JP2017032266A - Heat transfer pipe of fluidized bed boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer pipe of a fluidized bed boiler including a protector having sufficient durability under a corrosive wear environment while lowering initial costs by preventing a complicated structure, considering maintenance performance such as attachment and replacement, and reducing risks of cracking and deformation.SOLUTION: In a heat transfer pipe 1 used in a fluidized bed of a fluidized bed boiler, the heat transfer pipe 1 is composed of a water pipe 2 in which a fluid flows, a thin protector 4 and a thick protector 3 made of casting, disposed at an outer peripheral side of the water pipe 2 and protecting the water pipe 2, a heat insulating layer 6 disposed between the water pipe 2 and the thin protector 4, and a fixing jig 5. The fixing fig 5 is fixed to the thick protector 3, and the thin protector 4 disposed at the outer peripheral side of the water pipe 2 is pressed by the fixing jig 5.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a heat transfer tube used in a fluidized bed of a fluidized bed boiler that recovers combustion heat by burning fuel such as waste, RDF (garbage solidified fuel), and biomass.

  In recent years, utilization of energy resources has been demanded from the standpoint of dealing with rising prices of fossil fuels and global warming problems. In this situation, the importance of power generation systems that burn fuels such as waste, RDF, and biomass that play a role in thermal recycling is increasing. In this power generation system, there is a method in which heat energy generated when a fuel such as waste, RDF, or biomass is burned using a fluidized bed boiler is recovered by a heat transfer tube. In this method, when a fuel such as waste, RDF, or biomass is burned in a fluidized bed boiler, a severe corrosive environment may be formed by chloride derived from the fuel. The wear caused by the fluidized medium causes a significant reduction in the thickness of the protector of the heat transfer tube, shortens the life of the protector itself, and requires frequent maintenance.

As measures for prolonging the life of the protector, there are known methods for improving wear resistance by forming a hardened surface layer and for reducing the collision speed of particles by providing studs on the surface of the protector as disclosed in Patent Document 1. It has been.
Moreover, in patent document 2, a protector surface temperature is raised by providing a space | gap between a protector and a heat exchanger tube, an oxide film is formed in the surface, and abrasion resistance is improved. It is also reported in Patent Document 3 that when a stainless steel material such as SUS is used for the protector, an oxide film is formed due to temperature rise, wear resistance is improved, and the amount of thinning is reduced.

On the other hand, Patent Document 4 proposes a method in which an aluminum sprayed layer is provided between the protector and the heat transfer tube, and the aluminum is melted to improve adhesion and lower the surface temperature of the protector to suppress corrosion.
Also, providing the protector with a sufficient thickness reduction is one of the measures for ensuring the life. Since the thickness of the plate material and the pipe material is limited, and the processing of the thick plate is costly, it is common to use a casting.

Japanese Patent Laid-Open No. 2004-19965 JP-A-5-18504 JP-A-8-226601 Japanese Utility Model Publication No. 5-25101

  As described above, when the surface hardened layer is formed as a measure for prolonging the life of the protector, special treatment is required, leading to an increase in the cost of the protector. It is effective against simple erosion, but has limited effects in environments where corrosion is involved. Relaxation of wear conditions such as by surface studs is effective for both wear and corrosion wear phenomena. However, since the structure becomes complicated, the cost of the protector increases and the maintenance becomes complicated.

  With regard to increasing the wall thickness as a measure for prolonging the service life, castings can be easily increased in thickness and cost reduced, but there are cases where welding is difficult due to the material. In addition, the welding work at the site itself may be difficult, and it is desired that the welding work at the site is small from the viewpoint of maintainability. For example, when the entire surface of the heat transfer tube is protected by a protector, the number of welding points is increased and the work load is increased, leading to deterioration in installation / exchange workability. In particular, when it is necessary to protect the entire circumference of the heat transfer tube, the number of protectors increases, so a complicated protector not only increases costs but also decreases work efficiency. In addition, the workability of the thick protector is also reduced from the viewpoint of increasing the weight. Further, when a fitting structure is formed by combining thick protectors, a fluid medium enters between the protector and the heat transfer tube during operation, and there is a risk that excessive stress is generated during cooling and the protector breaks.

