EA040225B1 - REGULATION OF THE COMPOSITION OF THE PROCESS FLOW TO INCREASE THE PRODUCTIVITY OF THE ELECTROLYZER - Google Patents

Description

Cross-reference to related application

35 U.S.C. §119(e) this application claims priority of provisional patent application US 62/635731 entitled REGULATION OF PROCESS STREAM COMPOSITION FOR IMPROVED ELECTROLYZER#PERFORMANCE, filed Feb. 27, 2018, the contents of which are in full incorporated herein by reference for all purposes.

Technical field

In general, the aspects and embodiments discussed in this paper relate to electrochemical devices and, in particular, to electrochlorination cells and devices, systems and methods in which they are used.

Prior Art

Electrochemical devices used to obtain a solution of the product from the feed stream as a result of chemical reactions on the electrodes are widely used in industry and domestic industries. Examples of such reactions include the following.

A1. Electrochlorination to form sodium hypochlorite from sodium chloride and water.

Reaction at the anode: 2SG -E C1 ₂ + 2e

Reaction at the cathode: 2Na ⁺ + 2H ₂ O + 2e -E 2NaOH + H ₂

In solution: C1 ₂ + 2OIT -E SU' + SG + H ₂ O

Overall reaction: NaCI + H ₂ O -E NaOCI + H ₂

E ° _oh \u003d -1.36 V (Formation of chlorine)

E°red = -0.83 V (Hydrogen production)

E ° _YCH eyki \u003d -2.19V

A2. Precipitation reaction conditions.

Magnesium hydroxide: Mg ²⁺ + 2OIT -E Md (OH) ₂

Calcium carbonate: Ca ²⁺ + CO3 ² '-E CaCO3

B. The formation of sodium hydroxide and chlorine from sodium chloride and water, if the anode and cathode are separated from each other by a cation exchange membrane.

Reaction at the anode: 2SG -> C1 ₂ + 2e

Reaction at the cathode: 2H ₂ O + 2e ->2OH' + H ₂

Overall reaction: 2NaC1 + 2H ₂ O -> 2NaOH + C1 ₂ + H ₂

C. A redox vanadium energy storage battery in which the electrodes are separated by a proton-permeable membrane.

When charging:

Reaction on the first electrode: V ³⁺ + e V ²⁺

Reaction on the second electrode: V ⁴⁺ -> V ⁵⁺ + e

When discharging:

Reaction on the first electrode: V ²⁺ -E V ³⁺ + e

Reaction on the second electrode: V ⁵⁺ + e V ⁴⁺

In some embodiments, electrochlorination devices can be used to produce sodium hypochlorite from sodium chloride found in sea water.

The essence of the invention

One aspect of the present invention relates to an electrochemical cell. The electrochemical cell includes a housing having an inlet, an outlet and a central axis, as well as an anode-cathode pair located inside the housing essentially concentrically with respect to the central axis and limiting the active area between the anode and cathode of the anode-cathode pair, where the active surface area is at least the measure of one of the electrodes, including the anode and the cathode, exceeds the area of the inner surface of the housing, and the anode-cathode pair is designed and placed with the ability to direct the entire fluid flowing through the electrochemical cell in the axial direction through the active area.

In some embodiments, the overall density of the placement of electrodes in the electrochemical cell is at least about 2 mm ^-1 .

In some embodiments, the electrochemical cell further includes a central internal element located in the electrochemical cell and designed to block the flow of fluid through a portion of the electrochemical cell located along the central axis, and the central internal element is not associated with at least one of the electrodes of the anode- cathode.

In some embodiments, the anode-cathode pair is helically wound around a central axis.

- 1 040225

In some embodiments, the electrochemical cell further includes one or more helically wound bipolar electrodes. In some embodiments, the anode is offset laterally relative to the cathode along the length of the electrochemical cell.

In some embodiments, at least one of the anode and cathode electrodes is a rigid electrode. Both the anode and the cathode may include a titanium plate, and an oxidation resistant coating may be applied to the surface of the anode, the material of which is selected from the group consisting of platinum and mixed metal oxides. Both the anode and the cathode may include one or more of the following metals: titanium, nickel, and aluminum. The anode surface may be coated with an oxidation resistant coating material selected from the group consisting of platinum, mixed metal oxides, magnetite, ferrite, cobalt spinel, tantalum, palladium, iridium, gold and silver. At least one of the electrodes comprising an anode and a cathode may be fluid-permeable and/or may include a perforated titanium plate.

In some embodiments, the electrochemical cell further includes a separator designed to create a gap between the anode and cathode, and the separator is able to pass the electrolyte solution through the active area. The spacer may include a sleeve having slotted spokes that engage edges of at least one of the electrodes, including the anode and cathode. The sleeve may further include an electrical connector designed to form an electrical connection between one of the electrodes comprising an anode and a cathode and an electrical current source.

In some embodiments, the electrochemical cell further includes a sleeve including spokes in electrical contact with one of the electrodes, including an anode and a cathode. The spokes may have grooves that interact with the edges of one of the electrodes, including the anode and cathode, and maintain a gap between the turns of the spirally wound anode-cathode pair.

In some embodiments, the central inner member includes a non-conductive inner member located within the deepest turn of the anode-cathode pair.

In some embodiments, the anode-cathode pair includes a plurality of concentric tubular electrodes and gaps located between adjacent tubular electrodes. The set of concentric tubular electrodes may include one of the following sets: the set of tubular anodes (anode electrodes) and the set of tubular cathodes (cathode electrodes). One of the following sets: the set of tubular anodes and the set of tubular cathodes may consist of rigid electrodes.

In some embodiments, the plurality of concentric tubular electrodes includes a plurality of tubular anodes and a plurality of tubular cathodes.

In some embodiments, the electrochemical cell is designed to pass an electrical current (direct (direct) current and/or alternating current) through the electrolyte solution from the tubular anode to the tubular cathode in a single pass.

In some embodiments, the electrochemical cell further includes a bipolar tubular electrode positioned between the tubular anode and the tubular cathode.

In some embodiments, the tubular anode is laterally offset along the length of the electrochemical cell relative to a tubular cathode having the same diameter as the tubular anode. The electrochemical cell may include a tubular electrode including an anode half and a cathode half.

In some embodiments, the electrochemical cell further includes a plurality of bipolar tubular electrodes positioned between respective concentrically adjacent pairs of tubular anodes and tubular cathodes.

In some embodiments, at least one of the plurality of tubular anodes and the plurality of tubular cathodes is perforated and/or fluid-permeable.

