EP0616557B1

EP0616557B1 - Centrifugal separator

Info

Publication number: EP0616557B1
Application number: EP93923702A
Authority: EP
Inventors: Leonard Borgström; Claes-Göran Carlsson; Peter Franzen; Claes Inge; Torgny Lagerstedt; Hans Moberg
Original assignee: Alfa Laval Separation AB
Current assignee: Alfa Laval Separation AB
Priority date: 1992-10-19
Filing date: 1993-10-15
Publication date: 1999-02-03
Anticipated expiration: 2013-10-15
Also published as: ES2129524T3; JPH07502454A; JP3165443B2; EP0616557A1; DE69323416D1; DE69323416T2; SE470493B; SE9203056D0; WO1994008723A1; SE9203056L

Abstract

Centrifugal separator comprising a rotor, which forms an inlet chamber, a separation chamber (5) and an outlet chamber (10), in which a liquid separated during operation forms a rotating liquid body with a radially inwards directed free liquid surface, and a stationary discharge device (17) and means (20), which are arranged to entrain during the operation of the rotor the liquid present in the outlet chamber (10) in the rotation of the rotor and to admit flow of such liquid radially outwards to an inlet (19) in the discharge device (17). In order to entrain the liquid in the outlet chamber (10) efficiently and to admit flow of the liquid radially outwards to the inlet (19) with a small risk of air admixture, said means (20) comprise a number of elongated elements distributed around the rotational axis and rotating with the rotor, which between themselves form flow spaces, which extend axially, radially and in the circumferential direction.

