From sewage sludge to Hydrogen: Life cycle Techno-Environment-Economic assessment of combined system with supercritical water Gasification, organic Rankine cycle and carbon capture and storage

Abstract

Supercritical water gasification (SCWG) technology has attracted significant attention due to its advantages in efficiently treating high-moisture materials and producing hydrogen-rich gas, offering an attractive option for sewage sludge (SS) treatment. This study develops an efficient hydrogen production system that integrates SCWG, Organic Rankine Cycle (ORC), and carbon capture and storage (CCS) technologies. A comprehensive life cycle techno-environmental-economic assessment of SS to hydrogen (SStH) process with SCWG technology is conducted. The results indicate that gasification temperature and moisture content are the primary factors affecting H₂ yield and system efficiency, while gasification pressure has a minor impact. The system demonstrates favorable exergy efficiency (30.93 %) and a certain advantage in overall environmental impact (66.99 mPE). Electricity and natural gas particularly contributed to the environmental impact indicators. Reducing energy consumption or seeking alternative low-emission renewable energy sources will further reduce its environmental impact. The economic feasibility of SStH is sensitive to energy prices, with the cost of natural gas and the selling price of H₂ being critical factors. Strategies such as reducing reliance on natural gas, increasing hydrogen sales prices, and leveraging carbon tax credits and sludge subsidies are vital for enhancing the economic viability of SStH with SCWG technology. Renewable energy utilization and co-gasification are expected to further reduce the operating costs of SCWG.