WO1988002664A1

WO1988002664A1 - Centrifugal separator having a stationary discharge member

Info

Publication number: WO1988002664A1
Application number: PCT/SE1987/000471
Authority: WO
Inventors: Jon Eiken
Original assignee: Alfa-Laval Separation Ab
Priority date: 1986-10-15
Filing date: 1987-10-15
Publication date: 1988-04-21
Also published as: SE8604366L; SE454954B; SE8604366D0

Abstract

A centrifugal separator, which comprises a rotor with a separation chamber (5) and a discharge chamber (17) for the discharge of a liquid separated in the separation chamber. The centrifugal separator also comprises a stationary discharge member in the shape of a circular disc having a peripheral inlet (23) and a central outlet (25) arranged in the discharge chamber (17) coaxially with the rotor. The inlet (23) is formed by at least one projection projecting out from the periphery of the disc and having an inlet opening directed essentially tangentially in a direction opposite to the rotational direction of the rotor and an inlet channel (30) connecting the inlet opening (29) to a space within the disc. The liquid separated during operation and present in the discharge chamber (17) forms a rotating liquid body having a liquid surface directed radially inwards, which is kept at a predetermined radial level outside the circular disc. The space (27) in the circular disc is ring shaped and encloses the rotational axis of the rotor and extends radially essentially from the central outlet of the disc to the outer circumference of the disc.

Description

Centrifugal separator having a stationary discharge member

The present invention concerns a centrifugal separator having a rotor with a separation chamber and with a discharge chamber for a liquid separated in the separation chamber. The centrifugal separator also has a stationary discharge member comprising an essentially circular disc being arranged coaxially with the rotor in the discharge chamber and having a peripheral inlet and a central outlet. The inlet is formed by at least one projection projecting radially out from the periphery of the disc and having an inlet opening directed tangentially in a direction opposite to the rotational direction of the rotor and an inlet channel connecting the inlet opening to an internal space in the disc. Liquid separated during operation and present in the discharge chamber forms a rotating liquid body having a liquid surface directed radially inwards, and means are arranged to keep this liquid surface during operation at a predetermined radial level outside the circular part of the discharge member.

Centrifugal separators of this kind are used for many different purposes. One advantage with the same is that the described outlet device for a separated component forms a centripetal pump, which makes it possible to transport the discharged component in tubes connected to the stationary discharge member without use of separate pump devices.

However, a problem in connection with the operation of such centrifugal separators is that great losses of effect arise as a result of the discharge of the separated component if this has a very high flow resistance, i.e. has a high viscosity. In such cases the driving system of the centrifugal separator has to be over- dimensioned to an unwanted degree.

One example of a separation process, in which a separated component has a very high viscosity, can be found in connection with the refinery of vegetabilic oils containing fatty acids. At such refinery the fatty acids are neutralized by mixing natrium hydroxide and water into the oil to be neutralized, the natrium hydroxide reacting with the fatty acids and forming a soap mass. This soup mass, which normally is separated from the neutralized vegetabilic oil in centrifugal separators, has a very high flow resistance, and a large effect is needed just for the discharge of the soap mass out of the centrifugal separator.

The object of the present invention is to provide a centrifugal separator of the initially described kind, in which the problem discussed above concerning a great consumption of effect can be reduced.

This object may be achieved by designing the space within said circular disc, which constitutes a part of the stationary outlet member of the centrifugal separator, ring shaped such that it encloses the rotational axis of the rotor and extends radially essentially from the centre of the disc to the outer periphery of the disc.

In previously known so called paring discs of the type here in question said space within the disc is divided into separate channels, each of which usually extends spirally from the periphery of the disc to the centre of it and the central outlet located there.

It has proved that a disc according to the invention having a relatively large annular chamber offers substantially less through flow resistance to a liquid having a high flow resistance than a conventional paring disc of the type discussed above.

In a preferred embodiment of the invention the disc at said inlet opening is provided with a radially inner edge and a radially outer sharp edge, only the latter of which is situated at such a radial level that during operation it is immersed into the liquid body in the discharge chamber of the rotor. Hereby, the consumption of effect is reduced at the entrance of the separated liquid in the channel. In the following the invention will be described more in detail with reference to the accompanying drawings, in which

Fig. 1 schematically shows an axial section through a part of a centrifugal separator according to the invention,

Fig. 2 shows a section along the line II-II in figure 1, Fig. 3 shows in section an enlarged part of the centrifugal separator in fig 1, and

Fig. 4a, b and c shows axial sections along the line IV-IV through three alternative embodiments of the part shown in figure 3 of the centrifugal separator.

