JP6691834B2 - Heat transfer tube of fluidized bed boiler - Google Patents

Description

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

  In recent years, utilization of energy resources has been demanded from the viewpoint of responding to soaring prices of fossil fuels and global warming problems. Among these, the importance of power generation systems that burn fuel such as waste, RDF, and biomass that play a role in thermal recycling is increasing. In this power generation system, there is a system in which a heat transfer tube recovers thermal energy generated when a fuel such as waste, RDF, or biomass is burned using a fluidized bed boiler. In this method, when a fuel such as waste, RDF, or biomass is burned in the fluidized bed boiler, there is a case where a chloride caused by the fuel causes a severe corrosive environment. The wear due to the fluidized medium causes a significant wall thinning of the protector of the heat transfer tube, shortens the life of the protector itself, and requires frequent maintenance.

As measures for extending the life of the protector, there are known a method of improving wear resistance by forming a surface hardened layer, and a method of providing a stud on the surface of the protector to reduce the collision speed of particles as disclosed in Patent Document 1. Has been.
Further, in Patent Document 2, by providing a gap between the protector and the heat transfer tube, the protector surface temperature is increased, an oxide film is formed on the surface, and wear 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 generated due to a temperature rise, wear resistance is improved, and the amount of wall thinning is reduced.

On the other hand, Patent Document 4 proposes a method in which an aluminum sprayed layer is provided between a protector and a heat transfer tube to improve the adhesion by melting aluminum and lower the surface temperature of the protector to suppress corrosion.
Providing a sufficient thickness reduction amount on the protector is also one of the measures for ensuring the life. Since plate materials and pipe materials have a limited thickness, and it is costly to process thick plates, casting is generally used.

JP, 2004-19965, A JP, 5-18504, A 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 extending the life of the protector, a special treatment is required, which leads to an increase in the cost of the protector. It is effective against simple erosion, but its effect is limited in environments where corrosion is involved. Relaxation of wear conditions by means of surface studs is effective for both phenomena of wear and corrosive wear. However, since the structure becomes complicated, the cost of the protector increases and the maintenance becomes complicated.

  Regarding thickening as a measure to prolong the service life, castings are easy to thicken and are low cost, but welding may be difficult due to the material. In addition, there are cases where the welding work itself is difficult, and from the viewpoint of maintainability, it is desirable that the welding work on site be small. For example, when the entire surface of the heat transfer tube is protected by a protector, the number of welding points increases and the work load increases, which leads to deterioration of workability in installation and replacement. In particular, when it is necessary to protect the entire circumference of the heat transfer tube, the number of protectors increases, and thus a complicated protector causes not only an increase in cost but also a reduction in work efficiency. Moreover, the workability of the thick-wall protector is also reduced in terms of weight. Furthermore, in the case where a thick protector is combined to form a fitting structure, there is a risk that the fluid medium enters between the protector and the heat transfer tube during operation, excessive stress is generated during cooling, and the protector is cracked.

  From the viewpoint of wear resistance, it is effective to raise the temperature of the protector.However, if a space is provided between the protector and the heat transfer tube, the fluid medium will enter the expanded space during operation and will contract when stopped, resulting in excessive temperature. Such stresses will cause the risk of cracking or deformation of the protector. On the other hand, from the viewpoint of corrosion resistance, it has been proposed to lower the protector surface temperature, and no suitable means has been found for an appropriate condition in which both corrosion and wear are involved.

  The present invention has been made to solve these problems, reduces the initial cost by avoiding a complicated structure, and considers maintainability such as installation and replacement, and 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 equipped with a protector having sufficient durability in the environment.

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive research on means for extending the life of the protector, and the research process will be described below.
The thickening is an effective means for extending the life of the protector while avoiding the complication of the structure, and the best means for manufacturing the structure of the protector at low cost is casting. The test was performed using a heat transfer tube in which a thick protector and a fixing jig were fitted together and fixed to avoid welding. However, the fluidized medium intruded into the gap formed between the water pipe, the protector and the fixing jig, and excessive stress was generated during thermal contraction, and the protector was often broken. Therefore, cracks were prevented by making the fixing jig as small as possible to reduce the generated stress. Also, the smaller fixture reduces the weight and improves workability on site.

