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2013
Blast furnace hearth refractory and coke ash mineral interactions Phillp Drain University of Wollongong
Recommended Citation Drain, Phillp, Blast furnace hearth refractory and coke ash mineral interactions, Masters of Engineering thesis, Faculty of Engineering, University of Wollongong, 2013. http://ro.uow.edu.au/theses/3925
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Blast Furnace Hearth Refractory And Coke Ash Mineral Interactions
By
Phillip Brian Drain B(MATERIALS)E
A thesis submitted in fulfilment of the requirements for the award of the degree of
MASTERS OF ENGINEERING (Materials)
from
UNIVERSITY OF WOLLONGONG FACULTY OF ENGINEERING
September 2013
Certification
I, Phillip B. Drain, declare that this thesis, submitted in fulfilment of the requirements for the award of Masters of Engineering, in the Department of Engineering, University of Wollongong, is whole my own work unless otherwise referenced or acknowledged. This document has not been submitted for qualifications at any other academic institution.
Phillip Brian Drain
September 2013
I
Acknowledgments
I would like to acknowledge the support and guidance I have received from my academic supervisor Associate Professor Brian Monaghan throughout this project. For this I am very grateful.
I would like to acknowledge the support and assistance of Dr Robert Nightingale and Dr Michael Chapman. I would like to thank Jim Cummins, Greg Brown and John Spink of BlueScope Steel refractory services for the use of their laboratory and technical advice. I would also like to thank Greg Tillman, Dr Ray Longbottom and Hazem Labib of the University of Wollongong for technical support in terms of sample preparation and analysis.
Finally, I would like to thank my family and friends for all their support and encouragement that helped me get this thesis across the finish line.
II
Abstract
The by-products of coke dissolution in iron are primarily calcium aluminate minerals known as coke ash. These minerals are unreactive with the iron bath and can therefore deposit onto the blast furnace hearth refractories when they form below the iron-slag interface. This study was focused on understanding the interactions between these coke ash minerals and blast furnace hearth refractories. Improved understanding of these interactions may have implications for the campaign life of the blast furnace hearth refractory materials.
It was found that the aluminosilicate refractory followed the linear rate law and the alumina carbon refractory corresponded to the logarithmic rate law. Thermodynamic modelling was conducted and compared with the spot analysis results and micrographs to determine the phases likely to have formed. It was found that the formation of gehlenite (Ca2Al2SiO7) and anorthite (CaAl2Si2O8) were more likely in the reactions with the aluminosilicate refractory due to the higher silicon content in the refractory. This corresponds with the observation of this refractory following the linear rate law which is typical of a material which forms a non-protective reaction layer with high porosity or forms liquid phase reaction products. The rates of reaction were found to follow an Arrhenius relationship, demonstrating temperature dependence for the reactions between both hearth refractories and the calcium aluminates. The reaction rate was also observed to increase with the calcium content as predicted by Fick’s 1st law of Diffusion. The Kirkendall effect was demonstrated via an inert wire test indicating net mass transport of material into the refractory materials from the calcium aluminates. This suggests that the active species responsible for most the reactions observed was the calcium ion.
Detailed analysis using thermodynamic data was carried out to determine the possible reactions between the calcium aluminates and the refractory minerals. The formation of low liquidus temperature phases (anorthite and gehlenite) and the possible formation of liquid oxide phase were determined to increase the rate of refractory wear and limit the ability of the refractories to form a protective reaction layer. The formation of grossite (CaAl4O7) and hibonite (CaAl2O19) was found to make the refractory more susceptible to structural and thermal spalling due to the increased stress in the reaction layer cause by the volume change and variation in thermal expansion coefficients of the reaction products.
III
Contents Certification .......................................................................................................................... I Acknowledgments ............................................................................................................... II Abstract.............................................................................................................................. III Contents ............................................................................................................................. IV List of Tables .................................................................................................................... VII List of Figures................................................................................................................. VIII Definitions and Notation ............................................................................................... XIII 1.
