Patent Publication Number: US-9833756-B2

Title: Apparatus for mixing and pumping

Description:
TECHNICAL FIELD 
     The invention relates to an apparatus for mixing and pumping. The apparatus has a shear rotor, a stator and an impeller arranged in a housing for effecting the mixing and the pumping. 
     BACKGROUND ART 
     Today a number of techniques exist for inline mixing of a material and a liquid. Examples of materials include particles in e.g. powder form or granulate form, as well as liquids with significantly higher viscosity than the liquid to mix with. Inline mixing refers to continuously introducing the material in a stream of the liquid that the material shall be mixed with. The stream of liquid is typically generated by a pump and the material that is introduced in the stream must be adequately mixed with the liquid. The mixing may include that the material is dissolved in the liquid, either fully or in part. In either case, the material that is introduced into the stream is after its introduction transported as a part of the liquid. 
     The mixing is often affected by the rate of flow of the stream of liquid, which means that the design of both mixing equipment and pumping equipment must be considered in order to obtain adequate mixing. 
     Apparatuses with equipment for both mixing and pumping a liquid and material are disclosed in a number of patent documents, for example in U.S. Pat. Nos. 4,660,990, 4,850,704, 5,322,357 and US2004/0223407. 
     The disclosed apparatuses successfully accomplish mixing and pumping of liquid and material. However, they are quite bulky and they are not very versatile in respect of employment within in a wide range of processes where mixing is required. 
     SUMMARY 
     It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the prior art. In particular, it is an object to provide an apparatus that accomplishes adequate mixing of a liquid and a material, as well as efficient feeding of the liquid, the material and the liquid and material after they have been mixed. 
     To fulfill these objects an apparatus for mixing and pumping is provided. The apparatus comprises: a housing with an inlet and an outlet for receiving and expelling liquid and a material; a shear rotor rotatably arranged in the housing about a central axis and connected to a drive unit; a stator fixedly arranged in the housing and surrounding a periphery of the shear rotor such that an annular clearance is formed between the shear rotor and the stator, wherein the liquid and material pass the annular clearance and through openings in the stator when the drive unit is activated, thereby effecting mixing of the liquid and material; and an impeller rotatably arranged in the housing about the central axis and connected to the drive unit, such that the impeller pumps the liquid and material from the inlet, via the annular clearance, via the openings in the stator and to the outlet when the drive unit is activated. The apparatus further comprises a return conduit that is configured to return to the inlet a part of the liquid and material that is pumped via the annular clearance and the openings in the stator. This means that a part of the liquid and material that have been mixed, i.e. a part of a mixture of the liquid and material, is returned to the inlet. 
     The provided apparatus is advantageous since it is, by virtue of the shear rotor, the stator and the impeller, readily employed as a single unit that performs both mixing and pumping. This renders the apparatus versatile since it may be easily employed within in a wide range of different processes. Moreover, the return conduit assists the employment within in a wide range of different processes because no external means are necessary in order to ensure proper receipt of unmixed liquid and material at the inlet, since returning a part of the mixed liquid and material to the inlet typically has the effect that the returned part pushes or pulls unmixed material and liquid towards the inlet. In this context, mixed liquid and material refers to liquid and material that has passed through the apparatus, while unmixed liquid and material is liquid and material that has not passed through the apparatus. 
     For the apparatus the pumping is performed by in particular the impeller. However, it is possible to give the rotor a shape such that it assists in the pumping. Correspondingly, the impeller may to some extent assist in mixing the liquid and material. Still, the main function of the impeller is the pumping, which includes generating a stream of liquid and material from the inlet to the outlet of the housing. Thus, the impeller draws liquid and material towards the inlet, past the annular clearance and the openings in the stator where mixing is effected, and to the outlet where the now mixed liquid and material are expelled. 
     The housing may comprise a further outlet to which the return conduit is connected for receiving the part of the liquid and material to return to the inlet, while a remaining part of the liquid and material is conveyed via the outlet. Alternatively or additionally, the return conduit may be connected to the outlet of the housing and may comprise a first branch that conveys the part of the liquid and material in a direction towards the inlet, and a second branch that conveys a remaining part of the liquid and material in another direction. 
