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Material characteristics affecting formcoke Gill, Wayne William 1979

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MATERIAL CHARACTERISTICS AFFECTING FORMCOKE by WAYNE WILLIAM GILL B.A.Sc. U n i v e r s i t y of B r i t i s h Columbia, 1976 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of M e t a l l u r g i c a l Engineering) We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1979 0 Wayne William G i l l , 1979 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of Brit ish Columbia Vancouver 8, Canada Date P O M E 2 9 ^ 9*73 c ABSTRACT The influence of aggregate and binder phase c h a r a c t e r i s t i c s on formcoke products has been studied. This involved i n v e s t i g a t i n g the compaction k i n e t i c s of the system and determining the mechanical strength of the briquettes produced. The char phase was characterized i n terms of density, hardness, p o r o s i t y and r e s i d u a l v o l a t i l e matter content and the r h e o l o g i c a l proper-t i e s of the binder phases used were established elsewhere. The strength and wetting behaviour of the aggregate-binder i n t e r f a c e were studied using model materials (an SRC p i t c h binder and a graphite rod aggregate) as w e l l as those produced i n t h i s work. Analysis of compaction curves was c a r r i e d out using the CCWL Hot Compaction Model f o r Char-Binder Coal systems which was found to adequately describe the observed compaction behaviour. Briquette strength was characterized by ultimate compressive strength and comparisons were made for a constant briquette bulk p o r o s i t y of 35% (by volume). Results i n d i c a t e that binder phase f l u i d i t y a f f e c t s compaction v i s c o s i t y during the p a r t i c l e flow stage of compaction and that char p o r o s i t y influences f i n a l briquette bulk density by a f f e c t i n g the amount of t o t a l compaction required to obtain a given bulk density. In general, increased t o t a l compaction was shown to r e s u l t i n higher product bulk density and high bulk density was found to y i e l d higher gross composite strength. The l a t t e r r e l a t i o n s h i p was seen to be approximately l i n e a r - i i i -over the range of bulk p o r o s i t y encountered i n t h i s study. A higher briquette strength was found for systems with aggregates carbonized at lower temperatures. This was a t t r i b u t e d to a combination of higher p o r o s i t y and stronger char-binder i n t e r f a c i a l strength, although the former e f f e c t was considered to predominate i n the systems considered here. Binder phase f l u i d i t y was also seen to a f f e c t b riquette strength, higher f l u i d i t y r e s u l t i n g i n higher strength. I t was concluded that t h i s was due to increased binder penetration of the aggregate phase. With no s i g n i f i c a n t pore structure i n the aggregate, as found with high temperature char, briquette strength was seen to become approximately constant for the three binder coals used. I t was concluded that a good formcoke product was aided by a high-l y f l u i d binder and a char pore structure a c c e s s i b l e to the binder phase. - i v -ACKNOWLEDGEMENTS The author wishes to express h i s gratitude f o r the advice and encouragement of h i s research supervisor, Dr. A.CD. Chaklader. Thanks are also extended to f a c u l t y members, fellow graduate students and tech-n i c a l s t a f f . The assistance of Messrs. P. Gorog, I. F r a n k l i n , P. Wenman and P. Musil i s e s p e c i a l l y appreciated. F i n a n c i a l assistance, i n the form of a fellowship from The Aluminum Company of Canada, i s g r a t e f u l l y acknowledged. V TABLE OF CONTENTS Page 1. INTRODUCTION 1 1.1 P y r o l y t i c Behaviour of Coal 1 1.2 The Conventional Cokemaking Process 3 1.3 The Formcoke A l t e r n a t i v e 6 1.4 Previous Studies 9 1.4.1 Material C h a r a c t e r i s t i c s 9 1.4.2 Char-Binder In t e r a c t i o n 15 1.4.3 Compaction K i n e t i c s 18 1.5 Objectives of Present Study 21 2. EXPERIMENTAL 22 2.1 Aggregate Char C h a r a c t e r i z a t i o n 25 2.1.1 Hardness 26 2.1.2 Density 27 2.1.3 Porosity 27 2.2 Binder Coal C h a r a c t e r i z a t i o n 28 2.3 Char-Binder I n t e r a c t i o n 30 2.3.1 I n t e r f a c i a l Strength 31 2.3.2 W e t t a b i l i t y of Chars 33 2.3.3 Wetting Behaviour of Coal Extracts 33 2.4 The B r i q u e t t i n g Program 34 2.5 Briquette Strength 37 3. RESULTS AND ANALYSES 39 3.1 Char C h a r a c t e r i z a t i o n 39 3.1.1 Density 39 3.1..2 Hardness 39 3.1.3 Porosity 42 3.1.4 Residual V o l a t i l e Matter Content 50 3.2 Char-Binder I n t e r a c t i o n 50 3.3 Compaction Analysis 52 3.4 Briquette Strength 61 - v i -Page 4. DISCUSSION 70 4.1 A p p l i c a b i l i t y of Hot Compaction Model 70 4.2 E f f e c t of Material C h a r a c t e r i s t i c s on Compaction K i n e t i c s 71 4.3 E f f e c t of Material C h a r a c t e r i s t i c s on Briquette Strength 79 4.3.1 Char C h a r a c t e r i s t i c s 80 4.3.2 Binder C h a r a c t e r i s t i c s 83 5. CONCLUSIONS 87 6. BIBLIOGRAPHY 89 & APPENDICES 93 A. Derivation of CCWL Hot Compaction Model f o r Char/Binder Coal Systems 93 B. Normalized Compaction Curves 97 C. Glossary of Terms 106 - v i i -LIST OF TABLES Table Page I S p e c i f i c a t i o n s f or B l a s t Furnace Coke Requirements f o r Various Countries 8 II Values of Fixed Experimental Parameters 24 III Proximate Analyses of Coals Used 25 IV G i e s e l e r P l a s t i c i t y and Ruhr Dilatometer Data 29 V Char-Binder Composition of B r i q u e t t i n g Mixtures Used 35 VI Volume Contained i n Aggregate Char Pores Above Given Diameters 48 VII I n t e r f a c i a l Shear Strength of Binder-Graphite Rod Specimens 50 VIII a. Values of Experimental and Model Parameters For Mixtures Containing Binder B l 62 b, Values of Experimental and Model Parameters For Mixtures Containing Binder B2 63 c. Values of Experimental and Model Parameters For Mixtures Containing Binder B3 64 IX a. Average Values of Second Model Element R i g i d i t i e s 65 b. Average Values of Second Model Element V i s c o s i t i e s 65 X Values of Slopes and Y-Intercepts of Curves of T o t a l Compaction vs. Resultant Briquette Bulk Porosity 78 - v i i i -LIST OF FIGURES Figure Page 1 Schematic Cross-Section of a Conventional Coke Oven 5 2 Selected Relationships Between Char Strength and Carbonization Temperature 11 3 Selected Relationships Between Char Por o s i t y and Carbonization Temperature 14 4 Schematic E q u i l i b r i u m Contact Angle Force Balance 15 5 Schematic Representation of the Mechanical Analog of the CCWL Hot Compaction Model 20 6 Schematic Diagram of Binder-Graphite Rod I n t e r f a c i a l Strength Specimen 32 7 Schematic Diagram of S e s s i l e Drop Apparatus 33 8 Schematic Diagram of B r i q u e t t i n g Apparatus 36 9 Relationship Between True Char Density and Charring Temperature 40 10 Relationship Between Char Microhardness and Charring Temperature 41 11 Relationship Between E l a s t i c Behaviour of Char i n Microhardness Test and Temperature 43 12 Photomicrograph of Microhardness Indentation (1400X) 44 13 a. Cumulative Pore Size D i s t r i b u t i o n f o r Char A l (Carbonized at 750°C) 45 b. Cumulative Pore Size D i s t r i b u t i o n f o r Char A2 (Carbonized at 625°C) 46 c. Cumulative Pore Size D i s t r i b u t i o n f o r Char A3 (Carbonized at 500°C) 47 - i x -Figure Page 14. a. Photomicrograph Showing Macropore In Char A3 (Carbonized at 500°C) (160X) 49 b. Photomicrograph Showing Micropores In Char A l (Carbonized at 750°C) (16800X) 49 15. Relationship Between Residual V o l a t i l e Matter Content of Char and Charring Temperature 51 16. Relationship Between Contact Angle of an SRC P i t c h on Char and Temperature 53 17. Observed Strain-Time Curves of B r i q u e t t i n g Mixture 6 (Aggregate A2 - Binder B3) 58 18. Relationship Between Natural Logarithm of S t r a i n Rate and Time for Briquette 6 of Mixture 6 Superimposed On the Strain-Time Curve 59 19. Predicted and Observed Strain-Time Curves f o r Briquette 6 of Mixture 6 60 20. Relationships Between Briquette Ultimate Compressive Strength and Briquette Bulk Porosity f o r A l l Mixtures 66 21. a. Relationship Between Briquette Ultimate Compressive Strength and Charring Temperature f o r Mixtures Containing Binder B l 67 b. Relationship Between Briquette Ultimate Compressive Strength and Charring Temperature f o r Mixtures Containing Binder B2 68 c. Relationship Between Briquette Ultimate Compressive Strength and Charring Temperature f o r Mixtures Containing Binder B3 69 22. Relationship Between Second Model Element V i s c o s i t y and Binder Phase F l u i d i t y 73 23. a. Relationship Between T o t a l Compaction and Resultant Briquette Bulk P o r o s i t y f o r Mixtures Containing Char A l 75 b. Relationship Between T o t a l Compaction and Resultant Briquette Bulk Po r o s i t y f o r Mixtures Containing Char A2 76 - x -Figure 23. 24. Page Relationship Between To t a l Compaction and Resultant Briquette Bulk Porosity f o r Mixtures Containing Char A3 77 a. Photomicrograph Showing Aggregate-Binder I n t e r f a c i a l F a i l u r e (60X) 82 b. Photomicrograph Showing Binder Phase Fracture (130X) 82 - x i -LIST OF ABBREVIATIONS AND SYMBOLS A F r a c t i o n of t o t a l compaction a t t r i b u t e d to the f i r s t stage of compaction (instantaneous system compaction) i n CCWL model; a l s o , aggregate-binder i n t e r f a c i a l area. Al Aggregate material made from coal carbonized at 750°C. A2 Aggregate material made from coal carbonized at 625°C. A3 Aggregate material made from coal carbonized at 500°C. ANCIT Formcoke Process of Eschweiler Bergwerks Verein, an a f f i l i a t e company of ARBED, S.A., Luxemburg. B F r a c t i o n of t o t a l compaction a t t r i b u t e d to the second stage of compaction ( p a r t i c l e flow) i n CCWL model. B l , B2, B3 Binder materials; p r o p e r t i e s given i n Tables I I I and IV. BBF Bergbauforschung (formcoke process). C F r a c t i o n of t o t a l compaction a t t r i b u t e d to the t h i r d stage of compaction ( p l a s t i c deformation) i n CCWL model. CCWL Chow-Chaklader-Warren-Leeder (hot compaction model f o r char/ binder coal systems used to analyse compaction curves). DKS Didier-Kellogg-Sumitomo (formcoke process). DPH Diamond Pyramid Hardness. FMC Food Machinery and Chemicals Corporation (formcoke process). HBN H o u i l l e r i e s du Basin du Nord et du Pas-de-Calais (formcoke process). k T o t a l compaction i n CCWL model; f o r computations, taken to be compaction at three minutes a f t e r a p p l i c a t i o n of pressure. M^ R i g i d i t y of i - t h element i n CCWL model. M T T o t a l System R i g i d i t y i n CCWL model. P, Briquette Bulk Porosity, b RVM Residual V o l a t i l e Matter. SRC Solvent Refined Coal. - X l l -Time. Temperature. Ultimate Compressive Strength. Exponential c o e f f i c i e n t s i n 1st, 2nd and 3rd terms of experimental equation i n CCWL model r e s p e c t i v e l y (ct= M / f i ; 8 = M /n ; Y = M 3 / n 3 ) • 1 1 2 2 Liquid-vapour i n t e r f a c i a l energy. S o l i d - l i q u i d i n t e r f a c i a l energy. Solid-vapour i n t e r f a c i a l energy. Normalized compaction s t r a i n at time, t . V i s c o s i t y of i - t h element i n CCWL mdoel. Density. Contact angle. Applied s t r e s s . 1. INTRODUCTION Formcoke i s a manufactured carbonaceous product intended to replace conventional coke i n the ironmaking b l a s t furnace. The impetus for formcoke development comes from several sources. Among the major a t t r a c t i o n s i s the a b i l i t y to u t i l i z e a wider range of coal s , t h i s being e s p e c i a l l y important i n i r o n and s t e e l producing areas with l i t t l e or no indigenous reserves of c l a s s i c a l coking c o a l . Further advantages are seen i n a more c l o s e l y c o n t r o l l e d and reproducible product, a choice of con-tinuous or i n t e r m i t t e n t operation and g r e a t l y improved p o l l u t i o n c o n t r o l . To better understand the nature and requirements of formcoke, i t i s necessary to appreciate the nature and requirements of conventional coke, which formcoke i s intended to replace. I t i s therefore u s e f u l to f i r s t consider the process of conversion of coal to coke, both at the fundamental l e v e l and as i t i s conventionally p r a c t i c e d . The advantages of and problems associated with formcoke w i l l then be apparent. 1.1 The P y r o l y t i c Behaviour of Coal B l a s t furnace coke i s the major product of high temperature carboni-z a t i o n of c e r t a i n types of c o a l . Conventionally, these coking coals are of the bituminous caking type. The r o l e of coke i n the b l a s t furnace i s t h r e e f o l d : providing f u e l for combustion; supply reductant f o r smelting; and p h y s i c a l l y supporting the burden. To perform these functions properly, coke must meet a number of p h y s i c a l and chemical s p e c i f i c a t i o n s i n c l u d i n g - 2 -strength, abrasion r e s i s t a n c e , r e a c t i v i t y and maximum l i m i t s on sulphur, ash and r e s i d u a l v o l a t i l e matter contents. These parameters are i n turn determined by the type of coal used and the carbonization conditions employed. As coal i s heated, i t undergoes a number of reactions. The f i r s t of these i s removal of moisture which occurs between 100°C and 200°C. The major v o l a t i l e components are evolved between 400°C and 500°C, depend-ing on the rank of the c o a l . Between 500°C and 1000°C the remaining v o l a t i l e s are evolved, the structure undergoes d e n s i f i c a t i o n and a slow r e s i d u a l outgassing takes place. At 1000°C, the carbonization process i s e s s e n t i a l l y complete, the s o l i d product being carbon and the o r i g i n a l l y contained mineral matter which i s converted to ash. The stage of most i n t e r e s t i n cokemaking i s d e v o l a t i l i z a t i o n . The coal's behaviour during t h i s stage determines the p h y s i c a l properties of the r e s u l t i n g coke. The d e v o l a t i l i z a t i o n process c o n s i s t s of two consec-u t i v e r e a c t i o n s . The f i r s t of these i s a depolymerization r e a c t i o n i n which weaker oxygen linkages between aromatic lamellae are ruptured. The r e s u l t of t h i s r e a c t i o n i s the formation of a f l u i d or p l a s t i c mass termed mesophase or metaplast, the amount of p l a s t i c i t y being r e l a t e d to the degree of depolymerization. The second i s a cracking process i n v o l v i n g the evolution from the mesophase of gaseous products, such as hydrogen, carbon monoxide, methane and higher order hydrocarbons, and s o l i d i f i c a t i o n of the remainder i n t o a residue, semicoke. The two reactions can be written schematically as k l Coal ^-Mesophase + Minor Gaseous Products (1) k2 Mesophase ^-Evolved Gases + Semicoke (2) - 3 -where k^ and k^ represent the rate constants for the two reactions. At higher temperatures, the semicoke undergoes a s e r i e s of decom-p o s i t i o n and condensation reactions. These r e s u l t i n fur t h e r weight l o s s , d e n s i f i c a t i o n and a completely carbonized s o l i d product—coke. Temperatures of the order of 1000°C are necessary to obtain t h i s f i n a l product. Although material properties are c o n t i n u a l l y a l t e r e d during t h i s high temperature carbonization stage, the coal's behaviour i n the low temperature stages influences the f i n a l product to a large extent. The r e l a t i v e magnitudes of the rate constants of reactions (1) and (2) determine whether a given coal w i l l be p h y s i c a l l y acceptable for the production of m e t a l l u r g i c a l coke. I f k^ i s much l a r g e r than k^, there w i l l be an accumulation of the mesophase, r e s u l t i n g i n the development of a p l a s t i c character. A coal of t h i s type i s known as caking since i t w i l l fuse i n t o a s o l i d mass upon completion of r e a c t i o n (2). A c e r t a i n amount of caking behaviour i s required i n the conventional cokemaking process. I f k 2 i s much l a r g e r than k^, any mesophase that forms w i l l immediately transform to v o l a t i l e gases and semicoke. This i s the case of a non-caking coal where no p l a s t i c behaviour i s observed and the coal appears to be converted d i r e c t l y to semicoke or char. No agglomeration i s noticed with t h i s type of c o a l . 