FR3069451A1 - IMPROVED FILTRATION METHOD AND PRESS FILTER - Google Patents

Abstract

The invention relates to a filtration method and a filter press (10) implementing it, for filtering a mixture having a liquid phase and solid particles and the filter press comprises, n trays (12, 14, 16, 18, 20, 22, 24) each having two opposite walls (26, 28; 26 ', 28') to form n-1 housings; n-1 filtration chambers trapped respectively inside said n-1 housings and to be connected together to be fed said pressurized mixture when said n trays are compressed axially against each other, said filtration chambers retaining the solid particles in the form of cakes (140) while said liquid phase flows out of said filter chambers. The filter press further comprises n-1 pairs of electrodes (92, 94, 96, 90) respectively installed inside said n-1 housings, so as to increase the dryness of said cakes.

Description

Improved filtration process and filter press

The present invention relates to a filtration process and to a press filter in order to be able to filter a mixture having a liquid phase and solid particles suspended in said liquid phase.

A field of application envisaged is in particular, but not exclusively, that of the filtration of complex sludges which are difficult to filter, for example mineral sludges containing bentonite, or even sludges containing hydrocarbons.

Filter presses intended for the filtration of a liquid / solid mixture are well known. They include a plurality of plates successively joined to each other. Each of the plates has two hollow walls opposite one another and respectively delimited by a raised peripheral edge, so as to form successive housings between each pair of plates. The plates are compressed axially against each other, peripheral edge against peripheral edge, and inside each housing is trapped in a sealed manner a filtration chamber. The filtration chambers of all the successive housings, made for example of a woven synthetic material, are connected together through the plates so as to be able to be supplied under pressure with the liquid / solid mixture. Also, the plates each comprise a collection passage path for said liquid phase having an axial collection part opening into the opposite peripheral edges of said two opposite hollow walls and a radial part extending between said peripheral edges and said axial collecting part towards said hollow walls. In this way, the axial collecting parts of the plates compressed axially against each other form a single collector into which opens the radial part of each of the plates.

The liquid / solid mixture is then injected under pressure inside the filtration chambers and, while the liquid phase flows through the walls of the filtration chambers, the solid phase remains trapped inside the filtration chambers. . The liquid phase of each of the housings flows through the radial part of the plates, then into the collector and then is collected at one of the ends of the plurality of plates. As for the solid phase, they gradually accumulate inside the filtration chambers as the liquid / solid mixture flows, and the residue which it constitutes then forms a cake. When the cake of each of the filtration chambers is sufficiently thick with regard to the housings, the injection of the liquid / solid mixture is stopped and the plates are separated from one another in order to be able to release said cakes.

Certain liquid / solid mixtures are difficult to filter, and they must for example be injected inside the filtration chambers at high pressures, above 15 bars for example. However, such pressures consequently require significant pressurization means. Other mixtures, even more complex, cannot be filtered using a press filter, at acceptable costs. Also, the cakes obtained have a relatively low mass percentage of dry matter, ie a dryness. And the more the cakes are loaded with moisture, the more resources they need to store or process.

Also, a problem which arises and which the present invention aims to solve is to provide a method and a filter press for implementing it, making it possible to filter complex liquid / solid mixtures.

For this purpose, there is proposed, according to a first object, a filter press to be able to filter a mixture having a liquid phase and solid particles suspended in said liquid phase, said filter press comprising: n trays each having two opposite walls recessed, said n trays being successively joined to each other to form n-1 housings respectively between the facing walls of said n trays, n being greater than 1; n-1 filtration chambers intended to be sealed respectively inside said n-1 housings and to be connected together to be supplied with said mixture under pressure when said n trays are compressed axially against each other, said chambers being intended to retain the solid particles in the form of cakes while said liquid phase flows out of said filtration chambers. And the filter press further comprises, n-1 pairs of electrodes respectively installed inside said n-1 housings, in order to be able to induce an electric field through said n-1 filtration chambers so as to increase the dryness of said cakes.

Thus, a characteristic of the invention resides in the implementation of an electric field through each of the filtration chambers, which has the effect of improving the filtration process, ie the filterability of the mixture, even for mixtures liquid / solid complex and therefore increase the dryness of the residue and the cakes then obtained.

