US3421587A - Method for mine fire control - Google Patents

Description

OR 394219587 R METHOD FOR MINE FIRE CONTROL Filed Sept. 20, 1967 Sheet of 2 FIRE ORIGIN OUTCROP com. BED .R COAL REMOVED BY STRI PPING {E} FIRE EVIDENCE 15 -CENTER LINE OF BARRIER HOLES v Q MINE COLUMNS l 20 30 FIG 2 lllllfifi 1 2O INVENTORS JERRY L. HEAVILON,

DENNIS A. JONES 8:

ATTORNEYS 14, 1969 J. 1.. HEAVILON ETAL 3,421,587

METHOD FOR MINE FIRE CONTROL Filed Sept. 20, 1967 Sheet 2 or 2 FIG-3 36 35 48 5'3 44 United States Patent 3,421,587 METHOD FOR MINE FIRE CONTROL Jerry L. Heavilon, Dayton, Dennis A. Jones, Vandalia,

and Barton A. Thomas, Dayton, Ohio, assignors to Dayton Fly Ash Co., Inc., Dayton, Ohio, a corporation of Ohio Filed Sept. 20, 1967, Ser. No. 669,205

U.S. Cl. 169-2 Int. Cl. A62c 1 /08; A62e 1 /24; A62c 3/02 Claims ABSTRACT OF THE DISCLOSURE Background of the invention Underground fires burn for many years in the coal mining regions of the United States and other countries. The origin of the fire is not clearly known but usually it is started in a coal outcropping and continues to burn the tailings left in the coal shaft, the coal left as supporting columns in the mines, and small seams left because they were not economical to mine. The fire is fed with a continuous supply of oxygen through abandoned shafts, fissures in the stone outcrop or earth, and man-made entries such as sewer lines and abandoned wells, and they usually burn only in areas where the earth overburden is about sixty feet or less.

These fires are particularly undesirable when burning under populated areas. The fire destroys the supporting columns of the mines and thus removes the structural strength of the supporting earth so that roads, highways, homes and other buildings are subjected to a possible subsidence due to the collapse of the supporting earth. In addition, the heat generated from the combustion destroys the plant life on the surface and the sulfurous and carbon monoxide fumes escape into the atmosphere, as well as homes through basement cracks, and are thus dangerous to health.

The present practice of controlling these fires is to visually establish the area of the fire by observing the surface of the ground for dying vegetation. Once the general area has been determined, holes are drilled into the ground in this area. Through the use of thermocouples and air draft detecting equipment lowered into these holes the source of the fire is more precisely determined. The fire is contained by drilling a series of holes approximately at ten foot intervals in a grid pattern surrounding the fire areas. The holes penetrate the mine shafts, and a slurry of limestone dust and water is flushed under gravity into the holes. The limestone dust covers the surfaces of the mine shaft when the water drains off thus providing a coating through which the fire frequently will not burn. However, this procedure does not inhibit the supply of oxygen feeding the fire and past results provide no conclusive proof that this process will contain the fire.

Summary of the invention Method and apparatus for filling a mine with a granulated material for supporting the overburden and for con- Patented Jan. 14, 1969 ICC taining mine fires by creating a barrier through which the fire will not burn. Once the area of the fire is determined, a series of holes are drilled into the mine along the center line of the barrier. Fly ash or other equivalent powdered material is then blown under air pressure into the holes to completely fill the mine shaft in the area of the barrier thus blocking the flow of oxygen to the fire, sealing the cracks and fissures through which the air is supplied, and creating a barrier of non-combustible ma terial through which the fire will not burn. The apparatus includes mobile pneumatic bulk trailers and a source of air pressure which cooperates with the bulk carrier to entrain the fly ash in pressurized air which flows through a suitable easing into the mine shaft. In another embodiment, the fire is smothered by blowing the fly ash or its equivalent directly into the fire area through holes in order to reduce the time that the fire requires to burn out.

Brief description of the drawings FIG. 1 is a plan view partially in section of a typical area in which a fire is burning in an abandoned coal mine shaft;

FIG. 2 is a vertical sectional view through a typical mine shaft showing the filling thereof with fly ash;

FIG. 3 is another sectional view showing the apparatus for conveying the fly ash into the mine shaft; and

FIG. 4 is a sectional view showing a casing mounted in a bore hole.

Detailed description of the drawings FIG. 1 illustrates a plan view of a typical area 10 wherein an underground mine fire is slowly burning. The area includes a hill generally defined by the contour line 11 having a plurality of streets 12 in a populated area thereon. The buildings 13 are shown along the streets 12, and the shaded area 14 indicates an area where the coal has been removed by strip mining since it was relatively close to the surface. The small crosses 15 indicate areas wherein evidence of the mine fire has appeared on the surface in the form of dying vegetation, fast melting of snow, the smell of gases, or structural damages to buildings due to settling of supporting soil.

