Tubular reversal polarity self-cleaning tank

Abstract

A process for self-cleaning an electrolytic cell involves introducing a flow of seawater into an electrolytic cell having one or more cathodes and anodes. The cathodes and anodes are substantially completely coated with a coating composition. As seawater flows between the electrodes, a forward bias is applied between the anode and the cathode at a first current density. A reverse bias is then provided at the cathode. The reverse bias is provided at a second current density that is lower than the first current density. When the reverse bias is applied, the polarity of the cathode is reversed for a short period of time. This produces a small amount of hydrochloric acid on the surface that was the cathode, causing dissolution of calcium, magnesium, or other deposits on the surface of the electrode without damaging the coating composition on the electrode.

Description

Technical Field

[0001] The present invention relates to an electrolytic cell, and more particularly to an electrolytic cell for biocidal treatment of seawater in offshore, coastal, and shore facilities.

Background Art

[0002] The electrolysis of seawater or other dilute sodium chloride aqueous solutions, which involves the production of active chlorine, i.e., a mixture of hypochlorite and other oxidizing species, has found several industrial applications that utilize the biocidal and disinfectant properties of the products. Particular applications of interest are the biocidal treatment of seawater in cooling, fire fighting water, utility water, desalination, and other onshore and offshore applications. In those applications, it is necessary to treat the circulating seawater with a biocide to prevent fouling and blockage of pipes, vessels, and channels due to the growth of marine organisms. Preventive biocidal treatment may involve the in-situ generation of hypochlorite by using an electrolytic cell. Electrochlorination of seawater eliminates the storage, handling, and purchase of harmful chemicals.

[0003] During the electrolysis process, seawater passes through the electrolytic cell and exits the cell as a sodium hypochlorite solution and the by-product hydrogen gas. The solution is piped to a tank or cyclone where it is possible to remove the hydrogen from the solution. The resulting solution exiting the cell is a mixture of seawater, hypochlorite, and hypochlorous acid. The electrolysis of a sodium chloride solution (seawater) involves passing a direct current between an anode and a cathode to separate the salt and water into their basic elements. The chlorine generated at the anode immediately undergoes a chemical reaction to form hypochlorite and hypochlorous acid. Hydrogen and hydroxide are formed at the cathode, where the hydrogen forms a gas and the hydroxide helps in the formation of hypochlorite, raising the pH of the outlet stream to about 8.5.

[0004] The overall chemical reaction can be shown as follows. Salt + Water + Energy → Sodium Hypochlorite + Hydrogen NaCl + H2O + 2e → NaClO + H2 The electrolytic chlorine generation process can cause fouling of the electrolytic cell due to scale buildup. Scale is hardened calcium and magnesium deposits. If there is no active method to remove these deposits, periodic chemical-based cleaning is required. This cleaning may also involve physically removing the cell for cleaning, requiring the neutralization of the acid solution used.

[0005] A common technique for cleaning electrolytic cells involves periodically washing the electrodes with hydrochloric acid. While this is a simple procedure for a trained technician or operator, the entire process is extremely difficult and costly, not only in terms of equipment downtime but also in terms of operational and environmental considerations related to the procurement, storage, and safe disposal of chemicals in offshore facilities.

[0006] Several companies offer "self-cleaning" tank technology. This process is based on the principle of high-speed seawater flow, which can induce a "scouring" effect across the electrode surface, physically removing calcium and magnesium scale buildup. However, it has been found that periodic polishing only washes away small amounts of deposits. Unfortunately, this method does not eliminate the accumulation of hardness over time, ultimately leading to blockage of the tank's annular section and irreversible damage to the tank.

[0007] For these reasons, there is a need for a technically and economically viable solution that minimizes scale buildup on electrolytic cells while reducing downtime related to logistics maintenance. [Brief explanation of the drawing]

[0008] [Figure 1] A cross-sectional view of a tubular polarity reversal tank according to one embodiment. [Figure 2] A schematic diagram of a tubular polarity reversal tank assembly according to one embodiment. [Figure 3] A diagram showing the dissociation of sediments on a polarity reversal tank due to polarity reversal, according to one embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention relate to a controllable process for self-cleaning a seawater electrolytic cell or "electrolytic cell." The process depends on the local conductivity of seawater, which changes with temperature and salinity. The process involves automatic adjustment or modulation of the reverse-biased power supplied to the electrolytic cell.

