Automated lithium concentration reverse osmosis system

Abstract

A reverse osmosis fluid concentration system is provided. The system comprises a first pass reverse osmosis array operable to separate fluid into a concentrate stream output and a permeate stream output, and a second pass reverse osmosis array operable to generate a more concentrated concentrate stream output along with a permeate stream output. The second pass reverse osmosis array is connected in fluid series downstream of the first pass reverse osmosis array in a normal operating mode. The system typically includes a buffer tank, with a circulation circuit connecting the second reverse osmosis membrane with the buffer tank. In a saturation mode, the circulation circuit is operable to feed and return fluid between buffer tank and the second pass reverse osmosis array.

Description

AUTOMATED LITHIUM CONCENTRATION REVERSE OSMOSIS SYSTEMCROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This PCT Patent Application claims the benefit of U.S. Provisional Patent Application No. 63 / 651,469, filed May 24. 2024, the entire teachings and disclosure of which are incorporated herein by reference thereto.FIELD OF THE INVENTION

[0002] The present invention generally relates to reverse osmosis systems, and more specifically to reverse osmosis systems with multiple stages / passes.BACKGROUND OF THE INVENTION

[0003] Disclosures or attempts of reverse osmosis (RO) systems for separating and concentration lithium ions in water are known in various patent publications. For example, CN11210800 shows a first RO unit connected in series to at least one second RO unit to provide Li rich concentrated solution. Further disclosures similarly show and describe cascading systems as in CN 117585684; and US 1 1,174,532 and WO 2023063928. CN 214829199 as currently understood from a machine translation possibly may attempt to concentrate the brine solution from the first pass RO units through recirculation; however the recirculated brine is eventually directed to separate fresh separation units which do not appear saturated. Yet another reverse osmosis arrangement is shown in schematic form in CN217264876.

[0004] As exemplified by such patent publications, current lithium extraction technology requires reverse osmosis to remove water from an incoming lithium chloride solution. The maximum concentration possible is a function of how much water is removed from the incoming solution, limited by the maximum pressure a RO membrane can handle. The maximum rated membrane pressure currently in the market is 1800 psi.

[0005] The process for concentration is currently done by running water through a 1 st pass array of membranes to maximize water recovery. Typically, this can reach up to 80%. The remaining 20% concentrate water is then fed to a second pass array of membranes atmaximum pressure (1800 PSI). One disadvantage of this method is that it takes 2-3 hours for the concentration to reach 12% (i.e., 120,000 ppm) which is the current max possible concentration given the membrane limitations. This time required to reach concentration results in more water consumed along with more power needed to remove the excess water at lower concentration <12%. This inefficient concentration cycle must be repeated everytime the RO system is shutdown.

[0006] The present invention therefore is directed tow ard advancements over the state of the art to increase concentration of separated concentrate from permeate, reduce water consumption, reduce footprint for lithium extraction and / or reduce energy requirements.BRIEF SUMMARY OF THE INVENTION

[0007] A Reverse Osmosis (RO) system herein may be specifically designed to maximize the concentration of a Lithium Chloride solution.

[0008] The known systems designed for concentration purposes can be designed for specific feed concentrations, given that changes in feed conditions significantly affect performance. The proposed RO unit allows the system to automatically adjust to varying feed concentration allowing for ultimate flexibility for brine concentration anywhere in the world.

[0009] It is proposed to provide a specific automated process that runs a close loop during the concentration period allowing for concentration to be reached without consuming w ater. Once the unit is ready to be started in normal operation the end user will have max concentration limiting the power required compared to concentrations <12% which are present without this initial step. During shutdown the system can retain the concentration previously achieved allowing the system to be started again without the need to repeat a saturation cycle which is costly and consumes water.

[0010] The proposed system takes a lithium chloride feed solution and concentrates it to 12% by volume while conserving water, minimizing power consumed, and is fully automated allowing the system to self-adjust to varying incoming feed conditions which are difficult to manage without intricate knowledge of the process. It is the process that has been fine tuned to deliver optimum results. Embodiments of the invention may be based on a process by which maximum concentration is achieved more rapidly through an automated concentration cycle.

[0011] As illustrated herein, water is fed through the 1st pass array and discharged into a separate holding tank at higher concentration than it came in. This tank is then fed to the 2nd pass array and run at 1800 psi in a closed loop. Due to the large volume in the membrane vessels and the very low flow that comes out of the reject side of the membrane, the Lithium Chloride ions entering the membrane array do not equal those that exit the membrane array therefore concentrating the volume in the membrane array. It is this very concentration effect that allows the concentration cycle (reaching 12%) to be reached much quicker than if it was not run in a closed loop.

[0012] This effect of concentration in the membrane array is confirmed by the tank concentration which when measured overtime becomes diluted. Due to the external tank introduced during concentration and the closed loop cycle, all water used in the process can be conserved. All concentration can be retained in the membrane array and the water in the holding tank is recycled once it reaches a low enough concentration. The process is then repeated to achieve full concentration at 12% (i.e.. 120,000 ppm).

[0013] Once max concentration is reached, the system can now be run continuously in normal operation yielding the highest concentration of lithium chloride. At shutdown the system is designed to retain the concentration within the system while safely dissipating internal pressure which allows the end user to achieve max concentration immediately once the unit is restarted minimizing water consumed and power required during the conventional concentration cycle.

[0014] An inventive aspect and embodiment is directed toward a reverse osmosis fluid concentration system, comprising: (a) a first pass assembly of a first pass pump and first pass reverse osmosis array capable of separating a fluid stream into a concentrate stream and a permeate stream; (b) a second pass assembly of a second pass pump and second pass reverse osmosis array fluidly connected downstream of the first pass assembly, capable of separating the concentrate stream into a further concentrated stream and a concentrate permeate stream; and (c) a buffer tank i) fluidly connected to the first pass assembly so as to receive the concentrate stream from the first pass reverse osmosis array during a first pass RO mode, and ii) fluidly connected to the second pass assembly so as to receive and circulate the further concentrated stream and the concentrate permeate stream from the second pass reverse osmosis array during a saturation mode.