Below the surface of this entire area 10, the abandoned mine 17 exists, having been dug some time ago usually before the modern shoring technique and equipment were employed. These mines include the elongated shafts 18 having the connecting lateral corridors 19 :between the large posts 20 which are left in place to support the ground 22 (FIG. 2) above the mine. Generally speaking, these mine shafts and corridors have a width of about fifteen feet (Dimension B, FIG. 2) and a height of about six feet (Dimension C), whereas the posts 20 may be as large as sixty-eight feet on each side (Dimension A). These dimensions are cited only for the purpose of illustrating that a substantial amount of coal remains in the mines, especially in the posts 20.

Fly ash is used in this process and is a by-product of the burning of pulverized coal in power plants which is precipitated from the flue gases by mechanical or electrostatic precipitators. Its main constituents are the following compounds: SiO A1 0 Fe O Fe O S0 C, trace elements.

It has a specific gravity in the range of 2.2 to 2.6 and weighs approximately one ton per cubic yard. For use in the present process the fly ash should have a fineness such that 90% will pass through a SO-mesh screen and will pass through a 325-mesh screen thereby facilitating thefilling of cracks and voids regardless of their size. The molecular structure of fly ash is round thus increasing the fluidity thereof and permitting its easy mixing with air and flow into small voids and cracks. Most importantly, it is noncombustible (maximum allowable carbon is 8%) and capable of providing the structural strength to support the ground in the areas where the posts have been burned out.

The first step in containing the fire is to locate generally the fire in terms of the terrain, buildings, and other landmarks on the surface. Once the general location is determined, a center line 24 is drawn along which the barrier 25 will be formed and thorugh which the fire will not burn. This center line generally extends between between opposite sides of the coal bed so that the fire cannot burn around the barrier once it is created.

A series of holes 30 are bored into the ground 22 along the center line 24 of the proposed barrier 25 approximately thirty feet apart. Since the fire usually burns only in an area where the overburden is about sixty feet or less above the mine shaft, a simple well rig can be utilized to create these bore holes. After the holes 30 are dug, a casing 32 is inserted thereinto in the form of a metal pipe having a threaded upper end 33 and an outer diameter somewhat less than the diameter of the bore. Suitable packing 34, e.g., oakum, is provided around the casing near the top and bottom to support it and seal the bore except for flow through the interior of the casing. How ever, the casing 32 can be snugly fitted in the holes 30 so that the packing 34 can be eliminated. The upper end 33 of the casing is approximately ground level or slightly therebelow so that the casing can be capped and then covered with earth after the mine shaft has been filled.

Then the fly ash 35 is pumped into the mine shaft and corridors 18 and 19 from the bulk truck 36 (FIG. 3). This truck includes a tractor 37 and a tank trailer 38 adapted for transporting bulk materials. The tank 38 is air tight and pressurized by air supplied by the air pump 41 driven by the auxiliary motor 42. While one form of generating air pressure is shown and described, other sources of air pressure can be utilized without departing from the scope of the invention. For example, it is possible to use one bank of cylinders of a Diesel engine as an air compressor driven by the other bank of the cylinders.

The pressurized air flows through the lines 43 and 44 having the valves 45 and 46 therein into the space 48 above the mass of fly ash 35. The air under pressure also flows through the short pipes 56 and into the space 51 at the bottom of the tank 38 from where it blows upwardly through the perforated pads 52 through the fly ash 35 as indicated by the arrows 53 to loosen the fly ash and facilitate its removal. The fly ash 35 is discharged from the tank under the pressure existing on the top surface thereof through the short supply conduits 55 which are connected to the air conduit 56 at acute angles to facilitate mixing of the fly ash through the air. A throttle valve 57 is provided in the air conduit 43 immediately upstream of the supply conduits to regulate the amount of air and thus the ratio of air to fly ash. Generally speaking, this ratio is 50% air and 50% fly ash.

The fly ash 35 is thus blown through the flexible hose 60 through the casing adaptor 61 which has been screwed onto the top 33 of the casing 32 and into the casing. It flows at high velocity under pressure and the force of gravity into the mine cavity wherein it begins to accumulate. Practice has demonstrated that the fly ash supplied under pressure will travel up to fifty-one hundred feet in every direction. Since the air will initially escape through the cracks and fissures and other oxygen supplying means the air will carry fly ash toward the source of oxygen thereby tending to build a barrier with extra thickness in the areas where the air is escaping through the oxygen supply source. The cracks and fissures regardless of their size and shape will actually be filled as the air flows. therethrough and deposits fly ash therein. The fly ash is continually supplied through the casing until the bottom portion of the bore 30 is filled as indicated by a substantial back pressure. Then the truck 36 is moved to another adjacent hole 30 and this operation is repeated. In order to completely create the barrier 25 in a matter of one or two weeks, a large number of the bulk supply trucks are utilized.

