Thermodynamic and environmental analysis of heat supply in pig manure supercritical water gasification system

Pig manure, a high water content waste with massive annual output, must be treated in a clean and effective way to protect the environment. Supercritical water gasification (SCWG) is a high-moisture waste utilization technology that is both efficient and pollution-free. The study developed a thermodynamic equilibrium model of the SCWG of pig manure. The effects of operating conditions were examined on heat production and system efficiency. In addition, life cycle assessment (LCA) was used to perform the environmental significance. The results indicated that decreasing the amount of preheating water, increasing the slurry concentration, and the gasification temperature can increase the heat output and system efficiency. The system efficiency is 95.53% at the ratio of water to the slurry is 1:1 and 94.90% at the slurry concentration is 70 wt%. The detailed exergy analysis results showed that the exergy efficiency of the entire system could reach 39.8%. The primary exergy loss occurs in heat exchange and oxidation processes. Adopting reasonable operating conditions and optimizing the layout of heat exchangers can effectively reduce the exergy loss of the system. Besides, GWP has been significantly reduced to 7.4 kg CO₂-eq/t steam with carbon capture.