JPH06215788A - Control method of reformer temperature in fuel cell generating facilities - Google Patents

Abstract

PURPOSE:To provide a control method of reformer temperature capable of preventing the overheat of a reformer heat transfer part at the time of lowering the load of a fuel cell and circulating the whole quantity of CO2 gas from anode side to cathode side. CONSTITUTION:This device is provided with a combustion air control valve 22, an air heater 24 by a combustion exhaust gas 8, a combusting air line 14 for heating and supplying an air 12 to the combustor of a reformer 10, and a temperature sensor 16 for detecting the temperature of the reformer heat transfer part. The temperature rise of the reformer heat transfer part is detected by the temperature sensor 16, or the combustion air control valve 22 is opened by a preceding signal based on load change command to excessively send the air in disregard of the flow rate at general time. Thus, the temperature of the combustion gas in the reformer 10 is lowered, and the overheat of the reformer heat transfer part is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a reformer temperature in a fuel cell power generation facility, and more particularly to a control method for preventing overheating of a reformer heat transfer section when a load is reduced.

[0002]

2. Description of the Related Art Molten carbonate fuel cells have characteristics that conventional power generators do not have, such as high efficiency and little impact on the environment, and they are attracting attention as a power generation system following hydropower, thermal power, and nuclear power. Is currently being researched and developed all over the world. In particular, in a power generation facility using a molten carbonate fuel cell using natural gas as a fuel, a fuel gas 3 obtained by mixing natural gas 1 and steam 2 is converted to an anode gas 4 containing hydrogen as shown in FIG. A reformer 10 that produces a reforming gas and a fuel cell 20 that generates electric power from an anode gas 4 and a cathode gas 5 containing oxygen are generally provided. The anode gas 4 produced by the reformer 10 is supplied to the fuel cell 20. It is supplied and consumes most (for example, 80%) of it in the fuel cell to become the anode exhaust gas 6, and after separating its water content, it is supplied to the combustor of the reformer 10 as the combustion gas 7. In the reformer, combustible components (hydrogen, carbon monoxide, methane, etc.) in the combustion gas 7 are burned in the combustor to generate high temperature combustion gas, and the high temperature combustion gas heats the reforming pipe 10a. The fuel gas 3 passing through the reforming pipe is reformed. The combustion exhaust gas 8 that has left the reformer merges with the air 11 to become the cathode gas 5, and a part of this cathode gas 5 reacts in the fuel cell 20 to become the high-temperature cathode exhaust gas 9, and a part of it is recycled. The remaining power is recovered by the turbine 31 of the power recovery device 30, the heat is recovered by the boiler 35, and the heat is discharged to the outside of the system.

[0003]

The reformer heat transfer section is usually
For example, it is operated at a high temperature of around 900 ° C., and this temperature is extremely close to the strength limit of the heat transfer material. Therefore,
Temperature control of this part is extremely important for improving the reliability of the reformer. On the other hand, the main cell reactions in the fuel cell are the anode reaction of H ₂ + CO ₃ ^2- → H ₂ O + CO ₂ +2 e and the cathode reaction of 1/2 O ₂ + CO ₂ +2 e → CO ₃ ^2- . The CO ₂ gas generated at the anode needs to be circulated to the cathode of the fuel cell in order to be used for the cathode reaction. In the above-described power generation equipment, after the anode exhaust gas 6 emitted from the fuel cell is separated from water, the entire amount thereof is supplied to the combustor of the reformer 10 as the combustion gas 7. When the load of the fuel cell decreases in such a power generation facility, the supply amount of the fuel gas 3 to the reformer 10 is reduced in response to the load command, but the anode gas 4 supplied to the fuel cell 20 is actually reduced. There is a time lag before it decreases. Therefore, while the power generation load drops and the fuel (mainly hydrogen) consumption in the fuel cell decreases, the calorific value of the anode exhaust gas 6 transiently increases, and the entire amount of the anode exhaust gas 6 is reformed. Since it burns at 10, the burned combustion gas becomes high in temperature, and there is a problem that the reformer heat transfer part such as the reforming pipe 10a is overheated. Therefore, there are problems that hot spots are generated in the heat transfer section of the reformer to damage the heat transfer section, or the reforming catalyst filled in the reforming tube is deteriorated to shorten the life. Further, if a part of the anode exhaust gas 6 is temporarily exhausted to the outside of the system in order to avoid such a problem and reduce the load in a short time, energy loss and safety are impaired, and the cathode reaction described above is also performed. There is a problem that the amount of circulation of the CO ₂ gas used for is reduced and it takes time to return to the high load operation. Therefore, conventionally, when the power generation load of the fuel cell is lowered, the load is gradually lowered so that the temperature of the reformer heat transfer section falls within an allowable range. However, for this reason, the load response characteristics of the fuel cell are deteriorated, and there is a problem that it is not possible to cope with a load change in a short time.

