EP2078867B1 - Pressure exchanger for transferring pressure energy from one liquid flow to another liquid flow - Google Patents

Description

The invention relates to a pressure exchanger for transmitting pressure energy from a first liquid stream to a second liquid stream. A Deraltiger pressure exchanger is for example off EP 0 298 097 B1 is known and serves to transfer pressure energy from a first liquid stream to a second liquid stream. Such pressure exchangers are used in particular in seawater desalination plants. In such systems, salt water is supplied under pressure on the input side. The supplied salt water then flows through membranes through which the desalted water passes and is discharged as a second liquid stream. On the inlet side of the membrane creates a higher concentrated brine, which emerges under pressure from the plant. The task of the pressure exchanger is to recover some of the pressure energy, which contains these escaping brine, and to reintroduce it to the salt water supplied in order to reduce the energy requirement of the plant.

Problematic in such pressure exchangers of EP 0 298 097 B1 known type is that it can come in the pressure exchanger to an undesirable mixture of salt water and brine, since both liquid streams are not completely separated.

WO 2006/015682 A1 discloses a variable speed pressure exchanger for transferring pressure energy from a first fluid to a second liquid. In this case, the pressure exchanger is controlled so that there is a predominantly bumpless entry of the flow rate in the channels of the rotor of the pressure exchanger. However, this regulation can still lead to undesirable mixing.

EP 1 508 361 A1 also discloses a pressure exchanger having a rotor drivable by a drive motor. In this rotor channels are formed, in which a piston is movably arranged, which separates the two liquids from each other. The arrangement of the piston leads to a more complex structure of the rotor. In addition, the rotor becomes heavier overall, whereby the efficiency deteriorates.

WO 97/20134 shows a charging device for the charge air of an internal combustion engine, which is designed as a pressure exchanger for transmitting the pressure energy from the exhaust gas flow to the charge air. Also, this pressure exchanger has a rotor which is driven in rotation by an electric motor. In the rotor open channels are formed, so that even with this pressure exchanger presents the problem that it can lead to an undesirable mixing of the two air streams.

In view of this problem, it is an object of the invention to improve a pressure exchanger in such a way that at the same time a possible high efficiency and reliable operation of the pressure exchanger is achieved and unwanted mixing of the two liquid streams is avoided together.

This object is achieved by a pressure exchanger having the features specified in claim 1. Preferred embodiments will become apparent from the subclaims, the following description and the accompanying figures.

The pressure exchanger according to the invention serves to transfer pressure energy from a first liquid stream to a second liquid stream. For example, the first liquid stream may be a brine exiting a seawater desalination plant while the second liquid stream may be a liquid stream of brine which is supplied to the seawater desalination plant. However, the application of the pressure exchanger according to the invention is not limited to seawater desalination plants, but can also be used in other plants in which pressure energy is to be transferred from a first liquid jet to a second one.

The pressure exchanger according to the invention has a housing which has an inlet and an outlet for the first fluid flow and an inlet and an outlet for a second fluid flow. In this case, the inlet and the outlet for the first liquid stream are preferably arranged at a first axial end and the inlet and the outlet for the second liquid stream are arranged at a second axial end. Further, disposed in the housing is a rotor having a plurality of channels extending radially spaced from a rotational axis of the rotor from a first axial end of the rotor to an opposite second axial end of the rotor. That is, the channels connect the two axial sides of the rotor with each other. In this case, a plurality of channels is distributed over the circumference of the rotor. The rotor is arranged to the inputs and outputs for the first liquid stream and the second liquid stream such that the channels alternately the input for the first liquid stream with the output for the second liquid stream and the input for the second liquid stream with each rotation of the rotor connect to the outlet for the first liquid flow. The pressure exchanger has for this purpose at its axial ends preferably connecting elements on which the inputs and outputs described for the two liquid streams are formed. That is, a first connection element is provided for the first liquid flow at an axial end and a second connection element for the second liquid flow at the opposite axial end, wherein the rotor is located in the axial direction between the two connection elements. In addition, the connection elements are designed so that the inputs and outputs located in them are not directly connected to each other. Rather, the inputs and outputs are each facing the rotor, so you can be aligned with the channels in the rotor depending on the rotation angle of the rotor. This structure basically corresponds to the EP 0 298 097 B1 known structure.

