Factors influencing coke gasification with

carbon dioxide

Mihaela Grigore

A thesis submitted in fulfilment

of the requirements for the degree of

Doctor of Philosophy

School of Materials Science and Engineering

Faculty of Science

The University of New South Wales

August 2007

PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES

Thesis/Dissertation Sheet

Surname or Family name: Grigore

First name: Mihaela Other name/s:

Abbreviation for degree as given in the University calendar: Ph.D.

School: School of Materials Science and Engineering Faculty: Science

Title: Factors influencing coke gasification with carbon dioxide

Abstract 350 words maximum: (PLEASE TYPE)

Of all coke properties the influence of the catalytic mineral matter on reactivity of metallurgical cokes is least understood. There is limited information about the form of minerals in the metallurgical cokes and no information about their relative concentration. A comprehensive study was undertaken for characterisation of mineral matter in coke (qualitative and quantitative), which enabled quantification of the effect of catalytic minerals on the reaction rate, and establishment of the effect of gasification on the mineral phases. Also, the relative importance of coke properties on the gasification reaction rate was determined.

The reactivity experiments were performed at approximately 900ºC using 100% CO2 under chemically controlled conditions.

The mineralogical composition of the investigated cokes was found to vary greatly as did the levels of catalytic mineral phases. These were identified to be metallic iron, iron sulfides and iron oxides. The gasification reaction rate at the initial stages was strongly influenced by the content of catalytic mineral phases and also by the particle size of the catalytic mineral matter. The reaction rate increased as the contact surface between catalyst and carbon matrix increased.

Catalytic mineral phases showed a strong influence on the reaction rate at early stages of reaction. But their influence diminished during gasification. At later stages of reaction the influence of micropore surface area became more important.

The influence of the catalytic mineral phases diminished during gasification because the catalyst was inactivated to some degree and the contact surface between the catalyst and carbon matrix diminished due to the strong gasification of the carbon around the catalyst particles. The partial inactivation of the catalytic mineral phases occurred because metallic iron and pyrrhotite were oxidised by CO2 to iron oxide, and in turn iron oxide reacted with other mineral phases, which it is associated with, to form minerals that are not catalysts.

It is noteworthy that a significant percentage of the mineral matter present in the investigated cokes was amorphous (44 - 75%). The iron, potassium and sodium present in the amorphous phase did not appear to catalyse gasification, but their potential contribution to gasification could not be completely excluded.

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Certificate of Originality

I hereby declare that this submission is my own work and to the best of my knowledge

it contains no materials previously published or written by another person, nor material

which to a substantial extent has been accepted for the award of ant other degree or

diploma at UNSW or any other educational institution, except where due

acknowledgement is made in the thesis. Any contribution made to the research by

others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in

the thesis.

I also declare that the intellectual content of this thesis is the product of my own work,

except to the extent that assistance from others in the project’s design and conception or

in style, presentation and linguistic expression is acknowledged.

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Mihaela Grigore

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Acknowledgments

During my doctoral research I have been accompanied and supported by many people.

Now, I have the opportunity to express my gratitude to all of them.

I thank Dr. Richard Sakurovs (CSIRO Energy Technology – Newcastle, NSW) for his

enthusiasm and commitment to this project, which inspired me. I also thank him for his

guidance, lectures about “high quality research work” and invaluable discussions during

this project. He supported and encouraged me in my decisions, which gave me

confidence in my research abilities. I owe him lots of gratitude for showing me this way

of research.

I wish to thank Dr. David French (CSIRO Energy Technology – Lucas Heights, NSW)

for his insightful comments, guidance and expertise in mineralogy, which helped

tremendously in my project. Also, I thank him for his continual support and

encouragement during this project.

I would also like to thank Prof. Veena Sahajwalla (School of Materials Science and

Engineering – The University of New South Wales) for the opportunity to carry out this

project and for her suggestions and supervision during my doctoral research.

I wish to acknowledge the Cooperative Research Centre for Coal in Sustainable

Development (CCSD) for the financial support of the project. Also, I would like to

thank Dr. Lila Gurba (CCSD), Dr. John Mathieson (Bluescope steel-Woolongong) and

Jim Craigen (ACARP) for their interest in my project and feedback.

I like to thank Ms. Elizabeth Gawronski (CSIRO Energy Technology – Lucas Heights,

NSW) and Mr. Lindsay Burke (CSIRO Energy Technology – Newcastle, NSW) for

their assistance and support over the years. Elizabeth helped me with her expertise in

coal/coke petrography and Lindsay was involved in coke preparation and building the

maceral separation device. Also, thanks to Dr. Daniel Roberts (CSIRO Energy

iii

Technology – Pullenvale, Qld) for his help in the experimental part of the project and

technical discussions regarding the reactivity experiments. I am grateful to Mr. Ian

Campbell (CSIRO Energy Technology – Lucas Heights, NSW) for his assistance in

learning how to use the mineral matter quantification software (SIROQUANT).

My gratitude goes to Sorina Popescu for encouraging me to embark on this PhD. I also

like to thank some of my fellow PhD students Tsuey Cham and Kelli Kazuberns for

their friendship and sense of humour.

I would like to acknowledge Dr. Haiping Sun (UNSW), Dr. Sushil Gupta (UNSW) and

Mr. N. Saha-Choudury (UNSW) for their assistance on different occasions.

Last but not least, I would like to thank my husband, Adrian and my daughter, Laura for

their patience and support over all these years.

