Eng. Hossam Nassar - The Application of Anaerobic Thermal Desorption Unit for the Treatment of Hydrocarbon Contaminated Soils
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Eng. Hossam Nassar - The Application of Anaerobic Thermal Desorption Unit for the Treatment of Hydrocarbon Contaminated Soils

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  • 1. ‫الشركـــــــــة الوطنيــــــة للتنظيـــــف‬si National Cleaning Company ANEROBIC THERMAL DESORPTION UNIT (ATDU) hossam TOSHIBA 1/1/2008
  • 2. Anaerobic Thermal Desorption Unit National Cleaning CompanyContents1. Introduction......................................................................................................... 22. RLC ATDU ........................................................................................................ 23. ATDU Process Description ................................................................................... 3 3.1. Plant Components .......................................................................................... 3 3.2. Process Description ....................................................................................... 34. Typical Process Parameters ................................................................................... 85. Treatment level .................................................................................................... 96. Process Safety Measurements & Controls ............................................................. 10 Page 1 of 11
  • 3. Anaerobic Thermal Desorption Unit National Cleaning Company1. Introduction Thermal desorption is an environmental remediation technology that utilizes heat toincrease the volatility of contaminants such that they can be removed from the solidmatrix without thermally destroying it. It is a separation technology that volatilizedcontaminants and then either collecting or thermally destroying, them, therefore anythermal desorption system usually has two major components; the desorber itself and theoff gas treatment system. In general, thermal desorption is capable of treating various materials, includingsoil, sediment, sludge, and filter cake, contaminated with a wide range of organiccontaminants. Petroleum, volatile organic compounds (VOCs), semivolatile organiccompounds (SVOCs), pesticides, and other compounds with boiling points up to about315 °C are typically processed through direct - or indirect-contact thermal desorptionunits. 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 innovativetechnology is based on an Indirect-heatedrotary desorber system which employs theuse of an oxygen-deficient atmosphere whiledesorbing / separating volatile and semi-volatile organic compounds from the solids. The rotating system is capable ofmaintaining material temperatures ranging from 315 oC – 760 oC. Slightly negativepressure is continuously maintained on the desorber. This assists in removing processgases from the desorber and into the Vapor Recovery Unit (VRU). Within the VRU theprocess gases undergo treatment inside a series of scrubbers and separators whereentrained solids, water and hydrocarbon vapors are removed from the gas stream. The second step in the gas treatment is accomplished when the effluent from theprimary scrubber are passed through a heat exchanger / condenser where the gastemperature is further reduced to below 38 oC. The vapors exiting the heat exchanger at Page 2 of 11
  • 4. Anaerobic Thermal Desorption Unit National Cleaning Companythis point include residual non-condensable gasses and water vapor. Depending on thelocal regulatory guidelines and emission requirements, these vapors may be dischargeddirectly 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 beachieved using activated carbon, bio-filters or thermal oxidation in ATDU furnace. All condensed vapors from the VRU undergo a separation and cooling processonce inside the Water Treatment Unit (WTU). The output from the WTU has commercialvalue and consists of three separate streams: solids, oil, and water. The oil can be furthertreated and used to fire ATDU burners. The recovered water once cooled can be recycledthrough the plant as cooling / process water. RLC Technologies provides complete plants including feed system, AnaerobicThermal Desorption Unit (ATDU), Vapor Recovery Unit (VRU), Water Treatment Unit(WTU), and associated process controls.3. ATDU Process Description3.1. Plant ComponentsThe 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 DescriptionSchematic process flow diagram is shown in figure 3.1 The following is a briefdescription of the treatment processes throughout the plant. Page 3 of 11
  • 5. Anaerobic Thermal Desorption Unit National Cleaning CompanyPretreatment The feed entering the ATDU plant should be pretreated and screened to removeoversized material and should not contain material exceeding 50 mm in diameter. Liquidreduction of the feed material is not required but is highly desirable in order to decreasethe operating cost and increase production.Feed System The feed system is the process of introducing and metering the feed into theATDU plant. The feed system begins with a feed hopper, which has a variable speedscrew conveyor live bottom. The design insures a steady feed supply to the ATDU whileminimizing bridge formation. The material is conveyed from the feed hopper byconveyor belt equipped with a belt scale to determine the feed rate into the ATDU. Amagnet 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 doubletipping 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 Page 4 of 11
  • 6. Figure 3.1: Schematic Process Flow Diagram
