Effect of Natural Gas Fuel Addition on the Oxidation of Fuel Cell Anode Gas

The anode exhaust gas from a fuel cell commonly has a fuel energy density between 15 and 25% that of the fuel supply, due to the incomplete oxidation of the input fuel. This exhaust gas is subsequently oxidized (catalytically or non-catalytically), and the resultant thermal energy is often used elsewhere in the fuel cell process. Alternatively, additional fuel can be added to this stream to enhance the oxidation of the stream, for improved thermal control of the power plant, or to adjust the temperature of the exhaust gas as may be required in other specialty co-generation applications. Regardless of the application, the cost of a fuel cell system can be reduced if the exhaust gas oxidation can be accomplished through direct gas phase oxidation, rather than the usual catalytic oxidation approach. Before gas phase oxidation can be relied upon however, combustor design requirements need to be understood. The work reported here examines the issue of fuel addition, primarily as related to molten-carbonate fuel cell technology. It is shown experimentally that without proper combustor design, the addition of natural gas can readily quench the anode gas oxidation. The Chemkin software routines were used to resolve the mechanisms controlling the chemical quenching. It is found that addition of natural gas to the anode exhaust increases the amount of CH3 radicals, which reduces the concentration of H and O radicals and results in decreased rates of overall fuel oxidation

A Partial Oxidation Technique for Fuel-Cell Anode Exhaust-Gas Synthesis

This paper describes the performance of a gas generator used to synthesize the exhaust gas from the anode of a molten-carbonate fuel cell. The composition of this gas is estimated to be that of equilibrium at 1,250 ° F and 1 atm: 48% CO2 , 39% H2O, 5% CO, and 8% H2, with an energy content of approximately 39 Btu/scf (higher heating value). To synthesize a range of gas compositions around this point, the gas generator partially oxidizes a mixture of CH4 , O2 , and CO2 to generate energy densities between 20 and 60 Btu/scf at temperatures between 1,198 and 1,350 ° F. Results show that the technique provides a relatively high ratio of CO to H2 concentrations compared with the target composition (CO:H2 of 2, versus 0.71). A detailed chemical model shows that the likely cause is quenching of the CO and H2 chemistry below 2,000 ° F

A Partial Oxidation Technique for Fuel-Cell Anode Exhaust-Gas Synthesis

This paper describes the performance of a gas generator used to synthesize the exhaust gas from the anode of a molten-carbonate fuel cell. The composition of this gas is estimated to be that of equilibrium at 1,250 ° F and 1 atm: 48% CO₂ , 39% H₂O, 5% CO, and 8% H₂, with an energy content of approximately 39 Btu/scf (higher heating value). To synthesize a range of gas compositions around this point, the gas generator partially oxidizes a mixture of CH₄ , O₂ , and CO₂ to generate energy densities between 20 and 60 Btu/scf at temperatures between 1,198 and 1,350 ° F. Results show that the technique provides a relatively high ratio of CO to H2 concentrations compared with the target composition (CO:H₂ of 2, versus 0.71). A detailed chemical model shows that the likely cause is quenching of the CO and H₂ chemistry below 2,000 ° F