Patent Publication Number: US-10788273-B2

Title: Shell-and-tube equipment with antivibration baffles and related assembling method

Description:
This application is a national phase of PCT/EP2016/062607, filed Jun. 3, 2016, and claims priority to EP 15175397.7, filed Jul. 6, 2015, the entire contents of both of which are hereby incorporated by reference. 
     FIELD OF APPLICATION 
     The invention relates to the field of shell-and-tube equipment. 
     PRIOR ART 
     In shell-and-tube equipment it is known to provide a certain number of baffles which have essentially two tasks: the first is that of increasing the speed of the fluid flowing in the shell side and passing over the tubes, thus increasing the heat exchange coefficient; the second is that of providing the tubes with intermediate support points along the bundle so as to prevent vibrations. The need to prevent vibrations is more felt when speed of the fluid circulating inside the shell is higher. 
     Each baffle has openings intended to receive a single tube or a set of tubes, and may be realized for example with a series of bars fixed to an external frame or with a sheet-metal disc suitably perforated. The baffles are spaced by a given distance, called pitch; it is also known to alternate baffles having a different geometry so that adjacent baffles provide a support to different groups of tubes and/or in perpendicular directions. Another requirement for the baffles is to allow a suitable through-flow of fluid, generally a gas, through the shell side. 
     Shell-and-tube equipment provided with the aforementioned baffles is described for example in the prior art patents U.S. Pat. Nos. 5,058,664, 5,642,778 and FR 2 993 217. 
     The known construction technique involves essentially the following steps: providing a framework comprising the baffles and respective longitudinal bars; inserting the tubes by passing them through the various baffles; fixing the tubes to the tube plates. This technique, however, is problematic and has a number of drawbacks. Each tube has to match the corresponding through-holes in the baffles which have a fairly small tolerance (otherwise the baffles would not be effective in preventing vibrations); the operation is feasible for the first tubes when the set of baffles and longitudinal bars still has a certain mobility; however, as the tubes are gradually inserted, the assembly becomes more rigid and positioning of the tubes becomes more difficult; insertion of the last tubes is typically performed by forcing them with a hammer and this practice can damage the tubes themselves. For example it has been noticed that, with this assembly technique, the surfaces of the tubes are damaged owing to the friction with the baffles. The baffles are also damaged, with the risk of breakage during operation. Breakage during operation is dangerous since tubes would lack support and be exposed to vibrations. Moreover, assembly performed in the above way requires a lot of time and is therefore costly. 
     The prior art seeks a compromise between a precise fit between tubes and baffles, which is more effective in reducing the vibrations but greatly complicates the assembly, and a less precise fit, which makes the assembly easier, but reduces the effectiveness against vibrations. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to solve the aforementioned problems and facilitate the construction of shell-and-tube equipment provided with antivibration baffles. 
     This object is achieved with shell-and-tube equipment according to the attached claims. 
     The equipment comprises a shell; a tube bundle; a plurality of baffles arranged along the tube bundle, each baffle having a plurality of receiving seats for said tubes and each of said seats receiving at least one tube of the bundle, and is characterized in that: 
     said seats of the baffles are shaped so as to comprise at least a first region designed to receive said at least one tube with a given first play, and a second region designed to receive said at least one tube with a second play which is smaller than the first play, or with substantially no play,
 
each baffle is displaceable, with respect to the tube bundle, between a first position, termed assembly position, and a second position, termed working position,
 
each tube of the bundle is received in the first region of the respective seat when the baffle is in the assembly position, and is received in the second region when the baffle is in the working position.
 
     The invention provides that the baffles can be set in an assembly configuration and in a working configuration. The tubes receiving seats of a generic baffle are shaped and oriented so that the displacement of the baffle from the assembly position to the working position gives a substantial locking of the tubes relative to the baffle. The displacement of a baffle from the assembly position to the working position is such that the respective seats move collectively from the assembly position to the working position. 
     In greater detail, in the assembly position a play allowing free sliding movement exists between the tubes and the respective seats of the baffles. In the working position this play is reduced or preferably null and, consequently, the tubes are locked or substantially locked with respect to the baffles. 