Advantageously, each of said n-1 filtration chambers comprises two filtration fabrics back-to-back. Thus, each filtration chamber includes two flexible walls made of a textile material. They are back-to-back and compressed against each other in their peripheral edges by means of the raised peripheral edge of the plates as will be explained below. In this way, the two filtration fabrics are connected together in their peripheral edges and form a pocket inside the housing formed by the plates.

In addition, and according to a particularly advantageous embodiment, the electrodes of each of said n-1 pairs of electrodes are respectively installed on said walls opposite each of said n-1 housings. Thus, one of the electrodes, forming an anode for example, is installed on one of the walls of the housing, formed by a plate, while the other of the electrodes, then forming cathode, is installed on the other of the walls of the housing, formed by the adjoining plateau. In this way, the filtration chamber extends between the two electrodes and the electric field generated by the cathode and the anode induces field lines substantially perpendicular to the walls opposite the filtration chamber. Therefore, and as will be explained in more detail in the description below, the electric field is uniformly distributed inside the filtration chamber and its efficiency is then maximum.

In addition, and according to a preferred embodiment of the invention, each of said two opposite hollow walls comprises a central zone having a bottom and a peripheral edge raised relative to said bottom surrounding said central zone. Thus, the two bottoms and the two peripheral edges of the two opposite walls of the same plate respectively define planes substantially parallel to each other. In this way, when two contiguous trays are in abutment against one another, their two peripheral edges facing each other are in abutment flat against one another, while the two facing bottoms extend substantially parallel to one another.

Preferably, according to a particular embodiment of the invention, each of said n plates comprises at least one injection passage path having an axial injection part opening into the opposite peripheral edges of said two opposite hollow walls. Thus, when the plates are applied against each other, the axial injection parts of all the plates are aligned and they define a single injection channel. This injection channel extends longitudinally through the peripheral edges of the plates. It can extend through the corners of the n trays, or even through the middle areas of the peripheral borders.

According to another advantageous embodiment, the injection passage path is formed in the center of said n plates.

In addition, said at least one injection passage path has two opposite grooves extending radially in said opposite peripheral edges between said axial part and said central zone. In this way, when the plates are applied against each other, the two grooves of two contiguous plates define a radial injection duct then connecting said single injection channel to the housing extending between the walls opposite the plates. In the detailed description, the mode of cooperation between the filter cloths and the plates to explain the filtration chambers connected to each other by the injection channel will be explained.

In addition, each of said n plates comprises at least one collecting passage path for said liquid phase having an axial collecting part opening into the opposite peripheral edges of said two opposite hollow walls. Thus, in an area spaced from the axial injection part, the plates have an axial collection passage part, so that all the axial collection parts are aligned with each other when the plates are attached to each other to form a single collector. In this way, the liquid phase can flow longitudinally through said single collector towards one of the ends of the n plates placed side by side.

In addition, said at least one collection passage path has a radial part extending between said peripheral edges and from said axial collection part towards said central zones to open into said bottom of said central zones. Thus, each of the housings is connected to said single collector via the radial part of its collection passage path.

According to a particularly advantageous embodiment of the invention, the filter press further comprises n-1 deformable membranes respectively installed on one of said walls opposite said n-1 housings in order to be able to compress said n-1 filtration chambers. The deformable membranes are airtight. In this way, by precisely injecting air or water, between these and the wall against which they are applied, the compression chamber is compressed against the opposite wall. Consequently, after a filtration sequence, as soon as the cakes have reached their optimum thickness, the injection of the liquid / solid mixture is stopped, and the filtration chamber is thus compressed to then facilitate the release of the cakes.

According to another object of the invention, there is provided a method of filtering a mixture having a liquid phase and solid particles suspended in said liquid phase, said filtration method being of the type comprising the following steps: n trays, n being greater than 1, said n trays each having two opposite hollow walls; said n trays are joined successively to each other to form n-1 housings respectively between the opposite walls of said n trays, while n-1 filtration chambers are trapped in a sealed manner inside said n-1 housings; said n-1 filtration chambers are connected together and they are supplied with said mixture under pressure when said n trays are compressed axially against each other, said n-1 filtration chambers being intended to retain the solid particles in the form of cakes while that said liquid phase flows out of said filtration chambers. Furthermore, n-1 pairs of electrodes are supplied, and said n-1 pairs of electrodes are respectively installed inside said n-1 housings, so as to be able to induce an electric field through said n-1 filtration filtration chambers. so as to increase the dryness of said cakes.

