JP2016085928A - Composite power generation system and control method for composite power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite power generation system and control method for the composite power generation system that are capable of reducing a risk of further damage expansion of a cell stack caused by a fuel shortage disabling a fuel electrode from being kept in a reduction state at the time of leakage being generated in the cell stack.SOLUTION: A composite power generation system 10 comprises: a control valve 34 that is provided on an exhaust fuel supply line 32 and performs pressure adjustment so that pressure of a fuel system of a cell stack provided inside an SOFC 12 is higher than that of an air system of the SOFC 12; a flow rate adjustment valve 41 that is provided in the exhaust fuel supply line 32 and adjusts a flow rate of the exhaust fuel gas flowing in a re-circulation line 33; and a leakage determination unit for determining that leakage of a fuel gas has occurred in the cell stack, when it is detected that the degree of opening of the control valve 34 is equal to or lower than a predetermined value or opening/closing speed at the time of the control valve 34's closing operation is equal to or larger than a predetermined value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a combined power generation system that combines a fuel cell and an internal combustion engine, and a control method for the combined power generation system.

  2. Description of the Related Art Fuel cells that generate electricity by chemically reacting fuel gas and oxygen are known. Among these, solid oxide fuel cells (hereinafter referred to as “SOFC”) use ceramics such as zirconia ceramics as an electrolyte, such as city gas, natural gas, petroleum, methanol, and coal gasification gas. Is a fuel cell operated using as a fuel.

  A combined power generation system that generates power by combining a SOFC and an internal combustion engine such as a gas turbine is also known.

In Patent Document 1 below, in order to protect the SOFC by confining the SOFC aeration gas in the system when the power generation is stopped, the fuel system is supplied by supplying a pressure adjustment gas to the fuel supply system and the oxidizing gas supply system. And a technique for preventing the pressure difference between the air system from being suppressed.
Further, in Patent Document 2, in order to prevent the cell stack from being damaged during a normal or emergency stop, first, the air system is continuously supplied with oxidizing gas while purging the fuel system with an inert gas. A technique for preventing reductive expansion of the electrode and then purging the air system with an inert gas after the cell voltage reaches a predetermined voltage to prevent oxidative expansion of the fuel electrode is disclosed.

JP 2014-89823 A JP 2013-171882 A

  In a combined power generation system that generates power by combining an SOFC and a gas turbine, water generated by power generation is reused for fuel reforming in the exhaust fuel supply line that supplies the exhaust fuel gas discharged from the SOFC to the gas turbine. In order to use the sensible heat of the exhausted fuel to raise the temperature of the supplied fuel, a recirculation line for returning a part of the exhausted fuel gas to the SOFC is provided.

  The exhaust fuel supply line is provided with a control valve A on the upstream side of the branch point with the recirculation line, that is, on the SOFC side, and on the downstream side of the branch point with the recirculation line, that is, on the gas turbine side. B is provided.

  During normal operation, the fuel system is controlled to be higher by a predetermined pressure (for example, 0.5 kPa) than the SOFC cell stack air system. This differential pressure control is performed using the control valve A. In order to increase the differential pressure, the control valve A is adjusted in the closing direction.

  When the SOFC cell stack or cell cartridge is damaged, fuel leaks from the fuel system to the air system.

When a minute leak occurs, adjustment is performed by the flow rate adjustment valve B in an attempt to keep the recirculation flow rate constant. At this time, the control valve A remains open.
On the other hand, when fuel leaks from the fuel system to the air system where the differential pressure changes, the control valve A is partially closed or fully closed in order to detect that the differential pressure has decreased and increase the differential pressure. To do. As a result, although the fuel supply of the fuel system continues, the fuel does not flow in the exhaust fuel supply line, and the SOFC fuel system is closed. At this time, depending on the leak location, the fuel does not flow to the downstream side of the cell stack, and the portion becomes deficient in fuel and the reduced state of the fuel electrode cannot be maintained. As a result, a part of the fuel electrode is reoxidized to cause volume expansion and stress is generated, so that a part of the film such as the air electrode may be peeled off, thereby damaging or expanding the cell stack. There was sex.

  The present invention has been made in view of such circumstances, and when a leak occurs in the cell stack, it is impossible to maintain the reduced state of the fuel electrode due to fuel shortage without stopping the flow of fuel in the fuel system. An object of the present invention is to provide a combined power generation system and a control method for the combined power generation system that can reduce the risk of further damage expansion of the cell stack.

In order to solve the above problems, the combined power generation system and the control method for the combined power generation system of the present invention employ the following means.
That is, the combined power generation system according to the present invention is a combined power generation system including a fuel cell and an internal combustion engine that is operated using exhaust fuel gas discharged from the fuel cell. An exhaust fuel supply system that supplies exhaust fuel gas, a recirculation system that is branched from the branch point of the exhaust fuel supply system, and returns the exhaust fuel gas to the fuel cell, and the exhaust fuel supply system, The pressure is adjusted so that the fuel system of the cell stack provided inside the fuel cell is higher than the pressure of the air system of the fuel cell by a predetermined pressure difference. A control valve, a flow rate adjusting valve provided downstream of the branch point in the exhaust fuel supply system, for adjusting a flow rate of the exhaust fuel gas flowing through the recirculation system, and an opening degree of the control valve. Specified value Or when it is detected that the opening / closing speed during the closing operation of the control valve is equal to or higher than a specified value, the fuel gas leaks from the fuel system to the air system in the cell stack. A leakage determination unit for determining.

  According to this configuration, since the control valve controls the fuel system of the cell stack so that the pressure is higher than that of the air system, the opening degree of the control valve is less than a specified value or when the control valve is closed. When it is detected that the opening / closing speed is equal to or higher than the specified value, it can be determined that the differential pressure between the fuel system and the air system is approaching 0 kPa, that is, fuel gas leaks in the cell stack. As a result, the risk of cell stack damage expansion can be reduced.

  In the above invention, in the exhaust fuel supply system, a blower provided upstream from the branch point and downstream from the control valve, and an opening degree of the control valve is equal to or less than a specified value, or the control A rotation speed setting unit that sets the rotation speed of the blower to a predetermined minimum rotation speed when it is detected that the opening / closing speed during the closing operation of the valve is equal to or higher than a specified value may be further provided.

