JP4383118B2 - Cleaning method of heat exchanger - Google Patents

Description

The present invention relates to washing method of a heat exchanger used in the water heater and the like. More specifically, the present invention relates to a heat exchanger cleaning method capable of easily removing scale containing silica.

A heat exchanger used for a water heater has a water distribution pipe formed of a metal material such as copper and through which tap water circulates and a heat exchange medium pipe through which a heat exchange medium circulates. The tap water is heated by heat exchange with the heat exchange medium in the exchange medium pipe. Here, the tap water contains hardness components such as calcium and magnesium, silicon dioxide (SiO ₂ ), and the like. For this reason, in the water distribution pipe, by causing the tap water to circulate for a long period of time, metal corrosion products resulting from the corrosion of the water distribution pipe by the tap water adhere to the distribution pipe, and also due to hardness components, silicon dioxide, etc. in the tap water. Scale adheres.

Conventionally, a cleaning agent for removing metal corrosion products and scales in a water distribution pipe contains malic acid (see, for example, Patent Document 1). And when it flows in into a water pipe, the inside of a water pipe is wash | cleaned by melt | dissolving a metal corrosion product etc. with malic acid.
JP 2000-265196 A (pages 2 to 3)

  However, malic acid contained in this conventional cleaning agent can dissolve scales caused by metal corrosion products and hardness components in tap water, but cannot dissolve scales containing silica. . For this reason, the scale containing silica remains in the water distribution pipe after washing, and there is a problem that it is difficult to remove it.

The present invention has been made paying attention to such problems existing in the prior art. And an object thereof is to provide a method of cleaning the heat exchanger can be easily removed scales containing silica.

In order to achieve the above object, the heat exchanger cleaning method according to the first aspect of the present invention includes a fluid container and a heat exchanger provided inside the fluid container. of a cleaning method, the acid solution containing the organic acid or a salt thereof, wherein the scale deposited on the heat exchange member by causing to flow into the fluid container Rise Jun or is shed, then from the fluid container The acid solution is discharged, and then an alkaline solution containing at least one selected from potassium hydroxide and sodium hydroxide and having an alkali component content of 0.1 to 50% by mass flows into the fluid container. also the in which you dissolve and remove the silica contained in the swelling or flaking the scale by causing.

Akira originating according to claim 2 is the invention according to claim 1, wherein the acid solution are those containing a cleaning improver having a chelating action and scale dispersing action.

Inventions of claim 3 is the invention according to claim 1 or claim 2, wherein the alkaline solution is one which contains the suspending agent having a chelating action and scale dispersing action.

The inventions of claim 4, in the invention described in any one of claims 1 to 3, wherein the acid solution and alkaline solution is one that is constituted by a food additive.

The inventions of claim 5, wherein the claim 1 in the invention described in any one of claims 4, the acid solution discharged from the fluid container, after dissolution and removal of the scale by the alkali solution The alkaline solution is neutralized by flowing into a fluid container .

As described in detail above, the present invention has the following effects.
According to inventions set forth in claim 1, silica by a simple operation that is dissolved by the alkaline solution was allowed to swell or peeling off the acid solution scales including, a scale containing silica can be easily removed.

According to inventions set forth in claim 2, in addition to the effect of the invention of claim 1, to improve the cleaning efficiency.
According to inventions set forth in claim 3, prevent in addition to the effect of the invention according to claim 1 or claim 2, precipitate in an alkaline solution occurs when processing a scale containing silica can do.

According to inventions set forth in claim 4, in addition to the effect of the invention according to any one of claims 1 to 3, used for cleaning the heat exchanger used in the water heater or the like for beverages can do.

According to the invention described in claim 5 , it is possible to prevent the alkaline solution from remaining in the fluid container.

Hereinafter, embodiments embodying the present invention will be described.
The heat exchanger cleaning agent of the present embodiment is composed of an acid solution containing an organic acid or a salt thereof, and an alkaline solution containing at least one selected from potassium hydroxide (caustic potash) and sodium hydroxide (caustic soda). ing. And it is used for washing | cleaning of the heat exchanger used for a hot water heater etc. Here, the heat exchanger will be described.

  As shown in FIGS. 1 and 3, the heat exchanger 11 includes a heat exchange medium container 12 and a fluid container 13 disposed below the heat exchange medium container 12. The heat exchange medium container 12 includes a plurality of first heat exchange medium pipes 14 extending in a direction orthogonal to the first heat exchange medium pipes 14 and adjacent to each other at the center between the pair of first heat exchange medium pipes 14 extending in the same direction. Two heat exchange medium tubes 15 are arranged, and the end portions of the second heat exchange medium tubes 15 are attached to the peripheral walls of the first heat exchange medium tubes 14 to form an H shape.

