AU2013255986B2

AU2013255986B2 - Mixer settler column

Info

Publication number: AU2013255986B2
Application number: AU2013255986A
Authority: AU
Inventors: David Gordon Hulbert
Original assignee: Mintek
Current assignee: Mintek
Priority date: 2012-05-02
Filing date: 2013-04-30
Publication date: 2017-08-03
Anticipated expiration: 2033-04-30
Also published as: ZA201408728B; AU2013255986A1; AP4050A; WO2013166528A1; AP2014008094A0; CA2875600A1

Abstract

Mixer settler apparatus which includes a vertical column which is divided by a plurality of horizontal plates into a plurality of fluid-containing volumes, wherein each plate has a transfer duct to induce turbulence in a respective lower fluid-containing volume.

Description

INT1378/MAJR (with amendments) 1 2013255986 14 Μ 2017

MIXER SETTLER COLUMN BACKGROUND OF THE INVENTION

[0001] This invention relates to a mixer settler column which is capable of multistage mixing and settling.

[0002] Mixing and settling processes for fluids are usually aimed at transferring a maximum amount of a particular material from one fluid to another. A material which is transferred might be dissolved in, absorbed by, or otherwise associated with, each of the two fluids. Multiple mixer-settler stages and counter-current flows are commonly used to achieve effective operation. 1 [0003] The word “light” is used, for the sake of convenience herein, to designate a fluid which is less dense than another fluid which is referred to as a “dense fluid”.

[0004] Factors which determine the effectiveness of a counter-current multistage mixer-settler process include the following: 15 20 a) in the case of liquid-liquid extraction, small enough droplet sizes should be obtained, with high interfacial areas and short diffusion paths within the droplets, so that mass transfer is suitably fast; b) the degree of mixing should be such that elements of the fluids contact each other sufficiently closely under conditions of high shear; c) the residence time per stage during or after mixing should be long enough to ensure satisfactory mass transfer; d) the efficiency per stage (stage efficiency is the fractional extent towards equilibrium that mass transfer occurs in a stage) should be high - this factor depends on points b) and c) referred to;

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 2 2013255986 14 Μ 2017 e) the benefits of more stages and higher stage efficiencies, which are interdependent, should be optimised to give a satisfactory efficiency at a required throughput; and f) the velocities of rising or settling particles, droplets or bubbles should be high, for low rising or settling rates limit the throughput of a process.

[0005] A process which requires mixing and settling is usually carried out in separate mixing and settling units or in columns.

Separate Mixing and Settling Units for a Liquid-liquid Contacting Process [0006] Conventional mixer and settler units can provide independently for very 1 small droplets and adequate residence times for excellent mass transfer and adequate time and conditions for good settling. However the use of multiple stages can be expensive and requires a large floor area and large fluid inventories.

Separate Mixing and Settling Units for a Solid-liquid Contacting Process [0007] Counter-current decantation is commonly done using multiple thickeners 1u together with mixer units. This approach is, however, expensive and requires a large footprint. Each mixing and settling stage has limited efficiency for mass transfer and, in order to achieve efficient overall mass transfer, multiple stages, which can be expensive, and excessive dilution, are required.

Mixing and Settling in Columns 20 [0008] Multi-stage, counter-current mixing and settling can be done in suitably

designed columns which generally have packing material or include simple plates with perforations, or complex, custom-designed plates. Some column-based processes are fully continuous and have steady counter-current flows, while other 9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 3 2013255986 14 Μ 2017 column-based processes make use of pulsing techniques which promote desirable flow and mass transfer characteristics.

[0009] Although a column can provide for many mass transfer stages and have a small footprint, the operation of a column is subject to the constraints of conflicting needs for high mixing, for good mass transfer, for fast relative movement of fluids and high throughputs.

[0010] In continuous or pulsed columns counter-current fluent streams generally pass each other in each physical stage by the rise or fall of particles, droplets or bubbles of one fluid through the other fluid which is continuous. If the settling rate is 1 not sufficiently high to sustain the required counter-current flow a phenomenon such as flooding can ensue. This problem can be addressed by increasing the cross-sectional area of the column but not by increasing its length. The rising or settling of particles, droplets or bubbles of fluid is generally required in all of the stages of a column and no mechanism is provided for selectively bypassing one or more stages 1 so that groups of stages can be used in parallel. The terminal velocity of particles, droplets or bubbles in one fluid places a limit on the relative counter-current flows that are possible without the flooding process taking place. This flooding limit is sensitive to the smallness of the particles etc. and small sizes should thus be avoided. On the other hand, small sizes are needed for fast diffusion over the high 20 surface areas which are associated with small particles.

[0011] It is known in a column application to facilitate counter-current flow by means of a downcomer, which is a duct, between stages, that allows unidirectional downward flow of a dense stream. This, however, requires a lighter stream to flow upwards by some means other than through the same downcomer, or duct. The 25 downcomer always protrudes downwards to below the overflow level of a

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 4 2013255986 14 Μ 2017 downcomer of a lower plate. This causes the bottom of the downcomer to protrude into a body of dense fluid below. Consequently, the lighter fluid has to rise through holes in the plate, or through bubble caps attached to the plate, and then to pass through a layer of dense fluid above the plate. The passage of the light fluid through the layer of dense fluid constitutes a mixing process and a bulk transfer of the light fluid upwards, and has an inherent potential of flooding.

