JP2006095426A - Electrolyzing method and electrolyzation apparatus in circulation type cooling water system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyzing method and an electrolyzation apparatus in each of which a scale component in circulating water can be removed by utilizing that the scale is deposited on an electrode (a cathode) to repress a tendency to generate scale in a cooling water system and the deposited scale can easily be dissolved and discharged. <P>SOLUTION: At an electrolyzation step, the water from a water storage tank 51 is electrolyzed by impressing a voltage between an anode 3 and the cathode 4 and making the water from the water storage tank pass circularly through the electrolyzation apparatus 1. Hydrogen is generated and the water becomes alkaline in the vicinity of the cathode 4. A carbonate ion is dissociated from a bicarbonate ion and reacted with a Ca ion and a Mg ion in the vicinity of the cathode 4 to produce calcium carbonate and magnesium carbonate. The produced calcium carbonate and magnesium carbonate are deposited on the surface of the cathode to repress the tendency to generate scale. At a scale removal step, carbon dioxide-mixed water is supplied to a rear chamber 6 from an ejector 12 and carbon dioxide is supplied to a water passage space 5 from a pipeline 9. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a circulating cooling water-based electrolytic treatment method and an electrolytic treatment apparatus, and more particularly to an electrolytic treatment method and an electrolytic treatment apparatus that simultaneously suppress scale failure and slime failure with one electrolytic device.

  Waste heat generated in compressors and refrigerators in factories and buildings is cooled with cooling water (cooling medium) through a heat exchanger. In the heat exchanger, the cooling water whose temperature has risen due to heat exchange with waste heat evaporates by contacting with air in the open cooling tower, is dissipated and cooled, and is circulated again to the heat exchanger. Therefore, in such a circulation type cooling water system, operation is performed by supplying supplementary water corresponding to the amount of water reduced by evaporation or scattering in the cooling tower.

  However, as it is, the scale components contained in the make-up water are concentrated in the cooling water system, exceeding its solubility, and deposited as scale on the heat transfer surface of the heat exchanger, the filler, bottom of the cooling tower, or piping. However, various operational failures such as a decrease in heat exchange efficiency and an increase in water flow resistance are caused.

  Therefore, in order to operate the system with a hardness that does not cause scale precipitation, circulating cooling is performed by discharging concentrated cooling water out of the system as blow water from the bottom of the cooling tower and diluting the whole with make-up water. Operation and management of water at a certain quality is being carried out. Here, if the amount of blow water is increased and the scale component concentration in the system is lowered, operation requires a large amount of makeup water, resulting in excessive water charges. On the other hand, when the high concentration operation is performed with the amount of blown water reduced, the scale component in the cooling water exceeds the solubility, and the scale of the hardly soluble salt is deposited.

  Conventionally, in order to prevent such scale precipitation in the cooling water system, a scale inhibitor made of various polymers such as a phosphoric acid-based chemical and a carboxylic acid-based chemical has been added, but the cost of the drug increases. Moreover, since there existed a possibility that the melt | dissolved chemical | medical agent may affect the aquatic organism which lives in a discharge area, there also existed a problem that a sewer discharge or water treatment was needed. In addition, the medicine needs to be replenished regularly, and its personnel cost is also a problem.

  As a method not using such a scale inhibitor, a physical scale prevention technique has been proposed.

  For example, Japanese Patent Laid-Open No. 2003-190988 discloses that cooling water replenishment water or circulating water is passed through an electrolyzer having a bipolar electrode whose polarity is changed, and a scale component contained in the replenishing water or circulating water is formed into fine crystals The method of preventing the scale adhesion in a cooling water system, especially the scale adhesion in a heat-transfer surface is described.

  In this electrolysis apparatus, cations such as calcium ions and magnesium ions gather on the cathode side of the conductive particles, and carbonate ions and silica gather on the anode side. Since the pH near the cathode is high, scale is deposited near the cathode. When the positive and negative polarities are reversed, the cathode becomes the anode, and the pH of the electrode surface decreases. By doing so, the scale deposited on the cathode without becoming a nucleus can be dissolved, and electrolytic failure can be prevented. The scale deposited in the vicinity of the electrode flows out into the circulating water, and very fine crystals are dispersed in the cooling water. These fine crystals serve as nuclei, and the scale components in the circulating water are deposited around the nuclei rather than in the heat exchange section and cooling tower in the system. Although the nucleus gradually increases, it is discharged together with blow water, and scale adhesion to the heat transfer surface and the like is prevented.

