Heat exchanger with multiple pipelines

Abstract

The invention relates to a heat exchanger (1) having a plurality of pipes (3) through which a first medium to be cooled can flow, at least sections (3a) of the pipes (3) being each surrounded by a space (5), or sections (3a) of a plurality of the pipes (3) being arranged together in the space (5), through which a second heat-absorbing medium can flow, the pipes (3) have a constant outer diameter at least in the sections (3a), wherein the pipes each have an inner diameter that gradually decreases in the flow direction of the first medium at least in at least one sub-region of the respective section (3a).

Description

Technical Field

[0001] The invention relates to a heat exchanger according to the preamble of claim 1 . Background Art

[0002] Heat exchangers are used to transfer thermal energy from one process medium to a second process medium. In a recuperator, each medium has a space separated from the other mediums.

[0003] One commonly used type of heat exchanger is the so-called shell-and-tube heat exchanger, in which one medium is led through a plurality of parallel tubes arranged in a bundle. A second medium is led through the space surrounding the bundle of tubes.

[0004] Heat exchangers are used to cool high-temperature process gases, for example at 700° C. to 1500° C. In most cases, the process gas is led through pipes, with a heat-absorbing medium being located in the space surrounding the pipes and flowing around the pipes on the outside.

[0005] When process gases are cooled in pipes, fouling occurs, which is the accumulation of deposits and contaminants on the inside of the pipes. Fouling is caused by particles in the process gas or by condensation of the process gas on the cooled inner walls of the pipes.

[0006] Deposits are usually removed by cleaning the pipes, in which case the heat exchanger must be taken out of service, which results in undesirable interruptions. Summary of the invention

[0007] It is therefore an object of the present invention to provide a heat exchanger with reduced fouling.

[0008] The invention is defined by the features of claim 1 .

[0009] The heat exchanger according to the invention comprises a plurality of pipes through which a first medium to be cooled can flow. At least one section of each pipe is surrounded by a space, or a section of each of a plurality of pipes is arranged together in a space. A second medium absorbing heat can flow through the space, wherein the pipe has a constant outer diameter at least in the section. The invention is characterized in that each of the pipes has an inner diameter that tapers in the flow direction of the first medium at least in at least one sub-region of the respective section.

[0010] The heat exchanger according to the invention can have the structure of a shell and tube heat exchanger, in which a plurality of pipes extend through a common space. The constant outer diameter of the pipes, at least in the section located in the common space, ensures that the second medium can flow around the pipes in a fluid-favorable manner. At the same time, the equipment-related effort is kept at a relatively low level, since the heat exchanger according to the invention can be constructed largely like a conventional heat exchanger. In an alternative embodiment, the heat exchanger can also be configured so that each pipe extends through its own space, for example a space formed annularly around the individual pipes.

[0011] The fact that the pipe initially has an inner diameter which tapers in the flow direction of the first medium in each of the sub-regions of the respective segments means that even if the first medium cools and the density changes, the flow velocity of the first medium along the pipe does not decrease or only decreases slightly and the flow velocity does not drop below the limiting velocity. By being able to maintain a relatively high flow velocity in this way, a high shear stress on the flow inside the pipe can be achieved, thereby preventing the deposition of particles or enabling already deposited particles to detach from the wall. Thus, a relatively high flow velocity can make it possible to keep the pipe substantially free of deposits or even clean the pipe.

[0012] The invention thus makes use of the fact that the flow velocity of the first medium can be relatively increased by reducing the inner diameter of the pipe, thereby making it possible to counteract the decrease in flow velocity due to cooling and the resulting density change.

[0013] Preferably, the respective sub-regions of the pipeline form the end region of the pipeline in the respective section along the flow direction of the first medium. In other words, the sub-region of the pipeline in which the inner diameter gradually decreases is located at the tail of the pipeline in the flow direction of the first medium, which tail is located in the respective space. This has the following advantages: the inner diameter gradually decreases in the part of the pipeline that has been significantly cooled, and therefore gradually decreases in the area where the scaling tendency is particularly strong. Due to the gradual decrease in the inner diameter and the constant outer diameter, the wall thickness of the pipeline increases in this area. However, due to the gradual decrease in the inner diameter in the sub-region of the pipeline located in the relatively cold section, the influence of the wall thickness on the heat transfer from the already cooled first medium to the second medium can be ignored.

[0014] Preferably, the cumulative length of the sub-regions of the pipe where the inner diameter tapers is between 1 / 4 and 9 / 10 of the total length of the segment.

