JP2013164247A - Anticorrosive coating layer, thermoconductive pipe having the anticorrosive coating layer, and heat exchanger having the thermoconductive pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosive coating layer which can be formed into an elongate pipe without spending a time and effort and is excellent in thermal conductivity, a thermoconductive pipe (including a pipe with fins) having the anticorrosive coating layer, and a heat exchanger having the thermoconductive pipe.SOLUTION: In the thermoconductive pipe 24, fins 28 are fixedly arranged at an outer peripheral face of a cylindrical thermoconductive pipe body 26 at predetermined pitch intervals. Surfaces of the thermoconductive pipe body 26 and the fins 28 are covered with the anticorrosive coating layer 40. The anticorrosive coating layer 40 is formed of a fluorine resin mixture. The fluorine resin mixture is formed by mixing carbon fiber 43, a low melting point alloy 44 containing tin, graphite 45, and silicone carbide 46 into a fluorine resin 42. The fluorine resin 42, the carbon fiber 43, and the low melting point alloy 44 are stuck to the surface of the thermoconductive pipe 24 while being dispersed.

Description

  The present invention is provided with a corrosion-resistant coating layer having corrosion resistance and heat transfer applied to the surface of a metal member used in combustion gas discharged from a boiler or the like, a heat transfer tube having the corrosion-resistant coating layer, and the heat transfer tube. It relates to a heat exchanger.

  In general, in order to increase the thermal efficiency of a boiler or the like, a heat exchanger that recovers heat from high-temperature combustion gas generated in a furnace and heats boiler water is used. The combustion gas contains water vapor, sulfur oxide (SOx), etc., and depending on the amount of water vapor in the combustion gas, the concentration of sulfur oxide, etc., dew condensation occurs in an atmosphere of about 160 ° C. or lower. As a result, highly corrosive sulfuric acid is generated and adheres to the heat exchanger (hereinafter, the temperature at which sulfuric acid is generated is referred to as sulfuric acid dew point temperature). As a result, the heat exchanger is subjected to corrosion, so-called low temperature corrosion. Therefore, in order to prevent the generation of sulfuric acid, by operating at a temperature higher than the sulfuric acid dew point temperature (for example, 180 ° C. or more), it prevents the generation of sulfuric acid and avoids the occurrence of low temperature corrosion. Yes.

  By the way, in order to improve the efficiency of boilers and the like, it has been strongly desired to operate at a sulfuric acid dew point temperature or lower. Therefore, a heat exchanger having a corrosion-resistant coating layer containing a fluororesin or glass is used. However, since the corrosion-resistant coating layer containing fluororesin or glass has low heat conductivity, the heat recovery rate decreases. Therefore, in order to improve the heat recovery rate, the heat recovery rate has been improved by enlarging the heat transfer area by increasing the surface area of the heat exchanger or adopting a finned tube.

  However, when the heat transfer area is increased, there are problems that the manufacturing cost increases and it is difficult to downsize the entire boiler system.

Thus, for example, Patent Document 1 discloses a economizer having a corrosion-resistant coating layer that does not impair the heat recovery rate.
The economizer described in Patent Document 1 has a corrosion-resistant coating layer containing a carbon resin such as a carbon nanotube. This corrosion-resistant coating layer is formed by depositing an electrodeposition solution in which a carbon resin is dispersed in a synthetic polymer resin, which is an electrodeposition material, on the surface of a metal tube by electrodeposition, followed by heat curing. . When an anionic synthetic polymer resin is used as the electrodepositable synthetic polymer resin, it is neutralized with an inorganic alkali such as trimethylamine or diethylamine, solubilized in water, or electrodeposited in a water-dispersed state. To be served. Further, when a cationic synthetic polymer resin is used, it is neutralized with an acid such as formic acid or acetic acid and is subjected to electrodeposition in a state solubilized in water or in a water-dispersed state.

