JPH04167368A - Fuel cell generation system - Google Patents

Abstract

PURPOSE:To eliminate adverse effects on the life of a fuel cell by supplying a combustion exhaust gas of low oxygen density to the inlet of an air electrode at a sudden decrease in loads so as to rapidly decrease the oxygen density of air at the air electrode and shorten an overvoltage state. CONSTITUTION:During the normal rated operation of a fuel cell generating system, a valve 12 is completely closed and a combustion exhaust gas supplied from a line 10 is wholey given to a cell container 4 and used for purging. During the partially loaded operation of the system, a voltmeter 18 judges the state of the system and a controller 20B actuates valves 9, 22, 23 in response to signals from the voltmeter 18, an output meter 19 and flow meters 8, 21 respectively and mixes air into the combustion exhaust gas and supplies it to an air electrode 3 to restrain an overvoltage state. If loads are suddenly decreased, the controller 20B initiates set values for the flow meters 8, 21 in response to an output command and opens the valve 22 and closes the valve 9 by means of advanced control to rapidly lower oxygen density in air at the air electrode 3 so as to lower cell voltage, thereby preventing the overvoltage state from continuing.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a fuel cell power generation system, and particularly relates to a fuel cell power generation system that shortens the operating time of a fuel cell in an overvoltage region in response to a sudden load reduction. However, the present invention relates to a fuel cell power generation system in which the adverse effect on battery life is suppressed as much as possible.

(Prior Art) In fuel cells that use phosphoric acid as an electrolytic material, platinum-based noble metal catalysts are mainly used. It is known that particles of this catalyst aggregate when the fuel cell voltage (hereinafter referred to as cell voltage) is high, causing performance deterioration.

Furthermore, due to the current-voltage characteristics of the fuel cell, during partial load operation, the cell voltage inevitably increases and approaches the overvoltage range.

Therefore, in order to solve this problem, various methods have been proposed to suppress the battery voltage within an allowable range during partial load operation.

In general, battery voltage changes depending on operating temperature, operating pressure, oxygen concentration at the sorami electrode, hydrogen concentration at the fuel electrode, utilization rate, etc.

Utilizing these characteristics, during partial load operation, a portion of the air electrode outlet gas is returned to the air outlet, reducing the oxygen concentration.
This method is considered to be the most effective method to lower the battery voltage, and there are many practical examples of this method.

FIG. 4 shows such a conventional example, in which a fuel cell 1 includes a fuel electrode 2. It is assumed that the air electrode 3 is composed of an air electrode 3 and a battery container 4 that houses the air electrode 3. Fuel, which is one of the reaction gases, is supplied to the fuel electrode 2 from a fuel supply device 5 via a control valve 6 through a fuel supply line. Air, which is the other reaction gas, is supplied to the air electrode 3 from an air supply device 7 through an air supply line via a flow meter 8 and a control valve 9.

Also, when the fuel cell 1 is operated under pressure, the fuel electrode 2. A fuel electrode 2 is placed between the air electrode 3 and the battery container 4.
Also, an inert gas having a pressure higher than that of the air electrode 3 is sealed. N2 gas is often used as this inert gas, but as the capacity of fuel cell power generation systems increases,
As a means of saving N2 gas, the combustion exhaust gas generated within the system is used instead.

On the other hand, since the inert gas sealed in the battery container is mixed with N2 gas leaked from the fuel electrode, a flow is normally formed from the inlet side to the outlet side of the battery container 4, and the N2 gas is discharged. That's what I do.

The flue gas is normally used as the flue gas of a reformer (not shown) installed in a fuel power generation system or an auxiliary combustor (not shown) or a boiler (not shown) that may be used to supply steam to a fuel processing system. ) is applicable to combustion exhaust gas, etc.

Such combustion exhaust gas is transported through the combustion exhaust gas extraction line 10.
However, due to its high temperature, it is cooled by a heat exchanger 11 and supplied to the battery container 4 via a blower 12 and a combustion exhaust gas supply line.

In a fuel cell power generation system having such a configuration, conventionally, as a means for suppressing overvoltage of the fuel cell 1 when the load is reduced, a part of the outlet gas of the air electrode 3 is transferred to the air electrode recycling blower 13, the flow meter 14, and the control valve. A recycle line was provided to return the air to the inlet side of the air electrode 3 via the air electrode 15, thereby reducing the oxygen concentration of the air supplied to the air electrode 3.

