JPS5918577A - Control system of fuel cell power generating plant - Google Patents

Abstract

PURPOSE:To improve dynamic characteristics and decrease by-pass energy loss to increase heat efficiency by controlling an air supply apparatus which supplies air to a fuel cell by installing a heat balance controller. CONSTITUTION:A heat balance controller 8 is installed, and a detected pressure P and a setting pressure Po of discharge air are inputted to a signal converter 9. Its output and the output obtained by giving an added value of a detected value F and a reference value Fo of by-pass flow rate to a PI controller 11 are added and inputted to signal converters 13 and 14, and flow rate of auxiliary burner is controlled with output of the converter 13. Output of the converter 14 is inputted to a signal converter 16 with hydrogen gas temperature T and setting value T1. Fuel flow rate correction signal of a reformer is outputted through an adder 17 and an adder 19 which adds output LD3 of a PI controller 18 and a load follow- up controller. Dynamic characteristics of an air supply apparatus is improved and power generating efficiency is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for a fuel cell power generation plant, and particularly to a control method for an air supply device that supplies air to a fuel cell.

A fuel cell power generation plant uses oxygen in the air supplied from an air supply device and hydrogen-rich gas (hereinafter simply referred to as hydrogen gas) generated by reforming raw fuel using a reformer to feed it into a fuel cell. This is a system configuration that can effectively recover waste heat and improve heat balance in order to improve the overall thermal efficiency of the plant and increase power generation efficiency. Various proposals have been made. For example, there is a method of controlling the amount of air supplied to the fuel cell and the amount of recirculation according to the load power (see Japanese Patent Publication No. 48-41352), and a method of controlling the amount of raw fuel supplied to the reformer according to the load power and the reformer temperature. System configurations have been devised, such as a method of increasing the pressure of the reformer (Japanese Patent Publication No. 50-15058) or a method of making the pressure of the reformer higher than that of the battery (Japanese Patent Application Laid-Open No. 53-81923).

In conventional fuel cell power plants, including the examples mentioned above, waste hydrogen gas containing unreacted hydrogen discharged from the fuel cell is generally used as a fuel to heat other equipment in the plant, such as a reformer. It is used as a part. Also,
Since the combustion exhaust gas discharged from this reformer is high temperature, it is used to drive an exhaust heat turbine, and this turbine power is used to operate an air compressor to supply the air necessary for the plant. has been devised. However, an auxiliary burner device is provided because the energy of the combustion exhaust gas alone is insufficient to supply the required amount of air to the plant, and to ensure controllability of the air supply device.

Furthermore, energy from waste air discharged from the fuel cell is also recovered as drive energy for the turbine.

On the other hand, it is necessary to control the amount of hydrogen gas, gas, and air supplied to the fuel cell in response to fluctuations in the power load, and in order to maintain the reaction efficiency within the fuel cell, it is necessary to control the amount of hydrogen gas, gas, and air supplied to the fuel cell. Pressure and air pressure must be maintained at specified values. Therefore, the above-mentioned air supply device driven by combustion exhaust gas, etc., can supply the required amount of air and control the discharge pressure at a constant level even if part of the drive energy fluctuates due to changes in the electric power load. It has to be possible. Therefore, it has been devised to follow the excess or deficiency of drive energy by controlling the fuel flow rate of the auxiliary burner device. However, the dynamic characteristics of such a control method include a control delay element in the auxiliary burner device, so controlling the air discharge pressure to follow load fluctuations requires only controlling the fuel flow rate of the auxiliary burner device. It is inferior in terms of responsiveness. Therefore, a bypass control valve is provided in the discharge system of the air supply device or the turbine inflow gas system of the air supply device to release the discharge air or the turbine inflow gas to the outside of the system, thereby improving responsiveness.

However, since the drive energy supplied to the air supply device due to power load fluctuations and the form of fluctuations in the required air amount have a complex causal relationship, the above-mentioned auxiliary burner fuel control and bypass flow control With the control system for the air supply device consisting of the three systems described above, it has been difficult to coordinate these controls. For this reason, in the past, bypass flow rate control was mainly used, which had the disadvantage that a large amount of effective energy was released outside the system (for example, into the atmosphere), resulting in a decrease in thermal efficiency.

