Membrane device

Abstract

Membrane device comprising a first rod (2) and a strip made of a material semi-permeable to a liquid phase of a fluid and permeable to a vapor phase of the fluid, wherein the strip extends widthwise between a first edge and a second edge, wherein the strip is folded over itself along a crease (3) separating the strip into a first flap (1) and a second flap (4), wherein the first rod (2) is disposed between the first flap (1) and the second flap (4), wherein the first flap (1) is fixed flat on the first rod (2) and wherein the second flap (4) is fixed flat on the first rod (2), the first rod being separated from the crease. Figure 1.

Description

Title of the invention: Membrane device TECHNICAL FIELD OF THE INVENTION

[0001] The present application relates to the general field of flexible membranes, generally porous, semi-permeable in the sense of being highly permeable to a vapor phase of a natural element such as water and weakly permeable to a liquid phase of the same element, more or less trapped in the pores and which are used in industrial heat and mass exchangers or membrane exchangers.

[0002] More particularly, the present application relates to membrane exchangers using a nozzle, separated from vapor phase condensers by a pair of membranes which must not come into contact with each other or with the condensers and must essentially remain flat, i.e. without folds or undulations of surface or without contact with other neighboring elements in the membrane exchangers to which they belong. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] To avoid deformations of a membrane in an industrial membrane exchanger using a semi-permeable membrane, this membrane is conventionally mounted on a four-sided frame, considered mechanically necessary, and stretched over this frame.

[0004] The membrane is stretched so as to be free of surface folds and to compensate for deformations caused by variations in membrane temperature and pressure on either side of the membrane, preventing the membrane from relaxing and contaminating a purified distillate by contact. Indeed, for example, a porous membrane in contact with a distillate, which contains in its pores possibly partially purified retentate or permeate, and which comes into contact with a distillate present on a condenser or condensate, contaminates the distillate with the contents of the pores.

[0005] A membrane adapted to a membrane exchanger must therefore be free of surface folds or creases or undulations in all circumstances, to guarantee the production of ultrapure liquid and it must finally be sufficiently taut, i.e. stretched flat, so as not to deform enough to touch the elements of the exchanger which are adjacent to it.

[0006] This pollution problem is inherent in the use of flexible, therefore thin, membranes, because they are also deformable in the absence of tension or when they are poorly tensioned or relaxed.

[0007] The greater the number of membranes on a frame, the more pronounced the problem becomes. To keep two membranes flat and parallel, one can either stretch the membranes on each side of the frame or stack two frames one on top of the other with each one a single membrane without reducing the risks of folds on the membranes and the associated risks of pollution.

[0008] Moreover, for industrial heat exchangers possibly including many plastic parts, especially frames, these are more easily deformed, particularly during temperature variations, and putting membranes under tension without deforming these frames is a difficult problem.

[0009] This problem is made even more acute in the prior art by the need to increase the dimensions of the membranes in order to increase the efficiency of the heat exchangers by increasing the exchange surface area. For large membranes, typically exceeding one meter in height, the risk of surface folds appearing during operation, rendering them unsuitable for use in the production of ultrapure liquids, is very high.

[0010] Furthermore, it is also not possible to increase the tension on the membranes indefinitely without risking tearing or fatigue, thereby reducing their lifespan.

[0011] Consequently, in the prior art, frames of more than one meter in length seem technically inconceivable in a membrane exchanger, whereas they are desirable to increase the performance of such an exchanger in the production of an ultrapure liquid phase from a natural liquid phase such as seawater. Summary of the invention

[0012] One aspect of the invention relates to a membrane device comprising a first rod and a strip made of a material semi-permeable to a liquid phase of a fluid and permeable to a vapor phase of the fluid, in which the strip extends in width between a first edge and a second edge, in which the strip is folded over itself along a crease separating the strip into a first flap and a second flap, in which the first rod is disposed between the first flap and the second flap, in which the first flap is fixed flat on the first rod and in which the second flap is fixed flat on the first rod, the first rod being separated from the crease.

[0013] In one or more embodiments, the fold is parallel to the first stem.

[0014] In one or more embodiments, the fold is perpendicular to the first edge.

[0015] In one or more embodiments, the fluid is seawater.

[0016] In one or more embodiments, the first stem is in the shape of parallelepiped extending in thickness between a first face fixed to the first flap and a second face fixed to the second flap.

[0017] Another aspect of the invention relates to a membrane exchanger comprising at least one membrane device as defined above.