In some embodiments, the electrochemical cell further includes at least one spacer positioned between adjacent tubular electrodes, wherein the at least one spacer is configured to limit and maintain a gap between adjacent tubular electrodes. The separator may allow the electrolyte solution to flow through a gap formed between adjacent tubular electrodes.

In some embodiments, the electrochemical cell further includes a metal sleeve including spokes electrically connected to the edges of the array of concentric tubular electrodes. Each spoke may include slots that engage with the edges of the concentric tubular electrode array to maintain gaps between adjacent tubular electrodes in the concentric tubular electrode array.

In some embodiments, the central inner member includes an end plug located at the end of the deepest concentric tubular electrode of the electrochemical cell.

In some embodiments, the electrochemical cell has a rounded cross section.

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In some embodiments, the electrochemical cell further includes an electrical connector electrically connected to one of the anode and cathode electrodes, wherein the electrical connector includes at least two materials having different resistances to chemical attack by the electrolyte solution. The at least two materials may include a first material and a second material, and the electrical connector may include a fluid-permeable piece made from the first material. The fluid-permeable part may include a plurality of holes.

In some embodiments, the electrochemical cell includes a plate or piece of a second material connected to a fluid-permeable piece made of a first material by one or more mechanical fasteners.

In some embodiments, the electrochemical cell includes a plate or piece of a second material connected to a fluid-permeable piece made of the first material by an interference fit.

In some embodiments, the electrochemical cell includes a plate or piece of a second material connected to a fluid-permeable piece made from the first material via a thread formed on the edge of the fluid-permeable piece made from the first material.

In some embodiments, the electrochemical cell includes a piece made from a second material connected to a fluid-permeable piece made from a first material by a thread formed on a cylindrical portion of the piece made from a second material.

In some embodiments, the electrochemical cell includes a piece made from a second material welded to a piece made from a first material.

Another aspect relates to a system including an electrochemical cell. The electrochemical cell includes a housing having an inlet, an outlet and a central axis and an anode-cathode pair located inside the housing substantially concentrically with respect to the central axis and delimiting the active area between the anode and cathode of the anode-cathode pair, where the active surface area of at least one of the electrodes, including the anode and cathode, exceeds the area of the inner surface of the housing, and the anode-cathode pair is designed and placed with the ability to direct all the fluid passed through the electrochemical cell in the axial direction through the active area. The system additionally includes an electrolyte source in fluid communication with the electrochemical cell. The electrochemical cell is designed to generate one or more reaction products from an electrolyte supplied from an electrolyte source and to release one or more reaction products. The system further includes a site for applying one or more reaction products generated by the electrochemical cell. One or more reaction products may include a disinfectant. The disinfectant may include sodium hypochlorite or essentially consist of sodium hypochlorite.

In some embodiments, the source of the electrolyte includes one of the following: saline (brine, brine) or sea water.

In some embodiments, the system is installed either on a ship or on an oil platform.

In some embodiments, the application site includes one of the following systems: a water cooling system or a ballast tank.

In some embodiments, the system is installed in a surface oil production system, with the site of application being the downhole portion of the oil production system.

Another aspect relates to an electrochemical cell. The electrochemical cell includes a cathode and an anode located in the housing, between which the gap is limited, and both the cathode and the anode include arcuate curved parts; the active surface area of the anode exceeds the area of the inner surface of the housing, and the active surface area of the cathode exceeds the area of the inner surface of the housing, and at the same time the cathode and the anode are designed with the ability and placed with the ability to direct the entire fluid flowing through the electrochemical cell in the axial direction through the gap.

In some embodiments, the anode includes a plurality of plates disposed away from the arcuate base, and the cathode includes a plurality of plates disposed away from the arcuate base, the plurality of anode plates being in alternation with the plurality of cathode plates.

Another aspect relates to an electrochemical cell. The electrochemical cell includes a cathode and an anode located in the housing, between which the gap is limited, and both the cathode and the anode include a part corresponding in shape to the corresponding parts of the inner surface of the housing; the active surface area of the anode exceeds the area of the inner surface of the housing, and the active surface area of the cathode exceeds the area of the inner surface of the housing, and at the same time the cathode and the anode are designed with the ability and placed with the ability to direct the entire fluid flowing through the electrochemical cell in the axial direction through the gap. At least

- 3 040225 one of the electrodes, including the anode and cathode, may include a profiled part.

Another aspect relates to the electrochlorination system. The system includes an electrolyser that is configured to be hydraulically connected between a source of supplied fluid and an outlet for the resulting fluid, and a subsystem designed to perform one of the following operations: increase the pH of the supplied fluid or increase the ratio of the content of monovalent ions to the content of divalent ions in supplied fluid, where the subsystem is located upstream relative to the cell.

In some embodiments, the subsystem includes a nanofiltration unit having an inlet configured to be hydraulically coupled to a source of feed fluid, where the unit is designed to separate the feed fluid into retentate and permeate (filtrate), where the retentate has a higher ratio of divalent ions to monovalent ion content than the permeate, and the plant has a permeate outlet designed to supply permeate to the cell inlet.

In some embodiments, the nanofiltration unit is designed to produce a permeate in which the concentration of monovalent ions is 2 to 10% lower than the concentration of monovalent ions in the feed fluid.

In some embodiments, the nanofiltration unit is designed to produce a permeate in which the concentration of divalent ions is 50 to 90% lower than the concentration of divalent ions in the feed fluid.

In some exemplary embodiments, the subsystem includes an electrodialysis unit having an inlet configured to be hydraulically connected to a supply fluid source, where the electrodialysis unit includes one or more monovalent ion selective membranes and an outlet for the concentrate stream located in the hydraulic interaction with the cell inlet. The electrodialysis unit may be designed such that it is capable of separating the feed fluid into a dilute solution stream and a concentrate stream and transfer predominantly monovalent ions from the dilute solution stream to the concentrate stream. The electrodialysis unit can be designed in such a way that its operation leads to an increase in the concentration of monovalent ions in the concentrate stream by 3 to 400% compared to the feed liquid.

In some exemplary embodiments, the subsystem includes an electrodialysis unit having an inlet configured to be hydraulically connected to a supply fluid source, and the electrodialysis unit includes one or more bipolar membranes and has an outlet designed to direct fluid flow having increased acidity along compared with the supplied fluid, into the cell inlet.

In some embodiments, the subsystem includes an electrodialysis unit having an inlet configured to be in fluid communication with a source of fluid supply, where the electrodialysis unit includes one or more bipolar membranes and an outlet designed to direct a fluid stream having an increased acidity compared to with the supplied fluid, into the inlet of the nanofiltration unit located upstream of the electrolytic cell. The nanofiltration plant can be designed to separate the fluid stream into retentate and permeate, where the retentate has a higher ratio of divalent ions to monovalent ions than the permeate, and the nanofiltration plant includes a permeate outlet designed to supply the permeate to the inlet electrolyzer.

