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Factors affecting the mechanical properties of blast furnace coke Grant, Michael G. K. 1986

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FACTORS AFFECTING THE MECHANICAL PROPERTIES OF BLAST FURNACE COKE by MR. MICHAEL G.K. GRANT, B.A.SC. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Metals and Materials Engineering We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December 1986 © Mr. Michael G.K. Grant, B.A.Sc, 1986 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British 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 or her 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 British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) Abstract The influence of coking conditions, with respect to position in a commercial coke-oven, on the mechanical behaviour of blast furnace coke has been studied. This involved the determination of density, porosity, the characterization of microstructure and assessing the influence of a l l three on the compressive strength of coke. The plastic flow properties were also investigated at temperatures greater than 1000°C. Three coke batches, originating in a 5m commercial coke-oven at three different positions with respect to height (0.8m, 3.3m and 5m below the coal line), along with three coke batches produced in a 460mm test-oven, were supplied by Energy, Mines and Resources (CANMET) in Ottawa. A- warf coke batch was also provided as a control sample. Several hundred core-drilled specimens (*1.3cm diameter and 1.3cm length) were produced from the seven coke batches. The bulk density of each cylindrical coke specimen was determined. Also, a detailed microstructural analysis, using a Leitz Image Analyzer, of the flat faces of the coke cylinders was performed to quantitatively characterize the pore and c e l l wall size, and the pore geometry. The compressive strength of each coke cylinder was determined both at ambient temperature and at 1400°C. In addition, the plastic flow behaviour of the commercially produced coke batches was studied. Results indicate that the coke product bulk density was affected by the coke-oven pressure (static load). Studies of the test-oven coke batches revealed that coke bulk density increased with higher oven presure. Furthermore, the pore size was found to be larger for cokes produced at lower oven pressures. The c e l l wall size did not appear to be affected by coke-oven pressure. The bulk density of the commercially produced samples increased with depth below the coal line. This was attributed to a higher temperature and static load that existed at the bottom of the battery. The pore size was larger in cokes extracted from higher regions. No correlation of c e l l wall size with depth below the coal line was found. However, an oven size effect on the pore and wall size was noticed. Both the pore and wall size was smaller in the test-oven coke batches. The compressive strength of coke was higher in batches subjected to higher coke-oven pressures. Similarly,' the compressive strength of commercial coke batches was higher for coke batches extracted from regions near the sole of the coke-oven, than that for coke batches extracted from higher regions. It was concluded that high oven pressures resulted in cokes exhibiting a lower porosity and small pores which had the combined effect of producing stronger coke. Coke strength was generally shown to be higher at 1400°C than at room temperature. The test-oven cokes were always stronger than cokes produced in the 5m commercial coke-oven. i i i Constant load tests revealed that coke exhibited plastic flow behaviour at temperatures above 1000°C. The time dependent strain data was described using an interactive-double-Kelvin element visco-elastic model. Acknowledgements The author wishes to express his gratitude to his research supervisor, Dr. A.CD. Chaklader for his advice and encouragement during this project. Thanks are also extended to the faculty, staff and fellow graduate students. The assistance of J. Arblaster and A. Darnbrough are especially appreciated. Financial assistance from the Energy, Mines and Resources (CANMET) in Ottawa, is gratefully acknowleged. v Table of Contents Abstract i i Acknowledgements v Table of Contents vi List of Tables x List of Figures x i i List of Abbreviations and Symbols xvi 1 . Introduction 1 1.1 Role of Coke in the Blast Furnace 3 1.1.1 Coke as a Fuel 4 1.1.2 Coke as a Reducing Agent 4 1.1.3 Coke as a Physical Support for the Burden ..6 1.2 Coke Characteristics necessary for the Blast Furnace 10 1.3 Production of Blast Furnace Coke 13 1.3.1 Coal Characteristics 13 1.3.1.1 Coal Chemistry 13 1.3.1.2 Coal Rank .....13 1.3.1.3 Coal Minerals 15 1.3.1.4 Reflectance 17 1.3.2 Coal Pyrolysis 18 1.3.2.1 Pyrolysis Reaction 18 1.3.2.2 Fluidity during Pyrolysis 19 1.3.3 Conventional Cokemaking Process 20 1.4 Testing Methods for Coke 24 1.4.1 Porosity and True Specific Gravity 24 1.4.2 Tumbler Tests 27 1.4.3 Reactivity Tests 29 vi 1.4.4 Coke Strength after Gasification 30 1.4.5 Shatter Tests 31 1.5 Previous Strength Tests and Analysis 32 1.5.1 High Temperature Tumbler Tests 32 1.5.2 Fundamental Strength Tests 33 1.5.2.1 Ambient Temperature Tests 33 1.5.2.2 High Temperature Tests 36 1.5.3 Pore Structure and Coke Strength 37 1.5.4 Coke Mechanical Properties in Relation to Position in Coke Oven 41 1.6 Objectives of this Research Project 41 2. Experimental ...44 2.1 Sample Identification 48 2.1.1 Positioning of Coke Lumps 48 2.1.2 Selection of Test Lumps 51 2.1.3 Sectioning of Test Lumps 51 2.1.4 Core D r i l l i n g of Coke Specimens 53 2.2 Preparation of Test Specimens 53 2.3 Bulk Density Measurement 53 2.4 Test Sample Selection 55 2.5 Microstructural Analysis 55 2.5.1 Photomicrograph Preparation 57 2.5.2 Image Analysis 59 2.5.3 True Density 61 2.6 Mechanical Tests 62 2.6.1 Compression Test Apparatus 63 2.6.2 Procedure of Testing 63 2.6.3 Experimental Parameters 65 v i i 2.7 Graphitization Tests 65 Results and Analysis 67 3.1 General Comments 67 3.2 Density 67 3.2.1 Bulk Density 67 3.2.2 True Density 72 3.3 Microstructure 72 3.3.1 Sensitivity 74 3.3.2 Edge Effects 77 3.3.3 Cell Wall Size 79 3.3.4 Pore Size and Geometry 81 3.3.5 Representation of Pore Size and Geometry ..83 3.4 Compressive Strength of Coke Batches ....85 3.4.1 Coke Strength as a Function of Variables ..85 3.4.2 Bulk Density 85 3.4.3 Porosity 87 3.4.4 Microstructure 91 3.4.4.1 Cell Wall Size 91 3.4.4.2 Pore Size 94 3.4.4.3 Number of Pores 94 3.4.4.4 Pore Perimeter 100 3.4.5 Stat i s t i c a l Aspects of Coke Fracture 100 3.4.6 Theoretical Aspects of Coke Fracture 111 3.4.7 Stability and Hardness 115 3.5 High Temperature Creep 119 3.5.1 Graphitization 119 3.5.2 Isothermal Constant Load Tests 120 v i i i 3.5.3 Creep Behaviour of Coke 126 3.5.4 V i s c o - e l a s t i c Models ..127 3.5.5 A n a l y s i s of Creep Data 127 D i s c u s s i o n 137 4.1 Bulk D e n s i t y ........138 4.1.1 R e l i a b i l i t y of Bulk D e n s i t y R e s u l t s 138 4.1.2 Oven P r e s s u r e 1 139 4.1.3 True D e n s i t y 141 4.2 M i c r o s t r u c t u r e ..143 4.3 E f f e c t of Coking c o n d i t i o n s on M i c r o s t r u c t u r e ..145 4.3.1 C e l l Wall Thickness 145 4.3.2 Pore S i z e and Geometry .........146 4.3.3 Summary of M i c r o s t r u c t u r a l Dependence on Coking C o n d i t i o n s ...152 4.4 Coke Str e n g t h 1 52 4.4.1 E f f e c t of Temperature 153 4.4.2 E f f e c t of M i c r o s t r u c t u r e 154 4.5 Creep of Coke 157 C o n c l u s i o n 160 References 163 ix List of Tables Nominal Cokemaking Capacity of the Western World in 1981 Typical Properties of Blast Furnace Coke ASTM, JIS and ISO Standard Drum Tests Coking Conditions For Test Oven Cokes Characteristics of the As-received Test Oven Cokes As-received Algoma Coke Properties Values of Fixed Compression Test Properties Estimated Variation of Mean Bulk Density and Oven Wall Pressure with Depth Below Coal Line Variation of True Density as a Function of Coking Conditions Variation of the Arithmetic Mean Values of the Pore-parameters Measured using the Leitz TAS PLUS Image Analyzer for CPR-264 as a Function of the Number of Fields Analyzed Comparison of Porosity Values as Measured Using the Image Analyzer with Those Values Obtained From Pynometry The Effect of Edges on Microstructural Parameters Values of CPR-264 Comparison of Cell Wall Size Values For Different Cokes Mean and Standard Deviation of the Coke Porous Parameters for a l l Seven Coke Batches 82 XV Cummulative 80% Finer Values of the Seven Pore Parameters for the Seven Coke Batches 84 XVI Mean Compressive Strength Values for the Seven Coke Batches at Ambient Temperature and at 1400°C 86 XVII Parameters for the Equation: a=-ne+b 92 XVIII Parameters for the Equation: 0=ooexp(-be) 92 XIX Weibull Modulus Values of Seven Coke Batches at Ambient Temperature and at 1400°C 110 XX Calculated C r i t i c a l Stress Intensity Factors Using a Multiple Flaw Model 114 XXI Conditions for Creep Tests 123 XXII Probability that the Assumption of Differing Bulk Densities is Erroneous for Comparisons Between Coke Batches 140 XXIII Cell Wall Size Values as a Function of Coking Conditions 147 XXIV Pore Size and Geometry Values as a Function of Coking 148 Conditions xi List of Figures Figure Page 1 Schematic Representation of the Ironmaking Blast Furnace 5 2 Effect of Coke Size and Uniformity on Bulk Resistance to Air Flow 8 3 Schematic Representation of the Layers of Coke, Ore and Flux as They Occur in the Blast Furnace 9 4 Schematic Representation of the Coalification Process 14 5 Origins of Different Coal Macerals 16 6 ASTM Free Swelling Index 21 7a Schematic Representation of the Charge in a Conventional Coke-oven at Some Intermediate Stage During the Heat 22 7b Coke Lumps as They Would Be Positioned in a Coke-Oven Battery 23 7c Arrangement of Typical Commercial Coke-Oven Batteries 25 7d Cross-section of a Typical Coke-oven Battery (showing the r a i l car) 26 8 The Schematic Representation of the Diametral Compression Test 34 9 The Origin and Corresponding ASTM Properties of the Algoma Coke Batches 46 10 The Positions of Coke Lumps as They Were Assumed to be in the Coke-oven 49 11 An Example of Coke Lumps Selected for Further Study 52 x i i 12 Schematic Representation of the Procedure for Sectioning Coke Lumps 54 13 Schematic Representation of the Leitz TAS PLUS Image Analyzer 56 14 A Typical Coke Microstructure 58 15 A Flow Chart of the Software Used to Quantify Coke Microstructure 60 16 A Schematic Representation of the Compressive Testing Apparatus 64 17 The Distribution of Bulk Density Values for a l l Seven Coke Batches 69 18a A Summary of Mean Bulk Density Values For A l l Seven Coke Batches 70 18b Bulk Density versus Estimated Oven Pressure 71 19a Mean Compressive Strength vs Mean Bulk Density 88 19b Compressive Strength vs Bulk Density for CPR-264 at Room Temperature 89 20 Mean Compressive Strength vs Coke Porosity 90 21a Mean Compressive Strength vs Cell Wall Size 93 21b Mean Compressive Strength vs Pore Area 95 21c Mean Compressive Strength vs Pore Equivalent Diameter 96 21d Mean Compressive Strength vs Pore Mean Chord Length 97 21e Mean Compressive Strength vs Pore Maximum Feret's Diameter 98 21f Mean Compressive Strength vs Number of Pores Per Field 99 x i i i Mean Compressive Strength vs Pore Perimeter Weibull Distribution Plot of CPR-264 Mean Compressive Strength Values Weibull Distribution Plot of CPR-265 Mean Compressive Strength Values Weibull Distribution Plot of CPR-266 Mean Compressive Strength Values Weibull Distribution Plot of CPR-267 Mean Compressive Strength Values Weibull Distribution Plot of CPR-268 Mean Compressive Strength Values Weibull Distribution Plot of CPR-269 Mean Compressive Strength Values Weibull Distribution Plot of CPR-270 Mean Compressive Strength Values Mean Compressive Strength vs {Fmax-0'5exp[-2(Fmax/Fmin)0«5ep]} Calculated C r i t i c a l Stress Intensity Factors Using Ambient Temperature Compressive Strength Data Calculated C r i t i c a l Stress Intensity Factors Using Compressive Strength Data Obtained at 1400°C Stability and Hardness vs Mean Compressive Strength Normalized Creep Curves Produced at 1500°C and 6.0Mpa Creep of CPR-270 at 1500°C Under Varying Conditions of Applied Stress xiv Creep of CPR-270 at 9.29Mpa Under Varying Conditions of Temperature Single-Kelvin Unit Interactive-double-Kelvin Unit Three-non-interactive-Kelvin Units Variation in Visco-elastic Model Mechanical Parameters as a Function of Temperature For CPR-270 Variation in Visco-elastic Model Mechanical Parameters as a Function of Applied Pressure for CPR-270 Temperature Histories in the Algoma No.9 Coke-oven Battery at the Top, Middle and Sole Positions Pore Size as a Function of Estimated Coking Temperature Pore Size as a Function of Estimated Oven Pressure Cell Wall Size and Number of Pores Per Field vs Pore Size xv List of Abbreviations and Symbols A Fraction of the total creep attributed to the f i r s t exponent of the experimental creep equation a Crack half-length ASTM American Standard for Testing Materials A.T. Ambient Temperature B Fraction of the total creep attributed to the second exponent of the experimental creep equation BCRA British Carbonization Research Association CSR Coke Strength after Reaction in 100% C02 CSR* Coke Strength after Reaction in 10% C0 2 ECE European Commission for Europe Fmax Maximum Feret's diameter Fmin Minimum Feret's diameter H.V. High volatile bituminous coal ISO International Standards Organization JIS Japanese Industrial Standards K Total creep in visco-elastic model (at t=») K J C Calculated c r i t i c a l stress intensity factors L.V. Low volatile bituminous coal L.V.D.T. Linear Voltage Diferential Transformer m Weibull modulus M^  Spring constant in the i-th spring of the viso-elastic model xvi M.V. Medium Volatile Bituminous Coal P Oven-pressure P(a) Probability of failure s Laplace operator t Time U c(t) Step function of input stress Vf Volume fraction of porosity a,P Exponention constants of the f i r s t and second terms of creep equation e Strain «p Percent porosity determined using pynometric and bulk density values «I Percent porosity determined using the image analyzer rji Viscosity of the i-th dashpot in the visco-elastic model Pb Bulk Density Mpb Mean bulk density o-pb Standard deviation of bulk density values a Applied Stress o0 Nominal applied stress xvi i 1. INTRODUCTION The strength properties of coke from ambient temperature to * 1800°C is very important for efficient blast furnace operations. This research program was designed to determine the strength properties of coke both at ambient and high temperatures and then to correlate the strength properties with other coke parameters. The coke samples used in this study were supplied by CANMET, Ottawa, but were prepared both in a conventional coke-oven at the Algoma Steel Corporation at Sault Ste. Marie, Ontario and in a test-oven at the Energy Research Laboratories in Ottawa. However, before going into details of the research project, i t w i l l be worthwhile to outline some background on: 1. the importance and functions of coke, .2. how i t is produced, 3. significant properties normally determined for evaluating coke characteristics, and 4. performance. It is important to know some of these aspects as the relevance of this research project will be apparent with this background. Coke is a carbonaceous product made from a special type of coal known as metallurgical coal. Table I shows the nominal coke-making capacity of the Western World in 1981 (1). At least ninety-two percent of coke produced in the Western World in 1981 was from carbonizing coal and seventy-eight percent of that was used for the steel 1 2 COUNTRY Steel Industry Coal Industry Independent Total mmt(l) % mmt(l) % mmrtl) mmt(l) Algeria 1. 20 100.0 _ _ 1.20 Argentina 1. 28 too, .0 - - - 1.28 Australia 5. ,20 95.0 0.20 it.O 0.0K 1.0 i.kk Austria 2. 35 100. ,0 - 2.35 Belgium 6. SO 97, .2 - 0.20 2.8 7.00 Brazil <t. 18 96 ,5 • 0.15 3.5 <».33 Canada 6. . U 98 .2 0.11 1.8 _ 6.25 Chile 0. .32 100, .0 - - - 0.32 Colombia 0. 36 100, .0 - - - 0.36 Egypt 1. ,00 100, .0 - - 1.00 France 5. 35 i»6 .6 6. 12 53.<» - - 11.47 Germany F.R. 7. ,88 2,5 .5 23.09 7k. 5 - - 30.97 Greece 0. .50 100, .0 _ 0.50 India 15. .09 100, .0 - - - 15.09 Iran 0. ,«0 100, .0 - - - o.«o Italy 8. .18 80. ,2 _ 2.03 19.8 10.21 Japan kit, .80 79, .0 2.70 0.7 9.20 16.3 56.70 Korea.Republic of it. ,50 98, .0 0.10 2.0 - - ».60 Morocco 0. .48 100.0 0.48 Mexico 3. .12 90. .7 - 0.32 9.3 3.kit Netherlands 2. 2ft 76, .7 - 0.68 23.3 2.92 Norway - . - 0.38 100.0 0.38 Pakistan 0. .75 100. ,0 - - - 0.75 Peru 0. .65 100. ,0 - - - 0.65 Portugal 0. .51 100. .0 - - _ 0.51 South Africa 5. .60 92. .7 O.kk 7.3 - - 6.04 Spain k. .88 100.0 - - - 4.88 Sweden 1. 20 100. .0 _ _ 1.20 Taiwan 0. ,91 82. 3 - 3.19 17.7 1.10 Turkey It. .76 100. .0 - - - ft.76 United Kingdom 7. 2 3 (7) 6 Y ,7 3.32 . 30.2 *. 1 11.00 United States 52 . <»0 ( 2> 86. 9 0.70*"" 1.2 7 .20 U > 11.9 60.30 Yugoslavia 3. 58 100. ,0 - - - 3.58 Zimbabwe 0. .1)0 100. ,0 - - - 0.30 T O T A L 20<t. 1» 78. 0 36.78 11.0 20.SI 8.0 261.76 (I (Millions of metric tons (2) Blast Furnace coke producers (3) Plant using Beehive Ovens (4) Found'-y coke producers Table I. Nominal Cokemaking Capacity of the Western World in 1981 (ref. 1). 3 industry. As indicated in Table I, the vast majority of coke was produced for the steel industry where i t was used to make pig iron in the blast furnace. In pig iron production, coke, ore and fluxes are the ingredients charged into a blast furnace. Coke consumption in the blast furnace is more than 500kg per ton of pig iron (2). A smaller type of blast furnace is also normally used in producing lead from the roasted lead oxide. However, lower temperatures (^1200°C in the hearth) and a higher COj/CO ratio in the gas in the lead blast furnace, mean that coke consumption is considerably less in these furnaces, than in the iron blast furnace. The coke used in blast furnaces is derived from blends of low, medium and high volatile bituminous coals. Such coals which are used to produce blast furnace coke are often termed "metallurgical coals" and only metallurgical coals are suitable for blast furnace coke production. 1.1 ROLE OF COKE IN THE BLAST FURNACE Coke has three important functions: 1. provides fuel for combustion and supplies heat to the charge, 2. supplies reductant gases for smelting the iron ore, and 3. physically supports the burden while i t descends down the blast furnace shaft. 1.1.1 COKE AS A FUEL Figure 1 is a schematic representation of the ironmaking blast furnace (2). Shown are the temperatures varying with height in the shaft and the principle reactions that occur at each level. At the tuyere level, hot blast air between 900 and 1000°C is injected and this reacts with the coke to produce mainly carbon dioxide. The temperature in this region is between 1800 and 2000°C at which point, the only solid phase present is the coke. The carbon dioxide penetrates to the center of the furnace forming carbon monoxide via the Boudouard reaction. The heat involved from burning coke at the tuyeres is needed to achieve the minimum temperature required in this region (~1800°C). This temperature at the tuyere is necessary to ensure that the burden higher up in the furnace is heated sufficiently. 1.1.2 COKE AS A REDUCING AGENT Both carbon dioxide and carbon monoxide are produced above the tuyere region of the blast furnace. The carbon monoxide is the reducing agent needed to reduce the iron ore. The blast furnace can be divided into two separate reduction zones represented by the dotted line in Figure 1: the direct reduction zone (the lower half of the furnace) and the indirect reduction zone (the upper half). In the direct reduction zone, metal oxides are reduced by carbon monoxide to form carbon dioxide, however,the Boudouard reaction is also occuring to produce carbon monoxide and 5 Ore + coke • fluxes n r Top gas Stack 1000° C Bosh , > 1800° C , Tuyeres l o o o o o o o l Hearth I 1400° C 3 F e 2 0 j • C O 2 F e j 0 4 + C O F e 3 0 4 • C O = 3FeO + C 0 2 2CO = C 0 2 + C FeO + C O Fe + C 0 2 CaCOj = CaO + C O j C O j + C = 2CO ( FeO + C O = Fe • C O j f MnO + C = Mn + C O S i 0 2 • 2C = & + 2 C O C O j + C = 2CO \ c + o2 = C O j / S + CaO + C = CaS + C O C = c Slag Hot metal F i g u r e 1. Schematic R e p r e s e n t a t i o n B l a s t Furnace ( r e f . 