[0012] Column usage has mainly been confined to processes with liquids, but sometimes to relatively free-flowing solid particles, like resin beads, and has not been extended to solids such as ore or precipitated particles. Columns, continuous 1 or pulsed, are subject to unwanted accumulations of solids that possibly would not be flushed away adequately during normal column operation. For this reason, at least, continuous columns and pulsed columns have not normally been used for thickening, counter-current decantation, counter-current leaching or particle classification. 1 [0013] US3108859 describes the operation of a pulsed column in a mixer-settler mode or in an emulsion mode. In the former mode liquid settles into distinct layers during quiescent phases of an operational cycle. In the latter mode a dispersed liquid remains dispersed in relatively small droplets, throughout the column, with no substantial change in droplet sizes occurring during the operational cycle. The 20 patent describes an improvement that provides alternate physical regions in which the light liquid is dispersed within the dense liquid, and the dense liquid is dispersed within the light liquid, respectively, by means an arrangement in the column of various perforated plates, and upward- and downward-pointing nozzles on upper and lower sides of sets of sieve plates having different wetting characteristics. The 25 disclosure in this patent does not provide for only one flow direction to cause mixing,

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 5 2013255986 14 Μ 2017 nor the use of one of the flow directions to accomplish a bulk transfer of one of the liquids over a selectable number of plates. Counter-current flow is accomplished by droplets settling or rising through the continuous liquid at all stages within the column, a factor which limits throughput and does not provide for a selected compromise between throughput and the number of mass transfer stages.

[0014] US3979281 describes a pulsed column in which a light liquid flows upwards continuously and in which a dense liquid is introduced periodically in pulses, so that it is moved downwards from plate to plate. A downwards pulse is not aimed at producing mixing, as ducts associated with each plate have upward and downward 1 extensions from the plate so as make the down-coming dense liquid enter a lower body of dense liquid below rather than being caused to mix with light liquid. The light liquid is moved upwardly through perforations in each plate and so becomes dispersed and rises through the dense liquid above the plate.

[0015] Another pulsed column process known to the applicant provides for liquid 1 contacting operations in which the liquids flow counter-current in a column and flow pulses are superimposed so as to create and maintain the dispersion of droplets of one of the liquids within the other liquid. Plates in the column are shaped as discs and doughnuts so that liquid transfer between plates occurs through central holes and circumferential annuli in alternate plates. An operational cycle of the column 20 does not allow for a no-flow settling period. As the dispersed liquid must settle or rise through the other liquid, between all adjacent pairs of plates, a throughput limit exists due to possible flooding.

[0016] PCT/IB02/00501 describes a column with perforated plates, wherein each plate has a transfer duct that extends both upwards and downwards from the plate. 25 The plates and transfer ducts emulate quite closely the common use of a

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 6 2013255986 14 Μ 2017 downcomer in a column, for example in distillation, to facilitate the transfer of dense fluids downwards between stages in a column while light fluid is made to pass upwards through perforations in the plates or through bubble caps mounted on the plates. The downcomer is used to transfer dense fluids from one plate, from an overflow weir formed by the downcomer’s upper end, downwards to a body of dense fluid above the plate below. The bottom of the downcomer forms a seal with the heavier fluid on the plate below so as to prevent any flow of light fluid up the downcomer at any time. Instead, the light fluid flows upwards through the perforations of the plate and becomes dispersed in, and rises through, the dense 1 fluid located on top of the plate above. As the dispersed liquid must rise through the other liquid, between all adjacent pairs of plates, a throughput limit exists due to possible flooding. The mixing intensity possible in the column is determined by a pressure drop across the stages that can be applied to force the light fluid upwards and disperse it by the action of the perforations in the plates. This pressure drop is 1 limited in each stage by the head of dense fluid in the downcomer as the upper level of this fluid in the downcomer reaches the level of an upper weir of the downcomer.

[0017] US3719455 describes the simultaneous use of separate mixer and settler compartments for each stage in a complex arrangement. Use is made of a mechanical stirrer. The settler section operates continuously at a settling rate which 20 is determined by the requirement of settling in each stage at the full rate of the counter-current streams. The throughput rate is therefore not controllable over a wide range and can be affected by flooding when settling is incomplete and mixed liquids are transferred instead of separated liquids. Liquid transfers take place simultaneously through two ducts and at least one of the these modes depends on 25 the action of gravity in combination with fluid density differences. There are two

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 7 2013255986 14 Μ 2017 main exit ports and, depending on gravity, it might not be possible to ensure that the exiting liquids report to the correct exit ports.

[0018] US2665196 and US3804594 are, to a substantial extent, similar to the preceding citation. Other prior art documents are US2937078; US3325255; US3389969; US3984331; US3989467; US4541724; US5194152 and W0249736.

