air and noise pollution

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Air and Noise Pollution

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  • 1

    ATMOSPHERE

    The atmosphere is an envelope of gases that surrounds the earth. The air we breathe is the

    part of atmosphere. Scientists have divided the atmosphere into four main parts, each with its own

    characteristics. They are:

    1. Troposphere

    2. Stratosphere

    3. Mesosphere

    4. Thermosphere

    1. Troposphere:

    The layer of atmosphere that touches the surface of earth is called Troposphere. The

    troposphere extends to a height of about 8 to 18 kilometers above the surface of earth.

    Most of the living organisms come under troposphere. This layer contains most of the water

    vapors in the atmosphere and this is only the layer in the atmosphere where weather changes occur.

    2. Stratosphere:

    Beyond the troposphere, reaching at a height of about 50 kilometers above the surface of

    earth is Stratosphere. Most jet planes travels in the lower level of stratosphere. The upper level of

    stratosphere contains a layer of gases called OZONE.

    3. Mesosphere:

    After the layer of stratosphere, there is another layer called Mesosphere which is extended

    up to 85 kilometers above the surface of earth. The mesosphere is the coldest layer of the

    atmosphere. Its temperature can be as low as -100 oC.

    4. Thermosphere:

    Thermosphere is the most outer layer of atmosphere. Unlike the mesosphere, thermosphere

    has a very high temperature reaching up to 2000 oC

    Biosphere:

    The living environment, known as biosphere consist of Land (Lithosphere), Water

    (Hydrosphere) and Air (Atmosphere) is the basic layer to sustain Food and

    .

    AIR POLLUTION

    (1) Air:

    Atmosphere is the column of air that surrounds the earth, starting from the surface of earth

    to the altitude of 18 Km called Troposphere. Air is blanket of gases that contain:

    Nitrogen 78.09% by volume, Oxygen 20.94% by volume and other gases like Carbon, Argon,

    Neon, Helium, Methane, etc. These are in pure and perfect harmony.

  • 2

    (2) Pollution:

    Air polluted due to the presence of one or more than one contaminant present in the air in

    sufficient quantity, composition and characteristics which causes injury to life as well as damages

    the materials and properties.

    Organic are: Methane, Benzene, formaldehyde, chlorinated hydrocarbons

    AND

    Inorganic are: NOX, SOX, COX, H2S, HF, NH3.

    (3) Control:

    A. Naturally self cleansing way of the environment

    1. Dispersion

    2. Gravitational settling

    3. Natural Absorption process

    4. Rain out

    5. Adsorption

    B. Controlling Air Pollution source through engineering devices.

    1. Stationary Source and

    2. Mobile Source

    Stationary Source:

    a. Absorption

    1a.) - Wet Scrubbers

    2a.) - Dry Scrubbers

    b. Combustion

    c. Fuel Gas Desulphurization

    d. Particulate Pollutants

    Mobile Sources:

    a. Fundamentals of different available engines

    b. Control

    Dispersion:

    Dispersion of pollutants by winds reduces the concentrations of air pollutants by moving the

    smog from one place to another. This diluted the smoke but not remove it.

    To calculate it mathematically a model has been developed to estimate the concentration of

    the particular pollutant for the specific location and time.

  • 3

    Gravitational Settling:

    Gravitational Settling is the most important natural mechanism under which large particles

    from the ambient air settle down on the buildings, trees and other objects.

    This process helps in removing large amount of particles formed by uniting of the smaller

    particles over the large particles, till the united particles becomes large and heavy enough to settle

    down under the gravity.

    Natural Absorption Process:

    The gaseous as well as particulates pollutants from the air get collected in rain or mist and

    settle down with that moisture. This phenomenon takes place below the cloud level, when falling

    rain drops absorb pollutants also known as wash out or scavenging.

    This does not remove particles less than 1 micro meter. The gaseous pollutants are removed

    in dissolved state with moisture either with or without chemical damages.

    Rainout:

    In this process precipitation in the clouds where sub micro particles in the atmosphere in the

    clouds serve as a condensation nuclei around which drops of water may form and fallout as rain

    drops. This increases the rainfall and fog formation in the urban areas.

