GB2078542A - Process and apparatus for continuous processing under pressure - Google Patents

Abstract

Continuous processes involving counter moving materials, and apparatus for carrying out such processing, are applied to extraction and to the combining of substances. In a continuous extraction process, solid material is introduced into a feeding body 5 leading to one end of an impermeable housing 6 containing a conical screw 7 the pitch of which decreases towards an outlet 2 for solid material. A fluid solvent is injected at a point 3 close to the outlet 2 and follows a helical path 8 to solvent outlet filters 13 below the foot of the feeding body 5. The solid material contains a solute which is to be extracted and is driven and squeezed progressively by the screw 7 which transports the solid material along a substantially linear path to the outlet 2. The effect of the rotation of the screw is to produce a pressure gradient which promotes solvation so that the solvent leaving through the filters 13 contains extracted solute. The respective rates of flow of the solvent and the solid material can be independently controlled and depend on the injection at the point 3 and the rate of rotation of the screw 7. <IMAGE>

Description

SPECIFICATION Process and apparatus for continuous processing under pressure The present invention relates to continuous processing under pressure, especially continuous extraction by solvation under pressure, and can be used in chemical, mechanical, agricultural and metallurgical engineering for processing vegetable and animal raw materials (derived from agriculture and extractive industry), raw mineral materials (derived from the mining industry), or intermediate materials (derived from the chemical and metallurgical industries).

The complete treatment of raw or intermediate materials includes the following steps: first, the preparation of the material to undergo extraction (e.g.

disintegration, roasting, cooking, flaking, etc.); second, the lixiviation or extraction, predominantly in counter-flow, in an extractor; third, the recovery of the solution contained in the undissolved and, fourth, the solute-solvent separation of the rich solution or extract. The present invention provides a process which covers the whole of the second step or the extraction predominantly in counter-flow, and part of the third step: the recovery of the solution, which is effected by a process of mechanical separation: the expulsion or "expression" of the solution from within the raw material at the final stage of processing by the extractor.

The present invention also provides apparatus which effects the removal of a soluble fraction, in the form of a solution, from an insoluble and permeable solid with which it is associated by establishing a close and direct contact of the material fed to the apparatus (for extraction) with the extractor solvent, in such a way as to allow mass-transfer of the desired constituents from the fed-in material to the solvent. The apparatus of the present invention operates in a continuous manner and predominantly with counter-flow, pure (new) solvent entering at the point in the extractor which contains the most exhausted material and the solution or extract (solute + solvent) leaving at the point in the extractor which contains the new (richest) material.Another useful effect produced by the extractor of the invention is the mechanical separation of the two phases, the solvent (liquid or gaseous) being separated from the insoluble and permeable solid with which the solute was associated by the mechanical squeezing action, from which a pressure state results which, in accordance with particle and fluid mechanics, forces them to move in opposite directions (the solids in one direction and the fluids in another). Hence apparatus in accordance with the present invention may be considered, as a whole, as a "separator" which operates by chemical, physical and mechanical processes.

The solvation referred to herein is the association or combination of one unit of solute (ionic, molecular or particle) with molecules of the solvent. Solvent is a fluid which dissolves other materials (solutes) in forming a single homogeneous phase (solutions).

The present invention can operate with unusual solvents under conditions which are different from the normal ones as regards temperature and pressure. The solvents can be materials which are in the liquid or gaseous state, under specific conditions of temperature and pressure, and which may be injected under pressure into the extractor. Such solvent, when pure and fresh, enter continuously into the apparatus at a point which is practically exhausted of the desired component; the solvent undergoes continuous enrichment by mass transfer during the transport in counter-flow, and is removed continuously at the point of maximum enrichment.

The term extraction is used herein to refer to operations of lixiviation, leaching and extraction by solvent generally.

In order to implement liquid-liquid extraction, or more generally fluid-fluid, with the extractor according to the invention it is necessary to associate the fluid to be extracted with an insoluble and permeable solid material which serves as a transport vehicle. This material may be, for example, activated charcoal, infusion earths, sawdust, sand, etc.

Apparatus according to the present invention, in its final part, partially recovers solutions (liquid or gaseous) from the solid material which had, originally, the solutes extracted, or which were utilized as vehicles for the liquids or gases which underwent the extraction and, throughout most of its length, performs a continuous extraction under pressure in counter-flow.

