Hydrophilic coating agent and hydrophilic coating method

Abstract

To provide a hydrophilizing coating agent and a hydrophilizing coating method capable of forming a spray dry film containing a silica nanoparticle having a hydrophilic surface over a wide area of a heat transfer pipe even if a heat transfer pipe is left to be attached, thereby becoming hard to be contaminated by foreign matters such as dust.SOLUTION: A hydrophilizing coating agent that forms a hydrophilic coating film on a surface of a plurality of heat transfer pipes constituting an air-cooling steam condenser, includes water, a silica nanoparticle that exists in a state dispersed in water, and a surface active agent, where the content of the surface active agent is in a range of more than 0.10 pts.mass and less than 2.50 pts.mass to 100 pts.mass of water, and the hydrophilic coating film is a spray dry film of the hydrophilizing coating agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrophilic coating agent and a hydrophilic coating method, and more particularly to a hydrophilic coating agent and a hydrophilic coating method for forming a hydrophilic coating film on the surfaces of a plurality of heat transfer tubes that constitute an air-cooled condenser or the like. [Background technology]

[0002] The cooling medium for the condensers in steam turbine plants is mainly seawater, fresh water, cooling tower water, etc., but air-cooled condensers are used in areas with scarce cooling water resources.Air-cooled condensers do not cause an increase in the water temperature of rivers or oceans, and environmental assessments to evaluate the impact on ecosystems are relatively easy.As a result, they have the advantage of being able to complete the process from new power plant design to power generation operation in a short period of time, and are often adopted regardless of the amount of cooling water resources.

[0003] However, air-cooled condensers generally have a dense structure in which heat transfer tubes are arranged in multiple layers and fins are formed on each of the heat transfer tubes. If foreign matter such as dust from the surrounding environment adheres to these tubes, the heat exchange efficiency of the air-cooled condenser may decrease, causing problems in the operation of the steam turbine plant.

[0004] Patent Document 1 describes an air-cooled condenser that includes a steam manifold to which exhaust steam from a steam turbine is supplied, a plurality of heat transfer tubes that branch off from the steam manifold and distribute and condense the exhaust steam, a condensate pipe that collects the plurality of heat transfer tubes and supplies condensed water to a boiler, a blower mechanism that forcibly supplies cooling air to the heat transfer tubes, and a water supply device that supplies water to the outer surfaces of the heat transfer tubes, and in which a ceramic coating is formed on the outer surfaces of the heat transfer tubes.The air-cooled condenser described in Patent Document 1 claims that dust adhesion can be reduced by forming a ceramic layer made of silicon oxide or the like and having a hydrophilic surface on the outer surfaces of the heat transfer tubes in particular.

[0005] On the other hand, as a coating agent for forming a ceramic layer made of silicon oxide and having a hydrophilic surface on the surface of a substrate, for example, Patent Document 2 describes a coating composition containing 0.5 to 99 wt% water, 0.1 to 20 wt% silica nanoparticles having an average particle size of 40 nm or less, 0 to 20 wt% silica nanoparticles having an average particle size of 50 nm or more, an acid having a pKa of <3.5 in an amount sufficient to lower the pH to less than 5, and 0 to 20 wt% tetraalkoxysilane, wherein the concentration of the silica nanoparticles is 0.1 to 20 wt%.

[0006] Furthermore, Patent Document 3 describes a water-based paint obtained by mixing alumina sol, water-soluble acrylic resin, polyethylene glycol, and fluororesin particles as a coating agent for forming a ceramic layer on the surface of aluminum by baking, and this water-based paint is applied to the outer surface of fin material or heat transfer tubes in a coating amount of 0.3 to 0.8 g / m 2 After coating in the range, the coating is heated and dried to obtain a highly hydrophilic, antifouling baked coating film, and then the coating is washed with water or hot water to form a highly hydrophilic, antifouling baked coating film. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-24411 [Patent Document 2] Patent No. 5587871 [Patent Document 3] Patent No. 6964489 Summary of the Invention [Problem to be solved by the invention]

[0008] However, Patent Document 1 does not describe a means for forming a ceramic layer on the outer surface of the heat transfer tube, so it was necessary to form the ceramic layer using a known coating agent, such as that described in Patent Document 3.

[0009] In this regard, silica-based coating agents generally take the form of a dispersion liquid in which nanosilica particles are dispersed in water, but heat transfer tubes are usually made of aluminum-based materials, and their outer surfaces have a dense fin structure with numerous aluminum fins formed on them.The surfaces of untreated aluminum fins in particular have poor hydrophilicity, so even if a coating agent whose main component is water is applied to the outer surface of a heat transfer tube, the water is repelled by surface tension and does not spread evenly, making it impossible to form a ceramic coating film with good adhesion, resulting in the problem of areas on the outer surface of the heat transfer tube where the coating film is not formed.

[0010] Furthermore, the coating agent in Patent Document 2 is not a coating agent for heat transfer tubes made of aluminum-based materials, but is a coating agent for non-metallic substrates such as PET and ceramic tiles, and the surface properties of the substrates are different from those of heat transfer tubes. Therefore, it was unclear whether an appropriate coating film could be formed even if the coating agent was applied to heat transfer tubes made of aluminum-based materials with a natural oxide film.

[0011] In particular, the multiple heat transfer tubes that make up an air-cooled condenser have a dense fin structure on the outer surface of each heat transfer tube, with numerous aluminum fins densely arranged at intervals of several millimeters, making it difficult to distribute the coating agent throughout the narrow gaps between the aluminum fins.

[0012] Furthermore, when the heat transfer tubes constituting the air-cooled condenser are arranged in multiple stages in the left-right and front-rear directions to improve heat exchange efficiency, the air-cooled condenser has a structure in which multiple heat transfer tubes are stacked on top of each other and a heat transfer tube arrangement structure with depth in the rear stage direction, which poses a problem that it becomes even more difficult to spread the coating agent over the outer surfaces of all of the heat transfer tubes.

[0013] Furthermore, when using a coating agent such as that described in Patent Document 3, the heat transfer tube to which the coating agent is applied must be baked at a high temperature to prevent the coating film from peeling off from the outer surface of the heat transfer tube. Also, a useful conventional means for preventing the coating film from peeling off from the outer surface of the heat transfer tube is to apply the coating agent after chemically treating the surface of the heat transfer tube with a silane coupling agent.