The operation of the pressure transmitter is such that from the inlet for the first fluid flow whose higher pressure is transmitted via one or more channels in the rotor to the outlet for the second fluid flow. In this way, pressure energy is transferred from the first liquid stream to the second liquid stream. As the rotor continues to rotate, the channels responsible for the pressure energy transfer described above come to a position where they are aligned with the second fluid stream inlet and the first liquid stream outlet. In this case, then pressure energy from the input of the second liquid stream transmitted to the output of the first liquid stream.

Usually, the volume flow of the first liquid flow with a higher pressure is less than the volume flow of the second liquid flow with a lower pressure. A mixing of the liquid streams according to the invention should be avoided in particular between the inlet for the liquid flow with a higher pressure and the outlet for the liquid flow with a lower pressure. When used in a seawater desalination plant, the output for the second liquid stream, i. the liquid flow with the lower pressure, the salt water fed to the seawater desalination plant. For this reason, it should be prevented that a part of the brine, which emerges from the seawater desalination plant and has a higher pressure, in this second liquid stream passes, since in this case the seawater desalination plant an unnecessarily increased salt concentration would be supplied. On the other side of the pressure exchanger between the outlet for the first fluid flow and the inlet for the second fluid flow, however, it is less problematic if the fluid flows to a part mix, as this would only cause liquid from the second fluid flow in the first fluid flow transgresses. In the case of use in a seawater desalination plant, this would mean that fresh salt water passes into the escaping brine, which is usually unproblematic. If the volume flow of the second liquid stream is greater, there will usually always be a mixing and a certain transfer of the second liquid into the outlet for the first liquid stream on this side.

For rotation of the rotor, a drive motor, preferably an electric drive motor is provided according to the invention. Essential to the invention is that adjusting means are provided by means of which the speed of the rotor is changeable. This can be done in particular by changing the speed of the drive motor. These adjustment means allow the rotor speed to be adapted to the current boundary conditions of the installation, in particular to the current volume flow of the first liquid stream and the second liquid stream. The speed of the rotor can be adapted to the volume flows so that an optimal pressure transfer takes place without the liquid streams mix more than necessary with each other. In the operation of such a pressure exchanger forms in the channels a mixing zone in which the two liquid streams come into contact with each other. When replacing the pressure energy, this mixing zone migrates in the channels in the axial direction. In order to avoid a real mixing of the liquid streams between the inlet for the first liquid stream and the outlet for the second liquid stream, however, this mixing zone must advantageously always remain in the interior of the channel. At the same time, in order to achieve a high efficiency of the pressure exchanger, the path by which this mixing zone travels in the axial direction should be as large as possible, preferably corresponding to almost the entire length of the channel in the axial direction. However, the movement of the mixing zone depends on external parameters, in particular the pressure differences and the volume flows and the rotational speed of the rotor. Now, if the speed of the rotor is variable, it is possible to always adjust the speed of the rotor so that the mixing zone remains inside the channel and at the same time the efficiency is maximized.

For this purpose, a control or regulating device is provided, via which the rotational speed of the rotor is adjustable. This is further preferably automatically to operate the pressure exchanger always with a rotor speed, which allows the maximum efficiency at given flow rates and pressure differences.

Furthermore, the control or regulating device is designed such that it adjusts the rotational speed of the rotor so that a mixing zone, in which there is a mixture between the first liquid stream and the second liquid stream, is always located in the interior of the channels. As a result, mixing of the liquid streams is prevented as described. At the same time, the controller preferably performs the control such that the axial distance that the mixing zone moves as the rotor rotates is maximized. This ensures the highest possible efficiency.

According to the invention, a sensor for detecting at least one parameter of at least one of the liquid streams is present and the control or regulating device is designed such that the rotational speed of the drive motor is set as a function of the detected parameter. Thus, an automatic adjustment of the rotor speed to the detected parameters is possible and the operation of the pressure exchanger can be done depending on the detected parameter in the range with maximum efficiency. The setting and adjustment of the rotor speed via the setting of the speed of the drive motor can be done automatically depending on the detected parameter or the detected parameters. Preferably, a plurality of sensors are provided to detect parameters of the liquid streams at different locations, for example, at the inlet and outlet for the respective liquid flow.