[0019] US3549332 discloses three distinct timed sub-operations for mixing and for the transfers of light and heavy fluids in opposite directions. Inter stage ducts connect the bottom of one stage to the top of another stage so as to facilitate different transfers forwards and backwards. The ducts are not used for mixing. 1 There is no suggestion in this patent of the possibility of using multiple physical stages per operational stage. Liquid transfers always involve one liquid entering another liquid. Thus a transfer of a liquid volume greater than the normal operating volume of that liquid, in a stage, requires the liquid to settle or rise quickly through the other liquid. This can possibly cause adverse mixing and entrainment. This is 1 an important factor in large scale systems for adverse mixing can be problematic as flow cross-sectional areas in the stages scale up only in proportion to flow rates raised to 2/3, for similar residence times. In this citation mixing is done by mechanical stirring and there is no suggestion of eliminating a separate mixing step. The technique described in this citation is not applicable to liquid/solid operations 20 because the transfer of any fluid entails a transfer from deep within a settled bed of solids where blockages can easily occur.

[0020] US2228434 describes a solvent extraction process in which a tower is partitioned into a plurality of vertically spaced components by means of a number of plates. Each plate includes a first duct in the form of a phase spray and a second 9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 8 2013255986 14 Μ 2017 duct which extends in an opposite direction to the first duct which is in the form of a spout. It is not seen that this process is suitable for the handling of slurries.

[0021] US4247521 describes a liquid-to-liquid contacting system in which zones are defined by plates in a column and each plate has a downcomer and an up-duct. These ducts are of constant cross-section and do not affect the velocity of a liquid flowing through a duct.

[0022] US1741519 discloses a fractionating column in which partitioning decks carry multiple nozzles, each of which exhibits a venturi type action.

[0023] An object of the present invention is to provide a mixer settler column which 1 allows for mixing, settling and counter-current transfers of fluid to be done cyclically in a plurality of distinct modes of operation. The operations of mixing, settling and transfer are carried out in different time periods in the same physical regions, instead of using different physical regions for the various operations. The feature holds particular benefits including a capability for flexibility and functionality that is not 1 possible in other columns known to the applicant.

[0024] A further object of the invention is to provide a mixer settler column which can be configured and operated to implement any of a number of processes such as liquid-liquid contacting operations, counter-current decantation, counter-current leaching, thickening, ion exchange, distillation, gas liquid contacting operations, and 20 classification.

SUMMARY OF INVENTION

[0025] The invention provides apparatus for the processing of dense and light fluids that includes an elongate column which, in use, is vertically disposed and which has a longitudinally extending axis, a plurality of plates located at spaced intervals from

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 9 2013255986 14 Μ 2017 one another inside the column, each plate extending transversely to the longitudinal axis, wherein each plate forms at least part of a respective fluid-containing volume which tends to trap fluid and which prevents the trapped fluid from flowing towards an adjacent plate and wherein each plate includes at least one respective transfer duct with a first end attached to the plate and a second end, which is spaced from the first end, a first aperture with a cross-section of a first area at the first end and a second aperture with a cross-section of a second area which is larger than the first area at the second end, characterised in that fluid flow from one fluid-containing volume to an adjacent fluid-containing volume takes place only through the said at 1 least one transfer duct.

[0026] It is to be noted, by way of contrast, that in one conventional distillation column for example, a transfer duct extends upwards and downwards from a plate so as to provide for an overflow of dense fluid that moves down through the duct to join a similar dense fluid below, without mixing. Upwards flow through the duct of a 1 light fluid is blocked and the light fluid must, instead, go through holes in the plate for dispersion into the dense fluid above.

[0027] Depending on the mode of operation of the column of the invention it may be orientated so that the respective first ends of the transfer ducts are lower than the respective second ends of the transfer ducts. Preferably, the transfer ducts are 20 positioned e.g. by suitable placement of the plates so that, with respect to a first plate which is adjacent a second plate inside the column, the transfer duct or ducts on the first plate are displaced in a circumferential sense relative to the transfer duct or ducts in the second plate i.e. a transfer duct in the first plate is not aligned nor in register with a transfer duct in the second plate, viewed in a longitudinal direction 25 through the column.

9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 10 2013255986 14 Μ 2017 [0028] Preferably each plate forms at least part of a fluid-containing volume which tends to trap fluid and which prevents the trapped fluid from flowing towards an adjacent plate.

[0029] The fluid-containing volume may be formed, at least, by at least one duct, at least part of the respective plate and a portion of a wall from which the column is made. This volume may be orientated to face downwardly or upwardly (with reference to the respective plate) depending on the mode of operation of the column.

[0030] Preferably each transfer duct is shaped and sized so that fluid flow at a suitable velocity through the duct from the second end towards the first end induces 1 turbulence inside a fluid-containing volume associated with a plate adjacent the first end, and fluid flow, at a suitable fluid velocity through the transfer duct from the first end towards the second end, causes laminar or near-laminar flow of the fluid over a fluid-containing volume of the respective plate.

[0031] The invention also extends to a method of using the aforementioned column 1 which is orientated so that the longitudinal axis is vertical and so that, in respect of each plate, the respective first aperture is lowermost and the respective second aperture is uppermost, the method including the steps of processing dense and light fluids in a cyclical sequence of mixing, settling and counter-current transfers.

