DE20307913U1 - Laboratory bench rotary vacuum concentrator comprises internal magnetic drive, for slow removal of solvent in test tube scale preparations - Google Patents

Abstract

A rotary vacuum concentrator has an internal magnetic drive. Preferred Features: A centrifugal separator is adapted to undertake evaporation under reduced pressure, without rotating shaft penetration of the vacuum enclosure. The unit may be provided with external heating or cooling and also an imbalance detection (25).

Description

DESCRIPTION
Device for concentrating mixtures of substances

The invention relates to a device according to the preamble of claim 1.

Such devices are known, for example, in the form of so-called rotary vacuum concentrators and are usually designed to remove at least one or more components from a mixture of substances by gentle evaporation under vacuum, thus lowering the boiling point, whereby the mixture of substances is set in rotation and the gravitational field generated in this way prevents delayed boiling. This type of concentration is used in the extraction of heat-sensitive products, in the isolation of components of an extract, in the screening of new compounds and also in general evaporation applications in the laboratory. The component to be removed by evaporation is often a solvent.

It is also known to introduce the mixture of substances to be concentrated into a vessel that is open at the top and which is inserted into the holders of a rotor that is itself arranged to rotate within a housing that encloses a vacuum space. The component to be separated is discharged in the vapor phase through the opening at the top of the vessel. To drive the rotor, preferably electric drives are used that are arranged outside the housing and are connected to the rotor via a vacuum-tight wall feedthrough or that are only magnetically or inductively coupled to the rotor to avoid feedthroughs that cause sealing problems. Finally, regulated magnetic coils arranged in a circle are also used to avoid such feedthroughs.

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The bearings of the rotor are problematic, particularly for the concentration process taking place within these devices, since the vacuum means that partial evaporation of lubricants is unavoidable, which not only leads to contamination of the housing, in particular the vacuum space, but also of the mixture of substances to be treated. Depending on the composition of this mixture of substances, in particular the properties of the component to be evaporated, there may also be damaging effects in the area of the bearings, for example if the component in question is a chemically aggressive solvent. This can, under certain circumstances, interact with the bearings and/or with the lubricant used in the bearings and significantly impair their function.

The use of rotary unions is also problematic, as the sealing materials or media can also evaporate or be attacked by the components being evaporated. The vacuum space and the mixture of substances can also be contaminated by sealing material or sealing media components.

It is known that the evaporation process from the vessels in the peripheral area of the rotor is often not uniform. This means that even if the rotor starts up unbalanced at the beginning of the concentration process, static and/or dynamic imbalances can occur later. It is also possible that, despite the rotor being unbalanced at the beginning of the process and despite the evaporation process being uniform, a static and/or dynamic imbalance can occur as the evaporation progresses, due to vessels of unequal weight or due to vessels with unequal mass distribution. This means that the bearings of the rotor within the housing are subjected to extremely high mechanical stress, which reduces their service life.

A further effect can be the (premature) termination of the process due to an unacceptably large imbalance.

2823/34 ., ,. ·« ,. Martin Christ Freeze-Drying Systems GmbH

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Against this background, the object of the invention is to improve a device of the type described at the outset while avoiding the disadvantages inherent in the prior art with regard to a design that is appropriate to the load and stable operating conditions. This object is achieved in such a device by the features of the characterizing part of claim 1.

The essential feature of the invention is that the rotor is mounted on a fixed axle within the housing via at least one magnetic bearing. The bearing is thus contact-free, friction-free and lubricant-free, simply by means of an appropriately applied magnetic field, so that the interactions described at the beginning between a component evaporating from the mixture of substances, the vacuum, the plain or roller bearings and a lubricant cannot occur.

The stator systems of the magnetic bearing are connected to the axle according to the features of claims 2 and 3. The axle can be designed as a hollow axle, so that the stator systems are located on the inside of this hollow axle and in this case surround the radially inner rotor systems. However, the stator systems can also be arranged on the outside of the axle and in this case be surrounded by radially outer rotor systems. In any case, the axle is arranged fixedly within the housing, so that there is no need for rotary feedthroughs through the housing wall.

In the same way, the rotor and stator systems of the electric drive of the rotor are integrated into the outside or inside of the axle as well as the inside of the hub or the outside of parts of the hub, so that an extremely simple structural design of the device is achieved. Electrical supply and control lines are conveniently accommodated in the axle and do not form an obstacle to the interior of the housing. The electrical concept of the drive can, for example, be designed in the manner of an asynchronous or synchronous motor, whereby a speed control can preferably be provided. The magnetic bearings enable high rotational speeds.

