WO1988002663A1

WO1988002663A1 - Centrifugal separator

Info

Publication number: WO1988002663A1
Application number: PCT/SE1987/000470
Authority: WO
Inventors: Karl Laigar
Original assignee: Alfa-Laval Separation Ab
Priority date: 1986-10-17
Filing date: 1987-10-15
Publication date: 1988-04-21
Also published as: SE454571B; SE8604420D0

Abstract

A certain type of centrifugal separator has a rotor (1) with a hollow driving shaft (5), whereby the rotor can be charged with a liquid mixture to be separated. According to the invention a thin tube (12) extends through the cavity (6) of such a driving shaft (5) for the supply of another liquid to the rotor (1). Two mechanical seals (24, 25; 26, 27) surround the driving shaft (5), one on each side of a radial opening (15) therein. The opening (15) communicates with the passage (13) in the tube (12).

Description

Centrifugal separator

The present invention concerns a centrifugal separator of the kind that has a rotor, forming a separation chamber, and a hollow driving shaft supporting the rotor, said driving shaft enclosing a first channel, which opens into the rotor and is arranged to supply a liquid mixture to be separated in diffe¬ rent components in the separation chamber, and a second channel opening into the rotor separately from the opening of the first channel and arranged for the supply of another liquid to the rotor.

Especially in connection with centrifugal separators of this kind, the rotor of which is to be charged with a liquid mixture via its driving shaft, difficulties arise in certain separation cases when another liquid has to be supplied to the rotor during operation, which liquid must not be mixed with said liquid mixture. Such other liquid sometimes has to be supplied to the rotor, e.g. for diluting a heavy component of said liquid mixture separated therein, so that it becomes less viscous and more easily can be removed from the rotor. If the diluting liquid is supplied to said liquid mixture before the latter is supplied to the rotor, in certain cases un undesired product in the form of an emulsion can be formed, which makes the separa¬ tion within the rotor more difficult.

The said difficulties arise because at this kind of centrifugal separators few other possibilities are left for the supply of said other liquid than via the hollow driving shaft. However, the driving shaft is needed for the supply of said liquid mixture.

In practice, the following arrangement is used for the supply of the other liquid. Inside the hollow driving shaft there is a tube extending coaxially therewith, leaving a very narrow gap between itself and the circumferential wall of the shaft. At the lower end of the shaft the interior of the central tube communi- cates with an inlet for said liquid mixture, while the inter¬ space between the tube and the driving shaft communicates with an inlet for the other liquid. Sealing means coaxial with the tube and the driving shaft are arranged at both of said inlets.

The arrangement thus used in practice means that a relatively large part of the available cross sectional area of the driving shaft cavity has to be used for the central tube, since this cannot be made too thin. Further, the arrangement means a complication in connection with assembling of the centrifuge rotor and each time it should be disassembled at service operations, since the central tube then has to be removed from the said sealing means and is not quite easy to get into place again.

ϊhe object of the present invention is to provide an improved solution of the problem discussed above, so that a larger part of the interior of the driving shaft can be used for the supply of liquid mixture to the rotor and so that the complications in connection with service operations are reduced.

According to the invention this object can be achieved in a centrifugal separator of the kind initially defined by means of 1) a tube extending within said first channel and which has a through passage forming said second channel for the other liquid, the tube at its end remote from the rotor being so supported by and sealingly connected to the driving shaft around a through opening in the circumferential wall thereof that the opening communicates with the passage within the tube, 2) a sealing device comprising two sealing members, which are mounted around the driving shaft and arranged to seal against its out¬ side axially on both sides of said opening, and a sealing housing, which together with the sealing members forms an annular chamber around the driving shaft in communication with the opening, and 3) means for the supply of said other liquid to the said chamber. By this invention a tube having very thin walls can be mounted within the driving shaft, whereby a largest possible part of the driving shaft interior can be used for the supply of liquid mixture to the rotor. As a consequence of the fact that the tube is supported by the driving shaft and does not have to be removed upon disassembling of the centrifuge rotor, the tube does not have to be dimensioned to resist ungentle mechanical treatment. Furthermore, all problems concerning mounting of it in connection with repeated service operations are avoided. A fundamental difference between the invention and the previously known technique described above is that the separate tube within the driving shaft is used according to the invention for the supply of said other liquid but, according to previously known technique, is used for the supply of liquid mixture to be separated in components in the separation chamber of the rotor.