  It is effective to raise the temperature of the protector from the viewpoint of wear resistance. However, if a gap is provided between the protector and the heat transfer tube, the fluidized medium will enter the expanded gap during operation and shrink at the time of stoppage. Stresses occur and risks such as breakage and deformation of the protector occur. On the other hand, from the viewpoint of corrosion resistance, it has been proposed to lower the protector surface temperature, and no appropriate means has been found for appropriate conditions in which both corrosion and wear are involved.

  The present invention has been made for these problems, and avoids complicated structures, lowers initial cost, considers maintainability such as installation and replacement, reduces the risk of cracking and deformation, and corrosive wear. An object of the present invention is to provide a heat transfer tube of a fluidized bed boiler provided with a protector having sufficient durability in the environment.

In order to achieve the above-described object, the present inventors have conducted research on means for prolonging the life of the protector, and the research process will be described below.
Thickening is an effective means for extending the life of the protector while avoiding the complexity of the structure, and casting is the best means for producing the structure of the protector at a low cost. In order to avoid welding, the test was conducted using a heat transfer tube in which a thick protector and a fixing jig were fitted and fixed in a structure. However, the fluid medium entered the gap formed between the water pipe, the protector, and the fixing jig, and excessive stress was generated at the time of thermal contraction, resulting in frequent trouble that the protector was broken. Therefore, cracks were prevented by reducing the generated stress by making the fixing jig as small as possible. Also, by reducing the size of the fixture, the weight was reduced and the workability on site was improved.

On the other hand, the problem with thin protectors is durability. In the prior art, it has been proposed to increase the surface temperature from the viewpoint of wear resistance, and it has been proposed to decrease the temperature from the viewpoint of corrosion resistance.
In response to this contradiction, the present inventors have used SUS310 and SCH13 as protectors for one year on actual machines, and found that SUS310 causes severe thinning, although SUS310 is superior in corrosion resistance in terms of material. It was. SUS310 was a thin plate and was in close contact with the heat transfer tube, but SCH13, which was a casting, was inferior in adhesion and thick, and was operated in a situation where SUS310 was several hundred degrees lower when compared with the surface temperature. In other words, it has been found that raising the metal temperature is effective in suppressing thinning in a corrosive wear environment. Based on this knowledge, it discovered that the surface temperature of a thin protector can be raised by providing a heat insulation layer between a thin protector and a water pipe, and thickness reduction can be suppressed. In order to prevent damage to the thin protector due to stress, it is desirable to prevent the fluid medium from entering between the thin protector and the water pipe.

The present invention is completed by the above knowledge and tests based thereon, and provides the following means for protecting the entire circumference of the heat transfer tube in a corrosive wear environment.
A heat transfer tube of a fluidized bed boiler according to the present invention is a heat transfer tube used in a fluidized bed of a fluidized bed boiler, wherein the heat transfer tube is provided on the outer peripheral side of the water tube and a water tube through which a fluid flows, and protects the water tube. A thin-wall protector for casting and a thick-wall protector made of casting, a heat insulating layer provided between the water tube and the thin-wall protector, and a fixing jig, and fixing the fixing jig to the thick-wall protector, The thin protector provided on the outer peripheral side of the water pipe is pressed by a fixing jig. The thickness of the thick protector is 10 mm to 50 mm, and the thickness of the thin protector is 2 mm to 6 mm.

In a preferred aspect of the present invention, the fixing jig is fitted to the thick protector and fixed with a structure.
In a preferred aspect of the present invention, the fitting structure includes a guide groove provided on one of the fixing jig and the thick protector, and a protrusion provided on the other of the fixing jig and the thick protector. It is characterized by comprising.
A preferred embodiment of the present invention is characterized by having a structure for preventing a fluid medium from entering the heat insulating layer.

In a preferred aspect of the present invention, the thin protector has a double structure, and the heat insulating layer is provided between the thin protectors.
In a preferred aspect of the present invention, the heat insulating layer is made of heat insulating paper.
In a preferred aspect of the present invention, the fixing jig is made of a casting.
In a preferred aspect of the present invention, the area of the thin protector covered by the fixing jig is 50% or less of the area of the outer peripheral surface of the thin protector.

In a preferred aspect of the present invention, the thin protector is provided with fins.
The fluidized bed boiler of the present invention is a fluidized bed boiler that burns fuel in a fluidized bed and collects combustion heat with a heat transfer tube, wherein the heat transfer tube is the heat transfer tube.
In a preferred aspect of the present invention, the fluidized bed boiler includes a combustion chamber for burning fuel, and a heat recovery chamber in which an in-layer heat transfer tube is disposed to recover combustion heat, and the fluidized air in the heat recovery chamber The fluidized medium is an internal circulating fluidized bed boiler that circulates between the combustion chamber and the heat recovery chamber with an air amount of u ₀ / u _mf = 2.0 to 4.0.

