NO831661L - PROCEDURE AND DEVICE FOR TRANSMISSION BRAND STILL - Google Patents

Abstract

Method and device for separating liquid components from a solution by transferring these into the vapor phase and the vapor subsequently being condensed, where the solution and distillate (condensate) are separated by a porous partition (2) which is only permeable to the vapor and touches it partition. The solution is heated to a higher temperature than the condensate, whose temperature is below its boiling point. Transfer to the vapor phase takes place on the solution side (la), the vapor diffuses through the pores of the partition (2) to the distillate side (lb) and possibly condenses there. According to the invention, during the duration of the separation by pressure and/or temperature control, at least in a partial area of the porous partition (2)'s immediate surroundings, on the solution side, at least the area for the current boiling point of the solution is achieved. The pressures on the solution side (la) and the distillate side (lb) can also be set higher or lower than atmospheric pressure. The porous partition can be a membrane and/or have a mesh-like pore structure, which makes it possible to set a pressure that corresponds to the maximum extent to the current vapor pressure of the solution exclusively in the pores of the porous partition (2). The procedure can also be carried out with recovery of heat from the condensate.

Description

The invention relates to a method and an apparatus for at least partial separation of at least one liquid component of a solution by transferring this into the vapor phase, where the solution and the distillate are kept separated by a porous partition wall, which is only permeable to the vapor-form distillate and any gases present, and with which the solution and the distillate are kept in contact, where the transfer to the vapor phase occurs on the solution side of the pores of the porous partition and the vaporized distillate diffuses through the pores to the distillate side.

From US-PS 3 361 645, a device for extracting drinking water from saline water is known, where water vapor from the solution diffuses through water vapor-permeable silicone rubber tubes to the interior of the tubes and is transported from there to a condenser with a draft gas, e.g. air. The vapor transport by means of the draft gas is effected either by means of a fan or by wide creation of a vacuum. There is thus no condensation of the water vapor already inside the pipes. The saline water is heated to a temperature that lies between the ambient and the boiling temperature.

German Offenlegungsschrift 25 37 780 discloses a method for separating phenols from aqueous mixtures with an organic polymer membrane, which is selectively permeable to phenol, where the aqueous coating stream is brought into contact with the membrane, either in liquid or vapor phase, and where the permeate can be present in the form of a phenol vapour, a phenol solution or as a phenol complex solution. With this known method, the absolute pressure in the coating and permeation zones can vary greatly, i.e. negative and positive pressure from a few torr to 35-70 kg/cm can be used. According to the aforementioned publication, pressure is generally not a significant factor when the permeation zone is exposed to liquid phase conditions. If, on the other hand, steam coating mixtures or membrane evaporation conditions are used, higher pressure at the coating zone can create a higher chemical potential, which is desirable. If the permeate in this known method is in the vapor phase, an overpressure is usually set on the coating side of the membrane and a negative pressure in relation to the atmospheric pressure on the permeate side of the membrane.

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From German Offenlegungsschrift 16 19 749 a method is known for the separation of liquid solutions and mixtures using porous bodies, which are in contact with the liquid, e.g. a lyophobic, porous foil, where work can also be done under negative pressure, since significantly less heat is then required to achieve the same effect as when operating under normal or positive pressure.

The permeate flows that have been achieved with these known methods have so far been considered the maximum achievable. Now, however, surprisingly enough, it has been shown that significantly higher permeate flows can in reality be achieved with methods of the aforementioned type (it is the amount of distillate that per unit time and per unit area of effective, porous partition wall diffuses from the solution side through the pores of the porous partition wall to the distillate side) than has so far been achieved and considered possible.

The present invention is thus based on the task of improving this method so that the amount of distillate or condensate that is obtained per surface unit of porous partition and per unit of time is significantly greater than what has been achieved so far with this method.

This task is solved by the aforementioned method according to the invention in that during the separation process duration, with the help of pressure and/or temperature control at all times, at least in a partial area of the immediate surroundings of the porous partition wall, on the solution side at least the area is achieved for the boiling point of the solution in question.

The driving force of the membrane distillation process

lation according to the invention is the vapor pressure difference between the solution side and the distillate side. Such a vapor pressure difference is achieved by either the distillate in vapor form being continuously led away from the porous partition wall or by the distillate side of the porous partition wall being continuously applied to a liquid that has a lower temperature than the solution and which absorbs the distillate which is then condensed on the distillate side of the pores of the porous partition, i.e. by a temperature difference between the solution and the condensate. Preferably, this cooling

:or transport liquid of condensed, cooled distillate. In this way mixing of the distillate with another liquid is prevented. This is particularly advantageous when the distillate itself is the actual product of the process and does not have to be treated as a waste product.

It must be regarded as completely surprising that the transmembrane distillate flow rate at the same vapor pressure difference between the solution side and the distillate side can be increased to a multiple, e.g. solely by the fact that on the dissolution side a negative pressure is formed in relation to the ambient pressure, and that it is sufficient if one. with such a pressure reduction according to the invention, at least in a partial area of the immediate surroundings of the porous partition wall in the solution, at least the area for the solution's current boiling point is achieved.

By "current boiling point" here is meant the solution's boiling point depending on the solution's temperature, pressure and concentration. This boiling point usually changes constantly. The place where the actual boiling point or the area for this boiling point is reached can also change.

Preferably, the pressure course or the temperature course on the solution side is controlled so that everywhere on the solution side at least the area for the current boiling point of the solution is achieved, but at least this is achieved along the entire porous partition. By the range of the relevant boiling point, according to the invention, it is understood that the absolute temperature of the solution is a maximum of 3% below the boiling temperature which corresponds to the pressure prevailing at the measuring point in question, expressed in Kelvin, or in other words that the temperature T of the solution is at least 0.97- T where TV is the boiling point of the solution at the measurement location in question.

The method according to the invention is not comparable to the conventional vacuum evaporation or distillation methods, where the evaporation at all times takes place in the direction where the device that generates the vacuum is located. With the method according to the invention, there will be an increase in the amount of distillate that diffuses through the pores of the porous partition towards the distillate side, even if a vacuum is set on the solution side, in particular the boiling pressure, by connecting the vapor space above the solution to a vacuum device. A further decisive difference between these methods of another type, which work with a vacuum and the method according to the invention consists in that the transition of the liquid component of the solution to be separated from, to vapor phase from the liquid phase, in the method according to the invention takes place on liquid surfaces which. protrudes into the pores of a porous partition and is thus exposed to capillary forces. Also when it comes to the result, the method according to the invention differs greatly from said methods of another type as the distillates (condensates) that can be obtained with the help of the invention have a degree of purity, which in the said methods is not obtained with just one evaporation step, i.e. for example without subsequent rectification or further distillation.

As is known, a liquid's boiling point is only reached when the liquid's vapor pressure is equal to the ambient pressure. A liquid's vapor pressure rises with increasing liquid temperature. At a certain ambient pressure, the boiling point can thus be reached by increasing the liquid's temperature; at a fixed temperature, the boiling point is reached by reducing the ambient pressure. In the case of a quiescent column of liquid, the static pressure in the lower area of the column is higher than on the surface, so that the boiling point will be reached at a higher temperature in the lower area of the column than at the surface. If one connects a liquid column with a negative pressure source, the boiling point - provided that the temperature is evenly distributed in the column - will be reached by achieving a certain negative pressure on the surface of the liquid column, but not in the lower areas. This means that by simply creating negative pressure above a column of liquid with a uniform temperature distribution, boiling is not achieved throughout the column. For example, the pressure in a 10 m high water column is 0.98l bar higher at the deepest point than at the highest point. If a 10 m high water column is under atmospheric pressure, the boiling temperature at the deepest point of the water column is thus increased to approx. 120°C. If such a water column is in contact with a vertically arranged, likewise 10 m high, hydrophobic, porous partition wall, and if this water column is brought to boiling by increasing the temperature or by reducing the ambient pressure, the necessary prerequisites for the greatest possible steam flow through the porous partition wall will thus only present in the upper area of the water column.

