AU5735199A

AU5735199A - Improved slurry pump

Info

Publication number: AU5735199A
Application number: AU57351/99A
Authority: AU
Inventors: Graham Ison; Frank Muller; Tony Murray; John Robinson; David Smirk; David Sutherland
Original assignee: Alusuisse Lonza Services Ltd; Alusuisse Technology and Management Ltd
Current assignee: 3A Composites International AG
Priority date: 1998-07-22
Filing date: 1999-07-10
Publication date: 2000-02-14
Anticipated expiration: 2019-07-10
Also published as: AU747171B2

Description

WO 00/05505 PCT/EP99/05984 1 IMPROVED SLURRY PUMP Technical Field The present invention relates to centrifugal pumps and more particularly to centrifugal pumps for processing and pumping fluids containing solid and 5 semi-solid scale and aggregates. Background Art In a variety of industrial applications pumps are required to transfer fluids that contain a collection of solid and semi-solid material. Such fluids are 10 commonly known as slurries and a number of different arrangements have been proposed to avoid choking or clogging of the impeller in centrifugal pumps employed to handle slurries. Some such arrangements include an aggregate screen or scale trap on the pump suction line to catch and retain scale and aggregate which would otherwise block the impeller assembly reducing flows 15 and incurring extensive maintenance. The trouble with this arrangement however is that these scale traps must be cleaned on a regular basis. As well as being labour intensive and time consuming, such cleaning can also expose workers to hazardous conditions including corrosive fluids and heavy lifting. For example, in the alumina refining process bauxite is first dissolved in 20 a hot caustic soda solution. The resulting bauxite/caustic slurry is then graded on a size fraction with the fine fraction directed to a settling or thickening stage to remove the undissolved impurities in the slurry from the alumina rich liquor. At this thickening stage the settled mud slurry is extracted with the aid of a rake assembly, polymer addition and diluting streams via dual underflow pumps with 25 associated scale traps. The scale traps are designed to protect the underflow pumps from oversized aggregates that can block and/or damage the pump impeller assembly. These scale traps must be cleaned on a regular basis to ensure maximum life is achieved from the thickener tanks. To clean a scale trap the underflow pump must be brought off-line. Then, after isolation, the trap 30 can be cleaned. As most scale traps are elevated at a height of approximately 1 metre, this involves manually pulling the scale basket from the trap at that height and supporting the weight of the basket (typically 15 to 20 kilogram) as it WO 00/05505 PCT/IEP99/05984 2 swings to the ground. After the basket has been up-ended to remove all the scale the clean basket is then inserted back into the trap and the underflow pump is re-commissioned. This manual cleaning of the scale traps exposes the operators to both a caustic hazard and to the risk of back injury. 5 Another pump configuration for handling solids-laden slurries include recessed or open impellers which attempt to pass whole solids. Clearly, however, such so-called "non-clog" pumps are limited in the size of the entrained solids with which they can cope by the dimensions of the impeller. Some of these pumps include cutter attachments added to standard non-clog 10 impellers. These, however, tend to increase shaft overhang and bearing loads and result in a reduction of seal life. There is clearly therefore a need for an improved arrangement for pumping slurries. 15 Summary of the Invention According to one aspect of the present invention there is provided a device for attachment to a centrifugal pump for processing and pumping a slurry containing solid and semi-solid scale and aggregate, the device being adapted to minimise choking and/or clogging of the pump impeller and 20 including grading means and attrition means, both of which are to be located at a pump suction line upstream of the impeller. The grading means is adapted to prevent scale and aggregate which are greater than a predetermined size from passing to the impeller and the attrition means is adapted for reducing any oversized material prevented by the grading means from passing to the impeller 25 to a size less than or equal to the predetermined size. That is, the attrition means is able to reduce any oversized scale and aggregate to a size that the impeller is capable of pumping. According to another aspect of this invention there is provided a centrifugal pump for processing and pumping a slurry containing solid and 30 semi-solid scale and aggregate, the pump including a device located at the pump suction line upstream of the pump impeller for minimising choking and/or clogging of the impeller. The device includes grading means adapted to WO 00/05505 PCT/EP99/05984 3 prevent scale and aggregate of greater than a predetermined size from passing to the impeller and attrition means adapted for reducing any oversized scale and aggregate material prevented by the grading means from passing to the impeller to a size that the impeller is capable of pumping. 5 In one form of the invention the attrition means includes a pair of members between which the oversized solid and semi-solid scale and aggregate can be abraded and disintegrated to a pumpable size. In one form of the invention the attrition means includes a rotatable member which is preferably adapted to be mounted on a shaft for rotation with 10 the pump impeller. In use the rotatable member grinds or abrades any oversized scale and aggregate in the slurry against a second, preferably stationary member of the attrition means. In one form of the invention the grading means includes a partition or panel in the pump suction line upstream of the impeller having a plurality of 15 apertures therethrough providing fluid communication with the impeller, the apertures defining the predetermined size of scale and aggregate in the slurry which is admissible to the impeller. The panel or partition is preferably in the form of a perforated plate-like member or grate. In a particularly