Hard Coal


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hard coal

[′härd ¦kōl]
(mineralogy)

Coal, Hard

 

a solid combustible mineral of plant origin; a type of mineral coal with a higher carbon content and greater density than brown coal (lignite). Hard coal is a dense rock of black and sometimes gray-black color with a shiny mat or semi-mat surface. It contains 75– percent and more carbon, 1.5–.7 percent hydrogen, 1.5– percent oxygen, 0.5– percent sulfur, up to 1.5 percent nitrogen, and 45– percent volatile matter; the amount of moisture varies between 4 percent and 14 percent; ash constitutes usually between 2– percent and 45 percent. The highest heat of combustion figured for a moist ashless mass of hard coal is 23.8 megajoules per kg (5, 700 kilocalories per kg).

Hard coals are formed from products of the decay of the organic remains of higher plants; these products have undergone changes (metamorphism) under the pressure of surrounding rocks in the earth’s crust at comparatively high temperatures. With an increase in the degree of metamorphism in the combustible mass of hard coal the carbon content increases consistently and, at the same time, the amount of oxygen, hydrogen, and volatile matter decreases; there are also changes in the heat of combustion and clinkering capacity. The industrial classification of hard coals by ranks that has been adopted in the USSR is based on changes in these qualities as determined by the results of the thermal decomposition of coal (the discharge of volatile matter and the characteristics of the nonvolatile remainder). The ranks are long flame, or candle (LF); gas, or bottle (G); gasmetabituminous (GF); metabituminous, or fat (F), coking metabituminous (CF); coking (C); lean clinkering (LC); lean (L); weak clinkering (WC); subanthracite (S); and anthracite (A). Anthracite coals are sometimes singled out as a separate group. Coals of ranks G, F, C, LC, and, to some extent, LF and L are generally used for coking. Between coal of rank LF and coal of ranks L-A there is a gradual decrease in moisture in the working fuel from 14 percent in LF coal to 4.5–5.0 percent in ranks L-A; at the same time the oxygen content (in the combustible mass) decreases from 15 percent to 1.5 percent and the hydrogen content drops from percent 5.7 to 1.5 percent. The content of sulfur, nitrogen, and ash does not depend on the rank to which the particular coal belongs. The heat of combustion of the combustible mass of coal rises steadily from 32.4 megajoules (MJ) per kg, or 7,750 kilocalories (kcal) per kg, for rank LF to 36.2–36.6 MJ/kg (8, 650–8,750 kcal/kg) for rank C and then decreases to 35.4–33.5 MJ/kg (8,450–8,000 cal/kg) for ranks S and A.

Hard coals are also classified by the size of the pieces obtained during extraction. The categories are slab (S) for more than 100 mm, macrofragmental (M) for 50– mm, nut (N) for 26– mm, fine (F) for 13– mm, seed (S) for 6– mm, chip (C) for less than 6 mm, and run-of-mine (R), which is not limited by size. Combinations of letters, such as LM, are used to indicate the rank and size of pieces for the coals.

The classifications of hard coals in a number of western European countries are based on approximately the same principles as those used in the USSR. The United States has the most extensive classification of hard coals, which is based on the release of volatile matter and the heat of combustion. The coals are divided into subbituminous, with a high discharge of volatile matter (corresponding to Soviet ranks LF and G); bituminous with moderate discharge of volatile matter (corresponding Soviet ranks F and C); bituminous with a low discharge of volatile matter (LC and L); and anthracite coals, which are divided into semianthracites (some L and A) and anthracites proper and meta-anthracites (A). In addition, there is an international classification of hard coals based on the content of volatile matter, the clinkering capacity, the coking capacity, and the industrial properties of the coals.

The formation of coal typifies all geological systems since the Silurian and Devonian; coal is very common in the deposits of the Carboniferous, Permian, and Jurassic systems. Coal occurs in the form of seams of varying thickness (from fractions of a meter to several dozen meters and more). The depth at which coals occur may vary; in some cases it emerges on the surface and in others it may occur as deep as 2, 000–, 500 m and lower. With the present level of mining technology, coal may be extracted by the open-pit method at depths to 350 m. The total geological reserves of hard coal in the USSR come to about 4, 700 billion tons (1968 estimate), which breaks down by rank (in billions of tons) to 1, 719 LF, 331 LF-G, 475 G, 69.4 GF, 156 F, 21.5 CF, 105 C, 88.2 LC, 634 WC, 205 L, 540 L-A, and 139 S and A. The largest reserves of hard coal in the USSR are found in the Tun-guska Basin. The largest developed coal basins in the USSR are the Donets, Kuznetsk, Pechora, and Karaganda basins. Major basins in other countries include the Appalachian and Pennsylvania Anthracite in the USA; Upper Silesia in Poland and its continuation into Czechoslovakia, the Ostrava-Karvina; the Ruhr in the Federal Republic of Germany; the Greater Hwang Ho Basin in China; South Wales in Great Britain; Valenciennes in France; and Brabant in Belgium. Coal has many uses: as home-heating and power fuel, as raw material for the metal and chemical industries, and for the extraction from the coal itself of rare and dispersed elements.

REFERENCES

Gapeev, A. A. Tverdye goriuchie iskopaemye. Moscow, 1949.
Zhemchuzhnikov, Iu. A., and A. I. Ginzburg. Osnovy petrologii uglei. Moscow, 1960.
Energeticheshoe toplivo SSSR: Spravochnik. Edited by T. A. Zikeev.Moscow, 1968.

A. K. MATVEEV

References in periodicals archive ?
While Germany's last hard coal mine has been shut down, Poland is currently expanding the country's hard coal mining activities in an effort to reduce its dependence on imports.
Meanwhile, the region that has now decommissioned all its hard coal mines - as opposed to the soft brown coal mines that continue to operate across Germany, despite ongoing negotiations for a full coal phase-out - is proudly showcasing its coal heritage.
The self-heating phenomenon occurs when the heat emitted as a result of contact between hard coal and oxygen is accumulated.
If the high coal margins persist, Reuters research shows that Germany could produce almost 130 terawatt-hours (TWh) of electricity from hard coal in 2012, up from 114.5 TWh last year.
The use of hard coal rose particularly in separate production of electricity.
Since the 12th century, galena ores have been excavated and used to extract silver and lead in the area of Olkusz near Krakow, whereas gold and hard coal have been excavated in the west of the country, in Lower Silesia.
Mixtures of hard coal and selected wastes were pyrolyzed in the laboratory model unit HOR2 (Kriz and Buchtele, 2003) built in IRSM AS CR Prague.
The report added that inland deliveries of hard coal were "continuing their slow decline," even though deliveries to the electricity generating industry rose slightly in 2001 and were "expected to show a further marginal increase in 2002, taking an increasing share of hard coal deliveries (70 per cent in 2000, 71 per cent in 2001 and 72 per cent in 2002)." Deliveries to coking plants were forecast to fall further in 2002, maintaining a downward that started in 1985, (interrupted only by a surge in deliveries in 2000).
Heating with this appliance involved filling it with hard coal through a hopper at the top and emptying the pan of clinkers and ashes, which was reached through a door at the bottom.
Proven coal reserves total some 984,211 Mt, of which 509,491 are hard coal (anthracite and bituminous) and 474,720 Mt are sub-bituminous and lignite.
The three German companies concerned are the country's only remaining hard coal producers and were cleared to merge on condition that they agreed to dispose of part of their coal importing business and divided the remainder of the coal trading operation into domestic and importing arms.
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