With the method according to the invention, this disadvantage does not exist, because the boiling point is at least approximately reached by controlling the solution's pressure and/or temperature on the solution side and/or on the distillate side, at least in the immediate vicinity of the entire porous partition if possible. In the case of a vertically arranged, e.g. 10 m high, porous partition wall, this can e.g. happen by the solution being guided from below upwards, along the porous partition wall, where the solution already has the boiling temperature^ which corresponds to the pressure when it is guided towards the porous partition wall, and where it is cooled on its way from below upwards so that the boiling temperature which corresponds to the local pressure at all times is reached. A cooling will then at least take place by the evaporation that takes place through the porous partition. If it is too strong, so that the temperature in the solution drops below the boiling temperature which corresponds to the relevant (level-dependent) pressure at any given time, this can be countered by applying heat to the relevant location or by increasing the flow rate of solution. If, on the other hand, the amount of evaporation is too small in relation to the flow-through amount of solution, the solution will, on reaching a certain height, begin to boil intensely, with strong steam bubble development. This can be avoided, for example, by reducing the flow-through amount of solution that is carried along the porous partition on the solvent side.

In the same way as when changing the flow rates, the pressure conditions can also be adapted to the possibly determined temperature conditions by installing additional flow resistors.

The same applies in the event that the solution is guided essentially horizontally along the, in this case likewise horizontally arranged, porous partition wall. In this case, essentially only the occurring, possibly only very small, pressure losses (flow losses) will lead to pressure differences in the solution along the porous partition wall and thus to only slightly deviating boiling temperatures. If the pressure difference along a horizontally arranged, porous partition wall, which can only be achieved by loss of flow, is too small in relation to the evaporation through the porous partition wall and due to a reduction in the temperature of the solution due to any non-occurring heat loss, the boiling point of the solution can is not achieved or maintained along the entire porous partition. In this case too, heat supply from outside, increase of the flow rate on the solvent side or installation of artificial flow resistances can lead to such a mutual adaptation of the temperature loss in the solution and the pressure flow in it that the relevant boiling point of the solution, or at least the area for this boiling point is achieved at least in a sub-range.

If, for example, the porous partition wall is formed by one or more pipes, the flow resistance in the pipes can, for example, be increased by making the internal diameter of the pipes correspondingly small or by filling the pipes with filler. This move can also bring additional benefits, as e.g. the residence time of the liquid flowing through the pipes is reduced, that with low flow rates at least a quasi-turbulent flow is achieved in the pipes, that disturbing boundary layers on the inner walls of the pipes are more easily broken up, etc. For the same purpose, the space surrounding the pipes as acting as a porous partition is filled with filler cells.

When it comes to the question of what kind of control is most suitable, it must be taken into account that at higher temperatures on the dissolution side, higher evaporation quantities are generally achieved. If heat supply at the same time as the transfer of at least one liquid component of the solution in the vapor phase is not possible or can only take place to a limited extent, the boiling point can be achieved and maintained with the help of the above-mentioned (negative) pressure control on the solution side, without simultaneous heat supply in the resolution.

The above-mentioned possibilities for pressure and temperature control on the solvent side to keep the solution at least as close to the boiling point as possible along the entire porous partition wall, as indicated according to the invention, can be realized with the help of measuring and regulation devices for controlling the pressure and temperature of solvent side and of the flow rate of solution. Preferably, the temperatures, pressures and flow rates on the distillate side are also regulated with corresponding devices. Under certain circumstances, discussed below, one can waive the above-mentioned mutually coordinated pressure-temperature regulation to achieve the boiling point and still achieve a comparatively only slightly reduced distillate flow.

Namely, surprisingly enough, it has been shown that - based on the previously known methods - it is possible to achieve a significant increase in the amount of distillate simply by the necessary pressure (negative pressure) for creating the boiling point only being created in the pores of the porous partition. This can e.g. in a simple way is effected by only the porous partition wall being immediately connected to a pressure (negative pressure) generating device. Although the solution and the distillate (condensate) e.g. has atmospheric pressure and both parts exhibit a temperature below the usual boiling temperature at this pressure, it is still possible, at a corresponding pressure (negative pressure) in the pores of the porous partition, to achieve at least an approximate boiling point in the solution in the immediate vicinity of the partition.

Often, this embodiment of the method according to the invention is so effective that one can dispense with additionally creating a corresponding boiling pressure (negative pressure) on the dissolution side. Thus, this method constitutes a particularly preferred embodiment of the method according to the invention.

Depending on the size and type of the porous partition, it may be appropriate to connect the porous partition to the device for generating (negative) pressure in several places.

Creation of the vapor pressure in the pores of the porous partition which corresponds to the temperature of the solution in the manner mentioned above is then possible, if the porous partition is constructed in a net-like manner, i.e. if there is a pore system where the pores are connected to each other via gas or vapor-permeable openings, channels, pores, etc. This embodiment of the invention can be carried out in a particularly efficient way, has the form of a microporous, cellular body of a thermoplastic polymer, selected from the group of olefin polymers, condensation polymers and oxidation polymers or mixtures thereof . The body then has an isotropic stroke with a majority of spherical cells, which are evenly distributed throughout the structure, and the adjacent cells are interconnected by pores, which have a smaller diameter than the first-mentioned cells. Preferably, the spherical cells in such a microporous cellular body have an average diameter C of 0.5 to 100 µ, sharpness factor ("Schårfefaktor") Sl - 30 and a ratio between average cell size and average diameter P of the pores connecting the cells C/P 2:1

to 200:1, and log C/P is 0.2 to 2.4 and log S/C is -1.4 to 1. The sharpness factor "S" (S factor) is then determined by analysis of a mercury intrusion curve. Such a microporous, cell-shaped body, which for carrying out the present invention can be in the form of at least a flat partition wall, a flat membrane, a tube, a hose or a hollow wire, as well as a method for its production is known from German Offenlegungsschrift 27 37 745- This publication also describes the calculation method of the S-factor (page 53).

Other bodies which are suitable for carrying out the method according to the invention, for use as a porous partition wall, and which, due to their special pore structure, are particularly suitable for carrying out the last mentioned embodiment of the method according to the invention, where only a pressure is set in the porous the pores of the partition wall, which correspond to a high degree to the vapor pressure of the solution, as well as methods for their production are known from German Offenlegungsschrift 28 33 493, German Offenlegungsschrift 28 33 623 and German Offenlegungsschrift 30 49 557.

A porous partition wall, for example of biaxially reinforced polytetrafluoroethylene (PTE) is only suitable to a limited extent for carrying out the method according to the invention, as the last mentioned embodiment of the method according to the invention cannot be carried out with such material or possibly only with poor results. This is due to the different shape and arrangement of the pores and the deviant structure of this porous material.

The method according to the invention can be carried out so that on the solution side, in the pores of the porous partition or on the distillate side (condensate side) there is a pressure that is equal to, greater or less than the atmospheric pressure, where as a rule there will be different pressures locally. This means that on the resolution side, e.g. if a pressure is set that is higher than the atmospheric pressure and the vapor pressure of the solution, that in the pores of the porous partition - under the conditions described

- a pressure is set which corresponds to a high degree to the vapor pressure of the solution, where this can also be higher than the atmospheric pressure, and that a pressure is set on the distillate side which is

higher than the pressure on the dissolution side. To maintain the required vapor pressure gradient, the (local) temperature of the distillate (condensate) must be lower than the (local) temperature of the solution. Also in this embodiment of

the method according to the invention, in the immediate vicinity of the porous partition, at least approximately the boiling point of the solution will be achieved, as mentioned above, that the solution is under atmospheric pressure and a negative pressure is set in the pores of the partition which corresponds to a high degree to the vapor pressure of the solution.

An important prerequisite for achieving high perpeat flows is that, in the method according to the invention, no transport gas is used on the distillate side. Namely, it has been shown that the high distillate flows which are characteristic of the method according to the invention are not reached in the presence of a transport or foreign gas.

The increase in effect that can be achieved with the present invention, compared to the hitherto known methods, i.e. the increase in the amount of distillate that diffuses through the porous partition per area unit of the membrane surface and per unit time, often amounts to more than the 7-fold.

