Development and Parametrization of a Novel Reactor Concept for the Supercritical Water Gasification Process

A novel reactor concept for supercritical water gasification was developed where cold biomass is mixed with supercritical water for heating. This approach enhanced the gasification efficiency and reduced solid deposition. Following proof of concept over 100 h, a parametric study was conducted, varying biomass type, dry matter content (1.3-8.2 wt %), temperature (550-700 °C), pressure (240-300 bar), potassium addition (0-3750 ppm), and residence time (0-42 s). Results showed that biomass type, pressure, and potassium addition had a minimal impact on the process. Higher biomass concentration reduced carbon efficiency (CE) but maintained levels around 80%. Increasing the residence time at the reaction temperature significantly improved CE up to 8 s at 650 °C (τ = 0 s, CE = 27%; τ = 8 s, CE = 72%), beyond which gains plateaued. Temperature strongly influenced CE (<i>T</i> = 550 °C, CE = 58%; <i>T</i> = 700 °C, CE = 91%) and gas composition, with higher temperatures reducing organic carbon and tar formation but increasing methane (<i>T</i> = 550 °C, 9.5 vol % CH₄; <i>T</i> = 700 °C, 15.9 vol % CH₄) and C₂₊ (<i>T</i> = 550 °C, 2.3 vol % C₂₊; <i>T</i> = 700 °C, 5.1 vol % C₂₊) contents. Deviations in gas composition from equilibrium calculations, conducted with ASPEN HYSYS, suggest insufficient steam reforming, potentially addressable with a nickel catalyst. An empirical multilinear regression model was developed, accurately predicting outcomes for studied biomasses and reducing experimental effort for process optimization. Overall, the study demonstrates the reactor concept's superior performance and provides a strong foundation for further developing and optimizing supercritical water gasification processes that could potentially be applied to other feedstocks.