Reverse osmosis system

Abstract

System (100) for reverse osmosis, RO, comprising: a first RO stage (10) with a first feed inlet (11), a first saline outlet (12) and a first permeate outlet (13); a second RO stage (20) with a second feed inlet (21), a second saline outlet (22) and a second permeate outlet (23); an isobaric pressure exchanger, pressure exchanger - PE, (40), connected between the second brine outlet (22) and the first feed inlet (11), wherein a means (50, 60) configured to generate a first pressure difference Δp1 as one of a pressure rise and a pressure drop is connected between the first brine outlet (12) and the second feed inlet (21) and a means (50, 60) configured to generate a second pressure difference Δp2 as the other of a pressure rise and a pressure drop is connected between the second brine outlet (22) and the isobaric pressure exchanger (40), wherein the system is configured such that the first pressure difference Δp1 and the second pressure difference Δp2 automatically adjust to each other so that they correspond to each other, such that the first pressure difference Δp1 between the first saline outlet (12) and the second feed inlet (21) corresponds to approximately 80% to 120% of the second pressure difference Δp2 between the second saline outlet (22) and the isobaric pressure exchanger (40).

Description

Field of the invention

[0001] The invention relates to a system for reverse osmosis, in particular a system for multi-stage reverse osmosis which has improved energy efficiency. Technological background

[0002] Osmosis is a process in which a solvent moves across a partially permeable membrane from the side of the membrane facing a lower solute concentration to the side facing a higher solute concentration. The movement of solvent particles is driven by diffusion, and generally, more solvent particles diffuse toward a higher solute concentration, i.e., the lower water potential, resulting in a net movement of the solvent. This naturally occurring process also underlies the reverse osmosis process, as described below.

[0003] In reverse osmosis, a pressure exceeding the osmotic pressure is applied to the side of higher solute concentration, reversing the energy balance of the osmotic system. This induces an overall net diffusive movement from the high solute concentration side through the membrane to the low solute concentration side, thereby increasing the solute concentration on the pressurized membrane side. Reverse osmosis systems comprise at least two chambers separated by a semipermeable membrane, with the inflow and outflow of the chambers being controllable to establish volumetric flow conditions as well as pressure gradients across the membrane.

[0004] Reverse osmosis (RO) is often used for water purification or desalination applications, where a highly concentrated salt solution is produced alongside the purified and / or desalinated water. The salt solution remains on the pressurized side of the membrane, while the purified and / or desalinated water (permeate) is removed from the other side of the membrane at a low pressure. The pressurized salt solution is removed from the reverse osmosis chamber to prevent an excessive increase in osmotic pressure and to allow the flow of fresh feed solution into the chamber. It is also known to use energy recovery devices, such as hydraulic turbines, for the purpose of transferring hydraulic energy from the pressurized salt solution to the feed solution to improve the overall energy efficiency of the reverse osmosis process.

[0005] Combining multiple RO stages is also known to improve energy efficiency and freshwater yield in such a system. In such multi-stage RO systems, the RO chambers are typically combined in a linear fashion. Within these chambers, the brine is typically pressurized before entering a subsequent stage to compensate for the increased solvent concentration of the brine. Hydraulic turbines are also used for energy recovery and improved efficiency in multi-stage RO systems.

[0006] The use of turbines typically requires the conversion of hydraulic energy into mechanical energy on the motor side, followed by conversion into electrical energy for energy transfer. The pump side then requires the reconversion of electrical energy into mechanical energy and then into hydraulic energy. This typically reduces the overall energy efficiency of an RO system. Pressure exchangers, which allow direct energy transfer between fluids, avoid such conversion losses, but tend to have narrow windows for optimal transfer efficiency, which are often not achieved in RO systems.

[0007] It is therefore an object of the present disclosure to overcome or at least reduce the disadvantages of the prior art and to provide a reverse osmosis system with improved energy efficiency. Brief description of the invention

[0008] By the subject matter of the present invention, ie by a system for reverse osmosis, RO, according to the appended claims, the object of the disclosure is solved and the disadvantages of the prior art are overcome or at least reduced.

[0009] One aspect of the present disclosure relates to a system for reverse osmosis, RO, comprising a first RO stage having a first feed inlet, a first brine outlet, and a first permeate outlet. The first RO stage comprises a first high-pressure RO chamber and a first low-pressure RO chamber separated by a first RO membrane. These chambers preferably form an RO tank configured to accommodate the first RO process and withstand the pressures encountered. The first RO stage may comprise multiple inlets and / or outlets, for example, multiple first feed inlets, multiple first brine outlets, and / or multiple first permeate outlets. For the sake of brevity, only one of these inlets or outlets will be discussed below. In a first RO stage comprising multiple inlets and / or outlets, the following explanations may refer to relationships between individual inlets and / or outlets and / or to relationships between multiple inlets and / or outlets.

[0010] The (at least one) first feed inlet is configured to supply a feed solution stream to the first high-pressure RO chamber, and the (at least one) first brine outlet is configured to remove the brine from the chamber. The first low-pressure RO chamber is configured to receive a permeate, i.e., the feed solution with a reduced solute concentration, via the first RO membrane. The (at least one) first permeate outlet is configured to remove the permeate from the first low-pressure RO chamber. The concentrated feed solution (brine) is removed via the (at least one) first brine outlet at a pressure approximately equal to the pressure of the feed solution at the (at least one) first feed inlet.The permeate is discharged via the (at least one) first permeate outlet at a pressure that is significantly lower than the feed pressure, preferably as low as possible to ensure an optimal pressure difference across the membrane.

[0011] The first RO membrane is designed to allow the diffusion of the solvent of the feed solution under an external pressure applied to the first high-pressure RO chamber. In a preferred embodiment, the feed solution is salt water, for example, seawater, and the first RO membrane is designed to allow water to diffuse through the membrane while preventing salt ions such as Na + and CI -permeate the membrane. Preferably, the first RO membrane is designed to prevent organic substances, bacteria, and pyrogens from permeating the membrane, although such components may already be removed in a pretreatment step prior to the RO chamber. The first RO chamber is preferably made of a cellulose acetate (CA) membrane or a polysulfone membrane, which may be coated with aromatic polyamides. Also preferably, the first RO membrane is nanostructured, a zeolite membrane, and / or a coil wrapped around the RO membrane.

[0012] The RO system of the present disclosure further comprises a second RO stage having a second feed inlet, a second brine outlet, and a second permeate outlet. The second RO stage comprises a second high-pressure RO chamber and a second low-pressure RO chamber separated by a second RO membrane. These chambers preferably form a second RO tank configured to accommodate the second RO process and withstand the pressures encountered. The second RO stage may comprise multiple inlets and / or outlets, for example, multiple second feed inlets, multiple second brine outlets, and / or multiple second permeate outlets. For brevity, reference will be made below to only one of these inlets or outlets.In a second RO stage comprising multiple inlets and / or outlets, the following explanations may refer to relationships between individual inlets and / or outlets and / or to relationships between multiple inlets and / or outlets.