  That is, in the cooling water system provided with the electrolysis apparatus of JP-A-2003-190988, the cooling water containing fine particles generated in the electrolysis apparatus is sent to a heat exchanger or a cooling tower, where the solubility is supersaturated. Become. In the supersaturated state, the energy required for generating new crystal nuclei and the energy required for crystal growth based on the existing crystals require much less energy to grow based on the existing crystals. Therefore, the scale component precipitates on the fine particles of the flowing scale component as seed crystals. The fine crystals are discharged from the blow line without growing until they are deposited.

  In JP-T-2001-502229, a pair of electrodes made of graphite is disposed in a cylindrical container, and conductive particles made of a carbonaceous material such as graphite, silica, glass, and the like are disposed between the electrodes. A method is described in which scale formation is reduced by mixing and filling non-conductive particles such as plastic and allowing water to flow through a cylindrical container while energizing between the electrodes. According to the description of the same issue, alkali is generated by this energization treatment, crystal nuclei are generated by this alkali, and the scale generation tendency is reduced. In this scale prevention method, the scale adheres to the electrodes as well as the generation of the scale fine crystals in the alkaline region, and periodic cleaning is required. As this cleaning method, there is a technique in which the polarity of the electrode is changed over a certain period of time, and the electrode adhered to the scale on the alkali side becomes an acidic region to peel and dissolve the scale.

  However, in the method of changing the polarity of the electrode, since the anode and the cathode are inverted by the polarity change, the electrode itself is repeatedly oxidized and reduced, and the electrode is likely to deteriorate. Most of the electrodes are used for either oxidation or reduction, but when used in both electrodes, the time for functioning as an electrode becomes very short depending on the time of polarity change. For example, in the case of a graphite electrode, the electrode itself is oxidized at the anode, and graphite powder flows out and deteriorates. A titanium electrode coated with platinum oxide or iridium oxide, which is often used as an insoluble electrode, is resistant to oxidation at the anode, but the oxide is peeled off at the cathode, and deterioration tends to proceed. Although the above problem can be solved by frequently replacing the electrode, the electrode replacement cost required for this is excessive.

  Japanese Patent Application Laid-Open No. 2000-140849 discloses an apparatus for depositing a scale component on a cathode surface through water to be treated in an electrolytic apparatus equipped with an uneven metal electrode unit, and further removing the deposited scale component out of the system by reversing the polarity. And methods are described. The problem with this method is that the electrode is likely to deteriorate due to the polarity change, and that the attached scale is not sufficiently removed by the polarity change alone. That is, when the polarity is changed after a certain amount of scale is attached to the electrode, the portion to which the scale is attached becomes non-conductive and the current is distributed. Therefore, an acidic region where the scale dissolves is formed from a portion where the scale is not attached, and it takes time to peel and dissolve the scale.

As a scale cleaning method that avoids electrode deterioration, Japanese Patent Application Laid-Open No. 9-141266 describes a method and an apparatus for cleaning an electrolytic cell to which a scale is attached using acid water generated in a sub electrolytic cell. . However, in this case, scale is deposited in the sub-electrolysis tank that generates acidic water. In addition, when acidic water is excessively supplied to enhance the cleaning effect, or when the hydrogen ion concentration of acidic water is increased, the pH of the discharged water becomes 5 or less, and the sewerage law pH 5.8 to 8.6. There is also the problem of going out of range.
Japanese Patent Laid-Open No. 2003-190988 Special table 2001-502229 gazette JP 2000-140849 A JP-A-9-141266

  The present invention is a method and apparatus for conducting electrolytic treatment by passing water of a circulating cooling water system through an electrolysis device, utilizing the fact that scale is deposited on an electrode (cathode), removing scale components in circulating water, An object of the present invention is to provide an electrolytic treatment method and an electrolytic treatment apparatus capable of reducing the scale formation tendency in the system and easily dissolving and discharging the deposited scale.

  The circulating cooling water system electrolytic treatment method according to claim 1, wherein water to be treated comprising circulating water and / or makeup water of the circulating cooling water system is passed through an electrolysis apparatus having an electrode to be electrolyzed, and the surface of the electrode And a scale removing step of removing scales deposited on the electrodes by supplying carbon dioxide to the electrolysis apparatus.

