Environmental Engineering-II - PowerPoint Presentation

Slide1

Environmental Engineering-II

Prof. Rajesh

Bhagat

Asst. Professor,

CED, YCCE

,

Nagpur

B.

E. (Civil

Engg

.) M. Tech. (

Enviro

.

Engg

.)

GCOE

, Amravati VNIT, Nagpur

Achievement

Selected Scientist, NEERI-CSIR, Govt. of India.

GATE Qualified Three Times.

UGC - NET Qualified in First Attempt.

Selected Junior Engineer, ZP

Washim

.

Three Times Selected as UGC Approved Assistant Professor.

Assistant Professor, PCE, Nagpur.

Assistant Professor, Cummins College of

Engg

. For

Women.

Topper of

PhD

Course Work at UGC-HRDC, RTMNU

Nagpur.

Mobile No

.:-

8483002277 / 8483003474

Email

ID

:-

rajeysh7bhagat@gmail.com

Website:-

www.rajeysh7bhagat.wordpress.com

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UNIT-VI

Introduction to Air Pollution,

Meteorological Parameters.

Monitoring Methods.

Techniques of Air Pollution Control.

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What is Environment ?

Natural world

Surrounding in which we liveLife sustaining system in which various living and non-living things are inter-relatedCollection of all the external factors or conditions influencing the life of the organisms

3

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Why it is important to study air pollution:-

Man can Survive for 5 weeks without food,

For 5 days without water,

But cant survive 5 minutes without air

Man consumes 2 liters water per day

Man breaths on an avg. 25000 times a day at a rate of 1-2 liters per breath

It means requires enormous quantity of air for his survival and it goes into direct contact with the most sensitive organs of the human body.

In water Conc. Of lead More than 300000ug/m3 is harmful.

In air conc. Of lead more than 1.5ug/m3 is harmful.

Once it is discharged in the atmosphere then it is impossible to control.

Air pollutants can transfer from one point to other and can give adverse effect

…..

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Pollution

is defined as the excessive discharge of undesirable substances into the environment, adversely altering the natural quality of the environment and causing damage to humans, plants and animals.

Water Pollution

Soil Pollution

Air Pollution

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What is Air Pollution ?

Perception

(When did you last say – Hey, that is air pollution ?)

Visible

(smoke, dust, chimney smoke) (Grey Scale)

Odour

(petrol, diesel, H

2

S, bleaching powder)

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How will you define Air Pollution?

Air pollution

is the presence of one or more contaminants in the ambient atmosphere which is injurious to living and non-living things or which unreasonably interfere with the comfortable enjoyment of life and property.

Air pollution

is the presence of foreign matter in the air either gaseous or particulate or combination of both which is dangerous to the health and welfare of human beings.

Air pollution

is the excessive concentration of foreign matter in the air which adversely affects the human-being or living things or causes damages to property.

Air pollution

is the presence of substances in air in sufficient concentration and for sufficient time, so as to be, or threaten to be injurious to human, plant or animal life, or to property, or which reasonably interferes with the comfortable enjoyment of life and property. Air pollutants arise from both manmade and natural processes.

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What is clean air ?

:- 78.1% Nitrogen + 20.9% Oxygen + 1% Trace

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Composition of Dry Atmospheric Air

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Natural and Artificial Sources of Air Pollution

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Air pollutant:-

A substance in the air that can cause harm to humans and the environment is known as an air pollutant.

The ambient air quality

may be defined by the concentration of a set of pollutants which may be present in the ambient air we breath in. These pollutants may be called criteria pollutants.

Ambient air quality

refers to the quality of outdoor air in our surrounding environment. It is typically measured near ground level, away from direct sources of

pollution.

Emission standards

express the allowable concentrations of a contaminant at the point of discharge before any mixing with the surrounding air.

Emission standards

are legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes.

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Types of Air Pollutants:

Primary Air Pollutant:

Harmful substance that is emitted directly into the atmosphere.

Ex. Natural Contaminants, Particulate Matter (PM), Sulfur dioxide, Oxides of Nitrogen, Carbon Monoxide, Carbon Dioxide, Hydrogen Sulfide, Hydrogen Fluoride, Hydrocarbons, Volatile Organic Compounds (VOC), Toxic M

etals

, such as

lead

,

cadmium

and

copper

,

Chlorofluorocarbons (CFCs), Ammonia (NH3), Odors, Noise, etc.

Secondary Air Pollutant:

These are not emitted directly but formed in the atmosphere when a primary air pollutant reacts with substances normally found in the atmosphere or with other air pollutants.

Examples

are ground level Ozone, Smog (Photochemical Smog),

Peroxy-Acytyl

Nitrate (PAN), Formaldehyde, Acid Mist, etc.

Some pollutants may be both primary and secondary

: that is, they are both emitted directly and formed from other primary pollutants.

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17

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Table 6.1 Air Pollutants (16)

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Major Classes of Air Pollutants:

Particulate Material (Dust, Fog, Mist, Fumes)

Oxides of Nitrogen ( NO, NO

2, NO

3

)

Oxides of

Sulphur

( SO

2

, SO

3

,

etc)Oxygen compound (CO, CO2, O3)Hydrocarbons (VOC, CH4, Non CH4)

Slide20

Air Pollutants:-

Natural Contaminants:-

Ex. Natural Fog, Pollen grains, bacteria, and product of volcanic eruption.

Pollen is important because of its peculiar properties irritating to some individuals.

