WO2003106006A1

WO2003106006A1 - Device and method for continuous mixing of components

Info

Publication number: WO2003106006A1
Application number: PCT/SE2003/000968
Authority: WO
Inventors: Jan-Olov Forslund; Per Stenson; Johan Sjöholm
Original assignee: Land & Sjö Food Technology AB
Priority date: 2002-06-12
Filing date: 2003-06-06
Publication date: 2003-12-24
Also published as: SE522476C2; DK1534415T3; EP1534415B1; SE0201816D0; AU2003239008A1; DE60331075D1; EP1534415A1; SE0201816L; ATE455586T1

Abstract

A device for continuous mixing of at least two components, which device is characterised by mixing chamber (3) for receiving a volume (V) of said components, means (4) for continuously conveying an inflow (P1) of said components to the mixing chamber (3), means (5) for continuously conveying an outflow (P2) of a mixture of said components from the mixing chamber (3) and a stirring means (6). The mixing chamber (3) has a bottom portion (7) which tapers from a polygonal base (8) to a bottom (9), and the stirring means (6) is adapted to generate, in said volume (V) a mass flow (P3) directed to said bottom (9). The present invention also relates to a corresponding method for continuous mixing of components.

Description

DEVICE AND METHOD FOR CONTINUOUS MIXING OF COMPONENTS

Field of the Invention

The present invention generally relates to a device and a method for mixing at least two components and, more specifically, to such a device and such a method for con- tinuously mixing said components.

Background Art

When mixing components, such as liquids and/or powders, the components are usually brought together in a container, such as a tank, followed by stirring.

This conventional mixing method is well suited for batchwise mixing, provided that the components are apt to mix, and results in homogeneous mixing of the components.

However, this method is less well suited for con- tinuous mixing, since in that case homogeneous mixing of the components is difficult to obtain.

Therefore various methods have been developed for continuous mixing of components.

According to one conventional method, a device is used for continuous feeding of a powder component into a continuous flow of a liquid component.

According to another conventional method, two liquid components are brought together and then subject to a turbulent flow. In these prior-art methods, the continuous mixing of the components is almost random, which means that homogeneous mixing of the components cannot be ensured. Difficulties arise in particular if a small flow of one component is to be mixed with a great flow of another component .

Consequently, there is a need for a better method for continuous mixing of components. Summary of the Invention

In view of that stated above, one object of the present invention is to provide a better device and a better method for continuous mixing of components. Another object is that the device and the method should ensure homogeneous mixing of said components.

Preferably, both the device and the method allow continuous mixing of liquid components and/or powder components. The method and the device preferably also allow mixing of liquid components and gas components.

It is also preferable for the device and the method to allow continuous mixing of comparatively great flows of said components .

To achieve these objects as well as other objects mentioned in the description below, a device having the features stated in claim 1 and a method having the features stated in claim 10 are provided according to the present invention. Preferred embodiments of the device are stated in claims 2-9 and preferred embodiments of the method are stated in claims 11 and 12.

Thus, according to the present invention, a device is provided for continuous mixing of at least two components, which device is characterised by a mixing chamber for receiving a volume of said components, means for continuously conveying an inflow of said components to the mixing chamber, means for continuously conveying an outflow of a mixture of said components from the mixing chamber and a stirring means, the mixing chamber having a bottom portion which tapers from a polygonal base to a bottom, and the stirring means being adapted to generate, in said volume, a mass flow directed to said bottom.

This results in a device which allows continuous mixing of two or more components. The outflow of components in mixed condition conveyed from the mixing chamber is a homogeneous mixture of said components. The expression continuous mixing, as used above and hereinafter, refers to simultaneous supply of said components and discharge of said mixture.