Thus, a characteristic of the filtration process according to the invention resides in the implementation of an electric field through each of the filtration chambers as will be explained in more detail below.

Other particularities and advantages of the invention will emerge on reading the description given below of a particular embodiment of the invention, given by way of indication but not limitation, with reference to the appended drawings in which:

- Figure 1 is a schematic exploded axial sectional view of a filter press according to the invention;

- Figure 2 is a schematic front view of an element of the filter press shown in Figure 1;

- Figure 2A is a schematic sectional view of a detail of the element shown in Figure 2 along the plane IIA-IIA;

- Figure 2B is a schematic sectional view of another detail of the element shown in Figure 2 along the plane IIB-IIB;

- Figure 2C is a schematic sectional view of yet another detail of the element shown in Figure 2 according to the IIC-IIC plan;

- Figure 3 is a schematic front view of another element of the filter press shown in Figure 1;

- Figure 3A is a schematic sectional view of a detail of the element shown in Figure 3 along the plane IIIA-IIIA;

- Figure 3B is a schematic sectional view of another detail of the element shown in Figure 3 along the plane IIIB-IIIB;

- Figure 3C is a schematic sectional view of yet another detail of the element shown in Figure 3 along the plane 11IC-IIIC;

- Figure 4 is a schematic detail view of two elements illustrated in Figure 1; and,

- Figure 5 is a schematic front view of elements shown in Figure 1.

Figure 1 schematically illustrates a filter press 10 in an axial exploded section and in accordance with a simplified mode of implementation for better understanding. It includes here n = seven internal plates, 12, 14, 16, 18, 20, 22, and 24. Among the internal plates, the first four, 12, 16, 20, 24 are of a first type and they each have two opposite recessed walls 26 ′, 28 ′, while three second recessed walls 14, 18, 22 are of a second type and they each have two other opposite recessed walls 26, 28. The internal plates of the first type are distinguished in particular in that that they each comprise two deformable membranes 29, 31 installed respectively on the two opposite hollow walls 26 ', 28'. The deformable membranes 29, 31 are for example made of an elastomer of the polyurethane type.

We will first describe with reference to Figures 2, 2A, 2B, 2C, the trays of the second type, then the trays of the first type with reference to Figures 3, 3A, 3B, 3C before returning to Figure 1.

Thus, Figure 2 illustrates from the front, a plate of the second type, on the side of one 26 of its two opposite hollow walls 26, 28. The plate defines substantially a regular quadrilateral. Its sides have a length for example equal to 1 m.

The hollow wall 26 comprises a central zone 30 and a peripheral border 32 surrounding the central zone 30. The central zone 30 has a flat bottom 34 substantially octagonal, while the peripheral border 32 is raised relative to the flat bottom 34 so as to form a ledge. The peripheral edge 32 defines a plane substantially parallel to the flat bottom 34. The surface of the flat bottom 34 is then connected to the surface of the peripheral edge 32 by an inclined edge 36 extending around the flat bottom 34.

The tray shown in Figure 2 includes two projecting side ears 38, 40 for suspending it from two parallel bars 42, 44 spaced from one another. One 40 of the lateral ears 38, 40 has a pair of centering lugs 46, 48 straddling one of the two parallel bars 42, 44. The other 38, of the ears, has a single lug of centering 50.

Also, the plate shown in Figure 2 has an upper right corner 52 comprising an injection passageway 54. The latter has an axial circular orifice 56 and a radial groove 58 formed in the peripheral edge 32. The radial groove 58 has a width substantially equal to the diameter of the axial circular orifice 56 and it extends from the latter towards the central zone 30, up to the inclined edge 36. In FIG. 2A is found partially in section the upper right corner 52 of the plate shown in FIG. 2. There are the peripheral edge 32, the axial circular orifice 56, the inclined edge 36 and the flat bottom 34 of the wall 26.

