WO2013121965A1

WO2013121965A1 - In-bed heat transfer tube for fluidized bed boiler

Info

Publication number: WO2013121965A1
Application number: PCT/JP2013/052843
Authority: WO
Inventors: 吉田　裕; 阪本　英之; 恭久本田
Original assignee: 荏原環境プラント株式会社
Priority date: 2012-02-13
Filing date: 2013-02-07
Publication date: 2013-08-22
Also published as: EP2821697A4; EP2821697B1; KR101998448B1; JP6085570B2; CN104136842A; KR20140127861A; EP2821697A1; JPWO2013121965A1; CN104136842B

Abstract

The present invention pertains to an in-bed heat transfer tube installed in the fluidized bed of a fluidized bed boiler that burns fuels such as refuse-derived fuel (RDF) and waste with a high calorific value, including biomass and plastic, and recovers combustion heat. This in-bed heat transfer tube (5) for a fluidized bed boiler is installed in the fluidized bed (3) of the fluidized bed boiler (1), and the in-bed heat transfer tube (5) consists of: a water tube (6) through which a fluid flows; a protector (8) for protecting the water tube (6), said protector (8) being disposed on the outer circumferential side of the water tube (6); and a filler layer (7) disposed between the water tube (6) and the protector (8).

Description

Heat transfer tube in fluidized bed boiler

The present invention relates to an in-bed heat transfer pipe installed in a fluidized bed of a fluidized bed boiler that burns fuel such as biomass and plastic, high calorific value RDF (waste solidified fuel) and waste, and recovers combustion heat. .

BACKGROUND ART In recent years, utilization of energy resources is required from the viewpoint of rising prices of fossil fuels and responses to global warming problems and the like. Among these, RDF, which plays a role in thermal recycling, and the power generation system that burns waste are increasing in importance. In this power generation system, there is a system in which thermal energy generated when RDF and waste are burned using a fluidized bed boiler is recovered by a heat transfer pipe in a bed. In this method, when fuel such as RDF or waste is burned in the fluidized bed boiler, some chlorine is transferred to the fluid medium (fluid sand) because the RDF and waste contain chlorine. It adheres to the heat transfer tube and causes molten salt corrosion of the in-layer heat transfer tube. The in-bed heat transfer tube suffers from the molten salt corrosion in addition to the wear because it is worn by the intense flow of the flow medium (flowing sand), and there is a problem that the amount of thinning of the heat transfer tube is large.

In the past, measures to reduce the thickness of the heat transfer tube installed in the fluidized bed were carried out by thermal spraying of a self-fluxing alloy (Ni-based) or overlaying a stainless steel material, but sufficient effects can be obtained. It was not done.
Japanese Patent Application Laid-Open No. 5-187789 (Patent Document 1) discloses a wear resistant structure of a heat transfer tube in which the thickness reduction of the heat transfer tube is reduced by covering the heat transfer tube with a stud and a refractory. However, in the structure disclosed in Patent Document 1, covering the heat transfer tube with a refractory lowers the heat transfer coefficient and requires a large heat transfer area. In addition, the diameter of the heat transfer tube and the refractory increases, which makes it difficult to arrange the heat transfer tube.
On the other hand, in JP-A-7-217801 (Patent Document 2), a method of attaching a protector and a method of overlaying or thermal spraying are proposed as a method of preventing thickness reduction due to wear of a heat transfer tube. And the problem that heat transfer is significantly impeded, and that there was a problem that build-up and thermal spraying were expensive (see paragraph [0004]), and pointed out the problems with conventional thinning measures. It has been proposed that the heat transfer tube itself be made of high chromium steel or stainless steel excellent in wear resistance. However, although the method described in Patent Document 2 can prevent thickness reduction due to wear, there is a problem that the durability is inferior in an environment directly subjected to molten salt corrosion simultaneously with wear.

Japanese Patent Application Laid-Open No. 5-187789 Japanese Patent Application Laid-Open No. 7-217801

As described above, in the conventional fluidized bed boiler, various measures have been taken, such as providing a buildup or protector against the thickness reduction due to the wear of the heat transfer tube in the bed or molten salt corrosion. The heat transfer tube as a whole is focused on enhancing heat transfer and rapidly transferring the heat of the fluidizing medium to the can water flowing in the heat transfer tube.

