Design and thermodynamic study of a supercritical CO2 gasification process coupled with steam reforming for spent mushroom substrate

To overcome the limitations posed by tar products during biomass gasification and to achieve a tar-free gas stream rich in CO and H2, this paper proposes and investigates a two-step process comprising biomass gasification and steam reforming in a supercritical carbon dioxide (SC-CO2) atmosphere. Both biomass gasification and steam reforming are currently considered state-of-the-art technologies. In this study, supercritical carbon dioxide and N2 were used as gasification agents to gasify spent mushroom substrate, yielding solid, liquid and gaseous products. The gaseous and liquid products were subsequently subjected to steam reforming to produce high-value-added gases. The results indicate that when the gasification temperature is 700 °C, the ratio of liquid-phase to gas-phase products increases further, which is beneficial for the subsequent steam reforming process. During the steam reforming stage, the CO yield increases with rising temperature, whilst the H2 yield is influenced by multiple factors, and its trend is not constant. The total yield of CO and H2 showed an upward trend, with the total yield under the SC-CO2 atmosphere being 1.38 times that under the N2 atmosphere. Energy and thermal analysis results indicated that, compared to the N2 atmosphere, the process under the SC-CO2 atmosphere required additional energy consumption, but thermal efficiency was improved by approximately 30%. This study provides a theoretical basis for process optimisation and offers theoretical support for the efficient, low-carbon conversion of biomass into gaseous fuels.