  According to a second aspect of the present invention, there is provided a circulating cooling water system electrolytic treatment method according to the first aspect, wherein carbon dioxide gas and / or carbon dioxide dissolved water is supplied to the electrolysis apparatus in the scale removing step.

  The circulating cooling water-based electrolytic treatment method according to claim 3 is characterized in that in claim 1 or 2, the electrolytic treatment in the electrolytic treatment step generates oxidant from the electrode to sterilize the cooling water. Is.

  According to a fourth aspect of the present invention, there is provided an electrolytic treatment method for a circulating cooling water system according to any one of the first to third aspects, wherein the electrode is made of a porous body.

  A circulating cooling water system electrolytic treatment method according to a fifth aspect is the method according to any one of the first to third aspects, wherein a plurality of electrodes are arranged in the electrolysis apparatus, and water is passed between the electrodes. And at least one electrode is made of a porous body. In the electrolytic treatment step, water to be treated is passed through the water passage space, and in the scale removal step, carbon dioxide is introduced. The electrode made of the porous material is transmitted from the opposite side of the water passage space to the water passage space side.

  The method for electrolytic treatment of a circulating cooling water system according to claim 6 is the method according to any one of claims 1 to 5, wherein in the scale removal step, carbon dioxide gas is supplied into the electrolysis apparatus, whereby the scale attached to the electrode is It is made to peel.

  The method of electrolytic treatment of a circulating cooling water system according to claim 7 is characterized in that, in any one of claims 1 to 5, carbon dioxide gas or carbon dioxide dissolved water is supplied into the electrolysis apparatus in the scale removing step. It is what.

  [Claim 8] The circulating cooling water system electrolytic treatment method according to claim 8 is characterized in that, in any one of claims 1 to 7, carbon dioxide flowing out of the electrolyzer in the scale removing step is recovered and supplied to the electrolyzer again. It is characterized by this.

  The circulating cooling water-based electrolytic treatment method according to claim 9 is the electrolysis method according to any one of claims 1 to 8, wherein in the scale removal step, carbon dioxide having 1 to 3 moles of scale deposited on the electrode is electrolyzed. It supplies to an apparatus.

  The processing apparatus of the circulating type cooling water system according to claim 10 includes an electrolysis apparatus having an electrode, means for passing water to be treated made of circulating water or makeup water of the circulating cooling water system into the electrolysis apparatus, and the electrolysis Carbon dioxide is supplied to the apparatus, and carbon dioxide supply means for removing scale deposited on the electrode is provided.

  The processing device of the circulating type cooling water system according to claim 11 is characterized in that, in claim 10, the carbon dioxide supply means is a supply means of carbon dioxide gas and / or carbon dioxide dissolved water.

  According to a twelfth aspect of the present invention, there is provided a circulating cooling water treatment apparatus according to the tenth or eleventh aspect, wherein the electrode is made of a porous body.

  The processing apparatus of the circulating type cooling water system according to claim 13 is the processing apparatus according to claim 10 or 11, wherein a plurality of electrodes are arranged in the electrolysis apparatus, and a space for water to be treated is provided between the electrodes. One electrode is made of a porous body, and as the carbon dioxide supply means, means for supplying carbon dioxide gas and / or carbon dioxide gas to the opposite side of the water passage space of the electrode made of the porous body is provided. It is.

  The processing apparatus of the circulating type cooling water system according to claim 14 is the processing apparatus according to any one of claims 10 to 13, wherein the carbon dioxide supply means mixes carbon dioxide gas and water with an ejector and supplies the mixture to the electrolysis apparatus. It is characterized by being comprised.

  The circulating cooling water treatment apparatus according to claim 15 is characterized in that, in any one of claims 10 to 14, a means for recovering carbon dioxide flowing out from the electrolyzer and supplying it to the electrolyzer again is provided. It is what.

  In order to prevent scale precipitation in the circulating cooling water system by the electrolysis method and apparatus of the present invention, water in the circulating cooling water system is passed through the electrolyzing device for electrolytic treatment.