JP 2011-2110 A

  However, in order to form the corrosion-resistant coating layer described in Patent Document 1, as described above, the synthetic polymer resin must be neutralized with an inorganic alkali or acid and solubilized in water, or in a water-dispersed state. In other words, many work steps and a lot of time are required, and it is difficult to construct the long pipe.

  Therefore, the present invention is an invention made under the state of the prior art as described above, and can be formed on a long tube without trouble, and the corrosion-resistant coating layer having excellent heat conductivity and the corrosion-resistant coating. It aims at providing the heat exchanger tube (including a tube with a fin) which has a layer, and a heat exchanger which has the heat exchanger tube concerned.

The present invention has been invented to solve the above-described problems in the prior art, and the corrosion-resistant coating layer of the present invention is a metal member used in a combustion gas containing moisture and sulfur oxide. A corrosion-resistant coating layer that adheres to the surface and prevents corrosion of the metal member,
A fluororesin mixture containing a fluororesin, carbon fiber, and a low melting point alloy (for example, a solder material),
The fluororesin, the carbon fiber, and the low melting point alloy are dispersed.

According to the said corrosion-resistant coating layer, since it contains a fluororesin, it has corrosion resistance against sulfuric acid.
Moreover, since carbon fiber, graphite, and a low melting point alloy are included, heat conductivity can be made higher than the corrosion-resistant coating layer which consists only of a fluororesin. Thereby, it can have the outstanding heat conductivity. Further, the fluororesin, the carbon fiber, and the low melting point alloy are adhered to the metal surface in a dispersed state. Thereby, corrosion resistance and thermal conductivity can be made uniform over the entire surface of the metal.
In addition, the fluororesin mixture can be prepared in a short time without trouble because only the carbon fiber and the low melting point alloy are mixed with the fluororesin. And the installation to a long pipe becomes easy.

Moreover, in the said invention, the said fluororesin mixture adheres to the surface of the said metal by being baked after electrostatic coating,
The low melting point alloy may have a melting point lower than the baking temperature.

  In this way, since a low melting point alloy having a melting point lower than the baking temperature is used, when baking is performed, the low melting point alloy melts and spreads over the entire metal surface, and also in the thickness direction in the coating layer. Due to the spread, the thermal conductivity can be increased uniformly over the entire surface of the metal.

  In the above invention, the fluororesin mixture may include 40 to 60% by weight of the fluororesin, 10 to 40% by weight of the carbon fiber, and 10 to 40% by weight of the low melting point alloy.

  Thus, since the corrosion-resistant coating layer contains 40 to 60% by weight of the fluororesin, 10 to 40% by weight of the carbon fiber, and 10 to 40% by weight of the low melting point alloy, the corrosion-resistant coating layer is more than the corrosion-resistant coating layer made of only the fluororesin. In addition, the corrosion resistance can be improved and the thermal conductivity can be increased.

  In the above invention, the fluororesin mixture may contain at least one of graphite and silicon carbide.

  When graphite is included, thermal conductivity and corrosion resistance can be further improved. Further, when silicon carbide is included, the corrosion resistance can be further improved.

  In the above invention, the fluororesin mixture may contain 0 to 15% by weight of the graphite and 0 to 15% by weight of the silicon carbide.

  Thus, since the corrosion-resistant coating layer contains 0 to 15% by weight of graphite and 0 to 15% by weight of silicon carbide, the corrosion resistance is improved as compared with the corrosion-resistant coating layer made of only a fluororesin, and the thermal conductivity is increased. Can be high.

  The heat transfer tube of the present invention is characterized by having a corrosion-resistant coating layer made of the above-mentioned fluororesin mixture on the surface.

