JPH0393166A - Fuel cell system - Google Patents

Abstract

PURPOSE:To prevent a drop in concentration of phosphoric acid at the time of battery stop by heating and drying air for being fed to an electrode while closing the feeding and exhausting valves of the electrode in the state where dry air is filled inside the electrode after supply of fuel gas is stopped. CONSTITUTION:In a fuel battery system using a phosphoric acid electrolyte, after supply of fuel gas is stopped, air is heated for being dried to be supplied to the electrode 10 while closing the feeding and exhausting bulbs 18, 20 and 26 in a state where dried air is filled in the gas space inside the electrode 10. Accordingly, a temperature drop of the electrode is suppressed so as to continue moisture evaporation at the reaction time in the phosphoric acid electrolyte after a stop of reaction. A drop of concentration of the phosphoric acid electrolyte at the time of operation stop, thereby, is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a phosphoric acid fuel cell system. (Background of the Invention) Phosphoric acid fuel cells generate electromotive force by introducing reactive gases into the electrodes, that is, hydrogen into the negative electrode and oxygen into the positive electrode.
The water produced by this reaction is exhausted as steam during high-temperature (approximately 200°C) operation, so the concentration of the phosphoric acid electrolyte does not decrease during operation. However, when the temperature drops due to battery shutdown, the water dissolved in the electrolyte does not evaporate and remains in the electrolyte. Also, water vapor remaining in the gas space of the electrode condenses and mixes with the phosphoric acid electrolyte. Therefore, when the battery is stopped, the phosphoric acid concentration decreases,
There was a problem that battery performance deteriorated. (Prior art) As a method to prevent the concentration of phosphoric acid from decreasing when the battery is stopped,
When shutting down a battery, a method has been proposed in which outside fresh air is sealed in the gas space of the electrode to preserve it (Japanese Unexamined Patent Publication No. 6
3-26962). However, even in this case, the highly hygroscopic phosphoric acid electrolyte will absorb this small amount of moisture in the enclosed air, and in fuel cells that are frequently operated intermittently, the decrease in the concentration of the phosphoric acid electrolyte cannot be ignored. There was the problem of becoming a thing. It is also possible to provide a moisture absorbent inside the electrode, but since the phosphoric acid electrolyte itself is highly hygroscopic, complete moisture absorption is not possible.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and is designed to prevent the concentration of the phosphoric acid electrolyte from decreasing when the operation is stopped.
The first purpose is to provide a method for stopping a fuel cell system. A second object of the present invention is to provide a fuel cell system for use in the implementation.

(Structure of the Invention) This object of the present invention is to provide a fuel cell system using a phosphoric acid electrolyte by heating and drying air after stopping the supply of fuel gas and supplying it to the electrodes. This is achieved by a method 6 for stopping a fuel cell system, which is characterized by closing the supply/discharge valves of the electrodes while the gas space inside the fuel cell system is filled with dry air.

A second object of the present invention is to provide a fuel cell system using a phosphoric acid electrolyte, including an electrode, first and second air supply lines for supplying air to the electrode, and a fuel cell system in the middle of the second air supply line. a moisture absorbing means provided in the air that absorbs moisture in the air when the temperature is low and releases moisture when the temperature is high; a heating means that directly or indirectly heats the moisture absorbing means; and a first air supply line that cuts off the first air supply line. What is claimed is: 1. A fuel cell system comprising: a second valve for cutting off an electrode exhaust line; and a third valve for cutting off a second air supply line between the electrode and the moisture absorption means.

