JP5701233B2 - Operation method of solid oxide fuel cell, operation method of combined power generation system, solid oxide fuel cell system, and combined power generation system - Google Patents

Description

  The present invention relates to a method for operating a solid oxide fuel cell, a solid oxide fuel cell system, a method for operating a combined power generation system including the solid oxide fuel cell, and a combined power generation system.

  A cylindrical solid oxide fuel cell is known as an example of the solid oxide fuel cell. In a cylindrical solid oxide fuel cell, a plurality of cylindrical cell stacks are electrically connected in parallel and accommodated in the fuel cell. In each cell stack, for example, a plurality of cells in which a fuel electrode, a solid electrolyte membrane, and an air electrode are stacked are formed on a porous substrate tube made of calcium-stabilized zirconia (CSZ), and adjacent cells are connected to each other. Connected with a connector.

In the cell, the fuel electrode is generally a mixture of Ni and yttria stabilized zirconia (YSZ). The air electrode is an oxide having conductivity, and for example, a LaMnO ₃ based material, a LaFeO ₃ based material, a LaCoO ₃ based material or the like is used.

The solid oxide fuel cell is operated at around 900 ° C. During operation of the solid oxide fuel cell, since fuel gas (H ₂ gas, CH ₄ gas, etc.) is flowing through the fuel electrode, Ni in the fuel electrode is maintained in a reduced state. However, when the fuel cell is stopped, such as during an emergency stop, the supply of fuel gas is interrupted. In this case, when an oxidizing gas (such as air) containing oxygen is circulated on the air electrode side, the oxidizing gas reaches the fuel electrode without being consumed by the solid electrolyte membrane. In a high temperature state close to the operating temperature, Ni reacts with oxygen to produce NiO, but this reaction is accompanied by a large volume change. For this reason, a large stress is generated in the fuel electrode, which leads to breakage of the base tube.

  In this case, if the solid oxide fuel cell is cooled to a low temperature (for example, 150 ° C. or less) at which the oxidation rate of Ni is low, it is possible to prevent NiO generation and damage to the base tube. However, when the fuel cell is restarted, it is necessary to reheat the cell stack to the operating temperature, resulting in a large energy loss and an increase in startup time.

  On the other hand, Patent Document 1 discloses that when the solid oxide fuel cell is stopped at a high temperature near the operating temperature, the supply of the fuel gas and the oxidizing gas is stopped and the fuel electrode side is purged with an inert gas. Disclosure.

JP 2006-100153 A (Claim 1, paragraph [0031])

  In the method described in Patent Document 1, since the supply of the oxidizing gas on the air electrode side is stopped, the fuel gas remaining on the fuel electrode side at the beginning of the inert gas purge diffuses to the air electrode side. The air electrode material is reduced by the fuel gas. At this time, a large volume change occurred in the air electrode, and the air electrode might be damaged. Further, the reduced cathode material does not return to the original material even if it is exposed to an oxygen atmosphere during re-operation. For this reason, the conductivity of the air electrode is lost, and the power generation performance of the solid oxide fuel cell deteriorates.

  An object of the present invention is to provide a solid oxide fuel cell operating method and a solid oxide fuel cell system capable of preventing the cell stack from being damaged even during a normal stop or an emergency stop. Another object of the present invention is to provide a method for operating a combined power generation system including the solid oxide fuel cell and a combined power generation system.

  The present invention includes one or a plurality of cell stacks having a plurality of cells, the fuel gas is supplied to the fuel electrode side of the cell stack, and the oxidizing gas containing oxygen is supplied to the air electrode side of the cell stack. An operation method of a solid oxide fuel cell that generates electricity by reacting the fuel gas and the oxidizing gas at a high temperature in the electrolyte membrane of the cell, and stops the supply of the fuel gas at a high temperature A first inert gas purge step of supplying an inert gas to the fuel electrode side at a predetermined flow rate and continuing to supply the oxidizing gas to the air electrode; and the fuel electrode in the cell; When the voltage between the air electrode reaches a predetermined voltage, the supply of the oxidizing gas is stopped in a high temperature state, and the inert gas is supplied to the air electrode side at a predetermined flow rate, so that the solid Stop operation of oxide fuel cell Providing a second method of operating a solid oxide fuel cell comprising an inert gas purge step of.

  The present invention includes a solid oxide fuel cell including one or a plurality of cell stacks having a plurality of cells, a fuel gas supply unit that supplies fuel gas to a fuel electrode side of the cell stack, and the cell stack. An oxidizing gas feeding unit that feeds an oxidizing gas containing oxygen to the air electrode side of the fuel cell; an inert gas feeding unit that feeds an inert gas to the fuel electrode side of the cell stack; and the cell stack An air electrode side inert gas supply unit that supplies an inert gas to the air electrode side of the air electrode, and stops the supply of the fuel gas to the fuel electrode side and sends the inert gas to the fuel electrode side. When the voltage between the fuel electrode and the air electrode in the cell reaches a predetermined voltage, the supply of the oxidizing gas to the air electrode side is stopped at a high temperature and the air electrode side is stopped. A solid acid comprising a control unit for feeding the inert gas Providing an object type fuel cell system.

  Thus, in the present invention, in the normal stop and the emergency stop of the solid oxide fuel cell, first, the fuel electrode side is purged with the inert gas, and the supply of the oxidizing gas is continued on the air electrode side. This prevents the fuel gas remaining on the fuel electrode side from diffusing and reaching the air electrode, thereby preventing the air electrode from being reduced. Then, after the cell voltage between the fuel electrode and the air electrode reaches a predetermined voltage, the air electrode side is purged with an inert gas. By doing so, the fuel electrode is prevented from being oxidized by the oxidizing gas (oxygen) diffused from the air electrode side. Therefore, according to the present invention, damage to the cell stack due to reductive expansion of the air electrode or oxidative expansion of the fuel electrode can be avoided in the shutdown process of the solid oxide fuel cell system. In addition, when the fuel electrode side is purged with an inert gas, the supply of the oxidizing gas is continued on the air electrode side, so that the fuel cell can be cooled by supplying the oxidizing gas. The time required for stopping the fuel cell is shortened.

  In the above operation method, the method further includes a voltage measuring step of measuring the voltage while supplying an inert gas to the fuel electrode side and supplying the oxidizing gas to the air electrode side, the second inert gas In the gas purge step, when the measured voltage becomes constant, it is preferable that the supply of the oxidizing gas is stopped at a high temperature and the inert gas is supplied to the air electrode side.

  In the solid oxide fuel cell system, it is preferable that a voltmeter for measuring the voltage is installed in the solid oxide fuel cell.

  Thus, if the cell voltage is monitored while the fuel electrode side is purged with the inert gas, and the air electrode side is purged with the inert gas when the cell voltage reaches a predetermined value, the cell stack is damaged. It can be avoided reliably.

  In the above operation method, a cell temperature measuring step for measuring the temperature of the cell, an oxidation-reduction equilibrium potential of the material of the fuel electrode at the measured temperature is calculated, and an oxidation with the oxidation-reduction equilibrium potential as the predetermined voltage is calculated. It is preferable to further include a reduction equilibrium potential calculation step.

  In the solid oxide fuel cell system, a thermometer for measuring the temperature of the cell is installed in the solid oxide fuel cell, and the controller is configured to control the fuel electrode at a temperature measured by the thermometer. It is preferable to calculate the redox equilibrium potential of the material and set the redox equilibrium potential to the predetermined voltage.

