Shell-and-tube heat exchanger with special (s type) baffles

Abstract

A heat exchanger (10) with a shell (11), a tube bundle (16) arranged inside the shell (11) between two tubular plates (17, 18) and flow-diverting partitions between the tubes of the bundle (16) has the tubes of the bundle which are arranged in concentric rings (31) and the flow-diverting partitions comprise at least intermediate partitions (26) which are arranged between neighbouring pairs of rings (31) of tubes and which are corrugated so as to have ridges (32) distributed along the tubes (16) and which are situated close to or touching the tubes of the bundle (16). An undulating - mainly longitudinal but turbulent - flow of fluid which improves the performance of the exchanger is thus formed and at the same time the tubes of the bundle are laterally supported.

Description

[0001] “Shell-and-tube heat exchanger with special (S type) baffles”

[0002] Description

[0003] The present invention relates to an innovative shell-and-tube heat exchanger with improved baffling.

[0004] A problem affecting shell-and-tube heat exchangers is that of not managing to optimize the heat exchange efficiency owing to the formation of preferential flow paths of the fluid flowing along the bundle inside the shell which negatively affect the heat exchange coefficient of the exchanger (for example the throughflow rates).

[0005] Furthermore, in chemical plants in some applications the fluid outside of the bundle may be “dirty”, namely contain solid elements which are deposited on the outside of the tubes or between the tubes and which prevent the correct flow of the fluid, hindering it and / or diverting it in an uncontrolled manner and / or locally modifying the surface temperature of the exchange tubes. Generally, in fact, if during the movement of the fluid inside the shell, stagnation zones occur, in these zones there is a further increase in the fouling on the shell side with a consequent further deterioration in the circulation of the fluid, with an increasingly worse performance of the exchanger over time.

[0006] In applications involving ethylene, if the hot fluid (cracking vapour) flows inside the tubes at a high temperature and the cooling fluid is the same fluid at lower temperatures, the stagnation / soiling also causes local overheating such that the wall temperature is increasingly situated within the creep / viscous flow range, with further problems due to deterioration of the mechanical resistance properties of the materials. Another extremely critical problem of shell-and-tube heat exchangers is that of preventing both damage to the tubes owing to high vibration amplitudes which may cause wear / fretting of the tubes in the region of the support elements (typically baffles) and the generation of problematic sound waves if a gaseous fluid is present inside the shell.

[0007] The fluid-dynamic vibrations may be typically caused by fluid-dynamic instability, vortex shedding and turbulent buffeting and are accompanied by a vibration amplitude of the tubes.

[0008] Acoustic resonance may instead be produced by an oscillation of the gaseous column with a bothersome sound effect even if not associated with vibration amplitude of the tubes.

[0009] In both cases it is necessary to ensure both adequate supporting of the tubes along their length and suitable conduction of the flow inside the shell as well as separation between the acoustic frequencies of the shell and exciting frequencies of the fluid (turbulent buffeting and vortex shedding).

[0010] Exchangers of the so-called FEHE (Feed-Effluent Heat Exchanger) type are for example very much subject to the aforementioned problems. Said reactors are widely used in the systems of high-temperature, exothermic, adiabatic reactors in order to save energy.

[0011] Generally, in the case of applications downstream of the cracking furnaces, the hot fumes enter the exchanger from below via a supply cone and are extracted from above via a further extraction cone.

[0012] The hot effluent exiting the furnace proceeds into a pre-heater in order to provide the energy required to pre-heat the supply to the optimum temperature. The fluid which is heated is therefore the same fluid (molar chemical composition) which is cooled (in terms of mass flowrate, while the pressure conditions may instead vary). The flow of the two fluids forms a counter-flow.

[0013] Typically the exchangers involved use low-pressure gas (if the plants in question produce ethylene) or medium-to-high pressure gas (if the plants in question are used for the production of hydrogen).

[0014] In the specific case of ethylene cracking, the gaseous fumes (effluent) which enter into the exchange tubes are at high temperatures (850-900°C) and exit, depending on the recovery level, typically at temperatures of 500°C or less. The fluid (charge) which enters into the shell of the exchanger is at a temperature typically of 300°C and exits at a temperature of about 700°C.

