHOR YEAR REF.# YUN 1961, 83 IRON OXIDE SIZE IN [vm] Fe203 (R.G.) <147; 0.5 q REDUCTANT (% C) SIZE IN Urn] Graphite (R.G.) <147 REDUCTANT PRE-TREATMEMT Degassed C/Fe, C/0 1.42 3.30 EXPERIMENTAL SYSTEM Balance Vacuum T RANGE [°C] 700-1100 [kcal/mole] N.A. BICKNESE 1966, 92 FeO (Synthetic) <1 12 g Coconut charcoal 95 N.A. N.A. N.A. I . 8 8 N 2 + CO Balance C02 wt. 980-1165 13.9 OTSUKA Fe203 (99%) Electrode Graphite 1969, 90 43 to 147; 0.8 g (99.8%); 43 to 208 None O.U-0.62 Gas Analysis 1050-0.83 200 cm3/m1n N2 1150 (0.2 f) 15-24 (0.6 F) 55-75 EL-GUINDY FeO-T102 (pure) Graphite 1970, 103 Finely ground 0.8 g N.A. None 0.08-1.16 0.28-4.05 Balance 1075-1140 Non-1 sot. 64 * 6 RAO 1971, 91 Fe203 (R.G.) 80% <1; 0.8 g Amorphous Carbon (R.G.);-44,135,270 None 0.16-0.96 Balance 0.37-2.23 600 cnt3/min Ar 850-1087 72 FRUEHAN Fe203, FeO (R.G.) Coconut charcoal, 1977, 96 <74; 0.8 g char & coke; 74, 500, 1600 0.16-0.23 1 hr at 600°C 0.56-0.93 Balance 1000 cm3/n1n Ar or He 900-1200 70-80 ABRAHAM Fe 20 3 (R.G.) 1979, 93 43 4 1800 11 9 Electrode Graphite 68 None 0.65 1.50 Fe203 apart from C. CSZ cell 880-1042 Non I sot. (0.2 f) 72 (0.6 F) 55 WRIGHT 1981, 94 Fe203 (BF Pellets) Coal char (82.3%) 1200, 12 g -800 + 100 20 h, up to 850^ 0.36 1.25 Char around pel let 900- 70-80 SUNDAR MURT1 Fe0>Cr203 (pure) 1982, 104 <45 0.8 g Graphite (99.9%) N.A. None 0.79-1.71 Balance 2.44-5.97 1150 1300 57 SEATON Fe203 « Fe304 (BF) Bituminous char 1983, 99 1400. N.A. (83.3); <47 N.A. 0.31 & 0.35 Horizon. Tube 800-0.72 A 0.65 800 cm/min N2 1200 Fe 20 3 : 30-57 Fe304 : 38 RAO Fe3<>4 (Concentrate) Coke (85.6) 1984, 116 <250; 8g <50 0.25 Gas Analysis 900-2 h. at 600°C 0.65 200 cm3/min N2 1000 73 42-75 (Cat) ro 27 E q u a t i o n s (2.1) and (2.2), and c o n s i d e r i n g that a l l the CO was consumed in the r e d u c t i o n , the rate Equation was found to be log (1.743 - f R ) = l o g 1.743 - R t (2.7) 2.303 Equation (2.7) f i t t e d the experimental r e s u l t s well except f o r the e a r l y p a r t o f the r e a c t i o n , i n agreement with e a r l i e r f i n d i n g s . 8 6 - 9 0 By way of e x p l a n a t i o n , i t was suggested that the c a r b o n g a s i f i c a t i o n d i d not f o l l o w E q u a t i o n (2.6) d u r i n g the e a r l y stages, but was c o n t r o l l e d by some other mechanism. The c a t a l y s i s of the Boudouard r e a c t i o n by i r o n and L i 2 O was a l s o demonstrated, as well as the i n h i b i t i n g e f f e c t of FeS a d d i t i o n s . The chemical r e a c t i o n c o n t r o l , exerted by the carbon g a s i f i -c a t i o n , was a l s o i n f e r r e d by Bicknese and C l a r k 9 2 from the observation that there was no measurable d i f f e r e n c e i n the r a t e of r e d u c t i o n f o r d i f f e r e n t c o a l p a r t i c l e s i z e s . They also introduced the concept t h a t , i n a s t a t i c system, the r e l a t i v e rates of the reduction r e a c t i o n and the g a s i f i c a t i o n o f carbon depend upon the r e a c t i v i t i e s of the oxide and carbonaceous m a t e r i a l . More r e c e n t experimental s t u d i e s , a p p l i c a b l e to t h i s work, have been undertaken. In one instance, the r e d u c t i o n and the g a s i f i c a t i o n r e a c t i o n s are i s o l a t e d from one another, but contained i n the same ves-s e l . 9 3 I t was found that the o v e r a l l rate of reduction i s an order of magnitude lower under these c o n d i t i o n s , as compared to the case where both s o l i d s are i n t i m a t e l y mixed. Thus the e f f e c t s of mixing and/or i r o n c a t a l y s i s have been i l l u s t r a t e d . In another work, by Wright et 28 a l . , 9 4 the reactants were kept separate u n t i l the d e s i r e d r e a c t i o n tem-perature was reached, then the f i n e reductant was poured over the i r o n -o x i d e p e l l e t . In t h i s c a s e , the r e s u l t s agreed well with an e a r l i e r study i n a l a b o r a t o r y k i l n by the same a u t h o r s 9 5 and with those of works by F r u e h a n , 9 6 Turkdogan e t a l . , 9 7 and Gransden et a l . 9 8 I t was deter-mined, from the a c t i v a t i o n energies obtained f o r these s i m i l a r r e a c t i o n systems, that the o v e r a l l reduction r e a c t i o n i s c o n t r o l l e d by the chemi-cal r e a c t i o n of the carbon g a s i f i c a t i o n up to about 1000°C, whereupon mass t r a n s f e r mechanisms s t a r t to assume c o n t r o l . The above f i n d i n g has been f u r t h e r c o r r o b o r a t e d by Seaton e t a l . 9 9 They have a l s o mentioned that heat t r a n s f e r e f f e c t s , manifested as temperature g r a d i e n t s through the Fe2t)3 p e l l e t s , play a part in the reduction r e a c t i o n . Among other aspects s t u d i e d , the p r e t r e a t m e n t o f the carbonaceous material has been found to have a noticeable e f f e c t on the r e d u c t i o n r e a c t i o n , 100-101 a n ( j a n increase i n the reduction r a t e , through the c a t a l y s i s of the Boudouard r e a c t i o n by a l k a l i c a r b o n a t e s , has a l s o been reported by Rao and Han.l° 2 Studies on the r e d u c t i o n k i n e t i c s o f FeO, o f m a t e r i a l s whose main components were T i 0 2 and 0 2 0 3 , have y i e l d e d d i f f e r e n t r e a c t i o n mechanisms however.103-104 S o l i d - s t a t e reduction control i s reported by E l - G u i n d y and Davenport, 103 to have predominated i n the reduction of Fe0-Ti02 up to 1020°C, whereupon gaseous reduction by CO takes over the c o n t r o l . An important f i n d i n g i n t h i s study i s the o b s e r v e d i n f l u e n c e o f the i n e r t - g a s f l u s h i n g on the reduction r a t e . Back d i f f u s i o n of the i n e r t gas i n t o the s o l i d s bed was r e c o g n i z e d , even a t low f l o w r a t e s such as 20 cm3/rnin. In the reduction of Chromite, on the other hand, 29 Sundar M u r t i and Seshadri'104 r e p o r t the reduction to be c o n t r o l l e d by d i f f u s i o n of oxygen towards the surface of the p a r t i c l e s , i n the tempe-rature range from 1150 to 1300°C. The complex nature of the two p a r a l l e l r e a c t i o n s , i r o n reduction and carbon g a s i f i c a t i o n , has l e d to the development of more t h e o r e t i c a l models w i t h d i f f e r i n g degrees o f c o m p l e x i t y . These models have had varying l e v e l s of success i n representing the experimental r e s u l t s , un-der g i v e n c o n s t r a i n t s . Thus, a general mathematical model of r e a c t i o n between s o l i d s , through gaseous intermediates, was proposed by Sohn and S z e k e l y . 1 0 5 T h e i r model i s r e s t r i c t e d to the case of chemical c o n t r o l and under the f o l l o w i n g assumptions: i ) A porous p e l l e t made up of u n i f o r m l y d i s t r i b u t e d p a r t i c l e s of any of the f o l l o w i n g geometries: f l a t p l a t e , l o n g c y l i n d e r o r sphere. i i ) Steady-state c o n d i t i o n s with respect to gas c o n c e n t r a t i o n . The rate of r e a c t i o n was expressed as a f u n c t i o n o f FeO c o n c e n t r a t i o n , carbon c o n c e n t r a t i o n , p a r t i c l e s s i z e r a t i o , e q u i l i b r i u m constants f o r the FeO reduction and Boudouard r e a c t i o n and the shape of the p a r t i c l e s . On the other hand, by a l s o c o n s i d e r i n g mass-transfer mechanisms, Raol06_ 109 developed a model which f i t t e d his experimental r e s u l t s from a pre-v i o u s study r e a s o n a b l y well.91 The model was e s t a b l i s h e d f o r the f o l -lowing c o n d i t i o n s : 30 i ) The o v e r a l l r e a c t i o n was assumed to proceed i n three stages: i n i t i a t i o n , propagation and termination, i i ) The gaseous d i f f u s i o n was assumed to be u n i d i r e c t i o n a l i n t o a stagnant i n e r t gas; t h i s gas i s considered not to d i f f u s e back i n t o the s o l i d s bed. i i i ) There were no s t r u c t u r a l changes i n the sample, i v ) The gas-phase compositions were tho s e f o r e q u i l i b r i u m c o n d i -t i o n s . The r a t e s o f CO and CO2 p r o d u c t i o n were e s t a b l i s h e d on the basis of a two-step r e a c t i o n sequence, formation and d i f f u s i o n , based on E q u a t i o n (2.6). The equations f o r the rates are: 2 (1 - 6) h P C Q 2 R C O = T 1 m p -(2.8) 1 + m a P C 0 2 (23 - 1) I a P C 0 2 R C 0 ? = (2.9) I + m a P C 0 2 where 6 denotes the f r a c t i o n of CO u t i l i z e d i n r e d u c t i o n , 1\ i s a spe-c i f i c rate constant and ma i s a fun c t i o n of the i n t r i n s i c rate constants and of the e q u i l i b r i u m constant. By co n s i d e r i n g the mechanism o f v i s -cous f l o w , s l i p f l o w and ordinary and surface d i f f u s i o n , the d i f f e r e n -t i a l equations e s t a b l i s h e d were numerically solved. Again, the o v e r a l l r e d u c t i o n p r o c e s s was found to be mass-transfer c o n t r o l l e d , determined 31 by the a v a i l a b i l i t y of CO, above 1000°C. These r e s u l t s were c o r r o b o r a t -ed by a s i m i l a r model, where the e v a l u a t i o n o f the d i f f u s i v e f l o w was s i m p l i f i e d to one i n v o l v i n g molecular d i f f u s i o n and forced gas flow to obeying P o i s e u i l i e ' s e q u a t i o n . 1 1 ^ Summarizing, as shown i n Table VI, the majority of the reduction k i n e t i c s studies share the f o l l o w i n g s i m i l a r i t i e s : small sample weight ( l e s s than 12 g) of pure m a t e r i a l s and considerable amounts of i n e r t gas f l u s h i n g during the r e a c t i o n ; and s t a t i c s o l i d s c o n d i t i o n s i n a l l cases. The o v e r a l l r e d u c t i o n r e a c t i o n has been proved to proceed through the gaseous i n t e r m e d i a t e products, CO and C02» with the Boudouard r e a c t i o n c o n t r o l l i n g i t at lower temperatures. At h i g h e r t e m p e r a t u r e s , mass-t r a n s f e r mechanisms such as gas d i f f u s i o n play an i n c r e a s i n g l y important r o l e . The a c t i v a t i o n energies o b t a i n e d , f o r the Boudouard r e a c t i o n , vary i n the range of 15 to 80 kcal/mole at temperatures between 800 and 1165°C, with most of the values f a l l i n g i n the narrower range of 45 to 75 kcal/mole. This range agrees with t h a t reported f o r the o x i d a t i o n of c a r b o n a c e o u s m a t e r i a l s with C O 2 , 1 1 1 the higher values corresponding to purer, l e s s r e a c t i v e , m a t e r i a l s such as coke and graphite,97,112-113 a n f j the lower values to those of c h a r s 1 1 4 and of c a t a l y z e d r e a c t i o n s . 1 1 5 " 1 1 8 2.4 Laboratory s c a l e s t u d i e s i n r o t a r y r e a c t o r s Several s t u d i e s have been performed i n l a b o r a t o r y - s i z e r o t a r y reactors.8,80-81,95, 1 1 0-129 j h e i r p r i n c i p a l aim was to determine the best c o n d i t i o n s f o r the reduction of i r o n - b e a r i n g m a t e r i a l s , under r o -t a t i n g c o n d i t i o n s , with r e l a t i v e l y l a r g e r s i z e samples. An o v e r a l l view of the c h a r a c t e r i s t i c s and operational d e t a i l s of each rotary r e a c t o r i s 32 summarized i n Table VII; a b r i e f account of t h e i r f i n d i n g s i s given be-low. The e a r l i e s t study by Williams et a l . 1 1 9 i s worthy of a more de-t a i l e d d e s c r i p t i o n since the range of o p e r a t i n g f a c t o r s and v a r i a b l e s t e s t e d was b r o a d . The study o f d i r e c t reduction of i r o n ore, c a r r i e d out p r o g r e s s i v e l y i n muffles, i n d i r e c t l y - h e a t e d r o t a t i n g tubes o f d i f -f e r e n t s i z e s and d i r e c t l y f i r e d drums and p i l o t - p l a n t s i z e k i l n s , y i e l d -ed the f o l l o w i n g important f i n d i n g s : i ) Under s u i t a b l e c o n d i t i o n s , sponge i r o n could be produced on a commercial s c a l e at about 900°C, with a reduction degree h i g h e r than 95 percent. i i ) The Boudouard r e a c t i o n appeared to be the rate c o n t r o l l i n g step i n the process. i i i ) Since the process r e q u i r e s a large heat input, and as the charge i s a poor heat conductor, heat t r a n s f e r i n t o the bed appeared to be a l i m i t i n g f a c t o r i n a successful l a r g e - s c a l e operation. i v ) Although the gas stream above the r o l l i n g charge in the k i l n was o x i d i z i n g w i t h r e s p e c t to i r o n , the hot carbon p a r t i c l e s main-tained a s t r o n g l y reducing atmosphere within the charge, v) Rapid heating and thorough s t i r r i n g were obtained; no d i f f e r e n c e was observed between 1 and 12 r.p.m; a l t h o u g h t h i s does not agree with more recent s t u d i e s . v i ) Low-grade, non-coking bituminous and l i g n i t i c c o a l s proved to be good r e d u c i n g agents; coking c o a l s could not be used since they caked and formed a c c r e t i o n s . TABLE VII. CHARACTERISTICS OF LABORATORY-SIZE ROTARY KILN EXPERIMENTS FOR IRON ORE REDUCTION AUTHOR D x L L/D 3/p ^ c ^ F e cFIx/ p e Year, Ref.# [mn] [mm] Max. F i l l T . [t] [r.p.m.] [°C] COMMENTS WILLIAMS 1927, 119 THEMELIS 1964, 120 MOELLER 1967, 122 MEADOWCROFT 1973, 123 NIXON 1973, 128 REUTER 1975, 121 PETERSON 1976, 124 MORRISON 1978, 95 SUCRE 1979, 8 HAUSLER 1951, 129 N.A. 0.45 Wide range 483 x 838 1.74 2.35 915 x 152 1.67 N.A. 145 x 1450 10.0 14.5 152 x 610 4.0 12 25 x 245 9.69 1.25 150 x 680 4.53 9 0.36 - 1.25 0.4 - 0.8 0.375 0.40 - 0.56 178 x 381 2.14 15 0.95 0.58 485 x 280 0.58 12 0.39 0.3 - 1.0 64 x 310 4.8 0.15 3.12 0.39 - 0.91 150 x 680 4.53 0.4 0.5 18 12 16 16 13 11 13 16 1.5-12 900 - 1050 0.4 -1.5 800 - 1100 1000- 1050 1.5-5 800 - 1000 1 - 10 900 - 1150 1020 N.A. 1000 -1150 10 - 30-8 950 - 1070 920 - 1000 Heat then charge. Internal firing with fuel o i l . Charge ore under Inert atmo-sphere, heat up, charge coal. External firing. Preheat to 800 then charge. Char. External heating. Flow of N£. Gas analysis. 1010- 1120 Induction heating. External electric heating. Continuous gas analysis. Continuous feed. Gas re-duction. Preheat to 600°, charge, then heat to T. Induction heat-ing. Green pellets. External elec-tric heating. 5 /min N2-External electric heating. Charge ore then heat the charge char. Heat then charge. Induction heating. Induction heating. 833 cm3/min N2-oo oo 34 v i i ) At ore s i z e s smaller than 5 mm, the reduction rate hardly v a r i e d with respect to the p a r t i c l e s i z e , v i i i ) Best m i x i n g r e s u l t s were o b t a i n e d when the reductant and ore were of the same s i z e ; f i n e r coal f l o a t e d on top of the bed. i x ) When f i n e i r o n - o r e , l e s s than 147 ym i n s i z e , was processed, i t s i f t e d through the bed and s i n t e r e d on the hot k i l n w a l l s . A l t h o u g h the c o n d i t i o n s of the experiments did not allow a very p r e c i s e e v a l u a t i o n o f the r e s u l t s of the p r o c e s s , e.g., p o i n t s ( v ) , ( v i i ) and ( v i i i ) , good general trends were e s t a b l i s h e d . Other studies have been performed on several aspects of the pro-cess on the l a b o r a t o r y s c a l e . S i m i l a r i t y c r i t e r i a were a p p l i e d to s c a l e down a pre-reduction k i l n , by Themelis et al.,120 W h e r e i t was concluded that the rate of generation and mass t r a n s f e r of CO, are the most impor-t a n t s t e p s i n the r e d u c t i o n p r o c e s s and depend strong l y on the s i z e , d e n s i t y , and r e a c t i v i t y of the coal used. The density and s i z e are ob-v i o u s l y i m p o r t a n t i n d e t e r m i n i n g the mixing patterns of the p a r t i c l e s w i t h i n the bed and t h e r e f o r e were the s u b j e c t o f two f u r t h e r s t u -d i e s . 4»121 in h i s i n v e s t i g a t i o n of t r a n s p o r t i n and mixing behaviour of r o t a r y k i l n beds f o r the production of sponge i r o n , Reuterl21 evaluated the e f f e c t s of r o t a t i o n a l speed, c y l i n d e r s i z e , m i x i n g t i m e , tempera-t u r e , p a r t i c l e shape and s u r f a c e c o n d i t i o n s , percent loading and the s i z e and density r a t i o s of the raw m a t e r i a l s on the r e d u c t i o n o f the i r o n o x i d e . Optimum r e s u l t s were reported f o r the reduction of p e l l e t s when the d c / d F e r a t i o was 0.36, and the C F l- x/Fe r a t i o was 0.4 at 1050°C. A l s o , the mixing patterns f o r a broad range of p a r t i c l e s and c y l i n d e r 35 sizes, at room temperature, were studied in depth by Henein 4 who conclu-sively determined the boundaries between slumping and ro l l ing motions in the bed of sol ids. He also investigated the kidney-shaped segregations of smaller particles formed in the centre of the bed; he showed as well that the Froude Number by i t s e l f (w2R/g) is not sufficient for scaling up purposes. The influence of coal reactivity on the SL/RN process also has been studied on a laboratory scale. The react iv i ty , coupled with redu-c i b i l i t y of iron oxide pel lets , was studied by Moeller et a l . . 1 2 2 For a coal size of -1 + 0.5 mm, previously devol at i 1 i z ed , they examined the following: i) Influence of ash on reducibi l i ty . i i ) Reactivity of coal as a function of ash content, i i i ) Softening behaviour of the ash. Dolomite was used as a desulphurizer and the reaction was conducted in an e l e c t r i c a l l y heated cylinder and monitored by gas analysis of CO. A high ash content was found to raise the temperature at which the soften-ing of the charge commences but, at the same time, to decrease produc-t i v i t y . The sui tabi l i ty of a broad range of Canadian coals, particular-ly l i g n i t e and sub-bituminous, for the SL/RN process was assessed by Meadowcroft et a l . . * 2 3 A standard test was performed by reacting 2 Kg of -15 + 9 mm fired pellets and 675 g of fixed carbon, as charred c o a l , in an externally heated rotary reactor. It was found that the lower the rank of the coal , the higher the degree of reduction obtained; a l s o , 36 t a k i n g i n t o account the gas composition, the temperature and f i x e d c a r -bon content of the char, the r e l a t i v e r e a c t i v i t y of l i g n i t e i s 180 times g r e a t e r than t h a t o f b i t u m i n o u s coal which, i n t u r n , i s 12 times more r e a c t i v e than a n t h r a c i t e . The r e a c t i v i t i e s of a broad range of c o a l s have been r e p o r t e d , i n g r a p h i c a l form, by Reuter e t a l . . 2 8 These are shown i n F i g u r e 2.6 and c o r r o b o r a t e the f i n d i n g s o f Meadowcroft e t al..123 Further aspects considered i n l a b o r a t o r y - s i z e k i l n s , when reduc-ing iron-oxide p e l l e t s , have been: i ) S t a t i s t i c a l optimization.95 i i ) Comparison of green vs. f i r e d pel lets.124 i i i ) Comparison of f i r e d p e l l e t s vs. ore lumps.125 i v ) Tendencies towards s i n t e r i n g of f i n e m a t e r i a l s . 8 0 v) Heat t r a n s f e r character!'sties. 126 v i ) A c c r e t i o n b u i l d up on the k i l n w a l l . 8 1 A set of isothermal e x p e r i m e n t s was performed by M o r r i s o n e t a l . , 9 5 where the e f f e c t s of three independent v a r i a b l e s , at f i v e l e v e l s each, were s t a t i s t i c a l l y evaluated. The v a r i a b l e s were: time, from 60 to 240 minutes; temperature, from 1000 to 1150°C and C p i x / F e r a t i o , from 0.3 to 1.0. Optimum c o n d i t i o n s , f o r a reduction higher than 95 percent, were o b t a i n e d between 1040 and 1100°C and at C F i x / F e r a t i o between 0.7 and 0.9. I t was suggested that long residence times, high C p i x / F e r a -t i o s and r e l a t i v e l y lower temperatures w i l l produce a well reduced p e l -l e t . On the other hand, the e f f e c t of heating rate and type of p e l l e t 1 f 37 2 0 I 0 Brown coal,Rhein,Germany >^ Huntly,New Zealand Forestburg,Canada 0.5 0.3 9 0 0 \ Gallup,U.S. "\_ Ch a r c o a l , B r a z i l X>^  Sama, Turkey O^eao . B r a z i l KQ S ingar en i , Ind i a „ „ n , OCharquedas,Brazil Cotgrave,England ^ ^ ' B l a i r A t h o l , A u s t r a l i a O Tavistock,South A f r i c a 0 > Anthrac ite,Germany Coke Breeze ^ » 1 I 1 9 5 0 1000 1050 Temperature of reduction (°C) 1100 2.6 R e a c t i v i t i e s o f d i f f e r e n t c a r b o n a c e o u s m a t e r i a l s as a f u n c t i o n o f t e m p e r a t u r e * 3 ! . 38 was t e s t e d by P e t e r s o n and P r a s k y , 1 ^ on a sample of 700 g of p e l l e t s (>67 p e r c e n t Fe) and 800 g of l i g n i t e ( C p i x = 33 percent) at 1020°C and 5 r.p.m., under a stream of 5 £/min of ni t r o g e n . The highest m e t a l l i z a -t i o n o b t a i n e d was 96 percent and the main d i f f i c u l t y encountered, when green p e l l e t s were reduced, was dust formation. Another set of compara-t i v e experiments, but t h i s time between p e l l e t s and ore lumps, was per-formed by Chatterjee and C h a k r a v a r t y . 1 2 5 By changing one v a r i a b l e at a time, they t e s t e d the f o l l o w i n g : temperatures from 900 to 1150°C, times of r e d u c t i o n from 120 to 150 minutes and ore/coal r a t i o from 1 to 1.2; the best c o n d i t i o n s found were f o r a p e l l e t / c o a l r a t i o o f 1.2, f o r 150 minutes a t 1050°C. The r e d u c t i o n o f f i n e r iron-oxide m a t e r i a l s has not been given much a t t e n t i o n to date. In t h e i r study of the reduction of s i n t e r , -3 + 0.8 mm, performed i n a continuously fed r o t a t i n g r e a c t o r and using gas-eous reducing agents, M u l l e t e t a l . 1 2 7 and N i x o n 1 2 8 claimed that a y i e l d of 90 percent reduction could e a s i l y be obtained without s t i c k i n g of the charge o r soot formation. This study was aimed at developing a process s i m i l a r t o the ACCAR p r o c e s s . 2 1 - 2 2 The r e s u l t s were analyzed by l i n e a r curve f i t t i n g the percent reduction to the temperature, time, ore s i z e , presence of unreacted hydrocarbons i n the reducing gas, r a t i o of H/C in the gas and to the reducing c a p a c i t y of the gas; out of these v a r i a b l e s , o n l y the temperature showed a l o g a r i t h m i c r e l a t i o n s h i p with the percent r e d u c t i o n . It was suggested t h a t s t i c k i n g of the charge i s r e l a t e d t o the formation of "hot spots," i . e . , l o c a l i z e d heating at c e r t a i n p o i n t s , owing to the heat t r a n s f e r c h a r a c t e r i s t i c s of the process. 39 In a study o f the r e d u c t i o n o f t i t a n i f e r o u s f i n e ores, Sucre-G a r c i a 8 concluded that a mixed con t r o l governed the r e d u c t i o n - and c a r -bon g a s i f i c a t i o n r e a c t i o n s at temperatures below 1000°C. The r e a c t a n t s used were d i f f e r e n t -149 ym t i t a n i f e r o u s ores and -600 +149 ym charred l i g n i t e , and the v a r i a b l e s studied were r o t a t i o n a l speed, c h a r - t o - o r e r a t i o , t emperature and pre-oxidation of the ores. The k i n e t i c s of the r e a c t i o n s were followed by a n a l y s i s of the e x i t gases f o r CO. A c c r e -t i o n s were observed to form, and hardly any change i n the reduction rate was observed with a change i n the r o t a t i o n a l speed from 18 to 30 r.p.m., i n d i c a t i n g t h a t good mixing'was achieved. F i n a l l y , the p o s s i b i l i t y of using a f i n e i r o n - o r e i n d i r e c t r e d u c t i o n was r e c e n t l y examined by ri a u s l e r , 1 2 9 - j n p i l o t - p l a n t r o t a r y k i l n s , a scanning e l e c t r o n microscope and r o t a r y c y l i n d e r s . The operational l i m i t a t i o n s were l o o k e d a t and the most important f i n d i n g s were: i ) The s i z e f r a c t i o n smaller than 300 ym should be kept at the low-e s t l e v e l p o s s i b l e , i i ) S u f f i c i e n t reduction was achieved with l i g n i t e coal at 900°C. i i i ) Between 700 and 800°C a s t r o n g d i s i n t e g r a t i o n of the m i n e r a l takes place, enhancing a c c r e t i o n s , i v ) The agglomerating behaviour of the sponge i r o n i s advantageous since i t y i e l d s up to 90 percent m e t a l l i z a t i o n , v) The agglomeration phenomenon decreases with the increment i n the amount o f h i g h r e a c t i v i t y c o a l ; i n other words, an absence of reductant at the end of the r e d u c t i o n p r o c e s s w i l l produce a strong s i n t e r i n g tendency in the charge due to r e o x i d a t i o n . 40 v i ) A d d i t i o n o f i r o n - s a n d s to the charge of f i n e i r o n concentrate i n h i b i t s the agglomeration tendencies. In summary, as can be seen i n T a b l e V I I , most of the s t u d i e s have focussed on the reduction of p e l l e t s i n e x t e r n a l l y heated r e a c t o r s , a t t e m p e r a t u r e s from 900 to 1150°C. As might be expected, the highest r e d u c t i o n has been o b t a i n e d a t higher temperatures and higher Cp-j x/Fe r a t i o s . At these temperatures however, the formation of undesirable ac-c r e t i o n s i s more l i k e l y . The amounts of excess carbon used, with r e -spect to the ' s t o i c h i o m e t r i c ' value, are high which produces a f a v o u r -able e f f e c t on the reduction rate but may reduce the reactor throughput. Furthermore, the rate of the reduction process v a r i e s c o n s i d e r a b l y , e s -p e c i a l l y a t the d e s i r e d lower t e m p e r a t u r e s , between p e l l e t s and f i n e i ron-ore concentrates. F i n a l l y , the formation of a c c r e t i o n s on the r e -a c t o r w a l l i s d i f f e r e n t i n the m e t a l l i c chamber used i n most of the ex-periments as compared to i t s r e f r a c t o r y material counterpart. 41 CHAPTER 3 SCOPE OF THE PRESENT WORK AND OBJECTIVES It becomes apparent from the foregoing d i s c u s s i o n t h a t the ma-j o r i t y of the previous research has been performed, e i t h e r on the reduc-t i o n k i n e t i c s of very small amounts of rather pure m a t e r i a l s Under s t a -t i c c o n d i t i o n s , i . e . , thermobalances, or on r e l a t i v e l y large r o t a r y r e -actors u s u a l l y i n v o l v i n g p e l l e t s , where the o p e r a t i o n a l parameters f o r r e d u c t i o n have been t e s t e d . C l e a r l y , n e i t h e r of the above two systems providesthe reduction k i n e t i c s information necessary to a i d i n the de-velopment o f a p r o c e s s f o r the r e d u c t i o n of unagglomerated i r o n ore f i n e s , with a low rank coal i n a rotary k i l n , which was the aim o f t h i s work. The d i f f e r e n c e s i n the reduction k i n e t i c s of the above mentioned two systems, when compared to the present work, are based e s s e n t i a l l y on the f o l l o w i n g c o n s i d e r a t i o n s : 1) The p a r t i c l e s s i z e , and consequently the r e a c t i n g surface area, d i f f e r s g r e a t l y between an average 12 mm diameter p e l l e t and the p a r t i c l e s to be studied here, with s i z e s smaller than 0.5 mm. L o g i c a l -l y , mass t r a n s f e r mechanisms w i l l play a l a r g e r r o l e i n the case of the reduction of p e l l e t s with the consequently lower o v e r a l l r a t e . 2) Good mixing c o n d i t i o n s are a c h i e v e d i n a r o t a t i n g system, f a c i l i t a t i n g intimate contact of the r e a c t i n g s o l i d s with t h e i r gaseous 42 r e a c t a n t s ; t h i s may be contrasted to s t a t i c - b e d systems where concentra-t i o n gradients within the s o l i d s m i x t u r e are more l i k e l y to d e v e l o p . F u r t h e r m o r e , the use of i n e r t gases to f l u s h the bed i n the l a t t e r case i s l i k e l y to have an e f f e c t on the l a t e r stages of r e d u c t i o n . 3) The r e a c t i v i t y of coal s t r o n g l y depends on i t s rank and, to a l e s s e r extent, on the d e v o l a t i l i z a t i o n t r e a t m e n t a p p l i e d to i t . In g e n e r a l , i t can be s a i d that the lower the coal rank the higher i t s r e -a c t i v i t y , which enhances the p o s s i b i l i t y of i t s g a s i f i c a t i o n a t lower t e m p e r a t u r e s . However, d i f f e r e n t r e a c t i v i t i e s f o r c o a l s of the same rank and subject to i d e n t i c a l d e v o l a t i l i z a t i o n treatments have been ob-s e r v e d ; t h i s d i f f e r e n c e can be a t t r i b u t e d to the g e o l o g i c a l o r i g i n of the c o a l . Thus, i t becomes necessary to u t i l i z e , i n the k i n e t i c s study; the c o a l type t h a t would most l i k e l y be used f o r an i n d u s t r i a l s c a l e process, since the i n f l u e n c e of the coal r e a c t i v i t y on the Boudouard r e -a c t i o n , and consequently on the reduction process, has been proved to be of utmost importance. A d e v o l a t i l i z a t i o n treatment f o r the c o a l , p r i o r to the r e d u c t i o n experiments, i s a l s o necesary. The presence of v o l a -t i l e s would make the r e d u c t i o n k i n e t i c s more d i f f i c u l t to f o l l o w and analyze. B e a r i n g i n mind the s e c o n s i d e r a t i o n s , the o b j e c t i v e s of t h i s work were: i ) To study the r e d u c t i o n k i n e t i c s of an unagglomerated iron-ore concentrate, u t i l i z i n g d e v o l a t i l i z e d low-rank c o a l s as r e d u c -t a n t , under well mixed c o n d i t i o n s approximating those of an i n -d u s t r i a l s c a l e rotary k i l n . 43 i i ) To e v a l u a t e the e f f e c t s o f s e v e r a l v a r i a b l e s on the reduction k i n e t i c s , namely temperature, f i x e d c a r b o n - t o - i r o n r a t i o , p a r -t i c l e s i z e , r o t a t i o n a l speed, type of c o a l , percent loading and the presence of a c a t a l y s t f o r the carbon g a s i f i c a t i o n r e a c -t i on. i i i ) To c h a r a c t e r i z e the agglomeration of the f i n e p a r t i c l e s w i t h i n the s o l i d s bed and against the furnace wall during r e d u c t i o n , i v ) To determine the most a p p r o p r i a t e o v e r a l l reduction k i n e t i c s model, i n v o l v i n g a l s o the carbon g a s i f i c a t i o n r e a c t i o n . Before the reduction experiments were c a r r i e d out, i t was essen-t i a l to define the optimum s o l i d s mixing c o n d i t i o n s , at room temperature and i n the same r e a c t o r , as an a i d to understanding the bed behaviour i n the reduction t e s t s . The ranges of some o f the o p e r a t i o n a l v a r i a b l e s were s e l e c t e d a c c o r d i n g to s i m i l a r i n d u s t r i a l c o n d i t i o n s and, although every e f f o r t was made to achieve mixing c o n d i t i o n s i n the bed that were the same as i n a la r g e k i l n , no attempt was made to obtain complete s i -m i l a r i t y between the la b o r a t o r y r e a c t o r and i t s i n d u s t r i a l c o u n t e r p a r t ; the g e o m e t r i c and heat t r a n s f e r c h a r a c t e r i s t i c s of a rotary k i l n have been proved d i f f i c u l t to sc a l e u p . 4 , 6 7 ' 1 2 0 Nonetheless, the reduction k i n e t i c s r e s u l t s obtained w i l l be the same r e g a r d l e s s o f the r e a c t o r s c a l e , provided the same well mixed c o n d i t i o n s p r e v a i l i n the bed and an equivalent heat source i s furni s h e d to maintain bed temperature. S i m i -l a r l y , the d e v o l a t i l i z a t i o n treatment a p p l i e d to the coal was performed under the same temperature c o n d i t i o n s as thos e p r e s e n t i n the r o t a r y k i l n . 44 CHAPTER 4 EXPERIMENTAL 4.1 Introduction A d e t a i l e d a c c o u n t o f the experimental techniques i s presented i n t h i s chapter. It includes the c h a r a c t e r i s t i c s o f the raw m a t e r i a l s used and t h e i r p r e p a r a t i o n , a d e s c r i p t i o n of the apparatus used i n the mixing and reduction experiments, the p r o c e d u r e s f o r the e x p e r i m e n t s t h e m s e l v e s and the e x p e r i m e n t a l d e s i g n f o r the v a r i a b l e s and l e v e l s t e s t e d . The m a t e r i a l s s t u d i e d , a s p i r a l i r o n - o r e concentrate from Carol Lake Mine, Quebec, and a sub-bituminous coal from Forestburg C o l l i e r i e s , A l b e r t a , were s e l e c t e d f o r t h i s study on the basis of t h e i r being r e a d i -l y a v a i l a b l e and i n p l e n t i f u l reserves; moreover, the r e l a t i v e l y h i gh r e a c t i v i t y o f the l a t t e r renders i t more s u i t a b l e , as was pointed out i n the previous chapter, f o r an i n d u s t r i a l operation a t lower temperatures, with i t s obvious advantages. A l a b o r a t o r y - s i z e r o t a r y k i l n was designed f o r the purposes of the mixing and the reduction experiments. The main feature of the k i l n was i t s heating system: an a x i a l l y p o s i t i o n e d s i l i c o n carbide r a d i a t i n g element which provided the energy r e q u i r e d to c a r r y out the r e a c t i o n s but, at the same time, d i d not i n t e r f e r e with the atmosphere produced by 45 the r e a c t i o n s . T h i s l a t t e r f a c t , c o u p l e d w i t h the hermetic s e a l i n g achieved i n the e n t i r e system, allowed a c a r e f u l g a s - f l o w measurement and a n a l y s i s to be performed throughout each experiment i n order to f o l -low the k i n e t i c s of the o v e r a l l reduction r e a c t i o n . The s i z e of the r e -a c t i o n chamber was l a r g e and able to contain a maximum of approximately 1.5 kg of s o l i d s . This amount was big enough to p e r m i t the assessment o f the e f f e c t s of the mixing v a r i a b l e s throughout the reduction and the mixing experiments; c l e a r l y , t h i s could not be a c h i e v e d u t i l i z i n g the t r a d i t i o n a l thermogravimetric approach. The room-temperature mixing experiments were h e l p f u l not only to determine the optimum mixing c o n d i t i o n s , as pointed out i n the p r e v i o u s chapter, but a l s o to a i d i n minimizing the number of experimental l e v e l s during the subsequent reduction t e s t s . Nevertheless, d e t e r m i n a t i o n s to o b t a i n the b e s t m i x i n g c o n d i t i o n s , i n the reduction experiments, were performed as w e l l . Furthermore, an experimental design was u t i l i z e d i n both c a s e s to a i d i n r e d u c i n g the l a r g e number of experiments which otherwise would have been necessary. 