Ultrafiltration system and method with pressure exchange

Abstract

The invention provides a semi-batch method and an ultrafiltration system for treating raw water. The ultrafiltration system is adapted to switch between two modes: a recirculation mode in which a concentrate stream from the ultrafiltration element is recirculated; and a flushing mode that expels the concentrate stream. The ultrafiltration system includes an energy recovery device adapted to recover energy from the concentrate stream during the flush mode. The liquid flows through the energy recovery device during at least a portion of the recirculation mode. Preferably, the energy recovery device is an isobaric energy recovery device or a pressure exchanger.

Description

Technical Field

[0001] The present invention relates to a method and system for semi-batch treatment of raw water using ultrafiltration. Background Art

[0002] A number of patents, patent applications, and publications are cited in this specification to more fully describe the state of the art to which the present invention pertains. The entire disclosure of each of these patents, patent applications, and publications is hereby incorporated by reference.

[0003] Climate change and water resource shortages together have increased the need for purified alternative water supplies for beneficial use with less energy consumption. Currently, conventional reverse osmosis is mainly used to meet this need. Conventional reverse osmosis (RO) is a quasi-steady-state ultrafiltration membrane process in which a pressurized feed stream is continuously split into two streams, namely a permeate stream and a retentate stream. Additional recovery of the feed stream is accomplished by adding additional ultrafiltration membrane elements in series. Semi-batch reverse osmosis is a novel method for desalinating water using ultrafiltration that utilizes two different main operating modes. During the first mode, the retentate stream is recycled and mixed with the feed stream before entering a pressure vessel containing the membrane. Thus, the salt concentration increases during the first mode of operation. In the second mode, the concentrate is directed to waste, thereby allowing the salt concentration in the vessel to be reduced.

[0004] The semi-batch reverse osmosis system consumes less energy than a conventional reverse osmosis system. In U.S. Patent No. 7,695,614 B2, Efraty describes a semi-batch ultrafiltration system in which the energy consumption is lower than that of a conventional reverse osmosis system, and an energy recovery device is not used in the semi-batch process. Efraty describes that the process is attractive for high recovery ultrafiltration (about 75%-95%) of low-concentration brine. At lower recovery rates, the advantages of the process are less attractive. To address the inefficiencies associated with the process, Efraty developed the process described in U.S. Patent No. 7,628,921 B2. In this process, a "side conduit" is added to extend the advantages of the semi-batch process to lower recovery rates, thereby allowing the process to be used for seawater desalination and similar high osmotic strength solutions. As a further improvement, Efraty also proposed (U.S. Patent No. 11,198,096 B1) a system that uses a pressure exchange type of energy recovery device (ERD) without using a "side conduit", thereby improving efficiency, reducing footprint, and reducing capital costs in some cases.

[0005] There are several different high-efficiency ERDs on the market. A pressure exchanger is a device commonly used in conventional ultrafiltration systems (systems including reverse osmosis membranes or nanofiltration membranes) to transfer energy from a high-pressure concentrate stream to a low-pressure feed stream. U.S. Patent No. 2,675,173 describes an early pressure exchanger that uses a cylindrical rotor to create a pressure exchange between a high-pressure stream and a low-pressure stream. Similarly, U.S. Patent No. 4,887,942A and European Patent No. 1,508,361B1 also describe a motor-driven pressure exchanger with a similar flow path. U.S. Patent No. 7,306,437B2 describes a system in which tangential flow entering a low-pressure inlet port provides a velocity vector that applies rotational momentum to the rotor. Other rotating isobaric devices apply rotational momentum to the rotor from a high-pressure port. Piston-based ERDs (such as double working energy exchange rotors (DWEERs)), rotating vane ERDs (U.S. Patent No. 9,708,924), and other isobaric ERDs also offer similar advantages.

[0006] However, there is a desire to provide an improved system suitable for treating water that can increase water recovery, reduce energy consumption, and have higher reliability. Summary of the Invention

[0007] A method for treating raw water, comprising:

[0008] providing a semi-batch ultrafiltration system 2, comprising:

[0009] a raw water source 4;

[0010] a feed line assembly 6, comprising a first feed path 10 extending from the raw water source 4 to a high-pressure pump 14, a second feed path 12, and a first junction 8 located on the first feed path 10 that connects the first feed path 10 to the second feed path 12;

[0011] a pressure vessel assembly 22, comprising a feed inlet 24, a concentrate outlet 26, a permeate outlet 28, and at least one pressure vessel 23 containing a plurality of ultrafiltration elements 54;

[0012] A recirculation loop 20, which includes a second connection point 18 connecting to the high-pressure pump 14; the recirculation loop 20 further includes a feed flow path from the feed inlet 24 through the pressure vessel assembly 22 to the concentrate outlet 26, and a return path 32 outside the pressure vessel assembly 22, the return path being adapted to enable flow from the concentrate outlet 26 to the feed inlet 24; wherein, a first section 32' of the return path 32 connects the concentrate outlet 26 with the third connection point 34, and a second section 32'' of the return path 32 connects the fourth connection point 38 with the feed inlet 24; wherein, the second section 32'' includes the second connection point 18 and the recirculation pump 40; and

