Use of pressure recovery devices as reinjection pumps for brine concentration nanofiltration systems

Abstract

Embodiments disclosed herein are nanofiltration membranes, systems, and methods to handle high concentration brine streams while minimizing the corrosive effects on the pumps used to move these high concentration brine streams. In an embodiment, a brine concentration nanofiltration system includes one or more first sets of nanofiltration elements, one or more second sets nanofiltration elements, and one or more pressure recovery devices. A pressure recovery device of the one or more pressure recovery devices includes a low-pressure side through which at least a portion of a filter permeate flow from the one or more second sets of nanofiltration elements is fed and a high-pressure side through which at least a portion of a process feed brine from a high-pressure process feed pump is fed. Outputs of the pressure recovery device include a high-pressure filter permeate output and a low-pressure feed fluid output.

Description

USE OF PRESSURE RECOVERY DEVICES AS REINJECTION PUMPS FOR BRINE CONCENTRATION NANOFILTRATION SYSTEMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 594.638 titled ‘USE OF PRESSURE RECOVERY DEVICES AS REINJECTION PUMPS FOR BRINE CONCENTRATION NANOFILTRATION SYSTEMS’’ filed on October 31, 2023, the disclosure of which is incorporated herein, in its entirety, by this reference.BACKGROUND

[0002] Demand by various industries has grown in recent years for systems that concentrate salt brine to near saturation while limiting energy usage and associated costs requiring less energy' than evaporation. Examples of such industries include, but are not limited to, chlor-alkali and zero-liquid-discharge water treatment industries.

[0003] Salt concentration by evaporation is a common process but is energy intensive. Salt concentration by reverse osmosis is, in general, a relatively low energy process, but is limited in the salinity achievable. A method for membrane concentration of brines to high salinities is described in the U.S. Published Patent Application No. 2015 / 0014248 by Herron et.al, which is incorporated herein, in its entirety, by this reference. This method uses high pressure nanofiltration membranes, which allows a limited amount of salt to permeate the membranes, creating a saline permeate. High pressure nanofiltration is ty pically performed at a pressure between 40 bar and 80 bar. Filtration retentate with osmotic pressures well above the applied pressures are achievable because water flows from the feed side through the membrane to the permeate side until the difference in osmotic pressures between the feed and the permeate equals the applied pressure. By passing the filter retentate through a series of nanofiltration membranes, water can be extracted from the feed to achieve total dissolved solids (TDS) levels in the retentate near saturation. The permeate will have lower TDS than the feed and can be dewatered by reverse osmosis or added back into the nanofiltration feed.

[0004] Additionally, International Patent Application PCT / 2022 / 016927, published as WO / 2022 / 178217, describes that when concentrating to high salinities, it is advantageous to reinject later stage permeate back into the feed at points where the feed and permeate salinities are similar. The brine is sequentially processed through a multitude of filter elements. The retentate brine concentration increases in each successive element and thepermeate from each element also increases in concentration. Typically, it is convenient to reinject the permeate from later filtration stages at locations having similar salinity to the salinity in the retentate process brine stream. The overall process efficiency generally increases with the number of permeate reinjection points.

[0005] Reinjection of permeate back into the brine process stream utilizes individual pumps for each reinjection point, which may cause one or more of the following difficulties:• Each additional reinjection pump adds to the cost and complexity of the system.• The reinjection pumps are typically multistage centrifugal pumps that are much smaller than the main feed pump which, due to the nature of centrifugal pumps, leads to markedly lower efficiencies.• The salinities of the later stage reinjection brines are high. For example, if NaCl is being concentrated to a salinity of 260,000 mg / L then some reinjection lines may have a salinity of more than 200,000 mg / L operating at temperatures as high as 40°C. This is a very corrosive environment even for the super-duplex stainless steels commonly used in such pumps and can result in reduced performance / efficiency, increased noise and vibration, overheating, contamination of the salts, increased repairs and downtime, increased energy usage, and increased running and replacement costs.SUMMARY

[0006] Embodiments disclosed herein are nanofiltration membranes and systems, and related methods, to handle high concentration brine streams while minimizing the corrosive effects on the pumps used to move these high concentration brine streams. In an embodiment, a brine concentration nanofiltration system includes one or more first sets of nanofiltration elements, one or more second sets of nanofiltration elements, and one or more pressure recover}' devices, a pressure recovery device of the one or more pressure recovery devices including a low-pressure side through which at least a portion of a filter permeate flow from a set of nanofiltration elements of the one or more second sets of nanofiltration elements is fed and a high-pressure side through which at least a portion of a process feed brine from a high-pressure process feed pump is fed, wherein outputs of the pressure recovery device include a high-pressure filter permeate output and a low-pressure feed fluid output.

