Fundamental Investigation of Slag/Carbon Interactions in Electric Arc Furnace Steelmaking Process

230 Pages·2010·4.2 MB·English

The University of New South Wales
Faculty of Science
School of Materials Science and Engineering
Fundamental Investigation of Slag/Carbon
Interactions in Electric Arc Furnace Steelmaking
Process

A Thesis in
Materials Science and Engineering
By
Muhammad Mahfuzur Rahman

Submitted in Partial Fulfilment
of the requirements for the Degree of
DOCTOR OF PHILOSOPHY
March 2010
i(cid:2)
(cid:2)
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 any 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.

Signed ……………………………………
Muhammad Mahfuzur Rahman
ii(cid:2)
(cid:2)
COPYRIGHT STATEMENT
‘I hereby grant the University of New South Wales or its agents the right to archive and to
make available my thesis or dissertation in whole or part in the University libraries in all
forms of media, now or here after known, subject to the provisions of the Copyright Act
1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in
future works (such as articles or books) all or part of this thesis or dissertation.
I also authorize University Microfilms to use the 350 word abstract of my thesis in
Dissertation Abstract International (this is applicable to doctoral theses only).
I have either used no substantial portions of copyright material in my thesis or I have
obtained permission to use copyright material; where permission has not been granted I
have applied/will apply for a partial restriction of the digital copy of my thesis or
dissertation.'

Signed ……………………………………………...........................
Date ……………………………………………...........................
AUTHENTICITY STATEMENT
‘I certify that the Library deposit digital copy is a direct equivalent of the final officially
approved version of my thesis. No emendation of content has occurred and if there are any
minor variations in formatting, they are the result of the conversion to digital format.’

Signed ……………………………………………...........................
Date ……………………………………………...........................
iii(cid:2)
(cid:2)
ACKNOWLEDGEMENTS
I wish to express my deepest sense of gratitude and appreciation to my supervisors
Professor Veena Sahajwalla, Dr Rita Khanna and Mr. Paul O’Kane for their unrelenting
support and guidance throughout my research. Their encouragement and enthusiasm were a
constant source of motivation. My sincerest gratitude goes to them for their excellent
guidance and for providing valuable advice, comments and suggestions at various points
during the course of this research. Their expertise was also invaluable in interpreting the
results and in providing suggestions on preparing papers and research documents. I also
wish to acknowledge the financial support provided by the Australian Research Council
and OneSteel, Sydney.

I wish to acknowledge the support of OneSteel, Sydney for all their help with carrying out
the industrial trials, in particular Catherine Skidmore, Mr. Kannan Thangaraj and other
OneSteel personnel for their whole hearted support and commitment to this research work,
through holding regular discussions and meetings to analyze and interpret the results, and
conducting industrial trials for the experimental work.

I am grateful to Mr Narendra Saha Chaudhury for his valuable assistance in setting up and
maintaining the experimental apparatus. In addition, special thanks to Philip Chatsfield for
providing training and valuable assistance in repairing/maintaining all the equipments.
I would also like to thank staff and colleagues at the School of Materials Science and
Engineering for their help throughout the course of this project. Special thanks to Dr.
Pramod Koshy, Ikram, James Dankwah, James Dongmin Jang, Nick, Anup, for the coffee
breaks and laughing sessions to keep me sane. Finally, I express my deepest gratitude to my
wife Emon and family for motivation, patience, sacrifices and forever love through the
period. I also thank my lovely daughter Mehjabeen Mahfuz, who is my beautiful gift from
God, for bearing with me during the course of my Ph.D.

