Pressure exchange ultrafiltration system and method

Abstract

The present invention provides a semi-batch method and an ultrafiltration system for treating raw water. The ultrafiltration system is suitable for switching between two modes: a recirculation mode in which a concentrate stream from the ultrafiltration element is recycled, and a flash mode in which the concentrate stream is sent to a discharge. The ultrafiltration system includes an energy recovery device suitable for recovering energy from the concentrate stream during the flash mode. 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 technology]

[0002] Several patents, patent applications, and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains, and the entire disclosure of each of these patents, patent applications, and publications is incorporated herein by reference.

[0003] The combination of climate change and water scarcity has increased the need to purify alternative water supplies for beneficial use with lower energy consumption. Currently, conventional reverse osmosis (RO) is widely used to meet this need. Conventional RO is a quasi-steady-state ultrafiltration membrane process in which a pressurized feed stream is continuously split into two streams: a permeate stream and a retentate stream. Further recovery of the feed stream is achieved by adding additional ultrafiltration membrane elements in series. Semi-batch reverse osmosis (SBR) is a novel method of desalination using ultrafiltration that utilizes two distinct primary modes of operation. During the first mode, the retentate stream is recycled and mixed with the feed stream before entering a pressure vessel containing the membrane. As a result, the salt concentration increases over the duration of the first mode operation. During the second mode, the concentrate is directed to waste, allowing for deconcentration of salts from the vessel.

[0004] Semi-batch reverse osmosis systems allow for lower energy consumption than conventional reverse osmosis systems. In U.S. Patent No. 7,695,614, Efraty describes a semi-batch ultrafiltration system that does not use an energy recovery device in the semi-batch process and consumes less energy than conventional reverse osmosis systems. Efraty describes this process as attractive for high-recovery ultrafiltration (approximately 75% to 95%) of low-concentration brackish water. At lower recovery rates, the benefits 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. The addition of a "side conduit" in the process extends the benefits of the semi-batch process to much lower recovery rates, allowing the process to be used for seawater desalination and similar high osmotic strength solutions. As a further improvement, Efraty has also proposed a system that uses a pressure exchange energy recovery device (ERD) instead of a "side conduit," potentially improving efficiency, reducing footprint, and lowering capital costs (U.S. Pat. No. 11,198,096).

[0005] Several different high-efficiency ERDs are available on the market. Pressure exchangers are commonly used in conventional ultrafiltration systems (systems with reverse osmosis or nanofiltration membranes) to transfer energy from a high-pressure concentrate stream to a low-pressure feed stream. U.S. Pat. No. 2,675,173 describes an early pressure exchanger that uses a cylindrical rotor to provide pressure exchange between high-pressure and low-pressure streams. Similarly, U.S. Pat. App. Pub. No. 4,887,942 and European Patent No. 1,508,361 also describe motor-driven pressure exchangers with similar flow paths. U.S. Pat. No. 7,306,437 describes a system in which tangential flow into a low-pressure inlet port provides a velocity vector that imparts rotational momentum to the rotor. Other rotary isobaric devices impart rotational momentum to the rotor from a high-pressure port. Piston-based ERDs such as dual-work energy exchangers (DWEERs), rotary vane ERDs (U.S. Pat. No. 9,708,924), and other isobaric ERDs also offer similar benefits. Summary of the Invention [Problem to be solved by the invention]

[0006] Nevertheless, it is desirable to provide an improved system suitable for water treatment that allows for higher water recovery, lower energy usage, and has high reliability. [Means for solving the problem]