[0014] However, these methods have the problem that it is difficult to carry out baking treatment or chemical treatment on an existing air-cooled condenser without removing the heat transfer tubes.

[0015] The present invention has been made in view of the above-described circumstances, and aims to provide a hydrophilic coating agent and a hydrophilic coating method that can form a sprayed dry film containing silica nanoparticles with a hydrophilic surface over a wide area of ​​the outer surface of a heat transfer tube, even when the heat transfer tube is in a mounted state, thereby making it difficult for foreign matter such as dust to adhere to the surface. [Means for solving the problem]

[0016] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that by using a hydrophilic coating agent containing water, silica nanoparticles dispersed in the water, and a surfactant, and by adjusting the content of the surfactant to be more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water, it is possible to form a sprayed dry film containing silica nanoparticles with hydrophilic surfaces over a wide area of ​​the outer surface of a heat transfer tube while the heat transfer tube is still attached, and have completed the present invention. That is, the gist of the present invention is as follows.

[0017] (1) A hydrophilic coating agent that forms a hydrophilic coating film on the surfaces of a plurality of heat transfer tubes that constitute an air-cooled condenser, the hydrophilic coating agent containing water, silica nanoparticles dispersed in the water, and a surfactant, the content of the surfactant being in the range of more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water, and the hydrophilic coating film being a sprayed and dried film of the hydrophilic coating agent.

[0018] (2) A hydrophilic coating method for forming a hydrophilic coating film on the surfaces of a plurality of heat transfer tubes constituting an air-cooled condenser, the hydrophilic coating method comprising a spraying step of spraying the hydrophilic coating agent described in (1) above onto the outer surfaces of the heat transfer tubes.

[0019] (3) The hydrophilic coating method according to (2) above, wherein the heat transfer tubes have a heat transfer tube arrangement structure in which they are arranged in multiple stages in the left-right direction and the front-rear direction, the heat transfer tubes constituting the heat transfer tube arrangement structure have gaps separating them from each other, and the spraying step sprays the hydrophilic coating agent in chunks or rods toward the heat transfer tubes located in the frontmost stage constituting the heat transfer tube arrangement structure.

[0020] (4) The hydrophilic coating method according to (2) or (3) above, further comprising a drying step of drying the sprayed hydrophilic coating agent to form a hydrophilic coating film after the spraying step. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a hydrophilic coating agent and a hydrophilic coating method that can form a sprayed dry film containing silica nanoparticles with a hydrophilic surface over a wide area of ​​the outer surface of a heat transfer tube even when the heat transfer tube is still attached, thereby making it difficult for foreign matter such as dust to adhere to the surface. [Brief explanation of the drawings]

[0022] [Figure 1]FIG. 1 is a graph showing the mass of carbon powder remaining on the surface of a heat transfer tube when eight different coating agents, each with a surfactant content varying between 0.00 and 5.00 parts by mass per 100 parts by mass of water, were used to form coating films on the tube by dip coating, and the coating films were then dried. Carbon powder, a foreign object, was then placed on the coating films and shaken off. [Figure 2] FIG. 2 is a schematic perspective view showing an example of the main part of an air-cooled condenser to which the hydrophilic coating agent of the present invention is sprayed. [Figure 3] FIG. 3 shows an example of a heat transfer tube array composed of multiple heat transfer tubes, where FIG. 3(a) is a front view, FIG. 3(b) is a cross-sectional view taken along line II in FIG. 3(a), and FIG. 3(c) is a partially enlarged view showing a portion of a heat transfer tube that composes the heat transfer tube array. [Figure 4] FIG. 4 is a schematic diagram showing the positional relationship between the coating agent discharge port and the heat transfer tube when the hydrophilic coating agent is sprayed onto the heat transfer tube in Examples 5 to 12 of the present invention. [Figure 5] FIG. 5 is a graph showing the mass of carbon powder remaining on the surface of each heat transfer tube (heat transfer tubes 2A, 2B, and 2C from the side closest to the coating agent outlet) when the hydrophilic coating agent was sprayed onto the heat transfer tubes in rod-like and mist-like forms to form a hydrophilic coating film on a triple-ply heat transfer tube in Examples 11 and 12 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0024] <Hydrophilic coating agent> The hydrophilic coating agent according to the present invention forms a hydrophilic coating film on the surfaces of a plurality of heat transfer tubes constituting an air-cooled condenser. The hydrophilic coating agent contains water, silica nanoparticles dispersed in the water, and a surfactant, the surfactant content being in the range of more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water, and the hydrophilic coating film is a sprayed and dried film of the hydrophilic coating agent.

[0025] In the hydrophilic coating agent of the present invention, by setting the surfactant content in the range of more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water, water is less likely to be repelled by surface tension, even on materials that are prone to forming oxide films and have poor surface hydrophilicity, such as aluminum, which is commonly used for heat transfer tubes. This allows the hydrophilic coating agent to spread approximately uniformly over the surface of the heat transfer tube, thereby forming a hydrophilic coating film over a wide area of ​​the outer surface of the heat transfer tube, including the fins, even if the outer surface of the heat transfer tube is provided with fins. Furthermore, by setting the surfactant content in the range of more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water, even in a structure in which multiple heat transfer tubes are arranged in multiple stages in the left-right and front-back directions in an air-cooled condenser, for example, the coating agent can be spread over the entire outer surface of the heat transfer tubes in the latter stages, thereby forming a hydrophilic coating film on the outer surface of all heat transfer tubes. Furthermore, since the hydrophilic coating film is a sprayed and dried film of the hydrophilic coating agent, the hydrophilic coating film can be formed on the outer surface of the heat transfer tube simply by drying, without performing a baking process at high temperature or a chemical treatment using a silane coupling agent on the surface of the heat transfer tube, and therefore there is no need to remove the heat transfer tube from an air-cooled condenser, etc. Therefore, by using the hydrophilic coating agent of the present invention, it is possible to provide a hydrophilic coating agent and a hydrophilic coating method that can form a hydrophilic coating film over a wide area of ​​the outer surface of a heat transfer tube, even when the heat transfer tube is still attached to an air-cooled condenser, etc.