On the other hand, the problem with thin wall protectors is durability. In the prior art, it has been proposed to increase the surface temperature from the viewpoint of wear resistance, and to reduce the temperature from the viewpoint of corrosion resistance.
In response to this contradiction, the inventors of the present invention have used SUS310 and SCH13 as protectors for one year in an actual machine, and found that SUS310 causes severe metal thinning even though 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 is a casting, had poor adhesion and was thick, and SUS310 was operated in a situation where the surface temperature was several hundred degrees lower. In other words, it has been found that increasing the temperature of the metal is effective for suppressing the metal loss in the corrosive wear environment. Based on this finding, it was found that by providing a heat insulating layer between the thin wall protector and the water pipe, the surface temperature of the thin wall protector can be increased and the thinning can be suppressed. In order to prevent the thin protector from being damaged by 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 the test based on the above knowledge, and provides the following means for protecting the entire circumference of the heat transfer tube in a corrosive wear environment.
One mode of the heat transfer tube of the fluidized bed boiler of the present invention is a heat transfer tube used in a fluidized bed of a fluidized bed boiler, wherein the heat transfer tube is a water tube through which a fluid flows, and the water tube provided on the outer peripheral side of the water tube. The protector is made of a thin wall protector and a thick wall protector made of casting, a heat insulating layer provided between the water pipe and the thin wall protector, and a fixing jig. The thickness of the thick wall protector is the thin wall protector. It is thicker than the thickness of the protector, the fixing jig is fixed to the thick protector, the fixing jig presses the thin protector provided on the outer peripheral side of the water pipe, and the thin protector has a double structure. The heat insulating layer is provided between the thin protectors .
One mode of the heat transfer tube of the fluidized bed boiler of the present invention is a heat transfer tube used in a fluidized bed of a fluidized bed boiler, wherein the heat transfer tube is a water tube through which a fluid flows, and the water tube provided on the outer peripheral side of the water tube. The protector is made of a thin wall protector and a thick wall protector made of casting, a heat insulating layer provided between the water pipe and the thin wall protector, and a fixing jig. The thickness of the thick wall protector is the thin wall protector. The thickness is larger than the thickness of the protector, the fixing jig is fixed to the thick protector, and the fixing jig presses the thin protector provided on the outer peripheral side of the water pipe. It is characterized by
One mode of the heat transfer tube of the fluidized bed boiler of the present invention is a heat transfer tube used in a fluidized bed of a fluidized bed boiler, wherein the heat transfer tube is a water tube through which a fluid flows, and the water tube provided on the outer peripheral side of the water tube. A thin protector for protecting and a thick protector made of casting, a heat insulating layer provided between the water pipe and the thin protector, and a fixing jig, and the thickness of the thick protector is the thin wall. The thickness is larger than the thickness of the protector, the fixing jig is fixed to the thick protector, the fixing jig presses the thin protector provided on the outer peripheral side of the water pipe, and the thin protector is provided with fins. A heat transfer tube for a fluidized bed boiler, which is characterized in that
A preferred embodiment of the present invention, the thickness of the thick protector is 10 mm to 50 mm, the thickness of the thin protector is characterized by a 2 mm to 6 mm.

A preferred aspect of the present invention is characterized in that the fixing jig is fixed to the thick protector by a fitting 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 consisting of.
A preferred aspect 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 fixing jig is made of 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.

A fluidized bed boiler of the present invention is a fluidized bed boiler in which fuel is burned in a fluidized bed and combustion heat is recovered by 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 arranged to recover combustion heat, and the fluidized air in the heat recovery chamber is It is characterized in that an air amount is set to u ₀ / u _mf = 2.0 to 4.0 and the fluid medium is an internal circulation fluidized bed boiler which circulates in the combustion chamber and the heat recovery chamber.

  According to the present invention, welding work is minimized, so that installation / replacement work is easy, cost is reduced by manufacturing a casting that can manufacture thick products at low cost, and long life with reduced damage due to corrosive wear It is possible to provide a heat transfer tube of a fluidized bed boiler equipped with the protector.

FIG. 1 is a schematic 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 the heat transfer tube according to the present invention. FIG. 3 is a sectional view taken along line III-III in FIG. FIG. 4 is an exploded perspective view showing an assembling procedure of the heat transfer tubes 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 designated by the same reference numerals, and duplicate description will be omitted.
FIG. 1 is a schematic 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, a fluidized bed boiler 11 includes a furnace body 12 having a substantially rectangular tube shape. Inside the furnace body 12, a pair of left and right partition walls 13, 13 is provided in a central combustion chamber 14 And two heat recovery chambers 15, 15 on both sides. A fluidized bed 20 for thermally reacting fuel such as waste and RDF is formed in the combustion chamber 14, 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 that is high in the center and gradually lowers toward both side edges. The hearth bottom plate 30 is provided with a large number of diffuser nozzles for ejecting fluidizing air as fluidizing gas into the furnace. 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. The hearth bottom plate 31 is provided with an air diffuser nozzle for ejecting fluidizing air as fluidizing gas into the furnace.

