Multi-tube heat exchanger

Abstract

To provide a heat exchanger with reduced fouling. [Solution] The heat exchanger 1 includes a plurality of tubes 3 through which a first medium to be cooled can flow. At least one section 3a of each of the tubes 3 is surrounded by a space 5, or certain sections 3a of each of the plurality of tubes 3 are located together in the space 5. A second medium that absorbs heat can flow within the space 5. The outer diameter of the tubes 3 is constant at least in the section 3a. The inner diameter of each of the tubes 3 narrows in the direction of the flow of the first medium in a portion 3b within at least one of the sections 3a.

Description

[Technical Field]

[0001] The present invention relates to a heat exchanger as defined in the preamble of claim 1 . [Background technology]

[0002] Heat exchangers are used to transfer thermal energy from one process medium to another. In dividing wall heat exchangers, each medium is spaced apart from the other.

[0003] A commonly used type of heat exchanger is the so-called shell-and-tube heat exchanger, in which a medium is guided through a number of parallel tubes arranged in a bundle, and another medium is guided through the space surrounding the tube bundle.

[0004] Heat exchangers are used to cool process gases at high temperatures, for example, 700 to 1500° C. In most cases, the process gas is guided through a tube, and a heat absorption medium is placed in the space surrounding the tube and flows around the outside of the tube. Summary of the Invention [Problem to be solved by the invention]

[0005] As the process gas cools within the tubes, fouling can occur, which is the buildup of deposits and contaminants on the inside of the tubes. Fouling can be caused by particles in the process gas or the condensed phase of the process gas cooling inside the tubes.

[0006] Typically, deposits are removed by cleaning the tubes, which requires the heat exchanger to be taken out of service, resulting in undesirable downtime.

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

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

[0009] The heat exchanger according to the present invention comprises a plurality of tubes through which a first medium to be cooled can flow. At least one section of each of the tubes is surrounded by a space, or a section of each of the plurality of tubes is located together within the space. A second medium that absorbs heat can flow within the space. The outer diameter of the tubes is constant at least within the section. The present invention is characterized in that the inner diameter of each of the tubes narrows in the direction of flow of the first medium within at least one of the sections.

[0010] The heat exchanger according to the present invention may have a shell-and-tube heat exchanger structure in which multiple tubes extend within a common space. The outer diameter of the tubes is constant, at least in the area within the common space, ensuring that the second medium can flow favorably around the tubes. At the same time, the heat exchanger according to the present invention can be constructed in much the same way as conventional heat exchangers, requiring relatively little equipment work. Alternatively, the heat exchanger may be configured such that each tube extends within its own space, for example, formed in an annular shape around the tube.

[0011] The initial inner diameter of each of the tubes narrows in the direction of flow of the first medium in the zone within the zone, meaning that the flow velocity of the first medium along the tube does not decrease, or decreases only slightly, below the ultimate velocity when the first medium cools and its density changes as a result. In this way, a relatively high flow velocity can be maintained, which achieves high shear stresses on the inside of the tube, preventing particle deposition and removing already deposited particles from the wall. As a result, the relatively high flow velocity can keep the tube substantially free of deposits and even wash away deposits.

[0012] Thus, the present invention takes advantage of the fact that by reducing the inner diameter of the tube, the flow velocity of the first medium can be relatively increased, thereby reducing the flow velocity reduction due to cooling and the resulting density change.

[0013] Preferably, the inner section of the tube constitutes an end region of the section of the tube in the direction of flow of the first medium. That is, the inner section of the tube with the reduced inner diameter is located in the rear part of the tube in the direction of flow of the first medium, which is located in the space. This has the advantage that the inner diameter is reduced in a section of the tube where the first medium has already been significantly cooled, i.e., where the tendency to fouling is greatest. A reduced inner diameter while maintaining a constant outer diameter would increase the wall thickness of the tube in this section. However, due to the reduced inner diameter in a section of the tube located at a relatively low temperature, the wall thickness is negligible for the heat transfer from the already cooled first medium to the second medium.

[0014] Preferably, the total length of the portion of the tube within the at least one zone where the inner diameter is reduced is 1 / 4 to 9 / 10 of the total length of the zone.

[0015] The inner diameter of the pipe may be continuously reduced in the zone, or may be stepped in the zone, or may be reduced in the zone by alternating conically tapered pipe elements with constant inner diameters. In principle, it is also possible to use a combination of various diameter reduction variants.