In Table I below, "A" is the material which is to undergo the extraction, "X" the component to be extracted, "B" the solvent and "V" a possible transport vehicle for "A". Various combinations of physical states (under pre-stabilised conditions of temperature and pressure) are thus provided.

TABLEI Is "V" Combination "A" "X" "B" required7 1 solid solid liquid no 2 solid liquid liquid no 3 solid gaseous liquid no 4 solid solid gaseous no 5 solid liquid gaseous no 6 solid gaseous gaseous no 7 liquid solid liquid yes 8 liquid liquid liquid yes 9 liquid gaseous liquid yes 10 liquid solid gaseous yes 11 liquid liquid gaseous yes 12 liquid gaseous gaseous yes 13 gaseous solid liquid yes 14 gaseous liquid liquid yes 15 gaseous gaseous liquid yes 16 gaseous solid gaseous yes 17 gaseous liquid gaseous yes 18 gaseous gaseous gaseous yes The distribution of pressures inside the extractor depends, amongst other variables, on the geometry of the parts, the speed of rotation and the pressure of injection of the solvent.This pressure of injection is determined by hydraulic pumps for liquid solvents or compressors for gaseous solvents, and must be pulsating.

Known equipment for extraction now available may be classified into two main classes: those which operate by percolation, i.e., infiltration of solvent into a layer of the solid, and those which operate by the dispersion of solids by agitation, i.e., the solid is in the form of particles and is dispersed within the extractor liquid and later separated from it. In both classes, there are designs for continuous operation, and batch or intermittent load operation.

An example of percolation in batches is the preparation of coffee in a percolator (extraction by repetition) or in a modern filter (a single fiitering). The continuous percolators use the principle of a movable layer implemented by baskets which carry the solid through sprays of solvent, or by belt (or screw) conveyors which move through solvent showers, or harrows which transport it along a line of cavities full of solvents. Examples of such designs are: the Rotocell extractor (rotating baskets on annular fixed perforated disc); the Boll man extractor (alternated baskets arranged in a bucket elevator); the Hildebrandt extractor (endless screws in a vertical "U" shape route;) the Kennedy extractor (harrows or shovels acting on lined cavities).

The extractors which operate by dispersion of solids (agitation) are particularly useful for solids which disintegrate during the extraction. They include non-continuous tanks and continuous extractors.

The continuous processes are implemented in tanks for mixing-sedimentation by gravity (thickeners) or vertical extractors, plate extractors. Examples are: the Dorr agitator .which combines a harrow with air thrust in order to wash precipitates in batches); the Bonotto extractor (circular plates with unaligned openings superimposed in a vertical column, on each plate a rotary radial blade operates); the Oldshue-Rushton extractor (column with baffles, fixed compartment disks and rotary impellor turbine along the whole column); the Sheibel-Vork extractor (also with impellor turbine, the dispersion of light ascending liquid is caused by stationary screens); the pulsing extractor (also with vertical column with Fixed perforated disks; the agitation is caused by fast superimposition of mechanical agitation, of about 201100 hertz, on the natural flow of liquids).

In some extractors, for example, the Kennedy and the Hildebrandt extractors although the main action is percolation, there is also some solid dispersion due to agitation caused by the solid transporters. In the extractor according to the present invention, the two effects are present: percolation and solid dispersion, and, mainly in the initial portion (preextraction portion), depending upon the project and/or operational adjustment, it is possible to have predominance of the solid dispersion effect.

On analysing the existing equipments, a characteristics is found to be common to all of them: the exit of the solution is always forced by the action of a potential field, most often the action of gravity and, sometimes, the action of centrifuge accelerations created by the extractor. This is a defect in design because while in practice there are almost always controlling conditions on the speed of flow of solid, there is almost never the capacity of acting on the speed of flow of the solution. This fact is reflected in the efficiency of the extractors and is an obstacle to the reduction of their size (and, therefore, of capital costs) because although it is possible to increase the speed of displacement of the solid, increasing the flow of the solution can only be achieved by increas ing the size of the equipment.

The basic problem is: how to make a solid displace itself in one direction and the fluid flow insthe oppo site direction, acting on the speeds of the two flows? The present invention is based on a solution of this problem utilising the properties of Archimedes' screw: a variable pitch and/or conical screw rotating inside a closed housing develops a distribution of increasing pressures upon the solid which is pushed by the screw; injecting the solvent near the higher pressure portion, the solvent flows towards the other end in a direction contrary to that of the solid.