[0018] In one or more embodiments, the membrane exchanger is a device for purifying a fluid in the liquid phase comprising:

[0019] - a nozzle for distributing said fluid in the form of drops into an atmosphere;

[0020] - a condenser wall; and

[0021] a membrane device as defined above, in which the nozzle is located between the two flaps of the membrane device;

[0022] in which the condenser wall and a flap among the first flap and the second flap of the membrane device delimit a first space, the first flap and the second flap of the membrane device delimit a space comprising the nozzle, and in which the condenser includes a refrigerant circulation circuit, the condenser wall separating the refrigerant circulation circuit and said first space, the condenser wall being impermeable to the fluid in liquid and gaseous phases and being configured to condense the gaseous phase fluid passed through a flap of the membrane device into a liquid phase of purified fluid.

[0023] In one or more embodiments, the rod is called the first rod, the membrane exchanger further comprising a second rod positioned at the fold of the membrane device and a tensioning system connected to the second rod, the tensioning system being configured to apply a tension at the fold in an opposite direction to the first rod.

[0024] Another aspect of the invention relates to a method for obtaining a membrane device as defined above, comprising:

[0025] - fold the membrane strip back on itself to form the first flap, the fold and the second flap;

[0026] - insert the rod between the first flap and the second flap;

[0027] - fix the first flap flat onto the stem; and

[0028] - fix the second flap flat on the stem.

[0029] In one or more embodiments, the stem is parallel to the fold.

[0030] In one or more embodiments, the first edge is parallel to the second edge and the membrane is folded over itself by overlapping the first edge on itself and overlapping the second edge on itself to obtain a fold perpendicular to the first edge.

[0031] Another aspect of the invention relates to a method of using a membrane device as defined above, in which the rod is called the first rod, the method comprising:

[0032] - insert a second rod between the fold and the first rod;

[0033] - press the second rod against the fold to flatten the membrane and obtain a first flap parallel to the second flap. BRIEF DESCRIPTION OF THE FIGURES

[0034] The [Fig. 1] describes a membrane in the form of a strip with parallel edges, folded over itself along a fold separating a first flap and a second flap on the membrane on either side of the fold, a first rod is inserted between the flaps and the flaps are fixed flat, i.e. without surface folds on this first rod which is rectilinear or straight or extends lengthwise along a straight line.

[0035] Figure 2 shows the assembly of the two flaps mounted on a first and a second rod, inside a membrane heat exchanger. The two flaps are initially folded without any particular shape, then one of the rods is inserted between the condensers and they are immobilized in a plane by means of springs.

[0036] Fig. 3 shows the shimming outside their plane of stretched flaps thanks to the invention and which are held in place in an exchanger by a comb shimming the different elements of the exchanger (membrane and condensers) in relative position.

[0037] Figure 4 represents a fluid purification device according to an embodiment of the invention. DETAILED DESCRIPTION

[0038] One aspect of the invention relates to a membrane device for use in a membrane system (also called a "membrane exchanger"), such as a heat exchanger or a fluid purification system, or any other system using two membranes positioned opposite each other, each membrane being permeable to a fluid in the gaseous phase and impermeable (or semi-permeable) to the fluid in the liquid phase. The membrane device according to the present invention can be used to replace a pair of conventional membranes in such systems. In particular, the membrane device according to the invention can be used for a fluid purification system, for example, for seawater, as shown in [Fig. 4].

[0039] A membrane device according to one embodiment is detailed with reference to [Fig. 1]. This membrane device 50 is made from a membrane strip for purifying a fluid or any other device using a membrane permeable to a fluid in the gaseous phase (i.e., it is permeable to the vapor of this fluid) and semi-permeable to the fluid in the liquid phase.

[0040] It is understood that the term "semi-permeable to fluid in the liquid phase" corresponds, in the context of the invention, to a property of the membrane according to which liquid droplets do not pass through the membrane when these droplets come into contact with the membrane when the latter is arranged in a substantially perpendicular to the ground. However, the membrane can become permeable to liquid when subjected to significant liquid pressure (for example, sending a jet of liquid against the membrane). For example, a non-absorbent membrane for liquid droplets, a membrane made of a water-repellent material or coated with a water-repellent material, which do not allow liquid droplets to pass through, falls within the scope of the present invention.

[0041] The membrane strip can be obtained by cutting a length from a roll of the membrane. This membrane strip can thus comprise two parallel edges of the membrane. The parallel strip is then folded back on itself (for example, by folding each edge back on itself) so as to form a first flap 1 and a second flap 4 separated by a fold 3.