[0013] The (at least one) second feed inlet is configured to supply a feed solution stream to the second high-pressure RO chamber, and the (at least one) first brine outlet is configured to remove the brine from the chamber. Therein, the feed solution supplied to the at least one feed inlet is (at least partially) the brine removed from the (at least one) first brine outlet. The second low-pressure RO chamber is configured to receive a permeate via the second RO membrane. The (at least one) second permeate outlet is configured to remove the permeate from the second low-pressure RO chamber. The permeate from the first and second low-pressure chambers can be removed together.Also in the second RO stage, the brine is discharged via the (at least one) second brine outlet at a pressure approximately equal to the pressure of the feed solution (first-stage brine) at the (at least one) second feed inlet, while the permeate is discharged via the (at least one) second permeate outlet at a lower pressure, preferably at a pressure significantly lower than the feed pressure, even as low as possible. The second RO membrane is designed in the same or a similar manner as the first RO membrane.

[0014] The system of the present disclosure further comprises a pressure exchanger (PE) connected between the second saline outlet and the first supply inlet. In other words, the pressure exchanger comprises an inlet, in particular a high-pressure (HP) inlet, configured to receive a saline flow discharged from the second saline outlet, and an outlet, in particular a high-pressure (HP) outlet, configured to provide a supply solution flow to the first supply inlet. The pressure exchanger further comprises another outlet, in particular a low-pressure (LP) outlet, configured to discharge the reduced-pressure saline flow, and another inlet, in particular a low-pressure (LP) inlet, configured to receive a pressurized supply solution flow.

[0015] In the system of the present disclosure, a first pressure difference Δp1 between the first brine outlet and the second feed inlet corresponds to a second pressure difference Δp2 between the second brine outlet and the pressure exchanger. In other words, the first pressure difference Δp1 refers to a difference between the pressure of the brine discharged via the first brine outlet and the pressure of the feed solution entering the second RO stage via the second feed inlet. The feed solution entering the second RO stage via the second feed inlet consists at least partially, preferably entirely, of the brine discharged via the first brine outlet.Consequently, the first and second pressure differences Δp1 and Δp2 are not independent of each other, but correspond to each other in that the first pressure difference Δp1 is set to a value that depends on a value of the second pressure difference Δp2, or the second pressure difference Δp2 is set to a value that depends on a value of the first pressure difference Δp1.

[0016] The system of the present disclosure thus enables operation in which a pressure between the first saline outlet and the second supply inlet is varied by the first pressure difference Δp1, and a pressure between the second saline outlet and the pressure exchanger is varied by the second pressure difference Δp2, which corresponds to the first pressure difference Δp1, and wherein hydraulic energy is thus advantageously transferred from a second saline stream flowing out of the second saline outlet to a first supply stream provided to the first supply inlet via the pressure exchanger with improved efficiency. The improved efficiency is enabled by the pressure configuration, i.e., corresponding to the first and second pressure differences, of the disclosed system, which allows operation of the pressure exchanger with optimal transfer efficiency.According to the present disclosure, the first pressure difference Δp1 and / or the second pressure difference Δp2 may have a positive pressure value or a negative pressure value.

[0017] According to a preferred embodiment of the RO system, the pressure exchanger, PE, has a high-pressure inlet, HP inlet, connected to the second brine outlet, and a PE-HP outlet connected to the first feed inlet, and the second pressure difference Δp2 occurs between the second brine outlet and the PE-HP inlet. Consequently, in the RO system of the present disclosure, the second pressure difference Δp2 is established before the brine stream is fed to the pressure exchanger in order to feed the brine stream to the pressure exchanger at an optimized pressure. In this way, a transfer efficiency of hydraulic energy in the pressure exchanger, which is configured to pressurize the feed stream provided to the first feed inlet, is advantageously improved. Also advantageously, in the embodiment, a booster pump is provided downstream of the second brine outlet.

[0018] Further preferably, in the system of the present disclosure, the first pressure difference Δp1 is used to generate the second pressure difference Δp2. In other words, hydraulic energy associated with the first pressure difference Δp1 is extracted and used to generate the second pressure difference Δp2. Likewise preferably, the second pressure difference Δp2 is used to generate the first pressure difference Δp1. This in turn refers to a transfer of hydraulic energy in connection with the first pressure difference Δp1 and the second pressure difference Δp2. Generating the second pressure difference Δp2 by utilizing the first pressure difference Δp1 does not necessarily mean that energy is provided to generate the second pressure difference Δp2, because in a similar way, the second pressure difference Δp2 can be generated by extracting hydraulic energy from the system using the first pressure difference Δp1.The transfer of hydraulic energy associated with the first pressure difference Δp1 and the second pressure difference Δp2 can occur directly or indirectly by converting it into other forms of energy. For example, hydraulic energy can be converted into mechanical and / or electrical energy to be transferred between the first pressure difference Δp1 and the second pressure difference Δp2.

[0019] In a particularly preferred embodiment of the system of the present disclosure, the pressure exchanger is an isobaric pressure exchanger. Further preferably, the pressure exchanger is configured to transfer pressure from the pressurized saline stream, downstream of the second saline outlet, to the low-pressure feed solution, upstream of the first feed inlet, using the principle of positive displacement. In such an isobaric pressure exchanger, pressure is transferred from a high-pressure stream (saline stream) to a low-pressure stream (feed stream) by bringing these streams into direct, instantaneous contact. Such an isobaric pressure exchanger is known to those skilled in the art and is disclosed in early forms, e.g., in US Pat. No. 2,675,173 B or EP0298097A1. A modern example of an isobaric pressure exchanger is the pressure exchanger within the Danfoss iSave device.

[0020] The energy efficiency of an isobaric pressure exchanger increases as the pressure differences in the pressure exchanger decrease. In particular, the smaller the pressure difference between a high-pressure inflow and a high-pressure outflow, the better the energy efficiency. Furthermore, the smaller the pressure difference between a low-pressure inflow and a low-pressure outflow, the better the energy efficiency of the isobaric pressure exchanger. The system of the present disclosure advantageously reduces these pressure differences.

[0021] Preferably, the pressure exchanger is a rotary pressure exchanger, more preferably comprising a cylindrical rotor with longitudinal channels aligned parallel to the rotational axis. Pressure transfer preferably occurs in rotor channels, with, in a particular case, a portion (e.g., one half) of the rotor channels being exposed to the high-pressure flow and another portion (e.g., the remaining portion or half) being exposed to the low-pressure flow. During rotation of the rotor, the channels pass through a sealing region that separates high and low pressure. In the channels, there is no physical barrier between the high-pressure flow (brine flow) and the low-pressure flow (feed flow), and the isobaric pressure exchanger is preferably designed such that the interface between the HP and LP flows cannot reach the end of the rotor channel before it is sealed.As a result, a "plug" of fluid remains in the rotor channel and moves from one end of the rotor to the other and back again. As the flow increases, the speed of the plug increases, but the speed of the rotor also increases, giving the plug less time to move through the channel. The plug advantageously serves as a barrier, reducing the mixing of the HP and LP flow in the channel.