  According to this configuration, when it is detected that the opening degree of the control valve is equal to or less than the specified value or the opening / closing speed when the control valve is closed is equal to or greater than the specified value, the rotational speed of the blower is set to the minimum rotational speed. Therefore, leakage of the oxidant gas from the air system to the fuel system from the leaked portion of the cell stack can be minimized.

  In the above invention, the opening degree of the control valve before determining that the fuel gas leaks from the fuel system to the air system in the cell stack is stored as a normal opening degree, and the rotational speed of the blower May be further provided with a control valve control section for returning the opening degree of the control valve to the normal opening degree when the predetermined minimum rotational speed is set.

  According to this configuration, since the opening degree of the control valve is returned to the original state while the rotation speed of the recirculation blower is set to the minimum rotation speed, the flow of fuel gas is created in the fuel system. No stagnation of fuel gas occurs.

  In the above invention, when the number of rotations of the blower is set to the minimum number of rotations, it further includes a flow rate adjusting valve control unit that shuts off the flow rate adjusting valve, and the control valve control unit flows through the recirculation system. The opening degree of the control valve may be adjusted so that the flow rate of the exhaust fuel gas becomes a predetermined flow rate.

  According to this configuration, the exhaust fuel gas does not flow to the internal combustion engine, and the exhaust fuel gas returns to the fuel cell via the recirculation system. Further, the pressure on the fuel system side is lower than that on the air system, and the fuel system is distributed from the air system to the fuel system at the leak location of the cell stack. However, since the rotation speed of the blower is set to the minimum rotation speed, an increase in circulation from the air electrode to the fuel electrode can be suppressed.

  In the above invention, the hydrogen concentration detected by the hydrogen concentration detection unit for detecting the hydrogen concentration in the exhaust fuel gas flowing through the exhaust fuel supply system, or detected by the battery voltage detection unit for detecting the voltage of the fuel cell. An operation determination unit that determines whether or not the fuel cell can continue to be operated may be further provided based on the voltage that has been generated.

  According to this configuration, for example, when the hydrogen concentration in the exhaust fuel gas or the voltage of the fuel cell is lower than a predetermined value, it can be determined that the degree of damage is large, so the continuation of operation is stopped.

  In the above invention, when the operation of the fuel cell is continued based on the determination result of the operation determination unit, the control valve control unit is configured so that the flow rate of the exhaust fuel gas flowing through the recirculation system becomes a predetermined flow rate. The opening degree of the control valve may be increased, and the rotation speed setting unit may increase the rotation speed of the blower after the control valve is fully opened.

According to this configuration, the recirculation flow rate can be increased by opening the control valve, and in this state, the recirculation flow rate can be further increased by increasing the rotational speed of the blower. In this way, by increasing the recirculation flow rate, it is possible to increase the pressure of the fuel system relative to the air system, increase the S / C ratio, and increase the fuel distribution to each cell stack.
If the rotational speed of the blower is increased before the control valve is opened, the pressure on the fuel system side becomes lower than that on the air system, and leakage from the air system side to the fuel system side increases, which is not preferable.

  A control method for a combined power generation system according to the present invention is a control method for a combined power generation system that includes a fuel cell and an internal combustion engine that is operated using exhaust fuel gas discharged from the fuel cell. And supplying the exhaust fuel gas to the fuel cell in a step of supplying the exhaust fuel gas from the fuel cell to the internal combustion engine and a recirculation system provided by branching from a branch point of the exhaust fuel supply system. And a control valve provided upstream of the branch point in the exhaust fuel supply system with respect to the pressure of the air system of the fuel cell, of the cell stack provided in the fuel cell. Adjusting the pressure so that the fuel system is increased by a predetermined pressure difference; and in the exhaust fuel supply system, a flow rate adjusting valve provided downstream of the branch point is configured to cause the exhaust gas flowing through the recirculation system to flow. The step of adjusting the flow rate of the feed gas, and when it is detected that the opening of the control valve is equal to or less than a specified value or the opening and closing speed during the closing operation of the control valve is equal to or greater than a specified value, Determining that fuel gas leaks from the fuel system to the air system in the cell stack, and if it is determined that the fuel gas leaks, the exhaust fuel In the supply system, there is a step of setting the rotational speed of a blower provided upstream of the branch point and downstream of the control valve to a predetermined minimum rotational speed, and leakage of the fuel gas. Storing the opening of the control valve before determining as a normal opening, returning the opening of the control valve to the normal opening, and shutting off the flow regulating valve, Flow rate of the exhaust fuel gas flowing through And a step of adjusting an opening degree of the control valve so that a predetermined flow rate.

  According to the present invention, when a leak occurs in the cell stack, when the leak occurs in the cell stack, the risk of further damage expansion of the cell stack due to failure to maintain the reduced state of the fuel electrode due to fuel depletion is reduced. be able to.

It is a block diagram which shows the combined power generation system which concerns on one Embodiment of this invention. It is a block diagram which shows the operation control apparatus of the combined power generation system which concerns on one Embodiment of this invention. It is a flowchart which shows operation | movement of the operation control apparatus of the combined power generation system which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the opening degree of a control valve, and time, and the rotation speed of a recirculation blower, and time. It is a partial expanded sectional view which shows the cell stack which concerns on one Embodiment of this invention. It is a perspective view which shows the SOFC module which concerns on one Embodiment of this invention. It is sectional drawing which shows the SOFC cartridge which concerns on one Embodiment of this invention.

Hereinafter, a combined power generation system according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of a combined power generation system 10 according to the present embodiment.
The combined power generation system 10 generates power by combining a fuel cell and an internal combustion engine that is operated using fuel gas discharged from the fuel cell. The combined power generation system 10 is constantly monitored.

  The SOFC 12, which is a fuel cell, generates power by supplying an oxidizing gas (air in the present embodiment) to the air electrode and supplying a fuel gas to the fuel electrode. The SOFC 12 is covered with the pressure vessel 14. The SOFC 12 is provided with a pressure sensor 15A that measures the pressure in the pressure vessel 14 and a temperature sensor 15B that measures the temperature in the pressure vessel 14.

The internal combustion engine is a small gas turbine (hereinafter referred to as “micro gas turbine” or “MGT”) 16 as an example.
The MGT 16 is supplied with a compressor 18 that supplies compressed air to the air electrode of the SOFC 12, exhaust air discharged from the air electrode, exhaust fuel gas and fuel gas (city gas in this embodiment) discharged from the fuel electrode, A combustor 20 that generates high-temperature combustion gas, and a turbine 22 that is rotationally driven by the combustion gas discharged from the combustor 20 are provided.

