1. Unit -3 AIR POLLUTION CONTROL 3.1. Concepts of control 3.2. Principles and design of control measures 3.3.Particulates control by gravitational, centrifugal, filtration, scrubbing, electrostatic precipitation 3.4. Selection criteria for equipment 3.5. Gaseous pollutant control by adsorption, absorption, condensation, combustion 3.6. Pollution control for specific major industries. 1MZCET/CIVIL/IV/CE6011/APM/3

2. 3.1 Concepts of control It cannot be fully prevented but can be controlled. 1.Preventative measures 2.Control measures using equipments. 1.Preventative measures (source control): Selection of suitable fuel. (Low sulphur coal in power plant, using of CNG). Modification in industrial process. Selection of suitable site and zoning for industrial unit. 2MZCET/CIVIL/IV/CE6011/APM/3

3. [A] Mobile Sources 1. Cleaner/Alternative Fuel: Vaporization of Gasoline should be reduced. Oxygen containing additives reduce air requirement e.g., ethanol, MTBE (Hazardous). – Methanol: (Less photochemically reactive VOC, but emits HCHO (eye irritant), difficult to start in winters: Can be overcome by M85 (85% methanol, 15% gasoline) – Ethanol: GASOHOL (10% ethanol & 90% Gasoline), – CNG: Low HC, NOx high, inconvenient refueling, leakage hazard. – LPG: Propane, NOx high 3.1 Concepts of control contd… 3MZCET/CIVIL/IV/CE6011/APM/3

4. 2. Three Way Catalytic Converter A three-way catalytic converter has three simultaneous tasks: Reduction of nitrogen oxides to nitrogen and oxygen. Oxidation of carbon monoxide to carbon dioxide. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water. 3.1 Concepts of control contd… 4MZCET/CIVIL/IV/CE6011/APM/3

5. [B] Stationary Sources Pre-combustion Control – Switching to less sulphur and nitrogen fuel Combustion Control – Improving the combustion process – New burners to reduce Nox – New Fluidized bed boilers – Integrated gasification combined cycle Post-Combustion Control – Particulate collection devices – Flue gas desulphurization 3.1 Concepts of control contd… 5MZCET/CIVIL/IV/CE6011/APM/3

6. 2. Control measures When source control not possible some measures taken to prevent pollution. Collecting pollutants by using equipments. Destroying the pollutants by thermal or catalytic combustion. Changing the pollutants to less toxic form. By releasing the pollutants through tall chimneys for greater dispersion. 3.1 Concepts of control contd… 6MZCET/CIVIL/IV/CE6011/APM/3

7. Preventation by laws Various laws has been established for the menace of air pollution. Air (Prevention & control of pollution ) Act,1981. Air (Prevention & control of pollution ) Amendment Act,1987. Motor vehicle Act, 1988. Air (Prevention & control of pollution) Union Territories Rules, 1983. Environment Protection Act, 1986. 3.1 Concepts of control contd… 7MZCET/CIVIL/IV/CE6011/APM/3

8. The government is trying to : Remove the use of leaded petrol, a major cause of air pollution. The industrial acts are implemented to control the harmful emission of gases. The natural management team work to minimize the effect of various natural disaster like forest fire, volcanic eruption that are causes of air pollution. 3.1 Concepts of control contd… 8MZCET/CIVIL/IV/CE6011/APM/3

9. 3.2. Principles and design of control measures (ref : http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Environmental%20Air%20Pollution/air%20pollution%20(Civil)/Module- 3/3b.htm) Source Control Technology Air quality management sets the tools to control air pollutant emissions. Control measurements describes the equipment, processes or actions used to reduce air pollution. The extent of pollution reduction varies among technologies and measures. The selection of control technologies depends on environmental, engineering, economic factors and pollutant type. 9MZCET/CIVIL/IV/CE6011/APM/3

10. 1. Settling Chambers Settling chambers use the force of gravity to remove solid particles. The gas stream enters a chamber where the velocity of the gas is reduced. Large particles drop out of the gas and are recollected in hoppers. Because settling chambers are effective in removing only larger particles, they are used in conjunction with a more efficient control device. 3.2. Principles and design of control measures contd… 10MZCET/CIVIL/IV/CE6011/APM/3

11. 2. Cyclones The general principle of inertia separation is that the particulate- laden gas is forced to change direction. As gas changes direction, the inertia of the particles causes them to continue in the original direction and be separated from the gas stream. The walls of the cyclone narrow toward the bottom of the unit, allowing the particles to be collected in a hopper. The cleaner air leaves the cyclone through the top of the chamber, flowing upward in a spiral vortex, formed within a downward moving spiral. 3.2. Principles and design of control measures contd… 11MZCET/CIVIL/IV/CE6011/APM/3

12. Cyclones are efficient in removing large particles but are not as efficient with smaller particles. For this reason, they are used with other particulate control devices. 3.2. Principles and design of control measures contd… 12MZCET/CIVIL/IV/CE6011/APM/3

13. The difference in velocity and pressure resulting from the constriction causes the particles and water to mix and combine. The reduced velocity at the expanded section of the throat allows the droplets of water containing the particles to drop out of the gas stream. Venturi scrubbers are effective in removing small particles, with removal efficiencies of up to 99 percent. 3.2. Principles and design of control measures contd… 13MZCET/CIVIL/IV/CE6011/APM/3

