Coal

is a black or brownish-black, formed as  called. Coal is mostly with variable amounts of other {{w|chemical elements]], chiefly {{w|hydrogen}}, {{w|sulfur}}, {{w|oxygen}}, and {{w|nitrogen}}. Coal is formed when dead {{w|plant matter}} decays into {{w|peat}} and is converted into coal by the heat and pressure of deep burial over millions of years. On {{Terra}} vast deposits of coal originate in former wetlands—called {{w|coal forest}}s—that covered much of the planet’s tropical land areas during the late {{w|Carboniferous}} ({{w|Pennsylvanian (geology)|Pennsylvanian}}) and {{w|Permian}} times. However, many significant coal deposits are younger than this and originate from the {{w|Mesozoic}} and {{w|Cenozoic}} eras.

Coal is primarily used as a fuel. While coal has been known and used for thousands of years. The extraction and use of coal causes premature deaths and illness.

Etymology
The word originally took the form col in, from *kula(n), which in turn is hypothesized to come from the  root *g(e)u-lo- "live coal". cognates include the kole,  cole,  kool,  chol,  Kohle and  kol, and the  word gual is also a cognate via the  root.

History


The earliest recognized use is from the area of China where by 4000 BC  inhabitants had begun carving ornaments from black lignite. Coal from the Fushun mine in northeastern China was used to smelt copper as early as 1000 BC., the Italian who traveled to China in the 13th century, described coal as “black stones ... which burn like logs”, and said coal was so plentiful, people could take three hot baths a week. In Europe, the earliest reference to the use of coal as fuel is from the geological treatise On Stones (Lap. 16) by the Greek scientist (c. 371–287 BC):

"Among the materials that are dug because they are useful, those known as anthrakes [coals] are made of earth, and, once set on fire, they burn like charcoal [anthrakes]. They are found in Liguria ... and in Elis as one approaches Olympia by the mountain road; and they are used by those who work in metals."

- Theophrastus, On Stones (16)

coal was used in Britain during the (3000–2000 BC), where it formed part of funeral pyres. In, with the exception of two modern fields, “the were exploiting coals in all the major coalfields in  and  by the end of the second century AD”. Evidence of trade in coal, dated to about AD 200, has been found at the, near ; and in the of , where coal from the  was transported via the  for use in drying grain. Coal cinders have been found in the hearths of and, particularly in , dated to around AD 400. In the west of England, contemporary writers described the wonder of a permanent brazier of coal on the altar of at  (modern day ), although in fact easily accessible surface coal from what became the  was in common use in quite lowly dwellings locally. Evidence of coal's use for iron-working in the city during the Roman period has been found. In, , deposits of were used by the Romans for the smelting of.

No evidence exists of coal being of great importance in Britain before about AD 1000, the. Coal came to be referred to as “seacoal” in the 13th century; the wharf where the material arrived in London was known as Seacoal Lane, so identified in a charter of granted in 1253. Initially, the name was given because much coal was found on the shore, having fallen from the exposed coal seams on cliffs above or washed out of underwater coal outcrops, but by the time of, it was understood to derive from the way it was carried to London by sea. In 1257–1259, coal from was shipped to London for the  and -burners building. Seacoal Lane and Newcastle Lane, where coal was unloaded at wharves along the, still exist.

These easily accessible sources had largely become exhausted (or could not meet the growing demand) by the 13th century, when underground extraction by or  was developed. The alternative name was “pitcoal”, because it came from mines.

Cooking and home heating with coal (in addition to firewood or instead of it) has been done in various times and places throughout human history, especially in times and places where ground-surface coal was available and firewood was scarce, but a widespread reliance on coal for home hearths probably never existed until such a switch in fuels happened in London in the late sixteenth and early seventeenth centuries.

Coking coal and use of coke to smelt iron
Coke is a solid carbonaceous residue derived from (a low-ash, low-sulfur bituminous coal, also known as metallurgical coal), which is used in manufacturing  and other iron products. Coke is made from coking coal by baking in an oven without oxygen at temperatures as high as 1,000 °C, driving off the volatile constituents and fusing together the fixed carbon and residual ash. Metallurgical coke is used as a and as a  in   in a. The carbon monoxide produced by its combustion reduces (an ) to.

Waste carbon dioxide is also produced together with, which is too rich in dissolved carbon so must be treated further to make steel.

Coking coal should be low in ash,, and , so that these do not migrate to the metal. The coke must be to resist the weight of overburden in the blast furnace, which is why coking coal is so important in making steel using the conventional route. Coke from coal is grey, hard, and porous and has a heating value of 29.6 MJ/kg. Some cokemaking processes produce byproducts, including, , light oils, and.

Use in foundry components
Finely ground bituminous coal, known in this application as sea coal, is a constituent of. While the molten metal is in the, the coal burns slowly, releasing at pressure, and so preventing the metal from penetrating the pores of the sand. It is also contained in ‘mould wash’, a paste or liquid with the same function applied to the mould before casting. Sea coal can be mixed with the clay lining (the “bod”) used for the bottom of a. When heated, the coal decomposes and the bod becomes slightly friable, easing the process of breaking open holes for tapping the molten metal.

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