Abstract:
A combustor includes a combustor housing defining a combustion chamber having a plurality of combustion zones. A plurality of temperature detectors are disposed in communication with the combustion chamber. The plurality of temperature detectors detect a temperature in the plurality of combustion zones. A controller communicating with the plurality of temperature detectors is programmed to determine an occurrence of a flame holding condition or a flashback condition in the plurality of combustion zones based on signals from the plurality of temperature detectors.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to detecting combustor flashback/flame holding using a temperature sensor. 
         [0002]    In a gas turbine, fuel is burned with compressed air, produced by a compressor, in one or more combustors having one or more fuel nozzles configured to provide a premixing of fuel and air in a premixing zone located upstream of a burning zone (main combustion zone). A gas-turbine combustor is essentially a device used for mixing large quantities of fuel and air and burning the resulting mixture. Gas-turbines with combustion systems designed to reduce NOx emissions to levels below 40 ppm without water or steam injection employ a combustion process in which fuel is uniformly mixed with air prior to the combustion process. In the premixing zone, ignition of the fuel and air occasionally occurs. This event, regardless of its cause, is called a “flashback.” Due to the design of most premix systems, the combustion of fuel and air in the premix section usually causes considerable damage to components. For various reasons, it is often not practical to design a low NOx combustor to operate satisfactorily with a flame in the premix section. 
         [0003]    Previously, flashback/flame holding had been prevented by having a flame holding margin and limiting the type of fuel that can be burned. Catastrophic damage to the fuel nozzles (and potentially any gas turbine hardware downstream) can be avoided by detecting the occurrence of flashback and by quickly taking remedial action. Additionally, with the use of a flashback detecting sensor, fuel flexibility can be enabled so that higher-order hydrocarbon fuels and/or fuels containing a portion of pure hydrogen can be burned. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In an exemplary embodiment, a combustor includes a combustor housing defining a combustion chamber having a plurality of combustion zones. A plurality of temperature detectors are disposed in communication with the combustion chamber. The plurality of temperature detectors detect a temperature in the plurality of combustion zones. A controller communicating with the plurality of temperature detectors is programmed to determine an occurrence of a flame holding condition or a flashback condition in the plurality of combustion zones based on signals from the plurality of temperature detectors. 
         [0005]    In another exemplary embodiment, a gas turbine includes a compressor configured to compress air, and the noted combustor in flow communication with the compressor. The combustor receives the compressed air from the compressor and combusts a fuel stream to generate a combustor exit gas stream. 
         [0006]    In yet another exemplary embodiment, a combustor includes a premixing device that mixes fuel and air into a gaseous premix and introduces the gaseous premix into a combustion chamber; a plurality of temperature detectors communicating with the combustion chamber that monitor a temperature rise in the combustion chamber; and a controller communicating with the plurality of temperature detectors and being programmed to determine an occurrence of a flame holding condition or a flashback condition in the combustion zone based on signals from the plurality of temperature detectors. The plurality of temperature detectors are disposed in an orientation that monitors temperature upstream from the premixing device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic illustration of a gas turbine; 
           [0008]      FIG. 2  is a schematic illustration of a combustor having a premixing device employed in the gas turbine system of  FIG. 1 ; 
           [0009]      FIG. 3  is a side and sectional view showing pertinent parts of a combustor; 
           [0010]      FIG. 4  is a flow chart showing a method for operating a combustor; and 
           [0011]      FIG. 5  is sequence/timing graph for desired flashback sensing and accommodation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Exemplary embodiments described herein include structure for detecting and remedying flashback/flame holding in a gas turbine fuel nozzle via temperature sensing provided by temperature sensors routed into and placed, for example, near the exit of the fuel nozzles. Monitoring flame/wall temperatures enables the detection of any abnormalities including flame-out or flashback. When flame holding/flashback is detected, it is desirable to take appropriate action and prevent damage to the gas turbine. 
         [0013]    With reference to  FIG. 1 , a gas turbine  10  having a combustor  12  is illustrated. The gas turbine  10  includes a compressor  14  configured to compress ambient air  16 . The combustor  12  is in flow communication with the compressor  14  and is configured to receive compressed air  18  from the compressor  14  and to combust a fuel stream  20  to generate a combustor exit gas stream  22 . The gas turbine  10  includes a turbine  24  located downstream of the combustor  12 , which is configured to expand the combustor exit gas stream  22  to drive an external load such as a generator  26 . In the illustrated embodiment, the compressor  14  is driven by the power generated by the turbine  24  via a shaft  28 . The combustor  12  employs a temperature detection device and controller configured to detect flame holding/flashback in a gas turbine combustion chamber and to take appropriate action to prevent damage to the gas turbine  10 . 
         [0014]      FIG. 2  is a schematic illustration of an exemplary configuration  40  of the combustor  12  having a temperature detection device  60  employed in the gas turbine system  10  of  FIG. 1 . As illustrated, the combustor  40  includes a premixing device  42  configured to mix fuel  20  and air  18  to form a gaseous pre-mix  44 . The combustor  40  includes a combustion chamber  46  configured to combust the pre-mix fuel  44  to form the combustor exit gas stream  22 . The combustor exit gas stream  22  is directed to a downstream process  48  such as to the turbine  24  (see  FIG. 1 ) for driving the external load  26  (see  FIG. 1 ). The premixing device  42  can further include a plurality of swirler vanes  50  configured to provide a swirl movement to the fuel  20  and/or air  18  to facilitate mixing of the fuel  20  and air  18 . In exemplary embodiments, the combustor  40  includes the temperature detection device  60 , which can be coupled to and in communication with either or both of the premixing device  42  and the combustion chamber  46 . The temperature detection device  60  can be any such device suitable for the described purpose, including, without limitation, a thermocouple, optical pyrometer, or via communication using fiber optics, etc. 
