Lignite
Lignite often referred to as brown coal.
It is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat.
It has a carbon content around 40 to 55%, and is considered the lowest rank of coal due to its relatively low heat content.
When removed from the ground, it contains a very high amount of moisture which partially explains its low carbon content.
Lignite is mined all around the world and is used almost exclusively as a fuel for steam-electric power generation.
The combustion for lignite produces less heat for the amount of carbon dioxide and sulfur released than other ranks of coal.
As a result lignite is the most harmful coal to human health.
Depending on the source, various toxic heavy metals, including naturally occurring radioactive materials, may be present in lignite which are left over in the coal fly ash produced from its combustion, further increasing health risks.
The energy content of lignite ranges from 10 to 20 MJ/kg on a moist, mineral-matter-free basis.
Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than higher-ranking coals.
Unfortunately, its high moisture content and susceptibility to spontaneous combustion can cause problems in transportation and storage.
Processes which remove water from brown coal reduce the risk of spontaneous combustion.
However, removing the moisture increases the cost of the final lignite fuel.
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