It discharged into atmosphere from plant, vegetation, weeds, trees grass, etc.

Many people suffers from

asthama

or hey fever & bronchitis.

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Aerosols (Particulate Matter):-

(200

ug/m3)

Ex. Dust, Smoke, Mist, Fog, & Fumes.

Solid or liquid particle of microscopic size suspended and dispersed in a gas or atmosphere.

They range from 0.01 to 500 u.

Aerosol also defined as a colloidal system in which the dispersion medium is a gas and the dispersed phase is a solid or liquid.

They differs widely in terms of particle size, particle density and their importance as pollutants.

PM

10

& PM

2.5

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Dust:-

Small solid particle generated by crushing, grinding, blasting of material. range from 1u to 200u.

Can settle under gravity.

Ex. Fly Ash, Cement, Foundry dust, etc

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Smoke:-

Aerosol particle resulting from incomplete combustion.

size less than 1u.

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Fog:-

Liquid particle formed by condensation of vapour.

Visible aerosol

Dispersed phase is liquid

Reduces visibility less than 0.5 km

Size range from 1u to 40u.

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Mist:-

Liquid particle formed by condensation of vapour.

Water droplet in air of size 40u to 500u

Visibility

upto

1km or more

Low concentration of dispersion of liquid particle of large size.

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Fumes:-

Very fine solid particle.Size 0.001 to 1u.

Unpleasant smelling airborne effluent.

Generated by condensation from the gaseous state and often accompanied by a chemical reaction such as oxidation.

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Gases:-

Ex.

Sulphur Dioxide,

Oxide of Nitrogen,

Hydrogen

sulphide

,

Carbon Monoxide,

Carbon Dioxide,

Hydrogen Fluoride,

Hydrogen Chloride,

Hydrocarbons,

Aldehydes

, Radio active gases, CFC, etc.

Slide28

Sulphur

Dioxide:- 80ug/m3

Principal constituents of air pollutants.Combustion of fuel specially coal.

Sulphur content of fuel.

Crude petroleum product contain1% to 5% of

sulphur

content.

Fuel gases contain

sulphur

but small quantity.

Another source is metallurgical operations.

Many ores like zinc, copper, lead are primarily

sulphides

.Sulphuric acid plant.Paper manufacturing plant.Incinerator.

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29

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Oxides of Nitrogen:- 80ug/m3

2

nd most abundant atmospheric contaminants.Highest conc. Of

NOx in effluent from industry where nitric acid is used.

Next highest conc. is in automobile exhaust.

Large power plant, low heat burners, furnace etc. also contribute.

High temp. processes.

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Carbon Monoxides:- 2000ug/m3 (0.03%)

Odourless & colourless gas.

Dangerous gaseous pollutant.

Produced from incomplete combustion of carbonaceous matter.

Chief source is automobile exhaust.

Loss of consciousness, concentration, headache, retardation of mental activity, weakness,

etc

Reacts with

haemoglobin

of blood to give

carboxy

haemoglobin.

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Hydrogen

Sulphide

:- 2ug/m3 (Rotten egg emits.)

highly toxic, flammable & Foul smelling gas.

Anaerobic biological decay processes.

Volcanoes & water springs.

Kraft pulp industry, petroleum refineries, coke-oven plants & chemical processes.

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Carbon Dioxide:- CO

2

Occurs naturally in the atmosphere.Essential ingredient in photosynthesis, the process by which plants make food and energy,

Released due to respiration by animal & plant.

Deforestation and the burning of fossil fuels such as coal

Eruption of volcanoes, forest fires, biological decay, etc.

Green house gas increase mean ambient temp & mean sea level.

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Hydrogen Fluoride:- HF

Major- Manufacturer of phosphate fertilizer, aluminum industry, brick plants, etc.

Minor - Other metallurgical operations & burning of coal.More important in terms of injury to vegetation & animal than human

.

Hydrogen Chloride:-

HCl

Industrial Chemical processes.

Effects on respiratory irritation from chlorine.

Damage to vegetation.

Corrosion

.

Chloro

Fluro Carbon:- CFCNon-toxic, non-flammable & non-carcinogenic.But harmful or damages to ozone layer allows UV rays to reach the earth surface.

A.C., Refrigerator, Sprays, etc.

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Aldehydes:-

Combustion of gasoline, diesel, oil, fuel, & natural gas.

Incomplete oxidation of motor fuel & lubricating oils.Irritates to eyes

.

Radioactive Gases:-

Nuclear power reactor & related fuel handling facilities.

Experimental accelerator, testing of nuclear bombs, agricultural, industrial , medical use of radioactive isotopes.

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Ozone:-O

3

In the earth’s upper atmosphere ozone plays imp. role by providing a shield from UV rays but Ozone at GL is harmful air pollutant.

Not emitted directly in the air but it is created by chemical reaction between

NOx

& VOC in presence of sunlight.

3O

2

  

( + NO2 catalyst & Sunlight)

    ==>   2O

3

Breathing Ozone trigger health problems like asthama, chest pain, coughing, throat irritation & congestion.Reduces lung function & inflame the lining of lungs.

Slide37

Smog:-

Combination of smoke & fog.

Photochemical & Coal Induced smog.

Restricted & highly motorized area in metro cities.

Occurs under adverse meteorological condition when air movement is restricted.

Reduces visibility, causes eye irritation, damages to vegetation & cracking of rubber.

Prolonged exposure may result high mortality rate.

