homework assignment help is most useful online help portal for the students that providing all Online Combustion and Pollution assignment help Services.Fossil fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years.The fossil fuels, which contain high percentages of carbon, include coal, petroleum, and natural gas. Fossil fuels range from volatile materials with low carbon:hydrogen ratios like methane, to liquid petroleum to nonvolatile materials composed of almost pure carbon, like anthracite coal. Methane can be found in hydrocarbon fields, alone, associated with oil, or in the form of methane clathrates. It is generally accepted that they formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth's crust over millions of years. This biogenic theory was first introduced by Georg Agricola in 1556 and later by Mikhail Lomonosov in the 18th century.
With Man's ever increasing need for energy, he has been using fossil fuels indiscriminately. In the process, harmful materials contributing to air pollution are being produced.
Coal is mainly elemental carbon with small amounts of hydrogen, oxygen, sulphur and nitrogen.
On complete combustion of coal, carbon dioxide is the main product formed. This is non-toxic, but contributes to the green house effect if produced in excess.
Small amounts of oxides of nitrogen and oxides of sulphur formed are responsible for acid rain.
On incomplete combustion of coal, carbon monoxide and unburnt carbon particles are also formed. This causes carbon monoxide poisoning and formation of smog, blackening of buildings etc.
Petroleum is a mixture of hydrocarbons. On combustion, it produces mainly carbon dioxide and water vapour. However, on incomplete combustion, they produce carbon monoxide, unburnt hydrocarbons etc. They also produce oxides of nitrogen.
Petrol is an important fraction of petroleum used in motor vehicles. To increase the efficiency of petrol engines, an anti-knock agent, lead tetra ethyl is added to slow down the rate of combustion. Lead tetra ethyl releases harmful lead compounds into the atmosphere. Lead being a cumulative poison, is extremely toxic.
From the above, we can infer that pollution caused by petroleum based fuels is more harmful than that of coal. Moreover, coal is generally used in a fixed place while petrol is used in vehicles which are constantly on the move. Thus, it is easier to control pollution due to combustion of coal as compared to that of petrol.
All fossil fuels, generally produce a large amount of green houses gases on burning. These gases include carbon dioxide, sulfur dioxide and nitrogen oxide gas etc.
The carbon dioxide gas is responsible for producing green house effect. Thus, increasing the temperture of the earth and causing global warming
On the other hand, gases such as nitrogen oxide and sulfur are mainly responsible for causing acid rain. These gases tends to affect the soil, water and forest resources. The acid rain is responsbile for causing damage the building made up of marble.
Burning of coal also prodoces these harmful gases. In addition , it also releases large amount of smoke which gets suspended in it. Moreover, the ash produced , during the combustion of fossil fuels is quite difficult to dispose off.
It may be noted in this regard that the pollution and ash produced by the combustion of fossil fuels is mainly due to the inefficency of the combution process. We can reduce the escape of these harmful gases and ash etc, by using various latest techniques. The use of alternative sources of energy, further, reduces the burden on the combustion of the fossil fuels.
The combustion of fossil fuels is done to obtain energy stored in them. The amount of energy released during the combustion of fossil fuels is used for domestic as well as for the industrial purposes. The use of fossil fuel is associated with good techniques and also causes air pollution. Therefore, there is need to look for alternative sources of energy as it is likely to reduce burden on the fossil fuel, which are available in limited amount.
The major problem that the atmosphere is being subjected to is pollution. In India, about 100 million tons of pollutants are being added to the atmosphere annually. This figure is likely to go up in future. Polluted air is harmful to man and the biosphere on the whole, as well. This problem needs to be tackled urgently. Since all of us contribute to it directly or indirectly, we must study air pollution in detail and discuss the means of controlling and preventing it.
Air pollution can be defined as 'the change of composition of air by the addition of harmful substances like the industrial and automobile gases and particulate matter.'
Most of the sources of air pollution are related to man's activities as a result of the modern lifestyle. Added to this are also natural causes like the volcanoes, anaerobic decomposition of organic matter, atmospheric reactions, etc.
Fossil fuels include petroleum and coal. Burning of coal produces a lot of smoke and dust whereas burning of petrol mainly produces sulphur dioxide. In addition to these, the pollutants include carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, hydrocarbons, particulate matter and traces of metals.
