JP5854632B2 - How to remove scale - Google Patents

Description

  The present invention relates to a method for removing scale adhered to a heat transfer surface of a heat exchanger in a water heater or the like.

  The hot water heater supplies hot water by applying heat from a heat source to water passing through the heat transfer tube of the heat exchanger or water around the heat transfer tube to raise the temperature. However, when the temperature of tap water or the like is increased, mineral components (for example, calcium and the like) in the water are concentrated under specific conditions and adhere as a scale to the surface of the heat transfer tube. The adhesion of the scale may reduce the heat exchange efficiency of the heat exchanger and may interfere with the water flow through the heat transfer tube.

  Various techniques have been proposed and put into practical use as a method for solving the problem of scale adhesion. For example, a method of dissolving and removing the attached scale by treating with a chemical (for example, see Patent Document 1), and a method of removing the attached scale by a physical method such as ultrasonic vibration (for example, see Patent Document 2). and so on. In addition, there is a method for reducing mineral components in water.

JP-A-6-154790 JP 2010-175160 A

However, the method using a drug often requires an acidic aqueous solution or a special chemical solution, and has a problem that it cannot be easily used in a general household. Moreover, the method using a physical method has a problem that it is difficult to reliably and sufficiently remove the scale attached to the heat transfer surface of the heat exchanger having a complicated structure. Further, the scale removal effect cannot be obtained reliably and sufficiently by other methods.
The present invention has been made to solve the above-described problems, and a scale removal method and a water heater that can easily and effectively remove the scale attached to the heat transfer surface of the heat exchanger. The purpose is to provide.

  As a result of diligent research to solve the above problems, the present inventors contacted the aqueous solution in which a specific water-soluble polymer is dissolved with the heat transfer surface of the heat exchanger and dried it, so that the water content of the aqueous solution was reduced. It has been found that the scale shrinkage caused by evaporation and the scale adhering to the heat transfer surface of the heat exchanger can be easily and effectively removed together with the water-soluble polymer film.

That is, the present invention is a method for removing scale adhered to the inner surface of a heat exchanger tube of a heat exchanger, wherein an aqueous solution in which two kinds of water-soluble polymers that are polyvinyl alcohol and polyvinyl pyrrolidone are dissolved is brought into contact with the inner surface. Forming the liquid film, and drying the liquid film to form the water-soluble polymer film on the inner surface, and the water-soluble polymer by volume contraction accompanying the drying of the liquid film. Removing the scale from the inner surface while taking the scale into the film, and injecting water into the heat transfer tube to dissolve the water-soluble polymer film, And removing the scale from the inner surface .

  ADVANTAGE OF THE INVENTION According to this invention, the scale removal method and water heater which can remove the scale adhering to the heat-transfer surface of a heat exchanger simply and effectively can be provided.

It is sectional drawing of the heat exchanger tube of the heat exchanger for demonstrating the removal method of the scale of Embodiment 1. FIG.

Embodiment 1 FIG.
The scale removal method of the present embodiment (hereinafter referred to as “scale removal method”) is intended for the scale attached to the heat transfer surface of the heat exchanger.
As used herein, “heat exchanger” means a device that efficiently transfers heat from a high temperature object to a low temperature object. The heat exchanger is not particularly limited as long as it is generally provided in a water heater, an air conditioner, a boiler, and the like. Moreover, in this specification, the "heat exchanger surface of a heat exchanger" means the surface of the heat transfer part (for example, heat exchanger tube etc.) which bears the heat exchange effect | action of a heat exchanger. The heat transfer surface of the heat exchanger is not particularly limited, and examples thereof include an inner surface or an outer surface of a heat transfer portion such as a tubular shape, a spherical shape, a cylindrical shape, and a box shape, and a surface of a flat heat transfer portion. .

  When the temperature of tap water is raised in a water heater, the concentration of mineral components (for example, calcium) in water gradually increases, and when the saturation point is exceeded, the mineral components are deposited on the heat transfer surface of the heat exchanger as a scale. . This scale adheres to the heat transfer surface of the heat exchanger in the form of fine crystals in the initial stage, but the scale gradually grows as time elapses and covers the entire heat transfer surface of the heat exchanger thickly. It becomes like this. The scale removal method of the present embodiment is not a scale attached so as to cover the entire heat transfer surface of the heat exchanger thickly, but an initial scale (that is, dot-like crystals on the heat transfer surface of the heat exchanger). Target).

