Patent Application
20240100481
This application claims foreign priority benefits under 35 U.S.C. § 119 from European Patent Application No. 22197408.2, filed Sep. 23, 2022, the content of which is hereby incorporated by reference in its entirety.
The invention relates to a system for reverse osmosis, particularly to system for a multi-stage reverse osmosis having an improved energy efficiency. The invention further relates to a method for the operation of such a system, exemplarily for producing fresh water.
Osmosis is a process wherein a solvent moves across a semipermeable membrane from the membrane's side facing a lower solute concentration towards the membrane's side facing a higher solute concentration. Therein, the movement of the solvent particles is driven by diffusion and, overall, more solvent particles diffuse towards the higher solute concentration, i.e., the lower water potential, resulting in a net movement of the solvent. This naturally occurring process is also underlying the reverse osmosis process as described below.
In reverse osmosis, a pressure exceeding the osmotic pressure is applied to the side of the higher solute concentration thus reverting the energy balance of the osmotic system causing an overall net diffusion movement from the high solute to the low solute concentration across the membrane, thus increasing solvent concentration at the pressurized membrane side. Reverse osmosis systems comprise at least two chambers that are separated by a semipermeable membrane, wherein inflow and outflow of said chambers can be controlled for setting volumetric flow conditions as well as the pressure gradient across the membrane.
Reverse osmosis, RO, is frequently applied for water purification or desalination applications where it yields a highly concentrated brine next to the purified and/or desalinated water. The brine remains at the pressurized side of the membrane, whereas the purified and/or desalinated water (permeate) is removed from the other membrane side at a low pressure. The pressurized brine is removed from the reverse osmosis chamber in order to avoid an excessive increase in osmotic pressure and to allow for inflow of the fresh feed solution into the chamber. It is further known to use energy recovery devices, such as hydraulic turbines, for the purpose of transferring hydraulic energy from the pressured brine to the feed solution in order to improve the overall energy efficiency of the reverse osmosis process.
It is also known to combine multiple RO stages for improving energy efficiency and freshwater yield in such a system. In such multi-stage RO systems, the RO chambers are usually combined in a linear manner. Therein, the brine is usually pressurized before entering a subsequent stage in order to compensate for the increased solvent concentration of the brine. Hydraulic turbines are also used in multi-stage RO systems for energy recovery and improved efficiency.
The use of turbines usually requires conversion of hydraulic energy to mechanical energy in the motor side as well as conversion to electrical energy for energy transmission. At the pump side, back conversion from electrical energy to mechanical energy and further to hydraulic energy is then required. This usually reduces the overall energy efficiency of a RO system. Pressure exchangers that allow for a direct energy transfer between liquid flows avoid such conversion losses but have rather narrow windows of optimal transfer efficiency, which are often not met in RO systems.
It is thus an object of the present disclosure to overcome or at least reduce the drawbacks of the prior art and to provide a system for reverse osmosis with an improved energy efficiency.
The objective of the disclosure is solved and the disadvantages of the prior art are overcome or at least reduced by the subject-matter of the present invention, i.e., by system for reverse osmosis, RO, according to the appended claims and by a method for operating such system.
An aspect of the present disclosure relates to a system for reverse osmosis, RO, comprising a first RO stage with 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 that are separated by a first RO membrane. These chambers preferably form a RO tank that is configured to house the first RO process and to withstand the occurring pressures. The first RO stage may comprise more inlets and/or outlets, such as multiple first feed inlets, multiple first brine outlets and/or multiple first permeate outlets. For the sake of conciseness, following it is only referred to one of these inlet and outlets, respectively. In a first RO stage comprising multiple inlets and/or outlets the following explanations can refer to relations between individual inlets and/or outlets and/or to relations between multiple of inlets and/or outlets.
The (at least one) first feed inlet is configured to supply a feed solution flow to the first high-pressure RO chamber and the (at least one) first brine outlet is configured to discharge the brine solution from said chamber. The first low-pressure RO chamber is configured to receive a permeate, i.e., the feed solution with reduced solute concentration, via the first RO membrane. The (at least one) first permeate outlet is configured to discharge the permeate from the first low-pressure RO chamber. The up-concentrated feed solution (brine) is discharged via the (at least one) first brine outlet at a pressure that is about the same as 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 significantly lower than the feed pressure, preferably as low as possible for having an optimal pressure difference at the membrane.