     The return conduit may be configured to return to the inlet less than one third of the liquid and material pumped by the impeller. Returning more than one third is of course possible. However, returning more than one third does not appear to improve feeding of unmixed liquid and material to any larger extent, even if this may be the case. The liquid and material pumped by the impeller is the same liquid and material that is pumped via the annular clearance and the openings in the stator. 
     The shear rotor and the impeller may be arranged to rotate about a horizontal, geometrical axis. Additionally, the apparatus may comprise a horizontally arranged drive axle that connects the shear rotor and the impeller to the drive unit. These specific arrangements improve the feeding of in particular the material. 
     The apparatus may comprise a liquid conduit arranged to convey the liquid to the inlet, and a material conduit arranged to convey the material to the inlet, wherein the return conduit is connected to the material conduit, such that a flow of the material in the material conduit is facilitated by the part of the liquid and material that is returned by the return conduit. 
     The material conduit may comprise an outer conduit, an inner conduit and a chamber that is formed between the outer conduit and the inner conduit, the inner conduit being arranged to convey the material and the return conduit being connected to the chamber such that the chamber may receive the part of the liquid and material that is returned by the return conduit, the chamber comprising an opening that surrounds at least a part of an outlet of the inner conduit, such that the liquid and material returned by the return conduit pass through the opening and come into contact with and thereby transport material from the inner conduit. This particular embodiment is advantageous in that it provides quite efficient feeding of the material. 
     The material conduit may be connected to the liquid conduit, such that material from the material conduit is conveyed to the inlet of the housing via the liquid conduit. 
     The liquid conduit may have a horizontal extension such that it conveys liquid in a horizontal direction towards the inlet of the housing, and the material conduit may have a vertical extension such it conveys material in a vertical direction towards the liquid conduit. For this embodiment, the material conduit is, as seen in the vertical direction, connected to an upper side of the liquid conduit. Such connection improves the feeding of the material. 
     The material conduit may comprise a first manual valve and the liquid conduit may comprise a second manual valve. The valves are advantageous in that they provide an apparatus that may be employment as a single mixing and pumping unit within a wide range of different processes. The valves are also advantageous in that they may create pressure differences when they are opened and closed, which effectively facilitates feeding of material that might have got stuck e.g. in a liquid or material conduit leading to the inlet of the housing. 
     The apparatus may be mounted on a frame that comprises a number of wheels for transporting the apparatus. The frame with the wheels is advantageous since it assists in providing an apparatus that may be employment within a wide range of different processes, typically because of increased mobility. Moreover, the frame and wheels allows an operator to easily access various components of the apparatus from various sides, which is advantageous if e.g. material gets stuck somewhere and actions must be taken in order to facilitate proper feeding of material. Also, the wheels are advantageous in that the apparatus may be easily shaken for releasing material that has got stuck e.g. in a conduit leading to the inlet of the housing, which in turn facilitates proper feeding of material. 
     The apparatus may comprise a hopper that is connected to the material conduit, and a table that is arranged adjacent the hopper. The hopper and the frame assist in providing an apparatus that may be employment within a wide range of different processes, since they contribute to a increasing the apparatus capability to operate as a stand-alone unit. Also, both the hopper and the table facilitate proper feeding of the material. Typically, the hopper and the table may be supported by the frame. 
