heat exchanger

Abstract

To provide a heat exchanger that does not require bend pipes. [Solution] In a heat exchanger 1 according to one embodiment, a plurality of heat transfer tubes 3 are arranged such that a group of heat transfer tubes 30, in which the heat transfer tubes 3 are aligned in a direction perpendicular to the gas flow direction A, is aligned in the gas flow direction A. The heat transfer tubes 3 are U-shaped tubes 3A, 3B having first straight sections 31, 34 and second straight sections 32, 35 that penetrate the first tube sheet 21 and the second tube sheet 22, as well as bent sections 33, 36 on the outside of the second tube sheet 22. The outer surface of the first tube sheet 21 is covered with a cover plate 4, and a plurality of recesses 41, 42, 43 aligned in the gas flow direction are formed in the cover plate 4. Recess 41 forms a first chamber 61 through which the first straight sections 31, 34 communicate, recess 43 forms a second chamber 62 through which the second straight sections 32, 35 communicate, and recess 42 forms an intermediate chamber 63 through which the first straight sections 31, 34 and the second straight sections 32, 35 communicate.

Description

Technical Field

[0001] This application relates to a heat exchanger that performs heat exchange between a gas and a liquid.

Background Art

[0002] Conventionally, a heat exchanger has been known that includes a plurality of heat transfer tubes crossing a flow path through which a gas flows, and performs heat exchange between a liquid flowing through these heat transfer tubes and the gas. For example, Patent Document 1 discloses a heat exchanger used as a feed water preheating device for a boiler.

[0003] Specifically, in the heat exchanger of Patent Document 1, heat transfer tubes with fins are arranged such that a row of heat transfer tubes in which the heat transfer tubes are arranged in the flow direction of the combustion exhaust gas is arranged in four rows in a direction orthogonal to the flow direction of the combustion exhaust gas. The heat transfer tubes of two heat transfer tube rows on one side and the other side of the four heat transfer tube rows are connected by bend tubes so as to form a continuous water flow path that alternately repeats a horizontal U-shaped path and a vertical U-shaped path.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, bend tubes are joined to heat transfer tubes by welding. Therefore, there is a desire to eliminate bend tubes.

[0006] Therefore, an object of this application is to provide a heat exchanger that does not require bend tubes.

Means for Solving the Problems

[0007] This application relates to a heat exchanger for performing heat exchange between a gas and a liquid, comprising: a first tube sheet and a second tube sheet facing each other across a gas flow path; a U-shaped heat transfer tube having a first straight section and a second straight section penetrating the first tube sheet and the second tube sheet, and a bend section connecting the first straight section and the second straight section on the outside of the second tube sheet; a plurality of heat transfer tubes arranged such that the heat transfer tubes are aligned in the direction of gas flow, with the heat transfer tubes aligned in a direction perpendicular to the direction of gas flow; and a cover plate covering the outer surface of the first tube sheet, wherein a plurality of recesses aligned in the direction of gas flow are formed on the surface of the cover plate facing the first tube sheet. The present invention provides a heat exchanger in which the second straight section is located downstream of the first straight section in the gas flow direction, the recess located furthest upstream in the gas flow direction forms a first chamber through which the first straight section of the heat transfer tube group located furthest upstream in the gas flow direction communicates, the recess located furthest downstream in the gas flow direction forms a second chamber through which the second straight section of the heat transfer tube group located furthest downstream in the gas flow direction communicates, and the other recesses form intermediate chambers through which the first straight section and the second straight section of adjacent heat transfer tube groups in the gas flow direction communicate. [Effects of the Invention]

[0008] According to this application, a heat exchanger that does not require bend pipes is provided. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1(a) is a front cross-sectional view of a heat exchanger according to one embodiment, and Figure 1(b) is a side view of the heat exchanger. [Figure 2] Figure 2 is a cross-sectional view along the line II-II in Figure 1. [Figure 3] Figure 3 is a cross-sectional view along the line III-III in Figure 1. [Modes for carrying out the invention]

[0010] Figures 1(a) and (b) show a heat exchanger 1 according to one embodiment. The heat exchanger 1 performs heat exchange between a gas and a liquid. For example, the heat exchanger 1 is used as a feedwater preheating device for a boiler. In this case, the heat exchanger 1 heats water with combustion exhaust gas.