In figure 1 there is shown a part of a centrifugal separator comprising a rotor, which has a lower part 1 and an upper part 2, which are joint together axially by means of a locking ring 3. In the shown example there is an axially movable valve slide 4 arranged inside the rotor. This valve slide delimits together with the upper part 2 a separation chamber 5 and is arranged to open and close an upper passage towards the outlet openings 6 for a component, which has been separated from a mixture supplied to the rotor and been accumulated 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 so called closing liquid. Upon rotation of the rotor the valve slide 4 is pressed by the pressure from the closing liquid present in the closing chamber 7 by the influence of the centrifugal force into sealing abutment against an annular gasket 10 arranged in the upper part 2.

Within the separation chamber there is arranged a stack of discs 11 comprising a number of conical separating discs between a distributor 12 and an upper disc 13. In the example shown in figure 1 the rotor is mounted on a hollow shaft, through which the liquid mixture, which is to be centrifugally treated, can be supplied to the separation chamber 5. The upper disc forms at its in the figure shown upper end a centrally located first discharge chamber 15 for a specific lighter liquid component separated in the separating chamber 5. This first discharge chamber 15 is in connection with the separation chamber 5 via a first overflow outlet 16, over which the specific lighter component can flow out of the separation chamber 5.

The upper part 2 of the rotor forms a centrally located second discharge chamber 17, to which a specific heavier separated liquid component can flow out of the radially outermost part of the separation chamber 5 via a passage 18 and a second overflow outlet 19.

In each discharge chamber there is arranged a stationary outlet member, a first discharge member 20 and a second discharge member 21, respectively. These discharge members are formed as circular discs provided with peripheral inlets, a first inlet 22 and a second inlet 23, which are connected to central outlets, a first outlet 24 and a second outlet 25, respectively. The discharge members 20, 21 extend essentially perpendicularly to the axis of rotation radially so far out that they during operation partly are located in a rotating liquid body present in the discharge chamber 15j 17, respectively.

The second discharge member 21 has a projection 26 projecting radially out of the periphery of the disc (fig. 2), in which a second inlet 23 is arranged with an inlet opening directed towards the rotational direction of the rotor.

As can be seen in fig. 1 and 2 there is a space 27 surrounding the rotational axis of the rotor inside the circular disc of the discharge member 21. The annular space 27 extends radially essen¬ tially from the central outlet 25 at the centre of the disc to the radially outermost part of the disc. Furthermore, the discharge chamber 17 is provided with internal wings 28 directed radially inwards for the entrainment of the liquid present in the discharge chamber. The design of the projection 26 can be seen in figure 3, which shows an enlarged section through the same. The projection 26 forms an inlet opening 29 directed towards the rotational direction of the rotor and an inlet channel 30, which connects the inlet opening 29 to the space 27 of the disc 21.

As shown in fig. 4a, b and c the inlet opening 29 is delimited by a radially inner edge 31, which is parallel to the axis of rotation of the rotor and during operation is located radially inside the liquid body rotating in the discharge chamber 17, and a radially outer sharp edge 32 located radially outside this liquid surface and consequently it is immersed into the liquid body. The form of the outer edge 32 is then preferably arcuated or designed such that it together with the inner edge forms a triangle or a rectangle.

At the first circle sector 33 upstream the inlet opening 29 the radius of the circular disc increases in the rotational direction of the rotor. The circumferential surface of the circular disc can be planned or arcuated in this circular sector 33. At the opposite side of the inlet opening the projection 34 is designed in a second circular sector with a radius which decreases from the inlet opening in the rotational direction of the rotor.

The centrifugal separator according to the invention shown in the figures functions in the following manner:

In connection with starting of a centrifugal separator of this kind and bringing the rotor to rotate, the separation chamber 5 is closed by supplying closing liquid to the closing chamber 7 through the inlet 8. As soon as the separation chamber 5 is closed, the liquid mixture, which is to be centrifugally treated, is supplied to the separation chamber through the hollow shaft 14. When the rotor has reached the rotational speed of operation and the separation chamber 5 has been filled up, the components contained in the liquid mixture are separated by the influence of centrifugal forces acting on the same. The separation is then mainly taking place in the intermediate spaces between the conical discs in the disc stack 11. During separation a specific heavier liquid component is thrown radially out towards the periphery of the separation chamber 5 where it is accumulated, while a specific lighter liquid component flows radially inwards in these intermediate spaces.

If the centrifugally treated liquid mixture also contains specific heavy particles, these are accumulated at the outermost periphery of the separation chamber 5.

The specific lighter liquid component flows over to the first discharge chamber 15 via the overflow outlet 16, which thereby will be determining for the radial level of the free liquid surface in the separation chamber 5. The light liquid component is discharged under pressure out of the centrifugal rotor via the stationary discharge member 20, which in this case consists of a conventional paring disc.

