JPS62222571A - Fuel cell power generating plant - Google Patents

Abstract

PURPOSE:To keep oxygen concentration in an oxidizing agent or hydrogen concentration in fuel in a specified range to operate a plant by comparing a flow rate detected with a flow rate detector with a setting flow rate, and controlling the opening of a flow rate control valve. CONSTITUTION:When a load 26 varies, oxygen concentration in an oxidizing agent electrode outlet gas varies. In a control circuit 35, a converter 32 receives a load setting value signal (measured value signal) 26, and converts a load signal into a flow rate signal based on a function which specifies the relation of perviously set recycle flow rate and the load so that cell voltage is in a stable range. The deviation of the flow rate signal from an actual flow rate signal sent from a flow rate detector 28 is calculated with an adder 33, and the obtained signal is converted into an opening signal with an adjustor 24 and inputted into a flow rate control valve 27 to operate a valve. As a result, recycle flow rate is controlled in an optimum value. by controlling the flow rate in the recycling line, power generation is performed with steady cell performance retained, and exhaust gas in each electrode outlet is efficiently utilized.

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 in which the flow rate of exhaust gas at the outlet of a battery that is fed into a long cycle line can be adjusted. Regarding the system.

[Technical background of the invention and its problems]

In recent years, fuel cell power generation systems have become known as systems that directly convert energy contained in fuel into electrical energy. This fuel cell power generation system usually consists of a pair of porous electrodes arranged with an electrolyte in between, and a fuel such as hydrogen is brought into contact with the back of one electrode, and oxygen is brought into contact with the back of the other electrode. It is designed to extract electrical energy from between the electrodes by bringing an oxidizing agent such as, and utilizing the electrochemical reaction that occurs.
As long as the above fuel and oxidizer are supplied, electrical energy can be extracted with high conversion efficiency.

FIG. 3 shows the basic configuration of a typical fuel cell power generation system of this type. 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 control valve 3 and the steam control valve 4, respectively, so that the mixing molar ratio of steam and carbon is about 3 to 5. It is controlled and introduced into the reforming contact tube 6 in the fuel reformer 5. Here, the steam and fuel 1 are heated to about 500 to 600°C to perform a reforming reaction, and then pass through the shift converter 7 to become reformed fuel with a high hydrogen content. This reformed fuel with a high hydrogen content is
After being sent to the fuel gas steam/water densifier 8 to remove surplus steam from reforming, the reformed fuel is sent to the auxiliary burner 9 via the auxiliary burner fuel control valve 10 and to the fuel electrode 11A of the fuel cell 11. The control valve 12 controls the flow rate and sends the respective fluids.

The reformed fuel that has flowed into the fuel electrode 11A of the fuel cell 11 undergoes a catalytic reaction with the air flowing into the oxidizer (~11B), and as a result, a portion of the fuel is consumed and electrical energy and water produced by the reaction are generated. The fuel exhaust gas that exits the fuel electrode 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. On the way, the gas passes through a steam/moisture ISIl device 16 in order to recover moisture in the gas.

The fuel exhaust gas sent to the main burner 13 is burned in the fuel reformer 5, heats the reforming catalyst tube 6, and is then discharged as high-temperature exhaust gas 17. Roughly, after combining with the air exhaust gas sent from the oxidizer electrode 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 reformed fuel sent to the auxiliary burner 9 is combusted within the auxiliary burner 9, and the combustion gas passes through the mixer 18 to drive the turbine 19A of the turbo compressor 19.

On the other hand, the discharge air of the compressor 193 connected to and driven by the turbine 19A is sent to the auxiliary burner 9 and the main burner 13 with the air-fuel ratio controlled by ti by the auxiliary burner air control valve 20 and the main burner air control valve 21, respectively. At the same time, the air control valve 22 controls the oxidizer electrode 1 of the fuel cell 11.
1B, and the surplus is sent to the mixer 18 as part of the energy for driving the turbo compressor 19. A part of the air sent to the oxidizer electrode 11B is
After it is consumed by reacting with the hydrogen of A, it is discharged containing the moisture generated in the oxidizer electrode 11B. This discharged air exhaust gas is partially condensed in the air exhaust gas steam/water separator 25 in the same manner as the fuel F31 exhaust gas, and then is converted into high-temperature exhaust gas from the fuel reformer 5. 1
Join up with 7.

