JP2006098003A - Circulating cooling water system electrolytic treatment method and electrolytic treatment apparatus - Google Patents

Abstract

The present invention provides an electrolytic treatment method and an electrolytic treatment apparatus capable of keeping the scale component concentration and chlorine concentration of an aqueous system within appropriate ranges in a method and an apparatus for conducting electrolytic treatment by passing circulating cooling water through an electrolytic device. To do.
In an electrolytic treatment process, a voltage is applied between an anode 3 and a cathode 4, and water from a water storage tank 51 is circulated through the electrolysis apparatus 1 to perform an electrolytic treatment. In the vicinity of the cathode 4, hydrogen is generated and becomes alkaline. 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, thereby reducing the scaling tendency. The current density is controlled so that the oxidation-reduction potential in the electrolyzed water is within a predetermined range.
[Selection] Figure 1

Description

  The present invention relates to a circulating cooling water-based electrolytic treatment method and an electrolytic treatment apparatus, and in particular, an electrolytic treatment method in which a scale is deposited in an electrolytic device and removed from the aqueous system, and a chlorinated oxidant is generated. The present invention relates to an electrolytic treatment apparatus.

  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, the upper limit is the conductivity corresponding to the concentration ratio at which scale precipitation does not occur in the system, and when that conductivity is reached, the concentrated cooling water is discharged from the bottom of the cooling tower as blow water to the outside of the system. The operation of the circulating cooling water is controlled with a constant quality by diluting the whole with make-up water. Here, if the amount of blow water is increased and the scale component concentration in the system is decreased, a large amount of makeup water is required, resulting in excessive water and sewerage 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 chemical and a carboxylic acid has been added.

  Since these chemical treatments are continuously infused at a constant concentration where the effect is recognized, if the load fluctuation occurs in the makeup water concentration, the chlorine consumption rate fluctuates depending on the season, the treatment effect is insufficient or overtreatment Cases arise. In general, due to insufficient treatment, scale adhesion and slime adhesion often occur, which is problematic. Therefore, not only the cost of the drug is excessive, but the blow water in which the drug is dissolved contains COD and phosphorus compounds, which may affect aquatic organisms living in the discharge area. There was also a problem that was necessary.

  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. For this reason, the deposited scale dissolves near the electrode and flows out into the solution. As a result, very fine crystals are dispersed in the cooling water. These fine crystals serve as nuclei and precipitate scale components. By continuing the electrolysis while converting the polarity, the scale component in the water to be treated is deposited on the fine crystals, thereby reducing the scale tendency of the circulating water and preventing the scale from adhering to the heat transfer surface. .

  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 electrodes, the electrode 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.

JP-A-2004-132592 discloses processes the circulating water by electrolysis, while measuring the electrical conductivity of the water to be treated so that the scale is not attached to the electrode surface, so as to be less 250 mg / L in terms of CaCO ₃ The method of holding is described. However, in this method, the amount of chlorine generated cannot be controlled, and if the chlorine consumption of the water to be treated is extremely low, the piping and heat exchanger may be corroded.
Japanese Patent Laid-Open No. 2003-190988 Special table 2001-502229 gazette JP 2000-140849 A JP 2004-132592 A

  The present invention relates to a method and an apparatus for electrolytic treatment by passing circulating cooling water system water through an electrolysis device, removing an appropriate amount of scale components in the system, and a chlorine-based oxidant in the effluent water from the electrolysis device. An object of the present invention is to provide an electrolytic treatment method and apparatus capable of performing an electrolytic treatment so that an appropriate amount is contained.

  Another object of the present invention is to provide an electrolytic treatment method and an electrolytic treatment apparatus that can easily remove scale deposited on electrodes of the electrolytic apparatus.

  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 In the circulating cooling water system electrolytic treatment method having an electrolytic treatment step of depositing scale on the surface and generating a chlorinated oxidant, the residual chlorine concentration or redox potential of the circulating water in the circulating cooling water system is measured, The current density between the electrodes is controlled so that the residual chlorine concentration or the oxidation-reduction potential falls within a predetermined range.