     The tubes receiving seats are oriented so that the locking of the tubes (i.e. the transition from the assembly position to the working position) is performed with a displacement or a rotation. Accordingly, the tube locking system may be named “shift-lock” when it occurs with a linear displacement of the baffles, and “twist-lock” when it occurs with a rotation. During locking, the tube receiving seats move along a linear path in the shift-lock embodiments or follow a circular arc in the twist-lock embodiments. 
     For example, in a preferred embodiment of the baffles with shift-lock system, the receiving seats are oriented so as to obtain locking of the tubes with a displacement of the baffles in a plane perpendicular to the axis of the tube bundle; in a preferred embodiment of the twist-lock type the seats are oriented so as to lock the tubes with a rotation of the baffles relative to said axis. 
     According to one aspect of the invention, two or more series of baffles with different locking movements are alternated. In particular, according to a preferred embodiment, at least two series of baffles configured to lock the tubes with opposite movements are provided. Said term of “opposite movements” refers respectively to translations along the same axis having opposite direction (shift-lock), or rotations about the same axis having opposite sense (twist-lock). 
     Preferably, the receiving seats comprise at least one effective surface which, in the assembly position, is spaced from a respective tube and, in the working position, comes into contact with said tube obtaining the desired locking effect. Said effective surface is advantageously inclined with respect to the locking direction. The term “locking direction” is understood as meaning the direction of movement of said surface towards the respective tube. Said locking direction is for example the direction of displacement of the baffles in the shift-lock embodiments and is the tangent to the arc travelled by the receiving seat in the twist-lock embodiments. 
     More advantageously, each tube receiving seat comprises two effective surfaces which converge forming a wedge-like zone where the tube is locked. For example a seat in accordance with this embodiment may have a trapezoidal shape. 
     The seats may be designed to receive a single tube or several tubes each, depending on different embodiments of the invention. 
     In some embodiments each baffle is a flat plate (for example a sheet-metal disc) and the seats are windows formed in the baffle using a suitable method, for example by laser cutting or water cutting, or by punching which is a particularly low-cost technique. 
     In the twist-lock embodiments, tubes receiving seats having a different shape depending on their distance from the axis of rotation may be provided. Said measure provides a uniform tube locking effect, compensating for the fact that arcs travelled by the seats closer to the axis of rotation are shorter than that of the seats away from the axis. For example, the above mentioned effective surfaces may have a greater inclination (greater locking angle) close to the axis. 
     The twist-lock embodiments allow the tubes to be arranged on concentric circles instead of being arranged in a square or triangular pitch. According to a particular embodiment of the invention, the tubes are arranged in concentric rows and the baffles comprise a plurality of concentric rings in which each ring comprises the tube receiving seats. For example, the seats intended to receive the tubes may be realized substantially as recesses formed in the edges of said rings. 
     Another aspect of the invention relates to a method for assembling shell-and-tube equipment comprising antivibration support baffles for the tubes, according to the accompanying claims. Said method for example comprises the steps of: 
     providing baffles in a provisional assembly configuration where the tubes of the bundle can be inserted being received with play in the first region of the respective seats of the baffles; 
     inserting the tubes until the tube bundle is completed; 
     displacing the baffles into a working configuration where the tubes are received in the second region of the seats of each baffle, with a small or substantially null play (locked tubes). 
     In the assembly configuration the baffles are preferably kept in position with a template or equivalent provisional means. For example in the assembly configuration the baffles are already spaced by the working pitch, but they are offset so that each tube encounters the receiving seats in the respective first region, that is with play. Optionally, the baffles may have a certain axial mobility in the assembly configuration. 
     Preferably, the definitive locking of the baffles in the working configuration is performed by the shell itself of the equipment, by means of a direct structural cooperation between the baffles and the shell. In accordance with this further preferred aspect of the invention, after displacement of the baffles into the respective working positions, the assembly of the tube bundle and the baffles is assembled together with the shell of the equipment and the baffles are locked in the respective working positions directly by said shell. 
     It should be noted that the shell does not have any play with respect to the baffles. Assembly is for example performed by assembling two or more halves of the shell or by constructing the shell using a fairly thin metal sheet which can be wrapped around the tube bundle. In other embodiments, locking of the baffles may be performed using a conventional technique, for example using tie bars; in this case the bundle does not cooperate structurally with the shell and may be simply inserted into the shell. 
