WO2005084814A1

WO2005084814A1 - A centrifuge for the separation of a supplied liquid comprising an emulsion of two liquid phases with different densities into a light liquid phase and a heavy liquid phase

Info

Publication number: WO2005084814A1
Application number: PCT/DK2005/000151
Authority: WO
Inventors: Carl Aage Nicolajsen; Tue Korremann Nielsen; Bent Madsen
Original assignee: Alfa Laval Copenhagen A/S
Priority date: 2004-03-09
Filing date: 2005-03-08
Publication date: 2005-09-15
Also published as: DE602005001698T2; EP1725337A1; ATE367207T1; DK200400388A; DE602005001698D1; EP1725337B1; DK1725337T3

Abstract

The centrifuge comprises an elongated drum (1) with an inlet (3) for the supply of an emulsion of liquid phases to a separation chamber (2) and a first and second outlet (4 and 5) from the separation chamber (2) for a light and a heavy liquid phase, respectively. Several barrier plates (6, 9, 10) are arranged for guiding the flow of liquid from the inlet (3) to the outlets (4, 5), which barrier plates (6, 9, 10) have respective overflow and/or underflow edges at different radial distances from the rotational axis (CL) and provide a first, second and third separation area (8, 11, 14) between the inlet (3) and the outlet (4) for the light liquid phase. The arrangement of the barrier plates contributes to prevent re-mixing of an already separated emulsion.

Description

A centrifuge for the separation of a supplied liquid comprising an emulsion of two liquid phases with different densities into a light liquid phase and a heavy liquid phase

