GB2116637A - Improvements in and relating to conveying systems - Google Patents

Abstract

The present invention relates to a conveying system particularly but not exclusively for conveying a slurry comprising particulate material, e.g. sand, and a liquid, e.g. water, to a gun for providing a high pressure abrasive jet. The high pressure jet is created in the gun (3) to which the slurry at low pressure and high pressure water are provided separately in pipes (2, 5). To assist flow of slurry to the gun at spaced intervals along the slurry carrying pipe (2), the high pressure water pipe (5) is connected to it by bleed devices (6, 7, 8, 9) providing high pressure jets of liquid in the slurry pipe in the direction of flow of slurry therealong. <IMAGE>

Description

SPECIFICATION Improvements in and relating to conveying systems The present invention relates to improvements in systems for conveying a particulate material and liquid mixture along a pipe, for example to apparatus for producing a jet of particulate material and liquid mixture, for example a sand blast gun using a sand/water mixture.

The problem with such systems, which are generally used to provide an abrasive jet, is that, if the particulate materiallliquid mixture is supplied to the gun at sufficient pressures to produce the required abrasive jet, the mixture will itself severely abrade and wear the gun itself, the supply pipe work and any pump which provides the mixture at the required pressures. This problem is solved by supplying the apparatus with the high pressure liquid and the particulate materials separately, the particulate material being mixed with some liquid to increase its fluidity. The problem then is howto induce the particulate material to flow to the apparatus without using a pump.This may be done by supplying the high pressure liquid to the apparatus in such a way as to create a zone of reduced pressure in the path of the particulate material in the gun, for example as described in U.K.

Specification No. 1403528. The resulting pressure differential along the particulate material supply pipe will produce a flow of the material to the gun which is sufficient if the source of the particulate material is relatively close to the gun, for example of the order of 2 to 3 meters away. To increase this distance it has been proposed to take a proportion of the high pressure liquid supply and feed it to the outlet of a hopper containing the particulate material, for example as described in U.K. Specification No. 1424896. However aithough this does materially improve the situation, it only increases the distance between the particulate material supply and the apparatus to at most 30 meters.

Systems of this type have particular application to under water work but, because of the limitation on distance between the particulate material supply and jet producing apparatus, heretofore the hopper containing the particulate material had to suspended under water over the side of a work boat an appropriate distance from the operator. This has proved to be most inconvenient and time consuming because of the need to move the hopper as the location of the operator moves.

According to one aspect of the present invention, there is provided a system for conveying a particulate material and liquid mixture comprising first pipe means for the particulate material and liquid mixture, means for supplying liquid under a pressure substantially greater than that of the mixture, and bleed means connected to the first pipe means at spaced intervals therealong and to the pressurised liquid supply means for supplying at the spaced intervals the pressurised liquid to the first pipe means so as to at least assist flow of the mixture therealong.

Advantageously the bleed means comprises a plurality of bleed devices provided at spaced intervals along the first pipe means, each bleed device interconnecting the first pipe means with a second pipe means for the pressurised liquid at spaced intervals along the second pipe means.

The bleed means may be arranged to permit liquid to flow from the second pipe means to the first pipe means at a predetermined pressure relative to the pressure of the pressurised liquid in such a way as to create in the first pipe means a localised zone of reduced pressure which draws particulate material along the first pipe means.

For supplying a particulate material and liquid mixture to apparatus for producing a jet thereof, the first and second pipe means would be connected to the apparatus, the pressurised liquid being supplied to the second pipe means at a relatively high pressure, e.g. of the order of 500 bar, and the first pipe means would be connected at its inlet end to a containerfor receiving the particulate material and liquid mixture.

According to another aspect of the present invention there is provided a bleed device for interconnecting two pipes comprising first and second connectors for connection into first and second pipes, the second connector having a lateral extension providing a passage for fluid from the second pipe and extending through the first pipe connector, the passage in the lateral extension opening into the first pipe connector axially thereof for providing an axial jet of fluid therein.