It will be observed that the opposite recessed wall 28 is symmetrical with the recessed wall 26 relative to a mean plane Pm of the plate. It will also be observed that the axial circular orifice 56 crosses the latter right through. Also, the plate represented in FIG. 2 has an opposite radial groove 59, symmetrically opposite to the radial groove 58 relative to the mean plane Pm of the plate and forming part of the injection passageway 54. The plate also has an edge opposite peripheral 33, symmetrically opposite with respect to the mean plane Pm at the peripheral edge 32, an opposite inclined edge 37, symmetrically opposite to the inclined edge 36, and an opposite flat bottom 35, opposite symmetrically to the flat bottom 34.

Returning to FIG. 2, it will be observed that the tray also has an upper left corner 60 and a lower left corner 62. Also, the tray comprises a first upper collection passage path 64 in the upper left corner 60 and a second path lower collection passage 66 in the lower left corner 62.

We find in FIG. 2C, the lower left corner 62 of the tray shown in FIG. 2, partially in section along the plane IIC-IIC and showing in detail the second lower collection passage path 66. There are the opposite peripheral edges 32, 33, the inclined edges 36, 37 and the flat bottoms 34, 35. Also, the second collection passage path 66 has an axial collection part 68 opening into the opposite peripheral edges 32, 33. The second collection passage path 66 also has a radial part 70, which extends in the thickness of the plate along the mean plane Pm. It extends from the axial collection part 68 into which it opens, to a thin zone 72 situated beyond the opposite inclined edges 36, 37, between the two flat bottoms 34, 35. The radial part 70 then has , in the thin zone 72, a plurality of orifices 74 opening both into the two opposite flat bottoms 34, 35.

Also, the first upper collection passage path 64 of the upper left corner 60 of the tray shown in FIG. 2, is identical to the second lower collection passage path 66.

Also, the plate shown in Figure 2 has a lower right corner 76 having a pneumatic axial channel 78 which is found in detail in Figure 2B. This pneumatic axial channel 78 crosses the lower right corner 76 right through and thus opens respectively into the two opposite peripheral edges 32, 33. We will explain its role in the following description. Also, the tray comprises, in the lower right corner 76, an auxiliary lower collection passageway 80 passing axially right through the tray, opening respectively into the opposite peripheral edges 32, 33. We will explain in the following description the role of this auxiliary collection passageway 80.

The plates of the first type will now be described with reference to Figures 3, 3A, 3B and 3C. Given their similarities with the second type trays, similar parts will have identical references with a premium sign: "'".

Thus, Figure 3 illustrates from the front, a tray of the first type, on the side of one 26 'of its two opposite hollow walls 26', 28 '. This plate also defines a regular quadrilateral, having the same dimensions as that of the second type. The hollow wall 26 'includes a central zone 30' and a peripheral edge 32 '. The central zone 30 'has a flat bottom 34' substantially octagonal, while the peripheral edge 32 'is raised relative to the flat bottom 34' forming a rim. The surface of the flat bottom 34 'is connected to the surface of the peripheral edge 32 by a straight edge 36' extending around the flat bottom 34 '.

The tray shown in Figure 3 includes two projecting lateral ears 38 ', 40' for suspending it from the two parallel bars 42, 44 above. One 40 'of the lateral ears 38', 40 'has a pair of centering lugs 46', 48 'straddling one 44' of the two parallel bars 42 ', 44', while the other 38 'of the ears has a single centering lug 50'.

Also, the plate has an upper right corner 52 ′ comprising an injection passage path 54 ′. The latter has an axial circular orifice 56 'and a radial groove 58' formed in the peripheral edge 32 '. The radial groove 58 'has a width close to the diameter of the axial circular orifice 56' and it extends from the latter towards the central zone 30 ', to the right edge 36'.

Figure 3A partially illustrates in section the upper right corner 52 'of the plate shown in Figure 3. There is the peripheral edge 32', the axial circular opening 56 ', the right edge 36' and the flat bottom 34 'of the wall 26 '. There is also the deformable membrane 29 applied against the flat bottom 34 'and which extends to the right edge 36'.