Any suitable type of sealing device can be used within the scope of the invention. However, it is preferred that the sealing device comprises two mechanical seals, each of which has a sealing ring connected to the driving shaft and arranged to abut axially against a sealing ring, which is connected to the sealing housing.

The sealing between the tube and the driving shaft can be arranged in many different manners. Preferably the tube is permanently joined to the driving shaft around the opening in the same, for instance by soldering or by welding. For avoiding relative movements between the tube and the driving shaft during operation, the former preferably abuts the inside of the latter along the main part of its length and is inserted into the opening in the driving shaft with an end portion forming an angle with the driving shaft. In the following the invention will be described more in detail with reference to the accompanying drawing, which in Fig 1 shows one embodiment of the same. Fig 2 shows an enlarged part of Fig 1.

In Fig 1 there is shown a centrifuge rotor 1, in which a separation chamber 2 is confined. A stack of conical separation discs 4 rests on a distributor bottom 3 in the separation chamber 2. The rotor is supported by a hollow driving shaft 5, which has a through-passing central channel 6. The channel 6 is in connection to the separation chamber 2 via passages 7 in the rotor and holes 8 in the distributor bottom 3. The driving shaft is supported by a frame 9 via an upper bearing device 10 and a lower bearing device 11. Between the bearing devices 10 and 11 there is means (not shown) for the driving of the driving shaft 5 and consequently the rotor 1.

Within the channel 6 of the driving shaft a small tube 12 extends with a through passage 13. The tube 12 has bent end portions, which extends into two through-passing openings 14, 15, respectively, in the circumferential wall of the driving shaft 5. The end portions of the tube 12 are tightly connected to the driving shaft 5 around said openings 14 and 15 e.g.by welding. The main part of the tube 22 abuts against the inside of the driving shaft 5.

In the rotor 1 there is formed a channel 16 and a space 17 beneath the distributor bottom communicating therewith. The opening 14 and consequently the passage 13 in the tube 12 is in connection with the separation chamber 2 via the channel 16 and the space 17.

Around the lower part of the driving shaft 5 in the area at the lower opening 15 the frame 9 supports a sealing device 18, which is arranged for separate supply of different liquids to the channel 6 in the driving shaft 5 and the passage 13 in the tube 12, respectively. Thus, the sealing device 18 is connected to a pump 20 via a conduit 19 for the supply of a liquid mixture, which is to be divided up into two components in the separation chamber 2, and connected to a second pump 22 via a conduit 21 for the supply of another liquid to the separation chamber via the tube 12.

The sealing device 18, which is shown enlarged in fig 2, comprises a housing 23, which surrounds the lower end portion of the driving shaft 5 and is connected to the frame 9. Inside the housing 23 the driving shaft 5 is surrounded axially on each side of the above mentioned opening 15 by two mechanical sealings. The one (upper) mechanical sealing has a rotatable sealing ring 24 connected to the driving shaft and a stationary sealing ring 25 connected to the frame 9. The sealing rings 24 and 25 sealingly abut axially against each other. The other (lower) mechanical sealing has a rotatable sealing ring 26 connected to the driving shaft and a stationary sealing ring 27 connected to the housing 23. The sealing rings 26 and 27 sealingly abut axially against each other. A helically coiled spring 28 is arranged between the two rotatable sealing rings 24, 26 and presses these from each other into abutment against the stationary sealing rings 25 and 27, respectively. The rotatable sealing rings 24 and 26 consequently are axially movable relative to the driving shaft 5 sealingly abutting against the outside of the same.