The present inventors obtained the following knowledge in the process of performing continuous operation over a long period of time using various in-bed heat transfer tubes in a fluidized bed boiler. That is, when chlorine is contained in the fuel like biomass-based RDF and wastes, when part of the chlorine is transferred to the fluid medium (fluid sand) after the fuel is burned, the chlorine in the fluid medium becomes the fluid bed. When operated at a temperature of 700.degree. C. to 850.degree. C., it produces eutectic salts with alkali metals (Na, K etc.) contained in the fuel. The condensation temperature at which this eutectic salt condenses in the molten state is, for example, 650 to 700.degree. Therefore, if the surface temperature of the in-layer heat transfer pipe is higher than the condensation temperature, condensation of the eutectic salt on the surface of the in-layer heat transfer pipe can be suppressed, and the reduction in thickness due to molten salt corrosion can be reduced. On the other hand, in the case of the in-layer heat transfer tube whose durability has been enhanced by providing a protector made of a stainless steel such as SUS310S on the outer peripheral side of the water tube, the present inventors have found that the surface temperature of the in-layer heat transfer tube It has been discovered that corrosion loss due to corrosion wear can be reduced at lower temperatures and above a predetermined temperature (e.g., 450 <0> C).

The inventors of the present invention based on the above findings, in order to adjust the surface temperature of the protector to a temperature range where molten salt corrosion is suppressed and thickness reduction is difficult, (1) heat transfer between the fluidized bed and the protector It was conceived that it was effective to increase the rate and (2) to lower the heat transfer coefficient between the protector and the water pipe, and the invention was achieved.

That is, according to the present invention, although the heat transfer coefficient between the protector and the water pipe is lowered, the heat transfer pipe is reduced in the amount of thickness reduction by suppressing the molten salt corrosion of the heat transfer pipe while securing the economical heat transfer amount It is an object of the present invention to provide an in-bed heat transfer pipe of a fluidized bed boiler excellent in durability.

In order to achieve the above object, the in-bed heat transfer pipe of the fluidized bed boiler of the present invention is an in-bed heat transfer pipe disposed in the fluidized bed of the fluidized bed boiler, wherein the in-bed heat transfer pipe A water pipe, a protector provided on the outer peripheral side of the water pipe for protecting the water pipe, and a packed bed provided between the water pipe and the protector are characterized.
According to the invention, the heat of the flowing medium is transferred to the water pipe via the protector and the packed bed, and the fluid in the water pipe is heated. The heat transfer coefficient between the protector and the water pipe can be lowered by setting the filler layer interposed between the water pipe and the protector to a low thermal conductivity. Therefore, the temperature difference between the protector surface and the water tube surface can be increased. Thereby, the molten salt corrosion of the heat transfer pipe can be suppressed, the amount of thickness reduction can be small, and the in-layer heat transfer pipe excellent in durability can be obtained.

According to a preferred embodiment of the present invention, the surface temperature of the protector is maintained at 450 to 650.degree.

According to a preferred embodiment of the present invention, the packed bed is formed by packing a solid particle filler.
According to the present invention, since the air gap of the packed bed is made of air having a low thermal conductivity, it is possible to lower the heat transfer coefficient between the protector and the water tube. In this case, the material, shape, and thickness of the filler of the filling layer are set such that the surface temperature of the protector becomes 450 to 650 ° C., preferably 480 to 620 ° C., because the heat transfer coefficient becomes inefficient if lowered too much. Select as appropriate.

According to a preferred aspect of the present invention, the packed bed is characterized in that the packing ratio of the solid particle filler is 0.5 or more and 0.9 or less. Here, the filling rate is a value obtained by dividing the volume [m ³ ] occupied by the filling by the volume [m ³ ] of the space between the outer surface of the water pipe and the inner surface of the protector.
According to the present invention, when the protector is thermally expanded, a gap formed between the surface (upper surface) of the packed bed and the inner surface of the protector by gravity settling of the filler by adopting the filling rate in the above range. That is, the thickness of the air layer can be reduced to ensure heat transfer to the water pipe.

According to a preferred embodiment of the present invention, the packed bed has a thermal conductivity of 0.4 to 1.4 W / mK.
According to the present invention, since the thermal conductivity of the packed bed is 0.4 to 1.4 W / mK, the heat transfer coefficient between the protector and the water pipe can be lowered. Therefore, the temperature difference between the surface of the protector and the surface of the water tube can be increased, and the surface temperature of the protector can be maintained at a high temperature of 450 to 650.degree.
According to a preferred embodiment of the present invention, the thickness of the filler layer is 2 to 4 mm.

