WO2011020474A1

WO2011020474A1 - Agitator

Info

Publication number: WO2011020474A1
Application number: PCT/DK2010/050197
Authority: WO
Inventors: Poul Gaardsted; Michael Juhl FØNS
Original assignee: Alfa Laval Corporate Ab
Priority date: 2009-08-19
Filing date: 2010-07-28
Publication date: 2011-02-24
Also published as: DK200900938A

Abstract

An agitator (1) for stirring a process media inside an enclosure (2) comprising: -a drive shaft (3), -a stirrer (4) suspended from the drive shaft (3), -means (5) for rotating the drive shaft, -a bearing arrangement (6) comprising at least one thrust bearing (7) and two radial bearings (8, 9) for holding the drive shaft (3) rotatably within the enclosure (2), wherein each bearing (7, 8, 9) is an electromagnetic bearing, and wherein the bearing arrangement (6) comprises active control means (16) and an enclosure (2) for such an agitator (1).

Description

Agitator

Field of the Invention

The present invention relates to an agitator for stirring a process media inside an enclo- sure comprising:

- a drive shaft,

- a stirrer suspended from the drive shaft,

- means for rotating the drive shaft,

- a bearing arrangement comprising at least one thrust bearing and two radial bearings for holding the drive shaft rotatably within the enclosure wherein each bearing is an electromagnetic bearing, and wherein the bearing arrangement comprises active control means.

Furthermore the invention relates to an enclosure adapted for containing a process me- dia comprising an agitator for stirring the process media inside the enclosure comprising:

- a drive shaft,

- a stirrer suspended from the drive shaft,

- means for rotating the drive shaft,

Background of the Invention

In the process industry there is a common need for agitators of the type as initially described for stirring a liquid process media inside a container or enclosure.

It is known to provide driving means and a bearing arrangement for the agitator out- side the container or enclosure. In case of a closed enclosure the shaft is introduced through an opening in the enclosure and sealed with a shaft seal. Especially in the medical industry there is a requirement for aseptic and extremely clean operation without introducing event the smallest amount of bacteria from outside the enclosure and other foreign objects to the process within such enclosure.

It is a problem to locate the bearings and the driving means outside the enclosure be- cause then the process cannot be aseptic even though a shaft seal between the shaft and the enclosure is provided. The shaft seal will be subject to wear followed by leakage.

A known example of a stirrer is provided with GB 934,793, in which an apparatus for driving a stirrer inside a space adapted to contain process media comprises a housing containing said apparatus and partly defining said space. The stirrer is suspended from a driven shaft part of which is provided inside said space and the remainder being inside said housing. Bearings are provided for the shaft inside a lubricant chamber which is inside said housing but outside said space. A seal is provided between the lubricant chamber and the housing. Means for driving the shaft is provided inside the chamber. The electrical connection for the driving means pass through the wall of the chamber.

GB 934,793 provides a way of substantially avoiding bacteria from the outside of the enclosure to get into the enclosure. However the lead-in for the electrical connection all though sealed may provide a path for bacteria. The seal between the lubricant chamber and the space will be subject to wear. Thus foreign objects stemming from the lubricant chamber will be introduced to the process media. These foreign objects are both the lubricant and metal particles which is released be the metal to metal contact within the bearing. This is unacceptable for medicine for ingestion, and in particular for medicine for injection.

WO 03/089799 discloses a mixing system comprising drive shaft, which is fitted with an agitator and means for rotating the drive shaft. A plurality of non-contact magnetic bearings are located about the drive shaft. The bearings are supplied with power through a control system, which is provided with control feedback from three sensors that monitors the position of the driveshaft. During operation the drive shaft is rotating inside an enclosure with a gab to any part of the enclosure. When the system is shut down the gab will close and the shaft will rest in whatever position it has fallen. Object of the Invention

The object of the present invention is to provide an agitator stirring a process media inside an enclosure, while maintaining aseptic conditions and without adding foreign matter to the suspension.

