Wet oxidation is an aqueous-phase oxidation process brought about when an organic and/or oxidizable inorganic-containing liquid is mixed thoroughly with a gaseous source of oxygen (usually air) at temperatures of 150 to 325 °C. Gauge pressures of 20 to 210 bar (300 to 3,000 psi) are maintained to promote reaction and control evaporation (Copa and Gitchel, 1988).
In wastewater treatment, wet oxidation in the temperature range of 150 to 200 °C improves sludge dewaterability. Intermediate temperatures of 200 to 280 °C are used in such applications as spent activated-carbon regeneration and conversion of refractories to biodegradable substances. Still higher temperatures (280 to 325 °C) provide essentially complete oxidation. Residence times of 15 to 60 min are required for 95 to 99% oxidation. Adjustment of pH, especially to lower values, accelerates rates.
In most cases where wet oxidation is applied to hazardous wastes, the treatment objectives are the detoxification of the wastewater for subsequent biological treatment, which can be accomplished in a publicly owned treatment works (POTW) facility or an industrial treatment plant. Wet oxidation is very effective in treating wastes containing inorganic and organic cyanides and sulfides at temperatures less than 250 °C and gauge pressures below 140 bar. Wastes containing halogenated aromatic compounds with at least one non-halogen functional group, e.g., pentachlorophenol or 2,4,6-trichloroaniline, are effectively treated by wet oxidation at temperatures of 250 to 320 °C and gauge pressures of up to 205 bar.
The wet oxidation unit is modeled in this program as a stoichiometric reactor. The user specifies the stoichiometry of oxidation reactions on a mass or molar basis. The extent of reaction represents the fractional conversion of the limiting or reference component. The oxygen supply (usually in the form of air) is adjusted by the model based on the excess % that is specified by the user. The excess amount of oxygen is calculated based on the stoichiometrically required amount. For more information on the material balances calculations, see Stoichiometric Reaction Operations: Modeling Calculations.
In Design Mode of calculation, the user specifies the residence time of the liquid in the system and the program calculates the vessel volume and the number of units. If the calculated vessel volume exceeds its maximum possible value (specified through the Equipment tab), the program assumes multiple, identical units operating in parallel with a total vessel volume equal to the calculated. In Rating Mode, the user specifies the volume and the number of vessels and the program calculates the residence time of the liquid in the system.
1. Copa, W.M. and W.B. Gitchel, 1988, “Wet Oxidation” in “Standard Handbook of Hazardous Waste Treatment and Disposal’, Harry M. Freeman (ed), McGraw-Hill, pp. 8.77 - 8.90.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Wet Air Oxidation: Oper. Conds Tab
● Reactions, see Stoichiometric Reaction/Fermentation Operation: Reactions Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab