Method for operating gas turbine combustor

In a method for operating a combustor of an embodiment, before ignition in the combustor, a mixed gas containing oxygen is circulated through the combustor as a circulating gas. Then, in an operating time from the time of ignition in the combustor to the time of a rated load of a turbine, from the time of ignition until reaching stable combustion conditions allowing stable combustion, a combustion gas in which a controller controls a flow rate of a fuel supplied from a fuel supply part and a flow rate of an oxidant supplied from an oxidant supply part to maintain the same oxygen concentration as an oxygen concentration in the mixed gas is circulated as the circulating gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-102469, filed on Jun. 21, 2021; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally a method for operating a gas turbine combustor.

BACKGROUND

In recent years, in power generation plant including a gas turbine combustor, increasing efficiency is in progress in response to demands for reduction of carbon dioxide, resource conservation, and the like. Under such circumstances, a gas turbine facility in which a part of carbon dioxide discharged from a turbine is circulated through a combustor is under consideration.

FIG.8schematically illustrates a vertical section of a combustor310provided in a conventional gas turbine facility300. As illustrated inFIG.8, the combustor310includes a combustor casing320, a combustor liner330, a fuel-oxidant supply part340, and a carbon dioxide supply pipe350.

In the combustor casing320, the combustor liner330and the fuel-oxidant supply part340are provided. The combustor liner330is constituted by a cylindrical member in which a fuel and an oxidant are combusted.

The fuel-oxidant supply part340is provided at one end (upstream end) of the combustor liner330. Note that at the other end (downstream end) of the combustor liner330, a transition piece360which guides a combustion gas discharged from the combustor liner330to a turbine is provided.

The fuel-oxidant supply part340includes a fuel supply pipe341and an oxidant supply pipe342. The fuel supply pipe341supplies the fuel into the combustor liner. The oxidant supply pipe342is provided around an outer periphery of the fuel supply pipe341, and supplies the oxidant into the combustor liner. A double-pipe structure is formed by the fuel supply pipe341and the oxidant supply pipe342.

The carbon dioxide supply pipe350is connected to the combustor casing320. The carbon dioxide supply pipe350supplies carbon dioxide to be circulated through the combustor310between the combustor casing320, and, the fuel-oxidant supply part340and the combustor liner330.

Here, flow rates of the fuel and the oxygen supplied to the combustor liner330are regulated so as to have a stoichiometric mixture ratio (equivalence ratio 1). The equivalence ratio which is mentioned here is calculated on the basis of the fuel flow rate and the oxygen flow rate. Note that the equivalence ratio is calculated by dividing a fuel-air ratio by a stoichiometric fuel-air ratio.

In the gas turbine facility300, the combustion gas discharged from the turbine, from which water vapor is separated, circulates through the combustor310. Most of components of the combustion gas from which the water vapor has been removed are carbon dioxide. Hence, the combustion gas circulated from the carbon dioxide supply pipe350to the combustor310is carbon dioxide.

The carbon dioxide circulated through the combustor310functions as a cooling medium and a dilution medium. The circulated carbon dioxide is heated by exchanging heat with the combustion gas discharged from the turbine through a regenerative heat exchanger, for example. Further, in the gas turbine facility300, carbon dioxide pressurized to a critical pressure or more is circulated to the combustor310, for example.

The carbon dioxide flowing between the combustor casing320and the combustor liner330is introduced from, for example, cooling holes331and a dilution hole332formed in the combustor liner330into the combustor liner330.

In the above-described gas turbine facility300, before initiating combustion in the combustor310, the carbon dioxide which is filled is circulated to the combustor310. Then, in a state in which the carbon dioxide is circulated through the combustor310, the operation of the combustor310is started.

In the time of turbine starting operation from the combustion initiation (ignition) in the combustor310to a turbine initial load, a pressure in the above-described combustor liner330is low in an initial time of turbine starting operation from the ignition to a predetermined time. In the low pressure state in the combustor liner330, a turbulent burning velocity is small. Hence, stable combustion cannot be obtained, which sometimes extinguishes flames.

Further, since the flow rates of the fuel and the oxygen supplied to the combustor liner330are set to the stoichiometric mixture ratio, the flow rate of oxygen is the minimum flow rate necessary for complete combustion. Moreover, carbon dioxide which is an inert gas is introduced around flames from the cooling holes331and the dilution hole332. Hence, the carbon dioxide flows into the flames, which makes the flames unstable.

As described above, in the initial time of turbine starting operation, in the combustor liner330, the turbulent burning velocity is small, and the combustion is performed in the state of mixing with the inert gas in addition to the absence of excess oxygen. Hence, the stable combustion cannot be obtained, which sometimes extinguishes the flames.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will be described in reference to the drawings.

In one embodiment, in a method for operating a gas turbine combustor, the gas turbine combustor includes: a casing; a combustor liner which is disposed in the casing and combusts a fuel and an oxidant; a fuel supply part which supplies the fuel to the combustor liner; an oxidant supply part which supplies the oxidant to the combustor liner; and a controller which controls a flow rate of the fuel supplied from the fuel supply part and a flow rate of the oxidant supplied from the oxidant supply part, in which through a circulation system connecting an outlet of a turbine and the casing, an exhaust gas discharged from the turbine is circulated in the casing as a circulating gas, and the circulating gas is introduced into the combustor liner through through holes provided in the combustor liner.

In the method for operating the gas turbine combustor, before ignition in the gas turbine combustor, a mixed gas containing oxygen in a predetermined concentration is circulated as the circulating gas. Then, in an operating time from a time of ignition in the gas turbine combustor to a time of a rated load of the turbine, from the time of ignition until reaching stable combustion conditions allowing stable combustion, a combustion gas is circulated as the circulating gas. The combustion gas is maintained a same oxygen concentration as an oxygen concentration in the mixed gas by controlling the flow rate of the fuel supplied from the fuel supply part and the flow rate of the oxidant supplied from the oxidant supply part by the controller.

FIG.1is a system diagram of a gas turbine facility1in which the method for operating the combustor of the embodiment is performed. As illustrated inFIG.1, the gas turbine facility1includes a combustor10, a fuel supply part40, an oxidant supply part50, a gas circulation system60, a turbine70, a generator75, a regenerative heat exchanger80, and a controller100. Note that the combustor10functions as a gas turbine combustor.

The fuel supply part40supplies a fuel to the combustor10. The fuel supply part40includes a pipe41. The pipe41is provided between a fuel supply source (not illustrated) and the combustor10. Further, the pipe41is provided with a flow rate regulating valve42which regulates a flow rate of the fuel.

Here, as the fuel, for example, hydrocarbon such as methane or natural gas is used. Further, as the fuel, for example, a coal gasification gas fuel containing carbon monoxide, hydrogen, and the like can also be used.

The oxidant supply part50supplies an oxidant to the combustor10. The oxidant supply part50includes a pipe51. The pipe51is provided between an air separating apparatus (not illustrated) which separates oxygen from the air and the combustor10, for example. The pipe51is provided with a flow rate regulating valve52which regulates a flow rate of the oxidant.

Here, as the oxidant, for example, oxygen, a mixed gas in which carbon dioxide is mixed with oxygen, or the like can be cited. As the carbon dioxide contained in the mixed gas, for example, a part of carbon dioxide flowing through the gas circulation system60is used.

Note that a compressor which pressurizes the oxidant is provided in the pipe51though not illustrated. For example, even when a circulating gas pressurized to a critical pressure or more depending on operating conditions flows through the gas circulation system60, this compressor can pressurize the oxidant to a pressure allowing supply to the combustor10.

Further, the oxidant may be heated by passing the pipe51through the regenerative heat exchanger80and supplied to the combustor10. In this case, the flow rate regulating valve52is provided on a more upstream side than the regenerative heat exchanger80.

The gas circulation system60includes a pipe61which circulates a circulating gas discharged from the turbine70through the combustor10. The pipe61is provided between an outlet of the turbine70and the combustor10.

Here, when the fuel and the oxidant are combusted in the combustor10, a combustion gas circulates as the circulating gas. Note that this combustion gas is a mixed gas of the combustion gas produced by the combustion of the fuel and the oxidant and the circulating gas introduced into a later-described combustor liner20.

Further, before starting the turbine (before combusting the fuel and the oxidant in the combustor10), the mixed gas with which the gas circulation system60is filled beforehand and which contains oxygen in a predetermined concentration in carbon dioxide circulates as the circulating gas.

The pipe61is provided with a condenser62which removes water vapor contained in the combustion gas. Note that the water vapor in the combustion gas passes through the condenser62, thereby condensing into water. The water is discharged through a pipe (not illustrated) to the outside, for example.

Further, the pipe61is provided with a compressor63which pressurizes the circulating gas. The compressor63pressurizes the combustion gas from which the water vapor has been removed in the condenser62, for example. The compressor63can pressurize the combustion gas from which the water vapor has been removed to, for example, the critical pressure or more depending on the operating conditions. The condenser62and the compressor63are provided in the pipe61in an area through which the combustion gas cooled by the regenerative heat exchanger80flows.

The pipe61is provided to pass through the regenerative heat exchanger80twice. That is, the pipe61passes through the regenerative heat exchanger80once between the turbine70and the condenser62. Then, the pipe61passes through the regenerative heat exchanger80again between the compressor63and the combustor10.

Here, the combustion gas (circulating gas) discharged from the turbine70is cooled by passing through the regenerative heat exchanger80. At this time, the circulating gas passing through the pipe61to circulate through the combustor10is heated by heat release from the combustion gas.

Note that the pipe61between the compressor63and the regenerative heat exchanger80is provided with a pipe branching from the pipe61though the pipe is not illustrated. Thus, a part of the circulating gas is discharged through the branch pipe to the outside.

The turbine70is rotationally moved by the combustion gas discharged from the combustor10. For example, a generator75which generates electricity by making use of the rotational movement of the turbine70is connected to the turbine70.