That is, in this electrolysis apparatus, the cooling water is electrolyzed as follows.
Anode: 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻
Cathode: 4H ₂ O + 4e ⁻ → 4OH ⁻ + 2H ₂

  By this reaction, hydrogen is generated near the cathode and becomes alkaline. For this reason, bicarbonate ions dissociate into carbonate ions in the vicinity of the cathode, and calcium carbonate and magnesium carbonate are produced from Ca ions and Mg ions, which are deposited on the electrode surface as scales, reducing the tendency to scale the cooling water system Is done. Therefore, the scale formation tendency of the circulating cooling water is reduced by passing the circulating cooling water or makeup water through the electrolyzer.

  According to the electrolytic treatment apparatus and method of the present invention, since scale components in the circulating cooling water are not deposited without using chemicals and can be operated at a constant concentration without causing corrosion, scales are formed in the heat exchange section and the cooling tower. Precipitation can be prevented or suppressed and corrosion can be reduced. In regions where the makeup water hardness is high, highly concentrated operation is possible, leading to water saving.

  Note that since the makeup water contains chlorine components such as chloride ions, an oxidizing agent such as hypochlorous acid is generated by the electrolytic treatment. Thereby, the sterilization of the water in a circulation type cooling water system can be performed.

  If scale removal is continued by this electrolytic treatment, the amount of scale attached to the electrode increases, so carbon dioxide is supplied to the electrolytic treatment apparatus at regular intervals to remove the scale.

The scale is mainly composed of calcium carbonate, calcium hydroxide, magnesium carbonate, and magnesium hydroxide, and these are dissolved and removed by reacting with carbon dioxide as follows.
CO ₂ + H ₂ O → H ₂ CO ₃ + H ⁺ + HCO ₃ ⁻ (dissolution of carbon dioxide in water)
CaCO ₃ + CO ₂ + H ₂ O → Ca ²⁺ + 2HCO ₃ ⁻ (dissolution of calcium carbonate)
Ca (OH) ₂ + 2H ⁺ → Ca ²⁺ + 2H ₂ O (dissolution of calcium hydroxide)
MgCO ₃ + CO ₂ + H ₂ O → Mg ²⁺ + 2HCO ₃ ⁻ (dissolution of magnesium carbonate)
Mg (OH) ₂ + 2H ⁺ → Mg ²⁺ + 2H ₂ O (dissolution of magnesium hydroxide)

  According to this carbon dioxide dissolution method, there is no need to purchase acid cleaning chemicals or dangerous carry-in work, which reduces chemical costs and improves work safety. In addition, when carbon dioxide is dissolved in city water, the pH of the water does not fall below 5, and the solution in which the scale is dissolved becomes pH 6 or higher, so that the sewer can be discharged.

  When carbon dioxide is supplied to the electrolytic treatment in the scale removal process, carbon dioxide may be supplied as carbon dioxide, carbon dioxide dissolved water may be supplied, or carbon dioxide dissolved water in which carbon dioxide bubbles are dispersed is supplied. May be.

  Carbon dioxide gas may be supplied to the electrolytic treatment as bubbles dispersed in water as described above, or may be supplied directly to the electrolytic treatment as a gas. Scale from the electrode surface using the impact of gas or bubbles on the electrode surface by supplying gas directly to the electrolysis process or by flowing water containing carbon dioxide bubbles into the electrolysis process at a relatively high flow rate. It is also possible to peel off.

  In order to supply water containing carbon dioxide gas bubbles to the electrolytic treatment apparatus, it is preferable to use an ejector. By supplying the ejected water of the ejector directly to the electrolytic treatment apparatus, it is possible to peel the scale from the electrode using the water flow.

  When the electrode of this electrolytic treatment apparatus is composed of a porous body, the contact area with water increases, and water can be efficiently subjected to electrolytic treatment.

  When the electrode is a porous body, carbon dioxide gas or carbon dioxide-dissolved water is supplied to the back side of the electrode made of the porous body in the scale removing step, and the scale attached to the electrode is removed by allowing the electrode to pass therethrough. It can be removed efficiently. In this case, it is possible not only to dissolve the scale but also to efficiently peel the scale from the electrode surface.

  In the present invention, carbon dioxide that could not be dissolved in water may be recovered and supplied to the electrolytic treatment again, and used for scale removal, thereby reducing the carbon dioxide cost and reducing the burden on the environment. Can be planned.

