JPH10281402A - Metal attachment to heating tube and heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the structure resistant to cracking under fatigue or creep even when thermal stress works on the weld between a heating tube and a metal attachment. SOLUTION: Relating to a metal attachment 2 in the prevention of mutual movement and contact of heating tubes 1, 1 provided side by side and constituting a heat exchanger and in the support of part of the dead load of the heating tubes 1, 1, the constitution is to obtain a set of metal attachments 2 with tapering parts for the heating tubes, the inclined sides 2b of the metal attachment 2 which adjoins the joint of the metal attachment 2 to the heating tube 1 making an angle θ of 45 deg. or less to the joint 2a of the heating tube 1, to obtain a heat exchanger using the metal attachment 2, and to obtain a boiler using this heat exchanger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube attached to a heat exchanger to prevent the heat transfer tubes from moving and contacting each other at a predetermined interval and to partially support the load of the heat transfer tubes. The present invention relates to a heat exchanger including a metal heat transfer tube group and a boiler having the heat exchanger.

[0002]

2. Description of the Related Art In a heat exchanger such as a boiler for thermal power generation, a large number of heat transfer tube groups are arranged to exchange heat between high-temperature combustion gas and steam or water. This heat transfer tube group is composed of several to several tens of heat transfer tube groups arranged side by side along the flow direction of the high-temperature combustion gas.

[0003] When the boiler is started or stopped, a difference in temperature distribution in the furnace and a non-uniform flow of the combustion gas causes a temperature difference among the heat transfer tubes. Occurs. Due to the temperature distribution of the heat transfer tube (group), the elongation of the heat transfer tube (group) becomes non-uniform as a whole,
This causes thermal deformation of the heat transfer tubes and greatly changes the positional relationship between the heat transfer tubes.

When the positional relationship between the heat transfer tubes deviates from a predetermined position, the heat transfer performance changes significantly. For this reason, as shown in FIG. 7, the metal fitting 2 is attached to the heat transfer tube 1 by welding or the like to prevent its movement. The metal deposit 2 also has an effect of supporting the weight of the heat transfer tube.
Further, the header 4 is connected to the plurality of heat transfer tubes 1, and the fluid inside the heat transfer tubes 1 can be collected in the header 4.

[0005] Figs. 8 and 9 show a typical method of attaching a plate-like attached hardware to a heat transfer tube. 8 (FIG. 8 (a) is a side view of the heat transfer tube portion, and FIG. 8 (b) is a view taken along the line AA in FIG. 8 (a)). The L-shaped plate-shaped metal member 2 is welded, and the metal member 2 having the same shape as the L-shaped plate-shaped metal member 2 is welded to the downstream side of the gas flow of the other heat transfer tube 1 with the welding metal 3. The L-shaped attachments 2 are engaged with each other, and a stopper 5 is welded to one of the heat transfer tubes 1 so that the engaged attachment 2 does not come off. With such a structure, the heat transfer tubes 1 and 1 are prevented from moving in the gas flow direction and the direction perpendicular to the gas flow, and the heat transfer tubes 1 and 1 are prevented from contacting each other.

FIG. 9 (FIG. 9A is a side view of the heat transfer tube, and FIG.
9B is a view taken along the line AA in FIG. 9A.
The metal fitting 6 having a U-shaped cross section is welded upstream with respect to the gas flow with the welding metal 3, and the same metal fitting 6 having the U-shaped cross section is formed on the downstream side of the gas flow of the other heat transfer tube 1. The deposited metal 6 is welded. At this time, the two metal fittings 6, 6 are arranged so as to overlap each other in the up-down direction, and the overlapping portion of the metal fittings 6 is provided with a projection 6a having a size that can be inserted into the U-shaped space of each other. Therefore, they are welded to the heat transfer tubes 1 and 1 in a state where they are inserted into the U-shaped space of the metal attachment 6 on the other side. With such a structure, the mutual movement and contact of the heat transfer tubes 1 and 1 can be prevented as in the case of FIG. 8, and a part of the weight of the heat transfer tube 1 can be supported by the metal deposit 6.

When the boiler is started or stopped, the heat transfer tube 1 is different from the deformation at the time of steady operation of the boiler described above.
That is, when the boiler is started, high-temperature steam starts to flow rapidly on the inner surface of the normal-temperature heat transfer tube 1, and when the boiler is stopped, the high-temperature steam flowing in the heat transfer tube 1 stops flowing rapidly. A sudden temperature change occurs in the heat transfer tube 1,
A large temperature difference occurs between the outer and inner surfaces of the heat transfer tube 1. For example, at the time of start-up, the outer surface of the heat transfer tube 1 is heated by the deposited metal 2 at the welded portion between the heat transfer tube 1 and the deposited metal 2, so that the temperature gradient in this portion becomes large and a large thermal stress is generated in the welded portion. .