As described above, in the fuel cell 11, the oxidizer electrode tiB becomes a positive electrode (cathode) and the fuel electrode 11A becomes a negative electrode (anode) through a catalytic reaction between hydrogen in the fuel electrode 11A and oxygen in the oxidizer electrode 11B. , generates electrical energy and supplies the electrical energy to an electrical load 26 connected between both electrodes 11A and 118.

At this time, the hydrogen and oxygen supplied to both N poles 11A and 113 react in approximately proportion to the current value absorbed by the electric load 26, and reaction product water is obtained, and water containing this steam is produced. The reactant gas will be discharged from the exits of both electrodes 11^ and 11B.

On the other hand, a recirculation line (recycle line) 14 is branched from the outlet of the fuel electrode 11A, and a portion of the fuel exhaust gas is returned to the inlet line of the fuel electrode 11A via a recycle blower 15. Similarly, from the outlet of the oxidizer electrode 11B,
A recirculation line (recycle line) 23 is branched, and a portion of the air exhaust gas passes through a recycle blower 24 and is returned to the inlet line of the oxidizer electrode 11B. In addition, the recycling blower installed in the recycling line generally operates at a constant rotation speed.
Operated at constant discharge flow rate.

These recycle lines at both poles are designed to circulate and reuse the unreacted gas after the cell reaction, and have the effect of effectively using fuel gas and air.Obtaining reformed fuel If the thermal energy of the fuel reformer 5 required for this can be saved, the energy efficiency of the entire fuel cell power generation system can be increased. In addition, in order to save the driving energy of the turbo compressor 19, it is better to secure as much recycled air as possible to branch to the recycle line 23. It is desirable to keep the required amount of air supplied by compressor 19 low.

However, the conventional recycling line configuration as shown in FIG. 3 has the following problems.

For example, the recycle line on the oxidizer electrode side will be explained.

In the battery oxidizer electrode 11B, an amount of oxygen corresponding to the electrical load applied to the electrical load 26 is consumed, so that the oxygen concentration in the oxidizer electrode outlet exhaust gas becomes lower than the oxygen concentration in the oxidizer electrode inlet gas. There is. In order to recycle a part of this exhaust gas with a low oxygen concentration to the oxidizer electrode inlet pipe through the recycle line 23, the oxygen concentration in the oxidizer electrode inlet pipe after merging with the recycle line is adjusted by adjusting the oxidizer electrode flow rate. The oxygen concentration is lower than the oxygen concentration in the oxidizing agent supplied from the valve 22. Therefore, if we try to effectively utilize the unreacted battery gas by reducing the oxidizing agent supplied from the oxidizing agent extreme flow control valve 22 and taking a large amount of the battery exhaust gas flowing through the recycling line 23, the recycle line 23
The oxygen concentration in the pipe leading to the oxidizing agent electrode inlet after merging with No. 3 may become extremely low.

By the way, it is generally well known that a fuel cell has a voltage drooping characteristic in which the terminal voltage decreases as the electric load (1) increases. On the other hand, for the same electrical load, when the oxygen concentration in the oxidizer increases, the amount of oxygen supplied to the reaction surface of the electrode increases, so the battery voltage increases, and conversely, the oxygen concentration in the oxidizer decreases. When the voltage drops below the limit level, the battery voltage has a characteristic of decreasing because the oxidizing mother supplied to the reaction surface of the electrode decreases. Therefore, in a certain region where the battery load m is large, if the oxygen concentration falls below a certain level, the voltage may drop too much and stable power generation may become impossible.

Conversely, in certain areas where the electrical load is small, oxygen
! It is said that when the temperature is high, the voltage of the unit cells that make up the battery becomes too high, exceeding a certain value, and as a result, the activation of the catalyst supported on the electrode surface may deteriorate. .

Therefore, depending on the level of electrical load, the oxygen concentration in the oxidizer electrode inlet gas can be kept within a certain range, that is, the battery voltage will not drop too much, and the voltage per unit cell will not become too high beyond a certain value. The amount of oxidizing material exhaust gas flowing through the recycle line 23 must be adjusted so that it falls within an appropriate range.

However, in the conventional recycle line configuration as shown in FIG. The flow rate of the gas branched from the exhaust gas pipe at the pole outlet and flowing through the recycle line 23 is constant regardless of the load amount of the battery, and therefore, the above-mentioned problem is that the appropriate recycle line gas flow rate cannot be adjusted. was there.