[0007] In some embodiments of the brine concentration nanofiltration system, the high- pressure filter permeate output is reinjected into nanofiltration retentate process brine from a set of nanofiltration elements of the one or more first sets of nanofiltration elements at a point where the high-pressure filter permeate output has a similar salinity as the nanofiltration retentate process brine. In some embodiments of the brine concentration nanofiltration system, a permeate outlet pressure of the high-pressure filter permeate output of the pressure recovery device is higher than a process brine pressure of the nanofiltration retentate process brine where the high-pressure filter permeate is being reinjected. In some embodiments, the brine concentration nanofiltration system includes a system reinjection port and a control valve between the high-pressure filter permeate output and the system reinjection port, the control valve being configured to control the filter permeate flow from the high-pressure filter permeate output, the system reinjection port positioned for reinjection of the high-pressure filter permeate output into the nanofiltration retentate process brine.

[0008] In some embodiments of the brine concentration nanofiltration system, the one or more second sets of nanofiltration elements include a plurality of sets of nanofiltration elements and the high-pressure filter permeate output is reinjected into nanofiltration retentate process brine from an additional set of nanofiltration elements of the plurality of second sets of nanofiltration elements different from the set of nanofiltration elements at a point where the high-pressure filter permeate output has a similar salinity as the nanofiltration retentate process brine. A permeate outlet pressure of the high-pressure filter permeate output of the pressure recovery device may be higher than a process brine pressure of the nanofiltration retentate process brine where the high-pressure filter permeate is being reinjected. The system also may include a system reinjection port and a control valve between the high-pressure filter permeate output and the system reinjection port, the control valve being configured to control the filter permeate flow from the high-pressure filter permeate output, the system reinjection port positioned for reinjection of the high- pressure filter permeate output into the nanofiltration retentate process brine.

[0009] In some embodiments of the brine concentration nanofiltration system, the one or more pressure recovery devices are made entirely from one or more brine contact materials more resistant to corrosion than stainless steel. In some embodiments of the brine concentration nanofiltration system, the one or more brine contact materials include one or more of ceramic, fiberglass, titanium, or plastic materials. In some embodiments of the brine concentration nanofiltration system, the process feed brine includes seawater.

[0010] In some embodiments of the brine concentration nanofiltration system, monovalent ions are concentrated to high salinities including salinities up to 90% of saturation in the nanofiltration retentate process brine. In some embodiments of the brine concentration nanofiltration system, divalent ions are concentrated to high salinities including salinities up to 90% of saturation in the nanofiltration retentate process brine.

[0011] In an embodiment, a method for reinjecting filter permeate of a nanofiltration brine concentration system by use of one or more pressure recovery devices is disclosed. The method includes supplying high-pressure fluid to a pressure recovery device of the one or more pressure recovery devices, the high-pressure fluid being supplied from a main process feed pump of the nanofiltration brine concentration system. The method also includes transferring energy from the high-pressure fluid from the main process feed pump to a low-pressure filter permeate to create high-pressure filter permeate where outputs of the pressure recovery' device are a high-pressure filter permeate output and a low-pressure feed fluid output. The method also includes reinjecting portions of the high-pressure filter permeate into a nanofiltration retentate process brine stream at locations where salinity’ of the high-pressure filter permeate is similar to the nanofiltration retentate process brine stream.

[0012] In some embodiments of the method, a pressure of the high-pressure filter permeate leaving the pressure recovery device is higher than a pressure of a nanofiltration retentate process brine at a point of reinjection. In some embodiments of the method, the one or more pressure recovery' devices are made entirely from one or more brine contact materials more resistant to corrosion than stainless steel. In some embodiments of the method, the one or more brine contact materials more resistant to corrosion include one or more of ceramic, fiberglass, titanium, or plastic materials.

[0013] In some embodiments of the method, permeate flow from the high-pressure filter permeate output of the pressure recovery device is controlled by a control valve between the high-pressure filter permeate output and a system reinjection port. In some embodiments of the method, the process feed brine is seawater. In some embodiments of the method, the high-pressure fluid from the main process feed pump includes seawater.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings illustrate one or more embodiments of the present disclosure, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings.

[0015] FIG. 1 is a block diagram of a brine concentration nanofiltration systemcontaining pressure recovery devices, according to an embodiment.

[0016] FIG. 1A is a block diagram of a sea water reverse osmosis system of the prior art containing a pressure recovery device.

[0017] FIG. 2 is a isometric illustration of a spinning cylinder of a rotating pressure recovery7device, according to an embodiment.