  The first and second heat exchange medium tubes 14 and 15 are respectively formed in a cylindrical shape, and each second heat exchange medium tube 15 is set to have an outer diameter and an inner diameter smaller than those of the first heat exchange medium tube 14 and the first heat exchange medium tubes 15. They are located on a plane passing through the axis of the heat exchange medium tube 14. The insides of the first and second heat exchange medium tubes 14 and 15 are communicated, and a bottomed cylindrical lid 16 is attached to one end of each first heat exchange medium tube 14. And, as shown by the arrow A in FIG. 1, the heat exchange medium container 12 has a heat exchange medium flowing into the first heat exchange medium pipe 14 from the other end of the first heat exchange medium pipe 14. After flowing through each second heat exchange medium tube 15, it flows into the other first heat exchange medium tube 14 and is discharged from the other end. Specific examples of the heat exchange medium include carbon dioxide, ethylene, ethane, and nitric oxide.

  The fluid container 13 is formed in a bottomed square box shape by forming a U-shaped cross section at the center of the long square plate member and bulging the first accommodating recess 17 extending in the longitudinal direction of the long square plate member. A fluid container body 18. A first opening 19 having a semicircular cross section is formed at both ends of one side edge in the longitudinal direction of the fluid container body 18 so as to bulge in the same direction as the first receiving recess 17. The 1 accommodation recessed part 17 is connected. On the bottom wall of the first housing recess 17, a plurality of partition walls 20 having a rectangular column shape extending in the short direction of the fluid container main body 18 are projected at regular intervals. At one end of each partition wall 20, a notch 21 is formed so as to form a staggered shape in the adjacent partition wall 20, and the end of each partition wall 20 is the notch 21. Therefore, the first receiving recess 17 is separated from the side wall.

  A lid plate 22 having a square plate shape is attached to the opening of the fluid container body 18, and the fluid container 13 is formed in a plate shape. A plurality of second receiving recesses 23 having a U-shaped cross section and extending in the short direction of the cover plate 22 are spaced apart from each other at a position corresponding to the partition wall 20 of the fluid container body 18 at the center of the cover plate 22. As shown, it is formed to bulge outward. For this reason, the inside of the fluid container 13 is partitioned into a plurality of flow chambers by the respective housing recesses 17 and 23 and the partition wall 20, and the flow chambers communicate with each other by a notch 21 formed at the end of the partition wall 20. ing.

  In the cover plate 22, a second opening 24 having a semicircular cross section is formed at a position corresponding to the first opening 19 in the same direction as the second receiving recess 23, and the second opening 24 and the second opening 24 are formed. The housing recess 23 communicates. For this reason, a cylindrical flow pipe 25 is formed by the openings 19 and 24 at both ends of one side edge of the fluid container 13. As shown by the arrow B in FIG. 1, the fluid container 13 is configured so that the fluid that has flowed into the fluid container 13 from one of the flow pipes 25 is orthogonal to the flow direction of the heat exchange medium in each flow chamber. And is circulated so as to meander through the fluid container 13 through the notches, and then is discharged from the other circulation pipe 25. Further, as shown in FIGS. 1 and 2, the fluid container 13 performs heat exchange so that the upper surface of the portion corresponding to each second accommodation recess 23 in the lid plate 22 contacts the second heat exchange medium tube 15. It is disposed below the medium container 12. The heat of the heat exchange medium flowing in the heat exchange medium container 12 after being heated is transmitted to the fluid via the second heat exchange medium pipe 15 and the fluid container 13.

  As shown in FIGS. 2 and 3, the heat exchanger 26 is formed by cutting a predetermined portion into a substantially trapezoidal cross section after making cuts in the long square plate material at regular intervals so as to be parallel to the short direction. By doing so, it is formed in the shape of a long square plate that is curved in a wave shape over the entire surface. The bent portions are formed so that the positions thereof are slightly shifted from each other along the diagonal line of the heat exchanger 26 so that a space is formed between the bent portions adjacent to each other in the longitudinal direction of the heat exchanger 26. Each is configured as an exchange member 27.

  The heat exchanger 26 is disposed in each flow chamber 28 so that each heat exchange member 27 extends in the short direction of the fluid container 13, that is, the fluid flow direction, and the fluid in the flow chamber 28 exchanges each heat. It is configured to circulate between the members 27. When the heat of the heat exchange medium is transmitted to the fluid container 13, a part of the heat exchange medium is transmitted to the fluid via each heat exchange member 27 of the heat exchange body 26.

  Here, in each heat exchange element 26, the interval D between the heat exchange members 27 in the fluid flow direction is preferably 2 mm or less. When the distance D between the heat exchange members 27 exceeds 2 mm, it becomes difficult to uniformly contact the entire fluid with the heat exchange member 27 in the fluid flow direction, and heat transfer from the heat exchange member 27 to the fluid is not possible. May be uniform.