The opposite recessed wall 28 'is symmetrical with the recessed wall 26' with respect to a mean plane P'm of the plate. The axial circular orifice 56 ′ crosses the latter right through. Also, the plate shown in Figure 3 has an opposite radial groove 59 ', symmetrically opposite the radial groove 58' relative to the midplane P'm of the plate and forming part of the injection passageway 54 '. The tray also has an opposite peripheral edge 33 ', symmetrically opposite with respect to the mid-plane P'm to the peripheral edge 32', an opposite straight edge 37 ', symmetrically opposite the inclined edge 36', and an opposite flat bottom 35 ', symmetrically opposite the flat bottom 34'. In addition, in FIG. 3A, we find the opposite deformable membrane 31, opposite to the deformable membrane 29.

Returning to FIG. 3, it will be observed that the plate also has an upper left corner 60 'and a lower left corner 62'. Also, the tray includes another first upper collection passage path 64 'in the upper left corner 60' and another second lower collection passage path 66 'in the lower left corner 62'. The other collection passage paths 64 ′, 66 ′, pass right through the plate, opening respectively into the opposite peripheral edges 32 ′, 33 ′ in a position relative to the plate itself, identical to that in which the paths collection passage 64, 66 pass through the plate of the second type of plate.

The tray shown in Figure 3 has, in addition, a lower right corner 76 'in which is formed another auxiliary collection passage path 80' having an axial auxiliary part 82 and a radial auxiliary part 84 extending in the thickness of the plate, from the axial auxiliary part 82 towards the lower left corner 62. The axial auxiliary part 82 has a relative position relative to the plate identical to that of the auxiliary lower collection passage path 80 of the plate of the second type illustrated on the Figure 2. Also, the radial auxiliary part 84 extends over a length close to the half-length separating the axial auxiliary part 82 from the other second collection passage path 66 'extending in the lower left corner 62' .

The radial auxiliary part 84, which is found seen in section in FIG. 3C, also has another plurality of orifices 74 ′ opening both into the two opposite flat bottoms 34 ′, 35 ′, respectively between the straight edges 36 ', 37' and the edge of the deformable membranes 29, 31.

Also, it will be observed in FIG. 3 and in the upper left corner 60 ′ that another radial auxiliary part 84 ′ extends in the thickness of the tray, from the collection passage path 64 ′ to yet another plurality of orifices 74 ”, opening themselves both into the 2 opposite flat bottoms 34 ', 35'.

Also, the plate shown in Figure 3 has a lower right corner 76 'having another pneumatic axial channel 78' which is found in detail in Figure 3B. This pneumatic axial channel 78 'crosses the lower right corner 76' right through and thus opens respectively into the two opposite peripheral edges 32 ', 33'. In addition, the plate shown in FIG. 3B has a pneumatic radial channel 86 extending along the mean plane P′m, from the other pneumatic axial channel 78 ′ and also opening into the two opposite flat bottoms 34 ′, 35 ′ , under the deformable membranes 29, 31.

With reference to FIG. 1, and on the strength of the teaching of the description of the trays of the first type and of the second type shown in FIGS. 2 and 3, we will describe the arrangement of the first four internal trays, 12, 16, 20 , 24 between which are alternately interposed, the three second internal plates 14, 18, 22. Figure 1 is an exploded figure clearly showing the relative position of the elements of the filter press 10. As will be explained below, the elements are applied against each other for the implementation of the filter press 10.

Each of the internal plates, 12, 14, 16, 18, 20, 22, and 24 is equipped with a pair of fine mesh grids forming an electrode. Thus, each of the first four internal plates, 12, 16, 20, 24, is equipped with a first pair of grids 90, 92 intended to form cathodes from which the electric current comes out as will be explained below, while each of the three second internal plates 14, 18, 22 is equipped with a second pair of grids 94, 96 intended to form anodes from which the electric current enters.

Thus, the grids of the first pairs of grids 90, 92 will come to apply respectively against the deformable membranes 29, 31, of plates of the first type, while the grids of the second pairs of grids 94, 96 will come to apply respectively against the flat bottoms 34, 35 of the trays of the second type.

In addition, between the plates of each of the pairs of contiguous internal plates, 12, 14; 14, 16; 16, 18; 18, 20; 20, 22; 22, 24, two filter cloths 98, 100 are attached to one another and carried between the grids 92, 94; 96, 90 respectively forming anode and cathode.

