Heat exchanger baffle

Abstract

A heat exchanger baffle having angled edges for carrying leaf seals.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to heat exchangers that have a longitudinal baffle that divides the internal volume of the heat exchanger into at least two sections. More particularly this invention relates to shell and tube heat exchangers with removable tubes and multiple shell side fluid passes that require longitudinal and transverse baffles.

2. Description of the Prior Art

This invention is applicable to numerous styles of shell and tube heat exchangers (exchangers or exchanger) such as a floating head exchanger, a U-tube exchanger, and other known types of shell and tube exchangers. However, for sake of brevity, this invention will be described in detail primarily in respect of U-type exchangers.

Heretofore, exchangers as described above, whether of the floating head or U-tube style, have carried internally of the shell thereof, a plurality (group) of tubes. This multitude of tubes generally traverses the length of the interior of the shell, and the individual tubes are held in a spaced apart relation by a tubesheet and tube supports. The tubes rest inside of a liquid tight volume of the shell known as the shellside of the exchanger which typically consists of a hollow cylinder (shell) which is enclosed at one end by a shell cover and at the opposing end of the shell by a tubesheet. The U part of each of the tubes is located at the shell cover end of the exchanger. The opposing ends of the U part of each tube carries, in spaced apart relation, a longitudinally extending, essentially straight tube part (leg) that reaches essentially from the shell cover end of the exchanger to the longitudinally opposite, channel end of the exchanger. This channel end of the exchanger carries a hollow channel. The channel, together with its outer channel cover and opposed tubesheet, closes that opposite end of the exchanger. The interior of the channel and the interior of the tubes is known as the tubeside of the exchanger, while the interior of the shell between the shell cover and the tubesheet is known as the shellside of the exchanger and defines the internal, liquid tight volume of the shell in which the tubes rest when the exchanger is in operation.

Between the end of the channel nearest the shell and the nearest shell end itself is disposed an essentially flat, transverse plate known as the tubesheet. The tubesheet supports in apertures there through the tube leg ends at the channel end of the tubes. Such support is in an open fluid communication with the interior of the channel so that fluid reaching the interior of the channel can flow into the interior of the tubes, and vice versa, i.e., the tubeside. The tube sheet also closes its adjacent end of the channel thereby defining the internal volume of the channel between the walls of the channel and the spaced apart channel cover and tubesheet.

A shell and tube exchanger is typically an elongated device that has a distinct longitudinal (long) axis and a shorter transverse axis so that the internal volume of its shell extends longitudinally a greater distance than its transverse axis. The tubes carried within that internal volume extends along most of the length of the longitudinal axis of the shell, and, therefore, are longitudinally extending with their U-shaped ends approaching, but not touching, the far shell cover end of the shell. In order to make the shellside of this exchanger a multiple pass device, the internal volume of both the channel and shell are physically divided into at least two sections by longitudinally extending members. On the side of the tubesheet where the channel is located, the longitudinally extending member is known as the pass partition. On the side of the tubesheet where the tubes are located, i.e., the shellside, the longitudinally extending member is a baffle known as the long baffle. This long baffle is an essentially flat member that is disposed between the spaced apart legs of the tubes, and extends from essentially the U-part of the tubes to the tubesheet. The pass partition of the channel extends in the interior of the channel from the tube sheet to the channel cover. The pass partition and the long baffle, in combination, divide the interior volumes of the channel and shell, the tubeside of the exchanger, into at least two sections except for the shell cover end of the shell which contains the U-parts of the tubes. The shell cover end is left open so shellside fluid can pass between the two sections of the interior volume of the shell formed by the long baffle.

The interior volume of the shell carries spaced apart along the shell's long axis a plurality of baffles that extend along the transverse axis of the shell (transverse baffles). The transverse baffles serve to support the tubes and provide a means to cause fluid flow within the shell to be circuitous by having to flow around the transverse baffles in order to keep flowing. The transverse baffle closest to the shell cover end is carried short of the U-part of the tubes thereby leaving the internal volume of the shell cover end open for fluid flow between the two sections of the internal volume of the shell. Certain of the transverse baffles are contiguous with the shell but not the long baffle, while alternate transverse baffles are contiguous with the long baffle and not the shell to cause the circuitous flow of a fluid through the shellside interior of the shell. In this manner a first fluid introduced into a first section of the interior of the shell near, and downstream of, the tubesheet must pass in a snakelike manner around the various transverse baffles to reach the shell cover end of the shell. The first fluid then passes from the first section past the U-part of the tubes and into the second section of the shell's interior, and follows a second circuitous path around the transverse baffles in that second section to reach the tubesheet. The first fluid is drawn out of the second section of the shell near the tubesheet, and by the time of its withdrawal has, in effect, made two passes through most of the length of the shell. Hence the term two pass exchanger.

