CENTRIFUGAL SEPARATOR HAVING A DEVICE FOR THE TRANSFORMATION OF KINETIC ENERGY TO PRESSURE ENERGY

Abstract: Centrifugal separator having a device for the transformation of kinetic energy of a liquid rotating in a chamber around a rotational axis to pressure energy. The device comprises an element for the discharge of liquid out of the chamber, which element has a surface (20) surrounding the rotational axis arranged to be so located in the rotating liquid body that liquid flows in a predetermined direction along and in contact with the surface (20). The discharge element forms at least one outlet channel (21), which has an inlet opening (22) located in said surface (20) and which from this inlet opening (22) extends a bit essentially in said flow direction. Seen in the flow direction the inlet opening (22) is delimited by two opposite side edges (23, 24) and a cross edge (25) located downstreams of these. In order to make the energy transformation more efficient the opposite side edges (23, 24) of the inlet opening (22) diverge in said flow direction along an essential part of its extension and at least one of the side edges has such a direction that liquid crossing the same flows into the inlet opening (22).

Description: Centrifugal separator having a device for the transformation of kinetic energy to pressure energy. The present invention relates to centrifugal separators having a device for the transformation of kinetic energy of a liquid rotating in a chamber around a rotational axis to pressure energy. This device comprises an element for the discharge of liquid out of the chamber, which element has a surface sur¬ rounding the rotational axis arranged to be so located in the rotating liquid body that liquid flows in a predetermined direc¬ tion along and in contact with the surface. The element forms at least one outlet channel, which has an inlet opening located in said surface and which from this inlet opening extends a bit essentially in said flow direction. Seen in the flow direction of the liquid the inlet opening is limited by two opposite side edges and a cross edge located downstreams of these. In a centrifugal separator which is provided with an energy transformation device of said kind, parts of the rotor of the centrifugal separator form an outlet chamberj in which liquid rotates. The outlet chamber is arranged to receive a separated liquid continuously from the separation chamber of the centri¬ fugal rotor. This liquid forms a rotating liquid body in the outlet chamber. Centrally in the outlet chamber an outlet device is arranged, through which liquid is discharged out of the out¬ let chamber and further out of the centrifugal rotor. A centri¬ fugal separator of this kind is shown in WO 88/7893, for instance. In many cases it is important that the energy transformation device can transform as? much as possible of the energy stored in the rotating liquid to pressure energy. How high pressure you then can achieve as a maximum is determined by the equation of Bernoullis for the pressure along a flow line of the liquid. p stat + p dyn = kons The static pressure P g ^at at tιe -*- n -*- et opening is composed by the pressure from the part of the rotating liquid body, which is located radially inside the inlet opening, and the pressure which acts on this part of the liquid body. The dynamic pressure P< jyil is in each point along a flow line determined by the equation P,jyn = ~~^ in which i is the density of the liquid and W is the flow rate of the liquid in the point looked upon. Outside the inlet opening the liquid has a total pressure which is the sum of the static and dynamic pressure there. However, in the device in a centrifugal separator known by WO 88/7893 only a minor part of the dynamic pressure can be recovered in the form of a liquid pressure in the outlet. Therefore, another device has been suggested for separators for the recovery of the kinetic energy of the rotating liquid, which is to be discharged out of the chamber of the centrifugal rotor. This device com¬ prises a discharge device, which has a radial extension and an inlet opening in its radial outer portion facing the flow direc¬ tion of the liquid. By directing the inlet opening in this way a greater part of the dynamic pressure of the rotating liquid outside the discharge device can be recovered in the form of a liquid pressure. However, a discharge device designed in this manner has a great slowing down effect on the liquid in the chamber. Furthermore it has a heavy agitating effect on the liquid^ which results in partly a great risk for the admixture of air in the discharged liquid, partly a possibly damaging mechanical influence on the liquid. The object of the present invention is to accomplish a centri- fugal separator having a device of the kind initially described for the transformation of kinetic energy of a rotating liquid to pressure