This is achieved by

(Example) Figure 1 is a conceptual diagram of a battery system according to an example of the present invention. In this figure, numeral 10 is an electrode. This electrode 1
0 sandwiching an electrode matrix impregnated with a phosphoric acid electrolyte, an air electrode (anode) is formed on one side, and a hydrogen electrode (cathode) is formed on the other side, forming a cell stack in which these electrodes are stacked one after another. FIG. 1 shows the supply/discharge route of reaction air supplied to and discharged from the air electrode. Air sent from the air blower 12 is supplied to the air gas space of the electrode 10 through a first air supply line 14, and after reacting at the electrode 10, is exhausted through an exhaust line 16. 18 is air supply line 1
The first valve 20 shuts off the exhaust line 16, and the second valve 20 shuts off the exhaust line 16. The first air supply line 14 is branched in the middle to provide a second air supply line 22 that enters the gas space of the air electrode of the electrode 10 . A moisture absorbing means 24 for removing moisture from the reaction air is provided in the middle, and a third valve is provided further downstream. The moisture absorbing means 24 has a heat exchanger-like structure in which a chamber covering the exhaust line 16 is filled with a moisture absorbing agent.
The reaction air flowing through the air supply line 22 absorbs moisture and dries there, is heated by exhaust heat from the exhaust line 16, and is supplied to the electrode 10. That is, in this embodiment, the moisture absorbing means 24 also serves as a heating means for heating the reaction air. The moisture absorbent filled in the moisture absorbing means 24 is preferably one that can be reversibly regenerated by applying heat, and for example, silica gel, alumina type, or zeolite type moisture absorbent can be used.

28 is a fourth valve that shuts off the second air supply line upstream of the moisture absorption stage 24.

Next, the operation of this embodiment will be explained.

During operation, all the valves 18, 20, 26, 28 are open, and the reaction air supplied from the supply air lines 14, 22 reacts at the electrodes, and then flows into the exhaust line 1 together with the generated water vapor.
It is exhausted by 6. Here, the second air supply line 22 has a moisture absorbing stage 24, which acts as a flow path resistance for the supply air.
During operation, the first air supply line serves as the main air supply passage.

When shutting down the operation, the fuel gas supply is stopped to stop the power generation reaction, and in this state the air supply and exhaust valves are operated.
First, the valve 18 is closed to cut off only the first air supply line l4. Only the heated dry air that has been absorbed by the moisture absorbing means 24 is supplied to the electrode 10 via the second air supply line. This suppresses the temperature drop of the electrode and allows water evaporation during the reaction in the phosphoric acid electrolyte to continue even after the reaction has stopped. Further, as the moisture absorbing function of the moisture absorbing means 24 increases as the exhaust heat from the exhaust line 16 decreases, the slight amount of water dissolved in the phosphoric acid electrolyte of the electrode 10 is evaporated and removed. When the inside of the electrode 10 is filled with dry air after a suitable period of time,
All remaining valves 20, 26, and 28 are also closed to seal the electrode 10. In this state, the battery operation shutdown work is completed and can be saved. When restarting operation, all valves 1
8, 20, 26. Open 28 and start power generation. The moisture absorbing means 24 that absorbed moisture when the operation was stopped is connected to the exhaust line 16.
The temperature is raised and dried by the high-temperature exhaust gas flowing through the
You can prepare for the next outage. At this time, the moisture released from the moisture absorbing means 24 is led to the electrode 10 through the second air supply line 22, but since the phosphoric acid during the battery reaction is at a high temperature and does not absorb moisture, this The moisture is directly discharged out of the system through the exhaust line 16.
When restarting operation, only valve 18.20 is opened to generate electricity using only the first air supply line, and after the exhaust gas has reached a sufficient temperature, valve 26.28 is opened and the second air supply line is also used. It may be activated to maintain steady operation.