When the heat transfer tube 1 is used for a superheater, the internal fluid temperature is about 1100 ° C. during a steady operation.
The heat transfer tube 1 is cooled by the internal fluid, but the deposited metal 2 is exposed to a high-temperature gas, so that a large temperature difference (temperature gradient) occurs between the heat transfer tube 1 and the deposited metal 2.
As a result, a large thermal stress is generated at the welded portion between the heat transfer tube 1 and the metal deposit 2.

[0009]

In the prior art described above, the heat stress generated in the welded portion at the time of starting / stopping the boiler or at the time of steady operation is reduced with respect to the structure in which the heat transfer tube 1 and the attached metal 2 are welded. Was not taken into account. Such a problem was found in a weld between the heat transfer tube 1 and the metal deposit 2 used in a boiler for thermal power generation, particularly a fluidized bed boiler. The object of the present invention is to solve the above-mentioned disadvantages of the prior art,
An object is to provide a structure in which fatigue cracks and creep cracks are unlikely to occur even when thermal stress acts on a weld between the heat transfer tube and the deposited metal. Further, an object of the present invention is to provide a heat transfer tube support metal which is less likely to generate fatigue cracks and creep cracks even when thermal stress accompanying repeated start / stop of the boiler or thermal stress during steady operation is applied. Is to provide a boiler.

[0010]

The above object of the present invention is attained by the following constitution. That is, to the heat exchanger tubes arranged side by side constituting the heat exchanger, to prevent the heat exchanger tubes from moving and contacting each other, and to adhere to the outer surface of the heat exchanger tubes to partially support the weight of the heat exchanger tubes, The heat transfer tube-attached metal member has a tapered portion in which an angle formed by a side portion of the metal member adjacent to the joint between the metal member and the heat transfer tube with respect to the joint portion of the heat transfer tube is 45 degrees or less. The height of the tapered portion of the side portion is set to be equal to or greater than the thickness of the side portion of the deposited piece, so that the height of the side portion of the deposited piece adjacent to the joint between the deposited piece and the heat transfer tube is equal to or greater than the thickness of the side portion. Can be eliminated. Further, the present invention includes a heat exchanger including a heat transfer tube group using the heat transfer tube-attached hardware, and a boiler using the heat exchanger. The heat exchanger of the present invention is particularly suitable for a heat exchanger of a fluidized-bed boiler that is buried in a fluidized medium, has a high flow resistance due to the fluidized medium, and is under a high temperature.

[0011]

FIG. 2 (a) is a side view of the heat transfer tube portion, and FIG. 2 (b) is a sectional view taken on line AA of FIG. 2 (a).
A heat transfer tube 1 and an attached metal 2 are represented by a model shown in FIG.
FIG. 3 and FIG. 4 show the results of analytically determining the thermal stress generated at the joint (for example, the weld toe by welding) using the finite element method. Here, it is assumed that the inner surface of the heat transfer tube 1 and the outer surface of the heat transfer tube 1 (the surface on the side of the bonded metal joint) are kept at a constant temperature, and at this time, the joint between the heat transfer tube 1 and the bonded metal 2 (the transfer of the bonded metal 2). Side part 2 joined to heat tube 1
The thermal stress generated in a) is defined as a parameter of the height H of the metal part 2 from the joint or the angle θ formed by the side 2b of the metal part 2 adjacent to the joint with the joint of the heat transfer tube 1. I'm asking.

FIG. 3 shows a change in thermal stress generated at the joint between the heat transfer tube 1 and the deposited metal 2 when the height H from the joint of the deposited metal 2 is fixed and the angle θ is changed. The generated stress is normalized by the generated stress when θ = 90 degrees (θ
== 90 degrees and takes a value of 1.0). The thermal stress generated at the joint decreases as the angle θ decreases, and the angle θ
Above 45 degrees, the generated stress hardly changes. In other words, if the angle θ is set to 45 degrees or less, it is possible to reduce the thermal stress generated at the joint. For example, if the angle θ is 40
In the case of degrees, the generated stress is about 90% of that in the case of 90 degrees. Thereby, for example, the fatigue life is increased by about 5 to 50 times.

FIG. 4 shows that the angle .theta. Is fixed at 60 degrees and the thermal stress generated at the joint between the heat transfer tube 1 and the metal deposit 2 when the height H of the metal deposit 2 from the junction is changed. It shows the change. The generated stress is normalized by the generated stress when the height is 50 mm (when the height H is 50 mm, 1.
FIG. 4 shows that the generated thermal stress hardly changes even if the height H of the metal deposit 2 changes. As is clear from FIGS. 3 and 4, in order to reduce the thermal stress generated at the joint between the heat transfer tube 1 and the metal deposit 2, the angle θ may be reduced.

