JPH08285489A - Heat exchanging method and heat exchanger - Google Patents

Abstract

PURPOSE: To provide a heat exchanging method and a heat exchanger capable of preventing a tube welded part from being damaged owing to a metal dusting phenomenon, and manufacture it inexpensively. CONSTITUTION: In a heat exchanger in which gas to be cooled is caused to flow to a tube side and gas to be heated to a shell side, and a tube and a tube plate are welded and mounted, on the upstream side of a front tube plate 32 a partition plate 54 is provided substantially parallely to the front tube plate 32 to form a partition chamber 56. A short tube (ferrule) 58 of a smaller outer diameter than a tube inner diameter is mounted on the partition plate 54 such that the tip end is inserted into a tube inlet tube part 44 of the front tube plate 32, and a cooling steam introduction tube 60 is connected with the partition chamber 56. A low temperature steam is made to flow through an annular space 64 between an outer surface of the short tube 58 and an inner surface of the tube 38 to cool the tube inlet tube part including a shell side surface of the front tube plate and a tube welded part 46.

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 exchange method for exchanging heat between fluids and a heat exchanger for implementing this method.

[0002]

2. Description of the Related Art A low temperature gas (about 100 ° C.) supplied to a heat exchanger between fluids, for example, a dehydrogenation reactor in a styrene monomer production apparatus is heated, and at the same time, a high temperature gas leaving the dehydrogenation reactor is heated. The multi-tube gas-gas heat exchanger for cooling (500 to 600 ° C.) needs to be integrated in series with the heat exchanger immediately downstream of the fluid on the pipe side because of the equipment layout required for the process. In addition, since there is a large difference in average temperature between the tube side and the shell side during operation, it is necessary to absorb the difference in expansion due to thermal expansion between the heat transfer tube (tube) and the shell. Therefore, this heat exchanger is conventionally a heat exchanger with one pass from the tube shell side and the rear tube sheet being a floating type, or a fixed tube sheet provided with an expansion joint outside or inside the shell. It is common to use a form heat exchanger.

Conventionally, in the above heat exchanger, as described in Japanese Utility Model Laid-Open No. 2-70868, in the front tube sheet, the heat transfer tube 1 and the tube sheet 2 are welded as shown in FIG. A mounting structure (hereinafter referred to as type D) is adopted, and in the rear tube sheet, a heat transfer tube 1 that also uses expansion as shown in FIG.
A welded attachment structure (hereinafter referred to as type C) between the tube sheet 2 and the tube sheet 2 was adopted. That is, the type D has a structure in which the end portion of the heat transfer tube 1 is inserted into the end opening 3 of the tube sheet 2 and welded, and the type C has the heat transfer tube 1 in the hole 4 of the tube sheet 2 and the tip of the heat transfer tube. Is inserted so as to project from the tube sheet 2, the tip of the heat transfer tube and the tube sheet are welded, and the portion of the heat transfer tube inserted into the tube sheet is expanded before or after welding. Reference numerals 5 and 6 are welded portions.

In the heat exchanger in the above-mentioned styrene monomer producing apparatus, carbon contained in the gas is deposited as carbon particles in the vicinity of the tube plate where the gas flow tends to stay on the shell side due to the nature of gas and operating conditions. It is in an easy environment. In the type C welded mounting structure shown in FIG. 6 and the type D welded structure shown in FIG. 7, the gap between the heat transfer tube 1 and the tube sheet 2 cannot be completely eliminated, and a gap remains in a minute range. For this reason,
When carbon precipitates, carbon particles intrude into this gap, and over a long period of operation, the carbon that grows and solidifies in the gap between the heat transfer tube and the tube sheet presses the heat transfer tube inward and deforms it. (Necking phenomenon of heat transfer tube), eventually the heat transfer tube-tube plate welded portion or the heat transfer tube is damaged, leading to gas leakage between the tube shells. It is known that such a phenomenon is generally likely to occur in the front tube sheet, but since a similar phenomenon can occur in the rear tube sheet, the heat transfer tube-tube sheet welded portion or heat transfer tube caused by the carbon precipitation is generated. Needed to fix the corruption issue.