[0010] According to one embodiment, a process for self-cleaning an electrolytic cell is disclosed. The electrolytic cell comprises cathode and anode electrodes. The electrodes are substantially completely coated with a coating composition. A stream of seawater is introduced between the electrodes. As the seawater stream flows between the electrodes, a forward bias is applied between the anode and the cathode. The forward bias is applied at a relatively high first current density. The self-cleaning process further involves applying a reverse bias to the cathode at a variable potential (relative to a fixed potential) to achieve a reduced second current density. In one embodiment, the second current density is 5% or more of a predetermined forward bias current. The reverse bias is applied periodically at a predetermined frequency. For example, the reverse bias is provided over a predetermined period of no more than 24 hours / every 24 hours. The current can be alternating in an internal power supply. When the reverse bias is applied, the polarity of the cathode is reversed for a short period of time so that the cathode functions as an anode. This generates a small amount of hydrochloric acid (HCl) on the cathode surface. This short-duration "in situ" generation of HCl at low current densities and a predetermined normal frequency causes dissolution of calcium, magnesium, or any other scale deposited on the electrode surface. This also prevents further scale buildup and permanent damage to the electrode and the coating composition on it. This ensures optimal forward-biased operation with significant HCl generation.

[0011] According to another embodiment, a tubular reverse polarity ("TRP") or reverse bias electrolytic cell comprises an electrically conductive outer tubular sleeve formed from (A) a tubular terminal anode and (B) a tubular terminal cathode, and a bipolar tubular electrode having a cathode end and an anode end. The terminal electrodes (anode / cathode) have a diameter slightly larger than that of the bipolar tubular electrode. This allows each terminal electrode to be fitted onto the bipolar electrode. The terminal anode and terminal cathode are separated by a central coupling mechanism. In addition, the ends of the terminal electrodes also have coupling mechanisms. The terminal electrodes and the bipolar electrode are separated by an annular space. The terminal electrodes and the bipolar electrode are substantially covered with a coating composition configured to withstand periodic changes in forward and reverse current bias on the electrodes. According to another embodiment, the TRP electrolytic cell system comprises two or more TRP electrolytic cells, a casing surrounding the TRP electrolytic cells, and a control panel for automatically supplying forward and reverse bias currents to the TRP electrolytic cells.

[0012] The present invention may be described in more detail below and with reference to the accompanying drawings, all of which illustrate or relate to the apparatus, systems, and methods of the present invention. In drawings not intended to be drawn to a specific scale, each similar component shown in various drawings is represented by the same numbers.

[0013] Depending on the context, all of the following references to “invention” may in some cases refer to only a specific embodiment. In other cases, it may be recognized that references to “invention” may refer to the subject matter described in one or more (but not necessarily all) of the claims.

[0014] Figure 1 shows an example of a TRP electrolytic cell (or, synonymously, "TRP cell" or simply "cell") 100. The TRP cell 100 comprises an electrically conductive, elongated outer tubular sleeve 110. The tubular sleeve 110 includes a tubular terminal anode electrode 115A and a terminal cathode electrode 115C (collectively referred to as "terminal electrodes 115"). A bipolar tubular electrode 120 is enclosed within the tubular sleeve 110. The bipolar electrode 120 has a cathode end and an opposing anode end.

[0015] The terminal electrode 115 has a diameter slightly larger than that of the bipolar electrode 120, such that an annular space is formed between the inner surface of the terminal electrode 115 and the outer surface of the bipolar electrode 120. This allows the terminal electrode 115 to be fitted onto the bipolar electrode 120. The terminal anode 115A and terminal cathode 115C are separated by a central coupling mechanism 115B. In addition, the ends of the terminal electrodes also have coupling mechanisms 115D and 115E. The coupling mechanisms may include seals. The seals may include one or more seal rings.

[0016] The TRP tank 100 includes an inlet and an outlet. The TRP tank 100 is configured to have connection nodes for electrodes, allowing for fluid flow of liquid throughout the tank. The bipolar electrode 120 and terminal electrode 115 are substantially coated with a suitable composition capable of withstanding reversal of electrode polarity. In one embodiment, the coating composition / coating may contain one or more metals selected from the group of platinum group metals (e.g., ruthenium and / or iridium). In another embodiment, the coating may also contain one or more metals selected from the group of valve metals. In yet another embodiment, the coating may contain one or more elements selected from the group including nickel, iron, and cobalt, either alone or in combination. However, it is understood that the coating may contain other suitable and stable mixtures capable of withstanding periodic current reversals.

[0017] The TRP tank 100 is configured to be self-cleaning. Therefore, the need for external acid cleaning of the TRP tank 100 is eliminated. This also eliminates any related logistics problems and operational downtime.

[0018] According to one embodiment, as shown in Figure 2, the TRP tank system 200 comprises a casing 210 surrounding a plurality of TRP tanks 100A-100D ("100") as described with respect to Figure 1. In one embodiment, the casing 210 may be made of stainless steel. The casing 210 may be configured to surround 2 to 16 tanks. However, it will be understood by those skilled in the art that the number of tanks can be modified as needed. In one or more embodiments, the tank system 200 may be skid-mounted.

