WO2009144452A1

WO2009144452A1 - Pump system

Info

Publication number: WO2009144452A1
Application number: PCT/GB2009/001321
Authority: WO
Inventors: Richard Julian Collings; Pavol Loderer
Original assignee: Weir Minerals Europe Limited
Priority date: 2008-05-27
Filing date: 2009-05-27
Publication date: 2009-12-03
Also published as: GB0809504D0; EA201071364A1; GB2472338B; GB201018213D0; UA100421C2; GB2472338A

Abstract

A pump system (10) for a pipeline (100) is disclosed that incorporates a pump (12) connectable to a supply pipe (101) and a discharge pipe (102) of the pipeline (100). The system (10) further includes a flow impeding device (22) which in one form is part of a valve (14) operative to selectively establish a plurality of restricted flow passages (30) at a first portion (105) of the discharge pipe (102). The restrictive flow passages (30) increase the resistance to flow of the medium at the first portion of the discharge pipe so as to restrict the flow rate of the medium being discharged by the pump (12) to below a threshold level. A valve (14) and valve member (22) is also disclosed. The system (10) has particular application for mining operations and methods of controlling a pump operation and retrofitting a pump system are also disclosed.

Description

Pump System

Technical Field

The present invention relates generally to a pump system and to valves and components and to associated methods for use with such systems. The invention has been developed especially for pump systems for use in long pipelines, particularly for mining operations, and the invention is herein described in that context. However, it is to be appreciated that the invention has broader application and is not limited to that use.

Background

In the operation of a typical pump, there is a known relationship between head (H, metres) and flow (Q, litres/sec). The head (H) is normally a combination of some physical height through which fluid needs to be pumped and the friction between the fluid and the pipe walls to be overcome. A pump will deliver a required flow rate (Q) over a given amount of head at a particular set operating speed (the so-called "design point" of the pump). The size of the pump motor is selected based on the operating speed needed.

In some instances, such as in mining operations, the pumps are required to pump media, such as slurry, over relatively long distances in an enclosed pipeline (for example, in the order of two to ten kilometres long). In such circumstances, the calculated head on which the pump motor is selected would typically be based on that required once the pipeline is fully charged and, accordingly, the friction head (being the component of the calculated head (H) resulting from the friction between the slurry and the pipe walls) is calculated when the pipeline is in this condition. However, if the pipeline is empty or only partially filled (such as may occur when the pump first starts), then there is very little friction head and, accordingly, the pump may immediately start operating (racing) at very high "flow rates". In practice, the motor and the pump will operate at these very fast rates until the pipeline if fully charged and the associated friction head has increased to its assumed level to restore the operation of the pump to the design point (or at least close to it).

The operation of the pump at these very high flow rates can cause the pump to become overloaded, consequently overloading the motor power. The NPSHR (Net Positive Suction Head Required) at these flows may exceed the NPSHA (Net Positive Suction Head Available), resulting in cavitation damage to the impeller and consequential severe vibration, as well as some pipeline vibration effects that are fed back into the pump. This can reduce bearing life and provide stresses on the other components more than would normally be expected. Often these pipeline pumps are typically driven by very large motors (for example 1.6MW or 3.2MW), so the energy levels are relatively very high with consequential high vibration damage.

US 6,241,685 discloses a sewerage pumping apparatus that incorporates a downstream pinch valve which is controllable under a programmable digital process controller to throttle the flow through a downstream section of pipe to create backpressure so as regulate the flow through a pump. Whilst such an arrangement is able to assist in regulating flow through the pump, it is not well suited to mining applications where the abrasive effects of a mining slurry can substantially limit the service life of the throttle valve and cause excessive wear to the pipe in the vicinity of the valve.

