CENTRIFUGAL SEPARATOR

Abstract: In a centrifuge rotor for separation of two liquids having different densities from a mixture thereof a stack of conical separation discs (21) is arranged in the separation chamber (13) with the base portions of the separation discs turned towards one end and with the apex portions of the separation discs turned toward the other end of the separation chamber. According to the invention the separation chamber (13) has an inlet for mixture situated at the end, towards which the separation discs turn their apex portions, and an outlet for separated relatively heavy liquid situated at the opposite end. The inlet for liquid mixture as well as both outlets for the separated liquids are situated at the same axial end wall of the centrifuge rotor.

Description: This invention relates to a centrifugal separator for separating a mixture of two liquids having different densities. The centrifugal separator includes a rotor body enclosing a separation chamber and including a stack of conical separation discs arranged coaxially with the rotor in the separation chamber, the base portions of the discs facing one end and the apex portions of the discs facing the other end of the rotor, a central inlet chamber, inlet passages connecting the inlet chamber with the separation chamber at the said other end of the rotor, and respective outlets for the relatively light and relatively heavy separated liquids, which outlets are situated both at the same end of the rotor, and the inlet passages having substantially the same inclination relative to the rotor axis as the separation discs. A centrifugal separator of this form is disclosed, for example, in the Swedish Patent No. 19666 from the year 1904. It is unknown whether a centrifugal separator of this kind has been produced and used in practice. Since the turn of the century centrifugal separators have not usually been designed as mentioned above. Instead, the inlet of the separation chamber has been situated at the one end of the separation chamber, i.e. that towards which the base portions of the separation discs face. A conventional centrifugal separator of this kind is disclosed for example in U.S.-A-3,986,663. Even centrifugal separators of the latter kind have the outlets for the two separated liquids situated at one and the same axial end of the rotor. This has several advantages. Among other things the outlet members of the rotor, which may have to be replaced or adjusted, are more easily accessible. Furthermore, use of stationary so-called paring members for the discharge of the separated liquids from the rotor is thereby facilitated. A principle advantage of a centrifugal separator as initially described, in which a mixture is introduced in the separation chamber at the said other end thereof, i.e. that towards which the apex portions of the separation discs are directed is that maximum advantage can be taken of a pre-separation which takes place in the inlet passages before the mixture enters the separation chamber. Thus, part of the relatively heavy liquid component and solids possibly included in the mixture, may be separated when the mixture passes through the inlet passages extending between the central inlet chamber and the inlet of the separation chamber. Relatively heavy component of the supplied mixture, separated in the inlet passages, may slide along the outer walls of the inlet passages directly out into the outermost part of the separation chamber radially outside the separation discs without being disturbed by or disturbing the flow of the rest of the mixture into the separation chamber. In a conventional centrifugal separator, in which the liquid mixture is instead introduced through inlet passages at the one end of the separation chamber, i.e. that end towards which the base portions of the separation discs face (see e.g. U.S.-A-3,986,663), relatively heavy component of the mixture separated in the inlet passages is forced to cross the flow of the rest of the mixture entering the separation chamber. This is a consequence of the fact that the inlet passages have an inclination relative to the rotor axis just about the same as that of the conical separation discs. Thus, the result of the pre-separation in the inlet passages is spoiled wholly or partly. This undesired effect of the cross flow will be greatest when all the mixture is introduced into the separation chamber at the outer edge of the separation disc situated closest to the inlet passages. In WO-A-86/04270 there is proposed a centrifugal separator for separating a discontinuous phase from a continuous phase, which separator comprises a rotor with four radial separation chambers uniformly distributed around the rotor axis and having a common central inlet chamber. A pack of double lamellae is accommodated in each separation chamber between the inlet chamber and an outer compression zone, the lamellae being downwardly and outwardly inclined towards the compression zone. Separated light phase passes inwardly through the spaces defined by the double lamellae and is discharged through an outlet at the upper end of the rotor. A respective conduit containing a screw conveyor is connected to each compression zone and extends radially inwardly to deliver