  As shown in FIG. 1, four air boxes 32, 32, 33, 33 are formed below a mountain-shaped hearth bottom plate 30, and these air boxes 32, 32, 33, 33 are provided from outside the furnace. Fluidized air is supplied. By adjusting the opening of a control valve (not shown) to adjust the flow rate of the air supplied to the air boxes 32, 32, 33, 33, the air diffuser nozzle above the two air boxes 32, 32 in the central portion. Fluidizing air is jetted so as to give a substantially low fluidizing speed, and the diffuser nozzles above the two air boxes 33, 33 on both sides provide a substantially high fluidizing speed. The fluidized air is jetted to. As a result, a moving layer 21 is formed above the central portion of the hearth bottom plate 30 so that the fluidized medium moves from the upper side to the lower side at a relatively slow speed. A fluidized bed 22 moving upward is formed. Therefore, in the lower part of the fluidized bed 20, the fluidized medium moves from the moving bed 21 to the fluidized bed 22, and in the upper part of the fluidized bed 20, the fluidized media moves from the fluidized bed 22 to the moving bed 21, thereby forming the moving bed 21 and the fluidized bed 22. A circulation flow in which the fluid medium circulates is formed on the left and right. The inclined portion of each partition wall 13 functions as a deflector that makes it easier for the ascending fluidized medium to invert 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 input port (not shown). At this time, the opening of the control valve is adjusted so that the amount of fluidizing air supplied to the moving bed 21 is smaller than the amount of fluidizing air supplied to the fluidized bed 22. In this embodiment 2~3u ₀ / _{u mf} air amount of the fluidizing air supplied to the moving bed 21, and the air quantity of the fluidizing air supplied to the fluidized bed 22 and 4~6u ₀ / _{u mf.} Where 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 fluidized medium and moves downward together with the fluidized medium. At this time, the fuel is thermally decomposed by the heat of the fluidized medium, combustible gas is generated from combustible components in the fuel, and becomes a brittle thermal decomposition residue. The pyrolysis residue typically contains incombustibles and unburned matter (char) that has become brittle due to pyrolysis. When the pyrolysis residue generated in the moving bed 21 reaches the hearth bottom plate 30 together with the fluidized medium, it goes to the fluidized bed 22 along the inclined hearth bottom plate 30. The pyrolysis residue reaching the fluidized bed 22 comes into contact with the fluid medium that flows violently, the unburned substances are separated from the incombustible substances, and the incombustible substances left after the unburned substances are separated are incombustible substances together with a part of the flowing medium. It is discharged from the discharge port 17.

  On the other hand, the unburned material separated from the incombustible material moves upward together with the fluidizing medium that flows as the fluidizing air is supplied. At this time, the unburned matter is combusted by the supplied fluidized air, generates combustion gas while heating the fluidized medium, and becomes fine unburned matter and ash particles that are transported to the gas. .. A part of the high-temperature fluidized medium reaching the upper part of the fluidized bed 22 flows into the moving bed 21. The fluidized medium is raised in the fluidized bed 22 to a temperature at which thermal decomposition of the fuel can be appropriately performed when it flows into the moving bed 21. The fluidized medium that has flowed into the moving bed 21 receives the fuel supplied 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.