When the first fluid is first introduced near the tubesheet into the first section within the shell's internal volume and later removed from near the tubesheet from the second section within the shell's internal volume, the first section will naturally be at a higher pressure than the second or subsequent section.

If, at the same time the first fluid is introduced into the interior of the shell, a physically separate second fluid is introduced into a first internal volume of the channel, as defined by the channel cover, pass partition and tubesheet, this fluid, in order to keep flowing, can only pass through the tubesheet into the hollow interiors of the various tubes. This second fluid then passes along the interior of the first legs of the tubes to their corresponding U-part ends and back toward the channel by means of the interiors of the opposing legs to enter the second internal volume of the channel. Thus, this second fluid, as it passes through the channel and tubes, also makes two passes through most of the length of the shell. It should be noted here that it is possible that a fluid may have more that two passes on the tubeside. At the same time the second fluid is in indirect heat exchange relationship with the first fluid that is passing through the internal volume of the shell. The second fluid, after passing through the tubes and reaching the second or final internal section of the channel, is removed from the channel for other use. In this manner a hot first fluid can be efficiently contacted with a cooler second fluid, or vice versa, in order to exchange heat between the two fluids for desired operational benefits.

The long baffle is an essentially flat (planar) member that not only extends longitudinally, but also traverses the interior of the shell, and has longitudinally extending opposing edges that approach, but do not touch, the interior surface of the shell thereby leaving a gap between such edges and the shell. A long seal is carried by each such long baffle edge and is disposed between each such edge and the interior surface of the shell in order to effect a fluid tight separation of the first and second internal sections formed within the shell by the long baffle, maintain the pressure difference between such internal sections, and force the fluid flowing within the shell to navigate around the transverse baffles as described above.

The tubesheet, tubes, transverse baffles and long baffle with its opposed long seals are often made into a unitary system that is normally referred to by those skilled in the art as “the bundle.” This is done so that the bundle can be fabricated separately from the shell, and can also be removed from the interior of the shell for maintenance and other purposes. After initial fabrication of the bundle, or after the bundle has been removed from the shell for whatever purpose, and the exchanger is desired for reuse, the bundle must be inserted into the interior of the shell with the long baffle seals engaging the inner surface of the shell, and here lies the problem that this invention addresses.

The end of the shell that is nearest the channel is terminated by a shell flange for removably fixing the shell to the channel once the bundle is in place. The internal corner of the shell flange at the interior surface of the shell has a right angle configuration that defines a relatively sharp edge. This sharp edge is the first part of the shell that the long seals of the long baffle meet when the bundle is inserted into the shell's interior. At this point of the insertion of the bundle into the shell the long seals of the long baffle undergo severe three-dimensional distortion. This sharp edge coupled with this severe distortion can damage either or both of the long seals initially and/or as the insertion of the bundle progresses thereby rendering the long baffle/long seal combination ineffective to separate the interior volume of the shell into two separate fluid tight sections that are at different pressures.

If the long seals of the long baffle are made sufficiently stout to maintain a fluid tight seal within the shell, insertion of the bundle into the shell becomes a difficult job since the long seals on both long edges resist the insertion of the bundle due to resistance of the long seals as they meet and are distorted by the aforesaid sharp edge, and since the drag effected by the long seals increases as more and more of the bundle is inserted into the shell.

If the long seals are made sufficiently compliant so as to make damage to those seals, upon insertion, unlikely, and insertion of the bundle a relatively easy job, then the ability of those seals to maintain a fluid tight seal between the higher and lower pressure sections within the shell is compromised.

In accordance with this invention, a long baffle configuration, and a long baffle/long seal combination is provided which results in easier insertion of the bundle into a shell, and consequently reduces damage to the long seals upon such insertion. This invention also provides for improved sealing effectiveness between the long baffle and the shell, and improved assurance that the long seals, upon insertion of the bundle into the shell, are flexed in the correct direction.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a configuration for an exchanger long baffle, and a long baffle/long seal combination that solves the aforesaid problems and provides the aforesaid advantages by employing longitudinal edges of the long baffle that are angled at a finite angle along the longitudinal axis of the long baffle away from the essentially flat plane of the long baffle. In the long baffle/long seal embodiment, each of the so angled edges carries at least one leaf seal that bridges the gap between the angled edges of the long baffle and the inner surface of the shell in a fluid tight manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross sectional side view of a U-tube exchanger with two shellside fluid passes and a removable bundle.