[0018] FIG. 3 is an end view of the spinning cylinder of FIG. 2.

[0019] FIG. 4 is a simplified isometric view of a cylinder housing containing cylinder housing end caps enclosing the spinning cylinder of FIG. 2.

[0020] FIG. 5 is an end view of one of the cylinder housing end caps of FIG. 4.

[0021] FIG. 6 is a section view taken along section line C-C in FIG. 5.DETAILED DESCRIPTION

[0022] Embodiments of brine concentration nanofiltration systems described herein may include one or more pressure recovery devices replacing the multistage centrifugal pumps or other pumps used for reinjection of high salinity' permeate into the process brine stream in brine concentration nanofiltration systems. The process brine stream includes the feed fluid fed to the system by the main high-pressure feed pump, the retentate from each successive membrane element, and the pressurized permeate after reinjection. The one or more pressure recovery' devices may include at least a low-pressure side and a high-pressure feed. For simplicity, the sy stem feed solution may be referred to as seawater through some of the detailed description, however, this is not intended to be limiting and other brine streams may be used as an alternative to seawater. The permeate may be fed to the low- pressure side of the pressure recovery device and a portion of the flow from the large process feed pump may be used as the high-pressure feed to the one or more pressure recovery devices. A drawing of a system for making 250,000 TDS NaCl brine from seawater is shown in FIG. 1.

[0023] Pressure recovery devices (e.g., pressure exchangers) are commercially available devices. Essentially, a pressure exchanger transfers pressure from a high-pressure fluid to a low-pressure fluid without allowing the fluids to mix. As shown in FIG. 1A, pressure exchangers are widely used in conventional, prior art seawater RO desalination systems to transfer the pressure from the concentrated brine into the seawater reverse osmosis (SWRO) feed, which can reduce the required pump power by 50%. There are three general designs for pressure exchangers. The first is the spinning cylinder ty pe like the PX* pressure exchanger made by Energy Recovery, Inc. These pressure exchanges have a rapidly rotating ceramic cylinder which has numerous channels running in the axialdirection. The ceramic cylinder spins inside a close-fitting, cylindrical, fiberglass cavity. The high-pressure seawater and low-pressure seawater ports are at the same end of the cylinder. The high-pressure permeate and low-pressure permeate are both at the opposite end of the cylinder. The clearance between the cylinder and housing ensures that there is minimal to no leakage between the high-pressure seawater feed solution and low-pressure seawater feed solution and there is minimal to no leakage between the high-pressure permeate and the low-pressure permeate. The two high-pressure ports are oriented so they are fluidly connected by the passages in the cylinder. The two low-pressure ports are oriented so they are fluidly connected by the passages in the cylinder. The high-pressure seawater is at a slightly higher pressure than the high-pressure permeate, and the low- pressure seawater is at a slightly lower pressure than the low-pressure permeate. The slight pressure difference causes pressurized seawater to flow through the cylinder toward the high-pressure permeate port. However, before the seawater reaches the exit of the channel, the rotation of the cylinder brings it into contact with the low-pressure port. Since the low- pressure permeate is at a higher pressure than the low-pressure seawater, the flow reverses and the cylinder fills with low-pressure permeate. Continued rotation of the cylinder repeats the process with the net effect of pressurizing the permeate while depressurizing the seawater. The rotation of the cylinder is induced by the fluid flow.

[0024] The second style of pressure exchanger device used in conventional seawater RO desalination is the dual cylinder type like the DWEER™ made by Flowserve Corporation. In this design, there are two cylinders with a moveable piston in each cylinder. One cylinder is the low-pressure cylinder and has low-pressure seawater on one side of the piston and low-pressure permeate on the other side of the piston. The other cylinder is the high-pressure cylinder and has high-pressure permeate on one side of the piston and high- pressure seawater on the other side of the piston. The high-pressure permeate starts as low- pressure permeate and is converted to high-pressure permeate when the piston is exposed to the high-pressure seawater. A valve control system ensures at all times low-pressure permeate is pushing the movable piston along the inside of one of the cylinders, forcing the lower pressure seawater out of the pressure exchanger and. at the same time, the other cylinder has high-pressure seawater forcing the piston to move in the opposite direction pressurizing the low-pressure permeate to become high-pressure permeate and forcing the high-pressure permeate out. When the pistons reach the end of the cylinders, the valving changes so that the high-pressure cylinders becomes the low-pressure cylinder and the low- pressure cylinder becomes the high pressure cylinder, and the flows reverse. High-pressureseawater and low-pressure permeate continuously enter while low-pressure seawater and high-pressure permeate continuously exit the pressure exchanger.

