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8/8/2019 Power Plant Presentation

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30/10/2010

ENVIRONMENTAL POLLUTION

DUE TO POWER GENERATION

& ITS CONTROL


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Introduction

The electric power demand iscontinuously increasing.Simultaneously the electric utilities

are faced with harmful impuritiesejected by the power plants. Thepower engineering specialists aretrying to develop and implement theeffective means in the field ofenvironmental protection from harmfuleffects of power plants.


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Introduction contd

The mainly affected parts ofenvironment are air, water and land.

It can be avoided if power plants are

located far from the populated areas.The pollution from nuclear power

plants is the radio active based in the

form of gases liquids and solidswhose radio active property may

retain for no. of years.


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STEAM POWER PLANTS

POLLUTANTS

Conventional fuels for steam power

plants are coal oil and gas whichcontributes in a large measure to air

pollution.


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Water Softening & Ash handling

Fly Ash are the ash particles which are mixed

with the flue gases. Fly ash is one of the

residues generated in the combustion of coal.Fly ash is generally captured from the

chimneys of coal fired power plants, and is one

of two types of ash that jointly are known as

coal ash; the other, bottom ash

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FLY ASH REMOVAL

The flue gases coming out of the boiler are mixed

with the AMMONIA (NH3), so that the ash particles

present will react with ammonia and forms

ammonium sulphate ((NH3)2SO4), which is wet andhence when passed through electrostatic

precipitator, under the influence of the electric field

produced, attracts these small particles together and

forms big clusters or lumps which are then

separated out. These lumps are then sent to thestorage tanks or silos and hence can be USED FOR

cement and brick manufacturing.

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Bottom Ash Removal

Bottom ash are the ash particles, which are the direct

ash obtained under the boilers bottom portion.

Bottom ash is removed by mixing it with the water. This is

treated in the EFFLUENT TREATMENT PLANT, where this

ash mixed water is fed to large tanks and gravity settling

process or natural sedimentation is carried out

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Water Treatment

Natural Water supplies contains solid,

liquid and gaseous impurities and as

such this water cannot be used for

generation of steam in boilers.

The various impurities are:

Dissolved salts of calcium, sodium and

magnesium

Dissolved gases such as CO2, SO2 and

oxygen

Mineral acids30/10/2010


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The salts of calcium and magnesium

are extremely harmful

When water containing them isheated and steam is generated they

precipitate as solid residue and form

hard scale on wall surface, this scale

hampers the process of heat transfer.

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Water softening is the act of reducing

the dissolved calcium, magnesium,

and to some degree manganese andferrous iron ion concentration in hard

water. A common water softener is

sodium carbonate (Na)2CO3

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The main pollutants are

CO

CO2

SO2

Nitrogen Oxides(NO,NO2)

Dust

Fly ash


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Effects of Pollutants:1-Carbon monoxide

With incomplete combustion of fuel,

hydrocarbons(CH4,C2H4) CO is

produced it combines with the

haemoglobin in the red blood cellsand thus interfere with their function

of supplying Oxygen to the blood

tissues. In this way CO is veryinjurious to health causing respiratory

problems.


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2-Carbon Dioxide

Thermal power plants contribute

substantially CO2 which has harmful

effects on atmospheric climate which

could turn fertile land into deserts if inexcess amount and also causes

green house effect. Therefore the

implications and control of CO2 need

priority study.


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3-SO2

SO2 is the main pollutant from steam

power plants its primary source is

combustion of bituminous coal and

residual oil fuel. Vegetables are mostsensitive to the SO2 gas. Its toxic

effect is associated with deterioration

of the surfaces of leaves due todestruction of their chlorophyll.


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4-Nitrogen Oxides

Nitrogen Oxides are collectivelyreferred to Nitrogen Dioxide (NO2)

and Nitric Oxide (NO).

Both are toxic and produce sharpirritating effect. People living in NO2

contaminated areas suffer from

reduced respiratory function and have

higher probability of respiratory

diseases.


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Acid rains is another effect caused by

thermal power plants.

Three main constituents of flue gases

which mainly effect the acidity of rain

are SO2, CO2 and Nitrogen Oxides

which are readily converted intoSulphuric acid 60%, Carbonic acid

5% and Nitric acid 35%. These affect

the acidity of lake, well water andrivers.


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Dust

The further detrimental effect ofpower plants is the yielding of smoke,dust and fly ashes. The quantity of

ash per Kg of fuel burnt is given byQ=K*W/100(1+P/(100-P))

where K=fraction of solid particlescarried off from furnace

W=ash contents in % age

P=contents of combustible in fly ashin %age


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Fly ash

It emits heat to the atmosphere aswell as small particles . Large quantity

of heat discharged also causes

pollution. Toxic substances canproduce harmful effect on biosphere.

Biosphere is the atmospheric layer

near the earth surface.


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During high temp. combustion the

pollution can be minimised by suitablesolution of following

1)-Combustion process

2)-burning gas with excess air3)-correct stabilisation of flame

4)-choice of proper length and

diameter of furnace chamber.


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Control of Particulate Matter

Steam power plants use followingmechanical arrestors for removal of

dust particles.

Fabric filters

Electrostatic precipitators

A high degree of pollution control is

obtained over particles larger than 2

to 3 microns. About 95% of fly ash

which is under 2 microns is difficult

to remove.


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Irrespective of the all the steps taken

to remove the particulates from

exhaust gases about 1% is alwaysdischarged to the atmosphere.

The particulates effect can be

reduced byCoal cleaning

Using improved electrostatic

precipitator designTo control the dust this is done by

increasing the height of the chimney

thus reducing the concentration.


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Furnaces burning coal throw dust in

the form of fly ash and collector must

be installed to remove ash particles.

Smoke has deadly effect on vegetation

because of the sulphur products in it.

Smoke corrodes metals and darkenspaints.

Fuels should be completely burnt to

reduce the quantity of dust particlesinto the atmosphere.

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