Effect Mechanism of Auxiliary Fuel in Supercritical Water: A Review

Abstract

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.

Numerical study of the counterflow diffusion flames of methanol hydrothermal combustion: The real-fluid effects and flamelet analysis

“…Hydrothermal flames can provide an internal heat source in the SCWO reactor, which is favourable for the process in many ways, for example, the lower preheat temperatures, the less corrosion/plug problems and the higher energy output [6][7][8]. On the other hand, if the hydrothermal flame is generated by an auxiliary fuel, abundant free radicals in the flame can promote the oxidation of the refractory organic wastes [9]. The ignition and extinction limits are always the main concerns in the hydrothermal combustion research [10][11][12][13][14].…”

Review on Mechanisms and Kinetics for Supercritical Water Oxidation Processes

“…The oxidation of short-chain chloride calls for chloroform as the dominant intermediate [30], while the degradation of PCBs had a more complex pathway. Since PCBs are barely soluble in water at normal temperature and pressure, organic solvents such as methanol and benzene are necessary to transport them into the SCWO reactor [46]. Anitescu et al [47] compared the difference of methanol and benzene as co-solvents on reaction products of 4-chlorobiphenyl in the SCWO process.…”

“…solvents such as methanol and benzene are necessary to transport them into the SCWO reactor [46]. Anitescu et al [47] compared the difference of methanol and benzene as co-solvents on reaction products of 4-chlorobiphenyl in the SCWO process.…”

Effluent recirculation enables near-complete oxidation of organics during supercritical water oxidation at mild conditions: A proof of principle

“…While the oxidation efficiency of organic carbon increases if treated at reaction conditions far beyond the critical point (e.g., 500 Ce750 C (Cocero et al, 2000)), corrosion of the reactor material becomes more severe (Fang, 2014;Tan et al, 2014). Moreover, high-temperature SCWO typically requires an auxiliary fuel, like methanol or ethanol (Shimoda et al, 2016;Zhang et al, 2019b), considerably increasing the operating costs ( Fig. 1a).…”