  In the present invention, the scale can be sufficiently removed by supplying the electrolytic treatment apparatus with about 1 to 3 moles of carbon dioxide equivalent to the dissolution equivalent of the scale deposited on the electrode.

  Hereinafter, embodiments will be described with reference to the drawings. 1 and 2 are system diagrams of the scale removing device according to the embodiment, respectively. FIG. 3 is a schematic system diagram of the cooling water system.

  As shown in FIG. 3, the water is cooled by the cooling tower 50 and stored in the water storage tank 51. This cooling water is sent to the heat exchanger 53 via the circulation pump 52, cooled by the cooling tower 50 after the heat exchange, and returned to the water storage tank 51.

  The water in the water storage tank 51 is passed through the electrolysis apparatus 1 or 20 via the pump 55 and subjected to electrolysis, and then returned to the water storage tank 51. The water in the water storage tank 51 is appropriately blown, and makeup water is supplied instead.

  Next, the configuration of the electrolysis apparatus 1 will be described with reference to FIG.

  The electrolysis apparatus 1 is configured such that an anode 3 and a cathode 4 are disposed in a casing 2, and water from a water storage tank 51 is passed through a water passage space 5 between the anode 3 and the cathode 4 for electrolytic treatment. ing. In this embodiment, the cathode 4 is made of a porous body, and a back chamber 6 for receiving carbon dioxide is formed on the opposite side of the water flow space 5 with the cathode 4 interposed therebetween.

  A pipe 7 for introducing water from the water storage tank 51 is connected to one end side of the water flow space 5 via a valve 8 and a pipe 9 for introducing carbon dioxide gas is connected via a valve 10. ing. A pipe 16 for returning the electrolyzed water to the water storage tank 51 is connected via the valve 15 to the other end side of the water flow space 5.

  Outflow water from the ejector 12 can be introduced into the back chamber 6 via a valve 13. A water supply pipe 11 for dissolving carbon dioxide gas and a carbon dioxide supply pipe 14 are connected to the ejector 12.

  In the electrolytic treatment process, a voltage is applied between the anode 3 and the cathode 4, the valves 10 and 13 are closed, and the valves 8 and 15 are opened. Water from the water storage tank 51 is passed through the pump 55 to the water flow space 5 through the pipe 7 and the valve 8, subjected to electrolytic treatment, and then returned to the water storage tank 51 through the valve 15 and the pipe 16. .

  In this electrolytic treatment process, hydrogen is generated near the cathode 4 in the water flow space 5 and becomes alkaline. For this reason, bicarbonate ions dissociate into carbonate ions in the vicinity of the cathode 4, and calcium carbonate and magnesium carbonate are generated from Ca ions and Mg ions, which are deposited on the electrode surface as scales. Is reduced.

  Therefore, the scale generation tendency of the circulating cooling water is reduced by passing the water in the water storage tank 51 through the electrolyzer. Instead of the water in the water storage tank 51, makeup water may be supplied to the water storage tank 51 after being treated by this electrolyzer.

  In addition, when a scale mainly precipitates as a carbonate, not only the hardness component in the system but also bicarbonate ions can be removed to lower the pH of the circulating water.

The Langerian index (hereinafter referred to as LSI), which is an index for measuring the corrosion / scale tendency of a solution, shows a tendency for scale precipitation as the value becomes positive, and a tendency toward corrosion as the value becomes negative. Also not shown. It is preferable to control the LSI so as to have a slight scale tendency of 0.5 to 1.0 by removing both hardness components and bicarbonate ions by the electrolysis apparatus 1 and lowering the pH. By managing LSI with a positive value of about 0.5 to 1.0 and leaving the scale component at a concentration close to supersaturation where no scale precipitates, the rate of corrosion on piping and heat exchangers in the system is reduced. Is possible. The calcium hardness in the circulating water is preferably 80 to 120 mg CaCO ₃ / L which does not cause the scale to deposit on the heat exchange section and piping of the cooling water system, the filler of the cooling tower, etc., and further the M alkalinity is 80 to 120 mg CaCO ₃ / L. The saturation index LSI is preferably set to 0.5 to 1.0 by controlling to L.

  In this embodiment, since the cathode 4 is composed of a porous body, the contact area between water and the cathode 4 is large, and the scale component can be efficiently deposited.

