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4-5j..Oxidation ,. _ r . Page ] of 5 4.57 Oxidation mediation Technologies Screening Matrix (Off-Gas Treatment Technology) and Reference Guide, Version 4.0 Description Synonyms Applicability Limitations Site Information Points of Contact Data Needs Performance Cost References Vendor Info. Health&Safety Technology>> Air Emissions/Off-Gas Treatment of Contents >>3.14 Air Emissions/Off-Gas Treatment Introduclion »4.57 Oxidation Introduction>> Organic contaminants are destroyed in a high temperature 1,000°C (' combustor. Trace organics in contaminated air streams are destroyec temperatures, 450 °C (842 °F), than conventional combustion by pas, mixture through a catalyst. j, Appendices Description. Figure_4-57: TV ical Oxidation Diagram Oxidation equipment(thermal or catalytic) is used for destroying contaminants in the exhaust gas from air strippers and SVE systems. Thermal oxidation units are typically single chamber, refractory-lined oxidizers equipped with a propane or natural gas burner and a stack. Lightweight ceramic blanket refractory is used because many of these units are mounted on skids or trailers. If gasoline is the contaminant, heat exchanger efficiencies are limited to 25 to 35%, and preheat temperatures are maintained below 180 °C (530 °F) to minimize the possibility of ignition occurring in the heat exchanger. Flame arrestors are always installed between the vapor source and the thermal oxidizer. Burner capacities in the combustion chamber range from 0.5 to 2 million Btus per hour. Operating temperatures range from 760 to 870 °C (1,400 OC to 1,600 °F), and gas residence times are typically 1 second or less. J. Catalytic oxidation is a relatively recently applied alternative for the treatment of VOCs in air streams resulting from remedial operations. The addition of a catalyst accelerates the rate of oxidation by adsorbing the oxygen and the contaminant on the catalyst surface where they react to form carbon dioxide, water, and hydrochloric gas. The catalyst enables the oxidation reaction to occur at much lower temperatures than required by a conventional thermal oxidation. VOCs are thermally destroyed at temperatures typically ranging from 320° to 540° C (600° to 1,000° F) by using a solid catalyst. First, the contaminated air is directly preheated (electrically or, more frequently, using natural gas or propane)to reach a temperature necessary to initiate the catalytic oxidation [310 °C to 370 OC (600 °C to 700 ° F)] of the VOCs. Then the preheated VOC-laden air is passed through a bed of solid catalysts where the VOCs are rapidly oxidized. Thermal oxidizers can often be converted to catalytic units after initially high influent contaminant concentrations decrease to less than 1,000 to 5,000 ppmv. > CataVic Oxidation Catalyst systems used to oxidize VOCs typically use metal oxides such as nickel oxide, copper oxide, manganese dioxide, or chromium oxide. Noble metals such as platinum and palladium may also be used. Most commercially available catalysts are proprietary. http://w-ww.frtr.gov/matrix2/section4/4-59.htmi 10/22/2004