RU2743930C1 - Shell and tube heat exchanger - Google Patents

Abstract

FIELD: heat exchangers.

SUBSTANCE: invention relates to heat exchangers and can be used in heat exchangers of different technological processes especially when the temperature of the coolant exceeds the maximum allowable temperature for the material of heat exchange tubes and walls of the heat exchanger body. The shell-and-tube heat exchanger consists of a housing with inlet and outlet nozzles, bundles of heat exchange tubes placed in it, consisting of heat exchange tubes fixed in tube sheets, each having an autonomous input and output of the pipe medium. All inlets and outlets of the pipe medium are installed on the inner surfaces of the walls of the casing and cover from 60% to 90% of the wall areas, all bundles are made with the same geometric parameters. Each subsequent bundle of heat exchange tubes is at an angle of 90 degrees relative to the previous one. All bundles are installed in a pre-tensioned state along the heat-exchange tubes and some of the bundles are connected by direct flow by means of crossover and outlet pipes, and some of the bundles are connected in counter flow with respect to the direction of the intertubular medium. The proportion (%) of the bundles connected by direct flow γ_D or counter flow γ_C is determined by calculation.

EFFECT: invention makes it possible to ensure operational manufacturability and maintainability, to remove restrictions on the temperature of the annular medium, to ensure gravitational independence and rational use of the heat exchanger volume.

1 cl, 7 dwg

Description

The invention relates to heat exchangers and can be used in heat exchangers of various technological processes, especially when the temperature of the coolant exceeds the maximum allowable temperature for the material of the heat exchange tubes and the walls of the heat exchanger body.

The main characteristics of heat exchangers (TA) are well studied and widely covered in numerous publications, for example, A.S. Tsygankov “Calculations of ship heat exchangers, reference manual. State Union publishing house of the shipbuilding industry. Leningrad, 1956, or Case V.M., London A.L. "Compact heat exchangers", M .: Energiya, 1967. In these publications, in particular, considerable attention is paid to the consideration of optimization of the characteristics of heat exchangers by choosing various schemes for connecting sections-bundles of heat exchange tubes, a method of protecting structural elements from overheating, reducing metal consumption constructions, etc. Advantages of "countercurrent" schemes for connecting beam sections with an insignificant temperature gradient of the coolants and the advantages of "direct-flow" schemes with a significant excess of the critical temperatures of heat-exchange tube materials by the coolant are disclosed in detail.

A known heat exchanger (Inventor's certificate SU No. 172142 A1, IPC G06G 5/00, F15C 3/14, publ. 1965), containing a rectangular body with flanges for supplying and removing the coolant, installed inside the body of the coil, and a device for protecting the body from burnout, made in the form of a screen of a number of pipes connected by jumpers located between the walls and the coils, while between one of the peripheral packages of the coils and the adjacent package there are hollow rods fixed on the cover with removable nozzles connected to the inlet manifold of the cooling medium. The known heat exchanger has the following disadvantages:

- structurally complex due to the presence of an additional element in the form of a protective screen;

- does not provide uniform heat removal in the cross-sectional plane due to the localization of the inlets of the cooling medium on one wall of the case;

- does not provide uniform heat removal along the flow of the annular medium due to a decrease in the driving force between the heat exchange media;

- is gravitationally dependent due to the possible sagging of the heat exchange tubes when working on the side or vertically;

- to protect the elements of heating from overheating, it requires the consumption of a cooling medium, which significantly increases operating costs.

The closest in technical essence and technical result is a shell-and-tube heat exchanger (Patent RU No. 2090816, IPC F28D 7/00, F28F 1/00, publ. 09/20/1997), taken as the closest analogue (prototype) containing a housing with an inlet and outlet nozzles for directing the intertubular medium and placed therein sections-bundles of heat exchange tubes, consisting of heat exchange tubes fixed in tube sheets, and each having an autonomous input and output of the tube medium.

In the above patent, solutions are proposed that make it possible to align heat transfer both in the cross-sectional plane and along the TA. However, the known shell-and-tube heat exchanger has the following disadvantages:

- lack of interchangeability of sections-bundles due to different - variable pitch between the tubes, which complicates the design and reduces its operational manufacturability and maintainability;

- limiting the temperature of the annular medium, the maximum permissible temperature of the material of the side walls of the casing;

- it is gravitationally dependent due to the possible sagging of the heat exchange tubes when operating in a lateral or vertical position, therefore, requires additional fixation of the tubes inside the body when they are relatively long;

- introduces additional hydraulic losses of the annular fluid flow on the tube fixing elements;

- irrational use of the volume of the heat exchanger due to the increased distance between the tubes of the first - inlet rows of sections-bundles.

