Lignite
It is categorized as the lowest rank of coal owing to its lowest heating value and lowest carbon content carbon is about 25-35%. It is sometimes referred as brown coal, about 250 million years old.
Lignite is mainly used to generate electricity but can be used to generate synthetic natural gas and fertilizer products.
It retains more moisture and is thus very expensive and dangerous to mine and transport. It is susceptible to accidental combustion and has very high carbon emissions when burned. Most lignite coal is used in power stations very close to where it was mined.
Sub-Bituminous Coal
It contains more carbon than lignite, about 35-45%, and like lignite sometimes considered “brown coal”. It is mainly used as fuel for generating electricity.
Bituminous
It derives its name from a sticky, tar-like substance called bitumen which is also found in petroleum. It contains about 45-86% carbon. It is intermediate in rank and sometimes called soft coal. It is the most abundant kind of coal. Although it has a high heating value. but has high sulfur content. It is used as coke which serves as the raw material for blast furnace iron making in iron and steel industries. It is also used in the cement, textile, and plastic industries. Its by-products in different chemicals form are used to make paint, nylon, etc.
Bituminous coal can be further classified into smithing coal, cannel coal, and coking coal.
Smithing coal is used in forging because of its low ash content.
Cannel coal served as a source of coal oil which was used as fuel for illumination in the 19th century but later got replaced by kerosene in the 20th century.
Coking coal is used especially in the iron and steel industry where the coal is converted to coke by heating to high temperature in the absence of oxygen.
Anthracite
It is the highest rank of coal and possess highest heating value and highest carbon content (up to 97%). It is hard, deep black, and lustrous in nature. It burns longer, with more heat and less soot as compared to other forms of coal. Being expensive it rarely found its usage in power plants and is mainly used in stoves and furnaces.
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