energy, which device is able to recover a greater part of the static and the dynamic pressure in the rotating liquid than previously known such devices without involving an increasing risk for the admixture of air in the liquid. The object is furthermore that the device shall be able to do this without resulting in a too great slowing down effect and too heavy stresses on the liquid. This is achieved according to the present invention by providing a centrifugal separator with an energy transformation device of said kind, in which the opposite side edges of the inlet opening diverge in said flow direction along an essential part of its extension, at least one of said side edges having such a direc- tion that liquid flowing cross the same flows into the inlet opening. With the expression along an essential part of its extension it is hereby meant preferably along at least half of its extension. By designing the device in this manner a substantially greater part of the dynamic pressure in the rotating liquid can be recovered than in hitherto known devices. This means that a higher pressure in the outlet of the centrifugal separator can be achieved whereby a pump arranged in an outlet conduit can possibly be avoided, or the radial dimensions of the discharge device be diminished, whereby a desired liquid pressure in the outlet can be achieved by less energy losses. This is possible without involving a greater risk for the admixture of air and causing heavy stresses on the separated liquid. In a preferred embodiment of the invention each one of said side edges has such a direction that liquid flowing cross the same flows into the inlet opening. At least one of the side edges then can possess a curved shape, the radius of the curvature of the side edges preferably varying along the side edges in a way such that in the flow direction from being convex towards the inlet opening it turns to be concave towards the same. In a special embodiment of the invention the outlet channel has two inlet openings, each of which being delimited by two diver¬ ging opposite side edges, one of which extending in the flow direction along essentially the whole inlet opening and the other one having a shorter extension in the flow direction than the inlet opening. The inlet opening is in all embodiments of the invention pre¬ ferably arranged symmetrically of a midline in the predetermined flow direction. In the following the invention will be described more closely with reference to the accompanying drawing, in which Fig 1 schematically shows an axial section through a part of a centrifugal separator] which is provided with a device according to the invention Fig 2-6 schematically show three dimensional views of different embodiments of a part in a device according to the invention. A centrifugal separator shown in fig 1 comprises a rotor , which has a lower part 1 and an upper part 2 which are joined together axially by means of a locking ring 3. Inside the centrifugal separator shown as an example, there is arranged an axially movable valve slide 4. This valve slide 4 delimits together with the upper part 2 a separation chamber 5 and is arranged to open and close an annular gap towards the outlet openings 6 for a componen , which during operation is separated out of a mixture supplied to the rotor and is collected at the periphery of the separation chamber 5. The valve slide 4 delimits together with the lower part 1 a closing chamber 7, which is provided with an inlet 8 and a throttled outlet 9 for a closing liquid. Inside the separation chamber 5 there is arranged a disc stack 10 consisting of a number of conical separation discs between a distributor 11 and the upper part 2. The upper part forms at its upper end, shown in the figure, a chamber 12, to which in this case a specific lighter liquid component of the mixture can flow from the separation chamber 5 via an inlet 13. The liquid present in the chamber 12 during operation of the rotor forms a rotating liquid body having a radially inwards facing free liquid surface 14. Centrally through the chamber 12 a stationary inlet tube 15 extends, which opens in the internal of the distributor 11. Around the inlet tube 15 there is arranged a stationary outlet tube 16 for the specific lighter liquid component in the chamber 12. In the chamber a discharge element 17 is arranged around the inlet tube and connected to the outlet tube 16. The discharge element 17 is stationary but in an alternative outlet arrange¬ ment a similar outlet element can be arranged to rotate with a rotational speed which is lower than the rotational speed of the rotor. The discharge element 17 extends radially outwards and has outside the radial level of the free liquid surface 14 of the rotating liquid body a part, which has at least one inlet opening 18. This inlet opening 18 is connected to the internal of the outlet tube 16 via an outlet