4.2 M a t e r i a l s and t h e i r preparation 4.2.1 Iron-ore concentrate The i r o n ore used i n the e x p e r i m e n t s was a commercial s p i r a l concentrate from Carol Lake Mine, Quebec. The s i z e d i s t r i b u t i o n and c h e m i c a l composition of the concentrate are shown i n Figure 4.1 and Ta-ble VIII r e s p e c t i v e l y . The main i r o n - b e a r i n g m i n e r a l o g i c a l component was specular hematite which had a high degree of c r y s t a l i n i t y , as shown Particle size (/im) P a r t i c l e s i z e d i s t r i b u t i o n o f s p i r a l i r o n - o r e c o n c e n t r a t e 47 TABLE VIII . CHEMICAL ANALYSIS OF SPIRAL IRON-ORE CONCENTRATE, FULL SIZE RANGE AND TWO SIZE FRACTIONS, -420 +300 and -106 +74 ym ~ - - - ~ _ J ^ t e r i a l F u l l s i z e range -420 +300 ym -106 +74 ym Species [<716 ym] d = 358 ym 3" = 90 ym Fe (Total) 65.80 66.7 66.5 FeO - 11.9 8.3 P 0.009 0.006 0.013 Mn 0.12 0.10 0.08 S i 0 2 4.70 3.60 2.90 Al 2 0 3 0.20 0.10 0.10 CaO - 0.40 0.30 MgO - 0.40 0.30 S - 0.002 0.002 N a 2 ° - 0.005 0.005 K 2 ° - 0.005 0.005 F e 2 0 3 ( c a l c ) - 82.20 85.90 H 20 3.50 0.06 0.20 48 i n Figure 4.2. The second most important i r o n species was magnetite and the gangue m a t e r i a l s were b a s i c a l l y s i l i c e o u s , mostly quartz. The ore was o v e n - d r i e d o v e r n i g h t and then sieved, i n t o narrow s i z e f r a c t i o n s , i n a G i l son p i l o t - p l a n t f a c i l i t y . The s i z e f r a c t i o n s chosen, among the e i g h t o b t a i n e d , were four: - 841 + 600 ym, - 420 + 300 ym, - 210 + 149 ym and - 106 + 74 ym. The amounts of m a t e r i a l r e -q u i r e d i n each s i z e f r a c t i o n were rather l a r g e owing to the number of experiments planned. Each f r a c t i o n was sampled f o r c h e m i c a l a n a l y s i s and i t s b u l k d e n s i t y was measured f o l l o w i n g the technique reported by H e n e i n . 4 The chemical a n a l y s i s and bulk d e n s i t i e s , i n the random loose and packed c o n d i t i o n s , f o r the d i f f e r e n t f r a c t i o n s r e l e v a n t to the ex-periments, are presented i n Table VIII and Table IX, r e s p e c t i v e l y . 4.2.2 Low rank c o a l s The c o a l used i n most o f the experiments was a sub-bituminous 'C type c o a l , from Forestburg C o l l i e r i e s , A l b e r t a . The proximate and ultimate analyses of the coal are presented i n Table X. The coal i n the as- r e c e i v e d c o n d i t i o n was d r i e d overnight i n a warmed-floor room, then c r u s h e d i n a hammer m i l l and screened i n t o narrow s i z e f r a c t i o n s , using the f a c i l i t y mentioned above. Again, each s i z e f r a c t i o n was sampled f o r c h e m i c a l a n a l y s i s and i t s bulk d e n s i t y was determined with the same technique as f o r the ore described above; bulk d e n s i t i e s f o r the s i z e f r a c t i o n s u t i l i z e d i n the experiments are presented i n Table IX. A l i g n i t i c c o a l , from Estevan, Saskatchewan, was used i n a few c o m p a r a t i v e e x p e r i m e n t s ; i t s proximate and ultimate analyses are pre-sented i n Table X. 4.2 SEM photograph of s p i r a l i r o n - o r e concentrate (lOOx) TABLE IX. RANDOM LOOSE AND PACKED BULK DENSITIES OF THE IRON-ORE CONCENTRATE AND THE FORESTBURG COAL, FOR DIFFERENT PARTICLE SIZES Material Mean P a r t i c l e Size Density [ y. m] [kg/m3] Loose Dense Iron ore 358 2455 2747 254 2439 2717 180 2384 2632 90 2504 2703 Coal 716 632 682 180 652 725 90 653 728 51 TABLE X. PROXIMATE AND ULTIMATE ANALYSES OF FORESTBURG COAL AND SASKATCHEWAN LIGNITE MEAN PARTICLE SIZES 718, 180 AND 90 ym M e a n W t i c l e Forestburg L i g n i t e s i z e [ym] 718 180 90 180 Proximate A n a l y s i s % % % % H 20 22.54 15.22 15.37 28.5 Ash 26.10 37.00 33.70 11.0 V o l a t i l e s 34.10 29.70 32.00 27.4 Fixed C 39.80 33.30 34.30 32.7 Ultimate A n a l y s i s (d.b) Carbon 51.91 44.53 45.52 60.80 Hydrogen 3.65 3.25 3.09 4.00 Nitrogen 1.10 0.96 0.98 0.10 Sulphur 0.62 0.57 0.60 0.70 Ash 26.10 37.00 33.70 15.90 Oxygen 16.62 13.69 16.11 18.50 52 4.2.3 C a t a l y s t Lithium, sodium and potassium carbonates of chemical p u r i t y were u t i l i z e d to prepare a c a t a l y s t mixture a c c o r d i n g to the t e c h n i q u e r e -p o r t e d by R a o . 1 3 0 An e q u i m o l a r m i x t u r e of the t h r e e carbonates was ground, melted and held a t 700°C f o r three hours under an i n e r t - g a s a t -mosphere. The melt was cooled, s o l i d i f i e d and ground again to a p a r t i -c l e s i z e l e s s than 150 vm, then stored under dry c o n d i t i o n s . The t o t a l amount of c a t a l y s t needed f o r the c a t a l y z e d experiments was produced i n a s i n g l e batch, to ensure that the mixture had the same p r o p e r t i e s i n every experiment. 4.3 Reduction Apparatus P r i o r to d e s c r i b i n g the a p p a r a t u s i n d e t a i l , a b r i e f o u t l i n e w i l l be given to provide an o v e r a l l p i c t u r e . The r e a c t o r , shown i n F i g -ure 4.3, c o n s i s t e d e s s e n t i a l l y of a short c y l i n d r i c a l s t e e l s h e l l , i n -side of which r e f r a c t o r y material was c a s t to give shape to the i n t e r n a l w orking chamber. The r e a c t o r could be s p l i t i n t o two s e c t i o n s , along i t s a x i s , to empty i t s contents a f t e r each experiment, and then b o l t e d back t o g e t h e r b e f o r e the next t e s t . The s t e e l s h e l l had openings at both ends on i t s a x i s , through which a heating element was p o s i t i o n e d . Two s t e e l p i p e s , f i r m l y supported by the support frame were attached to each of the openings of the r e a c t o r , to provide a route f o r the f l u s h i n g o f the i n e r t gas before the experiment was s t a r t e d , and f o r the e x i t i n g of the gaseous r e a c t i o n p r o d u c t s i n t o the f l o w r a t e measurement and a n a l y s i s t r a i n . The frame a l s o supported the trunnions upon which the Sampling point-* To exhaust hood flowmeters support Steel shell clamp •• •%•'•:•:/ AI 2Q 3 shield Teflon insert Castable AUO. v. -HlLSiljcone rubber gasket 1_ SiC heating element 4.3 Overall view of experimental set-up f o r reduction t e s t s 54 r e a c t o r r o t a t e d , powered by a chain and sprocket and motor system, l o -cated beneath the r e a c t o r . The r e a c t o r had t h r e e r a d i a l openings f o r purposes of s o l i d s feeding and sampling and i n t r o d u c i n g the thermocouple probe and the a c c r e t i o n s probe, r e s p e c t i v e l y . 4.3.1 Heating system The c o r e o f the h e a t i n g system was a s i l i c o n carbide r a d i a t i n g element p o s i t i o n e d along the a x i s of the r e a c t i o n chamber, as shown i n F i g u r e 4.3. A r e c r y s t a l l i z e d alumina tube, supported from one of the chamber ends, surrounded the element to p r o t e c t i t from f a l l i n g p a r t i -c l e s . The h e a t i n g element was secured i n p o s i t i o n by two water-cooled copper b u s - b a r s , one a t each end, which i n t u r n were h e l d by s t e e l b r a c k e t s , w i t h T e f l o n i n s u l a t i o n s l e e v e s , secured to the frame of the support assembly. Obviously a l l the d i f f e r e n t r o t a t i n g and s t a t i c parts of the system had to be c o n c e n t r i c around the heating element, since clearances between some parts were of the order of 5 mm. Even a minor m i s a l i g n m e n t c o u l d be o f d i s a s t r o u s consequences f o r the f r a g i l e e l e -ment, as was witnessed i n one i n s t a n c e . The power s o u r c e was a m u l t i -tap A.C. transformer, with proportional c o n t r o l , capable of d e l i v e r i n g 3 kW. 4.3.2 S e a l i n g system S e a l i n g was one o f the most important design f e a t u r e s , as well as the most d i f f i c u l t to achieve, c o n s i d e r i n g the c h a r a c t e r i s t i c s of the r o t a t i n g high temperature system, Figure 4.4. The system had to be a i r t i g h t because the reduction k i n e t i c s were to be assessed through the 4.4 Top view of rotary reactor showing s e a l i n g areas . 56 measurement of the flow rate and composition of gaseous products. Thus i f e i t h e r a i r leaked i n or gas leaked out, serious e r r o r s would be i n -troduced i n the k i n e t i c s e v a l u a t i o n . D i f f e r e n t m a t e r i a l s and c o n f i g u r a -t i o n s were t e s t e d i n terms of both minimum leakage and minimum bending s t r e s s on the heating element at the e x i t of the end pipes, regions A-A' i n Figure 4.4. The material chosen was a s i l i c o n e sponge, c a p a b l e of w i t h s t a n d i n g r e l a t i v e l y high temperatures 200°C) without l o s i n g i t s e l a s t i c p r o p e r t i e s . Thus s i l i c o n e sponge s l i c e s were l o c a t e d i n regions A-A 1 to provide s e a l s . Another key l o c a t i o n to be sealed was the j o i n t between the s t a t i c end-pipes flanges and the r o t a t i n g r e a c t o r , B-B' i n Figure 4.4. Here 15 x 15 mm s i l i c o n e sponge rings were f i x e d by glueing one of t h e i r faces unto a groove i n the steel s h e l l of the k i l n , w h i l e the opposite face was l u b r i c a t e d with a high-temperature M0S2 grease and s l i d compressed aga i n s t the face of each end-pipe f l a n g e . This compres-s i o n was a c h i e v e d by s i m u l t a n e o u s l y h a n d - f a s t e n i n g both e n d - p i p e s against the r i n g s through the use of two t h r e a d e d rods w i t h n u t s , as shown i n F i g u r e 4.4. The t h i r d i m p o r t a n t l o c a t i o n where the s e a l i n g sponge was used, seen as C-C i n Figure 4.4, was i n the j o i n t between the two s e c t i o n s of the s t e e l s h e l l comprising the r e a c t o r body. Here, a s t r i p of the material was glued to the edge of one o f the s h e l l s s e c -t i o n s b e f o r e the r e a c t o r was c l o s e d ; the s t r i p had to be replaced a f t e r every experiment, as opposed to the other seals which l a s t e d f o r several r u n s , because the combined e f f e c t o f compression and temperature de-stroyed i t s e l a s t i c i t y . The r e s t of the system gas l i n e s were s e a l e d w i t h s t a n d a r d vacuum g r e a s e . The e f f i c i e n c y of s e a l i n g achieved, as 57 w i l l be exp l a i n e d i n d e t a i l i n se c t i o n 4.7 of t h i s chapter, was qu a n t i -f i e d i n every experiment and was higher than 95 percent i n a l l cases. 4.3.3 B u i l d i n g m a t e r i a l s and dimensions The body of the rotary r e a c t o r i s shown i n F i g u r e 4.5 A and B and c o n s i s t e d of a c y l i n d r i c a l steel s h e l l 9.3 mm t h i c k , 512 mm long and 406 mm i n t e r n a l diameter. It could be s p l i t apart i n t o two s e c t i o n s , as shown i n Figure 4.5 A; the sect i o n s were j o i n e d at t h e i r edges by b o l t -ing the flanges together. The c i r c u l a r openings a t each end were 54 mm i n d i a m e t e r and the grooves around them f o r s e a l i n g purposes were 6 mm deep, 12.4 mm wide and 120 mm i n circumference. The i n t e r n a l r e f r a c t o r y l i n i n g , shown with f i n a l dimensions i n Figure 4.5 B, c o n s i s t e d of two co n c e n t r i c l a y e r s of casta b l e m a t e r i a l s . The i n n e r working l a y e r was 20 mm t h i c k made from C a s t o l a s t G, a high alumina material with thermophysical p r o p e r t i e s p r e s e n t e d i n T a b l e XI which can withstand higher temperatures but possesses a r e l a t i v e l y high thermal c o n d u c t i v i t y . The e x t e r n a l l a y e r was 113 mm t h i c k c a s t from P l i c a s t LWI24, w i t h p r o p e r t i e s presented i n Table XI, which provided the necessary thermal i n s u l a t i o n . The thickness of the r e f r a c t o r y l a y -e r s was determined by performing a heat balance on the system given the fo l l o w i n g c o n s t r a i n t s : i ) A maximum inner face temperature of 1100°C (1373 K). i i ) The need to contain about 1.5 kg of charge m a t e r i a l s i n the r e -ac t i o n chamber at 20 percent f i l l i n g . Steel tire \ T/c Slip ring L Cold junction ''dewar at AI2Q3tube End ^pipe 0-Brocket Rollers Figure 4.5. (A) Side view of open rotary reactor. 400 mm 406 mm PliCQSl _fc±. / / L.W.I. 2 4 •112 mm *| N" Feeding port -280 mm •! thermocouple ' y probe ~ M II 4 ^ . T T 140 I8C 54 0 1 0 mm A l 2 0 3 castable Charge Figure 4.5. (B) Central cross-sections of rotary reactor 59 TABLE XI. THERMOPHYSICAL PROPERTIES OF REFRACTORY MATERIALS USED IN THE REACTOR P l i c a s t LW1 24R C a s t o l a s t G Composition 46% A 1 2 0 3 , 38% S i 0 2 , 1.5% F e 2 0 3 , 94% A 1 2 0 3 1.5% T i 0 2 , 9% CaO, 1% MgO, 2% A l k a l i e s 6% Phosphates Density 1282 Kg/m3 2650 Kg/m3 Thermal c o n d u c t i v i t y 0.40 W/m K (at 815°C) 8.8 W/m K (1000°C) Maximum temperature 1050°C 1200°C 60 i i i ) A r e a s o n a b l y low e x t e r n a l s h e l l temperature of approximately 200°C (573 K). This was to enable use o f s i l i c o n e base mate-r i a l s to seal the system. The heat balance c a l c u l a t i o n s are presented i n Appendix A. The ends o f the r e a c t i o n chamber were c a s t i n a 45° c o n i c a l shape, as shown i n Figure 4.5 B, to minimize dead-zones which could a f -f e c t the mixing o f the p a r t i c l e s as the rea c t o r r o t a t e d . The r e f r a c t o r i e s , once they were c a s t i n s i d e the s h e l l , were f i r e d using the heating element f o l l o w i n g the manufacturer's s p e c i f i c a -t i o n s . However, when pr e l i m i n a r y t e s t s were conducted with the rea c t o r sealed, considerable amounts of water were found to deposit a t the co n -de n s e r s and even at the e x i t end-pipe. This was concluded to be due to the f a c t that the external l a y e r s of the r e f r a c t o r y were never a b l e t o reach the temperature necessary to release t h e i r water of c r y s t a l l i z a -t i o n , i . e . , about 400°C, thus the water could only be slowly released by d i f f u s i o n i n t o the r e a c t i o n chamber. Consequently, the whole r e a c t o r was baked i n a g a s - f i r e d furnace, at 500°C f o r 72 h o u r s , t o ensure a l l the water had been e l i m i n a t e d . Even then, i n subsequent t r i a l s , t r a c e amounts of water were s t i l l found which, most l i k e l y , r e s u l t e d from ad-s o r p t i o n from the s u r r o u n d i n g s d u r i n g i n t e r v a l s when the reactor was open. This f i n a l problem was f u l l y overcome by k e e p i n g the r e a c t o r c l o s e d and a t 500°C d u r i n g i d l e periods; needless to say that mainte-nance of a dry rea c t o r was e s s e n t i a l f o r the study of reduction using c o a l . 61 4.3.4 Rotating system A 1/4 h.p. v a r i a b l e speed motor with a 16 tooth d r i v i n g sprock-e t , shown i n Figure 4.3, was used to impart the r o t a t i o n to the r e a c t o r . A s t a n d a r d c h a i n , 25.4 mm p i t c h , l i n k e d the d r i v i n g sprocket to i t s 80 tooth counterpart that was b o l t e d to the r e a c t o r . Rotation was achieved v i a s t e e l t i r e s , seen i n F i g u r e 4.5 A, which rested on r o t a t i n g s t e e l trunnions supported by s t e e l b a l l bearings whose p i l l o w blocks were s e -cured to the frame of the s t r u c t u r a l assembly. Special care was paid to the f a c t that several attachments were to be protruding from the s h e l l , so enough c l e a r a n c e had to be allowed f o r them to r o t a t e f r e e l y . The maximum r o t a t i o n a l speed that could be i m p a r t e d to the r e a c t o r was 25 r.p.m.. 4.3.5 Feeding, sampling and emptying systems The r e a c t o r was provided with one feeding p o r t , shown in Figure 4.5 B, which a l s o c o u l d be used f o r s o l i d s sampling. The port was de-signed i n such a way as to feed the charging m a t e r i a l s i n a t a n g e n t i a l d i r e c t i o n , thus avoiding any p o s s i b l e damage to the f r a g i l e heating e l e -ment by thermal shock and chemical a t t a c k . A sampling probe, d e s c r i b e d below, c o u l d a l s o be i n t r o d u c e d through t h i s port i n t o the s o l i d s bed without the p o s s i b i l i t y of touching the element. The sampling probe, p r e s e n t e d i n Figure 4.6, c o n s i s t e d of two c o n c e n t r i c s t a i n l e s s s t e e l pipes, one of 9.3 mm and the other of 25.4 mm d i a m e t e r . The o u t e r p i p e , s l i g h t l y t a p e r e d f o r ease of i n t r o d u c t i o n through the feeding port, was c l o s e d at i t s top by a threaded cap which 62 4.6 Sampling probe configuration 63 allowed the movement of the inner pipe f o r purposes of opening and c l o s -ing the probe to take a s o l i d s sample. Argon gas was blown through the i n n e r p i p e and e x i t e d c l o s e to the s o l i d s sample to f a c i l i t a t e quench-ing and c e s s a t i o n of the r e a c t i o n . The i n e r t gas e x i t e d the o u t e r p i p e a t p o i n t B 5 shown i n F i g u r e 4.6. The s i z e of the sample obtained was between 1 and 3 grams. One more probe, i t s l o c a t i o n shown i n F i g u r e 4.5 B, was c a s t i n t o the r e f r a c t o r y to c h a r a c t e r i z e the p o s s i b l e formation of a c c r e t i o n s a g a i n s t the w a l l . The probe was made with the same r e f r a c t o r y thickness as the r e s t of the k i l n , to transmit the same heat by c o n d u c t i o n ; i t s exposed area at the r e a c t i o n chamber was 4.5 cm 2. In order to empty the r e a c t o r contents and to v i s u a l l y i n s p e c t the r e a c t i o n chamber a f t e r every experiment, the short end of the reac-t o r could be separated from the l a r g e r s e c t i o n , as shown i n F i g u r e 4.5 A, by f a s t e n i n g the former with two bolted brackets to i t s corresponding end-pipe f l a n g e . The end-pipe rested on a heavy p l a t f o r m t h a t had the c a p a b i l i t y to r o l l , l o n g i t u d i n a l l y with respect to the heating element, on four b a l l bearings over the s t r u c t u r a l assembly, to a l l o w a s e p a r a -t i o n of approximatley 25 cm between the two s e c t i o n s . 4.3.6 Temperature monitoring and c o n t r o l A quick response thermocouple probe, l o c a t e d at p o i n t A i n F i g -ure 4.5 B, was implemented a c c o r d i n g to previous work in t h i s depart-ment. 131 T h i s probe was used to monitor the temperature of the system during the t e s t s and contained three i n d i v i d u a l t h e r m o c o u p l e s : two a t the inner surface of the r e a c t i o n chamber and the other protruding 15 mm 64 i n t o the chamber. The d u p l i c a t e i n n e r - s u r f a c e thermocouples ensured c o r r e c t temperature measurement at t h i s p o i n t . The the r m o c o u p l e s were c h r o m e l - a l umel type 'K' wires of 0.76 mm diameter and t h e i r beaded ends were protected from erosion and chemical attack by applying a t h i n l a y -e r , l e s s than 1 mm t h i c k , o f alumina ceramic p a i n t . The thickness of the c o a t i n g , given the r e l a t i v e l y high c o n d u c t i v i t y of the alumina, i n -t r o d u c e d a n e g l i g i b l e thermal r e s i s t a n c e to the heat flow. The c o l d j u n c t i o n f o r the thermocouples, shown i n Figure 4.5 A, was an i c e f i l l e d thermos f l a s k r o t a t i n g with the r e a c t o r . The voltage s i g n a l s from any of the three thermocouples were t r a n s m i t t e d to a s l i p r i n g , w i t h the h e l p of a m u l t i p o s i t i o n s w i t c h , which i n t u r n t r a n s m i t t e d them to a chart recorder. The e l e c t r i c signal was al s o fed to the c o n t r o l l e r o f the power source. 4.3.7 Gas flow measurement and a n a l y s i s The gas flow measurement and sampling set-up i s shown i n F i g u r e 4.3. Above the gas-exit end-pipe a s o l i d s trap and c o o l e r were l o c a t e d . This was a water cooled copper pipe, 31 mm i n t e r n a l diameter, t h a t con-t a i n e d an i n t e r w o v e n mesh tof copper i n s i d e to trap s o l i d p a r t i c l e s en-t r a i n e d by the gas stream. A subsequent g l a s s condenser trapped most of the remaining dust and cooled the gas down to room temperature. The gas flow was d i r e c t e d , v i a tygon tubing, i n t o a s e t of b a l l rotameters, Gilmont s e r i e s 1, 2, 3 and 4. The rotameters were previous-l y c a l i b r a t e d , f o r a standard gas mixture of composition s i m i l a r to that e x p e c t e d to be obtained from the experiments, u t i l i z i n g a l i q u i d - s e a l e d gas meter f o r the higher flows and the soap-bubble method f o r the low 65 f l o w r a t e s . C a l i b r a t i o n curves f o r the rotameters are presented i n Ap-pendix B. The gas f l o w was d i v e r t e d a c c o r d i n g to i t s magnitude, by changing the tygon tubing coming from the second condenser, i n t o the ap-p r o p r i a t e flowmeter with the help of quick t e f l o n connectors which every r o t a m e t e r had a t i t s i n l e t end. The flows were always measured i n be-tween 15 and 80 percent of the maximum r e s p e c t i v e flowmeter c a p a c i t y w h ich, f o r the set of flowmeters, encompassed a flow rate range between 20 and 36000 cm 3/min. The pressure head at the flowmeter's i n l e t was measured with a u-tube manometer and ranged between 0.5 and 4 cm of wa-t e r ; the gas temperature was al s o measured at t h i s point with a thermo-meter. The gas sampling p o i n t , shown i n Figure 4.3, was l o c a t e d a f t e r the s e t of rotameters. The r e t e n t i o n time from the e x i t of the re a c t o r up to t h i s point v a r i e d , according to flow r a t e , between a few seconds and 8 minutes since the condensers and gas l i n e s had a volume of approx-i m a t e l y 3000 cm 3. The gas samples, of 60 cm 3, were taken with syringes through a rubber s e c t i o n of the gas l i n e , b e f o r e the gaseous p r o d u c t s were exhausted i n t o a fume hood. The sampling procedure i s explained i n d e t a i l i n s e c t i o n 4.7.3 of t h i s chapter. 4.4 Apparatus f o r Room-Temperature Mixing Experiments The same ro t a r y r e a c t o r , with some m o d i f i c a t i o n s f o r v i s u a l ob-s e r v a t i o n , was u t i l i z e d f o r the mixing experiments as was mentioned at the beginning of t h i s chapter. The arrangement, shown i n F i g u r e 4.7, c o n s i s t e d of removing the short s e c t i o n of the re a c t o r and r e p l a c i n g i t with a transparent, c o n i c a l l y shaped s e c t i o n , that corresponded to that 66 (b) 4.7 Equipment f o r room-temperature mixing experiments (A) Gen-er a l view; (B) D e t a i l view of a c r y l i c blade . 67 end of the r e a c t i o n chamber. It was p o s s i b l e i n t h i s manner to observe the way the s o l i d s bed behaved under d i f f e r e n t c o n d i t i o n s . An a u x i l i a r y device, shown i n Figure 4.7 B, was used to observe the degree of mixing at the c e n t r a l cross s e c t i o n of the bed. The de-v i c e c o n s i s t e d of a transparent p l a s t i c blade i n the shape of a segment s i m i l a r to the cross s e c t i o n a l area of the bed. A handle p e r p e n d i c -u l a r to the blade was used to p o s i t i o n and hold i t in place while a pho-tograph was taken. A 35 mm camera, with a macro l e n s , was u t i l i z e d to record the p a r t i c l e s d i s t r i b u t i o n behind the blade. 4.5 Coal Charring Equipment A s c h e m a t i c view o f the set-up to perform the coal d e v o l a t i l i -z a t i o n i s presented i n Figure 4.8. The set-up c o n s i s t e d i n a p r e - o x i d -i s e d s t a i n l e s s - s t e e l t r a y , able to contain 1 kg of c o a l . The tray was placed on the bone-ash f l o o r of a t o p - f i r e d gas furnace, above the e x i t of the p i p e which c a r r i e d i n e r t gas. The coal c o n t a i n i n g tray was co-vered with a l a r g e r , heavy Inconel tray t h a t , placed upside down against the furnace f l o o r , acted as a l i d to maintain an i n e r t atmosphere around the c o a l . A small opening was l e f t i n the bone ash a t one o f the c o r -n e r s , as shown i n F i g u r e 4.8, to allow the v o l a t i l e products to escape from the system and to be burnt o f f by the furnace flame. Four chromel-alumel thermocouples, marked i n Figure 4.8 as A,B, and C,D, were placed along the l o n g i t u d i n a l mid-section of the c o a l bed: two a t the c e n t e r and the o t h e r two a t one of the ends of the bed. In each of the l o c a -t i o n s , one thermocouple was p o s i t i o n e d a t the bottom and the o t h e r a t the mid-height of the bed. It was p o s s i b l e , i n t h i s way, to record the 68 Top view Thermocouples Gos exit Bone ash floor \ Burner Inconel cover Coal bed K ~ — 1 Inert gas IT ^S.S.'trdy Side view 4.8 Schematic view of coal d e v o l a t i l i z a t i o n equipment 69 t e mperature g r a d i e n t s c r u d e l y within the bed during the coal c h a r r i n g experiments. 4.6 Experimental Design and Va r i a b l e s The v a r i a b l e s and t h e i r l e v e l s , summarized i n Table XII and de-s c r i b e d below, were chosen i n order to obtain an o v e r a l l p i c t u r e o f the r e d u c t i o n p r o c e s s , under f e a s i b l e c o n d i t i o n s f o r an i n d u s t r i a l - s i z e operation. In p a r t i c u l a r , e f f e c t s on the mixing patterns, on the reduc-t i o n k i n e t i c s and on the agglomeration c h a r a c t e r i s t i c s of the iron - o r e and coal p a r t i c l e s were of concern. The v a r i a b l e s are presented i n the f o r t h c o m i n g sub-sections. The sequence of t e s t i n g the d i f f e r e n t l e v e l s and the r a t i o n a l e , are presented i n the ensuing Chapters 5 and 6. 4.6.1 V a r i a b l e s i n room-temperature mixing experiments The room-temperature m i x i n g e x p e r i m e n t s were performed u s i n g o n l y m i x t u r e s o f i r o n ore and F o r e s t b u r g c o a l ; the mixtures with the other carbonaceous m a t e r i a l s were assumed to follow the same m i x i n g be-h a v i o u r , s i n c e t h e i r d e n s i t i e s and s u r f a c e c h a r a c t e r i s t i c s were very s i m i l a r . The v a r i a b l e s and t h e i r r e s p e c t i v e l e v e l s t e s t e d were: i ) Coal to ore s i z e r a t i o , dc/d*F e. For each of the four ore p a r t i -c l e s i z e s , * 358, 254, 280 and 90 ym, four coal p a r t i c l e s i z e s * P a r t i c l e s i z e h e r e a f t e r d e f i n e d as the a r i t h m e t i c mean value between the two c l o s e s t U.S. s e r i e s screen openings. 70 TABLE XII. SUMMARY OF VARIABLES AND LEVELS TESTED. USING FORESTBURG COAL Experiments V a r i a b l e Symbol Levels Mixing Iron-ore mean p a r t i c l e d/p e 358, 254, 180, s i z e [ ym] 90 Coal to ore s i z e r a t i o d c / d p e 4, 2, 1, 0.5 F i x carbon to i r o n r a t i o Cpj x/Fe 0.45, 0.58, 0.71, 0.84 Rotational speed [r.p.m.] w 5, 15 Percent volume f i l l e d [%] % L 12, 20 Reduction Temperature of r e a c t i o n [°C] Rotational speed [r.p.m.] F i x carbon to i r o n r a t i o Percent volume f i l l e d [%] Iron-ore mean p a r t i c l e s i z e [ym] Coal to ore s i z e r a t i o T 800, 850. 900, 950 a) • 7, 11, 14, 17, 20 Cpix/Fe 0.16. 0.24, 0.32 0.48, 0.64 % L 7, 14 " d / F e 358, 90. d c / d F 0.5, 1, 2 71 were used i n o r d e r to obtain d c/dp e r a t i o s of approximately 4, 2, 1 and 0.5. Adding together the we i g h t of t h e s e s i z e f r a c -t i o n s accounts f o r approximately three quarters of the weight of the a s - r e c e i v e d ore. i i ) F i x e d carbon to i r o n r a t i o , CFix/Fe. Four l e v e l s were t e s t e d : 0.45, 0.58, 0.71 and 0.84 which correspond to 180, 260, 340 and 400 p e r c e n t e x c e s s o f c a r b o n , r e s p e c t i v e l y , according to the stoichiometry of Equations (2.1) and (2.2). i i i ) R o t a t i o n a l speed, u> • Two l e v e l s were t e s t e d , 5 and 15 r.p.m. which cover the range of i n d u s t r i a l c o n d i t i o n s , when the Froude Number (Fr = w 2 R/g) - j S u s e c j a s a s i m i l a r i t y c r i t e r i o n . The me-dian p o i n t , 10 r.p.m., was t e s t e d i n some experiments. i v ) P e r c e n t l o a d i n g , % L. Two l e v e l s were t e s t e d , 12 and 20 per-cent, which again covers the range of volume f i l l i n g i n i n d u s -t r i a l o p e r a t i o n . 4.6.2 V a r i a b l e s i n reduction experiments The v a r i a b l e s t e s t e d i n the reduction experiments were: i ) Coal t y p e . The reduction k i n e t i c s were c h a r a c t e r i z e d f u l l y f o r the Forestburg, sub-bituminous c o a l . Comparative t e s t s were performed w i t h the Saskatchewan L i g n i t e and, i n one case, with electrode-grade g r a p h i t e , i i ) R e d u c t i o n Temperature, T. Four i s o t h e r m a l temperatures were t e s t e d , 800, 850, 900 and 950°C. Although they are comparative-l y low w i t h respect to present i n d u s t r i a l o p erations, the reac-t i v i t y o f the F o r e s t b u r g c o a l r e p o r t e d i n the 1 i t e r a t u r e ! 2 3 72 i n d i c a t e d t hat carbon g a s i f i c a t i o n , and the corresponding reduc-t i o n , were f e a s i b l e a t these temperatures a t r e a s o n a b l e r a t e s and with l e s s p a r t i c l e agglomeration, i i i ) F i x e d carbon to i r o n r a t i o , C p i x / F e . Again f i v e l e v e l s were t e s t e d : 0.16, 0.24, 0.32, 0.48 and 0.64 which correspond to 0, 50, 100, 200 and 300 percent excess carbon with respect to the minimum s t o i c h i o m e t r i c r e q u i r e m e n t s o f E q u a t i o n s (2.1) and (2.2). i v ) Coal to ore s i z e r a t i o , d c / d p e a Two l e v e l s , 0.5 and 2, were tested f o r the 358 ym ore p a r t i c l e s and one l e v e l , 1, was t e s t e d f o r the 90 ym ore p a r t i c l e s , v) Rotational speed, co . Five speeds were t e s t e d , 7, 11, 14, 17 and 20 r.p.m. u n t i l no f u r t h e r a p p r e c i a b l e e f f e c t was o b s e r v e d on the reduction r a t e . v i ) P e r c e n t l o a d i n g , % L. Two l e v e l s were t e s t e d , 7 and 14 per-cent. 4.6.3 Experimental design As can r e a d i l y be o b s e r v e d from the number o f v a r i a b l e s and l e v e l s involved f o r each type of the experiments c o n s i d e r e d above, the number o f p o s s i b l e e x p e r i m e n t a l combinations i s rather high: l a r g e r than 250 f o r the mixing t e s t s and about 600 f o r the r e d u c t i o n e x p e r i -ments. C l e a r l y , some c o n s i d e r a t i o n s had to be a p p l i e d i n order to r e -duce those f i g u r e s and y e t obtain the o v e r a l l p i c t u r e of the experiment-al system here s t u d i e d . Thus: 73 i ) D u r ing the room-temperature m i x i n g e x p e r i m e n t s , the extreme values of the v a r i a b l e s were f i r s t t e s t e d and, i f a s i g n i f i c a n t e f f e c t on the m i x i n g was not observed, the intermediate values were discarded. The f u l l range of the v a r i a b l e s was checked a t l e a s t once f o r one i r o n - o r e s i z e however, i i ) In the reduction experiments, the e f f e c t of the r o t a t i o n a l speed was a s s e s s e d o n l y a t the Cp-j x/Fe r a t i o s of 0.16 and 0.64 and 900°C of temperature. This temperature ensured an a p p r e c i a b l e r a t e and the two v a l u e s o f the Cp-j x/Fe r a t i o enclose the f u l l range to be t e s t e d , i i i ) A l s o i n the r e d u c t i o n experiments, the e f f e c t of Cp-j x/Fe r a t i o was evaluated, again, at the high temperature (900°C) to ensure an a p p r e c i a b l e r a t e a t a l l the Cp-j x/Fe l e v e l s . In t h i s case however, the r o t a t i o n a l speed was kept a t the lower l e v e l (7 r.p.m.) because the e f f e c t o f Cp-i x/Fe was g r e a t e r a t low speeds. The above c o n s i d e r a t i o n s reduced the number of experiments to a manageable s i z e , and replaced the experimental design which had o r i g i n -a l l y been planned, f o r the reduction experiments. This was a f r a c t i o n a l f a c t o r i a l design of four v a r i a b l e s a t f o u r l e v e l s each, t h a t was a l s o discarded f o r the f o l l o w i n g reasons: i ) The i n t e r a c t i o n s between some p a i r s of v a r i a b l e s could not be neglected, as i s assumed i n that kind of design. 