Thermal oxidation relies on the combination of high temperature (typically 1350 to 1600 °F), sufficient residence time (0.6 to 1.0 second) and effective gas phase mixing to achieve VOC destruction in the target range of 98-99%. Because fuel is so expensive, virtually all thermal oxidizers come equipped with some capacity for heat recovery to minimize fuel consumption. When the heat exchanger is an integral part of the oxidizer, the hot, clean exhaust preheats the incoming, solvent laden air. This is known as primary heat recovery. The closer the preheated air temperature from the exchanger is to the final oxidation temperature, the less fuel is used.
There are two categories of thermal oxidizers: Recuperative and regenerative.
Recuperative oxidizers use direct transfer of heat from the clean exhaust to the incoming process gases (typically via a shell and tube or plate style heat exchanger). Recuperative heat exchangers efficiencies typically vary from 40-80% depending on the expected solvent loading conditions.
Regenerative thermal oxidizer systems differ from recuperative in that heat is transferred from the cleaned exhaust air stream to the incoming process gases via a ceramic heat exchange media. The regenerative designation is due to the fact that the ceramic media is alternately heated and cooled by the clean exhaust airflow and process gases respectively. The process airflow is first directed through one media bed, where the heated media heats the incoming air stream to near the operating control temperature. The second media bed absorbs heat from the clean high temperature exhaust stream, cooling the stream prior to discharge to atmosphere. At least two regenerative beds are required so that process air can be cycled back and forth between the beds, alternately heating and cooling the media. Regenerative heat exchanger efficiency picks up where recuperative technology leaves off (i.e. at 80-95% efficiency). Regenerative thermal oxidizers have an advantage as pre-combustion within the exchange media does not harm the oxidizer.