FIG. 2 shows a cross sectional side view of the bundle when removed from the interior of the exchanger shell of FIG. 1. For sake of clarity, this Figure shows the long baffle and only a single tube, and not the associated transverse baffles and multitude of tubes that would typically be present in the system that composes the bundle.

FIG. 3 shows a top view of the system of FIG. 2 as it is about to be inserted into the shell of the exchanger of FIG. 1. This Figure also shows only the long baffle and a single tube and not the transverse baffles and plurality of tubes that would normally be present.

FIG. 4 shows an end view of a portion of the long baffle and associated long seal prior to insertion of same into the shell of FIG. 1.

FIG. 5 shows a top view of the long baffle with associated long seal after partial insertion of the long baffle into the interior volume of the shell of FIG. 1, and further shows flexing of that portion of the seal that is associated with the portion of the long baffle that has been so inserted.

FIG. 6 shows an end view of the bundle of FIG. 2 after insertion into the shell and shows the more normal severe distortion of the long seal when it is flexed into sealing engagement with the inner surface of the shell of FIG. 1.

FIG. 7 shows a front view of an angled long baffle pursuant to this invention.

FIG. 8 shows a top view of the long baffle of FIG. 7.

FIG. 9 shows a partial end view of an angled edge long baffle of this invention carrying a leaf seal that is not so severely distorted when flexed into sealing engagement with the inner surface of a shell such as the shell of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a conventional shell and tube exchanger with a removable bundle and baffles designed for two shellside fluid passes. More particularly, FIG. 1 shows exchanger 1 to be composed of a shell 2 that is closed by a rounded shell cover 3 at one end and tubesheet 15 at the opposing end thereby defining an internal volume 5 of shell 2. Shell interior 5 contains U-tube 6 which is carried by a plurality of transverse baffles 7 and 8. Normally a plurality, e.g., from about 50 to about 5,000, U-tubes are employed in a bundle. FIG. 1 shows a single tube only for sake of clarity and brevity. Tube 6 has a U-part 9 which carries opposed, spaced apart essentially straight parts or legs 10 and 11. The ends of tube 6 that oppose U-part 9 are fixed to upstanding tubesheet 15 in fluid flow communication through tubesheet 15. Tubesheet 15 closes its end of shell 2 thereby defining the interior volume 5 of shell 2 between the walls of shell 2, tubesheet 15 and fixed shell cover end 3.

Hollow channel 16 is carried by shell 2 contiguous with tubesheet 15 and is closed by an opposing outer channel cover 12. The hollow interior of channel 16 is separated into independent, fluid tight sections 18 and 19 by pass partition plate 26. The interior 5 of shell 2 is separated into independent sections 20 and 21 by longitudinally extending (long) baffle 17. Long baffle 17 extends from just short of U-part 9 to tubesheet 15, and extends between legs 10 and 11 of tube 6. Thus, the interior volume of channel 16 is separated into separate fluid tight sections 18 and 19 by pass partition 17, and interior volume 5 of shell 2 is separately divided into two sections 20 and 21 by long baffle 17.

Fluid communication between channel sections 18 and 19 is achieved by flow through the interior of tube 6. Thus, when a first fluid 22 is injected through a standard inlet channel nozzle (not shown) into first channel section 18, this fluid passes through tubesheet 15 into the interior of tube 6 as shown by arrow 23 and flows through leg 10, U-part 9, and leg 11 into second channel section 19 as shown by arrow 24. Thus, this fluid makes two passes (legs 10 and 11) through most of the interior length of shell 2. This first fluid is then removed from section 19 by way of another standard channel nozzle (not shown) as indicated by arrow 25. This is known as the tubeside because first fluid flows through the interiors of the channel and the tubes.

Fluid communication within shell 2 between separate sections 20 and 21 is accomplished by flow around long baffle end 30 and U-part 9. An elongate seal (see FIG. 3) on each longitudinal edge of long baffle 17 removably seals baffle 17 to the interior surface 39 (see FIG. 6) of shell 2. Thus, when a second, separate fluid is injected into section 21 by way of a standard shell nozzle (not shown) as indicated by arrow 31, that fluid is forced to follow a circuitous, serpentine flow route 32 around a plurality of transverse baffles 7 and 8 in order to reach U-part 9. Once U-part 9 is reached, the second fluid leaves section 21 and passes into section 20 to continue its circuitous flow path back towards tubesheet 15. Thus, this second fluid passes two times through essentially the full length of shell 2. The second fluid is removed from section 20 by a standard shell nozzle (not shown) as indicated by arrow 33. Because of the circuitous path 32 that the second fluid follows, the pressure in section 21 is higher than the pressure in section 20.