Description

The present invention concerns a centrifugal separator comprising a rotor, which forms a inlet chamber for liquid mixture of components, a separation chamber connected to the inlet chamber, an outlet chamber, which via a passage communicates with the separation chamber for the reception of a liquid separated in the separation chamber during operation of the rotor, and which is so designed that liquid present therein during operation forms a rotating liquid body with a radially inwards directed free liquid surface. The centrifugal separator also comprises a stationary discharge device extending radially inwardly from the said liquid body to a central outlet, at least one outlet channel being formed in the discharge device one end of the outlet channel having an inlet located in said liquid body, and the other end of the outlet channel opening into an outlet connected to the discharge device. Furthermore, the centrifugal separator comprises elongate elements connected to the rotor for entraining separated liquid present in the outlet chamber to rotate with the rotary during operation of the rotor, said members defining there between spaces extending in the axial and radial directions to permit flow of said liquid in said directions in the outlet chamber for said liquid to flow to the inlet of the outlet channel, said elongate elements being distributed in a group disposed around the rotational axis.
In a known centrifugal separator of this kind said passage from the separation chamber opens into the outlet chamber at a level radially inside the free liquid surface. As described in WO 89/03250, in the outlet chamber a number of elongate elements in the form of wings are fixedly connected to extend axially between the end walls of the chamber and radially inwardly from the circumferential wall of the outlet chamber. Separated liquid entering the outlet chamber is hereby thrown radially outwards and collides either directly with the free liquid surface or with one of said wings thereafter to be thrown further radially outwards to the free liquid surface. The flow of the separated liquid radially outwards in the rotating liquid body to the inlet of the outlet channel takes place mainly in thin layers along the wings and one of the end walls of the outlet chamber.
The described collision between the separated liquid and the free liquid surface, or between the liquid and a wing, result in splashes, which means there is a great risk of air or gas, which is located radially inside the free liquid surface in the outlet chamber, being admixed in the separated liquid which flows radially outwards to the inlet of the outlet channel and further to the outlet. Also the locally high liquid flow velocity which occurs near the free liquid surface in the layers, in which the liquid flows radially outwards in the liquid body, results in a great risk of admixture of air or gas with the liquid.
In order to decrease the high liquid flow velocities in the layers in which the liquid flows radially outwards, it has been suggested in WO 89/03250 to have in the outlet chamber radially inside the wings at least one disc fixed concentrically to the rotor. Hereby the outwardly directed liquid flow in the outlet chamber is distributed in more layers having a large total cross-sectional area, whereby the flow velocities in the layers and consequently the risk of air admixture decreases. However, the disc or discs according to the suggested known solution is unable to decrease the air admixture sufficiently and at the same time satisfactorily entrain the separated liquid in the rotation of the rotor.
The object of the present invention is to provide a centrifugal separator of the kind initially described, in which the risk of air admixture in the discharged separated liquid is less than in hitherto known centrifugal separators of this kind with corresponding capability to entrain the separated liquid in the outlet chamber.
This is accomplished according to the present invention by such a centrifugal separator characterised in that said elongate elements are separated from adjacent elements in different directions and a plurality of interconnected flow spaces are formed between the elements enabling liquid also to flow circumferentially between the elements within the volume of the outlet chamber occupied by the group of elongated elements.
In a preferred embodiment of the invention the elongate elements are straight and regularly oriented and they extend substantially parallel to the rotor axis, but they can alternatively be directed substantially radially.
In another embodiment of the invention the elongate elements are irregularly oriented and they can with advantage abut against each other.
In a particular embodiment of the invention the elongate elements can be supplemented by at least one wing fixedly connected to the rotor, the wing extending radially and axially in the outlet chamber, in a way such that an efficient entrainment of the liquid in the outlet chamber is obtained.
In the following the invention will be described more closely with reference to the attached drawings in which:
Figure 1 schematically shows an axial section through a part of a centrifugal separator according to the invention,
Figure 2 shows a view of the detail in a centrifugal separator according to the invention, and
Figure 3 shows a section along the line III-III in Figure 2.
The part of the centrifugal separator shown in Figure 1 comprises a rotor, which has a lower part 1 and an upper part 2, which are joined together by a locking ring 3. Inside the rotor an axially movable valve slide 4 is arranged. This valve slide delimits together with the upper part 2 a separation chamber 5 and is arranged to open and close an outlet passage between the separation chamber 5 and outlet openings 6 to discharge intermittently a component, which has been separated from a mixture supplied to the rotor and has accumulated at the periphery of the separation chamber. The valve slide 4 delimits together with the lower part 1 a closing chamber 7, which is provided with an inlet and a throttled outlet for a closing liquid. These inlets and outlets are not shown in the figure.
Inside the separation chamber 5 a disc stack 8 consisting of a number of conical separation discs is arranged between a distributor 9 and the upper part 2. The upper part 2 forms in its upper end (as illustrated) a outlet chamber 10, to which a specific lighter liquid separated during operation from a mixture supplied to the rotor can flow from the separation chamber 5 via a passage 11. In the outlet chamber the liquid forms a rotating liquid body with a radially inwards directed free liquid surface at a certain radial level. The outlet chamber 10 is delimited by two axial end walls 12, 13 and a circumferential wall 14 which extends between the end walls.
Centrally through the outlet chamber 10 a stationary inlet tube 15 is arranged, which opens in the interior of the distributor 9. Around this inlet tube 15 a stationary outlet tube 16 is arranged for the specific lighter liquid in the supplied mixture. The outlet tube 16 extends into the outlet chamber 10. Inside the outlet chamber 10 a stationary discharge device 17 is arranged around the inlet tube 15. The discharge device 17 extends radially inwardly from the rotating liquid body to the inlet tube 15 and forms inside itself at least one outlet channel 18, one end of which has a peripheral inlet 19, and the other end of which opens in the interior of the outlet tube 16.
In the outlet chamber 18 an entraining device 20 is arranged fixedly connected to the end walls 12 and 13. This device 20 is arranged to entrain the liquid present in the outlet chamber 10 during operation in the rotation of the rotor and admit flow of the same radially outwards to the inlet 19 of the outlet channel 18.
Figure 2 and 3 show more in detail the design of said device 20. According to this embodiment of the invention the device 20 comprises an annular circular disc 21, which is fixedly connected to an end wall 12 or 13 and concentric with the rotation axis. On the axial side of the disc, which is directed towards the stationary discharge device 17 several elongated elements 22 are distributed in an array around the rotational axis and these elements form between themselves flow spaces, which extend axially, radially and in the circumferential direction of the rotor allowing the liquid to flow in these directions within the volume occupied by the elongated elements. In the illustrated embodiment the elongated elements 22 are fixedly connected to each other via the disc 21 and are directed axially. The flow spaces between the elongated elements 22 are open in the direction toward the stationary discharge device 17.
In order to increase the entraining capability of the entraining device, three wings are fixedly connected to the disc 21 to extend radially and axially in the outlet chamber 10.
A centrifugal separator which is designed according to the invention works in the following manner:
Upon start of the centrifugal separator the rotor is brought to rotate and the separation chamber 5 is closed by supplying a closing liquid to the closing chamber 7 through an inlet (not shown). After the separation chamber 5 has been closed the liquid mixture, which is to be centrifugally treated is supplied to the separation chamber 5 through the inlet tube 15 and the distributor 9. Gradually the separation chamber 5 is filled up, the rotor reaches the operational rotational speed and the conditions are stabilized inside the separation chamber. The components contained in the liquid mixture are separated under the influence of the centrifugal forces acting on the same.
The separation takes place mainly in the inter-spaces between the conical discs in the disc stack 8. During separation the specific heavier component is thrown radially outwards and is accumulated in the radially outermost part of the separation chamber, whereas the specific lighter liquid flows radially inwards in these interspaces.
The specific heavier component is intermittently discharged during operation by causing the valve slide 4 to uncover the peripheral outlet openings 6.
The specific lighter liquid flows out through the separation chamber 5 through the passage 11 to the outlet chamber 10, in which it forms a rotating liquid body with a radially inwards directed free liquid surface. The liquid present in the outlet chamber 10 is discharged through the outlet channel 18 in the stationary discharge device 17 via its inlet 19. The entrainment of the liquid present in the outlet chamber 10 effected gently by the device 20 rotating with the rotor and by other internal surfaces of the walls of the outlet chamber. The liquid located closest to the discharge device 17 is slowed down by the contact with the external surfaces of the discharge device 17. Thereby, different parts of the liquid volume located in the outlet chamber 10 will obtain different rotational speeds. The contact between the liquid and the external surfaces of the discharge device 17 results in that a circulating flow is generated in the outlet chamber 10, the liquid flowing radially inwards along the external surfaces of the discharge device 17 and radially outwards in layers, which extend along and connect the elongated elements 22 and along internal surfaces of the walls of the outlet chamber 10. In the case that said device 20 also comprises a wing 23, liquid also flows radially outwards in layers along this wing.
This flow radially outwards is distributed over relatively large layers. Hereby the local maximum flow velocities can be kept low, which is especially important at the free liquid surface as the risk of air admixture is especially high there.
If the passage 11 is arranged at essentially the same radius as the radius at which the inlet 19 of the outlet channel 18 is located the radial outwardly directed flow is to be referred to the internal circulation in the outlet chamber 10.
However, sometimes it is necessary to place the passage 11 radially inside said inlet 19 in order to be able to keep the different liquid levels inside the separation chamber 5 at wanted radii. Then the radially outwards directed flow which this location of the passage 11 gives rise to, is added.