[0005] In order to solve this problem, the actual Kaihei 2-7
As described in Japanese Patent No. 0868, the following welding structure has been proposed. That is, as shown in FIGS. 4 and 5, the rear tube sheet is of a floating type so that the tube 1 side and the shell side each have one pass and the difference in expansion due to thermal expansion between the heat transfer tube 1 and the shell can be absorbed. In a multi-tube heat exchanger having a structure or a fixed tube plate type structure in which an expansion joint is provided outside or inside the shell, the front tube sheet and the rear tube sheet are
In order to eliminate the gap between the heat transfer tube 1 and the tube plate 2, a welding attachment structure of the following type A (see FIG. 4) or / and the following type B (see FIG. 5) heat transfer tube and tube sheet is used. I have. (A) The welded mounting structure between the type A heat transfer tube and the tube sheet is
As shown in FIG. 4, a hole 13 having the same inner diameter as that of the heat transfer tube 1 is provided in the tube sheet 2, and a peripheral edge 14 slightly thicker than the outer diameter of the heat transfer tube 1 is projected at one end of the hole, and the inside of the peripheral edge is The heat transfer tube 1 is formed by forming a stopper 15 into which the heat transfer tube is inserted and abutted by cutting out in a circular shape and inserting one end of the heat transfer tube into this stopper.
And tube plate 2 are welded together. The upper side of the center line of the heat transfer tube 1 shows the state before welding, and the lower side of the center line of the heat transfer tube 1 shows the state after welding. 16 is a welded part, 17
Is a groove. (B) The welded mounting structure between the type B heat transfer tube and the tube sheet is
As shown in FIG. 5, the tube sheet 2 is provided with a tapered hole 18 and a straight tubular small-diameter hole 20 communicating with the small-diameter portion of the hole. The structure in which the heat pipe 1 is inserted by the length of the notch 24 and the small diameter hole 20 and the tip of the heat transfer pipe are welded. The upper side of the center line of the heat transfer tube 1 shows the state before welding, and the lower side of the center line of the heat transfer tube 1 shows the state after welding. Reference numerals 21, 22, and 23 are welded portions, and 24 is a cutout portion.

Further, Japanese Patent Laid-Open No. 6-170532 discloses a necking phenomenon and a metal dusting phenomenon (CO
_In order to prevent a metal in a gas atmosphere containing ₂ and CO from being a starting point of a welded portion having a structural change (having a bentonite structure) and being corroded by simultaneous carburization and high temperature oxidation), In a multi-tube gas-gas heat exchanger, ferrite-based chromium as tubes and tube plates
Using molybdenum steel, insert the tip of the tube into the hole provided in the tube sheet, and use a nickel alloy of nickel alloy so that the back wave is formed all around the tube sheet surface on the side that comes into contact with the gas in the shell. It describes a configuration in which the tube tip and the tube sheet are joined by welding using a filler.

[0007]

As described above, in Japanese Utility Model Laid-Open No. 2-70868, the attachment of the tube and the tube sheet is shown in FIG. 4 in order to prevent the welded portion from being damaged by the necking of the tube. A heat exchanger having a welded structure of type A or type B shown in FIG. 5 is described. Further, Japanese Patent Laid-Open No. 6-170532 discloses a welding rod having a welding structure similar to the type B welding structure shown in FIG. 5 in order to prevent the tube welded portion from being damaged by necking of the tube and metal lasting. The use of nickel alloys is described.