74 i i ) In o r d e r to f u l f i l l the symmetry of the design, some v a r i a b l e s would have had to have been t e s t e d a t a number of l e v e l s t h a t was not necessary, i i i ) In order to perform the s t a t i s t i c a l a n a l y s i s of the experimental design, and thus make f u l l p r o f i t of i t s p r o p e r t i e s , a t l e a s t one r e p l i c a t i o n of each experiment would have been required and so, again, the number of experiments would have been doubled. 4.7 Experimental Procedures A d e s c r i p t i o n o f each o f the t h r e e t y p e s of experiments, f o r mixing-, c h a r r i n g - and reduction s t u d i e s , i s presented i n t h i s s e c t i o n . 4.7.1 Room-temperature mixing experiments This group of experiments was c a r r i e d out i n the equipment de-s c r i b e d i n s e c t i o n 4.4 above. The aim of the testwork was, as has been stated i n s e c t i o n 4.1 of t h i s chapter, to determine optimum m i x i n g con-d i t i o n s o f the coal-ore mixtures previous to the reduction experiments. This was achieved through v i s u a l observation of the type of bed motion and photographic recording of the d i s t r i b u t i o n of s o l i d p a r t i c l e s . The sequence of operation was as f o l l o w s . The i r o n - o r e and c o a l p a r t i c l e s mixture was prepared, with the p r e d e t e r m i n e d d c / d p e s i z e r a t i o , by adding small amounts of each com-ponent i n t o a 1000 cm 3 graduated c y l i n d e r , and hand mixing them c a r e f u l -l y each time, u n t i l the volume necessary f o r the d e s i r e d percent loading was f i l l e d . A graph, shown i n Figure 4.9, was prepared i n advance f o r easy reference to e s t a b l i s h the r e l a t i o n s h i p s amongst percent l o a d i n g , 75 4.9 Graph showing bed volume and depth as a fun c t i o n of per-cent loading f o r a r e a c t o r 14 cm in diameter . 76 bed volume and bed depth f o r the r e a c t o r . The weights of each component were r e c o r d e d f o r subsequent t e s t s with the same d c/dp e and Cpix/Fe r a -t i o s . The mixture was then fed i n t o the r e a c t o r and the r o t a t i o n s t a r t -ed a t the d e s i r e d r.p.m. (measured with a hand tacometer), kept f o r 30 minutes and stopped. The bed behaviour was taken to be t h a t o b s e r v e d d u r i n g the l a s t f i v e minutes o f r o t a t i o n . There i s evidence i n the 1 i t e r a t u r e l Z l t h a t complete mixing i s obtained i n l e s s than 25 r e v o l u -t i o n s ; t h i s c o n d i t i o n was achieved even a t the low r o t a t i o n a l s p e eds, i . e . , 5 r.p.m. The type of bed motion observed was recorded according to the c l a s s i f i c a t i o n of s l i p p i n g , slumping and r o l l i n g r e p o r t e d by He-n e i n . 4 The t r a n s p a r e n t end of the chamber was removed and the p l a s t i c blade was c a r e f u l l y placed at the c e n t r a l cross s e c t i o n area of the so-l i d s bed, as has been shown i n Figure 4.7 A. The p a r t i c l e s which r e -mained i n f r o n t were brushed away with great care, i n order not to d i s -t u r b the bed b e h i n d the b l a d e , and a photograph was taken. (A great advantage f o r t h i s purpose was the f a c t that there was a l a r g e c o n t r a s t i n c o l o r between the two t y p e s o f p a r t i c l e s . ) The reactor was then emptied and the m a t e r i a l s discarded. 4.7.2 Coal c h a r r i n g experiments One k i l o g r a m o f c o a l , t h a t had been stored a f t e r screening i n t i g h t l y c l o s e d p l a s t i c bags, was put i n t o the s t a i n l e s s ste e l tray which then was placed i n the set-up described i n s e c t i o n 4.5 and shown i n F i g -ure 4.8. The argon flow was s t a r t e d a t 1500 cm 3/min and the gas f i r e d furnace was l i t . The valves f o r gas and a i r were c o n t r o l l e d i n order to produce a heating rate of approximately 9°C/min, which has been reported 77 to be the h e a t i n g r a t e f o r the m a t e r i a l s i n an i n d u s t r i a l s i z e r o t a r y k i l n , 1 u n t i l the center region of the coal bed temperature reached 900°C (1173 K); t h i s was achieved i n approximately 100 m i n u t e s , and the c o a l was then kept at t h i s temperature f o r the d e s i r e d period of time, a f t e r which, the furnace was turned o f f and the char was allowed to cool over-night with the argon flowrate maintained at 1000 cm^/min. Once the char reached room temperature, i t s weight was recorded, a 10 gram sample was taken and stored again i n a sealed p l a s t i c bag. 4.7.3 Reduction experiments The c o r e o f t h i s study was the reduction experiments. Several p r e l i m i n a r y t r i a l s had to be c a r r i e d out, with an ever i n c r e a s i n g degree of success, u n t i l the optimum procedure was a t t a i n e d ; the d e s c r i p t i o n of t h i s procedure f o l l o w s . The amount of the i r o n - o r e and coal mixture, f o r a given Cpix/Fe and d c / d p e r a t i o s , was prepared f o l l o w i n g the same procedure as the one used f o r the room-temperature mixing experiments, j u s t described i n sec-t i o n 4.7.1. The only n o t i c e a b l e d i f f e r e n c e was the weight r a t i o of ma-t e r i a l s , since the f i x e d carbon content i n the char had obviously chang-ed during the d e v o l a t i l i z a t i o n process. The r e a c t o r , which was kept at 500°C during the i d l e periods to prevent re-adsorption of m o i s t u r e , was s e t the n i g h t p r e v i o u s to the e x p e r i m e n t , a t 75°C above the d e s i r e d t e s t temperature. Thus by the time the experiment was s t a r t e d the l a r g e r e f r a c t o r y mass of the r e a c t o r had already a t t a i n e d near steady-state thermal e q u i l i b r i u m with i t s sur-roundings. The reason f o r superheating the r e f r a c t o r y was the f a c t t h at 78 when the charge m a t e r i a l s were introduced, a sharp drop i n the set tem-perature in the r e a c t i o n chamber was o b s e r v e d . The r e a c t o r was then sealed, paying s p e c i a l a t t e n t i o n to the c r i t i c a l s e a l i n g areas, designed by A-A' and B-B1 i n f i g u r e 4.4. Argon flow was s t a r t e d to f l u s h the a i r from the system f o r about 45 minutes; meanwhile the a i r and standard gas samples of composition shown i n T a b l e X I I I , were a n a l y z e d i n the gas chromatograph, a P e r k i n - E l m e r , Sigma 38 dual column gas chromatograph whose operating c o n d i t i o n s are presented i n T a b l e XIV. The chromato-graph had a peak a r e a i n t e g r a t o r and a c h a r t recorder attached to i t . The columns were a 0.3 x 180 cm f i l l e d with Porapak 1N' material f o r CO2 a n a l y s i s and a 0.3 x 300 cm column f i l l e d with a molecular s i e v e , MS 5A, f o r the a n a l y s i s of hydrogen, oxygen, n i t r o g e n , and carbon monoxide. At l e a s t three samples of each gas were run and the r e s p e c t i v e peak a r e a counts f o r each gas component were averaged. The r e l a t i v e e r r o r between the counts was, i n almost a l l cases, smaller than one percent. The a i r - t i g h t n e s s e f f i c i e n c y of the r e a c t o r , h e r e a f t e r r e f e r r e d to as e f f i c i e n c y , was then a s s e s s e d by comparing the amount of argon g o i n g i n to t h a t g o i n g out of the system, using two i d e n t i c a l flowme-t e r s , at an input flowrate of 7000 cm3/min; the e f f i c i e n c y was c a l c u l a t -ed, by s u b t r a c t i n g the output from the input and d i v i d i n g by the i n p u t , and r e c o r d e d as the s t a r t i n g value. The c o l d j u n c t i o n f l a s k was f i l l e d with crushed i c e and the two thermocouples at the chamber face were com-pared a g a i n s t each other, as a check to ensuring both were working. At t h i s p o i n t , the temperature control was turned down to the s e t tempera-t u r e and, i m m e d i a t e l y , the f e e d i n g port opened and the s o l i d s mixture q u i c k l y but s t e a d i l y poured i n t o the r e a c t o r with the help of a f u n n e l . TABLE XIII. CERTIFIED-GRADE STANDARD GAS COMPOSITION Gas % Ar 1.07 H 2 4.04 C0 2 20.10 CO 74.79 TABLE XIV. GAS CHROMATOGRAPH OPERATING CONDITIONS C a r r i e r gas Argon Oven temperature 105°C In j e c t o r and detector temperatures 130°C Pressure of i n j e c t i o n 22 p.s. 80 The p o r t was t i g h t l y c l o s e d , the r o t a t i o n s t a r t e d to the des i r e d r o t a -t i o n a l speed and the argon f l o w s t o p p e d ; the measurements were thus i n i t i a t e d . The chamber and s o l i d s temperature, shown i n Figure 4.10, dropped sharply but, because of the superheating provided, r e c o v e r e d t o the s e t temperature w i t h i n 10 minutes and at the higher temperatures, before 6 minutes. The gas f l o w r a t e measurement at every time i n t e r v a l , was f o l -lowed by a gas sample, w i t h i n a maximum of 10 seconds. The f i r s t meas-urement and sample were taken, i n v a r i a b l y , 2 minutes a f t e r the s t a r t and then, i n most cases, every 2 minutes u n t i l 20 minutes, e x c e p t when the r e a c t i o n was expected to proceed f a s t e r , whereupon the measurements were taken every minute. From then on, the r e a d i n g s were spaced a t l a r g e r i n t e r v a l s , up to a maximum o f 30 minutes which was maintained f o r the r e s t of the experiment. The gas flow was p r o g r e s s i v e l y d i v e r t e d t o the smaller c a p a c i t y flowmeters as the r e a c t i o n rate dropped, but since most of the gas f l o w r a t e s produced were between 2000 and 12000 cm 3/min and at the higher rates there was some small entrainment of very f i n e c o a l d u s t , two flowmeters w i t h t h i s c a p a c i t y were used, a l t e r n a t e l y being cleaned i n between measurements. The gas samples s t a r t e d to be analyzed i n the gas chromatograph before 30 minutes had elapsed from the time of taking them, which i s well w i t h i n the considered safe storage p e r i o d o f one h o u r . 1 3 2 The measurements continued u n t i l the r e a c t i o n p r a c t i c a l l y stop-ped, i . e . , at flow rates of about 80 cm 3/min. The argon flow was s t a r t -ed, the power turned o f f and the e f f i c i e n c y o f the system d e t e r m i n e d again; the o v e r a l l e f f i c i e n c y was considered to be the a r i t h m e t i c mean 9 5 0 T Charge introduction 5 10 Time (min) 4.10 Reaction chamber temperature as a fun c t i o n of time oo 82 of the i n i t i a l and f i n a l values. The r o t a t i o n was stopped then, and the reac t o r l e f t to cool overnight with an argon flow of approximately 1000 cm^/mi n. The r e a c t o r was s p l i t a p a r t, a f t e r the argon flow had been stop-ped, and the contents were c a r e f u l l y emptied onto a t r a y . They were im-mediately t r a n s f e r r e d i n t o a f l a s k t h at was t i g h t l y c l o s e d with a rubber stopper, to avoid any r e o x i d a t i o n o f the f r e s h p r o d u c t s . The s e a l , shown by C - C i n f i g u r e 4.4, was replaced, the rea c t o r c l o s e d back and the power s t a r t e d again. The r e a c t i o n s o l i d products were sieved i n t o narrow s i z e f r a c -t i o n s , from 2000 ym down to 74 pm, in standard T y l e r screens. The d i f -ference between the ir o n - o r e and coal p a r t i c l e s s i z e was a b i g advantage f o r t h i s purpose, except at the f i n e s t s i z e s (smaller than 140 ;pm) when a sample had to be taken and separated magnetically to obtain the pro-ducts d i s t r i b u t i o n ; t h i s was a l s o the case when the e x p e r i m e n t s w i t h d c / d p e o f 1 were p e r f o r m e d . In a l l cases, a sample of about 20 grams was taken from each s i z e f r a c t i o n , t o be examined under the s c a n n i n g e l e c t r o n m i c r o s c o p e ; t h e s e samples were kept i n s i d e t i g h t l y sealed v i a l s . 83 CHAPTER 5 RESULTS OF ROOM-TEMPERATURE MIXING EXPERIMENTS The r e s u l t s of the room-temperature mixing experiments are p r e -sented i n t h i s chapter. The experiments were performed i n the apparatus described i n Section 4.4 (Figure 4.7) f o l l o w i n g the technique p r e s e n t e d i n S e c t i o n 4.7.1. A summary of the experimental c o n d i t i o n s and r e s u l t s i s t abulated i n Appendix C, and only a synopsis of the r e s u l t s , to i l -l u s t r a t e the o b s e r v e d p a t t e r n s , the type of bed motion and degree of mixing, i s presented i n the forthcoming s e c t i o n s . The type o f bed motion and the corresponding mixing of the par-t i c l e s were determined by v i s u a l observation. Bed motion was c a t e g o r -i z e d according to the d e f i n i t i o n s of s l i p p i n g , slumping, r o l l i n g and ca-t a r a c t i n g , as given by Henein e t al..133 p a r t i c l e mixing was c h a r a c t e r -i z e d i n terms of three defined 'degrees' o f m i x i n g , as i l l u s t r a t e d i n Figure 5.1, namely: i ) S e g r e g a t e d c o n d i t i o n : i n which there e x i s t e d a sharply defined c o r e , or " k i d n e y , " 4 o f i r o n - o r e p a r t i c l e s w i t h i n the bed, (A) and (B) i n Figure 5.1. (A) (B) D e f i n i t i o n o f b o u n d a r i e s o f degree o f m i x i n g . C o n d i t i o n s d =358ym; C_. /Fe=0.45; 15 r.p.m.; 20% l o a d i n g ; d /d„ r e r I X c Fe f o r ( A ) , 4.464; (B) , 2.000 ; (C) , 1. 285; (D) , 1,000; (E) 0.714; and ( F ) , 0.503. (A) and ( B ) , s e g r e g a t e d bed; (C) and (D), t r a n s i t i o n a l c o n d i t i o n and (E) and ( F ) , w e l l -mixed bed. F i g u r e 5.1 (Continued) Figure 5.1 (Continued) 87 i i ) T r a n s i t i o n a l c o n d i t i o n : i n which some regions i n the c r o s s -s e c t i o n of the bed showed a h i g h e r c o n c e n t r a t i o n o f i r o n - o r e p a r t i c l e s , without well defined boundaries, (C) and (D) i n F i g -ure 5.1. i i i ) Well mixed c o n d i t i o n : i n which a l l the iron-ore p a r t i c l e s were evenly d i s t r i b u t e d over the c r o s s - s e c t i o n o f the bed, (E) and (F) i n Figure 5.1. The degree o f m i x i n g was estimated at the conclusion of the experiment and a l s o checked agai n s t photographs which were taken. I t i s i m p o r t a n t to s t a t e a t t h i s p o i n t t h a t a x i a l segregation was not measured within the s o l i d s bed. Axial s e g r e g a t i o n was not ex-p e c t e d f o r t h i s r e a c t o r s i z e ; 134 moreover, the c o n i c a l shape of the chamber ends, and the c a r e f u l l e v e l i n g of the r e a c t o r p r i o r to each ex-p e r i m e n t , helped to minimize a x i a l e f f e c t s . This f a c t was corroborated by the observation of the same s i z e of segregation kidney, at the t r a n s -parent end of the r e a c t o r and at the c e n t r a l c r o s s - s e c t i o n of the s o l i d s bed, during the experiments. 5.1 E f f e c t of p a r t i c l e - s i z e r a t i o The s i n g l e most important v a r i a b l e to a f f e c t bed motion patterns and degree of mixing was the d i f f e r e n c e i n s i z e between the iron-ore and c o a l p a r t i c l e s . C o n s e q u e n t l y , o f the v a r i a b l e s s t u d i e d , the l a r g e s t number o f v a l u e s were t e s t e d f o r the d c/dp e s i z e r a t i o throughout the e x p e r i m e n t a l programme. Nine v a l u e s o f d^/dp e were s t u d i e d , i n the range between 4 and 0.5, f o r the four s i z e s of i r o n - o r e p a r t i c l e s . F o r 88 the t e s t s i n v o l v i n g the l a r g e s t i r o n - o r e p a r t i c l e s i z e , 358 ym, the other v a r i a b l e s were maintained constant a t the f o l l o w i n g values: r o t a -t i o n a l speed a t 5 and 15 r.p.m., C F i x / F e r a t i o a t 0.45 and 0.84, and percent l o a d i n g at 12 and 20 percent. For the remaining three i r o n - o r e p a r t i c l e s i z e s , the other v a r i a b l e s were t e s t e d only at 5 and 15 r.p.m., Cpix/Fe r a t i o of 0.45 and 20% percent l o a d i n g . I t was observed during these t e s t s that r o l l i n g motion predomi-n a t e d a t the l a r g e r v a l u e s o f dc/cfFe and o f i r o n - o r e p a r t i c l e s i z e . Slumping, on the other hand, appeared a t lower l e v e l s o f these v a r i -a b l e s . An uneven type of motion, a l t e r n a t i n g between unsteady slumping and c a t a r a c t i n g , was observed, a t 15 r.p.m. f o r the smallest d c/dp e r a -t i o , i n each t e s t ; an assessment of t h i s behaviour i s p r e s e n t e d i n the di s c u s s i o n s e c t i o n . The d c / d p e s i z e r a t i o exerted a strong i n f l u e n c e on the degree of p a r t i c l e mixing as w e l l , as can be seen i n Figure 5.1. The best mix-ing was obtained f o r the smaller values of both 3 c/dp e and iron- o r e par-t i c l e s i z e . As shown i n Figure 5.2 r e l a t i v e l y good mixing, was obtained even a t a d c/cip e of 4 f o r the small coal p a r t i c l e s i z e . Segregation i n the bed was p r e s e n t with l a r g e r values of d c/dp e and ir o n - o r e p a r t i c l e s i z e ; see Figure 5.1, (A) to (D). 5.2 E f f e c t of r o t a t i o n a l speed At 5 and 15 r.p.m. l e v e l s , there was a no t i c e a b l e e f f e c t of the r o t a t i o n a l speed on the type of bed motion. The four i r o n - o r e p a r t i c l e s i z e s (358, 254, 180 and 90 ym) were t e s t e d , at a l l the other v a r i a b l e 89 E f f e c t of d /d siz e r a t i o on the degree of mixing for 90 ym iron-8re p a r t i c l e s . Conditions: c F i x / F e = 0.4 5; 15 r.p.m. and 20% loading. 90 l e v e l s , . f o r each r o t a t i o n a l speed. At 5 r.p.m. the bed motion a l t e r n a t -ed, w i t h i n each experiment, between slumping and r o l l i n g a t the l a r g e r v a l u e s o f ore s i z e and cT c/^Fe r a t i o . At the smaller values, however, the bed motion was e s s e n t i a l l y slumping; some uneven bed motion was ob-s e r v e d i n t e s t s i n v o l v i n g the smalles t coal p a r t i c l e s (90 ym). At 15 r.p.m., on the other hand, the bed motion o b s e r v e d was r o l l i n g under most c o n d i t i o n s . Some slumping motion was obtained, however, when the smallest coal p a r t i c l e s were t e s t e d . Some experiments were c a r r i e d out a t 10 r.p.m., to a i d i n d e f i n i n g more s h a r p l y the s l u m p i n g - r o l l i n g boundary, but they revealed the same motion as at 15 r.p.m.. The degree of mixing of p a r t i c l e s was not a f f e c t e d by r o t a t i o n -al speed i n the range of 5 to 15 r.p.m. even though d i f f e r e n t t y p es o f bed motion were o b s e r v e d . T h i s i s c l e a r l y i l l u s t r a t e d i n Figure 5.3, which shows close-up photographs of the bed, without the p l a s t i c b l a d e , a f t e r being subjected to the minimum and maximum r o t a t i o n a l speeds. 5.3 E f f e c t of fixed-carbon to i r o n r a t i o The C p i x / F e has no appreciable e f f e c t on the type of bed motion over the range 0.45 to 0.84. The l e v e l s a t which the o t h e r v a r i a b l e s were m a i n t a i n e d d u r i n g t h e s e t e s t s , were ^ c/dpe °f 4, 2, 1, and 0.5; percent loading of 12 and 20; r o t a t i o n a l speed of 5 and 15 r.p.m.. The degree of m i x i n g of p a r t i c l e s was a f f e c t e d by athe C p i x / F e r a t i o , as shown i n Figure 5.4, but only with respect to the depth of the c o a l s u r f a c e l a y e r , i n the experiments where segregation was present; the c o a l surface l a y e r was s l i g h t l y deeper when C p i x / F e was 0.84. This e f f e c t was not observed when well-mixed c o n d i t i o n s were present. 5 r.p.m. 15 r.p.m. 5.3 E f f e c t of r o t a t i o n a l speed on t h e degree of m i x i n g f o r 180 um i r o n - o r e p a r t i c l e s . C o n d i t i o n s : d c / d F e = 0.5; C„. /Fe = 0.4 5 and 20% l o a d i n g . F i x 92 C: . /Fe - 0.84 F i x ' 5.4 E f f e c t o f f i x e d - c a r b o n t o i r o n r a t i o on t h e degree o f m i x i n g f o r 358 ym i r o n - o r e p a r t i c l e s . C o n d i t i o n s : d /d = 4 ; 20% l o a d i n g and 15 r.p.m. 93 5.4 E f f e c t of percent loading At l e v e l s of 12 and 20 percent, no appreciable e f f e c t of percent loading on the type of bed motion was observed v i s u a l l y . T h i s was the case f o r the extreme v a l u e s o f each of the o t h e r v a r i a b l e s , namely ~d c/dp e of 4 and 0.5, C p i x / F e of 0.45 and 0.84 and r o t a t i o n a l speeds of 5 and 15 r.p.m.. S i m i l a r l y , percent loading had no e f f e c t on the degree of mixing of p a r t i c l e s , as i l l u s t r a t e d i n Figure 5.5. A s e g r e g a t e d bed i s found a t 12 and 20 p e r c e n t f i l l , w i t h o t h e r c o n d i t i o n s held constant. The same r e s u l t s were obtained when the p a r t i c l e s were well mixed. 5.5 Preliminary d i s c u s s i o n of r e s u l t s from room-temperature mixing experiments The r e s u l t s of the room-temperature mixing experiments are d i s -cussed i n t h i s s e c t i o n , only w i t h i n the context of relevance to the sub-sequent reduction experiments, that were c a r r i e d out using the same r e -a c t o r and m a t e r i a l s . Further d i s c u s s i o n as to the a p p l i c a b i l i t y of the mixing r e s u l t s obtained, to d i f f e r e n t s i z e s of systems and m a t e r i a l s , i s presented i n Chapter 8. I t i s a p p a r e n t from the r e s u l t s obtained that the s i n g l e most important v a r i a b l e a f f e c t i n g the mixing and motion of the bed i s the r a -t i o of p a r t i c l e s i z e s ; t h i s e f f e c t i s i l l u s t r a t e d by the c o n s t r u c t i o n of predominance-area diagrams shown i n Figures 5.6 and 5.7, (The points des-ignated by the l e t t e r s F, G, R and S i n Figure 5.6 w i l l be discussed l a -t e r i n the t e x t ) . It i s seen that the areas c o r r e s p o n d i n g t o s e g r e g a -t i o n and r o l l i n g motion and to slumping motion and a well-mixed bed are nearly c o i n c i d e n t . 20% loading 5.5 E f f e c t of percent loading on the degree of mixing for 358 ym iron-ore p a r t i c l e s . Conditions: d /d =4.0; C F i x/Fe=0.4 5 and 15 r.p.m. c Fe > 1 1 1 1 \ \ • • Transition \ \ \ v . Segregated o \ \ \ \ Well mixed \ * \ * s _ € OF O " C . © O o oR o J L 100 200 300 400 d F e (fj.m) 6 Predominance area diagram f o r the degree of mixing as a functio n of d c/dp e s i z e r a t i o and iron - o r e mean p a r t i c l e s i z e , dp e. Co n d i t i o n s : Cp-|x/Fe = 0.45; 5 to 15 r.p.m. and 20% loading . 5 rpm 9 Slumping^ Transition \ \ \ \ \ v \ Rolling \ « \ \ t ransi t ion © © • Slumping \ s s \ • • o ^ © N v ^ © — . — - © - © o o o 100 200 300 400 dFe(/xm) Predominance areajdiagram f o r the type of bed motion as a funct i o n of d c/dp e s i z e r a t i o and ir o n - o r e mean p o a r t i c l e s i z e , a p e . Con d i t i o n s : Cf^/Fe = 0.45; 5 and 15 r.p.m., and 20% loading . 97 T h i s behaviour can be explained i n terms of a p e r c o l a t i o n mech-anism operating during r o t a t i o n a l movement of the bed. A c c o r d i n g t o t h i s mechanism, heavier and/or f i n e r p a r t i c l e s s i f t through the l i g h t e r and/or l a r g e r p a r t i c l e s , s e g r e g a t i n g i n t o a c o r e i n the s o l i d s bed; t h e s e d i f f e r e n c e s and the p a r t i c l e shape and surface c h a r a c t e r i s t i c s have been reported to be among the main f a c t o r s which f a v o u r s e g r e g a -t i o n . 4 ' 1 3 5 By p r o g r e s s i v e l y d e c r e a s i n g the s i z e of the l i g h t e r p a r t i c l e s , the mixing i s a f f e c t e d because, at a c r i t i c a l s i z e r a t i o , the v o i d s be-tween the l i g h t e r p a r t i c l e s w i l l be too small to allow the heavier par-t i c l e s to pass through. This was the c a s e , as can be seen i n F i g u r e 5.6, f o r i r o n - o r e p a r t i c l e s l a r g e r than 254 ym, where a c r i t i c a l d c/dp e of about 1.0 was obtained. According to geometric p r i n c i p l e s alone, the c r i t i c a l s i z e r a t i o should be between 2.41 and 6.46 f o r orderly-arranged homogeneous s p h e r e s , 1 2 1 or greater than 1.2 f o r i r r e g u l a r , homogeneous s o l i d s . 1 3 * * The c r i t i c a l r a t i o i s t h e refore expected to be lower, i f the d i f f e r e n c e i n d e n s i t i e s a l s o i s considered; t h i s was c l e a r l y the case i n the p r e s e n t s t u d y . A l s o , a c r i t i c a l s i z e r a t i o of about 0.5 has been reported f o r mixtures of i r o n - o r e p e l l e t s and c o a l . 1 2 1 In the present study, the c r i t i c a l s i z e r a t i o f o r the c o a l / i r o n -ore mixture was estimated as f o l l o w s . F i r s t , a sample of coal p a r t i c l e s with 1595 ym mean p a r t i c l e s i z e was mounted i n r e s i n ; vacuum was a p p l i e d to ensure that the r e s i n f i l l e d the i n t e r p a r t i c l e v o i d s . A g r i d of 20 x 20 mm, with 2 mm d i v i s i o n s , was drawn on the f l a t surface of the s p e c i -men; the d i s t a n c e s between the edges of the p a r t i c l e s were measured, with a s t e r e o s c o p i c m i c r o s c o p e , i n the two p e r p e n d i c u l a r d i r e c t i o n s 98 a l o n g the l i n e s o f the g r i d . The averaging of over a hundred measure-ments y i e l d e d a v o i d s i z e of 1.025 mm. Thus, i f i t i s assumed t h a t s m a l l e r p a r t i c l e s m a i n t a i n the same shape, the average void s i z e , £, should be r e l a t e d to the mean coal p a r t i c l e s i z e , d c , as follows a = a cTc . (5.1) where a i s a p r o p o r t i o n a l i t y constant t h a t depends m a i n l y on p a r t i c l e shape; i n the p r e s e n t c a s e , a has a v a l u e of 0.643. By applying the above r e l a t i o n s h i p to d i f f e r e n t p a r t i c l e s i z e s , the v o i d s i z e c o r r e -sponding to each p a r t i c l e s i z e i s obtained; t h i s i s shown i n Figure 5.8. Also shown i n Figure 5.8 are the t h e o r e t i c a l values c a l c u l a t e d f o r two d i f f e r e n t p a r t i c l e shapes: a sphere with diameter '"dc and a slab with dimensions 0.5 d c x d c x 2 cf c. The t h e o r e t i c a l void s i z e s were obtained based on the f o l l o w i n g assumptions: i ) The number of voids i s the same as the number of p a r t i c l e s , i i ) The voids are s p h e r i c a l , with the l a r g e s t d i a m e t e r to f i t be-tween p a r t i c l e s . i i i ) The average s i z e of the voids i s obtained by d i v i d i n g the meas-ured void f r a c t i o n by the number of p a r t i c l e s . For example, f o r c o a l p a r t i c l e s w i t h d c = 0.716 mm the void s i z e i s 0.283 mm f o r s p h e r i c a l p a r t i c l e s , and 0.566 mm f o r s l a b - l i k e p a r t i c l e s . I t i s seen i n F i g u r e 5.8 t h a t the measured void s i z e s f i t between the two t h e o r e t i c a l l y c a l c u l a t e d values. 1500 lOOOr-600 1 400 o I — S 2 00 in •a o > 100 60 30 i r /I Slab shaped y / -i particles / / / / Spherical / I / A / / i / / / / / / ^J§_ particles / 50 100 200 400 _ 1000 2000 Coal particle size , dc (^ im) Void s i z e between p a r t i c l e s as a fun c t i o n of coal par-t i c l e s i z e i n a loose bed . 100 T h i s diagram can thus be used to p r e d i c t the s i z e of the ore p a r t i c l e s that w i l l r e s u l t i n s e g r e g a t i o n , f o r a g i v e n c o a l p a r t i c l e s i z e . From knowledge of the coal s i z e , the corresponding v o i d s i z e can be obtained. If the ore p a r t i c l e s are smaller than t h i s , they w i l l tend to s e g r e g a t e ; i f they are l a r g e r , they w i l l stay well mixed. For exam-p l e , the void s i z e s f o r 0.356 and 0.127 mm coal p a r t i c l e s are 0.235 and 0.082 mm r e s p e c t i v e l y ; thus a 0.254 mm ore p a r t i c l e w i l l segregate i n a bed c o n t a i n i n g 0.356 mm coal p a r t i c l e s and be well mixed i n the presence of 0.127 mm coal p a r t i c l e s . These two c o n d i t i o n s can be a s c e r t a i n e d by re-examining Figure 5.6, points G and R r e s p e c t i v e l y . The c o r r e s p o n -dence i s s e l f explanatory. At ore s i z e s smaller than t h i s however, the well-mixed boundary i n Figure 5.6 i s d i s p l a c e d toward higher d c/dp e r a t i o s . Therefore other f a c t o r s must have exerted an i n c r e a s i n g l y stronger i n f l u e n c e on bed mix-i n g . Among the l i k e l y f a c t o r s may be the e l e c t r o s t a t i c charging and/or an increased f r i c t i o n c o e f f i c i e n t of the coal p a r t i c l e s , that were c o r -r e s p o n d i n g l y s m a l l e r . The former f a c t o r would cause the coal p a r t i c l e s to clump together hindering the f r e e motion of the ore p a r t i c l e s and l e a v i n g them randomly disseminated through the bed. The l a t t e r f a c t o r would produce a s i m i l a r e f f e c t by the r e s p e c t i v e i n c r e a s e of the f r i c -t i o n c o e f f i c i e n t between ore and coal p a r t i c l e s . This mechanism would a l s o e x p l a i n the correspondence between slumping and well-mixed b e h a v i -our that was obtained always f o r smaller coal p a r t i c l e s i z e s . Results of angle of repose measurements, using the cone method, 4 are presented i n Table XV f o r d i f f e r e n t p a r t i c l e s i z e s of coal by i t s e l f and mixed w i t h 254 ym ore p a r t i c l e s , at a C F i x / F e of 0.32. A s l i g h t 101 tendendy o f i n c r e a s i n g angle of repose, f o r the coal p a r t i c l e s by them-s e l v e s , i s obtained as coal p a r t i c l e s i z e decreases. An increased angle of repose was obtained f o r the ore/coal mixtures, at l a r g e r coal s i z e s , as would be e x p e c t e d . T h i s e f f e c t however was not p r e s e n t f o r the smaller coal p a r t i c l e s s i z e s . From the f o r e g o i n g , i t i s apparent that the type of bed motion i s p r i m a r i l y determined by the coal p a r t i c l e s i z e , f o r the range t e s t e d , TABLE XV ANGLE OF REPOSE FOR DIFFERENT COAL PARTICLE SIZES AND ORE/COAL MIXTURES WITH 254 m ORE PARTICLE SIZE d c d c/dp e $ r j C $r,mix $r,mix-$r,c [vm] [°] [°] [°] 1016 4.0 37.0 39.5 2.5 510 2.0 37.0 38.5 1.5 358 1.4 37.5 38.5 1.0 254 1.0 38.0 38.0 0.0 127 0.5 38.0 38.0 0. dp e = 254 vm, $ r,Fe = 35° whereas the p a r t i c l e s s i z e r a t i o , d c/dp e, determines the degree of mix-ing at coal s i z e s l a r g e r than 254 ym; a t s m a l l e r s i z e s , e l e c t r o s t a t i c and f r i c t i o n a l forces become predominant. The above d i s c u s s i o n i s based on experiments at room temperature •and when no r e a c t i o n i s taking p l a c e . However, the main d i f f e r e n c e with respect to a r e a c t i n g system, to be encountered i n the reduction e x p e r i -ments, i s the d e c r e a s i n g c o a l p a r t i c l e s i z e as the r e a c t i o n s proceed. 102 This w i l l only but enhance the degree of mixing of the bed since the ore p a r t i c l e s are expected to m a i n t a i n a p p r o x i m a t e l y t h e i r i n i t i a l s i z e . F i n a l l y , the gases g e n e r a t e d by the r e a c t i o n may produce an e f f e c t on the bed mixing; t h i s w i l l be discussed i n Chapter 8. 103 CHAPTER 6 RESULTS OF REDUCTION EXPERIMENTS The r e s u l t s of the reduction experiments are p r e s e n t e d i n t h i s chapter. The r e s u l t s of the coal d e v o l a t i l i z a t i o n experiments f o l l o w i n g the technique o u t l i n e d i n Section 4.7.2 are p r e s e n t e d f i r s t . T h i s i s followed by the presentation of the r e s u l t s of the reduction experiments arranged i n t o three s e c t i o n s : the p r e l i m i n a r y runs to d e t ermine the ranges of v a r i a b l e s , the main e x p e r i m e n t a l block and the comparative experiments. A l l three sets were performed i n the equipment d e s c r i b e d i n S e c t i o n 4.3, f o l l o w i n g the procedure e s t a b l i s h e d i n Section 4.7.3. 