Thus, it can be seen that the first fluid introduced at 22 flows in indirect heat exchange relation with the second fluid introduced at 31 through essentially two lengths of shell 2.

FIG. 2 shows the channel/tubes/baffle system (bundle) of FIG. 1 when removed from shell 2 except that, for sake of clarity, transverse baffles 7 and 8 are not shown. Normally transverse baffles 7 and 8 would be a part of this system when removed from the interior of shell 2. It is common for the channel to be a separate part and removable from the tubesheet and the bundle. FIG. 2 shows the long axis 34 of long baffle 17 to be essentially parallel to legs 10 and 11 as well as the long axis of shell 2. It is this system (bundle), including the transverse baffles, that is desirably removable from the interior of shell 2 for easy access for maintenance and the like.

FIG. 3 shows a top view of the bundle of FIG. 2 as it is about to be inserted into interior 5 of shell 2. In this Figure shell 2 is shown to carry a shell flange 41 at its channel end that extends transversely to the long axis 34 of long baffle 17 and the long axis of shell 2. Shell flange 41 is designed to mate with a corresponding transverse channel flange 42 for removably fixing the bundle of FIG. 2 to shell 2. Transverse flange 41 forms a relatively sharp right angle edge at 35.

The longitudinally extending edges 35 and 36 of long baffle 17 carry an elongate seal 37 and 38, respectively. Long seals 37 and 38 are designed to meet with the inner surface 39 of shell 2 in fluid sealing engagement so that the second fluid hereinabove is kept within section 21 (FIG. 1) until it reaches end 30 of long baffle 17. Because of this requirement, long seals 37 and 38, when not inserted into interior 5 extend beyond inner surface 39, and engage sharp edge 35 upon insertion of the bundle into interior 5. This is shown better in FIGS. 4 and 5.

FIG. 4 shows long baffle 17 carrying long seal 37 by means of a plurality of fasteners 40. A conventional seal 37 is one or more strips of stiff metal. One such seal is a 1.5 inch wide, 0.004 inch thick strip of 302 stainless steel (full hard temper), see Mechanical Design of Heat Exchangers And Pressure Vessel Components by K. P. Singh and A. I. Soler, Arcturus Publishers, Inc., Cherry Hill, N.J., 1984, ISBN: 0-916877-00-0, page 21. Such a seal is a very resilient member which, once flexed and inserted into interior 5, presses out against surface 39 with vigor. Accordingly, before being bent for insertion into interior 5, seals 37 and 38 extend a finite distance beyond inner surface 39, as is shown at 43 in FIG. 4.

When the bundle of FIG. 3 is inserted into interior 5, as shown in FIG. 5, the first point of resistance flexed (bent) seals 37 and 38 meet from shell 2 is sharp edge 35. As seen in FIG. 6 bent seal 37 is flexed considerably when in place in interior 5 thereby filling the gap 44 between edge 36 of long baffle 17 and inner surface 39 of shell 2. Gap 44 is generally no more than about 0.5 inches.

FIG. 5 shows that, as the bundle is forced into interior 5, more and more of the area of each of long seals 37 and 38 is forced against edge 35. Since long baffles are typically many feet long, e.g., 20 feet, a significant amount of force can be required to force the entire bundle into interior 5. Also, as more and more of the bundle is inserted into the shell, the drag from the ever greater quantity of the flexed seals increases thus requiring more force toward the end of the insertion step, all of which adversely impacts the long seals as and when they meet sharp edge 35. Edge 35 can tear or otherwise abrade the seals thereby at least shortening their operational life, if not breaching the seals and ruining their sealing capacity in at least certain areas of one or both of the seals before the exchanger is even put into operation. Further, seals 37 and 38, being long and very springy are, of necessity, difficult to bend and keep bent prior to the insertion of the system into the shell thereby complicating and possibly extending the insertion step.

