METHOD AND DEVICE FOR DESALTING SOLUTIONS

Description

AREA OF INVENTION

[0001] The present invention relates to a method for desalting a suspension and to a device for use with such a method. STATE OF THE ART

[0002] Membrane distillation devices and processes with coupled crystallization are already well known in the prior art.

[0003] In the membrane distillation process, vapor, which is produced by heating a liquid in a pipe, is separated from the liquid by using a pipe designed as a gas-permeable membrane, so that the gaseous components can pass through the membrane, but not the liquid components.

[0004] The crystallization process is also well known in the prior art. A salt-containing solution in the saturation or supersaturation range crystallizes, i.e., .The salts present are no longer merely dissolved in the solution, but form solid crystals. The crystallization process is facilitated or accelerated by the addition of crystallization nuclei.

[0005] KR 2016 / 0149545 discloses a method and a device in which a solution is first heated in a container and the solvent vapor is then removed in a separate container using a membrane. The concentrated solution is then crystallized.

[0006] US 2017 / 0096355 A1 also discloses a method and apparatus in which distillation and crystallization are carried out in separate containers.

[0007] US 2017 / 036937 discloses a process or apparatus in which salts are first separated by precipitation and then subsequently distilled in a separate container.

[0008] DE 10 2007 012 774 A1 discloses a method for crystallizing a salt, wherein the crystallization takes place in a circuit comprising a distillation module, and salt solution is added either to the reactor or to the solution circuit. The device comprises two separate circuits: one for heating the solution to produce a distillate, and a second with a coolant to produce condensate. DE 10 2007 012 774 AT does not show a distillation unit in which the heating section and distillation section are combined.

[0009] WO 00 / 72947 A1 also discloses a method for crystallizing a salt using a distillation module comprising modules in which liquid is introduced countercurrently through conduits and subsequently returned through conduits via the same module. WO 00 / 72947 A1 thus discloses a distillation unit with interlocking conduits of the heating section and the distillation section. WO 00 / 72947 A1 therefore does not show a heating section that is separate from the distillation section to prevent the heating medium from entering the distillation section.

[0010] The publication "Review of thermal efficiency and heat recycling in membrane distillation processes", ZHANG YONGGANG ET AL, DESALINATION, ELSEVIER, AMSTERDAM, NL, (20150418), vol. 367, pages 223 - 239, discloses various processes for membrane distillation, in one of which the resulting solvent vapor is used to heat the solution.

[0011] US Patent 4,476,024 A relates to a distillation process using a composite membrane through which evaporation and condensation occur.

[0012] EP 2 606 953 A1 relates to a membrane distillation system in which several distillate modules are connected in series and each downstream module operates at a lower pressure than the preceding module.

[0013] US 2017 / 361277 A1 shows a system comprising several membrane distillation modules, a heat exchanger and an evaporator required to generate steam for distillation. TASK OF INVENTION

[0014] The object of the invention is to provide an improved device and an improved method for the desalination of suspensions, whereby the distillation and crystallization are carried out in the most space-saving and energy-saving way possible. PRESENTATION OF THE INVENTION

[0015] The object of the invention is achieved by a method for desalting a suspension according to claim 1.

[0016] The present invention is used for the desalination of suspensions. Suspensions within the meaning of the invention are defined as saline media, in particular those that are close to saturation, containing dispersed solid particles.

[0017] Dissolved salts are in particular inorganic salts such as NaCl, CaCO 3 , CaSO 4 , CaCl 2 , Mg(OH) 2 , MgSO 4 etc. or organic salts such as calcium citrate, sodium acetate and others.

[0018] Suitable solid particles suspended in the medium are those that are capable of serving as crystallization nuclei and causing the precipitation or crystallization of the salts after reaching saturation or supersaturation.

[0019] Suitable nucleation sites include, in particular, undissolved similar salt particles, undissolved foreign salt particles, or quartz sand.

[0020] Preferably, the crystallization nuclei are added before the start of distillation, but it is of course not excluded to add them continuously or to add further crystallization nuclei only as needed after the start of distillation if not enough crystallization nuclei are produced due to the interruption and disintegration of the crystals that are formed.

[0021] Any liquid that can contain dissolved salts can be used as the medium for the suspension. Water is particularly suitable.

[0022] An advantage of the device and method according to the invention is that the suspension is circulated, so that supersaturation does not occur, but rather, once the saturation concentration of a salt is reached, salt crystallizes on the crystallization nuclei to the same extent as solvent vapor is removed by evaporation of the suspension. Crystallization thus takes place within the distillation unit.

[0023] Hollow distillate lines for carrying out distillation are already known in the prior art. In particular, hollow distillate lines made of plastic are suitable.

[0024] Hollow means that the distillate lines have an internal volume for receiving and conveying a volume of liquid or gas.

[0025] The distillation unit according to the invention is divided into a heating section and a distillation section, but otherwise forms a single structural unit in order to carry out distillation and the associated concentration of the suspension as efficiently as possible. "Divided" means that the heating section and the distillation section are separate from each other, so that no heating medium comes into contact with the solvent vapor, and vice versa, but they are nevertheless connected to each other in a liquid-conducting manner with respect to the suspension.

[0026] The heating section and the distillation section in the distillation unit are arranged such that, viewed in one direction of suspension flow, there is no gap between them. Alternatively, there may be a gap smaller than the dimensions of the heating section and / or the distillation section when viewed in the direction of suspension flow. Within this gap, for example, a liquid collection chamber, preferably heated, may be arranged, the cross-section of which is larger than that of a heating line or a distillate line.