Inside the housing 23 there is formed an annular chamber 29, which communicates with the previously mentioned opening 15 in the driving shaft 5. The conduit 21 opens in the chamber 29.

At its lower end the housing 23 has a central through-passing bore hole 30, to which the conduit 19 is connected. The bore hole 30 communicates with the channel 6 in the driving shaft 5. The lower mechanical sealing 26, 27 around the driving shaft 5 prevents communication between the annular chamber 29 and the bore hole 30 in the housing 23. The liquid, which is supplied to the chamber 29 via the conduit 21 serves as sealing liquid for the two mechanical sealings in the housing 23. A draining channel 31 is formed in the frame 9 to lead away liquid, which possibly passes the upper mechanical sealing 24, 25.

The arrangement shown in Fig 1 and 2 is used in the following manner.

In connection with starting of the centrifugal rotor 1 the pump 22 is activated, so that liquid is supplied to the chamber 29 in the housing 23. Thereby, the functional wetting of the mechanical sealings 24, 25 and 26, 27 is ensured. When the wanted rotational speed has been achieved for the centrifugal rotor, the pump 20 is activated, so that a liquid mixture is supplied to the separation chamber of the rotor via the conduit 19, the bore hole 30, the channel 6, the passages 7 and the holes 8.

In the separation chamber 2 there is formed an interface at the radial level of the holes 8 between two separated components of the supplied liquid mixture. The other liquid, which is supplied to the separation chamber 2, by means of the pump 22 via the conduit 21, the chamber 23, the opening 15, the passage 13, the opening 14, the channel 16 and the chamber 17, will consequently be mixed up with the heavier one of the two separated components in the separation chamber 2. In that way the viscosity of this component can be lowered, which thereby easier than otherwise ca be discharged out of the rotor via an outlet, which is not shown on the drawing.

Claims

1. Centrifugal separator having a rotor (1), forming a sepa¬ ration chamber (2), and a hollow driving shaft (5) supporting the rotor, the driving shaft (5) enclosing a first channel opening into the rotor and arranged for the supply of a liquid mixture to be separated in different components in the sepa¬ ration chamber (2), and a second channel opening into the rotor separately from the opening of the first channel and arranged for the supply of another liquid to the rotor, c h a r a c t e r i z e d b y

- a tube (12) which extends within said first channel (6) and which has a through passage (13) forming said second channel for the other liquid, the tube at its end remote from the rotor being so supported by and sealingly connected to the driving shaft (5) around a through opening (15) in the circumferential wall thereof that the opening (15) communi¬ cates with the passage (13) within the tube (12),

- a sealing device (18) comprising two sealing members mounted around the driving shaft (5) and arranged to seal against its outside axially on each side of said opening (15), and a sealing housing (23), which together with the sealing members forms an annular chamber (29) around the driving shaft (5) in communication with the opening (15), and

- means (12, 22) for the supply of said other liquid to the said chamber (29).

2. Centrifugal separator according to claim 1, c h a r a c ¬ t e r i z e d i n that the sealing device (18) comprises two mechanical seals (24, 25; 26, 27), each of which has a sealing ring (24; 26) connected to the driving shaft and arranged to abut axially against a sealing ring (25; 27) connected to the sealing housing (23).

3. Centrifugal separator according to claim 1 or 2, c h a ¬ r a c t e r i z e d i n that the end of the tube (12) is per¬ manently connected to the driving shaft (5) around the opening (15) in the same, e.g. by soldering or welding.

4. Centrifugal separator according to any of the preceding claims, c h a r a c t e r i z e d i n that the tube (12) abuts against the inside of the driving shaft (5) along the main part of its length and is inserted into the opening (15) in the driving shaft with an end portion, which forms an angle with the driving shaft (5).