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Abstract

Any improvement of the blast furnace efficiency operated under current technologies,

and any implementation of new technologies will make new demands on coke quality.

In order to prepare coke of suitable quality to address these requirements a better

understanding of the factors that affect coke degradation in the furnace is required.

Since gasification has been identified as an important factor that affects coke

degradation, a better understanding of coke gasification is necessary.

Coke properties such as microtexture, surface area and mineral matter have been

reported as the main factors that affect coke reactivity. Although many studies have

investigated the effect of microtexture and surface area on coke reactivity there is not a

complete agreement regarding their influence. Moreover, the influence of mineral

matter is least understood. Previous studies have concentrated on elemental ash

composition, however it has been recognized that the forms of the mineral matter in the

coke play an important role in controlling coke reactivity. There is currently limited

information available in the literature about the form of minerals present in the

metallurgical cokes and no information about their relative concentration, which would

assist to quantify the effect of catalytic minerals on coke reactivity. To address this issue

a comprehensive study on coke properties and their role in gasification reaction was

undertaken. Also, the influence of coal properties such as rank and maceral composition

on coke properties was also investigated.

The reactivity experiments were designed to measure the reaction rate of coke with

carbon dioxide under chemically controlled conditions and minimise the inhibiting

effect of the product gas on the reaction rate. The cokes used in this project were

prepared from nine Australian bituminous coals of a broad range of rank, maceral

composition and ash chemistry. Also, five coals of different rank were selected for

preparation of maceral-enriched fractions to investigate the influence of coal maceral on

coke properties and reactivity. The cokes and the carbonised maceral-enriched fractions

were subjected to reactivity test. The reactivity experiments were performed using a

v

fixed-bed reactor at approximately 900ºC and the reactant gas was 100% carbon

dioxide.

It was found that the reactivity of the cokes from this series could not be predicted by

the coal rank and maceral composition even though the effect of coal rank on coke

microtexture was obvious; the size of the anisotropic microtexture increased as the coal

rank increased. At the nanometre scale, the effect of coal rank on the degree of ordering

of carbon structure (Lc ranged between 1.46-1.66 nm) was not noticeable. Coal rank did

not affect the crystallite length (La ranged between 3.60-4.18 nm) of the cokes either.

The influence of coal rank on Lc of the cokes was diminished by the content of non-

fusible inertinite present in the parent coal. Lc increased as the levels of non-fused

inertinite decreased in the series carbonised vitrinite-rich fraction, coke and carbonised

inertinite-rich fraction prepared from the same parent coal in similar carbonisation

conditions. The effect of non-fusible inertinite was significant on the Lc of the cokes

made from medium volatile coals and minor on the Lc of the cokes prepared from high

volatile coals. The decrease of Lc of the cokes is due to the content of non-fused

inertinite, which has a much lower Lc than of the reactive derived maceral component.

Also, the non-fusible inertinite in the coals may affect the development of the carbon

crystallites during carbonisation.

Optical microscopy data showed that the non-fused inertinite was the most reactive

microtextural component. The study on the carbonised maceral-enriched fractions

showed that the carbonised inertinite-rich fractions had greater reactivity than their

corresponding carbonised vitrinite-rich fractions. The increased reactivity of the

carbonised inertinite-rich fractions was mainly due to their greater levels of catalytic

mineral phases and to some extent due to greater micropore surface area.

A consistent change in crystallite height (Lc) of the cokes was observed during

gasification. Lc increased slightly at the initial stages but a significant increase was

noticed at greater carbon conversion levels (approximately 75% burn-off). The increase

of Lc during gasification was not due to a temperature effect: the crystallite size (Lc and

La) of coke samples annealed in inert atmosphere, at a temperature similar with the

vi

reaction temperature, was not affected significantly. It was concluded that the increase

of Lc during gasification was due to selective removal of the non-fused inertinite

component, since the carbonised inertinite-rich fractions had smaller Lc than their

corresponding carbonised vitrinite-rich fractions. Therefore, the preferential removal of

the non-fused inertinite would result in an increase of the average crystallite height (Lc)

of the cokes.

The initial apparent and intrinsic rates of the cokes were not significantly influenced by

Lc. At approximately 15% carbon conversion, a trend was observed between crystallite

height (Lc) of the reacted cokes and apparent rate; the apparent reaction rate decreased

as Lc increased.

Crystallite length (La) was found not to be determined by either coal rank or maceral

type. Crystallite length of the raw cokes did not vary significantly between cokes and it

did not show any consistent behaviour during gasification.

During gasification the micropore and mesopore surface area increased dramatically at

about 15% carbon conversion. The initial apparent rate was slightly affected by the

micropore and mesopore surface area, but the reaction rate was strongly influenced by

the micropore surface area at approximately 15% burn-off. This indicates that the

influence of micropore surface area became more important at a higher carbon

conversion. The mesopore surface area of the reacted cokes did not affect significantly

the reaction rate.

Ash chemistry was found to be an unreliable indicator for coke reactivity because it

does not provide information about the levels of catalysts in the coke and their particle

size. Also, the mineralogical characterisation of the cokes showed that not all the iron,

calcium, potassium and sodium mineral phases are catalysts of the gasification reaction.

The mineralogical composition varied strongly between cokes. The catalytic mineral

phases identified in the cokes used in this project were metallic iron, iron sulfides and

iron oxides. The catalytic mineral phases showed a strong influence on the apparent

rates of the cokes prepared in the 9 kg oven and the cokes and carbonised maceral-

vii

enriched fractions made in the 70 g oven at the initial stages of reaction. Also, the

particle size of the catalytic mineral matter was found to be an important factor that

affected coke reactivity. The reaction rate increased as the contact surface between

catalyst and carbon matrix increased.