14. 3. Venturi scrubbers Venturi scrubbers use a liquid stream to remove solid particles. In the venturi scrubber, gas laden with particulate matter passes through a short tube with flared ends and a constricted middle. This constriction causes the gas stream to speed up when the pressure is increased. 3.2. Principles and design of control measures contd… 14MZCET/CIVIL/IV/CE6011/APM/3

15. One drawback of this device, however, is the production of wastewater. Fabric filters, or baghouses, remove dust from a gas stream by passing the stream through a porous fabric. The fabric filter is efficient at removing fine particles and can exceed efficiencies of 99 percent in most applications. The selection of the fiber material and fabric construction is important to baghouse performance. 3.2. Principles and design of control measures contd… 15MZCET/CIVIL/IV/CE6011/APM/3

16. 3.2. Principles and design of control measures contd… The fiber material from which the fabric is made must have adequate strength characteristics at the maximum gas temperature expected and adequate chemical compatibility with both the gas and the collected dust. One disadvantage of the fabric filter is that high-temperature gases often have to be cooled before contacting the filter medium. 16MZCET/CIVIL/IV/CE6011/APM/3

17. 4. Electrostatic Precipitators (ESPs) An ESP is a particle control device that uses electrical forces to move the particles out of the flowing gas stream and onto collector plates. The ESP places electrical charges on the particles, causing them to be attracted to oppositely charged metal plates located in the precipitator. The particles are removed from the plates by "rapping" and collected in a hopper located below the unit. 3.2. Principles and design of control measures contd… 17MZCET/CIVIL/IV/CE6011/APM/3

18. The removal efficiencies for ESPs are highly variable; however, for very small particles alone, the removal efficiency is about 99 percent. Electrostatic precipitators are not only used in utility applications but also other industries (for other exhaust gas particles) such as cement (dust), pulp & paper (salt cake & lime dust), petrochemicals (sulfuric acid mist), and steel (dust & fumes). 3.2. Principles and design of control measures contd… 18MZCET/CIVIL/IV/CE6011/APM/3

19. 3.3 Particulates controlling equipments 1. Gravitational settling chamber Gravitational settling chambers are generally used to remove large, abrasive particles (usually >50 μm) from gas stream. It provides enlarged areas to minimize horizontal velocities and allow time for the vertical velocity to carry the particle to the floor. The usual velocity through settling chambers is between 0.5 to 2.5 m/s. Velocity of flue gas reduced in large chamber. Particles settle under gravitational force. 19MZCET/CIVIL/IV/CE6011/APM/3

20. Design of a gravitational settling chamber If we assume that Stokes law applies we can derive a formula for calculating theminimum diameter of a particle collected at 100% theoretical efficiency in a chamber of length Where v t =terminal settling velocity, m/s 3.3 particulates controlling equipment contd… 20MZCET/CIVIL/IV/CE6011/APM/3

21. Advantages Low initial cost. Easy to design. Low pressure drop. Low maintenance cost. Dry and continuous disposal of solid particulates. Disadvantages Require large space. Less collection efficiency. Only larger size particles can be collected. 3.3 particulates controlling equipment contd… 21MZCET/CIVIL/IV/CE6011/APM/3

22. 2. Cyclone separator Centrifugal force is utilized to separate the particulate matter. It can remove 10 to 50 μm particle size. Used mostly in industries. 3.3 particulates controlling equipment contd… 22MZCET/CIVIL/IV/CE6011/APM/3

23. A cyclone separator consists of a cylindrical shell, conical base, dust hopper and an inlet where the dust-laden gas enters tangentially. Under the influence of the centrifugal force generated by the spinning gas, the solid particles are thrown to the wall of the cyclone as the gas spirals upward at the inside of the cone. The particles slide down the walls of the cone and into the hopper. The operating efficiency of a cyclone depends on the magnitude of the centrifugal force exerted on the particles. The greater the centrifugal force, the greater the spreading efficiency. 3.3 particulates controlling equipment contd… 23MZCET/CIVIL/IV/CE6011/APM/3

24. Advantages Low initial cost. Require less floor area. Simple construction and maintenance. Can handle large volume of gas at high temp. Disadvantages Requires large head room. Less efficiency for smaller particles (<10μm). Sensitive to variable dust load and flow rate. 3.3 particulates controlling equipment contd… 24MZCET/CIVIL/IV/CE6011/APM/3

25. 3. Electrostatic precipitators The electrostatic precipitator is one of the most widely used device for controlling particulate emission at industrial installations ranging from power plants, cement and paper mills to oil refineries. Electrostatic precipitator is a physical process by which particles suspended in gas stream are charged electrically and, under the influence of the electrical field, separated from the gas stream. Works on the principle of electrical charging of particulate Matter (-ve) and collecting it in a +ve charged surface. 3.3 particulates controlling equipment contd… 25MZCET/CIVIL/IV/CE6011/APM/3

26. The precipitator system consists of a positively charged collecting surface and a high voltage discharge electrode wire suspended from an insulator at the top and held in passion by weight t the bottom. At a very high DC voltage, of the order of 50kV, a corona discharge occurs close to the negative electrode, setting up an electric field between the emitted and the grounded surface. 99% efficiency. Can remove particle size range of 0.1 μm to 1 μm. 3.3 particulates controlling equipment contd… 26MZCET/CIVIL/IV/CE6011/APM/3