Condensation of the vapor that penetrates from the solution through the porous partition wall can take place immediately, on the surface of the partition wall facing the distillate side, so that the formed, liquid condensate is in contact with the porous partition wall. However, the distillate can also first be led away from the porous partition in vapor form and condensed in another place. Then the liquid distillate (condensate) will not come into contact with the partition. This type of condensation can take place in an ordinary condenser. In order to promote the removal of the vaporized distillate to such a condenser, a pressure drop, generated by a negative pressure source, e.g. a vacuum pump, particularly efficient. Instead of the usual condensation, you can also use steam condensation, which is known per se. The energy efficiency of the method according to the invention can be increased significantly in this way, e.g. by mechanical steam condensation with rotary piston condensers or radial fans.

When the distillate is to be led away from the porous partition wall in vapor form, this must take place without transport gas, or if condensation of the distillate is to take place on a condensing surface opposite the porous partition wall, the intermediate space which is filled with distillate vapor must not additionally contain a gas that does not condense at the given temperature and pressure conditions.

The method according to the invention is not only suitable for treating so-called true solutions, such as salt water, acids or the like, but also for liquid mixtures and liquids containing organic or inorganic particles in undissolved form. also in the sub-microscopic area, microorganisms etc. and for extracts, emulsions, etc. All liquids where, with the method described according to the invention, there is at least a partial separation of at least one liquid component of the liquid, thus apply as solutions in the sense of the invention. This means that the desired product does not always have to be the condensed distillate, but can also be the concentrated solution or both.

The boiling point of solutions is often different from that of the pure solvent or of the various liquid mixture components in their pure form. For this reason, the boiling point of the solution, which depends on the concentration, often changes during the implementation of the method according to the invention. This must be taken into account when controlling pressure or temperature.

The porous partition can consist of porous or micro-porous materials which have the property that they are permeable exclusively to the steam, but not to the solution or

the condensate.

Porous partitions, which have proven to be suitable for carrying out the method according to the invention and which can also be in membrane form, consist of nylon, cellulose acetate, polypropylene, polytetrafluoroethylene, polyethylene, polyvinylidene fluoride, polyvinyl chloride, cellulose, asbestos, silicates, mineral substances. or mixtures thereof.

These materials are preferably not wettable by one of the two liquids. This property of the porous partition usually only has to be present under the conditions under which the method is carried out. It can optionally be achieved by corresponding pre-treatment of the porous partition wall.

Surprisingly, the method according to the invention can be carried out with great success, partly even with solutions, where the solution, but not the condensate, leads to wetting of the porous partition wall at atmospheric pressure, as only a negative pressure corresponding to the solution's vapor pressure is set on the solution side.

The porous partition can be in plane or not plane, e.g. curved, corrugated or closed shape, i.e. e.g. such as flat membrane (flat foil), hose membrane (hose foil), pipe or hollow wire or hollow fibre.

For carrying out the method according to the invention, an artificially produced, porous or microporous membrane will generally be preferred as a porous partition.

In an advantageous continuation of the method of the invention, the solution and/or condensate flows along the porous partition wall, where the present amount of solution and/or condensate quantity or only a part of them is moved one or more times along the porous partition wall by natural convection or forced, f .ex. by natural pressure difference or per se known transport means, such as pumps etc. The solution and condensate can flow in the same direction, in counter-flow, cross-flow or in any mixed-flow ratio.

The possibly necessary heating or cooling of the solution and/or condensate can take place immediately in the area of the porous partition wall or in separate steps. An at least partial recovery of the amount of heat that has been transferred from the solution to the condensate as a result of condensation of the distillate vapor and by heat transfer through the porous partition wall is also possible in other ways than the aforementioned. te precautions and can also be beneficial like this, e.g. using heat pumps.

The method according to the invention can be carried out in one or more steps, i.e. the solution can in turn be led along several and possibly different porous partitions and at the same time condensed step by step and/or the condensed distillate from a previous step can be used as a solution in a subsequent step, when in this way an even purer distillate can be obtained than with a one-step process.

The method according to the invention can also be used as a preceding, intermediate or final step in a multi-step method, where, for various reasons, other distillation, evaporation or similar methods are connected before or after.

At higher temperatures on the solution side or greater temperature differences between the solution and the condensate, the amount of distillate that passes through the porous partition is larger due to the prevailing larger vapor pressure drop, than at lower temperatures or temperature differences. This also applies when the boiling point has not yet been reached in the solution. For this reason, a pressure drop on the solution side or in the pores of the porous partition, until the boiling point is reached, will in these cases cause a minor increase in the amount of distillate. In the case of aqueous solutions and water as condensate and a temperature in the solution of e.g. only 25°C and a temperature in the condensate of e.g. 14°C, on the other hand, the amount of distillate in the method according to the invention will amount to more than 7.5 times, compared to an operating mode at atmospheric pressure, e.g. at 23% NaCl solution.

In order to achieve the boiling point of the solution, at least in the immediate vicinity of the porous partition, it is generally not absolutely necessary to create a negative pressure also on the distillate side, if the distillate is present in liquid form there, i.e. as condensate. But if this is desirable for other reasons, it has proven advantageous to set a higher hydrostatic pressure on the condensate side than on the solution side to prevent a sudden leak in the porous partition wall leading to solution entering the condensate, if this must be extracted in its purest form.

A leakage flow that may arise from such a leakage as a result of this precaution, and go from the condensate side to the solution side (return flow), will quite simply reduce the amount of distillate obtained, but will not, as a rule, disturb the process, up to a certain limit, as the condensate is not non-species for the resolution.

On the other hand, a difference between the hydrostatic pressure on the solution side and on the condensate side can lead to a mechanical deformation or even to a break in the porous partition wall. This can especially happen when the porous partition has the form of one or more very thin membranes. In order to avoid such unwanted deformations due to hydrostatic pressure difference, common devices and precautions can be used for cushioning or strengthening the porous partition wall. As a result of these precautions/organs, however, there should not be a significant weakening of the specific evaporation effect of the porous partition wall. In many cases, however, it has proven far more advantageous to set the hydrostatic pressure (negative pressure) at approximately the same low level on both sides of the porous partition wall. The hydrostatic pressure difference which then acts on the porous partition wall will be zero or nearly zero. According to the invention, the hydrostatic pressures are said to be approximately equal, when the difference between the two pressures is in the range 0-10% of the lower of the two pressures.

Due to the high degree of purity of the distillate that can be achieved with the method according to the invention, the good thermal efficiency and because the method can also be carried out at low temperatures in the boiling area, it is, for example, very well suited for extracting drinking water and even from boilers -feed water (completely desalinated water), even from salt water, so that it is suitable for use on board ships. Other areas where the method according to the invention can be advantageously used are the treatment of electroplating wastewater, also as a preliminary step in metal recycling, concentration of caustic soda, fruit juice, sugary juice from sugar extraction, milk etc., treatment of whey, production of sterile water for and in laboratories, pretreatment or manufacture of pharmaceutical products, extraction of drinking water from urine during space travel, steaming of spinning baths, e.g. in rayon spinning mills and other comparable processes.

The device according to the invention, which is suitable for carrying out the method according to the invention, essentially consists of at least one container, which is divided into at least two chambers by means of at least one porous partition, of which one chamber is intended for absorption of the solution and the other for absorption of the distillate or condensate. According to the invention, the chamber for receiving the solution and/or the chamber for receiving the distillate and/or the porous partition wall are provided with organs, by means of which each of the mentioned parts can be connected to a device for creating negative pressure (vacuum) or positive pressure.

At least the parts of the device which, according to the invention, are operated with underpressure or overpressure, are made in an outwardly closed construction.

In order to create the negative pressure for achieving the boiling point at low temperatures, as proposed according to the invention, the container with the two chambers can also be barometrically set up and connected. This means that the container is arranged at a level that corresponds to the desired boiling pressure and that the supply and outlet lines are designed as rising or falling lines, which open into vessels, which are arranged at a lower level than the container and are filled with liquid ( solution or condensate), so-called immersion vessels. The lines open below the liquid level in these vessels and thus form a so-called barometric lock.

The chambers must then be designed in an outwardly closed form and can, for example, in the same way as the porous partition, be connected to a common or separate negative pressure or vacuum device for ventilation.

The device according to the invention further comprises the measuring, adjusting and monitoring devices which are necessary and in and of themselves usual as needed. These will not be discussed in more detail as they will be known to professionals and are self-explanatory, once you are familiar with the requirements that are being made.