  The electrolytic treatment method for a circulating cooling water system according to claim 2 is characterized in that, in claim 1, the current density is controlled within a range of current density in which no scale is deposited in the system and no corrosion occurs. is there.

Electrolytic treatment method for recycling the cooling water system of claim 3, in claim 1 or 2, characterized in that control within a current density of 0.1~1.5A / dm ^2.

The range of the current density is particularly preferably 0.1~1.5A / dm ² depending on the system, more preferably 0.2~1A / dm ^2.

  According to a fourth aspect of the present invention, there is provided a circulating cooling water system electrolytic treatment method according to any one of the first to third aspects, wherein a scale of a predetermined amount or more adheres to the electrode by the electrolytic treatment in the electrolytic treatment step. The removal process is performed, and then the process returns to the electrolytic treatment process.

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

  The method for electrolytic treatment of a circulating cooling water system according to claim 6 is the electrolytic treatment method according to any one of claims 1 to 5, wherein in the electrolytic treatment step, the electrical conductivity in the circulating water of the circulating cooling water system is measured, The amount of blow water and / or the amount of makeup water is controlled so as to be within a predetermined range.

  The circulating cooling water treatment apparatus according to claim 7 comprises an electrolysis apparatus having an electrode, and means for passing water to be treated made of circulating water or makeup water in the circulation cooling water system into the electrolysis apparatus. A circulating cooling water treatment apparatus comprising: means for measuring residual chlorine concentration or redox potential (ORP) of circulating water in the circulating cooling water system; and the measured residual chlorine concentration or redox potential is within a predetermined range. And a means for controlling the energization amount to the electrode.

  The processing device for the circulating cooling water system according to claim 8 is the processing device according to claim 7, wherein the means for controlling the energization amount to the electrode is a means for controlling the energization amount so that no scale is deposited in the system and corrosion does not occur. It is characterized by.

  According to a ninth aspect of the present invention, there is provided the processing apparatus for circulating type cooling water system according to the seventh or eighth aspect, wherein the means for measuring conductivity in the circulating water of the circulating type cooling water system and the amount of blow water and / or so that the electric conductivity falls within a predetermined range. Or a means for controlling the amount of makeup water is provided.

[Claims 1 and 7]
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. Scale is deposited by this 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 the scale component of the circulating cooling water can be operated at a constant concentration without using chemicals, it is possible to prevent or suppress the scale from being deposited on the heat exchange section or the cooling tower. Corrosion can be reduced. In regions where the makeup water hardness is high, highly concentrated operation is possible, leading to water saving.

  Further, since the cooling 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.

  In the present invention, when the operation is performed in a current density range in which the amount of scale deposition on the electrode can be properly maintained, and the residual chlorine concentration or ORP measured value exceeds a certain range, (if the power is turned on / off) It is preferable that the chlorine generation rate is adjusted by changing the current density within the range of the current density so that the residual chlorine concentration is controlled within a certain range.

[Claims 3, 6 and 9]
Note that there is a relationship schematically shown in FIG. 3 between the current density of this electrolyzer and the chlorine generation rate and scale deposition rate. That is, the current density and the chlorine generation rate are almost proportional. The scale deposition rate is substantially proportional in the range where the current density is small, but eventually reaches a peak, and when the current density becomes greater than a certain value, the scale deposition rate decreases. There is such a peak or inversely proportional relationship between the current density and the scale deposition rate. If the current density is increased too much, too much OH ⁻ is generated in the vicinity of the electrode, preventing the scale components from approaching. As a result, scale nuclei generated on the cathode surface flow into the system without adhering to the electrode surface, so that the scale deposition rate decreases.

[Claims 4 and 5]
If this electrolytic treatment is continued, the scale adhesion amount of the electrode increases, so the scale removal step is performed.