According to a preferred aspect of the present invention, the protector is made of stainless steel.
According to a preferred embodiment of the present invention, the stainless steel is SUS304 or SUS316 or SUS310S.
According to the present invention, by forming the protector from stainless steel such as SUS304, SUS316, or SUS310S, it is possible to suppress thickness reduction due to molten salt corrosion.

According to a preferred aspect of the present invention, the protector is provided with fins on the outer surface.
According to the present invention, since the fins with excellent heat exchange efficiency are provided on the outer surface of the protector, the heat transfer coefficient from the fluid medium to the protector can be enhanced. Therefore, economical heat transfer can be secured.
According to a preferred aspect of the present invention, the fin is a spiral fin.
According to a preferred aspect of the present invention, the fin is a pin-shaped fin.

The fluidized bed boiler according to the present invention is a fluidized bed boiler in which fuel is burned in a fluidized bed and combustion heat is recovered by an in-bed heat transfer pipe, wherein the in-bed heat transfer pipe is any one of claims 1 to 11. The in-bed heat transfer tube according to the present invention is characterized in that the temperature of the fluidized bed is controlled to 700 to 900 ° C.
According to the present invention, the temperature of the fluidized bed is controlled to 700 to 900 ° C. by adjusting the amount of air of the fluidizing air supplied to the fluidized bed according to the fuel calories and the like. Then, the heat of the fluidized bed maintained at 700 to 900 ° C. is transferred to the water pipe through the protector and the packed bed, and the saturated water in the water pipe is heated. The heat transfer coefficient between the protector and the water pipe can be reduced by the packed bed interposed between the water pipe and the protector. Therefore, the temperature difference between the surface of the protector and the surface of the water tube can be increased, and the surface temperature of the protector can be maintained at a high temperature of 450 to 650.degree.

According to a preferred aspect of the present invention, the air amount of the fluidizing air of the portion provided with the in-bed heat transfer pipe of the fluidized bed is u ₀ / u _mf = 2.0 to 4.0.
According to the present invention, by setting the fluidization condition of the fluidized bed (moving bed) in which the in-bed heat transfer pipe is arranged to u ₀ / u _mf = 2.0 to 4.0, Fluidization can be activated to increase the heat transfer coefficient from the fluid medium to the protector. As a result, even in the case of an in-layer heat transfer tube in which the packed bed is interposed between the protector and the water tube, the overall heat transfer coefficient and the total heat passing amount can be maintained to be similar to the in-layer heat transfer tube. Therefore, economical heat transfer can be secured.

According to a preferred aspect of the present invention, the fluidized bed boiler includes a combustion chamber for burning a fuel, and a heat recovery chamber in which the heat transfer pipe in the bed is disposed to recover combustion heat, and the flow of the heat recovery chamber The internal circulation fluidized bed boiler is characterized in that the air amount of the liquefaction air is set to u ₀ / u _mf = 2.0 to 4.0 and the fluidizing medium circulates between the combustion chamber and the heat recovery chamber.
According to the present invention, since the combustion chamber which burns the fuel and the heat recovery chamber which recovers heat are separated, troubles such as incombustibles in the fuel entwining in the in-layer heat transfer pipe do not occur. In addition, by controlling the air amount of the fluidizing air in the heat recovery chamber, it is possible to control the heat recovery amount of the in-layer heat transfer pipe.

The present invention has the following effects.
(1) The heat transfer coefficient between the protector and the water pipe can be lowered by forming the in-layer heat transfer pipe with the water pipe, the filler and the protector, and installing the filling layer interposed between the water pipe and the protector. Therefore, the temperature difference between the surface of the protector and the surface of the water tube can be increased, and the surface temperature of the protector can be maintained at a high temperature of 450 to 650.degree. As a result, it is possible to provide an in-layer heat transfer pipe with reduced durability and reduced amount of thickness reduction while suppressing molten salt corrosion of the heat transfer pipe.
(2) By forming the protector from stainless steel such as SUS304, SUS316, or SUS310S, it is possible to suppress thickness reduction due to molten salt corrosion.
(3) Fluidization of the fluidized bed (moving bed) is _{achieved by} setting the fluidization conditions of the fluidized bed (moving bed) in which the heat transfer pipes in the bed are arranged to u ₀ / u _mf = 2.0 to 4.0. Actively increases the heat transfer coefficient from the fluid medium to the protector. As a result, even in the case of an in-layer heat transfer tube in which the packed bed is interposed between the protector and the water tube, the overall heat transfer coefficient and the total heat passing amount can be maintained to be similar to the in-layer heat transfer tube. Therefore, economical heat transfer can be secured.
(4) Since the fin which was excellent in heat exchange efficiency was provided in the outer surface of a protector, the heat transfer coefficient from a fluid medium to a protector can be raised. Therefore, economical heat transfer can be secured.

