Abstract:
A gas turbine which can detect ignition in a combustor regardless of startup conditions of the gas turbine, such as the hot startup or the cold startup. An ignition detecting method for the gas turbine comprises the steps of calculating a difference between the exhaust temperature detected at a particular time before outputting of an ignition command for a combustor and the exhaust temperature detected after the outputting of the ignition command, and determining that the combustor is ignited, when the calculated difference is not less than a predetermined value. As an alternative, the method includes a step of determining that the combustor is ignited, when a change amount or rate of the exhaust temperature exceeds a predetermined value in a predetermined period from the outputting time of the ignition command.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an ignition detecting method for a multi-chamber gas turbine provided with a plurality of combustors.  
         [0003]     2. Description of the Related Art  
         [0004]     One example of known techniques for detecting an ignition failure at the startup of a gas turbine combustor without using a flame sensor is disclosed in, e.g., Patent Reference 1; JP-A-59-15638. According to JP-A-59-15638, if the exhaust temperature is still low even after the lapse of a certain time from the startup, this is determined as indicating the occurrence of an ignition failure, and fuel supply is stopped.  
       SUMMARY OF THE INVENTION  
       [0005]     The startup mode of a gas turbine is mainly divided into hot startup and cold startup depending on a temperature condition at the startup of the gas turbine. Between the hot startup and the cold startup, there is a large difference in output of an exhaust temperature sensor, i.e., exhaust temperature, immediately prior to ignition. For example, the exhaust temperature in the cold startup is equal to about the atmospheric temperature, and the exhaust temperature in the hot startup is about 200-300° C. Because of such a large difference in exhaust temperature at the time of ignition between the hot startup and the cold startup, it is difficult or uncertain to reliably determine an ignition failure in both the hot startup and the cold startup with the above-mentioned known technique of determining an ignition failure based on an absolute value of the gas turbine exhaust temperature, as disclosed in JP-A-59-15638.  
         [0006]     Accordingly, an object of the present invention is to provide an ignition detecting method for a gas turbine, which can detect ignition in a combustor regardless of startup conditions of the gas turbine, such as the hot startup or the cold startup.  
         [0007]     When calculating, on the basis of an exhaust temperature at a certain particular time (e.g., an ignition command outputting time) before ignition, a difference between an exhaust temperature after ignition and the reference exhaust temperature, and looking at an increase of the difference, the difference is increased with the establishment of ignition regardless of the hot startup or the cold startup, and exceeds a predetermined value after the lapse of a predetermined time. With attention paid to the above point, the present invention is featured in determining that ignition has been established, when the increase of the exhaust temperature after the ignition exceeds a predetermined value.  
         [0008]     Practically, an ignition detecting method for a gas turbine according to the present invention comprises the steps of calculating a difference between the exhaust temperature detected at a particular time before the outputting of an ignition command for a combustor and the exhaust temperature detected after the outputting of the ignition command, and determining that the combustor is ignited, when the calculated difference is not less than a predetermined value.  
         [0009]     As an alternative, the ignition detecting method may comprise the steps of calculating a change amount (rate) of the exhaust temperature with respect time after the particular time, and determining that the combustor is ignited, when the calculated change rate is not less than a predetermined value. Further, the ignition detecting method may comprise the steps of calculating a change amount (rate) of the exhaust temperature with respect a revolution speed of the gas turbine after the particular time, and determining that the combustor is ignited, when the calculated change rate is not less than a predetermined value.  