2 ) . of the Ironmaking 6 consuming coke at the same time. For example: FeO + CO = Fe + C 0 2 C 0 2 + C = 2 C O (A) FeO + C = Fe + CO The Boudouard reaction in [A] controls the CO2/CO ratio so the net reaction results in the consumption of coke. The indirect reduction zone is characterized by the consumption of carbon monoxide to produce carbon dioxide. This zone exists above the 900°C isotherm (dotted line in Figure 1). Below 900°C , the Boudouard reaction is sluggish and therefore provides no significant contribution to the reduction mechanisms. In the upper regions of the stack Fe 2 0 2 and F e 3 0 4 are reduced to FeO. It is interesting to note that a "sooting" reaction also occurs in the upper regions of the furnace forming carbon dioxide and carbon from carbon monoxide. This is undesirable because i t consumes carbon monoxide needed for the the reduction of the ore, thereby increasing the need for a higher coke consumption rate. 1.1.3 COKE AS A PHYSICAL SUPPORT FOR THE BURDEN Perhaps the most important function of coke in the iron blast furnace is its a b i l i t y to physically support the burden as i t descends down the shaft. The blast furnace is a counter current reactor where, as mentioned before, hot reducing gases formed at the tuyere region must find their 7 way to the top of the shaft while the burden progresses downward. An evenly distributed upward gas flow is necessary for stable blast furnace operation. This ensures an evenly reduced burden as well as even heat exchange between the hot gas and the descending burden. Figure 2 demonstrates how gas flow is impeded by a decrease in the harmonic mean size of coke lumps (3). It i s , therefore, desirable to use a coke which degrades as l i t t l e as possible during i t s descent. This is particularly important in the lower half of the furnace where, between 1100°C and 1400°C, the burden fuses and melts leaving coke as the only solid phase present. Figure 3 shows in some detail how the burden behaves in the blast furnace. The burden in the melting zone fuses into s t r a t i f i e d layers of coke, ore, and flux (4). The gases moving upward rely on the coke layers (coke s l i t s ) to allow these to escape into the lumpy zone at the top half of the furnace. Closer to the raceway, the phases present are liquid metal, slag, and coke. In this region, the coke lumps are supporting the entire burden while allowing hot metal to percolate to the hearth and the combustion gases to penetrate to the center of the furnace. Coke fines near the raceway w i l l prevent adequate penetration of gases to the center of the furnace, therefore forcing the gases upward near the wall and trapping molten metal and slag from flowing downward resulting, in insufficient tapping volume and increasing tapping frequency. Coke fines suspended in 8 HARMONIC MEAN SIZE Sh(mm) F I G U R E 2 . E F F E C T O F C O K E S I Z E A N D U N I F O R M I T Y O N B U L K R E S I S T A N C E TO A I R F L O W 9 C O K E Figure 3. Schematic Representation of Layers of Coke, Ore, and Flux as They Occur in The Blast Furnace (ref. 4 ) . 10 the slag and liquid metal can result in uneven tapping. It is apparent that the blast furnace w i l l operate more effic i e n t l y i f the coke lumps maintain their integrity as much as possible while physically supporting the burden and being attacked by carbon dioxide and alkali vapours. For this reason, coke must be physically strong without losing its strength while being subjected to the harsh conditions in the lower part of the furnace. 1.2 COKE CHARACTERISTICS NECESSARY FOR THE BLAST FURNACE The carbon content of coke is the primary agent, in addition to the small concentrations of hydrogen, for the reduction of iron ore. Therefore, i t is desirable to reduce the impurity components in the coke such as moisture, ash, and sulfur as much as possible. A good coke should be reactive enough to supply the reducing gas required for a particular ore (5). It is generally better, however, to have an ore which is very reactive and a coke which has low reactivity. This lowers the coke consumption by reducing the effect of the Boudouard reaction. A coke with low reactivity is more likely to maintain i t s mechanical strength in the direct reduction zone of the blast furnace. The impurities in the coke have detrimental effects other than lowering the coke-carbon content. A low sulfur content is prefered since this impurity generally ends up in the pig iron which makes refining to steel more d i f f i c u l t . Moisture escaping from the coke in the upper regions of the 11 furnace w i l l disturb the reducing gases as they pass upward through the burden. Perhaps the most detrimental impurity in coke is ash which has two negative effects on the performance of coke: catalyzing the Boudouard reaction and reacting internally with the carbon in the matrix. The presence of minerals is known to affect the reactivity of coke to C0 2 (6). In these investigations various ash components commonly found in coal were separately added to a very low ash coal (less than 1.0%) to determine their effect on reactivity with CO^. The results show that reactivity increased with the following order of effect: K & Na > Ca > Fe > Mg > (Si, Al, Ti) The alk a l i oxides greatly increased the reactivity of coke with S i , Al, and Ti having a much lower effect. Ash-carbon reactions were found to occur at temperatures between 1600 and 1800°C. It was shown that a l l the oxides in the minerals (ash) contained in the coke were reduced producing carbon monoxide as a product (6). Silicon was found to react most readily with the carbon producing silicon carbide and carbon monoxide. These reactions a l l contributed to carbon loss thereby weakening the coke matrix. Typical blast furnace coke characteristics are given in Table II (5). The f i r s t two columns are strength indices from drum tests. These indices w i l l be explained later. Coke characteristics must be closely controlled for optimum blast furnace operation. 12 Metallurgical Coke Property I > go mm II > 60 mm III > 40 mm Tumbler strength (%)* 85 85 85 Abradability, M„ (%)" 6 6 6 Moisture (% of raw product) 1.5 +0.5 2.5 ±0.5 3.5 ±0.5 Ash (%) 8.5 +0.3 8.5 ±0.3 8.5 ±0.3 Sulfur (% of dry product) 0.9 ±0.03 0.9 ±0.03 0.9 ±0.03 Volatile matter (% of dry < 1 < 1 < 1 product) Alkali (% of dry product)* 0.26 0.26 0.26 Bulk density (kg/m*) 438 • According to DIN 51 717, conforming with ISO/R—1967. * Content of Na,0 and K,0 determined in different plants. Table II. Typical Properties of Blast Furnace Coke (ref. 5 ) . 13 1.3 PRODUCTION OF BLAST FURNACE COKE Since the major fraction of coke produced in the world is made from metallurgical coal, i t is important to know the coal characteristics suitable for coke-making. 1.3.1 COAL CHARACTERISTICS 1.3.1.1 Coal Chemistry Coal is composed of organic minerals containing carbon, hydrogen, oxygen, and small amounts of sulfur and nitrogen. Studies have shown that coal is made up of both aromatic and aliphatic molecules (7). Aromatic molecules consist of rings of six carbon atoms joined to form a hexagonal shape - the simplest type being benzene. Aliphatic molecules are chains of hydro-carbons - the simplest form is methane. There is a definite relationship between carbon content of the coal and the relative amounts of aliphatic and aromatic molecules. The carbon content of the coal increases with the aromatic/aliphatic ratio. 1.3.1.2 Coal Rank There are several classifications of coal depending on their origins. Figure 4 shows the stages of metamorphosis to form various types of coal (5). The metamorphosis of coal increases with increasing time and pressure inside the earth. The term most often used to represent the degree of metamorphosis is rank, which 1 4 ANTHRACITE F i g u r e 4. Schematic Representation Process (ref. 5 ) . of the Coali f ication 15 increases with increasing metamorphic change. In other words, anthracite has a high rank, whereas lignite is a low rank coal. In general, rank increases with increasing carbon content, decreasing volatile matter content, decreasing moisture content, and increasing c a l o r i f i c value. To form a high rank coal (low volatile matter content), extreme depths and times of the order of 150 million years are needed. The best coals for making metallurgical coke are generally a combination of high volatile coal for low bulk density , and a medium or low volatile coke for high strength (5). 1.3.1.3 Coal Minerals Coal is not a homogeneous substance, but is comprised of metamorphized organic minerals (from different sources) called macerals. The origins of different macerals are listed in Figure 5 (5). During metamorphosis, the chemical composition and the percent aromatic structures changes but the proportion of each maceral in the coal change very l i t t l e . The most common maceral shown in Figure 5 is v i t r i n i t e (5). This along with resinite and exinite are termed "reactive" due to their a b i l i t y to become plastic and release volatiles during pyrolysis. V i t r i n i t e makes up 75 to 80 percent of coals in the bituminous range. Reactive macerals are noted for their high H/C ratio. The other important macerals are called "inerts" -which are high carbon macerals that release small 16 Source Material "Wood" Waxy Exines Resins Inorganic Ions Mineral Grains Peat Swamp Humified — "Decomposed"-"Charred" -Incorporated Incorporated -"Chelated" -Precipitated -Coal Components Vitrinite ( *» Micrinite fc Fusinite r — Exinite r „ . / ^, fc. Resmite Incorporated -fc- Minerals -»> Minerals Figure 5 . Origins of Different Coal Macerals (ref. 5) 17 amounts of volatile compounds and do not become plastic during pyrolysis. Macerals such as fusinite and micrinite are classi f i e d under the name inertinite. These originate from charred or decomposed plant matters. 1.3.1.4 Reflectance Coal scientists have found that a l l macerals exhibit distinguishing optical properties when viewed under an optical microscope. Each maceral reflects and absorbs light differently. A special microscope is used in which the light reflected off the specimens can go either to the eye-piece or to a photomultiplier tube (8,9). The incident light is polarized at an angle of 45° and a f i l t e r with a peak transmittance of 546 nm (monochromatic green) is used at any position along the path of light. A drop of immersion o i l is added on the sample to provide more contrast between the various phases. The percent reflectance (in oil) of each phase is measured by the photomultiplier and is based on glass standards. Since 75-80% of the coal is v i t r i n i t e , i t is possible to represent the rank of the coal by its v i t r i n i t e reflectance as described above. In general, the higher rank materials have higher reflectance values. The best coking coal blends have reflectance between 1.3 and 1.5 (percent) in o i l . 18 1.3.2 COAL PYROLYSIS Coal p y r o l y s i s (or carbonization) i s the term used to describe the transformation of coal to coke. As coal i s heated in the absence of oxygen, many reactions occur up to 1000°C. Between 110°C and 150°C, absorbed moisture i s released. Gases, such as H2S, are released between 150°C and 350°C. The coal i t s e l f begins to decompose between 300°C and 350°C. Above 350°C, thermal decomposition becomes rapid with the release of primary v o l a t i l e gases and the s o l i d mass begins to l i q u e f y (mesophase). Between 500°C and 1000°C the s o l i d mass undergoes a polymerization reaction which causes the l i q u e f i e d coal to s o l i d i f y , when densifcation and shrinkage occur simultaneously with the release of secondary v o l a t i l e components such as methane and carbon monoxide. At 1000°C, the coking process i s v i r t u a l l y complete with the product being coke containing mineral matter (ash). 1.3.2.1 Pyrolysis Reaction The p y r o l y s i s reaction has been represented by three s i m p l i f i e d consecutive reactions (10): K, P—\>M (B) K 2 M •R + G, (C) K, R — > S + G 2 (D) where P denotes the o r i g i n a l c o a l , M denotes the 19 mesophase (or liquid phase) , R is the semi-coke, S is the f i n a l coke product, G, and G 2 are the primary and secondary volatile gases, respectively. These reactions have been treated as being f i r s t order, but in reality they are probably more complex since each reaction [B-D] represents a large number of separate reaction steps (7). It has been shown that the relative magnitude of each of these reaction rates determines whether or not a coal is suitable to make metallurgical coke (10). A good coal should be fusable (good bonding characteristics) and this is determined by the amount of mesophase produced and by i t s f l u i d i t y . If there is an accumulation of mesophase, the coal is said to be caking and w i l l produce coke. This will occur i f K^  is much larger than K2. If K2 is larger than K,, a char (non-fusible product) wi l l be formed. It is important to realize that a l l metallurgical coals are caking coals but not a l l caking coals w i l l produce metallurgical coke. 1.3.2.2 Fluidity during Pyrolysis Fluidity is commonly measured using a Gieseler plastometer (11). It essentially consists of a st i r r e r , which has an electric motor, and a hysteresis brake controlling the torque. Each rotation is counted photo-electrically and the f l u i d i t y is measured by the di a l divisions per minute (100 dial divisions per 20 revolution). Another method of assessing the mesophase is the Free Swelling Index. The Free Swelling Index is measured by placing one gram of coal in a s i l i c a crucible and visually comparing the coke button produced afterward with a set of standards (see Figure 6) (39). Good metallurgical coal has a Free Swelling Index between five and seven. 1.3.3 CONVENTIONAL COKEMAKING PROCESS Figure 7a is a schematic representation of the charge in a conventional coke-oven at some intermediate stage during the heat. The coke-oven consists of a vertical retort approximately 6m high, 15m long, and 0.5m wide. Coal is charged into the chamber between two externally heated refractory walls. The charge mass closest to the wall experiences a higher temperature than at the center. Near the wall, the mass softens and then s o l i d i f i e s into coke where the temperature is above 600°C. The plastic zone moves toward the center of the coke-oven as the charge heats up and the particulate coal near the center liquefies and decomposes. The large fissures shown in Figure 7a are a result of differential contraction during resolidification of the charge near the oven wall. The final coke product is a highly porous, carbonaceous product containing large fissures throughout. Figure 7b shows the arrangement of coke lumps with respect to their position in a coke- oven • 350* C above 5 0 0 ° C i - 5 0 0 ° C Coke Material less than 350 # C Coal particles Intcrstfctt Refractory wot Figure 7a. Coke Ptoitk etoge Ptxtkulou Cfcarft coal centra Schematic Representation of the Charge in a Conventional Coke-oven at some Intermediate Stage During the Heat (ref 52). Figure 7b. Coke Lumps as They Would Be Positioned in a Coke-oven B a t t e r y ( r e f . 4 ) . 24 battery(arrangements were suggested by CANMET). The coking chambers are arranged in batteries as illustrated in Figure 7c. Between two oven walls there is a flue chamber which heats two oven walls simultaneously. The flue is often fueled by the volatile gases from the coking process i t s e l f . When the charge has reached the final temperature (1000-1200°C ), the mass is "pushed" out of the slot into r a i l cars and subsequently water quenched (see Figure 7d). The coking process from charging to pushing can take up to twenty one hours. 1.4 TESTING METHODS FOR COKE Three characteristics of coke are normally used to predict its performance in the blast furnace: 1. porosity and true specific gravity 2. reactivity to carbon dioxide, and 3. tumbler strength tests. Porosity is studied due to its contribution to the weakening of coke and to coke reactivity. Reactivity assessment is important for minimizing the coke consumption rate. Tumbler tests are used as general information on the ab i l i t y of coke to resist volumetric breakage and abrasion. 1.4.1 POROSITY AND TRUE SPECIFIC GRAVITY In North America, coke porosity and true specific gravity are normally assessed in accordance with ASTM designation Dl67-73 (12). The apparent specific gravity is F i g u r e 7d . Cross-section of a T y p i c a l Coke-oven Battery (showing the r a i l car) (ref. 4 ) . 27 f i r s t measured by a water displacement method. The true specific gravity is determined using pycnometry. The porosity is then calculated using the measured true and apparent specific gravity values. Some workers have begun to explore ways of measuring porosity using computerized image analyzers. Such methods rely on the subjective way the operator determines the level of greyness (explained later) the pore features appear on the computer monitor. Since this work is s t i l l in the development stage, no standard has yet been presented. 1.4.2 TUMBLER TESTS Tumbler testing of coke is the most common method used in industry for determining coke quality. There are many accepted standards for measuring the drum strength of coke. Leeder, Price, and Gransden have made comparisons of different drum standards as given in Table III (13). From Table III, i t is apparent that the four standards shown, vary significantly from one another. Variations include coke lump size, sample weight, drum dimensions, drum rotational speed, duration of the test, moisture content of the coke, and the number and widths of the l i f t s . L i f t s are slats in the drum which l i f t the coke lumps upward with the revolution of the drum until the angle of the l i f t s is large enough to cause lumps to f a l l . These variations have made i t d i f f i c u l t to make correlations between the different standard drum tests, and such correlations are unreliable Test Designation Test Method Strength Indices Coke Drum Dimensions Drum RPM Test Duration (min) Total Rev 8 Breakage Abrasion Size Weight Moisture Width Dlam L i f t e r s Width ASTM JIS Drua Test Mlcua* IRSID* D 294-64 2151-72 R 556 R 1881 3x2 In. +5 Omm +60mm +20mm 22 lb 10 kg 50 kg (Not 50 kg dry dry <5 .e half m: <3 18 In. 1.5m 1.0m .cum t c 1.0m 36 In. 1.5m 1.0m ! S t us< 1.0m 2 6 4 >s half i 4 2 In. 250mm 100mm :he wei 100mm 24±1 15 25±1 ght ar 25±1 58 2 10 4 d a drum 20 1400 30 150 100 0.5m : 500 Z>1" S t a b i l i t y Factor Z>15mm-DI Z>15nm-DI Z>40am, M*»o n width) X>40,20mm I«»0.l20 Z> V Hardness Factor 30 15 150 15 Z<10ssi KlOmm IlO *Round-hole sieves used - other tests use square-hole sieves Table III. ASTM, JIS, and ISO Standard Coke Drum Tests (ref. 1 3 ) . w 29 (13). Two types of breakage mechanisms occur during drum tests: volume breakage and surface abrasion. Peirce and Horton (14,15) and Peirce et al (16) have shown that the volume breakage is associated with the propagation of large fissures and that surface abrasion is due to localized stress at contact points between the lumps. Considering this, as well as observing Table III, i t is obvious that the ASTM drum test relies more on abrasion than on impact to degrade coke since i t only has two small l i f t s . In contrast, the JIS, Micum and IRID standards specify six or four wide l i f t s respectively, which i n f l i c t more impact breakage. 1.4.3 REACTIVITY TESTS There has been no ASTM standard proposed to date for determining the reactivity of coke. Three methods are worth noting: the ECE test (European Commision for Europe) (6), the NSC test (Nippon Steel Corporation) (17), and a test used by Jeulin et al (18). The ECE test requires 7 grams of -3+1mm particles to be reacted in pure C0 2 for thirty minutes. The reactivity is expressed as a reaction rate constant by monitoring the C0 2 in the off gas. The NSC test uses 200 grams of +l9-21mm coke reacted in pure C0 2 for 120 minutes at 1100°C. The reactivity is calculated as the weight present lost during the test. 30 Jeulin et al (18) used -30+20mm coke lumps which were gasified in a gas mixture containing 10% C02, 20% CO, 10% H2, and 60% N 2 . The sample was heated to 650°C under nitrogen and from 650 to 1200°C at 200°C per hour in the reactive gas. The sample weight was continuously monitored during the experiment. The relevant parameter studied was the gasification threshold temperature. This is defined as the temperature where the rate of weight loss due to gasification becomes significant. The importance of the gasification threshold temperature stems from the fact that the Boudouard reaction consumes heat. Therefore, a low gasification threshold w i l l decrease the length of indirect reduction zone of the blast furnace and a shift in i t s thermal profile will occur. The ECE and the NSC tests are similar in principle but the ECE test uses a small coke particle size. The use of larger particle sizes in the NSC test distinguishes mass transfer rates between cokes as well as reactivity of the solid i t s e l f . The method used by Jeulin et a l (18) helps to predict the effect the coke wi l l have on the thermal profile of the blast furnace. 1 .4.4 COKE STRENGTH AFTER GASIFICATION A test which is gaining increased popularity is the coke strength after reaction test (CSR). This involves measuring the strength of -21+19mm coke after i t has been gasified at 1100°C for two hours in 100% carbon dioxide. 31 Nippon Steel Corporation employs an I-drum for 600 revolutions at 20 revolutions per minute and this has become the most commonly used CSR test. The CSR test has been employed by Fellows and Wilmers (17), and by BCRA workers (19). Both groups found approximately negative linear relationships between reactivity and post reaction strength. Brown et al (6) found that the CSR test exaggerates the extent of reaction * occuring in the blast furnace. So the CSR test was developed using 10% C0 2 and 90% N 2 which more closely represented the extent of reaction of tuyere coke. It was * found that l i t t l e correlation existed between CSR and CSR tests. The results show a general weakening of coke after gasification. 