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Lignite (derived from Latin lignum meaning 'wood'), often referred to as brown coal, [1] is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% [ 1 ] [ 2 ] and is considered the lowest rank of coal due to its relatively low heat content .
Bituminous coal is dark brown to black, [3] hard, [9] but friable. [10] It is commonly composed of thin bands of alternating bright and dull material. [9] Though bituminous coal varies in its chemical composition, a typical composition is about 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur, on a weight basis. [11]
The grade of coal produced depended on the maximum pressure and temperature reached, with lignite (also called "brown coal") produced under relatively mild conditions, and sub-bituminous coal, bituminous coal, or anthracite coal (also called "hard coal" or "black coal") produced in turn with increasing temperature and pressure. [2] [22]
An anthracite pile in Trevorton, Pennsylvania. Anthracite derives from the Greek anthrakítēs (ἀνθρακίτης), literally "coal-like". [9] Other terms which refer to anthracite are black coal, hard coal, stone coal, [10] [11] dark coal, coffee coal, blind coal (in Scotland), [7] Kilkenny coal (in Ireland), [10] crow coal or craw coal, and black diamond.
The behaviour of the coal's ash residue at high temperature is a critical factor in selecting coals for steam power generation. Most furnaces are designed to remove ash as a powdery residue. Coal which has ash that fuses into a hard glassy slag known as clinker is usually unsatisfactory in furnaces as it requires cleaning. However, furnaces can ...
Soft coal may refer to several lower quality types of coal, primarily used for power generation: Lignite, or brown coal; Sub-bituminous coal; Bituminous coal, ...
This word refers to a large, dark-brown animal that lives in (or around) African rivers. They are renowned for their barrel-shaped bodies, enormous heads and short legs.
Densified coal is the product of the Coldry Process coal upgrading technology that removes moisture from low-rank coals such as sub-bituminous and lignite/brown coal.The densification process raises the calorific value of low-rank coal to equal or exceed that of many export-grade black coals.
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