Hydrogen generation by supercritical water gasification of biomass: Process optimization

Supercritical water gasification of distillery wastewater as a real biomass feedstock for hydrogen production was modeled by Aspen Plus®. A non-stoichiometric approach was used to assess the reactor’s conditions in a continuous process, which was verified by comparison to empirical data. The results of sensitivity analysis showed that the optimum feed concentration is dependent to reactor temperature. Moreover, the highest temperature was correspondent to the least energy consumption per mole of produced hydrogen. Hence, the highest temperature (700 °C) and the corresponding optimum feed concentration (90 wt%) at 240 bar were determined as the optimum reactor conditions. Separation process at the downstream of reactor was optimized with the goal of reaching the highest hydrogen purity in gaseous product and the results implied that the lowest cooler temperature (30 °C) and the highest pressure in flash separator (235 bar) delivers gas with 64% hydrogen purity and 93.3% separation efficiency. Another optimization was done for obtaining the highest hydrogen flow in gaseous product, by which the highest cooler temperature (100 °C) and the lowest pressure in separator (5 bar) were determined as the optimum conditions to reach 99.9% separation efficiency at the expense of hydrogen purity reduction to 44%.