1.4.5 SHATTER TESTS The drop shatter test for coke is perhaps the most primitive of the coke quality assessment techniques. The ASTM standard (20) for measuring the shatter strength of coke requires that f i f t y pounds of coke be dropped from a height of six feet . The minus half inch is removed from the sample and the procedure is repeated three more times. A sieve analysis is then performed on the coke sample. The shatter test has the disadvantage that i t only measures the coke's resistance to impact and not abrasion. 32 1.5 PREVIOUS STRENGTH TESTS AND ANALYSIS With the realization that the quality of coke affects the operation of the blast furnace , coke researchers have been turning towards a more fundamental approach to assessing coke quality. High temperature drum tests are being used to see how impact and abrasion resistance are affected by high temperatures. Also, since drum tests induce very complex stress states, more simple states of stress such as uniaxial compressive and tensile stresses are being used to characterize coke strength. Microstructural techniques have recently been employed to determine the effect of microstructural variations on the strength of coke. 1.5.1 HIGH TEMPERATURE TUMBLER TESTS A comprehensive review made by Reeve, Price, and Gransden (21) produced several conclusions about the tumbler strength of coke at high temperatures: coke strength is lower at high temperatures than at ambient temperature, there is no correlation between cold and hot strength tests, and the higher the cold Micum index value, the lower the reduction in hot Micum values at elevated temperatures. Patrick and Wilkinson (22) and other workers at the BCRA (19) found a general decrease in the drum strength indices as temperature increased. This suggests that resistance to volume and surface breakage is reduced as temperature of testing is increased. 33 1.5.2 FUNDAMENTAL STRENGTH TESTS The nature of stresses induced in coke during tumbler tests is d i f f i c u l t to assess. Therefore, more fundamental test methods such as uniaxial compressive and tensile strength tests are being more frequently used. Both these tests on coke specimens have been performed at ambient and elevated temperatures. 1.5.2.1 Ambient Temperature Tests Perhaps the f i r s t group to consider testing coke on a fundamental basis was Holoway and Squarcy (23). They performed compressive strength tests on 1.27cm cubical specimens and obtained strengths ranging from 4.41MPa to 31.83MPa for a l l cokes tested. However, only three tests were performed on each coke specimen, thereby raising doubt as to the credibility of these values for representing the whole population. The BCRA researchers (19) performed tensile strength tests on 16 industrial cokes using the diametral compression test. This test is shown schematically in Figure 8a. The tensile stress is calculated using the equation: at = 2w/(rrDt) (1 ) where w is the applied load, D is the specimen diameter, and t is the thickness of the disk. Fifty specimens were used for each coke where mean tensile strengths ranged 34 lot (cl w The Schematic Representation of the Diametral Compression Test Showing: a. The Disc Sample b. The Typical Fracture Pattern, and c. The Stress Field Within The Disc (ref. 25). 35 between 1.62 and 6.0MPa. Similar tests were conducted by Patrick and Wilkinson (22) yielding nearly the same results. Klose and Suginobe (24) measured tensile strengths of industrial cokes also using diametral compression. Strengths ranged between 2.0 and 7.0MPa. There was a definite strength dependence on specimen size with larger samples tending towards being weaker. No s t a t i s t i c a l evidence showing an effect of cross-head speed (ie. strain rate) was found. The diametral testing method has two serious drawbacks which affect the practicality of i t s use for assessing coke quality. The theory from which equation 1 was derived, states that for the method to yield the correct tensile strength, the material being tested must be homogeneous and elastic (24). It is well known that coke is a very heterogeneous material. Samples which do not exhibit the fracture pattern in Figure 8b, can not be included in the test results. The stress fi e l d shows that the compressive stress at the points of loading tends toward in f i n i t y (Figure 8c), and that an uneven tensile stress f i e l d is induced in the specimen. Furthermore, the tensile strength is measured by the fracture stress at the point of loading. In most cases, small tributary cracks occur at the point of loading which raises question as to the mode of fracture (25). Klose and Suginobe (24) found that only 25% of the coke discs tested produced the fracture pattern in Figure 8b. 36 Therefore, a very large number of tests are needed for s t a t i s t i c a l r e l i a b i l i t y of the data. Also, by discarding 75% of the tests made, there wi l l be a bias toward the homogeneous samples which may not be representative of the coke as a whole. 1.5.2.2 High Temperature Tests High temperature compressive and tensile strengths of coke have been less widely studied than tests at ambient temperature due to the inherent d i f f i c u l t y of performing the large number of tests needed to characterize coke. The earliest work encountered was that of Holoway and Squarcy (23). Compression tests were performed on 0.635cm (edge length) cubes at 1650°C. They found that the compressive strength was higher than that observed at room temperature. However, only three to six samples were tested for each coke on a different testing machine than the Baldwin tensile machine used at room temperature. The test sample size was smaller than those tested at room temperature. This is not a good practice since coke has been shown to exhibit a strength dependence on specimen size (24). Patrick and Wilkinson (22), BCRA workers (19), and Jeulin et al (18), a l l observed a strength increase as temperature increased. They attributed this behaviour to the possibility that coke continued to graphitize after exceeding the final coking temperature. This is in accordance with dilatometer tests performed by Golezka and Roberts 37 (26,27), Golezka et a l (3), and Fellows and Willmers (17). These workers have shown that coke expands upon heating to the final coking temperature and subsequently contracts as graphitization continues above this temperature. 1.5.3 PORE STRUCTURE AND COKE STRENGTH With the avai l a b i l i t y of automated microscopes with attached image analytical f a c i l i t i e s , a new technique of coke quality assessment is being developed. This technique can quickly examine the pore structure of a coke sample, and with the aid of computerized image processing, can st a t i s t i c a l l y quantify such features as pore size, shape, area fractioning, and c e l l wall thickness. Klose and Suginobe (24) used a Leitz TAS system to determine the porosity and maximum pore size by examining half of each fractured tensile specimen. They found that coke tensile strength correlated well with the porosity and maximum pore size according to the semi-empirical relation: a = (K//dp)[exp(-Be)] (2) where dp is the maximum pore size, e is the porosity (pore fraction), and K and B are empirical constants. This equation is a modified form of porosity dependence on strength equation developed by Knudsen (28) for porous alumina: 38 o = a0 exp (-be) (3) where o0 is the strength of the non-porous body. The term K/Vdp is derived from the G r i f f i t h crack theory. Pitt and Rumsey (30) claimed to have estimated the strength of the non-porous coke by extrapolation of strength-porosity relationships developed by previous workers. These values differed by an order of magnitude depending on the equation used, with values ranging between 16MPa and 524MPa for one type of coke tested. They also attempted to measure the strength of non-porous coke by crushing 0.13mm coke particles between two steel plates. The values obtained were within the range of values calculated by extrapolation, but were determined on the assumption that the coke particles cruched were spherical. Jeulin et al (18) used a texture analyser to measure pore volume fraction and specific pore surface area. They found that the best correlation between tensile strength and pore volume fraction was obeyed by equation 2. However, their derivation of this equation was more theoretically based than that of Klose and Suginobe (24). The most detailed studies made to date were those of Patrick et al (31-36). These studies included a very detailed analysis of the porous structure of coke by employing a Quantimet 720 Image Analyzer. The analysis was divided into two sections: f i e l d data (values describing each f i e l d of view as a whole), and feature data (individual 39 features were examined separately). In an earlier work (32), pore and wall sizes were assessed by horizontal chord sizing. The analysis also included the number of pores per f i e l d . Porosity was determined as the area fraction of the pores. It was found that thirty to forty fields of view were needed to characterize the pore structure of a particular coke type. Most pores were found to occur in the size range 1 urn to 120Aim and a definite positive skewness was observed in the pore size distribution. Tensile strengths of some cokes were found to f i t the Knudsen equation (28), but variations from the relationship were found to occur when a variety of coke types were tested (33). Patrick (31), and Patrick and Stacey (35), found definite trends between coke structure and coking conditions. They concluded that preheating coal charges produced a greater number of smaller pores and decreased porosity which resulted in a stronger coke. Additions of up to 30% of petroleum coke decreased the porosity, increased the wall thickness, and increased the number of smaller pores which had the combined effect of increasing tensile strength. The strength.was found to be related to pore and wall size by equation 4: a N = 105 (W/P2) - K (4) where o is the tensile strength, N is the number of pores per f i e l d , W is the wall size, P is the pore size, and K is 40 a constant. It is clear that equation 4 has no theoretical basis, and is therefore not reliable for predicting the strength of cokes outside the range of cokes tested. Patrick and Stacey (35) and other workers at the BCRA (34) both realized the inadequacy of equation 4 and derived another equation which is more theoretically based. They utiliz e d an equation of the form proposed by Jeulin et al (18), and by Klose and Suginobe (24) which is similar to equation 2. The crack length (dp in equation 2) was assumed to be the mean maximum Feret's diameter of the pores. The Quantimet 720 Image Analyzer used is capable of measuring the maximum and minimum caliper dimensions (Feret's diameter) of a feature (in this case individual pores). The constant b (in equation 2) was assumed (34,35) to be the stress concentration factor: 2( Fmax / Fmin ) 0 , 5 of an e l i p t i c a l crack perpendicular to the applied stress. The resulting equation used was then: a = 450 (Fmax)"0*5 exp[ -2( Fmax / Fmin ) 0 , 5 p ] (5) where Fmax and Fmin are the mean maximum and mean minimum Feret's diameters respectively, and p is the porosity. This equation was found to predict the strength of various cokes with a standard error of =«10%. It should be noted that the feature analysis was only performed on pores greater than 2 0.015mm in area, and is therefore, biased toward the larger 41 pores. This is theoretically valid since larger flaws (pores) are considered to be the origin of most failures. 1.5.4 COKE MECHANICAL PROPERTIES IN RELATION TO POSITION IN  COKE OVEN Nishioka and Yoshida ( 3 7 ) performed experiments to evaluate the effect of position with respect to the oven width on coke mechanical properties. The coke was made in a 250kg coke-oven with a width of 0.450m. Temperature measurements were made at ten positions across the oven width. The general trend was a decrease in tensile strength of coke toward the center of the coke-oven. Porosity reached a minimum at the 1/4 width position in the oven, but increased to a maximum at the oven center. There appears to be no information available on the effect of coke quality as a function of position for commercial coke-ovens. Furthermore, no information on the coke quality as a function of vertical position in the coke-oven has been reported in the literature. 1.6 OBJECTIVES OF THIS RESEARCH PROJECT It is clear from the discussion above that coke is a very complex material. This complexity and diversity arise for several reasons: 1. Blendings of High Volatile,Medium Volatile and Low Volatile coals are used, which determine the pore volume content and pore size distributions. 42 2. Cokes at the bottom of the coke-oven batteries are denser (less porous) because of the static load (burden) present during coking on these cokes. 3. Cokes nearer the refractory walls are subjected to higher temperatures than those which are present at the center of the battery. Thus, a large number of coke samples for commercial cokes have to be tested to get a representive value of any property. The properties of warf coke (aggregated commercial coke) vary widely from sample to sample. On the other hand, most coke quality studies have been performed to date on "test-oven" cokes which generally exhibit relatively uniform properties throughout. In this research program, experiments have been performed to f u l f i l the following objectives: 1. The effect of coking conditions on the microstructure of coke was assessed using an image analyzer. The analysis was performed on industrial coke batches extracted from three different heights in an Algoma 5m coke-oven. These microstructural characteristics were compared with those obtained from coke batches produced using the same coal blend, but under various conditions in a 460mm test-oven at CANMET Laboratories in Ottawa. 2. The mean strength values of the aforementioned seven coke batches were determined both at ambient temperature and at 1400°C. These results were treated statisticaly and were correlated with microstructural parameters and 43 coking conditions. 3. The plastic behavior of some coke samples have also been qualitatively evaluated as this property may have significant influence on the coke performance in a blast furnace. 2. EXPERIMENTAL The coke samples used in this study were supplied by the Energy Research Laboratory (CANMET) in Ottawa, Ontario. The samples originated from two sources: CANMET-a 460mm test-oven, and an Algoma 5m industrial oven at Sault Ste. Marie. The test-oven coke was produced from the same coal blend used in the 5m oven at Algoma. The blend consisted of 35% low volatile (LV) coal and 65% high volatile (HV) coal. The conditions of coking are listed in Table IV for the test-oven cokes. Sample CPR-264 CPR-265 CPR-266 Coal Moisture, % 5.9 4.1 1.2 Coal Bulk Density, gm/cm 0.578 0.863 0.976 Coking Time, h 17.2 17.15 18.1 Oven Wall Pressure, kPa 3.2 5.9 17.8 Table IV. Coking Conditions For Test-oven Cokes The as-received test-oven cokes have the standard ASTM characteristics as shown in Table V (values determined at CANMET) (38). The coke samples produced in the 5m industrial oven were sampled from 44 45 Sample CPR-264 CPR-265 CPR-266 Apparent Specific Gravity 0.781 0.903 0.936 Stability 59.5 59.2 57.4 Hardness 69.3 70.2 71.1 Table V. Characteristics of the As-received Test-oven Cokes. steel mesh cages (28x28x35.6cm) that had been lowered into the oven through the center charging hole as illustrated in Figure 9a(38). On the f i r s t day of testing, a basket was lowered to the bottom of the empty coke-oven before charging. On the second day, charging was interrupted after the oven was half f u l l and another basket was placed in the oven. Finally, on the third day, a third basket was placed in the coke-oven after 80% charging. Figures 9(b-d) show the variation in coke properties as a function of height as measured by CANMET. The as-received coke properties are summarized in Table VI. The sample CPR-270 is wharf coke (ie. from the same battery in which cages were positioned). Wharf coke is refered to as the representative 46 a ) Approximate Location of Cages b) 73-7 0-798 634 0-888 64*3 0-947 %*90mm Coka,Wharf - 68 2 Apparant Specific Gravity,Wharf - 0-C) 46 4 37-2 48 2 63-3 S3 6 71-2 ASTM Stability .Wharf - 58 5 ASTM Hafdness.Wharf - 69 8 d) 34 6 43-1 32 3 48-9 28 3 59-5 Reactivity, Wharf - 23-7 Stranffh aftar Reaction,Wharf . 64-Figure 9. The Origin and Corresponding ASTM Properties of the Algoma Coke Batches. 47 Sample CPR -267 CPR -268 CPR -269 CPR -270 Apparent Specific Gravity 0. 947 0. 880 0. 798 0. 888 ASTM Stability 53 .6 48 .2 46 .4 58 .5 ASTM Hardness 71 .2 63 .3 57 .2 69 .8 Height Below Coal Line, m 5 .0 3 .3 0 .8 Table VI. As-received Algoma coke properties. coke for the whole oven. The parameters liste d in Table IV,V,and VI were considered to be independent variables to be used in this study. The dependent variables (to be determined) in this study are: 1. Bulk density (apparent specific gravity) 2. True density (true specific gravity) 3. Porosity 4. Ambient temperature compressive strength 5. High temperature compressive strength, and 6. Microstructure Variables (1-3) and (6) were also used as independent variables to assess their influence on ambient and high temperature compressive strength of the cokes used in this study. The procedures used for sample preparation and for determining properties (1-6) are described in the following sections of this chapter. These methods were necessary to 48 minimize inconsistencies attributed to variations in experiental procedure. 2.1 SAMPLE IDENTIFICATION A systematic procedure for identifying the seven coke packages received from CANMET has been developed . The method involved four steps: 1. Positioning the coke lumps according to their approximate position along the width of the oven 2. Selection of suitable lumps to be used 3. Sectioning each of the selected test lumps by a diamond saw, and then 4. Core-drilling specimens from each lump section. 2.1.1 POSITIONING OF COKE LUMPS Each of the seven coke packages were examined and each lump was positioned according to i t s approximate location across the coke-oven width. Positions were determined by the visual appearance of each lump. For example, lumps with a cauliflower type structure at one end were located at the wall of the coke-oven as shown in Figure 10. This was earlier suggested by Dr. W.R. Leeder of Denison Mines. In contrast, lumps with darker coloring were considered to be "coked" to a lesser degree, and therefore, were assumed to have originated close to the center of the oven. The approximate position of the coke lumps of the seven coke batches are shown in photographs (Figure 10a-g). These lumps Figure 10. The positions of Coke Lumps as they were Assumed to be in the Coke-oven. Figure 1 0 . Continued. 51 were numbered and photographed for further reference. The lumps considered suitable for further study were selected from each of the seven coke batches. 2.1.2 SELECTION OF TEST LUMPS The selection of test lumps was based mainly on their size, position, and their as-received condition. Larger lumps which exhibited the cauliflower structure were preferred because the structural variation according to distance from the oven wall can be more readily compared in large lumps. The position in the oven of smaller lumps not exhibiting the cauliflower structure is less certain. Coke lumps which contained a large number of fissures were generally not used due to the d i f f i c u l t y of sectioning them. It was also desirable to, wherever possible, select an equivalent number of each wall and center coke lumps. The best example of large lump selections are those of CPR-267 as shown in Figure 11. These lumps contain both the cauliflower structure and darker center regions. This enabled classification, according to distance from the wall, to be more easily performed. 2.1.3 SECTIONING OF TEST LUMPS Each selected coke lump was sectioned into several 2cm thick sections. Attempts were made to cut the coke lumps in such a way that the faces of each section were approximately parallel to the coke-oven wall. Each section was numbered 52 Figure 11. An Example of Coke Lumps Selected for Further Study. 53 and the position with respect to the coke-oven wall (or oven center for some lumps) was recorded. Figure 12 is a schematic diagram of the sectioning procedure used for a l l selected test lumps. 2.1.4 CORE DRILLING OF COKE SPECIMENS Individual test samples were made by core-drilling specimens from each of the sections described above. This is illustrated in Figure 12. The d r i l l cores were approximately 1.3cm in diameter. The variation in the properties of drill-cored specimens is sufficiently large, so the exact position of the specimen within the slice was not taken into consideration. 2.2 PREPARATION OF TEST SPECIMENS The core d r i l l e d cylindrical specimens were each inserted into a hardened steel die with a 1.3cm diameter hole, then ground and polished down to 1.3cm in length using polishing wheels between 80 and 600 g r i t . This method ensured that each specimen had smooth parallel faces at both ends of the coke cylinder. The parallel faces are essential for good alignment during compression testing. 