In this embodiment, the valve 28 that communicates the moisture absorbing means 24 with the atmosphere is closed, but after restarting the operation, the moisture absorbing means 24 is closed.
This valve 28 may be omitted if the moisture absorbent No. 4 can be sufficiently regenerated. However, if the moisture absorbing means is also stored isolated from the atmosphere as in this embodiment, the moisture absorption of the moisture absorbent will be reduced and it will be easier to regenerate during the next operation.
In this embodiment, the first and second air supply lines 14 and 22 are each independently connected to the electrode 10, but each line 14.
Reference numeral 22 indicates the first and third valves 1 as shown in the phantom lines in FIG.
8. The electrodes are merged downstream of 26 as one line.
The present invention also includes such a connection. FIG. 2 is a conceptual diagram of a battery system according to another embodiment of the present invention. In this embodiment, the air flowing through the second air supply line 14A is not heated by the exhaust line 16A, but by an independent heating means 30A comprised of an electric heater. During operation, only the first and second valves 18A and 20B are opened, and the battery is operated through the first air supply line 14A and exhaust line 16A. When stopped, the first valve 18
Only valve A is closed, and the remaining valves 2OA, 26A, and 28A are all opened to allow air to flow through the second air supply line 22A. The air is heated by the heating means 30A, while the moisture absorbing means 2
4A and introduced into the gas space of the electrode IOA as heated dry air. After a suitable period of time, heating means 3
0A is stopped, the moisture absorption function of the moisture absorption means 24A is increased, and the introduced air is dried. Once the electrode is filled with dry air, close all valves to stop and save the system. When restarting operation, only valves 18A and 2OA may be opened, but
In order to regenerate the moisture absorption means 24A, the temporary valve 26A
．． 28A is also opened and the heating means 30A is operated while air is flowing, and when the regeneration is completed, the valves 26A and 28 are opened again.
It is preferable to close A and stop the heating means 24A.
In the above embodiment, the heating means is provided only in the second air supply line in which the moisture absorption means is provided, but the heating means is also provided in the first air supply line, and when the operation is stopped, the heating means is provided in the first air supply line. It is also possible to first send heated air from the line to evaporate the moisture in the electrolyte and then fill it with dry air through the second air supply line, and the present invention also includes such a system. (Effects of the Invention) As described above, the present invention has the advantage of stopping the supply of one of the reactive gases, fuel gas or air, and then heating the other reactive gas and supplying it to the electrode. While the moisture was evaporated, the other reaction gas was dried and supplied to the electrode, and the supply/discharge valves of the electrode were closed with the dry reaction gas filling the gas space within the electrode. Therefore, stop
The electrolyte does not absorb water during storage and the phosphoric acid concentration does not decrease.

Furthermore, in the fuel cell system of the present invention, since the moisture absorbing means and the electrode are separated by a valve, the moisture absorbed by the moisture absorbing means does not transfer to the phosphoric acid electrolyte of the electrode during stoppage and storage. Furthermore, the moisture absorbing means can be regenerated by heating with the heating means, so that it can be used repeatedly.

4.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a battery system according to an embodiment of the present invention;
The figure is a conceptual diagram of a battery system of another embodiment. 10, IOA... Electrode, 14.14A... First air supply line, 16.16A.
...Exhaust line, 22.22A...Second air supply line, 24...Heat exchanger as a moisture absorption means and heating means, 24A...Moisture absorption means. 30A...Heating means

Claims (2)

[Claims] (1) In a fuel cell system using a phosphoric acid electrolyte, after stopping the supply of fuel gas, air is heated and dried before being supplied to the electrodes, filling the gas space inside the electrodes with dry air. A method for stopping a fuel cell system, characterized by closing the supply/discharge valves of the electrodes. (2) In a fuel cell system using a phosphoric acid electrolyte, the electrodes, the first and second air supply lines that supply air to the electrodes, and the air supply line that is installed in the middle of the second air supply line to supply air at low temperatures. Moisture absorbing means that absorbs moisture inside and releases moisture at high temperatures,
A heating means that directly or indirectly heats the moisture absorption means, a first valve that cuts off the first air supply line, a second valve that cuts off the exhaust line of the electrode, and a heating device that directly or indirectly heats the moisture absorption means, a first valve that cuts off the first air supply line, a second valve that cuts off the electrode exhaust line, and a A fuel cell system comprising: a third valve that shuts off the second air supply line.