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Photochemical Smog

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Fig. 6.2 Air Pollutant Sources (16)

Slide40

Acid Mist / Acid Rain:-

Acid mist or acid rain

is any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure.

Slide41

PAN (

Peroxy

Acytyl Nitrate):-

Produced from the combination of hydrocarbons, and nitrogen dioxide in the presence of sunlight and heat.

Hydrocarbons + O

2

+ NO

2

+ light → CH

3

COOONO

2

(PAN)

The general equation is CxHyO3 + NO2 → CxHyO3

NO

2

Cause eye irritation, damages to plant, skin cancer, etc.

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Formaldehyde:-

It is organic chemical prevalent in environment.Colourless gas with pungent odour from family of gases aldehyde.

It is formed by numerous natural sources & anthropogenic activities.Released from through biomass combustion / forest fires, decomposition & through volcanoes.

Power plant, incineration, automobile exhaust, etc.

Cause cancer.

Irritation to respiratory tract.

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Effects of Air Pollution on Human Health:-

Man easily affected by air pollution. Inhalation of air pollutants through respiratory system gives direct impact on human health.

Factors affecting impact of air pollutants on man are :-

Type of air pollutant.

Concentration of air Pollutant.

Duration of exposure of air pollutant.

Health condition of the receptor.

Age group of the receptor.

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Effects of Air Pollution on Human Health:-

Cause irritation to the eye.Cause nose & throat irritation.SO2 & PM: Irritate respiratory tract and causes damages to lungs.

NO2: Causes airway restriction

CO: reduces

oxygen

carrying capacity of blood, Causes headache, fatigue, drowsiness, death.

CO increase stress on those suffering from cardio-

vascullar

& pulmonary disease.

Ozone: Causes burning eyes, coughing, and chest discomfort

Gases like H

2

S, amonia, etc. cause odour nuisance.Increases mortality rate & morbidity rate.Pollen initiate asthamatic attack.Chronic pulmonary disease like bronchitis & asthama are aggravated by SO2, NO2, PM, Smog, etc.

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Effects of Air Pollution on Human Health:-

HF cause diseases of the bone (fluorosis) & molting of teeth.Carcinogenic agents causes cancer.PM (Dust) cause respiratory disease like silicosis, asbestosis, etc.

Heavy metals like lead cause poisoning.Retardation of mental activity.

Loss of concentration, weakness, etc.

Cause skin cancer.

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Effects of Air Pollution

Table 6.2 Air Pollutant Effects (16)

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Effects of Air Pollution on Animal:-

Two step process:-Accumulation of the air borne contaminant in the vegetation & forage.Subsequent poisoning to the animals when they eat it.

3 Pollutants responsible for damage are Fluorine, Dust & Lead.Fluorine can cause rapid loss in weight, decline in health, poisoning, etc.

It may increase bone failure.

Arsenic in dust or spray on plants lead to poisoning of animal

Air pollutants can causes salivation, thirst, vomiting, uneasiness, irregular pulse & respiration.

Depressing effect on central nervous system.

Animal becomes dull & losses weight.

Can result in paralysis and death.

Acid rain falling in rivers, killing fish that are sensitive to pH fluctuations.

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Effects of Air Pollution on Plant :-

Interfere with plant growth.weakens plants and makes them more susceptible to insect infestation.Reduces the amount of light reaching the leaf by clogging the stomata & reduces CO2

intake & thus interfere with photosynthesis.Damages to leaves ( bleaching of leaves, collapse of leaf, necrosis of leaves, etc.)

Retard the yield.

Acute & chronic injury to plant.

Spoil the appearance of plant.

Air Pollutants affecting Plant:- SO

2

, PM, HF, O

3

,

NOx

, HCl, etc.

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Effects of Air Pollution on Material :-

Damages the material or metals by corrosion. SO2---SO3----H2SO4

CO2 in presence of moisture produces Carbonic acid, which is then leached out as water soluble bicarbonate.

PM adhere to building surfaces to produce unsightly coating.

Paint is also affected & requires frequent painting.

H

2

S is common cause of darkening of surfaces covered with paint.

SO

2

cause deterioration of natural & some synthetic textile fibers.

O3 cause pronounced fading of certain dyes on cotton & rayon fabrics.

Rubber can be damaged by cracking.SOx causes lather to lose its strength & ultimately disintegrate.

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Air Pollutants cause damage to material by 5 mechanism :-

Abrasion:-Solid particle of sufficient size & travelling at high velocities can cause abrasion action & accelerate wear.Deposition & Removal:-

Particle deposited on a surface may spoil appearance & also may cause some deterioration.

Direct Chemical Attack:-

React directly & irreversibly with material to cause deterioration. Ex. Bleaching of marble by SO

2

& etching of a metallic surface by acid mist.

Indirect Chemical Attack:-

Certain material absorbs some pollutants & get damaged when the pollutants undergo chemical changes. Ex. SO

2

absorbed by leather is converted to H

2

SO4, which deteriorates the leather.Corrosion:-Atmospheric deterioration of ferrous metal is by an electro-chemical process ie corrosion.

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Table 6.3 Air Pollutant effects (16)

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Table 6.4 Air Pollutant Effects (16)

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Effects of Air Pollution on Atmosphere

:Inversion.

Acid Rains.Climate Change.

Green

house

effects / Global warming.

Heat

Islands.

Photochemical

Smog.

Depletion of Ozone layer.

