Coal

What Is Coal?

Coal is an 'Ancient Gift Serving Modern Man'. About 300 million years ago, plants and trees grew in swamps that covered much of the earth. As this vegetation died, it drifted down to the bottom of the swamps and formed a soggy, sponge like material called peat. Over millions of years and through the forces of heat and pressure, the peat became coal. Coal is classified as a non-renewable energy source because it takes millions of years to form. The energy we get from coal today comes from the energy that plants absorbed from the sun by photosynthesis millions of years ago . After the plants die, this energy is released as the plants decay. During coal formation, however, the decay process is interrupted, preventing the further release of the stored solar energy.

Coal is found in underground coal mines in seams.Seams of coal--range in thickness from a fraction of an inch to hundreds of feet and they may represent hundreds or even thousands of years of plant growth. There are two ways to remove coal from the ground.

  • Surface mining -This is done when a coal seam is relatively close to the surface, usually within 200 feet.

  • Underground mining This is done when the coal seam is buried several hundred feet below the surface. In underground mining, workers and machinery go down a vertical "shaft" or a slanted tunnel called a "slope" to remove the coal. Mine shafts may sink as much as 1,000 feet deep.

After coal comes out of the ground, it typically goes on a conveyor belt to a preparation plant that is located at the mining site. A "prep" plant cleans and processes coal to remove dirt, rock, ash, sulfur, and other impurities. Removing the impurities increases the calorific value of coal.

Types of coal

The rank of coal is based on the degree to which the orginal plant material has been transformed into carbon and can be seen as a rough indication of how old the coal is: the older the coal the higher the carbon content (generally). The coal with the highest carbon content is the best and cleanest type of coal to use. As one moves down the coal rank the calorific value of the coal decreases.As geological processes apply pressure to peat over time, it is transformed successively intothe following:

Lignite

Used almost exclusively for electric power generation lignite is a young type of coal. Lignite is brownish black, has a high moisture content (up to 45 %), and a high suphur content. Lignite is more like soil than a rock and tends to disintegrate when exposed to the weather. Lignite is also called brown coal. This type of coal contains a lot of moisture and breaks apart easily. Lignite has a calorific value of less than 5kW/kg approximately.

Sub-bituminous coal

Sub-bituminous coal is also called black lignite. Sub-bituminous coal black and contains 20-30 % moisture. Sub-bituminous coal is used for generating electricity and space heating.It has calorific values ranging from 5 - 6.8 kW/kG approximately.

Bituminous coal

Bituminous coal is a soft, dense, black coal. It often has bands of bright and dull material in it. Bituminous coal is the most common coal and has a moisture content less than 20 %. Bituminous coal is used for generating electricity, making coke.

Anthracite

Anthracite is coal with the highest carbon content, between 86 and 98 percent, and a heat value of nearly 15,000 BTUs-per-pound.

Coal Use

Coal was used for cooking mainly and for baking pottery items. Coal is still used for cooking in many countries like India,Korea, Nepal,China, Africa for cooking and baking or for making pottery.

Then people started using coal to power railway steam engines and steam ships and boats.It is now used mainly for generating electricity and in iron and steel factories.
Materials that may be extracted from one ton of coal:

PRODUCT USES
Lump Coke =metallurgical coke, copper smelting, iron smelting, lead smelting and iron and steel casting.
Calcium Carbide=acetylene chemicals.
Water Gas= heating homes and industry chemical processing.
Industrial= chemical processing, lime burning, beet sugar refining, manufacturing of mineral wool.
Screenings or Breeze=iron-ore agglomeration, chemical processing, steam generation
Coal Tar=Tar Coal carbolic acids, pharmaceuticals, cresole, lysol, photo developer, plastics, phenols, detergents, drugs, dyes, food preservatives, perfumes, rubber chemicals, weed killer.
Tar Bases=pyridine bases, antiseptics, disinfectants, paint thinner, pyridine, clothes water proofing, sulfa drugs, synthetic vitamins.
Napthaline=insecticides, fungicides, plastic dolls, explosives, moth balls, synthetic fibres.
Heavy Oil dyes, embalming fluid, laxatives, wood preservatives.
Pitch=electrodes, insulating, paving, roofing, storage batteries, water proofing.
Light Oil
Benzene= synthetic fibres, nylon, aniline dyes, food preservatives, motor fuel, plastics, synthetic rubber, tanning fluids.
Toluene=antiseptics, fingernail polish, printing ink, saccharine, TNT explosives, aviation gas, detergents.
Xylene=motor fuel, gasoline solvents, herbicides.
Solvent Naptha= rubber solvent, electrical - insulation, linoleum, varnish.

What happens when coal is burned


Combustion of coal, like any other fossil fuel, produces carbon dioxide (CO2) and nitrogen oxides (NOx) along with varying amounts of sulfur dioxide (SO2) depending on where it was mined. Sulfur dioxide reacts with oxygen to form sulfur trioxide (SO3), which then reacts with water to form sulfuric acid.The sulfuric acid is returned to the Earth as acid rain. Scrubbing systems, which use lime to remove the sulfur dioxide can reduce or eliminate the likelihood of acid rain.

Coal and the Environment

When coal became an important energy source, concern for the environment was not at the forefront of public attention. For years, smokestacks from electrical and industrial plants emitted pollution into the air. Coal mining left some land areas barren and destroyed.