  Examples of the material of the heat exchange medium container 12, the fluid container 13, and the heat exchange body 26 include metal materials, but a metal material having high heat conductivity such as copper is effective in heat conduction from the heat exchange medium to the fluid. Is preferable because of its high value. Specific examples of the fluid include drinking water such as tap water (clean water), industrial water, and the like, but drinking water is preferable because the heat exchanger 11 can be used as a water heater for beverages.

  Here, drinking water such as tap water generally contains hardness components such as calcium and magnesium, silicon dioxide and the like. For this reason, when the fluid container 13 or the like is made of copper, the drinking water circulates in the fluid container 13 for a long period of time, so that the inner surface of the fluid container 13 or the surface of the heat exchange member 27 The copper corrosion product which is a metal corrosion product resulting from corrosion by drinking water adheres. Furthermore, the scale (henceforth a silica scale) containing the silica resulting from the hardness component in a drinking water and silicon dioxide adheres. Specific examples of the silica scale include a scale composed of a mixture of colloidal silica having silicon dioxide as a polymerization unit, magnesium silicate, calcium silicate, a hardness component, and silicon dioxide.

Next, the heat exchanger cleaning agent of this embodiment will be described.
The organic acid or a salt thereof swells or peels off the silica scale attached to the inner surface of the fluid container 13 or the like. Furthermore, it dissolves the scale caused by metal corrosion products and hardness components. The swelling of the silica scale is a concept including the wetting of the silica scale, and the silica scale may be peeled off after being swollen. Here, the inorganic acid or a salt thereof can swell or peel off the silica scale in the same manner as the organic acid, but has high corrosiveness to a metal material or the like. For this reason, the acid solution needs to contain an organic acid or a salt thereof instead of an inorganic acid or a salt thereof.

  Specific examples of organic acids include those generally used for washing heat exchangers, and specific examples of salts include sodium salts, potassium salts, ammonium salts and the like. These may be contained alone or in combination of two or more. Among organic acids, citric acid, acetic acid, formic acid, propionic acid, malic acid, gluconic acid or glutamic acid used as food additives can be used for washing heat exchangers used in water heaters for beverages The citric acid is more preferable because it has a high effect of swelling or peeling off the silica scale and has a low irritating odor. Here, the food additive is a concept including those generally used for food, and includes FDA (Food and Drug Administration) approved products.

  Content of the organic acid or its salt in an acid solution becomes like this. Preferably it is 0.1-50 mass%, More preferably, it is 0.5-20 mass%, More preferably, it is 2-12.5 mass%. When the content of the organic acid or salt thereof is less than 0.1% by mass, the content of the organic acid or salt thereof in the acid solution is low, and the silica scale cannot be sufficiently swollen or peeled off. On the other hand, even if it exceeds 50 mass%, the effect commensurate with cost cannot be acquired and it is uneconomical.

  The acid solution preferably contains a detergency improver as another additive component. The detergency improver has a chelating action and a scale dispersing action, prevents dissolved metal corrosion products and the like from reattaching to the inner surface of the fluid container 13, and improves the dispersibility of the peeled silica scale. This improves the cleanability. Specific examples of the detergency improver include maleic acid compounds such as polymaleic acid, phosphonocarboxylic acids, phosphonic acid compounds such as 2-phosphonobutane-1,2,4-tricarboxylic acid, sodium polyphosphate, potassium polyphosphate And EDTA salts such as ethylenediaminetetraacetic acid (EDTA) -2Na. These may be contained alone or in combination of two or more.

  Among these, polymaleic acid, polyphosphoric acid or their sodium salts, potassium salts or calcium salts used as food additives can be used for washing heat exchangers used in water heaters for beverages. Preferably, polymaleic acid is more preferable because it has a high effect of improving detergency.

  The content of the detergency improver in the acid solution is preferably 10 to 100,000 ppm, more preferably 20 to 10,000 ppm, and still more preferably 50 to 1000 ppm. If the content of the detergency improver is less than 10 ppm, the detergency cannot be sufficiently improved because the content of the detergency improver in the acid solution is low. On the other hand, even if it exceeds 100000 ppm, an effect commensurate with the cost cannot be obtained, which is uneconomical.

  At least one selected from potassium hydroxide and sodium hydroxide (hereinafter also referred to as an alkali component) dissolves silica scale swollen or peeled off by an organic acid or a salt thereof in an acid solution. Here, weak alkali components such as lithium hydroxide have little solubility in silica scale or the like and cannot dissolve silica scale. For this reason, the alkaline solution needs to contain the above-mentioned alkaline component instead of a weak alkaline component.

