Patent Publication Number: US-2020284194-A1

Title: Process for controlling oxidant flows in operation of a power generation plant

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-155406, filed on Jul. 26, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a gas turbine facility. 
     BACKGROUND 
     Increasing efficiency of power generation plants is in progress in response to demands for reduction of carbon dioxide, resource conservation, and the like. Specifically, increasing temperature of working fluid of a gas turbine and a steam turbine, employing a combined cycle, and the like are actively in progress. Further, research and development of collection techniques of carbon dioxide are in progress. 
       FIG. 5  is a system diagram of a conventional gas turbine facility in which a part of carbon dioxide generated in a combustor is circulated as working fluid. As illustrated in  FIG. 5 , oxygen separated from an air separator (not illustrated) is compressed by a compressor  310 , and its flow rate is controlled by a flow rate regulating valve  311 . The oxygen which has passed through the flow rate regulating valve  311  is heated by receiving a heat quantity from combustion gas in a heat exchanger  312 , and is supplied to a combustor  313 . 
     Fuel is regulated in flow rate by a flow rate regulating valve  314  and is supplied to the combustor  313 . This fuel is hydrocarbon. The fuel and oxygen react (combust) in the combustor  313 . When the fuel combusts with oxygen, carbon dioxide and water vapor are generated as combustion gas. The flow rates of fuel and oxygen are regulated to be of a stoichiometric mixture ratio in a state that they are completely mixed. 
     The combustion gas generated in the combustor  313  is introduced into a turbine  315 . The combustion gas which performed an expansion work in the turbine  315  passes through the heat exchanger  312  and then further through a heat exchanger  316 . When passing through the heat exchanger  316 , the water vapor condenses into water. The water passes through a pipe  319  and is discharged to the outside. 
     The carbon dioxide separated from the water vapor is compressed by a compressor  317 . A part of the compressed carbon dioxide is regulated in flow rate by a flow rate regulating valve  318  and is extracted to the outside. The rest of the carbon dioxide is heated in the heat exchanger  312  and supplied to the combustor  313 . 
     Now, the carbon dioxide supplied to the combustor  313  is used to cool wall surfaces of the combustor  313  and dilute the combustion gas. Then, the carbon dioxide is introduced into the combustor  313  and introduced into the turbine  315  together with the combustion gas. 
     In the system, the carbon dioxide and water generated by the hydrocarbon and oxygen supplied to the combustor  313  are exhausted to the outside of the system. Then, the remaining carbon dioxide circulates through the system. 
     In a power generating plant, the amount of generated power is often finely regulated depending on demands for electric power. In such cases, the fuel flow rate is finely regulated in a gas turbine. In the above-described conventional gas turbine facility, the fuel flow rate and the oxygen flow rate are regulated to be of the stoichiometric mixture ratio in a state that the both are mixed completely so that fuel and oxygen react (combust) in proper quantities. Accordingly, accompanying increase or decrease of the fuel flow rate, the oxygen flow rate should also be increased or decreased. 
     In the conventional gas turbine facility illustrated in  FIG. 5 , the flow rate regulating valve  311  is disposed on an upstream side of the heat exchanger  312 . Then, the distance between the flow rate regulating valve  311  and the combustor  313  is large. Depending on the size and disposition layout of the power generating plant, this distance can be a few tens of meters. In this case, when the fuel flow rate changes rapidly, the following ability of the oxygen flow rate worsens since the distance between the combustor  313  and the flow rate regulating valve  311  of oxygen is far. Thus, excess oxygen or excess fuel remains in the system. 
       FIG. 6  is a diagram illustrating changes in fuel flow rate and oxygen flow rate over time in the conventional gas turbine facility. The fuel flow rate changes by the amount of generated power. To maintain the stoichiometric mixture ratio, it is necessary that the oxygen flow rate changes accompanying the change in fuel flow rate, and the flow rate ratio of fuel and oxygen is maintained constant. However, as illustrated in  FIG. 6 , the change in oxygen flow rate is slightly late, and the flow rate ratio of fuel and oxygen is not maintained constant. 
     As described above, in the conventional gas turbine facility, the oxygen flow rates cannot follow the change in fuel flow rate. Accordingly, it has been difficult to maintain the flow rate ratio of fuel and oxygen constant. In particular, when the fuel flow rate changes to an increasing side, excess fuel remains in the combustion gas exhausted from the combustor. Thus, the fuel circulates through the system, resulting in that the fuel is discharged to the outside. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system diagram of a gas turbine facility of a first embodiment. 
         FIG. 2  is a diagram illustrating changes in fuel flow rate and oxygen flow rate over time in the gas turbine facility of the first embodiment. 
         FIG. 3  is a system diagram of a gas turbine facility of a second embodiment. 
         FIG. 4  is a system diagram of a gas turbine facility of a third embodiment. 
         FIG. 5  is a system diagram of a conventional gas turbine facility in which a part of carbon dioxide generated in a combustor is circulated as working fluid. 
         FIG. 6  is a diagram illustrating changes in fuel flow rate and oxygen flow rate over time in the conventional gas turbine facility. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, a gas turbine facility has a combustor combusting fuel and oxidant, a turbine rotated by combustion gas exhausted from the combustor, a heat exchanger cooling the combustion gas exhausted from the turbine, a working fluid supply pipe guiding a part of the combustion gas as working fluid to the combustor via the heat exchanger, and an exhaust pipe exhausting a remaining part of the combustion gas to an outside. 
     Further, the gas turbine facility has a fuel supply pipe supplying fuel to the combustor, an oxidant supply pipe supplying the oxidant to the combustor via the heat exchanger, and an oxidant bypass supply pipe branched from the oxidant supply pipe, bypassing the heat exchanger, and coupled to the oxidant supply pipe at a position between the heat exchanger and the combustor, so as to introduce the oxidant into the oxidant supply pipe. 
