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By Dr. Rakesh Govind

Air emissions from paint spray booths and composite manufacturing operations occur due to evaporation of organic solvents during the production process, such as during atomization and application of the coating, during initial air drying of the parts and after they leave the spray booth, and in the bake oven. Fugitive emissions occur when coatings are mixed and loaded into the application device, during transport of coated parts and during post curing. Many solvents used in spray booths are a health hazard and have the potential to contribute to atmospheric pollution. Volatile organics commonly encountered in spray booths and in composite manufacturing include benzene, xylene, styrene, and toluene, which are not only toxic with adverse health effects in humans, but also cause photochemical smog in the presence of nitrogen oxides and sunlight.

Technologies used to control emissions of volatile organics (VOCs) from spray booths and composite manufacturing operations includes: (1) thermal and catalytic oxidizers; (2) carbon adsorption; (3) condensers; and (4) biofilters. Thermal and catalytic oxidizers use high temperature to oxidize the chemicals to carbon dioxide and water. Typically, they use natural gas to effectively maintain the destruction temperature needed to prevent the emission of unburnt hydrocarbons. Due to increases in natural gas prices and due to high operating temperatures, thermal and catalytic oxidizers have a high investment and operating cost. Carbon adsorption removes the organic vapors by selective adsorption on activated carbon. While this is not a treatment system, the activated carbon is periodically removed when saturated and either destroyed or regenerated using high temperature to desorb the organics from the carbon surface and reactivate the carbon. Activated carbon replacement is a recurring cost which can be substantial especially if the organic concentrations in the gas phase are high. Also, activated carbons saturated with hydrocarbons are a fire hazard that have to be handled carefully to prevent fugitive air emissions of the adsorbed compounds. Condensers, utilize a low temperature to condense the organics into a liquid phase which can be separated from the gas phase. Typically, condensers can only reduce the concentration of volatile organics but not eliminate them and they cannot reduce the concentrations enough for direct discharge into ambient air.