US3688901A - Method of and apparatus for sorting crystals according to size - Google Patents

Abstract

A device for sorting crystals according to their size comprises a separation chamber divided into two parts; a fluid carrying the crystals to be sorted passes into a first of these parts while a separate driving fluid is passed into the second, the flow-rate of fluid passing out of the second part being less than the flowrate of driving fluid which passes into the second part, while the flow-rate of fluid passing out of the first part is higher than the flow-rate of carrier fluid passing into the first part, whereby at least a portion of the driving fluid passes across an interface separating the two parts, in counter-flow to the largest crystals to be sorted; the crystals to be sorted tend to flow from the first part to the second but the upward speed of the driving fluid in the separation chamber prevents such flow except for the crystals having the desired diameter, regulated by the speed of the fluid.

Description

United States Patent Laurenty [451 Sept. 5, 1972 [72] Inventor: Francois Laurenty, Le Touquet,

France [73] Assignee: C.O.C.E.I. SA, Paris, France; a part interest [22] Filed: Nov. 10, 1969 [21] App1.No.: 875,096

[30] Foreign Application Priority Data Nov. 15, 1968 France 173.845

[52] US. Cl. ..209/l57, 209/155, 209/158, 209/21 1 [51] Int. Cl. ..B03b 3/30 [58] Field otSearch ..209/l55161; 23/273 [56] References Cited UNITED STATES PATENTS 118,379 8/1871 Merrill ..209/l60 1,177,849 4/1916 De Kalb ..209/l60 X 3,219,186 11/1965 Polhemus et a]. ......209/172.5 3,295,677 1/1967 Condolios ..209/158 X FOREIGN PATENTS OR APPLICATIONS 987,908 3/ 1965 Great Britain ..209/ 158 Primary Examiner-Frank W. Lutter Assistant Examiner-Ralph J. Hill Attorney-Young & Thompson [57] ABSTRACT A device for sorting crystals according to their size comprises a separation chamber divided into two parts; a fluid carrying the crystals to be sorted passes into a first of these parts while a separate driving fluid is passed into the second, the flow-rate of fluid passing out of the second part being less than the flow-rate of driving fluid which passes into the second part, while the flow-rate of fluid passing out of the first part is higher than the flow-rate of carrier fluidpassing into the first part, whereby at least a portion of the driving fluid passes across an interface separating the two parts, in counter-flow to the largest crystals to be sorted; the crystals to be sorted tend to flow from the first part to the second but the upward speed of the driving fluid in the separation chamber prevents such flow except for the crystals having the desired diameter, regulated by the speed of the fluid.

8 Claims, 16 Drawing Figures Patented Sept. 5, 1972 2 Sheets-Sheet 2 FIG 12 METHOD OF AND APPARATUS FOR SORTING CRYSTALS ACCORDING TO SIZE The present invention has for its object a method of and a device for effecting the sorting of crystals, carried by a fluid of different density, according to their size, and is especially directed to the application of such a device to a crystallization installation.

A crystallization installation comprises, in a manner known per se, a crystallization circuit such as an evaporation circuit or a cooling circuit, and a circuit for removing excess liquid, and generally delivers crystals having a granular size distributed over an extensive range of diameters, from the finest to the largest, according to the usual laws of statistics in this matter.

Now, as is well known, it is of the greatest advantage to obtain crystals in which the granulometric distribution is as narrow as possible on each side of a welldefined mean diameter.

The method and the device forming the objects of the present invention achieve this purpose; they further enable the diameter of the crystals obtained to be regulated at will.

The invention provides for the utilization of a separation chamber having two parts, between which exists a force field, the said parts comprising a common interface and being each provided with a fluid inlet and outlet, in combination with regulating means permitting the variation of any one of the following parameters: useful area of the interface, flow-rate passing through this interface, intensity of the force field.

According to a static form of embodiment, that is to say according to a form of construction which only comprises static members, the separation chamber of the device according to the invention is confined in a tank subjected only to the force field, and divided into two parts by adjustable throttling means which enable the flow-rate of fluid from one of the said parts to the other to be modulated at will.