27. The particle laden gas enters near the bottom and flows upward. The gas close to the negative electrode is, thus, ionized upon passing through the corona. As the negative ions and electrons migrate toward the grounded surface, they in turn charge the passing particles. The electrostatic field then draws the particles to the collector surface where they are deposited. Periodically, the collected particles must be removed from the collecting surface. This is done by rapping or vibrating the collector to dislodge the particles. The dislodged particles drop below the electrical treatment zone and are collected for ultimate disposal. 3.3 particulates controlling equipment contd… 27MZCET/CIVIL/IV/CE6011/APM/3

28. 3.3 particulates controlling equipment contd… 28MZCET/CIVIL/IV/CE6011/APM/3

29. Advantages High collection efficiency. Particles may be collected dry or wet. Can be operated at high temp. (300-450˚c). Maintenance is normal. Few moving parts. Disadvantages High initial cost. Require high voltage. Collection efficiency reduce with time. Space requirement is more. Possible of explosion during collection of combustible gases or particulates. 3.3 particulates controlling equipment contd… 29MZCET/CIVIL/IV/CE6011/APM/3

30. 4. Fabric filters Flue gas is allowed to pass through a woven Fabric, which filters out Particulate matter. Small particles are retained on the fabric. Remove particles up to 1 μm. Its efficiency up to 99%. 3.3 particulates controlling equipment contd… 30MZCET/CIVIL/IV/CE6011/APM/3

31. In a fabric filter system, the particulate-laden gas stream passes through a woven or felted fabric that filters out the particulate matter and allows the gas to pass through. Small particles are initially retained on the fabric by direct interception, inertial impaction, diffusion, electrostatic attraction, and gravitational settling. After a dust mat has formed on the fabric, more efficient collection of submicron particle is accomplished by sieving. 3.3 particulates controlling equipment contd… 31MZCET/CIVIL/IV/CE6011/APM/3

32. Filter bags usually tubular or envelope-shaped, are capable of removing most particles as small as 0.5μm and will remove substantial quantity of particles as small as 0.1μm. Filter bags ranging from 1.8 to 9 m long, can be utilized in a bag house filter arrangement. As particulates build up on the inside surface of the bags, the pressure drop increases. Before the pressure drop becomes too severe, the bag must be relieved of some of the particulate layer. Fabric filter can be cleaned intermittently, periodically, or continuously 3.3 particulates controlling equipment contd… 32MZCET/CIVIL/IV/CE6011/APM/3

33. Fabric and Fibre Characteristics: Fabric filter may be classified according to filtering media: Woven fabric or felt cloth. Woven fabrics have a definite long range repeating pattern and have considerable porosity in the direction of gas flow. These open spaces must be bridged by impaction of interception to form a true filtering surface. Felted cloth consists of randomly oriented fibres, compressed into a mat and needled to some loosely woven backing material to improve mechanical strength. 3.3 particulates controlling equipment contd… 33MZCET/CIVIL/IV/CE6011/APM/3

34. The choice of fabric fiber is based primarily on operating temperature and the corrosiveness or abrasiveness of the particle. Cotton is the least expensive fiber, and is preferably used in low temperature dust collection service. Silicon coated glass fiber cloth is commonly employed in high temperature applications. The glass fibre must be lubricated to prevent abrasion. All fibre may be applied to the manufacture of woven and felt type fabrics. 3.3 particulates controlling equipment contd… 34MZCET/CIVIL/IV/CE6011/APM/3

35. Fabric filter systems typically consist of a tubular bag or an envelope, suspended or mounted in such manner that the collected particles fall into hopper when dislodged from fabric. The structure in which the bags are hanged is known as a bag- house. Generally, particle laden gas enters the bag at the bottom and passes through the fabric while the particles are deposited on the inside of the bag. The cleaning is accomplished by shaking at fixed intervals of time. 3.3 particulates controlling equipment contd… 35MZCET/CIVIL/IV/CE6011/APM/3

36. Advantages Higher collection efficiency for smaller than 10 μm particle size. Performance decrease becomes visible, giving prewarning. Normal power consumption. Disadvantages High temp. gases need to be cooled. High maintenance and fabric replacement cost. Large size equipment. Fabric is liable to chemical attack. 3.3 particulates controlling equipment contd… 36MZCET/CIVIL/IV/CE6011/APM/3

37. 5. Wet gas Scrubbers Wet scrubber removes particulate matter from gas streams by incorporating the particles into liquid droplets directly on contact. The basic function of wet scrubber is to provide contact between the scrubbing liquid, usually water and, the particulate to be collected. This contact can be achieved in a variety of ways as the particles are confronted with so-called impaction target, which can be wetted surface as in packed scrubbers or individual droplets as in spray scrubbers 3.3 particulates controlling equipment contd… 37MZCET/CIVIL/IV/CE6011/APM/3

38. The basic collection mechanism is the same as in filters: inertial impaction, interception and diffusion. Generally, impaction and interception are the predominant mechanism for particles of diameter above 3 μm, and for particle of diameter below 0.3μm diffusion begins to prevail. There are many scrubber designs presently available where the contact between the scrubbing liquid and the particles is achieved in a variety of ways. 3.3 particulates controlling equipment contd… 38MZCET/CIVIL/IV/CE6011/APM/3

39. The major types are: 1.plate scrubber, 2.packed-bed scrubber, 3.spray scrubber, 4.venturi scrubber, 5.cyclone scrubber, 6.baffle scrubber, 7.impingement-entrainment scrubber, 8.fluidized-bed scrubber. 3.3 particulates controlling equipment contd… 39MZCET/CIVIL/IV/CE6011/APM/3