[0032] Mixing may be carried out for a predetermined period by introducing a fluid 20 with a suitable flow rate into the column at or near its upper end thereby to cause a downward flow of fluid in the column and mixing of dense and light fluids between each adjacent pair of plates within the column.

[0033] The fluid which is introduced at the upper end may be a light fluid, a dense fluid or a mixture thereof.

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 11 2013255986 14M2017 [0034] Settling may be carried out within the column, for a defined period, by the step of imposing a net zero flow of fluid through the column.

[0035] After the settling mode has been completed bulk transfer of the light fluid within the column may be effected for a defined period by introducing fluid at a suitable flow rate into the column near or at a lower end of the column thereby to cause upward flow of only light fluid in the column while maintaining the dense fluid, substantially unmoved, within the respective fluid-containing volumes of the plates.

[0036] The fluid which is introduced to the lower end of the column could be a light fluid, a dense fluid or a mixture thereof. 1 [0037] The apparatus may be inverted so that the column, still in a vertical orientation, has the first apertures which are associated with the respective plates higher than the second apertures which are associated with the respective plates. In this form of the invention a mixing step may be effected by introducing a fluid into the column at or near a lower end of the column. 1 [0038] Settling in this mode of operation may be effected by imposing a net zero flow of fluid through the column for a defined period.

[0039] In order to carry out the step of bulk transfer (in the second mode of operation) a fluid is introduced into the column at or near an upper end of the column. This fluid, which may be a light fluid, a dense fluid or a combination of light 20 and dense fluids, may be introduced at a flow rate which does not displace, to any substantial extent, fluid contained within any of the fluid-containing volumes associated with the respective plates.

[0040] The aforementioned process can be carried out to achieve counter-current, liquid-to-liquid contacting operations such as those employed in solvent extraction.

9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 12 2013255986 14 Μ 2017

In a different application, the light and dense fluids are a liquid, and a slurry of solid particles and a liquid, respectively, and the process is carried out to achieve counter-current decantation.

[0041] As used herein “fluid” designates a gas, or a liquid, or a slurry of solid particles and a liquid.

[0042] In another application the light and dense fluids are liquid, and a slurry of solid particles and a liquid respectively. With the column in the first mode of orientation the settling step and the bulk transfer step are repeated between each pair of consecutive mixing steps, with the process being aimed at thickening. 1 [0043] With the column in the first mode of orientation the light and dense fluids may be liquid, and a slurry of solid particles and a liquid, respectively, and the process may be aimed at counter-current leaching.

[0044] In another application, again one in which the light and dense fluids are liquid, and a slurry of solid particles and a liquid, respectively, the process is aimed 1 at counter-current leaching and the column is positioned between adjacent mixing tanks.

[0045] In another application, one fluid is a liquid, or a slurry of a liquid and particles, and the other fluid is a slurry of ion-exchange beads or fibres and a liquid, and the process is aimed at a counter-current ion exchange. 20 [0046] With the column in the inverted form, in one application, the light and dense

fluids are vapour or gas, and liquid, respectively, and the process is aimed at counter-current distillation or gas-liquid contacting operations. In another application, the light and dense fluids are a liquid containing slow settling particles, 9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 13 2013255986 14 Μ 2017 and a liquid containing fast settling particles, respectively, and the process is aimed at counter-current classification.

[0047] The invention also extends to a material handling process wherein, within a vertically orientated column, mixing of light and dense fluids is achieved by concurrent flow in a first direction, at suitable velocities, of the fluids through the column, settling is carried out by reducing to zero, for a defined period, the net flow of fluid through the column, and counter-current bulk transfer is carried out by directing the light fluid in a second direction opposite to the first direction through the column thereby to leave the dense fluid substantially undisturbed and within a 1 plurality of fluid-containing volumes which are longitudinally spaced from one another within the column.

[0048] The column provides for mixing, settling and counter-current transfers of fluid to be done cyclically, in three or more distinct modes of operation in the same physical regions, and not in different physical regions. The column has plates with 1 specially shaped transfer ducts that facilitate turbulent mixing of the fluids when the flow rate is high and downwards, and that facilitate near-laminar flow of only the light settled fluid when the flow rate is relatively low and upwards. The plates and ducts, and possibly also the column walls, are arranged in a way that provides a containing volume in each physical stage that tends to dam the dense fluid, so that it normally 20 does not flow downwards. In an inverted version of the column, mixing would occur with upward flow, transfer of the dense fluid would occur with downward flow, and the column would have a containing volume in each physical stage that tends to collect the light fluid so that it normally does not flow upwards. The column is operated with controlled flow rates of fluids into and out of the column, so as to 25 obtain the desired conditions for mixing, settling and counter-current transfers of

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 14 2013255986 14M2017 fluids. The top and the bottom of the column have special structures (internally or externally) designed to facilitate the required operation of the column.