The controller100controls the flow rate regulating valve42, the flow rate regulating valve52, and the like to regulate the flow rates of the fuel and the oxidant supplied to the combustor10, and the like.

Here,FIG.2is a block diagram illustrating a configuration of a controller100which executes the method for operating the combustor10of the embodiment. The controller100includes an input unit110, a storage unit120, a calculation unit130, and an output unit140.

To the input unit110, for example, an ignition request signal and a load request signal from an input device or the like, a timer signal from a timer or the like, detection signals from various detection units, and the like are input.

The storage unit120is constituted by storage mediums such as read-only memory (ROM) and random access memory (RAM). The storage unit120stores turbine starting operation-time data121indicating a relationship between an operating time in the time of turbine starting operation from combustion initiation (ignition) in the combustor10to a turbine initial load, and, the fuel flow rate and the oxidant flow rate, and the like, for example. That is, in the turbine starting operation-time data121, for example, data of the flow rates of the fuel and the oxidant supplied to the combustor10every predetermined time from the time of ignition to the time of the turbine initial load is stored.

Further, the storage unit120stores turbine load operation-time data122indicating a relationship between the fuel flow rate and the oxidant flow rate corresponding to a turbine load in the time of turbine load operation from the turbine initial load to a rated load, or the like, for example.

Note that in the respective pieces of the above-described data, information of valve opening degrees of the flow rate regulating valves corresponding to the flow rates or the like is also stored.

Here, the time of turbine starting operation is referred to as an operating period from the time of combustion initiation (the time of ignition) in the combustor10to the time of the turbine initial load. Further, in the time of turbine starting operation, the time from the ignition to a predetermined time entering a stable combustion zone is referred to as an initial time of turbine starting operation. Note that the stable combustion zone is a range satisfying stable combustion conditions allowing combustion in which combustion conditions are stable, and the stable combustion zone will be described later.

The turbine starting operation-time data121is data obtained in a turbine starting operation test in an actual machine. Further, the turbine load operation-time data122is data obtained in a turbine load operation test in the actual machine.

The calculation unit130executes various kinds of calculation processing by using input signals from the input unit110, programs and the data stored in the storage unit120, and the like, for example. The calculation unit130includes an elapsed time determining unit131, a fuel-oxidant flow rate determining unit132, and the like.

The elapsed time determining unit131determines an elapsed time from the time of ignition, or the like on the basis of the timer signal from the input unit110.

The fuel-oxidant flow rate determining unit132specifies the flow rates of the fuel and the oxidant supplied to the combustor10in the time of turbine starting operation on the basis of a determination result in the elapsed time determining unit131and the turbine starting operation-time data121.

Further, the fuel-oxidant flow rate determining unit132performs a calculation operation of the flow rates of the fuel and the oxidant supplied to the combustor10in the time of turbine load operation on the basis of the load request signal in the time of a turbine load and the turbine load operation-time data122.

The output unit140outputs control signals from the calculation unit130to, for example, the flow rate regulating valves42,52, or the like. Note that the output unit140is communicably connected with the flow rate regulating valves42,52, or the like.

Here, the processing executed by the above-described controller100is implemented by, for example, a computer device or the like.

Next, a configuration of the combustor10will be described.

FIG.3schematically illustrates a vertical section of the combustor10in which the method for operating the combustor of the embodiment is performed. As illustrated inFIG.3, the combustor10includes a combustor casing15, a combustor liner20, and a fuel-oxidant supply part30.

The combustor casing15is constituted by a cylinder body housing the combustor liner20and the fuel-oxidant supply part30.

The combustor liner20is constituted by a cylindrical member in which the fuel and the oxidant are combusted. One end (upstream end) of the combustor liner20is blocked by an upstream end wall21, and the other end (downstream end) thereof is opened. Note that at the other end (downstream end) of the combustor liner20, a transition piece90which guides the combustion gas discharged from the combustor liner20to the turbine70is provided.

The combustor liner20is constituted by a linearly extending cylinder body or the like, for example. Note that the combustor liner20may be constituted by a partially curved cylinder body or the like, for example.

In a side portion of the combustor liner20, cooling holes22and a dilution hole23which introduce the circulating gas introduced from the pipe61into the combustor casing15into the combustor liner20are formed. Note that the cooling holes22and the dilution hole23function as through holes.

The cooling hole22is constituted by a cooling hole for film cooling, or the like, for example. Further, the dilution hole23is constituted by the through hole formed in a direction perpendicular to a direction of the center axis of the combustor liner20, or the like, for example.

The fuel-oxidant supply part30penetrates the combustor casing15, and the downstream end of the fuel-oxidant supply part30is disposed at the one end (upstream end) of the combustor liner20. Specifically, for example, the downstream end of the fuel-oxidant supply part30is fitted into a through opening21aformed in the upstream end wall21not to project into the combustor liner20.

The fuel-oxidant supply part30includes a fuel supply pipe31and an oxidant supply pipe32.