[0022] In a particularly preferred embodiment of the system of the present disclosure, a hydraulic motor is connected between the second saline outlet and the pressure exchanger high-pressure inlet. Further preferably, the hydraulic motor is an axial piston motor comprising a mechanical shaft connected either to a swashplate supporting a plurality of pistons disposed inside a cylinder block or directly to such a cylinder block. These pistons may be axially aligned (i.e., parallel to the shaft axis), and a cam angle between a normal vector of the swashplate (or an equivalent portion of the cylinder block) and the shaft axis determines a displacement of the motor. According to this embodiment, the pressurized second saline flow is applied to the pistons via the motor inlet and influences an extension and reciprocating movement of the pistons and a rotation of the cylinder block.The output speed (rotational speed) of the axial piston motor is proportional to the input flow, and its drive torque is proportional to the pressure difference between the motor inlet and the motor outlet, from which a (partially) reduced-pressure second saline solution flow is discharged. Consequently, in this embodiment, the second pressure difference Δp2 is the pressure drop across the hydraulic motor, and consequently, the pressure drop across the hydraulic motor corresponds to the first pressure difference Δp1.

[0023] In this preferred embodiment, a pressure at the first brine outlet is preferably lower than a pressure at the second feed inlet. For example, the first RO stage operates at a high-pressure level of approximately 60 bar, while the second RO stage operates at a high-pressure level of approximately 120 bar. Since the pressure difference in the high-pressure RO chambers is negligible, the pressure at the first brine outlet is approximately 60 bar, while the pressure at the second feed inlet is approximately 120 bar. Consequently, the first pressure difference Δp1 here is a pressure increase, and consequently the second pressure difference Δp2 is a pressure drop. More preferably, a hydraulic pump is interposed between the first brine outlet and the second feed inlet to provide the pressure increase of the first pressure difference Δp1 to the brine stream upstream of the second feed inlet.Further preferably, the hydraulic pump between the first saline outlet and the second supply inlet is (at least partially) powered by the hydraulic motor, which provides the pressure drop of the second pressure difference Δp2 downstream of the second saline outlet, which is upstream of the pressure exchanger.

[0024] In another particularly preferred embodiment, a hydraulic pump is connected between the second saline outlet and the high-pressure inlet of the pressure exchanger. The hydraulic pump is preferably an axial piston pump comprising a mechanical shaft connected either to a swash plate carrying a plurality of pistons arranged inside a cylinder block or directly to such a cylinder block. The pistons can be aligned axially (parallel to the shaft axis). A cam angle between a normal vector of the swash plate (or an equivalent part of the cylinder block) and the shaft axis determines a displacement of the pump and causes an extension and reciprocating movement of the pistons based on rotation of the cylinder block.According to this embodiment, the movement of the pistons is used to pump the second saline flow from a pump inlet via a pump outlet toward the pressure exchanger, with the pump inlet and outlet being arranged in a connection and valve plate. Consequently, in this embodiment, the second pressure difference Δp2 is the pressure rise occurring at the hydraulic pump, and the pressure rise at the hydraulic pump corresponds to the first pressure difference Δp1.

[0025] In this preferred embodiment, a pressure at the first brine outlet is preferably greater than a pressure at the second feed inlet. For example, the first RO stage operates at a high-pressure level of approximately 120 bar, while the second RO stage operates at a high-pressure level of approximately 60 bar. Since the pressure difference in the high-pressure RO chambers is negligible, the pressure at the first brine outlet is approximately 120 bar, while the pressure at the second feed inlet is approximately 60 bar. Consequently, the first pressure difference Δp1 here is a pressure drop, while the second pressure difference Δp2 is a pressure increase. Preferably, a hydraulic motor is connected between the first brine outlet and the second feed inlet to provide the pressure drop as the first pressure difference Δp1.Furthermore, the hydraulic motor between the first saline solution outlet and the second supply inlet preferably supplies (at least partially) the hydraulic pump with energy, which provides the pressure increase of the second pressure difference Δp2 upstream of the pressure exchanger.

[0026] In the system of the present disclosure and in each of the embodiments described above, the first pressure difference Δp1 is preferably greater than 5 bar, preferably greater than 10 bar, more preferably greater than 15 bar, particularly preferably greater than 20 bar, also preferably greater than 30 bar, preferably greater than 40 bar, and even more preferably greater than 50 bar. In other words, the first RO stage and the second RO stage are preferably operated at high pressure levels that are different ("far apart") from each other. In the system of the present disclosure, a difference in high pressure levels is present as the first pressure difference Δp1, which corresponds to a second pressure difference Δp2 introduced upstream of the pressure exchanger.By connecting the first pressure difference Δp1 and the second pressure difference Δp2, the energy efficiency of the system is increased by manipulating the pressure levels of the pressure exchanger without the need for external energy. Consequently, the system of the present disclosure can be advantageously used when a rather high or variable difference exists in the high-pressure levels of a multi-stage RO system. A particularly advantageous method of connecting is described in more detail below.

[0027] Preferably, in the system of the present disclosure, the first pressure difference Δp1 is about 70% to 130% of the second pressure difference Δp2, also preferably, the first pressure difference Δp1 is about 80% to 120% of the second pressure difference Δp2, even more preferably, the first pressure difference Δp1 is about 90% to 110% of the second pressure difference Δp2, and most preferably, the first pressure difference Δp1 is about 95% to 105% of the second pressure difference Δp2. While it is particularly preferred that the first pressure difference Δp1 be equal to the second pressure difference Δp2, certain pressure losses occur in the high-pressure RO chambers of the first and second RO stages, the fluid lines, and other parts of the RO system. Consequently, it might be possible that an equal value of the first pressure difference Δp1 and the second pressure difference Δp2 cannot be maintained in all operating conditions of the system.

[0028] However, neither the first pressure difference Δp1 nor the second pressure difference Δp2 can be a constant value. In a multi-stage RO system, pressure losses occur in the RO chambers, the PE unit, and / or the piping. Although efforts will be made to keep them as low as possible, it is not possible to specifically set (i.e., strictly control) the first pressure difference Δp1 versus a second pressure difference Δp2; rather, these pressure differences are a consequence of the system design and the flow rate through the system. However, in the system of the present disclosure, any changes in pressure losses, e.g., due to increased flow rates, membrane aging, or the like, the first pressure difference Δp1 and / or the second pressure difference Δp2 automatically adjust with respect to each other so that they correspond to each other.Consequently, a pressure at an HP inlet of the pressure exchanger always matches an HP outlet pressure, with a pressure boost required in an additional booster using external power. Consequently, the system of the present disclosure advantageously provides a very flexible solution that can easily accommodate changes in flow rates or pressures within the system without any loss of efficiency.

[0029] In a preferred embodiment of the system of the disclosure, the hydraulic motor interposed between one of the first saline outlet and the second supply inlet, or between the second saline outlet and the PE-HP inlet, and the hydraulic pump interposed between the other of the first saline outlet and the second supply inlet, or between the second saline outlet and the PE-HP inlet, are mechanically connected to each other. This embodiment advantageously allows for direct transfer of energy from the hydraulic motor to the hydraulic pump without conversion losses, in particular without any losses due to the conversion of mechanical energy into electrical energy and vice versa.The mechanical connection between the hydraulic motor and the hydraulic pump is preferably a direct mechanical connection, for example, via a common drive shaft of the hydraulic motor and the hydraulic pump, via a pinion, a drive belt, and / or a drive shaft. Here, part of the common drive shaft can function as an output shaft of the hydraulic motor, and another part of the common drive shaft can function as an input shaft of the hydraulic pump. In such a scenario, energy can be transmitted via the direct mechanical connection, e.g., in the form of torque and / or speed. More specifically, hydraulic energy (volumetric flow, pressure) is converted by the hydraulic motor into mechanical energy (torque, speed) and transmitted via the direct mechanical connection to the hydraulic pump, where it is converted back into hydraulic energy (volumetric flow, pressure).