[0011] Specifically, the heat exchanger 1 includes a first tube sheet 21 and a second tube sheet 22 that face each other across a gas flow path, and a pair of side plates (not shown) that face each other across the gas flow path in a direction perpendicular to the opposing direction of the first tube sheet 21 and the second tube sheet 22. Furthermore, the heat exchanger 1 includes a plurality of heat transfer tubes 3 that traverse the gas flow path and through which liquid flows.

[0012] The first tube sheet 21, the second tube sheet 22, and the pair of side plates constitute a duct that forms a flow path for gas. The direction of gas flow A within the duct is downward in Figure 1(a), but it may also be upward or sideways.

[0013] Each heat transfer tube 3 is a U-shaped tube. In this embodiment, there are two types of U-shaped tubes: a first U-shaped tube 3A and a second U-shaped tube 3B that is sized to fit inside the first U-shaped tube 3A.

[0014] The first U-shaped pipe 3A has a first straight section 31 and a second straight section 32 that penetrate the first tube sheet 21 and the second tube sheet 22, and a bend section 33 that connects the first straight section 31 and the second straight section 32 on the outside of the second tube sheet 22. The second straight section 32 is located downstream of the first straight section 31 in the gas flow direction A.

[0015] Similarly, the second U-shaped tube 3B has a first straight section 34 and a second straight section 35 that penetrate the first tube sheet 21 and the second tube sheet 22, and a bend section 36 that connects the first straight section 34 and the second straight section 35 on the outside of the second tube sheet 22. The second straight section 35 is located downstream of the first straight section 34 in the gas flow direction A.

[0016] In this embodiment, the outer diameter of the heat transfer tube 3 is 15 mm or less. Therefore, a bare tube without fins can be adopted as the heat transfer tube 3. However, if the outer diameter of the heat transfer tube 3 is 20 mm or more, ring-shaped circumferential fins may be provided on the heat transfer tube 3.

[0017] The heat transfer tubes 3 are arranged such that a plurality of heat transfer tube groups 30 are aligned in the gas flow direction A. As shown in FIG. 2, each heat transfer tube group 30 is configured such that the first U-shaped tubes 3A are aligned in a specific direction B orthogonal to the gas flow direction A, and the second U-shaped tubes 3B are aligned in the specific direction B inside the first U-shaped tubes 3A. The specific direction B is the direction in which the pair of side plates described above face each other.

[0018] That is, the radius of curvature of the bend portion 33 of the first U-shaped tube 3A is larger than the value obtained by adding the outer diameter of the heat transfer tube 3 to the radius of curvature of the bend portion 36 of the second U-shaped tube 3B.

[0019] The pitch P at which the first U-shaped tubes 3A are aligned in the specific direction B is equal to the pitch P at which the second U-shaped tubes 3B are aligned in the specific direction B. When the outer diameter of the heat transfer tube 3 is 15 mm or less as in this embodiment, for example, the pitch P is 1.4 times or more and 2 times or less the outer diameter of the heat transfer tube 3. Further, the first U-shaped tubes 3A are inclined with respect to the gas flow direction A, and the second U-shaped tubes 3B are inclined in the opposite direction to the first U-shaped tubes 3A with respect to the gas flow direction A.

[0020] In the specific direction B, the first straight portions 31 of the first U-shaped tubes 3A and the first straight portions 34 of the second U-shaped tubes 3B are arranged in a staggered manner, and the second straight portions 32 of the first U-shaped tubes 3A and the second straight portions 35 of the second U-shaped tubes 3B are arranged in a staggered manner. In other words, in the specific direction B, the positions of the first straight portions 31 of the first U-shaped tubes 3A and the first straight portions 34 of the second U-shaped tubes 3B are shifted by P / 2, and the positions of the second straight portions 32 of the first U-shaped tubes 3A and the second straight portions 35 of the second U-shaped tubes 3B are shifted by P / 2.

