US3333896A - Method and apparatus for rock dusting during coal mining operations - Google Patents

Description

J. J. DlA'MANTl 3,333,896

METHOD AND APPARATUS FOR ROCK DUSTING DURING COAL MINING OPERATIONS Filed April 29, 1965 3 Sheets-Sheet l WAM AT TORNE YS Aug l, 1967 .1.J. DIAMANTI 3,333,896

METHOD AND APPARATUS FOR ROCK DUSTING DURING COAL MINING OPERATIONS Filed April 29, 1965 5 Sheets-Sheet c INVENTOR. JAMES J. DIAMANTI ATTORNEYS ugl, 1957 .1.J. DIAMANTI 3,333,896

METHUD AND APPARATUS FOR ROCK DUSTING DURING COAL MINING OPERATTONS med April 29, 1965 s sneets-sheet INVENTOR. JAMES J. DlAMANTI ATTORNEYS United States Patent O 3,333,896 METHOD AND APPARATUS FOR ROCK DUSTING DURING COAL MINING OPERATIONS James J. Diamanti, Carbon Fuel Company, Helper, Utah 84526 Filed Apr. 29, 1965, Ser. No. 451,836 Claims. (Cl. 299-12) ABSTRACT OF THE DISCLOSURE A method of rock dusting during coal mining operations that involves blowing a gaseous suspension of rock dust into a ow stream made up of air passed across a working face of a coal seam being mined and volatile materials entrained therein, at a location closely adjacent to the working face but without obscuring it, and without contaminating the coal being mined and damaging the continuous mining machine employed, to thereby insure maximum safety to workers. The preferred apparatus for practicing the method is a continuous mining machine equipped with a rock dust blower arranged to blow rock dust in accordance with the method and operable independently of the cutting wheels of the miner.

This invention relates to the mining of coal and to mechanical apparatus employed for the purpose.

Dangers involved in the mining of coal have long been recognized. Chief among these in modern ventilated mines is the accidental touching oi of major explosions of airborne coal dust, usually by reason of small and relatively harmless initial explosions of methane gas and/or coal dust at the working face of the coal seam due to a spark from cutting tools, static electricity, etc. A small explosion tends to raise settled coal dust and cause a chain of larger explosions throughout the mine workings.

To guard against this possibility, it is now standard practice-usually enforced by government regulation-to periodically spray a thick layer of rock dust, generally powdered limestone, over exposed coal areas, walls, ceilings, floors and other surfaces in the mine (up to within 40 feet of the working face) where coal dust tends to collect. This eliminates much of the airborne coal dust and reduces the danger inherent therein.

This spraying generally occurs at the end of each working day and requires a crew of men to perform. A very heavy coating of rock dust is applied, so that it will electively hold the settled coal dust on the ground should an explosion occur.

In recent years coal mining has become an almost completely mechanized operation. In addition to various cutting, drilling, and loading machines, there are face-working machines provided with huge jaws or with rotating cutter wheels, generally designated continuous miners, that are being increasingly utilized to more or less continuously cut into the working Vface of a coal seam and rip or chew out great quantities of the virgin coal at a rapid rate as compared with the old manual operations. Clouds of coal dust are inevitably formed at and in the vicinity of the working face during operation of a continuous miner.

In order to minimize the danger of explosions, water sprays are mounted at the cutting ends of these machines. Such water sprays tend to not only settle the dust, but to quench sparks as well.

Nevertheless, danger persists despite these precautions. An explosion, which took the lives of nine miners and extensively damaged workings at the particular mine concerned, was presumably due to a spark igniting a small pocket of methane gas and/or coal dust when the cutter wheels of a continuous miner cut into the pocket and into boundary rock simultaneously. The relatively small 3,333,896 Patented Aug. 1, 1967 ICC gas coal dust explosion apparently Asparked a larger coal p dust explosion near the working face, which resulted in a chain of increasingly larger explosions of the coal dust raised during a four hour working period, and of coal dust being carried by a conveyor belt, even though all normal safety precautions had been taken. Heavy dusting of the mine in accordance with this known process was credited with preventing the deaths of many more miners.

