In some embodiments, the system further comprises a controller configured to operate the parallel electrochemical cell at one of the first current density or the second current density.

In some embodiments, the system further comprises a controller configured to operate the parallel electrochemical cell at one of the first flow rate or the second flow rate.

In accordance with another aspect, there is provided an electrochlorination system. The system comprises a source of feed fluid, a product fluid outlet, a pair of parallel electrochemical cells fluidly connected in parallel to a fluid outlet of the source of feed fluid, a series electrochemical cell connected fluidically in series between the pair of parallel electrochemical cells and the product fluid outlet, and a controller configured to operate the pair of parallel electrochemical cells at one of a first current density or a first flow rate, and to operate the series electrochemical cell at a second current density or second flow rate different from the first current density or first flow rate.

In some embodiments, the controller is configured to operate each of the electrochemical cells in the pair of parallel electrochemical cells and the series electrochemical cell at a same current density.

In accordance with another aspect, there is provided a method of operating an electrochlorination system. The method comprises flowing a feed fluid through a first electrochemical cell and through a second electrochemical cell of the system, the second electrochemical cell being operated at one of a different current density or a different flow velocity than a respective current density or flow velocity of the first cell.

In some embodiments, the method comprises flowing the feed fluid through the first electrochemical cell and through the second electrochemical cell in series.

In some embodiments, the method comprises flowing the feed fluid through the first electrochemical cell and through the second electrochemical cell in parallel.

In some embodiments, the method further comprises flowing the feed fluid through a third electrochemical cell in series with the first and second electrochemical cells.

In some embodiments, the method further comprises one of flowing the feed fluid from both the first and second electrochemical cells into the third electrochemical cell, or flowing the feed fluid from the third electrochemical cell into both the first and second electrochemical cells.

In some embodiments, the flow velocity of the feed fluid through the third electrochemical cell is a sum of the flow velocities of the feed fluid through the first and second electrochemical cells.

In some embodiments, each of the first, second, and third electrochemical cells are operated at a same current density.

In some embodiments, the method comprises flowing the feed fluid through the first and second electrochemical cells at a same flow velocity.

In some embodiments, the method further comprises operating the first electrochemical cell at a higher current density than the second electrochemical cell.

In some embodiments, the method comprises flowing the feed fluid through the second electrochemical cell at a flow velocity higher than a flow velocity of the feed fluid through the first electrochemical cell.

In some embodiments, the method further comprises recirculating feed fluid from an outlet of the second electrochemical cell to an inlet of the second electrochemical cell.

In some embodiments, the method further comprises operating the first electrochemical cell at a higher current density than the second electrochemical cell. In some embodiments, the method further comprises recirculating feed fluid from an outlet of the second electrochemical cell to an inlet of the first electrochemical cell.

In some embodiments, the method further comprises operating the first electrochemical cell at a higher current density than the second electrochemical cell.

In some embodiments, the method further comprises flowing the feed fluid from a product tank into the first electrochemical cell, from the first electrochemical cell through the second electrochemical cell, and from the second electrochemical cell back into the product tank.

In some embodiments, the method further comprises operating the first electrochemical cell at a higher current density than the second electrochemical cell.

In some embodiments, the method further comprises flowing the feed fluid from the first electrochemical cell into a product tank.

In some embodiments, the method further comprises recirculating feed fluid from the product tank through the second electrochemical cell and then back into the product tank.

In some embodiments, the method further comprises operating the first electrochemical cell at a higher current density than the second electrochemical cell.

In accordance with another aspect, there is provided a method of operating an electrochlorination system. The method comprises flowing feed fluid through an electrolyzer at a first flow rate to produce a product solution, the electrolyzer including one or more electrochemical cells, flowing the product solution from the electrolyzer operating at the first flow rate into a product tank, recirculating the product solution from the product tank through the electrolyzer and back into the product tank at a second flow rate higher than the first flow rate, and flowing the product solution at a third flow rate higher than the second flow rate from the product tank and through an outlet of the electrochlorination system to a point of use.

Embodiments of methods disclosed herein may include electrochemically generating a product solution having a NaOCl concentration of at least 3000 ppm from the feed fluid.

