Gas turbine transition piece air bypass band assembly   

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Russian Patent Application No. 2010101978, entitled “GAS TURBINE TRANSITION PIECE AIR BYPASS BAND ASSEMBLY”, filed Jan. 15, 2010, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to gas turbine combustors, and, more particularly, to a gas turbine transition piece air bypass band assembly that allows for excess compressor discharge air to be bypassed during certain gas turbine operating conditions.

Gas turbines can be somewhat limited as to the amount that the combustor exit temperature can be reduced by the allowed levels of carbon monoxide (CO) produced by the gas turbine. Typically, the combustor exit temperature remains relatively high to ensure that the gas turbine does not exceed permitted levels of CO emissions. To keep combustor exit temperatures high enough to remain at relatively low CO emission levels requires that the fuel the customer is consuming remain “on-line,” that is, synchronized to the electrical power grid. If a primary contributor to CO production in the individual combustor cans is reduced, this would allow the gas turbine customer to further turn down the load on the gas turbine and, thus, reduce fuel consumption during periods of reduced electricity demand. This can replace the method of shutting down the gas turbine during periods of reduced electricity demand and later turning the gas turbine back on when the demand returns. This method of frequently turning the gas turbine on and off may reduce the reliability of the gas turbine.

In existing turndown regimes, the gas turbine still operates at the speed required to produce electricity at the desired frequency, and the flow rate of fuel and air to the combustors is reduced to reduce the amount of combustion gases generated in the combustors, thereby reducing the power produced by the gas turbine. However, the operating range of typical compressors limits the extent to which the air flow may be reduced, thereby limiting the extent to which the fuel flow may be reduced while maintaining the relatively preferred fuel to air ratio. When the fuel to air ratio is in the relatively preferred position, then the combustor emissions are relatively low and the combustion is stable. Bypassing excess air through the transition piece openings can allow for the preferred fuel to air ratio to be achieved at the combustor head end when the combustion process occurs, thereby reducing CO emissions.

According to one aspect of the invention, an air bypass band assembly includes a transition piece of a gas turbine, the transition piece having at least one opening therein to allow a flow of air to pass through the at least one opening. The air bypass band assembly also includes a band that is movable between at least two positions, a first one of the at least two positions being a closed position where the at least one opening is closed to prevent the flow of air from flowing through the at least one opening, a second one of the at least two positions being an open position where the at least one opening is opened to allow the flow of air to flow through the at least one opening. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions.

According to another aspect of the invention, an air bypass band assembly portion of a gas turbine includes a transition piece, the transition piece having a plurality of openings therein to allow a flow of air to selectively pass through the plurality of opening. The air bypass band assembly also includes a band that is movable between at least two positions, a first one of the at least two positions being a closed position where the plurality of openings are closed to prevent the flow of air from flowing through the plurality of openings, a second one of the at least two positions being an open position where the plurality of openings are opened to allow the flow of air to flow through the plurality of openings. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions.

According to still another aspect of the invention, an air bypass band assembly includes a transition piece of a gas turbine, the transition piece having at least one opening therein to allow a flow of air to pass through the at least one opening. The air bypass band assembly also includes a band located radially around at least a portion of the transition piece, the band being movable between at least two positions, a first one of the at least two positions being a closed position where the at least one opening is closed to prevent the flow of air from flowing through the at least one opening, a second one of the at least two positions being an open position where the at least one opening is opened to allow the flow of air to flow through the at least one opening. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross section of a combustor and transition piece portion of a gas turbine in which embodiments of an air bypass band assembly of the present invention may be located;

FIG. 2 is a perspective view of the forward end of the transition piece of FIG. 1 having the air bypass band assembly of embodiments of the invention located therein and with a manifold cover removed for clarity;

FIG. 3 is a perspective view of the air bypass band assembly of the embodiment of FIG. 2 shown in an open position;

FIG. 4 is a perspective view of the air bypass band assembly of the embodiment of FIG. 2 shown in a closed position;

FIG. 5 is a cross section view of the air bypass band assembly of the embodiment of FIG. 2 shown in an open position; and

FIG. 6 is a cross section view of the air bypass band assembly of the embodiment of FIG. 2 shown in a closed position.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION

FIG. 1 shows a gas turbine 10 having a combustor 12 and a transition piece 14 in which embodiments of an air bypass band assembly 16 of the present invention may be located, as described in detail hereinafter. The gas turbine 10 may be for land-based use for, e.g., generation of electricity, although it is not limited as such. That is, the turbine portion of the gas turbine may be connected with a generator for generating electricity. The transition piece 14 is typically located downstream of the combustor 12 and upstream of the turbine (not shown).

FIG. 2 shows the forward end 18 of the transition piece 14 of FIG. 1. FIG. 2 also shows a portion of the air bypass band assembly 16 of embodiments of the invention located therein and with a bypass manifold cover 24 (FIGS. 1, 3-6) removed for clarity. The air bypass band assembly 16 of embodiments of the present invention include a flexible band 20 and a mechanism 22 that moves the band 20 between at least two positions; for example, an open and closed positions with respect to a plurality of air bypass openings (e.g., circular) or holes 26 located in the transition piece 14 (FIGS. 3-6). The band 20 may comprise a flexible material, such as, for example, a nickel alloy that retains its elasticity at relatively elevated temperatures.

