CROSS-REFERENCE TO RELATED APPLICATION

[0001] This Patent Cooperation Treaty application claims the benefit of U.S. Provisional Application No. 61/375,006, filed on August 18, 2010, entitled "Heat Exchanger Radial Seal" and assigned to the assignee of the present application. The disclosure of this application is hereby incorporated herein by reference in its entirety.

BACKGROUND

[0002] The present invention relates to heat exchangers and, more particularly, to sealing elements that reduce leakage between hot air conduits and cold air conduits of regenerative heat exchangers.

[0003] Heat exchangers transfer heat from a hot flow conduit to a cold flow conduit. For example, regenerative heat exchangers are used to provide preheated air to heavy machinery, such as fuel burning power plants, chemical processors, refineries, mills, and the like. These examples of heavy machinery typically will exhaust hot gas and will operate more efficiently when supplied with preheated air. For example, the boiler of a power plant will typically produce hot flue gases having a temperature of approximately 700 degrees Fahrenheit (370° C). A regenerative heat exchanger can preheat incoming air to a temperature of approximately 600 degrees Fahrenheit (315° C).

[0004] Generally, in a regenerative heat exchanger, two fluid flow passages extend through the heat exchanger, one passage comprising a hot gas conduit that communicates with a hot exhaust outlet of the heavy machinery, and the other passage comprising a cold air conduit that communicates with a cool air intake passage. Hot exhaust gases flow from the hot exhaust outlet into the hot gas conduit of the heat exchanger, and cool air flows from the cool air intake passage into the cold air conduit. In the heat exchanger, heat is extracted from the hot exhaust gas flow and is transferred to the cool air flow.

[0005] A rotary regenerative air heat exchanger performs the heat transfer using a rotor that turns continuously within a housing through the hot gas flow and cool air flow. The rotor comprises a heat exchanging body that includes multiple thermal transfer surfaces comprising radially extending plates or sheets that are attached to a central cylinder. A group of the plates or sheets may be segregated into sectors called diaphragms or baskets. The hot gas flow and cool air flow typically enter the housing from opposite ends of the heat exchanger and pass over the thermal transfer surfaces in opposite flow directions. During operation, the rotor rotates at a relatively slow speed (1-2 rpm) and thereby moves the thermal transfer surfaces within the housing from the hot gas flow where the surfaces absorb heat into the cool air flow where the surfaces give off heat into the cool air flow. The well-known configuration by Frederik

Ljungstrom dating from 1920 is an example of a rotary regenerative air heat exchanger. The description herein relates to a rotor that rotates about a vertical axis, but it should be understood that the considerations in this description can also relate to a horizontal axis rotor. [0006] Figure 1 is an illustration of a rotary heat exchanger 100 showing a rotor 102 that rotates within the heat exchanger housing 104. Figure 1 shows the thermal transfer plates 106 of the rotor divided into sectors 108. The rotor rotates on a shaft 110. For heat transfer efficiency, the hot gas flow 112 and cool air flow 114 must be kept sealed from each other within the heat exchanger housing. The two flows are kept separated by sealing elements mounted at the junctions between the rotor and the heat exchanger housing. The sealing elements comprise radial seals 118 mounted on the radially extending edges of the upper and lower surfaces of the rotor sectors, and perimeter seals 120 at the free ends of the rotor sectors. Sector plates 124, 126 block the flow of gas and air so as to form a hot gas side 128 and a cool air side 130. The perimeter seals may be mounted to the rotor sectors, in which case they are generally referred to as circumferential seals, or they may be mounted to the internal walls of the housing itself, in which case they are generally referred to as bypass seals. Some configurations may have both circumferential seals and bypass seals.

[0007] Because the hot exhaust gas flow 114 enters the rotary heat exchanger housing at one end and the cool air flow 114 enters at the other end, the hot exhaust inlet end is generally referred to as the hot end, and the cool air inlet end is generally referred to as the cold end. This results in an axial temperature gradient from the hot end to the cold end. As noted above, the temperature gradient of the air flow between the hot end and cold end during operation can be approximately 100 degrees Fahrenheit (about 40° C). The temperature gradient differential can be even greater when the heat exchanger is being brought from a non-operational condition (such as after installation or maintenance) up to an operating condition. The temperature gradient can expand and distort the rotor, and create sealing problems between the hot gas flow and the cool air flow. For large power plant boilers, a rotary heat exchanger can have a diameter of approximately 30 feet to 60 feet (about 10-20 meters). On that large scale, operating efficiency can be drastically effected by the rotor distortion.