6.1 Results of coal d e v o l a t i l i z a t i o n experiments A d e v o l a t i l i z a t i o n treatment of the coal was deemed n e c e s s a r y , p r i o r to the reduction experiments, f o r the f o l l o w i n g reasons. F i r s t l y , the presence of the v o l a t i l e c o n s t i t u e n t s i n the c o a l , i n c l u d i n g mois-t u r e , would complicate unduly the assessment of the reduction k i n e t i c s owing to the presence of p a r a l l e l r e a c t i o n schemes. Moreover, the ob-j e c t i v e o f t h i s work was to study the r e d u c t i o n k i n e t i c s with carbon alone, as i t would occur i n the reduction s e c t i o n o f an i n d u s t r i a l r o -t a r y k i l n . As was s t a t e d e a r l i e r , Section 2.2.1, most of the v o l a t i l e c o n s t i t u e n t s i n the coal are r e l e a s e d i n the p r e h e a t i n g s e c t i o n of the 104 k i l n . I t i s important to note however, that the p o s s i b i l i t y of a small degree of reduction by hydrogen always e x i s t s i n the reduction s e c t i o n , since a t r a c e amount of hydrogen i s r e t a i n e d by the char. S i m i l a r l y , i n the present study, a small f r a c t i o n of r e d u c t i o n by hydrogen i s pos-s i b l e ; t h i s i s discussed i n d e t a i l i n Section 6.4.6. The second reason f o r d e v o l a t i l i z i n g the coal i s r e l a t e d to ex-perimental c o n s i d e r a t i o n s . The gas flowrate measurements during the r e -duction experiments would be impaired by the d e p o s i t i o n of l o w - m e l t i n g p o i n t compounds, i n the gas l i n e s as the gases discharged from the reac-t o r cooled down. These compounds would be r e l e a s e d i n c o n s i d e r a b l e amounts i f raw c o a l were used. Experiments t h e r e f o r e were conducted with the aim of e l i m i n a t i n g the major f r a c t i o n o f the v o l a t i l e s under temperature c o n d i t i o n s s i m i l a r to those i n an i n d u s t r i a l r o t a ry k i l n . A heating rate of 9°C/min was adopted f o r these t e s t s based on a v a i l a b l e i n f o r m a t i o n . ^ Coal soak per i o d s , at 900°C, from one to ten hours were t r i e d . The p a r t i c l e s i z e s studied were those to be u t i l i z e d i n the r e -duction experiments, namely: - 841 + 600, - 420 + 300, - 210 + 149, and - 106 + 74 ym. Two methods were adopted to evaluate v o l a t i l e s r e l e a s e : chemi-cal analyses and weight l o s s of the sample. Proximate and u l t i m a t e a n a l y s e s p r o v i d e d a p r e c i s e value of the v o l a t i l e matter and hydrogen remaining i n the char, r e s p e c t i v e l y . These were performed by S t e l c o I n c . . The weight-loss method, on the other hand, provided a reasonable estimate of the evolved v o l a t i l e s . T h i s method p e r m i t t e d the c o n s i s -t e n c y of the c h a r r i n g treatment f o r a l l coal used i n the reduction ex-periments to be monitored. 105 6.1.1. Temperature measurement i n the coal bed Considering the s i z e of the coal samples and the n a t u r e o f the f u r n a c e , d e s c r i b e d e a r l i e r , temperature gradients were expected to de-velop i n s i d e the coal bed. The measurement of the tempe r a t u r e a t d i f -f e r e n t l o c a t i o n s i n the bed, was t h e r e f o r e aimed a t e v a l u a t i n g these gradients since they might i n f l u e n c e char homogeneity. A temp e r a t u r e versus time p l o t , f o r an experiment with a 10 hour soaking-time i s shown i n Figure 6.1. Thermocouple l o c a t i o n s are al s o shown and c o r r e s p o n d t o t h o s e i n F i g u r e 4.8. The temperature at each point during the soaking period i s presented i n Table XVI f o r the four p a r t i c l e s i z e s t r e a t e d . The h e a t i n g rate ranged from 8.8°C/min at the bottom side l o c a -t i o n , p o i n t B i n Figure 6.1, up to 10°C/min a t the c e n t r a l p o s i t i o n , p o i n t D. As i s shown i n Table XVI, a maximum temperature d i f f e r e n c e of 40°C was observed between these points f o r the l a r g e s t c o a l p a r t i c l e s . S i m i l a r c o n d i t i o n s were o b t a i n e d with the smaller p a r t i c l e s , although the temperature gradients decreased s l i g h t l y with p a r t i c l e s i z e . 6.1.2 E f f e c t of soak time and p a r t i c l e s i z e V o l a t i l e and hydrogen r e l e a s e increased with soak t i m e , as was t o be e x p e c t e d . F i g u r e 6.2 shows the asymptotic pattern of hydrogen r e l e a s e . The major f r a c t i o n o f the hydrogen was e v o l v e d d u r i n g the h e a t i n g - u p period and the t o t a l f r a c t i o n was p r a c t i c a l l y independent of p a r t i c l e s i z e , w i t h i n the range t e s t e d . A minimum amount of hydrogen r e t a i n e d , about 0.3 percent, was obtained with 10 hours of treatment. 106 6.1 Temperature at four l o c a t i o n s i n the coal bed during d e v o l a t i l i z a t i o n treatment . 107 TABLE XVI. TEMPERATURES MEASURED AT FOUR LOCATIONS IN THE COAL BED, FOR PARTICLE SIZES OF - 841 + 600, - 420 + 300, - 210 + 149 and - 106 + 74 ym P a r t i c l e s i z e (ym) - 841 + 600 - 420 + 300 - 210 + 149 - 106 + 74 Location Temperature (°C) A 920 923 920 919 B 883 889 888 890 C 907 910 911 909 D 923 920 921 921 108 1 5 3.0 Particle size o 0.716 mm • 0.358 " A 0.180" Q 0.040 " 25 CVJ 5* 1.5 1.0 A 0.5 1 120 240 360 480 Charring time (min) 600 720 6.2 Percent hydrogen remaining i n char, a f t e r d e v o l a t i l -i z a t i o n treatment at 900°C, f o r four coal p a r t i c l e s i z e s : 716, 358, 180 and 90 ym . 109 The proximate and u l t i m a t e a n a l y s e s , f o r the d i f f e r e n t char p a r t i c l e s i z e s , are presented i n Table XVII, ash composition i s presented i n Ta-ble XVIII. 6.1.3 Discussion of coal d e v o l a t i l i z a t i o n r e s u l t s The 10 hour treatment was adopted as the s t a n d a r d f o r the c o a l samples to be used i n a l l the reduction experiments. From the trend i n Figure 6.2, i n order to reduce the hydrogen content a f u r t h e r 0.1 p e r -c e n t , a t l e a s t f i v e a d d i t i o n a l hours of treatment would have been r e -quir e d . P r a c t i c a l c o n s i d e r a t i o n s however prevented t h i s . Depending on the C F i x / F e r a t i o to be used i n the reduction experiments, a maximum r e -duction by hydrogen of 4.7 p e r c e n t might be e x p e c t e d , based on s t o i -c hiometric c o n s i d e r a t i o n s alone, f o r a 0.3 percent H2 content. S i m i l a r -l y 0.45 p e r c e n t H 2 , o b t a i n e d w i t h a 5 hour t r e a t m e n t , might produce c l o s e to 7 percent reduction whereas 0.2 percent H2» to be obtained with a 15 hour t r e a t m e n t , would y i e l d about 3 p e r c e n t r e d u c t i o n . These amounts of reduction are obviously smaller when the e q u i l i b r i u m f o r the H 2 - H2° - CO - CO2 system i s considered. A d i s c u s s i o n on t h i s i s pre-sented i n Section 6.4.6. The range of heating r a t e s , 8.8 to 10°C/min, at d i f f e r e n t l o c a -t i o n s i n the coal bed have been demonstrated i n the l i t e r a t u r e ! 3 7 - 1 3 8 to a f f e c t n e i t h e r the rate of v o l a t i l e s r e l e a s e nor the s t r u c t u r e of the char to any g r e a t d e g r e e . S i m i l a r l y , the temperature gradients found i n s i d e the bed are not considered s i g n i f i c a n t at the c h a r r i n g tempera-ture of 900°C. Gradients might have played a more important r o l e had 110 TABLE XVII. PROXIMATE AND ULTIMATE ANALYSES OF FORESTBURG COAL AND SASKATCHEWAN LIGNITE AFTER 10 HOUR CHARRING TREATMENT. MEAN PARTICLE SIZES: 718, 180 and 90 ym Coal Forestburg L i g n i t e Mean P a r t i c l e 718 180 90 180 si z e [ym] Proximate A n a l y s i s H 20 0.62 0.83 0.58 0.08 Ash 49.50 56.10 52.10 28.40 V o l a t i l e s 2.50 3.10 2.50 4.64 Fixed C 48.00 40.84 45.40 66.96 U l t i mate Analysi s (d.b.) Carbon 48.07 42. 76 46. 72 69.57 Hydrogen 0.51 0. 31 0. 33 0.43 Nitrogen 0.48 0. 29 0. 34 0.40 Sulphur 0.66 0. 71 0. 71 0.85 Ash 49.50 56. 10 52. 10 28.40 Oxygen 0.78 - - 0.35 TABLE XVIII. ASH COMPOSITION OF FORESTBURG COAL AND SASKATCHEWAN LIGNITE IN % WEIGHT Fe 203 P2O5 S i 0 2 Al2O3 CaO MgO NagO K 2 0 T i 0 2 Forestburg 6 . 0 0 0.83 55.80 2 1 . 2 0 12.30 1.80 1.23 0.68 0.19 L i g n i t e 3.60 0.36 51.80 23.60 1 1 . 1 0 2.80 4.60 0.99 0.64 I l l the temperature been lower, of the order of 600°C, or f o r shorter soak-ing periods.137-138 The temperature of 900°C chosen f o r the d e v o l a t i l i z a t i o n t r e a t -ments was lower than the maximum value of 950°C to be te s t e d i n some o f the r e d u c t i o n experiments. This d i f f e r e n c e , however, should not r e s u l t i n a major change i n the r e a c t i v i t y of the charred product f o r the f o l -lowing reason. It has been demonstrated that n e i t h e r g r a p h i t i z a t i o n nor a f u r t h e r change i n pore surface area i s obtained by t r e a t i n g s u b - b i t u -minous c o a l s beyond 900°C, a t l e a s t up to 1300°C.l 1 1 Therefore, since pore surface area exerts a ve r y s t r o n g i n f l u e n c e on r e a c t i v i t y , t h i s property i s not expected to change d r a m a t i c a l l y by i n c r e a s i n g the t r e a t -ment temperature by 50°C. The l a r g e s t o p ening of the pores i n th e s e c o a l s , hence h i g h e s t r e a c t i v i t y , 1 3 7 i s o b t a i n e d by t r e a t i n g them at 700°C. Therefore, d e v o l a t i l i z a t i o n a t t h i s temperature would be advo-cated f o r reduction purposes, i f i t were not f o r the f a c t that the major p o r t i o n of the hydrogen i s not relea s e d unless heated above t h i s temper-a t u r e . 1 1 1 Moreover, i f the coa l had been d e v o l a t i l i z e d at 700°C, the hydrogen content remaining i n the char would have been r e l a t i v e l y l a r g e and a l s o the reduction achieved v i a hydrogen. By co n s i d e r i n g the above f a c t o r s a temperature of 900°C was therefore adopted f o r the d e v o l a t i l -i z a t i o n of the coal samples throughout a l l the reduction program. 6.2 C a l c u l a t i o n of f r a c t i o n a l reduction The r e s u l t s o f the r e d u c t i o n experiments are presented as the s t a n d a r d p l o t s of f r a c t i o n a l r e d u c t i o n , fR, versus time. The slopes of 112 the r e d u c t i o n c u r v e s represent the f r a c t i o n a l rates of r e d u c t i o n . The f r a c t i o n a l reduction was c a l c u l a t e d using the f o l l o w i n g r e l a t i o n s h i p : where ( O x ) ^ i s the moles of oxygen removed up to time t , and ( 0 x ) j o t i s the t o t a l moles of oxygen i n the o r i g i n a l concentrate. ( 0 x ) y o t was ob-tai n e d from the chemical composition of the ore, Table VIII, and al s o by c o n s i d e r i n g the Fe203 content i n the coal ash, Table XVIII. (Ox)t was c a l c u l a t e d by the f o l l o w i n g procedure: i ) The CO and CO2 mole f r a c t i o n s , Xco and XQO » were obtained from the r e s u l t s of gas a n a l y s i s . ( I t was assumed the gas sample had the same composition as that coming o f f the bed, as w i l l be d i s -cussed i n Section 6.4.6.) An example of the gas c o m p o s i t i o n as a f u n c t i o n of reduction time i s shown i n Figure 6.3. i i ) The measured gas f l o w r a t e , QR 0t> was c o r r e c t e d f o r the s e a l i n g e f f i c i e n c y of the system, E f f , as defined i n Section 4.7.3, and f o r the density d i f f e r e n c e with respect to the standard gas, as p r o v i d e d by the manufacturer of the flowmeters, using Equation (6.2): ( 0 x ) t (6.1) (Ox) Tot c o r r Q Tot (6.2) where E. f f 2 10 8 0 -£ 6 0 o o o 4 0 u 2 0 — CO \ O $ A co/co 2 , H 2 T = 8 5 0 ° C C f j x / F e = a32 d c /d F e=0.5 rpm = I 4 % f i l l = l 4 0 toCr-Q - Q - 4 - o h 1 8 (NJ O u 4 O i 4 0 8 0 120 160 200 240 2 8 0 Time (min) 6.3 Gas composition as a functi o n of r e a c t i o n time f o r a reduction experiment; c o n d i t i o n s as shown . M 114 and (1 - V s ) 1 7 2 p. c o n r (1 - p s t d ) 1 / 2 whereupon the flowrate of each gaseous s p e c i e s c o u l d be c a l c u -l a t e d , QC0 = <W ' XC0 ( 6' 3 ) QC0 2 = Q T o t ' XC0 2 ( 6' 4 ) together with t h e i r corresponding molar r a t e s , mC0 = QCO P T / R T f ( 6- 5) mC0 2 = QC0 2 P T / R T f (6-6) i i i ) The molar rates of oxygen and carbon were c a l c u l a t e d by c o n s i dering t h a t , C + 1/2 0 2 = CO (6.7) C + 0 2 = C02 (6.8) Thus % = 1/2 \ o + "to (6.9) 2 mC = \ o + \ o 2 (6.10) 115 i v ) Then, by numerical i n t e g r a t i o n 1 3 9 of the oxygen and carbon molar r a t e s t h e i r r e s p e c t i v e amounts removed up to time t , (Ox)-t and (C)t» c o u l d be o b t a i n e d . By s u b s t i t u t i n g ( 0 x ) t i n Equation (6.1) the f r a c t i o n a l reduction was obtained. A computer program was implemented to perform the c a l c u l a t i o n s described above; the program l i s t i n g and a sample o u t p u t are p r e s e n t e d i n Appendix D. The program a l s o gave the o v e r a l l mass balance f o r each species: i r o n , oxygen, hydrogen, carbon and i n e r t m a t e r i a l s . The over-a l l material balances c l o s e d w i t h i n 6 percent i n a l l cases, the majority being within 4 percent. A summary of the mass balances i s p r e s e n t e d i n Appendix E. 6.3 Results of experiments to determine v a r i a b l e s ranges The purpose of t h i s s e t of e x p e r i m e n t s was to d e t ermine the ranges o f operational v a r i a b l e s w i t h i n which an e f f e c t on the reduction rate could be obtained. These v a r i a b l e s were: f i x e d c a r b o n - t o - i r o n r a t i o , r o t a t i o n a l speed and percent l o a d i n g . The approach followed was to change p r o g r e s s i v e l y the l e v e l of the t e s t e d v a r i a b l e , i n s e p a r a t e experiments, u n t i l no f u r t h e r e f f e c t was observed on the reduction r a t e . In each case, the other v a r i a b l e s were m a i n t a i n e d a t c o n s t a n t l e v e l s chosen under the c o n s i d e r a t i o n s stated i n Section 4.6.3. The p a r t i c l e s i z e r a t i o was maintained at 0.5 i n a l l c a s e s , c o r r e s p o n d i n g to wel 1-mixed c o n d i t i o n s . This i s shown by point R in Figure 5.6. A tempera-ture of 900°C was used i n a l l t e s t s , f o r the reasons s t a t e d i n S e c t i o n 4.6.2. 116 6.3.1 E f f e c t of f i x e d - c a r b o n - t o - i r o n r a t i o The e f f e c t o f C p i x / F e r a t i o on the reduction r a t e , f o r values between 0.16 and 0.64, i s i l l u s t r a t e d i n Figure 6.4. The c o n d i t i o n s f o r t h e s e t e s t s were: r o t a t i o n a l speed of 7 r.p.m. and 14 percent l o a d i n g . I t . can be seen t h a t the reduction rates beyond C p i x / F e = 0.32 are very s i m i l a r , e s p e c i a l l y up to 0.5 f r a c t i o n a l r e d u c t i o n . At 0.16 however, the r a t e i s c o n s i d e r a b l y slower. A small divergence of the 0.48 curve i s observed a t a l a t e r stage of re d u c t i o n . 6.3.2 E f f e c t of r o t a t i o n a l speed The e f f e c t o f the r o t a t i o n a l speed on the reduction r a t e , f o r values from 7 to 20 r.p.m., i s shown i n F i g u r e 6.5. Two v a l u e s o f C p j x / F e were t e s t e d : 0.64 and 0.16; 14 percent f i l l i n g was used i n a l l cases. It can be seen that p r a c t i c a l l y no d i f f e r e n c e between the r a t e s was produced by changes i n the r o t a t i o n a l speed. At the 0.16 l e v e l , a s l i g h t l y f a s t e r r e d u c t i o n r a t e was p r e s e n t a t the h i g h e r speed, 14 r.p.m. The experiment at 17 r.p.m. was i n t e r r u p t e d due to operational problems i n the d r i v i n g motor. 6.3.3 E f f e c t of percent loading The e f f e c t o f 7 and 14 percent l o a d i n g i s shown i n Figure 6.6, f o r Cp-j x/Fe r a t i o s of 0.64 and 0.16. The r o t a t i o n a l speed was maintain-ed constant at 7 r.p.m.. I t can be seen t h a t a t the lower v a l u e o f C p i x / F e , the i n i t i a l r a t e was f a s t e r a t 7 percent loading than at 14 percent. The opposite was true at l a r g e r f r a c t i o n s reduced. At the 117 l 1 1 — i 1 1 r ,b i i l I I L _ 0 80 160 240 Time (min) 6.4 P l o t of f r a c t i o n a l reduction versus time showing the e f f e c t of Cpix/Fe r a t i o ; c o n d i t i o n s as shown . Time (min) P l o t of f r a c t i o n a l reduction versus time showing the e f f e c t of r o t a t i o n a l speed a t two Cp-jx/Fe r a t i o s ; c o n d i t i o n s as shown . ! ^ }C f i x/Fe=0.64 C f i „/Fe =0.16 14% Temp-900°C rpm -7 dc/dFe=05 1 1 0 80 160 Time (min) 240 P l o t of f r a c t i o n a l reduction versus time showing the e f f e c t of percent f i l l a t two C p i x / F e r a t i o s ; c o n d i t i o n s as shown . 120 0.64 v a l u e of the Cp n- X/Fe r a t i o , on the other hand, p r a c t i c a l l y no e f -f e c t of the percent loading was observed. 6.3.4 Preliminary d i s c u s s i o n of r e s u l t s from e x p e r i - ments to determine v a r i a b l e s ranges" The f i x e d carbon-to-iron r a t i o showed a strong e f f e c t on the r e -duction rate as was to be expected. The value of 0.32 could be taken as the optimum, since no improvement was achieved by i n c r e a s i n g the Cp-j x/Fe value to 0.64. The s l i g h t l y slower rate shown at the 0.48 v a l u e might be a t t r i b u t e d to e i t h e r experimental e r r o r or d i f f e r e n c e s i n the s o l i d s composition. This might al s o account f o r the r e l a t i v e l y l a r g e d i f f e r -ence o b t a i n e d when the o v e r a l l mass balance was performed, 5.4 percent, as shown i n Appendix E. The optimum value of 0.32, i . e . 100 percent ex-c e s s w i t h respect to the minimum s t o i c h i o m e t r i c requirements, i s c o n s i -derably lower than the f i g u r e s reported f o r f i x e d - b e d r e d u c t i o n ( T a b l e V I ) , where e f f e c t s o f the Cp-j x/Fe r a t i o were s t i l l found at values as high as 0.96. This can undoubtedly be a t t r i b u t e d to two f a c t o r s : b e t -t e r m i x i n g i n the r o t a r y r e a c t o r , and the char r e a c t i v i t y was higher than those of the carbonaceous m a t e r i a l s used i n some of the s t u d i e s mentioned e a r l i e r . 9 0 " 9 3 When the value of 0.32 f o r Cp-j x/Fe i s compared to those studied i n s i m i l a r works using rotary r e a c t o r s (Table V I I ) , i t i s found that i t i s again lower than those studied p r e v i o u s l y . This can be due to a more intimate contact between the r e a c t i n g gases and s o l i d s , a c h i e v e d i n the reduction of the f i n e m a t e r i a l s i n t h i s work. The 0.32 value was adopted f o r use i n the main experimental b l o c k , as the s t a n -dard C F i x / F e r a t i o . 121 The e f f e c t caused by the percent loading on the reduction rate can be analyzed as f o l l o w s . F i r s t l y , f o r shallower beds the p a r t i c l e s have been r e p o r t e d to spend longer o v e r a l l times at the surface of the bed.4.121 S e c o n d l y , the a r e a to volume r a t i o (A/V) has been found to e x e r t a s t r o n g e f f e c t on the heat t r a n s f e r i n t o the bed;? the shallower the bed, the l a r g e r the A/V r a t i o becomes with i t s consequent enhance-ment of heat t r a n s f e r i n t o the bed. At 14 percent f i l l i n g the A/V r a t i o was 48 m - 1 whereas at 7 percent, i t was 85 m _ 1. Therefore, at the lower Cp-jx/Fe l e v e l the shallower bed reacted f a s t e r i n i t i a l l y due to the f a c t t h a t , although the temperature at the c e n t e r o f the bed was 900°C, an i n c r e a s e d f r a c t i o n of the r e a c t i o n was o c c u r r i n g at the bed's surface because of the combined e f f e c t s of longer exposure times at the s u r f a c e and o f the s l i g h t l y h i g h e r temperature p r e v a i l i n g t h e r e . The slowing down of the rate as the r e a c t i o n advanced i s but a consequence of the i n i t i a l l y f a s t e r consumption of carbon.. At the higher C F i x / F e r a t i o however, the l a r g e excess of carbon must have overcome th e s e e f f e c t s s ince the i r o n - o r e p a r t i c l e s were surrounded by more coal char. Fourteen percent loading was adopted f o r the experiments o f the main b l o c k f o r two reasons. F i r s t l y , t h i s value i s c l o s e s t to the range used i n an i n -d u s t r i a l o p e r a t i o n . S e c o n d l y , as was mentioned above, a 0.32 C p i x / F e r a t i o was to be used i n t h e s e e x p e r i m e n t s and t h e r e f o r e the p e r c e n t f i l l i n g was not expected to play a p a r t . The l a c k of an e f f e c t on the reduction rate of r o t a t i o n a l speed i s i n agreement with what was found i n the room-temperature m i x i n g ex-p e r i m e n t s . In t h o s e e x p e r i m e n t s , good mixing c o n d i t i o n s had been ob-t a i n e d a t speeds as low as 5 r.p.m. p r o v i d e d t h a t the r i g h t p a r t i c l e 122 s i z e r a t i o was u t i l i z e d . N o n e t h e l e s s , to ensure that good g a s - s o l i d c o n t a c t i n g was achieved, a r o t a t i o n a l speed of 14 r.p.m. was adopted f o r a l l the subsequent reduction t e s t s . 6.4 Results of main experimental block T h i s s e t o f e x p e r i m e n t s was designed to assess the e f f e c t s of temperature and p a r t i c l e s i z e r a t i o , on the reduction r a t e , i n o r d e r t o determine the rate c o n t r o l l i n g step f o r the o v e r a l l reduction r e a c t i o n . Based on the d i s c u s s i o n given i n Section 6.3.4, these e x p e r i m e n t s were c a r r i e d out at a r o t a t i o n a l speed of 14 r.p.m., 14 percent loading and a C p i x / F e r a t i o o f 0.32. The s t o i c h i o m e t r i c Cp-j x/Fe r a t i o , 0.16, was tes t e d f o r only one set of temperatures. A summary of the c o n d i t i o n s studie d i s shown i n Figure 6.7. The r e s u l t s are presented as f r a c t i o n a l r e d u c t i o n - v e r s u s - t i m e p l o t s and as P c o/ pC0 2 r a t i o - v e r s u s - f r a c t i o n a l -r e duction p l o t s . 6.4.1 E f f e c t of temperature: the base case The c o n d i t i o n s f o r t h i s sub-set of experiments were: i r o n - o r e p a r t i c l e mean s i z e o f 358 ym and dc/cTpg of 0.5, which are i n the w e l l -mixed region i n Figure 5.6; these r e s u l t s were taken as the base c a s e . A d i s c u s s i o n on t h i s choice i s given i n Section 6.4.6. The e f f e c t of temperature, from 800 to 950°C, on the rate of r e -d u c t i o n and on the gas composition i s shown i n Figures 6.8 and 6.9, r e -s p e c t i v e l y . It i s seen that the reduction rate increased with tempera-t u r e , as was to be e x p e c t e d . The f r a c t i o n a l r e d u c t i o n obtained was greater than 0.9 f o r temperatures above 850°C. At 800°C, the reduction / d Fe 0.5 0.5 1 . 0 2.0 Temperature (°C) 8 0 0 8 5 0 9 0 0 9 5 0 3 58/1 m — 358/xm — 90/xm 358/im - * C f j x / F e 0.16 0.32 0.32 0.32 V a r i a b l e s i n main experimental block 124 T i m e (min) .8 P l o t of f r a c t i o n a l reduction versus time showing the e f f e c t of temperature: the base case. Conditions as shown . 125 100 950 °C 50 Boudouard equil 900°C 850°C 0.2 0.4 0.6 0.8 Fractional reduction .0 .9 Change i n Pcn/Pco? r a t i o with f r a c t i o n a l reduction during experiments of^base case; c o n d i t i o n s as shown . 126 was c o n s i d e r a b l y slower and therefore the f r a c t i o n a l reduction d i d not reach 0.5. Temperature produced a marked e f f e c t on gas c o m p o s i t i o n as w e l l . With i n c r e a s i n g t e m p e r a t u r e the Pco/'3C02 r a t 1 0 S w e r e s r n ' f t e d 0 f u r t h e r away from the values i n e q u i l i b r i u m w i t h the i r o n o x i d e s . A d i s c u s s i o n on the shapes o f the Pco/pCG2 c u r v e s 1 S given i n Section 6.4.6. 6.4.2 E f f e c t of Cp-j x/Fe s t o i c h i o m e t r i c r a t i o Conditions i n these e x p e r i m e n t s were i d e n t i c a l to those j u s t d e s c r i b e d i n Section 6.4.1, except f o r the Cpj x/Fe r a t i o t hat was 0.16. Results of f r a c t i o n a l reduction obtained from 850 to 950°C are shown, compared to those of the base case, i n Figure 6.10. It i s seen that at a C p i x / F e o f 0.16 slower reduction rates were obtained at a l l tempera-tures and f u l l reduction was not accomplished. The e f f e c t on gas c o m p o s i t i o n i s shown i n Figure 6.11. It i s observed that the PCQ/PQQ^ r a t 1 0 S remained c l o s e r to the reduction e q u i -l i b r i a values, over a smaller extent of r e d u c t i o n , as compared t o the base case, Figure 6.9. 6.4.3 Reduction of f i n e r p a r t i c l e s under well-mixed c o n d i t i o n s The only d i f f e r e n c e s i n the c o n d i t i o n s o f thes e e x p e r i m e n t s , when compared to the base case, are the ir o n - o r e mean p a r t i c l e s i z e of 90 ym and the d c/dp e r a t i o of 1.0. These c o n d i t i o n s are a l s o within the well-mixed r e g i o n , as shown by point F i n F i g u r e 5.6. R e s u l t s of the f r a c t i o n a l r e d u c t i o n o b t a i n e d from 850 to 950°C, are shown i n Figure 6.12. An i n t e r e s t i n g e f f e c t i s observed: at 850°C the reduction rate 127 6.10 P l o t of f r a c t i o n a l redution versus time showing the e f f e c t of s t o i c h i o m e t r i c Cp-,-x/Fe r a t i o ; c o n d i t i o n s as shown 128 100 50 20 T 950 °C T Boudouard equil _ 900°C 850°C CJ O O CL \ o o 0_ 950Q,—°-o o o.0P ,900°C ' —o 0.5 0.2 f Cfix/Fe=0.l6 d_c/dFe=0-5 d F e = 358 /xm i ' Fe304 / FeO equil 0. 0 0.2 0.4 0.6 0B Fractional reduction 1.0 .11 Change i n Pcn/Pco? r a t i o with f r a c t i o n a l reduction during experiments with s t o i c h i o m e t r i c Cpix/Fe r a t i o ; con-d i t i o n s as shown . 129 Time (min) 6.12 P l o t of f r a c t i o n a l r eduction versus time showing the e f f e c t of f i n e r p a r t i c l e s ; c o n d i t i o n s as shown . 130 i s s l o w er than t h a t of the standard case whereas at 950°C the opposite was obtained. At 900°C a behaviour s i m i l a r to the l a t t e r p r e v a i l e d . The gas compositions obtained are shown i n Figure 6.13. At a l l t h r e e t e m p e r a t u r e s i t i s seen that the Pco/pC02 r a t i o s remained c l o s e r to the FeO/Fe e q u i l i b r i u m values than i n the base c a s e , t h r o u g h o u t a l l the r e d u c t i o n . 6.4.4 Reduction under bed s e g r e t a t i o n c o n d i t i o n s F o r t h e s e e x p e r i m e n t s the d c/dp e was changed to 2.0 as opposed to 0.5 f o r the base case. For the i r o n - o r e p a r t i c l e s i z e used, 358 ym, bed s e g r e g a t i o n c o n d i t i o n s were expected, as shown by point S i n Figure 5.6. Results of f r a c t i o n a l r e d u c t i o n o b t a i n e d from 850 to 950°C are shown i n F i g u r e 6.14. I t can be seen t h a t the r e d u c t i o n rates were c l e a r l y slower than those of the base case; t h i s e f f e c t was more marked the lower the temperatures. The e f f e c t o f bed s e g r e g a t i o n , i . e . , l a r g e r coal p a r t i c l e s , on gas c o m p o s i t i o n i s shown i n Figure 6.15. It i s seen that the Pco/PCGv, r a t i o s remained c l o s e r to the FeO/Fe e q u i l i b r i u m v a l u e s , than t h o s e o f the base case, during the i n i t i a l stages of r e d u c t i o n . At l a t e r stages, they showed a stronger d e p a r t u r e , from t h e s e e q u i l i b r i u m v a l u e s , t h a n those of the base case. 6.4.5 R e p r o d u c i b i l i t y t e s t s T e s t s of experimental r e p r o d u c i b i l i t y were performed throughout the main experimental block. Tests were repeated f o r the base case a t 800°C and 900°C and f o r the s t o i c h i o m e t r i c Cp^/Fe r a t i o at 900°C. The 131 100 5 0 -2 0 I 0 (VI O o Q. \ o 0° 0.5 0.2 0 Boudouard equil 900 °C 850°C Ov o 950°C / " - / i 9 50°C 900°C 850°C 'FeO'/Fe equil * * i ' FeJD./FeO' equil • !950°C ~ 4 Cfjx/Fe =0.32 dc/dF,= 1.0 d F e =90^m 1 0 0.2 0.4 0.6 0.8 Fractional reduction ID 6.13 Change i n Pco/pCQo r a t 1' 0 w l ' t h f r a c t i o n a l r e d u c t i o n during experiments with f i n e r p a r t i c l e s ; c o n d i t i o n s as shown 132 Time (min) 6.14 P l o t of f r a c t i o n a l r e d u c t i o n versus time showing the e f f e c t of bed segregation; c o n d i t i o n s as shown . 133 100 50 20 10 CM O o Q. 1 ' 950°C ' 1 — Boudouard equil 900°C — 850°C y / — 0.5 0.2 0.1 9 50°C, o 900°C^ • 850°C dpe= 358 fj. m Fe304/Fe0 equil 0.2 0.4 0.6 0.8 Fractional reduction 1.0 6.15 Change i n Pco/pCOo r a t i o with f r a c t i o n a l reduction during experiments with segregated bed; co n d i t i o n s as shown . 134 f r a c t i o n a l reduction r e s u l t s are shown i n Figure 6.16. It i s seen that the agreement between the repeated experiments i s w i t h i n 1.5 p e r c e n t , e x c e p t i n the 900°C base case experiment. The unusual pattern followed by experiment number R12 r e q u i r e d that i t be r e p e a t e d . Experiment R58 was the r e s u l t and was used f o r a l l subsequent c a l c u l a t i o n s . 6.4.6 Preliminary d i s c u s s i o n of r e s u l t s from  the main experimental block" B e f o r e the r e s u l t s presented above can be discussed, c o n s i d e r a -t i o n must be given to several c h a r a c t e r i s t i c s of the r e a c t i n g system, namely: i ) Sample gas a n a l y s i s as r e l a t e d to the time-lag, i . e . , the time the gases leave the s o l i d s - b e d to the moment of sampling, i i ) P o ssible reduction by hydrogen remaining i n the char, i i i ) Stoichiometry of the o v e r a l l reduction r e a c t i o n , i v ) P o s s i b l e e f f e c t of the SiC heating element o x i d a t i o n on the gas r e a c t i o n s (discussed i n Appendix F ) . The t i m e - l a g i s a f u n c t i o n of the gas flowrate f o r a given v o l -ume of r e a c t o r and gas t r a i n . The r e t e n t i o n time o f the gaseous p r o -d u c t s i n the gas f l o w system c o u l d t h e r e f o r e vary, within one e x p e r i -ment, from a few seconds up to several minutes with the d e c l i n e of reac-t i o n r a t e s , as was mentioned i n S e c t i o n 4.3.7. The longer r e t e n t i o n times are of concern because there e x i s t e d the p o s s i b i l i t y of i n t e r m i x -i n g o f the gaseous products from d i f f e r e n t stages of the r e a c t i o n . The gas l i n e was comprised e s s e n t i a l l y of three s e c t i o n s : the end-pipe, the 135 1.0 0.9 0.8 0.7 0.6 0.5 1 / I V Lll o* 900°C, Cfjx/Fe = 0.32 AA 900°C,Cfjx/Fe = 0.16 • • 800°C,Cfjx/Fe = 0.32 ^ R 52 :B^-R45 rpm =14 % f i l l =14 d c / d F c = 0.5 dFe= 358 .^m 0 8 0 160 Time (min) 240 6.16 P l o t of f r a c t i o n a l r e duction versus time f o r experimental r e p r o d u c i b i l i t y ; c o n d i t i o n s as shown . 136 c o o l e r and the p l a s t i c tubing, as were described i n Section 4.3.7. Re-s u l t s of c a l c u l a t i o n s of the r e t e n t i o n times i n each s e c t i o n of the gas system, f o r the lower gas f l o w r a t e s at 0.80, 0.90 and 0.95 f r a c t i o n a l reduction are presented i n Table XIX. The assumed gas t e m p e r a t u r e s i n each s e c t i o n were: 950°C i n the freeboard, 500°C i n the end pipe, 100°C i n the c o o l e r and room temperature i n the p l a s t i c t u b i n g . I t can be o b s e r v e d t h a t the r e t e n t i o n time i n the e n t i r e system was about 7 min-u t e s a t fR = 0.95, 2 minutes at f ^ = 0.90 and l e s s than 1 minute at f ^ = 0.80. Furthermore, i f i t i s c o n s i d e r e d t h a t the gases s p e n t o n l y about 60 p e r c e n t o f t h i s time i n the freeboard, where mixing might be more l i k e l y to occur because i n the gas l i n e s plug flow would be expect-ed to dominate, the mixing e f f e c t i s even s m a l l e r . Since samples were taken every 30 minutes at these r e a c t i o n stages, the gas m i x i n g e f f e c t can be s a f e l y neglected below a f r a c t i o n a l reduction of 0.95. The extent of reduction c a r r i e d out by the trace amounts o f hy-drogen remaining i n the char i s considered next. F i r s t , the worst case i n t h i s regard, i . e . , the l a r g e s t amount of hydrogen c o n t a i n e d i n the i r o n - o r e / c h a r admixture, i s the 0.32 Cf-\x/Fe experiments where the max-imum weight r a t i o of c h a r to ore was used. In t h i s c a s e , the c h a r weight was 313 g with 0.31 percent hydrogen, which y i e l d s 0.485 moles of hydrogen p o t e n t i a l l y i n v o l v e d i n the r e d u c t i o n . Since the only p r o d u c t o f r e d u c t i o n by hydrogen c o u l d be water vapor, the maximum number of oxygen moles removed from Fe2°3 i s 0.243, which corresponds to 4.7 per-cent of the t o t a l oxygen present. It i s r e c o g n i z e d t h a t r e d u c t i o n by hydrogen i s more e a s i l y achieved than with carbon monoxide. The extent TABLE XIX. RETENTION TIME OF THE PRODUCT GASES AT DIFFERENT SECTIONS IN THE REACTOR Section D V [cm] [cm 3] Freeboard 11.5 3435 End-pipe 7.6 817 Cooler 2.5 147 Tubing 0.9 120 [cnw/min] [ s ] 0.80 8200 25 0.90 2870 72 0.95 820 251 0.80 5190 9 0.90 1820 27 0.95 519 94 0.80 2510 4 0.90 880 10 0.95 250 35 0.80 2000 4 0.90 800 9 0.95 200 36 138 o f t h i s can be e s t i m a t e d c o n s i d e r i n g , by way of i l l u s t r a t i o n , the f o l -lowing e q u i l i b r i a ! 