1.2 The Conventional Cokemaking Process Conventional cokemaking i s c a r r i e d out i n e x t e r n a l l y heated r e f r a c -tory l i n e d slot-type ovens operated i n batch mode. The modern version of the s l o t oven i s approximately 15 m long, 6 m high and 0.5 m wide. Gaseous carbonization products are c o l l e c t e d and processed into u s e f u l f r a c t i o n s , g i v i n g the assembly i t s common name: the by-product coke oven. These _ 4 -are u s u a l l y arranged i n b a t t e r i e s with heating f l u e s a l t e r n a t i n g with oven chambers to conserve f u e l and maximize heating e f f i c i e n c y . A schematic representation of a standard coke oven i s shown i n figu r e 1. Heat from the long walls of the oven passes through the coal charge toward i t s centre. As the charge temperature adjacent to the wall reaches the softening point of the c o a l , a p l a s t i c zone develops and moves inward. The width of t h i s zone depends on the p l a s t i c range of the coal while the speed at which i t moves depends on the heat t r a n s f e r conditions. In the p l a s t i c region, the coal swells causing compaction of the untrans-formed charge ahead of i t and pressure on the oven wall behind. As the zone moves toward the centre of the oven, the semicoke l e f t behind con-tinues to transmit t h i s pressure. The agglomerated mass curves away from the w a l l , f i s s u r e s appear and the charge may break i n t o a number of pieces. Resultant coke p r o p e r t i e s vary considerably across the width of the oven due to a s i g n i f i c a n t temperature gradient from wall to centre. F i n a l p o r o s i t y i n the coke i s the r e s u l t of evolution of v o l a t i l e matter into the p l a s t i c phase. In conventional p r a c t i c e , the balance required between v o l a t i l e matter content, p l a s t i c character and mechanical strength has r e s t r i c t e d s u i t a b l e coal supplies to the low v o l a t i l e (14%-22%) bituminous caking type. Modern improvements to the conventional process such as charge blending and preheating now allow medium v o l a t i l e (22%-30%) bituminous coals to be used as w e l l . A stamp charging technique, i n v o l v i n g formation of the charge i n t o a compact before p l a c i n g i t i n the oven, has proved successful i n u t i l i z i n g a proportion of high v o l a t i l e c o a l . However, only low and low-medium v o l a t i l e bituminous caking coals are r e f e r r e d to as prime coking co a l s . - 5 -Flue gases Semi coke Green coal Sem coke Oven wall Plastic zone Plastic zone Oven wall Figure 1: Schematic C r o s s - S e c t i o n of a Conventional Coke Oven - 6 -Numerous surveys and estimates [1-6] have been made of the size of coal resources through the world and demand f o r coking grade types. These i n d i c a t e that small f r a c t i o n s of t o t a l supply can be considered of coking q u a l i t y and that three quarters of these are located i n North America, the U . S . S . R . and China. To meet projected future demands i t w i l l be necessary to further broaden the m e t a l l u r g i c a l coal base. This i s e s p e c i a l l y true for areas with l i t t l e or no indigenous coking coal supplies, such as Japan, but i s al s o s i g n i f i c a n t on a more l o c a l scale within North America. 1.3 The Formcoke A l t e r n a t i v e A number of a l t e r n a t i v e processes to the conventional by-product coke oven are now being developed. These are c o l l e c t i v e l y termed formcoke processes. Although many d i f f e r e n t processes have been developed, they a l l follow a common approach. Conventionally unsuitable coal i s briquetted with a carbonaceous binder and the product i s carbonized to y i e l d a coherent b l a s t furnace feedstock. The coal may be mixed and briquetted d i r e c t l y with a binder followed by carbonization steps. This i s the approach of the HBN [7], A n c i t [8], DKS [9], Iniex and Auscoke [10] processes. A l t e r n a t i v e -l y , the coal may be charred at a low temperature (400 oC _600°C) and subse-quently mixed with a binder and briquetted. A high temperature carboniza-t i o n stage follows to complete the coking operation. This i s the route followed by such processes as FMC [11] and BBF [12]. The type of binder used also v a r i e s from system to system. This may be: t a r or p i t c h , as i n Auscoke, Iniex or D K S ; a caking c o a l , as i n BBF or Ancit; or the condensate t a r by-products recovered i n a previous charring stage, as i s pr a c t i c e d i n one version of the FMC operation. Further d i f f e r e n c e s may be discerned i n the heating methods employed. _ 7 -These include f l u i d i z e d sand or a i r beds f or the charring operation and shaft furnaces, rotary k i l n s and f l u i d i z e d beds i n the f i n a l high tempera-ture stage. Extensive l i s t s of formcoke processes can be found i n r e f e r -ences 3 and 13. A number of these are now i n the p i l o t plant stage and construction of commercial operations i s reported [5]. Formcoke must equal or exceed the performance of conventional coke i n the b l a s t furnace i f i t i s to be used as a substitute and is, therefore , subject to the same p h y s i c a l and chemical requirements as the conventional product. Table I shows b l a s t furnace coke s p e c i f i c a t i o n s for various countries [2] and formcoke briquette p r o p e r t i e s f o r d i f f e r e n t processes [14]. With adoption of formcoking techniques, the caking c h a r a c t e r i s t i c s of the char-producing coal become unimportant. S e l e c t i o n of coal f o r m e t a l l u r g i c a l coke production can then be based on chemical composition alone. This w i l l expand the s u i t a b l e coal base to include almost a l l a n t h r a c i t i c , bituminous and sub-bituminous types. The s u i t a b i l i t y of more widely a v a i l a b l e , l e s s expensive coals , holds the greatest a t t r a c t i o n f o r i n t r o d u c t i o n of formcoke technology. The cost of coal has been estimated [3] as 70% of t o t a l coke cost. At the same time, there appears to be agreement [2-4,15] that formcoke operating and c a p i t a l costs w i l l equal or bet t e r those of the conventional route. Consistent with t h i s a t t i t u d e i s the f a c t that improvements to the conven-t i o n a l oven battery, such as preheating, p i p e l i n e charging and dry quench-ing, are expensive and d i f f i c u l t to implement. E x i s t i n g coking f a c i l i t i e s w i l l l i k e l y be operated without major improvement f o r t h e i r projected l i f e . In a g r e e n f i e l d s i t e s i t u a t i o n , formcoking provides a t t r a c t i v e a l t e r n a t i v e s i n many regions. - 8 -TABLE I SPECIFICATIONS FOR BLAST FURNACE COKE REQUIREMENTS FOR VARIOUS COUNTRIES PROPERTIES OF METALLURGICAL COKE PROPERTY UNITED KINGDOM CANADA JAPAN Moisture (%) *3 Shatter Index 0.5 in.>90% 0.5 in.>90% -M,„ Index 40 >75% ASTM Stab.{55 DI (30/15) >93.5 M^Q Index <7% ASTM Hard. 70 DI (150/15) >81.5 Ash (%) 11-12 Sulphur (%) } 0.6 \ 0.7 0.55-0.65 V.M. (%) =0.8 = 0.7 = 0.7 Size Range (mm) 20-65 13-65 30-75 BRIQUETTE PROPERTIES PROPERTY BBF (GERMAN) BBF (BRITISH) FMC (USA) DKS (JAPAN) Moisture (%) 3.0 4.9 4.7 3.1 Fixed Carbon (mf)* 81.5 81.2 89.9 80.3 Ash (mf) 5.5 12.1 5.5 12.6 V o l a t i l e Matter (mf) 9.1 6.0 3.9 6.5 Sulphur (mf) 0.9 1.0 0.7 0.5 -3 Bulk Density (kgm ) 578 622 554 779 M„„ Index 40 84 86 - -M Index 9.3 10.9 5.1 5.6 * (mf) - moisture free basis - 9 -As a f u e l and reductant formcoke r e l i e s on the chemical nature of the parent c o a l , while as a burden support i t depends on the p h y s i c a l nature of the b r i q u e t t e composite. Mechanical parameters c h a r a c t e r i z i n g formcoke may be divided i n t o three groups: those of the aggregate phase, strength (hardness and d e n s i t y ) , texture (porosity) and surface chemical nature; those of the binder phase, strength and f l u i d i t y ; and those of aggregate binder i n t e r a c t i o n , i n t e r f a c i a l strength, wetting and spreading behaviour and gross composite strength. L i t t l e fundamental work on formcoking has appeared to date. A survey of the a v a i l a b l e l i t e r a t u r e shows that some r e l a t i o n s h i p s between process parameters and material p r o p e r t i e s have been es t a b l i s h e d . More recent work has involved studying the compaction behaviour during briquet-t i n g to i d e n t i f y the mechanisms of the composite forming process. 1.4 Previous Studies Comprehensive reviews of b r i q u e t t i n g theory and p r a c t i c e have been published, i n c l u d i n g that by Rhys Jones [16] on binderless b r i q u e t t i n g p r a c t i c e and the general overview of coal b r i q u e t t i n g by Berkowitz [17]. The supplementary volume of Chemistry of Coal U t i l i z a t i o n [18] i s an e x c e l l e n t general reference source. Aside from the state of the a r t summaries noted e a r l i e r [1-15], studies concerning the i n d i v i d u a l aspects of c h a r a c t e r i z a t i o n and i n t e r a c t i o n of the char-binder system have been reported. These may be grouped according to the material property con-sidered. 1.4.1 Material C h a r a c t e r i s t i c s 1.4.1.1 Char Strength and Hardness Smith and Reynolds [19] found that coke strength, measured as a - 10 -r e l a t i v e 1/4" tumbler index, increased with carbonization temperature. Dainton [20] used a simple beam-bending apparatus to measure the Young's modulus of semi-coke and found i t increased from 400 MPa at 500°C to 1700 MPa at 800°C. Gryaznov et a l . [21] found s i m i l a r increases from 290 MPa at 500°C to 1400 MPa at 1000°C, suggesting t h i s was due to polycondensa-t i o n brought about by continuing p y r o l y s i s . Toda and Toyoda [22] c a l c u l a t e d values of Young's modulus from c o m p r e s s i b i l i t y p l o t s and compared them with measured Knoop hardness values. They stated the d i r e c t p r o p o r t i o n a l i t y observed was reasonable because both Knoop hardness and Young's modulus are r e f l e c t i o n s of the binding energy between molecules. Chaklader et a l . [23] showed the 136° diamond pyramid hardness of char to increase from DPH 20 at 500°C to DPH 200 at 750°C f o r a sub-bituminous coal char. A summary of these r e s u l t s i s shown i n fig u r e 2. 1.4.1.2 Char Density Studies of true char density have shown i t to increase with carbon-i z a t i o n temperature. Evans and Hermann [24] found values of 1.4 gem ^ -3 at 400°C increasing to 1.9 gem at 1000°C. White and Zimmer [25] -3 measured a higher value of 2.2 gem at the higher temperature, while -3 Jacienko [6] found the 1000°C density to be between 2.0 and 2.1 gem 1.4.1.3 Char Porosity Toda et a l . [26] followed the f i n e structure of both caking and non-caking coals as a function of heat treatment temperature using adsorp-t i o n isotherms, d i f f e r e n c e s i n volume i n mercury and methanol, and mercury penetration porosimetry. They concluded that the micropore structure i s closed o f f up to 400°C due to oozing out of t a r r y material from the char. This caused a decrease i n pore volume with increasing temperature. From 2000 o Q_ 500 LU CO =| 1000 o E cn c O >-500 0 300 T o T 200 (20) 35%VM. coal •° Young's modulus ° (21) Russian coal Young's modulus 100 i CL* Q 500 700 900 0 Carbonization temperature (°C) Figure 2: Selected Relationships Between Char Strength and Carbonization Temperature - 12 -400°C to 600°C, an increase i n pore volume was noted, a t t r i b u t e d to removal of the t a r r y material and such reactions as demethanation and de-hydrogenation. Pore volume decreased again above 600°C due to thermal shrinkage of the pore str u c t u r e . The authors also showed mercury penetra-3-1 3-1 t i o n volume decreased i n a caking coal from 75 mm g at 400°C to 25 mm g at 800°C. March and Rand [27] considered that microporosity i n char arose from n o n - p a r a l l e l j o i n i n g of sheets of the coal molecular structure and from evo l u t i o n of low molecular weight materials such as water, methane and hydrogen. They found experimentally that micropore volume i n the carbons studied increased with carbonization temperature from 400°C to 700°C and then decreased upon furt h e r heating. Gregg et a l . [28] measured adsorption isotherms of butane and found r e s u l t s that i n d i c a t e d c o n s t r i c t i o n s i n micropores obstructed passage of the measuring f l u i d i n t o l a r g e r c a v i t i e s . McCartney [29] employed a scanning e l e c t r o n microscope to i n v e s t i -gate bubbles s i z e s i n conventional coke. P a t r i c k et a l . [30] developed an automated procedure f o r t e x t u r a l c h a r a c t e r i z a t i o n of coke using a Quantimet 720 Image Analyser. They measured t o t a l pore volume, number of pores, pore w a l l thickness, pore perimeter and pore diameter. Good agree-ment between t h i s procedure and the density d i f f e r e n c e method of pore volume determination was demonstrated. They c o r r e l a t e d increasing char strength with in c r e a s i n g pore wall thickness and decreasing perimeter per pore and t o t a l pore volume. Toda and Toyoda [22] studied the p o r o s i t y of 17 d i f f e r e n t coals comparing r e s u l t s of mercury penetration and density d i f f e r e n c e c a l c u l a t i o n s . - 13 -Good agreement was found and the suggestion made that increases i n pore volume measured i n the penetration program above 100 atm, corresponding to a pore diameter