The adhesion state of the scale on the heat transfer surface of the heat exchanger can be confirmed by visual observation, but can also be confirmed by various measurement methods. Examples of measurement methods include optical measurement methods such as reflectance and transmittance, electrical measurement methods such as electric resistance and electric field, and measurement methods such as heat capacity and thermal conductivity. Those skilled in the art can also predict the state of scale adhesion based on the amount and experience of mineral components in the water.
The scale removal method of the present embodiment can obtain a desired effect by being carried out at regular intervals, but by confirming or predicting the state of scale adhesion as described above, and carrying out at an appropriate timing. A desired effect can be obtained without waste.

Hereinafter, the scale removal method of the present embodiment will be described with reference to the drawings.
Fig.1 (a)-(d) is sectional drawing of the heat exchanger tube of a heat exchanger. In this figure, the inner surface of the heat transfer tube is assumed as the heat transfer surface, but it goes without saying that it can be applied to other portions (for example, the outer surface).
By using a device (for example, a water heater) provided with a heat exchanger, the scale 2 adheres to the heat transfer surface (inner surface in FIG. 1) of the heat transfer tube 1 of the heat exchanger <FIG. 1 (a)>. In the initial stage, the scale 2 is attached to the inner surface of the heat transfer tube 1 of the heat exchanger in the form of dots as fine crystals. If the scale 2 continues to adhere to the surface of the heat exchanger tube 1 of the heat exchanger, the scale 2 covers the entire inner surface of the heat exchanger tube 1 of the heat exchanger thickly, and it becomes difficult to remove the scale 2. Therefore, before the scale 2 covers the entire inner surface of the heat transfer tube 1 of the heat exchanger thickly, it is necessary to perform the scale removal method of the present embodiment.

  In order to remove the scale 2 in the form of fine crystals adhering to the inner surface of the heat transfer tube 1 of the heat exchanger, first, an aqueous solution in which a water-soluble polymer is dissolved is brought into contact with the inner surface of the heat transfer tube 1 < FIG. 1 (b)>. Thereby, the aqueous solution in which the water-soluble polymer is dissolved coats the inner surface of the heat transfer tube 1 of the heat exchanger and forms a liquid film 3 incorporating the scale 2.

  As the water-soluble polymer, at least one selected from polyvinyl alcohol and polyvinyl pyrrolidone is used. These substances are highly safe for the human body and do not corrode metals or the like, so there are few problems in use. In addition, since these substances are not insolubilized by the presence of calcium ions or the like unlike natural hydrophilic polymers, they are advantageous when washing and removing a water-soluble polymer film as described in detail below. is there. In particular, when polyvinyl alcohol and polyvinylpyrrolidone are used in combination, the water-soluble polymer film can be quickly removed by washing with water.

The polyvinyl alcohol preferably has a saponification degree of 90% or less from the viewpoint of solubility in water. If the saponification degree exceeds 90%, the solubility in water may not be sufficient.
The polyvinyl alcohol and polyvinyl pyrrolidone preferably have a degree of polymerization of 300 or more and 30,000 or less. If the degree of polymerization is less than 300, the strength of the water-soluble polymer film decreases, and as a result, the removal effect of scale 2 may not be sufficiently obtained. On the other hand, if the degree of polymerization exceeds 30,000, it may take too much time to remove the water-soluble polymer film with water.

  The concentration of the water-soluble polymer in the aqueous solution in which the water-soluble polymer is dissolved is not particularly limited, but is preferably 1.5% by mass to 30% by mass, more preferably 3% by mass to 20% by mass. . If the concentration of the water-soluble polymer is less than 1.5% by mass, the film of the water-soluble polymer may become thin, and the scale 2 removal effect may not be sufficiently obtained. On the other hand, when the concentration of the water-soluble polymer exceeds 30% by mass, the fluidity of the aqueous solution is lowered, and it may be difficult to bring the aqueous solution into contact with the surface of the heat transfer tube 1.

Known components such as chelating agents, pH adjusters, and surfactants can be blended in the aqueous solution as optional components.
The chelating agent has an effect of easily removing the scale 2 by ionizing and dissolving the metal constituting the scale 2. The chelating agent also provides an effect of suppressing insolubilization of the water-soluble polymer. The chelating agent is not particularly limited. For example, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), methylglycine diacetic acid (MGDA) , And derivatives and salts thereof. Moreover, even if it is not generally classified as a chelating agent, those that interact with the metal ion component, for example, carboxylic acids such as oxalic acid and polyacrylic acid, various amino acids and proteins, and the like can also be used. These can be used alone or in combination of two or more.
The concentration of the chelating agent in the aqueous solution in which the water-soluble polymer is dissolved is not particularly limited as long as it does not inhibit the effect of the present invention, but is generally 0.1% by mass or more and 5.0% by mass or less.

