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Waste Gas; Types and Treatments

Waste Gas; Types and Treatments. Outline. Overview Air pollutants Waste gas treatmens Biofilters. Definition. Air pollution may be defined as : the presence in the air (outdoor atmosphere) of one or more contaminants or combinations there of in such quantities and of such durations

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Waste Gas; Types and Treatments

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  1. Waste Gas; Types and Treatments

  2. Outline • Overview • Air pollutants • Waste gas treatmens • Biofilters

  3. Definition Air pollution may be defined as: • the presence in the air (outdoor atmosphere) of one or more contaminants or combinations thereofin such quantities and of such durations • as may be or tend to be injurious to human, animal or plant life, or property, • unreasonably interferes with the comfortable enjoyment of life or property or conduct of business.

  4. The Composition of Atmosphere

  5. Air Pollution Index Value

  6. Outline • Overview • Air pollutants • Waste gas treatmens • Biofilters

  7. Outline • Overview • Air pollutants • Waste gas treatments • Biofilters

  8. Waste Gas Treatments Waste gas treatments Source control: Raw product substitution Reduction Recycle Secondary control: Treatment after it has been produced -may reduce quality - Increase cost • Choice of tech dictated by: • Economic • Ecological const.

  9. Types of waste gas treatments • Condensation • Incineration • Adsorption • Absorption • Membrane systems • Biological Treatments

  10. 1. Condensations • Applicable for waste contaminant that are: -> concentrated and have a high boiling point -> have recycle or recovery value -> recovery is impossible for mixed pollutant stream • Mechanism: -> waste gas are treated by simultaneous cooling and compressing

  11. 2. Incineration • Widely used, suitable for moderate flow rate waste • Mechanism: -> thermal incineration involves combustion at tempt of 700-1400 0C -> catalytic incineration (used platinum, palladium, rubidium) at 300-7000C • Drawbacks: -> high cost esp for low conc. Waste -> need a large amount of fuel -> produce another pollutant (Nox, dioxins)

  12. 3. Adsorption • Most efficient for: -> low concentration vapour -> low vapour pressure -> high molecular weight waste gas • Common methods: -> fixed or fluidized bed of material such as activated carbon or zeolite • Function of effectiveness: -> air flow rate -> total VOC loading

  13. 3. Adsorption • Limitations: -> misjudgment of bed saturation often encountered, bed maybe renewed before it is necessaru -> the saturated bed materials are often treated as hazardous material -> increasing operational cost for its treatment -> generaly it is treated by: a. Desorption with steam or hot air b. Disposal c. incineration

  14. 4. Absorption • Process: -> removes contaminant with a scrubbing solutions (water mostly used) -> gas enters a large contactor -> gas are transferred to a liquid phase -> silicon oil maybe used for hydrophobic pollutant -> after gas are transfered to liqiud, additional treatment need to be apllied. • Drawbacks: -> need additional treatment for liquid phase (incineration. Additional wwtp)

  15. Vertical Venturi Scrubber

  16. Packed Bed Scrubber

  17. 5. Membrane Systems • The subsequent process of condensation • Process: -> gas stream are compressed to 310-1400 kPa -> the pressure diferential drives the membrane separation process -> the membrane pores remain filled with water -> the organic vapour transfered through the membrane -> the process than requires treatment of liquid permeate for final VOC disposal

  18. 6. Biological treatments • Utilize microbial metabolic reactions • Effective and economical for low concentrations of contaminant in large quantities of air. • The contaminant maybe used as energy or carbon source for microbial growth • Most succesfull for low molecular weight and highly soluble organic compound with simple bond structure (H2S or Ammonia)

  19. 6. Biological treatments • The appropiate industries: - Animal husbandary (slaugterhouse) - Composting - Crematorium - Food Processing - Fragnance - Furniture - Landfill gas extraction - Pulp and paper - Petroleum industries

  20. 6. Biological treatments

  21. Operational Concerning Factors • Characteristics of supporting medium (porosity, degree of compaction, water retention capability, ability to host microbial populations) • Microbial inoculum • Medium pH • Temperature • Medium moisture • Nutrient content

  22. Operational Cost • include: 1) nutrients andwater expenses 2) electricity for the blower and therecycle pump and miscellaneous electrical equipment 3) maintenance 4) costs associated withcontrolling the growth of biomass 5) capital costs

  23. Applicability of various air pollution control

  24. Case Studies • 98% H2S RE • 50-70% (toluene, benzene, xylene)

  25. Case Studies • 85-99% H2S RE

  26. Case Studies • >90 % H2S RE • >90 % RE aromatic compounds • >95% RE ketones

  27. Thank You

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