Patent Publication Number: US-8535000-B2

Title: Centrifugal pump for slurries

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119(e) to U.S. provisional patent application No. 61/172,490 filed Apr. 24, 2009. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to pumps and more specifically to centrifugal pumps for slurries containing solid particles. 
     BACKGROUND OF THE INVENTION 
     Centrifugal pumps are commonly used for pumping liquids. For some liquids, such as those that contain hydrocarbons and/or water, corrosion problems arise. If the liquid is a slurry that contains solid particles suspended in it, such as an oil sand/water slurry, a tailings/water slurry, a coke/water slurry, etc. the solid particles can cause erosion/corrosion or other forms of wear to the components of the pump. Additionally, because of how centrifugal pumps operate, different components may be subjected to different forms and severity of wear and/or corrosion. Even different surfaces of the same component may be subjected to different conditions causing different forms and severity of wear and/or corrosion. 
     Often these centrifugal pumps are critical components of a larger system and in some cases these pumps may be the run-limiting component in these systems with respect to system reliability. Once the centrifugal pump fails, needs maintenance or components of the pump need replacing, the entire system may have to be shut down while the pump is being repaired or components replaced. Any extension of pump life that can be achieved can greatly increase the efficiency of the systems these pumps are used in. 
     Currently, the wet end components of these centrifugal pumps are cast as single components, requiring a single material, typically chromium white iron (CWI), to be used for these components. This can greatly limit the ability to surface engineer the various components and surfaces to tailor the performance of these parts for the operating conditions in the pump. 
     SUMMARY OF THE INVENTION 
     In a first aspect, an impellor for use in a centrifugal pump is provided. The impellor has a central hub, a plurality of vanes spacedly attached to the hub, and at least one side plate attached to the vanes, whereby each vane is individually wear protected prior to attaching each vane to the hub. In one embodiment, the wear protection comprises tungsten carbide. In another embodiment the wear protection could be any suitable corrosion resistant/wear resistant material as appropriate. The wear material may be integral or may be attached by welding, brazing, adhesion, some form of mechanical attachment or other suitable method, or any combination thereof. 
     In a second aspect, a centrifugal pump is provided having a volute casing having a discharge conduit, an impeller provided in the volute casing, and a suction sideliner enclosing the impeller in the volute casing, the suction sideliner being at least partially covered with sintered tungsten carbide tiles. 
     In a third aspect, a centrifugal pump is provided having a volute casing having a discharge conduit, an impeller provided in the volute casing, the impeller assembled from a plurality of vanes joined to a central hub and connected between a first side plate and a second side plate, a suction sideliner enclosing the impeller in the volute casing, the suction sideliner having a coating on the interior surface and an intake conduit directed towards the impeller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein: 
         FIG. 1  is a side view of a pump in accordance with the present invention; 
         FIG. 2  is a front view of the pump in  FIG. 1 ; 
         FIG. 3  is a side sectional view of a volute casing of the pump shown in  FIG. 2  along sectional line AA′; 
         FIG. 4  is a perspective view of an impeller; 
         FIG. 5  is an exploded view of the impeller shown in  FIG. 4 ; 
         FIG. 6  is a front view of an impeller vane; 
         FIG. 7  is a side sectional view of the impeller vane shown in  FIG. 6 , along line BB; and 
         FIG. 8  is a perspective view of a sideliner having tungsten carbide tiles attached to its inner surface. 
     
    
    
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. 
       FIGS. 1 and 2  illustrate a centrifugal pump  10 . The centrifugal pump  10  has a motor  20 , such as electric motor, turbine, etc., that drives the pump  10  and is connected to an impeller (not shown) by a shaft  25 . The impeller is provided in a volute casing  30 . An intake conduit  32  is provided in the volute casing  30  to route liquid into the pump  10 , where the liquid will be subsequently discharged from the pump  10  through a discharge conduit  34  provided in the volute casing  30 . A suction sideliner  40  is provided to allow access to the inside of the volute casing  30 . 
