Thermodynamic and environmental analysis of an integrated multi-effect evaporation and organic wastewater supercritical water gasification system for hydrogen production

Abstract

Organic wastewater poses significant environmental and human health risks. Supercritical water gasification (SCWG) presents a promising approach for converting organic waste into hydrogen-rich mixed gases. Nevertheless, the high moisture content present in organic wastewater hampers the energy efficiency of the SCWG process. To tackle this challenge, we have designed and developed an organic wastewater SCWG hydrogen production system incorporating a multi-effect evaporator. The developed system demonstrates the ability to achieve autothermal conditions for the treatment of swine wastewater with a solids concentration of 4.3%. Notably, this system exhibits impressive energy efficiency, reaching a maximum value of 44.88%, along with an exergy efficiency of 33.90% when processing 7% swine wastewater. Exergy analysis further reveals that the incorporation of a multi-effect evaporator leads to a reduction in exergy destruction within the gasification unit, oxidation unit, and heat exchanger. These improvements highlight the positive impact of the multi-effect evaporator on the overall performance of the supercritical water gasification system. Sensitivity analysis indicated that suitable concentrated concentration and an appropriate amount of preheated water can improve hydrogen production. The system minimum GWP reaches 5.27 kgCO2-eq/kgH2 after adding the CCUS. This work expands the range of applicable feedstocks for the autothermal SCWG process.