         [0010]     According to the present invention, it is possible to provide an ignition detecting method for a gas turbine, which can reliably determine ignition in a combustor regardless of startup conditions of the gas turbine, such as the hot startup or the cold startup. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a block diagram of principal components of a gas turbine for use with an ignition detecting method according to each embodiment of the present invention;  
         [0012]      FIG. 2  is a schematic view of an exhaust duct in a gas turbine of lateral-flow exhaust type;  
         [0013]      FIG. 3  is a schematic view of an exhaust duct in a gas turbine of axial-flow exhaust type;  
         [0014]      FIG. 4  is a sectional view of combustors in a multi-chamber gas turbine;  
         [0015]      FIG. 5  is a graph showing one example of behavior of the gas turbine exhaust temperature at the time of ignition;  
         [0016]      FIG. 6  is a graph showing one example of behavior of a change amount of the gas turbine exhaust temperature at the time of ignition;  
         [0017]      FIG. 7  is a graph for explaining how to calculate a change rate ΔT/dt of the exhaust temperature per unit time at the time of ignition;  
         [0018]      FIG. 8  is a graph showing one example of behavior of the change rate ΔT/dt of the exhaust temperature per unit time at the time of ignition;  
         [0019]      FIG. 9  is a graph for explaining how to calculate a change rate ΔT/dn of the exhaust temperature per unit revolution speed at the time of ignition; and  
         [0020]      FIG. 10  is a graph showing one example of behavior of the change rate ΔT/dn of the exhaust temperature per unit revolution speed at the time of ignition. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]      FIG. 1  schematically shows the construction of a gas turbine for use with an ignition detecting method according each embodiment of the present invention. The illustrated gas turbine comprises a plurality (six in this embodiment, but only one is shown in  FIG. 1 ) of combustors  2  for burning fuel supplied through a fuel pipe  9  and air supplied through a compressed air channel  7 , a turbine  3  driven for rotation by combustion gases produced in the combustors  2  and supplied through respective combustion gas channels  8 , a compressor  1  driven for rotation by the turbine  3  through a turbine shaft  6  and sending compressed air to the compressed air channel  7 , a generator  4  driven for rotation by the turbine  3  through the turbine shaft  6  and generating electric power, an exhaust gas channel  5  through which the combustion gases after having been used to drive the turbine  3  is discharged, and a control unit  28  for controlling the flow rate of fuel supplied to the combustors  2 .  
         [0022]     Further, the gas turbine of the illustrated embodiment comprises an exhaust temperature sensor  21  for detecting the exhaust temperature in the exhaust gas channel  5 , a revolution speed sensor  23  for detecting the revolution speed of the turbine shaft  6 , a load sensor  24  for detecting the load of the generator  4 , and a fuel flow adjuster  25  disposed in the fuel pipe  9  and adjusting the flow rate of fuel. Output signals from those various sensors  21 ,  23  and  24  are converted to digital signals by A/D converters  26   a - 26   c , respectively, and the digital signals are transmitted to the control unit  28 . In accordance with the detected signals from those various sensors, the control unit  28  outputs a control signal for the fuel flow adjuster  25 . The output signal from the control unit  28  is converted to an analog signal by a D/A converter  27  and transmitted to the fuel flow adjuster  25 .  
         [0023]     The exhaust temperature sensor  21  for detecting the gas turbine exhaust temperature is a temperature detecting means prepared using an ordinary temperature sensor, such as a thermocouple. In practice, the exhaust temperature sensor  21  is disposed plural along a circumference in the exhaust gas channel to measure the temperatures of the gas turbine exhaust gases at a plurality of points. Each exhaust temperature sensor  21  outputs an analog signal depending on the exhaust temperature. The analog signal is converted to a digital signal of a predetermined voltage by the A/D converter  26   c , and the digital signal is sent to the control unit  28 .  
         [0024]     The revolution speed sensor  23  detects the turbine revolution speed. For example, a part of the turbine shaft  6  on the inlet side of the compressor  1  is machined into the form of a gear, and analog signals are outputted depending on magnetic conditions at mountains and valleys of the gear by using a magnetic sensor or the like. Those analog signals are each converted to a digital signal of a predetermined voltage by the A/D converter  26   b , and the digital signal is sent to the control unit  28 .  
         [0025]     In addition to the above-mentioned sensors  21 ,  23  and  24 , the gas turbine may further optionally include, like the illustrated embodiment, a flame sensor  22  as a means for detecting a flame. In that case, the flame sensor  22  may be disposed for each of any suitable number (two in the illustrated embodiment) of the combustors instead of being disposed in one-to-one relation to all the combustors. An output signal of the flame sensor  22  is transmitted as an input signal to the control unit  28  through an A/D converter  26   d . The flame sensor  22  is mounted plural to each monitoring window of the plurality of associated combustors and outputs a current depending on the intensity of light emitted from a combustion flame by using a photosensor, for example. Then, the A/D converter  26   d  outputs a digital value of 1 when the output current from the flame sensor  22  exceeds a certain value, and a digital value of 0 when the output current from the flame sensor  22  does not exceed the certain value. The thus-obtained digital signal is outputted to the control unit  28 .  
