Coal is a multifaceted resource which differs in composition even inside the same deposit. There are four different types or ranking based on various levels of coal with differences in energy output as a result of increased temperature,pressure & time
Lignite is a brownish-black coal with great moisture and ash content and the lowest heating value of the four types of coal. It is used for generating electricity.
Subbituminous coal is a dull black coal consisting a higher heating value than lignite and used for electricity and space heating.
Bituminous coal is the most commonly used type of coal for electric power . Bituminous Coal is a dark, hard coal that has a higher heating value than lignite and subbituminous coal, but it has a lower heating value than anthracite.
Anthracite also known as "hard coal", hard and shiny and compact, thus consumed highest energy content of the all the four levels of coal discussed here. It is used for space heating and generating electricity.
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