  The present invention minimizes welding and minimizes damage by reducing wear and damage due to corrosion and wear by making castings that can produce thick-walled products at a low cost. It is possible to provide a heat transfer tube of a fluidized bed boiler equipped with a protector.

FIG. 1 is a schematic cross-sectional view showing an embodiment of a fluidized bed boiler provided with a heat transfer tube according to the present invention. FIG. 2 is a perspective view of a heat transfer tube according to the present invention. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is an exploded perspective view showing an assembly procedure of the heat transfer tube shown in FIGS. 2 and 3.

Hereinafter, an embodiment of a heat transfer tube of a fluidized bed boiler according to the present invention will be described with reference to FIGS. 1 to 4. 1 to 4, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.
FIG. 1 is a schematic cross-sectional view showing an embodiment of a fluidized bed boiler provided with a heat transfer tube according to the present invention. As shown in FIG. 1, the fluidized bed boiler 11 includes a furnace body 12 having a substantially rectangular tube shape, and the inside of the furnace body 12 is a single combustion chamber 14 in the center by a pair of left and right partition walls 13 and 13. And two heat recovery chambers 15 on both sides. In the combustion chamber 14, a fluidized bed 20 that thermally reacts fuel such as waste and RDF is formed, and the fluidized bed 20 is supported by a hearth bottom plate 30. The hearth bottom plate 30 installed in the furnace body 12 has a mountain shape in which the center is high and gradually lowers toward both side edges. A large number of diffuser nozzles for ejecting fluidized air as fluidized gas into the furnace are disposed on the bottom floor plate 30. A fluidized bed 23 is formed in each heat recovery chamber 15, and the fluidized bed 23 is supported by a hearth bottom plate 31. A diffuser nozzle for ejecting fluidized air as fluidized gas into the furnace is disposed on the hearth bottom plate 31.

  As shown in FIG. 1, four air boxes 32, 32, 33, and 33 are formed below the mountain-shaped hearth bottom plate 30, and these air boxes 32, 32, 33, and 33 are formed from outside the furnace. Fluidized air is supplied. By adjusting the opening of a control valve (not shown) to adjust the flow rate of air supplied to the air boxes 32, 32, 33, 33, an air diffuser nozzle above the two air boxes 32, 32 in the central portion. From the above, the fluidized air is ejected so as to give a substantially small fluidization speed, and the air diffuser nozzles above the two air boxes 33 on both sides are given a substantially large fluidization speed. Fluidized air is jetted out. As a result, a moving bed 21 in which the fluid medium moves from the upper side to the lower side at a relatively slow speed is formed above the center portion of the hearth bottom plate 30, and the fluid medium flows from the lower side above both sides of the hearth bottom plate 30. A fluidized bed 22 moving upward is formed. Accordingly, the fluidized medium moves from the moving bed 21 to the fluidized bed 22 at the lower part of the fluidized bed 20, and the fluidized medium moves from the fluidized bed 22 to the moving bed 21 at the upper part of the fluidized bed 20. A circulation flow in which the fluid medium circulates between the left and right is formed. The inclined portion of each partition wall 13 functions as a deflector that makes it easier for the rising fluid medium to reverse to the inside of the furnace body 12.

In the internal circulating fluidized bed boiler 11 configured as shown in FIG. 1, fuel is supplied to the moving bed 21 from an inlet (not shown). At this time, the amount of fluidized air supplied to the moving bed 21 is adjusted so as to be smaller than the amount of fluidized air supplied to the fluidized bed 22 by adjusting the opening of the control valve. In the present embodiment, the amount of fluidized air supplied to the moving bed 21 is 2 to ₃ u ₀ / u _mf , and the amount of fluidized air supplied to the fluidized bed 22 is 4 to ₆ u ₀ / u _mf . Here, u ₀ is the superficial velocity, and u _mf is the minimum fluidized superficial velocity.