         [0026]     The control unit  28  receives the digital signals from the various sensors  21 - 24 , monitors those signals, and executes arithmetic/logical operations based on them. Then, the control unit  28  outputs, as digital signals, the control signal to the fuel flow adjuster  25 , an alarm command signal to an alarm device, etc.  
         [0027]     The fuel flow adjuster  25  is mounted to the fuel pipe  9 . The digital signal outputted from the control unit  28  is converted by the D/A converter  27  to an analog signal for adjusting the opening degree of a fuel valve. The fuel flow adjuster  25  adjusts the opening degree of the fuel valve in accordance with that analog signal, thereby adjusting the flow rate of fuel.  
         [0028]     The shape of the exhaust duct will be described below with reference to  FIGS. 2 and 3 .  FIG. 2  is a schematic view of an exhaust duct in a gas turbine of lateral-flow exhaust type, and  FIG. 3  is a schematic view of an exhaust duct in a gas turbine of axial-flow exhaust type.  
         [0029]     The shape of the exhaust duct is classified into two types, as shown in  FIGS. 2 and 3 , depending on the type of gas turbine. An exhaust duct  16   a  shown in  FIG. 2  is called the lateral-flow exhaust type in which combustion gases  14  introduced from the combustor  2 , not shown in  FIG. 2 , pass nozzles  12  and blades  13  and become exhaust gases  15 , which are bent in a direction perpendicularly to the turbine shaft in the downstream side of the exhaust gas channel. The exhaust temperature sensor  21  is disposed in the downstream side of the exhaust gas channel (downstream of a duct bent portion in the illustrated example) such that a sensor unit of the exhaust temperature sensor  21  is projected into the channel parallel to the direction of the turbine shaft.  
         [0030]     Also, an exhaust duct  16   b  shown in  FIG. 3  is called the axial-flow exhaust type in which the exhaust gases  15  discharged after passing the nozzles  12  and the blades  13  flow in the direction of the turbine shaft without being bent. In the case of the exhaust duct  16   b  shown in  FIG. 3 , the exhaust temperature sensor  21  is disposed in the downstream side of the exhaust gas channel such that a sensor unit of the exhaust temperature sensor  21  is projected into the channel in a direction perpendicular to the turbine shaft.  
         [0031]      FIG. 4  is a sectional view of combustors in a multi-chamber gas turbine. Each combustor  2  mixes and burns fuel and compressed air delivered from the compressor  1 , thereby producing high-temperature and high-pressure combustion gases. Energy of the produced high-temperature and high-pressure combustion gases is converted to energy of rotation by the turbine.  
         [0032]     In the example shown in  FIG. 4 , combustors  2   a - 2   f  are mounted within a casing  11  having a circular cross-section so as to lie on a circumference in concentric relation to the casing  11 , and each of the combustors  2   a - 2   f  is coupled to adjacent one through any of flame propagating pipes  10   a - 10   f . At the startup of the gas turbine, some of the combustors ( 2   a  and  2   f  in the illustrated example) are ignited by ignition plugs  29  mounted to those combustors  2   a ,  2   f . A flame produced with the ignition in the combustor  2   a  is propagated to the adjacent combustor  2   b  through the flame propagating pipe  10   a . Likewise, a flame produced in the combustor  2   f  is propagated to the adjacent combustor  2   e  through the flame propagating pipe  10   e . Subsequently, the flame is propagated from the combustor  2   b  to the combustor  2   c  through the flame propagating pipe  10   b , while the flame is propagated from the combustor  2   e  to the combustor  2   d  through the flame propagating pipe  10   d . In this way, the flame is successively propagated from one combustor to the next adjacent combustor in two opposite directions so that all the combustors are eventually ignited.  