The coal industry's most troublesome problem today is removing organic sulfur, a substance that is chemically bound to coal. All fossil fuels, such as coal, petroleum, and natural gas, contain sulfur. When these fuels are burned, the organic sulfur is released into the air where it combines with oxygen to form sulfur dioxide. Sulfur dioxide is an invisible gas that has been shown to have adverse- effects on the quality of air we breathe. It also contributes to acid rain, an environmental problem that many scientists think adversely affects wildlife (especially fish) and forests.

However, the coal industry is doing something to solve this problem. One method uses "scrubbers" to remove the sulfur in coal smoke. Scrubbers are installed at coal-fired electric and industrial plants where a water and limestone mixture reacts with sulfur dioxide to form a sludge. Scrubbers eliminate up to 98 percent of the sulfur dioxide, but they are very expensive to build.

The coal industry is also concerned about the carbon dioxide that is produced when coal is burned. Carbon from burning coal reacts with air to form carbon dioxide- causing greenhouse effect.

Scientists and others are concerned about the greenhouse effect because it is causing a change in the earth's climate. Some say the earth is already experiencing a climate change due to the greenhouse effect; others are not so sure yet. While northern part of the world will experience warmer climate,it could cause drought in some areas of the world India, Africa etc and the erosion of ocean coasts due to rising sea levels in all areas.

How does coal burning contribute to global warming


Emissions from coal-fired power plants represent one of the two largest sources of carbon dioxide emissions, which are the primary cause of global warming. Coal mining and abandoned mines emit methane, which is another cause of global warming. Since the carbon content of coal is higher than oil, burning coal is a serious threat to the stability of the global climate, as this carbon forms CO2 when burned. Many other pollutants are present in coal power station emissions, as solid coal is more difficult to clean than oil, which is refined before use. To eliminate CO2 emissions from coal plants, carbon capture and storage has been proposed but has yet to be commercially used.

Coal and coal waste products including fly ash, bottom ash, boiler slag, and flue gas desulferization contain many heavy metals, including arsenic, lead, mercury, nickel, vanadium, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, selenium and radium, which are dangerous if released into the environment. Coal also contains low levels of uranium, thorium, and other naturally-occurring radioactive isotopes whose release into the environment may lead to radioactive contamination. While these substances are trace impurities, enough coal is burned that significant amounts of these substances are released, resulting in more radioactive waste than nuclear power plants. Coalization is the mass use of coal-fired power plants to produce electricity, as happens in China and USA.

If Coal is so polluting then why use Coal as a Energy Source


As the price of crude oil climbs higher, the world's energy-intensive economy –especially the US – are seeking viable alternatives.
Renewable sources like wind, hydro and bio-fuel will certainly play a role. But one of the most viable alternatives for countries which have ample coal reserves will be coal. Since 1970, energy from coal has become increasingly clean, and the technologies to make coal energy even cleaner will be available in the future. Demand for energy has grown dramatically over the last three decades, and the need for energy will continue to grow. Electricity from coal energy plays a crucial role in today's energy mix. At present coal provides over 23% of global primary energy need and generates about 39% of the world's electricity.

Clean Coal Technologies


New technologies are creating new opportunities for using this fossil fuel . High prices of oil and natural gas are leading to increased interest in "BTU Conversion" technologies such as gasification, methanation and liquefaction. These processes will solve coal's obvious environmental problems.

Coal gasification breaks down the coal into its components, usually by subjecting it to high temperature and pressure, using steam and measured amounts of oxygen. This leads to the production of syngas, a mixture mainly consisting of carbon monoxide (CO) and hydrogen (H2).In the past, coal was converted to make coal gas, which was piped to customers to burn for illumination, heating, and cooking. At present, the safer natural gas is used instead. South Africa still uses gasification of coal for much of its petrochemical needs.

Gasification is also a possibility for future energy use, as the produced syngas can be cleaned-up relatively easily leading to cleaner burning than burning coal directly (the conventional way). The cleanliness of the cleaned-up syngas is comparable to natural gas turbine.

Liquefaction-coal can also be converted into liquid fuels like gasoline or diesel by several different processes. Bergius process (liquefaction by hydrogenation), The Fischer-Tropsch process of indirect synthesis of liquid hydrocarbons etc. Syngas can also be converted to methanol, which can be used as a fuel, fuel additive, or further processed into gasoline via the Mobil M-gas' process.

-United States of America, India have made coal gasification and liquefaction projects high priorities in its national energy strategy. USA and India have formed a Coal Working Group. This group will be co-developing technologies to exploit coal-bed methane, coal gasification and liquefaction, and other clean-coal-related technologies.

China's government also in a desperate need to cut coal emissions made a zero-emissions coal-fired power plant one of its goals. So to achieve this goal China is also developing proprietary technology for coal liquefaction and gasification. If these clean coal technologies become commercially viable then there will be more efficient and cleaner
use of an abundant energy resource-coal. In fact General Electric owns the patent on a coal-gasification technique that's used in over 60 coal-gasification plants worldwide. That process removes usable gas from coal without the harmful emissions. The gas can then be used to generate power. The whole process is called the "integrated gasification combined cycle" - or IGCC for short.

Contributors

User:Grant Ballard-Tremeer 15 January 2007
User:Karabi Dutta 23 May 2007
User:Karabi Dutta 28 August 2007






Last edited by Miriam Hansen , based on work by Grant Ballard-Tremeer .
Page last modified on Tuesday 28 of September, 2010 10:35:08 GMT. @HEDON: UJFB

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