According to the heat transfer tube, since the above-described corrosion-resistant coating layer is provided on the surface, heat exchange can be performed more efficiently than a conventional corrosion-resistant coating layer made of only a fluororesin. That is, the heat recovery rate can be improved. Furthermore, since the heat recovery rate is excellent, it is possible to reduce the size of the heat transfer tube that has been enlarged to increase the heat recovery rate.
Moreover, since it has the corrosion-resistant coating layer mentioned above on the surface, the corrosion resistance with respect to a sulfuric acid is improved rather than the conventional corrosion-resistant coating layer, and corrosion can be reduced rather than the conventional heat exchanger tube.

  The heat exchanger according to the present invention is characterized in that the above-described heat transfer tube is provided in a portion where the combustion gas containing moisture and sulfur oxide is cooled to be below the dew point and sulfuric acid is generated.

According to the above heat exchanger, the combustion gas containing water and sulfur oxide is cooled to have a dew point or lower and the above-described heat transfer tube is provided at a site where sulfuric acid is generated. Is improved, and the amount of corrosion can be reduced as compared with the conventional heat transfer tube.
In addition, since the above-described heat transfer tube is used only at a site where sulfuric acid is generated, a heat exchanger can be manufactured at a lower cost compared to the case where the above-described heat transfer tube is provided at all sites.
And since the heat exchanger tube mentioned above is provided, it can be used for a long time, improving a heat recovery rate rather than the conventional heat exchanger.
Furthermore, since the above-described heat transfer tube is provided, the heat exchanger that has been increased in size to increase the conventional heat recovery rate can be reduced in size.
Moreover, since it becomes possible to operate a boiler etc. even below sulfuric acid dew point temperature, the efficiency of a boiler can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, it can form also in a long pipe without taking an effort, and is a heat-resistant coating layer excellent in heat conductivity, the heat-transfer tube (including a finned tube) which has the said corrosion-resistant coating layer, and the said heat-transfer tube Can be provided.

It is a figure which shows the waste heat recovery apparatus of the boiler which concerns on embodiment of this invention. It is a sectional side view of the heat exchanger tube which has a corrosion-resistant coating layer concerning the present invention. It is a schematic diagram which shows the fluororesin, carbon fiber, graphite, silicon carbide, and low melting point alloy which were disperse | distributed in the corrosion-resistant coating layer. It is a figure which shows the relationship between the compounding quantity of graphite, and thermal conductivity. It is a figure which shows the relationship between the material contained in a corrosion-resistant coating layer, and a heat transfer rate. It is a conceptual diagram which shows the effect by this invention.

Hereinafter, embodiments of the present invention will be described in more detail based on the drawings.
However, the scope of the present invention is not limited to the following embodiments. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments are merely illustrative examples and are not intended to limit the scope of the present invention only unless otherwise specified.

FIG. 1 is a diagram illustrating a boiler exhaust heat recovery apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the fuel supplied to the furnace 4 by the burner 2 of the boiler 1 is mixed with the air supplied from the air duct 6 to generate high-temperature combustion gas in the furnace 4. The hot combustion gas is recovered by the superheater 10, the reheater 12, and the economizer 14 installed in the furnace 4 and the exhaust gas passage 8. The temperature of the combustion gas gradually decreases as it passes through the superheater 10, the reheater 12, and the economizer 14.

The water vapor evaporated in the brackish water drum 16 is fed to the superheater 10. And the water vapor | steam heated with the superheater 10 is supplied to a high pressure turbine.
Further, the steam that has worked in the high-pressure turbine is supplied to the reheater 12. Then, the steam heated by the reheater 12 is supplied to the intermediate pressure turbine.

Further, boiler water supplied from the condensate pump is supplied to the economizer 14 by the water supply pump 22. Then, the boiler water heated by the economizer 14 is supplied to the brackish water drum 16.
The boiler water in the heat transfer tube 24 is heated by exchanging heat between the combustion gas passing around the heat transfer tube 24 of the economizer 14 and the boiler water in the heat transfer tube 24.