     Hereinafter, embodiments will be described with reference to drawings. 
     First Embodiment 
       FIG. 1  is a system diagram of a gas turbine facility  10  of a first embodiment. As illustrated in  FIG. 1 , the gas turbine facility  10  has a combustor  20  combusting fuel and oxidant, and a pipe  40  supplying fuel to this combustor  20 . The fuel supplied to the combustor  20  is regulated in flow rate by a flow rate regulating valve  21  interposed in the pipe  40 . Note that the pipe  40  functions as a fuel supply pipe. Here, for example, hydrocarbon such as methane or natural gas is used as the fuel, but coal gasification gas fuel containing carbon monoxide and hydrogen and the like can also be used. 
     The oxidant is separated from the atmosphere by an air separating apparatus (not illustrated) and is compressed by a compressor  22  interposed in a pipe  41 . The compressed oxidant is regulated in flow rate by flow rate regulating valves  23 ,  33  interposed in the pipe  41 , passes through a narrowed part  24  such as an orifice and a heat exchanger  25 , and is supplied to the combustor  20 . Passing through the heat exchanger  25 , the oxidant obtains a heat quantity from combustion gas exhausted from a turbine  28 , which will be described later, and is heated thereby. Note that the oxidant which passed through the heat exchanger  25  is supplied to the combustor  20  together with oxidant introduced into the pipe  41  from a pipe  42 , which will be described later. Here, oxygen is used as the oxidant. 
     The fuel and the oxidant guided to the combustor  20  are introduced into a combustion area. Then, the fuel and the oxidant occur a combustion reaction to generate combustion gas. Here, in the gas turbine facility  10 , it is preferred that no excess oxidant (oxygen) and fuel remain in the combustion gas exhausted from the combustor  20 . Accordingly, the flow rates of fuel and oxidant are regulated to be of, for example, a stoichiometric mixture ratio (equivalence ratio  1 ). Note that the equivalence ratio mentioned here is an equivalence ratio (overall equivalence ratio) assuming that fuel and oxygen are homogeneously mixed. 
     The gas turbine facility  10  has a pipe  42  which branches from the pipe  41  in downstream of the flow rate regulating valve  23 , bypasses the heat exchanger  25 , and is coupled to the pipe  41  between the heat exchanger  25  and the combustor  20 . In this pipe  42 , a flow rate regulating valve  27  regulating the flow rate of oxidant flowing through a compressor  26  and the pipe  42  is interposed. This pipe  42  is provided to introduce the oxidant into the pipe  41  in the vicinity of the combustor  20  corresponding to the amount of change in fuel flow rate when the fuel flow rate changes. Note that the flow rate regulating valve  27  has a certain intermediate opening, and constantly introduces a certain amount of oxidant from the pipe  42  to the pipe  41 . 
     Here, the compressor  26  operates constantly so that the oxidant can be introduced from the pipe  42  into the pipe  41  in the vicinity of the combustor  20  instantly when the fuel flow rate changes to an increasing side. The oxidant more than the flow rate passing through the flow rate regulating valve  27  flows through the pipe  42  on an upstream side of the compressor  26 . Then, a part of the oxidant exhausted from an exit of the compressor  26  passes through a pipe  43  and is returned to the entrance of the compressor  26 . When the oxidant is circulated from the exit to the entrance of the compressor  26 , the oxidant is cooled by cooling means (not illustrated) such as a heat exchanger with water, air, or a different medium. 
     When the fuel flow rate changes to the increasing side, the flow rate of oxidant introduced from the pipe  42  into the pipe  41  in the vicinity of the combustor  20  is, for example, 20% or less of the flow rate of the entire oxidant. Further, the pipe  41  is provided with the narrowed part  24 . Moreover, the pipe  41  passes through the heat exchanger  25 . Thus, a passage resistance in the pipe  41  is larger than a passage resistance in the pipe  42 . Further, as described above, the flow rate of oxidant flowing through the flow rate regulating valve  27  is smaller than the flow rate entering the compressor  26 . Thus, when the flow rate flowing through the flow rate regulating valve  27  increases abruptly, the flow rate flowing through the pipe  43  decreases or becomes zero. From these points, when the oxidant flows from the pipe  42  to the pipe  41  in the vicinity of the combustor  20 , the flow rate of oxidant flowing through the pipe  41  passing through the heat exchanger  25  barely changes. 
     On the other hand, when the fuel flow rate changes to a decreasing side, the flow rate of oxidant flowing through the flow rate regulating valve  27  also decreases. Thus, the flow rate of oxidant passing through the pipe  43  and returns to the entrance of the compressor  26  increases. 
     The pipe  42  bypasses the heat exchanger  25 . Accordingly, the oxidant lower in temperature than the oxidant flowing through the pipe  41  is introduced from the pipe  42  into the pipe  41  in the vicinity of the combustor  20 . However, since the flow rate of oxidant introduced from the pipe  42  into the pipe  41  in the vicinity of the combustor  20  is small as described above, its influence on combustibility is small. 
     Here, the pipe  41  functions as an oxidant supply pipe, the pipe  42  functions as an oxidant bypass supply pipe, and the flow rate regulating valve  27  functions as an oxidant bypass flow rate regulating valve. 
     The gas turbine facility  10  has a turbine  28  rotated by combustion gas exhausted from the combustor  20 . For example, a generator  29  is coupled to this turbine  28 . The combustion gas mentioned here exhausted from the combustor  20  contains combustion product, generated by fuel and oxidant, and dry combustion gas (carbon dioxide), which will be described later, supplied to the combustor  20  and exhausted together with the combustion product from the combustor  20 . 
