Performance evaluation of a supercritical water oxidation cogeneration system using hydrogen peroxide as oxidant

Abstract

Supercritical water oxidation (SCWO) is widely used for organic waste for its fast degradation rate and higher efficiency. As a kind of wastewater treatment system with high energy density, its energy utilization of SCWO is a hot issue of great concern. In this paper, 35 % concentration of hydrogen peroxide was employed as the oxidation medium, combined with the organic Rankine cycle (ORC), a hybrid system based on the SCWO system was constructed. From the perspective of efficient energy utilization within the SCWO system, parameter sensitivity analysis, exergy and economic analyses were performed for the proposed system. It can be found from the results that when operated with organic wastewater mass flow rate of 5020 kg/h (12% w.t.), the obtained net power of the system was 668.06 kW, the heat generated for heat consumer was 2918.20 kW. The electrical and thermal efficiencies of the system were 14.96% and 65.34%, the cogeneration efficiency was 62.28% and exergy efficiencies were 34.54%, respectively. Exergy analysis results showed that the four components that consumed the most exergy destruction in the whole system were: heat exchanger for recovering waste heat from the oxidation reaction solution to the heat user, primary preheater for heating organic wastewater, and primary preheater for heating hydrogen peroxide, and the reactor which accounting for 32.05%, 17.85%, 14.87% and 13.99% of the total exergy destruction of the system, respectively. Economic analysis results showed that the annual net income of the system was 7490.37 k$/year. The system with compressed air as the oxidation medium was used to compare with the proposed system. The results showed that the proposed system with higher electrical efficiency, heat efficiency as well as revenue from electricity and hot water.