1. ‫الشركـــــــــة الوطنيــــــة للتنظيـــــف‬
si
National Cleaning Company
ANEROBIC THERMAL
DESORPTION UNIT
(ATDU)
hossam
TOSHIBA
1/1/2008

2. Anaerobic Thermal Desorption Unit National Cleaning Company
Contents
1. Introduction......................................................................................................... 2
2. RLC ATDU ........................................................................................................ 2
3. ATDU Process Description ................................................................................... 3
3.1. Plant Components .......................................................................................... 3
3.2. Process Description ....................................................................................... 3
4. Typical Process Parameters ................................................................................... 8
5. Treatment level .................................................................................................... 9
6. Process Safety Measurements & Controls ............................................................. 10
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3. Anaerobic Thermal Desorption Unit National Cleaning Company
1. Introduction
Thermal desorption is an environmental remediation technology that utilizes heat to
increase the volatility of contaminants such that they can be removed from the solid
matrix without thermally destroying it. It is a separation technology that volatilized
contaminants and then either collecting or thermally destroying, them, therefore any
thermal desorption system usually has two major components; the desorber itself and the
off gas treatment system.
In general, thermal desorption is capable of treating various materials, including
soil, sediment, sludge, and filter cake, contaminated with a wide range of organic
contaminants. Petroleum, volatile organic compounds (VOCs), semivolatile organic
compounds (SVOCs), pesticides, and other compounds with boiling points up to about
315 °C are typically processed through direct - or indirect-contact thermal desorption
units. Contaminants with boiling points above 315 °C, such as polychlorinated biphenyls
(PCBs), dioxins, and furans, may be treatable with higher-temperature systems.
2. RLC ATDU
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 315 oC – 760 oC. 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 38 oC. The vapors exiting the heat exchanger at
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4. Anaerobic Thermal Desorption Unit National Cleaning Company
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.
3. ATDU Process Description
3.1. Plant Components
The plant consists of the following main parts:
 Pretreatment
 Feed System
 Anaerobic Thermal Desorption Unit (ATDU)
 Solid Discharge and Conditioned System
 Vapor Recovery Unit (VRU)
 Water Treatment Unit (WTU)
3.2. Process Description
Schematic process flow diagram is shown in figure 3.1 The following is a brief
description of the treatment processes throughout the plant.
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5. Anaerobic Thermal Desorption Unit National Cleaning Company
Pretreatment
The feed entering the ATDU plant should be pretreated and screened to remove
oversized material and should not contain material exceeding 50 mm 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.
Feed Hopper Screening Grid over Feed Hopper
Conveyor Belt Outlet Hopper
Pretreatment & Feed System
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6. Figure 3.1: Schematic Process Flow Diagram

7. Anaerobic Thermal Desorption Unit National Cleaning Company
Anaerobic Thermal Desorption Unit (ATDU)
The material enters the ATDU and depending on the application, can be heated up
to 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 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 30 - 140 m3/min.
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8. Anaerobic Thermal Desorption Unit National Cleaning Company
Cyclone (Dry Dust Collector) Vapor Recovery Unit
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 90oC. The gasses are then further scrubbed utilizing a
Venturi Scrubber where the temperatures are nominally reduced to below 55 oC. 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 55 oC 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 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
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9. Anaerobic Thermal Desorption Unit National Cleaning Company
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.
Oil Water Separator Unit
4. Typical Process Parameters
The process has been designed to meet a wide range of contaminated soil types
and levels to serve as much clients as possible without affecting the quality of the final
treated soil. The present plant has the capability of treating the following materials:
 Crude oil tanker bottom's and other marine waste
 Oily sludge
 Tank bottom's
 Refinery waste
 Drill cuttings
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10. Anaerobic Thermal Desorption Unit National Cleaning Company
 Contaminated filter cakes
 Polyaromatic hydrocarbon's (PAH's)
 Polychlorinated biphenyl's (PCB's)
 Pesticides
 Trichloroethane (TCE)
 Perchloroethene (PCE)
 Other chlorinated organic compounds
 Other contaminated materials & waste
The following are summery of process parameters:
Feed Type range
Max. Bed Temperature 700 oC
Total Residence Time 5 – 45 min
Soil 30 to 80%
Feed Soil content Oil 0 to 50%
Water 10 to 80%.
Feed Particles size Less than 50 mm (large sizes are screened and crushed
through a size reduction screw conveyer)
Output:
 Soil TPH
 Recovered Diesel
< 10,000 ppm
 Hydrocarbon in
> 80%
recovered Water < 100 ppm
Processing Capacity 2 – 15 ton/hours (Depend on feed quality and
contamination level)
5. Treatment level
Soil: Treated soil is tested using the petroflag test kit and results are maintained and
supplied to clients upon request. Typical value of treated soil is less than 10,000 ppm
which is in compliance with KEPA standards.
Oily Water: Vapor and gases are condensed as described above. The condensed gas
contains fine sand, oil, and waters. The mixture pass to a water treatment unit where the
solid particles precipitate down and the oil is separated from the water. The water is
recycled back to the process. The oil collected is of high value and is collected and stored
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11. Anaerobic Thermal Desorption Unit National Cleaning Company
in HDPE lined collection pit and maybe used for heating the process or sold. The sludge
is either recycled back to the plant or further treated via a three phase separator. The
recovered oil is of a high commercial value which is stored, the sludge is sent back to the
ATDU as feed, and the water is reused again as process water.
Air Emission: Generated gases and vapors pass through a series of treatment processes
prior to discharge to atmosphere. Throughout the mechanical collector, prescrubber,
venture scrubber, Demister, and indirect heat exchanger/ condenser with chiller, and the
carbon filters, the air emission is minimum and meeting local regulations and standard.
6. Process Safety Measurements & Controls
The overall plant operations and processes are connected and automatically
monitored and controlled via SCADA system. All control actions are performed
automatically by programmable logic controllers ("PLCs") and the SCADA system
allows operators to change the set points for the process parameters, and enable alarm
conditions, such as loss of flow, high temperature, pressure change,…..etc, to be
displayed and recorded.
Plant Control Room
The following are the emergency shutdown procedures:
1. Switch off both feed and discharger burners.
2. Switch appropriate valves to vent process gases to the carbon packs or atmosphere
and not to the ATDU furnace.
3. Switch on steam, water injection or nitrogen purge valves.
4. Switch off all main electrical disconnects.
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12. Anaerobic Thermal Desorption Unit National Cleaning Company
5. In case of power loss or possibility thereof, the auxiliary drive (Air motor) for the
claciner should be turned on to prevent warping of the calciner.
6. Turn off appropriate fuel valves (in case of fire) such as:
A. LPG – pilot and main burner supplies.
B. #2 fuel at the reservoir tank.
C. Natural Gas Supply.
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