  In this way, the cell temperature is measured while the fuel electrode side is purged with the inert gas, and the cell while the fuel electrode side is purged with the inert gas based on the redox equilibrium potential calculated from the cell temperature. By monitoring this voltage, damage to the cell stack can be reliably avoided.

  In the above operation method, a correlation between the inert gas supply time and the voltage when the inert gas at the predetermined flow rate is supplied to the fuel electrode side is acquired in advance, and the predetermined flow rate is obtained based on the correlation. A purge time determining step for obtaining the feed time at which the predetermined voltage is reached, and in the second inert gas purge step, when the feed time set by the purge time determining step is reached, the temperature is high. The supply of the oxidizing gas may be stopped in a state, and the inert gas may be supplied to the air electrode side.

  In the solid oxide fuel cell system, a correlation between the supply time of the inert gas and the voltage when the inert gas having the predetermined flow rate is supplied to the fuel electrode is stored in the control unit in advance. The control unit may determine when to stop the supply of the oxidizing gas and start the supply of the inert gas to the air electrode based on the correlation.

  As described above, if the correlation between the inert gas supply time and the cell voltage is acquired in advance, it is not necessary to monitor the voltage and temperature in the stopping process. For this reason, the process of stopping the above-mentioned solid oxide fuel cell system is further simplified.

  The present invention relates to a combined power generation in which a solid oxide fuel cell including one or a plurality of cell stacks including a plurality of cells and a gas turbine power generation facility including a combustor, a compressor, a turbine, and a generator are connected. A method of operating a system, wherein when the solid oxide fuel cell and the gas turbine power generation facility are in operation, fuel gas is supplied from the first fuel gas source to the fuel cell in a high temperature state. A first inert gas purge step of stopping and supplying an inert gas to the fuel electrode side of the cell at a predetermined flow rate and continuing to supply the oxidizing gas from the compressor to the air electrode side of the cell And when the voltage between the fuel electrode and the air electrode in the cell reaches a predetermined voltage, the supply of the oxidizing gas to the fuel cell is stopped in a high temperature state and the air electrode is not connected to the air electrode. Active gas And feeding at a predetermined flow rate, to provide a method for operating a combined cycle power generation system comprising a second inert gas purge process of stopping the operation of the solid oxide fuel cell.

  The present invention relates to a solid oxide fuel cell including one or a plurality of cell stacks having a plurality of cells, a turbine, a generator connected to the turbine, and a combustor for supplying combustion gas to the turbine. A gas turbine power generation facility including a compressor capable of supplying an oxidizing gas to the combustor and an air electrode of the cell stack, and a first fuel for supplying a fuel gas to the fuel electrode side of the cell stack A gas supply unit, a second fuel gas supply unit for supplying fuel gas to the combustor, a fuel electrode side inert gas supply unit for supplying inert gas to the fuel electrode side, and An air electrode side inert gas supply unit for supplying an inert gas to the air electrode side, and a control unit, so that the oxidizing gas discharged from the air electrode is supplied to the combustor, The air electrode and the combustor are connected and discharged from the fuel electrode. In addition, the fuel electrode and the combustor are connected so that the fuel gas is supplied to the combustor, and the control unit is configured to operate the solid oxide fuel cell and the gas turbine power generation facility. The fuel gas is supplied from the first fuel gas supply unit to the fuel electrode, and the fuel gas discharged from the fuel electrode is supplied to the combustor and is oxidized from the compressor to the air electrode. The gas is supplied and the oxidizing gas discharged from the air electrode is supplied to the combustor. When the solid oxide fuel cell is stopped, the fuel electrode is supplied from the first fuel gas supply unit. The fuel gas to the fuel electrode side, the inert gas is supplied from the fuel electrode side inert gas supply unit to the fuel electrode side, and the fuel electrode and the air electrode in the cell When the voltage between them reaches the specified voltage The combined power generation for stopping the supply of the oxidizing gas from the compressor to the air electrode in a high temperature state and for supplying the inert gas from the air electrode side inert gas supply unit to the air electrode side Provide a system.

  In a combined power generation system combining a solid oxide fuel cell and a gas turbine power generation facility, if the solid oxide fuel cell is normally stopped or urgently stopped in the above-described steps, the air electrode is reduced or expanded or the fuel electrode is oxidized. Damage to the cell stack due to expansion can be avoided. In addition, the fuel cell can be cooled by supplying the oxidizing gas, and the time taken to stop the solid oxide fuel cell can be shortened.

  In the operation method of the combined power generation system, in the first inert gas purge step, supply of fuel gas from the second fuel gas source to the combustor is started, and in the second inert gas purge step, It is preferable to supply the oxidizing gas directly from the compressor to the combustor to continue the operation of the gas turbine power generation facility.

  In the combined power generation system, when the control unit stops the supply of the fuel gas from the first fuel gas supply unit to the fuel electrode, the control unit outputs the second fuel gas supply unit from the second fuel gas supply unit. Preferably, fuel gas is supplied to the combustor, and when the supply of the oxidizing gas from the compressor to the air electrode is stopped, the oxidizing gas is preferably supplied from the compressor to the combustor. .

  When shifting to the step of stopping the solid oxide fuel cell in this way, if the fuel gas and the oxidizing gas are fed directly to the combustor of the gas turbine power generation facility and the operation of the gas turbine power generation facility is continued, A stable power supply can be implemented.

  According to the present invention, the solid oxide fuel cell system can be cooled in a short time while preventing damage to the cell stack without causing oxidation or reduction in a high temperature state during a normal stop or an emergency stop. Can be stopped.

1 is a schematic view of a solid oxide fuel cell system. It is a flowchart explaining the driving | running method which concerns on 1st Embodiment. Feeds send a N ₂ gas to the fuel electrode side is a graph showing changes with time of the average cell voltage in the case of stopping the solid oxide fuel cell system while feeding air to the air electrode side. It is a flowchart explaining the driving | running method which concerns on 2nd Embodiment. Is a graph showing an example of a change with time of the cell voltage when changing the flow rate of N ₂ gas fed to the fuel electrode. It is a flowchart explaining the driving | running method which concerns on 3rd Embodiment. 1 is a schematic diagram of a combined power generation system.

<First Embodiment>
The solid oxide fuel cell system according to the first embodiment will be described below.
FIG. 1 is a schematic view of a solid oxide fuel cell system according to the present embodiment. A cylindrical solid oxide fuel cell 12 is applied to the solid oxide fuel cell system 1 of the present embodiment. One or a plurality of cylindrical cell stacks are housed inside the solid oxide fuel cell 12. When a plurality of cell stacks are stored, the cell stacks are electrically connected in parallel.

A plurality of cells are formed on the cell stack, and one cell is configured by laminating a fuel electrode, a solid oxide film, and an air electrode from the base tube side. Alternatively, one cell is configured by laminating an air electrode, a solid oxide film, and a fuel electrode from the base tube side. In the following description, a cell stack in which a fuel electrode, a solid oxide film, and an air electrode are purely stacked on a base tube is used.
Adjacent cells are connected by an interconnector. In the present embodiment, the anode of the solid oxide fuel cell 12 contains Ni, for example, a mixture of Ni and YSZ. The solid electrolyte membrane is generally YSZ. The air electrode of the solid oxide fuel cell 12 is an oxide such as a LaMnO ₃ -based material, a LaFeO ₃ -based material, or a LaCoO ₃ -based material. The interconnector is made of a perovskite oxide such as SrTiO ₃ or a LaCrO ₃ based material.

