JPS62119869A - Control system for fuel cell power generation plant - Google Patents

Abstract

PURPOSE:To stabilize the state of electricity generation over the entire range of load and increase the efficiency of the generation, by keeping the flow rate of hydrogen gas and the coefficient of utilization of fuel or the flow rate of oxygen gas within prescribed ranges to provide a function of controlling the flow rate of recycling. CONSTITUTION:When a load command 100 is entered, a setting calculator 42 computes the flow rate of hydrogen gas needed by a fuel cell 11 and determines a set flow rate signal 52. The flow rate of hydrogen gas currently supplied to a fuel electrode 11A is computed by a calculator 40 in terms of a fuel gas flow rate signal 50 from a fuel gas flow meter 30 and a hydrogen gas concentration signal 51 from a hydrogen gas concentration meter 31, and a measured flow rate signal 53 is determined by the calculator. A comparator 43 compares the signals 52, 53 with each other and determines a flow rate deviation signal 54. An appropriate calculating function is previously set in a second calculator 41 which receives the deviation signal 54 from the comparator 43 and sends out a valve opening degree target signal 55 to make the degree of opening of a recycled fuel flow rate control valve 32 appropriate. The signal 55 is converted into a valve opening degree control signal 56 through a controller 44 to regulate the degree of opening of the control valve 32. The flow rate of recycled fuel is thus altered so that the flow rate of the fuel gas to the fuel electrode 11A is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell power generation system, and more particularly, to a fuel cell power generation system that controls the flow rate of reactant gas in a fuel cell using a recirculation flow lid for fuel exhaust gas containing hydrogen or air exhaust gas containing oxygen. This invention relates to a control system for a fuel cell power generation plant that performs the following adjustments.

[Technical background of the invention and its problems]

In recent years, fuel magnetoelectric power generation systems have become known as systems that directly convert the energy contained in fuel into electrical energy. This fuel cell power generation system usually configures a fuel (magnetic) by arranging a pair of porous membranes sandwiching an electrolyte, and also brings a fuel such as hydrogen into contact with the rear surface of one of the membranes. On the other hand, the back side of IIE (2) is to bring an oxidizing agent such as oxygen into contact with each other and use the electrochemical reaction that occurs to extract electrical energy from the above-mentioned Electrical energy can be extracted with a low conversion efficiency as long as the oxidizing agent is supplied.

FIG. 7 shows the basic configuration of this type of alternative fuel cell power generation system. In the figure, natural gas,
Alternatively, the fuel 1 made of fossil fuel such as coal gas and the steam from the steam supply device 2 are controlled by the fuel flow control valve 3 and the steam flow control valve 4, respectively, so that the mixing molar ratio of steam and carbon is 3 to 5. The internal reforming contact tube is introduced into the fuel reformer iLS under controlled conditions.

Here, the steam and the fuel 1 are heated at about 500 to 600°C to perform a reforming reaction, and then (-) the shift converter 7 becomes a fuel gas with a high hydrogen content. The fuel gas is sent to the fuel gas steam water separator 8 (:) and after removing excess steam from reforming, it is sent to the auxiliary burner 9 via the auxiliary burner fuel flow rate l54W!J valve 10.
Further, the fuel gas flow rate tA to the fuel electrode 11A of the fuel cell 11 is
Each biL child is controlled and sent by the intermediary 12.

Hydrogen in the fuel gas that has flowed into the fuel electrode 11A of the fuel cell 11 undergoes a medium reaction with oxygen in the air into which the oxidizer 11B current is flowing, and as a result, a portion of the fuel is consumed and 7 electrical energy is generated. and reaction product water are obtained.

The fuel exhaust gas that exits the fuel i 11A and contains a portion of the reaction product water produced in the fuel cell 11 is sent as fuel to the main burner 13 of the fuel reformer 5 described above.
During this process, the fuel exhaust gas passes through a steam/water separator 16 in order to recover moisture in the gas.