Where the pressure of the jet of fluid is to be less than that of the fluid in the second pipe, restriction means may be provided in the passage in the extension for reducing the pressure of the fluid as it issues into the first pipe. The restriction means may include a first restriction for controlling the quantity of fluid flowing into the passage and a second restriction for controlling the pressure.

Advantageously the first pipe connector is shaped downstream of the opening to facilitate, in use, transfer of kinetic energy from the jet issuing from the opening to fluid flowing in the first pipe connector.

The first pipe connector may have a venturi shaping downstream of the opening.

Preferably the flow cross section of the first pipe connector is substantially constant from its inlet end to the region of emergence of the jet and the portion of the lateral extension in the first pipe connector may be provided with a streamlined shape to minimise disturbance of flow of fluid in the first pipe connector.

The present invention will be more fully understood from the foilowing description of embodiments thereof, given by way if example only, with reference to the accompanying drawings, in which: Figure lisa diagrammatic view of an embodiment of a system according to the present invention; Figure 2 is a section through an embodiment of bleed device according to the present invention and for use in the system of Figure 1; Figure 3 is a section on the line Ill-Ill of Figure 2; Figure 4 is a section on the line IV-IV of Figure 2; Figure 5 is a diagrammatic view of part of the embodiment of Figure 1 showing a modification thereof; and Figure 6 is a diagrammatic view of a system similarto that of Figure 1 showing further modifications thereof.

The system shown in Figure 1 is for conveying or supplying sand and water to a sand blast gun 3 which is used under water. The system comprises a container 1, for example a hopper, which is in use mounted on a boat or other surface support. The hooper 1 receives sand and water. A mixture of sand and water, which we will hereafter refer to as slurry, is taken from hopper 1 by pipe 2 and supplied to the slurry inlet of the gun 3, which has been shown very diagrammatically but may be as described in U.K.

Specification No. 1403528. The inlet end of pipe 2 is closed and the end portion 4 is perforated to provide a pluarlity of inlets for slurry such that blockage of one or more by sand particles will not substantiaiiy affect flow of slurry to the gun. The perforated end portion 4 may for example be made of stainless steel, the pipe 2 being made of reinforced rubber.

Simultaneously high pressure water is supplied from a pump (not shown) by pipe 5 to the gun 3.

While as mentioned above, the gun may be as described in U.K. Specification No. 1403528 in which a zone of reduced pressure is created in the gun by the flow of high pressure water, to draw the slurry to the gun, it is not essential that the gun include an arrangement within it to induce flow of slurry to it.

To induce the slurry to flow along pipe 2, a plurality of bleed devices 6,7,8 and 9 are provided at intervals along pipe 2 and connect pipe 2 with pipe 5 at these spaced intervals. While a system with four such bleed devices has been shown, the actual number of devices provided will depend on the length ofthe pipe 2 and the maximum distance between the hopper 1 and the gun 3. These bleed devices permit a small flow of high pressure water from pipe 5 to flow into pipe 2 in effect to supply kinetic energy to the slurry in pipe 2 to cause itte flow along the pipe.

Advantageously the water flowing from pipe 5 to pipe 2 in each bleed device is arranged to issue in the pipe 2 as a high pressure jet which creates a localised zone of reduced pressure in the pipe 2 to draw the slurry along the pipe.

A particular embodiment of a bleed device for use in the above described system is shown in Figures 2 to 4. As shown the bleed device comprises a connector 10 for connection in pipe 2 and a connector 11 for connection in pipe 5. Each connector comprises a body 12, 13 having a throughbore 14, 15 to provide a continuation ofthe respective pipe, and portions 16, 17 with which the pipes 2, 5 respectively are engaged. As shown portions 16 of connector 10 are provided with external enlargements for frictional engagement with pipe 2 and portions 17 of connector 11 are externally threaded for engagement with threaded end portions on pipe 5. It will be appreciated that the precise arrangement of portions 16, 17 will depend on the particular types of pipes used.

Connector 11 has a lateral extension 18 providing a passage 19 for fluid to flow from pipe 5. A metering device 20 is provided in passage 19, the device 20 defining a metering orifice 21 which is arranged to permit a preset quantity of liquid flow from pipe 5.