     The return conduit may be configured to return the part of the liquid and material to the inlet without passing the returned part of the liquid and material via any further pumping equipment. Thus, for this embodiment the return conduit may not be seen as a fluid line that incorporates a pump. The further pumping equipment is here any other pumping equipment that in addition to the apparatus would pump the liquid and material. Arrangements within the housing of the apparatus are however not considered to be a further pumping equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which 
         FIG. 1  is a perspective view of an apparatus for mixing and pumping, 
         FIG. 2  is cross-sectional view of the apparatus of  FIG. 1 , 
         FIG. 3  is an enlarged, cross-sectional view the apparatus of  FIG. 1 , 
         FIGS. 4-5  illustrate a stator of the apparatus of  FIG. 1 , 
         FIGS. 6-7  illustrate a shear rotor of the apparatus of  FIG. 1 , 
         FIGS. 8-9  illustrate an impeller of the apparatus of  FIG. 1 , 
         FIG. 10  is a perspective view of the apparatus of  FIG. 1 , when mounted on a frame with wheels, 
         FIG. 11  is a schematic view of the apparatus of  FIG. 1 , and 
         FIGS. 12-13  are schematic views of further embodiments of an apparatus for mixing and pumping. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2  an apparatus  1  for mixing and pumping is shown. The apparatus  1  comprises a pump and mixing unit  2  and a piping arrangement  4 . The apparatus effects mixing of a liquid L and a material P, where the material P typically is a dry material in powder or granulate form. The mixing may include dissolving the material P in the liquid L, either fully or in part. The material P may also have the form of a liquid with significantly higher viscosity than the liquid L to mix with. The pump and mixing unit  2  also effects pumping of the liquid L and material P prior they are mixed as well as pumping of the liquid L and material P after they have been mixed. When the liquid L and material P have been mixed, they are pumped in combination in the form of a mixture M 1 , M 2 . The piping arrangement  4  is connected to the pump and mixing unit  2  and ensures that liquid L and material P are effectively fed to the pump and mixing unit  2 . In its most basic form the apparatus comprises the pump and mixing unit  2  and the piping arrangement  4 , but may, as will be described, include additional components. 
     The pump and mixing unit  2  has an inlet  201  where both liquid L and material P are received. The liquid L and the material P are mixed in the pump and mixing unit  2  and a part M 1  of the resulting mixture is expelled via an outlet  202 , while, in one embodiment, another part M 2  of the resulting mixture is expelled via a further outlet  203 . The part M 1  of the mixture expelled via the outlet  202  is referred to a “the process mixture” M 1 , while the other part M 2  of the mixture is referred to as a “return mixture” M 2 . Typically, a flow of process mixture M 1  that is expelled via the outlet  202  is twice as big as a flow of return mixture M 2  that is expelled via the further outlet  203 . In the illustrated embodiment the pump and mixing unit  2  comprises both the outlet  202  and the further outlet  203 . The outlet  202  may be referred to as a first outlet and the further outlet  203  may be referred to as a second outlet. 
     The piping arrangement  4  comprises a material conduit  412  and a liquid conduit  411  that are joined at a joining section  404 . In the shown embodiment this joining has been accomplished by connecting the material conduit  412  to an upper side  426  of the liquid conduit  411 . The liquid conduit  411  has an inlet  401  for the liquid L and the material conduit  412  has an inlet  402  for the material P. The liquid L and the material P are brought together at the joining section  404  and are transported to an outlet  403  of the piping arrangement  4 , which outlet  403  is connected to the inlet  201  of the pump and mixing unit  2 . Even though the liquid L and the material P are brought together at the joining section  404  they are not considered to be mixed here, since bringing them together at the joining section  404  typically does not fulfill conventional requirements for adequate mixing. Thus, adequate mixing must be performed, which for the described embodiment is accomplished by the pump and mixing unit  2 . 
     The piping arrangement  4  also comprises a return conduit  413  that is connected to the further outlet  203  and to the material conduit  412 . The return conduit  413  conveys the return mixture M 2  from the further outlet  203  and to the material conduit  412 . Thus, the return mixture M 2  is, together with the material P, brought together with the liquid L at the joining section  404  and is thereafter introduced in the pump and mixing unit  2  via the inlet  201 . As will be described, the return mixture M 2  effectively assists in feeding the material P to the joining section  404  as well as assists in feeding the liquid L and the material P to the inlet  201 . 
