JPH02244559A - Method of stopping operation of fuel cell - Google Patents

Abstract

PURPOSE:To prevent drop of the output power by blocking the inlet and outlet of a fuel path after stopping supply of the electric power, supplying an inert gas to this blocked fuel path while its pressure is controlled by a pressure adjusting valve, and by supplying oxidation gas to an oxidating agent path. CONSTITUTION:When power generation of a fuel cell 1 is to be stopped, switches 22, 23 are closed to turn on load resistance circuits 24, 25, and an inlet valve 10 and outlet valve 11 for the fuel gas are shut. Further a nitrogen supply valve 13 is opened to supply nitrogen to a blocked fuel path 5 via a nitrogen supply line 12. The residual hydrogen encapsulated by the valve 10, 11 reacts with air to generate power, and the current flows through resistances 20, 21. At this time, hydrogen is consumed to cause drop of the pressure in the fuel path 5, that is however compensated with the nitrogen flowing through the line 12, and a pressure adjusting valve 14 make control so that the pressure in the fuel path 5 gets a specified value. This the generated voltage sinks with reduction of the hydrogen concentration in the fuel path 5. This should preclude drop of the output power associate with start and stop of the fuel cell.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to the production of fuel cells, especially phosphoric acid fuel cells! The present invention relates to a method of stopping a fuel cell by stopping the supply of electric power to an external load.

[Conventional technology]

A fuel cell, such as a phosphoric acid fuel cell, generates electricity by causing a cell reaction with a fuel gas and an oxidant gas supplied through a fuel flow path and an oxidant flow path within the fuel cell. In this case, a reformed gas rich in hydrogen is used as the fuel gas, and air is used as the oxidizing gas. For power generation in phosphoric acid fuel cells, the operating temperature is 150°C to 230°C, and the output voltage per cell is O,
The voltage is 5V to 0.8V, and a fuel cell usually includes a cell stack in which a plurality of single cells are stacked, and the power generated in this cell stack is supplied to an external load.

By the way, in a stopped state where the fuel cell is disconnected from the external load and the supply of electricity generated by the fuel cell to the external load is stopped, the hydrogen remaining inside the fuel cell is replaced by nitrogen as an inert gas at a temperature of 130°C or less. It is in a state where it is replaced with gas. This is because if the temperature is high and the voltage of the unit cell is left at 0.8 V or higher, the output characteristics of the fuel cell will gradually decrease. For this reason, when disconnecting the fuel cell from the external load and transitioning to the stopped state, the following operation mode is implemented so that the above-mentioned stopped state can be reached quickly. In other words, the output supplied from the fuel cell to the external load is gradually reduced, and the operating temperature is controlled to a low level of 150°C to 14°C.
When the temperature reaches 0° C., the output is cut off and disconnected from the external load, and nitrogen gas as an inert gas is supplied to the fuel flow path and the oxidizer flow path to purge the fuel gas and air. In this case, a load resistor is connected to the output end of the fuel cell to form a load resistor circuit, and electricity generated by the cell reaction between the remaining fuel gas and oxidant gas is passed through the load resistor to quickly reduce the voltage. ing.

[Problem to be solved by the invention]

Even in the above-mentioned operation mode in which the fuel cell is in a stopped state, there is a problem in that the output characteristics of the fuel cell gradually decrease when starting and stopping are repeated. this is.

This is because the nitrogen gas supplied to the fuel cell is excessive and dry, causing the electrolyte in the fuel cell to evaporate and scatter, and the movement of the electrolyte due to volume changes to prevent normal power generation reactions.

An object of the present invention is to provide a method for stopping a fuel cell that can reduce evaporation and scattering of electrolyte when replacing the fuel gas remaining in the fuel cell with inert gas after disconnecting the fuel cell from an external load. It is to provide the following.