Then, the fuel exhaust gas sent to the main burner 13 is burned in the fuel reformer IJt device 5, heats the reforming catalyst tube 6, and then is discharged as high-temperature exhaust gas 17.

Furthermore, after combining with the air exhaust gas sent from the oxidizer 11B of the fuel cell 11, it is sent to the mixer 18 and used as part of the energy for driving the turbo compressor 19. On the other hand, the fuel gas sent to the auxiliary burner 9 is combusted within the auxiliary burner 9, and the combustion gas passes through the mixer 18 and enters the turbo compressor. 19 turbines 19A are driven.

On the other hand, the air discharged from the compressor 19B that connects the two turbines 19A and 19B to the auxiliary burner 9 and the main burner 13 is adjusted to adjust the auxiliary burner air flow to the main burner air flow mA and the main burner air flow mA to the auxiliary burner valve 21 (- The air is sent to the oxidizer electrode 11B of the fuel cell 11 by the air flow rate regulator 22, and the surplus is used as part of the energy for driving the turbo compressor 19. As & divider 1
Sent to 8. A part of the oxidizer 4fAIIBI=7'C air is consumed in contrast to the hydrogen of the fuel value 11A, and then is discharged containing the moisture generated in the oxidizer IIB. This discharged air exhaust gas is similar to the fuel exhaust gas (i.e., after a part of the steam in the air exhaust gas is condensed by the air exhaust gas steam/water separator 25, it joins with the high-temperature exhaust gas 17 from the fuel reformer 5).

As described above, the fuel cell 11 generates 4-ki energy so that the oxidizer electrode IIB becomes the positive electrode and the fuel electrode 1 becomes the negative electrode due to the catalytic reaction between the hydrogen in the fuel electrode 11A and the oxygen in the oxidizer electrode UB. A 70-ryo electric shock occurred and 11A was fired.

The electrical load C2 connected between 11B and 11B supplies the energy. At this time, the current value absorbed by the 4-air load 26 (2) is approximately proportional to both the electrodes 11A, IIB inlet (; the supplied hydrogen and oxygen react to obtain reaction product water, and this steam A large amount of unreacted gas containing gas is discharged from the exits of both 1! 11A and IIB.

On the other hand, a recycle pipe 14 connected to a fuel recirculation device is branched from the outlet of the fuel electrode 11A, and a portion of the fuel exhaust gas is passed through a fuel recirculation fan 15 to the inlet of the fuel waste 11A.

Alternatively, an air recycle pipe connected to an air recirculation device is branched from the outlet of the oxidizer electrode 11B, and a part of the air exhaust gas passes through an air recirculation fan and is then discharged to the inlet of the oxidizer electrode 11B.

These bipolar recirculation devices adjust the hydrogen concentration of the fuel exhaust gas and the oxygen concentration of the air exhaust gas, and adjust the cell generated voltage by the concentration distribution effect of the fuel cell. Also, they utilize the unreacted gas after the cell reaction. Since a larger amount of reactant gas can be supplied to the cells than batteries, the fuel cell plant can be operated at a higher load and has the effect of increasing the efficiency of the fuel cell plant.

In such a retraction state of the fuel cell system, in order for the fuel cell to maintain a stable output voltage and continue outputting the load/magnetic force according to the load command, the fuel supplied to the fuel pole inlet is The amount of hydrogen gas contained in the gas,
It is necessary that the amount of oxygen gas contained in the air supplied to the oxidizing agent inlet is adjusted to an appropriate amount. The appropriate amount here is the amount of reactant gas consumed in the cell reaction plus a certain amount of surplus unreacted gas.In general, in the case of hydrogen gas, this surplus is 2O4 for 2 reactants gas. In the case of oxygen gas, it is desirable to add a valence of about 40 or more to the reactive gas mass. Here, the fuel utilization rate is calculated by dividing the amount of hydrogen gas consumed by the reaction by the total amount of hydrogen gas contained in the fuel gas at the anode, and the amount of acid gas consumed by the reaction is calculated by dividing the amount of hydrogen gas contained in the oxidizer electrode fuel gas. The value divided by the amount of oxygen gas is called the air utilization rate. Regardless of the load current level of the fuel cell, if the reactant gas flow rate is not maintained at an appropriate value, that is, if the fuel utilization rate or air utilization rate is not maintained, an abnormal drop in the magnetoelectric voltage will occur. The inner fan is now required to continue stable power generation operation.