In some exemplary embodiments, the subsystem includes a nanofiltration unit having an inlet configured to be hydraulically connected to a supply fluid source and an outlet in fluid communication with the electrodialysis unit, where the electrodialysis unit includes one or more monovalent selective membranes. ions, and a concentrate flow outlet in fluid communication with the cell inlet. The system may further include an oxygenation unit in fluid communication with and between the electrodialysis unit and the electrolyser, configured to supply oxygen to the concentrate stream prior to introducing the concentrate stream into the inlet of the electrolyzer.

In some embodiments, the subsystem includes an electrodialysis unit having an inlet configured to be in fluid communication with a source of fluid, one or more monovalent ion selective membranes, a dilute solution flow outlet in fluid communication with the inlet. nanofiltration plant, concentrate flow inlet, on

- 4 040225 in fluid communication with the permeate outlet of the nanofiltration unit, and the concentrate flow outlet in fluid communication with the cell inlet.

Another aspect relates to the method of operation of the electrochlorination system. The method includes the operation of a subsystem that is in hydraulic interaction with the source of the supplied fluid and the electrolyzer and located between them, where the operation includes performing one of the following operations: increasing the pH of the supplied fluid or increasing the ratio of the content of monovalent ions to the content of divalent ions in the supplied fluid, which results in the production of a modified feed fluid and introduction of the modified feed fluid into the cell.

In some embodiments, the operation of the subsystem includes separating the feed fluid in the nanofiltration plant into a retentate and a permeate, where the retentate has a higher ratio of divalent ions to monovalent ions than the permeate. The method may include obtaining a permeate, in which the concentration of monovalent ions is from 2 to 10% lower than the concentration of monovalent ions in the supplied fluid. The method may include obtaining a permeate, in which the concentration of divalent ions is from 50 to 90% lower than the concentration of divalent ions in the supplied fluid.

In some embodiments, the operation of the subsystem includes treating a feed fluid in an electrodialysis unit comprising one or more monovalent ion selective membranes. The method may include separating the feed fluid into a dilute solution stream and a concentrate stream and preferentially moving monovalent ions from the dilute solution stream to the concentrate stream in an electrodialysis unit. The concentration of monovalent ions in the concentrate stream increases by 3 to 400% compared to the feed liquid.

In some embodiments, operation of the subsystem includes treating a feed fluid in an electrodialysis unit including one or more bipolar membranes and supplying a fluid stream having an increased acidity compared to the feed fluid from the outlet of the electrodialysis unit to an inlet of the cell.

In some exemplary embodiments, operation of the subsystem includes treating a feed fluid in an electrodialysis unit comprising one or more bipolar membranes and supplying a fluid stream having an increased acidity compared to the feed fluid from an outlet of the electrodialysis unit to an inlet of a nanofiltration unit located upstream of the cell. The method may further include separating the fluid stream into retentate and permeate using a nanofiltration unit, where the retentate has a higher ratio of divalent ions to monovalent ions than the permeate, and feeding the permeate into the cell inlet.

In some exemplary embodiments, operation of the subsystem includes treating a feed fluid in a nanofiltration unit whose outlet is in fluid communication with an electrodialysis unit, where the electrodialysis unit includes one or more monovalent ion selective membranes, and supplying a concentrate stream from the electrodialysis unit to electrolyzer inlet. The method may further include adding oxygen to the concentrate stream prior to introducing the concentrate stream into the cell inlet.

In some exemplary embodiments, operation of the subsystem includes treating a feed fluid in an electrodialysis unit comprising one or more monovalent ion selective membranes, feeding a dilute solution stream from the electrodialysis unit into an inlet of a nanofiltration unit, feeding permeate recovered from the nanofiltration unit into a concentrate stream inlet provided in the electrodialysis unit; and feeding a concentrate stream from the electrodialysis unit to the electrolyzer inlet.

Brief description of graphic materials

The accompanying graphics are not necessarily to scale. All identical or substantially identical components depicted in the various graphics are identified with the same number. For clarity, not every component may be labeled on every drawing. In graphics:

in fig. 1A is a perspective view of one embodiment of an electrolyzer cell including an array of concentric tubular electrodes;

in fig. 1B is a side view of the concentric tubular electrode cell shown in FIG. 1A;

in fig. 1C is a cross-sectional view of the concentric tubular electrode cell shown in FIG. 1A;

in fig. 2 shows an electrolyzer system comprising 20 electrochemical cells connected in series via a hydraulic connection;

- 5 040225 in FIG. ZA presents a table of representative parameters of the cell system;

in fig. 3B is a table of representative mass flow rates in the cell system;

in fig. 3C is a table of representative volumetric hydrogen production rates in the cell system;

in fig. 3D is a table of representative mass production rates of substances in the cell system;

in fig. 4 shows a system for controlling the composition of the stream fed to the cell system by means of nanofiltration;

in fig. 5 shows the removal rates of selected compounds in one example of a nanofiltration system;

in fig. 6 shows a system for controlling the composition of the stream fed to the cell system by means of electrodialysis;

in fig. 7A shows relative concentrations of Cl ^- and SO4 ^{2 -} versus total dissolved solids (TDS) in a seawater-derived concentrate in one example of an electrodialysis module;

in fig. 7B shows relative concentrations of Cl ^- and SO4 ^{2 -} versus percent desalting in one example of an electrodialysis module;

in fig. 8A shows relative concentrations of selected cations versus total TDS in a seawater-derived concentrate in one example of an electrodialysis module;

In FIG. 8B shows relative concentrations of selected cations versus percent desalting in one example of an electrodialysis module;

in fig. 9A shows a system for adjusting the pH of a stream fed to an electrolytic cell by means of electrodialysis;

in fig. 9B is a more detailed view of the bipolar electrodialysis module shown in FIG. 9A;

in fig. 10 shows a system for adjusting the pH of the flow fed to the cell by nanofiltration;

in fig. 11A shows a system in which a combination of nanofiltration and electrodialysis is used to control the composition of the stream fed to the cell;

in fig. 11B shows another system that uses a combination of nanofiltration and electrodialysis to control the composition of the electrolyser feed stream;

in fig. 12A shows a feed composition control system coupled to an electrolytic cell designed to improve the reaction product;

in fig. 12B shows the relative effectiveness of reducing the hydrogen yield when various solutions are fed into the cell;

in fig. 13 shows a control system suitable for the embodiments of the electrochemical cells and systems discussed in this paper;

in fig. 14 shows a memory system suitable for the control system shown in FIG. 13;

in fig. 15A is a diagram of a test system suitable for evaluating the efficiency of an electrolyser recirculation system;

in fig. 15B shows the composition of the solution supplied to the system shown in FIG. 15A; and in FIG. 15C shows test results for the system shown in FIG. 15A.