Along with the crystalline mineral phases an amorphous phase was identified. The

content of the amorphous phase varied between 44 and 75%. The amorphous phase

formed due to decomposition of aluminosilicates such as kaolinite, montmorillonite,

illite and chamosite. The iron, potassium and sodium present in the amorphous phase

did not appear to catalyse gasification, but they may have a potential contribution to

gasification.

During gasification the catalysts underwent transformations due to oxidation by carbon

dioxide. Oxidation of the catalysts enabled their reaction with other minerals, which

they were in contact with, transforming the catalyst into a non-catalytic mineral. Also,

as the gasification proceeds, the carbon in contact with the catalyst is consumed,

diminishing the contact between the catalyst and the carbon matrix. Therefore, during

gasification the effect of catalyst on the reaction rate diminishes gradually.

It can be concluded that the reaction rate at the initial stages of reaction was mainly

controlled be the catalytic mineral matter. As the reaction proceeds the catalytic effect

diminishes and the surface area of the micropores becomes more important.

This study has shown the critical importance of mineral matter transformation in cokes

in determining coke behaviour in blast furnaces. This conclusion is supported by the

application of quantitative mineralogical analysis. The quantitative mineralogical

analysis also made possible quantification the effect of catalytic mineral matter on

gasification rate and established the importance of catalytic mineral matter during

gasification. Although coal rank and maceral composition affected coke properties, the

influence of coke microtexture and surface area on the reaction rate was overshadowed

by the influence of the catalytic mineral phases at the initial stages of reaction. The

effect of surface area on gasification rate became more important at higher carbon

conversion levels.

viii

Table of contents

Certificate of Originality ................................................................................................ii

Acknowledgments ..........................................................................................................iii

Abstract ........................................................................................................................v

Table of contents ............................................................................................................ix

List of figures ................................................................................................................xiii

List of tables..................................................................................................................xix

Bibliography and Achievements .................................................................................xxi

Nomenclature .............................................................................................................xxiii

CHAPTER 1 – Introduction ........................................................................................1

CHAPTER 2 – Literature Review...............................................................................6

2.1 Blast furnace.....................................................................................................6 2.1.1 Overview of the Blast Furnace process – coke importance in the

furnace................................................................................................6 2.1.2 Coke gasification in the blast furnace ..................................................9

2.2 Coke characterisation.....................................................................................12 2.2.1 Coke microtexture ..............................................................................13 2.2.2 Coke microstructure ...........................................................................18 2.2.3 Mineral matter ....................................................................................19

2.3 Coke gasification ............................................................................................20 2.3.1 Gas-solid reactions .............................................................................20 2.3.2 Mechanism of reaction.......................................................................22 2.3.3 Reaction rate measurement ................................................................24

2.4 Factors influencing coke gasification.............................................................25 2.4.1 Coke microtexture ..............................................................................25 2.4.2 Coke microstructure ...........................................................................28 2.4.3 Mineral matter ....................................................................................31

2.5 Factors influencing coke properties ...............................................................37 2.5.1 Coal properties ...................................................................................37 2.5.2 Carbonization process ........................................................................44

2.6 Methods of measuring coke reactivity ............................................................51

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2.7 Chapter overview............................................................................................55

CHAPTER 3 – Thesis Objectives ..............................................................................58

CHAPTER 4 – Experimental.....................................................................................60

4.1 Parent coals ....................................................................................................60

4.2 Preparation of maceral-rich fractions ...........................................................62

4.3 Coke preparation............................................................................................67 4.3.1 The large scale coke ovens.................................................................67 4.3.2 The 70 g coke oven ............................................................................70

4.4 Coke reactivity test .........................................................................................74 4.4.1 Coke reactivity reactor system...........................................................74 4.4.2 Reaction rate calculation ....................................................................77 4.4.3 Activation energy measurement.........................................................78

4.5 Coke samples characterisation.......................................................................79 4.5.1 Optical microscopy ............................................................................79 4.5.2 Surface area........................................................................................82 4.5.3 Carbon structure .................................................................................82 4.5.4 Qualitative and quantitative analysis of mineral phases ....................83 4.5.5 Visual analysis of mineral matter using FESEM ...............................85 4.5.6 Analysis of mineral matter in coal using QEMSCAN .......................87

CHAPTER 5 – Kinetics of the Coke – Carbon dioxide reaction ............................88

5.1 Apparent reactivity experiments: Coke – Carbon dioxide reactions..............89

5.2 Coke surface area and intrinsic reactivity .....................................................93

5.3 Coal properties – Coal rank and Maceral composition.................................98

5.4 Coke properties – Coke microtexture...........................................................102

5.5 Coke properties – Carbon structure.............................................................105

5.6 Coke properties – Ash composition ..............................................................111

5.7 Summary .......................................................................................................113

CHAPTER 6 – Influence of coal macerals on coke properties .............................116

6.1 Effect of carbonisation conditions on coke reactivity and coke properties..117 6.1.1 Surface area and intrinsic reactivity .................................................119 6.1.2 Coke microtexture ............................................................................120 6.1.3 Carbon structure ...............................................................................123

6.2 Effect of macerals on coke reactivity............................................................125 6.2.1 Surface area and intrinsic reactivity .................................................131 6.2.2 Carbon structure ...............................................................................134