However, the structure described in Japanese Utility Model Laid-Open No. 2-70868 solves the problem of tube necking, but does not solve the problem of metal dusting unless expensive stainless steel is used as a manufacturing material. Further, the configuration described in Japanese Patent Laid-Open No. 6-170532 solves both the problems of necking and metal dusting,
Due to the welding overlay of the tube sheet and the partial use of the nickel alloy, there remains a problem that it is not sufficiently inexpensive and that the dissimilar material combination causes excessive thermal stress in the dissimilar material welded portion. The present invention has been made in view of the above points, and an object of the present invention is to prevent damage to a tube welded portion and a front tube sheet due to a metal dusting phenomenon and to manufacture the heat exchange method at low cost. And to provide a heat exchanger.

[0009]

In order to achieve the above object, the heat exchange method of the present invention heat-exchanges by flowing a fluid to be cooled on the tube side and a fluid to be heated on the shell side. In the method, a steam having a temperature lower than the temperature of the heated fluid at the shell outlet is introduced into the tube inlet tube portion near the front tube sheet, and the shell side surface of the front tube sheet and the tube and the front tube sheet. The tube inlet pipe part including the welded part is cooled. Further, another heat exchange method of the present invention is a method of performing heat exchange by flowing gas to be cooled on the tube side and gas to be heated on the shell side, in which a short tube is provided at the tube inlet tube portion of the front tube sheet. The gas to be cooled is inserted into the short pipe, and steam having a temperature lower than the temperature of the heated gas at the shell outlet is introduced into the annular space between the short pipe and the tube inlet pipe portion. After cooling the shell side surface of the front tube sheet and the tube inlet tube section including the welded portion between the tube and the front tube sheet, the tube inlet tube section is mixed with the gas to be cooled. Further, another heat exchange method of the present invention is a method of performing heat exchange by flowing gas to be cooled on the tube side and gas to be heated on the shell side, in which the gas is to be exchanged on the rear side of the tube inlet tube of the front tube sheet. A partition plate is provided substantially parallel to the front tube sheet to form a partition chamber, and steam having a temperature lower than the temperature of the heated gas at the shell outlet is introduced into the partition chamber to remove the front tube sheet. After cooling the tube inlet tube section including the shell side surface and the welded section of the tube and the front tube sheet,
It is characterized by being mixed with a heated gas.

The heat exchanger of the present invention is a heat exchanger having a structure in which a tube and a tube plate are welded and attached, in which a fluid to be cooled is flowed to the tube side and a fluid to be heated is flowed to the shell side to exchange heat. A partition chamber surrounded by the front tube plate and a partition plate is provided in the tube inlet pipe section near the front tube plate, and a cooling steam introducing pipe is connected to the partition chamber. Further, another heat exchanger of the present invention is a heat exchanger having a structure in which a tube and a tube plate are welded and attached, in which the gas to be cooled on the tube side is exchanged with the gas to be heated on the shell side for heat exchange. , A partition plate is provided on the upstream side of the front tube sheet in a direction substantially parallel to the front tube sheet to form a partition chamber, and the inner diameter of the tube is inserted so that the tip is inserted into the tube inlet tube section of the front tube sheet. A short pipe having a smaller outer diameter is attached to the partition plate, and a cooling steam introducing pipe is connected to the partition chamber. Furthermore, another heat exchanger of the present invention is
In a heat exchanger having a structure in which a tube and a tube sheet are welded and attached, in which a gas to be cooled on the tube side and a gas to be heated are made to flow on the shell side to perform heat exchange, the front portion is provided on the downstream side of the front tube sheet. A partition plate is provided in parallel with the tube plate to form a partition chamber.
A cooling steam introduction pipe is connected to this partition chamber, and the tip of the partition plate and the inside of the shell through which the heated gas passes are connected so that the heated steam after cooling is mixed with the heated gas. Is configured to do.

The welding structure of the tube and the front tube sheet (high temperature side tube sheet) is, for example, the above-mentioned type A (see FIG. 4), type B (see FIG. 5), type C (see FIG. 6),
Type D (see FIG. 7), welded structures similar to these can be mentioned. Explaining the operation in the above configuration, the steam at a temperature lower than the temperature of the heated fluid at the shell outlet is introduced into the tube inlet pipe portion near the front tube sheet, and the shell side surface of the front tube sheet and the tube. The tube inlet tube, including the weld between the tube and the front tube sheet, is cooled and the steam used for cooling is mixed with the fluid in the tube or the fluid in the shell.