Information confirming the possibility of carrying out the invention

Considered in this work, the aspects and examples of the invention are not limited to the details of structures and the location of components presented in the following description or shown in the drawings. Considered in this work aspects and examples of the invention can be embodied or applied in other ways. In addition, the phraseology and terminology used herein is for the purpose of description and should not be construed as limiting. As used herein, the terms including, having, and containing, and their various variations, include the items listed after the specified term and their equivalents, as well as additional items.

This paper discusses various embodiments of systems including electrochlorination cells and electrochlorination devices, however, this work is not limited to systems including electrochlorination cells or devices, and the aspects and embodiments discussed in this paper are applicable to systems including electrolytic and electrochemical cells used for any variety of purposes.

In currently commercially available cells for electrochlorination, one or two electrodes are usually designed in the form of concentric tubes (English concentric tube electrode, abbr. CTE) and parallel plates (English parallel plate, abbr. PPE).

Aspects and examples of implementation discussed in this paper generally relate to the system

- 6 040225 topics, including electrochemical devices in which disinfectants such as sodium hypochlorite are obtained. It should be understood that the terms electrochemical device and electrochemical cell and their grammatical variants include electrochlorination devices and electrochlorination cells and their grammatical variants. Aspects and examples of the implementation of electrochemical cells, discussed in this work, include one or more electrodes.

Embodiments of the electrochemical cells installed in the systems discussed in this work may include metal electrodes, such as one or more anodes, one or more cathodes and/or one or more bipolar electrodes. As used herein, the term metal electrodes, or grammatical variants thereof, includes electrodes made from or consisting of one or more metals, such as titanium, aluminum, or nickel, although the term metal electrode does not exclude electrodes comprising or consisting of other metals or alloys. In some embodiments, the metal electrode may include a plurality of layers of different metals. The metal electrodes used in one or more of the embodiments discussed herein may include a highly conductive metal core, such as copper or aluminum, which is coated with a metal or metal oxide that is highly resistant to chemical attack by electrolyte solutions, such as a layer from platinum, mixed metal oxide (COM, English mixed metal oxide, abbr. MMO), magnetite, ferrite, cobalt spinel, tantalum, palladium, iridium, silver, gold or other coating materials. Metal electrodes may be coated with an oxidation resistant coating, examples of which materials include, without limitation, platinum, mixed metal oxide (MMO), magnetite, ferrite, cobalt spinel, tantalum, palladium, iridium, silver, gold, or other coating materials. Mixed metal oxides used in the embodiments discussed herein may include an oxide or oxides of one or more of the following metals: ruthenium, rhodium, tantalum (optionally alloyed with antimony and/or manganese), titanium, iridium, zinc, tin, antimony, titanium-nickel alloy, titanium-copper alloy, titanium-iron alloy, titanium-cobalt alloy, or other suitable metals or alloys. The anodes used in the embodiments discussed herein may be coated with platinum and/or an oxide or oxides of one or more of the following metals: iridium, ruthenium, tin, rhodium, or tantalum (optionally alloyed with antimony and/or manganese). The cathodes used in the embodiments discussed herein may be coated with platinum and/or an oxide or oxides of one or more of the following metals: iridium, ruthenium and titanium. The electrodes used in the exemplary embodiments discussed herein may include a backbone of one or more of the following materials: titanium, tantalum, zirconium, niobium, tungsten, and/or silicon. The electrodes for any of the electrochemical cells in any of the systems discussed in this paper can be made in the form of or from plates, sheets, foils, extruded materials and/or sintered materials.

In some aspects and embodiments, it is indicated that the electrochemical cells installed in the systems discussed in this paper include rigid electrodes. As used herein, the term rigid object refers to an object that, in the absence of an applied force, retains its shape at normal operating temperature and/or at elevated temperature. As used herein, the term rigid electrode refers to an electrode having sufficient mechanical strength to allow it to maintain its shape and spacing between adjacent electrodes or coils of electrodes in various embodiments of the electrochemical cells and devices discussed in this paper without the need for spacers. For example, a flexible film having a metal coating is not considered a rigid electrode according to the present invention.

As used herein, the term tube (tubular) includes cylindrical pipes, but does not exclude pipes having a cross-section of a different shape, such as pipes having a cross-section of a square, rectangular, oval or rounded shape, or a cross-section in the form of a regular or irregular polygon.

As used herein, the terms concentric tubes or concentric coils include tubes or alternating (interleaved) coils having a common central axis, but does not exclude tubes or alternating coils surrounding a common central axis, which does not necessarily run through the center of each of the concentric tubes. or alternating coils in a set of concentric tubes or alternating coils.

In some embodiments, a line drawn from the central axis of the electrochlorination cell to the periphery of the electrochlorination cell in a plane perpendicular to the central axis passes through the array of plate electrodes. The plate electrode array may include an anode array and/or a cathode array and/or a bipolar electrode array. The central axis may be parallel to the average direction of fluid flow through the electrochemical cell.

In the embodiments of electrochemical cells installed in the systems discussed in this work, including a set of tubular anodes or cathodes, a set of tubular

- 7 040225 anodes may be generically referred to as an anode or an anode tube, and a plurality of tubular cathodes may be generically referred to as a cathode or cathode tube. In embodiments of electrochemical cells installed in systems including a plurality of tubular anodes and/or a plurality of tubular cathodes, a plurality of tubular anodes and/or a plurality of tubular cathodes may be collectively referred to as an anode-cathode pair.

In some aspects and embodiments of electrochemical cells installed in the systems discussed in this work, including concentric tubular electrodes, for example one or more of the anodes and/or cathodes discussed in this work, the electrodes are designed and placed with the ability to direct the fluid through one or more gaps present between the electrodes in a direction parallel to the central axis of the electrochemical cell. In some aspects and embodiments of electrochemical cells comprising concentric tubular electrodes, such as one or more of the anodes and/or cathodes discussed in this work, the electrodes are designed and placed with the ability to direct all fluid supplied to the electrochemical cell through one or more gaps available between the electrodes, in a direction parallel to the central axis of the electrochemical cell.

