JP2002343370A - Fuel cell system and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact bi-temperature-control combination solid oxide fuel cell system which can maintain operation temperature constant of a solid oxide fuel battery cell without using an outside thermal supply or a combustor in a fuel battery. SOLUTION: The fuel cell system provided with a low-temperature solid oxide fuel cell 12 which uses hydrocarbon system gas as fuel and generates power by draining carbon monoxide, hydrogen and unreacted hydrocarbon system gas, and a high-temperature solid oxide fuel cell 14 which generates power with drainage gas 13 from the low-temperature solid oxide fuel cell 12 as fuel, is also provided with a flow divider 21 which divides flow of hydrocarbon system gas 11 supplied from outside into two branches in any ratio, one of which 22 is supplied to the low-temperature solid oxide fuel cell 12 and the other 23 is supplied to the high-temperature solid oxide fuel cell 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel cell system and a control method thereof, and more particularly to a solid oxide fuel cell system and a control method thereof.

[0002]

2. Description of the Related Art Conventionally, as a solid oxide fuel cell system using a hydrocarbon-based gas as a fuel, a fuel cell system comprising a low-temperature solid oxide fuel cell and a high-temperature solid oxide fuel cell, That is, a two-temperature control connection type solid oxide fuel cell system is known.

FIG. 4 shows a conventional dual-temperature controlled solid oxide type.
FIG. 2 is a diagram illustrating a fuel cell system. In the figure,
The fuel cell system according to
And the partial oxidation reaction C_nH_{2n + 2} + 0.5nO₂ → nCO + (n +
1) H₂  -Temperature solid oxide fuel cell 12 for power generation
And the exhaust gas 13 from the fuel cell 12
Of the low-temperature solid oxide fuel cell in
Reforming Reaction of Hydrocarbon Gas C_nH_{2n + 2} + NH₂O → nCO + (2n + 1)
H₂  And oxidation reaction of carbon monoxide CO + 0.5O₂ → CO₂  And hydrogen oxidation reaction H₂ + 0.5O₂ → H₂O 2 and a high-temperature solid oxide fuel cell 14 for generating electricity
Dual temperature control connection type solid body characterized by being connected
It is an oxide fuel cell system.

In this case, the fuel cells 12 and 14 are also thermally connected, and a part of the heat generated in the fuel cell 14 flows to the fuel cell 12 to help maintain the temperature of the fuel cell 12.

A similar system is disclosed in, for example,
No. 2,688,832.

[0006]

When the fuel cell system cannot stand alone thermally, it is heated from the outside or a part of the fuel is burned, and the heat of reaction is used to maintain the temperature of the system. There is a need.

The above low-temperature type solid oxide fuel cell 12
The power density of the partial oxidation reaction in
Oxidation reaction using CH as fuel CH₄ + 0.5O₂ → CO + 2H₂  Currently achieved with solid oxide fuel cells using
Maximum power density is 0.3 W / cm at single cell level²Degree (luck
(The turning temperature is 800 ° C. and the operating voltage is about 0.4 V). Up
The theoretical open circuit voltage of the low temperature type solid oxide fuel cell 12 is
Since it is as high as about 1.2 V, a high voltage of about 1 V is actually used.
It is expected to drive in. When driving at a voltage of 1V
Assuming that the power density is 0.1 W / cm at best
²It is about.

On the other hand, at present, the high-temperature type solid oxide fuel cell 14 has a high output density of about 0.5 W / cm ² at a single cell level (operating temperature of 1000 ° C. and operating voltage of about 0.7 V). Has been obtained.

Therefore, in the conventional dual-temperature controlled solid oxide fuel cell, the cell area of the low-temperature solid oxide fuel cell 12 may be increased, and the system may be enlarged. For example, the conventional system shown in FIG.
Methane is supplied as 1 and 95% of the methane supplied to the system in the low-temperature type solid oxide fuel cell 12 undergoes a partial oxidation reaction, and all the hydrogen and carbon monoxide generated by the partial oxidation reaction are converted into a high-temperature type. It is assumed that the system is thermally independent by burning the remaining 5% of methane that has reacted in the solid oxide fuel cell 14 and has not reacted in the low-temperature solid oxide fuel cell 12. When the low-temperature type solid oxide fuel cell 12 is operated at a voltage of 1 V and a temperature of 800 ° C., and the high-temperature type solid oxide fuel cell 14 is operated at a voltage of 0.7 V and a temperature of 1000 ° C., the overall efficiency is about 63%. Assuming that the total output is 100 kW, the output of the low-temperature solid oxide fuel cell 12 is about 32 kW, and that of the high-temperature solid oxide fuel cell 14 is about 68 kW. Assuming that the power density of the low-temperature solid oxide fuel cell 12 is 0.1 W / cm ² and that of the high-temperature solid oxide fuel cell 14 is 0.5 W / cm ² , the cell area is roughly calculated. The physical fuel cell 12 has a cell area of 32 m ² , and the high-temperature solid oxide fuel cell 1
4 has a cell area of 13.6 m ² , and the volume of the low-temperature solid oxide fuel cell 12 is large. It is necessary to suppress such an increase in the fuel cell volume and downsize the system.
Issues.

