JPH0381971A - Operating method for fuel cell - Google Patents

Abstract

PURPOSE:To shorten the starting time by starting a cell with heating, supplying a high temp. modified gas when a specified temp. is attained, and allowing this modified gas to assist heating of the cell. CONSTITUTION:At starting, a fuel cell 1 is first heated by the heat of a starting burner 12 through a cooling chamber 18. When the temp. has attained a point which is a proximity temp. over the dew point o a modified gas and where the temp. of modifier becomes TR1, the high temp. modified gas is introduced to a fuel chamber 16 to assist heating of the fuel cell 1. When the fuel cell 1 has attained the temp TC1 with this heating, discharging is started, and the temp. of the fuel cell 1 rises further being assisted by the heating due to discharging, to attain the steady operating temp. TC2 at the time t1. That is, the post-start steady operating condition is obtained in the time t1 which is shorter than t2 in case no heating assist is given by the heat of modified gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for operating a fuel cell that operates at a temperature higher than room temperature, and particularly to a method for starting a fuel cell.

[Conventional technology]

A fuel cell that uses methanol or a reformed natural gas such as methane or ethane as a fuel and oxygen or air as an oxidant gas is generally equipped with a cell stack at the bottom of the tank as shown in Figure 3. . In other words, a fuel cell consists of a matrix 5 impregnated with an electrolyte, a porous fuel electrode 2 and an oxidizer electrode 3 sandwiching the matrix 5 and having gas diffusion and electrolyte permeability, and a current collector in contact with these electrodes. A cell stack 6 is constructed by stacking a plurality of single cells, which are connected to a separator 4 at the bottom of the tank and connected to a separator 4 for supplying a reaction gas to each electrode. It is equipped with

The electrode is a porous thin film to facilitate gas diffusion or permeation, and supports a noble metal such as platinum to facilitate electrode reaction.

In such fuel cells, an electrode reaction (Hg
= 2H" + 2e) is an electrode reaction (AOz
+2H" +2e-■mO) becomes an electromotive reaction, and the total reaction generates water from hydrogen and oxygen to generate electricity. The above reaction progresses at the location of the catalyst added to each electrode, The hydrogen ions generated at the fuel electrode are transported to the oxidizer electrode through the electrolyte in the matrix, and the generated electrons are transported to the oxidizer electrode through a load circuit connected to the battery, where they react with oxygen. Produce water.

The hydrogen that causes the above electrogenic reaction is hydrogen in the reformed gas obtained by reforming the reformed raw material into a hydrogen-rich gas in a fuel reformer, and the oxygen contained in the air is used. ,
These reformed gases and air are supplied to the cell stack as reaction gases to generate electricity. Therefore, when extracting electricity from a fuel cell, a fuel cell power generation device is usually constructed by combining a fuel reformer and a fuel cell, and the reformed gas generated by the fuel reformer is supplied to the fuel cell, and the reformed gas is supplied at the same time. The generated air is used to generate electricity in a fuel cell.

By the way, fuel cells generally improve the efficiency of catalytic reactions.

An appropriate rated operating temperature is determined based on the heat resistance of the constituent members, and this temperature is higher than normal temperature, for example, approximately 190° C. for a phosphoric acid fuel cell. Therefore, it takes time to heat up the fuel cell from startup to rated operating temperature.
This is called startup time. From the viewpoint of the usability of the fuel cell as a plant, it is preferable for the startup time to be short. Conventionally, in order to shorten this time, methods such as heating the cell stack immediately after startup using a heating heater installed in the cell stack have been used. has been adopted. For example, as shown in FIG. 4, a cooling plate 10 having a cooling passage 9 is inserted between the cells in the cell stack 6, and this cooling passage 9, a starting burner 12 having a heat transfer tube 11, and a cooling plate 10 are inserted between the cells in the cell stack 6. A temperature raising device including a circulation system 14 connected to a pump 13 for feeding a liquid heat medium (hereinafter referred to as circulating fluid) is provided in the flow path 9, and the circulating fluid is circulated to the circulation system 14 by this temperature raising device. The heat exchanger tube 1 is circulated by the pump 13 and burned by the starting burner 12.
1, and this high temperature circulating fluid cools the cooling plate 10.
After the cell stack 6 is heated to a certain temperature (130°C in the case of a phosphoric acid fuel cell), the reformed gas and air from the fuel reformer are supplied to the fuel cell to discharge it. The resulting internal heat generation accelerates the temperature rise of the fuel cell, shortening startup time.