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and are considered to be almost free of losses due to contact-free and therefore friction-free operation, so that measures for possible bearing cooling are unnecessary. As a result of the contact-free operation of the magnetic bearing, there is also no abrasion that could potentially lead to contamination of the vacuum space or the mixture of substances to be treated.

The axis supporting the rotor is arranged vertically in the housing according to the features of claim 4, wherein the housing can be closed by a cover in a pressure-tight or vacuum-tight manner.

According to the features of claims 5 and 6, two axially spaced magnetic bearings are provided, namely two radially effective bearings and one axially effective bearing. The bearings are operatively connected to a higher-level electrical control in the same way as the drive mentioned. This control can also contain means for visually displaying the operating state of the device, in particular the drive and the magnetic bearings, but also the ongoing process, such as vacuum, temperature, rotor speed, imbalance of the rotor, etc.

The rotor can be designed as a fixed angle rotor according to the features of claims 7 and 8, in which the vessels receiving the substance mixture are arranged at a fixed angle to the axis of the rotor - however, a holder for the vessels that can be freely swiveled out or that can be limited in terms of a swivel angle according to a stop can also be considered. Finally, rotors that are designed directly to receive the substance mixture to be treated, i.e. that simultaneously fulfill the function of the vessels mentioned, can also be considered.

The features of claims 9 to 11 are directed to particular advantageous features resulting from the magnetic bearing of the rotor, which relate to the operating sequence, in particular the concentration process, but also the rotational movement of the rotor.

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2823/34 Martin Christ Freeze Drying Systems GmbH

The fixed, vertically arranged axis that supports the rotor within the housing makes it possible to determine the mass of the rotor, including that of the mixture of substances held in the peripheral vessels, by evaluating the bearing force applied via the axial magnetic bearing and/or the radial magnetic bearing(s). This mass changes during the concentration process depending on the mass of the components evaporating as a result of the vacuum within the housing, which are removed with the help of a vacuum source. It is known that in such processes the evaporation rate changes during the concentration process in such a way that it decreases sharply from an initial maximum value, since the concentration of the remaining components in the mixture of substances increases sharply in relation to the evaporated component. The temporal progression of the axial and/or radial bearing force thus enables the evaporation rate to be continuously observed or recorded over time, and thus the determination of how far the concentration process has progressed or that the end of the concentration process has been reached. This process can be visually reproduced in digital, analogue or graphical form or can be further evaluated as a measured value in automated systems.

The magnetic bearings, whose electrical concept can be designed in the same way as that of the drive, for example in the manner of a synchronous machine, enable the rotor position to be calculated based on the counter voltage induced in the phases that are temporarily not energized. If the electrical concept of the magnetic bearings is designed in the manner of an asynchronous machine, it is also possible to calculate the rotor position based on the stator currents in connection with the motor speed. However, these electrical concepts are only to be understood as examples. Those based on the type of electronically commutated or brushless DC motors and the use of special sensor systems to detect the position of the rotor are also equally possible. The balanced state of the entire system, consisting of the rotor and vessels and the mixtures of materials used in them, is known to be characterized by the fact that its axis of rotation runs through the center of gravity and that

2823/34 . Martin Christ Freeze Drying Systems GmbH

the axis of rotation corresponds to a main axis of inertia. This state is also characterized by an air gap between the rotor and stator systems that is uniform in the circumferential direction of the individual magnetic bearings. However, the non-uniform evaporation rates in individual vessels during the concentration process lead to unavoidable imbalances occurring, which lead to the displacement of the main axis of inertia relative to the axis of rotation (static and/or dynamic imbalance) and the corresponding non-uniformities of the air gap between the rotor and stator systems of the magnetic bearings. This means that by evaluating the operating parameters of the magnetic bearings, the size and position of an imbalance can be determined in addition to the rotor position. According to the invention, this circumstance is used to compensate for the imbalance state by means of a local field control adapted to the position of the imbalance or by controlling other operating parameters of the magnetic bearings that determine the local bearing force. Monitoring of the imbalance state and compensation by appropriate control of the magnet layers can be carried out continuously throughout the entire concentration process, so that a stable, imbalance-free state of the rotor can be maintained throughout the entire process, regardless of any uneven evaporation rates of the individual vessels. This in turn has the advantage of low vibrations of the device and lower noise compared to conventional devices.