Additionally, due to abnormalities in the system components of fuel cell power generation plants, the exhaust gas salinity and flow rate of the reformer, which is the driving energy for the air supply device, may decrease, or the required amount of air may increase abnormally. For example, even if the fuel flow rate of the auxiliary burner is increased to the rated flow rate, the air discharge pressure may not be restored to a predetermined pressure. In this case,
Since the air pressure inside the fuel cell is reduced, there is a risk that the reaction will be slowed down and the power generation efficiency will be reduced.

An object of the present invention is to provide a fuel cell power generation system that can improve thermal efficiency and power generation efficiency by improving the dynamic characteristics of control of an air supply device, reducing bypass flow rate, and further suppressing abnormal decreases in air pressure. The objective is to provide a plant control system.

The present invention provides a reformer that supplies hydrogen gas to a fuel cell;
Air that is formed from an auxiliary burner device, a turbine whose driving gas is the combustion exhaust gas of the auxiliary burner device and the combustion exhaust gas of the reformer, and an air compressor driven by the turbine and supplies air to the fuel cell. A supply device, a pressure detector for the discharge air pressure of the air supply device, and a bypass control valve that bypasses at least one of the discharge air and the turbine drive gas to outside the system when the detected pressure is equal to or higher than a predetermined set pressure. In the fuel cell power generation plant configured, a first signal converter outputs a pressure deviation signal according to a deviation between the detected pressure and the set pressure, a bypass flow rate detector for the bypass flow rate, and the detected bypass flow rate. a first adder which inputs the reference value of a predetermined minimum bypass flow rate by one person; a PI regulator which receives the output signal of the adder; and an output signal of the PI regulator and the pressure deviation. a second adder that receives a signal as an input; and a fuel control signal for the auxiliary burner device in which the output signal of the adder increases in proportion to the output signal up to a predetermined set value and then remains at a constant value. a second signal converter that outputs a signal, and a third signal converter that outputs a signal that is increased in proportion to the output signal of the second adder when the output signal is greater than or equal to the predetermined set value; and a fourth signal converter that outputs a fuel flow rate correction signal for the reformer according to the output signal of the signal converter, thereby reducing the bypass flow rate and maintaining the air discharge pressure at a predetermined pressure. The aim is to improve thermal efficiency and power generation efficiency.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 shows an overall system configuration diagram of a fuel cell power generation plant according to an embodiment of the present invention.

As shown in FIG. 1, each of the reaction section IA, combustion chamber IB, and auxiliary burner device 4 of the reformer 1 has a flow control valve FCV.
I and F'CV2. Raw fuel 100 is supplied via POY3. Hydrogen gas 1 generated in this reaction part IA
04 is supplied to two fuel chambers of the fuel cell 2, and waste hydrogen gas 105 containing unreacted hydrogen gas is discharged from this fuel chamber 2A, and this waste hydrogen gas 105 is supplied to the pressure control valve PCV'.
1 to the combustion chamber IB of the reformer 1 (9
) Ru. Air supply device 3Fi, air compressor 3A and turbine 3
B, and a flow control valve FCV4°POY5. P
Air is supplied to the air chamber 2B of the fuel cell 2, the combustion chamber IB of the reformer 1, and the auxiliary burner device 4 via the OY6. Further, the air discharge system of the air supply device 3 is opened to the atmosphere via a bypass control valve PCV2. The combustion exhaust gas 106 of the combustion chamber IB of the reformer i, the combustion exhaust gas 107 of the auxiliary burner device 4, and the waste air 108 from the air chamber 2B of the fuel cell 2 flow into the turbine 3B via the pressure control valve PCV3. ing.

A load 5 is connected to the electrodes 2C and 2D of the fuel cell 2.