The homogeneous mixing is ensured by the manner in which the components are circulated in the mixing chamber, the circulation being provided owing to the geometric design of the bottom portion in combination with the mass flow which is generated by the stirring means and directed to the bottom of the bottom portion. The bottom portion tapers from the polygonal base to the bottom. The mass flow directed to said bottom will thus, when reaching the bottom, be divided into partial flows which are forced upwards in the mixing chamber. Owing to this, it is possible to ensure that the partial flows substantially follow a corner edge each of the bottom portion and then, while being further divided, continue upwards in the mixing chamber until they recombine and sink back down in the volume, under the influence of gravity, for repeated downward feeding in the volume by means of the mass flow generated by the stirring means. Consequently, the design of the bottom portion in combination with said mass flow produces a flow pattern that promotes homogeneous mixing of the components. The flow pattern in the mixing chamber also prevents forming of turbulence or a vortex, which makes it possible to avoid undesirable introduction of air into the volume.

Moreover, the design of the bottom portion prevents the partial volume of the components contained therein from being set in rotation by the stirring means. As a result, the force of the stirring means, depending on the geometric design of the rest of the housing, can be more or less focused on the generation of said mass flow, whereby the energy required to provide said mass flow can be reduced. This in turn means that the inventive device has a high degree of efficiency and thus comparatively low energy consumption in operation. This is a great advantage since little energy is added to the volume, which means that no undesirable rise in temperature occurs .

According to a particularly preferred embodiment of the inventive device, the stirring means is adapted to generate a mass flow which is considerably higher than the inflow and the outflow. This ensures a comparatively high internal turnover of the components in the mixing chamber, which further promotes homogeneous, continuous mixing of the components. In particular, it is possible to ensure homogeneous mixing of an inflow of components even if the inflow comprises a small flow of one of the components and a considerably greater flow of one of the other components. The mass flow is preferably at least ten times greater than said inflow and said outflow. According to yet another preferred embodiment of the inventive device, the mixing chamber is defined by a substantially cubic housing, said bottom portion being formed ^'by a corner portion of said housing. This ensures that the entire volume contained in the mixing chamber cannot be set in rotation by the stirring means, which implies that substantially all the force of the stirring means can be focused on the generation of said mass flow.

The device is preferably adapted for mixing components of which at least one is a liquid component. Alternatively, the device can be adapted for mixing components of which at least one is a powder component.

According to a preferred embodiment of the present invention, the bottom portion of the device has a triangular base. According to another preferred embodiment, the bottom portion of the device has a quadrangular base.

According to still another preferred embodiment, the base of the bottom portion tapers towards a bottom in the form of a point . Furthermore, according to the present invention, a method is provided for continuous mixing of at least two components, comprising the steps of continuously con- veying an inflow of said components to a mixing chamber with a bottom portion which tapers from a polygonal base to a bottom, generating a mass flow, directed to said bottom, in a volume which is contained in said mixing chamber and which is formed by the components conveyed to the mixing chamber, and continuously conveying an outflow of a mixture of said components from the mixing chamber.

Owing to this, an improved method is obtained for continuous mixing of at least two components. By pro- ceeding according to the inventive method, a flow pattern is provided in the mixing chamber such that homogeneous mixing of the components is promoted. More specifically, this is achieved by the step of generating a mass flow towards a bottom of a bottom portion tapering from a polygonal base to said bottom. The mass flow will be divided into partial flows and forced upwards in the mixing chamber, after which they sink back down in the mixing chamber under the influence of gravity.

According to a preferred embodiment of the inventive method, the step of generating a mass flow comprises adjusting of the mass flow so as to make it considerably higher than said inflow and said outflow. This results in an advantageously high internal turnover of the components, which further promotes homogeneous mixing of the components. Advantageously, the mass flow is adjusted so as to be at least ten times greater than said inflow and said outflow.

Preferred embodiments of the present invention will be described below for the purpose of exemplification and with reference to the accompanying drawings.

Brief Description of the Drawings

Fig. 1 is a schematic perspective view of an inventive embodiment of an inventive device. Fig. 2 is a side view of a preferred embodiment of an inventive device. Fig. 3 is a side view of the device in Fig. 2 with some parts cut away.

Fig. 4 is a side view of the device in Fig. 2 in operation with some parts cut away.

Description of Embodiments

Below some embodiments of the present invention will be described for the purpose of exemplification. The same reference numerals are used in the different embodiments when referring to substantially similar parts.

