HK1060079B - Method and device for desalting water - Google Patents

Description

Method and apparatus for desalination of water

Technical Field

The invention relates to a method for desalting water by reverse osmosis; it also relates to a device for carrying out the method.

Background

Such a method and such a device are described in german patent application No. 19933147.2. Here, the brine is fed into the pressure compensation device under the action of a first pressure; and fed from the pressure compensating device to a diaphragm assembly under the action of a second, higher pressure; while the desalinated water and the concentrated brine are removed from the membrane module. Desalinated water is understood to be water having a salt content that is low relative to the salt content of the brine fed to the apparatus. In order to improve the efficiency and energy balance of the method and the device, it is proposed that the concentrated brine removed from the membrane module is continuously fed into the pressure compensation device under the action of the second pressure and is used to add the second pressure to the brine fed into the pressure compensation device and to feed the brine into the membrane module. The feeding of the brine into the pressure compensation device is performed by means of a one-way valve, while the outflow of the brine from the pressure compensation device is performed by means of a controlled main valve. These controlled main valves are preferably actively controllable and are placed on the connecting lines between the membrane module and the pressure compensation device or between the pressure compensation device and the outlet of the concentrated brine.

The method described at the beginning and the apparatus described therein are also described in EP 0028913. In this case, a pump is provided to compensate for the pressure loss.

DE 2448985 discloses the use of a hydraulic motor driven by such a liquid for recovering energy from a highly pressurized liquid. The cylinder/piston combination, which operates in opposite phases, is mechanically connected to a crankshaft by means of a connecting rod, which is in turn driven by a drive in order to compensate for the pressure loss. This system has several disadvantages. However, since the crankshaft drives the piston and the connecting rod to move in two directions, the supporting method and the guide of the piston and the connecting rod are complicated.

In the known method and device, a high pressure acts on the main valve. When the main valve is in operation, a great mechanical stress is generated at the moment when the main valve starts to open or at the last moment of closing. However, since these main valves are designed for large flows, they are correspondingly large in size and heavy.

The main valves are slow to act because of their size and mass, and are therefore exposed to large pressure variations for a longer time, especially at the beginning of the opening process and at the end of the closing process. Since it is desirable that such devices operate without interruption, these main valves are subjected to large stresses over time due to the magnitude and duration of the stresses and the frequency of the load variations.

Disclosure of Invention

The present invention has been made to solve the above problems, and an object of the present invention is to overcome the above disadvantages and to improve the above method and apparatus so that the main valve is less worn.

This problem of the above-described method and apparatus can be solved by the following method and apparatus. That is, the present invention provides a method for desalinating seawater using reverse osmosis, wherein saltwater is fed into a pressure compensation device under a first pressure and from the pressure compensation device into a membrane module under a second, higher pressure; wherein the desalinated water and the concentrated brine are discharged from the membrane module, wherein the concentrated brine discharged from the membrane module is continuously fed into the pressure compensating device under the action of a second pressure, and the second pressure is applied to the brine fed into the pressure compensating device, and the brine is fed into the membrane module; and wherein a controlled main valve is used to feed the strong brine into the pressure compensation device and to discharge the strong brine from the pressure compensation device; wherein the control of the auxiliary valves arranged in parallel with the main valves enables the reduction of load peaks during the opening and/or closing of the main valves, for which purpose the auxiliary valves open at least during the opening or closing of the respective main valves arranged in parallel therewith; wherein the pressure fluctuations are compensated by means of a pressure accumulator which is mounted at the input of the pressure compensation device, and the concentrated brine can be discharged from the membrane module via the pressure accumulator. Also, the present invention provides an apparatus for carrying out the above method, which has a feed pump for feeding brine into a pressure compensating means, and a membrane module for separating the brine discharged from the pressure compensating means into desalted water and concentrated brine; wherein, a connecting pipeline which is continuously under the pressure action in work is arranged between the diaphragm assembly and the pressure compensation device and is used for respectively sending the strong brine discharged from the diaphragm assembly into the pressure compensation device and sending the brine from the pressure compensation device to the diaphragm assembly; the main valve is used for feeding the strong brine into the pressure compensation device and discharging the strong brine from the pressure compensation device; wherein auxiliary valves are provided in parallel with the main valves, such that load peaks during opening and/or closing of the main valves are reduced, for which purpose the auxiliary valves open at least during opening or closing of the respective main valves arranged in parallel therewith; the pressure fluctuation is compensated by a pressure accumulator arranged at the input end of the pressure compensation device, and the strong brine can be discharged from the membrane assembly through the pressure accumulator.