preferred form of the invention the plate-like member of 20 the grading means cooperates with the rotatable member of the attrition means in such a way that the grading means plate also actually forms part of the attrition means. The rotatable member of the attrition means is preferably arranged adjacent to and upstream of the plate member such that the rotatable member is able to abrade any oversized scale and aggregate against the 25 perforated plate, disintegrating the oversized solid and semi-solid material until it is reduced to a size capable of passing through the apertures in the plate member. Thus, the present invention provides a device which is able to be retro fitted to existing pumps which previously relied upon scale traps and aggregate 30 screens to prevent choking of the impeller. The present invention also provides an entire pump assembly which incorporates this device. The present invention removes the need for a scale basket or aggregate screen since the solid and WO 00/05505 PCT/EP99/05984 4 semi-solid scale and aggregate material can be reduced to a size that can be pumped using the existing tolerances within the pump impeller and casing. With no scale trap there is no need for cleaning, reducing pump down-time, labour and the risks to workers associated with cleaning the scale traps. 5 Brief Description of the Drawings The above and further features and advantages of the present invention will be more fully appreciated from the following detailed description of a preferred embodiment of the invention with reference to the accompanying 10 drawings, in which like reference numerals designate like features, and in which: Fig. 1 is a perspective view of a device according to a preferred embodiment of the present invention; and Fig. 2 is a partially sectioned schematic top view of a pump according to 15 a preferred embodiment the invention incorporating the device of Fig. 1. Detailed Description of Preferred Embodiment of the Invention Referring to Fig. 1 and Fig. 2 of the drawings, a preferred form of device 10 according to the present invention can be incorporated in a centrifugal pump 20 20 for processing and pumping a slurry containing solid and semi-solid scale and aggregate. The device 10 is located in the pump suction line 21 upstream of the pump impeller 22 at an inlet 23 to the impeller housing 24. The device 10 includes a grading means 11 and an attrition means 12 and is adapted to minimise choking and/or clogging of the pump impeller 22. The grading means 25 11 is a means for grading the solid and semi-solid scale and aggregate in the slurry being delivered to the pump to prevent scale and aggregate which are greater than a predetermined size from passing to the impeller 22. The grading means 11 includes a partition or panel in the form of a plate member 13 across the suction line at the inlet 23 to the impeller housing. The plate member 13 30 includes a plurality of substantially uniformly sized apertures 14 therethrough providing fluid communication with the pump impeller 22. The size of the apertures 14 define the predetermined maximum size of the scale and WO 00/05505 PCT/EP99/05984 5 aggregate in the slurry which is admissible to the impeller. The perforated plate member or grate 13 is typically formed from a robust and durable material such as stainless steel. The attrition means 12 is a means for reducing the size of any oversized 5 scale and aggregate material prevented by the grading means 11 from passing to the impeller. The oversized scale and aggregate is ground down or abraded by the attrition means to a size less than or equal to the predetermined size such that it can pass through to and be handled by the pump impeller 22. The attrition means 12 includes a rotatable member 15 which is adapted to be 10 mounted on the impeller shaft 25 for rotation with the pump impeller. The rotatable member includes a pair of blade portions 16 which extend radially in opposite directions from a central hub 17. The blade portions 16 extend across substantially the full diameter of the suction line 21 or impeller housing inlet 23. It is the central hub 17 of the rotatable member which is connected for rotation 15 with the impeller shaft 25. The rotatable member 15 of the attrition means is arranged adjacent to and upstream of the plate member 13 and cooperates in use with the plate member in such a way that the attrition and abrasion which disintegrate the oversized scale and aggregate is largely due to the shear forces created by the member 15 rotating relative to the stationary plate 20 member 13. The edges 18 of the apertures 14 formed in the partition plate also enhance attrition of the oversized material. Thus, the grading means plate member 13 may also actually function as part of the attrition means 12. The rotatable member or tool 15 is also desirably robust and durable and may be formed from a material such as stainless steel. 25 The mounting plate 26 surrounding the device 10 in Fig. 1 is for connection of the suction line feed pipe 21. In operation, slurry is directed along the suction line to the pump 20 where it meets the rotating blade portions 16 of the rotary tool 15. Scale, aggregate and plasticised mud which are too large to pass through the apertures 14 in the plate member 13 are ground down 30 and disintegrated by the action of the rotating tool 15 until they are reduced to a size which is able to pass through the apertures in the plate member. The WO 00/05505 PCT/EP99/05984 6 ground down slurry can then pass into the impeller housing 24 and be pumped as normal. The device 10 illustrated in Fig. 1 has been fitted to a GlW (Georgia Iron Works) KL 3x3/4 LSA 21 underflow pump and the maximum additional load 5 afforded by the device when used in the alumina refining process described previously has been found to be less than 1kW, maintaining efficiency yet still achieving the required flow and head conditions. Finally, it is to be appreciated that various modifications and/or additions may be made to the construction and arrangement of the parts previously 10 described without departing from the spirit or ambit of the present invention as disclosed herein.

