Pollution Control Techniques

Pollution Control Techniques

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  FATIMAH JINNAH WOMENUNIVERSITY POLLUTION CONTROL TECHNIQUES ASSIGNMENT
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  POLLUTION CONTROL TECHNIQUES 2 ollutionis outlined because the presence of impurities or waste product substances in sufficient concentration levels, inflicting harmful effects on persons, animals, and flora or material resources once exposed for a sufficient length of your time, therefore reducing the standard of life within the surroundings. Pollution is that the impact of undesirable changes in our surroundings that have harmful effects on plants, animals and persons. Pollutants embrace solid, liquid or gasified substances gift in larger than natural abundance, manufacture because of act that have a determined impact on the environment. POLLUTANTS FROMINDUSTRIES: The nature and concentration of a waste product verify the severity of its harmful effects on human health. Impurities discharged directly from the supply of origin area unit called primary pollutants, for instance, CO, SO2, and NO. once contaminants like HC, NO, O3, mix within the atmosphere (moisture, sunlight) to create new merchandise like PAN (per-oxy acetyl group nitrate), organic compound air pollution, gas, that area unit called secondary pollutants. From an ecological perspective, pollutants are often classified as degradable, slowly degradable and non-degradable. The Degradable or known as as non-persistent pollutants are often apace counteracted by process. for instance domestic sewerage, discarded vegetables, slowly degradable or persistent pollutants area unit pollutants that stay within the surroundings for several years in an unchanged condition and take decades or longer to degrade. For example, insecticide (pesticides) and most plastics, the non-degradable pollutants can't be degraded by process. Once they're discharged into the surroundings they're troublesome to eradicate and still accumulate: for instance, toxic components like lead or mercury, and nuclear wastes. CAUSES: The ultimate reason for pollution is act itself. Pollution could be a human contribution to nature. Human activities principally include: industries for varied human desires each directly and indirectly, agriculture for food production and industrial desires, health look after health of persons and animals, transport for quality of persons, living accommodations for settlement in town or villages, energy for varied direct human and industrial desires. All of those activities contribute to pollution in a method or different and so causes miseries. All of them area unit aimed to be a part of human welfare programs. Together with welfare, all of them have brought the maladies of pollution. A vast array of industries will cause pollution contrary to fashionable perception that solely a industry will cause pollution. The character and intensity of pollution could also be completely different in numerous trades. In others, it's going to be invisible, indirect or negligible. In such a broad sense, no trade is freed from pollution. Table shows the classified list of industries inflicting differing kinds of pollution. P
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  POLLUTION CONTROL TECHNIQUES 3 Table:List of Industries causing different types of pollution Type of industries Type of pollution Manufacture of chemicals, pesticides, medicines Water pollution, air pollution Manufacture of gases Air pollution Cement, steel and other mine based industries Air pollution and solid wastes, noise pollution Textile industries and their ancillaries Water pollution, air pollution, noise pollution Transport vehicle manufacturing Solid wastes, noise pollution, air pollution Petroleum based industries Water pollution, air pollution Forest dependent industries Air pollution, solid wastes and sound pollution Food industries Water pollution, air pollution, food pollution Paper industries Water pollution, air pollution, solid wastes, sound pollution Sugar industry Water pollution, air pollution, solid wastes Brick industry Air pollution, water pollution Aircraft industry Solid wastes, water pollution, air pollution Electrical appliances and electric goods industries Solid wastes, air pollution IT based industries Air pollution Telecom industries Solid wastes and air pollution EFFECTS OF POLLUTION: Pollution produces physical and biological effects that vary from mildly irritating to lethal. The more serious of the two are the biological effects. The physical effects of pollution are those that we can see, but they include effects other than actual physical damage. Oils spills, killing fish birds, coal produce sox, particulates etc., are considered as physical effects. Air pollutants speed the erosion of statues and buildings, which in some instances, destroys works of art. The most serious result of pollution is its harmful biological effects on human health and on the food- chain of animals, birds, and marine life. Pollution can destroy vegetation that provides food and shelter. It disrupts the balance of nature, and, in extreme cases, can cause the death of humans. Pesticides, which include herbicides and insecticides, can damage crops; kill vegetation; and poison birds, animals, and fish. Most pesticides are non-selective; they kill or damage life forms other than those intended For example, pesticides used in an effort to control or destroy undesirable vegetation and insects often destroy birds and small animals. The biological effect of water pollution is its danger to our water supplies. Water pollutants are also dangerous to all forms of marine life. SOURCES OF POLLUTION: Nature contributes to pollution by eroding the soil casing silt to build up in streams and by volcanic eruptions that pollute the atmosphere. However, people cause most pollution problems in the world. The main sources of pollutants are agricultural, industrial, municipal and transportation operations.
