Abstract:
The disclosed device disperses a substance in a liquid. The device has at least one dispersing chamber, which has at least one liquid inlet, at least one substance inlet, and at least one outlet. At least one driving means is placed inside the dispersing chamber while serving to set the liquid inside the dispersing chamber in motion so that at least one cavity with varying volume forms in the liquid for drawing in the substance through the substance inlet and forcing the substance made wet with liquid through the outlet.

Description:
The present application is a National Phase Application of PCT/CH2005/000579 filed on Oct. 5, 2005, which claims priority to European Patent Application 04405801.4 filed on Dec. 23, 2004, both aforementioned applications being incorporated herein by reference in their entireties. 
     BACKGROUND 
     The present invention relates to a device for dispersing a substance in a liquid. 
     Devices of this type serve to form a dispersion by finely distributing the substance in a liquid. The substance can be present as a solid, liquid or gaseous phase or also as a mixture of different phases. Wetting and homogeneously distributing the substance during the mixing process is often problematic. If the substance is a powder, there is also the risk of dust comprising unwetted powder undesirably forming in the environment. 
     It is known to supply liquid and substance to a dispersing chamber and to work them intensively by means of a dispersing tool in order to achieve fine distribution of the substance (see e.g. patent specifications EP-B1-436 462 and EP-B1-648 537 by the same applicant or patent specification EP-B1-587 714). However, it has been shown that wetting the substance with liquid is problematic and can result in undesired inhomogeneities in the dispersion. If, for example, a powdered substance is supplied, lumps can form in the mixing zone, i.e. the zone in which the substance comes into contact with the liquid, and these lumps clog the substance supply line or impede homogeneous distribution of the substance in the liquid. The known dispersing devices also have the disadvantage that the suction capacity is dependent upon the liquid throughput and the pressure at the outlet, with the result that the suction capacity may be too low to be able to suck in and wet a sufficient quantity of the substance to be dispersed. 
     Devices for producing a dispersion of gas and liquid are known from patent specifications U.S. Pat. No. 3,119,339 and U.S. Pat. No. 3,932,302. These devices comprise an eccentrically arranged gearwheel with internal teeth which mesh with a pinion, and a crescent-shaped insert. Devices of this type have inter alia the disadvantage that they are unsuitable for the dispersal of powdered substances. As the latter are virtually incompressible, the meshing of the internal teeth with the pinion would generate forces so great that the device would be damaged, e.g. the walls of the teeth or the pinion or possibly the bearings would be damaged. It is also disadvantageous that the throughput and therefore the dispersion volume producible per unit time are relatively low. 
     Devices which have radially displaceable vanes for producing a variable working volume are known from patent specifications U.S. Pat. No. 3,936,246 and U.S. Pat. No. 6,616,325 B1. This has the disadvantage that narrow gaps are formed, which can cause accumulation of the substance to be dispersed. Especially if the substance is a powder, this accumulation can lead to the vanes jamming in the guides and, ultimately, to failure of the device. 
     A device which has a cylinder rotating in a tube for the production of an emulsion is known from patent application US-A1-2002/0089074. The device has inter alia the disadvantage that it is poorly suited to the dispersal of powdered substances because pumping means of complex design have to be provided for the introduction of these substances. 
     Starting from this prior art, an object of the present invention is to propose a device which allows a substance to be sucked in and distributed in a liquid as homogeneously as possible in a simplified and improved manner. 