The fuel supply pipe31supplies the fuel into the combustor liner20. The fuel supply pipe31is constituted by a cylindrical pipe or the like, for example. The fuel supply pipe31is coupled to the pipe41which supplies the fuel. An outlet31aof the fuel supply pipe31provides a function as a fuel nozzle, for example. The outlet31ais constituted by a single-hole fuel injection hole, a multi-hole fuel ejection hole, or the like, for example. The fuel is ejected from the outlet31aof the fuel supply pipe31into the combustor liner20.

The oxidant supply pipe32supplies the oxidant into the combustor liner20. An outer periphery at a downstream end of the oxidant supply pipe32is fitted into the through opening21aof the upstream end wall21. The oxidant supply pipe32is constituted by a cylindrical pipe having an inside diameter larger than an outside diameter of the fuel supply pipe31, or the like, for example.

The oxidant supply pipe32is provided around an outer periphery of the fuel supply pipe31, as illustrated inFIG.3, for example. For example, the center axis of the oxidant supply pipe32is on the same axis as the center axis of the fuel supply pipe31. This causes an annular passage to be formed around the outer periphery of the fuel supply pipe31.

Thus, for example, the fuel supply pipe31and the oxidant supply pipe32are formed in a double-pipe structure. The fuel is ejected from the central fuel ejection hole and the oxidant is ejected from the annular flow passage formed around the central fuel ejection hole. That is, a diffusion combustion system is adopted to the combustor10.

At an outlet32aof the annular passage between the fuel supply pipe31and the oxidant supply pipe32, for example, a swirler33which forms swirling flow of the oxidant is provided. The swirler33is provided with a plurality of blades in a circumferential direction in the annular passage. The blades are disposed to be inclined at a predetermined angle to the axial direction of the annular passage.

The oxidant passes through the swirler33, and thereby the swirling flow having a circumferential velocity component is ejected into the combustor liner20. Thus, shaping the oxidant into the swirling flow causes mixing of the fuel and the oxidant to be promoted to form stable flames in the combustor liner20.

The pipe61which circulates the circulating gas is connected to the combustor casing15. The pipe61is connected to a side portion of the combustor casing15on a side where the fuel-oxidant supply part30penetrates it, for example.

The pipe61supplies the circulating gas between the combustor casing15, and, the fuel-oxidant supply part30and the combustor liner20. The circulating gas is introduced from the previously-described cooling holes22and dilution hole23of the combustor liner20into the combustor liner20as a cooling medium or a dilution medium.

The circulating gas introduced into the combustor liner20is introduced around or down flames formed in the combustor liner20. The flames burn while catching the introduced circulating gas. In other words, a combustion reaction progresses while the circulating gas is mixed in a combustion zone where the flames are formed.

Next, a method for operating the combustor10will be described.

FIG.4is a time chart for explaining the method for operating the combustor10of the embodiment.FIG.5is a flow chart for explaining the method for operating the combustor10of the embodiment.

Here, a horizontal axis inFIG.4indicates a time. A vertical axis inFIG.4indicates a pressure ratio in the combustor10, a fuel flow ratio, an oxidant flow ratio, an equivalence ratio, and an oxygen concentration (wt %) of the circulating gas. Note that in a portion indicating the pressure ratio in the combustor10inFIG.4, a range of the later-described stable combustion zone is indicated with oblique lines.

Here, the pressure ratio in the combustor10is a pressure ratio in the combustor liner20. In the pressure ratio in the combustor10, a pressure in the combustor liner20at each time, when the pressure in the combustor liner20at the time of the rated load of the turbine is set to 1, is indicated by a ratio. In the fuel flow ratio, a fuel flow rate at each time, when the fuel flow rate at the time of the rated load of the turbine is set to 1, is indicated by a ratio. In the oxidant flow ratio, an oxidant flow rate at each time, when the oxidant flow rate at the time of the rated load of the turbine is set to 1, is indicated by a ratio.

Further, the oxygen concentration is an oxygen concentration in the circulating gas introduced to the combustor10. That is, it is the oxygen concentration in the circulating gas introduced from the pipe61into the combustor casing15.

As the equivalence ratio, a local equivalence ratio φl in the fuel-oxidant supply part30and a total equivalence ratio φt in the combustor10(combustor liner20) are indicated.

The local equivalence ratio φl is an equivalence ratio calculated on the basis of flow rates of the fuel and the oxygen supplied to the fuel-oxidant supply part30. In other words, the local equivalence ratio φl is the equivalence ratio calculated on the basis of the flow rate of the fuel ejected from the fuel supply pipe31into the combustor liner20and the flow rate of the oxygen ejected from the oxidant supply pipe32into the combustor liner20.

The total equivalence ratio φt is an equivalence ratio calculated on the basis of flow rates of the fuel and the oxygen supplied to the combustor10. That is, the total equivalence ratio φt is calculated also in consideration of a flow rate of oxygen contained in the circulating gas supplied into the combustor liner20. In other words, the total equivalence ratio φt is the equivalence ratio calculated on the basis of the flow rate of the fuel ejected from the fuel supply pipe31into the combustor liner20, and the flow rates of the oxygen ejected from the oxidant supply pipe32into the combustor liner20and the oxygen contained in the circulating gas introduced into the combustor liner20.

