SIGMA INSTITUTE OF ENGINEERING VADODARA-19

Mechanical department

Class :m11 Semester : IGUIDED BY :

PREPARED BY : Khushwant Labana Enrollment no:140500119048

Class:M 11 Sem 1

Air Pollution: causes and

control

AIR POLLUTION

Air is one of the vital part of life .Air supplies with oxygen is essential for our bodies to live. Air is 99.9% nitrogen, oxygen, water vapors and inert gases. Due to man made activities along with some natural processes many physical addition of material that turn the air impure or unclean. That is called air pollution.

AIR POLLUTIONAir pollution primarily comes from burning fossil fuels such as natural gas, petroleum, and coal. Humans are the main cause of air pollution. Industry, including factories and power plants, burn large quantities of fuel. Burning coal and petroleum releases sulfur oxides and nitrogen oxide into the air. Airplanes, boats, and cars burn petroleum, releasing carbon monoxide and carbon dioxide.

Primary vs Secondary pollutants• Not all of the pollutants found in the

atmosphere are the direct result of emissions.

• Many pollutants arise from chemical reactions in the atmosphere with other substances or light (photochemical reactions).

•Pollutant substances that are directly emitted into the atmosphere = primary pollutants. •Substances not directly emitted into the atmosphere, formed by chemical reactions in the atmosphere = secondary pollutants.

TYPES OF POLLUTION INDOOR POLLUTION Indoor air pollution occurs inside our homes, office and

schools. The main types of indoor pollutants are tobacco smoke, gases

from stoves and furnaces, household chemicals, small fiber particles, and hazardous fumes given off by building materials like insulation , glue, and paint .

In high amounts it causes headache, eye irritation, etc. OUTDOOR POLLUTION Gases and particulates form of pollutants pour into the

atmosphere from the burning of fuel to motor vehicles, heat buildings, business and industrial processes , burning of garbage etc…

Outdoor pollution make huge impacts on atmosphere and the organisms

Acid rain , global warming, etc are some of its consequences .

TYPES OF POLLUTANTS Aerosols

Particulates solid phase Dust Ash Fumes

Solid and liquid Smoke (from combustion) Coastal aerosols

Liquid Aggregate gases (sulfate,

nitrate)

GasesCOxSOxNOxPAH

SIX PRIMARY OR “CRITERIA” AIR POLLUTANTS

Carbon monoxide (CO) Sulfur oxides (SOx) Nitrogen dioxide (NO2) Ozone (O3) Hydrocarbons Particulate matter(PM2.5

_PM10)

Carbon Monoxide

•colorless, odorless, tasteless, non irritating gas

•produced when carbon does not burn in fossil fuels,ie incomplete combustion.

•Commonly present in automobile exhaust

•deprives body of O2 causing headaches, fatigue, and impaired vision, it may lethal when continually inhale concentration above 1000ppm over a period of 4 hours.

Sulfur Dioxide

•Colourless gas with penetrating and pungent odour

•produced mainly when coal and fuel oil are burned

•present in power plant exhaust

•narrows the airway, causing wheezing and shortness of breath, especially in those with asthmaThe formation of SO2, SO3, and sulfuric acid

S + O2 SO2

2 SO2 + O2 2SO3

SO3 + H2O H2SO4

Nitrogen Dioxide

•reddish, brown gas

•produced when nitric oxide combines with oxygen in the atmosphere

•present in car exhaust and power plants

•affects lungs and causes wheezing; increases chance of respiratory failure.

•Smokers may readily develop lung disease as cigarettes and cigars containing 330 to 1,500 ppm nitrogen oxides. Prolonged exposure at 1 to3 ppm or even less may fatal. •It also react with water to cause acid rain 4NO2+2H2O+O2 ------- 4HNO3

Methods of air pollution control can be divided into two categories: •THE CONTROL OF PARTICULATE EMISSIONS •THE CONTROL OF GASEOUS EMISSIONSThe term particulate refers to tiny particles of matter such as smoke, soot, and dust that are released during industrial, agricultural, or other activities.Gaseous emissions are industrial products such as sulfur dioxide, carbon monoxide, and oxides of nitrogen also released during various manufacturing operations.

Control of Air Pollutants

1. Particulates – Cyclones separation by centrifugation –

Cyclone utilise centrifugal force generated by a spinning gas stream to separate the particulate matter from the carrier gas.The general principle of inertia separation is that the particulate-laden gas is forced to change direction. As gas changes direction, the inertia of the particles causes them to continue in the original direction and be separated from the gas stream.

THE CONTROL OF PARTICULATE EMISSIONS

3.Particulates – Filtration

Fibre bags commonly used for control of particulate emissions with very high dust loadings and smaller particles.

• Filters consist of porous structure composed of granular or fibrous material which tends to retain the particulate matter as the carrier gas passes through the voids of the filter.

• The dust is collected on the inside of the bag surface and the filtered gas is discharged to the atmosphere -

99% efficient

4.Particulates – Wet Scrubbers

spray systems where fine water droplets are sprayed at high velocity at right angles to the emerging gas

Most of the particles in the gas stream are scavenged by the water droplets, which fall and are collected along with the particles

relatively low efficiencies (80-90%) and is usually employed as a pre-cleaner to remove particles larger than 5m

pass dirty gas through a series of fine wires (coronas) charged with DC current – causes particles to aggregate & precipitate

Alternatively corona produces negative ions that cause particles in the gas stream to become negatively charged, and attracted to positive terminal – where they aggregate and fall into a collection hopper

Large precipitators and low gas flow rates give better results

5.Particulates – Electrostatic Precipitators

charged electrodes soot laden smoke inlet

soot free gas escape

removal of soot particles earth point

GASEOUS POLLUTANTS –PROCESS MODIFICATIONS

simplest and least expensive methods for the control of gaseous pollutants

fuel substitution e.g. low sulfur coal, or fuel oils in place of cheaper coal can greatly reduce the amount of SO2 emissions at the source

This type of source control is always the best approach wherever possible

Gaseous pollutants - Combustion involves a series of complex chemical reactions in

which oxygen is combined with organic molecules, to form CO2 and H2O

commonly referred to as incineration or afterburning

GASEOUS POLLUTANTS - ADSORPTION physical adsorption to solid surfaces Reversible - adsorbate removed from the adsorbent

by increasing temp. or lowering pressure widely used for solvent recovery in dry cleaning,

metal degreasing operations, surface coating, and rayon, plastic, and rubber processing

limited use in solving ambient air pollution problems – with its main use involved in the reduction of odour

Adsorbents with large surface area to volume ratio (activated carbon) preferred agents for gaseous pollutant control

Efficiencies to 99%

GASEOUS POLLUTANTS - ABSORPTION Scrubbers remove

gases by chemical absorption in a medium that may be a liquid or a liquid-solid slurry

water is the most commonly used scrubbing medium

Additives commonly employed to increase chemical reactivity and absorption capacity

CONTROL OF AIR POLLUTIONMinimize activities which are causes the pollution like transportation and burning of fossil fuels. Modification of Equipments.By using the low sulphur coal in industries.Removing the sulphur from coal (by washing with the help of bacteria)By using the biological and bio-scrubbers.Plantation more trees.