An innovative system by integrating the gasification unit with the supercritical water unit to produce clean syngas for solid oxide fuel cell (SOFC): System performance assessment

Abstract

Existence of impurities in the product gas hinders the application of the system which combines gasification with solid oxide fuel cell (SOFC). A new method is proposed to produce qualified syngas, which integrates the gasification unit with the supercritical water unit (SWU). The SWU contains supercritical water mixer, separator, reactor (SWR) and expander. To analyze performance of the proposed process from a systematic perspective, downstream operating units primarily including SOFC, burner, heat recovery steam generation and steam cycle are designed. Model for the whole system is developed by using Aspen Plus and a mathematical model for the SOFC. Sensitivity analysis regarding the fuel utilization factor (Uf) and the mass ratio of tars to supercritical water (T/W) are conducted in terms of system electrical efficiency, SOFC electrical efficiency and cell voltage. Results show that combustible components in the obtained syngas mainly contain CH4, H2, and CO. Tars are completely decomposed and only slight amount of light hydrocarbons (except CH4) are present. One SWR can undertake the functions of water gas shift, tar reforming and methane synthesis concurrently. The integrated process can offer a combustible components efficiency of 78.2%, and the system electrical efficiency is predicted to be 46.3%. Uf has a significant influence on the SOFC electrical efficiency, while it has slight influence on system electrical efficiency. As the T/W rises from 1.6% to 2%, system electrical efficiency, SOFC electrical efficiency and cell voltage slightly increase.