JP2002005592A - Multipipe heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce thermal stress of heat exchanger tubes effectively under a simple structure without requiring any special design technology while avoiding significant increase in the manufacturing cost of a multipipe heat exchanger. SOLUTION: In a multipipe heat exchanger, e.g. a shell and tube heat exchanger, heat exchanger tubes 7 are secured to a high temperature side tube sheet 3 by welding and heat source fluid guide tubes 9 made of a heat resistant material are held while being spaced apart from the heat exchanger tubes 7 with the outlet side end part thereof being inserted into the heat exchanger tube 7 and arranged in a high temperature side header 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tube heat exchanger called a shell-and-tube heat exchanger, and more particularly to piping of heat transfer tubes in a high-temperature header into which a high-temperature heat source fluid flows. Regarding the configuration.

[0002]

2. Description of the Related Art In recent years, a multi-tube type heat exchanger capable of efficiently performing heat exchange between a heat source fluid and a preheating fluid in a high pressure range and a high temperature range under a robust structure has been recently developed. The demand for exchangers is increasing rapidly. A typical prior art regarding a shell-and-tube heat exchanger that can meet such demands is as follows.
It is disclosed in JP-A-10-62079 and JP-A-11-51588.

In this type of shell-and-tube heat exchanger, a portion near a tube sheet which is a boundary portion separating a high-temperature heat source fluid and a low-temperature preheating fluid, particularly a welded portion for fixing the heat transfer tube and the tube sheet. The occurrence of breakage due to thermal stress due to a temperature difference is a problem. This is because the temperature of the heat transfer tube rises due to the flow of the high-temperature heat source fluid, and the temperature rise is suppressed because the tube sheet is in contact with the low-temperature fluid.

The first prior art disclosed in Japanese Patent Application Laid-Open No. H10-62079 employs means for relaxing the thermal stress by controlling the flow rate of preheated air. A second prior art disclosed in U.S. Pat.
5b adopts a means for cooling the welded portion by arranging the doubled portions 5b, all of which are intended to reduce the thermal stress due to the temperature difference of the welded portion.

[0005]

However, none of the techniques can completely eliminate the thermal stress caused by the temperature difference at the weld. In addition, there are disadvantages such as extremely high processing cost and extremely difficult design.

Further, in the second prior art, a device has been devised to reduce the thermal stress in the welded portion.
This will be described with reference to FIG. 5 and FIG. 6 which is an enlarged view of a main part of the structure, in the vicinity of the tube sheet. The heat insulating effect from the heat source near the opening of each heat transfer tube 16 is increased, and the cooling effect is improved. In order to increase the height, a collar tube 17 and a heat insulating board 19 are provided. In particular, the tube sheet 15b and the heat transfer tube 16 are fixed at the welded portion 18 by welding via the collar tube 17. However, as a result of heat conduction from the heat transfer tube 16 heated by the high-temperature fluid through the welding portion 18, the collar tube 17 itself has a large temperature gradient at the top of the welding portion 18 between the collar tube 17 and the tube sheet 15b. Thermal stress occurs in this part.
In addition, since the collar tube 17 is located on the hot gas side of the tube sheet 15b, and therefore has a very large thermal stress, there is a great concern that breakage due to this will occur.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a special design technique while avoiding a significant increase in the manufacturing cost of a heat exchanger. It is an object of the present invention to provide a multi-tube heat exchanger capable of effectively reducing thermal stress on a heat transfer tube with a simple structure without requiring a heat exchanger.

[0008]

The present invention has the following configuration to achieve the above object. That is, the invention of claim 1 in the present invention is a method of introducing and supplying a preheating fluid.
A tube body having an outlet, a high-temperature side tube sheet and a low-temperature side tube sheet provided to be closed at both ends of the tube body, and inlets of heat source fluids provided on both sides of the tube body with the respective tube sheets interposed therebetween. A high-temperature side header having a heat source fluid outlet and a low-temperature side header having a heat source fluid outlet, and a plurality of heat transfer tubes extending through the tube body with the tube ends inserted through the tube ends so that the opening faces both headers. In a multi-tube heat exchanger that transfers the heat of the heat source fluid circulated through the heat transfer tubes to the preheating fluid via the heat transfer tubes, the heat transfer tubes are welded and joined by a high-temperature side tube sheet. On the other hand, a heat source fluid guide tube made of a heat-resistant material tube,
While being held apart from the heat transfer tube,
A multi-tube heat exchanger having a heat source fluid guide tube, wherein the outlet side end is inserted into the heat transfer tube and disposed in the high temperature side header.