The fact that the extractor of the present invention allows the control of the two flow speeds, gives it the following advantages over the known extractor equipments: a greater extracting efficiency; more compact structure and therefore less expense; possibility of extraction by solvation in small scale pro duction; compensation for eventual higher operational costs, due to the use of higher energy in the process, by the greater efficiency and by lower capital and maintenance costs.

The possibilities in applying the process according to the invention and for configurations of the apparatus which are capable of performing it are numerous, as shown by the 18 combinations of Table I. Embodiments of the invention can be used for extraction of sugars and other soluble con stituents of sugar cane, sorghum and other veget ables, for the purpose of producing fuel and indus trial alcohol; extraction of oils and fats from veget able and animal products for non-alimentary pur poses, mainly as fuels; extraction in the treatment of minerals, in metallurgy, chemical industries, pet rochemical, alcohol-chemical, carbon-chemical, nuc lear industries, etc.; and in reaction vessels where, in a continuous process under controlled conditions of temperature and pressure, close contact is achieved in counter-flow for reagents and catalysts in the 18 combinations of physical state described in Table I, for example, in a reaction vessel for the acid hyd rolysis of biomass in a continuous process.

The invention will now be described in more detail solely by way of example, with reference to the accompanying drawings, in which:~ Fig. 1 is a schematic side view of an extractor with natural feeding, and without "stopper", embodying the invention; Fig. 2 is a schematic side view of an extractor, with forced feeding and with external "stopper", embodying the invention; Fig. 3 is a schematic side view of an extractor, with natural feeding, internal "stopper" and external "stopper", embodying the invention; Fig. 4 is a schematic side view of an extractor which is a preferred embodiment, with forced feed ing, internal "stopper", external "stopper", and independent shafts for two screws (7) and (7a), driv ing of three screws being by three independent motors;; Fig. 5 is a side view of the extractor of Fig. 4 show ing its basic components, Fig. 6 is a sectional view at the Section AA indicated in Fig. 5; and Fig. 7 is a plan view of the extractor of Fig. 5.

In the drawings, corresponding elements of the various embodiments have the same reference numerals.

Fig.,1 shows an extractor having an inlet 1 for disintegrated solid which initially contains the solute, or which serves as a vehicle for transporting a fluid which contains the solute, and an outlet 2 for the disintegrated solid with a controlled content of solution.

This content depends upon how much energy can be expanded in squeezing the solid, which is a function of: value of the solvent, subsequent use of the solid (for example: as animal food which must not become rancid, as fuel, as a transport vehicle which must undergo recovery for re-utilization, etc.), the value of the residual solute, etc. An inlet 3 is provided for the solvent in the impermeable casing of the extractor. Near this inlet point there is a perturbation in the distribution of pressures in the mixture which is being transported. To the right of it, there is the final portion c of the extractor, where the solidsolution separation is exclusively mechanical.To the left is the portion b where the extraction is predominantly by forced percolation of the solution; this intermediate portion extends to the initial portion having filters 13, where the housing is no longer impermeable. In Fig. 1 there is practically no initial portion a or portion a and b merge, depending upon the geometry of the screw. Outlet points 4 are provided for the extract or solution for later use. Except for Fig. 1, in all other figures there are outlet points for extract or solution which is to be recirculated to the portion a. The speed of such recirculation must be greater than the speed of solid flow. In this region, the extraction is effected by solid dispersion (agitation), mainly in the case of solids which disintegrate during leaching. At the inlet 1 the extractor has a feeding body 5 integrally connected to the casing which houses the screw.In some embodiments, e.g., Figs. 2, 4 and 5, the body 5 serves as impermeable housing for a forced feeding screw 15. Forced feeding may be effected by means other than a screw. The union of the funnel constituted by the body 5 with the housing 6 of the screw 7 should avoid sharp curves, and should be grooved when forced feeding is effected with a squeezertransporter screw. The housing 6 of the screw 7 is impermeable and has internal longitudinal grooves 19. The space existing between the screw 7 and the housing 6 is important in several respects. The fact that this housing is impermeable is a principal feature which distinguishes the present extractor from the screw press ("expeller") conventionally known, which has a permeable housing and consequently does nof develop a distribution of pressures as in the present extractor. The expeller operates exclusively by mechanical separation.In the present extractor, variation of the pitch and/or conicity of the squeezer-transporter screw enables the screwimpermeable housing combination to form closed chambers which undergo reduction of volume, and consequently an increase in pressure along the assembly. In ideal operation the solid does not stick to the screw and the screw does not transfer any rotation to the solid, due to the lack of friction, so that the course of the solid is longitudinal only. To implement solely longitudinal displacement of the solid under real conditions, the friction between the solid and the housing is selectively increased, for example, by providing longitudinal grooves 19 in the housing. In the embodiment of Fig. 3, the screw thread is interrupted so that an internal "stopper" 16 may operate.The screws in the figures have righthand threads and, therefore, in order to push from the left-hand side to the right hand side of the figure, they have to rotate in the counter clockwise direction, indicated by an arrow 10, as seen from the left towards the right-hand side in Fig. 2. In the embodiment of Fig. 4, two aligned screws operate independently, a screw 7a operating in the portion a, and a screw 7 operating in the portions b and c as shown.