The inventive device will be described for continuous mixing of a liquid component and a powder component. It will be understood, however, that the present invention is not limited to continuous mixing of this combination of components. The invention is also applicable to continuous mixing of more than two components and continuous mixing of, for example, exclusively liquid components. The invention also comprises applications, in which one or more gas components are mixed with one or more liquid components.

In Fig. 1, to which reference is now made, an inventive device 1 for continuous mixing of components, such as a liquid component and a powder component, is schematically illustrated. The device 1 comprises a housing 2 which internally defines a mixing chamber 3 for receiving a volume of said components, means 4 for continuously conveying an inflow of said components to the mixing chamber 3, which means 4 is hereinafter referred to as a supply means 4, means 5 for continuously conveying an outflow of a mixture of said components from the mixing chamber 3, which means 5 is hereinafter referred to as a discharge means 5, and a stirring means 6.

The housing 2 is designed such that the mixing chamber 3 has a bottom portion 7 which tapers from a base 8 to a bottom 9. As to the rest, the housing 2 can be designed in optional manner, which is indicated by dashed lines. In the shown embodiment, the base 8 of the bottom portion 7 forms a quadrangle, but according to the present invention the base 8 may also have some other polygonal design. The bottom 9 is in the form of a point 10, but it will be appreciated that the bottom 9 may have another design. The bottom can, for example, constitute the narrow end of a bottom portion in the form of a truncated pyramid. The supply means 4 comprises a supply pipe 11 which is connected to the mixing chamber 3 in an upper portion thereof. It will be understood that the supply means can be arranged for supplying said components in the form of separate partial flows and that the supply means does not necessarily have to be connected to the mixing chamber in the upper portion thereof.

The discharge means 5 comprises a discharge pipe 12 which is connected to the bottom portion 7 of the mixing chamber 3. Naturally, the discharge means can also be connected to the mixing chamber in some other position.

The stirring means 6 comprises a shaft 13, which is rotatable by means of a driving mechanism (not shown) and which extends vertically towards the point 10 of the bottom portion 7, and an agitator or blade means 14, which is supported by the shaft and which is arranged substantially in the centre of the mixing chamber 3. This blade means can be designed in a number of ways and the blade means 14 shown in Fig. 1 is only a non-limiting example of a convenient design. When using the inventive device 1, the supply means 4 is activated. This results in a continuous inflow of the components to the mixing chamber 3 through the supply pipe 11, which will fill the mixing chamber 3 to a given volume consisting of said components. At the same time, the stirring means 6 is activated, the shaft 13 causing the blade means 14 to rotate. The blade means 14 is adapted to engage the volume of compo- nents contained in the mixing chamber 3 to generate a mass flow directed to the bottom 9 of the mixing chamber 3.

As mentioned above, the bottom 9 of the mixing chamber 3 is formed by the narrow end of the bottom portion 7.

The stirring means 6 thus generates a mass flow directed to the bottom 9. From there, the mass flow is deflected and forced upwards in the mixing chamber 3. Now the mass flow is divided into partial flows, which substantially follow a corner edge 15 each of the pyramid-shaped bottom portion 7. The different mass flows are then continuously forced upwards in the mixing chamber 3 until they finally sink back down, under the influ- ence of gravity, into the rest of the volume contained in the mixing chamber 3. The mass flow generated in the mixing chamber 3 is preferably so intense that the partial flows are pressed all the way up to the top of the mixing chamber, where they recombine and then sink down in the volume. The components are thus circulated cyclically in the mixing chamber 3, thereby ensuring homogeneous mixing of the components.

When the mixing chamber 3 is filled with the given volume of said components, the discharge means 5 is activated. This causes a continuous flow of the homogeneous mixture to leave the mixing chamber 3 through the discharge pipe 12. To ensure that the volume of said components in the mixing chamber 3 is substantially constant during the operation of the inventive device 1, the inflow of components should substantially equal the outflow of the homogeneous mixture .