Petrol on combustion produces carbon monoxide, hydrocarbons, nitrogen oxides, aldehydes, sulphur compounds, organic acids and ammonia and carbon particles. Incomplete combustion of petrol produces a hydrocarbon, 3,4 benzpyrene. There is more pollution during acceleration and deceleration than during constant speed.
They produce oxides, sulphur, nitrogen, hydrocarbons, particulate matter and fluorine.
Since they are coal based the pollutants are fly ash, soot and sulphur dioxide.
They produce cotton dust, nitrogen oxides, chlorine, naphtha vapours, smoke and sulphur dioxide.
They produce carbon monoxide, carbon dioxide, sulphur dioxide, phenol, fluorine, cyanide, particulate matter, etc.
Volcanic eruptions release oxides of nitrogen that pollute the atmosphere.
Decomposition of organic matter under anaerobic conditions produces methane which on being oxidised in the atmosphere produces carbon monoxide. Decomposition of these matter also produces foul smelling gases.
Photochemical oxidation of marine organic matter and biological oxidation by marine organisms produce lot of carbon monoxide on the surface of the oceans which enters the atmosphere.
There are six main categories of air pollutants:
The various categories of air pollutants and their harmful effects are summarised in the given table:
| Pollutant | Source/Cause | Effect |
|---|---|---|
| Carbon monoxide | Automobile exhaust, photochemical reactions in the atmosphere, biological oxidation by marine organisms, etc. | Affects the respiratory activity as haemoglobin has more affinity for Co than for oxygen. Thus, CO combines with HB and thus reduces the oxygen-carrying capacity of blood. This results in blurred vision, headache, unconsciousness and death due to asphyxiation (lack of oxygen). |
| Carbon di oxide | Carbon Burning of fossil fuels,depletion of forests (that remove excess carbon dioxide and help in maintaining the oxygen-carbon dioxide ratio). | Global warming as it is one of the greenhouse gases. |
| Sulphur dioxide | Industries, burning of fossil fuels, forest fires, electric generation plants, smelting plants, industnal boilers, petroleum refineries and volcanic eruptions. | Respiratory problems, severe headache,reduced productivity of plants, yellowing and reduced storage time for paper, yellowing and damage to limestone and marble, damage to leather, increased rate of corrosion of iron, steel, zinc and aluminium. |
| Hydrocarbons Polynuclear Aromatic Compounds(PAC) and Polynuclear Aromatic Hydrocarbons(PAH) | Automobile exhaust and industries,leaking fuel tanks, leaching from toxic waste dumping sites and coal tar lining of some water supply pipes. | Carcinogenic (may cause leukemia) |
| Chlorofluoro carbons (CFCs) | Refngerators, air conditioners, foam shaving cream, spray cans and cleaning solvents. | Destroy ozone layer which then permits harmful UV rays to enter the atmosphere. |
| Nitrogen Oxides | Automobile exhausts, burning of fossil fuels, forest fires,electric generation plants, smelting plants, industnal boilers, petroleum refineries and volcanic eruptions | Forms photochemical smog, at higher concentrations causes leaf damage or affects the photosynthetic activities of plants and causes respiratory problems in mammals. |
| PAN - peroxylacetyl -nitrate | Photochemical reactions of hydrocarbons and nitrogen oxides. | Irritation of eye, throat and respiratory tract, damage to clothes, paint and rubber articles, damage to leaves and stomatal tissue in plants. |
| Particulate matter Lead halides (lead pollution) | Combustion of leaded gasoline products | Toxic effect in man. |
| Asbestos particles | Mining activities | Asbestosis - a cancerous disease of the lungs |
| Silicon dioxide | Stone cutting, pottery, glass manufacturing and cement industries. | Silicosis, a cancerous disease. |
| Biological matter like the pollen grains | Flowers | Allergy |
| Fungal spores, bacteria, virus, etc | Microbes | Infectious deseases |
Most of the solar radiation entering the earth's atmosphere is reflected back into the space. However some of the heat is absorbed by the gases like the carbon dioxide. This serves to keep the earth warm much like the greenhouses. Greenhouses are glasshouses which maintain a temperature higher than the surroundings for the plants to grow and yield better. The other gases that contribute to this are water vapour, methane, chlorofluorocarbons (CFCs) and nitrous oxide. These gases are called the greenhouse gases.
While greenhouse effect is a necessary and natural phenomenon. Every year teh temperature are going up due to pollution and the levels of these greenhouse gases is also going up. This is called global warming. According to estimates, at the current rate of increase, the average global temperature will go up by 3oC to 8oC in the next 100 years.