[0025] The third style of pressure exchanger uses a turbine or pelton wheel to recover energy from the high-pressure brine. The work done on the turbine by the high-pressure brine is used to drive a centrifugal pump to pressurize seawater. The turbine and pelton wheel energy recovery devices are similar in design to centrifugal pumps and have the same problems with corrosion so they are not desirable for use as a ven' high salinity reinjection feed pump.

[0026] Pressure exchangers used in conventional seawater RO desalination process, as shown in FIG. 1A. utilize the pressurized retentate stream to pressurize the low-pressure seawater feed stream. In the proposed system, the pressure exchangers are used as reinjection pumps, in place of conventionally used multistage centrifugal pumps, to pump nanofiltration permeate into locations of the process retentate brine stream where the salinities of the permeate and process brine are similar. For the rotating cylinder ty pe pressure exchanger, low-pressure nanofiltration permeate is input into the pressure exchanger and high-pressure seawater is input into the opposite side of the pressure exchanger. The high-pressure seawater causes the cylinder to rotate thereby transferring energy' to, and increasing the pressure of, the nanofiltration permeate passing through the cylinder. This increase in nanofiltration permeate pressure is such that a multistage centrifugal pump or pumps or similar pump or pumps is no longer required to reinject the nanofiltration permeate stream back into the process brine stream. The process brine stream includes the feed fluid fed to the system by the main high-pressure feed pump, the retentate from each successive membrane element, and the pressurized permeate after reinjection. For the dual cylinder type pressure exchanger, one cylinder is the low-pressure cylinder and has low-pressure nanofiltration permeate on one side of the piston and low-pressure seawater on the other side of the piston. The other cylinder is the high-pressure cylinder and has high-pressure seawater on one side of the piston and high-pressure nanofiltration permeate on the other side of the piston. The high-pressure nanofiltration permeate starts as low-pressure nanofiltration permeate and is converted to high-pressure nanofiltration permeate when the piston is exposed to the high-pressure seawater.

[0027] One of the motivations for the use of pressure exchangers as the reinjection feed pumps is corrosion resistance. Multistage centrifugal pumps for desalination are cast from specialty alloys and precision machined to exacting tolerances. The issue with using these pumps as reinjection pumps is the salinity of reinjection brines is very' high. Super-duplexpumps are widely used in seawater desalination. However, in seawater desalination the pumps operate at salinities of around 35,000 TDS. In contrast, the salinity of reinjection brines can be over 200,000 TDS. Even for super-duplex stainless steel this causes problems with pitting and crevice corrosion that may limit the life of the pumps.

[0028] Casting and machining multistage centrifugal pumps from more corrosion resistant materials such as titanium would be an extremely expensive undertaking and likely not economically feasible.

[0029] The use of a spinning ceramic cylinder style pressure exchanger may be beneficial because the housing and cylinder may be all fiberglass composite and / or ceramic and / or titanium and / or plastic. Likewise, the dual cylinder design may utilize a plastic or other non-corrodible or minimally corrodible piston material moving in a fiberglass composite housing or other non-corrodible or minimally corrodible material housing. There are metallic valves and pipe connections associated with the spinning cylinder and dual cylinder designs, but these components are commercially available manufactured from titanium.

[0030] One or more embodiments of the systems disclosed herein include a single large high-pressure seawater input pump and pressure exchangers instead of a slightly smaller high-pressure seawater input pump and several small reinjection pumps. The overall energy7efficiency of the system is improved as one large pump combined with the higher than 95% efficient pressure exchangers have a higher mechanical efficiency than a slightly smaller pump combined with multiple smaller reinjection pumps.

[0031] The efficiency of the overall brine concentration process may also be improved by increasing the number of reinjection points as this minimizes the amount of mixing between brine streams of differing concentration. However, increasing the number of permeate injection points using multiple small pumps and drivers rapidly increases the cost and complexity7of the system. Using pressure exchangers to accomplish the reinjection may reduce these costs, allowing for more reinjection points and higher overall process efficiency.

[0032] Another advantage of the use of pressure recovery devices as reinjection pumps for brine concentration nanofiltration systems is they do not require pressure boosting pumps at the high-pressure outlet of the device. The high-pressure inlet of the device is at the system feed pressure, which is higher than the pressure of the system at the reinjection point. Pressure drops induced by the energy recovery device are smaller than the pressure loss between the system process brine high-pressure feed and the reinjection point, so thepressure recovery' device operation can be controlled by a control valve rather than a booster pump. This is a cost savings and is also more corrosion resistant.