It will be appreciated that the supply means 4 and the discharge means 5 can be arranged for intermittent operation. However, in order to provide continuous mixing, they have to be activated for simultaneous continuous supply and discharge, respectively. It goes without saying that exceptions are made for the start when the mixing chamber 3 is to be filled with the components and the terminal phase when the components are to be evacuated from the mixing chamber 3 in mixed condition. The stirring means 6 should be adapted to generate a mass flow that is considerably greater than the inflow of components to the mixing chamber 3 and the outflow of the homogeneous mixture from the mixing chamber 3. Advantageously, the mass flow is at least ten times greater than said inflow and said outflow. The design of the bottom portion 7 contributes to producing a flow pattern in the mixing chamber 3 that is favourable for homogeneous mixing of the supplied components . This in combination with the comparatively high internal turnover of the components in the mixing chamber 3 ensures homogeneous mixing of the components. As already mentioned, the comparatively high internal turnover is achieved by ensuring that the mass flow generated by the stirring means 6 is considerably higher than the inflow of components and the outflow of the homogeneous mixture.

The inventive device 1 thus allows continuous mixing of components. Furthermore, the inventive device 1 has a comparatively high degree of efficiency. This again is due to the design of the bottom portion 7. Its quadran- gular base 8 imparts a geometric shape to the bottom portion 7 such that the partial volume of the components contained therein cannot be set in rotation when the stirring means 6 engages said partial volume. Provided that the rest of the housing 2 has a suitable design, it will thus be possible to ensure that substantially all the force is focused on the generation of the mass flow when the blade means 14 engages the components.

Figs 2 and 3, to which reference is now made, illustrate a preferred embodiment of an inventive device 1. In Fig. 3, the device 1 shown in Fig. 2 is illustrated with some parts cut away. In conformity with the device described above with reference to Fig. 1, the device 1 comprises a housing 2, which internally defines a mixing chamber 3, supply means 4, discharge means 5 and a stirring means 6. The housing 2 is substantially in the form of a cube placed on its edge, which results in the mixing chamber 3 having a bottom portion 7 formed by a corner edge of the housing 2. The bottom portion 7 thus tapers from a triangular base 8 to a bottom 9 in the form of a point 10. The base 8 is indicated by a dot-dashed line.

In the shown embodiment, the supply means 4 is arranged in an upper portion 16 of the mixing chamber 3 in the form of a bevelled part of the housing 2.

According to the shown embodiment, the supply means 4 comprises a first supply pipe 11a and a second supply pipe lib, which is concentrically arranged inside the first supply pipe 11a. It will be appreciated, however, that the supply means can be arranged in other positions and be designed differently. The discharge means 5 is arranged in the bottom portion 7 of the mixing chamber 3.

The discharge means 5 comprises a discharge pipe 12 which is connected to the bottom portion 7 of the mixing chamber 3. The stirring means 6 comprises a rotatable shaft 13, which extends from the upper portion 16 into the mixing chamber 3, and a blade means 14, which is supported by the shaft 13 and which is arranged substantially in the centre of the mixing chamber 3. The shaft 13 thus extends through a central portion of said upper portion towards the point of the bottom portion. The stirring means 6 also comprises a driving mechanism (not shown) for rotating the shaft 13. It goes without saying that the shaft can also support two or more blade means . The blade means 14 can also be arranged closer to the bottom so that the inventive device can be operated at a lower degree of filling. The supply means 4 can also comprise connecting pipes and pumps (not shown) .

The discharge means 5 can also comprise connecting pipes and pumps (not shown) . The preferred embodiment of the inventive device 1 is intended for mixing of a liquid component and a powder component. The liquid component is added continuously to the mixing chamber 3 through the first supply pipe 11a whereas the powder component is added continuously through the second supply pipe lib.

Fig. 4, to which reference is now made, illustrates the device 1 described with reference to Figs 2 and 3 in operation.

