Иностранный язык (английский яз)

Coal 

Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons. Coal is a non-renewable energy source because it takes millions of years to create. The energy in coal comes from the energy stored by plants that lived hundreds of millions of years ago, when the Earth was partly covered with swampy forests.

For millions of years, a layer of dead plants at the bottom of  the swamps was covered by layers of water and dirt, trapping the energy of the dead plants. The heat and pressure from the top layers helped the plant remains turn into what we today call coal.

Coal is classified into four main types, or ranks (anthracite, bituminuos, subbituminous and lignite), depending on the amounts and types of carbon it contains and on the amount of heat energy it can produce. The rank of a deposit of coal depends on the pressure and heat acting on the plant debris as it sank deeper and deeper over millions of years.

Anthracite contains 86 97 % carbon, and generally has a heating value slightly higher than bituminous coal. It accounts for less than 0,5 % of the coal mined in the United States.

Bituminous coal contains 45 – 86 % carbon. Bituminous coal was formed under high heat and pressure. Bituminous coal in the United States is between 100 to 300 million years old. It is the most abundant  rank of coal found in the United States. Bituminous coal is used to generate electricity and is an important fuel and raw material for the steel and iron industries.

Subbituminous coal has a lower heating value than bituminous coal.  It typically contains 35 45 % carbon. Most subbituminuos coal  in the United States is at least 100 million years old. About 46 % of the coal  produced in the United States is subbituminous.

Lignite is the lowest rank of coal with the lowest energy content. Lignite coal deposits tend to be relatively young coal de­posits that were not subjected to extreme heat or pressure, contain­ing 25 – 35 % carbon. It is crumbly and has high moisture content.

Coal miners use giant machines to remove coal from the ground. They use two methods: surface or underground mining. Modern mining methods allow us to easily reach most of our coal reserves.

Surface mining is used to produce most of the coal in the US be­cause it is less expensive than underground mining. Surface mining can be used when the coal is buried less than 200 feet underground.

Underground mining, sometimes called deep mining, is used when the coal is buried several hundred feet below the surface. Some underground mines are 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. The plant cleans and processes coal to remove other rocks and dirt, ash, sulfur, and unwanted materials, increasing the heating value of the coal.

After coal is mined and processed, it is ready to be shipped to market.

Coal is used to create almost half of all electricity generated in the US. Power plants bum coal to make steam. The steam turns turbines that generate electricity.

A variety of industries use coal's heat and by-products. Sepa­rated ingredients of coal (such as methanol and ethylene) are used in making plastics, tar, synthetic fibers, fertilizers, and medicines.

Coal is also used to make steel. Coal is baked in hot furnaces to make coke, which is used to smelt iron ore into iron needed for making steel. It is the very high temperatures created from the use of coke that gives steel the strength and flexibility for things like bridges, buildings, and automobiles. The concrete and paper indus­tries also use large amounts of coal.

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