GB2034195A - Contacting solids and liquids - Google Patents

Abstract

A solids/liquid contactor comprises a container through which the phases flow, a rotor therein, discs rotatable with the rotor dividing the container into a plurality of interconnected compartments and, in at least some of the compartments, receptacles extending between the discs to effect phase transfer. At least one of the compartments is free of receptacles or has receptacles arranged on a smaller diameter than in the other compartments to form a settling chamber. The contactor may be used in the extraction of oil-sands or purification of china clay. <IMAGE>

Description

SPECIFICATION Apparatus for and methods of contacting materials This invention relates to apparatus for, and methods of, contacting materials, and is particularly concerned with a solids/liquid or slurry/liquid contactor and contacting method.

More specifically, the invention is concerned with a solids/liquid contactor which comprises a container through which the phases can flow, a rotor within the container which rotor is mounted for rotation within or with, the container and which includes a plurality of discs which divide the container into a series of compartments, a passage or passages in and/or round each disc enabling the phases to move from compartment to compartment, and, for each of at least some of the compartments, a plurality of receptacles extending between the discs of the compartment and designed to receive material of one phase and to discharge it into the other phase as the rotor turns. Such a contactor will be referred to hereinafter as "a contactor of the type described" and is exemplified by the apparatus described and illustrated in British Patent Specification Nos.

972,035.

The presence of solids in contacting processes can raise problems in settling. In many mixing and other processes such as uranium extraction and china clay purification, a large proportion of the operating costs lies in providing means for dewatering the solids present, especially in the fuel used for such a purpose. Using conventional extraction systems high dilutions are employed to prevent the formation of crud and thus large quantities of water have to be subsequentt removed.

According to this invention, we provide a solids/liquid contactor comprising a container through which the phases can flow, a rotor mounted for rotation within or with the container, a plurality of discs rotatable therewith dividing the container into a plurality of interconnected compartments and, for each of at least some of the compartments, a plurality of receptacles extending between the discs to transfer material from one phase to the other phase, one or more of the interdisc compartments being free of receptacles or having receptacles arranged on a smaller diameter than in the other compartments so as to form one or more settling chambers.

Preferably the discs have passages therethrough which are aligned with receptacles on opposite sides of the disc, the passages in some of the discs being staggered in relation to those of others; the passages permit the movement of solids from receptacles of one compartment to the receptacles of an adjacent compartment and enhance the flow of phases through the contactor. Such a contactor is described inter alia in U.K. specification No.

7917804 Serial No.2026889.

in any compartment in which the buckets are omitted or on a smaller diameter, there may be stirring rods to retain the solids in suspension.

Preferably, the passages in successive discs are staggered so that, in any one compartment, some of the receptacles are connected to the aligned receptacles in one adjacent compartment and the receptacles not so connected are connected to receptacles in the other adjacent compartment.

Provision may be made for restricting the flow of the lower density phase through the gaps between the discs and the container at the top of the contactor. Thus, baffles may be appropriately carried by the container to overlie the discs at the upper portion of the contactor. Alternatively, the rotor may be mounted eccentrically of the container with the result that the container-discs gaps are greater at the top of the container than at the bottom.

The invention also includes a method of treating solids with a treatment liquid in which the solids with a carrier liquid are passed through a contactor as specified above, a treatment liquid, which is immiscible with the carrier liquid,. is passed through the contactor in counter-direction, the treated solids and carrier liquid are first allowed to settle in a settlement chamber, are removed at or adjacent one end of the contactor and the treatment liquid is removed at or adjacent the other end. For example, a slurry of oil-sand and water and a treatment liquid consisting of, or including, a solvent for the bitumen oils of the oil-sand may be passed counter-current through the contactor in order to extract the bitumen oils.

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 an axial section through a contactor of the type described, Figure 2 is a radial section on the line Il-Il of Figure 1, Figure 3 is a radial section on the line Ill-Ill of Figure 1, and Figure 4 is a modified radial section.

The contactor shown in the drawings is employed for contacting solids, or a slurry, with a liquid. The example to be described concerns the solvent extraction of oil-sand but the treatment of other solids can be similarly accomplished.