FIG. 1 is a schematic cross-sectional view showing an embodiment of a fluidized bed boiler provided with an in-bed heat transfer tube according to the present invention. FIG. 2 is a schematic sectional view showing another embodiment of the fluidized bed boiler provided with the in-bed heat transfer tube according to the present invention. FIG. 3 is a schematic cross-sectional view of the in-layer heat transfer tube. FIG. 4A is a diagram showing experimental results of a conventional in-layer heat transfer pipe in which a stainless steel is built on a water pipe. FIG. 4B is a diagram showing experimental results of the in-layer heat transfer tube of the present invention. FIG. 5 is a front view of the in-layer heat transfer tube. FIG. 6 is a longitudinal sectional view of the in-layer heat transfer tube. FIG. 7A is a view showing another form of the in-layer heat transfer tube, and FIG. 7A is a front view of the in-layer heat transfer tube. FIG. 7B is a view showing another form of the in-layer heat transfer tube, and FIG. 7B is a longitudinal sectional view of the in-layer heat transfer tube. FIG. 8A is a view showing still another form of the in-layer heat transfer tube, and FIG. 8A is a front view of the in-layer heat transfer tube. FIG. 8B is a view showing still another form of the in-layer heat transfer tube, and FIG. 8B is a longitudinal sectional view of the in-layer heat transfer tube.

Hereinafter, an embodiment of the in-bed heat transfer tube of the fluidized bed boiler according to the present invention will be described with reference to FIGS. 1 to 8. In FIG. 1 to FIG. 8, the same or corresponding components are given the same reference numerals, and duplicate explanations are omitted.
FIG. 1 is a schematic cross-sectional view showing an embodiment of a fluidized bed boiler provided with an in-bed heat transfer tube according to the present invention. As shown in FIG. 1, the fluidized bed boiler 1 comprises a furnace main body 2 having a substantially cylindrical shape or a substantially square cylinder shape, a fluidized bed 3 for burning waste or fuel such as RDF, and a hearth bottom plate supporting the fluidized bed 3 In the fluidized bed 3, an in-bed heat transfer pipe 5 is installed. The fluidized bed 3 is filled with a fluidized medium, which is a fluidized sand such as silica sand, so as to fill the intra-bed heat transfer pipe 5. The hearth bottom plate 4 is formed with a large number of aeration nozzles for injecting fluidizing air as fluidizing gas into the furnace.

In the fluidized bed boiler 1 configured as shown in FIG. 1, fuel is supplied to the fluidized bed 3 from an inlet (not shown). At this time, fluidizing air having a uniform amount of air is ejected from the aeration nozzle of the hearth bottom plate 4 over the whole of the fluid bed 3, and in the fluid bed 3, the fluid medium is up and down. It becomes a so-called bubbling fluidized bed that flows actively. The fuel supplied into the furnace is thermally decomposed and burned in the fluidized bed 3, and the heat of combustion heats the fluidized medium to a high temperature, and the temperature of the fluidized bed 3 is maintained at 700 to 900.degree. The temperature of the fluidized bed 3 is controlled by adjusting the amount of fluidization air. The fluid medium that has become high temperature comes into contact with the in-bed heat transfer tube 5, and the fluid (can water) in the in-bed heat transfer tube 5 exchanges heat with the fluid medium to recover heat from the fluid medium.