     SUMMARY 
     A device which achieves this object is set out in claim  1 . Preferred developments are set out in the remaining claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described hereinbelow with the aid of preferred embodiments and with reference to drawings, wherein: 
         FIG. 1  shows a part-sectional side view of the device according to the invention; 
         FIG. 2  shows the device according to  FIG. 1  in the section plane II-II; 
         FIG. 3  shows the device according to  FIG. 1  in the section plane III-III; 
         FIG. 4  shows a hydraulic diagram of the device according to the invention; 
         FIG. 5  shows another variant of a hydraulic diagram of the device according to the invention; 
         FIG. 6  shows a part-sectional side view of a further embodiment of the device according to the invention; 
         FIG. 7  shows a hydraulic diagram of the device according to  FIG. 6 ; 
         FIG. 8  shows another variant of a hydraulic diagram of the device according to  FIG. 6 ; 
         FIG. 9  shows a side view of a further embodiment of the driving means for the device according to the invention; 
         FIG. 10  shows a perspective view of the driving means according to  FIG. 9 ; and 
         FIG. 11  shows another variant of the openings  30 ′,  35 ′ and  40 ′ in the device according to  FIG. 1  in the section plane II-II. 
     
    
    
     As can be seen from  FIGS. 1 and 2 , the dispersing device comprises a dispersing chamber  10  which is preferably bounded laterally by a cylindrical wall  11 . The dispersing chamber  10  contains a driving means  12 , by means of which liquid can be set into motion. 
     DETAILED DESCRIPTION 
     The driving means is preferably formed as an impeller  12 . The latter comprises a hub  13  which is rotatable about the rotation axis  16  and on which a plurality of vanes  14  is mounted. The impeller  12  is eccentrically arranged in the dispersing chamber  10  so that the rotation axis  16  lies adjacent to the centre  18  of the dispersing chamber  10 . Owing to this arrangement, the distance between the base  15  of a vane  14  and the wall  11  of the dispersing chamber  10  changes recurrently between a minimum value and a maximum value during rotation of the impeller  12 . The axis passing through the points  16  and  18  extends substantially in the neutral region, where neither the suction effect generated in the dispersing chamber  10  nor the pumping effect predominates. 
     The impeller  12  is fixed to a shaft  19  which can be set into rotation by means of a drive (not shown). In the embodiment shown in  FIG. 1 , the shaft  19  is arranged vertically. It is also possible to place the dispersing device in a different position, for example so that the shaft  19  is arranged horizontally. 
     The dispersing chamber  10  is provided at the top with a cover  29  which contains a substance inlet  30  for introducing a substance into the dispersing chamber  10  and an outlet  35  for discharging the product from the dispersing chamber  10 . The substance inlet  30  and the outlet  35  are each connected to a feed line  31  and  36  respectively. If, as mentioned hereinabove, the shaft  19  is arranged horizontally, it is advantageous to dispose the substance inlet  30  at a higher level than the outlet  35 . 
     As can be seen from  FIG. 2 , the substance inlet  30  and the outlet  35  are substantially sickle-shaped so that the distance between the edges  32  and  33  of the substance inlet  30  increases in the direction of rotation  17  and the distance between the edges  37  and  38  of the outlet  35  decreases in the direction of rotation  17 . The inner edge  32  of the substance inlet  30  and the inner edge  37  of the outlet  35  lie approximately on a circle, the centre of which lies on the rotation axis  16  of the impeller  12 . The outer edge  38  of the outlet  35  lies on a circle  39  located substantially concentrically with the wall  11  of the dispersing chamber  10 . The outer edge  33  of the substance inlet  30  is likewise formed in a substantially circular manner and is arranged so that it lies within the circle  39 . During operations this arrangement counteracts the risk of liquid ingressing from the dispersing chamber  10  into the substance inlet  30  and the risk of the supplied substance forming lumps. 
     If the feed line  31  leading to the substance inlet  30  has a cylindrical shape, the transition of the feedline  31  to the sickle shape of the substance inlet  30  can, if necessary, be optimised so that liquid cannot spray into the substance inlet  30  from the dispersing chamber  10 , even if turbulence is high. For this purpose, the transition is not abrupt in cross-section, but e.g. in the form of a ramp so that, when seen in the flow direction, the middle part of the substance inlet lies higher than its two ends. 