The first RO membrane is configured for allowing 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, e.g., sea water, and the first RO membrane is configured to allow water to diffuse through the membrane while not letting salt ions, such as Na+ and Cl−, pass through the membrane. Preferably, the first RO membrane is configured to not let organics, bacteria, and pyrogens pass through the membrane, however such components may already be removed in a pre-treatment stage prior the RO chamber. The first RO membrane preferably is one of a cellulose acetate, CA, membrane, or a polysulfone membrane which may be coated with aromatic polyamids. Also preferred, the first RO membrane is nano-structured, a zeolithe membrane, and/or a spiral wound RO membrane.
The RO system of the present disclosure further comprises a second RO stage with 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 that are separated by a second RO membrane. These chambers preferably form a second RO tank that is configured to house the second RO process and to withstand the occurring pressures. The second RO stage may comprise more inlets and/or outlets, such as multiple second feed inlets, multiple second brine outlets and/or multiple second permeate outlets. For the sake of conciseness, following it is only referred to one of such inlet and outlets, respectively. In a second RO stage comprising multiple inlets and/or outlets the following explanations can refer to relations between individual inlets and/or outlets and/or to relations between multiple of inlets and/or outlets.
The (at least one) second feed inlet is configured to supply a feed solution flow to the second high-pressure RO chamber and the (at least one) first brine outlet is configured to discharge the brine solution from said chamber. Therein, the feed solution fed to the (at least one) second feed inlet is (at least partially) the brine solution discharged 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 discharge the permeate form the second low-pressure RO chamber. The permeate from the first and second low-pressure chamber may be commonly discharged. Also in the second RO stage, the brine is discharged via the (at least one) second brine outlet at a pressure that is about the same as 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 configured in same or similar manner as the first RO membrane.
The system of the present disclosure further comprises a pressure exchanger, PE, that is connected between the second brine outlet and the first feed inlet. In other words, the pressure exchanger comprises an inlet, particularly a high-pressure, HP, inlet, that is configured to receive a brine flow discharged from the second brine outlet and an outlet, particularly a high-pressure, HP, outlet, that is configured to provide a feed solution flow to the first feed inlet. The pressure exchanger further comprises another outlet, particularly a low-pressure, LP, outlet, that is configured to discharge the depressurized brine flow and another inlet, particularly a low-pressure, LP, inlet, that is configured to receive a feed solution flow to be pressurized.
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 relates to a difference between the pressure of the brine solution discharged via the first brine outlet and the pressure of the feed solution entering the second RO stage via the second feed inlet. Therein, the feed solution entering the second RO stage via the second feed inlet consists at least partially, preferably completely from the brine solution discharged via the first brine outlet. Hence, the first and second pressure differences Δp1 and Δp2 are not independent of each other but rather correspond to each other in that the first pressure difference Δp1 is set to a value depending on a value of the second pressure differences Δp2 or the second pressure differences Δp2 is set to a value depending on a value of the first pressure differences Δp1.
The system of the present disclosure thus enables an operation, wherein a pressure between the first brine outlet and the second feed inlet is changed by the first pressure difference Δp1 and a pressure between the second brine outlet and the pressure exchanger is changed by the second pressure difference Δp2 corresponding to the first pressure difference Δp1 and wherein hydraulic energy is thus advantageously transferred from a second brine flow effluent from the second brine outlet to a first feed flow provided to the first feed inlet via the pressure exchanger with an improved efficiency. The improved efficiency is enabled by the pressure configuration, i.e., corresponding first and second pressure differences, of the disclosed system that allows the operation of the pressure exchanger with an optimal transfer efficiency. According to the present disclosure, the first pressure difference Δp1 p2 and/or the second pressure differences Δp2 can have a positive pressure value or a negative pressure value.
