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DEMONSTRATION BULLETIN: THERMAL DESORPTION SYSTEM - CLEAN BERKSHIRES, INC.
Citation:
McPherson, J. AND J. Hockeneir. DEMONSTRATION BULLETIN: THERMAL DESORPTION SYSTEM - CLEAN BERKSHIRES, INC. EPA/540/MR-94/507, 1994.
Impact/Purpose:
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Description:
A thermal desorption system (TDS) has been developed by Clean Berkshires, Inc. (CBI), Lanesboro, Massachusetts for ex-situ treatment of soils and other media contaminated with organic pollutants. The TDS uses heat as both a physical separation mechanism and as a means to destroy contaminants. The process is continuous and is composed of three different operations: feed preparation, contaminant volatilization, and gas treatment. Feed preparation begins with a sequence consisting of crushing, shredding, and screening excavated or dredged waste material to reduce maximum particle size to 3/4-inch. Next, using a front- end loader, the waste is repeatedly folded into itself in an attempt to distribute moisture and pollutants evenly. This step is particularly important since it helps protect the system from severe, sudden thermal shocks caused by "hot spots" in the waste. The prepared material is then dumped into surge bins and fed into a kiln through a two-stage conveyor belt system. Contaminant volatilization begins after the prepared material enters the kiln. The temperature of the soil is increased through contact with an air stream heated by a natural gas burner located at the entrance of the kiln. The kiln is equipped with specially designed flights which lift and veil the soil, exposing greater surface area to the hot gases, improving volatilization. Treated soil exits the kiln and enters a pug mill which combines the material with solid residuals from gas treatment. Water recycled from the quench tower is added at this time to cool the treated materials and to control fugitive dust emissions. The solids are deposited onto a discharge conveyor and stockpiled. Gas treatment begins when the gas stream from the kiln, which contains volatilized contaminants and entrained paniculate, enters a multi-stage treatment sequence. The sequence uses the following: a cyclone to remove coarse particulate, a high-efficiency afterburner to destroy organics, a quench tower to cool the gas stream, and a baghouse to remove filterable particulate still suspended in the gas stream. A scrubber could be added to remove sulfur dioxide if levels are high enough to impact air quality standards. Treated gases exit the system through a 75-foot high stack. Solid residuals from gas treatment are transferred by a screw auger to the pug mill and are combined with the treated waste material. The TDS is transportable and is monitored and controlled by a computer-based data acquisition system.