     The pump and mixing unit  2  accomplishes mixing primarily by a shear rotor  60  and a stator  70  that is arranged about the shear rotor  60 . Pumping is accomplished primarily by an impeller  50 . However, depending on how the shear rotor  60  is embodied, it may assist more or less in the pumping. Correspondingly, the impeller  50  may assist in the mixing. The shear rotor  60 , the stator  70  and the impeller  50  are arranged in the pump and mixing unit  2 . In detail, the pump and mixing unit  2  comprises a housing  220  in which the shear rotor  60 , the stator  70  and the impeller  50  are arranged. Typically, the housing  220  comprises the inlet  201  for the liquid L and material P, the outlet  202  for the process mixture M 1 , and the further outlet  203  for the return mixture M 2 . The liquid conduit  411  has a horizontal extension such that it may convey the liquid L a horizontal direction x towards the inlet  201  of the housing  220 . The material conduit  412  has a vertical extension such it may convey the material P in a vertical direction y towards the liquid conduit  411 . 
     Both the shear rotor  60  and the impeller  50  are rotatable arranged about a geometrical, central axis A 1  and are connected to a horizontally arranged drive axle  31  that in turn is connected to a drive unit  3 . The central axis A 1  extends in a horizontal direction and defines a radial direction R. The drive unit  3  may have the form of e.g. a conventional, electrical motor. The pump and mixing unit  2  has a conventional gasket  33  arranged about the drive axle  31  at a location where it extends into the pump and mixing unit  2 , such that leakage from the pump and mixing unit  2  is prevented. When the drive unit  3  is operated the drive axle  31 , the shear rotor  60  and the impeller  50  rotates with the same rotational speed. A cover  32  is arranged about the drive axle  31  for preventing that the drive axle  31  is touched by e.g. an operator. The cover  32  also acts as a support that connects the pump and mixing unit  2  to the drive unit  3 . 
     A hopper  5  is connected to the inlet  402  of the material conduit  412  for feeding the material P into the material conduit  412 . A table  51  may be arranged adjacent the hopper  5  for e.g. more convenient handling material P that shall be fed into the hopper  5 . Each of the drive axle  31 , the drive unit  3  and the hopper  5  may be seen as comprised in the apparatus  1  for mixing and pumping. 
     A first manual valve  505  is arranged between the material conduit  412  and the hopper  5 , which allows an operator to stop a flow of material P into the material conduit  412 . A second manual valve  506  is connected to the inlet  401  of the liquid conduit  411 . Typically, liquid L is introduced into the piping arrangement  4  by connecting a source of liquid (not shown) to the second manual valve  506 . The second manual valve  506  allows an operator to e.g. stop a flow of liquid L into the liquid conduit  411 , or to prevent that liquid L flows out from the piping arrangement  4  when a source of liquid is disconnected from the second manual valve  506 . 
     With reference to  FIG. 3  an enlarged, cross-sectional view the apparatus  1  is illustrated. The pump and mixing unit  2  comprise the housing  220 , which in turn comprises, as seen in a horizontal direction x, a front section  221 , a first intermediate section  222 , a second intermediate section  223 , an impeller section  224  and a backsection  225 . Of course, two or more of these sections  221 - 225  may be embodied as one, unitary section. The sections  221 - 225  are attached to each other, e.g. by welding them together or by using conventional bolts that extend from the frontsection  221  to the backsection  225  and hold the sections  221 - 225  together. In the illustrated embodiment, the impeller section  224  comprises the outlet  202  for the process mixture M 1  and the further outlet  203  for the return mixture M 2 . 
     The further outlet  203  is embodied as an opening in the impeller section  224 . The impeller section  224  comprises a corresponding opening for the outlet  202 . The opening for the outlet  202  may not bee seen in  FIG. 3  since it is arranged on the “backside” the cross-sectional view of  FIG. 3 . However, it is possible to arrange the opening for the outlet  202  directly opposite the further outlet  203  or at some other location in the impeller section  224 . 
     The sections  221 - 225  form an interior space of the pump and mixing unit  2  and are, apart from the outlet  202  and the further outlet  203 , symmetrical about the central axis A 1 . The stator  70 , the shear rotor  60  and the impeller  50  are arranged in the interior space formed by the sections  221 - 225  and are symmetrically arranged about the central axis A 1 . 