If the temperature of the solid oxide fuel cell cannot be kept constant when the internal conditions or environmental conditions of the fuel cell system change, the thermal stress generated by the temperature change may cause the solid oxide fuel cell to fail. Damage the cell.

[0011] In a solid oxide fuel cell system designed based on a solid oxide fuel cell that does not deteriorate so that the heat for maintaining its own temperature and the excess heat of the reaction are balanced. When the performance of the fuel cell degrades and the output decreases, the heat loss of the system increases and the temperature of the entire system increases. The thermal stress generated by this temperature change damages the solid oxide fuel cell. Another problem is to prevent the fuel cell from being damaged by thermal stress.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to reduce the size of a small-sized solid oxide fuel cell by keeping the operating temperature of the cell constant without using external heat supply or a combustor in the fuel cell. An object of the present invention is to provide a solid oxide fuel cell system coupled with temperature control.

[0013]

According to the present invention, in order to solve the above-mentioned problems, a hydrocarbon-based gas is used as fuel, and carbon monoxide, hydrogen and unreacted hydrocarbons are used. A low-temperature solid oxide fuel cell that generates power by discharging system gas; and a high-temperature solid oxide fuel cell that generates power using the exhaust gas from the low-temperature solid oxide fuel cell as fuel. A fuel cell system comprising:
The entire flow of hydrocarbon-based gas supplied from the outside is branched into two at an arbitrary ratio, one branch is supplied to the low-temperature solid oxide fuel cell, and the other branch is the high-temperature solid oxide. A fuel cell system comprising a flow divider for supplying the fuel cell to the fuel cell.

According to a second aspect of the present invention, there is provided a method for controlling a fuel cell system for controlling a fuel cell system according to the first aspect, wherein the low-temperature type of the shunt is provided. The ratio of the hydrocarbon-based gas to be supplied to the solid oxide fuel cell is reduced when the temperature of the low-temperature solid oxide fuel cell is lower than a set temperature, and the low-temperature solid oxide fuel cell is reduced. When the temperature of the fuel cell becomes higher than the set temperature, the temperature is increased to constitute a control method of the fuel cell system.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In a dual temperature controlled solid oxide fuel cell system according to the present invention, the entire flow of a hydrocarbon-based gas supplied from the outside is bifurcated at an arbitrary ratio, and Is supplied to the low-temperature solid oxide fuel cell, and the other branch is supplied to the high-temperature solid oxide fuel cell. The volume of the solid oxide fuel cell can be reduced compared to the conventional one, the system can be downsized, and the operating temperature of the low-temperature solid oxide fuel cell can be kept constant, Damage due to thermal stress can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a view for explaining a dual temperature control connection type solid oxide fuel cell system according to the present invention.

A hydrocarbon-based gas 11 such as methane, ethane, propane, and butane supplied to the system is divided into two at an arbitrary ratio by a flow divider 21, and one is used as a hydrocarbon-based gas 22 to perform a partial oxidation reaction and power generation. It flows into the low-temperature type solid oxide fuel cell 12 and the other flows into the hydrocarbon-based gas 23.
As a high-temperature solid oxide fuel cell 14 for performing a power generation by oxidation of carbon monoxide and hydrogen gas and a reforming reaction of a hydrocarbon-based gas using water vapor generated by oxidation of hydrogen.
Flows into. In this case, the carbon monoxide and the hydrogen gas are contained in the exhaust gas 13 from the low-temperature solid oxide fuel cell 12 flowing into the high-temperature solid oxide fuel cell 14.