With reference to FIG. 5, the filter cloths 98, 100 will be described. These filter cloths 98, 100 are identical and they are made from a woven fabric of synthetic fibers. For example, these synthetic fibers are made of polyester, and of the monofilament type. The fibers can also be made of polypropylene or else of polyamide. The textile thus woven constitutes a filter whose mesh opening is variable as a function of the diameter of the fibers and of the weaving; it is for example between 20 pm and 220 pm.

Thus, the filter cloth 98 shown flat in Figure 5 has an edge 102 substantially defining a regular quadrilateral. The sides of the filter cloth 98 have lengths substantially greater than that of the sides of the plates, for example of the order of 1.10 m.

In addition, the filter cloth 98 has a right upper cloth corner 104 in which is formed a circular injection recess 106 whose diameter is close to those of the injection passage paths 54, 54 ′ of the plates of first and of the second type. In addition, the filtration fabric 98 has a neck 108 surrounding the circular injection recess 106. In addition, the filtration fabric 98 has, a top left fabric corner 110, a bottom left fabric corner 112 and a corner of lower right fabric 114 having respectively, an upper left collecting recess 116, a lower left collecting recess 118 and a lower right collecting recess 120. The relative position of the collecting recesses 116, 118, 120, and the recess injection circular 106 is identical to that of the collection passageways 64, 64 ′; 66, 66 '; 80, 80 'of the first and second type trays.

In addition, the filter cloth 98 has a pneumatic channel recess 122 in the position corresponds to that of the pneumatic axial channels 78, 78 'of the first and second type plates.

In this way, as shown in Figure 1, the filter cloths 98, 100 are arranged on each of the opposite hollow walls 26, 28 of the plates 12, 14, 16, 18, 20, 22, and 24 so as to that the collection recesses 116, 118, 120, the circular injection recess 106 and the pneumatic channel recess 122, coincide respectively with the collection passageways 64, 64 '; 66, 66 '; 80, 80 ', the injection passageways 54, 54' and pneumatic axial channels 78, 78 '.

Also, the plates 12, 14, 16, 18, 20, 22, and 24 are then brought into contact with each other and then compressed axially against each other. In this way, the peripheral edges 32, 32 ′ of the plates 12, 14, 16, 18, 20, 22, and 24 come in pairs to compress the pairs of filter cloth 98, 100, in a sealed manner, forming seven minus one , ie six housings 124 in each of which extends a filtration chamber 126, as partially illustrated in FIG. 4.

It will be observed that the axial pressure exerted on the plates 12, 14, 16, 18, 20, 22, and 24 is adapted to ensure the sealing of the filtration chambers 126 around their periphery, but also to ensure their sealing at the level of the paths injection passage 54, 54 ', so that there is continuity between the adjoining filtration chambers 126. At this level, the facing radial grooves 59, 58 ’; 59 ', 58, define conduits between the pairs of filtration cloths 98, 100, extending between the interior of the filtration chambers 126 and the injection passageways 54, 54', while the necks 108 are engaged injection injection paths 54, 54 '.

Also, thanks to the axial compression of the plates 12, 14, 16, 18, 20, 22, and 24, the collection passageways 64, 64 '; 66, 66 '; 80, 80 ', and the pneumatic axial channels 78, 78', respectively define sealed axial conduits extending longitudinally in the filter press 10.

FIG. 4 illustrates in detail the housing 124 formed by two opposite hollow walls 26 ′, 28 of two contiguous plates, and the filtration chamber 126 formed by two filtration fabrics 98, 100, extends inside the housing 124.

Also found in Figure 4, the grid 96 intended to form anode and which extends between the flat bottom 34 of the second type plate and one of the filter cloths 98, and the grid 90 intended to form cathode and which extends between the other of the filter cloths 100 and one of the deformable membranes 29. The grid 96 forming anode and the grid 90 forming cathode are connected respectively, via conductive wires 130, 132 passing through the plates so waterproof, to a DC generator not shown. It will be observed that the other grids 94, 92 respectively forming the anode and cathode of the two contiguous plates are respectively connected together. Also, it is understood that the succession of interior plates makes it possible to form a succession of housings 124 suitable for respectively receiving a filtration chamber 126.

