THERMODYNAMIC ANALYSIS OF HYDROGEN-PRODUCTION FROM BIOGAS FOR PHOSPHORIC-ACID FUEL-CELL

The utilization of low-cost biogas in stand-alone phosphoric acid fuel cells (PAFCs) offers a great potential for electric Power generation. Digester biogas is processed via steam reformation and water-gas shift to generate H-2-rich gas for feeding the PAFC anodes. In this paper, the thermodynamics of steam reformation, shift and carbon deposition as a function of temperature are compared for a typical digester biogas feed (60% CH4, 40% CO2) and a pure methane feed. Equilibrium calculations are performed with identical steam-hydrocarbon ratios (1.54) for the two feeds at a total system pressure of 1 atm (0. 1 MPa). The effect of CO2 present in biogas on CH4-conversion, H-2-yield and CO-content of the anode feed gas has been analysed. On this basis, optimum reformation and shift conditions for biogas feed have been identified. Threshold steam-hydrocarbon feed ratios for preventing carbon deposition in the reformer, shift converters and PAFC anodes have also been determined.