In an alternative embodiment, according to a dynamis form of construction, the separation chamber is ar ranged downstream of a small wheel rotatably mounted in a fixed cylindrical chamber, this wheel ensuring the setting in rotation of the fluids which pass into the two parts of the said volume, so that in this latter, the said fluids are subjected to a centrifugal force field different from the normal force field and generally higher than this normal field.

However this may be, the separation chamber receives, according to the invention, two fluids which are hereinafter known, for convenience of the description, as the driving fluid or fluid A, and the carrier fluid or fluid B. The crystals to be sorted, carried by the fluid B pass into a first of the parts of the separation chamber and are subjected in this chamber to a force field; they thus tend to flow from this first part of the said chamber to the second. Conjointly, in this second part of the separation chamber passes the fluid A, of which at least a portion tends to pass from this second part to the first across the interface. The resulting flow-rate of fluid across this interface opposes the flow referred to above of the crystals to be sorted or classified, so that only the crystals having a sufficient diameter effectively flow across.

The method and the device according to the invention result advantageously in simple and effective constructions which can very readily be added to any previously existing crystallization installation. For that purpose, it is only necessary to place the device according to the invention in shunt on the one hand with the concentration circuit and on the other hand with the excess liquid-removal circuit of such a crystallization installation.

When this has been done, by virtue of the device according to the invention, the too-fine crystals are re-cycled while the too-large crystals can either be sieved in the excess liquid removal circuit or elsewhere, or reduced to smaller dimensions, by crushing for example.

By this means, the installation only delivers crystals of well-defined dimensions.

The characteristic features and advantages of the invention will be further brought out in the description which follows below, given by way of example only, reference being made to the accompanying diagrammatic drawings, in which:

FIG. I is a perspective view with parts broken away, of a device according to the invention;

FIG. 2 is a diagram illustrating the inclusion of this device in a crystallization installation;

FIG. 3 is a diagrammatic view in elevation, illustrating the operation of this device;

FIGS. 4A, 4B and 4C are partial views which relate to one of the elements utilized in the device according to the invention, and which each illustrate one form of construction of this element;

FIG. 4D is a view in cross-section of the form of construction shown in FIG. 4C, taken along the line D-D of this figure;

FIG. 5 is a perspective view similar to FIG. I, and relates to an alternative construction of the device ac cording to the invention;

FIG. 6 is a perspective view illustrating the combination in parallel of a plurality of devices according to the invention;

FIG. 7 is a view in axial section of an alternative form of construction of the device according to the invention, employing a small rotating wheel;

FIGS. 8 and 9 are views in transverse section of the construction shown in FIG. '7, taken respectively along the lines VIII-VIII and IX-IX of FIG. 7;

FIG. 10 is a view similar to FIG. 8 and relates to an alternative form of construction;

FIGS. 11 to 13 are views similar to FIG. 7, and each relates to another alternative form of construction.

In accordance with the form of embodiment chosen and shown in FIG. 1, the device according to the invention comprises a tank 10 of generally parallelepiped shape, the internal space of which constitutes the separation chamber V according to the invention. This chamber is divided horizontally into two parts, a lower part HA and an upper part 11B, by adjustable throttling shutters 13, the actuation of which will be described in detail later, and which more or less intercept the passage of fluid from the lower part 11A to the upper part 1 1B of this volume.

The lower part 11A of the tank 10 is provided with a fluid-inlet 14A and a fluid-outlet 15A located in the extension of that preceding. Similarly, the upper part I I8 of the tank comprises an inlet 14B and an outlet 158 which, in the example shown, are respectively parallel to the inlet 14A and to the outlet 15A of the lower part 1 1A.

Reference will now be made to FIG. 2, in which a cryatallization installation has been shown diagrammatically.

An installation of this kind generally comprises a crystallization body 20, such as an evaporator or cooler.

As shown in heavy lines in FIG. 2, the 'outlet 21 of this body is coupled to the inlet 14B of the tank 10 of the device according to the invention, while the outlet 158 of this tank is connected to the supply 22 of the body 20, through the intermediary of a pump 23.