[0030] In such an embodiment, the hydraulic energy provided by the hydraulic pump and / or the hydraulic energy consumed by the hydraulic motor can be adjusted to correspond to each other, thereby allowing a flawless direct mechanical connection. For example, a pressure drop across the hydraulic motor can be adjusted (e.g., lowered) to adjust (e.g., reduce) the hydraulic energy converted into mechanical energy there. In the same way, a pressure rise across the hydraulic pump can be adjusted (e.g., increased) to correspond to the mechanical energy provided via the common shaft. Such adjustments can be performed using adjustable values.

[0031] Furthermore, the mechanical connection is preferably an indirect mechanical connection, for example via a gearbox, a transmission and / or a clutch. In such an embodiment, an output shaft of the hydraulic motor is preferably mechanically connected to an input shaft of the hydraulic pump via the gearbox, the transmission and / or a clutch. An indirect mechanical connection advantageously allows a more efficient adjustment of the power output of the hydraulic motor and the power consumption of the hydraulic pump without the need to regulate the flow processes at these components. For example, via a gearbox, a speed and / or a torque provided via the output shaft of the hydraulic motor can be adjusted to a speed and / or a torque required by the input shaft of the hydraulic pump. At the same time, the hydraulic processes at the hydraulic pump and the hydraulic motor can remain the same.In this way, an indirect mechanical connection allows for error-free operation of the system, e.g., by avoiding overloading of mechanical components, as well as power distribution. Further preferably, at least one of the hydraulic motor and the hydraulic pump comprises a swash plate, and the power output of the hydraulic motor and the power input of the hydraulic pump are advantageously adjusted by adjusting a swash plate angle of the hydraulic motor and / or pump.

[0032] In a preferred embodiment, the system of the present disclosure further comprises an induction motor, in particular an AC asynchronous electric motor, having a stator and a rotor. Preferably, the induction motor is a three-phase squirrel-cage motor configured to operate at a substantially constant (rotational) speed, assuming a given AC input frequency and winding configuration (pole matching). More preferably, the induction motor is a double-fed electric machine (DFIM) such as a double-fed induction generator (DFIG) or a double-fed wound rotor asynchronous machine (DASM) configured to operate at a variable (rotational) speed, assuming a specific winding configuration (pole matching).In a DFIM, a DFIG, or a DASM, the stator is preferably directly connected to an AC power source such as an energy storage device or a power grid, while the rotor is connected to it via a frequency converter. In other words, the induction motor is configured either as a fixed-speed generator (FSG) or an adjustable-speed generator (ASG), the latter of which can be configured as a direct-in-line ASG system or a DFIG-ASG system, preferably including an IGBT converter.

[0033] Those skilled in the art will be familiar with many designs of such an induction motor, which are commonly used in various industrial applications, such as wind turbines. Exemplary designs, diagrams, and circuit diagrams are disclosed, for example, in S. MÜLLER; S.; et al. (2002). "Doubly Fed Induction Generator Systems for Wind Turbines" (PDF). IEEE Industry Applications Magazine. IEEE. 8(3): 26-33. doi:10.1109 / 2943.999610, and in Roberts, Paul C. (2004). "Study of Brushless Doubly-Fed (Induction) Machines; Contributions in Machine Analysis, Design and Control" (PDF). Emmanuel College, University of Cambridge. The entire contents of the above-mentioned documents are incorporated herein by reference.

[0034] According to this preferred embodiment, the rotor of the induction motor is mechanically connected to (an input shaft) of the hydraulic pump and also mechanically connected to (an input shaft) of the hydraulic motor(s). In other words, in this embodiment, an indirect mechanical connection exists between the hydraulic pump and the hydraulic motor. In the context of this application, an input / output shaft refers to any mechanical component (e.g., a pinion gear) configured to transmit mechanical energy input / output through a specific device. The mechanical connection of the rotor to the hydraulic motor and / or the hydraulic pump is either a direct mechanical connection (e.g., via a common shaft of the induction motor) or an indirect mechanical connection (e.g., via a gearbox).Particularly preferably, the induction motor is a two-shaft induction motor or a dual-shaft induction motor, wherein the rotor is connected to two shafts, one of which is then preferably connected to the hydraulic motor and the other to the hydraulic pump. In the system according to this embodiment, the hydraulic pump and the hydraulic motor are mechanically connected via the rotor of the induction motor. This in turn allows direct transmission from the hydraulic motor to the hydraulic pump without conversion losses, in particular without losses due to the conversion of electrical power in power converters, such as AC-DC, AC-AC, or DC-DC converters or variable frequency drives.

[0035] Furthermore, the combination of hydraulic motor, induction motor, and hydraulic pump can be (or be designed to be) operated with a net positive energy production, wherein the produced energy can be advantageously distributed and / or used to operate other electrical consumers in the system, e.g., feed pumps, etc. Furthermore, the configuration of the system allows for simple compensation of energy differences between the hydraulic motor and the hydraulic pump by supplying or withdrawing electrical energy to or from the system. Preferably, the induction motor can be operated with a variable slip, wherein a positive slip corresponds to an operating mode in which energy is consumed by the induction motor, for example, to compensate for pressure losses, and wherein a negative slip corresponds to an operating mode in which electrical energy is generated by the induction motor, i.e.in which the induction motor acts as a generator.

[0036] Further preferably, the system according to the present disclosure comprises a third RO stage interposed between the first RO stage and the second RO stage, which comprises a third feed inlet, a third brine outlet, and a third permeate outlet. The third RO stage has the same or similar components as the first RO stage and the second RO stage. Specifically, the third RO stage comprises a third high-pressure RO chamber and a third low-pressure RO chamber separated by a third RO membrane. These chambers preferably form a third RO tank configured to accommodate the third RO process and withstand the pressures encountered. The third RO stage may comprise multiple inlets and / or outlets, for example, multiple third feed inlets, multiple third brine outlets, and / or multiple third permeate outlets.For the sake of brevity, only one of these inlets or outlets will be referred to below. In a third RO stage comprising multiple inlets and / or outlets, the following explanations may refer to relationships between individual inlets and / or outlets and / or to relationships between multiple inlets and / or outlets.

[0037] The (at least one) third feed inlet is configured to supply a feed solution to the third high-pressure RO chamber, and the (at least one) third brine outlet is configured to discharge the brine from the chamber. The feed solution supplied to the (at least one) third feed inlet is (at least partially) the brine discharged from the (at least one) first brine outlet. The third low-pressure RO chamber is configured to receive a permeate via the third RO membrane. The (at least one) third permeate outlet is configured to discharge the permeate from the third low-pressure RO chamber. The permeate from the first to third low-pressure chambers can be discharged together.Also in the third RO stage, the brine is discharged via the (at least one) third brine outlet at a pressure approximately the same as the pressure of the feed solution (first-stage brine) at the (at least one) third feed inlet, while the permeate is discharged at a lower pressure via the (at least one) third permeate outlet. The brine discharged via the (at least one) third brine outlet is (at least partially) the feed solution provided to the (at least one) second feed inlet. The third RO membrane is configured in the same or a similar manner as the first and / or second RO membranes.