[0027] This makes the inventive method or device both space- and energy-saving, because no long connecting paths are required between the heating section and the distillation section. Additional connecting paths would, on the one hand, require further lines, thus requiring more space, and on the other hand, the suspension would have to be heated in these additional lines to prevent the heated suspension from cooling down on its way to distillation, which would require more energy.

[0028] The heating section comprises at least one heating element for conducting the suspension, typically a plurality of heating elements. The distillation section comprises at least one distillate line, typically a plurality of distillate lines. Preferably, the heating section comprises the same number of heating elements as the distillation section comprises distillate lines, in order to ensure particularly easy transfer of the heated suspension from the heating section to the distillation section. Since the liquid is transferred from the heating section to the distillation section, the invention provides that the two sections are connected to each other by a liquid conductor.

[0029] In the heating section of the distillation unit, the suspension in the heating line is heated, while distillation or separation takes place in the distillation section. Separation means that the solvent vapor generated by heating in the at least one heating line or the distillation line can escape through a gas-permeable membrane in the distillation section, but the liquid itself cannot. The remaining liquid is thus concentrated.

[0030] The heating section according to the invention serves to heat the suspension located in the at least one heating conductor. The suspension is heated to 40°C to 200°C, preferably 40°C to 100°C, and particularly preferably to about 70°C.

[0031] The distillation unit further includes at least one vapor outlet with which the solvent vapor can be extracted from the distillation section.

[0032] In principle, any pipe that is impermeable to liquids and gases can be used as a heating pipe according to the invention. Pipes made of metal or plastic are particularly preferred.

[0033] The at least one distillate line according to the invention is designed as a gas-permeable membrane. In particular, membranes made of a gas-permeable plastic or ceramic are suitable as gas-permeable membranes.

[0034] In order to exhibit gas permeability, the membrane must have pores. Preferably, these are membranes with a pore size between 0.1 µm and 0.5 µm, particularly approximately 0.2 µm.

[0035] According to the invention, both the at least one heating line and the at least one distillate line are straight. This means that neither the heating line nor the distillate line has one or more bends that would deflect the flow direction of the suspension. The at least one heating line and the at least one distillate line are arranged in the same direction and thus run straight through the heating section and the distillation section, respectively, so that the suspension flows straight through the distillation unit.

[0036] According to the invention, the distillation unit has a casing that surrounds the at least one heating element and the at least one distillate line. The casing of the at least one heating element and the at least one distillate line is designed such that a volume remains between the casing and the heating element and the distillate line, respectively. However, the volume of the heating section is in any case separated from the volume of the distillation section.

[0037] Any suitable casing according to the prior art is suitable, but preferably it is a casing made of metal or plastic.

[0038] Between the casing and the at least one heating line or the at least one distillate line, there is a space comprising a volume into which a gas or a liquid can be received.

[0039] To efficiently remove solvent vapor from the space between the casing and the distillate line, the device preferably includes a vacuum pump. The vacuum pump's function is to generate and maintain a vacuum and to remove non-condensable gases, such as CO₂, O₂, N₂, etc. The vacuum allows the solvent to evaporate at lower temperatures, resulting in increased energy efficiency of both the process and the device.

[0040] Any commercially available vacuum pump, in particular ejectors or water ring pumps, suitable for use in conjunction with the device according to the invention, can be used. By removing the solvent vapor, continuous distillation and thus concentration of the suspension can be carried out.

[0041] In order to be able to supply a heating medium between the sheathing and the at least one heating line, the invention provides that the heating section further comprises at least one heating medium supply line and at least one heating medium outlet.

[0042] Suitable heating media include liquids or gases, with water and steam being particularly preferred due to their good thermal conductivity and low cost of purchase.

[0043] By introducing hot heating medium, the cold suspension is heated by heat transfer in at least one heating line. The cooled heating medium is then removed via the heating medium outlet and replaced with hot heating medium via the heating medium supply line.

[0044] In principle, a process according to the invention proceeds as follows: Before the distillation or crystallization process begins, the suspension is prepared in a container by adding crystallization nuclei to the suspension medium, preferably water containing salts, which is to be desalinated. In particular, suspension media that are close to saturation are used. Preferably by means of a pump, the suspension to be desalinated is then pumped via a line into the distillation unit, whereby the suspension first enters the heating section, more precisely the at least one heating line, of the distillation unit.

[0045] The heating medium is fed into the space between the casing and the at least one heating element via the heating medium supply line, thereby heating the cold suspension contained within the heating element. As the heating medium transfers heat to the suspension, the suspension warms up while the heating medium cools down. The cooled heating medium is then drained via the heating medium outlet and replaced with fresh, hot heating medium to ensure continuous heating of the suspension. The heated suspension is then transferred to the distillation section.The heated suspension is transferred from at least one heating line to at least one distillate line. The heating line is impermeable to gas and liquids, while the distillate line is gas-permeable, allowing the resulting solvent vapor to permeate from the distillate line through pores into the space between the distillate line and the casing. This process concentrates the remaining suspension in the distillate line until it reaches the saturation or supersaturation point and begins to crystallize, partly due to the crystallization nuclei. The suspension is then discharged from the distillation unit. Subsequently, at least a portion of the suspension is returned to the distillation unit.By returning the suspension to the distillation unit, the suspension is constantly in motion and never stagnates, allowing distillation and crystallization to be carried out in a single line or distillation unit. This constant movement of the suspension also prevents scaling on the membranes of the distillation unit. In one embodiment of the invention, crystallization nuclei are added to the suspension, enabling crystallization of concentrated salts in the distillate line and thus facilitating particularly efficient desalination of the suspension.

