Heat Exchanger

Abstract

A device for exchanging heat between first and second fluid streams is disclosed. The device includes a core housing configured to channel the first stream through heat exchange elements and out through a first half exhaust port. A shell housing encloses the core housing and is configured to channel the second stream past the heat exchange elements, the shell housing being isolated from the core housing by a space. A second half exhaust port is formed on the shell adjacent with the first half exhaust port, the first and second half exhaust ports being separated by a gap. An expansion joint couples 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. The expansion joint includes a flexible ring flange having an inner edge mounted to the core housing adjacent the first half exhaust port and a peripheral edge mounted to the shell housing at a circular attachment point surrounding the second half exhaust port.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No. 13/644,037 filed Oct. 3, 2012, which is incorporated herein by reference

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.

Another 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 an aspect of the present invention, there is provided a heat exchanger for exchanging heat between a first and second fluid streams. The device includes a core housing configured to channel the first stream through heat exchange elements and out through an exhaust port formed as a first and second half exhaust ports. A shell housing encloses the core housing and is configured to channel the second stream around the heat exchange elements, the shell housing being isolated from the core housing by a space. The first half exhaust port is formed on the core housing while the second half exhaust port is formed on the shell housing adjacent to the first half exhaust port, the first and second halves exhaust ports being separated by a gap. A circular expansion joint bridges the gap between the first and second half exhaust ports. The inner circumferential edge of the expansion joint attaches around the first half exhaust port while the outer edge is attached to the shell housing surrounding the second half exhaust port. The flexibility of the joint derived from its circular corrugations and elbows permits the core housing to float within the shell housing.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a heat exchanger made in accordance with the present invention and showing the expansion joint.

FIG. 2 is the expansion joint in more detail.

FIG. 3 is a cross sectional view taken along line C-C of FIG. 1 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.

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

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 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 11. 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 by a gap (or space) 9 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 32. Baffle 25 is an annular flange which ensures that the second stream of fluid contacts the full length of heat exchange tubes 16 on its way from intake 28 to exhaust 32. 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.

Referring now to FIG. 2, heat exchanger 10 has an axis 11 on which core housing 14 is formed. Core housing 14 is formed with exhaust port 19 having halve ports 34 and 29. Half port 34 is formed on core housing portion 22 while half 29 is formed on shell housing circular portion 42 surrounding port 29. Halves ports 34 and 29 are separated by a gap 40. Gap 40 is dimensioned to ensure that that the core housing and the shell housing are free to move relative to each other as a result of the heating and cooling of the heat exchanger during operation.

Gap (space) 40 is bridged by ring flange (expansion joint) 18. The inner circumferential edge 38 of ring flange 18 attaches around half port 34 on core housing portion 22 while the outer circumferential edge 36 is attached at circular contact point 30 of shell housing portion 42 surrounding half port 29. Ring flange 18 has corrugations and elbows ribs between its circumferential edges 34 and 36 and is adequately flexible to permit the core housing to float within the shell housing. Item 44 is the joint assembly internal liner.

The above described expansion joint permits that the heat exchanger outer diameter be made smaller and less bulky because there is no need for a greater diameter shell to absorb thermal expansion/contraction. Instead, the flexibility of flange 18 of the joint absorbs the thermal expansion/contraction of the shell and core housings. Essentially, the core housing via flange 18 floats within the isolated shell. Flange 18 is preferably designed according to the pressure differential between the two fluid streams rather than the usual higher pressure code requirements. This allows flange 18 to be thinner and more flexible because it only has to compensate for the pressure difference between the two fluid streams.

Referring now to FIG. 1 and 3, heat exchanger 10 has opposite ends 48 and 50 and fluid A inlet/outlet ports 27 and 29. Shell housing 12 has a cylindrical portion 52 which extends from end 48 towards where it meets Bulged portion 54 of the shell housing adjacent end 50 and surround port 32. Bulged portion 54 extends away from axis 11 in such that the diameter of the shell housing at bulged portion 54 is asymmetrical such that the diameter of the shell housing increases continuously as it progresses from side 58 towards side 56 of the bulged portion. This permits fluid B current to flow more freely and evenly around heat exchange tubes 16 at the vicinity of port 32.

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 fluids being at different temperature, the heat exchanger comprising:

a core housing configured to channel the first stream through heat exchange elements and out through a first half exhaust port, this first half exhaust port being mounted on the core housing;

a second half port to complete the exhaust of the first stream;

the first half exhaust port being separated from the second half exhaust port by a gap;

an expansion joint bridging the above gap and coupling the core housing to the shell housing;

an inner edge of the expansion joint mounted to the first half port mounted on the core housing;

an outer edge of the expansion joint mounted to the shell housing at a circular point surrounding the second half exhaust port;

the expansion joint comprising a flange with circular corrugations and elbow ribs for flexibility;

the flexibility of the joint allowing the core housing to float within the shell.

2. 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 core housing configured to channel the first stream through heat exchange elements and out through a first exhaust port;

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

a second exhaust port formed on the shell adjacent to and coaxially aligned with the first exhaust port, the first and second exhaust ports being separated by a gap;

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, the expansion joint comprising a corrugated ring flange having an inner edge mounted to the core housing adjacent the first exhaust port and a peripheral edge mounted to the shell housing at a circular attachment point surrounding the second exhaust port.

3. The heat exchanger of claim 1 wherein the shell housing has opposite first and second ends and a central axis, the secondary port being formed on the first end of the shell housing, a peripheral port formed on the shell housing adjacent the second end of the shell housing, the shell housing configured to pass the second fluid stream through the peripheral port, the shell having a first cylindrical portion extending from the first end of the shell housing to a second portion of the shell housing surrounding the peripheral port where the shell housing bulges asymmetrically away from the central axis.

4. The heat exchanger defined in claim 1 wherein the expansion joint has a thickness, the thickness of the expansion joint being selected to compensate for the relative movement between the core and shell housing as a result of a difference in pressure between the first and second fluid streams.