WO2005089914A1

WO2005089914A1 - Method and device for distilling solutions using a membrane

Info

Publication number: WO2005089914A1
Application number: PCT/EP2005/002874
Authority: WO
Inventors: Wolfgang Heinzl
Original assignee: Wolfgang Heinzl
Priority date: 2004-03-19
Filing date: 2005-03-17
Publication date: 2005-09-29
Also published as: DE102004013647A1

Abstract

The invention relates to a method for distilling solutions, in particular for producing fresh water from sea water or brackish water. Said method is characterised in that: a) a stream of liquid containing the relevant solution is delimited on at least one side by a microporous, hydrophobic membrane (20); b) part of the liquid from the stream of liquid that comes into contact with the membrane is evaporated and the resultant vapour passes through said membrane into a vapour channel (22), in which the absolute pressure lies below the ambient pressure at all points; c) a vapour- and liquid-proof condensation partition (24), which is separated from the membrane by the vapour channel, is used, whereby vapour condenses at least partially on said partition; and d) the side of the condensation partition facing away from the vapour channel comes into contact again with a stream of liquid containing the relevant solution, the opposite side of said stream being delimited by the microporous, hydrophobic membrane (20) in such a way that the condensation energy that is supplied to the stream of liquid is reconverted at least partially into evaporation energy. The invention also relates to a corresponding distillation device and to a distillation device of this type comprising parallel condensation channels, which are delimited on opposing sides by a respective condensation partition (24).

Description

METHOD AND DEVICE FOR DISTILLING SOLUTIONS ON A MEMBRANE

The invention relates to a method and a device for the distillation of solutions, in particular for the production of fresh water from sea or brackish water.

There are basically three different processes in the field of conventional thermal desalination:

Multi-stage flash evaporation (MSF = Multi Stage Flash) - multiple effect desalination (MED = Multi Effect Desalination) vapor compression, a combination of mechanical and thermal processes (VC = Vapor Compression).

All previously known membrane distillation processes (MD) use the MSF process.

During the distillation, a liquid is evaporated and the vapor condensed. Thus distillation is suitable e.g. for the separation of liquids with different vapor pressure and for the complete or partial separation / separation of liquids from salt solutions.

A distillation device that can be implemented in practice must be both inexpensive and energy-efficient. A corresponding distillation process only makes sense if both conditions are met. These requirements can be implemented using the membrane distillation mentioned above. Such a membrane distillation uses a porous, vapor-permeable material. No. 3,340,186 describes a device in which an air-filled microporous, hydrophobic membrane is used, so that a so-called direct contact membrane distillation can be carried out. The warm sea water stream and the cold distillation stream come into direct contact with the membrane.

EP 0 088 315 AI describes a device for the continuous distillation of hot saline solutions or of liquid mixtures with different vapor pressure. This known device consists of a thermally conductive vapor-impermeable layer, which forms an elongated wall, and a hydrophobic vapor-permeable membrane, which forms an adjacent or opposite wall, the two walls together forming an elongated distillation collection chamber or a corresponding or distillation collection channel. The chamber or channel has an outlet for the distillate. In a preferred embodiment of this known membrane distillation, a spiral wrap configuration is used. Cold sea water (feed) flows in a spiral chamber in the center and absorbs heat from the condensation surface. This sea water (feed), which has been preheated by the condensation process of the distillate, is then further heated by a heater and then conducted in a concentrate channel. The hot solution then flows out through the channel delimited by the membrane. When flowing through the concentrate channel, part of the solution evaporates through the membrane. EP 1 185 356 describes a process for purifying a liquid by membrane distillation, in which steam arising from a liquid flow passes through a porous wall which limits the liquid flow. The steam condenses on a cool condenser surface and forms a condensate flow. The condenser surface separates a supplied liquid stream from the distillation stream. This supplied liquid stream flows in countercurrent to the vapor-emitting liquid stream. In order to increase the distillation flow per driving force unit, a pressure is maintained in the gas channel which is below the ambient pressure. however, is above the vapor pressure of the liquid emitting the vapor.