There are two main reasons why the above-described angle θ is reduced to reduce the thermal stress generated at the joint between the heat transfer tube 1 and the metal deposit 2. When the angle θ is reduced, the stress concentration coefficient at the joint between the heat transfer tube 1 and the deposited metal 2 where the thermal stress occurs is reduced. When the heat of the metal deposit 2 is transmitted to the heat transfer tube 1, when the angle θ is small, the gap that hinders the heat transfer is reduced, so that the heat flow becomes smooth, the temperature gradient becomes gentle, and the heat generated at the joint is reduced. The stress is reduced.

As described above, the metal fittings 2 are bonded to the heat transfer tubes 1 for the purpose of preventing mutual movement and contact of the heat transfer tubes 1 and 1 arranged side by side and for the purpose of supporting the heat transfer tubes 1 and 1. In this case, by attaching the metal fitting 2 having a shape such that the angle θ is 45 degrees or less to the heat transfer tube 1, the thermal stress generated at the joint between the heat transfer tube 1 and the metal fitting 2 is reduced by an angle as in the related art. As compared with the case of welding at θ of 90 degrees, the fatigue strength or creep strength of the entire structure including the metal deposit 2 increases.

[0016]

Embodiments of the present invention will be described. INDUSTRIAL APPLICABILITY The present invention is applied to a heat transfer tube of a boiler for thermal power generation or other heat exchangers and the like, in which it is necessary to prevent movement and mutual contact of heat transfer tubes such as heat transfer tubes arranged in a high-temperature gas flow, heat transfer tubes Applies to those who need to support. In particular, a heat transfer tube such as a fluidized-bed boiler is disposed in a fluidized medium, and thus is easily moved by the fluidized medium. Therefore, the present invention is suitable for preventing this.

The metal deposit of the present invention is a metal deposit provided for preventing movement and mutual contact of the heat transfer tubes and for supporting the heat transfer tubes, and the shape thereof is not limited.
It is desirable to use a plate.

FIG. 1 shows an embodiment of the present invention. FIG.
(A) is a side view of a heat transfer tube used for a heat exchanger in a boiler, and FIG. 1 (b) is a view taken along the line AA in FIG. 1 (a).
The metal fitting 2 having an L-shaped cross section on the upstream side of the gas flow of one of the heat transfer tubes 1 and having a tapered side portion 2b adjacent to a side portion (weld portion) 2a for welding is welded with a welding metal 3. Further, on the downstream side of the gas flow of the other heat transfer tube 1, an attachment 2 having an L-shaped cross section having substantially the same shape as the above-mentioned attachment 2 is welded, and these L-shaped attachments 2, 2 are engaged with each other. Further, the stopper 5 is welded by using the weld metal 3 so that the metal fitting 2 engaged with one of the heat transfer tubes 1 does not come off.
With such a structure, the heat transfer tubes 1 and 1 can slide freely in the tube axis direction, but are prevented from moving in the gas flow direction and the direction perpendicular to the gas flow. Mutual contact is prevented.

The manufacturing conditions are as follows. Dimensions of heat transfer tube 1: diameter 50.8 mm x thickness 10.8 mm Material of heat transfer tube 1: 2.25Cr-1Mo steel Dimensions of metal attachment 2: width 50 mm x height 50 mm x thickness 1
0 mm Angle θ = 30 degrees formed by the side 2b of the metal fitting 2 adjacent to the welded part (side 2a) of the metal fitting 2 to the heat transfer tube 1 with respect to the joint surface of the heat transfer tube 1. : 2.25Cr-1Mo steel

A welded portion (side portion 2a) exerting on a thermal stress generated in a welded portion (side portion 2a) between the heat transfer tube 1 and the metal deposit 2
In order to confirm the influence of the angle θ formed between the side edge 2b and the side edge 2b, the thermal stress generated at the weld toe (the end of the side edge 2a) was determined by finite element analysis.

The analysis conditions are based on the assumption that the boiler is in a steady operation, and the inner surface of the heat transfer tube 1, the outer surface of the heat transfer tube 1,
Was maintained at a constant temperature, and the stress generated at the weld toe was determined. For comparison, analysis was also performed for a case where the angle θ was 60 degrees, which was obtained by general welding. The details of the analysis conditions are as follows. Internal fluid temperature: 350 ° C. Inner surface heat transfer coefficient: 1700 kcal / m ² · hr · ° C. Atmospheric temperature: 900 ° C. Outer surface heat transfer coefficient: 450 kcal / m ² · hr · ° C.

As a result of analysis, the present embodiment (angle θ = 30 degrees)
The thermal stress generated at the weld toe of the heat transfer tube 1 and the metal attachment 2 is 205 Mpa, which is about 75% compared to 265 Mpa in the case of θ = 60 degrees (corresponding to the conventional construction method) performed for comparison. Had declined. This corresponds to an increase of about seven times in fatigue life.