According to a preferred embodiment of the RO system, the pressure exchanger, PE, has a high-pressure, HP inlet that is connected to the second brine outlet and a PE HP outlet that is connected to the first feed inlet and the second pressure difference Δp2 is occurring between the second brine outlet and the PE HP inlet. Thus, in the RO system of the present disclosure the second pressure difference Δp2 is created before the brine flow is fed to the pressure exchanger in order to feed the brine flow to the pressure exchanger with an optimized pressure. In that way a transfer efficiency of hydraulic energy in the pressure exchanger that is configured to pressurize the feed flow that is provided to the first feed inlet is advantageously improved. Also advantageously, in the embodiment a booster pump downstream the second brine outlet.
Further preferred, in the system of the present disclosure, the first pressure difference Δp1 is utilized to create the second pressure difference Δp2. In other words, hydraulic energy associated with the first pressure difference Δp1 is harvested and utilized to the create second pressure difference Δp2. Also preferred, the second pressure difference Δp2 is utilized to create the first pressure difference Δp1. Again this essentially refers to a transfer of hydraulic energy associated with the first pressure difference Δp1 and the second pressure difference Δp2. Therein, creating the second pressure difference Δp2 by utilizing the first pressure difference Δp1 does not necessarily mean that energy is provided to create the second pressure difference Δp2 but in a same manner the second pressure difference Δp2 can be created by removing hydraulic energy from the system utilizing the first pressure difference Δp1. The transfer of hydraulic energy related to the first pressure difference Δp1 and the second pressure difference Δp2 may occur directly or indirectly by conversion to other forms of energy. Exemplarily, hydraulic energy may be converted to mechanic and/or electric energy for being transferred between the first pressure difference Δp1 and the second pressure difference Δp2.
In a particularly preferred embodiment of the system of the present disclosure, the pressure exchanger is an isobaric pressure exchanger. Further preferred, the pressure exchanger is configured to transfer pressure from the pressurized brine flow downstream the second brine outlet to the low-pressure feed solution upstream the first feed inlet utilizing the principle of positive displacement. In such an isobaric pressure exchanger, pressure transfer occurs from a high-pressure (brine) flow to a low-pressure (feed) flow by putting these flows in direct, momentary contact. Such isobaric pressure exchanger is known to the skilled person and, in early forms are disclosed e.g., in U.S. 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.
The energy efficiency of an isobaric pressure exchanger increases when the pressure differences in the pressure exchanger decreases. Particularly, an energy efficiency is the better, the less a pressure difference between a high-pressure inflow and a high-pressure outflow is. Further, the energy efficiency of the isobaric pressure exchanger is the better the less a pressure difference between a low-pressure inflow and a low-pressure outflow is. The system of the present disclosure advantageously reduces these pressure differences.
Preferably, the pressure exchanger is a rotary pressure exchanger, particularly preferred having a cylindrical rotor with longitudinal ducts oriented parallel to the rotational axis. Therein, the pressure transfer preferably occurs in rotor ducts, wherein at any given instant, one part (e.g., half) of the rotor ducts are exposed to the high-pressure flow and another part (e.g., the remaining part or half) of the rotor ducts are exposed to the low-pressure flow. During the rotation of the rotor, the ducts pass a sealing area that separates high and low pressure. In the ducts, there is no physical barrier between the high pressure (brine) flow and the low pressure (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 duct before it is sealed. Hence, a “plug” of liquid remains in the rotor duct and travels from one end of the rotor to the other and back again. As flow increases, the velocity of the plug increases but the rotor also speeds up which gives the plug less time to move in the duct. The plug advantageously serves as a barrier that is reducing mixing of the HP and LP flows in the duct.