In the case of a feeder line, the device according to the invention comprises feeding means for supplying and removing solution and/or distillate or condensate to and from the respective chambers, as well as possibly return lines with corresponding regulation means, which enable repeated circulation of all or parts of the solution and/or or the condensate flow.

Furthermore, the device according to the invention can include devices for heating and/or cooling the solution and/or the condensate. These devices can, according to need or desire, be arranged inside or outside the chambers for the solution or the distillate or the condensate.

The device according to the invention can. further include several chambers for the solution and/or several chambers for the distillate or condensate. The chambers for the solution and the chambers for distillate or condensate can flow-technically be connected in parallel or in series. When both the chambers for the solution and the chambers for condensate are connected in series, the solution and condensate can preferably be directed in counter-flow, so that, if there is no intermediate heating or intermediate cooling of the two liquids, a different temperature level is indeed set in each pair of chambers. If desired, an equally large but only slightly different temperature difference between solution and condensate can be set in each pair of chambers.

If the method according to the invention is to be carried out intermittently, i.e. charge-wise, circulation pumps etc. can be dispensed with. In order for solution and condensate to be equally kept in motion, stirring or mixing devices can be arranged for this purpose. Heating and cooling devices can also be beneficial.

If such high boiling temperatures are desired that they require overpressure, the chambers can be connected with correspondingly high risers, so that the desired overpressures can be set using correspondingly high liquid columns. The same can be achieved without risers, by means of gas cushions or with correspondingly dimensioned circulation pumps and throttling devices. In the case of containers with closed construction, the vapor pressure which corresponds to the temperature of the liquid and which, in the absence of gases, corresponds to the boiling pressure, will set itself.

Preferably, the device according to the invention comprises

a porous partition, which has a net-like construction,

i.e. where the pores that open on the solution and distillate side and are open throughout, so that vaporized distillate from the solution side can diffuse through the pores to the distillate side, are connected to each other by means of gas- or vapor-permeable openings, channels, capillary tubes, pores, etc. cross connections, as discussed in detail above, in connection with the general description of the method according to the invention.

If gases are dissolved in the solution, it may be appropriate to release the solution from gases in a manner known per se even before it is brought into contact with the porous partition wall. This can be particularly advantageous when the boiling point of the solution is first reached in the area of the partition wall and not before. For this purpose, a corresponding degassing device is arranged in front of the chamber which is to absorb the solution.

If the device according to the invention comprises a net-like structure, porous partition, which is suitable for setting a pressure in the pores which corresponds to the greatest extent to the actual vapor pressure of the solution, it is advantageous that at least this partition is connected to . a vacuum and overpressure device.

The invention and the results that can be achieved with it will now be described in more detail with reference to examples of the device according to the invention and the method according to the invention, which are reproduced in the drawing., •

In Figures 1-10, some embodiments of the apparatus according to the invention and various measuring devices are shown in simplified, schematic representations, partly in sections or in sections.

In fig. 11-18 the measurement results are reproduced graphically. In detail shows

fig. 1 an embodiment of the device according to the invention which is suitable for continuous operation,

fig. 2 a series connection of four distillation devices according to the invention,

fig. 3 an embodiment, where the device according to the invention is set up barometrically,

fig. 4 an embodiment of the device according to the invention with heat energy recovery, suitable for continuous operation,

fig. 5 a particularly preferred embodiment of the distillation apparatus according to the invention, which makes it possible to set different pressures in the pores of the porous partition opposite the solution side and/or the condensate side,

fig. 5a an embodiment of the distillation apparatus according to fig. 5,

fig. 5b a measuring device for measuring the pressure in the pores of the porous partition wall using pressure measuring probes,

fig. 6 is a side view of an embodiment of the distillation apparatus according to the invention, suitable for continuous operation, with a non-tubular, porous partition, which makes it possible to set a deviating pressure in the pores of the partition, opposite the solution side and/or the condensate side,

fig. 7 is an elevation of the device according to fig. 6,

fig. 7a and 7b are embodiments of measuring points for recording the pressure in the pores of a porous partition, such as the device shown in fig. 6 and 7,

fig. 8 a measuring device for recording the pressure or the pressure distribution in the pores of a (tubular) porous partition wall,

fig. 9 a distillation apparatus according to the invention, which is suitable for continuous and intermittent operation, with an agitator,

fig. 10 a distillation device according to the invention with two stirrers and suitable for intermittent operation,

fig. 11 is a graphical representation of the increase in the transmembrane distillation flow obtainable under otherwise equal conditions by lowering the pressures that affect the porous partition under atmospheric pressure until the boiling point is reached in the solution,

fig. 12 a graphical representation for comparison purposes of obtainable transmembrane distillation currents at different

equal temperatures and atmospheric pressure or when the boiling point is reached on the solution side,

fig. 13 a graphical representation of the increase in the transmembrane distillation flow obtainable under otherwise equal conditions by reducing the pressure on the solution side until the boiling point of the solution is reached,

fig. 14 for comparison purposes a graphical representation of the achievable increase in the transmembrane distillation flow at increasing temperatures, at atmospheric pressure on the solution side and a pressure in the pores of the porous partition corresponding to the pressure on the solution side, and alternatively at a pressure in the pores corresponding to that of the solution current vapor pressure,

fig. 15 is a graphical rendering of achievable transmembrane distillation flows in an otherwise identical mode of operation as indicated for fig. 14, but with a porous partition of a different nature,

fig. 16 for comparison purposes the graphical rendering of achievable transmembrane distillation flows in a mode of operation not according to the invention and different modes of operation according to the invention,

fig. 17 a graphic representation of the pressure distribution in the pores in different sized (long) (tubular) porous partitions,

fig. 18 for comparison purposes the graphical representation of the achievable transmembrane distillation flows in an operating mode that is not according to the invention and an operating mode according to the invention with two different solutions.

In the embodiments of the device according to the invention shown in fig. 1-10, all position numbers with the addition "a" relate to parts on the solution side and all position numbers with the addition "b" to parts on the distillate or condensate side. Equal parts have the same position number in all figures. In fig. 1, the following parts of the device according to the invention are reproduced: The container 1, which is divided into the two chambers la by means of the porous partition wall 2; lb (la for solution, lb for condensate), the ring lines 3a; 3b, the supply line 4a for the solution, the outlet lines 5a; 5b, the heat exchangers 6a; 6b, the pumps 7a; 7b, the valve 8a, the connections 9a; 9b to a common or separate, although not shown, device for generating underpressure (vacuum) or overpressure, as well as the throat organs

13a; 13b. The implementation of the method according to the invention with this device appears from the above description of the method. The individual arrows indicate the flow directions in the individual pipelines. The pumps 7a; 7b makes it possible to circulate an possibly much larger volume flow through the ring lines 3a; 3b than what corresponds to the amount of solution that is supplied through the supply line 4a or the amount of condensate that is led away through the outlet line 5b. The amount of solution supplied to the device can be set to the desired value by means of the valve 8a. The temperatures of solution or condensate can be brought to the desired level with the help of the heat exchangers 6a and 6b. The pressure level in the chambers la and lb can be set to the same or different values by means of the devices not shown for generating negative or positive pressure via the connecting lines 9a and 9b respectively. The concentrated solution is led away through outlet line 5a, while the formed distillate (condensate) is led away through outlet line 5b. The heat exchangers 6a and 6b can also be arranged in the chambers la and lb. Instead of ordinary heat exchangers, others can also be used, e.g. electrically powered heating or cooling devices (peltier elements). In a particularly advantageous way, they will also enable heat supply or heat removal in the immediate vicinity of the porous partition. The wall of the container 1 itself can also be used as a heat transfer surface. Furthermore, a negative pressure can be created on the porous partition 2 without the negative pressure devices, not shown, and the connection lines 9a.'; 9b to them. This can happen by corresponding adjustment of the throat organs 13a; 13b on the suction side of the pumps 7a; 7b, a sufficiently high negative pressure is generated which also becomes effective in the chambers la; lb. In the embodiment of the device according to the invention shown in fig. 1, the solution and distillate flow in counter-current along the porous partition 2. In that the throat devices 13a; 13b is placed behind the chambers la or lb, it can generate

res an overpressure in the chambers la; lb by means of the pumps 7a; 7b.