[0012]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications can be made as appropriate. Example 1 FIG. 1 shows a heat exchanger in which steam is blown into the tube side in this example, and FIG. 2 shows an enlarged main part in FIG. FIG. 1 and FIG. 2 show, as an example, a multitubular system in which a feed gas to the dehydrogenation reactor is preheated in the dehydrogenation reaction section of a styrene monomer production apparatus, and at the same time, the reactor gas leaving the dehydrogenation reactor is cooled. The heat exchanger is shown.

Reference numeral 30 is a shell (body), 32 is a front tube sheet (high temperature side tube sheet), 34 is a rear tube sheet (low temperature side tube sheet), and 36 is a channel, which is a front tube sheet 32 and a rear tube sheet 34. A large number of tubes (heat transfer tubes) 38 are arranged in the horizontal direction between and. The front tube sheet 32 is provided with openings 40 corresponding to a large number of tubes 38 and short cylinders 42 communicating with these openings, and these short cylinders 42 and one end of the tubes 38 are the above-mentioned type A. To D, or a welded structure similar thereto, to form the tube inlet tube portion 44. 46 is a tube weld, 48 is a baffle, 50 is a supply gas inlet, and 52 is a supply gas outlet.

A partition plate 54 is provided on the upstream side (channel side) of the tube plate 32 so as to be substantially parallel to the front tube plate 32, and a partition chamber 56 is formed between the partition plate 54 and the front tube plate 32. Tube sheet 32
A plurality of short tubes (ferrules) 58 having an outer diameter slightly smaller than the inner diameter of the tube 38 are provided in the partition plate 54 so as to be inserted into the tube inlet tube portion 44 of the tube 38. A steam introducing pipe 60 for cooling is attached to the partition chamber 56. 62 is a spacer. The short pipe 58 is preferably provided so as to be detachable from the partition plate 54.

In the above heat exchanger, the tube opening 40 on the front tube plate surface is not in contact with the reactor gas by the partition plate 54. The reactor gas is introduced into the short pipe 58 and flows in the tube 38, and low-temperature steam is introduced into the partition chamber 56 surrounded by the partition plate 54 and the front tube plate 32, and this steam is the short pipe. It is mixed with the reactor gas in the tube 38 through an annular space 64 between the outer surface of 58 and the inner surface of the tube 38. Since a large amount of steam is originally contained in the reactor gas, even if a small amount of steam is mixed, it does not have a bad influence. In this example, the feed gas is introduced at, for example, 100 ° C., exchanges heat with the reactor gas at, for example, 580 ° C. and is preheated to the feed gas at, for example, 530 ° C. In this case, the steam will increase the cooling effect,
The temperature is preferably 400 ° C or lower, and more preferably 200 to 300 ° C.

As a material for manufacturing the heat exchanger in this embodiment, for example, 21 / 4Cr-1Mo steel which is a low alloy steel is used. Further, it is preferable that the tube and the tube sheet are attached on the front tube sheet (high temperature side tube sheet) 32 side by the welding structure of type A or type B described above. With this structure, the necking phenomenon of the tube can be prevented. As a material for manufacturing the partition plate 54 and the short tube 58, 304 stainless steel is used, for example. The partition plate 54 is divided into a plurality of parts, and is attached inside the channel 36 by bolting so that the partition plate 54 can be disassembled. Further, the divided members are sized so that they can be inserted and removed from the manhole. Short pipe 58
Has a structure that can be detached from the partition plate 54 so that the surface of the tube plate can be easily inspected when disassembled.