The specific heavier liquid component, which has been accumulated at the periphery of the separation chamber, flows radially inwards through the passage 8 and further via the overflow outlet 19 into the outlet chamber 17. Herein it forms a cylindrical liquid body, which is kept In rotation inter alia by means of the entraining means 28 (fig. 2). Upon operation the discharge member 21 is immersed into the rotating liquid body only with its radially projecting projection 26, while the circular disc of the discharge member is located ra¬ dially inside the rotating liquid body. Hereby, the friction between the outside of the discharge member 21 and the rotating liquid body will be low.

Specific heavier component flows into the internal space 27 of the circular disc through the Inlet opening 29 of the projection 26. Therefrom it flows further out through the central outlet 25. According to the invention the space 27 is designed such that it encloses the rotational axis of the rotor and extends radially from the centre outlet 25 to the radially outermost part of the circular disc. By this design of the space 27 the specific heavier component is permitted to choose by itself the flow path through the discharge member 21 between the inlet channel 30 and the central outlet 25. This seems to result in the lowest possible flow resistance for the discharge of the heavy liquid component.

It is important that the through flow area for the heavy component, when it has passed through the inlet opening 29, is larger than the cross section area of the inlet opening.

If the specific heavier liquid component consists of a liquid flowing with a very high resistance, the free liquid surface of the liquid body in the discharge chamber 17 can take a form, which differs from the pure circular cylindrical. In order to prevent that the central disc of the discharge member 21 in such cases comes into contact with the liquid body, the radius of the circumferential surface of the circular disc increases in the rotational direction of the liquid body in a circular sector upstream the inlet opening 29. Hereby, the discharge capacity of the inlet opening 29 can be used maximally without any risk for the circular disc coming into contact with the liquid body.

To minimize the contact of the projection 26 with the rotating liquid body the projection suitably has such a form that it behind the inlet opening 29 extends in the rotational direction of the rotor along a circular sector which is less than 45°, and its outer radius being decreasing successively behind the inlet opening 29. Hereby, the rotating liquid body leaves the projection close to the inlet opening 29. It is also possible to design the projection with a sharp edge (not shown) located in the rotational direction of the liquid body after the inlet opening 29, from which the liquid body leaves the projection 26. In the shown example an interface between the specific lighter and the specific heavier liquid component in the separation chamber is adjusted during operation, the radial position of which Is determined inter alia by the position of the two overflow outlets 16 and 19. However, it is quite possible to design a centrifugal separator according to the invention without the overflow outlet 19 and to have the liquid level in the discharge chamber to be determining for the radial position of the interface.

Claims

1. Centrifugal separator comprising a rotor, which forms a separation chamber (5) and a discharge chamber (17) for a liquid separated in the separation chamber (5); a stationary discharge member (21) with an essentially circular disc, which is arranged in the discharge chamber (17) coaxially with the rotor and which has at least one projection (26) projecting radially from the periphery of the disc; and means arranged to keep a liquid surface of a liquid body rotating in the discharge chamber (17) during operation at a predetermined level radially outside the circular disc; said projection (26) forming an inlet with an Inlet opening (29) directed essentially tangentially in a direction opposite to the rotational direction of the rotor and an inlet channel (30) connected to the inlet opening (29), the inlet channel communicating with a central outlet (25) at the centre of the disc via an internal space in the disc, c h a r a c t e r i z e d i n that said space (27) in the circular disc is ring shaped so that it encloses the rotational axis of the rotor and extends radially essentially from the centre of the disc to the outer periphery of the disc.

2. Centrifugal separator according to claim 1, c h a r a c t e ¬ r i z e d i n that the inlet opening (29) is delimited by a radially inner edge (31) and a radially outer sharp edge (32), of which edges only the latter is located at such a radial level that it during operation is immersed in liquid in the discharge chamber (17).

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 circumferential surface of the disc has a radius, which increases in the rotational direction of the rotor over a circle sector (33) just in front of (upstream) the inlet opening (29).

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 discharge member (21) is designed such that the cross sectional area of the inlet opening constitutes the smallest through-flow area for liquid in the discharge member (21).

5. Centrifugal separator according to any of the previous claims, c h a r a c t e r i z e d i n that the projection (26) has a radial extension, which decreases in the rotational direction of the rotor from the inlet opening (29), and an extension in the circum¬ ferential direction of the rotor from the inlet opening (29) along a circle sector (34) smaller than 45°.

6. Centrifugal separator according to any of the previous claims, c h a r a c t e r i z e d i n that said inlet opening (29) has the shape of a rectangle.

7. Centrifugal separator according to any of the claims 1-5, c h a r a c t e r i z e d i n that said inlet opening (29) has the shape of a triangle, in which one of the sides of the triangle constitutes a radially inner edge (31) of the inlet opening and extends essentially axially.

8. Centrifugal separator according to any of the claims 1-5, c h a r a c t e r i z e d i n that the inlet opening (29) is formed by a radially inner straight edge (31), which extends essen- tially axially and a radially outer curved edge (32), which connects the ends of the inner straight edge (31).