  The content of the alkali component in the alkaline solution is preferably 0.1 to 50% by mass, more preferably 0.5 to 20% by mass, and still more preferably 0.5 to 5% by mass. When the content of the alkali component is less than 0.1% by mass, since the content of the alkali component in the alkali solution is low, it takes time to dissolve the silica scale, and the cleaning efficiency may be lowered. On the other hand, even if it exceeds 50 mass%, the effect commensurate with cost cannot be acquired and it is uneconomical.

  The alkaline solution preferably contains a suspending agent as another additive component. The suspending agent has a chelating action and a scale dispersing action similar to the detergency improver, and improves the dispersibility of the peeled silica scale, and the dissolved silica scale and the like are deposited in the alkaline solution as a precipitate. To prevent. Specific examples of the suspending agent and the content of the suspending agent in the alkaline solution are the same as those of the detergency improver. When the content of the suspending agent is less than 10 ppm, precipitation may occur in the alkaline solution because the content of the suspending agent in the alkaline solution is low. On the other hand, even if it exceeds 100,000 ppm, the dispersibility of the silica scale cannot be further improved.

  Specific examples of the acid solution and the alkali solution include water such as drinking water and industrial water. Among these, drinking water is preferable because it can be used for washing a heat exchanger used in a hot water supply for beverages. The content of the solvent in the acid solution or alkaline solution is the remaining amount with respect to the other components. The acid solution or alkali solution may contain a bactericidal agent as another additive component.

  The disinfectant prevents bacteria from being generated in the acid solution when contained in the acid solution, and the fluid container 13 is sterilized by washing the fluid container 13 with an acid solution or an alkali solution containing the disinfectant. To do. Specific examples of the disinfectant include thiabendazole, sodium hypochlorite, chlorine dioxide, ethyl formate, benzalkonium chloride and the like. These may be contained alone or in combination of two or more. Among these, thiabendazole, sodium hypochlorite, chlorine dioxide, and ethyl formate used as food additives are preferable because they can be used for washing heat exchangers used in water heaters for beverages. Is more preferable because of its high value.

  The content of the bactericide in the acid solution or alkali solution is preferably 1 to 50000 ppm, more preferably 5 to 10000 ppm, and still more preferably 10 to 1000 ppm. If it is less than 1 ppm, the content of the bactericide is low, so that the bactericidal effect cannot be sufficiently exhibited. On the other hand, even if it exceeds 50000 ppm, the bactericidal effect cannot be exhibited any more.

  Now, when cleaning the fluid container 13 to which the metal corrosion products, silica scale, etc. are attached using the heat exchanger cleaning agent, first, the acid solution is introduced into the fluid container 13. At this time, the acid solution can dissolve the scale caused by the metal corrosion product and the hardness component with the organic acid or a salt thereof, and can swell or peel off the silica scale. Subsequently, after discharging the acid solution from the fluid container 13, the alkaline solution is introduced. At this time, the alkali solution dissolves silica scales swollen or peeled off by the alkali component.

  For this reason, the heat exchanger cleaning agent can clean and remove the fluid container 13 by dissolving and removing scales such as metal corrosion products and silica scale. Here, the heat exchanger cleaning liquid can clean the fluid container 13 even at room temperature (20 ° C.), but in order to improve the cleaning efficiency, an acid solution or an alkali solution may be heated.

The effects exhibited by the above embodiment will be described below.
-The heat exchanger cleaning agent of embodiment is comprised from the acid solution containing an organic acid or its salt, and the alkali solution containing an alkali component. The organic acid or a salt thereof swells or peels off the silica scale, and the alkaline component can dissolve the swollen or peeled silica scale. For this reason, the cleaning agent for heat exchangers can easily remove the silica scale. Furthermore, the organic acid or its salt can dissolve the scale caused by the metal corrosion products and hardness components. For this reason, the cleaning agent for heat exchangers of this embodiment can easily remove the scale caused by the metal corrosion product and the hardness component together with the silica scale.

  The fluid container 13 constituting the heat exchanger 11 is formed in a plate shape, and a plurality of heat exchanging members 27 are formed over the entire surface of the heat exchanging body 26 in the heat exchanging bodies 26 disposed in the respective circulation chambers 28. Has been. And it is comprised so that a fluid may circulate between each heat exchange member 27. For this reason, the heat conduction efficiency from the fluid container 13 to the fluid can be improved, and the heat transfer to the fluid can be made uniform. Here, when a metal corrosion product, silica scale, or the like adheres to the surface of each heat exchange member 27 in which the distance D is set to 2 mm or less, the space between the heat exchange members 27 is blocked by silica scale or the like. . In this case, by cleaning with the heat exchanger cleaning agent of the present embodiment, the space between the heat exchange members 27 closed by dissolving the silica scale and the like adhering to the surface of each heat exchange member 27 can be easily obtained. Can be opened.