Embodiments of methods disclosed herein may include electrochemically generating a product solution having a NaOCl concentration of at least 6000 ppm from the feed fluid.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1A is a perspective view of an embodiment of a concentric tube electrolyzer cell;

FIG. 1B is a side view of the concentric tube electrolyzer cell of FIG. 1A;

FIG. 1C is a cross-sectional view of the concentric tube electrolyzer cell of FIG. 1A;

FIG. 2A is a perspective view of an embodiment of a multi-tube concentric tube electrolyzer cell;

FIG. 2B is a side view of the concentric tube electrolyzer cell of FIG. 2A;

FIG. 2C is a cross-sectional view of the concentric tube electrolyzer cell of FIG. 2A;

FIG. 3 includes tables listing different design parameters of a 20-cell electrolyzer system;

FIG. 4 illustrates examples of different arrangements of fluidic connections between cells in an electrolyzer system;

FIG. 5 illustrates examples of different arrangements of electrical connections between cells in an electrolyzer system;

FIG. 6 illustrates examples of different arrangements recirculation lines between cells in an electrolyzer system;

FIG. 7 illustrates recirculation of fluid from a product tank through an electrochemical cell in an electrolyzer system.

FIG. 8 depicts an example of a once-through electrolyzer system;

FIG. 9 depicts an example of a feed-and-bleed electrolyzer system;

FIG. 10 depicts an example of a once-through electrolyzer system including a plurality of CTE cells in series;

FIG. 11 depicts another example of a once-through electrolyzer system including a plurality of CTE cells in series;

FIG. 12 depicts an example of a once-through electrolyzer system including a first plurality of CTE cells operated in parallel and a second plurality of CTE cells operated in series;

FIG. 13 depicts another example of a once-through electrolyzer system including a plurality of CTE cells in series;

FIG. 14 depicts an example of an electrolyzer system including a first plurality of CTE cells operated in series and a parallel CTE cell disposed in a feed-and-bleed line from a product tank;

FIG. 15A depicts another example of a feed-and-bleed electrolyzer system;

FIG. 15B is a table of operating parameters of the system of FIG. 15A;

FIG. 16 illustrates a control system for embodiments of electrochemical cells and systems disclosed herein; and

FIG. 17 illustrates a memory system for the control system of FIG. 16.

DETAILED DESCRIPTION

Aspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects and embodiments disclosed herein are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

This disclosure describes various embodiments of systems including electrochlorination cells and electrochlorination devices, however, this disclosure is not limited to systems including electrochlorination cells or devices and the aspects and embodiments disclosed herein are applicable to systems including electrolytic and electrochemical cells used for any one of multiple purposes.

Current commercially available electrochlorination cells are typically based on one of two electrode arrangements, concentric tubes (CTE) and parallel plates (PPE).

Aspects and embodiments disclosed herein are generally directed to systems including electrochemical devices to generate disinfectants such as sodium hypochlorite. The terms “electrochemical device” and “electrochemical cell” and grammatical variations thereof are to be understood to encompass “electrochlorination devices” and “electrochlorination cells” and grammatical variations thereof. Aspects and embodiments of electrochemical cells disclosed herein are described as including one or more electrodes.

Embodiments of electrochemical cells included in systems disclosed herein may include metal electrodes, for example, one or more anodes, one or more cathodes, and/or one or more bipolar electrodes. The term “metal electrodes” or grammatical variation thereof as used herein is to be understood to encompass electrodes formed from, comprising, or consisting of one or more metals, for example, titanium, aluminum, or nickel although the term “metal electrode” does not exclude electrodes including of consisting of other metals or alloys. In some embodiments, a “metal electrode” may include multiple layers of different metals. Metal electrodes utilized in any one or more of the embodiments disclosed herein may include a core of a high-conductivity metal, for example, copper or aluminum, coated with a metal or metal oxide having a high resistance to chemical attack by electrolyte solutions, for example, a layer of titanium, platinum, a mixed metal oxide (MMO), magnetite, ferrite, cobalt spinel, tantalum, palladium, iridium, silver, gold, or other coating materials. “Metal electrodes” may be coated with an oxidation resistant coating, for example, but not limited to, platinum, a mixed metal oxide (MMO), magnetite, ferrite, cobalt spinel, tantalum, palladium, iridium, silver, gold, or other coating materials. Mixed metal oxides utilized in embodiments disclosed herein may include an oxide or oxides of one or more of ruthenium, rhodium, tantalum (optionally alloyed with antimony and/or manganese), titanium, iridium, zinc, tin, antimony, a titanium-nickel alloy, a titanium-copper alloy, a titanium-iron alloy, a titanium-cobalt alloy, or other appropriate metals or alloys. Anodes utilized in embodiments disclosed herein may be coated with platinum and/or an oxide or oxides of one or more of iridium, ruthenium, tin, rhodium, or tantalum (optionally alloyed with antimony and/or manganese). Cathodes utilized in embodiments disclosed herein may be coated with platinum and/or an oxide or oxides of one or more of iridium, ruthenium, and titanium. Electrodes utilized in embodiments disclosed herein may include a base of one or more of titanium, tantalum, zirconium, niobium, tungsten, and/or silicon. Electrodes for any of the electrochemical cells in any of the systems disclosed herein can be formed as or from plates, sheets, foils, extrusions, and/or sinters.