Preferably, the concentrated brine discharged from the diaphragm assembly is fed under a second pressure to the outlet chamber of one of the at least two piston/cylinder arrangements of the pressure compensation arrangement; and acts on the piston to cause the brine fed into the inlet chamber of the same piston/cylinder unit to be fed into the diaphragm assembly under the action of a second pressure.

Preferably, the brine is alternately fed into the output chamber of one of the piston/cylinder units, while brine is discharged from the corresponding input chamber of the same piston/cylinder unit into the diaphragm assembly; and in that brine is simultaneously fed into the inlet chamber of the other piston/cylinder unit under a first pressure, and brine is discharged from the outlet chamber of the same piston/cylinder unit under a lower pressure.

Preferably, the piston/cylinder devices of the pressure compensation device are controlled such that brine can be fed into the inlet chamber of at least one piston/cylinder device simultaneously; discharging the strong brine from an output cavity of the same piston/hydraulic cylinder device; feeding the concentrated brine into the output chamber of at least one further piston/cylinder device; and feeding brine from the input chamber of the same piston/cylinder assembly into the diaphragm assembly.

Preferably, the pressure compensation means comprises two piston/cylinder arrangements operating in opposite phases; and the pistons of the piston/cylinder devices are connected by connecting rods.

Preferably, the connecting rod is driven by a drive means. The auxiliary valve has a smaller cross-section than the main valve. The maximum flow through the auxiliary valve is controlled by means of a flow restrictor on the liquid supply line to the auxiliary valve. The auxiliary valve is opened only during the opening or closing of the respective main valve arranged in parallel therewith. Preferably, the main valve and the auxiliary valve are controlled such that the main valve is switched in the absence of pressure. Preferably, the position of the piston is determined continuously.

Preferably, the pressure compensating means comprises pairs of piston/cylinder arrangements, each pair being connected by a connecting rod; also, several pairs of devices are operated in a phase-offset manner.

The basis of the present invention is that load peaks are known to occur during the opening and closing of the main valve and should be avoided as much as possible. According to the invention this is achieved by means of an auxiliary valve, called a bypass valve, which bypasses the main valve a part of the pressure generated during opening and closing of the main valve. For this purpose, an auxiliary line for mounting an auxiliary valve is provided around the main valve.

Preferably, the auxiliary valves are controlled so that they open shortly before the main valve opens or closes; and/or only during opening or closing of the main valve. At other times, the auxiliary valve is normally closed.

In a preferred construction, the auxiliary valve is narrower in cross-section than the main valve. The cross-section of the auxiliary valve can be significantly smaller than the cross-section of the main valve, and therefore the pressure resistance of the auxiliary valve is much larger. Thus, by properly controlling the auxiliary valve, the stress on the main valve is significantly reduced and its life is proportionally extended.

In another embodiment of the invention, the cross-section of the auxiliary valve can be chosen arbitrarily. With a suitable control, the liquid can be delivered through the cross section of the auxiliary valve. This means that the auxiliary valve can be opened or closed simultaneously with its corresponding main valve arranged in parallel, except that the auxiliary valve is opened slightly earlier than the main valve arranged in parallel and closed slightly later than the main valve arranged in parallel in order to relieve the load acting thereon.

In a preferred embodiment of the invention, the pressure accumulator is connected to the outlet of the concentrated brine from the membrane module and to the inlet of the pressure compensation device. Therefore, the pressure accumulator is at the same pressure as the brine itself. The purpose of this pressure accumulator is to compensate for pressure fluctuations that inevitably occur during operation of the valve due to volume losses; thereby establishing an optimally fixed working pressure in the diaphragm assembly.