In a particularly preferred embodiment of the system of the present disclosure, a hydraulic motor is connected between the second brine outlet and the pressure exchanger high-pressure inlet. Further preferred, the hydraulic motor is an axial piston motor comprising a mechanical shaft that is connected either to a swash plate carrying a plurality of pistons arranged inside a cylinder block or directly to such cylinder block. These pistons may be axially oriented (i.e., parallel to the shaft axis) and 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 motor. According to this embodiment, the pressurized second brine flow is applied to the pistons via the motor inlet and affects protruding and reciprocating movement of the pistons and a rotation of the cylinder block. The output (rotational) speed of the axial piston motor is proportional to the input flow and its drive torque is proportional to the difference in pressure between the motor inlet and the motor outlet, from which a (partially) depressurized second brine flow is discharged. Hence, in this embodiment the second pressure difference Δp2 is the pressure drop occurring at the hydraulic motor and thus the pressure drop at the hydraulic motor is corresponding to the first pressure difference Δp1.
In this preferred embodiment, a pressure at the first brine outlet is preferably smaller than a pressure at the second feed inlet. Exemplarily, the first RO stage operates at a high-pressure level of about 60 bar, while the second RO stage operates at a high-pressure level of about 120 bar. As the pressure difference in the high-pressure RO chambers is neglectable, the pressure at the first brine outlet is about 60 bar, while the pressure at the second feed inlet is about 120 bar. Hence, the first pressure difference Δp1 here is a pressure rise and thus the second pressure difference Δp2 is a pressure drop. Particularly preferred, a hydraulic pump is interconnected between the first brine outlet and the second feed inlet for providing the pressure rise of the first pressure difference Δp1 to brine flow upstream the second feed inlet. Further preferred, the hydraulic pump between the first brine outlet and the second feed inlet is powered (at least partially) by the hydraulic motor providing the pressure drop of the second pressure difference Δp2 downstream the second brine outlet upstream the pressure exchanger.
In another particularly preferred embodiment, a hydraulic pump is connected between the second brine outlet and the pressure exchanger high-pressure inlet. The hydraulic pump preferably is an axial piston pump comprising a mechanical shaft that is either connected to a swash plate carrying a plurality of pistons arranged inside a cylinder block or directly to such cylinder block. The pistons may be axially oriented (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 effects protruding and reciprocating movement of the pistons based on a rotation of the cylinder block. According to this embodiment, the movement of the pistons is used to pump the second brine flow from a pump inlet via a pump outlet towards the pressure exchanger, with pump inlet and outlet being disposed in a port and valve plate. Hence, 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 is corresponding to the first pressure difference Δp1.
In this preferred embodiment, a pressure at the first brine outlet is preferably larger than a pressure at the second feed inlet. Exemplarily, the first RO stage operates at a high-pressure level of about 120 bar, while the second RO stage operates at a high-pressure level of about 60 bar. As the pressure difference in the high-pressure RO chambers is neglectable, the pressure at the first brine outlet is about 120 bar, while the pressure at the second feed inlet is about 60 bar. Hence, the first pressure difference Δp1 here is a pressure drop, while the second pressure difference Δp2 is a pressure rise. Preferably, a hydraulic motor is connected between the first brine outlet and the second feed inlet for providing the pressure drop as the first pressure difference Δp1. Further preferred, the hydraulic motor between the first brine outlet and the second feed inlet is powering (at least partially) the hydraulic pump providing the pressure rise of the second pressure difference Δp2 upstream the pressure exchanger.
In the system of the present disclosure and in each of the above described embodiments, the first pressure difference Δp1 preferably is larger than 5 bar, preferably larger than 10 bar, further preferred larger than 15 bar, particularly preferred larger than 20 bar, also preferred larger than 30 bar, preferably larger than 40 bar and further preferred larger than 50 bar. In other words, the first RO stage and the second RO stage are preferably operated at high-pressure levels that are distinct (“far away”) from each other. In the system of the present disclosure, a difference in high-pressure levels is present as the first pressure difference Δp1 that corresponds to a second pressure difference Δp2 which is introduced upstream to the pressure exchanger. By coupling 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 requiring external energy. Hence, the system of the present disclosure can be advantageously used, if there is a rather high or variable difference in high-pressure levels of a multi-stage RO system. A particularly advantageous method of coupling will be described in more detail below.
