JP2005288238A - Cooling water treatment device and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform scale deposition in an electrolyzer for reducing scale generating tendency; to perform removing and cleaning of scale sufficiently at a low cost. <P>SOLUTION: A main electrolyzer 2 for reducing the scale generating tendency is installed in piping 1 for cooling water. In the main electrolyzer 2, an anode 5a and a cathode 5b made of a porous body are disposed opposite to each other in a casing 3. A sub-electrolyzer 11 for generating acidic water for acid cleaning of the main electrolyzer 2 is installed. In the sub-electrolyzer 11, its inside is divided into an anode chamber 12 and a cathode chamber 13 by a diaphragm 16, and an anode 14 is installed in the anode chamber 12 and a cathode 15 is installed in the cathode chamber 13. When the operation of the main electrolyzer 2 continues, the scale adheres to the cathode in it, so that the main electrolyzer 2 is acid cleaned periodically or when current-carrying resistance between the electrodes exceeds the prescribed value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cooling water treatment apparatus for preventing scale adhesion in a cooling water system and an operation method thereof.

  In the cooling water system, cooling water (circulated water) heated by cooling with a heat exchanger is sent to a cooling tower and cooled by evaporating a part, and the cooled cooling water is circulated through the heat exchanger. Cooling is repeated. In such a cooling water system, the circulating water is concentrated by evaporation in the cooling tower. Hardness components such as calcium and magnesium and other scale components contained in the cooling water makeup water or concentrated circulating water are deposited on the heat transfer surface of the heat exchanger and are scaled to cause a decrease in thermal conductivity.

  As a method for preventing the scale, a method of adding a drug such as polyphosphoric acid or a low molecular weight polymer is performed, but the drug cost is high. As a water treatment method for cooling water that does not require the use of chemicals, Japanese Patent Application Laid-Open No. 2003-190988 discloses that replenishing water or circulating water in a cooling water system is passed through an electrolyzer having a bipolar electrode whose polarity is changed. A method for preventing scale adhesion in a cooling water system, particularly scale adhesion on a heat transfer surface, by precipitating scale components contained in water or circulating water as fine crystals 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 changing 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 the above-mentioned Japanese Patent Application Laid-Open No. 2003-190988, the cooling water containing fine particles generated in the electrolysis apparatus is sent to the heat exchange section or the cooling tower, and the solubility becomes supersaturated at that portion. . 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.

  JP-T-2001-502229 discloses that 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 plastic between the electrodes. A method is described in which scale formation is reduced by mixing and filling non-conductive particles such as water and passing water between the electrodes while passing water through a cylindrical container. 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 this method, 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. 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 at the cathode, the oxide is exfoliated and easily deteriorates.

Japanese Patent Application Laid-Open No. 2000-140849 discloses an apparatus for depositing a scale component on a cathode surface by passing water to be treated through an electrolytic device 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 problems with this method are that the electrodes are likely to deteriorate due to the polarity change, and that the attached scales are 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.
Japanese Patent Laid-Open No. 2003-190988 Special table 2001-502229 gazette JP 2000-140849 A

  In the cooling water treatment apparatus that reduces the scale formation tendency by depositing the scale component on the cathode by the electrolytic treatment of water as described above, in particular, in the flat plate facing type, the electrolysis apparatus is put into the electrolytic apparatus with the progress of operation in a short time. A scale adheres and narrows the flow path of the water to be treated. Moreover, it is necessary to remove this, but the scale could not be efficiently and sufficiently removed while avoiding the deterioration of the electrode.

  An object of the present invention is to perform the scale removal cleaning of the electrolysis apparatus for reducing the scale generation tendency sufficiently and at low cost.

  The cooling water treatment apparatus of the present invention is a cooling water treatment apparatus comprising an electrolytic device for reducing scale generation tendency in which supply water or circulating water of a circulating cooling water system is passed between an anode and a cathode. It consists of a porous body.