In another preferred embodiment of the present invention, a flow restrictor is installed on the supply line of the auxiliary valve, which prevents the pressure from being suddenly balanced by restricting the maximum flow rate therethrough, so that gradual pressure compensation and a slow pressure change can be performed without sudden fluctuation. These flow restrictors are sized differently to create different magnitudes of "flow resistance". Due to the narrow cross-section, the flow restrictor may be integrated with the auxiliary valve.

In the elongated structure of the invention, the pressure compensating device comprises two piston/cylinder combinations operating in opposite phases, and the pistons of the piston/cylinder arrangements are connected by a connecting rod. Such a link and its function are known from EP 0028913. However, unlike the known connecting rod, in the refined structure of the present invention, there is no pump that compensates for the pressure loss.

Instead, in the second embodiment of the invention, a drive of the connecting rod is provided to compensate for the pressure loss. This drive is constructed such that teeth are formed at the center portion of the connecting rod, and a driven pinion gear is engaged with these teeth. In this way, the desired working pressure can be maintained.

In the device according to the invention, the high-pressure pump which generates the high pressure can be dispensed with entirely, and if the pressure necessary for the concentrated brine at the output of the membrane module can be achieved by continuously feeding the concentrated brine back into the pressure compensation device in order to add the pressure to the brine pumped into the pressure compensation device, a pump which generates a much lower pressure can be used instead. It is of utmost importance that the above process is carried out continuously, since otherwise the pressure in the brine supply line from the pressure compensating device to the membrane assembly would decrease and must be recovered by the high pressure pump. Thus, continuous production of desalinated water is not possible.

Drawings

The invention will be explained below on the basis of the drawings. Wherein:

FIG. 1 is a schematic circuit diagram for illustrating the method according to the present invention;

FIG. 2 is an embodiment of the apparatus according to the invention in a first operating state;

FIG. 3 shows this embodiment in a second operating state;

figure 4 shows the operation of this embodiment during a full duty cycle.

Detailed Description

FIG. 1 is a schematic representation of a pressure at a first pressure P₁Next, brine 10 is fed to one of the feed pumps 1 in the pressure compensation device 2. The same brine 11, at a high operating pressure, is fed from the pressure compensation device 2 to the membrane module 3. A portion of the saltwater 11 (e.g., 25% saltwater 11) passing through the membrane 6 is desalinated in the process and discharged as desalinated water 12. The remaining brine 11 (e.g. 75%) cannot pass through the membrane 6 and is used as a still almost high pressure P by means of the connecting line 5₂The concentrated brine 13 is returned to the pressure compensation device 2. This high pressure is applied to the brine 10 fed to the pressure compensating device 2 and fed to the input of the membrane module 3 in a manner to be described. At the same time, this pressure is used in the pressure compensation device 2 in the manner to be explained, where the concentrated brine 14 is finally discharged through the discharge pipe 4 and the less concentrated brine 10 is fed into the pressure compensation device 2. All the described processes are carried out simultaneously and continuously, so that no high-pressure pumps supplying high working pressures are required and desalinated water 1 is continuously obtained2。

Next, the structure and operation of the pressure compensation device 2 will be described based on the embodiment of the present invention shown in fig. 2. Here, the pressure compensation means comprises two identical piston/cylinder arrangements 401, 402 with two cylinders placed in line opposite each other, each cylinder comprising an inlet chamber 201, 202 for brine 10 and an outlet chamber 101, 102 for brine 13. Within the piston/cylinder units 401, 402 there are respective special pistons 301, 302, which divide the interior of the piston into chambers as described above and which are movable in the horizontal direction in the figure. The respective feed lines with the (passive) non-return valves 7 lead from the feed pump 1 to the inlet chambers 201, 202. When the pressure in the feed line is greater than the pressure in the inlet chambers 201, 202, the check valve 7 opens to allow flow therethrough. In the feed lines from the feed chambers 201, 202 to the membrane module 3, a check valve 8 is provided for comparison in the other flow direction.