[0015] In general, the permissible head losses are fairly low (effluent side <10kPa; charging side <50kPa) and the heat exchange coefficient of the two fluids is comparable.

[0016] In an attempt to solve the initially mentioned problems (i.e. maximize the exchange efficiency and prevent the occurrence of vibrations or acoustic resonance), in a conventional exchanger the flow into the shell is directed by suitably shaped baffles which have both the function of directing the flow and the function of supporting the exchange tubes in order to prevent deflection thereof when fluid-dynamically excited.

[0017] In the prior art various types of baffles have been proposed, each with their particular advantages and drawbacks: for example, single segmental baffles, double segmental baffles, disk-and-doughnut baffles, triple segmental baffles which provide a certain amount of support for the tubes, but subject the flow to relatively sudden changes in direction resulting in a velocity component which is transverse to the tubes - or cross flow (X-flow) - which develops between a pair of baffles, and a velocity component which is parallel to the axis of the tubes - or longitudinal flow (W-flow) - which develops in windows of the baffles themselves through which the tubes pass. This may result in turbulence and dead zones in the flow mainly due to the sudden vectorial speed change, with consequent vibration and soiling deposits.

[0018] Another solution which has been proposed is single segmental baffles without tubes in the windows, which allow the vibrations to be reduced, since the main baffles may have, inserted between them, intermediate baffles for supporting and rigidifying the tubes (raising their natural frequency) without significantly increasing the head losses. However, the problem of sudden changes in direction remains.

[0019] In an attempt to improve the situation, baffles of the so-called “disk-doughnut” type have also been proposed, these making it possible to achieve a compromise between the head losses of double segmental baffles and the heat exchange coefficient of single segmental baffles. The result obtained is, however, a compromise which is not always satisfactory, there still remaining a sudden change in direction of the flow and dead zones in the centre of the exchanger (axis of symmetry).

[0020] In order to eliminate the sudden changes in direction in the flow which are present in the aforementioned baffles, the use of helical baffles (with single or double helices) has also been proposed. This solution is able to achieve a helical flow, without sudden changes in direction of the flow and consequently without dead zones, but has the drawback of a lack of symmetry of the flow and an intrinsic constructional difficulty due to the perforation of the helices in order to seat the tubes and support them, this making the manufacture of the exchanger very complex and costly.

[0021] With regard to the suppression of the acoustic resonance of cross-flow exchangers, the prior art also envisages the additional use of one or more solid or porous deresonating (or “detuning”) baffles which are arranged parallel to the flow and in a direction perpendicular to the stationary waves, or Helmholtz resonators or resonating cavities, helical spacers between the tubes, an irregular arrangement of the tubes, surface treatments for favouring acoustic damping, etc. This makes the manufacture of the exchanger even more complicated.

[0022] In order to avoid the problems associated with the use of deflectors having a surface extending in the manner of a disk, segments or helices, the use of so-called Tod baffle” technology has also been proposed, this using instead of the deflector baffles (plates) a cage which is formed by thin straight bars arranged intersecting each other in planes transverse to the tubes of the bundle and which has the function of supporting the tubes against the transverse movements without hindering the flow of the fluid, which becomes purely longitudinal (or axial) inside the shell. The support for the tubes, which is provided by the bars, is satisfactory (the small mesh, which is repeated along the whole length of the tubes, consists of four series of horizontal and vertical bars, which are welded to a peripheral ring and are regularly spaced, so as to form a square which embraces each tube, the spacing between the tubes being in fact square) and eliminates the problems of vibrations, but on the other hand the movement of the purely longitudinal flow without turbulence results in a number of disadvantages regarding the heat exchange coefficient. Furthermore, the entry into the shell occurs through an annular distributor such that sudden changes in the direction of the flow and right-angled velocity components nevertheless remain at the inlet and outlet.

