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.
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.
A device which achieves this object is set out in claim 1. Preferred developments are set out in the remaining claims.
The invention will be described hereinbelow with the aid of preferred embodiments and with reference to drawings, wherein:
As can be seen from
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
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
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
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
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
The cavity 50 then passes through the region of the cavities designated by the reference numerals 52 and 53 in
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
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
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.
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.
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.
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
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
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
If the dispersion is produced in a single pass, an arrangement as shown in the hydraulic diagram according to
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:
Number | Date | Country | Kind |
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04405801 | Dec 2004 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/CH2005/000579 | 10/5/2005 | WO | 00 | 11/30/2007 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2006/066421 | 6/29/2006 | WO | A |
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