WO2023282775A1

WO2023282775A1 - A shell-and-tube heat exchanger with helical baffles

Info

Publication number: WO2023282775A1
Application number: PCT/PL2022/050041
Authority: WO
Inventors: Janusz PRZYBYŁA
Original assignee: Famet Spółka Akcyjna
Priority date: 2021-07-07
Filing date: 2022-06-24
Publication date: 2023-01-12
Also published as: PL438374A1; PL244117B1; EP4367464A1

Abstract

A shell-and-tube heat exchanger with helical baffles wherein the shell (1) includes inside an outer continuous helical baffle (8) to support the tubes (4) of the outer bundle of tubes (2), and an integrated inner discontinuous helical baffle (23) to support the tubes (4) of the inner bundle of tubes (22). The outer continuous helical baffle (8) is formed of many main flat segments (11) and many intermediate flat segments (14) or(16). The inner discontinuous helical baffle (23) is formed of flat segments (25). The flat segments (25) with the intermediate flat segments (14) or (16) form together common flat segments (27) or (27A). The heat exchanger according to the present invention solves the problem of optimal continuous helical flow characterized by highly efficient heat transfer.

Description

A shell-and-tube heat exchanger with helical baffles

The present invention relates to a shell-and-tube heat exchanger with helical baffles, used in a variety of industry sectors, particularly in refinery and petrochemical systems, power industry, metallurgical industry, and others.

The main component of the heat exchanger is typically a cylindrical outer shell with inlet and outlet nozzles. Inside the shell, there is placed a bundle of tubes the ends thereof are fixed in tubesheets. One fluid flows inside the tubes whereas second fluid flows in the shell, in the inter-tube space, so that heat transfer takes place between them. A very significant role is played by so called baffles of the tube bundle. The function of the baffles is to support the tubes and to direct the flow of the second fluid in the shell, so as to obtain high heat transfer rates, reduce fouling in the shell space and eliminate tube vibration. Apart from traditional segmental baffles perpendicular to the tube bundle, heat exchangers with helical flow inside the shell have also begun to be increasingly used in the last several dozen years.

In the solutions known so far, the helical flow in the shell is provided with the use of discontinuous helical baffles in the form of many, typically quarter segments arranged at an angle in relation to the heat exchanger axis. Such solutions are presented in patent applications EP1668306, US2693942, CS269165, US1525094, US4493368, and CN2655156Y. The discontinuous helical baffles described in those patents cause that the helical flow in the shell occurs only partially because a significant portion of the fluid moves between the quarter segments in the axial direction, meandering along the tubes. Moreover, the pressure drop inside the shell increases and the heat transfer deteriorates in such a situation. The publication of the authors R.J. Jibb et ah, "Helixchanger Heat Exchanger - Field Experience And Ongoing Development", conference: Heat Exchanger Fouling and Cleaning - 2019 2-7 June 2019, Jozefow (Warsaw), describes all aspects of the helical flow in heat exchangers of the Helixchanger type with the use of a discontinuous helical baffle. In such apparatuses, in practice, the fluid flow in the shell is similar to the helical flow in the outer part only while in the inner - central part a longitudinal flow dominates, characterized by low surface film conductance. As a result, the whole heat exchanger has lower efficiency.

Another known solution for conducting a helical flow in the shell of a heat exchanger is to use a continuous helical baffle. Such solutions are known from patent applications US20080190593, US4360059 and CN100386586C. In the publication of the authors Jiang-Feng Yang et ah, "Investigation on combined multiple shell-pass shell-and-tube heat exchanger with continuous helical baffles" www.elsevier.com Energy 115 (2016) 1572-1579, various aspects of the use of a continuous helical baffle are described.