[0021] Further, each first U-shaped tube 3A is inclined such that the center-to-center distance between the first straight portion 31 and the second straight portion 32 in the specific direction B is P / 2, and each second U-shaped tube 3B is inclined such that the center-to-center distance between the first straight portion 34 and the second straight portion 35 in the specific direction B is P / 2.

[0022] Both ends of the first U-shaped tube 3A, that is, the ends on the side opposite to the bend portion 33 of the first straight portion 31 and the second straight portion 32, are fixed to the first tube sheet 21 by tube expansion. Similarly, both ends of the second U-shaped tube 3B, that is, the ends on the side opposite to the bend portion 36 of the first straight portion 34 and the second straight portion 35, are fixed to the first tube sheet 21 by tube expansion.

[0023] In this embodiment, since the first tube sheet 21 receives the pressure of the liquid, the thickness of the first tube sheet 21 is set to be relatively thick. The outer surface of the first tube sheet 21 on the side opposite to the second tube sheet 22 is covered with a cover plate 4.

[0024] Also, in this embodiment, a seal plate 5 is sandwiched between the first tube sheet 21 and the cover plate 4. The cover plate 4 is fixed to the first tube sheet 21 by bolts 11 and nuts in a state where the seal plate 5 is sandwiched between the cover plate 4 and the first tube sheet 21.

[0025] On the surface of the cover plate 4 on the side of the first tube sheet 21, a plurality of depressions 41, 42, 43 arranged in the gas flow direction A are provided. Also, on the seal plate 5, openings having the same size as the depressions 41, 42, 43 are provided at positions corresponding to the depressions 41, 42, 43.

[0026] As shown in FIG. 3, each of the depressions 41, 42, 43 is a rectangular depression extending in the specific direction B. The length of the depressions 41, 42, 43 in the specific direction B is longer than the length of the heat transfer tube group 30 in the specific direction B.

[0027] Furthermore, the width of the recesses 41 and 43 located at both ends in the gas flow direction A is greater than the cross-sectional width of one side of a single heat transfer tube group 30 in the gas flow direction A (the distance between the centers of the first straight sections 31 and 34 in the gas flow direction A plus the outer diameter of the heat transfer tube 3). The width of the other recesses 42 in the gas flow direction A is greater than twice the cross-sectional width of one side of a single heat transfer tube group 30 in the gas flow direction A.

[0028] The recess 41 located on the upstream side in the gas flow direction A, together with the opening provided in the seal plate 5, forms a first chamber 61 through which the first straight sections 31 and 34 of the heat transfer tube group 30 located on the upstream side in the gas flow direction A are connected.

[0029] The recess 43 located furthest downstream in the gas flow direction, together with the opening provided in the seal plate 5, forms a second chamber 62 through which the second straight sections 32 and 35 of the heat transfer tube group 30 located furthest downstream in the gas flow direction A are connected.

[0030] The other recesses 42, together with the openings provided in the seal plate 5, form an intermediate chamber 63 through which the first straight sections 31, 34 and the second straight sections 32, 35 of the heat transfer tube group 30, which are adjacent to each other in the gas flow direction A, are connected.

[0031] A cover plate 4 having such recesses 41, 42, and 43 can be manufactured by cutting and polishing a flat plate. In this embodiment, the cover plate 4 is made of stainless steel (for example, SUS304). This prevents corrosion of the cover plate 4. However, the material of the cover plate 4 is not limited to this and can be changed as appropriate.

[0032] In this embodiment, there are multiple intermediate chambers 63 (two in the illustrated example), and the bolts 11 described above are arranged to surround two adjacent intermediate chambers 63 as a whole, as well as to surround the first chamber 61 and the second chamber 62 individually.

[0033] The cross-sectional area A1 of the first chamber 61 in the direction perpendicular to the specific direction B, that is, the area shown in Figure 1(a), is larger than the sum of the internal cross-sectional areas of the first straight sections 31 and 34 of one heat transfer tube group 30. In other words, when the inner diameter of the heat transfer tube 3 is Di, and the number of first U-shaped tubes 3A and second U-shaped tubes 3B in one heat transfer tube group 30 are N1 and N2, respectively, the cross-sectional area A1 of the first chamber 61 is (N1 + N2) × Di 2 It is greater than / 2.