The invention relates to a centrifuge for the separation of a supplied liquid comprising an emulsion of two liquid phases with different densities into a light liquid phase and a heavy liquid phase, comprising an elongated drum adapted for rotation about its longitudinal axis, the drum having a substantially cylindrical separation chamber with an inlet for the supply of liquid for the separation chamber; first and second outlets from the separation chamber for the light and heavy liquid phases, respectively, the outlet for the light liquid phase being arranged at a first radial distance from the longitudinal or rotational axis, and the outlet for the heavy liquid phase being arranged at a second, greater radial distance from the rotational axis; and the separation chamber having arranged in it several radially extending barrier plates between the inlet and outlets in order to guide the flow of liquid from the inlet to the outlets, the barrier plates having respective overflow and/or underflow edges at different radial distances from the rotational axis, where a first barrier plate extends from a level above, or closer to the rotational axis than, the highest level of filling for the liquid in the separation chamber to a third radial distance from the rotational axis, the third radial distance being smaller than the distance from the rotational axis to the inner wall in the separation chamber of the drum and greater than the second radial distance in order to define a first separation area in the separation chamber, in that, during operation of the centrifuge, the first barrier plate determines the greatest distance from the rotational axis for an interface between the light and heavy liquid phases in the separation chamber, and where a second barrier plate is placed between the first barrier plate and the outlet for the heavy liquid phase, in relation to the flow, and has an underflow edge at a fourth radial distance from the rotational axis greater than the second radial distance in order to force the heavy liquid phase to pass the fourth radial distance before reaching its outlet. Usually, the rotational axis will be horizontal. The first barrier plate ensures that the liquid entering the centrifuge passes through the first separation area. A centrifuge of this type is known from US-A-4 362 620, which describes a centrifuge (Figure 6 of the document) having a drum, through which a central co-axial body extends, in which the inlet is placed. The first and second barrier plates extend radially from the body and the outlet for the light liquid phase is placed between the two barrier plates. The first barrier plate together with an end wall in the separation chamber form an inlet compartment or first separation area, which is closed radially inwardly but open radially outwardly towards the remaining part of the separation chamber. An emulsion guided into the inlet compartment through the inlet will have a certain residence time there and will be separated into the light and the heavy liquid phases. The light liquid phase will accumulate radially at the innermost of the inlet compartment and force the inflowing emulsion out at a greater radius and thus to an area with greater G force, which will accelerate the separation of the heavy and the light liquid phases. While the heavy liquid phase can flow freely out of the inlet compartment, the light liquid phase will be trapped therein, until the inlet compartment is filled with light-phase-liquid. Thus, when the inlet compartment is filled with light liquid phase, this will begin to flow "under" the edge of the first barrier plate and "up" into a discharge compartment for the light liquid phase defined by the first and second barrier plates, in that the light liquid phase thus flows some of the way through an area with heavy liquid phase to an interface between the light and heavy liquid phases in this discharge compartment. The fact that the light liquid phase must flow some of the way through the heavy liquid phase renders this prior art disadvantageous, since a risk of re- mixing of the two liquid phases is involved which would impair the efficiency of the separation. US-A-4 362 620 corresponds to EP-A-18 474, the novelty report of which mentions US-A-1 870 608, which disclose a centrifugal separator with a separa- tion chamber, from the inner area of which a separated liquid phase is guided some of the way radially outwards through a tube discharging into a small chamber in flow communication with the part of the separation chamber containing the heavy liquid phase. From the small chamber, the light liquid phase is guided back towards the centre of the separator to an outlet . Other examples of centrifuges for the separation of emulsions are known from US-A-5 156 751 and US-A-5 624 371. US-A-5 156 751 discloses a centrifuge where the light liquid phase is discharged directly from the inlet compartment in accordance with the above- mentioned technique. The centrifuge disclosed in this document is a decanter centrifuge with a transportation worm for guiding a heavier solid phase to a third outlet located outside the separation chamber, as this is defined by a baffle plate at its one end, which is thus located between the separation chamber and the third outlet, and is defined by a barrier plate at its other