Further, the invention of claim 2 of the present invention provides:
With regard to the multi-tube heat exchanger according to claim 1, the heat transfer tube is configured such that a tube end corresponding to a required length of a welded portion at the time of welding is projected into the high-temperature side header. It is characterized by being configured to be fixed to the high temperature side tube sheet by welding.

[0010] The invention of claim 3 in the present invention provides:
Regarding the multitubular heat exchanger according to claim 1 or 2,
A heat insulating material surrounding the welded portion between the high-temperature side tube sheet and the heat transfer tube and the heat source fluid guide tube is stretched.

[0011] The invention of claim 4 in the present invention provides:
The multi-tube heat exchanger according to the first, second or third aspect is characterized in that a heat insulating material is interposed between the heat transfer tube and the heat source fluid guide tube.

Further, the invention of claim 5 in the present invention provides:
The multi-pipe heat exchanger according to claim 4, wherein the heat insulating material is provided so as to change the heat insulating property by decreasing the heat insulating property from a high temperature side to a low temperature side. I do.

[0013] The invention of claim 6 in the present invention provides:
The multi-tube heat exchanger according to claim 5 is characterized in that the thickness of the heat insulating material is gradually reduced from a high temperature side to a low temperature side.

[0014] The invention of claim 7 in the present invention provides:
The multi-tube heat exchanger according to the first, second, third, fourth, fifth or sixth aspect is characterized in that the heat source fluid guide tube is made of a stainless steel tube.

According to the present invention, since a heat source fluid guide tube is newly provided and is fixed to neither the heat transfer tube nor the tube sheet, welding at a high temperature portion can be avoided. Thereby, the thermal stress at the welded portion can be reduced.

The heat source fluid guide tube extends to a lower temperature side than the tube sheet, and a heat insulating material such as an air layer is interposed between the heat transfer tube and the heat source fluid guide tube. The replacement can be performed at a location remote from the tube sheet, so that the thermal stress at the welding portion between the tube sheet and the heat transfer tube can be reduced.

In the present invention, the thermal stress that is expected to easily occur in a transient state during the heat exchange operation, that is, in a state where the temperature inside the heat exchange device is sharply increased is remarkably reduced. In the steady state where there is no change in temperature inside the equipment after long-term operation, heat exchange is performed by radiation between the heat transfer tube and the heat source fluid guide tube. Expected

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. Figure 1
FIG. 2 is a front view showing a cross section of a multi-tube heat exchanger to which the present invention is applied, and FIG. 2 is a cross-sectional view of a portion near a tube sheet of the multi-tube heat exchanger according to the first embodiment of the present invention. FIG.

The multi-tubular heat exchanger 1 shown in FIG. 1 has a pipe 2 having a preheating fluid inlet 2A and an outlet 2B near both ends, respectively, and is provided by closing both ends of the pipe 2. A high-temperature side tube sheet (tube sheet) 3 and a low-temperature side tube sheet (tube sheet) 4 and a heat source fluid inlet 5 integrally mounted immediately above the tube 2 with the high-temperature side tube sheet 3 interposed therebetween.
A, a low-temperature header 6 having a heat source fluid outlet 6A integrally attached immediately below the tube 2 with the low-temperature tube sheet 4 interposed therebetween, and a tube in both tube sheets 3, 4. It is configured to include a plurality of heat transfer tubes 7 that are inserted into the ends and extend into the tube 2 with the openings facing the headers 5 and 6. In FIG. 1, reference numeral 8 denotes a plurality of baffle plates arranged at equal intervals and in a staggered manner on the inner wall surface from one end to the other end of the tube 2.