[0026] (Composition of hydrophilic coating agent) The hydrophilic coating agent of the present invention contains water, silica nanoparticles dispersed in water, and a surfactant, i.e., the hydrophilic coating agent of the present invention is an aqueous dispersion of silica nanoparticles.

[0027] The surfactant contained in the hydrophilic coating agent stably disperses silica nanoparticles in water and enhances the wettability between the heat transfer tube and the hydrophilic coating agent. By spraying the hydrophilic coating agent containing a surfactant, the surface tension of the hydrophilic coating agent droplets can be reduced when the hydrophilic coating agent is applied to the surface of the heat transfer tube or fin, allowing the hydrophilic coating agent to be spread evenly over a wide area on the outer surface of the heat transfer tube or the surface of the fin.

[0028] The type of surfactant is not particularly limited as long as it is water-soluble, and at least one of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants can be used. Among these, nonionic surfactants are preferred from the viewpoint of improving wettability to heat transfer tubes. Nonionic surfactants can be further classified into three types: ethylene oxide condensation type, polyhydric alcohol ester type, and polyhydric alcohol condensation type. Ethylene oxide condensation type nonionic surfactants are preferred from the viewpoint of ease of handling and enhanced wettability to heat transfer tubes. As the ethylene oxide condensation type nonionic surfactant, polyoxyethylene alkyl ethers are preferred, for example, because they can contribute to wettability to heat transfer tubes even with a small amount. The HLB value of the polyoxyethylene alkyl ether is preferably in the range of 8 to 15, as described below. Furthermore, branched polyoxyethylene alkyl ethers are preferred as the polyoxyethylene alkyl ether. In this case, the carbon atoms attached to the branched side are preferably linear, and the number of moles of the carbon atoms is more preferably in the range of 4 to 6.

[0029] The HLB value of the surfactant, such as polyoxyethylene alkyl ether, contained in the hydrophilic coating agent is preferably 8 or more, more preferably 10 or more, from the viewpoint of increasing the solubility of the surfactant in water and improving wettability to the heat transfer tube. On the other hand, the upper limit of the HLB value of the surfactant, such as polyoxyethylene alkyl ether, contained in the hydrophilic coating agent is preferably 15 or less, from the viewpoint of achieving both high wettability and solubility in water by suppressing a decrease in wettability to the heat transfer tube.

[0030] The surfactant content is in the range of more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water. In particular, by increasing the surfactant content to more than 0.10 parts by mass per 100 parts by mass of water, the surface tension of the hydrophilic coating agent applied to the surface of the heat transfer tube or fin is weakened, allowing droplets of the hydrophilic coating agent to spread over a wide area of ​​the surface of the heat transfer tube or fin, even if the surface of the heat transfer tube or fin is made of aluminum, which has poor hydrophilicity. Therefore, the surfactant content is preferably 0.25 parts by mass or more per 100 parts by mass of water. On the other hand, by increasing the surfactant content to less than 2.50 parts by mass per 100 parts by mass of water, the surfactant is less likely to remain in the sprayed and dried film of the hydrophilic coating agent, thereby increasing the wettability of the coating to foreign matter, thereby reducing the likelihood of foreign matter adhering to the coating. Furthermore, by setting the surfactant content to less than 2.50 parts by mass per 100 parts by mass of water, the COD components contained in the hydrophilic coating agent are reduced, thereby reducing the environmental impact caused by the excess chemical waste liquid that is generated when the hydrophilic coating agent is sprayed. Therefore, the surfactant content is preferably 1.50 parts by mass or less per 100 parts by mass of water.

[0031] Figure 1 shows a graph showing the mass of carbon powder remaining on the surface of a heat transfer tube when eight different coating agents, each with a surfactant content varying between 0.00 and 5.00 parts by mass per 100 parts by mass of water, were used to form coating films on aluminum heat transfer tubes by dip coating, and the coating films were then dried. A foreign substance, carbon powder (powdered activated carbon, manufactured by Kurita Water Industries Ltd., model number: Krykol WD-712, 90% particle size: 0.075 mm or less), was then placed on the coating film and the same vibration was applied to shake off the carbon powder.

[0032] Here, as shown in Figure 1, when a hydrophilic coating film is obtained by applying a hydrophilic coating agent containing more than 0.10 parts by mass of surfactant to 100 parts by mass of water and then drying it, even if carbon powder (a foreign substance) is placed on the surface, vibration can remove a large amount of the carbon powder, thereby reducing the amount of carbon powder remaining on the surface of the hydrophilic coating film. On the other hand, when a hydrophilic coating agent containing 0.10 parts by mass of surfactant to 100 parts by mass of water is used, a large amount of carbon powder remains on the surface even when the heat transfer tube with the carbon powder on its surface is vibrated. Similarly, when a hydrophilic coating agent containing 2.50 parts by mass of surfactant to 100 parts by mass of water is applied to a heat transfer tube, a large amount of carbon powder remains on the surface even when the heat transfer tube with the carbon powder on its surface is vibrated.

[0033] The silica nanoparticles contained in the hydrophilic coating agent are particles made of silica (SiO2) and are mainly composed of particles with a particle size of less than 1 μm. When the hydrophilic coating agent contains silica nanoparticles, a hydrophilic coating film made of silica can be formed on the outer surface of the heat transfer tube when the hydrophilic coating agent is sprayed and the silica nanoparticles are deposited on the outer surface of the heat transfer tube and dried.

[0034] Here, the particle size of the silica nanoparticles is not particularly limited. However, from the viewpoint of more stably dispersing the hydrophilic coating agent in water and reducing clogging of nozzles and other discharge parts when spraying the agent onto the surfaces of heat transfer tubes and fins, the average particle size can be set to, for example, 5 nm to 100 nm. In particular, by setting the average particle size of the silica nanoparticles to 5 nm or more, the availability of the silica nanoparticles can be increased. Furthermore, by setting the average particle size of the silica nanoparticles to 100 nm or less, clogging of nozzles and other discharge parts when spraying the agent onto the surfaces of heat transfer tubes and fins can be reduced. As the silica nanoparticles, one type of silica nanoparticle having an average particle size in the range of 5 nm to 100 nm can be used alone, or two or more types of silica nanoparticles having the same or different average particle sizes can be used in combination.