Some aspects and embodiments of electrochemical cells included in systems disclosed herein are described as including rigid electrodes. As the term is used herein, a “rigid” object is one that maintains its shape in the absence of an applied force at a normal operating temperature and/or at an elevated temperature. A “rigid electrode,” as the term is used herein, is considered to have sufficient mechanical stiffness such that it maintains its shape and separation between adjacent electrodes or electrode windings in the various embodiments of electrochemical cells and devices disclosed herein without the need for spacers. For example, a flexible film including a metal coating is not to be considered a “rigid electrode” as the term is used herein.

The term “tube” as used herein includes cylindrical conduits, however, does not exclude conduits having other cross-sectional geometries, for example, conduits having square, rectangular, oval, or obround geometries or cross-sectional geometries shaped as any regular or irregular polygon.

The terms “concentric tubes” or “concentric spirals” as used herein includes tubes or interleaved spirals sharing a common central axis but does not exclude tubes or interleaved spirals surrounding a common axis that is not necessarily central to each of the concentric tubes or interleaved spirals in a set of concentric tubes or interleaved spirals.

In some embodiments, a line passing from a central axis of an electrochlorination cell toward a periphery of the electrochlorination cell in a plane defined normal to the central axis passes through multiple electrode plates. The multiple electrode plates may include multiple anodes and/or multiple cathodes and/or multiple bipolar electrodes. The central axis may be parallel to an average direction of flow of fluid through the electrochemical cell.

In embodiments of electrochemical cells included in systems disclosed herein including multiple anode or cathode tube electrodes, the multiple anode tube electrodes may be referred to collectively as the anode or the anode tube, and the multiple cathode tube electrodes may be referred to collectively as the cathode or the cathode tube. In embodiments of electrochemical cells included in systems including multiple anode and/or multiple cathode tube electrodes, the multiple anode tube electrodes and/or multiple cathode tube electrodes may be collectively referred to herein as an anode-cathode pair.

In some aspects and embodiments of electrochemical cells included in systems disclosed herein including concentric tube electrodes, for example, one or more anodes and/or cathodes as disclosed herein, the electrodes are configured and arranged to direct fluid through one or more gaps between the electrodes in a direction parallel to a central axis of the electrochemical cell. In some aspects and embodiments of electrochemical cells including concentric tube electrodes, for example, one or more anodes and/or cathodes as disclosed herein, the electrodes are configured and arranged to direct all fluid introduced into the electrochemical cell through the one or more gaps between the electrodes in a direction parallel to a central axis of the electrochemical cell.

Electrochlorination cells are used in marine, offshore, municipal, industrial and commercial applications. The design parameters of electrochlorination cells including a plurality of concentric electrode tubes, for example, inter-electrode spacing, thickness of electrodes and coating density, electrode areas, methods of electrical connections, etc., can be selected for different implementations. Aspects and embodiments disclosed herein are not limited to the number of electrodes, the space between electrodes, the electrode material or spacer material, number of passes within the electrochlorination cells or electrode coating material.

PCT application PCT/US2016/018210 is incorporated herein by reference in entirety for all purposes.