Disclosure of the Invention

According to the present invention, this is achieved by an agitator of the type specified in the introduction and which is peculiar in that, the drive shaft has a parking position, where the drive shaft is in contact with the enclosure and an active position, where the drive shaft is without contact with the enclosure, and where the position of the drive shaft during transition between the parking position and the active position is controlled by the active control means.

Alternatively this is achieved by an enclosure of the type specified in the introduction and which is peculiar in that, the drive shaft has a parking position, where the drive shaft is in contact with the enclosure and an active position, where the drive shaft is without contact with the enclosure, and where the position of the drive shaft during transition between the parking position and the active position is controlled by the active control means.

The parking position is a power off position for the electromagnetic bearings in the agitator, to be used optionally when the agitator is inactive, the enclosure is empty or during transportation. The enclosure may be adapted for providing a seat for the drive shaft. The contact surface between the seat and the drive shaft has a complimentary shape.

The active position is a power on position for the electromagnetic bearings in the agitator, to be used during operation of the agitator, when there is process media inside the enclosure or during emptying of the enclosure. The position of the drive shaft is controlled during transition between the two positions for controlling the speed of the drive shaft. When the agitator is changing from the active position to the parking position the drive shaft should be non-rotating. The speed of the drive shaft towards the seat is controlled by the active control means such that the impact when the drive shaft is contacting the seat of the enclosure is very small.

The means for rotating the drive shaft may be locked, such that the drive shaft is non- rotating.

It is herewith avoided that material is loosened during changing from active to parked position, thus foreign objects will not be added to the process media.

When the agitator is changing from the parked position to the active position the posi- tion of the drive shaft is also controlled, such that the drive shaft and the stirrer is not impacting against any other part of the agitator or enclosure.

By providing the agitator with electromagnetic bearings for the drive shaft it is achieved to provide bearings with a gap between the rotating part of the bearing and the static part of the bearing. There is no contact between the drive shaft and the enclosure during rotation of the drive shaft. This avoids the need for lubrication of the bearing. Furthermore there is no metal to metal contact. The agitator inside the enclosure may therefore operate completely aseptic without adding foreign objects to the process.

Each electromagnetic bearing comprise a stator and a rotor, where the rotor is part of the drive shaft and the stator is located outside the enclosure. Each stator may be advantageously composed of at least two, preferably at least four separately powered electrical coils associated with a magnetic yoke and an even radial distribution around the stator.

The active control means ensure that the drive shaft is always centred within the bearings, by controlling the power supply to the electrical coils of the stators separately, thus maintaining the gap within acceptable tolerances. This allows the agitator to be used for processing media, which contain crystals which are to be kept in liquid suspension without being crushed. The size of the gap around the drive shaft and the stirrer should exceed the largest crystal size. The size of the gap is limited by the achiev- able magnetic forces of a particular magnetic bearing. Thus an agitator with a relatively large gap would require relatively larger bearings.

The x, y, z position of the drive shaft relative to the enclosure is controlled by the active control means.

During emptying of the enclosure it may be tilted. To maintain the process media in a homogeneous suspension the agitator may continue to operate. This is possible due to the active control means ability to maintain the gap by biasing the power supply to the stator.

The agitator is especially suited for use in enclosures for processing insulin, which contain needle crystals as carriers for the insulin. There is an absolute requirement for aseptic processing with zero tolerance towards added foreign objects to the process media. The needle crystals must be maintained in liquid suspension without being crushed.

The bearings may be submerged into the process media, because of the contact free operation. Therefore the radial bearings may be located at the same end of the enclosure or one at each end.

