High Temperature Removal of H2S from Coal Gasification Process Streams Using an Electrochemical Membrane System: Final Technical Report

High Temperature Removal of H₂S from Coal Gasification Process Streams Using an Electrochemical Membrane System
Final Technical Report - 2003

LIST OF TABLES			5
LIST OF FIGURES			7
NOMENCLATURE			8
SUMMARY			10
CHAPTER 1. INTRODUCTION			13
1.1	Significance of H₂S Removal		13
1.2	Hot-gas Clean-up in Coal Gasification Processes		14
1.3	Objectives		18
CHAPTER 2. BACKGROUND			19
2.1	Theory		19
	2.1.1	Electrochemical Membrane Separation	19
	2.1.2	Steps in Removal	21
	2.1.3	Sulfide Diffusion Limitation across the Membrane	22
	2.1.4	Gas Mass Transfer Limitations	23
	2.1.5	Stoichiometric Limitations	23
	2.1.6	Application of Theory	24
	2.1.7	Theoretical Potentials	25
	2.1.8	Overpotentials	27
	2.1.9	H₂ Solubility and Diffusivity in the Electrolyte	28
	2.1.10	Carbon Deposition	28
2.2	Previous Work		29
	2.2.1	Sulfur Removal Calculations	29
	2.2.2	Sulfide Reaction Kinetics	30
	2.2.3	Mechanism of Sulfide Reaction	32
	2.2.4	Cathode Materials Selection	33
	2.2.5	Cobalt Sulfide Cathode	34
	2.2.6	Metal Oxide Cathodes	35
	2.2.7	Cell Housing Passivation	35
	2.2.8	Optimal Electrode Design	36
CHAPTER 3. TECHNICAL APPROACH AND EXPERIMENTAL METHODS			38
3.1	Technical Approach		38
	3.1.1	Fundamental Sulfur Transport Limitations	38
	3.1.2	Analysis of Cathode Materials	39
	3.1.3	Novel Metal Oxide Cathode Materials	39
	3.1.4	Evaluation of Cathode Performance	41
3.2	Experimental Methods		41
	3.2.1	Cell Components	41
	3.2.2	Equipment	43
	3.2.3	Electrode Fabrication	46
	3.2.4	Conductivity Samples	48
	3.3.3	Cell Housing Fabrication and Passivation	49
	3.2.5	Assembly of Cell Housing, Electrodes, Membrane, and Electrolyte	50
	3.2.6	Analytical Techniques	52
	3.2.7	Cathode Material Stability Test	52
CHAPTER 4. RESULTS			54
4.1	Full Cell Runs		54
	4.1.1	CO₂ Transport	54
	4.1.2	H₂S Removal	55
	4.1.3	H₂S Removal - Effect of Membrane Thickness	57
	4.1.4	CO₂ Purge Stream	59
	4.1.5	Dynamics of Cell Operation	59
	4.1.6	Pre-mixing Sulfide Electrolyte	60
4.2	Cathode Stability Analysis		60
	4.2.1	Stability Results in Full Cell Runs for Previously Used Cathode Materials	60
	4.2.2	Internal Heat Production - Ohmic Losses	64
	4.2.3	Stability Run Results	66
	4.2.4	Stability Results in Full Cell Runs for Novel Cathode Materials	71
CHAPTER 5. DISCUSSION			76
5.1	H₂S Removal		76
	5.1.1	Temperature Effects	76
	5.1.2	Effect of Membrane Thickness	76
5.2	Membrane Optimization		78
5.3	Electrolyte Loss and Gas Crossover		78
5.4	Catalytic Reaction Scheme		79
5.5	Nernstian Effects		79
5.6	Using CO₂ as the Purge Stream		81
5.7	Model of Sulfide Membrane Diffusion-Limited System		81
5.8	Preliminary Economic Study		82
5.9	Development of Cathode Materials		85
	5.9.1	Cathode Stability	85
	5.9.2	Novel Oxide Cathode Materials	85
CHAPTER 6. CONCLUSIONS AND RECOMMENDATIONS			87
6.1	Conclusions		87
6.2	Recommendations		88
	6.2.1	Chemical Combustion Vapor Deposition (CCVD)	88
	6.2.2	Sol-Gel Processing of Membrane	88
	6.2.3	Future Cathode Possibilities	89
	6.2.4	Full Cell Runs at Higher Temperature	90
	6.2.5	Full Cell Runs at Higher Pressure	90

CHAPTER 6. CONCLUSIONS AND RECOMMENDATIONS	87
6.1 Conclusions	87
6.2 Recommendations	88
6.2.1 Chemical Combustion Vapor Deposition (CCVD)	88
6.2.2 Sol-Gel Processing of Membrane	88
6.2.3 Future Cathode Possibilities	89
6.2.4 Full Cell Runs at Higher Temperature	90
6.2.5 Full Cell Runs at Higher Pressure	90
REFERENCES	91
APPENDIX A. Successful Run Descriptions	94
APPENDIX B. Unsuccessful Run Descriptions	106
APPENDIX C. Stability Results of Poor Cathode Candidates	109
APPENDIX D. Derivation of Ionic Flux Equation	114
APPENDIX E. Error Analysis	118
APPENDIX F. Algorithm of Sulfur Species Diffusion Model	119
APPENDIX G. Operating Costs Calculations	119