When the portion a of the extractor operates mainly on the solid dispersion or agitation principle, it may be convenient to replace the screw 7a by a high speed blade agitator.

The helical route of the extract, counter-clockwise as viewed from the left to the right-hand side, is indicated by a broken line 8. Since the solid has a tendency to move longitudinally with a degree of small rotation in following the screw, in addition to the flow of solution being a counter-flow in the longitudinal direction, it flows alongside the thread, opposing the solid. An example of the recirculation route of extract or rich solution is indicated at 8a. The longitudinal flow of solid is indicated by an arrow 9. It is parallel to the shaft of the screw except when there are conicities. The direction of rotation of the squeezer-transporter screws is indicated by arrows 10. The screws are intended to operate at a constant rate of rotation the value of which depends upon the characteristics of the solids and fluids which are flowing.It is evident that the higher the rate of rotation, the higher the rates of flow, and consequently the larger the nominal capacity of the apparatus. In the case of Fig. 4, with two independent axial screws with independent drive, operation with different rotations can be carried out. The direction of rotation of the screw 15 for forcing the feeding is indicated by an arrow 11 and corresponds to rotation of a righthand thread in the counter-clockwise direction as viewed from top to bottom in Fig. 4. The rate of rotation of the screw 15 is variable so that depending upon the raw material, the pressures in section a can be stabilised. A pressure regulator-stabiliser device 12 is also provided at outlet which acts by choking the flow of solids, and is termed the "stopper". The regulating effect of the stopper 12 is achieved by the static axial separation, and the stabilising effect is achieved by a dynamic axial separation controlled by springs which respond to the oscillations in the pressure being stabilised. The stopper 12 does not turn with shaft of the screw 7; its only movement relative to the shaft is axial.

Efficient filters 13, for example filters formed of sintered metal powder with a porosity adequate to retain solids and allowing the extract or solution rich in solute to flow through are provided at the input end of portion a. In the case of solids which disintegrate during the extraction and/or quite viscous extracts, such mechanical separation (filtering) may become a problem. For example, the castor bean (Ridnus Communis) is quite friable and also has 55% content (by mass) of high viscosity oil. In this case, portion a - in this case termed the pre-extraction portion - of an extractor embodying the invention operates mainly by solid dispersion with efficient filters under pressure. The main disadvantage of the sintered metal powder filter, in this case, is its low resistance to traction.It is essential to dimension the structure of portion a so as to minimise the exposure of the filters to traction stresses, for example, by embedding them in cast-metal housings. The filters are arranged to be continuously scraped by the screw, and the extract collectors, after the filters, are arranged to allow the injection of steam for periodic maintenance and cleaning of the filters, including during the operation of the extractor, if necessary.

Points for inlet of the extract or recirculated rich solution are indicated in Figs. 2 to 5 by references 14. Such recirculation is forced at high speeds of flow by hydraulic pumps which preferably are surging pumps. It is important to be able to regulate the injection pressures in order to accommodate the variations of raw material. The squeezing-transporting screw 15 forces the input of solids and pressurises the portion a of the extractor. At the initial point of the screw a space, of approximately 20%, should exist, between the screw and its impermeable housing, in this case the feeding body 5. This space must diminish progressively to about the mid-point of the length of the screw, where it must be equal to the normal screw to housing fit.

A pressure regulating-stabilizing device 16 is preferably provided inside the extractor (as an internal "stopper"). This internal stopper 16 operates by choking the flow in a manner similar to the effect of the outlet stopper 12. The stopper 16 may be made of metal, with a diaphragm shutter type design, or with stabilizing movements based upon the deformation of an elastomeric member which may be hollow and pressurizable or solid.