[0046] The crystallization nuclei can, in principle, be added before the start of the distillation and crystallization process, or continuously or as required.

[0047] In one embodiment of the invention, it is provided that the solvent vapor is extracted from the distillation section via the vapor discharge using a vacuum pump in order to enable particularly efficient extraction of the solvent vapor.

[0048] Any commercially available vacuum generator, in particular ejectors or water ring pumps, that is suitable for use in connection with the invention can be considered as a vacuum pump.

[0049] The vacuum pump extracts the solvent vapor from the space between the casing and the at least one distillate line, allowing new solvent vapor to permeate from the distillate line.

[0050] In one embodiment of the invention, it is provided that the heating section is heated using water or gas as the heating medium in order to enable particularly efficient and cost-effective heating of the suspension.

[0051] In order to enable the separation of the resulting salt crystals from the remaining suspension, it is provided according to the invention that the resulting salt crystals are separated by means of a classifying device, wherein the classifying device is arranged downstream of the distillation unit in the direction of flow of the suspension.

[0052] After the suspension is passed from the distillation unit, it usually already contains a large number of heavy or large crystals because crystallization occurs within the membrane distillation module, i.e., in the distillation unit itself. To separate these crystals, a classifying device is provided that removes salt crystals of a specific weight or size from the suspension.

[0053] In order to condense the solvent vapor after it has been drawn from the space between the casing and the at least one distillate line, one embodiment of the invention provides for the solvent vapor to be condensed by means of a condenser, the condenser being arranged downstream of the distillation unit in the direction of flow of the solvent vapor. A heat exchanger is particularly suitable as the condenser. By using a heat exchanger, it is possible to obtain pure solvent and make it easily reused or further processed.

[0054] The solvent vapor is extracted from the space and fed to a condenser, where it condenses again so that the solvent can be used elsewhere or returned to the distillation cycle as a heating medium.

[0055] In order to enable a particularly energy-efficient implementation of the invention, one embodiment of the invention provides that several distillation units are arranged in series and connected to each other, and that at least a part of the solvent vapor from the previous distillation unit is used to heat the subsequent distillation unit.

[0056] The solvent vapor permeating from the at least one distillate line is not, in this case, discharged or fed to a condenser, but is at least partially fed back to the subsequent distillation unit, more precisely, to the heating section of the distillation unit, as a heating medium. The solvent vapor is thus passed through the vapor outlet of the preceding distillation unit into the subsequent distillation unit, with the vapor outlet of the preceding distillation unit serving as the heating medium supply line for the subsequent distillation unit. Using the solvent vapor from the preceding distillation unit to heat the subsequent distillation unit is made possible by the fact that the pressure and temperature decrease after passing through each distillation unit, so that the pressure and temperature are always higher in the preceding distillation unit than in the subsequent one.

[0057] It is known that different salts present in salt mixtures crystallize at different concentrations. In one embodiment of the invention, therefore, the salt concentration of the suspension increases further with each pass through several distillation units due to the removal of solvent vapor after each distillation unit, and different salts are separated after at least two distillation units. It is self-evident that the concentration of the suspension to be desalted is higher after passing through the distillation unit than before, due to the concentration process, so that the salt concentration naturally increases further with each distillation unit passed through.The increasing salt concentration after each distillation unit allows for separate salt separation. At lower concentrations, the sparingly soluble salts, such as CaCO₃ and CaSO₄, crystallize and are separated first, while at higher concentrations, the more soluble salts, such as NaCl, precipitate and are separated. This separation can then be achieved, for example, using classification devices, each connected downstream of a distillation unit, so that a different salt is separated after each distillation unit.

[0058] For example, sparingly soluble salts such as CaCO₃ or CaSO₄ can be separated after a first distillation unit, while readily soluble salts such as NaCl are separated after the subsequent distillation unit. Of course, it is also possible to arrange further distillation units in series to achieve an even more specific separation of the salts.

[0059] Alternatively, instead of continuously adding new suspension to the distillation unit, a specific quantity of suspension is added only once at the beginning of the distillation process, and the apparatus is operated in batch mode. This means that the suspension is completely returned to the distillation unit after leaving it. In such batch operation, it is possible to crystallize different salts present in the salt mixture of the suspension at varying concentrations. In a first pass, the suspension passes through the distillation unit, and in this initial pass, one or more salts can be separated and crystallize out.Due to the removal of solvent vapor after passing through the distillation unit, the salt concentration naturally increases after the first pass, so that in the subsequent pass, a different salt or salts can be separated from the first salt(s). It goes without saying that the concentration of the suspension to be desalted is higher after passing through the distillation unit than before, due to the concentration process, so that with each new pass through the distillation unit, the salt concentration naturally increases further.The increasing salt concentration with each pass through the distillation unit allows for separate salt separation. As in fractional distillation, the sparingly soluble salts, such as CaCO₃ and CaSO₄, crystallize and are separated first at lower concentrations, while the more soluble salts, such as NaCl, precipitate and are separated at higher concentrations. Separation can then be carried out after each pass through the distillation unit using the same downstream classifying device, so that a different salt is separated after each pass.