[0038] According to this embodiment, the first pressure difference Δp1 comprises a pressure difference Δp 3,1 between the first saline outlet and the third supply inlet and a pressure difference Δp 3,2between the third saline outlet and the second supply inlet. In other words, the first pressure difference Δp1 is determined by several pressure differences Δp 3,1 and Δp 3,2 The system of the present disclosure may further comprise a fourth RO stage interposed between the third RO stage and the second RO stage. Then, the pressure difference Δp 3,2 in pressure differences Δp 4,1 and Δp 4,2 The system may further comprise a fifth RO stage located between the fourth RO stage and the second RO stage. The pressure difference Δp is then divided 4,2 in pressure differences Δp 5,1 and Δp 5,2etc. Also in such an embodiment, the second pressure difference Δp2 corresponds to the first pressure difference Δp1, which is then formed by several pressure differences between several RO stages in order to operate in at least one pressure exchanger at optimal high and low pressure levels with minimal pressure differences. Furthermore, such a multi-stage RO system can preferably comprise several pressure exchangers, wherein individual pressure exchangers are connected between the brine outlet of at least one of the RO stages, preferably the last RO stage, and a feed inlet of at least one further RO stage (in addition to the first feed inlet). Furthermore, in such a multi-stage RO system, at least one of the pressure differences Δp 3,1 and Δp 3,2 (and / or pressure differences Δp 4,1 and Δp 4,2 , pressure differences Δp 5,1 and Δp 5,2and so on) via a hydraulic motor and a hydraulic pump. In other words, even in a system with three or more RO stages, not all hydraulic energy transfer is enabled by pressure exchangers; rather, the adjustment of pressure levels to achieve optimal energy efficiency of these pressure exchangers is achieved by introducing a hydraulic motor(s) and / or a hydraulic pump(s) for introducing pressure drops and / or pressure increases. Some embodiments of such a multi-stage RO system are described below with reference to the accompanying figures.

[0039] The system according to one aspect of the present disclosure can be used in a method for operating a reverse osmosis (RO) system. Herein, an exemplary method comprises at least the step of changing a pressure between the first brine outlet and the second supply inlet by a first pressure difference Δp1, optionally via one of a hydraulic motor (pressure drop) and a hydraulic pump (pressure increase). The first pressure difference Δp1 can be influenced at least partially or completely by one of the hydraulic pump and the hydraulic motor. The method further comprises the step of changing a pressure between a second brine outlet and the pressure exchanger by a second pressure difference Δp2, wherein the second pressure difference Δp2 corresponds to the first pressure difference Δp1, optionally via the other of the hydraulic motor (pressure drop) and a hydraulic pump (pressure increase).Here, the second pressure difference Δp2 is optionally influenced at least partially or completely by the other of the hydraulic pump and the hydraulic motor. The method also includes the step of transferring hydraulic energy from the second brine stream flowing out of the second brine outlet to a first feed stream provided to the first feed inlet via the pressure exchanger. The method enables such energy transfer with optimal transfer efficiency.

[0040] The method optionally relates to operating a system further comprising a third RO stage interposed between the first RO stage and the second RO stage, and comprising a third feed inlet, a third brine outlet, and a third permeate outlet. Accordingly, the method further comprises the steps of varying a pressure between the first brine outlet and the third feed inlet by a pressure difference Δp 3,1 and changing a pressure between the third saline outlet and the second supply inlet by a pressure difference Δp 3,2 . Here is the sum of the pressure difference Δp 3,1 and the pressure difference Δp 3,2 at least equal to the first pressure difference Δp1. Furthermore, at least one of the pressure difference Δp 3,1 and the pressure difference Δp 3,2via one of a hydraulic motor and a hydraulic pump, while the second pressure difference Δp2 is influenced by the other of the hydraulic motor and the hydraulic pump. If necessary, if one of the pressure difference Δp 3,1 and the pressure difference Δp 3,2via one of a hydraulic motor and a hydraulic pump, it is assumed that the pressure between the first brine outlet and the second feed inlet is changed by a first pressure difference Δp1 (also) via the one of the hydraulic motor and the hydraulic pump. In other words: In such a case, a first pressure difference Δp1 can be influenced partly by one of a hydraulic motor and a hydraulic pump and partly by other means, e.g., a pressure exchanger. The same applies to RO systems that include further RO stages, for example, a fourth RO stage, a fifth RO stage, and so on, and thus further pressure differences Δp 4,1 and Δp 4,1 , Δp 5,1 and Δp 5,1 and so on. Then some of these pressure differences could also be introduced by hydraulic pumps or motors and / or pressure exchangers.

[0041] Further aspects and preferred embodiments of the invention are disclosed by the dependent claims, the drawings, and the following description of the drawings. Various disclosed embodiments are advantageously combined with one another unless expressly stated otherwise. Short description of the drawings

[0042] The features of the invention will become apparent to those skilled in the art from the detailed description of exemplary embodiments with reference to the attached drawings. It shows: Fig. 1 a system for RO according to a first embodiment; Fig. 2 a system for RO according to a second embodiment; Fig. 3 a system for RO according to a third embodiment; Fig. 4 a system for RO according to a fourth embodiment; Fig. 5 a system for RO according to a fifth embodiment; Fig. 6 a system for RO according to a sixth embodiment; and Fig. 7 a system for RO according to a seventh embodiment. Detailed description of the invention

[0043] Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. Effects and features of the exemplary embodiments, as well as methods of implementation thereof, will be described with reference to the accompanying drawings. Throughout the drawings, like reference numerals denote like elements, and redundant descriptions will be omitted. The present invention may be embodied in various embodiments and should not be construed as limited to the embodiments illustrated herein. These embodiments are provided as examples so that this disclosure will be complete and will fully convey the aspects and features of the present invention to those skilled in the art.

[0044] Accordingly, elements that are not necessary for one skilled in the art to fully understand the features of the present invention may not be described.

[0045] The term "and / or," as used herein, encompasses any combination of one or more of the elements listed in this context. Furthermore, the use of "may" in describing embodiments of the present invention refers to "one or more embodiments of the present invention." In the following description of embodiments of the present invention, terms in the singular may also include the plural, unless the context clearly indicates otherwise.

[0046] It should be understood that while the terms "first" and "second" are used to describe various elements, these elements are not intended to be limited by these terms. These terms are used merely to distinguish one element from another. For example, a first element may be referred to as a second element, and likewise, a second element may be referred to as a first element without departing from the scope of the present invention. As used herein, the terms "substantially," "approximately," and similar terms are used as terms of approximation rather than of degree, and are intended to account for inherent variations in measured or calculated values ​​that would be recognized by one of ordinary skill in the art.Furthermore, where the term ‘essentially’ is used in combination with a characteristic that can be expressed by a numerical value, the term ‘essentially’ means a range of + / - 5% of the value, with the value at its centre.

[0047] Fig. 1 schematically shows a reverse osmosis (RO) system 100 according to a first embodiment, wherein the system 100 comprises a first RO stage 10 and a second RO stage 20.

[0048] The first RO stage 10 includes a first feed inlet 11, a first brine outlet 12, a first permeate outlet 13, and a first high-pressure RO chamber 15 and a first low-pressure RO chamber 16, which are separated by a first RO membrane 14 and together form a first RO tank. A first feed stream 17 is fed to the first high-pressure RO chamber 15 via the first RO feed inlet 11, and a first brine stream 19 is discharged via the first brine outlet 12. Furthermore, a first permeate stream 18 is discharged from the first low-pressure RO chamber 16 via a first permeate outlet 13.

