Claims:We claim:
1. A heat recovery steam generator (HRSG) to arrest gas bypass during differential expansion between two headers (1, 2), the HRSG comprising:
at least two heater header (1,2) positioned adjacent to each other;
a plurality of spacer bars (3, 4) provided on each of the at least two heater header (1, 2) along length;
a baffle plate (5) with pivot mechanism is mounted on the plurality of spacer bars (3) mounted on any of heater header (1 or 2) of the at least two heater header (1, 2) to arrest has bypass from a gap (8) between the at least two heater header (1,2).

2. The HRSG as claimed in claim 1, wherein the baffle plate (5) with pivot mechanism comprising:
the baffle plate (5);
a plurality of knuckles (6) mounted on the baffle plate (5) at corresponding location of the plurality of spacer bars (3,4); and
a plurality of pins (7) passes through barrel of the plurality of knuckles (6) to provide pivot mechanism.

3. The HRSG as claimed in claim 2, wherein the plurality of pins (7) are welded at ends with the plurality of spacer bars (3, 4) to allow pivot movement of the baffle plate (5).

4. The HRSG as claimed in claim 2, wherein middle knuckle (6) from the plurality of knuckles is mounted on middle spacer (3) from the plurality of spacers (3) mounted on the heater header (1).

5. The HRSG as claimed in claim 1, wherein length of the baffle plate (5) matches with the length of the at least two heater header (1,2).
6. The HRSG as claimed in claim 1, wherein length of the plurality of pins (7) depends on length of the plurality of spacer bars (3, 4).

7. The HRSG as claimed in claim 1, wherein number of pins (7) and knuckles (6) depend upon number of plurality of spacer bars (3) mounted on the heater header (1).

8. The HRSG as claimed in claim 1, wherein the baffle plate (5) covers complete gap (8) between the at least two heater header (1, 2).

9. The HRSG as claimed in claim 1, wherein the heater header (1) traverse vertically more distance downward than the heater header (2) from the at least two heater header (1, 2).

10. The HRSG as claimed in claim 1, wherein one longitudinal end of the baffle plate (5) is mounted with the pivot mechanism on the heater header (1) and other longitudinal free end is seated on the spacer bar (4) of the heater header (2) and exhaust gas pressure ensures the baffle plate (5) remains seated on the spacer bar (4) during hot condition.
, Description:SWINGING BAFFLE SYSTEM BETWEEN ADJACENT MOVING HEADERS TO ARREST GAS BYPASS INSIDE HEAT RECOVERY STEAM GENERATOR

FIELD OF INVENTION

[001] The present subject matter described herein, relates to a swinging baffle system between adjacent headers to arrest gas bypass during differential expansion between headers in heat recovery steam generator.