[0035] The content of silica nanoparticles in the hydrophilic coating agent can be set to, for example, a range of 0.1 to 10 parts by mass per 100 parts by mass of water, from the viewpoint of preventing aggregation of silica nanoparticles and clogging of the discharge section when spraying the hydrophilic coating agent, and from the viewpoint of facilitating the formation of a sprayed and dried film containing silica nanoparticles by spraying and drying an appropriate amount of the hydrophilic coating agent.

[0036] Examples of silica nanoparticles that can be used include the Snowtex series manufactured by Nissan Chemical Industries, Ltd., the Quartron PL series manufactured by Fuso Chemical Co., Ltd., the SI series manufactured by JGC Catalysts and Chemicals Co., Ltd., TCSOL800 manufactured by Tama Chemicals Co., Ltd., and the Adelite AT series manufactured by ADEKA Corporation, all of which have a particle size in the range of 5 nm to 100 nm.

[0037] Silica nanoparticles may be contained in the hydrophilic coating agent in the form of colloidal silica.Here, the colloidal silica may be a water-dispersed silica sol such as a Na ion-stabilized type, an acid sol, an ammonium ion-stabilized type, a surface alumina-coated type, or lithium silicate, or an organosilica sol dispersed in a hydrophilic solvent, or a silica-containing sol in which silica nanoparticles and other particles such as alumina particles are dispersed.One of these may be used alone, or two or more of these may be used in combination.

[0038] The hydrophilic coating agent of the present invention may contain any conventionally known compound as an additional component other than those mentioned above.

[0039] More specifically, the hydrophilic coating agent of the present invention can contain, as other components, sols such as alumina sol (such as the AS series manufactured by Nissan Chemical Industries, Ltd.) or zirconia sol (such as the ZR series or OZ series manufactured by Nissan Chemical Industries, Ltd.) dispersed in a hydrophilic solvent. The hydrophilic coating agent of the present invention can also contain emulsions such as acrylic emulsions, urethane emulsions, and modified epoxy emulsions. One of these may be used alone, or two or more of these may be used in combination.

[0040] The hydrophilic coating agent of the present invention may also contain a thickener as another component. Examples of thickeners include cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; ammonium salts or alkali metal salts of the above cellulose compounds; polycarboxylic acids such as poly(meth)acrylic acid and modified poly(meth)acrylic acid; alkali metal salts of the above polycarboxylic acids; polyvinyl alcohol (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; and water-soluble polymers such as saponified copolymers of vinyl esters with unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid. Among these, alkali metal salts of carboxymethyl cellulose and alkali metal salts of poly(meth)acrylic acid are particularly preferred as thickeners.

[0041] The pH (hydrogen ion concentration) of the hydrophilic coating agent is not particularly limited, but can be, for example, in the range of 10.0 or less to obtain a stable aqueous dispersion. When spraying the hydrophilic coating agent on an aluminum heat transfer tube, the pH of the hydrophilic coating agent may be 9.0 or less to prevent corrosion of the aluminum. When spraying the hydrophilic coating agent on a heat transfer tube, the pH is preferably in the near-neutral range of 7.0 to 8.5 to prevent the hydrophilic coating agent from scattering around the heat transfer tube and affecting surrounding equipment, thereby ensuring worker safety. The lower limit of the pH of the hydrophilic coating agent is not particularly limited, but can be, for example, 5.0 or more to obtain a stable aqueous dispersion. The pH of the hydrophilic coating agent can be adjusted, for example, by adjusting the blend of acidic colloidal silica and basic colloidal silica, or by bubbling an acidic gas such as carbon dioxide through basic colloidal silica.

[0042] (Configuration of air-cooled condenser to which hydrophilic coating agent is applied) The hydrophilic coating agent is sprayed onto the surfaces of the heat transfer tubes constituting the air-cooled condenser, thereby forming a hydrophilic coating film, which is a sprayed and dried film of the hydrophilic coating agent, while the heat transfer tubes remain attached to the air-cooled condenser.

[0043] Fig. 2 is a diagram showing an example of an air-cooled condenser to which a hydrophilic coating agent is applied. Fig. 3 is a diagram showing an example of a heat transfer tube array composed of a plurality of heat transfer tubes, where Fig. 3(a) is a front view, Fig. 3(b) is a cross-sectional view taken along line II in Fig. 3(a), and Fig. 3(c) is a partially enlarged view showing a portion of a heat transfer tube constituting the heat transfer tube array.

[0044] Here, the air-cooled condenser 1 to which the hydrophilic coating agent is applied condenses exhaust steam, such as water vapor, supplied from the outside into a liquid such as water. Although the air-cooled condenser 1 is often installed outdoors, its structure means that the entire air-cooled condenser 1 is rarely washed away by rainwater, making it difficult to remove dirt adhering to the surface of the heat transfer tubes by simply applying a conventional hydrophilic coating. However, spraying the above-mentioned hydrophilic coating agent on the surface of the heat transfer tubes of the air-cooled condenser 1 provides an antistatic effect to the surface of the heat transfer tubes of the air-cooled condenser 1, thereby reducing the adhesion of dirt to the surface of the heat transfer tubes.

[0045] As shown in FIG. 2 , an example of an air-cooled condenser 1 includes a steam manifold 3 to which exhaust steam is supplied, a plurality of heat transfer tubes 2 that branch from the steam manifold 3 and distribute the exhaust steam to condense it into a liquid, and a condenser tube 4 that collects the heat transfer tubes 2 and supplies the condensed liquid to the outside. The air-cooled condenser 1 may further include a blower mechanism 6 having a fan 5. The air-cooled condenser 1 may also include a mechanism (not shown) that supplies cooling water to the plurality of heat transfer tubes 2. In this air-cooled condenser 1, exhaust steam supplied from the outside is sent to the steam manifold 3, where it branches off and is distributed to the plurality of heat transfer tubes 2. In the plurality of heat transfer tubes 2, the exhaust steam condenses as it loses heat to the atmosphere outside the heat transfer tubes 2, and the condensed liquid is supplied to the outside through the condenser tube 4. In particular, when the air-cooled condenser 1 is equipped with a blower mechanism 6, the fan 5 of the blower mechanism 6 is configured to generate an airflow in the atmosphere outside the heat transfer tubes 2, and the airflow hits the multiple heat transfer tubes 2 to remove heat from the surfaces of the heat transfer tubes 2.