The technical problem, the solution of which is provided in the implementation of the proposed invention and cannot be implemented using the prototype, is:

- the impossibility of ensuring the interchangeability of the sections of the beams;

- the impossibility of increasing the temperature of the intertubular medium above the maximum allowable temperature for the material of the side walls of the body;

- the impossibility of ensuring the performance of the heat exchanger in different spatial positions without introducing additional hydraulic losses in the flow of the annular medium.

- impossibility of rational use of the volume of the heat exchanger.

The technical objective of the present invention is to ensure operational manufacturability and maintainability, removing restrictions on the temperature of the annular medium, ensuring gravitational independence and rational use of the volume of the heat exchanger.

The technical problem is solved by the fact that in a shell-and-tube heat exchanger containing a housing with inlet and outlet nozzles for directing the intertubular medium and the sections-bundles of heat exchange tubes placed in it, consisting of heat exchange tubes fixed in the tube sheets, and each having an autonomous input and output of the tube medium , according to the invention, all inlets and outlets of the pipe medium are installed on the inner surfaces of the walls of the casing and cover from 60% to 90% of the wall areas, all sections-bundles are made with the same geometric parameters, each subsequent section-bundle of heat exchange tubes is deployed at an angle of 90 ° relative to the previous one, all sections-bundles are installed in a pre-tensioned state along the heat-exchange tubes and some of the sections-bundles are connected in direct flow by means of crossover and outlet pipes, and some of the sections-bundles are connected in counterflow with respect to the direction of the intertubular medium and the proportion of sections-bundles connected by direct flow γ _D or countercurrent γ _C determined by the formula:

Where

N _D - the number of sections-bundles connected by direct flow;

N is the total number of bundle sections in the heat exchanger;

- критическая температура, обусловленная требованием длительной прочности материала, °С;

- critical temperature due to the requirement for long-term strength of the material, ° С;

- температура горячего и холодного теплоносителя на входе в теплообменник, соответственно, °С.

- temperature of the hot and cold heat carrier at the inlet to the heat exchanger, respectively, ° С.

a, b - empirical constants depending on the thermophysical properties of the heat carrier flows.

The shell-and-tube heat exchanger contains a housing with inlet and outlet nozzles for directing the intertubular medium and the sections-bundles of heat exchange tubes placed in it, consisting of heat exchange tubes fixed in the tube sheets, and each having an autonomous input and output of the tube medium.

Unlike the prototype, all inlets and outlets of the pipe medium are installed on the inner surfaces of the walls of the body and cover from 60% to 90% of the wall areas, all sections-bundles are made with the same geometric parameters, each subsequent section-bundle of heat exchange tubes is deployed at an angle of 90 ° relative to the previous one, all section-bundles are installed in a pre-tensioned state along the heat-exchange tubes and some of the sections-bundles are connected in direct flow by means of crossover and outlet pipes, and some of the sections-bundles are connected in counterflow with respect to the direction of the intertubular medium and the proportion of sections-bundles connected by direct flow γ _D or countercurrent γ _C is determined by the formula:

N _D , pcs. - the number of sections-bundles connected by direct flow;

N, pcs. - the total number of sections-bundles in the heat exchanger;

°С - критическая температура, обусловленная требованием длительной прочности материала;

° С - critical temperature due to the requirement for long-term strength of the material;

°С - температура горячего и холодного теплоносителя на входе в теплообменник, соответственно.

° С is the temperature of the hot and cold heat carrier at the inlet to the heat exchanger, respectively.

a, b - empirical constants depending on the thermophysical properties of the heat carrier flows.

All inlets and outlets of the pipe medium are installed on the inner surfaces of the casing walls and cover from 60% to 90% of the wall areas, thereby protecting them from overheating and increasing heat transfer to the heated medium due to additional heat exchange surfaces.

Section-bundles are made the same in all geometric parameters (diameters, lengths, etc.), which allows you to install any section-bundle in any place both during repair and when replacing failed ones with new ones, thereby increasing the operational manufacturability and maintainability of TA.

