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Air Emissions Treatment

Air Emissions Treatment. Because air pollutants vary in size many orders of magnitude, many different types of treatment devices are required for emissions treatment.

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Air Emissions Treatment

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  1. Air Emissions Treatment

  2. Because air pollutants vary in size many orders of magnitude, many different types of treatment devices are required for emissions treatment.

  3. Air pollutant devices can be treated as black box separators, like we studied in Chapter 3. Recovery efficiency can be described by the equation: R1 = (x1/x0) x 100 R1 = recovery of component 1, % x1 = amount of pollutant collected by the device per unit time, kg/sec x0 = amount of pollutant entering the device per unit time, kg/sec

  4. Feed x0 Escaped x2 Pollution control device Removed x1 Example An air pollution control device removes a particulate that is being emitted at a concentration of 125,000 :g/m3 at an air flow rate of 180 m3/sec. The device removes 0.48 metric toms per day. What are the concentration of the emission and the recovery of collection? At steady state the mass balance is: Rate of particulates in = rate of particulates out Rate of particles in = rate of particles removed + rate of particles escaping

  5. Particulates in: 180 m3/sec x 125,000 :g/m3 x 10-6:g/g = 22.5 g/sec Particles collected: 0.48 tons/day x 106 g/ton x 1 hr/3600 sec x 1 day/24 hr = 5.5 g/sec Mass balance: 22.5 = 5.5 + particles that escape Particles that escape = 17 g/sec Emission concentration: (17 g/sec x 106:g/g)/ 180 m3/sec = 94,000 :g/m3 Recovery: R = (x1 x 100)/x0 = (5.5 x 100)/22.5 = 24%

  6. Treatment Devices Settling Chambers The simplest of treatment devices. Wide spot in the exhaust flue that allows particles to settle out. Only very large particles (> 100 :m) will settle effectively.

  7. Cyclones

  8. Bag Filter or Bag House

  9. Spray Tower or Scrubber

  10. Electrostatic Precipitators

  11. Electrostatic Precipitators

  12. Process Selection • Settling Chamber • Simple Cyclone • High-efficiency Cyclone • Electrostatic Precipitator • Spray Tower wet scrubber • Venturi Scrubber • Bag Filter

  13. Control of Gaseous Pollutants Wet Scrubbers Adsorption Incineration or flaring Catalytic Combustion

  14. Venturi Scrubber Wet Scrubber

  15. Wet Scrubbers

  16. Adsorption

  17. Carbon Adsorption System

  18. Incineration and Flaring

  19. Control of Sulfur Oxides (SOx) Emission of SOx one of the major causes of acid precipitation Major source of SOx is coal-fired power plants Several options for control: Change to Low-sulfur fuel Desulfurize the coal Sulfur in coal is either organic (usually about 60%) or inorganic (about 40%). The inorganic form is iron pyrite (FeS2) that can be removed from the coal by washing. The removal of organic sulfur requires a chemical reaction that is accomplished best if the coal is gassified first. Gasified coal is like natural gas.

  20. SOx Control Options (continued) Tall Stacks Flue-Gas Desulfurization Contact with lime SO2 + CaO  CaSO3 Contact with limestone SO2 + CaCO3 CaSO4 + CO2 Calcium sulfite (CaSO3) and calcium sulfate (CaSO4) are solids that have low solubilities so they can be removed from the water by settling, but then there is a disposal problem

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