[0034] Similarly, the cross-sectional area A2 of the second chamber 62 in the direction perpendicular to the specific direction B, that is, the area shown in Figure 1(a), is the sum of the internal cross-sectional areas of the first straight sections 31 and 34 of one heat transfer tube group 30 ((N1 + N2) × Di 2 It is greater than ( / 2).

[0035] On the other hand, the cross-sectional area A3 of the intermediate chamber 63 in the direction perpendicular to the specific direction B, that is, the area shown in Figure 1(a), is twice the sum of the internal cross-sectional areas of the first straight sections 31 and 34 of one heat transfer tube group 30 ((N1 + N2) × Di 2 It is larger than ).

[0036] By setting the cross-sectional area A1 of the first chamber 61, the cross-sectional area A2 of the second chamber 62, and the cross-sectional area A3 of the intermediate chamber 63 as described above, obstruction of liquid flow within the first chamber 61, the second chamber 62, and the intermediate chamber 63 is suppressed.

[0037] In this embodiment, liquid flows from the heat transfer tube group 30 located furthest downstream in the gas flow direction A to the heat transfer tube group 30 located furthest upstream in the gas flow direction A. For this reason, the cover plate 4 is provided with a plurality of inlet passages 44 extending from the second chamber 62 to the side opposite the first tube sheet 21, and a plurality of outlet passages 45 extending from the first chamber 61 to the side opposite the first tube sheet 21. In other words, the second chamber 62 is the inlet chamber, and the first chamber 61 is the outlet chamber.

[0038] Furthermore, on the side of the cover plate 4 opposite to the first tube sheet 21, an inlet header 71 that communicates with the inlet passage 44 is attached, and an outlet header 72 that communicates with the outlet passage 45 is also attached.

[0039] In the heat exchanger 1 with the configuration described above, the intermediate chamber 63 functions as a liquid return channel between adjacent heat transfer tube groups 30 in the gas flow direction A. Therefore, a bend pipe is unnecessary. Moreover, since the liquid that has flowed through each heat transfer tube 3 is mixed in the intermediate chamber 63, the heat exchange efficiency can be improved. Furthermore, in this embodiment, the second chamber 62 functions as a liquid distribution chamber to the heat transfer tube group 30 located at one end, and the first chamber 61 functions as a liquid confluence chamber from the heat transfer tube group 30 located at the opposite end. Therefore, the structure related to liquid distribution and confluence can also be simplified.

[0040] Furthermore, in this embodiment, since the cover plate 4 is fixed to the first tube sheet 21 by bolts 11 and nuts, not only are problems due to welding distortion, as would occur when the cover plate 4 is fixed to the first tube sheet 21 by welding, avoided, but the manufacturing cost of the heat exchanger 1 can be reduced compared to when the cover plate 4 is fixed to the first tube sheet 21 by welding. In particular, when the heat exchanger 1 is used as a feedwater preheating device for a boiler, the design of the cover plate 4 and the size, number, and position of the bolts 11 can be determined based on strength calculations, and boiler structural standards can be met.

[0041] Furthermore, since a sealing plate 5 is sandwiched between the first tube sheet 21 and the cover plate 4, the sealing plate 5 can prevent liquid from leaking from between the first tube sheet 21 and the cover plate 4.

[0042] <Variation> This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure.

[0043] For example, the second U-shaped tube 3B may be omitted, and the heat transfer tube group 30 may consist only of the first U-shaped tube 3A. However, if the heat transfer tube group 30 consists of the first U-shaped tube 3A and the second U-shaped tube 3B as in the above embodiment, one heat transfer tube group 30 can be composed of many heat transfer tubes 3.