end. Baffle plates of the type disclosed in US-A-5 156 751 are known in many forms, among others from WO-A-97/22411. US-A-5 624 371 discloses a centrifuge with no central body in the drum, in which light and heavy liquid phases are guided from an inlet compartment above or below barrier plate edges, respectively, to discharge compartments, from which the liquid phases are removed by means of scoop elements . It is an object of the invention to provide a centrifuge enabling more reliable separation of a heavy and a light liquid phase in an emulsion. This is achieved by a centrifuge of the kind mentioned in the introduction, which is characterized in that a third barrier plate between the first barrier plate and the outlet for the light liquid phase extends from a fifth radial distance from the rotational axis, which is smaller than the first radial distance but greater than the radius of the highest level of filling, to a sixth radial distance from the rotational axis, which is greater than the third radial distance, whereby the third barrier plate and the first barrier plate define a second separation area in the separation chamber, and in that the outlet for the light liquid phase is arranged downstream from the third barrier plate from a third separation area in the separation chamber. By this arrangement of the third barrier plate a space or second separation area between the first and the third barrier plate is achieved, from which the light and the heavy liquid phases flow in separate directions on to the remaining separation chamber or the third separation chamber, and the interface between the heavy and the light liquid phases in the second separation area may be brought close to the underflow edge of the first barrier plate, by means of appropriate dimensioning of said radial distances relative to the densities of the two liquid phases, thus avoiding the light liquid phase having to flow far through the heavy liquid phase. The inlet may appropriately be placed at one end of the separation chamber and the outlets may appropriately be placed at the other end of the separation chamber. This results in the emulsion having to flow through the separation chamber, whereby a certain uniform residence time in the separation chamber is achieved for each emulsion volume . The centrifuge may be a decanter centrifuge with an elongated central body located in the separation chamber and co-axial in relation to the drum, the body containing the inlet and carrying a transportation worm for the transportation of a heavy relatively solid phase towards a third outlet. Thus, the body preferably carries a baffle plate between the inlet and the third outlet, the baffle plate bridging the space between two adj acent worm windings and blocking part of this space, as it extends from the body to a radial distance from the rotational axis, which is greater than the third radial distance over the entire extent of the baffle plate from one worm winding to the other. Thus, flow of light liquid phase out of the required end of the inlet compartment is ensured. Preferably, the barrier plates are substantially imperforated, and in case a central body is present, the first barrier plate may be tightly fitted to the body. Preferably, along the flow path of the emulsion, surface members are provided for the provision of a larger area of friction. These surface members are thus members whose only function in relation to the emulsion is to increase the area it sweeps (the area of friction) on its way from the inlet to the outlets. Such 'an increased area of friction will enhance the emulsion separating attributes of the centrifuge. In the following, the invention will be explained by means of examples of embodiments with reference to the schematic drawings, in which: Figure 1 illustrates the principles of a centrifuge in accordance with the invention; Figure 2 shows a section through a decanter centrifuge in accordance with the invention; Figure 3 shows a section through a variant of the decanter centrifuge of Figure 2; Figure 4 shows a section through another decanter centrifuge in accordance with the invention; and Figure 5 illustrates another embodiment of a centrifuge with no transportation worm. The figures all show a centrifuge for the separation of a light liquid phase and a heavy liquid phase in a supplied liquid, the liquid containing or being an emulsion of two liquid phases with different densities. In all the examples shown, the centrifuge has an elongated drum 1, which in a manner known per se is journalled and provided with a drive in order for it to be able to rotate about its horizontal longitudinal axis C_L. In the following, reference is made to Figure 1 in order to explain the invention in general . In the drum 1, a cylindrical separation chamber 2 with an inlet 3 for the supply of liquid is located. There are outlets 4 and 5 from the separation chamber 2 for the light and the heavy liquid phases, respectively, and the Outlet 4 for the light liquid phase is arranged at a first radial distance R_x from the longitudinal or rotational axis C_L, whereas the outlet 5 for the heavy liquid phase is arranged at a second, greater radial distance R from the rotational axis C_L. In the separation chamber 2, between the inlet 3 and the outlets 4 and 5, several barrier plates 6,