According to the invention, the sensor is a sensor for detecting the concentration of a substance and in particular the salt content in the liquid. About such a sensor can be monitored directly, whether it comes to a mixing of the two liquid streams. Should this be determined, the speed of the drive motor can then be adjusted so that such mixing no longer occurs, what then in turn detected by the sensor or sensors for concentration detection.

Further, according to the invention for each at least one of the two liquid streams both in the input and in the output of a sensor for detecting the substance concentration is provided and the control or regulating device is for detecting the difference between the concentrations of substances at the input and the output and for setting the Speed of the drive motor formed as a function of the detected difference. If the pressure exchange between two liquids or liquid streams, which have different concentrations of a substance, for example, a different salt content, takes place, it can be determined in this way, if it comes to a mixing of the liquids. If the liquids do not mix, at the exit and entrance of a liquid stream, the concentration of the substance should be substantially the same, respectively. H. the detected difference have a minimum. If the difference becomes larger, this indicates that there is an undesirable mixing of the two fluid streams and the speed of the drive motor can be adjusted by the controller accordingly to adjust the speed of the drive motor so that it does not a mixing of the liquid flows comes.

The control device is designed such that it controls the speed of the drive motor so that the difference of the substance concentrations reaches a minimum. In this way, the pressure exchanger is always operated so that it comes to the least possible mixing of the two liquid streams and at the same time the maximum efficiency can be achieved.

According to a further preferred embodiment, means for detecting the rotational speed of the rotor may be present, in particular a Speed sensor can be arranged on the rotor. This makes it possible to detect the current rotor speed and to take into account in the control or regulation of the speed. The controller can thus receive feedback on how high the actual rotor speed is. Thus, an even more accurate control or regulation of the speed of the drive motor and thus adaptation to the current operating conditions is possible.

Fig. 1

eine schematische perspektivische Ansicht des erfindungsgemäßen Druckaustauschers, wobei eines der axialen Anschlusselemente abgenommen ist,

Fig. 2

eine perspektivische Ansicht eines Anschlusselementes des Druckaustauschers gemäß Fig. 1,

Fig. 3

eine Schnittansicht des Druckaustauschers,

Fig. 4

eine Kurve, welche eine Differenz des Salzgehaltes aufgetragen über die Rotordrehzahl zeigt und

Fig. 5

eine Schnittansicht eines Druckaustauschers gemäß einer zweiten Ausführungsform der Erfindung.

The invention will now be described by way of example with reference to the accompanying drawings. In these shows:

Fig. 1

a schematic perspective view of the pressure exchanger according to the invention, wherein one of the axial connection elements is removed,

Fig. 2

a perspective view of a connection element of the pressure exchanger according to Fig. 1 .

Fig. 3

a sectional view of the pressure exchanger,

Fig. 4

a curve showing a difference of the salt content plotted against the rotor speed and

Fig. 5

a sectional view of a pressure exchanger according to a second embodiment of the invention.

The geometric structure of the pressure exchanger essentially corresponds to the example of EP 0 298 097 B1 known pressure exchanger. The pressure exchanger has a cylindrical housing 2, in the interior of which a rotor 4 is rotatably arranged. In this case, the rotor 4 is rotatable about the longitudinal axis X of the housing 2 and the rotor 4. At the two axial sides, the housing 2 is closed in each case by a connecting element 6. Both connection elements 6 are identical, for distinction, the two connection elements are referred to below with 6a and 6b. If no distinction is made, the description refers to identically formed parts. The connection elements 6 are screwed to the housing 4.

The rotor 4 has a plurality of channels 10, which extend in the rotor in the axial direction parallel to the longitudinal axis X. The channels 10 are arranged in a circle around the longitudinal axis X. In the example shown, two concentric rings of channels 10 are provided. This arrangement of two rings of channels is chosen for stability reasons. It should be understood that other arrangements, for example, only a ring of z. B. for larger channels or more than two rings of channels can be selected. The channels 10 connect the two axial ends of the rotor 4 with each other.