[0013] An energy recovery device (ERD) 42, which includes four ports:

[0014] A first ERD inlet port 44, which is fluidly connected to the second feed flow path 12,

[0015] A first ERD outlet port 46, which is adapted to supply pressurized raw water to the recirculation loop 20 through the fourth connection point 38,

[0016] A second ERD inlet port 48, which is adapted to receive a pressurized concentrate stream from the recirculation loop 20 through the third connection point 34,

[0017] A second ERD outlet port 50, which is fluidly connected to the brine outflow pipeline 52 and is adapted to supply a depressurized concentrate stream to the brine outflow pipeline 52; and

[0018] Repeatedly switching between a first operating mode and a second operating mode, wherein,

[0019] The first operating mode is characterized by enabling flow between the first section 32' and the second section 32'' of the return path 32 and allowing the concentrate fluid from the concentrate outlet 26 to mix with the flow from the high-pressure pump 14 at the second connection point 18, such that the combined flow is conveyed to the pressure vessel inlet 24; and the liquid flows through the ERD 42 during at least a portion of the first mode; and

[0020] The second operating mode is characterized by preventing flow between the first section 32' and the second section 32'' of the return path 32; causing a portion of the fluid from the raw water source 4 to sequentially pass through the inlet to the second feed path 12, the first ERD inlet port 44, the first ERD outlet port 46, the fourth junction 38, and the second section 32'' of the return path 32; and causing the concentrate fluid from the concentrate outlet 26 to sequentially pass through the inlet to the first section 32' of the return path 32, the third junction 34, the second ERD inlet port 48, the second ERD outlet port 50, the brine outflow line 52, and the brine discharge port 68.

[0021] The advantages and features that characterize the novelty of the present invention are particularly pointed out in the appended claims and form a part of the claims. However, for a better understanding of the present invention, its advantages, and the purposes obtained by its use, reference should be made to the accompanying drawings, which form another part of the present invention, and to the accompanying descriptive matter, in which one or more preferred embodiments of the present invention are shown and described. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 a and Figure 1 b show the configurations of two operating modes (recirculation and flush, respectively) of a prior art semi-batch system including energy recovery.

[0023] Figure 2 A pressure vessel assembly including a plurality of parallel containers is shown.

[0024] Figure 3 a to Figure 3 c show an embodiment of the system of the present invention, in which valves are configured to allow different flow paths for different operating steps. In Figure 3 a and Figure 3 b, the recirculation mode is enabled, in which the concentrate fluid is recycled to the feed inlet of the pressure vessel assembly. In Figure 3 b, liquid is caused to flow through the ERD simultaneously. In Figure 3 c, the flush mode is enabled, in which the concentrate fluid passes through the energy exchange unit and is sent to the brine discharge port.

[0025] Figure 4 a to Figure 4 c show an alternative embodiment of the system of the present invention, showing steps corresponding to the steps in Figure 3 a to Figure 3 c, but in which the liquid flow (raw water) within the ERD in Figure 4 b is achieved by an internal bypass.

[0026] Figure 5 a to Figure 5Figure c shows another embodiment of the present invention, which shows a three-way valve and Figure 5 the recirculation of the flow achieved in b to the feed tank.

[0027] Figure 6a Figures 6a to 6c show alternative embodiments of the system of the present invention, showing steps corresponding to the steps in Figure 3 a to Figure 3 c, but wherein the flow of liquid (concentrate) within the energy exchange device (Figure 6b) is achieved by an internal bypass. Detailed Description

[0028] A system and method for operating a semi-batch ultrafiltration system are provided herein. The systems described herein, for example, reduce energy consumption and achieve additional water recovery compared to other configurations that combine batch reverse osmosis with energy recovery (such as the system described in U.S. Patent No. 11,198,096 B1).

[0029] Referring now to the drawings, wherein like reference numerals represent corresponding structures in all the drawings, and particularly to Figure 1 Figure 2a, which shows a configuration corresponding to a prior art semi-batch system that operates part of the time in a recirculation (closed loop) mode, wherein the concentrate from the ultrafiltration element is mixed with the raw water and recirculated to the ultrafiltration element. The prior art semi-batch system also operates part of the time in a flush mode ( Figure 1 Figure 2b), wherein the concentrate from the ultrafiltration element is directed to a brine discharge port. Figure 2 The pressure vessel assembly 22 is shown. In Figure 3 Figures 2 to 6, several embodiments of the system of the present invention are shown and will be described in more detail hereinafter.