The flow control valves FCVl, FCV2. POY3. P.O.Y.
4゜POY5. POY6 is a flow rate detector F'TI,
FT2゜FT3. FT4. FT5. To FT6, line 201
202, 203, 204, 205, 206. Further, the pressure control valve pcvi.

POY3. POY3 U, lines 207, 208, 2 respectively
09, the pressure detectors PTI, PT2. To PT3 (
10) Connected. A load power detection signal LD from the load 5 is input to the load following controller 6 via a line 210. This load following controller 6 is connected to the PCI and FC4 by lines 211 and 212, respectively, and is connected to the PCI and FC4 by lines 21
3 to the air ratio controller 7 and by line 214 to the heat balance controller 8. The air ratio controller 7 includes the flow rate detectors FTI, F'l'2. FT3, each line 20
1 and 20 are connected by 203. moreover,
This air ratio controller 7 is connected to the flow controllers FC5, FC6 by lines 215, 216, respectively. The input end of the heat balance controller 80 is connected by a line 217 to a hydrogen gas temperature sensor TTI provided at the outlet of the reformer 1.
By a line 218 to a flow rate sensor FT7 provided downstream of the bypass control valve PCV2, and also to said pressure sensor PT.
2 by wires 208, respectively. The output end of this heat balance controller 8 is connected to the flow rate controllers F'C2, FC3 by lines 219, 220, respectively.

A detailed configuration diagram of the heat balance controller 8 is shown in FIG. 2 (11). ing.

In FIG. 2, the first signal converter 9 includes the line 208.
A detected pressure P of the discharge air pressure and a set pressure P0 of the discharge air pressure are inputted from the pressure detector PT2 via the pressure detector PT2. The detected flow rate F of the bypass flow rate is inputted to one input terminal of the first adder 10 from the flow rate detector FT7 via a line 218.
The reference value F of the minimum bypass reference flow rate is at the input terminal. is input, and the output of this adder 10 is input to a second adder 12 via a PI adjuster 11. This adder 12
The output signal Sm of the first signal converter 9 is inputted to the adder 12, and the output signal Sl of the adder 12 is inputted to the second signal converter 13 and the third signal converter 14, respectively. There is. A set value 5110 is input to the second signal converter 13, and an output signal Sc is input to the flow rate controller FC3 through a line 220. Said third signal converter 1
The set value Si6 is input to the fourth signal converter 1, and the output signal SD is converted to a signal 8m via the coefficient multiplier 15.
6 is input. Furthermore, the detected temperature T and the set value T of the hydrogen gas temperature are input to the fourth (12) signal converter 16 via a wire 217 stranded in the temperature detector TT1. One input terminal of the third adder 17 receives the detected temperature T, and ten input terminals receive the output signal 8y of the fourth signal converter and the set value T.

is entered. The output of this adder 17 is input to a fourth adder 19 via a PI adjuster 18. Further, the other input end of this adder 19 is connected to the load following controller 6 by a line 214, and the output end is connected to the flow rate controller FC2 by a line 219.

The operation of the embodiment configured in this way will be described below.

In the reformer 1, raw fuel 101 flows into the reaction chamber IA.
The heat given to combustion chamber IB causes hydrogen gas 10
4 and is supplied to two fuel chambers of fuel cell 2. In the fuel cell 2, a voltage is generated across the electrodes 2C and 2D due to an electrochemical reaction between the air 113 supplied to the air chamber 2B from the air supply device 3 and the hydrogen gas 104. Electric power generated in this fuel chamber (13) pond 2 is output to a load 5.

Waste hydrogen gas 1 that was not consumed by the reaction of the fuel cell 2
05 is sent to the combustion chamber IB, and waste air 108 is sent to the turbine 3.
It is discharged to B.

In the combustion chamber IB of the reformer, heat is supplied to the reaction chamber IA by combusting the waste hydrogen gas 105 and the raw fuel 102. This combustion exhaust gas 106 is generated by the turbine 3B.
is being discharged. The turbine 3B uses the waste air 108
, and is driven by a driving gas 109 mixed with combustion exhaust gas 106 and combustion exhaust gas 107 of the auxiliary burner device 4.