The present invention is designed to greatly minimize if not entirely eliminate the danger .accompanying use of all types of mining machines at the working face. I have found that rock ldust, sprayed or atomized into the air adjacent the cutting or drilling operation, will mingle with the coal dust and render it incapable of propagating such small explosions as may take place during cutting or drilling operations. It will also promote rapid settling of the coal dust along with the rock dust, so that the settled dust is an intimate intermixture of the two, rather than the usual distinct layers.

During normal min-ing operations using conventional techniques, coal dust is withdrawn from the vicinity of the working face by an air duct constituting a return for the forced air ventilation system of the mine. In accordance with the invention, rock dust is placed in suspension in the air current near the face for intimate intermixture with coal dust being drawn into the return air duct.

The rock dust is ejected as an airborne suspension in the vicinity of the entrance to this air duct near the face, preferably from a device mounted on the particular mining machine concerned, so it will comingle with coal dust being drawn into the air duct but will not contaminate the coal being mined nor inltrate into bearings and other parts of the machine which are susceptible to damage from abrasion, and so that it is not moistened by the water sprays and settled out before it can perform its intended purpose.

This immediate, intimate comingling of rock dust particles with the coal dust raised during Working operations insures that as the coal dust settles it is thoroughly intermixed with a layer of rock dust that will prevent the coal dust rising should an explosion occur. In addition, the interspersion of rock dust in the suspended coal dust Virtually eliminates the possibility of the air suspension propagating an explosion.

Except where the return air duct is very short, it is preferred that additional rock dust be injected thereinto at strategic locations along its length for complete protection. This insures coverage of the coal dust regardless of the distance it is carried in the return air duct.

The method and apparatus of the present invention are presently being used in the same mine in which nine miners were killed. During recent operations a methane gas pocket was again ignited, but this time only one miner, standing at one side of and approximately mid-way of the continuous miner machine was even injured-and his injuries were considered not serious. Other miners in the immediate vicinity were not injured, and many did not even know that an explosion had occurred. This invention was credited by the miners with preventing another lifetaking disaster.

There is shown in the accompanying drawings a portion of typical coal mine workings and one type of continuous miner with required modifications, representing what is presently regarded as the best mode of carrying out the invention. From the following detailed description, other specific objects and features of the invention will become apparent.

In the drawings:

PIG. 1 represents a schematic layout in plan of a fragmentary portion of a typical coal mine, showing a continuous miner equipped for prac-tice of the invention and operating at the face of a coal seam, and a return duct of the mine-Ventilating system having its intake opening nearby, intermediate potrions of the illustrated fragmentary portion of the mine being broken out for convenience of illustration;

FIG. 2, a fragmentary elevation taken from the standpoint of the line 2-2 of FIG. 1 and drawn to a considerably larger scale, showing the rock dust discharging unit mounted on the continuous miner;

FIG. 3, a fragmentary vertical section taken on the line 3 3 of FIG. 2 to show the injector and discharge nozzle of the rock dust discharging unit;

FIG. 4, fragmentary vertical section taken on the line 4-4 of FIG. 3, and showing interior details of one embodiment of rock-dust feed hopper;

FIG. 5, a schematic illustration of the drive and control means of the apparatus of the invention;

FIG. 6, a view like FIG. 4, but showing the interior details of another form of rock dust feed hopper; and

FIG. 7, a horizontal section taken on the line 7-7 of FIG. 6.

Referring to the drawings:

The schematic showing of FIG. 1 includes a haulageway 10 of customary character, along one side of which a brattice cloth partition 11 divides off a longitudinal passageway or duct 12 in usual fashion for the flow of Ventilating air to the exhaust stack (not shown) of the conventional Ventilating system of the mine.

