Emission Concentrators Information
Emission concentrators route contaminants from large-volume, low-concentration exhaust streams into low-volume, higher-concentration streams, so that smaller, more efficient downstream processing equipment can be used. A rotor concentrator is divided into three zones. The process zone adsorbs volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) from the high-volume process stream while exhausting purified gas. About 90% of the incoming airstream is expelled as clean air. A desorption zone then activates the VOCs and HAPs with a low volume heated airstream. The produced high concentration airstream decreases fuel consumption in the oxidizer and can produce free energy to drive the concentrator. A cooling zone is then used to stabilize the adsorbent material after VOCs and HAPs have been desorbed.
A concentrator—which may be available as an integral unit or as a set of individual components—consists of a concentrator wheel, desorption air heater, and an oxidizer.
The concentrator wheel contains adsorbent materials such as a zeolite, activated carbons, polymer adsorbents, or a mixture of zeolite and activated carbon or polymer adsorbents. The adsorbent material is able to strip VOCs and HAPs from the high-volume exhaust stream. The captured VOCs and HAPs are then thermally released by the heated air stream as the wheel is rotated into the desorption zone.
Zeolites are volcanic minerals. They are a microporous aluminosilicate whose natural structure is conducive to adsorption. Natural zeolites are de-aluminized in order to make it hydrophobic and more conducive to the adsorption of non-polar substances such as VOCs. Although zeolites are a natural occurring mineral they may also be synthesized. A pre-filter is often used in conjunction with zeolite concentrator wheels in order to prevent particulates from masking the microporous material. Zeolites are most commonly used due to the fact they are completely inert and able to withstand thermal stress while maintaining their physical integrity.
Activated carbons are made of a variety of materials, the most common of which are bituminous coal and lignite. They have specific properties that are a function of the material source and the mode of activation. They are generally cheaper than zeolites and plastic adsorbents, but must be replaced more frequently due to thermal breakdown and water sensitivity.
Polymer adsorbents include a wide range of porous plastic materials. They are available in a wider range of pore sizes, which can help captures larger molecules that fail to get trapped by zeolites.
Desorption Air Heater
The desorption air heater generates a highly concentrated airstream consisting of VOCs and HAPs that have been adsorbed by the concentrator wheel. The heater may consist of a heat exchanger or electric duct heater and is fed by the exhaust of the cooling air stream. The cooling airstream helps stabilize the adsorbent material in order to collect more pollutants.
The oxidizer is an air pollution control device that incinerates VOCs and HAPs producing CO2 and water. There are several different types of oxidizers including catalytic, regenerative, or recuperative thermal oxidizers. Catalytic oxidizers incorporate a catalyst that allows lower operating temperatures. Regenerative oxidizers incorporate heat exchanges and are able to harness thermal energy and reuse it for other processes. Recuperative oxidizers use a heat exchanger to heat the intake airstream and reduce fuel consumption. In some cases the abated air may feed through a solvent recovery system rather than the oxidizer. To learn more about oxidizers visit Engineering360’ s Thermal Oxidizers and Catalytic Oxidizers specification guide.
United States Environmental Protection Agency—Choosing an adsorption system for VOC (pdf)