channel 19 formed in the discharge element 17. In figures 2-6 there is shown in more detail some examples of how the discharge element shown in fig 1 can be designed accor¬ ding to the present invention. The discharge element shown in fig 2 has a circular cylindrical surface 20, which during operation is located in the rotating liquid body in the chamber 12 and along which the liquid flows in a predetermined direction. Inside the discharge element an outer channel 21 extends, which has an inlet opening 22 in said surface 20 and in its opposite end is connected to the internal of an outlet tube (not shown). In this example the inlet opening 22 seen in the flow direction is delimited by two opposite side edges 22 and 24, which diverge from a common point and forwards in the flow direction in a way such that liquid crossing the side edges flows into the inlet opening 22. Downstreams the inlet opening 22 is delimited by a cross edge 25, which is con- nected to the two side edges 23 and 24. In the example shown in this figure, as in the examples shown in figures 3-6, the outlet channel has a confining surface 26 which at the end of the inlet opening 22 upstreams forms a continuation of circular cylindri¬ cal surface 20 of the discharge element. The discharge element shown in fig 3 differs from the one shown in fig 2 in that the side edges 27 and 28 in this example are curved having a radius of curvature which varies along the side edges and that this inlet opening 29 in the flow direction is delimited by two parallel cross edges 30 and 31. The curved side edges 27 and 28 turns in the flow direction from being convex towards the inlet opening 29 to be concave towards the same. Each one of the inlet openings 22 and 29 in the discharge element shown in figures 2 and 3 is formed symmetrically of a midline extending in the flow direction, which midline in the same time constitutes a midline in the circular cylindrical surface of the discharge element respectively. Fig 4 shows a discharge element according to the invention] which is designed with an outlet channel 32 and has two inlet openings 33 and 34. Each one of these inlet openings has the same shape as the inlet opening 29 shown in fig 4. The two inlet openings 33 and 34 are suitably located symmetrically of a mid- line of the circular cylindrical surface extending in the flow direction. Fig 5 shows a discharge element having an asymmetric inlet opening 35. This inlet opening 35 is delimited perpendicular towards the flow direction by two side edges 36 and 37 and in the flow direction by two cross edges 38 and 39. As in the embodiments according to figures 2, 3 and 4, the side edges 36 and 37 diverge in this example. The side edge 36 is straight and is directed essentially parallel to the flow direction while the other side edge 37 has a curved shape in the same manner as each one of the side edges in the examples shown in figures 3 and 4. The cross edges 38 and 39 in this example are perpendicular towards the flow direction. Fig 6 shows a discharge element having an outlet channel 40, which has two inlet openings 41A and 41B. Each inlet opening has a shape which is similar to the shape of the inlet opening 35 shown in fig 5, and is delimited perpendicular to the flow direction by two side edges 42 and 43, 44 and 45, respectively, which diverge in the flow direction. One 42, 44, respectively, of these two side edges is straight and directed in the flow direction while the other side edge 43, 45, respectively, has a curved shape similar to the curved side edge 33 shown in fig 5. As shown in fig 6 the two inlet openings are preferably turned such that their curved side edges meet. Upstreams each inlet opening is delimited by a cross edge 46] 47, respectively, which connects the straight side edge of the inlet opening to its curved side edge. In the shown example the two inlet openings 41A and 41B do not form closed contours. Downstreams the inlet openings are delimited by a common cross edge 48, which is connected to the two straight side edges 42 and 44 of the inlet openings. By designing a centrifugal separator having an energy transfor¬ mation device of the kind initially described in this way] the kinetic energy of the rotating liquid can be recovered and transformed into pressure energy much more effectively than previously has been possible. This might depend on that liquid flowing cross a side edge in a direction into the inlet opening, creates a whirl along the side edge. This whirl then gets such a direction that it by means of shear forces influences the liquid around the discharge element to flow into the outlet channel. In all shown embodiments the inlet openings are formed in a circular cylindrical surface and facing radially. However] the invention is quite applicable in devices of this kind, the inlet openings of which facing in another direction, for instance axially.