Furthermore, the tank 10 is also included by its inlet 14A and its outlet 15A in an excess liquid removal circuit 30 comprising for example a centrifuge 31 and a circulation pump 32.

In an installation of this kind, the introduction of the fresh liquor, non-saturated but rich in dissolved product and therefore dense, can be effected for example in the centrifuge dryer, as indicated by the arrow 35 in broken lines, or alternatively it can be made at any point of the drying circuit 30 as indicated by the arrow 36 in full lines.

With regard to the extraction of exhausted liquor, this can be done at any appropriate point of the circulation circuit 25, as shown diagrammatically by the arrow 37, or alternatively at any suitable point of the crystallization body 20.

Reference will now be made to FIG. 3, which is a simple diagram representing the device according to the invention.

A liquor B arrives at 14B containing the crystals which have been formed or which have been increased in size in the crystallization body 20. The density of this liquor is obviously less than that of the crystals.

Due to the effect of gravity alone, the crystals carried by this liquor B have therefore a tendency to settle in the tank 10.

A liquor A arrives at 14A coming from the drying circuit; this liquor is composed on the one hand of the liquid volume which travels in a closed circuit in this drying circuit, and on the other hand, of the unsaturated liquid volume introduced either at 35 or at 36. The density of this liquor A is higher than that of the liquor B but is still less than that of the crystals. Thus the liquors A and B define a range of densities which excludes that of the crystals, that is, the density of the crystals lies outside the range of densities of the liquids.

The flow-rate of liquor A passing out at 15A is made smaller than the flow-rate passing in at 14A; conjointly the flow passing out at 158 is made higher than the flow-rate of liquor B passing in at 14B. There is therefore an upward flow of liquor A in the tank 10 in the direction of the arrow 40 of FIG. 3, this upward flow taking place in the direction opposite to that along which the crystals passing into 148 have a tendency to flow into the tank 10.

In consequence, by regulating the upward speed of this flow, it is possible to effect a choice between the crystals, some of these crystals being effectively able to flow through while others are prevented from flowing through.

This selection is made as a function of the speed of flow of the crystals with respect to this upward speed of the liquor A in the tank 10, and in consequence as a function of the diameter of these crystals, the other conditions, such as viscosity in particular, being assumed to be the same.

Thus, a liquor passes out at 158 which has lost its lar gest crystals, these crystals being found on the other hand in the liquor which passes out at 15A.

Everything takes place as if in the tank Ill there existed an interface 8 between the liquor B passing in at 148 and the liquor A passing in at 14A, and as if there were a transfer of crystals from one liquor to the other across this interface, as a function of the diameter of the said crystals.

In FIG. 3, this interface S has been arbitrarily represented by a broken line at the level of the shutters 13.

However this may be, the liquor which passes out at 15A and which is sent to the dryer comprises only crystals having a diameter greater than a given diameter which is a function of the upward speed of the liquor in the tank 10.

In order to vary this diameter, it is thus only necessary to modify this upward speed.

This modification of speed can be effected in two ways:

either, the area of the interface S between the parts 11A and 11B of the tank 10 remaining equal, by modifying the flow-rate of the liquor introduced into the tank 10, or in a more general manner, the difference of flow-rate between the flow passing-in at 14A and the flow passing-out at 15A;

or, this flow-rate or this difference in flow-rate remaining equal, by modifying this section by acting on the throttling shutters 13.

To this end, and as shown by way of example in FIGS. 1 and 3, each shutter 13 is rotatably mounted about its longitudinal axis 41 which extends transversely with respect to the tank 10.

There will now be described by way of example various constructions permitting the actuation of the shutters 13.

In accordance with FIG. 4A, each shutter 13 is articulated on two parallel operating rods 45A, 458, common to all the shutters l3 and forming articulated parallelograms with these latter. These rods 45A, 45B are in turn articulated on a common operating lever 46.

As will be readily understood, actuation of the lever 46 causes all the shutters 13 to pivot simultaneously about their axes 41.

A similar simultaneous operation could be obtained if the lever 46 and any element parallel to this lever, for example a shutter 13, were each respectively articulated at any two fixed points located on the same parallel to the sides, forming a parallelogram with the said lever and the said element.