[0044] Furthermore, in the above embodiment, the first straight section 31 of the first U-shaped pipe 3A and the first straight section 34 of the second U-shaped pipe 3B were arranged in a staggered pattern, and the second straight section 32 of the first U-shaped pipe 3A and the second straight section 35 of the second U-shaped pipe 3B were also arranged in a staggered pattern. However, the first U-shaped pipe 3A and the second U-shaped pipe 3B may not be inclined with respect to the gas flow direction A, and the first straight section 31 and the second straight section 32 of the first U-shaped pipe 3A and the first straight section 34 and the second straight section 35 of the second U-shaped pipe 3B may be arranged in a grid pattern.

[0045] However, as in the above embodiment, if the first straight section 31 of the first U-tube 3A and the first straight section 34 of the second U-tube 3B are arranged in a staggered pattern, and the second straight section 32 of the first U-tube 3A and the second straight section 35 of the second U-tube 3B are also arranged in a staggered pattern, a turbulence-promoting effect on the gas can be obtained. As a result, the heat transfer coefficient can be improved. Moreover, if the first U-tube 3A and the second U-tube 3B are inclined in opposite directions, the turbulence-promoting effect on the gas can be made greater compared to the case where the first U-tube 3A and the second U-tube 3B are not inclined.

[0046] Conversely to the above embodiment, liquid may flow from the heat transfer tube group 30 located furthest upstream in the gas flow direction A to the heat transfer tube group 30 located furthest downstream in the gas flow direction A. In this case, the first chamber 61 functions as a liquid distribution chamber to the heat transfer tube group 30 located at one end, and the second chamber 62 functions as a liquid confluence chamber for the liquid from the heat transfer tube group 30 located at the opposite end.

[0047] Furthermore, it is not necessary for the sealing plate 5 to be sandwiched between the first tube sheet 21 and the cover plate 4. Alternatively, annular grooves may be formed on the surface of the cover plate 4 facing the first tube sheet 21, surrounding each of the recesses 41, 42, and 43, and annular sealing material may be held in these annular grooves.

[0048] <Summary> In a first aspect, the present disclosure relates to a heat exchanger for performing heat exchange between a gas and a liquid, comprising: a first tube sheet and a second tube sheet facing each other across a flow path through which the gas flows; a U-shaped heat transfer tube having a first straight section and a second straight section penetrating the first tube sheet and the second tube sheet, and a bend section connecting the first straight section and the second straight section on the outside of the second tube sheet, wherein a plurality of heat transfer tubes are arranged such that a group of heat transfer tubes arranged in a direction perpendicular to the direction of gas flow are aligned in the direction of gas flow; and a cover plate covering the outer surface of the first tube sheet, wherein the surface of the cover plate on the first tube sheet side has a plurality of recesses aligned in the direction of gas flow. A heat exchanger is provided, wherein the second linear section is located downstream of the first linear section in the gas flow direction, the recess located furthest upstream in the gas flow direction forms a first chamber through which the first linear section of the heat transfer tube group located furthest upstream in the gas flow direction communicates, the recess located furthest downstream in the gas flow direction forms a second chamber through which the second linear section of the heat transfer tube group located furthest downstream in the gas flow direction communicates, and the other recesses form intermediate chambers through which the first linear section and the second linear section of adjacent heat transfer tube groups in the gas flow direction communicate.

[0049] According to the above configuration, the intermediate chamber functions as a return flow channel for liquid between adjacent heat transfer tube groups in the gas flow direction. Therefore, a bend tube is unnecessary. Moreover, since the liquid flowing through each heat transfer tube is mixed in the intermediate chamber, the heat exchange efficiency can be improved. Furthermore, one of the first and second chambers functions as a liquid distribution chamber to the heat transfer tube group located at one end, while the other functions as a liquid confluence chamber for the heat transfer tube group located at the opposite end. Therefore, the structure related to liquid distribution and confluence can also be simplified.

[0050] In a second embodiment, the cover plate may be made of stainless steel, as in the first embodiment. This configuration makes it possible to prevent corrosion of the cover plate.

[0051] In a third embodiment, in the first or second embodiment, the cover plate may be fixed to the first tube sheet by bolts and nuts. This configuration not only avoids problems caused by welding distortion, as occurs when the cover plate is fixed to the first tube sheet by welding, but also reduces the manufacturing cost of the heat exchanger compared to when the cover plate is fixed to the first tube sheet by welding.