In order to remove the scale, carbon dioxide is preferably supplied to the electrolytic treatment apparatus to remove the scale. For example, in the case of a flow of 5 hours electrolysis and 1 hour CO ₂ cleaning, the scale component concentration of the circulating water in the system increases and the residual chlorine concentration decreases because electrolysis is not performed for 1 hour of CO ₂ cleaning. The temporary load fluctuation can be dealt with by the operation control of the present invention.

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.

  The carbon dioxide gas may be supplied to the electrolytic treatment apparatus as bubbles dispersed in water as described above, or may be directly supplied to the electrolytic treatment as a gas. By supplying gas directly to the electrolytic processing apparatus, or by introducing water containing carbon dioxide gas bubbles into the electrolytic processing apparatus at a relatively high flow rate, the surface of the electrode is utilized by using the impact of the gas or bubbles on the electrode surface. It is also possible to peel the scale from.

  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.

  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.

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

  As shown in FIG. 2, 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 through the pump 55 and the pipe 56, subjected to electrolytic treatment, and then returned to the water storage tank 51 through the pipe 57. The water in the water storage tank 51 is appropriately blown, and makeup water is supplied instead.

  The water storage tank 51 is provided with a conductivity meter 58 and an ORP meter (oxidation reduction potential meter) 59, and these detected values are input to the controller 60. The controller 60 controls the current density of the electrolysis apparatus 1 based on these detected values and also controls a blow valve (not shown).

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

  In the electrolysis apparatus 1, two anodes 3 and three cathodes 4 are alternately arranged in a casing 2, and water from a water storage tank 51 is passed through a water passage space 5 between the anodes 3 and the cathodes 4. Then, it is configured to perform electrolytic treatment. In this embodiment, three cathodes 4 made of a porous plate are arranged with a space between each other, and a plate-like anode 3 is arranged between each of the cathodes 4 and 4.

  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-plated 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.

  A pipe 56 for introducing the water to be treated is connected to the lower end side of the casing 2 via a valve 56a, and a pipe 57 for flowing out the electrolyzed water is connected to the other end side via a valve 57a.

  Two perforated plates 6 and 6 made of punching metal or the like are arranged on the lower end side in the casing 2 with the plate surface substantially horizontal so that the inflowing water from the pipes 56 is dispersed in each space 5 and flows in. Yes. A space 7 between the perforated plates 6 and 6 serves as an inflow space 7 for carbon dioxide dissolved water.

  A perforated plate 8 made of punching metal or the like is disposed on the upper end side in the casing 2 with the plate surface being substantially horizontal, and a space 9 for collecting carbon dioxide-dissolved water is formed above the perforated plate 8. Thus, by arranging the porous plate 8 on the outflow side, the flow of each space 5 can be made more uniform.

  A carbon dioxide-dissolved water supply device 20 that supplies carbon dioxide-dissolved water into the casing 2 in order to dissolve the scale attached to the cathode 4 is installed. The carbon dioxide dissolved water supply device 20 includes a dissolution tank 23 to which a liquid carbon dioxide cylinder 21 is connected via a valve 22, a pump 24 for sending carbon dioxide dissolved water from the dissolution tank 23, and a discharge side of the pump 24. And a carbon dioxide supply pipe 26 that communicates the intake port of the ejector 25 and the upper part of the dissolution tank 23. The dissolution tank 23 is provided with a pressure gauge 27.

  The discharge side of the ejector 25 is connected to the inflow space 7 of the casing 2 via a valve 29 and a pipe 28. The collecting space 9 of the casing 2 and the upper part of the dissolution tank 23 are connected via a pipe 30 and a valve 31.