[0008] The rotor distortion due to the temperature gradient is commonly referred to as rotor turndown, and causes the radial edge of the rotor sectors to assume a shape similar to that of an inverted bowl or dish. Rotor turndown can also cause the outer edge (peripheral edge or circumferential edge) of the rotor sectors to distort into a curved edge. As a result of the rotor turndown, the radial seals mounted on the hot end of the rotor are pulled away from the sector plates of the housing with the greater separation occurring at the outer radius of the rotor. This opens a gap which allows flow and results in an undesired intermingling of the hot gas and the cool air.

[0009] Figure 2 is a side view of the Figure 1 heat exchanger 100 in an initial cold operating condition. Figure 3 is a side view of the Figure 1 heat exchanger 100 at operating temperature. Figure 2 and Figure 3 illustrate the phenomenon of rotor turndown. The radial seals 118 are shown in Figure 2 forming an effective seal with the sector plates 124, 126 at the top end in the cold condition, whereas there is a gap 204 at the bottom end between the lower radial seals 218 and the bottom sector plates 224, 226. Conversely, Figure 3 shows that a gap 302 is created between the upper radial seals 118 and sector plates 124, 126 at the heat exchanger upper end in the heated operational condition, but the gap is closed at the bottom end between the lower radial seals 218 and the bottom sector plates 224, 226. [0010] It is important to maintain the seal between the movable heat exchanging body and the heat exchanger housing to thereby maintain the separate hot gas and cool air flows. A flexible and resilient construction of the seals helps the seals to maintain a seal over the operational temperature gradient. Unfortunately, the seals are often subjected to severe demands and harsh operating conditions. In a power plant, for example, the seals are typically exposed to corrosive fly ash and soot that attack the sealing surfaces. As the heat exchanging body moves with respect to the housing or vice versa, the seals are also exposed to mechanical wear because the seals are positioned to maintain sliding contact with the stationary surfaces. Consequently, the seals can wear down relatively quickly and require periodic maintenance and cleaning.

[0011] From the discussion above, it should be apparent that there is a need for a resilient sealing element that maintains an effective seal over a temperature gradient and that resists corrosion, mechanical wear, and thermal distortion. The present invention satisfies this need. SUMMARY

[0012] Embodiments of the present invention provide a heat exchanger sealing element that comprises a radial seal having two elongated sealing elements that are joined together and enclose one or more memory plates between them. One sealing element comprises a backing assembly having a lip or ridge projecting outwardly from its inner surface, and the other sealing element comprises a slotted assembly having a slot that receives the lip of the backing assembly for mating engagement. The memory plates have a resilient construction such that the memory plates tend to return to their initial condition after flexing. Enclosing the memory plates between the backing assembly and the slotted assembly helps protect the memory plates from harsh environments. The memory plates can be constructed for maximum resiliency so as to maintain their shape through a greater range of temperature and physical forces. The components of the backing assembly and slotted assembly can be selected for maximum durability, to withstand harsh environments. The assembled components provide a radial seal that maintains an effective seal over a wide temperature gradient and that resists corrosion, mechanical wear, and thermal distortion.

[0013] Other features and advantages of the present invention should be apparent from the following description of exemplary embodiments, which illustrate, by way of example, aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a perspective view of a prior art rotary heat exchanger.

[0015] Figure 2 is a cut-away view of the Figure 1 heat exchanger in an initial cold operating condition. [0016] Figure 3 is a depiction of the Figure 2 representation illustrating rotor turndown.

[0017] Figure 4 is a perspective view of a rotary heat exchanger radial seal constructed in accordance with the present invention, showing the radial seal separated into a backing assembly and a slotted assembly.

[0018] Figure 5 is a perspective view of the base plate shown in Figure 4. [0019] Figure 6 is a perspective view of the mount plate shown in Figure 4.

[0020] Figure 7 is a perspective view of the slotted sealing edge plate shown in Figure 4.