The present invention was devised to solve the above-mentioned various problems. That is, it is an object of the present invention to prevent overheating of the reformer heat transfer section when the load of the fuel cell is reduced and to circulate the entire amount of CO ₂ gas from the anode side to the cathode side. It is to provide a temperature control method.

[0005]

When the load of the fuel cell drops, the amount of air required for the cathode gas also decreases, and excess air is generated with respect to the supply capacity of the air supply equipment. The present invention utilizes such surplus air and supplies more air than required by the reformer to the combustor of the reformer to burn the combustion gas 7 with excess air in the reformer. It is intended to lower the combustion temperature. That is, according to the present invention, the fuel cell is provided with a reformer for reforming a fuel gas containing water vapor into an anode gas containing hydrogen, and a fuel cell for generating electricity from the anode gas and a cathode gas containing oxygen. In the fuel cell power generation facility in which the entire amount of the anode exhaust gas is supplied to the combustor of the reformer and burns, and the entire amount of the combustion exhaust gas is supplied to the cathode side of the fuel cell, the combustion air control valve and the combustion exhaust gas An air heater, which is provided with a combustion air line for heating air to supply the combustor of the reformer and a temperature sensor for detecting the temperature of the reformer heat transfer section. The temperature sensor detects the temperature rise of the heat section, or the preceding signal based on the load change command opens the combustion air control valve to send excess air above the normal flow rate, thereby burning the reformer. Gas temperature The lowered, to prevent overheating of the reformer heat transfer unit, the control method of the reformer temperature is provided in the fuel cell power plant, characterized in that. According to a preferred embodiment of the present invention, a cathode air control valve is further provided, and an air supply line for supplying air to the cathode gas is further provided, and the cathode air control valve is closed at the same time when the combustion air control valve is opened. Reduce the amount of air supplied to the cathode. Further, it is preferable that a bypass line having a bypass valve and bypassing the air heater is further provided, and the bypass valve is fully opened at the same time as the opening operation of the combustion air control valve.

[0006]

According to the present invention, the temperature rise in the reformer heat transfer section is detected by the temperature sensor, or the advance signal based on the load change command is used to open the combustion air control valve to ignore the normal flow rate. Since excessive air is sent, the combustion gas temperature of the reformer is lowered by this excess air, and it is possible to prevent overheating of the reformer heat transfer section. Further, according to this method, the entire amount of the anode exhaust gas is supplied to the cathode side of the fuel cell via the reformer, so that the circulation of CO ₂ gas necessary for the cathode reaction can be reliably performed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing a power generation facility of a molten carbonate fuel cell for carrying out the method according to the present invention. In this figure, the same parts as those in FIG. 2 are designated by the same reference numerals. 1, a fuel cell power generation facility includes a reformer 10 for reforming a fuel gas 3 containing water vapor into an anode gas 4 containing hydrogen, and a fuel cell 20 for generating electricity from an anode gas 4 and a cathode gas 5 containing oxygen. So that the entire amount of the anode exhaust gas 6 discharged from the fuel cell 20 is supplied to the combustor of the reformer 10 and burned, and the entire amount of the combustion exhaust gas 8 is supplied to the cathode side C of the fuel cell 20. Has become. The fuel cell 20 is composed of an anode side A through which the anode gas 4 passes and a cathode side C through which the cathode gas 5 passes, and is composed of hydrogen and carbon monoxide in the anode gas and oxygen and carbon dioxide in the cathode gas. Electricity is generated by a chemical reaction. As described above, due to this cell reaction, CO ₂ gas is generated on the anode side and CO ₂ gas is consumed on the cathode side.

The fuel cell power generation system further includes a combustion air line 1 for heating the air 12 and supplying it to the combustor of the reformer 10.
4 and a temperature sensor 16 for detecting the temperature of the heat transfer section of the reformer
With. In the combustion air line 14, a combustion air control valve 22 and an air heater 24 for the combustion exhaust gas 8 are provided in the middle thereof.
And are provided. The air heated by the combustion air line 14 can be supplied to the combustor of the reformer, and the combustion of the anode exhaust gas 6 can be stably performed. 1 further includes an air supply line 18 for supplying air 12 to the cathode gas 5 and a bypass line 1 for bypassing the air heater 24 and supplying air to the reformer 10.
9 is equipped. A cathode air control valve 26 is provided in the middle of the air supply line 18, and the bypass line 19 is provided.
Is provided with a bypass valve 27 in the middle thereof. The power generation facility further includes a control device 28. Combustion air control valve 2
2, the cathode air control valve 26 is a flow rate control valve, the bypass valve 27 is an opening / closing valve, and these are opened / closed by a control signal from the control device 28. Control device 28
Further, the load command signal 15 of the entire power generation equipment and the detection signal of the temperature sensor 16 are input to the.
Other points are the same as those of the power generation equipment shown in FIG. 2, and the description thereof will be omitted here to avoid duplication.