[0023] A subsequent development, known as “EM Baffles” technology, i.e. expanded metal baffles, attempted to maintain the advantages of the rod baffles rigidifying cage, while creating a local turbulence in the various bar planes so as to increase the heat exchange coefficient and obtain the advantages of the “rod baffles” cage, with regard to vibrations, and the advantages of a conventional X-W flow baffling, as regards the heat exchange coefficient. In order to achieve this, perforated and stretched metal sheets are used, instead of simple intersecting bars, in order form a meshwork. The constructional complexity, however, increases and it is more difficult to assemble the tube bundle through the meshes with also a satisfactory contact between the meshes and the bundle tubes.

[0024] The general object of the present invention is to provide a shell-and-tube heat exchanger with an innovative internal structure for supporting the tubes and type of movement flow inside the shell.

[0025] In view of this object the idea which has occurred is to provide, according to the invention, a heat exchanger with a shell, a tube bundle arranged inside the shell between two tube plates and flow-diverting partitions between the tubes of the bundle, characterized in that the tubes of the bundles are arranged in concentric rings and the flow-diverting partitions comprise at least intermediate partitions which are arranged between neighbouring pairs of tube rings and which are corrugated so as to have ridges distributed along the tubes and which are situated close to or touching the tubes of the bundle.

[0026] Advantageously, a heat exchanger according to the invention may also comprise at least one peripheral partition which is arranged between the shell and the outermost ring of tubes and which is corrugated so as to have ridges distributed along the tubes and situated close to or touching alternately the tubes of the outermost ring of tubes of the bundle and the shell.

[0027] Advantageously, a heat exchanger according to the invention may also comprise at least one innermost partition which is arranged more towards a main axis of the exchanger than the tubes of the bundle and which is corrugated so as to have ridges distributed along the tubes which are situated close to or touch the tubes of the bundle of the innermost concentric ring.

[0028] In order to illustrate more clearly the innovative principles of the present invention and its advantages compared to the prior art, possible examples of embodiment applying these principles will be described below with the aid of the attached drawings. In the drawings:

[0029] - Figure 1 shows a schematic cross-sectioned side view of an exchanger made in accordance with the invention;

[0030] - Figure 2 shows a partial, schematic, enlarged side elevation view of a zone of an exchanger according to the invention;

[0031] - Figure 3 shows a schematic cross-sectioned view, along the line Ill-Ill of Figure 1 , of a possible embodiment of an exchanger according to the invention;

[0032] - Figure 4 shows a possible, partial, schematic cross-sectioned view, along the line IV-IV of Figure 2, of a second possible embodiment of an exchanger according to the invention;

[0033] - Figure 5 shows a schematic view of a possible embodiment of an end zone of the exchanger.

[0034] With reference to the figures, Figure 1 shows an exchanger, denoted overall by 10, made in accordance with the principles of the present invention.

[0035] The exchanger 10 comprises a casing or shell 11 which has, at its opposite ends, headers 12, 13 to which inlet and outlet ducts 14, 15 for the fluid to be cooled (for example high-temperature ethylene vapours) are connected.

[0036] A tube bundle 16 is arranged inside the casing between tube plates 17 and 18 so as to be immersed in the exchange fluid (for example, low-temperature ethylene vapours) which circulates in the exchanger through inlet and outlet ducts 19 and 20.

[0037] The tubes of the bundle 16 are arranged in several concentric rings 31 and, in accordance with the principles of the invention, intermediate partitions 26 are arranged between the tubes of two neighbouring rings, said partitions extending parallel to the tubes and being corrugated in the direction parallel to the tubes so as to be situated alternately close to and spaced from the tubes of the two neighbouring rings.

[0038] In particular, these intermediate partitions 26 may have the ridges of their corrugations which rest alternately on tubes of the outermost ring and on tubes of the innermost ring of the two neighbouring rings.

[0039] Preferably at least one innermost partition 27 is arranged in the space inside the innermost ring of tubes of the exchanger and in the direction parallel to the tubes is corrugated so as to be situated alternately close to and spaced from the tubes of the innermost ring. In particular, the at least one innermost partition 27 may have the ridges of their corrugations directed towards the tubes which rest on tubes of the innermost ring of the exchanger. In the space in the direction closer to the axis of the exchanger than the innermost partition 27, namely in the space extending axially and central inside the exchanger, heat exchange tubes are not present.