  The fuel supplied to the moving bed 21 is swallowed by the fluid medium and moves downward together with the fluid medium. At this time, the fuel is thermally decomposed by the heat of the fluidized medium, and combustible gas is generated from the combustible component in the fuel, resulting in a brittle thermal decomposition residue. The pyrolysis residue typically includes incombustible material and unburned material (char) that has become brittle by thermal decomposition. When the pyrolysis residue produced in the moving bed 21 reaches the hearth bottom plate 30 together with the fluidized medium, it goes toward the fluidized bed 22 along the inclined hearth bottom plate 30. The pyrolysis residue that has reached the fluidized bed 22 comes into contact with the fluid medium that flows violently, the unburned material is peeled off from the incombustible material, and the unburned material left after the unburned material is peeled off together with some of the fluidized medium. It is discharged from the discharge port 17.

  On the other hand, the unburned material peeled from the incombustible material moves upward together with the fluid medium that flows as fluidized air is supplied. At this time, the unburned material is combusted by the supplied fluidized air, generates a combustion gas while heating the fluidized medium, and becomes fine unburned material and ash particles that are conveyed to the gas. . A part of the high-temperature fluid medium that reaches the top of the fluidized bed 22 flows into the moving bed 21. The fluid medium is raised in the fluidized bed 22 to a temperature at which the fuel can be thermally decomposed appropriately when it flows into the moving bed 21. The fluid medium flowing into the moving bed 21 receives the supplied fuel again and repeats the thermal reaction in the moving bed 21 and the fluidized bed 22 described above. The temperature of the moving bed 21 is maintained at 700 to 900 ° C, and the temperature of the fluidized bed 22 is maintained at 700 to 900 ° C.

A part of the high-temperature fluid medium above the fluidized bed 22 enters the heat recovery chamber 15 beyond the upper part of the partition wall 13. A large number of screen water tubes 2 are installed between the combustion chamber 14 and the heat recovery chamber 15 in a substantially vertical direction so as to surround the heat recovery chamber 15. It enters the recovery chamber 15. The fluid medium that has entered the heat recovery chamber 15 forms a fluidized bed 23 that moves downward from above. The hearth bottom plate 31 of the heat recovery chamber 15 is inclined downward from the inner wall side of the furnace body 12 toward the combustion chamber side, and an opening 18 is provided in the lower portion of the heat recovery chamber 15. The fluid medium that has entered sinks while forming the fluidized bed 23 and circulates from the opening 18 to the combustion chamber 14. The temperature of the fluid medium that enters the heat recovery chamber 15 is 700 to 900 ° C., but the in-layer heat transfer pipe 16 is disposed in the fluidized bed 23 of the heat recovery chamber 15, The fluid (can water) in the in-layer heat transfer tube 16 recovers heat from the flowing medium by exchanging heat with the flowing medium. By controlling the amount of fluidized air ejected from the diffuser nozzle of the hearth bottom plate 31 of the fluidized bed 23 to 2-4 u ₀ / u _mf , the heat recovery amount of the in-layer heat transfer tube 16 can be controlled. . The fluidized medium circulated to the combustion chamber 14 joins the fluidized bed 22 and rises together with the fluidized medium in the fluidized bed 22, and a part of the fluidized medium enters the heat recovery chamber 15 again, and the inside of the above-described in-layer heat transfer tube 16. Repeat heat exchange with the fluid.

An embodiment in which the heat transfer tube according to the present invention is applied to the screen water tube 2 of the fluidized bed boiler 11 shown in FIG. 1 will be described with reference to FIGS.
2 is a perspective view of a heat transfer tube according to the present invention, and FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is an exploded perspective view showing a procedure for assembling the heat transfer tubes shown in FIGS. 2 and 3.
As shown in FIGS. 2 and 3, the heat transfer tube 1 is provided so as to surround a cylindrical water tube (screen water tube) 2 through which a fluid (canned water) flows and a part of the circumferential surface of the water tube 2. The U-shaped thick protector 3, the U-shaped thin protector 4 provided to surround the circumferential surface of the water pipe 2 on the opposite side of the thick protector 3, and the thin protector 4 are pressed from above. And a fixing jig 5 having a U-shaped cross section that is fitted and fixed to the thick-wall protector 3. That is, the entire circumference of the water pipe 2 is surrounded and protected by the thick protector 3 and the thin protector 4. The thickness of the thick protector 3 is 10 mm to 50 mm, and the thickness of the thin protector 4 is 2 mm to 6 mm.