When all of the holes 30 have been filled, the barrier of fly ash completely fills the mine shaft from the floor to ceiling and between adjacent posts, as shown in FIG. 1. The barrier 25 extends through the shaft 18 and into the adjacent corridors 19 with the shaft 18 being substantially completely filled and the fly ash tapering downwardly therefrom in the corridors 19. Thus when the fire reaches the barrier 25, there will be no way that it can continue through the barrier as the fly ash will not burn and any tendency to burn through the posts or trailings will be suffocated for lack of oxygen.

Once the barrier 25 is completed, the fire will eventually burn itself out when it reaches the barrier if not before. Should the barrier block the flow of oxygen to the fire, it is possible that the fire would be extinguished prior to actually reaching the barrier. The casings can be utilized for lowering thermocouples or other temperature sensing equipment to determine the temperature of the overburden thereby indicating when the fire has been extinguished.

Th process of letting the mine burn itself out usually consumes many months, and if more immediate results are required, a grid work of holes 30 are drilled approximately thirty feet apart over the entire area wherein the fire is burning. The burning can be accurately determined by the use of thermocouples lowered into the casings 32 to indicate that the temperature of the ground is elevated above normal. Then, the mixture of air and fly ash is forced into the holes in the manner described above to blanket the fire completely and fill the mine shafts and corridors and any other voids created by the burning. By blanketing the burning areas and covering the adjacent unburned areas, it is impossible for the fire to continue and it suflocates for lack of oxygen. This blanketing operation accordingly produces much faster results although it may require a substantial increase in the amount of fly ash utilized.

While the invention has been shown and described as utilizing fly ash, it is possible that other granular relatively fine materials which are non-combustible can be utilized without departing from the scope of the invention. Certain fine clays, silts, and the like can thus be utilized within the scope of the invention although fly ash produces preferred results. Likewise, the equipment utilized to force the air-fly ash mixture into the ground is preferred but other types of equipment can be utilized without departing from the scope of the invention.

The method and apparatus provided herein thus provide a method of inexpensively filling a mine to control a fire and/ or supporting the earth above the mine thereby ob viating the possible dangers to health and safety. This is accomplished by pumping an air-fly ash mixture into the abandoned shafts or voids. A fire is extinguished by creating a barrier through which the fire will not burn and which will block the supply of oxygen to the fire. If it is desired to immediately extinguish the fire, a grid work of holes is drilled directly into the fire area and a blanket of fly ash created in this area to smother the fire.

While the methods and form of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and form of apparatus, and that changes may be made therein Without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A process of controlling a fire in or supporting the earth above an underground mine shaft or other earth cavity, comprising the steps of drilling a plurality of spaced holes through the overburden into the mine shaft, mixing air and finely granulated non-combustible fly ash having a size which permits at least 90% to pass through a 50- mesh screen and 75% to pass through a 325-mesh screen, injecting said mixture into the holes to fill the mine shaft beneath the holes with the fly ash, said injecting step having a sufiicient volume and pressure of air so that the fly ash is carried by the air into the cracks and voids through which the air escapes to fill such cracks and voids with the fly ash, said injecting step including filling the mine shaft with fly ash along a substantial length of mine shaft to a depth equal to the vertical height of the mine shaft to create a fly ash barrier through which fire cannot burn and to provide vertical support for the earth above the mine shaft, and then closing and sealing the holes.

2. A process of controlling a fire as defined in claim 1 comprising the step of extinguishing a mine fire by creating a barrier by drilling said spaced holes along the centerline of the barrier.

3. A process of controlling a fire as defined in claim 1 comprising the step of blanketing the fire by drilling said spaced holes directly into the area of the fire and injecting the mixture of air and fly ash thereinto to smother the fire.

4. A process of controlling a fire as defined in claim 1 wherein said mixing step uses fly ash having specific gravity in the range of 2.2 to 2.6.

5. A process of controlling a fire as defined in claim 1' wherein said injecting step includes mixing step including mixture 50% air with 50% fly ash.

References Cited UNITED STATES PATENTS 1,261,922 4/1918 Grasty et al. 169-2 1,435,957 11/1922 Ellery 169-2 1,556,879 10/1925 Reid 169-2 Re. 16,914 3/1928 Trent 1692 2,368,209 l/1945 Fahey et a1. 1692 3,186,490 6/1965 Jamison et a1. 16915 3,194,443 7/ 1965 Gurney 1692 3,333,896 8/1967 Diamanti 299-12 FOREIGN PATENTS 1,112,032 8/1961 Germany.

OTHER REFERENCES R.I. Bureau of Mines Report of Investigations 6453 by John Nagy et a1.

Bulletin 590 Bureau of Mines by F. E. Grifiith et al., noting pp. 41, 42, 44.

EVERETT W. KIRBY, Primary Examiner.

US. Cl. X.R.

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