[0040] The central empty space of the exchanger may also be filled, if necessary, with a suitable filling material, for example a wool mattress made of suitable material able to withstand the specific conditions inside the exchanger.

[0041] Advantageously, the innermost partition 27 may be connected to the two plates 17 and 18 so as to continue the sinusoidal movement avoiding vectorial discontinuity in the velocity of the fluid flowing into and out of the shell, as will become clearer below. Alternatively, the partition 27 may also be advantageously connected to a suitable diffuser or flow deflector mounted both on the inlet plate and on the outlet plate, as shown schematically in broken lines and indicated by 30 in Figure 1 . Preferably, at least one peripheral partition 28 is arranged in the space between the lateral shell of the exchanger and the outermost ring of tubes, said peripheral partition extending parallel to the tubes and being corrugated in the direction parallel to the tubes so as to be situated alternately close to and spaced from the tubes of the outermost ring.

[0042] In particular, the at least one peripheral partition 28 may have the ridges of the corrugations which rest alternately on tubes of the outermost ring and on the inner wall of the shell (or which are situated close to them with a small amount of play).

[0043] In particular, in an advantageous embodiment according to the invention, the peripheral partition 28 may have the ridges directed towards the wall of the shell which allow a fluid flow to pass through between the partition and shell in the direction parallel to the shell wall, as indicated schematically by the thin-line arrows in Figure 1 . This throughflow (which in the embodiments of the prior art is a throughflow which is inefficient and has an adverse effect on the heat exchange) in the solution of the present invention becomes advantageously a fluid flow which is useful for cooling the shell. This throughflow between shell and peripheral partition may allow for example the design temperature of the shell to be kept to values which avoid damaging creep effects (for example, again with reference to exchangers of the effluent charging type downstream of the cracking ovens). For example, the shell may be kept at a temperature approximately equal to the inlet temperature of the fluid flowing into the shell.

[0044] If required, the peripheral partitions 28 may also be advantageously made with a double wall (namely, for example with two metal sheets 28a, 28b which define an intermediate cavity 28c, as shown schematically in broken lines in the enlarged view of Figure 2), so as to increase the heat insulation between the two faces of the peripheral partition. The cavity which is created in the double-wall partition may simply contain stagnant air or a suitable heat insulant (for example insulating paper), if an even greater heat insulation between the two walls is required.

[0045] As can be clearly seen in Figure 1 , preferably but not necessarily, all the corrugated partitions may have corrugations arranged in the same direction (namely so as to be in “phase alignment”) in the planes transverse to the central axis of the exchanger (axis 25 in Figure 1 ) parallel to the tubes, so as to create a corrugated space with a substantially constant transverse dimension between two radially adjacent partitions and with, inside, the tubes of a ring of tubes.

[0046] The corrugations of the corrugated partitions create a correspondingly undulating flow of the fluid along the tubes of the bundles, as indicated for example by arrows in the exchanger of Figure 1 .

[0047] As again shown in Figure 1 , the partitions may be preferably made with their ends facing the two plates 17 and 18 which are gradually increasingly spaced from the respective facing plate in the direction from the centre of the exchanger towards the periphery of the exchanger, so as to better guide at one end of the exchanger the fluid flow from the peripheral inlets 19 towards the corrugated spaces containing the tubes and from these corrugated spaces towards the peripheral outlets 20 at the other end of the exchanger.

[0048] The ends of the partitions at the two ends of the exchanger are spaced from the plates and have a corrugation which is formed so as to gently accompany the fluid flow from the inlet into the shell to the cavities between the partitions and from the cavities between the partitions to the outlets from the shell with a variation of the velocity vectors preferably having a continuous derivative without angled points.