[0060] This means that, according to the invention, the desalination or crystallization of the salts can be carried out either continuously in a single distillation unit or in several distillation units connected in series, whereby the suspension to be desalted is continuously added to at least one or the first distillation unit. Alternatively, the desalination or crystallization of the salts can also be carried out in batch operation. In this case, the suspension to be desalted is added only once at the beginning of the desalination process to the first distillation unit, which then passes through the distillation unit(s) at least once, preferably several times.

[0061] The object of the invention is further solved by a device according to claim 10 for desalting a suspension for use with a method according to the invention.

[0062] To enable particularly efficient transfer of the suspension from the heating section to the distillation section, one embodiment of the invention provides that the at least one heating line transitions into the at least one distillate line. Typically, each of the several heating lines transitions into one of the several distillate lines.

[0063] To facilitate particularly simple manufacturing of the casing, the heating element and the distillate line are enclosed in a common casing. Even with this shared casing, the heating section remains separate from the distillation section, preventing any heating medium from entering the distillation section. The casing could, for example, be a cylinder whose length is at least equal to the length of one distillate line plus the length of one heating element. Of course, other casing shapes are not excluded; the casing could also be a cuboid or similar.

[0064] In one embodiment of the invention, a liquid collection chamber, preferably heatable, is arranged between the heating section and the distillation section. The cross-section of this liquid collection chamber is larger than that of a heating conductor or a distillate line. This allows for the use of varying numbers of heating conductors and distillate lines. In this case, the at least one heating conductor terminates, viewed in the direction of suspension flow, at the inlet or within the liquid collection chamber, while the at least one distillate line begins in or at the outlet of the liquid collection chamber. The heating conductor and distillate line are spaced apart from each other in the direction of suspension flow. The liquid collection chamber is preferably heatable to prevent the suspension, previously heated in the heating section, from cooling down again and thus preventing subsequent distillation in the distillation section.Since the heating section and the distillation section share a common casing, the liquid collection chamber preferably has a diameter that is no larger than that of the casing.

[0065] To provide a particularly large distillation surface, one embodiment of the invention provides that the at least one distillate line has a diameter between 3 mm and 10 mm, preferably between 4 mm and 8 mm, and particularly preferably about 5 mm. Using distillate lines with a diameter in the aforementioned range ensures that as much permeable membrane surface area as possible is available, through which the resulting solvent vapor can permeate into the space between the casing and the distillate line, thus resulting in particularly effective distillation. A line diameter that is too small would lead to clogging by crystallization nuclei or the growing crystals, while a line diameter that is too large would result in a reduced membrane surface area.

[0066] To enable rapid heating of the suspension, one embodiment of the invention provides that the at least one heating line has a diameter between 3 mm and 10 mm, preferably between 4 mm and 8 mm, and particularly preferably about 5 mm. A diameter that is too small would lead to clogging by crystallization nuclei or growing crystals, while a diameter that is too large would result in a reduced heat exchange surface area.

[0067] In order to enable rapid permeation of the solvent vapor through the membrane, but to prevent liquid or unwanted ions from passing through the membrane, the invention provides that the gas-permeable membrane of the distillate line has a thickness of 0.3 mm to 2 mm, preferably 0.7 mm to 1.7 mm and particularly preferably between 1 mm and 1.5 mm.

[0068] To enable efficient permeation of the solvent through the membrane while simultaneously making it impermeable to liquids, one embodiment of the invention provides that the gas-permeable membrane of the distillate line is made of a gas-permeable plastic or a gas-permeable ceramic. Suitable gas-permeable plastics include, in particular, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or polypropylene (PP).

[0069] In order to prevent the suspension from entering the heating medium or the heating medium from entering the suspension, one embodiment of the invention provides that the at least one heating line is made of liquid- and gas-impermeable plastic or metal.

[0070] In one embodiment of the invention, the sheathing is made of plastic to ensure simple manufacturing. In particular, this allows for the particularly simple production of a common sheathing for the distillate and heating lines.

[0071] In one embodiment of the invention, the device further comprises a condenser, wherein the condenser is arranged downstream of the distillation unit in the direction of flow of the solvent vapor in order to condense the solvent vapor.

[0072] In one embodiment of the invention, the device further comprises at least one classification unit for separating the suspension crystals, wherein the classification unit is arranged downstream of the distillation unit in the direction of suspension flow in order to separate crystals that have reached a specific size or weight. Concentrating the suspension brings the suspension medium to the saturation or supersaturation range. The existing crystallization nuclei then crystallize the salts present, leading to the growth of these nuclei and / or the formation of new crystals.

[0073] To enable the most energy-efficient design of the device, one embodiment of the invention provides that the device comprises several interconnected distillation units arranged in series, with the vapor outlet of the preceding distillation unit serving as the heating medium supply line for the subsequent distillation unit. This arrangement of the distillation units allows the solvent vapor from the preceding distillation unit to be used as the heating medium for the subsequent unit and is itself condensed. Furthermore, this arrangement enables the highly efficient desalination of large quantities of the suspension. By using the solvent vapor from the preceding distillation unit to heat the suspension in the subsequent unit, energy costs are kept particularly low.

[0074] In one embodiment of the invention, it is provided that, in the case of several interconnected distillation units arranged in series, at least one classifying device is arranged downstream of at least two distillation units in order to separate different salts. Such an arrangement enables better separation of various salts present in the suspension, thereby simplifying, for example, further use or facilitating subsequent purification.

[0075] In one embodiment, a line is provided through which at least a portion of the suspension can be returned to the distillation unit after leaving it. In this case, the device for desalting a suspension preferably comprises a container for the suspension, a pump, and at least one line connecting the container to the pump and the at least one distillation unit.