In fig. 2 are four chamber pairs la; lb shown connected in series. The solution flows through the four chambers la in turn, from left to right in the image plane. The distillate (condensate) flows through the chambers lb from right to left. The two fluids thus flow in countercurrent. The inlet temperature t^ of the solution is higher than its outlet temperature t^, the inlet temperature of the condensate is lower than its outlet temperature t^. Also, t^is higher than and t^higher than t-^. It is possible to choose the setting of the liquid flows so that you get approximately t^ - t2= tj, - t-^, i.e. that in each of the four stages there is approximately the same temperature difference between solution and distillate (condensate). It is also possible, in one or more places, to divert a condensate partial flow such as e.g. can correspond to the amount of condensate produced in each stage. Likewise, it is possible to mix fresh solution in any quantity in the solution stream between the individual stages (chamber pairs). If desired, heat exchangers can also be arranged for heating or cooling the liquid flows between the individual stages. As this figure is only intended to illustrate the possibility of a series connection of several porous partitions in a schematic way, additional devices, such as the connections for connecting devices that generate negative or positive pressure, pumps, measuring and regulating instruments and organs etc. not shown.

In fig. 3 shows the barometric arrangement of the container

1 with the chambers la; lb and the porous partition 2. The containers lea; 12b and 14a are designed as immersion vessels, where the riser line 10a for solution and the drop lines 11b or lia for condensate or the concentrated solution open below the liquid mirror in these vessels and where the aforementioned containers via lines 4a4b or 15a can be filled or emptied continuously or intermittent. The negative pressure that prevails in chamber la; lb depends on the height of the riser line 10a or the fall lines 1a; 11b. The pumps 7a; 7b act as circulation pumps for solution or condensate. The amount of fresh solution supplied to chamber la depends on the level difference between immersion vessels 12a and l4a and can be throttled by means of valve 13a. Beg ge the chambers la; lb can also be connected to negative pressure devices, even if it is only for aeration. Heat exchangers can also be arranged in the riser line 10a, the ring lines 3a; 3b and/or the fall leads lia; 11b. Furthermore, the upper side of the chamber can allow for the solution, e.g. be designed as a solar collector and the underside of chamber lb for condensate can be equipped with cooling fins. Finally, feed or dosing pumps can be arranged in the riser line 10a and/or the drop lines. Ila; 11b.

If the containers 12a; 12b and 14a are not arranged below, but above the container 1 (high-level containers), the chambers la and lb can be operated with excess pressure. The height of the overpressure then appears from the level difference between the liquid mirrors in the (high-level) containers 12a; 12b or l4a and the porous partition 2. The fall lines 10a; 11a and 11b from fig. 3 become risers with this arrangement. The (height level) containers 12a; 12b and 14a can act as storage containers with a sufficiently large volume, or they can only act as level vessels with a smaller volume. This applies similarly to the arrangement of the three containers as immersion containers according to fig. 3.

The embodiment of the apparatus according to the invention which is shown in fig. 4 includes, in addition to the parts that are also included in the embodiment shown in fig. 1 and which for this reason also have corresponding reference numbers, also the following parts: A supply pump 16a for dissolution, a filter 17a for dissolution and a heat exchanger 18, by means of which recovery of a part, possibly the majority of the energy transferred to the distillate (the condensate) from the solution in the transmembrane distillation (heat of vaporization) is possible. The required amount of heat to achieve the nominal inlet temperature of the solution is supplied to the solution immediately before it enters the chamber 1a by means of the heat exchanger 6a. Also in this embodiment of the device according to the invention, the solution and the condensate are pumped in a circuit through the ring lines 3a and 3b respectively by means of the circulation pumps 7a and 7b. The amount of distillate that exits the circuit through outlet line 5b corresponds to the amount of distillate that passes through the porous partition 2. The amount of solution that exits the circuit through outlet line 5a corresponds to the amount of solution supplied to the circuit through supply line 4 minus the amount of condensate that emerges through the discharge line 5b. As fig. 4 further shows, in this embodiment the concentrated solution is taken out at a place where the concentration of the solution is greatest and its temperature is lowest. Condensate is removed at a place where the condensate has the lowest temperature.

In fig. 5 shows a particularly preferred embodiment of the container 1 for carrying out the method according to the invention. In this embodiment, the porous partition wall is formed by a plurality of tubes. The pipes which form the porous partition are at their ends embedded in pipe bottoms 21, which can for example consist of a molding compound which is common for such purposes and which acts as partitions between the individual chambers. The container 1 further has an inlet opening 24a (24b) and an outlet opening 25a (25b) for solution (or for distillate or condensate) and an inlet opening 22b (22a) and an outlet opening 23b (23a) for distillate or condensate (or solution) . The solution can thus be led through the tubes. Then the distillate (condensate) will flow around the pipes, but it can also be arranged the other way around. In fig. 5, this is indicated by the fact that the alternative meaning, also for the two chambers la and lb in reverse mode of operation, is indicated in brackets. The pipes which form the porous partition and thus the container 1 can have any length and be arranged horizontally, as shown in fig. 5, or vertically. With a vertical device, a difference in the hydrostatic pressure corresponding to the pipe length and thus also with the boiling temperatures between the highest and lowest point is achieved, while with a horizontal device a pressure difference occurs between the inlet and outlet side, essentially only as a result of the unavoidable equal flow loss. For the sake of completeness, it should also be mentioned that also an inclined device - ie a device between the horizontal and vertical - of the container 1 which is shown in fig. 5 and also in other figures, can be advantageous. If an embodiment is chosen, where the container 1 can be swung from a horizontal to a vertical arrangement and vice versa, the pressure conditions can be changed in a simple way, possibly during the operation of the device. This can, for example, be very advantageous for experimental or laboratory devices, especially because such installations often work with hoses instead of rigid pipelines.

An essential feature of the container 1 shown in fig. 5 and 5a is the (negative) pressure chamber 19, which can be connected via the coupling 9c to a device for generating negative or positive pressure. By means of this device 19; 9c, in a particularly advantageous way, a pressure can be created in the pores of the partition, which corresponds to the highest degree to the vapor pressure of the solution, even if there is a higher pressure in the chambers la and lb than that which corresponds to the vapor pressure. A prerequisite for this is that the wall of the pipes that form the porous partition consists of a material that is suitable for this mode of operation, i.e. that the wall e.g. is net-like constructed. It has already been mentioned previously, what is understood by this in the present context. If necessary, it may be appropriate to arrange several short containers in succession instead of a long container 1 with a (under)pressure chamber 19. Such a chamber 19 can also be arranged on both sides of the container 1, i.e. two chambers 19 for a container 1. Finally, more than two such chambers 19 can also be arranged in a container 1. For the chambers 19 which are not arranged at the ends of the pipes, a diversion 35 must be arranged for the liquid that flows around the pipes, as shown in fig. 5. To check the pressure (negative pressure) prevailing in the 2 pores of the porous partition, it is recommended to arrange a manometer 20, which is connected to one of the pipes. In fig. 8 shows details of such a connection between a porous pipe and a manometer. In the embodiment of the container 1 shown in fig. 5 solution and distillate (condensate) can be carried as shown in (crossing) countercurrent, or by reversing the direction of flow for one of the liquids in (crossing) common direction.

A detailed description of fig. 5 with regard to the reference numbers will be redundant. Reference number 36 also indicates filling or displacement bodies.

In the case of wetting liquids, these preferably flow around the pipes, as there is otherwise a risk of such a liquid being sucked through the pipe walls and into the chamber 19.

Figures 6 and 7 show an embodiment of the device according to the invention in two different views. Here, the porous partition wall 2 is designed as a flat plate or membrane and consists of a material that allows the generation of the steam pressure alone in the pores of the porous partition wall 2. The (low) pressure chamber 19 here has the shape of an annular channel, where the porous partition wall 2 opens with its four sides. The annular channel-shaped chamber 19 is gas-tightly sealed against the chambers la and lb. The other parts of

this embodiment appears from the reference numbers, so that a repeated description of these parts is unnecessary. The generation of the (under)pressure which corresponds to the vapor pressure of the solution alone in the 2 pores of the porous partition has the additional advantage that between the solution side la and the condensate side lb at least no significant pressure difference occurs, which could possibly become dangerous for the porous partition 2.