Electrochlorination cells are used in offshore, coastal, municipal, industrial and commercial applications. Appropriate design parameters for electrochlorination cells including a plurality of concentric tubular electrodes, such as electrode spacing, electrode thickness and coating density, electrode areas, electrical connection methods, etc., can be selected for various applications. The aspects and embodiments discussed herein are not limited to the number of electrodes, the distance between the electrodes, the material of the electrodes or the material of the separators, the number of passages within the cells for electrochlorination, or the material of the coating of the electrodes.

The content of PCT/US2016/018210 is hereby incorporated by reference in its entirety for all purposes.

Aspects and examples of implementation discussed in this work include systems and methods for controlling the composition of the stream supplied to the cell. The application of the considered methods allows to reduce the rate of precipitate formation and increase the concentration of hypochlorite produced in the cell.

Concentric tubular electrode (CTE) electrolytic cell configurations suitable for improving system efficiency have been discussed in US 62/633790, the contents of which are incorporated herein by reference in their entirety for all purposes. Electrolytic systems incorporating various variations of electrochemical cells (eg, CTE systems comprising a plurality of CTE cells) are discussed in PCT/US2019/019072, the contents of which are incorporated herein by reference in their entirety for all purposes. However, in addition to possible designs and placement of electrochemical cells, the efficiency of a CTE system strongly depends on the composition of the flow fed into it.

CTE systems are designed to operate with a seawater feed stream having a wide range of compositions such as those shown in Tables 1 and 2 below. may include the following components.

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Table 1. Components of typical sea water and their concentrations

Name Symbol mg/l (ppm) Chloride CI 19350 Sodium Na 10750 Sulfate SO ₄ 2700 Magnesium mg 1290 Calcium Sa 410 Potassium TO 380 Bicarbonate HCO3 140 Bromide Vg 65 Strontium Sr 13 Aluminum Al 1.9 Silicon Si 1.1 Fluoride F 0.8 Nitrate NO ₃ 0.8 Bor IN 0.4 Barium Ba 0.2 Iron Fe 0.1 Manganese Μη 0.1 Copper Xi 0.1 Lithium Li 0.1 Phosphorus P 0.06 Iodide 1 0.04 Silver Ag 0.02 Arsenic As <0.01 Nitrite NO ₂ <0.01 Zinc Zn <0.01 Total: 35000 (excluding H and O)

The various ionic components of seawater from various locations are listed in Table 1 below. 2.

Table 2. Main ions contained in sea water (mg/l)

And he typical sea water Eastern Mediterranean Arabian Gulf in Kuwait Red Sea off Jeddah Chloride (SG) 18980 21200 23000 22219 Sodium (Na ⁺ ) 10556 11800 15850 14255 Sulfate (SO ₄ ² ') 2649 2950 3200 3078 Magnesium (MD ²⁺ ) 1262 1403 1765 742 Calcium (Ca ²⁺ ) 400 423 500 225 Potassium (K ⁺ ) 380 463 460 210 Bicarbonate (HCO ₃ ') 140 - 142 146 Strontium (Sr ²⁺ ) 13 - - - Bromide (VG) 65 155 80 72 Borate (BO ₃ ³ ') 26 72 - - Fluoride (F') 1 - - - Silicate (SiO ₃ ² ') 1 - 1.5 - Iodide (G) <1 2 - - Other - - - - Total Dissolved Solids (TDS) 34483 38600 45000 41000

The conditions for the overall electrochemical reaction of forming NaOCl from sea water in the CTE system are indicated in the Background section of this description in equations A1 and A2.

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The main product of the reaction at the anode of the CTE system, in which NaOCl is formed from sea water, is Cl ₂ . The rate of formation of Cl ₂ depends on the magnitude of the anode current and the concentration of NaCl in the solution, and this rate, in turn, determines the amount of NaOCl formed in the solution. The dependence of the amount of NaOCl formed on the volume flow in the system determines the total concentration of the product.

The main reaction products at the cathode of the CTE system, in which NaOCl is formed from sea water, are H ₂ and OH ^- . The current, and thus the cathodic current density, governs the rates of product formation, and these rates of formation affect the pH in the system.

Although the pH of the bulk sea water is typically 7.5-8.4, the pH in the system is affected by the kinetics of the above reactions, as well as other factors.

When the hydrogen solubility threshold is exceeded, as it is generated, it begins to be released in the CTE cell, displacing the fluid medium and shielding the cathode. Reducing the local volume of the liquid (fluid) while maintaining the same rate of production of OH ^- increases the local pH at the cathode.

The local concentration of OH ^- at the cathode of the CTE cell is also velocity dependent, since turbulence and thus mixing are functions of velocity. Thus, reducing the flow rate also increases the local pH at the cathode.

Upon reaching a pH value of 8, sea water is supersaturated with CaCO ₃ . Upon reaching a pH value of 10.7-11, Mg(OH) ₂ begins to form. Both of these compounds adversely affect the efficiency of the CTE cell.

Varying the concentrations of Mg ²⁺ and Ca ²⁺ in solution also affects both the rate and the amount of precipitate formation.

Changes in the TDS (Total Dissolved Solids) of the process stream affect its conductivity and thus the overall power consumption of the cell, since the cell voltage is inversely proportional to the conductivity.

In FIG. 1A-1C show the Evoqua CTE cell according to the current state of the art. In FIG. 2 shows an example of a system including twenty CTE cells connected in series with a hydraulic connection. Particularly important parameters include seawater volume flow (FIG. 3A), mass flow rates shown in FIG. 3B, the space rates of H ₂ formation (FIG. 3C) and the mass production rates shown in FIG. 3D.

At a flow rate of 2-3 m/s, the system shown in FIG. 2 is capable of self-cleaning, provided that the feed stream has Na ⁺ concentrations of approximately 10,000 to 16,000 ppm, Cl ^- concentrations of approximately 18,000 to 23,000 ppm, Mg ²⁺ concentrations of approximately 750 to 1800 ppm , and Ca ²⁺ concentrations are approximately 200 to 500 ppm.

With these feed parameters, NaOCl output concentrations of about 2000 ppm to about 3000 ppm can be achieved. In this case, the concentration of the product is theoretically limited by the rate of precipitate formation and the amount of NaCl in solution. To improve the efficiency of the electrochlorination system, for example, the following can be done:

reducing precipitation (by adjusting the pH or removing Mg ²⁺ /Ca ²⁺ ); and/or increasing the concentration of NaCl in the feed stream.

Regulation of the composition of the process flow.

There are techniques to compensate for the stiffness caused by divalent ions and/or increased salt concentrations of monovalent ions. However, for the systems discussed above, many methods are impractical. Examples of suitable and inappropriate methods are given below.

