CN107941052A - A kind of two-tube double tube plate heat exchanger tube to plate welding method - Google Patents

Abstract

The invention proposes a tube sheet calculation method for a double-tube double-tube-sheet heat exchanger, which belongs to the technical field of heat exchanger tube-sheet design. Tube-sheet heat exchanger: an outer heat exchanger composed of an outer tube sheet and an inner heat exchange tube, and an inner heat exchanger composed of an inner tube sheet and an outer heat exchange tube, and then perform relevant calculations in accordance with relevant national standards . In the calculation, the constraint effect of the inner tube sheet and the outer heat exchange tube on the cylinder is considered for the outer heat exchanger, and the constraint effect of the outer tube sheet and the inner heat exchange tube on the cylinder is considered for the inner heat exchanger. The design and calculation method of the tube sheet of the double-tube double-tube-sheet heat exchanger proposed by the present invention provides a brand-new technical solution for the design and calculation of this type of heat exchanger, and solves the key technical problem that has plagued technicians in related fields for a long time.

Description

A Calculation Method for Tube Sheet of Double Tube Double Tube Sheet Heat Exchanger

technical field

The invention relates to a design calculation method of a heat exchanger tube sheet, in particular to a design calculation method of a double tube double tube sheet heat exchanger tube sheet.

Background technique

Shell-and-tube heat exchangers are widely used in the heat exchange process between hot and cold media in the process industry. Leakage is one of the common faults of heat exchange equipment. For ordinary heat exchangers, once leakage occurs, it will cause The two media are in contact with each other. In the general chemical process, a small amount of leakage of the heat exchanger is usually allowed, but in many special occasions such as polysilicon, organic silicon and fluorine chemical industry, it is required that the two media involved in heat exchange must not be mixed and contacted, otherwise it will endanger the equipment. safety, and even lead to catastrophic accidents. Therefore, those skilled in the related art have developed a safety heat exchanger with double tubes and double tube sheets. There are gaps; there are two tube sheets at the front and rear ends of the heat exchanger, the two ends of the inner heat exchange tube of the heat exchanger are respectively connected with two outer tube sheets, and the two ends of the outer heat exchange tube are respectively connected with two inner tube sheets ; There are gaps between the inner and outer tube sheets at both ends of the heat exchanger, and the gaps communicate with each other through the gaps between the inner and outer heat exchange tubes to form a closed cavity. In this way, when a leak occurs in the heat exchanger, the leaked medium will first enter the closed cavity, causing the pressure of the closed cavity to change. By monitoring the pressure change of the closed cavity, the leakage of the heat exchanger can be found in time and effective measures can be taken, which can effectively prevent the cold and hot media in the heat exchanger from contacting each other due to leakage, and ensure the safety of the equipment.

At present, domestic and foreign researches on double-tube double-tubesheet heat exchangers mainly focus on structure selection, double casing type, heat transfer analysis and leakage monitoring, etc. The research on tubesheet strength design is still relatively lacking. At present, there are no relevant standards for the strength design of double-tube double-tube sheets, and no relevant research institutions have proposed reliable design methods. Many designs mainly rely on engineering experience or experimental methods, and these design methods may have higher requirements for design departments. High, or the economic investment is large, and the design cycle is long. The designed heat exchanger tube sheet also often has problems such as insufficient strength and potential safety hazards, or the phenomenon of material selection that is too thick and wasteful is very serious.

Contents of the invention

The object of the present invention is to propose a calculation method for the tube sheet of a double-tube double-tube-sheet heat exchanger, and to provide a reliable design method for the design of this type of heat exchanger.

The technical scheme adopted by the present invention is: a design and calculation method for a tube sheet of a double-tube double-tube-sheet heat exchanger, which is characterized in that it includes the following steps:

Step 1, the double-tube double-tube-sheet heat exchanger is disassembled into two ordinary fixed tube-sheet heat exchangers: an outer heat exchanger and an inner heat exchanger, and the outer heat exchanger consists of an inner heat exchange tube and two outer heat exchangers. The inner heat exchanger is composed of an outer heat exchange tube and two inner tube sheets;

Step 2. Calculate according to the calculation method for the fixed tube-sheet heat exchanger tube sheet specified in the relevant national standards.

