Thermodynamic, environmental analysis and comprehensive evaluation of supercritical water gasification of biomass fermentation residue

Abstract

In this paper, a residue from a simultaneous saccharification and fermentation (SSF) process using corn stover as the feedstock was taken as the material to study the thermodynamic and environmental performance of supercritical water gasification for hydrogen production . The supercritical water gasification system of the SSF residue (SSF-SCWG) was simulated by Aspen Plus. Taking temperature (600 °C, 650 °C, 700 °C) and residue concentration (5 wt%, 10 wt%, 15 wt%) as independent variables, the gasification yield and thermodynamic performance of the system under different working conditions were studied, and two methods to improve energy efficiency were proposed, including recycling waste heat by organic Rankine cycle and reheating cycle. The results show that increasing the temperature and decreasing the residue concentration are beneficial to increasing the hydrogen production rate. Among all the working conditions, the system has the highest energy efficiency of 36.8% and exergy efficiency of 39.5%, when the reaction temperature is 700 °C and the mass concentration is 15 wt%. On this basis, the energy efficiency was further improved by 5.68% by integrating the organic Rankine cycle and 9.2% by integrating the reheat cycle . The life cycle assessment of the system was carried out by SimaPro . The scope of life cycle study is the operation stage of the SSF-SCWG system and the functional unit is 1 ton of SSF residue. The environmental burden of the system was quantified with the impact assessment methods of ReCipe Endpoint and ReCipe Midpoint . The life cycle results show that the system is environmentally friendly, with global warming potential of −216.6 kg CO 2 -eq/functional unit and acidification potential of −8.9 kg SO 2 -eq/functional unit. Finally, considering thermodynamic and environmental indexes comprehensively, entropy weight method and technique for order preference by similarity to ideal solution model were adopted to make multi-attribute decision for all working conditions, and the optimal conditions for the SSF-SCWG system were obtained. • A novel system of supercritical water gasification of a fermentation residue is designed. • The organic Rankine cycle and reheat cycle are used to increase energy efficiency. • The life cycle environmental burden of the system is quantified. • A multi-attribute decision making method is used for the optimal operation conditions.