For all, known so far from patent applications and scientific publications, heat exchangers with a continuous helical baffle, many theoretical advantages have been demonstrated, but they have one fundamental disadvantage. This problem is the practical industrial technology for manufacturing a continuous helical ribbon as a support for the entire bundle of tubes because it is not possible in practice to precisely make all coaxial holes for each of the tubes in the bundle. Even if a central pipe or separate segments of a discontinuous baffle in the central flow of the heat exchanger are used to fix such a helical baffle, these solutions will be very difficult and expensive in practical implementation. In order to practically solve the problem of the industrial manufacture technology of a continuous helical baffle, various kinds of bent or overlapped segments are applied that are next joined together to impose a helical-like flow in the heat exchanger shell. The majority of solutions, known among others from patent applications CN105202948, CN104019694 and CN105973040, do not solve the issue of the optimal utilization of the central flow in the heat exchanger. This means that, as a result of the intense longitudinal central flow, the remaining, most often definitely larger part of the heat transfer surface shows low efficiency. Moreover, the production of such baffle segments is extremely complicated and very expensive. Another, similar solution is presented in the patent application CN110081762. In this case, for better utilization of the central flow, a separate bundle of tubes with a specially shaped surface, different in relation to the other tubes, has been used. This solution increases costs and is problematic for cleaning the heat exchanger. In addition, the above-mentioned solutions of the heat exchanger structure may be used for apparatuses of small sizes and low heat transfer efficiency.

The object of the present invention is to provide the structure of a shell-and-tube heat exchanger with an outer continuous helical baffle and with the use of a central pipe, as well as the structure of an outer continuous helical baffle integrated with an inner discontinuous helical baffle placed in the central flow, in order to achieve higher heat transfer efficiency and the reduction of flow resistance, thus the reduction of energy consumption together with the reduction of C02 emission. Another object of the present invention is also to achieve high stiffness of said structure as well as a simple and cheap method to precisely make tube holes in large heat exchangers including several hundred or even several thousand tubes.

The essence of the present invention is the structure of a continuous helical baffle for the outer bundle of tubes of the shell-and-tube heat exchanger including a central pipe or, in place of the central pipe, having additionally an inner bundle of tubes supported by an inner discontinuous helical baffle. The outer continuous helical baffle is formed of many main flat segments in the shape of an isosceles triangle with the base thereof of the shape of a convex arc facing the inner surface of the heat exchanger shell and the apex of said triangle is located on a circle of a diameter equal to the outside diameter of the central pipe or, respectively, to the diameter of the central flow, as well as of many intermediate flat segments of the shape of an isosceles triangle with the base thereof of the shape of a concave arc facing the X-X axis of the heat exchanger, or many intermediate flat segments of the shape of an isosceles trapezium with one base thereof of the shape of a convex arc facing the inner surface of the heat exchanger shell and the other base thereof of the shape of a concave arc facing the X-X axis of the heat exchanger. The main flat segments and the intermediate flat segments alternately adjoin each other along their legs and are arranged in relation to each other at an alternating angle a lesser than 180°, and, at the same time, respectively, every other main flat segment or every other intermediate flat segment of the shape of an isosceles triangle, or every other flat segment of the shape of an isosceles trapezium are mutually parallel. The intermediate flat segments are located at an angle b lesser than 90° in relation to the X-X axis of the heat exchanger. On the other hand, the inner discontinuous helical baffle is formed of many flat segments with one side thereof of the shape of a convex arc congruent with the concave arc of the intermediate flat segment of the shape of an isosceles triangle or to a concave arc of the intermediate flat segment of the shape of an isosceles trapezium, and they form with the intermediate flat segments of the outer continuous helical baffle many common flat segments, where the flat segment of the inner discontinuous helical baffle has the area F larger than the area S of a flat geometric figure similar to an isosceles triangle with the base thereof of the shape of a convex arc congruent with a concave arc of the intermediate flat segment of the shape of an isosceles triangle or to a concave arc of the intermediate flat segment of the shape of an isosceles trapezium whereas the apex of said triangle is located on the X-X axis of the heat exchanger. The projection of said geometric figure on a plane perpendicular to the X-X axis of the heat exchanger corresponds to one fourth or one sixth of the cross-sectional area of the central flow contained in a circle of a diameter equal to the diameter of the central flow. The flat segments of the inner discontinuous helical baffle have the area F larger than the area S of a flat geometric figure in order to accommodate all tube holes located within the flat geometric figure and at least all complete boundary tube holes located at the edge of the flat geometric figure and arranged in accordance with the layout of the inner bundle of tubes. The flat segments of the inner discontinuous helical baffle can have the area F larger than the area S of the flat geometric figure in order to accommodate, apart from all tube holes located within the flat geometric figure and the boundary tube holes, additional tube holes arranged in accordance with the layout of the inner bundle of tubes. The main flat segments together with the intermediate flat segments form couples of segments that, consecutively repeated n-fold, form one full pitch P of the outer continuous helical baffle along the X-X axis of the heat exchanger, where n equals 4 or 6. The essence of the present invention is also that the main flat segments together with the associated flat segments form couples of segments which, consecutively repeated n-fold, form one full pitch P of the outer continuous helical baffle integrated with the inner discontinuous helical baffle, where n equals 4 or 6.