40. [A] Plate scrubber It contains a vertical tower containing one or more horizontal plates (trays). Gas enters the bottom of the tower and must pass through perforations in each plate as it flows countercurrent to the descending water stream. Collection efficiency increases as the diameter of the perforations decreases. A cut diameter, that collected with 50% efficiency, of about μm aerodynamic diameter can be achieved with 3.2-mm-diameter holes in a sieve plate. 3.3 particulates controlling equipment contd… 40MZCET/CIVIL/IV/CE6011/APM/3

41. [B] Packed –bed scrubber Operates similarly to packed-bed gas absorber. Collection efficiency increases as packing size decreases. A cut diameter of 1.5 μm aerodynamic diameter can be attained in columns packed with 2.5 cm elements. 3.3 particulates controlling equipment contd… 41MZCET/CIVIL/IV/CE6011/APM/3

42. [ C] Spray scrubber Particles are collected by liquid drops that have been atomized by spray nozzles. Horizontal and vertical gas flows are used, as well as spray introduced co-current, countercurrent, or cross-flow to the gas. Collection efficiency depends on droplet size, gas velocity, liquid/gas ratio, and droplet trajectories. For droplets falling at their terminal velocity, the optimum droplet diameter for fine particle collection lies in the range 100 to 500 μm. Gravitational settling scrubbers can achieve cut diameters of about 2.0 μm. The liquid/gas ratio is in the range 0.001 to 0.01 m3/ m3 of gas treated. 3.3 particulates controlling equipment contd… 42MZCET/CIVIL/IV/CE6011/APM/3

43. [D] Venturi scrubber A moving gas stream is used to atomize liquids into droplets. High gas velocities (60 to 120 m/s) lead to high relative velocities between gas and particles and promote collection. [E] Cyclone scrubber Drops can be introduced into the gas stream of a cyclone to collect particles. The spray can be directed outward from a central manifold or inward from the collector wall. 3.3 particulates controlling equipment contd… 43MZCET/CIVIL/IV/CE6011/APM/3

44. Spray tower Cyclone scrubber 3.3 particulates controlling equipment contd… 44MZCET/CIVIL/IV/CE6011/APM/3

45. [F] Impingement-Entrainment Scrubber: The gas is forced to impinge on a liquid surface to reach a gas exit. Some of the liquid atomizes into drops that are entrained by the gas. The gas exit is designed so as to minimize the loss of entrained droplets. [G] Fluidized-bed scrubber A zone of fluidized packing is provided where gas and liquid can mix intimately. Gas passes upward through the packing, while liquid is sprayed up from the bottom and/or flows down over the top of the fluidized layer of packing 3.3 particulates controlling equipment contd… 45MZCET/CIVIL/IV/CE6011/APM/3

46. Advantages Simultaneously remove particulates and gaseous pollutants. Hot gases can be cooled down. Corrosive gases can be recovered and neutralize. Disadvantages Lot of waste waters produced. Poses freezing problem in cold countries. Maintenance cost is high when corrosive materials are collected. 3.3 particulates controlling equipment contd… 46MZCET/CIVIL/IV/CE6011/APM/3

47. 3.4. Selection criteria for equipment There are a number of factors to be considered prior to selecting a particular in air pollution control equipment. In generally, they can group into three categories: 1.environmental, 2.engineering, and 3. economic 47MZCET/CIVIL/IV/CE6011/APM/3

48. (1) Environmental Equipment location, availability space, ambient conditions, availability of adequate utilities and ancillary system facilities. Maximum allowable emissions (air pollution regulation) Contribution of air pollution control system to wastewater and solid waste. Contribution of air pollution control system to plant noise levels. (2) Engineering Design and performance characteristics of the particular control system(size and weight, pressure drop, reliability and dependability, temperature limitation, maintenance requirement 3.4. Selection criteria for equipment contd… 48MZCET/CIVIL/IV/CE6011/APM/3

49. Gas stream characteristics (volume. flow rate, temperature, pressure, humidity.composition, viscosity m density, reactivity,corrosiveness, and toxicity ) Contaminant characteristics ( physical and chemical properties, concentration, particulate shape and size distribution in the case of particulates) (3) Economic Capital cost (equipment, installation, engineering, etc.) Operating cost (utilities, maintenance, etc.) Expected equipment lifetime and salvage value 3.4. Selection criteria for equipment contd… 49MZCET/CIVIL/IV/CE6011/APM/3

50. 3.5. Control of gaseous pollutants from stationary sources The most common method for controlling gaseous pollutants is the addition of add-on control devices to recover or destroy a pollutant. There are four commonly used control technologies for gaseous pollutants: - Absorption, - Adsorption, - Condensation, and - Incineration (combustion) 50MZCET/CIVIL/IV/CE6011/APM/3

51. 1. Absorption The removal of one or more selected components from a gas mixture by absorption is probably the most important operation in the control of gaseous pollutant emissions. Absorption is a process in which a gaseous pollutant is dissolved in a liquid. As the gas stream passes through the liquid, the liquid absorbs the gas, in much the same way that sugar is absorbed in a glass of water when stirred. Absorbers are often referred to as scrubbers, and there are various types of absorption equipment. 3.5. Control of gaseous pollutants contd… 51MZCET/CIVIL/IV/CE6011/APM/3