     As  FIG. 1  also shows, the bottom of the dispersing chamber  10  contains a disc  41  with a liquid inlet  40  for the introduction of liquid into the dispersing chamber  10 . As can be seen from  FIG. 2 , the liquid inlet  40  is substantially arranged between the substance inlet  30  and the outlet  35 , wherein the substance inlet  30  is arranged upstream of the liquid inlet  40  and the latter is arranged upstream of the outlet  35  when seen in the direction of rotation  17 . In the example shown in  FIG. 2 , the liquid inlet  40  has a substantially circular shape. For the sake of greater clarity, in  FIG. 1  the position of the liquid inlet  40  is shown rotated through 90 degrees in relation to the position shown in  FIG. 2 . 
     The disc  41  is preferably rotatably arranged so that the position of the liquid inlet  40  is variable in relation to the neutral axis passing through the points  16  and  18 . The dispersing device also comprises pumping means  61  for conveying liquid through the liquid inlet  40  into the dispersing chamber  10 . 
     The dispersing device described thus far functions as follows: 
     The impeller  12  is set into rotation in the direction  17  indicated in  FIG. 2  and liquid is pumped through the liquid inlet  40  into the dispersing chamber  10  by the pumping means  61 . The liquid is also set into rotation by the rotating impeller  12  and is driven outwards by the centrifugal force so that it is lifted from the hub  13  and forms a rotating liquid ring  47  which is substantially concentric with the wall  11  of the dispersing chamber  10 . In FIG.  2 , the transition between the ring  47  of rotating liquid and the liquid-reduced inner region is indicated by a dot-dash line  39 . The position of this transition  39  and therefore the thickness of the liquid ring  47  is substantially determined by the position of the outer edge  38  of the outlet  35  because—as explained hereinbelow—liquid located in the inner region is conveyed through the outlet  35  by the pumping effect. 
     Between the base  15  of adjacent vanes  14  and the liquid ring  47  is formed a respective cavity  50 - 57 , the volume of which is recurrently increased and decreased by the rotation of the impeller  12 , there by generating a pumping effect. If, for example, the cavity provided with the reference numeral  50  in  FIG. 2  is taken as a starting point, first of all its volume increases when it moves towards the position of the cavity  51 . This volume increase produces a decrease in pressure, which has the effect that substance is sucked through the substance inlet  30  into the dispersing chamber  10  and, lastly, wetted and mixed with the liquid. The generated suction effect ensures that the substance does not come into contact with the liquid while still in the substance inlet  30  and does not clog the substance inlet  30  by forming lumps. 
     The cavity  50  then passes through the region of the cavities designated by the reference numerals  52  and  53  in  FIG. 2 , where its volume barely changes, so that neither a suction effect nor a pumping effect is generated. The liquid inlet  40  is arranged in this neutral zone. The cavity  50  subsequently moves towards the position of the cavity  54  so that its volume is reduced again and the product consisting of liquid and substance contained therein is expelled through the outlet  35 . The cavity  50  then passes through a further neutral zone between the pressure side and the suction side in the region of the cavities  55  and  56 . 
     The dispersing chamber  10  is designed so that the flow conditions are usually turbulent and fine distribution of the substance in the liquid is favoured. 
     The mixing ratio of substance and liquid can be adjusted by rotating the disc  41 . The position of the liquid inlet  40  is thus displaced either more towards the pressure side or more towards the suction side so that the amount of liquid flowing into the dispersing chamber  10  per unit time is regulated accordingly. 
     By rotation of the driving means  12 , the substance in the dispersing chamber  10  is intensively wetted. Consequently, the risk of lumps forming is virtually eliminated, especially in the case of powdered substances. This is also effectively avoided by the fact that the dispersing chamber  10  can be designed so as to be free of narrow apertures or other narrow gaps. In particular, the vanes  14  do not need to be radially displaceably arranged, but can be fixedly connected to the hub  13 . Furthermore, a high vacuum with a simultaneous high suction capacity is generated during operation and this is substantially independent of the liquid throughput and, to a certain extent, also independent of the pressure at the outlet  35 . In this way, dust-free incorporation into the liquid is ensured, especially in the case of powdered substances. It has been shown that the generatable suction capacity is sufficiently high that heavy powders, e.g. metal-containing powders, can also be sucked in. 