In addition, the reference numeral 16 in the same figure is a thermometer for measuring the temperature of the combustion exhaust gas on the outlet side of the heat exchanger 11, and the reference numeral 17 is provided on the outlet side of the cooling water of the heat exchanger 11, and a thermometer is provided to measure the temperature of the combustion exhaust gas on the outlet side of the heat exchanger 11. A control valve that controls the flow rate of cooling water according to the signal from the thermometer 16 so that the flow rate is within the range; 18 is a voltmeter that measures the voltage of the fuel cell 1; and 19 is an output that measures the output of the fuel cell 1. A meter 2OA is a control device that receives signals from the flowmeters 8 and 14, voltmeter 18, wattmeter 19, etc., and controls the control valves 9 and 15.

(Problems to be Solved by the Invention) As the capacity of fuel cells increases, the internal volume of the fuel cell 1 also increases. Therefore, in the above-described method of returning the outlet gas of the air electrode 3 to the inlet of the air electrode 3 to reduce the oxygen concentration, it is necessary to further increase the recycling flow rate, and the blower capacity required for this recycling must be increased. In addition, it takes a very long time for the oxygen concentration to decrease,
In particular, there is a problem in that the overvoltage state of the fuel cell 1 continues for a long time in response to a sudden load reduction, which adversely affects the fuel cell 1.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fuel cell power generation system in which, when a sudden load decrease occurs in the fuel cell power generation system, the overvoltage state of the fuel cell is suppressed for a short period of time, and the adverse effect on the fuel cell life is reduced. It is in.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a fuel cell having an air electrode and a fuel electrode, and a reformer that converts raw fuel, which is a reaction gas for one of the fuel cells, into a hydrogen-rich one. A fuel cell power generation system equipped with a fuel supply device that supplies purified gas to the fuel electrode, an air supply device that supplies air that will become the other reaction gas to the air electrode, and a combustor that includes a combustion section attached to a reformer. In the system, a combustion exhaust gas merging line is provided to merge part or all of the combustion exhaust gas from the combustor into the air supply line that connects the air supply device and the air electrode via a control valve, and is used during partial load operation or when sudden loads are applied. A control device is provided that controls the voltage of the fuel cell to be within a predetermined allowable range by adjusting the flow rate of combustion exhaust gas supplied to the air electrode via a control valve when the fuel cell voltage decreases.

(Function) In particular, when the load decreases rapidly, the oxygen concentration in the air electrode can be rapidly reduced by quickly supplying combustion exhaust gas with a low oxygen concentration to the inlet of the air electrode. Thereby, the overvoltage state of the fuel cell can be suppressed for as short a time as possible, and the adverse effect on the fuel cell life can be reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a configuration diagram of an embodiment of the present invention.

In the figure, 1 is a fuel cell, 2 is a fuel electrode, 3 is an air electrode, 4 is a battery container, 5 is a fuel supply device, 6 is a control valve, 7 is an air supply device, 8 is a flow meter, and 9 is a control valve. This is the same as the conventional configuration described above.

In addition, when the fuel cell 1 is operated in a pressurized state as in the conventional configuration described above, the fuel electrode 2. Inert gas (N2 gas) is sealed between the air electrode 3 and the battery container 4 at a pressure higher than that of the fuel electrode 2 and the air electrode 3, but as fuel cell power generation systems increase in capacity, N2 gas can be saved. In this embodiment as well, combustion waste generated within the same system is used as a means.

In this embodiment, as in the conventional configuration described above, the combustion exhaust gas may be the combustion exhaust gas from the reformer (not shown) installed in the fuel cell power generation system or the combustion exhaust gas from the auxiliary combustor (not shown). The target is combustion exhaust gas from boilers (not shown) that are sometimes used in fuel cell cooling water systems.

This combustion exhaust gas is supplied from the combustion exhaust gas take-off line 10 in the same manner as in the conventional configuration described above, is cooled to within an allowable temperature range by a heat exchanger 11, and then enters the blower 12. The combustion exhaust gas that has exited the blower 12 is branched into a combustion exhaust gas merging line, which joins between the control valve 9 of the air supply line and the inlet of the air electrode 3 via a flow meter 21 and a control valve 22, and a combustion exhaust gas supply line. do.

A flow meter 21 and a control valve 22 are provided in this combustion exhaust gas confluence line, and the combustion exhaust gas is mixed with air and supplied to the inlet of the air electrode 3. Further, a control valve 23 is provided in the combustion exhaust gas line that supplies the battery container 4, and is controlled in a mutual relationship with the control valve 22 described above.

Note that the code 20B indicates the flowmeters 8 and 2+, and the voltmeter 18.
, a wattmeter 19, etc., and controls the control valves 9, 22 and 23.

Next, the operation of the embodiment configured as above will be explained.

