WO2008139023A1

WO2008139023A1 - Pump and a method for disassembling the pump

Info

Publication number: WO2008139023A1
Application number: PCT/FI2008/050119
Authority: WO
Inventors: Eero Ekman; Juhani Lyyra; Pertti Pekkala; Bror Nyman; Stig-Erik Hultholm
Original assignee: Outotec Oyj
Priority date: 2007-05-16
Filing date: 2008-03-17
Publication date: 2008-11-20
Also published as: FI20070383A0; PE20090259A1; FI20070383A; FI121091B; CL2008001394A1

Abstract

A pump comprising a body (1) that is a cylindrical vertical container (10), which is upwards open, its interior (2) being defined by a planar bottom (11) that comprises a central inlet (3), and by a first side wall (12) that comprises an outlet (4) in the lower part thereof in the vicinity of the bottom (11). An impeller (5) is arranged to rotate around a verti- cal axis in the vicinity of the inlet (3) and centrally with respect to the container (10). A flush cover (13) is adapted in the interior (2). The flush cover includes a cylindrical second side wall (14). Between the first side wall and the second side wall, an upwards open annular first space (15) is formed. A bottom cone (16) has a frusto-conical shape and it extends to the vicinity of the impeller (5). A through pipe (17) extends from the bottom cone (16) upwards, a drive shaft (8) being placed inside the pipe, and a second space (18) being defined around the drive shaft. A vertical scroll wall (19) surrounds the impeller (5) and forms, with the bottom cone (16), a scroll cover (7) that surrounds the impeller (5) and expands towards the outlet (4).

Description

PUMP AND A METHOD FOR DISASSEMBLING THE PUMP

FIELD OF THE INVENTION

The invention relates to a pump that is de- fined in the preamble of Claim 1. The invention further relates to a method of disassembling the pump, which is defined in the preamble of Claim 13.

In particular, the invention relates to a pump, which can be used for pumping large volume flows of liquid, especially extraction solution, in hydro- metallurgical recovery processes of metals, which utilize liquid-liquid extraction.

BACKGROUND OF THE INVENTION In the hydrometallurgical recovery of metals, the following stages can be distinguished: leaching of concentrate or ore, liquid-liquid extraction, and precipitation or reduction of metal. In the leaching, the ore or the concentrate is typically leached with min- eral acid, whereby a valuable metal is obtained in an aqueous solution. In the extraction, the aqueous solution containing the valuable metal and numerous impurities originating in the leach are mixed with an organic solution containing an extraction agent in an extraction apparatus, or which typically is a mixer- settler cell or column. In that case, the metal to be refined reacts selectively with the extraction agent in an ion exchange reaction or by another chemical mechanism, dissolving in the organic phase as an or- ganometallic complex, whereby the metal can be separated from the aqueous solution in a pure form. The aqueous solution, from which the value metal was separated, can be returned to the leaching stage. The extraction solution, in turn, is conveyed to a stripping stage, where the precious metal that was bound to the same is returned to the aqueous solution by a reaction reverse to the extraction reaction, from which solution it can be processed to form a product by precipitating it into a metallic compound or electrolytically reducing it into metal. In the liquid-liquid extraction, thus, two liquids, which are insoluble in each other, are mixed in the mixer of the extraction apparatus so that one liquid is dispersed into drops in the other liquid, forming a dispersion, whereby an effective mass trans- fer between the liquids is enabled. The mixing takes place in the mixer-settler in the pumping section, which, at the same time, maintains the flow of solutions between the process stages. The liquids that were mixed are separated from each other in the set- tling section of the extraction apparatus by means of the drops combining and the gravity. Typically, the process of the extraction plant contains several series-connected extraction and stripping stages and, possibly, other additional stages, such as the washing and regeneration stages of the extraction solution.

In the extraction plant, while the extraction solution in the process continuously circulates through the various stages, its volume in the stages varies, among others, as a result of the variation in the velocity of decomposition in the settling section of the liquid-liquid dispersion. To equalize the variations in volume, a storage tank with a wide surface area is placed in the process, wherein the surface of the solution can rise and lower. Depending on the capacity of the process, the volume flow of the extraction solution can be in the order of 500 to 2500 m³/h.