In the preferred embodiment, the angle b ranges from 30° to 75° whereas the angle a is within the range from 120° to 170°.

In the optimal embodiment, each couple of the flat segments is cut out from a single plate sheet and bent at the angle a along the legs of the main flat segments. The convex arcs of the intermediate flat segments shaped into an isosceles trapezium and located at the angle b in relation to the X-X axis of the heat exchanger and the convex arcs of the main flat segments are fragments of an ellipse, and all said arcs in the projection on a plane perpendicular to the X-X axis form a circle of a diameter lesser by 2 to 20 mm than the inside diameter of the shell. Concurrently, the concave arcs of the intermediate flat segments of the shape of an isosceles triangle or the concave arcs of the intermediate flat segments of the shape of an isosceles trapezium are fragments of such an ellipse which in the projection on a plane perpendicular to the X-X axis forms a circle of a diameter equal to the outside diameter of the central pipe or the diameter of the central flow.

The shell-and-tube heat exchanger according to the invention with the use of the central pipe and the outer continuous helical baffle formed of many main flat segments of the shape similar to an isosceles triangle and connected one to the other with the intermediate flat segments of the shape similar to an isosceles triangle or to an isosceles trapezium enables the implementation of a uniform optimal plug flow of the second fluid in the heat exchanger shell.

The shell-and-tube heat exchanger according to the invention with the outer continuous helical baffle and integrated therewith the inner discontinuous helical baffle in the central flow, as a consequence of the use of the segments of the inner discontinuous helical baffle of a larger area F, enables to reduce the velocity of the central flow and, concurrently, to increase the velocity of the helical flow in the outer bundle of tubes. This change has a beneficial effect on the equalization of the velocity and on the increase of the heat transfer capacity in the entire heat exchanger because the heat transfer in the outer bundle of tubes increases. Increasing the area of the segments of the inner discontinuous helical baffle provides the opportunity to optimize the flow-and-thermal parameters of a heat exchanger at the stage of design and thermal calculations. As a result, the size of the entire heat exchanger for a particular task can be significantly reduced, even by over a dozen percent, retaining all so far known advantages of the helical flow in the shell of a heat exchanger, namely elimination of fouling, reduction of tube vibrations and the increase of the operational time in between overhauls. The heat exchanger according to the invention can be successfully used in place of existing traditional tube bundles with segmental baffles or in place of the so called Helixchanger heat exchanger. In such cases, the reduction of energy consumption or the increase of flexibility - efficiency of the entire installation will be achieved.

The shell-and-tube heat exchanger according to the invention is presented in the drawings, where:

Fig. 1 shows schematically an axial section of a heat exchanger with the central pipe. Fig. 2 shows schematically a cross-section of a heat exchanger with the central pipe.

Fig. 3 shows schematically an axial section of a heat exchanger with the inner discontinuous helical baffle located in the central flow.

Fig. 4 shows schematically a cross-section of a heat exchanger with the inner discontinuous helical baffle located in the central flow.

Fig. 5 shows an example of the flat development of one scroll (360°) of the outer continuous helical baffle comprising four couples of flat segments - without tube holes.

Fig. 5A shows an example of a different embodiment of the flat development of one scroll (360°) of the outer continuous helical baffle comprising four couples of flat segments - without tube holes. Fig. 6 shows an example of the flat development of one scroll (360°) of the outer continuous helical baffle integrated with the segments of the inner discontinuous helical baffle comprising six couples of flat segments - without tube holes.

Fig. 6A shows an example of a different embodiment of the flat development of one scroll (360°) of the outer continuous helical baffle integrated with the segments of the inner discontinuous helical baffle comprising four couples of flat segments - without tube holes.