[0007] 1. A process for treating raw water, comprising: 1. A semi-batch ultrafiltration system 2, comprising: Raw water source 4 and a supply line assembly 6 including a first supply line 10 extending from a raw water source 4 to a high-pressure pump 14 and a second supply line 12; a first junction 8 located on the first supply line 10 and connecting the first supply line 10 to the second supply line 12; a pressure vessel assembly 22 including 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) including a second junction (18) connected to the high-pressure pump (14), the recirculation loop (20) further including a feed flow path through the pressure vessel assembly (22) from the feed inlet (24) to the concentrate outlet (26), and a return path (32) external to the pressure vessel assembly (22) suitable for permitting flow from the concentrate outlet (26) to the feed inlet (24), a first section (32') of the return path (32) joining the concentrate outlet (26) to the third junction (34), a second section (32'') of the return path (32) joining the fourth junction (38) to the feed inlet (24), the second section (32'') housing the second junction (18) and a recirculation pump (40); Four ports, namely: a first ERD inlet port 44 fluidly connected to the second feed flow path 12; a first ERD outlet port 46 suitable for supplying pressurized raw water to the recirculation loop 20 through the fourth junction 38; a second ERD inlet port 48 adapted to receive the pressurized concentrate stream from the recirculation loop 20 through the third junction 34; a second ERD outlet port 50 fluidly connected to the brine discharge line 52 and adapted to provide a reduced pressure concentrate stream to the brine discharge line 52; an energy recovery device (ERD) 42 including: providing a semi-batch ultrafiltration system 2 comprising: repeatedly switching between the first and second modes of operation; a first mode of operation is characterized by permitting flow between the first section 32′ of the return path 32 and the second section 32″ of the return path 32, and permitting concentrate fluid from the concentrate outlet 26 to mix with flow from the high-pressure pump 14 at the second junction 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; A process characterized by a second mode of operation: blocking flow between the first section 32' of the return path 32 and the second section 32'' of the return path 32; passing a portion of fluid from the raw water source 4 sequentially through the second supply 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 passing the concentrate fluid from the concentrate outlet 26 sequentially through 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 discharge line 52, and the brine discharge 68.

[0008] The advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its uses, reference should be made to the drawings which form a further part of this specification and to the accompanying descriptive matter which illustrates and describes one or more preferred embodiments of the invention. [Brief explanation of the drawings]

[0009] [Figure 1a] 1A-1D show configurations for two modes of operation (recirculation mode and flash mode) of a prior art semi-batch system including energy recovery. [Figure 1b] 1A-1D show configurations for two modes of operation (recirculation mode and flash mode) of a prior art semi-batch system including energy recovery. [Figure 2] FIG. 1 illustrates a pressure vessel assembly comprising multiple parallel vessels. [Figure 3a] 3a and 3b show an embodiment of the system of the present invention where the valves are configured to allow different flow paths for different operational steps: In Fig. 3a, a recirculation mode is enabled in which the concentrate fluid is recycled to the feed inlet of the pressure vessel assembly; [Figure 3b]3a and 3b show an embodiment of the system of the present invention where the valves are configured to allow different flow paths for different operational steps. In Fig. 3b, a recirculation mode is enabled in which the concentrate fluid is recycled to the feed inlet of the pressure vessel assembly. In Fig. 3b, liquid flow is simultaneously enabled through the ERD. [Figure 3c] 3c shows an embodiment of the system of the present invention where the valves are configured to allow different flow paths for different operational steps. In FIG. 3c, a flush mode is enabled where the concentrate fluid passes through the energy exchange unit and into the brine discharge. [Figure 4a] Steps corresponding to those in Figures 3a to 3c are shown. [Figure 4b] FIG. 4b shows an alternative embodiment of the system of the present invention, showing steps corresponding to those in FIGS. 3a-3c, but in which the flow of liquid (raw water) within the ERD is enabled by an internal bypass. [Figure 4c] Steps corresponding to those in Figures 3a to 3c are shown. [Figure 5a] 5a and 5b show another embodiment of the invention showing a three-way valve and flow recycle enabled to the supply tank. [Figure 5b] 5a and 5b show another embodiment of the invention showing a three-way valve and flow recycle enabled to the supply tank. [Figure 5c] 5a and 5b show another embodiment of the invention showing a three-way valve and flow recycle enabled to the supply tank. [Figure 6a] Steps corresponding to those in Figures 3a to 3c are shown. [Figure 6b] 6A-6C show steps corresponding to those in FIGS. 3a-3c, but depict an alternative embodiment of the system of the invention in which the flow of liquid (concentrate) within the energy exchange device (FIG. 6b) is enabled by an internal bypass. [Figure 6c]Steps corresponding to those in Figures 3a to 3c are shown. DETAILED DESCRIPTION OF THE INVENTION

[0010] Provided herein are systems and methods for operating a semi-batch ultrafiltration system that reduces energy consumption and allows for 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.

[0011] Referring now to the drawings, in which like reference numerals indicate corresponding structure throughout the figures, and particularly to FIG. 1a, there is shown a configuration corresponding to a prior art semi-batch system that operates part of the time in a recirculation (closed circuit) mode, in which concentrate from the ultrafiltration element is mixed with raw water and recycled to the ultrafiltration element. The system also operates part of the time in a flush mode (FIG. 1b), in which concentrate from the ultrafiltration element is directed to a brine discharge. FIG. 2 shows the pressure vessel assembly 22. Several embodiments of the system of the present invention are shown in FIGS. 3-6, which will be described in more detail below.

