JP2023081179A - Solid oxide ful cell system - Google Patents

Abstract

To reduce a stack temperature of a fuel cell stack without increasing a total amount of an oxidant gas supplied to the fuel cell stack.SOLUTION: A solid oxide fuel cell system comprises: a ratio determination unit (216) for determining, in accordance with a stack temperature (CB), a ratio (RM) of an oxidant supply amount from a first oxidant supply pump with respect to a total amount (XT) of an oxidant gas; a target value determination unit (218) for determining a first target value and a second target value of the oxidant supply amount based on the ratio and the total amount; and a pump control unit (220) which controls a first oxidant supply pump (34) based the first target value and controls a second oxidant supply pump (36) based on the second target value, thereby causing the pumps to supply the oxidant gas.SELECTED DRAWING: Figure 2

Description

The present invention relates to solid oxide fuel cell systems.

Patent Literature 1 discloses a fuel cell device. A fuel cell device has a cell stack (fuel cell stack) and a reformer. Air is supplied from the first blower to the fuel cell stack. When heating the fuel cell stack, air is supplied to the reformer from the second blower. A partial oxidation reforming reaction occurs inside the reformer, generating heat. The fuel cell stack is heated by a reformer.

JP 2016-25005 A

According to the fuel cell device disclosed in Patent Document 1, the balance between the generated heat generated in the fuel cell stack and the heat transmitted to the reformer in which the steam reforming reaction occurs is maintained, so that the fuel cell stack It is maintained at a temperature suitable for power generation. However, when the fuel cell stack deteriorates, the stack temperature may increase in an attempt to maintain power generation output. If the amount of air supplied to the fuel cell stack is increased in order to lower the stack temperature, there is a problem that the offset of the power output due to the increase in blower drive power cannot be ignored.

An object of the present invention is to solve the problems described above.

An aspect of the present invention is a solid oxide fuel cell system, comprising: a fuel cell stack that generates electricity through an electrochemical reaction between a fuel and an oxidant gas; and a fuel exhaust gas and an oxidant exhaust gas emitted from the fuel cell stack are burned a combustor that outputs combustion exhaust gas; a stack temperature detection unit that detects the stack temperature of the fuel cell stack; a first oxidant supply pump that supplies the oxidant gas to the fuel cell stack; a second oxidant supply pump different from the first oxidant supply pump for supplying the oxidant gas to the fuel cell stack; a heat exchanger that raises the temperature of the combustion exhaust gas before it is supplied to the stack; and when the stack temperature exceeds a predetermined temperature, the first a ratio determination unit that determines a ratio of the oxidant supply amount of the oxidant gas from the oxidant supply pump according to the stack temperature; a target value determination unit that determines a first target value of the oxidant supply amount and a second target value of the oxidant supply amount from the second oxidant supply pump; controlling the first oxidant supply pump and controlling the second oxidant supply pump based on the second target value to supply the oxidant gas to the first oxidant supply pump and the second oxidant supply pump; and a pump control unit for supplying from to the fuel cell stack.

According to the present invention, the stack temperature of the fuel cell stack can be lowered without increasing the total amount of oxidant gas supplied to the fuel cell stack.

FIG. 1 is a diagram showing a solid oxide fuel cell system in one embodiment. FIG. 2 is a functional block diagram of the control device. FIG. 3A is a diagram schematically showing how the stack temperature and the reformer temperature change over time. FIG. 3B is a diagram schematically showing how the current in the fuel cell stack changes over time. FIG. 3C is a diagram schematically showing how the raw fuel supply amount changes over time. FIG. 3D is a diagram schematically showing how the total amount of oxidant gas changes over time. FIG. 4 is a diagram showing types of oxidant gas supply amounts calculated for each system state of the solid oxide fuel cell system. FIG. 5 is a diagram showing the basis for calculating the supply amount of the oxidant gas for each type. FIG. 6 is a flow chart showing a processing procedure for determining the target value of the supply amount of the oxidant gas. FIG. 7 is a flow chart showing a processing procedure for determining a target value for the total amount of oxidant gas. FIG. 8A is a diagram schematically showing how the power generated by the fuel cell stack remains constant regardless of the passage of time. FIG. 8B is a diagram schematically showing how the stack temperature changes over time. FIG. 8C shows how the oxidant supply amount from the first oxidant supply pump and the oxidant supply amount from the second oxidant supply pump change over time, and the total amount of oxidant gas changes over time. FIG. 10 is a diagram schematically showing how the constant changes regardless of the progress of . FIG. 9 is a diagram exemplifying a map that defines the correspondence between the ratio of the oxidant supply amount from the first oxidant supply pump to the total amount of oxidant gas and the stack temperature. FIG. 10 is a flowchart showing a processing procedure for determining a first target value of the oxidant supply amount from the first oxidant supply pump and a second target value of the oxidant supply amount from the second oxidant supply pump. .