Incidentally, the above-described local equivalence ratio φl and total equivalence ratio φt are each calculated by dividing a fuel-air ratio by a stoichiometric fuel-air ratio.

InFIG.4, the time of turbine starting operation is from a time t1to a time t4(the time t1or more to less than the time t4). In the time of turbine starting operation, the initial time of turbine starting operation is from the time t1to a time t3(the time t1or more to less than the time t3). The time of turbine load operation is from the time t4to a time t5(the time t4or more to less than the time t5).

In the gas turbine facility1, before starting the turbine, that is, before initiating combustion in the combustor10(less than the time t1), the mixed gas with which the gas circulation system60is filled beforehand is circulated through the combustor10as the circulating gas. That is, the mixed gas circulates through the pipe61, the combustor10, and the turbine70. The mixed gas is pressurized by the compressor63in the circulation.

Here, the mixed gas is carbon dioxide in which oxygen is contained in a predetermined concentration. The oxygen concentration in the mixed gas is set in a range of 10 to 15 wt %.FIG.4illustrates one example when the oxygen concentration in the mixed gas is set to 15 wt %. Incidentally, the reason why the oxygen concentration in the mixed gas is set in this range is described later.

In a state in which the mixed gas is circulated through the combustor10, the oxidant and the fuel are supplied to the combustor10, and ignited by an ignition device. Here, the time of ignition (time t1) functions as a first time.

As illustrated inFIG.5, the fuel-oxidant flow rate determining unit132of the controller100determines whether or not an ignition start signal is input in the input unit110(Step S10).

In the determination of Step S10, when the ignition start signal is determined not to be input (No in Step S10), the fuel-oxidant flow rate determining unit132executes the processing of Step S10again.

In the determination of Step S10, when the ignition start signal is determined to be input (Yes in Step S10), the fuel-oxidant flow rate determining unit132executes control for ignition (Step S11).

In Step S11, the fuel-oxidant flow rate determining unit132specifies the flow rates of the fuel and the oxidant supplied to the combustor10at the time of ignition in reference to the turbine starting operation-time data121. Then, the fuel-oxidant flow rate determining unit132outputs signals for supplying the oxidant and the fuel to the fuel-oxidant supply part30of the combustor10to the output unit140.

The output unit140outputs the signals from the fuel-oxidant flow rate determining unit132to the flow rate regulating valve52and the flow rate regulating valve42. This causes adjustment of opening degrees of the flow rate regulating valve52and the flow rate regulating valve42and supply of the fuel and the oxidant at predetermined flow rates through the fuel-oxidant supply part30into the combustor liner20.

At this time, the local equivalence ratio is set to be a first equivalence ratio. Here, the first equivalence ratio is set in a range of 0.8 to 0.9.FIG.4illustrates one example when the first equivalence ratio is set to 0.84. Incidentally, the reason why the first equivalence ratio is set in this range is described later.

Hence, the fuel and the oxidant are ejected from the fuel supply pipe31and from the oxidant supply pipe32into the combustor liner20, and ignited by the ignition device to form flames. (Time t1to time t2)

As illustrated inFIG.5, the fuel-oxidant flow rate determining unit132determines whether or not a detection signal from a flame detector is input in the input unit110(Step S12).

In the determination of Step S12, when the detection signal is determined not to be input during a predetermined time (No in Step S12), the fuel-oxidant flow rate determining unit132stops the supply of the fuel and the oxidant to the combustor10, for example. Then, for example, the operation of the combustor10is stopped.

In the determination of Step S12, when the detection signal is determined to be input (Yes in Step S12), the fuel-oxidant flow rate determining unit132executes control of reducing the local equivalence ratio φl (Step S13).

In Step S13, as illustrated inFIG.4, the fuel-oxidant flow rate determining unit132executes the control of reducing the local equivalence ratio φl from after detecting the detection signal from the flame detector which is input in the input unit110, that is, after the ignition (after the time t1) to a second time (time t2) later than the time t1(from after the time t1to less than the time t2), for example. Note that the time t2functions as the second time.

Here, in the combustor10, the local equivalence ratio φl is gradually reduced from the first equivalence ratio to a second equivalence ratio smaller than the first equivalence ratio while the fuel flow rate and the oxidant flow rate are increased.

At this time, the oxygen concentration in the circulating gas circulated through the combustor10is maintained in the same concentration as the oxygen concentration in the mixed gas circulated through the combustor10before the ignition (15 wt % inFIG.4). In other words, the local equivalence ratio φl is reduced while the total equivalence ratio φt is maintained constant.

Here, the second equivalence ratio is set in a range of 0.35 to 0.45.FIG.4illustrates one example when the second equivalence ratio is set to 0.40. Incidentally, the reason why the second equivalence ratio is set in this range is described later.

Specifically, the elapsed time determining unit131determines an elapsed time from the time t1on the basis of an output signal from the timer, and outputs its determination information to the fuel-oxidant flow rate determining unit132. The fuel-oxidant flow rate determining unit132specifies the flow rates of the fuel and the oxidant supplied to the combustor10, which correspond to the elapsed time from the time t1, on the basis of the determination information from the elapsed time determining unit131and the turbine starting operation-time data121.