     With further reference to  FIGS. 5 and 6  the stator  70  is shown in detail. As may be seen, the stator  70  has the shape of a circular collar with an inner diameter D 1 . A number of openings  72  are evenly arranged in the stator  70  and the stator  70  is attached to a frontplate  226  of the frontsection  221 . The openings  72  are embodied as elongated openings in the stator  70 , but may also have the form of slits or cut-outs in the stator  70 , typically on the side of the stator  70  that faces away from the frontsection  221 . 
     With further reference to  FIGS. 7 and 8  the shear rotor  60  is shown in detail. The shear rotor  60  comprises a circular plate  63  with a centre hole  66  into which the drive axle  31  extends (see  FIG. 2 ). The shear rotor  60  may be locked to the drive axle  31  by e.g. a small key (not shown) or by any other suitable means. At a periphery  61  of the plate  63  a number of teeth  62  are arranged. When the shear rotor  60  is arranged in the pump and mixing unit  2 , the teeth  62  extends from the plate  63  in a direction towards the inlet  201 , parallel to the central axis A 1 . As may be seen from the figures, the teeth  62  are separated by openings  65 . The openings  65  have the form of interspaces  65  between the teeth  62 . The shear rotor  60  is symmetrically arranged about the central axis A 1  and the plate  63  of the shear rotor has a diameter D 2  that is smaller then the inner diameter D 1  of the stator  70 . The teeth  62  of the shear rotor  60  are, as seen in the radial direction R, aligned with the stator  70  (see  FIG. 3 ). Thus, an annular clearance  71  is formed between the stator  70  and the shear rotor  60 , which allows the shear rotor  60  to rotate and liquid to pass through the interspaces  65 , past the annular clearance  71  and through the openings  72  in the stator  70 . When liquid L and material P pass between the interspaces  65  of the shear rotor  60  and the openings  72  of the stator  70  shear forces act on the material P in the liquid L, which effectively provides adequate mixing of the liquid L and material P. When the liquid L and the material P has passed the annular clearance  71  and the stator  70  they are conveyed through the pump and mixing unit  2  as a mixture M 1 , M 2 . 
     Instead of arranging teeth  62  that are separated by interspaces  65 , a collar with openings (e.g. similar to the stator) may be arranged on the plate  63  of the shear rotor  60 . However, the outer diameter D 2  of the shear rotor  60  must always be smaller then the inner diameter D 1  of the stator  70 , such that the annular clearance  71  has a radial extension of that may be calculated as D 1 −D 2 . 
     With further reference to  FIGS. 9 and 10  the impeller  50  is shown in detail. The impeller  50  comprises a plate  53  with a number of vanes  52 . On the vanes  52  curved ridges  55  are arranged, such that each vane has a respective curved ridge. The impeller  50  is symmetrical about a centre hole  54  through which the drive axle  31  extends (see  FIG. 2 ). The impeller  50  may be locked to the drive axle  31  by e.g. a small key (not shown) or by any other suitable means. When the impeller  50  is arranged in the pump and mixing unit  2 , the curved ridges  55  protrudes from the plate  53  an in a direction towards the inlet  201 . The impeller  50  is, as seen in the direction towards the inlet  201 , arranged behind the shear rotor  60  and stator  70 , i.e. the shear rotor  60  and the stator  70  are arranged intermediate the inlet  201  and the impeller  50 . The impeller  50  is symmetrical about the central axis A 1  and performs the same function as an impeller in a conventional centrifugal pump. 
     Turning back to  FIG. 3 , the housing  220  of the pump and mixing unit  2  comprises a first peripheral chamber  231  that is, as seen in the radial direction R, located outside the stator  70 . The first intermediate section  222  has basically the form of a ring and allows fluid to flow from the first peripheral, annular chamber  231  and in a direction towards the central axis A 1  and to an annular passage  232  in the impeller section  224 . The passage  232  is located near to the central axis A 1  such that the mixture M 1 , M 2  that passes the passage  232  comes into contact with the curved ridges  55  of the impeller  50  at a location close to the centre hole  54  of the impeller  50 . Then, by rotating the impeller  50 , a flow of mixture M 1 , M 2  is generated since mixture M 1 , M 2  entering the impeller  50  near to the central axis A 1  is accelerated by the impeller  50  in an outward, radial direction R towards a second peripheral, annular chamber  233  that is formed by the impeller section  224  and backsection  225 . 