[0049] The second RO stage 20 includes a second feed inlet 21, a second brine outlet 22, a second permeate outlet 23, and a second high-pressure RO chamber 25 and a second low-pressure RO chamber 26, separated by a second RO membrane 24 and together forming a second RO tank. A second feed stream 27 is fed to the second high-pressure RO chamber 25 via the second RO feed inlet 21, and a second brine stream 29 is discharged via the second brine outlet 22. Furthermore, a second permeate stream 28 is discharged from the second low-pressure RO chamber 26 via a second permeate outlet 23. Each of the inlets and outlets can be valve-controlled, with active valves and passive valves (e.g., check valves) being possible. The system further comprises a further liquid source (not shown) to compensate for the permeate withdrawn from the system 100 via permeate outlets 13, 23, iealso to supplement the first feed stream 17.

[0050] The RO system 100 further comprises a pressure exchanger, PE, 40, in particular an isobaric and / or rotary pressure exchanger 40. The pressure exchanger 40 comprises a PE high-pressure inlet 41, a PE-HP outlet 42, a HP low-pressure (LP) inlet 43, and a PE-LP outlet 44. The PE-HP inlet 41 is connected to the second brine outlet 22, i.e., is arranged downstream of the second brine outlet 22, and receives the brine stream 29 discharged from the second brine outlet 22. The PE-HP outlet 42 is connected to the first feed inlet 11, i.e., is arranged upstream of the first feed inlet 11 and provides the first feed stream 17 to the first feed inlet 11. Consequently, the PE 40 is connected between the second saline outlet 22 and the first supply inlet 11.

[0051] As in Fig. 1, a first pressure difference Δp1 between the first saline solution outlet 12 and the second supply inlet 21 corresponds to a second pressure difference Δp2 between the second saline solution outlet 22 and the pressure exchanger 40. A pressure at the first saline solution outlet 12 differs from a pressure at the second supply inlet 21 by the first pressure difference Δp1. Furthermore, a pressure at the second saline solution outlet 22 differs from a pressure at the PE-HP inlet 41 by the second pressure difference Δp2. Here, the first pressure difference Δp1 is preferably greater than 20 bar, particularly preferably greater than 35 bar, and likewise preferably even greater than 50 bar. Since the second pressure difference Δp2 corresponds to the first pressure difference Δp1, the second pressure difference Δp2 also preferably exceeds these values.The first pressure difference Δp1 may be exactly the same as the second pressure difference Δp2, but corresponds to at least about 80% to 120%, preferably about 90% to 110%, and most preferably about 95% to 105% of the second pressure difference Δp2.

[0052] Setting the first and second pressure differences Δp1 and Δp2 in such a corresponding manner provides the additional advantageous effect that the isobaric pressure exchanger 40 is advantageously operated with optimal energy transfer efficiency. This is achieved when pressure differences, in particular a pressure difference between pressure levels at the PE-HP inlet 41 and the PE-HP outlet 42, as well as a pressure difference between pressure levels at the PE-LP inlet 43 and the PE-LP outlet 44, are the same or at least almost the same. This achieves optimal pressure conditions and, consequently, optimal transfer efficiency, regardless of specific system pressures.

[0053] Fig. 2 schematically shows a system for RO 100 according to a second embodiment, wherein, as in the first embodiment, like components are designated by the same reference numerals and a repeated description of these components is omitted for the sake of brevity.

[0054] In the system of Fig. 2, the first pressure difference Δp1 is realized by a (second) hydraulic pump 60.2, and the second pressure difference Δp2 is realized by a hydraulic motor 50. In other words: The first pressure difference Δp1 corresponds to the pressure increase at the second hydraulic pump 60.2 and the second pressure difference corresponds to the pressure drop at the hydraulic motor 50. In the system of Fig. 2, the hydraulic motor 50 and the second hydraulic pump 60.2 are connected to each other via a connection designed to allow energy transmission, as in Fig. 2 is represented by a dashed line. Energy transfer via this connection can be realized hydraulically, mechanically, and / or electrically.

[0055] The RO System 100 from Fig. 2 also differs from the system of Fig. 1, that a further (first) hydraulic pump 60.1 is arranged in the first feed stream 17 in order to pressurize a portion of the feed stream 17. A portion of the feed stream 17 is separated from it at a point upstream of the first hydraulic pump 60.1 and provided to the PE-LP inlet 43. This portion is then pressurized in the isobaric pressure exchanger 40 and provided to the first feed inlet 11 via the PE-HP outlet 42. In this way, it can also advantageously be ensured that the volumetric flow into the PE-LP inlet 43 corresponds to a volumetric flow into the PE-HP inlet 41, which also improves the efficiency of the PE 40.

[0056] In the embodiment of Fig. 2, the first RO stage 10 operates at a high pressure level of approximately 60 bar, and the second RO stage 20 operates at a high pressure level of approximately 120 bar. In other words, a pressure at the first feed inlet 11 and the first brine outlet 12 is approximately 60 bar, and a pressure at the second feed inlet 21 and the second brine outlet 22 is approximately 120 bar. A pressure rise at the second hydraulic pump 60.2 is approximately 60 bar, which corresponds to the pressure drop across the hydraulic motor 50, from which power is transferred to the second hydraulic pump 60.2. A pressure of the second brine stream 29 upstream of the hydraulic motor 50 is about 120 bar and downstream of it about 60 bar, and a pressure at the PE-HP inlet 41 is about 60 bar, which is approximately equal to a pressure at the first feed inlet 11 and the PE-HP outlet 42.

[0057] The feed solution can be provided by a feed solution container at a pressure of 2 bar, which corresponds to a pressure at the PE-LP inlet 43 and a pressure at a pump inlet of the first hydraulic pump 60.1. A pressure at the PE-LP outlet 44 also corresponds to 2 bar, and a pressure at a motor outlet of the first hydraulic pump 60.1 is also about 60 bar. Consequently, in the system of Fig. Two pressure levels are ensured to operate the pressure exchanger 40 with optimal transfer efficiency. Furthermore, the hydraulic energy removed from the system 100 via the hydraulic motor 50 to ensure these pressure levels is reintroduced into the system 100 via the second hydraulic pump 60.2 to increase the pressure for the second RO stage 20.

[0058] Fig. Figure 3 schematically shows a system for RO 100 according to a third embodiment. As in the previous embodiments, like components are designated by like reference numerals, and a repeated description of these components is omitted for the sake of brevity.