On the other hand, in the configuration of the recycle line 14 on the fuel electrode side, based on the same concept, it is necessary to appropriately adjust the flow rate of the exhaust gas flowing through the recycle line 14 and branched from the fuel electrode outlet exhaust gas pipe. In the recycling method using the recycle blower 15 driven at a constant discharge flow rate, the recycle flow rate remains constant regardless of the electrical load, so it is expected that the same problem as the oxidizer electrode side will occur. .

[Purpose of the invention]

The present invention has been made in view of the above problems, and its purpose is to cover the entire range of electrical loads,
Oxygen concentration in the oxidizer or hydrogen in the fuel flowing through the oxidizer electrode or fuel maximum port pipe after joining the recycle line
To be able to drive within a certain range of A degrees,
The flow rate of gas flowing through the recycle line is adjusted according to the electrical load at that time, and as a result, it is possible to maintain stable battery characteristics and generate electricity, and the exhaust gas at the outlet of each electrode can be used efficiently. Our objective is to provide a fuel cell power generation system.

[Summary of the invention]

A battery cell is constructed by stacking a plurality of battery cells in which a pair of electrodes, a fuel electrode and an oxidizer electrode, are arranged with an electrolyte layer in between, and a fuel is brought into contact with the fuel electrode, and an oxidizer such as air is placed in the oxidizer electrode. A fuel cell stack that extracts DC output from between the electrodes by making use of the electrochemical reaction that occurs when the electrodes are in contact with each other, and an electrode that is discharged through an electrode outlet exhaust gas piping of at least one of the fuel electrode and the oxidizer electrode. In a fuel cell power generation plant comprising a recirculation line configured to branch off a part of the outlet exhaust gas and recirculate it to the respective electrode inlet side lines via a recirculation blower, A flow control valve provided therein, a flow rate detector which is also provided on the recirculation line and detects the flow rate of gas flowing through the line, and a maximum flow value detected by this flow rate detector are compared with a set flow rate value. and a control device that controls the valve opening of the control valve based on the comparison result, so that the flow rate of gas flowing through the recycle line can be adjusted according to the amount of electrical load. Features.

(Embodiments of the invention) (Structure) The present invention will be explained in detail below with reference to the drawings. Fig. 1 is a block diagram of a fuel cell power generation system according to an embodiment of the invention. Fig. 1 shows an oxidizing agent. Although only the recycle line on the pole side is shown, the configuration on the fuel pole side is also exactly the same.In the text below, we will explain the recycle line on the oxidizer pole side as an example.Note that Figure 1 is the same as Figure 3. to act/
Components b are given the same reference numerals, so their explanation will be omitted.

The difference between FIG. 1 and FIG. 3 is that a flow rate detector 28 and a flow rate control valve 27 are provided in the recycle line 23.
Furthermore, a control device 35 is provided.

The flow rate detector 28 is branched from the oxidizer pole outlet exhaust gas,
It has a function to measure the flow rate of gas that passes through the recycle line 23 and is returned to the oxidizer electrode inlet pipe, and also has a function to measure the flow rate of the gas returned to the oxidizer electrode inlet pipe.
7 has a function of adjusting the flow a of gas that passes through the recycle line 23 and is returned to the oxidizer electrode inlet pipe according to the opening degree of the valve.

Further, the control circuit 35 has the following configuration.

The converter 32 that receives the electric load signal 26 converts the electric load @26 into a set flow signal according to a function that schedules a target value of the recycle flow rate according to a preset electric load amount. . The adder 33 that receives this set flow rate signal determines the flow rate deviation between the actual flow set signal from the flow rate detector 28 and the set flow rate signal. and,
The adjustment section 34 that receives this flow rate deviation signal outputs a flow rate control valve opening signal corresponding to this flow rate deviation, and provides this to the flow rate control valve 27.

(Operation) In the configuration shown in FIG. 1 described above, the present invention operates as follows. In the operating state of this fuel cell power generation system, when the electrical load changes, the oxygen concentration in the cell oxidizer electrode outlet gas changes, and the cell voltage changes. In the converter 32 that receives the measured value signal) 26, the electrical load amount signal is converted into a flow rate signal according to a function that determines the relationship between the recycling flow rate and the electrical load amount, which is set in advance so that the battery voltage characteristics are within a stable range. . The adder 33 calculates the deviation between this flow rate signal q and the actual flow rate signal from the flow rate detector 28, converts this into an opening signal in the adjustment section 34, and gives this to the flow rate control valve 27 to operate the valve. let

As a result, the recycle flow rate is controlled to an appropriate value.