6.3 Factors influencing reactivity of carbonised inertinite-rich fractions and carbonised vitrinite-rich fractions...........................................................138

6.3.1 Carbonised inertinite-rich fractions..................................................138 6.3.2 Carbonised vitrinite-rich fractions ...................................................145

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6.4 Summary .......................................................................................................152

CHAPTER 7 – Mineralogical characterization of cokes and parent coals..........154

7.1 Coal mineralogy ...........................................................................................154

7.2 Coke mineralogy and its relationship to coal mineralogy ...........................158

7.3 The effect of carbonization conditions on mineral matter in the coals ........172

7.4 Mineral phases deportment in the carbonised maceral-enriched fractions and cokes prepared in the 70 g oven ..............................................................178

7.5 Summary .......................................................................................................183

CHAPTER 8 – Relationship between catalytic mineral phases in coke and coke reactivity....................................................................................................185

8.1 Relationship between catalytic mineral phases and reactivity for cokes prepared in the 9 kg oven ........................................................................186

8.1.1 Initial apparent rate ..........................................................................186 8.1.2 Final apparent rate............................................................................194

8.2 Influence of catalytic mineral phases on reactivity of cokes and carbonised maceral-enriched fractions prepared in the 70 g oven ...........................197

8.2.1 Initial apparent rate ..........................................................................197 8.2.2 Effect of preparation conditions on catalytic mineral phases and their

reactivity.........................................................................................201

8.3 Relationship between catalytic mineral phases and intrinsic rate ...............204 8.3.1 Initial intrinsic rate ...........................................................................204 8.3.2 Final intrinsic rate ............................................................................207

8.4 Amorphous mineral phase ............................................................................209

8.5 Summary .......................................................................................................211

CHAPTER 9 – Mineral reactions during gasification...........................................213

9.1 Mineral phases transformation during gasification.....................................213

9.2 Effect of temperature and carbon dioxide on the mineralogy of the coke....216

9.3 Transformation of mineral phases in coke during gasification....................224

9.4 The effect of mineral phase transformation on coke reactivity ....................237

9.5 Summary .......................................................................................................251

CHAPTER 10 – Summary and Conclusions ...........................................................252

10.1 Coal rank ....................................................................................................252

10.2 Coal macerals.............................................................................................253

10.3 Carbon structure of the coke ......................................................................254

10.4 Coke surface area.......................................................................................255

10.5 Coke mineral matter ...................................................................................255

CHAPTER 11 – References .....................................................................................258

xi

Appendix A: Mineral matter identification in the coals.........................................274

Appendix B: Mineral matter identification in the raw, reacted and annealed cokes....................................................................................................................284

Appendix C: Mineral matter identification in the carbonised maceral-enriched fractions, cokes and carbonised SLACs .................................................303

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List of figures

Figure 1.1 The influence of coke quality in the blast furnace..........................................4

Figure 2.1 Schematic of the Blast Furnace ......................................................................8

Figure 2.2 A theoretical diagram of temperature distribution of gas and solids along the height of the blast furnace and the chemical reactions within these zones ..11

Figure 2.3 Nomenclature and classification of the anisotropic carbon by different laboratories ...................................................................................................14

Figure 2.4 Coke microtextures.......................................................................................15

Figure 2.5 Schematic presentation of MOD ..................................................................16

Figure 2.6 Classification of Molecular Orientation Domains........................................16

Figure 2.7 A schematic picture of a crystallite of graphite ............................................18

Figure 2.8 Ideal representation of the three controlling zones of carbon gasification...22

Figure 2.9 Gasification of coke microtexture ................................................................26

Figure 2.10 Crystallite size (Lc and La) of a metallurgical coke function of temperature under inert gas (Ar) and reactive gas (Ar-CO-CO2) ....................................27

Figure 2.11 Variation of surface area (N2 adsorption) and porosity during gasification......................................................................................................................29

Figure 2.12 Reactivation of metallic iron during gasification by CO and H2................33

Figure 2.12 Distribution of � electrons in the aromatic rings (a) not affected by catalyst and (b) influenced by catalyst ......................................................................37

Figure 2.13 Schematic representation of coal structure made by Hirsch.......................39

Figure 2.14 A typical reflectance distribution of macerals in coking coal ....................42

Figure 2.15 Reactions of cracking and aromatisation of coal components....................45

Figure 2.16 Transformation of coal during pyrolysis ....................................................46

Figure 2.17 Deposition of pyrolytic carbon ...................................................................48

Figure 2.18 Schematic diagram of an experimental system using a thermogravimetric analyser ........................................................................................................53

Figure 2.19 Schematic diagram of a fixed-bed reactor system......................................54

Figure 4.1 Schematic of the maceral separation device.................................................63

Figure 4.2 The concentration of macerals and mineral matter in the separated fractions of coal F........................................................................................................64

Figure 4.3 A diagram of the 9 kg coke oven..................................................................68

xiii

Figure 4.4 A schematic diagram of (a) the 70 g coke oven and (b) the calcination furnace..........................................................................................................73

Figure 4.5 A schematic diagram of the fixed-bed reactor system..................................75

Figure 4.6 Typical results from a FBR experiment........................................................76

Figure 4.7 Different type of microtexture shown by (a) coke C and (b) coke F............81

Figure 4.8 Identification of the mineral phases present in coke F using Bruker Eva search/match software ..................................................................................84