In fig. 8 shows a measuring device, by means of which different pressures (underpressure) can be set in the pores of a porous partition wall with a corresponding pore structure. The pressures that then occur at different distances from the pressure connection point 26 can also be measured. At the connection point 26, the porous, tubular partition wall 2 is surrounded by a ring 27 with an annular channel 28, where the annular channel 28 is gas-tightly sealed against the surroundings by means of gaskets 29. Via the pipeline 30, the annular channel 28 can be connected to a (negative) pressure generating device (not shown). At measuring point 31, the same parts are 27; 28; 29; 30 is arranged, as at the connection point 26. The pipeline 30 is, however, connected to a pressure gauge 20. The measuring point 31 is displaceably arranged on the tubular, porous partition 2, so that at optional distances from the connection point 26 one can measure

the (negative) pressure that prevails in the pores of the porous partition wall

2 and which is created when an under- or over-pressure of any size is produced in the annular channel 28 of the connection point 26. For measurement, the porous partition wall 2 is immersed in a liquid, e.g. water, which does not wet the partition wall, i.e. does not penetrate into the pores, and which can be in a container 32. The liquid will then also penetrate into the interior of the pipe due to the liquid-repellent property (non-wettability) of the porous partition wall, but not in the pores of the partition. The device shown as an example in fig. 8 for measuring the pressure in the 2 pores of the partition wall, can also be used for embodiments of the device according to the invention which corresponds to the one shown in fig. 5. Por planar, porous partitions 2, such as e.g. shown in fig. 6 and 7j, the measuring device 27, 28, 29 must be reshaped accordingly and adapted to the flat shape of the partition wall 2, e.g. as shown in fig. 7a and 7b. These figures need no further mention.

The pressure in the 2 pores of the porous partition wall, which is measured with the measuring device as shown in fig. 8, is a mean value of the actually slightly varying pressures that prevail in the individual pores. However, it has been shown that the recording of this mean value when carrying out the method according to the invention or operation of the device according to the invention as a rule satisfies the stated requirements and enables good control and monitoring of the method. However, it is also possible to find out the pressures prevailing in the pores very locally limited by means of pressure measuring probes 37 with dimensions which only constitute a fraction of the thickness of the porous partition 2. For this purpose, a recess (bore) can be arranged at the desired location, which corresponds to the probe's dimensions (diameter) to a depth in the porous partition 2, where the pressure is to be recorded. The probe 37 is introduced into this depression (bore) and the depression (bore) is gas-tight sealed to the outside with the probe in place.

Fig-5b shows such a measuring device.

In the embodiment of the device according to the invention shown in fig. 9, the porous partition 2 consists of at least one spiral tube (tube), through which the distillate (or the condensate or the solution) can be led. Chamber lb for distillate or condensate (or chamber la for dissolution in reverse mode of operation) is formed here by the interior of the porous partition's 2 tubes. Chamber la for solution or lb for distillate or condensate in the reverse mode of operation is formed by the inner space of the container 1. In order to keep the liquid in the container 1 moving, the stirring device 34 is arranged. The operation of this stirring device 34 is not shown. In addition, the container 1 is designed with a double wall in the lower area, and the formed space 33 can be operated with a cooling or heating fluid as needed. This embodiment of the device according to the invention is particularly suitable for intermittent operation, i.e. so-called charge operation. In this way, a very gentle concentration of a solution is made possible, which is then suitably filled into the container 1. If desired, the container 1 can also be operated continuously with solution (or with distillate or condensate in the case of reverse mode of operation). For this purpose, the inlet and outlet openings 24a (24b) 25a (25b) can be used, which are otherwise used for filling and emptying the container 1. If the distillate or the condensate of this type of device according to the invention is led through the pipeline, the boiling point can in the immediate surroundings of the partition wall 2 on the dissolution side can be achieved in a simple way, e.g. in that the lowest possible pressure is set on the distillate or condensate side lb, i.e. in the pipeline, e.g. a (negative) pressure that corresponds to the condensate's vapor pressure. If the distillate is to be led away in vapor form, an even lower pressure can be set in the pipeline. Moreover, this embodiment in a correspondingly reduced form is also very good as a laboratory apparatus, where the temperature of the solution in the container (vessel) 1 can be brought close to the boiling point with a bunsen burner or an electric hot plate and the pipe forming the partition 2 can be connected to a water line , when the distillate does not have to be collected separately.

The embodiment of the apparatus according to the invention shown in fig. 10 is also suitable for intermittent operation. The container 1 is here divided into the two chambers la and lb for solution and condensate by means of the planar, vaulted or optionally designed porous partition 2. In both, chambers la and lb, stirrers 34a and 34b are mounted, which keep the solution and condensate in motion. In addition, a heating device 6a is arranged in chamber la, e.g. a heat exchanger, and in chamber lb a cooling device 6b is arranged. For starting this device, it may be appropriate that the chamber 1b is initially at least partially filled with condensate or a condensate-like liquid. Chamber lb can be provided with an overflow at the top (not shown), so that it becomes possible at all times to keep chamber lb completely filled with condensate and thus keep the porous partition wall completely covered.

Instead of the heat transfer devices 6a and 6b, the chambers la and lb can also be provided with a heating or cooling jacket, as shown in fig. 9 (designated as 33). Conversely, other heating or cooling devices can also be mounted with the device according to fig. 9.

According to the invention, the chambers la and lb, as well as the porous partition wall 2 in the embodiments according to fig. 9 and 10 also be connected to a device that generates underpressure or overpressure. Likewise, measuring devices can be arranged for monitoring the pressure in the 2 pores of the porous partition, as shown in fig. 5-8 and discussed in connection with these figures.

In fig. 1 to 7, 9 and 10, the chambers la and lb are made in a closed construction. A chamber that is not operated with negative or positive pressure can, however, also be designed as an open vessel. For reasons of clarity, any necessary additional measuring, regulating or monitoring devices for pressure, temperature, liquid flow rates, concentrations etc. are also not shown.

When the device according to the invention is first started, there is usually no condensate, so that the condensate side lb should initially be filled with a liquid that is equal to the condensate, provided that the distillate is not to be led away in vapor form. It has often proved particularly advantageous to fill the distillate side lb with a cooler liquid first.

In fig. 11, the amount of condensate that is obtained by reducing the pressure on the solution and condensate side under atmospheric pressure is shown graphically as a percentage of the amount of condensate that can be obtained at atmospheric pressure. This applies to the case that approximately the same negative pressure prevails on both sides of the porous partition. It can be seen that the amount of distillate that diffuses through the porous partition wall, which corresponds to the achievable condensate quantity, rises approximately fivefold, when the pressure on both sides of the partition wall is reduced to approx. 200 mbar, and rises to approximately the sevenfold belt at a pressure of approx. 100 mbar. This relationship has been found to be approximate for different porous partitions and different solutions. For example, the measurements were carried out with a 45% LiCl solution and with a device where the porous partition wall was arranged at a higher level than the storage container for the solution and the collection containers for condensate or the concentrated solution. The device was similar to that shown in fig. 3, but the aforementioned containers were made in a closed construction with shorter riser or faller lines. The chamber for absorbing the solution and the chamber for absorbing the condensate were each connected to a separate negative pressure device. The porous partition wall consisted of 6 tubes of a mesh-like constructed, porous polypropylene, as detailed above. The tubes were 420 mm long and had an external diameter of 6.1 mm and an internal diameter of 4.2 mm. The solution flowed around the pipes and the condensate through the pipes. With the help of circulation pumps, 250 l/hour of solution and condensate was circulated by pumping and led along the porous partition wall. At atmospheric pressure, the amount of condensate that passed through the partition was 103 ml/hour and at 100 mbar absolute pressure it was 720 ml/hour. The temperature of the solution was approx. 77°C, on the condensate side the average temperature was approx. 15°C. The solution's boiling point at 100 mbar was approx. 77°C

Fig. 12 shows an arrangement of condensate quantities which

can be achieved with the method according to the invention and with another method, expressed in l/m h. The lower curve was obtained by the transmembrane distillation being carried out at atmospheric pressure and different temperatures. It can be clearly seen that the increase in the amount of condensate that passes through the porous partition initially increases slightly with increasing temperature of the solution. Striking is the disproportionately strong increase in the amount of condensate in the method according to the invention,

i.e. when a temperature is reached in the solution that is at most slightly below the boiling temperature, as defined above. The lower curve thus reproduces the method according to the invention only in the far right part. The upper curve was obtained by setting a vapor pressure corresponding to each temperature of the solution at all times on the solution side according to the invention, so that a boiling point was achieved on the solution side at all temperatures. At approx. At 100°C, the two curves overlap (not shown), as the boiling point is reached in both operating modes at this temperature. A comparison of the two curves

also makes it clear that in the lower temperature ranges, e.g. at 50°C, a doubling of the amount of condensate is achieved by the method according to the invention (upper curve), while the difference in amounts of condensate at higher temperatures is admittedly greater, but percentageally smaller. The temperature of the condensate was here set constant at approx. 20°C.