  The economizer 14 includes an upper block 14a, a middle block 14b, and a lower block 14c. Boiler water supplied from the water supply pump 22 is supplied into the heat transfer tube 24 from a water supply port 32 provided at the end of the heat transfer tube 24 at the lower end of the lower block 14c. Then, after passing through the lower block 14c, the middle block 14b, and the upper block 14a, the water is supplied to the brackish water drum 16 from the water supply port 32 provided at the end of the heat transfer tube 24 at the upper end of the upper block 14a.

The boiler water is gradually heated as it moves from the lower block 14c to the upper block 14a. Therefore, the temperature of the combustion gas gradually decreases as it goes from the upper block 14a to the lower block 14c.
For example, the temperature of the combustion gas passing near the upper end of the economizer 14 is about 373 ° C., and the temperature of the combustion gas after passing through the economizer 14 is about 163 ° C. Moreover, the temperature of the boiler water supplied to the economizer 14 was about 145 ° C. Therefore, in the middle block 14b or the lower block 14c, the sulfuric acid dew point temperature (about 160 ° C.) or lower is generated, and a site where sulfuric acid is generated is generated. When sulfuric acid is generated, the heat transfer tube 24 undergoes low temperature corrosion. In view of this, a heat transfer tube 24 having a corrosion-resistant coating layer according to the present invention, which will be described later, is disposed at a site that is equal to or lower than the sulfuric acid dew point temperature. The arrangement location is determined in advance by calculating a position where the sulfuric acid dew point temperature is lower than the design. In the present embodiment, for example, the corrosion-resistant coating layer according to the present invention is applied to the heat transfer tube 24 of the lower block 14c. Therefore, the upper block 14a and the middle block 14b are provided with general heat transfer tubes.
In this embodiment, the temperature of the combustion gas passing near the upper end of the economizer 14 is about 373 ° C., and the temperature of the combustion gas after passing the economizer 14 is about 163 ° C. and supplied to the economizer 14. Although the temperature of the boiler water made was about 145 degreeC, it is not limited to these values.

FIG. 2 is a side sectional view of the heat transfer tube 24 having the corrosion-resistant coating layer 40 according to the present invention.
As shown in FIG. 2, in the heat transfer tube 24, fins 28 are fixed to the outer peripheral surface of a cylindrical heat transfer tube main body 26 at a predetermined pitch interval. The surfaces of the heat transfer tube body 26 and the fins 28 are covered with a corrosion-resistant coating layer 40 according to the present invention.

FIG. 3 is a schematic diagram showing the fluororesin 42, the carbon fibers 43, the graphite 45, the silicon carbide 46, and the low melting point alloy 44 dispersed in the corrosion resistant coating layer 40.
As shown in FIG. 3, the corrosion-resistant coating layer 40 is formed from a fluororesin mixture. This fluororesin mixture is formed by mixing carbon fiber 43, low melting point alloy 44 containing tin, graphite 45 and silicon carbide 46 with fluororesin 42. The fluororesin 42, the carbon fiber 43, the low melting point alloy 44, the graphite 45, and the silicon carbide 46 are all in the form of powder, fiber, and paste.

  In the fluororesin mixture, the fluororesin 42 is 40 to 60 wt%, the carbon fiber 43 is 10 to 40 wt%, the low melting point alloy 44 is 10 to 40 wt%, the graphite 45 is 0 to 15 wt%, and the silicon carbide 46 is 0 to 15% by weight is contained.

  In the present embodiment, a powdery tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is used as the fluororesin 42, but is not limited thereto. For example, polytetrafluoroethylene (PTFE), Tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polybilinidene fluoride (PVDF), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene copolymer (ETFE), etc. It may be used.

  As the carbon fiber 43, powdery pitch-based carbon fiber 43 made of petroleum pitch or coal tar pitch was used. This is because the pitch-based carbon fiber 43 is excellent in corrosion resistance and heat conductivity and has high rigidity.

