Thermodynamic analysis of natural-gas fuel processing for fuel cell applications

A detailed thermodynamic analysis of equilibrium products was conducted for natural gas fuel processing under simultaneous partial oxidation (POX) and steam reforming (SRF) processes. Fuel processing by this arrangement requi res no extra heat from external sources and the required thermal energy for endothermic SRF is obtained from the exothermic POX; assuming adiabatic PO X and SRF reactions. The equilibrium product composition and the equilibriu m temperature are both dependent on the air-fuel ratio and water-fuel ratio . A computer program developed at NASA Lewis Research Center was adopted an d modified in this study for calculating the complex chemical equilibrium c omposition. With different combinations of the molar air-fuel ratio and mol ar water-fuel ratio in the fuel-air-water reaction system, it is possible t o obtain a maximum hydrogen yield with minimum productions of carbon monoxi de and solid carbon. Results showed that an optimal hydrogen yield of 36.3- 36.6% can be achieved when the molar air-fuel ratio and molar water-fuel ra tio are set to 3.5 and 2.5-4, respectively, and one mole of natural gas can produce 2.19-2.22 moles of hydrogen. Under this condition, the formations of carbon monoxide and residue methane are 2.24-4.38% and 0.55-0.96%, respe ctively; while the formation of solid carbon is effectively suppressed to z ero. The product's temperature under the assumption of adiabatic reaction c orresponding to this condition is 820-871 K. (C) 2000 International Associa tion for Hydrogen Energy. Published by Elsevier Science Ltd. All rights res erved.