     The combustion gas exhausted from the turbine  28  is cooled by passing through the heat exchanger  25 . The combustion gas which passed through the heat exchanger  25  further passes through a heat exchanger  30 . By passing through the heat exchanger  30 , water vapor contained in the combustion gas is removed, and thereby the combustion gas becomes dry combustion gas. Here, by passing through the heat exchanger  30 , the water vapor condenses into water. The water passes through the pipe  44  for example and is discharged to the outside. Note that the heat exchanger  30  functions as a water vapor remover removing water vapor. 
     Here, as described above, when the flow rates of fuel and oxidant are regulated to be of the stoichiometric mixture ratio (equivalence ratio  1 ), components of the dry combustion gas are mostly carbon dioxide. Note that the dry combustion gas also includes the case where, for example, a minute amount of carbon monoxide of 0.2% or less is mixed in. 
     The dry combustion gas is compressed by a compressor  31  interposed in a pipe  45 . A part of the compressed dry combustion gas flows into a pipe  46  branched from the pipe  45 . Then, the dry combustion gas flowing through the pipe  46  is regulated in flow rate by a flow rate regulating valve  32  interposed in the pipe  46 , and is guided to the combustor  20  via the heat exchanger  25 . Note that the pipe  46  functions as a working fluid supply pipe and the flow rate regulating valve  32  functions as a working fluid flow rate regulating valve. 
     The dry combustion gas flowing through the pipe  46  obtains in the heat exchanger  25  a heat quantity from the combustion gas exhausted from the turbine  28  and is heated thereby. The dry combustion gas guided to the combustor  20  cools, for example, a combustor liner and is guided into a downstream side of a combustion area in the combustor liner via a dilution hole or the like. This dry combustion gas rotates the turbine  28  together with the combustion gas generated by combustion, and hence functions as working fluid. 
     On the other hand, a remaining part of the dry combustion gas compressed by the compressor  31  is exhausted to the outside from an end of the pipe  45 . The end of the pipe  45  exhausting the dry combustion gas to the outside also functions as an exhaust pipe. 
     Further, the gas turbine facility  10  has a flow rate detecting unit  50  detecting the flow rate of fuel flowing through the pipe  40 , a flow rate detecting unit  51  detecting the flow rate of oxidant flowing through the pipe  41 , a flow rate detecting unit  52  detecting the flow rate of oxidant flowing through the pipe  42 , and a flow rate detecting unit  53  detecting the flow rate of dry combustion gas (working fluid) flowing through the pipe  46 . Each flow rate detecting unit is constituted of, for example, a flowmeter such as a venturi tube or a Coriolis flowmeter. 
     Here, the flow rate detecting unit  50  functions as a fuel flow rate detecting unit, the flow rate detecting unit  51  functions as an oxidant flow rate detecting unit, the flow rate detecting unit  52  functions as an oxidant bypass flow rate detecting unit, and the flow rate detecting unit  53  functions as a working fluid flow rate detecting unit. 
     The gas turbine facility  10  has a control unit  60  which controls openings of the respective flow rate regulating valves  21 ,  23 ,  27 ,  32 ,  33  based on, for example, detection signals from the respective flow rate detecting units  50 ,  51 ,  52 ,  53 . This control unit  60  mainly has, for example, an arithmetic unit (CPU), a storage unit such as a read only memory (ROM) and a random access memory (RAM), an input/output unit, and so on. The CPU executes various arithmetic operations using, for example, programs, data, and the like stored in the storage unit. 
     The input/output unit inputs an electrical signal from an outside device or outputs an electrical signal to an outside device. Specifically, the input/output unit is connected to, for example, the respective flow rate detecting units  50 ,  51 ,  52 ,  53  and the respective flow rate regulating valves  21 ,  23 ,  27 ,  32 ,  33 , and so on in a manner capable of inputting/outputting various signals. Processing executed by this control unit  60  is realized by, for example, a computer apparatus or the like. 
     Next, operations related to flow rate regulation of the fuel, the oxidant (oxygen), and the dry combustion gas (carbon dioxide) as the working fluid to be supplied to the combustor  20  will be described with reference to  FIG. 1 . 
     While the gas turbine facility  10  is operated, an output signal from the flow rate detecting unit  50  is inputted to the control unit  60  via the input/output unit. Based on the inputted output signal, it is judged whether the fuel flow rate has changed or not. 
     When it is judged that the fuel flow rate has not changed, the control unit  60  repeats the judgment of whether the fuel flow rate has changed or not based on the inputted output signal. 
     When it is judged that the fuel flow rate has changed to the increasing side, output signals from the flow rate detecting unit  50 , the flow rate detecting unit  51 , and the flow rate detecting unit  52  are inputted to the control unit  60  via the input/output unit. Then the control unit  60  calculates an equivalence ratio from the flow rates of fuel and oxygen in the arithmetic unit by using programs, data, and the like stored in the storage unit. 
     When the calculated equivalence ratio is 1, the judgment of whether the fuel flow rate has changed or not is repeated again. 
     When the calculated equivalence ratio exceeds 1, the control unit  60  calculates an oxygen flow rate to be introduced from the pipe  42  into the pipe  41  to make the equivalence ratio be 1 in the arithmetic unit by using output signals from the flow rate detecting unit  50 , the flow rate detecting unit  51 , and the flow rate detecting unit  52  and programs, data, and the like stored in the storage unit. The control unit  60  outputs an output signal for regulating a valve opening from the input/output unit to the flow rate regulating valve  27  so that the calculated oxygen flow rate can be introduced into the pipe  41 . Note that in this case, the flow rate regulating valve  27  is regulated in a direction to increase the valve opening. 
