Patent Publication Number: US-2011072826-A1

Title: Can to can modal decoupling using can-level fuel splits

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to gas turbines and more particularly to can combustor de-tuning and frequency de-coupling via multi-circuit fuel manifolds. 
     In a gas turbine, multi-can combustors communicate with each other acoustically due to connections between various cans. Large pressure oscillations, also known as combustion dynamics, result when the heat release fluctuations in the combustor couple with the acoustic tones of the combustor. Some of these combustor can acoustic tones may be in phase with the adjacent can, while other tones could be out of phase with the adjacent can. In-phase tones are particularly a concern because of their ability to excite the turbine blades in the hot gas path if they coincide with the natural frequency of the blades impacting the blade life. The in-phase tones are particularly of concern when the instabilities in different cans are coherent (i.e., there is a strong relationship in the frequency and the amplitude of the instability in one can to the next can). Such coherent in-phase tones can excite the turbine buckets leading to durability issues and thereby limiting the operability of the gas turbine, and can ultimately crack the turbine buckets. 
     Current solutions to the potential damaging in-phase coherent tones are to ensure that the in-phase coherent tones near the bucket natural frequency are of much smaller amplitude compared to the typical design practice limits. This approach means that the operability space could be limited by the in-phase coherent tones. Another current approach includes changing the fuel splits to either shift the combustor instability frequency away from the turbine blade natural frequency or to lower the amplitude. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In exemplary embodiments, a gas turbine system is provided. The gas turbine can include a compressor configured to compress air and combustor cans in flow communication with the compressor, the combustor being configured to receive compressed air from the compressor and to combust a fuel stream. The gas turbine can also include a multi-circuit manifold coupled to the combustor cans and configured to provide a split fuel stream from the fuel stream to the combustor cans. 
     In exemplary embodiments, a gas turbine is provided. The gas turbine can include a first group of combustor cans, a second group of combustor cans and fuel nozzles disposed in each of the first group and second group of combustor cans. The gas turbine can further include a multi-circuit manifold coupled to the first group of combustor cans and the second group of combustor cans. 
     In exemplary embodiments, a method of decoupling in-phase coherent tones between the first and second combustor cans in a gas turbine, the first and second combustor cans having groups of fuel nozzles. The method can include providing a fuel stream to the first and second combustor cans and splitting the fuel stream in at least one of, between the first and second combustor cans and between the groups of nozzles in both the first and second combustor cans. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       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  diagrammatically illustrates a side view of a gas turbine system in which exemplary multi-circuit manifolds can be implemented. 
         FIG. 2  diagrammatically illustrates the gas turbine system of  FIG. 1  including an exemplary multi-circuit manifold configuration coupled to the combustor cans. 
         FIG. 3  diagrammatically illustrates a front view of an exemplary multi-circuit manifold configuration similar to the multi-circuit manifold of  FIG. 2 . 
         FIG. 4  illustrates a front perspective view of an example of a nozzle arrangement within a combustor can. 
         FIG. 5  diagrammatically illustrates an example of groupings of fuel nozzles within a combustor can. 
         FIG. 6  diagrammatically illustrates an exemplary multi-circuit manifold configuration. 
         FIG. 7  diagrammatically illustrates a front view of an exemplary multi-circuit manifold configuration. 
         FIG. 8  illustrates an example of a time series data plot of pressure versus time for an out of phase tone in a gas turbine. 
         FIG. 9  illustrates an example spectra plot of amplitude versus frequency for the out of phase tone of  FIG. 8 . 
         FIG. 10  illustrates an example of a time series data plot of pressure versus time for an in-phase tone in a gas turbine. 
         FIG. 11  illustrates an example spectra plot of amplitude versus frequency for the in-phase tone of  FIG. 10 . 