  • 7. Anaerobic Thermal Desorption Unit National Cleaning CompanyAnaerobic Thermal Desorption Unit (ATDU) The material enters the ATDU and depending on the application, can be heated upto 760oC. The ATDU is equipped with a variable speed rotary drum drive and adjustableslope. The rotational speed and the slope of the rotary desorber control the flow of thefeed through the unit. Depending on throughput,material residence times over sixty minutes can berealized. Heat is supplied to the ATDU by a seriesof burners that are strategically located foreffective heat transfer through the desorber’sexterior surface area. The furnace has twochambers and is designed in a way that thecombustion gases heat the outside of the rotating desorber and the heat is transferredthrough the cylinder shell to the material. The combustion gases from the burners do notcome in contact with the material inside the ATDU. They are vented directly to theatmosphere through two stacks. This indirect heating greatly reduces the volume of theprocess gasses that have to be treated; therefore, resulting in substantially reduced vaportreatment system when compared to direct fired thermal treatment systems such asincinerators.Solid Discharge and Conditioned System The processed solids leave the ATDU via a high temperature resistant screwconveyor through a double tipping valve (airlock). The airlock ensures that oxygen-deficient conditions within the ATDU are maintained. The solids are cooled and hydratedin a mixing chamber. Water is introduced in the mixer/cooler to prevent fugitive dust andto protect equipment and personnel from the hot solids. Conveyor then transfers theconditioned material to a storage area.Vapor Recovery Unit (VRU)The process gasses leaving the ATDU are normally between 430oC - 540oC. The volumeof 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. Page 6 of 11
  • 8. Anaerobic Thermal Desorption Unit National Cleaning Company Cyclone (Dry Dust Collector) Vapor Recovery UnitThe gases exiting the ATDU pass through a mechanical collector designed to removeapproximately 50 - 60 percent of the dust from the ATDU. It collects the larger particulate matter from the exhaust gas stream prior to theScrubbers. 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 mostof the oil and the remaining particulate matter. In the pre-scrubber, the temperatures ofthe gasses are reduced to below 90oC. The gasses are then further scrubbed utilizing aVenturi Scrubber where the temperatures are nominally reduced to below 55 oC. Theventuri scrubber will remove almost all the remaining particulate from the gas stream.However, to achieve greater removal efficiency an additional separator with Demister isimplemented after the Venturi. At or below approximately 55 oC temperature rangevirtually all hydrocarbon vapors in the gas stream have been condensed out. The VRUemploys an indirect Heat Exchanger/Condenser in conjunction with a chiller to furtherreduce the process gas temperature and any remaining hydrocarbon residues in the gasstream. After the Heat Exchanger/Condenser, the volume of the gases will be reduced toless 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 activatedcarbon, bio-filter or thermal oxidation inside the ATDU furnace. Process water quality is of the utmost importance when considering a trouble-freeoperation. High process water temperature can result in poor separation of oil and solids Page 7 of 11
  • 9. Anaerobic Thermal Desorption Unit National Cleaning Companyand can greatly affect the performance of the entire process. Having adequate coolingcapacity 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-solidmixture after the VRU into three separate streams of oil, water, and solids and to cool thestream of process water for further use in the VRU scrubber system.The process mixture undergoes a primary separation through an Interceptor beforeentering 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 Unit4. Typical Process Parameters The process has been designed to meet a wide range of contaminated soil typesand levels to serve as much clients as possible without affecting the quality of the finaltreated soil. The present plant has the capability of treating the following materials:  Crude oil tanker bottoms and other marine waste  Oily sludge  Tank bottoms  Refinery waste  Drill cuttings Page 8 of 11
  • 10. Anaerobic Thermal Desorption Unit National Cleaning Company  Contaminated filter cakes  Polyaromatic hydrocarbons (PAHs)  Polychlorinated biphenyls (PCBs)  Pesticides  Trichloroethane (TCE)  Perchloroethene (PCE)  Other chlorinated organic compounds  Other contaminated materials & wasteThe following are summery of process parameters:Feed Type rangeMax. Bed Temperature 700 oCTotal 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 ppmProcessing Capacity 2 – 15 ton/hours (Depend on feed quality and contamination level)5. Treatment levelSoil: Treated soil is tested using the petroflag test kit and results are maintained andsupplied to clients upon request. Typical value of treated soil is less than 10,000 ppmwhich is in compliance with KEPA standards.Oily Water: Vapor and gases are condensed as described above. The condensed gascontains fine sand, oil, and waters. The mixture pass to a water treatment unit where thesolid particles precipitate down and the oil is separated from the water. The water isrecycled back to the process. The oil collected is of high value and is collected and stored Page 9 of 11
  • 11. Anaerobic Thermal Desorption Unit National Cleaning Companyin HDPE lined collection pit and maybe used for heating the process or sold. The sludgeis either recycled back to the plant or further treated via a three phase separator. Therecovered oil is of a high commercial value which is stored, the sludge is sent back to theATDU as feed, and the water is reused again as process water.Air Emission: Generated gases and vapors pass through a series of treatment processesprior to discharge to atmosphere. Throughout the mechanical collector, prescrubber,venture scrubber, Demister, and indirect heat exchanger/ condenser with chiller, and thecarbon 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 automaticallymonitored and controlled via SCADA system. All control actions are performedautomatically by programmable logic controllers ("PLCs") and the SCADA systemallows operators to change the set points for the process parameters, and enable alarmconditions, such as loss of flow, high temperature, pressure change,…..etc, to bedisplayed and recorded. Plant Control RoomThe 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. Page 10 of 11
  • 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. Page 11 of 11