     The invention is applicable to equipment with straight tubes and equipment with U-shaped tubes. In the latter, the baffles are mounted along the straight sections of the U-shaped tubes. 
     The great advantage of the invention consists in a simplified assembly without adversely affecting the effectiveness against vibrations. The tubes may be positioned without difficulty since assembly is performed with play relative to the baffles; in operation, however, said play is substantially removed and the tubes finds a precise support on the baffles. These and other advantages of the invention will emerge more clearly with the aid of the detailed description below relating to a number of preferred embodiments. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a simplified diagram of shell-and-tube equipment comprising a series of antivibration baffles. 
         FIG. 2  shows in schematic form a series of baffles of the equipment shown in  FIG. 1 , according to a first embodiment of the invention. 
         FIGS. 3 and 4  show locking of a tube in a respective window of one of the baffles, according to the embodiment of  FIG. 2 . 
         FIGS. 5 to 7  are similar to  FIGS. 2 to 4  and show another embodiment of the invention. 
         FIG. 8  shows a preferred embodiment for the windows of the baffles, in particular for the embodiments of the type shown in  FIGS. 5-7 . 
         FIGS. 9 and 10  show other embodiments of the windows of the baffles intended to receive the tubes. 
         FIGS. 11 and 12  show an example with baffles having windows designed to receive a plurality of tubes, with free and locked tubes, respectively. 
         FIG. 13  shows a preferred arrangement of the windows in consecutive baffles of the type shown in  FIG. 11 . 
         FIG. 14  shows another embodiment of the invention in which the baffles consist essentially of concentric rings. 
         FIG. 15  shows a detail of  FIG. 14  illustrating locking of a tube. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows in schematic form a shell-and-tube equipment  1  comprising a shell  2 ; a bundle  3  of straight tubes  4 ; a plurality of baffles  5  spaced by a pitch p and acting as antivibration supports for the tubes  4 ; two tube plates  6 .  FIG. 1  shows only the axes of the tubes for the sake of simplicity. 
       FIG. 2  relates to a first embodiment of the invention and, for the sake of simplicity, shows a single tube  4  passing through the baffles  5 . Each baffle  5  comprises a series of passing-through openings in the form of windows  7  which allow the passage of tubes. The reference number  5  denotes collectively the set of baffles and the reference number  7  denotes collectively the windows formed in the baffles. In the example according to  FIG. 2  the windows  7  have a trapezoidal form, more preferably the form of an isosceles trapezium. 
     As shown in  FIGS. 3 and 4 , a trapezoidal window  7  comprises a region  8  in the proximity of the long base which may receive a tube  4  with a certain play g and a second region  9  close to the short base of the trapezium in which, instead, a tube  4  is received substantially with no play (i.e. locked), bearing against internal surfaces  10  defined by the two converging sides of the window  7  ( FIG. 4 .). 
     The play g allows the tube  4  to freely slide through the window  7 . A slight misalignment between tube and window is in fact compensated for by the play g during the assembly. In the region  9  instead the converging sides of the trapezoidal window  7  form a wedge-like zone which eliminates the play g and lock the tube  4  which finds two points of contact  11  with said surfaces  10 . Therefore, it can be noted that the arrangement shown in  FIG. 3  allows easier assembly while the arrangement shown in  FIG. 4 , during operation, ensures an effective action against the vibrations thanks to the bearing contact of the tube against the surfaces  10 . 
     Locking of the tube  4  inside the window  7  (i.e. the passage of the tube from the receiving region  8  with play to the substantially locked region  9 ) is the result of a linear displacement f of the window  7  with respect to said tube. 
     It should be noted that the locking is the result of a suitable inclination β of the surfaces  10  relative to the locking direction ( FIG. 4 ). Here, said surfaces  10  are termed “effective surfaces” since they provide the tube with the desired antivibration support. The locking direction may be defined as being the direction in which the tube moves towards the region  9  (and therefore towards the surfaces  10 ) which, in this example, is the direction of the displacement f. For short, said angle β is also called locking angle. 
     In the example, for each tube  4  there are two surfaces  10  which converge defining a wedge-like locking zone. More generally it is preferable to provide at least one surface inclined with respect to a locking direction of the tubes. 