The multi-tubular heat exchanger 1 has a heat source fluid flowing through each heat transfer tube 7 through the high temperature side header 5 and a space around each heat transfer tube 7 in the tube 2 from the inlet 2A. Heat is exchanged with the circulated preheating fluid, and the heat of the heat source fluid is transferred to the preheating fluid via each heat transfer tube 7, so that the preheating fluid is heated to a predetermined temperature and the outlet 2B is heated.
It is designed to be taken out from.

Referring to FIG. 2, the structure of the tube type heat exchanger 1 in the vicinity of the tube sheet, in particular, the high temperature side tube sheet 3 will be described with reference to FIG. The heat transfer tube 7 is formed by projecting a tube end corresponding to a required length of the welded portion 12 at the time of welding connection from the corresponding tube insertion hole of the high temperature side tube sheet 3 into the high temperature side header 5. The outer peripheral wall surface of the end portion is fixed to the high temperature side tube sheet 3 by a welded portion 12 to be welded.

Although not shown, the multi-tube heat exchanger 1
In the above, there is a structure in which the high temperature side tube sheet 3 is provided in a plurality of stages such as two stages. Welded part 12 to be welded at the place where
While the uppermost high-temperature side tube sheet 3 provided facing the high-temperature side header 5 is not projected into the high-temperature side header 5 from the corresponding tube insertion hole. In some cases, it is fixed to the high temperature side tube sheet 3 by welding in a state where it is slightly retracted.

On the other hand, in the multi-tube heat exchanger 1 shown in FIG. 1, a short tube having an outer diameter slightly smaller than the inner diameter of the heat transfer tube 7 is formed by a heat-resistant material such as a stainless steel tube. The heat source fluid guide tube 9 is held at a distance from the heat transfer tube 7, and is preferably held with a small gap to the extent that heat is not easily transferred to the heat transfer tube 7. The heat transfer tube 7 is provided in the high-temperature side header 5 in a coaxial arrangement with the heat transfer tube 7 by inserting the portion into the heat transfer tube 7 so as to be wrapped with a length substantially corresponding to the outer diameter. In this case, the outlet side end of the heat source fluid guide tube 9 extends to the low temperature fluid side through the welding portion 12 and the high temperature side tube sheet 3. In this case, between the heat transfer tube 7 in contact with the high temperature side tube sheet 3 and the heat source fluid guide tube 9, a heat insulating layer 11 made of an extremely thin air layer that does not cause air convection is formed. , So-called insulated state.

A heat insulating material 10 such as a heat insulating board is stretched around the welded portion 12 between the high temperature side tube sheet 3 and the heat transfer tube 7 and the heat source fluid guide tube 9. The heat-insulating treatment is performed so that the welding portion 12 and the heat-source fluid guide tube 9 are not heated by the high-temperature heat-source fluid being in direct contact.

In the shell-and-tube heat exchanger 1 according to the first embodiment of the present invention having the above-described structure, the high-temperature heat flowing into the high-temperature side header 5 and flowing into the heat transfer tube 7 via the heat source fluid guide tube 9 is used. The heat source fluid guide tube 9 that rises in temperature by directly contacting the heat source fluid (open arrow line in FIG. 2) is not fixed to the heat transfer tube 7,
In the wrapped portion 9, the heat insulating layer 11 is provided with a gap that does not cause air convection, so that the temperature does not directly affect the heat transfer tube 7, and the heat source fluid guide tube The heat transfer from 9 to the welded portion 12 of the high-temperature side tube sheet 3 is suppressed only to heat radiation. Therefore, the heat transfer tube 7 balances the temperature of the low temperature fluid, and the heat source fluid guide tube 9 balances the temperature of the high temperature heat source fluid. Here, the temperature distribution of the heat transfer tube 7 is a point where the high-temperature heat source fluid is directly blown in the vicinity of the cut (end on the outlet side) of the heat source fluid guide tube 9, and becomes lower as it approaches the high-temperature side tube sheet 3. If the wrap length of the heat source fluid guide tube 9 is appropriately selected, the temperature of the welded portion 12 of the high temperature side tube sheet 3 can be kept low, and the temperature difference is substantially eliminated, and the thermal stress in the welded portion 12 is remarkably reduced. Breakage due to this thermal stress is prevented.