FIG. 1 shows a solid oxide fuel cell system 10 in one embodiment. The solid oxide fuel cell system 10 includes a power unit 20, a raw fuel supply pump 30, a water supply pump 32, a first oxidant supply pump 34, a second oxidant supply pump 36, a first valve 44, It has a second valve 46 , a power conditioner system (PCS) 50 and a controller 60 . In the present embodiment, the fuel includes raw fuel, water, and reformed gas, which will be described later.

Raw fuel supply pump 30 outputs a raw fuel containing hydrocarbons to a flow channel in power unit 20 . The raw fuel is, for example, natural gas, petroleum gas, or liquefied petroleum. Raw fuels include hydrocarbons such as methane, ethane, propane, or butane. Water supply pump 32 outputs water to the flow path in power unit 20 . The first oxidant supply pump 34 and the second oxidant supply pump 36 output the oxidant gas to flow paths in the power unit 20, respectively. The oxidant gas is air, for example. The oxidant gas contains oxygen.

A first valve 44 is arranged in the first flow path 40 connecting the second oxidant supply pump 36 and the partial oxidation reformer 70 . The first valve 44 switches whether to supply the oxidant gas from the second oxidant supply pump 36 to the partial oxidation reformer 70 . The second valve 46 is arranged in the second flow path 42 connecting the second oxidant supply pump 36 and the fuel cell stack 90 . The second valve 46 switches whether to supply the oxidant gas from the second oxidant supply pump 36 to the fuel cell stack 90 .

Power unit 20 generates power using fuel and oxidant gas, and outputs DC power to power conditioner system 50 . The power unit 20 includes a partial oxidation reformer (POx) 70, a steam reformer (SR) 72, a combustor 74, a first heat exchanger 76, a second heat exchanger 78, and an exhaust catalyst 80. , and a fuel cell stack 90 . The partial oxidation reformer 70 and the steam reformer 72 are provided close to each other or integrally.

The raw fuel supplied by the raw fuel supply pump 30 and the oxidant gas supplied by the second oxidant supply pump 36 flow into the partial oxidation reformer 70 . The partial oxidation reformer 70 generates a reformed gas containing hydrogen gas and carbon monoxide gas by partially oxidizing hydrocarbons contained in the raw fuel with oxygen contained in the oxidant gas. A catalyst is used for this reforming. The reformed gas produced by the partial oxidation reformer 70 flows through the steam reformer 72 into the fuel cell stack 90 .

A mixed gas containing raw fuel supplied by the raw fuel supply pump 30 and steam flows into the steam reformer 72 . The steam reformer 72 reforms the hydrocarbon contained in the raw fuel to generate and output a reformed gas containing hydrogen gas and carbon dioxide gas. A catalyst is used for this reforming. A portion of the mixed gas remaining without being reformed is also output from the steam reformer 72 . The reformed gas and part of the mixed gas produced by the steam reformer 72 flow into the fuel cell stack 90 . Note that water vapor is generated by raising the temperature of the water supplied by the water supply pump 32 by the first heat exchanger 76 .

The combustor 74 combusts the fuel exhaust gas and the oxidant exhaust gas from the fuel cell stack 90 and outputs high-temperature combustion exhaust gas. The fuel exhaust gas and the oxidant exhaust gas begin to burn when ignited by the ignition device 100 . The flue gas flows through the steam reformer 72, the partial oxidation reformer 70, the first heat exchanger 76, the second heat exchanger 78, and the exhaust catalyst 80, and is exhausted to the outside of the power unit 20. . The flue gas raises the temperatures of the steam reformer 72 , the partial oxidation reformer 70 , the first heat exchanger 76 , the second heat exchanger 78 and the exhaust catalyst 80 .

The flue gas increases the temperature of the partial oxidation reformer 70 and the steam reformer 72 . The steam reformer 72 can perform steam reforming when warmed to the temperature required for steam reforming.

The flue gas increases the temperature of the first heat exchanger 76 . The first heat exchanger 76 heats the raw fuel supplied from the raw fuel supply pump 30 and the water supplied from the water supply pump 32 . This causes the water to evaporate and turn into steam. Thus, a mixed gas containing raw fuel and steam is obtained. The mixed gas passes through the partial oxidation reformer 70 whose reforming has stopped and flows into the steam reformer 72 .

The combustion exhaust gas increases the temperature of the second heat exchanger 78 . The second heat exchanger 78 raises the temperature of the oxidant gas supplied by the first oxidant supply pump 34 . The oxidizing gas heated by the second heat exchanger 78 flows into the fuel cell stack 90 to raise the temperature of the fuel cell stack 90 .

The fuel cell stack 90 generates power through an electrochemical reaction between fuel (reformed gas) and oxidant gas. The fuel cell stack 90 has a laminate in which a plurality of fuel cells 110 are stacked. The plurality of fuel cells 110 are separated from each other by separators (not shown).

The fuel cell 110 has an anode electrode (fuel electrode) 112 , a cathode electrode (air electrode) 114 and an electrolyte membrane 116 . The fuel (reformed gas) reformed by the partial oxidation reformer 70 or steam reformer 72 enters through the fuel gas inlet 120 of the fuel cell stack 90 and is distributed to the anode electrode 112 of each fuel cell 110 . be done.