Next, the control method will be explained.

Flow rate control valve 11'CV1~6 and pressure control valve PCVI~
3, the opening degree is controlled by the corresponding flow rate controllers FC1 to FC6 and pressure controllers PC1 to PC3, respectively.

Since the reaction of the fuel cell 2 reduces the power generation efficiency when the pressure is low, the hydrogen gas pressure in the two fuel chambers is controlled by PCVI, and the air pressure in the air chamber 2B is controlled to a constant value by POY3. has been done.

(14) Hydrogen gas 104 and air 1 consumed by fuel cell 2
13 varies depending on the load power, so the flow rate of the raw fuel 101 is determined by the signal LD1°LD, which is determined in correlation with the detected values T and D of the load power output from the load following controller 6. , and the flow rate of air 113 is F'
This is handled by controlling with CV4.

For example, when the load power increases, the FCVI
is opened and the flow rate of raw fuel 101 is increased. As a result, in order to prevent the temperature of the hydrogen gas 104 from decreasing, the flow rate of the raw fuel 102 flowing into the combustion chamber IB is determined by the load input to the third adder 19 of the heat balance controller 8. The detected temperature T and the set temperature T are subjected to shifted forward control by the signals L I) and i from the follow-up controller 6, and further output from the temperature detector TTI. It is corrected according to the deviation from At this time, in order to control the amount of combustion air of the waste hydrogen gas 105 and the raw fuel 102, the air ratio controller 7 calculates the theoretical air amount A from the respective flow rates output from the flow rate detectors FT1 and FT2. 15) It's out. For example, if the raw fuel is methane gas, the flow rate of the raw fuel 101 is FGI (Nm”/s), and the raw fuel 1
The theoretical air amount A? (Nm”/S) is calculated using the following formula 4% (1) The flow rate control valve FCV5 is controlled by a control signal obtained by multiplying the theoretical air amount calculated by the air ratio controller 7 by the excess air ratio (for example, 1.3). By controlling the combustion chamber IB, the combustion chamber IB is controlled in accordance with the increase in the load power.

Moreover, when the air consumption increases, the discharge air pressure of the air compressor 3A is reduced. Since this decrease in air pressure reduces the reaction efficiency of the fuel cell as described above, the heat balance controller 8 sets the detected pressure P of the discharged air detected by the pressure detector PT to a set pressure P. The flow rate of the raw fuel 103 of the auxiliary burner device (16) 4 is controlled so as to match the auxiliary burner device (16) 4.

This will be explained in detail using FIGS. 2 and 3.

The first signal converter 9, as shown in FIG. 3(A),
It outputs an output signal S on the vertical axis that is decreased in response to an increase in the detected pressure P of the input signal on the horizontal axis, and the detected pressure P is the set pressure P of the discharge air pressure. If it is above, the output signal S is O
becomes. As shown in FIG. 3 [F]), the second signal converter 13 increases the input signal Sm on the horizontal axis in proportion to 8++ when it is less than the set value S++6. In the above cases, the flow rate control signal Sc on the vertical axis is outputted as a constant value.

The signal converter 14 of FIG. 3, as shown in FIG.
When the input signal S11 on the horizontal axis is less than the set value 810, the output signal is O, and when it is more than 810, the output signal SD on the vertical axis is increased in proportion to S++. As shown in FIG. 3(C), the signal converter 16 in FIG. 4 has the detected temperature T input from the temperature detector TTI on the horizontal axis.
When T is lower than the upper limit reference temperature T, the signal Sm input from the coefficient unit 15 is output as the output signal Sy on the vertical axis (17), and when T is 78 or higher, the output signal is obtained by gradually decreasing the Sg. It outputs SF.