[0049] The transfer duct attached to a plate comprises a weir which extends in one direction only, namely upwards or downwards from the plate. The transfer duct is not a downcomer (as referred to in the prior art) that dips below the level of the overflow of a lower plate. Thus an inter-stage transfer duct is used to transport dense fluid downwards and light fluid upwards under circumstances and during time periods when settling rates impose no limit on the extent of the fluid flow rates. Any reasonable mixing intensity, for example to obtain small bubbles or droplets, is 1 possible without the associated settling velocities having a direct effect on the counter-current flow rates. The flow of dense fluids downwards occurs during mixing and the flow simultaneously entrains light fluid that moves downwards too, without any need for differential flow rates to be effected by a settling mechanism. The flow of light fluid upwards during a transfer period bypasses the heavier fluid and occurs 1 when the fluids are not required to mix or to be mixed. The flow of light fluid upwards exceeds the downwards flow during mixing so that the net flow of light fluid is upwards. It is to be borne in mind that the different cross-sectional areas of opposed ends of each transfer duct are required to ensure that the high and low fluid flow rates, in opposing directions, are achieved in order to facilitate mixing and bulk 20 transfer.

[0050] The column of the invention allows for the use of multiple plates or stages, in the column, in a parallel sense. This is achieved by making the mixing and transfer fluid movements go over more than one plate at a time. Prior art columns, known to the applicant, have counter-current fluids interacting with each other similarly in each 25 stage and it is therefore not possible to provide a facility of bypassing stages

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 15 2013255986 14 Μ 2017 selectively to make the plates operate in parallel and so extend the throughput efficiency optimization range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figure 1 is a side view in section of a mixer settler column according to one form of the invention;

Figure 2 is a side view in section and on enlarged scale of part of the column in Figure 1, illustrating fluid flow during a mixing phase; 1 Figure 3 is similar to Figure 2 illustrating fluid flow during a bulk transfer phase;

Figure 4 shows the column of Figure 1 in an inverted mode for a different application; Figures 5, 6 and 7 depict different types of transfer ducts which can be used in the column of the invention; and

Figures 8, 9, 10 and 11 are side views in cross-section illustrating different forms of 1 the column of the invention in different applications.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0052] Figure 1 shows in cross-section and from one side a general structure of a mixer settler column 10 according to the invention. The column includes an elongate 20 tubular body 12 with a surrounding wall 14 which encloses an elongate volume 16.

The body has a longitudinally extending axis 18. An upper end 20 of the body has a dense fluid feed inlet connection 22, a light fluid return connection 24, and a light fluid outflow connection 26. A lower end 28 of the body has a bottom fluid return 9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 16 2013255986 14 Μ 2017 connection 30, a mixed or dense fluid outflow connection 32, and a light fluid connection 34.

[0053] A plurality of plates 36 are provided at spaced intervals from one another at respective positions which are displaced along the longitudinal axis. Each respective plate has at least one transfer duct 38 which allows for fluid flow between the plates which define plate stages within the column.

[0054] The plates 36 are spaced closely enough to give adequately short settling distances for small particles or droplets of a dense fluid to settle in a reasonable time. Each transfer duct has, at a first end 40 (see Figure 2), a first aperture 42 of a 1 first area and, at a second end 44, a second aperture 46 of a second area which is greater than the first area.

[0055] The transfer ducts can have various types of construction and Figures 5 to 7, referred to hereinafter, illustrate possibilities in this regard. The shaping of each duct is such that a reasonably high downward fluid flow rate in the column leads to high 1 velocity entry and turbulent mixing in the stage below, as is shown in Figure 2.

Additionally, as each duct widens in cross-section towards its upper end (the aperture 46), a reasonably low upwards fluid flow rate in the column leads to a low flow velocity and near laminar flow, of light fluid, above settled beds of dense fluid (associated with the various plates), without causing unwanted mixing of the fluids, 20 as is shown in Figure 3.

[0056] Each transfer duct may be of any convenient three-dimensional shape which allows for the aperture 42 to be smaller in cross-sectional area than the second aperture 46.

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 17 2013255986 14 Μ 2017 [0057] Each plate is associated with and helps to define a respective fluid-containing volume 50 which, with the column vertically orientated as in Figure 1, is for the collection of dense fluid on the plate. The size of the volume is determined, at least, by the distance between the first end 40 and the second end 44 of the transfer duct. If the dense fluid level is too high, then dense fluid above the level of the second end 44 can overflow the second end and can pass through the transfer duct to the plate below. In a simple form of construction each plate has one transfer duct. The plates are positioned so that successive ducts are on alternating sides of the column, as is shown in Figure 1. Also, the transfer ducts, in adjacent plates, are not 1 aligned in a longitudinal sense with one another but rather are displaced circumferentially from one another. Depending on factors such as cost and specific operating conditions, a plate may have one large transfer duct or multiple transfer ducts.

[0058] Figure 5 for example illustrates two plates 36A and 36B which have opposed 1 ducts 38A and 38B respectively, each of which extends over a circumferential arc of the respective plate. Figure 6 shows a plate 36C which has a plurality of funnel-shaped ducts 38C at spaced intervals over its surface. Additionally, the ducts are grouped in quadrants by means of transversely extending partitions 54 and 56 respectively. In the arrangement shown in Figure 7 a plate 36D has three channel-20 shaped transfer ducts 38D, 38E and 38F.

[0059] In each case adjacent plates are orientated so that, within the column, no duct on one plate is immediately above or below a duct on an adjacent plate.