BACKGROUND AND PRIOR ART
[002] Heat recovery steam generators have become an essential part of gas turbine based power plants. These steam generators extract heat from GT exhaust gas, and the steam generated is used either in process industry or in power plants. They act as a critical thermal link between the gas turbine and steam turbine in combined cycle power plants. In HRSG’s heat transfer surfaces known as modules are arranged vertically or horizontally, perpendicular to the direction of gas flow. As, the GT exhaust gas passes over module tubes, heat is absorbed by water/ steam flowing in the module tubes. All the heat transfer sections are constructed of either single, double or triple row modules. Each consists row of tubes, welded to top and bottom headers. Tubes are either bare/ finned for increasing heat transfer in convection mode. As the temperature of the gases progressively drops, the superheater (SH), the reheater (RH), the Evaporator (EVAP), and the Economiser (ECON) tube modules for each pressure level are arranged accordingly.
[003] The modules are supported from the top beams by means of tie rod and thermal expansion takes place at the bottom. Header spacer bars are provided for maintaining the horizontal gap between the headers which avoids direct rubbing of header with one another. Further, it also serves as component for transferring seismic load to the nearest support. Baffles are normally located direct within the flow of hot exhaust gas through the heated surfaces of the HRSG. These baffles minimize gas bypassing the modules and maximize the exchange of heat in the modules where steam is generated. These baffles help in effective distribution of gas flow over the boiler tubes, maintaining optimum flue gas velocity and Elimination of hot spots caused by bypassing flue gas. Different type of baffles such as Attic and basement baffles, header baffles, Side gas baffles, Centre gas baffles, Flow baffles and Sound baffles are provided in heat recovery steam generator.
[004] The expansion at top header location is minimum and maximum thermal expansion occurs at the bottom header level. Stationary header baffle welded to spacer bars is found to be satisfactory at top header level as there is no or little thermal expansion at the top. Due to temperature difference between adjacent modules belonging to different heat transfer sections, thermal expansion isn’t the same in adjacent bottom headers. This differential thermal expansion between adjacent bottom headers, creates gap between headers during operation, allowing gas to by-pass through the gap, effectively reducing the heat transfer.
[005] US Patent publication US4427058A discloses a method to inhibit gas flow along the sidewalls of an HRSG by utilizing baffles to obstruct the gas flow path between the tube bundle and adjacent sidewalls. This redirects the sidewall gas flow through the tube bundle thereby increasing the efficiency of the heat exchanger. The problem of clearances between the sidewalls and baffles under conditions of tube bundle thermal growth has been solved by mounting the baffles on the tube bundle itself. The positioning of the baffles on the tube bundle has been optimized and the means for mounting the baffles to the tube bundle are disclosed.
[006] US Patent publication US3300787A discusses baffle seals for boilers, and has for its object to provide a device of this character whereby the opposite sides of the baffle plate are providing with laterally movable members for engaging inner periphery of the shell of the heat exchanger for forming a seal between the edges of the baffle plate and the shell. Also to provide means in connection with laterally movable packing means for extending or retracting the same when it is desired to seal the plate or to remove the plate with the tube bundle for cleaning or repair purposes.
[007] US Patent publication US4183401 A recites an apparatus comprising a combination tube support for supporting tubes within a shell and tube type heat exchanger and baffle for directing fluid flow within the heat exchanger. A baffle lip is mounted on a baffle body to provide a seal with the interior surface of the heat exchanger shell. A foot having support surfaces of varying heights is used to support the baffle body to prevent the weight of the baffle body and the tubes contained therein as well as other forces from collapsing a portion of the baffle lip.
[008] For, maximum thermal efficiency, it is imperative to design the HRSG in such a way that, most of the exhaust gas is channelled past the module tubes. One attempt at solving the problem, is to use stationary baffle, welded to both header spacer bars. However, this solution will not effectively serve the purpose when the thermal expansion is not identical in adjacent headers, resulting in failure of baffle due to thermal stresses. This would create gap between headers during operation, causing gas to bypass.
[009] All the above mentioned patents deal with baffle seals for boilers, however, the question of differential thermal expansion is not addressed in the above mentioned patents. Whereas, in the present invention, swinging baffle arrangement deals with differential thermal expansion between adjacent headers for arresting gas bypass. Because of the foregoing discovery, in the present invention, a dynamic configuration of baffles is envisaged to arrest the gas bypass through the gap between adjacent bottom headers during operation.
OBJECTS OF THE INVENTION
[0010] The principal object of the present invention is to provide an improved dynamic baffle arrangement to prevent gas slippage between bottom headers during operation of a heat recovery steam generator.
[0011] Another object of the present invention is to arrest by-pass of exhaust gas by sealing the gap between headers during both hot and cold conditions.
[0012]
SUMMARY OF INVENTION
[0013] The subject matter disclosed herein relates to a new configuration of dynamic baffles which is provided to seal the physical gap between adjacent bottom headers. This objective is achieved by designing a baffle with swinging joint or pivot joint, which is dynamic in nature. Depending on the relative expansion of the headers, the baffle will move in desired direction to block the gas from flowing through the gap.
[0014] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0015] [0026] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0016] Fig. 1 shows overall elevation view of a Heat recovery steam generator, in accordance with the present subject matter;
[0017] Fig. 2 illustrates bottom headers with only spacer bars, in accordance with the present subject matter;
[0018] Fig. 3 illustrates bottom headers with spacer bar and swinging baffle, in accordance with the present subject matter;
[0019] Fig. 4 illustrates headers with swinging baffle in cold condition, in accordance with the present subject matter;
[0020] Fig. 5 illustrates enlarged view of swinging baffle with spacer bar in cold condition, in accordance with the present subject matter; and
[0021] Fig. 6 illustrates headers with swinging baffle in hot condition, in accordance with the present subject matter.
[0022] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE INVENTION
[0023] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0024] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0025] Present innovation deals with horizontal configured HRSG’s. The figures given may be referred for better understanding of the configuration. Fig.1 shows a typical arrangement of modules inside a heat recovery steam generator. The assembly of heat transfer tubes along with top and bottom header is called a module. The modules are vertically assembled inside the steam generator and supported from the top. Typically, the module height ranges from five to twenty-five meters. Mostly, module tubes are finned for better heat transfer. Bare tubes are also used at certain locations depending on the heat transfer co-efficient and exhaust gas temperature. The module tubes are welded with both top and bottom headers either by full strength or full penetration weld. As the modules are an integrated entity, the total expansion of the module due to its length, takes place at the bottom, which is free. Hot Exhaust gases from gas turbine are channelled through the modules and heat transfer takes place. Superheater, reheater, evaporator, economiser are the main heat transfer sections in a HRSG, often water preheater is added as a downstream process need.

