TECHNICAL FIELD

The present inventive concept relates to the field of centrifugal separators. More particularly it relates to a method for eliminating air locks in a centrifugal separator.

BACKGROUND

Centrifugal separators are generally used for separation of liquids and/or solids from a liquid mixture or a gas mixture. During operation, fluid mixture that is about to be separated is introduced into a rotating bowl and due to the centrifugal forces, heavy particles or denser liquid, such as water, accumulates at the periphery of the rotating bowl whereas less dense liquid accumulates closer to the central axis of rotation. This allows for collection of the separated fractions, e.g. by means of different outlets arranged at the periphery and close to the rotational axis, respectively.

When processing pharmaceutical products such as fermentation broths, it may be desirable to eliminate the need for cleaning-in-place processes of the rotating bowl and the separator parts that have contacted the processed product. More useful may be to exchange the rotating bowl as a whole, i.e. to use a single use solution. This is advantageous from a hygienic perspective of the process.

WO 2015/181177 discloses a separator for the centrifugal processing of a flowable product comprising a rotatable outer drum and an exchangeable inner drum arranged in the outer drum. The inner drum comprises means for clarifying the flowable product. The outer drum is driven via drive spindle by a motor arranged below the outer drum. The inner drum extends vertically upwardly through the outer drum which has fluid connections arranged at an upper end of the separator.

However, when using a separator with a single use insert, several issues may arise. One such issue is that low pressures are used. That means that common methods to remove trapped air in the centrifuge are not applicable. Air locks cannot be compressed by external pressure nor be removed by intermittent discharge of the separator rotor bowl. Thus, there is a need in the art for improved ways for venting or eliminating air in a centrifugal separator, and especially for a centrifugal separator that is for use in single use applications.

SUMMARY

It is an object of the invention to at least partly overcome one or more limitations of the prior art. In particular, it is an object to provide a centrifugal separator bowl that facilitates an easy removal of trapped air.

As a first aspect of the invention, there is provided a centrifugal separator bowl comprising

a rotor casing enclosing a separation space in which a stack of frustoconical separation discs is arranged, the rotor casing being arranged to rotate around a vertical axis (X) of rotation, wherein the separation discs are arranged with the imaginary apex pointing to the axially lower end of the rotor casing;

a feed inlet at the axially lower end for receiving the fluid mixture to be separated;

a distributor for distributing the fluid mixture from the inlet to the separation space, said distributor being arranged for guiding the fluid mixture to be separated continuously from an axially lower position at the inlet to an axially upper position in the separation space;

a light phase outlet for discharge of a separated phase of a first density and a heavy phase outlet for discharge of a separated phase of a second density higher than said first density, said heavy phase outlet being arranged at the axially upper end of the rotor casing;

at least one outlet conduit for transporting separated phase of the second density from the separation space, said conduit extending from a radially outer position of said separation space to said second liquid outlet; said conduit having a conduit inlet arranged at the radially outer position and a conduit outlet at a radially inner position.

The rotor casing encloses a separation space in which the separation of the fluid mixture, such as a gas mixture or a liquid mixture, takes place. The rotor casing may be a rotor casing and be free of any further outlets for separated phases. Thus, the rotor casing may be solid in that it is free of any peripheral ports for discharging e.g. a sludge phase accumulated at the periphery of the separation space. However, in embodiments, the rotor casing comprises peripheral ports for intermittent or continuous discharge of a separated phase from the periphery of the separation space.

In embodiments of the first aspect of the invention, the rotor casing is free of any further outlets for separated phases.

Thus, the rotor casing may be solid in that it is free of any peripheral ports for discharging e.g. a sludge phase accumulated at the periphery of the separation space. Thus, the exchangeable insert may comprise solely the light phase and the heavy phase outlet.

In embodiments of the first aspect of the invention, the separation space extends from a first axial position to a second axial position, and wherein the inner diameter of the separation space continuously increases from said first to said second axial position. As an example, the heavy phase collection space of the separation space may extend from a first axial position to a second axial position, and the inner diameter of the separation space may continuously increase from said first to said second axial position. The separation space may thus comprise a heavy phase collection space, which is a space that is radially outside the stack of separation discs. The separation space may also comprise a radially inner portion, which is thus formed by the interspaces between the discs of the stack of separation discs.