     On the other hand, when it is judged that the fuel flow rate has changed to the decreasing side, output signals from the flow rate detecting unit  50 , the flow rate detecting unit  51 , and the flow rate detecting unit  52  are inputted to the control unit  60  via the input/output unit. Then, the control unit  60  calculates the equivalence ratio from the flow rates of fuel and oxygen in the arithmetic unit by using programs, data, and the like stored in the storage unit. 
     When the calculated equivalence ratio is 1, the judgment of whether the fuel flow rate has changed or not is repeated again. 
     When the calculated equivalence ratio is smaller than 1, the control unit  60  calculates the oxygen flow rate to be introduced from the pipe  42  into the pipe  41  to make the equivalence ratio be 1 in the arithmetic unit by using output signals from the flow rate detecting unit  50 , the flow rate detecting unit  51 , and the flow rate detecting unit  52  and programs, data, and the like stored in the storage unit. The control unit  60  outputs an output signal for regulating a valve opening from the input/output unit to the flow rate regulating valve  27  so that the calculated oxygen flow rate can be introduced into the pipe  41 . Note that in this case, the flow rate regulating valve  27  is regulated in a direction to decrease the valve opening. 
     Subsequently, in the arithmetic unit of the control unit  60 , the flow rate of dry combustion gas (carbon dioxide) supplied to the combustor  20  as working fluid is calculated based on output signals from the flow rate detecting unit  50  and the flow rate detecting unit  53  which are inputted from the input/output unit. Note that the flow rate of dry combustion gas (carbon dioxide) can also be calculated based on output signals from the flow rate detecting unit  51 , the flow rate detecting unit  52 , and the flow rate detecting unit  53 . 
     Here, the flow rate of dry combustion gas (carbon dioxide) supplied as working fluid is determined based on, for example, the flow rate of fuel supplied to the combustor  20 . For example, the amount equivalent to the generated amount of carbon dioxide generated by combusting fuel in the combustor  20  is exhausted to the outside via the end of the pipe  45  functioning as an exhaust pipe. For example, when the flow rate of fuel is constant, the flow rate of carbon dioxide supplied to the entire combustor  20  is controlled to be constant. That is, when the flow rate of fuel is constant, carbon dioxide circulates at a constant flow rate in the system. 
     Next, the control unit  60  outputs an output signal for regulating the valve opening from the input/output unit to the flow rate regulating valve  32  so that the calculated flow rate of carbon dioxide flows into the pipe  46  based on an output signal from the flow rate detecting unit  53  which is inputted from the input/output unit. 
     By controlling as described above, the fuel, the oxidant, and the dry combustion gas as working fluid are supplied to the combustor  20 . By performing such control, for example, even when the fuel flow rate changes to the increasing side, the flow rate of oxidant introduced from the pipe  42  to the pipe  41  is regulated instantly. 
     Now,  FIG. 2  is a diagram illustrating changes in fuel flow rate and oxygen flow rate over time in the gas turbine facility  10  of the first embodiment. As illustrated in  FIG. 2 , for example, when the fuel flow rate changes, the flow rate regulating valve  27  is controlled to regulate the flow rate of oxygen (denoted as bypass oxygen in  FIG. 2 ) introduced from the pipe  42  into the pipe  41  corresponding to the amount of change in fuel flow rate. Note that the flow rate of oxygen passing through the narrowed part  24  and the heat exchanger  25  and flowing through the pipe  41  is maintained constant even after the valve opening of the flow rate regulating valve  27  is regulated. 
     By regulating the bypass oxygen flow rate, the oxygen flow rate changes in a manner to follow with almost no time delay from the change in fuel flow rate as illustrated in  FIG. 2 . Accordingly, the flow rate ratio of fuel and oxygen supplied to the combustor  20  is maintained constant, and for example, the stoichiometric mixture ratio (equivalence ratio  1 ) is maintained. 
     As described above, in the gas turbine facility  10  of the first embodiment, by providing the pipe  42 , even when the flow rate regulating valve  23  regulating the flow rate of oxidant is provided at a separate distance from the combustor  20  for example, the oxidant corresponding to the amount of change in fuel flow rate is introduced instantly into the pipe  41  in the vicinity of the combustor  20  when the fuel flow rate changes. Thus, when the fuel flow rate changes, the flow rates of fuel and oxidant are regulated instantly to the stoichiometric mixture ratio (equivalence ratio  1 ). 
     Further, since the pipe  42  bypasses the heat exchanger  25 , the oxidant at high temperature will not flow through the pipe  42 . Accordingly, it is not necessary to use an expensive valve for high temperature as the flow rate regulating valve  27  interposed in the pipe  42 . 
     Second Embodiment 
       FIG. 3  is a system diagram of a gas turbine facility  11  of a second embodiment. Note that the same components as those of the gas turbine facility  10  of the first embodiment are designated by the same reference numerals, and overlapping descriptions are omitted or simplified. 
     The gas turbine facility  11  of the second embodiment differs from the gas turbine facility  10  of the first embodiment in a structure having a combustion gas supply pipe. Here, this different structure will be mainly described. 
     As illustrated in  FIG. 3 , the combustion gas exhausted from the turbine  28  passes through the heat exchanger  30  where water vapor contained in the combustion gas is removed, and thereby becomes dry combustion gas (carbon dioxide). A part of the dry combustion gas flows into a pipe  70  branched from the pipe  45  in which the dry combustion gas flows. Then, the dry combustion gas which flowed into the pipe  70  is regulated in flow rate by a flow rate regulating valve  80  interposed in the pipe  70 , and is introduced to a downstream side of the position on the pipe  41  where the pipe  42  is branched. Accordingly, mixed gas constituted of the oxidant (oxygen) and the dry combustion gas flows through the pipe  41  on a downstream side of the position where the pipe  70  is coupled. Here, the pipe  70  functions as a combustion gas supply pipe. 