Thus, the plates 12, 14, 16, 18, 20, 22, and 24 shown in Figure 1 are intended to be arranged one against the other successively in pairs as illustrated in Figure 4. In addition, the filter press 10 comprises two end plates 134, 136 each having a single hollow wall 138 of the type of that of the second type of plate illustrated in FIG. 2. According to a particular embodiment of the invention, one of the end plates 134 has a single inlet for a mixture to be filtered situated opposite the injection passageway 54 ′ and a single air inlet facing the other pneumatic axial channel 78 ′, of the first plate of the first type 12. And the other of the end trays 136 have three single collection outlets extending respectively opposite the other collection passage paths 64 ′, 66 ′ and auxiliary 80 ′ of the last first type tray 24.

Also, the two end plates 134, 136 are respectively equipped with grids 96, 94 intended to form anode and filter cloths 98, 100, while the first first type plate 12 and the last first type plate 24 are respectively equipped with grids 90, 92 forming cathode and filter cloths 100, 98.

Consequently, the plates 12, 14, 16, 18, 20, 22, and 24 are compressed axially against one another by applying axial pressure to the terminal plates 134, 136 which themselves make it possible to form housings 124 to inside which filter chambers 126 can extend.

Obviously, the filter press 10 comprises a plurality of plates, the number of which is usually odd and greater than or equal to three and is adapted as a function of the mixture to be filtered.

Thus, the mixture to be filtered, which comprises a liquid phase, generally water, inside which solid particles are in suspension, is injected under pressure through said single inlet of mixture to be filtered. The injection pressure can vary for example between 5 bars and 20 bars. According to a particular mode of implementation, the injection pressure is 15 bars. Also, the mixture to be filtered flows between the plates inside the filtration chambers 126.

Also, in parallel, a potential difference is applied between the grids forming anodes 94, 96 and respectively the grids forming cathode 90, 92 so as to apply an electric field uniformly distributed inside each of the filtration chambers, along lines of field oriented substantially axially. According to a particularly advantageous embodiment, the current density inside the filtration chambers is between 10 A / m ² and 100 A / m ² In this way, the uneasy sludge to be filtered is more easily thanks to the application of an electric field in the filtration chambers.

Thus, the liquid phase migrates more easily inside the solid phase. The solid phase accumulates inside the filtration chambers, while the liquid phase is easily separated therefrom and passes through the filtration cloths 100, 98, in order to then join the plurality of orifices 74, 74 ', then respectively, the first and second collection passageways 64, 64 ', 66, 66', and the auxiliary collection passageways 80, 80 'via the radial auxiliary portions 84, to flow through the only three or four collection outlets from the terminal platform 136.

The potential difference applied between the grids forming anodes 94, 96 and respectively the grids forming cathode 90, 92, is such, that one observes a localized heating around the electrodes and in particular around the anodes 94, 96. Also, in order to dissipate the thermal energy which accumulates around the anodes 94, 96, water under pressure is injected into the first collection passageways 66, 66 'and which will emerge in the second collection passageways 64, 64' . This water, which then flows around the anodes 94, 96, makes it possible not only to dissipate thermal energy, but also to carry with it by suction effect, the liquid phase of the mixture which passes through the filter cloths 100 , 98.

Likewise, it is possible to inject pressurized water through the auxiliary collection passageways 80, 80 ′ so as to be able to dissipate the thermal energy which accumulates around the cathodes 90, 92.

Advantageously, and with the aim of rebalancing the pHs in the vicinity of the electrodes 90, 92, 94, 96, in addition to evacuating thermal energy, the water recovered from the first and second collection passage paths 80, 80 ′ can be reinjected as it is or mixed with water having a suitable pH through the auxiliary collection passageways 66, 66 ', while in a crossed manner, the water recovered from the auxiliary collection passageways 64, 64' are reinjected through the first and second collection passage paths 80, 80 ′.

When the filtration chambers 126 are full, the injection under pressure of the mixture is stopped, and advantageously, air, or water, is injected under pressure through the possible air inlets 78, or water, from the terminal plate 136. The air, or water, flows under pressure between the deformable membranes 29, 31 and respectively the opposite flat bottoms 34 ', 35', of the plates of the first type, and then comes to bulge the deformable membranes 29, 31. Consequently, the latter compress the cakes then formed axially inside the filtration chambers 126.

Then, the end trays 134, 136 and the internal trays 12, 14, 16, 18, 20, 22, and 24, are separated from one another in order to be able to remove cakes 140, which are found schematically illustrated on the Figure 1.