The pH adjuster has an effect of facilitating dissolution of the scale 2. The scale 2 has a pH condition that facilitates dissolution. For example, in the case of calcium carbonate as a main component, the solubility of the scale 2 is improved by lowering the pH. Although it does not specifically limit as a pH adjuster, For example, organic acids, such as an acetic acid, an oxalic acid, and a citric acid, are mentioned. These can be used alone or in combination of two or more.
The concentration of pH adjustment in the aqueous solution is not particularly limited as long as the effect of the present invention is not impaired, but is preferably 0.05% by mass or more and 2% by mass or less, more preferably 0.1% by mass or more and 1% by mass. It is as follows. In particular, the content of the pH adjuster in this aqueous solution is less than the content of the pH adjuster in the general scale remover, which suppresses problems such as cost, waste liquid treatment, and occurrence of corrosion on the heat transfer surface. Is possible. When the concentration of the pH adjuster is less than 0.05% by mass, the blending amount is too small, and the effect of adding the pH adjuster cannot be sufficiently obtained. On the other hand, when the concentration of the pH adjusting agent exceeds 2% by mass, problems such as corrosion may occur when a metal is used for the heat transfer surface.

  The surface and heat transfer surface of the scale 2 may be water repellent due to contamination or the like, and it may be effective to make the heat transfer surface water repellent in advance as described later. In order to bring the aqueous solution into sufficient contact with the water repellent surface, it is preferable to add a surfactant to the aqueous solution. Further, if the foaming property of the surfactant is utilized and the aqueous solution is bubbled and then brought into contact with the inner surface of the heat transfer tube 1, the amount of the aqueous solution used can be reduced.

The surfactant is not particularly limited as long as it is soluble in water at room temperature (25 ° C.). For example, nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants are used. An agent or the like can be used. Examples of nonionic surfactants include higher alcohols, alkylphenols, fatty acids, polyhydric alcohols, alkylamines, oils and fats, polyethylene glycol adducts such as polypropylene glycol, glycerol, pentaerythritol, sorbitol, sorbitan, sucrose, polyvalent Examples include alcohols and fatty acid esters of alkanolamine. Examples of anionic surfactants include carboxylates, sulfate esters, sulfonates, phosphate esters and the like. Examples of the cationic surfactant include amine salt type and quaternary ammonium salt type. Examples of amphoteric surfactants include amino acid types and betaine types. These can be used alone or in combination of two or more.
The concentration of the surfactant in the aqueous solution is not particularly limited as long as it does not inhibit the effects of the present invention, but is generally 0.05% by mass or more and 5.0% by mass or less.

A method for bringing the aqueous solution into contact with the inner surface of the heat transfer tube 1 is not particularly limited, but the aqueous solution may be injected into the heat transfer tube 1. In addition, when the heat transfer surface is the outer surface of the heat transfer tube 1 of the heat exchanger or the like, the aqueous solution may be applied by a known method such as spray coating or flow coating.
The degree of contact of the aqueous solution with the inner surface of the heat transfer tube 1 is not particularly limited as long as the aqueous solution can cover the inner surface of the heat transfer tube 1 and form the liquid film 3 incorporating the scale 2.

Next, the liquid film 3 formed on the inner surface of the heat transfer tube 1 is dried to form a water-soluble polymer film 4 having no fluidity (FIG. 1C). At this time, since the scale 2 is taken into the liquid film 3, the adhesiveness with the water-soluble polymer is high, and the scale 2 taken into the liquid film 3 due to volume contraction accompanying water evaporation of the aqueous solution. Also contraction force acts. As a result, the scale 2 is peeled off from the inner surface of the heat transfer tube 1 and removed. Along with the scale 2, the water-soluble polymer film 4 is also peeled off from the inner surface of the heat transfer tube 1.
The drying method of the liquid film 3 formed from the aqueous solution is not particularly limited, but if air is sent into the heat transfer tube 1 or the heating function of the heat exchanger is used to promote drying. Good.

  The film thickness of the water-soluble polymer film 4 formed by drying the liquid film 3 is preferably 1 μm or more, more preferably 5 μm or more. Here, the film thickness means the film thickness of the water-soluble polymer film 4 obtained by drying the liquid film 3 under an air current of about 60 ° C. When the film thickness of the water-soluble polymer film 4 is less than 1 μm, the contraction force acting on the scale 2 is reduced, and the scale 2 may not be sufficiently removed from the inner surface of the heat transfer tube 1.