[0076] Any container known in the prior art and suitable for suspensions can be used. However, a plastic container is preferred.

[0077] Any pump known in the prior art that is suitable for pumping the suspension through a pipe can be used. However, a centrifugal pump is preferably used in connection with the present invention.

[0078] Any pipe known in the prior art that is suitable for conveying the suspension to be desalinated can be used for this purpose. Preferably, however, it is a pipe made of metal or plastic.

[0079] By at least partially recirculating the suspension back into a distillation unit according to the invention, desalination can be carried out continuously, and the distillation and crystallization processes can be performed in a single line, specifically in the heating line or the distillate line. Upon exiting the distillation unit, crystals of a specific size or weight can thus be directly separated from the suspension. A membrane distillation unit in which distillation and crystallization occur simultaneously, made possible by recirculating the suspension back into the distillation unit and maintaining its constant movement, is not previously known in the art.

[0080] In the event that the temperature of the generated solvent vapor is insufficient to heat the heating section of the subsequent distillation unit, one embodiment of the invention provides either a device comprising an injector for carrying out thermal vapor compression of the solvent vapor or a device comprising a compressor for carrying out mechanical vapor compression of the solvent vapor.

[0081] In connection with the device according to the invention, which comprises more than one distillation unit, either thermal or mechanical solvent vapor compression can be carried out, depending on which appears more suitable in the application area of ​​the device.

[0082] If thermal vapor compression is used to increase the solvent vapor temperature, the device according to the invention additionally includes a device comprising an injector, wherein the injector draws steam from another steam generator as its motive medium. A portion of the solvent vapor from the last distillation unit is compressed by means of the injector. This compression raises the temperature of this portion of the solvent vapor. The drawn-in solvent vapor is mixed with the motive steam, and the resulting mixture is used to heat the heating section of the first distillation unit, where it is completely condensed. The amount of condensate corresponding to the motive steam is returned to the steam generator to produce new motive steam, while the remaining condensate from all distillation units is collected and discharged.The advantage of using thermal vapor compression is that a higher energy yield is achieved.

[0083] If mechanical vapor compression is used to increase the solvent vapor temperature, the device according to the invention additionally includes a device comprising a compressor.

[0084] If a system includes a compressor for mechanical vapor compression, a condenser is not required, since the solvent vapor from the last distillation unit is compressed by the compressor to such an extent that the first distillation unit can be heated again with this solvent vapor and the solvent vapor then condenses again.

[0085] Due to this cycle, mechanical compression is only suitable for one or two distillation units. An advantage, however, is that no cooling medium is required; a disadvantage is that mechanical compression using a compressor requires electrical energy. BRIEF DESCRIPTION OF THE FIGURES

[0086] The invention will now be explained in more detail using exemplary embodiments. The drawings are exemplary and are intended to illustrate the inventive concept, but in no way to restrict or even exhaustively represent it.

[0087] This shows: Fig. 1 a line representation of a distillation unit according to the invention Fig. 2 a flow diagram of a device according to the invention comprising a container, a pump, a distillation unit, a condenser and a classification device Fig. 3 a device according to the invention with several distillation units connected in series Fig. 4 a device according to the invention with several distillation units connected in series, comprising a device for carrying out thermal vapor compression Fig. 5 a device according to the invention comprising a device for carrying out mechanical vapor compression. WAYS TO IMPLEMENT THE INVENTION

[0088] Fig. 1 Figure 1 shows a distillation unit 4 according to the invention, which is used in conjunction with a device 1 according to the invention for desalting a suspension. The distillation unit 4 is divided into a heating section 6 and a distillation section 7, the two sections being separated from each other by the space between the heating lines 8 and the distillate lines 9, but connected to each other via the interior of the heating lines 8 and distillate lines 9. The heating section 6 is used to heat the suspension. The heating section 6 comprises seven heating lines 8, shown here, for guiding the suspension, these heating lines 8 being impermeable to liquid and gas. The heating lines of the Fig. 1 are made of thermally conductive plastic.

[0089] The distillation section 7 also includes seven distillate lines 9, as shown here, for conveying the heated suspension. The distillate lines 9 of the Fig. 1 are made of polypropylene.

[0090] A heatable liquid collection chamber 18 is arranged between the heating lines 8 and the distillate lines 9, so that the heated suspension from all heating lines 8 is collected there before being passed on to the distillation section 7.

[0091] Fig. 1 further shows that the seven heating lines 8 and the seven distillate lines 9, as well as the liquid collection chamber 18, are surrounded by a common casing 11. The casing, which is in the Fig. 1 The casing shown is made of polyvinyl chloride (PVC). Between the casing 11 and the heating lines 8 or the distillate lines 9 there is a space with a volume that can hold liquid or gas.

[0092] A heating medium is supplied between the casing 11 and the seven heating lines 8 via a heating medium supply line 12 to heat the suspension in the heating lines 8. Since the heating medium cools down through heat exchange with the suspension in the heating lines 8, heating medium is continuously supplied and the cooled heating medium is simultaneously discharged via a heating medium outlet 13.

[0093] The heated suspension is then directed into the heated liquid collection container 18 and from there into the distillation section 7, specifically the seven distillate lines 9. The distillate lines 9 are designed as gas-permeable membranes, allowing the solvent vapor generated by heating the suspension to permeate through the membrane pores. The solvent vapor passes from the interior of the distillate lines 9 between the casing 11 and the distillate lines 9. The Fig. 1 The distillation section shown here comprises two vapor outlets 10 through which the solvent vapor can be discharged. Preferably, the solvent vapor is discharged by means of a vacuum pump (not shown).