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  POLLUTION CONTROL TECHNIQUES 4 Agriculturalpollutants include insecticides, herbicides, pesticides, natural and chemical fertilizers, drainage from animal feedlots, salts from field irrigation, and silts from uncontrolled soil erosion. Industrial operations produce a wide variety of pollutants. Industrial pollutants include acids from mines and factories, thermal discharges from power plants and radioactive wastes from mining and processing certain ores. Industries create pollutants by producing food, chemicals, metals, petroleum products, and poisons, as well as countless other by-products of our country’s technology. The primary municipal pollutants are raw or inadequately treated sewage. Other municipal pollutants include refuse, storm-water overflows and salts used on streets in wintertime. Transportation pollutants include emissions from aircraft, trains, waterborne vessels, and cars and trucks. Motor vehicles create most of our air pollutants through their release of unburned fuel vapors (hydrocarbons). POLLUTION CONTROL EQUIPMENT: Sometimes pollution control at source is not possible by preventing the emission of pollutants. Then it becomes necessary to install pollution control equipment to remove the gaseous pollutants from the main gas stream. The pollutants are present in high concentration at the source and as their distance from the source increases they become diluted by diffusing with environmental air. Pollution control equipment’s are generally classified into two types: (a) Control devices for particulate contaminants. (b) Control devices for gaseous contaminants. In the present book only the control devices for particulate contaminants are dealt with. CONTROL DEVICES FOR PARTICULATE CONTAMINANTS: (1) GRAVITATIONAL SETTLING CHAMBER: For removal of particles exceeding 50 µm in size from polluted gas streams, gravitational settling chambers are put to use. This device consists of huge rectangular chambers. The gas stream polluted with particulates is allowed to enter from one end.
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  POLLUTION CONTROL TECHNIQUES 5 Thehorizontal velocity of the gas stream is kept low (less than 0.3 m/s) in order to give sufficient time for the particles to settle by gravity. The particulates having higher density obey Stroke’s law and settle at the bottom of the chamber from where they are removed ultimately. The several horizontal shelves or trays improve the collection efficiency by shortening the settling path of the particles. (2) CYCLONE SEPARATORS (REVERSE FLOW CYCLONE): Instead of gravitational force, centrifugal force is utilized by cyclone separators, to separate the particulate matter from the polluted gas. Centrifugal force, several times greater than gravitational force, can be generated by a spinning gas stream and this quality makes cyclone separators more effective in removing much smaller particulates than can possibly be removed by gravitational settling chambers. A simple cyclone separator consists of a cylinder with a conical base. A tangential inlet discharging near the top and an outlet for discharging the particulates is present at the base of the cone. Mechanism of Action: The dust laden gas enters tangentially, receives a rotating motion and generates a centrifugal force due to which the particulates are thrown to the cyclone walls as the gas spirals upwards inside the cone (i.e. flow reverses to form an inner vortex which leaves flow through the outlet). The particulates slide down the .walls of the cone and are discharged from the outlet. (3) FABRIC FILTERS (BAGHOUSE FILTERS): In a fabric filter system, a stream of the polluted gas is made to pass through a fabric that filters out the particulate pollutant and allows the clear gas to pass through. The particulate matter is left in the form of a thin dust mat on the insides of the bag.
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  POLLUTION CONTROL TECHNIQUES 6 Thisdust mat acts as a filtering medium for further removal of particulates increasing the efficiency of the filter bag to sieve more sub micron particles (0.5 µm). A typical filter is a tubular bag which is closed at the upper end and has a hopper attached at the lower end to collect the particles when they are dislodged from the fabric. Many such bags are hung in a bag-house. For efficient filtration and a longer life the filter bags must be cleaned occasionally by a mechanical shaker to prevent too many particulate layers from building up on the inside surfaces of the bag. (4) ELECTROSTATIC PRECIPITATORS: The electrostatic precipitator works on the principle of electrostatic precipitation i.e. electrically charged particulates present in the polluted gas are separated from the gas stream under the influence of the electrical field. A typical wire and pipe precipitator consists of: (a) A positively charged collecting surface (grounded). (b) A high voltage (50 KV) discharge electrode wire. (c) Insulator to suspend the electrode wire from the top. (d) A weight at the bottom of the electrode wire to keep the wire in position. Mechanism of Action: The polluted gas enters from the bottom, flows upwards (i.e. between the high voltage wire and grounded collecting surface). The high voltage in the wire ionizes the gas. The negative ions migrate towards the grounded surface and pass on their negative charge to the dust particles also. Then these negatively charged dust particles are electro-statically drawn towards the positively charged collector surface, where they finally get deposited. The collecting surface is rapped or vibrated to periodically remove the collected dust-particles so that the thickness of the dust layer deposited does not exceed 6 mm, otherwise the electrical attraction becomes weak and efficiency of the electrostatic precipitator gets reduced. As
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  POLLUTION CONTROL TECHNIQUES 7 theelectrostatic precipitation has 99 + percent efficiency and can be operated at high temperatures (600°C) and pressure at less power requirement, therefore, it is economical and simple to operate compared to other devices. (5) WET COLLECTORS (SCRUBBERS): In wet collectors or scrubbers, the particulate contaminants are removed from the polluted gas stream by incorporating the particulates into liquid droplets. Common wet scrubbers are: (i) Spray Tower (ii) Venturi Scrubber (iii) Cyclone Scrubber (I) SPRAY TOWER: Water is introduced into a spray tower (Fig. 5.5.) by means of a spray nozzle (i.e. there is downward flow of water). As the polluted gas flows upwards, the particulates (size exceeding 10 µm) present collide with the water droplets being sprayed downward from the spray nozzles. Under the influence of gravitational force, the liquid droplets containing the particulates settle to the bottom of the spray tower. (II) CYCLONE SCRUBBER: The dry cyclone chamber can be converted into a wet cyclone scrubber by inserting high pressure spray nozzles at various places within the dry chamber. The high pressure spray nozzles generate a fine spray that intercepts the small particles in the polluted gas. The centrifugal force throws these particles towards the wall from where they are drained downwards to the bottom of the scrubber. REFERENCES:  www.yourarticlelibrary.com/essay/pollution  www.environmentalpollution  www.fibre2fashion.com  www.conserve-energy-future.com