JPH06170532A - Heat exchanger - Google Patents

Abstract

PURPOSE:To provide a heat exchanger not generating necking phenomenon and metal dusting phenomenon, having the advantage for welding work and replaceability of vibration preventive plate/tube and having low production cost. CONSTITUTION:A multi tube type heat exchanger is arranged with plural tubes 5 and tube plates 3, 4 installed therewith in a cylinder 2 being gas flow passage. A ferritic chrome molybdenum steel is used for a tube 5 and tube plate 3, a tip of the tube 5 is inserted into a hole 3a arranged on the tube plate 3, further, a tip of the tube 5 and tube plate 3 is welded with using a nickel alloy filler such that reverse side bead is formed on the surface 3e of the tube plate on the side coming into contact with gas in the cylinder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shell-and-tube type heat exchanger for exchanging heat between fluids in the petrochemical industry and the like.

[0002]

2. Description of the Related Art A multi-tube heat exchanger is shown in FIG.
As in the heat exchanger 11 shown in FIG.
4 and many tubes (heat transfer tubes) 5, baffles (baffles)
7 and the like are arranged. In the tube sheets 3 and 4, not only are the tubes 5 attached integrally, but also the tubes 5
It is a plate having a hole 3a connected to the inside of the. Baffle 7
A fluid such as a gas is supplied into the body 2 (heat exchange portion) whose flow path is defined by, and at the same time, another fluid is passed from the outside of one tube plate 3 into each tube 5 to remove the tube wall of the tube 5. It exchanges heat between those two kinds of fluids. Each tube 5 has an outer diameter of several tens of millimeters, a thickness of one to three millimeters, and a length of several meters to ten meters.
They range in diameter from a few hundred millimeters to a few meters.

The material of each part of the heat exchanger must be selected in consideration of operating pressure, temperature, kind of fluid (corrosion, etc.), and is provided, for example, in the dehydrogenation reaction part of the styrene monomer production apparatus. the heat exchanger, 2 _^1/4 Cr-
Ferritic chromium molybdenum steel such as 1Mo steel is often used. This is because that type of steel has heat resistance and corrosion resistance suitable for the above-mentioned applications, even though it is low in price.
The heat exchanger for the above-mentioned application is a low temperature gas supplied to the dehydrogenation reactor (about 100 to 200 ° C. It contains ethylbenzene and steam as main components and may contain a trace amount of CO ₂ and CO).
And the high temperature gas (about 550 ° C or higher; mainly composed of styrene monomer and water vapor) exiting the same reactor, the former is flown into the barrel 2 and the temperature is raised to about 500 ° C or higher. While heating, pass the latter through the tube 5 for approximately 30
Cool to 0-400 ° C.

In the multi-tube heat exchanger, the joining of each tube and the tube sheet, that is, the construction of the X portion in FIG. 4 (a) is conventionally the same (b), the same (c) or the same (d). ) Is done. In the same (b), the tube 5 is passed through the hole 3a of the tube sheet 3 and the tip end of the tube 5 and the surface of the tube sheet 3 (body 2
The surface opposite to the heat exchange part inside. Hereafter, the outer surface of the tube sheet 3) 3d is welded. The same (c) shows the peripheral edge portion 3f having a slightly larger outer diameter than the tube 5 on the surface of the tube sheet (the surface facing the heat exchange portion in the body 2 and in contact with the gas in that portion. (Referred to as the inner surface of the tube) 3e, and the tip of the tube 5 is fitted into the inlay portion 3g and welded over the entire circumference. And the same (d)
In this method, only the tip 5a of the tube 5 is inserted into the hole 3a of the tube sheet 3 to melt the inside and outside of the tube 5 and weld the entire circumference.
The ones shown in FIGS. 4 (c) and (d) are the actual Kaihei 2-7086.
No. 8 gazette or Japanese Utility Model Laid-Open No. 4-92173, the welding itself between the tube 5 and the tube sheet 3 is non-filler welding performed only by melting the base metal,
It is general to perform co-gold welding using a filler (filler material) equivalent to the base material (the above-mentioned ferritic chromium molybdenum steel).

[0005]

The joint mode between the tube and the tube sheet shown in FIGS. 4 (b) to 4 (d) is a heat exchanger for the dehydrogenation reaction section of the above-mentioned styrene monomer production apparatus (described later). As described above, when applying CO ₂ or a gas containing CO into the body 2), there are the following inconveniences.