  The screen water pipe 2 that divides the combustion chamber 14 and the heat recovery chamber 15 becomes severe on the combustion chamber side in both corrosive environment and wear conditions. The more severe combustion chamber side was protected with a thick protector 3 made of casting. On the other hand, the relatively mild heat recovery chamber side is protected by the thin protector 4, and the fixing jig 5 has a minimum size necessary for holding the thin protector 4. Thereby, the stress which generate | occur | produces in the fitting part of the thick protector 3 and the fixing jig 5 can be suppressed, and the crack of the thick protector 3 can be prevented. In addition, the overall weight is reduced and the maintainability is improved. From the viewpoint of improving work efficiency, the size of one fixing jig 5 is reduced in order to make it lighter, and the fixing jig 5 has a two-stage structure as a whole.

  In the present invention, the thick protector 3 and the fixing jig 5 are stainless steel castings such as SCS13, SCS14, SCS18, SCH13, SCH21, and SCH22 or heat-resistant cast steel, and the thin protector 4 is stainless steel such as SUS304, SUS310, and SUS316. And steel such as SS400. In the present embodiment, in consideration of manufacturing cost and ease of attachment, the thick protector 3 is manufactured from a casting, and the thin protector 4 is manufactured from a plate material of SUS310 stainless steel.

  The present inventors have found that when the thin protector 4 exposed to the atmosphere in the fluidized bed and the screen water pipe 2 are in direct contact, the metal surface temperature is lowered and corrosion wear reduction is promoted in the exposed portion. For this reason, an insulating layer is provided between the thin protector 4 and the screen water pipe 2 to prevent excessive cooling. The heat insulating layer provided between the thin protector 4 and the water pipe 2 is formed of a heat insulating material, a heat insulating castable or the like, and prevents the flowing medium from flowing into the heat insulating layer. In this case, the shape of the heat insulating material is not particularly limited, and may be, for example, paper, fiber, powder, or bulk. In this embodiment, the heat insulation paper 6 is employ | adopted as a heat insulation layer. When the heat insulating layer is an air layer, a cap formed of cast metal or steel may be provided above the thick protector 3 or the thin protector 4 in order to prevent the flowing medium from flowing into the heat insulating layer. The thickness of the heat insulating layer is desirably 0.25 mm or more. The thin protector 4 may have a double structure, and a heat insulating layer may be provided between the thin protector having the double structure and the thin protector. In order to increase the surface temperature of the thin protector 4, fins may be provided on the thin protector.

  In the present invention, the thick protector 3 and the fixing jig 5 are fitted and fixed with a fitting structure, so that they can be easily attached without welding. A guide groove is provided in one of the thick protector 3 or the fixing jig 5, and the protruding portion of the fixing jig 5 or the thick protector 3 is fitted into the guide groove. However, since thermal stress is generated in the portion where the guide groove is provided, it is preferable to attach the guide groove to the thick protector side having a large area from the viewpoint of preventing cracking. In this embodiment, the thick protector 3 having a U-shaped cross section is provided with guide grooves 3g, 3g on the inner surfaces of both side portions, and the fixing jig 5 having a U-shaped cross section is a protrusion on both side portions on the opening side. 5a, 5a. The fixing jig 5 is fixed to the thick protector 3 by fitting the projections 5 a and 5 a of the fixing jig 5 into the guide grooves 3 g and 3 g of the thick protector 3. Note that a cut hole may be provided in the fixing jig 5 and the thick protector 3 and fixed with bolts and nuts.

  If the fixing jig 5 is large, the entire body including the protectors 3 and 4 becomes heavy and difficult to handle, and the thermal stress generated in the guide groove portion increases, so a smaller one is desirable. The area of the portion covered with 4 is 50% or less, preferably 30% or less of the area of the outer peripheral surface of the thin protector 4. The area of the portion where the thin protector 4 is covered by the fixing jig 5 is 20% or more of the area of the outer peripheral surface of the thin protector 4. The fixing jig 5 may be one stage or a plurality of stages. During maintenance, only necessary parts such as thin protectors or heat insulation layers can be replaced.

  Next, a procedure for attaching the protector to the screen water pipe 2 will be described with reference to FIG. As shown in FIG. 4, the heat insulating paper 6 is first wound around the screen water tube 2, and then the thick protector 3 and the thin protector 4 are combined, and finally fixed to the guide groove 3 g provided in the thick protector 3. The fixing jig 5 is attached to the thick protector 3 by fitting the protrusion 5 a of the tool 5.