The at least one thrust bearing may be located at one end of the enclosure. One thrust bearing is sufficient for an agitator with a substantially horizontal drive shaft or with a drive shaft with an angle of inclination between 45° and vertical. Two thrust bearings, one at each end of the enclosure or drive shaft, are required for an agitator with a drive shaft having an angle of inclination between horizontal and 45°. According to a further embodiment, the agitator according to the invention is peculiar in that the means for rotating the drive shaft is an electromagnetic motor, where the motor comprises a stator and a rotor, where the rotor is part of the drive shaft, and where the stator is located free located outside the enclosure.

It is herewith achieved that the drive shaft may be driven with no mechanical contact between the means for rotating the drive shaft and the drive shaft itself. The drive shaft with the agitator will be levitating inside the enclosure.

Furthermore this embodiment avoids the need for passing the electrical connection for the driving means or any part of the drive shaft through the wall of the enclosure.

According to a further embodiment, the agitator according to the invention is peculiar in that the active control means comprise

- a position sensor for detecting the position of the drive shaft,

- a control unit, which is coupled to the position sensor and each stator for controlling the position of the drive shaft.

It is herewith achieved that the location of the drive shaft inside the enclosure may be controlled by the position sensor continuously providing feedback to the control unit for controlling each stator and thereby the position of the drive shaft.

The position sensor may be a mechanical sensor, an inductive sensor or an optic sensor. According to a further embodiment, the agitator according to the invention is peculiar in that the bearing arrangement is located within a housing adapted for being mounted to the enclosure.

It is herewith achieved that the agitator may be provided as a unit. The agitator may be manufactured separately from the enclosure. The agitator and the enclosure are brought together for assembly utilizing a shared interface. The agitator may therefore be replaceable, such that the agitator may be repaired. According to a further embodiment, the agitator according to the invention is peculiar in that the drive shaft is in a substantially vertical position.

In this embodiment only one thrust bearing is required. The thrust bearing may be Io - cated at the top of the enclosure, in which case the thrust bearing is pulling the drive shaft into position during operation.

Alternatively the thrust bearing may be located at the bottom of the enclosure, in which case the thrust bearing is pushing the shaft into position during operation.

The stirring is most advantageously performed with the drive shaft in an orientation where the surface of the process media is perpendicular to the drive shaft, compared to an orientation where the surface of the process media is parallel to the drive shaft. This applies in particular to a situation where the enclosure is partly filled with process me- dia.

On a horizontal drive shaft the stirrer will move into and out of the process media once every revolution, causing the process media to be whipped and mixed with air. This is alleviated with a vertical drive shaft.

According to a further embodiment, the agitator according to the invention is peculiar in that drive shaft has a first part with a first diameter and a second part with a second diameter, wherein the first diameter is smaller than the second diameter, and wherein the transition between the first diameter and second diameter is providing an abutment surface which is complimentary to a seat surface of the enclosure.

The abutment and seat surfaces are in contact when the drive shaft is in the parking position. It is herewith achieved that the drive shaft is supported and in contact with the enclosure when in the parking position.

According to a further embodiment, the agitator according to the invention is peculiar in that a radial bearing is positioned about each end of the drive shaft. This will provide a distance between the bearings and thus a large moment arm. This is advantageous when the agitator is subject to large shear forces or when the bearings need to be as small as possible. According to a further embodiment, the agitator according to the invention is peculiar in that the radial bearings are positioned about one end of the drive shaft.

It is hereby achieved that an outlet may be positioned at the bottom of the enclosure, because this area is not taken up by the drive shaft. It is thereby possible to provide an outlet of little complexity, which allow for complete emptying of the enclosure.

According to a further embodiment, the enclosure according to the invention is peculiar in that a radial bearing is arranged at each end of the enclosure. It is hereby achieved that a distance between the two radial bearings are provided, such that the forces required by the radial bearing to control the gap are small. This is advantageous when the agitator is subject to large shear forces or when the bearings need to be as small as possible. According to a further embodiment, the enclosure according to the invention is peculiar in that the bearing arrangement, the means for rotating the drive shaft and the active control means are provided on the top of the enclosure, wherein a discharge opening is provided in the bottom of the enclosure, and wherein means for opening/closing the discharge opening are provided.