A method of controlling the reformer temperature in the fuel cell power generation facility shown in FIG. 1 will be described below. When the load of the fuel cell drops in such power generation equipment, a preceding signal based on the load change command is issued. The temperature sensor 16 detects an increase in the temperature of the reformer heat transfer section, or the preceding signal based on a load change command is used to open the combustion air control valve 22 and send air in excess of the normal flow rate. Due to this excess air, the temperature of the combustion gas in the reformer 10 is lowered, and it is possible to prevent overheating of the reformer heat transfer section. Further, according to this method, since the entire amount of the anode exhaust gas 6 is supplied to the cathode side C of the fuel cell 20 via the reformer, it is possible to reliably circulate the CO ₂ gas required for the cathode reaction. it can. Further, it is preferable to close the cathode air control valve 26 at the same time as the opening operation of the combustion air control valve 22 to reduce the amount of air supplied to the cathode C. As a result, the amount of air reduced by the cathode air control valve 26 can also be sent to the combustor of the reformer 10 via the combustion air control valve 22 to further lower the combustion gas temperature. When the load drops, the amount of air required by the cathode also decreases, so the above operation is possible, and the excess air supplied to the reformer 10 via the combustion air control valve 22 is Since the entire amount returns to the cathode side C of the fuel cell 20, it is possible to immediately cope with the subsequent load fluctuation. Further, it is preferable that the bypass valve 27 is fully opened at the same time when the combustion air control valve 22 is opened. As a result, low-temperature air bypassing the air heater 24 can be supplied to the combustor of the reformer 10, and the cooling effect can be further enhanced.

[0010]

As described above, according to the present invention, the temperature rise of the reformer heat transfer section is detected by the temperature sensor, or the combustion air control valve is normally opened by the preceding signal based on the load change command. Since the excess air is sent while ignoring the flow rate at the time, the combustion gas temperature of the reformer is lowered by this excess air, and it is possible to prevent overheating of the reformer heat transfer section. Further, according to this method, since the entire amount of the anode exhaust gas is supplied to the cathode side of the fuel cell via the reformer,
It is possible to reliably circulate the CO ₂ gas necessary for the cathode reaction. Therefore, according to the present invention, it is possible to prevent overheating of the reformer heat transfer portion when the load of the fuel cell is lowered, and to make it possible to circulate the entire amount of CO ₂ gas from the anode side to the cathode side. A control method can be provided.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a power generation facility for carrying out a method according to the present invention.

FIG. 2 is an overall configuration diagram showing a conventional power generation facility.

[Explanation of symbols]

 1 natural gas 2 steam 3 fuel gas 4 anode gas 5 cathode gas 6 anode exhaust gas 7 combustion gas 8 combustion exhaust gas 9 cathode exhaust gas 10 reformer 10a reforming pipe 11 air 12 air 14 combustion air line 15 load command signal 16 temperature Sensor 18 Air supply line 19 Bypass line 20 Fuel cell 22 Combustion air control valve 24 Air heater 26 Cathode air control valve 27 Bypass valve 28 Control device 30 Power recovery device 31 Turbine 35 Boiler

Claims (3)

[Claims] 1. An anode exhaust gas discharged from a fuel cell, comprising a reformer for reforming a fuel gas containing water vapor into an anode gas containing hydrogen, and a fuel cell for generating electricity from the anode gas and a cathode gas containing oxygen. In a fuel cell power generation facility in which all of the fuel gas is supplied to the combustor of the reformer and burns, and the total amount of the combustion exhaust gas is supplied to the cathode side of the fuel cell, a combustion air control valve and an air heater using the combustion exhaust gas Equipped with a combustion air line that heats air to supply it to the combustor of the reformer, and a temperature sensor that detects the temperature of the reformer heat transfer section. Is detected by the temperature sensor, or by a preceding signal based on a load change command, the combustion air control valve is opened to supply excess air above the flow rate at the normal time, thereby lowering the temperature of the combustion gas in the reformer. ,
A method for controlling a reformer temperature in a fuel cell power generation facility, comprising preventing overheating of a reformer heat transfer section. 2. An air supply line having a cathode air control valve for supplying air to the cathode gas, the air being supplied to the cathode by closing the cathode air control valve simultaneously with the opening operation of the combustion air control valve. Reduce the amount,
The method for controlling the reformer temperature in the fuel cell power generation facility according to claim 1, wherein. 3. A bypass line having a bypass valve for bypassing the air heater is further provided, and the bypass valve is fully opened simultaneously with the opening operation of the combustion air control valve. A method for controlling the reformer temperature in the fuel cell power generation facility according to.