When the structure of the present invention shown in FIGS. 2 to 4 and a fixing jig having the same size as the thick protector is used instead of the thin protector (Comparative Example 1), a heat insulating layer is provided between the thin protector and the water pipe. When there was not (Comparative Example 2), it evaluated by the actual machine. A summary of the verification results is shown in Table 1.
As shown in Table 1, although there was no problem with the product of the present invention and Comparative Example 2, cracks were seen in Comparative Example 1. As for the thickness reduction, the thickness reduction rate was small for the thick protector and the fixing jig, and a sufficient life was expected. On the other hand, with regard to the thin protector, in Comparative Example 2 in which the heat insulating layer was not provided, severe thinning was observed in a portion exposed to an environment without a fixing jig. In the product of the present invention, it was confirmed that the protector had a sufficient thickness and had a sufficient life as a protector. As for maintainability, Comparative Example 2 is the easiest, and the product of the present invention increases the man-hour for the work of attaching the heat insulating paper as compared with Comparative Example 2, but it is not a great effort. On the other hand, in Comparative Example 1, since the heavy thick protector and the fixing jig were combined, the workability was poor, and further, it took time to remove the fluid medium that was bitten during operation.
As described above, the product of the present invention was comprehensively judged and proved to be excellent in durability and maintainability.

  Although the embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention may be implemented in various different forms within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 Heat transfer tube 2 Screen water tube 3 Thick protector 3g Guide groove 4 Thin protector 5 Fixing jig 5a Protrusion part 6 Heat insulation paper 11 Fluidized bed boiler 12 Furnace main body 13 Partition wall 14 Combustion chamber 15 Heat recovery chamber 16 In-layer heat transfer tube 17 Noncombustible Material outlet 18 Opening 20 Fluidized bed 21 Moving bed 22 Fluidized bed 23 Fluidized bed 30 Furnace bottom plate 31 Furnace bottom plate 32 Air box 33 Air box

Claims (11)

In heat transfer tubes used in the fluidized bed of a fluidized bed boiler,
The heat transfer pipe is provided between a water pipe through which a fluid flows, a thin protector provided on the outer peripheral side of the water pipe to protect the water pipe and a cast-type thick protector, and the water pipe and the thin protector. It consists of a heat insulation layer and a fixing jig,
A heat transfer tube of a fluidized bed boiler, wherein the fixing jig is fixed to the thick protector, and the thin protector provided on the outer peripheral side of the water tube is pressed by the fixing jig.   The heat transfer tube of a fluidized bed boiler according to claim 1, wherein the fixing jig is fitted to the thick protector and fixed with a structure.   The fitting structure includes a guide groove provided on one of the fixing jig and the thick protector, and a protrusion provided on the other of the fixing jig and the thick protector. A heat transfer tube of a fluidized bed boiler according to claim 2.   The heat transfer tube of a fluidized bed boiler according to any one of claims 1 to 3, further comprising a structure for preventing fluid medium from entering the heat insulating layer.   The heat transfer tube of a fluidized bed boiler according to any one of claims 1 to 4, wherein the thin protector has a double structure, and the heat insulating layer is provided between the thin protectors.   The heat transfer tube of a fluidized bed boiler according to any one of claims 1 to 5, wherein the heat insulating layer is made of heat insulating paper.   The heat transfer tube of a fluidized bed boiler according to any one of claims 1 to 6, wherein the fixing jig is made of a casting.   8. The flow according to claim 1, wherein an area of the portion of the thin protector covered by the fixing jig is 50% or less of an area of an outer peripheral surface of the thin protector. Layer boiler heat transfer tube.   The heat transfer tube of a fluidized bed boiler according to any one of claims 1 to 8, wherein fins are provided on the thin protector. In a fluidized bed boiler that burns fuel in a fluidized bed and collects the heat of combustion with a heat transfer tube,
The fluidized bed boiler, wherein the heat transfer tube is the heat transfer tube according to any one of claims 1 to 9. The fluidized bed boiler includes a combustion chamber for burning fuel, and a heat recovery chamber in which an in-layer heat transfer tube is arranged to recover combustion heat, and the amount of fluidized air in the heat recovery chamber is u ₀ / u. _The fluidized bed boiler according to claim 10, wherein the fluidized medium is an internal circulation fluidized bed boiler that circulates between the combustion chamber and the heat recovery chamber with _mf = 2.0 to 4.0.

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