Heat Exchanger

Abstract

A device for exchanging heat between the two fluid streams is disclosed. The device includes parallel heat exchange tubes arranged in an annular pattern, the first and second ends of the tubes being coupled to first and second halves of a core housing configured to channel the first gas stream through the heat exchange tubes between a first intake formed on the first half of the core housing and a first exhaust formed on the second half of the core housing. The device further includes a shell enclosing the core housing and separated from the core housing by a space, the shell configured to channel the second gas from a second intake, then between the heat exchange tubes, and then through a second exhaust. The heat exchanger device includes an expansion joint coupling the core housing and the shell housing such that the core housing floats within the shell.

Description

FIELD OF THE INVENTION

The invention relates generally to a heat exchanger for exchanging heat between a cooler fluid and a hotter fluid, and in particular for exchanging heat between two separate streams of gas.

BACKGROUND OF THE INVENTION

Heat exchangers are often used in industrial applications to transfer heat from one gas or liquid to another. One type of heat exchanger uses a plurality of tubes to carry one of the fluids. The tubes are usually arranged in a circular fashion around a central opening, as seen in U.S. Pat. No. 5,355,945 to Sanz et al. The parallel tubes are generally mounted to headers at their ends and can be held in a substantially vertical orientation. The other gas is then passed over and between the tubes in a current or counter current arrangement to effect the transfer of heat from the hotter gas (or fluid) to the cooler gas (or fluid). One stream of gas (or fluid) enters the heat exchanger through an intake port which then passes the gas through the heat exchange tubes and then out of an exhaust. The other stream of gas (or fluid) enters the heat exchanger through another intake port, then passes over and between the heat exchange tubes and then out another exhaust port. Heat is exchanged between the two fluids through the walls of the heat exchange tubes as the two currents pass each other in opposite directions.

While this sort of heat exchanger is heat transfer wise effective, it suffers from a series of drawbacks, such as complexity of design, difficulty in assembling, bulkiness and the need to periodically repair leaks in the heat exchange mechanism, particularly where the heat exchange tubes are secured to their headers. One factor necessitating the large bulk associated with heat exchangers is the cyclical heating and cooling of portions of the heat exchanger. During the operation of the heat exchanger, heat from the fluids passing through the heat exchanger tends to cause the heat exchange tubes and the housings enclosing the heat exchange tubes to expand. When the heat exchanger cools down when the flow of hot fluid is stopped, the tubes and housings contract. This constant expanding and contracting generally requires the housings to be built large enough to absorb the expansions and contractions without causing faults in the system. As a result, heat exchangers tend to be large and bulky.

In order to control the temperature exciting the heat exchanger, external piping is generally provided so that a portion of one of the gas (fluid) streams can be shunted directly towards the exhaust port without going through or between the heat exchange tubes. The piping required for the shunting adds to the overall size and bulk of the heat exchanger.

One factor contributing to the complexity and cost of building shell and tube heat exchangers is the necessity of mounting a series of baffles around the heat exchange tubes. These baffles generally take the form of annular metal members which surround the bundle of heat exchange tubes and extend between the tubes and the outer housing. Mounting these baffles often involves many steps, which in turn increases the overall cost of the heat exchanger.

One factor contributing to the maintenance requirements of the heat exchanger is the failure of the joints holding the ends of the heat exchange tube to their respective headers. As a result of the joints being repeatedly heated and cooled by exposure to the hotter and cooler gases and in conjunction with the thermal stresses in the heat exchanger, the welded or rolled in joints are prone to failure from cracking This in turn requires periodic inspection and occasional repair. Another factor contributing to the maintenance requirements and limiting the service life of these heat exchangers is the failure of tubes at a result of fluid impingement causing erosion and tube vibration failures at the proximity of the shell ports of the vessels.

