Effect Mechanism of Auxiliary Fuel in Supercritical Water: A Review

Supercritical water oxidation is a promising alternative for treatment of wastewater and sludge. The addition of auxiliary fuel can achieve the optimization of the system. Owing to the discrepancy in the fuel parameter and reaction condition, the auxiliary fuel presents two different behavior mechanisms in supercritical water, co-oxidation and hydrothermal combustion. The process mechanism, kinetics analysis, and effect behavior for these two processes were systematically reviewed in this work. The co-oxidation between auxiliary fuel compounds, such as methanol, ethanol, isopropyl alcohol, etc. and ammonia, polychlorinated biphenyls was analyzed, and the mixing kinetics models and mechanism investigation approaches were summerized. Besides, the process analysis, kinetics model, and interaction during the supercritical hydrothermal combustion with higher concentration of auxiliary fuel were discussed. Finally, a supercritical water oxidation system with optimized auxiliary fuel was proposed and evaluated by the mechanism-based kinetics simulation, and further research needs were put forward.