[0015] Any of these above aspects and / or embodiments may be used in connection with one or more features either alone or in combination with each other as presented in the paragraphs below.

[0016] It is a feature that the system may be operational during a fill mode to direct a water stream through the first pass assembly to fill the first pass assembly and the second pass assembly with water.

[0017] It is a feature the system may be operational through the first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank.

[0018] It is a feature that the system may be operational through the saturation mode to circulate the concentrate stream from the buffer tank through the second pass assembly to saturate the second pass reverse osmosis array with concentrate.

[0019] It is a feature that the may be is operational through a normal mode to direct the concentrate stream from the first pass assembly to the second pass assembly, and direct the further concentrated stream from the second pass assembly with the saturated reverse osmosis array as a concentrated output stream of the system.

[0020] It is a feature that the system may be operational during a fill mode to direct a water stream through the first pass assembly to fill the first pass assembly and the second pass assembly with water; then operational through the first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank; then operational through the saturation mode to circulate the concentrate stream from the buffer tank through the second pass assembly to saturate the second pass reverse osmosis array with concentrate; then operational through a normal mode to direct the concentrate stream from the first pass assembly to the second pass assembly, and direct the further concentrated stream from the second pass assembly with the saturated reverse osmosis array as a concentrated output stream of the system.

[0021] Another inventive aspect and embodiment is directed toward a reverse osmosis fluid concentration system, comprising: a first reverse osmosis membrane operable to separate fluid into a first concentrate stream output and a first permeate stream output: and a second reverse osmosis membrane operable to generate a second concentrate stream output and a second permeate stream output. The second reverse osmosis membrane is connected in fluid series downstream of the first reverse osmosis membrane in a normal operatingmode to receive the first concentrate stream output from the first reverse osmosis membrane. The reverse osmosis fluid concentration system further comprises a buffer tank; and a circulation circuit connecting the second reverse osmosis membrane with the buffer tank in a saturation mode. The circulation circuit is operable in the saturation mode to feed and return fluid between buffer tank and the second reverse osmosis membrane.

[0022] The above aspects and / or embodiments may be used in connection with one or more features either alone or in combination with each other as presented in the paragraphs below or in prior paragraphs above.

[0023] It is a feature that the second permeate stream output may be connected and fed to the buffer tank in the saturation mode.

[0024] It is a feature that the second concentrate stream output may be connected and fed to the buffer tank in the saturation mode.

[0025] It is a feature that the reverse osmosis fluid concentration system may further comprise a first stage pump operable to pump fluid to the first reverse osmosis membrane.

[0026] It is a feature that the reverse osmosis fluid concentration system may further comprise a second stage pump operable to pump fluid to the second reverse osmosis membrane.

[0027] It is a further feature in relation to the above feature that (a) in the normal mode, the second stage pump may be operable to pump the first concentrate output from the first reverse osmosis membrane to the second reverse osmosis membrane; and (b) in the saturation mode, the second stage pump may be operable to pump fluid contained in the buffer tank to the second reverse osmosis membrane.

[0028] It is a feature that the reverse osmosis fluid concentration system may further comprise an inlet supply conduit adapted to deliver a supply of feedstock fluid to be separated toward the first reverse osmosis membrane; a first permeate outlet conduit adapted to cany' away the first permeate stream output; a first concentrate conduit adapted to connect the first reverse osmosis membrane with the second reverse osmosis membrane in the normal mode for supplying the first concentrate stream output to the second reverse osmosis membrane; a second permeate outlet conduit adapted to cany' away the second permeate stream output; a second concentrate outlet conduit adapted to cany' the first concentrate stream output toward a final product outlet.

[0029] In the above feature, it is a further feature that the reverse osmosis fluid concentration system may further comprise a permeate return branch conduit operable to connect the second permeate outlet conduit to the buffer tank in the saturation mode; and a concentrate return branch conduit operable to connect the second concentrate outlet conduit to the buffer tank in the saturation mode.

[0030] In any of the two above features, it is a further feature that the reverse osmosis fluid concentration system may further comprise an inlet branch operable to connect the first concentrate conduit and the buffer tank in an first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank.

[0031] It is a feature that the first reverse osmosis membrane may be part of a first pass assembly, comprising a plurality of first pass membrane elements contained in a plurality of first vessels, respectively. Further, the second reverse osmosis membrane may be part of a second pass assembly comprising a plurality of second pass membrane elements contained in a plurality of second vessels, respectively.

[0032] It is a feature the system may comprise a fill mode wherein the reverse osmosis fluid concentration system is operable during the fill mode to direct the supply of feedstock fluid through the first pass assembly to fill the first pass assembly and the second pass assembly with water.

[0033] It is a feature that the reverse osmosis fluid concentration system may further comprise a booster pump connected with a tank outlet of the buffer tank. The booster pump is operable to pump fluid from the buffer tank toward the / a second stage pump that is operable to pump fluid to the second reverse osmosis membrane (preferably, through a particulate filter arranged between in fluid series between the tank outlet and the second reverse osmosis membrane).

[0034] Another inventive aspect and embodiment is directed toward a reverse osmosis fluid concentration system comprising a first reverse osmosis membrane operable to separate fluid into a first concentrate stream output and a first permeate stream output; and a second reverse osmosis membrane operable generate a second concentrate stream output and a second permeate stream output. The second reverse osmosis membrane is connected in fluid series downstream of the first reverse osmosis membrane in a normal operating mode to receive the first concentrate stream output from the first reverse osmosis membrane. The reverse osmosis fluid concentration system further comprises a circulationcircuit operable in the saturation mode recirculate the second permeate stream output and the second concentrate stream output to the second reverse osmosis membrane.

[0035] The above aspects and / or embodiments may be used in connection with one or more features either alone or in combination with each other as presented in the paragraphs below or in prior paragraphs above.

[0036] It is a feature that the circulation circuit may be operable in the saturation mode to recirculate the second permeate stream output and the second concentrate stream output only to the second reverse osmosis membrane and not the first second reverse osmosis membrane.

[0037] It is a feature that the reverse osmosis fluid concentration system may further comprise a buffer tank, with the circulation circuit connecting the second reverse osmosis membrane with the buffer tank in the saturation mode.