Claims

A centrifugal separator comprising

a rotor forming an inlet chamber for a liquid mixture of components, a separation chamber (5) connected to the inlet chamber, and an outlet chamber (10), which via a passage (11) communicates with the separation chamber for the reception of a liquid separated in the separation chamber during operation of the rotor, and which is so designed that liquid present therein during operation forms a rotating liquid body with a radially inwards directed free liquid surface,

a stationary discharge device (17) extending radially inwardly from the said liquid body to a central outlet, at least one outlet channel (18) being formed in the discharge device, one end of the outlet channel having an inlet (19) located in the said liquid body, and the other end of the outlet channel opening at an outlet connected to the discharge device, and

elongate elements (22) connected to the rotor for entraining separated liquid present in the outlet chamber (10) to rotate with the rotor during operation of the rotor, said elements defining therebetween flow spaces extending in the axial and radial directions to permit flow of said liquid in said directions in the outlet chamber (10) for said liquid to flow to the inlet (19) of the outlet channel (18),
said elongate elements (22) being distributed in a group disposed around the rotational axis, characterized in that the elements are separated from adjacent elements in different directions and a plurality of interconnected flow spaces are formed between the elements enabling liquid also to flow circumferentially between the elements within the volume of the outlet chamber occupied by the group of elongated elements (22).
A centrifugal separator according to claim 1, characterised in that the elongate elements (22) are fixedly connected to each other.
A centrifugal separator according to claim 1 or 2, characterised in that the elongate elements (22) are substantially straight and regularly oriented.
A centrifugal separator according to claim 2 or 3, characterised in that at least some of the elongate elements (22) extend substantially parallel to the rotor axis.
A centrifugal separator according to claim 2 or 3, characterised in that at least some of the elongate elements (22) extend substantially radially in the outlet chamber.
A centrifugal separator according to claim 1 or 2, characterised in that the elongate elements (22) are irregularly oriented.
A centrifugal separator according to claim 6, characterised in that elongate elements (22) abut against each other.
A centrifugal separator according to any of the previous claims, characterised in that in addition to the elongate elements (22) at least one wing (23) is fixedly connected to the rotor and extends radially and axially in the outlet chamber (10).
A centrifugal separator according to any of the previous claims, characterised in that the spaces between the elongate elements are open in a direction towards the stationary outlet device (17).