Centrifugal separator having a forcing device to create a radial leak flow

A centrifugal separator includes a frame and a rotating part including a spindle and a centrifuge rotor enclosing a separation space. An inlet channel provides fluid communication into the separation space and includes a rotary channel part, a frame channel part, and a first seal at the interface between the rotary and frame channel parts. An outlet channel provides fluid communication out from the separation space and includes a rotary channel part, a frame channel part, and a second seal at the interface between the rotary and frame channel parts. The inlet and outlet channels are arranged concentrically with each other. A forcing device is provided to generate a leak flow through one of the first and second seals in a first direction from the outlet channel to the inlet channel and to counteract leakage in the opposite direction.

TECHNICAL FIELD OF THE INVENTION

The present invention refers to a centrifugal separator according to the preamble of claim1, see U.S. Pat. No. 4,759,744.

PRIOR ART

The centrifugal separator disclosed in U.S. Pat. No. 4,759,744 comprises a frame (illustrated as stationary members), and a rotating part comprising a spindle and a centrifuge rotor enclosing a separation space. The rotating part is supported by the frame to rotate around an axis of rotation. A drive member (not shown in the drawing) rotates the rotating part. An inlet channel provides fluid communication into the separation space and comprises a rotary channel part attached to the centrifuge rotor, a frame channel part attached to the frame, and sealing means provided at the interface between the rotary channel part of the inlet channel and the frame channel part of the inlet channel. An outlet channel provides fluid communication out from the separation space and comprises a rotary channel part attached to the centrifuge rotor, a frame channel part attached to the frame, and sealing means provided at the interface between the rotary channel part of the outlet channel and the frame channel part of the outlet channel. A further outlet channel provides fluid communication out from the separation space and comprises a rotary channel part attached to the centrifuge rotor, a frame channel part attached to the frame, and sealing means provided at the interface between the rotary channel part of the further outlet channel and the frame channel part of the further outlet channel.

In centrifugal separators, such as the one disclosed in U.S. Pat. No. 4,759,744, it is important that the sealing means ensures that no leakage can occur. Leakage from the inlet channel into one of the outlet channels will severely reduce the efficiency of the centrifugal separator, and can under certain circumstances destroy one of the separated products. Consequently, the costs for the sealing means and for the maintenance of the sealing means are significant.

Furthermore, in centrifugal separators, such as the one disclosed in U.S. Pat. No. 4,759,744 where all bearings and the drive motor are positioned on the spindle side, there is a difficulty to ensure a proper functioning of the sealings of the communication channels at the side of the centrifuge rotor turned away from the spindle. This is due the to pivoting of the spindle and the centrifuge rotor during operation of the centrifugal separator. These sealings require a complex design since they have to provided a proper sealing of movements in several directions.

WO 2007/133161 discloses another centrifugal separator comprising a frame and a rotating part comprising a spindle and a centrifuge rotor enclosing a separation space. The rotating part is supported by the frame to rotate around an axis of rotation. An inlet channel, comprising a rotary channel part attached to the centrifuge rotor, provides fluid communication into the separation space. An outlet channel, comprising a rotary channel part attached to the centrifuge rotor, provides fluid communication out from the separation space. A possible further outlet channel provides fluid communication out from the separation space.

EP-B-37210 discloses a mechanical seal with two pairs of opposite seal surfaces. One seal surface in one of the pairs is provided with spiral pumping grooves for forcing a medium in one determined direction through the seal between the opposite seal surfaces.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the problems discussed above, and to provide a centrifugal separator, that may ensure a high separation efficiency, low costs for the sealing means and low maintenance costs.

This object is achieved by the centrifugal separator initially defined, which is characterized in

that the inlet channel and the outlet channel are arranged adjacent to and concentrically with each other, and

that forcing means are provided to generate a leak flow through one of the sealing means in a first direction from the outlet channel to the inlet channel and thus to counteract, or prevent, leakage in the opposite direction from the inlet channel to the outlet channel.

