JPH0337966A - Transferring method to no-load operation for fuel cell - Google Patents

Abstract

PURPOSE:To transfer to no-load operation without worrying about breaking of a combustor by controlling the flow rate of anode gas and that of cathode gas according to increase in load current. CONSTITUTION:Anode gases 7-11 and cathode gases 16-19 are supplied to a fuel cell. A part or the whole of anode exhaust gas is recycled to an anode 2 and the remainder is burned in a combustor 12 to convert it into cathode gas, then it is supplied to a cathode 3. A specified amount of load current is supplied to a load unit 4 from the fuel cell. When the fuel cell is transferred from load operation to no-load operation, load current in the load unit 4 is gradually decreased to zero so that the output temperature of the combustor 12 does not exceed a specified value, and the flow rate of anode gas and that of cathode gas are controlled according to decrease in load current. Increase in anode gas concentration in the combustor is prevented and the fuel cell is transferred to no-load operation without applying unreasonable load to the combustor.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for transitioning a molten carbonate fuel cell to no-load operation, and in particular to a method for transitioning a fuel f:4 battery having a gas recycling system from load operation to no-load operation. The present invention relates to a method of transitioning from no-load operation to operation.

[Prior art] A fuel cell is a reaction that is the reverse of water electrolysis, in which hydrogen and oxygen are chemically reacted to produce electricity and water at the same time, and an electrolyte plate is used as a fuel electrode (anode). The cells are stacked in multiple layers, sandwiched from both sides by the picture electrodes of the air electrode (cathode).

In molten carbonate fuel cells, hydrogen.

- Anode gas containing carbon oxide, etc. is supplied to the anode of the fuel cell via the anode gas supply system, and oxygen,
By supplying a cathode gas containing carbon dioxide or the like to the cathode via a cathode gas supply system, hydrogen and oxygen react via an electrolyte plate to generate electricity. At this time, the anode exhaust gas and cathode exhaust gas from the anode and cathode were simply thrown away, but since the gas consumption rate of this type of fuel cell is low at about 60 to 80%, it is necessary to use them effectively. A gas recycling system was invented. This gas recycling system recycles some or all of the anode exhaust gas to the anode, and burns (oxidizes) the remainder in a combustor such as a catalytic combustor connected to the cathode gas supply system to produce cathode gas, which is then sent to the cathode. and the cathode exhaust gas is recycled to the cathode via the catalytic combustor.

[Problems to be Solved by the Invention] By the way, the conventional method for transitioning from load operation to no-load operation of a fuel cell is to cut off the load with a load device connected to the fuel cell and stop the fuel cell from generating power. (Reaction> is stopped, but in the case of a fuel cell with a gas recycling system,
Because the anode exhaust gas from the anode enters the combustor,
In the conventional transition method, the anode gas concentration in the combustor increases, which causes abnormal combustion in the combustor and increases the combustor outlet temperature (in the worst case, an explosion occurs in the combustor). Therefore, an excessive load is applied to the combustor, and there is a risk that the combustor may be damaged.

Therefore, the present invention has been made to solve the above problems, and when a fuel cell with gas recycling is transferred from load operation to no-load operation, the present invention has been made to solve the above problem. The purpose is to provide a load operation transition method.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a fuel cell connected to supply power to a load device, and a supply system that supplies hair node gas and cathode gas of the fuel cell, respectively. , an anode gas recycling system that recycles part or all of the anode exhaust gas to the anode and supplies the remainder to a combustor connected to a cathode gas supply system where it is combusted as cathode gas, When transitioning from load operation to no-load operation, the load current of the load device is gradually lowered to zero so that the outlet temperature of the combustor does not exceed a predetermined value, and the anode gas is reduced in accordance with the decrease in the load current. The gas flow rates from the and cathode gas supply systems are controlled respectively.

[Operation] By supplying the fuel cell hair node gas and cathode gas respectively, recycling part or all of the anode exhaust gas to the anode, and burning the remainder in a combustor to make cathode gas, the fuel is supplied to the cathode. A predetermined load current flows from the battery to the load device. At this time, in order to shift the fuel cell from load operation to no-load operation, the load current of the load device is gradually lowered to zero so that the combustor outlet temperature does not exceed a predetermined value, and the load current is By controlling the flow rates of anode gas and cathode gas accordingly, the concentration of anode gas in the combustor is prevented from increasing, allowing the fuel cell to operate without load without placing an unreasonable load on the combustor. You can move to

[Example] A preferred embodiment of the present invention will be described based on the accompanying drawings.

First, a power generation system using a molten carbonate fuel cell employed to carry out the method of the present invention will be described.

