air quality management module five ppt for engineerrs

air quality management for engineers

1. AIR QUA 1 LITY MANAGEMENT CET464 M0DULE 5 1

2. SYLLABUS 5.1 CONTROL OF AIRPOLLUTION 5.2 PARTICULATE EMISSION CONTROL- METHODS 5.3 SCRUBBING- CYCLONES 5.4 FILTRATION- ELECTROSTATIC PRECIPITATION 5.5 GASEOUS EMISSION CONTROL 5.6 ADSORPTION, ABSORPTION, THERMAL METHODS 5.7 THERMAL METHODS 2

3. 5.1 CONTROL OF AIR Pollutants A. NATURAL CONTROL (Natural Self Cleansing Capacity)  The nature itself has a capacity to clean out the pollutants coming into the atmosphere with natural forces of climate and ecology.  The following natural phenomena tries to reduce the pollutants and remove the Pollutants from the air : 1 . Dispersion  Dispersion of the pollutants from the source to larger area by wind so that the concentrations are diluted.  The pollutants emitted through tall chimneys is only a means of spreading our own pollutant around our neighbors. 2. Gravitational settling with or without flocculation  Large heavy SPM from ambient air settle down on building, trees & other surfaces. This process also helps in removing flocculated particles formed in the atmosphere 3

4. 3. Precipitation  Precipitations like rain water washes away some of air pollutants such as particulate matter, suspended in air When the pollutants emitted to the atmosphere are more than the natural self cleansing capacity of the atmosphere, the pollutants remain in the air for long periods in a sustainable manner which results into various ill effects to all the living & non living things on the earth. CONTROL METHODS A) PREVENTION :  Most effective means of dealing with the problem of air pollution is to prevent the formation of pollutants  Select the process which do not contribute pollution or have minimum pollution potential B) SOURCE CORRECTION METHODS o Raw material change, o Operational change, o Modification of process equipment, o Replacement of equipment 4

5. i ) Raw material change  Use purer grade of raw materials & reduce formation of undesirable pollutants as by- products  Burning of natural gas instead of Coal  Fuel desulphurization ii) Process change 1.Chemical and petroleum refining volatile substances are recovered by condensation Non condensable gases are recycled for additional reactions 2. Cement plants Dust control in Rotary kilns By adjusting operating conditions in Rotary kilns. 3. Smelting in Paper industries High pollution potential(emits highly objectionable sulphurous materials) This is replaced by hydro metallurgical separation of ores. 4. Steel Industry Sulphur bearing fuel, lime stone & air are injected into a molten iron bath 5

6. iii) Equipment Modification or replacement 1. Automobiles Unburnt hydrocarbons & CO can be burnt by injecting air into hot exhaust manifolds of engine 2. Petroleum Refineries Direct evaporation of HCs from storage tanks and filling can be minimized by floating roof tanks or by pressurizing the tanks 3. Steel industry Replacement of open hearth furnace by oxygen furnace) C. EMISSION CONTROL i )Dilution Method Dispersion of the pollutants from the source to larger area by wind through high rise chimneys so that the concentrations are diluted. Thereby reducing the pollution near the emission source D) CLEANING OF GASEOUS EFFLUENTS Applied to those cases where emissions of pollutants cannot be prevented and pollution control equipment's are necessary to remove them 6

7. 5.2 PARTICULATE EMISSION CONTROL-METHODS Particulate matters emitted in gaseous streams consist of discrete and minute suspended particles. Particle size generally from 100 micrometer to 0.1 micrometer. METHODS 1. Gravitational settling chambers Generally used to remove large, abrasive particles (usually >50µm) They offer low pressure drop and require simple maintenance Less efficient for particles less than 50µm Used as pre-cleaners prior to passing the gas through high efficiency collection devices Settling chambers uses the force of gravity to remove solid particles The gas stream enters a chamber where the velocity of gas is reduced. Large particles drop out of the gas and are recollected in hoppers 7

8. Advantages: 1. Simple construction 2. Low initial cost, maintenance cost, pressure drop 3. Dry and continuous disposal of solid particulates Disadvantages: 1. Large space requirement 2. Only comparatively large particles can be collected 8

9. 2.Cyclone Separators 9

10. Other cyclone types: 1. Straight through flow cyclone • Inner vortex of air leaves at the bottom (rather than reversing direction), with initial centrifugal motion being imparted by vanes at top • Advantage: low pressure drop and high volumetric flow rates 2. Impeller collector: • Gases enter normal to an impeller and are swept out by the impeller around its circumference while the particles are thrown into an annular slot around the periphery of the device. 3.Filters 10