2.3 BULK DENSITY MEASUREMENT Since the polished core-drilled specimens were near perfect cylinders, the volume could easily be determined from the dimensions (measured by a caliper). Each recorded sample 54 Figure 1 2 . Schematic Representation of the Procedure for Sectioning Coke Lumps (ref. 4). 55 diameter was the mean of three such measurements and the recorded height was the average of two measurements. The separate measurements rarely differed by more than 0.025mm (0.001 in). The bulk density was easily determined by dividing the sample weight by i t s measured volume. 2.4 TEST SAMPLE SELECTION The samples used for compression testing, creep testing, and microstructural analysis were grouped on the basis of their bulk density. The samples selected from each of the seven batches f e l l inside the range of bulk densities described by: Mpb " "pb ? "pb * Mpb + apb ( 6 ) where is the mean bulk density and a ^  is the sample standard deviation. This method was used in order to minimize the effect of bulk density variation on coke strength amongst test samples in each of the seven coke batches studied. 2.5 MICROSTRUCTURAL ANALYSIS The microstructure of the seven coke batches was analyzed using a Leitz TAS PLUS computerized image analyzer. This image analyzer has the capability of quantitatively measuring textural features of optical images and determining their quantity, size distribution, area, form, and other optically distinguishable parameters. Figure 13 56 Storage Dts* Imagt Memories POP-I I Computer Grty L t v t l Discriminator T V Monitor High Resolution TV Camera Operator Input Keyboard Lint Printer External Main-Frame Computer Photograph Macrostand Coke Photomicro-graph F i g u r e 13 . Schematic R e p r e s e n t a t i o n of t h e L e i t z TAS PLUS Image A n a l y z e r . 57 schematically illustrates the Leitz TAS PLUS image analyzer. The system at U.B.C. has both an optical microscope and a macrostand for analyzing photographs. The macrostand was used in this study to analyze photomicrographs of the coke texture. This method was chosen due to the ease with which the photographs can be used with the image analyzer. Also, specimens can be re-examined without additional polishing and after the specimens have undergone compression testing. 2.5.1 PHOTOMICROGRAPH PREPARATION Each of the coke specimens selected for further study based on their bulk density, were photographed for quantitative examination using the image analyzer. The samples were prepared by f i r s t lightly dry polishing each end using Carborundum 3/0 Flexbac polishing paper. The surface pores were then coated with soot from a luminous candle flame to eliminate any internal reflection (from the shallow pore channels in the coke) which may affect the accuracy of the texture analysis. Each end of the coke cylinder was then photographed at a magnification of 12.8X on polaroid films with an exposure time of two minutes for high contrast between pore walls and pore channels. An example of the excellent contrast achievable using this method is shown in Figure 14 in which the dark regions are pores and the light regions are pore walls 58 F i g u r e 14. A T y p i c a l Coke M i c r o s t r u c t u r e . m a g n i f i c a t i o n (12.82) 59 2.5.2 IMAGE ANALYSIS The Leitz image analyzer is easily automated using software to analyze the porous structure of coke. This software has been developed indigenously to measure seven parameters of coke structure. The parameters that are considered important for characterizing the porous structures are pore (channel) perimeter, c e l l wall thickness, pore area, equivalent diameter, mean chord length, form factor, maximum and minimum Feret's diameters. Mean chord length (also used to determine c e l l wall thickness) was determined by averaging the chord lengths of the features at three orientations (0°, 60° and 120° to the horizontal). Form factor is used to characterize shape using area and perimeter measurements (ie. form 2 factor=47r(area)/perimeter ). Maximum and minimum Feret's diameters were determined by measuring the caliper dimensions at 12 orientaions (15° intervals) and taking the maximum and minimum values of these. A l l of these measurements were performed on each individual pore in the photographs. A flow chart of this program is presented in Figure 15. A second software program has been developed to do field-based mean chord measurements for c e l l walls. The image analyzer detects features by their grey-levels on a black and white TV monitor. The TAS PLUS image analyzer has a grey level range between 1 (white) and 100 (black). Measurements are performed on objects which Deflno Arroyt Input Calibration Factor Input Numbor of Flo Idi Anion Output Flit Dofl HJttog no rami 60 Mtatoro Volumo of Porotlty Ellmlneto Small Poroi Porform 7 Moowro-montt on toch Port Figure 15. A Flow Chart of the Software Coke Microstructure. Used to Quant i fy 61 f a l l inside the specified grey-levels. This method is called threshold detection. However, another method of detection (edge detection) was found to be more suitable for analyzing coke microstructure. This method util i z e s the sharp contrast between pore and wall grey levels and detects pores by these abrupt changes. Edge detection eliminates errors associated with judging grey levels of features by an operator. The image analyzer makes measurements on features by counting hexagonal pixel points. Very small features are therefore inaccurately measured. For this reason, features with dimensions less than 12MITI in diameter were not included in these measurements. This was done by a series of image erosions followed by a series of dilations to reconstruct the remaining larger pores. The seven parameters measured were cla s s i f i e d into seven different histograms describing their size distribution. It should be noted that measurements made on individual features of the porous structure, may not be absolute but can be regarded as being relative because image analyzer results are resolution dependent (section 4.2). 2.5.3 TRUE DENSITY The true density of each of the seven coke types was measured to enable porosity calculations based on bulk density to be made. This was done to verify the porosity measurements made using the image analyzer. The true density was determined using the pycnometric method. 62 The coke slices, sectioned 2cm from the cauliflour end, were ground to minus 75jxm in a Spex Mixer M i l l . Approximately 2gm of this powder was used for true density determination. The fine powder was needed to eliminate any closed pores that might be present in the coke. The 2gm sample was placed in a 25ml pycnometric flask and evacuated or boiled to remove trapped a i r . Both d i s t i l l e d water and methanol were used as the measuring fluids for a l l seven coke batches. The true density of the coke powders was calculated using the following equation: W2 - W, Density = (W.-W,)-(w7~W2) (7) P i P i where W, = Weight of Pycnometer bottle, W2 = Weight of Pycnometer bottle + sample, W3 = Weight of Pycnometer + sample + flu i d , W„ = Weight of Pycnometer f i l l e d with f l u i d alone,and p,= Density of fl u i d . The porosity was calculated from the relative density, which was obtained by dividing the average bulk density by the measured true density. 2.6 MECHANICAL TESTS A l l mechanical tests on coke cylinders were performed under compression. Compression strengths were determined both at ambient temperatures and at 1400°C. Some tests were also carried out at 1000°C for three of the seven coke batches. 6 3 Constant load tests were performed on a l l four of the Algoma coke samples. 2.6.1 COMPRESSION TEST APPARATUS These studies were made using the apparatus illustrated schematically in Figure 16. The coke sample was positioned between two graphite plungers which acted as suseptors in the induction c o i l . The graphite plungers and the specimen were enclosed in a quartz tube with two water cooled copper disks at each of the top and bottom ends of the tube. The system was flushed with argon to prevent oxidation of the coke specimen and the graphite plungers. It is important that the oxidation of the specimens was kept to a minimum so that the pore structure of the coke remained unchanged during the test. The temperature of the specimen was monitored using a Pt-lO%RdPt thermocouple inserted through the bottom plunger to an approximate distance of 2mm away from the specimen. 2.6.2 PROCEDURE OF TESTING The load was applied using a hydraulic system. The loading rate can be controlled using a leak valve which allows a linear build-up of pressure in the piston chamber. The loading rate used on a l l strength and constant load tests was approximately 1.2MPa/sec. The load was recorded using a load c e l l made by A.L. Design Inc. of Tonawanda, N.Y. situated at the bottom of the assembly. The load c e l l 64 To Chart R t c o r d t r Grophite Plungers' Argon Outlet-To Load R t c o r d t r Tronsductr Meehonical Dial Indicator -Air Inlet Valvt A r g o n In te t Coke Specimen Induction Coil • Load Washer -Thermocouple Te T e m p e r a t u r e C o n t r o l l e r Figure 16. A Schematic Representation of the Compression Testing Apparatus. 65 was connected to a Kipp and Zonen BD-41 chart recorder set to an 800 pound f u l l scale load. The c e l l was calibrated using an Instron testing machine with an FR tension-compression c e l l . The linear dimensional change was monitored by an LVDT mechanically connected to the top of the plunger. The transducer was connected to a second pen on the same chart recorder. The heating rate was arbitrarily set at =*200°C/min. and used in a l l experiments. For both high temperature strength and constant load tests, specimens were heated to the desired temperature and maintained at that temperature for ten minutes before the load was applied. The constant load tests were carried out normally between thirty and sixty minutes. 2.6.3 EXPERIMENTAL PARAMETERS The fixed experimental parameters used for a l l compression and constant load tests are summarized in Table VII. Room temperature compression strength tests were also performed in accordance with Table VII except without the argon atmosphere which was unnecessary. 2.7 GRAPHITIZATION TESTS To determine the extent of coke shrinkage during heating, graphitization tests were also performed. These tests involved placing a sample in the strength testing apparatus, 66 Parameter Value Sample Diameter 1 . 3cm Sample Length 1 . 3cm Loading Rate 1.2MPa/sec Heating Rate ~200°C/min. Time at Temperature 10 min. (before testing) Atmosphere Argon Number of Compression 12-25 Tests per Condition Table VII. Values of Fixed Compression Test Parameters. and heating to 1400°C for thirty minutes without applying any load to the coke sample. The dimensions of the sample were measured after cooling. 3. RESULTS AND ANALYSIS 3.1 GENERAL COMMENTS It should be noted that because of the wide va r i a t i o n in microstructure and other properties of coke even within a single lump, a l l properties (physical and mechanical) should be treated s t a t i s t i c a l l y . This wide va r i a t i o n of properties arises from the method of coke production where temperature variatio n s of =«200oC exists from the center of the batteries to the refractory wall, and from the top of the battery to the sole (M |a<300oC). Furthermore, the coke at the top of the batteries i s not subjected to as much a s t a t i c load as the coke at the bottom ( i e . s i g n i f i c a n t differences in oven wall pressure are encountered). In addition to these, the raw material used in coke-making (coal) i s extremely heterogeneous. So, i t i s not surprising that coke has such a complex texture with wide variati o n s in properties. In spite of t h i s f a c t , very few results reported in the l i t e r a t u r e are treated s t a t i s t i c a l l y . In t h i s project, almost a l l res u l t s (except the creep data) are treated s t a t i s t i c a l l y . 3.2 DENSITY 3.2.1 BULK DENSITY Bulk density was used as an i n i t i a l c r i t e r i o n for characterizing the seven d i f f e r e n t coke batches. The bulk de n s i t i e s were c l a s s i f i e d into histograms for each coke type 67 68 from which their mean bulk densities and standard deviations were obtained. Figure 17 is the distribution of bulk densities for a l l seven coke batches (CPR-264-CPR-270). The histograms for the individual coke batches are included in the Appendix A. Figure 18a is a summary of the mean bulk density as a function of coke type. The error bars correspond to the standard deviations. The mean bulk densities range between 0.779gm/cm (CPR-269) and 0.947gm/cm (CPR-266). The variation between oven wall pressure and bulk density for the test-oven cokes is illustrated in Figure 18b. There is a strong correlation between bulk density and oven wall pressure when plotted in a semi-logarithmic scale. Also included are the bulk density values of three industrial cokes on the straight line obtained from the test-oven cokes. The best f i t curve which describes the relationship between oven pressure and bulk density of the test-oven coke is : Pb(gm/cm3)=0.11[loglQP(KPa)1+0.808 r=0.997 (8) where p^ is the bulk density and P is the oven wall pressure. Table VIII shows the relationship between estimatedCfrom Figure 18b) static load pressure and depth below the coal line for the industrial cokes. As expected, there is an increase of static load with increasing depth below the coal line, resulting in a higher coke bulk density. 69 Coke Type * All Coke Samples Density (gm/cc) •643 •654 •665 •676 •686 •698 •709 •720 •731 •742 •753 •764 •770 •776 •787 -798 •809 •820 •831 •841 •853 •864 • 8 7 5 •886 •897 •908 •9 I 9 •930 •941 •952 •963 •973 •984 •995 1006 1018 1029 I 040 10 51 1062 Percent 3 4-9 J 6-4 3 4-3 • 3-8 3 3-6 Mean* -861 gm/cc Standard Deviation 083 gm/cc Figure 17 . The D i s t r i b u t i o n of Bulk Density Values for a l l Seven Coke Batches. 70 I 00 1 1 r -Test Furnace-Coke 1 i r r Commercial Oven—^ Coke I to E o ^ 0 90 o> to c 0) O 0 80 CD o O A v 0 70 ± 264 265 266 267 268 269 270 CPR Coke Type Figure 18a. A Summary of Mean Bulk Density Values for a l l Seven Coke Batches. 71 1-0 E o \ E 0-9 w >* *— «/> c Q) a Bu! 0-8 c o 0) 2 I I I I I 1 1—I—I I I I I 266. 267 . 264 s 2 6 8 A / 6 "l 269, ' K s Correlation Coef. r -0 .997 A O Test Oven Cokes A Industrial Oven Cokes 0-7' * 1 » 1 1 J L I t I I . I 0-5 5 10 Oven Pressure (kPa) 20 Figure 18b. Bulk Density versus Oven Wall Pressure (Points for i n d u s t r i a l oven cokes estimated the using l i n e a r l i n e and bulk density values). 72 3.2.2 TRUE DENSITY The true densities of a l l seven coke batches have been determined. These values are presented in Table IX. There is no apparent correlation between the true density and the oven wall pressure (or static load). The true density values of a l l seven cokes vary within five percent of each other. These values are lower than that of graphite (2.266 gm/cm3 (40)) which indicate that these cokes are not well graphitized. Since CPR-270 is the wharf coke, i t would require a large number of true density measurements to get a representative value for a l l wharf coke, so i t s true density was calculated from the average of CPR-267, CPR-268 and CPR-269 true density values. 3.3 MICROSTRUCTURE The microstructure of the seven coke batches used in this project was examined quantitatively using a Leitz TAS PLUS image analyzer, as discussed in section 2.5.2. Since this analysis was performed on two dimensional photographs with the intention of representing a three dimensional system, an effort was made toward improving the accuracy of the method employed. This includes determining the sensitivity of the results towards the number of fields (photographs of circular faces) analyzed and assessing the effect of large pores crossing the outside boundaries of the fields. The analysis of the porous structure proceeded in the following manner: 1) the sensitivity analysis was performed to Coke Depth Below Est imated Mean Type Coal Line S t a t i c Load Bulk CPR-(m) Pressure (kPa) Density gm/cm' 267 5.0 10.2 0.919 26B 3.3 4.9 0.884 269 0.8 5.4(10"') 0.779 Table VIII . Estimated V a r i a t i o n of Mean Bulk Density and Oven Wall Pressure with Depth Below The Coal L i n e . Coke Depth Oven Wall True Standard Type Below Pressure Density Deviation CPR- Coal Line <Ol) (kPa) (gm/cm3) (gm/cm1) 264 - 3.2 1 .9672 0.0784 265 - 5.9 2.0229 0.0918 266 - 17.8 1.9009 0.0729 267 5.0 10.2* 1.9167 0.0326 268 3.3 * 4.9 2.0163 0.0216 269 0.8 5.4(10"')* 1.9194 0.0640 270 Warf - ** 1 .9470 0.0621 Table IX. Var iat ion of True Density as a Function of Coking Condi t ions. * Calculated. • * Average of true dens i t ies of CPR-267,268 and 269. 74 determine the minimum number of fields required to represent the whole microstructure; 2) the effect of pores situated on the borders of the f i e l d was assessed; 3) distributions of pore area, equivalent diameter, mean chord length, form factor (4jr(area)/(perimeter) ), pore perimeter, maximum and minimum Feret's diameters along with a mean chord sizing of coke c e l l walls were determined; and 4) a s t a t i s t i c a l analysis was performed on the results. 3.3.1 SENSITIVITY Table X shows the measured parameters obtained from measuring 4,10,20 and 40 fields (photographs) of a batch of coke. As shown, some variables are more sensitive to the number of fields analyzed than others with pore perimeter being the most sensitive, while the mean chord length (averaged over three orientations) varying the least. The values appear to converge when more than twenty fields of view have been analyzed. Therefore, i t was decided that an analysis of thirty or more fields of view would represent each coke batch adequately. The porosity was also measured using the same software. These values are compared in Table XI, with those calculated from the measured bulk and true density values. The values obtained from the image analyzer were consistently higher Number pore Equivalent Mean Chord Form Pore Maximum Minimum of Area Diameter Length Factor Per imeter F e r e t ' i Feret' • F i e l d s Diameter Diameter Analyzed (mm1) (mm) (mm) (mm) (mm) <-> 4 0. 174 0.298 0. 178 0.858 1 .483 0.427 0.273 10 0. 180 0.310 0.178 0.847 1.596 0.449 0.283 20 0. 133 0.261 0. 176 0.879 l .251 0.403 0.250 40 0.130 0.285 0.177 0.877 1.248 0.404 0.253 Table Variation of The Arithmetic Mean Values of The Pore-parameters Measured Using The Leitz TAS PLUS Image Analyzer for CPR -264 as a Funct ion of Number of Fields Analyzed. Coke Number Porosity Porosity Type of Frames f rom from CPR- Analyzed Image Analyzer Pycnometry ( % ) ( % ) 264 40 60.54 55.50 265 33 59.29 54.32 266 40 56.05 51.34 267 40 57. 12 52.05 268 40 57.91 56. 16 269 40 59.03 59.41 270 40 57.54 55.88 Table XI Comparison of Analyzer with Porosity Values as Measured using the Image Those Values Obtained From Pycnometry. 77 than those found by pycnometry. The differences between the two methods follow the best f i t relationship: ep= 0.944ej- 0.023 r=0.994 (9) where and C j are the porosities (in percent) measured by pycnometry and by the image analyzer, respectively. In order to calculate the porosities of the test-oven cokes (CPR-264 to CPR-266) a single averaged true density value was used. This average true density was obtained from eighteen different true density measurements of a l l three cokes. The justification in using such a method is that the oven wall pressure should not affect the true density of the coke (5). 3.3.2 EDGE EFFECTS One form of inaccuracy, that affects the optical methods of quantitatively characterizing microstructure, is the effect of edges. Often, large features cross over the boundaries of the photographs. This allows only a fraction of their size to be analyzed. The Leitz TAS PLUS image analyzer has the capability of eliminating features which cross the boundaries of the frame being analyzed. This effect was examined by analyzing four and twenty fields. The arithmetic mean values of seven parameters are listed in Table XII. The mean values for a l l seven microstructural parameters are consistently lower for the data obtained in the absence of features bordering the f i e l d edges as Parameter 4 F i e l d s 4 F i e l d s 20 F i e l d s 20 F i e l d s Edge Pores Containing Edge Pores Containing El iminated Edge Pores El iminated Edge Pores Pore Area (mm) 0.085 0.174 0.073 0.133 Equivalent D i a . (mm) 0.25B 0.298 0.241 0.281 Mean Chord Length (mm) 0.170 0.178 0.162 0.175 Form Factor 0.894 0.858 0.913 0.879 Pore Perimeter (mm) 1 .016 1 .483 0.925 1.251 Max. Fere t ' s Dia (mm) 0.352 0.427 0.330 0.403 Min. Fere t ' s Dia (mm) 0. 174 0.273 0.178 0.250 Table XII . The Effect of Edges on Micros truc tura l Parameters of CPR-264. 79 compared to those values obtained when edge features are included. This is not surprizing as the larger features are expected to be more frequently intercepted by the f i e l d boundaries than the smaller ones. Since larger pores are considered likely to be the cause for mechanical failure in coke, i t was decided that further microstructural analysis would be carried out including a l l the edge pores. This decision is based on the assumption that edge effects will be similar for a l l seven coke batches and, therefore, the results produced by the image analyzer w i l l be relatively consistent. 