According to H6. 45, at least one of the operating rods 45A, 458, the rod 45A for example is replaced by a cord A which passes through each shutter 13 and is provided on each side of the shutter with two fixed stops 48, in the same way as so-called Venetian blinds.

in accordance with the alternative form of construction shown in FIG. 4C, at least one of the operating rods 45A, 45B, the rod 45B for example, is replaced by a rack 245B comprising for each shutter 13 an angular slot 50 in which the shutter 13 is pivotally mounted in the same way as a blade, the corresponding edge of the said shutter being sharpened for that purpose.

This latter arrangement has the advantage of minimizing or even eliminating the consequences of a possible jamming of crystals in the control-rod system of the shutters 13.

As illustrated in FIG. 4D, the edges of the slot 50 in the rack 2458 are advantageously bevelled.

According to various alternatives (not shown), the shutters 13 are replaced by a single shutter, or in a more general way by valve or throttling means of any kind.

According to the form of construction shown in FIG. 5, the tank is cylindrical and the throttling means which are associated with it are not shutters as previously, but a variable-volume chamber 55, an inflatable chamber for example. This chamber is arranged in the central zone of the tank 10, and, depending on its degree of inflation, it intercepts a more or less large portion of the transverse section of this tank.

As illustrated by FIG. 6, it is possible to associate a number of tanks I0 in parallel, each tank 10 comprising as previously its inlets and its outlets for liquor, MA, MB and A, 158 respectively.

In an association of this kind, some of the tanks 10 may not comprise any variable throttling means.

It has been assumed up to this point, when considering the application of the invention to a crystallization installation, that the liquor A was a non-saturated liquor which is rich in dissolved product, heavier than the liquor B which, derived from the crystallization circuit, is relatively exhausted in dissolved product although it carries crystals.

It has also been assumed that these crystals were heavier than the liquors A and B.

The invention will also be applicable, in a more general way, to the case in which the crystals to be sorted are lighter than the carrier fluid and the driving fluid employed, and would therefore have a tendency to float. The fluid A being assumed for example to be lighter than the fluid B, it is then only necessary to cause the crystals to be conveyed by the fluid A, to cause the latter to pass into the base of the separation chamber and to ensure at 148 an entering flow-rate of fluid B greater than the outlet flow-rate at 158, so as to have a flow of fluid B from the top to the bottom, in opposition to the floating movement of the particles.

In all cases, the densities of the fluids A and B define a range of densities which excludes the density of the crystals to be sorted. The devices described above with reference to FIGS. 1 to 6 are static devices, that is to say devices which only comprise parts which are stationary, apart from the periods of adjustment.

There will now be described with reference to FIGS. 7 to 13 alternative forms of dynamic construction, that is to say alternatives comprising a moving part for the creation of a force field independent of the field of normal gravity and most frequently greater than this latter.

To this end, a small wheel 60 is mounted so as to be freely rotatable inside a cylindrical chamber 61.

In accordance with the form of embodiment shown in FIGS. 7 to 10, the axis of the chamber 61 and of the wheel 60 is horizontal.

This wheel comprises an axial conduit 62 partitioned by radial blades 63 and provided externally, as can be more clearly seen from FIG. 8, with driving blades 64 which are slightly curved in the same way as the blades of a Pelton wheel. Each blade 64 is parallel to the axis of the wheel and carries a portion 65 of an annular wall which is extended up to the vicinity of the adjacent blade 64, each blade 64 being itself extended up to the vicinity of the chamber 61. These wall portions 65 form with the axial conduit 62 an annular space 66 closed on the upstream side by a front plate 67, and open on the downstream side.

The wheel 60 occupies only a part of the internal space of the chamber 61, the part of this internal space which is free forming the separation chamber V according to the invention proper, as will become apparent later.

The mounting of the wheel 60 in the chamber 61 is effected by single fluid bearings 68, 69 at each extremity of the said wheel, these bearings being capable of permitting the passage of leakage.