[0012] The semi-batch ultrafiltration system 2 of the present invention includes a raw water source 4 containing raw water to be treated. The source can be a pressurized source or a reservoir (e.g., a tank or rake). A supply line assembly 6 includes a first supply path 10 extending from the raw water source 4 to a high-pressure pump 14. The supply line assembly 6 also includes a second supply path 12 connecting with the ERD 42. The supply line assembly 6 includes a first junction 8 located within the first supply path 10 and connecting the first supply path 10 to the second supply path 12.

[0013] System 2 includes a pressure vessel assembly 22. Pressure vessel assembly 22 includes a feed inlet 24, a concentrate outlet 26, a permeate outlet 28, and at least one pressure vessel 23 housing a plurality of ultrafiltration elements 54. In some embodiments (not shown), pressure vessel assembly 22 may include two or more permeate outlets 28, with different qualities of permeate being removed from two or more ends of vessel 23 (see, e.g., U.S. Pat. No. 4,046,685). Pressure vessel assembly 22 must include at least one pressure vessel 23 and preferably includes multiple pressure vessels 23 arranged in series and / or parallel. While FIG. 2 illustrates pressure vessel assembly 22 with a one-dimensional array of vessels 23, two-dimensional arrays of parallel pressure vessels 23 are also common. Feed inlet 24 provides fluid to be treated to the plurality of vessels 23. Similarly, pressure vessel assembly 22 is configured such that permeate outlet 28 and concentrate outlet 26 receive permeate fluid and concentrate fluid, respectively, from the plurality of vessels 23.

[0014] The pressure vessel 23 contains multiple ultrafiltration elements 54 in series, preferably two to eight ultrafiltration elements 54 in series. The ultrafiltration elements ("membrane elements") are cartridges containing reverse osmosis (RO) or nanofiltration (NF) membranes. Most commonly, they take the form of spirally wound elements in which membrane sheets, feed spacers, and permeate spacers are each wound around a central permeate tube (see, e.g., U.S. Pat. No. 10,717,050). The feed spacer regions within each ultrafiltration element 54 allow feed flow from one end of the vessel to the other, connecting the feed inlet 24 and concentrate outlet 26 of the system. Similarly, within each vessel, the permeate tubes of multiple ultrafiltration elements 54 are joined and fluidly connected to the permeate outlet 28.

[0015] Continuing with reference to FIGS. 3a-3c, system 2 includes a recirculation loop 20 that allows the concentrate fluid from concentrate outlet 26 to be recirculated to feed inlet 24. Specifically, recirculation loop 20 includes a feed flow path through pressure vessel assembly 22 from feed inlet 24 to concentrate outlet 26. This feed flow path through pressure vessel assembly 22 may include simultaneous paths through multiple different vessels 23. Recirculation loop 20 further includes a return path 32 external to pressure vessel assembly 22 that is adapted to allow flow from concentrate outlet 26 to feed inlet 24. A first section 32' of return path 32 joins the concentrate outlet to a third junction 34, and a second section 32'' of return path 32 joins a fourth junction 38 to feed inlet 24. Second section 32'' includes a recirculation pump 40 and second junction 18. A second junction 18 in the recirculation loop 20 is connected downstream of the high-pressure pump 14 to provide fresh raw water to the recirculation loop 20 .

[0016] The semi-batch system of the present invention includes an energy recovery device (ERD) 42 for recovering energy from the pressurized concentrate stream during flash mode. Various energy recovery units are known, such as pressure exchange units, rotary vane units, and isobaric units (see, for example, EP 1,508,361 and U.S. Pat. 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 technologies can be described as positive displacement energy exchangers, including piston-based ERDs (such as Clark pumps, dual-work 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. The first ERD inlet port 44 is fluidly connected to the second feed flow path 12 to receive raw water. The second ERD inlet port 48 may be connected to the third junction 34 and is intended to receive a pressurized concentrate stream from the recirculation loop 20 during the flash mode. The first ERD outlet port 46 may be connected to the fourth junction 38 and is suitable for providing pressurized raw water to the recirculation loop 20 during the flash mode. The second ERD outlet port 50 is fluidly connected to the brine discharge line 52 and provides a reduced pressure concentrate stream to the discharge line 52. During the flash 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.