Then, the fuel-oxidant flow rate determining unit132outputs signals for supplying the oxidant and the fuel at predetermined flow rates to the fuel-oxidant supply part30of the combustor10to the output unit140every predetermined elapsed time.

The output unit140outputs the signals from the fuel-oxidant flow rate determining unit132to the flow rate regulating valve52and the flow rate regulating valve42. This causes adjustment of the opening degrees of the flow rate regulating valve52and the flow rate regulating valve42and supply of the fuel and the oxidant at the predetermined flow rates through the fuel-oxidant supply part30into the combustor liner20.

As illustrated inFIG.5, the elapsed time determining unit131determines whether or not to reach the time t2on the basis of an output signal from the timer (Step S14).

In the determination of Step S14, for determination not to reach the time t2(No in Step S14), the elapsed time determining unit131outputs a determination result thereof to the fuel-oxidant flow rate determining unit132. Then, the fuel-oxidant flow rate determining unit132continues the processing of Step S13.

In the determination of Step S14, for determination to reach the time t2(Yes in Step S14), the elapsed time determining unit131outputs a determination result thereof to the fuel-oxidant flow rate determining unit132. Then, the fuel-oxidant flow rate determining unit132executes control for maintaining the local equivalence ratio φl constant (Step S15).

In Step S15, as illustrated inFIG.4, the fuel-oxidant flow rate determining unit132executes the control of maintaining the local equivalence ratio φl constant from the time t2to a third time (time t3) later than the time t2(from the time t2or more to less than the time t3). Note that the time t3functions as the third time.

Here, in the combustor10, the local equivalence ratio φl is maintained at the second equivalence ratio while the fuel flow rate and the oxidant flow rate are increased.

At this time, the oxygen concentration in the circulating gas circulated through the combustor10is maintained in the same concentration as the oxygen concentration in the mixed gas circulated through the combustor10before the ignition (15 wt % inFIG.4). In other words, the local equivalence ratio φl is maintained at the second equivalence ratio while the total equivalence ratio φt is maintained constant. Note that at the time t3, combustion conditions satisfy the stable combustion conditions, and a combustion state reaches the later-described stable combustion zone.

Further, the elapsed time determining unit131determines an elapsed time from the time t2(or the elapsed time from the time t1) on the basis of an output signal from the timer, for example. The elapsed time determining unit131outputs determination information of the elapsed time to the fuel-oxidant flow rate determining unit132.

The fuel-oxidant flow rate determining unit132specifies the flow rates of the fuel and the oxidant supplied to the combustor10, which correspond to the elapsed time from the time t2, on the basis of the determination information from the elapsed time determining unit131and the turbine starting operation-time data121.

Then, the fuel-oxidant flow rate determining unit132outputs signals for supplying the oxidant and the fuel at predetermined flow rates to the fuel-oxidant supply part30of the combustor10to the output unit140every predetermined elapsed time.

The output unit140outputs the signals from the fuel-oxidant flow rate determining unit132to the flow rate regulating valve52and the flow rate regulating valve42. This causes adjustment of the opening degrees of the flow rate regulating valve52and the flow rate regulating valve42and supply of the fuel and the oxidant at the predetermined flow rates through the fuel-oxidant supply part30into the combustor liner20.

As illustrated inFIG.5, the elapsed time determining unit131determines whether or not to reach the time t3on the basis of an output signal from the timer (Step S16).

In the determination of Step S16, for determination not to reach the time t3(No in Step S16), the elapsed time determining unit131outputs a determination result thereof to the fuel-oxidant flow rate determining unit132. Then, the fuel-oxidant flow rate determining unit132continues the processing of Step S15.

In the determination of Step S16, for determination to reach the time t3(Yes in Step S16), the elapsed time determining unit131outputs a determination result thereof to the fuel-oxidant flow rate determining unit132. Then, the fuel-oxidant flow rate determining unit132executes control for increasing the local equivalence ratio φl (Step S17).

In Step S17, as illustrated inFIG.4, the fuel-oxidant flow rate determining unit132executes the control of increasing the local equivalence ratio φl from the time t3to a fourth time (time t4) later than the time t3(from the time t3or more to less than the time t4).

Here, in the combustor10, there is illustrated one example in which the local equivalence ratio φl is increased from the second equivalence ratio to a third equivalence ratio larger than the second equivalence ratio by increasing the flow rate of the fuel while the flow rate of the oxidant is maintained constant. Note that also by increasing the flow rate of the fuel while the flow rate of the oxidant is increased, the local equivalence ratio φl may be increased from the second equivalence ratio to the third equivalence ratio larger than the second equivalence ratio.

At this time, the oxygen concentration in the circulating gas circulated to the combustor10is lowered from the same oxygen concentration as the oxygen concentration in the mixed gas circulated to the combustor10before the ignition (15 wt % inFIG.4).

