JP3570570B2 - Molten carbonate fuel cell power generator - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a fuel cell power generator that suppresses a differential pressure generated between an anode and a cathode and between the anode and the cathode and the inside of a storage container within an allowable value at the time of shutdown.
[0002]
[Prior art]
Molten carbonate fuel cells have features that are not found in conventional power generators, such as high efficiency and little impact on the environment, and have attracted attention as a power generation system following hydro, thermal and nuclear power. Is underway.
[0003]
FIG. 5 is a diagram showing an example of a power generation facility using a molten carbonate fuel cell using natural gas as a fuel. In the figure, a power generation facility includes a reformer 10 for reforming a fuel gas 1 obtained by mixing a natural gas 8 and steam 9 into an anode gas 2 containing hydrogen, a cathode gas 3 containing oxygen, and an anode gas containing hydrogen. And an anode gas 2 produced in the reformer 10 is supplied to the fuel cell 20, and the anode gas 2 is largely consumed in the fuel cell 20 to become the anode exhaust gas 4, and the anode exhaust gas 4 is burned. It is supplied to the combustion chamber Co of the reformer 10 as a use gas.
[0004]
In the reformer 10, combustible components (hydrogen, carbon monoxide, methane, etc.) in the anode exhaust gas 4 are burned in the combustion chamber Co to generate high-temperature combustion gas, and the combustion gas heats the reforming chamber Re. In the reforming chamber Re, the fuel gas 1 is reformed by the reforming catalyst to obtain the anode gas 2. The anode gas 2 exchanges heat with the fuel gas 1 by the fuel preheater 11 and is cooled and supplied to the anode A of the fuel cell 20. Further, the combustion exhaust gas 5 that has exited the combustion chamber Co is cooled by the air preheater 32, and after removing moisture, merges with the air 6 to become the cathode gas 3. A part of the cathode gas 3 reacts in the fuel cell 20 to become a high-temperature cathode exhaust gas 7, and a part of the cathode exhaust gas 7 a is mixed with the cathode gas 3 and circulated through the cathode C, and another part of the cathode exhaust gas 7 a. The exhaust gas 7 b is supplied to the combustion chamber Co of the reformer 10, and the rest is recovered by a turbine drive compressor 36 that compresses the air 6, and then heat energy is recovered by a waste heat recovery steam generator (not shown). It is discharged out of the system. The steam 9 generated by the steam generator is mixed with the natural gas 8 to form the fuel gas 1.
[0005]
The fuel cell 20 is stored in the storage container 22, and is operated in a pressurized state. Due to the strength of the fuel cell, the differential pressure between the cathode C and the anode A, the internal pressure of the storage container 22, and the differential pressure between the cathode C and the anode A must be controlled to 800 to 1000 mmAq or less, and controlled to 400 mmAq or less during normal operation. Have been. When an emergency stop of the fuel cell power generator is performed, the supply of the fuel gas 1 is stopped, the high-temperature blower 23 and the low-temperature blower 35 are stopped, and the inside gas is exhausted and replaced with nitrogen gas. In this case, the anode exhaust gas 4 and a part 7b of the cathode exhaust gas enter the exhaust gas supply line 13 through the combustion chamber Co and are discharged from the discharge line 16, and the gas in the containment vessel enters the circulation line 14 from the container discharge line 18 and the cathode The gas is discharged from the turbine supply line 19 through the turbine and the bypass line 40 together with the exhaust gas 7c.
[0006]
[Problems to be solved by the invention]
In order to limit the differential pressure between the cathode C and the anode A at the time of the emergency shutoff, and the differential pressure between the internal pressure of the storage container 22 and the cathode C or the anode A to 800 to 1000 mmAq or less, the differential pressure between the internal pressure of the storage container and the cathode C is reduced. There is provided a high temperature differential pressure control valve 50 for controlling, and a high temperature differential pressure control valve 51 for controlling a differential pressure between the cathode C and the anode A. These high temperature differential pressure control valves 50 and 51 are used only when the plant is stopped, and are considerably more expensive than commercially available control valves due to high temperature specifications. For this reason, it has been one of the components that raises the cost of the plant.