  When the cooling water treatment apparatus of the present invention is equipped with an acid generation electrolyzer that generates an acid for acid cleaning, the operation method of the cooling water treatment apparatus of the present invention, An operation process for reducing scale generation tendency and an acid cleaning process for supplying acid to the scale generation tendency reducing electrolyzer to perform acid cleaning are alternately performed. is there.

According to the cooling water treatment apparatus and the operation method thereof of the present invention, the cooling water is electrolyzed in the scale generation tendency reducing electrolysis apparatus as follows.
Anode: 2H ₂ O → O ₂ + 4H ⁺ + 4OH ⁻
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 generated from Ca ions and Mg ions, which are precipitated as scale fine particles, thereby reducing the scaling tendency.

  In addition, when the water containing the scale fine particles flows in the supersaturated region of the scale components such as the heat exchanger in the cooling water system, the dissolved scale components are deposited on the scale fine particles, so that the water is applied to the surface of the equipment such as the heat exchanger. Scale adhesion is remarkably suppressed. Therefore, the scale formation tendency of the circulating cooling water is reduced by passing the circulating cooling water or makeup water through the electrolyzer.

  In the present invention, since the cathode is a porous body, the contact area between the cathode and water is large, and dissolved scale components in water are deposited on the surface of the cathode and in the cathode, and the scale formation tendency of water is sufficiently reduced. .

  By reducing the porosity of the porous body to 30 to 97%, the reduction in scale generation tendency becomes more remarkable.

  When scale accumulates on the cathode of this scale generation tendency reducing electrolyzer, acid cleaning is performed to remove the scale. For this purpose, acid is removed from the acid generation electrolyzer for reducing scale formation tendency. It is preferable to introduce into an electrolytic apparatus and perform acid cleaning. By providing this electrolytic device for acid generation, it becomes unnecessary to purchase and store an acid for acid cleaning, and the processing cost is reduced. Moreover, since the cathode is made of a porous material and has a large surface area, the thickness of the scale attached is small. For this reason, the scale can be sufficiently removed by acid cleaning. In the operation method of the cooling water treatment apparatus, the scale can be reliably removed by alternately performing the operation process and the acid cleaning process.

  According to the cooling water treatment apparatus and the operation method thereof of the present invention, the scaling tendency of the cooling circulating water can be lowered, so that the deposition of scale in the heat exchange section, the cooling tower, etc. is prevented or suppressed. In addition, the scale generation tendency reducing electrolyzer is sufficiently acid cleaned, and the acid cleaning cost is reduced.

  In the present invention, after a certain amount of scale is attached to the porous body electrode constituting the cathode of the scale generation tendency reducing electrolyzer, the electrolytic acid water is used for reducing the scale formation tendency from a separate acid generation sub-electrolyzer. It is supplied to the electrolyzer and the scale is acid cleaned and discharged. By providing this electrolytic apparatus for acid generation, it is possible to eliminate the purchase of chemicals for acid cleaning and dangerous carrying-in work, and to improve the chemical cost and safety. Furthermore, the use of a porous electrode having a high porosity increases the adhesion area of the scale and improves the contact efficiency between the electrolytic acid water and the scale, thereby shortening the cleaning time. In addition, by performing acid cleaning with electrolytic acid water, polarity conversion is not required, and electrode deterioration can be greatly suppressed.

  Hereinafter, the cooling water treatment apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an electrolysis apparatus of a cooling water treatment apparatus according to an embodiment.

  A main electrolysis device 2 for reducing scale generation tendency is installed in the middle of the cooling water pipe 1. In the pipe 1, the upstream side of the main electrolyzer 2 is 1a, and the downstream side is 1b, 1c.

  The main electrolysis apparatus 2 has an anode 4 and cathodes 5 a and 5 b made of a porous body disposed in a casing 3. In this embodiment, two plate-like cathodes 5 a and 5 b are arranged so as to face both plate surfaces of the plate-like anode 4. Cooling water from the pipe 1a flows between the anode 4 and the cathode 5a from the inlet 3a, flows around the tip side of the anode 4, flows between the anode 4 and the cathode 5b, and flows out from the outlet 3b to the pipe 1b. To do. A blow water outlet 3c is provided so as to face the tip side of the anode 4, and a blow pipe 6 is connected thereto. The blow pipe 6 is provided with a valve 6a.