Dynamic continuous balancing of the rotor also enables the use of vessels with weight differences, as an imbalance that would otherwise be caused by these can be compensated for almost automatically. It is also possible to dynamically balance rotors and vessels whose masses are unequal or which have a different mass distribution before the start of the process, i.e. when empty.

The containers intended to hold the mixture of substances can be made of plastic or metal. However, they are often made of glass. They are subject to high mechanical stress during operation of the device. Glass breakage cannot therefore be completely ruled out and leads to uncontrolled

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Distribution of the mixture of substances within the housing. However, by evaluating the bearing forces of the magnetic bearings, such glass breakage, which may involve the destruction of one or more vessels, can be recognized very quickly by a relatively rapid and spontaneous increase in the imbalance, so that appropriate measures or decisions can be taken at an early stage. An evaluation of the forces absorbed by the magnetic bearings over time also makes it possible to obtain information about the damage to individual vessels.

Furthermore, the size and position of existing imbalances can be detected and corrective measures can be taken if necessary.

The influence of the forces to be absorbed via the magnetic bearings with the aim of causing displacements of the axis of rotation of the rotor relative to the axis can also be used to transmit a controlled radial or axial oscillating movement to the rotor according to the features of claim 12. In this way, the evaporation process of the mixture of substances absorbed in the vessels can be effectively supported by the fact that the resulting curled and thus enlarged free surface of the mixture of substances to be treated improves the transfer of substances from the mixture into the interior of the housing.

The axis, which is fixedly arranged within the housing, is designed to accommodate electrical supply and control lines for both the bearings and the drive, in accordance with the features of claim 13. This is not a problem, since this measure does not involve vacuum-tight passages in the housing wall.

To further support the evaporation process, the housing, the walls of which mostly consist of metallic materials, can be equipped with heating elements according to the features of claim 14.

2823/34 Martin Christ Freeze Drying Systems GmbH

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According to the features of claim 15, cooling elements with which the housing is equipped can also be advantageous.

The support bearings according to the features of claims 16 and 17 are preferably designed as almost maintenance-free plastic or ceramic bearings and only come into operation when the rotor is at rest or in emergencies during run-down.

According to the features of claim 18, the stator systems of both the bearings and the drive and preferably the rotor systems of the bearings and the drive are completely encapsulated, preferably vacuum-tight cast. This results in not only high reliability and service life, but also the possibility that the interior of the housing can be cleaned, in particular rinsed, without dismantling the rotor bearing.
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Overall, the device according to the invention provides a working tool which, in addition to effective process control, is characterized by largely maintenance-free operation and a stable operating sequence which compensates for any unbalance conditions that may occur.
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The invention will be described below with reference to the drawings
schematically reproduced embodiments are explained in more detail. It
show:

Fig.1 shows a first embodiment of a device according to the invention in a
vertical section;

Fig.2 shows a second embodiment of a device according to the invention in a
Vertical section.
30

In Fig. 1, 1 designates a housing that is rotationally symmetrical with respect to a central axis 2 and is closed at the top by a cover 3. The upper edge of the housing 1 is characterized by a circumferential flange 4,

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on which, with the interposition of a sealing ring 5, the cover is fixed in a manner not shown in detail in the drawing. A fixed axis 6, to be described in more detail below, projects into the housing 1 from the bottom side, essentially as far as its upper region 7. The axis 6, which extends coaxially to the central axis 2, is fastened to the bottom 8 of the housing 1 in a manner not shown in the drawing. This design of the housing and the arrangement of the cover and the axis are to be understood merely as examples. The housing can also be cuboid-shaped. The cover can also be arranged laterally instead of on top of the housing. Finally, the axis mentioned can also protrude into the housing from above and be fastened on the top or cover side.

Reference numeral 9 designates a horizontally extending pipe socket, which is arranged, for example, at the upper region 7 of the housing 1 and is connected to a vacuum source (not shown in the drawing), via which a defined negative pressure can be set in the interior of the housing 1.

10 designates a hub which is mounted on the axle 6 in a manner to be described in more detail below and which carries a rotor 11 on the outside. This is equipped with several holders 12 provided in a uniform circumferential distribution, each for a vessel 13 which is open at the top and is intended to hold a mixture of substances 14 to be concentrated.