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 preferred the first pressure difference Δp1 is about 80% to 120% of the second pressure difference Δp2, further preferred the first pressure difference Δp1 is about 90% to 110% of the second pressure difference Δp2, and particularly preferred 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 has an equal amount as the second pressure difference Δp2, some pressure losses occur in the high-pressure RO chambers of the first and second RO stage, the fluid conduits and other parts of the RO system. Thus, an equal amount of the first pressure difference Δp1 and the second pressure difference Δp2 might not be maintained in all operational states of the system.
However, neither the first pressure difference Δp1 nor the second pressure difference Δp2 may be a constant value. In any multi-stage RO system, there will be pressure losses occurring in the RO chambers, the PE unit and/or the pipes. Although one will strive to keep them as low as possible, it is not possible to deliberately set (i.e., control in a strict sense) the first pressure difference Δp1 vis-à-vis the second pressure difference Δp2 but these pressure differences are rather a consequence of the system design and the flow rate through it. However, in the system of the present disclosure, any change in pressure losses, e.g., due to increased flow rates, aging of membranes, or the like, the first pressure difference Δp1 and/or the second pressure difference Δp2 automatically adjust with respect to each other such that they match each other. Hence, a pressure at a HP inlet of the pressure exchanger always fits a HP outlet pressure with requiring a pressure addition in an additional booster with external energy. Hence, the system of the present disclosure advantageously provides a very flexible solution that can easily handle changes in flowrates or pressures in the system without any efficiency losses.
In a preferred embodiment of the system of the disclosure, the hydraulic motor interconnected between—one of—the first brine outlet and the second feed inlet or the second brine outlet and the PE HP inlet and the hydraulic pump interconnected between—the other one of—the first brine outlet and the second feed inlet or the second brine outlet and the PE HP inlet are mechanically connected to each other. This embodiment advantageously allows for a direct transfer of energy from the hydraulic motor to the hydraulic pump without any conversion losses, particularly without any losses due to conversion of mechanical energy to electrical energy and vice versa. The mechanical connection of the hydraulic motor and the hydraulic pump preferably is 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 propeller shaft. Therein, a part of the common drive shaft may function as an output shaft of the hydraulic motor and another part of the common drive shaft may function as an input shaft of the hydraulic pump. In such a scenario, energy may be transferred via the direct mechanical connection, e.g., in the form of torque and/or rotation speed. In more detail, hydraulic energy (volumetric flow, pressure) is converted into mechanical energy (torque, rotational speed) by the hydraulic motor and transferred via the direct mechanical connection to the hydraulic pump, where it is again back converted to hydraulic energy (volumetric flow, pressure).
In such embodiment, the hydraulic energy provided by the hydraulic pump and/or the hydraulic energy consumed by the hydraulic motor may be adapted in order to match each other, thus allowing for a faultless direct mechanical connection. Exemplarily, a pressure drop at the hydraulic motor may be adjusted (e.g., lowered) in order to adapt (e.g., reduce) the hydraulic energy that is converted there into mechanical energy. In the same manner, a pressure rise at the hydraulic pump may be adjusted (e.g., increased) in order to match a mechanical energy provided via the common shaft. Such adaptions may be carried out using adjustable valves.
Further preferred, the mechanical connection is an indirect mechanical connection, for example via a gear box, a transmission, and/or a clutch. In such embodiment, preferably an output shaft of the hydraulic motor is mechanically connected to an input shaft of the hydraulic pump via the gearbox, transmission, and/or a clutch. An indirect mechanical connection advantageously allows for matching the power output of the hydraulic motor and the power intake of the hydraulic pump more efficiently and without the necessity to control the flow processes at these components. Exemplarily, via a gear box a rotation speed and/or torque provided via the output shaft of the hydraulic motor may be adapted to a rotation speed and/or 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 may remain the same. In such a manner, an indirect mechanical connection allows for a faultless operation of the system, e.g., by avoiding overload of mechanical components, as well as for power distribution. Further preferred, 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 intake of the hydraulic pump are advantageously adjusted by adjusting a swash plate angle of the hydraulic motor and/or pump.
