Thermodynamic analysis of hydrogen production via supercritical water gasification of coal, sewage sludge, microalga, and sawdust

This study investigates the thermodynamic equilibrium analysis of the supercritical water gasification (SCWG) involving several typical feedstocks (coal, sewage sludge, microalga, and sawdust). The effects of various parameters including feed concentrations, temperatures, and pressures are analyzed. It is observed that temperature and feed concentration play a determining role in the yield of hydrogen, while the effect of pressure is very limited. Results show that the feed concentration of 15–20 wt% is optimal for hydrogen production. Furthermore, the effects of composition (hydrogen to carbon ratio and oxygen to carbon ratio) of the feedstock on the yield of product gases are investigated, which is useful for screening potential feedstock for SCWG. The results show that maximum H₂ and CH₄ molar yields are achieved at a low O/C and a high H/C ratio.