The contactor comprises a stationary, cylindrical, container or shell 12, and a rotor within the shell consisting of a number of radially arranged, and spaced, circular discs 13, which are carried on a central shaft 14 and the edges of which are spaced from the inner wall of the container 12 to leave an annular gap between the rotor and the container. The rotor shaft is mounted in bearings in the end plates 1 5, 1 6 of the container and is driven at one end. The container is arranged with its axis slightly inclined to the horizontal from left to right.

A slurry of oil-sand and water is continuously introduced into the container 12 through a connection 17 at one end and is discharged through connection 18 at the other, connections 1 7, 1 8 being near the bottom of the container.

Simultaneously, a treatment stream which is immiscible with water and which consists of a solvent for the bitumen oils of the oil-sand, is fed into the other end through connection 20 and passes in countercurrent to the flow of the oilsand slurry, before leaving the container through connection 21 at the first end. The two streams the slurry and the treatment liquid - move countercurrent through the container 12 in two separate phases, the lighter solvent phases being uppermost and the interface being approximately at the axis of the container.

Each of the compartments, into which the container 12 is divided by the discs 13, carries receptacles or buckets 22, of which six are shown by way of example in Figure 2; the buckets extend between the discs. There is the same number of buckets in each compartment and corresponding buckets in the compartments are aligned with one another in a direction parallel to the rotor axis. As the rotor turns, the buckets raise the lower phase and discharge it into the upper phase so that the tarsand material comes into intimate contact with the solvent. The buckets also draw the lighter phase downwards into the heavier phase.

The oil-sand solids are largely carried through the contactor with the flow of the water of the slurry. In order to increase the movement of the oil-sand solids through the container 12 (from left to right in Figure 1), each of the discs 13 has passages 23 aligned with buckets 22 on either side of the disc. Thus, Figure 2 shows three such passages in disc 13A, which passages are aligned with each second bucket. The buckets which are not aligned with passages 23 in the disc 13A are aligned with passages through the other disc 13B (Figure 1) of the compartment. In other words, in each compartment, every second bucket is aligned with passages of one disc and the other three buckets are aligned with passages in the other disc.

As the rotor turns, some of the oil-sand solids scooped up by the buckets of each compartment migrates into the buckets of the next compartment so that flow of the solids through the contactor is not limited to the annular gap between the discs and the shell. Staggering the passages in successive discs ensures that the solids are frequently showered from the buckets through the solvent phase during their passage through the contactor.

Figure 1 shows that at both ends of the contactor the final compartment is formed as a settlement chamber to allow phase settlement prior to solids discharge so that treatment liquid is not carried out with the solids.

The buckets in these end compartments 27, 28 of the rotor have been dispensed with. However the rods 25 on which the buckets are carried and which are shown as extending from end to end of the rotor are advantageously retained to act as stirrers which maintain the solids in suspension and thus enable the solids to be discharged from the contactor. Further, for a discharge at 28 intermediate the ends of the contactor, as described for example in our U.K. patent application No. 35906/78, a similar settlement chamber 29 is formed by the omission of the buckets in the intermediate chamber while retaining the rods for stirring.

Instead of removing the buckets entirely from the settling compartment or compartments, buckets may be provided but on a smaller diameter than the buckets in the remaining compartments as shown in Figure 4 where smaller buckets 30 are provided.ln those settling compartment or compartments, the buckets scoop up little or none of the solids, which therefore do not entrain and remove from the contactor the treatment liquid. At the same time the buckets cause intermingling of the treatment liquid with the carrier liquid for the solids. That arrangement is particularly useful where the solids originally carry a constituent to be removed but are spent by the time they arrive at the settlement compartments. Even when the settlement compartments have buckets on a reduced diameter, the rods 25 are continued into those compartments to act as stirrers for the solids.Thus for example, in a contacting system for the extraction of uranium, the required uranium values are stripped from the solids into the aqueous carrier in the first third or so of the contactor and thereafter contact between the aqueous liquid and extractant only is required. If the buckets remain on the same diameter the spent solids continue to be distributed through the liquid phases and can be entrained thereon unnecessarily.