Next, if necessary, the water-soluble polymer film 4 is brought into contact with water <FIG. 1 (d)>. Accordingly, the water-soluble polymer film 4 is dissolved in water, and the water-soluble polymer and the scale 2 are removed from the inner surface of the heat transfer tube 1 together with water.
A method for bringing the water-soluble polymer film 4 into contact with water is not particularly limited, but water may be injected into the heat transfer tube 1. When the heat transfer surface is the outer surface of the heat transfer tube 1 of the heat exchanger, water may be applied by a known method such as spray coating or flow coating.

  The scale removal method of the present embodiment performed as described above can remove the scale 2 together with the water-soluble polymer film 4 by volume contraction accompanying water evaporation of the aqueous solution containing the water-soluble polymer. The scale 2 attached to the heat transfer surface of the heat exchanger having a complicated structure that cannot be processed by the conventional physical scale removal method can be removed.

In the scale removal method of the present embodiment, it is preferable to form a water-repellent coating in advance on the heat transfer surface from the viewpoint of facilitating peeling of the scale 2 and the water-soluble polymer film 4.
The method for forming the water-repellent coating is not particularly limited. For example, hydrophobic treatment using a reactive agent such as a fluorine-based silane coupling agent, hydrophobic plating treatment such as nickel plating combined with PTFE, silicone, For example, painting with fluororesin. Among these, in consideration of water resistance and heat resistance of the heat exchanger, it is preferable to perform coating with a fluororesin. In particular, various fluororesin coating agents using a fluorine-based solvent as a solvent, for example, polytetrafluoroethylene (PTFE) paint, fluoroethylenepropylene (FEP) paint, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) paint It is preferable to carry out baking coating using a PTFE / PFA composite paint, other modified paints, and the like.

Next, an actual specific example in the case where the scale removal method of the present embodiment is applied to a water heater having a heat exchanger for heating water injected into the hot water tank will be described.
The heat exchanger provided in the hot water tank heats the water in the hot water tank by the heat exchanger, and is generally formed from a copper pipe, and the copper pipe is coiled or uneven on the conduit surface. Has been. Therefore, it is difficult to remove the scale 2 formed on the surface of the copper tube by a physical method or the like.
In the scale removal method of the present embodiment, first, the hot water tank is drained, and then an aqueous solution in which the water-soluble polymer is dissolved is introduced into the hot water tank and brought into contact with the surface of the copper pipe. Next, the liquid film 3 formed on the surface of the copper tube is dried.
When a hydrophobic coating is formed in advance on the surface of the copper tube, the water-soluble polymer film 4 incorporating the scale 2 is peeled off naturally from the surface of the copper tube. The peeled water-soluble polymer film 4 can be removed from the opening.
When a hydrophobic coating is not formed in advance on the surface of the copper tube, the water-soluble polymer film 4 incorporating the scale 2 is difficult to peel off from the surface of the copper tube, but by injecting water into the hot water tank, The water-soluble polymer film 4 can be dissolved and removed.

Next, an actual specific example in the case of applying the scale removing method of the present embodiment to a water heater having a heat exchanger for heating water passing through the pipe will be described.
As the scale removal method of the present embodiment, there is a method in which the tube of the heat exchanger is once removed, or a method in which a dedicated inlet for injecting an aqueous solution in which a water-soluble polymer is dissolved is provided in the water heater.
When a dedicated inlet is provided, it is preferable to inject the aqueous solution after removing the water filled in the tube, but the water filled in the tube may be pushed out by injecting the aqueous solution. After the injection of the aqueous solution, air (heated air if necessary) is introduced into the tube to form the water-soluble polymer film 4. At this time, the formation of the water-soluble polymer film 4 may be promoted by heating. Next, the water-soluble polymer film 4 incorporating the scale 2 may be dissolved and removed by injecting water into the tube.

Embodiment 2. FIG.
The water heater of the present embodiment has an optimum structure for carrying out the above-described scale removal method, and an aqueous solution in which at least one water-soluble polymer selected from polyvinyl alcohol and polyvinyl pyrrolidone is dissolved. And volume shrinkage accompanying water evaporation of the aqueous solution by providing at least one inlet for supplying air to the heat transfer surface of the heat exchanger and drying the aqueous solution in contact with the heat transfer surface The scale is peeled off from the heat transfer surface while incorporating the scale into the water-soluble polymer film .
The inlet may be common to both the water-soluble polymer and air, or may be dedicated to each of the aqueous solution and air.
Thus, by providing the inlet for supplying the aqueous solution or air to the heat transfer surface of the heat exchanger, the removal of the scale 2 in the heat exchanger of the water heater can be performed efficiently.