The holders 12 are formed by aligned bores 15, 16 of two axially spaced-apart annular disks 17, 18 that are coaxial with one another and with the axis 6, the axes of these bores 15, 16 each extending at the same angle to the axis 6. The axes of the said bores 15, 16 are thus all located on the outer surface of a pyramid with a circular base, the tip of which lies on the central axis 2. These bores are each intended to accommodate a vessel 13, which is inserted via the bore 15 of the upper annular disk 17 and rests on the bottom side on a third annular disk 19 that is axially spaced from the lower annular disk 18.

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The rotor 11 with the ring disks 17 to 19 attached to it can be arranged interchangeably on the hub 10. Furthermore, the ring disks 17 to 19 can themselves be detachably connected to the rotor 11.

20 designates the electrical drive of the rotor 11, which can be designed in the manner of an asynchronous or synchronous motor and consists of a fixed stator system 21 integrated into the structure of the axis 6 and, on the other hand, a rotor system 22 surrounded by the latter while leaving an air gap, which is designed in accordance with the electrical functional principle of the drive 20, for example, as a rotor winding system, as a permanent magnet system or as a squirrel-cage rotor.

Two axially spaced magnetic radial bearings 23, 24 are used to support the hub 10 on the axle 6. A magnetic axial bearing 25 is also provided at the lower end of the hub 10. These magnetic bearings are known as such and consist of winding systems that are magnetically linked to one another via an air gap - interlinked systems made up of permanent magnets and magnetic coils are also possible - whereby in the case of the radial bearings 23, 24 mentioned above, one radial air gap is formed and in the case of the axial bearing 25, one or two axially oriented air gaps are formed.

The winding systems of such magnetic bearings, which are comparable to the rotor and stator system of electrical machines, can also be designed in the manner of synchronous and asynchronous motors.

During normal operation, the hub 10 is supported exclusively by the magnetic bearings 23, 24 and 25 mentioned above. A radial support bearing 26 at the upper end of the hub 10 and a combined radial and axial support bearing 27 at the lower end of the hub are only provided for emergencies and when the machine is at a standstill. These support bearings 26, 27 can be designed as rolling bearings or as plain bearings, preferably with ceramic or plastic sliding elements. They should be operated with little or no lubricant.

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The distribution of the magnetic bearings 23 to 25 described above can be varied so that an axial magnetic bearing 25 is located at the upper end of the axis 6. The same applies to the distribution of radial and axial support bearings along the axis 6.
5

It is important that the hub 10 is a hat-like closed structure, placed on the top of the axis 6 and only open on the bottom, and that, due to the drive of the rotor, no rotary feedthroughs through the walls of the housing 1 are required. Electrical feedthroughs are limited to functional elements that are firmly connected to the axis 6 and can therefore be relocated into the structure of the axis 6.

28 indicates a higher-level control system which is connected to the magnetic bearings 23, 24, 25 mentioned above and to the drive 20 and which is designed in particular to monitor the operating sequence of this device, to visually display parameters characterizing the ongoing operation, etc. Finally, 29 designates flat heating elements which interact with the preferably metallic housing walls and via which the temperature of the interior of the housing can be adjusted to support the concentration process.

These heating elements 29 can be designed as heating sleeves. In addition, radiation elements known per se, such as infrared radiators, which are not shown in the drawing, can also be used, which are arranged on the housing and/or the cover in accordance with the irradiation of the mixture of substances to be treated.

Finally, the housing and/or the cover can also be provided with cooling elements that are also not shown in the drawing.
30

The embodiment shown in Fig. 2 differs from that of Fig. 1 only in that the axis 6 supporting the rotor 11 is designed as a hollow axis which is fixedly arranged on the bottom of the housing 1.

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Identical functional elements are designated by the same reference numbers, so that a repeated description can be dispensed with.

In the drawing, only the axial magnetic bearing 25 is located at the upper end of the axis 6 there. With regard to the distribution of the magnetic bearings 23 to 25 and also the support bearings, the above statements regarding the embodiment according to Fig. 1 also apply.