Claims (10)

1. Filter press (10) in order to be able to filter a mixture having a liquid phase and solid particles suspended in said liquid phase, said filter press (10) comprising: - n trays (12, 14, 16, 18, 20, 22, 24) each having two opposite hollow walls (26, 28; 26 ', 28'), said n trays being joined successively to each other to form n -1 housings (124) respectively between the opposite walls (28, 26 '; 28', 26) of said n plates, n being greater than 1; - n-1 filtration chambers (126) intended to be sealed respectively inside said n-1 housings (124) and to be connected together to be supplied with said mixture under pressure when said n trays (12, 14 , 16, 18, 20, 22, 24) are compressed axially against each other, said filtration chambers (126) being intended to retain the solid particles in the form of cakes (140) while said liquid phase flows in outside of said filtration chambers (126); characterized in that it further comprises n-1 pairs of electrodes (92, 94; 96, 90) respectively installed inside said n-1 housings (124), in order to be able to induce an electric field through said n -1 filtration chambers (126) so as to increase the dryness of said cakes. 2. Filter press according to claim 1, characterized in that each of said n-1 filtration chambers (126) comprises two filtration cloths (98, 100) leaning against each other. 3. Filter press according to claim 1 or 2, characterized in that the electrodes of each of said n-1 pairs of electrodes (92, 94; 96, 90) are respectively installed on said facing walls (28 ', 26 ; 28, 26 ') of each of said n-1 housings (124). 4. Filter press according to any one of claims 1 to 3, characterized in that each of said two opposite hollow walls (26, 28; 26 ', 28') comprises a central zone (30; 30 ') having a background (34, 35; 34 ’, 35’) and a peripheral border (32, 33; 32 ’, 33’) raised relative to said bottom surrounding said central area. 5. Filter press according to claim 4, characterized in that each of said n plates (12, 14, 16, 18, 20, 22, 24) comprises at least one injection passage path (54; 54 ') having an axial injection part (56; 56 ') opening into the opposite peripheral edges (32, 33; 32', 33 ') of said two opposite hollow walls. 6. Filter press according to claim 5, characterized in that said at least one injection passage path (54; 54 ') has two opposite grooves (58, 59; 58', 59 ') extending radially in said opposite peripheral edges (32, 33; 32 ', 33') between said axial part and said central zone. 7. Filter press according to any one of claims 4 to 6, characterized in that each of said n plates (12, 14, 16, 18, 20, 22, 24) comprises at least one collection passage path for said liquid phase (64, 66, 80; 64 ', 66', 80 ') having an axial collection part opening into the opposite peripheral edges (32, 33; 32', 33 ') of said two opposite hollow walls. 8. Filter press according to claim 7, characterized in that said at least one collection passage path (64, 66, 80 ') has a radial part (70, 84) extending between said peripheral edges and, from said axial collecting part towards said central zones to open into said bottom of said central zones. 9. Filter press according to any one of claims 1 to 8, characterized in that it further comprises n-1 deformable membranes (29, 31) respectively installed on one of said facing walls (26 '; 28 ') of said n-1 housings (124) in order to be able to compress said n-1 filtration chambers (126). 10. Method for filtering a mixture having a liquid phase and solid particles in suspension in said liquid phase, said filtration process being of the type comprising the following steps: - n trays are provided (12, 14, 16, 18, 20, 22, 24), n being greater than 1, said n trays each having two opposite hollow walls (26, 28; 26 ’, 28’), - said n trays are joined successively to each other to form n-1 housings (124) respectively between the facing walls (28, 26 '; 28', 26) of said n trays, while n-1 chambers are trapped filtration (126) in a sealed manner inside said n-1 housings (124), - said n-1 filtration chambers (126) are connected together and they are supplied with said mixture under pressure when said n plates are compressed axially against each other, said n-1 filtration chambers (126) being intended to retain the solid particles in the form of cakes (140) while said liquid phase flows out of said filtration chambers (126); characterized in that further n-1 pairs of electrodes (92, 94; 96, 90) are provided, and in that said n-1 pairs of electrodes are respectively installed inside said n-1 housings (124), to be able to induce an electric field through said n-1 filtration chambers (126) so as to increase the dryness of said cakes (140).