[0038] Another inventive aspect and embodiment is directed toward a process for concentrating a product of a fluid stream, comprising passing a feedwater fluid stream through a first pass assembly comprising a first reverse osmosis membrane to separate fluid into a first concentrate stream output and a first permeate stream output, with a second pass assembly arranged downstream. The second pass assembly comprises a second reverse osmosis membrane with the second pass assembly operable to generate a second concentrate stream output and a second permeate stream output. The process further comprises: (a) operating in a saturation mode, which comprises recirculating the second concentrate stream output and the second permeate stream output through the second pass assembly to increase concentration of a concentrate product in the second concentrate stream; and (b) switching from the saturation mode to operating in a normal operating mode, which comprises passing the first concentrate stream through the second pass assembly thereby separating the first concentrate stream into the second concentrate stream output and the second permeate stream output.

[0039] The above aspects and / or embodiments may be used in connection with one or more aspects / features either alone or in combination with each other as presented in the paragraphs below or in prior paragraphs above.

[0040] It is a feature that the process may further comprise buffering the recirculating with a buffer tank that receives the second concentrate stream output and the secondpermeate stream output and feeds fluid contained in the buffer tank to the second pass assembly during the saturation mode.

[0041] It is a feature that the process may further comprise operating in a fill mode before operating in the saturation mode by filling the first pass assembly and the second pass assembly with the feedwater fluid stream (in this fill mode instance, the first concentrate stream output may be considered the feedwater fluid stream as little if any separation is occurring during filling).

[0042] It is a feature that the process may further comprise operating in a first pass RO mode after the fill mode and before the saturating mode by directing the first concentrate stream output from the first pass assembly to the buffer tank to initially fill the buffer tank.

[0043] It is a feature that the process may further comprise concentrating lithium chloride feed solution in the saturation mode and the normal operating mode.

[0044] The above feature may concentrate the lithium chloride feed solution to produce a lithium chloride concentrate to a desired set point of the operator.

[0045] It is therefore a feature that the process may further involve switching from saturation mode to normal operating mode at a set point once a contrate level is reached, preferably the concentrate level at least 10% (i.e., 100,000 ppm), and more preferably at least 12% (i.e., 120,000 ppm).

[0046] According to an embodiment / aspect. a reverse osmosis fluid concentration system, comprises: (a) a first pass assembly of a first pass pump and first pass reverse osmosis array capable of separating a fluid stream into a concentrate stream and a permeate stream; (b) a second pass assembly of a second pass pump and second pass reverse osmosis array fluidly connected downstream of the first pass assembly, capable of separating the concentrate stream into a further concentrated stream and a concentrate permeate stream; (c) a buffer tank i) fluidly connected to the first pass assembly so as to receive the concentrate stream from the first pass reverse osmosis array during a first pass RO mode, and ii) fluidly connected to the second pass assembly so as to receive and circulate the further concentrated stream and the concentrate permeate stream from the second pass reverse osmosis array during a saturation mode. The system is operational during a fill mode to direct a water stream through the first pass assembly to fill the first pass assembly and the second pass assembly with water; then operational through the first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank; thenoperational through the saturation mode to circulate the concentrate stream from the buffer tank through the second pass assembly to saturate the second pass reverse osmosis array with concentrate; then operational through a normal mode to direct the concentrate stream from the first pass assembly to the second pass assembly, and direct the further concentrated stream from the second pass assembly with the saturated reverse osmosis array as a concentrated output stream of the system.

[0047] According to an embodiment / aspect, a process for concentrating a product of a fluid stream uses a first pass assembly of a first pass pump and first pass reverse osmosis array capable of separating a fluid stream into a concentrate stream and a permeate stream; a second pass assembly of a second pass pump and second pass reverse osmosis array fluidly connected downstream of the first pass assembly, capable of separating the concentrate stream into a further concentrated stream and a concentrate permeate stream; a buffer tank i) fluidly connected to the first pass assembly so as to receive the concentrate stream from the first pass reverse osmosis array during a first pass RO mode, and ii) fluidly connected to the second pass assembly so as to receive and circulate the further concentrated stream and the concentrate permeate stream from the second pass reverse osmosis array during a saturation mode; the process comprising the steps of: directing a water stream through the first pass assembly during a fill mode to fill the first pass assembly and the second pass assembly with water; then directing the concentrate stream from the first pass reverse osmosis array during the first pass RO mode to the buffer tank; then directing the concentrate stream from the buffer tank to the second pass assembly during the saturation mode, and circulating the further concentrated stream through the second pass assembly to saturate the second pass reverse osmosis array with concentrate; and then directing the concentrate stream from the first pass assembly to the second pass assembly and directing the further concentrated stream from the second pass assembly with saturated second pass reverse osmosis array as a concentrated output stream of the system during a normal mode.

[0048] Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

[0050] FIG. 1 is a front-left comer isometric view of a reverse osmosis fluid concentration system in accordance with an embodiment of the present invention;

[0051] FIG. 2 is a front-right comer isometric view of the reverse osmosis fluid concentration system shown in FIG. 1;

[0052] FIG. 3 is a top view of the reverse osmosis fluid concentration system shown in FIG. 1;

[0053] FIG. 4 is a front elevation view of the reverse osmosis fluid concentration system shown in FIG. 1 ;

[0054] FIG. 5 is a left side elevation view of the reverse osmosis fluid concentration system shown in FIG. 1 ;

[0055] FIG. 6 is a right side elevation view- of the reverse osmosis fluid concentration system shown in FIG. 1 ;

[0056] FIG. 7 is the first part of a schematic fluid circuit diagram of the first stage of the reverse osmosis fluid concentration system shown in FIG. 1;

[0057] FIG. 8 is the second part of the schematic fluid circuit diagram of the second stage of the reverse osmosis fluid concentration system shown in FIG. 1 (and completing the remainder of the first part of the schematic fluid circuit diagram of FIG. 7);

[0058] FIG. 9 is a schematic, simplified process diagram of the reverse osmosis fluid concentration system of FIG. 1 (and according to the schematic fluid circuit diagram of FIGS. 7-8);

[0059] FIG. 10 is the schematic, simplified process diagram shown in FIG. 9, but shown in a Fill Mode (bolded lines showing open flow passages);

[0060] FIG. 11 is the schematic, simplified process diagram shown in FIG. 9, but shown in a 1stPass RO Mode (bolded lines showing open flow passages);

[0061] FIG. 12 is the schematic, simplified process diagram shown in FIG. 9, but shown in a Saturation Mode (bolded lines showing open flow passages);

[0062] FIG. 13 is the schematic, simplified process diagram shown in FIG. 9, but shown in a Normal Operation Mode (bolded lines showing open flow passages);

[0063] While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.DETAILED DESCRIPTION OF THE INVENTION

[0064] Referring to FIGS. 1-13, an embodiment of the present invention has been shown as a reverse osmosis fluid concentration system 10.