By the way, the problem with the fuel cell power generation plant having the above-mentioned recirculation system is how to adjust the flow rate of the reactant gas at the fuel cell inlet. The flow rate varies hourly (2) depending on the reaction characteristics of the fuel reformer 5 and shift converter 7, and when part of the exhaust gas is recirculated, the amount of unreacted limescale gas in the exhaust gas decreases depending on the load current of the fuel cell. As well as changing, it also depends on the mixing ratio with the fuel gas reformed in the reformer 5. In other words, the fuel utilization rate fluctuates due to these fluctuation factors, and the
- There is a possibility that the permissible range will be exceeded depending on the situation. Similarly, the flow rate of oxygen gas that is electrolytically eroded in the air at the oxidizer image inlet varies depending on the load's magnetic current and the mixing ratio with the compressed air of the compressor 19 when part of the exhaust gas is recirculated. In other words, the air utilization rate will fluctuate, and in some cases it may exceed the allowable range.

In other words, the hydrogen gas flow rate and fuel utilization rate in the fuel gas supplied to the fuel cell, or the oxygen gas flow rate and air utilization rate in the air supplied to the oxidizer electrode inlet are:
It is subject to constant changes due to the characteristics of the gas supply system, the load of the fuel cell, the magnetic current, or the recirculation and filtering. In other words, the load command (
2. In order to continue outputting the corresponding load current, as mentioned above, some method is required to adjust the amount of hydrogen gas at the inlet of the fuel electrode and the amount of oxygen gas at the inlet of the oxidizer electrode to an appropriate level. .

[Purpose of the invention]

The purpose of the present invention is to maintain the drowsiness load (accordingly, the weight of hydrogen gas contained in the fuel gas at the inlet of the fuel cell and the fuel utilization rate, or the flow rate of oxygen gas contained in the air and the air utilization rate) within a predetermined range. C2. By providing a control system for a fuel cell plant with a function to adjust the recirculation flow rate,
As a result, it is possible to obtain a stable starting state of the fuel cell over the entire range of cell load levels (;, and to ensure the maximum recirculation flow rate in range C2 where the above utilization rate is permissible). The objective is to realize the effect of increasing the efficiency of fuel cell plants.

[Overview of Kaimei]

The present invention is designed to adjust the recirculation flow rate using the gas detection value of the gas detector installed at the inlet or outlet of the fuel cell. A method in which the flow rate is directly adjusted using a flow joint valve C2 provided, and a portion of the discharge flow rate of the recirculation fan is returned to the suction side for recirculation through a bypass flow control valve provided between the suction side and the discharge side of the recirculation fan. A method of adjusting the flow rate at FA, - A method of adjusting the recirculation flow rate by installing a recirculation fan (knee rotation speed control device) to adjust the rotation speed of the recirculation fan and changing the discharge flow rate. The flow rate can be adjusted by one or combination C2.

[Implementation sequence of the invention]

Embodiments of the present invention will be described in detail below based on the drawings.

Note that the same parts in the drawings are designated by the same reference numerals.