As a preferred solution, for the disassembled outer heat exchanger, when calculating the axial stiffness of the cylinder, the constraint effect of the outer heat exchange tube and the two inner tube sheets on the cylinder is considered. For the disassembled inner heat exchanger, When calculating the axial stiffness _of the cylinder, the constraint effect of the inner heat exchange tube and the two outer tube sheets on the cylinder is considered. The stiffness ratio Q ₂ of the inner heat exchanger heat exchange tube bundle and the cylinder is calculated according to the following formula:

where L is the distance between the two outer tube sheets,

L ₁ is the distance between the inner tube sheet and the outer tube sheet,

L ₂ is the distance between the two inner tube sheets,

a ₁ is the cross-sectional area of the inner heat exchange tube wall metal of a single heat exchange tube,

a ₂ is the cross-sectional area of the tube wall metal of a single heat exchange tube of the outer heat exchange tube,

n is the number of heat exchange tubes,

E ₁ is the elastic modulus of the isolation cavity between the inner and outer tube sheets,

E ₃ is the elastic modulus of the heat exchanger shell,

E _t1 is the elastic modulus of the inner heat exchange tube material,

E _t2 is the elastic modulus of the material of the external heat exchange tube,

A ₁ is the cross-sectional area of the connection pup between the inner and outer tube sheets,

A ₃ is the cross-sectional area of the heat exchanger cylinder.

Compared with the prior art, the beneficial effect of the present invention is to propose a design and calculation method for the tube sheet of a double-tube double-tube-sheet heat exchanger, which solves the key technology of this type of heat exchanger design that has long plagued those skilled in the related art problem.

Description of drawings

Figure 1 is a schematic diagram of the structure of a double-tube double-tube-sheet heat exchanger.

Figure 2 is a schematic diagram of the structure of the disassembled external heat exchanger.

Figure 3 is a schematic diagram of the disassembled internal heat exchanger

Figure 4 is the equivalent cylinder diagram of the external heat exchanger

Figure 5 is the equivalent cylinder diagram of the internal heat exchanger

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The structure of the double-tube double-tube-sheet heat exchanger is shown in Figure 1. Its main structure includes two outer tube sheets 1 and two inner tube sheets 2. Each group of heat exchange tubes consists of two tubes nested together. They are the inner heat exchange tube 4 and the outer heat exchange tube 5 respectively, wherein the two ends of the inner heat exchange tube 4 are respectively connected with two outer tube plates 1 , and the two ends of the outer heat exchange tube 5 are respectively connected with two inner tube plates 2 . There is a gap between the inner heat exchange tube 4 and the outer heat exchange tube 5, and there is no constraint between the two. The outer tube sheet 1 and the inner tube sheet 2 at both ends of the heat exchanger are respectively connected by short joints 6 . The heat exchanger can be disassembled to obtain a fixed tube-sheet heat exchanger consisting of the inner heat-exchange tube 4 and the outer tube-sheet 1 as a fixed tube-sheet heat exchanger—the outer heat exchanger (as shown in FIG. 2 ), and A fixed tube-sheet heat exchanger consisting of an outer heat-exchanging tube 5 and an inner tube-sheet 2 that does not double as a flange—an inner heat exchanger (as shown in FIG. 3 ).

For the disassembled external heat exchanger, its shell 3-1 is actually restrained by the external heat exchange tube 5 and the inner tube sheet 2, which is different from the ordinary fixed tube sheet heat exchanger, and it needs to be found A suitable computational model. An equivalent cylinder is assumed for it, and the equivalent cylinder is composed of two cylinders 7, two hypothetical rigid bodies 10, a cylinder 8, and a cylinder 9, as shown in FIG. 4 . Among them: the cylinder 7 is the short joint 6 of the original double-tube double-tubesheet heat exchanger, its thickness δ _s1 , length L ₁ , cross-sectional area is A ₁ , and elastic modulus is E ₁ . The axial elongation under force is ΔL ₁ ; cylinder 8 is an equivalent cylinder evolved from the outer heat exchange tube bundle of the original double-tube double-tubesheet heat exchanger, and should have the same rigidity as the original heat exchange tube bundle and the same linear expansion coefficient, its elastic modulus is E ₂ , and its cross-sectional area is A ₂ , assuming that under the action of unit axial force, the axial force component it receives is F ₂ , and its axial elongation The volume is ΔL ₂ ; the cylinder 9 is the cylinder 3 of the original double-tube double-tubesheet heat exchanger, its thickness δ _s , length L ₂ , cross-sectional area A ₃ , and elastic modulus E ₃ , assuming that in the unit Under the action of axial force, the axial force component it receives is F ₃ , and its axial elongation is ΔL ₃ ; assuming that the rigid body 10 is composed of the inner tube plate 2 of the original double-tube double-tube-sheet heat exchanger Approximately, it is assumed to be an absolute rigid body.

