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“Our civilization is founded on coal, more completely than one realizes until one stops to think about it. The machines that keep us alive, and the machines that make machines, are all directly or indirectly dependent upon coal." - George Orwell in his essay “Down The Mine".
Our main energy source has been coal since the invention of the steam engine, through the Industrial Revolution and continues to be so today. With Global warming taking the center stage, the question asked is should coal be our main energy source?
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Consider these three facts about coal combustion.
- Coal gives us energy in the form of heat. Heat release takes place by the exothermic reaction of carbon in coal with oxygen in air to form carbon dioxide. Therefore, if coal is to give heat, then there will be carbon dioxide. 3.67 mols of CO2 will be formed for every mol of carbon burned - no more and no less. This reaction has made coal the biggest energy supplier.This has also made coal the biggest producer of CO2, the green house gas affecting Global Warming. This is the inevitable truth.
- Coal exists in nature not as pure carbon, but as a mineral rock containing predominantly carbon with ash and water. It also includes small amounts of hydrogen, sulphur, and other elements. Depending on the rank of coal and the location of the mines, the carbon percentages vary. When coal burns, it is only the carbon and the hydrogen that contributes to the heat energy. All other components convert to residue (ash) and gaseous emissions like sulphur dioxide, nitrogen oxides and carbon dioxide. These along with trace elements like mercury disperse into the atmosphere. This residue and emissions is what earned coal the tag “dirty fuel."
- Coal lies deep below the earths surface. To mine or reach the coal layer the top layers of soil have to be moved. This destroys the vegetation, trees, and agriculture above. This also works against the clean coal image.
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For a given coal, the elimination or reduction of the residual matter and emissions are not possible. These are chemically fixed. What can change is only the method of capture and its disposal. What the proponents of Clean Coal Technology are doing is only this.
In earlier days, dispersion of the ash and gaseous emissions to the atmosphere was through the chimney. The after effects were disastrous, affecting a large population base. Acid rain, ground level ozone, respiratory diseases, and reduced visibility all were a result of this. Strict environmental regulations helped in developing technology to capture these emissions.
Today electrostatic precipitators collect almost all of the ash particles. Flue gas Desulphurization Units and Selective Catalytic Reduction units capture most of the emissions.
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The captured ash and residues will turn out to be environmental issues as these coal fired power plants age.
The collected ash or the sulphate from the desulphurization units over the years make massive piles that will lead to environmental issues. A 600 MW Coal fired power plant produces almost a million tons of ash in three years. It affects agriculture, groundwater, and the health of the people living nearby. It may take many years to notice the effects. This does not make the coal clean.
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NOx and CO
The process of combustion itself generates some undesirable gaseous emissions like NOx and CO. These, though not necessarily a part of the basic reaction, are present in everyday combustion. Advances in combustion technology and operation philosophy have seen considerable reduction of these emissions. This is really eliminating an unwanted emission and a success of clean coal technology.
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CO2 still emits into the atmosphere. Commercial scale capturing of CO2 ( Carbon Sequestering Systems ) and sending it to underground reservoirs is yet to be viable. CO2 emission will continue to be the main burden of coal, unless large scale forestry takes place to absorb the emissions.
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New Combustion Process
Advanced technologies like Integrated Coal Gasification, Circulating Fluidized Bed technology, and coal washeries improve the utilization and efficiency of coal combustion. This also makes it easy for capturing the emissions and residues.
Even though these are termed clean coal technologies, they are in fact only making the coal combustion cleaner.
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Utilizing the captured residue, substituting for other natural resources, is an environmentally better disposal method.
- Mixing fly ash in cement,
- Using fly ash for road laying
- Using fly ash to make bricks
- Using sulphate from flue gas desulphurization for making gypsum boards
Even though this is only a smaller percentage of the residue or emissions captured, this is a constructive clean coal method.
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Nature has taken millions of years to sequester the carbon into coal. In a few milliseconds, man has found the means to release it back to the atmosphere. The Pandora’s box has been opened, and we can only wait for Hope.
A real clean coal with no emissions or environmental effects is impossible, but a cleaner coal is a must.