One major consideration for CTE cells is that of cathodic scaling, which limits the overall strength of hypochlorite that can be generated. As local pH at the cathode approaches 10.7-11, magnesium in solution will precipitate to form magnesium hydroxide and occlude the electrode surface. Without being bound to a particular theory, it is believed that the following reactions may occur at the cathode of a CTE cell to generate scale:

CaCl₂)+2HCO₃+2 NaOH→CaCO₃+2H₂O⁻+2NaCl

2NaOH+MgCl₂→2NaCl+MG(OH)₂

The potential for scale can also increase due to the presence of excessive hydrogen (reduced volume) and high temperature (faster kinetics). If scale deposits are continuously allowed to form, they can occlude the CTE electrode gap, causing the system to fail.

Two measures for the prevention of scale are:

- Turbulence: Velocities above 2 m/s are considered to clean scale
- Current Density: 3000 A/m²is nominal, but can be reduced to about 1500 A/m²

Aspects and embodiments disclosed herein provide for the operation of systems including multiple CTE cells to produce product with a higher concentration of NaOCl than previously achievable without build up of scale in the CTE cells of the systems. Aspects and embodiments may achieve these advantages by selection of appropriate configurations of CTE cells with appropriate flow velocities and current densities. Other parameters that may be selected or adjusted to achieve high product concentration without cell scaling include feedwater composition (e.g., TDS, pH, etc.) and/or kinetics (e.g., temperature, flow rate, etc.).

Another aspect of cell design is that of volumetric footprint, since larger footprints have higher relative operating expense (OPEX) costs. Previous state of the art CTE cells, for example, as illustrated in FIGS. 1A-1C contained an anode surface area of about 0.138 m²within an approximate volume of 0.02 m³. Current state of the art CTE cells including multiple alternating concentric anodes and cathodes, for example, as illustrated in FIGS. 2A-2C, however, contain an anode surface area of about 0.85 m²within the same volume. This represents a roughly 6× increase for the same volumetric footprint.

In some examples, previous state of the art CTE cells operating in regions with high temperatures (40° C.-45° C.) and with seawater having higher than average levels of dissolved solids (TDS) were limited with respect to the concentration of sodium hypochlorite product that could be produced and a flow rate that should be maintained to avoid scaling. In one example of an installation of previous state of the art CTE cells located in the Middle East, the cells could produce a product solution with 1000 ppm NaOCl, but were operated at a flowrate of 8 m³/hr with a current density of 3000 A/m²and still accumulated scale that was removed in cleaning operations performed every two to three months. Under similar conditions, current state of the art CTE cells could produce a product solution with 1000 ppm NaOCl and be operated at a flow rate of 7.5 m³/h and not require cleaning due to scale build up after 8 months of operation. In another example, current state of the art CTE cells as described in PCT Application No. PCT/US2018/027564, incorporated by reference herein, are capable of operating with the same high temperature/high TDS seawater to produce a product solution with 2500-3000 ppm NaOCl while operated at a flow velocity of 2-3 m/s and 3000 A/m²and be self-cleaning and not generate scale.

Different electrochemical cell configurations disclosed herein may operate in accordance with different design parameters. FIG. 3 includes tables listing design parameters from four different examples of systems each including 20 electrochemical cells operating in series. Example 1 is a system including two-tube electrochemical cells with diameters of about 50 mm and lengths of about 1 m. Example 2 is a system including three-tube electrochemical cells with diameters of about 50 mm and lengths of about 1.2 m. Example 3 is a system including three-tube electrochemical cells with diameters of about 100 mm and lengths of about 1.2 m. Example 4 is a system including five-tube electrochemical cells with diameters of about 100 mm and lengths of about 1.2 m. The NaOCl production (PROD. RATE, CELL OUTPUT parameters in FIG. 3) of each example system was calculated assuming a 3000 A/m²current density across the electrodes of each electrochemical cell. Each example has a recommended maximum flow rate, which may be set based on the associated pressure drop across the electrochemical cells and their mechanical strength, and a recommended minimum flow rate, which may be set at a rate that avoids scale build-up in the electrochemical cells. The systems may be operated with a failsafe that cuts flow of current to the electrochemical cells if the flow rate through the cells drops below a minimum (LIMIT TRIP parameters in FIG. 3).