All of the above limitations add to the expense and inconvenience of utilizing these types of heat exchanges. An improved heat exchanger design which overcomes these limitations is therefore required.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is provided a heat exchanger for exchanging heat between a first stream of gas and a second stream of gas, the two gas streams being at different temperatures. The heat exchanger includes a plurality of parallel heat exchange tubes arranged in an annular pattern, the heat exchange tubes having opposite first and second ends, the first and second ends being coupled with a first and second halves of a core housing, the first and second halves of the core housing is configured to channel the first gas stream through the heat exchange tubes between a first intake formed on the first half of the core housing and a first exhaust formed on the second half of the core housing. The heat exchanger further includes a shell enclosing but isolated from the core housing by a space. The shell is configured to channel the second gas from a second intake, then between the heat exchange tubes, and then through a second exhaust. The heat exchanger further includes a three part flanged flued expansion joint.

With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the preferred typical embodiment of the principles of the present invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a heat exchanger made in accordance with the present invention showing the heating exchange tubes mounted between the upper and lower pair of headers and within the housing shell of the heat exchanger.

FIG. 2 is a sectional view of a heat exchanger made in accordance with the present invention and showing the inner shunt mechanism.

FIG. 3 is a cross sectional view taken along line C-C of FIG. 2 showing the orientation of the heat exchange tubes in relation to the outer housing shell and the inner core housing and showing also the shell guide plates mounted around the upper tube plate.

FIG. 4 is a view of the tie bar portion of the present invention.

FIG. 5 is a top view of a portion of a baffle used in the construction of the heat exchanger shown in FIG. 2.

FIG. 6 is a cross sectional view of a anti acid condensation shield portion of a heat exchanger made in accordance with one aspect of the present invention.

FIG. 7 is a side view of a portion of the heat exchanger showing part of the valve mechanism for the shunt.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 a heat exchanger made in accordance with the present invention, shown generally as item 10, includes an outer shell housing 12, an inner core housing 14 contained within shell housing 12 and a plurality of heat exchange tubes 16 arranged in an annular fashion around a central space 18 and axis 1. Core housing 14 is divided into first portion (or half) 20 and second portion (or half) 22. Headers (also called tubesheet) 24 and 26 are formed on the first and second core housing portions 20 and 22, respectively. The tubesheets are configured to form a header causing a first stream of fluid, shown by arrows A, to pass from an intake 27 formed on one portion of the core housing to exhaust 29 formed on the other portion of the core housing by passing through heat exchange tubes 16. Shell housing 12 is isolated from core housing 14 and is further configured to cause a second stream of fluid, indicated by arrows B, to flow from an intake 28 on shell 12 to an exhaust 30. Baffle 25 is an annular flange which ensures that the second stream of fluid passes between and the full length of heat exchange tubes 16 on its way from intake 28 to exhaust 30. The direction of flow of the first and second streams can be reversed if required. Of course, the two fluids enter heat exchanger 10 at different temperatures, with the hotter fluid passing a majority of its heat to the second fluid while passing through the heat exchanger.

Heat exchanger 10 is provided with a flange & flued bellows expansion joint assembly shown generally as item 32. Flange 34 joins to shell 12, flange 38 joins to an adjacent component (not shown) connected to shell exhaust 29. Flange 36, located between flanges 34 and 38, joins to core housing 14. Item 32 is the joint assembly internal liner. The thickness of flanges 34 and 38 are configured for the expansion/contraction to be compensated for derives from the local Pressure code requirement while the thickness of flange 36 derives from the pressure differential between streams A and B. It will be appreciated that because the pressure differential is smaller than the design pressure (i.e. desired pressure rating) of the exchanger that it is possible there from to obtain a greater flexibility for flange 36 by making this flange thinner than flanges 34 and 38.

The above described expansion joint permits the heat exchanger's outer diameter be made smaller and less bulky because there is no need for a greater diameter shell to absorb thermal expansions/contractions. Instead, the flexibility of flange 36 of the joint absorbs the expansion/contraction of the core housing. Essentially, the second half portion core 22 via flange 36 floats within the isolated shell.