52. The principal types of gas absorption equipment include spray towers, packed columns, spray chambers, and venture scrubbers. In general, absorbers can achieve removal efficiencies grater than 95 percent. One potential problem with absorption is the generation of waste-water, which converts an air pollution problem to a water pollution problem. 3.5. Control of gaseous pollutants contd… 52MZCET/CIVIL/IV/CE6011/APM/3

53. When a gas or vapor is brought into contact with a solid, part of it is taken up by the solid. The molecules that disappear from the gas either enter the inside of the solid, or remain on the outside attached to the surface. The former phenomenon is termed absorption (or dissolution) and the latter adsorption. The most common industrial adsorbents are activated carbon, silica gel, and alumina, because they have enormous surface areas per unit weight. Activated carbon is the universal standard for purification and removal of trace organic contaminants from liquid and vapor streams. 2. Adsorption 3.5. Control of gaseous pollutants contd… 53MZCET/CIVIL/IV/CE6011/APM/3

54. Carbon adsorption systems are either regenerative or non- regenerative. - Regenerative system usually contains more than one carbon bed. As one bed actively removes pollutants, another bed is being regenerated for future use. - Non-regenerative systems have thinner beds of activated carbon. In a non-regenerative adsorber, the spent carbon is disposed of when it becomes saturated with the pollutant. 3.5. Control of gaseous pollutants contd… 54MZCET/CIVIL/IV/CE6011/APM/3

55. 3. Condensation Condensation is the 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. They can be used ahead of absorbers, absorbers, and incinerators to reduce the total gas volume to be treated by more expensive control equipment. Condensers used for pollution control are contact condensers and surface condensers. 3.5. Control of gaseous pollutants contd… 55MZCET/CIVIL/IV/CE6011/APM/3

56. In a contact condenser, the gas comes into contact with cold liquid. In a surface condenser, the gas contacts a cooled surface in which cooled liquid or gas is circulated, such as the outside of the tube. Removal efficiencies of condensers typically range from 50 percent to more than 95 percent, depending on design and applications. 3.5. Control of gaseous pollutants contd… 56MZCET/CIVIL/IV/CE6011/APM/3

57. 4. Direct combustor Direct combustor is a device in which air and all the combustible waste gases react at the burner. Complete combustion must occur instantaneously since there is no residence chamber. A flare can be used to control almost any emission stream containing volatile organic compounds. Studies conducted by EPA have shown that the destruction efficiency of a flare is about 98 percent. 3.5. Control of gaseous pollutants contd… 57MZCET/CIVIL/IV/CE6011/APM/3

58. In thermal incinerators the combustible waste gases pass over or around a burner flame into a residence chamber where oxidation of the waste gases is completed. Thermal incinerators can destroy gaseous pollutants at efficiencies of greater than 99 percent when operated correctly. 3.5. Control of gaseous pollutants contd… 58MZCET/CIVIL/IV/CE6011/APM/3

59. Catalytic incinerators are very similar to thermal incinerators. The main difference is that after passing through the flame area, the gases pass over a catalyst bed. A catalyst promotes oxidation at lower temperatures, thereby reducing fuel costs. Destruction efficiencies greater than 95 percent are possible using a catalytic incinerator. 3.5. Control of gaseous pollutants contd… 59MZCET/CIVIL/IV/CE6011/APM/3

60. 3.6. Pollution control for specific major industries Environment pollution accompanies each stage of any industrial process, starting with raw material and fuel production and ending with waste treatment. Some of the industries are 1.Petroleum Industry 2.Energy Production from Fossil Fuels 3.Inorganic chemical technology 4.Cement Industry 5.Organic Chemical Industry 6.Pulp and Paper 7.Iron and steel industry 8.Nonferrous metal industry 60MZCET/CIVIL/IV/CE6011/APM/3

61. 1. Petroleum Industry The petroleum industry includes various activities to explore for, produce, and transport oil and petroleum products worldwide. Besides the production of fuels and lubricating oils, large refineries integrated with petrochemical plants may produce many different synthetic derivatives— from pure chemicals to additives for fuels and lubricants, synthetic polymers, elastomers, etc. However, the world petroleum industry produces around 67 million tons of waste annually. 3.6. Pollution control for specific major industries contd… 61MZCET/CIVIL/IV/CE6011/APM/3

62. A. Pollution from Exploration and Production of Crude oil and Natural Gas: Air pollution from the production of oil and gas is by volatile hydrocarbons in fugitive emissions (mainly methane), as well as emissions from storage and manipulation. Exhaust combustion emissions are generated from compressors, pumps, drill engines and engines of servicing vehicles. Gas flaring is the major source of combustion emissions. The major source of secondary emissions is the water separated from the natural gas and crude oil. 3.6. Pollution control for specific major industries contd… 62MZCET/CIVIL/IV/CE6011/APM/3

63. B. Pollution from Storage, Manipulation, and Transportation of Petroleum Liquids: Air emissions from storage and transportation are mainly evaporative hydrocarbon emissions from manipulation— loading/unloading—and transit losses from storage tanks and tanks of transporting vehicles. Ballast water from transporting vessels and especially ocean- going tankers is the major source of secondary emissions, but also a major source of marine water pollution. Another source polluting underground water is leaking liquids from pipelines. Solid waste generated in storage and transportation is mainly sludge from the storage and transportation tanks. 3.6. Pollution control for specific major industries contd… 63MZCET/CIVIL/IV/CE6011/APM/3