Figure 4.9 A typical SIROQUANT plot ........................................................................85

Figure 4.10 A typical SEM image (top) and EDS analysis (bottom).............................86

Figure 5.1 The apparent reaction rate at 900ºC versus carbon conversion (100% CO2)89

Figure 5.2 Arrhenius plots obtained using data recorded during furnace cooling .........90

Figure 5.3 Relative density as a function of burn-off ....................................................92

Figure 5.4 Total surface area of raw and reacted cokes (approximately 15% burnout) (a) measured using N2 adsorption (b) measured using CO2 adsorption.......94

Figure 5.5 Dependence of apparent rates on total surface area measured using both N2 and CO2 (a) initial apparent rate and (b) final apparent rate ........................96

Figure 5.6 Relationship between the rank of parent coal (expressed as mean maximum vitrinite reflectance in oil) and (a) initial and final apparent rates, (b) initial and final intrinsic rates calculated using CO2 surface area and (c) initial and final intrinsic rates calculated using N2 surface area....................................99

Figure 5.7 Relationship between inertinite content in the parent coal and (a) initial and final apparent rates, (b) initial and final intrinsic rates calculated using CO2 surface area and (c) initial and final intrinsic rates calculated using N2 surface area.................................................................................................101

Figure 5.8 Microtexture of cokes made form coals of different rank (a) Coke B (R0max–1.00%), (b) Coke D (R0max–1.18%) and (c) Coke F (R0max–1.27%) ........................................................................................................103

Figure 5.9 Microtexture of coke F during gasification (a) raw coke, (b) 15% burnout coke and (c) 75% burnout coke..................................................................104

Figure 5.10 Lc and La of the raw cokes versus rank of parent coal..............................106

Figure 5.11 Variation of (a) Lc and (b) La during gasification.....................................108

Figure 5.12 (a) Initial and final (15% burn-off) apparent rates of the nine cokes vs. Lc and (b) initial and final intrinsic rates of the nine cokes, calculated using CO2 surface area, vs. Lc..............................................................................110

Figure 5.13 Initial and final apparent rates of the nine cokes against total iron, calcium, potassium and sodium concentration in the cokes .....................................112

Figure 6.1 The apparent reaction rate at 900ºC versus carbon conversion (100% CO2) of the cokes B, C, D, F and G prepared in the 70 g and 9 kg ovens ..........118

Figure 6.2 The initial intrinsic reaction rates of cokes B, C, F and G prepared in the 70 g and 9 kg ovens.........................................................................................120

xiv

Figure 6.3 Percentage of non-fused inertinite in the cokes B, C, D, F and G prepared in the 70 g and 9 kg ovens compared to percentage of inertinite in the coal .121

Figure 6.4 Microtexture of (a) coke B, (b) coke C, (c) coke F and (d) coke G prepared in the 70 g (top) and 9 kg (bottom) ovens ..................................................122

Figure 6.5 Crystallite size (Lc and La) of the raw cokes B, C, F and G carbonised in the 70 g and 9 kg ovens....................................................................................124

Figure 6.6 The apparent reaction rate of the cokes produced from the original coals (B, C, D, F and G) and their corresponding maceral-enriched fractions versus carbon conversion ......................................................................................127

Figure 6.7 Anisotropic microtexture of (a) carbonised inertinite-rich fraction B (left) and carbonised vitrinite-rich fraction B (right) and (b) carbonised inertinite-rich fraction G (left) and carbonised vitrinite-rich fraction G (right) ........128

Figure 6.8 The initial apparent reaction rate of the cokes produced from the original coals (B, C, D, F and G) and their corresponding maceral enriched fractions versus their content of non-fused inertinite................................................130

Figure 6.9 Surface area of the raw cokes made from the original coals (B, C, F and G) and their corresponding carbonised maceral-enriched fractions versus the concentration of non-fused inertinite (left-side charts). The right-side charts shows the initial intrinsic rates of the cokes made from the original coals (B, C, F and G) and their corresponding carbonised maceral-enriched fractions....................................................................................................................133

Figure 6.10 Crystallite height (Lc) of the raw cokes made from the original coals (B, C, F and G) and their corresponding carbonised maceral-enriched fractions versus the concentration of non-fused inertinite (left-side charts). The initial apparent rates versus Lc (right-side charts) ................................................135

Figure 6.11 Crystallite length (La) of the raw cokes made from the original coals (B, C, F and G) and their corresponding carbonised maceral-enriched fractions versus the concentration of non-fused inertinite (left-side charts). The initial apparent rates versus La (right-side charts) ................................................137

Figure 6.12 Initial apparent rate of the raw cokes made from the original coals (B, C, F and G) and their carbonised maceral-enriched fractions versus Lc............138

Figure 6.13 The apparent reaction rate of the carbonised inertinite-rich fractions against carbon conversion ......................................................................................139

Figure 6.14 Microtexture of the carbonised inertinite-rich fractions of (a) coal B, (b) coal C, (c) coal F and (d) coal G ................................................................141

Figure 6.15 Initial apparent rate of the carbonised inertinite-rich fractions versus both non-fused inertinite and rank of the parent coal.........................................142

Figure 6.16 Surface area measured by carbon dioxide against non-fused inertinite ...143

Figure 6.17 Initial apparent and intrinsic rates of the carbonised inertinite-rich fractions....................................................................................................................143