3.3.3 CELL WALL SIZE The thickness of the c e l l wall was determined using the image analyzer to perform intercept sizing. This method is similar to the manual technique but is performed on a series of lines oriented at 0°, 60°, and 120° relative to the horizontal axis. The mean chord length is found by counting the number of intercepts of each line and dividing the length of each line by the number of intercepts for each of the three angles. The fin a l value results from an average of the chord sizing of the three orientations. The wall size values of the seven coke batches are listed in Table XIII. The c e l l wall width of the cokes produced in 460mm test-oven are thinner than those for the cokes produced in the 5m industrial coke-oven. coke CPR-264 CPR-265 CPR-266 CPR-267 CPR-268 CPR-269 CPR-270 Type Wall Size 0.131 0.122 0.131 0.154 0.152 0.168 0.169 (mm) Table XIII. Comparison of Cell Wall Size Values for Different Cokes. CD 81 3.3.4 PORE SIZE AND GEOMETRY The analysis of pore size and geometry was carried out by measuring a l l seven parameters of each pore on a l l photographs. The number of pores analyzed per coke batch ranged between 3500 and 5500 depending on the coke being analyzed. The seven pore-parameters which were expected to have an influence on coke mechanical properties are listed in section 2.5.2. Each pore measurement has been classified into histograms and the distribution statistics were calculated using the PDP-11 computer attached with the image analyzer. In addition, a l l pore measurements were transferred to the main AMDAHL computer for further s t a t i s t i c a l analysis. The calculated mean values and their corresponding standard deviations are liste d on Table XIV and the histograms for CPR-264 are included in Appendix B as an example. There is a general decrease in the pore dimension values from CPR-264 to CPR-266 for the test-oven cokes while an increase in pore dimensions is observed from CPR-267 to CPR-269. The mean pore size (as described by equivalent diameter, mean chord, maximum and minimum Feret's diameters) is found to be larger for the commercially produced coke than that for the test-oven cokes. The standard deviations of each parameter is shown to be larger than the arithmetic mean values. This is characteristic of heavily skewed distributions. The histograms shown in the appendix are seen to have a positive skewness (there is a very large number of Coke Pore Area Equivalent Mean Chord Length Form Pore Maximum Minimum CPR- Diameter Factor Perimeter F e r e t ' s Diameter F e r e t ' s Diameter (mm') (mm) (mm) (mm) (mm) (mm) u o u o u o u o u o u o u o 264 0 . 1 3 0 0 . 5 1 7 0 . 2 8 5 0 . 2 9 0 . 0 . 1 7 7 0 . 1 0 6 0 . 8 7 7 0 . 2 4 3 1 . 2 4 8 2 . 6 4 2 0 . 4 0 4 0 . 5 0 6 0 . 2 5 3 0 . 2 9 9 2 6 5 0 . 1 0 5 0 . 3 5 6 0 . 2 7 0 0 . 2 4 8 0 . 1 7 3 0 . 0 9 6 0 . 8 8 5 0 . 2 3 6 1 . 1 1 6 1 . 8 4 5 0 . 3 7 6 0 . 4 2 3 0 . 2 4 0 0 . 2 5 2 2 6 6 0 . 1 0 0 0 . 3 0 1 0 . 2 6 9 0 . 2 3 4 0 . 1 7 0 0 . 0 8 6 0 . 8 7 4 0 . 2 4 3 1 . 1 4 0 1 . 8 6 4 0 . 3 7 8 0 . 4 0 8 0 . 2 3 9 0 . 2 4 1 2 6 7 0 . 1 2 8 0 . 4 7 8 0 . 2 8 7 0 . 2 8 4 0 . 1 8 0 0 . 1 0 6 0 . 8 7 7 0 . 2 4 4 1 . 2 4 4 2 . 4 2 2 0 . 4 0 7 0 . 4 9 8 0 . 2 5 5 0 . 2 9 1 2 6 8 0 . 1 5 0 0 . 4 9 3 0 . 3 0 7 0.311 0.189 0 . 1 2 0 0 . 8 6 7 0 . 2 4 9 1 . 3 5 0 2 . 4 5 1 0 . 4 3 5 0 . 5 3 5 0 . 2 7 4 0 .315 2 6 9 0.184 0 . 7 5 1 0 . 3 2 3 0 . 3 6 1 0 . 1 9 6 0 . 1 4 0 0 . 8 6 2 0 . 2 4 8 1 . 4 4 6 2 . 9 2 9 0 . 4 6 3 0 . 5 9 6 0 . 2 8 9 0 . 3 6 8 2 7 0 0 . 1 6 4 0 . 5 9 5 0 . 3 1 4 0 . 3 3 2 0 . 1 9 3 0 . 1 2 5 0 . 8 6 6 0 . 2 4 3 1 . 3 8 0 2 . 6 7 2 0 . 4 4 0 0 . 5 4 5 0 . 2 7 8 0 . 3 3 3 Table XIV Mean (y)and Standard Deviations (a)of The Coke Porous Parameters for a l l Seven Coke Batches. 00 83 small pores). This raises doubt as to the validity of using the arithmetic mean as a representative value. 3.3.5 REPRESENTATION OF PORE SIZE AND GEOMETRY The s t a t i s t i c a l problems (associated with skewed distributions) mentioned in section 3.3.4 can be avoided by considering cummulative distributions. For the purpose of this project, the seven parameters used to characterize coke structures were represented arbitrarily by the cummulative 80% finer values (values at which 80% are smaller). The cummulative 80% finer values at the 95% confidence limit are shown in Table XV. The values shown for Form Factor a l l exceed the theoretical maximum of 1.0 (for a circle) and therefore can not be relied upon. With this in mind, the ratio of maximum Feret's diameter to minimum Feret's diameter was used to characterize pore shape as previously suggested by other workers (32-36). CPR-265 exhibits the smallest pore dimensions of the test oven cokes, whereas CPR-267 exhibits the same(ie. smallest pore dimensions) for the cokes produced in the 5m industrial coke-oven. Another parameter which has been considered important is the number of pores per f i e l d (see Table XV). It can be seen the test-oven cokes contain a larger number of smaller pores when compared with cokes produced at Algoma. Coke Number of Pore Equivalent Hean Chord Form Pore Maximum Minimum Ratio of Mai Type Pores Area Diameter Length Factor Perimeter F e r e t ' s F e r e t ' s to Min CPR- per F i e l d Diameter Diameter F e r e t ' s (mm1) (mm) (mm) (mm) (mm) (-"> Diameter 264 121 0 104 0.363 0.229 1.10 1.378 0.518 0.310 1.771 266 140 0 093 0.343 0.222 1. 10 1.290 0.482 0.301 1.7)4 266 126 0 098 0.353 0.224 1.10 1 .345 0.506 0.310 1.755 267 115 0 105 0.365 0.231 1.10 1.410 0.530 0.310 1.749 268 101 0 105 0.365 0.231 1.10 1.574 0.573 0.352 1.754 269 89 0 134 0.413 0.255 1.10 1.629 0.603 0.352 1.766 270 97 0 I 25 0.399 0.251 1.09 1 .531 0.566 0.350 1.766 T a b l e XV Cummulat i v e 80% F i n e r V a l u e s of the Seven P o r e Parameters f o r t h e Seven Coke B a t c h e s . CO 85 3.4 COMPRESSIVE STRENGTH OF COKE BATCHES T a b l e X V I i n c l u d e s the mean c o m p r e s s i v e s t r e n g t h v a l u e s of t h e seven coke b a t c h e s , both a t ambient t e m p e r a t u r e and a t 1400°C. A l s o g i v e n a r e t h e i r s t a n d a r d d e v i a t i o n v a l u e s . S e v e r a l c o n c l u s i o n s can be drawn from t h i s d a t a : 1. Coke i s s t r o n g e r a t h i g h t e m p e r a t u r e , 2. T e s t - o v e n cokes (CPR-264 t o CPR-266) a r e s t r o n g e r than t h e Algoma cokes,and 3. The s t a n d a r d d e v i a t i o n f o r each mean s t r e n g t h v a l u e i s l a r g e (up t o 50% of t h e mean s t r e n g t h ) . The l a r g e s t a n d a r d d e v i a t i o n s show the l a r g e v a r i a t i o n i n coke s t r e n g t h v a l u e s w i t h i n each coke b a t c h . T h i s s c a t t e r i n t h e d a t a w i l l be d e s c r i b e d i n more d e t a i l i n s e c t i o n 3.4.5.. 3.4.1 COKE STRENGTH AS A FUNCTION OF VARIABLES The independent v a r i a b l e s used t o c h a r a c t e r i z e ambient and h i g h t e m p e r a t u r e coke s t r e n g t h have been l i s t e d i n s e c t i o n 2.0. The e f f e c t s of the s e v a r i a b l e s on coke s t r e n g t h a r e i l l u s t r a t e d i n F i g u r e s 19-21 ( a - g ) . A l l s t r e n g t h r e s u l t s show a s i g n i f i c a n t amount of s c a t t e r which i s a s s o c i a t e d w i t h the heterogenous n a t u r e of coke. 3.4.2 BULK DENSITY The p o s i t i o n of coke i n the Algoma coke-oven w i t h r e s p e c t t o h e i g h t was found t o a f f e c t the b u l k d e n s i t y of the f i n a l coke p r o d u c t ( s e c t i o n 3.2.1). The r e s u l t s show t h a t b u l k d e n s i t y r i s e s w i t h i n c r e a s i n g d epth i n t h e Coke Type Mean Strength Standard Mean Strength Standard at Ambient Deviation at 1400°C Deviat ion CPR- Temperature (MPa) (MPa) (MPa) (MPa) 264 12.76 4.09 16.41 5.06 265 14.34 6.26 17.81 7.17 266 17.57 6.90 18.72 7.71 267 10.72 4.74 13.32 5.41 268 10.64 5.95 13.84 7.55 269 8.16 4.06 6.29 2.40 270 9.93 3.56 11 .35 5.78 Table XVI. Mean Compressive Strength Values for the Seven Coke Batches at Both Ambient Temperature and at 1400°C. 87 coke-oven. Figure 19a shows the effect of mean bulk density on mean compressive strength. There was no correlation found between the strength of individual specimens, within a coke batch, and their respective bulk densities as shown in Figure 19b. Figure 19b shows the strength versus bulk density for the range of bulk density values (mean ± standard deviation) chosen for this strength study. This further confirms the need for a s t a t i s t i c a l approach to the treatment of coke strength data. The error bar in Figure 19a represents the 95% confidence limit for estimating the mean strength. Despite the large scatter, definite trends are noticable as indicated by the "best f i t " lines. The results suggest a linear relationship between bulk density and strength for the range of cokes studied. The coke strength appears to be greater for cokes extracted from the lower regions of the Algoma coke-oven than those sampled from the top of the oven. 3.4.3 P O R O S I T Y Porosity has previously been reported to affect the strength of materials (28). Figure 20 is the relationship between strength and porosity. The strength was found to decrease with increasing porosity. Two empirical relationships, as postulated previously, were used to test the data: a = ~ n cp + D and a - o0 exp(-be ) (ref 28) — 2 2 o Q. 5 2 0 S 1 8 c £ \ 6 g 1 4 in o> 2 » * i — f — i — i i | i i i i TEST OVEN ALGOMA A 1400 # C A I400*C - o- R.T • R.T O Q) 8 0 7 5 0 7 9 I ' ' • ' I i i I i i i i i 0 8 3 0 - 8 7 0 * 9 1 3 Mean Bulk Density ( g / c m ) 0 - 9 5 Figure 19a. Mean Compression Strength versus Mean Bulk Density. 89 2 0 o C L 5 c g 15 to > V) </> 0) k_ CL o O 1 o 0 o - ° o -o o 1 o o o 0 0 o o . Bulk Density Figure 19b. Compressive Strength vs Bulk Density for CPR-264 at Ambient Temperature. 90 22 ~ 18 c 16 0) _> to 0) 12 o. 10 E o u s 1 1 — - r -TEST OVEN ALGOMA I 4 0 0 * C R.T. • A -o o 5 6 -50 52 _L 54 56 P o r o s i t y (%) 56 60 F i g u r e 20. Mean Compressive Strength versus Coke Porosity. 91 where i s t h e p o r o s i t y , a i s the c o m p r e s s i v e s t r e n g t h and o 0 i s an e m p i r i c a l c o n s t a n t . The e m p i r i c a l parameters of t h e s e e q u a t i o n s a r e shown i n T a b l e s XVII and X V I I I , r e s p e c t i v e l y . J u d g i n g by the v a l u e s of t h e c o r r e l a t i o n c o e f f i c i e n t s , the l i n e a r r e l a t i o n s h i p more a c c u r a t e l y d e s c r i b e d the v a r i a t i o n of c o m p r e s s i v e s t r e n g t h w i t h p o r o s i t y t h a n the e x p o n e n t i a l e q u a t i o n p r o p o s e d by Knudsen ( 2 8 ) . 3.4.4 MICROSTRUCTURE I t i s o b v i o u s from s e c t i o n 3.4.3 t h a t t h e c o r r e l a t i o n between c o m p r e s s i v e s t r e n g t h and p o r o s i t y i s s i g n i f i c a n t but not v e r y s a t i s f a c t o r y (as i n d i c a t e d by the c o r r e l a t i o n c o e f f i c i e n t s ) . So, t o o b t a i n a b e t t e r c o r r e l a t i o n between the s t r e n g t h and some m i c r o s t r u c t u r a l f e a t u r e s , a t t e m p t s have been made t o t e s t the dependence of t h e s t r e n g t h d a t a on the parameter v a l u e s d e t e r m i n e d u s i n g t h e image a n a l y z e r . 3.4.4.1 C e l l W a l l S i z e The e f f e c t of c e l l w a l l s i z e on t h e c o m p r e s s i v e s t r e n g t h v a l u e i s shown i n F i g u r e 21a, f o r the d a t a b o t h a t ambient te m p e r a t u r e and a t 1400°C. E r r o r bars a r e not shown s i n c e the 95% c o n f i d e n c e l i m i t s f o r mean c o m p r e s s i v e s t r e n g t h a r e the same as i n F i g u r e s 19 and 20. There i s a s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n between the s t r e n g t h and the c e l l w a l l s i z e as shown by t h e c a l c u l a t e d l i n e a r r e g r e s s i o n l i n e s . These r e s u l t s a r e i n dis a g r e e m e n t w i t h P a t r i c k e t a l (32) who found a Test ing Condit ion n b C o r r . (MPa) (MPa) Coeff . Test Oven Cokes, Ambient Temp. 1. 14 76 .25 -0.999 Test Oven Cokes, 1400°C 0. 51 44 .92 -0.934 Algoma Cokes, Ambient Temp. 0. 33 28 .50 -0.845 Algoma Cokes, 1400°C 0. 91 61 .94 -0.794 Table XVII Parameters for the Equation: o » - n e * b . Test ing Condit ion o 0 b C o r r . (MPa) Coeff . Test Oven Cokes, Ambient Temp. 837. 98 0 .075 -0 .996 Test Oven Cokes, 1400°C 82. 85 0 .029 -0 .927 Algoma Cokes, Ambient Temp. 71 . 45 0 .036 -0 .842 Algoma Cokes, 1400°C 2435. 73 0 .097 -0 .801 Table XVI11 Parameters for the Equation: a*o 0exp(-b< ) . Mean Compressive Strength ( M P a ) — « — — — ro to o a * a > o r o - ( * 0 > a > o r o £6 94 p o s i t i v e c o r r e l a t i o n between c e l l w a l l t h i c k n e s s and t e n s i l e s t r e n g t h . 3.4.4.2 Pore S i z e The pore s t r u c t u r e was r e p r e s e n t e d by f i v e d i f f e r e n t p a r a m e t e r s : pore a r e a , e q u i v a l e n t d i a m e t e r , mean c h o r d l e n g t h , and maximum and minimum F e r e t ' s d i a m e t e r s . P l o t s of c o m p r e s s i v e s t r e n g t h v e r s u s t h e s e parameters a r e shown i n F i g u r e s 2 l ( b - e ) . The e f f e c t of minimum F e r e t ' s d i a m e t e r on s t r e n g t h was not p l o t t e d due t o t h e s m a l l v a r i a t i o n of v a l u e s between the seven coke b a t c h e s . In F i g u r e s 2 1 ( b - e ) , e r r o r b a r s r e p r e s e n t i n g the 95% c o n f i d e n c e i n t e r v a l of the 80% cummulative f i n e r v a l u e s a r e o n l y shown f o r the ambient t e m p e r a t u r e p o i n t s s i n c e t h e s e i n t e r v a l s a r e the same f o r the h i g h t e m p e r a t u r e d a t a as w e l l . The "best f i t " l i n e s r e p r e s e n t t h e g e n e r a l t r e n d s of the d a t a . From t h e s e p l o t s , i t i s app a r e n t t h a t the s t r e n g t h d e c r e a s e d w i t h i n c r e a s i n g p ore a r e a and pore s i z e , but t h e l i n e a r c o r r e l a t i o n s o b t a i n e d i n a l l f o u r p l o t s a r e poor. S i m i l a r t r e n d s have been o b s e r v e d i n p r e v i o u s s t u d i e s (32-36) 3.4.4.3 Number of Po r e s L a r g e r pore and w a l l s i z e have been found t o d e c r e a s e the c o m p r e s s i v e s t r e n g t h of co k e . I t i s a p p a r e n t , t h e r e f o r e , t h a t the number of p o r e s p e r u n i t volume might a l s o c o r r e l a t e w i t h s t r e n g t h . T h i s r e l a t i o n s h i p i s shown i n F i g u r e 2 1 f . I n t h i s f i g u r e , the 96 22 T T T CL20-I 18 c 0) 55 16 14 > vt I 2 </> 0) c i i o E o <~> 8 0) O 033 A I400°C (r--0-859) o R T . (r--0-821) 0-35 0-37 0-39 0-41 Equiva len t D iame te r (mm) Figure 21c. Mean Compressive Strength versus Pore Equivalent Diameter. 0-43 -0-917) - 0 8 4 9 ) 0 21 0-22 0-23 0-24 0-25 Mean Chord Length (mm) F i g u r e 21d. Mean Compressive S t r e n g t h v e r s u s P o r e Mean Chord L e n g t h . 0-26 to - i — — i 1 r « r A l 400°C( r - -0 906) o R.T. (r-0-833) 6 -1 1 1 1 0-48 0-50 0-52 0-54 0-56 0-58 0-60 Maximum Feret's Diameter (mm) F i g u r e 2 1 e . Mean Compressive S t r e n g t h v e r s u s Pore Maximum F e r e t ' s D i a m e t e r . o I - J I I I I L. ^ 8 0 9 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 Number of Pores per Field Figure 2 1 f . Mean Compressive Strength versus Number of Pores per Field. vo V O 100 coke strength appears to rise with increasing number of pores per f i e l d . This result agrees with previous observations (32-36). 3.4.4.4 Pore Perimeter The compressive strength has been shown in the past (32-36) to be a function of the pore perimeter. This parameter is thought to represent the pore surface area. Plotting mean compressive strength versus pore perimeter (see Figure 2lg), yields a negative correlation indicating that strength decreased with increasing pore perimeter. However, this correlation does not describe the coke strength more accurately than other correlations shown in Figures 2l(a-f). 3.4.5 STATISTICAL ASPECTS OF COKE FRACTURE The Weibull statistics have provided a useful tool to test the strength data of b r i t t l e solids. An attempt has been made to assess the variability of compressive strength values of coke (that has been encountered in this study for different coke batches) using the Weibull model of failure. The failure behaviour is represented by a probability curve, which is expressed mathematically as: PU) = 1 - exp[-Kom] (10) where P is the probability of failure, a is the failure stress, K is an empirical constant and m is the Weibull Pore Perimeter (mm) Figure 21g. Mean Compressive Strength versus Pore Perimeter. 102 modulus ( a l s o an e m p i r i c a l c o n s t a n t ) . T h e o r e t i c a l l y , t h i s e q u a t i o n was d e v e l o p e d from the weakest l i n k t h e o r y (18) and, t h e r e f o r e , was not t r u e l y meant t o be a p p l i e d t o c o m p r e s s i v e s t r e n g t h d a t a of coke where the f a i l u r e mechanism may be a p r o g r e s s i v e c o o p e r a t i o n of f l a w s . However, e q u a t i o n 10 can be used as a cummulative d i s t r i b u t i o n f u n c t i o n of the p r o b a b i l i t y of f a i l u r e v e r s u s f a i l u r e s t r e s s t o d e s c r i b e the v a r i a t i o n s of s t r e n g t h between coke specimens. F i g u r e s 22(a-g) a r e the W e i b u l l d i s t r i b u t i o n p l o t s of c o m p r e s s i v e s t r e n g t h f o r a l l seven coke t y p e s b o t h a t ambient and a t h i g h t e m p e r a t u r e s . The d i s t r i b u t i o n of coke s t r e n g t h i s l a r g e and sometimes v a r i e s by an o r d e r of m agnitude(normal f o r b r i t t l e s o l i d s ) . The parameter of t h e W e i b u l l f u n c t i o n which most a c c u r a t e l y d e s c r i b e s t h e v a r i a t i o n i n s t r e n g t h v a l u e s i s t h e W e i b u l l modulus(m) ( s l o p e of the W e i b u l l p l o t ) . These v a l u e s were c a l c u l a t e d u s i n g l i n e a r r e g r e s s i o n and a r e compared i n T a b l e XIX. For t e s t s a t ambient t e m p e r a t u r e , the W e i b u l l modulus v a l u e s of the t e s t - o v e n cokes (CPR-264 t o CPR-266) a r e c o n s i s t e n t l y h i g h e r than t h o s e v a l u e s found f o r the Algoma oven c o k e s . T h i s shows t h a t the t e s t - o v e n cokes appear t o be s l i g h t l y more u n i f o r m i n s t r e n g t h p r o p e r t i e s a t ambient t e m p e r a t u r e than t h o s e of the Algoma c o k e s . T h i s p a t t e r n , however, does not a p p l y t o the d a t a a t 1400°C. A l l v a l u e s of the W e i b u l l modulus found i n t h i s p r o j e c t f a l l w i t h i n t h e range r e p o r t e d i n t h e l i t e r a t u r e ( 1 8 ) . 103 0 98 0-95 0-90 0 80 0-60 S 0 - 4 0 o JO o OL <D 0-20 o L L 0 1 0 0 08 0 06 0 0 4 T—r—r A l 4 0 0 ° C ( r - 0 958) o R.T. (r-0987) 1 J _ J . 2 3 4 5 10 20 30 Fai lure Stress (MPa) 50 F i g u r e 22a. W e i b u l l D i s t r i b u t i o n P l o t of CPR-264 Mean Compressive S t r e n g t h V a l u e s . 104 I 2 3 4 5 10 20 SO 50 Failure Stress (MPa) Figure 22b. Weibull D i s t r i b u t i o n Plot of CPR-265 Mean Compressive Strength Values. 105 0 9 8 0 9 5 0 9 0 0 - 8 0 0 - 6 0 o n o 0) 0 - 2 0 ix 0 1 0 0 0 5 0 0 4 — i — r ~ n 1 A - — | 4 0 0 ° C ( r - 0 - 9 6 1 ) o R T . ( r - 0 9 9 2 ) 1 2 3 4 5 1 0 2 0 3 0 5 0 Fai lure S t r e s s (MPa) F i g u r e 22c. W e i b u l l D i s t r i b u t i o n P l o t of CPR-266 Mean Compressive S t r e n g t h V a l u e s . 106 0 98 0 95 0- 90 0- 80 0 60 E 0-40 o o 0. 0- 20 ^ 0 1 0 0- 08 0- 06 0- 04 1 - 1 1 1 1 1 1 - — I400 #C (r-0955) °/r -0 R.T. (r-0 974) c o/i j ft O A A*' • a /° i / O A j / o f ol A / / / Ol A 7 / O / / A / / / 1 O / A / / _ / / — / / « / / — » / O / A • . • I I 1 1 1 1 ,. 2 3 4 5 10 20 30 50 Fai lure Stress (MPa) F i g u r e 22d. W e i b u l l D i s t r i b u t i o n P l o t of CPR-267 Mean Compressive S t r e n g t h V a l u e s . 107 JD O O 0) O Li. 0 98 0 95 0 -90 0 80 0- 60 0- 40 2 0 20 0 I 0 0- 08 0 0 6 0 04 0 n — r - r — i 1 — I400°C (r-0 990) /<*/ -J I I I 1 1 J L 2 3 4 5 10 20 30 50 Fa i lure S t r e s s (MPa) F i g u r e 22e. W e i b u l l D i s t r i b u t i o n P l o t of CPR-268 Mean Compressive S t r e n g t h V a l u e s . 108 O L i . 0 98 0 95 0 - 9 0 0 • 80 0 • 60 0 -40 o .o o 0. o> 0 - 2 0 0 10 0 • 08 0 • 06 0 • 04 I A « . . . o i i I n — l400°C(r-0-979)* / ( R.T. (r-0 9 7 7 ) A y ; 1 r — i — r 3 4 5 10 J I L 20 30 50 Failure Stress (MPa) F i g u r e 2 2f. W e i b u l l D i s t r i b u t i o n P l o t of CPR-269 Mean Compressive S t r e n g t h V a l u e s . 