GB2114526A - Method and apparatus for conveying abrasive solids - Google Patents

Abstract

Apparatus and method for conveying abrasive solids to a backfilling location wherein the solid materials are delivered to a blow-pot type loader 26, a vibratory feeder 29 receives the discharge from the loader, and delivers the same to a pressurised conduit 13 where air under pressure suspends the solid material and delivers it to the backfill location. A reciprocable slide valve is disposed between the delivery means 14 and the loader 26, the slide valve 17 providing a substantially air-tight closure for the loader and eliminating the necessity for rotary feeding and metering apparatus which are subject to frequent replacement and repair. <IMAGE>

Description

SPECIFICATION Method and apparatus for conveying abrasive solids This invention is in the field of conveying solids in a batch type process wherein said solids are delivered through a slide valve, and then dropped through an opening in a blow tank, whereupon they are vibrated and discharged into a pressurised airstream.

In the mining of coal or metals, there are substantial environmental and safety hazards which relate to the disposal of the waste material produced during underground mining. The problem is particularly severe where the waste material is a hard rock such as the high density quartz which is a by-product of gold mining. Lifting the rock to the surface for disposal involves great expense, particularly since some gold mines are many thousands of feet below the surface of the earth. Even if the rock is lifted to the surface, it must then be stored somewhere and this often creates.an environmental problem. Furthermore, deep mines become quite hot, and the areas where the rock has been removed must be ventilated and cooled, considerably increasing the cost of the mining operation.

One of the most serious harzards in mining is known as "rock burst". As the depth of the mine increases, the pressure increases and the stresses on the rock at the sides and in the roof of the mined out areas also increase. When the stress reaches the limit which the rock can stand, it simply explodes or bursts.

As soon as an area is mined, compression of the side walls and a sagging of the roof begin, creating a condition known as "closure". As the amount of closure increases, rock stress increases. Blowing waste rock in at very high velocities and packing in this material up to the roof before closure becomes appreciable causes the packed material to compress with subsequent closure and gradually carry the load of the unsupported material. Filling the mined out areas pneumatically will pack the fill material to densities approaching 80% of the original rock density, thereby reducing closure to about 20%. With other types of supports, such as timber packs and the like, closure is as high as 75%.

The most desirable solution is thus to extract the ore and move the waste rock around underground to areas which have been previously mined. This eliminates the expense and the problems associated with bringing the rock to the surface. It also reduces the volume of the mine which has to be ventilated and cooled, and further has the additional benefit of decreasing the length of mine cavities which have to be shored up with timbers to prevent collapse, a time consuming and expensive procedure.

Commercial machinery for moving rock around in a mine normally utilises a rotary feeding and metering apparatus which operates continuously.

The waste rock is metered into a pipe and is blown to a remote location where it is piled into so-called "stopes" which are excavations resulting from the removal of ore.

The difficulty with rotary feeders in this environment is that they have a very short service life and are impractical. High density quartz rock, for example, is very abrasive. Since the vanes on rotary feeders are continuously rotating, the rate of wear is greatly accelerated. In order to reduce wear, rotary feeders are often operated with air pressures in the conveying pipes of about 5 to 6 psig (0.35 to 0.42 Kg/sq. cm). This pressurised air is introduced on the upstream side of the rotary feeders to carry the rock along the pipe for conveyance to a remote location for backfilling a stope. Lower air pressures are used to minimise danger to rotary air locks and lower pressures require larger diameter pipes, which are more costly and difficult to handle to convey the same amount of material.

The following U.S. patent specifications are of general interest in connection with the handling of solid residues by means of fluid streams.

U.S. Patent Specification No. 1,347,358 describes a lifting apparatus for solids making use of a closed receiver and a plurality of air pipes which act on the material to loosen and break up the mass to such an extent that it will enter into the lower open end of a discharge pipe.

U.S. Patent Specification No. 2,536,869 involves first breaking the ground by a modified shrinkage method of stoping, and then introducing waste fill at the top of the stope as the fragmented ore is withdrawn from the bottom and as its upper surface subsides within the stope.

In U.S. Patent Specification No. 3,253,865 there is described a pneumatic conveyor pipe line for conveying bulk material utilising passageways which connect the gas duct to the bulk material duct throughout the length of the conveyor pipe line.

U.S. Patent Specification No. 3,268,264 also deals with a pneumatic conveyor in which the solid flows through the conveyor in a dense state resembling a liquid-like flow.

U.S. Patent Specification No. 3,268,266 is also directed to a pneumatic conveyor system utilising a rotary feeder. The vanes of the feeder are provided with wipers at their extremities. The hub of the rotor is provided with caps which have fingers entering into the spaces between the vanes and which carry annular ribs which are radially spaced to provide a seal between the rotor and a lining of synthetic resin which faces the end walls of the chamber.