Figure 6.18 Crystallite size (Lc and La) of the carbonised inertinite-rich fractions B, C, F and G.......................................................................................................144

xv

Figure 6.19 Initial apparent rate versus crystallite size (Lc and La) of the carbonised inertinite-rich fractions...............................................................................145

Figure 6.20 The apparent reaction rate of the carbonised vitrinite-rich fractions against carbon conversion ......................................................................................146

Figure 6.21 Microtexture of the carbonised vitrinite-rich fractions of (a) coal B, (b) coal C, (c) coal F and (d) coal G........................................................................147

Figure 6.22 Initial apparent rate of the carbonised vitrinite-rich fractions versus both rank of the parent coal and non-fused inertinite.........................................148

Figure 6.23 Initial apparent and intrinsic rates of the carbonised vitrinite-rich fractions....................................................................................................................149

Figure 6.24 Crystallite size (Lc and La) of the carbonised vitrinite-rich fractions .......151

Figure 6.25 Initial apparent rate versus crystallite size (Lc and La) of the carbonised vitrinite-rich fractions.................................................................................151

Figure 7.1 The XRD patterns of the nine raw cokes and the LTA of coke C..............160

Figure 7.2 Plot of quartz/fluorapatite/crystalline titanium dioxide (rutile, anatase, brookite) in the coke versus quartz/fluorapatite/crystalline titanium dioxide (rutile, anatase, brookite) in the coal ..........................................................162

Figure 7.3 Percentage of total quartz associated with kaolinite and illite in coals ......163

Figure 7.4 Mineral matter behaviour of a thermal coal, equivalent of coal A in this work, during heating in vacuum.................................................................164

Figure 7.5 The percentage of Si, Al, Ca, Fe and K present in crystalline mineral phases....................................................................................................................172

Figure 8.1 Total iron present in the mineral phases known as catalysts of gasification (Fe, Fe1-xS, Fe2O3, Fe3O4 and FeO)............................................................187

Figure 8.2 Relationship between initial apparent rate against (a) catalytic iron, (b) catalytic calcium and (c) total catalytic iron and calcium..........................188

Figure 8.3 Catalytic calcium against catalytic iron in the raw cokes...........................189

Figure 8.4 FESEM images of a pyrrhotite particle (figure A) and a metallic iron particle (figure B) in coke C....................................................................................190

Figure 8.5 FESEM images of a pyrrhotite particle (figure A) and metallic iron particles (figures B and C) in coke I .........................................................................191

Figure 8.6 Initial apparent rate against (a) iron content present in the catalytic iron phases and (b) total iron .............................................................................193

Figure 8.7 Final apparent rate (approximately 15% carbon conversion) of cokes B, C, F and G versus (a) catalytic iron, (b) catalytic calcium and (c) total catalytic iron and calcium.........................................................................................196

Figure 8.8 Total iron present in the catalytic mineral phases (Fe, Fe1-xS, Fe2O3, Fe3O4 and FeO), identified in the cokes prepared in the 70 g oven and the carbonized maceral-enriched fractions (vitrinite and inertinite) and carbonised SLACs......................................................................................198

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Figure 8.9 Initial apparent rate versus (a) catalytic iron, (b) catalytic calcium and (c) total catalytic iron and calcium ..................................................................199

Figure 8.10 Total iron present in the mineral phases known as catalysts of gasification (Fe, Fe1-xS, Fe2O3, Fe3O4 and FeO) in the cokes prepared in the 9 kg and 70 g ovens .......................................................................................................202

Figure 8.11 Initial apparent rate against catalytic iron present in the cokes prepared in the 9 kg and 70 g ovens..............................................................................203

Figure 8.12 SEM images and EDS spectrum of pyrrhotite particles in coke F prepared in the 9 kg oven ..........................................................................................203

Figure 8.13 Initial intrinsic rate of cokes prepared in the 9 kg oven versus (a) catalytic iron, (b) catalytic calcium and (c) total catalytic iron and calcium............205

Figure 8.14 Initial intrinsic rate of cokes prepared in the 70 g oven versus (a) catalytic iron, (b) catalytic calcium and (c) total catalytic iron and calcium...........206

Figure 8.15 Final intrinsic rate (approximately 15% carbon conversion) of cokes B, C, F and G against (a) catalytic iron, (b) catalytic calcium and (c) total catalytic iron and calcium.........................................................................................208

Figure 8.16 Initial apparent rate of the nine cokes versus (a) both iron content in the amorphous mineral phase and catalytic iron, (b) potassium content in the amorphous mineral phase and (c) sodium content in the amorphous mineral phase...........................................................................................................210

Figure 8.17 (a) Total Fe+K+Na in the amorphous mineral phase in cokes A and B and (b) initial apparent rates of cokes A and B.................................................211

Figure 9.1 Desorption of CO2 and CO during annealing of coke F in nitrogen ..........220

Figure 9.2 The iron-oxygen phase diagram taken from Biswas ..................................220

Figure 9.3 The content of the major elements (Si, Al, Fe and Ca) in the mineral phases identified in the raw, annealed and 75% burn-off F cokes ........................223

Figure 9.4 The Fe-O-C equilibrium curves and the superimposed Boudouard curve .224

Figure 9.5 The deportment of iron in the catalytic mineral phases identified in the raw, 15 % burn-off and 75% burn-off cokes......................................................226

Figure 9.6 The deportment of catalytic calcium in the mineral phases identified in the raw, 15 % burn-off and 75% burn-off cokes..............................................227

Figure 9.7 Systems ‘SiO2–Al2O3–FeO’ [152] and ‘SiO2–Al2O3–CaO’ [153] .............229