  -The acid solution preferably contains a detergency improver. In this case, the cleaning efficiency of the heat exchanger cleaning agent can be improved by preventing the reattachment of the dissolved metal corrosion product or the like to the inner surface of the fluid container 13 or the like. Furthermore, by improving the dispersibility of the peeled silica scale, clogging of the heat exchanger 26 and the like due to the peeled silica scale can be suppressed.

  -It is preferable to contain a suspending agent in the alkaline solution. In this case, it is possible to prevent the dissolved silica scale or the like from being precipitated in the alkaline solution as a precipitate. Furthermore, by improving the dispersibility of the peeled silica scale, clogging of the heat exchanger 26 and the like due to the peeled silica scale can be suppressed.

  -It is preferable that the acid solution and the alkaline solution are constituted by food additives. In this case, the heat exchanger cleaning agent can be used for cleaning the fluid container 13 of the heat exchanger 11 used in the hot water supply for beverages. Here, for example, when the fluorine compound is contained in the heat exchanger cleaning agent, the fluid container 13 can be cleaned, but the fluorine compound may remain in the fluid container 13. For this reason, it is difficult to use the cleaning agent for a heat exchanger containing a fluorine compound for cleaning the fluid container 13 of the heat exchanger 11 used in a hot water supply for beverages.

  -The organic acid is preferably citric acid. In this case, since the effect of swelling or exfoliating the silica scale is high, the heat exchanger cleaning agent can remove the silica scale more easily.

In addition, this embodiment can also be changed and embodied as follows.
Before discharging the alkaline solution from the fluid container 13, the already discharged acid solution may be flowed into the fluid container 13 to neutralize the alkaline solution. In the case of such a configuration, it is possible to prevent the alkaline solution from remaining in the fluid container 13 by discharging after neutralizing the alkaline solution.

  -You may use the said heat exchanger cleaning agent for washing | cleaning of heat exchangers other than the heat exchanger 11 of this embodiment.

  In Example 1, first, citric acid as an organic acid was dissolved in water to prepare an acid solution, and potassium hydroxide and sodium hydroxide were dissolved in water to prepare an alkaline solution. Here, the content of citric acid in the acid solution is 1% by mass, 5% by mass or 10% by mass, the content of potassium hydroxide in the alkaline solution is 0.8% by mass and the content of sodium hydroxide The amount was 0.9% by mass. Furthermore, the temperature of the acid solution and the alkali solution was set to 20 ° C.

  Next, the fluid container 13 formed of copper and having a metal corrosion product, silica scale, or the like attached to the surface of the heat exchange member 27 or the like was cut on a plane passing through the center portion in the thickness direction. Then, it cut | disconnected to the magnitude | size of 2 cm long and 3 cm wide, and formed the test piece. Then, the test piece was immersed in the stirred acid solution for 10 minutes.

  As a result, metal corrosion products and the like could be dissolved and removed by the acid solution, and the silica scale could be peeled off from the test piece as the citric acid content in the acid solution increased. In particular, when the content of citric acid in the acid solution was 10% by mass, the silica scale could be completely removed from the surface of the heat exchange member 27 and the like. Further, the test piece was immersed while stirring an acid solution having a citric acid content of 2.5 mass%. As a result, the silica scale began to peel off 20 to 30 minutes after the start of immersion, and the silica scale could be completely removed 30 to 40 minutes after the start of immersion. The test was performed three times. Subsequently, as a result of adding an amount of 25000 ppm to the alkali solution after recovering the peeled silica scale, the entire silica scale was dissolved.

  In Example 2, first, citric acid as an organic acid was dissolved in water to prepare an acid solution, and sodium hydroxide was dissolved in water to prepare an alkaline solution. Here, the content of citric acid in the acid solution was 12.5% by mass, and the content of sodium hydroxide in the alkaline solution was 7.5% by mass. Furthermore, the temperature of the acid solution and the alkali solution was set to 20 ° C.

  Next, 4 liters of water was introduced into the fluid container 13 of Example 1, and then an acid solution diluted five times with water (weight ratio) was introduced for 90 minutes. Subsequently, the acid solution was discharged from the fluid container 13, and then an alkaline solution diluted 5 times (weight ratio) with water was flowed in for 60 minutes. Then, the acid solution discharged from the fluid container 13 was again flowed into the fluid container 13 to neutralize the alkaline solution, and then discharged from the fluid container 13 to wash the fluid container 13. Here, the flow into the fluid container 13 is performed using an MD-20RZ-N type pump (max.flow 11 liter / min, max.ahead 6.9 m, 100 V, 50 W), and the temperature of each fluid is 20 ° C. It was.