of 0.1 ym, were due to c o m p r e s s i b i l i t y of the specimens. In a l a t e r study, Toda [31] found an increase i n pore volume up to 400°C followed by a decrease up to 800°C. This was the case f o r both caking 3-1 3-1 (a drop from 80mm g at 400°C to 20 mm g at 800°C)and non-caking 3-1 3-1 coals (a drop from 90 mm g at 400°C to 60 mm g at 800°C). Figure 3 shows the porosity-temperature r e l a t i o n s h i p s established i n various studies. In more recent work, Spi t z e r et a l . [32] compared various methods of pore structure a n a l y s i s and reconfirmed t h e i r close agreement. Chaklader et a l . [33] used the mercury penetration technique and concluded that pore volume i n non-caking coal char does not vary widely, but does decrease with heat treatment temperature so that only micropores (<0.003ym) remain above 900°C. 1.4.1.4 Coal Extracts The organic solvent soluble f r a c t i o n s produced at carbonization temperatures have been associated with the intermediate p l a s t i c phase which i s seen to accumulate i n caking coals at these elevated temperatures. Loison et a l . [34], i n t h e i r review of the p l a s t i c p r o p e r t i e s of co a l , pointed out that a number of fa c t s support t h i s a s s o c i a t i o n . The concen-t r a t i o n of chloroform-soluble extr a c t increased with temperature, passed through a maximum, and d e c r e a s e d — i n a manner p a r a l l e l with measured p l a s t i c i t y . The y i e l d of extract was increased by pressure, as was p l a s t i c i t y and the extract was decomposed to gas and an in s o l u b l e residue under heat.. However, the f l u i d i t y maximum was reached a f t e r that of extract concentration. The authors concluded that t h i s d i d not disprove the - 14 -Figure 3: Selected Relationships Between Char Porosity and Carbonization Temperature 150 ro CL) £ JD O > i _ O C L D O I (27) PFA carbon C0 2 adsorption E E lOOl 50 0 0 (26) Caking coal Hg penetration I 400 800 Carbonization temperature (°C) - 15 -a s s o c i a t i o n because f l u i d i t y may be somewhat dependent on pore structure which developed with time. They also noted that chloroform-soluble extracts were only a f r a c t i o n of the metaplast. In another review, Howard [35] compared Gieseler P l a s t i c i t y curves at a constant temperature with the rate of formation of chloroform-, soluble e x t r a c t . I t was found that the extract was formed much fa s t e r than f l u i d i t y and concluded that the chloroform extract per se was not respons-i b l e f o r f l u i d i t y . 1.4.2 Char-Binder In t e r a c t i o n As formcoke i s a two-phase composite ma t e r i a l , f i n a l p roperties are dependent on aggregate-binder i n t e r a c t i o n . The extent to which the binder phase wets the aggregate c o n t r o l s the spreading and d i s t r i b u t i o n of the binder matrix around the aggregate p a r t i c l e s . Char p o r o s i t y and roughness a l s o influence t h i s binder d i s t r i b u t i o n . In considering wetting phenomena i n the t e x t i l e industry, Wenzel [36] began with the Young-Dupre" equation f o r e q u i l i b r i u m contact angles: Y = Y - Y cos 0 TSL TSV TLV where y i s the i n t e r f a c i a l energy of the boundaries corresponding to the su b s c r i p t s : S - s o l i d L - l i q u i d , V-vapour; and 0 i s the angle between s o l i d and l i q u i d at t h e i r point of contact. The p h y s i c a l s i t u a t i o n i s shown i n f i g u r e 4. Figure 4: Schematic E q u i l i b r i u m Contact Angle Force Balance Vapour ^/^Uquid S O L I D XSL Xsv - 16 -He modified the equation to account f o r the e f f e c t of surface roughness by introducing a roughness c o e f f i c i e n t , r, being the r a t i o of apparent to true contact area Y S L = Y s v - I LV COS 0 r A thermodynamical d e r i v a t i o n of t h i s modified form has been given by Good [37] . Adam [38] summarized i t s importance by s t a t i n g that the e f f e c t of surface roughness was to increase the d i f f e r e n c e between the contact angle and 90°. That i s , i f the r e a l angle was l e s s than 90°, the apparent angle would be l e s s than the r e a l value and i f the r e a l angle was greater than 90°, the apparent value would be greater than the r e a l value. Sukhorukov et a l . [39] studied the w e t t a b i l i t y of carbonaceous materials by p i t c h and found the contact angle decreased sharply with temperature to below 20° i n a l l cases. They considered the e f f e c t of c a p i l l a r y penetration, f i n d i n g a negative c a p i l l a r y pressure up to about 150°C which prevented penetration. However, the pressure was seen to become p o s i t i v e above 150°C and therefore a s s i s t the penetration process. The authors also found that a more ordered carbonaceous surface (ranging from crude to c a l c i n e d petroleum coke to roasted material to a r t i f i c i a l graphite) l e d to a weaker bond, the adhesion forces being van der Waals and chemisorption. Agrawal and Berkowitz [40] measured e q u i l i b r i u m contact angles between binders made from a s p h a l t i c materials and various coal and char substrates. They found that a l l the binders studied stopped j u s t short -2 of complete wetting and c a l c u l a t e d energies of adhesion of around 90 mJm - 17 -This was shown to be i n s e n s i t i v e to the i d e n t i t y of the substrate. Dmitrieva et a l . [41] showed that adhesion energy could be increased by a d d i t i o n of a surface a c t i v e agent ( o l e i c acid) and Vetyukov et a l . [42] have agreed that the nature of the carbon material i s r e l a t i v e l y unim-portant. They concluded that the extent of surface roughness was more important. D e l l and Peterson [43] , i n studying Soderberg anodes, found that at low temperatures, high v i s c o s i t y of the binder p i t c h prevented substan-t i a l penetration i n t o remote pores. From the accompanying strength measurements they concluded composite strength was the r e s u l t of mechani-c a l i n t e r l o c k i n g of the binder and aggregate. Therefore, a pore structure a c c e s s i b l e to the binder was deemed e s s e n t i a l f o r a good bond. Lahaye and Aubert [44] c a r r i e d out two i n v e s t i g a t i o n s i n t o the i n t e r a c t i o n between a coke and a t a r . In the f i r s t they studied the e f f e c t of the surface chemical state, concluding that as the oxygen surface functions increased, the contact angle decreased. When a c r i t i c a l value of oxygen function was exceeded, the contact angle would remain constant at a low value. This c r i t i c a l value corresponded to that producing complete s a t i s f a c t i o n of a l l po s s i b l e hydrogen bonds. In the second paper they found the l i m i t i n g pore diameter i n t o which the t a r would penetrate to be 5-6 ym for non-outgassed and 1-2 ym for outgassed char. Greenhalgh and Moyse [45] showed that penetration of the porous structure would occur for a contact angle l e s s than 90° i f given s u f f i c i e n t time. In a d d i t i o n , they found that once the p i t c h had spread mechanically, i t would not recede to i t s eq u i l i b r i u m contact angle. Chaklader et a l . [23] measured contact angles of p i t c h on various chars and found that the - 18 -angle d i d not drop to zero i n a l l cases. Some systems were seen not to f a l l below 40°. 1.4.3 Compaction K i n e t i c s F i t z g e r a l d [46] has modelled the v i s c o e l a s t i c response of a caking coal i n the p l a s t i c state to an applied s t r e s s using a s e r i e s coupling of a Maxwell and a K e l v i n element. He suggested the retarded e l a s t i c i t y observed i n the coal was associated with the many po s s i b l e configurations of the cross l i n k s between molecular lamellae. Habberjam [47] studied compaction of binderless char mixtures at the carbonization temperature. A model was developed employing two K e l v i n elements and an a d d i t i o n a l spring i h s e r i e s . In an attempt to determine i f compaction behaviour observed i n char systems was due to the presence of a v i s c o e l a s t i c component, Jayasinghe and P i l p e l [48] coated char p a r t i c l e s with a v i s c o e l a s t i c poly-mer, polyisobutane. They found close c o r r e l a t i o n between the model system and char behaviour, concluding a t h i n f i l m of v i s c o e l a s t i c m a terial i s formed on the char surface during compaction. Bradford et a l . [49] measured e l e c t r i c a l r e s i s t a n c e and change i n volume with pressure to in v e s t i g a t e p a r t i c l e behaviour during compaction. They found that without a binder, deformation of the p a r t i c l e s was e l a s t i c (shape a l t e r i n g ) , but with s u f f i -c i e n t binder present, compaction was i s o s t a t i c and r e l a t i v e l y small. A c r i t i c a l binder content of 27% was found necessary to obtain the l a t t e r c o ndition. Recently, C o l l e t t and Rand [50] have i n d i c a t e d that c o a l - t a r p i t c h can be considered a Newtonian l i q u i d at low temperatures, but non-Newtonian above 380°C. They suggested p i t c h be thought of as an emulsion: i n i t i a l l y - 19 -as one of mesophase i n an i s o t r o p i c l i q u i d and then as one of i s o t r o p i c l i q u i d i n mesophase as temperature r i s e s . The above models were concerned with binderless systems or i d e a l -ized aggregate-binder materials. Chow et a l . [51] developed a hot compac-t i o n model for char-binder coal systems (the CCWL model). They found that experimental compaction curves could be f i t t e d s a t i s f a c t o r i l y with an equation expressing compaction s t r a i n , E , as the sum of three exponen-t i a l time terms: e t = k (1 - A e " a t - B e ~ B t - Ce" Y t) where k, A, B, C, a, 6 and yare experimentally determined constants. A t h i r d order d i f f e r e n t i a l equation, shown below, was generated from the experimental equation following the procedure described by Bradbeer and Chaklader [52]. "c + ME + Ne + Te = P O + Q O + R O Various mechanical analogs c o n s i s t i n g of spring and dashpot com-binations were considered and i t was found that the response of a s e r i e s coupling of three K e l v i n v i s c o e l a s t i c elements (each being a spring and dashpot i n p a r a l l e l ) to an applied s t r e s s was given by an equivalent expression. This model i s shown schematically i n f i g u r e 5. In employing t h i s mechanical analog, i t was recognized that f o r the case of successive element h a l f - l i v e s , the three model elements could be considered non-i n t e r a c t i n g . The values of the model parameters, n^, n^r n^ ' t M2 a n < ^ M^, were determined from the experimental constants, k, A, B, C, a, 3, and which were determined from the isothermal compaction curves. Based on the observation that only two of the Kelvin elements were - 20 -Figure 5: Schematic Representation of the Mechanical Analog of the CCWL Hot Compaction Model M ^ 1 M. M ;////////// - 21 -t e m p e r a t u r e s e n s i t i v e , i t w a s c o n c l u d e d t h a t t h e m o d e l e l e m e n t s c o u l d b e a s s o c i a t e d w i t h o n e o f t h r e e c o m p a c t i o n m e c h a n i s m s : i n s t a n t a n e o u s s y s t e m c o m p a c t i o n , p a r t i c l e f l o w a n d p l a s t i c d e f o r m a t i o n . T h e h a l f - l i v e s o f t h e s e e l e m e n t s w e r e s u g g e s t e d t o b e 0; 0.5; a n d 3-10 m i n u t e s , r e s p e c t i v e l y . A m o r e t h o r o u g h d e r i v a t i o n o f t h i s m o d e l i s p r e s e n t e d i n A p p e n d i x A . 1.5 O b j e c t i v e s o f P r e s e n t S t u d y D e s p i t e t h e i m p o r t a n c e o f t h e m e c h a n i c a l s t a b i l i t y o f f o r m c o k e i n t h e b l a s t f u r n a c e , n o c o m p r e h e n s i v e s t u d y o f t h e i n f l u e n c e o f i n g r e d i e n t m e c h a n i c a l p a r a m e t e r s o n f o r m c o k e c o m p o s i t e s t r e n g t h h a s b e e n r e p o r t e d . T h e e f f e c t s o f c a r b o n i z a t i o n c o n d i t i o n s o n c h a r p r o p e r t i e s h a v e b e e n s t u d i e d ; e x p e r i m e n t a l t e c h n i q u e s h a v e b e e n d e v e l o p e d t o q u a n t i f y b i n d e r c h a r a c t e r i s t i c s ; a n d c h a r b i n d e r i n t e r a c t i o n s h a v e b e e n i n v e s t i g a t e d . H o w e v e r , t h e s e h a v e g e n e r a l l y b e e n i n d i v i d u a l s t u d i e s o f d i f f e r e n t p a r a m -e t e r s i n ' v a r y i n g s y s t e m s . T h e o b j e c t o f t h i s w o r k i s t o s t u d y t h e f u n d a m e n t a l r e l a t i o n s h i p s b e t w e e n t h e a g g r e g a t e a n d b i n d e r m a t e r i a l c h a r a c t e r i s t i c s a n d t h e f o r m -c o k i n g p r o c e s s a n d i t s f i n a l p r o d u c t . T h i s i s c a r r i e d o u t b y i n v e s t i g a t i n g t w o w a y s i n w h i c h m a t e r i a l p r o p e r t i e s c a n a f f e c t t h e f i n a l b r i q u e t t e p r o d u c t : 1) b y i n f l u e n c i n g t h e c o m p a c t i o n k i n e t i c s o f t h e b r i q u e t t i n g p r o c e s s ; a n d 2) b y d i r e c t l y i n f l u e n c i n g t h e p h y s i c a l n a t u r e o f t h e f i n a l b r i q u e t t e p r o d u c t . - 22 -2. EXPERIMENTAL A non-caking coal char aggregate-caking coal binder system was chosen f o r study. Commercial process of t h i s type have shown promise [8/12] and t h i s type of system i s suited to the Canadian coal resource s i t u a t i o n . The experimental v a r i a b l e s involved were i d e n t i f i e d as: Aggregate Phase Independent Variables (controlled) (i) rank of parent coal ( i i ) carbonization atmosphere ( i i i ) carbonization heating rate (iv) maximum carbonization temperature (v) soaking time at maximum temperature Dependent Variables (measured) (vi) char strength (hardness and density) ( v i i ) char p o r o s i t y ( v i i i ) equivalent char rank ( r e s i d u a l v o l a t i l e matter content) Binder Phase Independent Variable (controlled) (ix) rank of binder coal Dependent Variables (measured) (x) caking properties (xi) strength a f t e r b r i q u e t t i n g Briquettes Independent Variables (controlled) ( x i i ) aggregate-binder r a t i o ( x i i i ) p a r t i c l e s i z e d i s t r i b u t i o n 23 (xiv) charge s i z e (xv) b r i q u e t t i n g heating rate (xvi) b r i q u e t t i n g maximum temperature (xvii) b r i q u e t t i n g pressure ( x v i i i ) duration of b r i q u e t t i n g at temperature and pressure Dependent V a r i a b l e s (measured) (xix) aggregate-binder wetting conditions (xx) mixture v i s c o s i t y under compaction conditions (xxi) briquette bulk p o r o s i t y (xxii) briquette strength A l l independent v a r i a b l e s except aggregate carbonization tempera-ture and binder coal rank (variables (iv) and (ix)) were held constant at the values given i n Table I I . In the case of b r i q u e t t i n g temperature, the