FIG. 2 is a schematic sectional view showing another embodiment of the fluidized bed boiler provided with the in-bed heat transfer tube according to the present invention. As shown in FIG. 2, the fluidized bed boiler 11 is provided with a furnace main body 12 having a substantially square cylindrical shape, and the inside of the furnace main body 12 has one combustion chamber 14 in the center by a pair of left and

right partition walls

13 and 13. And two

heat recovery chambers

15, 15 at both sides. In the combustion chamber 14, a fluidized bed 20 for thermally reacting waste and fuel such as RDF is formed, and the fluidized bed 20 is supported by the hearth bottom plate 30. The hearth bottom plate 30 installed in the furnace body 12 has a mountain shape which is high at the center and gradually lowered toward the side edges. The hearth bottom plate 30 is provided with a number of aeration nozzles for injecting 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 the hearth bottom plate 31. The hearth bottom plate 31 is provided with an aeration nozzle for injecting fluidizing air as fluidizing gas into the furnace.

As shown in FIG. 2, four

air boxes

32, 32, 33, 33 are formed below the mountain-shaped heart floor bottom plate 30, and these

air boxes

32, 32, 33, 33 are formed from the outside of the furnace. Fluidized air is provided. Aeration nozzles above the two

central air boxes

32, 32 by adjusting the opening of a control valve (not shown) to adjust the air flow rate supplied to the

air boxes

32, 32, 33, 33 From there, the fluidizing air is jetted so as to give a substantially small fluidization velocity, and from the aeration nozzles above the two

air boxes

33, 33 on both sides, to give a substantially high fluidization velocity Erupt the fluidizing air. As a result, a moving bed 21 is formed above the central portion of the hearth floor plate 30 to move the flowing medium downward at a relatively slow speed from above, and the flowing medium flows from above below both sides of the hearth floor plate 30. A fluidized bed 22 moving upward is formed. Therefore, the moving medium moves from the moving bed 21 to the fluidized bed 22 in the lower part of the fluidized bed 20 and the moving medium from the fluidized bed 22 to the moving bed 21 in the upper part of the fluidized bed 20. A circulating flow is formed on the left and right through which the fluid medium circulates. The inclined portion of each partition wall 13 functions as a deflector which makes it easy for the rising fluid medium to be inverted to the inside of the furnace body 12.

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

The fuel supplied to the moving bed 21 is swallowed by the fluid medium and moves downward with the fluid medium. At this time, thermal decomposition of the fuel is performed by the heat of the fluid medium, and combustible gas is generated from the combustibles in the fuel to become brittle thermal decomposition residue. The pyrolysis residue typically contains incombustible matter and unburned matter (char) which has become brittle due to the pyrolysis. The pyrolysis residue generated in the moving bed 21 travels to the fluidized bed 22 along the inclined bottom floor plate 30 when it reaches the bottom floor plate 30 together with the fluid medium. The thermal decomposition residue that has reached the fluidized bed 22 comes in contact with the strongly flowing fluid medium, and the unburned matter is exfoliated from the incombustible matter, and the incombustible matter remaining after the unburned matter is exfoliated together with some fluid medium It is discharged from the discharge port 17.

On the other hand, the unburned material separated from the incombustible material moves upward with the flowing fluid medium as the fluidizing air is supplied. At this time, the unburned matter is combusted by the supplied fluidizing air, generates combustion gas while heating the fluid medium, and becomes fine unburned matter and ash particles which are carried to the gas. . A part of the high temperature fluid medium reaching the upper part of the fluid bed 22 flows into the moving bed 21. The fluidized medium is raised in the fluidized bed 22 to a temperature at which the fuel can be properly pyrolyzed when it flows to the moving bed 21. The fluid medium having flowed into the moving bed 21 receives the supplied fuel again, and repeats the thermal reaction in the moving bed 21 and the fluid 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 fluid medium in the upper part of the fluidized bed 22 passes the upper part of the partition wall 13 and enters the heat recovery chamber 15. The fluid medium that has entered the heat recovery chamber 15 forms a fluid bed 23 moving 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, and an opening 18 is provided in the lower portion of the heat recovery chamber 15. The inflowing fluid medium settles to form the fluid bed 23, and circulates from the opening 18 to the combustion chamber 14. The temperature of the fluidizing medium entering the heat recovery chamber 15 is 700 to 900 ° C., but the in-bed heat transfer pipe 5 is disposed in the fluidizing bed 23 of the heat recovery chamber 15. While moving downward, the heat transfer pipe 5 comes into contact with the in-bed heat transfer pipe 5, and the fluid (can water) in the in-bed heat transfer pipe 5 exchanges heat with the flowing medium to recover heat from the flowing medium. The amount of heat recovery of the heat transfer tube 5 can be controlled by controlling the amount of air of fluidizing air ejected from the aeration nozzle of the heart floor bottom plate 31 of the fluidized bed 23 to 2 to 4 u ₀ / u _mf. . The fluid medium circulated to the combustion chamber 14 joins the fluid bed 22 and ascends with the fluid medium of the fluid bed 22, and a part of the fluid medium enters the heat recovery chamber 15 again. Repeat heat exchange with the fluid.