[0007]
The present invention has been made in view of the above-described problems, and controls the discharge of cathode exhaust gas from a turbine to limit the differential pressure between the internal pressure of the containment vessel and the cathode C or the anode A to 800 to 1000 mmAq or less. And abolish the high temperature differential pressure control valve.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a fuel cell having an anode and a cathode and generating electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, a storage container for storing the fuel cell, and a cathode exhaust gas for the fuel cell A reformer that burns a part of the exhaust gas and reforms a fuel gas containing water vapor into an anode gas by the heat, an anode exhaust gas discharge line that supplies the anode exhaust gas to a combustion chamber of the reformer, and a cathode exhaust gas A cathode exhaust gas discharge line for supplying part to the combustion chamber, a circulation line for circulating a part of the cathode exhaust gas of the fuel cell to the cathode, and an exhaust gas supply line for cooling the combustion exhaust gas of the reformer and supplying it to the circulation line And a turbine supply line that supplies a portion of the cathode exhaust gas to a turbine-driven compressor that supplies pressurized air to the exhaust gas supply line. A discharge line which release more gas, and the storage container to the container supply for supplying the gas line, as the differential pressure between the storage vessel and the cathode provided in said container feed line is within the allowable value gas A low-pressure differential pressure control valve that regulates the supply of air, and a container discharge line that guides the gas in the storage container to the circulation line, and that the rotational speed of the turbine-driven compressor is controlled to be constant during an emergency operation stop. For example, the volume of the gas in the containment vessel is reduced to such an extent that the cathode exhaust gas is released earlier than the gas in the containment vessel and the differential pressure between the gas in the containment vessel and the cathode exhaust gas increases and exceeds an allowable value. in many molten carbonate fuel cell power plant, the pressure loss of the anode exhaust gas discharge line and the cathode exhaust gas discharge line is configured to be substantially equal during normal operation, before The discharge line is provided with a low-temperature differential pressure control valve for adjusting the discharge of exhaust gas so that the differential pressure between the anode exhaust gas and the cathode exhaust gas does not exceed an allowable value during an emergency operation stop, and the turbine supply line is provided with a turbine. A bypass line having a rotation speed control valve for controlling the flow rate of the cathode exhaust gas to control the rotation speed of the turbine is provided. A control device is provided that controls the valve opening of the rotation speed control valve to be smaller than the valve opening during normal operation so that the discharge of the cathode exhaust gas from the bypass line becomes gentle within a range where the rotation speed does not become a critical speed. , A molten carbonate fuel cell power generator is provided.
[0009]
[Action]
When the plant is stopped due to emergency shutoff or the like, the anode exhaust gas 4 and a part 7b of the cathode exhaust gas enter the exhaust gas supply line 13 through the combustion chamber Co, are discharged from the discharge line 16, and the gas in the containment vessel is circulated from the container discharge line 18 through the circulation line. 14 and is discharged from the turbine supply line 19 through the turbine and the bypass line 40 together with the cathode exhaust gas 7c. Since the volume of the gas in the storage container is large, the cathode exhaust gas 7c is more likely to be released first, and the pressure difference between the two increases, exceeding the allowable value. Furthermore, since the rotation speed of the turbine drive compressor 36 increases due to a decrease in load due to the stoppage of the plant, the rotation speed control valve 42 increases the opening of the cathode exhaust gas 7c to reduce the flow rate of the cathode exhaust gas 7c to the turbine to maintain the rotation speed. As a result, the cathode exhaust gas 7c easily escapes through the bypass line 40, so that the pressure difference between the gas in the storage container and the cathode exhaust gas 7c increases. Therefore, by reducing the opening of the rotation speed control valve 42 and gradually discharging the cathode exhaust gas 7c through a turbine having a large resistance, the pressure difference between the anode exhaust gas 7c and the gas in the containment vessel is reduced, and both are discharged from the turbine. go. At this time, since the amount of the cathode exhaust gas 7c flowing through the turbine increases, the rotation speed of the turbine drive compressor 36 increases, and there is a possibility that the speed may become a dangerous speed. Smaller. Since the anode exhaust gas 4 and a part 7b of the cathode exhaust gas are balanced in the combustion chamber Co, the pressure difference between the anode and the cathode is within an allowable value.