Further, a part of the high temperature fluidized medium in the upper part of the fluidized bed 22 enters the heat recovery chamber 15 over the upper part of the partition wall 13. A large number of screen water pipes 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, and the fluid medium passes between these screen water pipes 2 to generate heat. It is designed to enter the recovery chamber 15. The fluidized 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 part of the heat recovery chamber 15 to The fluid medium that entered enters the combustion chamber 14 through the opening 18 while settling while forming the fluidized bed 23. The temperature of the fluidized medium that enters the heat recovery chamber 15 is 700 to 900 ° C., but the in-layer heat transfer tube 16 is arranged in the fluidized bed 23 of the heat recovery chamber 15, and While moving downward, it contacts the in-layer heat transfer tube 16, and the fluid (can water) in the in-layer heat transfer tube 16 recovers heat from the fluid medium by exchanging heat with the fluid medium. By controlling the air amount of the fluidizing air is jetted from the air diffuser nozzle hearth bottom plate 31 of the fluidized bed 23 in 2~4u 0 _/ u _mf, it is possible to control the heat recovery amount of intra-layer heat transfer tube 16 .. The fluidized medium circulated to the combustion chamber 14 merges with the fluidized bed 22 and rises together with the fluidized medium in the fluidized bed 22. 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 to 4.
2 is a perspective view of a heat transfer tube according to the present invention, and FIG. 3 is a sectional view taken along line III-III of FIG. FIG. 4 is an exploded perspective view showing an assembling procedure of 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 in which a fluid (canned water) flows and a part of a circumferential surface of the water tube 2. The thick protector 3 having a U-shaped cross section, the thin protector 4 having a U-shaped cross section provided on the opposite side of the thick protector 3 so as to surround the circumferential surface of the water pipe 2, and the thin protector 4 are pressed from above. And a fixing jig 5 having a U-shaped cross section which is fixed to the thick protector 3 by fitting. 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 thick protector 3 has a thickness of 10 mm to 50 mm, and the thin protector 4 has a thickness of 2 mm to 6 mm.

  The screen water pipe 2 that separates the combustion chamber 14 and the heat recovery chamber 15 becomes strict on the combustion chamber side in both corrosive environment and wear conditions. The more severe side of the combustion chamber was protected by a thick protector 3 made of cast metal. On the other hand, the heat recovery chamber side under relatively mild conditions is protected by the thin protector 4, and the fixing jig 5 has a minimum size necessary for pressing the thin protector 4. Thus, the stress generated at the fitting portion between the thick protector 3 and the fixing jig 5 can be suppressed, and the thick protector 3 can be prevented from cracking. At the same time, the overall weight is reduced and the maintainability is improved. Further, from the viewpoint of improving workability 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, SCH22 or heat resistant cast steel, and the thin protector 4 is stainless steel such as SUS304, SUS310, SUS316. And steel such as SS400. In the present embodiment, the thick protector 3 is made of a casting and the thin protector 4 is made of a plate material of SUS310 stainless steel in consideration of manufacturing cost and ease of mounting.

  The present inventors have discovered that when the thin protector 4 exposed to the atmosphere in the fluidized bed and the screen water pipe 2 directly contact with each other, the metal surface temperature decreases and the corrosion wear thinning is promoted in the portion exposed to the atmosphere. Therefore, a heat 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, heat insulating castable, or the like to prevent 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, a paper shape, a fiber shape, a powder shape, or a bulk shape. In this embodiment, the heat insulating paper 6 is used as the heat insulating layer. When the heat insulating layer is an air layer, a shade made of cast metal or steel may be provided above the thick protector 3 and 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 preferably 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. The thin protector may be provided with fins in order to increase the surface temperature of the thin protector 4.

  In the present invention, the thick protector 3 and the fixing jig 5 are fixed to each other 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 and the fixing jig 5, and the protrusion 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 crack prevention. In the present 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 has a protruding portion on both side portions on the opening side. 5a, 5a. The fixing jig 5 is fixed to the thick protector 3 by fitting the protrusions 5 a, 5 a of the fixing jig 5 into the guide grooves 3 g, 3 g of the thick protector 3. The fixing jig 5 and the thick protector 3 may be provided with cut holes 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 becomes large. Therefore, it is preferable that the fixing jig 5 is small. The area of the portion where 4 is covered 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 have a single stage or a plurality of stages. Only the necessary parts such as a thin wall protector or heat insulating layer can be replaced during maintenance.

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

When a fixing jig having the same size as the thick wall protector is used in place of the structure of the present invention shown in FIGS. 2 to 4 and the thin wall protector (Comparative Example 1), a heat insulating layer is provided between the thin wall protector and the water pipe. When it did not exist (Comparative Example 2), it was evaluated side by side with an actual machine. Table 1 shows a summary of the verification results.
As shown in Table 1, there was no problem in cracking in the product of the present invention and Comparative Example 2, but in Comparative Example 1, cracking was observed. Regarding the metal thinning, the thick wall protector and the fixing jig had a small metal thinning rate, and a sufficient life was expected. On the other hand, regarding the thin protector, in Comparative Example 2 in which the heat insulating layer was not provided, a severe thinning was observed in the portion exposed to the environment without the fixing jig. Further, in the product of the present invention, it was confirmed that the protector had a sufficient wall thickness and had a sufficient life as a protector. Regarding the maintainability, Comparative Example 2 is the easiest, and the product of the present invention has more man-hours as compared with Comparative Example 2 by the work of attaching the heat insulating paper, but this is not a big labor. On the other hand, in Comparative Example 1, since a heavy protector with a heavy weight and a fixing jig were combined, the workability was poor, and the removal of the fluid medium caught during operation was troublesome.
As described above, the product of the present invention was comprehensively judged and proved to be excellent in durability and maintainability.