    Adsorption:

    This is the phenomenon in which gaseous or the liquids pollutants present in the ambient air

    we kept attracted, generally electro statically by a surface where they are concentrated and retained.

    Natural surface such as soil, rocks, leaves, and blades of grass, buildings and other objects

    can absorb and retain pollutants. The particles may come in contact with such surfaces either by

    gravitational settling or by internal impaction.

    Absorption:

    Control devices work on the principle that they absorb and transfer the pollutant smoke

    from gas to the liquid state.

    It is a mass transfer process in which gas is dissolved in the liquid. This conversion may or

    may not accompanied by a reaction with water.

    This is purely a diffusion process where pollutants move from higher concentration to the

    lower concentration.

  • 4

    Scrubbers:

    It is one of the most common pollution control device used by the industries. It is operated

    on a very simple principle that the polluted gas is brought into contact with the absorbent so that the

    pollutants can be removed.

    There are two types of Scrubbers: Wet Scrubbers and Dry Scrubbers. Mechanism of both

    the scrubbers is almost same. The only difference is in case of Dry Scrubbers End Product is in

    solid form while in case of Wet Scrubbers it is found in liquid form.

    Combustion:

    When the contaminant in the gas is oxidize able to an inert gas than combustion for

    contaminant control is used.

    There are two methods are used commercially as:

    1) Direct Flume Combustion

    2) Catalytic Combustion.

    Direct flume combustion:

    This method used when:

    1) The gas stream must have an energy concentration greater than 3.7 MJ/m3. At this

    concentration the gas flume will be self supporting after ignition, below this point the

    supplementary fuel is required.

    2) None of the by-products of combustion be toxic.

    In some cases the combustion byproducts may be more toxic than the original pollutant gas. For

    example the combustion of trichloroethylene will produce Phosgene, which was used as a war gas

    in World War I.

    Direct flume applied to Varnish cooking, meat smoke house and paint bake oven emission.

    Catalytic Combustion:

    Some catalytic materials enable oxidation to be carried out in gases that have an energy less

    than 3.7 MJ/m3.

    Active catalyst is a platinum or Palladium compound.

    Supporting lattice is usually a Ceramic.

    These are expensive, liable to poisoning by sulfur and lead compounds in trace amounts.

    Catalytic combustion has successfully applied to printing press, varnish cooking and asphalt

    oxidation emission.

  • 5

    Fuel Gas Desulphurization (FGD):

    The technology that employs absorbent, usually lime or limestone, to remove SO2 from the

    gases produced by burning fossil fuels. Flue gas desulphurization is the current technology for

    major SO2 emitters, like power plants.

    Lime is used to remove SO2 from coal fired power station gases (called FGD) the product is

    Gypsum.

    CaO(s) + SO2 (g) + 2H2O (1) + O2 (g) CaSO4. 2H2(s)

    This system may used with the scrubbers or in the towers through two broad ways.

    Regenerative (Reusable)

    Non regenerative. (Not reusable)

    In terms of the number and size of system installed, the non-regenerative system dominates.

    Cyclone:

    For particle size greater than above 10 um, the collector of choice is the cyclone.

    This is inertial collector with no moving parts.

    The particulate gas is accelerated through a spiral (round) Motion, which imparts a

    centrifugal force to the particles. Due to which the particles by force come out of the gas and

    impact on the cylinder wall of the cyclone. Then they slide to the bottom of the cone, where they

    are removed through an air tight valving system.

    The efficiency of collection of various particle sizes can be determined through an

    expression given below.

    [(9 B2 H)]

    d0.5=

    [p Qg ]

    As the diameter of the cyclone is reduced, the efficiency of collection increased, pressure

    drop also increases which ultimately increases the power requirement for moving the gas through

    the collector.

    With the increase in the efficiency tangential velocity remains constant and the efficiency

    increases with increase in the power consumption by using multiple cyclones in parallel.

    Filter:

    When the high efficiency controls of particles smaller than 5um are desired than we use

    filters.

    There are two types of filters in use 1 deep bed filters 2 the bag house.

  • 6

    The deep bed filters resembles like a furnace filter, having packing of fibers used to block

    the particles of the gas stream, used in air conditioner