Therefore, when the power load increases, the detected pressure P of the discharged air decreases as described above, and the first signal converter 9 sends a signal Sm corresponding to the deviation from the set pressure P0 to the second adder 12. is input. On the other hand, since the discharge air pressure is low, the detected flow rate F of the bypass flow rate is 0, so the reference value F0 of the minimum bypass reference flow rate is proportionally integrated by the PI controller and input to the second adder 12. There is. The adder 12 adds these input signals and outputs a signal S11. The second signal converter 13 sends a fuel control signal Sc for the raw fuel 103 of the auxiliary burner device 4 to the flow rate controller FC3 in response to the signal S++, thereby increasing the opening degree of the flow rate control valve FCV3. In this way, the combustion exhaust gas 107 discharged from the auxiliary burner device 4 is increased, and the driving gas 109 of the turbine 3B is increased, thereby increasing the discharge air pressure.

If the drop in discharge air pressure is large, close the flow control valve (18
) Even when FCV3 is fully opened, the discharge air pressure is the set pressure P.

may not be reached. The aforementioned setting value SBo is determined according to the upper limit output of the auxiliary burner device 4, and in the above-mentioned case, the signal SBo from the third signal converter 14 is
D is output to the coefficient unit 15.

The coefficient unit 15 is for coordinating the control characteristics of the flow control valves FCV2 and FCV3, and performs signal processing using the ratio of the maximum flow rates of these flow control valves as a coefficient.

The output signal Sv of the coefficient unit 15 is converted by a fourth signal converter 16 and sent to a third adder 17 as a signal 8y that increases the flow rate of raw fuel 10°1 flowing into the combustion chamber IB of the reformer. is input. Note that this signal converter 16 is
The signal S remains until the hydrogen gas temperature reaches the upper limit reference temperature T.
However, when the hydrogen gas temperature rises and exceeds T, the output signal Sy is decreased to protect the reformer. Note that the hydrogen gas temperature when the discharge air pressure is sufficiently controlled within the control range of the auxiliary burner device is input to the third adder 17. Normal setting temperature T.

Due to the deviation 16' between the detected temperature (19) and T, PIθl'! l Mj finger 1
8 is activated and burns through the fourth adder 19 ``41B
P control is performed by correcting the fuel control @ of the raw fuel 102.

Also, when the air consumption decreases and the discharge air pressure increases, the bypass control valve PCV2 operates and the bypass LM'
116, the increase in discharge air pressure is quickly suppressed. Subsequently, this bypass flow meter is detected by the flow detector FT7, and the detected flow tF is inputted to one input terminal of the first adder 10 shown in FIG.

The deviation from that is output. Standard fi11. Since F o is shortened to a value as close to 0 as possible within a controllable range, the output signal of the PI regulator is reduced by the PI operation. As a result, the output (if signal Sm) of the adder 12 is also reduced, and first, the output signal So of the third signal converter 14 is reduced.
is reduced to reduce the raw fuel flow value flowing into the combustion chamber IB of the reformer, and then the raw fuel control signal Sc of the auxiliary burner device is reduced by the second No. 18 converter 13, and the bypass The flow rate is kept to a minimum within a controllable range.

Note that an increase in discharge air pressure may cause surging of the air compressor or damage pressure piping, so as mentioned above, the highly responsive bypass system is used to quickly suppress the increase in discharge air pressure. Next, since it is desirable to control to reduce the bypass flow rate in order to improve thermal efficiency and to prevent mutual interference of control, the response time of the regulator 11 is It is desirable that the speed be at least twice as slow as PC2.

Therefore, according to this embodiment, when controlling the discharge air pressure of the air supply device to a constant value, the bypass control with excellent responsiveness is operated in response to an increase in air pressure, and then,
By controlling the drive energy of the turbine to be reduced to minimize the bypass flow rate, the increase in discharge air pressure is suppressed, which improves the dynamic characteristics of control, reduces energy loss associated with bypass, and improves thermal efficiency. You can see the effect of being treated.

(21) Furthermore, according to this embodiment, in response to a decrease in discharge air pressure,
To maintain the p air pressure constant by increasing the combustion exhaust gas of the auxiliary burner device, and to provide backup by increasing the combustion exhaust gas of the reformer within a certain limit in case of an abnormal drop in air pressure. This suppresses a drop in air pressure, which has the effect of improving the power generation efficiency of the fuel cell.