FIG. 3 is a cross-sectional view of a portion near a tube sheet of a multi-tube heat exchanger according to a second embodiment of the present invention. Regarding the multitubular heat exchanger according to the second embodiment, similar to the multitubular heat exchanger according to the first embodiment, the corresponding members are denoted by the same reference numerals. Avoid duplication and omit explanations. The second embodiment is characterized in that the heat source fluid guide tube 9 formed as a short tube having an outer diameter slightly smaller than the inner diameter of the heat transfer tube 7 is a heat transfer tube. 7, an air-convection does not occur, and a gap that does not easily conduct heat is held, and the outlet end thereof is inserted into the heat transfer tube 7 so as to be wrapped with a small length into the high-temperature side header 5. That is, the heat transfer tubes 7 are provided in a coaxial arrangement. In this case, the outlet side end of the heat source fluid guide tube 9 is located at substantially the same level as the welded portion 12 based on the flow direction of the high temperature heat source fluid, and does not extend to the low temperature fluid side.

In the second embodiment having such a configuration, the heat source fluid guide tube 9 is provided with the heat transfer tube 7.
In contrast, the heat transfer tube 7 is not directly affected by the temperature because the air gap is inserted with a small wrap length while maintaining a gap that does not generate air convection and is difficult to transfer heat. On the other hand, since the welded portion 12 of the high-temperature side tube sheet 3 is exposed to the high-temperature heat source fluid in the heat transfer tube 7 through the wall of the tube 7, there is no temperature difference from the end of the heat source fluid guide tube 9 and the temperature is high. Become. However, since the heat transfer tube 7 and the heat source fluid guide tube 9 are in a state where heat transfer is difficult as described above, the thermal stress in the welded portion 12 is alleviated, and breakage due to this thermal stress is prevented.

FIG. 5 is a cross-sectional view of a portion near a tube sheet of a multi-tube heat exchanger according to a third embodiment of the present invention. Regarding the multitubular heat exchanger according to the third embodiment, similar to the multitubular heat exchanger according to the first and second embodiments, corresponding members have the same reference numerals. The description is omitted here. In this third embodiment,
The characteristic configuration is that the heat insulating layer 11 has a heat insulating material interposed in place of the air layer.

In the third embodiment having such a configuration, heat radiation is suppressed by the heat insulating material of the heat insulating layer 11, and therefore, depending on the heat insulating properties including the thickness of the heat insulating material, the third embodiment is different from the second embodiment. A thermal stress relaxation effect is obtained. In this case, if necessary, the thickness of the heat insulating material of the heat insulating layer 11 may be gradually reduced from the high temperature side to the low temperature side, and the heat insulating property may be reduced from the high temperature side to the low temperature side so as to change. The temperature distribution of the heat transfer tube 7 can be appropriately controlled.

[0030]

The thermal stress Pa in each part of each embodiment of the present invention was examined by comparing the prior art example (shown in FIG. 6) and the comparative example (shown in FIG. 7) with each other. The results shown in Table 1 were obtained. Here, the comparative example shown in FIG. 7 is a reference example in which the above-described prior art example is improved, and the welded portion 18 with the heat transfer tube 16 is formed by extending the collar tube 17 to the low temperature fluid side. It is characterized by the structure provided on the low-temperature fluid side. The material used in each part was stainless steel, and a high-temperature fluid was used at a temperature of 85 at the inlet.
Using a gas at 0 ° C. and a low-temperature fluid as a gas at an outlet temperature of 650 ° C., the thermal stress Pa of each part was examined.

[0031]

[Table 1]

As is clear from Table 1, in the case of the first embodiment, the thermal stress in the heat transfer tube can be reduced only slightly as compared with the prior art example, but the welding point is reduced to one for each heat transfer tube. As a result, the cost can be reduced while relatively relaxing the thermal stress. On the other hand, in the case of Examples 2 and 3, it is shown that the thermal stress in the heat transfer tube is suppressed to about 2/5 of that of the conventional art, and contributes significantly to the relaxation of the thermal stress.

