AIR POLLUTION

DefinitionAir pollution may be defined as the presence

in the air (outdoor atmosphere) of one or more contaminants or combinations thereof in such quantities and of such durations as may be or tend to be injurious to human, animal or plant life, or property, or which unreasonably interferes with the comfortable enjoyment of life or property or conduct of business.

Sources of air pollution :

Natural - Dust storms, volcanoes, lightning, etc.

Man-made - industrial activities,automobile exhaust, agricultural,

domestic conditions,

Pollutants of air

Particulate pollutants - are solids or liquids with size

< 100 microns that remain suspended in the atmosphere.

Dust Fumes Smoke Mist Fog

Bacteria

Gaseous - Toxic and poisonouse.g. CO, chlorine, NH3, H2S, SO2, NO2, CO2.

POINT AND NONPOINT SOURCES

Point sources--- crusher, factories, etc

Non point sources ---- mobile sources – vehicles ,road traffic, air craft emissions etc.

Major PollutantsMajor Pollutants

OzoneOzone Transient damageTransient damagePermanent damagePermanent damage

-accelerated aging of the -accelerated aging of the lunglung Carbon monoxideCarbon monoxide

- heart disease - heart disease - lung diseases - lung diseases - central nervous system- central nervous system

response to external response to external stimuli stimuli (symptoms similar (symptoms similar of flu)of flu)

- Normal individual during - Normal individual during strenuous strenuous workwork

Nitrogen DioxideNitrogen Dioxide

Short term -Short term - respiratory infectionsrespiratory infections trigger asthmatrigger asthma

lung function lung functionrespiratory irritationrespiratory irritation

Long-term -Long-term - chronic damage (emphysema) chronic damage (emphysema)

Suppression of immune system Suppression of immune system

ability to fight off bacterial & viral ability to fight off bacterial & viral infectionsinfections

body's ability to generate antibodies body's ability to generate antibodies ability to remove foreign particles ability to remove foreign particles

LeadLead- - Nerve damage Nerve damage

IQ IQ perceptual motor skills perceptual motor skills

- Anemia- Anemia- Kidney damage - Kidney damage - High blood pressure - High blood pressure

Sulfur dioxideSulfur dioxide

- Trigger asthma especially in children- Trigger asthma especially in children

sulfur dioxide affects adults and children sulfur dioxide affects adults and children differently and that chronic and acute effects differently and that chronic and acute effects may also be differentmay also be different

Particulate MatterParticulate Matter

- Cancer - Cancer- Asthmatic attacks in children- Asthmatic attacks in children- Eye and throat irritation - Eye and throat irritation - Headache- Headache- Lightheadedness- Lightheadedness- Nausea - Nausea - Perception of unpleasant odors- Perception of unpleasant odors- Lung inflammation.- Lung inflammation.

Primary and secondary Primary and secondary pollutantspollutants

• Primary pollutant : put directly into the atmosphere Primary pollutant : put directly into the atmosphere by human or natural activity.by human or natural activity.

– Soot from smokeSoot from smoke

• Secondary Pollutant : forms in the atmosphere by Secondary Pollutant : forms in the atmosphere by chemical reactions with primary pollutants, air or chemical reactions with primary pollutants, air or both. An example would be ground level ozoneboth. An example would be ground level ozone

- ground level ozone: emissions from car - ground level ozone: emissions from car react with the UV rays and then mix with the O2 in react with the UV rays and then mix with the O2 in the atmosphere.the atmosphere.