64. C. Estimation of Pollution and Control Technologies for Petroleum Processing 1. Estimation of air pollution: Emissions to air from the petrochemical industry are usually presented as methane (CH4), carbon dioxide (CO2) and non-methane volatile organic compounds (VOCs). 1. Storage and handling emissions can be measured directly but are most often calculated. The most widely used control technologies include floating roofs, submerged filling, balancing the vapors from all tanks and collecting them in a separate tank, and condensation of excess vapors. 3.6. Pollution control for specific major industries contd… 64MZCET/CIVIL/IV/CE6011/APM/3

65. 2. Combustion emissions can be measured but on a larger scale are usually calculated from the amount and type of fuel burned in the particular burner. Typical control techniques are concentrated on improving the efficiency of combustion and diminishing heat losses. These include new types of burners, flue gases heat recovery, introducing new processes with lower energy consumption, etc. Flaring is used to control pressure and remove gas, which cannot be otherwise used. 3.6. Pollution control for specific major industries contd… 65MZCET/CIVIL/IV/CE6011/APM/3

66. 3. Fugitive emissions (equipment leak emissions) are the most difficult to characterize, because they come from an enormous amount of point sources. The control technologies include inspection and maintenance programs, and change of equipment with more advanced seal design modifications. 3.6. Pollution control for specific major industries contd… 66MZCET/CIVIL/IV/CE6011/APM/3

67. 4. Process emissions: Gas streams from all refinery processes are usually passed through gas treatment and sulfur recovery units to remove sulfur and recycle them to fuel gas. Particulates are captured in electrostatic precipitators or cyclone separators. Wet scrubbers may be used for catalytic cracking units in the future in order to eliminate catalyst fines. 3.6. Pollution control for specific major industries contd… 67MZCET/CIVIL/IV/CE6011/APM/3

68. The water systems of a production or processing site (tanks, ponds, sewer system drains, are the main source of secondary emissions. The main options for their control are diminishing the amount of wastewater and solid wastes and keeping wastewater and solid wastes in closed systems in order to control their release. 3.6. Pollution control for specific major industries contd… 68MZCET/CIVIL/IV/CE6011/APM/3

69. 2. Energy Production from Fossil Fuels Power production from burning fossil fuel led to extremely severe pollution of air, water and soil, through greenhouse gases and by damaging the land. Power generation is the most powerful source of emissions of sulfur dioxide and nitrogen oxides, non-comparable with any other industry. 3.6. Pollution control for specific major industries contd… 69MZCET/CIVIL/IV/CE6011/APM/3

70. a. Production, transportation and pre-combustion processing of fossil fuel and their contribution to environmental pollution: Coal is a major source of energy for power stations. Almost 40% of the world's electricity is generated from coal—more than twice the proportion from any other fuel. Coal causes environmental problems associated with the release of particulate matter (PM), soot, volatile organic compounds, carbon monoxide, and sulfur and nitrogen oxides. 3.6. Pollution control for specific major industries contd… 70MZCET/CIVIL/IV/CE6011/APM/3

71. b. Coal mining, its impact on environment and technologies for pollution control The environmental problems of power generation from coal combustion begin with its mining. Coal mining operations are sources of air pollution in the form of methane, coal or rock dust. Water pollutants are suspended and dissolved solids, sulfates, acidity and alkalinity. Acidity derives from oxidation of coal pyrites by the oxygen dissolved in water or contained in the pumped air. The overall effect of these reactions is the conversion of sulfur compounds into sulfuric acid. Back filling, grading, restoration, re-vegetation and post mining land uses are needed after surface mining. 3.6. Pollution control for specific major industries contd… 71MZCET/CIVIL/IV/CE6011/APM/3

72. C. Pre-combustion cleaning Pre-combustion cleaning is used to reduce the mineral and ash content in coal. Froth flotation is used for cleaning the fine classes of coal. Desulfurization, even partial, is a very important step in the pre-combustion cleaning of coal. Pyrites are removed (within 30-50%) by flotation. Distillate oils have negligible nitrogen and ash content with sulfur less than 0.3% (wt.). Residual oils contain significant quantities of metals, nitrogen, and sulfur. 3.6. Pollution control for specific major industries contd… 72MZCET/CIVIL/IV/CE6011/APM/3

73. Waste oils include used crankcase oils from automobiles and trucks, used industrial lubricating oils, and other spent industrial oils (i.e., heat transfer fluids). High levels of halogenated solvents are also often found in waste oil. The most common pre-treatment scheme for waste oil uses sedimentation followed by filtration. Blending of waste oil with a virgin fuel oil is practiced frequently and has the same effect as some of the pre- treatment processes. 3.6. Pollution control for specific major industries contd… 73MZCET/CIVIL/IV/CE6011/APM/3

74. d. Power generation from fossil fuels There are three main designs of combustion systems in which coal and air can be reacted, classified as fixed bed system, entrained (or suspended) bed system and fluidized bed system. The latter is characterized by sufficiently high velocity of the oxidizing gas to support or “float” the particles without carrying them out of the bed. A pressurized fluidized bed combustor (PFBC) system can drive both a gas turbine and a steam turbine. This arrangement is known as a combined cycle. 3.6. Pollution control for specific major industries contd… 74MZCET/CIVIL/IV/CE6011/APM/3

