Thermal oxidizer applications with higher VOC concentrations

Direct fired thermal oxidizers may find appropriate use when VOCs are fuel source

Economic realities and start-up expense can lead some companies to look for less capital intensive solutions when it comes to installation of a thermal oxidizer for control of volatile organic compounds (VOCs). While not preferred in many thermal oxidizer applications for its lack of recuperative heating ability, certain manufacturing situations allow for the simplest form of thermal oxidizer – direct fired thermal oxidizers.

Direct fired thermal oxidizers – also known as afterburners – represent the introductory technology for thermal oxidizers. Simply put, direct fired thermal oxidizers are specifically-designed ignition chambers fed a stream of VOC-laden gas before exposing the gas to turbulence and temperatures sometimes eclipsing 1,000-degrees Fahrenheit. The destructive capability of direct fired thermal oxidizers approaches 99 percent of VOCs incinerated as long as the gas is exposed for a pre-determined residence time and heat.

Typically this technology is the least expensive of thermal oxidizers to deploy, as it is the least sophisticated in design. However, unless specific industrial conditions are met, direct fired thermal oxidizers may represent the largest ongoing cost of any thermal oxidizer. They do not contain any regenerative or recuperative heat exchange devices, so the internal temperature is achieved solely through burning fuel. For that reason, direct fired thermal oxidizers are only recommended for processes with variable exhaust flow and with high VOC concentrations. Essentially, the VOCs in the air will supplement the combustion process as a secondary fuel source. Also, low-flow and turbulent gas flows are desired to lower temperatures and create optimal residence times in the combustion chamber.

If these specific conditions are met, there is also the possibility of adding heat exchangers as a post-combustion item to recapture steam and heat as a by-product of the afterburner to pre-heat some of the waste gas. Also available are heat recovery steam generators, which can take the heat used in the VOC destruction to recharge electrical power for the industrial process.

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