  Here, the flow rate per hour when the acid solution and the alkaline solution flowed into or discharged from the fluid container 13 was measured using a flow meter, and the pressure difference was measured using a pressure meter. As a result, for the acid solution, the flow rate at the time of inflow is 1.67 liters / minute, the pressure difference is 55 kPa or more (flow rate: 1.67 liters / minute), and the flow rate at the time of discharge is 70 liters / hour. In addition, the pressure difference was 55 kPa or more (flow rate: 1.67 liter / min). On the other hand, for the alkaline solution, the flow rate during inflow is 120 liters / hour, the pressure difference is 45.4 kPa (flow rate: 1.67 liters / minute), and the flow rate during discharge is 125 liters / hour. The pressure difference was 43.7 kPa (flow rate: 1.67 liter / min). For this reason, it was possible to increase the flow rate and reduce the pressure difference by washing the fluid container 13 using an acid solution and an alkaline solution. This is because the silica scale or the like attached to the inner surface of the fluid container 13 is dissolved and removed by washing with the acid solution and the alkaline solution, so that the fluid can easily flow into the fluid container 13 and This is because the pressure difference during discharge has become smaller.

Further, for acid solution and alkali solution, acidity or basicity before dilution and at the time of discharge is measured, and copper (Cu), iron (Fe), calcium (CaCO ₃ ), magnesium (MgCO ₃ ) and The content of silica (SiO ₂ ) was measured. These results are shown in Table 1. In Table 1, the numerical value of the content of each component is expressed in mg / liter.

表１に示すように、排出時における酸溶液は、希釈前に比べて銅等の含有量が高くなった。一方、排出時におけるアルカリ溶液は、希釈前に比べてシリカ等の含有量が高くなった。これは、酸溶液によって金属腐食生成物等を溶解させることができ、アルカリ溶液によってシリカスケール等を溶解させることができたためである。

As shown in Table 1, the acid solution at the time of discharge had a higher content of copper or the like than before dilution. On the other hand, the alkali solution at the time of discharge had a higher content of silica or the like than before dilution. This is because the metal corrosion product and the like can be dissolved by the acid solution, and the silica scale and the like can be dissolved by the alkaline solution.

(Test Examples 1 to 3 and Comparative Example 1)
In Test Example 1, an acid solution and an alkali solution were prepared in the same manner as in Example 1 except that the content of citric acid in the acid solution was changed to 2.5% by mass. Subsequently, silica scale or the like is placed in the fluid container 13 formed of copper and having an initial differential pressure of 27 kPa (flow rate: 1.67 liters / minute, temperature: 15 ° C.) and a maximum flow rate of 140 liters / hour. After adhering to increase the differential pressure and reduce the maximum flow rate, the acid solution and the alkali solution were sequentially introduced and washed. Here, inflow of the acid solution and the alkali solution into the fluid container 13 was performed using the same pump as in Example 1.

  Then, the time when the flow rate reaches the lowest limit (50 liters / hour) after flowing in the acid solution (hereinafter referred to as AH) is measured, and the flow rate is maximized (140 liters / hour) after flowing in the alkaline solution. The time to reach (hereinafter referred to as BH) was measured. As a result, AH was 60 minutes and BH was 10 minutes. Furthermore, the pressure difference of the fluid container 13 after washing is 27 kPa (flow rate: 1.67 liters / minute) and the maximum flow rate is 140 liters / hour, and the content of silica in the washed alkaline solution is 1200 ppm. Met. In addition, about 5 g of precipitate was generated during washing.

  In Test Example 2, an acid solution and polymaleic acid (Berkulin 200, Great Lakes Chemical Japan, Inc., molecular weight: 1000 or less) as a precipitation inhibitor were further dissolved in an alkaline solution in the same manner as in Test Example 1. An alkaline solution was prepared. Here, the content of polymaleic acid in the alkaline solution was 50 ppm. Subsequently, AH and BH were measured in the same manner as in Test Example 1. As a result, AH was 60 minutes and BH was 10 minutes. The pressure difference after washing, the maximum flow rate, and the content of silica in the alkaline solution were the same as in Test Example 1, and no precipitate was generated during washing.

  In Test Example 3, an acid solution and an alkali solution were prepared in the same manner as in Test Example 2, except that phosphonocarboxylic acid as a detergency improver was further dissolved in the acid solution. Here, the content of phosphonocarboxylic acid in the acid solution was 50 ppm. Subsequently, AH and BH were measured in the same manner as in Test Example 1. As a result, AH was 50 minutes and BH was 10 minutes. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2.

