Brown coal

BROWN COAL

BROWN COAL (EN: brown coal; DE: Braunkohle; FR: lignite, charbon brun; ES: lignito; RU: бурый уголь) is the combustible useful mineral of the plant origin, with the low degree of coalification, the transitional form from the peat to the mineral coal.

Within the USSR, there belong to the brown coals the coals with the highest heat of combustion from the wet ash-free mass of less than 24 megajoules per kilogram, and with the reflective ability of the vitrinite within the oil (R0) of less than 0.50 (the GOST 9276-72 governmental standard). The analogous value for the heat of combustion for the separation of the brown and mineral coals is prescribed by the international classification. The brown coals in the lump and powder forms (the streak on the porcelain plate, namely, "biscuit") have the colour from pale yellow to black; the density is 1200-1500 kilograms per cubic metre, the voluminous mass is 1.05-1.4 tonnes per cubic metre, the loose bulk mass is 0.70-0.97 tonnes per cubic metre. They distinguish the soft, earthy, matte, lignitic, and dense (lustrous) varieties. Within the air, the brown coal rapidly loses the moisture, cracks itself, and metamorphoses itself into the small pieces.

The overwhelming majority of the brown coals, according to their material composition, belong to the humites. The sapropelites, and the transitional humus-sapropel varieties, have the subordinate significance, and may be found in the form of the interlayers within the layers, which are formed by the humites. The majority of the brown coals is formed by the microcomponents of the vitrinite group (80-98%), and only within the Jurassic brown coals within the Central Asia, there prevail the microcomponents of the fusenite group (45-82%); for the Lower Carboniferous brown coals, there is characteristic the high content of the liptinite. Within the USSR (the GOST 21489-76 governmental standard), the brown coal is sub-divided according to the degree of the metamorphism (coalification) into the three stages, namely, O1, O2, and O3, and into the three classes, namely, 01, 02, and 03. As the basis for such sub-division, there is adopted the reflective ability of the vitrinite within the oil R0; its normalized value for the stage O1 is less than 0.30; for the stage O2 is 0.30-0.39; for the stage O3 is 0.40-0.49. By the industrial classifications of the USSR (the GOST governmental standard, the A 10 group) the brown coals are sub-divided according to the humidity of the working fuel (Wr) into the three technological groups (see the Table). The brown coals of Ukraine (the GOST 9280-75 governmental standard) are divided into the four groups according to the yield of the primary tar from the semi-coking (Tskdaf is more than 25%; 20-25%; 15-20%; 15% and less), and into the four subgroups according to the specific heat of combustion (Qsdaf is more than 31.5; 31-31.5; 29-31; and less than 26 megajoules per kilogram). According to the international classification, which has been adopted by the European Economic Commission (1957), the brown coals are sub-divided into the six classes according to the humidity (less than 20; 20-30; 30-40; 40-50; 50-60; 70-70), and into the five groups according to the yield of the tars from the semi-coking.

The average values for the indicators of quality for the brown coals of the USSR
The technological group The technical analysis, % The elementary composition, % The specific heat of combustion, megajoules per kilogram
Wr Ad Vdaf Sdf Cdaf Hdaf Qdaf Qsdaf Qri
Б1 40-58 12-40 44-60 0.2-4.0 64-70 4.5-5.9 20-28 25.5-29.2 6.06-12.8
Б2 30-40 7-45 44-56 0.3-8.0 65-76 3.8-5.7 17-26 25.6-29.2 9.08-15.9
Б3 19-30 14-40 32-50 0.3-3.0 67-78 4.0-6.0 16-22 26.58-31.2 11.66-18.8
Note.
Wr - the humidity of the working fuel;
Ad - the ash content in terms of the dry condition of the coal;
Vdaf - the yield of the volatile substances, is calculated for the dry ash-free condition of the coal;
Sdf - the total sulfur content for the dry condition of the coal;
Cdaf - the content of carbon within the combustible mass of the coal;
Hdaf - the content of hydrogen within the combustible mass of the coal;
Qdaf - the specific heat of combustion of the coal;
Qsdaf - the specific heat of combustion according to the bomb calorimeter method, is calculated for the dry ash-free condition of the coal;
Qri - the specific lower heat of combustion for the working fuel.

With the increase of the degree of metamorphism within the brown coals, there increase themselves the content of carbon, the specific heat of combustion, and decreases itself the content of oxygen. The brown coals are characterised by the higher content of the phenolic, carboxyl, and hydroxyl groups, by the existence of the free humic acids, the content of which decreases itself with the increase of the degree of metamorphism from 64 to 2-3%, and of the tars, the content of which decreases itself from 25 to 5%. At the certain deposits, the soft brown coals give the high yield of the benzene extract (5-15%), which is containing 50-75% of the waxes, and have the increased content of uranium and germanium.