Fig. 13 shows the amount of condensate that can be obtained at a constant solution temperature of 55°C at different negative pressures on the solution side. This diagram also shows the large increase in the amount of condensate that passes through the porous partition wall immediately before and when the boiling point of the solution is reached, i.e. when the method according to the invention is carried out. In this diagram, e.g. "-600 mbar" that the set pressure on the solution side was 600 mbar below atmospheric pressure.

In fig. 1H is a graphical representation of the results obtained with a device according to the invention, as shown in fig.

5. Lower curve reproduces the amount of condensate at atmospheric pressure and different solution temperatures. The method according to the invention takes effect above 90°C. This can be seen from the disproportionate increase in the amount of condensate that is achieved when, according to the invention, at least on the dissolution side, the area close to the boiling point is reached, as defined above. The upper curve reproduces the achievable condensate quantities at different solution temperatures, when the vapor pressure is set in the pores of the porous partition that corresponds to the current temperature at any given time, compared to atmospheric pressure thus a negative pressure, so that according to the invention, at least in the immediate vicinity of the porous partition (at least approximately) when.the boiling point. A comparison of the two curves here also shows very clearly that the method according to the invention (upper curve) at lower temperatures results in a relatively greater increase in the amount of condensate that can be achieved than at higher temperatures. At 50°C, a four-fold increase in the amount of condensate was thus achieved compared to methods that are not according to the invention, at 70°C a three-fold increase was reached and at 90°C somewhat more than a doubling. The absolute increase in the amount of condensate 1 l/m h was significantly more at higher temperatures than at low ones. The increase in the amount of condensate following the method according to the invention (upper curve) thus amounted, compared to another method, to 30 l/m ph at 90°C, but only approx. 9 1/m^h at 50°C. If reference is made to low dissolution temperatures, the method according to the invention will thus provide significant technical and economic advantages.

But even at higher temperatures, for example a doubling of the amount of condensate when operating according to the invention will mean a not inconsiderable improvement.

The results which are graphically shown in Figures 12-14 were obtained with an aqueous 0.1% NaCl solution. The porous partition wall consisted of 420 mm long tubes with an external diameter of 6.2 mm and an internal diameter of 4.1 mm and thus a wall thickness of 1.05 mm. The pipe wall consisted of a net-like constructed, porous polypropylene, as discussed in detail above. The pore volume was 80% and the largest pore diameter was 0.85 U. A total of 18 such parallel-connected tubes were connected to a unit (module construction, cf. Fig. 5). Here, the solution passed through the pipes, while the condensate flowed around the pipes on the outside. The amount of solution that was added to this distillation unit amounted to 250 l/h,

so did the amount of condensate, and the amount of solution leaving the still was reduced by the amount of distillate that diffused to the condensate through the porous partition, and the amount of condensate was increased by the same amount.

The results which are graphically reproduced in fig. 15 was obtained under otherwise the same conditions as those reproduced in fig. 14, but a different, porous partition was used. The pipes used here had an external diameter of 8.6 mm, an internal diameter of 5>5 mm, i.e. a wall thickness of 1.55 mm, a pore volume of only 75% and a maximum pore diameter of only 0.55 U • All other parameters were unchanged. The amounts of condensate obtained under these conditions were significantly lower. This can be attributed to the lower pore volume, the larger pipe wall thickness and the smaller pores (pore diameter). The conclusions that must be drawn from this are obvious.

Fig. 16 shows a compilation of the condensate quantities that can be obtained under different operating conditions. For this graphical presentation, the corresponding values obtained from several measurement series are the average. The inlet temperature of the solution was at all times 50°C, the inlet temperature of the condensate was 16°C. The other parameters correspond to those that were also present in the results according to fig. 12-14. Under the aforementioned conditions, the amount of condensate "1" was obtained by a method which was not according to the invention, in that atmospheric pressure was set on the solution side, the condensate side and in the pores of the porous partition wall. The amount of condensate "2" was obtained when a negative pressure was generated on the solution side corresponding to the solution's negative pressure, i.e. when the boiling point was reached and maintained on the solution side. The amount of condensate "3" was obtained when a pressure (vacuum pressure) corresponding to the vapor pressure of the solution at 50°C was created only in the pores of the porous partition wall, while atmospheric pressure was set on the solution and condensate side. The amount of condensate "4" was obtained when a pressure (negative pressure) corresponding to the vapor pressure of the solution at 50°C was set on the solution side and in the pores of the porous partition wall.

These results show very clearly that a significant increase in the amount of condensate can be achieved with the method according to the invention. By setting a pressure that corresponds to the temperature of the solution exclusively in the pores of the porous partition, such an increase in the amount of condensate that can be achieved can already be achieved that the generation of a corresponding (negative) pressure on the solution side can be waived, even if this also results in an increase in the amount of condensate, although the latter increase is less pronounced. This means that the maximum possible amount of condensate can in reality possibly already be achieved, at least approximately, when according to the invention, at least on the solution side and in the immediate vicinity of the porous partition, the relevant boiling point of the solution is reached, in the smallest area for this boiling point .

Fig. 17 shows the pressure drop in the pores of pipes, which are connected to a device that generates negative pressure and which admittedly consisted of the same material and had the same diameter as the pipes mentioned in connection with fig. 12-14, but which had a different length. One pipe had a total length of 0.5 m, the other a total length of 2 m. The two pressure drop curves were recorded with the measuring device shown in fig. 8 and discussed above, at room temperature and in water. At one end of the tubes, a negative pressure was generated that was 930 mbar below atmospheric pressure. The negative pressure that forms in the pores was measured by moving the measuring point (31 in Fig. 8) to different distances from the pipe end. The results from these measurements show that the pipe length has a large influence on the pressure drop in the pipes' pores. This applies similarly to flat plates, rods or differently designed bodies with a corresponding mesh-like constructed pore structure. This means that the vacuum, as with short pipes or plates with a small surface area, is generated in one place, e.g. at a pipe end, at an arbitrary distance from this place, acts stronger than in the case of a long pipe or a plate with a large surface.

Depending on the temperature profile created by the method according to the invention at the porous partition wall, and the resulting vapor pressure profile, a pressure distribution as shown in the lower curve can lead to the dissolution side, in the immediate vicinity of the entire porous partition wall, achieving the solution's current boiling point, at least the range for this that the invention prescribes. If the temperature difference on the solution side between the inlet and outlet side, and thus the vapor pressure difference, is however small, in order to achieve a pressure in the pores of the partition wall that corresponds to a high degree to the vapor pressure of the solution, it may be appropriate to connect the porous partition wall with a device for generating negative pressure with short length distances, as shown for example in fig. 5a.

The graphically reproduced measurement values in fig. 18 was registered when carrying out the transmembrane distillation method in an operation that was not according to the invention and in operation according to the invention. The upper curve was obtained with a 43% CaCl solution, the lower curve with a 33% LiCl solution. The measurements were carried out at a pressure on the solution side that was above atmospheric pressure, ie at 1065 mbar for the upper curve (CaCl solution) and at .1040 mbar for the lower curve (LiCl solution). The boiling temperatures were above 120°C. These measurements also show that only with the method according to the invention, i.e. in the area immediately around the boiling point, as defined above, can sufficiently high condensate quantities be reached. if the transmembrane distillation method is to be exploited economically. The porous partition that was used for these measurements was the same as that used for recording the measurement values that are reproduced in fig. 15 and which is described above.