FIG. 5 (FIG. 5 (a) is a side view of a heat transfer tube portion,
FIG. 5B shows another embodiment of the present invention in FIG. 5A taken along line AA. This differs from the embodiment shown in FIG. 1 in that the tapered portion is not the entire side portion 2b of the metal fitting 2, but a side portion for welding (weld toe) as shown in FIG.
Side portion 2a of side portion 2b adjacent to 2a (weld toe)
It is a metal fitting 2 having an L-shaped cross section provided only on a part of the side.
The metal fittings 2 and 2 welded to the adjacent heat transfer tubes 1 and 1 using the welding metal 3 are engaged with each other, and the metal fittings 2 engaged with one of the heat transfer tubes 1 are not detached. The stopper 5 is welded with the weld metal 3. Thus, the heat transfer tubes 1 and 1 are prevented from moving in the gas flow direction and the direction perpendicular to the gas flow, and the heat transfer tubes 1 and 1 are prevented from contacting each other.

The thermal stress generated on the weld toe side of the heat transfer tube 1 and the deposited metal 2 is greatly affected by the shape of the deposited metal 2 near the welded portion. Therefore, even if a taper is provided only in the vicinity of the welded portion of the metal deposit 2 to the heat transfer tube 1 without forming a taper on the entire metal deposit 2, the side portion of the metal deposit 2 bonded to the heat transfer tube 1 (a weld toe). Part 2) Attached hardware 2 adjacent to 2a
The angle formed by the side portion 2b with respect to the joint surface of the heat transfer tube 1 is 4
When the angle is set to 5 degrees or less, the thermal stress generated at the weld toe portion between the heat transfer tube 1 and the attached metal piece 2 is reduced as compared with the case where the angle θ is 60 degrees.

In the present embodiment, the effect of relaxing the stress at the welded portion is not changed as compared with the embodiment shown in FIG. 1 described above, but there is an advantage that the length L of the metal deposit 2 can be shortened. However, as shown in FIG. 6, it is desirable that the height H ′ of the tapered portion from the welded portion be equal to or greater than the thickness S of the metal deposit 2 where the influence of the height H is almost eliminated.

[0026]

According to the present invention, it is possible to reduce the thermal stress generated in the welded portion between the heat transfer tube and the deposited metal and the stress generated by the external load, thereby preventing the fatigue or creep crack occurring in the welded portion. In addition, it is possible to provide a high-reliability heat-deposited metal tube bundle for a heat transfer tube group that does not require maintenance, a heat exchanger including the heat transfer tube with the heat-deposited metal tube, and a boiler including the heat exchanger. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a state in which metal fittings welded and connected to heat transfer tubes arranged in parallel according to an embodiment of the present invention are engaged with each other.

FIG. 2 is a diagram showing a model used for analysis of the present invention.

FIG. 3 is a view showing a result of analyzing a thermal stress generated at a joint portion of an adhered metal piece welded and connected to the heat transfer tube shown in FIG. 2 by a finite element method.

FIG. 4 is a view showing a result of analyzing a thermal stress generated at a joint portion of a metal deposit welded and connected to the heat transfer tube shown in FIG. 2 by a finite element method.

FIG. 5 is a view showing a state in which metal pieces welded and connected to heat transfer tubes arranged side by side according to another embodiment of the present invention are engaged with each other.

FIG. 6 is a diagram showing an analysis result of thermal stress by a finite element method in a configuration of another embodiment of the present invention.

FIG. 7 is a side view of a boiler heat transfer tube.

FIG. 8 is a diagram showing a state in which metal pieces welded and connected to heat transfer tubes arranged side by side in the prior art are engaged with each other.

FIG. 9 is a view showing a state in which metal pieces welded and connected to heat transfer tubes arranged side by side according to the related art are engaged with each other.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat transfer tube 2 Adhesive metal 3 Weld metal 4 Header 5 Stopper

Claims (4)

[Claims] 1. A heat transfer tube, which is arranged side by side, constituting a heat exchanger,
In the metal fittings joined to the outer surface of the heat transfer tubes to prevent the heat transfer tubes from moving and contacting each other and partially support the weight of the heat transfer tubes, the metal fittings adjacent to the joint of the metal fittings with the heat transfer tubes A heat-transfer-tube-attached hardware, characterized in that the heat-transfer-tube-attached metal member has a tapered portion whose side portion forms an angle of 45 degrees or less with the joint of the heat-transfer tube. 2. A height of a tapered portion of a side portion of the deposited metal which is adjacent to a joint of the deposited metal with the heat transfer tube is equal to or greater than a thickness of the side portion of the deposited metal. The heat transfer tube-attached hardware according to 1. 3. A heat exchanger comprising a heat transfer tube group using the heat transfer tube attached metal according to claim 1. 4. A boiler using the heat heat exchanger according to claim 3.