iv(cid:2)
(cid:2)
ABSTRACT
This work investigates the interactions of carbonaceous materials (metallurgical coke,
natural graphite and HDPE/coke blends) with three EAF slags [FeO: 24% to 32%].
Experiments were conducted using the sessile drop technique (1500°C-1600°C) with off-
gases (CO, CO ) measured using an IR analyzer; the wetting behaviour was determined
2
from contact angle measurements. Estimation of slag foaming behaviour was determined
from the droplet volume changes calculated using specialized software. At 1550°C, all
slags were non-wetting with coke due to increased surface tension due to sulphur. At
1550°C, slag 1 was initially non-wetting on natural graphite due to gas entrapment in the
slag droplet; the wetting improved after that. Other slags showed comparatively better
wetting. At 1600°C, all slags were non-wetting with coke. Slags showed a shift from non-
wetting to wetting behaviour with natural graphite. Slag/coke reactions produced high off-
gases levels causing extensive FeO reduction; gas entrapment in the slag was poor (small
volume droplets). Slag/natural graphite interactions revealed both slow gas generation rates
and FeO reduction, and excellent gas entrapment (higher droplet volumes) with minor
changes in slag properties due to low ash levels. The iron oxide reduction rates were
determined to be 1.54x10-5 and 4.2x10-6 mol.cm-2/sec (Slag 1, 1550°C) for metallurgical
coke and natural graphite respectively. Slag interactions with coke/HDPE blends showed
increasing off-gas levels with increasing HDPE levels. Blend#3 produced the highest off-
gas levels, extensive FeO reduction and displayed significantly higher slag foaming and
better wetting compared to coke. Our line on trends compared well for slag/carbon
interactions and resulted in deceased specific energy consumption and carbon usage and
increased productivity. These findings have enhanced the possibility of utilizing polymeric
wastes in blends with coke in EAF steelmaking for slag/carbon interactions.

v(cid:2)
(cid:2)
TABLE OF CONTENTS
CERTIFICATE OF ORIGINALITY ii
COPYRIGHT & AUTHENTICITY STATEMENTS
iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
TABLE OF CONTENTS vi
LIST OF FIGURES x
LIST OF TABLES xix
LIST OF PUBLICATIONS AND AWARD xxi
Chapter 1 Introduction 1-1
1.1 Research objectives 1-3
Chapter 2 Literature review 2-1
2.1 Electric arc furnace (EAF) steel making – a brief overview 2-1
2.2 Electric arc furnace (EAF) slag 2-5
2.2.1 The structure of slags 2-7
2. 3 Slag foaming in EAF steelmaking 2-9
2.3.1 Carbonaceous injectant 2-12
2.3.2 Industrial importance 2-14
2.3.3 Mechanisms 2-15
2.3.4 The advantages of slag foaming 2-16
2.4 Slag foaming and carbon/slag interactions 2-21
2.4.1 Measurement of foaming 2-21
2.4.1.1 Viscosity and second phase particles 2-26
2.4.1.2 Basicity 2-28
2.4.1.3 Surface tension 2-31
2.4.1.4 Temperature 2-35
2.4.1.5 Kinetics of gas generation 2-38
vi(cid:2)
(cid:2)
2.5 Wettability 2-42
2.5.1 Previous wettability studies on carbon/slag systems 2-43
2.5.2 Mechanisms of wetting 2-46
2.5.3 Factors affecting wettability 2-48
2.5.3.1 Temperature 2-48
2.5.3.2 Surface active elements 2-49
2.5.3.3 Role of experimental conditions 2-50
2.5.3.4 Influence of sulphur 2-52
2.6 FeO reduction in EAF steelmaking slag 2-52
2.6.1 Previous studies on iron oxide reduction 2-54
2.6.2 Mechanism of iron oxide reduction in slag 2-62
2.7 Key objectives 2-67
Chapter 3 Experimental 3-1
3.1 Characterization of experimental materials 3-1
3.1.1 Electric arc furnace (EAF) slags 3-1
3.1.2 Slag characterization 3-2
3.1.2.1 Oxford LabX-3500 XRF for Slag Analysis 3-2
3.1.2.2 Field Emission Scanning Electron Microscopy (FESEM) 3-3
3.1.2.3 Optical Microscopy 3-3
3.2 Carbonaceous materials 3-5
3.2.1 Material preparation 3-5
3.2.1.1 Characterization of Carbonaceous Materials 3-7
3.2.1.2 Proximate/ultimate and ash analysis 3-7
3.2.2 X-Ray Diffraction Analysis 3-12
3.2.3 Visual/FESEM characterization 3-12
3.2.4 Carbon Percentage analysis using LECO SC444DR 3-13
3.3 Experimental Techniques 3-14
3.3.1 Sessile Drop Techniques 3-14
3.3.1.1 Dynamic Wettability and Interfacial Phenomena 3-16
vii(cid:2)
(cid:2)
3.3.1.2 Study of Interfacial Reaction Products 3-18
3.3.1.3 Infrared (IR) gas analysis 3-20
3.3.2 Reproducibility of experimental results 3-21
Chapter 4 Novel Sessile Drop Software for quantities estimation of slag 4-1
foaming in slag/carbon interaction
4.1 Dynamic volume and area measurement 4-3
4.2 Summary 4-9
Chapter 5 Slag/carbon interactions: metallurgical coke: 5-1
Results and Discussion
5.1 Dynamic wettability 5-1
5.1.1 Effect of temperature 5-2
5.1.2 Effect of slag composition 5-5
5.2 Dynamic slag foaming behaviour 5-9
5.2.1 Effect of temperature 5-10
5.2.2 Effect of slag composition 5-15
5.3 Reactivity studies 5-17
5.4 Interfacial phenomena 5-20
5.4.1 Optical microscopic studies 5-20
5.4.2 FESEM studies 5-23
5.5 Discussion 5-24
5.6 Summary 5-29
Chapter 6 Slag/carbon interactions: natural graphite: 6-1
Results and Discussion
6.1 Dynamic wettability 6-1
6.1.1 Effect of temperature 6-1
6.1.2 Effect of slag composition 6-4
6.2 Dynamic slag foaming behaviour 6-8
viii(cid:2)
(cid:2)
6.2.1 Effect of temperature 6-9
6.2.2 Effect of slag composition 6-13
6.3 Reactivity studies 6-15
6.4 Interfacial phenomena 6-17
6.4.1 Optical microscopic studies 6-18
6.4.2 FESEM studies 6-21
6.4 Discussion 6-22
6.5 Summary 6-26
Chapter 7 Experimental results: HDPE-cokes blends as a carbon resource 7-1
7.1 Dynamic wettability 7-1
7.2 Dynamic slag foaming 7-3
7.3 Reactivity studies 7-5
7.4 Microscopic investigations 7-7
7.5 Industrial trials 7-12
7.6 Discussions 7-14
7.7 Summary 7-18
Chapter 8 Discussion: Influence of carbonaceous materials 8-1
on slag/carbon interactions
Chapter 9 Summary and conclusion 9-1
Chapter 10 List of references 10-1
Appendix A Video image Library A-1