A number of problems arise in connection with the known membrane distillation processes. For all known membrane distillation processes (MD process), the energy density converted is low, which is due to the fact that the known processes always work above the boiling steam pressure of the solution to be concentrated and the resulting steam quantities are accordingly low. In addition, in the known MD methods, the heat of condensation released during the condensation of the steam generated is always absorbed by the heating of a liquid stream. In the process with a gas gap (air gap), the vapor is condensed on a vapor and liquid-tight surface and the heat of condensation released is transferred to the liquid by heat conduction and heat transfer. In the direct contact method, the vapor which arises at the interface between the warmer liquid and the membrane passes through the membrane and condenses in the colder liquid adjacent to the membrane wall. Here, the heat of vaporization is extracted from the liquid flow by cooling and then returned to the liquid flow supplied by heating. leads. In order to provide the heat of vaporization for one liter of distillate, at least 20 liters of aqueous liquid must be cooled from 80 ° C to 40 ° C. The solution stream must therefore be at least twenty times as large as the distillate stream generated.

In the known MD processes, the heat of condensation of the distillate is therefore always absorbed by heating the inflowing liquid, which requires a mass flow which is at least twenty times greater than that of distillate production.

For this purpose, in the known MD processes, large liquid mass flows have to be pumped around, which entails a high demand for auxiliary energy (pumps) per product produced. In addition, in an operation in which the solution is circulated for a higher concentration and only parts of the solution are discarded, the heat supplied on the hot side must essentially be removed again via a cooler.

The invention has for its object to provide an improved method and an improved device of the type mentioned, in which the aforementioned problems are eliminated. In particular, the energy density should be increased, the pumped liquid volume and the need for auxiliary energy reduced, the heat recovery improved and cooling as in the known multi-stage flash evaporation (MSF process) avoided.

With regard to the method, this object is achieved according to the invention by a) that a liquid flow containing a solution in question is limited on at least one side by a microporous hydrophobic membrane,

b) it is ensured that a part of the liquid evaporates from the liquid stream touching the membrane and the resulting steam passes through the membrane into a steam channel in which the absolute pressure is below the ambient pressure at all points,

c) that a vapor-tight and liquid-tight condensation wall is used, separated from the membrane, on which the vapor condenses at least partially, and

d) that the side of the condensation wall facing away from the steam channel is at least partially touched again by a liquid containing the solution in question, which is again delimited on the opposite side by a microporous hydrophobic membrane, so that the condensation energy supplied to the liquid flow is at least partially again in vaporization energy is implemented.

Process steps a) to d) are preferably repeated several times.

Part of the liquid is advantageously evaporated from the liquid flow on a respective membrane by a membrane distillation process with a continuous temperature profile. In particular, such an embodiment of the method is also conceivable, in which, in accordance with a membrane distillation process, crete stages with assigned temperature stages, part of the liquid is evaporated from the liquid stream.

At the end of the process, the remaining, still remaining steam is expediently condensed on the liquid stream supplied which contains the solution in question.

At the end of the process, in particular the escaping streams of concentrated solution and distillate are preferably cooled against the liquid stream supplied.

The problems mentioned in connection with the known methods can thus be eliminated, for example, by the following steps:

Part of the liquid is evaporated from a liquid flow, which is always or mostly delimited at least on one side by a microporous membrane, the evaporated part passing through the membrane as steam, in particular steam, and at a vapor and liquid-tight surface is condensed again. This condensation surface or wall is again opposed by a microporous hydrophobic membrane wall which, with the condensation surface or wall mentioned, has a narrow flow channel filled with solution and of a width in a range of, for example, about 1 to about 8 mm, preferably about 2 to 5 mm. limited. The condensation energy supplied to the condensation surface or wall is thus immediately converted back into evaporation energy in the region of the flow channel.

The absolute pressure of the vapor space used for the membrane distillation process can be below the ambient pressure at all points. The steam generated can then be Condense at the steam pressure / temperature corresponding point of the MD process.

In a membrane distillation process with a continuous temperature curve or in concrete steps with assigned temperature steps, salt solution is evaporated on a membrane wall. The steam enters through a microporous, hydrophobic membrane into a steam channel with negative pressure and condenses at a point on the condensation surface that corresponds to the temperature / steam pressure. The latent heat absorbed at the condensation surface is immediately used again to evaporate from the solution on the other side through a membrane. This process is repeated several times, with energy efficiency increasing with the number of repetitions.

At the end of the process, the remaining steam leaving the process is condensed on the supplied solution. In addition, the emerging streams of concentrated solution and distillate are cooled against the supplied solution.

With regard to the device, the previously specified object is achieved according to the invention in that

a) that a liquid stream containing a solution in question is bounded on at least one side by a microporous hydrophobic membrane,

b) that part of the liquid from the liquid stream touching the membrane evaporates through the membrane into a vapor channel in which the absolute pressure is below the ambient pressure at all points, c) that a vapor and liquid-tight condensation wall is provided, separated from the membrane, on which the vapor condenses at least partially, and

d) that the side of the condensation wall facing away from the steam channel is at least partially touched again by a liquid stream containing the solution in question, which is again delimited on the opposite side by a microporous hydrophobic membrane, so that the condensation energy supplied to the liquid stream is at least partially in again Evaporation energy is implemented.