[0010]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a fuel cell power generation device according to an embodiment. In this figure, the same components as those in FIG. 2 are represented by the same reference numerals. The fuel cell power generation device includes a reformer 10 for reforming a fuel gas 1 containing water vapor to an anode gas 2 containing hydrogen, and a storage container 22 for generating electricity from the anode gas 2 and the cathode gas 3 containing oxygen and carbon dioxide. The anode exhaust gas 4 discharged from the fuel cell 20 is supplied to the combustion chamber Co of the reformer 10 by the anode exhaust gas discharge line 12 and is together with a part 7 b of the cathode exhaust gas 7. The fuel is combusted, and the combustion exhaust gas 5 is supplied to the cathode C of the fuel cell 20 as the cathode gas 3 containing carbon dioxide via the exhaust gas supply line 13 and the circulation line 14.
[0011]
The natural gas 8 is pressurized by the fuel blower 25, is desulfurized by the desulfurizer 26, merges with the steam 9 via the fuel cutoff valve 27, becomes the fuel gas 1, is heated by the fuel preheater 11, and is supplied to the reformer 10. You. A valve 47 is provided on the outlet side of the fuel cutoff valve 27, and nitrogen gas is supplied at the time of a plant stop such as an emergency stop. The reformer 10 includes a combustion chamber Co that burns the anode exhaust gas 4 and the cathode exhaust gas 7b that have exited the fuel cell 20, and a reformer that reforms the fuel gas 1 by heat transfer from the combustion chamber Co to generate the anode gas 2. The room Re. The combustion chamber Co is filled with a combustion catalyst so that sufficient combustion is performed, and the reformer Re is filled with a reforming catalyst for reforming the fuel gas 1 into an anode gas 2 mainly composed of hydrogen. .
[0012]
From the combustion chamber Co, the flue gas 5 passes through the flue gas supply line 13 and enters the circulation line 14, but in the flue gas supply line 13 is cooled by the air preheater 32, and moisture is removed by the condenser 33 and the steam separator 34. The air is pressurized by the low-temperature blower 35, mixed with the air 6, heated by the air preheater 32, and enters the circulation line 14. The discharge line 16 provided with a flow control valve 44 is connected to the inlet side of the low-temperature blower 35, and discharges exhaust gas generated when the plant is stopped or the like to an exhaust gas treatment device (not shown). The differential pressure control valve 44 is operated so that the differential pressure between the anode exhaust gas 4 and the cathode exhaust gas 7 does not exceed an allowable value.
[0013]
A portion 7c of the cathode exhaust gas 7 drives a turbine T of a turbine drive compressor 36 via a turbine supply line 19, and is supplied to an exhaust heat recovery steam generator (not shown). The air 6 compressed by the turbine drive compressor 36 joins the combustion exhaust gas 5 at the outlet of the low-temperature blower 35. The turbine-driven compressor 36 is provided with a backup line 37 having an electric blower 38, and is used for backup when the capacity of the turbine-driven compressor 36 is insufficient. The turbine supply line 19 is provided with a bypass line 40 that bypasses the turbine T, and is controlled by a rotation control valve 42 to control the flow rate during normal operation to keep the rotation speed of the turbine T constant. The rotation speed of the turbine T is measured by the tachometer 41 and input to the control unit 43, which controls the rotation control valve 42.
[0014]
The fuel cell 20 includes an anode A through which the anode gas 2 passes, and a cathode C through which the cathode gas 3 passes. The fuel cell 20 is formed from hydrogen and carbon monoxide in the anode gas 2 and oxygen and carbon dioxide in the cathode gas 3. The reaction produces electricity.
[0015]
A part 7a of the cathode exhaust gas 7 is mixed with the combustion exhaust gas 5 and the air 6 heated by the air preheater 32 to become the cathode gas 3 and supplied to the cathode C by the circulation line 14. The circulation line 14 circulates the cathode gas 3 by the high-temperature blower 23. A valve 48 is provided on the outlet side of the high-temperature blower 23, and nitrogen gas is supplied at the time of plant stop such as an emergency stop. A container supply line 17 is provided on the outlet side of the low-temperature blower 35, and gas is supplied to the storage container 22 via a differential pressure control valve 46. The differential pressure control valve 46 adjusts the supply gas so that the differential pressure between the inside of the storage container and the cathode C is within an allowable value. Note that the differential pressure control valves 44 and 46 are for low temperatures and are not expensive. Further, a container discharge line 18 is provided from the storage container 22 to the cathode C outlet side of the circulation line 14 to discharge gas in the storage container 22.