[Means to solve the problem]

the above! In order to solve iB, according to the present invention, after stopping the supply of electric power generated by a fuel cell having a fuel flow path and an oxidizer flow path to an external load, the fuel gas remaining in the fuel cell is removed. In a method for stopping a fuel cell in which electricity generated by a cell reaction with an oxidizing gas is passed through a load resistance circuit to lower the starting pressure, after the power supply is stopped, the fuel gas population and outlet are closed and the fuel gas is inactivated. The gas is controlled to a predetermined pressure by a pressure regulating valve and is supplied to the closed fuel flow path, while the oxidant gas is supplied to the oxidizer flow path.

(Operation) After disconnecting the fuel cell from the external load, the inlet and outlet of the fuel flow path of the fuel cell are closed, and pressure-controlled inert gas is supplied to the closed fuel flow path, and the oxidizer flow path is closed. oxidant gas is supplied to cause a battery reaction to generate electricity, and this electricity is passed through a load resistance circuit connected to the outlet end of the fuel flow.
Consumes and eliminates hydrogen in remaining fuel gas.

In this case, since the inlet and outlet of the fuel flow path are closed, the pressure within the fuel flow path decreases due to consumption of hydrogen. Therefore, the inert gas is supplied while being controlled by the pressure regulating valve so that the pressure in the fuel flow path becomes a predetermined pressure so as to compensate for the consumption of hydrogen. On the other hand, the oxidant gas is supplied to the oxidant flow path so that the reaction with the residual hydrogen in the fuel wave path continues.

The supply amount of this oxidant gas may be 2 to 3 times the amount calculated from the current flowing through the load resistor.

In this way, while continuing the power generation reaction of the fuel cell, by replacing the closed fuel flow path of the fuel cell with inert gas, there is no need to supply an excessive amount of dry inert gas. This prevents evaporation and scattering of the electrolyte, and also controls the concentration of the electrolyte by generating water generated during the power generation reaction.

〔Example〕

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

FIG. 1 shows the connections between fuel cell systems when the fuel cell stopping method according to the embodiment of the present invention is applied. In FIG. 1, 1 is a phosphoric acid fuel cell, which is shown schematically, and includes an electrolyte chamber 2 containing phosphoric acid as an electrolyte, and a fuel electrode 3 and an oxidizer electrode 4 arranged on both sides of the electrolyte chamber 2. Further, the fuel passage 5 is disposed on both sides of the fuel passage 5 and includes a fuel passage 5 that supplies fuel gas to the fuel electrode 3 and an oxidizer passage 6 that supplies air as an oxidant gas to the oxidizer electrode 4. Reference numeral 7 denotes a fuel gas supply system, which includes a fuel gas supply pipe 8 that supplies fuel gas to the fuel flow path 5 of the fuel cell 1, and a fuel gas discharge pipe 9 that discharges fuel gas from the fuel flow path 5. .

Note that the fuel gas supply pipe 8 is provided with a large opening valve 10, and the fuel gas discharge pipe 9 is provided with an exit valve 11. A nitrogen supply system 12 is connected to the fuel gas supply pipe 8 at the outlet of the artificial valve 10, and includes a nitrogen supply valve 13 and a pressure regulating valve 14. Reference numeral 15 denotes an air supply system that supplies and discharges air to and from the oxidizer channel 6 of the fuel cell I.

A load circuit 17 is connected to the fuel electrode 3 and oxidizer electrode 4 of the fuel cell 1 through an external load via a power converter (not shown).
is connected. The load circuit 17 includes load resistors 20, 21 . and switch 22.
23 and 24, 25 respectively are read out. The load resistor 20 is a load with a large current capacity that consumes hydrogen in the fuel gas remaining in the fuel gas piping of the fuel cell and the gas flow path in the fuel flow path 5 immediately after power generation is stopped. The load resistor 21 is a load that subsequently consumes the small amount of hydrogen that remains.