It is herewith achieved that the enclosure may be emptied by gravity, while the stirring is maintained until the enclosure is completely empty.

In the embodiment above the agitator may advantageously be provided as unit inside a housing, which is plugged onto the enclosure and sealed. Description of the Drawing

The invention will be explained in more detail below with reference to the accompanying drawing, where: Fig. 1 shows in isometric ghost view of an agitator according to invention inside an enclosure,

Fig. 2 shows a side view of an enclosure with an agitator,

Fig. 3 shows a section view (A-A) of an agitator inside an enclosure according to

Fig. 2,

Fig. 4 shows a section cut of part of a first agitator housing,

Fig. 5 shows a section cut of part of a second agitator housing,

Fig. 6 shows the drive shaft in an active position,

Fig. 7 shows the drive shaft in a parking position, and

Fig. 8 shows a partial section view of a second embodiment of the agitator inside an enclosure.

Detailed Description of the Invention

In the explanation of the figures, identical or corresponding elements will be provided with the same designations in different figures. Therefore, no explanation of all details will be given in connection with each single figure/embodiment.

Fig. 1-3 shows an agitator 1 inside an enclosure 2 for a process media. The enclosure 2 is cylindrical with a conical top 18 and a conical bottom 19 and legs 20. In alternative embodiments of the invention the top 18 and bottom 19 may be flat, domed, polygonal or any other shape according to the intended use of the invention. The agitator 1 comprise a substantially vertical drive shaft 3 with a stirrer 4 suspended from said drive shaft 3. The agitator has means 5 for rotating the drive shaft 3, and a bearing arrangement 6 for supporting said drive shaft 3. The stirrer 4 has three spaced connections 17 to the drive shaft 3 in this embodiment. The stirrer 4 is extending within the conical bottom 19 and is shaped as a narrow spiral, which is conforming to the shape of the conical bottom 19. The stirrer 4 may be located at different positions inside the enclosure 2 and extend throughout the enclosure 2 substantially along the entire length of the drive shaft 2 depending on the application and process media.

The means 5 for rotating the drive shaft 3 is located on the top of the enclosure 2 in- side a first agitator housing 21.

The bearing arrangement 6 is partly arranged within the first agitator housing 21 and inside a second agitator housing 22 located on the bottom of the enclosure 2. The bearing arrangement 6 (see Figs. 4 and 5) comprises one electromagnetic thrust bearing 7 and two electromagnetic radial bearings 8, 9. The electromagnetic bearings 7, 8, 9 are controlled by active control means 16 for centring the drive shaft 3 within the bearings

7, 8, 9 such that a gap 23 (see fig. 4) is provided between the drive shaft 3 and any surrounding structure. One thrust bearing 7 and one radial bearing 8 is located in the first agitator housing 21 and one radial bearing 9 is located in the second agitator housing 22 providing a distance between the radial bearings 8, 9. The radial bearings 8, 9 are spaced to limit the forces required for centring the drive shaft 2. The forces required by the radial bearing

8, 9 are increasing as the distance becomes smaller.

The first and second agitator housings 21, 22 are connected to the enclosure 2 by flange connections 24 which are sealed.

Fig. 4 show a section cut of the first agitator housing 21 located on top of the enclo- sure 2. Mentioned from the top and downwards the first agitator housing 21 comprise the following major parts: active control means 16 for controlling the vertical position and radial position of the drive shaft 3, one thrust bearing 7, means 5 for rotating the drive shaft 3, and one radial bearing 8. Each bearing comprise a stator 10, 11, 12 and a rotor 13, 14, 15. Each stator 10, 11, 12 is divided into separately powered electrical coils associated with a magnetic yokes with an even radial distribution around the stator.