EXAMPLES Hereinafter, although an Example demonstrates the detail of this invention, this invention is not limited by these.
As the heat exchanger, a heat exchanger formed of a copper tube having a diameter of 10 mm and capable of raising the temperature of water passing through the copper tube to 60 ° C. by heating with boiling water from the outside of the copper tube was used. As water to be heated by the heat exchanger, calcium carbonate fine powder was added and mixed, and then filtered tap water was used. After passing water for 60 minutes, the copper tube was cut and the inner surface of the copper tube was confirmed by microscopic observation. As a result, it was confirmed that many calcium scale microcrystals were adhered.

(Examples 1-7 and Comparative Examples 2-3)
After injecting an aqueous solution having the composition shown in Table 1 below into the copper tube to which the calcium scale was attached as described above, the excess aqueous solution was discharged by flowing air, and the air was further flown for 5 minutes. A water-soluble polymer film was formed on the inner surface.
Next, the water-soluble polymer film was dissolved and removed by flowing water through the copper tube for 60 seconds.
In addition, Examples 1-3 and 5-7 are reference examples.
(Comparative Example 1)
The treatment with the aqueous solution was not performed, and the copper tube to which the calcium scale was attached as described above was used as it was.

  The effect of removing the calcium scale was evaluated by counting the number of calcium scale microcrystals remaining on the observation surface of the inner surface (1 mm square) of the copper tube using a microscope after cutting the copper tube. The results are shown in Table 1.

As shown in Table 1, the methods of Examples 1 to 7 using an aqueous solution in which a water-soluble polymer was dissolved had few calcium scale microcrystals attached to the inner surface of the copper tube, and the calcium scale was simplified and Could be removed effectively. Moreover, the method of Examples 5-7 which added the chelating agent, the pH adjuster, or surfactant further increased the calcium scale removal effect.
In Table 1, the significant results of the method of Example 4 using two types of water-soluble polymers relative to the methods of Examples 1 to 3 using one type of water-soluble polymer are not clear. However, when the water-soluble polymer film was dissolved and removed, water was passed through the steel pipe for 30 seconds for evaluation, but the method of Examples 1 to 3 showed that the water-soluble polymer film remained undissolved. In the method of Example 4, since the undissolved residue of the water-soluble polymer film was not confirmed, the use of two types of water-soluble polymers can increase the water washing removal efficiency of the water-soluble polymer film. all right.
On the other hand, in the methods of Comparative Examples 2 to 3 using an aqueous solution not using a water-soluble polymer, there were many calcium scale microcrystals attached to the inner surface of the copper tube, and the calcium scale could not be removed sufficiently. .

  As can be seen from the above results, according to the present invention, it is possible to provide a scale removing method and a water heater that can easily and effectively remove the scale attached to the heat transfer surface of the heat exchanger. .

  1 Heat transfer tube, 2 scale, 3 liquid film, 4 water-soluble polymer film.

Claims (5)

A method of removing scale adhered to the inner surface of a heat exchanger tube of a heat exchanger,
Forming a liquid film by bringing an aqueous solution in which two water-soluble polymers, polyvinyl alcohol and polyvinylpyrrolidone, are dissolved into contact with the inner surface;
By drying the liquid film, the water-soluble polymer film is formed on the inner surface, and the scale is taken into the water-soluble polymer film by volume contraction accompanying the drying of the liquid film. Peeling the scale from the inner surface;
Removing the scale from the inner surface while dissolving the water-soluble polymer film by injecting water into the heat transfer tube.   The method for removing a scale according to claim 1, wherein the saponification degree of the polyvinyl alcohol is 90% or less, and the polymerization degree of the polyvinyl alcohol and the polyvinyl pyrrolidone is 300 or more and 30,000 or less.   The scale removal method according to claim 1 or 2, wherein the aqueous solution further contains at least one component selected from a chelating agent, a pH adjusting agent, and a surfactant.   The method for removing a scale according to any one of claims 1 to 3, wherein the concentration of the water-soluble polymer in the aqueous solution is 1.5 mass% or more and 30 mass% or less.   The scale removal method according to any one of claims 1 to 4, wherein a water-repellent coating is previously formed on the heat transfer surface of the heat exchanger.

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