(cid:2)
(cid:2)
(cid:2)
ix(cid:2)
(cid:2)
List of Figures
Figure Name Page
2.1 Outline of an electric arc furnace (EAF). 2-2
2.2 EAF steelmaking process. 2-3
2.3 Schematic diagram of eaf steelmaking operations. 2-4
2.4 Schematic representation of the silica tetrahedron and crystalline and 2-7
molten silica. The oxygen atoms are shown white and the silica atoms
are black [Pretorius and Carlisle (1998)].
2.5 Schematic representation of a divalent metal oxide in molten silica. 2-9
Metal ions are represented by the shaded circles. The concentration of
metal oxide increases from left to right [Eisenhuttenleute (1981)].
2.6 Spherical bubbles shapes observed in a well-foamed slag [Yi et al 2-11
(2002)].
2.7 Illustration of slag foaming phenomena in eaf (courtesy of 2-12
Steeluniversity).
2.8 Lance prior to slag formation and foamy slag formations during 2-15
charcoal injection (courtesy of Sydney steel mill).
2.9 Schematic of slag foaming phenomenon. 2-16
2.10 Effect of slag foaming on heat loss in eaf steelmaking [Jones et al 2-17
(1998)].
2.11 Effect of slag foaming on electrical arc furnace (eaf) operation [Jones et 2-18
al (1998)].
2.12 Effect of slag foaming on energy loss with increase in power factor 2-18
[Jones et al (1998)].
2.13 Influence of slag foaming on reactance ratio with increasing power 2-19
factor.
2.14 Heat loss to eaf sidewalls for foaming and conventional slag [Jones et al 2-19
(1998)].

x(cid:2)
(cid:2)