Carbon dioxide gas is supplied from the cylinder 21 so that the gas pressure in the upper part of the dissolution tank 23 becomes a predetermined pressure. When the pumps 24 are operated with the valves 29 and 31 opened, the water in the dissolution tank 23 is supplied to the ejector 25, and the carbon dioxide gas sucked through the pipe 26 is caught in the discharge water of the ejector 25, and a part thereof Dissolves in water. After this carbon dioxide-dissolved water has passed through the casing 2 from the pipe 28, it is circulated to the dissolution tank 23 via the pipe 30. The circulation flow rate at this time is 0.05 to 3 m / sec, preferably 1 to 2 m / sec. The faster the flow rate, the thinner the diffusion layer on the scale surface and the easier it is for CO _{2 in} the water to reach the scale.

Next, the electrolytic treatment process using this electrolytic treatment apparatus will be described in detail.
[Electrolytic treatment process]
In the electrolytic treatment process, a voltage is applied between the anode 3 and the cathode 4, the valves 29 and 31 are closed, and the valves 56a and 57a are opened. Water from the water storage tank 51 is passed through the water passing space 5 through the pump 55, the pipe 56, and the valve 56a, subjected to electrolytic treatment, and then returned to the water storage tank 51 through the valve 57a and the pipe 57.

  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 a scale.

  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 scale deposition rate is a substantially constant rate within the range of a in FIG. 3, for example, a current density of 0.1 to 1.5 A / dm ² . This is because the scale deposition is rate-determining the diffusion of hardness components in the circulating water to the cathode surface. Increasing the flow rate can make the hardness component easily reach the cathode surface, but if the flow rate is increased too much, carbonate nuclei generated on the cathode surface in an alkaline atmosphere do not adhere to the surface of the cathode 4. In other words, it flows into the pipe 57, and the scale adhesion rate to the electrode decreases. Therefore, although the flow rate is related to the chlorine generation rate, it is preferably 0.01 to 1 m / sec, and particularly preferably 0.05 to 0.1 m / sec. If the water quality, flow rate, and current density are constant, the scale deposition rate per unit electrode area becomes constant, so that different cooling tower scales can be handled by increasing or decreasing the electrode area.

  In order to perform the automatic operation, it is preferable to perform concentration management by obtaining the ion concentration from the conductivity in the cooling water system. When the scale deposition rate is constant, the amount of hardness component to be removed can be derived from the scale of the cooling water system, the concentration factor, and the load factor. Accordingly, the operation is performed with the scale deposition rate equal to the required removal rate. Based on the conductivity at that time, if the conductivity is higher than the reference value, the blow device is operated to lower the concentration factor.If the conductivity is lower than the reference value, the blow device is stopped and the concentration factor is decreased. increase.

  When this electrolysis is performed, on the anode 5 side, chloride ions in the circulating water are oxidized and chlorine gas is generated. Above pH 4, the chlorine gas dissolves in the circulating water and becomes hypochlorous acid. When the pH of this hypochlorous acid becomes 8 or more, 80% dissociates into hypochlorite ions. Since these have strong oxidizing power, they can sterilize slime and mold in circulating water. This chlorine generation amount can be controlled by the current density.

In order to control the amount of generated chlorine, for example, the correlation between the residual chlorine concentration in the cooling water system and the ORP value is grasped in advance, and the residual chlorine concentration is set to 0.1 to 0.5 mgCl ₂ / L, for example. performing normal operating current density 0.7 a / dm ² as a reference. If the residual chlorine concentration is lower than 0.1 mgCl ₂ / L, the current density is increased to adjust the chlorine generation rate, and if it is 0.5 mgCl ₂ / L or more, the current density is decreased to decrease the chlorine generation rate. In the range of 0.1 to 1.5 A / dm ² , even if the current density changes, there is almost no influence on the scale deposition rate as shown in FIG. 3, so that simultaneous automatic management of scale and slime becomes possible.

  In general, the Langerian index (hereinafter referred to as LSI), which is an index for measuring the corrosion / scale tendency of a solution, shows a tendency of scale precipitation as the value becomes positive, and a tendency toward corrosion as the value becomes negative. It also shows no tendency. It is preferable to control the LSI to have a slight scale tendency of 0.5 to 0.8 by removing both hardness components and bicarbonate ions by the electrolyzer 1 and lowering the pH. If the LSI is managed with a positive value of about 0.5 to 0.8, the scale component in the circulating water does not reach supersaturation.