The exhaust stack, ordinarily equipped with a large and powerful fan or blower, returns to the atmosphere Ventilating air that is drawn into the mine through the usual access openings (not shown) at the end of haulageway 10. From such access openings, the fresh air flows along the various main drifts of the mine into and along the haulageway 10 until it reaches the working face 13, where it is deected into the open, intake end 14 of the air-return duct 12. It may be desirable to utilize one or more additional fans to direct the Ventilating air against all portions of the working face before it is carried out the air-return duct.

In accordance with normal practice, a cross-cut drift 15 intersects the haulageway at a distance back of the working faces determined by the working progress, and leads as directly as possible to the exhaust stack. It is customary to provide such cross-cuts at intervals, e.g. of eighty-five feet, along the length of theV haulageway and to advance the brattice cloth partition 11 accordingly as the mining progresses along the coal seam being mined. The distance along the cross-cut and to the: exhaust stack will vary in accordance with the location of the particular haulageway and the working face in the overall mine layout. Often the distance is quite long, e.g. several thousand feet.

Operably disposed at the working face 13 is a continuous miner 16, here shown as the type manufactured by the Lee-Norse Company of Charleroi, Pa., but any of the several face working machines on the market could be used instead. The miner 16 has an assembly 17 of coal cutter wheels projecting from its forward end as coal mining means, and has an operators seat 18 at one side of the machine. For purposes of this invention the seat 18 is at the side of the machine that is remote from the open intake 14 leading int-o air-return duct 12.

In accordance with the invention, a rock dust disi charging unit 19 is mounted on the miner 16 at the side opposite seat 18 and next to air-return intake 14 when the miner is in working position at the face. Ithas a discharge nozzle 20 directed outwardly of the machine and toward the intake 14. With unit 19 thus mounted, the rock dust discharged does not block the vision of the operator of the miner and it is not wetted down by the water spraying forwardly from jets on the miner.

Preferably, as illustrated, the nozzle 20 is directed forwardly and laterally at an acute angle to the longitudinal axis of the machine, so as to continuously discharge a cloud of rock dust 21 toward intake 14, as indicated by the appended arrows with plain tails, during operation of the machine and even during intermittant periods when the coal cutter wheels are idle. The cloud or gaseous suspension of rock dust 21 merges and mingles with airborne dust particles 22, carried by the ow of Ventilating air from the working face 13 (see appended arrows with barbs on their tails), as both such dust particles and the rock dust flow toward, and enter, intake 14.

The intermixed suspensions of rock dust and coal dust particles continue to travel with the Ventilating air along the return passageway or duct 12, with any settling out of coal dust being accompanied by at least part of the rock dust to provide a safely mixed deposit within such duct.

Whenever found desirable, a separate, portable, rock dust discharging unit 23 can be installed at the bend of duct 12 leading into cross-cut 15, or at some other suitable location, with its nozzle 24 directed into and longitudinally of such cross-cut, as a booster, to continue the intermixed nature of the airborne dust suspension a safe distance along such cross-cut toward the exhaust stack.

The rock dust discharging units 19 and 23 can be of any suitable types with any suitable sources of supply. Preferably, however, they embody a storage hopper for rock dust feeding by injection into a forced stream of air from a blower and discharging through the nozzle of the unit.

One embodiment that has proven to be a satisfactory construction for the continuous-miner-mounted unit 19 is shown in FIGS. 2, 3, and 4.

In this embodiment, the unit 19 is provided with a hopper-like bin 25 for feeding rock dust through a regulatable gate, volume control 26 into an injector feed pipe fitting 28. The position of gate 26 is set as desired by loosening and tightening bolts 26a which extend through slots 26b in the wall of the hopper. The feed end 27a of such pipe 27 is angularly directed into the outlet portion of such venturi throat 28a in the direction of air ow from an air-supply conduit 29 connected with an air compressor 30.

Bin 25 has a closed top 25a and a sloping bottom 25b that overlies an air chamber 25e and is perforated. A porous cloth 25d overlies the bin bottom 25b and supports a quantity of rock dust (not shown) therein while permitting compressed air to pass through and agitate the bed of rock dust. Compressed air is supplied to chamber 25C from the compressor, via a conduit 31 that intersects the injector pipe fitting 28.