Pursuant to this invention and referring to FIG. 7, flat, planar long baffle 50 is angled at its longitudinal edges 51 and 52 at a finite angle A away from the plane 53 of the baffle. Angle A can vary considerably depending on the fluid pressures, geometry, and physical size of the exchanger, but will generally be from about 20 to about 75 degrees. Angle A for long edges 51 and 52 can be the same or different for each of edges 51 and 52 in the same baffle. The width of angled edges 51 and 52 can also vary considerably, but will generally be a matter of up to about two inches. As an example, a long baffle that was 45 inches wide and 19 feet-4 inches long was employed using a bent length 51 and 52 of one and one-sixteenth inches and an angle A of about 30 degrees for each bent length. The angled edges preferably are bent in the same direction, although this is not a requirement of this invention. The angled edges preferably are bent toward the higher pressure section within interior 2, e.g., section 21 of FIG. 1, but this is not a requirement of this invention. Thus, in FIG. 7 bent edges 51 and 52 would point downward toward high pressure section 21 and away from upper section 20 which is at a lower pressure. This way the higher pressure section is employed to force the seal against surface 39 for better sealing engagement.

FIG. 8 shows a top view of long baffle 50 with its longitudinally extending, angled edges 51 and 52 carrying long seals 53 and 54, respectively. Angled long edges 51 and 52, and long seals 53 and 54 extend for essentially the entire length of baffle 50.

In FIG. 9 an end portion of baffle 50 is shown with its angled long edge 52. Long seal 54 is shown to be a leaf seal that is composed of a plurality of very thin springy metal strips, e.g., 2 inch wide, 0.005 inch thick stainless steel strips, which are fixed to angled edge 52 by a plurality of bolts 55. One stainless steel strip could be employed, if desired. Long seal 54 is flexed downward toward high pressure section 21 (FIG. 1) so that higher pressure section 21 pushes against seal 54 as shown by arrow 56 to force seal 54 into tight sealing engagement with surface 39.

It can be seen by comparing FIG. 9 (invention) with FIG. 6 (prior art) that with angled long edges pursuant to this invention, the distortion of seal members 54 is much more gradual and much less severe than with seal member 37 (FIG. 6). Accordingly, with this invention the amount of distortion of the long seal members when they are forced against sharp edge 35 of FIG. 5 is substantially reduced. This reduces substantially the strain put on seal members 54 during insertion of the bundle into a shell, and minimizes the possibility of damage to those seal members upon such insertion.

It should be noted here that, in the past, with long baffles that did not have angled long edges as contemplated by this invention, long baffles have actually been improperly installed with their long edges flexed in a direction that was opposite to that desired. For example, the long edges were flexed so as to be bent toward the low pressure section instead of toward the high pressure section as desired. This invention, with its permanently angled long edges substantially reduces the likelihood of an undesirable bundle installation.

Reasonable variation and modifications are possible within the scope of this disclosure without departing from the spirit and scope of this invention.

Claims

1. In a tube and shell heat exchanger that has longitudinal and transverse axes, said longitudinal axis being longer than said transverse axis, said shell enclosing an inner volume of said exchanger, said exchanger having associated with said shell and inner volume a removable bundle containing a channel having a pass partition, at least one longitudinally extending tube, a long baffle, and a tubesheet, said long baffle and said at least one tube extending into said inner volume, said long baffle extending in an essentially flat plane along said longitudinal and transverse axes and dividing said inner volume into at least two sections with a portion of said at least one tube in each section, said long baffle having opposed longitudinally extending edges, said long baffle extending across said transverse axis essentially to but spaced from said shell thereby defining a gap between each of said edges and said shell, the improvement comprising each of said longitudinally extending edges being angled away from said essentially flat plane of said long baffle at a finite angle, and each of said angled edges carrying at least one leaf seal that bridges said gap.

2. The apparatus of claim 1 wherein said angled edges are both angled in the same direction away from said plane of said long baffle.

3. The apparatus of claim 1 wherein said two sections in said inner volume are at different pressures and said leaf seal is curved toward the section that contains the higher pressure.

4. The apparatus of claim 1 wherein said finite angle is from about 20 to about 75 degrees.

5. The apparatus of claim 1 wherein said finite angle is essentially the same for both said edges.

6. A heat exchanger baffle that extends in an essentially flat plane and has opposed longitudinally extending edges, said edges being angled away from said essentially flat plane at a finite angle.

7. The device of claim 6 wherein said edges are angled in the same direction away from said plane and said finite angle is essentially the same for both edges.

8. The device of claim 7 wherein said finite angle is from about 20 to about 75 degrees.

9. The device of claim 6 wherein each of said angled edges carries at least one leaf seal.