[0042] A straight rod 2 is introduced between the two flaps 1, 4. The term "rod" is understood to mean any element having a dimension, along a principal direction, that is significantly greater (for example, at least 10 times greater) than its dimensions in other directions. "Straight" means that the rod has a straight shape along its principal direction. For example, the rod 2 may be positioned between the two flaps so that its principal direction is substantially perpendicular to the edges of the membrane strip. "Substantially perpendicular" means that the angle formed between the edges and the principal direction is between 80° and 100°. In some embodiments, the rod may be made of a material sufficiently rigid so as not to deform (in particular, not to bend or curve) when a force is applied at the fold 3 to tension the two flaps of the membrane device 50.For example, the stem could be a rectangular plastic plate.

[0043] In embodiments, the rod advantageously has a thickness e between 5 and 20 mm (cf. [Fig.1]).

[0044] The stem 2 is advantageously positioned at a distance from the fold 3, the edges (folded down), the stem 2 and the fold 3 forming a substantially rectangular space which defines a membrane zone (or "exchange zone", i.e. a zone in which exchanges can take place when the membrane device 50 is used in a membrane exchange system).

[0045] Once positioned between the two flaps 1, 4, the rod 2 is glued to the first flap 1 so that this first flap 1 is glued without any surface creases relative to the rod (i.e., there are no creases along the glued edge). The rod is also glued to the second flap 4 in the same way. For example, the rod can be glued to the first flap 1 and the second flap 4 "flat," that is, by placing the membrane strip and the rod 2 on a flat surface substantially parallel to the ground, so as to minimize glued creases. Any other fastening method than gluing is usable for the invention.

[0046] This gives us a membrane device 50 with parallel edges comprising two flaps (therefore two membrane flaps) fixed to the rod 2.

[0047] As mentioned previously, the membrane device 50 according to the invention can be used in a membrane system, such as a heat and / or mass exchanger, to replace two "simple" membranes (i.e., each consisting of a single flap) positioned opposite each other, for example, positioned between two condensers. In such systems, it can be difficult to obtain a sufficiently taut membrane that does not exhibit any waviness, folds, or waves on its surface. This problem can be overcome by means of the membrane element of the invention.

[0048] Indeed, the membrane device 50 of the invention can be used to replace two membranes of the system, and a second rod can be inserted at the fold to "stretch" the two flaps 1, 4 of the membrane device 50, so as to remove as much as possible the folds and undulations of the flaps of the membrane device 50 and to form two substantially parallel sheets of membranes positioned opposite each other.

[0049] The membrane device can, for example, be inserted between two condensers, so as to cross the condenser zone.

[0050] Then a second rod can be inserted between the flaps of the membrane device at the fold. According to some embodiments, a stress can be applied to the second rod outwards (i.e., in a direction opposite to the first rod 2, along a direction perpendicular to the fold 3). In other embodiments, equal and opposite tensile stresses can be applied to the two rods to tighten the two flaps of the membrane device.

[0051] The second rod is a straight rod, which may or may not be identical to the first rod. The second rod may have the same thickness as the first rod, to keep the two flaps parallel or substantially parallel.

[0052] The shape of the fold being materialized by the second rod, the adjustment of the fold will be equivalent to that of this second rod pressed on the fold, as soon as the second rod puts the flaps of the membrane device under tension.

[0053] This observation can be used in an embodiment of the fold adjustment during the mounting of the membrane device on this first rod. In this preferred method, a second rod of the same thickness as the first rod is inserted between the flaps, immobilized, and serves as a mechanical reference by pressing the fold against this second rod. The first flap is then fixed flat on the first rod without tension on the membrane device, and tension is applied to the membrane, which forces it onto the second rod. Then, all the folds on the membrane device are eliminated by adjustments, and the second flap, which is then necessarily fixed flat, is attached. There are no surface creases on the stem because the membrane device is completely crease-free across its entire surface. The applied tension can be chosen as the minimum tension that prevents creases on the membrane, given the selected settings.

[0054] To apply the equal and opposite or symmetrical constraints in the plane of the flaps, mentioned above, it is possible to use springs arranged between a frame that is more rigid than the existing rods and these rods. Advantageously, these springs can be adjustable to maintain the tension of the flaps.

[0055] To apply these equal and opposite or symmetrical constraints outside the plane of the membrane, it is possible to use shims which may have the form of combs that can accommodate the rods to immobilize them in a direction perpendicular to the flaps, as shown in [Fig.3] described in detail below.

