Membrane separation system using high-efficiency, closed-circuit membrane technology
The CCRO system is adapted for smaller-scale applications by omitting the feed pump and using a circulation pump for filtration and flushing, addressing cost and scalability issues in conventional systems, achieving efficient and cost-effective membrane separation.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- PANNON EGYETEM
- Filing Date
- 2025-12-08
- Publication Date
- 2026-06-18
AI Technical Summary
Conventional closed-circuit reverse osmosis (CCRO) systems are large-scale and require high-capacity feed pumps, making them unsuitable for smaller-scale applications like household use, and they incur high investment costs due to the need for booster pumps to operate at high transmembrane pressures.
Adapting the CCRO scheme for small-scale applications by omitting the feed pump when connected to a pressurized liquid source or using a lower-power feed pump, and employing a circulation pump for both filtration and flushing operations, with a closed-circuit design that includes a three-way valve system to manage liquid flow and reduce transmembrane pressure.
Enables efficient membrane separation using high-permeability membranes in smaller systems with reduced pump capacity and cost, enhancing fouling resistance and energy efficiency while maintaining high water yield and purification efficiency.
Smart Images
Figure HU2025050101_18062026_PF_FP_ABST
Abstract
Description
[0001] Membrane separation system using high-efficiency, closed-circuit membrane technology
[0002] The invention relates to a membrane separation system using high-efficiency, closed-circuit membrane technology.
[0003] In the last two to three decades, technological developments in the field of membrane technology have resulted in the development of reverse osmosis (RO) membranes with high permeability and selectivity, as well as nanofiltration (NF) membranes, which allow membrane separation to be carried out efficiently, i.e. with high pollutant removal and high flux, using very low transmembrane pressures (typically 2-6 bars). This transmembrane pressure corresponds to the usual pressure of pressurized liquid sources (e.g. mains tap water), which allows avoiding the use of expensive booster pumps in both RO and NF membranes.
[0004] The schematic diagram of a conventional closed-circuit reverse osmosis (CCRO) filtration system is shown in Figure 1 (source: Salt Separation Services Ltd. https: / / saltsep.co.uk / what- is-ccro-and-what-are-the-benefits). The CCRO filtration system 100 comprises a liquid inlet 102, a high-pressure feed pump 106, a membrane unit 108 connected to the feed pump 106 and including RO membranes in one or more parallel channels, a permeate outlet 110, a feedback branch 112 along which a circulation pump 114 is arranged, and a three-way valve 116, through which the concentrate can be returned to the inlet of the membrane unit 108 or can be conveyed from the system.
[0005] The above-mentioned CCRO scheme is used, among others, in the DesaliTec™ CCRO system of the DuPont company (https: / / www.dupont.com / brands / desalitec-ccro-high-efficiency- ro.html). This system is basically a technology for large-scale industrial (over 10 m3 / h) reverse osmosis-based desalination (over 10 m3 / h). The feed is provided here by a high-performance (high-pressure) pump, which also performs the flushing operation.
[0006] It is an object of the present invention to improve the conventional CCRO membrane separation systems in order to make the system suitable for carrying out smaller closed-circuit crossflow membrane separation apparatuses (even on a household scale), and to effectively perform filtration based on nanofiltration or reverse osmosis (or ultrafiltration, microfiltration). It is another object to provide a membrane separation device, the required feed pump capacity of which is smaller than that of the known CCRO systems, or which can be omitted in the case of a pressurized liquid source (e.g. tap water), thereby reducing the investment cost of the system.
[0007] To achieve the above objects, the CCRO scheme has been adapted to small and low-pressure membrane separation devices, especially to NF membranes and RO membranes. The conventional CCRO scheme has been modified by omitting the feed pump in the case of a pressurized liquid source, or using only a lower-power feed pump in the case of a nonpressurized liquid source, while arranging the circulation pump in the liquid circuit so that the flushing operation is performed by the circulation pump when cleaning the membrane unit.
[0008] The above objectives are achieved by providing a system according to claim 1. Preferred embodiments of the membrane separation system according to the invention are defined in the dependent claims.