In the axis of the axial conduit 62 of the wheel 60, the chamber 61, in accordance with the form of embodiment shown in FIGS. 7 to 9, is provided on the one hand with an axial supply pipe 1148 and on the other hand with an axial outlet pipe 1158, this latter being located beyond the separation chamber V or in this chamber.

In addition, at the level of the wheel 60, the chamber 61 is provided externally with supply nozzles 114A arranged tangentially and uniformly distributed around the periphery. These supply nozzles are preferably convergent and are arranged between the spaces defined by the fluid bearings 68 and 69.

Similarly, at its other extremity, the chamber 61 is provided externally with outlet nozzles 1 15A, similar to the supply nozzles 114A, but having a larger cross-section.

Finally, the wheel 60 is provided axially, at the upstream extremity of its axial conduit 62, with a hub 70 having the shape of a bullet.

The operation of this alternative form is as follows:

The liquor B carrying the crystals to be sorted is introduced to the pipe 1143, while the driving liquor A is introduced through the nozzles 114A.

As previously, the flow passing out at USA is made less than the flow entering at 114A; and the flow passing out at 1 15B is made greater than the flow entering at 1148.

The liquor A injected by the nozzles 1 14A strikes the driving nozzles of the wheel 60 and thereby causes the wheel to be set in rotation. From this time onwards, due to the uniform distribution of the said nozzles, the wheel 60 is maintained floating in a balanced manner in the chamber 61.

This latter being horizontal and the injection of the liquor A being made between the bearings 68 and 69, the wheel 60 is subjected only to slight axial reaction.

After contact with the driving blades 64 of the wheel 60, the liquor A injected by the nozzles 114A is directed by these blades towards the annular space 66 comprised between the axial conduit 62 and the portions of wall 65, in the direction of the arrows 71 of FIG. 8. This liquor A then leaves the wheel in rotation.

The liquor B which passes in at 114B, is directed towards the axial conduit 62 of the wheel 60 where the blades 63 also put this liquor into rotation.

At the outlet of the wheel 60 there are therefore in contact with each other along a cylindrical interface 8', on the one hand the liquor B in the axis of the chamber and on the other hand the liquor A located annularly round the said liquor B and rotating at the same speed as this latter.

Due to the rotation of the liquor B, the crystals carried by this latter are subjected to a force field which is the more intense as this speed of rotation is high, that is to say the more intense as the speed of rotation of the wheel 60 is high.

In this connection, the hub 70 has the purpose of deflecting slightly from the axis of the wheel, those crystals which pass-in axially and which for this reason could escape from the effects of centrifugal force.

By reason of this centrifugal force, the crystals have a tendency to pass radially through the interface 8' in the direction of the arrow 140 of FIG. 7, and by regulating the speed of rotation of the wheel 60 it is possible to determine the diameter of the crystals which will be subjected to a sufi'icient amount of centrifugal force to pass effectively through this interface S, in counterflow with the centripetal flow of liquor A resulting from the excess of the flow passing-in at 114A with respect to the flow passing out at USA.

The regulation of this speed is effected by adjusting the flow-rate of liquor injected through the nozzles lI4A, these nozzles being provided for that purpose with the usual flow-regulating means (not shown in the drawings).

At the downstream extremity of the chamber 61, the outlet nozzles 1 A of this latter evacuate a liquor into which have been transferred all the crystals having a diameter greater than a pre-determined diameter corresponding to the speed of rotation of the wheel 60.

At the same time, the liquor from which these crystals have been removed is evacuated through the axial pipe 1158.

FIG. 10 relates to an alternative form in which the inlet nozzles 114A are replaced by a diffuser 214A which is coupled to the chamber 61 along an annular surface partitioned by fins 72. These fins are extended up to the vicinity of the wheel 60 and the spaces between the fins can, at least in certain cases, be closed for the purpose of regulating the flow-rate.

A similar arrangement may be adopted for the outlet nozzles USA.

In accordance with an alternative form (not shown), the chamber 61 is vertical or oblique, so that the wheel 60 is subjected to its own weight.