         [0015]    The combustor  40  also includes a control unit  65  coupled to the temperature detector  60 . The control unit  65  receives signals from the temperature detectors that correspond to the flame holding/flashback in the combustion chamber  46 . The control unit  65  is further in communication with the source of the air  18  and the fuel  20 . As further described herein, if the control unit  65  receives signals that indicate there is flame holding/flashback in the combustion chamber  46 , the control unit  65  can take appropriate action to mitigate damage to the gas turbine. The appropriate action that the control unit  65  can take includes ceasing fuel and air flow to the combustion chamber or some modification of the air and fuel flow to reduce or eliminate the flame holding/flashback. 
         [0016]      FIG. 3  illustrates an exemplary gas turbine  100  including a plurality of temperature detectors  180 . The example of the gas turbine shows the temperature detectors coupled to and in communication with a combustion chamber  140  of the gas turbine and configured to detect temperatures within the combustion chamber  140 . 
         [0017]    Similar to  FIG. 1 , 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 . 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 , which includes a series of temperature detectors  180  affixed to the housing  170 . The temperature detectors  180  are coupled to and in communication with the combustion chamber  140  and the combustor exit gas stream  165 . 
         [0018]    The control unit  65  can detect the signal responses from multiple temperature detectors (e.g., the temperature detectors  180 ) and implement a voting algorithm to determine the type of action taken by the control unit  65  in response to a flame holding/flashback condition. For example, if two of the three detectors  180  determine that a flashback condition exists, the control unit  65  can then cut off or reduce the fuel to the combustor cans  120 . Similarly, if only one detector  180  detects flashback, the control unit  65  can decide to continue the fuel until the detectors  180  make another reading. Multiple detector elements can reside in an enclosure corresponding to the detectors  180 . The multiple detector elements can be multiplexed in order to aggregate the signals detected in the combustor cans  120 . In this way, the aggregate signal can be implemented to determine the results of the voting algorithm. 
         [0019]      FIG. 4  is a flow chart showing a method  700  for operating a combustor in accordance with exemplary embodiments. At block  705 , fuel nozzles (e.g.,  160   FIG. 3 ) introduce fuel into a premixing device (e.g.,  42   FIG. 2 ), and a compressor (e.g.,  110   FIG. 3 ) introduces air into the premixing device. At block  710 , the premixing device forms a gaseous pre-mix. At block  715 , the combustor (e.g., combustor cans  120   FIG. 3 ) combust the premix in a combustion chamber (e.g.,  165   FIG. 3 ). At block  720 , the temperature within the combustion chamber is monitored. If the temperature detectors detect a condition that evidences flame holding/flashback (Yes in block  725 ), then at block  730 , the controller can modify the fuel flow into the premixing device or other appropriate action described herein. If the temperature detectors do not detect such condition (No in block  725 ), then the process returns to block  705 . 
         [0020]      FIG. 5  is sequence/timing graph for desired flashback sensing and accommodation. Upon the occurrence of a flashback event, it is desirable for the sensors and controller to detect the event within three seconds and for the controller to take action within another three seconds. Mitigation actuation should take less than one-quarter second, and the flashback event should be eliminated within another quarter second. The values are exemplary and would be adjusted to assure that hardware damage and false alarms are avoided. 
         [0021]    Exemplary embodiments have been described for detecting flame holding/flashback in the combustion chamber  140  of the combustor cans  120 . Thermal emissions can be detected elsewhere in the system, for example from the fuel nozzles  160  (see  FIG. 3 ). By monitoring the thermal emissions from the fuel nozzles  160 , the system can determine if a flame is within the fuel nozzle  160  because the thermal emissions would indicate a higher temperature than would be expected in the fuel nozzles  160 . Thermal emissions indicating flame holding/flashback could be measured at the swirler vanes, burner tube, or diffusion tip of the fuel nozzles  160  or other downstream components such as in the combustor. The temperature detectors  180  are preferably oriented adjacent the fuel nozzles  160  or fuel nozzle circuit. Fuel from the premixed circuit could be redirected in full or part to another fuel circuit, vented or to an unused fuel circuit such as the diffusion flame circuit. Furthermore, optical pyrometer detectors  180  could be spaced such that each detector  180  shares a line of sight with one of the fuel nozzles  160 . As such, if two of the detectors indicate that there is a flame holding/flashback event, the control unit  65  therefore knows which of the fuel nozzles  160  is affected. In this way, the controller can selectively reduce the fuel or shut off the fuel to the one effected fuel nozzle  160 . It is appreciated that the combustor can  120  can experience minimal disruption when the control unit  65  acts upon only a single fuel nozzle  160 . As such, the affected fuel nozzle  160  can be serviced during the next scheduled outage. 
         [0022]    By including strategically placed temperature sensors within a gas turbine, undesirable flame holding/flashback can be detected, and catastrophic damage to the fuel nozzles can be avoided by quickly taking remedial action. Additionally, with the detectors in place, fuel flexibility can be increased enabling the use of higher-order hydrocarbon fuels and/or fuels containing a portion of pure hydrogen without risking damage due to flame holding/flashback. 
         [0023]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.