In the liquid supply line 5 from the diaphragm assembly 3 to the outlet chambers 101, 102 and in the discharge line 4 from the outlet chambers 101, 102, an actively switchable main valve V is arranged in each case₃、V₆And V₁、V₄. By means of these main valves, the flow of concentrated brine 13 from the membrane module 3 into the pressure compensation device 2 or of concentrated brine 14 from the pressure compensation device 2 can be controlled.

The pistons 301, 302 are permanently connected to each other by means of a connecting rod 30. To compensate for pressure losses, the connecting rod 30 and the pistons 301, 302 can be driven by a pinion 40, driven by, for example, a motor with gears, and meshing with teeth cut on the connecting rod 30.

The pistons operate in opposite phases. If a piston is in a position where the volume of the input chamber 202 is at a maximum and the volume of the output chamber 102 is at a minimum; the other piston connected by the connecting rod 30 is in a position where the volume of the input chamber 201 is minimum and the volume of the output chamber 101 is maximum (compare with fig. 2). In this state, the input chamber 202 is filled with water and the output chamber 101 is filled with brine. Controlling valve V as a representation of switch₁、V₃、V₄And V₆Let V be₃And V₄Closing, V₁And V₆And (4) opening.

In this specification, valve opening means that the valve is opened by purely mechanical means, creating a flow connection through which flow can pass. Similarly, valve closure means that the valve is closed purely mechanically, the flow connection is interrupted, and the flow is interrupted.

By opening the main valve V₁The pressure of the brine in the outlet chamber 101 is first removed. By opening the main valve V₆The output chamber 102 is subjected to pressure (e.g. 70 bar) and the brine flows into this chamber. At the same time, saline in the input chamber 202 is pressed toward the diaphragm assembly 3 by the pressure applied to the piston.

Since the pistons are arranged to operate in opposite phases, the pressurised concentrate (e.g. at 70 bar) is passed into the output chamber 102 and the other piston 301 can be moved by the connecting rod 30 to empty the output chamber 101 of no pressure. At the same time, a negative pressure is created in the input chamber 201, drawing in saline and filling this chamber.

If the output chamber 102 is full, the main valve is controlled accordingly and the reverse process can be performed.

Since the membrane module is preferably operated at approximately 80 bar in order to increase the yield of fresh water, a pressure loss of at most 10 bar occurs on the membrane when, as a pressure of the brine, at least the abovementioned pressure of 70 bar is present on the concentrate discharge line 5 of the membrane module 3.

In order to protect the main valve from large pressure variations that could cause wear, in particular during opening and closing, according to the invention a valve is provided in connection with the main valve V₁，V₃，V₄，V₆Parallel auxiliary or bypass valve V₂，V₂′，V₅，V₅'. These auxiliary valves have a significantly smaller cross section than the main valve and therefore have a higher pressure resistance. Thus, by properly controlling the auxiliary valve, the stress on the main valve is significantly reduced, resulting in a proportional increase in its life.

In addition, the pressure accumulator P is connected to the brine outlet of the membrane module 3, so that its pressure is the same as the pressure of the brine itself, for example, approximately 70 bar. In order to make the working pressure as constant as possible in the diaphragm assembly 3, it is necessary to compensate for pressure fluctuations that inevitably occur with the action of the valve due to volume losses.

Between the concentrated brine outlet of the membrane module 3 and the outlet chambers 101, 102, several flow restrictors R are placed which are divided into resistors₁，R₂，R₃. By limiting the flow, these flow restrictors can prevent sudden pressure compensation, allowing the pressure to gradually compensate, with the pressure changing slowly rather than fluctuating suddenly. These flow restrictors, which act as "flow resistors," are different sizes.