[0017] The system 2 may be repeatedly switched between a first or recirculation mode of operation and a second or flush mode of operation. The term "repeated," as used herein, refers to an action occurring more than once in a defined period of time, preferably more than once every three hours, and more preferably once every hour. The exact duration of the repetition period is determined by the length of time the system 2 operates in the recirculation mode. One skilled in the art can determine the operating time in the recirculation mode by modeling the pressure vessel assembly 22 to predict, for example, a target change in concentration within the ultrafiltration system. Alternatively, a system output, such as a target conductivity of the brine, may be monitored.

[0018] Referring now to FIG. 4b, in some ERDs, such as pressure recovery (PE) unit 42, an internal bypass allows some fluid to flow between first ERD inlet port 44 and second ERD outlet port 50, which can become the majority of the flow within the ERD when flow through first ERD outlet port 46 and / or second ERD inlet port 48 is blocked. The internal bypass is shown in FIG. 4b as a curved, broken arrow connecting second feed flow path 12 to brine discharge line 52 through ports 44 and 50. Commercially available ERDs with pressure exchangers available from Energy Recovery are similar to devices described in Hague (U.S. Pat. No. 7,306,437). Hague describes a system in which flow from a low-pressure inlet port has an inlet tangential velocity vector that imparts rotational momentum to the rotor rather than using a motor. As a result of the design, when the high-pressure port is blocked by a valve or other means and flow is introduced through the low-pressure inlet port, rotor rotation is induced and discharged to the low-pressure outlet port.

[0019] For each of the embodiments of Figures 3-6, the first valve assembly 36 can be configured to provide separate flow paths that allow multiple modes of operation, including at least a recirculation step and a flushing step, i.e., 1) FIGS. 3a-3b, 4a-4b, 5a-5b, and 6a-6b all illustrate a portion of a recirculation step in which flow is permitted between a first section 32′ of return path 32 and a second section 32″ of return path 32. In this step, concentrate fluid from concentrate outlet 26 is mixed with the raw water stream from high-pressure pump 14 at second junction 18, and the combined stream is delivered to pressure vessel inlet 24. In preferred embodiments, system 2 operates in this recirculation step at least 50%, more preferably 70%, and more preferably 90% of the time. During this recirculation step, permeate fluid having a lower concentration than the feed is removed from system 2 via outlet path 30, thereby increasing the concentration of the fluid in recirculation loop 20 over time. As shown in the valve configurations of FIGS. 3b, 4b, 5b, and 6b, liquid flows through ERD 42 during at least a portion of the recirculation step. In some embodiments, as shown in Figures 3b, 4b, and 5b, the recirculation step may further include operating a low-pressure pump 60 to provide a flow of raw water through at least a portion of the saltwater discharge line 52. 2) Figures 3c, 4c, 5c, and 6c illustrate a flushing step in which flow between the first section 32' of the return path 32 and the second section 32'' of the return path 32 is blocked. In the flushing step, fresh raw water is provided to the recirculation loop 20, and the concentrate fluid in the recirculation loop 20 is removed from the system 2. To provide the flush while recovering the energy (pressure) originally present in the recirculation loop 20, two fluid streams pass through the ERD 42. A portion of the fluid from the raw water source 4 is passed sequentially through the second supply 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. Simultaneously, the concentrate fluid from the concentrate outlet 26 is passed sequentially 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 discharge line 52, and the brine discharge 68. Preferably, the system operates in the flushing step less than 50% of the time.

[0020] During the two portions of the recirculation step shown in Figures 3a and 3b, the first valve assembly 36 blocks the flow of concentrate fluid from the concentrate outlet 26 to the ERD unit 42. However, in a preferred embodiment of the recirculation step, a portion of the fluid from the raw water source 4 is allowed to pass through the ERD 42, as shown in Figure 3b. It is also preferable that this portion can be recovered. In the system of Figures 3-5, a recovery path 64 allows flow from the fifth junction 62 located in the brine discharge line 52 to be directed to either a) the raw water source 4 or b) a sixth junction 66 located in the first supply path 10.

[0021] 3, 4, and 5, a second set of valves (second valve assembly 56) is adapted to direct flow from the brine discharge line 52 to either the brine outlet 68 or the return path 64. In its simplest embodiment, the second valve assembly 56 may consist of a single three-way valve located at the junction 62 (FIG. 5). Alternatively, the second valve assembly 56 may comprise two-way valves (56', 56'') located in both the return path 64 and the brine discharge line 52 (see FIGS. 3 and 4).