With such an arrangement of the inlet and outlet channels and the forcing means, it is possible to counteract or prevent leakage of the product fed to the separation space into the separated product leaving the separation space. A low degree of impurities in the separated product is thus achieved. Furthermore, the arrangement of the inlet and outlet channels adjacent to each other makes it possible to let all communication channels enter the separation space from one side, for instance through the spindle, thereby leaving the other side free with only one or completely from communication channels into or out from the centrifuge rotor and the separation space. Such an arrangement enables a very compact design of the centrifugal separator, where at least most of the sealing means and bearings may be provided on one side of the centrifuge rotor, which simplifies the design and construction of the centrifugal separator.

According to an embodiment of the invention, the inlet channel is configured to feed a product to be separated into the separation space and the outlet channel is configured to discharge a separated primary phase of the product from the separation space, wherein the forcing means are provided to generate said leak flow from the outlet channel to the inlet channel and thus to counteract, or prevent, leakage from the inlet channel to the outlet channel, i.e. into the primary phase of the separated product.

According to a further embodiment of the invention, the forcing means are comprised by said one of the sealing means. Advantageously, at least said one of the sealing means may then comprise a rotary seal surface on the respective rotary channel part and a frame seal surface on the respective frame channel part, and wherein the rotary seal surface and the frame seal surface are arranged opposite to each other. A small gap may be provided between the rotary seal surface and the opposite frame seal surface. Advantageously, the rotary seal surface and the frame seal surface both extend in parallel with a radial plane with respect to the axis of rotation.

According to a further embodiment of the invention, the forcing means comprises a plurality of at least partly non-radial pumping elements on at least one of the rotary seal surface and the frame seal surface. The pumping elements may comprises blades projecting from at least one of the rotary seal surface and the frame seal surface, or grooves in at least one of the rotary seal surface and the frame seal surface. Advantageously, the pumping elements may have a curved shape seen in the direction of the axis of rotation.

According to a further embodiment of the invention, the forcing means may be configured to generate an overpressure in the outlet channel with respect to the inlet channel, at least in an area around said one of the sealing means. Normally, centrifugal separators, in particularly with a closed separation space, i.e. of a so called hermetic type, are operated with an overpressure in the inlet channel with respect to the outlet channel.

According to a further embodiment of the invention, the forcing means may comprise a pump wheel provided to operate on the outlet channel and arranged to force the fluid communication through the outlet channel, and thus to generate said leak flow. The pump wheel may be located upstream said one of the sealing means. The pump wheel may be driven by means of a turbine wheel provided in the inlet channel. The pump wheel provides an example of advantageous forcing means for providing such an overpressure in the outlet channel.

According to a further embodiment of the invention, the spindle comprises the rotary channel part of the inlet channel and the rotary channel part of the outlet channel. Consequently, both the inlet channel and the outlet channel extend through the spindle, enabling a compact design of the centrifugal separator as mentioned above.

According to a further embodiment of the invention, the drive member comprises an electrical motor having a rotor and a stator, wherein the rotor is fixedly connected to the rotating part. Advantageously, the rotor of the electrical motor may be provided on or fixed to the spindle.

According to a further embodiment of the invention, the outlet channel is provided within the inlet channel. This is advantageous with respect to the energy consumption since the outlet flow may be provided at a smaller radius than the inlet flow.

According to a further embodiment of the invention, the inlet channel is provided within the outlet channel.

According to a further embodiment of the invention, the centrifugal separator comprises a further outlet channel configured to provide fluid communication out from the separation space and comprising a rotary channel part attached to the centrifuge rotor, a frame channel part attached to the frame, and sealing means provided at the interface between the rotary channel part and the frame channel part. Advantageously, the further outlet channel may be configured to discharge a separated secondary phase of the product from the separation space, wherein the forcing means are provided to generate a leak flow through the sealing means of the inlet channel from the further outlet channel into the inlet channel and thus to counteract, or prevent, leakage from the inlet channel into the further outlet channel.