1st Fuse Reli (Configuration) Figure 1 shows the configuration of the recirculation system for fuel speculation in the first example of the present invention. At the same time, a pair of electric oxidizers are arranged, and the oxidizer 11A is supplied with two fuel gases.
1B4 is a fuel cell which supplies air and extracts electrical energy from the space between the two 4's by an electrochemical reaction that occurs at this time; 15 is the fuel of the fuel cell 11 & the output of 11A
ll: Fuel that circulates part of the fuel exhaust gas discharged from the fuel value 11A back to the inlet side of the fuel electrode IIA? 4
The outlet 11111 of the recirculation fan is a recirculation fuel flow regulating valve for adjusting the discharge flow rate of the recirculation fan, and the valve is installed at the inlet line of the fuel electrode 11A.
A fuel gas flow meter 31 detects the flow rate of the fuel gas flowing through the line; 31 is a hydrogen gas concentration meter installed on the inlet line of the fuel electrode 11A to detect the hydrogen gas concentration of the fuel gas flowing through the line; 40 is the fuel gas concentration meter 40; The fuel gas flow rate signal (capital) detected by the flow meter (9) and the hydrogen gas mentioned above are connected to the straight needle 3.
1 is a computing unit that calculates the hydrogen gas (If) detected by No. 51 and supplied to the inlet side of the fuel electrode 11A; 41 is a computing unit that calculates the flow rate of the hydrogen gas detected by the computing unit; A second computing unit, which calculates the valve opening command signal port of the recirculation fuel flow ff1tA control valve 32 based on the comparison result, is reformed by the fuel reforming device d5, and is further modified by the shift converter 7, and This is a fuel gas flow rate control valve that adjusts the fuel gas that has passed through the fuel gas steam/water separator to fA'1rJ.

(action) ゛! J12 diagram is the fuel speculation flow of 5441 examples of the present invention! This is a block diagram showing the control, and shows the effect of the load command 100C2 corresponding to the output current and generated voltage of the fuel cell when the fuel fuel plant is in operation. Load command 1
When 00 is input, the setting calculator 42 selects the fuel cell 11.
The set flow rate signal 52 is obtained by calculating the required hydrogen gas flow rate. In addition, the calculator 40 calculates the current fuel value 11A i2 and the supplied hydrogen gas flow rate from the fuel gas flow rate signal from the fuel gas flow meter and the hydrogen gas concentration signal 51 from the hydrogen gas concentration meter 31, and generates a measured flow rate signal. Find 53. Next layer: The comparator section compares the set flow rate signal 52 and the defined flow f1 signal 53 to obtain the flow rate deviation signal 54. By using the flow 11 deviation signal 54 obtained by the comparator 43 as an input, the valve 32 of the recirculation fuel flow control valve 32 is opened so that it becomes an appropriate value, and the 1 target signal 55 is set. Here, for example, if the flow rate deviation signal 54 is positive (that is, the hydrogen gas flow rate at the battery inlet is too small), the valve opening degree 1 target signal 55 changes to increase the valve opening degree of the valve, Also, the flow rate deviation signal 54 is negative (that is, °(
If the flow rate of electrified hydrogen gas is excessive, the valve opening degree 1 target signal 55 can be determined to change so as to reduce the valve opening degree of the valve. Next, the valve opening degree 1 target signal 55 is PI
Through the regulator 44, which is composed of a D regulator, a limiter with a dead zone, etc., it is converted into a valve opening adjustment number 1d 56 for actually driving the valve with mechanical force, hydraulic pressure, or air pressure. I) Adjust the valve opening degree of the recirculation 4 fuel flow jtA face valve 32 by the signal.

+4 circulation 4 fuel flow jltfA By adjusting the valve opening degree of the control valve 32, the recirculation fuel flow rate changes, and the fuel gas miscarriage supplied to the fuel value 11A changes. Such adjustment of the valve opening is possible because the hydrogen gas measurement miscarriage signal 53 is a constant flow! This is repeated until the hydrogen gas approaches 1 to 52. As a result, the flow rate of hydrogen gas corresponding to the simulated load can be adjusted with the current command 100 so as to be supplied to the magnetic inlet.