Eutrophication

.

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Effects of Air Pollution on Atmosphere:

Can cause visibility reduction.Change in precipitation.

Fog formation.

Solar radiation can be reduced.

Can cause alternation in temp. and wind distribution.

Global warming.

Humid condition.

Depletion of ozone layer.

Life of mosquitoes can be increased.

Can cause Heat Islands.

Acid Rains.

Water Logging.

Change in mean sea level, energy supply & demand, water sources availability, and its consequences etc.

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Heat Islands :-

Cities are warmer than their rural surroundings. In highly urbanized & industrialized area a difference in temp of 6 to 10

0C.

Cities are warmer, rainier and foggier.

Heat energy release causes a significant climate change.

Thermal capacitance of street, buildings & Industries for solar input & Energy dissipation.

Artificial production of energy approaches nearly 1000 watts/m2 while the solar absorption by the atmosphere averages out to be only 25 watts/m2.

Energy release may occur through evaporation of water and direct heat of air.

Further cone. Of GHGs may increase the heat content of urban area.

Inevitably disrupt the climatological & ecological balance.

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Write a note on ozone layer depletion?

Chlorofluorocarbons (CFCs) and other halogenated substances are mainly responsible for

ozone depletion.

One of the greatest and most dangerous effects of pollution

on the

ozone layer

is that it creates holes in the atmosphere, which allow powerful ultraviolet rays from the sun to reach the Earth's surface.

When CFCs reach the stratosphere, the ultraviolet radiation from the sun causes them to break apart and release chlorine atoms which react with

ozone

, starting chemical cycles of

ozone

destruction that

deplete

the ozone layer. One chlorine atom can break apart more than 100,000 ozone molecules. Effects of ozone layer depletion.

Skin Cancer:

exposure to UV rays from sun can lead to increased risk for developing of several types of skin cancers.

Eye Damage:

UV rays are harmful for our eyes too.

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Air Pollution Episodes:-

1930 -3 Day Fog in Meuse Valley, Belgium1931 -9 Day Fog in Manchester, England

1948 -Plant Emissions in Donora, Penn, US

1952 -5 Day Smog in London, England

1970 –Radionuclide Emissions, Three Mile Island, US

1984 -Release of Methyl

Iso-Cynate

(MIC) in Bhopal, India

1986 -Radionuclide Releases, Chernobyl, Ukraine 

1997 – Haze Disaster in Indonesia

2001 – Wildfires in Sierra Nevada, US

2001 – Enormous Clouds of Dust in New York during Collapse of World Trade Center, US

2002 – Violent Dust Storm in Queensland, Australia2005 - Jilin Chemical Plant Explosions, Jilin city, China2007 – Wildfires in TALLAHASSEE Florida, US

2008 - Kingston Fossil Plant Coal Fly Ash Slurry Spill, Kingston, US

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Bhopal Gas Tragedy:

On the night of December 2, 1984, the Union Carbide Pesticide Plant in Bhopal, India began to leak methyl Iso-Cyanate

gas and other poisonous toxins into the atmosphere.About 40 tons of toxic gases had leaked and spread throughout the city.

The Bhopal Disaster was the worst episode in the history of industrial air pollution.

Over 5,00,000 were exposed and there were up to 15,000 deaths at that time.

In addition, more than 20,000 people have died since the accident from gas-related diseases.

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Bhopal Gas Tragedy:

The cause was the entry of water into Methyl Iso-Cyanate (MIC) storage tank.

Resulting exothermic reaction increase the temp. inside tank above 200

0

C and raised the pressure. (BP of MIC is 39

0

C)

Safety system failed.

Gases were blown by wind towards city Bhopal.

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The Great London Smog

:- (The Killer Smog) 4th Dec.

1952

With the advent of industry, London’s population was accustomed to seeing foggy, pollution laden air.

In 1952 however, this pollution took a tragic turn in winter.

Weather was cold & residents burned more coal in their fireplaces to reduce the chill.

High-pressure air mass created a subsidence & temperature inversion.

The smoke with sulfur dioxide & nitrogen oxides and left London cover in a black cloud of near total darkness.

The old and respiratory affected died first, but younger people exposed to the outside atmosphere were also affected.

The maximum daily SO

2

concentration recorded at that time was 4000 µg/m

3, smoke levels were 4.46 mg/m3 & PM were 5 times higher than normal. The Great London Smog lasted for five days and lifted on 9th

Dec, resulting in about 12000 deaths & 100,000 illnesses.

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The Los Angeles Smog

:- July 1973.

Photochemical Smog episode.

Slide73

Donora (Washington) Fog, 27

th

Oct. 1948:-Horror visited the US Steel company town of Donora.The fog started building up in Donora on October 27, 1948, on the night when a temp. inversion started and made sudden attack on the town.

Fluoride emissions from the Donora Zinc Works smelting operation and other sources containing

sulphur

, carbon monoxide and heavy metal dusts were trapped by weather conditions.

Causing coughing and other signs of respiratory distress (pain) for many residents of the community.

Illnesses, asthma and deaths had taken place.

The smog continued until it rained on October 31, by which time 20 residents of Donora had died and approximately 2000 residents had been suffered.

Another 50 residents died of respiratory causes within a month after the incident.

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Meuse Valley, Dec. 1930 (Inversion) :-

First week of December 1930, when a thick mist lay over large parts of Belgium Country.