         FIG. 12  illustrates a flow chart of a method of decoupling in-phase tones between the first and second combustor cans in a gas turbine. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  diagrammatically illustrates a side view of a gas turbine system  100  in which exemplary multi-circuit manifolds can be implemented. In exemplary embodiments, the gas turbine  100  includes a compressor  110  configured to compress ambient air. One or more combustor cans  120  are in flow communication with the compressor  110  via a diffuser  150 . The combustor cans  120  are configured to receive compressed air  115  from the compressor  110  and to combust a fuel stream from fuel nozzles  160  to generate a combustor exit gas stream  165  that travels through a combustion chamber  140  to a turbine  130 . Part of the combustion chamber  140  is included in a transition piece  145  that is coupled to the combustor cans  120 . The turbine  130  is configured to expand the combustor exit gas stream  165  to drive an external load. The combustor cans  120  include an external housing  170 , and an end cap  175  configured to couple with fuel hoses (not shown) from a fuel manifold (not shown). Currently, a single fuel manifold provides a single fuel flow to the end caps  175  of each of the combustor cans  120  and thus to the fuel nozzles  160 . 
     As described herein, adjacent combustors cans  120  communicate with each other acoustically through an opening at the exit of the transition piece  145  and a first stage of the turbine  130 . When the heat release fluctuations in the combustor cans  120  couple with combustor acoustic tones they tend to excite either an in-phase or an out of phase tone or both. In exemplary embodiments, the system  100  can include a multi-circuit manifold configured to detune the strong acoustic interactions (e.g., coupling of acoustic modes of adjacent cans) between the combustor cans  120  thereby shifting the frequencies of instability in the adjacent cans or decreasing the amplitude by reducing the combustion-acoustic interaction and reducing the coherence of the in-phase mode. 
       FIG. 2  diagrammatically illustrates the gas turbine system  100  of  FIG. 1  including an exemplary multi-circuit manifold configuration  200  coupled to the combustor cans  120 . In exemplary embodiments, the manifold configuration includes fuel lines  205  that provide fuel from the manifold  200  to the combustor cans  120 , thus intentionally introducing variation in operating conditions in the adjacent cans. In exemplary embodiments, the multi-circuit manifold  200  fuels adjacent cans from individual fuel manifolds included in the multi-circuit manifold  200 . In this way, adjacent fuel combustor cans can be fueled at different rates and direct control at the combustor can level to change the fuel split can be achieved. By adjusting the rates of the fuel flow to adjacent cans, the resulting frequencies, and thus the in-phase and out of phase tones, can also be controlled. Changing the fuel splits between adjacent cans changes the fuel system impedance and unstable frequencies in adjacent cans, which impacts the flame acoustic interaction and thereby shifts the instability frequencies in adjacent cans, lowers the instability amplitude, and thus disrupts the strong coherent relationship between the cans. In addition to changing fuel system impedance, varying combustor temperature between adjacent cans induces instability frequency differences, which in turn disrupts the strong coherence across cans. This asymmetry or de-synchronization results in suppressing the ability of the unstable tone to drive the turbine blades. In exemplary embodiments, in the event of a gas turbine turndown, one or more of the manifolds in the multi-circuit manifold can be turned off to turn off alternate cans. 
       FIG. 3  diagrammatically illustrates a front view of an exemplary multi-circuit manifold configuration  300  similar to the multi-circuit manifold  200  of  FIG. 2 . In exemplary embodiments, the multi-circuit manifold configuration  300  can include a first manifold  305  and a second manifold  310  concentric with the first manifold  305 . The first manifold  305  includes a first set of combustor cans  320  coupled to the first manifold  305  via fuel lines  321 . The second manifold  310  includes a second set of combustor cans  325  interleaved and adjacent to each of the first set of combustion cans  320 . The second set of combustion cans  325  are coupled to the second manifold  310  via fuel lines  326 . It to be appreciated that combustor cans can include multiple nozzles within the combustor cans as illustrated, for example, in  FIG. 1  (i.e., combustor can  120  shows nozzles  160 ) and described further herein. In the multi-circuit manifold configuration  300  example of  FIG. 3 , the fuel lines  321  provide fuel from the first manifold  305  to all nozzles within the first set of combustor cans  320 . Similarly, the fuel lines  326  provide fuel from the second manifold  310  to the second set of combustor cans  325 . It is therefore appreciated that the multi-circuit manifold configuration  300  provides a first fuel stream to the first set of combustor cans  320  and a second fuel stream to the second set of combustor cans  325 . As described herein, the first set of combustor cans  320  can be fueled at a different rate than the second set of combustor cans  325 . By having two separate manifolds  305 ,  310 , the fuel split to the respective first and second set of combustor cans  320 ,  325  can be controlled. By adjusting the rates of the fuel flow to one or both of the first and second sets of combustor cans  320 ,  325 , the instability frequencies can be adjusted and controlled. By having control of the fuel splits with the first and second manifolds  305 ,  310 , the flame acoustic interactions in the first and second sets of combustors is controlled to shift the instability frequencies and their tendency to drive to higher amplitudes, thereby disrupting the strong coherent relationships between the first and second sets of combustor cans  320 ,  325 . 