Summary of the Invention

According to a first aspect, there is provided a pump system comprising: a pump connectable to a supply pipe and a discharge pipe, the pump being operable to draw a medium from said supply pipe and to discharge that medium into the discharge pipe, and a flow impeding device operative to selectively establish a plurality of restricted flow passages at a first portion of the discharge pipe to increase the resistance to flow of the medium at the first portion of the discharge pipe so as to restrict the flow rate of the medium being discharged by the pump to below a threshold level. A pump system according to this aspect of the invention is able to selectively increase the resistance to flow of the medium at the discharge pipe. Accordingly, such a device is capable of increasing the friction head at the pump (which is a consequence of increasing the resistance to flow in the discharge pipe) and as such is capable of influencing the flow rate of the pump. The friction head component imparted by the flow impeding device can be used to effectively control the flow rate of the pump by supplementing a low friction head provided by the general condition of the discharge pipeline (such as would occur when the discharge pipeline is empty). With this supplementing effect, the system can safeguard the pump from becoming overloaded and as a result being damaged. In general, the damage to a pump during start up can radically shorten the operational life of a pump and therefore the ability to mitigate this occurring has substantial practical benefit. Moreover, having the flow impeding device able to be selectively operable to increase the resistance to flow provides an option, under normal operating conditions (for example, when the pipeline is fully charged), for the flow impeding device to be arranged to have no or minimal influence on flow through the pipeline, thereby ensuring no adverse impact on the pump operation during normal operating conditions.

Furthermore, the flow impeding device is operative to establish a plurality of restricted flow passages at the first portion of the discharge pipe. It is advantageous to use multiple smaller restrictive flow passages so as to reduce wear effects from the medium on the pipeline itself downstream from the flow impeding device. If there is one larger passage, the medium flow would tend to fan from the single passage and would impinge on a fixed, specific location on the interior of the pipe just downstream from the flow impeding device and thus cause the pipe to become worn in that location. In the case of multiple, smaller passages, the flow is advantageously diffused and therefore less likely to impinge on the downstream pipe work but rather to run more parallel with the pipe side walls.

In one form, the flow impeding device comprises a valve, having a valve body, and a valve member movable relative to the valve body between an open and a closed position, wherein the valve member establishes the restricted flow passages when in the closed position. In a particular form, when in the open position, the valve member does not impede the flow of medium through the discharge pipe.

In a particular form, the valve is in the form of modified gate-valve where, rather than having a solid plate (or gate) as is typically the case in a standard knife-gate valve, the valve incorporates a gate having a plurality of apertures that in use define the restrictive flow passages. In use, when the pump starts, the valve is "closed" with the aperture gate located across the pipeline, immediately downstream from the pump in the discharge pipe. With the plate in position across the pipeline, enough friction head is added to restrict the fluid flow and keep the pump motor operating without it overloading. However, the valve does not prevent fluid flow and over time the discharge pipe will become charged with the medium and this will result in the pressure basically equalising either side of the valve. At that time, the valve may be "opened" by withdrawing the aperture gate and leaving a full diameter open pipeline. An advantage of this arrangement is that the wearing parts (the aperture gate) are therefore out of the flow and not subject to wear under normal operating conditions. The normal gland seals of the valve are effective to seal the pipeline after the gate is withdrawn and the only weai' parts left in the flow are the rubber gate seals which are relatively inexpensive to replace.

In a second aspect, the invention is directed to a valve having a valve body including a port, and a valve member movable relative to the valve body between an open and closed position so as to regulate the flow of a medium through the port, wherein the valve member establishes a plurality of restricted flow passages at the port when in the closed position, and allows for unimpeded flow through the port when in the open position.

A valve according to this aspect may be in any form as described above in relation to the valve disclosed in respect of the pump system according to the first aspect of the invention. In a third aspect, the invention is directed to a valve member for use in the valve of the second aspect. The valve member forms part of a valve and is operative to establish a plurality of restricted flow passages through the valve when in a first condition, and the valve member includes a plurality of apertures which provide the restricted flow passages. In a particular arrangement the valve member is in the form of a plate and the plurality of apertures extends through that plate. In one particular arrangement the valve is a gate valve.

In a fourth aspect, the invention is directed to a method of controlling the operation of a pump arranged to pump a medium from a supply pipe into a discharge pipe, the method comprising the steps of: increasing the resistance to flow of the medium in the discharge pipe during a first stage of the pumping operation by establishing a plurality of restricted flow passages in the discharge pipe so as restrict the flow rate of the medium being discharged by the pump to below a threshold level; and reducing the resistance to flow in the discharge pipe during a second stage of the pumping operation.

In a particular form, the step of increasing the resistance to flow of the medium includes creating an increased pressure head in a first portion of the discharge pipe.

In one form, the first stage is during start up of the pumping operation. In one form, the second stage is when the discharge pipe is substantially charged with medium.

