6 Ways to Control Air Pollution in 2018
Control of air pollution basically means adopting ways and technique to stop the harmful emissions of gases into the ecosystem, thus creating a balanced ecosystem and thus establishing pillars for a healthy life. The control of air pollution is definitely one of the major principles adopted apart from control of land and water pollution.
Air is polluted only when there is a presence of certain substances in high concentrations and exposure for long durations causes harmful or undesirable effects.
Adverse effects on human life, health, ecosystem, property, and atmospheric visibility are its major drawbacks. Natural sources or manmade activities both can be the common reason for pollution.
Volcanic eruption or forest fires or any other natural phenomena may not an immediate effect on local or regional ecosystem but has an effect globally or worldwide. However natural occurrence such as industrialisation or excessive emission from vehicles aren’t in our control but only the man made reasons can be mitigated or eliminated
Combustion is the major reason for pollution or contamination of air. Burning of fossil fuels such as coal was the major cause of pollution in London and other European cities in middle age. With the wake up of Industrialisation in the 19th century, burning and use of fossil fuel increased which intensified the harmful effects caused.
The invention of mobile sources of pollution which is gasoline powered highway vehicles—had a disastrous impact on air quality and was the reason of pollution in cities. Not before the middle of 20th century the level of pollution was realised and attempts were made for its mitigation.
Protecting and preserving ambient, or outdoor, air quality is the primary focus of air pollution control in industrialized lands, cities and countries. Control of a small number of specific pollutants who contribute to smog and life threatening public health problems.
The pollutants include fine particulates, carbon monoxide, nitrogen dioxide, ozone and lead. Since the end of the 20th century, there also has been a trace of air toxics which basically cause hazardous effect on air. Most air toxics are organic chemicals containing carbon, hydrogen and other molecules.
Specific emission regulations are installed against those pollutants. In addition, the greenhouse effects are observed which has an everlasting and long term effect on the environment.
The greenhouse gases ozone, methane, CFCs, nitrous oxide etc. The U.S. Environmental Protection Agency implanted that greenhouse gases cause threat to human health and should be subject under regulation as a major source of air pollution.
The most suitable way to protect air quality is to reduce the emission of pollutants by making a swift change to cleaner fuels and processes. Pollutants which are not eliminated must be collected or filtered by a best air-cleaning device as soon as it is generated and before it can escape into the atmosphere polluting it.
Such types of devices are described below :
1. Controlling of Air Particulates
A variety of physical processes can help to trap the air borne particles and later filter them. Cyclones, electrostatic precipitators, scrubbers, bag house filters are common types of equipment for collecting fine particulates. Agglomerates are formed after collection where particles adhere to each other which can be later filtered and eliminated from the equipment and disposed of, in a landfill mostly. Each air pollution control level is separate and distinct and it is usually impossible to decide on the best type of particle collector device, it must be decided on case by case protocols.
Corrosivity, shape, density, reactivity and size distribution are the important characteristics which decides the selection of collector device. Temperature, viscosity, pressure, removal efficiency, flow rate are other factors kept in consideration. Cyclone collectors are often used for controlling the emission of industrial dust. Whereas wet scrubbers are preferred in case of flammable or explosive dusts. Electrostatic precipitators and baghouse filters are used in power plants mostly.
A dirty airstream is allowed to flow in a spiral pattern within a cylindrical chamber in a cyclone. A vortex is formed as the dirty air enters the chamber from a tangential direction. It basically swirls within the chamber. The particles having greater inertia which is a dependent factor on its size are forced against the chamber walls. They gradually slide downwards into a conical pattern at the bottom which happens because it is slowed by friction. The cleaned by air swirls in a narrower spiral and within the inner cylinder. The dust accumulated is periodically removed and disposed.
Wet scrubbers are devices responsible for trapping particles by spraying water or any other liquid. Basically, a scrubber does the job of washing the particles out of the airstream that contains dirt. This happens because they come in contact with various tiny water droplets. Scrubbers with variety of configurations are in use and depending on its need we can easily opt for the best one. Spray tower scrubber is known to remove 90 percent of particulates and is about 8 μm in diameter.