[0021] Figure 8 is a perspective view of the non-slotted sealing edge plate shown in Figure 4.

[0022] Figure 9 is a perspective view of the memory plate shown in Figure 4. [0023] Figure 10 is a detail perspective view of the backing assembly and slotted assembly shown in Figure 4 ready to be mated together.

[0024] Figure 11 is a detail perspective view of the backing assembly and slotted assembly shown in Figure 10 after mating together.

[0025] Figure 12 is a detail perspective view of the Figure 4 backing assembly showing the assembly inner surface .

[0026] Figure 13 is a detail perspective view of the Figure 4 backing assembly showing the assembly outer surface.

[0027] Figure 14 is a detail perspective view of the Figure 4 slotted assembly showing the assembly outer surface. [0028] Figure 15 is a detail perspective view of the Figure 4 slotted assembly showing the assembly inner surface.

DETAILED DESCRIPTION

[0029] Figure 4 shows an exploded perspective view of a heat exchanger sealing element comprising a radial seal 400 having two elongated sealing elements comprising a backing assembly 402 and a slotted assembly 404 that fit together and enclose a plurality of memory plates 405 between them. A basic component that is common to both assemblies 402, 404 is an elongated, planar main plate 406. A mount plate 408 is attached to each main plate and provides a surface for mounting the assembled radial seal 400 to a heat exchanger. The mount plates are fastened to the outer surfaces of the main plates, as illustrated in Figure 4. The inner surfaces of the main plates face each other. The main plates 406 are configured with mounting holes for attachment of the radial seal to a heat exchanger, and the mount plates 408 include mounting holes that align with the mounting holes of the main plates. Two different types of sealing edge plates are attached to the main plates, a slotted sealing edge plate 410 attached to the main plate of the slotted assembly 404 and a non-slotted sealing edge plate 412 attached to the main plate of the backing assembly 402. Thus, the slotted assembly 404 includes components comprising a main plate 406, a mount plate 408, and a slotted sealing edge plate 410. The backing assembly 402 includes components comprising a main plate 406, a mount plate 408, and a non-slotted sealing edge plate 412. The memory plates 405 are enclosed between the two assemblies 402, 404. The components may be attached with welding techniques, adhesives, or other means of fastening together so that the components remain together for easier handling of the two assemblies 402, 404 during installation and maintenance of the radial seal 400. [0030] Figure 5 is a perspective view of the base plate 406 and shows the mounting holes 502 for mounting the completed radial seal to a heat exchanger. A bolt or screw (not shown) or similar well-known means for mechanical attachment is typically used for securing a radial seal in a heat exchanger, and can be used with the radial seal configuration described herein. The mounting holes are typically positioned proximate a mounting edge 504 of the base plate 406. For example, the mounting holes 502 shown in Figure 5 are located approximately 0.25 inches (about 6 mm) from the mounting edge 504. Two slots are positioned proximate the sealing edge 506 of the base plate 406, opposite the mounting edge 504, comprising a first slot 508 and a second slot 510. The slots 508, 510 may be formed in the base plate 406 by a cutting and bending operation that first produces a cut in the base plate substantially parallel to the sealing edge 506 and two small cuts that are perpendicular to the slots, and then folds over the base plate, thereby forming a lip or ridge and creating the slots illustrated in Figure 5.

[0031] Figure 6 is a perspective view of the mount plate 408, the mount plate having a mounting edge 602 that is aligned with the mounting edge 504 of the main plate when the two components are assembled together. The mount plate includes mounting holes 604 that align with the mounting holes 502 of the main plate when the mounting edge 602 of the mount plate is aligned with the mounting edge 504 of the main plate. Figure 6 shows that the mounting holes 604 are located substantially equidistant from the mounting edge 602 and the opposite edge 606 of the mount plate 408, but other locations may also be selected. The mount plate provides increased strength to the assemblies 402, 404 in the area of mounting to the heat exchanger, but are optional depending on the construction of the main plate 406 and its resistance to flex and maintainability in a harsh operating environment. [0032] Figure 7 is a perspective view of the slotted sealing edge plate 410. The slotted sealing edge plate is mounted to the base plate 406 (Figure 4) such that a sealing edge 702 of the slotted sealing edge plate is aligned with the sealing edge 506 of the base plate when the two plates 406, 410 are joined together. The slotted sealing edge plate 410 includes a first slot 704 and a second slot 706 that are substantially parallel to the sealing edge 702, between the sealing edge and the opposite edge 708. When the slotted sealing edge plate 410 is attached to a base plate 406, the first slot 704 of the slotted sealing edge plate is aligned with the first slot 508 of the base plate, and the second slot 706 of the slotted sealing edge plate is aligned with the second slot 510 of the base plate. [0033] Figure 8 is a perspective view of the non-slotted sealing edge plate 412, which is mounted to the base plate 406 such that a sealing edge 802 of the slotted sealing edge plate is aligned with the sealing edge 506 of the base plate when the two plates 406, 412 are joined together.