Referring now to FIG. 2, heat exchanger 10 includes an internal passage 50 for by-pas purpose of fluid stream A. Flange 38 of expansion joint 32 is exhaust port 29. Passage 50 consists of an elongated tube 52 which is dimensioned to fit coaxially through central opening 54 formed within the heat exchanger. Central opening 54 is surrounded by heat exchange tubes 16 and is positioned along axis 51 of the heat exchanger. Space 53 separates heat exchange tubes 16 from shell housing 12 and permits fluid stream B to flow between heat exchange tubes 16 as the fluid stream passes from external space 53 to central passage 54. Baffle 25 ensures that the fluid is then directed to flow between the heat exchange tubes to space 64. Baffles 21 have a tube support function only. The top and bottom ends of central opening 54 is blocked by walls 43 and 45, respectively, to ensure that stream B does not mix with stream A. Elongated tube 52 is provided with an expansion joint 56 to ensure that changes in the length of tube 52 caused by the cooling or heating of the tube can be compensated for.

Tube 52 has a conical diffuser 58 formed on the end of tube 52 adjacent exhaust port 29. Conical diffuser 58 is cone shaped and has a plurality of apertures 60 formed thereon to permit the fluid passing through tube 52 to mix with the rest of fluid stream A flowing within the interior of first core housing 20 before the fluids exit exhaust port 29. Valve 80 is positioned at the entry of tube 52, adjacent intake port 27 to control the amount of stream A which by-passes through tube 52 as opposed to through heat exchange tubes 16 in order to maintain the specified temperature. In the event the temperature of the fluid exiting outlet port 29 is below its normal temperature valve 80 closes fully and the entirety of stream A passes between heat exchange tubes 16. Inversely, if the temperature of the fluid exiting outlet port 29 is above its normal temperature valve 80 opens partially and only part of stream A passes between heat exchange tubes 16. It will be appreciated that the portion of the stream passing through tube 52 will be at a different temperature than the portion of the stream passing through tubes 16, so conical diffuser 58 helps to mix the two portions of stream A in the interior of core housing portion 20 before the stream exits exhaust 29. This ensures that no “hot spots” are formed at exhaust 29.

Fluid stream B enters the heat exchanger, through intake port 28, decreases its velocity within space 62 and is distributed all around conical shape 14 at the circumference of annular space 63 separating shell 12 from core housing portion 20. Then, upon flowing through space 63 stream B enters and fills space 53 parallel and not transversely to tubes 16 before impinging transversely on and between the tubes. As a result of first flowing parallel to the tubes there is even less likelihood to cause the tubes to vibrate. In contrast, if stream B at the greater velocity of port 28 impinged on the tubes transversely, as it is generally done, the stream would induce vibrations in the tubes, causing additional strain at the tube joints and tube wall thinning damage at baffle 25 and as a result shorten the service life of the exchanger.

Fluid stream B passes from space 53 towards exhaust 30 by flowing through internal passage 54, around baffle 25 to space 64 to reach passage 65. Since port 30 is in this case positioned below tube plate 26, stream B is forced by annular passage 65 to again flow towards space 66 parallel to tubes 16. It will be appreciated that should a particular application of heat exchanger 10 require the direction of steams A and B to be reversed, then, passage 65 would also act to reduce vibration in the tubes by compelling the fluid stream to impinge on the tubes in a parallel orientation adjacent tube plate 26.

A portion of the core housing is positioned inwardly towards a longitudinal axis of the heat exchanger by means of wall 99. This extends the space separating housing 12 and core housing 14 at a position “below” tube plate 26 so as to accommodate two parallel conduits for carrying the first and second fluid stream, in this case exhaust port 30 and intake port 27.

Referring now to FIG. 3, a cross-sectional view shows the relationship between heat exchange tubes 16, central passage 54, baffle 25, space 53 and ports 27, 28 29 and 30. Space 53 is obstructed by baffle 25 in order to cause stream B to flow between the top and bottom halves of heat exchange tubes 16 as discussed above.

Referring now to FIGS. 4 and 5, flanges 25 and 21 are supported within the housing by a plurality of tie bars 67 which run up the length of the heat exchanger. Flanges 25 and 21 have a peripheral edge 69 with a plurality of notches 70 formed therein. Tie bars 67 are elongated members, usually made of steel, which have notches 68 formed along the length of the tie bar. To attach the tie bars 67 to the flange edge 69 the tie bar is positioned such that one of the notches 68 mates with a corresponding notch 70, the tie bar is then tack welded to the baffle. It will be appreciated that the heat exchanger may have several flanges 25 and 21 positioned one above the other, in which case a corresponding plurality of notches 68 are formed along the length of the tie bar. The above tie bars are located between tubes and have the advantage of not taking the place of heat transfer tubes—as is generally done.