For example, if the electrical load on the battery suddenly increases for some reason, if the recycling flow rate remains unchanged, the oxygen concentration in the recycled exhaust gas branched from the battery outlet will decrease, and The oxygen concentration in the oxidant gas after it is circulated to the side and combined with the air supplied from the oxidant extreme flow control valve 22 line will also decrease. However, in the configuration of the present invention as shown in FIG. 1, by appropriately selecting the heker output function of the converter 32, the set recycle flow rate from the converter 32 is reduced in response to a sudden increase in electrical load. A flow setting signal such as this will be outputted and will immediately work to reduce the opening degree of the flow control valve 27. As a result, the flow rate of gas circulating through the recycle line decreases, so that the oxygen concentration in the oxidant gas, which joins the air supplied from the oxidizer polar flow control valve 22 line and is introduced into the cell inlet, drops to a certain level. It will be suppressed. As a result, a decrease in battery voltage due to a decrease in oxygen concentration can be kept within a certain appropriate range.

(Effect) This action makes it possible to adjust the flow rate of recycled gas to a preset flow rate level according to the electrical load, thereby reducing the oxygen concentration in the gas flowing through the battery oxidizer electrode inlet pipe. It becomes possible to adjust the battery so that it can generate electricity in a stable voltage state. This makes it possible to utilize the exhaust gas at the electrode outlet to the maximum extent possible without deteriorating the battery characteristics.

In the above description with reference to FIG. 1, the recycle line on the oxidizer electrode side was used as an example, but the gist of the present invention can be applied in exactly the same way to the 1-noise cycle line on the oxidizer electrode side.

[Other embodiments of the present invention]

FIG. 2 shows a fuel cell power generation system according to another embodiment of the present invention. The same parts as those in FIG.

However, in FIG. 2, the flow rate control valve 27 will be referred to as a first flow rate control valve, and the control device 35 will be referred to as a first control device in order to avoid confusion in the following description.

The difference between FIG. 2 and FIG. 1 is that there is a new differential pressure detector 31 that measures the pressure difference at the outlet of the recycle blower, and a second 'a amount branched from the recycle line 23 on the discharge side of the blower 24. A control valve 30 is provided, and a line 29 (hereinafter referred to as the mini 70-line) whose outlet side is configured to communicate with the suction side line of the blower 24 is provided, and a differential pressure setting device 38 is added to adjust these. Vessel 3
7 and an adjustment section 36 are provided. The differential pressure setting device 38 sets an appropriate differential pressure for the blower 24 to operate normally. The adder 37 that receives this differential pressure set value signal determines the differential pressure deviation between the actual differential pressure signal from the differential pressure detector 31 and the differential pressure setter signal, and outputs this to the adjustment section 36. do. Upon receiving this differential pressure deviation signal, the adjusting section 36 operates to output an opening degree signal of the second flow rate regulating valve corresponding to this differential pressure deviation and applying this to the second flow rate regulating valve 30.

Next, the operation of this example will be explained. First flow control valve 2
7 and the second control device 35 are the same as in FIG. However, in the case of FIG. 1, the pressure on the discharge side of the blower 24 fluctuates greatly due to the opening/closing adjustment of the first flow rate control valve, so the pressure difference applied to both ends of the first flow rate control valve fluctuates and this becomes excessive. In this case, the accuracy and followability of flow rate control based on the valve opening degree may be reduced. Therefore, in FIG. 2, an attempt is made to adjust the recycle flow rate with better accuracy.

That is, in the second control circuit 39, the differential pressure setting device 3
The differential pressure detector 31 measures the differential pressure signal set in advance to a differential pressure suitable for operating the blower by step 8, and the pressure difference between the input and outlet of the blower that changes due to opening and closing of the first flow control valve. The adder 37 calculates the deviation from the actual pressure difference signal, and the adjustment section 36 converts this into an opening signal, which is applied to the second flow ω control valve 30 to operate the valve. By bypassing the gas flow rate changed by the second flow rate control valve to the blower inlet through the second flow rate control valve, the pressure difference at the air outlet of the blower is adjusted to a certain constant value. Thereby, the pressure on the upstream side of the first flow rate control valve 27 can be kept constant, so that the recycle flow rate can be accurately controlled by the first flow rate control valve.