The system according to the present embodiment includes a hydrocarbon-based system.
Methane is supplied as the gas 11,
And 50% of the methane supplied to the system
The fuel is supplied to the low-temperature solid oxide fuel cell 12,
Partial oxidation reaction in the part, the remaining 50 supplied to the system
% Methane supplied to high temperature solid oxide fuel cell 14
And inside the steam reforming reaction CH₄ + H₂O → CO + 3H₂  Water generated by the partial oxidation reaction and steam reforming reaction
All elements and carbon monoxide are high temperature solid oxide fuel cells 1
Let's say you want to react with 4. At this time, the low-temperature type solid oxide type
The fuel cell 12 is operated at a voltage of 1 V and a temperature of 800 ° C.
Type solid oxide fuel cell 14 at a voltage of 0.7 V and a temperature of 1
When operated at 000 ° C., the power generation efficiency is about 63%.
This efficiency is the same as that of the conventional system.
Methane is supplied as 1 and low-temperature solid oxide fuel
95% of the methane supplied to the system by battery 12
Oxidation reaction and hydrogen generated by partial oxidation reaction and monoxide
All carbon reacts in high-temperature solid oxide fuel cell 14
And burns 5% of the methane supplied to the system
Equivalent to the efficiency of a thermally independent stem.

Assuming that the total output of the system of this embodiment is 100 kW, the low-temperature solid oxide fuel cell 12 has a capacity of about 17 kW, and the high-temperature solid oxide fuel cell 1
4 gives an output of about 83 kW. When the power density of the low-temperature type solid oxide fuel cell 12 is set to 0.1 W / cm ² and the high-temperature type solid oxide fuel cell 14 is set to 0.5 W / cm ² , the cell area is roughly calculated. The cell of the oxide fuel cell 12 is 17 m ² , and the cell of the high-temperature solid oxide fuel cell 14 is 16.6 m ² .

In the system of the present embodiment, the hydrocarbon-based gas 2 is stored in the high-temperature solid oxide fuel cell 14.
3 reforming reaction. However, even in this case, the volume of the high-temperature type solid oxide fuel cell 14 is about the same as when the reforming reaction of the hydrocarbon-based gas 23 is not performed inside (that is, when the hydrocarbon-based gas 23 is not supplied). Can be suppressed. Accordingly, the cell area of the total in the system of 100kW is 33.6M ^2, miniaturization of about 27% as compared to the cell area 45.6 m ² total in the conventional system is realized.

The system according to the present embodiment has a flow divider 21
Controlling the ratio of the hydrocarbon-based gas (22 and 23) to be supplied to the low-temperature and high-temperature solid oxide fuel cells (12 and 14) The temperature of the batteries (12 and 14) is controlled.

As shown in FIG. 2, the temperature _TL of the low-temperature type solid oxide fuel cell 12 is measured, and when the _TL falls below the set operating temperature, the high-temperature type solid oxide fuel cell 12 is measured. The rate of supply to the battery 14 is increased (ie, the rate of supply to the low-temperature type solid oxide fuel cell 12 is reduced), and the temperature of the high-temperature type solid oxide fuel cell 14 is increased, and T _L is increased. Is higher than the set operating temperature, the supply rate to the low-temperature solid oxide fuel cell 12 is increased (that is, the high-temperature solid oxide fuel cell 1).
The temperature of the high-temperature type solid oxide fuel cell 14 is lowered (by reducing the ratio supplied to the fuel cell 4), and if the _TL matches the set operating temperature, the low-temperature type and high-temperature type solid oxide Is controlled so as to maintain the ratio of the hydrocarbon-based gas (22 and 23) supplied to the fuel cell (12 and 14). Since the temperature of the low-temperature solid oxide fuel cell 12 is maintained by the flow of heat from the high-temperature solid oxide fuel cell 14, the low-temperature solid oxide fuel cell is controlled by such a control method. The temperature of the fuel cell 12 is kept constant. If the temperature of the low-temperature solid oxide fuel cell 12 is kept constant, the high-temperature solid oxide fuel cell 1
Since the flow of heat from 4 to the low-temperature solid oxide fuel cell 12 also reaches a steady state, the temperature of the high-temperature solid oxide fuel cell 14 also becomes constant.

FIG. 3 shows a low-temperature type solid oxide fuel cell 1.
2 shows the total power generation efficiency of the fuel cell system when the ratio of the hydrocarbon-based gas 22 supplied to 2 is changed from 0 to 1.
The low-temperature type solid oxide fuel cell 12 is applied with a voltage of 1 V and a temperature of 8
It is assumed that the fuel cell is operated at 00 ° C. and the high-temperature solid oxide fuel cell 14 is operated at a voltage of 0.7 V and a temperature of 1000 ° C. As the ratio of the hydrocarbon-based gas 11 supplied to the low-temperature solid oxide fuel cell 12 increases, the system efficiency increases, and the amount of heat used to maintain the temperature of the system decreases. Conversely, as the ratio of the hydrocarbon-based gas 11 supplied to the low-temperature solid oxide fuel cell 12 decreases, the system efficiency decreases, and the heat used to maintain the temperature of the system increases. When the above ratio is 0 or 1, the flow of the hydrocarbon-based gas 11 supplied from the outside is set to 2
This is not to say that it is divided into two branches, and these cases are out of the scope of the present invention.