[0033] In many embodiments, a brine concentration nanofiltration system includes one or more first sets of nanofiltration elements and one or more second sets of nanofiltration elements. As described in greater detail below, permeate from the one or more first sets of nanofiltration elements may be directed to a feed tank, while permeate from the one or more second sets of nanofiltration elements may be passed to one or more tanks to be pressurized with one or more pressure recovery devices and reinjected into the feed flow upstream of one of the one or more first sets of nanofiltration elements or a different one of the one or more second sets of nanofiltration elements. A process-flow diagram of an example brine concentration nanofiltration system with pressure recovery devices is shown in FIG. 1. Feed brine 54 enters the system feed tank 10. Low-pressure process brine feed pump 11 and high-pressure process brine feed pump 12 work in tandem to pressurize the fluid from the feed tank 10 to high pressure, such as about 60 to about 80 bar. Most of the pressurized feed brine 13 passes through a series of seawater reverse osmosis (SWRO) elements 100. The permeate 101 from the SWRO elements 100 is desalinated water.

[0034] The fluid retentate 102 from SWRO elements 100 is passed on to a first set of nanofiltration (NF) elements 200. Fluid retentate 102 has an osmotic pressure of over about 60 bar and the permeability of the NF membrane 200 is selected so that the flux is appropriate for spiral-wound NF elements, such as about 5 to about 25 Imh. The permeate 201 is far less saline than fluid retentate 102 used as feed and has an osmotic pressure around 60 bar less than the fluid retentate 202. Permeate 201 is returned to tank 10 to be fed back into the system.

[0035] The fluid retentate 202 from NF elements 200 is passed on to a second set of nanofiltration elements 300. Fluid retentate 202 has an osmotic pressure and a TDS level substantially higher than fluid retentate 102 (such as, for example, about 25,000 TDS to about 35,000 TDS higher for sodium chloride, depending on the number of NF elements) and the permeability of the NF membrane 300 is selected so that the flux is appropriate for spiral-wound NF elements, such as about 5 to about 25 Imh. The permeate 301 is far less saline than fluid retentate 202 used as feed and has an osmotic pressure around 60 bar less than the fluid retentate 302. Permeate 301 is returned to tank 10 to be fed back into the system.

[0036] The fluid retentate 302 from NF elements 300 is passed on to a third set of nanofiltration elements 400. Fluid retentate 302 has an osmotic pressure and a TDS levelsubstantially higher than fluid retentate 202 (such as, for example, about 25,000 TDS to about 35.000 TDS higher for sodium chloride, depending on the number of NF elements) and the permeability of the NF membrane 400 is selected so that the flux is appropriate for spiral-wound NF elements, such as about 5 to about 25 Imh. The permeate 401 is far less saline than fluid retentate 302 used as feed and has an osmotic pressure around 60 bar less than the fluid retentate 402. Permeate 401 is returned to tank 10 to be fed back into the system. In addition to fluid retentate 302. permeate 501 from nanofiltration elements 500 is pressurized by the first pressure recovery device 22 and fed to elements 400. Permeate 501 has approximately similar osmotic pressure to fluid retentate 302.

[0037] The fluid retentate 402 from NF elements 400 is passed on to a fourth set of nanofiltration elements 500. Fluid retentate 402 has an osmotic pressure and a TDS level substantially higher than fluid retentate 302 (such as, for example, about 25,000 TDS to about 35,000 TDS higher for sodium chloride, depending on the number of NF elements) and the permeability of the NF membrane 500 is selected so that the flux is appropriate for spiral-wound NF elements, such as about 5 to about 25 Imh. The permeate 501 is far less saline than fluid retentate 402 used as feed and has an osmotic pressure around 60 bar less than the fluid retentate 502. Permeate 501 is passed to tank 20 to be pressurized with pressure recovery device 22 and reinjected into the feed flow upstream of elements 400. In addition to fluid retentate 402, permeate 601 from nanofiltration elements 600 is pressurized by the second pressure recovery device 32 and fed to elements 500. Permeate 601 has approximately similar osmotic pressure to fluid retentate 402.

[0038] The fluid retentate 502 from NF elements 500 is passed on to a fifth set of nanofiltration elements 600. Fluid retentate 502 has an osmotic pressure and a TDS level substantially higher than fluid retentate 402 (such as, for example, about 15,000 TDS to about 25,000 TDS higher for sodium chloride, depending on the number of NF elements) and the permeability of the NF membrane 600 is selected so that the flux is appropriate for spiral-wound NF elements, such as about 5 to about 25 Imh. The permeate 601 is far less saline than fluid retentate 502 used as feed and has an osmotic pressure around 60 bar less than the fluid retentate 602. Permeate 601 is passed to tank 30 to be pressurized with pressure recover}' device 32 and reinjected into the feed flow upstream of elements 500. In addition to fluid retentate 502, permeate 701 from nanofiltration elements 700 is pressurized by the third pressure recovery' device 42 and fed to elements 600. Permeate 701 has approximately similar osmotic pressure to fluid retentate 502.