Claims (18)

1. Device for concentrating mixtures of substances by evaporating at least one component of the mixture, comprising a housing ( 1 ) which can be closed pressure-tight with a lid ( 3 ) and can be connected to a vacuum source, within which a rotor ( 11 ) is arranged which can rotate about an axis ( 6 ) and is operatively connected to a drive ( 20 ), with vessels ( 13 ) which are intended to hold the mixture of substances to be treated and which are detachably received in holders ( 12 ) of the rotor ( 11 ) in accordance with a uniform circumferential distribution, characterized in that the rotor ( 11 ) is mounted via its hub ( 10 ) with at least one magnetic bearing on the fixed axis ( 6 ) extending within the housing ( 1 ), and that the electrical rotor and stator systems of both the said drive ( 20 ) and of the at least one magnetic bearing are integrated into the structure of the axis ( 6 ) or the structure of the hub ( 10 ). 2. Device according to claim 1, characterized in that the stator systems of said drive ( 20 ) and of the at least one magnetic bearing are connected to the axis and that said rotor systems are located radially outside the axis. 3. Device according to claim 1, characterized in that the axis ( 6 ) is designed as a hollow axis, that the stator systems of said drive ( 20 ) and of the at least one magnetic bearing are connected to the axis ( 6 ) and that said rotor systems are located radially inside the axis ( 6 ). 4. Device according to one of claims 1 to 3, characterized in that the axis ( 6 ) extends perpendicular to a bottom ( 8 ) of the housing ( 1 ) closable by the cover ( 3 ). 5. Device according to one of claims 1 to 4, characterized by two axially spaced radial magnetic bearings ( 23 , 24 ) and one axial magnetic bearing ( 25 ). 6. Device according to one of claims 1 to 5, characterized by an electrical control ( 28 ) which is in operative connection with the magnetic bearings ( 23 , 24 , 25 ) and the drive ( 20 ). 7. Device according to one of claims 1 to 6, characterized in that the holders ( 12 ) of the rotor ( 11 ) are designed and arranged to receive the vessels ( 13 ), namely in accordance with a fixed angle between the longitudinal axis of a vessel ( 13 ) and the axis ( 6 ). 8. Device according to one of claims 1 to 6, characterized in that the holders ( 12 ) of the rotor ( 11 ) are intended and arranged to receive the vessels ( 13 ), with the proviso that the vessels are each held so as to be freely or with a limited angle of rotation pivotable about axes which run in a plane perpendicular to the axis ( 6 ) and tangential to a circle around this axis. 9. Device according to one of claims 6 to 8, characterized in that the control ( 28 ) is arranged with the cooperation of the magnetic bearing(s) ( 23 , 24 , 25 ) for the continuous detection of the mass of the substance mixture held in the vessels ( 13 ). 10. Device according to one of claims 6 to 9, characterized in that the control ( 28 ) is set up with the cooperation of the magnetic bearings ( 23 , 24 , 25 ) for the continuous detection of a static and/or a dynamic imbalance of the rotor ( 11 ). 11. Device according to claim 10, characterized in that the control ( 28 ) is set up with the cooperation of the magnetic bearings ( 23 , 24 , 25 ) by a field control adapted to the position of the unbalance, correct for the angle of rotation or the like to compensate for a static and/or a dynamic imbalance. 12. Device according to one of claims 6 to 11, characterized in that the control ( 28 ) is arranged with the cooperation of the magnetic bearings ( 23 , 24 , 25 ) by means of a field control appropriate to the angle of rotation or the like for transmitting a controlled radial and/or axial oscillating movement to the rotor ( 11 ). 13. Device according to one of claims 1 to 12, characterized in that the axis ( 6 ) is designed to accommodate electrical supply and control lines both of the magnetic bearing(s) ( 23 , 24 , 25 ) and of the drive ( 20 ). 14. Device according to one of claims 1 to 13, characterized in that the housing ( 1 ) is equipped with heating elements. 15. Device according to one of claims 1 to 14, characterized in that the housing ( 1 ) is equipped with cooling elements. 16. Device according to one of the preceding claims 1 to 15, characterized by support bearings ( 26 , 27 ) arranged within the hub ( 10 ) and/or the axle ( 6 ). 17. Device according to one of the preceding claims 1 to 15, characterized by support bearings arranged outside the hub ( 10 ) and/or the axle ( 6 ). 18. Device according to one of the preceding claims 1 to 17, characterized by a completely encapsulated bearing of the rotor ( 11 ) within the housing ( 1 ) which otherwise has no rotary feedthroughs or the like.