2.
Introduction.................................................................................................................. 1 1.1.
Problem Definition..................................................................................................................... 1
1.2.
Aim ............................................................................................................................................ 2
1.3.
Objectives .................................................................................................................................. 3
1.4.
Methodology .............................................................................................................................. 3
Literature Review ........................................................................................................ 4 2.1.
The Ironmaking Blast Furnace ......................................................................................... 4
2.1.1.
Raw Materials ............................................................................................................................ 5
2.1.2.
Permeability in a Blast Furnace ................................................................................................. 5
2.1.3.
Key Reactions in the Blast Furnace Hearth ............................................................................... 6
2.1.4.
Hearth Liquid Flow .................................................................................................................... 8
2.2.
Coke ................................................................................................................................ 11
2.2.1.
Coke Composition and Mineralogy ......................................................................................... 11
2.2.2.
Coke Dissolution in Liquid Iron .............................................................................................. 11
2.2.3.
Mineral Layer Formation ......................................................................................................... 13
2.3.
Blast Furnace Hearth Refractories .................................................................................. 15
2.3.1.
Fabrication ............................................................................................................................... 16
2.3.2.
Composition and Microstructure.............................................................................................. 17
2.4.
Refractory and Mineral Systems .................................................................................... 19
2.4.1.
CaO-Al2O3 Binary System ....................................................................................................... 20
2.4.2.
Al2O3-SiO2 Binary System ....................................................................................................... 20
2.4.1.
CaO-SiO2 Binary System ......................................................................................................... 21
2.4.2.
Al2O3-CaO-SiO2 Ternary System ............................................................................................ 21
2.5.
Thermodynamics of Refractory and Mineral Matter Reactions ..................................... 22
2.6.
Kinetics of Refractory and Mineral Matter Reactions .................................................... 23
2.6.1.
Kinetics in Solid State Oxide Systems ..................................................................................... 23
2.6.2.
Temperature Dependence ........................................................................................................ 24
2.6.3.
Area of Reaction Interface ....................................................................................................... 25
2.6.4.
Kinetic Models in Solid State Oxide systems .......................................................................... 25
2.7.
Refractory Degradation Mechanisms in the Blast Furnace Hearth ................................ 27
2.1.
Summary ......................................................................................................................... 30 IV
3.
Experimental Method ................................................................................................ 31 3.1.
Reaction Couple Experiments ........................................................................................ 31
3.1.1.
Reaction Couple and Crucible Configuration .......................................................................... 32
3.1.2.
Reaction Couple Furnace Configuration .................................................................................. 33
3.1.3.
Experimental Heating Schedule ............................................................................................... 33
3.1.4.
Experimental Matrix ................................................................................................................ 34
3.1.5.
Experimental Repeatability ...................................................................................................... 34
3.1.6.
Experimental Outcomes ........................................................................................................... 35
3.2.
Reaction Couple Furnace Temperature Calibration ....................................................... 35
3.3.
Preparation of Refractories ............................................................................................. 37
3.3.1.
Coring and Cutting of Samples ................................................................................................ 37
3.3.2.
Sample Cleaning ...................................................................................................................... 37
3.3.3.
Grinding and Polishing of Refractories .................................................................................... 38
3.3.4.
Microstructure Characterisation ............................................................................................... 39
3.3.5.
Composition Characterisation .................................................................................................. 40
3.4.
Preparation of Calcium Aluminates................................................................................ 41
3.4.1.
Calcium Aluminate Synthesis .................................................................................................. 41
3.4.2.
Preparation of Calcium Aluminate Reaction Couple Disks ..................................................... 43
3.5.
Measurement of the Reaction Couple Interfacial Surface Roughness............................ 45
3.5.1.
Contact Atomic Force Microscopy .......................................................................................... 45
3.5.2.
Roughness Analysis using the Atomic Force Microscope ....................................................... 46
3.5.3.