         [0033]     Further, in the example shown in  FIG. 4 , the flame sensors  22  are mounted to the combustors  2   d ,  2   e  other than the combustors  2   a ,  2   f  provided with the ignition plugs  29 . When those two flame sensors  22  detect flames, it is determined that all the combustors have been ignited. With such a method of detecting a flame by the flame sensor  22 , however, the flame sensor  22  must be mounted to the combustor  2 . Also, since the combustor is subjected to an atmosphere at high temperatures under high pressures, the flame sensor  22  must be highly durable against such an atmosphere. Further, a cooling device (such as a water cooling jacket or an air cooling device) for cooling the flame sensor  22  is required in some cases.  
         [0034]     In view of the above-described situation, the gas turbine of the illustrated embodiment is intended to detect the establishment of ignition in the combustor by the following method with no need of using any flame sensor  22 .  
         [0035]      FIG. 5  shows one example of behavior of the gas turbine exhaust temperature at the time of ignition. Assuming that an ignition command is issued at a time indicated by (A) in  FIG. 1 , the exhaust temperature behaves as represented by a solid line  31   a  when ignition has succeeded in the case of the cold startup. When ignition has failed, the exhaust temperature behaves as represented by a one-dot chain line  32   a . On the other hand, in the case of the hot startup, the exhaust duct is not sufficiently cooled and high-temperature gases reside within the exhaust duct. Thus, since the exhaust temperature measured at the start of ignition is high, the exhaust temperature behaves as represented by a broken line  33   a  when ignition has succeeded, and behaves as represented by a two-dot chain line  34   a  when ignition has failed. As seen from  FIG. 5 , an absolute value of the exhaust temperature at the start of ignition greatly differs depending on the startup conditions of the gas turbine, and therefore it is difficult to determine the establishment of ignition based on the absolute value of the exhaust temperature.  
         [0036]     In order to avoid such a difficulty, one embodiment of the ignition detecting method is constituted as follows. Assuming that the exhaust temperature at a particular time not later than the issuance of the ignition command (at an ignition command outputting time (A) in this embodiment) is TX(A) and the exhaust temperature at a particular time after the issuance of the ignition command is TX, an exhaust temperature change amount (TX−TX(A)) is calculated on the basis of TX(A). As a result of the calculation, the respective behaviors of the exhaust temperature, shown in  FIG. 5 , are converted to behaviors of change amounts of the exhaust temperature as shown in  FIG. 6 . In other words, a solid line  31   b  represents the behavior of change amount of the exhaust temperature when ignition has succeeded in the case of the cold startup, and a one-dot chain line  32   b  represents that behavior when ignition has failed. Also, a broken line  33   b  represents the behavior of change amount of the exhaust temperature when ignition has succeeded in the case of the hot startup, and a two-dot chain line  34   b  represents that behavior when ignition has failed.  
         [0037]     Looking at a change of the exhaust temperature in terms of a change amount from a certain reference, as described above, the change amount of the exhaust temperature increases when ignition has succeeded, and it does not increase when ignition has failed, regardless of the startup conditions of the gas turbine, etc. In view of that point, the change amount of the exhaust temperature from the certain reference exhaust temperature TX(A) is computed and the establishment of ignition is determined when the change amount exceeds a predetermined value  41  within a certain ignition time as shown in  FIG. 6 . On the other hand, when the change amount from the reference exhaust temperature does not exceed the predetermined value  41  within the certain ignition time from the ignition command outputting time, this is determined as indicating an ignition failure.  
         [0038]     Further, as represented by  31   b  and  33   b , the change amounts of the exhaust temperature in the cases of the cold startup and the hot startup are varied substantially in the same way with the lapse of time when ignition has succeeded. Therefore, the predetermined value  41  of the change amount of the exhaust temperature, which is used as a reference for determining the establishment of ignition, can be set in common with both the cold startup and the hot startup. It is hence possible to eliminate the necessity of setting the predetermined value  41 , which is used to determine whether ignition has succeeded or not, for each of the cold startup and the hot startup. According to such a method, whether ignition has established in the combustor or not can be easily determined by using the exhaust temperature sensor. Additionally, when the change amount of the exhaust temperature does not reach the predetermined value  41  and an ignition failure is determined, the flow rate of fuel is reduced to 0 by the fuel flow adjuster  25  shown in  FIG. 1 .  