[0033]

The present invention is embodied in the form described above and has the following effects. According to the present invention, since a heat source fluid guide tube is newly provided and is fixed to neither the heat transfer tube nor the tube sheet, welding in a high temperature portion can be avoided, and the number of welding points can be reduced by half. This makes it possible to alleviate the thermal stress at the welded portion, reduce the welding cost and improve the productivity.

Further, the heat source fluid guide tube extends to a lower temperature side than the tube sheet in the heat transfer tube, and a heat insulating material such as an air layer is provided between the heat transfer tube and the heat source fluid guide tube. For example, the heat exchange of the high-temperature gas can be performed at a location away from the tube sheet, so that the thermal stress at the welded portion between the tube sheet and the heat transfer tube can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional front view of a multitubular heat exchanger.

FIG. 2 is a cross-sectional view of a portion near a tube sheet of the multitubular heat exchanger according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of a portion near a tube sheet of a multitubular heat exchanger according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of a portion near a tube sheet of a multitubular heat exchanger according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of a portion near a tube sheet of an example of a conventional multi-tube heat exchanger.

FIG. 6 is an enlarged view of a main part corresponding to FIG. 5;

FIG. 7 is a cross-sectional view of a portion near a tube sheet of a multitubular heat exchanger of a comparative example for the present invention.

[Explanation of symbols]

1 ... Multi-tubular heat exchanger 2 ... Cylindrical body 2A ... Inlet 2
B ... outlet 3 ... high temperature side tube sheet 4 ... low temperature side tube sheet 5 ... high temperature side header 6 ... low temperature side header 7 ... heat transfer tube 8 ... baffle plate 9 ... heat source fluid guide tube 10
... heat insulating material 11 ... heat insulating layer 12 ... welded part

Claims (7)

[Claims] 1. A tube having an inlet / outlet for a preheating fluid, a high-temperature tube sheet and a low-temperature tube sheet which are respectively closed at both ends of the tube, and the tube sandwiching each of the tube sheets. A high-temperature side header having a heat source fluid inlet and a low-temperature side header having a heat source fluid outlet provided on both sides of the tube, the tube ends are inserted through both tube sheets, and the opening faces both headers. A multi-tube heat exchanger that includes a plurality of heat transfer tubes that are extended and that transfers the heat of the heat source fluid circulated through the heat transfer tubes to the preheating fluid via the heat transfer tubes; The heat tube is fixed to the high-temperature side tube sheet by welding, while the heat source fluid guide tube made of a heat-resistant material is held apart from the heat transfer tube. Together, multitubular heat exchanger having a heat source fluid guiding tube characterized by comprising disposed on the high temperature side in the header by inserting the outlet end in the heat transfer tube. 2. The heat transfer tube is fixed to the high-temperature side tube sheet by welding and projecting a tube end corresponding to a required length of a welded portion at the time of welding connection into the high-temperature side header. A multi-tube heat exchanger having the heat source fluid guide tube according to claim 1. 3. The multiple heat source fluid guide tube according to claim 1, wherein a heat insulating material surrounding the welded portion between the high temperature side tube sheet and the heat transfer tube and the heat source fluid guide tube is stretched. Tube heat exchanger. 4. A multi-tube heat exchanger having a heat source fluid guide tube according to claim 1, wherein a heat insulating material is interposed between the heat transfer tube and the heat source fluid guide tube. 5. The multi-tubular heat exchanger having a heat source fluid guide tube according to claim 4, wherein the heat insulating material is provided so as to decrease and change the heat insulating property from a high temperature side to a low temperature side. . 6. The multi-tube heat exchanger having a heat source fluid guide tube according to claim 5, wherein the thickness of the heat insulating material gradually decreases from a high temperature side to a low temperature side. 7. A multi-tube heat exchanger having a heat source fluid guide tube according to claim 1, wherein the heat source fluid guide tube is made of a stainless steel tube.