Next, the in-bed heat transfer pipe 5 used in the bubbling fluidized bed boiler shown in FIG. 1 and the internal circulating fluidized bed boiler shown in FIG. 2 will be described.
FIG. 3 is a schematic cross-sectional view of the in-layer heat transfer tube 5. As shown in FIG. 3, the in-layer heat transfer pipe 5 includes a water pipe 6 through which a fluid (canned water) flows, a protector 8 provided on the outer peripheral side of the water pipe 6 to protect the water pipe 6, a water pipe 6 and a protector 8 And a filler layer 7 provided between the two. The water pipe 6 is composed of a steel pipe for a boiler or heat exchanger having a thickness of 4 to 8 mm, for example, STB 410S, and a fluid (water can flow) flowing in the water pipe 6 is saturated water of 2 MPa to 12 MPa. The filler layer 7 is filled with a filler of solid particles such as sand, stainless steel powder, magnesium oxide, iron, alumina and the like, and is formed in a cylindrical shape having a thickness of 2 to 4 mm. The thermal conductivity of the packed bed is, for example, 0.4 to 1.4 W / mK as calculated by the calculation shown in “Reaction of powder, Nikkan Kogyo Shimbun, p. 54-57”. As long as the thermal conductivity of the packed bed can be used by being packed within this range, fillers of types and materials other than those listed above can be used.
The filler is preferably particulate. The filling rate of the filler is preferably 0.5 or more and 0.9 or less, and more preferably 0.6 or more and 0.8 or less. Here, the filling factor at the time of filling the filler in the space between the water pipe 6 and the protector 8 is according to the following equation.
Packing ratio [-] = volume occupied by filling [m ³ ] / volume of void in water tube outer surface and protector inner surface [m ³ ]
A gap formed between the surface (upper surface) of the packed bed and the inner surface of the protector by gravity settling of the filler when the protector is thermally expanded by employing the filling factor of the filler in the above range, that is, the air layer Can be reduced in thickness to ensure heat transfer to the water pipe.

The protector 8 is made of stainless steel such as SUS304, SUS316, or SUS310S, which is excellent in wear resistance and corrosion resistance, and is formed in a cylindrical shape having a thickness of 3 to 6 mm. The protector 8 may be formed by cylindrically forming a stainless steel plate, or a stainless steel pipe may be used.

In the present invention, (1) the material of the protector 8 is stainless steel such as SUS304, SUS316, SUS310S, and (2) a thermal conductivity of 0.4 to 1.4 W / mK between the water pipe 6 and the protector 8 The formed packed bed 7 is formed to a predetermined thickness, that is, a thickness of 2 to 4 mm, and (3) the fluidized bed 3 (see FIG. 1) in which the in-layer heat transfer tube 5 is installed It is configured to maintain the temperature of 700.degree.-900.degree. C.).
In the present invention, the surface temperature of the protector 8 is maintained at a high temperature of 450 to 650 ° C., preferably 480 to 620 ° C., by adopting the configurations of (1) to (3).

FIGS. 4A and 4B are diagrams showing a comparison result of a conventional in-layer heat transfer pipe in which a stainless steel is accumulated on a water pipe, and the in-layer heat transfer pipe of the present invention having the configurations of (1) to (4) above. is there.
The conventional heat transfer pipe in the layer uses a 3 mm buildup made of stainless steel for surface modification of the water pipe. As shown in FIG. 4A, assuming that the temperature of the fluidized bed is 800 ° C. and the temperature of the can water is 300 ° C., and the amount of air in the fluidizing air supplied to the fluidized bed is u ₀ / u _mf = 1.5, the flow heat transfer rate from the medium (sand) into the cladding is 210W ^{/ m} 2 K, the surface temperature of the deposition is 320 ° C., overall heat transfer coefficient in the cladding inner surface reference (water pipe outer surface reference) is 222W ^{/ m} 2 K, The total heat passing rate is 111118 W / m ² . The temperature difference between the surface temperature of the overlay and the surface temperature of the water pipe is 20 ° C.