As one mechanism of the metal dusting phenomenon, the C component in the supply gas is deposited, and this C adheres to the metal surface to carburize the metal, resulting in corrosion damage from the metal surface due to simultaneous progress with oxidation. It is thought to go.
The temperature range where metal dusting occurs is 450 to 800 ° C.
However, the manufacturing material of this heat exchanger is 21 / 4Cr-1M.
For o steel, it is considered that metal dusting is most likely to occur at about 550 ° C. or higher, based on the results of investigations on a heat exchanger that was actually damaged. In a heat exchanger made of 21 / 4Cr-1Mo steel, if no partition chamber or short tube (ferrule) is provided, the tube weld will be the reactor gas (approximately 580
(° C) and the supply gas (about 530 ° C) on the outlet side, which exceeds 550 ° C depending on the part of the tube.
Metal dusting can occur. On the other hand, in the heat exchanger of the present embodiment, low-temperature steam (about 400 ° C. or less) is passed through the partition chamber 56 in the channel 36 to flow into the annular space 64 between the outer surface of the short tube 58 and the inner surface of the tube 38. Since the tube weld has a sufficiently low temperature of about 500 ° C. or lower, metal dusting can be prevented without using expensive stainless steel as a manufacturing material. Also,
The partition plate 54 and the short pipe 58 are easy to manufacture and attach,
Since only a small amount of material is required, the cost of manufacturing the heat exchanger is slightly increased as compared with the case where these parts are not attached.

Embodiment 2 In this embodiment, as shown in FIG. 3, low temperature steam is blown to the shell side to lower the temperature of the welded portion and prevent damage to the welded portion due to metal dusting. Is. That is, a partition plate (deflector plate) 66 is provided on the downstream side (right side in FIG. 3) of the front tube sheet (high temperature side tube sheet) 32 substantially parallel to the front tube sheet 32 and the front tube sheet 32. A partition chamber 68 is formed between these partition chambers 68
A cooling steam introducing pipe 70 is connected to the cooling steam introduction pipe 70, and the heated steam after cooling is mixed with the heated supply gas so that the leading end portion (lower end portion in FIG. 3) of the partition plate 66 and the heated supply gas are supplied. It is configured to communicate with the inside of the shell through which the gas passes. 72 is a communication part. Since a large amount of steam is originally contained in the supply gas, even if a small amount of steam is mixed, it does not have an adverse effect. In the heat exchanger of this embodiment, the partition plate 66 is provided in addition to the cooling of the welded portion 46 by the low temperature steam, so that the shell side surface of the front tube sheet 32 and the tube inlet pipe including the welded portion 46 are provided. The carburizing feed gas does not come into contact with the parts. Therefore, it is sufficient that the steam temperature is 500 ° C. or lower. Other configurations and operations are similar to those of the first embodiment.

[0019]

Since the present invention is configured as described above, it has the following effects. (1) Introduce steam at a temperature lower than the temperature of the heated fluid at the shell outlet into the tube inlet pipe section near the front tube sheet (high temperature side tube sheet), and the shell side surface of the front tube sheet and the tube. By cooling the tube inlet pipe part including the welded part between the front tube plate and the front tube plate, the temperature of the tube welded part becomes low, so metal dusting is prevented or reduced without using expensive stainless steel as a manufacturing material. can do. In this case, by setting the temperature of the cooling steam so that the tube weld will be about 500 ° C or less,
It is possible to reliably prevent metal dusting. (2) Partition plates and short tubes (ferrules) are easy to manufacture and install, and the material is small, so the cost of manufacturing heat exchangers is not so low compared to the case where these parts are not installed. . (3) When the steam is blown into the shell side, the fluid to be heated does not come into contact with the shell side surface of the front tube sheet and the tube inlet pipe portion including the tube welded portion. If it is a carburizing gas,
Metal dusting can be more reliably prevented in combination with the cooling of the shell side surface of the front tube sheet by the low temperature steam and the tube inlet tube section including the tube welded section.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a heat exchanger of the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part in FIG.

FIG. 3 is a vertical cross-sectional view of the essential parts showing another embodiment of the heat exchanger of the present invention.

[Fig. 4] Welded mounting structure for tube and tube sheet (Type A)
FIG.