By allowing the scale component to remain in the circulating water at a concentration close to supersaturation where no scale is deposited, it is possible to reduce the corrosion rate of the piping in the system and the heat exchanger. The calcium hardness in the circulating water is preferably 80 to 120 mg CaCO ₃ / L which does not cause the scale to precipitate in the heat exchange section of the cooling water system, the piping, the filler of the cooling tower, and the M alkalinity is 80 to 120 mg CaCO ₃ / L. Preferably, the saturation index LSI is controlled to 0.5 to 0.8.

Therefore, when performing the automatic concentration management of the cooling water, it is preferable that the M alkalinity of the cooling water system is operated and managed at 80 to 120 mg CaCO ₃ / L. The hardness component amount to be removed by the electrolyzer 1 can be derived by subtracting the hardness component amount discharged together with the blow water from the hardness component flowing into the cooling water system together with the makeup water. In order to perform the automatic concentration management, the electrical conductivity when the M alkalinity is 80 to 120 mg CaCO ₃ / L is measured, and blow water discharge and makeup water replenishment are managed so as to fall within the ranges. For example, if the conductivity when the M alkalinity is 80 mg CaCO ₃ / L is 80 mS / m, the conductivity when the M alkalinity is 120 mg CaCO ₃ / L is 140 mS / m, and the conductivity is lower than 80 mS / m, blown After the discharge is stopped, the portion that has evaporated is flown into the makeup water and concentrated, and when reaching 140 mS / m, the blow is started and the makeup water is allowed to flow. Thereafter, by repeating this, even if the load fluctuation of the makeup water occurs, it is possible to manage the Langeria index without causing the scale to precipitate or causing corrosion by the conductivity management.

[Scale removal process]
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 process, the valves 56a and 57a are closed, the valves 29 and 31 are opened, the pump 24 is started, and the water in the tank 23 is supplied to the ejector 25.

  Carbon dioxide-dissolved water in which carbon dioxide bubbles from the ejector 25 are entrained flows into the water flow space 5 and dissolves 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.

  After the scale removal step is completed, the pump 24 is stopped, the valves 29 and 31 are closed, and the water in the dissolution tank 23 is discharged through a discharge line (not shown) provided in the tank 23. To discharge. 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.

  The water in the dissolution tank 23 can be used repeatedly for the scale removal process. When the water in the dissolution tank 23 becomes dirty, a part or all of the water may be discharged, and water may be supplied to the tank 23 instead.

[Example 1]
1 was installed in the open system circulating cooling water line shown in FIG.

When this was circulation line is installed in an open system circulating coolant line 300 frozen tons Atsugi City Water 5-fold concentrated, makeup water calcium hardness of 5-fold concentrated stoichiometric calcium hardness from 40mgCaCO ₃ / L becomes 200mgCaCO ₃ / L.

Automatic operation was started by setting the current density to 1.0 A / dm ² so that the calcium carbonate scale deposition rate in the electrolyzer 1 was 20 g CaCO ₃ / m ³ / hr and the residual chlorine concentration was 0.3 mgCl ₂ / L. . The electrical conductivity is controlled to be within 50 to 70 mS / m. If the electrical conductivity exceeds 70 mS / m, the blow is started, and the electrical conductivity is lowered by replenishing makeup water. Was maintained at around 100 mg CaCO ₃ / L.

The ORP at the start of operation was 0.3 mg Cl ₂ / L at 800 mV. In this state, even if the slime potential fluctuation in the system was 0.5 to 2 times, the residual chlorine concentration was stable in the range of 0.2 to 0.5 mg Cl ₂ / L.