[0015] The inner diameter of the pipe can taper continuously in the sub-regions. It is also possible to taper the inner diameter in steps in the sub-regions. The inner diameter can also be tapered by alternating tubular elements with conically taper inner diameters and elements with a constant inner diameter in the sub-regions. In principle, a combination of different variants of taper can also be used.

[0016] In the heat exchanger according to the present invention, an outer tube may be arranged around each pipe, each outer tube forming one of the plurality of spaces. Therefore, the heat exchanger may be configured in the form of a double-tube heat exchanger.

[0017] Alternatively, a plurality of pipelines may be arranged in parallel in a casing, and the casing forms a space.

[0018] In the heat exchanger according to the invention, the pipe can have a constant inner diameter in areas other than the sub-areas.

[0019] The material of the pipe or pipeline is selected according to the heat releasing medium and the heat absorbing medium. For example, if the heat absorbing medium is a liquid, water or a water / steam mixture, low alloy steel, high alloy steel or even stainless steel have proven to be advantageous pipe materials. If the heat absorbing medium is air, process gas or steam, the pipe material can be low alloy steel, high alloy steel or even stainless steel or nickel-based alloys. The pipeline can also consist of partial sections of different pipe materials.

[0020] An embodiment of the heat exchanger according to the invention may also have a pipe through which a first medium to be cooled can flow, wherein at least one section of the pipe is surrounded by a space through which a second heat-absorbing medium can flow, and wherein the pipe has a constant outer diameter at least in the section, wherein the pipe has an inner diameter that tapers in the flow direction of the first medium at least in a subregion of the section. In this embodiment of the heat exchanger according to the invention, the other features described above may also be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Hereinafter, the present invention is described in more detail with reference to the following drawings.

[0022] In the attached picture:

[0023] Figure 1 shows a schematic cross-sectional view of the heat exchanger according to the invention in general,

[0024] Figure 2a to Figure 2c Schematic cross-sectional views showing various embodiments of sub-regions of a tube of a heat exchanger according to the invention, and

[0025] Figure 3 A schematic detail diagram showing the tubes of a double-tube heat exchanger according to the invention. DETAILED DESCRIPTION

[0026] Figure 1 A schematic cross-sectional view of a heat exchanger 1 according to the invention is shown.

[0027] The heat exchanger comprises a plurality of pipes 3 arranged parallel to each other. The pipes 3 pass through a space 5 formed by a casing 7. Figure 1 In the exemplary embodiment shown, the pipe 3 is arranged vertically and the first medium to be cooled flows through the pipe 3 from top to bottom. In principle, a horizontal arrangement is also possible. The first medium is guided to the inlet chamber 11 through the inlet 9, flows through the pipe 3, is cooled therein, and then enters the outlet chamber 13. The now cooled first medium is discharged from the heat exchanger through the outlet 15.

[0028] The second medium for absorbing heat from the first medium is guided through the space 5. The second medium is introduced into the space 5 via the second inlet 17 and flows through the space to the second outlet 19. In this way, the second medium flows countercurrently with the first medium. Depending on the heat transfer task, the second medium can also alternatively flow cocurrently with the first medium, which is achieved by being introduced into the space 5 via the corresponding inlet and flowing through the space to the corresponding outlet.

[0029] The portion of the pipe 3 located in the space 5 is referred to as section 3a. At least in this section, the pipes 3 each have a constant outer diameter A.

[0030] In the sub-region of the respective section 3a, the pipe 3 has an inner diameter i which tapers in the flow direction of the first medium. The sub-region 3b of the pipe 3 with the taper inner diameter i extends, for example, to about 50% of the total length of the section 3a in the illustrated exemplary embodiment, wherein the respective sub-region 3b of the pipe 3 respectively forms the end region of the respective section 3a of each pipe 3. In the remaining regions of the pipes 3, they each have a constant inner diameter i.

[0031] The first medium now flows through the pipe 3 and is cooled by the second medium located in the space 5 and flowing around the pipe 3. This causes the density of the first medium to increase, so the flow velocity of the first medium in the pipe 3 begins to decrease. In order to prevent the flow velocity of the first medium from falling below the limit velocity, the inner diameter i of the pipe 3 is gradually reduced in the sub-area 3b, where the first medium has been significantly cooled and thus has a correspondingly reduced flow velocity. By gradually reducing the inner diameter of the pipe, the flow velocity of the first medium is relatively increased again, thereby offsetting the reduction in flow velocity caused by cooling. This can prevent the formation of deposits on the inside of the pipe, because the pipe flow velocity prevents this or the already deposited particles are carried away again.