     With reference still to  FIG. 2 , it is shown a preferred embodiment in which the set of baffles  5  comprises a first series of baffles  5 A with a first orientation of the windows  7 , and a second series of baffles  5 B with windows  7 B having a second orientation. As a result of the different orientation, the baffles of the two series denoted by A and B respectively have different locking directions, for example the baffles  5 A are locked with a displacement +f and the baffles  5 B are locked with an equal and opposite displacement −f. 
     It should be noted that the locking operation brings the baffles back into axial alignment with the tube bundle, i.e. eliminates the misalignment shown in  FIG. 2 .  FIG. 2  shows the centre of a baffle and the axis  12  of the equipment. The figure thus highlights the misalignment of the baffles during the assembly, which is eliminated by the displacement +f or −f. 
       FIGS. 5 to 7  are similar to  FIGS. 2 to 4 , and show an embodiment where the locking of the tubes is obtained with a rotation about the axis  12  of the equipment  1 . In particular, it is shown an embodiment with series of baffles A and B which can be locked with equal and opposite rotations +φ, −φ. 
     Locking of the tubes can be seen in  FIGS. 5 and 6 : the rotation of a baffle through an angle φ brings a tube  4  towards the wedge-like zone  9  of the associated window  7  where locking takes place. The angle β of inclination of the surfaces  10  in this case may be defined with respect to the line  13  tangential to the circular arc travelled by the window  7  upon rotation ( FIG. 7 ). 
     An embodiment of the type shown in  FIG. 2  is called “shift-lock”, while an embodiment of the type shown in  FIG. 5  is called “twist-lock”. 
     The windows  7  of a single baffle  5  may be all identical or may have different shape and/or orientation, depending on various embodiments of the invention. 
     In the twist-lock embodiments, the provision of windows  7  with a different shape depending on the distance from the axis of rotation may be preferred, in order to obtain uniform locking, thus compensating for the greater displacement of the peripheral windows with respect to those close to the axis. In order to compensate for this difference, preferably, the baffles  5  comprise two or more concentric rows of windows  7  with a varied shape. 
     For example, as shown in  FIG. 8 , a window  7 . 1  at a distance r 1  from the axis of rotation preferably has effective surfaces  10  with a locking angle greater than a window  7 . 2  situated at a greater distance r 2  from the axis. The greater locking angle compensates for the smaller arc travelled by the window  7 . 1  close to the axis, for the same rotation φ. In greater detail,  FIG. 8  has β 1 &gt;β 2  where β 1  is the locking angle of the window  7 . 1  close to the axis and β 2  is the locking angle of the window  7 . 2  distant from the axis. In other words, the windows close to the axis have a sharper wedge-like locking zone  9  so as to obtain the desired locking despite the relatively small displacement. 
     The twist-lock configuration according to  FIG. 5  is advantageously applicable to equipment with tubes arranged on concentric circumferences, rather than in a square or triangular pitch. Equipment with this arrangement of tubes is commonly used for example to realize heat exchangers inside reactors for the ammonia synthesis which have the tubes arranged on circular ranks. 
       FIGS. 2-4 and 5-7  show embodiments where the set of baffles  5  comprises a first series of baffles  5 A and a second series of baffles  5 B which can be locked with displacements or rotations of the same magnitude having opposite direction or sense. In both cases the baffles of the first series and the second series are alternated. Consequently the tubes  4  are supported alternately according to different planes. These embodiments are suitable for supporting tubes in a square or triangular arrangement, which fit most applications. Some embodiments may envisage a greater number of series of baffles having a different geometry, for example forming a sequence of baffles  5 ′,  5 ″, . . .  5   (n)  repeated along the tube bundle. 
       FIGS. 9 and 10  show variants in which the single windows  7 , for example trapezoidal, are connected without a solution of continuity, for example being formed by means of saw cuts  14  made in the baffles  5 . The variant of  FIG. 9  applies to the shift-lock embodiments and the variant of  FIG. 10  applies to the twist-lock embodiments. This variant may be preferred when the tubes are quite close to each other. 
     In the embodiments according to  FIGS. 1-10  the tube receiving seats are represented by the above described windows  7 , each intended to receive a single tube  4  of the bundle. Other embodiments are possible wherein each seat of the baffles  5  is configured to receive a plurality of tubes. 
     A preferred application of the invention relates to axial-flow heat exchangers, wherein the shell-side fluid passes through the baffles; in this case, in order to avoid an excessive obstruction of the section for the passage of fluid through the baffles (which would cause an excessive increase of the load losses) each seat advantageously receives a plurality of tubes. 
     For example,  FIG. 11  shows an embodiment of the invention in which the tube receiving seats are in the form of windows  27  designed to receive four tubes with shift-lock. 
     A window  27  has a substantially rectangular shape and comprises four corner lobes designed to receive respective tubes  4 . A lobe comprises a surface in the form of a circle arc which defines a zone  28  for receiving the tube  4  with play, and an effective surface  20  inclined with respect to the locking direction and defining a locking zone  29 . The point  21  ( FIG. 12 ) indicates the point of contact with the tube resulting from the displacement of the window  27  into the working position. 
       FIG. 11  shows the assembly position in which the tubes  4  are located in the regions  28  of the lobes and consequently are received with a certain play. The figure also shows some characteristic parameters of the window  27 , namely the length L of the effective surface  20  and the locking angle β. 
       FIG. 12  shows the working condition in which each of the four tubes is locked making contact at point  21  with a respective effective surface  20 . 
       FIG. 13  shows, respectively with continuous and broken lines, a preferred arrangement of windows  27 A and  27 B belonging to two adjacent baffles, which can be locked with opposite displacements during operation (for example two baffles  5 A and  5 B, as shown in  FIG. 2 ). It is noted that the windows of adjacent baffles are staggered horizontally and vertically by an offset distance equal to the tube pitch so as to receive different groups of tubes  4 . 
       FIGS. 14 and 15  show another embodiment of the twist-lock type, namely with tubes arranged in concentric rows and baffles lockable by rotation. In this embodiment a baffle is formed essentially by concentric rings connected by bridge portions. 
     The tube receiving seats are formed on the edges of the concentric rings, in the form of substantially semicircular recesses  37  comprising a straight portion inclined relative to the locking direction, which defines the effective surface  30 . The reference numbers  38  and  39  (similar to the reference numbers  8 ,  9  and  28 ,  29 ) indicate the receiving zones with play and the zones for locking the tubes in the recess  37 ; the reference numbers  31  (similar to the reference numbers  11  and  21 ) indicate the point of contact of the tube against the effective surfaces  30 . 
     In the example reference is made to two series of baffles denoted by A and B (in a similar manner to  FIGS. 2 and 5 ) and lockable by means of opposite rotations +φ, −φ. The Figure shows two rings  32 A of a first baffle  5 A and two rings  32 B of a second baffle  5 B with the respective bridge portions  33 A and  33 B. 
     It should be noted that each tube  4 , in the working position, rests alternately on a ring of a baffle  5 A belonging to the first series and on a ring of a baffle  5 B belonging to the second series. This is due to the fact that two adjacent rings of a single baffle are separated by a distance  34  which is twice the radial distance  35  between two consecutive rows of tubes and the fact that adjacent baffles are staggered by a distance equal to said radial distance  35  as shown for example in  FIG. 14 . 
     The method for assembling the equipment  1  comprises essentially the following steps. 
     The baffles  5  are arranged in a provisional assembly configuration such as for example the configuration of  FIG. 2  or  FIG. 5 . In said provisional configuration, the seats  7  are arranged so that the tubes  4  can be inserted through the baffles and received with play in the regions  8 . During this step the baffles  5  are advantageously kept at the correct distance (pitch p of  FIG. 1 ) via suitable provisional means. 
     The insertion of the tubes is greatly facilitated by the play existing between tubes and seats of the baffles, and also the last tubes of the bundle may be positioned without difficulty. After completing the tube bundle, the baffles  5  are displaced and moved into the working position, for example by means of the linear displacements +f, −f or the rotations +φ, −φ. As a result, the tubes  4  are locked in the regions  9  of the baffles. 
     An embodiment such as that of  FIGS. 11-13  or such as that of  FIGS. 14-15  is assembled in a similar manner. 
     In a particularly preferred embodiment, after reaching the working condition (locked tubes), the baffles  5  are blocked by the insertion of the bundle into the shell  2  and structural cooperation with said shell.