75. Coal gasification is one of the clean systems of power generation because sulfur, nitrogen compounds and particulates are removed before the fuel is burned. In an integrated combined cycle with coal gasification coupled with an advanced gas turbine, gas can be cleaned of more than 99% of its sulfur and ash and 90% of its nitrogen pollutants. The gas is burned in the gas turbine. Exhaust heat is used to produce steam for steam turbines. Coal gasification can also take place in situ. 3.6. Pollution control for specific major industries contd… 75MZCET/CIVIL/IV/CE6011/APM/3

76. 3. Cement Production from lime powder Besides steel and power the cement production of India is recognized as one of the most important industries. Cement industry is one of the 17 most polluting industries listed by the central pollution control board. It is the major source of particulate matter, SOx, NOx and CO2 emissions 76MZCET/CIVIL/IV/CE6011/APM/3

77. Cement dust contains heavy metals like chromium, nickel, cobalt, lead and mercury pollutants hazardous to the biotic environment with impact for vegetation, human health, animal health and ecosystem. India is the second largest producer of cement after China. The production process for cement consists of drying, grinding and mixing limestone and additives like bauxite and iron ore into a powder known as “raw meal”. 3.6. Pollution control for specific major industries contd… 77MZCET/CIVIL/IV/CE6011/APM/3

78. The raw meal is then heated and burned in a pre-heater and kiln and then cooled in an air cooling system to form a semi-finished product, known as a clinker. Clinker (95%) is cooled by air and subsequently ground with gypsum (5%) to form Ordinary Portland Cement (OPC). 3.6. Pollution control for specific major industries contd… 78MZCET/CIVIL/IV/CE6011/APM/3

79. Three criteria air pollutants are released to the air during cement manufacturing which includes particulate matter (PM), nitrogen oxides (NOX) and sulfur dioxide (SO2) which can be categorized into two headings: 1) Particulates 2) Gaseous pollutants 3.6. Pollution control for specific major industries contd… 79MZCET/CIVIL/IV/CE6011/APM/3

80. Particulates : Particulate air pollution is a complex mixture of small and large particles of varying origin and chemical composition. Larger particles, ranging from about 2.5 microns to 100 microns in diameter, usually comprise smoke and dust from industrial processes, agriculture, construction, and road traffic, as well as plant pollen and other natural sources. 3.6. Pollution control for specific major industries contd… 80MZCET/CIVIL/IV/CE6011/APM/3

81. The health effects of particulates are strongly linked to particle size. Small particles, such as those from fossil fuel combustion, are likely to be most dangerous, because they can be inhaled deeply into the lungs, settling in areas where the body’s natural clearance mechanisms can’t remove them. 3.6. Pollution control for specific major industries contd… 81MZCET/CIVIL/IV/CE6011/APM/3

82. S. No Particulate type Diameter 1 Cement Dust 80-90% greater than 30 µm 2Motor Vehicles 0.01-5000 µm 3`Urban road dust 3-100 µm 4Fly Ash 1-2000 µm 5 Coal Dust 3-100 µm 3.6. Pollution control for specific major industries contd… 82MZCET/CIVIL/IV/CE6011/APM/3

83. Gaseous pollutants Gaseous pollutants have major negative impacts on health. They also play an important role in environmental changes in atmospheric chemistry. SO2 and NO2 form acids through different chemical reactions in the atmosphere, and these acids are subsequently deposited on land and ocean surfaces as acid rain. 3.6. Pollution control for specific major industries contd… 83MZCET/CIVIL/IV/CE6011/APM/3

84. It is anticipated that the increasing load of atmosphere – sulfur dioxide (SO2), – nitrogen dioxide (NO2), – carbon dioxide (CO2), – carbon monoxide (CO), and – ozone (O3) will contribute to global climate change, consequently, it is necessary to quantify the emission in the very near future. 84MZCET/CIVIL/IV/CE6011/APM/3

85. Available air pollution control technologies and equipment Controlling particulate emissions from sources other than the kiln usually entails capturing the dust using a hood or other partial enclosure and transporting it through a series of ducts to the collectors. The type of dust collector used is based on factors such as particle size, dust loading, flow rate, moisture content, and gas temperature. The best disposal method for collected dust is to send it through the kiln creating the clinker. 85MZCET/CIVIL/IV/CE6011/APM/3

86. However, if the alkali content of the raw materials is too high, the dust must be discarded, or must be pre-treated before introduction into the kiln. The highest allowable alkali content is 0.6% (as sodium oxide). 1.Flexible Pulse Jet Filters Raw gas enters the filter compartments via inlet ducts equipped with guide vanes that distribute the gas uniformly across the filter bags. 86MZCET/CIVIL/IV/CE6011/APM/3

87. This arrangement creates a downward gravimetric gas flow along the filter bags, precipitating the dust into the hopper below. In contrast to filters where raw gas enters through dampers located in the hoppers, the design of the flexible pulse jet filter gas distribution system prevents the creation of high can velocities (or vertical, upward gas flow). High gas velocities prevent fine particulate from settling into the hoppers during on-line cleaning cycles. The raw gas is filtered by the fabric from the outside, and the clean gas exits at the top of the bag. The fan is located on the clean gas outlet side of the filter 87MZCET/CIVIL/IV/CE6011/APM/3