On the other hand, the in-layer heat transfer tube of the present invention uses a 2 mm thick filler layer filled with magnesium oxide particles and a 3 mm thick protector made of SUS310S on the outer periphery of the water tube. There is. As shown in FIG. 4B, assuming that the temperature of the fluidized bed is 800 ° C. and the temperature of the can water is 300 ° C., and the amount of air of fluidizing air supplied to the fluidized bed is u ₀ / u _mf = 2.5, the flow The heat conductivity from the medium (sand) to the protector is 390 W / m ² K, the thermal conductivity of the protector is 16.2 W / m K, the thermal conductivity of the packed bed filled with magnesium oxide (thickness 2 mm) is 1.3 W / mK, surface temperature of the protector 513 ° C., the surface temperature of the packed bed 491 ° C., overall heat transfer coefficient (protector inner surface reference) is 246W ^{/ m} 2 K, total heat transfer amount is 122957W / ^{m 2.} The temperature difference between the surface temperature of the protector and the surface temperature of the packed bed is 22 ° C., and the temperature difference between the surface temperature of the packed bed and the surface temperature of the water pipe is 191 ° C.
Incidentally, the overall heat transfer coefficient is 263 W / m ² K and the total heat passing amount is 131,586 W / m ^{2 on the} basis of the outer surface of the water pipe.

As shown in the comparison results of FIGS. 4A and 4B, an in-layer heat transfer pipe provided with a filler and a protector on the outer periphery of the water pipe is used, and the air amount of fluidizing air is u ₀ / u _mf = 2.5 or more. (1) Increase the heat transfer coefficient between the fluid medium (sand) and the protector by activating the fluidization of the fluid bed (moving bed) and appropriately selecting the thickness and thermal conductivity of the packed bed, ) The heat transfer rate between the protector and the water tube can be reduced. Thereby, the protector surface temperature can be set to 450 ° C. or higher while maintaining the overall heat transfer coefficient and the total heat passing amount to the same level as the in-layer heat transfer pipe of the buildup.

As is apparent from FIGS. 4A and 4B, the conventional in-bed heat transfer tube is designed to quickly transfer the heat of the fluid medium in the fluidized bed to the fluid (water can) in the heat transfer tube. On the other hand, in the in-layer heat transfer tube 5 of the present invention, by providing the filling layer 7 between the water tube 6 and the protector 8, the surface temperature of the protector 8 is raised by gentle heat transfer. Thereby, it is possible to suppress the molten salt corrosion of the heat transfer tube, reduce the thickness reduction of the heat transfer tube, and extend the heat transfer tube life.

Next, an example of the detailed structure of the in-bed heat transfer pipe used in the fluidized bed boiler shown in FIGS. 1 and 2 will be described with reference to FIGS. 5 and 6.
FIG. 5 is a front view of the in-layer heat transfer tube 5. FIG. 5 shows a heat transfer tube group in which two in-layer heat transfer tubes 5 are arranged in parallel. The in-layer heat transfer pipe 5 has a straight pipe portion and a bent pipe portion, and a large number of fins 9 are installed in the straight pipe portion.
FIG. 6 is a longitudinal sectional view of the in-layer heat transfer tube 5. Similar to the in-layer heat transfer tube 5 shown in FIG. 3, the in-layer heat transfer tube 5 shown in FIG. 6 includes fins 9 on the outer periphery of the protector 8 in addition to the water tube 6, the filling layer 7 and the protector 8. Have. The fins 9 are made of stainless steel plates such as SUS304, SUS316, and SUS310S, and are fixed to the upper and lower sides of the outer peripheral surface of the protector 8.

7A and 7B are views showing another form of the in-layer heat transfer tube 5, FIG. 7A is a front view of the in-layer heat transfer tube 5, and FIG. 7B is a longitudinal sectional view of the in-layer heat transfer tube 5. In the in-layer heat transfer tube 5 shown in FIGS. 7A and 7B, spiral fins 34 are attached to the entire outer periphery of the protector 8 by welding. The spiral shape facilitates the attachment of the fins and significantly reduces the construction period.