The SOFC 12 is supplied with reducing gas (hydrogen gas in the present embodiment), water vapor, inert gas (nitrogen gas in the present embodiment), and fuel gas (city gas in the present embodiment) via the fuel supply line 24. It can be supplied. The reducing gas supply line is provided with a pressure reducing valve 28A, and the supply lines corresponding to the respective gases are provided with on-off valves 28B to 28E.
As fuel gas, in addition to city gas (CNG), for example, liquefied natural gas (LNG), hydrocarbon gas such as hydrogen (H2) and carbon monoxide (CO), methane (CH4), and carbonaceous materials such as coal It is also possible to use a gas produced by a raw material gasification facility. The fuel gas is preheated by the fuel preheater 26 and then supplied to the SOFC 12.

The exhaust fuel gas discharged from the SOFC 12 is cooled by the cooler 30 and supplied to the combustor 20 by the exhaust fuel supply line 32, and part of the exhaust fuel gas is returned to the SOFC 12 through the fuel recirculation line 33. It is. The exhaust fuel supply line 32 includes a control valve 34 and a recirculation blower 36 that supplies gas to the combustor 20 while circulating the gas discharged from the SOFC 12 to the SOFC 12. During normal operation, the control valve 34 performs differential pressure control so that the fuel system is higher than the air system of the cell stack of the SOFC 12 by a predetermined pressure (for example, 0.5 kPa).
The exhaust fuel supply line 32 is provided with an on-off valve 40 and a flow rate adjustment valve 41 on the downstream side of the branch point with the fuel recirculation line 33. The flow rate adjustment valve 41 adjusts the flow rate of the exhaust fuel gas flowing through the recirculation line 33 to be constant during normal operation.

  The exhaust fuel supply line 32 is branched between the fuel preheater 26 and the cooler 30, and the exhaust fuel gas can be purged (discharged out of the system) by the exhaust line 42. The discharge line 42 is provided with an open / close valve 44. Thereby, the fuel gas in the combined power generation system 10 is purged when the on-off valve 44 is opened.

The SOFC 12 is compressed by the compressor 18, and air preheated by the air preheater (regenerative heat exchanger) 48 is supplied via the air supply line 46. The air supply line 46 is provided with a control valve 50 that controls the flow rate of air from the compressor 18.
An air / nitrogen gas supply line including a pressure reducing valve 47 and an opening / closing valve 49 is connected downstream of the control valve 50. The illustrated air / nitrogen gas supply line is a flow path for supplying either air or nitrogen gas.

The air exhausted from the SOFC 12 is supplied to the combustor 20 through the exhaust air supply line 56. The exhaust air supply line 56 is provided with an on-off valve 60.
The exhaust air supply line 56 is branched, and air can be purged by the exhaust line 62. The discharge line 62 is provided with an open / close valve 64. Thereby, the air in the combined power generation system 10 is purged when the on-off valve 64 is opened.

  FIG. 2 is a block diagram showing an electrical configuration of the operation control device 80 according to the present embodiment. The operation control device 80 includes, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a computer-readable recording medium. A series of processes for realizing various functions is recorded on a recording medium or the like in the form of a program as an example, and the CPU reads the program into a RAM or the like to execute information processing / arithmetic processing. As a result, various functions are realized.

  The operation control device 80 includes an opening degree detection unit 81, a leak determination unit 82, a recirculation blower rotation speed setting unit 83, a control valve control unit 84, a flow rate adjustment valve control unit 85, and an operation determination unit 88. Prepare.

  The opening detection unit 81 detects the opening of the control valve 34 or the opening / closing speed when the control valve 34 is closed. The detected opening degree or the opening / closing speed at the time of closing is sent to the leak determination unit 82.

  When the opening degree of the control valve 34 detected by the opening degree detection unit 81 is equal to or less than a specified value or when the opening / closing speed when the control valve 34 is closed is equal to or more than a specified value, It is determined that fuel gas leaks in the cell stack. On the other hand, when the opening degree of the control valve 34 detected by the opening degree detection unit 81 exceeds a specified value, or the opening / closing speed when the control valve 34 is closed is less than the specified value, the leak determination unit 82 Does not determine that fuel gas leaks in the cell stack. In this case, normal operation is continued. The determination result of the leak determination unit 82 is sent to the recirculation blower speed setting unit 83.

  When the recirculation blower rotation speed setting unit 83 receives a signal indicating that a leak has occurred from the leak determination unit 82, the recirculation blower rotation speed setting unit 83 ensures a recirculation flow rate to maintain the rotation speed of the recirculation blower 36 as the combined power generation system 10. Set to the minimum number of revolutions. The recirculation blower rotation speed setting unit 83 confirms that the rotation speed of the recirculation blower 36 is set to the minimum rotation speed. Further, when it is confirmed that the rotation speed of the recirculation blower 36 is set to the minimum rotation speed, the control valve control unit 84 is notified that the rotation speed of the recirculation blower 36 is set to the minimum rotation speed. .

  The control valve controller 84 indicates that the rotation speed of the recirculation blower 36 is set to the minimum rotation speed, and the recirculation blower rotation speed setting section 83 sets the rotation speed of the recirculation blower 36 to the minimum rotation speed. When the signal is received, the opening degree of the control valve 34 in the closed state is returned to the opening degree during the normal operation before closing. At this time, the control valve control unit 84 refers to the opening degree during normal operation of the control valve 34 separately stored in a storage unit such as a memory.

  The flow rate adjusting valve control unit 85 is set to the minimum rotation speed at which the recirculation blower 36 is set, and the recirculation blower rotation speed setting unit 83 sets the rotation speed of the recirculation blower 36 to the minimum rotation speed. Is received, the flow rate adjustment valve 41 is shut off.

The hydrogen concentration detection unit 86 is provided in the exhaust fuel supply line 32 and detects the hydrogen concentration in the exhaust fuel gas. The hydrogen concentration detection unit 86 sends the detection result to the operation determination unit 88.
The battery voltage detection unit 87 detects the voltage of the SOFC 12. The battery voltage detection unit 87 sends the detection result to the operation determination unit 88.