  On the other hand, in Comparative Example 1, a sulfamic acid was dissolved in water to prepare a heat exchanger cleaning agent. Here, the content of sulfamic acid in the heat exchanger cleaning agent was 10% by mass, and the temperature of the heat exchanger cleaning agent was 20 ° C. Next, the heat exchanger cleaning agent was introduced into the fluid container 13 and AH and BH were measured. As a result, AH was 60 minutes, and BH could not be measured because the flow rate did not reach 140 liters / hour. The pressure difference of the fluid container 13 after cleaning is 180 kPa (flow rate: 1.67 liters / minute) and the maximum flow rate is 50 liters / hour, and the content of silica in the heat exchanger cleaning agent after cleaning is It was 200 ppm. In addition, no precipitate was generated during washing.

  For this reason, in Test Examples 1 to 3, the differential pressure and the maximum flow rate of the fluid container 13 could be recovered by washing with an acid solution and an alkaline solution, respectively. Furthermore, in Test Example 2 and Test Example 3, since the alkaline solution contains polymaleic acid, it is possible to prevent the generation of precipitates during washing. In Test Example 3, the acid solution is a phosphonocarboxylic acid. As a result, AH was shortened to improve the cleaning efficiency. On the other hand, in Comparative Example 1, since the cleaning is performed using the heat exchanger cleaning agent containing only the acid, the silica scale cannot be dissolved and removed, and the differential pressure and the maximum flow rate of the fluid container 13 are restored. I couldn't.

  In Example 4, except that citric acid as an organic acid was changed as shown in Table 2, acid solutions and alkaline solutions were prepared in the same manner as in Test Example 2, and AH and BH were prepared in the same manner as in Test Example 1. It was measured. As a result, BH was all 10 minutes. On the other hand, the measurement results of AH are shown in Table 2. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2.

表２に示すように、クエン酸を他の有機酸に変更しても、流量を最下限にまで到達させることができるとともに最大限に到達させることができた。さらに、各酸溶液において流体用容器１３の差圧及び最大流量を回復させることができた。

As shown in Table 2, even when citric acid was changed to another organic acid, the flow rate could reach the lowest limit and the maximum could be reached. Further, the differential pressure and the maximum flow rate of the fluid container 13 can be recovered in each acid solution.

(Test Examples 4 to 8)
In Test Example 4, an acid solution was prepared in the same manner as Test Example 2, and only an alkali solution was prepared by dissolving sodium hydroxide alone, potassium hydroxide alone, or sodium hydroxide and potassium hydroxide in water. The temperature of the acid solution and the alkali solution was 20 ° C. Table 3 shows the content of each component in the alkaline solution. Subsequently, AH and BH were measured in the same manner as in Test Example 1. Further, the maximum amount of silica that can be dissolved by the alkaline solution (hereinafter referred to as BS) was measured. As a result, AH was all 60 minutes. On the other hand, the measurement results of BH and BS are shown in Table 3. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2.

表３に示すように、アルカリ溶液は水酸化カリウムを含有することにより、ＢＨを短縮することができるとともにＢＳを増加させることができた。さらに、各アルカリ溶液において流体用容器１３の差圧及び最大流量を回復させることができた。

As shown in Table 3, the alkaline solution was able to shorten BH and increase BS by containing potassium hydroxide. Further, the differential pressure and the maximum flow rate of the fluid container 13 can be recovered in each alkaline solution.

  In Test Example 5, an acid solution and an alkaline solution were prepared in the same manner as in Test Example 2 except that the temperature of the acid solution was changed to 50 ° C., and AH and BH were measured in the same manner as in Test Example 1. As a result, AH was 30 minutes and BH was 10 minutes. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2. For this reason, in Test Example 5, by heating the acid solution to 50 ° C., it was possible to shorten AH and improve the cleaning efficiency. Furthermore, the differential pressure and the maximum flow rate of the fluid container 13 could be recovered.

  In Test Example 6, an acid solution and an alkali solution were prepared in the same manner as in Test Example 2 except that the temperature of the alkaline solution was changed to 50 ° C., and AH and BH were measured in the same manner as in Test Example 1. As a result, AH was 60 minutes and BH was 3 minutes. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2. For this reason, in Test Example 6, by heating the alkaline solution to 50 ° C., it was possible to shorten BH and improve the cleaning efficiency. Furthermore, the differential pressure and the maximum flow rate of the fluid container 13 could be recovered.

  In Test Example 7, an acid solution and an alkaline solution were prepared in the same manner as in Test Example 2 except that the content of citric acid in the acid solution was changed as shown in Table 4, and AH was tested in the same manner as in Test Example 1. And BH were measured. Further, the maximum amount of copper corrosion product (hereinafter referred to as AC) that can be dissolved by the acid solution was measured. As a result, BH was all 10 minutes. On the other hand, Table 4 shows the measurement results of AH and AC. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2.