[0059] The System 100 from Fig. 3 differs from the system of Fig. 2, when the first RO stage 10 is operated at a high pressure level of approximately 120 bar, while the second RO stage 20 is operated at a high pressure level of approximately 60 bar. In other words, a pressure at the first feed inlet 11 and the first brine outlet 12 is approximately 120 bar, and a pressure at the second feed inlet 21 and the second brine outlet 22 is approximately 60 bar. The system of Fig. 3 also differs from that of Fig. 2, as the hydraulic motor 50 is arranged between the first RO stage 10 and the second RO stage 20, while the second hydraulic pump 60.2 is arranged downstream of the second brine outlet 22. Consequently, in the system 100 of Fig. 3, a pressure drop of approximately 60 bar is introduced via the hydraulic motor 50 between the first saline solution outlet 12 and the second feed inlet 21, which corresponds to a pressure increase at the second hydraulic pump 60.2 of approximately 60 bar. Consequently, a pressure of the second saline solution stream 29 upstream of the second hydraulic pump 60.2 is approximately 60 bar and downstream of it approximately 120 bar, and consequently, a pressure at the PE-HP inlet 41 is approximately 120 bar, which is approximately equal to a pressure at the first feed inlet 11 and the PE-HP outlet 42.

[0060] Again, the feed solution can be provided by a feed solution container with a pressure of 2 bar, which corresponds to a pressure at the PE-LP inlet 43 and a pressure at a pump inlet of the first hydraulic pump 60.1. A pressure at the PE-LP outlet 44 also corresponds to 2 bar, and a pressure at a motor outlet of the first hydraulic pump 60.1 is approximately 120 bar. Consequently, also in the system of Fig. 3 pressure levels to operate the pressure exchanger 40 with optimal transfer efficiency, and hydraulic energy removed from the system 100 via the hydraulic motor 50 is reintroduced into the system 100 via the second hydraulic pump 60.2 to increase the pressure of the second brine stream 29 upstream of the isobaric pressure exchanger 40.

[0061] Fig. Figure 4 schematically shows a system for RO 100 according to a fourth embodiment. As in the previous embodiments, like components are designated by like reference numerals, and a repeated description of these components is omitted for the sake of brevity.

[0062] The System 100 from Fig. 4 differs from that of Fig. 3, the connection between the hydraulic motor 50 and the second hydraulic pump 60.2 is realized via an induction motor 70. The induction motor 70 can be an asynchronous motor having a stator and a rotor. The second hydraulic pump 60.2 can be an axial piston pump, and the hydraulic motor 50 can be an axial piston motor. The rotor of the induction motor 70 can be mechanically connected to an input shaft of the axial piston pump 60.2 and to an output shaft of the axial piston motor 50. The rotor of the induction motor 70 can be connected to a motor shaft of the induction motor 70, which is connected to the input shaft and the output shaft. This motor shaft can either be a single continuous motor shaft or can be formed by a pair of two (a pair of) motor shafts.

[0063] Using the configuration of Fig. 4 advantageously allows the transfer of energy from the hydraulic motor 50 to the second hydraulic pump 60.2 in a particularly efficient manner, i.e., without conversion losses for converting mechanical to electrical energy, which could occur, for example, in a variable frequency drive or the like. Furthermore, the use of the induction motor 70 for mechanically connecting the hydraulic motor 50 and the second hydraulic pump 60.2 advantageously provides ways for efficient control of the system 100, e.g., by supplying additional energy required by a second hydraulic pump 60.2 to generate a desired pressure level at the PE-HP inlet 41. This can be varied by changing a slip of the induction motor 70. Furthermore, at least one of the hydraulic motor 50 and the second hydraulic pump 60.2 a swash plate and / or a mechanical gear to enable adjustment of a volume and / or a rotation ratio between the hydraulic motor 50 and the second hydraulic pump 60.2.

[0064] Fig. Figure 5 schematically shows a system for RO 100 according to a fifth embodiment. As in the previous embodiments, like components are designated by like reference numerals, and a repeated description of these components is omitted for the sake of brevity. The system 100 of Fig. 5 has the same configuration of hydraulic motor 50 and second hydraulic pump 60.2 connected to each other via an induction motor 70 as described with reference to Fig. 2, which describes the advantages as described with reference to Fig. 4 described.

[0065] Fig. 6 schematically shows a system for RO 100 according to a sixth embodiment. As in the previous embodiments, like components are designated by like reference numerals, and a repeated description of these components is omitted for the sake of brevity.

[0066] The RO System 100 from Fig. 6 further includes a third RO stage 30, which includes a third feed inlet 31, a third brine outlet 32, a third permeate outlet 33, and a third high-pressure RO chamber 35 and a third low-pressure RO chamber 36, separated by a third RO membrane 34 and together forming a third RO tank. A third feed stream 37 is fed to the third high-pressure RO chamber 35 via the third RO feed inlet 31, and a third brine stream 39 is discharged via the third brine outlet 32. Furthermore, a third permeate stream 38 is discharged from the third low-pressure RO chamber 36 via a third permeate outlet 33. The permeate from all three RO stages 10, 20, 30 can be provided jointly or separately to subsequent stages or uses.

[0067] In the system 100 of Fig. 6, a first pressure difference Δp1 between the first RO stage 10 and the second RO stage 20 is determined by a pressure difference Δp3,1 between the first RO stage 10 and the third RO stage 30 and by a pressure difference Δp 3,2 between the third RO stage 30 and the second RO stage 20. As described with reference to the embodiments of Fig. 7 and Fig. 8, at least one of the pressure differences Δp 3,1 and Δp 3,2 by one of a hydraulic motor and a hydraulic pump. The system 100 could further include additional RO stages between the third RO stage 30 and the second RO stage 20, e.g., a fourth RO stage (not shown) between the third RO stage 30 and the second RO stage 20 and a fifth RO stage (not shown) between the fourth RO stage (not shown) and the second RO stage 20. Then, the pressure difference Δp 3,2 further in pressure differences Δp 4,1 and Δp 4,2 be divided, and the pressure difference Δp 4,2 would be further converted into pressure differences Δp 5,1 and Δp5,2 at least some of which are generated by one of a hydraulic motor and a hydraulic pump. Again, the system 100 includes a further liquid source (not shown) to compensate for the permeate withdrawn from the system 100 via permeate outlets 13, 23, 33, ie, to also supplement the first feed stream 17.

[0068] Fig. Figure 7 schematically shows a system for RO 100 according to a seventh embodiment. As in the previous embodiments, like components are designated by like reference numerals, and a repeated description of these components is omitted for the sake of brevity.