[0030] The semi-batch ultrafiltration system 2 of the present invention includes a raw water source 4 containing raw water to be treated. The raw water source can be a pressurized source or a reservoir (such as a tank or cistern). The feed line assembly 6 includes a first feed path 10 extending from the raw water source 4 to the high-pressure pump 14. The feed line assembly 6 also includes a second feed path 12 connected to the ERD 42. The feed line assembly 6 includes a first connection point 8 located on the first feed path 10 that connects the first feed path 10 to the second feed path 12.

[0031] System 2 includes a pressure vessel assembly 22. The pressure vessel assembly 22 includes a feed inlet 24, a concentrate outlet 26, a permeate outlet 28, and at least one pressure vessel 23 containing a plurality of ultrafiltration elements 54. In some embodiments (not shown), the pressure vessel assembly 22 may include more than one permeate outlet 28, such as when different quality permeates are removed from more than one end of the vessel 23 (e.g., see U.S. Patent No. 4,046,685). Although the pressure vessel assembly 22 must include at least one pressure vessel 23, the pressure vessel assembly preferably includes a plurality of pressure vessels 23 arranged in series and / or parallel. Figure 2 A pressure vessel assembly 22 is shown having a one-dimensional array of vessels 23, but two-dimensional arrays of parallel pressure vessels 23 are also common. The feed inlet 24 supplies the fluid to be treated to the plurality of vessels 23. Similarly, the pressure vessel assembly 22 is configured such that the permeate outlet 28 receives permeate fluid from the plurality of vessels 23, and such that the concentrate outlet 26 receives concentrate fluid from the plurality of vessels.

[0032] The pressure vessel 23 contains a plurality of ultrafiltration elements 54 in series, preferably two to eight ultrafiltration elements 54 in series. The ultrafiltration element (“membrane element”) is a core containing a reverse osmosis (RO) membrane or a nanofiltration (NF) membrane. Most commonly, these elements take the form of spiral wound elements, where the membrane sheet, the feed spacer, and the permeate spacer are each wound around a central permeate tube (e.g., see U.S. Patent No. 10,717,050). The feed spacer zones within each ultrafiltration element 54 cause the feed to flow from one end of the vessel to the other end of the vessel, thereby connecting the feed inlet 24 and the concentrate outlet 26 of the system. Similarly, within each vessel, the permeate tubes of the plurality of ultrafiltration elements 54 are joined and fluidly connected to the permeate outlet 28.

[0033] Still referring to Figure 3 a to Figure 3c, The system 2 includes a recirculation loop 20 that recirculates the concentrated fluid from the concentrate outlet 26 back to the feed inlet 24. Specifically, the recirculation loop 20 includes a feed flow path that extends from the feed inlet 24 through the pressure vessel assembly 22 to the concentrate outlet 26. The feed flow path through the pressure vessel assembly 22 may include parallel channels through a plurality of different vessels 23. The recirculation loop 20 further includes a return path 32 outside the pressure vessel assembly 22 that is adapted to effect flow from the concentrate outlet 26 to the feed inlet 24. A first section 32' of the return path 32 connects the concentrate outlet to a third junction 34, and a second section 32'' of the return path 32 connects a fourth junction 38 to the feed inlet 24. The second section 32'' includes a recirculation pump 40 and a second junction 18. To supply fresh raw water to the recirculation loop 20, the second junction 18 within the recirculation loop 20 is connected to the downstream side of the high-pressure pump 14.

[0034] The semi-batch system of the present invention includes an energy recovery device (ERD) 42 that is configured to recover energy from the pressurized concentrated stream during the flushing mode. Various energy recovery units are known, such as pressure exchange units, rotary vane units, and isobaric units (e.g., see European Patent No. 1,508,361 and U.S. Patent Nos. 4,887,942; 5,338,158; 7,306,437; 7,799,221; 9,708,924; and 10,138,907). Some of these energy exchange techniques can be described as positive displacement energy exchangers, including piston-based ERDs (such as Clark pumps, double working energy exchangers (DWEERs), or axial piston devices) or progressive cavity ERDs (such as rotary vane units). The ERD 42 includes four ports: two inlet ports and two outlet ports. A first ERD inlet port 44 is fluidly connected to a second feed flow path 12 for receiving raw water. A second ERD inlet port 48 may be connected to the third junction 34 and is configured to receive the pressurized concentrated stream from the recirculation loop 20 during the flushing mode. A first ERD outlet port 46 may be connected to the fourth junction 38 and is adapted to supply pressurized raw water to the recirculation loop 20 during the flushing mode. A second ERD outlet port 50 is fluidly connected to the brine outlet line 52 and supplies a depressurized concentrated stream to the outlet line 52. During the flushing mode, most of the fluid entering the first ERD inlet port 44 flows to the first ERD outlet port 46, and most of the fluid entering the second ERD inlet port 48 flows to the second ERD outlet port 50, while energy (as pressure) is transferred within the ERD from the second ERD inlet port 48 to the first ERD outlet port 46.