In FIG. 1, reference numeral 1 denotes a fuel cell. Since this fuel cell has the same structure as the conventional example, the explanation will be omitted, and in this example, it is shown as an anode 2 and a cathode 3.

A load device 4 is connected to the anode 2 of the fuel cell 1, and when the fuel cell 1 generates power, a predetermined load current flows through the load device 4, and this load current value becomes zero! It is configured to be input to the L board 5.

An anode gas supply system 6 is connected to the anode 2, and this anode gas supply system 6 contains hydrogen (H2).

-Carbon oxide (Co), nitrogen (N2), carbon dioxide (CO
2), Supply system that supplies steam (H2O) 7゜8.9,1
0.11, these supply systems 78.9, 10.11
Hydrogen, carbon oxide, nitrogen, carbon dioxide, and steam are mixed in an anode gas supply system 6 and supplied to the anode 2 as anode gas.

A cathode gas supply system 13 having a combustor 12 such as a catalytic combustor is connected to the cathode 3, and a cathode exhaust gas exhaust system 15 having a cathode exhaust gas control valve 14 is connected to the cathode 3.
is connected. The cathode gas supply system 13 includes carbon dioxide (CO2), oxygen (02), air, and steam (H20).
and carbon dioxide from these feed systems 16.17.18.19.

Oxygen, air, and steam are mixed in the cathode gas supply system 13 and supplied to the cathode 3 as cathode gas. Further, the cathode gas supply system 13 is provided with a thermometer 20 for measuring the outlet temperature of the combustor 12, and the measured value of the thermometer 20 is inputted to the control panel 5.

In addition, each supply system 7 supplies the above-mentioned hydrogen, carbon oxide, nitrogen, carbon dioxide, and steam to the anode gas supply system 6.
, 8.9, 10.11 and the respective supply systems 16.17° and 18.19 that supply carbon dioxide, oxygen, air, and steam to the cathode gas supply system 13 are equipped with flowmeters FAI for measuring the flow rates. , FA2. FA3. FA4. F.A.
5゜PCI, Fe2. Fe2. Control valves VAI, VA2. for controlling Fe2 and supply gas flow rates M. VA3゜VA4
．． VA5. VCI, VO2, VO2° VO2 are interposed, and each flow meter FAI, FA2° FA3. FA4. FA5.
FCl, Fe2°Fe2. The measured value of Fe2 is input to the control panel 5, and each control valve VAI, VA2 . VA3゜VA4. VA5. VCI, VO2, VO2゜VO2 are each operated by the utilization rate control of the control panel 5, and the gas supply amount of each supply system 7, 8, 9, 10.11゜16.17.18.19 is controlled. It has become so.

Furthermore, the fuel cell 1 is equipped with a gas recycling system 21 for effectively utilizing gas.

This gas recycle system 21 consists of an anode gas recycle system 22 and a cathode gas recycle system 23. The anode gas recycle system 22 includes a first anode gas recycle system 27 connected to the anode gas supply system 6 via an anode exhaust gas control valve 24, an anode exhaust gas recycle blower 25, and a recycle control valve 26 in this order.
and a second anode recycle branched from the first anode recycle system 27 between the anode exhaust gas recycle blower 25 and the recycle control valve 26 and connected to the combustor 12 of the cathode supply system 13 via the cathode supply control valve 28. It consists of system 29.

On the other hand, the cathode gas recycle system 23 is branched from the cathode exhaust gas discharge system 15 and connected to the combustor 12 via a cathode exhaust gas recycle blower 30 and a recycle control valve 31 in this order. Note that the above-mentioned control valve is operated by a control panel.

Next, a method for transitioning to no-load operation of a fuel cell according to the present invention will be explained based on the power generation system using the molten carbonate fuel cell.

Hydrogen, carbon oxide, nitrogen, carbon dioxide, and steam are supplied to the anode gas supply system 6 via respective supply systems 7, 8.9, 10.11, mixed, and supplied to the anode 2 as anode gas. . Part or all of the anode exhaust gas from the anode 2 is recycled to the anode 2 via the anode gas recycling system 22, and the remainder is supplied to the catalytic combustor 12 where it is combusted (oxidized) to become cathode gas.

In addition, carbon dioxide, oxygen, air, and steam are supplied to the cathode gas supply system 13 via respective supply systems 16, 17, 18, 19, mixed, and supplied as cathode gas to the cathode 3 via the catalytic combustor 12. Supplied. A part of the cathode exhaust gas from the cathode 3 is supplied to the catalyst and combustor 12 via the cathode gas recycling system 23, and then recycled to the cathode 3, where hydrogen and oxygen react to generate electricity, and the load device A predetermined load current flows through 4.