[0065] The reverse osmosis fluid concentration system 10 generally comprises a first pass assembly 12 and a second pass assembly 14, each of which are operational for separating a fluid stream into a concentrate stream and a permeate stream. The reverse osmosis fluid concentration system 10 also comprises circulation circuit 16 that is operational to increase concentration of product (for example, lithium chloride) within the concentrate stream produced by the second pass assembly 14.

[0066] In particular, the recirculating circuit 16 is typically operated at low concentration level operating conditions such as during initial priming and start-up and / or perhaps at other times if product concentration level drops within concentrate stream. For example, during initial priming and start-up, the first pass assembly 12 and the second pass assembly 14 can be flooded with a substantial volume of a low concentration level water feedstock (e.g., such as raw water, feedstock feed water and / or minimally / low concentrated concentrate fluid stream). As a consequence, as fluid is slowly introduced under highpressures into the first pass assembly 12 and the second pass assembly 14, the initial concentrate stream (e.g., 2ndconcentrate stream output 36 as discussed below) is very low. This is due to low mixing within RO membrane vessels / elements, and slow displacement and purging of the initial fluid stream volume of low concentrate stream contained in the pressure vessels and piping of the system 10. Until such low concentrate fluid is purged to a sufficient degree, which takes some time, the initial concentration level of the 2ndconcentrate stream output 36 remains low but the concentration level gradually increases as the initial volume of feedstock gets pushed and / or purged through the system, due to the recirculation during operation of the circulation circuit 16. The circulation circuit 16 is able to recycle the 2ndconcentrate stream output 36 (and also combined with and recirculated with the second permeate stream output 36 in an embodiment), until the concentration level in the final output of the 2ndconcentrate stream output 36 is at a desired level for production output.

[0067] Turning in greater detail to the illustrated embodiment, the first pass assembly 12 comprise a first pass pump, indicated as first stage pump 18 and a first pass reverse osmosis array 20. In operation, the first pass reverse osmosis array 20 separates a fluid stream into a concentrate stream shown as first concentrate stream output 22 and a permeate stream shown as first permeate stream output 24.

[0068] For example, as shown best in FIGS. 6 and 7 (and indicated in FIGS. 9-13), the first pass reverse osmosis array 20 can comprise first stage tubular pressure vessels 26 that housing first stage reverse osmosis membrane elements 28 (e.g., spiral wound, single pass reverse osmosis membrane elements). Each membrane element 28 (and / or the elements 28 collectively) provide a first reverse osmosis membrane operable to separate fluid into the first concentrate stream output 22 and the first permeate stream output 24. For example, twelve first stage tubular pressure vessels 26 and first stage reverse osmosis membrane elements 28 are shown in the illustrated embodiment, although more or less may be provided in alternative embodiments.

[0069] The second pass assembly 14 comprise a second pass pump, indicated as second stage pump 30 and second pass reverse osmosis array 32. In operation, the second pass reverse osmosis array 32 separates a fluid stream into a further concentrate stream shown as second concentrate stream output 34 and a permeate stream shown as first permeate stream output 36.

[0070] For example, as shown in FIGS. 6 and 8 (also indicated in FIGS. 9-13_, the second pass reverse osmosis array 32 can comprise second stage tubular pressure vessels 38 that house second stage reverse osmosis membrane elements 40 (e.g., spiral wound, single pass reverse osmosis membrane elements). Each membrane element 40 (or the elements 40 collectively) provide a second reverse osmosis membrane operable to separate fluid into the second concentrate stream output 34 and the second permeate stream output 36. For example, six second stage tubular pressure vessels 38 and first stage reverse osmosis membrane 40 are shown in the illustrated embodiment, although more or less may be provided in alternative embodiments.

[0071] In the illustrated example and in an embodiment, the second stage preferably may be higher performance and more efficient at separating concentrate from permeate. The reason is the concentration level at the first stage is relatively low and can be operated with lower energy inputs therefore, while the second stage is to finish and produce much higher concentrations of desired product ion (e.g., lithium chloride) in the concentrate stream. For example, the stage tubular pressure vessels 26 and first stage reverse osmosis membrane elements 28 may be rated at 1200 PSI; whereas the second stage tubular pressure vessels 38 and second stage reverse osmosis membrane elements 40 may be rated at 1800 PSI (or alternatively the second pass / stage may also be rated at 1200 psi like the first pass / stage). The second stage tubular pressure vessels 38 and second stage reverse osmosis membrane elements 40 are therefore operating at much higher operating pressures that can force more permeate through the RO membrane of the second stage reverse osmosis membrane elements 40, thereby further concentrating product in the second stage concentrate stream output 34 toward a set desired level that may be referred to as maximum level.

[0072] For example, in the illustrated embodiment, some (e.g., nine) of the first stage tubular pressure vessels 26 and first stage reverse osmosis membrane elements 28 are arranged in parallel fluid circuit as shown in FIG. 7. However, each group of three vessels 26A and RO elements 28A that are arranged in parallel feed a single finish concentrating vessel 26B and RO element 28B arranged in fluid series circuit as also shown in FIG. 7. The collective output of the three single finish concentrating vessels 26B and RO elements 28B provide for the first concentrate stream output 22, as also shown in FIG. 7.

[0073] For example, in the illustrated embodiment, all six of the second stage tubular pressure vessels 38 and second stage reverse osmosis membrane elements 40 are arranged in parallel circuit as shown in FIG. 8, and collectively produce the second concentrate stream output 34.