[0035] System 2 can repeatedly switch between a first operating mode and a second operating mode, or between a recirculation operating mode and a flushing operating mode. As used herein, the term "repeatedly" refers to an action that occurs more than once within a defined time period (preferably more than once within a three-hour time period, more preferably once within a one-hour time period). The exact duration of the repeating time period is determined by the length of time that system 2 operates in the recirculation mode. A person skilled in the art can determine the operating time in the recirculation mode by modeling the pressure vessel assembly 22 to, for example, predict the target change in concentration within the ultrafiltration system. Alternatively, the system output (such as the target conductivity of the brine) can be monitored.

[0036] Now referring to Figure 4 b, in some ERDs (such as pressure exchanger (PE) units) 42, an internal bypass allows some fluid to flow between a first ERD inlet port 44 and a second ERD outlet port 50 such that when the flow through the first ERD outlet port 46 and / or the second ERD inlet port 48 is blocked, this fluid can become the majority of the flow in the ERD. The internal bypass depicted as a curved dashed arrow in Figure 4 b connects the second feed flow path 12 to the brine outlet line 52 through port 44 and port 50. Commercial ERDs including pressure exchangers available from Energy Recovery, Inc. are similar to the devices described in Hague (U.S. Patent No. 7,306,437). Hague describes a system in which the flow from a low-pressure inlet port has an inlet tangential velocity vector that imparts rotational momentum to a rotor, rather than using a motor. As a result of this design, when a valve or other device blocks the high-pressure port and flow is introduced through the low-pressure inlet port, the rotor rotates while the flow is discharged into the low-pressure outlet port.

[0037] For Figure 3 each of the embodiments in FIGS. 12 to 6, the first valve set 36 can be configured to provide different flow paths for implementing multiple operating modes. The multiple operating modes at least include a recirculation step and a flushing step:

[0038] 1) Figure 3 a to Figure 3 b, Figure 4 a to Figure 4 b, Figure 5 a to Figure 5 b, and Figure 6aThrough Figure 6b all show a part of the recirculation step, in which a flow is achieved between the first section 32' of the return path 32 and the second section 32" of the return path 32. In this step, the concentrate fluid from the concentrate outlet 26 is mixed with the raw water flow from the high-pressure pump 14 at the second junction 18, and the combined flow is delivered to the pressure vessel inlet 24. In a preferred embodiment, the time during which the system 2 operates in the recirculation step is at least 50%, more preferably 70%, and even more preferably 90%. During the recirculation step, the permeate fluid with a concentration lower than the feed concentration is removed from the system 2 via the discharge path 30, and this causes the fluid concentration within the recirculation loop 20 to increase over time. As depicted in Figure 3 b, Figure 4 b, Figure 5 b and the valve configurations of Figure 6b, during at least a part of the recirculation step, the liquid flows through the ERD 42. In some embodiments, as Figure 3 b, Figure 4 b and Figure 5 b shown, the recirculation step may further include operating the low-pressure pump 60 to provide a raw water flow through at least a part of the brine outlet line 52.

[0039] 2) Figure 3 c, Figure 4 c, Figure 5 c and Figure 6c show the flushing step, in which the flow between the first section 32' of the return path 32 and the second section 32" of the return path 32 is prevented. In the flushing step, fresh raw water is supplied to the recirculation loop 20 and the concentrate fluid within the recirculation loop 20 is removed from the system 2. The two fluid flows pass through the ERD 42 to provide flushing while recovering the energy (pressure) initially present in the recirculation loop 20. A part of the fluid from the raw water source 4 is caused to sequentially pass through the second feed path 12, the first ERD inlet port 44, the first ERD outlet port 46, the fourth junction 38, and the second section 32" of the return path 32. At the same time, the concentrate fluid from the concentrate outlet 26 is caused to sequentially pass through the first section 32' of the return path 32, the third junction 34, the second ERD inlet port 48, the second ERD outlet 50, the brine outlet line 52, and the brine discharge port 68. Preferably, the time during which the system operates in the flushing step is less than 50%.

[0040] In Figure 3 a and Figure 3 b, during the two parts of the recirculation step depicted, the first valve group 36 prevents the concentrate fluid from flowing from the concentrate outlet 26 into the ERD unit 42. However, in a preferred embodiment of the recirculation step, as Figure 3As shown in Figures 3 to 5 , a portion of the fluid from the raw water source 4 passes through the ERD 42. Additionally, it is also preferred that this portion can be recycled. In the

[0041] reference Figure 3 、 Figure 4 、and Figure 5 , the second set of valves (second valve set 56) is adapted to direct the flow from the brine outlet line 52 to either the brine discharge port 68 or the recycle path 64. In its simplest embodiment, the second valve set 56 can consist of a single three-way valve located at the junction 62 ( Figure 5 ). Alternatively, the second valve set 56 can include a two-way valve 56' located on the brine outlet line 52 and a two-way valve 56'' located on the recycle path 64 (see Figure 3 and Figure 4 ).