     The cavities produced are liquid-reduced regions which inter alia are bounded by the liquid itself (cf. the dot-dash line  39  in  FIG. 2 ). Therefore, there is no occurrence of sealing or lubrication problems such as those which arise in the known dispersing devices in which, in order to produce a variable working volume, a gearwheel meshes with a pinion. 
     The suction and pumping effect of the dispersing device described here is produced in much the same way as in water-ring pumps. Unlike these pumps, however, the dispersing device used here has the function of sucking in, wetting and dispersing a substance in the liquid in an optimum manner. For this purpose, the dispersing device has a liquid inlet  40  so that the liquid in the ring is continually replaced during operation. In contrast, water-ring pumps contain water as a working fluid, which remains permanently in the working chamber. 
     In a first development of the dispersing device, the outlet  35  is fluidly connected to the liquid inlet  40 . This allows the liquid to be conducted repeatedly through the dispersing chamber  10 . By means of this recirculation, it is possible e.g. to provide a gradual increase in the concentration of substance in the liquid and/or to obtain a particularly homogeneous distribution of the substance in the liquid. In the latter case, the substance inlet  30  is advantageously closed, e.g. by means of a valve, and the dispersion is conducted repeatedly through the dispersing chamber  10 . 
     In a second development of the dispersing device, which is also shown in  FIG. 1 , a second dispersing chamber  60  is provided. This is fluidly connected via the liquid inlet  40  to the first dispersing chamber  10  and, as shown in  FIG. 1 , is located underneath the latter. In the second dispersing chamber  60  is arranged at least one dispersing tool  61  which serves as a pumping means and as a working means for distributing the substance particularly finely in the liquid. 
       FIG. 3  shows an example of a dispersing tool  61  with two toothed rings  62   a  and  62   b  which form the rotor  62 , and two toothed rings  63   a  and  63   b  which form the stator  63 . The toothed rings  62   a ,  62   b ,  63   a ,  63   b  have slots  64 , through which liquid and substance contained therein can pass. The number and formation of the toothed rings  62   a ,  62   b ,  63   a ,  63   b  are selected according to the intended application. The inner region of the dispersing tool  61  is provided with a passage  69  which is fluidly connected to a supply chamber  70 . As shown in  FIG. 1 , this supply chamber  70  is located underneath the dispersing tool  61  and comprises an inlet  71 . If the dispersion is to be recirculated; the outlet  35  of the first dispersing chamber  10  is connected to the inlet  71 . 
     When the dispersing device is set into operation, liquid is first sucked out of the supply chamber  70  by means of the dispersing tool  61  and pumped via the liquid inlet  40  into the first dispersing chamber  10 , in which—as already described hereinabove—a liquid ring is formed. Substance is sucked in through the substance inlet  30  and dispersed in the liquid. The resulting dispersion is conducted back into the supply chamber  70  via the outlet  35  and the inlet  71 . On passing through the slots  64 , the liquid and the substance contained therein are accordingly worked by the rotor  62  and the stator  63  to produce improved and homogenised distribution of the substance. The liquid circulates repeatedly between the first and second dispersing chamber  10 ,  60  until the desired substance concentration has been reached and/or until a sufficiently homogeneous dispersion has been obtained. 
     The provision of two dispersing chambers  10  and  60  has the advantage that the processes of wetting the substance with liquid and working with the dispersing tool  61  are carried out in separate chambers and, therefore, the two processes do not affect one another. In this way, particularly homogeneous dispersions can be produced without the problems of lump formation and/or undesired dust formation in the case of powdered substances. 