[0056] The invention is capable of industrial application in large-scale heat and material exchangers requiring several semi-permeable flexible membranes that must remain parallel to each other.

[0057] The invention is particularly suited to the realization of a compact, lightweight and large-dimension membrane exchanger for each membrane as well as using several membranes for the industrial production of ultrapure liquids.

[0058] Throughout the application, a fold or crease is understood to mean a deformation zone of a surface resulting from a folding of the surface.

[0059] Throughout this application, a fold separating two flaps is understood to be parallel to a straight element such as a rod if the line furthest from the rod drawn on the fold is parallel to the straight element. The fold physically reduces to this line or fold axis when forces such as pinching are symmetrically applied to the flaps to bring them together and into contact. "Parallel" is always understood to mean "substantially parallel," meaning that a few degrees of difference between the directions (for example, less than 5° or less than 10°) is permissible.

[0060] Equivalently, it is understood that a straight element in length conforming to the shape of the fold, in mechanical contact with it, materializes a direction parallel to the straight fold and that this direction tends towards the straight fold when the section of the straight element perpendicular to its length decreases.

[0061] It is noted that folding a membrane by marking its crease is also a way of creating a straight fold, but with a risk of weakening the membrane strip at the fold. Supporting a second rod on the fold area allows the fold to be oriented relative to the first rod, without weakening the membrane strip at the fold.

[0062] It is understood that any means of fixing a rod to the membrane other than gluing, such as screwing, is usable for the present application.

[0063] One aspect of the invention relates to a system for purifying a fluid in liquid phase such as that shown in [Fig.4].

[0064] The system of [Fig. 4] comprises a plurality of membrane devices 50 permeable to the fluid in the gaseous phase, and semi-permeable to the fluid in the liquid phase. More specifically, the membrane devices 50 are impermeable to the fluid in the liquid phase when the latter is, for example, projected against the membrane devices 50 in the form of droplets, the aim being that, in the context of the invention, only gaseous particles of the liquid can pass through the membrane devices 50. The membrane devices 50 are, for example, membrane devices similar to those of [Fig. 1].

[0065] The system also includes a plurality of condensers (or cold traps) 90. "Condenser" is understood to mean a device configured to condense (or liquefy) vapor. For example, each condenser may be a flat-plate condenser comprising two walls 90a, 90b between which is a refrigerant circulation circuit. The walls 90a, 90b of the condenser 90 are advantageously impermeable to fluids (in both liquid and gaseous phases).

[0066] The system further includes nozzles 30 for distributing a fluid in the form of droplets between the two flaps 1,4 of the membrane devices 50. Thus, each membrane device 50 receives, between its two flaps 1,4, droplets distributed by a respective nozzle.

[0067] The flaps 1, 4 of the membrane devices 50 do not allow droplets of the liquid dispensed by the nozzles 30 to pass through. For example, the membrane devices 50 can be impermeable to liquid droplets. The membrane devices 50 can, for example, be made from membranes of one or more of the following materials: Teflon or PTFE, Polyvinyldiene Fluoride or PVDF, Polypropylene or PP, and Polyethylene or PE. The pore thickness of the membrane devices 50 can be determined by routine testing by a person skilled in the art, and in particular, pore sizes ranging from 60 micrometers to 60 nanometers can be used. In some embodiments, the membrane devices 50 can be made of a fabric coated with a treatment to make it impermeable.

[0068] The material used to make a wall of a condenser or cold trap can be a metal or a heat-conducting material. Stainless steel, for example, or a plastic, can be used, particularly if the cold liquid circulating in the condenser is salt water or corrosive water.

[0069] Referring again to [Fig.4], membrane devices 50 and condensers 90 are arranged alternately, so that exactly one membrane device 50 is arranged between two condensers 90.

[0070] A membrane device 50 disposed between two consecutive condensers 90 defines a space 40 between its two flaps 1, 4. This space is surmounted by a nozzle 30 configured to distribute a fluid in the liquid phase in the form of drops or droplets. This space constitutes a "first fluidic channel" 40 through which the fluid distributed by the nozzle 30 flows. "Fluidic channel" is understood to mean a volume through which a fluid can flow or circulate, in liquid or gaseous phase. A fluidic channel can advantageously be delimited by two separators (for example, flaps of a membrane device 50 and / or walls of condensers 90), which makes it possible to maximize the heat exchange or mass exchange surfaces, such as for vapor flow.