C'A button) Fuel part 11A (in the fuel gas into which current is supplied), stable magnetization will not occur unless the flow rate of hydrogen gas injected is appropriately adjusted by negative commands such as output current and generated magnetic pressure. If this happens, it will cause a decrease in the performance of the fuel tank '1.The first column is based on the fuel gas flow rate 1 added with *υ on the population side of the fuel section 11A and the detection signal of the hydrogen gas aV meter 31. By determining the flow rate deviation between the calculated hydrogen gas flow rate and the set hydrogen gas flow rate set corresponding to the load command and adjusting the recirculation fuel flow rate), the fuel flow rate lIAζ = hydrogen extremely close to the set hydrogen gas flow rate. Since the gas flow rate can be supplied (-), it is possible to ensure an appropriate fuel utilization rate, and the fuel cell can continue to output a 9-load flow in accordance with the load command value while maintaining a stable output voltage. You can get the effect of being able to do this.

Second implementation row (configuration) Figure 3 shows a configuration diagram of the recirculation system on the fuel section side of the second example of the present invention.
Instead of the recirculation fuel flow rate control valve of 2, a new C: Fuel recirculation R fan 15 has a suction side and a discharge side (two bypass lines are provided, and a fuel bypass flow rate 14-node valve is installed between them.
Congratulations on what you accomplished.

(Operation) FIG. 4 is a block diagram showing flow rate control on the fuel section side in a second example of the present invention. The difference from the first example in Figure 2 is that the second example
The computing unit 41 calculates the flow rate deviation signal 5 obtained by the comparator 43.
4 as an input, calculates and outputs a valve opening 2 target signal 57 so as to match the valve opening of the fuel bypass flow rate control valve 33,
Further, the valve opening 2 target signal 57 is passed through the regulator 44 and converted into a valve opening 2 adjustment signal 58 for actually driving the valve with mechanical force, hydraulic pressure, or air pressure, resulting in a fuel bypass flow! The control valve was set to 114 degrees. By appropriately setting the operational X function of the calculator 41 in advance, for example, when the flow rate deviation signal 54 is positive, the valve opening degree 2 target signal 57 changes to reduce the valve opening degree of the valve in question. It is possible to reduce the bypass amount of the flow rate discharged by the fuel recirculation fan 15 and increase the amount of fuel gas recirculated to the fuel section 11A. Further, when the flow rate deviation signal 54 is negative, the valve opening degree 2 target signal 57 changes to increase the valve opening degree of the valve concerned, and can act to reduce the amount of fuel gas recirculated to the fuel section 11A. .

(effect) The same effect as in Example 1 can be obtained.

s3 Example (Configuration) Figure 5 shows the present invention! This is a diagram showing the configuration of the fuel recirculation system for example P13.The difference from the first example in Figure 1 is that instead of the recirculation flow rate control valve, a fuel recirculation fan 15 is installed at tR7'c. It is noted that a rotation speed regulator 34 is provided in the structure.

(Operation) FIG. 6 is a block diagram showing flow rate control on the fuel section side of the W2B example of the present invention. The difference from No. 11yIl in FIG. Calculate and output 59,
In addition, the actual @(1
777 rotation speed is 11m.
This is achieved by determining the i signal 60 and adjusting the rotation speed of the fuel recirculation fan 15 to a14tftJ using the rotation speed adjustment device. By setting the computing unit iiL of the computing unit 41 appropriately in advance, for example, if the flow rate deviation signal is positive, the rotation number S 59 is set to the fuel recirculation fan 1.
5, the discharge flow rate of the fuel recirculation fan 15 is increased, thereby increasing the fuel recirculation fan 11A.
It can be operated to increase the amount of fuel gas that is recirculated. If the flow rate deviation signal is negative, the rotational speed target signal 59 changes to reduce the rotational speed of the fuel recirculation fan 15, thereby reducing the discharge flow rate of the fuel recirculation fan 15 and the amount of fuel gas recirculated to the fuel tank 11A. C2 can be used to reduce the

(effect) The same effects as in the first example can be obtained.

