Afterburners & Thermal Oxidizers Explained

Afterburners and Thermal oxidizers rely on the process of combustion to oxidize VOC’s to the hydrocarbon units of CO₂ and H₂O.  High temperatures and residence time, coupled with the proper amount of turbulence, allow this process to occur. Generally, these processes will be able to destroy over 95% of the VOC’s in the process gas. 

In order to increase the VOC destruction efficiency, higher temperatures and longer retention times are necessary.  When the destruction efficiencies are this high, the only products of this reaction are water and Carbon Dioxide.  These off-gases can be released to the atmosphere, so there are no removal costs. 

Another unique property of these incineration type devices is the ability to destroy both small particulate VOC’s as well as airborne VOC’s.  By combining an incinerator with other methods of VOC removal such as scrubbers, baghouse filters and boilers, 99%+ removal efficiency can be guaranteed.

In order to ensure high chemical reaction rates, reactions are conducted at elevated temperatures. A burner unit maintains these temperatures. This unit gives the process gas a place to mix with oxygen and flame in order to promote combustion.  Natural gas, propane and other fuels are used to supplement the process gas flow and maintain combustion. 

This is where the primary costs of running an Afterburner or Thermal Oxidizer unit comes from.  However, these requirements are generally reduced by the heat generated in the combustion heating of the new process gas and, if feasible, the use of a heat recovery system.

Incineration type destruction devices can be used over a fairly wide, but low, range of organic vapor concentrations.  However, the concentrations of the organics in the air must be substantially below the lower flammable level (lower explosive limit or LEL). The LEL is an expression of the concentration of solvent vapors in air. Generally all systems must operate at 25% or below of the LEL.  This is done to enhance the safety of the system and to prevent the possibility of overheating, flashbacks, fires, or explosions.