Thus, the inner surface of the separation space may gradually increase in an axial direction. As an example, the first axial position may be closer to the inlet and the second axial position may be closer to the outlets. A continuous increase of the inner diameter, with no intermittent decrease, may facilitate collection of the separated heavy phase at the second axial position of the separation space.

The separation space comprises a stack of separation discs arranged centrally around the axis of rotation. The separation discs have a frustoconical shape, which refers to a shape having the shape of a frustum of a cone, which is the shape of a cone with the narrow end, or tip, removed. A frustoconical shape has thus an imaginary apex where the tip or apex of the corresponding conical shape is located. The imaginary apex of the frustoconical separation discs points towards the lower axial end of the separator bowl.

The axis of the frustoconical shape is axially aligned with the rotational axis of the rotor casing. The axis of the frustoconical portion is the direction of the height of the corresponding conical shape or the direction of the axis passing through the apex of the corresponding conical shape.

The separation discs may e.g. comprise a metal or be of metal material, such as stainless steel. The separation discs may further comprise a plastic material or be of a plastic material.

The feed inlet is for receiving the fluid mixture to be separated from a stationary inlet pipe, and the distributor is for guiding the received fluid, such as a liquid, to the separation space. The distributor may thus be arranged at the inlet.

The distributor is further arranged to guide the fluid to be separated upwards to the separation space, i.e. from an axially lower position at the inlet to an axially upper position in the separation space. The distributor is arranged to guide the fluid upwards without any interruptions, i.e. the fluid is guided up to the separation space without being guided towards the axially lower end.

The light phase outlet is for discharging a separated phase of a lower density and the heavy phase outlet is for separating a phase of a higher density. The heavy phase outlet is arranged at the upper axial end of the rotor casing. The light phase outlet may be arranged at the lower axial end or at the upper axial end of the rotor casing.

There is further at least one outlet conduit arranged for transporting a separated heavy phase from the separation space to the heavy phase outlet. The at least one conduit extends from a radially outer position in the separation space to the heavy phase outlet, which is thus at a radially inner position. The conduit has a conduit inlet arranged at the radially outer position and a conduit outlet at a radially inner position. Further, the at least one outlet conduit is arranged with an upward tilt from the conduit inlet to the conduit outlet. Thus, relative the radial plane, the conduit is tilted axially upwards from the conduit inlet in the separation space to the conduit outlet at the heavy phase outlet. This may facilitate transport of the separated heavy phase in the conduit.

The conduit inlet may be arranged at an axially upper position in the separation space. The conduit inlet may be arranged at an axial position where the separation space has it largest inner diameter.

The outlet conduit may be a pipe. As an example, the rotor casing may comprise a single outlet conduit.

In embodiments, the at least one outlet conduit is arranged with an upward tilt from the conduit inlet to the conduit outlet.

In embodiments of the first aspect of the invention, the at least one outlet conduit is tilted with an upward tilt of at least 2 degrees relative the radial plane. As an example, the at least one outlet conduit may be tilted with an upward tilt of at least 5 degrees, such as at least 10 degrees, relative the radial plane.

The at least one outlet conduit may facilitate transport of the separated heavy phase in the separation space to the heavy phase outlet.

The first aspect of the invention is based on the insight that by arranging the inlet, distributor, separation discs and the outlet conduit as disclosed above, the centrifugal separator bowl is de-aerated automatically, i.e. the presence of air-pockets is eliminated or decreased so that any air present within the rotor casing is forced to travel unhindered upwards and out via the heavy phase outlet. Consequently, the design of the separator bowl as according to the first aspect of the invention provides for a bowl that is vented automatically. For example, if the bowl is filled up through the feed line, all air may be vented out through the heavy phase outlet.

According to embodiments, the distributor and the inlet are arranged to guide the fluid mixture to be separated solely along an upwards path from the stationary inlet conduit to the separation space. This means that air may easily escape via the outlet conduit and out via the heavy phase outlet.

Thus, the inlet, distributor, separation space, outlet conduit and heavy phase outlet are arranged so that they form a fluid path that extends solely axially upwards from the inlet to the heavy phase outlet. This is advantageous in that it minimizes the risk of air-pockets or air-locks within the separator. Such air locks may severely decrease the functionality and separation capacity and create unwanted air-liquid interphases during operation.