Each subsequent section-bundle of heat exchange tubes is deployed at an angle of 90 ° relative to the previous one, which protects both the side and the top from the bottom wall of the housing from overheating.

The total number of sections-beams is calculated according to well-known methods, given, for example, in the indicated sources to the application.

All sections-bundles are installed in a pre-tensioned state along the heat exchange tubes, which avoids sagging of the tubes during their thermal expansion and ensures gravitational independence.

The required tension force of the section-bundle to minimize the sagging of the tubes is determined by the well-known formula, for example, “Gantry cranes and overhead cranes. Cable type cranes ”, A.P. Kobzev, V.P. Ponomarev; ed. K. D. Nikitina, Krasnoyarsk: I1SCh KSTU, 2005, p. 33, 34:

where N, kg is the pre-tensioning force of the heat exchange tubes;

G, kg - weight of the filled heat exchange tube;

L, m - the length of the heat exchange tube;

f, m - permissible deflection arm of the heat exchange tube;

n is the number of heat exchange tubes in the section-bundle.

Some of the sections-bundles are connected by a forward flow by means of cross-over and outlet pipes, which makes it possible to avoid heating the walls of the heat exchange tubes above the critical temperature.

Some of the sections-bundles are connected by means of cross-over and outlet pipes in a countercurrent with respect to the direction of the annular medium, which makes it possible to equalize the thermal heads in the sections-bundles and thereby increase the compactness of the TA.

The calculation of the proportions of section-bundles connected by direct flow or counter-current according to the above formula optimizes their ratio, which makes it possible to determine the minimum required number of direct-flow sections-bundles to exclude possible heating of heat exchange tubes above the critical temperature while maximizing the average driving force, which ultimately determines compact design and efficiency of the TA as a whole.

Thus, the proposed invention makes it possible to ensure operational manufacturability and maintainability, to remove restrictions on the temperature of the annular medium, to ensure gravitational independence and rational use of the volume of the heat exchanger.

FIG. 1 shows a cross-section of a shell-and-tube heat exchanger.

FIG. 2 shows a diagram of the connection of sections-bundles and a diagram of the movement of heat exchange media.

FIG. 3 shows a view "B" on the walls of a shell-and-tube heat exchanger, explaining the degree of overlapping of the walls by inputs and outputs.

FIG. 4, 5, 6 show examples of flow around inputs or outputs at different degrees of wall overlap (60%, 75%, 90%).

FIG. 7 shows a fragment (section A-A) of a tube sheet with heat exchange tubes.

The positions in the drawings are given:

1 - shell-and-tube heat exchanger

2 - case

3 - inlet pipe

4 - outlet branch pipe

5 - the direction of the annular medium

6 - wall (bottom)

7 - heat exchange tube

8 - tube sheets

9 - inlet of the pipe medium

10 - outlet of the pipe medium

11 - wall (side)

12 - previous section-beam

13 - subsequent section-beam

14 - section-beam is connected by direct flow

15 - section-beam is connected in countercurrent

16 - outlet branch pipe

17 - crossover pipe

18 - supply pipe

19 - inner surface of the walls

20 - wall (top).

In the case 2 of the shell-and-tube heat exchanger 1 with inlet 3 and outlet 4 nozzles, sections-bundles 12, 13 of the same geometrical parameters are placed in a pre-tensioned position by a tension force (without position), each subsequent section 13-bundle is deployed at an angle of 90 ° relative to the previous 12, inlets 9 and outlets 10 of the pipe medium (without position) are installed on the inner surfaces 19 of the walls 11, 20, 6 (side, top, bottom) of the body 2, covering their area from 60% to 90%. Part of the sections-bundles 14 are installed in direct flow, part of the sections-bundles 15 are installed in counterflow with respect to the direction of the intertubular medium 5 with the help of crossover pipes 17, supply 18 and outlet 16 pipes.