During power generation, when the load on the battery 1 must be cut off to protect the fuel cell 1, such as when power generation is stopped or when an abnormality occurs in the process value of the fuel cell 1, the load operation changes from load operation to no-load operation. To migrate, as shown in Figure 2,
The load is gradually lowered to zero, and the flow rates of the anode gas and cathode gas are controlled in accordance with the decrease in load, as shown in FIGS. 3 and 4. This reduction in load and control of the flow rates of the anode gas and cathode gas are stored in the control panel 5, so that the current value input to the control panel 5 is converted into the supply gas flow rate using a conversion formula.

As shown in FIG. 5, the no-load operation transition operation is performed by firstly
8.19 each regulating valve VAI.

VA2. VA3. VA4. VA5. VCI.

Switch VO2, VO2, VO2 to utilization rate m.

Next, the load setting current value (2) of the load device 4 is gradually set to a smaller value in steps, and this set value is input into the control panel 5.

The current value input to the control panel 5 is converted into each supply gas flow rate by each conversion formula (shown below) built into the control panel 5 in advance.

Anode gas: Setting H2 flow rate = 'IXC ÷ Setting fuel utilization rate / 100 x Setting H2 composition ÷ Setting (N20 CO) Composition setting CO flow rate = IXC ÷ Setting fuel utilization rate / 100 x Setting Co composition ÷ Setting (N2 + CO) Composition setting N2 flow rate = + x C ÷ setting fuel utilization rate / 100 x
Setting N2 composition ÷ Setting (Hz + co) Composition setting C02 flow rate = IxC ÷ Setting fuel utilization rate / 100 × Setting CO2 Composition ÷ Setting (N2 + CO) Composition setting N20 flow rate = IXC ÷ Setting fuel utilization rate / 100 × Setting H20 ÷ Setting ( N2 + CO) composition cathode gas: Set CO2 flow rate = l/2 1XC ÷ Set oxygen utilization rate/
100 x setting CO2 composition ÷ setting (0 2 + air x 21/100) composition setting 0
2 flow rate = 1/2 1XC ÷ set oxygen utilization rate/100×
Setting 02 composition ÷ setting (0 □ 10 air x 21/100) composition setting air flow rate = [1/2 K2 x C ÷ setting oxygen utilization rate / 100 + 1/2 setting (N2 + CO) amount x (1 - fuel utilization rate) co x setting Air composition ÷ setting (02 + air x 21/100) composition setting N20
Flow rate = 1/2 1 C knee setting oxygen utilization rate/100X
Setting H20 composition ÷ setting (0 □ 10 air x 21/100) Jfl formation However,
To the current value set to: Set value converted from the amount of gas required for N2 purge
I≦1 to 2: Setting value converted from the amount of gas required for air purge
I≦2 C: 22.4x number of cells ÷ 53604 The above conversion formula converts the current I=2XFxx (c/s) generated from the supply amount of hydrogen x IIo Jl/s from /h), and the Faraday constant is F=
9.6485309 x10' (c/rgoj
) and obtained from X=22.4xT÷53603.

When the load setting current value is converted to each supply gas flow rate using each conversion formula, the control panel 5 converts each control valve VAI, VA2.
, VA3, VA4, VA5.

VCI, VO2, VO2, and VO2 are operated to reduce the amount of anode gas and cathode gas supplied to the fuel cell 1 according to the composition ratio. However, the anode gas nitrogen and the cathode gas air are flowed at the purge flow rate, that is,
When the set current value ■ satisfies I≦+, the nitrogen supply system 9
The control valve VA3 is held, N2 flows to the anode 2 as much as the N2 purge flow, and the set current value ■ becomes ■≦
2 is satisfied, the control valve VO2 of the air supply system 18 is held, and air flows to the cathode 3 at the air purge flow rate. All of these series of operations are automatically performed by the computer in the adjustment panel 5.

If the outlet temperature of the catalytic combustor 12 is below the set temperature as measured by the thermometer 20, the load set current value is arbitrarily lowered and the above operation is repeated to reduce the set current value to zero and shift to no-load operation. let

In this way, by controlling the flow rates of the anode gas and cathode gas according to the decrease in the load setting current value, the required amount of hydrogen and carbon oxide fuel gas in the anode gas is proportional to the load current value. , the utilization rate of the fuel gas at the anode 2 hardly changes. Therefore, the anode exhaust gas from the anode 2 enters the catalytic combustor 12 via the second anode recycling system 29, and the catalytic combustor 12 Since the fuel gas concentration with respect to the cathode gas in catalytic combustor 1 is almost the same ratio as in the load operation state,
Abnormal combustion at step 2 hardly occurs, and no unreasonable load is placed on the catalytic combustor 12. In addition, by controlling the anode gas and cathode gas flow rates, the cathode gas flow rate will also decrease as the anode gas flow rate decreases, so the differential pressure between the anode 2 and cathode 3 will hardly increase. , there is no need to worry about damaging the fuel cell 1 due to the pressure difference. Furthermore, each control valve VAI when the load current value is instantaneously reduced to zero by gradually lowering the load current value to zero.