[0019] The tank system 200 further comprises a transformer 230 configured to supply power to the control panel 240. The control panel 240 may include a current reversal device or mechanism 245.

[0020] During normal operation, a predetermined forward bias (DC current) is applied to the tank 100. The forward bias involves the application of a high-density current. For example, the current density is 0.5-4 kA / m³ when seawater flows through the tank 100. 2 It is possible that this occurs between these two states. Electrolysis generates a large amount of sodium hypochlorite. During this process, due to the specific properties of the source water and the electrolytic action, deposits form on the cathode surface of the tank. These deposits may include, but are not limited to, calcium and magnesium deposits. The accumulation of deposits degrades the performance of the electrodes.

[0021] According to another embodiment, the process for self-cleaning the tank 100 involves applying a reverse bias at a low current density (e.g., 5% or more of the forward bias) to generate a small amount of HCl that can be used to dissociate the sediment.

[0022] The reverse bias can be applied over a predetermined period of time such that the deposits dissolve without damaging the coating applied to the electrodes. In one embodiment, the reverse bias is applied at a predetermined low current density over a predetermined period of 24 hours each. Subsequently, it is possible to alternate the bias / DC current in the internal power supply in the same electrical connection to the cell. Such a self-cleaning process can be automated to eliminate the possibility of operator error. The self-cleaning process ensures a long operating life of the TRP cell and minimizes operational downtime.

[0023] An example of deposit dissociation by reverse polarity where the cathode surface operates as an anode is shown in FIG. 3. When the polarity is reversed, both the cathode end of the bipolar electrode and the terminal cathode operate as anodes for a short period of time. The polarity can be reversed at a frequency and for a period appropriate to produce a small amount of HCl on the surface that was the cathode of the electrolytic cell.

[0024] The short-time "in situ" generation of such HCl at a low current density and appropriate frequency dissolves the deposits or scale buildup on the electrodes before they become too thick and hard, preventing permanent damage to each electrode and ensuring optimal forward bias operation. This allows for the continuous free-flow operation of the electrolytic cell. In addition, the lower current density in the short-term reverse bias eliminates the accumulated hardness while not affecting the electrode life or performance.

[0025] In one or more embodiments, the self-cleaning process described herein can be applied to an electrolyzer with one or more electrolytic cells. For example, the electrolytic device can comprise a plurality of cathode and anode electrodes.

[0026] The TRP tank can be used on both large-scale facilities on land and at sea, as well as other small-scale facilities. Embodiments of the system can also be used in immersion water, cooling water, and fire-fighting water loops. Additionally, the TRP tank can be used in industrial power and coastal biofouling control applications. The TRP tank has an optimal design that requires only minimal operation and maintenance requirements. It has a once-through flow design that eliminates recirculation requirements. The TRP tank is composed of corrosion-resistant materials that make it durable. The TRP tank assembly, including the number of TRP tanks enclosed by the casing, can be customized to meet site-specific requirements. The TRP tank is configured to consume minimal power.

[0027] Therefore, the present invention may be well adapted to attain the recited objects and advantages, as well as those inherent therein. Since the invention may be modified and embodied in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein, the specific embodiments disclosed above are only illustrative. For example, a self-cleaning process can be used to remove accumulated deposits from any electrolytic cell having a fully coated cathode and anode, as disclosed herein. The process is independent of the tubular shape or size of the electrolytic cell. In addition, the process is independent of the presence of bipolar electrodes positioned within a sleeve having monopolar electrodes. For example, according to one embodiment, a process for self-cleaning an electrolytic cell comprises: (A) providing an electrolytic cell comprising (i) one or more cathode electrodes and (ii) one or more anode electrodes, the electrodes being substantially completely coated by a coating; and (B) applying a reverse bias to the cathode electrodes at a predetermined frequency and for a predetermined period within 24 hours. The process involves applying a reverse bias at 5% or more of a predetermined forward bias. The reverse bias causes the cathode electrodes to operate as anodes for a short period of time. The process generates hydrochloric acid (HCl) to dissolve the accumulation of scale on the electrodes.

[0028] All ranges described herein include endpoints that describe a range "between" two values. Terms such as "about," "generally," "approximately," and "substantially" should be interpreted as modifying a term or value, so as not absolute. Such terms may be defined by context, and the terms that context modifies them will be understood by those skilled in the art. The terms "approximately" and "substantially" and their variations are defined as, in most cases, not necessarily as a whole, but as explicitly stated so as understood by those skilled in the art.