  Moreover, as the low melting point alloy 44, for example, a lead-free solder alloy was used. The lead-free solder alloy is mainly composed of tin and added with copper, silver, aluminum, bismuth, zinc or the like. Although details will be described later, Sn-Ag-Cu, Sn-Al, Sn-Bi, Sn-Bi-Ag, etc. that can be melted when the fluororesin mixture is baked at about 150 to 200 ° C. after electrostatic powder coating The low melting point alloy is used. In this embodiment, a powdery lead-free solder alloy is used, but a paste-like one may be used.

  As the graphite 45, powdery diamond-like carbon (DLC) was used. Note that the graphite is not limited to DLC, and general graphite 45 may be used.

Since not only the fluororesin 42 but also the graphite 45 and silicon carbide 46 having high hardness are present in the corrosion-resistant coating layer 40 in a dispersed state as shown in FIG. 3, the corrosion resistance can be improved. Further, since the carbon fibers 43 and the graphite 45 having a high heat transfer coefficient are dispersed and are connected to the wire by the low melting point alloy 44, the heat transfer property can be improved. By mixing the powdered carbon fiber 43, the low melting point alloy 44, the graphite 45, the silicon carbide 46, and the fluororesin 42, it can be dispersed in the corrosion resistant coating layer 40.
The result of examining the influence on the thermal conductivity by including powdery graphite 45 will be described below.

FIG. 4 is a diagram showing the relationship between the blending amount of graphite 45 and the thermal conductivity.
As shown in FIG. 4, the thermal conductivity of each mixture was measured using a plurality of types of mixtures having different amounts of graphite 45. Specifically, a mixture obtained by melting and mixing graphite 45 and polyphenylene sulfide (PPS) resin 42 (hereinafter referred to as a molten mixture), powdered graphite 45 and powdered polyphenylene sulfide (PPS) resin 42 are powdered. A mixture (hereinafter referred to as powder mixture), graphite 45 and polyphenylene sulfide (PPS) resin 42 mixed in a solution (hereinafter referred to as solution mixture), graphite 45 and polyphenylene sulfide (PPS) resin A mixture (hereinafter referred to as a roll kneaded product) obtained by pressurizing and kneading 42 with a roll was used.

  In all the mixtures, it was confirmed that the heat transfer coefficient increased as the content of graphite 45 increased. Moreover, it has confirmed that a powder mixture showed the value whose heat conductivity is the highest than another mixture. For example, when the content of graphite 45 is 20% by weight, the heat transfer coefficient of the powder mixture shows the highest value. And the heat conductivity is low in the order of the solution mixture, the roll mixture, and the molten mixture. Therefore, it was confirmed that high thermal conductivity can be obtained by mixing the powdery graphite 45.

  By the way, the fluororesin mixture is attached to the heat transfer tube 24 by powder electrostatic coating. The heat transfer tube 24 to which the fluororesin mixture is adhered is placed in a baking and drying furnace and baked at about 150 to 200 ° C. By baking, the powder particles of the low melting point alloy 44 contained in the fluororesin mixture are melted and dispersed over the entire surface of the heat transfer tube 24, and then cured, whereby the corrosion-resistant coating layer 40 is formed.

  Since the carbon fiber 43, the low melting point alloy 44, the graphite 45 and the silicon carbide 46 are powder particles, the corrosion-resistant coating layer 40 is formed in a state of being dispersed on the surface of the heat transfer tube 24.

  Next, the result of having improved the heat transfer by including the carbon fiber 43, the low melting point alloy 44, the graphite 45, etc. will be described.

FIG. 5 is a diagram showing the relationship between the material contained in the corrosion-resistant coating layer and the heat transfer coefficient.
As shown in FIG. 5, a plurality of types of corrosion-resistant coating layers (hereinafter referred to as samples) having different blending materials were prepared, and the thermal conductivity of each sample was measured. For comparison, Samples 1 to 5 made of commonly used blending materials were also prepared. First, samples 1 to 5 that are generally implemented will be described, and then samples 6 to 8 made of the blended material according to the present invention will be described.