The operation determination unit 88 is configured to supply a specified amount of fuel, and when the concentration value detected by the hydrogen concentration detection unit 86 falls below a predetermined value, or the voltage value detected by the battery voltage detection unit 87. When the value falls below a predetermined value, the fuel supplied to the SOFC 12 is increased.
The operation determination unit 88 is based on at least one of the rotational speed of the recirculation blower 36, the recirculation flow rate, the concentration value detected by the hydrogen concentration detection unit 86, and the voltage value detected by the battery voltage detection unit 87. It may be determined whether or not the operation can be continued. For example, even if the rotational speed of the recirculation blower 36 is increased to a predetermined value or more, even when the recirculation flow rate is lower than a predetermined value, or even if the rotational speed of the recirculation blower 36 is increased to a predetermined value or more, the hydrogen concentration When the concentration value detected by the detection unit 86 is lower than the predetermined value, or when the voltage value detected by the battery voltage detection unit 87 is lower than the predetermined value, the operation of the SOFC 12 cannot be continued. to decide.
The operation determination unit 88 sends the determination result to the control valve control unit 84 and the recirculation blower rotation speed setting unit 83.

  When the control valve control unit 84 receives the determination result indicating that the operation is possible, the control valve control unit 84 opens until the opening degree of the control valve 34 reaches a predetermined value. When it is confirmed that the opening degree of the control valve 34 has been opened to a predetermined value, the control valve control unit 84 transmits to the recirculation blower rotation speed setting unit 83 that the opening degree of the control valve 34 has been opened to a predetermined value. To do. The predetermined value of the opening degree of the control valve 34 is the opening degree before the leak occurs, that is, the opening degree of the control valve 34 at the time of normal operation in which no leak occurs in the cell stack in the combined power generation system 10. The opening degree of the control valve 34 during normal operation is recorded in a storage unit such as a memory provided in the control valve control unit 84 or the like.

  When the recirculation blower rotation speed setting unit 83 receives the determination result that the operation is possible and receives a signal that the opening degree of the control valve 34 is opened to a predetermined value, the recirculation blower 36 rotates. Increase the number.

  Next, operations of the operation control device 80, the control valve 34, the recirculation blower 36, and the flow rate adjustment valve 41 according to the present embodiment will be described with reference to FIGS.

  Due to the deviation between the measured pressure difference (differential pressure) of the fuel system relative to the air system of the SOFC 12 and a specified pressure difference (differential pressure) (for example, 0.5 kPa), the opening of the control valve 34 is a specified value. When the value is below (for example, 10% or less with respect to full opening, 20% or less of the valve opening degree of normal operation), or the opening / closing speed when the control valve 34 is closed is a specified value (for example, normal when a leak occurs) When the opening degree is 50% or more and the opening / closing speed is reduced to 10%), it is determined that fuel gas leaks in the cell stack (step S1).

  At this time, when the control valve 34 provided in the exhaust fuel supply line 32 is closed, the fuel does not flow through the cell stack. Therefore, the recirculation blower 36 is set to the minimum rotational speed and operated (step S2), the control valve 34 is returned to a certain opening (for example, the opening during normal operation) (step S3), and the flow rate adjustment valve 41 is turned on. Shut off (step S4). By this control, the state is in the range <2> shown in FIG.

  At this time, the exhaust fuel gas is returned to the SOFC 12 and the pressure of the fuel system becomes lower than that of the air system, so that the gas flows from the air system to the fuel system at the leak location of the cell stack. However, since the recirculation blower 36 is operating at the minimum rotational speed, an increase in leakage from the air system to the fuel system is suppressed. If the measured pressure difference (differential pressure) of the fuel system with respect to the air system recovers at this time, the operation is continued. When the SOFC 12 voltage, module temperature, or hydrogen concentration of the exhaust fuel gas is measured and no major abnormality is observed, the operation is continued. On the other hand, even when the differential pressure cannot be recovered or when the differential pressure recovers, the operation shifts to the stop operation depending on the degree of damage.

  When you want to increase the differential pressure, increase the S / C ratio, increase the fuel distribution to the cell stack, etc. The control valve 34 is gradually opened and fully opened until it reaches a specified value (step S5). By this control, the state is in the range <3> shown in FIG.

When the recirculation amount is further increased, the rotational speed of the recirculation blower 36 is gradually increased to secure the recirculation flow rate (step S6). By this control, the state in the range <4> shown in FIG. 4 is obtained. If the rotational speed of the recirculation blower 36 is increased before the control valve 34 is opened, the pressure on the fuel system side becomes lower than that on the air system, and leakage from the air system side to the fuel system side increases. Therefore, it is not preferable.
On the other hand, when the recirculation flow rate cannot be secured, the operation is shifted to the stop operation of the SOFC 12.

  Even if the fuel gas is supplied in a specified amount, the supply amount of the fuel gas is increased if the hydrogen concentration in the exhaust fuel supply line 32 downstream of the cell stack or the voltage of the SOFC 12 falls below a specified value. If steam cannot be supplied while power is being generated, it is necessary to increase the recirculation flow rate so as to ensure the S / C ratio required for fuel reforming.

  In addition, when the rotation speed of the recirculation blower 36 is increased to a predetermined rotation speed or more, if the hydrogen concentration in the exhaust fuel supply line 32 downstream of the cell stack or the voltage of the SOFC 12 falls below a specified value, recirculation is performed. Without increasing the rotation speed of the blower 36, it is determined that the degree of damage is large, and the operation proceeds to the stop operation.

Next, the amount of water supplied to the recirculation line 33 of the SOFC 12, that is, the fuel supply side, will be described in order to obtain a prescribed S / C ratio required in accordance with the operating situation. Water is supplied by, for example, water vapor.
The supply amount of water vapor is set to a desired value for each start-up, rated operation, and stop operation as follows.

  The amount of water vapor supplied at the time of start-up is based on the recirculation flow rate of the exhaust fuel gas and the flow rate of the fuel gas newly supplied to the SOFC 12, and the flow rate required for the reforming reaction in the SOFC 12, for example, the S / C ratio is 4 The water vapor supply amount is determined so that

  In addition, the recirculation flow rate of the exhaust fuel gas at the time of start-up is (1) a flow rate that can ensure distribution to each cartridge, or (2) a gas temperature drop due to heat radiation of the piping of the recirculation line 33 to prevent drainage. Is set to one of the flow rates that can suppress the above. In addition, when the heat retention apparatus (for example, trace heater) is installed in the piping of the recirculation line 33, the flow rate setting in (2) may be excluded, and the flow rate setting in (1) is performed.