[0042] Figure 3 、 Figure 4 and Figure 5 , the first valve set 36 and the second valve set 56 together are preferably adapted to simultaneously prevent the concentrated fluid from the concentrate outlet 26 from entering the ERD 42 and to effect the circulation of the liquid (raw water) through the ERD unit 42. The recycle loop 58 for raw water circulation includes or consists of the following: a first portion from the second ERD outlet port 50 to the first ERD inlet port 44, which first portion includes the recycle path 64; and a second portion extending into the ERD 42 and allowing the raw water to be optionally transferred from the first energy recovery unit inlet port 44 to the second energy recovery unit outlet port 50 via a bypass line 92 and a valve 94. The recycle loop 58 includes a second feed path 12, a first ERD inlet port 44, a second ERD outlet port 50, a portion of the brine outlet line 52, the recycle path 64, and a portion of the first feed path 10. In these embodiments, at least one low-pressure pump 60 is located on the recycle loop 58, preferably downstream of the fifth junction 66 and upstream of the first ERD inlet port 44. The second valve set 56 includes at least one isolation valve 56'' located on the recycle loop 58.

[0043] In a preferred embodiment, such as Figure 3 b and Figure 4In some of the embodiments depicted in b, the low-pressure pump 60 is in fluid communication with at least one of the ports 44, 46, 48, 50 of the ERD 42, and the low-pressure pump 60 generates a raw water flow that sequentially passes through the first ERD port 44, the second ERD outlet port 50, and the brine outlet line 52 into the second feed path 12. The low-pressure pump 60 effects the flow within the recovery loop 58.

[0044] For Figure 3 a through Figure 3 c of the system shown, the flow path external to the ERD 42 can be used to cause fluid to flow from the first ERD inlet port 44 to the second ERD outlet port 50. In the embodiment shown, the bypass line 92 having the bypass valve 94 is adapted to provide a conduit for flow between the bypass junctions 90, 96, thereby connecting the first ERD outlet port 46 and the second ERD inlet port 48. When the bypass valve 94 is opened, the low-pressure pump 60 can initiate mechanical movement within the ERD 42 and the raw water can flow therethrough along a path that sequentially includes the first ERD outlet port 46, the bypass junction 90, the bypass line 92, the bypass junction 96, and the second ERD inlet port 48 to flow from the first ERD inlet port 44 to the second ERD outlet port 50.

[0045] Figure 3 a shows the valve positions for configuration when the system is in the first operating mode, in which the concentrate is recycled as feed to the pressure vessel 23. The valve 36' is in the open state while the remaining valves in the first valve set 36", 36''' are in the closed state. (The valves 56' and 56" are also shown in the closed state.)

[0046] As Figure 3 shown in b, prior to switching to the second operating mode, the system can be configured in a manner that allows fluid (raw water) to flow through the ERD (in this case the rotating pressure exchange (PE) unit 42). This can lubricate the internal components of the PE unit and initiate rotation of the internal rotor (see U.S. Patent No. 7,306,437). Figure 3b shows the valve positions in the second valve set 56 that effect the recovery of the flow into the ERD and the raw water discharged from the second ERD outlet port 50. Valve 56" is in the open state and valve 56' is in the closed state, such that at least a portion of the raw water flow from junction 8 passes through the ERD 42 and returns to junction 8. The illustrated recovery loop 58 includes a second feed path 12, a first ERD inlet port 44, a second outlet port 50, a portion of the brine outflow line 52, a recovery path 64, and a portion of the first feed path 10. (The recovery loop 58 can be designed to avoid the first feed path 10.) In these embodiments, the low pressure pump 60 is located on the recovery loop 58, preferably downstream of the fifth junction 66 and upstream of the first ERD inlet port 44. On the recovery loop 58, Figure 3 The embodiment shown in b also includes a portion external to the ERD 42 that includes a bypass line 92.

[0047] In Figure 3 b, the pumps and valves on the bypass line 92 allow for the control of the fluid flow through the ERD. The closed valve 56' prevents flow between the second ERD outlet port 50 and the brine discharge port 68 during at least most of the time while the liquid flows through the pressure exchange device 42 during the recirculation step. Preferably, the total flow of liquid through the PE during the first mode exceeds at least twice the flow of liquid entering the brine discharge port 68 during the same time period.

[0048] Figure 3 c shows the flushing or cleaning step, and once the ERD 42 rotor rotates, the system preferably enters the second operating mode. The figure shows that valves 36", 36"', and 56' are in the open state while valves 56" and 36' are in the closed state. In the second operating mode, energy is exchanged from the high-pressure concentrate entering the second ERD inlet port 48 to the fluid discharged from the ERD 42 at the first ERD outlet port 46. At the same time, the low-pressure fluid passing through the brine outflow line 52 is sent to the discharge port 68. This allows the high-pressure feed flow to enter the recirculation loop, thus replacing the flow that is sent from the concentrate outlet 26 to the brine discharge port 68.

[0049] The first set of valves (the first valve set 36) effect the switching between the recirculation operation mode and the flushing operation mode. This valve set 36 is adapted to control the flow between the second ERD inlet port 48 and the first section 32' of the return path 32; the flow between the first section 32' of the return path 32 and the second section 32" of the return path 32; and the flow between the first ERD outlet port 46 and the second section 32" of the return path 32. In Figure 3 and Figure 4In it, the valve groups 36 for these corresponding purposes are identified as 36″, 36′, and 36″′. In some embodiments, the valve 36″′ can be a check valve (shut-off valve).

[0050] Figure 4 a through Figure 4 c shows another embodiment of the system 2 of the present invention, in which the system has a flow path inside the ERD 42, and this flow path can enable the fluid to flow from the first ERD inlet port 44 to the second ERD outlet port 50. As indicated by the dashed lines shown, the flow from the first ERD inlet port 44 to the second ERD outlet port 50 through the pressure exchange unit 42 is generated by an internal bypass. Figure 4 The first valve group 36 in a is configured to allow the feed water to recirculate through the pressure vessel assembly 22. In Figure 4 b, the first valve group 36 and the second valve group 56 still allow the concentrated fluid to recirculate from the concentrate outlet 26 to the feed inlet 24 of the pressure vessel assembly 22. However, the configuration of the first valve group 36 and the second valve group 56 also supports the flow of liquid (raw water) from the first ERD inlet port 44 to the second ERD outlet port 50 through the ERD 42, which is suitable for initiating the rotational movement inside the ERD 42. Similar to Figure 3 b, Figure 4 the arrangement in b also shows a preferred embodiment, in which the raw water passing through the ERD 42 is recovered. (This configuration allows at least a part of the raw water from the connection point 8 to pass through the ERD 42 and return to the connection point 8 via the recovery loop 58.) Finally, Figure 4 c shows the flushing step.

[0051] Figure 4 The process shown in a shows a part of the recirculation step. In this process, the flow through the first ERD inlet port 44 and the flow through the second ERD outlet port 50 are blocked. Compared with Figure 4 b, Figure 4 the closed valve 56″ in a blocks the flow through the ERD inlet port 44. Since the other three ERD ports are only connected to closed paths, the flow through the ERD inlet port 44 is blocked.

[0052] Figure 4 b and Figure 5The process shown in b is also part of the recirculation step, and the liquid flows through only two of the four ports of the ERD. Small flows may also be allowed through nominally closed valves, but it is intended that the liquid mainly flows through only two of the four ports of the ERD. In both cases, there is a valve 56' or 56''' suitable for blocking the flow between the second ERD outlet port 50 and the brine discharge port 68, and blocking the flow to the brine discharge port 68 during at least most of the recirculation step when the liquid flows through the pressure exchanger device 42. Preferably, the total flow of liquid through the ERD during the first mode exceeds at least twice the flow of liquid entering the brine discharge port 68 during the same time period.

[0053] During the recirculation step, when passing the liquid through the ERD, it is preferred that no fluid is lost from the brine discharge port 68. In Figure 3 , Figure 4 , and Figure 5 , the brine effluent valve 56' or 56''' located on the brine effluent line 52 between the second ERD outlet port 50 and the brine discharge port 68 prevents this loss.

[0054] As Figure 5 shown, the three-way valve 36'''' in the first valve group 36 or the three-way valve 56''' in the second valve group 56 can replace the function of two (two-way) valves. In Figure 3 a to Figure 3 c and Figure 4 a to Figure 4 c, the flow from the first section 32' of the return path 32 can be directed to the second section 32'' of the return path 32 or the second ERD inlet port 48. Similarly, Figure 5 the three-way valve 36'''' in the valve group 36 in Figure 5 can also achieve a similar selection. Figure 3 and Figure 4 also shows a three-way valve 56''' replacing the two (two-way) valves 56', 56'' depicted in Figure 5 Finally,

[0055] Now referring to Figure 6a and Figure 6b, the first operating mode is shown. This configuration includes one or more pressure exchanger type energy recovery devices, where the flow from the high pressure concentrate inlet can cause the rotor to rotate. As Figure 6aAs shown, a large portion (potentially all) of the flow bypasses the ERD 42 through the control valve 37, which is located in the section of the return path 32 connecting the third junction 34 and the fourth junction 38. The control valve 37 can be adjusted during the first mode to change the rate of liquid flow through the ERD 42. During most of the first operating mode (first time interval), the control valve can be opened or substantially opened. As shown in FIG. 6b, reducing the flow through the control valve 37 increases the bypass flow through the ERD 42 from the second ERD inlet port 48 to the first ERD outlet port 46. This can be practiced during a portion of the first operating mode (second time interval). In a preferred embodiment, rotational momentum can be imparted to the rotor within the ERD 42, after which the second operating mode is initiated. In another preferred embodiment, the rotor rotates throughout the first mode. In yet another preferred embodiment, the rotor rotates at a faster rate during the second time interval compared to the first time interval of the first mode. By maintaining the valves 39 and 57 in the closed position, flow through the first ERD inlet port 44 and the second ERD outlet port 50 can be prevented during at least a portion (if not all) of the first mode. Preferably, during the first mode, the liquid mainly flows only through the other two ports 48, 46 of the ERD. Preferably, the first mode is divided into a first time interval and a second time interval, where the duration of the second time interval is shorter than the duration of the first time interval, but where the volume of liquid flowing through the ERD 42 is greater during the second time interval. The time portion of the internal bypass engagement in the ERD 42 is desirably less than the duration of the first operating mode, preferably less than 50% of the duration of the first operating mode, more preferably less than 25% of the duration of the first operating mode, and even more preferably less than 10% of the duration of the first operating mode.

[0056] Figure 6a Both FIG. 6b shows the effluent valve 57 closed. During at least most of the first mode in which liquid flows through the ERD 42, flow between the second ERD outlet port 50 and the brine drain 68 is preferably blocked. Preferably, the flow of liquid through the ERD 42 during the first mode exceeds at least twice the flow of liquid entering the brine drain 68 during the same time period.

[0057] Referring to FIG. 6c, during the second operating mode, the control valve 37 is closed to direct all flow in loop 32 into the second ERD inlet port 48 and out of the second ERD outlet port 50. The valve 39 is opened to establish a fluid path for raw water to the ERD inlet port 44. The effluent valve 57 is opened to allow the concentrate flow to pass between the second ERD outlet port 50 and the brine discharge port 68. The first fluid stream entering the first ERD inlet port 44 flows to the first ERD outlet port 46. The second fluid stream entering the second ERD inlet port 48 flows to the second ERD outlet port 50. The ERD 42 transfers pressure from the second fluid stream to the first fluid stream. The duration of the second operating mode is typically less than 100% of the duration of the first operating mode, more preferably less than 75%, more preferably less than 50%, and more preferably less than 25%.

[0058] To return to the first operating mode, the control valve 37 is opened and the valves 39 and 57 are closed to re - establish the recirculation loop.

[0059] All embodiments of the system 2 include a control unit. Those skilled in the art can select a suitable control unit. Non - limiting examples of suitable types of control units include computer systems, solid - state electronic systems (such as programmable logic controllers (PLCs)), and electromechanical systems. The control unit is adapted to position the respective valves (e.g., 37, 39, 57, 94) and valve assemblies 36, 56 to effect a switch between different operating modes. Preferably, the control unit also receives measurements from sensors at various locations within the system 2, such as flow, temperature, conductivity, turbidity, and pressure. While the control unit can switch between operating modes based only on a specific time interval, preferably, the control unit uses the measurements from the sensors to determine the moment to switch between different operating modes. The control unit preferably also engages the low - pressure pump 60 and can preferably generate liquid flow through the ERD 42 during at least a portion of the recirculation step. In some embodiments, liquid flow is caused to pass through the ERD 42 during a portion of the recirculation step and then immediately switched to the flushing step. In other embodiments, liquid flow is caused to pass through the recovery loop 58 during at least a majority of the recirculation step.

[0060] The present invention includes a method for operating the described system, the method including the various optional embodiments mentioned and their combinations. The method includes repeated switching between a recirculation step and a flushing step. In some embodiments, the recirculation step may further include: a first time interval in which liquid flow through the pressure exchange unit 42 is blocked; and a second time interval in which liquid flow through the pressure exchange unit 42 is caused, followed by switching to the flushing step.

[0061] In some embodiments, the ERD associated with a semi-batch ultrafiltration system can include a plurality of ERDs in a parallel configuration such that similar port types are connected together and function together. In some embodiments, the same ERD can be associated with more than one semi-batch ultrafiltration system. Preferably, different semi-batch ultrafiltration systems are operated in phases such that each PE is used in only one flush step at a time.

[0062] Although certain preferred embodiments of the invention have been described and specifically illustrated above, the invention is not intended to be limited to such embodiments. Rather, it should be understood that although many features and advantages of the invention have been set forth in the foregoing description, together with details of the structure and function of the invention, this disclosure is illustrative only, and changes can be made in detail, particularly in the shape, size, and arrangement of the parts, to the full extent indicated by the broad general meaning of the terms of the appended claims within the principles of the invention.