The active control means 16 comprise a position sensor 28 for detecting the vertical position of the drive shaft 3 and a plurality of radial position sensors 37 distributed around the drive shaft 3 for detecting the radial position of the drive shaft 3. The x, y, z position is continuously monitored. The position information is provided to an external control unit 38 (see Fig. 2) through control connections 39 (see Fig. X). The external control unit 38 (see Fig. 2) provides electrical control of each stator 10, 11, 12 individually through the control connections 39 (see Fig. 2).

If the gap 23 around the drive shaft 3 is decreasing on one side of the drive shaft 3, this will be detected by the radial position sensors 37, and corrected for by the external control unit 38 (see Fig. 2), which will bias the power for the electrical coils in the sta- tors 11, 12 of the radial bearings 8, 9, until the drive shaft 3 is in the correct position.

If the gap 23 above the drive shaft 3 is increasing, this will be detected by the position sensor 28, and corrected for by the external control unit 38 (see Fig. 2), which will adjust the power to the electrical coils in the stator 10 of the thrust bearing 7, until the drive shaft 3 is in the correct position.

Alternatively the control unit may be built into the first or second agitator housing 21, 22.

The thrust bearing 7 is provided with a stator 10, which is outside the enclosure 2, and a rotor 13, which is part of the drive shaft 3. This provides a gap 23 between the drive shaft 3 and the surrounding structure.

The means 5 for rotating the drive shaft 3 is an electromagnetic motor 25. The motor 25 comprise a stator 26, which is outside the enclosure 2, and a rotor 27, which is part of the drive shaft 3. This provides contact free rotation of the drive shaft 3. The radial bearing 8 is provided with a stator 11, which is outside the enclosure 2, and a rotor 14, which is part of the drive shaft 3. This provides a gap 23 between the drive shaft 3 and the surrounding structure.

The first agitator housing 21 is mounted to the enclosure 2 by a complimentary flange connection 24.

Fig. 5 show a section cut of the second agitator housing 22 located on the bottom of the enclosure 2. The second agitator housing 22 comprise a radial bearing 9. A plurality of radial position sensors 37, which are distributed around the drive shaft 3, are provided for continuously monitoring the radial position of the drive shaft 3. The radial position is continuously provided to the external control unit. The active control means 16 (see fig. 4) is in communication via the external control unit 38 (see Fig. 2) with the stator 12 of the radial bearing 9 for controlling the gap 23 around the drive shaft 3.

The second agitator housing 22 is mounted to the enclosure 2 by a complimentary flange connection 24. Surfaces of the agitator 1 and the enclosure 2 which is in contact with the process media, is made of stainless steel for hygienic purposes. Another suitable material may be titanium.

Fig. 6 and 7 shows a section cut of a detail of the drive shaft 3 in the active position and the parking position respectively.

The drive shaft 3 has a first part 29 with a first diameter and a second part 30 with a second diameter. The first diameter is smaller than the second diameter. In the embodiment shown on fig. 6 and 7 the transition 31 between the two diameters is conical. The surface of the transition 31 is providing an abutment surface 32, which is complimentary to a seat surface 33 of the enclosure 2. When the drive shaft 3 is in its active position power is applied to the bearing arrangement 6 (see fig. 1-5) via the active control means 16, such that the drive shaft 3 is free of mechanical contact with any part of the enclosure 2. The drive shaft 3 is levitating caused by the magnetic forces exerted by the stators onto the rotors.

When the drive shaft 3 is transiting from the active position to the parking position the power to the thrust bearing 7 (see fig 4) is adjusted. The gap 23 between the abutment surface 32 and the seat surface 33 is decreasing until the drive shaft 3 is in the parking position with the abutment surface 32 in contact with and resting on the seat surface 33 of the enclosure 2.

The motor 25 may be in a short circuit state such that the drive shaft 3 is locked in a radial position and prevented from rotating during transition from active to parking position.

In this way the agitator 1 may prepared for being stopped or transportation without the risk of freeing material by abrasion between the drive shaft 3 and the enclosure 2.