First, in the case of joining as shown in FIG. 4 (b), since there is a minute gap (clevis) 3q between the inner portion (right side in the figure) of the tube sheet 3 and the outer surface of the tube, necking is not possible. The tube 5 may be damaged due to the phenomenon called. Necking means that carbon particles penetrate into such a gap to promote the generation of metal oxide scale to grow and press the tube 5 inward, and after the deformation step, the tube 5
It is a phenomenon that leads to the damage of. Heat exchanger 1 for the above application
In No. 1, in the gas flowing in the body, in addition to ethylbenzene, which is the main component, and water, a trace amount of C as an impurity or derivative.
O ₂ and CO are contained, but it is known from the chemistry of such a gas that carbon components in the gas are likely to be deposited as carbon particles in the temperature range of about 400 to 600 ° C. Therefore, it is considered that precipitation of carbon particles is particularly likely to occur in the vicinity of the tube sheet 3 where the gas flow tends to have a low flow rate in addition to the temperature within this range.

In the case of the joining form shown in FIG. 4 (c), since there is no fine gap between the tube 5 and the tube sheet 3, the above-mentioned necking phenomenon does not occur, but the following inconveniences occur. That is, (a) The welded portion 6 between the tube 5 and the tube plate 3 may be corroded and damaged from the outer periphery, and eventually may be broken. According to a recent investigation, this phenomenon is caused by a metal portion in a gas atmosphere containing CO ₂ and CO that has undergone a structural change (being a bainite structure) as a starting point, and undergoes carburization and high-temperature oxidation at the same time to cause corrosion. It is clear that this is a so-called metal dusting phenomenon. Ferrite-based chromium / molybdenum steel is 550-6 depending on the gas composition.
Since it tends to be susceptible to this corrosion at 50 ° C,
In the heat exchanger 11 for the above-mentioned application, which is used for the tube 5 or the tube sheet 3 having a considerable temperature rise, this metal dusting phenomenon is very likely to occur depending on the conditions.

(B) The welding of the corresponding portion must be performed by a special means called inner surface bore welding. This is because many tubes 5 are attached to the tube sheet 3 extremely densely and welding from the outer periphery of the tubes 5 is impossible, and the position of the welded portion 6 is the outer end (left side in the figure). The reason is that the welding rod cannot be inserted at an appropriate angle (obliquely) because it is far from 3d.

C) When performing the above welding, an operator must enter the body 2 of the heat exchanger 11 in order to abut the tip of the tube 5 with the protruding peripheral edge 3f of the tube sheet 3. Since the inside of the case 2 is narrow and the working environment becomes worse due to preheating before welding, the burden on the worker in this case becomes considerably severe.

D) During welding, the worker does not use the body 2 as described above.
Since it is necessary to enter the inside, the baffle 7 for the tube 5, the support plate 8 and the like cannot be provided in the vicinity of the welded portion 6. For this reason, it may not be possible to take measures to prevent vibration of the tube 5 in the most desirable state.

(E) If the tube 5 needs to be removed for some reason, the tube sheet 3 is slightly larger than the outer diameter of the tube 5 in order to pull the tube 5 to the outside of the tube sheet 3 (to the left in the figure). That is, the holes must be re-drilled (larger than the original holes 3a). Therefore, it takes a lot of time and money to replace only the tube 5.

Further, in the case of joining as shown in FIG. 4 (d), although the disadvantages of (b) to (e) above are not present, the inconvenience a) due to the metal dusting phenomenon still occurs.

The object of the present invention is that, in addition to the above-mentioned necking phenomenon, metal dusting phenomenon does not occur, and there is an advantage in welding work, vibration prevention surface, tube replacement work, etc., and a rise in manufacturing cost is minimized. It is to provide a heat exchanger.

[0014]

A heat exchanger according to the present invention is a multi-tube heat exchanger in which a plurality of tubes and a tube plate to which they are attached are arranged in a hollow cylinder which is a gas flow passage. A) using ferritic chrome / molybdenum steel as a) tubes and tube sheets (at least the tube sheet on the high temperature side if there are more than one), and b-1) insert the tip of the tube into the hole provided in the tube sheet. B-2) Filler of nickel alloy (filling filler) so that a back wave is formed on the entire surface of the tube sheet (inner surface) on the side that comes into contact with the gas in the body. The tube tip and the tube sheet are joined by welding using a material or a weld metal).

As described in claim 2, the heat exchanger may be further provided with a nickel alloy layer on the surface of the tube sheet (inner surface) on the side in contact with the gas in the case. It is more preferable that the nickel alloy of this layer has a coefficient of thermal expansion close to that of the above-mentioned ferritic chromium molybdenum steel.