  In principle, the steam supply during the rated operation is unnecessary because the water generated by the power generation reaction of the SOFC 12 is supplied to the SOFC 12 via the recirculation line 33. Note that the recirculation flow rate of the exhaust fuel gas during the rated operation is set to a flow rate required for the reforming reaction in the SOFC 12, for example, a flow rate at which the S / C ratio is 4.

  The amount of water vapor supply during the stop operation is determined based on the recirculation flow rate of the exhaust fuel gas and the flow rate of the fuel gas newly supplied to the SOFC 12, such as the flow rate required for the reforming reaction in the SOFC 12, for example, the S / C ratio. The water vapor supply amount is determined to be 4.

  The recirculation flow rate of the exhaust fuel gas during the stop operation is set to either (1) a flow rate that can ensure distribution to each cartridge, or (2) a flow rate that is necessary for cooling the cell stack. The Note that (2) is set when it is desired to shorten the time required for a complete stop. When cooling by other heat radiation, the flow rate setting in (2) may be excluded, and the flow rate setting in (1) is performed.

In the above description, it is described that it is desirable to adjust the steam supply amount and the recirculation flow rate so that the S / C ratio is 4, but the present invention is not limited to this example.
For example, if the S / C ratio is 2 or more, it is preferable that S / C ≧ 2 because an effect of preventing carbon deposition is obtained. Further, if the value of the S / C ratio is too large, for example, if S / C ≧ 10 or more, the water in the exhaust fuel gas increases, and this latent heat is discharged out of the system as wasted heat. As a result, the system efficiency decreases. Therefore, the S / C ratio is preferably less than 10.

  As described above, according to the present embodiment, the flow of the exhaust fuel gas to the exhaust fuel supply line 32 is continued even when the cell stack is damaged and the fuel gas leaks. Therefore, there is no stagnation of fuel gas in the cell stack. Therefore, as in the conventional case, the fuel electrode is deficient and the reduced state of the fuel electrode cannot be maintained, and a part of the fuel electrode is reoxidized to cause volume expansion and stress is generated. The risk of expanding damage to the cell stack due to peeling can be reduced. Further, the expansion of damage to the cell stack can be minimized, and the SOFC 12 can be safely stopped if necessary.

Hereinafter, an example of the SOFC applied to the combined power generation system 10 according to the present embodiment will be described.
In the following, for convenience of explanation, the positional relationship of each component is specified using the expressions “upper” and “lower” on the basis of the paper surface, but this is not necessarily limited to the vertical direction. For example, the upward direction on the paper surface may correspond to the downward direction in the vertical direction. Moreover, you may respond | correspond to the horizontal direction where the up-down direction in a paper surface goes orthogonally to a perpendicular direction.
In the following description, a cylindrical shape is described as an example of a cell stack of a solid oxide fuel cell (SOFC). However, the cell stack is not necessarily limited to this, and may be a flat cell stack, for example.

(Cylindrical cell stack structure)
First, a cylindrical cell stack according to the present embodiment will be described with reference to FIG. Here, FIG. 5 shows one mode of the cell stack according to the first embodiment. The cell stack 101 includes a cylindrical base tube 103, a plurality of fuel cells 105 formed on the outer peripheral surface of the base tube 103, and an interconnector 107 formed between adjacent fuel cells 105. The fuel cell 105 is formed by stacking a fuel electrode 109, a solid electrolyte 111, and an air electrode 113. The cell stack 101 is connected to the air electrode 113 of the fuel cell 105 formed at the end in the axial direction of the base tube 103 among the plurality of fuel cells 105 formed on the outer peripheral surface of the base tube 103. A lead film 115 is electrically connected through the connector 107.

(Explanation of materials and functions of each component of cell stack)
The base tube 103 is made of a porous material, for example, CaO stabilized ZrO ₂ (CSZ), Y ₂ O ₃ stabilized ZrO ₂ (YSZ), or MgAl ₂ O ₄ . The base tube 103 supports the fuel battery cell 105, the interconnector 107, and the lead film 115, and supplies the fuel gas supplied to the inner peripheral surface of the base tube 103 through the pores of the base tube 103. Is diffused to the fuel electrode 109 formed on the outer peripheral surface of the electrode.

The fuel electrode 109 is made of an oxide of a composite material of Ni and a zirconia-based electrolyte material. For example, Ni / YSZ is used. In this case, in the fuel electrode 109, Ni that is a component of the fuel electrode 109 has a catalytic action on the fuel gas. This catalytic action reacts with a fuel gas supplied through the base tube 103, for example, a mixed gas of methane (CH ₄ ) and water vapor, and reforms it into hydrogen (H ₂ ) and carbon monoxide (CO). Is. Further, the fuel electrode 109 is an interface between the solid electrolyte 111 and hydrogen (H ₂ ) and carbon monoxide (CO) obtained by reforming and oxygen ions (O ²⁻ ) supplied via the solid electrolyte 111. It reacts electrochemically in the vicinity to produce water (H ₂ O) and carbon dioxide (CO ₂ ). At this time, the fuel cell 105 generates electric power by electrons emitted from oxygen ions.

The solid electrolyte 111 is mainly made of YSZ having gas tightness that prevents gas from passing through and high oxygen ion conductivity at high temperatures. The solid electrolyte 111 moves oxygen ions (O ²⁻ ) generated at the air electrode to the fuel electrode.

The air electrode 113 is made of, for example, a LaSrMnO ₃ oxide or a LaCoO ₃ oxide. The air electrode 113 generates oxygen ions (O ²⁻ ) by dissociating oxygen in an oxidizing gas such as air supplied near the interface with the solid electrolyte 111.

The interconnector 107 is composed of a conductive perovskite oxide represented by M _1-x L _x TiO ₃ (M is an alkaline earth metal element, L is a lanthanoid element) such as SrTiO ₃ system, and is composed of fuel gas and oxidation It is a dense film so that it does not mix with sex gases. Further, the interconnector 107 has stable electrical conductivity in both an oxidizing atmosphere and a reducing atmosphere. The interconnector 107 electrically connects the air electrode 113 of one fuel battery cell 105 and the fuel electrode 111 of the other fuel battery cell 105 in adjacent fuel battery cells 105, so that the adjacent fuel battery cells 105 are connected to each other. Are connected in series. Since the lead film 115 needs to have electronic conductivity and a thermal expansion coefficient close to that of other materials constituting the cell stack 101, the lead film 115 is made of Ni such as Ni / YSZ and a zirconia-based electrolyte material. Composed of composite material. The lead film 115 leads direct current power generated by the plurality of fuel cells 105 connected in series by the interconnector to the vicinity of the end of the cell stack 101.

