420D Thermal Desorption Unit

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PROCESS DESCRIPTION

The MSR 420D is a compact, low capacity thermal soil remediation system capable of process rates of up to 15 tons per hour. Contaminated materials are fed into a three cubic yard feed hopper by means of a front-end loader. The material is conveyed over a weigh scale and enters the “cool end” of the rotary desorber. As the contaminated soil travels through the desorber it is contacted with hot combustion gases flowing in the opposite direction. This counter-current flow of soil and hot combustion gases heat the soil and reduce the gas temperature to less than 500°F. As the soil temperature elevates, contaminants in the soil are volatilized and enter the gas stream. The rotary desorber is equipped with speed, slope and temperature controls to provide a variable soil retention time of 6 to 12 minutes. The unit can achieve soil discharge temperatures up to 800°F.

The contaminated and dust laden gasses exiting the desorber are routed to a pulsejet baghouse equipped with over 900 square feet of P84 filter cloth. Particulate collected in the baghouse is conveyed to the rotary discharge auger. The particulate-free gases exiting the baghouse are then routed to a secondary treatment unit located on a separate trailer. The secondary treatment unit booster fan draws the gas stream into a thermal oxidizer where the combination of high temperature and residence time converts virtually all of the organic contaminants to carbon dioxide (CO2), water vapor (H2O) and inorganic acids (HCL). The oxidizer is designed to provide a 2-second residence time at an oxidizer discharge temperature of 1,800°F.

When treating chlorinated compounds the oxidizer exhaust gases are routed to a quench duct that reduces the gas temperature to below 400°F. This rapid quench (milliseconds) minimizes the potential for dioxin formation. The cooled gas flows into a packed-bed scrubber where HCL formed in the oxidizer is neutralized with a caustic sodium hydroxide (NaOH) solution. Spent scrubber water containing mainly salts is used as dust control on processed soil thereby minimizing waste discharges.

The hot soils exiting the thermal desorber pass into the discharge auger where they are mixed with dust fines removed in the baghouse. The auger is equipped with water spray nozzles that cool and rehydrate the soil using the water described above. The treated soil is stockpiled using a front-end loader and allowed to cool before sampling.