Due to the flow restrictor R₂And R₃Can be adjacent to the auxiliary valve V₂，V₂' and V₅，V₅' on each occasion, pressure compensation is performed within an acceptable time, and therefore at node K, respectively₂And an auxiliary valve V₂，V₂' between and at node K₃And an auxiliary valve V₅，V₅' two flow restrictors R between₂，R₃The passing flow rate is compared with the node K₁And a flow restrictor R between the accumulator P₁The allowed flow is large. In another aspect, R₁Is always connected to the concentrate outlet of the membrane module 3, so that the pressure in the pressure accumulator P can be compensated for without interruption. Thus, the flow restrictor R₁The flow resistance of (2) is large, and only a small flow rate is allowed to pass through. The concentrate line is largely isolated from the membrane module 3, so that the pressure fluctuations have a negligible effect on the membrane module 3. In addition, it should also be noted that only when the auxiliary valve V is present₂And V₅At node K₁And node K₂，K₃Between which a pressure compensation is established, the main valve V₃And V₆Is started. Thus, the main valve V₃And V₆It always starts without pressure and therefore there is no pressure fluctuation.

In any case, the maximum flow is subject to the auxiliary valve V₂，V₂′，V₅，V₅The structure of' limits, therefore, these auxiliary valves automatically function as flow restrictors.

The working cycle of the device according to the invention will now be described on the basis of the schematic diagrams shown in fig. 2 and 3 and the process diagram shown in fig. 4. The values in the diagram shown in fig. 4 represent the pressure drop across the respective valve in operation.

The start state is the state shown in fig. 2. The pistons 301, 302 of the two piston/cylinder arrangements are in the leftmost end position. This is also shown in the process diagram shown in fig. 4 (see the two columns on the right). Main valve V₃And V₄Still open. Since the pressure drop across these valves is zero, the valves close in the absence of pressure (time t)₁). At the latest in this regard, the auxiliary valve V₂And V'₅Must also be shut down, respectively connecting node K₂And K₃Spaced from the outflow of concentrate and the concentrate outlet of the membrane module 3. At this point, all valves are closed.

To prepare the pistons 301, 302 for the opposite movement, the auxiliary valve V is now closed₂' on (time t)₂) Node K to₂The upper phase is reduced with respect to a pressure of about 70 bar of the concentrate outflow. Due to the valve V₂' is an auxiliary valve with a small cross section, and therefore, the volume flow is small. Using flow restrictors R₂Or auxiliary valve V₂' by itself, sudden pressure fluctuations can be suppressed.

At the same time, a main (as is, an auxiliary) valve V₅Node K, which is open, and which is pressurized to a pressure that is not present after the brine has been drained from the outlet chamber 102₃The above. Due to the flow restrictor R₃The flow is restricted and this pressure can be gradually added. Thus, at K₁Upper pressure is applied to node K₃The above.

Due to node K₁By means of a flow restrictor R with a large flow resistance₁And a main valve V₅The isolation is, therefore,the compensation being effected by accumulators P which in turn make use of node K₁Through a flow restrictor R₁Is filled. Therefore, the pressure fluctuation at the concentrate output end in the diaphragm assembly 3 is mainly caused by the flow restrictor R₁Is determined such that at node K₁A more constant pressure can be obtained.

When node K₂Upper pressure by an auxiliary valve V₂Is decreased, and at node K₃Upper pressure by an auxiliary valve V₅When set up, the main valve V₁And V₆Can be opened without pressure (time t)₃) And the opposite movement of the piston begins. This is indicated by the arrow pointing to the right in fig. 4.

At time t₄Auxiliary valve V₂' and V₅And is turned off again. At the latest at a time t when the pistons 301, 302 have reached their rightmost end position (see fig. 3)₅Auxiliary valve V₂' and V₅And closing.

Since the piston moves from the leftmost position to the rightmost position, causing the brine to flow into the output chamber 102, the brine is forced from the input chamber 202 into the diaphragm assembly 3 at a pressure of about 80 bar (70 bar from the incoming concentrate, 10 bar from the drive). At the same time, without pressure from the outlet chamber 101 on the concentrate discharge line, the brine is delivered, while the brine flows into the inlet chamber 201. At time t₅When all valves are closed again, the same process can be carried out in the opposite direction by appropriate control.