  In addition, the flow velocity (linear velocity) of the water in the water flow space 5 at the time of electrolytic treatment is 0.5 m / sec or less, for example, about 0.1-0.5 m / sec is suitable. When the flow rate is reduced in this way, the scale deposited on the surface of the cathode 4 is very soft and easy to remove.

  The material of the porous body constituting the cathode 4 is preferably a conductive material that is insoluble in acid. Specifically, a metal composite such as vitreous carbon, insoluble metal, metal oxide, and SUS is suitable. is there. The porosity of the porous electrode is preferably in the range of 30 to 97%, particularly preferably 80 to 97%. As the anode, an insoluble metal electrode or an oxidation resistant electrode is preferably used. Specifically, a titanium electrode coated with platinum or iridium, a platinum plating electrode, or the like is preferable. In addition, since the voltage applied to the anode 3 and the cathode 4 is not reversed in the electrolytic treatment step, a titanium electrode coated with platinum or iridium can be used for the anode.

  The distance between the anode 3 and the cathode 4 is preferably 3 to 20 mm, particularly 5 to 10 mm.

  If this electrolytic treatment is continued, the amount of scale attached to the cathode 4 increases, so the electrolytic treatment process is stopped and the scale removal process is performed. In this scale removal step, the valve 8 is closed, the valves 13 and 15 are opened, water is supplied to the ejector 12 through the pipe 11, and carbon dioxide gas is supplied through the pipe 14. The water supplied to the ejector 12 is preferably tap water, industrial water, groundwater or the like. A carbon dioxide gas cylinder is preferably used as the carbon dioxide gas source.

  Carbon dioxide-dissolved water in which carbon dioxide bubbles from the ejector 12 are entrained passes through the cathode 4 made of a porous body from the back chamber 6 and flows out to the water flow space 5 to dissolve the scale attached to the cathode 4. At this time, the air bubbles contained in the water also come into contact with the scale to be peeled off from the cathode 4.

  Furthermore, in this scale removal step, it is preferable that the valve 10 is opened and carbon dioxide gas is directly blown from the pipe 9 into the water space 5. As a result, the vicinity of the surface of the cathode 4 is vigorously stirred, and the scale attached to the cathode 4 is peeled off.

  In this scale removal step, the amount of carbon dioxide used is preferably about 1 to 3 times the molar amount of the adhesion scale. Such a small amount of carbon dioxide gas can sufficiently remove the scale, and the carbon dioxide gas cost is low. In the scale removal step, water flowing out from the pipe 16 is introduced into the water storage tank 51 and is appropriately discharged through a blow line (not shown) provided in the water storage tank 51. Generally, in tap water saturated with carbon dioxide, the pH is not lower than 4.8, and the pH of discharged water in which calcium carbonate is dissolved is higher than 5.8. It can be discharged without neutralization.

  Next, the electrolyzer 20 of FIG. 2 will be described.

  In the electrolyzer 20, an anode 22 and a cathode 23 are arranged facing each other at a predetermined interval in a casing 21, and a water passing space is formed between them.

  A pipe 24 for introducing water from the water storage tank 51 is connected to one end side of the water passage space via a valve 25, and an ejector 32 is connected via a valve 33.

  The ejector 32 is supplied with water in the water tank 40 via the pump 30 and the pipe 31, and carbon dioxide gas is supplied from above the water tank 40 via the pipe 36.

  A pipe 27 for returning the electrolyzed water to the water storage tank 51 is connected to the other end side of the water flow space via the valve 26, and drainage is caused to flow out of the casing 21 in the scale removal step. A pipe 35 is connected via a valve 34.

  The end of the pipe 35 is connected to the water tank 40.

  The water tank 40 is composed of a sealed tank, and carbon dioxide gas can be introduced into the upper part thereof from a carbon dioxide gas cylinder 41 through a pipe 42 and a valve 43. Further, a carbon dioxide gas release valve 44 is provided at the upper part of the water tank 40. The pressure of the carbon dioxide gas in the water tank 40 is detected by the pressure controller 45, and the valves 43 and 44 are controlled to open and close so that the pressure falls within a predetermined range. A trap 46 is provided at the bottom of the water tank 40 for collecting solid matter that has flowed in along with water from the pipe 35, and a solid matter discharge valve 47 is provided on the trap 46.

