AIR POLLUTION CONTROL

METHODS AND EQUIPMETS

PRESENTED BY

JINTO CV 1320214

LOVIN S ABRAHAM 1320217

What is Air Pollution Control ?

Air pollution control, the techniques employed to reduce or eliminate the emission into the atmosphere of substances that can harm the environment or human health.

The control of air pollution is one of the principal areas of pollution control, along with wastewater treatment, solid-waste management, and hazardous-waste management.

Top 20 polluted cities

PM2.5 refers to the

diameter measured in

microns of particulates

such as ammonia,

carbon, nitrates and

sulfate -- which are

small enough to pass

into the bloodstream

and cause diseases such

as emphysema and

cancer.

% contribution

What to control?

Control of particulate

Control of dangerous gases

Control system design

Design changes case by case

Influenced by Particulate characteristics

Corrosivity,

Reactivity,

Shape,

Density, and

Size

Other design factors

Air stream characteristics

Pressure

Temperature

Density

Flow rate

Control system design

continues….

Control of Particulate

1. Cyclones

2. Scrubbers

3. Electrostatic Precipitators

4. Bag house Filters

Waste goes to land fill

1.Cyclones

1.Cyclones

Advantages and Limitations

Best at removing relatively coarse particulates

Achieve 90% of efficiencies for particles larger than about 20 micrometers.

Cyclones are not sufficient to meet stringent air quality standards.

They are typically used as pre-cleaners and are followed by more efficient air-cleaning equipment such as electrostatic precipitators and baghouses

2.Scrubbers

Spray-tower scrubbers can remove 90 % of particulates larger than about 8μm.

3.Electrostatic precipitators

3.Electrostatic precipitators

Give electric charge to particulate

Remove particulates by electric field

1,00,000 Volts DC current is used for charging particles

can remove particulates as small as 1 μm with an efficiency exceeding 99 percent.

The effectiveness of electrostatic precipitators in removing fly ash from the combustion gases of fossil-fuel furnaces accounts for their high frequency of use at power stations.

4.Baghouse filters

4.Baghouse filters

A fabric-filter dust collector can remove very nearly 100 percent of particles as small as

1 μm and a significant fraction of particles as small as 0.01 μm.

Energy usage is high

Air should be cooled

Internet of things and cloud

CONTROL OF GASES

Absorption

Adsorption

Incineration

ABSORPTION

It includes transfer of a gaseous pollutant from the air into a contacting

liquid, such as water.

The liquid must be able either to serve as a solvent for the pollutant or to

capture it by means of a chemical reaction.

Wet scrubbers similar to those described above for controlling suspended

particulates may be used for gas absorption.

Gas absorption can also be carried out in packed scrubbers, or towers, in

which the liquid is present on a wetted surface rather than as droplets

suspended in the air

Thermoplastic materials are most widely used as packing for countercurrent scrubber towers.

These devices usually have gas-removal efficiencies of 90–95 percent.

FLUE GAS DESULPHURIZATION

Sulphur dioxide in flue gas from fossil-fuel power plants can be controlled by means of an

absorption process called flue gas desulfurization (FGD).

It can be wet scrubbing or dry scrubbing

In wet FGD systems, flue gases are brought in contact with an absorbent, which can be either a

liquid or a slurry of solid material.

In dry FGD systems, the absorbent is dry pulverized lime or limestone; once absorption occurs,

the solid particles are removed by means of bag-house filters

FGD systems are also classified as either regenerable or non-regenerable (throwaway),

depending on whether the sulphur that is removed from the flue gas is recovered or discarded.

ADSORPTION

When a gas or vapor is brought into contact with a solid, part of it is taken up by the solid. The

molecules that disappear from the gas either enter the inside of the solid, or remain on the

outside attached to the surface. The former phenomenon is termed absorption (or dissolution)

and the latter adsorption.

The most common industrial adsorbents are activated carbon, silica gel, and alumina, because

they have enormous surface areas per unit weight.

Activated carbon is the universal standard for purification and removal of trace organic

contaminants from liquid and vapor streams.

Carbon adsorption systems are either regenerative or non-regenerative.

- Regenerative system usually contains more than one carbon bed. As one bed actively removes

pollutants, another bed is being regenerated for future use.

- Non-regenerative systems have thinner beds of activated carbon. In a non-regenerative

adsorber, the spent carbon is disposed of when it becomes saturated with the pollutant.

CONDENSATION

Condensation is the process of converting a gas or vapor to liquid. Any gas can be reduced to a liquid by lowering its temperature and/or increasing its pressure.

Condensers are typically used as pre-treatment devices. They can be used ahead of absorbers, absorbers, and incinerators to reduce the total gas volume to be treated by more expensive control equipment. Condensers used for pollution control are contact condensers and surface condensers.

In a contact condenser, the gas comes into contact with cold liquid.

In a surface condenser, the gas contacts a cooled surface in which cooled liquid or gas is circulated, such as the outside of the tube.

Removal efficiencies of condensers typically range from 50 percent to more than 95 percent, depending on design and applications.

INCINERATION

Incineration, also known as combustion, is most used to control the emissions

of organic compounds from process industries.

This control technique refers to the rapid oxidation of a substance through

the combination of oxygen with a combustible material in the presence of

heat.

When combustion is complete, the gaseous stream is converted to carbon

dioxide and water vapor.

Equipment used to control waste gases by combustion can be divided in three

categories:

- Direct combustion or flaring,

- Thermal incineration and

- Catalytic incineration.

DIRECT COMBUSTOR

Direct combustor is a device in which air and all the combustible waste gases

react at the burner. Complete combustion must occur instantaneously since

there is no residence chamber.

A flare can be used to control almost any emission stream containing volatile

organic compounds. Studies conducted by EPA have shown that the

destruction efficiency of a flare is about 98 percent.

In thermal incinerators the combustible waste gases pass over or around a

burner flame into a residence chamber where oxidation of the waste gases is

completed. Thermal incinerators can destroy gaseous pollutants at

efficiencies of greater than 99 percent when operated correctly.

Catalytic incinerators are very similar to thermal incinerators. The main

difference is that after passing through the flame area, the gases pass over a

catalyst bed. A catalyst promotes oxidation at lower temperatures, thereby

reducing fuel costs. Destruction efficiencies greater than 95 percent are

possible using a catalytic incinerator.

REFERENCES

http://edition.cnn.com/2014/05/08/world/asia/india-pollution-who/

http://articles.economictimes.indiatimes.com/2015-02-

24/news/59460740_1_ceo-vishal-sikka-infosys-silicon-valley

http://www.britannica.com/EBchecked/topic/1589060/air-pollution-control

http://www.eng.utoledo.edu/~akumar/IAP1/Pollution%20Control.htm

http://www.envergy.co.in/air-pollution-control-equipment.html

http://nptel.ac.in/courses/105102089/air%20pollution%20(Civil)/Module-

3/3b.htm