[0069] The embodiment of Fig. 7 corresponds to that of Fig. 6, where each of the pressure differences Δp 3,1 and Δp 3,2by a hydraulic pump, namely a first hydraulic pump 60.1 and a second hydraulic pump 60.2. For example, the first RO stage 10 operates at a high pressure level of 60 bar, the third RO stage 30 operates at a high pressure level of 90 bar, and the second RO stage 20 operates at a high pressure level of 120 bar. In other words, a pressure at the first feed inlet 11 and the first brine outlet 12 is approximately 60 bar, a pressure at the third feed inlet 31 and the third brine outlet 32 ​​is approximately 90 bar, and a pressure at the second feed inlet 21 and the second brine outlet 22 is approximately 120 bar. A pressure increase at the first hydraulic pump 60.1 is therefore approximately 30 bar, and a pressure increase at the second hydraulic pump 60.2 is also approximately 30 bar. The sum of these pressure increases, ie 60 bar, corresponds to the pressure drop across the hydraulic motor 50, from which energy is supplied to both the first hydraulic pump 60.1 and the second hydraulic pump 60.2, as indicated by the dashed lines. A pressure of the second brine stream 29 upstream of the hydraulic motor 50 is approximately 120 bar and downstream thereof approximately 60 bar, and consequently, a pressure at the PE-HP inlet 41 is approximately 60 bar, which is approximately equal to a pressure at the first feed inlet 11 and the PE-HP outlet 42. Again, the system 100 comprises a further liquid source (not shown) to compensate for the permeate withdrawn from the system 100 via permeate outlets 13, 23, 33, i.e., to also supplement the first feed stream 17. Reference symbol 10 first RO stage 11 first feed inlet 12 first saline outlet 13 first permeate outlet 14 first RO membrane 15 first high-pressure RO chamber 16 first low-pressure RO chamber 17 first feed stream 18 first saline stream 19 first permeate stream 20 second RO stage 21 second feed inlet 22 second saline outlet 23 second permeate outlet 24 second RO membrane 25 second high-pressure RO chamber 26 second low-pressure RO chamber 27 second feed stream 28 second saline stream 29 second permeate stream 30 third RO stage 31 third feed inlet 32 third saline outlet 33 third permeate outlet 34 third RO membrane 35 third high-pressure RO chamber 36 third low-pressure RO chamber 37 third feed stream 38 third saline stream 39 first permeate stream 40 (isobaric) pressure exchangers 41 (first) PE-HP inlet 42 (first) PE-HP outlet 43 (first) PE-LP inlet 44 (first) (first) PE-LP outlet 45 (second) (isobaric) pressure exchanger 46 (second) PE-HP inlet 47 (second) PE-HP outlet 48 (second) PE-LP inlet 49 (second) PE-LP outlet 50 hydraulic motor 60 hydraulic pump 70 Induction motor 100 Reverse Osmosis System QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2,675,173 B

[0019] EP 0298097A1

[0019] Cited non-patent literature

[0000] S. MÜLLER; S.; et al. (2002). „Doubly Fed Induction Generator Systems for Wind Turbines“ (PDF). IEEE Industry Applications Magazine. IEEE. 8(3): 26-33. doi:10.1109 / 2943.999610

[0033] Roberts, Paul C. (2004). „Study of Brushless Doubly-Fed (Induction) Machines; Contributions in Machine Analysis, Design and Control“ (PDF). Emmanuel College, University of Cambridge

[0033]

Claims

[1] System (100) for reverse osmosis, reverse osmosis - RO, comprising: a first RO stage (10) having a first feed inlet (11), a first brine outlet (12) and a first permeate outlet (13); a second RO stage (20) having a second feed inlet (21), a second brine outlet (22) and a second permeate outlet (23); an isobaric pressure exchanger (PE) (40) connected between the second saline outlet (22) and the first feed inlet (11), wherein a means (50, 60) configured to generate a first pressure difference Δp1 as one of a pressure increase and a pressure drop is connected between the first saline outlet (12) and the second supply inlet (21), and a means (50, 60) configured to generate a second pressure difference Δp2 as the other of a pressure increase and a pressure drop is connected between the second saline outlet (22) and the isobaric pressure exchanger (40), wherein the system is configured such that the first pressure difference Δp1 and the second pressure difference Δp2 automatically adjust to correspond to one another such that the first pressure difference Δp1 between the first saline outlet (12) and the second supply inlet (21) corresponds to approximately 80% to 120% of the second pressure difference Δp2 between the second saline outlet (22) and the isobaric pressure exchanger (40). [2] The system (100) of claim 1, wherein the means (50, 60) configured to generate a first pressure difference Δp1 and the means (50, 60) configured to generate a second pressure difference Δp2 are connected to each other via a connection configured to enable energy transfer. [3] The system (100) of claim 1 or 2, wherein the isobaric pressure exchanger (40) comprises a PE high pressure inlet, PE-HP inlet, (41) connected to the second saline outlet (22) and a PE high pressure outlet, PE-HP outlet (42) connected to the first feed inlet (11), wherein the means for generating the second pressure difference Δp2 is connected between the second saline outlet (22) and the PE-HP inlet (41). [4] System (100) according to one of the preceding claims, wherein the first pressure difference Δp1 is used to generate the second pressure difference Δp2, or wherein the second pressure difference Δp2 is used to generate the first pressure difference Δp1. [5] System (100) according to one of the preceding claims, wherein the means (50, 60) for generating the first pressure difference Δp1 is configured to assist in generating the second pressure difference Δp2 by transmitting hydraulic energy associated with the first pressure difference Δp1 to the means (50, 60) for generating the second pressure difference (50, 60) and / or wherein the means (50, 60) for generating the second pressure difference Δp2 is used to assist in generating the first pressure difference Δp1 by transmitting hydraulic energy associated with the second pressure difference Δp2 to the means (50, 60) for generating the second pressure difference Δp2, the hydraulic energy being transmitted directly or indirectly by conversion into mechanical energy and / or electrical energy. [6] System (100) according to any one of the preceding claims, wherein the isobaric pressure exchanger (40) is a rotary pressure exchanger. [7] System (100) according to claim 2, wherein a hydraulic motor (50) is connected between the second saline outlet (22) and the PE-HP inlet (41), and wherein the pressure drop occurring at the hydraulic motor (50) is the second pressure difference Δp2, which corresponds to the first pressure difference Δp1. [8] System (100) according to claim 7, wherein a pressure at the first saline solution outlet (12) is lower than a pressure at the second supply inlet (21) and / or a hydraulic pump (60) is interposed between the first saline solution outlet (12) and the second supply inlet (21). [9] System (100) according to claims 2 to 8, wherein a hydraulic pump (60) is connected between the second saline solution outlet (22) and the PE-HP inlet (41), and wherein the pressure increase occurring at the hydraulic pump (60) is the second pressure difference Δp2, which corresponds to the first pressure difference Δp1. [10] System (100) according to claim 9, wherein a pressure at the first saline solution outlet (12) is greater than a pressure at the second supply inlet (21) and / or wherein a hydraulic motor (50) is interposed between the first saline solution outlet (12) and the second supply inlet (21). [11] System (100) according to one of the preceding claims, wherein the means (50, 60) for generating the first pressure difference Δp1 is configured such that the first pressure difference Δp1 is greater than 10 bar, preferably greater than 20 bar, and more preferably greater than 50 bar. [12] System (100) according to one of the preceding claims, wherein the first pressure difference Δp1 is about 80% to 120% of the second pressure difference Δp2, the first pressure difference Δp1 is preferably about 90% to 110% of the second pressure difference Δp2, and the first pressure difference Δp1 is particularly preferably about 95% to 105% of the second pressure difference Δp2. [13] System (100) according to claims 8 or 10, wherein the hydraulic motor (50) and the hydraulic pump (60) are mechanically connected to each other, preferably via an induction motor (70). [14] System (100) according to one of the preceding claims, further comprising a third RO stage (30) interposed between the first RO stage (10) and the second RO stage (20) and having a third feed inlet (31), a third brine outlet (32) and a third permeate outlet (33), wherein means for generating a pressure difference Δp 3,1 is connected between the first saline outlet (12) and the third supply inlet (31) and the first pressure difference Δp1 is a pressure difference Δp 3,1 between the first saline solution outlet (12) and the third supply inlet (31) and wherein a means for generating a pressure difference Δp 3,2between the third saline outlet (32) and the second supply inlet (21) and wherein the first pressure difference Δp1 further comprises a pressure difference Δp 3,2 between the third saline solution outlet (32) and the second supply inlet (21).

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