This action makes it possible to adjust the flow rate of recycled gas to a preset flow rate level according to the electrical load, and this allows the battery to stabilize the oxygen concentration in the gas flowing through the battery oxidizer electrode inlet pipe. It becomes possible to adjust the voltage so that it can generate electricity. This makes it possible to utilize the exhaust gas at the electrode outlet to the maximum extent possible without deteriorating the battery characteristics.

〔Effect of the invention〕

Since the present invention is configured as described above, the following effects of the invention can be expected. That is, by adjusting the recycling flow rate in a preset manner as a function of the electrical load of the battery, the concentration of oxygen and hydrogen in the gases flowing in the electrode inlet piping can be reduced over a range of electrical loads.
To provide a fuel cell power generation system capable of keeping the i degree within a certain range, thereby enabling stable power generation by maintaining good battery characteristics, and making maximum use of battery unreacted gas by recycling. be able to.

[Brief explanation of drawings]

FIG. 1 is a piping configuration diagram of a fuel cell power generation system showing an embodiment of the present invention, FIG. 2 is a piping configuration diagram of a fuel cell power generation system showing another embodiment of the invention, and FIG. 3 is a diagram of a conventional fuel cell power generation system. FIG. 2 is a main piping configuration diagram showing the configuration of the power generation system. 1...Raw fuel 2...Steam supply device 3.
...Raw fuel control valve 4...Steam control valve 5...
Fuel reformer 6... Reforming catalyst tube 7... Shift converter 8... Steam-water separator 9... Auxiliary burner 10... Fuel control valve 11... Fuel cell
11A... Fuel electrode 11B... Oxidizer electrode
12...Reformer fuel control valve 13...Main burner
14... Recycle line 15... Recycle blower 16... Steam water separator 17... High temperature exhaust gas
18...Mixer 19...Turbo compressor 1
9A...Turbine 19B...Compressor 20.
21.22...Air control valve 23...Recycle line 24...Recycle blower 25...Steam water separator 26...Electric load 27...First flow rate control valve 28...Flow rate Detector 29...Mini flow line
30...Second flow rate control valve 31...Differential pressure detector
32...Converter 33...Adder 34.
... Adjustment section 35 ... First control device 36 ... Adjustment section 37 ... Adder 38 ... Differential pressure setting device 3
9...Second control device agent Patent attorney Nori Chika Yudo Hirofumi Mitsumata

Claims (2)

[Claims] (1) A plurality of battery cells are stacked in which a pair of electrodes, a fuel electrode and an oxidizer electrode, are arranged with an electrolyte layer in between, and the fuel is brought into contact with the fuel electrode, and air is placed in the oxidizer electrode. A fuel cell stack that extracts DC output from between the electrodes by making use of the electrochemical reaction that occurs when the oxidizing agent of and a recirculation line configured to branch a part of the electrode outlet exhaust gas and recirculate it to the corresponding electrode inlet side line via a recirculation blower. A flow rate control valve provided on the line, a flow rate detector also provided on the recirculation line to detect the flow rate of gas flowing through the line, and the flow rate value detected by this flow rate detector as the set flow rate value. A fuel cell power generation plant comprising: a control device that compares and controls the valve opening of the control valve based on the comparison result. (2) A plurality of battery cells are stacked in which a pair of electrodes, a fuel electrode and an oxidizer electrode are arranged with an electrolyte layer in between, and the fuel is brought into contact with the fuel electrode, and the oxidizer electrode is exposed to air, etc. A fuel cell stack that extracts DC output from between the electrodes by making use of the electrochemical reaction that occurs when the oxidizing agent of and a recirculation line configured to branch a part of the electrode outlet exhaust gas and recirculate it to the corresponding electrode inlet side line via a recirculation blower. a first flow control valve provided on the line;
A flow rate detector is also provided on the recirculation line and detects the flow rate of gas flowing through the line, and the flow rate value detected by this flow rate detector is compared with a set flow rate value, and based on the comparison result, the above-mentioned a first control device that controls the opening degree of the first control valve; and a bypass line that branches from the discharge port side of the recirculation blower and connects to the suction port side; a second flow rate control valve; a differential pressure detector that detects a pressure difference between the inlet and the outlet of the recirculation blower; and a differential pressure value detected by the differential pressure detector is compared with a set differential pressure value. A fuel cell power generation plant comprising: a second control device that controls the opening degree of the second flow rate regulating valve based on the comparison result.