Under the action of unit axial force F, the axial elongation of each part is as follows:

The axial force should satisfy the following balance relationship:

F＝F ₂ +F ₃ (4)

Assuming that the total axial elongation of the system is ΔL, each axial elongation should satisfy the following deformation coordination relationship:

ΔL ₂ =ΔL ₃ (5)

ΔL=2ΔL ₁ +ΔL ₂ (6)

Combining formulas (1) to (6), the total elongation of the system under the action of unit axial force F can be obtained:

Assuming that the axial stiffness of the equivalent cylinder of the external heat exchanger is K _s1 , it can be seen that it satisfies:

Then, for the external heat exchanger, the stiffness ratio Q1 _of the heat exchange tube bundle and the equivalent shell cylinder should be calculated according to the following formula:

The unexplained symbols in the formula are as follows:

a ₁ : the cross-sectional area of the tube wall metal of one inner heat exchange tube, mm ² ;

E _t1 : elastic modulus of inner heat exchange tube material, MPa;

a ₂ : the cross-sectional area of the tube wall metal of one outer heat exchange tube, mm ² ;

E _t2 : Elastic modulus of the material of the external heat exchange tube, MPa;

n: number of heat exchange tubes.

Other calculations of the outer heat exchanger tube sheet obtained from the disassembly can be carried out according to the ordinary fixed tube sheet heat exchanger.

For the internal heat exchanger obtained by dismantling, its cylinder body 3-2 is actually constrained by the inner heat exchange tube 4 and the outer tube sheet 1, and an equivalent cylinder body is also assumed for it, and the equivalent cylinder body is composed of two cylinder bodies 11. Two hypothetical rigid bodies 14, cylinder 12 and cylinder 13 are formed, as shown in Fig. 5 . Among them: cylinder 11 and cylinder 13 are the same as the equivalent cylinder of the external heat exchanger, and cylinder 12 is the equivalent cylinder obtained by the evolution of the inner heat exchange tube bundle of the original double-tube double-tubesheet heat exchanger, which is the same as the original heat exchanger. The tube bundle should have the same stiffness and the same coefficient of linear expansion, its elastic modulus is E ₂ , and its cross-sectional area is A ₂ , assuming that under the action of unit axial force, the axial force component it receives is F ₂ , here Its axial elongation is ΔL ₂ ; assuming that the rigid body 14 is approximated by the outer tube sheet 1 of the original double-tube double-tube sheet heat exchanger, it is assumed to be an absolute rigid body.

Under the action of unit axial force F, the axial elongation of each part is as follows:

The axial force should satisfy the following balance relationship:

F＝F ₁ +F ₃ (14)

F ₁ =F ₂ (15)

The elongation of each axis should satisfy the following deformation coordination relationship:

2ΔL ₁ +ΔL ₃ =ΔL ₂ (16)

Combining formula (11) to formula (16), we can get:

Substituting into formula (13), the elongation of the inner heat exchanger cylinder 3 under the action of the unit axial force F is obtained:

Assuming that the axial stiffness of the equivalent cylinder of the inner heat exchanger is K _s2 ′, it can be seen that it satisfies:

Then for the internal heat exchanger, the stiffness ratio _Q2 of the heat exchange tube bundle and the equivalent shell cylinder should be calculated as follows:

Other calculations of the inner heat exchanger tube sheet obtained from the disassembly can be carried out according to the ordinary fixed tube sheet heat exchanger.

Claims (2)