To prevent the orifice 21 being inadvertently blocked by a particulate contaminant in the water in pipe 5, a filter 22 is provided upstream of device 20. As shown the filter is made of a fine metal mesh. The extension 18 projects through lateral openings in connector body 12 and through bore 14. Passage 19 is connected with a radial passage 23 which opens at 24 axially into passage 14. The flow cross section of passage 23 and opening 24 is arranged relative to that of orifice 21 so as to provide a jet of water having a predetermined rate of flow and therefore a predetermined pressure relative to the pressure of the water in pipe 5. Thus the kinetic energy provided to the fluid in pipe 2 by the jet issuing from opening 24 is predetermined by the relative flow cross sections of orifice 21 and opening 24 and the pressure in pipe 5.

While as shown in full lines in Figures 2 and 3, the bore 14 downstream of opening 24 has the same shape as it has upstream of opening 24, advantageously downstream of opening 24, the bore 14 is shown to maximise the efficiency of the transfer of kinetic energy from the jet to the sand flowing in pipe 2. For example, as shown in broken lines in Figures 2 and 3, the flow cross section of bore 14 downstream of jet 24 may be reduced and then progressively increase to that of the inlet end of connector 10. This shaping may be such as to provide a venturi effect in the zone of issuance of the jet which may be arranged to create a zone of reduced pressure in bore 14 which induces flow of slurry along pipe 2. The variation in shaping of the bore 14 downstream of opening 24 may be provided integrally with body 12 or by a separate liner 25, for example made of a ceramic material.

To prevent disturbance of flow of slurry in pipe 2 upstream of the zone of issuance of the jet from opening 24, bore 14 may be widened in the region of extension 18 to provide a constant flow cross section from the inlettothe point of issuance ofthe jetfrom opening 24 and the portion 18a of extension 18 lying within the bore 14 may have a modified cross section. As shown the portion 18a may be streamlined and generally oval, the plane of the longer axis of the oval including the axis of bore 14.

Because of the high pressures used for water in pipe 5, device 20 will be subject to wear and may therefore be made of hardened stainless steel or synthetic sapphire. Similarly passage 23 and opening 24 may also be provided by a hardened insert to minimise wear. Passage 19 in extension 18 for convenience of manufacture extends the full length of extension 18 and is closed at the end opposite its connection to connector 11 by a plug 19a which will also be subject to wear and may be made of a hardened material. The connectors 10,11 and extension 18 may be made for example of stainless steel.

With the above described arrangement, there is no positive control on the relative proportions of water and sand in the slurry flowing from the hopper 1, the initial proportion simply depending on the extent to which the sand in hopper 1 is suspended in the water. To control the proportion of sand to water in the output from gun 3, the first bleed device 6 may as shown in Figure 5 include an additional water inlet 26 (shown in broken lines in Figure 3) and which is connected to a pipe 27 provided with a valve 28 and connected to a water supply. For example the free end of pipe 27 may simply be dipped into the upper part of the hopper where there is mainly water.

Water will then be drawn along pipe 27, as will slurry along pipe 2, by the effect of the water jet issuing from opening 24 in the device 6. The amount of waterflowing along pipe 27 is controlled bythe valve 28 which may be manually operated or remotely controlled by the operator of the gun or on the instruction of the gun operator by a person on the boat in dependence on the mixture of the jet being produced by the gun 3.

Alternatively, the inlet end of pipe 27 may be connected, not to the upper part of the hopper, but to a source of pressurised liquid, e.g. water, for example at a relatively low pressure of between 1 to 20 bars, e.g. 10 bars or less. In such an enlargement, the outlet end of pipe 27 may be connected to pipe 2 upstream of the first deviceS, as shown in FigureS.