Note that the control method of the present invention is not limited to the above embodiments, and various applications are possible within the scope of the present invention.

For example, a bypass to maintain a constant discharge air pressure may release the driving gas of the turbine instead of releasing air, or a combination thereof. It is also possible to provide a pressure control valve at the turbine inlet to control the output of the turbine. Furthermore, the bypass flow rate can also be detected from the opening degree of the pressure control valve for bypass control.

As explained above, according to the present invention, the dynamic characteristics of the control of the air supply (22) supply device 4 are improved, the energy loss associated with bypass is reduced, and the thermal efficiency is improved.
Since abnormal decreases in air pressure can also be suppressed, power generation efficiency can be improved.

[Brief explanation of the drawing]

Fig. 1 is an overall system configuration diagram of a fuel cell power generation blunt according to an embodiment of the present invention, Fig. 2 is a detailed configuration diagram of the main control circuit of the embodiment shown in Fig. 1, and Fig. 3 (A). ~(I)
) is a diagram for explaining the operation. DESCRIPTION OF SYMBOLS 1... Reformer, 2... Fuel cell, 3... Air supply device, 3A... Air compressor, 3B... Turbine,
4... Auxiliary burner device, 9... First signal converter,
10... First benefit device, 11... PI adjuster, 12
...Second adder, 13...Second signal converter, 1
4... Third signal converter, 16... Fourth signal converter, PT2... Pressure detector, FT7... Bypass flow rate detector, POY3... fjJ t'. - 88' s, - JBo s, - Tt 1 pass

Claims (1)

[Claims] 1. A reformer that supplies hydrogen gas to a fuel cell, a turbine whose driving gas is combustion exhaust gas discharged from the reformer and the auxiliary burner device, and air driven by the turbine. an air supply device that is formed from a compressor and supplies air to the fuel cell; a pressure detector that detects the discharge air pressure of the air supply device; and when the detected pressure is equal to or higher than a predetermined set pressure, the discharge air and the turbine a bypass control valve that bypasses at least one of the drive gases to flow out of the system, in a fuel cell power generation plant configured to output a pressure deviation signal according to a deviation between the detected pressure and the set pressure. a first signal converter; a bypass flow rate detector for detecting the bypass flow rate; a first adder for determining the detected flow rate by one person and setting a reference value of a predetermined minimum bypass flow rate by one person; a PI controller that inputs the output signal of the PI controller; a second adder that inputs the output signal of the PI controller and the pressure deviation signal; a second signal converter that outputs a fuel control signal for the auxiliary burner device that is increased in proportion to the output signal when , and is kept at a constant value when it is or more. Control method for power generation plants. 2. A reformer that supplies hydrogen gas to the fuel cell, a turbine whose driving gas is combustion exhaust gas discharged from the reformer and the auxiliary burner device, and an air compressor driven by the turbine. an air supply device that is formed and supplies air to the fuel cell; a pressure detector that detects the discharge air pressure of the air supply device; and a pressure detector that detects the discharge air pressure of the air supply device; a bypass control valve that bypasses one side and flows out of the system; a first signal that outputs a pressure deviation signal corresponding to a deviation between the detected pressure and the set pressure; a converter, a bypass flow rate detector that detects the bypass flow rate, a first adder that uses the detected flow rate as input and has ten inputs as a reference value for a predetermined minimum bypass flow rate, and an output signal of the adder. a PI controller as an input; a second adder having ten inputs as the output signal of the PI controller and the pressure deviation signal; and when the output signal of the adder is below a predetermined set value, the output a second signal converter for outputting a fuel control signal for the auxiliary burner device, which is increased in proportion to the signal and otherwise kept at a constant value; a third signal converter that outputs a signal that is increased in proportion to the output signal when the output signal is greater than or equal to the set value of the signal converter;
and a fourth signal converter that outputs a correction signal for the fuel flow rate of the reformer according to the output signal of the signal converter. control method.