[0060] In operation of the column of Figure 1 the contents of the main body within the column are mixed in all local regions and are moved downwards by the fast entry 25 of a required volume of fluids into the top of the column. At this end a dense fluid

9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 18 2013255986 14 Μ 2017 feed and a light fluid return are fed through the respective connections 22 and 24. Flows can occur consecutively but preferably are simultaneously introduced into the column. Mixing within the column is induced by turbulent eddies caused by a high fluid flow rate, as illustrated in Figure 2. In each duct the downwards flow of the fluids through the first aperture 42, which is of relatively small cross-sectional area, causes a stream or jet of fluid to be directed, at an increased speed, into the respective underlying fluid-containing volume 50 in which turbulence is induced.

[0061] The magnitude of the total volume of fluids introduced during the mixing phase should be adjusted to fix the required volume in the column per mass transfer 1 stage. This could range from a fraction of a physical stage volume (i.e. the size of the volume bounded by two adjacent plates 36, extended though their respective first apertures 42, and the column wall 14) or any multiple, not necessarily an integer, of physical stage volumes.

[0062] During mixing the dense and light fluids both move between the physical 1 stages. The total volumes of the dense fluid feed and the light fluid return are introduced in the same ratio as is required for the contents of the main body of fluid in the column as a whole. This factor determines the volume fraction occupied by the dense fluid within a fluid-containing volume 50, rather than the size of the fluid-containing volume. Flowever, the ratio of dense to light fluid should not be so large 20 as to cause a higher dense-fluid volume per stage than can be dammed by the fluid- containing volume 50 of the stage. Generally, the containing volume 50 would be made a reasonably high percentage of the volume of a physical stage, by increasing the distance between the first end 40 and the second end 44 of a duct, so that operation over a wide range of fluid ratios is possible.

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 19 2013255986 14 Μ 2017 [0063] After the mixing phase a settling mode is implemented by stopping all flows into and out of the column. Sufficient time is allowed for settling to be completed or for segregation to be effected to the required extent e.g. for classification by particle size. As the plates 38 are closely spaced fast settling can take place even when particles, droplets or bubbles (as the case may be) are very small. The settled particles etc. accumulate in the respective fluid-containing volumes 50.

[0064] The settling phase is followed by a bulk transfer phase. During mixing, a volume of the light fluid would have been moved into and down the column together with the dense fluid. Thus, during the bulk transfer phase a similar volume of fluid, 1 drawn or extracted from the mixed fluid outflow at the connection 32, should be returned to the bottom of the column via the return 30 so that the light fluid is pushed back up the column to its position before mixing. Fresh light fluid is fed through the connection 34 to produce an additional upward movement so that the light fluid has a net upward flow over the full operational cycle. 1 [0065] In the main body of the column the light fluid, above each respective settled bed of dense fluid in the respective volumes 50, is moved upwards in near laminar flow by the moderate flow rate of a required volume of fluids into the bottom of the column. The light fluid feed at the connection 34 and the bottom fluid return at the connection 30 are made to enter the column at low to moderate flow rates. These 20 flows can occur simultaneously or consecutively, preferably with the light fluid feed entering through the connection 34 after the bottom fluid return.

[0066] Figure 3 illustrates near laminar flow 60, for the bulk transfer of the light fluids in the column, which is induced by low fluid velocities. Ideally the near laminar flow 60 should cause plug flow of all the light fluid up the column without any dead 25 volumes. In practice, with moderate flow rates that are not too low, some beneficial

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 20 2013255986 14 Μ 2017 local mixing takes place which tends to prevent dead volumes of the light fluid that is not transferred. In liquid-liquid contacting operations, surface tension effects help to prevent any mixing of the light and dense fluids during bulk transfer. In particulate processes, especially in classification, the flow rate of the light fluid during bulk transfer should be set carefully to regulate or minimize the degree of mixing between the light and dense fluids.

[0067] The mixed fluid outflow at the connection 32 should preferably be settled so as to produce a light fluid to be returned to the bottom of the column (via the connection 30) and a dense fluid product. The bottom of the column can have 1 features to facilitate this, or the separation can be done using a suitable external processing unit such as a thickener.

[0068] Some adaptations to the column may be required to adapt the column to be suitable for particular applications.

[0069] For example, the separation of fluids from, or within, the ends of the column, 1 and accurate timing and implementation of various forward and reverse flows in the column, require the upper and lower ends of the column and appropriate peripheral equipment to be customised according to the type of process to be implemented.

[0070] In most cases, the separation of the light and dense fluids at an end of the column, where a return flow is required, is best done within the end of the column, so 20 that no mixed light and dense fluids leave the column and so that there is no need to separate the mixed fluids externally. For this, the transfer ducts of one or more plates at the end of the column might be made wide and without any narrow aperture, or made to be just relatively large holes in the plates, so that further mixing tends not to occur there and so that those plates only serve to facilitate settling. In other cases,

9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 21 2013255986 14 Jul2017 for example in counter-current decantation, an external separator such as a thickener might be better.