[0094] The remaining suspension is concentrated by distillation and permeation of the solvent vapor through the membrane, reaching the saturation or supersaturation range. The existing crystallization nuclei trigger crystallization, leading to crystal formation and growth. The suspension is then discharged from the distillation unit.

[0095] Fig. 2 Figure 1 shows a flow diagram of a device 1 according to the invention. The device comprises a container 2 in which the suspension to be desalinated is placed. The suspension is pumped from the container into a distillation unit 4 by means of a pump 3. The distillation unit according to the invention is divided into a heating section 6 and a distillation section 7. The heating section 6 and the distillation section 7 have a common casing 11. The Figur 2 The heating section 6 shown symbolically has only one heating line 8 in which the suspension is heated. A heating medium is supplied to the heating section 6 via a heating medium supply line 12, with the heating medium being introduced between a sheath 11 and the heating line 8. The heating medium is continuously replaced by new heating medium, as it cools down through heat exchange with the suspension. The heating medium is discharged from the heating section via the heating medium outlet 13.

[0096] Unlike the Fig. 1 The suspension will be in Fig. 2 Directly, without liquid collection chamber 18, from the heating section 6 to the distillation section 7, i.e., directly from each heating line 8 into a distillate line 9, where the resulting solvent vapor can permeate through the distillate line 9, which is designed as a membrane, between the casing 11 and the distillate line 9. The solvent vapor is discharged via a vapor outlet 10 and fed to a condenser 14. Fig. 2 It can be seen that, viewed in the direction of flow 16 of the solvent vapor, the condenser 14 is located downstream of the distillation unit 4. The condensed solvent vapor can then be used for its further purpose.

[0097] The partially concentrated suspension remaining in distillate line 9 is discharged from the distillation unit. Due to the presence of crystallization nuclei, the concentration process leads to crystal formation and growth. Downstream of distillation unit 4, in the direction of suspension flow 17, a classifying device 15 is arranged, which separates crystals of a specific weight or size. The suspension is returned to the inlet of distillation unit 4 via line 5, located between container 2 and pump 3.

[0098] Fig. 3 Figure 1 shows a flow diagram of a device 1 according to the invention, in which four distillation units 4 are connected in series. The device is shown in the diagram. Fig. 2 The system is constructed with the difference that it comprises four distillation units 4. The suspension to be desalinated is pumped from the container 2 into the first distillation unit 4 by means of the pump 3, whereby the suspension is heated in the heating section 6 of the first distillation unit 4 and the solvent vapor produced by the heating is separated in the distillation section 7 of the first distillation unit 4. To heat the suspension, according to the Fig. 3 A heating medium, in this case steam, is supplied via a heating medium supply line 12 between the sheathing 11 and the heating cable 8. To ensure a constantly warm heating medium, the heating medium is continuously drained via a heating medium outlet 13 and new heating medium is supplied via the heating medium supply line 12.

[0099] The solvent vapor is discharged from the distillation section 7 via a vapor outlet 10, whereby the vapor outlet 10 of the first distillation unit 4 is used as the heating medium supply line 12 of the second and thus subsequent distillation unit 4, so that the solvent vapor separated from the suspension serves as a heating medium for the subsequent distillation unit 4.

[0100] The suspension, concentrated by passing through distillation unit 4, is discharged from the first distillation unit 4 via a line 5. Downstream of the first distillation unit 4, in the direction of flow 17 of the suspension, a classifying device 15 is arranged, which allows crystals of a specific size or weight to be separated. Since sparingly soluble salts precipitate first, salts such as CaCO₃ or CaSO₄ can be separated in a first step.

[0101] The remaining suspension can optionally be treated with new crystallization nuclei to ensure sufficient crystallization in subsequent steps. The remaining suspension is then fed via line 5 into a second, downstream distillation unit 4, which is structurally identical to the first distillation unit 4, and / or returned to the first distillation unit 4. In the second distillation unit, the suspension is reheated in the heating section 6, and the resulting solvent vapor is discharged via a vapor outlet 10 in the distillation section 7. The vapor outlet 10 of the second distillation unit 4 now corresponds to the heating medium supply line 12 of the subsequent third distillation unit 4.

[0102] The suspension, further concentrated by passing through two distillation units 4, is discharged from the second distillation unit 4 via a line 5. Downstream of the second distillation unit 4, in the direction of flow 17 of the suspension, a classifying device 15 is arranged to separate crystals of a specific weight or size. Since the salt concentration in the suspension is higher than after passing through the first distillation unit 4, salts that require a suspension with a higher salt concentration for precipitation precipitate out in this second step, along with the remaining sparingly soluble salts.

[0103] The remaining suspension can optionally be treated with new crystallization nuclei to ensure sufficient crystallization in subsequent steps. The remaining suspension is then fed via line 5 into a third, downstream distillation unit 4, which is structurally identical to the first and second distillation units 4, and / or returned to the second distillation unit 4. In the third distillation unit, the suspension is reheated in the heating section 6, and the resulting solvent vapor is discharged via a vapor outlet 10 in the distillation section 7. The vapor outlet 10 of the third distillation unit 4 now corresponds to the heating medium supply line 12 of the subsequent fourth distillation unit 4.