Here, the third equivalence ratio is set to 1.0. In the gas turbine facility1, excess oxygen and fuel preferably do not remain in the combustion gas discharged from the combustor10at the time of the rated load of the turbine. Therefore, from the time t3to the time t4, increasing the local equivalence ratio φl to 1.0 reduces the oxygen concentration in the circulating gas.

Further, the elapsed time determining unit131determines an elapsed time from the time t3(or the elapsed time from the time t1) on the basis of an output signal from the timer, for example. The elapsed time determining unit131outputs determination information of the elapsed time to the fuel-oxidant flow rate determining unit132.

The fuel-oxidant flow rate determining unit132specifies the flow rates of the fuel and the oxidant supplied to the combustor10, which correspond to the elapsed time from the time t3, on the basis of the determination information from the elapsed time determining unit131and the turbine starting operation-time data121.

Then, the fuel-oxidant flow rate determining unit132outputs signals for supplying the oxidant and the fuel at predetermined flow rates to the fuel-oxidant supply part30of the combustor10to the output unit140every predetermined elapsed time.

The output unit140outputs the signals from the fuel-oxidant flow rate determining unit132to the flow rate regulating valve52and the flow rate regulating valve42. This causes adjustment of the opening degrees of the flow rate regulating valve52and the flow rate regulating valve42and supply of the fuel and the oxidant at the predetermined flow rates through the fuel-oxidant supply part30into the combustor liner20.

As illustrated inFIG.5, the elapsed time determining unit131determines whether or not to reach the time t4on the basis of an output signal from the timer (Step S18).

In the determination of Step S18, for determination not to reach the time t4(No in Step S18), the elapsed time determining unit131outputs a determination result thereof to the fuel-oxidant flow rate determining unit132. Then, the fuel-oxidant flow rate determining unit132continues the processing of Step S17.

In the determination of Step S18, for determination to reach the time t4(Yes in Step S18), the elapsed time determining unit131outputs a determination result thereof to the fuel-oxidant flow rate determining unit132. Then, the fuel-oxidant flow rate determining unit132executes control for maintaining the local equivalence ratio φl constant (Step S19).

In Step S19, as illustrated inFIG.4, the fuel-oxidant flow rate determining unit132executes the control of maintaining the local equivalence ratio φl constant from the time t4to a fifth time (time t5) later than the time t4(from the time t4or more to less than the time t5).

Here, in the combustor10, the local equivalence ratio φl is maintained at the third equivalence ratio while the fuel flow rate and the oxidant flow rate are increased.

At this time, the oxygen concentration in the circulating gas circulated to the combustor10is lowered from the oxygen concentration in the circulating gas at the time t4. Then, the oxygen concentration in the circulating gas at the time t5becomes “0” wt %. That is, at the time t5, the circulating gas does not contain oxygen. Further, at the time t5, the total equivalence ratio φt becomes the third equivalence ratio (1.0) the same as the local equivalence ratio φl.

Note that a turbine load starts to be generated from the time t4. The time t5is the time of the rated load of the turbine.

From the time t4on (the time t4or more), control based on load regulating operation is executed. The fuel-oxidant flow rate determining unit132specifies the flow rates of the fuel and the oxidant supplied to the combustor10on the basis of the load request signal and the turbine load operation-time data to maintain the local equivalence ratio φl at the third equivalence ratio while the fuel flow rate and the oxidant flow rate are increased in the load regulating operation.

Then, the fuel-oxidant flow rate determining unit132outputs signals for supplying the oxidant and the fuel at predetermined flow rates to the fuel-oxidant supply part30of the combustor10to the output unit140.

The output unit140outputs the signals from the fuel-oxidant flow rate determining unit132to the flow rate regulating valve52and the flow rate regulating valve42. This causes adjustment of the opening degrees of the flow rate regulating valve52and the flow rate regulating valve42and supply of the fuel and the oxidant at the predetermined flow rates through the fuel-oxidant supply part30into the combustor liner20.

(Grounds for Ranges of Oxygen Concentration in Mixed Gas, First Equivalence Ratio, and Second Equivalence Ratio)

Here, the reason why the oxygen concentration in the mixed gas, the first equivalence ratio, and the second equivalence ratio are set in the previously described ranges will be described.

FIG.6is a chart for explaining a flame holding range in the initial time of turbine starting operation of the combustor10according to the embodiment.FIG.7is a chart for explaining the stable combustion zone in the combustor10according to the embodiment.

Here, inFIG.6, a horizontal axis indicates the oxygen concentration (wt %) in the circulating gas, and a vertical axis indicates the local equivalence ratio φl. InFIG.6, the flame holding range in the time of the time t1to the time t3which is the initial time of turbine starting operation is indicated with solid lines, and the flame holding range in the stable combustion zone is indicated with dotted lines.

Further,FIG.6illustrates a relationship between the oxygen concentration in the circulating gas and the local equivalence ratio φl in the time of the time t1to the time t3which is the initial time of turbine starting operation. At the time t1inFIG.6, the oxygen concentration in the mixed gas is 15 wt %, and the local equivalence ratio φl is 0.9. At the time t2and the time t3inFIG.6, the oxygen concentration in the mixed gas is 15 wt %, and the local equivalence ratio φl is 0.35.