109 CL 0) o LL. 0 98 0 95 0 90 0-80 0-60 - 0-40 o . O o 0-20 0 1 0 0 0 8 0 0 6 0 04 1 T T T 1 1 r - T A--~I400*C (r-0 987) / J I '\ 1 1 J l _ L 2 3 4 5 10 20 30 50 Failure Stress ( M P a ) F i g u r e 22g. W e i b u l l D i s t r i b u t i o n P l o t of CPR-270 Mean Compressive S t r e n g t h V a l u e s . Batch 264 265 266 267 268 269 270 m, A.T. 2 .881 2.039 2.184 2.008 1.709 1.997 2.630 m, 1400°C 3.499 2.018 2.310 2.607 1.519 2.752 1.714 Table XIX Weibull Modulus Values of Seven Coke Batches at Ambient Temperature and at 1400°C. 111 3.4.6 THEORETICAL ASPECTS OF COKE FRACTURE The e m p i r i c a l c o r r e l a t i o n s between coke s t r e n g t h and a number of m i c r o s t r u c t u r a l p arameters have been d i s c u s s e d above. The t r e n d s show t h a t a number of s t r u c t u r a l p a r ameters t o g e t h e r may d e t e r m i n e the coke s t r e n g t h . P a t r i c k e t a l (35) and o t h e r workers a t the BCRA (34) proposed an e q u a t i o n ( e q u a t i o n 5 ) : a=450(Fmax)"°' 5exp[-2 ( F m a x / F m i n ) 0 * 5 e p ] (5) where Fmax i s the mean maximum F e r e t ' s d i a m e t e r which i s t r e a t e d as t h e c r i t i c a l f l a w s i z e , and the term 0 5 2(Fmax/Fmin) * i s the s t r e s s c o n c e n t r a t i o n f a c t o r . U s i n g the d a t a g e n e r a t e d i n t h i s s t u d y , e q u a t i o n 5 was t e s t e d (see F i g u r e 23) where Fmax and (Fmax/Fmin) a r e t h e 80 p e r c e n t i l e v a l u e s . I t was assumed t h a t a l l f a i l u r e was i n t e n s i o n d u r i n g t h e c o m p r e s s i o n t e s t s (24) which j u s t i f i e s the use of e q u a t i o n 5 f o r t h e s e t e s t s . The s l o p e of t h e p l o t s a re 2385 and 3331 MPa f o r room tem p e r a t u r e and 1400°C, r e s p e c t i v e l y , which i s h i g h e r than 450MPa, r e p o r t e d by P a t r i c k e t a l ( 3 5 ) . I t s h o u l d be r e a l i z e d , however, t h a t the nominal c o m p r e s s i v e s t r e n g t h of b r i t t l e s o l i d s a r e always h i g h e r than the t e n s i l e s t r e n g t h ( t h e o r e t i c a l l y 8 t i m e s g r e a t e r ( 2 4 ) ) . A l t h o u g h P a t r i c k ' s e q u a t i o n d i d not c o r r e l a t e any b e t t e r than p l o t t i n g s t r e n g t h vs i n d i v i d u a l porous p a r a m e t e r s , i t has the m e r i t of p r e d i c t i n g the o b s e r v e d o r d e r of mean s t r e n g t h v a l u e s f o r the coke b a t c h e s . A c c o r d i n g t o the t h e o r y of f r a c t u r e mechanics, the f a i l u r e s t r e s s of a m a t e r i a l i s governed by i t s c r i t i c a l "1 1 1 1 1 I— l 4 0 0 ° C ( < r - 3 3 3 I F - 2 0 ) (r- 0 846) R.T (cr-2385F-l2) (r-0-821) )084 00090 F = ( F max) Figure 23. 0-0096 0-0102 0-0108 0-5 0-5 e x p ( - 2 ( F m a x / F m i n ) p ) Mean Compressive Strength versus {Fmax - 0 , 5exp[-2(Fmax/Fmin) 0 , 5p]}. 0-0M4 113 f l a w s i z e , and hence, i t s c r i t i c a l s t r e s s i n t e n s i t y f a c t o r ( 4 1 ) . The s t r e s s i n t e n s i t y f a c t o r K i s a f u n c t i o n of the n o m i n a l s t r e s s a p p l i e d and t h e f l a w s i z e , and when K reaches the c r i t i c a l s t r e s s i n t e n s i t y f a c t o r , K I C , f a i l u r e o c c u r s . N i e d and A r i n (42) d e v e l o p e d a model f o r c e r a m i c s which t r e a t e d s m a l l p o r e s as s p h e r i c a l f l a w s and d e v e l o p e d a r e l a t i o n s h i p t o c a l c u l a t e the s t r e s s i n t e n s i t y f a c t o r s by a c c o u n t i n g f o r the i n t e r a c t i o n of s t r e s s t r a j e c t o r i e s i n t h r e e d i m e n s i o n s : K = 2/rr {1/V f tan[ (*/2)V f ] } 1 / 2 a 0 / ( 2 a ) (11) where a i s t h e pore r a d i u s , i s t h e volume f r a c t i o n of p o r o s i t y , and o0 i s the nominal a p p l i e d s t r e s s . The' c r i t i c a l s t r e s s i n t e n s i t y f a c t o r s ( K I f^) f o r the seven coke b a t c h e s ar e shown i n T a b l e XX as c a l c u l a t e d u s i n g e q u a t i o n 11. The v a l u e s of K J C f o r cokes produced i n the e x p e r i m e n t a l t e s t - o v e n a r e h i g h e r than t h o s e f o r Algoma c o k e s . I t has been s u g g e s t e d p r e v i o u s l y t h a t pore shape i n f l u e n c e s the s t r e s s i n t e n s i t y f a c t o r ( 3 2 - 3 6 ) , but e q u a t i o n 11 makes no a c c o u n t f o r f l a w shape. The f l a w shape, however, i s d i f f i c u l t t o a s s e s s s t a t i s t i c a l l y i n a m a t e r i a l , such as c o k e , owing t o the complex system of p o r e s . I t i s i n t e r e s t i n g t o note t h a t the c a l c u l a t e d v a l u e s of the c r i t i c a l s t r e s s i n t e n s i t y f a c t o r s a r e s i m i l a r t o t h o s e v a l u e s c a l c u l a t e d f o r coke b a t c h e s of the same o r i g i n ( i e . t e s t - o v e n cokes have c r i t i c a l s t r e s s i n t e n s i t y f a c t o r v a l u e s c l o s e t o one a n o t h e r as do t h o s e of Algoma c o k e s ) . T h i s Coke Porosity Max. Feret's K I C Type V f Dia, 2a (MPa/mm) (mm) A.T. 1400°C CPR-264 0.555 0.518 8.560 11.006 CPR-265 0.543 0.482 9.205 11.431 CPR-266 0.513 0.506 11.341 12.084 CPR-267 0.521 0.530 7.112 8.835 CPR-268 0.562 0.573 7.542 9.810 CPR-269 0.594 0.603 6.081 4.686 CPR-270 0.559 0.566 6.980 7.982 Table XX. Calculated C r i t i c a l Stress I n t e n s i t y Factors Using a Multiple Flaw Model. 115 s u g g e s t s t h a t t h e t e x t u r a l c h a r a c t e r i s t i c s (pore s i z e ) have a s i g n i f i c a n t i n f l u e n c e on t h e m e c h a n i c a l b e h a v i o u r of coke (see s e c t i o n 4.5.2). F i g u r e s 24(a & b) i l l u s t r a t e the v a r i a t i o n of the c a l c u l a t e d K j ^ v a l u e s amongst the coke b a t c h e s t e s t e d a t room temperature and 1400°C, r e s p e c t i v e l y . The e r r o r b a r s r e p r e s e n t the range of K J (, v a l u e s t h a t would o c c u r from the mean s t r e s s range c a l c u l a t e d p r e v i o u s l y a t the 95% c o n f i d e n c e l i m i t . The t e s t - o v e n coke Kj^. v a l u e s i n c r e a s e w i t h i n c r e a s i n g oven p r e s s u r e , but t h i s t r e n d c o u l d not be found f o r t h e Algoma c o k e s . CPR-269 r e c o r d e d the l o w e s t K I (, v a l u e s a t both t e m p e r a t u r e s . 3.4.7 STABILITY AND HARDNESS Coke s t r e n g t h i s t r a d i t i o n a l l y a s s e s s e d i n N o r t h America i n a c c o r d a n c e w i t h the ASTM s t a b i l i t y and hardness s t a n d a r d ( 4 3 ) . T h i s s t a n d a r d has been p r e s e n t e d p r e v i o u s l y i n T a b l e I I I ( 1 3 ) . I t i s t h e r e f o r e d e s i r a b l e t o attempt t o d e v e l o p a r e l a t i o n s h i p d e s c r i b i n g s t a b i l i t y and hardness u s i n g c o m p r e s s i v e s t r e n g t h v a l u e s . F i g u r e 25 shows s t a b i l i t y and hardness (measured a t CANMET) v e r s u s t h e mean co m p r e s s i v e s t r e n g t h v a l u e s a t room t e m p e r a t u r e . No c o r r e l a t i o n c o u l d be ob s e r v e d between the s t a b i l i t y and ha r d n e s s and the c o m p r e s s i v e s t r e n g t h d a t a o b t a i n e d i n t h i s p r o j e c t . 116 15 13 o E E o 0. u Test-oven " Coke " U*—Algoma C o k e - e J o u v. o 6 -_L 264 265 266 267 268 269 270 CPR Coke Type F i g u r e 24a. C a l c u l a t e d C r i t i c a l S t r e s s I n t e n s i t y F a c t o r s u s i n g Ambient Temperature Compressive S t r e n g t h D a t a . 117 15 13 II O E E o 9 n 1 1 — r r r * - A l g o m a Coke-#»»i Test -oven . Coke I I ± 264 265 266 267 268 269 270 CPR Coke Type F i g u r e 24b. C a l c u l a t e d C r i t i c a l S t r e s s I n t e n s i t y F a c t o r s u s i n g Compressive S t r e n g t h Data O b t a i n e d a t 1400°C. -1 1 A A A 1 A 1 1 A A A O O O O 0 o Stability O A Hardness o 1 1 1 l i 6 8 10 12 14 16 IC Mean Compressive Strength ( M P a ) F i g u r e 25. S t a b i l i t y and Hardness v e r s u s Mean C o m p r e s s i v e S t r e n g t h . 119 3.5 HIGH TEMPERATURE CREEP A l i t e r a t u r e s u r v e y r e v e a l e d no r e f e r e n c e on t h e p l a s t i c b e h a v i o u r of b l a s t f u r n a c e coke. However, because of the e x i s t e n c e of ash h a v i n g low m e l t i n g t e m p e r a t u r e c o n s t i t u e n t s such as NajO, S i 0 2 , 1^0, e t c . (and t h e i r e u t e c t i c s ) ; some p l a s t i c d e f o r m a t i o n can be e x p e c t e d t o oc c u r when the specimens a r e h e a t e d t o t e m p e r a t u r e s g r e a t e r than 1000°C and s u b j e c t e d t o a l o a d . I n t h i s p r o j e c t , c o n s t a n t l o a d e x p e r i m e n t s were performed a t v a r y i n g t e m p e r a t u r e s ( g r e a t e r than 1000°C) and p r e s s u r e s t o d e t e r m i n e i f coke e x h i b i t s any h i g h t e m p e r a t u r e p l a s t i c i t y . Such e x p e r i m e n t s were found t o be d i f f i c u l t t o p e r f o r m as most of the specimens f a i l e d ( c o l l a p s e d ) d u r i n g l o a d i n g t o the d e s i r e d s t r e s s f o r t e s t i n g . However, a few c r e e p e x p e r i m e n t s were c a r r i e d out under a c o n s t a n t l o a d and i s o t h e r m a l c o n d i t i o n s . I n o r d e r t o e s t i m a t e the d i m e n s i o n a l change, which specimens may undergo due t o c o n t i n u e d g r a p h i t i z a t i o n above the f i n a l c o k i n g t e m p e r a t u r e , g r a p h i t i z a t i o n t e s t s were a l s o p e r formed. T h i s was n e c e s s a r y t o ensure t h a t d i m e n s i o n a l change d u r i n g c r e e p t e s t i n g was not caused by g r a p h i t i z a t i o n . 3.5.1 GRAPHITIZATION The maximum te m p e r a t u r e e n c o u n t e r e d i n a normal coke-oven i s i n the o r d e r of 1250°C, so i t i s q u i t e n a t u r a l t h a t when coke i s s u b j e c t e d t o a temperature h i g h e r than t h i s and f o r a p r o l o n g e d p e r i o d of t i m e , the specimens would 120 g r a p h i t i z e r e s u l t i n g i n an i n c r e a s e i n d e n s i t y w i t h an a s s o c i a t e d s h r i n k a g e . In o r d e r t o d e t e r m i n e the e x t e n t of s h r i n k a g e due to g r a p h i t i z a t i o n , coke specimens were heat t r e a t e d a t 1400°C as d e s c r i b e d i n s e c t i o n 2.7. The maximum l i n e a r s h r i n k a g e e n c o u n t e r e d i n the s e e x p e r i m e n t s was i n the range 0.96 t o 1.33%, which agrees w i t h d i l a t o m e t e r r e s u l t s o b t a i n e d by o t h e r w o rkers (3,23,26,27), who r e p o r t e d v a l u e s i n the range of 0.70 t o 1.0% a t t e m p e r a t u r e s r e a c h i n g 1400°C. 3.5.2 ISOTHERMAL CONSTANT LOAD TESTS The c o n s t a n t l o a d t e s t s were performed a t t e m p e r a t u r e s r a n g i n g between 1000 and 1600°C w i t h s t r e s s e s r a n g i n g from 5.0 t o 13.0MPa on the f o u r Algoma cokes (CPR-267 t o CPR-270). Such t e s t s c o u l d not be c a r r i e d out on the t e s t - o v e n cokes as t h e i r sample s i z e s were not s u f f i c i e n t l y l a r g e t o produce enough c y l i n d r i c a l specimens t o do both s t r e n g t h and c r e e p s t u d i e s . The c o n s t a n t l o a d t e s t s were performed u s i n g the h e a t i n g and l o a d i n g c o n d i t i o n s d e s c r i b e d i n s e c t i o n 2.6.2.. The d e f l e c t i o n was r e c o r d e d as a f u n c t i o n of time and was c o r r e c t e d f o r e l a s t i c s t r a i n , o b t a i n e d by removing the l o a d a t the end of the c r e e p e x p e r i m e n t s and n o t i n g t h e magnitude of t h e e l a s t i c " s p r i n g back". The f i r s t s e t of e x p e r i m e n t s performed was t o determine t h e r e p r o d u c i b i l i t y of the c r e e p c u r v e s . Three " s o - c a l l e d " s i m i l a r specimens from one b a t c h of coke (CPR-269) were 121 c r e e p t e s t e d under i s o t h e r m a l conditions(1500°C) and p r e s s u r e (6.0MPa). The n o r m a l i z e d c r e e p c u r v e s a r e shown i n F i g u r e 26. U n f o r t u n a t e l y , the c r e e p c u r v e s a r e not v e r y r e p r o d u c i b l e . S i m i l a r randomness i n c r e e p b e h a v i o r was e n c o u n t e r e d i n a l m o s t a l l o t h e r c a s e s . Because of the l a c k of a v a i l a b i l i t y of a l a r g e number of specimens h a v i n g i d e n t i c a l b u l k d e n s i t y and p r o p e r t i e s , no e x t e n s i v e c r e e p t e s t i n g c o u l d be c a r r i e d out i n t h i s program. The t e s t c o n d i t i o n s and t o t a l s t r a i n f o r a l l c r e e p e x p e r i m e n t s a r e l i s t e d i n T a b l e X X I . I t i s o b v i o u s (from F i g u r e 26) t h a t specimens were u n d e r g o i n g p l a s t i c d e f o r m a t i o n a t t e m p e r a t u r e s >1000°C and the t o t a l maximum s t r a i n t h a t c o u l d be i n t r o d u c e d was i n the o r d e r of 6 t o 8% (not t a k i n g i n t o c o n s i d e r a t i o n s h r i n k a g e due t o g r a p h i z a t i o n of ^ 1 % ) . Due t o the q u a l i t a t i v e n a t u r e of t h i s p a r t of the s t u d y , i t was c o n s i d e r e d unnessary t o a c c o u n t f o r g r a p h i t i z a t i o n s h r i n k a g e which c o u l d be v e r y d i f f i c u l t t o measure d u r i n g the c r e e p e x p e r i m e n t s . Most of the c r e e p c u r v e s a r e shown i n Appendix C, e x c e p t t h o s e of CPR-270, which were s e l e c t e d f o r f u r t h e r a n a l y s i s . The c r e e p c u r v e s of CPR-270 showed normal c r e e p b e h a v i o r w i t h r e s p e c t t o t e m p e r a t u r e and s t r e s s ( F i g u r e s 2 7 ( a - b ) ) . I n c r e a s i n g the t e m p e r a t u r e and p r e s s u r e of t e s t i n g s h o u l d produce a h i g h e r t o t a l s t r a i n , i f the assumption t h a t the m e l t i n g of ash c o n t r o l s the p l a s t i c b e h a v i o r of coke i s c o r r e c t . B o t h the c o n c e n t r a t i o n of the g l a s s y phase (ash) and i t s v i s c o s i t y s h o u l d be a f f e c t e d by t e m p e r a t u r e and qure 26. Normalized Creep Curves Produced at 1500 and 6.0MPa. 123 Coke Temperature Applied Stress Total Type of Tests During Stra in Tests (°C> (MPa) (%) 1000 12.6 6.55 CPR-267 1600 12.6 8.52 1600 12.6 6.42 1200 9.69 1.81 1400 9.69 6.08 CPR-268 1600 9.69 5.74 1600 6.0 3.22 1600 13.0 4.04 1 500 6.0 4.90 1 500 6.0 2.09 CPR-269 1500 6.0 2.30 1600 • 9.69 4,74 1500 5.0 1.71 1 100 9.29 1 .69 1 300 9.29 1 .86 CPR-270 1 500 9.29 3.12 1 500 6.0 1 .98 1 500 13.0 4.03 T a b l e X X I . C o n d i t i o n s f o r Creep T e s t s . F i g u r e 27a. Creep of CPR-270 at 1500°C Under V a r y i n g C o n d i t i o n s of A p p l i e d S t r e s s . 125 • 1500-C O 1300 # C A II00*C 20 30 40 Time (min) 50 60 F i g u r e 27b. Creep of CPR-270 a t 9.29MPa Under V a r y i n g C o n d i t i o n s of Temperature. 126 p r e s s u r e . R a i s i n g t h e t e m p e r a t u r e of coke s h o u l d have the e f f e c t of i n c r e a s i n g the c o n c e n t r a t i o n of g l a s s y phase and d e c r e a s i n g i t s v i s c o s i t y . D e v i a t i o n s from t h i s b e h a v i o r can be a t t r i b u t e d t o the v e r y complex n a t u r e of coke t e x t u r e ( l a r g e v a r i a t i o n s were e n c o u n t e r e d even i n the same b a t c h ) . An i n t e r e s t i n g o b s e r v a t i o n t h a t c o u l d be made from t h e s e c r e e p c u r v e s i s t h a t the temperature was found t o a f f e c t t h e shape of the c u r v e s . Creep c u r v e s g e n e r a t e d a t low e r t e m p e r a t u r e s (1000-1200°C) were found t o r e a c h t h e i r f i n a l s t r a i n v a l u e s ( l e v e l e d o f f ) more q u i c k l y than those produced a t h i g h e r t e m p e r a t u r e s . T h i s i n d i c a t e s a v i s c o u s t y p e f l o w ( s i m i l a r t o g l a s s ) a t h i g h e r t e m p e r a t u r e s which s u p p o r t s t h e c o n t e n t i o n t h a t i t i s t h e m e l t i n g of a s h components wh i c h produced the p l a s t i c s t r a i n . 3.5.3 CREEP BEHAVIOUR OF COKE The d e t e r m i n a t i o n of the mechanisms of t h e c r e e p b e h a v i o u r of coke i s beyond the scope of t h i s i n v e s t i g a t i o n and r e q u i r e s more e x t e n s i v e s t u d y . However, the shape of the c r e e p c u r v e s was found t o be s i m i l a r t o c r e e p c u r v e s of r e f r a c t o r i e s ( 4 4 , 4 5 ) . The c r e e p b e h a v i o r of r e f r a c t o r i e s a r e o f t e n a n a l y z e d by v i s c o - e l a s t i c models as the systems a r e t o o complex t o be a n a l y z e d u s i n g any a t o m i s t i c mechanisms. In alm o s t a l l c a s e s , t h e c r e e p of r e f r a c t o r i e s i s due t o t h e f o r m a t i o n of a g l a s s y phase produced by low m e l t i n g t e m p e r a t u r e c o n s t i t u e n t s ( 4 5 ) . F u r t h e r m o r e , i t was r e p o r t e d t h a t an 127 i n c r e a s e i n p o r o s i t y reduces t h e a b i l i t y of r e f r a c t o r i e s t o r e s i s t c r e e p ( 4 5 ) . S i n c e coke i s a h i g h l y porous s o l i d c o n t a i n i n g low m e l t i n g t e m p e r a t u r e phases (ash c o n s t i t u e n t s ) , i t i s n a t u r a l t h a t an attempt be made t o a n a l y z e the c r e e p d a t a of coke u s i n g a v i s c o - e l a s t i c model. A l s o , the complex n a t u r e of t h e coke s t r u c t u r e does not p e r m i t any i n t e r p r e t a t i o n of the c r e e p of coke u s i n g any a t o m i s t i c model. 3.5.4 VISCO-ELASTIC MODELS Three models a r e c o n s i d e r e d f o r the a n a l y s i s of t h e c r e e p b e h a v i o r of coke. These a r e a s i n g l e - K e l v i n u n i t ( F i g u r e 2 8 a ) , an i n t e r a c t i v e d o u b l e - K e l v i n element u n i t (46,47) ( F i g u r e 28b) and t h r e e - n o n - i n t e r a c t i v e - K e l v i n u n i t s (48) ( F i g u r e 2 8 c ) . Of th e s e t h r e e models, o n l y t h e i n t e r a c t i v e d o u b l e - K e l v i n element model i s found t o a d e q u a t e l y d e s c r i b e the response of coke s u b j e c t t o c o n s t a n t l o a d t e s t s . 3.5.5 ANALYSIS OF CREEP DATA The a n a l y s i s of the c r e e p d a t a was c a r r i e d out u s i n g a v i s c o - e l a s t i c model d e r i v e d p r e v i o u s l y (46,47) f o r h o t - p r e s s i n g of c e r a m i c powders. In F i g u r e s 27(a & b ) , t h e 128 Figure 28a. Single-Kelvin Unit. / / //)/////////////////////// F i g u r e 28b. I n t e r a c t i v e - d o u b l e - K e l v i n U n i t . 130 M, • M 2 • • u n n r i u mn Figure 28c. Three-non-interactive-Kelvin Units, 131 p o i n t s c o r r e s p o n d t o e x p e r i m e n t a l d a t a and the l i n e s as drawn can be r e p r e s e n t e d by an e q u a t i o n as f o l l o w s : e=AL/L o=K(1-Ae~ a t-Be" / 3 t) (12) The parameters K,A,B,a and 0 can be d e t e r m i n e d by d i g i t i z i n g e x p e r i m e n t a l c u r v e s and t h e n , u s i n g a computer, f i t t i n g the d a t a t o e q u a t i o n 12. I t i s a l s o p o s s i b l e t o f i t the c r e e p c u r v e s t o a s i x t h o r d e r p o l y n o m i a l ( 4 6 ) , but such an e q u a t i o n would not l e n d i t s e l f t o the development of a v i s c o - e l a s t i c model. The problem can be r e p r e s e n t e d u s i n g system dynamics (47) where a s t e p i n p u t s t r e s s : o = a 0 U c ( t ) (13) where 0 f o r t < 0 1 f o r t > 0 U c ( t ) = (14) produces a s t r a i n o u t p u t ( e q u a t i o n 12). T h e r e f o r e , the s t r a i n can be r e p r e s e n t e d by the p r o d u c t of s t r e s s and the system t r a n s f e r f u n c t i o n : e=xo (15) where x i s a t r a n s f e r f u n c t i o n . 132 A d i f f e r e n t i a l e q u a t i o n f o r t h e system can be found by a p p l y i n g t h e L a p l a c e t r a n s f o r m t o e q u a t i o n 15 (51) ( r e p r e s e n t e d by c a p i t a l l e t t e r s ) : E = X L (16) where « - * ( . < t » - f - J b ! - H K(s+a)(s+g)-KAs(s+fl)-KBs(s+g) s ( s + a ) ( s + 0 ) and I = £(U ( t ) ) • 1/s T h e r e f o r e , the L a p l a c e t r a n s f o r m of the t r a n s f e r f u n c t i o n i s found t o be ( t a k i n g i n t o c o n s i d e r a t i o n t h a t a t t=0, e ( t ) = 0, t h e r e f o r e , A+B=1): E _ x _ sK(Aa+B/3)+Kag (17) Z s 2+(g+ 0)s+ g 0 which can be a r r a n g e d t o g i v e : E [ s 2 + (g+0)s+g/3] = I[sK(Ag+B/3)+Kg/3] (18) T a k i n g t h e i n v e r s e L a p l a c e t r a n s f o r m of e q u a t i o n 18 produces t h e d i f f e r e n t i a l e q u a t i o n : + (a+p)— + g/3c = K(Ag+B/3) d^ + Kg/3a (19a) d t 2 d t d t T h i s d i f f e r e n t i a l e q u a t i o n i s s i m i l a r t o t h a t which 133 d e s c r i b e s t h e b e h a v i o r of t h e two i n t e r a c t i v e K e l v i n e l ements shown i n F i g u r e 28b (4 6 , 4 7 ) : i l l + [^(Mi+Mai+Man, ] de + [M,Ma ] £ d t 2 T7,T7 2 dt [ T 7 , 7 ? 2 ] = _1_d£ +. [MjMx] 0 { l 9 b ) The s p r i n g c o n s t a n t s and the dashpot v i s c o s i t i e s have been shown t o be r e l a t e d t o K, A, B, a, and 0 by: T)2 = l/K[Aa+B0] (20) M 2 = 7 7 2 [a+p,-Ka/377 2 ] (21) TJ 1 = M 2 2 /T? 2[Ka/3M 2-a/3] (22) M i » nyr\2a$M2 (23) T h i s m e c h a n i c a l analogue was used t o d e s c r i b e the components of c r e e p s t r a i n f o r t h e coke samples t e s t e d under a c o n s t a n t l o a d , and under i s o t h e r m a l c o n d i t i o n s . The v a l u e s of t h e s e m e c h a n i c a l parameters a r e c a l c u l a t e d u s i n g the v a l u e s of K, A, B, a, 0 of the e x p e r i m e n t a l c u r v e s and a r e shown i n the Appendix C. The te m p e r a t u r e and s t r e s s dependence of T J , , T ? 