temperature at which the mixture exhibited the greatest f l u i d i t y was used. This was found to be constant for a given binder. The higher b r i q u e t t i n g pressure for mixtures containing binder B2 was necessary to produce coherent briquettes of comparable bulk p o r o s i t y . Varying the aggregate charring temperature and the coal used as binder, produced v a r i a t i o n s i n the mechanical pro p e r t i e s of the system which were characterized and compared to i d e n t i f y those pr o p e r t i e s i n f l u -encing briquette strength. C h a r a c t e r i z a t i o n was performed as follows. - 24 -TABLE II VALUES OF FIXED EXPERIMENTAL PARAMETERS PARAMETER VALUE CARBONIZATION: HEATING RATE TIME AT TEMP. ATMOSPHERE BATCH SIZE 6°C min 120 min Argon ca. 40 g BRIOUETTING: HEATING RATE TEMPERATURE PRESSURE TIME AT TEMP. AND PRESSURE 80°C min Bl - 430°C B2 - 500°C B3 - 480°C 10 MPa (13.8 MPa f o r B2) 3 min CHARGE SIZE 0.75 g 2.1 Aggregate Char Cha r a c t e r i z a t i o n The aggregate phase of the b r i q u e t t i n g mixtures was produced by carbonization of a high v o l a t i l e sub-bituminous coal which had a low inherent moisture content and a lustrous non-banded appearance. The proximate a n a l y s i s of t h i s coal i s given i n Table I I I . TABLE III PROXIMATE ANALYSES OF COALS USED COAL COAL COAL COAL FOR FOR FOR FOR CHAR B l B2 B3 Moisture (%) 20.3 1.2 0.8 0.9 Ash (dry basi s %) 6.0 3.2 9.0 3.8 V o l a t i l e Matter (db %) 42 34.3 21.1 22.0 Fixed Carbon (db %) 52 62.5 69.9 74.2 The coal was i n i t i a l l y broken to -10 + 4 mm. This material was weighed i n t o a standard No. 13 p o r c e l a i n boat, batch s i z e s being approxi-mately 40 grams, and placed i n the 50 mm diameter tube furnace. With the sample thermocouple buried i n the coal and the furnace ends sealed, the tube was flushed with argon f o r 30 minutes. The programmed c o n t r o l l e r was then engaged to bring the charge up to the selected charring temperature at the constant rate of 6 (±0.2)°C min ^. A slow argon flow was maintained throughout the carbonizing/cooling cycle to prevent oxidation and to remove the v o l a t i l e matter evolved. The charring temperatures selected were 500°C, 625°C and 750°C, while soaking time at temperature was kept constant at the s p e c i f i e d two - 26 -hours. With the apparatus employed, i t was not po s s i b l e to accurately a t t a i n the programmed temperature, but i t was p o s s i b l e to accurately measure the temperature reached. Hence, charring temperatures va r i e d up to 13°C from the selected value. The temperature at the ends of the boat was approximately 20°C lower than at the centre. The sample thermocouple was located at the boat centre. A f t e r a two hour soaking at temperature, the furnace was shut o f f and the sample was allowed to cool under a slow argon flow with the furnace sealed. This c o o l i n g time was of the order of 15-18 hours. The char product was weighed a f t e r removal from the furnace to determine the weight l o s s due to d e v o l a t i l i z a t i o n . Nine char batches were produced at 750°C and f i v e were produced at each of 625°C and 500°C. 2.1.1 Hardness From each char batch, s i x specimens of approximately 5 mm s i z e were selected and mounted i n a quick-set mounting block. These were then polished to a 5 pm - alumina f i n i s h . A t h i n f i l m of carbon soot was deposited on the surface by passing the block through a candle flame. This allowed the diamond pyramid indentation made by a Tukon Microhardness Tester to be seen. An indentor weight of 300 g and a magnification of 20X were used. With t h i s technique i t was also p o s s i b l e to discern an e l a s t i c component i n the char's response to the indentation. Three separate hardness measurements were taken on each of the s i x pieces of char i n the samples, although some pieces were of too high a p o r o s i t y to provide a s u i t a b l e surface f o r hardness measurement. Only the' permanently deformed p o r t i o n of the indentation was used i n determining the DPH value. However, the amount of the indentation which appeared to 27 -be e l a s t i c i n nature was al s o recorded. This was done by recording the diagonals of the permanent indentation as a percentage of the diagonals of the area of the soot f i l m disturbance. 2.1.2 Density Approximately 2 grams of each char batch was used i n the determina-t i o n of true density. This was the density as measured when the e n t i r e pore structure was open to the measuring f l u i d . To eliminate any closed p o r o s i t y i n the sample, the char was ground to l e s s than 75 iim and weighed int o a 25 ml pycnometric f l a s k . The sample was covered with the measuring f l u i d , methanol, and evacuated to remove any trapped a i r and promote complete penetration of the sample by f l u i d . The true density of the char was c a l c u l a t e d i n the following manner: W2 " W l Density = (w4-w ) - (w 3-w 2) PCH 3OH PCH 3OH where: W^  = Weight of Pycnometer W2 = Weight of Pycnometer + Sample W^  = Weight of Pycnometer + Sample + F l u i d W^  = Weight of Pycnometer f i l l e d with F l u i d alone P C H 3 O H V ° - 7 9 2 g C m _ 3 2.1.3 Po r o s i t y Other char pieces were a l s o used as specimens i n the determination of char p o r o s i t y . For these experiments a Micromeritics Model 910 Mercury Penetration Porosimeter was used. This technique involved measur-ing the volume of mercury forced i n t o the pore structure of the sample as a function of the i s o s t a t i c pressure applied to the system. T o t a l pore volumes were equated to the penetrated mercury volume up to the maximum pressure of 345 MPa (50,.000 psi) . Quantitative values of pore s i z e s and - 28 -pore s i z e d i s t r i b u t i o n s could be made based on assumptions of a constant mercury-sample contact angle (130°) and the geometry of pore c r o s s - s e c t i o n ( c i r c u l a r ) . Five runs were c a r r i e d out on each char type. The remaining material was mixed according to charring temperature producing, from nineteen i n d i v i d u a l char batches, three char types: 500°C, 625°C and 750°C. Each of these was ground and separated i n t o three s i z e f r a c t i o n s : -300 + 150 ym; -150 + 75 ym and -75 + 37 ym. The f r a c t i o n s were then remixed i n selected proportion to produce the three Aggregate Batches used i n the b r i q u e t t i n g program: Aggregate Batch, A l : 50% 35% 15% Aggregate Batch,. A2: 50% 35% 15% Aggregate Batch, A3: 50% 35% 15% 2.2 Binder Coal Ch a r a c t e r i z a t i o n The binder phase of the b r i q u e t t i n g mixtures was composed of one of three caking coals which when heated was expected to f l u i d i z e and flow around the char aggregate. These were: (i) a high v o l a t i l e bituminous; ( i i ) a low v o l a t i l e bituminous with r e l a t i v e l y high ash and poor caking q u a l i t y ; and ( i i i ) a low v o l a t i l e bituminous with lower ash and better caking p r o p e r t i e s . These were designated as binders Bl,- B2 and B3, r e s -p e c t i v e l y . Their proximate analyses are given i n Table III while t h e i r p l a s t i c p r o p e r t i e s (in terms of Gieseler P l a s t i c i t y and Ruhr Dilatometer data) as determined by the Energy Research Laboratory, Ottawa, are present-ed i n Table IV. - 300 + 150 ym 750°C char - 150 + 75 ym 750°C char - 7 5 + 3 7 ym 750°C char - 300 + 150 ym 625°C char - 150 + 75 ym 625°C char - 7 5 + 3 7 ym 625°C char - 300 + 150 ym 500°C char - 150 + 75 ym 500°C char - 7 5 + 3 7 ym 500°C char - 29 -TABLE IV GIESELER PLASTICITY AND RUHR DIIATQMETER DATA GIESELER PLASTICITY B l B2 B3 S t a r t of p l a s t i c range (°C) 402 444 423 Fusion temperature (°C) 417 - 437 Temp, of maximum f l u i d i t y (°C) 442 465 462 F i n a l f l u i d temperature (°C) 472 483 492 S o l i d i f i c a t i o n temperature (°C) 476 492 494 Melting range (°C) 70 39 69 Maximum f l u i d i t y (dd m "S 994 4.6 127 Torque (g in.) 40 40 40 RUHR DILATOMETER B l B2 B3 Softening temperature, T^ (°C) 355 409 390 Maximum contraction temp., T ^ (°C) 419 474 441 Maximum dilatation temp., (°C) 457 474 Maximum contr a c t i o n (%) 27 22 25 Maximum d i l a t a t i o n (%) 109 61 39 - 30 -I n i t i a l l y , each binder was ground and separated i n t o the same s i z e f r a c t i o n s and remixed i n the same proportion as were the aggregate batches: Binder Batch, B l : 50% - 300 + 150 ym hvb coal 35% - 150 + 75 ym hvb coal 15% - 75 + 37 ym hvb coal Binder Batch, B2 50% - 300 + 150 ym lvb (poor caking) coal 35% - 150 + 75 ym lvb (poor caking) coal 15% - 7 5 + 3 7 ym lvb (poor caking) coal Binder Batch, B3: 50% - 300 + 150 ym lvb (good caking) coal 35% - 150 + 75 ym lvb (good caking) coal 15% - 7 5 + 3 7 ym lvb (good caking) coal This ensured that the b r i q u e t t i n g mixtures would be of a constant p a r t i c l e ' s i z e d i s t r i b u t i o n and therefore of a constant packing density. In a d d i t i o n to these aggregate and binder c h a r a c t e r i z a t i o n s , i t was necessary to i n v e s t i g a t e the nature of the aggregate-binder i n t e r f a c e . 2.3 Char-Binder I n t e r a c t i o n * Three experiments were performed to characterize the char-binder i n t e r f a c e : i ) The e f f e c t of p h y s i c a l i n t e r l o c k i n g of binder and aggregate was studied by measuring the strength of a bond between a binder and a model carbonaceous material (graphite) with varying degrees of surface roughness. i i ) The w e t t a b i l i t y of the chars was studied using a model binder material (an SRC pitch) on d i f f e r e n t char surfaces to study the e f f e c t of v a r i a t i o n i n char on the wetting c h a r a c t e r i s t i c s of the system. i i i ) Since a number of previous works had i n d i c a t e d a c o r r e l a t i o n between the p l a s t i c mesophase and the organic solvent soluble f r a c t i o n s formed at carbonization .temperatures, the wetting behaviour of one of these f r a c t i o n s (benzene-soluble) on a model substrate (amorphous carbon) was also studied. 2.3.1 I n t e r f a c i a l Strength For t h i s study, a set of 6.5 mm diameter graphite rods was used, the surfaces of which were prepared i n one of three ways: 1) Polished with a s o f t c l o t h to y i e l d a v i s u a l l y smooth surface. 2) Polished and then grooved r a d i a l l y with a razor blade (approximately 1 mm spacing between grooves). 3) Polished and then roughened with 100 g r i t sandpaper i n a r a d i a l manner. These were placed i n graphite moulds as shown i n f i g u r e 6. Five grams of a binder was added and the arrangement was heated to the p l a s t i c range of the binder phase and allowed to c o o l . The specimen was then supported by a f l a t d i s c with a 10 mm diameter hole through the center and the graphite rod was pushed out using an Instron machine with an FR tension-compression c e l l under the following conditions: f u l l scale load 200 l b (900 N); cross-head speed 0.005 i n . (0.127 mm) min" 1; chart speed 5 i n (127 mm) min The area of contact between binder and rod was measured as follows: A = surface area of rod embedded i n binder = II • (Diameter of rod) • (Depth of rod i n binder) = 20.42 (Depth) x 10~ 6 m2 The strength of the bond (in shear) was c a l c u l a t e d by: S = load to f a i l u r e A Binder B2 was used i n t h i s study. Binders B l and B3 were found to be unsuitable because t h e i r high f l u i d i t i e s led to f r o t h i n g during d e v o l a t i l i z a t i o n . - 32 -Figure 6: Schematic Diagram of Binder-Graphite Rod I n t e r f a c i a l Strength Specimen Graphite rod Induction coil o o o o o o o o Binder coa Graphite stand Thermocouple - 33 2.3.2 W e t t a b i l i t y of Chars In another set of experiments the w e t t a b i l i t y of the three char types by a s i n g l e model binder was studied. The model binder used was an SRC p i t c h , the same material used i n previous studies [23] on wetta-b i l i t y of various char substrates. Samples of each char type were polished f l a t and used as substrates onto which the SRC p i t c h binder was placed. Contact angle measurement was c a r r i e d out as follows. The binder p i t c h was placed on a char substrate and ins e r t e d i n a standard s e s s i l e drop apparatus (figure 7). -Molten specimen Heating coil Camera Argon 2 ^ Substrate Light source low O O O O O O O •Thermocouple Figure 7: Schematic Diagram of S e s s i l e Drop Apparatus The power supplied to the res i s t a n c e heating c o i l was adjusted to i n -crease the temperature i n a step-wise manner while the system was continu-a l l y flushed with argon. By a l i g n i n g the system so that the camera-f u r n a c e - l i g h t source axis f e l l i n the plane of the substrate, an accurate photographic record of the contact angle between extract and substrate was produced. 2.3.3 Wetting Behaviour of Coal Extracts The wetting behaviour of the benzene-soluble f r a c t i o n of each binder was i n v e s t i g a t e d . A five-gram sample of each binder batch was placed i n a No. 5 p o r c e l a i n c r u c i b l e and set i n the charring furnace. A f t e r f l u s h i n g with argon f o r 30 minutes, the sample was brought to i t s - 34 -temperature of maximum f l u i d i t y at a heating rate of approximately 70°C min ^. The sample was held at t h i s temperature f o r ten minutes and then withdrawn from the furnace and cooled q u i c k l y . The cooled material was f i r s t coarsely ground and dr i e d at 110°C for one hour and then ground further to pass a 75 ym screen. Ex t r a c t i o n of the benzene soluble f r a c t i o n was accomplished by p l a c i n g the ground material i n a 25 ml soxlet thimble, i n s e r t i n g i t i n the soxlet-type apparatus and r e f l u x i n g with 50 ml benzene f o r approximately 25 hours. With the water bath maintained at 98°C the benzene was seen to c i r c u l a t e f r e e l y through the r e f l u x c y c l e . The extract containing s o l u t i o n was poured i n t o a watchglass and the excess benzene removed by evaporation. The extr a c t l e f t was scraped from the watchglass, weighed and pressed into c y l i n d r i c a l p e l l e t s approximately 4 mm i n diameter and 10 mm long. The extr a c t p e l l e t was placed on a 10 mm x 15 mm substrate of vitreous carbon. This was inserted i n the s e s s i l e drop apparatus shown i n f i g u r e 7 and the r e l a t i o n s h i p between contact angle and temperature was determined i n the manner described above. 