       FIG. 4  shows a third development of the dispersing device in schematic form. The rectangle with the reference numeral  80  schematically represents the dispersing unit comprising the first dispersing chamber  10  and the driving means  12  and—if provided—the second dispersing chamber  60  and the dispersing tool  61 . Accordingly, the reference numeral  81  designates the liquid inlet  40  if a second dispersing chamber  60  is not provided or the inlet  71  if it is provided. The supply container  83  holding the substance to be dispersed is connected by a line  84  to the substance inlet  30 . A container  86 , which serves to separate gas and/or non-dispersed substance, is arranged in the recirculation line  85  connecting the outlet  35  of the dispersing unit  80  to the inlet  81 . A return line  87 , which connects the separating container  86  to the supply container  83  in order to feed back the separated gas or the separated substance, can optionally be provided, as indicated by the broken lines in  FIG. 4 . A supply line  88  connected to the inlet  81  serves to supply the liquid. A discharge line  89 , which joins the recirculation line  85 , serves to discharge the dispersion produced from liquid and substance. The lines  84 ,  88  and  89  are provided in a known manner with valves  90 ,  91  and  92  in order to be able to open and close the respective passage. 
     If a dispersing tool  61  is provided, measures have to be taken so that as little air as possible is contained in the liquid to be worked. Too large a proportion of air can result in no more liquid being conveyed through the slots  64  in the toothed rings and, consequently, operation being interrupted. If, in addition to the substance, the liquid leaving the outlet  35  also contains ambient air, the latter can be separated in the separating container  86  and reliable operation of the dispersing tool  61  can be ensured. 
     It is also possible to form the dispersing device as a closed system so that gas exchange with the environment is prevented. In this case, the supply container  83  and the separating container  86  have a closed formation. 
     The use of a closed system is advantageous e.g. when the substance to be dispersed is a very fine powder and undesired powder deposits in the environment are to be avoided. If the powder is difficult to disperse and/or very fine, the air in the separating container  86  may still contain non-dispersed powder. This can be fed back to the supply container via the return line  87 . 
     The use of a closed system is also advantageous when the dispersal of powdered substance entails the risk of dust explosions. In this case, the air in the dispersing device, in particular in the supply container  83  and the separating container  86 , is replaced by an inert gas, for example nitrogen. During operation, the inert gas is separated in the separating container  86  and fed back to the supply container  83  via the return line  87 . 
       FIG. 5  shows a variant of the dispersing device for batch operation. In  FIGS. 4 and 5 , like parts are provided with like reference numerals. The rectangle with the reference numeral  82  schematically represents a container in which the liquid is held. If the separation of gas and/or non-dispersed substance is not necessary, the separating container  86  can also be omitted. 
     To incorporate the substance into the liquid, the container is connected to the inlet  81  via the line  88 ′ and to the outlet  35  via the lines  89 ′ and  85 ′. The liquid is conducted repeatedly through the dispersing unit  80 , in which the substance from the supply container  83  is added, and through the container  82  until the desired substance concentration and homogeneity has been reached. Lastly, the dispersion thus produced is collected in the container  82 , and the latter is separated from the dispersing unit  80 . Defined batches of dispersions can thus be produced in a simple manner. 
     Depending upon the intended application, recirculation of the liquid or the dispersion through the dispersing unit  80  is not absolutely necessary. The dispersing unit  80  can e.g. be arranged in a processing line in which liquid is continuously fed through the inlet  81  and substance is continuously fed through the inlet  30  into the dispersing unit  80  and liquid and substance are mixed together, and the resulting dispersion is supplied for further processing via the outlet  35 . 
       FIG. 6  shows a further embodiment of the dispersing device, which essentially differs from the embodiment shown in  FIG. 1  in that the liquid inlet  40 ″ and the outlet  35 ″ have been interchanged and in that the dispersing tool  61 ′ is arranged so that a pumping effect is producible from the outlet  35 ″ to the outlet  71 ′. 
     The liquid inlet  40 ″ is disposed in the cover  29  and is located in the neutral zone or on the pressure side, i.e. in the region of the neutral axis extending through the points  16  and  18  shown in  FIG. 2  or to the left thereof. The liquid inlet  40 ″ can also be arranged in the wall  11  of the dispersing chamber  10  so that it opens laterally into the dispersing chamber  10 . 