In a preferred embodiment, the system of the present disclosure further comprises an induction motor, particularly an asynchronous AC electric motor, with a stator and a rotor. Preferably, the induction motor is a three-phase squirrel-cage motor that is configured to operate at a substantially constant (rotational) speed assuming a given AC input frequency and winding configuration (pole adjustment). Particularly preferred, the induction motor is a doubly-fed electric machine (DFIM), such as a double-fed induction generator (DFIG) or Doubly-fed wound rotor asynchronous machine (DASM) that is configured to operate at a variable (rotational) speed assuming a given winding configuration (pole adjustment). In a DFIM, DFIG, or DASM, the stator is preferably connected directly with an AC power source such as a power storage device or a power grid, while the rotor is connected thereto 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), wherein the latter can be configured as a direct-in-line ASG system or a DFIG ASG system, preferably comprising an IGBT converter.
The skilled person is aware of multiple designs for such an induction motor which are commonly used in various industrial applications, such as e.g., wind turbines. Exemplary designs, schematics and circuit diagrams are e.g., discloses 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, as well as 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 whole content of the aforementioned documents is incorporated herein by reference.
According to this preferred embodiment, the rotor of the induction motor is mechanically connected to (an input shaft of) the hydraulic pump and is also mechanically connected to (an output shaft of) the hydraulic motor. In other words, also 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., pinion) that is configured to convey mechanical energy that is input/output by a given 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 preferred, the induction motor is a dual-shaft induction motor or double 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 one 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 again allows for a direct transfer of energy from the hydraulic motor to the hydraulic pump without conversion losses, particularly without losses due to electric power conversion in power converters, such as e.g., AC/DC, AC/AC or DC/DC converters or variable frequency drives.
Further, the combination of hydraulic motor, induction motor and hydraulic pump can be (configured to be) operated with a net positive power production, wherein the produced power can be advantageously distributed and/or used to operate other electrical consumers in the system, e.g. feed pumps, etc. Further, the system's configuration allows for a simple compensation of energetic differences between the hydraulic motor and the hydraulic pump by adding or retrieving electric power to or from the system. Preferably, the induction motor can be operated with a variable slip, wherein a positive slip corresponds to an operation mode in which energy is consumed by the induction motor, e.g., in order to compensate for pressure losses, and wherein a negative slip corresponds to an operation mode in which electric energy is generated by the induction motor, i.e., in which the induction motor functions as generator.
Further preferred, the system according to the present disclosure comprises a third RO stage that is interconnected between the first RO stage and the second RO stage and that comprises a third feed inlet, a third brine outlet, and a third permeate outlet. The third RO stage has same or similar components as the first RO stage and the second RO stage. Particularly, the third RO stage comprises a third high-pressure RO chamber and a third low-pressure RO chamber that are separated by a third RO membrane. These chambers preferably form a third RO tank that is configured to house the third RO process and to withstand the occurring pressures. The third RO stage may comprise more inlets and/or outlets, such as multiple third feed inlets, multiple third brine outlets and/or multiple third permeate outlets. For the sake of conciseness, following it is only referred to one of such inlet and outlets, respectively. In a third RO stage comprising multiple inlets and/or outlets the following explanations can refer to relations between individual inlets and/or outlets and/or to relations between multiple of inlets and/or outlets.
The (at least one) third feed inlet is configured to supply a feed solution flow to the third high-pressure RO chamber and the (at least one) third brine outlet is configured to discharge the brine solution from said chamber. Therein, the feed solution fed to the (at least one) third feed inlet is (at least partially) the brine solution 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 may be commonly discharged. Also in the third RO stage, the brine is discharged via the (at least one) third brine outlet at a pressure that is about 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 via the (at least one) third permeate outlet at a lower pressure. 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 same or similar manner as the first and/or the second RO membrane.
