Experimental investigation and simulation optimization of a pilot-scale supercritical water oxidation system

Supercritical water oxidation (SCWO) technology has an excellent performance in treating high concentration and refractory organic wastes. While the high treatment cost is one of the key drawbacks currently restricting its large-scale application. In this study, a SCWO pilot system with a novel jet reactor (treatment capacity of 200 kg/ h) was experimentally investigated, and the process model was developed to optimize the system by Aspen Plus. The energy and exergy efficiency of the system was evaluated, and the wastewater treatment cost in different operating conditions was estimated. The results show that chemical oxygen demand (COD) removal efficiency could be increased with the increase of the temperature, pressure, and the excess oxygen coefficient. By locating the electric heater 1 (H1) before the heat exchanger 2 (H2), and improving the outlet temperature of the oxygen compressor (MP1), the wastewater treatment cost could be reduced to 53.5 $/t, and the energy and exergy efficiency of the SCWO system could be improved to 81.61% and 8.91%, which is 26.28% and 6.23% higher than that of the current system, respectively. Both the reaction temperature and COD concentration of the wastewater have positive effects on the wastewater treatment cost, e.g. the wastewater treatment cost could decrease from 80.88 $/t to 59.27 $/t when the reaction temperature increases from 380 degrees C to 420 degrees C, and the SCWO system could achieve the energy self-sufficient operation when the COD concentration is over 60,000 mg/L.