Thermodynamic analysis of a three-stage cascade reactor system with ejector-driven recirculation for supercritical water gasification

Supercritical water gasification (SCWG) is a promising clean technology for the conversion of fossil fuels, biomass, and solid wastes. However, efficient heat supply remains a critical bottleneck restricting its industrial application. Existing SCWG heat supply strategies largely neglect the heat exchanger requirements and the utilization of supercritical water in oxidized hot fluid. This study proposes a three-stage cascade reactor system integrated with ejector-driven recirculation to reuse oxidized hot fluid as the gasification agent and reduce heat transfer rate demand. Thermodynamic analysis demonstrates the optimized system's superiority over the single-stage reference system. Cold gas efficiency and power generation efficiency increase by 17.4 and 10.7 percentage points respectively, while oxygen demand is reduced to 30.2 % of the reference system. The optimized recuperation process lowers recycled water flux, cutting the water-heating duty to 0.476 MW, merely 8.5 % of the reference system's 5.581 MW, and the maximum heat exchanger temperature to 600 °C. Sensitivity analysis of feedstock properties shows that increasing the heating value and reducing the gasification temperature are beneficial to system performance. This study provides guidance for industrial system configuration and offers a practical heat integration solution for SCWG applications.