GB2153711A - Tubular bowl centrifuge - Google Patents

Abstract

A tubular bowl centrifuge has a rotor comprising a plurality of similar segments (10) movable between closed positions to form a closed tube and open positions for discharge of separated solids. It is not necessary for the bowl to be stopped completely for removal of collected solids; instead the bowl may be slowed to a suitable speed, eg about 3000 r.p.m., and the segments moved to their open positions for discharge of solids from the relatively slowly rotating bowl. The centrifuge can thus be operated in semi-continuous manner, increasing throughput. Longitudinal ribs (30) may be provided to promote laminar flow and to impart strength. An arrangement of locking lugs (38) and bolts (42) is provided to maintain the segments in closed position for high-speed rotation. <IMAGE>

Description

SPECIFICATION Tubular bowl centrifuge Field ofinvention This invention concerns a tubular bowl certrifuge.

Background to the invention A typical conventional tubular bowl centrifuge comprises a tubular steel bowl about 1 m in length arranged with its axis extending vertically, having an inlet at its lower end and an outlet at its upper end. In use, the bowl is rotated about its axis and liquid containing solids to be separated therefrom is fed, eg pumped, into the bowl via the inlet. Solids separate out under the action of centrifugal force and collect on the inner face of the bowl, and liquid is removed via the outlet. In order to remove collected solids the bowl is stopped completely and the solids removed, eg by scraping the bowl inner face or by removing a collector insert.

Because the centrifuge must be used in batch manner with significant downtime between batches, possible throughput is reduced. This is particularly so when separating liquid streams with high solids content. Further, tubular bowl centrifuges are commonly used for separating relatively small particles, such as various biochemical particles, where high rotation rates, e.g. 20000 r.p.m., are required to cause separation: a bowl rotating at such a speed takes about 15 minutes to stop and about 20 minutes to get up to speed again, resulting in a downtime between batches of at least about 35 minutes.

The invention According to the present invention there is provided a tubular bowl centrifuge comprising a tubular bowl arranged for rotation about an axis, wherein the bowl comprises a plurality ofsimilar segments movable between closed positions to form a closed tube and open positions for discharge of separated solids.

With a centrifuge in accordance with the invention it is not necessary for the bowl to be stopped completely for removal of collected solids; instead the bowl may be slowed to a suitable speed, eg about 3000 r.p.m., and the segments moved to their open positions for discharge of solids from the relatively slowly rotating bowl. The solids will normally be discharged automatically and relatively rapidly, eg within 1 second, underthe action of centrifugal force for collection on a suitable collecting surface.

Because the bowl does not have to be stopped completely, a centrifuge in accordance with the invention can be operated in semi-continuous manner, and this feature together with the rapid discharge rates which are possible means that throughput can be increased. Further, automatic discharge of solids simplifies operation.

The bowl will generally be arranged for rotation about a vertical axis. In this case the segments are conveniently arranged for hinging movement about respective vertical axes, producing a vertically extending slit between adjacent segments when open.

One preferred embodiment comprises four such segments of part circular cylindrical configuration.

Different numbers of segments may alternatively be used, e.g. six or eight, it generally being preferable to use an even number for reasons of symmetry and balance.

The segments when in their closed positions form a closed tube, sealed to prevent the escape of material being treated. To this end cooperating surfaces are conveniently provided on adjacent segments for sealing engagement, for example with opposed edges of the segments being suitably shaped to overlie one another in sealing manner.

Locking means is preferably provided for holding the segments in closed position, the locking means being releasable to permit opening movement of the segments. For example, a series of locking lugs may be provided for holding each segment in its closed position, the lugs being retractable for opening.

In one preferred embodiment the bowl comprises a plurality of segments arranged for hinging movement about respective vertical shafts, with a plurality of locking lugs fixed to each shaft. In order to open the segments the shafts are all simultaneously rotated in a appropriate direction to free the lugs from engagement with the relevent segment. The free segments can then move outwardly, by hinging movement on the relevant supporting shaft; in use centrifugal force would cause such outward movement of the segments to occur. The segments may then be closed by rotating the shafts in the opposite direction to move the lugs, and segments engaged thereby, inwardly.

With such an arrangement a series of locking bolts may also be provided for further securing the segments in their closed positions, the bolts being retractable to permit opening as described above.

Such bolts are conveniently solenoid operated. As a safety feature an interlock is preferably provided arranged to permit high speed rotation of the centrifuge only when the bolts are locked.

Control of the segments, e.g. by rotation of supporting shafts as discussed above, is conveniently effected hydraulically, with suitable linkages leading to remote actuating means and equipment.

Each segment is preferably of one piece construction, and is made of suitable material to withstand the high stresses to which it will be subjected in use.

Light, strong composite materials are preferred, e.g.

carbon fibre reinforced epoxy resin, or glass fibre reinforced materials.