(Description of SOFC module structure and function of each element)
Next, the SOFC module and the SOFC cartridge according to this embodiment will be described with reference to FIGS. Here, FIG. 6 illustrates one mode of the SOFC module according to the first embodiment. FIG. 7 shows a cross-sectional view of one aspect of the SOFC cartridge according to the first embodiment.

  As illustrated in FIG. 6, the SOFC module 201 includes, for example, a plurality of SOFC cartridges 203 and a pressure vessel 205 that stores the plurality of SOFC cartridges 203. The SOFC module 201 has a fuel gas supply pipe 207 and a plurality of fuel gas supply branch pipes 207a. The SOFC module 201 includes a fuel gas discharge pipe 209 and a plurality of fuel gas discharge branch pipes 209a. The SOFC module 201 includes an oxidizing gas supply pipe (not shown) and an oxidizing gas supply branch pipe (not shown). The SOFC module 201 includes an oxidizing gas discharge pipe (not shown) and a plurality of oxidizing gas discharge branch pipes (not shown).

  The fuel gas supply pipe 207 is provided outside the pressure vessel 205 (not shown), and is connected to a fuel gas supply unit that supplies a predetermined gas composition and a predetermined flow rate of fuel gas corresponding to the power generation amount of the SOFC module 201. The plurality of fuel gas supply branch pipes 207a are connected. The fuel gas supply pipe 207 is configured to branch and guide a predetermined flow rate of fuel gas supplied from the fuel gas supply unit described above to a plurality of fuel gas supply branch pipes 207a. The fuel gas supply branch pipe 207 a is connected to the fuel gas supply pipe 207 and is connected to a plurality of SOFC cartridges 203. The fuel gas supply branch pipe 207a guides the fuel gas supplied from the fuel gas supply pipe 207 to the plurality of SOFC cartridges 203 at a substantially equal flow rate, and makes the power generation performance of the plurality of SOFC cartridges 203 substantially uniform. .

  The fuel gas discharge branch pipe 209 a is connected to the plurality of SOFC cartridges 203 and also connected to the fuel gas discharge pipe 209. The fuel gas supply branch pipe 209 a guides the exhaust fuel gas discharged from the SOFC cartridge 203 to the fuel gas discharge pipe 209. The fuel gas discharge pipe 209 is connected to a plurality of fuel gas supply branch pipes 209 a and a part thereof is disposed outside the pressure vessel 205. The fuel gas discharge pipe 209 guides the exhaust fuel gas led out from the fuel gas discharge branch pipe 209a at a substantially equal flow rate to the outside of the pressure vessel 205.

  Since the pressure vessel 205 is operated at an internal pressure of 0.1 MPa to about 1 MPa and an internal temperature of atmospheric temperature to about 550 ° C., the pressure vessel 205 is resistant to corrosion and resistance to oxidizing agents such as oxygen contained in the oxidizing gas. The possessed material is used. For example, a stainless steel material such as SUS304 is suitable.

  Here, in the present embodiment, a mode has been described in which a plurality of SOFC cartridges 203 are assembled and stored in the pressure vessel 205. However, the present invention is not limited to this. It can also be set as the aspect accommodated in the container 205. FIG.

(Description of SOFC cartridge structure and functions of each element)
As shown in FIG. 7, the SOFC cartridge 203 includes a plurality of cell stacks 101, a power generation chamber 215, a fuel gas supply chamber 217, a fuel gas discharge chamber 219, an oxidizing gas supply chamber 221, and an oxidizing gas discharge chamber. 223. The SOFC cartridge 203 includes an upper tube plate 225a, a lower tube plate 225b, an upper heat insulator 227a, and a lower heat insulator 227b. In this embodiment, the SOFC cartridge 203 includes a fuel gas supply chamber 217, a fuel gas discharge chamber 219, an oxidizing gas supply chamber 221, and an oxidizing gas discharge chamber 223 as shown in FIG. The fuel gas and the oxidizing gas have a structure that flows between the inside and the outside of the cell stack 101, but this is not always necessary, for example, the inside and the outside of the cell stack flow in parallel. Alternatively, the oxidizing gas may flow in a direction orthogonal to the longitudinal direction of the cell stack.

  The power generation chamber 215 is an area formed between the upper heat insulator 227a and the lower heat insulator 227b. The power generation chamber 215 is an area in which the fuel cell 105 of the cell stack 101 is disposed, and electricity is generated by electrochemically reacting the fuel gas and the oxidizing gas. Further, the temperature in the vicinity of the central portion of the power generation chamber 215 in the longitudinal direction of the cell stack 101 is a high temperature atmosphere of about 700 ° C. to 1100 ° C. during the steady operation of the fuel cell module 201.

  The fuel gas supply chamber 217 is an area surrounded by the upper casing 229a and the upper tube plate 225a of the SOFC cartridge 203. The fuel gas supply chamber 217 communicates with a fuel gas supply branch pipe 207a (not shown) through a fuel gas supply hole 231a provided in the upper casing 229a. In the fuel gas supply chamber 217, one end of the cell stack 101 is arranged with the inside of the base tube 105 of the cell stack 101 open to the fuel gas discharge chamber 219. The fuel gas supply chamber 217 guides the fuel gas supplied from the fuel gas supply pipe branch 207a (not shown) through the fuel gas supply hole 231a into the base pipe 105 of the plurality of cell stacks 101 at a substantially uniform flow rate. The power generation performance of the plurality of cell stacks 101 is made substantially uniform.

  The fuel gas discharge chamber 219 is an area surrounded by the lower casing 229b and the lower tube plate 225b of the SOFC cartridge 203. The fuel gas discharge chamber 219 communicates with a fuel gas discharge branch pipe 209a (not shown) through a fuel gas discharge hole 231b provided in the lower casing 229b. In the fuel gas discharge chamber 219, the other end of the cell stack 101 is disposed with the inside of the base tube 105 of the cell stack 101 open to the fuel gas discharge chamber 219. The fuel gas discharge chamber 219 collects the exhaust fuel gas that passes through the inside of the base tube 105 of the plurality of cell stacks 101 and is supplied to the fuel gas discharge chamber 219, and is not shown through the fuel gas discharge hole 231b. It leads to the fuel gas discharge branch pipe 209a.