It is previously known that the extraction solution is pumped from the storage tank back to the process stages usually by large-size centrifugal pumps. Such a known pump includes a body having a hollow interior, an inlet for allowing the liquid to en- ter the interior, and an outlet for removing the liquid from the interior. There is an impeller in the interior, including a number of impeller blades that convert the kinetic energy of the impeller into pres- sure energy of the liquid in the outlet. A scroll cover is adapted to surround the impeller. The impeller is attached to a drive shaft, which is fitted with a bearing to rotate in the body. The drive shaft is rotated by a driving motor. Several pumps are used, connected in parallel, to provide the volume flow of a required size. Typically, the number of pumps that are used is two, while there are two additional pumps on standby for maintenance. The price of these pumps and the auxil- iary devices needed constitutes a significant portion of the total investment costs of a production plant.

As mixing and pumping affect the physical and chemical properties of the solution, the organic extraction solution should be treated as gently as pos- sible in the liquid-liquid processes. When the solution is pumped or mixed using high peripheral velocities of the impeller, as is the case with conventional centrifugal pumps, for example, shearing forces are exerted on the liquid, resulting in a decrease, by degradation, in the size of the residue drops of the aqueous phase, which are present in the extraction solution and originate in the liquid-liquid contact, whereby their natural separation, which is based on the gravity and the mutual combining of the drops, is decelerated or completely prevented. Thus, the drops of water and the soluble impurities therein can drift along with the extraction solution through the settling basins and forward in the process, all the way to the product of the process, decreasing its quality and commercial value.

The liquid that is pumped can further contain small solid matter particles or colloids. In metal re- fining processes, solid matter residue originating in ground ore or concentrate often exists in solutions. In that case, the shearing forces of the centrifugal pump may cause a formation of extraction deposits, which are called cruds . A crud is a stable structure formed by the organic extraction solution, the aqueous solution, and solid matter, accumulating in the settling basins of the extraction cells on the boundary layers of the aqueous and organic phases. When the amount of crud exceeds a certain boundary, it must be removed from the equipment. The expensive reagent contained in the extraction solution is bound to the crud, causing an increase in the operating costs of the plant.

PURPOSE OF THE INVENTION

The purpose of the invention is to eliminate the disadvantages mentioned above. In particular, the purpose of the invention is to disclose a novel pump, which treats the liquid to be pumped so gently that the pumping has no effect on the physical and chemical properties of the liquid.

Another purpose is to disclose a pump that is especially suitable to be used in the liquid-liquid extraction process of the hydrometallurgical recovery of metals for pumping an organic extraction solution between the extraction solution storage tank and the extraction process to replace the several separate centrifugal pumps, which are conventionally used, with one pump according to the invention.

A further purpose of the invention is to disclose a pump that has no harmful effects on the physical and chemical properties of the extraction solution that is pumped. SUMN[ARY OF THE INVENTION

The pump according to the invention is characterized in that which is disclosed in Claim 1. The method according to the invention for disassembling the pump is characterized in that which is disclosed in Claim 13.

According to the invention, the body is a cylindrical, vertical container, which is upwards open, its interior being limited downwards by an essentially horizontal, planar bottom that comprises a round central inlet, and the interior being limited laterally by a first vertical side wall, its lower part in the vicinity of the bottom comprising an outlet. An impel- ler is arranged around the vertical axis to rotate in a horizontal position in the close proximity of the inlet and centrally with respect to the container. The pump includes a flush cover, which is centrally adapted to the interior of the container, the flush cover including a second cylindrical, vertical side wall, its outer diameter being smaller than the inner diameter of the first side wall so that an upwards open, annular first space is formed between the first side wall and the second side wall. The pump further includes a bottom cone, which is frusto-conical in shape and extends converging downwards to the vicinity of the impeller; and a vertical through pipe that extends vertically upwards from the bottom cone, the drive shaft being arranged inside the pipe, an upward open, second space being limited inside the through pipe and around the drive shaft. The pump further includes a vertical scroll wall, which surrounds the impeller, forming jointly with the bottom cone a scroll cover that partly surrounds the impeller and expands towards the outlet. The scroll wall extends with its bending radius increasing from the first proximal end of the outer periphery of the impeller to the second proximal end of the first side wall of the container, the first end comprising a guide plate for guiding the liquid flow to the outlet. The flush cover closes the free fluid level of the liquid in the container so that, when the impeller rotates, a column is formed in the said first and second spaces to convert part of the pressure energy of the liquid into potential energy in the column to form hydrostatic pressure in the outlet . In one application of the pump, the impeller includes a round horizontal upper plate, which is attached to the drive shaft, and to which upper plate curved impeller blades have been attached at the upper edges thereof; an annular lower plate that has a round inlet hole in the middle thereof, the hole being located centrally with respect to the inlet to receive liquid into the impeller through the inlet hole, the impeller blades being attached to the lower plate at the lower edges thereof to circumferentially surround the inlet hole of the lower plate and to form blade passages, through which the liquid exits into the scroll cover from inside the impeller.

