After burners are an oxidation technology that oxidizes various compounds with the help of a fuel fired burner. They are used in the petroleum, petrochemical, and other industries that require the disposal of waste gases of high concentration of both a continuous or intermittent basis. As other thermal oxidation technologies, the three T's of combustion of time, temperature and turbulence are necessary to achieve adequate emission control

Flares ideally burn waste gas completely and smokelessly. Two types of flares are normally employed. The first is called the open flare, where as the second is called the enclosed flare. The major components of a flare consist of the burner, stack, water seal, controls, pilot burner and ignition system. Flares required to process variable air volumes and concentrations are equipped with automatic pilot ignition systems, temperature sensors and air and combustion controls.
Open flares have a flare tip with no restriction to flow. The flare tip being the same diameter of the stack. Open flares are effectively a burner in a tube. Combustion and mixing of air and gas take place above the flare with the flame being fully combusted outside of the stack.
Enclosed flares are composed of multiple gas burner heads placed at ground level in a stack like enclosure that is usually refractory or ceramic lined. Many flares are equipped with automatic damper controls that regulate the supply of combustion air depending on temperature which is monitored up stream of the mixing, but inside the stack. This class of flare is becoming the standard in the industry due to its ability to more effectively control emissions.
Requirements on emissions includes carbon monoxide limits and minimal residence time and temperature. Exhaust gas temperatures may vary from 1000 to 2000 F.

The main advantages being:

• Lower capital costs
• Effective solutions for high VOC concentration ( up to 50 % LEL)

The disadvantages being:

• High secondary emmissions ( Such as NOx, CO2, SOx)
• Very high operating cost with lower VOC concentrations.