separated heavy phase to an outlet chamber positioned below the separation chamber and extending about the rotor drive shaft. The aim of the present invention is to provide a centrifugal separator, the rotor of which firstly has the preferable arrangement, known at least since 1904, for introducing liquid mixture into the separation chamber and, secondly, has the outlets for both separated liquids at one and the same end of the rotor, which centrifugal separator has an improved design enabling more effective separation of two liquids than a centrifugal separator as described in the above mentioned Swedish Patent No. 19666. In accordance with the present invention there is provided a centrifugal separator for separating a mixture of two liquids having different densities, comprising a rotor body enclosing a separation chamber and including a stack of conical separation discs arranged coaxially with the rotor in the separation chamber, the base portions of the discs facing one end and the apex portions thereof facing the other end of the separation chamber, a central inlet chamber, inlet passages connecting the inlet chamber with the separation chamber at said other end of the latter, and respective outlets, both at the same axial outlet end of the rotor, for relatively light and relatively heavy separated liquid, said inlet passages having substantially the same inclination relative to the rotor axis as the separation discs, characterized in that at least one outlet channel extends from a radially outer part of the separation chamber towards the rotor center at the said one end of the separation chamber, and this outlet channel communicates with the rotor outlet for separated heavy liquid at said outlet end of the rotor. In a centrifugal separator according to the invention maximum advantage can be taken of the pre-separation in said inlet passages and, simultaneously, the relatively heavy liquid component of the mixture is ensured a long axial flow path in the separation chamber. Hereby, the relatively heavy liquid may be separated effectively from the relatively light liquid and simultaneously be freed from any solids present in the mixture and heavier than the relatively heavy liquid. Furthermore, both the separated liquids are discharged from the rotor at one and the same end thereof. It is possible to locate the two outlets for the separated liquids at either end of the rotor, with the rotor being conveniently connected with a driving shaft at the opposite end. However, in a preferred embodiment of the invention the two rotor outlets are situated at the said other end of the rotor, the end towards which the apex portions of the separation discs face, and outlet means having at least one through channel are arranged to conduct relatively heavy separated liquid from said outlet channel axially through the separation chamber to the rotor outlet for the separated heavy liquid. Hereby, the rotor can be connected with a driving shaft so that its point of gravity will be located as close a possible to the drive shaft and its bearings, in an axial sense. Some embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:- Fig. 1 shows partly in axial cross-section a preferred centrifugal separator according to the invention; Fig. 2 shows in enlarged plan view a part of the centrifugal separator of Fig. 1; Fig. 3 shows in axial section a modified part corresponding to that shown in Fig. 2; and Fig. 4 shows another modified part of the centrifugal separator in Fig. 1. Fig. 1 shows a centrifugal separator having a rotor 1, a vertical drive shaft 2 supporting the rotor, a driving device 3 in engagement with the drive shaft, a lower housing 4 for the driving device 3 and an upper housing 5 for the rotor. The upper housing 5 includes an inlet tube 6 for a mixture of two liquids having different densities and particles suspended therein. Further, the housing 5 forms a receiving chamber 7 having an outlet for separated relatively light liquid and a receiving chamber 9 having an outlet 10 for a separated relatively heavy liquid. The rotor comprises two rotor parts 11 and 12, which are kept axially pressed against each other and which surround a separation chamber 13. The rotor part 11, which forms the bottom of the separation chamber 13 and is connected with the driving shaft 2, has a central column 14 the upper part of which arrests the rotor part 12 by means of an annular locking member 15. The rotor part 12 forms a substantially cylindrical surrounding wall and a substantially conical upper end wall of the rotor. A narrow end portion of the inlet tube 6 extends axially through the locking member 15 into a central inlet chamber 16 formed in a tubular upper portion of the central column 14. This tubular portion of the column 14 has several openings 17 in its surrounding wall. The locking member 15 forms an upper annular end wall in the inlet chamber 16. Around the central column 14 there is arranged a partition member having a sleeve-like part 18 and a conical part 19. The sleeve part 18 surrounds the column 14 below said openings 17. An annular gasket seals between the sleeve part 18 and the column 14. The conical part 19 abuts against said upper end wall of the rotor. Radial recesses in the conical