In one application of the pump, the scroll cover is attached to the flush cover, preferably to the bottom cone.

In one application of the pump, the pump is a pump that is used in the liquid-liquid extraction process of the hydrometallurgical recovery of metals.

In one application of the pump, the pump is a pump that is connected to the equalizing tank of the extraction solution.

In one application of the pump, the pump is a pump that is situated between the equalizing tank of the extraction solution and the mixer-settler cell. In one application of the pump, the output of the pump is within a range of 10 to 10000 m³/h. In one application of the pump, the pressure produced by the pump is in the order of 500 to 1200 mm H₂O.

In one application of the pump, the pump is adapted to pump solutions, the densities of which are typically from 0.7 to 1.2 kg/dm³ and the dynamic viscosities from 1 to 8mPas .

In one application of the pump, the pump is constructed from a material that resists strongly cor- rosive aqueous solutions and chemically aggressive organic solutions.

In one application of the pump, the container, the flush cover, the impeller and/or the scroll wall are formed from acid-resistant steel. In one application of the pump, the container, the flush cover, the impeller and/or the scroll wall are formed from fibre-reinforced plastic.

In the method of disassembling the pump, the flush cover, the scroll wall, the impeller, the drive shaft and the driving motor are formed into a sub- assembly, which can be handled as one unity. To disassemble the pump, the said sub-assembly is detached and lifted out of the interior of the container as one unity, without having to detach the container from the pipework, to which the container has been connected, and without having to remove the liquid from the container .

In the method, kinetic energy is converted into pressure energy of the liquid by means of the rotatable impeller of the pump that works on the principle of centrifugal force. Part of the pressure energy provided by the impeller is converted directly into pressure energy on the delivery side and part of it is converted into potential energy by means of the column formed by the impeller rotating, to provide hydrostatic pressure on the delivery side. In one application of the method, the surface of the liquid that is to be pumped in the container on the suction side is arranged at such a height that the liquid covers the entire impeller. In one application of the method, the liquid pressure on the suction side is arranged so as to be positive during the operation of the pump.

In one application of the method, the rotation speed of the impeller is adjusted to adjust the output of the pump, when the level of pumped liquid in the container on the suction side varies and/or when the counterpressure of the delivery side varies.

In one application of the method, the volume flow of the liquid to be pumped is measured and the ro- tation speed of the impeller is adjusted on the basis of the value measured.

In one application of the method, the rotation speed of the impeller is adjusted so that the circumferential speed of the impeller is in the order of 3.5 to 4.5 m/s.

In connection with the hydrometallurgical recovery of metals the pump according to the invention can be used to pump the organic extraction solution so that smaller shearing forces are exerted on the extraction solution than when pumping by the centrifugal pump.

One pumping unit according to the invention can be used to pump the entire volume flow of the extraction solution that is needed in the extraction process, and thus replace the parallel-connected pumps of the equalizing tank of the extraction solution and the associated auxiliary devices, which are conventionally used. The pump can also be located in some other place in the liquid-liquid extraction process, where there is a need for a large volume flow with a relatively low pressure output.

On the basis of the experiences gained from the pumping units of the mixer-settler of a similar type, the pump can be freely dimensioned and built for the desired volume flow, which on a wide range is within 10 and 10000 m³/h. Typically, the pressure produced by the pump is fairly low, 500 to 1200 mmH₂0, which, however, is sufficient for the hydrometallurgical liquid-liquid extraction process, which is designed so that the existing counterpressures are of the same order. The equipment is used for pumping solutions that exist in extraction plants, of their properties the density typically from 0.7 to 1.2 kg/dm³ and the dynamic viscosity from 1 to 8 mPas .