Claims

1. A device for attachment to a centrifugal pump for processing and pumping a slurry containing solid and semi-solid scale and aggregate, the 5 device being adapted to minimise choking and/or clogging of the pump impeller and including: grading means adapted to prevent scale and aggregate which are greater than a predetermined size from passing to the impeller; and attrition means which is adapted to reduce any oversized material 10 prevented by the grading means from passing to the impeller to a size less than or equal to the predetermined size.

2. A device as claimed in claim 1 wherein the attrition means includes a pair of members between which the oversized solid and semi-solid scale and 15 aggregate can be abraded and disintegrated to a pumpable size.

3. A device as claimed in claim 1 or claim 2 wherein the attrition means includes a rotatable member which is adapted to grind or abrade any oversized scale and aggregate in the slurry. 20

4. A device as claimed in claim 3 wherein the attrition means further includes a stationary member against which the rotatable member is adapted to grind or abrade the oversized scale and aggregate to reduce it to a pumpable size. 25

5. A device as claimed in any one of the preceding claims wherein the grading means includes a partition in the pump suction line upstream of the impeller, the partition having a plurality of apertures therethrough providing fluid communication with the impeller, the apertures defining the predetermined size 30 of scale and aggregate in the slurry admissible to the impeller. WO 00/05505 PCT/EP99/05984 8

6. A device as claimed in claim 5 wherein the partition comprises a plate like member arranged transverse to a direction of flow for the slurry in the suction line of the pump. 5

7. A device as claimed in claim 6 wherein the plate like member of the grading means also forms part of the attrition means.

8. A device as claimed in claim 7 wherein the rotatable member of the attrition means is arranged adjacent to and upstream of the grading means 10 plate member such that the rotatable member is able to abrade any oversized scale and aggregate against the plate member thereby disintegrating the oversized solid and semi-solid material until it is reduced to a size capable of passing through the apertures in the plate member. 15

9. A device as claimed in claim 8 wherein the rotatable member includes a pair of blade portions which extend radially outwards in opposite directions from a central hub.

10. A device as claimed in claim 9 wherein the blade portions are configured 20 to rotate through an area which covers substantially all of the plate member apertures providing fluid communication with the pump impeller.

11. A device as claimed in claim 10 wherein the hub of the rotatable member is adapted to be mounted on the impeller shaft for rotation with the impeller. 25

12. A centrifugal pump for processing and pumping a slurry containing solid and semi-solid scale and aggregate, the pump including the device located at a pump suction line upstream of the pump impeller to minimise choking and/or clogging of the impeller, the device including: 30 grading means adapted to prevent scale and aggregate which have a greater than predetermined size from passing to the impeller; and WO 00/05505 PCT/EP99/05984 9 attrition means adapted to reduce any oversized material prevented by the grading means from passing to the impeller to a size less than or equal to the predetermined size. 5

13. A pump as claimed in claim 12 wherein the attrition means includes a pair of members between which the oversized solid and semi-solid scale and aggregate can be abraded and disintegrated to a pumpable size.

14. A pump as claimed in claim 12 or claim 13 wherein the attrition means 10 includes a rotatable member which is adapted to grind or abrade any oversized scale and aggregate in the slurry.

15. A pump as claimed in claim 14 wherein the attrition means further includes a stationary member against which the rotatable member is adapted to 15 grind or abrade the oversized scale and aggregate to reduce it to a pumpable size.

16. A pump as claimed in any one of claims 12 to 15 wherein the grading means includes a partition in the pump suction line upstream of the impeller, 20 the partition having a plurality of apertures therethrough providing fluid communication with the impeller, the apertures defining the predetermined size of scale and aggregate in the slurry admissible to the impeller.

17. A pump as claimed in claim 16 wherein the partition comprises a plate 25 like member arranged transverse to a direction of flow for the slurry in the suction line of the pump.

18. A pump as claimed in claim 17 wherein the plate like member of the grading means also forms part of the attrition means. 30

19. A pump as claimed in claim 18 wherein the rotatable member of the attrition means is arranged adjacent to and upstream of the grading means WO 00/05505 PCT/EP99/05984 10 plate member such that the rotatable member is able to abrade any oversized scale and aggregate against the plate member thereby disintegrating the oversized solid and semi-solid material until it is reduced to a size capable of passing through the apertures in the plate member. 5

20. A pump as claimed in claim 19 wherein the rotatable member includes a pair of blade portions which extend radially outwards in opposite directions from a central hub. 10

21. A pump as claimed in claim 20 wherein the blade portions are configured to rotate through an area which covers substantially all of the plate member apertures providing fluid communication with the pump impeller.

22. A pump as claimed in claim 21 wherein the hub of the rotatable member 15 is adapted to be mounted on the impeller shaft for rotation with the impeller.