When the agitator 1 is turned on, the drive shaft 3 may change position from the park- ing position to the active position. Power to the thrust bearing 7 is adjusted until the gap 23 between the abutment surface 32 and the seat surface 33 is within the desired limits. The drive shaft 3 should be locked against rotation during power up to prevent abrasion between the abutment surface 32 and the seat surface 33. In this way the agitator 1 is prepared for operation without the risk of freeing material by abrasion between the drive shaft 3 and the enclosure 2.

The monitoring, feedback and control by the active control means 16 is continuous when the drive shaft 3 is in the active position.

Fig. 8 shows a partial section view of a second embodiment of the agitator inside an enclosure. The agitator has one agitator housing 34 on the top of the enclosure 2. The housing contains the means for rotating the drive shaft 3, the bearing arrangement 6 with the thrust bearing 7 and the two radial bearings 8, 9. The radial bearings 8, 9 are sized to provide forces sufficient to achieve proper centring of the drive shaft 3 through the entire length of the drive shaft 3.

The two radial bearings 8, 9 are preferably spaced apart as much as possible by providing the means 5 for rotating the drive shaft 3 between the two.

The bottom of the enclosure 2 is occupied only by a discharge opening 35, for empty- ing the enclosure 2 through gravity. The discharge opening 35 is closed by a plug 36, which may be removed for emptying the enclosure 2.

Claims

1. An agitator for stirring a process media inside an enclosure comprising:

- a drive shaft,

- a stirrer suspended from the drive shaft,

- means for rotating the drive shaft,

- a bearing arrangement comprising at least one thrust bearing and two radial bearings for holding the drive shaft rotatably within the enclosure,

wherein each bearing is an electromagnetic bearing, and wherein the bearing arrangement comprises active control means characterised in that the drive shaft has a park- ing position, where the drive shaft is in contact with the enclosure and an active position, where the drive shaft is without contact with the enclosure, and where the position of the drive shaft during transition between the parking position and the active position is controlled by the active control means.

2. An agitator according to claim 1, wherein the means for rotating the drive shaft is an electromagnetic motor, where the motor comprises a stator and a rotor, where the rotor is part of the drive shaft, and where the stator is located outside the enclosure.

3. An agitator according to claim 1 or 2, wherein the active control means comprise - a position sensor for detecting the position of the drive shaft,

4. An agitator according to any of the preceding claims, wherein the bearing arrange- ment is located within a housing adapted for being mounted to the enclosure.

5. An agitator according to any of the preceding claims, wherein the drive shaft is in a substantially vertical position.

6. An agitator according to claim 5, wherein the drive shaft has a first part with a first diameter and a second part with a second diameter, wherein the first diameter is smaller than the second diameter, and wherein the transition between the first diameter and second diameter is providing an abutment surface which is complimentary to a seat surface of the enclosure.

7. An agitator according to any of the preceding claims, wherein a radial bearing is positioned about each end of the drive shaft.

8. An agitator according to any of the claims 1-6, wherein the radial bearings are positioned at one end of the drive shaft.

9. An enclosure adapted for containing a process media comprising an agitator for stirring the process media inside the enclosure comprising:

- a drive shaft,

- a stirrer suspended from the drive shaft,

- means for rotating the drive shaft,

wherein each bearing is an electromagnetic bearing, and wherein the bearing arrangement comprises active control means characterised in that the drive shaft has a parking position, where the drive shaft is in contact with the enclosure and an active posi- tion, where the drive shaft is without contact with the enclosure, and where the position of the drive shaft during transition between the parking position and the active position is controlled by the active control means.

10. An enclosure according to claim 9, wherein a radial bearing is arranged at each end of the enclosure.

11. An enclosure according to claim 9, wherein the bearing arrangement, the means for rotating the drive shaft and the active control means are provided on the top of the enclosure, wherein a discharge opening is provided in the bottom of the enclosure, and wherein means for opening/closing the discharge opening are provided.