11. 3.1 Packed Filters 11

12. 3.2.Fabric filters 4.Electrostatic precipitators

13. 5.Scrubbers Scrubber systems are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. It is a pollution control devices that use liquid to wash unwanted pollutants from a gas stream. Industrial Scrubbers can also be used for heat recovery from hot gases by flue gas condensation. Used for scrubbing the obnoxious fumes such as silicon tetrafluoride, HNO3, HCl, NH3, Phosphoric acid, super phosphate & Fluorine. Types of scrubbers: A) Dry scrubber U sed for the removal of odorous and corrosive gases. Can be categorized as dry sorbent injectors (DSIs) or as spray dryer absorbers (SDAs) DSI involves the addition of an alkaline material (usually lime or soda ash) into the gas stream to react with acid gases. Dry scrubbing systems are used to remove acid gases such as Sulphur dioxide and HCl, primarily from combustion sources. 13

14. B) Wet scrubber 14

15. 5.5 CONTROL OF GASEOUS EMISSIONS There are two classes of techniques by which gaseous pollutants may be removed from an effluent stream: 1. Sorption of pollutant Absorption in liquids Adsorption on a solid surface 2. Chemical alteration of pollutant Combustion Catalytic treatment 1. Absorption by liquids One of the most frequently used technique for controlling concentration of gaseous pollutants Absorption is a process in which a gaseous pollutant is dissolved in a liquid Involves transfer of pollutant from gas phase to liquid phase across the interface in response to a concentration gradient Water is the most commonly used absorbent liquid As the gas stream passes through the liquid , liquid absorbs the gas Efficiency of this process depends on: a. Amount of surface contact between gas and liquid b. Contact time c. Concentration of the absorbing medium d. Speed of reaction between the absorbent and the gases 15

16. Gas absorption equipments Packed towers The liquid is distributed over the packing which provides high interfacial surface area and flows down the packing surface in the form of thin films or subdivided streams Normally the liquid and gas flow countercurrent to each other, the gas flowing upward and liquid downward 2. Plate or tray tower 3. Venturi scrubbers 16

17. 2. Adsorption by solids Adsorption is a surface phenomenon by which gas or liquid molecules are captured by and adhere to the surface of a solid adsorbent The attractive forces holding the molecules at the surface may be either physical( physical adsorption ) or chemical( chemisorption ) in nature Physical adsorption: The gaseous material condenses upon the surface of the solid accompanied by an evolution of heat Adsorbed material can be removed or desorbed by reducing the pressure or by increasing temperature Reversible process Chemisorption: Result of a chemical interaction between the solid and adsorbed material Usually irreversible with the higher heat of adsorption than physical Molecules are held on solid surface by chemical bonds and the original material undergoes a chemical change. 17

18. Stages of adsorption: First stage : Diffusion of pollutant from bulk gas phase to the external surface of solid Similar to diffusion of gas to gas liquid interface in absorption Second stage: Diffusion of gas molecules into the pores of the solid Third stage : Actual adsorption on the active sites in the pores Relatively fast compared to other stages. Adsorption techniques are widely used in: • Odor control for removing small quantities of pollutants present in large volume of air • For collecting valuable organic substances that cannot be picked up by scrubbing methods. Rate of adsorption depends on: • Concentration of material around the adsorbent • Surface area of adsorbent • Pore volume of adsorbent • Temperature, molecular polarity, and chemical nature of adsorbent surface 18

19. 3. Thermal methods -Combustion 19

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21. (ⅰ)Thermal incineration: ( ⅰⅰ ) Catalytic oxidation: The catalytic combustion technique is recommended for gases that are free of metallic substances which could poison catalyst. The catalyst bed is cleaned periodically9quarterly or annually) by scrubbing with water or sometimes with acid and by heating to high temperatures 21

22. 4. Condensation • Process of converting a gas or vapor to liquid • Any gas can be reduced to a liquid by lowering its temperature and/ or increasing its pressure • Condensers are typically used as pretreatment devices • Can be used ahead of absorbers , adsorbers and incinerators to reduce the total gas volume to be treated • Condensers used are : contact condenser and surface condensers Contact condenser: • Gas comes in contact with cold liquid 22

23. Surface condenser Gas contacts a cooled surface in which cooled liquid or gas is circulated, such as the outside of the tube 23

24. Previous year questions: APRIL 2018 MAY 2019 Write a note on principles of air pollution control (10) Discuss the advantages and disadvantages of scrubbers (10) Discuss the method used for control of particulate matter (10) Explain the different techniques used for controlling gaseous contaminants (10) DECEMBER 2019 Explain high volume air sampler. (10) Describe the equipment’s used for the control of emission of particulate pollutants. (15) Describe the various control methods for the removal of gaseous pollutants. (15) SEPTEMBER 2020 Explain various control methods for the removal of gaseous pollutants. (12) Explain the working of an Electrostatic precipitator for particulate emission control. Also explain its advantage and disadvantage (8) Explain high volume air sampler (12) 24

25. THANKYOU 25