4 0 : Q?7 P P FeO + CO = Fe + C0 2 ; - , C 0 2 / , C 0 = 0.443 (6.11) FeO + H 2 = Fe + H 20 ; K ; j 2 7 = P H 2 0 / P H 2 = 0.633 (6.12) PC0 * PH 0 C0 ? + H 2 = CO + hLO ; K:? 2 7 = 2 = 1.428 (6.13) r C 0 2 K H 2 Methane may a l s o be formed but to such a small extent as to be s a f e l y neglected. In the present case, the molar r a t i o o f carbon t o hydrogen i s given by C = 40.6% / 12 „. R 9 p H 0.31% //2 ^.o^o-S i n c e t h e r e w i l l be one mole of (CO + CO2) f o r each mole of carbon, and one mole of (H 2 + H 2 0) f o r each mole of hydrogen, then -P + P K C 0 * C 0 ? — = 21.828 P H 2 + PH 20 Als o , since the gas mixture i s only comprised of the four gases, (PCO + PC0 2) + (PH 2 + PH 20) = 1 atm Therefore, by s o l v i n g simultaneously these two r e l a t i o n s h i p s , the f o l lowing i s obtained: (PCO + p C 0 2 ) = ° - 9 5 6 a t " i and ( P H 2 + P H 0 ) = 0.044 atm 139 F i n a l l y , by r e c a l l i n g the e q u i l i b r i u m constants, Ki and K 2, the p a r t i a l pressure (and volume f r a c t i o n ) can be obtained, namely: PCO = 0.6625 p c o 2 = 0.2937 pH = 0.0268 2 PH 0 = 0.0170 2 This value f o r the hydrogen volume f r a c t i o n l i e s w e l l w i t h i n the range of values obtained i n the gas analyses; see Figure 6.3. However, an i n -crease i n the hydrogen content i s observed as the r e a c t i o n p r o c e e d e d . T h i s can be e x p l a i n e d by the f a c t t h a t the CO contents were a l s o i n -c r e a s i n g , through the Boudouard r e a c t i o n , and thus the e q u i l i b r i u m given by E q u a t i o n (6.13) tends to be d i s p l a c e d to the reactants s i d e . More-over, upon the c o o l i n g of the gases along the gas l i n e s , the d i s p l a c e -ment of the e q u i l i b r i u m to the reactants s i d e , i n Equation (6.13), was al s o favoured. From the foregoing, the f o l l o w i n g can be concluded: i ) The r a t e o f r e d u c t i o n i s a f f e c t e d , t o a s i m i l a r extent f o r a given temperature f o r a l l c o n d i t i o n s t e s t e d , by the hydrogen contents of the char. The maximum extent of reduction by hydro-gen i s 1.8 percent, i i ) The P c o / P c o r a t i o s are s i m i l a r l y a f f e c t e d to a small extent; c o n s i d e r a t i o n to t h i s was given when the Pco/pCO w e r e P l o t t e d . 140 The s t o i c h i o m e t r y of the o v e r a l l reduction r e a c t i o n , of obvious importance to the amount of carbon required to reduce a given oxide, can be analyzed as f o l l o w s . The two r e a c t i o n s , C + C0 2 = 2 CO (2.1) F e 2 0 3 + 3C0 = 2 Fe + 3 C0 2 (2.2) have been a s c e r t a i n e d to occur i n p a r a l l e l . But, to what e x t e n t w i l l each gaseous s p e c i e s , CO and C0 2, be u t i l i z e d to ca r r y out i t s respec-t i v e r e a c t i o n ? Two l i m i t i n g cases can be e s t a b l i s h e d by combining Equa-t i o n s (2.1) and (2.2), namely: 1/3 F e 2 0 3 + C = 2/3 Fe + CO ( C / F e ) w t = 0.32 (6.14) 1/3 F e 2 0 3 + 1/2 C = 2/3 Fe + 1/2 C0 2 ( C / F e ) w t = 0.16 (6.15) E q u a t i o n (6.14) c o n s i d e r s t h a t C0 2 reacts instantaneously with carbon whereas Equation (6.15) i s obtained by assuming that the reduction by CO occurs much more r a p i d l y than carbon g a s i f i c a t i o n . C l e a r l y , the o v e r a l l reduction r e a c t i o n given by Equation (6.15) w i l l be the more carbon e f -f i c i e n t o f the two, and a l s o w i l l s e t the minimum carbon required to car r y out the complete reduction of the oxide. It can thus be i n f e r r e d t h a t the " s t o i c h i o m e t r i c " proportion of carbon and Fe 203, w i l l depend on the r e l a t i v e rates of both reduction and g a s i f i c a t i o n r e a c t i o n s as has been t h e o r e t i c a l l y d i s c u s s e d b e f o r e . 1 0 5 I t i s a l s o evident, on the other hand, that i n experimental (and i n d u s t r i a l ) r e a c t i o n systems the gaseous phase w i l l be formed of both CO and C0 2. Therefore, the f o l l o w -ing o v e r a l l reduction r e a c t i o n can be po s t u l a t e d , 141 1/3 ') F e 2 ° 3 + (• + *) C = 2 / 3 ( R + 4, Fe + *C0 + | CO, 2 (6.16) where R i s the e q u i l i b r i u m CO/COg r a t i o f o r e i t h e r the reduction or the Boudouard r e a c t i o n s and <j> i s the CO mole f r a c t i o n corresponding to that e q u i l i b r i u m . The s t o i c h i o m e t r i c r a t i o c a l c u l a t i o n s can thus be perform-ed under the f o l l o w i n g assumptions: i ) When the Boudouard r e a c t i o n i s rate c o n t r o l l i n g , R and <)> w i l l be those of the reduction e q u i l i b r i u m ; conversely, when the r e -duction r e a c t i o n c o n t r o l p r e v a i l s , R and <t> w i l l be those of the Boudouard e q u i l i b r i u m , i i ) R and <j> i n the r e d u c t i o n e q u i l i b r i u m are taken to be those of w u s t i t e r e d u c t i o n s i n c e t h i s i s the slowest stage i n the Fe203 reduction sequence. R e s u l t s o f these c a l c u l a t i o n s are presented i n Table XX and Figure 6.17 f o r each type of c o n t r o l l i n g r e a c t i o n , a t the temperatures r e l e v a n t t o t h i s work. From these r e s u l t s , a Cp-j x/Fe of 0.16 was adopted f o r t h i s work as the " s t o i c h i o m e t r i c " value. An a l t e r n a t e treatment of the s t o i -c h i o m e t r y o f the o v e r a l l reduction r e a c t i o n could be developed, on the basis of the concept of the "gas u t i l i z a t i o n f a c t o r , " B , mentioned i n Section 2.3, Equations (2.8) and (2.9). The c h o i c e of the experiments of the base case was based on the f o l l o w i n g . With respect to Cp-j x/Fe, the 0.32 value was s e l e c t e d because 142 TABLE XX. STOICHIOMETRIC RATIOS FOR REDUCTION OF F e 2 0 3 WITH CARBON, UNDER TWO TYPES OF REACTION CONTROL: BOUDOUARD AND REDUCTION BOUDOUARD CONTROL Molar Ratio Weight Ratio C0/C0 2 C/Fe C/O c F i x / p e L i m i t 0 0.750 0.500 0.161 800 1.841 1.109 0.739 0.238 850 1.976 1.123 0.749 0.241 900 2.155 1.139 0.759 0.245 950 2.311 1.152 0.768 0.248 1000 2.448 1.163 0.775 0.250 REDUCTION CONTROL Molar Ratio Weight Ratio C0/C0 2 C/Fe C/0 c F i x / p e 800 3.598 1.232 0.821 0.265 850 17.868 1.425 0.950 0.306 900 37.462 1.462 0.975 0.314 950 70.429 1.479 0.986 0.318 1000 120.000 1.488 0.992 0.320 Li m i t » 1.500 1.000 0.322 800 850 900 950 1000 Temperature (°C) 17 S t o i c h i o m e t r i c Cpj x/Fe r a t i o as a fu n c t i o n of temperature for the reduction of Fe203 with carbon . 144 no f u r t h e r enhancement i n the reduction rate was obtained by i n c r e a s i n g the amount of coal char. With respect to p a r t i c l e s i z e , the 358 ^ m ore p a r t i c l e s were the l a r g e s t , i n a c c o u n t a b l e weight p r o p o r t i o n , i n the concentrate s i z e range (see F i g u r e 4.1); s m a l l e r p a r t i c l e s s h o u l d be reduced f a s t e r , as was proved with the experiments using 90>wm p a r t i -c l e s . The cha r p a r t i c l e s ( d c = 180 ym) mixed with the 358 y m ore were the l a r g e s t p o s s i b l e , with which a well mixed bed was s t i l l obtained, as shown by p o i n t R i n Figure 5.6. The d c/dp e r a t i o of 0.5 provided then the most ' d i f f i c u l t ' s i z e of ore to reduce. The 90 y m ore p a r t i c l e s , c o n v e r s e l y , p r o v i d e d the s m a l l e s t s i z e of ore to be reduced; they ac-count f o r more than 40 percent of the t o t a l c o n c e n t r a t e w e i g h t . T h i s ore s i z e was t e s t e d mainly due to i t s expected enhancing e f f e c t on the agglomeration growth. The e f f e c t of temperature on the reduction rate presented common features throughout the main experimental block, as i l l u s t r a t e d by F i g -ure 6.8, namely: i ) A p r o g r e s s i v e l y i n c r e a s i n g o v e r a l l reduction rate was produced by i n c r e m e n t s i n the temper a t u r e o f r e a c t i o n , from 800 t o 950°C. i i ) F r a c t i o n a l reduction higher than 0.85 was obtained, i n a l l cases but the s t o i c h i o m e t r i c Cf^x/Fet f o r temperatures at and above 850°C. i i i ) At 900 and 950°C, the reduction rates e x h i b i t e d a constant per-i o d up to about 0.6 f r a c t i o n a l r e d u c t i o n . Beyond t h i s p o i n t , they slowed down. 145 i v ) At 850°C the r e d u c t i o n r a t e s showed a decrease at about = 0.2. The rates then s l i g h t l y i n c r e a s e d up to about 0.6 from where they again decayed, v) At 800°C the reduction rates were slow. The reduction obtained i n most cases d i d not proceed much beyond f ^ = 0.3 which c o r r e -sponds to the s t a r t of wustite r e d u c t i o n . The drop i n r e d u c t i o n r a t e , a t about 0.2 f r a c t i o n a l reduction was not confined to the t e s t s a t 850°C. T h i s phenomenon can be seen b e t t e r by p l o t t i n g f r a c t i o n a l reduction rate as a f u n c t i o n of f r a c t i o n reduced. This i s i l l u s t r a t e d i n F i g u r e 6.18 f o r the base case o n l y . S i m i l a r p a t t e r n s were a l s o o b t a i n e d f o r a l l other c o n d i t i o n s . It i s seen that a drop i n the rates occurred between 0.1 and 0.2 f r a c t i o n a l r e d u c t i o n . T h i s was f o l l o w e d by a r e c o v e r y p e r i o d up to about 0.3. From then on, a f a i r l y constant rate p r e v a i l e d , up to d i f f e r e n t e x t e n t s o f r e d u c t i o n , whereupon the rates d e c l i n e d u n t i l complete reduction was achieved. S i m i l a r patterns i n the reduction rate have been observed be-f o r e 9 0 » 9 8 and they can be explained on the basis of the stage-wise r e -duction of Fe203 as f o l l o w s . A f r a c t i o n a l r e d u c t i o n o f 0.1 c l o s e l y corresponds to the com-p l e t e r e d u c t i o n of Fe203 to Fe304. This value should be 0.111 f o r pure Fe203 b u t , s i n c e the ore contained a f r a c t i o n of Fe304 (Table V I I I ) , a value of 0.101 i s obtained. S i m i l a r l y , the f r a c t i o n a l r e d u c t i o n c o r r e -s p o n d i n g to the n o n - s t o i c h i o m e t r i c range of w u s t i t e , Fen.881° t 0 Feo.9530, i s found between 0.221 and 0.273 i n s t e a d of 0.243 and 0.300. Fractional reduction 18 F r a c t i o n a l reduction rate as a func t i o n of f r a n c t i o n a l reduction f o r experiments of the base case . 147 A c c o r d i n g l y , the drop i n rate between 0.1 and about 0.2 f r a c t i o n a l r e -d u c t i o n c o r r e s p o n d s to r e d u c t i o n o f Fe304 to F e n < g g i 0 . ^ n i s °-roP 1 S sharper, and p r o p o r t i o n a l l y smaller, the higher the t e m p e r a t u r e . Sub-s e q u e n t l y , i n f u r t h e r r e d u c i n g to Feo.9530, a recovery i n the rate i s observed, again, of a l a r g e r magnitude with higher t e m p e r a t u r e s . T h i s i s f o l l o w e d by a p e r i o d of reasonably constant r a t e , to l a r g e r extents of reduction the lower the temperature; f i n a l l y , a decaying r a t e i s ob-ta i n e d . When the gas c o m p o s i t i o n s o b t a i n e d are examined, Figures 6.9, 6.11, 6.13 and 6.15, three stages i n the PCO/POQ^ r a t i o are encountered i n most experiments. An i n i t i a l stage, up to the appearance of wustite, where the r a t i o s i n c r e a s e with f r a c t i o n a l r e d u c t i o n . This i s followed by a reasonably constant Pco/pCO P^ r i o d , i n d i c a t i v e of Boudouard reac-t i o n c o n t r o l by i t s proximity t o the o x i d e s e q u i l i b r i a . T h i s p e r i o d was s h o r t e r at 950° than a t 900°C and 850°C. The length of t h i s p e r i o d a l s o v a r i e d with the c o n d i t i o n s of the experiment. I t was l o n g e s t f o r the f i n e r p a r t i c l e s , followed i n decreasing order by the base case, the s t o i c h i o m e t r i c Cp-j x/Fe and the segregated bed experiments. F i n a l l y , a t h i r d stage of i n c r e a s i n g Pco/pCO r a t i o i s observed. From the foregoing observations, i t i s evident that a correspon-dence e x i s t s between the stages i n the reduction rates and Pco/pC02 r a" t i o s , as would be expected. The a n a l y s i s o f t h i s c o r r e s p o n d e n c e , i n Chapter 8, w i l l a i d i n d e t e r m i n i n g the r a t e c o n t r o l l i n g mechanism at each stage of the reduction r e a c t i o n . D e t a i l e d c o n s i d e r a t i o n w i l l be given to the p a r t i c l e s s i z e as w e l l . 148 6.5 Results of comparative experiments The aim of these experiments was to determine the e f f e c t s of ad-d i t i o n a l parameters, on the reduction r a t e s , i n order to f u r t h e r a s s e s s the s t a g e s o b s e r v e d i n the e x p e r i m e n t s of the main block. The para-meters t e s t e d separately were: a c a t a l y s t f o r the Boudouard r e a c t i o n , use o f l i g n i t e as r e d u c t a n t , use o f g r a p h i t e as reductant, i n e r t - g a s f l u s h i n g and reduction of hematite p e l l e t s . Operational c o n d i t i o n s were the same as i n the main experimental block, namely: 14 r.p.m., 14 per-cent l o a d i n g and 0.32 Cp n- X/Fe. 6.5.1 Reduction using a c a t a l y s t f o r the Boudouard r e a c t i o n The e f f e c t on the r e d u c t i o n r a t e s of a c a t a l y s t f o r the Bou-douard r e a c t i o n i s shown i n Figure 6.19. The c a t a l y s t was an equimolar mixture of l i t h i u m , sodium and p o t a s s i u m c a r b o n a t e s , p r e p a r e d as ex-p l a i n e d i n Section 4.23 and added i n an amount of 5 wt percent with r e -spect to the charge. I t i s seen i n F i g u r e 6.19 t h a t r e d u c t i o n r a t e s were c o n s i d e r a b l y f a s t e r than i n the base case. The high degree of r e -duction achieved at 800°C i s e s p e c i a l l y remarkable. The gas c o m p o s i t i o n f o r t h e s e e x p e r i m e n t s i s shown i n Figure 6.20. The Pco/pCO r a t i o s are markedly d i f f e r e n t than those of the base c a s e . The second stage, c h a r a c t e r i z e d by constant Pco/PfJOg r a t i o s , was n o n - e x i s t e n t at e i t h e r temperature with the c a t a l y s t . The Pr ,o/ pC0 2 r a~ t i o s were higher than i n the base case, throughout the e n t i r e r e d u c t i o n , a t both temperatures and the r a t i o s increased f a s t e r , than those of the base case, i n the l a s t stage. 149 Time (min) 6.19 P l o t of f r a c t i o n a l reduction versus time showing the e f f e c t of a c a t a l y s t of the Boudouard r e a c t i o n ; c o n d i t i o n s as shown . 100 50 900 °C 20 0 900°C Boudouard equil (catalyzed) 0' / 800°C (N2flush) O 0° o 0_° 800°C_ _ /• • ^ ©-®800eC _ e^r^ (catalyzed) ©rT . 3DD1Q. _ _ 0.5 0.2-0. 0 0.2 0.4 0.6 0.8 Fractional reduction .0 20 Change i n Pcrj/PcOo r at"»° with f r a c t i o n a l reduction durin c a t a l y z e d and ^ - f 1 u s r n n 9 experiments; c o n d i t i o n s as shown . 151 6.5.2 Reduction with l i g n i t e F r a c t i o n a l r e d u c t i o n p l o t s , using l i g n i t e , are shown i n Figure 6.21. The reduction rates were c o n s i s t e n t l y s l o w e r than those of the base case; t h i s can be seen by comparing Figures 6.8 and 6.21. This e f -f e c t was more marked the lower the temperature. The gas c o m p o s i t i o n , shown i n F i g u r e 6.22, d i f f e r e d from the base case p r i m a r i l y i n that the Pco/pCO c o n s t a i r t periods were s l i g h t l y s horter and c l o s e r to the FeO/Fe e q u i l i b r i a f o r the l i g n i t e c o a l . 6.5.3 Reduction with graphite R e d u c t i o n w i t h a low r e a c t i v i t y carbonaceous m a t e r i a l , such as graph i t e , i s expected to be minimal i n the range of temperatures t e s t e d . N o n e t h e l e s s , an e x p e r i m e n t was conducted with t h i s material to v e r i f y t h i s hypothesis. Temperature was v a r i e d from 875 t o 950°C d u r i n g the t e s t w i t h the r e s u l t s shown i n Figure 6.23. It i s seen that the reduc-t i o n rate was extremely slow, even at 950°C. The gas a n a l y z e d was a l -most pure C02* 6.5.4 E f f e c t of i n e r t - g a s f l u s h i n g In t h i s e x p e r i m e n t a 4000 cm 3/min f l o w of nitrogen was blown over the bed surface, shown by N-N1 i n F i g u r e 4.3. The e f f e c t on the r e d u c t i o n r a t e i s shown i n F i g u r e 6.23. It i s seen that the r e a c t i o n slowed down a f t e r a f r a c t i o n a l reduction of 0.8, and stopped completely, j u s t above a f r a c t i o n a l reduction of 0.9. The corresponding e f f e c t on gas composition i s shown i n F i g u r e 6.20. A s l i g h t decrease i n Pco/pCOo r a t i o i s seen during the reduction 152 A X 8 5 0 ° C Lignite C f i x/Fe=0.32 dc/d F e=0.5 d F e = 358/xm rpm =14 % f i l l = 14 160 Time (min) 240 6.21 P l o t of f r a c t i o n a l reduction versus time f o r reduction with Saskatchewan l i g n i t e ; c o n d i t i o n s as shown . N O 0 ° \ o 0.° 100 50 20 10 5 0.2 0.1 T 950°C Boudouard equil 900°C 850°C 950°C o — o — o 950°C FeO'/Fe equil 850°C 950°C Fe304/'FeO'equil Lignite Cfjx/Fe - 0.32 d c /dF, = 0.5 dpe = 358/i.m 0.2 0.4 0.6 0B Fractional reduction 1.0 .22 Change i n Pco/pCQo r a t i o with f r a c t i o n a l reduction f o r experiments with l i g n i t e ; c o n d i t i o n s as shown . 154 6.23 P l o t of f r a c t i o n a l reduction versus time showing the e f -f e c t s of N 2 - f l u s h i n g on r e d u c t i o n with Forestburg coal and reduction with graphite; c o n d i t i o n s as shown . 155 o f w u s t i t e , up to a f r a c t i o n a l r e d u c t i o n of about 0.8, whereupon the r a t i o increased d r a m a t i c a l l y . 6.5.5 Reduction of hematite p e l l e t s Commercial hematite p e l l e t s (67 percent i r o n ) were reduced, t o -gether with the concentrate, i n several of the experiments. Two p e l l e t s o f d i f f e r e n t s i z e s , 14 and 19 mm i n diameter, were reduced i n each of these t e s t s . P e l l e t s were reduced a t e v e r y t e m p e r a t u r e , from 800 t o 950°C, at l e a s t once. The extent of reduction of the p e l l e t s was deter-mined from t h e i r t o t a l weight l o s s , assumed to be oxygen removed. A summary o f the c o n d i t i o n s t e s t e d and the r e s u l t s obtained are presented i n Table XXI compared to the reduction of the r e s p e c t i v e concentrates. At 800°C, d u r i n g the segregated-bed c o n d i t i o n s , the f r a c t i o n a l reduction of the smaller p e l l e t was p r a c t i c a l l y the same as t h a t of the c o n c e n t r a t e ; the l a r g e r p e l l e t though, was 10 percent l e s s reduced. On the other hand, during the c a t a l y z e d experiment at the same temperature, both the l a r g e and small p e l l e t s were 40 percent l e s s reduced than the concentrate but were at l e a s t 15 percent more reduced than t h e i r coun-t e r p a r t s i n the s e g r e g a t e d - b e d c o n d i t i o n s . At 850°C, during both the base case and the f i n e r p a r t i c l e s r e d u c t i o n , p e l l e t s were reduced a t l e a s t 50 percent l e s s than the concentrates with a very small d i f f e r e n c e i n reduction between p e l l e t s . At 900°C, during the r e d u c t i o n of f i n e r p a r t i c l e s , the d i f f e r e n c e i n the extent of reduction was about 40 per-cent; again a minor d i f f e r e n c e was seen between p e l l e t s a t t r i b u t a b l e to t h e i r s i z e d i f f e r e n c e . F i n a l l y , at 950°C, the extent of p e l l e t reduc-t i o n , during the reduction of the f i n e r p a r t i c l e s was p r a c t i c a l l y the 156 TABLE XXI. CONDITIONS AND RESULTS FOR REDUCTION OF HEMATITE PELLETS T d c I n i t i a l weight F i n a l fR. Bed c o n d i t i i r c ] [ym] [g] P e l l e t s Ore 800 100 10.8293 6.6536 0.4358 0.4328 0.830 0.830 Catalyzed 90 9.9766 5.8585 0.1919 0.2912 0.297 0.297 Fine Mixture 850 90 9.7635 6.4264 0.3955 0.4203 0.932 0.932 Fine Mixture 180- 7.5026 0.4150 0.913 Base Case 900 90 8.5451 6.8137 0.4617 0.4358 0.861 0.861 Fine Mixture 950 716 12.4747 5.5047 0.7838 0.9294 0.973 0.973 Segregated 90 9.7947 6.7192 0.9592 0.9687 0.997 0.997 Fine Mixture 157 same f o r both the concentrate and p e l l e t s , without any e f f e c t of p e l l e t s i z e . However, during the segregated-bed experiment at the same tempera-t u r e , the smaller p e l l e t was 15 percent more reduced than the l a r g e r but 5 percent l e s s than the r e s p e c t i v e concentrate. 6.5.6 Preliminary d i s c u s s i o n of r e s u l t s from the comparative experiments The f a c t that the presence of a c a t a l y s t f o r the Boudouard reac-t i o n i n c r e a s e d the r e d u c t i o n r a t e , through i t s e f f e c t on gas composi-t i o n , i s not s u r p r i s i n g . That r e a c t i o n has been i d e n t i f i e d as the r a t e determining step by several of the i n v e s t i g a t i o n s reviewed i n Chapter 2. However, when comparing t h i s work with t h o s e p r e v i o u s l y r e p o r t e d , the m i x i n g c o n d i t i o n s , p a r t i c l e s s i z e and carbonaceous material r e a c t i v i t y are found to be s i g n i f i c a n t l y d i f f e r e n t . In a d d i t i o n an i n e r t - g a s d i -l u e n t was u t i l i z e d i n most of the e a r l i e r s t u d i e s . It might be a n t i c i -pated that d i f f e r e n t c o n t r o l l i n g mechanisms may be involved i n the p r e -s e n t i n v e s t i g a t i o n , p a r t i c u l a r l y i n the l a t e r reduction stages. This may a l s o be i n f e r r e d from a c a r e f u l study of the Pco/PCGv, r a t i ° obtained i n the experiment when a nitrogen f l u s h was used, see F i g u r e 6.20. In t h i s t e s t , the r a t i o followed very c l o s e l y the shape of the e q u i l i b r i u m l i n e s f o r the oxide r e d u c t i o n . This i n d i c a t e s that the Boudouard r e a c -t i o n p l a y e d a more i m p o r t a n t r o l e under diluent-gas c o n d i t i o n s . This can be analyzed as f o l l o w s . There i s e v i d e n c e t h a t back d i f f u s i o n o f i n e r t gas i n t o the s o l i d s bed i s p o s s i b l e i n the thermogravimetric ex-p e r i m e n t s reviewed i n S e c t i o n 2.3.103 j h i s was estimated to be the 158 case, by c a l c u l a t i o n s based on ordinary molecular d i f f u s i o n i n t o a stag-nant gas f o r two o f the t h e r m o g r a v i m e t r i c r e d u c t i o n s t u d i e s r e v i e w -ed. 96,102 i n these experiments, 8 and 0.85 g samples were reduced under i n e r t gas flows of 200 and 2000 cm^/min, r e s p e c t i v e l y . Inert gas flows of 15 and 1400 £/min would have had to have been used i n the p r e s e n t study i n o r d e r to o b t a i n s i m i l a r r a t i o s of i n e r t gas to sample weight. A lower flow of 4000 cm^/min was used i n the present study, based on evidence that i n e r t gas d i f f u s i o n i n t o the bed i s more e a s i l y a c h i e v e d i n a r o t a r y k i l n . 8 Moreover t h i s lower flow would correspond b e t t e r with the range of nitrogen flow, v i a i n j e c t e d a i r , i n an i n d u s t r i a l r o -t a r y k i l n . 7 T h e r e f o r e , the c o n d i t i o n s f o r nitrogen d i f f u s i o n i n t o the bed were p o s s i b l e i n the experiment. The d i l u t i o n of the r e a c t i n g gases w i t h i n the bed f a v o u r e d the Boudouard r e a c t i o n to be rate c o n t r o l l i n g over a l a r g e r extent of the r e d u c t i o n . The lower r e d u c t i o n rate obtained when l i g n i t e was used as r e -ductant can only be e x p l a i n e d on the b a s i s of the lower ash c o n t e n t o f t h i s m a t e r i a l as compared w i t h the sub-bituminous coal char. The c a t a l y t i c e f f e c t of ash on the Boudouard r e a c t i o n has been a s s e r t e d be-f o r e . ! 14,117 Therefore, since the Boudouard r e a c t i o n c o n t r o l s the over-a l l r eduction process to a c e r t a i n extent, a slower g a s i f i c a t i o n r e a c -t i o n w i l l r e t a r d the r e d u c t i o n . This stronger c o n t r o l by the Boudouard r e a c t i o n , during the f i r s t h a l f of the reduction process, can be c o r r o -b o r a t e d by the i n c r e a s e d c l o s e n e s s of the Pco/Pc^ r a t i o s to the 'FeO'/Fe e q u i l i b r i a i n the l i g n i t e experiments over the base c a s e , F i g -u res 6.22 and 6.9 r e s p e c t i v e l y . The minimal reduction obtained with 159 g r a p h i t e , even a t 950°C, again shows the importance of the Boudouard r e -a c t i o n when such a l o w - r e a c t i v i t y material i s used. Further d i s c u s s i o n on the e f f e c t o f the c a r b o n a c e o u s - m a t e r i a l r e a c t i v i t y on the o v e r a l l r e a c t i o n k i n e t i c s i s to be given i n Chapter 8. The e x p e r i m e n t s w i t h p e l l e t s were c a r r i e d out to compare the t o t a l extent of reduction of l a r g e r p a r t i c l e s with that of the f i n e ore. The p e l l e t s were expected to remain i n s i d e the bed, as was corroborated by v i s u a l i n s p e c t i o n a f t e r the experiments had ended. I t i s t h e r e f o r e assumed that the p e l l e t s encountered the same reducing c o n d i t i o n s as the ore concentrate. In general, the higher the t e m p e r a t u r e , the s m a l l e r the d i f f e r e n c e i n r e d u c t i o n between p e l l e t s and concentrate. This was to be expected since the Pco/Pcc^  r a t l 0 S i n t n e bed increased with tem-perature, and t h e r e f o r e the reducing p o t e n t i a l was higher. 160 CHAPTER 7 STUDY OF PARTICLES AGGLOMERATION DURING REDUCTION One of the o b j e c t i v e s of t h i s work was to c h a r a c t e r i z e the ag-g l o m e r a t i o n of the f i n e p a r t i c l e s w i t h i n the s o l i d s bed and on the f u r -nace wall during r e d u c t i o n . Since no a c c r e t i o n s were formed on the r e -a c t o r w a l l , most l i k e l y due to the r e l a t i v e l y low temperatures of opera-t i o n , only the agglomeration of p a r t i c l e s w i t h i n the bed i s examined i n t h i s c h a p t e r . The r e s u l t s are p r e s e n t e d as a comparison between the p a r t i c l e s i z e d i s t r i b u t i o n of the reduced p r o d u c t and the o r i g i n a l charge. These are complemented with observations using a scanning e l e c -tron microscope. 7.1 P a r t i c l e s i z e d i s t r i b u t i o n a f t e r reduction The p a r t i c l e s i z e of the i r o n - o r e concentrate b e f o r e r e d u c t i o n was - 410 + 305 ym ( d p e = 358 ym) i n a l l cases but one, where the s i z e was - 107 + 74 ym (dp e = 90 ym). The r e s u l t s of the p a r t i c l e s i z e d i s -t r i b u t i o n a f t e r reduction under d i f f e r e n t c o n d i t i o n s are shown i n F i g -ures 7.1 t h r o u g h 7.4. In each f i g u r e , the narrow s i z e range of the s t a r t i n g material i s shown by v e r t i c a l d o t t e d l i n e s . The p e r c e n t a g e u n d e r s i z e a t which the p a r t i c l e s - s i z e d i s t r i b u t i o n crosses the upper-s i z e l i m i t , provides a q u a l i t a t i v e measure of the agglomeration growth. 100 80 60 40 20 15 II A - i * K - ^ H / / ^ 800°C /i 850,900°C A / / / o / / / / /950°C / - a - P — Q ' I | I L 60 100 200 400 1000 2000 Agglomerate size (ft-m ) 4000 8000 P a r t i c l e s i z e d i s t r i b u t i o n a f t e r reduction of 90 y m p a r t i c l e s . 200 400 1000 2000 400 1000 3000 Agglomerate size (/xm) 2 P a r t i c l e s i z e d i s t r i b u t i o n a f t e r reduction, (a) base case; (b) c a t a l y z e d experiments . P a r t i c l e size d i s t r i b u t i o n a f t e r reduction. (a) Segregated bed (b) Stoichiometric C_. /Fe Agglomerate size ifim) .4 P a r t i c l e s i z e d i s t r i b u t i o n a f t e r r eduction. (A) base case; (B) L i g n i t e reductant . 165 On t h i s b a s i s , the l a r g e s t agglomeration of p a r t i c l e s was ob-t a i n e d when the dp e = 90 ym ore was reduced, as shown i n Figure 7.1. It i s seen that more agglomeration was produced the higher the temperature. At 900 and 850°C however, the extent of agglomeration was very s i m i l a r . A few of the agglomerates were as l a r g e as 10 mm. At 800°C, the p a r t i -c l e s agglomerated to a l e s s e r extent. In Figure 7.2 the p o s i t i v e e f f e c t of the c a t a l y s t on agglomeration i s i l l u s t r a t e d . T h i s e f f e c t was more pronounced a t h i g h e r temperature. By comparing Figure 7.3 with Figure 7.2(A) the e f f e c t s of C p i x / F e and bed segregation can be seen. S l i g h t l y more agglomeration was produced when the s t o i c h i o m e t r i c Cp-j x/Fe was em-ployed. Bed segregation, on the other hand, increased the agglomerating tendency o n l y at 850°C; at 900°C the extent of agglomeration was prac-t i c a l l y the same whereas at 950°C l e s s agglomeration was obtained i n the segregated bed. F i n a l l y , the e f f e c t of using a l i g n i t e reductant i s i l -l u s t r a t e d i n Figure 7.4. It i s seen that agglomerate s i z e s are l a r g e r w i t h l i g n i t e than t h o s e w i t h sub-bituminous coal at temperatures from 850 to 905°C. A q u a n t i t a t i v e measure of the agglomeration can be given by the f o l l o w i n g r e l a t i o n s h i p ^ : Agglomeration = ^ 2 9 (7.1) dFe where the average diameter of the agglomerates, d^gg, i s given by 166 X-j i s the amount of material r e t a i n e d between two sieve s i z e s and dn- i s the average s i z e of the openings i n those s i e v e s . A summary of the c a l -c u l a t i o n s based on the above, f o r a l l c o n d i t i o n s t e s t e d , i s presented i n F i g u r e s 7.5 and 7.6 f o r cTAgg and ^Agg/^Fe r e s p e c t i v e l y . In these f i g -ures the e f f e c t s described above can be c l e a r l y seen. The strong e f f e c t of s m a l l e r ore p a r t i c l e s on a g g l o m e r a t i o n , i n a b s o l u t e and r e l a t i v e terms i s evident. I t i s a l s o seen t h a t t e m p e r a t u r e d i d not e x e r t a marked e f f e c t when segregation i n the bed was present. 7.2 Scanning e l e c t r o n microscope observations The reduced products were examined under a scanning e l e c t r o n mi-croscope. An example of the agglomerates formed during the reduction of 90 m p a r t i c l e s i s shown i n Figure 7.7. I t was d e t e r m i n e d by the ob-s e r v a t i o n of several samples from non-catalyzed c o n d i t i o n s that the ag-glomerates were held together p r i m a r i l y by the i r o n whiskers which grow as a product of the r e d u c t i o n ; t h i s i s shown i n Figure 7.8. This pho-tograph shows two reduced g r a i n s , one on top and the o t h e r a t the b o t -tom, j o i n e d together. R e l a t i v e l y few non-metallic p a r t i c l e s were found between the reduced g r a i n s . P a r t i c l e s which were found i n t h i s r e g i o n , as i l l u s t r a t e d i n F i g u r e 7.9, appeared to be e n t a n g l e d by the i r o n -whiskers rather than being bonded to the reduced g r a i n s . A d i f f e r e n t p a t t e r n was observed when the agglomerates formed during reduction with the c a t a l y s t were examined. As shown i n Figure 7.10, c o n s i d e r a b l y more non-metallic p a r t i c l e s were found between the reduced g r a i n s . 1200 1000 8 0 0 E =L 6 0 0 Catalyzed cn 4 0 0 2 0 0 -Base case ° Stoichiometric'! |_ ( C f j x / F e ) 0 1 1 d F e =358/i. m d F e = 90/x m L 8 0 0 850 9 0 0 Temperature (°C) 950 .5 Agglomerates average s i z e as a fu n c t i o n of reduction temperature. Conditions of experiments as shown . 800 850 900 950 Temperature (°C) Agglomeration r e l a t i v e to the o r i g i n a l ore s i z e as a functio n of temperature. Conditions of experiments as shown . 