[0074] The circulation circuit 16 as shown preferably includes a buffer tank 42 to provide enough volume to facilitate the purge of low level concentrate fluid from the 2ndpass assembly and in particular form the second stage tubular vessels 38 and the RO membrane elements 40. The buffer tank 42 is shown to be (a) fluidly connected to the first pass assembly 12 that may receive the concentrate stream from the first pass reverse osmosis array 20 during a first pass RO mode (shown in FIG. 11), and (b) fluidly connected to the second pass assembly 14 so as to receive and circulate the further concentrated stream and the concentrate permeate stream from the second pass reverse osmosis array 32 during a saturation mode (shown in FIG. 12). The circulation circuit 16 connects the second reverse osmosis membrane provided by the second RO membrane elements 40 with the buffer tank 42 in the saturation mode. The circulation circuit 16 is operable in the saturation mode to feed and return fluid between buffer tank 42 and the second reverse osmosis membrane provided by the second RO membrane elements 40.

[0075] The second stage pump 30 can be used to pump fluid through the circulation circuit 16, to both draw fluid from the buffer tank 42 and piping of the circulation circuit 16 as well as push through the 2ndpass array 14. As the first pass array 12 may not be operating and providing pressure during this saturation mode as shown in FIG. 12, preferably a booster pump 44 is connected in fluid series with the second stage pump 30, at a location upstream of the second stage pump 30 and to initially receive and pump from the gravity fed outlet of the buffer tank 42.

[0076] As shown, the booster pump 44 is connected with a tank outlet 46 of the buffer tank 42. The booster pump 44 is operable to pump fluid from the buffer tank 42 toward the second stage pump 30, which second stage pump 30 is operable to pump fluid to the second reverse osmosis membrane provided by the second stage RO membrane elements 40. Preferably a particulate filter (e.g., five micron filter element(s) 48) is provided in the circulation circuit 16, such as in fluid series between the booster pump 44 and the second stage pump 30. The booster pump 44 is operable to pump tank fluid first through the filterelement(s) 48 before reaching the second pass assembly 14 and its second pass reverse osmosis array 32.

[0077] In operation, at least the second concentrate stream output 34 is recirculated (e.g, connected and fed to the buffer tank 42) in the saturation mode as shown in FIG. 12. Although RO purified water can be used for other purposes or otherwise output / removed from the system 10, preferably, the second permeate stream output 36 is combined therewith and also recirculated (e.g., connected and fed to the buffer tank 42) in the saturation mode.

[0078] Once saturation mode is finished (e.g., the desired and / or maximum level of concentration of concentrate product in the second concentrate is achieved), normal mode operation can commence as shown for example in FIG. 13. In the normal mode operation, the second stage pump 32 is operable to pump the first concentrate output from the first reverse osmosis membrane of the first pass reverse osmosis array 20 to the second reverse osmosis membrane of the second pass reverse osmosis array 32. In normal mode operation, the second concentrate stream output 34 may be finished product as far as the RO system 10 is concerned; and accordingly, the second concentrate stream output 34 can exit the system 10 as finished product, such as for further refining (e.g., in the case the system is used for lithium chloride production, evaporation of water typically in a subsequent separate processing area).

[0079] Referring in greater detail to the piping / plumbing and to accomplish an example of a more detailed embodiment as shown in FIGS. 7-8 (see also FIGS. 9-13), the reverse osmosis fluid concentration system 10 generally comprises an inlet supply conduit 50, a first permeate outlet conduit 52, first concentrate conduit 54, a second permeate outlet conduit 56, and a second concentrate outlet conduit 58.

[0080] The inlet supply conduit 50 is adapted to deliver a supply of feedstock fluid to be separated toward the first reverse osmosis membrane of the first pass RO array 20. The first stage pump 18 may be interposed along the inlet supply conduit 50 preferably along with first stage filter element(s) 60 (e.g., five micron particulate elements) upstream of the first pass RO array 20 to filter out and better prevent particulates from reaching the RO membrane elements thereof to prevent membrane clogging.

[0081] The first permeate outlet conduit 52 is adapted to carry away the first permeate stream output 22, which is RO purified water, which may be combined with the secondpermeate stream output 34 as shown in FIGS.7-8, which is also RO purified water. Such RO purified water can then exit the RO system 10 at permeate exit port 52 A and is itself can be considered a finished product that may be used by the end-user for such process water as solvent and / or for other purposes.

[0082] The first concentrate conduit 54 is generally interposed fluidly between the first pass RO array 20 and the second pass RO array 32. The first concentrate conduit 54 is adapted to connect the first reverse osmosis membrane of the first pass RO array 20 with the second reverse osmosis membrane of the second pass RO array 32 at least in the normal mode for supplying the first concentrate stream output to the second reverse osmosis membrane of the second pass RO array 32 for further concentrating the product concentrate stream.

[0083] The second permeate outlet conduit 56 is adapted to carry away the second permeate stream output 34, which like that of the first stage is RO purified water, which can be considered a finished product as far as the RO system 10 is concerned. The second permeate outlet conduit 56 is combined in this embodiment with the first concentrate conduit 54 and leads also to the permeate exit port 52A.

[0084] The second concentrate outlet conduit 58 is adapted to carry the first concentrate stream output toward a final product outlet port 58A as shown, which allows exit of high concentration concentrate which can be considered a finished product as far as the RO system 10 is concerned.

[0085] Additional details of plumbing and piping for buffer tank 42 and circulation circuit 16 are also shown. In the figures, it can be seen that the RO system 10 comprises a permeate return branch conduit 62, a concentrate return branch conduit 64, a first inlet branch conduit 66, and an outlet branch conduit 68.

[0086] The permeate return branch conduit 62 branches off and between the second permeate outlet conduit 56 and the buffer tank 42, with an operational valve opening and closing the branch as shown. The permeate return branch conduit 62 is normally closed during normal operation but open and operable during the saturation mode (e.g. FIG. 10) to connect and recirculate permeate from the second permeate outlet conduit 56 to the buffer tank 42 in the saturation mode.