Calibration of the Atomic Force Microscope ........................................................................... 48
3.6. 3.6.1.
Characterisation of Heat Treated Reaction Couple Materials ........................................ 48 Heat Treated Alumina-Carbon Refractory Changes ................................................................ 49
3.7.
Measurement of Bulk Density and Apparent Porosity ................................................... 51
3.8.
Microscopy Preparation of Reaction Couples ................................................................ 52
3.9.
Measurement of Reaction Layer ..................................................................................... 53
3.9.1.
Calibration of the Scanning Electron Microscope Scale Bar ................................................... 54
3.9.2.
Reaction Layer Measurement Error ......................................................................................... 56
3.9.3.
Identification of the Original Reaction Couple Interface ......................................................... 56
V
4.
Results ......................................................................................................................... 57 4.1.
Summary of Results........................................................................................................ 57
4.2.
Temperature Effect on Reaction Couple Kinetics .......................................................... 58
4.2.1.
Mass Change Measurements .................................................................................................... 58
4.2.2.
SEM Micrographs .................................................................................................................... 59
4.2.3.
Reaction Layer Thickness Measurements ................................................................................ 63
4.2.4.
Elemental Analysis of the Reaction Layer ............................................................................... 64
4.3.
5.
Time Effect on Reaction Couple Kinetics ...................................................................... 68
4.3.1.
Mass Change Measurements .................................................................................................... 68
4.3.2.
SEM Micrographs .................................................................................................................... 68
4.3.3.
Reaction Layer Thickness Measurements ................................................................................ 74
4.3.4.
Elemental Analysis of the Reaction Layer ............................................................................... 74
4.4.
Experimental Observations ............................................................................................. 79
4.5.
Phase Stability Diagrams ................................................................................................ 82
Discussion ................................................................................................................... 85 5.1.
Thermodynamics of Hearth Refractory and Coke Ash Interactions ............................... 85
5.1.1.
Reaction Couple Phase Formation with Temperature .............................................................. 86
5.1.2.
Reaction Couple Phase Formation with Time .......................................................................... 91
5.1.3.
Phase Identification and Energy Dispersive Spectroscopy Error ............................................. 96
5.1.4.
Alumina-Carbon Refractory Mass Loss ................................................................................... 96
5.2.
Kinetics of Hearth Refractory and Coke Ash Interactions ............................................. 97
5.2.1.
Aluminosilicate Refractory Reaction Kinetics ......................................................................... 97
5.2.2.
Alumina-Carbon Refractory Reaction Kinetics ..................................................................... 103
5.2.3.
Identification of the original Reaction Couple Interface ........................................................ 108
5.2.4.
Refractory – Coke ash reaction kinetics in the blast furnace hearth. ..................................... 109
5.3.
Influence of Reaction Products Properties on Refractory Degradation ........................ 110
5.4.
Consequences for Blast Furnace Hearth Refractories .................................................. 111
6.
Conclusions ............................................................................................................... 112
7.
Recommendations for Further Studies .................................................................. 114
8.