In order to overcome the effect of this weight, the outer surface of the annular portions of wall 65 may be made frusto-conical in order that the force resulting from the variations of pressure and speed of the liquor on the upstream and downstream sides of the wheel may substantially balance the weight of this latter.

As an alternative, the driving blades 64 may also be given an oblique profile on the axis of the wheel so as to balance the weight of the wheel.

In accordance with the alternative construction shown in FIG. 11, the injection of liquor A into the chamber 61 is efi'ected by nozzles 214A arranged axially at the upstream transverse extremity of this chamber, around the axial supply pipe 114B associated therewith, through which the liquor B passes-in. In this case, the wheel 60 is provided with driving blades 164 which are oblique on its axis and which extend radially between its axial conduit 62 and an annular peripheral wall 165 in the same way as the blades of a Francis turbine.

In addition, the axial conduit 62 is provided at its upstream extremity with an extension 162 engaged in a fixed axial pipe 1148 and its axial hub is provided on its downstream face with a dished portion 76 serving as a supporting surface for a fixed locking rod 77. This latter is carried on the chamber 61 by arms 78 and serves to compensate for the axial thrust to which the wheel 60 is subjected due to the axial injection of the liquor A.

At the same time, the outlet of the liquor A may be effected either through peripheral nozzles as previously, or through axial nozzles 215A, as shown, while the outlet of the liquor B is effected through an axial pipe 1 15B.

The operation of a construction of this kind is similar to that described above.

The arms 78 are preferably helicoidal to give a better adaptation of these arms to the flow of the liquor in which they are immersed, and extend into the axial pipe 1158 so as to form flow-straighteners by preventing the rotation of the liquid in this pipe.

In the alternative forms of construction described with reference to FIGS. 7 to I], the wheel 60 is mounted freely rotating in the chamber 61, and its rotation is effected by the injected liquor A, which corresponds to a certain loss of pressure in this liquor.

There will now be described with reference to FIGS. 12 and 13, alternative forms of construction according to which the wheel in accordance with the invention is driven mechanically, which results in a certain application of pressure to the liquids in which it is immersed.

According to the alternative form shown in FIG. 12. this wheel is a shell 160 having the general shape of a hemisphere or a paraboloid of revolution, or of any surface comprised between the hemisphere and the paraboloid, driven in rotation by a shaft 80 which passes axially through the chamber 161, with the interposition of a packing gland bearing 81. The shaft 80 is keyed on the output shaft of a motor, motor-reduction gear, motor speed-varying gear or the like (not shown).

On its concave face opposite to the shaft 80, the wheel 160 has two successive layers of centrifugal blades 82, 83 extending respectively between an axial inlet 84, 85 and a peripheral outlet 86, 87, the inlet 85 forming a ring round the inlet 84.

Facing these inlets 84, 85, the fixed chamber 16] carries two concentric inlet pipes, an axial pipe 314A through which the liquor A is introduced, and an annular pipe 314B through which the liquor B is introduced.

The fixed chamber 161 further comprises outlet conduits 3158 and 315A arranged annularly facing the outlets 86 and 85 of the centrifugal blades 82, 83 of the wheel 160.

According to this alternative form of construction, the liquors A and B are put into contact as previously at the outlet of the wheel along a substantially cylindrical interface S through which pass only those crystals having a sufficient diameter.

According to the alternative shown in FIG. 13, the supply of liquor A is efi'ected on the convex face of the wheel, this convex face being provided for that purpose with appropriate centrifugal blades, when so required.

At the same time, the inlet of the liquor B is effected as previously on the concave face of the wheel 160, in the axial zone of this latter, and this liquor is set in rotation, as previously, by centrifugal blades 183.

The wheel also carries on its free peripheral edge, cylindrical extensions 85, 86, between which is developed the cylindrical interface S representing the contact surface of the liquors A and B at the outlet of the wheel [60.

The operation of this alternative is similar to that of the preceding alternative construction.

It will of course be understood that the present invention is not limited to the forms of embodiment described and shown, but covers any alternative form of construction or of combination of their various elements.

ln addition, its field of application is not limited only to the crystallization installations of the type diagrammatically described with reference to FIG. 2, but extends to any type of crystallization installation.

