GB2592179A

GB2592179A - Seal assembly

Info

Publication number: GB2592179A
Application number: GB1914338.7A
Authority: GB
Inventors: Loderer Pavol; Locke Matthew; Clarence Paul
Original assignee: Weir Minerals Europe Ltd
Current assignee: Weir Minerals Europe Ltd
Priority date: 2019-10-04
Filing date: 2019-10-04
Publication date: 2021-08-25
Anticipated expiration: 2039-10-04
Also published as: GB2592179B; GB201914338D0; WO2021064533A1

Abstract

A seal assembly, especially for a centrifugal slurry pump, comprising a mechanical compound shaft sealant for creating an interface between a dry end and a wet end of a centrifugal pump; a gland seal stop for mounting on a shaft near the wet end of the centrifugal pump, and defining a discharge channel; a gas inlet channel in fluid communication with the discharge channel in the gland seal stop, and defining a gas cavity into which gas can be fed. In use, gas is introduced to the gas cavity and flows through the discharge channel to create a gas to liquid interface at the wet end of the pump to reduce liquid input to the mechanical compound shaft sealant from the wet end of the pump. A method of reducing water leakage from a gland seal is also described.

Description

SEAL ASSEMBLY

The invention relates to improvements in or relating to a seal assembly, and particularly, but not exclusively, to a seal assembly for use in a centrifugal pump.

A number of techniques are known for sealing centrifugal pumps, such as slurry pumps (which convey highly abrasive material, such as mixtures of at least 10% by weight of ore in water) and result in severe erosion to the centrifugal pump and parts thereof (such as the impeller, throatbush, and volute). Erosion is a form of wear involving the loss of surface material by the action of particles entrained in the liquid.

Mechanical seals are generally very expensive and if they fail then the slurry pump typically has to be stopped, thereby stopping the processing of ore at a mine, which is very expensive because of the lost productivity. Gland water seals are cheaper than mechanical seals and they do not require the slurry pump to be stopped if they fail. However, gland water seals have limitations on sealing pressure and if not regularly adjusted result in a relatively high volume of water leakage. On many mine sites, water is an expensive resource On some sites, all water used in processing equipment on a mine must be obtained from sea water) so using a gland water seal can result in a high cost of ownership that counteracts the initial lower cost.

US 5,427,500 discloses a pressurised air buffer located between two seals to prevent slurry from leaking from a wet end of a pump to a dry end. However, this design has the disadvantage that slurry will destroy the wet end seal (lift seal) very quickly.

Furthermore, the shaft seal will dry out very quickly (due to the air pressure in the air buffer) causing leakage therethrough. The dry end seal could be improved by using a mechanical seal, but this would bring the risk of having to shut the pump off in the event of a failure of the mechanical seal.

It is among the objects of embodiments of the present invention to overcome or mitigate one or more of the above disadvantages or other disadvantages of prior art seals. According to a first aspect there is provided a seal assembly comprising: a mechanical compound shaft sealant for creating an interface between a dry end and a wet end of a centrifugal pump; a gland seal stop for mounting on a shaft near the wet end of the centrifugal pump, and defining a discharge channel; a gas inlet channel in fluid communication with the discharge channel in the gland seal stop, and defining a gas cavity into which gas can be fed, whereby, in use, gas is introduced to the gas cavity and flows through the discharge channel to create a gas to liquid interface at the wet end of the pump to reduce liquid input to the mechanical compound shaft sealant from the wet end of the pump.

The mechanical compound shaft sealant may comprise a flexible, self-lubricating compound, such as a compound available from TOM-PAC Inc. (trade mark) of Montreal, Quebec, Canada, H41 1V6 (kti.vvv.toni-pac corn).

The seal assembly may further comprise a gas source. The gas source may store compressed air, compressed inert gas, or any other convenient gas.

The gland seal stop may comprise a ring defining radial slots through which gas and liquid may pass between the gas cavity and the wet end of the pump, where the slots form the discharge channel. This has the advantage of allowing water and air to pass through the gland seal stop to enable a gas to liquid interface to be created either inside the gas cavity or immediately outside the gland seal stop, but prevents passage of any large particulates.

The slots may take any shape, such as straight or curved sidewalls.