It should be noted that the pump 1 is not primarily intended for feeding saline 10 into the inlet chambers 201, 202, but for preventing so-called cavitation; i.e. a negative pressure region occurs in the stream of brine 10 flowing into the inlet chambers 201, 202. Such a region is unstable due to turbulent flow. The negative pressure draws ambient water into and through these areas. The water flows at such a high velocity that it can easily knock particles off the walls of the pipeline and its fittings, causing rapid damage to the parts, and requiring periodic replacement of the parts. In the two-chamber system of the invention, the pump 10 (as such; 1) does not have as high an operating pressure as in the known devices, but operates as a turbocharger of an internal combustion engine, with a low pressure sufficient to prevent cavitation when brine is sucked in.

Fig. 3 shows the start state. The pistons 301, 302 of the two cylinders are in the rightmost position. This is also shown in the process diagram shown in fig. 4. Valve V₁And V₆Still open. Both valves are closed in the absence of pressure (time t) due to zero pressure drop across the valves₅). At the latest in this regard, the auxiliary valve V₂' and V₅Must also be shut down so that node K₂And K₃Respectively, from the outflow of concentrate and the concentrate outlet of the membrane module 3. Now all valves are closed.

To prepare the pistons 301, 302 for opposite movement, the auxiliary valve V₅' on (time t)₆) Node K to₃A pressure drop of about 70 bar with respect to the output flow of the concentrate. Due to the valve V₅' is an auxiliary valve with a small cross section, and thus the volume flow is small. Flow restrictor R₃Suppressing sudden pressure fluctuations.

At the same time, the auxiliary valve V₂Open, apply pressure to node K where there is no pressure after draining the brine from the output chamber 101₂The above. Due to the flow restrictor R₂The flow is restricted and this pressure can be gradually added. Thus, at node K₁Upper pressure also at node K₂And (4) establishing. Flow restrictor R due to high flow resistance₁Let node K₁And an auxiliary valve V₂Isolation and therefore compensation is performed by the accumulator 70. The accumulator in turn passes through a flow restrictor R₁Is filled.

When the auxiliary valve V₅' let node K₃Upper pressure drop, auxiliary valve V₂At node K₂When pressure is built up, the main valve V₃And V₄Opening in the absence of pressure (time t)₇) The piston begins to actThe opposite movement. This is also indicated by the arrow pointing to the left in fig. 4.

At time t₈Time, auxiliary valve V₅' and V₂And is turned off again. At the latest at the time t when the pistons 301, 302 reach their extreme left positions (see fig. 2)₁Time, auxiliary valve V₅' and V₂It must be shut down.

As the piston moves from the rightmost position to the leftmost position, the brine flows into the outlet chamber 101, and is pressed out of the outlet chamber 201 into the membrane assembly 3 under a pressure of about 80 bar. At the same time, without pressure from the outlet chamber 102 acting on the concentrate discharge line, brine may be delivered and allowed to flow into the inlet chamber 202.

Thus, at time t of the next cycle₁All valves are closed again; by appropriate control, the same process can be performed in the opposite direction. Meanwhile, the chain line in fig. 4 indicates the end of one cycle and the start of the next cycle.

From the pressure of the individual valves it can be seen that the main valve is always switched without pressure, whereas an appropriately sized auxiliary valve is only exposed to high pressure when open. This is a very decisive advantage of the invention.

The sealing between the piston of the piston/cylinder device and the corresponding cylinder is not strictly necessary, since a slight mixing of the two liquids does not have a significant influence on the action of the device. On the other hand, the sealing of the hydraulic cylinder at the outlet point of the connecting rod is strictly necessary.

It is necessary to continuously detect the current position of the piston. This position must be detected because collision between the piston and the cylinder must be prevented to avoid damage. In this case, the position of the piston can be detected directly or indirectly, for example on the connecting rod.

The invention uses a drive link to replace such a pump substantially or completely, thereby compensating for pressure losses, since the pump used to compensate for pressure losses is exposed to great stress and risks damage due to the high pressure and the corrosive saline medium.

