Thermal oxidizers may also be called afterburners or direct flame thermal oxidizers. Thermal oxidation is a method of pollution control that can be applied to incineration as a method of pollution control for air polluted with small particles or combustible solids or liquids. Catalytic oxidization is an off-gas post treatment unit for control of organic compounds. Gas enters the unit and passes over a support material coated with a catalyst (commonly a noble metal such as platinum or rhodium) that promotes oxidation of the organics. Catalytic oxidizers can convert volatile organic compounds (VOC) to carbon dioxide and water at much lower temperatures than thermal oxidizers by using a catalyst inside the combustion chamber.
Thermal oxidizers are typically one of two types, regenerative or recuperative. Regenerative thermal oxidizers use an oxidation technology that uses two or more ceramic heat transfer beds that act as smaller heat exchangers and a retention chamber where the organics are oxidized. It can often recover 90 to 95% of the heat generated by oxidation. A recuperative thermal oxidizer uses an oxidation technology (thermal or catalytic) that uses a plate, shell, and tube, or other conventional type of heat exchanger to heat incoming air with air from the oxidation process. Recuperative systems can often recover 50 to 75% of the heat generated by oxidation. Another technology that can be found on the market are rotor concentrators. Rotor concentrators use an oxidation technology add-on that reduces air volume and increases VOC concentration. The process stream flows through a continuously rotating wheel impregnated with adsorbent. Here the VOCs are adsorbed and the clean air is exhausted into the atmosphere. The wheel is then regenerated by passing through a stream of warm, low volume desorption gas that produces a concentrated stream that can be more efficiently destroyed by an oxidizer.
Regenerative Thermal Oxidizer Operation
Important specifications for thermal oxidizers and catalytic oxidizers are destruction efficiency or capabilities. Oxidizers generally have destruction efficiency anywhere from 90 to greater than 99%. Some manufacturers specify the destruction efficiency in milligrams per cubic meter of VOCs. Many oxidizers can also destroy odors and particles causing opacity of air. Required airflow through the oxidizer is important when specific process airflows need to be treated. The temperature range of the oxidizer will determine the solvent load that may be oxidized. Typical temperature ranges are 400 to 600 °F for catalytic oxidizers and 1000 to 1800 °F for thermal oxidizers.
Catalytic oxidizers and thermal oxidizers may be mounted in one of several ways. These include outdoor ground mounted units, outdoor rooftop units and indoor units. Power sources for oxidizers include electric, natural gas, propane, and fuel oil.