Energy and exergy assessments of supercritical water oxidation of wet organic wastes under hydrothermal flames with a Y-shape reactor for power generation

Abstract

A novel Y-shape reactor combined the concepts of transpiring wall reactor (TWR) and hydrothermal flame was proposed for supercritical water oxidation (SCWO) of wet organic wastes. Hydrothermal flames can enhance feed degradation, and the Y-shaped structure enables the efficient gas–solid separation and allows extracting a part of uncooled supercritical fluids for power generation. The proposed reactor and corresponding system were simulated using Aspen Plus 8.2, and simulation results agree well with experimental flame temperatures and reaction products. Exergy analysis results indicate the reactor, heat exchanger 7, heat exchanger 1, and turbine contribute to the main destruction of the system, with exergy distribution coefficients of 18.65%, 17.75%, 11.95%, and 7.64%, respectively. The exergy destruction coefficient for the reactor has been greatly reduced compared with previous TWR-SCWO systems, indicating great improvement in exergy efficiency with the Y-shape reactor. The exergy efficiency can be increased from 24.83% to 40.50% when hot water output is replaced with steam production because of the great reduction in exergy destruction. Lower ratios of fuel flow to feed flow contribute to higher exergy efficiencies on the premise of the safety and economy of the system. The increases of separation efficiency and split coefficient are helpful for increasing system efficiency for more supercritical fluids can be converted into high-grade energy. The increase of feed concentration is beneficial for the increase of system economy even though at a relative low exergy efficiency.