[0052] In a fourth embodiment, in any of the first to third embodiments, for example, the number of intermediate chambers may be multiple, and the bolts may be arranged to surround two adjacent intermediate chambers as a single unit.

[0053] In a fifth embodiment, in any of the first to fourth embodiments, the outer diameter of the heat transfer tube may be 15 mm or less. With this configuration, a finless bare tube can be used as the heat transfer tube.

[0054] In a sixth embodiment, in any of the first to fifth embodiments, for example, the cover plate may be provided with an inlet channel extending from the second chamber to the surface opposite to the first tube sheet, and an outlet channel extending from the first chamber to the surface opposite to the first tube sheet.

[0055] In a seventh embodiment, in any of the first to sixth embodiments, the heat exchanger further comprises a sealing plate sandwiched between the first tube sheet and the cover plate, having a plurality of openings at positions corresponding to the plurality of recesses, wherein the plurality of recesses, together with the plurality of openings, form the first chamber, the second chamber, and the intermediate chamber. With this configuration, the sealing plate can prevent liquid leakage from between the first tube sheet and the cover plate. [Explanation of Symbols]

[0056] 1 heat exchanger 21 1st tube plate 22 2nd tube plate 3 Heat transfer tubes 3A 1st U-shaped tube 3B 2nd U-shaped tube 31,34 1st straight section 32,35 2nd straight section 33,36 Bend section 4 Lid plate 41, 42, 43 indentations 44 Inlet channel 45 Outlet channel 5. Seal plate 61 First Chamber 62 Second Chamber 63 Intermediate Chamber

Claims

1. A heat exchanger that performs heat exchange between a gas and a liquid, A first tube sheet and a second tube sheet facing each other across the flow path through which the aforementioned gas flows, A heat transfer tube that is a U-shaped tube having a first straight section and a second straight section penetrating the first tube sheet and the second tube sheet, and a bend section connecting the first straight section and the second straight section on the outside of the second tube sheet, wherein a plurality of heat transfer tubes are arranged such that the heat transfer tubes are aligned in the direction of gas flow, with the heat transfer tubes aligned in a direction perpendicular to the direction of gas flow, The first tube sheet comprises a cover plate that covers the outer surface of the tube sheet, Multiple recesses are formed on the surface of the cover plate on the first tube sheet side, aligned in the direction of gas flow. The second straight section is located downstream of the first straight section in the direction of gas flow, A heat exchanger in which, of the recesses, the recess located furthest upstream in the direction of gas flow forms a first chamber through which the first straight section of the heat transfer tube group located furthest upstream in the direction of gas flow is connected; the recess located furthest downstream in the direction of gas flow forms a second chamber through which the second straight section of the heat transfer tube group located furthest downstream in the direction of gas flow is connected; and the other recesses form intermediate chambers through which the first straight section and the second straight section of adjacent heat transfer tube groups in the direction of gas flow are connected.

2. The heat exchanger according to claim 1, wherein the cover plate is made of stainless steel.

3. The heat exchanger according to claim 1 or 2, wherein the cover plate is fixed to the first tube sheet by bolts and nuts.

4. The number of intermediate chambers is multiple, The heat exchanger according to claim 3, wherein the bolts are arranged to surround two adjacent intermediate chambers as a single unit.

5. The heat exchanger according to claim 1 or 2, wherein the outer diameter of the heat transfer tube is 15 mm or less.

6. The heat exchanger according to claim 1 or 2, wherein the cover plate is provided with an inlet channel extending from the second chamber to the surface opposite to the first tube sheet and an outlet channel extending from the first chamber to the surface opposite to the first tube sheet.

7. The device further comprises a sealing plate sandwiched between the first tube sheet and the cover plate, with a plurality of openings provided at positions corresponding to the plurality of recesses, The heat exchanger according to claim 1 or 2, wherein the plurality of recesses, together with the plurality of openings, form the first chamber, the second chamber, and the intermediate chamber.

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