     As described above, in-phase coherent combustion tones are a concern because of their ability to excite the turbine buckets. By having two manifolds in the multi-circuit manifold configuration  300  as described, the gas turbine can have can-level fuel split management to suppress the in-phase coherent nature of the gas turbine. By fueling the adjacent cans differently, the fuel system impedance and combustor temperature are modified and thus the flame-acoustic wave interactions and the instability frequency are influenced. The coherence of the instability around the gas turbine is thus reduced, accompanied by reduction in the instability amplitude, which in turn suppresses the ability of the tone to drive the turbine buckets, thereby reducing the chance of damage to the turbine buckets. It is to be appreciated that the grouping of combustor cans into two groups is just an example. In other exemplary embodiments, the combustor cans are grouped into additional adjacent groups. 
     Each combustor can includes multiple fuel nozzles. In exemplary embodiments, nozzles in all combustor cans can be grouped together for fuel split management and thus combustor can control and management. Each group of nozzles can be referred to as a circuit and a particular circuit can be fed fuel from a single manifold. In this way, each combustor can receives fuel from all manifolds but to different circuits within the combustor can. 
       FIG. 4  illustrates a front perspective view of an example of a nozzle arrangement  400  within a combustor can (e.g.,  320 ,  325  in  FIG. 3 ). It is to be appreciated that the number and groupings of nozzles described herein is used as an illustrative example. It is to be appreciated that other numbers and groupings of the nozzles are contemplated in alternate exemplary embodiments. The nozzle arrangement includes a center nozzle PM 1 , a first group of outer nozzles PM 2 _ 1 , PM 2 _ 2 , and a second group of outer nozzles PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3 .  FIG. 5  diagrammatically illustrates groupings  500  of the nozzles, PM 1 , PM 2 _ 1 , PM 2 _ 2 , PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3  within a combustor can.  FIG. 6  diagrammatically illustrates a front view of an exemplary multi-circuit manifold configuration  600 . The multi-circuit manifold configuration  600  includes a first manifold  605 , a second manifold  610  and a third manifold  615 . The manifolds  605 ,  610 ,  615  are each coupled to combustor cans  620 . For illustrative purposes one of the combustor cans  620  is diagrammatically illustrated showing the group of nozzles as shown in  FIG. 5  to illustrate the coupling of fuel lines  606 ,  611 ,  616  to the manifolds  605 ,  610 ,  615 . In exemplary embodiments, the first manifold  605  is coupled to each of the combustor cans  620  via a fuel line  606 . The second manifold  610  is coupled to each of the combustor cans  620  via fuel lines  611 . The third manifold is coupled to each of the combustor cans  620  via fuel lines  616 . It is further appreciated that in the multi-circuit configuration  600 , the fuel line  606  feeds the nozzle PM 1  as a first circuit. The fuel lines  611  feed the nozzles PM 2 _ 1 , PM 2 _ 2  as a second circuit. The fuel lines  616  feed the nozzles PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3  as a third circuit. It is therefore appreciated that the nozzles are grouped into discrete sub-groups and the multi-circuit manifold configuration provides discrete fuel streams to each of the sub-groups of nozzles. 
     The multi-circuit manifold configuration  600  addresses the concern of in-phase coherent combustion tones. By grouping nozzles into three circuits in this example, each of the circuits fed by a separate manifold, the gas turbine can have can-level fuel split management to suppress the in-phase coherent nature of the gas turbine. By fueling the groups of nozzles (circuits) differently, the fuel system impedance is modified and thus the flame-acoustic wave interactions and the instability frequency are influenced. In this way, the acoustic interaction and instability frequencies are controlled by controlling the fuel flow to the different circuits, thereby controlling cross talk between adjacent combustor cans via the circuits. The coherence of the instability around the gas turbine is thus reduced, which in turn suppresses the ability of the tone to drive the turbine buckets, thereby reducing the chance of damage to the turbine buckets. It is to be appreciated that the grouping of nozzles into three circuits is just an example. In other exemplary embodiments, the nozzles can be grouped into fewer or more circuits. 