FIG. 5: Welded mounting structure for tube and tube sheet (Type B)
FIG.

[Fig. 6] Welding mounting structure for tube and tube sheet (Type C)
FIG.

FIG. 7: Welded mounting structure for tube and tube sheet (Type D)
FIG.

[Explanation of symbols]

 30 Shell (Body) 32 Front Tube Sheet (High Temperature Side Tube Sheet) 34 Rear Tube Sheet (Low Temperature Side Tube Sheet) 36 Channel 38 Tube 40 Open 42 Short Cylinder 44 Tube Inlet Tube 46 Tube Weld 48 Baffle 50 Supply Gas Inlet 52 Supply Gas Outlet 54 Partition Plate 56 Partition Chamber 58 Short Pipe (Ferrule) 60 Steam Introducing Pipe 62 Spacer 64 Annular Space 66 Partition Plate (Deflector Plate) 68 Partition Chamber 70 Steam Introducing Pipe 72 Communication Port

Claims (6)

[Claims] 1. A method for performing heat exchange by flowing a fluid to be cooled on a tube side and a fluid to be heated on a shell side,
Introducing steam at a temperature lower than the temperature of the heated fluid at the shell outlet into the tube inlet tube near the front tube sheet,
A heat exchange method, comprising cooling a shell-side surface of a front tube sheet and a tube inlet tube section including a welded portion between the tube and the front tube sheet. 2. A method of heat exchange by flowing gas to be cooled on the tube side and gas to be heated on the shell side,
A short tube is inserted into the tube inlet tube section of the front tube sheet, and a gas to be cooled is caused to flow in the short tube, and the shell outlet is heated in an annular space between the short tube and the tube inlet tube section. After introducing steam at a temperature lower than the temperature of the generated gas to cool the shell side surface of the front tube sheet and the tube inlet tube section including the welded portion of the tube and the front tube sheet, A heat exchange method characterized by mixing. 3. A method of heat exchange by flowing gas to be cooled on the tube side and gas to be heated on the shell side,
A partition chamber is formed on the downstream side of the tube inlet tube of the front tube sheet by providing a partition plate substantially parallel to the front tube sheet to form a partition chamber.
After introducing steam having a temperature lower than the temperature of the heated gas at the shell outlet to cool the shell side surface of the front tube sheet and the tube inlet tube section including the welded portion between the tube and the front tube sheet, heating is performed. A heat exchange method, characterized in that the heat exchange method comprises mixing the gas with the gas. 4. A heat exchanger having a structure in which a tube and a tube plate are attached by welding, in which a fluid to be cooled on the tube side is caused to flow by flowing a fluid to be heated on the shell side, and the heat exchange is performed in the vicinity of the front tube plate. A heat exchanger characterized in that a partition chamber surrounded by the front tube plate and a partition plate is provided in the tube inlet pipe section, and a cooling steam introducing pipe is connected to the partition chamber. 5. A heat exchanger having a structure in which a tube and a tube sheet are attached by welding, in which a gas to be cooled on the tube side and a gas to be heated are flowed to the shell side to exchange heat, the upstream side of the front tube sheet. A partition plate is provided on this side to form a partition chamber substantially parallel to this front tube sheet, and a short tube with an outer diameter smaller than the tube inner diameter is inserted so that the tip is inserted into the tube inlet tube section of this front tube sheet. Is attached to the partition plate, and a steam introducing pipe for cooling is connected to the partition chamber. 6. A heat exchanger having a structure in which a tube and a tube sheet are attached by welding, in which a gas to be cooled on the tube side and a gas to be heated are made to flow on the shell side to exchange heat, the downstream side of the front tube sheet. A partition plate is provided on the side substantially parallel to the front tube plate to form a partition chamber, and a cooling steam introducing pipe is connected to this partition chamber, and the heated steam after cooling is mixed with the heated gas. Thus, the heat exchanger characterized in that the tip of the partition plate and the inside of the shell through which the heated gas passes are in communication with each other.