Claims

1. A method for treating raw water, comprising: providing a semi-batch ultrafiltration system 2, comprising: a raw water source 4; a feed line assembly 6, comprising a first feed path 10 extending from the raw water source 4 to a high-pressure pump 14, a second feed path 12, and a first connection point 8 located on the first feed path 10, the first connection point connecting the first feed path 10 and the second feed path 12; a pressure vessel assembly 22, comprising a feed inlet 24, a concentrate outlet 26, a permeate outlet 28, and at least one pressure vessel 23 containing a plurality of ultrafiltration elements 54; a recirculation loop 20, comprising a second connection point 18 connecting the high-pressure pump 14; the recirculation loop 20 further comprises a feed flow path from the feed inlet 24 through the pressure vessel assembly 22 to the concentrate outlet 26, and a return path 32 outside the pressure vessel assembly 22, the return path being adapted to enable flow from the concentrate outlet 26 to the feed inlet 24; wherein a first section 32' of the return path 32 connects the concentrate outlet 26 and a third connection point 34, and a second section 32" of the return path 32 connects a fourth connection point 38 and the feed inlet 24; wherein the second section 32" comprises the second connection point 18 and a recirculation pump 40; and an energy recovery device (ERD) 42, comprising four ports: a first ERD inlet port 44, which is fluidly connected to the second feed flow path 12, a first ERD outlet port 46, which is adapted to supply pressurized raw water to the recirculation loop 20 through the fourth connection point 38, a second ERD inlet port 48, which is adapted to receive a pressurized concentrate stream from the recirculation loop 20 through the third connection point 34, a second ERD outlet port 50, which is fluidly connected to a brine outlet line 52 and is adapted to supply a depressurized concentrate stream to the brine outlet line 52; and repeatedly switching between a first operating mode and a second operating mode, wherein, the first operating mode is characterized by enabling flow between the first section 32' and the second section 32" of the return path 32 and allowing the concentrate fluid from the concentrate outlet 26 to mix with the flow from the high-pressure pump 14 at the second connection point 18, such that the combined flow is conveyed to the pressure vessel inlet 24; and liquid flows through the ERD 42 during at least a portion of the first mode; and The second operating mode is characterized by preventing flow between a first section 32' of the return path 32 and a second section 32'' of the return path 32; causing a portion of the fluid from the raw water source 4 to sequentially pass through and enter the second feed path 12, the first ERD inlet port 44, the first ERD outlet port 46, the fourth junction 38, and the second section 32'' of the return path 32; and causing the concentrate fluid from the concentrate outlet 26 to sequentially pass through and enter the first section 32' of the return path 32, the third junction 34, the second ERD inlet port 48, the second ERD outlet port 50, the brine outflow line 52, and the brine discharge port 68.

2. The method according to claim 1, wherein, During at least most of the time in the first mode of liquid flow through the energy recovery device 4, flow between the second ERD outlet port 50 and the brine discharge port 68 is blocked.

3. The method according to claim 1 or claim 2, wherein The total liquid flow through the ERD during the first mode exceeds at least twice the liquid flow into the brine discharge port 68 during the same time period.

4. The method according to any one of the preceding claims, wherein, During the first mode, liquid mainly flows through only two of the four ports of the ERD.

5. The method according to any one of the preceding claims, wherein, The first mode is divided into a first time interval and a second time interval, the duration of the second time interval being shorter than the duration of the first time interval, and wherein, during the second time interval, the volume of liquid flowing through the pressure exchange device is greater.

6. The method according to claim 5, wherein The second time interval is less than 50% of the first time interval.

7. The method according to any one of the preceding claims, wherein, The control valve 37 is located in the section of the return path 32 connecting the third junction 34 and the fourth junction 38, and the control valve 37 is adjusted during the first mode to change the rate of liquid flow through the ERD.

8. The method according to any one of the preceding claims, wherein A valve (39 or 56'') prevents flow through the PE inlet port 44 during at least a portion of the first mode.

9. The method according to any one of the preceding claims, wherein, During at least a portion of the first mode, flow through the first ERD inlet port 44 and the second ERD outlet port 50 is prevented.

10. The method according to any one of the preceding claims, wherein, The effluent valve 57 is located on the brine outflow line 52 between the second ERD outlet port 50 and the brine discharge port 68.

11. The method according to any one of the preceding claims, wherein The semi-batch ultrafiltration system 2 further includes a recovery path 64 adapted to enable flow from a fifth junction 62 in the brine outflow line 52 to the raw water source 4 or to a sixth junction 66 in the first feed path 10; wherein the flow from the brine outflow line 52 is directed into the recovery path 64 during at least a portion of the first mode and into the discharge port 68 during the second mode.

12. The method according to any one of the preceding claims, wherein, The ERD includes an isobaric energy exchanger.

13. The method according to any one of the preceding claims, wherein, The ERD includes a pressure exchanger (PE).

14. The method according to any one of the preceding claims, wherein, The ERD includes a positive displacement energy exchanger.

15. The method according to claim 13, wherein, The PE includes a rotor, and the rotor rotates throughout the first mode.

16. The method according to claim 13, wherein, The PE includes a rotor, and the rotor rotates at a faster rate during the second time interval.

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