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Process Description
The MSR 945D Thermal Desorption Unit typically processes between 80 and 120 tons of contaminated soil per hour. The process begins with the placement of contaminated soil in the primary feed hopper via front end loader. All types of soil including clay, sand, silty clay, gravel, and aggregates can be treated. The feed soil immediately passes through a six inch grizzly bar screen that rejects debris and large aggregate before entering the system.
After proceeding through additional screens which reduce the soil size for processing, the soil then passes over a dual idler, in-motion weigh scale which has an electronic remote read-out and recorder which logs all soil tonnage entering the process. Soils then travel via slinger conveyor into the systems rotary desorber. The rotary desorber elevates soil temperature to a level necessary to convert contaminants, into a vapor state for removal by way of an exhaust gas stream. The rotary desorber is equipped with variable speed, slope and temperature control to permit soil retention time to vary from eight to twenty minutes to assure the remediation of contaminants.
The high temperature air stream containing the volatilized contaminants as well as any dust picked up from the rotary desorber then travels to the fabric filter baghouse. The dust and particulate fines from the baghouse are recycled to the thermal dust conductor where they are further treated by dwelling with high temperature soil from the rotary desorber in a tumbling motion. The intimate contact of high temperature soil from the rotary desorber with dust and particulates from the baghouse, allows conductive heat transfer to volatilize any remaining contaminants in the dust before exiting the thermal dust conductor. The volatilized contaminates are ducted back into the combustion zone for elimination. The fabric filter baghouse is equipped with filter bags that trap dust as the gas stream is drawn inside by an exhaust fan. As dust is trapped on the outside of the bags, the particulate free air exits the unit from inside the bags and is directed to the thermal oxidizer.
The thermal oxidizer receives the dust free air stream from the baghouse and elevates the gas to between 1,400°F and 1,800°F in order to destroy organic compounds contained within the gas stream at an efficiency rate exceeding 99%.
Soil exiting the thermal dust conductor enters into the soil cooler, which lowers soil temperatures and rehydrates the soil with water sprayed from high pressure jets. The cool, rehydrated soil exits the conditioner/cooler by gravity and is deposited on a stacking conveyor for stockpiling.
Upon completion of laboratory testing to confirm the removal of all VOC's to below the project clean-up objectives, the soil is ready for reuse. Treated soil is commonly placed into the original excavation as backfill to fulfill closure requirements and the treated soil can be compacted to a density above 95%.