9, 10 with different radial extents are arranged in order to block the flow path of the liquid from the inlet to the outlets at different distance intervals from the rotational axis C to thereby guide the flow of liquid from the inlet to the outlets. The barrier plates have respective overflow and/or underflow edges at different radial distances from the rotational axis C_L. As can be seen, an elongated central body 16 located in the separation chamber 2 and co-axial relative to the drum 1 carries, at least indirectly, some of the barrier plates and the inlet 3 discharges from the body 16. Thus, a first barrier plate 6 extends from a level above, or closer to the rotational axis C_L than, the highest level of filling R₀ for liquid in the separation chamber 2 and to an underflow edge at a third distance R₃ from the rotational axis C_L, which third radial distance R₃ is smaller than the distance from the rotational axis C_L to the inner cylindrical wall 7 in the separation chamber 2 of the drum and greater than the second radial distance R₂. The first barrier plate 6 may selectively be tightly fitted to the body 16. Thus, the first barrier plate 6 defines a first separation area 8 in the separation chamber at the inlet 3. During operation of the centrifuge, the first barrier plate 6 determines the greatest distance from the rotational axis C_L for an interface between the light and heavy liquid phases in the separation chamber 2. The first barrier plate 6 may extend into the body 16 or have an extension within the body 16, the highest possible level of filling being within the body. A second barrier plate 9 is placed between the first barrier plate 6 and the outlet 5 for the heavy liquid phase, and this second barrier plate 9 has an underflow edge located at a fourth radial distance R₄ from the rotational axis C_L, which at least is greater than the second radial distance R₂, as the second barrier plate 9 must ensure that the light liquid phase is not permitted access to the outlet 5 of the heavy liquid phase. A third barrier plate 10 is arranged between the first barrier plate 6 and the outlet 4 of the light liquid phase. This third barrier plate 10 extends from an overflow edge at a fifth radial distance R₅ from the rotational axis, which is smaller than the first radial distance Ri but greater than the radius of the highest level of filling R₀, to an underflow edge at a sixth radial distance R_s from the rotational axis, which is greater than the third radial distance R₃. The outlet 4 for the light liquid phase is arranged downstream from the second barrier plate 9. In this way, both the outlet 5 for the heavy liquid phase and the outlet 4 for the light liquid phase are arranged downstream from the second barrier plate 9. Therefore, a second' separation area 11 is provided between the first and the third barrier plate 6 and 10. With continued reference to Figure 1, the centrifuge operates as follows: During operation, an emulsion containing liquid is guided through the inlet 3 into the first separation area 8, in which the emulsion is separated into a heavy liquid phase seeking towards the wall 7 of the drum 1 and a light liquid phase gathering on top of the heavy liquid phase. Since R₃ is greater than R₂ (the radius of the outlet 5 for the heavy liquid phase) , the heavy liquid phase will fill the separation compartment 2 at the first separation area 8 up to a separation line 12 between the light and the heavy liquid phases. This separation line will position itself at the radius R3 , because the light liquid phase will flow under the first barrier plate 6 towards its outlet 4, if that radius is exceeded. From the first separation area 8, the light liquid phase flows to the second separation area 11. By appropriate dimensioning of the above radial distances Ri-Rε relative to the densities of the two liquid phases, it is possible for an interface 13 between the two liquid phases in the second separation area 11 to be close to the underflow edge of the first barrier plate 6, which is located at the radius R₃. Therefore, the light liquid phase from the underflow edge of the first barrier plate 6 does not have to flow through a thick layer of the heavy liquid phase in order to be united with the amount of light liquid phase in the second separation area 11, and therefore substantially no re-mixing of the two liquid phases occur at that point. From the second separation area 11, the heavy liquid phase flows under the underflow edge of the third barrier plate 10 at the radius R_s, and the light liquid phase flows over the overflow edge of the third barrier plate 10 at the radius R₅₎ in their respective paths towards the outlets 5, 4. The paths of the liquid phases do not cross each other, after the second separation area 11. From the second separation area 11, the two liquid phases flow into a third separation area 14, in which an interface 15 positions between them. From the third separation area 14, the light liquid phase flows directly to its outlet 4, whereas the heavy liquid phase passes under the second barrier plate 9 at a distance R from the rotational axis C_L. This distance must be so dimensioned that it is greater than the distance of the interface 15 from the rotational axis. The fourth radial distance R may thus appropriately equal the sixth radial distance R₆. It should be understood that in the surfaces of separation 12, 13, 15, yet unseparated emulsion might be present . In the embodiments shown in Figures 1-4, the inlet 3 is placed at one end of the separation chamber 2 and the outlets 4, 5 are placed at the other end of the separation chamber 2 so that the emulsion must pass through the entire separation chamber. In the embodiments shown in Figures 2-4, the centrifuge is formed in a manner known per se as a decanter centrifuge, as the body 16 located in the separation chamber 2 carries a transportation worm 17 for the transportation of a heavy, relatively solid phase 18 towards a third outlet 19, which is also indicated in Figure 1. The body 16 carries a baffle plate 20 between the inlet 3 and the third outlet 19, which baffle plate 20 bridges the space between two adjacent worm windings and blocks part of this space, as it extends from the body 16 to a seventh radial distance R₇ from the rotational axis C_L, which is greater than the third radial distance R₃ over the entire extent of the baffle plate 20 from one worm winding to the other. In the examples described, the barrier plates 6, 9 and 10 as well as the baffle plate 20 are imperforated . In the embodiment shown in Figure 2 , the baffle plate 20 is a plane circular disc and the first and the third barrier plate 6 and 10 extend axially between two adjacent windings of the transportation worm 17, which carries the third barrier plate 10 on its own, whereas the first barrier plate is also, besides the windings, fitted tightly to the body 16. In fig. 3, the baffle plate 20 is also a plane circular disc, and the first barrier plate 6 extends axially as in the embodiment of Figure 2. On the other hand, the third barrier plate 10 is formed as part of a worm winding with the opposite direction of pitch relative to the transportation worm 17. The overflow edge is provided at a recess 21 in the barrier plate 10. Furthermore, in the first separation area 8, along the flow path of the emulsion, a friction surface member in the form of a low worm winding 22 is provided for the provision of a larger area of friction for the emulsion between the inlet 3 and the first barrier plate 6_; The emulsion from the inlet can flow freely on all sides of the low worm winding 22. Alternatively or additionally, a friction surface member may be provided in the second separation area 11 or even in the third separation area 14. In Figure 4, the barrier plates 6 and 10 are formed in the same manner as in Figure 2, but the baffle plate 20' is formed as a worm winding extending from the upstream side of a transportation worm winding 17', follows the sense of rotation of the transportation worm but has a steeper pitch and joins the downstream side of a second transportation worm winding 17'' placed upstream from the first transportation worm winding 17' . At this point, upstream refers to the transportation direction of the transportation worm for solid phase towards the third outlet 19. In Figure 5, an embodiment with no transportation worm is shown, the outlets 4 and 5 for the light and the heavy liquid phases, respectively, are placed at either end of the drum 1. There is a certain symmetry in this construction of the centrifuge, as the inlet 3 and the first separation area 8 are placed approximately at the centre of the drum 1 relative to the longitudinal direction, the first separation area 8 is defined between two similar barrier plates 6 and 6' and there is a second separation area 11, 11' on either side of the first separation area 8 provided between two third barrier plates 10 and 10' and the first barrier plates 6 and 6'. Thus, two third separation areas 14 and 14' are also provided. In this embodiment, the second barrier plate 9 is placed adjacent the right, third separation area 14' in the figure. The two separation areas 14, 14' are in mutual flow communication: as for the light liquid phase through a tube connection 23 and as for the heavy liquid phase via the free connection along the inner wall 7 of the drum 1.