2 , M, , M 2 a r e i l l u s t r a t e d i n F i g u r e s 29 (a & b ) , r e s p e c t i v e l y . In b o t h f i g u r e s , t h e v i s c o s i t y parameter 77, has much h i g h e r v a l u e s than t h o s e of T J 2 , M,, and M 2. The parameter, T J , , a l s o a p p e a r s t o be both t e m p e r a t u r e and s t r e s s s e n s i t i v e whereas the o t h e r t h r e e parameters a r e r e l a t i v e l y i n s e n s i t i v e . The s i g n i f i c a n c e of t h i s b e h a v i o u r w i t h r e s p e c t t o te m p e r a t u r e 134 F i g u r e 29a. V a r i a t i o n i n V i s c o - E l a s t i c Model M e c h a n i c a l Parameters as a F u n c t i o n of Temperature f o r CPR-270. 135 20001 1 r 1 1 1 r o 1 1 1 r- 1 1 r~ 6 6 10 12 Applied Stress (MPa) F i g u r e 29b. V a r i a t i o n i n V i s c o - E l a s t i c M e c h a n i c a l Parameters as a F u n c t i o n of A p p l i e d P r e s s u r e f o r CPR-270. 136 and p r e s s u r e cannot be e x p l a i n e d a t p r e s e n t . However, any r e s i s t a n c e t o f l o w i m p l i e s t h a t v e r y h i g h v i s c o s i t y i n the system and t h e r e d u c t i o n of v a l u e s of TJ, w i t h t emperature may be a s s o c i a t e d w i t h the i n c r e a s i n g f l o w p r o p e r t i e s of 4. DISCUSSION In t h e p r e v i o u s c h a p t e r , t h e r e s u l t s o b t a i n e d i n t h i s s t u d y have been a n a l y z e d . However, i t i s w o r t h w h i l e t o c r i t i c a l l y e v a l u a t e some of the a t t e m p t e d c o r r e l a t i o n s a l r e a d y made. B e f o r e d o i n g t h i s e v a l u a t i o n , t h e t o t a l e f f o r t s w i l l be summarized f i r s t . As o u t l i n e d i n s e c t i o n 1 . 6 , an e f f o r t has been made t o s t u d y t h e v a r i a t i o n of coke p r o p e r t i e s ( m i c r o s t r u c t u r e and s t r e n g t h both a t ambient and h i g h t e m p e r a t u r e s ) as a f u n c t i o n of p o s i t i o n ( h e i g h t ) i n a coke-oven b a t t e r y . S e c o n d l y , a wharf coke sample t o r e p r e s e n t t h e oven-coke, as a whole, was a l s o used as the c o n t r o l sample. T h i s was done i n o r d e r t o compare t h i s wharf coke w i t h cokes e x t r a c t e d from v a r i o u s h e i g h t s i n Algoma's 5m coke-oven. F u r t h e r m o r e , t h r e e t e s t - o v e n samples made from the same c o a l b l e n d but p r e p a r e d under v a r y i n g c o k i n g c o n d i t i o n s were a l s o t e s t e d f o r f u r t h e r c o mparison w i t h t h e c o m m e r c i a l l y produced samples. The e x p e r i m e n t a l program i n v o l v e d q u a n t i f y i n g the m i c r o s t r u c t u r e of the coke u s i n g an automated image a n a l y z e r and c o r r e l a t i n g the m i c r o s t r u c t u r a l parameters w i t h c o m p r e s s i v e s t r e n g t h v a l u e s o b t a i n e d both a t ambient and h i g h t e m p e r a t u r e s . L a s t l y , the p l a s t i c b e h a v i o u r of the i n d u s t r i a l coke samples was q u a l i t a t i v e l y e v a l u a t e d a t t e m p e r a t u r e s above 1000°C. 137 138 4.1 BULK DENSITY I n i t i a l l y , t h e b u l k d e n s i t y of the coke samples was c o n s i d e r e d as a major parameter f o r d i s t i n g u i s h i n g each of t h e seven coke b a t c h e s (CPR-264 t o CPR-270).The b u l k d e n s i t y of coke depends on i t s ash c o n t e n t , the carbonaceous p r o d u c t , i t s t r u e d e n s i t y , and i t s p o r o s i t y . S i n c e t h e s e coke samples were produced from the same c o a l b l e n d , t h e i r a s h c o n t e n t s h o u l d be s i m i l a r i f not the same. For t h i s r e a s o n , the b u l k d e n s i t y was c o n s i d e r e d a good parameter f o r d i s t i n g u i s h i n g t h e coke b a t c h e s . 4.1.1 RELIABILITY OF BULK DENSITY RESULTS A c c o r d i n g t o t h e ASTM s t a n d a r d s ( 5 7 ) , a 50 pound sample of wharf coke must be used when d e t e r m i n i n g t h e sample b u l k d e n s i t y . Such a l a r g e sample s i z e i s n o r m a l l y c o n s i d e r e d n e c e s s a r y t o get a r e p r e s e n t a t i v e v a l u e . However, t h i s was not p o s s i b l e f o r the purpose of t h i s p r o j e c t s i n c e the l a r g e sample s i z e s needed and the n e c e s s a r y equipment were not a v a i l a b l e . The b u l k d e n s i t y was t h e r e f o r e d e t e r m i n e d by measuring t h e volume of n e a r - p e r f e c t d r i l l - c o r e specimens and t h e i r r e s p e c t i v e w e i g h t s . The r e s u l t s showed c o n s i d e r a b l e s c a t t e r as r e p r e s e n t e d i n F i g u r e 18a by t h e e r r o r b a r s ( s t a n d a r d d e v i a t i o n ) . The number of specimens measured i n t h i s way ranged between 32(CPR-265) and 131(CPR-269), which was governed by t h e s i z e of t h e sample b a t c h e s s u p p l i e d by CANMET. There i s a c o n s i d e r a b l e " o v e r l a p " of the b u l k d e n s i t y ranges ( e r r o r 1 39 b a r s ) of the seven coke b a t c h e s . T h i s r a i s e d c o n c e r n about the p o s s i b i l i t y t h a t p o p u l a t i o n mean bu l k d e n s i t i e s c o u l d be the same. An a n a l y s i s of v a r i a n c e of the b u l k d e n s i t y v a l u e s u s i n g the One-Way C l a s s i f i c a t i o n t e c h n i q u e (29) was employed a t 99% c o n f i d e n c e t o t e s t t h i s p o s s i b i l i t y . The r e s u l t s showed t h a t a t l e a s t two sample mean b u l k d e n s i t y v a l u e s d i f f e r e d . A more i n de p t h a n a l y s i s ( s i n g l e - d e g r e e - o f - f r e e d o m c omparisons (29)) r e v e a l e d t h a t the i n d i v i d u a l mean bu l k d e n s i t i e s do i n f a c t d i f f e r from one another i n most c a s e s . T a b l e XXII shows t h e p r o b a b i l i t y t h a t i n d i v i d u a l c o m p a r i s o n s have the same mean bu l k d e n s i t y . Blank spaces i n the t a b l e i n d i c a t e t h a t t h e r e i s no s i g n i f i c a n t d i f f e r e n c e between t h e two coke b a t c h e s . The coke b a t c h e s CPR-264, CPR-265, CPR-268 and CPR-270 p o s s e s s s i m i l a r mean b u l k d e n s i t y v a l u e s when compared a t a l e v e l of s i g n i f i c a n c e of 0.01. An i n t e r e s t i n g r e s u l t of t h i s a n a l y s i s i s t h a t the mean bu l k d e n s i t y v a l u e of CPR-270 (wharf coke) i s r e p r e s e n t a t i v e of the c o m b i n a t i o n of b u l k d e n s i t y v a l u e s o b t a i n e d from CPR-267, CPR-268, and CPR-269 (Algoma cokes) but i s not r e p r e s e n t a t i v e of the t e s t - o v e n c o k e s . F u r t h e r m o r e , the mean bu l k d e n s i t y v a l u e s of CPR-264, CPR-265, and CPR-266 as a group do not r e p r e s e n t t h o s e of CPR-267,CPR-268, and CPR-269 which they were i n i t i a l l y i n t e n d e d t o do (see Appendix D). 4.1.2 OVEN PRESSURE 1 Bulk d e n s i t y was shown t o be a f f e c t e d by the p r e s s u r e ' A l l p r e s s u r e s e x i s t i n g i n a b a t t e r y ( s t a t i c or o t h e r ) a r e r e f e r r e d t o as oven p r e s s u r e s . 264 265 266 267 268 269 270 264 — 0.01 0.01 0.01 265 — 0.01 0.05 0.01 0.05 266 0 .01 0.01 — 0.05 0.01 0.01 0.01 267 0 .01 0.05 0.05 — 0.01 0.01 0.01 268 0.01 0.01 — 0.01 0.05 269 0 .01 0.01 0.01 0.01 0.01 — 0.01 270 0.05 0.01 0.01 0.05 0.01 — Table XXII • Probabi1ity that The Assupmtion of Di f fer ing Bulk Densities i s Erroneous for Comparisons Between Coke Batches. 141 of the oven w a l l s d u r i n g c o k i n g i n the t e s t - o v e n s ( F i g u r e 18b). The r e l a t i o n s h i p between the b u l k d e n s i t y and the oven w a l l p r e s s u r e e x i s t i n g i n the coke-oven was found t o be: P b(gm/cm 3) = 0 . 1 1 [ l o g 1 Q P ( K P a ) ] + 0 . 8 0 8 T h i s e q u a t i o n , however, was d e r i v e d u s i n g o n l y t h r e e d a t a p o i n t s (from t e s t - o v e n cokes) s i n c e i t was i m p o s s i b l e t o d e t e r m i n e the p r e s s u r e i n an o p e r a t i n g i n d u s t r i a l coke-oven. Shown a l s o i n F i g u r e 18b a r e the e s t i m a t e d p o i n t s f o r the t h r e e Algoma cokes based on t h e i r b u l k d e n s i t y v a l u e s . The d i f f e r e n c e i n c o k i n g p r e s s u r e i n the i n d u s t r i a l coke-oven can be a t t r i b u t e d t o the s t a t i c l o a d e x i s t i n g on the c h a r g e . I t s h o u l d be mentioned, however, t h a t t h e r e may be o t h e r v a r i a b l e s (such as v e r t i c a l t e m p e r a t u r e g r a d i e n t s ) a f f e c t i n g the f i n a l b u l k d e n s i t y of the Algoma coke. F i g u r e 30 i l l u s t r a t e s t he v a r i a t i o n of t e m p e r a t u r e s as a f u n c t i o n of time i n the Algoma No.9 b a t t e r y f o r the t h r e e p o s i t i o n s from where cokes CPR-267(sole) t o CPR-269(top) were sampled ( 4 9 ) . The t e m p e r a t u r e h i s t o r i e s of the t h r e e p o s i t i o n s a r e somewhat v a r i e d w i t h f i n a l t e m p e r a t u r e s b e i n g 935°C, 1195°C, and 1262°C f o r the t o p , m i d d l e , and s o l e p o s i t i o n s , r e s p e c t i v e l y . The e f f e c t of f i n a l c o k i n g t emperature on the coke b u l k d e n s i t y i s u n c e r t a i n but i t i s p o s s i b l e t h a t the t e m p e r a t u r e e f f e c t may be s i g n i f i c a n t . 4.1.3 TRUE DENSITY The t r u e d e n s i t y of a l l seven coke b a t c h e s was d e t e r m i n e d from the samples t a k e n 2cm from t h e c a u l i f l o u r 142 O e 16001 1400 1200 1000 5 800 o S. 600 E £ 400 -200 0 — T — i — i — i — i — r Top 0-5m below Coal Line Mid- 2-5m below Cool Line — Sole 4-5m below ± 4 8 12 16 Time After Charge (hours) 20 F i g u r e 30. Temperature H i s t o r i e s Measured i n the Algoma No. 9 Coke-oven B a t t e r y a t the Top,Middle and So l e P o s i t i o n s . 143 edge.This was n e c e s s a r y as a p r e c a u t i o n a g a i n s t p o s s i b l e t r u e d e n s i t y v a r i a t i o n as a f u n c t i o n of p o s i t i o n a l o n g the oven w i d t h . Two f l u i d s were used i n the p y c n o m e t r i c d e t e r m i n a t i o n of t r u e d e n s i t y g i v i n g s i x measurements f o r each of the seven coke t y p e s . From T a b l e IX, t h e s t a n d a r d d e v i a t i o n ranged between 1.1% (CPR-268) and 4.5%(CPR-265). The v a r i a t i o n ( i e . s t a n d a r d d e v i a t i o n ) between measurements was seen t o be g r e a t e r f o r the t e s t - o v e n cokes than those e n c o u n t e r e d f o r the Algoma c o k e s . The t r u e d e n s i t y v a l u e s f o l l o w e d no p a r t i c u l a r t r e n d . T h e o r e t i c a l l y , t h e t e s t - o v e n coke s h o u l d a l l have s i m i l a r t r u e d e n s i t y v a l u e s s i n c e they were produced under s i m i l a r c o n d i t i o n s of c o k i n g time and t e m p e r a t u r e ( 5 ) . Algoma coke was e x p e c t e d t o show i n c r e a s i n g t r u e d e n s i t y v a l u e s toward the s o l e of the coke-oven as the t e m p e r a t u r e was h i g h e r i n t h i s r e g i o n . For t h e wharf coke (CPR-270), t h e t r u e d e n s i t y v a l u e was c a l c u l a t e d as an average of CPR-267, CPR-268 and CPR-269, s i n c e the sample r e q u i r e d t o a c h i e v e a r e p r e s e n t a t i v e v a l u e would have t o be e x t r e m e l y l a r g e . 4.2 MICROSTRUCTURE Two s o u r c e s of e r r o r a r e p o s s i b l e when making q u a n t i t a t i v e m i c r o s t r u c t u r a l a n a l y s i s from p h o t o g r a p h s : 1. I n a c c u r a c i e s a s s o c i a t e d w i t h r e p r e s e n t i n g a t h r e e 144 d i m e n s i o n a l system u s i n g a two d i m e n s i o n a l photographs, and 2. The e f f e c t of l a r g e p o r e s c r o s s i n g the b o u n d a r i e s of the measurable a r e a . The f i r s t problem i s e a s i l y t a k e n c a r e of by i n c r e a s i n g the a r e a of a n a l y s i s ( i e . i n c r e a s i n g the number of p h o t o g r a p h s ) . However, the problem of l a r g e p o r e s c r o s s i n g t h e b o u n d a r i e s of t h e measurable a r e a i s l e s s e a s i l y s o l v e d . T a b l e XII shows the d i f f e r e n c e s between t h e mean v a l u e s of seven m i c r o s t r u c t u r a l p arameters w i t h and w i t h o u t "edge" p o r e s . The r e s u l t s show a s i g n i f i c a n t d e c r e a s e i n mean v a l u e s when edge po r e s a r e e l i m i n a t e d . D e c r e a s i n g the m a g n i f i c a t i o n of the photographs c o u l d reduce t h i s e f f e c t but would d e c r e a s e t h e a c c u r a c y of such measurements, s i n c e t h e measurments a r e o n l y as a c c u r a t e as the s m a l l e s t " p i x e l p o i n t " on the T.V. m o n i t o r , and a r e , t h e r e f o r e , r e s o l u t i o n dependent. S i n c e s m a l l p o r e s a r e d i f f i c u l t t o r e s o l v e , the m a g n i f i c a t i o n of each photograph was s e t a t 12X. In a d d i t i o n , i t was d e c i d e d t h a t edge po r e s would a l s o be i n c l u d e d i n t h e a n a l y s i s because i t i s the l a r g e s t pore (or p o r e s ) which i s e x p e c t e d t o have the g r e a t e s t i n f l u e n c e on coke m e c h a n i c a l b e h a v i o u r . Comparison between p o r o s i t y v a l u e s measured u s i n g both pycnometry and image a n a l y s i s i s made i n T a b l e XI. The image a n a l y z e r c o n s i s t e n t l y produced h i g h e r p o r o s i t y v a l u e s than t h o s e o b t a i n e d by pycnometry. T h i s can be a t t r i b u t e d t o dark a r e a s p r e s e n t i n the pore w a l l s caused by i n s u f f i c i e n t 145 p o l i s h i n g ( i e . a r e a s w i t h rough s u r f a c e ) . A l t h o u g h the p o r o s i t y v a l u e s o b t a i n e d u s i n g pycnometry and t h o s e o b t a i n e d by t h e image a n a l y z e r d i f f e r , they do show e s s e n t i a l l y the same r e l a t i v e v a r i a t i o n between the d i f f e r e n t coke b a t c h e s and t h i s i s shown by e q u a t i o n 9 ( s e c t i o n 3.3.1). The p o r o s i t y v a l u e s c a l c u l a t e d u s i n g the r e s u l t s of b u l k d e n s i t y and t r u e d e n s i t y v a r i e d l i n e a r l y w i t h t h o s e v a l u e s d e t e r m i n e d u s i n g the image a n a l y z e r . T h i s j u s t i f i e d t h e a s s u m p t i o n t h a t the image a n a l y z e r d e s c r i b e d t h e m i c r o s t r u c t u r e s of t h e v a r i o u s coke b a t c h e s r e l a t i v e t o one a n o t h e r . T h i s i s i m p o r t a n t , s i n c e most of t h e e f f o r t was d i r e c t e d more toward v a r i a t i o n between coke t e x t u r e and i t s e f f e c t on t h e c o m p r e s s i v e s t r e n g t h than on t h e a c q u i s i t i o n of a b s o l u t e v a l u e s o f m i c r o s t r u c t u r a l p a r a m e t e r s . 4.3 EFFECT OF COKING CONDITIONS ON MICROSTRUCTURE The coke samples used i n t h i s s t u d y were a l l produced from the same c o a l b l e n d , but under a v a r i e t y of c o k i n g c o n d i t i o n s . The e f f e c t s of d i f f e r e n t c o k i n g c o n d i t i o n s on the pore s t r u c t u r e of coke a r e d e s c r i b e d below. 4.3.1 CELL WALL THICKNESS T a b l e X I I I summarizes the measured c e l l w a l l s i z e of a l l seven coke b a t c h e s . I t i s i m m e d i a t e l y a p p a r e n t t h a t the c okes produced i n t h e 460mm t e s t - o v e n p o s s e s s t h i n n e r c e l l w a l l s than t h o s e produced i n Algoma. T h i s i s c o n t r a r y t o the r e s u l t s of the BCRA ( 3 1 ) , where t h e y c l a i m e d t o f i n d no 146 s i g n i f i c a n t e f f e c t of oven s i z e on t h e c e l l w a l l t h i c k n e s s . However, t h e i r r e s u l t s showed c e l l w a l l s i z e s of 0.125, 0.134, and 0.137mm f o r t h e 250kg, 350kg, and 17 tonnes ovens, r e s p e c t i v e l y . T h i s may i n d i c a t e t h a t t h e r e was an o v e n - s i z e e f f e c t i n t h e i r r e s u l t s . The v a r i a t i o n i n t h e f i n a l c o k i n g t e m p e r a t u r e as a f u n c t i o n of h e i g h t i n an Algoma coke-oven, has been i l l u s t r a t e d i n F i g u r e 30. As can be seen i n T a b l e X X I I I , no d i r e c t dependence of c e l l w a l l s i z e on e s t i m a t e d f i n a l c o k i n g temperature was o b s e r v e d . P e r c h ( 5 ) , a l s o r e p o r t e d t h a t c e l l w a l l s i z e was independent of f i n a l c a r b o n i z i n g t e m p e r a t u r e f o r c o a l s c a r b o n i z e d above the r e s o l i d i f i c a t i o n t e m p e r a t u r e . Coke-oven p r e s s u r e and c o a l m o i s t u r e c o n t e n t showed no apparent e f f e c t on c e l l w a l l s i z e of the cokes examined. In c o n t r a s t , i t has been w e l l documented t h a t p r e h e a t i n g ( d r y i n g ) c o a l p r i o r t o c h a r g i n g has r e s u l t e d i n a f i n e r p o r e - w a l l t h i c k n e s s (31,50). 4.3.2 PORE SIZE AND GEOMETRY The pore s i z e and geometry v a l u e s of t h e seven coke b a t c h e s w i t h t h e i r r e s p e c t i v e c o k i n g c o n d i t i o n s a r e summerized i n T a b l e XXIV. For t h e purpose of t h i s d i s c u s s i o n , pore s i z e i s r e p r e s e n t e d as the 80% cummulative f i n e r mean c h o r d l e n g t h , and geometry i s r e p r e s e n t e d as the r a t i o of the maximum t o minimum F e r e t ' s d i a m e t e r s . Coke Oven Est imated Charge C e l l Sample Pressure Coking Moisture Wall Temperature Content Size CPR- kPa <°C) ( % ) (mm) 264 3.2 1250 5.9 0.131 265 5.9 1250 4.1 0.122 266 17.8 1250 1.2 0.131 267 10.2 1260 N/A 0.154 268 4.9 1200 N/A 0.152 269 0.54 940 N/A 0.168 270 — — N/A 0.169 Table XXIII. C e l l Wall Size Values as a Function of Coking Condit ions (Oven pressure estimated for Algoma Coke). Coke Oven Estimated Coal Mean Fmax Number Batch Pressure Coking Charge Chord Fmin of CPR- (kPa) Temperature Moisture Length Pores per (°C) ( % ) (mm) F i e l d 264 3.2 1250 5.9 0.229 1 .771 121 265 5.9 1250 4.1 0.222 1.714 140 266 17.8 1250 1.2 0.224 1 .755 126 267 10.2 1260 N/A 0.231 1 .749 115 268 4.9 1200 N/A 0.243 1 .754 101 269 0.54 940 N/A 0.255 1 .766 89 270 — — N/A 0.251 1 .766 97 T a b l e XXIV. Pore S i z e and Geometry Values as a Function of Coking C o n d i t i o n s . 149 Figures 31a and b i l l u s t r a t e the relationship between the pore size as a function of the estimated coking temperature and oven pressure, respectively. It appears that pore size decreases with increasing temperature and oven pressure. The existance of oven wall pressure during the production of the test-oven cokes seems to be p o s i t i v e l y correlated to the coal-charge bulk density (see table IV). This agrees with the obsevations of other workers (5,31) who have observed a similar decrease in the pore size r e s u l t i n g from an increase in the coal charge bulk density. The value of (Fmax/Fmin) did not show much va r i a t i o n between coke batches with values ranging between 1.7 and 1.766. This compares with values between 1.7 and 1.9 reported by Patrick (31-36) and other BCRA workers. Their studies showed that the value of the shape factor was found to be dependent on the number of orientations performed on each measurement. The BCRA (34) studies showed that the error for measuring maximum Feret's diameter ranged between 8.3% for four orientations, and 0.5% for sixteen orientations. In t h i s study, twelve measurements at 15° in t e r v a l s were made to obtain the maximum and minimum Feret's diameters since t h i s was the maximum number of orientations that could be performed using the L e i t z TAS PLUS image analyzer. A s t a t i s t i c a l analysis performed by BCRA (34) showed that the probable error of estimate for the determination of maximum Feret's diameter using twelve 150 E E 0-25 I?024 o> TJ k. O O o-23 c o CD 0-22. o Test-Oven Coke A Algoma Coke A O o o 900 K>00 1100 1200 1400 Estimated Coking Temperature ( ° C ) Figure 31a. Pore Size as a Function of Estimated Coking Temperature. 151 0-25 E E 0-24 a> _) o JC O c D IE 023 0-22 A Test-oven Coke O Algoma Coke -r—r A J _ l _ T T J _ J _ L 0-5 I 2 5 10 Estimated Oven Pressure (kPa) 20 F i g u r e 31b. Pore S i z e as a F u n c t i o n of E s t i m a t e d Oven P r e s s u r e . y 152 orientations was approximately 1%. The average number of pores per f i e l d of view i s also l i s t e d in Table XXIV for each of the seven coke batches studied. In general, cokes with smaller pores had a larger t o t a l number of pores than cokes containing larger pores. Thus, these values appear to be related to coking conditions where the number of pores i s found to increase with coking temperature and oven pressure. 4.3.3 SUMMARY OF MICROSTRUCTURAL DEPENDENCE ON COKING  CONDITIONS . It can be concluded from the above, that the c e l l wall thickness i s not greatly dependent on the conditions of coking. However, c e l l wall thickness was found to be greater for cokes produced in the Algoma coke-oven than those of the test-oven cokes. In contrast, the pore size was shown to increase at a lower f i n a l carbonization temperature and lower oven pressure (or lower coal charge bulk density). The temperature of coking and the e x i s t i n g oven pressure are lower near the coal l i n e of" a commercial coke-oven which re s u l t s in coke products exhibiting larger pores. 