With this configuration, when power generation by the fuel cell 1 is stopped, the power transmitted to the power converter I is cut off, the switch 22.23 is closed, the load resistance circuit 24.25 is utilized, and the fuel gas artificial valve is closed. 10. The outlet valve 11 is closed, and nitrogen is supplied to the closed fuel passage 5 via the nitrogen supply system 12 with the nitrogen supply valve 13 in between. On the other hand, air is made to flow through the oxidizer channel 6 via the air supply pipe 15. In this state, the residual hydrogen in the fuel flow path, etc., which is closed by the artificial valve 10 and the outlet valve 11, reacts with the air and generates electricity, and this generated electricity is generated by the load resistance 2O, 2
Flows through 1. Hydrogen corresponding to this removed current is consumed, and the pressure in the fuel flow path 5 decreases, but this pressure drop is compensated for by nitrogen flowing through the nitrogen supply system 12, and the pressure regulating valve 14 The pressure of No. 5 is controlled to be a predetermined pressure. In this way, while the pressure in the fuel flow path 5 is maintained at a predetermined pressure, the hydrogen in the remaining fuel gas undergoes a cell reaction with the air and is consumed, and as the hydrogen concentration in the fuel flow path 5 becomes thinner, the generated voltage decreases. descend. At this time, in order to uniformly reduce the hydrogen concentration inside the fuel cell, the load resistor 20 is repeatedly turned on and off by the switch 22 so that the cell voltage becomes 0.8 to 0.5 V.T! 1 When the voltage decreases and the ON time of the load resistor 20 is shortened to several seconds, the load resistor 20 is set to 0 F, and the load resistor 2 is turned on.
The remaining hydrogen is consumed by turning the switch 23 of No. 1 on and off.

Air supply is controlled by the load resistance 20.21 and the theoretical amount calculated from the battery voltage when the load resistance 20 is ON and OFF controlled.
Supply twice as much air. When controlled by the load resistor 21, the supply of air is stopped, but the oxygen remaining in the oxidizer flow path is used for the power generation reaction.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, after the power transmission to the external load of the fuel cell is stopped, the inlet and outlet of the fuel flow path inside the fuel cell are closed, and the closed fuel flow path is filled with nitrogen. While supplying and controlling the pressure to a predetermined pressure, the hydrogen in the fuel gas remaining in this fuel flow path is consumed by a battery reaction with the air flowing through the oxidizer flow path, and the electricity generated by this soil removal is sent to the load resistance circuit. By reducing the power generation voltage and stopping the fuel cell, the electrolyte is prevented from evaporating and scattering due to excessive dry inert gas, and since there is water produced during the cell reaction, the concentration of the electrolyte is reduced. This has the effect that the deterioration in output characteristics accompanying the start and stop of the fuel cell is reduced by being appropriately controlled. In addition, since the amount of inert gas that replaces the fuel gas is also reduced, there is also the effect that the equipment for the inert gas supply system is also reduced in size.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a fuel cell when a method for stopping a fuel cell according to an embodiment of the present invention is applied. 1: fuel cell, 5: fuel flow path, 6; oxidizer flow path, 10;
Population valve, 11: Outlet valve, 14-Pressure adjustment valve, 24°25
;Load resistance circuit. 1st generation rationalist Yamaguchi I5. (

Claims (1)

[Claims] 1) Electricity generated by causing a cell reaction of the fuel gas remaining in the fuel cell with an oxidant gas after the supply of power generated by a fuel cell having a fuel flow path and an oxidizer flow path to an external load is stopped. In the method for stopping a fuel cell in which the generated voltage is reduced by flowing the power through a load resistance circuit, after the power supply is stopped, the inlet and outlet of the fuel flow path are closed, and the inert gas is controlled to a predetermined pressure by a pressure regulating valve. A method for stopping a fuel cell, characterized in that the oxidant gas is supplied to the closed fuel flow path, and the oxidant gas is supplied to the oxidizer flow path.