The mixing chamber 3 contains a given volume V of the components. Advantageously, it is ensured that the continuous inflow PI of components is substantially identical to the outflow P2 of the mixture of the components so that the given volume V will be substantially constant over time. The blade means 14 of the stirring means 6 is adapted, when rotating the shaft 13, to engage the volume V contained in the mixing chamber 3 to generate a mass flow P3 directed to the bottom 9 of the mixing chamber 3. At the bottom 9 formed as a point 10, the mass flow P3 deflects and divides into small partial flows P4. To be more specific, the partial flows P4 are forced upwards substantially along a corner edge 15 each of the bottom portion 7. When the respective partial flows P4 reach a corner, they are divided into smaller partial flows P4/2 and continue upwards in the mixing chamber 3 along the corner edges 17 interconnected with the corner edges 15 of the bottom portion 7. When the smaller partial flows P4/2 reach the next corners, they recombine in pairs and continue upwards in the mixing chamber until they finally sink back down in the volume V under the influence of gravity. The mass flow P3 directed to the bottom 9 of the mixing chamber 3 is thus divided into three primary par- tial flows P4, which in turn are divided into six smaller secondary partial flows P4/2. Thus, when the secondary partial flows P4/2 recombine in pairs they originate from different primary partial flows P4. In this way, the con- tinuous, homogeneous mixing of the components is further promoted.

As mentioned above with reference to Fig. 1, the mass flow P3 is preferably so intense that the partial flows P4 reach the upper portion 16 of the mixing cham- ber 3, where they recombine and sink back down in the volume V under the influence of gravity.

As a result, a flow pattern is produced in the mixing chamber 3 which strongly promotes homogeneous mixing of the components. By ensuring that the mass flow P3 generated by the blade means 14 of the stirring means 6 is considerably higher than the inflow PI of components and the outflow P2 of the mixture, a high internal turnover is obtained which further promotes homogeneous mixing of the compo- nents. As mentioned above, the mass flow P3 is preferably at least ten times greater than the inflow PI and the outflow P2. By thus creating a comparatively high internal turnover in the mixing chamber 3 , a device 1 is provided for continuous mixing with a high capacity. In addition, reliable homogeneous mixing is obtained of an inflow PI comprising a small flow of one of the components and a great flow of one of the other components .

Furthermore, the geometric design of the mixing chamber 3 ensures that the volume V will not be set in rotation when engaged by the blade means 14. More specifically, this is achieved thanks to the fact that the mixing chamber 3 is not rotationally symmetric in the direction of rotation of the blade means 14. Consequently, substantially all the force can be focused on the generation of the mass flow P3 , which results in an inventive device with a comparatively high degree of efficiency. The powder component which is supplied to the mixing chamber 3 through the second supply pipe lib sinks down onto the surface of the volume V and is then drawn down into the volume V owing to the mass flow P3 generated by the blade means 14. Since the blade means 14 does not set the volume V in rotation, it is also ensured that the powder component falling down onto the surface of the volume V is not flung out to the sides of the mixing chamber 3 by the centrifugal force. The geometric design of the mixing chamber 3 thus ensures efficient introduction of the powder component into the volume V.

In some cases, the powder component tends to agglomerate. Such agglomerates will, however, be drawn down into the volume V to the blade means 14 to be disinte- grated before they are entrained by the mass flow P3 directed to the bottom 9.

According to the preferred embodiment of the inventive device 1, the liquid component is supplied through an annular supply pipe 11a which surrounds the supply pipe lib of the powder component. Owing to this, the powder component is wetted which prevents dust formation.

According to the present invention, a device 1 is thus provided which allows continuous mixing of at least two components. More specifically, a continuous inflow PI of the components is supplied to a mixing chamber 3, from which a corresponding outflow P2 of the components in mixed condition is discharged. The mixing chamber 3 has a bottom portion 7 which tapers from a polygonal base 8 to a bottom 9, a stirring means 6 generating a mass flow P3 which is directed to the bottom 9' and which advantageously is considerably higher than the inflow PI and the outflow P2 in the mixing chamber. The geometric design of the bottom portion 7 in combination with the compara- tively great mass flow P3 ensures homogeneous mixing of the components. The inventive device thus allows continuous mixing of two or more components, the expression continuous mixing implying that the components are supplied to the mixing chamber at the same time as the mixture consisting of said components is discharged from the mixing chamber. The expression continuous mixing thus also comprises cases where the supply and the simultaneous discharge occur intermittently.