According to a further embodiment of the invention, the outlet channel is provided within the inlet channel, wherein the inlet channel is provided within the further outlet channel at least at the interface between the rotary channel part of the inlet channel and the frame channel part of the inlet channel, and wherein the forcing means are provided to generate a leak flow through the sealing means of the inlet channel from the further outlet channel into the inlet channel and thus to counteract, or prevent leakage from the inlet channel into the further outlet channel. Advantageously, the rotary channel parts of the inner outlet channel, the intermediate inlet channel and the outer further outlet channel are all contained or comprised in the spindle. This embodiment is especially advantageous due to the possibility of complete dispense with any communication channels through the casing at the side turned away from the spindle.

FIG. 1discloses a centrifugal separator according to a first embodiment comprising a frame1and a rotating part2. The rotating part2is rotatably supported by the frame1to rotate around an axis x of rotation by means of suitable bearing means, for instance in the form of one or more bearings. In the first embodiment the bearing means comprises a first bearing3a, and a second bearing3b. The first and second bearings3a,3bmay comprise roller bearings or ball bearings. The first bearing3amay be elastically mounted to the frame1via a first resilient member4ahaving suitable elastic and damping properties. Also the second bearing3bmay be elastically mounted to the frame1via a second resilient member4bhaving suitable elastic and damping properties.

The frame1may be stationary, at least with respect to the rotating part2. For instance, the frame1may be located or mounted on the ground, possibly via an intermediate fundament that may be provided with damping means or configured to provide a damping function of vibrations or other movements of the centrifugal separator. The frame1comprises or carries a casing5.

The rotating part2comprises a spindle6and a centrifuge rotor7attached to the spindle6. The centrifuge rotor7is enclosed by the casing5. The centrifuge rotor7encloses or defines a separation space8. The centrifuge rotor7also comprises a plurality or a large number of separation discs9provided in separation space8. In the embodiments disclosed, the separation discs9are conical. However, as an alternative radial or even axial separation discs may be comprised by the centrifuge rotor7. The centrifugal separator of the embodiments disclosed is of a so called hermetic type with a closed separation space8.

The centrifugal separator also comprises a drive member10for rotating the rotating part2. The drive member10comprises, in the embodiments disclosed, an electric motor directly attached to the spindle6. The electric motor comprises a rotor11, which is attached to and extends around the spindle6, and a stator12, which is attached to the frame1. Alternatively, the drive member10may be provided beside the spindle6and rotate the rotating part2via a suitable transmission, such as a belt or a gear transmission.

In the embodiments disclosed, the first bearing3aand the second bearing3bare attached to the spindle6and provided on a respective side of the drive member10. The first bearing3ais provided on the spindle6between the drive member10and the centrifuge rotor7, whereas the second bearing3bis provided on the spindle6on the other side of the drive member10turned away from the centrifuge rotor7.

The centrifugal separator comprises an inlet channel20, an outlet channel30and a further outlet channel40.

The inlet channel20is configured to provide fluid communication into the separation space8and to feed a product to be separated into the separation space8. The inlet channel20comprises a rotary channel part21having an inner and outer surface, the rotary channel part attached to the centrifuge rotor7, a frame channel part22having an inner and outer surface, the frame channel part attached to the frame1, and sealing means23provided at the interface between the rotary channel part21of the inlet channel20, and the frame channel part22of the inlet channel20. The sealing means23contacts the outer surface of the rotary channel part21and frame channel part22.

The outlet channel30is configured to provide fluid communication out from the separation space8and to discharge a separated primary phase of the product from the separation space8. The outlet channel30comprises a rotary channel part31having an inner and outer surface, the rotary channel part attached to the centrifuge rotor7, a frame channel part32having an inner and outer surface, the frame channel part attached to the frame1, and sealing means33provided at the interface between the rotary channel part31of the outlet channel30, and the frame channel part32of the outlet channel30. The sealing means33contacts the outer surface of the rotary channel part31and frame channel part32.