表４に示すように、クエン酸の含有量が高くなるに伴い、ＡＨを短縮して洗浄効率を向上させることができるとともにＡＣを高めることができた。さらに、各酸溶液において流体用容器１３の差圧及び最大流量を回復させることができた。

As shown in Table 4, as the citric acid content increased, AH could be shortened to improve cleaning efficiency and AC could be increased. Further, the differential pressure and the maximum flow rate of the fluid container 13 can be recovered in each acid solution.

  In Test Example 8, an acid solution and an alkali solution were prepared in the same manner as in Test Example 2, except that the contents of sodium hydroxide and potassium hydroxide in the alkali solution were changed as shown in Table 5. Then, AH and BH were measured in the same manner as in Test Example 1, and BS was further measured. As a result, AH was all 60 minutes. On the other hand, the measurement results of BH and BS are shown in Table 5. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2.

表５に示すように、水酸化ナトリウム及び水酸化カリウムの含有量が高くなるに伴い、ＢＨを短縮して洗浄効率を向上させることができるとともにＢＳを高めることができた。さらに、各アルカリ溶液において流体用容器１３の差圧及び最大流量を回復させることができた。

As shown in Table 5, as the content of sodium hydroxide and potassium hydroxide increased, BH could be shortened to improve the cleaning efficiency and BS could be increased. Further, the differential pressure and the maximum flow rate of the fluid container 13 can be recovered in each alkaline solution.

  In Test Example 9, an acid solution and an alkali solution were prepared in the same manner as in Test Example 2, and the flow rate of the acid solution and the alkali solution was changed to twice that in Test Example 1 by changing the type of pump. Measured AH and BH in the same manner as in Test Example 1. As a result, AH was 40 minutes and BH was 7 minutes. The pressure difference after washing, the maximum flow rate, the silica content in the alkaline solution, and the generation of precipitates during washing were the same as in Test Example 2. For this reason, AH and BH could be shortened by increasing the flow rate, and the cleaning efficiency could be improved. Furthermore, the differential pressure and the maximum flow rate of the fluid container 13 could be recovered.

  In Example 6, an acid solution and an alkaline solution were prepared in the same manner as in Test Example 2 except that the bactericide was further dissolved in the acid solution, and then the acid solution was observed. Here, the content of the bactericide in the acid solution was 0.1 ppm, and chlorine dioxide, sodium hypochlorite, benzalkonium chloride, thiabendazole or ethyl formate was used as the bactericide. As a result, mold fungi were not generated in each acid solution when 67 days had passed since the preparation. Further, AH, BH, pressure difference after washing, maximum flow rate, content of silica in the alkaline solution, and generation of precipitates during washing were all the same as in Test Example 2. For this reason, in Example 6, the acid solution was sterilized by containing a bactericidal agent, and generation of mold fungi could be prevented.

Further, the technical idea that can be grasped from the embodiment will be described below.
- said organic acid is Ru citric Sandea. According to this structure, the scale containing silica can be removed more easily.

The perspective view which shows the heat exchanger of this embodiment. The principal part expanded sectional view which shows a heat exchange member. The disassembled perspective view which shows a heat exchanger.

Explanation of symbols

  D ... interval, 11 ... heat exchanger, 12 ... heat exchange medium container, 13 ... fluid container, 27 ... heat exchange member.

Claims (5)

A heat exchanger cleaning method comprising a fluid container and a heat exchange member provided inside the fluid container,
An organic acid, or an acid solution containing a salt thereof, wherein the scale deposited on the heat exchange member by causing to flow into the fluid container Rise Jun or is shed, then drained acid solution from the fluid container,
Thereafter, an alkaline solution containing at least one kind selected from potassium hydroxide and sodium hydroxide and having an alkali component content of 0.1 to 50% by mass is caused to swell or peel off by flowing into the fluid container. the method of cleaning the heat exchanger, wherein the benzalkonium to dissolve and remove the silica contained in the scales. The method for cleaning a heat exchanger according to claim 1, wherein the acid solution contains a detergency improver having a chelating action and a scale dispersing action. The method for cleaning a heat exchanger according to claim 1 or 2, wherein the alkaline solution contains a precipitation inhibitor having a chelating action and a scale dispersing action. The method for cleaning a heat exchanger according to any one of claims 1 to 3, wherein the acid solution and the alkali solution are constituted by food additives. The acid solution discharged from the fluid container is neutralized with the alkali solution by allowing the acid solution to flow into the fluid container after dissolution and removal of the scale with the alkali solution. The method for cleaning the heat exchanger as described .

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