Patent Publication Number: US-2013243615-A1

Title: Pump

Description:
FIELD OF THE INVENTION 
     The invention relates to the pump defined in the preamble to claim  1 . 
     BACKGROUND OF THE INVENTION 
     A pump mixer is known in the prior art e.g. in publication U.S. Pat. No. 5,662,871 (the Dispersion Overflow Pump, DOP®), with which two or more mutually insoluble liquid phases are mixed with each other into a dispersion. The pump feeds the dispersion via one or several mixers into a solvent extraction settler. 
     This kind of pump includes a suction tank comprising a bottom, which limits the internal space of the suction tank in the downward direction. The suction tank further includes a cylindrical vertical sidewall, which limits the internal space of the suction tank in the lateral direction. There is an opening for the first inlet channel in the sidewall, through which the first liquid phase is fed into the suction tank, and for the second inlet channel, through which the second liquid phase is fed into the suction tank. The suction tank further includes an upper wall, which limits the internal space of the suction tank in the upward direction and in which upper wall there is a central opening. Furthermore, the pump includes a pump section, which comprises an blade wheel housing, which is arranged on top of the suction tank so that the above-mentioned upper wall forms the bottom of the blade wheel housing, and where the central opening in the upper wall forms the suction opening for the pump section, and which blade wheel housing is limited laterally by a cylindrical sidewall. The pump section further comprises a blade wheel, in which there is a set of blades. The blade wheel is arranged so as to mix into a dispersion the first phase and second phase that are sucked into the internal space of the blade wheel housing from the suction opening. The blade wheel is fixed to the vertical drive shaft in order to rotate the drive motor. 
     In this DOP pump of the prior art the blade wheel housing is open at the top. The upper part of the blade wheel housing sidewall opens conically upwards so that the upper rim of the sidewall forms an “overflow” rim, over which the dispersion is discharged into the space surrounding the blade wheel housing. The suction tank and pump section are surrounded by an outer tank, which receives the dispersion discharging from the blade wheel housing into the space between the suction tank and the outer tank. In this space the mixing power is kept at a level at which the phases remain mixed. The remainder of the kinetic energy is changed into potential energy, with the purpose of moving the dispersion forwards via the discharge channel opening in the sidewall of the outer tank to the mixers and from there on to the solvent extraction settlers. 
     This type of DOP pump construction of the prior art acts as an excellent dispersion former. 
     However, in large-scale Cu extraction plants the DOP pump construction of the prior art creates some problems. With the construction described above the size of the DOP pump will be large. For example, the diameter of the outer tank that is required, which determines the physical size of the equipment, may be as much as the order of 6-7 m and the height over 4 m. The physical size of the equipment is therefore huge and causes large investment costs. There is a large empty space on top of the pump section in the outer tank, which is not needed apart from during process start-up, because the shaft bushing of the drive shaft through the lid of the outer tank is not sealed tight. This increases the size of the equipment and consequently the investment costs. The space for liquid between the outer tank and the suction tank increases the physical size of the equipment, increases the investment costs of the equipment and technically in terms of the process makes it difficult to dimension (dispersion residence time). Since there is a large volume of liquid in the DOP unit, which must be kept mixed before the dispersion flows to the mixers, the phases have to be over-mixed in the pump section. This increases the formation of small droplets in the pump that are hard to separate, and raises the power consumption of the DOP unit. A large unit and especially a large outer tank raise transportation costs and hamper transport, particularly for instance in mountain regions and in Africa, where the dimensions of the outer tank often exceed the permitted transportation dimensions. Since the drive motor is located a long way from the blade wheel, a long drive shaft is required. A long shaft will bend particularly in large production units and cause vibration in the blade wheel. Bending of the shaft hampers the mechanical dimensioning of the shaft and blade wheel. 
     PURPOSE OF THE INVENTION 
     The purpose of the invention is to eliminate the above-mentioned drawbacks. 
     In particular the purpose of the invention is to disclose a pump, which is considerably smaller in physical size and cheaper in price than earlier. 
     A further purpose of the invention is to disclose a pump, which enables the dimensioning of the pump so as to be transportable by ordinary means of transportation without requiring special transportation, and where the pump transportation costs are reasonable. 
     A further purpose of the invention is to disclose a pump where there is no need for a large empty space nor an outer tank, and whose liquid volume is thus as small as possible. 
     A further purpose of the invention is to disclose a pump where the dispersion residence time is as small as possible. 
     A further purpose of the invention is to disclose a pump, whose power consumption is smaller than earlier. 
     In addition, it is the purpose of the invention to disclose a pump where there is as little blade wheel vibration as possible. 
     SUMMARY OF THE INVENTION 
     The features of the pump accordant with the invention are made apparent in claim  1 . 
     In accordance with the invention, the inner space of the blade wheel housing is limited in the upward direction by a cover plate, in which there is a central shaft bushing for the drive shaft sealed with a mechanical shaft seal. The discharge channel opening is in the sidewall of the blade wheel housing. 
     In comparison with the DOP pump known in the prior art, the pump accordant with the invention has many advantages:
         No separate outer tank is required at all, because the dispersion is removed directly from the blade wheel housing of the pump section. This reduces the physical size and cost of the equipment by over 50%.   The pump is always full of liquid. There is no empty space inside the equipment nor is it needed. Thus there is no need for the expensive and troublesome butterfly valve intended for liquid level control of the current DOP pump.   The liquid volume of the pump is small i.e. the mixer residence time dimensioning will be accurate and easy to calculate.   Over-mixing is not required since as soon as the dispersion is formed, it is removed from the pump and is almost immediately in the mixer. This improves phase separation in the solvent extraction settler and decreases the power consumption of the pump.   A small-sized pump unit can be transported easily as a whole to the site, for instance by normal road transport. Several pumps with the new construction can be transported in the same transportation, whereas the current units require individual transportation pallets.   The blade wheel drive shaft is short, so it does not vibrate, which facilitates the dimensioning of the shaft and blade wheel and enhances mechanical durability.       