part 19 form between this part and the rotor end wall several passages 20, which connect the openings 17 with the separation chamber 13. Between the conical part 19 and the lower rotor part 11 there is arranged in the separation chamber 13 coaxially with the rotor axis a set of frusto-conical separation discs 21. The outer edges of the separation discs 21 are situated substantially at the same radial level as the outer edge of the previously mentioned conical part 19. The inner edges of the separation discs 21 are situated at some distance radially outside the sleeve part 18, so that a central space is formed in the separation chamber 13 radially inside the separation discs 21. This space is divided into parallel axial channels by radially and axially extending wings supported by the sleeve quart 18. The conical part 19 has a number of, for instance three, axial through-channels 22 and supports on its upper side an equal number of tubular members 23, the interiors of which communicate with respective channels 22. The rotor part 12 has an equal number of axial through-channels 24, which are situated such that they communicate through the tubular members 23 with the respective channels 22. An annular gasket is arranged to seal between the tubular members 23 and the rotor part 12 around each of the channels defined therethrough. On top of the rotor part 12 there is arranged an annular member 25, which together with the rotor part 12 forms a chamber, into which the channels 24 through the rotor part open. The chamber 26 has one or several peripheral outlets 27. In the lower part of the separation chamber 13 there is placed an annular member 28, which axially inwards and axially downwards seals against the rotor part 11 and extends radially outwards into the separation chamber 13 beyond the separation discs 21. On its underside the annular member 28 has a number of radial grooves which form channels 29 extending between the separation chamber 13 and an equal number of central radial channels 30 in the rotor part 11. The radial channels 30 communicate with a number of axial channels 31 in which axial tubes 32 are inserted. The tubes 32 extend through aligned holes in the separation discs 21, holes in the previously mentioned conical part 19, holes in the rotor part 12 and holes in the annular member 25. Sealing gaskets are arranged around said holes and around the tubes 32, between the rotor part 12 and each of the conical part 19 and the annular member 25. The interiors of the tubes 32, which through the channels 29-31 communicate with the separator chamber 13, open into a radially inwardly open groove 33 in the annular member 25. The upper edge of the groove 33 forms an overflow outlet 34 therefrom. From the radially innermost part of each channel 30 a draining channel 35 extends through the rotor part 11 to the outside of the rotor. A shielding member 36 is connected with the driving shaft 2 and is arranged to prevent liquid leaving the rotor through the draining channels 35 from flowing down into the housing 4 of the driving device. The rotor housing 5 has a separate outlet 37 for such liquid. Fig. 2 shows from the above partition member that comprises the conical part 19. Apart from the three previously mentioned tubular members 23, three further tubular members 38 are shown and through the openings of which the tubes 32 (Fig 1) are passed. As can be best seen from Fig. 2 the tubular members 38 are situated at a larger radius than the tubular members 23. Radially and axially extending ridges 39 on the upper of side the conical part a define the previously mentioned recesses which together with the rotor part 12 form the passages 20 in Fig. 1. Around its circumference the conical part 19 has a number of recesses 40, the function of which is described later. Corresponding recesses axially aligned with the recesses 40 are present in all of the separation discs 21 in the separation chamber 13. Fig. 3 shows a section through a somewhat modified partition member comprising a conical part 19a, a sleeve-like part 18a and tubular member 23a and 38a. The partition member shown in Fig 3 is intended to be made entirely of plastic, and as can be seen the tubular members 23a and 38a have been shaped in a way enabling a firm connection with the rotor part 12. Sleeve-like extension 41 and 42 having small external annular end flanges 43 and 44, respectively, are dimensioned and are resilient so that they will engage with a snap-fit when inserted in the holes in the rotor part 12 intended therefor. Fig. 4 shows the upper part of a rotor according to Fig. 1, comprising a partition member according to Fig. 3. The tubular members 23a and 38a are inserted into through-channels in the rotor part 12a. The walls of these channels have annular grooves for receiving the annular end flanges 43 and 44 (Fig. 3). The partition member is thus connected with the rotor part 12a by means of a so-called snap-lock connection. A further so-called snap-lock connection is present between the rotor part 12a and the annular member 25a. The latter has an internal annular flange 45 which engages in an external groove in the rotor part 12a. Instead of a fixed end wall the annular member 25a has a removable and thus exchangeable annular end wall 46, the inner edge of which forms an overflow outlet corresponding to the overflow outlet 34 in fig 1. Even the end wall 46 is secured to the annular member 25a by means of a so called snap lock connection. The centrifugal separator in Fig 1 is intended to operate in the following manner after the rotor 1 has been put in rotation by means of the driving device 3. Through the tube 6 a mixture of two liquids having different densities and solids suspended therein is introduced into the central inlet chamber 16. The mixture flows through the openings 17 and the passages 20 to the separation chamber 13. Mainly through the recesses 40 in the conical part 19 and corresponding recesses in the separation discs 21 the mixture is distributed between the separation discs. In the passages 20 a pre-separation of the three components forming the supplied mixtures takes place. A large part of the suspended solids and part of the heavier of the liquids move along the rotor part 12 out to the surrounding wall of the separation chamber 13 without disturbing the continued flow of the liquid mixture into the separation chamber. The liquid mixture together with possibly remaining solids is distributed after that between the separation discs 21. Between the separation discs the two liquids of different densities are separated, the lighter liquid flowing radially inwards and being conducted through the channels 22 and 24 to the chamber 26, whereas the heavier liquid flows radially outwards. Outside the separation discs 21 the latter liquid flows axially downwards in the separation chamber and out thereof through the channels 29. It is conducted further through the channels 30 and 31 and by the tube 32 to the annular groove 33. While the separated heavy liquid leaves over the overflow outlet 34 the separated light liquid leaves through the outlet 27 of the chamber 26. The outlet 27 thus is so large that the chamber 26 during normal operation is only partly filled. This means that the tubular members 23 and the radially outer limiting walls of the channels 22 and 24 form overflow outlets from the separation chamber 13 for the separated light liquid. The position of the interface layer formed between the two separated liquids in the separation chamber during operation is determined by the positions of the two said overflow outlets of the separation chamber. The position of the interface layer may be changed by exchange of the annular member 25 for another one, the overflow outlet 34 of which is situated at a different radial level. As an alternative, of course, an exchangeable so called gravity disc may be arranged in one of the chamber 26 and the groove 33. If desired, conventional distribution channels extending axially through the separation discs 21 and the conical part 19 may be situated at any desired distance from the rotor axis. If and when required, the annular member 28 at the bottom of the separation chamber may be exchanged for another one having a larger or smaller radial extension. For removal of separated solids from the separation chamber the locking member 15 has to be removed and the rotor parts 11 and 12 have to be separated. Since the channels 22 and 24 will serve during operation as over-flow outlets of the separation chamber 13, a free liquid surface will be formed in the separation chamber radially outside the sleeve part 18 around the central column 14. Any liquid possibly leaking past the gasket between the column 14 and the sleeve part 18 will therefore be directed away from the inlet chamber 16 to the separation chamber 13. Since the lower portion of the sleeve part 18 is situated at a substantial axial distance from the overflow outlet 24 for separated light liquid, any such leakage of small magnitude will not influence the separation in the rotor. In a preferred embodiment of the invention the component parts 11, 12 and 32 are made of metal, whereas the components parts 18, 19, 25 and 28 are made of plastic. Thereby, instead of separate sealing members such as gaskets placed between the tubular members 23, 38 and the rotor part 12, the tubular members 23 and 38 by being made of plastic can accomplish the necessary sealing themselves. Preferably this is achieved such that the members in question are shaped to provide a firm connection, for instance, a so-called snap-lock connection, between these members and the rotor part 12 (Fig. 4). This avoids the important seal between the tubular members 23, 38 and the rotor part 12 having to be broken each time the rotor is disassembled; in other words the sealing function will be more reliable and will not be jeopardized by wear or damage. Furthermore, the dismantling and reassembly of the rotor is facilitated by the fact that the latter will consist of a smaller number of parts. Also, the uppermost annular member 25 may be formed such that a firm connection may be obtained between this and the rotor part 12 (Fig. 4). The tubes 32 preferably are fixed to the rotor part 11, so that they can keep the separation discs 21 in fixed positions when the rotor part 12 is removed. The tubes 32 thus serve as guiding members for the separation discs 21 and prevent these from being turned relative to each other during rotation of the rotor.