     Since the outlet  202  and the further outlet  203  are located at the periphery of the impeller section  224 , mixture M 1 , M 2  that is accelerated by the impeller  50  exits the pump and mixing unit  2  at the outlets  202 ,  203 , where a process part of the mixture M 1 , M 2  is expelled from the outlet  202  as the process mixture M 1 , and where a return part of the mixture M 1 , M 2  is expelled from the further outlet  203  as the return mixture M 2 . 
     The return mixture M 2  is expelled into an inlet  405  of the return conduit  413  and is conveyed, by the return conduit  413 , to an outlet  406  of the return conduit  413 . The outlet  406  of the return conduit  413  is connected to the material conduit  412 . In detail, the material conduit  412  comprises an outer conduit  425  and an inner conduit  421 . The return conduit  413  is connected to the outer conduit  425  and the outer conduit  425  is at a first of its ends connected to the liquid conduit  411 . Specifically, the outer conduit  425  is joined to the liquid conduit  411  at the joining section  404 , at the upper side  426  of the liquid conduit  411 . At a second end of the outer conduit  425  the inner conduit  421  is inserted. The inner conduit  421  is attached to the outer conduit  425  by a threaded ring  427  that presses a flange  429  of the inner conduit  421  towards a threaded flange  428  of the outer conduit  425 , when the threaded ring  427  is screwed onto the threaded flange  428 . 
     The inner conduit  421  has an outer circumference that is smaller than an inner circumference of the outer conduit  425 . Thus, an annular chamber  422  is formed between the outer conduit  425  and inner conduit  421 , and the return mixture M 2  transported by the return conduit  413  is introduced into the chamber  422 . The chamber  422  has an opening  424  in form of an annular slit that is located at an outlet  423  of the inner conduit  421 . Thus, when the return mixture M 2  is continuously fed to the chamber  422 , the return mixture M 2  passes through the chamber  422  and exits the chamber  422  at the opening  424 . Material P is introduced into the inlet  402  of the piping arrangement  4 , which inlet  402  is an inlet of the inner conduit  421 . Hence, when material P passes into the inner conduit  421  and further to the outlet  423  of the inner conduit  421 , the material P meets the return mixture M 2  where the opening  424  of the chamber  422  meets the outlet  423  of the inner conduit  421 . As a result a kind of venturi effect is obtained, where the return mixture M 2  assists in feeding the material P into the liquid conduit  411 . This is advantageous in that there is a reduced risk of clogging of material P. 
     With reference to  FIG. 10  an alternative embodiment of the apparatus  1  is illustrated. In this embodiment the apparatus  1  is mounted on a frame  80  that comprises a number of wheels  85 . The apparatus  1 , which thus comprises the frame  80  and wheels  85 , may then easily be transported and used at a location where it is needed. 
     The frame  80  comprises two rectangular frames that are made of vertical bars  81  and horizontal bars  82 . These frames form two longsides of the frame  80  and are at their lower ends held together by a first set of horizontal bars  83  and a second set of horizontal bars  84 . The drive unit  3  is mounted on the second set of horizontal bars  84  and the cover  32  that is attached to the drive unit  3  supports the pump and mixing unit  2 . The hopper  5  and the table  51  are supported by upper sides of the two rectangular frames formed by the vertical and horizontal bars  81 ,  82 . The hopper  5  and the table  51  typically assist in holding the frame  80  together, e.g. by being welded or bolted to the frame  80 . A control unit  89  is mounted on the frame  80  and the first set of horizontal bars  83 . The control unit  89  is connected to the drive unit  3  and is arranged to control at least activation, deactivation and a rotational speed of the drive unit  3 . 
     As may be seen from the figures, the return conduit  413  is configured to return the return mixture M 2  to the inlet  201  without passing the return mixture M 2  via any other further pumping equipment. 