7.7 Agglomerate formed during reduction of 90 ym i r o n ore p a r t i c l e s (lOOx) 7.8 Iron whiskers produced during reduction j o i n i n g two reduced p a r t i c l e s (800x) 1 7 0 7.9 S i l i c a t e p a r t i c l e between two reduced gra i n s (800x) 7.10 Agglomerate formed during r e d u c t i o n under c a t a l y z e d c o n d i t i o n s (lOOx) 171 7.3 Preliminary d i s c u s s i o n on p a r t i c l e s  agglomeration during reduction Before the agglomeration of p a r t i c l e s within the bed i s d i s c u s s -ed, c o n s i d e r a t i o n must be given to the absence o f a c c r e t i o n growth on the i n n e r wall of the r e a c t o r . As was mentioned above, one of the main reasons f o r the lack of these a c c r e t i o n s i s the r e l a t i v e l y low tempera-t u r e s a t which the experiments were c a r r i e d out. The highest tempera-ture t e s t e d , 950°C, i s s t i l l c o nsiderably below the melting p o i n t of any o f the p o s s i b l e phases to be formed between the high-alumina wall and the components of the charge. These phases, E u t e c t i c s 5 and 6 g i v e n i n T a b l e V, have melting temperatures of 1070 and 1165°C r e s p e c t i v e l y . In a d d i t i o n , the smoothness of the r e f r a c t o r y surface may have hindered the growth of a c c r e t i o n s . The l a r g e agglomeration growth, r e l a t i v e to the i n i t i a l p a r t i c l e s i z e , when the 90 ym p a r t i c l e s were reduced can be explained as f o l l o w s . In Chapter 2, the mechanisms o f agglomeration during the reduction of i r o n ores were e s t a b l i s h e d to be s i l i c a t e and i r o n 'bridges' j o i n i n g the p a r t i c l e s t o g e t h e r . At the temperatures t e s t e d however, the s i l i c a t e bridges w i l l play but a minimal r o l e i n the n o n - c a t a l y z e d e x p e r i m e n t s , as was confirmed by the microscopic observations. Therefore the number of i r o n bridges w i l l p r i m a r i l y determine the agglomerate growth. The number o f bridges w i l l i n turn be d i r e c t l y proportional to the s p e c i f i c surface area (area per u n i t mass) of the reduced i n d i v i d u a l p a r t i c l e s . The r a t i o of s p e c i f i c surface area of the 90 ym with respect to the 358 ym p a r t i c l e s i s obtained as f o l l o w s . The volume of a 90 ym p a r t i c l e i s 172 64 times smaller than that of a 358 ym p a r t i c l e s . Therefore, by d i v i d -ing the s p e c i f i c surface area of 64 small p a r t i c l e s by that of one l a r g e p a r t i c l e , a r a t i o of 4 i s obtained. T h e o r e t i c a l l y then, the 90 ym par-t i c l e s should agglomerate 4 times more, w i t h r e s p e c t to the o r i g i n a l p a r t i c l e s i z e , than the 358 ym p a r t i c l e s . This i s the case at 850 and 900°C, see Figure 7.6. D i v i d i n g the d Agg?dp e of the 90 ym p a r t i c l e s by that of the 358 ym p a r t i c l e s (base c a s e ) , r a t i o s of 3.19 and 3.96 are o b t a i n e d f o r 900 and 850°C r e s p e c t i v e l y . At 950°C however, t h i s r a t i o i s 6.28. This i s l a r g e r agglomeration than p r e d i c t e d and i s l i k e l y due to a s t r o n g e r e f f e c t of temperature on the bonds between smaller p a r t i -c l e s . The l a r g e degree of agglomeration obtained when the c a t a l y s t was used can only be explained i n terms of an e f f e c t of the c a t a l y s t on the s u r f a c e o f the n o n - m e t a l l i c p a r t i c l e s . At the temperatures t e s t e d the c a t a l y s t was i n the l i q u i d s t a t e . Moreover, the a l k a l i i o n s , L i + , Na + and K + may have r e a d i l y d i s s o l v e d the surface of the non-metallic p a r t i -c l e s , forming phases which tended to bond the i r o n p a r t i c l e s t o g e t h e r . T h i s i s c o n f i r m e d by examining Figure 7.11. It i s seen that the non-m e t a l l i c p a r t i c l e s between i r o n g r a i n s p o s s e s s a more rounded shape; even some d r o p l e t s are observed, which would i n d i c a t e the molten s t a t e of the c a t a l y s t . The smaller degree of agglomeration obtained f o r other v a r i a b l e s when 358 m ore p a r t i c l e s were reduced, can be explained on the basis of the c h a r a c t e r i s t i c c o n d i t i o n s of each t e s t . The s l i g h t increase i n ag-g l o m e r a t i o n f o r Cpix/Fe = 0*16 over the base case r e f l e c t s the enhanced p r o b a b i l i t y that reduced grains would contact each other given that 7.11 Non-metallic p a r t i c l e s between reduced i r o n g r a i n s during reduction under c a t a l y z e d c o n d i t i o n s (200x) 174 t h e r e were fewer c h a r p a r t i c l e s i n the bed. Very l i k e l y agglomeration would have proceeded f u r t h e r had the reduction been c o m p l e t e d . D u r i n g r e d u c t i o n under s e g r e g a t e d - b e d c o n d i t i o n s a t 850°C, the i r o n grains would have been c l o s e r together i n the core and therefore contacted each o t h e r more e a s i l y with the consequent enhanced growth of agglomerates. At 900 and 950°C however, t h i s was not observed. The a g g l o m e r a t e s o b t a i n e d under a l l c o n d i t i o n s discussed above were e a s i l y broken up by applying a g e n t l e p r e s s u r e . Moreover, t h e i r s i z e s s h o u l d not ca r r y dramatic consequences f o r the reduction process. This w i l l be f u r t h e r discussed i n Chapter 8. 175 CHAPTER 8 OVERALL DISCUSSION OF RESULTS AND PROPOSED MECHANISMS An o v e r a l l d i s c u s s i o n of the r e d u c t i o n k i n e t i c s i n the r o t a r y r e a c t o r i s p r o v i d e d i n t h i s chapter, based on the pre l i m i n a r y d i s c u s -sions given i n Sections 5.5, 6.3.4, 6.4.6, and 6.5.6. This i s o b t a i n e d by a p p l y i n g a v a i l a b l e k i n e t i c s r e l a t i o n s h i p s , f o r d i f f e r e n t rate-con-t r o l l i n g mechanisms, to the d i s t i n c t stages o b s e r v e d i n the r e d u c t i o n r a t e s and gas compositions. A c t i v a t i o n energies f o r the two r e a c t i o n s , carbon g a s i f i c a t i o n and oxide r e d u c t i o n , are als o obtained and compared to the v a l u e s reported i n the l i t e r a t u r e . F i n a l l y , e s t i m a t i v e c a l c u l a -t i o n s are made as to how an i n d u s t r i a l - s c a l e r o t a r y k i l n would p e r f o r m , when p r o c e s s i n g the ma t e r i a l s u t i l i z e d i n t h i s study. P a r t i c l e mixing and agglomeration c h a r a c t e r i s t i c s are incorporated i n the estimations as w e l l . 8.1 T e s t i n g of a v a i l a b l e k i n e t i c s r e l a t i o n s h i p s f o r the reduction of iron-oxides with carbon The complexity of the two r e a c t i o n s , i r o n - o x i d e r e d u c t i o n and carbon g a s i f i c a t i o n , o c c u r r i n g i n p a r a l l e l , does not allow a s i n g l e mechanism to properly d e s c r i b e the r e d u c t i o n path over the ranges o f tem p e r a t u r e , gas composition, p a r t i c l e s i z e and chemical composition of 176 p r a c t i c a l and e x p e r i m e n t a l i m p o r t a n c e . 1 4 0 Among the k i n e t i c s subpro-cesses e x i s t i n g i n the p a r a l l e l r e a c t i o n s scheme, shown i n F i g u r e 2.5, p r e v i o u s workers have s i n g l e d out the Boudouard r e a c t i o n and the d i f f u -sion of the gases through the reduced l a y e r of the o x i d e p a r t i c l e s t o be rate c o n t r o l l i n g over a major f r a c t i o n of the reduction process. The r e l a t i v e i n f l u e n c e exerted by each of these subprocesses on the o v e r a l l reduction r a t e , depends p r i m a r i l y on the temperature of operation and on the r e a c t i v i t y and p a r t i c l e s i z e o f each m a t e r i a l . In a d d i t i o n , the i n t e r m i x i n g o f the r e a c t i n g s o l i d s and gases and the presence of a d i -l u t i n g i n e r t gas could be important. A c c o r d i n g t o the c h a r a c t e r i s t i c s o f the present experimental system, gaseous d i f f u s i o n mechanisms should play but a minimal r o l e on the o v e r a l l reduction rate mostly owing to the p a r t i c l e s i z e s u t i l i z e d . A l s o , the p o s s i b l e i n f l u e n c e of hydrogen on the o v e r a l l reduction can be d i s c a r d e d based on the f o l l o w i n g . According to Equation (6.12) the r e -duction of FeO could be c a r r i e d out by hydrogen thus producing water va-pour. The l a t t e r would i n t u r n r e g e n e r a t e hydrogen by the water-gas r e a c t i o n , Equation (6.13), a l l t h i s happening within the ore p a r t i c l e s . However, i f t h i s was the p r e v a i l i n g sequence of re d u c t i o n , an increase i n the amount of char ( r e l a t i v e to ore) and t h e r e f o r e i n the amount o f hydrogen present, would have increased the reduction r a t e . This was not observed when doubling the amount of char during the e x p e r i m e n t s , c . f . Figure 6.4. Therefore, the o v e r a l l reduction rate w i l l l i k e l y be deter-mined by the i n d i v i d u a l r e a c t i o n rates of carbon g a s i f i c a t i o n and o x i d e r e d u c t i o n , at d i f f e r e n t stages of the process. The s h i f t i n c o n t r o l l i n g 177 mechanism can be i n f e r r e d from the observed changes in the gas composi-t i o n , e xemplified by Figure 6.9, as well as from the patterns p r e s e n t e d i n the f r a c t i o n a l reduction r a t e , i l l u s t r a t e d by Figure 6.18, at d i f f e r -ent extents of r e d u c t i o n . Accordingly, the o v e r a l l r e d u c t i o n sequence w i l l be t r e a t e d as three d i s t i n c t stages: Stage I, from the beginning of the r e a c t i o n to the end of the n o n - s t o i c h i o m e t r i c range o f w u s t i t e ; Stage I I , from the beginning of reduction of wustite to the end of the constant rate p e r i o d ; and Stage I I I , from the end o f the c o n s t a n t r a t e p e r i o d onwards. In terms of f r a c t i o n a l r e d u c t i o n , Stage I ends at f ^ = 0.273 depending on the composition of the ore and Stage II extends from fR = 0.273 to varying extents of r e d u c t i o n , which changes with the con-d i t i o n s of the system. The two chemical r e a c t i o n s , Boudouard and r e d u c t i o n , can be con-sidered to occur n e i t h e r i n s e r i e s nor i n p a r a l l e l s i n c e both c h e m i c a l p o t e n t i a l s are b e i n g generated by the two r e a c t i o n s o c c u r r i n g s i m u l t a -neously. Therefore, the Boudouard r e a c t i o n having the h i g h e s t a c t i v a -t i o n energy o f the two, the o v e r a l l process can be assumed to be con-t r o l l e d by t h i s r e a c t i o n . As the r e d u c t i o n p r o c e s s advances however, t h e r e w i l l be l e s s wustite a v a i l a b l e and the reduction r e a c t i o n becomes i n c r e a s i n g l y more important, therefore rate c o n t r o l l i n g s i n c e t h e r e i s always an excess of carbon present. 8.1.1 Boudouard r e a c t i o n as rate c o n t r o l l i n g mechanism When the Boudouard r e a c t i o n i s assumed to be the r a t e - d e t e r m i n -i n g s t e p i n the o v e r a l l r e d u c t i o n process, as i s assumed in t h i s case f o r Stages I and I I , the r e s u l t s of f r a c t i o n a l reduction can be analyzed 178 •in terms of the f r a c t i o n a l consumption of carbon. Therefore, by c o n s i -d e r i n g the Boudouard r e a c t i o n to obey f i r s t order kinetics,91,96-97 t n e rate of carbon consumption i s given by dW - — = kg Wc (8.1) dt where Wc i s the mass of carbon remaining and kg i s the rate constant f o r the Boudouard r e a c t i o n i n m i n - 1 . I n t e g r a t i n g Equation (8.1) and ex-pressin g i t i n terms of f r a c t i o n a l conversion of carbon, f c , y i e l d s In (1 - f c ) = - K B t (8.2) Thus, by p l o t t i n g l n (1 - fr;) vs t the value of the rate constant i s obtained. This i s presented i n Figures 8.1 through 8.6 f o r the d i f f e r -ent c o n d i t i o n s s t u d i e d ; a summary of the rate constants obtained i s g i v -en i n T a b l e XXII. In those f i g u r e s , the f r a c t i o n a l r e d u c t i o n , f ^ , c o r -responding to the departure from l i n e a r i t y i s i n d i c a t e d . Care must be e x e r c i s e d i n a s s e s s i n g t h i s p o i n t of departure, given the l o g a r i t h m i c nature of the p l o t s . When comparing t h e s e f i g u r e s w i t h t h o s e o f gas c o m p o s i t i o n , F i g u r e s 6.9, 6.11, 6.13, 6.15, 6.20 and 6.22, the c l o s e c o r r e s p o n d e n c e between the values of fR at the departure from l i n e a r i t y and t h o s e a t which, the Pco/ pC0 2 r a t 1 ° s t a r t e d to increase i s evident. Taking the base case as an example, the points of departure from l i n e a r -i t y i n Figure 8.1 occur a t f R of 0.59, 0.61 and 0.74, at 950, 900 and 179 P l o t of l n ( l - f c ) vs t f o r the base case experiments (Boudouard c o n t r o l ) . Time (min) P l o t of In (1-fr,) vs t f o r the s t o i c h i o m e t r i c C p i X / F e experiments (Boudouard c o n t r o l ) . 181 8.3 P l o t of In ( 1 - f r ) vs t f o r the f i n e r p a r t i c l e s experiments (Boudouard c o n t r o l ) . 182 8.4 P l o t of l n ( 1 - f r ) vs t f o r the segregated bed experiments (Boudouard c o n t r o l ) . 183 I _ 900°C, • cat -1.5 Catalysed 8 N2 flushed 2.0 50 100 150 Time (min) 200 250 8.5 P l o t of In (1 -frj) vs t f o r the c a t a l y z e d and ^ - f l u s h e d experiments (Boudouard c o n t r o l ) 184 8.6 P l o t of l n (1 - f r ) vs t f o r the l i g n i t e reductant experiments (Boudouard c o n t r o l ) . 185 TABLE XXII. REACTION RATE CONSTANTS FOR STAGES I THROUGH III DURING REDUCTION EXPERIMENTS Conditions Temp Stage I Stage II Stage III [°C] k B (10)2 k B (10)2 k R (10)3 Base case 950 2.28 4.85 8.75 900 1.51 2.05 5.40 850 0.62 0.73 3.26 S t o i c h i o m e t r i c Cp-j x/Fe 950 2.71 5.06 -900 1.62 2.26 -850 0.48 0.79 -F i n e r p a r t i c l e s 950 3.71 8.72 -900 1.64 2.10 -850 0.50 0.59 -Segregated bed 950 1.55 3.02 5.70 900 1.05 1.53 3.72 850 0.32 0.41 2.23 L i g n i t e 950 1.92 3.87 -900 1.11 1.30 -850 0.49 0.41 -Catalyzed 900 2.60 4.75 5.13 800 1.11 0.39 2.00 186 850°C r e s p e c t i v e l y . The c o r r e s p o n d i n g values of f ^ f o r the change i n gas composition, shown i n Figure 6.9, are 0.45, 0.60 and 0.70. The r e -l a t i v e l y l a r g e d i f f e r e n c e observed at 950°C i s due to the closeness of the points i n Figure 8.1 whereby the p o i n t of d e p a r t u r e from l i n e a r i t y cannot be seen very c l e a r l y . The r a t e constants of Stage II w i l l be analyzed f i r s t , i n terms of a c t i v a t i o n energy, f o r the f o l l o w i n g reason. The r e d u c t i o n o f wus-t i t e accounts f o r over two t h i r d s of the t o t a l , and represents the most d i f f i c u l t step i n the Fe203/Fe304/'FeO' reduction sequence. The a c t i v a t i o n energy, A E, f o r the Boudouard r e a c t i o n i s o b t a i n -ed by c o n s t r u c t i n g Arrhenius p l o t s of l n Kg vs 10 4/T. These are shown i n F i g u r e 8.7 f o r c o n d i t i o n s of the base c a s e , the s t o i c h i o m e t r i c Cp-j x/Fe, r e d u c t i o n w i t h l i g n i t e and the c a t a l y z e d experiments during Stage I I . The a c t i v a t i o n energy f o r the Boudouard r e a c t i o n with F o r e s t -burg c o a l i s e s t a b l i s h e d to be about 224 KJ/mole (53.5 kcal/mole) from the base case and s t o i c h i o m e t r i c Cp-j x/Fe experiments. This agrees well with the reported v a l u e s , i n C h a p t e r 2, f o r s i m i l a r c o a l c h a r s , and c a t a l y z e d c o k e s . The s l i g h t l y higher a c t i v a t i o n energies obtained f o r l i g n i t e and the c a t a l y z e d r e a c t i o n , 264 KJ/mole (63.1 kcal/mole) and 257 KJ/mole (61.4 kcal/mole) r e s p e c t i v e l y , can be r e a d i l y explained i n terms of the c a t a l y s i s of the Boudouard r e a c t i o n . The c a t a l y t i c e f f e c t e x e r t e d by a l k a l i oxides and i r o n on the Boudouard r e a c t i o n has been recognized. Since both components are p r e -sent i n most of the reduction experiments, a l k a l i oxides i n the coal ash and i r o n as the product of the r e a c t i o n , the o v e r a l l c a t a l y t i c e f f e c t has to be the a d d i t i o n of the e f f e c t s of each. Fresh i r o n i s present i n 8.7 Arrhenius p l o t s f o r base case, s t o i c h i o m e t r i c Cp-jx/Fe, l i g n i t e reductant and c a t a l y z e d e x p e r i -ments. Stage II (Boudouard c o n t r o l ) . 188 i n c r e a s i n g l y l a r g e r q u a n t i t i e s as the reduction proceeds. However, the points of contact with the coal p a r t i c l e s are l i m i t e d to the e x t e r n a l s u r f a c e o f the p a r t i c l e s ; furthermore, i t has been e s t a b l i s h e d that the i r o n c a t a l y s t i s deactivated more e a s i l y at lower t e m p e r a t u r e s , of the o r d e r o f 9 0 0 ° C . 1 4 1 The a l k a l i oxides, on the other hand, although pre-sent as a very small f r a c t i o n of the coal ash, are much more f i n e l y d i -vided, and evenly d i s t r i b u t e d through the coal p a r t i c l e s . Therefore, i n s p i t e of the rather d i f f e r e n t amounts of each of the c a t a l y s t compo-n e n t s , the c a t a l y t i c e f f e c t due to the a l k a l i oxides i n the coal ash i s l i k e l y the most important. This hypothesis i s supported by the f o l l o w -i n g . F i r s t l y , a s t r o n g c a t a l y t i c e f f e c t of i r o n on the ox i d a t i o n of g r a p h i t e has been observed,142 D U t the i r o n had to be impregnated i n t o the carbon by using a s a l t s o l u t i o n (20 percent FeCl3 i n H 2 O ) . When the i r o n was i n simple contact w i t h the g r a p h i t e the r a t e i n c r e a s e d o n l y s l i g h t l y . In the same study, the c a t a l y t i c e f f e c t of i r o n on more reac-t i v e forms of carbon was l e s s s i g n i f i c a n t ; t h i s n e g l i g i b l e e f f e c t a l s o was c o r r o b o r a t e d by Fruehan,96 when reducing i r o n oxides with coke and coal chars. Secondly, the a c t i v a t i o n energy f o r l i g n i t e g a s i f i c a t i o n i s about 10 p e r c e n t h i g h e r than t h a t f o r the F o r e s t b u r g sub-bituminous c o a l , c . f . , Figure 8.7. On examination of the ash contents and composi-t i o n s o f each c o a l char, shown i n Tables XVII and XVIII, and by c o n s i -dering that 313 g of Forestburg coal char and 272 g of l i g n i t e char were used to o b t a i n a C p i x / F e of 0.32 i n each case, i t can be as c e r t a i n e d that there was about 60 percent more K 20 when using Forestburg coal char and about 60 percent more Na 20 when using l i g n i t e . However, the K 20 i s 189 a conside r a b l y stronger c a t a l y s t than N a 2 0 1 0 2 and th e r e f o r e enhances the Boudouard r e a c t i o n i n the Forestburg c o a l . The A r r h e n i u s p l o t s f o r Stage II (Boudouard c o n t r o l ) , f o r the segregated bed and f i n e r p a r t i c l e s are compared to the base case i n F i g -ure 8.8. The s p r e a d of the p o i n t s f o r the s e g r e g a t e d bed, and the s l i g h t l y l a r g e r a c t i v a t i o n energy obtained of 232.8 KJ/mole (55.6 k c a l / -mole) can both be e x p l a i n e d by the f o l l o w i n g . F i r s t l y , i t can be seen i n Figures 6.15 and 8.4 that control by the Boudouard r e a c t i o n s o l e l y was exerted only during a small f r a c t i o n of the t o t a l r e d u c t i o n . There-f o r e , the ev a l u a t i o n of the rate constants was more u n c e r t a i n . Second-l y , the de-mixing s t a t e of the s o l i d s bed hindered the small c a t a l y t i c e f f e c t of i r o n . The r e l a t i v e l y high a c t i v a t i o n energy obtained f o r the ex p e r i m e n t s w i t h f i n e r p a r t i c l e s of 277.8 KJ/mole (66.2 kcal/mole) can only be explained i n terms of the coal p a r t i c l e s i z e . At 90 ym, more ash p a r t i c l e s may have r e a d i l y been l i b e r a t e d from the char and there-fore t h e i r c a t a l y t i c e f f e c t on the Boudouard r e a c t i o n diminished. F i n a l l y , by o b t a i n i n g the a c t i v a t i o n energy f o r Stage I of r e -duction, when m e t a l l i c i r o n was not y e t present, the separate c a t a l y t i c e f f e c t of the ash can be estimated. The Arrhenius p l o t i s shown in F i g -ure 8.9 and the a c t i v a t i o n energy obtained i s 231.1 KJ/mole (55.2 k c a l / -m o l e ) . T h i s v a l u e i s only s l i g h t l y higher (about 3 percent) than that f o r Stage II when m e t a l l i c i r o n i s already present. T h i s c o r r o b o r a t e s the s t r o n g e r c a t a l y t i c e f f e c t exerted by the coal ash when compared to that of m e t a l l i c i r o n and that the Boudouard r e a c t i o n a l s o c o n t r o l s the Stage I of r e d u c t i o n . The l a t t e r would be expected since the a c t i v a t i o n Arrhenius p l o t s f o r base case, segregated bed and f i n e r p a r t i c l e s experiments. Stage II (Boudouard c o n t r o l ) 191 e n e r g i e s f o r the Fe203-Fe3U4 and Fe3U4 to 'FeO' reduction by CO are 69 KJ/mole (16.5 k c a l / mole) and 73 KJ/mole (17.1 k c a l / m o l e ) r e s p e c t i v e - • l y . 1 4 3 The l e v e l l i n g o f f of the temperature dependence of KB i n Stage I a t the h i g h e r t e m p e r a t u r e , t h a t has been observed bef o r e , 9 4 » 9 6 > 9 9 i s due, at l e a s t i n p a r t , to gas d i f f u s i o n e f f e c t s i n t o both the iron-oxide and c o a l char p a r t i c l e s which a t low e x t e n t s of r e a c t i o n are not so porous as l a t e r i n the r e a c t i o n . This s l i g h t d i f f u s i o n e f f e c t can be a s c e r t a i n e d f u r t h e r by o b s e r v i n g i n Figure 8.8 the stronger curvature e x i s t i n g during the experiments under s e g r e g a t e d bed c o n d i t i o n s which in v o l v e d l a r g e r coal p a r t i c l e s . 8.1.2 Reduction r e a c t i o n as rate c o n t r o l l i n g mechanism It has been shown i n the previous s e c t i o n that the Boudouard r e -a c t i o n does not c o n t r o l the o v e r a l l r e d u c t i o n process over the f u l l range of r e d u c t i o n ; the extent of t h i s c o n t r o l depends on the e x p e r i -mental c o n d i t i o n s . Therefore, i n the l a t e r stages of the process, the r e s i s t a n c e s of the two r e a c t i o n s act i n s e r i e s and the o v e r a l l r a t e o f r e d u c t i o n d e c l i n e s . A k i n e t i c equation f o r reduction control i s given i n terms of f r a c t i o n a l reduction by145 1 - (1 - f R ) 1 / 3 = k R t (8.3) where KR i s the rate constant i n m i n - 1 f o r the reduction of 'FeO' by CO, since i n Stage III wustite w i l l be the o n l y i r o n - c o n t a i n i n g s p e c i e s . Thus, by p l o t t i n g l - ( l - f R ) l / 3 vs t the values of the rate contants can be obtained. This i s shown i n Figures 8.10 through 8.12 and a summary 8.9 Arrhenius p l o t s f o r base case, s t o i c h i o m e t r i c Cp-j x/Fe and segregated bed experiments. Stage I (Boudouard c o n t r o l ) 193 o f the v a l u e s of KR i s given i n Table XXII. It can be seen that a rea-s o n a b l y good l i n e a r f i t i s obtained i n going from the fR value f o r the end o f the Boudouard c o n t r o l by i t s e l f up to above fR = 0.80 i n a l l cases. The segregated-bed c o n d i t i o n , Figure 8.11, and the c a t a l y z e d ex-periments, Figure 8.12, have been chosen as examples because they showed a stronger departure from l i n e a r i t y , when the Boudouard r e a c t i o n was c o n s i d e r e d to be the rate l i m i t i n g step, and t h e r e f o r e t h e i r rate cons-t a n t s could be evaluated with more ease. The a c t i v a t i o n energy f o r the reduction r e a c t i o n i s a l s o o b t a i n -ed through the c o n s t r u c t i o n of Arrhenius p l o t s of In KR VS 10 4/T. These are shown i n Figure 8.13. The energy of a c t i v a t i o n f o r the reduction of 'FeO' by CO i s found to be 116.4 KJ/mole (27.8 kcal/mole) f o r the base case and s l i g h t l y lower f o r the segregated-bed c o n d i t i o n . T h i s v a l u e f a l l s w i t h i n the range reported by Themelis and G a u v i n 1 4 6 of 63 to 126 KJ/mole (15 to 30 kcal/mole), and match very c l o s e l y the value r e p o r t e d by Y u * 4 5 o f 113 KJ/mole (27 kcal/mole). The a c t i v a t i o n energy f o r the c a t a l y z e d r e a c t i o n i s about 15 percent lower and a l s o f i t s w e l l w i t h i n the reported values. 8.2 Overall view of the reduction process It has been shown i n the preceding s e c t i o n s t h a t the Boudouard r e a c t i o n c o n t r o l s the o v e r a l l r a t e of r e d u c t i o n , a t temperatures of 900°C and lower and under well-mixed c o n d i t i o n s , up to extents of f r a c -t i o n a l reduction which vary from 0.50 to 0.80. At 950°C, however, the 194 8.10 P l o t of 1 - ( l - f ) 1 / 3 vs t f o r base case experiments. Stage III (Reduction c o n t r o l ) 8.11 P l o t of 1 - ( 1 - f ) 1 / 3 vs t f o r segregated bed e x p e r i -ments. Stage III (Reduction c o n t r o l ) 196 8.12 P l o t of 1 - ( 1 - f ) 1 / 3 vs t f o r c a t a l y z e d experiments. Stage III (Reduction c o n t r o l ) 197 T(°C) - 3 - 6 - 7 950 9 0 0 850 800 1 1 1 1 AE kJ/mole kcal/mole o 116.4 27.8 o 108.9 26.0 — 98.1 23.4 -jvBase Segregated \. Catalyzed 1 1 a o 8.5 9.0 9.5 I0 4 /T(K _ I ) 8.13 Arrhenius p l o t s f o r base case, segregated bed and c a t a l y z e d experiments. Stage III (Reduction c o n t r o l ) 198 e x t e n t o f c o n t r o l by the Boudouard r e a c t i o n does not go beyond fR = 0.50. This i s but an obvious p o s i t i v e e f f e c t of temperature on the k i -n e t i c s of the c a r b o n - g a s i f i c a t i o n r e a c t i o n . The reduction r e a c t i o n , on the other hand, p l a y s a more impor-t a n t r o l e i n the second part of the o v e r a l l reduction r e a c t i o n up to fR values of about 0.95, at temperatures of 900°C and lower. At 950°C the c o n t r o l by the reduction r e a c t i o n s t a r t s e a r l i e r (fR = 0.50) l i k e l y due again to the strong e f f e c t of temperature on the k i n e t i c s of the Boudou-ar d r e a c t i o n . At t h i s temperature however, the i n c r e a s i n g control ex-e r t e d by the r e d u c t i o n r e a c t i o n i s somewhat more uncertain above fR = 0.85 ( i n d i c a t e d i n Figures 8.10 and 8.13). This can be e x p l a i n e d based on the f o l l o w i n g c o n s i d e r a t i o n s . At that f r a c t i o n a l reduction the par-t i a l l y reduced p a r t i c l e s already must have agglomerated. A g g l o m e r a t i o n o f f i n e reduced p a r t i c l e s has been demonstrated to set in from the be-g i n n i n g o f the w u s t i t e r e d u c t i o n . 1 2 9 The i n c r e a s e i n p a r t i c l e s i z e would produce an increase not only of the d i f f u s i o n e f f e c t s , but also of the mass t r a n s f e r e f f e c t s through an increased boundary l a y e r thickness around the agglomerated p a r t i c l e s , because of t h e i r l a r g e r s i z e . The boundary l a y e r e f f e c t would be f u r t h e r enhanced by the lower r e a c t i o n r a t e , hence lower gas v e l o c i t y , present at t h i s l a s t stage of r e d u c t i o n . T h i s i n t e r p r e t a t i o n i s supported by the r e l a t i v e l y sharper drop observ-ed i n the reduction rate of f i n e r p a r t i c l e s , Figure 6.12, which e x h i b i t -ed the gr e a t e s t agglomeration, Figure 7.1. The c a t a l y z e d experiments aided i n c l a r i f y i n g the r e a c t i o n mech-anisms o f the ' u n c a t a l y z e d 1 r e d u c t i o n process. The c a t a l y s t presence a c c e l e r a t e d the reduction through i t s e f f e c t on the Boudouard r e a c t i o n ; 199 r e a s o n a b l e r e d u c t i o n was thus o b t a i n e d even a t 800°C. However, the u t i l i z a t i o n of t h i s c a t a l y s t i n an i n d u s t r i a l process i s hindered by i n -h e r e n t o p e r a t i o n a l problems, as w i l l be discussed i n the f o l l o w i n g sec-t i o n . 8.3 Estimative c a l c u l a t i o n s f o r the operation  of an i n d u s t r i a l - s i z e r o t a r y k i l n The reduction of iron-oxide with carbon i n an i n d u s t r i a l r o t a r y k i l n i n v o l v e s phenomena of p a r t i c l e mixing, gas flow, heat t r a n s f e r and r e a c t i o n k i n e t i c s . These phenomena are s t r o n g l y i n t e r r e l a t e d and can change a l o n g the r e a c t i o n path; t h i s renders an i n t e g r a t e d a n a l y s i s of the process d i f f i c u l t . For in s t a n c e , the degree o f m i x i n g i n the bed not o n l y w i l l a f f e c t the r e a c t i o n k i n e t i c s but als o the heat t r a n s f e r mechanisms wit h i n the bed; heat t r a n s f e r w i l l a f f e c t the a g g l o m e r a t i o n growth and t h e r e b y the reduction k i n e t i c s and the p a r t i c l e s mixing be-haviour; and so on. M i x i n g o f i r o n ore and co a l p a r t i c l e s together, at the s i z e s u t i l i z e d i n t h i s work, had not been s t u d i e d b e f o r e . As d i s c u s s e d i n Section 5.5, not only the density and s i z e r a t i o s are important but als o other f a c t o r s exert an i n c r e a s i n g e f f e c t as the coal s i z e d e c r e a s e s . These are the f r i c t i o n c o e f f i c i e n t and p o s s i b l y e l e c t r o s t a t i c forces be-tween the p a r t i c l e s . Since these are a l l i n t e n s i v e p r o p e r t i e s , t h e i r e f f e c t i n a l a r g e r s i z e o p e r a t i o n i s l i k e l y to p e r s i s t . However, one f u r t h e r f a c t o r has to be considered with respect t o p a r t i c l e m i x i n g i n an i n d u s t r i a l o p e r a t i o n . T h i s i s the p a r t i a l f l u i d i z a t i o n of the bed 200 caused by the p r o p o r t i o n a l l y l a r g e r flowrates of gases evolved. The bed surface area to volume r a t i o , A/V f o r instance, i n a 2.1 m diameter k i l n i s about 4 nr* whereas that f o r the present study i s 48 n r 1 . Therefore, tendency to f l u i d i z e the top l a y e r s of the bed would be l a r g e r i n an i n -d u s t r i a l k i l n ; f l u i d i z a t i o n of t h i s kind has been observed b e f o r e . 6 6 A l -so, there would be a propensity f o r the c o a l p a r t i c l e s to move to the upper l a y e r s i n the bed, e s p e c i a l l y as the r e a c t i o n s proceed and the coal p a r t i c l e s decrease i n s i z e . The f l u i d i z a t i o n tendency c o u l d be d i m i n i s h e d by u s i n g s l i g h t l y l a r g e r coal p a r t i c l e s , since the minimum f l u i d i z a t i o n v e l o c i t y i s i n f l u e n c e d by (d~ c)3. Thus, during the f i r s t stages of r e d u c t i o n where l a r g e volumes o f gases are g e n e r a t e d , the l a r g e r coal p a r t i c l e s would not be entrained as e a s i l y . As the r e a c t i o n proceeds, the coal becomes f i n e r but the gas f l o w r a t e s then are lower and the reduced p a r t i c l e s w i l l have s t a r t e d to agglomerate. These com-bined f a c t o r s may provide a well mixed bed along the k i l n . The s i z e of operation against which the r e s u l t s of the base case from t h i s work are compared below, i s that of a p i l o t - p l a n t operation of S t e l c o I n c . 7 The k i l n , 35 m long by 2.1 m i n t e r n a l diameter, i s capable of reducing to 95 percent completion 113 tons of h e m a t i t e p e l l e t s per day a t 14 p e r c e n t f i l l i n g (or 200 ton/day at 25 percent f i l l i n g ) , at a 1000°C and a Cp-j x/Fe o f 0.43. Furthermore, the movement of m a t e r i a l s w i l l be assumed to be i n plug flow. In order to assess the throughput of a 2.1 x 35 m k i l n using the present m a t e r i a l , i t s operational parameters must be d e t e r m i n e d i n ad-vance. F i r s t , w i t h r e g a r d to r o t a t i o n a l speed, a c r i t e r i o n has been developed to scale-up k i l n s based on the modified Froude number, ^ 2R/g, 201 and the r a t i o of diameters of the model and prototype r a i s e d to the one-h a l f power, as follows133. ' U 2 R 1/2 M / R D 1/2 (8.4) By s u b s t i t u t i n g numerical values i n Equation 8.4, a r o t a t i o n a l speed of 0.9 r.p.m. would be necessary i n the l a r g e k i l n i n o r d e r to o b t a i n the same bed behaviour as that i n the l a b o r a t o r y k i l n at 7 r.p.m. Secondly, a v a i l a b l e r e l a t i o n s h i p s e x i s t to determine the average r e t e n t i o n t i m e , T^, i n reduction kilns,146 such as K, mV 0.148 T k - S D N (8.5) where lr >m i s the angle of repose of the s o l i d s mixture, L i s the k i l n length i n m, S i s the k i l n slope i n percent, D i s the k i l n diameter i n m and N i s the number of r e v o l u t i o n s per minute. Thus, by s u b s t i t u t i n g the k i l n dimensions and the angle of repose of the m a t e r i a l s from T a b l e XV i n E q u a t i o n ( 8 . 5 ) , a r e t e n t i o n time of 360 min i s obtained f o r a k i l n slope of 4.5 percent. This i s the time r e q u i r e d to reduce the c o n c e n -t r a t e 95 p e r c e n t a t 850°C, as shown i n Figure 6.8, by a l s o c o n s i d e r i n g that the reduction zone i n the k i l n comprises about one h a l f o f the t o -t a l l e n g t h . D i v i d i n g the volume of the bed, of 17 m3 f o r 14 percent f i l l i n g , by the r e t e n t i o n t i m e , a volumetric flowrate of 68 m3/day i s obtained. The measured density of the i n i t i a l ore/char mixture i s 1.28 ton/m 3 and the d e n s i t y of the p r o d u c t s a f t e r 95 percent reduction i s 2.43 ton/m 3; t h e r e f o r e , an average value of 1.86 ton/m 3 can be c o n s i d e r -ed. Then by m u l t i p l y i n g the volumetric flowrate by the average d e n s i t y , 202 a k i l n t h r o u g h p u t of 126 ton/day i s obtained; t h i s i s equivalent to 83 tons of ore p r o c e s s e d per day at a Cp-j x/Fe of 0.32. By r e c a l l i n g t h at the same s i z e of k i l n i s capable of p r o c e s s i n g 113 ton of p e l l e t s per day a t 1000°C, the t h r o u g h p u t of the k i l n p r o c e s s i n g concentrate at 850°C i s about 25 percent lower. However, the same c a l c u l a t i o n s f o r r e -d u c t i o n o f the concentrate at 900°C show that a throughput of 125 ton/-day can be e a s i l y achieved, which i s about 10 percent h i g h e r than t h a t of the k i l n processing p e l l e t s . On b a s i s o f the above estimates, s i m i l a r throughputs can be ob-tain e d by t r e a t i n g f i n e ores and p e l l e t s . The c l e a r advantage i n the former case i s the conside r a b l y lower temperature of operation with the consequent decrease i n operational problems, e s p e c i a l l y lower a c c r e t i o n formation and waste-gas f l o w r a t e s . 