The discharge channel may be formed by a fluid permeable membrane instead of, or in addition to, one or more slots.

The seal assembly may further comprise an expeller located in the wet end of the pump and mounted on the shaft.

The expeller preferably extends radially (from the shaft) at least 20% of the radius of the impeller (measured from the centre of the shaft). This is to ensure that the expeller is able to create a centrifugal field that accelerates (or moves) slurry away from the shaft to create a liquid to air interface around the shaft during operation.

The gas cavity may comprise an air cavity, or a cavity of an inert gas.

The gas source may include a regulator (comprising a simple control system) to maintain a constant (or a minimum) pressure in the gas cavity. The regulator may be in communication with a pressure sensor located in or near the gas cavity. The regulator may comprise one or more valves.

The gas source may be part of a pressurising system The pressurising system may comprise the gas source, a regulator (comprising a simple control system) to maintain a generally constant (or a minimum) pressure in the gas cavity, at least one sensor for monitoring or sensing the pressure in the gas cavity during operation of the seal assembly and for activating the gas source to inject gas into the gas cavity upon detecting a decrease in pressure below a defined threshold.

Although the expeller should create a liquid to air interface around the shaft during operation; where high density slurries are being pumped, or where the shaft speed is relatively low, the expeller may not be able to create a sufficient air to liquid interface, so the addition of gas from the gas source improves performance.

The gland seal stop allows the injected gas to reach the expeller and help create a sufficient air to liquid interface to reduce slurry ingress into the mechanical compound shaft sealant.

It will now be appreciated by those of skill in the art that the above aspect provides a "waterless" gland seal that is an alternative to a gland water seal and a mechanical seal.

Instead of flushing a gland water seal with fresh water to keep it clear of slurry, the above aspect introduces a bubble of gas (such as air) between the slurry and the mechanical compound shaft sealant. The pressure in the gas cavity is maintained by the gas source (and a simple control system) and balanced so that the air bubble resides in the gas cavity or just outside the gland seal stop to provide a dynamic seal between the slurry and the waterless gland seal. A compound injector is provided to top-up the compound as the compound wears away over time.

According to a second aspect there is provided a centrifugal pump assembly comprising: a pump housing defining a pump cavity, a drive shaft rotatably mounted to the housing, an impeller disposed in the housing at a wet end of the pump and coupled to the drive shaft for rotation therewith, and a seal assembly according to the first aspect or any additional features thereof as described above.

According to a third aspect there is provided a method of reducing water leakage from a gland seal, the method comprising: (a) injecting a mechanical compound around a shaft to create an interface between a dry end and a wet end of a centrifugal pump; (b) providing a discharge channel between the mechanical compound and the wet end of the centrifugal pump; (c) providing a gas cavity in fluid communication with the discharge channel; and (d) injecting gas into the gas cavity to create a gaseous buffer between the mechanical compound and the wet end to reduce water leakage at the dry end.

The method may include the further step of creating a centrifugal field on the wet end side of the discharge channel that accelerates (or moves) liquid (or slurry) away from the shaft to create a liquid to air interface around the shaft during operation.

The centrifugal field may be implemented using a vortex generator, such as an expeller mounted on the shaft.

The mechanical compound may comprise TOM-PAC (trade mark) material, or any other convenient material.

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a simplified elevational, schematic cross-sectional view (without any shading, for clarity) of a centrifugal pump having a seal assembly in accordance with one embodiment of the present invention; Fig. 2 is a simplified schematic cross-sectional view of part of the centrifugal pump of Fig. 1, showing the seal assembly in more detail; and Fig. 3 is a pictorial diagram of part (the recessed lantern ring) of the seal assembly of Fig. 1.

Reference is now made to Fig. 1, which is an elevational schematic view (without any shading, for clarity) of a centrifugal pump 10 incorporating a seal assembly 12 according to one embodiment of the present invention.

The centrifugal pump 10 comprises a base 14 supporting a bearing assembly 16 and a pump housing 18 (comprising an outer half casing 20 and an inner half casing 22 clamped together by bolts 24). The pump housing 18 defines a pump cavity (generally indicated by numeral 26).