In the first to third embodiments described above, the fuel gas flow meter 30 or the hydrogen end direct meter 31 was provided on the inlet side of the fuel 11A (; however, its e direct is not limited to this;
Even if installed on the outlet side of the fuel tank 11A, the calculation unit 40 calculates and adds the amount of hydrogen gas consumed in the cell reaction according to the load current, etc. From C2, the hydrogen gas flow rate at the inlet of the fuel tank 11A can be estimated and calculated. The same applies if

In addition, although the embodiments from the 1st column to the 31st/IJ explain different configurations, these various methods can be combined depending on the case to reduce hydrogen in the fuel gas supplied. The gist of the present invention can also be applied even if the gas flow rate is adjusted.

The above is an example of the fuel tank 11A for a fuel cell.In the case of the air tank 11B, the same equipment is used and the oxygen gas source that supplies the air tank 11Bl2 with the same action is described. The gist of the present invention can be applied in that the air utilization rate can be reduced to gwJ.

〔Effect of the invention〕

As explained above, according to the present invention #y3, there is a fuel reformer that reformes the raw fuel as a mixed component into a fuel gas mainly composed of hydrogen, and an air supply device that supplies compressed air #i.

A fuel cell that outputs a magnetic current due to the reaction between hydrogen in the fuel gas and oxygen in the compressed air, a fuel cell cooling device that cools the reaction heat of the fuel cell, and an unreacted magnetic current that has passed through the fuel cell. A recirculation device configured to recirculate a portion of the fuel exhaust gas containing hydrogen and/or the air exhaust gas containing unreacted oxygen through the recirculation fan. In a fuel cell power generation plant configured with the above, a gas is provided at the inlet side line or outlet line of the fuel cell to detect the hydrogen gas concentration or oxygen gas concentration in the gas flowing through the line. a detector, a flow meter installed on the inlet side line of the fuel cell to detect the gas flow rate flowing through the line, and a gas concentration signal detected by the gas detector and a gas concentration signal detected by the flow meter (; A computing unit that computes the flow rate of a reactive gas such as aqueous gas or oxygen gas supplied to the fuel cell inlet based on the gas miscarriage signal, and a ratio of the flow rate of the computing unit to the set reactive gas flow rate @result By proposing a control system for a fuel cell power plant, which is characterized by comprising a controller that controls the recirculation flow rate of the recirculation device based on the The recirculation flow value is adjusted to directly match the hydrogen gas flow rate and fuel utilization rate contained in the fuel gas at the rX pond inlet, or the nitrogen gas flow rate and air utilization rate contained in the air, within a predetermined range. This makes it possible to realize a fuel cell plant with a high efficiency, which allows stable fuel cell power generation over the entire range of cell load levels. By ensuring the maximum recirculation flow rate with !/), it is possible to achieve the effect of increasing the efficiency of the fuel cell plant.

[Brief explanation of drawings]