Additional examples:

With a device according to the invention which in all essential parts corresponded to the device according to fig. 4, measurement series were carried out for different flow rates on the solution side and the condensate side. The set or achieved temperatures t, flow rates at all times

Q and pressure P were measured at locations A to D in fig. 4 (the letters are circled there). The results are shown in Table 1.

The porous partition here consisted of six 9.2 m long pipes of porous polypropylene with a net-like pore structure. The tubes' outer diameter was 9 mm, their inner diameter 6 mm. Measuring point A was on the inlet side for solution in the distillation apparatus, measuring point B at the outlet point for the solution, measuring point C at the inlet point for condensate and measuring point D at the outlet point for condensate from the distillation apparatus.

When recording the flow rate Q, only the amount of solution or condensate entering the distillation apparatus was measured at any time. The condensate that exited the overflow line (5b in Fig. 4) was collected and weighed. With the thus obtained values, it was calculated how much distillate was obtained per hour and per m porous partition. This distillate quantity D is indicated in the last column of the table. The solution then flowed through the interior (lumen) of the tubes, while the condensate flowed around the outside of the tubes. The condensate side was connected via the overflow line 5b to the surroundings, i.e. with atmospheric pressure, while the solution side was connected to a device for generating negative pressure.

The designations of the measured value symbols in table 1 indicate where the relevant value was measured. Thus, t„ B means the temperature that was measured at B, ie the temperature of the solution leaving the distillation apparatus.

The measurement series listed in table 1 clearly show the influence of the flow rates on the solution or condensate side on the amount of distillate that can be obtained.

Moreover, the measurement series show that the method according to the invention also leads to good results when a pressure is created on the solution side that is partly above atmospheric pressure, as long as the boiling point of the solution or at least the range for this is reached at least in places.

In table 2, for comparison purposes, the analysis values for tap water, for distillate obtained from tap water by the transmembrane distillation method according to the invention, of distillate obtained from a 0.1% NaCl solution and of completely desalted (VE) water, as used in laboratories.

In order to avoid misunderstandings, reference is made here again to the fact that a comparison between modes of operation which are not according to the invention and modes of operation according to the invention can only give statements under the assumption that there are comparable temperature conditions on the distillate side (condensate side), i.e. that in particular the inlet and the outlet temperature of distillate or condensate is largely the same for the operating modes to be compared. That only increasing the amount of solution at a constant inlet temperature for the solution or, increasing the flow rate on the distillate side, at a constant inlet temperature on this side, due to the higher average temperature differences that can thus be achieved between the solution side and the distillate side, also results in an increased distillate flow through it porous partition, is common knowledge and self-evident. An objective comparison of other methods with the method according to the invention would thus not be possible without taking these factors into account. When one thus e.g. by setting a negative pressure corresponding to the vapor pressure on the solution side or by increasing the temperature on the solution side according to the invention when the boiling point is reached, so that a higher transmembrane distillate flow is achieved, the outlet temperature of the condensate will rise with an unchanged flow rate on the distillate side (condensate), as the increased distillate amount is now taken up by the same amount of condensate and condensed and a correspondingly increased condensation heat energy is transferred to the condensate. As a result of this mode of operation, the average temperature difference between the solution side and the condensate side is thus reduced, so that a comparison of the two described modes of operation must lead to incorrect conclusions. A comparison is, on the other hand, possible when the flow rate on the condensate side, in the described method according to the invention, is set so high that the outlet temperature of the condensate remains unchanged and the average temperature difference between the solution side and the condensate side thus does not change either.

Claims (21)

1. Method for at least partial separation of at least one liquid component of a solution by transferring it into the vapor phase, where the solution and the distillate are kept separated by a porous partition, which is only permeable to the vaporized distillate and any gases present, and with by means of which solution and distillate are kept in touching contact, where transfer to the vapor phase takes place on the solution side of the pores of the porous partition, and the vapor-form distillate diffuses through the pores to the distillate side, characterized in that during the duration of the fraction separation, by pressure and/or temperature control at all times, at least in a partial area of the immediate surroundings of the porous partition on the solution side, at least the area of the solution's current boiling point is reached. 2. Method as set forth in claim 1, characterized in that at least in the immediate vicinity of the porous partition, on the solution side, at least the area of the solution's actual boiling point is reached. 3. Method as stated in claims 1 and 2, characterized in that a hydrostatic pressure is set on the distillate side of the porous partition, which is higher than the steam pressure on the distillate side, and that the distillate is brought to a temperature which, at this pressure, is below its boiling temperature, so that condensation of the vaporized distillate takes place on the distillate side of the pores of the porous partition. 4. Method as stated in claims 1-3, characterized in that at least on the solution side of the porous partition a hydrostatic pressure is set which is lower than the atmospheric pressure. 5. Method as stated in claims 1-4, characterized in that a hydrostatic pressure which is lower than the atmospheric pressure is also set on the distillate side of the porous partition wall. 6. Method as specified in claims 1-5" characterized in that a pressure is set at least in the pores of the porous partition wall, which corresponds to the maximum extent to the current vapor pressure of the solution. 7. Method as stated in claims 1-6, characterized in that a higher hydrostatic pressure is set on the distillate side of the porous partition wall than on the solution side of the porous partition wall. 8. Method as stated in claims 1-7, characterized in that the solution and/or the possibly condensed distillate flows along the porous "partition wall". 9. Method as stated in claims 1-8, characterized in that the porous partition wall is an artificially produced membrane. 10. Method as stated in claims 1-9, characterized in that the solution is supplied with heat energy before and/or at the same time that at least one liquid component of the solution is transferred into the vapor phase. 11. Method as stated in claims 1-10, characterized in that heat energy is extracted from the distillate (condensate) after and/or at the same time as at least one liquid component of the solution is transferred into vapor phase. 12. Method as specified in claims 1-11, characterized in that part of the heat energy that is added to the solution is extracted from the distillate or the condensate. 13. Apparatus which is suitable for carrying out the method as stated in claims 1-12 and 20, which consists of at least one container, which is divided into at least two chambers by means of at least one porous partition, of which one chamber is intended for absorption of the solution and the other for absorption of the distillate, characterized in that the chamber (la) for absorption of the solution and/or the chamber (lb) for absorption of the distillate and/or the porous partition (2) comprises organs (9a; 9b; 9c) ), by means of which each of the aforementioned parts (la; lb; 2) can be connected to a device for generating underpressure (vacuum) or overpressure. 14. Device as stated in claim 13, characterized in that only the porous partition (2), which is suitable for setting a pressure in the pores that corresponds to the highest possible degree to the relevant vapor pressure of the solution, can be connected to a device for generating of underpressure (vacuum) or overpressure. 15. Device as specified in claims 13 and 11!, characterized in that the chamber (la) for recording the solution can be connected to a device for generating negative pressure (vacuum) or positive pressure. 16. Device as stated in claims 13-15, characterized in that the container (1) with the two chambers (la; lb) and the porous partition wall (2) is barometrically set up and connected. 17. Device as specified in claims 13-16, characterized in that a device (6a) is arranged on the solution side for transferring heat energy to the solution. 18. Device as stated in claims 13-17, characterized in that a device for extracting heat energy from the distillate (condensate) is arranged on the distillate side (condensate side). 19. Device as stated in claims 13-18, characterized in that a heat transfer device (18) is arranged in front of the chamber (la) for recording the solution and behind the chamber (lb) for recording the distillate (condensate), by means of which heat energy from the condensate can be transferred to the solution for cooling the condensate and heating (preheating) the solution. 20. Method as set forth in claims 1-12, characterized by the use of a mesh-constructed, porous partition wall, where the continuous open pores, which open on the solution side and the distillate side, are connected to each other by gas- or vapor-permeable openings, channels, pores etc. cross connections. 21. Device as stated in claims 13-15, characterized by a net-like constructed, porous partition wall, where the through-open pores, which open on the solution side and on the distillate side, are connected to each other by gas- or steam-permeable openings, channels, pores beer. cross connections.