In the embodiment of Fig. 3, a single screw 7 extends through the whole extractor, and only the thread of this screw is interrupted over a region 17 near the internal stopper 16. It is then necessary to shield the rotating shaft from the flowing solid. If this is not done, clogging occurs at the internal stopper 16. A supporting bearing 18 shown in Fig. 4 resists the axial thrust of the screw 7 when there are two co-axial independent screws. When the screw 7 works under traction, the bearing 18 may be placed at the other end.

The longitudinal grooves 19 which have the purpose of increasing the friction acting against rotation of the solid and keeping it to a minimum in the longitudinal direction for the solid are shown in Fig. 6.

Hydraulic motors 20 are shown in Fig. 5 for driving the three screws, namely the screw7 in the portion where forced percolation under pressure predomi nates, the screw 7a in the portion where the solid dispersion (agitation) may predominate (this screw may be replaced by a bladed agitator with advantages in some cases), and the screw 15 in the feeding body 5. The feeding body 5 is equipped with funnel or hopper 2 for the feeding in of raw material.

A process embodying the invention will now be described in relation to the simple extractor represented in Fig. 1.

Disintegrated solid material 1 of a convenient particlesize, is fed in bythefeeding body5.T,he squeezing-transporting screw 7 receives this material within the cavities of its thread. The change of pitch and/or conicity of the screw results in the screw-impermeable housing combination forming closed chambers which reduce in volume along the route followed by the material. As the material is pushed within these chambers, the reduction in volume increases the pressure. Under ideal conditions, the route 9 of the solid is exclusively longitudinal and in a straight line. This route is axial and parallel to the screw's shaft except when there is conicity.

The impermeable housing 6 which forms the operative combination with the screw 7 has internal longitudinal grooves (as 19 in Fig. 6) for increasing the friction between the solid and the housing for rotation so to implement, physically, the above mentioned straight line route. The screw 7 transports the solid material, while squeezing it, from the feeding point at the foot of the body 5 to the outlet point 2 where there is a controllable content of solution, remaining in the solid. This remainder content depends upon how much energy is expended in squeezing the solid in recovering the solution.

The solvent fluid is injected through the impermeable housing at the point 3. This injection causes a perturbation in the distribution of pressures in the solid near the point 3. However, the gradient of pressure continues to cyclically increase towards the right of the point 3. Consequently, the solvent flows towards the left-hand side as a counter-flow relative to the flow 9 of solid material. In the first contact between the solute carried by the solid material and the solvent, mass transfer of solute occurs to the solvent, which becomes a solution. The main route 8 of the solution is helical along the screw threads.

Right-hand thread screws are rotated in the counter-clockwise direction 10, so that a flow 8 of the solution results having a helical route in the counter-clockwise direction. Since the route 9 of the solid material is mainly longitudinal, in addition to the flow of the solution being in the counter-flow longitudinal direction, it flows alongside the thread, opposing the solid. The solution flows from the region near the solvent intake 3 to the low pressure end of the extractor where the outlets 4 for the solution or extract are located. During this whole journey, mass-transfer occurs, in counter-flow, with a continuous repetition of the process of enrichment of the solution and corresponding weakening of the solid. Such enrichment and weakening relate to the content of solute (which is the object of the extraction) in the solution and the solid material, respectively.

The apparatus of Figs. 2, 3 and 4 add flexibility to the fundamental process just described with refer pence to Fig. 1.

The basic idea is to have more control overthe pressures and rates of flow, so that the process may be applied to several raw materials and solvents, in the 18 combinations of physical states shown in Table 1, and also so that the extractor may be used as a reaction receptacle.Such flexibility is achieved through use of the device 12 (stopper) acting as reguletor-stabilizer of the pressures at the outlet for the solid material; use of the device 16 (internal stopper) as regulator-stabilizer of pressures within the extractor; use of the squeezer-transporter screw 15 to force feed raw material, which enables flows to be controlled, because its rotation is variable; use of filters 13 of great efficiency, such as sintered metal powder filters in order to, under pressure, increase the efficiency of mechanical separation of the solution or extract from fine solids with which it is associated.

The use of such devices allows sufficient flexibility for determining, along the extractor, the corr,bina- tions of proportions of performance of the two basic classes of extraction: percolation and solid dispersion (agitation). Thus, in Figs. 2, 3 and 4 there is the portion a where it can be arranged that there is a predominance of solid dispersion, and the portion b, where forced percolation with fluid under pressure predominates. It is important to note this point, because the most used percolation process nowadays is the natural one, that is, the fluid flows under the action of the gravity and, for this reason, there are no conditions which act on the speed of such flow. The usual definition initial of percolation is infiltration of solvents in a solid layer.The region c of the extractor continues to be a region where the main separation process is mechanical separation of the solidfluid phases, but now with the stopper 12 there are more and better conditions with which to regulate, operationally, the content of the weak solution remaining in the solid material which leaves the extractor.