         [0039]     Another embodiment of the method for determining the establishment of ignition will be described with reference to  FIGS. 7 and 8 . This embodiment is intended to determine the establishment of ignition by measuring a change rate of the exhaust temperature per unit time after the outputting of the ignition command.  
         [0040]     In this embodiment, as shown in  FIG. 7 , a change rate ΔT/dt of the exhaust temperature per unit time after the outputting of the ignition command is calculated. As shown in  FIG. 8 , the change rate ΔT/dt of the exhaust temperature per unit time behaves as represented by a solid line  35  when ignition has been established, and behaves as represented by a one-dot chain line  36  when ignition has failed. When ignition has been normally established, the exhaust temperature is abruptly increased for a moment immediately after the outputting of the ignition command and so is the change rate ΔT/dt of the exhaust temperature as represented by the solid line  35 . Thereafter, the exhaust temperature rises while the temperature change rate gradually decreases. On the other hand, when ignition has failed, the exhaust temperature does not rise as a matter of course, and the change rate ΔT/dt of the exhaust temperature is not increased as represented by the one-dot chain line  36 .  
         [0041]     Thus, according to the method for determining the establishment of ignition with this embodiment, the establishment of ignition is determined when the calculated change rate ΔT/dt of the exhaust temperature per unit time exceeds a predetermined value  42  within a predetermined time from the outputting of the ignition command. When the calculated change rate does not reach the predetermined value  42  within the predetermined ignition time, this is determined as indicating an ignition failure and the flow rate of fuel is reduced to 0 by the fuel flow adjuster  25 .  
         [0042]     Thus, since the change rate ΔT/dt of the exhaust temperature is increased when ignition has succeeded and the change rate ΔT/dt of the exhaust temperature is not increased when ignition has failed, this embodiment can reliably detect the establishment of ignition in the combustor by comparing the change rate with a reference value regardless of the startup conditions of the gas turbine, etc., such as the cold startup or the hot startup.  
         [0043]     Still another embodiment of the method for determining the establishment of ignition in the combustor will be described with reference to  FIGS. 9 and 10 . This embodiment is intended to determine the establishment of ignition by measuring a change rate of the exhaust temperature per unit revolution speed after the outputting of the ignition command.  
         [0044]     In this embodiment, as shown in  FIG. 9 , a change rate ΔT/dn of the exhaust temperature per unit revolution speed of the gas turbine after the outputting of the ignition command is calculated. As shown in  FIG. 10 , the change rate ΔT/dn of the exhaust temperature per unit revolution speed behaves as represented by a solid line  37  when ignition has been established, and behaves as represented by a one-dot chain line  38  when ignition has failed. Then, according to the method for determining the establishment of ignition with this embodiment, the establishment of ignition is determined when the calculated change rate ΔT/dn of the exhaust temperature per unit revolution speed of the gas turbine exceeds a predetermined value  43  within a predetermined time from the outputting of the ignition command. When the calculated change rate of the exhaust temperature per unit revolution speed does not exceed the predetermined value  43  within a predetermined time from the outputting of the ignition command, this is determined as indicating an ignition failure and the flow rate of fuel is reduced to 0 by the fuel flow adjuster  25 .  
         [0045]     An ignition failure may also occur when the components of the gas turbine have no abnormality. If the gas turbine is completely stopped upon each ignition failure, it takes a substantial time until the next startup. In this embodiment, therefore, when an ignition failure is determined according to any of the above-described methods for determining the establishment of ignition in the combustor, the ignition command is outputted to the combustor again to repeat the ignition operation. Then, if an ignition failure is determined again with the second ignition operation, this is determined as indicating an abnormality in any component, and the operating mode is shifted the operation for stopping the gas turbine. As a result, reliability in operation of the gas turbine can be improved.  
         [0046]     With the embodiments described above, even when no flame sensors are installed, a highly reliable method for detecting a flame at the time of ignition can be provided by using a plurality of exhaust temperature sensors installed on the gas turbine outlet side. Also, a more reliable method for detecting a flame at the time of ignition can be provided by combination with the flame sensors.