8A and 8B show still another embodiment of the in-layer heat transfer tube 5, FIG. 8A is a front view of the in-layer heat transfer tube 5, and FIG. 8B is a longitudinal cross-sectional view of the in-layer heat transfer tube 5. . The in-layer heat transfer pipe 5 shown in FIGS. 8A and 8B is attached to the outer periphery of the protector 8 as a pin-shaped fin 35 instead of a plate (blade). A large number of pin-shaped fins 35 are welded to the outer peripheral surface of the protector 8.

As shown in FIGS. 5, 6, 7A, 7B and 8A, 8B, the heat transfer coefficient per inner surface of the protector can be increased by the protector 8 including the

fins

9, 34 or 35. . Therefore, the heat transfer coefficient between the fluid medium (sand) and the protector can be increased, and the surface temperature of the protector 8 can be increased to 450 ° C. or higher. The water pipe 6, the packed bed 7 and the protector 8 in the in-layer heat transfer pipe 5 shown in FIGS. 5, 7A, 7B and 8A, 8B have the same configuration as the in-layer heat transfer pipe shown in FIG.

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

The present invention relates to an in-bed heat transfer pipe installed in a fluidized bed of a fluidized bed boiler that burns fuel such as biomass and plastic, high calorific value RDF (waste solidified fuel) and waste, and recovers combustion heat. It is available.

Reference Signs List 1 fluidized bed boiler 2 furnace main body 3 fluidized bed 4 hearth bottom plate 5 in-layer heat transfer pipe 6 water pipe 7 packed bed 8

protector

9, 34, 35 fins 11 fluidized bed boiler 12 furnace main body 13 partition wall 14 combustion chamber 15 heat recovery chamber 17 Incombustible material discharge port 18 opening 20 fluid bed 21 moving bed 22 fluid bed 23 fluid bed 30 heart floor bottom plate 31 heart

floor bottom plate

32, 32, 33, 33 air box

Claims

In the in-bed heat transfer pipe disposed in the fluidized bed of the fluidized bed boiler,
The in-layer heat transfer pipe is composed of a water pipe through which the fluid flows, a protector provided on the outer peripheral side of the water pipe for protecting the water pipe, and a packed bed provided between the water pipe and the protector. An in-bed heat transfer tube of a fluidized bed boiler characterized in that
The in-bed heat transfer tube according to claim 1, wherein the surface temperature of the protector is maintained at 450 to 650 属 C.
The in-bed heat transfer tube according to claim 1, wherein the packed bed is formed by packing a solid particle filler.
The in-bed heat transfer pipe of a fluidized bed boiler according to claim 3, wherein the filling rate of the solid particle filling material is 0.5 or more and 0.9 or less.
The in-layer heat transfer tube according to claim 1, wherein the packed bed has a thermal conductivity of 0.4 to 1.4 W / mK.
The in-bed heat transfer tube according to claim 5, wherein the thickness of the packed bed is 2 to 4 mm.
The in-bed heat transfer tube according to claim 1, wherein the protector is made of stainless steel.
The in-layer heat transfer tube according to claim 7, wherein the stainless steel is SUS304 or SUS316 or SUS310S.
The in-bed heat transfer tube according to any one of claims 1 to 8, wherein the protector comprises fins on an outer surface.
The in-bed heat transfer tube according to claim 9, wherein the fin is a spiral fin.
The in-bed heat transfer tube according to claim 9, wherein the fins are pin-shaped fins.
In a fluidized bed boiler in which fuel is burned in a fluidized bed and heat of combustion is recovered by a heat transfer pipe in the bed,
The in-layer heat transfer pipe is the in-layer heat transfer pipe according to any one of claims 1 to 11,
A fluidized bed boiler characterized in that the temperature of the fluidized bed is controlled to 700 to 900 ° C.
The fluidized bed boiler according to claim 12, wherein an amount of air of fluidizing air in a portion provided with an in-bed heat transfer pipe of the fluidized bed is set to u 0 / u mf = 2.0 to 4.0.
The fluidized bed boiler includes a combustion chamber for burning fuel and a heat recovery chamber in which the heat transfer pipe in the layer is disposed to recover combustion heat, and the air amount of the fluidizing air of the heat recovery chamber is u 0 / The fluidized bed boiler according to claim 12, characterized in that it is an internal circulating fluidized bed boiler in which the flow medium circulates between the combustion chamber and the heat recovery chamber with u mf = 2.0 to 4.0.