During operation, the valve 28 is operated, as described above, to control the flow of liquid to the pipe 2 and therefore the relative proportions of liquid and particulate material in the slurry. At the normal relatively low flow rates which will be required to produce the required variations in the proportions of the slurry, the liquid from pipe 27 enters pipe 2 and mixes with the slurry flowing therethrough. However, if the pressure of the liquid in pipe 27 is sufficient in relation to the pressure of the mixture in pipe 2, the supply from pipe 27 may be used to stop flow of slurry from the hopper by increasing the flow of liquid from pipe 27 until flow along the part of pipe 2 upstream of its connection to pipe 27 is at least stopped and advatageously reversed.Since the pressure in pipe 2 at its connection to pipe 27 will be low and indeed may be negative, the pressure of liquid supplied to pipe 27 need not be particularly high to achieve reverse flow. This facility can be very useful to clear pipe 2 of particulate material, when it is required to temporarily interrupt flow of particulate material therealong or at the end of an operation, and may be the primary function of the supply to pipe 27.

The gun used with a system as described above is generally of the type in which, when a particulate jet is no longer required, either temporarily or at the end of an operation, the input of high pressure liquid to the gun is directed to a dump outlet. This has the immediate effect of reducing the pressure of the liquid in pipe 5 and therefore of the jets in pipe 2 issuing from the bleed devices 6-9. The slurry flowing in pipe 2 may therefore stop or flow so slowly that the particulate material settles out. If this occurs it can prove impossible to restart the gun without disconnecting the pipework and cleaning each section of particulate material. To prevent this occurring, a choke or restriction device 30 (Figure 6) may be provided immediately upstream of the gun or in the gun itself.The restriction provided thereby is less than that provided by the gun nozzle so that it has no effect on the particulate jet provided by the gun, but when the dump outlet of the gun is used, the restriction provided by the choke or restriction device is effective to maintain the pressure in pipe 5 at a level such that the jets from devices 6-9 continue to be effective to keep the slurry flowing to the gun. The slurry then issues harmlessly from the gun nozzle.

Where an arrangement as shown in Figure 6 is provided, wherein a particulate jet is no longer required and the particulate material isto be cleaned from the system, the valve 28 is opened as the gun is connected to dump. Liquid from pipe 27 prevents further flow of slurry from the hopper and also flows along pipe 2 towards the gun and is assisted in its passage by the jets from devices 6-9. Flow of liquid along pipe 5 is continued until clear liquid issues from the nozzle of the gun indicating that all particulate material has been cleared from pipe 2. At this point, the outlet of the hopper is permanently closed and supply to pipes 27 and 5 is shut off.

For start up this procedure may be reversed so that the system is fully primed with flowing liquid before the particulate material is added.

It will be appreciated that the above described system has advantages not only in operation of the system but also facilitates start-up and shut-down of the system because the bleed devices are permanently open and will operate so long as high pressure water is supplied to pipe 5.

In a preferred embodiment, the water in pipe 5 during operation of the gun is at a pressure of about 500 bars and has a flow rate of about 80 litres per minute. The jet issuing from the gun 3 thus has a pressure of about 500 bars and deiivers particulate material at a rate of about 8 kg per minute. Each bleed device is arranged to produce a jet of water at a pressure of about 150 bars and supply water to pipe 2 at a rate of about 7 litres per minute. When the gun is on dump, the pressure of liquid at the dump outlet is about 20 bar and, where a choke or restrictive device is provided, the pressure in pipe 5 is about 200 bar.

As concerns the spacing of the bleed devices 6,7 etc. along the pipes 2,5, this will of course depend on the likely arrangements of the two pipes, for example whether or not they will be mainly horizontal or mainly vertical etc. With a type of arrangement diagrammatically shown in Figure 1, the first bleed device may be arranged about 2 meters from the end of pipe 2 and the second, third etc. devices may be spaced apart by about 30 or 40 meters. lfgun3 includes an arrangement for inducing a flow of slurrytothe gun,then the spacing between the last bleed device and the gun may again be about 30 or 40 meters. If however the gun does not include such an arrangement, the last bleed device may be close to the gun.

While the above described system and devices has been described in terms of its use with a sand and water mixture, it will be appreciated that the system can be used with other particulate materials and other liquids. Additionaily of course the system is applicable to other uses than with the gun submerged, and for example may be used in an entirely iand based operation, and may be used to convey a particulate material and liquid mixture for other pur poses than to supply a gun. For such other purposes the liquid in pipe 5 may be provided simply and solely to supply the bleed devices and at the pressure required for the jets, for example at 50 - 100 bars.