     The dry combustion gas introduced into the pipe  41  from the pipe  70  mixes with the oxidant regulated in flow rate by flow rate regulating valves  23 ,  81 , and is compressed by the compressor  22  interposed in the pipe  41 . The compressed mixed gas passes through the narrowed part  24  and the heat exchanger  25  and is supplied to the combustor  20 . Passing through the heat exchanger  25 , the mixed gas obtains a heat quantity from the combustion gas exhausted from the turbine  28  and is heated thereby. Note that the mixed gas which passed through the heat exchanger  25  is supplied to the combustor  20  together with the oxidant introduced from the pipe  42  into the pipe  41 . 
     The fuel, the oxidant, and the mixed gas introduced into the combustor  20  are introduced into the combustion area. Then, the fuel and the oxidant occur a combustion reaction to generate combustion gas. Here, in the gas turbine facility  11 , it is preferred that no excess oxidant (oxygen) and fuel remain in the combustion gas exhausted from the combustor  20 . Accordingly, the flow rates of fuel and oxidant are regulated to be of, for example, the stoichiometric mixture ratio (equivalence ratio  1 ). 
     Here, the mixture ratio of the oxidant and the dry combustion gas (carbon dioxide) in the mixed gas is maintained constant. Further, from a viewpoint of stabilizing combustibility in the combustor  20 , for example, the ratio of oxidant to the mixed gas is preferably set in the range of 15 to 40 mass %. Further, the ratio of oxidant to the mixed gas is more preferably 20 to 30 mass %. 
     Note that in the dry combustion gas, a part other than that flowing through the pipe  70  is compressed by the compressor  31 . A part of the compressed dry combustion gas flows through the pipe  46 , and the rest is exhausted to the outside from the end of the pipe  45 . 
     The gas turbine facility  11  has a flow rate detecting unit  90  detecting the flow rate of oxidant flowing through the pipe  41  on an upstream side of the position where the pipe  42  is branched, a flow rate detecting unit  91  detecting the flow rate of dry combustion gas introduced into the pipe  41 , and a flow rate detecting unit  92  detecting the flow rate of mixed gas flowing through the pipe  41 . Each flow rate detecting unit is constituted of, for example, a flowmeter such as a venturi tube or a Coriolis flowmeter. 
     Here, the flow rate detecting unit  90  functions as an oxidant flow rate detecting unit, the flow rate detecting unit  91  functions as a combustion gas flow rate detecting unit, and the flow rate detecting unit  92  functions as a mixed gas flow rate detecting unit. 
     The input/output unit of the control unit  60  is further connected to, for example, the respective flow rate detecting units  90 ,  91 ,  92 , the respective flow rate regulating valves  80 ,  81 , and so on other than those illustrated in the first embodiment in a manner capable of inputting/outputting various signals. 
     Next, operations related to flow rate regulation of the mixed gas constituted of oxidant (oxygen) and dry combustion gas (carbon dioxide) supplied to the combustor  20 , the oxidant flowing through the pipe  42 , the fuel, and the dry combustion gas (carbon dioxide) as working fluid will be described with reference to  FIG. 3 . 
     While the gas turbine facility  11  is operated, an output signal from the flow rate detecting unit  50  is inputted to the control unit  60  via the input/output unit. It is judged whether the fuel flow rate has changed or not, based on the inputted output signal. 
     When it is judged that the fuel flow rate has not changed, the control unit  60  repeats the judgment of whether the fuel flow rate has changed to the increasing side or not based on the inputted output signal. 
     When it is judged that the fuel flow rate has changed to the increasing side, output signals from the flow rate detecting unit  50  and the flow rate detecting unit  90  are inputted to the control unit  60  via the input/output unit. Then the control unit  60  calculates the equivalence ratio from the flow rates of fuel and oxygen in the arithmetic unit by using programs, data, and the like stored in the storage unit. 
     When the calculated equivalence ratio is 1, the judgment of whether the fuel flow rate has changed or not is repeated again. 
     When the calculated equivalence ratio exceeds 1, the control unit  60  calculates an oxygen flow rate to be introduced from the pipe  42  into the pipe  41  to make the equivalence ratio be 1 in the arithmetic unit by using output signals from the flow rate detecting unit  50 , the flow rate detecting unit  52 , the flow rate detecting unit  91 , and the flow rate detecting unit  92  and programs, data, and the like stored in the storage unit. 
     Then, the control unit  60  outputs an output signal for regulating a valve opening from the input/output unit to the flow rate regulating valve  27  so that the calculated oxygen flow rate can be introduced into the pipe  41 . Note that in this case, the flow rate regulating valve  27  is regulated in the direction to increase the valve opening. At this time, the oxygen flow rate introduced from the pipe  42  into the pipe  41  is small, and thus its influence on combustibility is small. 
     On the other hand, when it is judged that the fuel flow rate has changed to the decreasing side, output signals from the flow rate detecting unit  50  and the flow rate detecting unit  90  are inputted to the control unit  60  via the input/output unit. Then, the control unit  60  calculates the equivalence ratio from the flow rates of fuel and oxygen in the arithmetic unit by using programs, data, and the like stored in the storage unit. 
     When the calculated equivalence ratio is 1, the judgment of whether the fuel flow rate has changed or not is repeated again. 