[0009] The invention will be described in detail below with reference to the drawings. In the drawings:
[0010] Figure 1 is a schematic diagram of a conventional CCRO membrane separation system; Figure 2 is a schematic circuit diagram of a first preferred embodiment of the membrane separation system according to the invention;
[0011] Figure 3 illustrates the circulation of the liquid in the normal operating mode (filtration phase) of the membrane separation system according to the invention shown in Figure 2;
[0012] Figure 4 illustrates the fluid flow path in the flushing mode (flushing phase) of the membrane separation system according to the invention shown in Figure 2;
[0013] Figure 5 is a schematic circuit diagram of a first preferred embodiment of the membrane separation system according to the invention, the three-way valve unit being formed by a pair of two-way valves;
[0014] Figure 6 is a schematic circuit diagram of a second preferred embodiment of the membrane separation system according to the invention; Figure 7 illustrates the circulation of the liquid in the normal operating mode (filtration phase) of the membrane separation system according to the invention shown in Figure 6; and
[0015] Figure 8 illustrates the fluid flow path in the flushing mode (flushing phase) of the membrane separation system according to the invention shown in Figure 6.
[0016] Preferred embodiments of the membrane separation system according to the invention are described below. The schematic circuit diagram of the first embodiment is shown in Figure 2. In this embodiment, which can be used when connected to a pressurized liquid source, for example, mains tap water, the membrane separation system 200 does not include a feed pump.
[0017] The membrane separation system 200 comprises a high-pressure liquid feed 202 from which fresh water is directed to a membrane unit 204 which comprises NF or RO membranes for filtering the fresh liquid. The permeate is conveyed from the membrane unit 204 through a conduit 206 which optionally includes a valve or tap 207. The valve 207 is preferably an electronically controlled, motorized valve.
[0018] The concentrate leaves the membrane unit 204 via a conduit 208, which is connected to a three-way valve unit 210, from where the concentrate is returned to the membrane unit 204 via a further conduit 209, thereby implementing a closed-circuit circulation of the liquid. The circulation pump 212 is arranged along the conduit 209, downstream of the three-way valve unit 210. The liquid feed 202 is connected to the conduit 209 downstream of the circulation pump 212, so that the fresh liquid and the returned concentrate enter the membrane unit 204 together.
[0019] The three-way valve unit 210 may be formed by a three-way diverting valve or a pair of two- way valves connected to a T-junction. In the latter case, the valve 231 on the waste liquid side is preferably of the normally closed (NC) type, and the valve 230 in the inner circuit is of the normally open (NO) type (see Figure 5).
[0020] The circulating pump 212 is preferably formed by a variable frequency drive (VFD) pump.
[0021] A pressure reducing valve 205 may be arranged along the conduit 203 connected to the liquid feed 202 if the network pressure is too high when using a high permeability membrane (high permeability NF membranes are currently available that operate ideally at a pressure of 2.5-4 bars).
[0022] In the membrane separation system 200, various measuring units may be arranged along each conduit. For example, as shown in Figure 2, a flow transmitter 220 may be placed along the permeate conduit 206, or, for example, a flow transmitter 221, a temperature transmitter 222, a conductivity transmitter 223, and pressure transmitters 224 and 225 may be placed along the conduit 208 exiting the membrane unit 204. The aforementioned measuring units are only examples; if necessary, these measuring units or even other measuring units, such as a turbidity meter, may be placed at other positions in the membrane separation system 200.
[0023] Figure 3 illustrates the circulation of the liquid in the normal operating mode (filtration phase) of the membrane separation system 200. The flow path of the liquid is indicated by dashed lines. In this operating mode, the transmembrane pressure is provided by the high-pressure liquid feed 202, while the crossflow in the membrane unit 204 is provided by the circulation pump 212. The circulation pump 212 is located in the low-pressure branch of the conduit 209 upstream of the connection of the conduit 203, so that pump with a relatively small capacity can be used for this purpose (because the high flow-rate flush is provided by the pressurized liquid feed). The three-way valve unit 210 is in a position to return the concentrate to the membrane unit 204. The tap 207 along the conduit 206 is in the open state, thereby continuously conveying the permeate from the membrane unit 204.
