Soaking process (mining)

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In the mining industry, an impregnation process , or coal impregnation , is a process that serves to bind the coal dust produced during the extraction of hard coal . The coal impregnation is intended to achieve a uniform moisture penetration of the coal. Impregnation processes are prescribed in the German hard coal mining industry by the mining ordinances .

Basics and history

Through reducing pressure in the Verhieb located seam pressure levels formed. This partially breaks up and grinds the coal and creates a large part of coal dust. There is more coal dust on the bad ones in the seam . The coal is moistened with water so that this coal dust does not get into the air stream when the coal is extracted, but rather is largely bound beforehand and prevented from being mobilized. This means that the dust is fought before it is released. The method was already described in 1890 by the mining engineer Meißner.

The basic procedure

First of all, a rotary drill is used to drill several holes in the coal face with a distance of three to ten meters, depending on the Tränkart. The boreholes can be carried out from the face , from the accompanying stretches or from a mine outside the extraction area. The holes have a diameter of 40 to 50 millimeters. They are drilled several meters into the seam and sealed with a soaking probe. When all of the required holes have been completed, pressurized water is applied to them via the probes. Depending on the pressure level of the water, a distinction is made between low pressure drinkers and high pressure drinkers. The seam is now exposed to water over a certain period of time, the soaking time. The water is pressed into the seam either continuously or discontinuously. Depending on the watering depth, between five and twelve liters of water are required per cubic meter of coal. Due to the pressure, the water penetrates into the coal in the finest crevices and columns , characterized the coal is wetted. In addition, the coal is partially loosened, which has a positive effect on the mining performance. However, it must be ensured that the Tränktiefe always be greater needs than the rate of utilization of the respective operating point.

differences

Over the years several methods have been developed which differ in terms of the water pressure used and the length of the borehole. A distinction is made between the near-soaking, the distant soaking, the deep soaking, the long-front soaking, the diagonal soaking and the pre-soaking. With the seam impregnation, the watering holes are drilled out of the longwall into the coal seam. The holes are then exposed to water until the coal begins to "sweat". In deep watering, the holes are made about ten meters deep in the seam. This makes it possible to soak the seam in advance for several days of mining. In remote watering, holes are drilled into the face from the face in staggered positions every day. They are drilled up to 30 meters deep into the seam. In all of these methods, the drill holes are made at right angles to the face joint. With long-front watering, holes up to 80 meters long are drilled into the seam from the accompanying stretches. In the case of pre-watering, the holes are made from another pit into the seam to be watered. In the case of diagonal watering, the boreholes are drilled into the seam with an angle of 66 to 77 gon up to a length of 40 meters.

Water pressures

Depending on the length of the borehole, the drinking water is introduced into the borehole at different pressures. In the case of low-pressure drinking, this is done with a water pressure of five to 20 bar . The normal operating pressure from the fresh water line is usually sufficient here. In the case of deeper boreholes, this pressure is not high enough; a significantly higher pressure has to be used so that the flow paths required for moistening the coal can open. In the process known as high pressure impregnation, impregnation pressures of 30 to 250 bar, sometimes even higher, are required. These high pressures, which can be up to 450 bar, can only be generated with special high-pressure pumps, such as differential or triple piston pumps. With these high pressures, the bad and pressure layers can be opened so that the water can penetrate the coal.

Cons and Problems

For the process to be most effective, the coal must be porous, but not too fissured. Problems with the structure and the load-bearing capacity of the coal can occur in sloping deposits . With very hard coal, it can happen that the drinking water does not penetrate sufficiently into the coal. This means that the coal remains dry even a short distance from the borehole. If the seams are not scratched, a sufficient amount of water cannot be injected into less porous coal. This is particularly a problem with deep drinking. The method is not suitable for water-sensitive adjacent rock with falling roof layers and slipping beds . If the coal is cracked, the water can escape too quickly, so that the coal is not sufficiently moistened. Due to wide cracks in the coal, the coal will be moistened unevenly. Drilling in the longwall hinders the work flow of the mining . The impregnation work can therefore only be carried out on a non-recoverable layer.

Individual evidence

  1. ↑ a b c d e f g h Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary . 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .
  2. ↑ Klaus-Peter Renner: The technical dust control in hard coal mining . In: Ministry of Economics, Energy, Building, Housing and Transport of the State of North Rhine-Westphalia. (Ed.): Annual report 2009 of the mining authorities of the State of North Rhine-Westphalia , Print Bezirksregierung Arnsberg, Düsseldorf 2010, pp. 44–48
  3. ↑ a b c d e f g h i j k l Ernst-Ulrich Reuther: Textbook of mining science. First volume, 12th edition, VGE Verlag GmbH, Essen 2010, ISBN 978-3-86797-076-1 , pp. 773-776.
  4. ↑ a b c d e f g h Carl Hellmut Fritzsche: Textbook of mining science. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962, pp. 607–610.
  5. ↑ a b c d Publication Service of the European Communities (ed.): The fight against silicosis . Robert Pfützner GmbH, Munich 1967.
  6. ↑ a b c d e Fritz Heise, Fritz Herbst: Textbook of mining science with special consideration of hard coal mining. First volume, fifth improved edition, published by Julius Springer, Berlin 1923, pp. 157–159.
  7. ↑ a b c d European Coal and Steel Community (Hrsg.): Technical dust control in mining. Status of research in the areas of occupational hygiene, occupational medicine and occupational safety on January 1, 1967, Luxemburg 1967, pp. 13-19.
  8. ↑ a b c European Coal and Steel Community (Ed.): Technical dust control in mining. Volume I, Report on the results of research carried out with the financial support of the High Authority of the ECSC (1960–1963) Luxembourg 1966, pp. 15–32.