A multiple arrangement of units each having the features a) to d) is preferably provided.

A preferred practical embodiment of the device according to the invention is characterized in that the liquid stream containing the solution in question is at least partially guided in a spiral liquid channel which is delimited on one side by a microporous hydrophobic membrane and on the opposite side by a vapor and liquid-tight condensation wall is, due to the spiral arrangement of the liquid channel between the turns of a corresponding spiral vapor channel is formed, which is bounded on one side by the membrane and on the opposite side by the condensation wall. A spiral arrangement ensures that the membrane surface always comes to lie opposite the condensation wall formed, for example, by a film. The vapor emerging from the solution through the membrane always hits a condensation surface. Such an execution form corresponds thermodynamically to a multiple-effect process with a continuous vapor pressure curve. The uncondensed steam leaving the module is condensed in a cooler or condenser which is cooled by the counter-flowing solution. The solution is preheated as desired. The resulting distillate is drawn off with a pump and passed over a cooler through which the solution flows, the solution again being preheated. Before the solution enters the membrane distillation device, it is further heated by a heat exchanger.

However, it is also conceivable, for example, for such an embodiment of the device according to the invention in which steam from a steam generator is fed to a first stage comprising a plurality of plates which has condensation channels which absorb the steam and are parallel to one another and which on opposite sides each have a vapor and liquid density Condensation wall are limited, with these condensation walls on the other hand each facing a microporous hydrophobic membrane in order to form together with the condensation wall a respective liquid channel for a liquid flow containing the solution in question. A vapor space is formed between two opposite membranes, in which the absolute pressure is below the ambient pressure at all points. In this case, at least two stages, each comprising a plurality of plates, are expediently connected in series. In this case, those leaving a previous stage can be the relevant one

Solution-containing liquid streams are fed to the liquid channels and the vapor emerging from a respective preceding stage is fed to the condensation channels of the respective subsequent stage. By connecting several such stages in series, a membrane distillation process can be implemented that uses thermodynamic mix corresponds to a multiple effects process. The increasing steam volume can be absorbed by a corresponding increase in the number of plates in the individual stages.

The steam generator connected upstream of the first stage can in particular comprise a plurality of parallel liquid channels for a liquid containing the solution in question, each delimited by two opposing microporous hydrophobic membranes, a vapor space adjoining each membrane in which the absolute pressure at all points below the Ambient pressure.

The non-condensed steam emerging from the spiral or plate module can be condensed in a cooler or condenser which is cooled by the liquid flow containing the solution in question.

At least one pump is expediently provided for withdrawing the distillate formed.

The resulting distillate can be passed through a cooler through which the liquid stream supplied flows.

The supplied liquid stream can expediently be additionally heated via a heat exchanger before the membrane distillation.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing; in this show:

1 shows an exemplary embodiment of a particularly for the production of fresh water from sea or brackish water-usable distillation device with a spiral channel for the liquid stream containing the solution in question, and

Figure 2 shows another exemplary embodiment of the distillation device with stages connected in series, each comprising several plates.

FIG. 1 shows a schematic illustration of an exemplary embodiment of a distillation device 10 which can be used in particular for the production of fresh water from sea or brackish water and has a spiral-shaped liquid channel 12 for the liquid stream containing the solution in question.

In contrast, FIG. 2 shows a schematic representation of an exemplary embodiment of a distillation device 10 with stages 14, 16 connected in series, each comprising several plates.

The following features are realized in each of the two embodiments:

a) a liquid channel 12 containing the solution in question is delimited on at least one side by a microporous hydrophobic membrane 20.

b) A part of the liquid from the liquid stream touching the membrane 20 is evaporated through the membrane 20 into a condensation channel 22 or into a vapor space 23, in which the absolute pressure is below the ambient pressure at all points.

c) In addition, a vapor and liquid-tight condensation wall 24 separate from the membrane 20 is provided, on which the vapor condenses at least partially.

d) The side of the condensation wall 24 facing away from the steam channel 22 is at least partially touched again by a liquid stream containing the solution in question. On the opposite side, the liquid channel 12 carrying this liquid flow is again delimited by a microporous hydrophobic membrane 20, so that the condensation energy supplied to the liquid flow is at least partially converted back into evaporation energy.

As can be seen from FIGS. 1 and 2, a multiple arrangement of units each having the features a) to d) is preferably provided.