[0049] Curved end deflectors may also be provided in the vicinity of the plates 17 and 18 in order to facilitate further the change in direction of the flow entering / exiting the spaces between the corrugated partitions. In particular, at the end inlet end where the fluid enters the shell, the curved deflectors may facilitate the change in direction of the fluid so that it enters into the space between the corrugated partitions (forming radial-annular deflectors) and at the outlet end where the fluid exits the shell the curved deflectors may facilitate the change in direction of the fluid at the outlet from the space between the corrugated partitions so as to direct it towards the outlets located on the periphery of the exchanger (forming annular-radial deflectors).

[0050] For the purposes of simpler illustration, these curved deflectors are shown by way of example (indicated by 29) only in a top left-hand zone in Figure 1. Based on Figure 1 , the person skilled in the art may nevertheless easily imagine the overall position and operation of the deflectors also in the other positions at the top and bottom ends of the exchanger in the vicinity of the plates. As can be seen more clearly in Figure 5, in the vicinity of the plates 17, 18 the curved deflectors 29 may comprise vanes for guiding the flow 33, which are extensions of the ends of the corrugated partitions and intermediate flow guide vanes 34. These vanes may be independent or may form part of the radial-annular or annular-radial diffuser. The vanes 33 which form an extension of the ends of the corrugated partitions may have curved ends which touch the tubes, while the intermediate vanes 34 may be perforated so as to allow the tubes of the bundle to pass through. As can be clearly see in Figure 5, the vanes may be situated further from the plate at the periphery and closer to the plate in the centre.

[0051] The outermost vane may also be arranged so as to have its end curved towards the periphery substantially flush with the fluid inlet (or outlet) opening in the shell. The curved deflectors and the vanes may also be connected together in the respective diffuser 30.

[0052] The flow guide vanes 33, which are extensions of the ends of the corrugated partitions, may be made as one piece with the corrugated partitions (by suitably shaping the partitions) or may be elements applied so as to extend the partitions such that the partitions may be made all with the same or similar length and the vanes may be extended in the axial direction with respect to the exchanger so as to complete the path between the end of the partition and the flow deflection position, namely the point where the vane curves, as schematically shown in Figure 5.

[0053] All or some of the partitions (including also if necessary the curved deflectors, even though these are better made using a static fusion process) may be made using shaped metal sheets. In particular, the corrugated form of the partitions may be obtained using any known technology suitable for the purpose, such as rolling, embossing, fluid pressure expansion against a shaped counter-surface or inside two coupled surfaces if each partition is in turn double, etc. The specific material used for the partitions and the deflectors will be chosen depending on the specific characteristics required, for example depending also on the fluid to be treated and the operating temperatures, as may be easily imagined by the person skilled in the art.

[0054] All or some of the partitions may also have small holes or channels through the thickness for equalizing the pressure on their two faces along the vertical extension of the exchanger.

[0055] Advantageously, the system may have a circular or square flow symmetry on the shell side (as will be described by way of example below) and this symmetry will preferably also be required at the fluid inlets and outlets in the shell, which must be preferably multiple in number (preferably four, or even better, multiples of four). In order to facilitate the distribution of the fluid inside the shell, the inlets 19 and the outlets 20 for the exchange fluid in the shell may be uniformly or symmetrically distributed along a circumference around the exchanger and, preferably, substantially flush with the corresponding tube plate 17 or 18.

[0056] Again preferably, the fluid inlets 19 and outlets 20 in the shell may be ducts formed with bends having a wide radius of curvature and connected to corresponding toroidal conduits 21 and 22 which coaxially surround the exchanger and are in turn connected to a corresponding main inlet pipe 23 and a corresponding main outlet pipe 24. This is shown by way of example in Figure 3 for an exchanger with a circular cross-section, but this solution is also valid for exchangers with different crosssections, as will be explained below.

[0057] Figure 2 shows schematically in greater detail a zone of the exchanger with the corrugated ducts between which the tubes are arranged. From this detail it can be better understood how the ridges of the partitions (indicated by 32) transversely support the tubes on the two sides. Using moreover preferably a series of partitions radially arranged alongside each other between the rings of tubes (as shown by way of example in Figure 1 ), the supporting action is transmitted from one ring to another and one partition to another, forming a particularly strong support structure, without the need for large continuous transverse supports as required by the solutions of the prior art.