LIST OF FIGURES

In the following, the invention is described in detail by means of embodiment examples and with reference to the appended drawing, in which

Fig. 1 shows schematically a cross-sectional side view of an embodiment of the pump according to the invention, Fig. 2 shows the section H-II of Fig. 1,

Fig. 3 shows a side view of the flush cover included in the embodiment of Fig. 1, a scroll wall being attached thereto,

Fig. 4 shows the flush cover of Fig. 3 as viewed from the direction IV-IV of Fig. 3,

Fig. 5 shows the section V-V of Fig. 3, Fig. 6 shows a side view of the entity formed by the impeller of the embodiment in Fig. 1, and its drive shaft, Fig. 7 shows the impeller of Fig. 6 as viewed from the direction VII-VII of Fig. 6,

Fig. 8 shows the section VIII-VIII of Fig. 7, Fig. 9 shows the section IX-IX of Fig. 8, Fig. 10 shows the pump according to the em- bodiment of Fig. 1, when connected to a container containing liquid, while the pump functions, and Fig. 11 shows the subassembly A of the system according to Fig. 10, when detached and lifted out of the container.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a pump, which is designed for use in the liquid-liquid extraction process of the hy- drometallurgical recovery of metals, in particular, but which is also suitable for any other purposes, where the pump is required to handle liquid gently without exerting, on the liquid, large shearing forces that would affect the physical and chemical properties of the liquid.

For example, the pump can be a pump that is between the equalizing tank of the extraction solution and the mixer-settler cell. In the liquid-liquid extraction process, the volume flow provided by the pump is typically within 10 and 10000 m³m/h and the pressure produced by the pump is in the order of 500 to 1200 mm H₂O. In particular, the pump is adapted to pump the extraction solutions existing in the liquid- liquid extraction process, their density typically being from 0.7 to 1.2 kg/dm³ and the dynamic viscosity from 1 to 8 mPas . The pump is made of a material that resists strongly corrosive aqueous solutions and chemically aggressive organic solutions, such as acid- resistant steel or fibre-reinforced plastic.

The pump body 1 is a cylindrical, vertical, upwards open container 10, its interior 2 being lim- ited downwards by an particularly horizontal, planar bottom 11 comprising a round central inlet 3. In the lateral direction, the interior of the container 10 is limited by a first vertical side wall 12, its lower part in the vicinity of the bottom 11 comprising an outlet 4. An impeller 5 that is rotated by a driving motor 9 by means of a vertical drive shaft 8 is arranged to rotate around the vertical axis in the hori- zontal position in close proximity to the inlet 3 a few millimetres away from it and centrally with respect to the container 10.

Referring to Figs. 1, 2 and 4, the pump fur- ther comprises a flush cover 13, which is adapted centrally in the interior of container 10. The flush cover 13 includes a second cylindrical vertical side wall 14, its outer diameter being smaller than the inner diameter of the first side wall 12 so that between the first side wall 12 of the container and the second side wall 14 of the flush cover 13, an upward open annular first space 15 is formed. The flush cover 13 is attached to the flange of the upper end of the container by a flanged joint. The flush cover 13 includes a bottom cone 16, which extends from the lower end of the second side wall 14 and has the shape of a truncated circular cone and extends, converging downwards, to the vicinity of the impeller 5. In the middle of the flush cover 13, there is a vertical through pipe 17 that extends upward from the bottom cone 16, the drive shaft 8 being arranged inside the pipe. Inside the through pipe 17 and around the drive shaft 8, an upward open second space 18 is defined.

A vertical scroll wall 19, which surrounds the impeller 5, forms, jointly with the bottom cone 16, a scroll cover 7 that partially surrounds the impeller 5 and expands towards the outlet 4. The horizontal lower edge of the scroll wall 19 rests against the bottom 11 of the container 10. With its bending radius increasing, the scroll wall 19 extends from the first proximal end 20 of the outer periphery of the impeller to the second proximal end 21 of the first side wall 12 of the container. At the first end 20, there is a guide plate 22, its purpose being to guide the flow of liquid to the outlet 4.