[0071] The space 130 between a condenser 90 and the flap of the membrane device 50 closest to the condenser 90 is called the "second fluidic channel" 130. Each second fluidic channel 130 may include a gutter 110 or any other means of recovering a liquid formed by condensation on the condenser 90. The gutter 110 may be connected to a purified or pure water collector 120.

[0072] Thus, in [Fig.4], the channel 40 and the condenser 90 are separated by a small tank or gutter 110 allowing water droplets to be collected as liquid water from the surface of the wall 90a, 90b of the condenser 90. The first channel 40, the nozzle 30, the gutter 110 and the condenser 90 form a periodic pattern repeated in [Fig.4], between a hot water distributor 20 and a hot water collector 60 connected via the channel 40 containing the nozzle 30 and between a cold water distributor 80 and a cold water collector 100 connected via the condenser 90.

[0073] One aspect of the invention can be implemented provided that the device comprises a nozzle 30, a membrane device 50 and a condenser 90, the membrane device 50 being located between the nozzle 30 and the condenser 90. Thus, the invention is not limited to a plurality of nozzles 30, condensers 90 and membrane devices 50. When the device comprises a plurality of these elements, the volume of purified liquid collected is greater, since purified liquid can be collected in parallel in several channels each bordered by a membrane device 50 and a wall 90a, 90b of condenser 90, for example via several gutters such as the gutter 110.

[0074] Fig. 4 thus shows a hot water supply 10 connected, in the fluidic sense, via a hot water distributor 20 to the nozzle 30 disposed internally to the membrane of the channel 40 and a hot water collector 60 extending the channel 40.

[0075] Fig. 4 also shows a cold water supply 70 connected to the condenser 90 via a cold water distributor 80 which is connected, in the fluidic direction, to a cold water collector 100 via the condenser 90.

[0076] In [Fig. 4], the membrane devices 50 and the walls 90a, 90b of the condensers 90 are vertical and parallel surfaces. It is understood that the degree of parallelism of these elements may, without departing from the scope of this application, be imperfect. In particular, it is essential that a fluid in the vapor phase be able to reach a wall of the condenser 90 via the channel 40. The verticality of the membrane devices 50 and the walls 90a, 90b of the condensers 90 are therefore to be understood in this application as a characteristic enabling the maximization of vapor-to-liquid conversion between the interior of the membrane device 50 of the first channel 40 and the surface of the wall 90a, 90b of the condenser 90, while facilitating the collection of condensate by the gutter and minimizing the overall size of the device.From this point of view, the "vertical" characteristic, in the geometric sense, can be understood in the context of the present invention and in all its embodiments as forming an angle, for example, between 70° and 110° with respect to the ground.

[0077] According to one aspect of the invention, a hot, unpurified liquid (the liquid may be a mixture, for example, of water and minerals or water and salt or solutes) is introduced by a feed 10, then distributed by a hot liquid distributor 20 to nozzles 30 which disperse it vertically in the form of droplets inside the channels 40. For example, the hot, unpurified liquid may be water from a water reservoir, for example a sea or a lake or a wastewater reservoir, possibly heated to a first temperature referred to as "hot".

[0078] A second liquid, called refrigerant liquid, which is colder than the hot liquid, is introduced by a feed 70, then distributed by a cold liquid distributor 80 which distributes it into the condensers 90 arranged in parallel on the [Fig.4],

[0079] By "hot liquid" is meant a liquid having a temperature higher than the maximum temperature of the refrigerant circulating in the condenser 90. For example, the difference between the temperature of the hot liquid (when dispensed as droplets from the nozzles 30) and the maximum temperature of the refrigerant circulating in the condenser 90 may be greater than 30°C. For example, the hot liquid may be dispensed as droplets at a temperature between 60°C and 90°C, and the refrigerant may have a temperature between 10°C and 30°C. Of course, the preceding temperatures are given by way of example, and other temperatures or temperature differences may be used.

[0080] After being dispensed as droplets by the nozzle 30, the hot, unpurified liquid flows through the channel 40 delimited by two flaps 1, 4 of a membrane device 50, and a portion of this hot, unpurified liquid passes, as vapor of purified fluid, through the flaps of the membrane device 50. For example, if the hot, unpurified liquid is salt water, a portion of this liquid passes in the form of pure water vapor and through the flaps of the membrane device 50. What remains in the channel 40 delimited by the two membrane devices 50 is liquid that is even less purified (i.e. more concentrated for at least one of its components, for example water with an even higher salt content, since some of the pure water has evaporated) and colder than at the nozzle outlet 30. This liquid, which is saltier and less hot than at the nozzle outlet, can then be collected in a collector 60.