Fig. 7 shows a part of a frontal view along the X-X axis of the outer continuous helical baffle - without tube holes. Fig. 8 shows the outer continuous helical baffle in the C-C cross-section made along a circle for the full circumference (360°).

Fig. 9 shows 1/4 of the full pitch of the outer continuous helical baffle integrated with 1/4 of the inner discontinuous helical baffle in the projection on a plane perpendicular to the X-X axis - without tube holes, of the area F of the flat segment (25) larger than the area S of the geometric figure (28).

Fig. 10 shows a common flat segment of the outer continuous and inner discontinuous helical baffles in the projection on a plane perpendicular to the X-X axis, of the area F large enough to accommodate complete boundary tube holes. Fig. 11 shows a common flat segment of the outer continuous and inner discontinuous helical baffles in the projection on a plane perpendicular to the X-X axis, of the area F significantly larger to accommodate additional tube holes arranged according to the layout.

Fig. 12 shows an axonometric view of three scrolls (3 x 360°) of the outer continuous helical baffle integrated with the inner discontinuous helical baffle - with tube holes and a fragment of the heat exchanger shell.

Fig. 13 shows an exemplary flat development of one scroll (360°) of the outer continuous helical baffle comprising six couples of flat segments for the use in a heat exchanger with the central pipe. List of designations in the drawings

1. Shell

2. Outer bundle of tubes

3. Tubesheet

4. Tube

5. Inlet nozzle

6. Outlet nozzle

7 Inside diameter of the shell

8. Outer continuous helical baffle

9. Central pipe

10. Tube hole

IOA. Boundary tube hole

IOB. Additional tube hole

11. Main flat segment

12. Convex arc

13. Inner surface of the shell

14. Intermediate flat segment

15. Concave arc

16. Intermediate flat segment

17. Convex arc

18. Concave arc

19. Leg of an isosceles triangle or an isosceles trapezium

20. Circle

21. Circle

22. Inner bundle of tubes

23. Inner discontinuous helical baffle

24. Central flow

25. Flat segment

26. Convex arc

27. Common flat segment 27A. Common flat segment 28. Flat geometric figure

29. Couple of flat segments 29A. Couple of flat segments

30. Couple of flat segments 30 A. Couple of flat segments

In the embodiment of a shell-and-tube heat exchanger according to the invention, shown in (Fig. 1), the heat exchanger has two tubesheets 3 in which the ends of tubes 4 are fixed. First fluid flows inside the tubes 4 of the entire outer bundle of tubes 2, excluding the central pipe 9. Second fluid is supplied to the shell 1 through the inlet nozzle 5. Inside the shell 1, on the central pipe 9, there is placed the outer continuous helical baffle 8 formed of four couples of flat segments 29A. The all couples of the flat segments 29A according to the development shown in (Fig. 5A) were cut out from a plate and bent appropriately in relation to each other or joined by welding at an angle a = 154° along the legs 19. Next, after the spatial structure corresponding to 1/4 of the circumference of the helicoid scroll had been formed as depicted above, the holes 10 for tubes 4 were made according to the planned layout. The parts thus prefabricated are assembled on the central pipe 9 in accordance with the diagram shown in the cross-section (Fig. 8), while maintaining the angle of inclination b = 60°. A total of four scrolls of the outer continuous helical baffle with a pitch P = 550 mm were made of sixteen main flat segments 11 and sixteen intermediate flat segments 16. For the correct and precise manufacture of all the shapes of the flat segments (Fig. 5A), the Inventor computer program for 3D design was used. As a result, all the arcs 17 and 12, after forming and final assembling of the outer continuous helical baffle, will create in the front view (Fig. 2) a circle 21 fitting the outside diameter of the central pipe 9 and a circle 20 of a diameter ten millimeters smaller than the inside diameter 7 of the shell 1. Second embodiment is a heat exchanger (Fig. 3 and Fig. 4) having two tubesheets 3 in which the ends of the tubes 4 of the outer bundle of tubes 2 and the inner bundle of tubes 22 are fixed. First fluid flows inside the tubes 4 of both bundles of tubes 2 and 22. Second fluid is supplied to the shell 1 through the inlet nozzle 5. Inside the shell 1, there is placed the outer continuous helical baffle 8 integrated with the inner discontinuous helical baffle 23. Both baffles 8 and 23 are constructed of main flat segments 11 and common flat segments 27. All the flat segments according to the development (Fig. 6) were cut out from a plate and bent appropriately in relation to each other or joined by welding at an angle a = 151° along the legs 19. Next, after the spatial structure corresponding to 1/4 of the circumference of the helicoid scroll had been formed as depicted above, the holes 10 for tubes 4 were made according to the planned layout. The parts thus prefabricated are assembled into the appropriate whole of the outer continuous helical baffle 8 integrated with the inner discontinuous helical baffle 23 whose example is presented in (Fig. 12). The assembly of the whole is carried out analogously to the diagram shown in the cross-section (Fig. 8), maintaining the angle b = 56° of inclination of the intermediate flat segments 14 in relation to the X-X axis of the shell 1. In this embodiment, twelve main flat segments 11 and twelve common flat segments 27 have been used in total to make three scrolls of the helical baffle of a pitch P = 900 mm. For the correct and precise manufacture of all the shapes of the flat segments 11 and 27 (Fig. 6A), the Inventor computer program for 3D design was used. As a result, all the arcs 12, after forming and final assembling of both mutually integrated helical baffles 8 and 23, will appropriately fit the inside diameter 7 of the shell 1, maintaining a five-millimetre assembly clearance. In the presented embodiment of the heat exchanger, the inner discontinuous helical baffle 23 is made of twelve flat segments 25 (Fig. 10), which have the area F adequately large to accommodate all tube holes 10 and additionally eleven complete boundary tube holes 10A. In this embodiment, the flat segments 25 together with the intermediate flat segments 14 form common segments 27 which were cut out from one plate sheet in a form of couples of flat segments 30 and subsequently bent along the legs 19 at the angle a = 151°.