[0104] The suspension, further concentrated by passing through three distillation units 4, is discharged from the third distillation unit via a line 5. Downstream of the third distillation unit 4, a classifying device 15 is arranged to separate crystals of a specific weight or size. Since the salt concentration in the suspension is even higher than after passing through the second distillation unit 4, salts that require an even higher concentration to precipitate than the concentration present after passing through the second distillation unit 4 now also precipitate.

[0105] The remaining suspension can optionally be treated with new crystallization nuclei to ensure sufficient crystallization in subsequent steps. The remaining suspension is then fed via line 5 into a fourth downstream distillation unit 4, which is essentially identical in design to the first, second, and third distillation units 4, and / or returned to the third distillation unit 4. In the fourth distillation unit 4, the suspension is reheated in the heating section 6, and the resulting solvent vapor is discharged via a vapor outlet 10 in the distillation section 7. The condensate obtained through the fourth condenser 14 is combined with the condensate from the upstream distillation units 4 and either used for further processing or discarded.

[0106] The suspension, further concentrated by passing through four distillation units 4, is discharged from the fourth distillation unit 4 via a line 5. Downstream of the fourth distillation unit 4, in the direction of flow 17 of the suspension, a classifying device 15 is arranged to separate crystals of a specific weight or size.

[0107] Since the salt concentration in the suspension is now even higher than after passing through the third distillation unit 4, readily soluble salts such as NaCl also precipitate, which require an even higher salt concentration to precipitate than the salt concentration present after passing through the third distillation unit 4.

[0108] By connecting several distillation units in series, partial salt separation can also be achieved, which facilitates further processing or subsequent purification of the salts.

[0109] The remaining suspension is fed back to the fourth distillation unit 4 via line 5 together with fresh suspension.

[0110] Fig. 4 Figure 1 also shows a flow diagram of a device 1 according to the invention, in which four distillation units 4 are connected in series. The device 1 is essentially the same as the device 1 in Figure 1. Fig. 3 set up. The device 1 according to the Fig. 4 differs from device 1 according to the Fig. 3 The device includes a means for carrying out thermal vapor compression. This means it includes an injector 19. By means of this injector 19, a portion of the solvent vapor is drawn off after the fourth distillation unit 4 and compressed using motive steam from another steam source. The motive steam mixes with the solvent vapor and is directed via the heating medium supply line 12 into the heating section 6 of the first distillation unit 4, where it heats the suspension and then condenses. A quantity of the condensate mixture, i.e., the mixture of the motive steam and the solvent vapor, corresponding to the original motive steam, is returned to the steam generator (not shown).The remaining condensate, which corresponds to the amount of suction steam, i.e., the solvent vapor after the fourth distillation unit 4, is carried off as distillate together with the condensate from the remaining distillation units 4.

[0111] Fig. 5 shows a device 1 as in Fig. 2The device is disclosed, with the difference that it additionally includes a device for carrying out mechanical vapor compression. The device for carrying out mechanical vapor compression comprises a compressor 20, which compresses the solvent vapor generated in the distillation unit 4. This compressed solvent vapor is then used as a heating medium for the heating section 6 and is supplied to the heating section 6 via heating medium supply line 12 to heat the suspension. Upon heating the suspension, the solvent vapor condenses, and the condensate is discharged via the heating medium outlet 13. The solvent vapor generated in the distillation section 7 of the distillation unit 4 is again compressed by compressor 20 and used as a heating medium, and so on.

[0112] Alternatively, a single distillation unit 4 can also be used for the crystallization of various salts (not shown in the figures). In this case, suspension is fed to the distillation unit 4 only once at the beginning of the crystallization process, and the apparatus is subsequently operated in so-called batch mode. After leaving the distillation unit 4, the suspension is completely returned to it and then passed through it again. In such batch operation, it is possible to crystallize different salts present in the salt mixture of the suspension at different concentrations, with the concentration of the suspension increasing after each pass through the distillation unit 4.In each pass through the distillation unit 4, other salts also crystallize, which can then be separated by the classification unit 15 downstream of the distillation unit 4.

[0113] This means that the desalination or crystallization of the salts can take place either in the continuous operation of a single distillation unit 4 or several distillation units 4 connected in series, whereby at least one or the first distillation unit 4 continuously receives the suspension to be desalted. Alternatively, the desalination or crystallization of the salts can also take place in batch operation, also called batch processing, of a single distillation unit 4 or several distillation units 4 connected in series. REFERENCE MARK LIST

[0114] 1 Device for desalting a suspension 2 Container for the suspension 3 Pump 4 Distillation unit 5 Line 6 Heating section 7 Distillation section 8 Heating line 9 Distillate line 10 Vapor outlet 11 Jacket 12 Heating medium supply line 13 Heating medium outlet 14 Condenser 15 Classifying device 16 Flow direction of solvent vapor 17 Flow direction of the suspension 18 Liquid collection chamber 19 Injector 20 Compressor