Unsuitable.

Adding an anti-scale agent: the cost of the reagent required to process the required mass is too high.

Chelation: the cost of the reagent required to process the required mass is too high.

Distillation: The cost of energy required to process the required volumes is too high.

Electrodeionization (English electrodeionization, abbr. EDI): the feed material must have a low hardness, the values of which are outside the range used in the method.

Ion exchange: requires human participation; the cost and danger of the chemicals required for regeneration are too high.

Water liming/Clark method: requires human intervention; too much mass required for processing, and too high a cost of disposal of suspended waste.

Magnetic water treatment (abbr. AMT): the method has not been proven, there is little supporting data.

- 10 040225

Suitable.

Adding Acid: Adding acid can lower the pH, which can reduce scale formation.

Capacitive deionization (abbr. CAPDI): can reduce the concentration of divalent ions and increase the concentration of monovalent ions; relatively low energy consumption (cyclic adsorption/desorption).

Nanofiltration/Reverse Osmosis: can reduce divalent ion concentrations while reducing monovalent ion concentrations; relatively low energy consumption.

Electrodialysis (English electrodialysis, abbr. ED): can selectively transfer monovalent ions and/or generate acid.

Description of non-limiting embodiments of the invention

In FIG. 4 shows a system for regulating the composition of the feed stream by means of nanofiltration (English nanofiltration, abbreviated as NF). The authors suggest that the use of NF to reduce the hardness created by divalent ions, in particular Mg ²⁺ and Ca ²⁺ , and thus prevent the formation of deposits in the cell is a new technique. The NF unit separates seawater into retentate and filtrate, where the retentate has a higher ratio of divalent ions to monovalent ions than the filtrate. The filtrate withdrawn from the filtrate outlet of the NF unit is sent to the inlet of the cell. Literature data on such an NF system are shown in Fig. 5 (copied from: Telzhensky, M., Birnhack, L, Lehmann, ^O. , Windier, E., Lahav, O. Selective separation of seawater Mg ²⁺ ions for use in downstream water treatment processes ⁺ from sea water to be fed into water treatment processes Chemical Engineering Journal 175 (2011) 136-143).

In this configuration, monovalent ion concentrations can be reduced by about 2 to 10%, while divalent ion concentrations can be reduced by about 50 to 90%.

In FIG. 6 shows an electrodialysis (ED) feed composition control system. In such a system, monovalent ion-selective membranes are used to preferentially move monovalent ions from a dilute solution into a concentrate stream. Literature data on this method are shown in Fig. 7A-8B. In FIG. 7A-7B are specifications for one example of an ED system using monovalent ion selective membranes. During treatment (reducing TDS or increasing desalting), monovalent ions (Cl, Na, K) quickly move from the dilute solution into the concentrate stream, while divalent ions (SO ₄ , Mg, Ca) remain in the concentrate stream until until a high degree of TDS removal/desalting is achieved. In this configuration, the concentrations of monovalent ions in the concentrate stream can be increased by about 3 to 400% while changing the concentration of divalent ions.

In FIG. 9A shows a system for adjusting the pH of the cell feed stream by performing ED. In this system, bipolar membranes are used to produce H ⁺ and OH- (FIG. 9A). H ⁺ can serve to adjust the pH either in the cell (FIG. 9B) or in the NF module (FIG. 10).

In FIG. 11A and 11B show systems using NF and ED techniques to control the composition of the cell feed stream. In the system shown in Fig. 11A, NF is used to reduce the stiffness created by divalent ions. The NF retentate stream is directed to the dilute solution stream and to the monovalent ion selective ED module concentrate stream. Since the bromide ions pass into the concentrate stream, the dilute solution stream from the monovalent ion selective ED module can be used for other purposes, such as service water or cooling water. The concentrate stream, in which the concentration of divalent ions is reduced and the concentration of monovalent ions is increased, may be a feed stream directed to the cell.

In the system shown in Fig. 11B, the dilute stream from the monovalent ion selective ED module is first used to reduce the concentration of monovalent ions in the feed stream. The dilute solution stream from the ED device is then sent as feed to the NF module to reduce divalent ion hardness. The permeate from the NF module is then fed into the concentrate stream of the ED device to maintain the total monovalent ion concentration.

In FIG. 12A shows a feed composition control system coupled to an electrolyzer having means to improve the reaction product. Previous experiments comparing the improvement in the quality of the reaction product depending on the composition of the feed material, namely, sea water and saline, showed that the presence of rigidity due to the presence of Mg ²⁺ led to shielding of the cathode and a decrease in the operating current density from approximately 2200 to 200 A/m ² (FIG. 12B) while shifting from oxygen consumption to hydrogen production. In FIG. 12V shift from oxygen consumption to hydrogen production occurs at the inflection point

- 11 040225 ba, marked on each of the lines. The line Salt solution - 3 m/s, air - 1 bar (10 ⁵ Pa) represents the technical data without improvement. The line Brine - 3 m/s, O ₂ - 6.9 bar (6.9-105 Pa) represents the specifications with the improvements fully realized. The line Sea water - 3 m/s, O ₂ - 5 bar (5-10 ⁵ Pa) represents the deterioration in performance caused by the influence of Mg. After removing the hardness created by divalent ions, in particular Mg ²⁺ , using, for example, the nanofiltration plant shown in FIG. 12A, it is possible to create an electrolyser system that can produce NaOCl without producing hydrogen. An oxygen saturation device can also be used to supply oxygen to the electrochemical reactor stream, which reacts with dissolved H ⁺ to form water and prevent H ⁺ from being removed from the solution.

The controller used to monitor and regulate the operation of the various elements of the exemplary system discussed in this paper may include a computerized control system. Various aspects of the controller may be implemented as custom software executable by general purpose computer system 1000, such as shown in FIG. 13. Computer system 1000 may include a processor 1002 coupled to one or more devices 1004 such as a magnetic disk drive, semiconductor memory, or other data storage device. Memory 1004 is typically used to store programs and data during operation of computer system 1000. Components of computer system 1000 may be connected via a coupling mechanism 1006, which may include one or more buses (eg, between components that are integrated within a single machine) and /or a network (for example, between components that are in separate machines). The connector mechanism 1006 allows information (e.g., data, instructions) to be exchanged between system components of system 1000. Computer system 1000 also includes one or more input devices 1008, such as a keyboard, mouse, trackball, microphone, touch screen, and one or more devices 1010 output, such as a printer, display, and/or speaker.