[0022] 3, 4, and 5 are preferably adapted to simultaneously prevent concentrate fluid from the concentrate outlet 26 from entering the ERD 42 and allow circulation of liquid (raw water) through the ERD unit 42. A recovery circuit 58 for circulating raw water comprises or consists of a first portion from the second ERD outlet port 50 to the first ERD inlet port 44, which includes a recovery path 64, and a second portion extending within the ERD 42 and allowing raw water to pass from the first energy recovery unit inlet port 44 to the second energy recovery unit outlet port 50, optionally via a bypass line 92 and a valve 94. The recovery circuit 58 comprises the second supply path 12, the first ERD inlet port 44, the second ERD outlet port 50, a portion of the brine discharge line 52, the recovery path 64, and a portion of the first supply path 10. In these embodiments, at least one low-pressure pump 60 is located in the recovery circuit 58, preferably downstream of the fifth junction 66 and upstream of the first ERD inlet port 44. The second valve assembly 56 includes at least one isolation valve 56'' located in the recovery circuit 58.

[0023] In preferred embodiments, such as those shown in Figures 3b and 4b, a 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 sequentially generates a flow of raw water through the first ERD port 44, the second ERD outlet port 50, and the brine discharge line 52 to the second supply path 12. The low-pressure pump 60 enables flow in the recovery circuit 58.

[0024] 3a-3c, a flow path external to the ERD 42 may be used to enable fluid flow from the first ERD inlet port 44 to the second ERD outlet port 50. In the embodiment shown, a bypass line 92 having a bypass valve 94 is adapted to provide a conduit for flow between bypass junctions (90, 96) connecting the first ERD outlet port 46 to the second ERD inlet port 48. When the bypass valve 94 is opened, the low-pressure pump 60 may induce mechanical movement within the ERD 42, causing raw water to flow from the first ERD inlet port 44 to the second ERD outlet port 50, passing 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.

[0025] Figure 3a shows the valve positions for the configuration when the system is in a first mode of operation, in which concentrate is recycled to the feed of pressure vessel 23. Valve 36' is open, while the rest of the valves in the first valve assembly (36", 36'") are closed. (Valves 56' and 56" are also shown as closed.)

[0026] As shown in FIG. 3b, before switching to the second mode of operation, the system may be configured to allow fluid (raw water) to flow through the ERD, in this case the rotary pressure exchange (PE) unit 42. This practice lubricates the internal components of the PE unit and may initiate spinning of the internal rotor (see U.S. Pat. No. 7,306,437). FIG. 3b illustrates valve positions in the second valve assembly 56 that allow flow to the ERD and recovery of the raw water discharged from the second ERD outlet port 50. Valve 56'' is open and valve 56 is closed, allowing at least a portion of the raw water flow from junction 8 to pass through the ERD 42 and return to junction 8. The illustrated recovery circuit 58 includes the second supply path 12, the first ERD inlet port 44, the second outlet port 50, a portion of the brine discharge line 52, a recovery path 64, and a portion of the first supply path 10. (Recovery circuit 58 may be designed to bypass first supply path 10.) In these embodiments, low-pressure pump 60 is located within recovery circuit 58, preferably downstream of fifth junction 66 and upstream of first ERD inlet port 44. Within recovery circuit 58, the embodiment shown in FIG. 3b also includes a portion external to ERD 42, including bypass line 92.

[0027] 3b, the pump and valve in bypass line 92 allow controlled flow of fluid through the ERD. Closed valve 56' prevents flow between second ERD outlet port 50 and brine outlet 68 during at least the majority of the time that liquid flows through pressure exchange device 42 in the recirculation step. Preferably, the total flow rate of liquid through the PE during the first mode exceeds at least twice the flow of liquid to brine outlet 68 during the same period.

[0028] FIG. 3c illustrates a flush or purge step, and the system preferably enters its second mode of operation once the ERD 42 rotor has spun. The diagram shows that valves 36", 36"', and 56' are open, while valves 56" and 36' are closed. In the second mode of operation, energy is exchanged from the high-pressure concentrate entering the second ERD inlet port 48 to the fluid exiting the ERD 42 at the first ERD outlet port 46. Simultaneously, low-pressure fluid passing through the brine discharge line 52 is sent to discharge 68. This allows high-pressure feed flow to the recirculation loop, replacing the flow from the concentrate outlet 26 sent to the brine discharge 68.