[0046] Here, the plurality of heat transfer tubes 2 may form a heat transfer tube array 20, as shown in Fig. 3(a), for example. The heat transfer tube array 20 preferably includes the plurality of heat transfer tubes 2, a steam branching section 21 that branches exhaust steam supplied from a steam manifold 3 and supplies the branched steam to the heat transfer tubes 2, and a liquid merging section 22 that merges liquid condensed in the plurality of heat transfer tubes 2 and supplies the liquid to a condensate tube 4. The heat transfer tube array 20 may further include a frame 23 that holds each of the plurality of heat transfer tubes 2. These heat transfer tubes 2 are connected to the steam manifold 3 and the condensate tube 4, respectively, and are configured so that their outsides are in contact with the atmosphere and the exhaust steam condenses inside to become a liquid.

[0047] The heat transfer tubes 2 in the air-cooled condenser 1 are preferably spaced apart from one another. This allows the hydrophilic coating agent, when sprayed from one side, to flow around to the other side of the heat transfer tubes 2, thereby forming a hydrophilic coating film over a wider area of ​​the heat transfer tubes 2. In particular, in the air-cooled condenser 1, the heat transfer tubes 2 are sometimes provided in the gaps between them to allow the passage of airflow generated by a blower mechanism 6 such as a fan 5. Therefore, the hydrophilic coating agent of the present invention can form a hydrophilic coating film over a wider area of ​​the heat transfer tubes 2 without removing the heat transfer tubes 2, while the heat transfer tubes 2 remain in the air-cooled condenser 1.

[0048] 3(b), the air-cooled condenser 1 preferably has a heat transfer tube arrangement structure in which a plurality of heat transfer tubes 2 are arranged in multiple stages in the left-right direction and the front-rear direction. The hydrophilic coating agent of the present invention spreads over a wider area of ​​the heat transfer tubes 2 with a smaller amount, so that even when the heat transfer tubes 2 are arranged in multiple stages in the left-right direction and the front-rear direction of the air-cooled condenser 1, it is possible to form a hydrophilic coating film over a wider area of ​​the heat transfer tubes 2.

[0049] 3(b) and 3(c), the heat transfer tube 2 preferably includes a tube section 2a through which exhaust steam and its condensed liquid flow, and fins 2b provided on the outer surface of the tube section 2a. In particular, providing the heat transfer tube 2 with fins 2b can promote heat transfer from the exhaust steam to the outside of the heat transfer tube 2. When the heat transfer tube 2 includes fins 2b, the fins 2b often form irregularities on the surface of the heat transfer tube 2. However, by using the hydrophilic coating agent of the present invention, the surface tension of the hydrophilic coating agent can be reduced on the surfaces of both the tube section 2a and the fins 2b. This allows the hydrophilic coating film to be formed over a wider area of ​​the outer surface of the tube section 2a inside the irregularities, without leaving any surfactant in the resulting hydrophilic coating film.

[0050] The material for the heat transfer tubes 2 and fins 2b is generally aluminum from the viewpoint of corrosion resistance and heat transfer characteristics, and its surface has poor wettability with water. However, by forming a hydrophilic coating film using the hydrophilic coating agent of the present invention, the wettability can be improved.

[0051] <Hydrophilic coating method> The hydrophilic coating method according to the present invention is a method for forming a hydrophilic coating film on the surfaces of multiple heat transfer tubes 2 constituting an air-cooled condenser, and includes a spraying step of spraying the above-described hydrophilic coating agent onto the outer surfaces of the heat transfer tubes 2. As a result, the hydrophilic coating agent spreads substantially uniformly over the surfaces of the heat transfer tubes 2 through the spraying step. Therefore, even if fins are provided on the outer surfaces of the heat transfer tubes 2, a sprayed dry film containing hydrophilic silica nanoparticles can be formed over a wide area of ​​the outer surfaces of the heat transfer tubes 2, including the fins. Furthermore, the increased adhesion between the hydrophilic coating agent and the outer surfaces of the heat transfer tubes 2 eliminates the need for high-temperature baking or chemical treatment of the heat transfer tube surfaces using a silane coupling agent or the like, eliminating the need to remove the heat transfer tubes from the air-cooled condenser or the like.

[0052] In the spraying step, the hydrophilic coating agent is sprayed onto the outer surfaces of the heat transfer tubes 2. Here, a spraying method is preferably used as the method for spraying the hydrophilic coating agent, from the viewpoint of being able to simultaneously apply the agent to a wide area. The spraying condition is preferably such that the hydrophilic coating agent is sprayed in chunks or rods rather than in a mist. Even in a heat transfer tube array structure in which a plurality of heat transfer tubes 2 are arranged in multiple stages in the left-right and front-rear directions, if the plurality of heat transfer tubes 2 constituting the heat transfer tube array structure have gaps separating them, spraying the hydrophilic coating agent in chunks or rods toward the plurality of heat transfer tubes located in the forefront stage of the heat transfer tube array structure allows the hydrophilic coating agent to pass through the gaps between the plurality of heat transfer tubes 2 and spread to the second and subsequent stages of the heat transfer tubes. Furthermore, the action of the hydrophilic coating agent allows a hydrophilic coating film to be formed over a wider area on the second and subsequent stages of the heat transfer tubes. Furthermore, even when the heat transfer tube 2 has fins 2b, the hydrophilic coating agent can be spread over the surface of the tube portion 2a behind the fins 2b of the heat transfer tube 2. In this specification, spraying the hydrophilic coating agent in a "lump or rod-like" manner means spraying droplets while suppressing the spreading of the liquid. Intermittent spraying is referred to as "lump" spraying, and continuous spraying is referred to as "rod-like" spraying. Spraying droplets of the hydrophilic coating agent in a lump or rod-like manner allows the droplets to be sprayed onto the heat transfer tube 2 at a high density without dispersing. The spray rate (discharge rate) of the hydrophilic coating agent onto the outer surface of the heat transfer tube 2 is not particularly limited, but is preferably in the range of 25 g / sec to 400 g / sec, more preferably 50 g / sec to 300 g / sec, and even more preferably 100 g / sec to 200 g / sec. In addition, when the heat transfer tube is small, the amount of the hydrophilic coating agent sprayed (discharged) onto the outer surface of the heat transfer tube may be less than 25 g / sec, and the lower limit may be, for example, 3.0 g / sec. Furthermore, it is preferable that the hydrophilic coating agent is sprayed onto the same location on the outer surface of the heat transfer tube 2 continuously for 10 seconds or more.

