Thermodynamic analysis and carbon footprint analysis of the system performance for supercritical water gasification of rice straw with different target products

Biomass supercritical water gasification (SCWG) technology holds highly promising prospects for application due to its ability to produce high-value products such as syngas and electricity. However, few studies have evaluated its thermodynamic and environmental performance from a system perspective for different target products. This paper develops three SCWG models for rice straw: pure syngas production, pure power generation, and syngas-power cogeneration. Through thermodynamic and carbon footprint analysis (CFA) comparisons of various target product routes models, it has explored system efficiency, exergy loss distribution, and environmental impacts. The cogeneration model exhibits higher efficiency, lower exergy loss, and better environmental performance, mainly because waste heat recovery for power generation improves energy utilization while reducing exergy loss and harmful emissions. At a gasification temperature of 700 °C, a rice straw slurry concentration of 60 wt%, a preheated water-to-slurry ratio of 1:2, and a gasification pressure of 25 MPa, the cogeneration system achieves an energy efficiency of 85.52 % and an exergy efficiency of 70.10 %, which is higher than the energy efficiency and exergy efficiency of the pure syngas system and the pure power generation system. CFA results indicate that direct CO₂ emissions are the primary factor affecting the system’s global warming potential (GWP), accounting for approximately 70.02 %–74.82 % of the total GWP. With CO₂ capture, the system’s GWP is reduced to 0.26 kg CO₂-eq/kg H₂, highlighting the significant environmental benefits of the cogeneration system. This study provides theoretical guidance and data support for assessing the feasibility of biomass SCWG systems.