The direct fired thermal desorption unit contains three major components; a primary kiln for soil treatment, a bag house for dust removal, and an afterburner operating from 1600 deg. F to 2150 deg. F with a 2 second gas retention time to destroy the volatilized organics from the primary. The system is self contained and powered by an on-board generator that is capable of handling all energy requirements for the system. The generator and both primary and secondary burners are fired on No. 2 diesel fuel or No. 2 heating oil. They can, however, be converted to propane or natural gas if desired.
The treatment process is simple and begins with the feeding of the soils into a hopper at the rear of the unit. A controlled feed-rate for soil is achieved by the use of a variable speed conveyor that moves the soil directly from the hopper onto a slinger belt. The belt virtually throws the soils into the rotating kiln drum. Once in the hopper, soil is moved down the kiln by gravity. A specially designed flighting system in the drum causes the soils to be dropped directly into the center of the main burner flame. The flame, positioned at the low side of the drum, provides the heat that is absorbed by the soil. This heat causes the volatile compounds to be released into the air stream and carried out of the kiln. The kiln temperatures can be controlled for the optimum efficiency of desorption, based upon contaminate concentration and soil type.
The air stream, laden with water and organic vapors and dust particles, exits the drum directly into the bag house. The dust is removed from the air stream to meet all standards for particulate emissions from the exhaust stack. The resulting air flow, carrying the vapors, is moved directly to an afterburner. The vapor-laden air passes through the afterburner at which point the organics are destroyed. The soils exit the kiln at temperatures of 600 deg. F to 900 deg. F. At the point of discharge, the soil is re-hydrated to suppress fugitive dust emissions.
Operation of the unit is performed primarily from the main control station. From here, the operator is able to start, operate, and shut the unit down. Process instrumentation process variables are displayed here, providing current information regarding all system parameters.