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hossam TOSHIBA 1/1/2008

AANNEERROOBBIICC TTHHEERRMMAALL

DDEESSOORRPPTTIIOONN UUNNIITT

((AATTDDUU))

الشركـــــــــة الوطنيــــــة للتنظيـــــف

National Cleaning Company

Anaerobic Thermal Desorption Unit National Cleaning Company

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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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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 o

C. The vapors exiting the heat exchanger at

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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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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.

Pretreatment & Feed System

Screening Grid over Feed Hopper Feed Hopper

Conveyor Belt Outlet Hopper

Figure 3.1: Schematic Process Flow Diagram

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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 - 540

oC. 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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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 o

C. 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 o

C 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

Cyclone (Dry Dust Collector)

Vapor Recovery Unit

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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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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

Feed Soil content Soil 30 to 80% 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 Hydrocarbon in recovered Water

< 10,000 ppm > 80% < 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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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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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.