FIGS. 3 and 5 show the air bypass band assembly 16 of the embodiment of FIG. 2 in an open position in which the plurality of air bypass openings are 26 uncovered by the band 20 (i.e., with the band 20 in a “relaxed” or loosened position as provided by the mechanism 16). In such an open position, a flow of bypass air as indicated by the line with an arrowhead 28 in FIG. 5, which may be provided as discharge air from the compressor of the gas turbine 10 or from some other air source within the gas turbine 10, flows within a cavity 30 of a forward ring 32 surrounding the transition piece 14. The flow of bypass air 28 then flows through the plurality of openings 26 located in the transition piece forward ring 32 and into a bypass manifold cavity 34 bounded by the bypass manifold cover 24. One or more bolts 35 may be used to retain manifold cover 24 on forward ring 32. The flow of bypass air 28 then flows through a plurality of floating tubes 36 and into an inner portion 38 of the transition piece 14. The floating tubes 36 connect the bypass manifold (cavity) 34 with the internal cavity portion 38 of the transition piece 14.

The air bypass band assembly 16 of embodiments of the present invention being in the open position, as illustrated in FIGS. 3 and 5, typically occurs when it is desired to operate the gas turbine 10 in a relatively “low” part load operation or regime. Operation in this manner allows an excess amount of the flow of air 28 to be bypassed, thereby reducing fuel consumption in the combustor 12. In this open position, it can be seen from FIGS. 3 and 5 that the band 20 moves away from the openings 26 and up against or adjacent to the inside of a radially outer wall of the bypass manifold cover 24.

FIGS. 4 and 6 show the air bypass band assembly 16 of the embodiment of FIG. 2 in a closed position. In this closed position, the plurality of air bypass openings 26 are covered by the band 20 (i.e., the band 20 is in a “tight” or closed position as provided by the mechanism 16). As such, the flow of air 28 flows through the cavity 30 in the transition piece forward ring 32 without being bypassed through the cavity 34 bounded by the bypass manifold cover 24. The air bypass band assembly 16 of embodiments of the present invention being in the closed position, as illustrated in FIGS. 4 and 6, typically occurs when it is desired to operate the gas turbine 10 in a relatively “high” or “base” load operation or regime. In this closed position, it can be seen from FIGS. 4 and 6 that the band 20 moves up against or adjacent to the inside of a radially inner wall of the bypass manifold cover 24 to block the openings 26. As such, the pressure in the cavities 34 and 38 are relatively the same, but lower than the pressure within the cavity 30. Then when the mechanism 16 starts to loosen the band 20, a positive pressure differential helps to open the band 20 and press it up against the inside of the radially outer wall of the bypass manifold cover 24.

FIGS. 1, 3 and 4 show the mechanism 16 for moving the band 20 radially between the open and closed positions described hereinabove may comprise, in an embodiment, a pair of levers 40, 42 interconnected by corresponding gears 44, 46 at one end of the levers 40, 42. The other end of each lever 40, 42 may connect to shackles 48, 50, which may connect to corresponding ends of the band 20 for opening and closing of the band 20. The gears 44, 46 may rotate on bearings 52, 54. The mechanism 16 may be at least partially enclosed by a box-like device 56, which itself may be a cap-like device or cover 57, shown in phantom in FIG. 3. The cap or cover 57 serves as a barrier for air inside and outside the bypass manifold cover 24.

FIG. 1 shows that the mechanism 16 may connect by a rod 58 to a gearbox 60, which may connect by another rod 62 to an actuator 64, such as, for example, a pneumatic cylinder 64. However, other suitable actuators may be utilized, such as motors. Also, other suitable mechanisms 16 may be utilized for moving the band 20 between open and closed positions, including those mechanisms that do not include gears. It suffices that the mechanism 16 used be able to move the band 20 between the at least two positions (i.e., the open and closed positions), as described hereinabove. Further, the band 20 may comprise between approximately 300-340 degrees of the overall 360-degree circumference of the transition piece 14. However, other angular amounts of the band 20 may be utilized, as deemed suitable.

Further, embodiments of the air bypass band assembly 16 of the present invention when utilized at the forward end 18 of the transition piece 14 may omit the transition piece forward ring 32. The flow of bypass air 28 may then instead flow through some other suitable cavity or flow channel.

Embodiments of the present invention allow for the reduction in the production of emissions, such as but not limited to, carbon monoxide (CO) in a gas turbine combustor (e.g., in the individual combustor cans). This allows the gas turbine load to be further turned down, thereby reducing the amount of fuel consumption by the gas turbine, during periods of reduced electricity demand, also providing for increased cost savings. Embodiments of the present invention also allow for a relatively good seal capability of the transition piece openings, thereby providing little or no sensitivity to thermal growth and little or no vibration-caused wear problems. This is because any expansion of the air bypass band is compensated for by actuator load and band spring force.

Embodiments of the air bypass band assembly of the present invention have been described and illustrated herein as being located at the forward end of the transition piece of the gas turbine (i.e., at the forward ring 32 of the transition piece 14). However, embodiments of the air bypass band assembly of the present invention may be located at other gas turbine locations, such as, for example, the combustor head end or the combustor liner aft section. In addition, embodiments of the present invention may be utilized in a gas turbine to modulate cooling airflow through components such as a turbine nozzle and blades. Also, embodiments of the present invention may be utilized to “tune” the combustor exit temperature profile during low load regimes.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.