[0039] The fluid retentate 602 from NF elements 600 is passed on to a sixth set of nanofiltration elements 700. Fluid retentate 602 has an osmotic pressure substantially higher (such as about 10,000 TDS to about 20,000 TDS higher) than fluid retentate 502 and the permeability of the NF membrane 700 is selected so that the flux is appropriate for spiral-wound NF elements, such as about 5 to about 25 Imh. The permeate 701 is far less saline than fluid retentate 602 used as feed and has an osmotic pressure around 60 bar less than the fluid retentate 702. Permeate 701 is passed to tank 40 to be pressurized with pressure recovery device 42 and reinjected into the feed flow upstream of elements 600.

[0040] Permeates 501, 601, and 701 are low-pressure filter permeate flows and may be fed into the low-pressure side of their respective pressure recovery devices 22, 32, and 42 as flows 24, 34, and 44, respectively. The high-pressure process feed brines 27. 37. and 47 from the high-pressure process feed pump 12 may be fed into high-pressure sides of pressure recover}' devices 22, 32, and 42, respectively. The outputs of the pressure recovery devices 22, 32, and 42 include high-pressure filter permeate outputs 25, 35, and 45, respectively, and low-pressure feed fluid outputs 26, 36, and 46, respectively. The high- pressure filter permeate outputs 25, 35, and 45 may then be reinjected into the nanofiltration retentate process brines 302, 402, and 502 at reinjection ports 29, 39, and 49, respectfully. The reinjected high-pressure filter permeate outputs 25, 35, and 45 have a similar salinity7to the nanofiltration retentate process brines 302, 402, and 502, respectfully. The reinjected high-pressure filter permeate outputs 25, 35, and 45 have higher pressures than the nanofiltration retentate process brines 302, 402, and 502, respectfully.

[0041] The operation of pressure recovery7devices 22, 32, and 42 are all similar, so device 22 with spinning cylinder sty le pressure recovery is used as an example. Alternatively, devices 22, 32, and 42 may be dual cylinder style pressure recovery7devices.

[0042] The essential parts of the ERI sty le pressure recovery device include a rotating cylinder and a cylindrical housing. The rotating cylinder is ceramic with holes in the axial direction extending the length of the cylinder. The rotating cylinder fits into the cylindrical housing with a small clearance on the walls and at least two isolated feed ports on the ends. Such devices have been available since the 1960s, as described in U.S. Pat. Nos. 3,431,747: 3,582,090 and 3,910,587. Improvements to the devices are described in U.S. Pat. Nos. 4,887,942; 5,338,158 and 5,988,993.

[0043] A simplified rotating pressure recovery device is shown in FIG. 2 to FIG. 6. FIG. 2 conceptually shows the spinning cylinder 90. preferably made of ceramic, of the rotating pressure recovery device 80. The cylinder 90 contains a multitude of holes, suchas cylinder holes 18 and 20, each extending the length of cylinder 90. Though not shown in FIG. 2, the cylinder 90 may include one or more of: other and / or different hole shapes, sizes, and / or numbers; a center hole for the axle; or an axle. As shown in FIG. 3, cylinder holes 18 and 20 are on opposite sides of cylinder 90.

[0044] FIG. 4 show s the cylindrical housing 70 of the pressure recovery device 80 with end caps 14 and 16. The cylinder 90, not shown in FIG. 4. is inside the housing 70. In FIG. 5, ports 26A and 27A are on opposite sides of endcap 14 and align with cylinder holes 18 and 20, respectively.

[0045] FIG. 6 show s the pressure recovery device 80 including the cylinder 90 with a multitude of cylinder holes including cylinder holes 18 and 20, the cylinder 90 inside hollow cylindrical housing 70 with endcap 14 having two ports 26A and 27A at one end of the hollow cylindrical housing 70 and endcap 16 with two ports 24A and 25 A at the other end of the hollow- cylindrical housing 70. The ceramic cylinder 90 rotates inside the hollow^ cylindrical housing 70.

[0046] The piping connections to the pressure recovery device in FIG. 6 are the low- pressure NF permeate feed for port 24A, the high-pressure nanofiltration permeate exit port 25A, the high-pressure seawater port 27A and the low-pressure seawater port 26A. The port numbers 24A, 25A, 26A and 27A correspond to flows 24, 25, 26, and 27 in FIG. 1 for pressure recovery device 22. In FIG. 1, flow 24 is the low-pressure permeate from the NF, flow 25 is the pressurized permeate exit, flow 27 is the pressurized seawater feed, and flow 26 is the low-pressure seawater exit.