  In the solid oxide fuel cell 1, the fuel gas supply unit 2 communicates with the inlet of the supply fan 4. The outlet of the feed fan 4 communicates with one of the inlets of the heat exchanger 11.

The fuel gas supply unit 2 includes a fuel gas source 2a, a flow rate adjusting valve 2b, and a flow rate detector 2c. The fuel gas source 2a contains H ₂ gas or CH ₄ gas as fuel gas.

In FIG. 1, the fuel electrode side inert gas supply unit 3 communicates between the supply outlet of the supply fan 4 and one of the reception inlets of the heat exchanger 11. Alternatively, the fuel electrode side inert gas supply unit 3 may be in communication with the receiving port of the supply fan 4. The fuel electrode side inert gas supply unit 3 includes a first inert gas source 3a, a flow rate adjusting valve 3b, and a flow rate detector 3c. The first inert gas source 3a contains an inert gas. The inert gas used here is a rare gas such as N ₂ gas or He gas, or combustion exhaust gas. The oxygen concentration in the inert gas is set to several hundred ppm or less, and the smaller the better. In view of operating costs, it is particularly preferable to use N ₂ gas as the inert gas.

  One outlet of the heat exchanger 11 communicates with the fuel gas supply chamber of the solid oxide fuel cell 12. The fuel gas supply chamber is connected to one end of a cell stack housed in the solid oxide fuel cell 12. Therefore, the fuel gas or the inert gas discharged from one of the outlets of the heat exchanger 11 is fed into the base tube from one end of the base tube of the cell stack.

  The other end of the cell stack of the solid oxide fuel cell 12 is connected to the fuel gas discharge chamber. The fuel gas discharge chamber of the solid oxide fuel cell 12 communicates with the inlet of the feed fan 4 and also with one of the inlets of the combustor 13.

  The discharge port of the combustor 13 communicates with one receiving port of the heat exchanger 14. One outlet of the heat exchanger 14 communicates with the exhaust gas inlet of the exhaust gas boiler 15. The exhaust gas outlet of the exhaust gas boiler 15 communicates with the chimney 16.

  The oxidizing gas supply unit 5 includes an air filter 5a, a flow rate adjusting valve 5b, and a flow rate detector 5c. The oxidizing gas supply unit 5 communicates with the receiving port of the supply fan 7. The outlet of the feeding fan 7 communicates with the other inlet of the heat exchanger 14. The air filter 5a takes in air from the external environment as an oxidizing gas.

In FIG. 1, the air electrode side inert gas supply unit 6 communicates between the supply port of the supply fan 7 and the other reception port of the heat exchanger 14. Alternatively, the air electrode side inert gas feeding unit 6 may be in communication with the receiving port of the feeding fan 7. The air electrode side inert gas supply unit 6 includes a second inert gas source 6a, a flow rate adjusting valve 6b, and a flow rate detector 6c. The second inert gas source 6a contains an inert gas. The inert gas used here is a rare gas such as N ₂ gas or He gas, or combustion exhaust gas. The oxygen concentration in the inert gas is set to several hundred ppm or less, and the smaller the better. In view of operating costs, it is particularly preferable to use N ₂ gas as the inert gas.

  The other outlet of the heat exchanger 14 communicates with the other inlet of the heat exchanger 11. The other outlet of the heat exchanger 11 communicates with the oxidizing gas supply chamber of the solid oxide fuel cell 12. The oxidizing gas or the inert gas discharged from the other outlet of the heat exchanger 11 is supplied around the cell stack.

  The oxidizing gas discharge chamber of the solid oxide fuel cell 12 communicates with the other inlet of the combustor 13.

  The flow rate adjustment valve 2b of the fuel gas supply unit 2, the flow rate adjustment valve 5b of the oxidizing gas supply unit 5, the flow rate adjustment valve 3b of the fuel electrode side inert gas supply unit 3, and the air electrode side inert gas supply The flow rate adjustment valve 6 b of the unit 6 is connected to the output unit of the control unit 20. The feeding fans 4 and 7 are connected to the output unit of the control unit 20.

  The flow rate detector 2c of the fuel gas feed unit 2, the flow rate detector 5c of the oxidizing gas feed unit 5, the flow rate detector 3c of the fuel electrode side inert gas feed unit 3, and the air electrode side inert gas feed The flow rate detector 6 c of the unit 6 is connected to the input unit of the control unit 20.

  In preparation for a case where power is lost due to an emergency stop of the solid oxide fuel cell 12, the control unit 20 is connected to an emergency power source (not shown).

  In this embodiment, the solid oxide fuel cell 12 is provided with a voltmeter 21 that measures the cell voltage. In the present embodiment, the voltmeter 21 is connected to the cell air electrode part or both ends (current collection part) of the cell stack, and measures the potential difference between the fuel electrode and the air electrode for one cell stack. That is, the voltmeter 21 measures the potential difference between the fuel electrode and the air electrode of a plurality of cells connected in series. When the solid oxide fuel cell 12 has a plurality of cell stacks, the potentials of all the cell stacks may be measured, or the potentials of arbitrary cell stacks may be measured. Moreover, you may measure the voltage of the specific cell of a cell stack by connecting to the arbitrary cell air electrode parts of a cell stack. The voltmeter 21 is connected to the input unit of the control unit 20. The voltmeter 21 is connected to an emergency power source (not shown) in case power is lost due to an emergency stop of the solid oxide fuel cell 12.

  An operation method of the solid oxide fuel cell system 1 according to the first embodiment will be described below. FIG. 2 is a flowchart of the operation method of the first embodiment.

  First, the operating state of the solid oxide fuel cell will be described. The control unit 20 operates the feed fans 4 and 7. The control unit 20 adjusts the flow rate adjusting valve 2b based on the signal from the flow rate detector 2c, and supplies the fuel gas from the fuel gas source 2a at a predetermined flow rate. The control unit 20 adjusts the flow rate adjustment valve 5b based on the signal from the flow rate detector 5c, and supplies the air taken in by the air filter 5a as the oxidizing gas at a predetermined flow rate. The fuel gas supplied to the heat exchanger 11 by the supply fan 4 is heated to about 900 ° C. to 1000 ° C. in the heat exchanger 11. The air supplied to the heat exchanger 14 by the supply fan 7 is heated to about 900 ° C. to 1000 ° C. in the heat exchanger 14.

  The heated fuel gas and air are supplied to the fuel gas supply unit and the oxidizing gas supply unit of the solid oxide fuel cell 12, respectively. The fuel gas is supplied from the fuel gas supply unit to the inside of the base tube of the cell stack and flows through the base tube toward the fuel gas discharge unit. At this time, part of the fuel gas diffuses from the inside of the base tube toward the outside. The air is supplied from the oxidizing gas supply unit to the periphery of the cell stack and is discharged from the oxidizing gas discharge unit. At this time, part of the air diffuses from the air electrode side toward the base tube. In each solid electrolyte membrane of the cell, the fuel gas and oxygen in the air react to generate electricity.