  Although not shown in the figure, a supply line for dissolving carbon dioxide gas such as tap water and industrial water is connected to the water tank 40, and a discharge line for scale dissolved water is also connected.

  The constituent materials of the anode 22 and the cathode 23 can be the same as those shown in FIG. Similarly, the distance between the anode 22 and the cathode 23 is preferably about 3 to 20 mm, particularly about 5 to 10 mm.

  Next, the operation of the electrolyzer 20 will be described.

  The water for dissolving carbon dioxide gas is stored in the water tank 40 up to a specified water level, and carbon dioxide gas is introduced into the upper part of the water tank 40 from the carbon dioxide gas cylinder 41 so as to have a specified pressure.

  In the electrolytic treatment process, a voltage is applied between the anode 22 and the cathode 23, the valves 33 and 34 are closed, and the valves 25 and 26 are opened. Water from the water storage tank 51 is passed through the pump 55 through the piping 24 and the valve 25 to the electrolysis apparatus 20, subjected to electrolysis, and then returned to the water storage tank 51 through the valve 26 and the piping 27.

  As in the case of the electrolysis apparatus 1 in FIG. 1, in this electrolytic treatment process, hydrogen is generated near the cathode 23 and becomes alkaline. For this reason, bicarbonate ions dissociate into carbonate ions in the vicinity of the cathode 23, and calcium carbonate and magnesium carbonate are generated from Ca ions and Mg ions, which are deposited on the cathode surface, thereby reducing the scaling tendency. Therefore, the scale generation tendency of the circulating cooling water is reduced by passing the water in the water storage tank 51 through the electrolyzer. Instead of the water in the water storage tank 51, makeup water may be supplied to the water storage tank 51 after being treated by the electrolysis device 20.

  If this electrolytic treatment is continued, scale adheres to the cathode 23, so the electrolytic treatment process is stopped and the scale removal process is performed. In this scale removal step, the valves 25 and 26 are closed, the valves 33 and 34 are opened, and the pump 30 is operated. Thereby, water in the water tank 40 is supplied to the ejector 32, and carbon dioxide-dissolved water in which carbon dioxide bubbles are involved is supplied from the ejector 32 into the electrolysis apparatus 20. Thereby, the scale adhering to the cathode 23 is dissolved.

  The liquid in the electrolyzer 20 and bubbles of carbon dioxide mixed therein are introduced into the water tank 40 through the pipe 35 and are separated into gas and liquid. Water is again supplied to the ejector 32 via the pump 30. The carbon dioxide gas released from the water in the water tank 40 is supplied again to the ejector 32 through the pipe 36. Solid matter contained in the water flowing into the water tank 40 from the pipe 35 is collected in the trap 46 and discharged by opening the valve 47 as appropriate. The carbon dioxide pressure in the upper part of the water tank 40 is maintained within a predetermined range by the controller 45.

  Even in the case of FIG. 2, the amount of carbon dioxide supplied to the electrolyzer 20 is preferably about 1 to 3 times the amount of the attached scale.

  After performing this scale removal step for a predetermined time, the pump 30 is stopped and the valves 33 and 34 are closed. Thereafter, the valves 25 and 26 are opened, and the process returns to the electrolytic treatment process.

  The water in the water tank 40 can be used repeatedly for the scale removal process. When the water in the water tank 40 becomes dirty, a part or all of the water is discharged, and water for dissolving carbon dioxide gas is supplied to the water tank 40 instead.

In the embodiment of FIG. 2, it is desirable to operate the electrolyzer 20 so that the M alkalinity of the cooling water circulating in the circulating cooling water system does not exceed 120 mg-CaCO ₃ / L. The amount of scale deposition in the electrolyzer 20 can be controlled by the value of the direct current that flows between the anode 22 and the cathode 23.

  In the circulation type cooling water system shown in FIG. 3 having the electrolyzer shown in FIG. 1, the scale treatment was performed for 5 hours and then the scale removal process was performed for 1 hour. Could be removed. The pH of the waste water in the scale removal process was 6.4. The volume of the electrolysis apparatus 1 was 0.75 L, and carbon dioxide gas was supplied to the electrolysis apparatus 1 from the pipe 9 at 12.5 L / Hr. Carbon dioxide gas was supplied to the ejector 12 at 20 L / Hr, and water for dissolving carbon dioxide gas was supplied at 100 L / Hr.