This expedient of having buckets on a reduced diameter can be utilised in settlement compartments at either end of the rotor, and/or in compartments intermediate the rotor ends where materials are injected into or drawn off from the contactor; the location of the buckets away from the peripheries of the discs has the added advantage that it facilitates the introduction or removal of flows of e.g. reagent, in that it enlarges the space between the shell and the buckets available for the necessary injection and/or drawoff equipment. The bucket shape can change with the change in diameter so that the buckets on the full diameter are more suitable for liquids/solids contacting while those on the reduced diameter are more suitable for liquid/liquid contacting.

in an alternative application of the invention to the purification of china clay, which has a minute particle size, we have found that the use of settlement chambers and a speed of the order of 1 5 to 20 r.p.m. allows some two-thirds of the solids to settle immediately. This compares very favourably with a conventional mixer settler in which only half the solids would be expected to settle.

Some compartments of the rotor may have a first set of buckets arranged as shown in the drawings and a second set on a reduced diameter.

The buckets may be of two types, suitable either for liquid/solids or liquid/liquid contacting and buckets of each type may alternate. That arrangement is of value where, for example, concurrent leaching and stripping is to be effected as described in U.K. patent application No.

491 78/77.

Although not illustrated in the drawings, the buckets may be formed by bucket tubes which pass from end to end through the contactor and which are arranged parallel to the rotor axis. In that case, each bucket tube passes through the discs 13 via slots, which closely confine the tube and which prevent the passage of liquids or solids therethrough, and via passages which permit that passage, the slots alternating with the passages in successive discs. As before the passages are relatively staggered in successive discs in order to prevent the possibility of the solids remaining in the bucket tubes and passing therein the entire length or a substantial part of the length of the contactor.

It is desirable that a substantial proportion of the treatment liquid entered throught connection 20 should pass through the passages 23 in the discs 13 so as to obtain proper contacting with the solids-containing phase. Particularly where the annular gaps between the discs 13 and the shell 12 are large to facilitate the movement of the solids, there is the danger that the treatment liquid will by-pass the compartments by flowing through the annular gaps at the top of the contactor. To avoid that danger, the shell may carry baffles which obstruct the gaps only at the upper half of the contactor. The baffles may be made of flexible material and each may extend over about two thirds of the periphery of the upper half of the shell. Each baffle may be formed with a partannular slot in which the rim of the disc is received without contact so that the baffle extends below the rim on either side.

The gaps between the edges of the disc and the internal wall of the shell at the top of the contactor cun alternatively be restricted to encourage flow of the treatment liquid through the passages in the discs by mounting the rotor slightly eccentrically of the shell i.e. the rotor axis is located slightly above the shell axis so that the gaps between the discs and shell are greater at the bottom of the contactor than at the top.

Claims (10)

1. A solids/liquid contactor comprising a container through which the phases can flow, a rotor mounted for rotation within or with the container, a plurality of discs rotatable therewith dividing the container into a plurality of interconnected compartments and, for each of at least some of the compartments, a plurality of receptacles extending between the discs to transfer material from one phase to the other phase, one or more of the inter-disc compartments being free of receptacles or having receptacles arranged on a smaller diameter than in the other compartments so as to form one or more settling chambers.

2. A contactor according to claim 1, wherein in any compartment in which the buckets are omitted or on a smaller diameter, stirring rods are provided to retain the solids in suspension.

3. A contactor according to claim 1 or 2, wherein a settling chamber is disposed adjacent that end of the container where solids are withdrawn.

4. A contactor according to claim 1, 2 or 3, wherein an intermediate settling chamber is provided adjacent an intermediate discharge station from the container.

5. A contactor according to any one of claims 1 to 4, wherein at least some of the discs comprise passages, aligned with receptacles on opposite sides of the disc, the passages in some of the discs being staggered in relation to those of the others.

6. A contactor according to any one of the preceding claims, comprising means for restricting flow of the lower density phase through the gaps between the discs and the container at the top of the contactor.

7. A contactor according to claim 6, wherein the means comprise baffles carried by the container to overlie the discs at the upper portion of the contactor.

8. A contactor according to claim 6, wherein the means comprises eccentric mounting of the rotor relative to the container.

9. A contactor according to claim 1, substantially as shown in the accompanying drawings and directed herein with reference thereto.

10. A method of treating solids with a treatment liquid, comprising passing solids with a carrier liquid through a contactor according to any one of the preceding claims, passing a treatment liquid, immiscible with the carrier liquid, through the contactor in counter-direction, allowing the treated solids and carrier liquid to settle in a settlement chamber prior to their removal at or adjacent one end of the contactor and removing treatment liquid at or adjacent the other end.