VA2. VA3. VA4. VA5. VCI.

This prevents variations in the amount of each gas supplied due to a delay in the response of VO2, VO2, and VO2.

Therefore, the fuel cell 1 with the gas recycling system 21
When transitioning from load operation to no-load operation, the load current of the load device 4 is gradually lowered to zero so that the outlet temperature of the combustor 12 does not exceed a predetermined value, and the anode By controlling the supply amount of gas and cathode gas, it is possible to avoid an increase in the anode gas concentration in the combustor 12, without worrying about damage to the combustor 2, and to reduce the differential pressure between the anode 2 and cathode 3. It is possible to shift to no-load operation without increasing the amount.

Note that automatic operation or manual operation may be used to shift from load operation to no-load operation. In the case of manual operation, the anode gas and cathode gas flow rates are controlled at the same time.
If the load current value is lowered so as not to exceed the response range of each control valve, the combustor outlet temperature will almost never exceed the set temperature, so the range of decrease in the load set IC flow value can be set to an excessive value.

Further, when the outlet temperature of the catalytic combustor 12 exceeds the set temperature, an interlock is applied to hold the load device 4 and, after a certain period of time, to each regulating valve VA1. VA2. V
A3. VA4. VA5゜VCl, VO2, VO2, V
The opening degree of O2 is held to ensure the safety of the fuel cell 1.

If the catalytic combustor 12 is not operating after the interlock, the load device 4 cuts off the load. At this time, the supply gas flow rate is held at the current composition flow rate, and after the hold, the operation is restarted or the system is shifted to a purge state according to the operator's judgment. On the other hand, when the catalytic combustor 12 is operating, the load is cut off by the load device 4, and at the same time each regulating valve VA1. V.A.
2゜VA3. VA4. VA5. VCI, VO2゜VO
2. Switch VO2 to utilization rate control and control the supply gas flow rate, that is, set the load setting current value to zero and shift to the purge state.

In addition, in this embodiment, when transitioning to no-load operation, the case where the supply amount of anode gas is reduced according to the composition ratio has been described. The operation may be shifted to no-load operation by supplementing with steam and keeping the total flow rate of the anode gas constant.

In this case, if the battery load reduction rate is set slowly, the rate of change in the gas supply flow rate that follows it will also be gradual, so the differential pressure between the anode and cathode will not increase.
Can shift to no-load operation.

[Effects of the Invention] In summary, according to the present invention, in order to shift a fuel cell having a gas recycling system from load operation to no-load operation,
Since the load current of the load device is gradually lowered to zero and the flow rates of the 7-node gas and cathode gas are controlled, an excellent effect is achieved in that the transition can be made without worrying about damage to the combustor.

[Brief explanation of drawings]

FIG. 1 is an elliptical diagram for explaining one embodiment of the method for transitioning to no-load operation of a fuel cell according to the present invention, FIG. 2 is a diagram showing the load on a load device according to the method according to the present invention, and FIG. FIG. 4 is a diagram showing the anode gas flow rate according to the method of the present invention, FIG. 4 is a diagram showing the cathode gas flow rate according to the method of the present invention, and FIG. 5 is a flowchart showing the no-load operation transition method of the present invention. In the figure, 1 is a fuel cell, 4 is a load device, 6 is an anode gas supply system, 12 is a combustor, 13 is a cathode gas supply system, 2
2 is an anode gas recycling system.

Claims (1)

[Claims] 1. A fuel cell connected to supply power to a load device, a supply system that supplies anode gas and cathode gas to the fuel cell, and a supply system that recycles some or all of the anode exhaust gas to the anode and supplies the remainder as cathode gas. and an anode gas recycling system that supplies the gas to a combustor connected to the system and burns it there to produce cathode gas.
When shifting the fuel cell from load operation to no-load operation, the load current of the load device is gradually lowered to zero so that the outlet temperature of the combustor does not exceed a predetermined value, and as the load current decreases, A method for transitioning to no-load operation of a fuel cell, characterized in that the flow rates of gases from the anode gas and cathode gas supply systems are controlled respectively.