88. 88MZCET/CIVIL/IV/CE6011/APM/3

89. 2. Ordinary Bag House Method This is a filtration method and is one of the oldest and most efficient methods of particulate control. The most commonly-used filtration device is known as a bag-house and consists of fabric bags through which the air stream is directed as shown in Figure. Particles become trapped in the fibre mesh on the fabric bags, as well as the filter cake which is subsequently formed 89MZCET/CIVIL/IV/CE6011/APM/3

90. 90MZCET/CIVIL/IV/CE6011/APM/3

91. 2 marks 1. Explain the principle behind settling chambers. Particles in the air or gas stream settle due to gravity 2. Write down the various types of Inertial Separation Baffle type, Louvre type, Dust trap 3. Name the common method of filter cleaning Rapping, Shaking, Reverse air low, Pulse jet 91MZCET/CIVIL/IV/CE6011/APM/3

92. 2 marks contd…. 4. State the Principle of cyclone filter. Control of gas borne pollution, particulates using centrifugal and inertial methods 5. What is adsorption? Removal of impurities from a gas stream by concentration on the surface of solid or liquid 6. What are the Advantages of ESP – High collection efficiency – Particle as small as 0.1 mm can be removed – Low maintained and operating cost – Low-pressure drop (0.25 – 1.25 cm of water – Treatment time is negligible (0.1 – 10. s) 92MZCET/CIVIL/IV/CE6011/APM/3

93. 7. What are the Disadvantages of Esp High initial cost Space requirement is more Possible explosion hazards during collection of combustible gases or particles Poisonous gas, ozone, is produce by the negatively charged electrodes during gas ionization. 8. Briefly explain Bag filter The most common type of collector is tubular type, consisting of tubular bags. A bag house or bag filter consists of numerous vertical bags. They are suspended with open ends attached to a manifolds 2 marks contd…. 93MZCET/CIVIL/IV/CE6011/APM/3

94. 9. List out the type of Scrubbers Spray towers Venturi scrubbers Cyclone scrubbers Packed scrubbers Mechanical scrubbers 10. Define Impinger A sampling instrument adopting the principle of impingement for the collection of particulate matters. 2 marks contd…. 94MZCET/CIVIL/IV/CE6011/APM/3

95. 11. What is Bag house An air pollution control device that traps gas borne particulate by forcing the gas through filter bags 12. Define the term Contaminant Unwanted material usually harmful or of a nuisance value are both. 13. Define Cyclone filter A type of particulate collector which depends upon centrifugal force for its action. 2 marks contd…. 95MZCET/CIVIL/IV/CE6011/APM/3

96. 14. What is meant by Dry bulb temperature? The actual temperature of the gas. Measured with a conventional thermometer. 15. Define Fumigation The phenomenon in which pollutants that are aloft in the air are brought rapidly to GL when the air destabilizes. 16. What is Incineration? Combustion of solid, liquid, or gases wastes under controlled condition. 2 marks contd…. 96MZCET/CIVIL/IV/CE6011/APM/3

97. 17. What is meant by Inertial separators? Air pollution control equipment that utilizes the principles of inertial to remove particulate matter from a stream of air or gas. 18. What Is the Chemical Composition of Air? Atmosphere is made up of only five gases: nitrogen, oxygen, water vapor, argon, and carbon dioxide. Several other compounds also are present. Although this CRC table does not list water vapor, air can contain as much as 5% water vapor, more commonly ranging from 1- 3%. The 1- 5% range places water vapor as the third most common gas 2 marks contd…. 97MZCET/CIVIL/IV/CE6011/APM/3

98. 19. What is a wind rose? A wind rose is a circular display of how wind speed and direction are distributed at a given location for a certain time period. 20. What causes condensation? Condensation is the formation of liquid drops of water from water vapor. It is the process which creates clouds, and so is necessary for rain and snow formation as well. Condensation in the atmosphere usually occurs as a parcel of rising air expands and cools to the point where some of the water vapor molecules clump together faster than they are torn apart from their thermal energy. 2 marks contd…. 98MZCET/CIVIL/IV/CE6011/APM/3

99. 21. Combustion Definition: Combustion is a chemical reaction chemical that occurs between a fuel and an oxidizing agent that produces energy, usually in the form of heat and light. 22. Define Atmospheric Stability and Instability Atmospheric stability : The resistance of the atmosphere to vertical motion. This is due in part to the greater molecular activity of denser, more compressed air at lower altitudes. These conditions change throughout a 24-hour period, as the daytime solar heating and nighttime heat loss to and through the atmosphere tend to modify the temperature distributions. 2 marks contd…. 99MZCET/CIVIL/IV/CE6011/APM/3

100. 23.Define Stable and Unstable Air Weather is strongly affected by how stable or unstable the atmosphere is. Stable air means that the weather is likely to be calm. It may rain or snow slowly and steadily, it may be sunny, but the weather will not change quickly. Unstable air means that the weather might change quickly with very little warning. Unstable air leads to sudden thunderstorms. 24.Briefly explain the Control equipment in air pollution Any apparatus, devices, equipment or system to control the quality and manner of emission of any air pollution and includes any devices used for securing the efficient operation of any industrial plant. 2 marks contd…. 100MZCET/CIVIL/IV/CE6011/APM/3

101. 25. Define Due point For air containing water vapor, it is the temperature at which liquid water begins to condense for a given state of humidity and pressure, as the temperature is reduced. 26. What is Dust fall The weight of particulate matter deposited due to gravitational action per unit time per unit area of the surface. 2 marks contd…. 101MZCET/CIVIL/IV/CE6011/APM/3