Common Vapor Treatment Technologies

Thermal Oxidation

Thermal oxidation equipment 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. Thermal oxidizers are often equipped with heat exchangers where combustion gas is used to preheat the incoming contaminated gas. If gasoline is the contaminant, heat exchanger efficiencies are limited to 25 to 35% and preheat temperatures are maintained below 530 °F (280 ^oC) and gas vapor concentrations well below the lower explosive limit (LEL) to minimize the possibility of ignition occurring in the heat exchanger. Flame arrestors are always installed between the vapor source and the thermal oxidizer. Operating temperatures range from 1,400 (760 ^oC) to 1,600 °F (870 ^oC) with higher temperatures needed for halogenated VOCs, and gas residence times are typically 1 second or less. In common with catalytic oxidation, thermal oxidation of halogenated VOCs produces acid vapor, e.g., hydrochloric acid. Off-gas scrubbing may be needed to control the acid vapor. Figure 1, below, shows a typical diagram for this type of equipment.

Figure 1: Schematic of Recuperative Thermal Oxidation Process (Adapted from "Choose the Best Heat-Recovery Method for Thermal Oxidizers," Chemical Engineering Progress, April 1995.)

In most cases, the thermal or catalytic oxidation process can be enhanced to reduce auxiliary fuel costs by using a heat exchanger to transfer heat from the exhaust gases to the incoming contaminated air. Typically, about 50% of the heat of the exhaust gases is recovered, though the efficiency of some designs is greater.

Thermal oxidation is effective for site remediation. Its use is increasing among remediation equipment vendors, and several variations in design are being marketed. Growing applications include treatment of air stripper and vacuum extraction gas-phase emissions. (Summary adapted from the Federal Remediation Technologies Roundtable.)

For more detail regard thermal oxidation, click on the following link to the Federal Remediation Technologies Roundtable FRTR Section 4 - Oxidation.