Each of the connection elements 6 has connecting pieces 12 (12a, 12b) and 14 (14a, 14b). As in Fig. 2 can be seen, the connecting pieces 12 and 14 are not connected to each other. Rather, in the interior of the connecting element 6, a partition wall 16 is formed, which is the interior of the connection element 6 divides into two parts. Thus, two arcuate recesses 18 (18a, 18b) and 20 (20a, 20b) separated from each other by the partition 16 are formed on the surface of the connecting element 6 facing the rotor 4. In this case, the recess 18 is connected to the connecting piece 12 and the recess 20 with the connecting piece 14.

As in FIG. 3 can be seen, an electric drive motor 22 is provided, which is connected via a coupling 24 with the rotor shaft 26. The rotor 4 is rotatably mounted on the rotor shaft 26 so that it can be rotated by the drive motor 22. At the rotor shaft 14, a shaft seal 28 is arranged. The shaft seal 28 is connected via the channel 30 with the recess 18 b to supply liquid for lubrication. Further, a channel 32 is provided, which leads from the recess 18a to the circumferential space 34 between the rotor 4 and the housing 2, to discharge liquid from this space. In this way, liquid which penetrates into this space can be dissipated and an excessive pressure in this space can be prevented. Also, a channel 36 is provided, which connects the recess 18a with the through hole in the rotor 4, in which the rotor shaft 26 is located. Thus, liquid can be removed from this through hole, in particular for cooling and lubrication of storage through the channel 30 entering liquid.

The operation of the pressure exchanger is as described below. The connecting pieces 12a and 14a serve for connection to a line system for a first liquid flow, while the connections 12b and 14b serve for connection to a line system for a second liquid flow. The first liquid stream is, for example, the brine stream emanating from a seawater desalination plant, which still has a high pressure energy, which is due to a second liquid stream, which, for example, is a flow of salt water is, which is to be supplied to a desalination plant is transmitted. The connection piece 14a forms an inlet for the first liquid stream under the pressure p ₂ , for example brine. The port 12a forms the outlet for the first liquid flow at a lower pressure p ₄ .

The port 14b forms the outlet for the second fluid stream, for example the salt water, while the port 12b forms the inlet for the second fluid stream. The first liquid flow enters the inlet 14a and the subsequent recess 20a at a pressure p ₂ . Since the pressure p _{2 is} greater than the pressure p ₁ , which has the liquid of the second liquid stream at the outlet 14 b, the liquid flows from the inlet 14 a into the channels 10 facing the recess 20 a and thus transfers the pressure to the second liquid, which is located in these channels, and the second liquid in the recess 20b and the subsequent to the output 14b line system, since these channels 10 are also aligned with the recess 20b.

In the channels 10, the two liquids come into contact with each other, being moved by the higher pressure p _2, this contact zone in the channels 10 to the axial end, which faces the recess 20b of the connecting element 6b. That is, in this position, the channels 10 are largely filled with the first liquid from the inlet 14a. Now, when the rotor 4 is rotated, these channels 10, which have first located between the recesses 20a and 20b, come to rest between the recesses 18a and 18b. In the recess 18b, the liquid pressure p _{3 of} the incoming second liquid prevails, which, although lower than the pressure p ₂ , but higher than the output pressure p _{4 of} the first liquid in the recess 18a. As a result, the second liquid flows into the channels 10 and presses the first liquid from the channels 10 largely into the recess 18a and via the connecting piece 12a in a subsequent pipeline. In this case, the mixing zone, in which the two liquids in the channels 10 come into contact with each other, moves to that axial end of the channels 10, which faces the connection element 6a and its recess 18a. Since the volume flow of the second liquid is greater than that of the first liquid, it comes on this side of the pressure exchanger to a mixing of the liquids, that is, a part of the second liquid enters the recess 18 a and the liquid emerging from the port 12 a is with a part of the incoming second liquid mixed. When the rotor now rotates back to the first described position so that said channels 10 are again between the recesses 20a and 20b, the first liquid flows back into the channels 10 there and pushes the second liquid to the outlet 14b for the second liquid , Thus, part of the pressure energy of the first liquid is transferred to the second liquid.