[0053] When spraying the hydrophilic coating agent using a spray method, the angle at which the hydrophilic coating agent spreads from a nozzle or other outlet is preferably between 0° and 5°, in order to spray droplets onto the heat transfer tube 2 at a high density without dispersing them. When spraying the hydrophilic coating agent using a spray method, the flow rate of the hydrophilic coating agent flowing through the nozzle or other outlet is preferably a rate that does not deform or damage the fins or outlet on the surface of the heat transfer tube 2, and more specifically, a flow rate of 1.20 m / s or less. When spraying the hydrophilic coating agent, the lower limit of the flow rate of the hydrophilic coating agent flowing through the outlet is preferably 0.45 m / s or more, in order to more reliably spread the hydrophilic coating agent over the surface of the tube portion 2a located behind the fins 2b of the heat transfer tube 2.

[0054] The hydrophilic coating agent may be sprayed in the spraying step using a general paint sprayer, but it is preferable to use equipment that exerts a stronger pressure to push out the hydrophilic coating agent, such as a high-pressure washer. This allows the hydrophilic coating agent to be spread over a wider area of ​​the surface of the heat transfer tubes 2, even if the heat transfer tubes 2 have a heat transfer tube arrangement structure in which multiple rows are arranged in the left-right and front-rear directions, or even if the heat transfer tubes 2 have fins 2b.

[0055] In the spraying process, excess chemical waste liquid may be generated when the hydrophilic coating agent is sprayed, and this chemical waste liquid may be collected and reused. Furthermore, as described above, by limiting the surfactant content to less than 2.50 parts by mass per 100 parts by mass of water, the environmental load can be reduced even when the chemical waste liquid is treated.

[0056] After the spraying step, a drying step is preferably performed in which the hydrophilic coating agent sprayed onto the heat transfer tube 2 is dried to form a hydrophilic coating film. The hydrophilic coating agent sprayed onto the heat transfer tube 2 in the spraying step can form a dried sprayed film containing hydrophilic silica nanoparticles on the outer surface of the heat transfer tube simply by drying, without the need for baking at high temperature or chemical treatment of the surface of the heat transfer tube with a silane coupling agent or the like.

[0057] Here, the drying conditions in the drying step are not particularly limited, and drying by air drying at room temperature may be used. Therefore, in the hydrophilic coating method of the present invention, the steps from forming the hydrophilic coating agent to drying can be carried out while the heat transfer tube is still attached to an air-cooled condenser or the like. [Example]

[0058] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0059] [Invention Examples 1 to 4, Comparative Examples 1 to 4] The heat transfer tube used was made of aluminum and had a diameter of 8.5 mm. The tubes were equipped with multiple tube sections 2a arranged in parallel at 25 mm intervals along the width direction, and multiple 0.1 mm-thick fins 2b attached to the outer surfaces of the multiple tube sections 2a at 1.2 mm intervals p along the extension direction X of the tube sections 2a to connect the multiple tube sections 2a. This heat transfer tube was cut out from a tube used in a residential air conditioner outdoor unit, and measured 120 mm in length along the extension direction X of the tube sections 2a and 120 mm in width. After cleaning and degreasing, the initial mass was measured using an electronic balance (Mettler-Toledo, model ME5002T / 00).

[0060] On the other hand, the hydrophilic coating agent was prepared by mixing 100 parts by mass of water with the surfactant polyoxyethylene isodecyl ether (HLB value: 12.5) in the amount shown in Table 1, and dispersing silica nanoparticles with an average particle size of 5 nm and silica nanoparticles with an average particle size of 15 nm in a mass ratio of 1:0.152, with the total amount shown in Table 1. The pH (hydrogen ion concentration) of this hydrophilic coating agent was adjusted to be in the range of 7.0 to 8.5.

[0061] Next, for Invention Examples 1 to 4 and Comparative Examples 1 to 3, the heat transfer tubes after measuring the initial mass were immersed in the hydrophilic coating agent and pulled up from the hydrophilic coating agent at a speed of 50 mm / s by dip coating, and then the coating film was formed on each heat transfer tube, and the coating film was air-dried at room temperature (air temperature 25°C) to form a coating film.Comparative Example 4 is an example of a blank heat transfer tube after measuring the initial mass, on which no coating film was formed.

[0062] Ten grams of carbon powder (powdered activated carbon, manufactured by Kurita Water Industries Ltd., model number: Krikol WD-712, 90% particle size: 0.075 mm or less) was placed on the surface of the heat transfer tube with the coating film formed and spread evenly with a spatula. The tube was then placed in the vibration section of a Powder Tester PT-E (manufactured by Hosokawa Micron Corporation) with the surface of the heat transfer tube with the carbon powder spread evenly facing up and the opening of the tube facing forward. The test tube was then vibrated at a frequency of 50 Hz and an intensity of 3 on the rheostat for 15 seconds to remove the carbon powder. The test tube was then turned over so that the opening on the front side of the test tube was facing upward, and vibrations at a frequency of 50 Hz and an intensity of 3 on the rheostat for 15 seconds were applied to further remove the carbon powder. The mass of the heat transfer tube after the carbon powder had been brushed off was measured using the electronic balance described above, and the amount of carbon powder adhered [g] was calculated by subtracting the initial mass from the measured mass. The results are shown in Table 1, and a graph showing the mass of carbon powder remaining on the surface of the heat transfer tubes in these invention examples and comparative examples is shown in Figure 1.