2.4 The Br i q u e t t i n g Program Nine b r i q u e t t i n g mixtures were made from combinations of the three aggregates and three binders. These are summarized i n Table V. In each case the proportion was 70% aggregate char to 30% binder coal by weight. The b r i q u e t t i n g apparatus i s shown i n f i g u r e 8. Approximately 0.75 g of a mixture was poured i n t o the die assembly which was then set i n the hot pressing arrangement shown i n the f i g u r e . The powder was i n i t i a l l y compacted cold by the same pressure as was to be used during the br i q u e t t i n g stage. Power was supplied to the inductive heating unit so - 35 -TABLE V CHAR-BINDER COMPOSITION  OF BRIQUETTING MIXTURES USED A G G R E G A T E A l A2 A3 B I B l MIX 1 MIX 4 MIX 7 N D E B2 MIX 2 MIX 5 MIX 8 R B3 MIX 3 MIX 6 MIX 9 36 -Split sleeve Spacer Char/ binder mixture Thermocouple F i g u r e 8: Schematic Diagram o f B r i q u e t t i n g Apparatus - 37 -as to maintain a constant heating rate of approximately 80°C min ^ up to the maximum f l u i d i t y temperature of the binder being used. This was found to be 430°C, 500°C and 480°C f o r binders B l , B2 and B3, r e s p e c t i v e l y . Upon reaching t h i s temperature a compacting pressure of 10 MPa was applied and a constant temperature was maintained. In the case of binder B2 mixtures, where a 10 MPa pressure was found to be i n s u f f i c i e n t to produce briquettes of comparable bulk density, the pressure was increased to 13.8 MPa. A pressing time of three minutes was used i n a l l cases. The c y l i n -d r i c a l b riquette product was approximately 10 mm i n diameter and 8 mm i n length. Compaction was recorded as a function of time on a Sargent model SR s t r i p chart recorder. This was c a l i b r a t e d to give a 10 mm pen d e f l e c -t i o n for a 0.25 mm compaction and the chart was run at 1.0 i n (25.4 mm) min ^. Volume and weight measurements were taken to determine bulk den-s i t i e s and bulk p o r o s i t i e s based on the true d e n s i t i e s determined i n the previous se c t i o n . 2.5 Briquette Strength The Ultimate Compressive Strength (UCS) of each briquette was determined using an Instron t e s t i n g machine. An FR tension-compression c e l l was used with a f u l l scale load of 500 l b . (2240 N). A cross-head speed of 0.01 i n min ^ (0.254 mm min "S and a chart speed of 5 i n min (127 mm min ^) were used. An ETEC Autoscan Scanning E l e c t r o n Microscope was used to i n v e s t i -gate the nature of the aggregate-binder i n t e r f a c e , the aggregate p a r t i c l e s themselves and the f r a c t u r e behaviour of a number of br i q u e t t e s . I t was necessary to deposit a t h i n gold f i l m on the surface of the specimens - 38 -due to the non-conducting nature of the ash content. A 20 kV e x c i t a t i o n voltage was employed. - 39 -3. RESULTS AND ANALYSES 3.1 Char C h a r a c t e r i z a t i o n The char material used was characterized by four parameters: density, hardness, p o r o s i t y and r e s i d u a l v o l a t i l e matter content. The r e l a t i o n s h i p s between these measured parameters and the independent v a r i a b l e - c h a r r i n g temperature, are presented i n f i g u r e s 9-14. A s i g n i f i -cant amount of s c a t t e r can be seen i n each of these p l o t s due to the heterogeneity of the material being studied. Coal i s a complex mixture of many components and therefore the s t a t i s t i c a l s i g n i f i c a n c e of the r e s u l t s obtained must be considered. Despite t h i s experimental d i f f i c u l t y , changes i n c h a r a c t e r i s t i c s from char to char are apparent. 3.1.1 Density The r e s u l t s of the pycnometric density measurements are shown i n f i g u r e 9. The i n d i c a t e d increase i n true density with carbonization temp-erature i s i n agreement with previous studies [6,24,25] mentioned e a r l i e r . Char density follows a sigmoid behaviour, increasing from that of the un--3 -3 treated coal (1.4 g cm ) to that of amorphous carbon (1.8-2.1 g cm ) produced at temperatures i n excess of 1000°C. 3.1.2 Hardness The v a r i a t i o n of char microhardness with charring temperature i s shown i n f i g u r e 10 where 136° Diamond Pyramid Hardness i s p l o t t e d against temperature. Increasing hardness i s seen to accompany an increase i n ' - 40 -400 600 800 Charring temperature (°C) F i g u r e 9: R e l a t i o n s h i p B e t w e e n T r u e C h a r D e n s i t y a n d C h a r r i n g T e m p e r a t u r e - 41 -250 200h n CL Q 400 600 800 Charring temperature (°C) Figure 10: Relationship Between Char Microhardness and Charring Temperature carbonization temperature, the r e l a t i o n s h i p being l i n e a r over the range considered. Each point on t h i s p l o t represents the mean of between 10 and 18 microhardness readings. This v a r i a t i o n was due to excessive char p o r o s i t y preventing t e s t i n g on some samples. The e l a s t i c behaviour of the char i n microhardness t e s t i n g i s shown i n f i g u r e 11 as a function of charring temperature. This was q u a n t i f i e d as percentage of the area disturbed by the indentor which r e -covered e l a s t i c a l l y . Figure 12 shows a photomicrograph (1400X) of a DPH indentation. The inner rectangle i s the permanent deformation from which the hardness values of f i g u r e 10 were determined. The outer rectangle marks the extent of the area disturbed by the indentor. The e l a s t i c nature of response to indentation was found to increase with charring temperature. 3.1.3 Po r o s i t y The penetration porosimetry technique allows determination of pore s i z e d i s t r i b u t i o n i n the char based on two assumptions. The contact angle of mercury on the samples must be known; i t was taken i n the present case to be 130°. The pore geometry must also be known. A c i r c u l a r c r o s s - s e c t i o n was assumed and p l o t s of cumulative pore volume against pore diameter were produced. These are presented i n f i g u r e s 13a, b and c, where upper and lower bounds are shown. Both mean pore s i z e and t o t a l pore volume were shown to decrease with in c r e a s i n g charring temperature. Table VI shows average pore volumes above various pore diameters. I t i s seen that the highest temperature char (750°) has v i r t u a l l y no pore structure above 1 ym diameter. Figure 14a and b show the type of pore structure found i n chars A3 and A l , r e s p e c t i v e l y . - 43 -Figure 11: Relationship Between E l a s t i c Behaviour of Char i n Microhardness Test and Charring Temperature 400 600 800 Charring temperature (°C) - 44 -i r Figure 13a. Cumulative Pore Size D i s t r i b u t i o n f o r Char A l (Carbonized at 750°C) Figure 13b.: Cumulative Pore Size D i s t r i b u t i o n f o r Char A2 (Carbonized at 625°C) - 4 7 -Pore diameter (/Am) Figure 1 3 c : Cumulative Pore Size D i s t r i b u t i o n f o r Char A3 (Carbonized at 500°C) - 48 -TABLE VI VOLUME CONTAINED IN AGGREGATE-CHAR PORES ABOVE GIVEN DIAMETERS DIAMETER (ym) Al (750°C) (mm g ) A2 (625°C) (mm g ) A3 (500°C) (mm g ) 15 0 4 14 5 0 7 18 1.0 2 10 22 0.1 20 23 67 0.01 54 55 90 - 49 -Figure 14b.: Photomicrograph Showing Micropores i n Char A l (Carbonized at 750°C) (16800X) - . 5 0 r 3.1.4 Residual V o l a t i l e Matter Content The r e s i d u a l v o l a t i l e matter (RVM) content of the char decreased with increasing carbonization temperature. This e f f e c t can be seen i n figur e 15 where RVM, being the d i f f e r e n c e between v o l a t i l e matter content of the char and that of the o r i g i n a l coal (42%), i s p l o t t e d against charring temperature. The RVM content appears tb follow a l i n e a r r e l a -t i o n s h i p , f a l l i n g from 42% with no heat treatment to approximately zero at carbonization temperatures above 1000°C. 3.2 Char-Binder In t e r a c t i o n The i n t e r f a c i a l strength measurements showed the binder-graphite bond to be very weak. The shear strengths measured f o r specimens with d i f f e r e n t surface preparations are presented i n Table VII. Graphite Rod Preparation Maximum (Load) (N) Calculated Area of Contact (mm ) I n t e r f a c i a l Strength (kPa) Polished 16 525 30 Grooved 29 435 67 Roughened 49 470 104 TABLE VII: INTERFACIAL SHEAR STRENGTH OF BINDER-GRAPHITE ROD SPECIMENS - 51 -Figure 15: Relationship Between Residual Volatile Matter Content of Char and Charring Temperature 20 c <D -*— C o o +— o E a> +— o o V) I 5 10 1 1 1 1 o o o o — o — o o o o CD o o o 1 1 1 o 1 5 400 600 800 Charring temperature ( °C ) - 52 -I t i s seen that the rod roughened with 100 g r i t sandpaper produced the highest shear strength, while the polished rod gave the lowest and the grooved rod gave an intermediate value. This i n d i c a t e s the r e l a t i v e e f f e c t of surface texture on the i n t e r f a c i a l shear strength. The contact angle-temperature r e l a t i o n s h i p s f o r the SRC p i t c h on each char i s presented i n fi g u r e 16. I n i t i a l softening of the p i t c h was seen to occur at approximately 200°C and the angle f e l l to a constant value of approximately 20° when the temperature was increased to 320°C. The y i e l d of benzene-soluble material a f t e r twenty-five hours ex-t r a c t i o n was found to be very small ^1.5% (±0.5%) f o r each binder c o a l . Complete- wetting of the amorphous carbon substrate was observed with each binder e x t r a c t and t h i s was seen to occur immediately a f t e r the extract became molten. The melting point of these materials was measured as 180°C ± 20°C i n each case. 3.3 Compaction Analysis The CCWL hot compaction model for char/binder coal systems i s composed of three K e l v i n v i s c o e l a s t i c elements i n s e r i e s , as discussed i n section 1.4.3. This model was o r i g i n a l l y derived using an e l e c t r i c a l analog with the equations formulated for the general case ( i . e . with no assumptions concerning i n t e r a c t i o n of model elements). I t was found that the simplest case to which t h i s general s o l u t i o n could be applied was that of three non-interacting elements and the s o l u t i o n f or a mechanical analog of t h i s type was obtained by s u b s t i t u t i n g springs for capacitors, dashpots f o r r e s i s t o r s and changing s e r i e s coupling to p a r a l l e l and p a r a l l e l to s e r i e s . From t h i s , the values of the mechanical model parameters (n. and M.) were r e l a t e d to the experimental constants. However, Contact angle, Q (deg) K> cr> o -O oo p o o o o Figure 16: Relationship Between Contact Angle of an SRC P i t c h on Char and Temperature - 54 -once t h i s non-interacting mechanical analog i s proposed, the r e l a t i o n s h i p s between model parameters and experimentally determined constants can be more d i r e c t l y solved as follows: The response of a s i n g l e K e l v i n element to an applied s t r e s s i s given by [53]: _g_ (1 - e M. (M/n)t, (l) where a i s the applied s t r e s s , M the e l a s t i c constant of the spring, n the v i s c o s i t y of the dashpot, and e the observed s t r a i n at any time, t . A s e r i e s of n of these elements w i l l have the response: n Z i = l _g_ (1 M. e - ( M i / n i ) t } (2) and, f o r the case of f i g u r e 5, ^ ( 1 _ e-Wi/mltj + ^ ( 1 M 2 e ^ 2 / n 2 ) t } + ^ ( 1 r ( M 3 / n 3 ) t . (3) Expanding t h i s expression and c o l l e c t i n g terms y i e l d s : 1 1 1 e " ( M l / n i ) t e " ( M 2 / T l 2 ) t e " ( M 3 / n 3 ) 1 :  M l + M 2 + M 3 " M l M 2 M 3 (4) The t o t a l r i g i d i t y of the system, M^, i s r e l a t e d to the i n d i v i d u a l element r i g i d i t i e s by: 1^_ A_ A_ A_ M M M 1 2 3 (5) Introducing and r e w r i t i n g gives: f M r ^ - ^ i / ^ t _ I M 2J ( M 2 / n 2 ) t M ^ | e - ( M 3 / n 3 ) t M 3J (6) - 55 and by d e f i n i n g : k = ; A E J*T_ ; B = J^jr ; C = _^T_ M T M x M 2 M 3 a E _ M l _ ' - e = _^2_r Y = M 3 , Hi ri2 13 (7) equation (6) can be written: e = k (1 - A e ~ a t - Be B t - Ce" Y t) (8) which i s the experimental equation (p. L9) By considering the boundary co n d i t i o n : e. = °o = k , (9) t=oo Mrp the t o t a l system r i g i d i t y i s seen to be given by: M T = _^o. = . (10) e. k t=oo S u b s t i t u t i n g equation (10) i n t o equations (7), the r e l a t i o n s h i p s between the v i s c o e l a s t i c parameters of f i g u r e 5 and the c o e f f i c i e n t s of equation (8) are given by: \ = _MT = _!°_ n = _^1_ = A kA a kAa M2 = _ ! ^ = ^ £ . n 2 = _ ^ l = ( I D B kB 8 kB 3 *3 = A = n = = _^o_ C kC Y k c Y This i s a p a r t i c u l a r s o l u t i o n of the more general form considered i n the o r i g i n a l model development. Equation (8) may be manipulated as follows to experimentally - 56 -determine the c o e f f i c i e n t s k, A, B, C, a , 3 and Y . An expanded form of equation (8), -at -Bt -Yt e = k - kAe - kBe - kCe (12) may be d i f f e r e n t i a t e d to y i e l d : -at „ -0t -Yt E = akAe + BkBe + YkCe (13) Taking the natural logarithm of both sides: ln(e) = -at + ln(akA) - Bt + ln(BkB) - Y t + ln(YkC) (14) Since the time i n t e r v a l s over which the three mechanisms predominate do not overlap, a p l o t of ln(e) vs. t w i l l have three s t r a i g h t - l i n e sections, the slopes of which correspond to -a, -B and - Y- The i n t e r c e p t s of the s t r a i g h t sections w i l l correspond to ln(akA), ln(BkB) and ln(YkC), r e s p e c t i v e l y . As i n d i c a t e d by equation (8), the constant, k, may be equated to the value of compaction s t r a i n at long times when the exponential terms go to zero. This model was used to quantify the compaction behaviour of each mixture. The second element i n the model—that associated with p a r t i c l e flow—was selected as being representative of char/binder i n t e r a c t i o n . S p e c i f i c a l l y , , the slope of the c e n t r a l portion of the ln(£) vs. t p l o t was equated to -B while the i n t e r c e p t was set equal to ln(kBB)/ allowing determination of the pre-exponential c o e f f i c i e n t , B. The r i g i d i t y and v i s c o s i t y of the compacting mixture during the p a r t i c l e flow stage was then c a l c u l a t e d , following the above d e r i v a t i o n : R i g i d i t y , M 2 = ( k B ) - 1 V i s c o s i t y , n = (kBB) ^ - 57 -T h e c h a r t r e c o r d e r a t t a c h e d t o t h e b r i q u e t t i n g a p p a r a t u s p r o d u c e d a c h a r t r e c o r d o f c o m p a c t i o n v s . t i m e . T h e s e c u r v e s w e r e s u p p l i e d t o a c o m p u t e r p r o g r a m i n t h e f o r m o f d i g i t i z e d x ( t i m e ) , y ( c o m p a c t i o n ) p a i r s . T h e p r o g r a m t h e n t r e a t e d t h e d a t a a s f o l l o w s : 1. N o r m a l i z e c o m p a c t i o n w i t h r e s p e c t t o i n i t i a l b r i q u e t t e l e n g t h , g i v i n g c o m p a c t i o n s t r a i n v s . t i m e d a t a . 2. D e t e r m i n e s l o p e ( £ ) o f z v s . t c u r v e a t v a r i o u s v a l u e s o f t a n d p l o t v a l u e s o f l n ( e ) a g a i n s t t . 3. D e t e r m i n e b e s t l e a s t s q u a r e s l i n e a r f i t f o r t h e s e c o n d r e g i o n , c a l c u l a t i n g v a l u e s o f (3 a n d B f r o m t h e s l o p e a n d i n t e r c e p t o f t h e c u r v e . 