As illustrated in FIG. 3, embodiments of an electrolyzer system may include, for example, 20 electrochemical cells arranged in series with all cells operating with the same flow velocity and current density. The current density of 3000 A/m²is one example. Other systems may operate with current densities of 1500-3000 A/m², 3000-6000 A/m², 500-1500 A/m², or 0-500 A/m². In some examples, the flow velocity of liquid through the electrochemical cells may be 2-3 m/s, but in other examples may be 0.5-2 m/2, 3-6 m/s, or 10-15 m/s. The identification of the different embodiments in FIG. 3 is not intended to indicate that these embodiments are each distinct. For example, electrolyzer systems including electrochemical cell operating with the current density of one or more of Embodiments 1-4 may operate with the cell velocities of any of Embodiments 5-9.

Embodiments of an electrolyzer system may include multiple electrochemical cells that may be fluidically and/or electrically connected in series and/or in parallel. FIG. 4 illustrates four different examples of arrangements of fluidic connections between electrochemical cells in an electrolyzer system. For all examples in FIG. 4, cells 1, 2, and 3 can have the same or different flow velocities, dependent upon on their respective flow areas, and the same or different current densities, dependent upon their respective electrode areas. It is to be appreciated that the examples illustrated in FIG. 4 show only connections between adjacent cells. The examples illustrated in FIG. 4 may be expanded to encompass electrolyzer systems with a greater number, for example, 20 or more electrochemical cells with adjacent electrochemical cells fluidically connected in accordance with one or more of the examples illustrated in FIG. 4.

Different arrangements of power connections to adjacent electrochemical cells of an electrolyzer system are illustrated in the examples shown in FIG. 5. As shown, adjacent electrochemical cells may be connected electrically in series, in parallel, in a combination of series and parallel, or may be each powered by a separate dedicated power source. For all examples in FIG. 5, cells 1, 2, and 3 can have the same or different Current Densities, dependent upon their respective electrode areas. The examples illustrated in FIG. 5 may be expanded to encompass electrolyzer systems with a greater number, for example, 20 or more electrochemical cells with adjacent electrochemical cells electrically connected in accordance with one or more of the examples illustrated in FIG. 5.

In some embodiments of electrolyzer systems disclosed herein, fluid may be recirculated between the output of a downstream electrochemical cell to the inlet of an upstream electrochemical cell. FIG. 6 illustrates three examples of recirculation of fluid through electrochemical cells in an electrolyzer system. In example 1, an upstream cell may include a recirculation line that recirculates at least some fluid from an outlet to the inlet of the upstream cell while a downstream cell is not coupled to a recirculation line. In example 2, a downstream cell may include a recirculation line that recirculates at least some fluid from an outlet to the inlet of the downstream cell while an upstream cell is not coupled to a recirculation line. In example 3, a downstream cell may include a recirculation line that recirculates at least some fluid from an outlet of the downstream cell to the inlet of an upstream cell. For each examples illustrated in FIG. 6, recirculation can occur for one or more cells, having the same or different flow velocities, dependent upon on their respective flow areas, and the same or different current densities, dependent upon their respective electrode areas. It is to be appreciated that recirculation may be performed through multiple electrochemical cells, and not just the limited number illustrated in FIG. 6. For example, either of cell 1 or cell 2 in FIG. 6 may be replaced with multiple electrochemical cells fluidically connected in series and/or parallel.

Embodiments of electrolyzer systems disclosed herein may include a product tank that receivers treated fluid from one or more electrochemical cells. As illustrated in the example of FIG. 7, the product tank may be fed by one or more cells, with one or more cells recirculating off the product tank. The one or more cells may have the same or different flow velocities, dependent upon on their respective flow areas, and may have the same or different current densities, dependent upon their respective electrode areas. It is to be appreciated that recirculation may be performed through multiple electrochemical cells, and not just the one cell illustrated in FIG. 7. For example, either of cell 1 or cell 2 in FIG. 7 may be replaced with multiple electrochemical cells fluidically connected in series and/or parallel.

FIG. 8 depicts a once-through electrolyzer system, comprised of three current state-of-art CTE cells 305 in series. A pump 310 is configured and arranged to pump feed liquid, for example, seawater, brine, or brackish water, from a source of feed liquid 315 through the cells 305. The pump 310, or any of the pumps in the different embodiments disclosed herein may include one or more sensors, for example, a flow meter or other sensor for one or more quality indicators, for example, sensors for measuring pH, temperature, oxidation-reduction potential (ORP), conductivity, or dissolved oxygen in fluid passing through the pump. The pump 310 and any included sensors may be in communication with a control system, for example, as illustrated in FIG. 16 for monitoring and controlling operation of the system. In other embodiments, an electrolyzer system does not utilize a controller, but rather, the flow velocity through the cells of the system and the current densities of the cells are set and operated at constant values.