203 CHAPTER 9 SUMMARY AND CONCLUSIONS The k i n e t i c s of d i r e c t reduction of a commercial unagglomerated i r o n o r e , wit h low-rank coal chars, have been i n v e s t i g a t e d i n the tem-perature range of 800-950°C (1073-1223 K). The r e a c t o r u t i l i z e d was a l a b o r a t o r y - s i z e b atch r o t a r y k i l n , capable of processing about 1 k i l o -gram of ore/char mixture. The o v e r a l l reduction k i n e t i c s were f o l l o w e d by measurement of gas a n a l y s i s and gas f l o w r a t e s . The extreme mean par-t i c l e s i z e s , 358 and 90 vm, from the f u l l s i z e range of the i r o n ore concentrate were reduced with three d i f f e r e n t coal char p a r t i c l e s i z e s . The mixing of the char/ore mixture was determined a t room tem-perature i n the same rea c t o r under d i f f e r e n t c o n d i t i o n s p r i o r to the r e -duction experiments. The c o n d i t i o n s s t u d i e d were: c h a r t o ore s i z e r a t i o from 0.5 to 4.0; r o t a t i o n a l speed o f 5 and 15 r.p.m.; percent f i l l i n g of 12 and 20 percent and f i x e d carbon-to-iron r a t i o from 0.45 to 0.84. The mixing studies y i e l d e d the f o l l o w i n g : i ) With an ore p a r t i c l e s i z e of 254 u m and l a r g e r , the degree o f bed mixing depends almost completely on the c o a l - t o - o r e s i z e r a -t i o ; best mixing i s achieved at a r a t i o of 1 and smaller. 204 i i ) At ore p a r t i c l e s i z e s s m a l l e r than 254 ym, the degree of bed mixing i s b e l i e v e d to be a f f e c t e d more strongl y by other f a c t o r s such as e l e c t r o s t a t i c and f r i c t i o n f orces between the coal par-t i c l e s . Good mixing i s obtained even at a c o a l - t o - o r e s i z e r a -t i o of 4 f o r 90 ym ore p a r t i c l e s , i i i ) Rotational speed, percent loading and f i x e d - c a r b o n - t o - i r o n r a t i o have n e g l i g i b l e e f f e c t s on the degree o f m i x i n g w i t h i n the ranges t e s t e d and f o r t h i s r e a c t o r s i z e , i v ) The bed motion c h a r a c t e r i s t i c s were al s o d e l i n e a t e d . R o l l i n g motion predominated at higher c o a l - t o - o r e s i z e r a t i o f o r l a r g e r p a r t i c l e s s i z e whereas slumping was obtained with a smaller coal p a r t i c l e s i z e ; bed motion depended almost c o m p l e t e l y on c o a l p a r t i c l e s i z e . The m i x i n g c o n d i t i o n s were f u r t h e r t e s t e d in the reduction experiments. At a f i x e d temperature and r o t a t i o n a l speed, no i n c r e a s e i n the r e d u c -t i o n r a t e was o b s e r v e d by v a r y i n g the f i x e d carbon-to-iron r a t i o from 0.32 to 0.64; a slower rate was obtained at a value of 0.16. At a f i x -ed temperature and f i x e d carbon-to-iron r a t i o s of 0.16 and 0.64, no im-provement i n the reduction rate was obtained by i n c r e a s i n g the r o t a t i o n -al speed from 7 to 20 r.p.m.. A bed with 7 percent f i l l i n g y i e l d e d a f a s t e r reduction rate i n i t i a l l y , over a bed w i t h 14 p e r c e n t f i l l i n g . This was due to combined e f f e c t s of mixing and heat t r a n s f e r . Having d e l i n e a t e d the best mixing c o n d i t i o n s , r e d u c t i o n e x p e r i -ments were c a r r i e d out to d e t ermine the r a t e c o n t r o l l i n g steps, and t h e i r energies of a c t i v a t i o n , comprising the o v e r a l l reduction p r o c e s s . 205 The P co/ pC02 r a t 1 0 P r o v e d t o D e a powerful tool e l u c i d a t i n g the rate c o n t r o l l i n g step. The o v e r a l l r e d u c t i o n p r o c e s s was found t o be con-t r o l l e d up to 0.5 to 0.8 f r a c t i o n a l reduction by the Boudouard r e a c t i o n , depending on the p a r t i c l e s i z e and temperature; from then on, the o v e r -a l l r e a c t i o n was c o n t r o l l e d e s s e n t i a l l y by the reduction r e a c t i o n . The a c t i v a t i o n energies obtained were 224 kJ/mole (53.5 k c a l / -mole) f o r the Boudouard r e a c t i o n , using sub-bituminous coal char, and 264 kJ/mole (63.1 k c a l / m o l e ) u s i n g l i g n i t e c o a l c h a r . These v a l u e s agree w e l l w i t h p r e v i o u s works and correspond to that of a c a t a l y z e d r e a c t i o n ; t h i s was corroborated by a r t i f i c i a l l y c a t a l y z i n g the Boudouard r e a c t i o n with a mixture of a l k a l i ( L i , Na and K) carbonates. The energy of a c t i v a t i o n obtained i n the reduction of wustite by CO was 116.4 k j / -mole (27.8 kcal/mole); t h i s a l s o agrees with p r e v i o u s l y reported values. The c a t a l y t i c e f f e c t of the coal ash, e s p e c i a l l y due to the K 20 content, on the Boudouard r e a c t i o n , was found to be much l a r g e r than the r e s p e c t i v e e f f e c t of m e t a l l i c i r o n produced by the r e d u c t i o n . In a d d i -t i o n , the presence of a d i l u e n t i n e r t gas blown over the bed, was found to e x tend the f r a c t i o n a l reduction over which Boudouard co n t r o l i s ex-e r t e d . The 90 urn ore p a r t i c l e s were found to agglomerate much more than those of 358 ym s i z e . The main cause o f a g g l o m e r a t i o n , i n the non-c a t a l y z e d e x p e r i m e n t s , was d e t e r m i n e d by SEM o b s e r v a t i o n s to be the whisker i r o n growth on the surface of the reduced p a r t i c l e s ; t h i s agrees w i t h p r e v i o u s l y r e p o r t e d s t u d i e s . The a d d i t i o n of a c a t a l y s t a l s o i n -creased the agglomeration by p a r t i a l l y melting the ash and gangue mate-r i a l s . In neither case d i d agglomeration r e t a r d the reduction rate to a 206 c o n s i d e r a b l e e x t e n t . No a c c r e t i o n growth was observed on the reactor w a l l , l i k e l y as a consequence of the low temperature of o p e r a t i o n . F i n a l l y , e s t i m a t i v e c a l c u l a t i o n s showed that s i m i l a r throughputs can be obtained by processing the unagglomerated c o n c e n t r a t e , as com-pared to o p e r a t i o n s which u t i l i z e indurated hematite p e l l e t s under the same c o n d i t i o n s . However, the advantage of using c o n c e n t r a t e s l i e s on the f a c t t h a t the p r o c e s s can be o p e r a t e d a t a temperature a t l e a s t 100°C lower. 207 LIST OF REFERENCES 1 Venkateswaran, V., & Brimacombe, J.K., "Mathematical Model of the SL/RN D i r e c t R e d u c t i o n P r o c e s s , " Met. T r a n s . 8B(3):387-398, (1977). 2 Lownie, H.W., J r . , " P r o s p e c t s f o r the F u t u r e o f D i r e c t Reduced I r o n " i n D i r e c t Reduced Iron—Technology and Economics of Pro- duction and Use, ISS-AIME, pp. 202-211, (1980). 3 Schnabel, W., Husain, R., & Schlebusch, D.W., " F l e x i b i l i t y of SL/RN Coal Based D i r e c t R e d u c t i o n i n Respect of Raw M a t e r i a l s and F u e l s , " MPT-Metall. Plant & Tech., 2:6-19, (1983). 4 Henein, H., Bed B e h a v i o u r i n Rotary C y l i n d e r s with A p p l i c a t i o n to Rotary K i l n s , Ph.D. T h e s i s , The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, (1980). 5 Gorog, J.P., Heat T r a n s f e r i n D i r e c t l y F i r e d Rotary K i l n , Ph.D. T h e s i s , The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, (1982). 6 Barr, P., Unpublished research, The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, (1982). 7 Venkateswaran, v., Mathematical Model of the SL/RN D i r e c t Reduction P r o c e s s , M.A.Sc. T h e s i s , The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, (1976). 8 Sucre-Garcia, G.A., K i n e t i c s of Reduction of T i t a n i f e r o u s Ores with L i g n i t e C o a l , M.Sc. Thesis, The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, (1979). 9 Stephenson, R.L., Ed., D i r e c t Reduced Iron, ISS-AIME, (1980). 10 M i l l e r , J.R., "Global S t a t u s of D i r e c t Reduction--1977," Iron & Steel Engnr., 54(9):45-50, (1977). 11 The Metals S o c i e t y , D i r e c t Reduction of Iron Ore. A B i b l i o g r a p h i c -al Survey, Order #262, London, (1979). 12 Union C a r b i d e , L i t e r a t u r e Search on D i r e c t Reduction, P r i v a t e Re-po r t , (1975). 13 Davis, C.G., M c F a r l i n , J.F., & P r a t t , H.R., "Direct-Reduction Tech-nology and Economics," Ironmak & Steelmak., 9_(3):93-129, (1982). 208 14 von Bogdandy, L., & E n g e l l , H.J., The Reduction of Iron Ores, Chap-t e r s 2-4. B e r l i n : S p r inger-Verlag, (1971). 15 Small, M., " D i r e c t Reduction of Iron Ore," J of Metals, A p r i l : 6 7 -75, (1981). 16 Midrex Corporation, "1983 DRI Capacity and Production," D i r e c t from Midrex, 9(3) :6, (1984). 17 Midrex C o r p o r a t i o n , "Midrex D i r e c t Reduction Process, l e a f l e t pub-l i s h e d by Midrex Co., p. 2, (1983). 18 Anonymous, " S i c a r t s a — M e x i c o ' s Latest Success Story," I. & S. Int., 50(1):13-17. (1977). 19 MacRae, D.R., "AISI Coal-based D i r e c t Reduction Processes Symposi-um," Summary r e p o r t to Bethlehem Steel Co., Sept. (1980). 20 LURGI, Report on SL/RN References, (1978). 21 A l b e r t , A.A., " A p p l i c a t i o n of ACCAR Tec h n o l o g y a t Sudbury M e t a l s Company and N i a g a r a F a l l s L i m i t e d , " Can. Met. Q., 18:97-104, (1979). ~~ 22 L e p i n s k i , J.A., "The ACCAR System and i t s A p p l i c a t i o n to D i r e c t Re-d u c t i o n o f Iron Ores," Iron & S t e e l Engnr., 57( 12):25-31, (1980). ~~ 23 Meyer, K., Heitmann, G., & Janke, W., "The SL/RN Process f o r Pro-d u c t i o n o f M e t a l l i z e d Burden," J of M e t a l s , 18(6):748-752, (1966). 24 Reuter, G., & S e r b e n t , H., "Raw M a t e r i a l s S e l e c t i o n C r i t e r i o n f o r the SL/RN Process," U.N. Econ. Comm. f o r Europe, S t e e l Commit-tee, Technical and Econ. Aspects, Romania (1972), 12 pp. 25 Reuter, G., "La Reduccion D i r e c t a de l o s M i n e r a l e s de F i e r r o . Su a p l i c a c i o n en America L a t i n a , " Redn. D i r e c t a en America L a t i n a , ILAFA, Mexico C i t y , (1973), 9 pp.. [Spanish]. 26 Serbent, H., & Reuter, G. "Estado actual del Proceso SL/RN," Conf. en Reduccion D i r e c t a , ILAFA, Porto ATegre, B r a z i l , pp. 89-104, (1975). [Spanish] 27 Liestmann, W.D., "Production of Sponge Iron with Rhenish L i g n i t e i n the Rotary K i l n , " Stahl E i s e n , 96(3):97-105, (1976). HB Trans. #9765. 28 Reuter, G., S e r b e n t , H., & S c h n a b e l , W. "SL/RN: La Clave para l a Reduccion D i r e c t a y E l a b o r a r i o n de Acero en America del Sur y C e n t r a l ," Uso y C o m e r c i a l i z a c i o n del F i e r r o Esponja, ILAFA, Ma-cuto, Columbia, pp. 211-216, (1977). [Spanish] 209 29 S i b a k i n , J.G., "Development o f the SL D i r e c t Reduction Process," AISI meeting, Technical s e s s i o n s , New York, May (1962). 30 Wild, R., "SL/RN D i r e c t R e d u c t i o n P r o c e s s , " Chem. and P r o c e s s Engng. (CEP), 51(1) :55, 57-58, (1970). 31 Thorn, G.G.W., & Wilson, K., "New SL/RN D i r e c t R e d u c t i o n P l a n t a t G r i f f i t h Mine," Iron and Steel Maker, (Oct.):30-34, (1976). 32 SALEM Co., Comparison between Salem and SL/RN P r o c e s s , 22 pp. (1976) . 33 Wilson, K., "The SL/RN Process at the G r i f f i t h Mine," Can. Met. Q., 18:105-109, (1979). 34 B a l i n s k i , A., & S i l v e i r a , M.A.B., "A Unidade de Reducao D i r e c t a SL/RN da P i r a t i n i , " Conf. en Reduccion D i r e c t a , ILAFA, P o r t o Alegre, B r a z i l , pp. 205-218, (1975). [Portuguese]. 35 B a l i n s k i , A., & V i l l a n o v a , R. de A., " R e l a t o r i o O p e r a c i o n a l da P l a n t a SL/RN da P i r a t i n i , " ILAFA, Uso y c o m e r c i a l i z a c i o n del  Hierro Esponja, Macuto, Colombia, pp. 15/-166, (1977). 36 Bongers, U., & Wetzel, R., "The Krupp Sponge Iron Process," In A l -t e r n a t i v e Routes t o S t e e l , P r o c . B I S I , London, pp. 55-58, (1971). 37 Anonymous, "150,000 Tons a Year of Prime Sponge Iron," Coal, Gold and Base Minerals of Southern A f r i c a , 21.(10): 16-19, (1973). 38 Meyer, G., and Bongers, U., "Krupp's D i r e c t R e d u c t i o n Route t o Sponge Iron Goes Commercial," Engng. & Min. J . , 174(6):159-164, (1973). 39 Meyer, G., Voppel , K.H., & J a n s s e n , W., " S o l i d Fuel Reduction i n the Krupp Sponge Iron Process w i t h S p e c i a l Emphasis on C o n d i -t i o n s i n the U.S.A.," ISS-AIME Ironmaking P r o c . 36:433-445, (1977) . ~ 40 Anonymous, "World's L a r g e s t Coal-based DR Plant," Iscor News, pp. 9-11, March, (1982). 41 G e l d e n h u i s , P.J., "Coal Based D i r e c t Reduction i n South A f r i c a -Some Results Already Achieved and A n t i c i p a t e d , " IISI 16th Annual M e e t i n g o f the Committee on T e c h n o l o g y , Johannesburg, South A f r i c a , March (1984), pp. 19. 42 Anonymous. "India's Exotic Coal-based DR Plant" I n d u s t r i a l World, pp. 10-11, Nov. (1981). 210 43 S c h l e b u s c h , D., Steinbacher, K., Anders, R., Wladen, H., & Magen-danz, N., "New Developments and C o n t r i b u t i o n s Towards Improved Energy Usage i n S t e e l P l a n t s , " SEAISI Conf., Sept. (1984), pp. 20. 44 Schnabel , W., & Schlebusch, D., "New Steelmaking Concepts Based on Low Grade Coal," MPT MET. PLANT & TECH. (2):30-37, (1984). 45 Schnabel, W., Formanek, L., Genge, U., & F r i t z s c h , K., "The Com-bismelt Technology f o r Steelmaking," CIM 23rd Conf. of M e t a l l u r -g i s t s , Quebec, Canada, Aug. (1984), pp. 28. 46 Schlebusch, D., "The Coal Based SL/RN D i r e c t R e d u c t i o n P r o c e s s , " L u r g i Symposium on D i r e c t Reduction, Moscow, March (1984), pp. 38. 47 Schnabel, W., Schlebusch, D., & Elsenheimer, G., "SL/RN Coal-based D i r e c t Reduction—The S t a t e of the A r t , " P r o c . 42nd Ironmak. Conf., A t l a n t a , U.S.A., A p r i l (1983), pp. 163-170. 48 Kanda, Y., Toyozawa, H., Yamada, Y., & Nakamura, M., " D i r e c t Reduc-t i o n Process f o r Iron Industries Waste Fines," ISS-AIME Ironmak. Proc. 36:398-410 (1977). 49 Yamada, Y., Kanda, Y., Toyozawa, H., & Mutsuta, A., "Planta y Ope-ra c i o n para l a Produccion de Hierro Esponja a P a r t i r de Oxidos de Desecho, P r o v e n i e n t e s de l a F a b r i c a c i o n de Arrabio y Acero Mediante el Metodo Sumitomo," Uso y c o m e r c i a l i z a c i o n del F i e r r o E s p o n j a , ILAFA, Macuto, Columbia, pp. 203-210, (1977), [Spa-n i s h ] . 50 S a i t o , Y., " D i r e c t R e d u c t i o n P r o c e s s f o r R e c y c l i n g S t e e l Plant Waste F i n e s , " ISS-AIME Ironmaking Proc. 34:464-481, (1975). 51 Muraki, J . , N i s h i d a , N., Otsuke, N., & Hara, Y., "Operation of the Nippon S t e e l D i r e c t Reduction 500 Ton/day Demonstration Plant," ISS-AIME Ironmaking P r o c , 38:266-276, (1979). 52 Shiramatsu, J . , & Yatsunami, K., " E f f e c t i v e Use of I n - p l a n t Gener-a t e d Dusts Using the SL/RN Process," Nippon Kokkan Research Re-port Overseas, (1977), 13 pp. 53 Shiramatsu, J . , & Yatsunami, K., " E f f e c t i v e Use of In-plant Gener-ated Dusts Using the SL/RN P r o c e s s , " ISS-AIME Ironmak. P r o c . 36:384-397, (1977). 54 Yatsunami, K., " O u t l i n e o f SL/RN Reduced P e l l e t Plant at Nippon Kokkan's Fukuyama Works i n Japan," Unknown procedence. 55 Yatsunami, K., Miyakado, S., Honda, A., Yamamoto, R., & Shiobara, K., "The Manufacturing of Reduced Iron Using the SL/RN Process," Nippon Kokkan Tech. B u l l . , (1976), 12 pp. 211 56 Janke, W., & Serbent, H., "Processing of Iron-bearing M e t a l l u r g i c a l Dust by the SL/RN Process," I n t ' l Iron & Steel Congress, Dussel-dorf, (1974), [STS. Trans. #15530]. 57 Serbent, H., Mackzek, H., & Rellermeyer, H., "Large Scale T e s t f o r the Treatment of BF Sludge and BOF Dust According to the Waelz Process," ISS-AIME Ironmak. Proc. 34:194-205, (1975). 58 Adams, C.J., "Recycling o f S t e e l P l a n t Waste 0 x i d e s - - A Review," CANMET Report 79-34, 11 pp., (1979). 59 Kerton, C P . , & Wood, J.R., " P i l o t Plant T r i a l of ' F i l t e r Cake Pro-c e s s ' f o r R o t a r y - k i l n R e d u c t i o n of E l e c t r i c Arc Steelmaking Fume," Ironmak. & Steelmak., 8(3):122-128, (1981). 60 Eichenberg, H., Lommert, H., & Serbent, H., "Manufacture o f Sponge Iron from M i l l Scale Using the SL/RN Process," Stahl E i s e n , May (1981), pp. 114-119. 61 Jessop, A.F., Medley, J . E . , & Sainsbury, D.J., "Steelmaking with New Zealand Ironsands," Proc. BISI, A l t e r n a t i v e Routes to S t e e l , London, (1971), pp. 50-54. 62 Bold, D.A., & Evans, N.T., " S e l e c c i o n y D e s a r r o l l o de l a Planta de Reduccion D i r e c t a SL/RN en New Zealand Limited," ILAFA, Semina-r i o de Reduccion D i r e c t a , B r a s i l , (1975), pp. 275-295 [Spa-n i s h ] . 63 Bold, D.A., & Evans, N.T., " D i r e c t Reduction Down Under: The New Zealand Story," Iron and Steel Int., 50(3):145-152, (1977). 64 Bates, C P . , " R e d u c t i o n with L i g n i t i c Coals," SEAISI Q., 6(4) :24-38, (1977). 65 Evans, N.T., "Development of the SL/RN Process at New Zealand Steel Limited," ISS-AIME Ironmak. Proc. 37:122-136, (1978). 66 Bracanin, B.F., Clements, R.J., & Davey, J.M., " D i r e c t R e d u c t i o n Technology--The Western Titanium Process f o r the Production of Synthetic R u t i l , F e r u t i l and sponge Iron," Aust. Ins. Min. Met., West. Aus., pp. 55-68, (1979). 67 Cassidy, P.W., & Mckay, J.M., "Development of the Hockin P r o c e s s and I t s A p p l i c a t i o n to the D i r e c t Reduction of Iron Ore," Proc. Commonw. Min. Metal. Congr. 11:335-340, (1979). 68 Keran, V.P., Baker, A . C , B o u l t e r , G.N., & R i d l e y , A . J . , "The D i -r e c t Reduction Corporation's Process Technology," ISS-AIME Iron-mak. Proc. 39:412-419, (1980). 212 69 McAdam, G.D., O ' B r i e n , D.J., & M a r s h a l l , T., "Rapid Reduction of New Zealand Ironsands," Ironmak. & Steelmak., 4U):l-9, (1977). 70 Crawford, G.P., "Innovative Ironmaking at New Zealand S t e e l , " ISS-AIME Ironmak. Proc. 40:225-232, (1981). 71 Bold, D.A., "Stage One to Increase Output F i v e f o l d , " I & S I n t . , Oct. (1982), pp. 243-254. 72 Geiger, G.H., & P o i r i e r , D.R., "Transport Phenomena i n M e t a l l u r -gy," New York: Addison Wesley P u b l i s h . Co., (1973), p. 570. 73 Meadowcroft, T.R., & Brimacombe, J.K., "Process Development Through R e s e a r c h , " The Darken Conference: Physical Chemistry i n Metal-l u r g y , pp. 121-145, U.S. Research Lab., P i t t s b u r g h , (1976). 74 . Ponghis, N., & Poos, A., " I n v e s t i g a t i o n s on the Mechanisms Govern-i n g Iron Ore S i n t e r i n g , " ISS-AIME, Ironmak. Proc. 36: 91-101, (1977). ~ 75 L e i s t e r , H., "Reducao D i r e t a de Minerio de Ferro em Forno Rotativo: Comportamenta da Cinza de Carvoes de Charqueadas—RS," M e t a l u r -gia ABM, 3(194) :25-29, (1979) [Portuguese]. 76 L e i s t e r , H., & Formoso, M., " S i n t e r i z a c a o na Carga de um Forno Ro-t a t i v o de Reducao D i r e t a . Formacao de Aglomerados," Metalurgia ABM, 36(268):179-185, (1980), [Portuguese]. 77 Gerbase, A.E., L e i s t e r , H., & B r i s t o t i , A., " S i n t e r i z a c a o de Mate-r i a l ' s F i n o s no Proceso SL/RN. Estudo em Laboratorio," Metalur-gi a ABM, 36(272):451-455,, (1980), [Portuguese]. 78 C h a t t e r j e e , A., & C h a k r a v a r t y , P.K., "Comparative E v a l u a t i o n o f Lump Ore and P e l l e t s as Raw M a t e r i a l s i n Sponge Iron Manufac-t u r e , " Iron & Steel Int., 50(4):245-252, (1977). 79 C h a t t e r j e e , A., & Pandey, B.D., "Mechanism of Ring F o r m a t i o n i n Rotary K i l n s Used f o r Sponge Iron M a n u f a c t u r e , " Ironmak. & Steelmak., 8(6):250-263 (1981). 80 Grosse, Daldrup H., " U n t e r s c h l i e d l i c h e Sinterneigung von Feinerzen be i der Red u k t i o n im Drehrohrofen," [ " D i f f e r i n g Tendencies To-wards S i n t e r i n g o f F i n e Ores D u r i n g R e d u c t i o n i n a Rotary K i l n " ] , Dr-Eng. T h e s i s , Rheinisch-Wesfalischen Technischen Hoch-schule, Aachen, West Germany, (1975). 213 81 S c h l e b u s c h , D.W., "Untersuchungen zur Ansatzbildung ander Feuer-f e s t e n Ausmauerung von D r e h r o h r o f e n z u r D i r e c t reduktion von  E i s e n e r z e n ,." [ " I n v e s t i g a t i o n on Ac c r e t i o n Build-up on the Re-f r a c t o r y W a l l s o f Rotary K i l n s f o r D i r e c t R e d u c t i o n o f Iron Ores"] Dr-Eng. T h e s i s , Rheinisch-Westfalischen Technischen Hoch-schule, Aachen, West Germany, (1978). T r a n s l a t e d by Maureen DeCamp., The U n i v e r s i t y of B r i t i s h Columbia, Canada, (1982). 82 Gudenau, H.W., S e r b e n t , H., & S c h l e b u s c h , D.W., " E i n f l u s s der E i n s a t z s t o f f e und Betriebs bedingungen auf die Ansatzbildung i n Drehrohrofen f u r die D i r e k r e d u c t i o n , " [ " I n f l u e n c e o f Charged M a t e r i a l s and Operating Conditions on the Formation of Scars i n Rota r y K i l n s f o r D i r e c t R e d u c t i o n " ] , Stahl E i s e n , 99(17):908-913, (1979). T r a n s l a t e d from the German by Cons u e l o Ivo, (1982). 83 Wenzel , W., Gudenau, H.W., & Grosse, Daldrup H., "Eisenauszchel-dungen a l s E i n f l u s s g r o s s e bei der Red u k t i o n von F e i n e r z e n im D r e h r o h r o f e n , " ["Iron P r e c i p i t a t e s as V a r i a b l e I n f l u e n c i n g the R e d u c t i o n o f F i n e Ores i n the Rotary K i l n " ] , S t a h l E i s e n , 97(15):741-746, (1979) [German-Spanish]. 84 Potebnya, Y.M., Tolstunov, Y.L., Rikhter, R.G., & G a v r i l k o , S.A., " S t r u c t u r a l T r a n s f o r m a t i o n s o f I r o n - o r e S i n t e r s During t h e i r R e d u c t i o n and S o f t e n i n g , " S t e e l i n the U.S.S.R., 2:176-178, March, (1978). 85 M o r r i s o n , A.L., W r i g h t , J.K., & Bowling, K.McG., "Microstructure of M e t a l l i z e d Iron-ore P e l l e t s Reduced by Coal Char i n a Rotary K i l n Simulator," Ironmak. & Steelmak, 5_(l):39-44, (1978). 86 Sohn, H.Y., & Wadsworth, M.E., Rate Processes of E x t r a c t i v e Metal-l u r g y , New York: Plenum Press, (1979), p. 258. 87 C a r t e r , R.E., " K i n e t i c Model f o r S o l i d - s t a t e R e a c t i o n s , " J . Chem. Phys., 34(6):2010-2015, (1961). 88 Yun, T.S., " D i r e c t Reduction o f F e r r i c Oxide by S o l i d Carbon i n Vacuum," Trans. ASM, 54:130-142, (1961). 89 Ross, H.U., "A Review of Problems i n Iron-ore R e d u c t i o n by S o l i d -state Processes," Can. Met. Q., 11.(4) :621-626, (1972). 90 Otsuka, K., & K u n i i , D., "Reduction of Powdery F e r r i c Oxide Mixed w i t h G r a p h i t e P a r t i c l e s , " J . Chem. Engng. (Japan), 2U):46-50, (1969). 91 Rao, Y.K., "The K i n e t i c s of Reduction of Hematite by Carbon," Met. Trans. 2:1439-1447, (1971). 214 92 Bicknese, E., & Clark, R., "Carbon Monoxide Reduction of FeO i n the Presence of Carbon," T r a n s . Met. Soc. AIME, 236(1):2-9, (1966). 93 Abraham, M.C., & Ghosh, A., " K i n e t i c s of Reduction of Iron Oxide by Carbon," Ironmak. & Steelmak., _1(1):14-23, (1979). 94 Wright, J.K., Bowling, K., & Morrison, A.L., "Reduction of Hematite P e l l e t s w i t h C a r b o n i z e d Coal i n a S t a t i c Bed," Trans. I S I J . , 21:149-155, (1981). 95 M o r r i s o n , A.L., Wright, J.K., & Bowling, K.McG., " D i r e c t Reduction of Iron Ore P e l l e t s w i t h Carbon i n a Rotary K i l n S i m u l a t o r , " Ironmak & Steelmak., 5U):32-38, (1978). 96 Fruehan, R.J., "The Rate of Reduction of Iron Oxides with Carbon," Met. Trans., 8(2):279-286, (1977). 97 Turkdogan, E.T., & V i n t e r s , J.V., " E f f e c t of Carbon Monoxide on the Rate o f Oxidation of Charcoal, Graphite, and Coke i n Carbon D i -oxide," Carbon, 8(l):39-53, (1970). 98 Grandsen, J.F., P r i c e , S.T., & Ramey, N.J., " R e d u c t i o n Rates o f Iron Ore-Char Briquets Used i n Cupola Smelting," CANMET Report, 78-30, Energy Mines and Resources, Canada, (1978), 15 pp. 99 Seaton, C.E., F o s t e r , J.S., & Velasco, J . , "Reduction K i n e t i c s of Hematite and Magnetite P e l l e t s C o n t a i n i n g Char," Trans I S I J , 23:490-496, (1983). 100 Stec, R., Mroz, J . , & Bu d z i k , R., " R e d u c t i o n of Hematite Ore by Carbon Reducers Degassed Within the Temperature Range 873-1273 K," Archiwum Hutnictwa, 26(3):489-500, (1981). [ P o l i s h ] . 101 Stec, R., Mroz, J . , & Budzik, R., " I n f l u e n c e of V o l a t i l e M a t t e r s and R e a c t i v i t y of Carbon Reducers on the Degree of Reduction and M e t a l l i z a t i o n o f Hematite Ore," Archiwum Hutnictwa, 27(4):429-439, (1982). [ P o l i s h ] 102 Rao, Y.K., & Han, H.G., " C a t a l y s i s by A l k a l i Carbonates of Carbo-thermic Reduction of Magnetite Concentrates," Ironmak & S t e e l -mak., 11(6):308-318. 103 E l - G u i n d y , M.J., & Davenport, W.G., " K i n e t i c s and Mechanisms of I l m e n i t e R e d u c t i o n w i t h G r a p h i t e , " Met. Trans., 1^:1729-1734, (1970). 104 Sundar, Murti N.S., & Seshadri, V., " K i n e t i c s of Reduction of Syn-t h e t i c Chromite with Carbon," Trans. I S I J , 22:925-933, (1982). 215 105 Sohn, H.Y., & Szekely, J . , "Reactions Between S o l i d s Through Gase-ous I n t e r m e d i a t e s — I. Reactions C o n t r o l l e d by Chemical K i n e -t i c s , " Chem. Engng. S c i . , 28:1789-1801, (1973). 106 Rao, Y.K., "A Physico-chemical Model f o r Reactions Between P a r t i c -u l a t e S o l i d s Occurring through Gaseous I n t e r m e d i a t e s — I. Reduc-t i o n o f Hematite by Carbon," Chem. Engng. S c i . , 29:1435-1445, (1974). 107 Rao, Y.K., & Chuang, Y.K., "A Physico-Chemical Model f o r Reactions Between P a r t i c u l a t e S o l i d s Occurring Through Gaseous I n t e r m e d i -a t e s — I I . General S o l u t i o n s , " Chem. Engng. S c i . , 29:1933-1938, (1974). ~~ 108 Rao, Y.K., & Chuang, Y.K., "Reactions Between P a r t i c u l a t e S o l i d s . V i s c o u s Flow and Knudsen D i f f u s i o n , " Met. Trans., 7B(3): 495-497, (1976). 109 Rao, Y.K., "Mechanism and the I n t r i n s i c Rates of Reduction of Me-t a l l i c Oxides," Met. Trans., 10B(2):243-255, (1979). 110 T i e n , R.H., & Turkdogan, E.T., "Mathematical A n a l y s i s of R e a c t i o n s i n Metal Oxide/Carbon M i x t u r e s , " Met. Trans., 8B(3) :305-313, (1977) . ~~ 111 Laurendau, N.M., "Heterogeneous K i n e t i c s of Coal Char G a s i f i c a t i o n and Combustion," P r o g . Energy Combust. S c i . , 4(4):221-270, (1978) . 112 Turkdogan, E.T., & V i n t e r s , J.V., " K i n e t i c s of Oxidation of Graph-i t e and Charcoal i n Carbon Dioxide," Carbon, 7_: 101-107, (1969). 113 Turkdogan, E.T., Koump, V., V i n t e r s , J.V., & Perzak, T.F., "Rate o f O x i d a t i o n o f G r a p h i t e i n Carbon D i o x i d e , " Carbon, 6:467-484, (1968). 114 F i e l d e s , R.B., & Hansen, C.J., "Char R e a c t i v i t y , " Dept. of Scien-t i f . and Ind. Research, New Zealand, Report #IPD/TS0/2002, May, (1982). 115 J a l a n , B.P., & Rao, Y.K., "A Study of the Rates of Catalyzed Bou-douard Reaction," Carbon, 16(3): 175-184, (1978). 116 Rao, Y.K.,. A d j o r l o l o , A., & Haberman, J.H., "On the Mechanism o f the C a t a l y s i s of Boudouard (C-CO?) Reaction by A l k a l i - M e t a l Com-pounds," Carbon, 20(3):207-212, (1982). 117 Rao, Y.K., " C a t a l y s i s i n E x t r a c t i v e M e t a l l u r g y , " J . of M e t a l s , 35(7):46-50, (1983). 216 118 A d j o r l o l o , A.A., & Rao, Y.K., " E f f e c t s o f P o t a s s i u m and Sodium Carbonate C a t a l y s t s on the Rate of G a s i f i c a t i o n of M e t a l l u r g i c a l Coke," Carbon, 22(2):173-176, (1984). 119 W i l l i a m s , C.E., B a r r e t t , E.P., & L a r s e n , B.M., " P r o d u c t i o n o f Sponge Iron," U.S. Bureau of Mines, B u l l . 270, (1927), 175 pp. 120 Themelis, N.J., Donaldson, J.W., & Udy, M.C., "Use of the S i m i l a r -i t y P r i n c i p l e i n P r e d i c t i n g the Optimum Performance of Iron Ore Reduction i n K i l n s , " Can. Inst, of Min. & Met. Trans., 67:74-82, (1964). ~~ 121 Reuter, G., "Das t r a n s p o r t — u n d Mischverhalten von Drehrohrofenmol-l e r b e i der Erzeugung von Eisenschwamm," ["The t r a n s p o r t and Mixing Behaviour of Rotary K i l n Beds d u r i n g the P r o d u c t i o n o f Sponge I r o n " ] Dr.-Eng. Thesis, Rheinisch-Westfalischen Techni-schen Hochschule, Aachen, W. Germany, ( 1975) [ T r a n s l a t i o n by A.W. Clotworthy, New Zealand]. 122 M o e l l e r , A., V i l l a n o v a , R.A., L e i s t e r , H., & B a l i n s k i , A., "Pro-c e s s o SL/RN—Ensaios com Materias-Primas Nacionais," Metalurgia ABM, 23(111):127-135, (1967) [Portuguese]. 123 Meadowcroft, T.R., Johnson, C.W.E., & W i l s o n , K., "Canadian Sub-b i t u m i n o u s and L i g n i t e C o a l s f o r the D i r e c t Reduction of Iron Ores," Proc. 26th Conf. on Coal, Energy Dev. Sector, EMR, O t t a -wa, Canada (1973), pp. 31-41. 124 Peterson, R.E., & Prasky, C , " M e t a l l i z a t i o n of P e l l e t i z e d , Domes-t i c , Iron Oxide Superconcentrates with L i g n i t e and Coal i n a Ro-tary K i l n , " U.S. Bureau of Mines, Report of Invs. #8179, (1976), 17 pp. 125 C h a t t e r j e e , A., & Chakravarty, P.K., "The Tisco S t u d y — D i r e c t Re-duction i n India," Iron & Steel Int., 49:210-214, (1976). 126 Schnabel , W., Zur Wa>meubertragung be i der D i r e k t r e d u k t i o n im D r e h r o h r o f e n L"0n Heat Transfer During D i r e c t Reduction in the Rotary K i l n " ] Dr-Eng. T h e s i s , Rheinisch-WesfSlischen Technischen Hochschule, Aachen, W. Germany, (1977). 127 M u l l e t t , W.A., Nixon, I.G., & Smith, J.D., "A Laboratory K i l n f o r Reduction of Iron Ore," J I S I , 211(4):278-283, (1983). 128 Nixon, I.G., " R e l a t i o n s h i p between Degree of Reduction o f Iron Ore and O p e r a t i n g V a r i a b l e s , " Ironmak. & Steelmak., _7(1):2-12, (1980). 217 129 HSusler, W.D., E i n s a t z Feinktirniger Eisenerze bei der Direcktreduk-t i o n im Drehrohrofen L"Use of Fine Grain Iron Ore f o r D i r e c t Re-d u c t i o n i n a Rotary K i l n " ] Dr-Eng. Thesis, R h e i n i s c h - W e s t f a i i -schen Technischen Hochschule, Aachen, W. Germany, (1981) [Trans-l a t i o n by Maureen DeCamp, 1982] 130 Rao, Y.K., Personal communication, U n i v e r s i t y of Washington, S e a t -t l e , WA, (Feb. 1983). 131 Barr, P., P e r s o n a l communication, U n i v e r s i t y of B r i t i s h Columbia, (Jan. 1982). 132 Gas Chromatography., Perkin Elmer Co. (1970. 133 Henein, H., Brimacombe, J.K., & Watkinson, A.P., "Experimental Stu-dy of T r a n s v e r s e Bed Motion i n Rotary K i l n s , : Met. T r a n s . 14B(6):191-203, (1983). 134 Donald, M.B., & Roseman, B., "Mixing and De-mixing of S o l i d P a r t i -c l e s , I: Mechanisms i n a H o r i z o n t a l Drum Mi x e r , " B r i t . Chem. Eng. 7(10):749-753, (1962). 135 D e t t w e i l e r , G., "Vermengen und Entmengen l o s e r Masen" A u f v e r e i -tungstechnik, 6:212-223, (1971) [ C i t e d i n Ref. 121]. 136 D e t t w e i l e r , G., "Vermengen und Entmengen l o s e r Masen" A u f v e r e i -tungstechnik, 6:347-354, (1971) [ C i t e d i n Ref. 121]. 137 A l - J a r a l a h , A. P y r o l y s i s of Some Western Canadian Coals i n a Spout-ed Bed Reactor. Ph.D. Th e s i s , The U n i v e r s i t y of B r i t i s h Colum-b i a , Vancouver, Canada, 1983. 138 Berkowitz, N. An Introduction to Coal Technology. New York: Aca-demic Press, (1979). 139 P o l l a r d , J.H. A Handbook of Numerical and S t a t i s t i c a l Techniques. Cambridge: Cambridge U n i v e r s i t y Press, (1977). 140 Ross, H.U. "Physical Chemistry," In D i r e c t Reduced Iron-Techno!ogy and Economics o f P r o d u c t i o n and Use, ISS-AIME, ppTI 9-26, ( 1 9 8 0 ) . 141 Walker, P.L., S h e l e f , M., & Anderson, R.A. Chemi s t r y and Physi cs o f Carbon, V o l . 4, pp. 287-383. New York: Marcel Dekker, ( 1 9 6 8 ) . 142 Turkdogan, E.T., & Vi n t e r s , J . V . Carbon 1 0 ( 1 ) : 9 7 - l l l , (1972). 143 Yu, K.O., & G i l l i s , P.P., "Mathematical Simulation of D i r e c t Reduc-t i o n , " Met. Trans. 12B(3):111-120, (1981). 218 144 L e v e n s p i e l , 0. Chemical Reaction Engineering. New York: John Wi-le y & Sons, (1972), pp. 350-351. 145 Doraiswamy, L.K., & Sharma, M.M. Heterogeneous Reactions: A n a l -y s i s , Examples and R e a c t o r DesTgn--Vol ume I: Gas-Sol i d and  S o l i d - S o l i d R e a c t i o n s . New York: John Wiley & Sons, (1984), 459 pp. 146 Themelis, N.J., & Gauvin, "A Generalized Rate Equation f o r the Reduction of Iron Oxides," Trans. AIME, 227(4):290-300, (1963). 