[0024] Figure 4 illustrates the fluid flow path of the membrane separation system 200 in the flushing mode (flushing phase), again in dashed lines. In this operating mode, no transmembrane pressure is required, and the tap 207 along the conduit 206 is preferably closed. In some embodiments, a check valve may be used instead of the tap 207, or the tap 207 may be omitted. In this case, the crossflow of the membrane unit 204 is provided by the high-pressure liquid feed 202. The three-way valve unit 210 is positioned to divert the flushing water from the membrane unit 204 via the conduit 208 from the membrane separation system 200.
[0025] The purpose of flushing is, on the one hand, to remove the concentrated water from the closed circuit and from the inside of the membrane unit 204 by means of the feed liquid, and on the other hand, to clean the impurities adhering to the surface of the membrane. Since the large flow rate of flushing liquid is provided by the water supply network in this embodiment, the circulation pump 212 can be sized smaller than what would be required for the flushing operation, which results in further cost savings.
[0026] As can be clearly seen in Figure 4, during the flushing phase, the flushing liquid does not flow through the circulation pump 212, thereby protecting the circulation pump 212, which ensures a longer service life for the pump.
[0027] If maximum energy efficiency is to be achieved, then at the beginning of the filtration process, it is advisable to operate the circulation pump 212 at a relatively low power, and as the circulated liquid (concentrate) becomes more concentrated, the power of the circulation pump 212 is gradually increased. This filtration method also results in a smaller transmembrane pressure increase during the filtration phase, which leads to a more timesteady permeate flux.
[0028] A schematic circuit diagram of the second embodiment is shown in Figure 6. In this embodiment, in which membrane separation of a liquid having low pressure or no pressure at all, such as a liquid fed from a liquid tank, can be performed, the membrane separation system 300 comprises a feed pump 301 that increases the pressure of the liquid coming from the low-pressure liquid feed 302 and supplies fresh water at an already increased pressure via the feed conduit 303 for cleaning.
[0029] The fresh water is fed through a conduit 309 to the membrane unit 304, which contains NF or RO membranes for filtering the fresh liquid. The permeate is from the membrane unit 304 conveyed through a conduit 306, along which a tap 307 is arranged. In some embodiments, a check valve may be used instead of the tap 307, or the tap 307 may even be omitted. Preferably, the tap 307 is formed by a controlled electric or pneumatic valve.
[0030] The concentrate exits the membrane unit 304 via a conduit 308, which is connected to a three- way valve unit 310, from where the concentrate is returned to the membrane unit 304 via the aforementioned conduit 309, which results in the closed-circuit circulation of the liquid. The circulation pump 312 is arranged along the conduit 309, downstream of the three-way valve unit 310. In this case, the conduit 303 transporting the fresh water from the liquid feed 302 is connected to the conduit 309 upstream the circulation pump 312, so that the fresh liquid and the returned concentrate flow together through the circulation pump 312 and thus reach the membrane unit 304. For the three-way valve unit 310, a three-way diverting valve or a pair of two-way valves connected to a T-junction may be used (similar to the first preferred embodiment).
[0031] The feed pump 301 and the circulation pump 312 are preferably equipped with a variable frequency drive (VFD) motor.
[0032] As shown in Figure 6, the membrane separation system 300 may include a by-pass branch connected in parallel to the feed pump 301, which, in this embodiment, is implemented by a conduit 330 and a check valve 331 disposed thereon. The by-pass branch may be necessary to use during flushing, as it will be described later.
[0033] In the membrane separation system 300, various measuring units may be arranged along the conduits. For example, as shown in Figure 6, a flow transmitter 320 may be arranged along the permeate conduit 306, or, for example, a flow transmitter 321, a temperature transmitter 322, a conductivity transmitter 323, and pressure transmitters 324 and 325 may be placed along the conduit 308 exiting the membrane unit 304. The measuring units mentioned here are only examples; if necessary, the aforementioned measuring units, or even other measuring units, may be placed at other positions of the membrane separation system 300.