Figure #1 is a configuration diagram of the first column of the present invention, and Figure #2 is a diagram of the first column of the present invention. lj control block diagram, FIG. 3 is a configuration diagram of the second example, FIG. 4 is a control block diagram of the second embodiment of the present invention, and FIG. 5 is an agreement diagram of the third embodiment of the present invention. , FIG. 6 is a control block diagram of a third embodiment of the present invention, and FIG. WI7 is a configuration diagram showing a conventional fuel supply system. 1 Fuel 7 Transformer 2 Steam supply device 8 Fuel gas steam water separator 3 Fuel flow rate 7m valve 9 Auxiliary burner 4 Steam flow key adjustment valve 10 Yanagibuki Nanen training - Utakyaku 5 En'4 + revised lX table direct 11 Fuel cell 6 Reforming contact tube IIA Fuel Association 11B Air electrode 3
2 Recirculation fuel flow control valve 12 Fuel gas flow control valve O Fuel bypass flow control valve 13 Main burner A Rotation speed regulator 14 Fuel recycling piping
40 Computing unit 15 Fuel recirculation fan 41
Second computing unit 16 Fuel exhaust gas A water separator 42
Setting YL armpit 17 High temperature exhaust gas 43 Comparator 18 Mixer 44 Adjuster 19
Turbo compressor 5o Fuel gas flow signal 1
9A turbine 51 hydrogen gas 1lII degree signal 19B compressor 52 set flow rate signal 20
try<-Kunuichishusho 53 Measured flow rate signal 21
Main Pursu Fallen Sabaguchi Shigamingo 8 Flow rate deviation signal section Air flow rate adjustment valve 55 Valve opening l target signal 23 Air retake piping 56 Valve opening l adjustment signal 24 to air recirculation fan 57 fP opening 2 target signal 25 Nitrogen exhaust gas steam/water separator 58 Valve opening degree 2 is electrical load 59 Number of revolutions - II (!9
Garden Fuel gas flow meter ω Rotation speed i, 11 node signal 31
Hydrogen gas concentration meter 100 load command figure 1 offshore, ? 2 Figure 2 Figure 3 X-33 Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) A fuel reformer that reforms raw fuel as a mixed component into fuel gas for hydrogen generation, an air supply device that supplies compressed air, and a reaction between hydrogen in the fuel gas and oxygen in the compressed air. A fuel cell that outputs current, a fuel cell cooling device that cools the reaction heat of the fuel cell, and either or both of a fuel exhaust gas containing unreacted hydrogen and an air exhaust gas containing unreacted oxygen that has passed through the fuel cell. A fuel cell power plant comprising a recirculation device configured to recirculate part of the exhaust gas of the fuel cell to the inlet side of the fuel cell through a recirculation fan, the inlet line or the outlet side of the fuel cell. a gas detector provided in the line to detect the hydrogen gas concentration or oxygen gas concentration in the gas flowing through the line; a flowmeter provided in the inlet side line of the fuel cell to detect the gas flow rate flowing through the line; a computing unit that computes a flow rate of a reactant gas such as hydrogen gas or oxygen gas supplied to the fuel cell inlet from a gas concentration signal detected by the gas detector and a gas flow rate signal detected by the flow meter; and the computing unit A control system for a fuel cell power generation plant, comprising: a controller that compares the calculated flow rate of the flow rate with a set reaction gas flow rate and controls the recirculation flow rate of the recirculation device based on the comparison result. . (2) In the control system for a fuel cell power generation plant according to claim 1, the controller includes a flow rate control valve in a line connected to the recirculation fan, and the calculated flow rate of the calculator and the set reaction gas. and a second calculator that calculates a valve opening command signal for the flow rate control valve based on the comparison result with the flow rate and outputs the signal to the control valve, thereby adjusting the recirculation flow rate of the recirculation device. A control system for a fuel cell power generation plant featuring: (3) In the control system for a fuel cell power plant according to claim 1, the controller includes a bypass flow rate control valve between the suction side and the discharge side of the recirculation fan, and a calculated flow rate of the arithmetic unit. A second calculator is provided which calculates a valve opening command signal for the bypass flow rate control valve based on the comparison result between the current flow rate and the set reaction gas flow rate, and outputs the signal to the control valve. A control system for a fuel cell power generation plant, characterized in that the control system adjusts. (4) In the control system for a fuel cell power generation plant according to claim 1, the controller includes a rotation speed control device for the recirculation fan and compares the calculated flow rate of the calculator with the set reaction gas flow rate. A fuel cell characterized in that a second computing unit is provided which calculates a rotation speed command signal of the recirculation fan from the result and outputs it to the rotation speed control device, thereby adjusting the recirculation flow rate of the recirculation device. Power plant control system.