4. ' C a l c u l a t e r i g i d i t y a n d v i s c o s i t y p a r a m e t e r s a n d . T h e s t r a i n - t i m e c u r v e s f o r m i x t u r e 6, s h o w n i n f i g u r e 17, a r e t y p i c a l o f t h e r e s u l t s o b t a i n e d ( t h e r e m a i n i n g n o r m a l i z e d c o m p a c t i o n c u r v e s a n a l y s e d a r e p r e s e n t e d i n A p p e n d i x B ) . A l t h o u g h t h e f i n a l c o m p a c -t i o n v a r i e s s o m e w h a t f r o m b r i q u e t t e t o b r i q u e t t e , t h e c o m p a c t i o n b e h a v i o u r i n t h e r e g i o n 0-1 m i n u t e a p p e a r s t o b e s i m i l a r . V a r i a t i o n s w i t h i n a m i x t u r e t y p e c a n a r i s e f r o m a n u m b e r o f s o u r c e s : s m a l l v a r i a t i o n s i n h e a t i n g r a t e , f i n a l t e m p e r a t u r e a t t a i n e d , a n d h o w c l o s e l y t h i s f i n a l t e m p e r a t u r e i s m a i n t a i n e d d u r i n g t h e c o m p a c t i o n p r o c e d u r e , d i m e n s i o n a l v a r i a t i o n s i n t h e d i e a s s e m b l y , a n d t h e h e t e r o g e n e o u s n a t u r e o f t h e m a t e r i a l s i n v o l v e d . T h e d e r i v e d p l o t o f l n ( £ ) v s . t f o r o n e b r i q u e t t e o f m i x t u r e 6 i s s h o w n s u p e r i m p o s e d o n t h e c o m p a c t i o n c u r v e i n f i g u r e 18 w h e r e t h e c i r c l e s c o r r e s p o n d t o t h e c a l c u l a t e d l n ( e ) v a l u e s . I n f i g u r e 19, t h e p r e d i c t e d c u r v e g e n e r a t e d f r o m t h e c a l c u l a t e d v a l u e s o f B a n d B i s p l o t t e d o n t h e s a m e a x e s a s t h e o r i g i n a l c o m p a c t i o n c u r v e . R e a s o n a b l e a g r e e m e n t i s s h o w n 1 03 Time (min ) Figure 17: Observed Strain-Time Curves of Br i q u e t t i n g Mixture 6 (Aggregate A2 - Binder B3) Figure 18: Relationship Between Natural Logarithm of S t r a i n Rate and Time for Briquette 6 of Mixture 6 Superimposed on the Strain-Time Curve 0.21 T — — i 1 1 1 1 r | 0.20 E E ~ 0.19 c •tmmm o • O-—o- Qd •Experimental Curve € f = 0 . 2 0 3 ( I - 0 . 2 7 e " 7 , 8 t ) cn o ( / ) 0.18 0.17 I 1 I I I L 0.2 0.4 Time (min) 0.6 0.8 Figure 19: Predicted and Observed Strain-Time Curves f o r Briquette 6 of Mixture 6 - 61 -for the region associated with the second compaction mechanism. The slow response of the compaction recorder prevented an accurate determination of the end of the f i r s t stage of compaction and i n i t i a t i o n of the second stage. The discrepancy between experimental and predicted p l o t s may be accounted for by t h i s inaccuracy. Measured values of 3, B, and n are given i n Tables V i l l a / b and c and summarized according to mixture type i n Tables IXa and b. 3.4 Briquette Strength Results of Ultimate Compressive Strength t e s t i n g are presented i n f i g u r e 20. Strength i s presented as a function of briquette bulk p o r o s i t y . For purposes of comparison/ the observed v a r i a t i o n of strength with bulk p o r o s i t y f o r each mixture type was extrapolated to a common bulk p o r o s i t y of 35%. The v a r i a t i o n s i n strength (at 35% porosity) with aggregate charring temperature are shown i n f i g u r e s 21a, b and c. E r r o r bars shown are f o r a 95% confidence i n t e r v a l on the strength value extrapolated to 35% bulk p o r o s i t y . This a n a l y s i s w i l l be elaborated fur t h e r i n the f o l -lowing section. MIX BRIQ k SLOPE (min~-M INTERCEPT 3 (min ) B RIGIDITY, M2 (MPa) VISCOSITY, n2 (MPa min) 1 1 0.249 -8.41 -0.52 8.41 0.28 141 16.7 2 0.277 -10.71 -0.71 10.71 0.16 217 20.3 CHAR 3 0.303 -9.62 -0.35 9.62 0.24 136 14.1 A l 4 MEAN 0.279 -8.73 -0.77 8.73 0.19 189 171 21.6 18.2 (3. 4 - 1 0.231 -18.2 -0.51 18.2 0.14 302 16.6 2 0.235 -14.5 -0.69 14.5 0.15 288 19.9 CHAR 3 0.255 -19.3 -0.51 19.3 0.12 322 16.6 A2 4 MEAN 0.235 -11.9 -0.79 11.9 0.16 261 293 22.0 18.8 (2. 7 1 0.229 -8.95 -0.69 8.95 0.24 178 19.9 2 0.220 -6.45 -1.06 6.45 0.24 186 28.9 CHAR 3 0.262 -11.3 -0.52 11.3 0.20 191 16.9 A3 4 0.221 -5.79 -1.01 5.79 0.28 159 27.5 5 0.256 -9.38 -0.64 9.38 0.22 178 19.0 6 0.190 -10.1 -0.97 10.1 0.20 266 26.3 7 0.283 -12.3 -0.46 12.3 0.18 194 15.8 MEAN 193 22.0 (5. l TABLE V i l l a : VALUES OF EXPERIMENTAL AND MODEL PARAMETERS FOR MIXTURES CONTAINING BINDER B l * Standard deviation i n parentheses. RIGIDITY, VISCOSITY, MIX BRIQ k SLOPE INTERCEPT 3 B M 2 n 2 (min~l) (min--'-) (MPa) (MPa min) 1 1 0.214 -6.91 -1.65 6.91 0.13 500 72.2 2 0.172 -8.13 -1.51 8.13 0.16 500 61.7 CHAR 3 0.206 -7.60 -1.58 7.60 0.13 510 67.5 Al 4 0.205 -5.48 -1.98 5.48 0.12 550 102.4 MEAN 520 76.0 (18. 5 1 0.186 -9.48 -0.69 9.48 0.28 261 27.5 2 0.189 -7.81 -0.97 7.81 0.26 286 36.6 CHAR 3 0.177 -8.20 -1.03 8.20 0.25 317 38.7 A2 4 0.206 -10.12 -0.45 10.12 0.31 218 21.6 5 0.203 -8.95 -0.59 8.95 0.31 223 24.9 6 0.203 -7.81 -0.86 7.81 0.27 253 32.5 MEAN 260 30.3 (6.2 8 1 0.164 .-9.06 -0.85 9.06 0.29 293 32.4 - 2 0.185 -9.59 -0.79 9.59 0.26 291 30.3 CHAR 3 0.201 -9.62 -0.95 9.62 0.20 342 35.5 A3 4 0.207 -8.62 -1.06 8.62 0.19 .. 243 39.8 MEAN 317 34.5 (4.1 > 5) TABLE V I I l b : VALUES OF EXPERIMENTAL AND MODEL PARAMETERS FOR MIXTURES CONTAINING BINDER B2 MIX BRIQ k SLOPE (min*"1) INTERCEPT 3 (min 1) B RIGIDITY, M2 (MPa) VISCOSITY, n2 (MPa min) 3 1 0.235 -6.80 -2.12 6.80 0.08 565 83.1 2 0.255 -9.90 -1.59 9.90 0.08 375 49.0 CHAR 3 0.252 -8.65 -2.04 8.65 0.06 667 77.1 Al 4 MEAN 0.247 -7.95 -1.90 7.95 0.08 532 535 67.0 69.0 (14. 6 1 0.217 -10.7 -0.91 10.7 0.17 265 25.3 2 0.248 -13.5 -0.29 13.5 0.22 180 13.6 CHAR 3 0.198 -11.9 -0.39 11.9 0.29 176 14.8 A2 4 0.207 -12.8 -0.54 12.8 0.22 221 17.2 5 0.208 -11.6 -0.28 11.6 0.31 153 13.4 6 0.201 -12.8 -0.39 12.8 0.26 189 15.0 MEAN 198 16.6 (4.5 9 1 0.225 -11.6 -1.33 11.6 0.10 437 37.8 2 0.197 -14.3 -0.63 14.3 0,19 267 18.7 CHAR 3 0.226 -9.83 -1.24 9.98 0.13 340 34.6 A3 4 0.230 -18.4 -1.09 18.4 0.08 550 29.5 5 0.199 -13.1 -0.92 13.1 0.15 329 25.1 MEAN 385 29.1 (7.5 1 TABLE V I H e : VALUES OF EXPERIMENTAL AND MODEL PARAMETERS FOR MIXTURES CONTAINING BINDER B3 - 65 -T A B L E I X ( a & b ) a . A V E R A G E V A L U E S O F S E C O N D M O D E L E L E M E N T R I G I D I T I E S ( M „ ) B l B 2 B 3 A l 1 7 1 5 2 0 5 3 5 A 2 2 9 3 2 6 0 1 9 8 A 3 1 9 3 3 1 7 3 8 5 b ' . A V E R A G E V A L U E S O F S E C O N D M O D E L E L E M E N T V I S C O S I T I E S ( n _ ) B l B2 B3 A l 18.2 76.0 69.0 A2 18.8 30.3 16.6 A3 22.0 34.5 29.1 cn 32 36 Bulk porosity of briquette (%) 4 0 Figure 20: Relationships Between Briquette Ultimate Compressive Strength and Briquette Bulk Pozosity For A l l Mixtures I -67-cn 450 550 650 7 50 Figure 21 a: Charring temperature (°C) Relationship Between Briquette Ultimate Compressive Strength and Charring Temperature for Mixtures Containing Binder B l . -68-O Q_ 00 3 4 50 550 650 750 Figure 21 b: Charring temperature (°C ) Relationship Between Briquette Ultimate Compressive Strength and Charring Temperature for Mixtures Containing Binder B2. - 6 9 -O Q-00 450 550 650 750 Charring temperature (°C) Figure 21 c: Relationship Between Briquette Ultimate Compressive Strength and Charring Temperature for Mixtures Containing Binder B3. - 70 -4 DISCUSSION As o u t l i n e d i n section 1.5, the o b j e c t i v e of t h i s work was to i n v e s t i g a t e the formcoke system on a more fundamental l e v e l than that attempted to date. The focus of the i n v e s t i g a t i o n has been on the e f f e c t s of material c h a r a c t e r i s t i c s on the f i n a l b riquette product. The p h y s i c a l c h a r a c t e r i s t i c s of the aggregate and binder phases may a f f e c t the f i n a l composite i n two ways: 1) by i n f l u e n c i n g the compaction k i n e t i c s of the b r i q u e t t i n g process, and 2) by d i r e c t l y i n f l u e n c i n g the p h y s i c a l nature of the f i n a l product. A range of aggregate c h a r a c t e r i s t i c s was produced by using chars produced at three d i f f e r e n t carbonization temperatures while v a r i a t i o n s i n binder p r o p e r t i e s were obtained by using three d i f f e r e n t caking c o a l s . The compaction k i n e t i c s of various mixtures of these phases were studied using a p r e v iously e s t a b l i s h e d model and the f i n a l formcoke composite was characterized by i t s ultimate compressive strength. I n t e r p r e t a t i o n of the r e s u l t s obtained w i l l follow the order established above. 4.1 A p p l i c a b i l i t y of Hot Compaction Model Analysis of the compaction curves was c a r r i e d out using the CCWL hot compaction model which has been described e a r l i e r (sections 1.4, 3.3 and Appendix A). I t should be noted here that i n the o r i g i n a l development - 71 -of the model, no e f f o r t was made to i n v e s t i g a t e the r e p r o d u c i b i l i t y of the compaction curves or the s e n s i t i v i t y of the c a l c u l a t e d model parameters to small v a r i a t i o n s i n these curves. One of the o b j e c t i v e s o f t h i s work was to e s t a b l i s h the v a r i a t i o n of model parameter values f o r one char-binder system over a wide range of b r i q u e t t i n g temperatures i n an attempt to iden-t i f y the i d e a l b r i q u e t t i n g conditions. In the present work, the model i s used to compare the model parameter values obtained under these i d e a l con-d i t i o n s for nine d i f f e r e n t char-binder systems and to i d e n t i f y the material c h a r a c t e r i s t i c s responsible for the observed v a r i a t i o n s . As can be seen from Tables VIII and IX some sc a t t e r i n the c a l c u l a t e d parameter values was found. R i g i d i t y values ranging from 171 MPa to 535 MPa were c a l c u l a t e d . The v i s c o s i t y values c a l c u l a t e d v a r i e d from 16.6 MPa min to 76.0 MPa min with standard deviations as shown i n parentheses i n the t a b l e . Considering the small sample s i z e a v a i l a b l e , these values were considered reasonable. During the course of t h i s study, conclusions concerning the associa-t i o n of p a r t i c u l a r compaction mechanisms with c e r t a i n model elements were drawn. These are presented i n the appropriate sections. In general, the model was found to describe the p h y s i c a l s i t u a t i o n quite well and to be s e n s i t i v e to small v a r i a t i o n s i n the compaction curves. The observed v a r i a t i o n i n c a l c u l a t e d values from d u p l i c a t e runs was a t t r i b u t e d to i n s e n s i t i v i t y of recording and d i g i t i z i n g equipment and material hetero-geneity. 4.2 E f f e c t of M a t e r i a l C h a r a c t e r i s t i c s  On Compaction K i n e t i c s Two material p r o p e r t i e s were found to a f f e c t the f i n a l product by i n f l u e n c i n g the compaction k i n e t i c s . Binder f l u i d i t y was shown to a f f e c t - 72 -compaction v i s c o s i t y during the second stage of compaction—that a s s o c i a t -ed with p a r t i c l e flow, and aggregate p o r o s i t y was shown to a f f e c t f i n a l compaction during the t h i r d stage—that associated with p l a s t i c deformation. A major influence on the compaction k i n e t i c s of the formcoke system comes from binder f l u i d i t y . By comparing the c a l c u l a t e d model parameters for the second stage of compaction (Tables IXa and b) with the r h e o l o g i c a l properties of the binders (Table IV) , i t can be seen that the observed compaction v i s c o s i t y increases as the binder f l u i d i t y drops. This i s shown g r a p h i c a l l y i n f i g u r e 22. Binder B l has the highest Gieseler f l u i d -i t y and d i s p l a y s the lowest compaction v i s c o s i t y values. F l u i d i t y de-creases from B l to B3 to B2 as the corresponding compaction v i s c o s i t i e s increase. Except for the case of mixture 6, t h i s i s true regardless of the char type used. The case of mixture 6 can be explained by loose spacer assembly allowing binder to be squeezed out during compaction as observed with t h i s mixture. This r e s u l t e d i n the c o n s i s t e n t l y low values of and observed f o r that mixture. This comparison r e i n f o r c e s the a s s o c i a t i o n of the second model element with a p a r t i c l e flow mechanism. As p l a s t i c phase f l u i d i t y de-creases, movement of aggregate p a r t i c l e s within the compact becomes more d i f f i c u l t and the compaction v i s c o s i t y of the mixture increases. The lack of s i g n i f i c a n t trends i n second element r i g i d i t y and t o t a l compaction values i n d i c a t e s that neither of these parameters i s g r e a t l y a f f e c t e d by mixture type. In the model, i s influenced by t o t a l com-paction, k, and the value of B, which i s the f r a c t i o n of the t o t a l model response a t t r i b u t a b l e to the second element Both of these remain approxi-mately constant throughout the study at 0.2 and 0.1 - 0.3, r e s p e c t i v e l y . - 73 -Figure 22: Relationship Between Second Model Element V i s c o s i t y and Binder Phase F l u i d i t y - 74 -Char p o r o s i t y i s seen to a f f e c t the b r i q u e t t i n g process by i n f l u -encing the amount of compaction necessary to a t t a i n a given bulk density i n the product. Although the value of k d i d not vary widely throughout the program, v a r i a t i o n s i n k within a mixture type were seen to c o r r e l a t e with changes i n briquette bulk density. When grouped according to char type, the e f f e c t of char p o r o s i t y on product bulk density can be seen. The r e s u l t s presented i n f i g u r e s 23a, b and c and summarized i n Table X, i n d i c a t e the r e l a t i o n s h i p between t o t a l compaction and re s u l t a n t briquette bulk p o r o s i t y to be l i n e a r . As expected, a la r g e r compaction r e s u l t s i n a lower bulk p o r o s i t y or, a l t e r n a t i v e l y , a higher bulk density. The slopes of these' curves represent the s e n s i t i v i t y of briquette bulk p o r o s i t y to t o t a l compaction. I t i s seen that f o r a given char type, t h i s slope i s approximately constant f o r each binder. However, for de-creasing temperature of char carbonization, the average slope i s seen to increase (see Table X). In a p h y s i c a l sense, an equal amount of compac-t i o n w i l l cause a greater increase i n bulk density f o r briquettes made with higher temperature char than f o r the lower temperature m a t e r i a l . This r e s u l t s from the need to eliminate the higher p o r o s i t y present within the lower temperature char. This may be accomplished by penetration of the binder phase i n t o the macropores (>5um) during the p a r t i c l e flow stage of compaction when the binder i s f l u i d and by collapse of the pore structure by p l a s t i c deformation i n the f i n a l compaction stage due to the applied s t r e s s . The y - i n t e r c e p t s of the k vs. P, curves (figures 23a, b and c) b correspond to the amount of compaction required to a t t a i n t h e o r e t i c a l density i n a briquet t e . This value i s also seen to increase with 28 32 36 40 Briquette bulk porosity (%) Figure 23 a: Relationship Between To t a l Compaction and Resultant Briquette Bulk Porosity f o r Mixtures Containing Char A l . E 0 . 3 0 0 -E E c o o o CL E o o o o 0 . 2 0 0 0 . 