Coal: Formation

Formation of Coal

To arrive at its present form, coal encountered enormous changes. It began long ago in the formation of plants and other organic material. Those plants died and were covered by layers of sediment. As time passed, heat, weight, and pressure built up on top of the plants, forcing them to change from plants to peat, to coal. Over time, this coal "matured" into higher rank coal. Higher rank coals have less moisture and higher carbon content.  Source: Illinois Department of Commerce.

American coal mining began in Virginia in 1748. Initially coal was used for home heating and cooking, and coal's use quickly expanded to power steam engines, steam boats, and the railroads. In 1882, the first coal-fueled electrical power station began operations in New York City. Since then, coal use has continued to grow. Today, coal provides approximately half of the electricity in the United States.

Coal mining in Alaska can be traced back to the early 1900s during the gold rush years. Visible coal in the Healy area was an obvious source of fuel for steam boats and the railroad operations between Anchorage and Fairbanks.
   

Ranks of Coal

  

There are four main ranks of coal:
1.
Anthracite  
Anthracite is the highest rank coal. It is hard, shiny (or lustrous) and has high heat content and little moisture. Anthracite is used in residential and commercial heating, as well as a mix of industrial applications. Some waste products from anthracite piles are used in energy generation. Anthracite is mined primarily in Pennsylvania.  
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 Oldest coal - over 300 million years  
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 High heat value  
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 High fixed carbon content - 90%  
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 Low volatile matter - less than 10%  
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 Burns slowly  
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 Home heating fuel  
•
 Least plentiful of all coals  
2.
Bituminous  
Bituminous coal is high-rank coal. It has high heat and low moisture contents and is harder than lower ranked coals. Bituminous coals are used in electricity generation and steel making processes, as well as, for industrial and municipal steam production applications. Bituminous coals are mined primarily in Appalachia, the Midwest and the West.  
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 Mined at Wishbone Hill Mine - Sutton, Alaska  
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 Old coal - 50 million to 300 million years  
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 Very little moisture  
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 Low volatile matter - less than 10%  
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 High heat value  
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 Generation of steam to produce electricity  
•
 Steel industry  
 
3.
Subbituminous  
Subbituminous coal is generally considered a soft coal. It has a lower moisture content and higher heat content than lignite. This rank of coal is typically used in electricity generation. Subbituminous coals are mined primarily in the Powder River Basin of Wyoming and Montana.  
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 Mined at Usibelli Coal Mine - Healy, Alaska  
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 Young coal - 10 million to 50 million years  
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 Medium to high moisture content  
•
 Generation of steam to produce electricity and district heat  
 
4.
Lignite  
Lignite, sometimes called "brown coal," is the lowest rank, or least mature coal. It has a high moisture and low heat content and is typically used in electricity generation. It is friable (easily broken up) and soft. As the name "brown coal" suggests, lignite can be brown in color. Lignite is primarily mined in Texas, North Dakota, Montana, and the Gulf States.  
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 Very young coal - less than 20 million years  
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 High moisture content  
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 Low carbon/energy content  
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 Brownish-black in color  
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 Crumbles easily  
•
 Generation of steam to produce electricity  
   

"Coking coal" describes a specific type of bituminous coal that "cokes" when exposed to high heat in the absence of air. The coking process involves heating coal to draw off volatile substances such as tars and aromatic hydrocarbons. This heating fuses the carbon and residual ash into a hard, grey, porous substance called "coke." Coke is used in the steel-making process as a fuel and reducing agent.

Usibelli coal is approximately 8 to 20 million years old. The age of the coal is one factor which determines its contained energy value. At 7,800 BTU Usibelli coal is well suited for use in power plants for steam production which is utilized to spin the electrical turbines and the steam can be utilized for space heat for commercial buildings and structures. This dual use of energy for electricity and heat is called “cogeneration.”

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