According to this embodiment, the first pressure difference Δp1 comprises a pressure difference Δp3,1 between the first brine outlet and the third feed inlet and a pressure difference Δp3,2 between the third brine outlet and the second feed inlet. In other words, the first pressure difference Δp1 is constituted by multiple pressure differences Δp3,1 and Δp3,2. The system of the present disclosure may further comprise a fourth RO stage interconnected between the third RO stage and the second RO stage. Then, the pressure difference Δp3,2 splits up in pressure differences Δp4,1 and Δp4,2. The system may further comprise a fifth RO stage interconnected between the fourth RO stage and the second RO stage. Then, the pressure difference Δp4,2 splits up in pressure differences Δp5,1 and Δp5,2 and so forth. Also in such embodiment, the second pressure difference Δp2 corresponds to the first pressure difference Δp1 that is then however constituted by multiple pressure differences between multiple RO stages in order to operate at least one pressure exchanger at optimal high- and low-pressure levels with minimal pressure differences. Also, such multi-stage RO system may preferably comprise multiple pressure exchangers, wherein individual ones of these 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 other RO stage (in addition to the first feed inlet). Further preferred, in such a multi-stage RO system at least one of the pressure differences Δp3,1 and Δp3,2 (and/or pressure differences Δp4,1 and Δp4,2, pressure differences Δp5,1 and Δp5,2 and so forth) is affected via one of a of a hydraulic motor and a hydraulic pump. In other words, also in a system with three or more RO stages not all hydraulic energy transfer is enabled by pressure exchangers but rather the adaption of the pressure levels for achieving optimal energy efficiency of these pressure exchangers is achieved by introducing hydraulic motor(s) and/or hydraulic pump(s) for introducing pressure drops and/or pressure rises. Some embodiments of such multi-stage RO system are described below with respect to the attached figures.
Another aspect of the present disclosure relates to a method for operating a system for reverse osmosis, RO, according to the present disclosure as described above. Therein, the method of the present disclosure comprises at least the step of changing a pressure between the first brine outlet and the second feed inlet by a first pressure difference Δp1, preferably via one of a hydraulic motor (pressure drop) and a hydraulic pump (pressure rise). Further preferred, the first pressure difference Δp1 is at least partially or fully affected by said one of hydraulic pump and hydraulic motor. The method further comprises the step of changing a pressure between the second brine outlet and the pressure exchanger by a second pressure difference Δp2 corresponding to the first pressure difference Δp1, preferably via another one of the hydraulic motor (pressure drop) and a hydraulic pump (pressure rise). Therein, the second pressure difference Δp2 preferably is at least partially or fully affected by said other one of hydraulic pump and hydraulic motor. The method also comprises the step of transferring hydraulic energy from a second brine flow effluent from the second brine outlet to a first feed flow provided to the first feed inlet via the pressure exchanger. The method of this disclosure enables such energy transfer with an optimal transfer efficiency.
In a preferred embodiment, the method of the present disclosure is for operating a system further comprising a third RO stage that is interconnected between the first RO stage and the second RO stage and comprises a third feed inlet, a third brine outlet, and a third permeate outlet. According to this embodiment, the method further comprises the steps of changing a pressure between the first brine outlet and the third feed inlet by a pressure difference Δp3,1 and of changing a pressure between the third brine outlet and the second feed inlet by a pressure difference Δp3,2. Therein, the sum of pressure difference Δp3,1 and pressure difference Δp3,2 amounts to at least the first pressure difference Δp1. Further, at least one of the pressure difference Δp3,1 and pressure difference Δp3,2 is affected via one of a of a hydraulic motor and a hydraulic pump, while the second pressure difference Δp2 is affected via the other one of the hydraulic motor and the hydraulic pump. Further preferred, if one of the pressure difference Δp3,1 and pressure difference Δp3,2 is affected via one of a of a hydraulic motor and a hydraulic pump, the pressure between the first brine outlet and the second feed inlet is considered to be changed by a first pressure difference Δp1 (also) via said one of the hydraulic motor and the hydraulic pump. In other words, in such case a first pressure difference Δp1 can be affected partially by one of a hydraulic motor and a hydraulic pump and partially by other means, e.g. a pressure exchanger. The same holds true for RO systems comprising even further RO stages, such as a fourth RO stage, a fifth RO stage and so forth and thus introducing further pressure differences Δp4,1 and Δp4,1, Δp5,1 and Δp5,1, and so forth. Also then, some of these pressure differences might be introduces by hydraulic pumps or motors and/or pressure exchangers.