  First, sample 1 consisting only of fluororesin 42, sample 2 in which 20% by volume of boron nitride is mixed in fluororesin 42, sample 3 in which 30% by volume of graphite 45 is mixed in fluororesin 42, and 30% by volume of copper in fluororesin 42 Sample 4 was mixed, and Sample 5 was prepared by mixing 50% by volume of aluminum with the fluororesin 42. The compounding material and the compounding ratio blended in these samples 1 to 5 are generally implemented when enhancing corrosion resistance and heat transfer.

  Next, sample 6 in which graphite 45 and silicon carbide 46 are mixed in PFA of fluororesin 42, sample 7 in which graphite 45, silicon carbide 46 and lead-free solder alloy are mixed in PFA, graphite 45, silicon carbide 46 and lead in PFA Sample 8 in which a free solder alloy and carbon fiber 43 were mixed was prepared. The combination of the blending materials blended in these samples 6 to 8, the blending ratio, etc. are newly invented this time in order to improve the corrosion resistance and heat transfer.

  The thermal conductivity of Sample 1 was 0.2 (W / mK), which was the smallest value among all the samples. The thermal conductivities of Samples 2, 3, 4, and 5 are 0.5, 1.0, 0.6, and 2.6 (W / mK), respectively, which are higher than the heat transfer coefficient of Sample 1. became. In particular, in the sample 5 containing aluminum, a high heat transfer coefficient was obtained. However, since aluminum contained 50% by volume, the cost becomes high.

The heat transfer coefficient of the sample 6 is 1.5 (W / mK), which is 7 times or more that of the sample 1.
Moreover, the heat transfer coefficient of the sample 7 is 13.9 (W / mK), which is the second highest heat transfer coefficient among the samples of this time.
Finally, the heat transfer coefficient of the sample 8 is 28.5 (W / mK), and has the highest heat transfer coefficient among the samples of this time.

  From these results, it was confirmed that the thermal conductivity could be increased by including graphite 45, carbon fiber 43, and lead-free solder alloy. In particular, high thermal conductivity can be obtained by including the carbon fiber 43 and the lead-free solder alloy.

According to the corrosion-resistant coating layer 40 according to the present invention described above, since the fluororesin 42 is contained in an amount of 40 to 60% by weight, it has corrosion resistance against sulfuric acid. And since it contains 0-15 weight% of silicon carbide 46, corrosion resistance can further be improved.
Further, since the carbon fiber 43 is contained in an amount of 10 to 40% by weight and the low melting point alloy 44 is contained in an amount of 10 to 40% by weight, the thermal conductivity can be made higher than that of the corrosion-resistant coating layer 40 made of only the fluororesin 42. And since it contains 0 to 15 wt% of graphite 45, it is possible to further increase the thermal conductivity and further improve the corrosion resistance.
Further, the fluororesin 42, the carbon fiber 43, and the low melting point alloy 44 are adhered to the surface of the heat transfer tube 24 in a dispersed state. Thereby, corrosion resistance and heat transfer property can be made uniform over the entire surface of the heat transfer tube 24.
Since the low melting point alloy 44 having a melting point lower than the baking temperature is used, the low melting point alloy 44 can be melted and the fluororesin mixture can be firmly attached to the surface of the heat transfer tube 24 when baking is performed. Further, the low melting point alloy 44 is melted and spreads over the entire surface of the heat transfer tube 24 by the action of binding carbon fibers, silicon carbide, etc. having high thermal conductivity. Thereby, the thermal conductivity can be made uniform over the entire surface of the heat transfer tube 24.
Furthermore, the fluororesin mixture can be prepared in a short time without trouble because only the carbon fiber 43 and the low melting point alloy 44 are mixed with the fluororesin 42. And the installation to a long pipe becomes easy.