[0016]

The heat exchanger of the present invention achieves the above object by the following actions. That is, 1) As described in b-1) and b-2) above, to weld between the tube sheet and the tip of the tube inserted into the hole, the entire inner surface of the tube sheet should be welded. Since the back wave is formed, there is no gap (such as the gap 3q in FIG. 4B) in the vicinity of the welded portion where the precipitated carbon particles enter from the gas side. Therefore, even when a gas containing carbon components such as CO ₂ and CO is put in the case and the temperature reaches 400 to 600 ° C., the necking phenomenon does not occur in the tube in this heat exchanger.

2) As described in b-3) above, since a nickel alloy filler is used for welding between the tube tip and the tube sheet, a metal dusting phenomenon occurs in the welded portion, the tube and the tube sheet. Absent. This phenomenon is thought to occur when carburization and high-temperature oxidation proceed simultaneously around the weld carburization, and in this heat exchanger, nickel with high carburization resistance (carburization resistance) is used. It is considered that the occurrence of the same phenomenon is prevented at the starting point by using the alloy as the welding filler. Therefore, in this heat exchanger, a carburizing gas is introduced and the temperature may rise to about 550 ° C. or higher.

3) Since the tip of the tube is inserted into the hole of the tube sheet as described in b-1), welding between the two can be performed relatively easily. That is, since the tip of the tube comes close to the outer surface of the tube sheet, it is possible in many cases to weld by inserting a welding rod into the hole of the tube sheet from the end, and the tube and tube sheet are butted ( Instead of the one shown in Fig. 4 (c), the tube is inserted into the hole.
It is not necessary for the worker to fit the tip of the tube into the correct welding position inside the body, and insertion work from outside the body is possible-
Therefore, welding is easy.

4) According to the above 3), since it is not necessary to secure a working space in the body, there is no restriction in providing the tube supporting member in the body, and the tube vibration preventing measure can be effectively applied. You can

5) If you need to remove the tube,
The tube can be easily pulled out to the outside of the tube sheet by removing only the welded part from the outside of the tube sheet by boring etc.Also, after inserting a new tube, the tube and tube can be welded by the same welding method as the original one. Can be joined to a board. That is, it is extremely easy to replace only the tube.

6) Instead of forming a tube or tube sheet with stainless steel having a high carburizing resistance (for example, 18Cr-8Ni steel) or the like, as described in a) above, an inexpensive metal material such as ferritic chrome molybdenum steel is used to form a metal. Since the dusting phenomenon is prevented, the manufacturing cost is almost the same as before.

According to experiments and investigations conducted by the inventors, it is extremely unlikely that the metal dusting phenomenon will occur in the tube or the tube sheet without using the welded portion as the starting point. There was a case where a slight carburization occurred near the inner surface. The heat exchanger according to claim 2 is constructed in consideration of that point, and since the nickel alloy layer having high carburization resistance is formed on the inner surface of the tube sheet, that is, the surface in contact with the gas, Completely prevent carburizing itself. The nickel alloy layer may be formed by a method such as build-up welding or thermal spraying, but if a metal having a thermal expansion coefficient close to that of the ferritic chromium molybdenum steel that is the material of the tube sheet (base material) is used, There is no risk of peeling or cracking of the same layer even when the temperature is large or the temperature changes drastically.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention is shown in FIGS.
The illustrated heat exchanger 1 is a multi-tube heat exchanger that is installed in a dehydrogenation reaction section of a styrene monomer production apparatus (not shown) and performs heat exchange between gases. As introduced above, a low-temperature (about 100 to 200 ° C.) gas containing ethylbenzene and steam as main components is introduced into the body 2 from the inlet 2a, and is heated to about 500 ° C. or higher by heat exchange. Moreover, it exits from the outlet 2b to be supplied to a dehydrogenation reactor (not shown). On the other hand, in a large number of tubes 5 arranged in the body 2, from the outside of the tube sheet 3 (on the left side in the figure), a high temperature (about 550 C.) reaction gas is passed through, cooled to about 300 to 400.degree. C. by heat exchange, and sent to the outside of the tube sheet 4.

The tube sheet 3 on the high temperature side (left side in the figure) into which the high temperature gas is introduced was fixed to the body 2 as a fixed tube sheet, while the tube sheet 4 on the low temperature side (right side in the figure) was the above-mentioned two. A so-called floating tube plate is used so as to absorb the difference in thermal expansion between the tube 5 and the body 2 due to the temperature difference between two fluids (gases). Further, baffles 7 (so-called NTIW baffles in this example) are attached to the tube 2 at a plurality of substantially equal intervals so that the gas flow in the tube 2 is cross-flowed with respect to the tube 5. Further, for the purpose of preventing the vibration of the tube 5, support plates 8 are also provided in the body 2 at a plurality of positions to support the tube 5. Tube 5
Therefore, both ends of the tube plate 3 and 4 are attached to both ends, and the baffle 7 and the support plate 8 support the intermediate portion.