The two embodiments presented above do not limit the possibilities of constructing other heat exchangers in accordance with the invention. Particularly, for large, not mentioned before, sizes of heat exchangers, a larger number of flat segments presented as an example in the drawing (Fig. 13) can be used. For joining the flat segments along the legs 19, other commonly known assembly techniques can be used. Moreover, basing on the segmental simple structure of the outer continuous helical baffle or integrated therewith the inner discontinuous helical baffle, heat exchangers with a double-scroll structure of the helical baffles can also be constructed. The invention described does not limit the construction of a heat exchanger with the use of only four or six couples of segments for one scroll of the helical baffle as well. For a relatively small pitch of the helicoid, three or even two couples of flat segments can be used.

Claims

1. A shell-and-tube heat exchanger with helical baffles that includes: a shell with an inlet and outlet nozzle, a central pipe or, instead of the central pipe, an additional inner bundle of tubes placed in the central flow, an outer bundle of tubes arranged parallel to the shell axis and around the central pipe or around the additional inner bundle of tubes, two tubesheets to fix the ends of tubes therein, an outer continuous helical baffle formed of flat segments and matched to the inside diameter of the shell, and, if there is the additional inner bundle of tubes instead of the central pipe, additionally an inner, discontinuous helical baffle placed in the central flow, and each baffle has numerous coaxial holes for each tube of one or both bundles of tubes respectively, characterized in that: the outer continuous helical baffle (8) is formed of many main flat segments (11) in the shape of an isosceles triangle whose base has the shape of a convex arc (12) facing the inner surface (13) of the heat exchanger shell (1), and the apex of this triangle is located on a circle (21) of a diameter equal to the outside diameter of the central pipe (9) or the diameter of the central flow (24), respectively, as well as of many intermediate flat segments (14) of the shape of an isosceles triangle whose base has the shape of a concave arc (15) facing the X-X axis of the heat exchanger, or of many intermediate flat segments (16) in the shape of an isosceles trapezium whose one base has the shape of a convex arc (17) facing the inner surface (13) of the heat exchanger shell (1) and the other base has the shape of a concave arc (18) facing the X-X axis of the heat exchanger, and the main flat segments (11) together with the intermediate flat segments (14) of the shape of an isosceles triangle or with the intermediate flat segments (16) in the shape of an isosceles trapezium alternately adjoin each other along the length of their legs (19) and are arranged in relation to each other at an alternating angle a lesser than 180° and at the same time every other main flat segment (11) or every other intermediate flat segment (14) of the shape of an isosceles triangle or every other intermediate flat segment (16) of the shape of an isosceles trapezium are mutually parallel, while the intermediate flat segments (14) or (16) are positioned at an angle b lesser than 90° in relation to the X-X axis of the heat exchanger, whereas the inner discontinuous helical baffle (23) is formed of many flat segments (25) whose one side has the shape of a convex arc (26) congruent with the concave arc (15) of the intermediate flat segment (14) of the shape of an isosceles triangle or with the concave arc (18) of the intermediate flat segment (16) of the shape of an isosceles trapezium, and which form together with the intermediate flat segments (14) or (16) of the outer continuous helical baffle (8) many common flat segments (27) or (27A), where the flat segment (25) of the inner discontinuous helical baffle (23) has the area F larger than the area S of a flat geometric figure (28) similar to an isosceles triangle whose base has the shape of a convex arc (26) congruent with the concave arc (15) of the intermediate flat segment (14) of the shape of an isosceles triangle or with the concave arc (18) of the intermediate flat segment (16) of the shape of an isosceles trapezium whereas the apex of this triangle is on the X-X axis of the heat exchanger, and where the projection of said geometric figure (28) on a plane perpendicular to the X-X axis corresponds to 1/4 or 1/6 of the cross-sectional area of the central flow (24) contained in the circle (21) of a diameter equal to the diameter of the central flow (24).

