Energy, exergy, economic, and environmental assessments of an advanced methanol and heat polygeneration system integrating supercritical water gasification and reverse water–gas shift

Abstract

Supercritical water gasification (SCWG) is a clean and efficient approach for transforming feedstocks into syngas. However, most previous studies have focused on hydrogen production or heat recovery, while the further conversion of SCWG-derived gas into liquid chemicals remains insufficiently explored. This work proposed and assessed a novel polygeneration system combining SCWG, reverse water–gas shift, and methanol synthesis. Under the design conditions of a gasification temperature of 620 ℃, a coal slurry concentration of 50 wt%, and a preheated water-to-coal slurry ratio of 3, the system produced 6.56 t/h of methanol and a heat output of 22.97 MW. The energy efficiency was 77.32% and the exergy efficiency was 54.49%. Economic analysis showed a total capital investment was 52,836.56 k$, a payback period of 4.30 years, a net present value of 116,077.95 k$, and a levelized cost of methanol of 272.82 $/t. The global warming potential was 569.28 kg CO2-eq/MWh under the design conditions. In general, this work gives a feasible route to turn SCWG-derived gas into methanol.

Keywords: Supercritical water gasification, Reverse water–gas shift, Methanol synthesis, Energy and exergy analysis, Economic analysis, Global warming potential