The flush cover 13 closes the free fluid level of the liquid in container 10 so that, while the impeller 5 rotates, a column 27 is formed in the first space 15 and the second space 18. Part of the pressure energy of the liquid is converted into potential energy in the column 27, causing hydrostatic pressure in the outlet 4.

Figs. 6 to 9 show in detail the structure of the impeller 5. The structure of the impeller 5 is similar to that of the closed-type turbines used in centrifugal pumps. The impeller 5 includes a round horizontal upper plate 23, which is attached to the drive shaft 8. Curved impeller blades 6 are attached, at their upper edges, to the round upper plate 23. The impeller blades 6 are attached, at their lower edges, to an annular lower plate 24, in the middle of which there is a round inlet hole 25, which is centrally aligned with respect to the inlet 3 for receiving the liquid into the impeller 5 through the inlet hole 25, as shown in Fig. 1. Impeller blades 6, curving outwards, surround peripherally the inlet hole 25 of the lower plate and form blade passages 26, through which the liquid exits from inside the impeller to the scroll cover 7 that surrounds the impeller.

As seen in Fig. 3, the scroll wall 19 is preferably attached to the flush cover 13, preferably to the bottom cone 16.

The outlet 4, through which the solution to be pumped is discharged to the pipework, is located on the side of the container 10 on the same level with the bottom 11 of the container. The pump is connected at its outlet 4 to the pipework, the counterpressure caused by the pipework being dimensioned to correspond to the pressure produced by the pump. When applying the pump to the hydrometallurgical recovery processes of metals, which utilize the liquid-liquid extraction, the device typically pumps the extraction solution to the following pumping section of the mixer-settler cell. As illustrated in Fig. 11, because of its structure, the pump can easily be disassembled, when needed, by detaching and lifting the entity that forms the subassembly A, which is formed by the flush cover 13, the scroll wall 19, the impeller 5, the drive shaft 8 and the driving motor 9, away from inside the container 10 without having to detach the container 10 from the pipework. In that case, the solution in container 10 can also be left in place. Referring to Fig. 10, the pump operates so that the liquid to be pumped enters the container 10 of the pump and the impeller 5 and its blade passages 26 through the inlet 3. While the impeller 5 rotates, it displaces liquid, causing suction in the inlet 3 of the pump, and brings the solution into a tangential circular motion in the space that surrounds the impeller 5 and expands like a scroll, whereby the solution is directed towards the outlet 4 of the pump. The mechanical energy provided by the impeller 5 is con- verted into the pressure energy of the solution. Part of this is directly converted into the kinetic energy of the liquid and part of it is converted into potential energy, when the column 27 is formed in the partially upward open container of the pump, its height causing hydrostatic pressure in the outlet 4 of the pump. The flush cover 13 closes the free fluid level of the pump container so that, while the pump operates and increases the liquid pressure, the fluid level is allowed to freely rise and lower in the narrow first space 15 between the flush cover 13 and the container 10, and in the second space 27 inside the through pipe of the drive shaft 8 of the impeller 5.

The pump is connected, at the suction side thereof, by a pipe to a container 28, from where the liquid is pumped. At the suction side, the level of the liquid that is to be pumped should be at such a height that the liquid covers the entire impeller. Also when the pump operates, the pressure of the solution in the inlet channel should be positive. The volume flow of the pump is adjusted by adjusting the rotation speed of the pump, when the level of the pumped liquid at the suction side varies or when the counter- pressure varies. The control system operates with a flow measuring sensor, which by means of a controller is connected to the frequency transformer that controls the rotation speed of the pump motor. The rotational speed of the impeller is such that the peripheral speed of the impeller is typically in the order of 3.5 to 4.5m/s. In that case, the shearing forces exerted on the liquid are fairly low and their harmful effects on the extraction solution are avoided.

The invention is not limited to the application examples disclosed above only, but many variations are possible within the inventive idea defined by the claims.

