The simplest technology of thermal oxidation is a direct-fired thermal oxidizer. The process exhaust stream of VOCs and HAPs is introduced into a firing chamber through/near a burner, and enough residence time is provided to achieve the desired destruction removal efficiency (DRE) of the VOCs. Most direct-fired thermal oxidizers operate at temperature levels between 1,800°F and 2,200°F, with air flow rates from 500 SCFM to 50,000 SCFM.
These systems, also called afterburners in certain cases, are the least capital intensive — but when applied incorrectly, the operating costs can be substantial, because there is no form of heat recovery. These oxidizers are best applied where there is a very high concentration of VOCs to act as the fuel source (instead of natural gas or oil burner fuel) for complete combustion at the targeted operating temperature.
Typical applications include treatment of flare gas or other streams having a BTU/SCF value of 500 or greater, such as landfill methane extraction offgas; or systems that require the mixing of upper flammability limit (UFL) gases with air in order to create an oxidizable VOC concentration. NESTEC has partnered with speciality burner manufacturers to ensure the required DRE.