     The outlet  35 ″ is an internal opening located between the first dispersing chamber  10  and the chamber  70 ′. Its shape and radial position are selected as shown in  FIG. 2  for the outlet  35  in the first embodiment. 
     During operation, liquid is conducted through the liquid inlet  40 ″ into the dispersing chamber  10 , where a liquid ring and the cavities are formed so that substance is sucked in through the substance inlet  30  and dispersed in the liquid. The dispersion is pumped via the outlet  35 ″ and the chamber  70 ′ into the second dispersing chamber  60 ′, where it is worked by the dispersing tool  61 ′ and, lastly, discharged via the outlet  71 ′. Fine dispersal in the second dispersing chamber  60 ′ therefore takes place after wetting in the first dispersing chamber  10  so that the dispersion is producible in a single pass. 
     However, where expedient, recirculation can also be provided, as shown in  FIG. 7 . To enable liquid to pass through the liquid inlet  40 ″ into the dispersing chamber  10 , pumping means  94  are necessary, for example in the form of a feed pump or by providing different liquid levels in order to generate a pressure difference. The reference numeral  80 ′ schematically represents the dispersing unit comprising the first dispersing chamber  10  and the driving means  12  and—if provided—the second dispersing chamber  60 ′ and the dispersing tool  61 ′. The reference numeral  95  designates the outlet  35 ″ if a second dispersing chamber  60 ′ is not provided or the outlet  71 ′ if it is provided. The other reference numerals have the same meaning as in the diagram according to  FIG. 4 . 
     If the dispersion is produced in a single pass, an arrangement as shown in the hydraulic diagram according to  FIG. 8  is sufficient. 
     The dispersing device according to the invention can be used in diverse ways for dispersing a substance in a liquid. The substance can be present as a solid, liquid or gaseous phase or as a mixture of different phases. The dispersing device according to the invention is especially suitable for the dispersal of free-flowing solid substances, e.g. powders, dyestuffs, fillers, substances from the foodstuffs industry and/or insoluble substances generally, e.g. poorly wettable powder such as metallic powder. 
     Starting from the above description, numerous modifications are available to the person skilled in the art without departing from the scope of the invention as defined by the claims. For example, the following modifications or broadenings are possible:
         The formation of the impeller is adapted to the flow to be generated in the dispersing chamber.  FIGS. 9 and 10  show a variant of the impeller  12 ′ in which the vanes  93  are arranged obliquely to the rotation axis. This arrangement permits the generation of particularly turbulent flows in the dispersing chamber  10  and thereby favours mixing of the substance in the liquid.   The shape of the openings  30 ,  35  and  40  does not need to be as precise as shown in  FIG. 2 .  FIG. 11  shows a variant in which the substance inlet  30 ′ and the outlet  35 ′ are sickle-shaped, wherein the respective front edge  34 ,  44  is substantially straight. The liquid inlet  40 ′ is substantially square.   It is also possible to provide a plurality of substance inlets  30 ,  30 ′, outlets  35 ,  35 ′,  35 ″, and/or liquid inlets  40 ,  40 ′,  40 ″, which are arranged in a suitable manner in the zones of increased pressure or decreased pressure or in the neutral zone.   Instead of an eccentric arrangement of the impeller  12 ,  12 ′, it is also possible to form the wall  11  elliptically and to arrange the impeller  12 ,  12 ′ in the middle. This formation of the dispersing chamber  10  results in four neutral zones, in which neither a suction effect nor a pumping effect is produced, and two zones each of increased pressure and decreased pressure.   The wall  11  of the dispersing chamber  10  can be roughened and/or be provided with additional obstacles in the form of depressions and/or projecting elements. In this way, a turbulent flow can also be generated in the vicinity of the wall  11 , thereby favouring liquid exchange within the liquid ring  47 . This is especially advantageous in the case of heavy substances because increased concentration in the outer region of the liquid ring  47  is avoided.   According to requirements, it can be necessary to use a plurality of dispersing tools instead of one dispersing tool  61 ,  61 ′ in order to be able to work the liquid and the substance contained therein in a suitable manner.