[0081] Indeed, the role of the membrane device 50 is to prevent the liquid distributed as droplets in the channel 40 from passing partially or totally into the zone 130 delimited by a condenser 90 and a flap of the membrane device 50. Only vapor from the liquid can pass through, thus preventing any contact between the hot liquid in the channel 40 and the vapor condensates formed in the zone 130 on the wall of the condenser 90. When a temperature difference is created between the two sides of the membrane device 50, a partial pressure difference of vapor appears, which drives the process. This causes the liquid to evaporate from the surface of the liquid on the hot side, generating vapor that passes through the membrane device 50 and condenses on the colder side where the condenser 90 is located.

[0082] The space between a condenser 90 and a flap of the membrane device 50 forms a channel through which the vapor from the hot liquid exiting the nozzle 30 and passing through the flap of the membrane device 50 diffuses. The role of the condensers 90 is to condense this vapor on one of their walls 90a, 90b to form purified liquid. This purified liquid is cooler than the vapor from which it originates, while conversely, the refrigerant liquid heats up through contact—via the wall 90a, 90b of the condenser 90—with the warmer vapor.

[0083] The refrigerant liquid can be collected at the outlet of the condenser circulation circuit 90 in a cold liquid collector 100, at a temperature higher than that which it had at the inlet of the condenser circulation circuit 90.

[0084] The condensate (purified water, for example) slides down the wall of the condenser 90 and can be collected in the gutter 110 placed, for example, on the wall (several gutters along the height of the condenser 90 can also be provided). The condensate can then be conveyed laterally to be collected in a pure water tank or collector 120.

[0085] According to alternative modes, the gutter or gutters 110 can either be brought to the condensers by mechanical fixing of the material composing this gutter or these gutters, or delimited by the external shape of the condenser or condensers by molding, that is to say delimited by the wall of a condenser, i.e. by the shape of its external surface on which condensation is obtained.

[0086] It is noted that in the example of [Fig. 4], the elements of the device are arranged in the following order, in a direction parallel to the membrane devices 50 and oriented from the cold water manifold 100 and the refrigerant distributor 80: the cold water manifold 100, the hot water distributor 20, the hot water manifold 60, and the refrigerant distributor 80. Such an arrangement allows for reverse or counter-current circulation of the liquids in the channel 40 and the refrigerant circulation circuit in the condenser 90. This counter-current circulation advantageously allows for particularly efficient heat exchange between the hot droplets produced by the nozzle 30 and the cold liquid via the membrane device 50 and the wall 90a, 90b of the condenser 90.

[0087] Other configurations are possible, and according to an alternative embodiment of the invention, the elements of the device can be arranged in the following order, in the direction parallel to the membrane devices 50 and oriented from the cold water collector 100 and the refrigerant distributor 80: the cold water collector 100, the hot water collector 60, the hot water distributor 20 and the refrigerant distributor 80. In this case, the circulation of the liquids in the channel 40 and the refrigerant circulation circuit in the condenser 90 is carried out in the same direction, and the invention is still functional, even if the heat exchanges are less efficient than in embodiments where the circulation of the liquids is in the opposite direction.

[0088] As mentioned above, the invention can be implemented by means of a supply 10 of hot water or hot fluid at a first temperature, distributed in the form of drops by a nozzle 30 and creating a vapor of the fluid (purified) and drops of the fluid (even less pure than the hot fluid distributed by the nozzle 30), the vapor of the fluid passing through the vapor-permeable and drop-impermeable membrane device 50, to reach a wall 90a, 90b impermeable to the fluid, the wall 90a, 90b being supplied with a refrigerant fluid via a cold water supply 70, the refrigerant fluid being injected between the walls of the condenser 90 at a second temperature lower than the first temperature. Thus, condensation of the fluid occurs into purified water droplets on a surface of the wall 90a, 90b, in contact with which flows cold water or a purified cold fluid at a temperature lower than the first temperature.

[0089] The invention can be used, for example, for membrane heat exchangers using two parallel semi-permeable membranes, opposite which a nozzle emits droplets of a liquid into air at atmospheric pressure, each membrane also being opposite a vapor condenser separated from each membrane by air at the same atmospheric pressure. It is It is then possible to replace the membranes of such an exchanger with membrane devices according to the invention.

[0090] For such an application, a minimum tension allowing compensation of mechanical deformations or variations in rigidity due to temperature differences of the membranes or of the structure of the exchangers is sufficient to ensure the absence of surface folds on the membranes and an absence of contact of the membranes with each other or with a condenser or cold wall.