[0047] As seen in FIG. 6, the low-pressure ports 24A and 26A are fluidly connected and the high-pressure ports 27 A and 25 A are fluidly connected. Fluid 24 is held at a higher pressure than fluid 26 so there is flow in cylinder hole 18 from port 24A toward port 26 A. Likewise, fluid 27 is held at a slightly higher pressure than fluid 25 so there is flow in cylinder hole 20 from port 27A toward port 25 A. The ceramic cylinder spins so the contact between cylinder hole 20 and ports 27A and 25 A is broken before the pressurized seawater feed can pass from port 27A to port 25A. As the cylinder rotates, cylinder hole 20 encounters ports 24A and 26A. The pressure differential causes flow from port 24A toward port 26A but the spinning causes the connection to be broken before the fluid entering from port 24A reaches port 26 A.

[0048] The net effect of the pressure recovery device is high-pressure seawater feed flows into port 27A, low-pressure seawater feed exits from port 26A, low-pressure NF permeate flows into port 24A, and high-pressure NF permeate flows from port 25 A. Thedevice requires no external energy input as the spinning of the cylinder is induced by the fluid flow.

[0049] In current SWRO systems, pressure recovery devices use the pressurized retentate brine stream to help pressurize incoming seawater thereby reducing the system energy7requirements. In one or more embodiments disclosed herein, the pressure recovery device is used to pressurize nanofiltration permeate by transferring energy from a portion of the nanofiltration feed stream from the system feed pump. Using pressure recovery devices in high salinity applications instead of multistage centrifugal high-pressure pumps avoids corrosion issues inherent in commonly used commercial high-pressure pumps.

[0050] The relative proportions of the cylinder and the holes in the drawings are not intended to reflect the actual device. And the number of holes may vary from the eight depicted. The gap between the cylinder and the end plates and housing, in reality7, is much tighter than that depicted and the gap is sized to practically eliminate bypass flow.

[0051] Flows in the device are balanced by keeping the pressure differential between ports 27 A and 25A approximately equal to that between ports 24A and 26 A.

[0052] In FIG. 1, flow 24 will be approximately equal to flow 501. The pressure of flow 24 is set by a variable frequency drive (VFD) on pump 21. If valve 23 is wide open, the pressure of flow 25 will be the same as the pressure of flow7302. The pressure of flow7302 is lower than the feed pressure 13 due to pressure drop in elements 100, 200, and 300. Device 22 is sized so that the pressure difference between port 27A and port 25A required to operate the system is less than that between port 27A and injection point 302. The required pressure at port 25 A can then be maintained by adjustment of control valve 23. A similar pressure differential between port 24A and port 26A can be maintained by a VFD on pump 21.

[0053] While the system in FIG. 1 is an example process flow diagram for concentrating sodium chloride, similar systems for concentrating ammonium sulfate, lithium chloride, sodium sulfate, and other monovalent and divalent ions are within the scope of this application. Salinities up to around 90% of saturation may be achieved.

[0054] FIG. 1 A is a process fluid diagram of an example SWRO system with pressure recovery according to the prior art. Seawater 154 enters the feed tank 150. Low-pressure seawater feed pump 151 and high-pressure seawater feed pump 152 work in tandem to pressurize the seawater from the feed tank 150 to high-pressure flow 153, preferably between 60 and 80 bar. A portion of flow 158 of the seawater from pump 151 is directed to the low-pressure inlet 158A of the pressure recovery device 180.

[0055] Pressurized seawater 157 coming from pressure recovery device 180 is further pressurized by booster pump 159 and combined with flow 153 from high-pressure pump 152. The combined flows are fed to RO filter 160. Permeate 161 from RO filter 160 is clean water. High-pressure retentate 155 from RO filter 160 is fed to port 155A of the pressure recovery device 180 and pressurizes flow 157. Low-pressure retentate 156 is the high salinity brine produced by the process.

[0056] As used herein, the term "about” or “substantially’7refers to an allowable variance of the term modified by “about” by ±10% or ±5%. Further, the terms “less than,” “or less,” “greater than”, “more than,” or “or more” include as an endpoint, the value that is modified by the terms “less than,” “or less,” “greater than,” “more than,” or “or more.”

[0057] While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting.