The further outlet channel40is configured to provide fluid communication out from the separation space8and to discharge a separated secondary phase of the product from the separation space8. The further outlet channel40comprises a rotary channel part41attached to the centrifuge rotor7, a frame channel part42attached to the frame1, and sealing means43provided at the interface between the rotary channel part41of the further outlet channel40, and the frame channel part42of the further outlet channel40.

In addition, the centrifugal separator may comprises a plurality of outlet openings, not disclosed in the figures, provided at the outer periphery of the centrifuge rotor7for discharge of a sludge or another further product from the separation space8. The openings may be permanently open or intermittently openable by means of a valve mechanism as known in the prior art.

Furthermore, each of the separation discs9may be provided with one or more feed holes9athrough which the product entering the separation space8may be fed into the package of separation discs9and distributed onto the separation discs9.

In the embodiment disclosed inFIG. 1, the primary phase of the product is a relatively light phase whereas the secondary phase of the product is a relatively heavy phase. Furthermore, the primary phase is the minor phase whereas the secondary phase is the main phase. These conditions may of course be the opposite in various variants of the first embodiment disclosed.

The inlet channel20and the outlet channel30are arranged adjacent to and concentrically with each other. In the first embodiment, the outlet channel30is provided within the inlet channel20. It is of course possible, as an alternative solution, to provide the inlet channel20within the outlet channel30.

The centrifugal separator also comprises forcing means provided to generate a leak flow through one of the sealing means, in the first embodiment the sealing means33of the outlet channel30, in a first direction from the outlet channel30to the inlet channel20, and thus to counteract or prevent leakage in the opposite direction from the inlet channel20to the outlet channel30. As the inlet channel20and outlet channel are concentrically arranged, leak flow through the sealing means33is in the radial direction.

The sealing means23,33and43comprise a respective rotary seal element25,35and45attached to the respective rotary channel part21,31and41, and provided with a respective rotary seal surface26,36and46, see alsoFIGS. 2-4. The sealing means23,33and43also comprise and a respective frame seal element27,37and47attached to the respective frame channel part22,32and42and provided with a respective frame seal surface28,38and48. The rotary seal surfaces26,36and46are arranged opposite to the respective frame seal surface28,38and48. The rotary seal surfaces26,36and46and the frame seal surfaces28,38,48are all plane and extend in parallel with a radial plane p with respect to the axis x of rotation. The rotary seal surfaces26,36and46may be arranged to abut the respective frame seal surface28,38and48for the rotary seal surface26, as indicated inFIGS. 2 and 4, and frame seal surface28, and for the rotary seal surface36and frame seal surface36, as indicated inFIG. 2. These abutting seal surfaces form a so called mechanical seal.

However, it is also possible to arrange the rotary seal surfaces26,36and46at a small distance to the respective frame seal surface28,38and48, leaving a gap, or a thin gap, therebetween as indicated inFIG. 2for the rotary seal surface36and the frame seal surface38. Such a gap will permit the leak flow mentioned above.

In the first embodiment, the forcing means comprises a plurality of at least partly non-radial pumping elements60on at least one of the rotary seal surface26,36and46and the frame seal surface28,38and48. In the embodiment disclosed inFIGS. 1-4, the pumping elements60are provided on the rotary seal surface36of the rotary channel part30of the outlet channel30. It is to be understood, that the pumping elements60alternatively may be provided on the frame seal surface28,38,48, or possibly on both the rotary seal surface26,36,46and the frame seal surface28,38,48.

InFIGS. 2 and 3, the pumping elements60are configured as blades projecting from the rotary seal surface36. InFIG. 2the pumping elements60are configured in such a way that the blades do not abut the opposite frame seal surface38. However, it is to be understood that it is possible to let the pumping elements60extend so that the blades will abut the opposite frame seal surface38.

As can be seen inFIG. 3, the pumping elements60extend in a non-radial direction. More precisely, the pumping elements60extend outwardly and rearwardly with respect to the rotary direction r of the rotary seal surface60seen in the direction of the axis x of rotation.