1 0 0 2 8 3 2 3 6 4 0 Briquette bulk porosity (%) F i g u r e 2 3 b ; R e l a t i o n s h i p B e t w e e n T o t a l C o m p a c t i o n a n d R e s u l t a n t B r i q u e t t e B u l k P o r o s i t y f o r M i x t u r e s C o n t a i n i n g C h a r A 2 . Briquette bulk porosity ( % ) F i g u r e 2 3 c : R e l a t i o n s h i p B e t w e e n T o t a l C o m p a c t i o n a n d R e s u l t a n t B r i q u e t t e B u l k P o r o s i t y f o r M i x t u r e s C o n t a i n i n g C h a r A 3 . SLOPE AVERAGE VALUE INTERCEPT AVERAGE VALUE CHAR BINDER MIX a - l (mm/mm % ) OF a FOR CHAR TYPE b (nun/mm) OF b FOR CHAR TYPE B l 1 -4.21 x 10~ 3 .418 A l B2 2 -7.37 x 10~ 3 -5.21 x 10~ 3 .465 .422 B3 3 -4.04 x 10~ 3 .383 B l 4 -1.06 x 10~ 2 .656 A2 B2 5 -7.85 x 10~ 3 -1.00 x 10~ 2 .502 .599 B3 6 -1.16 x 10~ 2 .640 B l 7 - 1.99 x 10~ 2 1.01 A3 B2 8 . - -1.63 x 10~ 2 - .846 B3 9 -1.26 x 10~ 2 .682 TABLE X VALUES OF SLOPES AND Y-INTERCEPTS OF CURVES OF TOTAL COMPACTION VS. RESULTANT BRIQUETTE BULK POROSITY - 79 -decreasing charring temperature. The i n t e r c e p t for the case of the high-est temperature char, A l , i s s i g n i f i c a n t since i n t h i s char, there i s v i r t u a l l y no a c c e s s i b l e p o r o s i t y . In t h i s case, the response of bulk p o r o s i t y to a change i n compaction i s associated with the binder phase alone. Increases i n the compaction required to a t t a i n t h e o r e t i c a l density above that seen f o r the case of aggregate A l correspond to the c o n t r i b u t i o n of the aggregate phase. Table X shows that a compaction of approximately 40% would be required to produce complete d e n s i f i c a t i o n with A l char and a d d i t i o n a l compactions of roughly 20% and 45% to cause the p l a s t i c deforma-t i o n required for chars A2 and A3 to reach t h e o r e t i c a l density. I t may be noted that 40% volume p o r o s i t y has been found to be the approximate normal packing density f o r a powder compact of random size d and shaped p a r t i c l e s [54] . This a n a l y s i s may be summarized i n three p o i n t s : 1) The aggregate phase of a formcoke does influence the compaction k i n e t i c s of the system and the f i n a l briquette product. 2) The greater macroporosity produced i n char at lower carboniza-t i o n temperatures requires more extensive binder penetration and p l a s t i c deformation i n the b r i q u e t t i n g operation to a t t a i n a product bulk density comparable to that obtained with higher temperature char. 3) The a s s o c i a t i o n of one of the elements of the CCWL hot com-paction model with a p l a s t i c deformation mechanism i s confirmed. 4.3 E f f e c t of Material C h a r a c t e r i s t i c s  On Briquette Strength The second o b j e c t i v e of t h i s work was to e s t a b l i s h how the aggregate - 80 -and binder c h a r a c t e r i s t i c s d i r e c t l y a f f e c t the formcoke product: t h i s required consideration of changes i n each component while the other was held constant. The basis of f i n a l product comparison was briquette Ultimate Com-pressive Strength (UCS). However, as established above, small v a r i a t i o n s i n compaction can lead to s i g n i f i c a n t d i f f e r e n c e s i n briquette bulk p o r o s i t y and the bulk p o r o s i t y of a specimen i s known to a f f e c t i t s gross strength. Therefore i t was f i r s t necessary to take account of v a r i a t i o n s i n b r i q u e t t e bulk p o r o s i t y . I t has been shown by Ryshkewitch [55] that the strength of a porous body can be r e l a t e d to i t s f r a c t i o n a l p o r o s i t y by an inverse exponential r e l a t i o n s h i p (UCS = Ae D ) over a large range of p o r o s i t y (3-60%). This empirical r e l a t i o n s h i p has also been v e r i f i e d by a number of other workers [56]. However, i t was found i n t h i s work that, over the range of p o r o s i t y encountered, strength appeared to vary l i n e a r l y with bulk p o r o s i t y . The l i n e a r r e l a t i o n s h i p f o r each mixture type was extrapolated to a common bulk p o r o s i t y f o r strength comparisons. T h i r t y - f i v e percent was chosen as being both a median f i g u r e f o r the experimental data a v a i l -able and a reasonable commercial value. The s t a t i s t i c a l r e l i a b i l i t i e s of these extrapolations were established using the 95% confidence l i m i t s f o r the predicted strength values [57]. From these r e s u l t s , the separate contributions of char and binder can be i s o l a t e d by considering f i r s t a constant binder and varying char and then a constant char with varying binder. 4.3.1 Char C h a r a c t e r i s t i c s To eliminate binder property e f f e c t s , b r i q u e t t i n g mixtures of a - 81 -singl e binder and d i f f e r e n t chars can be considered. In these cases, v a r i a t i o n s i n UCS are associated with v a r i a t i o n s i n char p r o p e r t i e s . Examination of briquette f r a c t u r e s showed separation to occur p r i m a r i l y along the char-binder i n t e r f a c e with some instances of binder fra c t u r e (figures 24a and b). Even i n briquettes made with 500°C char, where hardness and density studies i n d i c a t e d lowest char strength, f a i l u r e through the aggregate phase was not observed. From t h i s i t i s concluded that i n the systems studied, b r i q u e t t e strength i s not dependent on the mechanical strength of the aggregate phase. Both the p o r o s i t y and RVM content of the char were seen to decrease with charring temperature (Table VI and f i g u r e 15, r e s p e c t i v e l y ) , para-l l e l i n g the decrease i n briquette UCS. The t o t a l volume of space contained i n pores of la r g e r than a given diameter has been presented i n Table VI. These data i n d i c a t e that pore volume decreases with increasing carbonization temperature, e s p e c i a l l y for pores of 1 - 5 ym diameter and l a r g e r . Lahaye and Aubert [44] con-cluded that 5 ym diameter pores are the lower l i m i t of penetration of t a r i n non-outgassed coke. However i t i s f e l t that pores of diameter l e s s than 1 ym are not penetrated under any circumstances. Further to t h i s , volumes measured f o r diameters below 0.1 ym may only be r e f l e c t i o n s of char com-p r e s s i b i l i t y , as suggested by Toda and Toyoda [22]. In the present case, the roughly equal increases i n apparent volume from 0.1 to 0.01 ym (experimental lower l i m i t ) i n d i c a t e a s i m i l a r c o n t r i b u t i o n from t h i s material c o m p r e s s i b i l i t y f o r each of the char types used. These r e s u l t s i n d i c a t e that the. greater pore volume and mean pore s i z e found i n the lower temperature char contribute to a higher gross - 82 -Figure 24b.: Photomicrograph Showing Binder Phase Fracture (130X) 83 -composite strength. This i s confirmed by the i n t e r f a c i a l strength measure-ments performed on the binder-graphite rod specimens (section 2.3.1 - Table VIII) where i n t r o d u c t i o n of surface roughness r e s u l t e d i n increased shear strength. Other authors have found s i m i l a r r e s u l t s . For example, i n t h e i r work on Soderberg anodes, D e l l and Peterson [43] concluded that a pore structure a c c e s s i b l e to the binder i s e s s e n t i a l f o r a good bond and Vetyukov et a l . [42] have in d i c a t e d that surface roughness i s more important than the type of carbon material used. A l l the above studies were concerned with g r a p h i t i c or c a l c i n e d petroleum coke aggregates. I t has been in d i c a t e d that materials of t h i s type may show weaker aggregate-binder bond strengths than carbonaceous materials produced at lower temperatures. As carbonization temperature i s increased, the s o l i d product of p y r o l y s i s takes on an i n c r e a s i n g l y denser, l e s s r e a c t i v e and more ordered s t r u c t u r e . Sukhorukov et a l . [39], i n studying a range of materials from crude to c a l c i n e d petroleum coke to graphite, showed that the more ordered, higher temperature materials showed weaker adhesion bonds. Chaklader et a l . [33] found that briquette strength was lower where a higher rank coal-char material was used. The measured decrease i n RVM content with r i s i n g carbonization temperature may be considered as a concurrent phenomenon with t h i s ordering process. I t i s therefore p o s s i b l e that a part of the measured decrease i n briquette strength with increasing charring temperature (figures 2.1a, b and c) may have been due to a decrease i n char-binder i n t e r f a c i a l strength. 4.3.2 Binder C h a r a c t e r i s t i c s To eliminate char-property e f f e c t s , b r i q u e t t i n g mixtures of a s i n g l e char and d i f f e r e n t binders can be considered. In these cases, - 84 -v a r i a t i o n s i n UCS are associated with v a r i a t i o n s i n binder p r o p e r t i e s . For aggregate A3 (500°C char), briquette strength decreases for binders i n the order Bl - B2 - B3. For the higher temperature aggregates, A2 (625°C) and A l (750°C), there i s l i t t l e or no s i g n i f i c a n t v a r i a t i o n i n briquette strength from one binder to another. The lower temperature char case (mixtures 7, 8 and 9) i s considered f i r s t . As noted e a r l i e r , f a i l u r e occurred p r i m a r i l y at the char-binder i n t e r f a c e . With the char-type held constant, t h i s i n d i c a t e s two p o s s i b l e explanations for the measured v a r i a t i o n i n composite strength: the bond strength across the char-binder i n t e r f a c e v a r i e s with the binder used; and/or the extent of penetration i n t o the a v a i l a b l e pore structure v a r i e s with binder due to d i f f e r e n c e s i n f l u i d i t y . Although the former cannot be measured d i r e c t l y , a c o r r e l a t i o n i s seen between binder f l u i d i t y and b r i q u e t t e strength. By comparing Table IV and f i g u r e s 21a, b and c, i t i s seen that the decrease i n f l u i d i t y from binder B l to B3 p a r a l l e l s the decrease i n briquette strength. With lower f l u i d i t y , B3 was l e s s able to penetrate the a v a i l a b l e pore structure of the char, r e s u l t i n g i n l e s s binder-char i n t e r l o c k i n g and i n t e r f a c i a l area and a lower gross composite strength. The exception of binder B2 to t h i s pattern i s explained by the f a c t that a higher b r i q u e t t i n g pressure was used with those mixtures con-t a i n i n g B2. At the nominal b r i q u e t t i n g pressure of 10 MPa, i t was not p o s s i b l e to produce a coherent briquette using t h i s binder. This conclusion i s consistent with the r e s u l t s found with the higher temperature char mixtures. With v i r t u a l l y no large pore structure a v a i l a b l e f o r binder penetration, b r i q u e t t e strength i s seen to become r e l a t i v e l y i n s e n s i t i v e to binder f l u i d i t y . In f a c t , the average briquette - 85 -strength appears to be approximately the same for a l l binders with the higher temperature chars. The strength of briquettes made with aggre-gate A l (750°C) can be i n t e r p r e t e d as r e f l e c t i n g the strength of the char-binder i n t e r f a c i a l bond, which does not appear to be s i g n i f i c a n t l y d i f f e r e n t f or the binders i n v e s t i g a t e d . Hence i t appears that, for a given char, i t i s p r i m a r i l y binder phase d i s t r i b u t i o n that influences composite strength. In t h i s regard, the r e s u l t s of the wetting studies c a r r i e d out i n d i c a t e that there i s no d i f f i c u l t y i n a t t a i n i n g e quilibrium wetting con-d i t i o n s of the system. The benzene-soluble extracts of each binder were seen to wet the amorphous carbon substrate almost immediately upon melt-ing and the SRC p i t c h was seen to a t t a i n a c o n s i s t e n t l y low equilibrium contact angle on each of the chars studied. I t can therefore be s a i d that, thermodynamically, the system favours penetration of the aggregate by the binder phase and that i t i s the k i n e t i c s of the spreading and pene-t r a t i o n of the binder phase which c o n t r o l the aggregate-binder d i s t r i b u -t i o n . This leads to a further i n d i c a t i o n of the r e l a t i v e importance of the two c h a r - c h a r a c t e r i s t i c e f f e c t s on strength discussed e a r l i e r . Given that the primary e f f e c t of varying the binder i s to change the extent of binder penetration i n t o the a v a i l a b l e pore structure, the amount by which the slope (Astrength/Acharring temperature) of f i g u r e 21a (binder Bl) exceeds that of f i g u r e 21c (binder B3)can be associated with the d i f f e r -ence i n i n t e r f a c i a l strength from binder to binder. From t h i s i t appears that briquette strength i n t h i s study i s more s e n s i t i v e to the a v a i l a b i l i t y of char pore structure than to v a r i a t i o n i n char-binder i n t e r f a c i a l strength - 86 -from char to char. However, the c o n t r i b u t i o n of the l a t t e r e f f e c t cannot be e n t i r e l y r u l e d out because of the l i m i t e d range of binders investigated and the f a c t that a l l the char types were produced from a s i n g l e c o a l . I t should be further pointed out that two e f f e c t s may be respons-i b l e f o r the way i n which an increase i n char p o r o s i t y can lead to an increase i n briquette strength. The increased p o r o s i t y may simply provide greater contact area of the char-binder i n t e r f a c e or i t may cause fra c t u r e to occur through the binder phase. Binder f a i l u r e has been observed (figure 24b) and t h i s would i n d i c a t e some c o n t r i b u t i o n of binder strength to briquette strength. Although i t has not been p o s s i b l e to c l e a r l y determine the extent of these two co n t r i b u t i o n s , the comparative insen-s i t i v i t y of briquette strength to the binder involved implies t h i s c o n t r i b u t i o n was small i n the present i n v e s t i g a t i o n . I t i s suggested that future studies be c a r r i e d out to i n v e s t i ^ gate the strength p r o p e r t i e s of formcoke at b l a s t furnace temperatures. An associated problem i s the manner i n which the green briquette strength i n v e s t i g a t e d i n t h i s work i s a f f e c t e d by the po s t - b r i q u e t t i n g high temperature carbonization step. I t should be recognized that l a r g e r sample s i z e s w i l l be required to improve the s t a t i s t i c a l r e l i a b i l i t y of studies of t h i s type and that a wider range of aggregates and binders should be considered. I t may also be us e f u l to i n v e s t i g a t e the t h i r d stage of compaction i n d e t a i l . - 87 -5. CONCLUSIONS 1. The hot compaction behaviour of the char-binder systems studied has been shown to be influenced by the p o r o s i t y of the aggregate-char phase and the f l u i d i t y of the binder-coal phase. Char p o r o s i t y a f f e c t s the amount of t o t a l compaction necessary to a t t a i n a given briquette bulk density, greater p o r o s i t y r e q u i r i n g more compaction. This p o r o s i t y i s eliminated by penetration of the binder phase and by p l a s t i c deformation due to the applied s t r e s s . Binder f l u i d i t y influences compaction v i s c o s i t y during the second stage of compaction (that associated with p a r t i c l e flow), higher binder f l u i d i t y leading to lower compaction v i s c o s i t y . This i s due to the r e l a t i v e ease with which the binder phase can penetrate and surround the aggregate p a r t i c l e s . 