Claims

CLAIMS1. A brine concentration nanofiltration system, the system comprising one or more first sets of nanofiltration elements, one or more second sets of nanofiltration elements, and one or more pressure recovery devices, a pressure recovery device of the one or more pressure recovery devices including a low-pressure side through which at least a portion of a filter permeate flow from a set of nanofiltration elements of the one or more second sets of nanofiltration elements is fed and a high-pressure side through which at least a portion of a process feed brine from a high-pressure process feed pump is fed, wherein outputs of the pressure recovery device include a high-pressure filter permeate output and a low-pressure feed fluid output.

2. The brine concentration nanofiltration system of claim 1, wherein the high- pressure filter permeate output is reinjected into nanofiltration retentate process brine from a set of nanofiltration elements of the one or more first sets of nanofiltration elements at a point where the high-pressure filter permeate output has a similar salinity as the nanofiltration retentate process brine.

3. The brine concentration nanofiltration system of claim 2, wherein a permeate outlet pressure of the high-pressure filter permeate output of the pressure recovery device is higher than a process brine pressure of the nanofiltration retentate process brine where the high-pressure filter permeate is being reinjected.

4. The brine concentration nanofiltration system of claim 2, further comprising a system reinjection port and a control valve between the high-pressure filter permeate output and the system reinjection port, the control valve being configured to control the filter permeate flow from the high-pressure filter permeate output, the system reinjection port positioned for reinjection of the high-pressure filter permeate output into the nanofiltration retentate process brine.

5. The brine concentration nanofiltration system of claim 1, wherein the one or more second sets of nanofiltration elements include a plurality of sets of nanofiltration elements and the high-pressure filter permeate output is reinjected into nanofiltration retentate process brine from an additional set of nanofiltration elements of the plurality of second sets of nanofiltration elements different from the set of nanofiltration elements at a point where the high-pressure filter permeate output has a similar salinity as the nanofiltration retentate process brine.

6. The brine concentration nanofiltration system of claim 5, wherein a permeate outlet pressure of the high-pressure filter permeate output of the pressure recovery device is higher than a process brine pressure of the nanofiltration retentate process brine where the high-pressure filter permeate is being reinjected.

7. The brine concentration nanofiltration system of claim 5, further comprising a system reinjection port and a control valve between the high-pressure filter permeate output and the system reinjection port, the control valve being configured to control the filter permeate flow from the high-pressure filter permeate output, the system reinjection port positioned for reinjection of the high-pressure filter permeate output into the nanofiltration retentate process brine.

8. The brine concentration nanofiltration system of claim 1. wherein the one or more pressure recovery devices are made entirely from one or more brine contact materials more resistant to corrosion than stainless steel.

9. The brine concentration nanofiltration system of claim 8, wherein the one or more brine contact materials include one or more of ceramic, fiberglass, titanium, or plastic materials.

10. The brine concentration nanofiltration system of claim 1, wherein monovalent ions are concentrated to high salinities including salinities up to 90% of saturation in the nanofiltration retentate process brine.

11. The brine concentration nanofiltration system of claim 1, wherein divalent ions are concentrated to high salinities including salinities up to 90% of saturation in the nanofiltration retentate process brine.

12. The brine concentration nanofiltration system of claim 1, wherein the process feed brine includes seawater.

13. A method for reinjecting filter permeate of a nanofiltration brine concentration system by use of one or more pressure recovery devices, the method comprising: supplying high-pressure fluid to a pressure recovery device of the one or more pressure recovery devices, the high-pressure fluid being supplied from a main process feed pump of the nanofiltration brine concentration system; transferring energy7from the high-pressure fluid from the main process feed pump to a low-pressure filter permeate to create high-pressure filter permeate where outputs of the pressure recovery7device are a high-pressure filter permeate output and a low-pressure feed fluid output; andreinjecting portions of the high-pressure filter permeate into a nanofiltration retentate process brine stream at locations where salinity of the high-pressure filter permeate is similar to the nanofiltration retentate process brine stream.

14. The method of claim 13, wherein a pressure of the high-pressure filter permeate leaving the pressure recovery device is higher than a pressure of nanofiltration retentate process brine at a point of reinjection.

15. The method of claim 13, wherein the one or more pressure recovery devices are made entirely from one or more brine contact materials more resistant to corrosion than stainless steel.

16. The method of claim 15, wherein the one or more brine contact materials more resistant to corrosion include one or more of ceramic, fiberglass, titanium, or plastic materials.

17. The method of claim 13, wherein permeate flow from the high-pressure filter permeate output of the pressure recovery device is controlled by a control valve between the high-pressure filter permeate output and a system reinjection port.

18. The method of claim 13, wherein the high-pressure fluid from the main process feed pump includes seawater.

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