[0087] The concentrate return branch conduit 64 branches off and between the second concentrate outlet conduit 58 and the buffer tank 42, with an operational valve opening andclosing the branch as shown. The concentrate return branch conduit 64 is also open and operable to connect the second concentrate outlet conduit 64 to the buffer tank 42 in the saturation mode to connect and recirculate the second concentrate stream output 36 when in the saturation mode.

[0088] The first inlet branch conduit 66 can be used to initially bypass the first concentrate stream output 22 to initially fill (partially or fully) the buffer tank with partially concentrated concentrate that has passed the first pass RO array 20, so that a supply of concentrate may be used for saturation mode. The first inlet branch conduit 66 branches off and between the first concentrate outlet conduit 54 and the buffer tank 42, with an operational valve opening and closing the branch as shown. The inlet branch conduit 66 is operable to connect the first concentrate conduit 54 and the buffer tank 43 in an first pass RO mode ((FIG. 11) to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank.

[0089] The outlet branch conduit 68 is connected to the tank outlet 46 of the buffer tank 42, and feeds the inlet portion circulation circuit 14, in which the booster tank 42 is connected through the outlet branch conduit 68 to branch back into the first concentrate outlet conduit 54, which feeds the second pass RO array 32 (e.g., at location upstream of second stage pump 30).

[0090] Further details such as motors, controls, valves, pressure gauges, concentration sensors and the like are also shown in FIGS. 7-8, which will be recognized as by schematic symbols shown. Operation of valves for example are used to switch between the various modes shown in FIGS. 9-13.

[0091] With the system now understood, an example of operational modes and example of sequence of operation is provided.

[0092] First a fill mode may be conducted as shown in FIG. 10. The RO system 10 is operational during a fill mode to direct a water stream (e.g., typically feedstock fluid that contains product that has not been concentrated, which includes fluid that is minimally concentrate that may have passed relatively quickly through the first stage RO array 20 during fill mode (as such “feedwater fluid stream” means raw feedstock fluid and / or fluid that has passed a membrane vessel and may have some additional concentration, such as having passed through the first pass RO array 20 for example). As shown, in the fill mode, feedwater is primed through the system to fill the vessels / elements of the first pass assemblyand to fill vessels / elements of the second pass assembly with water (e.g., feedstock water that has some low level concentrate of product dissolved in solution therein).

[0093] After fill mode, the system is primed and ready to elevate hydraulic pressures. The RO system 10 is then operational through the first pass RO mode shown in FIG. 11 to direct the concentrate stream (i.e., first concentrate stream output 22) from the first pass reverse osmosis array 20 to the buffer tank 42. This will initially purge the first pass RO array 20 of low concentrate water and start to increase concentrate levels in the first concentrate stream output 22 (and to some extent in the buffer tank 42).

[0094] After the fill mode and / or the first pass RO mode, the RO system 10 is operational through the saturation mode shown in FIG. 12 to circulate the concentrate stream from the buffer tank 42 through the second pass assembly 14 to saturate the second pass reverse osmosis array 32 with concentrate.

[0095] After fill mode, the system 10 is operational through a normal mode as shown if FIG. 13, to direct the concentrate stream (first concentrate stream output 22) from the first pass assembly 12 to the second pass assembly 14, and direct the further concentrated stream (second concentrate stream output 34) from the second pass assembly 14 with the saturated reverse osmosis array (a saturated condition of the second pass RO array) as a concentrated output stream of the system 10, which can be delivered to second concentrate outlet port 58 A.

[0096] OPERATIONAL DESCRIPTION OF AN EXAMPLE

[0097] The system is designed to provide 31 GPM of concentrated product water with a LiCl content of 11% (110,000 ppm). The unit accomplishes this by processing raw water with nominal 14,400 ppm LiCl through two RO passes. The first pass will produce LiCl concentration of 60,000 ppm, and the second pass will produce LiCl concentration of 110,000 ppm. Before normal steady state production is performed, the unit needs to complete two preparatory operational stages as described herein.

[0098] System Priming. The first step is to prime the RO first pass and RO second pass with raw feedwater. The user supplied raw water should have the following characteristics: 14,400 ppm LiCl and 60-70 psi. The raw water feed should be capable of providing 250 gpm. This step does not require the RO pumps to operate, the feedwater pressure is sufficient to fill the RO first and second passes.

[0099] Saturation. Once system priming is complete, the second step prior to steady state production is saturation. Saturation is the process by which the 2nd pass RO membranes are fdled with sufficient LiCl ions to support the concentration of LiCl for steady state operation.

[0100] Steady State Production. Once the saturation cycle is complete, the unit automatically transitions to steady state production unless manually stopped by the operator. During steady state production, the RO first pass is continuously operating. The first pass concentrate bypasses T1 and is sent directly to the second pass pumps. The second pass is continuously operating and sends 2nd pass concentrate with 11% LiCl to product piping. The steady state production mode will operate continuously unless manually stopped by the operator, if the concentrate drops below 10% LiCl, or if another alarm occurs.

[0101] The process is fully automated to achieve high yield. Additionally, the system will self-adjust automatically to changes in feed concentrations while maintaining optimum yield. The knowledge base necessary to manage variating incoming feeds is programmed into the PLC's logic.

[0102] System parameters for one embodiment:

[0103] SYSTEM DESCRIPTION:

[0104] Production capacity of 1194 m3 / day (219 gpm) of less than 1000 ppm TDS permeate (filtrate) and 169 m3 / day (31 gpm) 1 1% concentrated (product) water with 460V / 60 Hz / 3 Phase power.

[0105] LITHIUM PRODUCTION:

[0106] At the normal system operating condition of 31 gpm Concentrate flow at 11% LiCl, capable of producing 28 lbs LiCl per minute (1,680 Ibs / hr or 40,320 Ibs / day).