References ................................................................................................................. 115
Appendix I - Atomic Force Microscopy and Roughness Results .................................... I Appendix II - AS1774.5-2001: The Determination of Density and Porosity .............. VII Appendix III - Reaction Couple Mass Change Results ...............................................XVI Appendix IV - Reaction Layer Thickness Measurements ...................................... XVIII Appendix V - Reaction Couple SEM Micrographs .....................................................XXI Appendix VI - Energy Dispersive Spectroscopy Line Analysis Results ................. XXVI VI
List of Tables Table 2.1: Ash composition of a typical BlueScope Steel coke by mass% of ash (total ash 11.6 mass%)[4] 11 Table 2.2: The characteristics of calcium aluminates [35-36] ......................................................................... 14 Table 2.3: Texture and mineralogy of different Alumina-Carbon refractories [38]. ....................................... 17 Table 2.4: Texture and mineralogy of different Aluminosilicate refractories [38]. ......................................... 18 Table 2.5: Composition of the Aluminosilicate and Alumina-Carbon refractories in mass% [39-40] ............ 19 Table 2.6: Free energy data for reactions in the coke ash and refractory minerals [46-47] ............................. 22 Table 2.7: The diffusion coefficients of Al3+, Ca2+ and Si2+ cations in alumina (99.85 mass%) at 1397˚C from [55] and calculated from data provided in [56] using equation 2-16...................................................... 24 Table 3.1: The Experimental Matrix testing the effect of time on reaction kinetics ........................................ 34 Table 3.2: The Experimental Matrix testing the effect of temperature on reaction kinetics ............................ 34 Table 3.3: Reaction couple experimental outputs ............................................................................................ 35 Table 3.4: Vertical tube furnace temperature calibration conditions. .............................................................. 36 Table 3.5: Fine grinding and polishing for the Alumina-Carbon refractory samples ...................................... 38 Table 3.6: Fine grinding and polishing for the Aluminosilicate refractory samples ........................................ 38 Table 3.7: Alumina-Carbon refractory EDS spot analysis results reported as oxides ..................................... 40 Table 3.8: Aluminosilicate refractory EDS spot analysis results reported as oxides ....................................... 40 Table 3.9: Base powders used for synthesis of calcium-aluminate phases [3, 4]............................................. 41 Table 3.10: Raw material powder quantities for calcium aluminate synthesis. ............................................... 41 Table 3.11: Fine grinding and polishing schedule for the calcium aluminate disks ........................................ 44 Table 3.12: Atomic Force Microscopy Average Roughness Measurements ................................................... 46 Table 3.13: Heat Treated Refractory and Calcium Aluminate mass loss data ................................................. 48 Table 3.14: Heat Treated Alumina-Carbon Refractory EDS spot analysis results .......................................... 49 Table 3.15: Average density and porosity of refractories and calcium aluminates. ......................................... 51 Table 3.16: Automatic grinding and polishing schedule for mounted refractory samples ............................... 53 Table 4.1: Aluminosilicate refractory temperature series reaction couples EDS spot analysis results ............ 60 Table 4.2: Alumina-Carbon refractory temperature series reaction couples EDS spot analysis results .......... 62 Table 4.3: Reaction layer phases consistent with EDS compositions observed in the Temperature Series Reaction couples in Figure 4.2 and Figure 4.3. ...................................................................................... 67 Table 4.4: Aluminosilicate refractory time series reaction couples EDS spot analysis results ........................ 70 Table 4.5: Aluminosilicate refractory time series reaction couples EDS spot analysis results ........................ 72 Table 4.6: Alumina-Carbon refractory temperature series reaction couples EDS spot analysis results .......... 73 Table 4.7: Reaction layer phases consistent with EDS compositions observed in the Time Series Reaction couples in Figure 4.15 and Figure 4.16. ................................................................................................. 78 Table 4.8: Reaction couple visual observations ............................................................................................... 79 Table 4.9: EDS Analysis of alumina weights and the observed glassy phase. ................................................ 80 Table 4.10: Material compositions used to model Phase Stability Diagrams .................................................. 82 Table 5.1: Predicted and observed interfacial phases in Aluminosilicate – CA reactions by temperature. Reaction time = 4 hours. ........................................................................................................................ 86 Table 5.2: Predicted and observed interfacial phases in Aluminosilicate – CA2 reactions by temperature. Reaction time = 4 hours. ........................................................................................................................ 86 VII
