Fuel Desulfurization
Sulfur-containing odorants are normally added to propane and natural gas supplies for leak detection. The sulfur in these fuels can poison the catalysts used in fuel cell fuel processing systems and inactivate the surfaces of the fuel cell anodes. This results in degraded power generation. The sulfur content of natural gas or any hydrocarbon fuel needs to be reduced to very low levels (typically parts per billion) to ensure long-term stable electrochemical performance for both high and low temperature fuel cells.
Operation of solid oxide fuel cell (SOFC) units using natural gas fuel has required sulfur selective sorbents for fuel desulfurization. Experience with physical sorbents has shown varying sulfur capacity during field operation. This has been puzzling and produced great uncertainty for selection of sorbents. This mystery of changing sorbent sulfur capacity has been partially solved (See Ref. 1). Measurements of considerably variable and unexpectedly high water vapor content in pipeline natural gas supplies appears to be a major contributor to competition for sulfur adsorption sites and results in variable sorbent performance.
The purpose of the desulfurization system is to remove contaminants from fuel to a level where they have no deleterious affect on the fuel cell performance. The desulfurization system will have different configurations depending upon the type of fuel to be cleaned. The two broad categories of fuel are:
1. Natural Gas Fuel Cleaning
Natural gas has only one contaminant of concern; sulfur compounds.
Contaminant Maximum after Cleaning
Sulfur (S), any form 100 ppbv
2. Coal Derived Synthesis Gas (Syngas) Fuel Cleaning
Syngas contains several contaminants. These are listed in the fuel cleaning metric below.
Contaminant Maximum after Cleaning 1
Sulfur (S), any form 100 ppbv
Phosphorus (P), any form 100 ppbv
Selenium (Se), any form 100 ppbv
Arsenic (As), any form 100 ppbv
Mercury (Hg), any form 5 ppmv
Methyl Chloride, CH3Cl 100 ppbv
Cadmium (Cd), any form 5 ppmv
Tin (Sb), any form 5 ppmv
Zinc (Zn), any form 5 ppmv
Hydrogen Chloride, (HCl) 5 ppmv
1 Contamination limits based upon test results reported in presentations at 9th Annual SECA Workshop, Pittsburgh PA, 7 August 2008 listed below:
“Effect of Coal Contaminants on Solid Oxide Fuel Cell Performance” by Gopala Krishnan
“SOFC Anode Interactions with Coal Gas Contaminants” by Olga Marina
“Coal Gas Testing of SOFCs at NETL” by Randall Gemmen
References:
1. Gordon Israelson, “Water Vapor Effects on Fuel Cell Desulfurizer Performance – A Decade of Field Experience”, FUELCELL2008-65131, Proceedings of FuelCell2008 Sixth International Fuel Cell Science, Engineering and Technology Conference, June 16-18, 2008, Denver, Colorado, USA
Sulfur-containing odorants are normally added to propane and natural gas supplies for leak detection. The sulfur in these fuels can poison the catalysts used in fuel cell fuel processing systems and inactivate the surfaces of the fuel cell anodes. This results in degraded power generation. The sulfur content of natural gas or any hydrocarbon fuel needs to be reduced to very low levels (typically parts per billion) to ensure long-term stable electrochemical performance for both high and low temperature fuel cells.
Operation of solid oxide fuel cell (SOFC) units using natural gas fuel has required sulfur selective sorbents for fuel desulfurization. Experience with physical sorbents has shown varying sulfur capacity during field operation. This has been puzzling and produced great uncertainty for selection of sorbents. This mystery of changing sorbent sulfur capacity has been partially solved (See Ref. 1). Measurements of considerably variable and unexpectedly high water vapor content in pipeline natural gas supplies appears to be a major contributor to competition for sulfur adsorption sites and results in variable sorbent performance.
The purpose of the desulfurization system is to remove contaminants from fuel to a level where they have no deleterious affect on the fuel cell performance. The desulfurization system will have different configurations depending upon the type of fuel to be cleaned. The two broad categories of fuel are:
1. Natural Gas Fuel Cleaning
Natural gas has only one contaminant of concern; sulfur compounds.
Contaminant Maximum after Cleaning
Sulfur (S), any form 100 ppbv
2. Coal Derived Synthesis Gas (Syngas) Fuel Cleaning
Syngas contains several contaminants. These are listed in the fuel cleaning metric below.
Contaminant Maximum after Cleaning 1
Sulfur (S), any form 100 ppbv
Phosphorus (P), any form 100 ppbv
Selenium (Se), any form 100 ppbv
Arsenic (As), any form 100 ppbv
Mercury (Hg), any form 5 ppmv
Methyl Chloride, CH3Cl 100 ppbv
Cadmium (Cd), any form 5 ppmv
Tin (Sb), any form 5 ppmv
Zinc (Zn), any form 5 ppmv
Hydrogen Chloride, (HCl) 5 ppmv
1 Contamination limits based upon test results reported in presentations at 9th Annual SECA Workshop, Pittsburgh PA, 7 August 2008 listed below:
“Effect of Coal Contaminants on Solid Oxide Fuel Cell Performance” by Gopala Krishnan
“SOFC Anode Interactions with Coal Gas Contaminants” by Olga Marina
“Coal Gas Testing of SOFCs at NETL” by Randall Gemmen
References:
1. Gordon Israelson, “Water Vapor Effects on Fuel Cell Desulfurizer Performance – A Decade of Field Experience”, FUELCELL2008-65131, Proceedings of FuelCell2008 Sixth International Fuel Cell Science, Engineering and Technology Conference, June 16-18, 2008, Denver, Colorado, USA