[0032] By providing a constant outer diameter A of the duct 3, a uniform flow around the duct in the space 5 may advantageously be achieved.

[0033] Figure 2a to Figure 2c Different variants of sub-regions of the pipe 3 with a gradually decreasing inner diameter i are shown. Figure 2a In the flow direction, the inner diameter i decreases continuously and gradually. Figure 2b It is shown that it gradually decreases. Figure 2cIn the embodiment, the tapering is achieved by alternating segments with conically tapering inner diameters and segments with a constant inner diameter.

[0034] Depending on the application, purpose and the first medium to be cooled used, the different variants have advantages and disadvantages. For example, a stepped taper can be produced easily and economically in terms of design, but in the case of a particle-laden first medium, the stepped shape can be prone to erosive effects or fluidically unfavorable. A continuously tapering cross section is more fluidically favorable, but leads to a higher effort in terms of manufacturing.

[0035] Figure 1 The heat exchanger 1 shown has the design of a classic shell and tube heat exchanger, in which parallel pipes 3 pass together through a space 5 formed by a jacket 7. In principle, the heat exchanger can also be configured as a double-tube heat exchanger. Figure 3 A schematic diagram of such a double pipe is shown, wherein the pipe 3 is surrounded by an outer pipe 21. The annular gap formed between the pipe 3 and the outer pipe forms a space 5 through which the second medium can flow.

[0036] The heat exchanger 1 according to the present invention has the following advantages: scaling inside the pipe can be reduced or avoided in a structurally simple manner, thereby reducing the downtime of the heat exchanger 1 caused by cleaning the pipe 3.

[0037] The first medium can be, for example, a process gas or air. The second medium absorbing heat can be a process gas, air, water, another liquid, steam or a water / steam mixture. The heat exchanger 1 according to the invention can be used, for example, to cool a high-temperature process gas of, for example, 700° C. to 1500° C.

[0038] Reference numerals list

[0039] 1 Heat exchanger

[0040] 3 Pipeline

[0041] Segment 3a

[0042] Sub-area 3b

[0043] 5. Space

[0044] 7 Casing

[0045] 9 Entrance

[0046] 11 Entrance Room

[0047] 13. Exit Room

[0048] 15 Exit

[0049] 17 Second Entrance

[0050] 19 Second Exit

[0051] 21 outer tube

Claims

1. A heat exchanger (1), comprising a plurality of pipes (3), through which a first medium to be cooled can flow, wherein at least one section (3a) of the pipes (3) is each surrounded by a space (5), or a plurality of pipes (3) are arranged together in a space (5) with respective sections (3a) through which a second medium absorbing heat can flow, and wherein the pipes (3) have a constant outer diameter (A) at least in the sections (3a), It is characterized in that The pipes (3) each have, at least in at least one sub-region (3b) of a respective section (3a), an inner diameter (i) which tapers in the flow direction of the first medium.

2. The heat exchanger according to claim 1, characterized in that: A respective sub-region (3b) of a pipeline (3) forms an end region of a respective section (3a) of the pipeline (3) in the flow direction of the first medium.

3. The heat exchanger according to claim 1 or 2, characterized in that: The length of the sub-region (3b) is between 25% and 90% of the total length of the segment (3a).

4. The heat exchanger according to any one of claims 1 to 3, characterized in that: The inner diameter (i) in the sub-region (3b) gradually decreases continuously.

5. The heat exchanger according to any one of claims 1 to 3, characterized in that: The inner diameter (i) in the sub-region (3b) gradually decreases in a step-by-step manner.

6. The heat exchanger according to any one of claims 1 to 3, characterized in that: The tapering of the inner diameter is achieved by alternating sub-areas (3b) with a conically tapering inner diameter (i) and elements with a constant inner diameter (i).

7. The heat exchanger according to any one of claims 1 to 6, characterized in that: An outer tube is arranged around each duct, one of the spaces being formed by each outer tube.

8. The heat exchanger according to any one of claims 1 to 6, characterized in that: A plurality of pipes are arranged in parallel in a casing, and the casing forms the space.

9. The heat exchanger according to any one of claims 1 to 8, characterized in that: The pipe has a constant inner diameter in regions other than the sub-regions.

10. A heat exchanger (1) comprising a pipe (3) through which a first medium to be cooled can flow, wherein at least one section (3a) of the pipe (3) is surrounded by a space (5) through which a second medium absorbing heat can flow, and wherein the pipe (3) has a constant outer diameter at least in the section (3a), It is characterized in that The pipeline (3) has, in at least one sub-region (3b) of the section (3a), an inner diameter (i) which tapers in the flow direction of the first medium.

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