[0034] The slotted sealing edge plate 410 and the non-slotted sealing edge plate 412 can be constructed of materials that provide improved abrasion resistance and increased service life in harsh operating environments. For example, the sealing edge plates 410, 412 can be constructed of high-strength steel that conforms to standards issued by the ASTM International (previously known as the American Society for Testing and Materials (ASTM)), such as ASTM A514 for tempered alloy steel plates. The sealing edge plates 410, 412 can be attached to their respective main plates 406 by spot welding techniques, adhesives, and other means for attachment so that the plates 406, 410, 412 remain together for easier handling of the two assemblies 402, 404 during installation and maintenance of the radial seal 400. Sealing edge plates 410, 412 constructed from steel that conforms to ASTM A514 provide plates that are resistant to abrasion in the environments described herein for heat exchangers and are capable of maintaining an effective seal on sector plates of heat exchangers as described herein.

[0035] Figure 9 is a perspective view of one of the memory plates 405 shown in Figure 4. Although Figure 4 shows three memory plates, it should be understood that a different number of memory plates may be used in a radial seal, depending on the size of the heat exchanger and corresponding dimensions of the radial seal. The memory plate is of a substantially planar, rectangular configuration, having four flat edges 902, 904, 906, 908. Other shapes may be suitable, depending on the configuration of the radial seal that is required for the intended heat exchanger application. Those skilled in the art will understand how to shape the memory plates to accommodate the configuration of the radial seal that is required for the heat exchanger.

[0036] The memory plates 405 are configured to have a great amount of resiliency so that they return to their original shape when flexed or otherwise subjected to bending forces. For example, the memory plates may be constructed of cold rolled spring steel. Such materials are widely available and can be specified according to a variety of industry standards. For example, the memory plates can be fabricated from material that conforms to the American Iron and Steel Institute (AISI) standard 1074 or 1075 for cold rolled, carbon strip, flat springs. Spring steel that conforms to AISI 1074 and 1075 specifications are available from a variety of suppliers, including Spring Engineers of Houston, Ltd. of Houston, Texas, USA. Such construction provides a memory plate that is bi-directional in the sense that the memory plate tends to retain its original shape despite being subjected to flexing or bending forces. This provides a radial seal that tends to retain its original sealing position and is bi-directional. As a result, the radial seal 400 can maintain constant positive contact with the sector plates of the heat exchanger, even through the temperature gradient experienced due to rotor turndown. Heat exchangers that are equipped with the radial seal described herein should be largely free of the gaps illustrated in Figures 2 and 3, described above. The lack of such gaps improves the operating efficiency of heat exchangers that are equipped with the radial seal described herein, as compared with radial seals of conventional configuration. [0037] During assembly of the radial seal 400, the memory plates 405 may be attached to one base plate or the other of the backing assembly 402 or the slotted assembly 404, or the memory plates may be loosely positioned between the respective assemblies 402, 404 without being attached to either base plate, while the respective assemblies are fastened together. Under the scenario in which the memory plates are loosely positioned during assembly, the memory plates will be held in position between the assemblies 402, 404 by virtue of the two assemblies being attached together such that the memory plates will remain substantially fixed in their initial positions. It should be apparent, however, that the memory plates 405 may experience a minimal amount of shifting relative to the respective assemblies as the radial seal undergoes flexing upon installation and operation in a heat exchanger. [0038] Figure 10 is a detail perspective view of the backing assembly 402 and slotted assembly 404 shown in Figure 4 ready to be mated together. Figure 10 shows the bent lip 1002 that is formed in the cutting and bending operation described above that forms a slot 1004 in the base plate 406 comprising the backing assembly 402. Figure 10 also shows the non-slotted sealing edge plate 412, mounted on the outer surface of the base plate. The slotted assembly 404 includes a base plate 406 having the slotted sealing edge plate 410 attached to the outer surface of the base plate. Figure 10 shows the bent lip 1006 of the base plate, which is visible in Figure 10 extending from the inner surface of the base plate through the slot in the slotted sealing edge plate 410. The slot in the slotted sealing edge plate has sufficient clearance to receive the lip 1006 of the backing assembly base plate and also the lip 1002 of the slotted assembly base plate.