The shell-and-tube heat exchanger works as follows. Hot coolant (without position) enters the heat exchanger 1 through the inlet pipe 3, passes through the bundle sections, gives off heat to them and exits through the outlet pipe 4. The cold coolant (without position) enters the heat exchanger 1 through the inlet pipe 18 and is divided into two streams , one of which is directed to section-bundles 14, connected by means of cross-over pipes 17 in direct flow, the other into section-bundles 15, connected in counterflow with respect to the direction of the intertubular medium 5. Pre-tension of sections-bundles 14 and 15 along the heat exchange tubes 7 ensures their stable position at any spatial position of the heat exchanger 1. The heat exchange tubes 7 are fixed in the tube sheets 8. Each subsequent section-bundle 13 of the heat-exchange tubes is deployed at an angle of 90 ° relative to the previous section-bundle 12, which makes it possible to protect both the side 11 and the upper 20 from the bottom 6 walls of housing 2 from overheating. A 90 ° rotation of the subsequent beam section 13 relative to the previous beam section 12 is performed both clockwise and counterclockwise, since the beam sections have the same geometry.

The location of the autonomous inputs 9 and outputs 10 of the pipe medium 3 on the inner surfaces 19 of the walls 11, 20, 6 of the housing 2 of the heat exchanger 1 allows to reduce the heat flux into the walls by absorbing and shielding it. The optimal degree of overlap (screening) of the walls 11, 20 and 6 of the housing 2 by the inlets 9 and outlets 10 of the tubular medium in the range from 60% to 90% is illustrated in FIG. 3. Here L is the size that determines the wall area, and 0.6L ÷ 0.9L is the size that determines the area of inputs 9 or outputs 10 overlapping the wall area.

FIG. 4, 5, 6 show flow patterns (examples of flow) of inlets 9 or outlets 10 of the pipe medium at three different degrees (%) of coverage (overlap) of the wall areas.

FIG. 4 it can be seen that with a degree of overlap of 60% of the wall areas, the main flow of the hot coolant (without position) creates a secondary vortex (vortex flow) (without position), in the space between inputs 9 and outputs 10 of the pipe medium, which touches walls 11, 20 and 6 heat exchanger and, therefore, intensively heats them, but at the same time the vortex flow washes also the shadow surfaces of inputs and outputs (out of position), (shaded surface) and thereby increases the intensity of heat exchange between hot and cold heat carriers.

With a degree of overlap of 90% (Fig. 6) of the wall areas, the main flow of the hot coolant (without position) does not create a vortex flow in the space between the inlets 9 and outlets 10 of the pipe medium, does not touch or heat the walls 11, 20 and 6 (side, bottom , upper) of the body 2 of the heat exchanger 1, but at the same time it does not wash the shadow surfaces (out of position) (the shaded surface) of the inputs 9 and outputs 10 of the pipe medium, which reduces the intensity of heat exchange between hot and cold heat carriers.

With a degree of overlap of 75% (Fig. 5), the main flow creates less intense secondary vortex flows than with an overlap of 60%, as well as tertiary vortices (vortex flows) (out of position) that wash the shadow surfaces (shaded surface) of bushings 9 and outlets 10 of the pipe medium, partially increasing the intensity of heat exchange between hot and cold heat carriers, and partially heating the walls 11, 20 and 6 of the heat exchanger 1.

Thus, by controlling the degree of overlap of the inputs 9 and outputs 10 of the pipe medium of the area of the inner surface of the walls 11, 20 and 6 of the housing 2 of the heat exchanger 1 (TA), the permissible limiting temperature of the material of the walls of the heat exchanger is ensured (for example, for alloy 12X18H10T the limiting temperature is 700 ° C, cm GOST 34347-17, "Steel welded vessels and apparatus. General technical conditions") and the intensity of heat exchange between hot and cold heat carriers is maximized by involving additional - shadow surfaces (without position) inlets 9 and outlets 10 of the pipe medium in heat exchange.

By turning each subsequent section-beam 13 relative to the previous section-beam 12 by 90 °, the upper 20 and lower 6 walls of the body are protected by each previous section-beam 12, and the side walls 11 are protected by each subsequent section-beam 12.

Experimental work has been successfully carried out on the claimed design of the shell-and-tube heat exchanger.

Examples of the implementation of the proposed invention are given - the calculation of the optimal proportion of straight-flow sections-beams in the TA.

Example 1: Initial data:

N = 32 pcs. - the total number of sections-bundles in the heat exchanger, calculated according to well-known methods for calculating TA, see, for example, A.S. Tsygankov "Calculations of ship heat exchangers", reference manual, State Union publishing house of the shipbuilding industry, Leningrad, 1956;

- критическая температура для сплава 12ХН1810Т;

- critical temperature for alloy 12XH1810T;

- температура холодного теплоносителя (без позиции) на входе в секции-пучки;

- temperature of the cold coolant (without position) at the entrance to the section-bundles;

- температура горячего теплоносителя на входе в теплообменник.