[0034] Figure 7 illustrates the fluid circulation in the normal operating mode (filtration phase) of the membrane separation system 300. The fluid flow path is indicated by dashed lines. In this operating mode, the transmembrane pressure is primarily provided by the feed pump 301. The crossflow of the membrane unit 304 is provided by the circulation pump 312, which also contributes slightly to the transmembrane pressure. The circulation pump 312 is located in the high-pressure branch of the conduit 309 downstream the connection of the conduit 303.
[0035] The 310 three-way valve unit is in a state in which it returns the concentrate to the membrane unit 304. The tap 307 along the conduit 306 is in the open state, thereby continuously conveying the permeate from the membrane unit 304.
[0036] Figure 8 illustrates the fluid flow path in the flushing mode (flushing phase) of the membrane separation system 300 with dashed lines. In this operating mode, no transmembrane pressure is required, and the tap 307 along the conduit 306 is closed. The crossflow of the membrane unit 304 is also provided by the circulation pump 312. The three-way valve unit 310 is in a state in which it conveys the flushing water coming from the membrane unit 304 via the conduit 308 from the membrane separation system 300. Since the feed pump 301 is typically a high-pressure, low-capacity (typically positive displacement) pump, its maximum flow rate is typically not sufficient for flushing. In such a case, the circulation pump 312 draws excess water into the conduit 309 via the by-pass branch, i.e. through the conduit 330. If the pressure of the feed fluid source is insufficient or negative (i.e. the fluid source is located at a lower position), then both the feed pump 301 and the circulation pump 312 must be of the self-priming type.
[0037] As can be clearly seen in Figure 8, during the flushing phase, the feed liquid for flushing primarily flows through the check valve 331 in the by-pass branch 330. The flushing liquid can flow passively through the feed pump 301, or the feed pump 301 may be operated to assist the flushing operation.
[0038] The flushing cycles may be controlled on the basis of the following conditions:
[0039] - Time-based control: flushing occurs automatically at programmed times.
[0040] - The value measured by the permeate flow transmitter 220 is lower than a pre-programmed minimum flow rate (mainly in the case of the first preferred embodiment of the system).
[0041] - The value measured by the conductivity transmitters 223, 323 is higher than a preprogrammed maximum conductivity.
[0042] - The pressure measured by the pressure transmitters 224, 225, 324, 325 exceeds a preprogrammed limit value (mainly in the case of the second preferred embodiment of the system).
[0043] - The pressure drop measured by the pressure transmitters 224, 225, 324, 325 of the membrane module (i.e. the difference between the pressures measured by the pressure transmitters 224 and 225, or 324 and 325) exceeds a pre-programmed limit value.
[0044] - The temperature measured bythe temperature transmitter exceeds a pre-programmed limit value.
[0045] - Signals sent by other optional sensors (e.g. turbidity meter).
[0046] Monitoring even one of the above conditions may be sufficient to initiate flushing, but the flushing cycle may even be controlled based on multiple signals if any of them reaches a critical value. The control based on the permeate flux is preferably performed according to values normalized with respect to the temperature and the conductivity data.
[0047] The advantages of the membrane separation system according to the invention are as follows.
[0048] The invention allows the use of hollow-fiber polyelectrolyte multilayer (PEM) direct nanofiltration (dNF) membranes and other high permeability membranes in practice in small- scale water purification devices, e.g. household water purification devices, with high water yield, good purification efficiency and minimal fouling.