  A part of the unreacted fuel gas discharged from the fuel gas discharge unit is supplied to one receiving port of the heat exchanger 11 and supplied to the solid oxide fuel cell 12 again. The remainder of the fuel gas is fed to the combustor 13 together with the air discharged from the oxidizing gas discharge section and burned. The exhaust gas after combustion is supplied to the heat exchanger 14, used as a heat source for heating air, and then discharged to the external environment via the chimney 16. The air heated by the heat from the exhaust gas is used as a heat source for heating the fuel gas in the heat exchanger 11.

  A system abnormality is detected in the solid oxide fuel cell system 1 in the above operating state (S1). The control unit 20 suddenly changes any of the value of the flow rate detector 2c, the value of the flow rate detector 5c, the value of the voltmeter 21 and the value of the thermometer that measures the cell temperature. If it is determined that a system error has occurred. A threshold value for determining system abnormality is set as appropriate. For example, when the above numerical value changes by more than ± 5% from the set value, the control unit 20 determines that the system is abnormal. As a result, the solid oxide fuel cell system 1 shifts to a stopped state (a state where the current load is interrupted by the control unit 20 and the electrochemical reaction via the electrolyte membrane is stopped).

  When the control unit 20 detects a system abnormality and the current load of the solid oxide fuel cell 12 is interrupted and shifts to the stop state, the control unit 20 outputs a signal from the flow rate detector 2c of the fuel gas supply unit 2. Based on this, the flow rate adjusting valve 3b is adjusted, and the supply of the fuel gas from the fuel gas source 2a is stopped (S2).

Next, the control unit 20 adjusts the flow rate adjustment valve 3b based on the signal from the flow rate detector 3c, and feeds an inert gas (N ₂ gas) from the first inert gas gas source 3a at a predetermined flow rate (S3). ). Thereby, the piping system on the fuel electrode side is purged with the inert gas. At this time, the supply of air to the air electrode side is continued. For this reason, part of the residual heat in the solid oxide fuel cell 12 is heat-exchanged by the supplied air, so that the power generation part of the cell stack is in a temperature region lower than its operating temperature of 950 ° C. It is cooled to some 650 ° C to 850 ° C. Further, the air supplied into the solid oxide fuel cell 12 can be supplied by bypassing the heat exchanger 14. Thereby, cooling in the solid oxide fuel cell 12 can be further promoted.

The voltmeter 21 measures the voltage of the cell stack at a predetermined time interval (S4). The measured voltage is transmitted to the control unit 20. The control unit 20 acquires an average cell voltage V _cell for the voltage of one cell stack. The average cell voltage V _cell is a value obtained by dividing the voltage of the cell stack by the number of cells formed on one cell stack. When the control unit 20 acquires voltages for a plurality of cell stacks, the control unit 20 acquires the average of the average cell voltages in each cell stack as V _cell .

Part of the air flowing outside the cell stack diffuses from the air electrode side toward the base tube. On the other hand, in the initial stop state (immediately after the fuel gas supply is stopped), the fuel gas remains in the piping in the system. The remaining fuel gas and inert gas are supplied to the base tube of the cell stack and diffuse from the inside of the base tube toward the outside. In the initial state of the trip state, oxygen diffused from the air side due to the difference in oxygen partial pressure between the fuel electrode and the air electrode reacts with the remaining fuel gas, so that the oxygen partial pressure P _O2Anode of the fuel electrode is equal to or lower than the Ni oxidation criteria. And Ni in the fuel electrode is not oxidized. The oxygen partial pressure criteria at this time is expressed by the equation (2) using the pressure equilibrium constant Kp of the oxidation reaction of Ni at the temperature in the trip state from the reaction equation (1).
2Ni + O ₂ → 2NiO (1)
P _{O2Anode | L} = 1 / Kp (2)
P _{O2Anode | L} is the oxygen partial pressure of the criteria at which Ni in the fuel electrode is oxidized. That is, when the oxygen partial pressure becomes P _{O2Anode | L} or more, Ni in the fuel electrode is oxidized.
Further, the potential difference between the fuel electrode and the air electrode (Ni redox equilibrium potential), that is, the electromotive force E _rev is expressed by Expression (3).
E _rev = RT / 4F × ln (P _O2Cathode / P _O2Anode ) (3)
R is a gas constant, T is a cell temperature in a trip state, and F is a Faraday constant. P _O2Cathode is the oxygen partial pressure at the air electrode and is 0.21 atm.

The fuel gas flow path in the system is replaced with the inert gas, the fuel gas remaining in the oxygen diffused from the air side, because we are consumed, the oxygen partial pressure P _O2Anode fuel in-electrode increases. When the residual fuel gas is consumed and the oxygen partial pressure of the fuel electrode becomes _{equal to} or higher than the Ni oxidation criteria P _O2Anode | _L , the oxygen diffused from the air electrode reacts with Ni. At this time, the reaction rate between Ni and oxygen is sufficiently higher than that of oxygen diffusing from the air electrode at high temperatures (100 ° C or higher). When the path is fully replaced with inert gas, P _O2Anode becomes a constant value P _{O2Anode | L.} Accordingly, the electromotive force E _rev is also constant.

The control unit 20 determines whether the acquired average cell voltage V _cell is constant (S5). The control unit 20 determines that the cell voltage is constant when the acquired average cell voltage is within ± 5% of the average cell voltage acquired immediately before.
When the average cell voltage V _cell is not constant, the control unit 20 continues to supply the inert gas to the fuel electrode side of the cell stack and continues to supply air to the air electrode side.
When the average cell voltage V _cell becomes constant, the control unit 20 determines that the voltage is the oxidation-reduction equilibrium potential of Ni. When the control unit 20 determines that the average cell voltage V _cell has reached the redox equilibrium potential of Ni, the control unit 20 adjusts the flow rate adjustment valve 5b based on the signal from the flow rate detector 5c of the oxidizing gas supply unit 5, The supply of air is stopped (S6).

FIG. 3 shows the change over time in the average cell voltage of the cell stack when N ₂ gas is supplied to the fuel electrode side and the solid oxide fuel cell system is stopped while air is supplied to the air electrode side. is there. In the figure, the horizontal axis represents the time for supplying N ₂ gas as an inert gas to the fuel electrode side (N ₂ purge time), and the vertical axis represents the average cell voltage of the solid oxide fuel cell. The solid oxide fuel cell from which the graph is obtained is one in which one cell stack is accommodated and 48 cells are formed in one cell stack. The voltage of the cell stack in the fuel cell was measured, and the average cell voltage V _cell was calculated.

“0 hour” in FIG. 3 represents the time point when the supply of the fuel gas to the fuel electrode is stopped and the supply of the N ₂ gas is started. The negative time in FIG. 3 means that the fuel gas (H ₂ gas) is supplied to the fuel electrode and the air is supplied to the air electrode. The positive time in FIG. 3 means a period in which N ₂ gas is supplied to the fuel electrode and air is supplied to the air electrode.
In the example of FIG. 3, power generation was performed at an average voltage of 1.0 V. However, when the supply of fuel gas to the fuel electrode was stopped and the supply of N ₂ gas was started, the voltage dropped sharply. About 2 hours after the start of the N ₂ gas supply, the average voltage became almost constant at 0.7V. This average voltage value (0.7 V) corresponds to the oxidation-reduction equilibrium potential of Ni.