[0071] Accurate timing and implementation of the various forward and reverse flows for the operation of the column require a means for flows to be started, regulated, stopped and, sometimes, reversed. This can be done by suitable combinations of process components such as pipes, valves, pumps, holding vessels, and pulsegenerating actuators; measuring devices such as interface detectors, level detectors and flow meters; and electronic or computer control systems. Where flows of fluid occur for relatively long times or need relatively large displacement volumes, 1 switched pumps or on-off valves might best be used. Alternatively, where flows of fluid occur for relatively brief times or need relatively small displacement volumes, for example as might be required for the mixing mode of the column, a pneumatic or mechanical pulse-generating actuator might best be used.

Liquid-liquid contacting operations 1 [0072] The normal, or the inverted, version of the column (i.e. Figure 1 or Figure 4) can be used for liquid-liquid contacting operations. When the ratio of light to dense liquid volumes in the column is required to be close to unity, the two orientations of the column tend to favour dense, and light continuous-phase liquids, respectively, otherwise the liquid of higher volume would tend to become the continuous-phase 20 liquid during settling. When the ratio of light to dense liquid volumes in the column is required to be very high or very low, the orientation of the column should be normal or inverted, respectively, to facilitate good liquid dynamics during the bulk transfer mode of operation.

9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 22 2013255986 14 Μ 2017 [0073] Figure 8 illustrates an example of customisation of the column for liquid-liquid contacting operations. In this case, the bottom of the column can conveniently be used to provide for separation of the dense and light liquids so that the bottom liquid return is separated dense liquid that pushes light liquid up the column. At the top of the column, a buffer volume 61 can be allocated to allow for the reverse-flow volume of the light liquid during mixing, and for excess light liquid there to overflow and to leave the column.

Counter-current decantation [0074] Figure 9 illustrates an example of customisation of the column for counter- 1 current decantation. In this case, the average slurry density in the column is made to be the same as that of the slurry feed, so there is no light fluid return at the top of the column. Generally, solids from the process are required to be thickened to a density much higher than that of the slurry feed, and a thickener is used downstream of the column to thicken the solids and provide a recycled thickener overflow that serves as 1 the bottom fluid return. If necessary, an upstream thickener can be used to thicken the feed slurry before it enters the column, in which case a downstream thickener might not be needed.

Counter-current leaching [0075] The use of the column for counter-current leaching is similar to the 20 application for counter-current decantation, but mass transfer rates, residence times

and solution addition points need attention. The column functions satisfactorily for leaching where the rate limiting step in mass transfer is diffusion within solid particles. Where the rate limiting step in mass transfer is diffusion in liquid films, the downward mixing flows should be short and frequent for optimum operation. By 9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 23 2013255986 14 Μ 2017 moderating the downward mixing flow rates optimally, the transfer of solids down the column could be made size-dependent so that larger particles have the longer residence times which are needed for adequate leaching. Different liquid streams can be added at the bottom of the column, and at positions higher up, to provide washing fluid that leaves with the exiting solids, and to provide one or more leaching solutions that should flow upwards, respectively.

Connecting unit between adjacent stirred tanks for counter-current leaching [0076] The column can be used to connect a pair of stirred leach reactors so as to transfer solids from a first tank to a second tank and liquid from the second tank to 1 the first tank. The column needs to have only one pipe connected at each of the two ends as shown in Figure 10. Liquid is pumped slowly from the top of the column to the first tank 62, with one or more breaks in pumping for settling if necessary, to ensure that only clear liquid leaves the top and solids are retained on the plates. Slurry from the first tank 62 is pumped at a fast rate into the top of the column, 1 causing the settled solids in the column to be mixed with the slurry and to move downwards towards the connection to the second tank 64. The mixing flow should push the contents of the column downwards by less than the full volume of the column, for example half of the volume, to give approximately two mass-transfer stages of counter-current decantation. 20 Thickening [0077] The operation of the column for thickening is illustrated in Figure 11. This requires a more complex cyclic operation. Between the mixing modes of successive operational cycles, several sub-cycles of settling and bulk transfer modes are implemented to build up the thicknesses of settled solids on the plates of the column.

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 24 2013255986 14 Μ 2017

Mixing is achieved by introducing slurry or recycled clear liquid at a high flow rate (66) at the top of the column. The bulk transfer is done by introducing slurry at a low or moderate flow rate (68) at the bottom of the column and by stopping the transfer when the slurry has displaced most of the clear liquid above the settled solids. The settling and bulk transfer sub-cycles are stopped when enough solids have been loaded onto the plates of the column.

[0078] The column can be regarded as an advanced form of pulsed column, but its structure and operation have special features that make it more effective and applicable to more processes than a conventional pulsed column. 1 [0079] A particular feature of the operation of the column is that sets of adjacent plates can effectively be made to operate in parallel, thus allowing a trade-off between throughput capacity and the number of mass-transfer stages. This is done dynamically simply by changing the volumes of fluids transferred upwards and downwards during the operating cycles. This versatility allows a tall and thin column, 1 with many plates, to be operated quite similarly to a shorter and wider column with fewer plates and the same total plate surface area. Because bulk counter-current movement of streams is not required during mixing or settling, the column can operate with small particles, droplets or bubbles, with good mixing and with efficient settling, without necessarily limiting throughput. 20 [0080] Splitting of the operation of the column into distinct time-delimited modes and the use of multiple plates per mass-transfer stage provide exceptional flexibility and functionality. The average feed rates of fluids, the degree of mixing in the column, and the ratio of fluids within the column, can all be set independently.