[0029] The first set of valves (first valve assembly 36) allows switching between a recirculation mode and a flushing mode of operation. This valve assembly 36 is suitable for controlling flow between the second ERD inlet port 48 and the first section 32′ of the return path 32, between the first section 32′ of the return path 32 and the second section 32″ of the return path 32, and between the first ERD outlet port 46 and the second section 32″ of the return path 32. In FIGS. 3 and 4, the valve assemblies 36 for these respective purposes are identified as 36″, 36′, and 36′″. In some embodiments, the valves 36′″ can be non-return valves (check valves).

[0030] 4a-4c illustrate another embodiment of the system 2 of the present invention, in which the system has a flow path internal to the ERD 42 that can enable fluid flow from the first ERD inlet port 44 to the second ERD outlet port 50. As indicated by the dashed lines in the figures, flow from the first ERD inlet port 44 to the second ERD outlet port 50 through the pressure exchange unit 42 is created by an internal bypass. The first valve assembly 36 in FIG. 4a is configured to enable recirculation of feed water through the pressure vessel assembly 22. In FIG. 4b, the first and second valve assemblies (36, 56) still enable this recirculation of the concentrate fluid from the concentrate outlet 26 to the feed inlet 24 of the pressure vessel assembly 22. However, the configuration of the first and second valve assemblies (36, 56) also supports liquid (raw water) flowing through the ERD 42 from the first ERD inlet port 44 to the second ERD outlet port 50, suitable for initiating rotational movement within the ERD 42. Similar to Figure 3b, the configuration in Figure 4b also illustrates a preferred embodiment in which raw water passing through ERD 42 is recovered. (This configuration allows at least a portion of the raw water from junction 8 to pass through ERD 42 and return to junction 8 via recovery circuit 58.) Finally, Figure 4c illustrates a flush step.

[0031] The process shown in Figure 4a illustrates one portion of a recirculation step, in which flow through both the first ERD inlet port 44 and the second ERD outlet port 50 is blocked. Compared to Figure 4b, the closed valve 56 in Figure 4a blocks flow through the ERD inlet port 44. The other three ERD ports are connected only to the closed path, thereby blocking flow through the ERD inlet port 44.

[0032] The processes shown in FIGS. 4b and 5b are also part of a recirculation step, in which liquid flows through only two of the ERD's four ports. A small flow through a nominally closed valve may also be permitted, but it is intended that liquid primarily flow through only two of the ERD's four ports. In both cases, a suitable valve (56' or 56''') is present to block flow between the second ERD outlet port 50 and the brine outlet 68, preventing this flow to the brine outlet 68 during at least the majority of the time during the recirculation step in which liquid flows through the pressure exchange device 42. Preferably, the total flow rate of liquid through the ERD during the first mode exceeds at least twice the flow of liquid to the brine outlet 68 during the same period.

[0033] During the recirculation step, when passing liquid through the ERD, it is preferable that there be no loss of fluid from the brine outlet 68. In Figures 3, 4, and 5, the brine outlet valve (56' or 56''') located in the brine outlet line 52 between the second ERD outlet port 50 and the brine outlet 68 prevents this loss.

[0034] As shown in FIG. 5, the three-way valve 36'''' or 56''' in the first or second valve assembly (36, 56) can be replaced with the function of two (two-way) valves. In FIGS. 3a-3c and 4a-4c, flow from the first section 32' of the return path 32 can be directed to either the second section 32'' of the return path 32 or the second ERD inlet port 48. Similarly, the three-way valve 36'''' in the valve assembly 36 in FIG. 5 also allows for a similar selection. FIG. 5 also shows a three-way valve 56''' replacing the two (two-way) valves (56', 56'') shown in FIGS. 3 and 4. Finally, FIG. 5 illustrates the possibility of returning raw water from the ERD 42 to a reservoir / tank.