Even if environmental conditions change, the amount of heat used for maintaining the temperature of the system can be adjusted by this control, so that the temperature of the solid oxide fuel cells 12, 14 can be kept constant, and the Damage to the solid oxide fuel cell can be prevented.

Even if the performance of the solid oxide fuel cell is deteriorated, if the ratio of the hydrocarbon gas 22 supplied to the low-temperature solid oxide fuel cell 12 by the flow divider 21 is increased, the output can be reduced. It is possible to prevent the temperature of the solid oxide fuel cell from lowering and prevent the solid oxide fuel cell from being damaged by thermal stress.

As described above, in the fuel cell system according to the present invention, the reaction amount in a low-temperature solid oxide fuel cell that performs a partial oxidation reaction of a hydrocarbon gas and power generation while maintaining power generation efficiency. Therefore, the area of the low-temperature solid oxide fuel cell can be reduced, and the size of the system can be reduced. Further, by using the control method of the fuel cell system according to the present invention, without burning the fuel, by adjusting the amount of heat used for maintaining the temperature,
It is possible to prevent the temperature of the solid oxide fuel cell from changing, and to prevent cell damage due to thermal stress.

[0028]

As described above, according to the present invention, a small two-temperature control connection type solid which keeps the operating temperature of the solid oxide fuel cell constant without using external heat supply or a combustor in the fuel cell. An oxide fuel cell system can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a dual temperature controlled solid oxide fuel cell system according to the present invention.

FIG. 2 is a diagram showing a method for controlling a solid oxide fuel cell system with dual temperature control according to the present invention.

FIG. 3 is a diagram showing the relationship between the ratio of hydrocarbon-based gas supplied to a low-temperature solid oxide fuel cell and the overall power generation efficiency of the system.

FIG. 4 is a diagram illustrating a conventional solid oxide fuel cell system with dual temperature control connection.

[Explanation of symbols]

11: hydrocarbon-based gas supplied to the system; 12: low-temperature solid oxide fuel cell; 13: exhaust gas from low-temperature solid oxide fuel cell; 14: high-temperature solid oxide fuel Battery, 21: Divider of hydrocarbon-based gas supplied to the system, 22: Hydrocarbon-based gas flowing from the diverter to the low-temperature type solid oxide fuel cell, 23: High-temperature type solid oxide from the diverter Hydrocarbon-based gas flowing into a fuel cell.

Continuation of the front page (72) Inventor Masayasu Arakawa 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Himeko 2-3-1 Otemachi, Chiyoda-ku, Tokyo Sun Inside the Telegraph and Telephone Corporation (72) Yoshitaka Tabata 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Satoshi Sugita 2-3-1 Otemachi, Chiyoda-ku, Tokyo No. Nippon Telegraph and Telephone Corporation (72) Inventor Akira Takeuchi 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Toshiaki Taniuchi 2--3, Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation (72) Inventor Kazuhiko Nozawa 2-3-1, Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Telegraph and Telephone Corporation (reference) 5H026 AA06 5H027 AA06 KK46 MM09

Claims (2)

[Claims] 1. A fuel comprising a hydrocarbon gas as a fuel, carbon monoxide,
A low-temperature solid oxide fuel cell that generates power by discharging hydrogen and unreacted hydrocarbon-based gas, and a high-temperature solid oxide fuel cell that generates power using the exhaust gas from the low-temperature solid oxide fuel cell as fuel. A solid oxide fuel cell, wherein the entire flow of hydrocarbon-based gas supplied from the outside is branched into two at an arbitrary ratio, and one of the branches is a low-temperature solid oxide fuel cell. A fuel cell system, comprising: a shunt for supplying a fuel cell and supplying the other branch to the high-temperature type solid oxide fuel cell. 2. The control method for a fuel cell system according to claim 1, wherein the flow of the hydrocarbon-based gas supplied to the low-temperature solid oxide fuel cell in the flow divider is performed. The ratio is decreased when the temperature of the low-temperature solid oxide fuel cell is lower than a set temperature, and when the temperature of the low-temperature solid oxide fuel cell is higher than the set temperature. Is a method for controlling a fuel cell system, characterized by increasing.