US 2924279 A
Description (OCR text may contain errors)
169-44. foR 2,9%2'79 .5R 6? C? Feb. 9, 1960 1. HoFBAuER Erm. 2,924,279
METHOD OF PREVENTING THE OUTBREAK OF ENDOGENOUS MINE FIRES Filed Jan. 4, 1957 2 sheets-sheet' 1 Febfs, 1960 l. HOFBAUER EIAL METHOD 0F PREVENTING THE OUTBREAK OF ENDOGENOUS MINE FIRES 2 Sheets-Sheet 2 Filed Jan. 4, 1957 United States Patent O METHOD OF PREVENTING THE OUTBREAK OF ENDOGENOUS MINE FIRES Ivo Hofbauer, Gustav ebor, Karel Betan, and Josef Novak, all of Vinarice, near Kladno, Czechoslovakia Application January 4, 1957, Serial No. 632,500
Claims priority, application Czechoslovakia January 5, 1956 11 Claims. (Cl. 169-1) The present invention relates Ito a method of preventing the outbreak of endogenous mine fires and a device for carrying out this method.
Endogenous mine res being the cause of great damage every year, the methods of preventing their outbreak have received considerable attention. The hitherto known method of preventing mine res consists in covering the coal walls with a thin lime mortar by a so-called injection process or by pressing a solution of lime milk or y ash into the walls. A drawback of this method is on the one hand the fact that the layer on the surface peels ofi soon, and on the other hand its ineiciency in the furrows under the injected layer, in particular when the coal walls are displaced under the influence of the pressure of the rock.
Etective substances, so-called inhibitors have, therefore been sought to reduce the tendency of coal towards self-ignition i.e. substances which suppress the oxidation of coal. These are for example boric acid, aluminium sulfate, sodium phosphate, calcium chloride, pyrocatechin and the like.
According to the invention an inhibitor for a deep injection process comprises a solution of hygroscopic calcium chloride which is a waste-product in chemical industry. As the solution of CaCl2 would not permanently till the gaps and cavities in the coal massif, a mineral iilling agent is added to the inhibitor, e.g. a tinely ground high-quality clay, bentonite or the like.
Preferably a solution of CaCl2 in a mixture with finely ground clay in a proportion of 40 to 45% of clay to 55 to 60% of calcium chloride is used for the deep injection process. V
The mixture of the inhibitor with clay is introduced through bores under pressure into the coal walls threatened by tire, by means of an injection needle which is sealed by tightened screws so as to prevent the mixture of CaCl2 with clay from flowing back from the bore.
The depth and spacing of the individual bore holes from each other depends from the hardness, cuts and temperature of the seam. The depth of the bore holes v amounts to 1 to 4 meters, the spacing of the individual bore holes to 2 to 4 meters and depends on the above mentioned circumstances. The pressure under which the mixture is pressed into the coal wall amounts usually to 4 to 12 atm. The mixture is pressed slowly'into the walls as long as the coal wall receives the inhibitor or until the mixture emerges from the coal wall in the vicinity of the bore-hole, indicating that the wall is saturated. The consumption of the mixture amounts to 50 to 500 litres, sometimes even more, per 1 m32 of the coal wall. The purpose of the deep injection process is to ll the cracks or cavities in the coal Wall with the inhibitor, but the latter must not impair the coal massif. In this the method according to the invention differs basically from the process of pressure water injection. The surface impregnation of coal walls by the inhibitor has for its purpose to prevent the ac- 2,924,279 Patented Feb. 9, 1960 cess of oxygen to the coal walls. It is carried out by a mixture of CaCl2 with clay in a proportion of about 1: 1, i.e. thicker than used for the deep injection process, the concentration of CaClz depending on the temperature and relative humidity of the working site and being selected to retain suicient moisture to keep the clay plastic. The mixture is applied to the coal walls in a layer of a thickness of about 5 to 7 mm. and the consumption for 1 m.2 of the coal wall amounts to 5 to 10 litres of mixture.
The present invention relates also to a device for carrying out the pressure injecting process and impregnation of the coal walls.
The mixing of the inhibitor with the mineral substance has originally been carried out in a mining truck provided with coiled pipes, arranged near the truck bottom. Air isinjected through apertures in the pipes, the air serving for stirring apertures in the pipes, the lair serving for stirring the mixture. A piston pump serves to produce the required pressure for the injection process, said pump being mounted on the undercarriage of the truck. This device suffers from numerous drawbacks, is liable to breakdowns and is very clumsy. The injection process may be carried out only in places, where rail transport is available.
According to the invention an improved device fo carrying out the process is provided. f
The accompanying drawings represent by way of example one embodiment of the device.
Fig. 1 shows a diagrammatic view of the overall arrangement and Fig. 2 shows in an elevational view a detail of lthe device.
The device according to the invention comprises a compressor 1 adapted to produce pressure of 15 to 2O atm., driven either by an air turbine 2 or an electromotor, and a pressure container 3 of a contents of about litres. The device is mounted on sleighs for easier transport.
The mixture of the inhibitor with the nely ground mineral substance is prepared either at the surface in a mixing apparatus or underground in a mixer shown diagrammatically in Fig. 2. The mixer 5 comprises substantially a double propeller driven either by a small electromotor or an air boring machine 6.
The mixture of CaCl2 with clay is pressed from the pressure container through a hose to an injection needle which may be similar to the injection needle used in the pressure water injection process. The main advantage of the relatively light, easily mobile device according to the invention rests therein, that iire preventing operations may be carried out even in localities which are inaccessible to transport.
The device according to the invention may be used in addition to the deep injection process and surface impregnation of coal walls also for pressure atomisation of various antipyrogenous substances and wet treatment of coal walls (pressure water injection).
1. A method of preventing endogenous fires in coal mines and the like, comprising adding to a solution of calcium chloride a ller selected from the group of clay and bentonite, and applying the suspension obtained under pressure upon and within coal walls.
2. A method according to claim 1, wherein said solution contains approximately 10% calcium chloride and ne clay in a proportion of 40:60 to 45:55 relative to said calcium chloride, the suspension obtained being applied upon and within the coal walls.
3. A method of preventing endogenous fires in coal mines and Ithe like, comprising adding mineral filling material of a plastic nature to a solution of a hygroscopic substance capable of retarding selfLigniton of coal so as to obtain a liquid composition, boring holes into the coal walls and injecting the liquid composition into the holes.
4. A method of preventing endogenous res in coal mines -and the like, comprising adding to a solution of approximately 10% calcium chloride nely ground clay, the proportion of calcium chloride and clay being approximately 1:1, and applying the liquid composition obtained upon a coal wall under pressure.
5. In the method according to claim 2, applying approximately 50 to 100 liters of said suspension per cu. m. of coal.
6. In the method according to claim 3, boring holes of approximately l to 4 meters depth and about 2 to 4 meters apart.
7. In the method according to claim 3, injecting the liquid composition under a pressure of about 4 to 12 atm.
8. In the method according to claim 3, sealing the holes upon completion of the injection.
9. In the method according to claim 4, applying a layer of about 5 to 7 mm. thickness.
10. The method according to claim 3, wherein the liquid composition is injected to a depth of at least one meter.
11. The method according to claim 3, wherein the liquid composition is injected until said wall is saturated with the liquid composition.
Swift et al July 15, 1941 Williamson et al. May 8, 1951