[0025] In the heat exchanger 1, using 2 _^1/4 Cr-1Mo steel as a material of the body 2 and the tube plate 3, 4 and the tube 5. This is because the ferritic chromium molybdenum steel typified by this is suitable for the application of this example because the maximum temperature that can be used is close to 600 ° C., and is extremely economical compared to stainless steel and the like.

However, the joining portion of the tube plate 3 and the tube 5 on the high temperature side of the heat exchanger 1 is slightly specially welded as follows. This is because the temperature during operation exceeds 500 ° C. in this portion, and thus the above-mentioned necking and metal dusting have been inconvenienced by the carbon component contained in the gas in the body 2 in the past. Now, the welding is performed as in 1) and 2) below.

1) As shown in the upper half of FIG. 1 (b), the tip of the tube 5 is inserted into the hole 3a from the inside of the tube sheet 3 (right side of the figure). The hole 3a is provided with a taper portion 3b on the outer side and a straight pipe portion 3c on the inner side, which is slightly larger than the outer diameter of the tube 5. However, the tip of the tube 5 has a penetration or a back wave during welding. Considering the formation, a small amount (about 1 mm) is inserted into the straight pipe portion 3c. Although the notch 5a is formed in a circular shape on the inner circumference of the distal end of the tube 5 so that the distal end easily melts during welding, other groove having the same action may be adopted. Besides, the tapered portion 3b is formed on the outer side in order to optimize the angle of the welding rod inserted from that side, and it is not necessary to form the tapered portion 3b when the diameter of the tube 5 or the hole 3a is large.

2) A filler material of Inconel, which is a nickel alloy, is inserted from the outside of the tube sheet 3 to form the tube sheet 3
TIG welding is performed between the tube and the tube 5 (see the lower half of FIG. 1B). The first layer 6a has a noclevis structure in which there is no fine gap around the tube 5 so that the inside surface 3e of the tube sheet 3 and the outer peripheral surface of the tube 5 can be fully penetrated so that a back wave appears all around. To do. Subsequently, the second layer 6b and the third layer 6c are welded with the same Inconel filler, but these other than the first layer 6a may not necessarily be the Inconel filler as long as the welding quality is not inconvenient.

In this heat exchanger 1 in which the tube plate 3 and the tube 5 are joined as described above, the necking phenomenon of the tube 5 does not occur because it is a noclevis, and the metal dusting phenomenon also occurs due to the action of the Inconel filler. do not do.

The effect of preventing the metal dusting phenomenon by the above-mentioned welded structure was also clarified by the following test. That is, a test piece as shown in FIGS. 3 (a) and 3 (b) is prepared by imitating the joint portion between the tube sheet 3 and the tube 5, and the test piece is placed in a high temperature gas containing a large amount of CO ₂ and CO. By exposing, the state of carburization closely related to the metal dusting phenomenon was investigated. The test was conducted as follows.

The type ‥‥ any specimens specimens also, the material of the tube plate 3 and the tube 5 and 2 _^1/4 Cr-1Mo steel welded structure is as follows specimen: FIG 3 (b) that is, as the same form as FIG. 4 (c), without using the filler (i.e. with non-filler) welding test piece: in the form of FIG. 3 (a), Kyokin ie 2 ^_1/4
Welding with a filler equivalent to that of Cr-1Mo steel (that is, the same structure as in Fig. 4 (d)) Test piece: Welding with Inconel filler as the form of Fig. 3 (a) (that is, the same as in Fig. 1 (b)) for structures) test conditions ‥‥ a so-called acceleration test, as described below, using gas stricter than the actual heat exchanger within 1: mixed gas of _{CO-CO 2 -N 2 (CO} -9.9
_{9 Vol%, CO 2 -3.31 Vol} %, N 2 - left) Temperature: 600 ℃ · 650 ℃ · 700 ℃ Test method: Distribution at very low flow rates to the gas mixture, the test device containing the test specimen Allowed test time: 200 hours (total time of mixed gas flow) Carburization investigation method ・ ・ ・ WDX ray analysis method Carburization investigation location ・ ・ ・ Each of the tube sheet 3 and tube 5 shown in the lower detailed drawings of FIGS. 3 (a) and 3 (b) Base material and weld 6 and heat affected zone 3
For x and 5x, there are two points on each of the inner peripheral surface and the outer peripheral surface (the inner surface (right side of the drawing) of the tube sheet 3) (total of 10 positions).