[0026] The present invention deals with top supported horizontal HRSG’s. Here, thermal expansion at the top is very small and highest at the bottom. Fig.1 & 2 shows two adjacent bottom headers, first header (1) can be superheater / evaporator /reheater /economiser /water-preheater header and the second header (2) can also be superheater/ evaporator/ economiser/ reheater/ water preheater header. Modules tubes are welded on the headers. For better visual clarity, only end module tubes are shown in Fig.2 and 3, instead of showing tubes throughout the header (1, 2) length.

[0027] As shown in Fig. 2, the header spacer bars (3,4) are provided for maintaining the horizontal gap between the headers which avoids direct rubbing of header with one another. In addition to maintaining the horizontal gap between headers, it also serves as a component for transferring seismic load to the nearest support. These spacer bars (3, 4) are not continuous along the header length instead segments are welded with the header at three to four locations to avoid overheating of a lengthy uncooled spacer bar (3, 4). Exhaust gas can pass through the gap between adjacent spacer bars as shown in Fig.2.

[0028] One attempt at solving this problem suggested providing a horizontal baffle plate, welded on the spacer bar, effectively sealing the header to header gap. But this arrangement will only work, if there is no relative movement between the headers. Since these two headers (1, 2) have working medium at different temperatures, their thermal expansion will also be different. As a result, there will be relative movement of one header (1) with respect to other header (2). Once the vertical movement of one header (1) is different from the adjacent header during hot condition, it cannot be welded to the baffle on both header spacer bars, because it will restrict the free downward movement, creating undue thermal stresses, leading to failure of the baffle plate. Another way to solve the issue is to weld the baffle plate on the spacer bar of any one header instead of both the headers. Again, in this case also, space will be formed below the baffle plate and above the spacer bar of the other header for gas to by-pass, once the vertical expansion of one header is different from the adjacent one.

[0029] The present invention deals with this issue, and the intention of the new design is to arrest by-pass of exhaust gas, by sealing the gap between the headers during both hot and cold conditions. For, maximum thermal efficiency, it is imperative to design the HRSG in such a way that, most of the exhaust gas is channelled past the module tubes, thus arresting gas by-pass at all conditions is of paramount importance.