In a particular form, the resistance to flow of the medium in the discharge pipe is regulated by a flow impeding device disposed in that discharge pipe. In the particular form, that flow impeding device is in the form of a valve member according to any of the forms described above in the first, second or third aspects.

In a fifth aspect, the invention is directed to a pipeline having a supply pipe, a discharge pipe and a pumping system according to the first aspect described above, the pump of the pumping system being operative to draw a medium from the supply pipe to discharge that medium into the discharge pipe, and the flow impeding device is disposed in the discharged pipe and operative to selectively increase the resistance to flow of the medium at a first portion of the discharge pipe so as to restrict the flow rate of the medium being discharged by the pump to below a threshold level.

In a sixth aspect, there is provided a method of retrofitting a pump system according to the first aspect described above to a pipeline having a supply pipe, a discharge pipe and a pump connected to the supply and discharge pipes and operative to draw a medium from the supply pipe and to discharge that medium into the discharge pipe, the method comprising the step of installing a valve in the discharge pipe, the valve including a flow impeding device that is operative to selectively increase the resistance to flow of the medium at a first portion of the discharge pipe so as to restrict the flow rate of the medium being discharged by the pump to below a threshold level.

In a particular form the step of installing the valve involves cutting the discharge pipe at a cut point and operatively coupling the valve to the discharge pipe at the cut point.

Brief Description of the Drawings

It is convenient to hereinafter describe an embodiment of the present invention with reference to the accompanying drawings. The particularity of the drawings and the related description is to be understood as not superseding the generality of the preceding broad description of the invention.

In the drawings:

Fig 1 is a schematic view of a pipeline having a pumping system according to an embodiment of the invention;

Fig 2 is a schematic view of a flow impeding device for use as part of the pumping system in the pipeline of Fig 1. Detailed Description of an Embodiment

Fig. 1 discloses a pipeline 100 which includes a pumping system 10 which is connected inline with a supply pipe 101 and a discharge pipe 102. The pumping system includes a pump 12 operable to draw a medium from the supply pipe 101 and to discharge that medium into the discharge pipe 102.

In the illustrated form, the pipeline 100 is for use in mining operations, for example to transport a solid-liquid slurry to a tailings dam. In such an application, the discharge pipeline 102 is long, typically in the order of four to eight kilometres and the pump 12 is arranged to pump the slurry through that pipeline. In view of the head (H) and flow rates (Q) required, the pump 12 is typically a large centrifugal pump driven by large motors (in the order of 1.6 MW or 3.2 MW).

The pump system 10 further comprises a valve 14 which is located in the discharge pipe 102 immediately downstream from the pump 12. The valve 14 incorporates a flow impeding device and the purpose of the flow impeding device is to be able to selectively increase the resistance to the flow of the slurry at the point in the discharge pipe 102 where the valve 14 is installed. In this way, the valve 14 is able to create a higher friction head over a first section 105 of the discharge pipe 102 as compared to a downstream section 106 of the pipe 102 during operation of the pump 12 when the discharge pipe 102 is not fully charged with slurry. Furthermore, because of the proximity of the valve 14 to the pump 12, the relatively higher friction head formed in the first section 105 of the discharge pipe can be established very quickly following start-up of the pump, even if the discharge pipe 102 is empty or substantially empty.

The level of resistance to flow created by the valve 14 will influence the resulting friction head generated over the discharge pipe portion 105. A variation in this level of resistance can be made so as to establish a desirable friction head for particular circumstances. In general the resulting friction head over the section 105 is designed so as to restrict the flow rate of the medium being discharged by the pump to below a threshold level regardless of the condition of the pipe downstream of the valve 14. If the pipeline is empty or only partially filled and there is little friction head in the discharge pipe 106, the pump may immediately start operating (racing) at very high flow rates. Operating the pump at these sorts of flow rates can cause the pump to become overloaded, consequently overloading the motor power, and the NPSHR (net 5 positive suction head required) at these flow rates may exceed the NPSHA (net positive suction head available) resulting in cavitation damage to the impeller and consequential severe vibration. The incorporation of the valve 14 can mitigate this occurring by causing a desirable friction head to form almost immediately after the pump starts, which will reduce the flow rate through the pump 12 to normal operating levels. 0

