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.