In the embodiment of FIG. 1, the liquid stream containing the solution in question is at least partially guided in a spiral liquid channel 12. This spiral-shaped liquid channel 12 is delimited on one side by a microporous hydrophobic membrane 20 and on the opposite side by a vapor and liquid-tight condensation wall 24.

As a result of the spiral arrangement of the liquid channel 12, there is a correspondingly spiral steam channel 22 between its turns formed, which is bounded on one side by the membrane 20 and on the opposite side by the condensation wall 24.

1, the membrane 20 is shown as a broken line and the condensation surface or wall 24 as a solid line.

The liquid stream 18 containing the solution in question, in particular sea water or brackish water, is supplied via a pump 26. The liquid flow flows through a heat exchanger 28, a condenser 30, a further heat exchanger 32 and is preheated in each case in the process. In a heat exchanger 34, the liquid containing the solution in question 18 is finally heated up to the upper process temperature.

At point A, the heated liquid flow enters the spiral module. The liquid channel 12 for the liquid flow is delimited on one side by the membrane 20 (broken line) and on the opposite side by the condensation surface or wall 24 (solid line). The channel on the side of the membrane that is not wetted by the saline solution, which on the other hand is delimited by the condensation wall 24, forms the steam channel 22. The distillate that collects in the channel CC is pumped out by a distillate pump 36. The residual steam is sucked off via the vacuum in the steam channel 22 by a vacuum pump 38 and is condensed in the condenser 30 to the incoming liquid stream containing the solution in question. The condensate is withdrawn from the condenser 30 by means of the distillate pump 36 via the heat exchanger 28. At the end of the liquid channel 12, the remaining liquid flow at B is drawn off, passed over the heat exchanger 32 and returned in the direction of the arrow to a suitable reservoir, for example in the sea during desalination.

In the embodiment according to FIG. 2, the steam is fed from a steam generator 40 to a first stage 14 with a plurality of plates, which has condensation channels 21, which receive the steam and are parallel to one another and which are respectively delimited by a vapor and liquid-tight condensation wall 24 on opposite sides.

On the other hand, each of these condensation walls 24 is opposite a microporous hydrophobic membrane 20 in order to form, together with the condensation wall 24 assigned to it, a respective liquid channel 12 for a liquid flow containing the solution in question. -. ^, , -

A vapor space 23 is again formed between two opposite membranes 20, in which the absolute pressure is below the ambient pressure at all points.

At least two stages 14, 16 each comprising several plates are connected in series.

The liquid streams emerging from a respective preceding stage 14 and containing the solution in question are fed to the liquid channels 12 of the respective subsequent stage 16 and the vapor from the steam rooms 23 emerging from a respective preceding stage 14 is fed to the condensation channels 21 of the respective subsequent stage 16. The steam generator 40 connected upstream of the stages 14, 16 comprises a plurality of parallel liquid channels 12, each delimited by two mutually opposite microporous hydrophobic membranes 20, for a respective liquid stream 18 containing the solution in question. A respective vapor space 23 adjoins a respective membrane 20, in which the absolute pressure is below the ambient pressure at all points.

The non-condensed steam emerging from the plate modules 14, 16 is condensed in a cooler or condenser 42, which is cooled by the liquid flowing through a pump 26 and containing the solution in question. A vacuum pump 38 is again connected to the cooler or condenser 42.

The resulting distillate is drawn off via a pump 36, it being passed through a cooler or heat exchanger 28 through which the supplied liquid stream flows. The solution leaving the plate module is passed through a heat exchanger 44 through which the supplied liquid stream flows.

Before the membrane distillation, the supplied liquid stream 18 is further heated via a heat exchanger 34. LIST OF REFERENCE NUMBERS

10 distillation device

12 liquid channel

14 first stage

16 second stage

20 membrane

21 condensation channel

22 steam channel

23 steam room

24 condensation wall

26 pump

28 heat exchangers

30 capacitor

32 heat exchangers

34 heat exchangers

36 The still pump

38 vacuum pump

40 steam generator

42 heat exchangers

44 heat exchangers

A entry point

B exit point

C C steam channel

Claims

Patent claims

1. A method for the distillation of solutions, in particular for the production of fresh water from sea or brackish water, characterized in that a) a liquid stream containing a solution in question is delimited on at least one side by a microporous hydrophobic membrane (20), b) it is ensured that a part of the liquid evaporates from the liquid contacting the membrane (20) and the resulting steam passes through the membrane (20) into a condensation or steam channel (21, 22) in which the absolute pressure is reached is below the ambient pressure at all points, c) that a vapor and liquid-tight condensation wall (24) is used, separated from the membrane (20), at which the vapor condenses at least partially, and d) that the condensation or vapor channel (21, 22) facing away from the condensation wall (24) at least in sections again from a liquid containing the solution in question Its stream is touched, which is again delimited on the opposite side by a microporous hydrophobic membrane (20), so that the condensation energy supplied to the liquid stream is at least partially converted back into evaporation energy.

