GB2088243A - Rotary contactor - Google Patents

Abstract

A continuous liquid/liquid or liquid/solids contactor comprises an outer shell 12 with a rotor therein having axially spaced partition discs 16 dividing the shell into compartments, at least some of which compartments have receptacles 17 carried by the rotor. Passages for phase flow between compartments are provided in or about the discs. At least one end settlement chamber free of receptacles is provided, having means therein, suitably in the form of a weir or funnel, for reducing vortex flow and/or turbulent flow in the settlement chamber. The weir may be attached to the lower half of the shell 12 (see 23, left-hand side) or the upper half (24, right-hand side) so as to face the respective inlet 18. Alternatively, inlet 18 may terminate in a divergent funnel to reduce the inlet velocity of liquid or solid. <IMAGE>

Description

SPECIFICATION Contactor This invention relates to a continuous liquid/liquid or liquid/solids contactor for purposes such as diffusional extraction, washing extraction, chemical extraction, leaching and chemical reaction. In particular, the invention is concerned with a continuous contactor of the type comprising an outer shell, a rotor within the shell having axially spaced partition discs separating the interior of the shell into compartments, receptacles carried by the rotor in at least some of the compartments, but not in the end settlement compartments, and passages in, or about, the discs for allowing movement of liquids from compartment to compartment. The contactor may operate in counter-current, in which case an inlet and an outlet are provided for each end settlement chamber.Alternatively, the contactor may operate in co-current, in which case one settlement chamber has two inlets and the other has two outlets. Such a contactor will be referred to as "a contactor of the type described".

In the operation of a contactor of the type described, two streams are passed in separate phases through the contactor. During the passage of the phases, gentle intermixing occurs by the action of the receptacles, which carry the heavier phase into the lighter phase, and vice versa.

Examples of contactors of the type described are given in British patent specifications Nos.

972,035, 1,145,894 and 1,527,269, and in British patent application No. 80.20345.

In the operation of contactors of the type described, and particularly when they are operated in counter-current, one "back mixing" has been observed, i.e. minor proportions of one phase has been carried out of the contactor entrained in the other phase, and vice versa, although ideally complete settlement of the two phases should take place in the settlement chambers prior to discharge. Back mixing is obviously to be avoided where possible, since in acute cases it necessitates further treatment of the discharged streams for removal of the entrained materials.

By experiment, we have found that much of the back mixing that does occur unexpectedly takes place in the settlement chambers. Thus, in counter-current operation, we have found that the speed at which an incoming stream enters a settlement chamber can give rise to vortices in that settlement chamber, causing mixing of the two phases and the discharge of material from the incoming stream with the outgoing stream.

Similar disturbance of flows can result from the speed at which an outgoing stream is discharged from a settlement chamber.

The present invention resides in one aspect in a continuous contactor of the type described, in which there are means in at least one of the settlement chambers at the ends of the contactor for reducing vortex flow and/or turbulent flow of at least one of the streams in the settlement chamber. Thereby, mixing of the streams in the settlement chamber, and therefore entrainment of one in the other, is minimized.

In one form of the invention, the means comprise a weir extending inwardly from the shell within the settlement chamber, and located and designed to reduce any vortex flow that may occur. Where the contactor is employed to bring into contact two liquid streams, the weir may extend from the lower part of the shell to a point below the designed interface between the two liquids in the settlement chamber. Such an arrangement of the weir is not possible where the lower stream in the contactor contains solids, since the weir would then prevent movement of the solids along the contactor, assuming that the density of the solids is greater than that of either of the liquids; in that case, the weir should extend downwardly from the upper part of the contactor or, preferably, the expedient described in the next paragraph should be adopted.

Alternatively, the said means may comprise a funnel diverging from an inlet or outlet and opening to the settlement chambers, in order to reduce the flow rate of the incoming or outgoing stream within the chamber. Such a funnel can be used when the two streams are liquids without included solids, or when one of the streams includes solids.

In another aspect, the invention, provides, in a contactor of the type described, a baffle plate closely adjacent one end of the rotor to close the interior of the shell apart from openings at top and bottom. The baffle plate serves to prevent interfacial baffles located between the phases from moving into the settlement chamber at the rotor end.

The invention will be more readily understood by way of example from the following description of contactors in accordance therewith, reference being made to the accompanying drawings, in which Figure 1 is a schematic axial section through a contactor employing weirs in the settlement chambers, Figures 2 and 3 are radial sections on the line Il-Il and Ill-Ill respectively, and Figure 4 is a schematic axial section of one end of the contactor and illustrates the use of a divergent funnel.

The contactor shown in Figures 1 to 3 is generally as described and illustrated in British patent specification No. 972035, except that there is a settlement chamber at each end, and except for the provision of means to be described for reducing vortices in the settlement chambers.

Thus, the contactor consists of a stationary shell 12 having end plates 13 and 14 and containing a rotor, which is constituted by a shaft 15 extending axially through the shell 12 and carrying a series of equally axially spaced partition discs 16. A ring of bucket-like receptacles 17 is carried in each compartment formed between successive discs 16, those receptacles being carried by, and rotating with, the discs 1 6. Each of the end plates 13 and 14 has an inlet and an outlet 18, one of which is disposed adjacent the bottom of the shell 12, and the other adjacent the top of the shell.

When the contactor is operated in counter current, the phase of greater density enters near the bottom of the left-hand end plate 1 3 and discharges at the bottom of the right-hand end plate 14, as indicated, while the lighter phase enters near the top of the right-hand end plate 14 and discharges near the bottom of the left-hand end plate 13. The two phases form an interface 20 approximately on the axis of the shell 12 and the rotor.