[0091] In other configurations of membrane exchangers in which the membranes are subjected to hydraulic pressure imposed by a pump on one side and to atmospheric pressure on the other, part of the overpressure applied to the membrane via the devices of the invention to keep it flat can also be used to compensate for deformations of the membranes caused by the pressure difference on either side of the membrane, in order to prevent contact between the membranes or between the membranes and other elements such as a condenser or cold wall.

[0092] In all cases of use of the invention within a membrane exchanger, the invention makes it possible to achieve, by adjustment during the assembly of the exchanger, a configuration of the membrane device in which all the flaps are taut without surface folds and are therefore flat, as during the assembly of the membrane device.

[0093] Advantageously, the first stem and the fold can extend in parallel directions, to allow simplified adjustments to remove folds on the flaps of the membrane device during its assembly.

[0094] Advantageously, the first stem or fold can extend in directions perpendicular to the edges of the parallel-edged strip used to form the membrane device, to simplify adjustments.

[0095] The desalination of seawater with large-dimension membranes or the purification of any liquid with a maximum efficiency-to-size ratio is permitted for membrane exchangers using the invention.

[0096] Furthermore, the dismantling of torn or worn membranes is made possible by the invention by carrying out the reverse operations of those carried out for assembly in an exchanger, which facilitates maintenance of exchangers using the invention.

[0097] Many embodiments using straight rods of any given invariant section along an axis or using different materials of variable rigidity are conceivable for the invention without departing from its teaching.

[0098] The invention is particularly suited to the production of exchangers using larger membranes exceeding one meter, such as two meters, and ensuring their operation with flat membranes in all circumstances provided for in a specification.

[0099] In all embodiments of the invention, plastic rods can be used to minimize the weight of the membrane device.

[0100] The invention thus makes it easy to obtain a taut membrane surface without any fold or undulation, and also makes it possible to obtain a plurality of membrane surfaces arranged opposite each other without any surface fold on any of these surfaces.

[0101] In certain embodiments, the first rod may be made of a deformable material. Indeed, adjusting the bend and the first rod to its shape during assembly ensures that restoring the same shape to this first rod and the bend in an industrial environment will achieve this result. For example, inserting a second rod, even a deformable one, between the first rod and the bend, in contact with the bend, and applying first mechanical means for adjusting the shape of the first rod and second means for adjusting the shape of the second rod relative to the first rod or to a common reference with the first rod, may be implemented to obtain the result of the invention.

[0102] It is observed that the element according to the invention can be inserted between two condensers of a membrane exchanger, by sliding the membrane between the condensers without passing the first rod between the condensers, which facilitates and secures the assembly and possible disassembly of the element according to the invention in the membrane exchanger.

[0103] Any membrane, particularly a flexible one, possessing the required permeability and semi-permeability properties can be used to obtain a membrane device according to the invention. Depending on the rigidity of the membrane, the thickness between the flaps at the fold can vary without being reduced to a folding axis; the fold will then be taken, for the purposes of adjusting the stem, as the line drawn on the fold that is furthest from the flaps.

[0104] The presence of the invention may be established in an element comprising a first rod connected on both sides to a strip, banner or streamer of a semi-permeable membrane, folded over itself along a fold and comprising a free space between the fold and the first rod, by positioning this first rod and then introducing a second rod, for example identical to the first rod, into the free space between the first rod and the fold and verifying that the surface of the membrane is free of folds everywhere in the presence of this second rod.

[0105] The principle of the invention is particularly applicable in membrane heat exchangers where the hot fluid is sprayed by a nozzle into several droplets, promoting the evaporation of vapor from the hot liquid. This vapor, passing through the membrane, condenses on the wall of a condenser. The efficiency of a membrane heat exchanger is maximized by the proximity between the condensers and the membranes and by the large dimensions of the membrane.

[0106] This proximity / density complicates the installation of a large, thin frame, whose membranes must be taut and without risk of contact between them or with the condensers.

[0107] The invention allows the production of a membrane exchanger without risk of folds and contact of the membrane by the following steps:

[0108] - Insert the membrane device between two condensers of the heat exchanger membranous;

[0109] - Pass the first rod through both sides of a frame of the heat exchanger membranous;

[0110] - Position the second rod on the first end of the frame and fix it;

[0111] - Position the 1st rod on the second end of the frame;

[0112] - Stretch the flaps by moving the first and second stems away from each other to The membrane device must be restored to its original shape upon assembly (i.e., with both flaps stretched flat, without creases or ripples). This tension can be applied at several points along its height using an adjustable system. This adjustable system can be a spring / threaded rod combination that allows for spring tension adjustment.