  The pipe 1a is provided with a valve 7, and a three-way valve 8 is provided between the pipes 1b and 1c. A pipe 9 connects the three-way valve 8 to the main electrolyzer inlet 3a side of the valve 1 in the pipe 1a.

  A secondary electrolysis device 11 is installed to generate acid water for acid cleaning. The sub electrolysis apparatus 11 is divided into an anode chamber 12 and a cathode chamber 13 by a diaphragm 16, an anode 14 is installed in the anode chamber 12, and a cathode 15 is installed in the cathode chamber 13.

  Water for electrolysis made of tap water or the like is introduced into the sub-electrolyzer 11, and acidic water flows out from the anode chamber 12 through a pipe 17 with a pump 17a and is supplied to the pipe 1a (the inlet 3a side from the valve 7). It is possible. A discharge line 18 is connected to the cathode chamber 13.

  The cooling water treatment apparatus configured as described above is installed in a cooling water circulation line of a cooling system, a cooling tower, or the like. In the cooling water treatment apparatus provided in this cooling system, in a steady state, the sub electrolysis apparatus 11 is stopped (energization and water flow is stopped), the valve 7 is opened, and the three-way valve 8 is connected to the pipes 1b and 1c. Water is passed only through the main electrolyzer 2. When a voltage is applied to the electrodes 4 and 5 of the main electrolyzer 2, scales are generated in the form of fine particles on the cathode sides 5a and 5b, and the fine particles flow through the circulating cooling water line while being mixed with the cooling water. When the water containing scale particles passes through the supersaturated region of the scale components such as heat exchangers, the scale deposits on the scale particles, thereby preventing the scale components from adhering to the surface of the equipment such as heat exchangers. Is done.

In a system in which the cooling water is not descaled at all, the calcium hardness of the cooling water is about 120 mg CaCO ₃ / L, so that the calcium hardness of the circulating cooling water should not exceed 100 mg CaCO ₃ / L. It is desirable to operate the electrolyzer 2. The amount of scale deposition in the main electrolysis apparatus 2 can be controlled by the current value of the DC power supply.

  If the operation of the main electrolysis apparatus 2 is continued, scales adhere to the surfaces of the cathodes 5a and 5b in the main electrolysis apparatus 2. Therefore, when the energization resistance between the electrodes becomes a predetermined value or more regularly, the main electrolysis The apparatus 2 is acid cleaned.

  In order to perform this acid cleaning, the valve 6a is opened, the valve 7 is closed, the three-way valve 8 is connected to the pipes 1b and 9, water is passed through the sub-electrolyzer 11, and a voltage is applied between the anode 14 and the cathode 15. To do. Thereby, acidic water is generated in the anode chamber 12. This acidic water is introduced into the main electrolysis device 2 through the pipe 17 and dissolves the scale component that has adhered. The acid cleaning waste liquid is discharged through the blow pipe 6.

  Alkaline water generated in the cathode chamber 13 of the sub-electrolysis device 11 is discharged from the discharge line 18. It is desirable to mix and neutralize the alkaline water from the discharge line 18 and the acidic waste water from the blow pipe 6.

  After completion of the acid cleaning, cooling water is circulated through the main electrolysis device 2 as necessary to perform rinsing.

  Then, it returns to steady operation.

  In this embodiment, after a predetermined amount of scale is attached to the porous electrodes constituting the cathodes 5a and 5b of the main electrolysis device 2, the electrolytic acid water is supplied from the acid generation sub-electrolysis device 11 to the main acid device. It is supplied to the electrolyzer 2 and the scale is acid washed and discharged. By providing this acid-generating sub-electrolysis device 11, there is no need to purchase acid cleaning chemicals or dangerous carry-in work, and it is possible to reduce chemical costs and safety. Furthermore, by using a porous electrode having a high porosity, the adhesion area of the scale is increased and the contact efficiency between the electrolytic acid water and the scale is improved, so that the cleaning time is shortened. In addition, by performing acid cleaning with electrolytic acid water, polarity conversion is not required, and electrode deterioration can be greatly suppressed.