[0058] Furthermore, the partitions, which may for example be made of sheet metal with a thickness typically of less than 6 mm, may be sufficiently flexible to withstand the thermal expansion of the tubes without causing local wear or fretting.

[0059] In order to reinforce the structure, the partitions may be easily kept in position by simple fixing means and / or thin rods or radial strips arranged at predefined axial distances (not shown, but which may be easily imagined by the person skilled in the art). Alternatively and more conveniently they may be connected to the deflectors 30 which are in turn keyed onto the tube plates 17 and 18.

[0060] The corrugated configuration of the partitions produces an undulating movement of the exchange fluid around the tubes which avoids dead points and optimizes the flow of the fluid and the heat exchange, with reduced head losses.

[0061] This enables a high efficiency of the exchanger to be obtained, while preventing or greatly reducing the soiling on the shell side which affects the solutions of the prior art.

[0062] Furthermore, the natural spectrum of the tubes is greatly raised (owing also to the reduced space between adjacent ridges) and therefore the critical vibrations in the exchange tubes and the possibility of acoustic resonance are prevented.

[0063] If preferred, the ridges of the partitions may be arranged as close to the tubes as required, but without touching them, thus leaving a small amount of play so as to allow, for example, thermal expansion movements transverse to the tubes, while limiting the possibility of transverse movement of the tubes, so as to provide an undulating flow of the fluids in the shell and ensure adequate support for the tubes and protection against excessive vibrations.

[0064] Figure 3 shows a first embodiment of the exchanger according to the invention with a structure of the partitions having a circular cross-section. In this embodiment, the partitions also have a generally cylindrical shape with their axis coinciding with the main axis 25 of the exchanger and with the side walls deformed so as to have an undulating progression in the direction of the axis 25 of the exchanger. As can be seen again in Figure 3, each concentric ring of tubes also has a correspondingly circular form with its centre along the axis 25 of the exchanger so as to match the circular arrangement of the partitions. In each ring the tubes are preferably equidistant from each other (namely with a practically identical “circular” pitch PI between the nth ring and the n+1 th ring).

[0065] The corrugated partitions with a circular cross-section may be made as a single cylindrical piece with a corrugated wall (for example a flat or corrugated metal sheet folded to form a cylinder) or by means of the juxtaposition of strips of corrugated cylindrical segments. For example, the partitions may be made from cylindrical sheet-metal tubes with a suitable diameter or may consist of curved strips so as to form cylindrical-wall segments which are deformed in order to obtain the required corrugation from the wall of the final cylinder in the axial direction of the cylinder thus formed.

[0066] Instead of the arrangement in circular rings, the tubes may also be arranged in rings configured to house between them partitions which are corrugated but have a straight cross-section with respect to the axis of the tubes. The partitions may thus form the sides of parallelepipeds with a convenient number of sides and the rings of tubes may have a corresponding polygonal cross-section. For example, the concentric rings may have a polygonal (square, hexagonal, octagonal, etc.) cross- sectional form. Obviously, the greater the number of sides of the polygon the closer the resemblance to a circular form.

[0067] Figure 4 shows in schematic form by way of example a zone, viewed along the cross-sectional line IV-IV of Figure 2, of an exchanger with corrugated straight partitions. In particular, Figure 4 shows the corner zone of square rings, where the corrugated sheet-metal partitions are joined together along their lateral edges to form the lateral comers of the parallelepiped with the sides parallel to the tubes in the rings. The construction with corrugated flat metal sheets may be easier to realize than the construction with partitions having a circular cross-section. In the case of corrugated flat metal sheets, the partitions may in fact be easily made from a completely flat metal sheet which is deformed (for example by means of rolling) so as to obtain the required corrugations in the lengthwise direction.