As also illustrated inFIG. 3, the pumping elements60have a curved shape seen in the direction of the axis x of rotation. It is to be noted that the pumping elements60instead may have a straight non-radial extension seen in the direction of the axis x of rotation.

In the first embodiment, eight such pumping elements60are provided. It is to be noted that the number of pumping elements60may be less or more than eight, for instance 2-7 or 9 or more.

InFIG. 4, the pumping elements60are, instead of comprising blades, configured as or comprising grooves formed in the rotary seal surface36. In this variant of the pumping elements60, the grooves may advantageously extend beyond the inner and outer side surfaces of the rotary seal element35. Furthermore, the rotary seal surface36may, but does not have to, abut the frame seal surface38as illustrated in EP-B-37210.

FIG. 5discloses a second embodiment of the centrifugal separator, which differs from the first embodiment in that the forcing means comprises a pump wheel70provided in or at the outlet channel30. The pump wheel70is and arranged to promote the fluid communication from the separation space8, and thus to force the fluid, i.e. the separated primary phase, through the outlet channel30. In such a way the leak flow through the sealing means33of the outlet channel30will be generated. The pump wheel70is located upstream the sealing means33of the outlet channel30.

In the second embodiment, the pump wheel70is driven by a turbine wheel71via a drive shaft72. The turbine wheel71is provided in the inlet channel20and driven by the fluid flow of the product fed through the inlet channel20into the separation space. However, as an alternative to the turbine wheel71, the pump wheel70may be driven by an electrical motor via the drive shaft72, or via a magnetic coupling, whereby the electrical motor may be provided inside or outside the rotating part2.

In the second embodiment it may be dispensed with the pumping elements60. The pumping effect of the pump wheel70may be sufficient to force a small part, i.e. the leak flow, of the primary phase through the sealing means33. However, it is to be noted that the pump wheel70may be combined with pumping elements60.

In the second embodiment, the rotary seal surface36and frame seal surface38of the outlet channel30are provided at a small distance from each other, i.e. with a gap therebetween, in order to permit the above mentioned leak flow therethrough.

FIGS. 7 to 9disclose a third embodiment of the centrifugal separator, which differs from the one in the first embodiment in that the inlet channel20is provided within the further outlet channel40along the rotary channel part21of the inlet channel20and along a substantial part of the frame channel part21of the inlet channel20. The outlet channel30is provided within the inlet channel20as in the first and second embodiments. Similar to the embodiment ofFIG. 2, each channel has a rotary channel part having an inner and outer surface and a frame channel part having an inner and outer surface.

The forcing means are provided to generate a leak flow through the sealing means23of the inlet channel20from the further outlet channel40into the inlet channel20, thereby preventing leakage from the inlet channel20into the further outlet channel40, and to generate a leak flow through the sealing means33of the outlet channel30into the inlet channel20, thereby preventing leakage in the from the inlet channel20to the outlet channel30. Each sealing means contacts an outer surface of the rotary channel part31and frame channel part32.

In the third embodiment, the forcing means comprises pumping elements60in the form of blades provided on the rotary seal surface26of the inlet channel26and the rotary seal surface36of the outlet channel30. The blades on the rotary seal surface26and/or the rotary seal surface36may of course be replaced by grooves as disclosed inFIG. 4. The blades and/or grooves have the same configuration as the blades disclosed inFIGS. 2 to 4. Also in this case it is possibly to provide the pumping elements60on the frame seal surface28and/or the frame seal surface38.

A fourth embodiment of the centrifugal separator differs from the one of the third embodiment in that the pumping elements60of the inlet channel20on the rotary seal surfaces26and/or the pumping elements60of the outlet channel30on the rotary seal surface36have been replaced by a pump wheel70of the second embodiment disclosed inFIG. 5. The seal surfaces26,28and/or36,38are arranged at a distance from each to permit the leak flow therethrough.

The present invention is not limited to the embodiments disclosed and described above, but may be varied and modified within the scope of the following claims.