Air is drawn into compressor 30 through an inlet conduit 32, having a filter 33 at its free end. Filter 33 is preferably positioned adjacent the end of miner 16 opposite the cutter wheels so that relatively pure air will be drawn into the compressor.

In operation, air entering air chamber 25e passes upwardly through perforated bottom 25b and porous cloth 25d to agitate and separate the rock dust particles in bin 25, at the same time rock dust is continuously drawn from hopper 25 by the injection action of the stream of air passing through venturi Ifitting 28 and is discharged as a gaseous suspension from nozzle 20. The air entering through the air chamber also creates a positive pressure within the bin that helps in forcing rock dust into the low pressure area formed by the venturi.

The compressor 30 is driven by a conventional hydraulic motor 34 which in turn is powered by the usual pump 35 of the miner. A valve 36 in the supply line 37 interconnecting pump 35 and hydraulic motor 34 con- =trols operation of the hydraulic motor, and therefore of the entire rock dust discharging unit. An exhaust line 38 from motor 34 discharges either directly as illustrated, or indirectly into the same reservoir 39 from which the hydraulic fluid that powers motor 34 is originally pumped.

Thus, when valve 36 is opened and pump 35 is operating, the rock dust will be discharged.

Pump 35 is driven by the electric motor 40 that powers the miner, and the pump will operate when ever the miner is in operation. However, since the cutting wheels are operated by separate hydraulic motors that are supplied and exhausted through lines 41 and 42, respectively, under the control of a valve 43 in line 41, the rock dust discharging unit will operate even though the cutter wheels may be stopped. It is thus possible to continue application of rock dust even after mining has stopped and no more coal dust is being created. This continued application of rock dust will allow a top coat of relatively pure rock dust to settle on the coal dust in the air-return duct 12.

In FIGURES 7 and 8 there is illustrated another form of bin that has been found satisfactory for use with a rock dust discharging unit.

In this embodiment, the bin, shown at 44, contains a pair of parallel, reversely turned worm screws 45 and 46. The screws are positioned at the bottom of the bin such that their flights 45a and 46a, respectively intermesh. This intermeshing relationship effectively breaks up, or agitates, the rock particles as the screws push them toward an opening 47. As in the previously disclosed embodiment a gate 48 is adapted to cover opening 47, and bolts 48a hold the gate in any pre-set position. As t-he rock dust is discharged through opening 47 the venturi picks it up and it is sprayed in the manner previously disclosed.

The screws can be driven through a gear 49 fixed to an output shaft 5t) of hydraulic motor 34 and meshing with ears 51 and 52, respectively xed to center shafts 45b and 46h of the screws 45 and 46, or a belt and pully arrangement, not shown, can be employed.

With either of the illustrated bin arrangemen-ts there is i.

an agitation and separation of rock dust particles and Y they are positively fed from the bin toward the discharge opening.

The method and apparatus of the invention have proved extremely useful in reducing the hazards incident to coal mining. Furthermore, since it is only necessary to replenish the feed hoppers during their continuous operation and it is no longer lnecessary to hand dust the mine at the end of each working -day a tremendous saving is realized in labor requirements. In addition, since the amount of rock dust applied in accordance with the invention is easily regulated and since the rock dust is moved with the coal dust to provide an even distribution, there is a consequent savings in the volume of rock dust used. In practice it has been found that rock dusting in accordance with the invention, in addition to providing extremely effective protection to the miners, requires only seventy to eighty percent of the amount of rock-dust previously used and only one-tenth the labor requirement. Obviously, the savings in labor and rock dust result in corresponding cost savings in the coal mining operation.

Whereas there are here illustrated and specifically described certain preferred constructions of apparatus which are presently regarded as the best modes of carrying out the invention, it should be understood that various changes may be made and other constructions adopted without departing from the inventive subject matter particularly pointed out and claimed herebelow.