Characterised by an upward flowing air stream that is washed by water sprayed from a collection of nozzles. In orifice, diameter is about 2 or even large. Efficiency is as high as 90 percent. Here the air and water mixture collides with a solid surface. Venturi scrubbers the most trusted scrubbers has a diameter of about 0.5 or larger and efficiency goes as high as 98%. It uses the principle of relative velocity that exists between the droplet and the particle.
3. Electrostatic Precipitators
For removing of fine particles from the airstream this method is preferred to a great extent. In this method the suspended particles in the airstream are given an electric charge on entering the unit and later with application of the phenomenon of electric field they are removed.
The unit comprises of baffles, electrodes and a dust clean out aperture and hoppers. The baffles are meant for distributing airflow. The electrodes are meant for discharge and collection. The hoppers are meant for collection. A direct current which is as high as 10000 volt is subjected to the discharge electrodes to charge the particle, on doing this they become charged negatively.
As a result the particles get trapped and are eliminated. The architecture of a typical electrode consists of large rectangular metal plates which are suspended vertically and stand parallel to each other. This forms a boxlike structure. In most cases, there exists hundred of such plates occupying a large area. The plates being grounded are negatively charged whereas the wires which hang between the collection plates are negatively charged, and thus gets attracted. Particles sticking to the collection plates are periodically shaken. This is also termed as rapping. Rapping is thus a technique of separating the trapped particles from the plate.
4. Bag-house Filters
For removing suspended particles from polluted air, the most easiest method is an assembly of fabric filter bags called as baghouse. A traditional baghouse is all about an collection of narrow or long bags. This bags are about 10 inches in diameter and are suspended in an upside fashion. By the help of the bottom enclosure of fan the dust laden air is blown upwards. Trapping of particles happens inside the bags, whereas through the fabric the clean air passes and exists at the top of baghouse. The efficiency of this is nearly about 100 percent and is thus preferred. The size ranges from 1 to as small as 0.01. They offer relatively higher resistance to airflow, which eventually ends up to substantial energy for the fan system. The air needs to be cooled in order to prolong the lifetime of fabric bag. At a single baghouse installation, several compartments of filter bags are often used. This allows cleaning of individual compartments while others remain in service. Regularly these bags need to be cleaned by eliminating the layers of dust. The ways of doing it are done either by mechanically shaking them,that is reversing the flow of air and leads to collapse. Not too much of the built up dust must be eliminated entirely.
5. Control of Gases
There are major three methods namely absorption, adsorption,and incineration when it comes to controlling gaseous criteria pollutants as well as volatile compounds. Apply them either in an individual way or in combination, they work both ways.
Control of major greenhouse gases can be combated that way. On top of this, there is another fourth technique known as carbon sequestration. It is mainly used as a means for controlling carbon dioxide levels.
This involves the transfer of a gaseous pollutant from air into a contacting liquid,such as water. The liquid acts as a solvent for the chemical reaction that is ought to happen.
5.1.1 Wet Scrubbers and Packed Scrubbers
Wet scrubbers are those which is used for absorption of particulate matter by dispersing water droplets. Whereas packed scrubbers are used for gas absorption.
5.1.2 Flue Gas Desulphurization
Flue gas from fossil fuel can be controlled by means of an absorption process called as flue gas desulphurisation.
Gas adsorption can be different from absorption and is a surface phenomenon. On the surface of the solid the gas molecules are sorbed and attracted and thus held.This is mainly used for odour control.
It is used to convert VOCs and other gaseous hydrocarbons pollutants to carbon dioxide and water. Hydrocarbon fumes usually is attained in a special incinerator called an after burner. To achieve the best proper amount of turbulence and burning time must be maintained at a sufficiently high temperature.
6. Carbon Sequestration
This is the principle of reducing the levels of carbon dioxide concentration in air and to use energy in a more productive way and reducing the emission of fossil fuels due to combustion by using alternative energy sources.
These are the few ways which can be used to control or reduce air pollution.