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Thermodynamic equilibrium analysis of water-gas shift reaction using syngases-effect of CO2 and H2S contents

Chein, Rei-Yu, Yu, Ching-Tsung
Energy 2017 v.141 pp. 1004-1018
Gibbs free energy, calcium oxide, carbon, carbon dioxide, catalysts, feedstocks, hydrogen, hydrogen production, hydrogen sulfide, methane, sorbents, synthesis gas, temperature
Thermodynamic equilibrium of water-gas shift reaction (WGSR) under various temperatures, pressures and steam-to-CO (S/C) ratios was analyzed by Gibbs free energy minimization method. Coal-derived syngases with various CO2 and H2S contents were used as the feedstock. Based on the obtained results, it was found that CH4 and carbon formations were enhanced when syngas CO2 content increases. Carbon-free WGSR can be resulted using high S/C ratio. However, CH4-free WGSR cannot be resulted even with low S/C ratios. From the H2O conversion and H2 yield variations, the temperature at which reverse WGSR occurs can be identified and found to decrease with the increase in S/C ratio. Solid CaO sorbent was employed for both CO2 and H2S removals in WGSR when sour syngas was used as the feedstock. It was found that WGSR performance was enhanced due to the CO2 and H2S removals by CaO. The H2S concentration can be decreased with decreased S/C ratio while increasing the reaction pressure was not favourable for H2 production and H2S removal in WGSR with CaO. Because WGSR performance enhancement due to CO2 and H2S removals occurred at high temperature, catalysts can be eliminated in sorption-enhanced WGSR.