Table 5.3: Predicted and observed interfacial phases in Aluminosilicate – CA6 reactions by temperature. Reaction time = 4 hours. ........................................................................................................................ 87 Table 5.4: Predicted and observed interfacial phases in Alumina-Carbon – CA reactions by temperature. .... 89 Table 5.5: Predicted and observed interfacial phases in Alumina-Carbon – CA2 reactions by temperature. .. 89 Table 5.6: Predicted and observed interfacial phases in Alumina-Carbon – CA6 reactions by temperature. .. 90 Table 5.7: Predicted and observed interfacial phases in Aluminosilicate – CA reaction couples by time. ...... 92 Table 5.8: Predicted and observed interfacial phases in Aluminosilicate – CA2 reaction couples by time. .... 92 Table 5.9: Predicted and observed interfacial phases in Aluminosilicate – CA6 reaction couples by time. .... 93 Table 5.10: Predicted and observed interfacial phases in Alumina-Carbon – CA reaction couples by time. .. 94 Table 5.11: Predicted and observed interfacial phases in Alumina-Carbon – CA2 reaction couples by time. 94 Table 5.12: Predicted and observed interfacial phases in Alumina-Carbon – CA6 reaction couples by time. 94 Table 5.13: k0 and Activation Energy for reaction layer formation for all CAx -Aluminosilicate reaction couples. ................................................................................................................................................ 101 Table 5.14: k0 and Activation Energy for reaction layer formation for all CAx –Alumina-Carbon reaction couples. ................................................................................................................................................ 105 Table 5.15: Unit cell volume and density of Coke Ash and Hearth Refractory minerals [74], [35], [44], [75], [45], [76] .............................................................................................................................................. 109 Table A 1: Atomic Force Microscopy Roughness trsults ................................................................................... I Table A-2: Temperature Series Reaction couple mass change data ............................................................. XVI Table A-3: Time Series Reaction couple mass change data ........................................................................ XVII Table A-4: Reaction layer Thickness Measurements for Temperature Series ........................................... XVIII Table A-5: Temperature Series Reaction couples with no observable reaction layer ................................ XVIII Table A-6: Reaction layer Thickness Measurements for Time Series .......................................................... XIX Table A-7: Time Series Reaction couples with no observable reaction layer ................................................ XX
List of Figures Figure 1.1: No.5 BF Port Kembla Hearth Refractory Design, diagram adapted from [1] Slag and iron levels within packed bed of coke are shown. Internal diameter of 10.55m at the taphole .................................. 1 Figure 2.1: Blast furnace key reaction zones and gas flow, adapted from [7] ................................................... 4 Figure 2.2: The change of SiO2 content in coke with increasing temperature in a blast furnace [8]. ................ 7 Figure 2.3: Simplified forces acting on the coke bed adapted from [15] ........................................................... 8 Figure 2.4: Diagrams of a) Static/sitting deadman b) Dynamic deadman c) Dynamic deadman with a complete coke free zone adapted from [15] ........................................................................................... 10 Figure 2.5: Fe-C phase diagram [21] ............................................................................................................... 12 Figure 2.6: Schematic representation of coke dissolution and mineral layer formation [32]........................... 13 Figure 2.7: Schematic diagram of a refractory microstructure made from powders with a large range of sizes [37]. ........................................................................................................................................................ 16 Figure 2.8: a) Microstructure of an Alumina-Carbon refractory, alumina grains (A), graphite flakes (G) light antioxidant Si metal grains (Si). b) Microstructure of Aluminosilicate refractory showing sintered porous alumina aggregate grains (A) bonded with fine alumina, glass and mullite [37]. ...................... 18 Figure 2.9: Al2O3-CaO phase diagram [44] ..................................................................................................... 20 VIII
Figure 2.10: Al2O3-SiO2 phase diagram [44] ................................................................................................... 20 Figure 2.11: SiO2-CaO phase diagram [45] ..................................................................................................... 21 Figure 2.12: Al2O3-SiO2-CaO phase diagram [44] .......................................................................................... 21 Figure 2.13: Comparative plot of diffusion coefficients for cations in Al 2O3 and CaO [49] ........................... 24 Figure 2.14: Comparative plot of the different kinetic models for the reaction layer formation, adapted from [57]. ........................................................................................................................................................ 26 Figure 2.15: a) Wetting material (θ