[0030] In the present invention, as shown in Fig. 3, 4, 5, & 6, swinging baffle arrangement is envisaged to tackle the issue of relative movement of headers during thermal expansion. In swinging baffle configuration, swinging joint includes baffle plate (5), knuckles (6) and pin (7) shown in Fig.4. During cold condition, shown in Fig.4, this baffle (5) just rests in its original position. The width of the baffle plate is optimised in such a way, that it does not touch the nearby module tubes under any circumstances. Sufficient clearance is also provided between the adjacent header (2) and baffle plate (5) for thermal expansion of the baffle plate (5). The knuckles (6) form the barrel through which the pin passes (7) as depicted in Fig. 4, 5, and 6.

[0031] End knuckles (6) are welded on the baffle plate, whereas middle knuckle (6) is welded on the spacer bar (3). Annular clearance is provided between knuckle (6) and pin (7) to allow the knuckles (6) to rotate freely, shown in Fig.5. Pin (7) is welded at the ends with header spacer bar (3). Pin (7) length is decided by the length of the spacer bar (3). Pin location and number is decided by spacer bar (3) location. Even during hot condition, the baffle will never open up space between baffle (5) and spacer bar (4) as the exhaust gas pressure ensures that baffle always remains seated on the spacer bar (4), shown in Fig. 5.

[0032] The swinging joint is the pivoting mechanism for baffle (5), just like our elbow joint is a pivoting mechanism for our arm. During hot condition, header (1) will vertically traverse more distance downwards, than the other header (2), as shown in Fig.6.This will result in rotation of the baffle plate (5), which is resting on the spacer bar (4), in clockwise direction. The rotation of the baffle plate (5) with respect to the barrel, will ensure no space opens up between spacer bar (4) and baffle (5). Thus the gap which was supposed to open up due to differential thermal expansion of the adjacent headers (1, 2) is effectively sealed by the baffle plate (5). Therefore, it is ensured that no gas by-passes at any stage of operation of the heat recovery steam generator and the swinging baffle arrangement redirects gas flow through the module tubes.

[0033] The present heat recovery steam generator (HRSG) to arrest gas bypass during differential expansion between two headers (1, 2). The HRSG includes at least two heater header (1,2) positioned adjacent to each other and a plurality of spacer bars (3, 4) provided on each of the at least two heater header (1, 2) along length. Further, a baffle plate (5) with pivot mechanism is mounted on the plurality of spacer bars (3) mounted on any of heater header (1 or 2) of the at least two heater header (1, 2) to arrest has bypass from a gap (8) between the at least two heater header (1,2). The baffle plate (5) with pivot mechanism includes the baffle plate (5), and a plurality of knuckles (6) mounted on the baffle plate (5) at corresponding location of the plurality of spacer bars (3,4). Further, the pivot mechanism comprises a plurality of pins (7) passes through barrel of the plurality of knuckles (6). The plurality of pins (7) is welded at ends with the plurality of spacer bars (3, 4) to allow pivot movement of the baffle plate (5).

[0034] Further a middle knuckle (6) from the plurality of knuckles is mounted on middle spacer (3) from the plurality of spacers (3) mounted on the heater header (1). Further, length of the baffle plate (5) matches with the length of the at least two heater header (1,2). Furthermore, length of the plurality of pins (7) depends on length of the plurality of spacer bars (3, 4). In the present HSRG, number of pins (7) and knuckles (6) depend upon number of plurality of spacer bars (3) mounted on the heater header (1). During hot condition, the heater header (1) traverse vertically more distance downward than the heater header (2) from the at least two heater header (1, 2). Further, one longitudinal end of the baffle plate (5) is mounted with the pivot mechanism on the heater header (1) and other longitudinal free end is seated on the spacer bar (4) of the heater header (2) and exhaust gas pressure ensures the baffle plate (5) remains seated on the spacer bar (4) during hot condition.

[0035] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.