Output devices 1010 may also include valves, pumps, or switches that may be used to introduce process water (e.g., brackish water or seawater) from a feed source to the electrochlorination system discussed in this paper or to an application site and/or to regulation of pumping speed. One or more sensors 1014 may also provide input to computer system 1000. These sensors may include, for example, pressure sensors, chemical concentration sensors, temperature sensors, fluid flow sensors, or sensors for any other electrochlorination system parameters required by the system operator. . These sensors may be installed anywhere in the system where they are desired, such as upstream of the application and/or electrochlorination system, or they may be in fluid communication with the feed source. In addition, computer system 1000 may include one or more interfaces (not shown) that connect computer system 1000 to a communications network along with or as an alternative to connection mechanism 1006.

Storage system 1012, shown in more detail in FIG. 14 typically includes a computer readable and writable durable recording medium 1102 that stores signals that determine the program being executed by the processor 1002 or information being processed by the program. The medium may include, for example, disk storage or flash memory. Typically, during operation, the processor reads data from the persistent storage medium 1102 into another memory 1104 that provides a faster processor access to information than the medium 1102. Such a memory device 1104 is typically a volatile random access storage device such as dynamic random access memory ( eng. dynamic random access memory, abbr. DRAM) or static storage device (eng. static memory, abbr. SRAM). It may reside in storage system 1012 or storage system 1004 as shown. Processor 1002 typically processes data in storage integrated circuit 1104 and copies the data to storage medium 1102 upon completion of processing. memory integrated circuit, and the aspects and examples of implementation discussed in this work are not limited to those listed. The aspects and examples of implementation discussed in this paper are not limited to a particular storage system 1004 or storage system 1012.

A computer system may include computer system hardware that is specially programmed for specific purposes, such as an application specific integrated circuit (ASIC). Aspects and exemplary embodiments discussed herein may be implemented in software, computer system hardware or firmware, or any combination thereof. In addition, such methods, activities, systems, system elements, and components thereof may be part of a computer system

- 12 040225 as above, or be an independent component.

While one type of computer system is exemplified by computer system 1000, with which various aspects and embodiments discussed herein can be implemented, it should be understood that the aspects and embodiments discussed herein are not limited to by means of the computer system shown in FIG. 13. The various aspects and embodiments discussed herein may be implemented using one or more computers having architectures or components other than those shown in FIGS. 13.

Computer system 1000 may be a general purpose computer system that can be programmed using a high-level computer programming language. The computer system 1000 may also be created using specially programmed dedicated hardware. Processor 1002 of computer system 1000 is typically a commercially available processor, such as the well-known Pentium™ or Core™ class processors available from Intel Corporation. Many other processors are also available which include programmable logic controllers. Such a processor typically runs on an operating system, which may be, for example, the Windows 7, Windows 8, or Windows 10 operating system supplied by Microsoft Corporation, MAC OS System X supplied by Apple Computer, the Solaris operating system supplied by Sun Microsystems, or UNIX. supplied by various companies. Many other operating systems may be used.

The processor and operating system together define the computer platform for which application programs are created in high-level programming languages. It should be understood that the invention is not limited to a particular computer platform system, processor, operating system, or network. In addition, those skilled in the art should understand that the aspects and embodiments discussed in this paper are not limited to a particular programming language or computer system. Additionally, it should be understood that other suitable programming languages and other suitable computer systems may also be used.

One or more of the parts of the computer system may be distributed in one or more computer systems (not shown) connected by a communications network. These computer systems may also be general purpose computer systems. For example, various aspects of the invention may be distributed across one or more computer systems designed to serve (eg, servers) one or more client computers or to perform a common task as part of a distributed system. For example, the various aspects and embodiments discussed herein may be executed on a client-server system that includes components distributed on one or more server systems that perform different functions in accordance with the various aspects and embodiments discussed herein. work. These components may be executable intermediate (eg, IL) or interpreted (eg, Java) code that is transmitted over a communications network (eg, the Internet) using a communications protocol (eg, TCP/IP). In some embodiments, one or more components of computer system 200 may communicate with one or more other components via a wireless network, including, for example, a cellular network.

It should be understood that the aspects and examples of implementation discussed in this paper are not limited to implementation using any particular system or group of systems. It should also be understood that the aspects and examples of implementation discussed in this paper are not limited to any particular distributed (provided, English distributed) architecture, network or communication protocol. The various aspects and embodiments discussed in this paper may be programmed using an object-oriented programming language such as SmallTalk, Java, C++, Ada, or C# (C-Sharp). Other object-oriented programming languages may also be used. Alternatively, functional, scripting, and/or logic programming languages, such as ladder logic, may be used. Various aspects and examples of implementation discussed in this paper can be executed in a non-programmable environment (for example, documents created in HTML, XML, or other formats that, when viewed in a viewer window, demonstrate aspects of a graphical user interface (English graphical- user interface, GUI for short) or perform other functions). The various aspects and embodiments discussed in this paper may be implemented as programmable or non-programmable elements, or any combination thereof.

Example.

In FIG. 15A shows the cell recirculation system under test.

In this plant, a 3.5% solution of synthetic sea salt was prepared in the product tank.

- 13 040225 Instant Ocean® water (Fig. 15B). When voltage was applied to the cell, this solution was recirculated through the cell for various periods of time (FIG. 15C, from 7 to 120 minutes). Gaseous H ₂ was removed as it was formed, accumulating the NaOCl product.

As noted in the discussion above, it is believed that the withdrawal of H ₂ avoids shielding of the cathode, which allows you to maintain local pH at the level of the value in the bulk solution and reduce the rate of precipitation of Mg(OH) ₂ . Indeed, the measured pH of the bulk solution was between 8.6 and 8.8 and no precipitation was observed either.

After continuous operation, the concentration of the NaOCl product was measured by iodometric titration. Product concentrations of approximately 750 to 6200 ppm were achieved (FIG. 15C). These results are significantly higher than in prior art installations.

The authors believe that the control of the composition of the feed stream, as well as the aspects and examples of implementation discussed in this paper, will achieve the same or greater efficiency.

The phrases and terms used in this work are for the purpose of description and should not be construed as limiting. As used in this work, the term collection means two or more objects or components. The terms including, carrying, having, and containing, as used in the specification or claims and like sections, are non-limiting terms, i.e. means inclusive without limitation. Thus, the use of such terms covers the objects listed after them and their equivalents, as well as additional objects. With respect to claims, only the transitional phrases consisting of and essentially consisting of have a limiting or semi-limiting meaning, respectively. The use of ordinal numbers, such as first, second, third, etc. in the claims for the definition of the claimed element does not in itself imply the priority, precedence or order of one claimed element with respect to another or the temporal order in which the operations of the method are performed; such designations are used as indicators to distinguish one claimed element having a certain name from another element having the same name (except for the use of the original term), to distinguish the claimed elements.