The chlorinated liquid generated in the cells may be stored in a product tank 320 until used as product. The chlorinated liquid generated in the cells may have a concentration of NaOCl of, for example, about 3000 ppm. In such a configuration, the nominal flow velocity would likely be 2-3 m/s, for example, 2 m/s, or 2 m/s or greater, the nominal current density would likely be 3000 A/m², and the nominal electrode area would be equivalent to approximately 18 previous state of art cells. The product tank 320, or any of the product tanks in any of the different embodiments disclosed herein may include one or more sensors S, for example, a flow meter or other sensor for one or more quality indicators, for example, sensors for measuring pH, temperature, oxidation-reduction potential (ORP), conductivity, or dissolved oxygen in fluid entering or present in the product tank 320. Any sensors included in the product tank 320 may be in communication with a control system, for example, as illustrated in FIG. 16 for monitoring and controlling operation of the system. It is to be appreciated that additional tanks, valves, or pumps may be included in the system illustrated in FIG. 8 or any of the other systems disclosed herein in appropriate positions as would be appreciated by one of ordinary skill in the art.

FIG. 9 depicts a feed-and-bleed electrolyzer system in which chlorinated liquid generated in the cells 305 may be returned upstream to mix with feed liquid entering the pump 310 through a recycle line 425. Recycle line 425 may include one or more pumps and/or valves (not shown). Again, the nominal flow velocity would likely be 2-3 m/s, for example, 2 m/s, or 2 m/s or greater, and the nominal current density would likely be 3000 A/m². In such a configuration, it is possible to increase the overall strength of hypochlorite in the product fluid produced, for example, up to about 6000 ppm NaOCl or more, however, as detailed above, consideration should be made to cathodic scaling as solution strength and pH increase.

From the above, and controlling for temperature/H₂production, alternative system orientations could be envisioned to compensate for increasing pH, and thus achieve a higher product strength. These systems would still have a smaller overall footprint, relative to the previous state of art.

FIG. 10 depicts a once-through electrolyzer system, comprised of a plurality, for example, six or more, or up to 20 or more, current state-of-art CTE cells 305 in series, although it should be appreciated that such systems may also have less than six cells 305, for example, four or five cells 305 in series. Lower current density, for example 1500 A/m², 1000 A/m², or 500 A/m²is applied across the electrodes of cells at the end of the system than at cells at the beginning of the system closer to the feed inlet to compensate for increasing pH. The applied current density may drop from a highest value, for example, 2500 A/m²at the furthest upstream cell 305, and may drop, for example, to 2000 A/m²and 1500 A/m²in the second and third cells 305 in series. The applied current density may continue to drop for cells further downstream or may attain a constant value, for example, 1500 A/m², 1000 A/m², or 500 A/m²for adjacent downstream cells 305. Fluid flow velocity may be the same, for example, 2-3 m/s, 2 m/s, or 2 m/s or greater for each cell 305 in the system.

In another embodiment, a system similar to that depicted in FIG. 10 may be provided, but the current density of all cells 305 may be reduced to below the nominal current density of the cells in the systems of FIGS. 8 and 9, for example, to 1500 A/m²as illustrated in FIG. 11. Fluid flow velocity may be the same, for example, 2-3 m/s, 2 m/s, or 2 m/s or greater for each cell 305 in the system.