[0016] In the heat exchanger according to the present invention, outer pipes may be disposed around each of the pipes, and each of the outer pipes may form one space. In other words, the heat exchanger may be configured in the form of a double-pipe heat exchanger.

[0017] Alternatively, a plurality of tubes may be arranged in parallel within a casing tube that defines the space.

[0018] In the heat exchanger according to the present invention, the inner diameter of the tube may be constant in portions other than the inner zone portion.

[0019] The tube or tube material is selected depending on the heat dissipating or 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 has proven to be an advantageous tube material. If the heat absorbing medium is air, process gas, or steam, the tube material can be low-alloy steel, high-alloy steel, or even stainless steel or a nickel-based alloy. The tube can also consist of partial sections made of different tube materials.

[0020] Furthermore, one embodiment of the heat exchanger according to the present invention may include a tube through which a first medium to be cooled can flow, at least one section of the tube is surrounded by a space, a second medium that absorbs heat can flow within the space, the outer diameter of the tube is constant at least in the section, and the inner diameter of the tube decreases in the direction of the flow of the first medium at least in a portion of the section. This embodiment of the heat exchanger according to the present invention may also realize other features described above.

[0021] The invention will now be explained in more detail with reference to the following drawings: [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of an overall view of a heat exchanger according to the present invention. [Figure 2a] 1 is a schematic cross-sectional view of one embodiment of an inner section of a tube of a heat exchanger according to the present invention. [Figure 2b] 4 is a schematic cross-sectional view showing another embodiment of the inner portion of a section of a heat exchanger tube according to the present invention. FIG. [Figure 2c]10 is a schematic cross-sectional view showing yet another embodiment of the interior of a section of a heat exchanger tube according to the present invention. FIG. [Figure 3] 1 is a schematic detailed view of a tube of a double-pipe heat exchanger according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 is a schematic cross-sectional view of a heat exchanger 1 according to the present invention.

[0024] The heat exchanger comprises a number of tubes 3 arranged parallel to one another, which pass through a space 5 formed by a casing tube 7. In the exemplary embodiment shown in FIG. 1, in which the tubes 3 are arranged vertically, the first medium to be cooled flows inside the tubes 3 from top to bottom. In principle, a horizontal arrangement is also possible. The first medium is guided through an inlet 9 into an inlet chamber 11, flows through the tubes 3 and is cooled, and then flows into an outlet chamber 13. The cooled first medium leaves the heat exchanger through an outlet 15.

[0025] A second medium is guided in the space 5, absorbing heat from the first medium. The second medium is introduced into the space 5 through a second inlet 17 and flows through the space 5 to a second outlet 19. In this way, the second medium flows countercurrently to the first medium. Alternatively, depending on the heat transfer task, the second medium may be introduced into the space 5 through a corresponding inlet and flow through the space 5 to a corresponding outlet, flowing cocurrently to the first medium.

[0026] The portion of the tube 3 located within the space 5 is referred to as a region 3a. The outer diameter A of each tube 3 is constant at least in this region.

[0027] The inner diameter i of the tube 3 narrows in the direction of flow of the first medium in the inner portion of the section 3a. In the illustrated exemplary embodiment, the inner portion 3b where the inner diameter i of the tube 3 narrows extends, for example, over about 50% of the entire length of the section 3a located in the space 5, and the inner portion 3b of the tube 3 constitutes an end region of the section 3a of the tube 3. The inner diameter i of each tube 3 is constant in the remaining portion of the tube 3.

[0028] The first medium flows inside the tube 3 and is cooled by the second medium arranged in the space 5 and flowing around the tube 3. This increases the density of the first medium, which initially reduces the flow velocity of the first medium inside the tube 3. To prevent the flow velocity of the first medium from decreasing below the critical velocity, the inner diameter i of the tube 3 is reduced in the zone 3b where the first medium has already cooled significantly and its flow velocity has correspondingly decreased. By reducing the inner diameter of the tube, the flow velocity of the first medium relatively increases again, thereby mitigating the decrease in flow velocity caused by cooling. This makes it possible to prevent deposits from forming on the inside of the tube, since the velocity of the tube either prevents this or carries away the deposited particles again.

