JPS6352311B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat exchanger, particularly a vertical fixed tube sheet heat exchanger. BACKGROUND OF THE INVENTION A vertical fixed tube plate heat exchanger as shown in FIG. 1 is conventionally known. This heat exchanger 1 is
Cylindrical vertical shell 2, upper end 2A of the shell
and the upper and lower fixed tube sheets 4 and 3 attached to the lower end portion 2B, respectively, and the upper and lower fixed tube sheets,
A number of stainless steel tubes 5 are attached along the length of the shell through them.
and a fluid inlet 6 and a fluid outlet 7 installed above and below the shell 2 to introduce fluid into the shell 2 and to draw out the introduced fluid;
and a lower channel 8 attached to the lower fixed tube sheet 3 for distributing and directing the fluid to the tubes 5 and an upper fixed tube sheet 4 attached to the upper fixed tube sheet 4 for collecting and discharging the heat exchanged fluid from the tubes 5. It consists of an upper channel 9. If necessary, a gas vent pipe 10 may be further attached above the shell 2. However, in this heat exchanger, cracks tend to occur in the portion 5A above the tube 5 where the tube 5 is held by the upper fixed tube plate 4. This is caused by, for example, residual stress when the tube is manufactured, stress applied when using a heat exchanger, dissolved oxygen in the fluid, other ions, etc., but it is also affected by the structure of the upper fixed tube sheet 4, temperature, etc. . Therefore, the present inventors have conducted extensive studies on obtaining a heat exchanger in which the occurrence of the above-mentioned cracks (referred to as stress corrosion cracking) is suppressed, and as a result, they have arrived at the present invention. Therefore, an object of the present invention is to provide a heat exchanger in which stress corrosion cracking is suppressed. This purpose is to provide a heat exchanger comprising the above-mentioned elements such that the fluid outlet port, preferably a plurality of fluid outlet ports, is such that the height of the flow surface of the fluid led out from the outlet port is the lower surface of the upper fixed tube plate. This is achieved by placing the heat exchanger at a height equal to or higher than the More preferably, the heat exchanger is provided with a jacket around the shell that collects and discharges the fluid led out from the outlet. The structure of the heat exchanger according to the present invention will be specifically explained with reference to FIG. The main elements of the heat exchanger of the present invention are the same as those of the conventional heat exchanger described above. That is, the heat exchanger 1 includes a shell 2, upper and lower fixed tube plates 4 and 3, a stainless steel tube 5, a fluid inlet, outlets 6 and 7, upper and lower channels 9 and 8, and the like. However, the position of the fluid outlet of the heat exchanger 1 according to the present invention is significantly different from that of the conventional heat exchanger. That is, the fluid outlet 7 is located so that the height of the flow surface of the fluid led out from the outlet is the same as or higher than the lower surface of the upper fixed tube plate 4, which is significantly different from the conventional method. different from that of The detailed explanation will be as follows with reference to FIG. FIG. 3 is a partially enlarged view of the vicinity of the fluid outlet 7, showing a case where the height of the fluid flow surface is the same as the height of the uneven surface of the upper fixed tube plate. That is, the fluid L flows through its outlet 7.
The outlet 7 is provided in the middle of the shell 2 so that the uppermost flow surface L _S is the same as the height (level) of the lower surface 4d of the upper fixed tube plate 4. In order to make the heights the same, the uppermost surface 7u of the fluid outlet 7 is the lower surface 4d of the upper fixed tube plate 4.
The number of fluid outlet ports provided in the middle of the shell 2 and the cross-sectional area of each outlet port must be the same as or higher than the fluid inlet port 6.
It is determined by considering the flow rate of the fluid introduced from the In the heat exchanger of the present invention, it is important not to form a space in the upper fixed tube plate 4 below the lower surface 4d that is not filled with fluid, so as long as this is followed, the shape of the fluid outlet, You can decide the number and size. In the heat exchanger of the present invention, a jacket 12 is preferably provided around the outer periphery of the shell 2 to collect the fluid discharged from the fluid outlet 7, and then the fluid is discharged through the discharge pipe 11. Discharge pipe 11
If the height of is increased as shown in FIG. 2, the flow surface Ls of the fluid outlet 7 can be located at the uppermost surface 7u of the fluid outlet tube 7. Furthermore, in the heat exchanger of the present invention, the material of the upper fixed tube plate 4 and the upper portion of the shell 2 that is in contact with the fluid in the tube is preferably a general structural carbon steel material, and the side of the tube that is in contact with the fluid is lined with stainless steel. Or use clad wood. Since the heat exchanger according to the present invention has the above-described structure, it exhibits the following functions and effects. (1) The space under the upper fixed tube plate inside the upper shell is eliminated. Therefore, the temperature of the upper fixed tube plate 4 can be lowered by the cooling fluid, and stress corrosion cracking of the stainless steel tube 5 at the contacting portion 5' can be suppressed. (2) Since the space is eliminated, the concentration of substances that cause stress corrosion cracking, such as salt, due to repeated drying and wetting of the cooling fluid in the contacting part 5' is prevented, and the stainless steel of the contacting part 5' is prevented from concentrating. Stress corrosion cracking of the tube 5 can be suppressed. Example 1 The structure shown in Fig. 1 has a heat transfer area of 5 m ² and a shell inner diameter.
250mm, number of tubes: 19, outer diameter: 27.7mm, length: 4
A process fluid at 150°C was introduced into the tube side of two vertical multitubular stainless steel heat exchangers. The exit temperature of this process fluid is 140°C. Industrial water at 20°C is passed through the shell side for heat exchange. This heat exchanger was operated at the same time, and when stress corrosion cracking occurred and the tube leaked, the operation was stopped, process fluid and industrial water were extracted, and stress corrosion cracking of the tube was investigated. The investigation method is an eddy current flaw detector (Electronic Magnetic Industry MT-
3450 model). The survey results are shown in Table 1.