Claims: 1. A centrifugal separator for separating a mixture of two liquids having different densities , comprising a rotor body enclosing a separation chamber (13) and including a stack of conical separation discs (21) arranged coaxially with the rotor in the separation chamber (13), the base portions of the discs facing one end and the apex portions thereof facing the other end of the separation chamber, a central inlet chamber (16), inlet passages (20) connecting the inlet chamber (16) with the separation chamber (13) at said other end of the latter, and respective outlets (27, 34), both at the same axial outlet end of the rotor, for relatively light and relatively heavy separated liquid, said inlet passages (20) having substantially the same inclination relative to the rotor axis as the separation discs (21), characterised in that at least one outlet channel (29) extends from a radially outer part of the separation chamber (13) towards the rotor centre at the said one end of the separation chamber, and this outlet channel (29) communicates with the rotor outlet (34) for separated heavy liquid at said outlet end of the rotor. 2. A centrifugal separator according to claim 1, wherein the outlet channel (29) extends inwardly from a level in the separation chamber (13) radially outside the outer edges of the conical separation discs (21). 3. A centrifuyal separator according to claim 1 or 2, wherein the outlets (27, 34) for the separated liquids are situated at the end of the rotor remote from the outlet channel (29), outlet means (28,32) having at least one through channel being arranged to conduct relatively heavy separated liquid from said outlet channel (29) axially through the separation chamber (13) to the rotor outlet (34) for the separated heavy liquid. 4. A centrifugal separator according to claim 3, wherein said outlet means (28,32) comprises several tubes (32) distributed around the rotor axis. 5. A centrifugal separator according to claim 3 or 4, wherein said outlet means (28, 32) extends throuyh the separation discs (21). 6. A centrifugal separator according to any one of claims 3-5, wherein a partition member (18,19) delimits said inlet passages (20) and is arranged between the stack of separation discs (21) and a part (12) of the rotor body at the said other end of the separation chamber, and said outlet means (28,32) extends axially through the partition member (18, 19). 7. A centrifugal separator according to claim 6, wherein the partition member (18, 19) has an outlet for separated light liquid provided by a number of through holes (22), said quart (12) of the rotor body having corresponding through holes (24), and tubular members (23) connect between the partition member (18, 19) and said part (12) of the rotor body around the respective through holes (22, 24), so that closed outlet channels from the separation chamber (13) are formed for the separated light liquid. 8. A centrifugal separator according to claim 7, wherein the tubular members (23) are formed in one piece with either said part (12) of the rotor body or the partition member (18, 19). 9. A centrifugal separator according to any one of the preceding claims, wherein the rotor (1) is supported at an end of a driving shaft (2), and the outlets for the separated liquids are at the rotor end remote form the driving shaft. 10. A centrifugal separator according to claim 9, wherein the rotor has at the end remote from the driving shaft an inlet for conducting mixture into the central inlet chamber (16).

Inventors: STROUCKEN, KLAUS
Applicants: ALFA-LAVAL SEPARATION AB
Application year: 1988
Main classification: B04B11
IPC codes: B04B1