[0016]
FIG. 2 is a block diagram showing a configuration of the control unit 43 of the rotation speed control valve 42. The output function unit 50 converts the output command into an output signal, and the adder 51 adds the output signal and the rotation speed of the tachometer 41. The proportional integrator 52 performs a proportional integration on the added value and outputs a control signal. 53 is a manual / automatic switch, and 54 is a switching relay. The setter 55 inputs the turbine speed from the tachometer 41, and when a plant stop command comes, a control command for decreasing the valve opening while keeping the speed of the turbine drive compressor 36 from becoming a critical speed. Is output to the switching relay 54. The switching relay 54 transmits this signal to the rotation control valve 42 preferentially when a signal from the setter 55 comes. Reference numeral 56 denotes a pneumatic converter for converting an electric signal into an air pressure for operating the rotation speed control valve 42.
[0017]
Next, the operation of this embodiment will be described. During normal operation, the fuel cell power generator is configured so that the anode exhaust gas exhaust line 12 through which the anode exhaust gas 4 passes and the cathode exhaust gas exhaust line through which a part 7b of the cathode exhaust gas 7 passes have substantially the same pressure loss. Since they are mixed and burned in the combustion chamber Co, the differential pressure between the anode A and the cathode C is within 400 mmAq. Further, the differential pressure between the inside of the storage container and the cathode C is controlled by the differential pressure control valve 46, and thus is within 400 mmAq. At the time of an emergency stop or the like, the fuel cutoff valve 27 is closed, and the fuel blower 25, the high temperature blower 23, and the low temperature blower 35 are stopped. At the same time, the differential pressure control valve 44, which is closed during operation, is opened to release the gas while monitoring the differential pressure between the cathode exhaust gas 7 and the anode exhaust gas 4. At the same time, the valves 47 and 48 are opened and nitrogen gas is injected.
[0018]
The turbine drive compressor 36 is controlled to keep the rotation speed constant during normal operation. When stopped, the load is reduced and the number of revolutions is increased, and the high temperature blower 23 and the low temperature blower 35 rotate by inertia even when the power is cut off. Increase. Therefore, the opening of the rotation speed control valve 42 is increased to increase the flow rate flowing through the bypass line 40. However, in this case, the cathode exhaust gas 7c is rapidly discharged through the bypass line 40, and the differential pressure between the internal pressure of the containment vessel and the cathode C exceeds the allowable value of 800 to 1000 mmAq. The opening of the rotation control valve 42 is made smaller than in the constant control, and the discharge of the cathode exhaust gas 7c is made slower to reduce the differential pressure. However, when the flow rate to the bypass line 40 approaches zero, the flow rate to the turbine T increases, and the rotation speed of the turbine drive compressor 36 may become a critical speed. Bring 42 closer to closure.
[0019]
FIG. 3 shows changes in the pressure in the containment vessel, the pressure in the cathode C, the pressure in the anode A, and the differences between the pressures during an emergency stop. Vp indicates the internal pressure of the container, Cp indicates the cathode pressure, and Ap indicates the anode pressure. Cp1 indicated by a broken line indicates the case where the rotation speed of the turbine T is controlled to be constant even after an emergency stop, and the cathode pressure Cp indicated by a solid line indicates that the rotation control valve 42 is operated within a range where the rotation speed of the turbine drive compressor 36 does not reach a critical speed. Indicates a closed state. With this control, the differential pressure between the cathode C and the anode A as well as the differential pressure between the internal pressure of the storage container and the cathode C is reduced.
[0020]
FIG. 4 shows the relationship between the opening of the rotation speed control valve 42 and the rotation speed of the turbine drive compressor 36. The horizontal axis indicates the opening degree of the valve 42 in percentage, and the vertical axis indicates the rotation speed of the turbine drive compressor 36. Since the critical speed is reached at the valve opening h0 close to full closure, the valve opening h1 with a predetermined margin is set as the allowable valve opening, and the valve opening is controlled between h1 and 100%.