     When the calculated equivalence ratio is smaller than 1, the control unit  60  calculates the oxygen flow rate to be introduced from the pipe  42  into the pipe  41  to make the equivalence ratio be 1 in the arithmetic unit by using output signals from the flow rate detecting unit  50 , the flow rate detecting unit  52 , the flow rate detecting unit  91 , and the flow rate detecting unit  92  and programs, data, and the like stored in the storage unit. 
     Then, the control unit  60  outputs an output signal for regulating a valve opening from the input/output unit to the flow rate regulating valve  27  so that the calculated oxygen flow rate can be introduced into the pipe  41 . Note that in this case, the flow rate regulating valve  27  is regulated in the direction to decrease the valve opening. 
     Note that when there is no change in fuel flow rate, the flow rate regulating valve  27  is in a state opened by a certain opening. 
     Subsequently, in the arithmetic unit of the control unit  60 , the flow rate of dry combustion gas (carbon dioxide) supplied to the combustor  20  as working fluid is calculated based on output signals from the flow rate detecting unit  50 , the flow rate detecting unit  53 , and the flow rate detecting unit  91  which are inputted from the input/output unit. 
     Here, the flow rate of dry combustion gas (carbon dioxide) supplied as working fluid is determined based on, for example, the flow rate of fuel supplied to the combustor  20 . For example, the amount equivalent to the generated amount of carbon dioxide generated by combusting fuel in the combustor  20  is exhausted to the outside via the end of the pipe  45  functioning as an exhaust pipe. For example, when the flow rate of fuel is constant, the flow rate of carbon dioxide supplied to the entire combustor  20  is controlled to be constant. That is, when the flow rate of fuel is constant, carbon dioxide circulates at a constant flow rate in the system. 
     Next, the control unit  60  outputs an output signal for regulating the valve opening from the input/output unit to the flow rate regulating valve  32  so that the calculated flow rate of carbon dioxide flows into the pipe  46 , based on an output signal from the flow rate detecting unit  53  which is inputted from the input/output unit. 
     By controlling as described above, the mixed gas, the oxidant, the fuel, and the dry combustion gas as working fluid are supplied to the combustor  20 . By performing such control, for example, even when the fuel flow rate changes to the increasing side, the flow rate of oxidant introduced from the pipe  42  to the pipe  41  can be regulated instantly. 
     Note that, although not illustrated, changes in fuel flow rate and oxygen flow rate over time in the gas turbine facility  11  of the second embodiment when the fuel flow rate changes, change similarly to the case of the gas turbine facility  10  of the first embodiment illustrated in  FIG. 2 . That is, by regulating the bypass oxygen flow rate, the oxygen flow rate changes in a manner to follow with almost no time delay from the change in fuel flow rate. Accordingly, the flow rate ratio of fuel and oxygen supplied to the combustor  20  is maintained constant, and for example, the stoichiometric mixture ratio (equivalence ratio  1 ) is maintained. 
     As described above, in the gas turbine facility  11  of the second embodiment, by providing the pipe  42 , even when the flow rate regulating valve  23  regulating the flow rate of oxidant is provided at a separate distance from the combustor  20  for example, the oxidant corresponding to the amount of change in fuel flow rate is introduced instantly into the pipe  41  in the vicinity of the combustor  20  when the fuel flow rate changes. Thus, when the fuel flow rate changes to the increasing side, the flow rates of fuel and oxidant are regulated instantly to the stoichiometric mixture ratio (equivalence ratio  1 ). 
     Further, since the pipe  42  bypasses the heat exchanger  25 , oxidant at high temperature will not flow through the pipe  42 . Accordingly, it is not necessary to use an expensive valve for high temperature as the flow rate regulating valve  27  interposed in the pipe  42 . 
     Third Embodiment 
       FIG. 4  is a system diagram of a gas turbine facility  12  of a third embodiment. Note that the same components as those of the gas turbine facility  10  of the first embodiment or the gas turbine facility  11  of the second embodiment are designated by the same reference numerals, and overlapping descriptions are omitted or simplified. 
     The gas turbine facility  12  of the third embodiment differs from the gas turbine facility  10  of the first embodiment in a structure having a combustion gas supply pipe and the structure of the pipe  42 . Here, this different structure will be mainly described. 
     As illustrated in  FIG. 4 , the combustion gas exhausted from the turbine  28  passes through the heat exchanger  30  where water vapor contained in the combustion gas is removed, and thereby becomes dry combustion gas (carbon dioxide). A part of the dry combustion gas flows into a pipe  70  branched from the pipe  45  in which the dry combustion gas flows. Then, the dry combustion gas which flowed into the pipe  70  is regulated in flow rate by a flow rate regulating valve  80  interposed in the pipe  70 , and is introduced into a mixing part  100  interposed in the pipe  41 . This mixing part  100  is, for example, a space in which a flow path cross-sectional area of the pipe  41  is enlarged. In this space, mixing of the oxidant (oxygen) and the dry combustion gas (carbon dioxide) is facilitated. 
     Accordingly, in the pipe  41  on a downstream side of the mixing part  100 , mixed gas constituted of oxidant regulated in flow rate by the flow rate regulating valve  23  and dry combustion gas flows. Here, the pipe  70  functions as a combustion gas supply pipe. 
     The mixed gas flowing out from the mixing part  100  and flowing through the pipe  41  is compressed by the compressor  22  interposed in the pipe  41 . The compressed mixed gas passes through the narrowed part  24  and the heat exchanger  25  and is supplied to the combustor  20 . Passing through the heat exchanger  25 , the mixed gas obtains a heat quantity from the combustion gas exhausted from the turbine  28  and is heated thereby. Note that the mixed gas which passed through the heat exchanger  25  is supplied to the combustor  20  together with the mixed gas introduced from the pipe  42  into the pipe  41 . 