  Corresponding to the power generation amount of the SOFC module 201, a predetermined gas composition and a predetermined flow rate of oxidizing gas are branched to the oxidizing gas supply branch pipe and supplied to a plurality of SOFC cartridges 203. The oxidizing gas supply chamber 221 is a region surrounded by the lower casing 229b, the lower tube plate 225b, and the lower support 227b of the SOFC cartridge 203. The oxidizing gas supply chamber 221 communicates with an oxidizing gas supply branch pipe (not shown) through an oxidizing gas supply hole 233a provided in the lower casing 229b. The oxidizing gas supply chamber 221 generates a predetermined flow rate of oxidizing gas supplied from an oxidizing gas supply branch pipe (not shown) through an oxidizing gas supply hole 233a through an oxidizing gas supply gap 235a described later. It leads to the chamber 215.

  The oxidizing gas discharge chamber 223 is a region surrounded by the upper casing 229a, the upper tube plate 225a, and the upper support 227a of the SOFC cartridge 203. The oxidizing gas discharge chamber 223 communicates with an oxidizing gas discharge branch pipe (not shown) through an oxidizing gas discharge hole 233b provided in the upper casing 229a. The oxidant gas discharge chamber 223 is shown through the oxidant gas discharge hole 233b for the exhaust oxidant gas supplied from the power generation chamber 215 to the fuel gas discharge chamber 223 via an oxidant gas discharge gap 235b described later. The third oxidizing gas discharge branch pipe 209b is not led.

  The upper tube plate 225a is arranged between the top plate of the upper casing 229a and the upper heat insulator 227a so that the upper tube plate 225a, the top plate of the upper casing 229a and the upper heat insulator 227a are substantially parallel to each other. It is fixed to the side plate. The upper tube sheet 225a has a plurality of holes corresponding to the number of cell stacks 101 provided in the SOFC cartridge 203, and the cell stacks 101 are inserted into the holes, respectively. The upper tube sheet 225a hermetically supports one end of the plurality of cell stacks 101 through one or both of a sealing member and an adhesive member, and also includes a fuel gas supply chamber 217 and an oxidizing gas discharge chamber 223. And is to be isolated.

  The lower tube plate 225b is disposed on the side plate of the lower casing 229b so that the lower tube plate 225b, the bottom plate of the lower casing 229b, and the lower heat insulator 227b are substantially parallel between the bottom plate of the lower casing 229b and the lower heat insulator 227b. It is fixed. The lower tube sheet 225b has a plurality of holes corresponding to the number of cell stacks 101 provided in the SOFC cartridge 203, and the cell stacks 101 are inserted into the holes, respectively. The lower tube sheet 225b hermetically supports the other end of the plurality of cell stacks 101 through one or both of a sealing member and an adhesive member, and also includes a fuel gas discharge chamber 219 and an oxidizing gas supply chamber 221. And is to be isolated.

  The upper heat insulator 227a is disposed at the lower end of the upper casing 229a so that the upper heat insulator 227a, the top plate of the upper casing 229a and the upper tube plate 225a are substantially parallel to each other, and is fixed to the side plate of the upper casing 227a. Yes. Further, the upper heat insulator 227a is provided with a plurality of holes corresponding to the number of cell stacks 101 provided in the SOFC cartridge 203. The diameter of the hole is set larger than the outer diameter of the cell stack 101. The upper heat insulator 227a has an oxidizing gas discharge gap 235b formed between the inner surface of this hole and the outer surface of the cell stack 101 inserted through the upper heat insulator 227a.

  The upper heat insulator 227a separates the power generation chamber 215 and the oxidizing gas discharge chamber 223, and the atmosphere around the upper tube sheet 225a is heated to reduce the strength and the corrosion caused by the oxidizing agent contained in the oxidizing gas. Suppresses the increase. The upper tube sheet 225a and the like are made of a metal material having high temperature durability such as Inconel, but the upper tube sheet 225a and the like are exposed to the high temperature in the power generation chamber 215, and the temperature difference in the upper tube sheet 225a and the like becomes large. This prevents thermal deformation. The upper heat insulator 227a guides the exhaust oxidizing gas exposed to a high temperature through the power generation chamber 215 to the oxidizing gas exhaust chamber 223 through the oxidizing gas discharge gap 235b.

  According to this embodiment, due to the structure of the SOFC cartridge 203 described above, the fuel gas and the oxidizing gas flow so as to face the inside and the outside of the cell stack 101. As a result, the exhaust oxidizing gas exchanges heat with the fuel gas supplied to the power generation chamber 105 through the inside of the base tube 105, and the upper tube plate 225a made of a metal material is buckled. It is cooled to a temperature that does not cause deformation and supplied to the oxidizing gas discharge chamber 223. In addition, the temperature of the fuel gas is raised by heat exchange with the exhaust oxidizing gas discharged from the power generation chamber 215 and supplied to the power generation chamber 215. As a result, the fuel gas preheated to a temperature suitable for power generation can be supplied to the power generation chamber 215 without using a heater or the like.

  The lower heat insulator 227b is disposed at the upper end of the lower casing 229b so that the lower heat insulator 227b, the bottom plate of the lower casing 229b, and the lower tube plate 225b are substantially parallel to each other, and is fixed to the side plate of the upper casing 227a. . Also, the lower heat insulator 227b is provided with a plurality of holes corresponding to the number of cell stacks 101 provided in the SOFC cartridge 203. The diameter of the hole is set larger than the outer diameter of the cell stack 101. The lower heat insulator 227b has an oxidizing gas supply gap 235a formed between the inner surface of this hole and the outer surface of the cell stack 101 inserted through the lower heat insulator 227b.

  The lower heat insulator 227b separates the power generation chamber 215 and the oxidizing gas supply chamber 221, and the atmosphere around the lower tube sheet 225b is heated to lower the strength and corrode by the oxidizing agent contained in the oxidizing gas. Suppresses the increase. The lower tube plate 225b and the like are made of a metal material having high temperature durability such as Inconel. However, the lower tube plate 225b and the like are exposed to a high temperature and the temperature difference in the lower tube plate 225b and the like is increased, so that the heat is deformed. It is something to prevent. The lower heat insulator 227b guides the oxidizing gas supplied to the oxidizing gas supply chamber 233 to the power generation chamber 215 through the oxidizing gas supply gap 235a.