Several thousand cases of acute pulmonary attacks occurred in the densely populated valley of the Meuse. Resulting in 60 deaths.

The cause was poisonous products in the waste gas of the many factories in the valley, in conjunction with unusual climatic conditions.

The disaster in all probability had been brought about by

sulphur

dioxide (SO

2

) or oxidation products of that compound.

During that time, the day temperature was a little above freezing point while at night it measured up to 10

o

C below, while the wind speed was only 1-3km/hr.

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Meuse Valley, 1930

Slide77

Atmosphere:-

Insulating blanket protecting the earth.

Softens the intense light & heat of the sun.Ozone layers acts as protecting umbrella that absorbs dangerous UV rays.

Atmosphere is bound to the earth by gravity.

As we go higher & higher, the characteristics & composition changes.

Atmosphere is divided into four sphere.

Troposphere

Stratosphere

Mesosphere

Thermosphere or Ionosphere

77

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Atmosphere is divided into four sphere:-

Troposphere

Stratosphere

Mesosphere

Thermosphere or Ionosphere

Atmospheric Layers:-

Slide80

Mesosphere:-

Region where few energy release reaction occur.

Lapse rate is +

ve

(decrease in temp.)

Coldest layer of atmosphere.

This layer has no significance in air pollution.

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Ionosphere:-

Thermosphere

Very high temp. 870

0

c over equator

143

0

c over north pole.

Highest & vastest zone of atmosphere.

Starting at 115km above the earth

upto

600km.

Region beyond 600km is termed as exosphere.

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Atmospheric stability:-

The resistance of the atmosphere to vertical motion or mixing.Lapse rate :-

(vertical temp. gradient) Rate at which temp. changes with elevation is called lapse rate.

Lapse rate in a Dry Adiabatic Atmosphere is called DALR (10

0

c/km) & (WALR 6

0

c/km).

Actual lapse rate is called Environmental Lapse Rate

ie

ELR may be greater or less than the DALR.

ELR determines whether the air or atmosphere is stable or unstable.

If the air is unstable, the vertical movement of air is encouraged, & If the air is stable, vertical movement of air is discouraged.Super Adiabatic Lapse rate = Rate is more than DALR.Inversion = -ve lapse rate.

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Stability of atmosphere depending upon the vertical air temperature distribution :-

Very stable : Temperature increases with increase in altitude. This is a -

ve lapse rate, or an inversion.

Stable

: Environmental lapse rate is less than the dry adiabatic lapse rate, but temperature decreases with altitude increase.

Neutral

: Environmental lapse rate is the same as the dry adiabatic lapse rate.

Unstable

: Environmental lapse rate is greater than the dry adiabatic lapse rate.

Very unstable

: Environmental lapse rate is much greater than the dry adiabatic rate, and is called super-adiabatic.

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Stability

is the degree to which the atmosphere will support, tolerate, or suppress vertical motions.

In a stable atmosphere, a parcel of air that is displaced upwards will tend to return to its original level while in an unstable atmosphere, a parcel of air displaced upwards will continue to rise.

Fig. 6.9 Lapse Rate (16)

Slide85

Lapse Rate Example

Que.1:-

Assuming the surface temperature is 15° at the surface of the earth, what is the temperature at 5510.5 m? Take ELR = 6.49°C/km

Solution:

5510.5 m = 5.5105 km

For each km the temperature decreases by 6.49°c

So the temperature decreases: 5.5105 x 6.49 = 35.76°c

Original temp was 15°,

temp at 5.5105 km = 15°c - 35.76°c = -20.76°C

Slide86

Plume:

Plume refers

to the path and extent in the atmosphere of the gaseous effluents, released from a source usually a stack (chimney

)

The

behavior of a plume emitted from any stack depends on localized air stability.

By

looking at the plume one can state stability condition and dispersive capacity

of atmosphere

.

The

behavior and dispersion of a

plume entirely

depend on the environmental lapse rate Effluents from stacks are often injected to an effective height of several 100m above ground. The spread of the plume is directly related to the vertical temperature gradient:

Looping

Coning

Fanning

Lofting

Fumigation

Trapping

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Coning plumes

Shaped like a cone roughly 10

0

c with horizontal axis.

Coning plume gets resulted in when the vertical air temperature gradient has been between dry adiabatic and isothermal, the air being slightly unstable with some horizontal and vertical mixing occurring.

Coning is most likely to occur during cloudy or windy periods.

Fig. 6.14 Coning Plumes (16)

Slide88

Fumigation Plume

causes the high pollutant concentration plume reaching the ground level along the length of the plume and is caused by a super-adiabatic lapse rate beneath an inversion.

The super-adiabatic lapse rate at the ground level occurs due to the solar heating.

This condition has been favored by clear skies and light winds.

Usually start when a fanning plume breaks up into a looping plume.

Fig. 6.15 Fumigating Plumes(16)

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Trapping:

In stable atmosphere both above & below stack with an unstable atmosphere in between two inversion layer.

Diffuse only in the limited vertical height

Occur at any time of the day in any season.

Slide90

Fanning

Plumes

form under very stable conditions. (extreme inversion condition)spread out horizontally but do not mix vertically. take place when the air temperature increases with altitude (inversion or –

ve lapse rate).

The plume rarely reaches the grounds level unless the inversion is broken by surface heating or the plume encounters a hill.

At night, with light winds and clear skies, fanning plumes are most probable.