There are no receptacles 17 between each end plate 13 or 14 and the adjacent disc 16, settlement chambers 21 and 22 being formed at the ends of the contactor, in order that the two phases may settle out by migration of entrained bubbles of one phase in the other back to the body of the first phase. However, as explained above, the entry of a stream at high velocity into either of the settlement chambers through the restricted respective inlet 18 can give rise to turbulence and the formation of vortices in the settlement chamber, to the detriment of the settling action and with the possibility of back mixing.

As shown in Figures 1 to 3, the occurrence of turbulence and vortices in the settlement chambers can be minimised by the location of a sector-shaped weir plate 23 or 24. The principle trouble occurs with the high velocity entry of the heavier phase and, in that case, the weir 23 is secured to the lower part of the shell 12 within the chamber 21, the weir plate 23 terminating below the interface 20. Weir plate 23 is displaced from end plate 13 by a distance between one third and one half of the axial width of the settlement chamber 21. By means of the weir, the high velocity jet entry through the inlet 1 8 has its velocity rapidly dissipated, without the formation of vortices, so that the settling action required in chamber 21 is not frustrated.

Similarly, the weir plate 24 may be provided as shown in the right-hand settlement chamber 22 opposite the inlet 18 for the lighter phase. In that case, the weir plate 24 is secured to the upper part of the shell 12 so as to mask the inlet. If the suction provided by the discharge through the outlets 18 creates disturbances, similar weirs may be provided adjacent them.

Where the heavier phase contains solids, it is impracticable to employ the weir plate 23, which would prevent the axial movement of the solids along the contactor. Instead, the velocity of the incoming jet is dissipated gradually by continuing the inlet 18 by a divergent funnel or horn 30 which opens into the chamber 21, with the result that the stream entering the mass of the lower phase in that chamber has a velocity which is sufficiently limited that turbulence and vortices do not occur. Similar funnels can be provided for the other inlets and outlets, where desired. The cone angle of the funnel 30 is preferably greater than 300.

The funnel 30 is usually provided where the heavier phase contains solids, which has a higher specific gravity than either of the liquids. However, funnels can be used in place of the weir 23 or 24 when no solids are involved. Also, a funnel 30 can be used in conjunction with an adjacent weir 23 or 24. Further, while the use of a weir 23 or 24 is prohibited when the shell 12 is mounted for rotation with the rotor 1 6, the use of funnels 30 can be used in that application.

It is not essential that the divergent funnel 30 should be located entirely within the settlement chamber. For example, the inlet pipe 18 may have a terminal part in the form of a divergent funnel, the mouth of which is at the end plate 13.

While the contactor is shown as having buckets similar to those described and illustrated in British Specification No. 972,035, it may equally have buckets presenting a smooth profile to the phases, as described in British Patent Application No.

80.20345.

Another cause of "back-mixing" is the creation in some instances of bubbles located between the two phases in the rotor. Where the lighter and heavier phases are respectively organic and aqueous in nature, the bubbles are usually aqueous with a certain amount of air rendering them less dense than the aqueous phase but more dense than the organic phase. The bubbles tend to move axially along the rotor into the settlement chamber from which the lighter phase is discharged, and to leave the contactor entrained in that phase.

To reduce the "back-mixing" resulting from the interfacial bubbles, it is further proposed to have within the contactor at least one baffle plate secured to the shell and located closely adjacent to a rotor end plate. The baffle plate closes off the shell interior except for segment-shaped gaps at top and bottom and prevents the movement of the bubbles out of the rotor. The area of each gap should be equal to half the area of the annular gap between a partition disc and the shell and the rotor end plate adjacent the baffle plate has preferably a smaller diameter than the partition discs to ensure that there is no restriction in flow of the phases through the contactor.

There may be a baffle plate adjacent each rotor end plate to confine the interfacial bubbles entirely within the rotor. The provision of the baffle plate or plates may be additional to the means for reducing vortex and/or turbulent flow described above.

Claims (12)

1. A continuous liquid/liquid or liquid/solids contactor comprising an outer shell, a rotor within the shell having axially spaced partition discs separating the interior of the shell into compartments, receptacles carried by the rotor in at least some of the compartments, passages in or about the discs allowing movement of liquids from one compartment to another and at least one end settlement chamber free of receptacles and provided with means for reducing vortex flow and/or turbulent flow of at least one of the streams in the settlement chamber.

2. A contactor according to claim 1 , wherein the means comprise a weir extending inwardly from the shell within the settlement chamber.

3. A contactor according to claim 2, intended for the contacting of liquid streams, wherein the weir extends from the lower part of the shell to a point below the intended interface between the liquids in the settlement chamber.

4. A contactor according to claim 3, wherein the weir is adjacent the entry of the heavier phase to the contactor.

5. A contactor according to claim 2, 3 or 4, comprising a weir extending downwardly from the upper part of the shell to a point above the intended interface between the liquids in the settlement chamber.

6. A contactor according to any one of the preceding claims, wherein the means comprise a funnel diverging from an inlet or outlet and opening to the end settlement chamber.

7. A contactor according to claim 6, wherein the funnel is arranged at the inlet for a heavier solids-containing phase.

8. A contactor according to any one of the preceding claims, further comprising a baffle plate closely adjacent one end of the rotor so as to close the interior of the shell except for gaps at the top and bottom of the shell, whereby interfacial bubbles located between the phases are prevented from moving into the settlement chamber.

9. A contactor according to claim 8, wherein the gaps in the baffle plate each have an area of about half the area of the annular gap between a partition disc and the shell.

10. A contactor according to claim 8 or 9 wherein a rotor end plate adjacent the baffle plate has a smaller diameter than the partition discs.

11. A contactor according to claim 1, substantially as described herein.

12. A contactor substantially as shown in Figures 1 to 3 or Figure 4 of the accompanying drawings and described herein with reference thereto.