It can be seen that the entire first liquid flow and the entire second liquid flow must be conveyed through the channels 10 of the rotor 4. According to the invention, the rotational speed of the rotor 4 can now be changed via the drive motor 22 in order to adapt the rotor speed to the first and the second fluid flow, so that an optimum efficiency is achieved, without causing a mixing of the two fluids on the side of the pressure exchanger with higher pressure that is, between the recesses 20a and 20b. Mixing would occur when the mixing region, in which both liquids come into contact with each other, leaves the channels 10 at one axial end. For example, if the rotor were rotating too slowly, it could happen that the first fluid flows through the channels 10 between the recesses 20b and 20a into the recess 20b before the rotor has continued to rotate. Here, the rotor speed should be adjusted so that such overflow does not occur. However, if the rotor speed is too fast, too little liquid enters the channels 10. Thus, for example, the channels 10 between the recesses 20a and 20b starting from the recess 20a would be filled only to a small extent with the first liquid before the rotor continues to rotate. This deteriorates the efficiency, because then the pressure energy can be transferred only to a small extent from the first liquid to the second liquid. Optimum efficiency is achieved when the contact or mixing region in which the two liquids in the channels 10 are in contact with each other upon rotation of the rotor from the position between the recesses 20a and 20b to the position between the recesses 18a and 18b migrates substantially over the full axial length of the channels 10.

In order to achieve an optimal control, sensors 38 for detecting the salt content are arranged in the recesses 18b and 20b. The sensors could also be designed to detect the concentration of another substance as salt, depending on the location of the pressure exchanger. The sensors 38 are connected by cable or wirelessly with a control or regulating device 39 which controls or regulates the rotational speed of the drive motor 22. The control device 39 determines from the output signals of the sensors 38 the difference between the substance concentrations or the salt contents. Thus, a change in the salt content can be detected in a second liquid flowing in through the connecting piece 12b and flowing out through the connecting piece 14b. If, for example, the first liquid, which is supplied through the connecting piece 14a and discharged through the connecting piece 12a, has a higher salt content than the second liquid, which is the case in the example described from a desalination plant, it would be in a mixing of first and second liquid to increase the salt content in the second liquid. When the first liquid is starting would flow from the recess 20a through the channels 10 into the recess 20b, this would result in the recess 20b to an increased salt content of the second liquid. That is, the salt content in the recess 20b would be higher than in the recess 18b in which the incoming second liquid is located. It would thus be possible to detect a difference in the salt content via the sensors 38.

In Fig. 4 the difference of the salt content 40 is plotted against the rotor speed 42. It can be seen that this curve 44 has a minimum 43. This minimum 43 is the optimum operating point at which there is the least possible mixing of the two fluid streams. If the rotational speed is too low, mixing occurs due to overflow of the liquid from the recess 20a into the recess 20b. If the speed is too high, there is also an increase in the difference in salt content between inlet and outlet for the second fluid, since there is an increasing mixing of the first and second fluids in the channels 10, since the channels 10 are not as before alternately substantially completely filled with the first and the second liquid. Rather, always a part of the liquid remains in the channels, so that here comes to a mixture and a slight increase in the salt content in the outlet for the second liquid.

The regulation of the rotational speed of the rotor 2 via the rotational speed of the drive motor 22 now takes place as follows. First, a speed is selected which is higher than the speed 47 at the minimum difference 43. Based on this speed, the speed is initially reduced, as long as the sensors 38 determine a decreasing difference in salinity. This is in the diagram in Fig. 4 indicated by the dashed arrows 45. If now an increase in the difference in salinity is detected, the rotor speed is increased again, as by the arrow 46 in Fig. 4 is shown. In this way, the speed can be adjusted to the speed 47 at the minimum 43 of the difference in salinity between the sensors 38.

In the event that the curve 44 runs so that it forms a straight line at a higher rotor speed and thus has no global minimum, the control can be carried out in such a way that the speed is set as low as possible. The speed is reduced so far that it just does not increase the difference of the salt content 40.