The inner face of each segment is conveniently provided with a longitudinally extending reinforcing rib. The rib is preferably integrally formed with the segment, and may be of hollow construction. Such a rib not only strengthens the arrangement but also acts to improve flow behaviour of liquid passing through the centrifuge, promoting laminarflow, which prevents collected solids from being removed from the bowl wall and also means that the centrifuge can be used for handling fragile material such as fragile animal and plant cells. The rib may be arranged to provide an over centre closing effect, to assist closing against centrifugal force.

Strengthening ribs may additionally or alternative ly be provided on the outer faces of the segments.

A suitable collecting surface for receiving discharged solids may be provided. Conveniently a collecting cylinder is located around the bowl on which solids collect and slide down under the action of gravity for collection at the base.

Suitable arrangements are provided at the ends of the bowl for introducing and removing liquid. For example, a disc-like end piece having an inlet or outlet as appropriate may be sealingly received within each end of the bowl to produce a closed, sealed arrangement from which liquid will not escape in use.

The present invention also includes within its scope a method of separating solids from liquid, comprising introducing a mixture to be treated to a centrifuge in accordance with the invention, the bowl of which is rotated art a suitable speed to cause separation; stopping the flow of mixture; slowing the bowl to a relatively slow speed of rotation (eg 3000 r.p.m.); opening the segments of the bowl; collecting solids discharged form the bowl; closing the segments of the bowl; increasing the speed of rotation; introducing to be centrifuge further mixture to be treated.

The relevant steps are repeated as appropriate.

The invention will be further described, by way of example, with reference to the accompanying drawings.

In the drawings Figure 1 is a schematic perspective view illustrating the segments of one embodiment of centrifuge in accordance with the present invention; Figure 2 is an enlarged scale view showing part of one of the segments of the arrangement of Figure 1; Figure 3 is a sectional view, to a further enlarged scale, of part of a further embodiment of centrifuge in accordance with the invention; and Figure 4 is a perspective view of part of the embodiment illustrated in Figure 3.

Detailed description of the drawings Figures 1 and 2 illustrate part of a tubular bowl centrifuge comprising four similar segments 10, each of part circular cylindrical configuration. Each segment is of one piece construction and is made of a light, strong composite material such as carbon fibre reinforced epoxy resin. Each segment is rigidly secured to a respective stainless steel former 12 and arranged for rotation about an associated vertical steel shaft 14.

The segments are arranged for hinging movement about the associated shafts for movement between closed positions, illustrated in dashed lines in Figure 1, in which they cooperate to form a closed, sealed tube, and open positions, illustrated in full lines in Figure 1, for discharge of separated solids.

The centrifuge further comprises upper and lower end pieces (not shown), each in the form of a disc shaped element with an inlet (at the base) or outlet (at the top), sealingly received within the tubular bowl formed by the segments when closed, to produce a closed, sealed arrangement from which liquid will not escape in use.

Figures 3 and 4 illustrate in more detail features of a further embodiment, which is generally similar to the embodiment of Figures 1 and 2.

The embodiment of Figures 3 and 4 comprises four similar segments, three of these designated by the reference numerals 16, 18 and 20 being illustrated in Figure 3. The segments are of similar material and construction to those of the Figure 1 and 2 embodiment, having associated formers such as formers 22 and 24 as shown. The segments are similarly mounted for rotation on associated shafts 26,28.

The main difference between the embodiments is that the segments of the Figure 3 and 4 embodiment each include a longitudinally extending internal rib 30,32 formed integrally with the segment. The ribs are for reinforcement and also have the effect of promoting laminar flow in liquid passing through the centrifuge.

Figures 3 and 4 also illustrate locking and sealing arrangements. The opposed major, vertical edges of the segments are formed with cooperating surfaces to overlie one another in sealing engagement when closed. For example, segment 16 includes a sealing lip 34 running along the length of the edge adjacent the associated shaft, with the adjacent edge 38 of segment 18 shaped for sealing engagement therewith. Similar sealing arrangements are provided at the three other join regions between adjacentseg- ments.

Locking means are also provided at each join region. These comprise a series of locking lugs eg 38,40 fixed in rotation to the associated shaft. As shown in Figure 4 lugs 38 are fixed to shaft 26. The lugs act to hold the segments in their closed positions, as illustrated in Figures 3 and 4. In order to open the segments the shafts are all simultaneously rotated in an appropriate direction to free the lugs from engagement with the relevant segment, ie clockwise as viewed in Figure 3. The freed segments can then move outwardly, by hinging movement on the relevant supporting shaft; in use centrifugal force would cause such outward movement of the segments to occur. The segments may then be closed by rotating the shafts in the opposite direction, ie. anti-clockwise as viewed in Figure 3, to move the lugs, and segments engaged thereby, inwardly.

The shafts and hence locking lugs are preferably hydraulically operated, with suitable linkages (not shown) leading to remote operating means and equipment.

A series of locking bolts 42, 44 is also be provided for further securing the segments in their closed positions, the bolts being rectractable to permit opening as described above. The bolts are conveniently solenoid operated. As a safety feature an interlock is provided arranged to permit high speed rotation of the centrifuge only when the bolts are locked.

Apparatus in accordance with the invention is used as follows.