[0029] The constant outer diameter A of the tube 3 advantageously allows for uniform flow around the tube in the space 5 .

[0030] Figures 2a to 2c show various examples of the interior of a region of a pipe 3 where the inner diameter i decreases. In Figure 2a, the inner diameter i decreases continuously in the direction of flow. In Figure 2b, a stepwise decrease is depicted. In Figure 2c, the decrease is achieved by alternating regions of conical decrease and constant diameter.

[0031] Depending on the application, purpose, and the first medium being cooled, each type has advantages and disadvantages. For example, a stepped reduction is simple and economical to design, but if the first medium is particle-rich, the stepped shape may be susceptible to erosion attack or may be unfavorable hydraulically. A continuous reduction in diameter section is more favorable hydraulically but requires more manufacturing effort.

[0032] The heat exchanger 1 shown in Figure 1 has the structure of a classic shell-and-tube heat exchanger, in which parallel tubes 3 pass together through a space 5 formed by a casing tube 7. In principle, the heat exchanger can also be configured as a double-tube heat exchanger. Figure 3 shows a schematic cross-section of such a double-tube heat exchanger, in which tube 3 is surrounded by an outer tube 21. The annular gap formed between tube 3 and the outer tube forms a space 5 through which the second medium can flow.

[0033] The heat exchanger 1 according to the present invention has the advantage that the construction can easily reduce or avoid fouling of the inside of the tubes, thereby shortening the downtime of the heat exchanger 1 for cleaning the tubes 3.

[0034] The first medium may be, for example, a process gas, air, etc. The second medium that absorbs heat may be a process gas, air, water, other liquid, steam, or a water / steam mixture. The heat exchanger 1 according to the present invention can be used to cool a high-temperature process gas, for example, at a temperature of 700 to 1500°C. [Explanation of symbols]

[0035] 1 heat exchanger 3 tubes 3a area 3b Inner area 5 Space 7 Casing tube 9 Entrance 11 Entrance room 13 Exit chamber 15 Exit 17 Second Entrance 19 2nd exit 21 outer tube

Claims

1. The device comprises multiple tubes (3) through which the first medium to be cooled can flow, Either at least one area (3a) of the pipe (3) is surrounded by a space (5), or a certain area (3a) of multiple pipes (3) is located within the space (5). The second heat-absorbing medium can flow within the space (5), In a heat exchanger (1) in which the outer diameter (A) of the pipe (3) is constant in at least the area (3a), A heat exchanger characterized in that the inner diameter (i) of each of the tubes (3) is reduced in the direction of the flow of the first medium in at least one portion (3b) of the region (3a).

2. A heat exchanger according to claim 1, characterized in that the portion (3b) of the tube (3) within the area constitutes the end region of the area (3a) of the tube (3) in the direction of flow of the first medium.

3. A heat exchanger according to claim 1 or 2, characterized in that the length of the at least one portion within the area (3b) is 25% to 90% of the total length of the area (3a).

4. A heat exchanger according to claim 1 or 2, characterized in that the inner diameter (i) continuously decreases in diameter within the area portion (3b).

5. A heat exchanger according to claim 1 or 2, characterized in that the inner diameter (i) is steppedly reduced in diameter in the portion (3b) within the area.

6. A heat exchanger according to claim 1 or 2, characterized in that the inner diameter is reduced by alternately providing a portion (3b) within a region where the inner diameter (i) is reduced in a conical shape and an element where the inner diameter (i) is constant.

7. A heat exchanger according to claim 1 or 2, characterized in that outer tubes are arranged around each tube, and a single space is formed by each of the outer tubes.

8. A heat exchanger according to claim 1 or 2, characterized in that a plurality of tubes are arranged in parallel within a casing tube that forms the space.

9. A heat exchanger according to claim 1 or 2, characterized in that the inner diameter of the pipe is constant in parts other than the portion within the area.

10. The device includes a tube (3) through which the first medium to be cooled can flow, At least one area (3a) of the pipe (3) is surrounded by a space (5), The second heat-absorbing medium can flow within the space (5), In a heat exchanger (1) in which the outer diameter of the pipe (3) is constant in at least the area (3a), A heat exchanger characterized in that the inner diameter (i) of the pipe (3) is reduced in the direction of the flow of the first medium in at least one portion (3b) of the region (3a).

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