[0068] In the case of straight partitions, the peripheral partition, i.e. the partition externally facing the inner wall of the shell may also be formed with a double wall having a straight corrugated inner wall, so as to follow the rectilinear progression of the corresponding part of the outermost ring of tubes, and a corrugated outer wall which is correspondingly curved to match the facing inner wall of the shell (for example with a cylindrical form), so as to maintain the contact or in any case the correct close arrangement of the ridges with respect to the tubes on one side and the shell on the other side. For example, in the case of tubes arranged in concentric squares, the peripheral partition may be advantageously formed with a square overall crosssection on the side towards the tubes and circular cross-section on the side towards the shell, which also has a circular cross-section.

[0069] Although the corrugation of the various partitions may have a varying progression, it may be advantageously sinusoidal or approximately sinusoidal.

[0070] For example, if x is the axis of the tubes, the surface of the partition in the direction x may be of the type y=y0*sin(2 % x / Lt); yo=(Pt, rings-d0) / 2), with y0which represents the height of the half-wave and Ltthe length of the wave, d0the outer diameter of the tubes and Ptthe transverse pitch, namely the radial distance between one ring of tubes and the next one (which is preferably constant between each concentric ring).

[0071] Obviously, the partition between two generic concentric rings (nth, n+1 th) may touch or be very close to the tubes located both on the outer ring and on the inner ring at m points depending on the wavelength. Advantageously, but not exclusively, it is possible to imagine a wavelength which is 4 to 8 times the height of the half-wave (and therefore for example less than 150 mm for conventional dimensions of the tubes).

[0072] The optimum wavelength is in any case that which maximizes the shearing force on the wall of the partition (therefore minimizing the soiling or sediments) at the cost of an accepable increase in the head loss with regard to the purely longitudinal flow between the various rings.

[0073] In the case of the sinusoidal form of the partition, the length Leffof the undulating path of the fluid in the space between two adjacent partitions, where L is the length of the exchanger, will be the length of the sinusoidal undulation between 0 and L of wavelength Lt.

[0074] Analytically expressed where y is the function which describes the undulation. The integral may be naturally resolved numerically for each desired waveform.

[0075] At this point it is clear how the objects of the invention are achieved, resulting in a heat exchanger of the shell-and-tube type, with internal baffling comprising corrugated partitions, able for example to prevent or gradually reduce shell side soiling, vibrations in the exchange tubes and acoustic resonance, and optimize the heat exchange.

[0076] Furthermore, the heat exchanger with an undulating flow according to the invention is substantially devoid of concentrated head losses due for example to flow contractions (Venturi effect) which occur in the case of the baffles / grids of the prior art.

[0077] The heat exchanger according to the invention may be intrinsically protected from fluid-dynamic vibrations and acoustic resonance also owing to the presence of multiple support points for the tubes in the axial and transverse direction owing to the supporting contact between the tubes and partitions. The partitions with their particular form and relationship with the tubes also behave as de-resonating baffles, without the drawbacks of the de-resonating baffles of the prior art.

[0078] Obviously the description given above of embodiments applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein.

[0079] For example, the exchanger according to the invention may also comprise further known elements, such as tie-rods (arranged both centrally and distributed) between the end plates of the tube bundle, flow diffusers mounted on the tube plate, for example on the hot fumes side, etc., as may now be easily imagined by the person skilled in the art.

[0080] The dimensions of the exchanger, the number of tubes in the bundle and in each ring, their arrangement, spacing and density, the number of rings, etc., may obviously vary depending on the specific requirements, as will be clear to the person skilled in the art. For example, in the case where a known flow diffuser installed on the tube plate on the hot fumes side (for example in the case of applications of the exchanger in ethylene plants), the first ring (namely the innermost ring) will have a greater diameter than the diffuser.

[0081] The tube plates may also be of the so-called “thin” type, namely sufficiently flexible that they tend to curve under the pressure present inside the shell. In this case, as is known, resistance to curving may be ensured by the same tube bundle welded between the plates. Known tie-rods between the plates may also be provided for a better resistance to curvature of the plates. Said tie-rods may be distributed between the tubes or also confined to only the central zone of the exchanger for example inside the innermost partition 27.

