Comparison of CO₂ with H₂O as the transport medium in a biomass supercritical water gasification system

Supercritical water gasification is a clean technology for biomass conversion and utilization. In supercritical water gasification systems, H₂O is often used as the transport medium. Decreases in the reaction temperature at the gasification area and in the heating rate of biomass may limit the gasification rate and efficiency. In this paper, CO₂ is used as the transport medium due to its relatively low critical point and specific heat capacity. Moreover, a corn stalk gasification system with different transport media is established in this paper, and the influences of various operating parameters, such as temperature, pressure and feedstock concentration, are investigated. The results show that the gas yield in the CO₂-transport system decreases by no more than 5 wt %. In addition, thermodynamic analysis reveals that a system with CO₂ as transport medium consumes approximately 25% less electricity than a system with H₂O as the transport medium. In addition, the reaction heat absorption decreases. The results show the superiority of CO₂ to H₂O as a transport medium.