Fig. 2 illustrates the valve 14 in more detail. In the illustrated form, the valve 14 is in the form of a modified gate valve that has been cut into the discharge pipeline and the flow impeding device is a modified gate 22 used in the valve 14. 5 The gate valve 14 includes a valve body 16 which has a first portion 18 incorporating a port (not shown) that is at least substantially the same size as the interior passage of the discharge pipe 102. The valve body 16 also includes a second portion 20 which is disposed above, and is contiguous with, the first portion 18. A valve member in the form of the valve gate 22 is mounted to the valve body 16 and o movable by sliding from a closed position wherein the valve gate is disposed within the first portion 18 of the valve body and across the port incorporated in the first portion 18 (thereby extending across the interior of the discharge pipe 102), to an open position wherein the valve gate 22 is moved by sliding into the second portion 20 of the valve body 16, wherein it does not impede the flow of the medium through the discharge5 pipe. The valve gate 22 includes a yoke 24 which typically includes an exterior thread that cooperates with an interior thread on an rotatable actuator 26 mounted at an upper end 28 of the valve body 16 to effect the sliding movement of the valve gate 22 by manual or automated means. 0 The valve gate 22 differs from a conventional sliding gate valve in that it incorporates a plurality of apertures 30 that act as restricted flow passages through the valve 14. Accordingly the valve 14 is not designed to shut off the flow when in its closed position but rather just impede the flow through the discharge pipe 102. In further embodiments the number and size of the apertures 30 can be altered, depending on the requirements for frictional head drop across the gate/orifice to suit the particular engineering circumstances of the application and the local site conditions.

In operation, when the pump 12 starts, the valve 14 is "closed" with the valve gate 22 located across the pipeline, which restricts the flow through the valve 14 by forcing the slurry to pass through the restricted flow passages 30 to add enough friction head to restrict the fluid flow and keep the pump 12 operating without overloading etc. When the discharge pipe 102 is full and the pressure is basically equalised on either side of the valve 14, the valve is "opened" by withdrawing the sliding gate 22 and leaving a full diameter open pipeline.

The wearing part (the gate 22) is therefore out of the flow and not subject to wear under normal operating conditions. A normal gland seal (not shown) of the valve 12 seals the pipeline after the gate 22 is withdrawn and the only wear parts left in the flow are the rubber gate seals (not shown ) which surround the valve port and which are relatively cheap to replace.

The valve gate 22 shown in the drawing uses multiple smaller holes 30 rather than a single, large hole so as to reduce wear effects from the slurry on the pipeline itself downstream from the valve 14. If there was one bigger hole in the slide gate, the valve 14 would still work for the function described, however the slurry flow would tend to fan out from the hole and would impinge on a fixed, specific ring-like location on the interior of the pipe 102, just downstream of the valve 14 and thus cause the pipe 102 to become worn in that position. In the case of multiple, smaller apertures 30, the flow is advantageously diffused so as not to impinge on the downstream pipe but rather to run parallel with the pipe side walls.

In some instances it is possible to supply a section of pipeline that has been pre- fitted with the valve 14 for positioning in a new pipeline situation where is it expected that such start-up issues can arise. In some instances it is possible to supply the valve 14 in combination with the pump 12 during the initial construction of the pipeline. In other circumstances it is possible for an operator to retrofit such a device by cutting a small section out of an existing pipeline to create a location for subsequent positioning of the valve 14. When a part becomes worn, for example the hole 30 in the slide gate 22 become worn to a larger individual diameter, an operator can replace that component of the valve 14.

For the most part the method of the present invention can be practiced whenever the pipeline is emptied and the pump deactivated, for example during maintenance or replacement of a tailings pump. In such a situation the method can be used to stabilise the operation at the time of restarting the pump.

In the claims which follow and in the preceding description of relative rotation stop means where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art in any country.

It will be appreciated that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A pump system comprising: a pump connectable to a supply pipe and a discharge pipe, the pump 5 being operable to draw a medium from said supply pipe and to discharge that medium into said discharge pipe, and a flow impeding device operative to selectively establish a plurality of restricted flow passages at a first portion of the discharge pipe to increase the resistance to flow of the medium at the first portion of the discharge pipe so as0 to restrict the flow rate of the medium being discharged by the pump to below a threshold level.

2. A pump system according to claim 1, further comprises a valve having a valve body, the flow impeding device forming part of the valve and comprising a5 valve member moveable relative to the valve body between an open and closed position, wherein the valve member establishes the restricted flow passages when in the closed position.