[0107] HIGH REJECTION & HIGH YIELD MEMBRANE ELEMENTS:

[0108] Frame Configuration Eight Element Length Membrane Element Vessels with Double Depth Membrane Rack

[0109] SALT REJECTION (CHLORIDE ION):[OHO] Per individual R.O. Membrane Element

[0111] Minimum 99.2%, Average 99.6%

[0112] SYSTEM FEED WATER:

[0113] FLOW - TABLE I:

[0114] SALINITY RANGE:

[0115] Up to 16,000 ppm TDS LiCl

[0116] TEMPERATURE RANGE: 0-38 degC

[0117] pH RANGE: 3-11

[0118] REVERSE OSMOSIS MEMBRANE:[0H9] TYPE: Selected aromatic tri-polyamid, thin film composite, spiral wound, single pass reverse osmosis membrane element.|0120] CHLORINE TOLERANCE: 0.1 PPM

[0121] SYSTEM FEED PRESSURE AND FLOW RATE - TABLE 2:

[0122] Flow rate 250 GPM|0123| METHODS / OPERATIONAL MODES

[0124] Fill mode (System priming) - at initial setup the unit is filled with water.

[0125] 1stPass RO mode - First pass of the unit is running to fill up the buffer tank with1stpass concentrate.

[0126] Saturation mode - 2ndpass of the unit is running in a closed loop with water coming in from the buffer tank and the 2ndpass concentrate and permeate returning to the buffer tank. LiCl saturates in the RO elements and this mode continues until the 2ndpass concentrate reaches maximum concentration of LiCl. The concentration of LiCl in the buffer tank is being reduced. When the buffer tank is depleted of LiCl below the conductivity setpoint, the buffer tank will be drained automatically, and the unit will automatically switch back to 1stpass RO mode to refill the buffer tank. The Saturation mode will continue again automatically when the buffer tank is full.

[0127] Automatic mode (Normal operation) - 1stand 2ndpass of the unit is running. The buffer tank is bypassed. Maximum concentration of LiCl is delivered to the customer in the 2ndpass concentrate. If the concentration of LiCl drops low, the saturation mode and / or 1stPass RO mode is repeated automatically. This mode can be run without doing 1stpass RO mode or Saturation mode prior. Automatic mode will run all necessary operations automatically.

[0128] 2ndPass Concentrate is the concentrated LiCl solution provided to customer as final product. 1stPass Permeate and 2ndPass Permeate are provided to customer as process water for other systems.

[0129] DEFINITIONS:

[0130] PERMEATE - The portion of the feedwater stream that passes through the RO membranes and is purified to low TDS levels. Also referred to as “filtrate”.

[0131] CONCENTRATE - The portion of the feedwater stream that flows around the RO membranes and receives the high concentration of LiCl ions. Also referred to as “product”.

[0132] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0133] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any nonclaimed element as essential to the practice of the invention.

[0134] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

WHAT IS CLAIMED IS:

1. A reverse osmosis fluid concentration system, comprising: a. a first pass assembly of a first pass pump and first pass reverse osmosis array- capable of separating a fluid stream into a concentrate stream and a permeate stream; b. a second pass assembly7of a second pass pump and second pass reverse osmosis array fluidly connected dow nstream of the first pass assembly, capable of separating the concentrate stream into a further concentrated stream and a concentrate permeate stream; and c. a buffer tank i) fluidly connected to the first pass assembly so as to receive the concentrate stream from the first pass reverse osmosis array during a first pass RO mode, and ii) fluidly connected to the second pass assembly so as to receive and circulate the further concentrated stream and the concentrate permeate stream from the second pass reverse osmosis array during a saturation mode.

2. The reverse osmosis fluid concentration system of claim 1, wherein the system is operational during a fill mode to direct a water stream through the first pass assembly to fill the first pass assembly and the second pass assembly with water.

3. The reverse osmosis fluid concentration system of any of claims 1-2, wherein the system operational through the first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank.

4. The reverse osmosis fluid concentration system of any of claims 1-3, wherein the system operational through the saturation mode to circulate the concentrate stream from the buffer tank through the second pass assembly to saturate the second pass reverse osmosis array with concentrate.

5. The reverse osmosis fluid concentration system of any of claims 1-4, wherein the system is operational through a normal mode to direct the concentrate stream from the first pass assembly to the second pass assembly, and direct the further concentrated stream fromthe second pass assembly with the saturated reverse osmosis array as a concentrated output stream of the system.

6. The reverse osmosis fluid concentration system of claim 1, wherein the system is operational during a fill mode to direct a water stream through the first pass assembly to fill the first pass assembly and the second pass assembly with water; then operational through the first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank; then operational through the saturation mode to circulate the concentrate stream from the buffer tank through the second pass assembly to saturate the second pass reverse osmosis array with concentrate; then operational through a normal mode to direct the concentrate stream from the first pass assembly to the second pass assembly, and direct the further concentrated stream from the second pass assembly with the saturated reverse osmosis array as a concentrated output stream of the system.

7. A reverse osmosis fluid concentration system, comprising: a first reverse osmosis membrane operable to separate fluid into a first concentrate stream output and a first permeate stream output; a second reverse osmosis membrane operable to generate a second concentrate stream output and a second permeate stream output; wherein the second reverse osmosis membrane is connected in fluid series dow nstream of the first reverse osmosis membrane in a normal operating mode to receive the first concentrate stream output from the first reverse osmosis membrane; a buffer tank; a circulation circuit connecting the second reverse osmosis membrane with the buffer tank in a saturation mode, the circulation circuit operable in the saturation mode to feed and return fluid between buffer tank and the second reverse osmosis membrane.

8. The reverse osmosis fluid concentration system of claim 7, wherein the second permeate stream output is connected and fed to the buffer tank in the saturation mode.

9. The reverse osmosis fluid concentration system of any of claims 7 and 8, wherein the second concentrate stream output is connected and fed to the buffer tank in the saturation mode.

10. The reverse osmosis fluid concentration system of any of claims 7-9, further comprising a first stage pump operable to pump fluid to the first reverse osmosis membrane.

11. The reverse osmosis fluid concentration system of any of claims 7-10, further comprising a second stage pump operable to pump fluid to the second reverse osmosis membrane.

12. The reverse osmosis fluid concentration system of claim 11, wherein:(a) in the normal mode, the second stage pump is operable to pump the first concentrate output from the first reverse osmosis membrane to the second reverse osmosis membrane; and(b) in the saturation mode, the second stage pump is operable to pump fluid contained in the buffer tank to the second reverse osmosis membrane.

