Thermal oxidizers burn pollutants in industrial exhaust air, with catalytic oxidation breaking down pollutants at lower temperatures. Regenerative thermal oxidizers recover more energy than recuperative ones, while rotor concentrators increase efficiency. Destruction efficiency is measured in milligrams per cubic meter of volatile organic compounds.
Thermal oxidizers are used as a pollution control method for process air containing small particles of combustible solids or liquids. The exhaust air in industrial environments can be highly polluted and it makes sense to oxidize (burn) it as much as possible, so that the exhaust consists of little but non-toxic carbon (soot). Thermal oxidizers are sometimes divided into non-flame oxidizers, which use slow heating to incinerate pollutants, and direct-flame thermal oxidizers, which use flame plumes. Thermal oxidizers can also include a process called catalytic oxidation. In catalytic oxidation, organic compounds pass over a support material coated with a catalyst, commonly a noble metal such as platinum or rhodium, which aids in the combustion of pollutants in the air. Catalytic oxidizers can break down pollutants at much lower temperatures than non-catalytic thermal oxidizers.
The most significant distinction between types of thermal oxidizers is whether they are regenerative or recuperative. Regenerative thermal oxidizers use ceramic heat transfer beds to recover as much energy as possible from the oxidation process, often 90% to 95%. These heat exchange beds act as heat exchangers, coupled to a retention chamber where organic substances are oxidized. A regenerative thermal oxidizer uses a heat exchanger in the form of a plate, shell or tube to heat the intake air with thermal energy from the oxidation process. These systems are less efficient than regenerative thermal oxidizers, recovering only about 50% to 75% of the heat generated.
One technology used to increase the efficiency of thermal oxidizers is that of rotor concentrators. Rotor concentrators reduce the overall amount of air flowing through the system and increase the concentration of organics in the oxidation stream. The incoming polluted air flows through a continuously rotating wheel covered with an adsorbent agent. Clean air flows into the atmosphere. The wheel is cleaned by exposing it to a desorption gas, producing a small, highly concentrated stream of organics which can then be efficiently oxidized.
The most important parameter for thermal oxidizers and catalytic oxidizers is their destruction efficiency, which commonly varies between 90% and 99%. The higher the destruction efficiency, the fewer pollutants are released into the atmosphere. The common unit for specifying destruction efficiency is in terms of milligrams per cubic meter of volatile organic compounds. To achieve these destruction efficiencies, catalytic oxidizers operate at 400-600°F (approximately 204-316°C), thermal oxidizers at 1000-1800°F (approximately 538-982°C).
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