Claims: Claims 1. Centrifugal separator having a device for the transformation of kinetic energy of a liquid rotating in a chamber around a rotational axis to pressure energy, comprising an element (17) for the discharge of liquid out of the chamber (12), which element (17) has a surface (20) surrounding the rotational axis arranged to be so located in the rotating liquid body that liquid flows in a predetermined direction along and in contact with the surface (20), and which element (17) forms at least one outlet channel (19, 21, 32, 40), which has an inlet opening (18, 22, 29, 33, 34, 35, 41A, 41B) located in said surface and which from this inlet opening extends a bit essentially in said flow direction, the inlet opening (18, 22, 29, 33, 34, 35, 41A, 41B), seen in the flow direction of the liquid along said surface (20), being delimited by two opposite side edges (23, 24, 27, 28, 36, 37, 42, 43, 44, 45) and a cross edge (25, 30, 38, 48), being located downstreams of these, c h a r a c t e r i z e d i n that the opposite side edges (23, 24, 27, 28, 36, 37, 42, 43, 44, 45) of the inlet opening diverge in said flow direction along an essential part of its extension, at least one of said side edges having such a direction that liquid crossing the same flows into the inlet opening (18, 22, 29, 33, 34, 35, 41A, 41B). 2. Centrifugal separator according to claim 1, c h a r a c ¬ t e r i z e d i n that said side edges (30, 31, 34, 35] 44, 49, 50, 51] 52) diverge in the flow direction along at least half of its extension. 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 each one of said side edges (23, 24, 27, 28, 42, 43, 44, 45) has such a direction that liquid crossing the same flows into the inlet opening (22, 29, 33, 34). 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 outlet channel (40) has two inlet openings (41A, 41B), each of which being delimited by two diverging opposite side edges (42, 43 and 44, 45, respectively), one of which extends in the flow direction along essentially the whole inlet opening (41A, 41B respectively) and the other has a shorter extension in the flow direction than the inlet opening (41A, 41B, respectively). 5. 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 outlet channel (19, 21, 32, 40) has a delimiting surface (26)] which at the end of the inlet opening located upstreams forms a continuation of said surface (20) of the discharge device (17). 6. 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 inlet opening (18, 22, 29, 33, 34, 35) is designed symmetrically of a midline in the flow direction. 7. 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 at least one (27, 28, 37] 43] 45) of the two side edges has a curved shape. 8. Centrifugal separator according to claim 7] c h a r a c ¬ t e r i z e d i n that the radius of curvature of the curved side edge (27, 28, 37, 43, 45) varies along the side edge. 9. Centrifugal separator according to claim 8, c h a r a c - t e r i z e d i n that the curved side edge (27, 28] 37, 43, 45) in the flow direction from being convex towards the inlet opening (18, 22, 29, 33, 34, 35] 41A, 41B) turns to be concave towards the same. 10. 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 outlet channel (19, 21, 32, 40) has a cross section perpendicular towards its longitudinal direction, the area of which gradually increases from the end of the outlet channel located upstreams. 11. Centrifugal separator according to claim 10, c h a r a c ¬ t e r i z e d i n that said cross section has an essentially rectangular shape. 12. 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 discharge device (17) consists of a circular cylindrical disc. 13. 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 said inlet opening (18] 22] 29] 33] 34] 35] 41A] 41B) is formed in an essentially radially facing surface of the discharge device (17). 14. 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 discharge device (17) is stationary. 15. 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 said chamber is formed in a part of a rotor body (2).

Inventors: BORGSTROEM LEONARD III, CARLSSON CLAES-GOERAN, FRANZEN PETER, INGE CLAES, LAGERSTEDT TORGNY, MOBERG HANS II, NAABO OLLE, BORGSTROEM, LEONARD, III, CARLSSON, CLAES-GOERAN, FRANZEN, PETER, INGE, CLAES, LAGERSTEDT, TORGNY, MOBERG, HANS, II, NAABO, OLLE
Applicants: ALFA LAVAL SEPARATION AB, ALFA-LAVAL SEPARATION AB
Application year: 1990
Main classification: B04B11
IPC codes: B04B1, B04B11