  According to this embodiment, due to the structure of the SOFC cartridge 203 described above, the fuel gas and the oxidizing gas flow so as to face the inside and the outside of the cell stack 101. As a result, the exhaust fuel gas that has passed through the power generation chamber 215 through the inside of the base tube 105 undergoes heat exchange with the oxidizing gas supplied to the power generation chamber 215, and the lower tube plate 225b made of a metal material. And the like are cooled to a temperature that does not cause deformation such as buckling, and supplied to the fuel gas discharge chamber 219. The oxidizing gas is heated by heat exchange with the exhaust fuel gas and supplied to the power generation chamber 215. As a result, the oxidizing gas heated to the temperature necessary for power generation can be supplied to the power generation chamber 215 without using a heater or the like.

  The direct-current power generated in the power generation chamber 215 is led out to the vicinity of the end of the cell stack 101 by the lead film 115 made of Ni / YSZ or the like provided in the plurality of fuel cells 105, and then the current collector rod (non-current) of the SOFC cartridge 203 The current is collected via a current collecting plate (not shown) to the outside of each SOFC cartridge 203. The electric power derived to the outside of the SOFC cartridge 203 by the current collector rod is connected to the generated power of each SOFC cartridge 203 in a predetermined series number and parallel number, and is derived to the outside of the SOFC module 201. It is converted into predetermined AC power by an inverter that does not, and supplied to the power load.

10 Combined power generation system 12 SOFC (fuel cell)
16 Gas turbine (internal combustion engine)
18 Compressor 20 Combustor 22 Turbine 24 Fuel supply line (fuel supply system)
32 Exhaust fuel supply line (Exhaust fuel supply system)
33 Recirculation line (recirculation system)
34 Control valve 36 Recirculation blower (blower)
41 Flow control valve

Claims (7)

A combined power generation system comprising a fuel cell and an internal combustion engine operated using exhaust fuel gas discharged from the fuel cell,
An exhaust fuel supply system for supplying the exhaust fuel gas from the fuel cell to the internal combustion engine;
A recirculation system provided by branching from a branch point of the exhaust fuel supply system and returning the exhaust fuel gas to the fuel cell;
In the exhaust fuel supply system, the fuel system of the cell stack provided inside the fuel cell is provided with a predetermined pressure difference with respect to the pressure of the air system of the fuel cell. A control valve that adjusts the pressure to be higher,
In the exhaust fuel supply system, a flow rate adjustment valve that is provided downstream of the branch point and adjusts the flow rate of the exhaust fuel gas flowing through the recirculation system;
When it is detected that the opening degree of the control valve is equal to or less than a specified value or the opening / closing speed during the closing operation of the control valve is equal to or greater than a specified value, the fuel stack is connected to the air system in the cell stack. A leakage determination unit that determines that fuel gas leakage has occurred;
A combined power generation system comprising: A blower provided upstream of the branch point and downstream of the control valve in the exhaust fuel supply system;
When it is detected that the opening degree of the control valve is equal to or less than a specified value, or the opening / closing speed during the closing operation of the control valve is equal to or greater than a specified value, the rotation speed of the blower is set to a predetermined minimum rotation speed. A rotation speed setting section;
The combined power generation system according to claim 1, further comprising: The opening degree of the control valve before determining that fuel gas leaks from the fuel system to the air system in the cell stack is stored as a normal opening degree,
3. The combined power generation system according to claim 2, further comprising a control valve control unit that returns the opening degree of the control valve to the normal opening degree when the rotation speed of the blower is set to the predetermined minimum rotation speed. A flow rate adjusting valve control unit that shuts off the flow rate adjusting valve when the rotation speed of the blower is set to the minimum speed;
The combined power generation system according to claim 2 or 3, wherein the control valve control unit adjusts an opening degree of the control valve so that a flow rate of the exhaust fuel gas flowing through the recirculation system becomes a predetermined flow rate.   The hydrogen concentration detected by the hydrogen concentration detection unit for detecting the hydrogen concentration in the exhaust fuel gas flowing through the exhaust fuel supply system, or the voltage detected by the battery voltage detection unit for detecting the voltage of the fuel cell The combined power generation system according to claim 4, further comprising an operation determination unit that determines whether or not the operation of the fuel cell can be continued based on the above.   When continuing the operation of the fuel cell based on the determination result of the operation determination unit, the control valve control unit controls the control valve so that the flow rate of the exhaust fuel gas flowing through the recirculation system becomes a predetermined flow rate. The combined power generation system according to claim 5, wherein the rotation speed setting unit increases the rotation speed of the blower after the control valve is fully opened. A control method for a combined power generation system comprising a fuel cell and an internal combustion engine operated using exhaust fuel gas discharged from the fuel cell,
Supplying the exhaust fuel gas from the fuel cell to the internal combustion engine in an exhaust fuel supply system;
Returning the exhaust fuel gas to the fuel cell in a recirculation system provided by branching from a branch point of the exhaust fuel supply system;
In the exhaust fuel supply system, a control valve provided upstream from the branching point has a predetermined fuel system of a cell stack provided in the fuel cell with respect to the pressure of the air system of the fuel cell. Adjusting the pressure to increase with the pressure difference;
A step of adjusting a flow rate of the exhaust fuel gas flowing through the recirculation system by a flow rate adjusting valve provided downstream of the branch point in the exhaust fuel supply system;
When it is detected that the opening degree of the control valve is equal to or less than a specified value or the opening / closing speed during the closing operation of the control valve is equal to or greater than a specified value, a leak determination unit is connected to the cell stack from the fuel system. Determining that fuel gas leaks to the air system;
With
When it is determined that the fuel gas has leaked, a predetermined number of revolutions of a blower provided upstream of the branch point and downstream of the control valve is determined in the exhaust fuel supply system. Step to set the minimum number of revolutions,
Storing the opening degree of the control valve before determining that the fuel gas has leaked as a normal opening degree, and returning the opening degree of the control valve to the normal opening degree;
Adjusting the opening degree of the control valve so that the flow rate of the exhaust fuel gas flowing through the recirculation system becomes a predetermined flow rate after shutting off the flow rate adjustment valve;
A control method for a combined power generation system comprising:

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