The bearing assembly 16 supports a drive shaft 30, on which is mounted an impeller 32 for rotation within the pump cavity 26. The pump cavity 26 is referred to as the wet end of the pump 10. The bearing assembly 16 is at the dry end (generally indicated by numeral 34) of the pump 10. The drive shaft 30 defines a longitudinal axis 36.

A frame plate liner 38 is mounted on an inner side of the inner half casing 22, rearwardly of the impeller 32. An expeller 40 is also mounted on the drive shaft 30 and is located rearwardly of the impeller 32 and the frame plate liner 38. An expeller ring 42 is mounted on an outer side of the inner half casing 22, rearwardly of the impeller 32.

Reference is now made to Fig. 2, which is a simplified, schematic, partial cross-sectional view of part of the centrifugal pump 10 showing the seal assembly 12 in more detail.

The space between the expeller ring 42 and the rear of the expeller 40 is referred to as the expeller ring cavity 43, which in this embodiment is vertically oriented. The expeller ring 42 defines a longitudinal elongate cavity 44 in which is located mechanical compound shaft sealant 45. In this embodiment, the sealant 45 is in the form of TOM-PAC (trade mark) sealing compound.

An axial end of the cavity 44 nearest the bearing assembly 16 is defined by an expeller ring end cover 46 on which is mounted a gasket 47 (the cover 46 and gasket 47 provide a sidewall), and the opposite axial end of the cavity 44 nearest the impeller 32 is defined by a gasket 48 abutting a pair of opposing wedge rings 50. The wedge rings 50 can deform to a small extent in response to a force applied thereto. The wedge rings 50 are held in place by a recessed lantern ring 51 (also referred to as a gland seal stop), which abuts against a wall of the expeller ring 42. The wedge rings 50 prevent ingress of large particles of slurry to the cavity 44.

The cavity 44 is radially defined by an inner sleeve 52, mounted on the drive shaft 30 and rotatable therewith; and is closed by an outer sleeve (also referred to as an expeller ring sleeve) 54 defining a compound inlet bore 56 therethough. A compound injector 58 is screwed into the inner bore 56, thereby allowing the TOM-PAC sealant 45 to be injected into the cavity 44 via the injector 58. The TOM-PAC sealant 45 is a flexible, self-lubricating compound similar in some respects to putty.

Injection of the TOM-PAC sealant 45 into the cavity 44 may be implemented manually, e.g. by a service engineer using an applicator to inject more TOM-PAC sealant 45 on a periodic basis (e.g. weekly or monthly, depending on the operational performance of the pump 10), or on an as needed basis, from a sealant source 60. Alternatively, injection of the TOM-PAC sealant 45 into the cavity 44 may be implemented automatically, e.g. by a solenoid actuated applicator injecting more TOM-PAC sealant 45 on a periodic basis (e.g. weekly or monthly) or in response to a sensor reading (e.g. a pressure sensor).

The opposing wedge rings 50 can deform to a small extent to accommodate any excess sealant 45 injected into the cavity 44.

The expeller ring 42 further defines a gas inlet bore 62 (also referred to as a gas inlet channel) opening in the vicinity of the recessed lantern ring 51. The gas inlet bore 62 has a longitudinal axis 64 shown in broken line. A source of compressed air (e.g. a compressor) 66 expels air through a flow meter 68 into the gas inlet bore 62. A pressure sensor 70 is provided to monitor the pressure of the compressed air.

The recessed lantern ring 51 performs two functions. The first function is to act as a gland seal stop to prevent the sealant 45 from moving the opposing wedge rings 50 along the inner sleeve 52. The second function is to provide a gas permeable interface between the gas inlet bore 62 and the expeller ring cavity 43 so that air from the compressor 66 can prevent, or significantly reduce, slurry from the expeller ring cavity 43 passing through the recessed lantern ring 51.

Reference is now made to Fig. 3, which illustrates the recessed lantern ring 51 in more detail. The lantern ring 51 (also referred to as a gland seal stop) includes a circular ring portion 80 having a rear face 82 adjacent the wedge rings 50 and a front face 84 adjacent a wall of the expeller ring 42. The lantern ring 51 defines a plurality (eight in this embodiment) of protrusions 86 radially spaced around the circular ring portion 80 and extending from the front face 84 away from the rear face 82. The lantern ring 51 defines a sleeve engaging surface 88 and an outer surface 90. When the lantern ring 51 is mounted on the sleeve 52, the sleeve engaging surface 88 is radially spaced therefrom by a small distance to prevent friction between the static lantern ring 51 and the rotating sleeve 52.