[0029] Furthermore, the limitations are not intended to impose any configuration or design details as shown herein. Therefore, it is clear that the specific exemplary embodiments disclosed above may be modified or altered, and all such variations are considered to fall within the scope and spirit of the invention. While systems and methods are described as "comprising" or "containing, including" various components or steps, systems and methods may also "consist essentially of" or "consist of" various components and steps.

Claims

1. A process for self-cleaning the electrolytic cell, (i) A step of introducing a seawater flow into the electrolytic cell, wherein the electrolytic cell is configured for offshore, coastal, and shore facilities, and the electrolytic cell is (i) One or more cathode electrodes, (ii) comprising one or more anode electrodes, The cathode electrode is completely coated with the coating composition, and the anode electrode is also completely coated with the coating composition, in the step of... (ii) A step of applying a forward bias at a first current density between the anode electrode and the cathode electrode when seawater flows between the anode electrode and the cathode electrode, (iii) A process comprising the step of providing a reverse bias in the cathode electrode, wherein the reverse bias is provided at a second current density less than the first current density, and the reverse bias is provided at a predetermined periodic frequency.

2. The first current density is 0.5–4 kA / m³. ２ The process according to claim 1, which is between the two.

3. The process according to claim 1, wherein the second current density is 5% or more of the first current density.

4. The process according to claim 2, wherein the reverse bias is provided at a variable potential to achieve a reduced second current density.

5. The process according to claim 4, wherein the reverse bias generates a small amount of hydrochloric acid compared to the amount of hydrochloric acid generated in the forward bias.

6. The process according to claim 5, wherein the hydrochloric acid generated in the reverse bias causes the dissolution of calcium deposits, magnesium deposits, or both accumulated on the anode electrode and the cathode electrode without damaging the coating composition on the electrodes.

7. The process according to claim 6, wherein the predetermined frequency is configured to prevent the long-term accumulation of the sediment.

8. The process according to claim 7, wherein the reverse bias is provided over a predetermined period of no more than 24 hours each.

9. The process according to claim 1, wherein the seawater flowing between the anode electrode and the cathode electrode has a fixed salinity / conductivity.

10. The process according to claim 1, wherein the electrolytic cell is a tubular cell.

11. A tubular inverted polarity ("TRP") electrolytic cell system, One or more TRP electrolytic cells, (i) Terminal cathode electrode, (ii) Terminal anode electrode and An electrically conductive outer tubular sleeve formed from, It comprises an inner tubular bipolar electrode having a cathode end and an anode end, The terminal cathode electrode, the terminal anode electrode, and the bipolar electrode are completely coated with a coating composition configured to withstand periodic reversals of polarity in a TRP electrolytic cell, A casing for surrounding the TRP electrolytic cell, The system includes a control panel for automatically supplying forward and reverse bias currents to the TRP electrolytic cell, The aforementioned control panel is Applying a forward bias at a first current density between the terminal anode electrode and the terminal cathode electrode, A TRP electrolytic cell system configured to provide a reverse bias at the terminal cathode electrode, wherein the reverse bias is provided at a second current density smaller than the first current density, and the reverse bias is provided at a predetermined periodic frequency.

12. The TRP electrolytic cell system according to claim 11, wherein the terminal cathode electrode and the terminal anode electrode have a larger diameter than the bipolar electrode.

13. The TRP electrolytic cell system according to claim 12, wherein the terminal cathode electrode and the terminal anode electrode are separated from the bipolar electrode by an annular space.

14. The TRP electrolytic cell system according to claim 11, wherein the terminal anode electrode and the terminal cathode electrode are separated by a central seal.

15. The TRP electrolytic cell system according to claim 11, wherein the opposing end faces of the terminal cathode electrode and the terminal anode electrode are provided with seals.

16. The process according to claim 1, wherein the electrolytic cell is of the skid-mount type.

17. The process according to claim 10, wherein the tubular vessel comprises an electrically conductive outer tubular sleeve formed from a terminal cathode electrode and a terminal anode electrode, and an inner tubular bipolar electrode having a cathode end and an anode end, the terminal cathode electrode, the terminal anode electrode, and the bipolar electrode are completely covered with a coating composition configured to withstand periodic reversals of polarity.

18. The process according to claim 17, wherein the terminal cathode electrode and the terminal anode electrode have a larger diameter than the bipolar electrode.

19. The process according to claim 17, wherein the terminal cathode electrode and the terminal anode electrode are separated from the bipolar electrode by an annular space.

20. The process according to claim 17, wherein the terminal anode electrode and the terminal cathode electrode are separated by a central seal.

21. The process according to claim 17, wherein the opposing end faces of the terminal cathode electrode and the terminal anode electrode are provided with seals.

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