Further, according to the heat transfer tube 24 according to the present invention, the heat transfer tube 24 according to the present invention has the corrosion resistance coating layer 40 according to the present invention, which has a higher thermal conductivity than the conventional corrosion resistance coating layer made of only the fluororesin 42, so that heat exchange can be performed efficiently can do. That is, the heat recovery rate can be improved. Furthermore, since the heat recovery rate is excellent, as shown in FIG. 6, it can be made smaller than a heat transfer tube that has been enlarged to increase the heat recovery rate.
And since it has the corrosion-resistant coating layer 40 according to the present invention, which is superior in corrosion resistance to the conventional corrosion-resistant coating layer, the corrosion resistance against sulfuric acid is improved, and corrosion can be reduced as compared with the conventional heat transfer tube. .

Moreover, according to the economizer 14 provided with the heat transfer tube 24 according to the present invention, the portion where the combustion gas is cooled to be below the dew point and sulfuric acid is generated, for example, the lower block 14c, has better corrosion resistance than the conventional heat transfer tube. Since the heat transfer tube 24 according to the present invention is provided, the amount of corrosion can be reduced as compared with the conventional heat transfer tube.
In addition, since the heat transfer tube 24 according to the present invention is used only in a portion where sulfuric acid is generated, the heat transfer tube 24 according to the present invention is provided in all the portions, for example, the upper block 14a, the middle block 14b, and the lower block 14c. In comparison, the economizer 14 can be manufactured at a low cost.
Moreover, since the heat transfer tube 24 according to the present invention is provided, it can be used for a long time while improving the heat recovery rate as compared with the conventional economizer.
Furthermore, since the heat transfer tube 24 according to the present invention is provided, it is possible to reduce the size of the conventional economizer to increase the heat recovery rate.
Moreover, since it becomes possible to drive the boiler 1 even if it is below a sulfuric-acid dew-point temperature, the efficiency of the boiler 1 can be improved.

1 boiler 2 burner 4 furnace 6 air duct 8 exhaust gas passage 10 superheater 12 reheater 14 economizer 14a upper block 14b middle block 14c lower block 16 brackish drum 22 water supply pump 24 heat transfer tube 26 heat transfer tube main body 28 fin 32 water supply port 40 Corrosion resistant coating layer 42 Fluororesin 43 Carbon fiber 44 Low melting point alloy 45 Graphite 46 Silicon carbide

Claims (7)

A corrosion-resistant coating layer that adheres to the surface of a metal member used in a combustion gas containing moisture and sulfur oxide and prevents corrosion of the metal member,
A fluororesin mixture containing a fluororesin, carbon fiber, and a low melting point alloy,
A corrosion-resistant coating layer in which the fluororesin, the carbon fiber, and the low melting point alloy are dispersed. The fluororesin mixture is attached to the surface of the metal by being baked after electrostatic coating,
The corrosion-resistant coating layer according to claim 1, wherein the low melting point alloy has a melting point lower than the baking temperature.   The said fluororesin mixture contains 40 to 60 weight% of the said fluororesin, 10 to 40 weight% of the said carbon fiber, and 10 to 40 weight% of the said low melting point alloy, It is characterized by the above-mentioned. Corrosion-resistant coating layer.   The said fluororesin mixture contains at least any one of graphite and silicon carbide, The corrosion-resistant coating layer as described in any one of Claims 1-3 characterized by the above-mentioned.   The corrosion-resistant coating layer according to claim 4, wherein the fluororesin mixture contains 0 to 15 wt% of the graphite and 0 to 15 wt% of the silicon carbide.   A heat transfer tube having a corrosion-resistant coating layer made of the fluororesin mixture according to any one of claims 1 to 5 on a surface thereof.   A heat exchanger comprising the heat transfer tube according to claim 6 at a site where the combustion gas containing moisture and sulfur oxide is cooled to be below the dew point and sulfuric acid is generated.

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