In this state, when the supply of N ₂ gas to the fuel electrode and the supply of air to the air electrode were continued, the average cell voltage decreased after about 6 hours. N After ₂ gas delivery starting from 9 hours, the feeding of _{N 2} gas to the fuel electrode is stopped, but resumed feeding of _{H 2} gas, the average voltage during the power generation in 0.925~0.926V there were. From this, it can be determined that the cell stack is damaged about 6 hours after the start of N ₂ gas supply.

Therefore, in the example of FIG. 3, the supply of air to the air electrode side is stopped between 2 hours and 6 hours from the start of N ₂ gas supply when the average cell voltage becomes constant. That is, in this embodiment, the supply of the oxidizing gas to the air electrode is stopped before the cell stack is damaged.

After stopping the supply of air to the air electrode, the control unit 20 adjusts the flow rate adjustment valve 6b based on the signal from the flow rate detector 6c, and the inert gas (N ₂₎ from the second inert gas source 6a. Gas) at a predetermined flow rate (S7). As a result, the inert gas is purged into the piping system on the air electrode side of the solid oxide fuel cell 12. When the air in the piping system on the air electrode side is sufficiently replaced with the inert gas, the solid oxide fuel cell system 1 stops (S8).

Second Embodiment
In the solid oxide fuel cell system according to the second embodiment, a thermometer for measuring the cell temperature is installed in the solid oxide fuel cell 12 of FIG. In the cell stack power generation section in the fuel cell system, a difference ΔT between the maximum temperature and the minimum temperature is about 100 ° C. to 300 ° C. For this reason, in consideration of the diffusion rate of oxygen from the air electrode, the temperature measured here is preferably the temperature of the highest temperature part of the cell part (for example, the central part in the cell stack axial direction). The thermometer is connected to the input unit of the control unit 20 in FIG.

  A method for operating the solid oxide fuel cell system according to the second embodiment will be described below. FIG. 4 is a flowchart of the operation method of the second embodiment. In the following, the same components as those in the first embodiment will be described with the same reference numerals as those in FIG.

  The trip state transition (S11), fuel gas supply stop (S12), feed of inert gas to the fuel electrode side (S13), and voltage measurement (S14) in FIG. 4 are the same as in the first embodiment. .

  The thermometer measures the temperature of the cell (S15). The measured temperature is transmitted to the control unit 20.

Based on the temperature acquired from the thermometer, the control unit 20 calculates the oxidation-reduction equilibrium potential E _rev of Ni in the trip state using Equation (3). The control unit 20 compares the average cell voltage V _cell acquired from the voltmeter 21 with the calculated E _rev and determines whether or not the acquired V _cell has reached E _rev (S16).

When the control unit 20 determines that V _cell has not reached E _rev (that is, V _cell > E _rev ), the control unit 20 continues to supply the inert gas to the fuel electrode side and to the air electrode side. Continue air supply.

When the control unit 20 determines that V _cell has reached E _rev (that is, V _cell ≦ E _rev ), the control unit 20 adjusts the flow rate adjustment valve 5b based on the signal from the flow rate detector 5c of the oxidizing gas supply unit 5. Then, the supply of air is stopped (S17).

Next, the controller 20 supplies an inert gas (N ₂ gas) from the second inert gas source 6a at a predetermined flow rate in the same manner as in the first embodiment (S18). When the air in the piping system on the air electrode side is sufficiently replaced with the inert gas, the solid oxide fuel cell system 1 stops (S19).

<Third Embodiment>
In the solid oxide fuel cell system according to the third embodiment, the voltmeter installed in the solid oxide fuel cell 12 of the first embodiment is omitted. Moreover, the thermometer of 2nd Embodiment is not installed.

  In the third embodiment, the correlation (voltage change with time) of the inert gas purge time to the fuel electrode and the cell voltage, the cell stack potential, or the cartridge potential that is an assembly of cell stacks is acquired in advance.

FIG. 5 is an example of a change with time of the cell voltage when the flow rate of the N ₂ gas supplied to the fuel electrode is changed. In the figure, the horizontal axis represents the time for supplying N ₂ gas (N ₂ purge time), and the vertical axis represents the cell voltage. The purge time at which the cell voltage is constant varies depending on the flow rate of N ₂ gas supplied to the fuel electrode side. The definition of “constant cell voltage” is the same as in the first embodiment. According to FIG. 5, when the N ₂ gas flow rate is 5000 mL / min, the cell voltage becomes constant after the N ₂ purge time is about 0.3 hours (about 18 minutes). When the N ₂ gas flow rate is 50 mL / min, the cell voltage becomes constant after the N ₂ purge time is about 0.6 hours (about 36 minutes).

In the third embodiment, for various inert gas flow rate, the data of the purge time t _d of the cell voltage respectively is constant is obtained. Data obtained purge time t _d is stored in the control unit.

  A method for operating the solid oxide fuel cell system according to the third embodiment will be described below. FIG. 6 is a flowchart of the operation method of the third embodiment. In the following, the same components as those in the first embodiment will be described with the same reference numerals as those in FIG.

  The trip state transition (S21), fuel gas supply stop (S22), and feed of inert gas to the fuel electrode side (S23) in FIG. 6 are the same as those in the first embodiment.

The control unit 20 manages the inert gas purge time t after the supply of the inert gas is disclosed. Control unit 20, from among the data stored, call the purge time t _d the cell voltage is constant with an inert gas supply flow rate in S23. The control unit 20 compares t with t _d and determines whether t has reached t _d (S24).

When the control unit 20 determines that the inert gas purge time t has not reached t _d (that is, t <t _d ), the control unit 20 continues to supply the inert gas to the fuel electrode side and the air electrode side. Continue to supply air to

When the control unit 20 determines that the inert gas purge time t has reached t _d (ie, t ≧ t _d ), the flow rate adjusting valve 5b is based on a signal from the flow rate detector 5c of the oxidizing gas supply unit 5. And the supply of air is stopped (S25).

Next, the control unit 20 supplies an inert gas (N ₂ gas) at a predetermined flow rate from the second inert gas source 6a in the same manner as in the first embodiment (S26). When the air in the piping system on the air electrode side is sufficiently replaced with the inert gas, the solid oxide fuel cell system 1 stops (S27).

<Fourth embodiment>
A combined power generation system 41 shown in FIG. 7 includes a solid oxide fuel cell 42 and a gas turbine power generation device 43. The combined power generation system 41 is a power generation system capable of obtaining high efficiency by combining power generation by the solid oxide fuel cell 42 and power generation by the gas turbine power generation facility 43.

  As a piping system for fuel gas, air gas, and inert gas used in the combined power generation system 41, a fuel gas supply flow path L1, an inert gas supply flow path L2 on the fuel electrode side, an exhaust fuel gas flow path L3, a recirculation Gas passage L4, fuel gas supply passage L5 for the combustor, oxidizing gas supply passage L6, exhaust passage L7, inert gas supply passage L8 on the air electrode side, exhaust oxidizing gas passage L9, oxidizing gas bypass flow A path L10, an exhaust fuel gas discharge channel L11, and an exhaust oxidant gas discharge channel L12 are provided.