3. A pump system according to claim 2, wherein when in the open position the o valve member does not impede the flow of medium through the discharge pipe.

4. A pump system according to claim 2 or 3, wherein the valve member is in the form of a plate incorporating a plurality of apertures that define said restricted flow passages. 5

5. A pump system according to any one of claims 2 to 4, wherein the valve is a gate valve.

6. A pump system according to any preceding claim, wherein the pump is a o centrifugal pump.

7. A valve having a valve body including a port, and a valve member movable relative to the valve body between an open and closed position so as to regulate the flow of a medium through the port, wherein the valve member establishes a plurality of restricted flow passages at the port when in the closed position, and allows for unimpeded flow through the port when in the open position.

8. A valve according to claim 7, wherein the valve member comprises a plate incorporating a plurality of apertures that define said restricted flow passages.

9. A valve according to either claim 7 or 8, wherein the valve is a gate valve.

10. A valve member for a valve operative to establish a plurality of restricted flow passages through the valve when in a first condition, the valve member including a plurality of apertures which defines the restricted flow passages.

11. A valve member according to claim 10, wherein the valve member is in the form of a plate and the apertures extend through said plate.

12. A valve member according to claim 10 or 11, wherein the valve is a gate valve.

13. A method of controlling the operation of a pump arranged to pump a medium from a supply pipe into a discharge pipe, the method comprising the steps of: increasing the resistance to flow of the medium in the discharge pipe during a first stage of the pumping operation by establishing a plurality of restricted flow passages in the discharge pipe so as restrict the flow rate of the medium being discharged by the pump to below a threshold level; and reducing the resistance to flow in the discharge pipe during a second stage of the pumping operation.

14. A method according to claim 13, wherein the step of increasing the resistance to flow of the medium includes creating an increased friction head in a first portion of the discharge pipe.

15. A method according to claim 13 or claim 14, wherein the first stage is during start up of the pumping operation.

16. A method of controlling the operation of a pump arranged to pump a medium from a supply pipe into a discharge pipe, the method comprising the steps of: introducing a flow impeding device into the discharge pipe that increases the resistance to flow of the medium in the discharge pipe during start up of the pumping operation so as restrict the flow rate of the medium being discharged by the pump to below a threshold level; and removing the flow impeding device from the discharge pipe during a second stage of the pumping operation.

17. A method according to claim 16, wherein the resistance to flow of the medium is increased by providing one or more restricted flow passages at a first portion of the discharge pipe.

18. A method according to claim 17, wherein the resistance to flow of the medium is increased by providing a plurality of restricted flow passages at a first portion of the discharge pipe.

19. A method according to any one of claims 13 to 15, wherein the resistance to flow of the medium in the discharge pipe is regulated by a flow impeding device disposed in the discharge pipe.

20. A method according to any one of claims 13 to 19, wherein the second stage is when the discharge pipe is substantially charged with medium.

21. A method according to claim 20, wherein the flow impeding device is in the form of valve member according to any one of claims 10 to 12.

22. A pipeline having a supply pipe, a discharge pipe and a pumping system according to any one of claims 1 to 6, the pump of the pumping system being operative to draw a medium from said supply pipe and to discharge that medium into said discharge pipe, and the flow impeding device being disposed in the discharge pipe and operative to selectively increase the resistance to flow of the medium at a first portion of the discharge pipe so as to restrict the flow rate of the medium being discharged by the pump to below a threshold level.

23. A method of retrofitting a pump system according to any one of claims 1 to 6 to a pipeline having a supply pipe, a discharge pipe and a pump connected to the supply and discharge pipes and operative to draw a medium from said supply pipe and to discharge that medium into said discharge pipe, the method comprising the step of: installing a valve in the discharge pipe, the valve including the flow impeding device of the pump system that is operative to selectively increase the resistance to flow of the medium at a first portion of the discharge pipe so as to restrict the flow rate of the medium being discharged by the pump to below a threshold level.

24. A method according to claim 23, wherein the valve is according to any one of claims 7 to 9.

25. A method according to claim 23 or claim 24, wherein the step of installing the valve involves cutting the discharge pipe at a cut point and operatively coupling the valve to the discharge pipe at the cut point.