[Problem to be solved by the invention]

Conventional methods such as those described above require a long start-up time, and there is a limit to the ability of the temperature-raising heater and starting burner to be increased. Therefore, simply increasing the heater capacity would result in uneven temperature distribution in the cell stack stacking direction, and increasing the number of inserted heaters would increase the size and weight of the cell stack, which was undesirable. On the other hand, in the method of heating the circulating fluid with a startup burner, there is a limit to increasing the flow rate of the heated circulating fluid due to dimensional constraints of the circulating fluid flow path in the cell stack, and at the same time, the capacity of the circulating pump increases. There is a drawback. In addition, increasing the combustion rate of the startup burner has the risk of partial boiling of the circulating fluid in the heat transfer tubes, and as with heaters, simply increasing the capacity has the disadvantage of increasing unevenness in temperature distribution in the stacking direction. be. In addition, even if a reactive gas is supplied to the cell stack and the temperature is raised due to internal heat generation, the cell stack does not discharge until it reaches a predetermined temperature (approximately 130°C for phosphoric acid fuel cells), so the startup time is reduced. A sufficient effect has not been obtained for the purpose of shortening the length.

An object of the present invention is to increase the temperature of the fuel cell at startup by using reformed gas from the fuel reformer in the fuel electrode of a fuel cell power generation device in which a fuel reformer and a fuel cell are combined. An object of the present invention is to provide a method of operating a fuel cell that can reduce time.

[! ! Means to solve the problem]

In order to solve the above problems, the present invention provides a fuel reformer that generates reformed gas by reforming a reformed raw material into hydrogen-rich gas, and a fuel reformer that generates reformed gas from the reformer and oxidizes the reformed gas from the reformer. In a method of operating a fuel cell equipped with a cell stack that generates electricity using an agent gas, after the temperature of the fuel cell reaches or exceeds the dew point of the reformed gas using a heating device, the reformed gas is supplied to the fuel cell to activate the fuel cell. shall be started.

[Effect]

After the temperature of the reformed gas generated in the fuel reformer is raised by the temperature raising device and the temperature of the fuel cell exceeds the dew point of the reformed gas, the reformed gas is supplied to the fuel cell to achieve high-temperature reforming. Since the fuel cell is heated from a relatively low temperature state called the dew point of the gas, the temperature of the fuel cell can be raised quickly without dew condensation occurring within the fuel cell.

〔Example〕

A fuel cell power generation device is constructed by combining a fuel reformer and a fuel cell, and has a system shown in FIG. In the figure, 1 is a fuel cell, which is shown schematically.
A matrix 5, a fuel electrode 2 and an oxidizer electrode 3 disposed on both sides of the matrix 5, a fuel chamber 16 disposed on both sides of the matrix 5 through which fuel gas circulates, and an oxidizer chamber 17 through which oxidizer gas flows;
Cooling plate 10 through which a cooling medium and a heat medium flow (see Fig. 4)
It is composed of a cooling chamber 18 equipped with.

A fuel reformer 20 includes a burner 21, a heating tube 22 for a reforming raw material, and a reforming tube 23 connected thereto and filled with a reforming catalyst. 24 is a reformed gas supply system that supplies the reformed gas sent out from the reforming pipe 23 to the fuel chamber 16;
25 is an off-gas exhaust system that guides off-gas containing residual hydrogen from the fuel chamber 16 to the burner 21, and 26 is an air supply system that supplies air to the oxidizer chamber 17. In addition, in the cooling room on the 1st, the 4th
A circulation system 14 having a starting burner 12 and a pump 13 shown in the figure is connected. 27 is a fuel tank 27a for fuel that is a reforming raw material, a fuel pump 27b, and a solenoid valve 27c.
It is a reforming raw material supply device equipped with this, and this supply device! !
27 and heating of the fuel reformer 20! A reforming material supply system 28 is provided in connection with the reforming material supply system 22. Reference numeral 29 denotes an auxiliary fuel supply device including an auxiliary fuel tank 29a for auxiliary fuel for combustion, an auxiliary fuel pump 29b, and a solenoid valve 29c.
0 is set. A combustion air supply system 31 supplies combustion air to the burner 19. Note that 32 is an electric circuit connected to a load and the like.

In the fuel cell power generation device having such a configuration, the fuel of the reforming material is supplied from the reforming material supply device 27 to the fuel reformer 20 via the reforming material supply system 28, and the heating tube 22. It flows into the reforming pipe 23. On the other hand, in the burner 21, the auxiliary fuel supplied from the auxiliary fuel supply device 29 through the auxiliary fuel supply system 30 is combusted by the air supplied through the combustion air supply system 31. The flame and combustion gas generated by this combustion cause the heating tube 22. The reforming tube 23 is heated and the heating tube 22. The reformed raw material flowing through the reforming pipe 23 is reformed into a hydrogen-rich gas to generate reformed gas. In this case, the temperature inside the fuel reformer is raised to 500°C or higher due to combustion in the burner 21, and the reformed gas also has a temperature of 250°C or higher.

