Desulfurization of coal by oxidation in alkaline solution

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Iowa State University Capstones, Theses and
Retrospective Theses and Dissertations
Dissertations
1979
Desulfurization of coal by oxidation in alkaline
solution
Kang-Chun Chuang
Iowa State University
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Chuang, Kang-Chun, "Desulfurization of coal by oxidation in alkaline solution " (1979).Retrospective Theses and Dissertations. 7272.
https://lib.dr.iastate.edu/rtd/7272
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CHUANG, KANG-CHUN
DESULFURIZATION OF COAL BY OXIDATION IN ALKALINE SOLUTION
Iowa State University PH.D. 1979
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Desulfurization of coal by oxidation
in alkaline solution
by
Kang-Chun Chuang
A Dissertation Submitted to the
Graduate Faculty in Partial Fulfillment of the
Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Major: Chemical Engineering
Approved:
Signature was redacted for privacy.
In Charge of Major Work
Signature was redacted for privacy.
For the Major Department
Signature was redacted for privacy.
For the Graduate College
Iowa State University
Ames, Iowa
1979
ii
TABLE OF CONTENTS
Page
NOMENCLATURE x
ABSTRACT xi
INTRODUCTION 1
LITERATURE REVIEW 6
Extraction of Sulfur from Pyrite and Other Sulfide
Minerals 6
Desulfurization of Coal 21
Leaching with solutions of ferric sulfate 21
Nitric acid leaching 23
Leaching with dissolved oxygen solutions 24
Atmospheric pressure method 24
Elevated pressure method 25
Hot aqueous solutions 25
Hot aqueous solutions with a promoter 29
Hot alkaline solutions 30
Leaching with caustic solutions 32
Extraction with molten caustic 33
Leciching with aqueous solutions of metal oxides 33
Treatment with gases 34
Sulfur dioxide 34
Chlorine 35
Ozone 35
KVB process 36
Hazen Magnex process 37
Other reviews and monographs 37
EXPERIMENTAL INVESTIGATION 39
Materials and Equipment Used 39
Autoclave 39
Pyrite cleaning apparatus 41
Coal and pyrite feedstock 41
Leaching Procedure 45
Calculations 46
iii
EXPERIMENTAL RESULTS AND DISCUSSION 48
Coal Desulfurization 48
Effect of stirring rate 48
Effect of oxygen flow rate 53
Effect of pulp density 53
Effect of leach solution and oxidant 56
Effect of alkali concentration 57
Effect of residence time 59
Effect of temperature 59
Effect of oxygen partial pressure 63
Effect of acid treatment 69
Sodium bicarbonate solution 71
Effect of temperature 71
Effect of concentration 73
Effect of sodium sulfate 73
Comparison of different alkalis 76
Removal of organic sulfur from precleaned coal 78
Two-step leaching 84
Desulfurization of Coal-Derived Pyrite 87
Conversion-time data 87
Modeling 88
Reaction kinetics 88
Selection of a model 99
Effective diffusivity calculation 104
Effect of Temperature 108
Effect of Oxygen Partial Pressure 110
Effect of Particle Size 114
CONCLUSIONS AND RECOMMENDATIONS 118
Conclusions 118
Coal desulfurization 118
Pyrite desulfurization 120
Recommendations 121
Coal desulfurization 121
Pyrite desulfurization 122
iv
LITERATURE CITED 123
ACKNOWLEDGMENTS 130
APPENDIX A. EXPERIMENTAL CONDITIONS AND RESULTS OBTAINED FOR
COAL DESULFURIZATION 131
APPENDIX B. STATISTICAL ANALYSIS OF COAL DATA 155
APPENDIX C. DETERMINATION OF SULFUR IN LIQUID SAMPLES 163
Procedure 163
Calculation Method 164
Sample Calculation of Sulfur Content 164
APPENDIX D. EXPERIMENTAL CONDITIONS AND RESULTS OBTAINED FOR
PYRITE DESULFURIZATION 166
APPENDIX E. NONLINEAR REGRESSION ANALYSIS OF PYRITE LEACHING
DATA 170
V
LIST OF FIGURES
Page
Figure 1. Schematic diagram of experimental apparatus 40
Figure 2. Pyrite cleaning apparatus 42
Figure 3. Effect of agitator speed on the removal of sulfur
from coal for 50 Ib./sq. in. (absolute) oxygen
partial pressure 50
Figure 4. The interaction of agitator speed and oxygen partial
pressure on pyritic sulfur removal 51
Figure 5. Effect of oxygen flow rate on leaching of coal 54
Figure 6. Effect of pulp density on leaching of coal 55
Figure 7. Effect of sodium carbonate concentration on oxy-
desulfurization of coal 58
Figure 8. Effect of leaching time on oxydesulfurization of
coal 60
Figure 9. Desulfurization of coal as a function of tempera­
ture at 50 Ib./sq. in. (absolute) oxygen pressure 61
Figure 10. Desulfurization of coal as a function of tempera­
ture at 200 Ib./sq. in. (absolute) oxygen pressure 62
Figure 11. Effect of oxygen partial pressure on oxydesulfuriza­
tion of Lovilia coal 65
Figure 12. Effect of oxygen partial pressure on leaching of
Western Kentucky coal 66
Figure 13. Effect of oxygen partial pressure on oxydesulfuriza­
tion of Western Kentucky coal by leaching with
alkaline, neutral or acidic solutions 68
Figure 14. Effect of temperature on leaching of coal with
sodium bicarbonate solution 72
Figure 15. Effect of sodium bicarbonate concentration on
leaching of coal 74
Figure 16. Effect of O2 pressure and reaction time on organic
sulfur removal at 1200C 81
vi
Figure 17. Effect of O2 pressure and time on organic sulfur
removal at 2000C 82
Figure 18. Organic sulfur removal versus heating value loss 83
Figure 19. Total sulfur conversion versus reaction time for
coarse particles 89
Figure 20. Total sulfur conversion versus reaction time for
fine particles 90
Figure 21. Partially reacted pyrite from chemical leaching
of c>-)a.l. A hematite (Fe203) reaction rim is
indicated by the arrows 92
Figure 22. The photomicrograph of a large leached pyrite
particle. P = unreacted pyrite. H = the reac­
tion rim of hematite 94
Figure 23. Representation of shrinking unreacted core model
for single particles 96
Figure 24. gCXg) and p(Xg) versus reaction time for coarse
particles 102
Figure 25. g(Xg) and p(Xg) versus reaction time for fine
particles 103
Figure 26. Arrhenius plot for the temperature effect 109
Figure 27. Effect of oxygen pressure on pyrite leaching 111
Figure 28. Effect of oxygen partial pressure on sulfur
conversion 113
Figure 29. Effect of particle size on sulfur conversion 115
Figure 30. Time for complete reaction of ppyyi rite (T)v ersus
square of the particle size (R/) 117
Figure B-1. Response of high sulfur coals to leaching condi­
tions 157
Figure B-2. Effect of sulfur content on response of high
sulfur coals to different leaching conditions 158
Figure B-3. Response of low sulfur coals to leaching condi­
tions 160
Figure B-4. Effect of sulfur content on response of low
sulfur coals to different leaching conditions 161