     During operation of the apparatus  1  a source of liquid is connected to the second manual valve  506 , material is fed into the hopper  5  and further past the first manual valve  505 , and a receptacle or mixture-conveying piping is connected to the outlet  202 . Any suitable source of liquid and receptacle or mixture-conveying piping may be used as long as they may convey liquid to the apparatus  1  respectively receive a mixture from the apparatus  1 . However, additional mixing or pumping equipment is not required for achieving adequate mixing and pumping or for ensuring that liquid and material are efficiently fed by the apparatus  1 . 
     Mixing and pumping is performed by the apparatus  1  alone when the drive unit  3  is activated and effects a rotation of the drive axle  31 , the impeller  50  and the shear rotor  60 . The rotation of the impeller  50  generates a suction at the inlet  201  such that the liquid L and the material P is “pulled” into the inlet  201 . The liquid L and material P is then pulled further past the shear rotor  60 , past the annular clearance  71  and past the stator  70  which effects mixing of the liquid L and material P, such that the liquid L and material P becomes mixed and forms a mixture M 1 , M 2 . The mixture M 1 , M 2  is then pulled further towards the impeller  50  where it is accelerated towards the outlet  202  and the further outlet  203 . The part of the mixture M 1  that exits via the outlet  202  is “pushed” or conveyed to a suitable receptacle or mixture-conveying piping, and is referred to as the process mixture M 1 . The part of the mixture M 2  that exits via the further outlet  203  is, via the return conduit  413 , “pushed” or conveyed to the chamber  422 , and is referred to as the return mixture M 2 . The return mixture M 2  assists in pulling the material P out from the inner conduit  421  and thereafter assists in pushing the material P as well as liquid L in the liquid conduit  411  towards the inlet  201 . The pushing or pulling of liquid and material may also be referred to as “feeding” the liquid and material. 
     For obtaining a suitable pushing or pulling effect on the liquid L and the material P up to one third of the mixture M 1 , M 2  may be returned as the return mixture M 2 . Thus, at least two thirds of the mixture M 1 , M 2  is advantageously fed as the process mixture M 1 . Other embodiments of the apparatus  1  may require different proportions between the return mixture M 2  and process mixture M 1 , and may be empirically determined for obtaining adequate feeding and mixing. 
     During operation liquid L is continuously fed into the liquid conduit  411  and material P is continuously fed into the hopper  5 . As a result, material is continuously mixed with liquid that flows in a steady stream, which may referred to as so called inline mixing. 
     With reference to  FIG. 11  a schematic drawing of the described apparatus  1  is shown. A second embodiment of the apparatus  1  is schematically illustrated by  FIG. 12 . The second embodiment differs from the previous one in that the further outlet  203  is omitted and in that the return conduit  413 ′ is connected to the outlet  202  via a connection point that is located downstream the outlet  202 . The connection point may be embodied as conventional flow divider, such that a predetermined part M 2  of the mixture enters the return conduit  413 ′ where it is conveyed as the return mixture M 2 , while a remaining part M 1  of the mixture is conveyed by a conduit  419  as the process mixture M 1 . In this embodiment the return conduit  413 ′ may be seen as comprising a first branch  413 ′ and a second branch  419 , where the first branch  413 ′ conveys a part M 2  of the mixture in a direction towards the inlet  201 , while the second branch  419  conveys a remaining part M 1  of the mixture in another direction. 
     With reference to  FIG. 13  a third embodiment of an apparatus  1  for pumping and mixing is shown. The third embodiment differs from the embodiment of  FIGS. 1-3  in that a return conduit  413 ″ is connected from the further outlet  203  and directly to the liquid conduit  411 . This allows the return mixture M 2  to push the liquid L in a direction towards the pump and mixing unit  2 . This is, in comparison to not returning any return mixture M 2  to the inlet  201 , advantageous in that the feeding of the liquid L is improved. Improved feeding of liquid L improves in turn feeding of material P towards the pump and mixing unit  2 , since the liquid L draws the material P. 
     From the description above follows that, although various embodiments of the invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims. In particular, the return conduit may be connected in several ways to the pump and mixing unit, as long as it somehow returns the return mixture to the inlet of the pump and mixing unit.