In embodiments of the first aspect, the feed inlet is at the rotational axis (X).

Furthermore, also the heavy phase outlet may be arranged at the rotational axis (X).

This may be advantageous in that it provides for a gentler treatment of the separated heavy phase. If the heavy phase is discharged at a small radius from the rotational axis (X), the rotational forces are fewer. This may be an advantage e.g. when separating a cell culture. Such cells may be shear sensitive, so it may be advantageous to be able to discharge them at a small diameter from the rotational axis.

Furthermore, it may be advantageous in allowing both the inlet and a liquid outlet to be arranged at the axis of rotation (X).

In embodiments of the first aspect, the centrifugal separator bowl is further comprising a mechanical hermetic seal for sealing said inlet to a stationary inlet pipe.

The inlet pipe may thus also be arranged at the rotational axis (X).

The mechanical hermetic seal is a rotatable seal for connecting and sealing the inlet to a stationary inlet pipe. A hermetic seal refers to a seal that is supposed to give rise to an air tight seal between a stationary portion and the rotor casing and prevent air from outside the rotor casing to contaminate the feed. Therefore, the rotor casing may be arranged to be completely filled with liquid during operation. This means that no air or free liquid surfaces is meant to be present in the rotor casing during operation.

This seal may be arranged at the border of the rotor casing and a stationary portion and may thus comprise a stationary part and a rotatable part.

Thus in embodiments, the mechanical hermetic seal comprises a stationary part arranged in a stationary portion and a rotatable part arranged in the axially lower end of the rotor casing.

Further, the rotatable part of the first rotatable seal may be arranged directly onto the axially lower portion of the rotor casing. In embodiments of the first aspect of the invention, the distributor is arranged to guide the fluid mixture to an axially upper position in the separation space, which is at a radial position that is outside the radial position of the outer circumference of the stack of frustoconical separation discs.

Liquid or fluid to be separated may thus be supplied to the separation space radially outside of the stack of separation discs.

However, the distributor may also be arranged to supply the liquid or fluid to be separated to the separation space at a radial position that is within the stack of separation discs, e.g. by axial distribution openings in the distributor and/or the stack of separation discs. Such openings may form axial distribution channels within the stack.

Furthermore, the stack of separation discs may form a stack on top of the distributor. The distributor may thus function as a support for the stack of separation discs. This may save space in the rotor casing.

Moreover, the distributor may have a conical outer surface with the apex pointing toward the axial lower end of the centrifugal rotor.

The conical outer and lower surface of the distributor may thus have the same angle relative the rotational axis as the separation discs. In the stack of separation discs. The conical shape of the distributor may have a diameter that is about the same or larger than the outer diameter of the separation discs in the stack.

The distributor may further comprise distribution channels arranged for guiding the fluid mixture to be separated continuously from an axially lower position at the inlet to an axially upper position in the separation space.

The distribution channels may for example be straight or curved. The distribution channels may further have a constant channel width or be diverging.

Furthermore, the distribution channels may extend along the outer surface of the distributor. The outer, and lower, surface of the distributor, as well as the distribution channels, may thus tilt upwards from the inlet to the separation space, thereby guiding the fluid mixture to be separated continuously from an axially lower position at the inlet to an axially upper position in the separation space.

In embodiments of the first aspect of the invention, the separator bowl forms part of an exchangeable separation insert for a centrifugal separator.

The exchangeable separation insert may thus be a pre-assembled insert ready for being inserted into a rotatable member, which may include rotatable support for the insert. Such a rotating assembly may also comprise a drive unit for rotating the rotatable member around the axis of rotation (X).

According to embodiments, the exchangeable separation insert is a single use separation insert. Thus, the insert may be adapted for single use and be a disposable insert. The exchangeable insert may thus be for processing of one product batch, such as a single product batch in the pharmaceutical industry, and then be disposed.

It is advantageous to have a self-deaerated insert in single use or pharmaceutical applications, since you may be prevented to open up the insert to get rid of air for hygienic reasons.