Fig. 6.11 Fanning Plumes (16)

Slide91

Lofting

Plumesform when there is a stable layer beneath unstable layer. diffuse upward but not downwards and occur when there is a super-adiabatic layer above a surface inversion.

generally not reach the ground surface.

a flat bottom and a rising top.

Fig. 6.12 Lofting Flumes (16)

Slide92

Looping plumes

take place when there has been a super-adiabatic lapse rate and solar heating. (Warm season)Wavy character occurs in a highly unstable atmosphere

bcoz of rapid mixing. (Day Time)

High turbulence disperse the plume rapidly but high conc. may occur close to the stack if plume touches the ground.

Fig. 6.13 Looping Plumes (16)

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94

Meteorology & Air Pollution:

Meteorology is the study and forecasting of weather changes resulting from large scale atmospheric circulationMeteorological parameter can trigger an air pollution episodes.

Once Pollutants Emitted:- Transported, Dispersed, Concentrated By meteorological conditions.

Parameters can be classified into primary and secondary depending upon importance.

Wind Direction & Speed

Atmospheric Stability

Temperature

Mixing Height

Precipitation

Humidity

Solar Radiation

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Wind Direction & Speed:-

Govern the drift & diffusion of air pollutants discharged.Higher the wind speed at or near the point of discharge, the more rapidly will carry away from the source and will disperse dilute with greater volume of air.

On the other hand, when wind speed are low pollutants tend to be concentrated near the area of discharge for longer periods.

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Temperature & Heat:-

Heat is the critical atmospheric variable.Comes from the sun as a short wave radiation.

After striking the earth it losses energy & reradiates to the space as a long wave radiation.

Some of radiation absorbed by the atmosphere & temp. increases

.

Atmospheric Stability:-

Ability to

resists

or enhance vertical motion.

Rate at which temp. changes is called lapse rate.

DALR = 10

O

C/Km & WALR = 6.5OC/Km (Neutral atmosphere)Reverse or -ve lapse means Inversion.

During Inversion, vertical air movement is stopped & pollution will be concentrated beneath the inversion layer.

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Mixing Height:-

Height above the earth surface to which related pollutants will extend.Primarily through the action of atmospheric turbulence.

Related to wind direction, wind speed & wind turbulence.

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Precipitation:-

Cleansing action on the air pollutants discharged onto the atmosphere.Removes the gaseous pollutants that are soluble in water.

Act as scrubbing fluid for the removal of air pollutants.

Thus it accelerates the deposition of pollutants on the ground.(water pollution & soil Pollution)

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Humidity:-

Measure of water vapour in atmosphere.

Always present in atmosphere & depends on temp.

Coastal regions & areas adjacent to huge water bodies are humid.

Moisture content of the atmosphere influence the corrosive action of air pollutants.

Also influence the potentiality for fog formation.

Humidity act as catalyst in the reaction of air pollutants like SO

2

, NO

2

, etc

.

Solar Radiation:-Depending on the location, solar radiation can have a pronounced effect on the type & rate of chemical reaction in the atmosphere.Photochemical smog formation at Los Angels is a typical example of the effect of solar radiation on air pollution.

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Stack Height & Effective Stack Height:-

Height

of the stack and the height of rise of the plume above the stack play a major role in the ground level conc. expected on the down wind side.The plume Rise depends upon many factors such as exit velocity, wind speed, diameter of stack, temp. of plume, lapse rate, etc.

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101

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H = h +

Δ

hWhere, H – effective height if stack h – Actual Height of stack Δh – The Rise of PlumeThere are several formulae are available to calculate the stack height.As per Emission regulation published by the central board for prevention and control of pollution, New Delhi, The chimney height is to be calculated according to the formulae.

PM :- H = 74 (Q) 0.27Where, Q = Particulate Matter Emission in

Tonnes

per Hour.

h = Height of Chimney in meters.

Gaseous Pollutants :- H = 14 (Q)

0.3

Where, Q = Gaseous Emission in Kg per Hour.

h = Height of Chimney in meters.

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Air Pollution Indices or Index (API)

It is system in which one can explain the quality of air to common man.

It is a scheme that transforms values of individual air pollution parameters into a single number.

Technical terms may not be known to public.

There must be easiest, understanding & simplified way to define quality of ambient air.

Criteria for Index:-

Easily understand by public

Include major air pollutants

Calculated in simpler manner

Based on scientific data

Meaningful

Relate to ambient air quality standards & goals

Can be forecasted a day in advance

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Air Pollution Indices or Index

API = ¼ (

Cspm /

Sspm

+

C

NOx

/

S

NOx

+ C

SO2

/ SSO2 + CCO / SCO) x 100 API =¼ (180.2 / 200 +98.5

/ 80 + 19.9

/ 80 + 2.55

/ 20) x 100

API = 89.84 ~ 90

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Air Pollution Indices or Index

Index Value

Remark

0-25Clean Air

26-50

Light Air pollution

51-75

Moderate Air Pollution

76-100

Heavy Air Pollution

>100

Severe Air Pollution

106

Other Rating:- Good, Acceptable, Satisfactory, Unsatisfactory, Unhealthy, Light Moderate, Heavy, Normal, Severe, etc.

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Wind Roses:-

Wind roses shows the prevailing direction of wind.

Defined as any diagram to show the distribution of wind direction experienced at a given location, over a considerable period.Wind data

ie Direction, duration, & intensity are graphically represented by a diagram called Wind Rose.