Furthermore, these additional devices enable there to be fast recirculation of the extract in the portion a between the exit area 13 and the inlet area 14 and possibly at some points of the portion b, if necessary.

Embodiments of the present invention are preferably used for the extraction of sugars and fats of vegetable nature. A prototype embodiment of apparatus in accordance with the invention should be able to process, on a micro-scale, at least sugar cane, sorghun and castor seed, with the least possible number of adjustments, the prototype being in accordance with Figs. 4, 5, 6 and 7.

Claims (14)

1. A process of continuous extraction by solvation under pressure, wherein independent control of two rates, namely the rate of movement of solid material which moves in substantially one direction and the rate of flow of a fluid which flows in substantially another direction both under pressure can be effected at the same time, the process including the steps of promoting forced movement of the fluid through a pressure gradient developed as a result of the structure of apparatus within which the movements take place and of effecting forced injection of solvent into the path of the said solid material.

2. A process according to claim 1, wherein the substance which is to undergo the extraction process is solid material and the constituents to be extracted from it are either solid, liquid or gaseous, and either liquid or gaseous solvents are used, under pressure, for the extraction.

3. A process according to claim 1, wherein the substance which is to undergo the extraction process is a liquid, and the constituents to be extracted from it are either solid, liquid or gaseous, either liquid or gaseous solvents are used, under pressure, forthe extraction, and the liquid which is to undergo the extraction process is associated with an insoluble and permeable solid material which acts as a transport vehicle.

4. A process according to claim 1, wherein the material which is to undergo the extraction process is a gas or vapour, and the constituents to be extracted from it are solid, liquid or gaseous, either liquid or gaseous solvents are used, under pressure, for the extraction, and the gas or vapour which is to undergo the extraction process is associated with an insoluble and permeable solid material which acts as a transport vehicle.

5. A process of continuous uniting or reacting under pressure, wherein initially separate substances are united or reacted together in a reaction process occuring under controlled conditions of temperature and pressure, through the close contact, in counteiflow, of reagents and catalysts, the reagents and catalysts being incorporated in a system comprising solid material which moves in one direction at a certain rate and a fluid which moves in another direction at another rate, the two rates of movement being independently controllable at the same time and forced movement of the fluid through a pressure gradient developed as a result of the structure of the apparatus in which the movements take place being promoted and forced injection of solvent into the path of the said solid material being effected.

6. A process according to claim 2, wherein the extraction of soluble constituents of the sugar cane, sorghum and other vegetables, for the production of alcohols, is effected.

7. A process according to claim 2, wherein the extraction of oils and vegetable fats and animal fats for industrial uses is effected.

8. A process according to any one of claim 1 to 5 applied to the processing or obtaining of industrial materials.

9. A process according to claim 1, wherein unusual solvents, in the liquid or gaseous state, are used in specific conditions of temperature and pressure and may be injected under pressure into the apparatus in which the extraction process takes place.

10. Apparatus for carrying out a process according to claim 1 or claim 5, the apparatus being such that the said solid material and the said fluid can move in opposite directions through the utilization of a variable and/or conical pitch screw which rotates within an impermeable housing.

11. Apparatus according to claim 10, wherein regulating devices are provided which stabilize the pressures at the exit of the solid and a squeezingtransporting screw is provided for the feed of raw material, and efficient filters are provided for, under pressure, increasing the efficiency of the mechanical separation of rich solution (or extract) from fine solids with which the rich solution may be associated.

12. Apparatus according to claim 11, wherein the apparatus is such that, along the flow path of the apparatus, combinations of required proportions of two basic types of extraction, namely percolation and solid dispersion, are established whereby in a first portion of the said path solid dispersion predominates and in a second portion of the said path mechanical separation of solid and liquid phases predominates.

13. A process according to claim 1, substantially as described hereinbefore with reference to any one of Figs. 1 to 3 orto Figs. 4 to 7 of the accompanying drawings.

14. Apparatus according to claim 10, substantially as described hereinbefore with reference to any one of Figs. 1 to 3 or to Figs. 4 to 7 of the accompanying drawings.