Claims

CLAIMS :

1. A pump for pumping liquid, comprising a body (1) comprising a hollow interior (2), - an inlet (3) for allowing the liquid to enter the interior (2)

- an outlet (4) for removing the liquid from the interior (2) ,

- an impeller (5) , which is in the interior and includes a number of impeller blades (6) to convert the kinetic energy of the impeller into the pressure energy of the liquid in the outlet,

- a scroll cover (7), which is adapted to surround the impeller, - a drive shaft (8), which the impeller is attached to and which is fitted with a bearing to rotate in the body, and

- a driving motor (9) for rotating the drive shaft, characterized in that the body (1) is a cylin- drical vertical container (10), which is upwardly open, its interior (2) being limited downwards by an essentially horizontal planar bottom (11), which comprises the central round inlet (3) , the interior being limited in the lateral direction by a first vertical side wall (12), its lower part in the vicinity of the bottom (11) comprising the outlet (4); that the impeller (5) is arranged around the vertical axis to rotate in the horizontal position in close proximity to the inlet (3) and centrally with respect to the container (10), and that the pump includes

- a flush cover (13), which is adapted centrally in the interior (2) of the container, the flush cover including a cylindrical vertical second side wall (14), its outer diameter being smaller than the inner diameter of the first side wall (12) so that between the first side wall and the second side wall, an upwardly open annular first space (15) is formed; a bottom cone (16), which is frusto-conical in shape and extends, converging downwards, to the vicinity of the impeller (5); and a vertical through pipe (17), which extends vertically upwards from the bottom cone (16) and inside which the drive shaft (8) is arranged, and an upwards open second space (18) being defined inside the through pipe around the drive shaft, and a vertical scroll wall (19), which surrounds the impeller (5), forming, jointly with the bottom cone (16), a scroll cover (7), which partly surrounds the impeller (5) and expands towards the outlet (4), the scroll wall extending with its bending radius increasing from the first proximal end (20) of the outer periphery of the impeller to the proximal second end (21) of the first side wall of the container, the first end (20) comprising a guide plate (22) for guiding the flow of liquid to the outlet (4) .

2. A pump according to Claim 1, characterized in that the impeller (5) includes a horizontal round upper plate (23) , which is attached to the drive shaft

(8), the curved impeller blades (6) being attached to the upper plate at their upper edges; an annular lower plate (24), comprising a round inlet hole (25) in the middle thereof, the hole being centrally located with respect to the inlet (3) to receive the liquid into the impeller through the inlet hole, the impeller blades (6) being attached to the lower plate at their lower edges to peripherally surround the inlet hole

(25) of the lower plate and to form blade passages (26), through which the liquid exits from inside the impeller into the scroll cover (7) .

3. A pump according to Claim 1 or 2, characterized in that the scroll wall (19) is attached to the flush cover (13), preferably to the bottom cone (16).

4. A pump according to any of Claims 1 to 3, characterized in that the pump is a pump that is used in the liquid-liquid extraction process of the hydro- metallurgical recovery of metals.

5. A pump according to Claim 4, characterized in that the pump is a pump that is connected to the equalizing tank of the extraction solution.

6. A pump according to Claim 4 or 5, characterized in that the pump is a pump between the equalizing tank of the extraction solution and a mixer- settler cell.

7. A pump according to any of Claims 1 to 6, characterized in that the output of the pump is within 10 and 10000 m³/h.

8. A pump according to any of Claims 1 to 7, characterized in that the pressure produced by the pump is in the order of 500 to 1200 mmH₂0.

9. A pump according to any of Claims 1 to 8, characterized in being adapted to pump solutions that typically have a density of 0.7 to 1.2 kg/dm3 and a dynamic viscosity of 1 to 8 mPas .

10. A pump according to any of Claims 1 to 9, characterized in that the pump is constructed from a material that resists strongly corrosive aqueous solutions and chemically aggressive organic solutions.

11. A pump according to any of Claims 1 to 10, characterized in that the container (10), the flush cover (13), the impeller (5) and/or the scroll wall (19) are formed from acid-resistant steel.

12. A pump according to any of Claims 1 to 11, characterized in that the container (10), the flush cover (13), the impeller (5), and/or the scroll wall (19) are formed from fibre-reinforced plastic.

13. A method of disassembling the pump according to any of Claims 1 to 12, characterized in that the flush cover (13), the scroll wall (19), the impeller (5), the drive shaft (8) and the driving motor (9) are joined to form a subassembly (A), which can be handled as one unity, and to disassemble the pump, the said subassembly (A) is detached and lifted out of the interior (2) of the container (10) as one unity, without having to detach the container from the pipework, which the container is connected to, and without having to remove the liquid from the container .