A method for starting a fuel cell according to the present invention is to supply thermal energy of reformed gas to the fuel cell from a low temperature state of the fuel cell to raise the temperature of the fuel cell, thereby shortening the heating time. That is, the circulating fluid whose temperature has been raised by the starting burner 12 is circulated through the circulation system 14 to raise the temperature of the fuel cell via the cooling chamber 17. The high-temperature reformed gas generated in the fuel reformer 20 is heated by the starting burner 12 and then heated to the fuel cell 1.
After the temperature of the reformed gas reaches the dew point or higher, the reformed gas is supplied to the fuel cell 1 via the reformed gas supply system 24 to raise the temperature of the fuel cell. Then, the temperature of the fuel cell is set to a predetermined temperature (approximately 130°C for phosphoric acid fuel cells).
℃), the fuel cell is discharged by the air supplied to the oxidizer chamber 17, and the temperature is further raised due to internal heat generation caused by this, and the temperature is raised to the operating temperature of the fuel cell. Note that the off-gas discharged from the fuel cell is sent to the burner 21 via the off-gas exhaust system 25 and is used as combustion fuel.

FIG. 2 is a graph showing the progress of the temperature rise of the fuel reformer and the cell stack of the fuel cell when the temperature of the fuel cell is increased by the startup burner and the above-mentioned reformed gas.
36 shows the temperature increase process of the fuel reformer from startup to the operating temperature, and 36 shows the temperature increase process of the cell and stack from startup to the operating temperature of the fuel cell according to the present invention. , - The dashed line 37 shows the temperature increase process of the cell stack by the conventional startup method. Note that Tll is the reforming start temperature of the fuel reformer, To is the operating temperature of the fuel reformer, and T
CI is the reformed gas supply start temperature for supplying reformed gas to the cell stack of the fuel cell, and To is the cell stack (fuel cell)
operating temperature.

The fuel reformer is directly heated and heated by combustion in the burner, so as shown in the temperature rise curve 35, the fuel reformer reaches the reforming start temperature T earlier than the temperature rise of the cell stack by the startup burner. □ is reached, and from this point the reformed gas can be supplied to the fuel cell to raise its temperature.

On the other hand, the temperature of the fuel cell is raised by the startup burner, and the reformed gas is supplied from point A of the temperature rise curve shown at 36 (the point at which the reformer temperature reaches T□), and the temperature of the fuel cell is raised. Note that the temperature at point A is higher than the dew point of the reformed gas. Then, the temperature of the fuel cell increases due to the increase in temperature caused by the reformed gas, and B
When the TCI temperature reaches the TCI point, discharge is caused by the supplied reformed gas and air, and the temperature of the fuel cell further rises due to the addition of internal heat generation due to the discharge, and at t8 hours, the operating temperature T'c is reached.
Reach t.

In addition, in the conventional startup method, the temperature of the fuel cell is raised by the startup burner as shown by the temperature increase curve 37 indicated by the dashed line, and when the temperature of the fuel cell reaches the 0 point T'c+, the reformed gas starts flowing. The fuel is supplied to the fuel cell and discharged, and from this zero point, internal heat generation due to the discharge is added, and the temperature of the fuel cell further rises, reaching the operating temperature T0 at time t8.

Therefore, the start-up method according to the present invention shortens the start-up time of the fuel cell by (tx t+) time than the conventional start-up method.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, when starting up a fuel cell, in addition to the conventional method of raising the temperature of a fuel cell, the reformed gas from the fuel reformer is heated so that the temperature of the fuel cell reaches the temperature of the reformed gas. By supplying fuel to the fuel cell to raise the temperature of the fuel cell after reaching the dew point of This has the effect of shortening the startup time since it can be heated.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a fuel cell power generation device when applying the fuel cell starting method according to the embodiment of the present invention, and Fig. 2 shows the progress of temperature rise of the fuel cell according to the fuel cell starting method according to the embodiment of the present invention. FIG. 3 is a sectional view of a cell stack of a fuel cell, and FIG. 4 is a system diagram for heating a conventional fuel cell. 1: Fuel cell, ■2: Starting burner, 20: Number of fuel':
$1 Eup 2nd Close

Claims (1)

[Claims] 1) A fuel reformer that generates reformed gas by reforming the reformed raw material into hydrogen-rich gas, and a cell stack that generates electricity by being supplied with the reformed gas and oxidizer gas from this reformer. A method of operating a fuel cell comprising: supplying reformed gas to the fuel cell to start the fuel cell after the temperature of the fuel cell becomes equal to or higher than the dew point of the reformed gas by a temperature raising device. how to drive.