[0035] Referring now to FIGS. 6a and 6b, a first mode of operation is shown. This configuration includes one or more energy recovery devices in the form of pressure exchangers, where flow from a high-pressure concentrate inlet can induce rotor rotation. As shown in FIG. 6a, a significant portion, potentially all, of the flow bypasses the ERD 42 through a control valve 37 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 at which liquid flows through 42. An open or largely open control valve can be implemented for most of the time (first time interval) of the first mode of operation. As shown in FIG. 6b, reducing 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 implemented during a portion of the first mode of operation (second time interval). In a preferred embodiment, rotational momentum may be imparted to the rotor within the ERD 42 prior to initiating the second mode of operation. In another preferred embodiment, the rotor spins throughout the entire first mode. In yet another preferred embodiment, the rotor spins at a faster rate during the second time interval compared to the first time interval of the first mode. By maintaining valves 39 and 57 in a closed position, flow through the first ERD inlet port 44 and the second ERD outlet port 50 may be prevented during at least a portion, if not all, of the first mode. Preferably, liquid flows primarily through only the other two ports (48, 46) of the ERD during the first mode. Preferably, the first mode is divided into a first time interval and a second time interval, the second time interval being of shorter duration than the first time interval, but with a greater volume of liquid flowing through the ERD 42 during the second time interval. The portion of time that the internal bypass is engaged in ERD 42 is desirably a short duration of the first mode of operation, preferably less than 50% of the duration of the first mode of operation, more preferably less than 25% of the duration of the first mode of operation, more preferably less than 10% of the duration of the first mode of operation.

[0036] 6a and 6b both show the discharge valve 57 closed. Flow between the second ERD outlet port 50 and the brine discharge 68 is preferably prevented at least most of the time during the first mode when liquid flows through the ERD 42. Preferably, the flow of liquid through the ERD 42 during the first mode exceeds by at least two times the flow of liquid to the brine discharge 68 during the same period.

[0037] Referring to FIG. 6c, during the second mode of operation, control valve 37 is closed, directing all of the flow in loop 32 to second ERD inlet port 48 and out second ERD outlet port 50. Valve 39 is opened to establish a fluid path for raw water to ERD inlet port 44. Discharge valve 57 is opened to allow the concentrate flow to pass between second ERD outlet port 50 and brine discharge 68. A first fluid stream entering first ERD inlet port 44 flows to first ERD outlet port 46. A second fluid stream entering second ERD inlet port 48 flows to second ERD outlet port 50. ERD 42 transfers pressure from the second fluid stream to the first fluid stream. The duration of the second mode of operation is typically less than 100%, more preferably less than 75%, more preferably less than 50%, and more preferably less than 25% of the duration of the first mode of operation.

[0038] To return to the first mode of operation, control valve 37 is opened and valves 39 and 57 are closed to re-establish the recirculation loop.

[0039] All embodiments of system 2 include a control unit. Those skilled in the art will be able to select an appropriate 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 suitable for positioning individual valves (e.g., 37, 39, 57, 94) and valve assemblies (36, 56) and enabling switching between different operating modes. Preferably, the control unit also receives measurements, such as flow rate, temperature, conductivity, turbidity, and pressure, from sensors located at various locations within system 2. While the control unit may switch between operating modes based only on specific time intervals, preferably, the control unit uses measurements from the sensors to determine when to switch between different operating modes. The control unit also preferably engages low-pressure pump 60, which preferably generates a flow of liquid through ERD 42 during at least a portion of the recirculation step. In some embodiments, liquid flows through ERD 42 during a portion of the recirculation step immediately prior to switching to the flushing step. In other embodiments, the liquid flows through the recovery circuit 58 during at least the majority of the recirculation step.

[0040] The present invention includes a process for operating the above-described system, including the various optional embodiments and combinations thereof mentioned. The process includes repeatedly switching between a recirculation step and a flushing step. In some embodiments, the recirculation step may further include a first time interval during which liquid is prevented from flowing through the pressure exchange unit 42 and a second time interval during which liquid is allowed to flow through the pressure exchange unit 42 before switching to the flushing step.

[0041] In some embodiments, an ERD associated with a semi-batch ultrafiltration system may include multiple ERDs configured in parallel so that similar port types are joined together and function as one. In some embodiments, the same ERD may be associated with two or more semi-batch ultrafiltration systems. Preferably, operation of the different semi-batch ultrafiltration systems is staged so that each ERD is used in only one flush step at a time.

