Thermodynamic and environmental analysis of two-stage series supercritical water gasification of biomass for hydrogen production

A system of two-stage series supercritical water gasification of biomass is proposed to achieve high hydrogen production. The system design and process simulation were implemented via Aspen plus, and the thermodynamic performance of the system was analyzed. Meanwhile, a life cycle environmental assessment under different conditions was performed using SimaPro. Based on the fixed reaction concentration, results of thermodynamic analysis reveal that the energy efficiency and exergy efficiency of the system are related to temperatures of the first-stage gasification reactor and the second-stage oxidation reactor. When temperatures of FGR and SOR are 603°C and 833°C respectively, the system could reach the highest hydrogen production. Moreover, the energy efficiency and exergy efficiency could reach 54.9 % and 56.2 % respectively, while changes of temperatures of the first-stage oxidation reactor and the second-stage gasification reactor have no effect on efficiency. In addition, the maximum recoverable energy loss is induced by the waste heat of the effluent from Cooler, indicating the path of system optimization. By using organic Rankine cycle, the energy efficiency and exergy efficiency could reach 57.7 % and 59.3 % respectively. Meanwhile, the data from SimaPro shows LCI and LCIA of the system, which identified the main environmental burdens. Overall, this work has great advantages in terms of thermodynamics and environmental impact, while it faces both opportunities and challenges. This research reveals the feasibility of TSCWG and provides theoretical guidance for biomass cleaning conversion.