13. The reverse osmosis fluid concentration system of any of claims 7-12. further comprising: an inlet supply conduit adapted to deliver a supply of feedstock fluid to be separated toward the first reverse osmosis membrane; a first permeate outlet conduit adapted to carry away the first permeate stream output; a first concentrate conduit adapted to connect the first reverse osmosis membrane with the second reverse osmosis membrane in the normal mode for supplying the first concentrate stream output to the second reverse osmosis membrane: a second permeate outlet conduit adapted to carry away the second permeate stream output; and a second concentrate outlet conduit adapted to carry the first concentrate stream output toward a final product outlet.

14. The reverse osmosis reverse osmosis fluid concentration system of claim 13, further comprising: a permeate return branch conduit operable to connect the second permeate outlet conduit to the buffer tank in the saturation mode; and a concentrate return branch conduit operable to connect the second concentrate outlet conduit to the buffer tank in the saturation mode.

15. The reverse osmosis fluid concentration system of any of claims 13 and 14, further comprising: an inlet branch operable to connect the first concentrate conduit and the buffer tank in an first pass RO mode to direct the concentrate stream from the first pass reverse osmosis array to the buffer tank.

16. The reverse osmosis fluid concentration system of any of claims 7-15, wherein the first reverse osmosis membrane is part of a first pass assembly, comprising a plurality of first pass membrane elements contained in a plurality of first vessels, respectively; and wherein the second reverse osmosis membrane is part of a second pass assembly comprising a plurality’ of second pass membrane elements contained in a plurality of second vessels, respectively.

17. The reverse osmosis fluid concentration system of claim 16, further comprising a fill mode wherein the system is operable during the fill mode to direct the supply of feedstock fluid through the first pass assembly to fill the first pass assembly and the second pass assembly with water.

18. The reverse osmosis system of any of claims 7-17, further comprising: a booster pump connected with a tank outlet of the buffer tank, and operable to pump fluid from the buffer tank toward the / a second stage pump that is operable to pump fluid to the second reverse osmosis membrane, and preferably through a particulate filter arranged between in fluid series between the tank outlet and the second reverse osmosis membrane.

19. A reverse osmosis fluid concentration system, comprising: a first reverse osmosis membrane operable to separate fluid into a first concentrate stream output and a first permeate stream output; a second reverse osmosis membrane operable generate a second concentrate stream output and a second permeate stream output; wherein the second reverse osmosis membrane is connected in fluid series dow n stream of the first reverse osmosis membrane in a normal operating mode to receive the first concentrate stream output from the first reverse osmosis membrane; a circulation circuit operable in a saturation mode to recirculate the second permeate stream output and the second concentrate stream output to the second reverse osmosis membrane.

20. The reverse osmosis fluid concentration system of claim 19, wherein the circulation circuit is operable in the saturation mode to recirculate the second permeate stream output and the second concentrate stream output only to the second reverse osmosis membrane and not the first second reverse osmosis membrane.21 The reverse osmosis fluid concentration system of any of claims 19-20, further comprising a buffer tank, the circulation circuit connecting the second reverse osmosis membrane with the buffer tank in the saturation mode.

22. A process for concentrating a product of a fluid stream, comprising: passing a feedwater fluid stream through a first pass assembly comprising a first reverse osmosis membrane to separate fluid into a first concentrate stream output and a first permeate stream output, with a second pass assembly arranged dow nstream of the first pass assembly, the second pass assembly comprising a second reverse osmosis membrane, the second pass assembly operable to generate a second concentrate stream output and a second permeate stream output, with the process further comprising:(a) operating in a saturation mode, which comprises recirculating the second concentrate stream output and the second permeate stream output through the second pass assembly to increase concentration of a concentrate product in the second concentrate stream; and(b) switching from the saturation mode to operating in a normal operating mode, which comprises passing the first concentrate stream through the second pass assembly thereby separating the first concentrate stream into the second concentrate stream output and the second permeate stream output.

23. The process of claim 22, further comprising: buffering the recirculating with a buffer tank that receives the second concentrate stream output and the second permeate stream output and feeds fluid contained in the buffer tank to the second pass assembly during the saturation mode.

24. The process of any of claims 22-23, further comprising: operating in a fill mode before operating in the saturation mode by filling the first pass assembly and the second pass assembly with the feedwater fluid stream.

25. The process of claim 24, further comprising operating in a first pass RO mode after the fill mode and before the saturating mode by directing the first concentrate stream output from the first pass assembly to the buffer tank to initially fill the buffer tank.

26. The process of any of claims 22-25, further comprising concentrating a lithium chloride feed solution in the saturation mode and the normal operating mode.

27. The process of claim 26, switching from saturation mode to normal operating mode at a set point once a contrate level is reached, preferably the concentrate level at least 10%. and more preferably at least 12%.

28. A process for concentrating a product of a fluid stream using a first pass assembly of a first pass pump and first pass reverse osmosis array capable of separating a fluid stream into a concentrate stream and a permeate stream; a second pass assembly of a second pass pump and second pass reverse osmosis array fluidly connected dow nstream of the first pass assembly, capable of separating the concentrate stream into a further concentrated stream and a concentrate permeate stream; a buffer tank i) fluidly connected to the first pass assembly so as to receive the concentrate stream from the first pass reverse osmosis arrayduring a first pass RO mode, and ii) fluidly connected to the second pass assembly so as to receive and circulate the further concentrated stream and the concentrate permeate stream from the second pass reverse osmosis array during a saturation mode; the process comprising the steps of: a. directing a water stream through the first pass assembly during a fill mode to fill the first pass assembly and the second pass assembly with water; then b. directing the concentrate stream from the first pass reverse osmosis array during the first pass RO mode to the buffer tank; then c. directing the concentrate stream from the buffer tank to the second pass assembly during the saturation mode, and circulating the further concentrated stream through the second pass assembly to saturate the second pass reverse osmosis array with concentrate; and then d. directing the concentrate stream from the first pass assembly to the second pass assembly and directing the further concentrated stream from the second pass assembly with saturated second pass reverse osmosis array as a concentrated output stream of the system during a normal mode.

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