What] claim is:

l. A device for sorting crystals according to their size, comprising a tank, means dividing said tank into two parts, said means permitting crystals to pass from one part to the other and permitting liquor to pass in the opposite direction, one of said parts having a fluid inlet for a carrier fluid and a fluid outlet, the other of said parts having a fluid inlet for a driving fluid and a fluid outlet, and means maintaining the flow rate of fluid passing out of said other part lower than the flow rate of driving fluid passing into said other part whereby a portion of said driving fluid passes through said dividing means in countercurrent flow to a portion of said crystals, said dividing means including an adjustable throttling means for altering the communication between said two parts of said tank.

2. A device as claimed in claim I, said two parts being vertically superposed and said dividing means being substantially horizontal.

3. A device as claimed in claim 1, said throttling means comprising at least one pivoted shutter extending across said tank.

4. A device as claimed in claim 3, at least one of the edges of said shutter being pivotally mounted in the manner of a knife blade in a slot formed in an operating rack member.

5. A device as claimed in claim 3, there being a plurality of said shutters actuated by a common control.

6. A device as claimed in claim 1, said inlet of said one part of said tank being smaller than said outlet of said one part of said tank, said inlet of said other part of said tank being larger than said outlet of said other part of said tank.

7. A method of sorting crystals according to their size, comprising establishing a pair of chambers separated by means through which fluid can pass in one direction and crystals can pass in the opposite direction, introducing carrier fluid containing crystals suspended therein into one chamber, withdrawing fluid from said one chamber at a flow rate greater than the rate of introduction of fluid into said one chamber, in-

tr ucin drivin flui it theot rs idchamber,and wfidraw mg drimg :2! rom said at er chamber at a rate of flow less than the rate of flow of driving fluid into said other chamber whereby fluid passes from said other chamber to said one chamber in countercurrent with crystals passing from said one chamber to said other chamber, said fluids having different densities, the density of said crystals lying outside the range of densities of said fluids.

8. A method as claimed in claim 7, the density of said driving fluid being higher than the density of said carrier fluid.

# i O I

Claims (8)

1. A device for sorting crystals according to their size, comprising a tank, means dividing said tank into two parts, said means permitting crystals to pass from one part to the other and permitting liquor to pass in the opposite direction, one of said parts having a fluid inlet for a carrier fluid and a fluid outlet, the other of said parts having a fluid inlet for a driving fluid and a fluid outlet, and means maintaining the flow rate of fluid passing out of said other part lower than the flow rate of driving fluid passing into said other part whereby a portion of said driving fluid passes through said dividing means in countercurrent flow to a portion of said crystals, said dividing means including an adjustable throttling means for altering the communication between said two parts of said tank.

2. A device as claimed in claim 1, said two parts being vertically superposed and said dividing means being substantially horizontal.

3. A device as claimed in claim 1, said throttling means comprising at least one pivoted shutter extending across said tank.

4. A device as claimed in claim 3, at least one of the edges of said shutter being pivotally mounted in the manner of a knife blade in a slot formed in an operating rack member.

5. A device as claimed in claim 3, there being a plurality of said shutters actuated by a common control.

6. A device as claimed in claim 1, said inlet of said one part of said tank being smaller than said outlet of said one part of said tank, said inlet of said other part of said tank being larger than said outlet of said other part of said tank.

7. A method of sorting crystals according to their size, comprising establishing a pair of chambers separated by means through which fluid can pass in one direction and crystals can pass in the opposite direction, introducing carrier fluid containing crystals suspended therein into one chamber, withdrawing fluid from said one chamber at a flow rate greater than the rate of introduction of fluid into said one chamber, introducing driving fluid into the other said chamber, and withdrawing driving fluid from said other chamber at a rate of flow less than the rate of flow of driving fluid into said other chamber whereby fluid passes from said other chamber to said one chamber in countercurrent with crystals passing from said one chamber to said other chamber, said fluids having different densities, the density of said crystals lying outside the range of densities of said fluids.

8. A method as claimed in claim 7, the density of said driving fluid being higher than the density of said carrier fluid.

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