Coal is the product of vegetable matter that has been formed by the action of decay, weathering, the effects of pressure, temperature and time millions of years ago.
Although coal is not a true mineral, its formation processes are similar to those of sedimentary rocks.
Structurally coal beds are geological strata characterized by the same irregularities in thickness, uniformity and continuity as other strata of sedimentary origin. Coal beds may consist of essentially uniform continuous strata or like other sedimentary deposits may be made up of different bands or benches of varying thickness.
Rack
^----------- t
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**i r*m f*? ~i*f~ ~^~^r nSW&nM
Fig. 3. Seam of coal
Fig. 4. Complex seam
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Thus, in Fig. 3 one can see a seam limited by two more or less parallel planes, a shape which is typical of sedimentary rocks.
The benches may be separated by thin layers of clay, shale, pyrite or other mineral matter, commonly called partings (Fig. 4).
Like other sedimentary rocks coal beds may be structurally disturbed by folding and faulting.
According to the amount of carbon coals are classified into: brown coals, bituminous coals and anthracite. Brown coals are in their turn subdivided into lignite and common brown coal.
Although carbon is the most important element in coal, as many as 72 elements have been found in some coal deposits, including lithium, chromium, cobalt, copper, nickel, tungsten and others.
Lignite is intermediate in properties between peat and bitumi nous coal, containing when dry about 60 to 75 per cent of carbon and a variable proportion of ash. Lignite is a low-rank brown-to-black coal containing 30 to 40 per cent of moisture. Developing heat it gives from 2,500 to 4,500 calories. It is easily inflammable but burns with a smoky flame. Lignite is liable to spontaneous combustion. It has been estimated that about 50 per cent of the world's total coal reserves are lignitic.
Brown coal is harder than lignite, containing from 60 to 65 per cent of carbon and developing greater heat than lignite (4,000-7,000 calories). It is very combustible and gives a brown powder. Bituminous coal is the most abundant variety, varying from medium to high rank. It is a soft, black, usually banded coal. It gives a black powder and contains 75 to 90 per cent of carbon. It weathers only slightly and may be kept in open piles with little danger of spontaneous combustion if properly stored. Medium-to-low volatile bituminous coals may be of coking quality. Coal is used intensively in blast furnaces for smelting iron ore. There are non-coking varieties of coal.
As for the thickness, the beds of this kind of coal are not very thick (1-1.5 metres). The great quantities of bituminous coal are found in the Russian Federation.
Anthracite or "hard" coal has a brilliant -lustre containing more than 90 per cent of carbon and low percentage -fit volatile matter. It is used primarily as a domestic fuel, although it can sometimes be blended with bituminous grades of coal to produce a mixture with improved coking qualities. The largest beds of anthracite are found in Russia, the USA and Great Britain.
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Unit 6______________________________________________ 153
Coal is still of great importance for the development of modern industry. It may be used for domestic and industrial purposes. Being the main source of coke, coal is widely used in the iron and steel industry. Lignite, for example either in the raw state or in briquetted form, is a source of industrial carbon and industrial gases.
There is a strong tendency now for increased research into new technologies to utilize coal. No doubt, coal will be used as a raw material for the chemical industry and petrochemical processes. All these processes involve coal conversion which include gasification designed to produce synthetic gas from coal as the basis for hydrogen manufacture, liquefaction () for making liquid fuel from coal and other processes.
28. , .
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1. Anthracite coals may be divided into lignite and common
brown coal.
2. Coals are ranked according to the percentage of carbon they
contain.
3. Peat, with the least amount of carbon is the lowest rank, then
comes lignite or brown coal.
4. Brown coal is hard and it is not liable to spontaneous combus
tion.
5. Bituminous coal weathers rapidly and one cannot keep it in
open piles.
6. Being intensively used in the Iron and steel industry bitumi
nous coal varies from medium to high rank.
7. Anthracite or hard coal, the highest in percentage of carbon,
can be blended with bituminous grades of coal.
29. :
1. What is the classification of coal based on?
2. Is carbon the only element in coal? (Prove it.)
3. Is lignite intermediate in properties between peat and bitumi
nous coal?
4. What heat value does lignite develop when burnt?
5. What coals are liable to spontaneous combustion?
6. What is the difference between lignite and brown coal?
7. Is bituminous coal high- or low-volatile?
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8. Does anthracite contain 90 per cent of carbon?
9. Where are the largest deposits of anthracite found? And what
can you say about bituminous coal?
10. What do you know about the utilization of coal?
30. )
:
1. spontaneous combustion, )
2. moisture and ash content 6)
3. the most abundant variety )
of coal )
4. in its turn )
5. the amount of volatile matter e)
6. easily inflammable gas. ) -
7. brilliant lustre
8. to smelt iron ore )
9. high-rank coal )
10. a smoky flame )
6) :
1. a) heat value
2. ) amount of caibon
3. ) coal rank
4. ) to store coal
5. ) to weather rapidly
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6. ) non-coking coal
7. ) blast furnace
8. ) of improved quality
9. ) to blend with other coals
31.
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