As an alternative to a speed control via the detection of the salt content in the manner described above, it is also possible to regulate the speed via the volume flow by the volume flows of the first and / or the second liquid are detected and depending on one or both volume flows, the speed be set. For this purpose, a table with an assignment of speeds to volume flows can be stored in the controller.

Fig. 5 shows a further embodiment of the invention, which differs from the preceding, with reference to Fig. 3 described embodiment differs only in that in the channels 10 spherical locking elements 48 are arranged. The blocking elements 48 are movable in the channels 10 along their longitudinal axis. At the axial ends of the channels 10 stop rings 50 are provided which prevent the locking elements 48 can escape from the channels 10 on the axial side. The blocking elements 48 prevent the first and second liquids in the channels 10 from coming into direct contact with each other. A small contact is tolerated, however, since it should be understood that the locking elements 48 can not always be arranged completely sealed in the channels due to their mobility. In operation of the pressure exchanger according to this embodiment, the blocking elements move 48, when the channels 10 are located between the recesses 20a and 20b, ideally first up to that axial end of the channels 10, which faces the connection element 6b, so that the locking elements 48 come to rest on the stop rings 50 at this axial end. When the rotor then rotates to a position such that these channels 10 are located between the recesses 18a and 18b, the locking elements 48 are moved to the opposite end of the rotor 4 and abut the stop rings 50 facing the terminal 6a. All other elements and the operation correspond to the above with reference to Fig. 3 explained operation.

LIST OF REFERENCE NUMBERS

2

- Casing

4

- Rotor

6a, 6b

- Connection elements

10

- Channels

12a, 12b 14a, 14b

- Connecting piece

16

- Partition wall

18a, 18b, 20a, 20b

- recesses

22

- Drive motor

24

- coupling

26

- Rotor shaft

28

- shaft seal

30, 32

- Channels

34

- room

36

- Channel

38

- Sensors

39

- Control or regulating device

40

- Difference in salinity

42

- Rotor speed

43

- minimum

44

- Curve

45, 46

- arrows

47

- Rotation speed

48

- blocking elements

50

- stop rings

X

- longitudinal axis

Claims (3)

1. A pressure exchanger for transmitting pressure energy from a first fluid flow to a second fluid flow, with a housing (2) which comprises an inlet (14a) and an outlet (12a) for the first fluid flow as well as an inlet (14b) and an outlet (12b) for the second fluid flow,
   with a rotor (4) which is arranged in the housing (2) and which comprises a multitude of channels (10) which extend in a manner radially distanced to a rotation axis (X) of the rotor (4) from a first axial end of the rotor (4) to an opposite, second axial end of the rotor (4), wherein the rotor (4) is arranged to the inlets and outlets (12, 14) in a manner such that on rotation of the rotor (4), the channels (10) alternately connect the inlet (14a) for the first fluid flow to the outlet (14b) for the second fluid flow and the inlet (12b) for the second fluid flow to the outlet (12a) for the first fluid flow, and
   with a drive motor (22) via which the rotor (4) is drivable in rotation, with adjusting means for changing the rotational speed of the rotor, wherein a control or regulation device is present, via which the rotational speed of the drive motor (22) can be adjusted and which is designed in a manner such that it adjusts the rotational speed of the rotor (4) such that a mixing zone, in which a mixing between the first fluid flow and the second fluid flow occurs, is always situated in the inside of the channels (10), characterised in that a sensor (38) for detecting the substance concentration of a substance in the fluid is present in the inlet (12b) as well as in the outlet (14b), at least for one of the two fluid flows and the control or regulation device is designed for detecting the difference (44) between the substance concentrations at the inlet (12b) and the outlet (14b) and for adjusting the rotational speed of the drive motor (22) in dependence on the detected difference (44) in a manner such that that it controls the rotational speed of the drive motor (22) with a closed loop, such that the difference (44) of substance concentration reaches a minimum (43).
2. A pressure exchanger according to claim 1, characterised in that the sensor is a sensor (38) for detecting the concentration of a substance and in particular of the salt content in the fluid.
3. A pressure exchanger according to one of the preceding claims, characterised in that means for detecting the rotational speed of the rotor (4) are present.

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