Claims

1. A method for the desalination of a suspension, - wherein the suspension is conducted into a distillation unit (4) which is divided into a heating section (6) and a distillation section (7), wherein the heating section (6) and the distillation section (7) are in fluid communication with each other, - wherein the suspension is initially directed into at least one liquid-impermeable and gas-impermeable heating conduit (8) of the heating section (6) of the distillation unit (4) and heated therein, wherein the heating section (6) is separated from the distillation section (7) so that no heating medium can gain access to the distillation section (7), - wherein the heated suspension is then transferred into at least one distillate conduit (9) of the distillation section (7) of the distillation unit (4) which is configured as a gas-permeable membrane, so that solvent vapour which is generated permeates out of the distillate conduit (9) via the gas-permeable membrane and is removed from the distillation section (7) via a vapour discharge conduit (10), - wherein the distillation unit (4) has a common casing (11) which surrounds the at least one heating conduit (8) and the at least one distillate conduit (9), - wherein the suspension is concentrated by the removal of the solvent vapour, and - wherein, after leaving the distillation unit (4), at least a portion of the suspension is fed back into the distillation unit (4) characterized in that the suspension flows through the distillation unit (4) in a straight line, because the heating conduit (8) and the distillate conduit (9) are disposed to run in a straight line in the same direction, wherein in the common casing (11) the heating section (6) is separated from the distillation section (7) so that no heating medium can gain access to the distillation section (7) and wherein the casing (11) is a cylinder or another shape of casing (11), the length of which corresponds at least to the length of a distillate conduit (9) plus the length of the heating conduit (8).

2. The method according to claim 1, characterized in that seed crystals are added to the suspension so that a crystallization of concentrated salts occurs in the distillate conduit (9).

3. The method according to claim 1 or claim 2, characterized in that the solvent vapour is discharged from the distillation section (7) via the distillate conduit (9) by means of a vacuum pump.

4. The method according to any one of claims 1 to 3, characterized in that the heating section (6) is heated by means of water or gas as heating medium.

5. The method according to any one of claims 1 to 4, characterized in that the salt crystals which are generated are separated by means of a screening means (15), wherein the screening means (15) is disposed downstream of the distillation unit (4) when viewed in the direction of flow (17) of the suspension.

6. The method according to any one of claims 1 to 5, characterized in that the solvent vapour is condensed by means of a condenser (14), wherein the condenser (14) is disposed downstream of the distillation unit (4) when viewed in the direction of flow (16) of the solvent vapour.

7. The method according to any one of claims 1 to 6, characterized in that several distillation units (4) are disposed one after the other and are connected together and in that at least a portion of the solvent vapour from the previous distillation unit (4) is used to heat the subsequent distillation unit (4).

8. The method according to any one of claims 1 to 7, characterized in that a salt concentration of the suspension increases further upon passage through several distillation units (4) by means of the removal of the solvent vapour after each distillation unit (4), and different salts are separated out after at least two distillation units (4).

9. The method according to any one of claims 1 to 8, characterized in that the method is carried out in continuous mode operation or in batch mode operation.

10. A device (1) for the desalination of a suspension for use with a method according to any one of claims 1 to 9, comprising a distillation unit (4) comprising at least one distillate conduit (9), wherein - the distillation unit (4) is divided into a heating section (6) and a distillation section (7), - wherein the heating section (6) and the distillation section (7) are in fluid communication with each other, but the heating section (6) is separated from the distillation section (7) so that no heating medium can gain access to the distillation section (7), - wherein the heating section (6) comprises at least one heating conduit (8) for conducting and heating the suspension, - wherein the distillation section (7) comprises at least one distillate conduit (9) for conducting the heated suspension and at least one vapour discharge conduit (10) for discharging the solvent vapour, - wherein the at least one heating conduit (8) as well as the at least one distillate conduit (9) are surrounded by a common casing (11), - wherein the heating section (6) comprises at least one heating medium supply conduit (12) as well as at least one heating medium discharge conduit (13), so that a heating medium can be supplied and discharged between the casing (11) of the heating section (6) and the at least one heating conduit (8), - wherein the at least one heating conduit (8) is impermeable to gases and liquids, - wherein the at least one distillate conduit (9) is configured as a gas-permeable membrane so that solvent vapour can pass through the gas-permeable membrane, and - wherein, after passing through the gas-permeable membrane, the solvent vapour is collectible between the casing (11) and the at least one distillate conduit (9), characterized in that the at least one heating conduit (8) and the at least one distillate conduit (9) are disposed in the same direction and therefore run in a straight line through the heating section (6) or the distillation section (7), so that the suspension runs through the distillation unit (4) in a straight line, wherein in the common casing (11) the heating section (6) is separated from the distillation section (7), so that no heating medium can gain access to the distillation section (7), and wherein the casing (11) is a cylinder or another shape of casing (11), the length of which corresponds at least to the length of a distillate conduit (9) plus the length of the heating conduit (8).

11. The device (1) according to claim 10, characterized in that the at least one heating conduit (8) merges into the at least one distillate conduit (9).

12. The device (1) according to claim 10 or claim 11, characterized in that a liquid collecting chamber (18), which can preferably be heated, is disposed between the heating section (6) and the distillation section (7) and has a cross section which is larger than a cross section of one heating conduit (8) or of one distillate conduit (9).

13. The device (1) according to any one of claims 10 to 12, characterized in that the device (1) furthermore comprises a condenser (14), wherein, when viewed in the direction of flow (16) of the solvent vapour, the condenser (14) is disposed downstream of the distillation unit (4) in order to condense the solvent vapour.

14. The device (1) according to any one of claims 10 to 13, characterized in that the device furthermore comprises at least one screening means (15) for separating the suspension crystals, wherein the screening means (15) is disposed downstream of the distillation unit (4) when viewed in the direction of flow (17) of the suspension.

15. The device (1) according to any one of claims 11 to 14, characterized in that the device (1) comprises several distillation units (4) which are disposed one after the other and are connected together, wherein the vapour discharge conduit (10) for the previous distillation unit (4) forms the heating medium supply conduit (12) for the subsequent distillation unit (4).