In some embodiments, the flow velocity of fluid through one or more cells in a system of CTE cells may be adjusted to a level that reduces or prevents scaling. In a system including multiple CTE cells in series, cells which would be expected to treat fluid with a higher pH, for example, cells in a downstream portion of the system, could be operated with the flow velocity of fluid through the cells set at a higher level that the flow velocity of fluid through cells which would be expected to treat fluid with a lower pH, for example, cells in an upstream portion of the system. In some embodiments, this may be achieved by operating upstream CTE cells in parallel and downstream CTE cells in series. For example, as illustrated in FIG. 12, there are four upstream cells 305U and two or more downstream cells 305D. A fluid inlet to the group of the downstream cells is in fluid communication with a combined fluid outlet of the upstream cells. A first group or a first parallel pair of upstream cells is in fluid communication upstream of a second group or second parallel pair of upstream cells. Fluid flow from the outlets of the second parallel pair of upstream cells is combined and enters an inlet of a first of a group of downstream cells. The fluid velocity of fluid entering the first of the group of downstream cells is the sum of the fluid velocities of fluid exiting the outlets of the second parallel pair of upstream cells. At least a second and, in some embodiments, more than two additional downstream cells are connected in series downstream of the first of the group of downstream cells. The fluid flow velocity through each of the upstream cells may be 2-3 m/s, for example, 2 m/s, or 2 m/s or greater. The fluid flow velocity through each of the downstream cells may be 4-6 m/s, for example, 4 m/s, or 4 m/s or greater. The current density applied to each of the upstream cells and each of the downstream cells may be equal, for example, 3000 A/m². In other embodiments, the current density applied across the electrodes of the upstream cells may be higher or lower than that applied to across the electrodes of the downstream cells. It is to be appreciated that system similar to that illustrated in FIG. 12 may include greater than two cells in parallel in each group of upstream cells, and/or may include greater than two groups of parallel cells. In some embodiments, the current density and/or flow rate in different CTE cells in a group of parallel CTE cells or in different series arranged CTE cells is different.

The velocity of fluid flow through CTE cells in a serial configuration, for example, as illustrated in FIGS. 10 and 11 may also be increased over a nominal fluid flow through cells in a system such as that illustrated in FIG. 13 or 14. The higher fluid flow velocity through the cells may allow each of the cells to operate at a higher current density than the cells in the systems of FIG. 10 or 11 while still exhibiting little or no scaling. As illustrated in FIG. 13, the higher flow velocity may be 4-6 m/s, for example, 4 m/s, or 4 m/s or greater. The applied current density applied to the cells in series operating at the higher fluid flow as illustrated in FIG. 12 may be, for example, 3000 A/m². The applied current density may be the same for each of the series arranged cells operated at the higher fluid flow velocity as illustrated in FIG. 13, but in other embodiments may be different for different cells, for example, lower for cells that are more downstream than other cells and higher for cells upstream of other cells in the system.

In another embodiment, a CTE cell may be provided in a feed-and-bleed fluid line. The feed-and-bleed fluid line may remove and return fluid to the product tank of a system such as illustrated in FIG. 8 which includes a plurality, for example, two, three, or more CTE cells in series that provide treated fluid to a product tank. One configuration of an embodiment in which a parallel CTE cell treats and recirculates fluid from the product tank is illustrated in FIG. 14. The treatment and recirculation of the fluid from the product tank 320 through the parallel CTE cell 905, pump 910, and feed-and-bleed fluid line 915 increases the concentration of NaOCl in the product tank 320 without increasing the risk of scaling in the series CTE cells 305. The series CTE cells 305 may operate at nominal fluid flow velocities of 2-3 m/s, for example, 2 m/s, or 2 m/s or greater and nominal current densities of 3000 A/m². The parallel CTE cell 905 may operate at a fluid flow of X m/s and a current density of Y A/m². The values of X and Y may be selected based on, for example, a desired concentration of NaOCl in the product tank 320. In some embodiments the fluid flow through the parallel CTE cell 905 may be 2-3 m/s, for example, 2 m/s, or 2 m/s or greater, or may be 4-6 m/s, for example, 4 m/s, or 4 m/s or greater. The current density applied across the electrodes of the parallel CTE cell may be, for example, any of 1500 A/m², 2000 A/m², 2500 A/m², or 3000 A/m², less than 1500 A/m², or more than 3000 A/m². The concentration of NaOCl in the liquid in the product tank 320 may be set or maintained at, for example, 3000 ppm or higher, for example, up to 6000 ppm or higher by recirculation of the product tank liquid through the parallel CTE cell 905. The system may operate under steady state conditions with treated fluid withdrawn from the product tank at the same velocity than fluid flows through the series CTE cells 305, for example, 2-3 m/s, 2 m/s, or 2 m/s or greater. The system may operate with treated fluid withdrawn from the product tank at a lower velocity than fluid flows through the series CTE cells 305 to build up a concentration of NaOCl in the product tank or may operate with treated fluid withdrawn from the product tank at a higher velocity than fluid flows through the series CTE cells 305, optionally with flow through the parallel CTE cell 905 suspended, to lower a concentration of NaOCl in the product tank.