Under such circumstances, the bleed device would not need means to control the pressure of the jet and therefore only a single restriction controlling the rate of flow of the liquid in the passage would need to be provided in the passage or at the opening of the passage into the pipe.

Claims (18)

1. A system for conveying a particulate material and liquid mixture comprising first pipe means for the particulate material and liquid mixture, means for supplying liquid under a pressure substantially greater than thatofthe mixture, and bleed means connected to the first pipe means at spaced intervals therealong and to the pressurised liquid supply means for supplying at the spaced intervals the pressurised liquid to the first pipe means so as to at least assistflow of the mixture therealong.

2. A system as claimed in claim 1, including second pipe means for the liquid under pressure.

wherein the bleed devices interconnect the first and second pipe means at spaced intervals therealong.

3. A system as claimed in either claim 1 or claim 2, wherein each bleed device is adapted to provide a jet of liquid in the first pipe means, at a predetermined pressure and rate of flow dependent on the pressure and flow of the liquid under pressure, and in the direction of flow of the mixture therealong.

4. A system as claimed in any one of the preceding claims, wherein each bleed device is arranged to provide a jet of pressurised liquid in the first pipe means, and is shaped so as to create a localised zone of reduced pressure in the first pipe means in the region of the jet and which draws the mixture along the first pipe means.

5. A system as claimed in any one of the preceding claims, including an additional liquid input connected to the first pipe means in the region of the first bleed device for supplying liquid to the first pipe means for adjusting the composition of the mixture, and means for controlling the supply of additional liquid.

6. A system as claimed in claim 5, wherein the additional liquid input is connected to the first pipe means at the first bleed device which is adapted to induce flow of the additional liquid into the first pipe means.

7. A system as claimed in any one of the preceding claims, including means for supplying liquid to the first pipe means at or upstream of the first bleed device for causing reverse flow of liquid along the first pipe means upstream thereofto prevent the mixture flowing along the first pipe means downstream thereof, and means for controlling the supply thereof.

8. A system as claimed in any one of the preceding claims for supplying particulate material and liquid to a gun for providing a high pressure jet of liquid and particulate material, wherein the first and second pipe means are connected to the gun at the downstream ends thereof and to a source of the mixture and of pressurised liquid respectively at the upstream ends thereof.

9. A system as claimed in claim 8, wherein the gun has a dump outlet to which the second pipe means is connected when the gun is not in operation, and a restriction is provided in the path of liquid flowing in the second pipe means upstream of the dump outlet which provides a lesser restriction than that provided by the gun in operation.

10. A system as claimed in any one of the preceding claims, wherein the pressure of the liquid under pressure is of the order of 500 bars, the pressure of the liquid supplied to the first pipe means by each bleed means is of the order of 150 bars.

11. A system substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings or as modified in accordance with Figures 5 or 6 of the accompanying drawings.

12. A bleed device for interconnecting two pipes comprising first and second connectors for connection into first and second pipes, the second connector having a lateral extension providing a passage for fluid from the second pipe and extending through the first pipe connector, the passage in the lateral extension opening into the first pipe connector axiallythereoffor providing an axial jet of fluid therein.

13. A bleed device as claimed in claim 12, including restriction means in the passage for controlling the pressure and volume of fluid flowing into the first pipe.

14. A bleed device as claimed in either claim 12 or claim 13, wherein the portion of the extension in the first pipe connector is provided with a streamline shape to minimise disturbance of the flow of fluid in the first pipe connector.

15. A bleed device as claimed in any one of claims 12 to 14, wherein the first pipe connector and the portion of the lateral extension therein are shaped to provide a substantially constant flow cross section for fluid therein from the inlet of the first pipe connector to the region of emergence of the jet thereinto.

16. A bleed device as claimed in any of claims 12 to 15, wherein the first pipe connector has a venturi shaping downstream of the opening in the lateral extension.

17. A bleed device substantially as herein described with reference to Figures 2 and 4 of the accompanying drawings.

18. A system as claimed in any one of claims 1 to 10, including bleed devices as claimed in any one of claims 12 to 17.