The largest basins and deposits of the brown coals are characteristic for the Mesozoic-Cenozoic depositions (see the Map). There comprise the exception the Lower Carboniferous brown coals of the Eastern European craton (the Moscow region basin). Within Europe, the depositions of the brown coals are associated almost exclusively with the depositions of the Neogene-Paleogene age, while within Asia, prevalently with the Jurassic age, to the lesser degree with the Cretaceous and Paleogene-Neogene ages, and on the remaining continents, with the Cretaceous and Paleogene-Neogene ages. Within the USSR, the major reserves of the brown coals are confined to the Jurassic depositions. The significant portion of the brown coals is embedded at the shallow depths within the coal layers (depositions) with the thickness of 10-60 metres, which fact permits to develop them with the opencast method. At the individual deposits, the thickness of the depositions is 100-200 metres.

The total worldwide resources of the brown coals are estimated (to the depth of 600 metres) at 4.9 trillion tonnes (1981). The worldwide reserves of the brown coals have been counted as the quantity of 1.3 trillion tonnes, of which the measured reserves (within the USSR, according to the A + B + C1 categories) are 0.3 trillion tonnes. The major reserves are concentrated within the USSR, West Germany, East Germany, Poland, Czechoslovakia, and Australia. The total geological reserves and resources of the brown coals within the USSR are estimated at 2090 billion tonnes (1981), including the reserves according to the A + B + C1 + C2 categories at 160 billion tonnes. The major basins within the USSR (there are within the parentheses the technological groups of the coals, and the reserves in the billions of tonnes): Kansk-Achinsk (B1-B2 - more than 115), Iliysk (B1-10), Moscow region (B2-4.0), Dnepr (B1-3.2), Southern Urals (B1-1.1), Chelyabinsk (B3-0.7), Turgaisk (B2-6.5), Irkutsk (B3-2.9), Maikubensk (B3-1.8), Uglovsk (B3-0.7). The largest deposits are: Nizhneiliyskoe (B1-B2-6.8), Angrenskoe (B2-1.9), Svobodnoe (B1-1.7), Bikinskoe (B1-B2-1.2), Kharanorskoe (B1-1.0). The major forecasted resources of the brown coals are concentrated within the Lena (B1-B3-941), and Kansk-Achinsk (B1-B3-508) basins (1980). The major basins within the foreign countries are: Latrobe Valley (Australia, lignite - 108); Fort Union, part of Alberta (USA, B2-B3-350); Lower Rhine (West Germany, B1-60); Thuringia-Saxony and Magdeburg (East Germany, B1-40); Mississippi and Texas (USA, lignite - 20); Maritskiy (Bulgaria, B1-3.1); Kosovo (Yugoslavia, B-4.5); Anatolian (Turkey, B1-B2-4.8); Neyveli (India, B1-3.3); Alta Amazon (Brazil, B-2200).

The worldwide extraction of the brown coals is 952.3 million tonnes (1980). The major coal-extracting countries (the extraction, million tonnes) are: East Germany (258), the USSR (165), West Germany (130), Czechoslovakia (95), USA (45), Poland (37), Australia (33). Within the USSR, the brown coal is extracted (1981, million tonnes) within the Moscow region (24.1), Dnepr (7.9), Chelyabinsk (13.2), Southern Urals (7.9), Kansk-Achinsk (35.2 ), Irkutsk (13.5), Uglovsk (1.7) basins, at the Angrenskoe (5.3), Kharanorskoe (6.3), Rajchikhinskoe (13.0), Bikinskoe (3.9), Pavlovskoe (2.3), and other deposits. The depth for the underground development does not exceed 600 metres, with the exception of the Chelyabinsk basin, and of the individual deposits within the Central Asia. For the majority of the deposits, the least thickness of the coal layers, which are developed with the opencast method, is 2 metres, and with the underground method is 0.8-1.3 metres.

The brown coal is delivered to the consumer in the unsorted (ordinary BR) or sorted form. The coals are used prevalently for the combustion in the powdered form, as the domestic fuel, and on the smaller scale, for the briquetting, gasification, production of the coal-alkaline reagents and montan wax (mineral wax). Within the East Germany, the brown coal is used for the obtainment of the metallurgical coke (of the coke briquettes). There is prospective the usage of the brown coals for the production of the liquid fuel, for the energy-technological processing, for the obtainment of the semi-coke and thermal coal. The requirements of the industry for the quality of the brown coals within the USSR are regulated within the basins (the GOST governmental standard, A13 group). There are normalized by the technical conditions for the brown coals the humidity, the ash content, the content of the lumps of coal with the size of more than 200 (300) millimetres, and the content of the visible rock. The greatest ash content of the brown coals, which are supplied for the combustion in the powdered form, must not exceed 40%, for the combustion in the layer form, must not exceed 37%, and for the briquetting, must not exceed 25%.

According to the classification within the USA, there correspond to the brown coals the B and C sub-bituminous coals, and the A and B lignites.