[0082] From the point of view of the constructional sequence, owing to the innovative principles of the present invention, in the case of long apparatus, it may be simple to arrange several short apparatus in series, such that the assembly of the cage formed by partitions 26 is easier (also in order to reduce the weight of the shaped partitions).

[0083] The desired performance could be obtained either with a long apparatus or more simply with k apparatus which are all identical and arranged in series (the outlet of one apparatus the inlet of the next one).

Claims

Claims1. Heat exchanger (10) with a shell (11 ), a tube bundle (16) arranged in the shell (11 ) between two tube plates (17, 18) and flow-diverting partitions between the tubes of the bundle (16), characterized in that the tubes of the bundle are arranged in concentric rings (31 ) and in that the flow-diverting partitions comprise at least intermediate partitions (26) which are arranged between neighbouring pairs of rings (31 ) of tubes and which are corrugated so as to have ridges (32) distributed along the tubes (16) and which are situated close to or touch the tubes of the bundle (16).

2. Heat exchanger (10) according to claim 1 , characterized in that it comprises at least one peripheral partition (28) which is disposed between the shell (11 ) and the outermost ring (31 ) of tubes and which is corrugated so as to have ridges (32) distributed along the tubes and alternately situated close to or touching the tubes of the outermost ring (31 ) of tubes of the bundle (16) and the shell (11 ).

3. Heat exchanger (10) according to claim 2, characterized in that the ridges (32) of the peripheral partition (28) do not touch the shell so as to allow a fluid flow between the peripheral partition and the shell.

4. Heat exchanger (10) according to claim 3, characterized in that the peripheral partition (28) is made double-walled with an intermediate cavity.

5. Heat exchanger (10) according to claim 1 , characterized in that it comprises at least one innermost partition (27) which is arranged more towards a main axis (25) of the exchanger than the tubes of the bundle (16) and which is corrugated so as to have ridges distributed along the tubes and situated close to or touching the tubes of the bundle (16) of the innermost concentric ring.

6. Heat exchanger (10) according to claim 5, characterized in that the tube plates (17, 18) centrally have a flow diverter (30) that is connected with a respective end ofthe at least one innermost partition (27).

7. Heat exchanger (10) according to claim 1 , 2 and / or 3, characterized in that the concentric rings are circular and the intermediate, central and / or peripheral partitions are also circular around a main axis (25) of the exchanger.

8. Heat exchanger (10) according to claim 7, characterized in that the intermediate, central and / or peripheral partitions are formed as cylinders with corrugated walls.

9. Heat exchanger (10) according to claim 1 , 2 and / or 3, characterized in that the rings (31 ) have a polygonal cross-section and the intermediate, central and / or peripheral partitions are straight in the plane transverse to a main axis (25) of the exchanger so as to follow the sides of the polygonal rings.

10. Heat exchanger (10) according to claim 1 , 2 and / or 3, characterized in that the corrugations of the intermediate, central and / or peripheral partitions are sinusoidal or approximately sinusoidal.

11. Heat exchanger (10) according to claims 1 and 2, characterized in that the intermediate partitions (26) and the at least one peripheral partition (28) have opposite ends facing the two tube plates (17 and 18) at a distance increasing in the direction from the innermost ring to the outermost ring of the concentric rings (31 ).

12. Heat exchanger (10) according to claim 11 , characterized in that close to the ends of the partitions flow diverters (29) are provided for directing the fluid flow into / out of the spaces between the partitions.

13. Heat exchanger (10) according to claim 12, characterized in that the flow diverters (29) comprise guide vanes (33, 34) for converting a radial flow into an annular flow at one end of the exchanger and for converting an annular flow into a radial flow at the other end of the exchanger.

14. Heat exchanger (10) according to claim, 1 , characterized in that it comprises around the shell two toroidal ducts (21 , 22) connected by means of respective conduits (23 and 24) with the inside of the shell near the two tube plates (17, 18) for entry and exit of the fluid flow into / out of the shell.

15. Heat exchanger (10) according to claims 1 , 2 and 3, characterized in that the corrugations of the intermediate, central and / or peripheral partitions are in phasealignment with each other in directions radial to a main axis of the exchanger.

Images