2. The heat exchanger according to claim 1 characterized in that: the flat segments (25) of the inner discontinuous helical baffle (23) have the area F larger than the area S of the flat geometric figure (28) in order to accommodate all tube holes (10) located within the flat geometric figure (28) and at least all complete boundary tube holes (10A) located at the edge of the flat geometric figure (28) and arranged in accordance with the layout of the inner bundle of tubes (22).

3. The heat exchanger according to claim 1 or 2 characterized in that: the flat segments (25) of the inner discontinuous helical baffle (23) have the area F larger than the area S of the flat geometric figure (28) in order to accommodate, apart from all tube holes (10) located within the flat geometric figure (28) and the boundary tube holes (10A), additional tube holes (10B) arranged in accordance with the layout of the inner bundle of tubes (22).

4. The heat exchanger according to claim 1 characterized in that: the main flat segments (11) together with the intermediate flat segments (14) of the shape of an isosceles triangle or with the intermediate flat segments (16) of the shape of an isosceles trapezium form couples of segments (29) or couples of segments (29A) respectively, which consecutively repeated n-fold form one full pitch P of the outer continuous helical baffle (8) along the X-X axis of the heat exchanger, where n = 4 or 6.

5. The heat exchanger according to claim 1 characterized in that: the main flat segments (11) together with the common flat segments (27) or with the common flat segments (27A) form couples of segments (30) or couples of segments (30A) respectively, which consecutively repeated n-fold form one full pitch P of the outer continuous helical baffle (8) integrated with the inner discontinuous helical baffle (23), where n = 4 or 6.

6. The heat exchanger according to claim 1 characterized in that: the angle b ranges from 30° to 75°, whereas the angle a is within the range from 120° to 170°.

7. The heat exchanger according to claim 1 characterized in that: each couple of the flat segments (29), (29A), (30) or (30A) is cut out from a single plate sheet and bent at the a angle along the legs (19) of the main flat segments (11).

8. The heat exchanger according to claim 1 characterized in that: the convex arcs (17) of the intermediate flat segments (18) of the shape of an isosceles trapezium, where these segments are located at the b angle in relation to the X-X axis of the heat exchanger, as well as the convex arcs (12) of the main flat segments (11) are fragments of an ellipse and all these arcs in the projection on a plane perpendicular to the X-X axis form a circle (20) of a diameter lesser by 2 to 20 mm than the inside diameter (7) of the shell (1), and concurrently the concave arcs (15) of the intermediate flat segments (14) of the shape of an isosceles triangle or the concave arcs (18) of the intermediate flat segments (16) of the shape of an isosceles trapezium are fragments of such an ellipse which in the projection on a plane perpendicular to the X-X axis creates a circle (21) of a diameter equal to the outside diameter of the central pipe or the diameter of the central flow (24).