     The multi-circuit manifold configuration  300  of  FIG. 3  illustrates a separate manifold for two groups of adjacent cans. The multi-circuit manifold configuration  600  of  FIG. 6  illustrates a separate manifold for each of three groups of nozzles within all combustor cans. In exemplary embodiments, a first group of manifolds can feed fuel to multiple circuits within a first group of combustor cans. Similarly a second group of manifolds can feed fuel to multiple circuits within a second group of combustor each adjacent to cans within the first group. 
       FIG. 7  diagrammatically illustrates a front view of an exemplary multi-circuit manifold configuration  700 . The multi-circuit manifold configuration  700  includes a first manifold  705 , a second manifold  710 , a third manifold  715 , a fourth manifold  730 , a fifth manifold  735  and a sixth manifold  740 . In exemplary embodiments, the second, third, fourth, fifth and sixth manifolds  710 ,  715 ,  730 ,  735 ,  740  are concentric with the first manifold  705 . The manifolds  705 ,  710 ,  715  are each coupled to combustor cans  720 . The manifolds  730 ,  735 ,  740  are each coupled to combustor cans  725 . For illustrative purposes one of the combustor cans  720  is diagrammatically illustrated showing a first group of nozzles  755  as shown in  FIG. 5  to illustrate the coupling of fuel lines  706 ,  711 ,  716  to the first group of manifolds  705 ,  710 ,  715 . In addition, for illustrative purposes one of the combustor cans  725  adjacent the combustor can  720 , is diagrammatically illustrated showing a second group of nozzles  760  as shown in  FIG. 5  to illustrate the coupling of fuel lines  731 ,  736 ,  741  to the second group of manifolds  730 ,  735 ,  740 . In exemplary embodiments, the first manifold  705  is coupled to each of the PM 1  nozzles of the combustor cans  720  via a fuel line  706 . The second manifold  710  is coupled to each of the PM 2 _ 1 , PM 2 _ 2  nozzles of the combustor cans  720  via fuel lines  711 . The third manifold  715  is coupled to each of the PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3  nozzles of the combustor cans  720  via fuel lines  716 . It is therefore appreciated that the first, second and third manifolds  705 ,  710 ,  715  form a first group fueling the first combustor cans  720 . In addition, each of the manifolds  705 ,  710 ,  715  fuels separate groups of nozzles within the combustor cans  720 . The fourth manifold  730  is coupled to each of the PM 1  nozzles of the combustor cans  725  via a fuel line  731 . The fifth manifold  735  is coupled to each of the PM 2 _ 1 , PM 2 _ 2  nozzles of the combustor cans  725  via fuel lines  736 . The sixth manifold  740  is coupled to each of the PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3  nozzles of the combustor cans  725  via fuel lines  741 . It is therefore appreciated that the fourth, fifth and sixth manifolds  730 ,  735 ,  740  form a second group fueling the first combustor cans  725 . In addition, each of the manifolds  730 ,  735 ,  740  fuels separate groups of nozzles within the combustor cans  725 . It is therefore appreciated that the multi-circuit manifold configuration therefore provides first fuel streams to the first set of combustor cans  720  and second fuel streams to the second set of combustor cans  725 . In addition the first fuel streams provide fuel to discrete sub-groups of nozzles in the first combustor cans  720  and the second fuel streams provide fuel to discrete sub-groups of nozzles in the second combustor cans  725 . 