     The fuel and the mixed gas introduced into the combustor  20  are introduced into the combustion area. Then, the fuel and the oxidant occur a combustion reaction to generate combustion gas. Here, in the gas turbine facility  12 , it is preferred that no excess oxidant (oxygen) and fuel remain in the combustion gas exhausted from the combustor  20 . Accordingly, the flow rates of fuel and oxidant are regulated to be of, for example, the stoichiometric mixture ratio (equivalence ratio  1 ). Note that the ratio of oxidant to mixed gas is as described in the second embodiment. 
     The pipe  42  branched from the mixing part  100  of the pipe  41  bypasses the heat exchanger  25  and is structured to be capable of introducing the mixed gas into the pipe  41  between the heat exchanger  25  and the combustor  20 . In the pipe  42 , a flow rate regulating valve  111  regulating the flow rate of mixed gas flowing through the compressor  26  and the pipe  42  is interposed. This pipe  42  is provided for introducing the mixed gas into the pipe  41  corresponding to the amount of change in fuel flow rate when the fuel flow rate changes. Note that the flow rate regulating valve  111  normally opens with a certain intermediate opening, and constantly introduces the mixed gas from the pipe  42  into the pipe  41  in the vicinity of the combustor  20 . 
     Here, the compressor  26  operates constantly so that the mixed gas can be introduced from the pipe  42  into the pipe  41  instantly when the fuel flow rate changes. Then, by the amount of a change in the flow rate passing through the flow rate regulating valve  111 , the flow rate passing through the pipe  43  which a part of mixed gas exhausted from the exit of the compressor  26  passes through changes also. 
     When the mixed gas is circulated from the exit to the entrance of the compressor  26 , the mixed gas is cooled by cooling means (not illustrated) such as a heat exchanger with water, air, or a different medium. 
     When the fuel flow rate changes to the increasing side, the flow rate of mixed gas introduced from the pipe  42  into the pipe  41  is, for example, 20% or less of the flow rate of the entire mixed gas. Further, the pipe  41  is provided with the narrowed part  24 . Moreover, the pipe  41  passes through the heat exchanger  25 . Thus, the passage resistance in the pipe  41  is larger than the passage resistance in the pipe  42 . From these points, when the mixed gas flows through the pipe  42 , the flow rate of mixed gas flowing through the pipe  41  barely changes. 
     Further, the pipe  42  bypasses the heat exchanger  25 . Accordingly, the mixed gas lower in temperature than the mixed gas flowing through the pipe  41  is introduced from the pipe  42  into the pipe  41 . However, since the flow rate of mixed gas introduced from the pipe  42  into the pipe  41  is small as described above, its influence on combustibility is small. 
     Here, the pipe  41  functions as an oxidant supply pipe, the pipe  42  functions as an oxidant bypass supply pipe, and the flow rate regulating valve  111  functions as a mixed gas bypass flow rate regulating valve. 
     Note that in the dry combustion gas, a part other than that flowing through the pipe  70  is compressed by the compressor  31 . A part of the compressed dry combustion gas flows through the pipe  46 , and the rest is exhausted to the outside from the end of the pipe  45 . 
     The gas turbine facility  12  has a flow rate detecting unit  90  detecting the flow rate of oxidant flowing through the pipe  41  on an upstream side of the position where the mixing part  100  is provided, a flow rate detecting unit  91  detecting the flow rate of dry combustion gas introduced into the mixing part  100 , a flow rate detecting unit  92  detecting the flow rate of mixed gas flowing through the pipe  41 , and a flow rate detecting unit  110  detecting the flow rate of mixed gas flowing through the pipe  42 . Each flow rate detecting unit is constituted of, for example, a flowmeter such as a venturi tube or a Coriolis flowmeter. 
     Here, the flow rate detecting unit  90  functions as an oxidant flow rate detecting unit, the flow rate detecting unit  91  functions as a combustion gas flow rate detecting unit, the flow rate detecting unit  92  functions as a mixed gas flow rate detecting unit, and the flow rate detecting unit  110  functions as a mixed gas bypass flow rate detecting unit. 
     The input/output unit of the control unit  60  is further connected to, for example, the respective flow rate detecting units  90 ,  91 ,  92 ,  110 , the respective flow rate regulating valves  33 ,  80 ,  111 , and so on other than those illustrated in the first embodiment in a manner capable of inputting/outputting various signals. 
     Next, operations related to flow rate regulation of the mixed gas constituted of oxidant (oxygen) and dry combustion gas (carbon dioxide) supplied to the combustor  20 , the mixed gas flowing through the pipe  42 , the fuel, and the dry combustion gas (carbon dioxide) as working fluid will be described with reference to  FIG. 4 . 
     While the gas turbine facility  12  is operated, an output signal from the flow rate detecting unit  50  is inputted to the control unit  60  via the input/output unit. The control unit  60  judges whether the fuel flow rate has changed or not, based on the inputted output signal. 
     When it is judged that the fuel flow rate has not changed, the control unit  60  repeats the judgment of whether the fuel flow rate has changed or not based on the inputted output signal. 
     When it is judged that the fuel flow rate has changed to the increasing side, output signals from the flow rate detecting unit  50  and the flow rate detecting unit  90  are inputted to the control unit  60  via the input/output unit. Then the control unit  60  calculates the equivalence ratio from the flow rates of fuel and oxygen in the arithmetic unit by using programs, data, and the like stored in the storage unit. 
     When the calculated equivalence ratio is 1, the judgment of whether the fuel flow rate has changed or not is repeated again. 