[0063] [Table 1]

[0064] As a result, in the hydrophilic coating films obtained in Examples 1 to 4 of the present invention, the mass of carbon powder remaining on the surface of the heat transfer tube was 0.10 g or less, and foreign matter was unlikely to adhere to the surface. On the other hand, in the hydrophilic coating films obtained in Comparative Examples 1 to 5, the mass of carbon powder remaining on the surface of the heat transfer tube exceeded 0.10 g, and foreign matter was likely to adhere to the surface.

[0065] [Examples 5 to 10] As shown in Fig. 4, three heat transfer tubes were used, each made of aluminum and having a diameter of 8.5 mm, each equipped with a plurality of tube sections 2a arranged in parallel at intervals of 25 mm along the width direction, and a plurality of fins 2b each having a thickness of 0.1 mm and provided on the outer surfaces of the plurality of tube sections 2a at intervals of 1.2 mm along the extension direction X of the tube sections 2a so as to connect the plurality of tube sections 2a, and these were designated as heat transfer tubes 2A, 2B, and 2C in order of proximity to the coating agent discharge port 7. The heat transfer tubes 2A, 2B, and 2C had a length of 120 mm along the extension direction X of the tube sections 2a, and a width of 120 mm. These heat transfer tubes 2A-2C were cut from tubes used in residential air conditioner outdoor units. The outer surface of each tube section 2a has a dense fin structure with numerous fins 2b arranged at a closer spacing p than the heat transfer tubes constituting an air-cooled condenser. Therefore, it is more difficult to spread a coating agent than with the heat transfer tubes constituting an air-cooled condenser. After cleaning and degreasing, these heat transfer tubes 2A-2C were arranged. For Examples 5 and 8, only the heat transfer tube 2A of the heat transfer tubes 2A, 2B, and 2C shown in FIG. 4 was placed, bundled with cable ties, and clamped to a stand. For Examples 6 and 9, only the heat transfer tubes 2A and 2B of the heat transfer tubes 2A, 2B, and 2C shown in FIG. 4 were placed so that the tube sections 2a were alternately arranged in the width direction. The tubes were bundled with cable ties and clamped to a stand. In Examples 7 and 10, the heat transfer tubes 2A and 2C in the odd-numbered rows (the first and third rows) and the heat transfer tube 2B in the even-numbered row (the second row) were bundled together with cable ties and clamped to the stand, with the tube sections 2a arranged alternately in the width direction, as shown in Fig. 4. The distance between the coating agent outlet 7 and the heat transfer tube 2A was 20 mm.

[0066] On the other hand, the hydrophilic coating agent was prepared by mixing 0.25 parts by weight of a surfactant, polyoxyethylene isodecyl ether (HLB value: 12.5), with 100 parts by weight of water, and dispersing 0.92 parts by weight of silica nanoparticles with an average particle size of 5 nm and 0.92 parts by weight of silica nanoparticles with an average particle size of 15 nm in a mass ratio of 1:0.152. The pH (hydrogen ion concentration) of this hydrophilic coating agent was adjusted to be in the range of 7.0 to 8.5.

[0067] As shown in Fig. 4, this hydrophilic coating agent was sprayed from the coating agent outlet 7 from the heat transfer tube 2A side toward the heat transfer tubes 2B and 2C (from one side of the heat transfer tube 2A toward the other side in the case of Invention Examples 7 and 10) by spraying while the heat transfer tube 2 was still in place. Here, a handheld pesticide sprayer (manufactured by Koshin Corporation, model number: GT-2D) was used to spray the hydrophilic coating agent H. 110 g of the hydrophilic coating agent H was sprayed from a 1 mm diameter hole (discharge port) in the nozzle of the handheld pesticide sprayer at a spray rate of 240 g to 400 g per minute (4.0 g to 6.7 g per second) in the spray pattern shown in Table 2 so that the hydrophilic coating agent H spread at the angle shown in Table 2. At this time, the flow velocity of the hydrophilic coating agent H flowing through the hole (discharge port) was in the range of 0.509 m / s or more and 0.853 m / s or less. When a predetermined amount of the hydrophilic coating agent H was sprayed, the amount of the hydrophilic coating agent H that passed through all of the heat transfer tubes 2A to 2C was measured. This measurement was performed three times, and the average of the three measurements is shown in Table 2 as the measured value.

[0068] [Table 2]

[0069] As a result, in Examples 5, 6, and 7 of the present invention, in which the hydrophilic coating agent was sprayed in a rod-like form, the proportion of hydrophilic coating agent passing through the heat transfer tubes was higher than in Examples 8, 9, and 10 of the present invention, in which the hydrophilic coating agent was sprayed in a mist form on heat transfer tubes of the same configuration. In particular, in Examples 6 and 7 of the present invention, in which two or three heat transfer tubes were arranged and the hydrophilic coating agent was sprayed in a rod-like form, the hydrophilic coating agent was able to pass through both the two and three heat transfer tubes. On the other hand, in Example 9 of the present invention, in which two heat transfer tubes were arranged and the hydrophilic coating agent was sprayed in a mist form, the amount of hydrophilic coating agent passing through the two heat transfer tubes was less than in Example 6, in which the hydrophilic coating agent was sprayed in a rod-like form. Furthermore, in Example 10 of the present invention, in which three heat transfer tubes were arranged and the hydrophilic coating agent was sprayed in a mist form, the hydrophilic coating agent was unable to pass through the three heat transfer tubes. Therefore, it can be seen that spraying the hydrophilic coating agent in a rod shape allows more of the agent to be distributed to the heat transfer tubes in the second and subsequent stages. In addition, spraying the hydrophilic coating agent in a rod shape allows the hydrophilic coating agent to pass through the second and third stages of heat transfer tubes, and therefore allows the hydrophilic coating agent to be distributed to the third and fourth stages of heat transfer tubes as well.