The current density was automatically changed according to the ORP value. ORP value varies from 500mV to 1300 mV, varied current density from 0.7 A / dm ² up to 1.4A / dm ² accordingly. In this current density range, the scale deposition rate was stably about 20 g CaCO ₃ / m ³ / hr. No scale or slime adhered to the heat exchanger during open inspection after 3 months of operation (see Table 1).

[Comparative Example 1]
As a comparative example, the control device was stopped in FIG. 2, and the operation was performed while maintaining the current density of the electrolysis device at a constant 1.0 A / dm ² . When the slime potential doubled in the summer when slime is likely to occur, the chlorine consumption also doubled. However, the operation was carried out at a constant current density, so the amount of chlorine generated was insufficient, and the slime grew. Therefore, as a result of increasing the slime load fluctuation by 0.1 to 2 times, the amount of generated chlorine was excessive when it was increased to 0.1 times, and corrosion of the carbon steel tube was observed.

  It was as Table 1 when the calcium hardness in the circulating water in Example 1 and the comparative example 1, residual chlorine concentration, and the efficiency fall degree to a heat exchanger were measured.

It is sectional drawing of the electrolysis apparatus used for embodiment. It is a systematic diagram of a circulation type cooling water system. FIG. 4 is a schematic correlation diagram of current density, scale deposition rate, and chlorine generation rate.

Explanation of symbols

1 Electrolyzer 2 Casing 3 Anode 4 Cathode 23 Dissolution Tank 25 Ejector

Claims (9)

Water to be treated consisting of circulating water and / or make-up water in a circulating cooling water system is passed through an electrolyzer having an electrode to be electrolyzed, thereby depositing scale on the electrode surface and generating a chlorinated oxidant. In an electrolytic treatment method of a circulating cooling water system having an electrolytic treatment step,
A circulation type characterized by measuring the residual chlorine concentration or oxidation-reduction potential of circulating water in the circulation-type cooling water system and controlling the current density between the electrodes so that the residual chlorine concentration or oxidation-reduction potential falls within a predetermined range. Cooling water system electrolytic treatment method.   2. The electrolytic process method for a circulating cooling water system according to claim 1, wherein the current density is controlled within a range of a current density in which no scale is deposited in the system and corrosion does not occur. According to claim 1 or 2, electrolytic treatment method of recycling cooling water systems and controls within the current density of 0.1~1.5A / dm ^2.   4. The scale removal step according to any one of claims 1 to 3, wherein a scale removal step is performed when a predetermined amount or more of scale adheres to the electrode by the electrolytic treatment in the electrolytic treatment step, and then the processing returns to the electrolytic treatment step. A method for electrolytic treatment of a circulating cooling water system.   5. The circulating cooling water system electrolytic treatment method according to claim 4, wherein in the scale removing step, carbon dioxide gas and / or carbon dioxide-dissolved water is supplied to the electrolysis apparatus.   In any 1 item | term of the Claims 1 thru | or 5, in the said electrolytic treatment process, the electrical conductivity in the circulating water of a circulation type cooling water system is measured, and the amount of blow water and / or make-up water amount are adjusted so that this electrical conductivity may become a predetermined range. A method for electrolytic treatment of a circulating cooling water system, characterized by controlling. 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;
In a circulating cooling water system treatment apparatus comprising:
Means for measuring the residual chlorine concentration or redox potential of the circulating water in the circulating cooling water system;
A circulating cooling water system processing apparatus comprising: means for controlling an energization amount to an electrode so that a measured residual chlorine concentration or oxidation-reduction potential is within a predetermined range.   8. The processing apparatus for a circulating cooling water system according to claim 7, wherein the means for controlling the energization amount to the electrode is a means for controlling the energization amount so that no scale is deposited in the system and corrosion does not occur.   9. The method according to claim 7, further comprising: means for measuring conductivity in circulating water of the circulating cooling water system; and means for controlling the amount of blow water and / or makeup water so that the conductivity falls within a predetermined range. A circulating cooling water system processing device.

Images