A method according to claim 1, characterized in that the process steps a) to d) are repeated several times.

3. The method according to claim 1 or 2, characterized in that part of the liquid is evaporated from the liquid flow on a respective membrane (20) after a membrane distillation process with a continuous temperature profile.

4. The method according to claim 1 or 2, characterized in that part of the liquid is evaporated from the liquid flow on a respective membrane (20) after a membrane distillation process in concrete steps with assigned temperature steps.

5. The method according to any one of the preceding claims, characterized in that at the end of the method the remaining, still remaining steam is condensed on the liquid stream supplied containing the solution in question.

6. The method according to any one of the preceding claims, characterized in that, at the end of the method, the escaping streams of concentrated solution and distillate are cooled against the liquid stream supplied.

7. Device (10) for the distillation of solutions, in particular for the production of fresh water from sea or brackish water, in particular for carrying out the method according to one of the preceding claims, characterized in that a) that a liquid flow containing a solution in question is limited on at least one side by a microporous hydrophobic membrane (20), b) that part of the liquid from the liquid touching the membrane (20) flows through the membrane (20) evaporates into a condensation or vapor channel (21, 22) in which the absolute pressure is below the ambient pressure at all points, c) that a vapor and liquid-tight condensation wall (24) separate from the membrane (20) is provided which at least partially condenses the steam, and d) that the side of the condensation wall (24) facing away from the condensation or steam channel (21, 22) is at least partially touched again by a liquid stream containing the solution in question, which is again on the opposite side is limited by a microporous hydrophobic membrane (20), so that the condensation energy supplied to the liquid flow is at least partially ise is converted back into vaporization energy.

8. The device according to claim 7, g e k e n n z e i c h n e t by a multiple arrangement of each having the features a) to d) units.

9. Device according to one of the preceding claims, characterized in that the liquid containing the solution in question flows at least partially in a spiral liquid channel (12) which on one side through a microporous hydrophobic membrane (20) and on the opposite side a vapor and liquid-tight condensation wall (24) is limited, whereby due to the spiral arrangement of the liquid channel (12) between its windings a corresponding spiral steam channel (22) is formed, which on one side through the membrane (20) and on the opposite side the condensation wall (24) is limited.

10. The device according to claim 7 or 8, characterized in that steam from a steam generator (40) is fed to a first stage (14) from a plurality of plates which has the steam-receiving, mutually parallel condensation channels (21) on opposite sides are each delimited by a vapor and liquid-tight condensation wall (24), these condensation walls (24) on the other hand each being opposite a microporous hydrophobic membrane (20) in order to close a respective channel (12) for a liquid stream containing the solution in question form, and in each case a vapor space (23) is formed between two opposing membranes (20) in which the absolute pressure is below the ambient pressure at all points.

11. The device according to claim 10, characterized in that at least two stages (14, 16) each comprising several plates are connected in series.

12. The device according to claim 11, characterized in that the emerging from a respective preceding stage (14), the liquid flows containing the solution in question are fed to the liquid channels (12) and the steam emerging from a respective preceding stage (14) is fed to the condensation channels (21) of the respective subsequent stage (16).

13. Device according to one of claims 10 to 12, characterized in that the steam generator (40) comprises a plurality of mutually parallel liquid channels (12), each delimited by two mutually opposite microporous hydrophobic membranes (20), for a respective liquid flow containing the solution in question, wherein a respective vapor space (23) adjoins a respective membrane (20), in which the absolute pressure is below the ambient pressure at all points.

14. Device according to one of the preceding claims, characterized in that the uncondensed steam emerging from the spiral module or the plate module is condensed in a cooler or condenser (30, 42) by the supplied liquid stream containing the solution in question is cooled.

15. Device according to one of the preceding claims, characterized in that at least one pump (36) is provided for withdrawing the distillate formed.

16. Device according to one of the preceding claims, characterized in that that the resulting distillate is passed through a cooler (28) through which the supplied liquid stream flows.

17. Device according to one of the preceding claims, characterized in that the supplied liquid stream can be further heated via a heat exchanger (34) before the membrane distillation.