[0049] Compared to conventional CCRO systems, the feed pump used in the system according to the invention should provide slightly lower pressure, since the circulation pump also increases the pressure of the liquid entering the membrane module. It should be noted, however, that the circulation pump must have a slightly higher capacity than in a conventional CCRO system. For small systems, this is advantageous from a point of view of costs, since either the feed pump may be omitted (as in the first preferred embodiment of the system) or a single high-pressure circulation pump with a capacity to provide the desired permeate flow rate is sufficient (as in the second preferred embodiment of the system). A higher volume flow rate can be achieved during flushing compared to conventional CCRO systems, since either the water supply network or the circulation pump can typically provide a higher volume flow rate than the feed pumps. This is particularly advantageous for some membrane modules (e.g. hollow fiber membranes).
[0050] If a feed pump is not used (see the first preferred embodiment above), the pressurized liquid can flow freely during flushing at the maximum volume flow rate specified by the membrane module manufacturer, which, due to the frequently used intensive flushing, greatly improves the fouling resistance of the membrane separation system as compared to the traditional CCRO systems.
Claims
Claims1. A closed-circuit membrane separation system (200, 300) comprising: a liquid feed (202, 302) for introducing fresh liquid; a membrane unit (204, 304); a conduit (206, 306) connected to the membrane unit (204, 304) for conveying the permeate; a conduit (208, 308) connected to the membrane unit (204, 304) for conveying the concentrate; a three-way valve unit (210, 310) for purging the concentrate / flushing liquid or returning the concentrate to the membrane unit (204, 304); and a circulation pump (212, 312); characterized by that the three-way valve unit (210, 310) is arranged upstream of the circulation pump (212, 312) in the direction of flow of the concentrate.
2. The closed-circuit membrane separation system (200, 300) according to claim 1, wherein the liquid feed (202) is connected to the conduit (209) arranged between the circulation pump (212) and the membrane unit (204).
3. The closed-circuit membrane separation system (200, 300) according to claim 1, wherein the liquid feed (302) is connected to the conduit (309) arranged between the three-way valve unit (310) and the circulation pump (312), through a conduit (303) along which a feed pump (301) is arranged.
4. The closed-circuit membrane separation system (200, 300) according to claim 3, wherein a conduit (330) forming a by-pass branch is provided in parallel to the feed pump (301), wherein a check valve (331) is arranged along said by-pass conduit (330).
5. The closed-circuit membrane separation system (200, 300) according to any one of claims 1-4, wherein the circulation pump (212, 312) and / or the feed pump (301) is in the form of afrequency-controlled motor pump or a pump with another type of power control, in particular an air-driven membrane pump.
6. The closed-circuit membrane separation system (200, 300) according to any one of claims 1-5, wherein a sensor is arranged at one or more positions of the system, wherein the one or more sensors are selected from the group of a pressure transmitter (324), a temperature transmitter (222, 322), a conductivity transmitter (223, 323) and a flow transmitter (221, 321).
7. The closed-circuit membrane separation system (200, 300) according to any one of claims 1-6, wherein a controllable motorized valve (207, 307) is arranged along the conduit (206, 306) for conveying the permeate.
8. The closed-circuit membrane separation system (200, 300) according to any one of claims 1-7, wherein the three-way valve unit (210, 310) is provided in the form of a three-way diverting valve or a pair of two-way valves connected to a T-junction, and wherein preferably, the waste liquid side valve (231) of the pair of two-way valves is of the normally closed (NC) type, and the valve (230) located in the inner circuit is of the normally open (NO) type.
9. The closed-circuit membrane separation system (200, 300) according to any one of claims 1-8, wherein the three-way valve unit (210, 310) is motorized or pneumatically controlled.
10. The closed-circuit membrane separation system (200, 300) according to any one of claims 1-9, wherein the membrane unit (204, 304) comprises any one of reverse osmosis membranes, ultrafiltration membranes, microfiltration membranes and nanofiltration membranes.
11. The closed-circuit membrane separation system (200) according to claim 1, wherein the liquid feed (202) is connected to the conduit (209) arranged between the circulation pump (212) and the three-way valve unit (210).
12. The closed-circuit membrane separation system (300) according to claim 1, wherein the liquid feed (302) is connected to the conduit (309) arranged between the membrane module and the circulation pump (312), through a conduit (303) along which a feed pump (301) is arranged.