Figure 9.8 The deportment of the major elements (Si, Al, Fe and Ca) in the mineral phases identified in the raw, 15 % burn-off and 75% burn-off B cokes ....233

Figure 9.9 The deportment of the major elements (Si, Al, Fe and Ca) in the mineral phases identified in the raw, 15 % burn-off and 75% burn-off C cokes ....234

Figure 9.10 The deportment of the major elements (Si, Al, Fe and Ca) in the mineral phases identified in the raw, 15 % burn-off and 75% burn-off F cokes ....235

Figure 9.11 The deportment of the major elements (Si, Al, Fe and Ca) in the mineral phases identified in the raw, 15 % burn-off and 75% burn-off G cokes....236

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Figure 9.12 SEM/EDS micrographs of isolated pyrrhotite particles in the raw coke F....................................................................................................................241

Figure 9.13 SEM/EDS micrographs of pyrrhotite particles in the raw coke F associated with aluminosilicates..................................................................................242

Figure 9.14 SEM/EDS micrographs of pyrrhotite particles in the raw coke F associated with silica ...................................................................................................243

Figure 9.15 SEM/EDS micrographs of metallic iron and pyrrhotite particles in the 15% burn-off coke F...........................................................................................244

Figure 9.16 SEM/EDS micrographs of a pyrrhotite particle in the 15% burn-off coke F....................................................................................................................245

Figure 9.17 SEM/EDS micrographs of iron oxide particles in the 15% burn-off coke F....................................................................................................................246

Figure 9.18 SEM/EDS micrographs of calcium minerals particles in the 15% burn-off coke F .........................................................................................................247

Figure 9.19 SEM/EDS micrographs of iron oxide particles in the 75% burn-off coke F....................................................................................................................248

Figure 9.20 SEM/EDS micrographs of iron oxide and iron minerals particles in the 75% burn-off coke F ..................................................................................249

Figure 9.21 SEM micrographs of (a) raw coke F, (b) 15% burn-off coke F and (c) 75% burn-off coke F...........................................................................................250

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List of tables

Table 4.1 Proximate, petrographic and ash analyses of the parent coals used for preparation of cokes in this work .................................................................61

Table 4.2 Petrographic analysis of the coal fractions and the original coal...................66

Table 4.3 Ash concentration in the vitrinite- and inertinite-rich fractions, the synthetic low ash coals and the original coals from the proximate analysis ...............67

Table 4.4 Proximate and ash analyses of the cokes prepared in the 9 kg oven .............69

Table 5.1 The measured apparent activation energy of the reaction with carbon dioxide of the cokes and their measured temperature ranges....................................90

Table 5.2 The effect of particle size and flow rate on the reaction rate.........................92

Table 5.3 The initial and final intrinsic rates of cokes with carbon dioxide measured using N2 and CO2 surface areas....................................................................98

Table 5.4 The content of isotropic microtexture in the raw and 75% burnout cokes ..102

Table 5.5 Crystallite size (Lc and La) of the raw cokes................................................105

Table 5.6 The Lc and La of the raw cokes and cokes annealed at 900ºC for 15 hours.107

Table 6.1 Surface area of the raw cokes B, C, F and G carbonised in the 70 g and 9 kg ovens ..........................................................................................................119

Table 6.2 Surface area of the raw cokes made from the original coals (B, C, F and G) and their corresponding carbonised maceral-enriched fractions................131

Table 6.3 The percentage of non-fused inertinite in the carbonised inertinite-rich fractions......................................................................................................140

Table 6.4 The percentage of non-fused inertinite in the carbonised vitrinite-rich fractions......................................................................................................148

Table 6.5 Surface area, measured by CO2, of the carbonised vitrinite-rich fractions..149

Table 7.1 Mineral phases identified in the low temperature ash (LTA) of the coals and their relative concentrations .......................................................................156

Table 7.2 Recalculated mineral phase compositions in the coals as weight percentages in the product cokes ...................................................................................157

Table 7.3 Mineral phases identified in the low temperature ash (LTA) of the cokes and their relative concentrations .......................................................................168

Table 7.4 Recalculated mineral phase compositions as weight percentages in the respective cokes .........................................................................................169

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Table 7.5 Recalculated mineral phase compositions as weight percentages in the respective cokes with bassanite and both jarosite and coquimbite being proportioned to oldhamite and pyrrhotite, respectively .............................170

Table 7.6 Elemental composition (mol fraction* 10-4 / 100 g coke) of crystalline and amorphous mineral forms in cokes ............................................................171

Table 7.7 Mineral phases identified in the low temperature ash (LTA) samples and their relative concentrations of cokes prepared in 70 g, 9 kg and 400 kg ovens 176

Table 7.8 Recalculated mineral phases composition identified in the low temperature ash (LTA) samples of cokes prepared in 70 g, 9 kg and 400 kg ovens .....177

Table 7.9 The ash yield of the carbonised maceral-enriched fractions and cokes.......178

Table 7.10 Mineral phases identified in the low temperature ash (LTA) samples and their relative concentrations of carbonised maceral-enriched fractions and original coal................................................................................................181

Table 7.11 Recalculated mineral phases composition identified in the low temperature ash (LTA) samples of carbonised maceral-enriched fractions and cokes prepared from the original coal ..................................................................182

Table 8.1 The relative concentrations (%, mass) of the catalytic mineral phases identified in the low temperature ashes (LTA) of the raw cokes B, C, F and G and their corresponding reacted cokes (15% burn-off) ..........................195