147 Hinze, J.W., & T r i p p , W.C. i n "Metal-Slag-Gas R e a c t i o n s and P r o -c e s s e s , " A. F o r o u l i s & W.W. Smeltzer (Eds.). The Electrochemi-cal Society (1975), pp. 391-408. 219 APPENDIX A. HEAT BALANCE OF THE LABORATORY KILN The heat that the Glo-Bar element has to provide in excess, account-ing for the need of the reaction, the heat losses and the heat stored, for different kiln characteristics, is calculated as follows: q i n + qgen ~ qred + qsto ^ q i n - q e l (ID V n = 0 %ut = ^gas + ^loss ( I V ) q r e d = AHj/At (V) II. q e l = aFA: ( T ^ - T^) where 1 + (1 J + A i i F + T, 1 - i (- - 1) BR 1 A 2 E 2 A2 F 2 and F g R = = ; in this case F g = 1. 1 + A2 2 F A" ~ B M l Several different dimensions, for the element and the cylinder, were tried. The data presented here are for the optimum found. Cylinder: 14 cm X. 32.8 cm, E 2 = 0.5; A 2 = 1450 cm2; 220' Element: 2.54 cm X 35.6 cm; Ej = 0.8; A 1 = 284 cm A 1/A 2 = 0.196; Fg = 1; F * 0.692 At T 2 = 1250°C = 1523 K $el = 5 , 6 7 4 (0.692) 284 cm2 [(1523K) 4 - (1373) 4] cm k q e l = 2035W Load = 7.17 W/cm2 At Jl = 1300°C = 1573K q , = 2860 W M e l Load = 10.1 W/cm2 Both temperatures and loads are within safe operational range, ac-cording to tables provided by the manufacturer. I I I . q g e n i s considered to be zero, since no a i r w i l l be introduced to help the combustion of CO. IV. q . = q + Qn  Hout Mgas H l o s s o,gas is taken to be 20% of the heat consumed by the reaction. q - j o s s i s calculated considering conduction through the refractory l i n i n g and convection from the external s h e l l . The formula and data used are (ne g l e c t i n g end e f f e c t s ) : 221 c a q ] o s s 1m (R 3/R 2) , In (R 4/R 3) In (Rg/R4) + — + - — — + 2TTLK 2 2TTLK 3 2TTLK 4 2TTL h where T 2 = 1100°C = 1 3 7 3 K Too = 20°C = 2 9 3 K R 2 = 7 cm R 3 = 8cm ( 1 cm of alumina) R 4 = 1 4 to 3 0 cm (Castable plicast) R 5 = R 4 + 0 . 9 5 cm ( 0 . 9 5 cm of steel shell) L = 3 3 cm k 2 = 8.8 ( 1 0 ) " 2 W/cm°C (at 1000°C) k 3 = 3 . 4 ( I O ) " 3 W/cm°C (at 700°C) k 4 = 0 . 4 3 W./cm°C (at 200°C) P„ = 0 . 7 0 6 r 3 Gr = S i ^ T 5 " T O ° ) L W N E R E L = 7 T R 5 v 2 and Nu = 0 . 5 3 ( G r ' P r ) 0 - 2 5 The calculations were performed iteratively, for a given diameter, 2 R 4 , and with an initial assumed temperature of the external shell, Tr-. A q, was .Qbta.ined, ;;ahdaa"new Tr-! was back'calculated from q, b ^loss - b ^loss repeating until a reasonable convergence. The results are presented in Figure Al . V. q r e ( J at 900°C A H Fe 20 3 + 3C = 2Fe + 3C0 900°C = AH298 +r!173 A C p d t + J298 Z 222 AH 2 9 8 = 3(-26.42kcal) - (-197kcal) = 117740 cal/mole ACp = 2Cp(Fe) + 3Cp(C0) - Cp(Fe 20 3) - 3Cp(C) 2Cp(Fe) = 17.746 + 2.948(10)"3T -113.84T~ 1 / 2 3Cp(C0) = 20.370 + 2.940(10)"3T - 0.330(10)V2 - Cp(Fe 20 3) = 23.490 - 18.600(10)"3T - 3.550(10) 5T~ 2 - 3Cp (C) = -0.078 - 27.920(10)"3T + 1.062(10) 5T - 2 + 12.465(10)" 6T 2 AC = 14.548-40.632(10)"3T + 4.282(10) 5T" 2 - 113.84T" 1 / 2 + 12.465(10)" 6T 2 r ^ACpdT = 14.548 (Tg-Tj) - 40.632(10)~ 3 (T 2 - T 2) + 4.282(10) 5 {1-1) 2 T l T2 -113,84 [ 2 ( T 2 1 / 2 -T^ 7 2) + 12.465(10)" 6 (T 3 - T 3) JACpdt = -9619.3 cal/mole L t = 2(1220) + 2(160) = 2760 cal/mole q r e d = 117740-9619.3 + 2760 = 110881 cal/mole for 95% reduction, and transforming to grams of Fe reduced: • _ 110881(0 95) _ q qo Cal _ . q 4 f i J  q r e d 2(55,85) y y j gFe red g Fe red So i t can be said that the element w i l l provide enough heat to f u l f i l l the requirements of the system. 6 8 10 12 14 16 18 20 22 Refractory thickness (cm) A . l Heat losses and surface temperature f o r d i f f e r e n t inner diameters and i n s u l a t i o n thicknesses APPENDIX B. CALIBRATION CURVES FOR FLOWMETERS 20 40 60 80 Scale reading B . l C a l i b r a t i o n curve f o r gas-standard flowrate in flow-meter Gilmont #1 20 40 60 Scale reading 100 B.2 C a l i b r a t i o n curve f o r gas-standard flowrate in flow-meter Gilmont #2 Scale reading B.3 C a l i b r a t i o n curve f o r gas-standard flowrate i n flow-meter Gilmont #3 ro ro Scale reading B.4 C a l i b r a t i o n curve f o r gas-standard flowrate in flow-meter Gilmont #4 229 APPENDIX C. CONDITIONS FOR ROOM-TEMPERATURE MIXING EXPERIMENTS Run # Ore d c/dp e C p i X / F e Load- Ore wt Coal wt Bed Mix Bed Mix siz e ing Motion deg Motion deg [ym] [%] [g] [g] C 01 358 4.464 0.45 12 386 289 S + R 0 R a C 02 0.58 20 644 483 S + R a R a C 03 0.58 12 318 307 S + R a R a c 04 20 530 512 S + R a R a c 05 0.71 12 270 319 S + R a R a c 06 20 450 532 S + R a R 0 c 07 0.84 12 235 328 S a R a c 08 20 391 547 S + R a R a c 10 2.000 0.45 20 651 484 s + R a R* a c 16 0.84 20 396 554 s a R a c 17 1.285 0.45 12 387 290 s + R T R* T c 18 20 645 484 s + R T R* T c 20 1.000 20 654 491 s + R T R + C T c 22 0.714 20 654 491 s + R M R + S M c 24 1.285 0.84 20 391 548 s + R M R* M c 25 0.503 0.45 12 398 298 s + R M R M c 26 20 663 497 R M R M c 31 0.84 12 242 339 s + C M S + C +R M c 32 20 404 565 s + C M S + C M c 34 254 3.984 0.45 20 650 487 R + s a R a c 42 2.008 656 492 R + S a R a c 44 1.414 656 492 R + S a R a c 50 1.000 665 498 S + R T S + R T c 58 0.504 668 500 S M S + C M c 66 180 3.984 0.45 20 646 484 R + S a R a c 74 1.996 638 478 R + S T R + S T c 82 1.000 658 493 R + S M R + S M c 90 0.500 658 493 S M S + C M c 98 90 3.984 0.45 20 646 484 S + R T S+R + C T c 104 0.84 20 387 541 S • T S+R + C T c 106 2.825 0.45 20 666 499 s M S + R M c 113 1.000 12 398 298 s M S M c 79 0.325 0.45 20 638 478 s M R M * Some behaviour at 10 r.p.m. S = Slumping a = Segregated R = R o l l i n g T = T r a n s i t i o n a l C = C a t a r a c t i n g M = Well mixed APPENDIX D LISTING OF PROGRAM TO PROCESS REDUCTION EXPERIMENTS DATA AND SAMPLE OUTPUT 231 L i s t i n g of EXPERCO at 16:01:23 on DEC 23, 1984 f o r CCid=GM07 Page 1 1 C EXPERIMENTS OF DIRECT REDUCTION OF 2 3 C C UNAGGLOMERATED IRON ORE WITH COAL 4 5 C C THIS PROGRAM CALCULATES, FOR THE REDUCTION EXPERIMENTS 6 C THE OUTLET GAS COMPOSITION, THE FLOWRATES OF EACH GAS, 7 c THE BOUDOUARD AND REDUCTION RATES AND THE FRACTIONAL 8 Q C c REDUCTION OF THE IRON OXIDE AND CARBON REACTED. 10 A 4 c '*** NOMENCLATURE AND UNITS *** 1 1 12 c FRACTION OF ASH IN CHAR ASH 13 c FRACTION OF FIXED CARBON IN CHAR CFIX 14 c FE203 IN CHAR ASH. AS FRACTION OF ASH CFE203 15 c CARBON IN CHAR AT START OF REACTION. IN MOLE CIN 16 c CARBON MOLECULAR WEIGHT, IN G/MOLE CMWT 17 c CARBON MONOXIDE MOLECULAR WEIGHT, IN G/MOLE COMWT 18 c CARBON DIOXIDE MOLECULAR WEIGHT, IN G/MOLE C02MWT 19 c CHAR WEIGHT FED IN, IN G CHARWT 20 c FIXED CARBON TO IRON RATIO CTOFE 21 c CARBON MONOXIDE TO CARBON DIOXIDE RATIO C0C02 22 c CARBON MONOXIDE TO HYDROGEN RATIO C0H2 23 c CARBON MONOXIDE FLOWRATE. IN L/MIN COFLW 24 c CARBON DIOXIDE FLOWRATE, IN L/MIN C02FLW 25 c CARBON MONOXIDE RATE OF PRODUCTION, IN MOLE/MIN CORATE 26 c CARBON OIOXIDE RATE OF PRODUCTION. IN MOLE/MIN C02RAT 27 c CARBON RATE OF TRANSFER, IN MOLE/MIN CRATE 28 c CARBON REACTED FROM START OF REACTION, IN MOLE CAC 29 c OXYGEN TRANSFERRED, EXTRAPOLATING, IN MOLE EX02 30 c TOTAL OXYGEN TRANSFERRED, EXTRAPOLATING, IN MOLE EX02AC 3 1 c CARBON TRANSFERRED, EXTRAPOLATING, IN MOLE EXC 32 c TOTAL CARBON TRANSFERRED, EXTRAPOLATING, IN MOLE EXCAC 33 c FE203 MOLECULAR WEIGHT, IN G/MOLE FE203M 34 c FEO MOLECULAR WEIGHT, IN G/MOLE FEOMWT 35 c FE203 FRACTION IN ORE FFE203 36 c FEO FRACTION IN ORE FFEO 37 c FRACTION OF GAS MEASURED, AT EXPERIMENT START FRABEG 38 c FRACTION OF GAS MEASURED, AT EXPERIMENT END FRAEND 39 c AVERAGE FRACTION OF GAS MEASURED FRAGAS 40 c FRACTIONAL REDUCTION OF IRON OXIDES FRARED 41 c FRACTIONAL REACTION OF CARBON FRACAR 42 c FRACTIONAL RATE OF REDUCTION, 1/MIN FRAT02 43 c FRACTIONAL RATE OF BOUDOUARD, 1/MIN FRATEC 44 c TOTAL IRON INPUT, IN MOLE FEIN 45 c FRACTION OF GANGUE IN ORE GANGUE 46 c TOTAL GAS FLOWRATE, IN L/MIN GA5FLW 47 c FRACTION OF HYDROGEN IN CHAR H2CHAR 48 c HYDROGEN FLOWRATE. IN L/MIN H2FLW 49 c RATE OF HYDROGEN RELEASED, IN MOLE/MIN H2RATE 50 c HYDROGEN RELEASED FROM START OF REACTION, IN MOLE H2AC 5 1 c INERT MATERIALS IN ORE AND CHAR INERT 52 c RUN NUMBER I RUN 53 c TIME OF REACTION, IN MIN ITIME 54 c TEMPERATURE OF REACTION. IN DEGREES CENTIGRADE ITEMP 55 c ROOM TEMPERATURE, IN K I TGAS 56 c HYDROGEN TRANSFERRED PER TIME INTERVAL, IN MOLE M0LH2 57 c OXYGEN REACTED PER TIME INTERVAL. IN MOLE M0L02 58 c CAR80N REACTED PER TIME INTERVAL, IN MOLE MOLC •232 L i s t i n g of EXPERCO a t 16:01:23 on DEC 23, 1984 f o r CCid=GM07 Page 2 59 C WEIGHT OF IRON ORE, IN G OREWT 60 C OXYGEN MOLECULAR WEIGHT, IN G/MOLE 02MWT 61 C TOTAL OXYGEN IN OXIDES AT START OF REACTION,IN MOLE 02IN 62 C RATE OF OXYGEN TRANSFER, IN MOLE/MIN 02RATE 63 C OXYGEN TRANSFERRED FROM START OF REACTION, IN MOLE 02AC 64 C ATMOSPHERIC PRESSURE P 65 C FRACTION OF HYDROGEN IN OUTLET GAS PCTH2 66 C FRACTION OF CARBON MONOXIDE IN OUTLET GAS PCTCO 67 C FRACTION OF CARBON DIOXIDE IN OUTLET GAS PCTC02 68 C FRACTION OF OXYGEN IN OUTLET GAS PCT02 69 C FRACTION OF NITROGEN IN OUTLET GAS PCTN2 70 C GAS CONSTANT, IN ATM*L/MOLE*K R 71 C HYDROGEN DENSITY, IN G/CM3 R0H2 72 C CO DENSITY, IN G/CM3 ROCO 73 C C02 DENSITY, IN G/CM3 R0C02 74 C ARGON DENSITY, IN G/CM3 ROAR 75 * C ROTAMETER READING ROTAM 76 C GAS DENSITY, IN G/CM3 ROGAS 77 C CORRECTION FACTOR FOR DENSITY ROCORR 78 C SUM OF GAS FRACTIONS, ACCORDING TO ANALISYS SIGMA 79 C SIZE RATIO OF ORE TO CHAR SIZERA 80 C GAS FLOWRATE OF STANDARD GAS. IN L/MIN STDFLW 81 C TOTAL REDUCTION OF ORE, AFTER EXTRAPOLATION TOTRED 82 C TOTAL CARBON REACTION, AFTER EXTRAPOLATION TOTCAR 83 C 84 C ****** DECLARATION OF VARIABLES ********** 85 C 86 IMPLICIT REAL*8(A-H,0-Z) 87 REAL*8 M0L02,MOLC,M0LH2,INERT 88 INTEGER I,I RUN,ITIME.I TEMP,ITGAS.N,KTH2,KTCO,KTC02,KT02,KTN2 89 INTEGER KTSH2,KTSCO,KTSC02,KTS02,KTSN2 90 DIMENSION TIME(30) ,VOL(30),ITIME(30),PCTH2(30),PCTCO(30) 91 DIMENSION PCTC02(3O),PCT02(30),PCTN2(30),SIGMA(30),GASFLW(30) 92 . DIMENSION H2FLW(30),COFLW(30),C02FLW(30),H2RATE(30),CORATE(30) 93 DIMENSION C02RAT(30),02RATE(30),CRATE(30),C0C02(30),C0H2(30) 94 DIMENSION M0L02(30),MOLC(30),M0LH2(30),H2AC(30),FRAT02(30) 95 DIMENSION 02AC(30),CAC(30),FRARED(30),FRACAR(30),KTH2(30) 96 DIMENSION KTCO(30),KTC02(30),KT02(30),KTN2(30),FRATEC(30) 97 DIMENSION PCCH2(30),PCCCO(30),PCCC02(30),SIGMAC(30),PCTAR(30) 98 DIMENSION C0CC02(30),C0CH2(30),PCFH2(30),PCFCO(30),PCCAR(30) 99 DIMENSION PCFC02(30),SIGMAF(30),C0FC02(30),C0FH2(30) 100 DIMENSION ROGAS(30),ROTAM(30),ROCORR(30),STDFLW(30),BOUCON( 30) 101 C 102 C ****** READING AND WRITING OF DATA ******* 103 C 104 C OPERATIONAL 105 READ(5,10)IRUN,I TEMP,ITGAS,P,R,CTOFE,SIZERA,OREWT 106 READ(5,20)CHARWT,CFIX,ASH,GANGUE,FRABEG,FRAEND,F ET 107 10 FORMAT(1X,I2,2X,I3,2X,I3,2X,F4.2,2X,F5.3,2X,F4.2,2X, 108 1 F5.3.2X,FS. 1 ) 109 20' FORMAT( 1X.F5. 1,2X,F5.3,2X,F5.3,2X,F6.4,2X,F4.2,2X,F4.2, 110 1 2X.F5.3) 111 C STOCHIOMETRIC: 112 READ(5,3O)02MWT,FE203M,FE0MWT,CMWT,C0MWT,C02MWT 113 READ(5,40)H2MWT,FFE203,FFEO,CFE203,H2CHAR,FEOUT.CINOUT 114 READ(5.45)R0H2,R0C0,R0C02,R0AR,R0STD 115 30 FORMAT(1X.F5.2,2X,F6.2,2X,F5.2,2X,F5.2,2X,F5.2,5X,F5.2) 116 40 FORMAT(1X,F4.2,2X.F6.4.2X.F6.4,2X.F6.4.2X,F6.4, 233 L i s t i n g of EXPERCO at 16:01:23 on DEC 23, 1984 f o r CCid=GM07 Page 3 1 17 1 2X,F6.2,2X,F6.2) 1 18 45 FORMAT(1X,E10.4.2X,E10.4,2X,E10.4.2X,E10.4,2X,E10.4) 1 19 C CHROMATOGRAPH STANDARDS 120 READ(5,50)KTSH2,KTSC0,KTSC02,KTS02,KTSN2 121 READ(5,60)STDH2,STDCO,STDC02,STD02,STDN2 122 50 FORMAT( 1X.15,2X, 15,2X,15,2X,15,2X,15) 123 60 FORMAT(1X,F4.2,2X,F5.2,2X,F5.2,2X,F5.2,2X,F5.2) 124 C EXPERIMENTAL DATA 125 READ(5,75)N 126 DO 65 1=1,N 127 READ(5,80-)ITIME( I ) , ROTAM( I ) , STDFLW( I ) , 128 1 KTH2(I),KTCO(I),KTC02(I),KT02(I),KTN2(I) 129 65 CONTINUE 130 75 FORMAT(1X,12) 131 80 FORMAT(1X,I3.2X.F4.1,1X.F6.3, 132 1 3X,I5.2X. I5.2X, I5.2X,I5.2X,15) 133 C WRITING OF DATA 134 WRITE(6, 105)IRUN,ITEMP,ITGAS,CTOFE,SIZERA,OREWT 135 WRITE(6,110)CHARWT,CFIX,FET.ASH,GANGUE,FRABEG,FRAEND 136 WRITE(6, 130)FFE203 , FFEO,CFE203,H2CHAR 137 WRITE(6, 135)R0H2,R0C0,R0C02,R0AR,R0STD 138 WRITE(6,14O)KTSH2,KTSC0,KTSC02,KTS02.KTSN2 139 WRITE(6,150)STDH2,STDCO,STDC02,STD02,STDN2 140 WRITE(6,160) 141 DO 100 I=1,N 142 WRITE(6,165)I,ITIME(I),ROTAM(I),STDFLW(I),KTH2(I), 143 1 KTCO(I),KTC02(I),KT02(I),KTN2(I) 144 100 CONTINUE 145 105 FORMAT( 1H1,///,5X, 'EXPERIMENT R' . I2.//.5X, 'ITEMP. . . ' , 13, 146 1 1X, ' C ,/,5X, 'ITGAS. . . . ' , I3.2X, 'K' ,/,5X, 'CTOFE . . • • ' t 147 2 F4.2./.5X, 'SIZERA. . . ',F5.3,/.5X, 'OREWT. F6 . 1 . 1X, 148 3 'G' ) 149 1 10 FORMAT(5X,'CHARWT...',F5.1,1X,'G',/,5X,'CFIX '. F5 . 3./.5X. 150 1 ' FET ' ,F5.3,/,5X, 'ASH ' , F5.3./.5X, 151 2 'GANGUE...',F5.3./,5X,'FRABEG.. . ' , F4 . 2 , / , 5X , ' FRAEND 152 3 F4.2) 153 130 FORMAT(5X, 'FFE203. . . ' ,F6.4,/,5X, 'FFEO ' ,F6.4,/. 5X , 154 1 'CFE203. . . ' ,F6.4,/,5X, 'H2CHAR. . . ' ,F6.4) 155 135 FORMAT(//,5X , 'GAS DENSITIES: ' ,/,5X, 'R0H2. . . ' .E10.4, 3X , 156 1 'ROCO . . . ' ,E10.4,3X, 'R0C02 . . ' ,E10.4,3X, 'ROAR . . . ' , E10.4. 157 2 3X, 'ROSTD. . ' ,E10.4) 158 140 FORMAT(//,5X. 'GAS STANDARDS: './,5X, 'KTSH2. . ',16,3X, 'KTSCO..', 159 1 16.3X, 'KTSC02 . ' , 16,3X, 'KTS02. . ' ,16,3X, 'KTSN2 .16) 160 150 FORMAT(5X, 'STDH2. . . ' , F5.2,3X, 'STDCO. . . ' ,F5.2,3X , 161 1 'STDCO . . . ' , F5.2,3X, 'STD02. . . ' ,F5.2,3X, 'STDN2 ' ,F5.2) 162 160 FORMAT(//,5X.'DATA:',//,2X.' I',3X,'ITIME',2X,'ROTAM', 2X, 163 1 ' STDFLW ' , 4X , ' KTH2',3X,' KTCO ' , 3X , ' K.TC02 ' , 3X KT02',4X 164 2 '. KTN2 ' ,/,8X, 'MIN' ,6X, '%' ,3X, 'L/MIN' ) 165 165 FORMAT(2X,I 2,4X, I 3,4X,F4. 1, 1X,F6.3,4X, 16, 166 1 2X, 16, 2X , I6..3X . I6.3X, 16) 167 C 168 C ****** CALCULATION OF GAS COMPOSITION AND DENSITY ************ 169 C 170 WRITE(6,220) 171 DO 200 I=1,N 172 PCTH2(I)=STDH2*KTH2(I)/KTSH2 173 PCTCO(I ) =STDCO*KTCO(I)/KTSCO 174 PCTC02(I ) = STDC02*KTC02(I)/KTSC02 234 L i s t i n g of EXPERCO at 16:01:23 on DEC 23, 1984 f o r CC1d=GM07 Page 4 175 PCT02(I)=STD02*KT02(I)/KTS02 176 PCTN2(I)=STDN2*KTN2(I)/KTSN2 177 SIGMA(I)=PCTH2(I)+PCTC0(I)+PCTC02(I)+PCT02(I)+PCTN2(I) 178 PCTAR(I)=100.DO-SIGMA(I) 179 C0C02(I)=PCTCO(I )/PCTC02(I) 180 C0H2(I)=PCTCO(I)/PCTH2(I) 181 WRITE(6,240)ITIME(I ) ,PCTH2(I),PCTCO(I),PCTC02(I),PCT02(I), 182 1 PCTN2(I),SIGMA(I),PCTAR(I),C0C02(I),C0H2(I) 183 CORREC=(SIGMA(I )-PCT02(I)-PCTN2(I)+PCTAR(I))/100.DO 184 PCCH2(I )=PCTH2( I )/CORREC 185 PCCCO(I)=PCTCO(I )/CORREC 186 PCCC02(I)=PCTC02(I )/CORREC 187 PCCAR(I)=PCTAR(I )/CORREC 188 SIGMAC(I)=PCCH2(I)+PCCCO(I)+PCCC02(I) 189 C0CC02(I)=PCCCO(I )/PCCC02(I) 190 C0CH2(I)=PCCCO(I)/PCCH2(I) 191 CORREF=SIGMAC(I)/100.D0 192 PCFH2(I)=PCCH2(I)/CORREF 193 PCFCO(I)=PCCCO(I )/CORREF 194 PCFC02(I )=PCCC02( I )/CORREF 195 SIGMAF(I)=PCFH2(I)+PCFCO(I)+PCFC02(I) 196 C0FC02(I) = (PCFCO(I ) + PCFH2(I))/(PCFC02(I)-PCFH2(I ) ) 197 C0FH2(I)=PCFCO(I )/PCFH2(I) 198 ROGAS(I) = ((PCCH2(I)*R0H2)+(PCCCO(I)*ROCO)+(PCCC02(I)'R0C02)+ 199 1 (PCCAR(I)*ROAR))/100.DO 200 200 CONTINUE 201 WRITE(6,245) 202 DO 215 I = 1 , N 203 WRITE(6,250)ITIME(I),PCCH2(I),PCCCO(I),PCCC02(I), 204 1 SIGMAC(I ) ,PCCAR(I),C0CC02(I),C0CH2(I),ROGAS(I) 205 2 15 CONTINUE 206 WRITE(6,255) 207 DO 219 1=1,N 208 WRITE(6,260) ITIME(I ) ,PCFH2(I),PCFCO( I) ,PCFC02( I ) , 209 1 SIGMAF(I ) ,C0FC02(I),C0FH2(I) 210 219 CONTINUE 21 1 220 FORMAT(1H1,//,5X,'GAS COMPOSITION',//,5X.'ORIGINAL', 212 1 //,2X,'ITIME',3X, 'PCTH2' ,3X, 'PCTCO' ,3X, 'PCTC02 ' .3X , 213 2 'PCT02' ,3X, 'PCTN2',3X, ' SIGMA' ,3X, 'PCTAR' ,3X, 'C0/C02' 214 3 3X,'C0/H2',/,3X,'MIN') 215 240 FORMAT(3X,I3,4X.F5.2,3X,F5.2,4X,F5.2,3X,F5.2. 216 1 3X,F5.2,3X,F6.2,3X,F5.2,4X,F5.2,3X,F5.2) 217 245 FORMAT(/,5X,'WITHOUT AIR'.74X,'ROGAS(G/CM3)'./) 218 250 FORMAT(3X,13,4X,F5.2,3X,F5.2. 219 1 4X,F5 . 2, 19X,F6.2,3X,F5.2,4X,F5.2,3X,F5.2,9X,E10.4) 220 255 FORMAT(1H1,/.5X.'WITHOUT ARGON' ,/) 221 260 FORMAT(3X,I3,4X,F5.2,3X, 222 1 F5.2.4X.F5.2, 19X.F6.2.12X,F5.2.3X,F5.2) 223 C 224 C ************* CALCULATION OF GAS FLOWRATES ************* 225 C 226 FRAGAS=(FRABEG+ FRAEND)/2.DO 227 WRITE(6,310) 228 DO 300 I=1,N 229 ROCORR(I) = (DSORT( 1 .DO/ROGAS(I)))/(DSQRT( 1.DO/ROSTD)) 230 GASFLWfI)=STDFLW(I)*ROCORR(I)/FRAGAS 231 H2FLW(I)=GASFLW(I )*PCCH2(I)/100.DO 232 COFLW(I)=GASFLW(I)*PCCCO(I)/100.DO 235 L i s t i n g o f EXPERCO at 16:01:23 o n DEC 23, 1984 f o r CCid=GM07 Page 5 233 C02FLW(I)=GASFLW(I ) *PCCC02(I)/100.D0 234 WRITE(6,320)ITIME(I ) ,GASFLW(I),H2FLW(I),COFLW( I) ,C02FLW( I ) 235 300 CONTINUE 236 310 FORMAT( 1H 1 ,//,5X , ' GAS FLOWRATES' ,//, 237 1 2X,'ITIME',5X,'GASFLW,5X,'H2FLW,5X,'COFLW,5X, 238 2 'C02FLW ,/3X, 'MIN' ,7X, 'L/MIN' ,5X, 'L/MIN' ,5X, 'L/MIN' , 239 3 6X,'L/MIN',/) 240 320 F0RMAT(3X,I 3,6X,F6.3,5X,F5.3,5X,F6.3,5X,F5.3) 241 C 242 C ******************* CALCULATION OF MOLAR RATES ******************* 243 C 244 C OXYGEN AND CARBON AMOUNTS IN FEED 245 02IN=((OREWT*((FFE203*48.00/159.70) + (FFEO*16.DO/7 1.85) 246 1 ))+(CHARWT*ASH*CFE203*48.00/159.70))/32.00 247 CIN = CHARWT*CFIX/12.DO 248 FEIN=((0REWT*FET)+(CHARWT*ASH*CFE203))/55.85 249 WRITE(6,410) 250 DO 400 1=1,N 251 H2RATE(I)=H2FLW(I)/(R*ITGAS) 252 CORATE(I)=COFLW(I)/(R*ITGAS) 253 C02RAT(I)=C02FLW(I)/(R*ITGAS) 254 02RATE(I)=CORATE(I)/2.DO+C02RAT(I) 255 CRATE(I)=C0RATE(I)+C02RAT(I) 256 FRAT02(I)=02RATE(I)/(02IN*60.DO) 257 FRATEC(I)=CRATE(I)/(CIN*60.DO) 258 WRITE(6,420)ITIME(I),H2RATE(I),CORATE(I),C02RAT(I),02RATE(I), 259 1 CRATE(I),FRAT02(I ) ,FRATEC(I ) 260 400 CONTINUE 261 410 FORMAT(//,5X,'MOLAR RATES',//, 262 1 2X, 'ITIME' ,5X, 'H2RATE',5X, 'CORATE' ,5X, 'C02RAT' ,5X, 263 2 '02RATE' ,5X, 'CRATE' ,8X, 'FRAT02', 10X, 'FRATEC. 264 3 /,3X,'MIN',5X,'MOL/MIN',4X, 265 4 'MOL/MIN',4X,'MOL/MIN',4X,'MOL/MIN',4X,'MOL/MIN', 266 5 7X, ' 1/SEC , 11X, ' 1/SEC ,/) 267 420 FORMAT(3X,I3,6X,F5.3,6X,F5.3,6X,F5.3,6X,F5.3,6X, 268 1 F5.3.6X.E10.4.6X.E10.4) 269 C 270 C ***** CALCULATION OF FRACTIONAL REDUCTION AND CARBON REACTED ********* 271 C (INTEGRATION IS PERFORMED USING TRAPEZOIDAL RULE) 272 C 273 C FIRST INTERVAL APPROXIMATION 274 WRITE(6,510) 275 M0L02(1)=02RATE(1)/2.DO*ITIME(1) 276 02AC( 1 )=M0L02( 1 ) 277 FRARED(1)=02AC(1)/02IN 278 MOLC(1)=CRATE(1)/2.00*ITIME(1) 279 CAC(1)=MOLC( 1 ) 280 FRACAR(1)=CAC( 1 )/CIN 281 M0LH2(1)=H2RATE(1)/2.DO*ITIME(1) 282 H2AC(1)=M0LH2(1) 283 8=1.DO-FRACAR(1) 284 BOUCON(1)=DLOG(B) 285 WRITE(6,520)ITIME( 1 ) ,M0L02( 1 ),02AC( 1 ) ,FRARED(1),MOLC(1). 286 1 CAC( 1),BOUCON( 1 ) , FRACAR(1),M0LH2(1),H2AC( 1) 287 C INTEGRATION 288 DO 500 d=2,N 289 M0L02(J) = (( 0 2 R A T E ( J - 1 )+02RATE(J))/2.DO)*(ITIME(J) 290 1 - I T I M E ( d - l ) ) .236 L i s t i n g o f EXPERCO at 16:01:23 on DEC 23, 1984 f o r CCid=GM07 Page 6 291 02AC(d)=02AC(d~1)+M0L02(J) 292 FRARED(d)=02AC(d)/02IN 293 M O L C ( d ) = ( ( C R A T E ( J - 1 ) + C R A T E ( J ) ) / 2 . D O ) * ( I T I M E ( J ) - I T I M E ( d - 1 ) ) 294 CAC(d)=CAC(d-1)+MOLC(J) 295 FRACAR(d)=CAC(d)/CIN 296 M0LH2(d )= ( (H2RATE(d -1 )+H2RATE(d ) ) /2 .D0) * ( IT IME(d ) 297 1 -ITIME(J-O) 298 H2AC(d)=H2AC(d-1)+M0LH2(d) 299 B=1.DO-FRACAR(d) 300 BOUCON(d)=DLOG(B) 301 WR ITE(6 .520)1T IME(d ) ,M0L02(d ) ,02AC(J ) ,FRARED ( d) , MOLC ( d) , 302 1 CAC(d) , FRACAR(d') .BOUCON(d) ,M0LH2(d) ,H2AC(d) 303 500 CONTINUE 304 C LAST INTERVAL EXTRAPOLATION (ONE AND A HALF TIMES LAST INTERVAL) 305 ITIMEX=1 .5 * ( I T IME (N ) - IT IME(N-1) ) 306 ITIMFI=ITIME(N)+ITIMEX 307 EX02=(02RATE(N)/2,DO)* IT IMEX 308 EX02AC=02AC(N)+EX02 309 T0TRED=EX02AC/02IN 310 EXC=(CRATE(N)/2.D0)* IT IMEX 311 EXCAC=CAC(N)+EXC 312 TOTCAR=EXCAC/CIN 313 EXH2=H2RATE(N)*ITIMEX 314 EXH2AC=H2AC(N)+EXH2 315 BC=1.DO-TOTCAR 316 BOUCOT=DLOG(BC) 317 WRITE(6,520) IT IMF I ,EX02,EX02AC,TOTRED,EXC,EXCAC, 318 1 T0TCAR,B0UC0T,EXH2,EXH2AC 319 510 FORMAT( 1 H 1 , / / / , 5 X , ' F R A C T I O N A L R E D U C T I O N ' , / / / , 320 1 2 X , ' I T I M E ' , 5 X , ' M 0 L 0 2 ' , 5 X , ' 0 2 A C ' , 5 X , ' F R A R E D ' , 5 X , ' M O L C ' , 321 2 7X, ' C A C ' , 5 X , ' FRACAR ' ,5X , ' L N ( 1 - F ) ' , 5 X , 'M0LH2' ,5X, 'H2AC ' , / , 322 3 3 X , ' M I N ' , / ) 323 520 F O R M A T ( 3 X , I 3 , 6 X , F 5 . 3 , 5 X , F 5 . 3 , 5 X , F 5 . 3 , 5 X , F 5 . 3 , 4 X , F G . 3 , 324 1 5 X , F 5 . 3 , 5 X , E 1 0 . 3 , 5 X , F 5 . 3 , 5 X , F 5 . 3 ) 325 C 326 C * * * * * * MASS BALANCE * * * * * * * * 327 C 328 TOTFED=OREWT+CHARWT 329 FEIN=FEIN*55.85 330 02IN=02IN*32.DO 331 H2IN=CHARWT*H2CHAR 332 CIN=CIN*12.D0 333 INERT=(OREWT*GANGUE)+(CHARWT*ASH*(1.D0-CFE203)) 334 CININ=CIN+INERT 335 T0TIN=FEIN+02IN+H2IN+CIN+INERT 336 020UT=EX02AC*32.DO 337 H20UT=EXH2AC*2.DO 338 CIN0UT=CIN0UT+(EXCAC*12.DO) 339 T0T0UT=FE0UT+020UT+H20UT+CIN0UT 340 XTOT=(TOTFED-TOTOUT)/T0TFED 341 XFE = ( FE IN -FEOUT) /FE IN 342 X02=(02 IN-020UT)/02 IN 343 XH2=(H2IN-H20UT)/H2IN 344 XCIN=(CININ-CINOUT)/CININ 345 XTOTAL=(TOTIN-TOTOUT)/TOTIN 346 WRITE(6,62O)T0TFED 347 620 FORMAT( / / / / / , 7 X , ' * * * * MASS BALANCE * * * * ' / / , 2 4 X , ' F E ' , 348 1 7 X . ' 0 2 ' , 7 X , ' H 2 ' , 7 X , ' C , 6 X , ' I N E R T ' , 4 X , 237 L i s t i n g of EXPERCO at 16:01:23 on DEC 23, 1984 f o r CCid=GM07 Page 7 349 2 'C+INERT' ,3X, 'TOTAL' ,//,5X, 'FEED' .67X.F7.2) 350 WRITE(6,630)FEIN,02IN.H2IN,CIN,INERT,CININ.TOTIN, 351 1 FE0UT,020UT,H20UT,CIN0UT,T0T0UT, 352 2 XT0T,XFE,X02,XH2,XCIN.XT0TAL 353 630 FORMAT( 5X,'IN *',13X,F6.2,3X,F6.2,3X,F6.2,3X, 354 1 F6.2,3X,F6.2,3X,F6.2,3X,F7.2,/,5X, 355 2 'OUT **' , 1 1X,F6.2,3X.F6.2,3X,F6.2.21X, 356 3 F6.2,3X,F7.2,///,5X, '(FEED-OUT)/FEED' , 357 4 56X,F6.3,/,5X, '(IN-OUT)/IN' ,6X , 358 5 F6.3,3X,F6.3,3X,F6.3,21X,F6.3, 359 6 3X,F6.3,//,5X,'* FROM SOLIDS ANALYSES',/,5X, 360 7 '** FROM GAS ANALYSIS AND SOLIDS SEPARATION') 361 RETURN 362 END EXPERIMENT R58 ITEMP....900 C ITGAS....294 K CTOFE....0.32 SIZERA . . .0.500 OREWT.... 600.0 G CHARWT...313.0 G CFIX 0.408 FET 0.667 ASH 0.561 GANGUE...0.058 FRABEG...0.99 FRAEND...0.96 FFE203...0.8220 FFEO 0. 1 190 CFE203...0.0460 H2CHAR...0.0031 GAS DENSITIES: R0H2. . .0.8300E-04 ROCO. . .0. 1 165E-02 R0C02. .0. 1831E-02 ROAR. . .0. 1665E-02 ROSTD. .0. 1260E-02 GAS STANDARDS: KTSH2.. 4540 KTSCO.. 7435 KTSC02. 1924 KTS02.. 2103 KTSN2.. 6992 STDH2... 4.04 STDCO . . .74.79 STDCO . . .20.10 STD02...21.00 STDN2. . .78.00 DATA: I ITIME ROTAM STDFLW KTH2 KTCO KTC02 KT02 KTN2 MIN ° L/MIN 1 2 17 0 1 600 385 0 3407 0 252 1 2 4 42 0 4 650 911 3475 4124 0 0 3 6 62 0 7 550 14 50 5606 2468 0 787 4 8 50 0 5 800 1669 6376 2131 0 0 5 10 37 0 4 050 1569 6552 2054 0 0 6 12 34 0 3 550 1591 6315 1946 60 200 7 14 37 0 4 050 1700 6600 1900 0 0 8 16 37 0 4 050 1800 6700 1900 0 0 9 21 38 0 4 200 1855 6852 1873 0 0 10 25 38 0 4 200 1958 6961 1917 0 O 1 1 30 35 0 3 800 2108 6720 2032 0 0 12 35 26 0 2 650 2403 6719 1919 0 0 13 41 18 0 1 750 3075 7190 1584 0 0 14 66 56 0 1 100 4620 7272 1555 0 0 15 96 40 0 0 710 5615 7033 1433 7 1 235 16 126 20 0 0 285 7600 7300 1200 94 270 GAS COMPOSITION ORIGINAL ITIME PCTH2 -PCTCO PCTC02 PCT02 PCTN2 SIGMA PCTAR C0/C02 C0/H2 MIN 2 0 . 34 0 .0 35 .59 0 .0 28 , 12 64 .06 35 .94 0 .0 0 .0 4 0, .81 34 .96 43 .08 0 .0 0. .0 78 .85 21 . 15 0 .81 43 . 12 6 1 . . 29 56 . 39 25 . 78 0 .0 8 . 78 92 . 24 7 . 76 2 . 19 43 .70 8 1 . . 49 64 . 14 22 . 26 0 .0 0. .0 87 .89 12 . 1 1 2 .88 43 . 18 10 1 .40 65 .91 21 .46 0 .0 0. .0 88 .76 1 1 .24 3 .07 47 .20 12 1 . 42 63 . 52 20 . 33 0 .60 2 . 23 88 . 10 1 1 .90 3 . 12 44 .87 14 1 .51 66 . 39 19 .85 0. .0 0. .0 87 . 75 12 . 25 3 . 34 43 . 89 16 1 .60 67 . 40 19. .85 0. .0 0. .0 88. . 85 1 1 . . 15 3 . 40 42 .08 21 1 .65 68 .93 19 .57 0 .0 0 .0 90 . 14 9 . 86 3 .52 41 .76 25 1 . 74' 70 .02 20 .03 0 .0 0 .0 91 . 79 8 . 21 3 .50 40 . 19 30 1 . 88 67 .60 21 , 23 0. .0 0. 0 90 , 70 9 . 30 3 . 18 36 .04 35 2 . 14 67 . 59 20 .05 0. .0 0. .0 89 .77 10. . 23 3 . 37 3 1 .61 41 2 . 74 72 . 33 16 .55 0. 0 0. 0 91 .61 8 . 39 4 . 37 26 . 43 66 4 . 1 1 73 . 15 16 . 25 0. .0 0. .0 93 .51 6 . 49 4 . 50 17 . 79 96 5 .00 70 . 75 14 . 97 0. .71 2 . 62 94 .04 5 . 96 4 . 73 14 . 16 126 6 . 76 73 . 43 12 . 54 0. .94 3 . 01 96. .68 3 . 32 5 . 86 10 .86 WITHOUT AIR R0GAS(G/CM3 2 0. . 48 0 .0 49 . 52 50. .00 50. .00 0. .0 0 .0 0. 1740E-02 4 0 .81 34 .96 43 .08 78 .85 21 . 15 0 .81 43 . 12 0. 1549E-02 6 1 . 4 1 61 . 82 28 . 26 91 .50 8 . 50 2 . 19 43 .70 0. 1380E-02 8 1 . . 49 64 . 14 22 . 26 87 . 89 12 . 11 2 .88 43 . 18 0. 1358E-02 10 1 .40 65 .91 21 .46 88 . 76 1 1 . 24 3 . ,07 47 . 20 0. 1349E-02 12 1 .46 65 . 37 20 .92 87 . 75 12 . 25 3 . 12 44 .87 0. 1350E-02 14 1 . .51 66 . 39 19 . 85 87 . 75 12 . 25 3 , 34 43 .89 0. 1342E-02 •16 1 . . 60 67 . 40 19 . 85 88 . 85 1 1 . 15 3 . 40 42 .08 0. 1336E-02 21 1 . .65 68 .93 19 . 57 90. 14 9 . 86 3 . 52 41 . 76 0. 1327E-02 25 1 . 74 70 .02 20 .03 91 . , 79 8 , 21 3 . 50 40 . 19 0. 1321E-02 30 1 . . 88 67 .60 21 . 23 90. .70 9. 30 ' 3 . 18 36 .04 0. 1333E-02 35 2 . 14 67 . 59 20. .05 89 . 77 10. 23 3 . 37 31 . 61 0. 1327E-02 41 2 . 74 72 .33 16 . 55 91 . 61 8 . 39 4 . 37 26 .43 0. 1288E-02 66 4 . 1 1 73 . 15 16 . 25 93 , .51 6 . 49 4 . 50 17 . 79 0. 1261E-02 96 5 . 17 73 . 18 15 . 49 93 . 84 6. 16 4 . 73 14 . 16 0. 1243E-02 126 7 .04 76 . 45 13 . 05 96 . 55 3 . 45 5 . 86 10 . 86 0. 1193E-02 CO VO WITHOUT ARGON 2 0 .95 0. .0 99 .05 100. .00 0. .01 0 .0 4 1 .03 44 .33 54 .64 100 00 0 . 85 43 . 12 6 1 . 55 67 . 56 30, . 89 100, ,00 2 . 36 43 . 70 8 1 .69 72 .98 25 , . 33 100, 00 3 16 43 . 18 10 • 1 . . 57 74 . 25 24 , . 17 100. .00 3 . 35 47 . 20 12 1 .66 74 . 50 23 . 84 100. .00 3 . 43 44 . 87 14 1 . 72 75 .66 22 .62 100 .00 3 . 70 43 . 89 16 1 . .80 75 .86 22 . 34 100. .00 3 . 78 42 . 08 21 1 .83 76 .46 21 , .71 100 .00 3 , .94 4 1 . 76 25 1 .90 76 . 28 21 , .82 100 .00 3 , .92 40. . 19 30 2 .07 74 . 53 23 , . 40 100 .00 3 , 59 36 . 04 35 2 . 38 75 . 29 22 . 33 100 00 3 , 89 31 61 4 1 2 .99 78 .95 18 .06 100 .00 5 . 43 26 . 43 66 4 .40 78 .23 17 . 37 100 .00 6 . 37 17 .79 96 5 .51 77 .99 16 .50 100 .00 7 .59 14 . 16 126 7 . 29 79 . 19 13 . 52 100. .00 13 , . 89 10 .86 c o c n c n - . u i o u ' — c n . u r o o c o c n . u r o O O O O O O O O O O O O O O O O b b b b o b b b b b b b b b b b O O O O O O O O O O O O O O O O - ^ r o r o r o r o c o u c o c o u r o r o . f c . b . - i . o »-» H-1 -1 z - t HH r o c o c n .u c o c o r o r o HH HH Z 3 2 ff> CO CO — Ul O Ul _* c n ^ r o o c o c n & r o z o m o m > C/l > n t~ 2 73 a o I > CO K. t o H O O-'-'NU* *. ^ C J . t » u i ~ j r - > 73 \ XI m \ (/l > 2 > c n c o - J - J c n - J t o _ i . O O c n O - J CO CO CO s -n —i -I O U M NI t I D O CD c o r o - * CO CO O CO I - m z m O CO CD CD CO O CD CO Ul Ul CO 4i -* c o - * -sj z (/) O O O O O O O O O O O O O O O O b b b b b - - - ^  ^  b - -- -- o b — r o c o u i - J O r o r o - . - . c o - ' U i c o c n O r o * c o J i C o r o O c o - - u i O t o O r o o o r o \ 73 2 > O O O O O O O O O O O O O O O O o o o o o b o o o o o o o - ^ o g rocox^ j ^ u i - j - j c n c n c r i o i u i c o o c o o - ' O o c n c o - j - ' - c o c o c n - ' - ' C n u i u i u i - o z c O O O O O O O O O O O O O O O O o o o o b b b o o o o b b b o b O O O - ' M U U U O U C O U O l O v l M t o u i o o r o r o c o u i f k c o c o - ^ c n c o - j - i c o 2 o n r- o v. ro 2 73 •-t > Z - I r- o O O O - ' - ' M M M M M U r O U ^ - ' O \ o 2 -n r o u i o o t o ^ i u i c o c D - J c n c j c n c n u i u i o c o c o r o c o c o c n t . c o - ' - J O ^ N i - i O O - o - t n ^ o r o a i c o c o r o o a i u i c o i . z c O O O O O O O O O O O O O O O O o b o o b o b o o b b b - - > - ' 0 O - ^ r o c o u i o o c o c o c o o o ^ i c o f o c o o r o c n c n u i c D i D - j a i i . o c o c o . - ' C o r o c o c o o o r~ ro \ 73 2 > >-• H Z m O O O O O O O O O O O O - r o - O O - . - ' i o u i c o c o c D c o - o - j c o i o o c o c n CO - '00(DCOO^UO(OCOO>1IO(I1(D c o ^ c o i » - . u i c o - ' - ' C O f f ) - ' C n - ' C o r o n r- o \ ro 2 -n i-i r— Z « O O O O O O O O O O O O O O O O O O O O O -•• — — to ro — O - . r o A < n c o ^ u i u i 4 i . A r o * . o - J c o r o -»-jfouicno~<-ucn.t>0">uiu )0">coco o o r- 73 \ > 2 —i O O O O O O O O O O O O O O O O ro ui - J . to CO CO ro to ro ro Ul CO CO -n O O CO ro co -J O O to co Ul CO CO .b _ t \ 73 A - J .u CO -J - j CO CO O O CO _>. CO oo (/) > cn — — t CO O ff) ro CO <n Ul Ul £- O Ul m H m m m m m m m m m m m m m m m m O O O O O O O O O b O O b O O O b O ro 4^  CO CO CO CO CO CO CO CO CO CO CO CO O O O O O O O O O O O O O O O O _ . 4 > . f f ) - ^ - » r o r o r o r o i o - > . r o c o 4 ^ r o 4 ^ - J t o o i o u i - . t i i i o i o co-ro ro co — M O t ( O O U I D ^ C O O l - J - O — ro oo co - J C O C O U I C D ~ 4 — - c O N a u i r o c o c o c o — co r n r T i r n r n n i r n r n r T i r n r n r n r n r n r f i r n r n i i i i i i O O O O O O O O O O O O O O O O 4 i £ . J ^ C O C O C O C O C O C O C O C O C O C O U 3 C O J ^ — 73 C/) > m -i O m O FRACTIONAL REDUCTION ITIME MOL02 02AC FRARED MOLC CAC FRACAR LN(1-F) MOLH2 H2AC MIN 2 0. 029 0 .029 0. .006 0. .029 0 ,029 003 0. 270E-02 0 ,000 0, 000 4 0. 137 0 . 165 0. 032 0. 168 0 . 197 0. 018 -o. 186E-01 0 .002 0. ,002 6 0. 290 0. . 455 0. 087 0. .416 0 .612 0. 058 -o. 593E-01 0, .006 0. 008 8 0. 311 0 . 766 0. 147 0. .482 1 .094 0. 103 -0. 108E+00 0, .008 0. 016 10 0. 220 0 .986 0. 189 0. .351 1 . . 445 0 136 -0. 146E+00 0 .006 0. 022 12 0. 169 1 . . 154 0. 222 0. .271 1 . .716 0. 161 -0. 176E+00 0, .004 0. 026 14 0. 167 1 .321 0. 254 0. . 270 1 .986 0. 187 -0. 207E+00 0 .005 0. 031 16 0. 178 1 . 499 O. 288 0 290 2 . 276 0. ,214 -o. 24 1E+00 o .005 0. 036 2 1 0. 459 1 .959 0 . 376 0 . 750 3 .027 0, , 284 -0. 335E+00 0 ,014 0 050 25 0. 380 2 . 339 0. . 449 0. 623 3 .649 0. , 343 -0. 420E+00 0 .012 0. 062 30 0. 456 2 . 795 0, "537 0. , 742 4 . 391 0, 4 13 -0. 532E+00 • 0 ,015 0. 077 35 0. 364 3 . 159 0. .607 0. . 590 4 . 981 0. 468 -0. 631E+00 0 .013 0. .090 41 0. 294 3 .453 0. .663 0. . 485 5 .466 0. ,514 -0. 721E+00 0, .013 0. , 103 66 0. ,794 4 . 248 0 . 816 1 .341 6 .807 0. .640 -0. 102E+01 0, .049 0, 152 96 0. 608 4 .856 0. .933 1. .032 7 . 839 0. ,737 -0. 133E+01 0 .052 0. , 205 126 0. 333 5 . 189 0. .997 0. , 572 8 .411 0. 790 -0. 156E+01 0 .037 0, 24 1 17 1 0. . 144 5 . 333 1 . .025 0 . 251 8 .661 0. ,814 -0. 168E+01 0 .039 0, 281 **** MASS BALANCE **** FE 02 H2 C INERT C+INERT TOTAL FEED 913.00 IN * 408.28 166.57 0.97 127.70 202.56 330.26 906.07 OUT ** 436.00 170.65 0.56 265.44 872.65 (FEED-OUT )/FEED 0.044 (IN-OUT)/IN -0.068 -0.025 0.421 0.196 0.037 * FROM SOLIDS ANALYSES ^ ** FROM GAS ANALYSIS AND SOLIDS SEPARATION 4=> APPENDIX E SUMMARY OF OVERALL MASS-BALANCES FOR REDUCTION EXPERIMENTS* Conditions Base case S t o i c h i o m e t r i c C F l- x/Fe Fi n e r p a r t i c l e s Segregated bed L i g n i t e Catalyzed N2--flushed CF- = 0.48 CF-i x / p e = 0.64 c F . • X/Fe = 0.16; 7 r.p.m. C F i X/Fe = 0.64; 7 r.p.m. C F i X/Fe = 0.64; 11 r.p.m. C F I X/Fe = 0.64; 20 r.p.m. CF I X/Fe = 0.16; 1% f i l l C F i x / F e = 0.64; 7% f i l l Temperature (In-0ut)/I [°C] 950 0.060 900 0.037 850 0.031 800 0.041 950 0.039 900 0.051 850 0.027 800 0.022 950 -0.037 900 0.033 850 0.025 800 0.022 950 0.048 900 0.056 850 0.035 800 0.014 950 0.038 900 0.022 850 -0.021 900 -0.020 800 -0.058 900 0.022 900 0.054 900 0.031 900 0.027 900 0.015 900 0.041 900 0.040 900 0.032 900 0.037 *A11 experiments at 14 percent f i l l , 14 r.p.m. and 0.32 C F l- x/Fe l e s s otherwise i n d i c a t e d . 244 APPENDIX F . CALCULATIONS FOR THE OXIDATION OF S i C HEATING ELEMENT. The r e a c t i o n s c o n s i d e r e d to take p l a c e i n s i d e the r o t a r y r e a c t o r and t h e i r r e s p e c t i v e f r e e energy e q u a t i o n s and e q u i l i b r i u m c o n s t a n t s , a r e : (1) C+ C0 2 =2C0 A G £ = 3 9 8 1 0 - 4 0 . 8 7 T K ^ t P c o ) 2 (Pco 2 ) (2) S iC+3C0 2 =Si0 2 +4C0 A G ° = - 2 4 9 3 0 - 4 1 . 4 9 T K 2 = ( P c o ) 4 2 ( P c o 2 ) 3 (3) SiC+2C0 =Si0+3C0 A G ° = 9 9 5 2 0 = 8 2 . 7 9 T K 0 = ( P c o ) 3 ( P s i O ) ( P c o 2 ) ^ The c a l c u l a t e d P c o / P c o 2 r a t i o s f o r these e q u a t i o n s are t a b u l a t -ed below f o r a t o t a l p r e s s u r e o f one atmosphere, and f o r the temperatures r e l e v a n t to t h i s c a s e . T (K) (1) (2) (3) P c o / P c o 2 P c o / P c o 2 P c o / P c o 2 Ps iO 1100 11.46 4 . 7 6 U 0 ) 4 11.38 1. 73 (10) -4 1200 49.05 3 . 5 1 ( 1 0 ) 4 48.69 3. 94 (10) -4 1300 174.63 2 . 6 3 ( 1 0 ) 4 17 3.34 7. 21(10) -4 1400 523.00 2 . 0 6 ( 1 0 ) 4 519.00 1. 33(10) -4 1500 1356.00 1 . 7 1 ( 1 0 ) 4 1346.00 2. 14 (10) -4 1600 3124.00 1 . 4 3 ( 1 0 ) 4 3101.00 3. 2 3 (10) -4 1700 6525.00 1 . 2 2 ( 1 0 ) 4 6477.00 4 . 70(10) -4 245 Thermodynamically then, the p o s s i b i l i t y e x i s t s of the o x i d a t i o n of the S i C h e a t i n g element, i n t o e i t h e r S i O or SiC>2, by the small f r a c t i o n o f CO2 generated. K i n e t i c a l l y , on the other hand, the r e a c t i o n i s very slow and i t s r a t e can be a s s e s s e d w i t h a v a i l a b l e data.147 p o r l a m i n a r f l o w of gas at 1477 °C, and under an oxygen p r e s s u r e of IO" 5 atm [these are the extreme ox-i d i s i n g c o n d i t i o n s that could be faced by the system], the r a t e c o n s t a n t f o r o x i d a t i o n of the SiC element i s 10~ 4 g/cm^min.. In t h i s case the element sur-f a c e a r e a i s 284 cm 2, and by c o n s i d e r i n g s t o i c h i o m e t r y , the rate of CO pro-duced w i l l be: 1 0 " 4 Hh- X 2 8 4 ™ X 4x281g/mo1 x 2 2' 4 iioT = ^ ( l O ) " 3 ^ (STP) whi c h , f o r an e x p e c t e d CO e v o l u t i o n from r e a c t i o n s (1) and (2) of about 5 V m i n , represents about 1 percent of the t o t a l gas to be analyzed. I t i s a l s o w o r t h w h i l e mentioning that a f t e r some o x i d a t i o n has taken p l a c e , the element surface w i l l be p a s s i v a t e d slowing some more the r a t e . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0096744/manifest

Comment

Related Items