The results of this test are shown in the table below. Although carburization was observed in many places in the test piece, it is understood that carburization did not occur in almost all the investigated places in the test piece having the same welded structure as in this example, that is, FIG. 1 (b). Remarks 1) ○: No carburizing, ×: Carburizing, −: No investigation 2) “Outer” refers to the outer peripheral surface, “Inner” refers to the inner peripheral surface, but tube plate 3
“Outside” refers to the inner surface (right side in FIG. 3) of the tube sheet 3.

Although carburization is partially observed on the inner surface of the tube sheet 3 in the test piece as well, carburizing at the base metal portion does not necessarily lead directly to metal dusting. Further, as shown in FIG. 2, if an Inconel layer (overlay) 3p is formed on the inner surface 3e of the tube sheet 3 by overlay welding or the like, carburization of the tube sheet 3 is prevented, so that the metal dusting It is more effective in prevention. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted here.

[0034] In addition, to prevent metal dusting effectively is, 2 _^1/4 Cr-1Mo further carburized high resistance chromium molybdenum steel than steel, for example 5Cr- _^1/2 M
o Steel or the like may be used. Similar to the case as shown in FIG. 2, this material is still economically advantageous as compared with the case where stainless steel such as 18Cr-8Ni is used for (the base material of) the tube sheet 3 and the tube 5. is there.

[0035]

According to the heat exchanger of the present invention, 1) the necking phenomenon of the tube does not occur even when the high temperature gas containing the carbon component is introduced, and 2) the metal dusting phenomenon is prevented. . In addition, there are advantages such as 3) easy welding between the tube and the tube plate, 4) easy vibration prevention by the support member, and 5) easy tube replacement.
6) Manufacturing cost does not rise compared to conventional heat exchangers. Particularly, according to the heat exchanger of the second aspect, the metal dusting phenomenon is prevented more effectively.

[Brief description of drawings]

FIG. 1 (a) is an overall vertical cross-sectional view of a heat exchanger according to an embodiment of the present invention, and FIG. 1 (b) is a detailed view of a portion b in the same (a).

FIG. 2 is a cross-sectional view of an essential part showing another embodiment of the present invention.

FIG. 3 shows a cross section of a test piece regarding a comparative test of effects of the example of FIG. 1 and a conventional example.

FIG. 4 is an overall longitudinal sectional view of a general heat exchanger (FIG.
(a)) and a detailed view showing the conventional welding structure for the X part (that is, the joint between the tube and the tube sheet) (the same (b))
・ (C) ・ (d)).

[Explanation of symbols]

 1 heat exchanger 2 body 3 tube plate 3a hole 5 tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Takeuchi, Inventor Hiroyuki Takeuchi 3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo Kawasaki Heavy Industries Ltd. Kobe factory (72) Inoue Fujii Higashi-kawasaki, Chuo-ku, Kobe-shi, Hyogo 3-1-1, Kawasaki Heavy Industries Ltd., Kobe Factory (72) Inventor Masaki Kamimon 1-1, Kawasaki-cho, Akashi City, Hyogo Prefecture Kawasaki Heavy Industries Ltd., Akashi Factory (72) Inventor Yoshihito Nakajima Miyamae, Tokuyama City, Yamaguchi Prefecture Ichiko Petroleum Chemicals Co., Ltd. (72) Inventor Hiroshi Yoshida 1-1, Miyamaecho, Tokuyama City, Yamaguchi Prefecture Idemitsu Petrochemicals Co., Ltd. (72) Inventor Etsu Tanaka 1 Miyamaecho, Tokuyama City, Yamaguchi Prefecture No. 1 Idemitsu Engineering Co., Ltd. (72) Inventor Kuniaki Umezu No. 1 Miyamae-cho, Tokuyama City, Yamaguchi Prefecture Idemitsu Engineering Co., Ltd.

Claims (2)

[Claims] 1. A multi-tube heat exchanger in which a plurality of tubes and a tube plate having the tubes are arranged in a hollow body which is a gas flow passage, and the tube and the tube plate are ferrite-based heat exchangers. Using chrome molybdenum steel, insert the tip of the tube into the hole provided in the tube sheet,
The heat characterized by joining the tube tip and the tube sheet by welding using a nickel alloy filler so that a back wave is formed around the tube sheet surface on the side in contact with the gas in the body. Exchanger. 2. The heat exchanger according to claim 1, wherein a nickel alloy layer is formed on the surface of the tube sheet on the side in contact with the gas in the body.