  The fuel gas supply channel L1 connects the fuel gas supply source 44 and the solid oxide fuel cell 42 via a flow rate adjusting valve 45 that adjusts the flow rate of the fuel gas. In addition, an inert gas supply flow path L2 for supplying an inert gas at the time of starting or stopping is connected to the fuel gas supply flow path L1. The inert gas supply flow path L2 on the fuel electrode side is connected to an inert gas supply source 46 on the fuel electrode side via a flow rate adjusting valve 47 that adjusts the flow rate of the inert gas.

The fuel gas used for power generation of the solid oxide fuel cell 42 is discharged to the exhaust fuel gas flow path L3. The exhaust fuel gas flow path L3 is connected to the combustor 51 of the gas turbine power generation device 43 via the heat exchanger 48 for the fuel gas and the exhaust fuel gas, the exhaust fuel gas recirculation blower 49, and the flow rate adjustment valve 50. .
The heat exchanger 48 heats the fuel gas supplied from the fuel gas supply flow path L1 and the high-temperature exhaust fuel gas used for power generation discharged from the solid oxide fuel cell 42 to the exhaust fuel gas flow path L3. The fuel gas supplied to the solid oxide fuel cell 42 is preheated. The exhaust fuel gas recirculation blower 49 supplies the unused fuel contained in the exhaust fuel gas discharged from the solid oxide fuel cell 42 to the exhaust fuel gas passage into the fuel gas supply passage L1 through the recirculation gas passage L4. Recirculating. The flow rate adjustment valve 50 controls the gas flow rate of the exhaust fuel gas that flows through the exhaust fuel gas flow path L <b> 3 supplied to the combustor 51 of the gas turbine power generation equipment 43.

  The oxidizing gas supply flow path L6 connects the compressor 54 of the gas turbine power generation equipment 43 and the solid oxide fuel cell 42 via the heat exchanger 52 and the flow rate adjusting valve 53. The oxidizing gas supply flow path L6 is connected to an inert gas supply flow path L8 on the air electrode side that supplies an inert gas at the time of starting or stopping. The inert gas supply flow path L9 on the air electrode side is connected to an inert gas supply source 57 on the air electrode side via a flow rate adjusting valve 58 that adjusts the flow rate of the inert gas. The heat exchanger 52 exchanges heat between the oxidant gas pressurized by the compressor 54 and the exhaust combustion gas discharged from the turbine 55 to the exhaust combustion gas flow path L7, and supplies the solid oxide fuel cell 42 to the solid oxide fuel cell 42. The temperature of the supplied oxidizing gas is raised. The flow rate adjustment valve 53 controls the flow rate of the oxidizing gas supplied from the compressor 54.

  The oxidizing gas used for power generation of the solid oxide fuel cell 42 is discharged to the exhaust oxidizing gas flow path L9. The exhaust oxidant gas flow path L9 is connected to the combustor 51 of the gas turbine power generator 43, and the exhaust oxidant gas is supplied to the combustor 51. In addition, an oxidizing gas bypass channel L10 is connected to the exhaust oxidizing gas channel L9. The oxidant gas bypass flow path L10 is used to supply the oxidant gas to the combustor 51 by bypassing the solid oxide fuel cell 42 when the combined power generation system 41 is started and stopped or when the gas turbine power generation facility 43 is operated alone. This is a piping system.

  The gas turbine power generation equipment 43 includes a compressor 54 that compresses the oxidizing gas, a combustor 51 that generates combustion gas for driving the gas turbine, and a turbine 55 that rotates by expanding the combustion gas. ing. The compressor 54 is connected to the turbine 55 coaxially. Further, the generator 56 is connected to the turbine 55 coaxially.

  The combustor 51 burns the fuel gas and the oxidizing gas discharged from the solid oxide fuel cell, and supplies a high-temperature and high-pressure combustion gas to the turbine 55. In addition to the exhaust fuel gas flow path L3, a combustor fuel gas supply flow path L5 for supplying fuel gas directly is connected to the combustor 51. The combustor fuel gas supply flow path L <b> 5 connects the combustor 51 and the fuel gas source 59 via the flow rate adjusting valve 60.

Next, the operation of the combined power generation system configured as described above will be described.
The discharged air (oxidized gas) compressed and discharged by the compressor 54 of the gas turbine power generator 43 is supplied to the air electrode of the solid oxide fuel cell 42 through the oxidizing gas flow path L6.
The discharged air (oxidizing gas) is used as an oxidant in the solid oxide fuel cell 42 for power generation, then discharged to the exhaust oxidizing gas flow path L9 and supplied to the combustor 51 of the gas turbine power generator 43.

  The flow rate adjustment valve 53 interposed in the oxidizing gas supply flow path L6 is used to separate the solid oxide fuel cell 42 and the gas turbine power generation device 43, and is provided with a normally closed flow rate adjustment valve. Similarly, the flow rate adjustment valve 61 interposed in the exhaust oxidation gas flow path L9 is used for separating the solid oxide fuel cell 42 and the gas turbine power generation equipment 43, and is provided with a normally closed automatic valve. .

  Further, for example, city gas (natural gas) or the like is supplied to the fuel electrode of the solid oxide fuel cell 42 as the fuel gas from the fuel gas supply flow path L1. A part of the fuel gas is used as a reducing agent for power generation in the solid oxide fuel cell 42 and then discharged from the fuel electrode side of the solid oxide fuel cell 42 to the exhaust fuel gas passage L3. The exhaust fuel gas is supplied to the combustor 51 through the exhaust fuel gas flow path L3. The exhaust fuel gas flow path L3 is provided with a flow rate adjusting valve 50 for adjusting the pressure of the exhaust fuel gas, and is provided with a normally closed automatic valve.

  In the combustor 51 of the gas turbine power generation device 43, the exhaust gas supplied from the exhaust fuel gas passage L3 using the exhaust oxidation gas from the exhaust oxidation gas passage L9 and the fuel gas passage L5 for the combustor are supplied. A fuel gas such as city gas (natural gas) is combusted, and the generated high-temperature and high-pressure combustion gas is supplied to the turbine 55.

  The turbine 55 that has been supplied with the combustion gas rotates with the energy generated when the combustion gas expands to generate a shaft output. This shaft output is mainly used for driving the generator 56 and converted into electric energy, but a part thereof is used as a drive source for the compressor 54. After being used in the turbine 55, the combustion gas is discharged into the exhaust combustion gas flow path L7 in order to exchange heat with the discharge air (oxidizing gas) in the heat exchanger 52.

  As described above, a part of the exhaust fuel gas discharged from the solid oxide fuel cell 42 is returned to the fuel electrode side of the solid oxide fuel cell 42, and a part of the remaining exhaust fuel gas is gasified. It may be configured to be sent to the combustor 51 of the turbine power generator, or may be configured to send all of the exhaust fuel gas discharged from the solid oxide fuel cell 42 to the combustor 51 side of the gas turbine power generator. It may be.

  The operating state of the combined power generation system will be described. The control unit 62 activates the turbine 55 by supplying fuel gas and oxidizing gas to the combustor 51 of the gas turbine power generation equipment 43. The control unit 62 detects the startup state of the turbine 55 and starts supplying air to the solid oxide fuel cell 42 by the compressor 54. The air exchanges heat with the exhaust combustion gas of the turbine 55 in the heat exchanger 52, and is heated to about 200 to 500 ° C. at the outlet of the heat exchanger 52. The compressor 54 feeds the oxidizing gas by taking in air from the outside air and compressing it.