[0042] While certain preferred embodiments of the present invention have been described and specifically exemplified above, it is not intended that the present invention be limited to such embodiments. Rather, while many of the features and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, it is to be understood that the present disclosure is merely illustrative, and that changes may be made in details, particularly with respect to the shape, size, and arrangement of parts, within the principles of the invention to the fullest extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. 1. A process for treating raw water, comprising:

1. A semi-batch ultrafiltration system 2 comprising: Raw water source 4 and a supply line assembly (6) including a first supply line (10) extending from the raw water source (4) to a high-pressure pump (14) and a second supply line (12); a first junction (8) located within the first supply line (10) and connecting the first supply line (10) to the second supply line (12); a pressure vessel assembly 22 including 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) including a second junction (18) connected to the high pressure pump (14), the recirculation loop (20) further including a feed flow path through the pressure vessel assembly (22) from the feed inlet (24) to the concentrate outlet (26), and a return path (32) external to the pressure vessel assembly (22) suitable for permitting flow from the concentrate outlet (26) to the feed inlet (24), a first section (32') of the return path (32) joining the concentrate outlet (26) to a third junction (34), a second section (32'') of the return path (32) joining a fourth junction (38) to the feed inlet (24), the second section (32'') housing the second junction (18) and a recirculation pump (40); Four ports, namely: a first ERD inlet port 44 fluidly connected to the second feed flow path 12; a first ERD outlet port 46 suitable for supplying pressurized raw water to the recirculation loop 20 through the fourth junction 38; and a second ERD inlet port 48 adapted to receive a pressurized concentrate stream from the recirculation loop 20 through the third junction 34; a second ERD outlet port 50 fluidly connected to a brine discharge line 52 and adapted to provide a reduced pressure concentrate stream to said brine discharge line 52; an energy recovery device (ERD) 42 including: providing a semi-batch ultrafiltration system (2) comprising: repeatedly switching between the first and second modes of operation; the first mode of operation is characterized by permitting flow between the first section 32′ of the return path 32 and the second section 32″ of the return path 32, and permitting concentrate fluid from the concentrate outlet 26 to mix with flow from the high-pressure pump 14 at the second junction 18, such that a 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; the second mode of operation is characterized by blocking flow between the first section 32′ of the return path 32 and the second section 32″ of the return path 32; passing a portion of fluid from the raw water source 4 sequentially through the second supply 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 passing concentrate fluid from the concentrate outlet 26 sequentially through 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 discharge line 52, and the brine discharge 68.

2. 2. The process of claim 1, wherein flow between the second ERD outlet port and the saltwater discharge is prevented during at least a majority of the time in the first mode when liquid flows through the energy recovery device.

3. 3. The process of claim 1 or 2, wherein the total flow rate of liquid through the ERD during the first mode is at least twice the flow of liquid to the brine outlet 68 during the same period.

4. The process of any one of claims 1 to 3, wherein liquid flows primarily through only two of the four ports of the ERD during the first mode.

5. 5. The process of claim 1, wherein the first mode is divided into a first time interval and a second time interval, the second time interval being of shorter duration than the first time interval, and wherein a greater volume of liquid flows through the pressure exchange device during the second time interval.

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

7. 7. The process of any one of claims 1 to 6, wherein a control valve 37 is located in a section of the return path 32 connecting the third junction 34 and the fourth junction 38, and wherein the control valve 37 is adjusted to change the rate at which liquid flows through the ERD during the first mode.

8. The process of any one of claims 1 to 7, 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 process of any one of claims 1 to 8, wherein flow through the first ERD inlet port 44 and the second ERD outlet port 50 is prevented during at least a portion of the first mode.

10. The process of any one of claims 1 to 9, wherein a drain valve (57) is located in the brine drain line (52) between the second ERD outlet port (50) and a brine drain (68).

11. 11. The process of any one of claims 1 to 10, wherein the semi-batch ultrafiltration system 2 further comprises a return path 64 suitable for allowing flow from a fifth junction 62 located on the brine discharge line 52 to the raw water source 4 or to a sixth junction 66 located on the first supply path 10, wherein flow from the brine discharge line 52 is directed to the return path 64 during at least a portion of the first mode and to the discharge 68 during the second mode.

12. The process of any one of claims 1 to 11, wherein the ERD comprises an isobaric energy exchanger.

13. The process of any one of claims 1 to 11, wherein the ERD comprises a pressure exchanger (PE).

14. The process of any one of claims 1 to 11, wherein the ERD comprises a positive displacement energy exchanger.

15. The process of claim 13 , wherein the PE includes a rotor, and the rotor spins throughout the first mode.

16. The process of claim 13 , wherein the PE includes a rotor, the rotor spinning at a faster speed during the second time interval.

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