[Table] Next, the stress corrosion cracked tube was replaced with a new tube, and one of the heat exchangers was connected to the circumferential shell near the upper fixed tube plate with several outlet ports for discharging the fluid inside the shell. The structure was improved to a jacket type for collectively discharging the fluid discharged from the outlet (heat exchanger according to the present invention), and the heat exchanger was operated simultaneously with another conventional heat exchanger. The results are shown in Table 2. In normal vertical heat exchangers, stress corrosion cracking occurs in 9 to 12 months, leading to tube leakage, but in the heat exchanger of the present invention, which has an improved structure, no stress corrosion cracking occurs for 3 years. A significant effect was observed.

[Table] Example 2 A process fluid at 130° C. was introduced into the tube side of two stainless steel vertical multitubular heat exchangers with a heat transfer area of 275 m ² . The outlet temperature of this process fluid is 120℃
It is. Industrial water at 20°C is passed through the shell side at 30°C.
Remove at °C. When this heat exchanger was operated at the same time, stress corrosion cracking occurred in the tubes from the second year onwards. Table 3 shows the occurrence situation. When renewing one of the two units after five years of operation, several outlet ports were installed in the circumferential shell near the upper fixed tube plate to draw out the fluid inside the shell, and the fluid was discharged from these outlets. The structure was improved to a jacket system (heat exchanger according to the present invention) for collectively discharging the collected fluid, and operation began. To investigate whether stress corrosion cracking was occurring, we removed the upper channel during annual inspections, filled the tube with water, and applied air pressure to the shell side to visually inspect the tube. Further investigation was conducted using an eddy current flaw detector (Denshi Magnetic Industry Model MT-3450). In normal vertical heat exchangers, stress corrosion cracking occurs after 2 to 3 years of operation, and the number of stress corrosion cracks tends to increase every year.
The heat exchanger of the present invention, which has an improved structure, did not suffer from stress corrosion cracking for 4 years, and was found to be highly effective.

【table】 [Brief explanation of the drawing]

FIG. 1 is a fragmented longitudinal sectional view of a conventional vertical fixed tube plate heat exchanger. FIG. 2 is a fragmented longitudinal sectional view of the heat exchanger according to the present invention. FIG. 3 is a partially enlarged view of the vicinity of the fluid outlet. DESCRIPTION OF SYMBOLS 1... Heat exchanger, 2... Shell, 3... Lower fixed tube sheet, 4... Upper fixed tube sheet, 5... Stainless steel tube, 6... Fluid inlet, 7... Fluid outlet, 8 ... lower channel, 9 ... upper channel, 10 ... gas vent pipe, 11 ... discharge pipe, 12
...jacket.

Claims (1)

[Claims] 1. A cylindrical vertical shell, an upper and lower fixed tube sheet attached to the upper and lower ends of the shell, and a tube plate that is passed through the upper and lower fixed tube sheets in the longitudinal direction of the shell. a number of stainless steel tubes installed along the shell, and liquid inlets and outlets installed above and below the shell for introducing fluid into the shell and for removing the introduced fluid. and a lower channel attached to the lower fixed tubesheet for distributing and directing fluid to said tube and an upper channel attached to said upper tubesheet for collecting and discharging heat exchanged fluid from said tube. In the heat exchanger, the liquid outlet is positioned such that the height of the flow surface of the fluid led out from the outlet is the same as or higher than the lower surface of the upper fixed tube plate. A vertical fixed tube plate heat exchanger featuring: