RLC Technologies innovative technology is based on an Indirect-heated rotary desorber system which employs the use of an oxygen-deficient atmosphere while desorbing / separating volatile and semi-volatile organic compounds from the solids. The rotating system is capable of maintaining material temperatures ranging from 600ºF - 1400ºF (315ºC - 760ºC). Slightly negative pressure is continuously maintained on the desorber. This assists in removing process gases from the desorber and into the Vapor Recovery Unit (VRU). Within the VRU the process gases undergo treatment inside a series of scrubbers and separators where entrained solids, water and hydrocarbon vapors are removed from the gas stream.

The second step in the gas treatment is accomplished when the effluent from the primary scrubber are passed through a heat exchanger / condenser where the gas temperature is further reduced to below 100ºF (38ºC). The vapors exiting the heat exchanger at this point include residual non-condensable gasses and water vapor. Depending on the local regulatory guidelines and emission requirements, these vapors may be discharged directly into the atmosphere. Should it be determined that additional treatment of the off-gases are required, final gas treatment to remove any residual contaminants can be achieved using activated carbon, bio-filters or thermal oxidation in ATDU furnace.

All condensed vapors from the VRU undergo a separation and cooling process once inside the Water Treatment Unit (WTU). The output from the WTU has commercial value and consists of three separate streams: solids, oil, and water. The oil can be further treated and used to fire ATDU burners. The recovered water once cooled can be recycled through the plant as cooling / process water.

RLC Technologies provides complete plants including feed system, Anaerobic Thermal Desorption Unit (ATDU), Vapor Recovery Unit (VRU), Water Treatment Unit (WTU), and associated process controls.

Pretreatment
The feed entering the ATDU plant should be pretreated and screened to remove oversized material and should not contain material exceeding 50 mm (2 inches) in diameter. Liquid reduction of the feed material is not required but is highly desirable in order to decrease the operating cost and increase production.

Feed System
The feed system is the process of introducing and metering the feed into the ATDU plant. The feed system begins with a feed hopper, which has a variable speed screw conveyor live bottom. The design insures a steady feed supply to the ATDU while minimizing bridge formation. The material is conveyed from the feed hopper by conveyor belt equipped with a belt scale to determine the feed rate into the ATDU. A magnet located above the belt conveyor, prevents tramp metal from entering the ATDU. In order to prevent air leakage into the ATDU, the feed material passes through a double tipping valve (airlock) before entering into the ATDU chamber for thermal processing.

Anaerobic Thermal Desorbtion Unit (ATDU)
The material enters the ATDU and depending on the application, can be heated up to 1,400ºF (760ºC). The ATDU is equipped with a variable speed rotary drum drive and adjustable slope. The rotational speed and the slope of the rotary desorber control the flow of the feed through the unit. Depending on throughput, material residence times over sixty minutes can be realized.

Heat is supplied to the ATDU by a series of burners that are strategically located for effective heat transfer through the desorber’s exterior surface area. The furnace has two chambers and is designed in a way that the combustion gases heat the outside of the rotating desorber and the heat is transferred through the cylinder shell to the material. The combustion gases from the burners do not come in contact with the material inside the ATDU. They are vented directly to the atmosphere through two stacks. This indirect heating greatly reduces the volume of the process gasses that have to be treated; therefore, resulting in substantially reduced vapor treatment system when compared to direct fired thermal treatment systems such as incinerators.

Solid Discharge and Conditioned System
The processed solids leave the ATDU via a high temperature resistant screw conveyor through a double tipping valve (airlock). The airlock ensures that oxygen-deficient conditions within the ATDU are maintained. The solids are cooled and hydrated in a mixing chamber. Water is introduced in the mixer/cooler to prevent fugitive dust and to protect equipment and personnel from the hot solids. Conveyor then transfers the conditioned material to a storage area.

Vapor Recovery Unit (VRU)
The process gasses leaving the ATDU are normally between 800ºF - 1000ºF (430ºC - 540ºC). The volume of gasses to be treated depends on the contaminants and the feed rate through the plant. The off-gas flow rate can range at approximately 1000-5000 ACFM (30 - 140 m3/min). The gases exiting the ATDU pass through a mechanical collector designed to remove approximately 50 - 60 percent of the dust from the ATDU. It collects the larger particulate matter from the exhaust gas stream prior to the Scrubbers. The collected dust is then discharged through air-sealed valve into the soil-conditioned system. After the mechanical collector, the gases first pass through the Pre-Scrubber, where they are scrubbed with water to reduce the temperature and remove most of the oil and the remaining particulate matter. In the pre-scrubber, the temperatures of the gasses are reduced to below 200ºF (90ºC). The gasses are then further scrubbed utilizing a Venturi Scrubber where the temperatures are nominally reduced to below 130ºF (55ºC). The venturi scrubber will remove almost all the remaining particulate from the gas stream. However, to achieve greater removal efficiency an additional separator with Demister is implemented after the Venturi. At or below approximately 130ºF (55ºC) temperature range virtually all hydrocarbon vapors in the gas stream have been condensed out. The VRU employs an indirect Heat Exchanger/Condenser in conjunction with a chiller to further reduce the process gas temperature and any remaining hydrocarbon residues in the gas stream. After the Heat Exchanger/Condenser, the volume of the gases will be reduced to less than 100 ACFM (3 m3/min). In cases where volatile light ends are still detected in the gas stream, they may undergo a final treatment through one of several options including activated carbon, bio-filter or thermal oxidation inside the ATDU furnace.

Process water quality is of the utmost importance when considering a trouble-free operation. High process water temperature can result in poor separation of oil and solids and can greatly affect the performance of the entire process. Having adequate cooling capacity and solids separation equipment is paramount in the design of the system.

Water Treatment Unit (WTU)
The Water Treatment Unit is designed to separate the process oil-water-solid mixture after the VRU into three separate streams of oil, water, and solids and to cool the stream of process water for further use in the VRU scrubber system.

The process mixture undergoes a primary separation through an Interceptor before entering the Oil / Water Separator(s) for more fine separation.

The solids collected in the water treatment system are pumped into a separate area for re-treatment into the ATDU feed or for disposal.