Each protrusion 86 extends from the sleeve engaging surface 88 part-way towards the outer surface 90. The area between the edge of the protrusion 86 and the outer surface 90 defines a recessed area 92.

In this embodiment, the protrusions 86 all extend the same distance, which is approximately 50% of the distance from the sleeve engaging surface 88 to the outer surface 90. In other embodiments, the protrusions may extend 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or more of the distance from the sleeve engaging surface 88 to the outer surface 90. In other embodiments, some or each of the protrusions 86 may have different heights.

Adjacent protrusions 86 define a discharge gap 94 through which compressed air can flow as it exits the gas inlet bore 62. In this embodiment, the discharge gap 94 (that is, the distance between adjacent protrusions 86) is approximately 6mm. The recessed areas 92 and the discharge gaps 94 provide a gas leakage (or discharge) channel.

The operation of the seal assembly 12 will now be described. During operation of the pump 10, slurry is circulated by the impeller 32. Although not desired, some slurry typically enters between the back of the impeller 32 and the frame plate liner 38. This slurry may approach the sealant 45 (by flowing between the expeller ring 42 and the sleeve 52), and potentially reach and damage the bearing assembly 16.

To prevent this happening, the cavity 44, sealant 45, the end cover gasket 47, the wedge ring gasket 48, and the wedge rings 50 form a gland seal 49 to protect the bearing assembly 16 from ingress of slurry.

The expeller 40 extends radially (from the drive shaft 30) approximately 70% of the radius of the impeller 32 (measured from the drive shaft 30). When the expeller 40 rotates, it creates an area of low pressure in the expeller ring cavity 43. This ensures that the expeller 40 is able to create a centrifugal field that accelerates (or moves) slurry away from the drive shaft 30, such that the area around the drive shaft 30 only contains gas.

However, even with the expeller 40 operating, some slurry will inevitably make its way through the gap between the expeller ring 42 and the sleeve 52.

To prevent this slurry from reaching the sealant 45, the compressed air source 66 charges the gas inlet bore 64 with gas On this embodiment, compressed air) until the pressure sensor 70 reaches a preset value On this embodiment 1 Bar).

The flow rate meter 68 may be used as a diagnostic or monitoring tool to check that the mechanical compound seal is working effectively.

When the gas inlet bore 64 is pressurised, the gas leaks through the recessed lantern ring 51 discharge channel (the recessed areas 92 and the discharge gaps 94) towards the expeller ring cavity 43. This creates a gas to liquid boundary in the expeller ring cavity 43, which prevents, or greatly hinders, the liquid (or slurry) from reaching the sealant 45.

The TOM-PAC sealant 45 is selected so that it does not dry out in the presence of the gas in the gas cavity 96, so the gland seal 49 performance is not compromised, unlike

in prior art systems.

Furthermore, the TOM-PAC sealant 45 does not require water, so the seal assembly provides a waterless gland seal solution.

It is believed that this seal assembly has particular advantages when used in thickener applications because of the relatively low shaft speeds, and low heads, used.

The TOM-PAC sealant 45 operates most effectively when the linear tangential velocity of the shaft inner sleeve 52 is less than twelve metres per second, which is typical in thickener applications.

In the foregoing description of certain embodiments, specific terminology has been used for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "upper" and "lower, "above" and "below" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms, nor to imply a required orientation of the seal assembly.

In other embodiments, the compressed air source 66 may be manually operated to charge the gas inlet bore 64 with gas until a desired pressure is reached.

In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

The preceding description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combined with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments.

In addition, the foregoing describes only some embodiments of the inventions, and alterations, modifications, additions and/or changes can be made thereto without departing from the scope of the disclosed embodiments, the embodiments being illustrative and not restrictive.