4.4 COKE STRENGTH The importance of coke strength on the e f f i c i e n c y of a blast furnace has already been outlined. One of the main objectives of t h i s project i s to determine the factors which 153 i n f l u e n c e the coke s t r e n g t h and t o r e l a t e t h e s e t o c u r r e n t coke p r o d u c t i o n p r a c t i c e s . 4.4.1 EFFECT OF TEMPERATURE T a b l e XVI i n c l u d e s t h e mean c o m p r e s s i v e s t r e n g t h v a l u e s f o r t h e seven coke b a t c h e s both a t ambient t e m p e r a t u r e and at 1400°C. The coke s t r e n g t h i n c r e a s e d i n e v e r y case except w i t h the coke b a t c h CPR-269 when t e s t e d a t 1400°C. The cause of t h i s d i s c r e p a n c y (CPR-269) can not be e x p l a i n e d but may be due t o a n o n - r e p r e s e n t a t i v e sample used i n t h i s i n v e s t i g a t i o n . A s i m i l a r e f f e c t of i n c r e a s i n g s t r e n g t h a t h i g h t e m p e r a t u r e has a l s o been obse r v e d by p r e v i o u s workers s t u d y i n g coke (19) and g r a p h i t e ( 4 0 ) . The i n c r e a s e i n coke s t r e n g t h when heated above the c a r b o n i z a t i o n temperature i s e x p l a i n e d by i t s c o n t i n u e d g r a p h i t i z a t i o n above the c o k i n g t e m p e r a t u r e s . In g r a p h i t e , t h i s s t r e n g t h i n c r e a s e a t h i g h e r t e m p e r a t u r e s has been a t t r i b u t e d t o r e l i e v i n g the r e s i d u a l s t r e s s e s formed d u r i n g the i n i t i a l g r a p h i t i z a t i o n - and subsequent c o o l i n g ( 4 0 ) . The h i g h t e m p e r a t u r e s t r e n g t h t e s t s performed i n t h i s p r o j e c t were o n l y c a r r i e d out i n an i n e r t gas ( A r ) . I t i s p r o b a b l e t h a t the i n c r e a s e i n s t r e n g t h would be a f f e c t e d or even n o n - e x i s t e n t i f t h e s e t e s t s were performed i n a C 0 2 atmosphere, s i n c e the pore w a l l s would be s u b j e c t e d t o a t t a c k by the Boudouard r e a c t i o n . No such e x p e r i m e n t s have y e t been r e p o r t e d i n t h e l i t e r a t u r e . 154 4.4.2 EFFECT OF MICROSTRUCTURE As with most porous s o l i d s , the strength has been shown to be reduced with increasing porosity (Figure 20) and conversely the strength increased l i n e a r l y with bulk density (Figure 19a). These trends have been extensively studied in the past, p a r t i c u l a r l y in the f i e l d of ceramics. Though these parameters (porosity and bulk density) generally have provided a q u a l i t a t i v e c o r r e l a t i o n with coke strength, i t is important to explore the cause of these observed variations in coke strength. It has been demonstrated in section 4.1.1 that the coke batches CPR-264, CPR-265, CPR-268, and CPR-270 have sim i l a r bulk densities (using one-degree-of-freedom comparisons) but they vary in compressive strength both at ambient and high temperatures. These differences may be caused by variations in pore size d i s t r i b u t i o n s and pore geometry. Figures 22(a-g) show that a r i s e in compressive strength correlates with decreasing c e l l wall s i z e , pore s i z e , and with increasing number of pores. It i s surprising that strength rises with decreasing c e l l wall size and increasing number of pores, but t h i s effect can be explained by considering the pore size to be the dominant factor a f f e c t i n g the strength. For example, i f two cokes have the same porosity, the coke with larger pores w i l l contain a smaller number of pores which are, on average, more widely spaced than a coke with smaller pores. Figure 32 i l l u s t r a t e s how the c e l l wall size and the number of pores per f i e l d are 155 Figure 32. C e l l Wall Size and Number of Pores per F i e l d as a Function of Pore Size. 1 56 just a consequence of the pore s i z e . This observation disagrees with the implications of Patrick's equation (equation 4, section 1.5.3) that pore size, c e l l wall size and the number of pores per f i e l d are independent of one another (37,42). It can be concluded, therefore, that the pore size has perhaps the greatest effect on coke strength compared with a l l other pore parameters. This supports the arguement that the c r i t i c a l flaw size governing f a i l u r e may be related to pore s i z e . Patrick et a l (35) also proposed an equation which suggests that there i s a strength dependence on the pore shape factor (equation 5). This equation was tested with the present data (Figure 23) and, as can be seen, the c o r r e l a t i o n was poor. This may be due to the d i f f i c u l t y of s t a t i s t i c a l l y describing the shape of the pores. Furthermore, no interaction of stress around pores was considered in the derivation equation 5. For t h i s reason, i t was decided to apply an equation developed by Neid and Arin (42) which i s a multiple flaw model that can predict the c r i t i c a l stress i n t e n s i t y factor (K J C) f ° r porous materials. Using porosity values and maximum Feret's diameter as the flaw s i z e , the values of R I C were calculated for a l l seven coke batches. Judging by the compressive strength values of coke, qu a l i t y of coke in the Algoma coke-oven i s better for samples extracted from the sole region of the oven than those obtained at higher positions. This may be due to both 157 the effect of a less porous product, and smaller pores in cokes produced at the sole l e v e l . Porosity and pore size appear to be affected by the following factors: s t a t i c load (oven pressure), f i n a l coking temperature and oven s i z e . To produce a stronger coke, i t i s best to increase the s t a t i c load on the charge and increase the f i n a l coking temperature. 4.5 CREEP OF COKE A preliminary study on the p l a s t i c flow behaviour of coke above 1000°C has been car r i e d out. From the knowledge of the fact that ash i s made up of low melting point constituents which are l i k e l y to melt at temperatures encountered at the tuyere region of the blast furnace, i t i s expected that coke should deform p l a s t i c a l l y , as do r e f r a c t o r i e s . Thus, the formation of a glassy phase should decrease the load bearing capacity of coke, which may result in creep. The complex structure of coke prohibits any interpretation of the creep data in any fundamental way. For t h i s reason, a v i s o - e l a s t i c model was used to describe the creep behaviour of coke above 1000°C. It was found that an in t e r a c t i v e double-Kelvin-element model (Figure 28b) described the behaviour most accurately. Figures 29(a-b) i l l u s t r a t e s the effect of temperature and applied pressure on the mechanical parameters T j 1 r M, , 772, M 2 of the two interactive Kelvin element model. Only the parameter, TJ,, varied with temperature and pressure and i t 158 had very high values when compared with the other three parameters: M, , T J 2 and M 2. If i t i s considered that the resistance to deformation can be attr i b u t e d to the very high values of the viscous parameter, r j 1 f (as the other parameters have low values) the temperature e f f e c t on thi s parameter should be the c o n t r o l l i n g factor describing the viscous deformation of coke at high temperatures (>1000°C) Thus, Tj 1, may represent the e f f e c t i v e v i s c o s i t y of the glassy phase (ash) c o n t r o l l i n g the flow behaviour of the system. The parameters, M, , M 2, and T J 2 , may somehow be related with the carbon structure and/or the machine response which explains their r e l a t i v e i n s e n s i t i v i t y to temperature and applied pressure. As expected, the v i s c o s i t y 771, i s lowered when the temperature r i s e s . This i s t y p i c a l of most glassy materials and i t should result in a decrease in the load bearing c a p a b i l i t i e s of coke at higher temperatures. There is also a de f i n i t e dependence of the v i s c o s i t y , r j 1 r on the applied pressure which i s shown to decrease with a r i s e in the applied stress. This i s c h a r a c t e r i s t i c of a non-Newtonian f l u i d . In summary, a time dependent s t r a i n has been observed at temperatures greater than 1000°C. This behaviour has been described using an interactive-double-Kelvin element v i s c o - e l a s t i c model. It should be noted that some of the ash constituents, such as Na , 0 , K , 0 , and SiO,, should also vaporize in the 159 highly reducing atmosphere ex i s t i n g in the blast furnace ( 6 ) . This may somehow counteract the weakening of coke due to melting of ash. In addition, the loss of carbon from coke by the Boudouard reaction should be taken into consideration when determining the strength properties of coke, as that would relate more cl o s e l y to blast furnace conditions. 5. CONCLUSION In t h i s project, seven coke batches s p e c i a l l y prepared by CANMET were studied. These samples originated from three sources: 1. Three coke batches were prepared in a 460mm test-oven, each with d i f f e r e n t coke-oven pressures. 2. Three coke batches were sampled from three d i f f e r e n t positions, with respect to height, in a 5m coke-oven at Algoma Steel Corporation. 3. A warf coke sample was prepared to be compared with the other six batches. The experimental program was carr i e d out in four major steps: 1. Bulk and true density determinations, 2. Quantitative microstructural analyses, 3. Compressive strength value determinations for a l l seven coke batches at ambient temperature and at 1400°C (these values were then related to coking conditions and to the microstructural r e s u l t s ) , and 4. Creep test experiments above 1000°C. The following conclusions can be made from t h i s study: 1. The bulk density of the Algoma cokes was higher for cokes extracted from the bottom of the coke-oven than those sampled close to the top. This increase in density can be attributed to an increase in s t a t i c load, due to the weight of the burden, which was greatest at the oven sole. This e f f e c t may also have been aided by the higher 160 161 f i n a l coking temperatures near the bottom of the coke-oven, but there i s i n s u f f i c i e n t evidence to make a d e f i n i t e comment. Coke pore and wall size were also found to be affected by coking conditions. The pore and wall size were smaller in test-oven cokes than those in Algoma cokes. This implies that there i s an oven size a f f e c t on the microstructure of coke. Furthermore, an increase in pore size was observed with height in the Algoma coke-oven. No apparent trend could be established between c e l l wall size and height. The coke compressive strength was found to be greater for the specimens obtained from regions close to the sole of the 5m Algoma oven. Cokes produced at the sole region exhibited lower porosity values and smaller pores than the cokes situated higher in the oven. This resulted in a stronger coke for the samples produced at the sole of the coke-oven. Coke batches produced in the test-ovens were always stronger than the Algoma cokes and were also more uniform in properties ( i e . higher Weibull modulus values) at ambient temperature. Coke strength was shown to be higher at 1400°C than at room temperature for six of the seven coke batches. This was thought to be due to continued graphitization a f t e r the coke exceeded i t s f i n a l coking temperature. The c r i t i c a l stress intensity factor values ( K I C ) of the test-oven coke batches were shown to increase with oven 162 wall pressure, but thi s trend was not so apparent for values of Kj^ obtained from the strength data of the Algoma coke batches. It was concluded that since K J C i s material property, the differences in these values may be due to variations in the mechanical properties of the s o l i d coke ( i e . pore walls) and to large hidden fissures that may have been present inside some of the samples. However, these differences were s l i g h t and, therefore, i t i s probable the coke mechanical behaviour i s largely governed by the porous structure. The coke exhibited p l a s t i c flow behaviour when subject to a constant load at temperatures greater than 1000°C. The creep data were interpreted by using an interactive-double-Kelvin element v i s c o - e l a s t i c model. The value of the dashpot v i s c o s i t y , 7 j 1 f was decreased with increasing temperature. The v i s c o s i t y of t h i s dashpot i s thought to be related with the presence of a glassy phase (ash) in coke which may govern i t s creep behavior. 6. REFERENCES 1. "Western World CokemakingtCapacity and Operating Practices"; Commission on Raw Materials and Technology Brussels, 1983;International Iron and Steel I n s t i t u t e , 1 983 2. Terkel Rosenquist;"Principles of Extractive Metallurgy" .'Copyright 1984 by McGraw-Hill Inc. (McGraw-Hill series in Materials Science and Engineering),pp 273-283 3. J.Goleczka, J.Tucker and T.L. Roberts;"Further Studies of the Properties of Coke at High Temperature"; ECSC  Round Table Meeting on Coke-Oven and Coke Research,  Luxemburg,6-7, October,1980;Luxembourg,Commission of the  European Communities,pp 249-275 4. Chaklader, A.CD.; Private Communications 5. Chemistry of Coal Utilization,Second Supplementary Volume,Martin A. E l l i o t (Ed.),John Wiley and Sons,1981 6. N.A. Brown, CD.A. Coin, M.R. Mahoney, W.W. Gill,"Improved Evaluation of Australian Coking Coals and Blast Furnace Cokes",End-of-Grant Report,NERDDP Grant  82/2326 7. I.G.C. Dryden,"Chemistry of Coal and i t s Relation to Coal Carbonization",J.Inst. of Fuel,April,1957,pp 193-213 8. ASTM Standards,1980,Part 26, Designation D2797-72,"Standard Method of Preparing Coal Samples for Microscopical Analysis by Reflected Light". 9. ASTM Standards,1980,Part 26.Designation D2798-79,"Microscopical Determination of the Organic Components in a Polished Specimen of Coal". 10. H.A.G Chermin and D.W. Van Krevelen,"Chemical Structure and Properties of Coal XVII-A Mathematical Model of Coal 163 164 Pyrolysis",Fuel,London,Vol 36, 1957,pp 85-104 11. ASTM Standards,1980,Part 26,Designation D2639-74,"Standard Method for P l a s t i c Properties of Coal by the Constant-Torque Gieseler Plastometer". 12. ASTM Standards,1980,Part 26Resignation D167-73, "Specific Gravity and Porosity of Lump Coke". 13. W.R. Leeder, J.T. Price , J.F. Gransden,"Coke Strength-Comparison of Different Methods",Symposium on Blast Furnace Coke,Quality,Cause and Effeet,Hamilton,Ontario,Canada, 21-22 May,1980 14. A.E. Horton and T.J Peirce,"An Interpretation of the Breakage Behaviour of Metallurgical Coke",Coal:Pheonix  of the 80's-Proceedings of 64th CIC Coal  Symposium-A.M.Al Taweel,(ed.),C.S.Ch.E.,Ottawa(1982) pp568-576 15. T.J Pierce and A.E. Horton,"Interpretation of Coke Strength Results", ECSC Round Table Meeting on Coke-Oven  and Coke Research, Luxembourg,6-7,Oct 1980; Luxembourg,Commission of the European Communities,pp 213-247. 16. T.J. Pierce, A.E. Horton, and J . Tucker,"Coke Breakage in Relation to i t s Structure", J.Phys.D:Appl.Phys.,13(1980) pp 953-67 17. P.M. Fellows and R.R. Willmers,"High Temperature Testing of Coke and i t s Relevance to the Blast Furnace",Ironmaking Proc. Vol 44,1985,pp 239-251 18. S t e i l e r , J.M. ;Duchene, J.M.; Daniel I s l e r ; and J e u l i n , D.;"New Means for the Evaluation of Coke Quality in the Blast Furnace";41st Annual Ironmaking Conference. Pittsburg,PA,U.S.A.,28 Mar.,1982;Proc. Ironmaking  Conf.;41;pp 436-450(1982) 19. B r i t i s h Carbonization Research Association,"Studies of the Mechanical and Chemical Properties of Coke at High Temperature",(Report on ECSC Contract  7220-EB/818),Luxembourg Commission oT the European  Communities,pp 74 (1984). 165 20. ASTM S t a n d a r d s , 1 9 8 0 , P a r t 2 6 R e s i g n a t i o n D3038-72;"Standard Method of Drop S h a t t e r T e s t of Coke". 21. D.A. Reeve, J.T. P r i c e , and J.F. Gransden,"High-Temperature B e h a v i o u r of B l a s t Furnace Coke-A Review",Ottawa,Canada C e n t e r f o r M i n e r a l s and  Energy T e c h n o l o g y ( 1 9 7 7 ) . 22. P a t r i c k , J.W. and W i l k i n s o n , H.C.,"High Temperature P r o p e r t i e s of M e t a l l u r g i c a l Coke" , I ronmaking P r o c , V o l 42,1983,pp 333-345 23. M.O. Holowaty and C M . S q u a r c y , " H i g h Temperature T e s t i n g of B l a s t Furnace Coke",Ironmaking P r o c e e d i n g s ; A I M E , V o l Jj6,pp 249-270, 1 957 24. W. K l o s e and H. Suginobe, "Comments on Coke Q u a l i t y C h a r a c t e r i z a t i o n by T e n s i l e S t r e n g t h " , A r c h i v Fur das  E i s e n h u t t e n w e s e n , V o l 56,1985,pp 19-24 25. S. Ragan and H. Marsh,"A C r i t i q u e of I n d u s t r i a l Methods of Measurement of S t r e n g t h of M e t a l l u r g i c a l Coke",J.Phys.D;Appl.Phys.,13(1980),pp 983-993 26. J . G o l e c z k a and T.L. Roberts,"Coke Q u a l i t y and i t s Assessment i n the L a b o r a t o r y " , I n t . C o n f . on C o a l , Coke  and the B l a s t Furnace,Middelsbrough,UK,June,1977.  London,UK,The M e t a l s S o c i e t y , p p 74-82(1978) ~ 27. J . G o l e c z k a and T.L. R o b e r t s , " H i g h Temperature P r o p e r t i e s of M e t a l l u r g i c a l Coke".In P r o c . of Round T a b l e M e e t i n g  on Coke-Oven Techniques,Round T a b l e M e e t i n g on Coke-Oven  T e c h n i q u e s , Luxembourg,Commission on the European  Communities,pp 221-240(1979) 28. F.P. Knudsen,"Dependence of M e c h a n i c a l S t r e n g t h of B r i t t l e P o l y c r y s t a l l i n e Specimens on P o r o s i t y and G r a i n Size",J.Amer.Ceram.Soc. 42(1959),No 8, ,pp 376-87 29. R.E. Wa l p o l e and R.H. M y e r s , " 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 E n g i n e e r s and S c i e n t i s t s " , 2 e d . , M a c M i l l a n P u b l i s h i n g Co. I n c . , C o p y r i g h t 1972 30. G.J. P i t t and J.C.V. Rumsey,"Some F e a t u r e s of t h e 1 66 Structure of Metallurgical Cokes and Their E f f e c t s on Strength",J.Phys.D.,13(1980),pp 969-81 31. J.W. Patrick, "Coke Structural Studies and Their Relevance to Coal Blending", ECSC Round Table Meeting on  Coke Oven and Coke Research, Luxembourg, 6-7 Oct. 1980;  Luxembourg, Commission of The European Communitles,pp 213-247 32. J.W. Patrick, M.J. Sims, and A.E. Stacey,"Quantitative Characterization of the Texture of Coke",Journal of  Microscopy,Vol 109,Pt 1,Jan. 1977, pp 137-143 33. J.W. Patrick, M.J. Sims and A.E. Stacey,"The Relation Between the Strength and Structure of Me t a l l u r g i c a l Coke",J.Phys.D:Appl.Phys,13(1980),pp 937-51 34. B r i t i s h Carbonization Research Association,"Studies of Coke Texture Using a Computerized Microscope for Automatic Image Analysis:Part 3",Chesterfield,UK,  B r i t i s h Carbonization Research Association,pp 34(Nov 1979) 35. Patrick, J.W. and Stacey, A.E.,"The E f f e c t s and Control of Coke Porosity", Trans.Iron and Steel Soc,AIME Vol 3,l983,pp 1-12 36. J.W. Patrick and A. Walker,"Preliminary Studies of the Relation Between the Carbon Texture and the Strength of Me t a l l u r g i c a l Coke",Fuel,1985,Vol 64, (January), P136-138 37. Nishioka, K. and Yoshida, S.,"Strength Estimation of Coke as a Porous Material", Trans.I SIJ,Vol 23,1 983, pp 387-392 38. M. Khan, J.F. Gransden, and J.T. Price,"Variation of Coke Properties in an Industrial Coke Oven",Unpublished Work 39. ASTM Standards,1980,Part 26Resignation  D720-67,"Free-Swelling Index of Coal" 40. F i t z e r , E.and Heym, M.;High Temperature Mechanical 167 Properties of Carbon and Graphite (A Review)";High  Temperature-High Pressure,1978, Vol 10,pp 29-66 41. Broek. D; Elementary Engineering Fracture Mechanics,Third Ed.,Martinus Nijhoft Publishers,1982 42. H.A. Nied and K. Arin,"Multiple Flaw Fracture Mechanics Model For Ceramics,Plenum Press 3,l977,pp 323-345 43. ASTM Standards,1980,Part 26,Designation D3402-76,"Standard Method of Tumbler Test For Coke". 44. R.W. Evans, B.J. Scharning and B.Wilshire,"Constitutive Equations for Creep of a Fired Doloma Refractory",J. and  Trans. B r i t i s h Ceramic Society, Vol 85(2),pp 36-75(1986) 45. F.H. Norton,Refractories,McGraw-Hill Book Company Copyright 1968,pp 231-243 46. A.CD. Chaklader and M.G.K. Grant,"Fluid Phase Densification and Reactive Hot-Pressing of Alumina", Agglomeration-85,pp 665-73,( 1 985),C.E. Capes(ed.),Toronto,Canada,The Iron and Steel Society Inc. 47. R.S. Bradbeer and A.CD. Chaklader, "Reactive Hot-pressing of C o l l o i d a l Boehmite", Materials Science  Research, Vol 6, G.C Kuczynski (Ed.), Plenum Publishing  Corporation, New York, 1980, 48. W.W. G i l l and A.CD. Chaklader, "Material Chara c t e r i s t i c s Affecting Formcoke",Fuel, Vol. 63,  October, 1984,, pp1385-1392 49. A. Burgess, Personal Communication on the temperature history of the coal charge during experimental measurements of a coke oven at three d i f f e r e n t heights at Algoma Steel Corp. 50., J.W. Patrick,"Studies of the Factors C o n t r o l l i n g the Formation and Development of the Porous Structure of Coke",BCRA,Information Symposium on Coke Oven  Techniques,1981;Luxembourg,Belgium 168 51. D.R. Coughanowr and L.R. K o p p e l . P r o c e s s Systems A n a l y s i s  and C o n t r o l . M c G r a w - H i l l Book Company, 1965. 52. D. M e r r i c k , " M a t h e m a t i c a l Models of The Thermal D e c o m p o s i t i o n of C o a l , P a r t 3", F u e l , 1983, V o l 62, May, pp547-552. 

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