The accumulator can smooth out pressure fluctuations in the diaphragm assembly. By placing a plurality of devices according to the invention in each diaphragm assembly, i.e. at least two pressure compensation devices in each diaphragm assembly, each pressure compensation device comprising a pair of piston/cylinder devices, in particular which are operated in a phase-shifted manner with respect to each other, additional smoothing of the pressure fluctuations is achieved. Thus, at a given point in time t, only the piston of one pressure compensating device is in the extreme right or left end position. Depending on the design, all pressure compensation devices can be equipped with one drive or each pressure compensation device can be equipped with a separate drive.

The invention is not limited to the described embodiments, in particular the pressure compensation means can be designed differently. For example, a design with several pairs of piston/cylinder arrangements and/or with piston/hydraulic arrangements of different designs is possible. The pressure values given are exemplary values for the purpose of illustrating the invention, and the piston geometry may vary, and other pressure conditions may be present.

With the device and the method according to the invention, the efficiency of energy recovery is very high, up to at least 90%. Only a part of the operating pressure of the liquid feed pump, which is about 70 to 80 bar, has to be used for reverse osmosis, which varies with the amount of water sucked in, so that the costs and maintenance costs can be considerably reduced. Thus, the production costs of water desalination plants and of preparing drinking water can generally be significantly reduced. The geometry of the piston is not limited to just one possibility. The osmotic pressure may or should be adjusted according to the salt content of the water. For brackish water-water with the lowest salt content-a lower osmotic pressure can be chosen.

Claims (15)

1. A method for desalinating saltwater by reverse osmosis, wherein the saltwater (10) is subjected to a first pressure (P)₁) Is fed into a pressure compensation device (2) under the action of pressure and is at a second, higher pressure (P)₂) Under the action of the pressure compensation device, the pressure is sent into the diaphragm assembly (3) from the pressure compensation device (2); wherein the desalinated water (12) and the concentrated brine (13) are discharged from the membrane module (3), wherein the concentrated brine (13) discharged from the membrane module (3) is at a second pressure (P)₂) Is continuously fed into the pressure compensation device (2) under the action of the pressure and the second pressure (P) is fed₂) Salt applied in the feeding pressure compensating device (2)Water (10) and brine (11) into the membrane module (3); and wherein use is made of a controlled main valve (V)₁，V₃，V₄，V₆) Feeding the concentrated brine (13) into the pressure compensation device (2) and discharging the concentrated brine (14) from the pressure compensation device (2); wherein the control and main valve (V)₁，V₃，V₄，V₆) Parallel arranged auxiliary valves (V)₂，V₂′，V₅，V₅') main valve (V) can be reduced₁，V₃，V₄，V₆) Load peaks during opening and/or closing, for which purpose the auxiliary valve (V)₂，V₂′，V₅，V₅') at least at each main valve (V) arranged parallel thereto₁，V₃，V₄，V₆) Open during the opening or closing process; the pressure fluctuation is compensated by means of a pressure accumulator (P) which is arranged at the input of the pressure compensation device (2), and the concentrated brine (13) can be discharged from the membrane module (3) via the pressure accumulator.

2. A method according to claim 1, characterized in that the concentrated brine (13) discharged from the membrane module (3) is at a second pressure (P)₂) Is operatively fed into the output chamber (101, 102) of one of at least two piston/cylinder devices (401, 402) of the pressure compensation device (2); and acts on the pistons (301, 302) to bring the brine (10) fed into the input chambers (201, 202) of the same piston/cylinder unit (401, 402) at a second pressure (P)₂) Is fed into the membrane assembly (3).

3. A method according to claim 2, characterized in that the brine (13) is alternately fed into the outlet chamber (101, 102) of one of the piston/cylinder arrangements (401, 402), while the brine (11) is discharged from the respective inlet chamber (201, 202) of the same piston/cylinder arrangement (401, 402) into the membrane module (3); and in that the brine (10) is at a first pressure (P)₁) Is simultaneously fed into the inlet chamber (2) of another piston/cylinder unit (401, 402)01, 202) and the brine (14) is discharged from the output chamber (101, 102) of the same piston/cylinder unit (401, 402) at low pressure.