List of reference numerals: Centrifugal pump 10 Seal assembly 12 Base 14 Bearing assembly 16 Pump housing 18 Outer half casing 20 Inner half casing 22 Bolts 24 Pump cavity 26 Drive shaft 30 Impeller 32 Dry end 34 Longitudinal axis 36 Frame plate liner 38 Expeller 40 Expeller ring 42 Expeller ring cavity 43 Elongate cavity 44 Mechanical compound shaft sealant 45 Expeller ring end cover 46 End cover gasket 47 Wedge ring gasket! 48 Gland seal 49 Wedge rings 50 Lantern ring 51 Inner sleeve 52 Outer sleeve 54 Compound inlet bore 56 Compound injector 58 Sealant source 60 Gas inlet bore (gas inlet channel) 62 Longitudinal axis (gas inlet bore) 64 Compressed air source 66 Flow meter 68 Pressure sensor 70 Circular ring portion 80 Rear face 82 Front face 84 Protrusions 86 Sleeve engaging surface 88 Outer surface 90 Recessed area 92 Discharge gaps 94 Gas cavity 96

Claims

CLAIMS1. A seal assembly comprising: a mechanical compound shaft sealant for creating an interface between a dry end and a wet end of a centrifugal pump; a gland seal stop for mounting on a shaft near the wet end of the centrifugal pump, and defining a discharge channel; a gas inlet channel in fluid communication with the discharge channel in the gland seal stop, and defining a gas cavity into which gas can be fed, whereby, in use, gas is introduced to the gas cavity and flows through the discharge channel to create a gas to liquid interface at the wet end of the pump to reduce liquid input to the mechanical compound shaft sealant from the wet end of the pump.
2. A seal assembly according to claim 1, wherein the mechanical compound shaft sealant comprises a flexible, self-lubricating compound.
3. A seal assembly according to claim 1 or 2, wherein the seal assembly further comprises a gas source in communication with the gas inlet channel.
4. A seal assembly according to any preceding claim, wherein the gland seal stop comprises a ring defining radial slots between adjacent protrusions, whereby the radial slots form the discharge channel through which gas and liquid may pass between the gas cavity and the wet end of the pump.
5. A seal assembly according to claim 4, wherein the slots are dimensioned such that a slot is at least 25% of the width of a protrusion.
6. A seal assembly according to claim 4 or 5, wherein the protrusions extend to at least 30% of the distance from an inner surface of the ring to an outer surface of the ring, thereby defining a recessed area between an edge of the protrusion nearest the outer surface of the ring, and the outer surface of the ring.
7. A seal assembly according to any preceding claim, wherein the seal assembly further comprises an expeller located in the wet end of the pump and mounted on the shaft.
8. A seal assembly according to claim 7, wherein the expeller extends radially, from the shaft, at least 20% of the radius of the impeller, measured from the shaft to ensure that the expeller is able to create a centrifugal field that moves particles away from the shaft, such that the area around the shaft only contains water or water carrying fine particles.
9. A seal assembly according to any preceding claim, wherein the gas cavity comprises an air cavity.
10. A seal assembly according to any preceding claim, wherein the gas source comprises a source of compressed air, and includes a regulator to maintain a generally constant pressure in the gas cavity.
11. A seal assembly according to claim 10, wherein the regulator comprises a valve, and the regulator is in communication with a pressure sensor located in or near the gas cavity, and a flow rate meter.
12. A centrifugal pump assembly comprising: a pump housing defining a pump cavity; a drive shaft rotatably mounted to the housing; an impeller disposed in the housing at a wet end of the pump and coupled to the drive shaft for rotation therewith; and a seal assembly according to any preceding claim.
13. A centrifugal pump assembly according to claim 12, further comprising a gas source
14. A method of reducing water leakage from a gland seal, the method comprising: (a) injecting a mechanical compound around a shaft to create an interface between a dry end and a wet end of a centrifugal pump; (b) providing a discharge channel between the mechanical compound and the wet end of the centrifugal pump; (c) providing a gas cavity in fluid communication with the discharge channel; and (d) injecting gas into the gas cavity to create a gaseous buffer between the mechanical compound and the wet end to reduce water leakage at the dry end.
15. A method of reducing water leakage according to claim 14, wherein the method includes the further step of creating a centrifugal field on the wet end side of the discharge channel that moves particles away from the shaft, such that the area around the shaft only contains water or water carrying fine particles.