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

1 Heat Transfer Tube 2 Screen Water Tube 3 Thick Wall Protector 3g Guide Groove 4 Thin Wall Protector 5 Fixing Jig 5a Projection 6 Heat Insulation Paper 11 Fluidized Bed Boiler 12 Furnace Main Body 13 Partition Wall 14 Combustion Chamber 15 Heat Recovery Chamber 16 Intralayer Heat Transfer Tube 17 Material discharge port 18 Opening part 20 Fluidized bed 21 Moving bed 22 Fluidized bed 23 Fluidized bed 30 Hearth bottom plate 31 Hearth bottom plate 32 Air box 33 Air box

Claims (11)

In the heat transfer tube used in the fluidized bed of the fluidized bed boiler,
The heat transfer tube is provided between a water tube through which a fluid flows, a thin wall protector provided on the outer peripheral side of the water tube to protect the water tube and a thick wall protector made of casting, and between the water tube and the thin wall protector. It consists of a heat insulating layer and a fixing jig,
The thickness of the thick protector is greater than the thickness of the thin protector,
The fixing jig is fixed to the thick protector, and the fixing jig presses the thin protector provided on the outer peripheral side of the water pipe ,
A heat transfer tube for a fluidized bed boiler , wherein the thin wall protector has a double structure, and the heat insulating layer is provided between the thin wall protectors . In the heat transfer tube used in the fluidized bed of the fluidized bed boiler,
The heat transfer tube is provided between a water tube through which a fluid flows, a thin wall protector provided on the outer peripheral side of the water tube to protect the water tube and a thick wall protector made of casting, and between the water tube and the thin wall protector. It consists of a heat insulating layer and a fixing jig,
The thickness of the thick protector is greater than the thickness of the thin protector,
The fixing jig is fixed to the thick protector, and the fixing jig presses the thin protector provided on the outer peripheral side of the water pipe,
The thermal insulating layer, the heat transfer tube of to that flow Doso boiler characterized in that it consists of heat-insulating paper. In the heat transfer tube used in the fluidized bed of the fluidized bed boiler,
The heat transfer tube is provided between a water tube through which a fluid flows, a thin wall protector provided on the outer peripheral side of the water tube to protect the water tube and a thick wall protector made of casting, and between the water tube and the thin wall protector. It consists of a heat insulating layer and a fixing jig,
The thickness of the thick protector is greater than the thickness of the thin protector,
The fixing jig is fixed to the thick protector, and the fixing jig presses the thin protector provided on the outer peripheral side of the water pipe,
Heat transfer tube of to that flow Doso boiler characterized in that a fin on the thin protector.   The heat transfer tube of the fluidized bed boiler according to any one of claims 1 to 3, wherein the thick protector has a thickness of 10 mm to 50 mm, and the thin protector has a thickness of 2 mm to 6 mm. .. The heat transfer tube for a fluidized bed boiler according to any one of claims 1 to 4, wherein the fixing jig is fixed to the thick wall protector by a fitting structure. The fitting structure includes a guide groove provided in one of the fixing jig and the thick protector, and a protrusion provided in the other of the fixing jig and the thick protector. The heat transfer tube of the fluidized bed boiler according to claim 5 . The heat transfer tube for a fluidized bed boiler according to any one of claims 1 to 6 , further comprising a structure for preventing a fluidized medium from entering the heat insulating layer. The heat transfer tube for a fluidized bed boiler according to any one of claims 1 to 7 , wherein the fixing jig is made of casting. The area of the portion of the thin protector covered by fixture has a flow according to any one of claims 1 to 8, characterized in that said more than 50% of the area of the outer peripheral surface of the thin protector Heat transfer tube for multi-layer boiler. In a fluidized bed boiler that burns fuel in a fluidized bed and recovers combustion heat with a heat transfer tube,
A 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 disposed 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 circulating fluidized bed boiler that circulates in the combustion chamber and the heat recovery chamber with _mf = 2.0 to 4.0.

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