Thermal Desorption


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Thermal Desorption

  1. 1. Thermal Desorption An Overview Andre Akiyode
  2. 2. The basics• A physical treatment and separation process. Does not destroy contaminants.• Wastes are heated enough to volatilize water and organic contaminants.• A carrier gas or vacuum system transports volatilized water and organics to the gas treatment system.
  3. 3. Treat and Control• Things to consider:Treatment is to remove dangerous contaminants. Therefore cross-media release should be avoided. - Organics are volatilised at low temperature (100-800°C ) and cleaned soils separated - Off-gases are treated to capture or destroy the volatilized contaminants, for example GAC, Afterburner / Thermal oxidiser, Catalyctic oxidiser
  4. 4. Thermal Desorption Process
  5. 5. Types of TD• Direct Fired Rotary Desorber – Treats high boiling point (BP) organics e.g. TCE – Flame in direct contact with contaminated media• Indirect Fired Rotary Desorber – Treats high to low BP contaminants e.g. DDT – Air stream is heated & directly applied on media. Heated air, on contact causes volatilization• Indirect Heated Rotary Desorber – Treats low BP contaminants e.g. Petroleum Hydrocarbon, BTEX – Externally heated rotary dryer (above diagram) heats contaminated media within dryer
  6. 6. Suitability Check• Thermal desorption is effective for treating: - dry soil, sludge, solid waste; - contaminated with: fuel oil, coal tar, volatile chemicals and metals, pesticides and solvents.• Low Temp. TD for BP < 300°C (e.g. BTEX)• High Temp. TD for BP > 300°C (e.g. PCBs)
  7. 7. Suitable ContaminantsPotentially Suitable • Unlikely to be suitable for:contaminants: - Non-volatile metals• VOCs (e.g. BTEX - Corrosives - Halogenated- hydrocarbons (e.g. TCE), - Asbestos - Non-halogenated - Oxidising agents hydrocarbons (e.g. TPH)• SVOC - Reducing agents - PAHs )e.g. naphthalene, benzo(a)pyrene etc) - PCBs, pesticides and herbicides - Explosive compounds (e.g. TNT)• Phenolics• Cyanides
  8. 8. Good Practices & Soil Pre-Treatment• In most cases, soil should be pre-treated to: – Remove rubble/scrap metal & contraries – Improve handling process – improve structure / remove large clumps – Reduce moisture content – Reduce calorific value – Reduce SOx/NOx/HCL emissions – Prevent damage to treatment plant
  9. 9. Good Practices & Off-Gas Treatment• Additional off-gas control should be implemented to: – Remove dusts: Bag filters and cyclones – Limit volatile metals: Electrostatic Precipitator & GAC injection – Reduce HCL emissions: alkaline scrubber – Control SOx: wet or dry scrubbers – Control NOx: scrubbers – VOCs: GAC, Thermal Oxidizer Note: In majority of cases, more than one abatement systems will be required to deal with the different releases, e.g. dust/particulates, gasses
  10. 10. Good Practices & Residuals Management• Post-treatment measures should be in place to deal with treated materials as well as residuals including: Treated soil Clean off-gas Spent carbon Concentrated contaminants Waste water Catalyst
  11. 11. Advantages• Potential for high removal efficiencies/ to meet stringent remedial targets• Can treat large volumes of soil• Effective – against a wide range of contaminants – Against unknown mixtures of volatile/ semi volatile contaminants
  12. 12. Limitations• High energy use – high cost• Air emission control – usually multiple control systems• Soil structure is usually destroyed – limits re-use• Potential generation of dusts/silt• Extremes of soil pH can corrode internal systems• Tightly aggregated soils can reduce the system performance