The design of the bottom portion also makes it pos- sible to ensure that the volume contained in the mixing chamber is not set in rotation by the stirring means. As a result, the frictional losses in the mixing chamber will be low and substantially all the force can be focused on the generation of the mass flow directed to the bottom, which results in a high degree of efficiency of the device. This reduces the energy transmitted to the volume and thus also a resultant temperature increase in the volume .

When operating the inventive device, a central down- wardly directed mass flow is divided and deviated to peripheral upwardly directed partial flows. This flow pattern yields efficient cooling of the volume, if needed, by cooling of the walls defining the mixing chamber.

As the stirring means does not set the volume in ro- tation, no conventional turbulence or vortex forms at the surface of the volume. This makes it possible to prevent air from being added to the volume, which may be preferable in some applications.

The comparatively high internal turnover in the mixing chamber also allows reliable continuous and homogeneous mixing of components if the inflow to the mixing chamber comprises a great flow of a first component and a small flow of a second component.

The inventive device also allows reliable continuous and homogeneous mixing of components already at a comparatively low degree of filling of the mixing chamber. Consequently, the volume of components contained in the mixing chamber may have a considerably lower surface level than that shown in Fig. 4. It should be noted, however, that the flow pattern may be somewhat different if the inventive device operates at a lower filling degree .

It will be appreciated that the present invention is not limited to the described embodiments.

The inventive device can, for example, be used for mixing a gas component with a liquid component. As men- tioned above, the device is not apt to let in air into the volume. Thus, if a gas component is to be mixed with a liquid component, the gas component has to be introduced into the liquid component under the surface thereof . Many modifications and variations are conceivable, and therefore the scope of the present invention is defined only by the appended claims.

Claims

1. A device for continuous mixing of at least two components, c h a r a c t e r i s e d by a mixing chamber (3) for receiving a volume (V) of said components, means (4) for continuously conveying an inflow (PI) of said components to the mixing chamber (3) , means (5) for continuously conveying an outflow (P2) of a mixture of said components from the mixing chamber (3) and a stirring means (6) , the mixing chamber (3) having a bottom portion (7) which tapers from a polygonal base (8) to a bottom (9) , and the stirring means (6) being adapted to generate, in said volume (V) , a mass flow (P3) directed to said bottom (9) .

2. A device as claimed in claim 1, in which said mass flow (P3) is considerably higher than said inflow (PI) and said outflow (P2) .

3. A device as claimed in claim 2, in which said mass flow (P3) is at least ten times greater than said inflow (PI) and said outflow (P2) .

4. A device as claimed in any one of claims 1-3, in which said mixing chamber (3) is defined by a substantially cubic housing (2) , said bottom portion (7) being formed by a corner portion of said housing (2) .

5. A device as claimed in any one of the preceding claims, in which the device is adapted uor mixing components of which at least one is a liquid component.

6. A device as claimed in any one of the preceding claims, in which the device is adapted for mixing compo- nents of which at least one is a powder component.

7. A device as claimed in any one of the preceding claims, in which said bottom portion (7) has a triangular base (8) .

8. A device as claimed in any one of claims 1-6, in which said bottom portion (7) has a quadrangular base (8) .

9. A device as claimed in any one of the preceding claims, in which the base (8) of the bottom portion (7) tapers towards a bottom (9) in the form of a point (10) .

10. A method for continuous mixing of at least two components, comprising the steps of continuously conveying an inflow (PI) of said components to a mixing chamber (3) with a bottom portion (7) which tapers from a polygonal base (8) to a bottom (9) , generating a mass flow (P3), directed to said bottom (9) , in a volume (V) which is contained in said mixing chamber (3) and which is formed by the components conveyed to the mixing chamber (3) , and continuously conveying an outflow (P2) of a mixture of said components from the mixing chamber (3) .

11. A method as claimed in claim 10, in which the step of generating a mass flow (P3) comprises adjusting of the mass flow (P3) so as to make it considerably higher than said inflow (PI) and said outflow (P2) .

12. A method as claimed in claim 11, in which said mass flow (P3) is adjusted so as to be at least ten times greater than said inflow (PI) and said outflow (P2) .