4. A method according to claim 3, characterized by controlling the piston/cylinder devices (401, 402) of the pressure compensating device (2) such that brine (10) can be fed simultaneously into the inlet chambers (201, 202) of at least one piston/cylinder device (401, 402); discharging the concentrated brine (14) from the output chamber (101, 102) of the same piston/cylinder arrangement (401, 402); feeding the concentrated brine (13) into the outlet chamber (101, 102) of at least one further piston/cylinder device (401, 402); and feeding brine (11) from the inlet chambers (201, 202) of the same piston/cylinder arrangement (401, 402) into the diaphragm assembly (3).

5. A method according to claim 1, characterized in that the pressure compensating device (2) comprises two piston/cylinder devices (401, 402) operating in opposite phases; and in that the pistons (301, 302) of the piston/cylinder devices (401, 402) are connected by a connecting rod (30).

6. A method according to any of claims 2-4, characterized in that the pressure compensating device (2) comprises two piston/cylinder devices (401, 402) operating in opposite phases; and in that the pistons (301, 302) of the piston/cylinder devices (401, 402) are connected by a connecting rod (30).

7. A method according to claim 5, characterized in that the connecting rod (30) is driven by a drive means.

8. Method according to claim 6, characterized in that the connecting rod (30) is driven by a drive means.

9. Method according to any of the preceding claims 1-5, characterized in that the auxiliary valve (V)₂，V₂′，V₅，V₅') cross-sectional ratio of main valve (V)₁，V₃，V₄，V₆) Has a small cross section.

10. Method according to any of the preceding claims 1-5, characterized in that, by means of an auxiliary valve (V)₂，V₂′，V₅，V₅') the maximum flow rate is determined by a flow rate limiter (R) on the liquid delivery line leading to the auxiliary valve₁，R₂，R₃) And (5) controlling.

11. Method according to any of the preceding claims 1-5, characterized in that the auxiliary valve (V)₂，V₂′，V₅，V₅') only in the respective main valves (V) arranged parallel thereto₁，V₃，V₄，V₆) Open during opening or closing.

12. A method according to any of claims 1-5, characterized in that the main valve and the auxiliary valve are controlled such that the main valve switches in the absence of pressure.

13. A method according to any of the preceding claims 1-5, characterized in that the position of the piston (301, 302) is determined continuously.

14. A method according to any of the preceding claims 1-5, characterized in that the pressure compensating device (2) comprises several pairs of piston/cylinder devices (401, 402), each pair being connected by a connecting rod (30); and is further characterized in that the pairs of devices are operated in a phase-offset manner.

15. A device for carrying out the method according to any one of the preceding claims, having means for feeding brine (10) into the pressure compensation device (2)And a membrane module (3) separating the brine (11) discharged from the pressure compensation device (2) into desalinated water (12) and concentrated brine (13); wherein, between the diaphragm assembly (3) and the pressure compensation device (2), a pressure (P) is provided which is continuously present during operation₂) A connecting pipeline (5) under action and used for respectively sending the strong brine (13) discharged from the membrane assembly (3) to the pressure compensation device (2) and sending the brine (11) from the pressure compensation device (2) to the membrane assembly (3); wherein the main valve (V) is controlled₁，V₃，V₄，V₆) For feeding the concentrated brine (13) into the pressure compensation device (2) and for discharging the concentrated brine (14) from the pressure compensation device (2); wherein a main valve (V) is arranged₁，V₃，V₄，V₆) Parallel auxiliary valves (V)₂，V₂′，V₅，V₅') in the main valve (V)₁，V₃，V₄，V₆) The load peak during opening and/or closing is reduced, for which purpose the auxiliary valve (V)₂，V₂′，V₅，V₅') at least at each main valve (V) arranged parallel thereto₁，V₃，V₄，V₆) Open during the opening or closing process; the pressure fluctuation is compensated by means of a pressure accumulator (P) which is arranged at the input of the pressure compensation device (2), and the concentrated brine (13) can be discharged from the membrane module (3) via the pressure accumulator.