Referring now to FIG. 6, condensation can occur when a hot SO3 gas is cooled by a cold SO2 gas. The bulk gas temperature may be above the acid dew point but the temperature of the tube wall can be below the acid dew point because the incoming cold stream temperature is below the acid dew point. As a preventive measure FIG. 6 shows one insulating space formed by a heat shield 71, however two or more insulative spaces could also be used.

Heat shield 71 consists of a flat sheet of metal which is provided with a plurality of apertures dimensioned to accept heat exchange tubes 16. Tube extensions 72 preferably, (temperature permitting) consists of a non-metallic or insulative material (such as Teflon) which is mounted around heat exchange tube 16. In this example, heat shield 71 is mounted to tube plate 26 by bolts 73 to have an insulating space 74 between cold stream A and hot tube plate 26. The intent is to prevent as much as possible, the cooling down by stream A of the tube wall temperature of the inlets of tubes 16 within tube plate 26 and thereby prevent acid condensation.

Referring back to FIG. 2, a recess 31 is formed within shell 12 to obtain an internal passage for port 27. Inwardly extended port 27 fills partially recess 31 and is attached thermal expansion free to internal wall 99 separating stream A from steam B. Thus, recess 31 has eliminated the need for a traditional expansion joint within the inwardly extension of port 27.

Referring now to FIG. 7, valve 80 attached to by-pass tube 52; this valve being located within A stream does not require a seal at the valve as is generally done, instead, the valve stem 81 passes through a void 82 provided within space 65. Void 82 is partially filled by tube 100 around valve stem 81. Further, the valve stem and seal block the space within tube 100.

A specific embodiment of the present invention has been disclosed; however, several variations of the disclosed embodiment could be envisioned as within the scope of this invention. It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims

Claims

1. A heat exchanger for exchanging heat between a first stream of fluid and a second stream of fluid, the two fluid streams being at different temperatures, the heat exchanger comprising:

a plurality of parallel heat exchange tubes coupled to a core housing, the core housing configured to channel the first stream through the heat exchange tubes;

a shell enclosing the core housing and isolated from the core housing by a space, the shell configured to channel the second stream between the heat exchange tubes;

an expansion joint coupling the core housing to the shell housing, the expansion joint configured such that the expansion joint allows the core housing to float within the shell.

2. The heat exchanger of claim 1 wherein the heat exchange tubes have opposite first and second ends, the first and second ends being coupled with a first and second halves of the core housing, the first and second halves of the core housing configured to channel the first stream through the heat exchange tubes between a first intake formed on the first half of the core housing and a first exhaust formed on the second half of the core housing;

the shell configured to channel the second stream from a second intake, then between the heat exchange tubes, and then through a second exhaust.

3. A heat exchanger of claim 1 wherein the expansion joint comprises a flanged and flued expansion joint having a middle flange positioned between near side and far side flange portions, one of said near side and far side flange portions being mounted to the shell housing with the middle flange being mounted to the core housing.

4. A heat exchanger of claim 3 wherein the far side and near side flange portions each have a thickness selected to permit the near side and far side flange portions to resiliently flex sufficiently to compensate for expansion and contraction of the shell housing relative to an adjacent component, the middle flange having a thickness selected to permit it to flex sufficiently to compensate for the relative motion between the core housing and the shell housing.

5. A heat exchanger of claim 4 wherein the thickness of the middle flange is less than the thicknesses of the near side and far side flange portions.

6. A heat exchanger of claim 3 wherein the far side and near side flange portions have a thickness selected to permit the heat exchanger to operate at a desired pressure rating, the thickness of the third flange being selected by referencing a difference in pressure between the first and second fluid streams.

7. A heat exchanger as defined in claim 2 further comprising an internal shunt for diverting a portion of the first stream such that said portion of the first stream does not pass through the heat exchange tubes and instead flows directly towards the first exhaust, the internal shunt comprising a central passage extending through a center of the core housing, the central passage having a first port communicating with the first intake and a second port communicating with the second exhaust and a valve for controlling the flow through the internal shunt.