Further preferred embodiments of the method of the present disclosure correspond to the preferred embodiments of the system of the present disclosure as described above and provided the advantages as described above with respect to the system of the disclosure. Further aspects and preferred embodiments of the invention are disclosed by the dependent claims, the drawings and the following description of the drawings. Different disclosed embodiments are advantageously combined with each other if not explicitly stated otherwise.
The features of the invention become apparent to those skilled in the art by the detailed description of exemplary embodiments with reference to the attached drawings in which:
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, and implementation methods thereof will be described with reference to the accompanying drawings. In the drawings, like reference numerals denote like elements, and redundant descriptions are omitted. The present invention, may be embodied in various different forms, and should not be construed as being limited to only the illustrated embodiments 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.
Accordingly, elements not considered necessary to those having skill in the art for a complete understanding of the features of the present invention may not be described.
As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the use of “may” when 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, the terms of a singular form may include plural forms unless the context clearly indicates otherwise.
It will be understood that although the terms “first” and “second” are used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element may be named a second element and, similarly, a second element may be named a first element, without departing from the scope of the present invention. As used herein, the term “substantially”, “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, if the term “substantially” is used in combination with a feature that could be expressed using a numeric value, the term “substantially” denotes a range of +/−5% of the value centered on the value.
The first RO stage 10 comprises a first feed inlet 11, a first brine outlet 12, a first permeate outlet 13 as well as a first high-pressure RO chamber 15 and a first low-pressure RO chamber 16 that are separated by a first RO membrane 14 and, together, form a first RO tank. A first feed flow 17 is fed to the first high-pressure RO chamber 15 via the first RO feed inlet 11 and a first brine flow 19 is discharged via the first brine outlet 12. Further, a first permeate flow 18 is discharged from the first low-pressure RO chamber 16 via a first permeate outlet 13.
The second RO stage 20 comprises a second feed inlet 21, a second brine outlet 22, a second permeate outlet 23 as well as a second high-pressure RO chamber 25 and a second low-pressure RO chamber 26 that are separated by a second RO membrane 24 and, together, form a second RO tank. A second feed flow 27 is fed to the second high-pressure RO chamber 25 via the second RO feed inlet 21 and a second brine flow 29 is discharged via the second brine outlet 22. Further, a second permeate flow 28 is discharged from the second low-pressure RO chamber 26 via a second permeate outlet 23. Each of the inlets and outlets may be valve controlled, wherein active valves or passive valves (e.g., check valves) may be used. The system further comprises another source of liquid (not shown) to compensate for permeate taken out of system 100 via permeate outlets 13, 23, i.e., to also add to the first feed flow 17.
The RO system 100 further comprises a pressure exchanger, PE, 40, particularly 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 disposed downstream of the second brine outlet 22, and receives the second brine flow 29 discharged from the second brine outlet 22. The PE HP outlet 42 is connected to the first feed inlet 11, i.e., is disposed upstream of the first feed inlet 11 and provides the first feed flow 17 to the first feed inlet 11. Hence, the PE 40 is connected between the second brine outlet 22 and the first feed inlet 11.
As illustrated in
Setting the first and second pressure difference Δp1 and Δp2 in such corresponding manner provides the advantageous effect that the isobaric pressure exchanger 40 is advantageously operated with optimal energy transfer efficiency. This is achieved as pressure differences, particularly 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. By this, optimal pressure conditions and thus transfer efficiency is achieved independent of specific system pressures.
In the system of
The RO system 100 of
In the embodiment of
The feed solution may be provided by a feed solution reservoir with a pressure of 2 bar which corresponds to a pressure at the PE LP inlet 43 and to 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. Hence, in the system of
The system 100 of
Again, the feed solution may be provided by a feed solution reservoir with a pressure of 2 bar which corresponds to a pressure at the PE LP inlet 43 and to 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 here about 120 bar. Hence, also in the system of
The system 100 of
The use of the configuration as of
The RO system 100 of
In the system 100 of
The embodiment of
| Number | Date | Country | Kind |
|---|---|---|---|
| 22197408.2 | Sep 2022 | EP | regional |