Thus, after considering certain aspects of at least one exemplary embodiment, it should be understood that various changes, modifications, and improvements to these aspects may be made by those skilled in the art. Any feature discussed in any embodiment may be included in any feature of any other embodiment or replaced by any feature of any other embodiment. Such changes, modifications and improvements should form part of the present invention and be included within the scope of the invention. Accordingly, the above description and drawings are provided by way of example only.

Claims (22)

CLAIM 1. An electrochlorination system, including: an electrolyser configured to be hydraulically connected between a source of supplied fluid and an outlet for discharging the resulting fluid; and a subsystem including an electrodialysis unit having an inlet configured to be hydraulically connected to a source of supplied fluid, one or more monovalent ion selective membranes, and a concentrate flow outlet in fluid communication with the inlet. cell, where the subsystem is designed to perform one of the following operations: increase the pH of the supplied fluid or increase the ratio of the content of monovalent ions to the content of divalent ions in the supplied fluid, and is located upstream of the cell. 2. The system of claim 1, wherein the electrodialysis unit is configured to separate the feed fluid into a dilute solution stream and a concentrate stream and to preferentially move monovalent ions from the dilute solution stream to the concentrate stream. 3. The system of claim 2, wherein the electrodialysis unit is designed to increase the concentration of monovalent ions in the concentrate stream compared to the feed liquid by an amount ranging from 3 to 400%. 4. The system of claim 1, wherein the subsystem includes an electrodialysis unit having an inlet configured to be in fluid communication with a supply fluid source, one or more bipolar membranes, and an outlet configured to direct fluid flow having increased acidity compared to the fluid supplied to the cell inlet. 5. The system of claim 1, wherein the subsystem includes an electrodialysis unit having an inlet - 14 040225 an opening configured to be hydraulically connected to a source of supplied fluid, one or more bipolar membranes, and an outlet designed to direct a fluid flow having an increased acidity compared to the supplied fluid into the inlet of the nanofiltration unit, located upstream of the cell. 6. The system of claim 5, wherein the nanofiltration unit is configured to separate the fluid stream into retentate and permeate, where the retentate has a higher ratio of divalent ions to monovalent ions than the permeate, and the nanofiltration unit includes a permeate outlet, designed to supply permeate to the cell inlet. 7. The system according to claim 1, in which the subsystem includes a nanofiltration unit having an inlet made with the possibility of hydraulic connection with a source of supplied fluid, and an outlet in fluid communication with the electrodialysis unit, where the electrodialysis unit includes one or more membranes , selective with respect to monovalent ions, and has an outlet for the flow of the concentrate, which is in fluid communication with the inlet of the cell. 8. The system of claim 7, further comprising an oxygenation unit that is in fluid communication with, and is located between, the electrodialysis unit and the electrolyser, and is configured to add oxygen to the concentrate stream prior to introducing the concentrate stream into the inlet of the electrolyzer. 9. The system of claim 1, wherein the subsystem includes an electrodialysis unit having an inlet configured to be hydraulically connected to a source of fluid to be supplied, one or more monovalent ion selective membranes, a dilute solution flow outlet located in fluid communication with the inlet of the nanofiltration unit, a concentrate flow inlet in fluid communication with the permeate outlet of the nanofiltration unit, and a concentrate flow outlet in fluid communication with the inlet of the cell. 10. The method of operation of the electrochlorination system according to claim 1, which includes: the operation of a subsystem that is in hydraulic interaction with the supply fluid source and the electrolyzer and located between them, in order to perform one of the following operations: increase the pH of the supplied fluid or increase the content ratio monovalent ions to the content of divalent ions in the supplied fluid, resulting in a modified supplied fluid; and introducing the modified feed fluid into the cell. 11. The method of claim 10, wherein operation of the subsystem includes separating the feed fluid in the nanofiltration plant into a retentate and a permeate, wherein the retentate has a higher ratio of divalent ions to monovalent ions than the permeate. 12. The method according to claim 11, including obtaining a permeate, in which the concentration of monovalent ions is from 2 to 10% lower than the concentration of monovalent ions in the fluid supplied. 13. The method according to claim 11, including obtaining a permeate, in which the concentration of divalent ions is from 50 to 90% lower than the concentration of divalent ions in the fluid supplied. 14. The method of claim 10, wherein operating the subsystem includes treating a feed fluid in an electrodialysis unit comprising one or more monovalent ion selective membranes. 15. The method of claim 14, comprising separating the fluid supplied to the electrodialysis unit into a dilute solution stream and a concentrate stream, and preferentially moving monovalent ions from the dilute solution stream to the concentrate stream. 16. The method according to claim 15, comprising increasing the concentration of monovalent ions in the concentrate stream compared to the feed liquid by an amount ranging from 3 to 400%. 17. The method of claim 10, wherein operating the subsystem includes treating a feed fluid in an electrodialysis machine including one or more bipolar membranes and supplying a fluid stream having an increased acidity compared to the feed fluid from an outlet of the electrodialysis machine to electrolyzer inlet. 18. The method of claim 10, wherein operating the subsystem includes treating a feed fluid in an electrodialysis machine including one or more bipolar membranes and supplying a fluid stream having an increased acidity compared to the feed fluid from an outlet of the electrodialysis machine to the inlet of the nanofiltration unit located upstream of the electrolytic cell. 19. The method of claim 18, further comprising separating the fluid flow into a retentate and a permeate in the nanofiltration plant, wherein the retentate has a higher ratio of divalent ions to monovalent ions than the permeate, and supplying the permeate to the inlet - 15 040225 cell opening. 20. The method of claim 10, wherein operating the subsystem includes treating the feed fluid in a nanofiltration unit whose outlet is in fluid communication with the electrodialysis unit, where the electrodialysis unit includes one or more monovalent ion selective membranes and supplying the concentrate flow from the electrodialysis unit to the cell inlet. 21. The method of claim 20, further comprising adding oxygen to the concentrate stream prior to introducing the concentrate stream into the cell inlet. 22. The method of claim 10, wherein operating the subsystem includes treating a feed fluid in an electrodialysis unit comprising one or more monovalent ion selective membranes, feeding a dilute solution stream from the electrodialysis unit to an inlet of the nanofiltration unit, supplying permeate, withdrawn from the nanofiltration unit, into the concentrate flow inlet of the electrodialysis unit, and feeding the concentrate stream from the electrodialysis unit into the inlet of the electrolyzer.