Table 9.1 Mineral phases identified in the low temperature ashes (LTA) of the raw cokes B, C, F and G and their corresponding reacted cokes (15% and 75% burn-off), and their relative concentration .................................................214

Table 9.2 Recalculated mineral phase composition in the raw and reacted cokes as weight percentages in the product cokes....................................................215

Table 9.3 Mineral phases identified in the low temperature ashes (LTA) of the raw coke F and the corresponding annealed coke and reacted coke to 75% burn-off, and their relative concentrations ................................................................217

Table 9.4 Recalculated mineralogy of the raw, annealed and reacted cokes as weight percentages in the product cokes................................................................218

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Bibliography and Achievements

Journals

1. M. Grigore, R. Sakurovs, D. French and V. Sahajwalla Influence of mineral matter on coke reactivity with carbon dioxide ISIJ (The Iron and Steel Institute of Japan) International Vol.46, No.4, 503-512 (2006).

2. M. Grigore, R. Sakurovs, D. French and V. Sahajwalla Effect of carbonisation conditions on mineral matter in coke ISIJ International Vol.47, No.1, 62-66 (2007).

3. R. Sakurovs, D. French and M. Grigore Quantification of mineral matter in commercial cokes and their parent coals International Journal of Coal Geology – in press.

4. S. Gupta, D. French, R. Sakurovs, M. Grigore, H. Sun, T. Cham, T. Hilding, M. Hallin, B. Lindblom and V. Sahajwalla Coke minerals and ironmaking reactions in blast furnace Progress in Energy and Combustion Science (An International Review Journal) – in press

Conferences

1. V. Sahajwalla, R. Sakurovs, M. Grigore, S.T. Cham and M. Dubikova Reactionrates and properties of cokes during reaction with carbon dioxide and liquid iron Science and Technology of Innovative Ironmaking for aiming at Energy Half Consumption [Halving Energy Consumption], Tokyo, Japan, 39-48 (2003).

2. R. Sakurovs, V. Sahajwalla, S.T. Cham, and M. Grigore The impact of advancing BF technology on coke quality requirements 2nd China International Coking Technology and Coke Market Congress, Beijing, P.R. China,192-203 (2004) (in English and Chinese).

3. T. Hilding, V. Sahajwalla, S. Gupta, B. Bj�rkman, R. Sakurovs, M. Grigore and N. Saha-Chaudhury Study of Gasification Reaction of Cokes Excavated from Pilot Blast Furnace SCANMET II 2nd International Conference of Process Development in Iron and Steelmaking, Luleå, Sweden, 467-478 (2004).

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4. M. Grigore, R. Sakurovs, D. French and V. Sahajwalla Mineral matter in coke and its effect on gasification rate 2005 International Conference on Coal Science and Technology, Okinawa, Japan [CD] (2005).

5. M. Grigore, D. French, R Sakurovs, S. Gupta and V. Sahajwalla Effect of coke mineralogy on the gasification behaviour and their implications for innovative blast furnace operations Australia-China-Japan Symposium on Iron and Steelmaking, Beijing, P.R. China, 66-74 (2006).

6. S. Gupta, B. Kim, M. Grigore, D. French, R Sakurovs and V. Sahajwalla Effect of iron-bearing minerals on gasification behaviour of coke The Iron & Steel Technology (AISTech), Indianapolis, USA, (2007).

Poster

M. Grigore, R. Sakurovs and V. Sahajwalla Carbon dioxide and steam gasification of coke Hearth and Raceway Symposium, Wollongong, Australia, (2002).

Achievement

‘Coalin Q Award for Outstanding Presentation’ – 2005 International Conference on Coal Science and Technology – Okinawa, Japan, October 2005

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Nomenclature

A – pre-exponential factor, g g-1 s-1

B – width of the peak at half maximum intensity, radian

[CO] – instantaneous concentration of carbon monoxide, ppm

Ea – activation energy, kJ mol-1

F – gas flow rate, L s-1

K – constant depending on reflection plane

La – average length of carbon crystallite, nm

Lc – average height of carbon crystallite, nm

mo – initial mass of carbon in the sample, g

�m – total mass of carbon loss, g

nco – instantaneous production of carbon monoxide, mol s-1

P – pressure, atm

r – instantaneous rate of carbon consumption, g s-1

R – universal gas constant, J K-1 mol-1

R0max – mean of maximum reflectance of vitrinite in oil, vol.%

t – time, s

T – temperature, K

w – instantaneous mass of carbon in the sample, g

Greek symbols

� – wavelength of incident X-rays, �

� – diffraction angle

�a – apparent chemical reaction rate, g g-1 s-1

� - chi-squared factor

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Acronyms

BET – Brunauer, Emmet and Teller

BF – Blast Furnace

BSE – backscattered electrons

BSU – Basic Structural Units

CRI – Coke Reactivity Index

CSR – Coke Strength after Reaction

EDS – energy dispersive X-ray analyser

FBR – fixed-bed reactor

FESEM – Field Emission Scanning Electron Microscopy

IMDC – Inert Maceral Derived Component

LTA – Low Temperature Ashing

MOD – Molecular Orientation Domain

NSC – Nippon Steel Corporation (test)

RMDC – Reactive Maceral Derived Component

SEM – Scanning Electron Microscopy

SLAC – Synthetic Low Ash Coal

XRD – X-ray Diffraction