U.S. Patent Specification No. 3,478,520 addresses itself to a method of filling mine cavities by means of a filler material such as an expandable plastics. The expandable material is placed in the abondoned mine cavity, and sufficient heat is applied to cause the material to expand and completely fill the cavities to thereby reinforce the ground about it.

U.S. Patent Specification No. 3,480,331 describes a fluidising conveyor apparatus including a gate valve for metering the flow of fluidised material along the conveyor. The gate valve has a blade which moves vertically to adjust the size of the passage through which the fluidised material flows.

U.S. Patent Specification No. 3,602,551 deals with an underground fluid conveyor transportation system particularly designed for removing fines and the like from coal mining installations.

U.S. Patent Specification No. 3,656,661 describes a measuring device for a pneumatically operated system including a compartmentalised dosage disc which has a discharge side leading to an air duct with an ejector unit mounted therein. This side is sealed by a flexible lip seal and the reverse side is sealed by a gasket. The discharge side of the dosage disc is an area of low pressure so that the granular material is drawn into the conveyor air duct.

U.S. Patent Specification No.3,871,711 describes a method for pneumatically conveying solid materials by means of gas jets located along a conveying pipeline. Valves are provided for synchronising the gas jets with the closing of each pipeline section to cause an intermittent movement of the discrete solid material along the pipeline.

In U.S. Patent Specification No. 3,937,522 there is described an apparatus for continously feeding granular material to a conveyor pipeline which includes a vertical cylindrical chamber with means in the chamber at different levels which act to alternately lift and release successive portions of the material, thereby preventing grains from interlocking and forming clumps.

In U.S. Patent Specification NO. 3,955,853 there is disclosed a system for the pneumatic conveyance of solid materials by pneumatic pulse waves without the necessity of pressurising the container.

Finally, in U.S. Patent Specification No. 4,059,963 there is described a method of backfilling a mine by dewatering a slurry so that it can be used more conveniently as a backfill either alone or in combination with cement to provide a mortar.

According to the invention there is provided apparatus for conveying abrasive solids to a backfilling location including a blow-pot type loader, delivery means for delivering said solids to said loader, a vibratory feeder receiving the discharge from said loader, a pressurised conduit receiving the discharge from said feeder, and a reciprocable slide valve disposed between said delivery means and said loader, said slide valve when closed providing a substantially air-tight closure for said loader.

The loader as well as the conduit may be pressu rised.

In a preferred form of the invention, the loader has a generally conical discharge end and said vibratory feeder is located in close proximity to the discharge end. The vibratory feeder is preferably located in a pressurised housing of its own.

The present invention also provides a method for conveying abrasive solids which comprises: drop ping said solids through an open slide valve, deliver ing said solids into a blow-pot loader, vibrating the solids to discharge the same from said blow-pot loader into a conduit, and introducing air under pressure into said conduit at a sufficient mass velocity to propel said solids as a suspension through said conduit.

In a preferred form of the invention, the air is introduced into the conduit in sufficient amounts to form a suspension containing about 3% to 10% by volume solids. One of the features of preferred embodiments of the invention is that higher press ures can be used in conveying, and the pressures in the conduit may be at least 10 psig (0.7 Kg/sq.cm).

The following is a detailed description of a preferred embodiment of the invention, reference being made to the accompanying drawings in which: Figure 1 is a view partly in elevation and partly in cross-section illustrating a conveyor assembly according to the present invention, Figure 2 is a cross-sectional view taken substantially along the line ll-il of Figure 1, Figure 3 is a pian view o; the slide valve, and Figure 4 is a fragmentary cross-sectional view of the slide valve assembly used in accordance with the present invention.

In Figure 1, reference numeral 10 indicates generally a support structure including a plurality of legs 12 for positioning a dispensing device relative to a pressurised conduit 13. A rock material in the form of granules or the like is delivered by means of a conveyor (not shown) to a hopper 14 which is securely mounted on a pair of opposed channel beams 15 and 16. The bottom for the hopper is provided by a reciprocable slide valve 17. As best seen in Figures 2 and 4, the slide valve 17 is arranged to slide between opposite sets of plates 18 and 19. A hydraulic cylinder 20 has a piston 21 mounted for reciprocation therein, the piston 21 carrying an actuating rod 22 which is connected to the slide valve 17 by means of a connector 23 as shown in Figure 3. The other end of the cylinder 20 is fixedly secured to the frame by means of a connection 24.

The actuator for the slide valve 17, including the hydraulic cylinder 20 and its operative parts, are supported by means of superstructure 25.