Here, the flame holding range is a range where flames can be maintained in the combustor10. The flame holding ranges are between the two solid lines and between the two dotted lines.

InFIG.7, a horizontal axis indicates a time from the time of ignition (time t1) to the time of the rated load of the turbine (time t5), and a vertical axis indicates a turbulent burning velocity ratio. InFIG.7, the turbulent burning velocity ratio from the time of ignition (time t1) to the time of the rated load of the turbine (time t5) is indicated with a solid line. Further, inFIG.7, the stable combustion zone is indicated with oblique lines.

Here, in the turbulent burning velocity ratio, a turbulent burning velocity in the combustor liner20at each time, when the turbulent burning velocity in the combustor liner20at the time of ignition (time t1) is set to 1, is indicated by a ratio. Note that the turbulent burning velocity is obtained by a numerical analysis.

Further, the flame holding ranges illustrated inFIG.6and the stable combustion zone illustrated inFIG.7are obtained on the basis of the test results in the actual machine.

As illustrated inFIG.6, the flame holding range in the initial time of turbine starting operation is smaller than the flame holding range in the stable combustion zone. Further, the flame holding range with respect to the local equivalence ratio φl in the initial time of turbine starting operation increases as the oxygen concentration in the circulating gas increases.

In a range where the oxygen concentration in the circulating gas is 10 to 15 wt %, in a state of maintaining the oxygen concentration in the circulating gas constant, even the local equivalent ratio φl is reduced to the local equivalent ratio φl at time t2and time t3, the condition will still be in the flame holding range.

Further, setting the local equivalence ratios φl and the oxygen concentration in the circulating gas at the time t1, the time t2and the time t3in the previously described ranges allows the flame holding range to be maintained even though the respective conditions vary in presumable ranges.

From such reasons, the oxygen concentration in the mixed gas, the first equivalence ratio, and the second equivalence ratio are set in the previously described ranges.

Here, as illustrated inFIG.7, the turbulent burning velocity ratio increases rapidly in the initial time of turbine starting operation (the time t1to the time t3) after the ignition (after t1). This increase in the turbulent burning velocity ratio results from an increase in the turbulent burning velocity with a rise in pressure in the combustor10(in the combustor liner20).

In general, the stability of flames improves with an increase in turbulent burning velocity. In the combustor10, the stable combustion zone can be obtained in a range where the turbulent burning velocity ratio is five or more. That is, the combustion conditions of the stable combustion zone satisfy the turbulent burning velocity ratio of five or more which is under the stable combustion conditions.

This stable combustion zone is a zone where stable flames can be obtained in the time of turbine starting operation and the time of turbine load operation regardless of the condition of the oxygen concentration in the circulating gas. In the stable combustion zone, for example, the stable flames can be obtained even under the zero condition of the oxygen concentration in the circulating gas.

Here, in general, a turbulent burning velocity increases when a pressure in a combustor is increased. In the combustor10, as illustrated inFIG.4, the pressure is increased from the time t1toward the time t5, and thereby the turbulent burning velocity also increases. The reason for falling within the stable combustion zone from the time t3on (the time t3or more) is considered to be that the turbulent burning velocity becomes a velocity equal to or more than a certain constant level, which is unlikely to extinguish flames.

The combustion conditions in the initial time of turbine starting operation (the time t1to the time t3) in the combustor10do not fall within the stable combustion zone. However, the stable flames are maintained by setting the combustion conditions in the initial time of turbine starting operation to the oxygen concentration in the mixed gas, the first equivalence ratio, and the second equivalence ratio which are previously described.

That is, in the initial time of turbine starting operation (the time t1to the time t3), as illustrated inFIG.4, by maintaining the oxygen concentration in the circulating gas in the range of 10 to 15 wt %, oxygen is sufficiently supplied to flames to maintain the stable flames even in the range where the turbulent burning velocity ratio is less than five.

Further, the combustion conditions from the time t3to the time t5fall within the stable combustion zone, thereby maintaining the stable flames even though the oxygen concentration in the circulating gas is set to less than 10 wt %, and further zero.

As described above, according to the method for operating the gas turbine combustor of the embodiment, in the time of turbine starting operation, by containing oxygen in the circulating gas, oxygen is supplied by the circulating gas introduced to the combustion area in the combustor liner20also in addition to oxygen supplied from the fuel-oxidant supply part30. This allows oxygen to be sufficiently supplied to flames to maintain the stable flames.

Further, in the initial time of turbine starting operation when the turbulent burning velocity is low and flames become unstable, maintaining the oxygen concentration in the circulating gas constant in the range of 10 to 15 wt % allows oxygen to be sufficiently supplied to flames to prevent the flames from being extinguished. Hence, the stable flames can be maintained even in the initial time of turbine starting operation.

According to the above described embodiment, it becomes possible to perform stable combustion in the initial time of turbine starting operation.