This will have the following effects:
When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight, smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it is called the photochemical smog. The word 'smog' is derived from the two words-smoke and fog.
It forms a yellowish brown haze especially during winter and hampers visibility. It also causes many respiratory disorders and allergies as it contains polluting gases.
Sulphur dioxide and nitrogen oxides react with water in the atmosphere producing sulphuric acid and nitric acid. These acids come down along with the rain. This phenomenon is called acid rain. The pH of acid rain varies from 3-6. The composition of acid rain is sulphuric acid, nitric acid and weak carbonic acid.
It has the following adverse affects on the environment:
Aerosol is formed by the dispersion of solid or liquid matter in the atmosphere. There are natural aerosols also in the atmosphere. However, polluting aerosols are formed by the pollutant particulate matter like carbon particles.
If the aerosols form a thick layer in the troposphere, they affect the weather conditions by blocking the solar radiation. Aerosols are also deposited on the leaves and affect the photosynthesis. Aerosols disperse the organic metallic pollutants far and wide.
The stratosphere of the atmosphere has ozone (O3). Ozone is known to absorb the Ultraviolet (UV) rays present in the sun's radiation. The UV rays are believed to cause skin cancer and mutations. Thus, the ozone protects us from the harmful effects of the UV rays.
However, hydrocarbons such as the chlorofluorocarbons (CFCs) destroy the ozone molecules which deplete the ozone layer. Ozone holes have been detected in the atmosphere which permit the UV rays to reach the earth's surface. The harmful effects of the UV rays are visible in the countries such as Australia and New Zealand where the rate of skin cancer is higher than the other regions of the world.
Air pollution can be controlled by different methods depending on the source and the pollutant. The different methods are:
One of the major causes of air pollution are the automobiles. The fuels being used should be lead-free as this will reduce the level of lead in the atmosphere. The carburetor should be cleaned regularly and good quality fuel should be used. This reduces the smoke emission from the exhaust pipes of the vehicles. Efforts to introduce vehicles running on alternate sources (for example solar energy) of energy should be made. These methods will go a long way in reducing the occurrence of photochemical smog.
The industrial pollution is best controlled at source. The polluting gases should be passed through filters and other devices such as cyclone collectors, scrubbers, precipitators, etc. so that the particulate matter is removed before the waste gases are released out. The toxic gases should be detoxified.
The domestic and industrial smoke producing units should have long chimneys to take the polluting gases far above and then disperse over a larger area. They should also invest in solar cookers or bio gas.
The pollution by sulphur dioxide is mainly due to coal-based industries. Alternate non-sulphur containing fuel must be used. It is also possible to remove the sulphur from the fuel before use.
There are many plant species like the neem (Azadirachta indica), bel (Aegle marmelos), gulmohur (Delonix regia), etc. that clean the atmosphere. More trees of such types should be planted.
For effective control and prevention of air pollution it is important to educate people and create public awareness about the ill-effects of air pollution.
The following are some methods that may be adopted to control pollution on a large scale:
Pollutants in the form of organic gases or vapours can be burnt to convert them into water vapour and relatively less harmful products, such as carbon dioxide.
The gaseous effluents may be made to pass through scrubbers or absorbers. These contain a suitable liquid absorbent, which removes or modifies one or more of the pollutants present in the gaseous effluents making it comparitively harmless.
The gaseous effluents are passed through porous solid adsorbents kept in suitable containers. The organic and inorganic constituents of the effluent gases are trapped at the interphase of the solid adsorbent. Adsorbents hold (molecules of a gas or liquid or solute) to its surface, causing a thin film to form.
Particulate emissions may be controlled by using mechanical devices that generally work on the basis of the following:
In this process, the particles settle down by gravitational force. Sudden changes in the direction of the gas flow causes the particles to separate out due to greater momentum.
The gases containing dust are passed through a porous medium. which is usually woven fabrics. The particles present in the gas are trapped and collected in the filters. The gases freed from the particles are then discharged.
A Typical Bag Filter
Wet scrubbers are used in chemical, mining and metallurgical industries to trap sulphur dioxide, ammonia, metal fumes, etc.
When a gas or an air stream containing aerosols in the form of dust, fumes or mist, is passed between two electrodes, then, the aerosol particles get precipitated on the electrode.
Electrostatic Precipitator
The following practices also help in controlling air pollution
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