[0021]
【The invention's effect】
As is clear from the above description, the present invention suppresses the differential pressure between the gas in the containment vessel and the cathode to an allowable value by reducing the flow rate of the cathode exhaust gas discharged from the turbine supply line when the plant is stopped. Can be. Thus, there is no need to use an expensive high-temperature differential pressure valve conventionally used.
[Brief description of the drawings]
FIG. 1 is an overall view of a fuel cell power generator according to the present embodiment.
FIG. 2 is a block diagram illustrating a detailed configuration of a control unit.
FIG. 3 is a diagram showing the pressure in a containment vessel and the pressures of a cathode and an anode during an emergency stop of a plant.
FIG. 4 is a diagram showing a relationship between a valve opening degree of a rotation speed control valve and a critical speed of a turbine compressor.
FIG. 5 is an overall configuration diagram of a conventional fuel cell power generator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel gas 2 Anode gas 3 Cathode gas 4 Anode exhaust gas 5 Combustion exhaust gas 6 Air 7 7a, 7b, 7c Cathode exhaust gas 8 Natural gas 9 Steam 10 Reformer 11 Fuel preheater 12 Anode exhaust gas exhaust line 13 Exhaust gas supply line 14 Circulation line Reference Signs List 16 discharge line 17 container supply line 18 container discharge line 19 turbine supply line 20 fuel cell 22 containment container 23 high temperature blower 25 fuel blower 26 desulfurizer 27 fuel cutoff valve 32 air preheater 33 condenser 34 gas water separator 35 low temperature blower 36 Turbine drive compressor 37 Backup line 38 Electric blower 40 Bypass line 41 Revolution meter 42 Revolution control valve 43 Control units 44, 46 Differential pressure control valves 47, 48 Valve 50 Output function unit 51 Adder 52 Proportional integrator 53 Manual / Automatic switching device 54 Switching relay 55 Setting device 5 6 Static converter A Anode C Cathode Co Combustion chamber Re Reforming chamber

Claims (1)

A fuel cell having an anode and a cathode, generating electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, a storage container for storing the fuel cell, and burning the anode exhaust gas of the fuel cell with a part of the cathode exhaust gas. A reformer for reforming a fuel gas containing steam into anode gas by the heat, an anode exhaust gas discharge line for supplying anode exhaust gas to a combustion chamber of the reformer, and a part of cathode exhaust gas for the combustion chamber. A cathode exhaust gas discharge line to be supplied, a circulation line that circulates part of the cathode exhaust gas of the fuel cell to the cathode, an exhaust gas supply line that cools the combustion exhaust gas of the reformer and supplies it to the circulation line, and supplies compressed air to the exhaust gas A turbine supply line that supplies a part of the cathode exhaust gas to the turbine-driven compressor that supplies the line, and a discharge line that discharges exhaust gas from the exhaust gas supply line. Line and, with the containment vessel to the vessel supply for supplying a gas line, low temperature pressure difference between the storage vessel and the cathode provided in said container feed line to adjust the feed of gas to be within the allowable value Differential pressure control valve, and a container discharge line for guiding the gas in the containment vessel to the circulation line, and if the rotation speed of the turbine drive compressor is controlled to be constant during an emergency operation stop, the inside of the containment vessel Molten carbonate fuel in which the volume of gas in the containment vessel is so large that the cathode exhaust gas is released earlier than the gas and the differential pressure between the gas in the containment vessel and the cathode exhaust gas increases and exceeds the allowable value. In battery power generators,
During normal operation, the pressure loss of the anode exhaust gas discharge line and the cathode exhaust gas discharge line are configured to be substantially equal,
The discharge line is provided with a low-temperature differential pressure control valve that regulates discharge of exhaust gas so that the differential pressure between the anode exhaust gas and the cathode exhaust gas does not exceed an allowable value during an emergency operation stop,
The turbine supply line is provided with a bypass line having a rotation speed control valve for controlling the flow rate of the cathode exhaust gas to the turbine to control the rotation speed of the turbine, and the rotation speed control valve stops the fuel cell power generator. When the rotation speed of the turbine drive compressor does not reach the critical speed, the valve opening of the rotation speed control valve is made smaller than the valve opening during normal operation so that the discharge of the cathode exhaust gas from the bypass line becomes gentle. and which, characterized the molten carbonate to form a fuel cell power plant that includes a controller for controlling the.

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