2. The bulk density of the formcoke product i s a f f e c t e d by the t o t a l compaction attained during the b r i q u e t t i n g process. For the materials used i n t h i s study, i t i s found that compactions from 15 to 25% produce briquettes from 60 to 70% bulk density and that the s e n s i t i v i t y of bulk density to compaction appears to be independent of the binder phase. I t i s p redicted that compaction of 40% would be necessary to a t t a i n 100% bulk density for the char material without s i g n i f i c a n t p o r o s i t y . This value increases with in t r o d u c t i o n of p o r o s i t y i n the char phase. 3. Briquette f a i l u r e was found to occur p r i m a r i l y at the char-binder i n t e r f a c e with occasional binder phase f r a c t u r e . This i n d i c a t e s that the - 88 -strength of the briquette systems studied i s independent of the strength of the char phase. Briquette strength i s a f f e c t e d by char p o r o s i t y and by the bond strength across the char-binder i n t e r f a c e , the former e f f e c t predominating i n the systems studied. Higher char p o r o s i t y leads to higher strength by increasing aggregate-binder i n t e r f a c i a l area and by promoting p h y s i c a l i n t e r l o c k i n g of the two phases. The e f f e c t of i n t e r f a c i a l bond strength i s i n f e r r e d from the r e s u l t s of other authors, which i n d i c a t e that use of char material carbonized at higher temperatures leads to lower i n t e r f a c i a l strength. Higher binder f l u i d i t y increases composite strength by allowing more extensive penetration of the char pore structure by the binder phase. 4. The CCWL hot compaction model f o r char-binder coal systems was found to be a p p l i c a b l e to the systems i n v e s t i g a t e d . A s o l u t i o n of the mechanical analog of t h i s model was developed and shown to be compatible with the o r i g i n a l s o l u t i o n . A nalysis of the experimental compaction curves using t h i s model r e i n f o r c e s the assumption of non-interaction of compaction mechanisms and the a s s o c i a t i o n of the second and t h i r d compaction stages with p a r t i c l e flow and p l a s t i c deformation, r e s p e c t i v e l y . 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"Characterization of Formed Cokes and Factors A f f e c t i n g Form-Coking," Third Annual  Report, EMR Research Agreement No. 2239-2-68-77, Dept. Energy, Mines and Resources, Ottawa, 1978. 34. Loison, R., Peytavy, A., Boyer, A.F., G r i l l o t , R. "The P l a s t i c Properties of Coal," Chemistry of Coal U t i l i z a t i o n , Supplementary Volume, Chpt. 4, 184, J . Wiley and Sons, 1963. 35.. Howard, H.C. " P y r o l y t i c Reactions of Coal," Chemistry of Coal U t i l i z a t i o n , Supplementary Volume, Chpt. 9, 392, J . Wiley and Sons, 1963. 36. Wenzel, R.N. "Resistance of S o l i d Surfaces to Wetting By Water," I n d u s t r i a l and Engineering Chemistry, 28, No. 8,. 988-994, 1936. 37. Good-, R.J. "A Thermodynamic Derivation of Wenzel's Modification of Young's Equation f o r Contact Angles; Together With a Theory of Hysteresis," J. Am. Chem. Soc. 74_, 5041-2, 1952. 38. Adam, N.K. " P r i n c i p l e s of Penetration of Liquids Into S o l i d s , " Discussions of the Faraday Society, 3_, 5-11, 1948. 39. Sukhorukov, I.F., Babenko, E.M., Gavrina, M.V. "Surface Phenomena At the Carbonaceous M a t e r i a l - Coal Tar P i t c h Boundary," Tsvetnye  Mettaly, 38, 70-73, 1965. 40. Agrawal, D.P., Berkowitz N. "On the Wetting of Carbon Surfaces By Carbonaceous Binders," Proceedings of the 9th B i e n n i a l B r i q u e t t i n g  Conference, 104-114, 1965. 41. Dmitrieva, G.V., Rhys, M.A., Smirnova A.S., Shuraeva, E.A. "Wet t a b i l i t y and Impregnability of Carbon Materials By Coal Tar P i t c h , " International Chemical Engineering, 7_, No. 2, 252-255, 1967. 42. Vetyukov, M.M., Ofit s e r o v , V.F.. Chalik, S.M., Sv e r d l i n , V.A., N i k u l i n , V.N. "Wetting of Carbon E l e c t r o n Materials By Coal-Tar Pitches," Tsvetnye Mettally, 47, 23-26, 1974. 43. D e l l , M.B., Peterson, R.W. "Wettability of Petroleum Cokes By P i t c h , " I n d u s t r i a l and Engineering Chemistry Prod. Res, and Dev., 9_, No. 2, 190-194, 1970. - 92 -44. Lahaye, J . , Auber, J.-P. "Interaction Between a Coke and a T a r — 1. Influence of the Surface Chemical Functions of Coke. 2. Limit of Tar Penetration i n Coke Poro s i t y , " F u e l, 56, 185-191, 1977. 45. Greenhalgh, E., Moyse, M.E., "Contact Angle of P i t c h On Carbon Surfaces," Third Conference on I n d u s t r i a l Carbons and Graphite, 539-549, 1971. 46. F i t z g e r a l d , D. " V i s c o e l a s t i c Properties of Coal During Carboniza-t i o n , " Fuel, 36, 389-394, 1957. 47. Habberjam, G.M. "Compaction Phenomena In Char B r i q u e t t i n g , " B r i t i s h Journal of Applied Physics, 15, 1233-1242, 1964. 48. Jayasinghe, S.S., P i l p e l , N. "The Cohesive Properties of Coal When Heated," Journal of the I n s t i t u t e of Fuel, 51-55, February, 1970. 49. Bradford, D.J., Doyle, A.J., Fahy, B.A., Greenhalgh, E. " D i s t r i b u t i o n of P i t c h Binder In Binder/Coke Mixtures," Third Conference On  I n d u s t r i a l Carbons and Graphite, London, SCI, 528-538, 1971. 50. C o l l e t t , G.W., Rand, B. "Rheological Investigation of Coal-Tar P i t c h During I t s Transformation To Mesophase," Fuel, 57, 162-170, 1978. 51. Chow, C , Chaklader, A.CD. , Warren, I.H., Leeder, W.R. "Hot Com-paction Behaviour of Char/Binder Coal Systems," Fuel, 57, 387-393, 1978. 52. Bradbeer, R.S., Chaklader, A.CD., "Reactive Hot Pressing of C o l l o i d a l Boehemite," M a t e r i a l Science Research, 6_, 395, 1973. 53. Krokosky, E. "Behaviour of Time-Dependent Composite Ma t e r i a l s , " Modern Composite M a t e r i a l s , Broutman and Krock (ed.), Chpt. 4, 122, Addison-Wesley, 1967. 54. a. McGeary, R.K. Journal of the American Ceramic Society, 44, 513, 1961. b. Smith, W.O., Foote, F.D. Phys. Rev., 34, 1272, 1929. 55. Ryshkewitch, E. "Compression Strength of Porous Sintered Alumina and Z i r c o n i a , " Journal of the American Ceramic Society, 36, 65, 1953. 56. Knudsen, F.P. Journal of the American Ceramic Society, 45, 94, 1962. 57. Walpole, R.E., Myers, R.H. P r o b a b i l i t y and S t a t i s t i c s f o r Engineers  and S c i e n t i s t s , 292, Macmillan, 1972. - 93 -7. APPENDICES APPENDIX A. Der i v a t i o n of CCWL Model For Hot Compaction  of Char/Binder Systems The system considered i s one whose response to an input stress i s time varying. The s t r e s s input i s considered to be characterized by a step function, u^_(t), such that a = a u (t) o t where: u (t) 0 for t 0 1 f o r t 0 + The response of the system to t h i s s t r e s s input i s described by the r e l a t i o n s h i p : e = k (1 - A e " a t - B e ~ B t - Ce~ y t) (1) or, introducing the t r a n s f e r function, x, e = x a Therefore, the problem i s to determine the t r a n s f e r function f or the system concerned. The response of a l i n e a r system to a u n i t pulse input, U q ( t ) i s the d e r i v a t i v e of the system response to a u n i t step function, u t ( t ) . The d e r i v a t i v e of equation (1) i s -at -8t -Yt i = kAae + kB6e + kCYe - 94 -and a Laplace transformation ^ J ( E ) > can be applied 4/ \ x = E = 7 (e) = s + a s + B S + Y where: a = kAa x = transform operator b = kBB c = key ij; = str e s s i n transform space = 1 s = independent v a r i a b l e i n the Laplace space, [F(t)]-»-f(s By considering the boundary c o n d i t i o n : A + B + C = 1, x = a(s+g) (S+Y) + b(s+q)(S+Y) + c (s+B)(s+q) (s+a)(s+B)(S+Y) 2 = s [a+b+c] + s[a(B+Y) + b(Y+a) + c(B+ct)] + kaBY 3 2 s + s [CX+8+Y] + s[aB+BY+Yc] + aBY It can be seen from the definitions of a, b and c that: kaBY = a 3 Y + bya + cBa And by introducing the following terms: M = a + B + Y P = a + b + c Q = a(B+Y) + b(Y+a) + c(B+a) R = kaBY N = (aB + BY + Yd) T = aBY equation (2) can be rewritten: 2 x = E = s P + sO + R 3 2 s + S M + S N + T The d i f f e r e n t i a l equation which describes the stress-strain response of the system i s given by the inverse of the Laplace transform, i e . : e + M E + Ne + T E = Pa + Qo + Ro - 95 -An e l e c t r i c a l analog may be obtained by re p l a c i n g e and a by q and v r e s p e c t i v e l y (q = / i d t ) : i + Mi + Ni + T / i d t = Pv + Qv + Rv with the corresponding time d e r i v a t i v e : i + Mi + Ni + T i = Pv + Qv + Rv . In the Laplace transform space, 3 2 I = s P + S Q + sR V 3 2 S + S M + S N + T (4) Of the various c i r c u i t s possessing the co r r e c t t r a n s f e r function, the simplest i s symmetric coupling: whose mechanical equivalent, with C -«->- _1_ and R«-»- n, i s : M M, M„ M. 77777777777777777 - 96 -Subs t i t u t i n g the mechanical equivalents i n t o the s o l u t i o n of equation (4) shows the constants of equation (3) to be given by: M = M 3 + M2 N = M M M 1 2 3 V2*3 n l ^2 T = M 1 M 2 M 3 V2 n3 P = 1 1 — + + Q = i + — M. 1 1 — + — R = MjM2 + M 2 M 3 + M 3 M i Since M, N, T, P Q and R are determined from experiment, the values of M^, M 2 ' M 3 ' r | l ' r i 2 ' ^3 C a n k 6 f ° u n i ^ ky solv i n g these s i x equations simultaneously. - 97 -APPENDIX B. NORMALIZED COMPACTION CURVES Strain (mm/mm) H-c ro 03 I Ln 03 O H-o a o o 3 XI P> n rt H-o 3 o c < > vQ (D ^ cn n> ai rt n> o Ml s CD rt cr H o ro 3 H- r—' N (t> CL 0) rt H 3* a> 3 3 * - 86 -0.4 T i m e (min) Figure B-2: Compaction Curves of Mixture 2 (Binder Bl - Aggregate Carbonized at 625°C) I 2 3 Time (min) Figure B-3 Compaction Curves of Mixture 3 (Binder Bl - Aggregate Carbonized at 500°C) 0.4 E 0.3 E E ^0.2 c o in 0.1 t—* o Time (min) Figure B-4: Compaction Curves of Mixture 4 (Binder B2 - Aggregate Carbonized at 750°C) Figure B-5• Compaction Curves of Mixture 5 (Binder B2 - Aggregate carbonized at 625°C char) 0 I 2 3 Time (min) Figure B-6: Compaction Curves of Mixture 7 (Binder B3 - Aggregate Carbonized at 750°C) 0.4 0 o Time (min) Figure B-7; Compaction Curves of Mixture B (Binder B3 - Aggregate Carbonized at 625°C) S t ra in (mm/mm) H-i Q C M ro CD i CO Cu — r t CD H-Ln 3 O QJ O CD o K. O — CO LO O O 3 XI a> o rt o 3 n c M < CD cn 3s in iO M i Q o CU M i r t CD S o Cu M cr o 3 H-N ro CD 3 3 * - SOT -- 106 -APPENDIX C. GLOSSARY OF TERMS Aggregate - that p o r t i o n of a b r i q u e t t i n g mixture which acts e f f e c t i v e l y as an i n e r t f i l l e r — made by low temperature carbonization of a non-caking c o a l . Anthracite - highest rank coal; l e s s than 14% v o l a t i l e matter; NCB group 100; I n t e r n a t i o n a l C l a s s i f i c a t i o n code 100. Binder - that p o r t i o n of a b r i q u e t t i n g mixture which takes on f l u i d p r o p e r t i e s under compacting conditions and forms the matrix of the f i n a l product. Bituminous - coals which demonstrate agglomerating properties; ranging from low (14-22%) to medium (22-30%) to high (above 30%) v o l a t i l e . By-Product Oven - the standard conventional coking oven; t y p i c a l modern dimensions: 6 m high x 15 m long x 0.5 m wide; heating i s from external f l u e s , preventing d i l u t i o n of gases produced. Caking Coal - a coal i n which an accumulation of the p l a s t i c phase i s ob-served during p y r o l y s i s . Char - the s o l i d product of low temperature (450°C-700°c) carbonization of c o a l . Coal Extr a c t - that f r a c t i o n of a coal which i s soluble i n an organic solvent, t y p i c a l l y chloroform, pyridene or benzene. Coke - the s o l i d product of high temperature carbonization of a coking coal conforming to a set of i n d u s t r i a l chemical and p h y s i c a l standards. Coking Coal - a caking coal which f a l l s within a range of acceptable p l a s t i c and chemical properties or one which does when blended with other c o a l s . Formcoke - the product of any of a number of a l t e r n a t i v e processes for producing b l a s t furnace coke from t r a d i t i o n a l l y unacceptable coals; u s u a l l y i n the form of b r i q u e t t e s . G i e s e l e r Plastometer - an apparatus i n which a constant torque i s applied to a s t i r r e r rod imbedded i n the coal sample. Rotation of the s t i r r e r i s p o s s i b l e only when the coal i s i n i t s p l a s t i c s t a t e . The amount of r o t a t i o n i s measured with increasing tempera-ture and used to i n d i c a t e sample f l u i d i t y parameters. - 107 -K e l v i n Element - v i s c o e l a s t i c model element c o n s i s t i n g of a spring and dashpot connected i n p a r a l l e l . Mesophase (Metaplast) - intermediate f l u i d phase of coal formed as a r e s u l t of depolymerization of the coal macromolecule. Proximate Analysis - an a n a l y s i s which breaks coal composition i n t o four p a r t s : moisture, v o l a t i l e matter, f i x e d carbon, and ash; covered by ASTM D 271 68. Rank - the order of a coal on any of a number of c l a s s f i c a t i o n systems; c l a s s f i c a t i o n s are based on v o l a t i l e matter content, caking prop e r t i e s and c a l o r i f i c value. Generally, rank increases with f i x e d carbon and decreasing v o l a t i l e matter. Ruhr Dilatometer - a device which follows the length of a coal sample under s p e c i f i c heating conditions; the sample may be brought q u i c k l y to temperature and the c o n t r a c t i o n / d i l a t a t i o n followed with time or i t may be heated slowly, both procedures y i e l d i n g a number of r h e o l o g i c a l parameters. Sub-bituminous - coals which do not demonstrate agglomerating p r o p e r t i e s , but with v o l a t i l e matter contents greater than 33%; c l a s s i f i -c a t i o n i s by c a l o r i f i c value: A - 10500-11500 BTU l b - 1 (24.4-26.8 MJkg ) B - 9500-10500 BTU l b - 1 (22.1-24.4 MJkg - 1) C - 8300-9500 BTU l b - 1 (19.3-22.1 MJkg"l) Tumbler Index - value a r r i v e d at by r o t a t i n g a c l o s e l y s i z e d coal sample i n a drum a s p e c i f i e d number of revolutions and s i z i n g the degrad-ed product to give percentage passing or standing on a given screen. V o l a t i l e Matter Content - the weight f r a c t i o n of a moisture-free coal which i s l o s t as gaseous products of p y r o l y s i s ; these t y p i c a l l y i n -clude combustible (hydrogen, carbon monoxide, methane and other hydrocarbons) and incombustible (carbon dioxide and water vapour) gases and t a r vapours. 

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