Thermodynamic modeling and analysis of biomass gasification for hydrogen production in supercritical water

Biomass gasification in supercritical water is a promising technology for hydrogen production by utilizing wet biomass. A new experimental system of biomass gasification in supercritical water was built in SKLMF. In this paper, a comprehensive thermodynamic analysis, including chemical equilibrium in the reactor, gas–liquid equilibrium in the high-pressure separator, exergy and energy analysis of the whole system, was conducted. Chemical equilibrium model is based on minimizing Gibbs free energy. By chemical equilibrium analysis in the reactor, rules of the main parametric effects on biomass gasification in supercritical water are obtained. Simultaneously, a high-pressure gas–liquid equilibrium model was proposed based on modified universal functional activity coefficient (UNIFAC) model, Soave–Redlich–Kwong (SRK) equation of state and modified Huron–Vidal second-order (MHV2) mixing rule. Effects of pressure, temperature and water recycled ratio on gas–liquid equilibrium in high-pressure separation were discussed. Finally, results from energy and exergy analysis show that energy and exergy efficiencies of the whole system are in excess of 40% and increase with increasing heat transfer efficiencies. Energy loss of the system is caused mainly by heat transfer and exergy loss is mainly caused by heat transfer and chemical reaction. Our research provided a thermodynamic tool for improvement of design and operation optimization of biomass gasification system in SKLMF, which may be also applicable to other biomass gasification system.