The slide valve 17 also forms an air-tight closure for a blow-pot loader generally indicated at reference numeral 26. The blow-pot loader 26 has a flange 27 which is also arranged to be secured to the superstructure 25.

The blow-pot loader 26 has a generally conical bottom 28 which discharges into a vibrating tray 29 of a vibrating type feeder such as the commercially available "Syntron" feeders. The feeder is actuated by a motor 30 which is enclosed in its own pressurised housing 32. A spring 31 serves to isolate the motor 30 from the housing 32. A shaft 32 transmits high frequency, low amplitude pulsations from the motor 30 to the vibrating tray 29. The tray 29 is likewise isolated mechanically from its support by means of a spring 34 extending between the tray 29 and the conduit 13. It will also be noted that the forward edge 29a of the tray 29 extends beyond the intersection of the tray with the angle of repose identified at reference 35. The material falling through the feeder will not be entrained in the airstream in the conduit 13 until the vibrating feeder is started.

Pressurised air is supplied into the conduit by means of a blower 36. The same blower may supply air under pressure to the blow-pot loader 26 by means of an inlet line 37.

The blower 36 provides air in sufficient volume to form a suspension containing about 3% to 10% by volume solids. The suspension is conveyed through the conduit 13 as a pressure of at least 10 psig (0.7 Kg/sq.cm), and typically about 11 to 12 psig (0.78 to 0.85 Kg/sq.cm). This permits a smaller diameter conduit 13 to be used, the typical conduit being about 8 inches (20.3 cm) in diameter. At an air velocity in the conduit of about 120 to 150 ft/sec (36.6 to 45.7 m/sec), the equipment can convey about 30 to 50 tons per hour (30545 to 50910 Kg/hr). The conduit is shown discharging into a heap 38 which is backfilling a mined out area.

The sequence of operation of the assembly is as follows. The blower 36 is started with no air passing through the conduit 13 and the slide valve 17 is opened. The blow-pot 26 is filled, and the slide valve 17 is closed. The filling of the blow-pot is controlled either by weighing the flow on the conveyor belt or by running the belt for a specific time. After the slide valve 17 closes, suitable valves (not shown) are opened so that the airflow passes into the conveying circuit 13. The vibrating pan feeder motor 30 is started and is run until the blow-pot 26 is empty. The vibrating feeder is then shut off and the system is ready for another cycle.

In apparatus according to the present invention, the expensive rotary air lock previously used in such systems has been eliminated and replaced with a simple and inexpensive slide valve. Such valves operate only once per cycle which usually means about once every 3 or 4 minutes. Such slide valves, therefore, do not experience the wear of rotary air locks which are operating continuously.

The slide valve operates only when the air has been cut off from the system, and this also reduces wear. In contrast, rotary air locks operate continuously at full system operating pressure. Furthermore, the wearing surfaces on the slide valve are flat plates or strips which are inexpensive and are easy to replace. Air leakage through the slide valve of this system is also substantially less than leakage through a rotary feeder. Power requirements for the feeder are quite small.

Claims (10)

1. Apparatus for conveying abrasive solids to a backfilling location including a blow-pot type loader, delivery means for delivering said solids to said loader, a vibratory feeder receiving the discharge from said loader, a pressurised conduit receiving the discharge from said feeder, and a reciprocable slide valve disposed between said delivery means and said loader, said slide valve when closed providing a substantially air-tight closure for said loader.

2. Apparatus according to claim 1, further including means for pressurising the interior of said loader.

3. Apparatus according to claim 1 or claim 2, wherein said blow-pot type loader has a generally conical discharge end and said vibratory feeder is located in close proximity to said discharge end.

4. Apparatus according to any one of claims 1 to 3, including hydraulic means coupled to said slide valve for opening and closing the same.

5. Apparatus according to any of claims 1 to 4, including a pressurised housing in which said vibratory feeder is enclosed.

6. A method for conveying abrasive solids which comprises: dropping said solids through an open slide valve, delivering said solids into a blow-pot loader, vibrating the solids to discharge the same from said blow-pot loader into a conduit, and introducing air under pressure into said conduit at a sufficient mass velocity to propel said solids as a suspension through said conduit.

7. A method according to claim 6, wherein said air is introduced in sufficient amount to form a suspension containing about 3% to 10% by volume solids.

8. A method according to claim 6 or claim 7, wherein said suspension is conveyed through said conduit at a pressure of at least 10 psig (0.7 Kg/sq.cm).

9. Apparatus for conveying abrasive solids substantially as hereinbefore described with reference to the accompanying drawings.

10. A method for conveying abrasive solids substantially as hereinbefore described with reference to the accompanying drawings.