  When the temperature detector 68 detects that the temperature of the solid oxide fuel cell 42 is raised to a predetermined temperature due to the supply of air to the solid oxide fuel cell 42, the fuel gas supply channel L1 is interposed. The supply of the fuel gas from the fuel gas source 44 is started by adjusting the flow rate adjusting valve 45.

  The fuel gas and the oxidizing gas are supplied to the fuel gas supply unit and the oxidizing gas supply unit of the solid oxide fuel cell 42, respectively. The fuel gas is supplied from the fuel gas supply unit to the inside of the base tube of the cell stack in the solid oxide fuel cell 42 and flows through the base tube toward the fuel gas discharge unit. The air is supplied from the oxidizing gas supply unit to the periphery of the cell stack and is discharged from the oxidizing gas discharge unit. The fuel gas and air flowing inside and outside the cell stack react in each solid electrolyte membrane of the cell to generate electricity.

  The exhaust fuel gas and the exhaust oxidant gas discharged from the solid oxide fuel cell 42 are supplied to the combustor 51 through the exhaust fuel gas passage L3 and the exhaust oxidant gas passage L9, and burned in the combustor 51. Yes.

  A system abnormality is detected in the combined power generation system 41 in the above-described operation state. Thereby, the combined power generation system 41 shifts to a stopped state.

When shifting to the stop state, the control unit 62 adjusts the flow rate adjustment valve 45 based on the signal from the flow rate detector 63 of the fuel gas supply flow path L1, and stops the supply of fuel gas from the fuel gas source 44.
When shifting to this stop state, the flow rate adjusting valve 60 interposed in the fuel gas supply flow path L5 is adjusted, and the fuel gas is supplied from the fuel gas source 59 to the combustor 51 of the gas turbine power generator. By starting, the turbine 55 is operated alone. In FIG. 7, the fuel gas source 59 is illustrated separately from the fuel gas source 46, but may be connected to the same fuel gas source.

  Next, the control unit 62 adjusts the flow rate adjustment valve 47 based on the signal from the flow rate detector 64 and supplies the inert gas at a predetermined flow rate from the purge gas supply source 46 on the fuel electrode side. Thereby, the piping system (L1, L2, L3, L4) on the fuel electrode side is purged with the inert gas. At this time, the supply of air to the air electrode side is continued. For this reason, part of the residual heat in the solid oxide fuel cell 42 is heat-exchanged by the supplied air, so that the power generation unit of the cell stack is in a temperature region lower than its operating temperature of 950 ° C. It is cooled to some 650 ° C to 850 ° C. In addition, the air supplied into the solid oxide fuel cell 42 can be supplied (not shown) by bypassing the heat exchanger 52. As a result, cooling in the solid oxide fuel cell 42 can be further promoted. When purging the inert gas to the fuel electrode side piping system, the fuel electrode side piping system is purged by closing the flow rate adjusting valve 50 interposed in the exhaust fuel gas flow path L3.

Similar to the first embodiment, the voltmeter 67 measures the voltage of the cell stack at a predetermined time interval. The measured voltage is transmitted to the control unit 62. The control unit 62 acquires the average cell voltage V _cell for the voltage of one cell stack.

When the average cell voltage V _cell is not constant, the control unit 62 continues to supply the inert gas to the fuel electrode side of the cell stack and continues to supply air to the air electrode side.
When the average cell voltage V _cell becomes constant, the control unit 62 determines that the voltage is the oxidation-reduction equilibrium potential of Ni. When the control unit 62 determines that the average cell voltage V _cell has reached the oxidation-reduction equilibrium potential of Ni, the control unit 62 adjusts the flow rate adjustment valve 53 based on a signal from the flow rate detector 65 of the oxidizing gas supply path L6. In this state, the oxidizing gas is supplied to the combustor 51 through the oxidizing gas bypass flow path L10 by opening the flow rate adjustment valve 69 interposed in the oxidizing gas bypass flow path L10. In addition, the stop determination of the solid oxide fuel cell 42 in consideration of the average cell voltage in the control unit 62 is performed in the same manner as in the first embodiment.

  The supply of air to the air electrode of the solid oxide fuel cell 42 is stopped by opening the flow rate adjustment valve interposed in the oxidizing gas bypass flow path L10 and simultaneously closing the flow rate adjustment valve 53. As a result, the oxidizing gas supplied from the compressor 54 is continuously supplied to the combustor 51, so that the gas turbine power generation equipment 43 can be continuously operated without stopping. The operation may be stopped by a predetermined stop operation.

Next, the control unit 62 opens the flow rate adjustment valve 58 based on a signal from the flow rate detector 66 and supplies an inert gas (N ₂ gas) from the inert gas source 57 on the air electrode side at a predetermined flow rate. Further, the flow rate adjustment valve 71 interposed in the exhaust oxidation gas flow path L12 is opened, and the flow rate adjustment valve 61 interposed in the exhaust oxidation gas flow path L9 is closed, thereby purging the piping system on the air electrode side. . When the pressure on the air electrode side becomes higher than the pressure on the fuel electrode side, oxygen ions easily pass from the air electrode side of the cell to the fuel electrode side, and the fuel electrode is reoxidized, thereby reducing the robustness of the cell. Therefore, the flow rate of the gas passing through each of the flow rate adjusting valves 70 and 71 is adjusted so that the pressure on the fuel electrode side is equal to or higher than the pressure on the air electrode side.

  The outlets of the exhaust fuel gas purge flow path L11 and the exhaust oxidation gas purge flow path L12 may be joined and connected to a catalytic combustor (not shown) so that the exhaust may be discharged while controlling the differential pressure by the catalytic combustor. May be released to the atmosphere by performing exhaust gas treatment (not shown).

  Purge piping system on the fuel electrode side of the solid oxide fuel cell 42 (from the solid oxide fuel cells L1 and L3 to the flow control valve 50, L4) and the purge piping system on the air electrode side (solid oxidation of L6 and L9) When the physical fuel cell (from the fuel cell to the flow control valve 61) is replaced with an inert gas, the flow control valves 70 and 71 are closed and the solid oxide fuel cell 42 is stopped.

  In the above description, the solid oxide fuel cell is stopped in the same manner as in the first embodiment. However, even if the solid oxide fuel cell is stopped in the same process as in the second embodiment or the third embodiment. good.

DESCRIPTION OF SYMBOLS 1 Solid oxide fuel cell system 2 Fuel gas supply part 2a, 59 Fuel gas source 2b, 3b, 5b, 6b, 45, 47, 50, 53, 58, 60, 61 Flow control valve 2c, 3c, 5c, 6c, 63, 64, 65, 66 Flow rate detector 3 Fuel electrode inert gas feed unit 3a First inert gas source 4, 7 Feed fan 5 Oxidizing gas feed unit 5a Air filter 6 Air electrode inert gas Feed unit 6a Second inert gas source 11, 14, 48, 52 Heat exchanger 12 Solid oxide fuel cell 13, 51 Combustor 15 Exhaust gas boiler 16 Chimney 20, 62 Control unit 21, 67 Voltmeter 41 Composite Power generation system 42 Solid oxide fuel cell 43 Gas turbine power generation device 44 Fuel gas supply source 46, 57 Inert gas supply source 49 Waste fuel gas recirculation blower 54 Compressor 55 Turbine 56 Power generation Machine 68 Temperature detector 69, 70, 71 Flow rate adjusting valve L1, L5 Fuel gas supply flow path L2, L8 Inert gas supply flow path L3 Waste fuel gas flow path L4 Recirculation gas flow path L6 Oxidation gas supply flow path L7 Exhaust Flow path L9 Exhaust oxidation gas flow path L10 Oxidation gas bypass flow path L11 Exhaust fuel gas discharge flow path L12 Exhaust oxidation gas discharge flow path