[0070] [Examples 11 and 12] Three heat transfer tubes identical to those used in Examples 5 to 10 of the present invention were used, designated as heat transfer tubes 2A, 2B, and 2C in order of proximity to the coating agent outlet 7. After cleaning and degreasing, these heat transfer tubes 2A to 2C were measured for their initial mass using an electronic balance (Mettler-Toledo, Model ME5002T / 00). Next, as shown in Figure 4, the odd-numbered (first and third) heat transfer tubes 2A and 2C and the even-numbered (second) heat transfer tube 2B were alternately arranged in the width direction, and then bound together with cable ties and clamped to a stand. The distance between the coating agent outlet 7 and the heat transfer tube 2A was 20 mm.

[0071] On the other hand, the hydrophilic coating agent was prepared by mixing 0.25 parts by weight of a surfactant, polyoxyethylene isodecyl ether (HLB value: 12.5), with 100 parts by weight of water, and dispersing 0.92 parts by weight of silica nanoparticles with an average particle size of 5 nm and 0.92 parts by weight of silica nanoparticles with an average particle size of 15 nm in a mass ratio of 1:0.152. The pH (hydrogen ion concentration) of this hydrophilic coating agent was adjusted to be in the range of 7.0 to 8.5.

[0072] This hydrophilic coating agent was sprayed from the coating agent outlet 7 from the heat transfer tube 2A side toward the heat transfer tubes 2B and 2C while the heat transfer tube 2 was still in place, as shown by hydrophilic coating agent H in Figure 4. The same handheld pesticide sprayer as in Invention Examples 5 to 10 was used to spray hydrophilic coating agent H. 500 g of hydrophilic coating agent H was sprayed from a 1 mm diameter hole (outlet) in the nozzle of the handheld pesticide sprayer at a rate of 240 to 400 g per minute (4.0 to 6.7 g per second) in the spray pattern shown in Table 2, so that the hydrophilic coating agent H spread at the angle shown in Table 3. The flow velocity of the hydrophilic coating agent H flowing through the outlet was in the range of 0.509 m / s to 0.853 m / s. After spraying a predetermined amount of hydrophilic coating agent H, the heat transfer tubes 2A to 2C were air-dried at room temperature (air temperature 25°C) to form a hydrophilic coating film on the outer surfaces of the heat transfer tubes 2A to 2C.

[0073] The heat transfer tubes 2A-2C with the coating film formed were removed from the stand, the three stacked heat transfer tubes were untied, and the masses of each of the heat transfer tubes 2A-2C were measured using the electronic balance described above. The initial masses were then calculated from the measured masses. Ten grams of carbon powder (powdered activated carbon, manufactured by Kurita Water Industries Ltd., model number: Krikol WD-712, 90% particle size: 0.075 mm or less) was placed on the surface of each tube and spread evenly with a spatula. The tubes were then placed in the vibration section of a Powder Tester PT-E (manufactured by Hosokawa Micron Corporation) with the carbon powder-coated surface facing upward and the tube opening facing forward. Vibrations were applied at a frequency of 50 Hz and an intensity of 3 on the rheostat for 15 seconds to remove the carbon powder. The specimen was then turned over so that the opening at the front of the heat transfer tube was facing upward, and vibrations at 50 Hz and rheostat setting 3 were applied for 15 seconds to further remove the carbon powder. After the carbon powder was removed, the mass of each heat transfer tube 2A-2C was measured using the electronic balance described above, and the amount of carbon powder deposited on each tube (g) was calculated by subtracting the initial mass from the measured mass. The results are shown in Table 3, and Figure 5 shows a graph showing the mass of carbon powder remaining on the surfaces of each of the three stacked heat transfer tubes 2A-2C when the hydrophilic coating agent was applied in both rod and mist form to form a hydrophilic coating film on the tubes.

[0074] [Table 3]

[0075] As a result, in Inventive Example 11, in which the hydrophilic coating agent was sprayed in a rod-like form, the mass of carbon powder remaining on the second and third heat transfer tubes was reduced, and the mass of carbon powder remaining on the third heat transfer tube was particularly significantly reduced, compared to Inventive Example 12, in which the hydrophilic coating agent was sprayed in a mist-like form. This shows that spraying the hydrophilic coating agent in a rod-like form can reduce the amount of carbon powder remaining on the second and subsequent heat transfer tubes, especially the third heat transfer tube. [Explanation of symbols]

[0076] 1 Air-cooled condenser 2, 2A~2C heat transfer tubes 2a pipe section 2b fins 20 Heat transfer tube array 21 Steam branch 22 Liquid confluence section 23 frames 3 Steam manifold 4 Condenser pipe 5 Fans 6. Blower mechanism 7 Coating agent outlet H Hydrophilic coating agent r diameter of heat transfer tube d The size of the gap between adjacent heat transfer tubes p Fin spacing along the extension direction of the heat transfer tube t is the thickness of the fin along the diameter of the heat transfer tube X: Extension direction of heat transfer tube

Claims

1. A hydrophilic coating agent for forming a hydrophilic coating film on the surfaces of a plurality of heat transfer tubes constituting an air-cooled condenser, The hydrophilic coating agent is Water and silica nanoparticles present in a dispersed state in the water; a nonionic surfactant having an HLB value in the range of 10 to 15; Contains the content of the nonionic surfactant is in the range of more than 0.10 parts by mass and less than 2.50 parts by mass per 100 parts by mass of water, The hydrophilic coating film is a sprayed and dried film of the hydrophilic coating agent.

2. A hydrophilic coating method for forming a hydrophilic coating film on the surfaces of a plurality of heat transfer tubes constituting an air-cooled condenser, comprising: A hydrophilic coating method, comprising a spraying step of spraying the hydrophilic coating agent according to claim 1 onto the outer surface of the heat transfer tube.

3. The plurality of heat transfer tubes have a heat transfer tube arrangement structure in which they are arranged in multiple stages in the left-right direction and the front-rear direction, the plurality of heat transfer tubes constituting the heat transfer tube arrangement structure have gaps separating them from one another, 3. The hydrophilic coating method according to claim 2, wherein the spraying step sprays the hydrophilic coating agent in the form of lumps or rods toward a plurality of heat transfer tubes located at the frontmost stage of the heat transfer tube array structure.

4. 4. The hydrophilic coating method according to claim 2, further comprising a drying step, after the spraying step, of drying the sprayed hydrophilic coating agent to form a hydrophilic coating film.

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