1. a double tube double tube sheet heat exchanger tube sheet calculation method is characterized in that comprising the steps: Step 1, the double-tube double-tube-sheet heat exchanger is disassembled into two ordinary fixed tube-sheet heat exchangers: an outer heat exchanger and an inner heat exchanger, and the outer heat exchanger consists of an inner heat exchange tube and two outer heat exchangers. The inner heat exchanger is composed of an outer heat exchange tube and two inner tube sheets; Step 2. Calculate according to the calculation method for the fixed tube-sheet heat exchanger tube sheet specified in the relevant national standards. 2. The method for calculating the tube sheet of a double-tube double-tube-sheet heat exchanger according to claim 1, characterized in that: for the disassembled external heat exchanger, when calculating the axial stiffness of the cylinder, the external heat exchange tubes and The restraining effect of the two inner tube sheets on the shell, for the disassembled inner heat exchanger, the restraining effect of the inner heat exchange tube and the two outer tube sheets on the shell is considered when calculating the axial stiffness of the shell, step 2 The stiffness ratio Q ₁ of the heat exchange tube bundle of the outer heat exchanger and the cylinder dismantled in , and the stiffness ratio Q ₂ of the heat exchange tube bundle of the inner heat exchanger disassembled and the cylinder are calculated according to the following formula: <mrow><msub><mi>Q</mi><mn>1</mn></msub><mo>=</mo><mfrac><mrow><msub><mi>E</mi><mrow><mi>t</mi><mn>1</mn></mrow></msub><msub><mi>na</mi><mn>1</mn></msub></mrow><mi>L</mi></mfrac><mo>&amp;lsqb;</mo><mfrac><mrow><mn>2</mn><msub><mi>L</mi><mn>1</mn></msub></mrow><mrow><msub><mi>E</mi><mn>1</mn></msub><msub><mi>A</mi><mn>1</mn></msub></mrow></mfrac><mo>+</mo><mfrac><msub><mi>L</mi><mn>2</mn></msub><mrow><mo>(</mo><msub><mi>E</mi><mrow><mi>t</mi><mn>2</mn></mrow></msub><msub><mi>na</mi><mn>2</mn></msub><mo>+</mo><msub><mi>E</mi><mn>3</mn></msub><msub><mi>A</mi><mn>3</mn></msub><mo>)</mo></mrow></mfrac><mo>&amp;rsqb;</mo></mrow> <mrow><msub><mi>Q</mi><mn>2</mn></msub><mo>=</mo><mfrac><mrow><msub><mi>E</mi><mrow><mi>t</mi><mn>2</mn></mrow></msub><msub><mi>na</mi><mn>2</mn></msub></mrow><mrow><msub><mi>E</mi><mn>3</mn></msub><msub><mi>A</mi><mn>3</mn></msub></mrow></mfrac><mo>&amp;CenterDot;</mo><mfrac><mrow><mo>(</mo><mfrac><mi>L</mi><mrow><msub><mi>E</mi><mrow><mi>t</mi><mn>1</mn></mrow></msub><msub><mi>na</mi><mn>1</mn></msub></mrow></mfrac><mo>+</mo><mfrac><mrow><mn>2</mn><msub><mi>L</mi><mn>1</mn></msub></mrow><mrow><msub><mi>E</mi><mn>1</mn></msub><msub><mi>A</mi><mn>1</mn></msub></mrow></mfrac><mo>)</mo></mrow><mrow><mo>(</mo><mfrac><mrow><mn>2</mn><msub><mi>L</mi><mn>1</mn></msub></mrow><mrow><msub><mi>E</mi><mn>1</mn></msub><msub><mi>A</mi><mn>1</mn></msub></mrow></mfrac><mo>+</mo><mfrac><mi>L</mi><mrow><msub><mi>E</mi><mrow><mi>t</mi><mn>1</mn></mrow></msub><msub><mi>na</mi><mn>1</mn></msub></mrow></mfrac><mo>+</mo><mfrac><msub><mi>L</mi><mn>2</mn></msub><mrow><msub><mi>E</mi><mn>3</mn></msub><msub><mi>A</mi><mn>3</mn></msub></mrow></mfrac><mo>)</mo></mrow></mfrac></mrow> where L is the distance between the two outer tube sheets, L ₁ is the distance between the inner tube sheet and the outer tube sheet, L ₂ is the distance between the two inner tube sheets, a ₁ is the cross-sectional area of the inner heat exchange tube wall metal of a single heat exchange tube, a ₂ is the cross-sectional area of the tube wall metal of a single heat exchange tube of the outer heat exchange tube, n is the number of heat exchange tubes, E ₁ is the elastic modulus of the isolation cavity between the inner and outer tube sheets, E ₃ is the elastic modulus of the heat exchanger shell, E _t1 is the elastic modulus of the inner heat exchange tube material, E _t2 is the elastic modulus of the material of the external heat exchange tube, A ₁ is the cross-sectional area of the connection pup between the inner and outer tube sheets, A ₃ is the cross-sectional area of the heat exchanger cylinder.