       FIG. 3  illustrates an impeller  50  provided in the volute casing  30 . The impeller  50  is connected to the shaft  25  and is rotated during operation of the pump  10 . 
     Referring to  FIGS. 1-3 , in operation, liquid enters the centrifugal pump  10  through the intake conduit  32  where it is routed to the impeller  50 . The impeller  50  is rotated by the motor  20  causing the incoming liquid to be drawn into the impeller  50  through an eye  58  of the impeller  50 . From the eye  58  of the impeller  50 , the rotation of the impeller  50  causes vanes  60  in the impeller  50  to force the liquid that has entered the impeller  50  through the eye  58  outwards to a periphery of the impeller  50  and out into the volute casing  30 . The vanes  60  of the impeller  50  impose radial forces on the liquid that has entered the impeller  50 , forcing the liquid to the periphery of the impeller  50  and out into the volute casing  30 . The volute casing  30  collects the liquid that exits the impeller  50  and directs it out the discharge conduit  34 . Typically, the liquid exiting the impeller  50  has a relatively high velocity and the volute casing  30  is shaped to convert this relatively high velocity into pressure. 
     Because of the operation of the pump  10 , the components of the pump  10  are subjected to various loads and forces depending on their use in the pump  10 . Some components, such as wetted surface  31  of the volute casing  30 , wetted surface  42  of the sideliner  40  and the impeller  50  come into direct contact with the liquid being pumped by the pump  10 . In some applications the liquid may be corrosives, such as when the liquid pumped includes hydrocarbons or water. Additionally, when the liquid being pumped is a slurry, such as an oil sand/water slurry, tailing/water slurry, coke/water slurry, etc., the presence of solids in the liquid can have a abrasive effect on the components of the pump  10  that come into direct contact with the liquid, causing wear problems with these components. However, because of the operation of the different components in the pump  10 , the different components are subjected to different forces, loads, etc. which can result in the components being subjected to different corrosion/erosion and/or wear conditions. Even those components that come into direct contact with the liquid may be subjected to different conditions. The components of the pump  10  can therefore be chosen and manufactured to address each component&#39;s operating conditions. 
     The liquid passing through the pump  10  comes into direct contact with the wetted surface  31  of the volute casing  30 . Because of the action of the impeller  50  which forces the liquid outwards out of the impeller  50  and against the interior surface  32  of the volute casing  30 , the volute casing  30  can be exposed to significant wear and/or corrosion by the liquid constantly being forced against its wetted surface  31 . This can be especially true when the liquid contains solid particles such as when the liquid is a slurry. In one aspect, the volute casing  30  of the pump  10  can be made of chromium white iron, such as being cast in chromium white iron. 
     The sideliner  40  connects to an end  35  of the volute casing  30  and has a wetted surface  42  that can come into contact with liquid passing through the pump  10 . Liquid entering the inlet conduit  32  is routed through the sideliner  40  to the eye  58  of the impeller  50 . The wetted surface  42  of the sideliner  40  faces the impeller  50 . When the pump  10  is in operation, liquid entering the pump  10  through the inlet conduit  32  can pass between the impeller  50  and the wetted surface  42  of the sideliner  40 . If the liquid is corrosive and/or contains solid particles making it abrasive, the interior surface  42  of the sideliner  40  can be subjected to significant wear. This wear may be significant because the impeller  50  is rotating during the operation of the pump  10 , while the sideliner  40  is stationary resulting in a relative rotational motion between the impeller  50  and the interior surface  42  of the sideliner  40 . In addition, local re-circulation may occur, dramatically increasing local wear rates. 
     To address the fact that the interior surface  42  of the sideliner  40  can be subjected to significant wear from the liquid passing through the pump  10 , the sideliner  40  can be made of a material such as carbon steel and in one aspect the sideliner  40  may be cast of ASTM A487 CA6NM, carbon steel, or other suitable material. Additionally or in the alternative, the wetted surface  42  of the sideliner  40  can have a wear and/or corrosion resistant material applied to it, such as by a coating. In one aspect, the wetted surface  42  of the sideliner  40  can have a layer of tungsten carbide applied to it, such as by having tungsten carbide tiles attached to the wetted surface  42  such as by adhesion, brazing, mechanical fastening, etc. The tungsten carbide tiles can provide a protective layer for the interior surface  42  of the sideliner  40 .  FIG. 8  shows a perspective view of a sideline  140 , for example, from a GIW TBC 57.5 pump, which has been tiled with tungsten carbide tiles  141 . The carbon tungsten tiles  141  were vacuum bonded to the interior surface  142  of the sideliner  140 , which is made of a chromium white iron base material. 
     The impeller  50  comes into direct contact with the liquid passing through the pump  10  during the operation of the pump  10 . It is the impeller  50  and specifically the vanes  60  that impart energy to the liquid, causing the liquid to accelerate towards the periphery of the impeller  50  and out into the volute casing  30 . The components of the impeller  50  can therefore be affected by this contact with the liquid/slurry. Additionally, the different components of the impeller  50  come into contact with the liquid/slurry under different conditions. For example, during the operation of the pump, the vanes  60  are forced directly against the liquid/slurry, while other components of the impeller  50  have the liquid flowing along them and traveling laterally relative to them. This can result in different components of the impeller  50 , itself, being subjected to different conditions as a result of contact with liquid passing through the pump  10 . Rather than casting the impeller as a single component, as is commonly done, the impeller  50  can be made of a number of components that are formed separately and then assembled together to form the completed impeller  50 . This allows each component of the impeller  50  to be individually tailored to that component&#39;s specific function in the impeller  50 . 
       FIG. 4  illustrates the impeller  50  in a perspective view and  FIG. 5  illustrates the impeller  50  in an exploded view. The impeller  50  has a first side plate  52  and a second side plate  54 . Positioned between the first side plate  52  and the second side plate  54  are a plurality of vanes  60 . Each of the vanes  60  are connected to a central hub  70 . The central hub  70  can have a number of tails  72 , with each tail  72  mateable with a pin  68  on one of the vanes  60 . In an aspect, the pin  68  can extend outwards as it extends from the vane  60  with the tails  72  shaped to mate with the pins  68 . In this manner, when a pin  68  on one of the vanes  60  is slid sideways into one of the tails  72  in the central hub  70 , the vane  60  cannot be pulled radially out of the central hub  72 . The vanes  60  and the central hub  70  are positioned between the first side plate  52  and the second side plate  54  and the first side plate  52  and the second side plate  54  are mechanically connected, compressing and holding the vanes  60  in place in the completed impeller  50 . 
     The first side plate  52  and the second side plate  54  can be formed of wear and/or corrosion resistant material. In one aspect, the first side plate  52  and the second side plate  54  could be formed of a material such as carbon steel, for example, ASTM A487 CA6NM, stainless steel, or any other similar material, preferably a material that is compatible with the application of additional wear protection. Because the first side plate  52  and the second side plate  54  are formed separately from the other components of the impeller  50 , the inner surfaces  53 ,  55  can be coated, such as having an wear protection of material provided over them, before the impeller  50  is assembled. 
     The central hub  70  can be formed, cast, machined, forged, etc. of a corrosion/wear resistant material, such as chromium white iron, CANGM stainless steel, carbon steel, stainless steel, etc., preferably a material that is compatible with additional wear protection. 
     Impeller  50  is shown as a closed vane impeller. Closed vane impellers, also called enclosed or shrouded impellers, provide benefits in certain applications over open or semi-open vane impellers. However, the vanes of a closed vane impeller are enclosed in passages running between the sides of the impeller, making it hard to apply wear protection or other surface treatments to the surfaces of the vanes. In a closed vane impeller that has been formed as a single piece, it is often hard, if not impossible, to apply a coating to the entire surface of the vanes because the surfaces of the vane located proximate the center of the impeller are not easily accessible or even accessible at all to the person or device applying the coating. Because impeller  50  is formed of a number of components that are then assembled into the completed impeller  50 , the vanes  60  can be separately formed before they are assembled with other components into the completed impeller  50 . 
       FIGS. 6 and 7  illustrate one of the vanes  60  before the vane  60  is assembled into a completed impeller  50  as shown in  FIG. 4 . The vane  60  has a profile that is selected for the operating characteristics desired for the pump  10 . The vane  60  imparts energy to the liquid passing through the impeller  50  to accelerate the liquid towards the periphery of the impeller  50 . This energy is imparted by the rotation of the impeller  50  during operation of the pump  10  which forces the vanes  60  against the liquid. Because of this, the vanes  60  can be subjected, to significant wear including erosion/abrasion by the liquid passing through the pump  10 , especially if there are solid particles present in the liquid. The vanes  60  move substantially perpendicularly to the flow of liquid passing through the pump  10 . This can impose a force from the liquid directly on a leading surface  62  of each vane  60 . If the liquid contains solid particles suspended in it, these solid particles can subject the vanes  60  to increased wear by the vanes  60  being impacted and abraded by the solid particles. The vanes  60  may therefore be subjected to different conditions than other components in the pump  10 . 
     By forming the vanes  60  separately from the other components in the impeller  50 , the material(s) of the vane  60  can be chosen separately from the materials used for the other components of the impeller  50  and constructed with suitable manufacturing techniques. The vane  60  can be cast, forged, machine, etc. In one aspect, a body  67  of the vane  60  can be formed from a first material and then a tip  65  can be attached to the body  67 . In one aspect, the tip  65  can be formed of solid sintered tungsten carbide. 
     The body  67  of the vane  60  can, in a further aspect, be provided with a surface treatment to increase its wear resistance. In one aspect, this surface treatment could be a wear resistant coating, such as a tungsten carbide coating, with the leading surface  62  having a first coating  61  and the trailing surface  64  having a second coating  63  applied over them. The wear resistant coating may be applied using any compatible technology such as by thermal spraying of coating, weld wear protectioning, etc. If desired, the first coating  61  on the leading surface  62 , which is forced against the liquid by the rotation of the impeller  50 , can be applied thicker than the second coating  63  applied to the trailing surface  64  and/or can consist of a different material. In another aspect, this coating could be ceramic tiles, carbide tiles, etc, that are applied to the surface vane  60 , such as by use of adhesives, mechanical attachment, brazing, etc. 
     Because the vane  60  is formed separately from the other components in the impeller  50 , the leading surface  62  and the trailing surface  64  are easily accessible to a person or device applying the surface treatment. This allows the person or device to easily apply a surface treatment, such as a wear resistant coating to the desired thickness and coverage. Alternatively, the part may be manufactured as a monolithic component, such as a solid sintered carbide, etc. 
     Referring again to  FIGS. 4 and 5 , once the vanes  60  have been formed and any surface treatment, such as surface coatings, etc. have been applied to the vanes  60 , the vanes  60  can be attached to the central hub  70 , by sliding the pins  68  on the vanes  60  into one of the tails  72  on the central hub  70 , to join the vanes  60  to the central hub  70 . The central hub  70  and the connected vanes  60  can then be positioned between the first side plate  52  and the second side plate  54  and the first side plate  52  and the second side plate  54  can be connected together, forming the completed impeller  50 . With the vanes  60 , central hub  70 , first side plate  52  and second side plate  54  in place, a number of passages  59  are formed. The liquid that has entered the impeller  50  through the eye  58  flows through these passages  59 . Each passage  59  is defined by the trailing surface  64  of a vane  60 , the leading surface  62  of an adjacent vane  60  and the inner surfaces  53 ,  55  of the first side plate  52  and the second side plate  54 , respectively. In this manner, each surface defining one of the passages  59  can be formed of a different material. This completed impeller  50  can then be installed in the pump  10 . 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.