The use of electricity has been an essential part of the U.S. economy since
the turn of the century. Coal power, an established electricity source that
provides vast quantities of inexpensive, reliable power has become more important as supplies of oil and natural gas diminish. In 1995, Coal burning
produced about 55% of the electricity generated in the U.S. In addition,
know coal reserves are expected to last for centuries at current rates of usage.
Coal power is a rather simple process. In most coal fired power plants, chunks of coal are crushed into fine powder and are fed into a combustion
unit where it is burned. Heat from the burning coal is used to generate steam that is used to spin one or more turbines to generate electricity.
Coal has played a major role in electrical production since the first power
plants that were built in the United States in the1880's. The earliest power plants used hand fed wood or coal to heat a boiler and produce steam.
This steam was used in reciprocating steam engines which turned generators
to produce electricity. In 1884, the more efficient high speed steam
turbine was developed by British engineer Charles A. Parsons which replaced the use of steam engines
to generate electricity. In the 1920s, the pulverized coal firing was developed. This process brought
advantages that included a higher combustion temperature, improved thermal
efficiency and a lower requirement for excess air for combustion. In the 1940s, the cyclone furnace was developed. This new technology allowed
the combustion of poorer grade of coal with less ash production and greater
Presently, coal power is still based on the same methods started over 100 years ago, but improvements in all areas have
brought coal power to be the inexpensive power source used so widely today.
Coal Fired Power Generation Technologies:
* Pulverized Coal System :
The concept of burning coal that has been pulverized into a fine powder stems from the belief that if the coal is made fine
enough, it will burn almost as easily and efficiently as a gas. The feeding rate of coal
according to the boiler demand and the amount of air available for drying and transporting the pulverized coal fuel is controlled by computers. Pieces
of coal are crushed between balls or cylindrical rollers that move between
two tracks or "races." The raw coal is then fed into the pulverizer along with air heated to about 650 degrees F from the boiler. As the coal gets
crushed by the rolling action, the hot air dries it and blows the usable fine coal powder out to be used as fuel. The powdered coal from the
pulverizer is directly blown to a burner in the boiler. The burner mixes the
powdered coal in the air suspension with additional pre-heated combustion air and forces it out of a nozzle similar in action to fuel being atomized
by a fuel injector in modern cars. Under operating conditions, there is enough heat in the combustion zone to ignite all the incoming fuel.
* Cyclone Furnaces:
Cyclone furnaces were developed after pulverized coal systems and require less processing of the coal fuel. They can burn poorer grade coals with
higher moisture contents and ash contents to 25%. The crushed coal feed is
either stored temporarily in bins or transported directly to the cyclone furnace. The furnace is basically a large cylinder jacketed with water pipes
that absorb the some of the heat to make steam and protect the burner itself
from melting down. A high powered fan blows the heated air and chunks of coal into one end of the cylinder. At the same time additional heated
combustion air is injected along the curved surface of the cylinder causing
the coal and air mixture to swirl in a centrifugal "cyclone" motion. The whirling of the
air and coal enhances the burning properties producing high heat densities (about 4700 to 8300kW/m2) and high combustion temperatures.
The hot combustion gases leave the other end of the cylinder and enter the
boiler to heat the water filled pipes and produce steam. Like in the pulverized coal burning process, all the fuel that enters the cyclone burns
when injected once the furnace is at its operating temperature. Some slag remains on the walls insulating the burner and directing the heat into the
boiler while the rest drains through a trench in the bottom to a collection
tank where it is solidified and disposed of. This ability to collect ash is
the biggest advantage of the cyclone furnace burning process. Only 40% of the ash leaves with the exhaust gases
compared with 80% for pulverized coal burning. Cyclone furnaces are not without disadvantages. The coal used must
have a relatively low sulfur content in order for most of the ash to melt for collection. In addition, high power fans are required to
move the larger coal pieces and air forcefully through the furnace, and more nitrogen oxide
pollutants are produced compared with pulverized coal combustion. Finally,
the actual burner requires yearly replacement of its liners due to the erosion caused
by the high velocity of the coal.
and International Electric hold in dispute many of the commonly held
concepts about the environmental impacts of coal fired electrical
generation. We believe that the benefits far outweigh any potential
negative impacts. IECG and CRPG work with the community and with
recognized experts to minimize and eliminate any potential environments
hazards such as:
* Coal mining causes severe erosion, resulting in the leaching of toxic chemicals into nearby streams and aquifers, and
* About two-thirds of sulfur dioxide, one-third of carbon dioxide emissions and one quarter of the nitrogen oxides emissions in the U.S. are
produced by coal burning.
* Coal burning also results in the emission of fine particles matter into the
atmosphere. Nitrogen oxide and fine airborne particles exacerbate asthma, reduce lung function and cause respiratory diseases and premature
death for many thousands of Americans.
* Smog formed by nitrogen oxide and reactive organic gases causes crop, forest and property damage. Sulfur dioxide and nitrogen oxides both
combine with water in the atmosphere to create acid rain. Acid rain acidifies the soils and water killing off plants, fish, and the animals that
depend on them.
* Global warming is mainly caused by carbon dioxide emissions and is responsible for at least half of the warming.
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