- temperature of the hot coolant at the inlet to the heat exchanger.

Heat exchange media:

- cold heat carrier - CO ₂ at a pressure of 65 bar;

- hot coolant - Products of combustion of hydrocarbon fuels with a pressure of 1.2 bar.

The empirical coefficients for the indicated heat transfer fluids are:

- a = 29.4;

- b = 11.2.

Let's calculate the proportion of straight-flow sections-beams according to the formula:

Then the number of straight-flow sections of the beams will be equal to:

N _D = 54.42 * 32/100 = 17.4 pcs., Round up to a larger integer - 18 pcs.

Example 2. In the same TA, we will raise the temperature of the hot heat carrier to 1500 ° C.

N = 32 pcs.

- критическая температура для сплава 12ХН1810Т;

- critical temperature for alloy 12XH1810T;

- температура холодного теплоносителя на входе в секции-пучки;

- temperature of the cold coolant at the entrance to the section-bundles;

- температура горячего теплоносителя на входе в теплообменник.

- temperature of the hot coolant at the inlet to the heat exchanger.

Heat exchange media:

- cold heat carrier - CO ₂ at a pressure of 65 bar;

- hot coolant - Products of combustion of hydrocarbon fuels with a pressure of 1.2 bar.

The empirical coefficients for the indicated heat transfer fluids are:

- a = 29.4;

- b = 11.2.

Let's calculate the proportion of straight-flow sections-beams according to the formula:

Then the number of straight-flow sections of the beams will be equal to:

N _D = 93.08 * 32/100 = 29.8 pcs., Round up to a larger integer - 30 pcs.

Example 3. In the same TA, we will reduce the temperature of the hot heat carrier to 800 ° C.

N = 32 pcs.

- критическая температура для сплава 12ХН1810Т;

- critical temperature for alloy 12XH1810T;

- температура холодного теплоносителя на входе в секции-пучки;

- temperature of the cold coolant at the entrance to the section-bundles;

- температура горячего теплоносителя на входе в теплообменник.

- temperature of the hot coolant at the inlet to the heat exchanger.

Heat exchange media:

- cold heat carrier - CO ₂ at a pressure of 65 bar;

- hot coolant - Products of combustion of hydrocarbon fuels with a pressure of 1.2 bar.

The empirical coefficients for the indicated heat transfer fluids are:

- a = 29.4;

- b = 11.2.

Let's calculate the proportion of straight-flow sections-beams according to the formula:

Then the number of straight-flow sections of the beams will be equal to:

N _D = 1.93 * 32/100 = 0.62 pcs., Round up to a larger integer - 1 pc.

A positive technical result was obtained in all the above examples of implementation.

Thus, the proposed invention with the above distinctive features, in conjunction with the known features, allows to ensure operational adaptability and maintainability, remove restrictions on the temperature of the annular medium, ensure gravitational independence and rational use of the volume of the heat exchanger.

Claims (7)

A shell-and-tube heat exchanger containing a housing with inlet and outlet nozzles for directing the intertubular medium and placed in it sections-bundles of heat exchange tubes, consisting of heat exchange tubes fixed in tube sheets, and each having an autonomous input and output of the tube medium, characterized in that all inputs and the outlets of the pipe medium are installed on the inner surfaces of the walls of the body and cover from 60% to 90% of the wall areas, all sections-bundles are made of the same geometric parameters, each subsequent section-bundle of heat-exchange tubes is deployed at an angle of 90 ° relative to the previous one, all sections are bundles installed in a pre-tensioned state along the heat exchange tubes and a part of the bundle sections by means of crossover and outlet pipes are connected in direct flow, and a part of the bundle sections are connected in countercurrent with respect to the direction of the intertubular medium and the proportion of the bundle sections connected by direct flow γ _D or countercurrent γ _C is determined by formula

N _D - the number of sections connected by direct flow; N is the total number of sections in the heat exchanger;

- critical temperature due to the requirement for long-term strength of the material, ° С;

- temperature of the hot and cold heat carrier at the inlet to the heat exchanger, respectively, ° С. a, b - empirical constants depending on the thermophysical properties of the heat carrier flows.

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