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Wind Roses:-

For accurate estimation of the dispersion of air pollutants in the atmosphere a knowledge of the frequency distribution of wind direction as well as wind speed is essential.

This type of information varies from city to city and varies for given city from month to month.

Wind data should be collected for a period of atleast

5 years and preferably of 1o years, so as to obtain an avg. data with sufficient accuracy.

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Wind Rose Construction:-

The most common form consist of circle from which eight or sixteen lines emerge, one for each direction.

Length of each line is proportional to the frequency of wind from that direction and frequency of calm conditions is entered in the entre.

There are many variation in the construction of wind roses. Some indicates the range of wind speeds from each direction & some relates wind direction with other meteorological condition.

Line or bar extending to the north on the wind rose indicates the frequency of winds blowing from the north.

Wind rose diagram is prepared using an appropriate scale to represent % frequencies of wind direction and appropriate index shades, lines, etc. to represent various wind speeds.

Observation corresponding to wind speed below 1Km/

Hr

are recorded as Calm.

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Special Pollution Wind roses are:-

Precipitation Wind Rose

Smoke Wind RoseSO2 Wind Rose

HC Wind Rose

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Air Pollution Controlling Technology:-

Air pollutants pose a great danger to the environment.

A removal of air pollutants from flue gases by a proper technology has a greater significance.

There are 3 broad approaches to the control of air pollutants:-

Control at source.

Control by using pollution control equipments.

Dilution in the atmosphere.

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1) Control at source:-

Most effective is to prevent emission at the source itself.

This can be achieved by investing various approaches at early stages of process design and development,

Selecting those methods which do not contribute to air pollution or have the minimum air pollution potential.

Control at source can be accomplished by:

Raw Material change

Process Change

Equipment Modification or Replacement

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a) Raw Material Change:-

Some raw materials are primarily responsible for causing air pollution.

Use of pure grade raw material is often beneficial and may reduce the formation of undesirable impurities and by-products or may even eliminate the trouble some effluents.

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b) Process Changes:-

Changing the process being used is still another important method of controlling emission at their source.

Ex. Washing the coal before pulverization to reduce the fly ash emission.

Ex. Reduction of the formation of NOx

in combustion chambers by low excess air combustion in two stages, fuel gas recirculation and water injection.

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c) Equipment Modification or Replacement:-

Another approach of control of pollutants at the source involves the proper use of existing equipments, modification and replacement of equipments.

Ex. The un-burnt CO & HC in the cylinders of an automobile engine can be burnt by injecting into hot exhaust manifold of the engine.

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2)

Dilution:-

Dilution of PM & gases can be accomplished by the use of tall stacks.Pollution released from taller stacks disperse easily & hence low ground level concentration are observed.

Thus, dilution is only a short term control measure & tends to bring about highly undesirable long range effects.

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3) Control by using Pollution Control Equipments:-

Particulates Air Pollution Controlling Devices

Gaseous Air Pollution Controlling DevicesTo remove the particulates from flue gases, various types of control equipments are available.

Controlling devices are divided into five major groups:

Gravity Settling Chamber,

Cyclone,

Fabric Filter,

Wet Scrubber &

Electrostatic Precipitator.

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Selection of Equipments depends on:-

Quantity of gas & its variation.

Nature & concentration of particulates.Temp. & pressure of the gas stream.

Quality of the treated effluent.

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Objectives of Air Pollution Controlling Equipment:-

Prevention of physical damage to property.

Elimination of health hazards.Recovery of valuable waste product.

Improvement of product quality.

Prevention of nuisance.

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Gravitational settling Chamber:-

The force of gravity removes only large PM by allowing them to settle in the chamber.

Gas stream enters a chamber where the velocity of gas is reduced to drop out the large particles from the gas stream.

Settled large size PM are collected in hopper at the bottom.

Used in conjunction with a more efficient control devices because this chamber removes only larger particles.

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Gravitational settling Chamber:-

Constructed as long horizontal box with inlet, outlet & dust collection hoppers.

Velocity of the particle laden gas stream is reduced in the chamber.All the particles are subjected to the force of gravity.

At reduced gas velocity in the chambers, the larger particles > 40u are settled into hoppers.

It mainly used as a pre-cleaner for other particle emission control devices to remove very large particles.

> 100um --- 25cm/s

10um --- 0.3cm/s

1 um --- 0.003 cm/s

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Cyclones:-

Simple mechanical device.

Used to remove relatively large particles from gas streamsUsed as pre-cleaner for more sophisticated air pollution control equipment. (ESP)

More efficient than settling chamber.

Forces are responsible for removal are centrifugal & gravitational.

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Cyclones:-

Shape of cyclones causes the gas stream to rotate in a spiral motion.

Larger particles move towards the outside of the wall by virtue of their momentum.Particles loss kinetic energy there & are separated from the gas stream.

After this because of gravitational force it falls down to get collected.

> 25um

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Wet Collectors :- (Wet Scrubber)

In wet scrubbing processes, liquid or solid particles are removed from a gas stream by transferring them to a liquid.

The liquid most commonly used as water.PM collection efficiency over 95%.

Requires low energy.

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Wet Collectors :- (Wet Scrubber)

Consist of a open vessel with one or more sets of spray nozzles to distribute the scrubbing liquid.

Gas stream enters at the bottom & passes upward through the sprays.The most common high energy wet scrubber is the

venturi scrubber.

Rain is the natural process of cleaning atmosphere or environment.

