Energy, exergy and economic analyses and performance assessment of a trigeneration system for power, freshwater and heat based on supercritical water oxidation and organic Rankine cycle

The chemical energy contained in organic sewage is not fully utilized. By using organic sewage as a renewable energy source, a novel trigeneration hybrid system consisting of a supercritical water oxidation process and an organic Rankine cycle system for power, freshwater and heat is proposed. The system is evaluated by multiple approaches including parametric sensitivity analysis, exergy and economic analyses. It is found that the proposed hybrid system with the organic sewage mass flow of 5020 kg/h (12% mass fraction) has a power capacity of 286.5 kW and heat capacity of 1081 kW. The electricity efficiency, thermal efficiency, energy efficiency and exergy efficiency could reach up to 9.56%, 44.93%, 53.47% and 22.45%, respectively. The overall exergy flow destruction of the hybrid system is 1706.1 kW. The four components with the highest exergy destruction are reactor, valve, the first stage of preheater and the evaporator of organic Rankine cycle system. The calculated net annual income value is 739.861 k$. The four components with the highest equipment cost are two turbines, cooling water pump and reactor, with the equipment costs of 571.31 k$, 1554.65 k$, 670.50 k$ and 460.91 k$, which account for 32.09%, 19.40%, 8.37% and 5.75%, respectively. The dynamic payback period and the simple payback period of the system are 16.41 and 11.02 years. These results reveal that the proposed hybrid system is efficient, self-sufficient and clean for both power, heat and freshwater generation, which could be a promising candidate as advanced energy conversion technology in practical applications.