     When the calculated equivalence ratio exceeds 1, the control unit  60  calculates a mixed gas flow rate to be introduced from the pipe  42  into the pipe  41  in the vicinity of the combustor  20  to make the equivalence ratio be 1 in the arithmetic unit by using output signals from the flow rate detecting unit  50 , the flow rate detecting unit  90 , the flow rate detecting unit  91 , the flow rate detecting unit  92 , and the flow rate detecting unit  110  and programs, data, and the like stored in the storage unit. Note that the mixture ratio of oxidant (oxygen) and dry combustion gas (carbon dioxide) in the mixed gas formed in the mixing part  100  is constant. 
     Then, the control unit  60  outputs an output signal for regulating a valve opening from the input/output unit to the flow rate regulating valve  111  so that the calculated mixed gas flow rate can be introduced into the pipe  41 . Note that in this case, the flow rate regulating valve  111  is regulated in the direction to increase the valve opening. 
     On the other hand, when it is judged that the fuel flow rate has changed to the decreasing side, output signals from the flow rate detecting unit  50  and the flow rate detecting unit  90  are inputted to the control unit  60  via the input/output unit. Then, the control unit  60  calculates the equivalence ratio from the flow rates of fuel and oxygen in the arithmetic unit by using programs, data, and the like stored in the storage unit. 
     When the calculated equivalence ratio is 1, the judgment of whether the fuel flow rate has changed or not is repeated again. 
     When the calculated equivalence ratio is smaller than 1, the control unit  60  calculates the mixed gas flow rate to be introduced from the pipe  42  into the pipe  41  in the vicinity of the combustor  20  to make the equivalence ratio be 1 in the arithmetic unit by using output signals from the flow rate detecting unit  50 , the flow rate detecting unit  90 , the flow rate detecting unit  91 , the flow rate detecting unit  92 , and the flow rate detecting unit  110  and programs, data, and the like stored in the storage unit. 
     Then, the control unit  60  outputs an output signal for regulating a valve opening from the input/output unit to the flow rate regulating valve  111  so that the calculated mixed gas flow rate can be introduced into the pipe  41 . Note that in this case, the flow rate regulating valve  111  is regulated in the direction to decrease the valve opening. 
     Note that when there is no change in fuel flow rate, the flow rate regulating valve  111  is in a state opened by a certain opening. 
     Subsequently, in the arithmetic unit of the control unit  60 , the flow rate of dry combustion gas (carbon dioxide) supplied to the combustor  20  as working fluid is calculated based on output signals from the flow rate detecting unit  50 , the flow rate detecting unit  53 , and the flow rate detecting unit  91  which are inputted from the input/output unit. 
     Here, the flow rate of dry combustion gas (carbon dioxide) supplied as working fluid is determined based on, for example, the flow rate of fuel supplied to the combustor  20 . For example, the amount equivalent to the generated amount of carbon dioxide generated by combusting fuel in the combustor  20  is exhausted to the outside via the end of the pipe  45  functioning as an exhaust pipe. For example, when the flow rate of fuel is constant, the flow rate of carbon dioxide supplied to the entire combustor  20  is controlled to be constant. That is, when the flow rate of fuel is constant, carbon dioxide circulates at a constant flow rate in the system. 
     Next, the control unit  60  outputs an output signal for regulating the valve opening from the input/output unit to the flow rate regulating valve  32  so that the calculated flow rate of carbon dioxide flows into the pipe  46 , based on an output signal from the flow rate detecting unit  53  which is inputted from the input/output unit. 
     By controlling as described above, the mixed gas flowing through the pipes  41 ,  42 , the fuel, and the dry combustion gas as working fluid are supplied to the combustor  20 . By performing such control, for example, even when the fuel flow rate changes to the increasing side, the flow rate of mixed gas introduced from the pipe  42  into the pipe  41  can be regulated instantly. 
     Note that, although not illustrated, changes in fuel flow rate and oxygen flow rate over time in the gas turbine facility  12  of the third embodiment when the fuel flow rate changes, change similarly to the case of the gas turbine facility  10  of the first embodiment illustrated in  FIG. 2 . That is, by regulating the flow rate of mixed gas flowing through the pipe  42 , the oxygen flow rate changes in a manner to follow with almost no time delay from the change in fuel flow rate. Accordingly, the flow rate ratio of fuel and oxygen supplied to the combustor  20  is maintained constant, and for example, the stoichiometric mixture ratio (equivalence ratio  1 ) is maintained. 
     As described above, in the gas turbine facility  12  of the third embodiment, by providing the pipe  42 , even when the flow rate regulating valve  23  regulating the flow rate of oxidant is provided at a separate distance from the combustor  20  for example, the mixed gas containing the oxidant corresponding to the amount of change in fuel flow rate is introduced instantly into the pipe  41  in the vicinity of the combustor  20  when the fuel flow rate changes. Thus, when the fuel flow rate changes, the flow rates of fuel and oxidant are regulated instantly to the stoichiometric mixture ratio (equivalence ratio  1 ). 
     Further, since the pipe  42  bypasses the heat exchanger  25 , mixed gas at high temperature will not flow through the pipe  42 . Accordingly, it is not necessary to use an expensive valve for high temperature as the flow rate regulating valve  111  interposed in the pipe  42 . 
     Note that in the above-described embodiment, an example is presented in which hydrocarbon is used as fuel and oxygen is used as oxidant, but hydrogen may be used as fuel and oxygen may be used as oxidant. In this case, the heat exchanger  30  and the pipe  44  become unnecessary. Further, in this case, a branching part of the pipe  46  branching from the pipe  45  may be on an upstream side of the compressor  31 . Then, the compressor  31  may be interposed on an upstream side of the flow rate detecting unit  53  of the pipe  46 . 
     In the embodiment as described above, the oxidant flow rate follows changes in fuel flow rate appropriately, and it is possible to maintain the flow rate ratio of fuel and oxidant constantly. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.