8. A heat exchanger as defined in claim 7 wherein the internal shunt further comprises a conical diffuser formed on the second port adjacent the first exhaust, the conical diffuser separating the diverted first stream to a portion of the first stream which was not diverted, the conical baffle having a plurality of apertures through which the diverted first stream can mix with the portion of the first stream which was not diverted.

9. The heat exchanger as defined in claim 8 further comprising a second expansion joint mounting the central passage at one of the first and second ports to the core housing such that an end of the central passage floats within the core housing.

10. The heat exchanger as defined in claim 1 further comprising at least one baffle surrounding the heat exchange tubes and extending between the heat exchange tubes and the shell, the baffle comprising a flat annular sheet having openings through which the heat exchange tubes extend perpendicularly there through, the baffle having peripheral edges with a plurality of notches formed there along, the flange being supported by a plurality of tie bars extending perpendicular to the flange, each of the tie bars having a plurality of notches formed thereon, the notches of the tie bars mating with the notches on the baffle.

11. The heat exchanger as defined in claim 2 wherein the first end of the heat exchange tubes are mounted to a header formed on the first half of the core housing, at least one heat shield baffle being mounted parallel to the header and held at a distance from the header by a plurality of support members, the heat shield baffle comprising a flat sheet of metal having a plurality of apertures formed thereon dimensioned and configured to permit the heat exchange tubes to pass through the flat sheet of metal and mate thereto.

12. The heat exchanger as defined in claim 11 further comprising an extension tube formed on an end of each heat exchange tube and extending between the header and the heat baffle, the extension tube being made of an insulative material.

13. The heat exchanger as defined in claim 1 wherein the core housing and shell housing are configured such that the second stream is directed to impinge on the heat exchange tubes in a parallel fashion where the second stream first contacts the heat exchange tubes.

14. The heat exchanger as defined in claim 2 wherein the shell housing immediately adjacent one of the exhausts and intakes is recessed sufficiently to reach the core housing and form a void surrounding said exhaust or intake such that said exhaust or intake does not contact the shell housing.

15. The heat exchanger as defined in claim 7 wherein the valve comprises a movable baffle contained within the central passage coupled to an elongated valve stem passing through the core housing and the shell housing, the shell housing immediately adjacent the valve stem being recessed sufficiently to reach the core housing and form a void surrounding the valve stem such that the valve stem does not contact the shell housing.

16. A heat exchanger for exchanging heat between a first stream of fluid and a second stream of fluid, the two fluid streams being at different temperatures, the heat exchanger comprising:

a plurality of parallel heat exchange tubes coupled to a core housing, the core housing configured to channel the first stream through the heat exchange tubes;

a shell enclosing the core housing and isolated from the core housing by a space, the shell configured to channel the second stream between the heat exchange tubes;

an expansion joint coupling the core housing to the shell housing, the expansion joint configured such that the expansion joint compensates for the thermal expansion and contraction of the shell housing relative to an adjacent component, the expansion joint being further configured to compensate for the expansion and contraction of the core housing relative to the shell housing.

17. A heat exchanger of claim 16 wherein the expansion joint comprises a flanged and flued expansion joint having a third flange positioned between near side and far side flange portions, one of said near side and far side flange portions being mounted to the shell housing with the flexible flange being mounted to the core housing.

18. A heat exchanger for exchanging heat between first and second fluid streams, the heat exchanger comprising:

a core housing mounted within a shell housing by a thermal expansion joint, the core and shell housings being configured to keep the first and second fluid streams separate but in thermal contact;

the shell housing being isolated from the core housing by a space dimensioned to permit the core housing to move relative to the shell housing as a result of thermal expansion;

the thermal expansion joint configured to compensate for the relative motion of the shell and core housings, and

the expansion joint being further configured to compensate for the thermal expansion of the shell housing relative to an adjacent component.

19. A heat exchanger of claim 2 wherein a portion of the core housing is positioned inwardly towards a longitudinal axis of the heat exchanger to accommodate two parallel conduits carrying the first and second fluid streams.