International Journal of Hydrogen Energy, Vol.44, No.45, 24459-24470, 2019
Supercritical water gasification of sewage sludge and combined cycle for H-2 and power production - A thermodynamic study
An integrated system of supercritical water gasification (SCWG) and combined cycle has been developed for H-2 production and power generation. Sewage sludge and lignite coal were selected as raw material in this simulation. The effects of feed concentration (10 -30 wt%) and lignite coal addition (0-50 wt%) on syngas yield and H-2 yield were also investigated in the temperature range of 500 degrees C-700 degrees C. Several heat exchangers were considered in the proposed integrated system to minimize energy loss. High pressure syngas was expanded by using turbo-expander to produce electricity, resulting in the improvement of the total efficiency. The results showed that the minimum feed concentrations of 14.25 wt%, 18.75 wt%, and 25.50 wt% were required to achieve selfsufficient energy at 500 degrees C, 600 degrees C, and 700 degrees C, respectively. However, the lower feed concentration and higher temperature were preferable for syngas production. The highest syngas and H-2 yield were obtained at 700 degrees C and 10 wt% feed concentration. The SCWG could produce 178.08 kg syngas from 100 kg feed and 9.06 kg H-2 were obtained after H-2 separation. The total power generation from turbo-expander and combined cycle module was 48.37 kW. By combining SCWG and combined cycle, the total efficiency could reach 63.48%. It worth mentioning that the addition of lignite coal could help reduce the minimum feed concentration to achieve autothermal condition, but did not have significant improvement on H-2 production. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.