[0113] For example, with reference to [Fig. 2], the membrane device is first inserted into a membrane system, so that the first rod 2 and the second rod 22 are brought together (a). Then, the first rod 2 is moved away from the second rod 22 by unfolding the flaps 1, 4 of the membrane device to a second position (b). Finally, the first rod 2 and the second rod 22 are pulled by a tensioning system (here, at least one spring 23) to bring the membrane device into a flat position (c).

[0114] The longitudinal tension is associated with a lateral physical separation (in the form of a comb) to maintain the planned geometric spacings between the condensers and the frames.

[0115] For example, with reference to [Fig.3], a condenser 31 and a membrane frame receiving a membrane device 50 flat in a plane are held apart by a comb 33 alternately receiving and blocking these condensers and frames in a plane perpendicular to the condensers and the membrane frames.

[0116] Throughout the application, a strip of a semi-permeable membrane adapted to the invention will preferably have parallel edges to facilitate its winding into a roll, although the invention also applies to a strip with non-parallel edges mounted flat on a rod.

[0117] It will be understood throughout the application that the liquid phase of a natural element is synonymous with the liquid phase of a fluid.

[0118] It is understood throughout the application that if a semi-permeable membrane has two flaps separated by a fold, attaching a rod to one of the flaps prevents the rod from coming into contact with the fold, these elements being distinct. In all embodiments of the invention, the greatest possible distance will be left between the rod and the fold to allow exchanges via the semi-permeable membrane and to enable this membrane to perform its function.

[0119] It is understood throughout the application that a flat attachment on a material element such as a rod of a semi-permeable membrane means without surface folds for the membrane or with a smooth surface of this membrane.

Claims

1.

2.

3.

4.

5.

6. Demands Membrane device comprising a first rod (2) and a strip made of a material semi-permeable to a liquid phase of a fluid and permeable to a vapor phase of the fluid, in which the strip extends in width between a first edge and a second edge, in which the strip is folded over itself along a fold (3) separating the strip into a first flap (1) and a second flap (4), in which the first rod (2) is arranged between the first flap (1) and the second flap (4), in which the first flap (1) is fixed flat on the first rod (2) and in which the second flap (4) is fixed flat on the first rod (2), the first rod being separated from the fold. Membrane device according to claim 1, wherein the fold (3) is parallel to the first rod (2). Membrane device according to any one of claims 1 to 2, wherein the fold is perpendicular to the first edge. Membrane device according to any one of claims 1 to 3, wherein the first rod is in the form of a parallelepiped extending in thickness between a first face fixed to the first flap and a second face fixed to the second flap. Membrane exchanger comprising at least one membrane device according to any one of claims 1 to 4. Membrane exchanger according to the preceding claim, wherein the exchanger is a device for purifying a fluid in the liquid phase comprising: - a nozzle (30) for distributing said fluid in the form of drops into an atmosphere; - a wall (90a, 90b) of a condenser (90); and - a membrane device according to any one of claims 1 to 4, in which the nozzle (30) is located between the two flaps of the membrane device; in which the condenser wall (90) and a flap between the first flap and the second flap of the membrane device (50) delimit a first space (130), the first flap and the second flap of the membrane device delimit a space (40) including the nozzle (30), and in which the condenser (90) includes a refrigerant circulation circuit, the condenser wall (90) separating the refrigerant circulation circuit and said first space (130), the condenser wall (90) being impermeable to the fluid in liquid and gaseous phases and being configured to condense the gaseous phase fluid passed through a flap of the membrane device into a liquid phase of purified fluid.

7. Membrane exchanger according to the preceding claim, wherein the rod is called the first rod, the membrane exchanger further comprising a second rod positioned at the fold of the membrane device and a tensioning system connected to the second rod, the tensioning system being configured to apply tension at the fold in an opposite direction to the first rod.

8. A method for obtaining a membrane device according to any one of claims 1 to 4, comprising: - folding the membrane strip over itself to form the first flap, the fold and the second flap; - inserting the rod between the first flap and the second flap; - fixing the first flap flat on the rod; and - fixing the second flap flat on the rod.

9. Method according to claim 8, wherein the stem is parallel to the fold.

10. A method according to claim 8 or 9, wherein the first edge is parallel to the second edge and the membrane is folded over itself by overlapping the first edge over itself and overlapping the second edge over itself to obtain a fold perpendicular to the first edge.

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