The exchangeable separation insert may comprise a polymeric material or consist of a polymeric material. As an example, the rotor casing and the stack of separation discs may comprise, or be of a polymeric material, such as polypropylene, platinum cured silicone or BPA free polycarbonate. The polymer parts of the insert may be injection moulded. However, the exchangeable separation insert may also comprise metal parts, such as stainless steel. For example, the stack of separation discs may comprise discs of stainless steel.

The exchangeable insert may be a sealed sterile unit.

Further, if the centrifugal separator bowl is an exchangeable separation insert, the centrifugal bowl may be arranged to be solely externally supported by external bearings. Thus, the rotor casing, as well as the whole centrifugal separator bowl, may be free of any bearings.

Furthermore, the exchangeable separation insert may be free of any rotatable shaft that is arranged to be supported by external bearings.

Thus, as a configuration of the first aspect of the invention, there is provided a modular centrifugal separator configured for separating a liquid feed mixture into a heavy phase and light phase, the modular centrifugal separator comprising a base unit and an exchangeable separation insert, wherein the exchangeable separation insert comprises a centrifugal separator bowl as disclosed herein. The base unit may comprise a stationary frame, a rotatable member configured to rotate about an axis of rotation arranged in the stationary frame, and a drive unit for rotating the rotatable member about the axis of rotation. The rotatable member may have a first axial end and a second axial end, and may delimit an inner space at least in a radial direction, the inner space being configured for receiving at least one part of the exchangeable separation insert therein. The rotatable member may be provided with a first through opening to the inner space at the first axial end and configured for a first fluid connection of the exchangeable separation insert to extend through the first through opening. The rotatable member may also comprise a second through opening to the inner space at the second axial end and configured for a second fluid connection of the exchangeable separation insert to extend through the second through opening.

However, in embodiments of the first aspect of the invention, the centrifugal separator bowl is comprising a spindle arranged to rotate coaxially with said separator bowl and further arranged to be rotatably supported by a stationary frame.

Thus, as a configuration of the first aspect of the invention, there is provided a centrifugal separator for separating a fluid mixture, the centrifugal separator comprising a stationary frame, a spindle rotatably supported by the frame, a centrifugal separator bowl as disclosed above mounted to a first end of the spindle to rotate together with the spindle around an axis (X) of rotation. The centrifugal separator may further comprise drive means for rotating the centrifugal separator bowl around the axis of rotation.

As a second aspect of the invention, there is provided a method of separating a liquid mixture comprising

a. providing a centrifugal separator comprising the centrifugal separator bowl according to any embodiment of the first aspect above;

b. supplying a liquid to said feed inlet at standstill and withdrawing liquid from said heavy phase outlet to eliminate any air-locks within said centrifugal separator bowl;

c. rotating said centrifugal separator bowl around the axis of rotation (X);

d. supplying said liquid mixture to be separated to said feed inlet.

The second aspect may generally present the same or corresponding advantages as the former aspect. The terms and definitions used in relation to the second aspect are the same as discussed in relation to the first aspect above.

The method of the second aspect is further advantageous in that liquid may be supplied at standstill of the separator bowl, i.e. when the centrifugal separator bowl does not rotate, in order to discharge any air present within the rotor casing out via the heavy phase outlet before rotation of the bowl.

In embodiments of the second aspect of the invention, the liquid mixture to be separated is a cell culture mixture.

The liquid supplied at standstill may be any type of liquid. As an example, if a cell culture is to be separated, the liquid supplied in step b) may be buffer liquid for the cell culture mixture.

In embodiments of the second aspect of the invention the liquid supplied in step b) is the liquid mixture to be separated. Thus, the liquid mixture to be separated may be supplied to the centrifugal separator bowl at standstill to eliminate air locks, and then the rotation of the centrifugal separator bowl may start when the liquid mixture to be separated is present within the centrifugal separator bowl.

As a third aspect of the invention there is provided a system for separating a cell culture mixture, comprisinga centrifugal separator comprising the centrifugal separator bowl according to the first aspect of the invention;a fermenter for hosting a cell culture mixture;a connection from the bottom of the fermenter to the centrifugal separator arranged so that the cell culture mixture to be separated is supplied to the inlet at the axially lower end of the centrifugal separator bowl.

The fermenter may be a fermenter tank.

The connection may be any suitable connection, such as a pipe. The connection may be a direct connection between fermenter and the centrifugal separator.