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Fabric Filter:- (Bag Filter or

Baghouses

)It uses a filter material such as nylon or wool to removes particles from the dust laden gases.The particles retained on the fabric material, while clean gas passes through the material.

Collected particles are then removed from the fabric filter by a cleaning mechanism which is either the mechanical shaking or by use of air blast.

Removed particles are the stored in a collection hopper.

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Fabric Filter:- (Bag Filter or

Baghouses

)Cyclones have lower collection efficiency than fabric filter.Depending upon the design & choice of fabric, PM control efficiency can be more than 99%.

Fabric filter are better able to reduce fine PM when they are not overloaded with larger PM.

Therefore best application of a bag filter includes a cyclone in a sequence.

Cyclone is good at removing larger particles, it complements the fabric filter well.

> 0.1um

Wet filter is better filter.

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Electro Static Precipitators :- (ESP)

Widely used in power plant.

PM is removed by the use of +vely charged & -

vely charged electrodes. (Electromagnetic field).

ESP have no moving parts.

Requires electricity.

Extremely effective in removing sub micron PM.

Expensive.

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Electro Static Precipitators :- (ESP)

At periodic intervals, the PM from charged plates are removed by rappers or hammers or vibrators depending on the design & collected into the bottom hopper.

Collection efficiency more than 98% for PM10.

ESP can handle hot flue gases at temp. up to 5700

C.

Compare to fabric filter ESP uses less energy & lower maintenance requirements.

Better separation efficiency.

> 0.1 um

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Control of Gaseous Pollutants :-

The control of gaseous pollutants from stack gases depends on their properties.

The methods of control include:

Combustion

Absorption

Adsorption

Condensation.

Bio-filter.

Advanced Oxidation by UV, O3,

HPO,etc

.

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Combustion :-

Organic compounds from different manufacturing operations are converted to innocuous carbon dioxide & water.

Devices are designed to push oxidation reactions to leave minimum unburned compounds.

Three methods of combustion commonly used in air pollution control are:-

Direct combustion

Thermal Combustion

Catalytic Combustion

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Direct Combustion :-

Gaseous air pollutants are burned directly in a combustor with or without aid of additional fuel such as natural gas.

Combustion process should be designed in such a way that the flame burns at any wind speed & any gas flow rate.

Mostly used in refineries & petrochemical plants.

Relatively safe method of highly combustible waste gases.

Economical only if the waste gases itself contribute more than 50% of total heating value required for incineration.

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Thermal Combustion :-

When conc. Of combustible pollutants is below the lower explosive limit, thermal incinerator is one of the choice for combustion.

This method is often used when the heating value of the waste gas in the range of 50-750 KJ/m3.

Waste gas stream is preheated in a heat exchanger & then passed through the combustion zone of a burner supplied with supplemental fuel.

Properly designed & operated incinerator can completely destroy the organic vapor from the exist gases.

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Catalytic Combustion :-

Accelerates the rate of a chemical reaction

Waste gas stream need not to be heated to high temp. as in thermal incineration.

Catalytic oxidation proceed through:-

Adsorption of the gas on the active surface

Chemical reaction of combustible with oxygen

Desorption of reaction product from the surface

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Absorption :-

Effluent gases are passed through absorber (scrubber) which contain liquid absorbents that remove one or more of the air pollutants.

Absorbent are being used to remove SO2, H2

S, SO3

, F &

NOx

.

Some of the absorbents are regenerative while other are of non-regenerative.

Some of the absorbing solution that are used in the removing different gaseous pollutants from gas stream are:-

SO

2

– Ammonia

Sulphate

, Alkaline Water, Calcium SulphateNOx -- Water, Nitric AcidH2S --

NaOH

& Phenol Mix

HF – Water &

NaOH

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Absorption :-

Efficiency of process depends upon:-

Amount of surface contact between gas & liquid.

Contact time

Conc. Of the absorbing medium

Speed of reaction between absorbent & gases

Major Equipments:-

Packed Bed

Plate Tower

Bubble Cap Tower

Spray Tower

Liquid Jet Scrubber

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Adsorption :-

Effluent gases are passed through adsorbent which contain solids of porous structure

Commonly used adsorbent include Activated Carbon, Silica Gel, Activated Alumina, Lithium Chloride, etc.

Adsorption is a surface phenomenon and requires very large solid surface area.

Adsorption equipment is generally the packed bed of some porous adsorbing material.

Efficiency of removal of gases depends on:-

Physical & chemical characteristics of the adsorbent.

The conc. & nature of the gas to be adsorbed.

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Adsorption :-

The commonly used adsorbent for removal of gases are:

SO2 --- Limestone

NOx

--- Silica Gel

VOCs ---- Activated Carbon

H

2

S --- Iron Oxide

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Condensation :-

Process of converting a gas to liquid.

Any gas can be reduced to a liquid by lowering its temp. and/or increasing its pressure.

Used as pretreatment device ahead of absorption, adsorption & combustion.

Condenser are of two types contact condenser & surface condenser.

Contact Condenser:- contact with cold liquid

Surface Condenser :- contact with cooled surface

Removal efficiency ranges from 50 to 95 % depending upon design & application.

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Bio-filter :- ( Biological Oxidation)

Used to destroy VOCs & odor by microbial oxidation of these problem compounds.

Most effective on water soluble material.

Polluted air passed is passed through a wetted bed, which support a biomass of bacteria that adsorb & metabolize pollutants.

Efficiency over 98% are possible.

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