  The main electrolyzer 2 can be incorporated in any position of the cooling water circulation line (line 54 in FIG. 2). Further, as shown in FIG. 2, the water in the water storage tank 51 of the cooling tower 50 may be installed so as to be introduced into the main electrolysis apparatus 2 through the pump 52 and the pipe 1 for processing. In FIG. 2, reference numeral 53 denotes a double-pipe heat exchanger, 54 denotes a circulation line, and 55 denotes a circulation pump.

  The material of the porous body electrode constituting the cathodes 5a and 5b of the main electrolysis device 2 is preferably an electrode that is conductive and insoluble in acid, and is a metal composite such as vitreous carbon, insoluble metal, metal oxide, and SUS. Is preferred. The porosity of the porous body electrode is preferably in the range of 30 to 97%, more preferably 80 to 97%.

  As the electrode material of the other electrodes 4, 12, 13 of the electrolysis apparatuses 2, 11, a material that does not elute by electrolysis is used, and in particular, a titanium electrode or a platinum plating electrode coated with platinum or iridium is suitable. .

[Example 1]
1 was installed in the open circulation cooling water line shown in FIG. This circulating water line is an open system circulating cooling water line of 300 refrigeration tons with 5 times concentration of Atsugi City water. Although makeup water calcium hardness of 5-fold concentrated stoichiometric calcium hardness from 40mgCaCO ₃ / L becomes 200mgCaCO ₃ / L, in the main electrolysis system 2, calcium carbonate scale deposition rate of the cooling water circulating solution is 20gCaCO ₃ / ^m ₃ / hr When the electrolysis conditions were set as described above, the calcium hardness in the circulating cooling water solution was stable at around 100 mg CaCO ₃ / L, and scale adhesion to the heat exchanger during open inspection was not observed.

[Comparative Example 1]
As a comparative example, the cooling water system was operated with the pump 52 stopped in FIG. As a result, the calcium hardness of the circulating cooling water stabilized at _{120mgCaCO 3 / L, 80mgCaCO 3 /} L min had precipitated to the heat exchanger and cooling tower.

In addition, when the scale deposition rate to the heat exchanger in Example 1 and Comparative Example 1 was measured, the amount of calcium carbonate scale (mg) adhered to 1 cm ² per month was as follows.
Example 1 1-2 (mg / cm < ² > / month)
Comparative Example 1 50 (mg / cm ² / month)

  As is clear from the above examples and comparative examples, according to the present invention, metal ion scale components such as calcium and magnesium ions dissolved during the treatment are removed to a saturation concentration or less to prevent scale deposition in the cooling water system. can do.

It is a systematic diagram of the cooling water treatment apparatus concerning an embodiment. It is a systematic diagram of the cooling water circulation system incorporating the cooling water treatment apparatus of FIG.

Explanation of symbols

2 Main electrolyzer (electrolyzer for reducing scale formation tendency)
4 Anode 5a, 5b Cathode 11 Sub-electrolyzer (electrolyzer for generating acid water for acid cleaning)
12 Anode chamber 13 Cathode chamber

Claims (4)

In a cooling water treatment apparatus comprising an electrolytic device for reducing scale generation tendency in which makeup water or circulating water in a circulating cooling water system is passed between an anode and a cathode,
A cooling water treatment apparatus, wherein the cathode is made of a porous material.   The cooling water treatment apparatus according to claim 1, wherein the porosity of the porous body is 30 to 97%.   3. The cooling water treatment apparatus according to claim 1, further comprising an acid generating electrolyzer that generates an acid for acid cleaning the electrolyzer.   The method for operating the cooling water treatment apparatus according to claim 3, wherein the scale generation tendency reducing operation step and the acid generated by the acid generation electrolyzer are supplied to the scale generation tendency reducing electrolyzer to perform acid cleaning. A method for operating a cooling water treatment apparatus, wherein the cleaning process is alternately performed.

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