I claim:

1. A method of safety mining coal by use of mechanical mining equipment, wherein a current of Ventilating air is blown against the working face of the coal seam to pick-up and remove coal dust caused by cutting action of said equipment on the working face and is'removed by a duct whose intake is located adjacent to said face, comprising blowing a gaseous suspension of rock dust into said current of air between said `face and said intake of the duct during operation of said equipment.

2. A method recited in claim 1, wherein the blowing is continued after the cutting action is stopped.

3. The method recited in claim 1, wherein the blowing is carried out from the side of the equipment adjacent to the duct intake, and wherein the equipment is operated from the side opposite the blowing.

4. The method recited in claim 1, wherein a gaseous suspension of rock dust is additionally blown into the duct at a location distant along the length of the duct from the working face, as a booster to provide continued protection within said duct from explosion of coal dust carried therethrough.

5. The combination with a continuous miner having forwardly projecting coal mining means and an operators seat, of a rock dust discharging unit mounted on said miner for `movement therewith, said unit having a discharge nozzle directed forwardly and outwardly with respect to the longitudinal axis of the said miner and away from said seat.

6. In combination, a continuous miner having a power source, a hydraulic reservoir, cutting means for cutting ore from the working face of a mine, a pump driven by the power source and supplying fluid from said reservoir to drive the cutting means, an operators area at one side o of the miner and control means at the operators area for regulating flow from said pump to the cutting means; and a rock dust discharging means including a hopper for rock dust, and outlet opening fro-m said hopper, means for agitating rock dust in the hopper and for moving it toward the outlet opening, venturi means for drawing rock dust from said hopper, and a nozzle positioned at the side opposite the operators area to direct rock dust entering the venturi means forwardly and laterally of the miner at an acute angle to the longitudinal axis thereof.

7. The combination of claim 6, further including a motor driven by the pump, and a compressor driven by the motor, said compressor supplying air for the venturi means.

8. The combination of claim 7, further including control valve means for controlling flow from the pump to the motor.

9. The combination -of claim 8, wherein the means for agitating rock dust in the hopper and for moving it toward the outlet comprises a bottom in the hopper that is perforated and sloped downwardly toward the outlet opening; -a porous sheet of material overlying said -bottom to support rock-dust thereon; an air chamber positioned beneath substantially the entire bottom; and conduit means for supplying compressed air to the said air chamber from the compressor.

10. The combination of claim 8, wherein the means for agitating rock dust in the hopper and for moving it toward the outlet comprises a pair of worm screws eX- tending across the hopper at the Ibottom thereof; means mounting s-aid screws such that their iiights intermesh; and means driving said screws such that they coact to move rock dust in the hopper toward the outlet.

References Cited UNITED STATES PATENTS 1,568,281 l/l926 Jones 169-2 1,862,396 6/1932 Gray et al 169-2 2,258,117 10/ 1941 Lamb et al. 169-2 OTHER REFERENCES The ABCs of Ventilation for Continuous Miners, Coal Age, February 1959, pages 96-101 inclusive.

Face Ventilation with Continuous Mining, Mechanization, September 1962, pages 39-43 inclusive.

ERNEST R. PURSER, Primary Examiner.

Claims (1)

1. A METHOD OF SAFETY MINING COAL BY USE OF MECHANICAL MINING EQUIPMENT, WHEREIN A CURRENT OF VENTILATING AIR IS BLOWN AGAINST THE WORKING FACE OF THE COAL SEAM TO PICK-UP AND REMOVE COAL DUST CAUSED BY CUTTING ACTION OF SAID EQUIPMENT ON THE WORKING FACE AND IS REMOVED BY A DUCT WHOSE INTAKE IS LOCATED ADJACENT OF SAID FACE, COMPRISING BLOWING A GASEOUS SUSPENSION OF ROCK DUST INTO SAID CURRENT OF AIR BETWEEN SAID FACE AND SAID INTAKE OF THE DUCT DURING OPERATION OF SAID EQUIPMENT.

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