Another embodiment of a feed-and-bleed type electrochemical cell system is illustrated in FIG. 15A. In this configuration, valves CV1 and CV2 are opened while valves CV3 and CV4 are closed. The electrolyzer, which may include one or more CTE cells fluidically and/or electrically coupled in series and/or parallel, and which may include a group of CTE cells arranged in accordance with any of the previously described embodiments, are operated via Pump A to draw feed fluid from the inlet of the system until the product tank is filled. During the tank fill or make-up operation, Pump A may operate at, for example, 12 m³/hr or to flow fluid through the electrolyzer at 2-3 m/s. The nominal concentration of NaOCl in the product tank would be between about 1500 to 1800 ppm. Once the product tank is full, valve CV1 is closed and valve CV3 is opened. The electrolyzer is again operated, via Pump A and the fluid solution in the product tank is recycled back through the electrolyzer and back into the product tank. Operation during the recycle operation would be at a higher flow velocity, to enhance self-cleaning of the CTE cells of the electrolyzer. In some instances, the fluid flow velocity through the electrolyzer during the recycle operation would be 4-5 m/s (Pump A operating at, for example, 24 m³/hr), and in others it would be higher. The maximum fluid flow velocity may be dependent upon the pressure rating of the CTE cells of the electrolyzer. The system would be continuously operated to achieve higher product strength. In some instances, the NaOCl product strength would reach 3,000 ppm. In other instances, higher NaOCl concentrations could be achieved. The peak concentration of NaOCl in the product tank may depend upon the balance between Mg and Ca precipitation against the maximum self-cleaning velocity. For dosing of the product to a point of use, valves CV1 and CV2 are closed, while valves CV3 and CV4 are opened. Pumps A and B are then used to externally shock dose the point of use, using the bulk product tank solution. The table in FIG. 15B shows example flow rates and valve and electrolyzer conditions during make-up, recycle, and shock dose operations.

In some embodiments, for example, as illustrated in FIG. 15A, the product tank, or the product tank(s) of any of the systems disclosed herein may include a lower end having sloped, for example, conical, sidewalls 325 and a precipitate outlet 330 that may be opened or closed with, for example, valve CV5. Calcium and magnesium deposits have a higher specific gravity than sodium hypochlorite or seawater and may tend to settle out in the product tank. The settled deposits may be flushed from the product tank at a desired interval or after achieving an unacceptable level, for example, by fluid, for example, seawater pumped into the product tank via Pump A. Valve CV5 may be opened during flushing of the product tank to allow the precipitates to flow outward.

The systems disclosed herein may draw feed, process liquid, or electrolyte, which in some embodiments is seawater, brine, or brackish water from sources external and/or internal to the systems. For example, if a system is a sea-based system, an external source may be the ocean and an internal source may be, for example, a ballast tank in a ship. In a land-based system, an external source may be the ocean and an internal source may be brackish wastewater from an industrial process performed in the system. The electrochlorination systems disclosed herein may produce chlorinated water and/or a solution including sodium hypochlorite from the water from the feed sources and may distribute it to a point of use. The point of use may be a source of cooling water for the system, a source of disinfection agent for a ballast tank of a ship, a downhole of an oil drilling system, or any other system in which chlorinated water may be useful. Various pumps, for example, pumps 310 and 910, may control the flow of fluid through the systems. One or more sensors may monitor one or more parameters of fluid flowing through the systems, for example, ionic concentration, chlorine concentration, temperature, or any other parameter of interest. The pumps and sensors may be in communication with a control system or controller which communicates with the sensors and pumps and controls operation of the pumps and other elements of the systems to achieve desired operating parameters.

The controller used for monitoring and controlling operation of the various elements of system may include a computerized control system. Various aspects of the controller may be implemented as specialized software executing in a general-purpose computer system 1000 such as that shown in FIG. 16. The computer system 1000 may include a processor 1002 connected to one or more memory devices 1004, such as a disk drive, solid state memory, or other device for storing data. Memory 1004 is typically used for storing programs and data during operation of the computer system 1000. Components of computer system 1000 may be coupled by an interconnection mechanism 1006, which may include one or more busses (e.g., between components that are integrated within a same machine) and/or a network (e.g., between components that reside on separate discrete machines). The interconnection mechanism