     In some embodiments of the pump, the opening of the discharge channel in the sidewall of the blade wheel housing is tangential. 
     In some embodiments of the pump, the drive includes a motor. 
     In some embodiments of the pump, the drive includes a gear, which is arranged between the motor and the drive shaft. 
     In some embodiments of the pump, the output is in the order of magnitude of 50-10 000 m3/h, the peripheral speed of the blade wheel is of the order of magnitude of 5 m/s and the overpressure of the dispersion in the discharge channel is of the order of magnitude of 5-50 kPa. This overpressure causes the majority of the hydrostatic pressure in the mixer that comes after the pump. The overpressure required for the dispersion to flow from the pump is 3-8 kPa. 
    
    
     
       LIST OF DRAWINGS 
       The invention is described in detail below by means of example embodiments with references to the attached drawings, where 
         FIG. 1  presents a diagram of one arrangement equipped with one embodiment of the pump accordant with the invention, and 
         FIG. 2  presents a diagram of a cross-section of one embodiment of the pump accordant with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  presents a diagram of an arrangement consisting of pump  1 , two mixers  2  and solvent extraction settler  3 . There may be a different number of mixers than two. Two or more liquid phases that are insoluble in each other are mixed together into a dispersion in pump  1 . Pump  1  feeds the dispersion to mixer  2 , from where it is routed on to the second mixer  2  and from there on via rise channel  24  to solvent extraction settler  3 . The phases to be mixed into a dispersion in the arrangement may be for instance water and an organic solution. In dispersion the extraction reaction transfers for example metals from one phase to the other. The phases are separated from each other in settler  3 . 
     In  FIG. 2  the basic structure of pump  1  from  FIG. 1  is shown in more detail. Pump  1  includes suction tank  4 . The inner space of suction tank  4  is bounded by bottom  5  in the downward direction. The inner space of suction tank  4  is bounded by cylindrical, vertical sidewall  6  in the lateral direction. The inner space of suction tank  4  is bounded by upper wall  9  in the upward direction. There is a central opening  10  in the upper wall. Sidewall  6  of suction tank  4  has an opening for first inlet channel  7  through which the first liquid phase is fed into the suction tank, and an opening for the second inlet channel  8 , through which the second liquid phase is fed into the suction tank. 
     Further, pump  1  includes pump section  11 , which is immediately on top of suction tank  4 . Pump section  11  includes blade wheel housing  12 , which is arranged on top of suction tank  4  so that upper wall  9  forms the bottom of blade wheel housing  12 , and in which upper wall  9  central opening  10  forms a suction opening from which the phases are sucked into blade wheel housing  12 . Blade wheel housing  12  is bounded laterally by vertical, cylindrical sidewall  13  as an upward continuous extension of sidewall  6  of suction tank  4 . The opening of discharge channel  18  is perpendicular or tangential in sidewall  13  of blade wheel housing  12 . Blade wheel  14 , in which there is a set of rotor blades  15 , is arranged in the inner space of blade wheel housing  12  so that as the blade wheel rotates, the first phase and second phase sucked out of suction tank  4  through suction opening  10  are mixed together into a dispersion, which can be discharged along discharge channel  18  to the mixer. The inner space of blade wheel housing  12  is bounded in the upward direction by cover plate  19 , in which central shaft bushing  21  is sealed with mechanical shaft seal  20 , through which vertical drive shaft  16  extends into blade wheel housing  12  and blade wheel  14  is fixed to the lower end of drive shaft  16 . Drive  17  is arranged to rotate drive shaft  16 , which may consist of electric motor  22  and reduction gear  23 . 
     Pump  1  is particularly suitable for use in large-scale Cu extraction plants. 
     As an example of pump size and key figures, it can be mentioned that the output of pump  1  may be in the order of 50-10 000 m 3 /h. Drive  17  may be adapted to rotate blade wheel  14  at a peripheral speed of the order of 5 m/s. The pressure of the dispersion in discharge channel  18  may be of the order of 50 kPa. 
     As an example of the physical dimensions, if the outer dimensions of a DOP unit with a structure accordant with the prior art were a diameter of 6.7 m and a height of 4.01 m, then correspondingly for a structure accordant with the invention the diameter is 3.4 m and the height 1.75 m. In comparison with a DOP unit of the prior art, the equipment volume of a pump accordant with the invention falls by 88%, the diameter decreases by 49% and the height decreases by 56%. The volume of the solution contained in the pump falls by approx. 75%. 
     The invention is not restricted only to the example applications presented above, but many variations are possible while remaining in the framework of the inventive concept defined in the patent claims.