Claims (12)

Including one or a plurality of cell stacks having a plurality of cells, supplying a fuel gas to a fuel electrode side of the cell stack, and supplying an oxidizing gas containing oxygen to an air electrode side of the cell stack, A method for operating a solid oxide fuel cell that generates electricity by reacting the fuel gas and the oxidizing gas at a high temperature in an electrolyte membrane of a cell,
A first inert gas that stops the supply of the fuel gas in a high temperature state, supplies the inert gas to the fuel electrode side at a predetermined flow rate, and continues the supply of the oxidizing gas to the air electrode. A gas purge step;
When the voltage between the fuel electrode and the air electrode in the cell reaches a predetermined voltage, the supply of the oxidizing gas is stopped at a high temperature, and the inert gas is supplied to the air electrode at a predetermined flow rate. A solid oxide fuel cell operating method comprising: a second inert gas purge step of feeding and stopping the operation of the solid oxide fuel cell. A voltage measuring step of feeding an inert gas to the fuel electrode side and measuring the voltage while feeding the oxidizing gas to the air electrode side;
In the second inert gas purge step, when the measured voltage becomes constant, the supply of the oxidizing gas is stopped in a high temperature state and the inert gas is supplied to the air electrode side. 2. A method for operating the solid oxide fuel cell according to 1. A cell temperature measuring step for measuring the temperature of the cell;
The oxidation-reduction equilibrium potential of the material of the said fuel electrode in the measured temperature is further calculated, The oxidation-reduction equilibrium potential calculation process which uses this oxidation-reduction equilibrium potential as the said predetermined voltage is further included. Operating method of solid oxide fuel cell. A correlation between the inert gas supply time and the voltage when the inert gas at the predetermined flow rate is supplied to the fuel electrode side is acquired in advance, and the predetermined voltage at the predetermined flow rate is obtained based on the correlation. A purge time determining step of acquiring the feeding time to be
In the second inert gas purge step, when the delivery time set in the purge time determination step is reached, the supply of the oxidizing gas is stopped at a high temperature state, and the inert gas is introduced to the air electrode side. The operation method of the solid oxide fuel cell according to claim 1, wherein Method of operating a combined power generation system in which a solid oxide fuel cell including one or a plurality of cell stacks having a plurality of cells and a gas turbine power generation facility including a combustor, a compressor, a turbine, and a generator are connected Because
When the solid oxide fuel cell and the gas turbine power generation facility are in operation, the supply of fuel gas from the first fuel gas source to the fuel cell is stopped in a high temperature state, and the fuel electrode of the cell A first inert gas purge step of supplying an inert gas to the side at a predetermined flow rate and continuing to supply an oxidizing gas from the compressor to the air electrode side of the cell;
When the voltage between the fuel electrode and the air electrode in the cell reaches a predetermined voltage, the supply of the oxidizing gas to the fuel cell is stopped in a high temperature state, and the inert gas on the air electrode side And a second inert gas purge step of stopping the operation of the solid oxide fuel cell. In the first inert gas purge step, the supply of fuel gas from the second fuel gas source to the combustor is started,
The method of operating a combined power generation system according to claim 5, wherein, in the second inert gas purge step, the oxidizing gas is directly supplied from the compressor to the combustor to continue the operation of the gas turbine power generation facility. . A solid oxide fuel cell comprising one or more cell stacks having a plurality of cells;
A fuel gas supply unit for supplying fuel gas to the fuel electrode side of the cell stack;
An oxidizing gas supply unit for supplying an oxidizing gas containing oxygen to the air electrode side of the cell stack;
A fuel electrode-side inert gas feeding unit for feeding an inert gas to the fuel electrode side of the cell stack;
An air electrode side inert gas supply unit for supplying an inert gas to the air electrode side of the cell stack;
The supply of the fuel gas to the fuel electrode side is stopped and the inert gas is supplied to the fuel electrode side, and the voltage between the fuel electrode and the air electrode in the cell reaches a predetermined voltage. A solid oxide fuel cell system comprising: a controller that stops the supply of the oxidizing gas to the air electrode side at a high temperature and supplies the inert gas to the air electrode side.   The solid oxide fuel cell system according to claim 7, wherein a voltmeter for measuring the voltage is installed in the solid oxide fuel cell. A thermometer that measures the temperature of the cell is installed in the solid oxide fuel cell,
9. The control unit according to claim 7, wherein the control unit calculates an oxidation-reduction equilibrium potential of the material of the fuel electrode at a temperature measured by the thermometer, and sets the oxidation-reduction equilibrium potential to the predetermined voltage. Solid oxide fuel cell system. The controller stores in advance a correlation between the inert gas supply time and the voltage when the predetermined flow rate of the inert gas is supplied to the fuel electrode side,
8. The solid oxide fuel according to claim 7, wherein the control unit determines a timing for stopping the supply of the oxidizing gas and starting the supply of the inert gas to the air electrode based on the correlation. Battery system. A solid oxide fuel cell comprising one or more cell stacks having a plurality of cells;
A turbine, a generator connected to the turbine, a combustor for supplying combustion gas to the turbine, and a compressor capable of supplying oxidizing gas to the air electrode of the combustor and the cell stack. A gas turbine power generation facility;
A first fuel gas supply unit for supplying fuel gas to the fuel electrode side of the cell stack;
A second fuel gas supply unit for supplying fuel gas to the combustor;
A fuel electrode-side inert gas supply unit for supplying an inert gas to the fuel electrode side;
An air electrode side inert gas feed unit for feeding an inert gas to the air electrode side;
A control unit,
The air electrode and the combustor are connected so that the oxidizing gas discharged from the air electrode is supplied to the combustor.
The fuel electrode and the combustor are connected so that the fuel gas discharged from the fuel electrode is fed to the combustor,
The control unit is
During operation of the solid oxide fuel cell and the gas turbine power generation facility, fuel gas is supplied from the first fuel gas supply unit to the fuel electrode, and the fuel gas discharged from the fuel electrode is discharged. The oxidant gas is supplied from the compressor to the air electrode, and the oxidant gas discharged from the air electrode is supplied to the combustor.
When the solid oxide fuel cell is stopped, the supply of the fuel gas from the first fuel gas supply unit to the fuel electrode is stopped and the fuel from the fuel electrode side inert gas supply unit is stopped. Send the inert gas to the pole side,
When the voltage between the fuel electrode and the air electrode in the cell reaches a predetermined voltage, the supply of the oxidizing gas from the compressor to the air electrode is stopped in a high temperature state, and the air electrode side A combined power generation system that feeds the inert gas from an inert gas feeding unit to the air electrode side. The control unit is
When the supply of the fuel gas from the first fuel gas supply unit to the fuel electrode is stopped, the fuel gas is supplied from the second fuel gas supply unit to the combustor,
The combined power generation system according to claim 11, wherein when the supply of the oxidizing gas from the compressor to the air electrode is stopped, the oxidizing gas is supplied from the compressor to the combustor.

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