During normal rated operation, the control valve 22 is fully closed, and all the combustion exhaust gas supplied from the combustion exhaust gas extraction line 10 is supplied to the battery container 4 for purging.

Also, during partial load operation, it is determined whether or not there is an overvoltage state from the measured value of the voltmeter 18, and the voltmeter 18. Output meter 19. A control device 20 into which signals from flow meters 8 and 21 etc. are input.
At B, the control valves 9, 22, and 23 are operated, and the combustion exhaust gas is mixed with air and supplied to the air electrode 3 so as to suppress the overvoltage state of the fuel cell 1.

Furthermore, when a sudden load decrease occurs, the control device 20B creates set values for the flowmeters 8 and 2I based on the output command, and uses advance control to operate the control valve 22 in the opening direction and the control valve 9 in the closing direction. . As a result, in response to a sudden load reduction, the oxygen concentration in the air at the air electrode 3 can be rapidly reduced, and the battery voltage is accordingly reduced to prevent the overvoltage state from continuing. I can do it.

Therefore, by configuring as described above, it is possible to quickly shift the battery operating state to a stable current-voltage region in response to a sudden load decrease, and it is possible to prevent the battery life from being adversely affected. can.

Note that the present invention is not limited to the above-described embodiment (hereinafter referred to as the first embodiment), and can be implemented in various modifications.

FIG. 2 is a configuration diagram showing another embodiment of the present invention. A feature of this embodiment is that combustion exhaust gas is supplied from the battery container 4 to the inlet side of the air electrode 3. That is, using the combustion exhaust gas as a purge gas for the battery container 4 is the same as in the first embodiment described above, or the battery container 4 is used between the battery container 4 and the downstream side of the control valve 9 of the air supply line. A combustion exhaust gas merging line for merging the combustion exhaust gases from the combustion exhaust gases is provided, and a flow meter 21 and a control valve 22 are provided in this combustion exhaust gas merging line to perform control in the same manner as in the first embodiment described above. Note that the configuration that overlaps with the first embodiment described above is
The explanation will be omitted.

FIG. 3 is a configuration diagram showing still another embodiment of the present invention. In this embodiment, the combustion exhaust gas is transferred to an auxiliary combustor 24 installed downstream of the reformer combustion section 23 and a turbine 25.
The combustion exhaust gas is taken out from between the heat exchanger 11. and supplied to the combustion exhaust gas extraction line 10. The air supply line joins the air supply line via the blower 12 and the control valve 22 on the downstream side of the control valve 9, and is controlled in substantially the same manner as in the first embodiment described above.

Note that as the purge gas for the battery container 4, either N2 gas as in the conventional case or combustion exhaust gas as in the above embodiment may be used.

In addition, a device is provided that branches off from the outlet line of the combustor and compresses and stores a portion of the combustion exhaust gas via a compressor, and from this device via a control valve (which has the same function as the control valve 22 described above). It may also be mixed into the air in the air line.

[Effects of the Invention] As explained above, according to the present invention, when a sudden load decrease occurs, the air supply is quickly reduced and combustion exhaust gas is mixed in to reduce the oxygen concentration at the air electrode. Therefore, it is possible to provide a fuel cell power generation system in which the operating time in the fuel cell overvoltage region is made as short as possible, and the adverse effect on the fuel cell life is reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 is a block diagram showing yet another embodiment of the present invention. FIG. 4 is a configuration diagram showing a conventional fuel cell power generation system. 1...Fuel cell 2...Fuel electrode 3...
- Air electrode 4...Battery container 5...Fuel supply device 7...Air supply device 9, 22.
23...Control valve 10...Combustion exhaust gas extraction line 11...Cooler 12...Blower 1
8...Voltmeter 19...Output meter 20
B...Control device (7317) Agent Patent attorney Aide Kensuke Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A fuel cell having an air electrode and a fuel electrode, a fuel supply device for supplying, to the fuel electrode, gas obtained by reforming the raw fuel, which is a reaction gas for one of the fuel cells, into a hydrogen-rich gas in a reformer, and a reaction gas for the other one of the fuel cells. In a fuel cell power generation system comprising an air supply device that supplies air to become a gas to the air electrode, and a combustor including a combustion section attached to the reformer, part or all of the combustion exhaust gas of the combustor is A combustion exhaust gas merging line is provided that joins the air supply line connecting the air supply device and the air electrode via a control valve, and the combustion exhaust gas is connected to the air electrode during partial load operation or when the load decreases rapidly. A fuel cell power generation system comprising: a control device that controls the voltage of the fuel cell to be within a predetermined allowable range by adjusting the supply flow rate via the control valve.