Claims

P A T E N T C L A I M S 1. A centrifuge for the separation of a supplied liquid comprising an emulsion of two liquid phases having different densities into a light liquid phase and a heavy liquid phase, comprising an elongated drum (1) arranged to rotate about its longitudinal axis (C_L) having a substantially cylindrical separation chamber (2) with an inlet (3) for the supply of liquid to the separation chamber (2) , a first and a second outlet (4 and 5) from the separation chamber (2) for the light and the heavy liquid phase, respectively, the outlet (4) for the light liquid phase being arranged at a first radial distance (Ri) from the longitudinal or rotational axis (C_L) , and the outlet (5) for the heavy liquid phase being arranged at a second, greater radial distance (R₂) from the rotational axis (C_L) , and where several radially extending barrier plates (6, 9, 10) are arranged in the separation chamber (2) between the inlet (3) and the outlets (4 and 5) in order to guide the flow of liquid from the inlet to the outlets, which barrier plates have respective overflow and/or underflow edges at different radial distances from the rotational axis (C_L) , a first barrier plate (6) extending from a level above, or closer to the rotational axis (C_L) than, the highest level of filling (R₀) for liquid in the separation chamber (2) and to a third radial distance (R₃) from the rotational axis (C_L) , which third radial distance (R₃) is smaller than the distance from the rotational axis (C_L) to the inner wall (7) in the separation chamber (2) of the drum and greater than the second radial distance (R₂) in order to define a first separation area (8) in the separation chamber, in which first separation area (8) the inlet (3) discharges, as the first barrier plate (6) determines the greatest distance from the rotational axis (C_L) , during operation of the centrifuge, for an interface (12) between the light and the heavy liquid phases in the separation chamber (2) , and a second barrier plate (9) , which is placed between the first barrier plate (6) and the outlet (5) for the heavy liquid phase relative to the flow and has an underflow edge at a fourth distance (R ) from the rotational axis greater than the second radial distance (R₂) in order to force the heavy liquid phase to pass the fourth radial distance (R₄) before reaching its outlet (5) , c h a r a c t e r i z e d in that a third barrier plate (10) between the first barrier plate (6) and the outlet (4) for the light liquid phase extends from a fifth radial distance (R₅) from the rotational axis, which is smaller than the first radial distance (Ri) but greater than the radius for the highest level of filling (R₀) , to a sixth radial distance (R_s) from the rotational axis, which is greater than the third radial distance (R₃) , whereby the third barrier plate (10) and the first barrier plate (6) define a second separation area (11) in the separation chamber (2), and in that the outlet (4) for the light liquid phase is arranged downstream from the third barrier plate (9) from a third separation area (14) in the separation chamber (2) .

2. The centrifuge of claim 1, c h a r a c t e r i z e d in that the inlet (3) is placed at one end of the separation chamber (2) .

3. The centrifuge of claims 1 or 2, c h a r -a c t e r i z e d in that the outlets (4, 5) are placed at the other end of the separation chamber (2) .

4. The centrifuge of any of the claims 1-3, c h a r a c t e r i z e d by an elongated central body (16) arranged in the separation chamber (2) and co-axial in relation to the drum (1) , the body containing the inlet (3) and carrying a transportation worm (17) for the transportation of a heavy relatively solid phase (18) towards a third outlet (19) .

5. The centrifuge of claim 4, c h a r a c t e r i z e d in that the body (16) carries a baffle plate (20, 20') between the inlet (3) and the third outlet (19), which baffle plate (20, 20') bridges the space between two adjacent worm windings and blocks part of this space, as it extends from the body (16) to a seventh radial distance (R₇) from the rotational axis (C_L) , which is- greater than the third radial distance (R₃) over the entire extent of the baffle plate (20, 20') from one worm winding to the other.

6. The centrifuge of one of the claims 1-5, c h a r a c t e r i z e d in that the barrier plates (6, 9, 10) are substantially imperforated.

7. The centrifuge of one of the claims 4-6, c h a r a c t e r i z e d in that the first barrier plate (6) is fitted tightly to the body (16) .

8. The centrifuge of one of the claims 1-7, c h a r a c t e r i z e d in that a friction surface member (22) is provided along at least part of the flow path of the emulsion for the provision of a larger friction area.

9. The centrifuge of claim 8, c h a r a c t e r i z e d in that the friction surface member (22) is provided in the first and/or second separation area (8; 11).