Effects of Air Pollution and Global Warming

-Rising Sea Level

-Change of precipitation and local climate conditions; acid rain

-Alteration of forests and crop yields

-Expansions of deserts into existing rangelands

-More intense rainstorms

-Not all long-term effects can be determined

Environmental Effects of Air pollution

Ecosystem effects Property damage Quality-of – life effects Global climate change

What Is Being Done: Alternatives

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Renewable Energy Sources

Solar EnergiesWind Power

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Biomasshttp://www.ca.blm.gov/news/images/geothermal.gif

Geothermal

Changes In Vehicle Systems

Hybrid

Fuel Cell

Battery-Electric

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Particulate Pollutants Cyclone Bag Filters Scrubbers Electrostatic precipitation (ESP)

CYCLONE Rotating motion of gas stream generates a

centrifugal force and throws the particle outside radially towards the wall

Gas moves up from inner portion of the cyclone chamber

Particle slides down the cyclone and are collected Centrifugal force or the particle separation factor

depends upon the inlet velocity (V) and radius (R) of the cyclone as V2/gR

Efficiency increases when the diameter of the cyclone is less

Cyclones have an efficiency range from 60 to 90% but may not effectively remove particles of less than 20 micron size

No moving parts and can be easily installed for handling large volumes of gas

Performance of a cyclone is affected by Temperature of influent gas variations in flow velocity and volume Humidity conditions shape, size of influent particle concentration

Cyclone Installation at Wood Working Planthttp://www.fkinc.com/cyclones.htm

ESP (electrostatic precipitator)

ESP Used in cement, power and metallurgical industries High capability to treat large gas flows under high

temp Corrosive environment Removal of sub micron particles Effluent gas passes in a high electric field and gets

ionized Negatively charged particulates move towards

positively charged collecting electrodes and attached to the surface

Two steps while using the precipitator To setup an electric field between the

electrodes for the formation of ions To charge the particles and the

electrodes oppositively to create migration and attachment of particles

STEPS INVOLVED IN ESP Impart electrostatic charge to particles Create electric field in flow region Particles develop force of attraction Particles migrate towards oppositively

charged electrodes Electrodes collect the impurities Particulate dust is removed by shaking

electrodes Dry particulate matter is collected in the

hopper below

TWO ESP’S PIPE AND PLATE TYPE In pipe type discharge electrode is a wire suspended in a pipe

with sufficient weights to maintain the position Precipitation takes on the inner wall surface In plate type precipitator collecting electrodes and discharge

electrodes are kept in parallel position Corona forms between the plates Dust particles become highly charged and migrate and

attached to the collecting electrodes Removes particle greater than and less than 1 micron size Efficiency of removal almost 100% High capital cost Sensitivity to inflow variations

ESP

http://www.powerspancorp.com/news/precipitator.shtml

BAG FILTERS These filters consist of porous structure material,

which has the property to retain the particulate matter as the dirty gas passes through the voids of filter

Air flows from the bottom and flow out along its sides

Forming a dust cake inside the filter Common packing material used is nylon, wool ,

Teflon etc Filter material should be resistant to gas temp and

the nature of gas and it has to resist abrasion and chemical reactions

95-99% efficiency Removal of fine particles 1 micron size Cleaning is done by shaking or sending air

in reverse direction with high velocity at periodic intervals

Fine particles penetrate through fabric and also cause rupture of cloth which may be difficult to locate, repair or replace

Reactive gases and chemical particles attack the filter media

As the filter cannot withstand high temperature suitable coatings should be provided on the filter surface

Humidity should be controlled since hygroscopic dust creates problems

WET SCRUBBERS These are collecting devices where water captures

dust particles and drain to sump 0.1 to 20 micron size particles are removed in this

units Preferred in foundries, mining operations and

metallurgical industry Spray towers, venturi scrubbers, cyclone and

packed bed scrubbers are usually used In simple spray chamber water may be flowing in

the downward direction and traps the impurities

The chamber may be packed to improve the contact and collection efficiency

In cyclone scrubber polluted air is tangentially swirled around whereas water sprinkles in to the chamber continuously

In venturi scrubber high velocities at the throat section atomize the liquid

Particle strikes against moving droplets because of the velocity difference between the droplets and particles ,droplets accelerate in the throat section

Very efficient for the removal of particulate greater than 0.5 microns

CYCLONE WITH VENTURI

Better capture between the high velocity collision particles and atomized water droplets

Reliable with high collection efficiency Removes corrosive chemical dusts that may

be difficult to remove in filters or ESP’s Highly soluble gases like NH3,HCL, HF are

also removed