9278895 1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 25 2013255986 14 Μ 2017 [0081] Although the use of conventional pulsed columns is generally confined to liquid-liquid contacting operations, the column of the invention can be used for liquid-liquid contacting operations as well as several other processes, by customization of the time-delimited modes. The column can be used for counter-current decantation, with many stages of washing, less dilution and lower costs than with multiple conventional thickeners. Thickening in the column can be achieved by multiple subcycles of slurry feeds and settling periods, with the build-up of solids on the plates and the displacement of clear liquid upwards, and then a downwards mixing flow to drive the thickened pulp downwards. Ion exchange and leaching operations in the 1 column can in some cases be very effective, particularly when the rate-limiting step of mass transfer tends to be diffusion, or reactions, within resin or solid particles. Under well-controlled conditions, the column can be used to do counter-current, multi-stage classification of solid particles based on their settling velocities.

[0082] The column does not have the problem of counter-current fluid streams 1 needing to pass each other in each physical stage by the rise or fall of particles, droplets or bubbles of one fluid through the other continuous fluid. Larger counter-current flows are effected simply by larger fluid transfers per operational cycle, independently of the settling part of the process.

[0083] The versatility of the column provided by the degrees of freedom available 20 for its operation allows a single column with standard plates to be used for any of a number of processes, and at any of a wide range of operating conditions. Three distinct process operations, namely mixing, settling and transfer, in a time cycle, are carried out in the same place in the column in simple stages and with no internal moving parts. Of importance in the present invention is the step of making one or 25 both of the transfers induce mixing to eliminate the need for a separate mixing step.

9278895_1 (GHMatters) P98797.AU INT1378/MAJR (with amendments) 26 2013255986 14M2017

The column also has the advantage of providing for essentially instantaneous shutdowns and instantaneous restarts after any reasonable length of delay, with no process disruption, by freezing the column’s operation in the settling phase.

[0084] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 1 [0085] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

9278895_1 (GHMatters) P98797.AU

Claims

1. Apparatus for the processing of dense and light fluids that includes an elongate column which, in use, is vertically disposed and which has a longitudinally extending axis, a plurality of plates located at spaced intervals from one another inside the column, each plate extending transversely to the longitudinal axis, wherein each plate forms at least part of a respective fluid-containing volume which tends to trap fluid and which prevents the trapped fluid from flowing towards an adjacent plate and wherein each plate includes at least one respective transfer duct with a first end attached to the plate and a second end, which is spaced from the first end, a first aperture with a cross-section of a first area at the first end and a second aperture with a cross-section of a second area which is larger than the first area at the second end, in which the at least one transfer duct is positioned so that, with respect to a first plate which is adjacent a second plate inside the column, the transfer duct or ducts on the first plate are displaced in a circumferential sense relative to the transfer duct or ducts in the second plate, when viewed in a longitudinal direction through the column, and the at least one transfer duct is funnel-shaped and having a cross-sectional area which decreases from the second end towards the first end, the only fluid communication path between one fluid-containing volume and an adjacent fluid-containing volume is formed by the said at least one transfer duct, and the transfer duct defines at least part of the volume for the collection of dense fluid on the respective plate whereby, in operation, dense fluid in excess of the volume passes into the at least one transfer duct via the second aperture.

2. Apparatus according to claim 1 in which each transfer duct is shaped and sized so that the velocity of fluid flow through the duct increases from the second end towards the first end and decreases from the first end towards the second end.

3. A method of using the apparatus of claim 1 or 2, wherein the column is orientated so that the longitudinal axis is vertical and so that, in respect of each plate, the respective first aperture is lowermost and the respective second aperture is uppermost, the method including the steps of processing dense and light fluids in a cyclical sequence of mixing, settling and counter-current transfers.

4. A method according to claim 3 wherein mixing is carried out for a predetermined period by introducing a fluid with a suitable flow rate into the column at or near an upper end thereby to cause a downward flow of fluid in the column and mixing of dense and light fluids between each adjacent pair of plates within the column.

5. A method according to claim 3 or 4 wherein settling is carried out within the column, for a defined period, by the step of imposing a net zero flow of fluid through the column.

6. A method according to claim 3, 4 or 5 wherein, after settling is completed, bulk transfer of the light fluid within the column is effected for a defined period by introducing fluid at a suitable flow rate into the column near or at a lower end of the column thereby to cause upward flow of only light fluid in the column while maintaining the dense fluid, substantially unmoved, within respective fluid-containing volumes associated with the plates.

7. A method of using the apparatus of claim 1 or 2, wherein the column is orientated so that the longitudinal axis is vertical and so that, in respect of each plate, the respective first aperture is higher than the respective second aperture, the method including the steps of processing dense and light fluids in a cyclical sequence of mixing, settling and counter-current transfers.

8. A method according to claim 7 wherein mixing is effected by introducing a fluid into the column at or near a lower end of the column, settling is effected by imposing a net zero flow of fluid through the column for a defined period, and bulk transfer is carried out by introducing a fluid into the column at or near an upper end of the column.