With the segments closed and secured in position with the locking lugs and bolts, the centrifuge is rotated at a suitable operating speed for separation.

For example speeds of about 20000 r.p.m. are required when dealing with relative small particles for example certain biological and microbial materials such as cell debris and fine protein precipitates.

Liquid containing solids to be separated therefrom is introduced via the inlet in the lower end piece.

Separation occurs within the tubular bowl, with separated solids collecting on the bowl inner face.

When sufficient material has been collected and the solids are to be recovered the supply of liquid is stopped and the centrifuge is slowed to a relatively slow speed, eg 3000 r.p.m. The locking bolts re released to permit opening of the segments. The segments are then opened by simultaneously rotating the four shafts in a clockwise direction, as viewed in Figure 3). This allows the segments to move outwardly under the action of centrifugal force, as explained above, and open.

With the segments open the collected solids discharge under the action of centrifugal force, with discharge typically taking about 1 second or less.

The discharged solids are collected on a suitable surface (not shown) such as a collecting cylinder located around the bowl on which solids collect and slide down under the action of gravity for collection at the base.

The segments are then closed again by reverse rotation of the shafts, and the locking bolts reengaged. The centrifuge is then brought up to operating speed again and a further supply of liquid is introduced.

The embodiments described above are about 1 m in length and about 0.1 m in a diameter. When the segments are open a slit about 10mm wide is produced between adjacent segments. The capacity is about 61. Other sizes of machine can be course also be constructed.

Claims (25)

1. Atubularbowl centrifuge comprising a tube lar bowl arranged for rotation about an axis, wherein the bowl comprises a plurality of similar segments movable between closed positions to form a closed tube and open positions for discharge of separated solids.

2. A centrifuge according to claim 1, wherein the bowl is arranged for rotation about a vertical axis and the segments are arranged for hinging movement about respective vertical axes.

3. A centrifuge according to claim 2, comprising four segments of part circular cylindrical configuration.

4. A centrifuge according to claim 1, 2 or 3, wherein cooperating surfaces are provided on adjacent segments for sealing engagement when the segments are in their closed positions.

5. A centrifuge according to claim 4, wherein opposed edges of the segments are suitably shaped to overlie one another in sealing manner.

6. A centrifuge according to any one of the preceding claims, wherein locking means is provided for holding the segments in closed position, the locking means being releasable to permit opening movement of the segments.

7. A centrifuge according to claim 6, wherein a series of locking or closing lugs are provided for holding each segment in its closed position, the lugs being retractable for opening.

8. A centrifuge according to any one of the preceding claims, wherein the bowl comprises a plurality of segments arranged for hinging movement about respective rotatable vertical shafts, with a plurality of locking or closing lugs fixed to each shaft.

9. A centrifuge according to claim 8, additionally comprising a series of locking bolts for further securing the segments in their closed positions, the bolts being retractable to permit opening.

10. A centrifuge according to claim 9, wherein the bolts are solenoid or pneumatically operated.

11. A centrifuge according to claim 9 or 10, further comprising an interlock arranged to permit high speed rotation of the centrifuge only when the bolts are locked.

12. A centrifuge according to any one of the preceding claims, wherein control of the segments is effected hydraulically, with suitable linkages leading to remote actuating means and equipment.

13. A centrifuge according to any one of the preceding claims, wherein each segment is of one piece construction.

14. A centrifuge according to any one of the preceding claims, wherein the segments are of carbon fibre reinforced epoxy resin, or glass fibre reinforced materials.

15. A centrifuge according to any one of the preceding claims, wherein the inner face of each segment is provided with a longitudinally extending reinforcing rib.

16. A centrifuge according to claim 15, wherein each rib is integrally formed with the associated segment.

17. A centrifuge according to claim 15 or 16, wherein each rib is of hollow construction.

18. A centrifuge according to claim 15, 16 or 17, wherein each rib is arranged to provide an over centre closing effect, to assist closing against centrifugal force.

19. A centrifuge according to any one of the preceding claims, additionally comprising strengthening ribs on the outer faces of the segments.

20. A centrifuge according to any one of the preceding claims, additionally comprising a suitable collecting surface for receiving discharged solids.

21. A centrifuge according to claim 20, wherein a collecting cylinder is located around the bowl.

22. A centrifuge according to any one of the preceding claims, wherein a respective disc-like end piece having an inlet or outlet as appropriate is sealingly received within each end of the bowl.

23. Atubular bowl centrifuge substantially as herein described with reference to, and as shown in, the accompanying drawings.

24. A method of separating solids from liquid, comprising introducing a mixture to be treated to a centrifuge in accordance with any one of the preceding claims, the bowl of which is rotated at a suitable speed to cause separation; stopping the flow of mixture; slowing the bowl to a relatively slow speed of rotation opening the segments of the bowl; collecting solids discharged form the bowl; closing the segments of the bowl; increasing the speed of rotation; introducing to the centrifuge further mixturn to be treated.

25. A method of separating solids from liquid, substantially as herein described with reference to the accompanying drawings.