  On the other hand, in the same electrolysis apparatus, when the scale removal step was performed for 4 hours with the polarity reversed, the scale remaining rate was as high as 5%, and deterioration of the electrodes was observed. The pH of the waste water was 9.4.

  In the same electrolyzer, when the scale removal step was performed by passing electrolytic acid water (pH 2.5) at 100 L / Hr, the scale remaining rate was 3%, and the wastewater pH was 5.2. there were. Deterioration of the electrode was not recognized.

It is sectional drawing of the electrolysis apparatus used for embodiment. It is sectional drawing of the electrolysis apparatus used for another embodiment. It is a systematic diagram of a circulation type cooling water system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 Electrolyzer 2,21 Casing 3,22 Anode 4,23 Cathode 12,32 Ejector 40 Water tank 45 Controller

Claims (15)

Electrolyzing process for circulating treated water consisting of circulating water and / or make-up water in a circulating cooling water system through an electrolysis apparatus having an electrode for electrolysis, and depositing scale on the electrode surface;
And a scale removal step of removing scale deposited on the electrode by supplying carbon dioxide to the electrolysis apparatus.   2. The circulating cooling water system electrolytic treatment method according to claim 1, wherein carbon dioxide gas and / or carbon dioxide-dissolved water is supplied to the electrolysis apparatus in the scale removing step.   3. The circulating cooling water system electrolytic treatment method according to claim 1, wherein an oxidizing agent is generated from the electrode to sterilize the cooling water by electrolytic treatment in the electrolytic treatment step.   4. The circulating cooling water system electrolytic treatment method according to claim 1, wherein the electrode is made of a porous body. In any one of Claims 1 thru | or 3, the some electrode is arrange | positioned in the said electrolysis apparatus, Between these electrodes is the water flow space of to-be-processed water,
At least one electrode comprises a porous body;
In the electrolytic treatment step, water to be treated is passed through the water flow space.
In the scale removal step, the circulating cooling water system electrolytic treatment method is characterized in that carbon dioxide is permeated from the opposite side to the water flow space of the porous electrode to the water flow space side.   6. The circulating cooling water system electrolytic treatment according to claim 1, wherein in the scale removing step, the scale attached to the electrode is peeled off by supplying carbon dioxide into the electrolysis apparatus. Method.   6. The circulating cooling water system electrolytic treatment method according to claim 1, wherein in the scale removing step, carbon dioxide gas or carbon dioxide-dissolved water is supplied into the electrolysis apparatus.   8. The circulating cooling water system electrolytic treatment method according to claim 1, wherein carbon dioxide flowing out of the electrolyzer in the scale removing step is recovered and supplied to the electrolyzer again. 10.   9. The circulating cooling water system according to claim 1, wherein in the scale removing step, 1 to 3 times as much mole of carbon dioxide as the scale deposited on the electrode is supplied to the electrolyzer. Electrolytic treatment method. An electrolysis device having an electrode;
Means for passing water to be treated comprising circulating water or makeup water in a circulating cooling water system into the electrolyzer;
A circulating cooling water processing apparatus comprising carbon dioxide supply means for supplying carbon dioxide to the electrolyzer and removing scales deposited on the electrodes.   11. The processing apparatus for a circulating cooling water system according to claim 10, wherein the carbon dioxide supply means is a supply means for carbon dioxide gas and / or carbon dioxide dissolved water.   12. The circulating cooling water processing apparatus according to claim 10, wherein the electrode is made of a porous body. In Claim 10 or 11, a plurality of electrodes are arranged in the electrolysis device, and the space between the electrodes serves as a water passage space for water to be treated.
At least one electrode comprises a porous body;
An apparatus for circulating cooling water system, characterized in that, as the carbon dioxide supply means, means for supplying carbon dioxide gas and / or carbon dioxide gas to the side opposite to the water passage space of the electrode made of the porous body is provided.   The circulating cooling water system according to any one of claims 10 to 13, wherein the carbon dioxide supply means is configured to mix carbon dioxide gas and water with an ejector and to supply the mixture to the electrolyzer. Processing equipment.   15. The processing apparatus of the circulating type cooling water system according to any one of claims 10 to 14, further comprising means for recovering carbon dioxide flowing out from the electrolyzer and supplying it again to the electrolyzer.

Images