[0039] Figure 11 is a detail perspective view of the backing assembly 402 and slotted assembly 404 shown in Figure 10 after mating together. Visible in Figure 11 is the outer surface of the slotted assembly 404, showing the outer surface of the base plate 406 and the outer surface of the slotted sealing edge plate 410. Figure 11 also shows the bent lip 1002 of the base plate 406 from the backing assembly 402 and the bent lip 1006 of the base plate from the slotted assembly

404 extending through the slot of the slotted sealing edge plate 410. The inner surfaces of the backing assembly 402 and the slotted assembly 404 are facing each other, and the memory plates

405 are held between the two assemblies. The memory plates, being held internally between the two assemblies 402 and 404, are not visible in Figure 11.

[0040] Figure 12 is a detail perspective view of the Figure 4 backing assembly 402 showing the assembly inner surface of the base plate 406. The bent lip 1002 of the base plate is visible in Figure 12, as is the non-slotted sealing edge plate 412. The slot 1004 in the base plate 406 is shown in Figure 12, with the non-slotted sealing edge visible through it. The mount plate 408 and the non-slotted sealing edge 412 are attached to the base plate 406 using spot welding techniques. Other suitable fastening means may be used.

[0041] Figure 13 is a detail perspective view of the Figure 4 backing assembly 402 showing the assembly outer surface, the reverse side of the backing assembly from that shown in Figure 12. The assembly components visible in Figure 13 include a portion of the base plate 406, as well as the outer surface of the mount plate 408 and the non-slotted sealing edge plate 412.

[0042] Figure 14 is a detail perspective view of the Figure 4 slotted assembly 404 showing the assembly outer surface. The assembly components visible in Figure 14 include the base plate 406 and the mount plate 408, as well as the slotted sealing edge plate 410. Also visible in Figure 14 is the bent lip 1006 of the slotted assembly base plate, formed by the previously described cutting and bending operation, which also forms the slot 1402. The mount plate 408 and the slotted sealing edge 410 are attached to the base plate 406 using spot welding techniques. Other suitable fastening means may be used.

[0043] Figure 15 is a detail perspective view of the Figure 4 slotted assembly 404 showing the assembly inner surface, the reverse side of the slotted assembly from that shown in Figure 14. The only assembly component visible in Figure 15 is the base plate 406, comprising the inner surface of the slotted assembly 404 to which the memory plates are mounted. Also visible in Figure 15 is the bent lip 1006 formed in the base plate, as well as the slot 1504, through which the attached slotted sealing edge plate 410 is visible. [0044] A heat exchanger equipped with the radial seal described herein can experience improved separation of the hot gas and cool air flows because of reduced gaps under cold start conditions and under temperature gradients experienced during rotor turndown. In addition, the materials selected for construction of the radial seal can be selected for improved durability and resistance to abrasion, as a result of improved resiliency from the memory plates, which are protected from the harsh operating environment by being enclosed between the backing assembly and the slotted assembly.

[0045] While certain exemplary embodiments have been described in detail and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not intended to be restrictive of the broad invention, and that this invention is not to be limited to the specific arrangements and constructions shown and described, since various other modifications may occur to those with ordinary skill in the art.

[0046] In the drawings, particular examples of structures are identified by reference numerals without identifying all such structures in each drawing, for simplicity of illustration. It is to be understood that like descriptions apply to like structures in the drawings. [0047] As used herein, the use of "a", "an" or "the" is intended to mean "at least one", unless specifically indicated to the contrary.