     The multi-circuit manifold configuration  700  addresses the concern of in-phase coherent combustion tones. By having two groups of manifolds in the multi-circuit manifold configuration  700  as described, as well as grouping nozzles into three circuits within each of the two groups of manifolds, the gas turbine can have can-level fuel split management to suppress the in-phase coherent nature of the gas turbine. By fueling both the groups of nozzles (circuits) within adjacent cans differently, the fuel system impedance and combustor temperature are modified and thus the flame-acoustic wave interactions and the instability frequency are influenced. In this way, the interaction between cans and instability frequencies are controlled by controlling the fuel flow to the different circuits, thereby controlling interaction between adjacent combustor cans via the cans and fuel circuits. The coherence of the instability around the gas turbine is thus reduced, which in turn suppresses the ability of the tone to drive the turbine buckets, thereby reducing the chance of damage to the turbine buckets. It is to be appreciated that the grouping of manifolds into two groups, and grouping the nozzles into three circuits is just an example. In other exemplary embodiments, the manifolds can be grouped into fewer or more groups and the nozzles can be grouped into fewer or more circuits. 
     As described herein, out of phase tones are not of the greater concern in gas turbines from the turbine life point of view.  FIG. 8  illustrates an example of a time series data plot  800  of pressure versus time for out of phase tone in a gas turbine.  FIG. 9  illustrates an example spectra plot  900  of amplitude versus frequency for the push-pull tone of  FIG. 8 . In this example, the instability tone is at about 340 Hz. The plot  800  illustrates that the tones of the adjacent cans, as indicated by lines  805 ,  810  tend are out of phase with adjacent combustor can.  FIG. 9  illustrates the corresponding spectral lines  905 ,  910  for combustor can  1  and combustor can  2  respectively. 
     In contrast, when the frequency of the in-phase coherent tones match the natural frequency of turbines buckets, these in-phase tones could potentially cause damage to the turbine buckets.  FIG. 10  illustrates an example of a time series data plot  1000  of pressure versus time for an in-phase tone in a gas turbine.  FIG. 11  illustrates an example spectra plot  1100  of amplitude versus frequency for the in-phase tone of  FIG. 10 . In this example, the instability tone is at about 60 Hz. The plot  1000  illustrates that the tones of the adjacent cans, as indicated by lines  1005 ,  1010  tend to be in phase. When these in-phase tones are strongly coherent between adjacent cans, they can drive the turbine buckets.  FIG. 11  illustrates the corresponding spectral lines  1105 ,  1110  for combustor can  1  and combustor can  2  respectively. The exemplary embodiments described herein therefore adjust the fuel flows, which as described above, can directly affect the tones of adjacent cans, causing a shift in the instability frequencies of adjacent cans, thereby decreasing coherence and thus reducing the ability of the tones to drive the turbine buckets. 
       FIG. 12  illustrates a flow chart of a method  1200  of decoupling in-phase tones between the first and second combustor cans in a gas turbine. At block  1205 , a fuel stream is provided to the first and second combustor cans such as the combustor cans  320 ,  325 . At block  1210 , the fuel stream is split as discussed herein. In exemplary embodiments, the fuel stream is split between two manifolds  305 ,  310  supplying a first stream to the first combustor cans  320  and a second fuel stream to the second combustor cans as in  FIG. 3 . In exemplary embodiments, the fuel stream is split between groups of fuel nozzles such as PM 1 , PM 2 _ 1 , PM 2 _ 2 , PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3  in combustors  620  as in  FIG. 6 . In exemplary embodiments, the fuel stream is split between adjacent combustor cans such as combustor cans  720 ,  725  in  FIG. 7 . In addition, the fuel stream is split among groups of nozzles PM 1 , PM 2 _ 1 , PM 2 _ 2 , PM 3 _ 1 , PM 3 _ 2 , PM 3 _ 3  in each of the combustor cans  720 ,  725 . 
     It is to be appreciated that many acoustical instabilities observed in the combustor near the turbine bucket natural frequencies is a design and operability concern and thus can be subject to stringent design limits. Thus, the ability to control the system level behavior of the in-phase coherent frequencies, for example, results in exercising more design options and improved operability space by eliminating these restrictions. As such, increased designs and operability can be considered in gas turbines. In addition, the combustion system can be optimized, to a large extent, independent of turbine structural design. It is to be appreciated that the exemplary embodiments described herein can address other acoustical instabilities that can be controlled by managing the fuel flows into combustor cans thereby providing active mitigation of a variety of acoustical instabilities. 
     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.