The oxidant gas supplied by the first oxidant supply pump 34 and heated by the second heat exchanger 78 flows through the oxidant gas inlet 122 of the fuel cell stack 90 and flows into the cathode electrode of each fuel cell 110 . 114. Electrolyte membrane 116 is sandwiched between anode electrode 112 and cathode electrode 114 . The material used for the electrolyte membrane 116 is an oxide such as stabilized zirconia having oxygen ion conductivity.

Oxygen ions, which are negative ions, are generated from the oxidant gas that has flowed into the cathode electrode 114 . Therefore, cathode electrode 114 functions as a positive electrode. Oxygen ions generated at the cathode electrode 114 permeate the electrolyte membrane 116 . Hydrogen gas and carbon monoxide gas contained in the reformed gas that has flowed into the anode electrode 112 react with oxygen ions that have permeated the electrolyte membrane 116 to produce water (water vapor), carbon dioxide gas, and electrons. . Therefore, the anode electrode 112 functions as a negative electrode.

The oxidant gas that has not reacted at the cathode electrode 114 corresponds to the oxidant exhaust gas described above. The water (water vapor) and carbon dioxide gas generated at the anode electrode 112 correspond to the fuel exhaust gas described above. Fuel exhaust gas and oxidant exhaust gas generated at the anode electrode 112 and cathode electrode 114 of each fuel cell 110 are respectively collected and output from the fuel gas outlet 124 and the oxidant gas outlet 126 of the fuel cell stack 90, respectively. The fuel exhaust gas and the oxidant exhaust gas output from the fuel cell stack 90 are directed to the combustor 74 respectively.

High-temperature flue gas flows into the exhaust catalyst 80 from the combustor 74 . Exhaust catalyst 80 removes hydrocarbons, carbon monoxide and nitrogen oxides contained in the hot flue gas and exhausts remaining gases and moisture.

The power conditioner system 50 converts the DC power output from the power unit 20 into AC power and outputs the AC power to the outside. The power conditioner system 50 applies a current between the anode electrode 112 and the cathode electrode 114 of each fuel cell 110 to cause each fuel cell 110 to generate electricity.

The controller 60 controls the solid oxide fuel cell system 10 as a whole. The solid oxide fuel cell system 10 further includes a stack temperature detection section 130 , a catalyst temperature detection section 140 and a reformer temperature detection section 150 .

Stack temperature detection unit 130 is a temperature sensor that detects a stack temperature, which is a typical temperature of fuel cell stack 90 . This temperature sensor is installed, for example, near the oxidant gas outlet 126 of the fuel cell stack 90 . Catalyst temperature detection unit 140 is a temperature sensor that detects the catalyst temperature of exhaust catalyst 80 . The reformer temperature detection unit 150 is a temperature sensor that detects the reformer temperatures of the partial oxidation reformer 70 and the steam reformer 72 .

The controller 60 acquires the detected stack temperature, catalyst temperature, and reformer temperature by receiving sensor signals from the plurality of temperature sensors described above. The control device 60 controls the raw fuel supply pump 30, the water supply pump 32, the first oxidant supply pump 34, and the second oxidant supply pump 36 based on the acquired temperature, thereby controlling the temperature of the fuel cell stack 90 and power generation. Adjust power.

In order for the fuel cell stack 90 to stably generate power, the stack temperature must reach a predetermined temperature. Therefore, first of all, the control device 60 controls the raw fuel supply pump 30 , the first oxidant supply pump 34 and the second oxidant supply pump 36 . Thereby, the raw fuel supply pump 30 and the second oxidant supply pump 36 supply the raw fuel containing hydrocarbon and the oxidant gas to the partial oxidation reformer 70 . Also, the first oxidant supply pump 34 supplies the oxidant gas to the fuel cell stack 90 .

As described above, the partial oxidation reformer 70 produces reformed gas through partial oxidation reaction between hydrocarbons and oxygen. Since this partial oxidation reaction generates high heat of several hundred degrees Celsius, the reformed gas becomes hot. Since the hot reformed gas passes through the steam reformer 72 and flows into the fuel cell stack 90, the temperatures of the steam reformer 72 and the fuel cell stack 90 are raised.

While the reformed gas is being generated in the partial oxidation reformer 70, the stack temperature has not reached the predetermined temperature. The oxidant gas hardly electrochemically reacts in each fuel cell 110 . Therefore, the reformed gas and the oxidant gas pass through the fuel gas outlet 124 and the oxidant gas outlet 126, respectively, toward the combustor 74 as fuel exhaust gas and oxidant exhaust gas, respectively.

The flue gas obtained by combusting the fuel exhaust gas and the oxidant exhaust gas in the combustor 74 passes through the steam reformer 72, the partial oxidation reformer 70, the first heat exchanger 76, and the second The heat exchanger 78 is heated. Thereby, the oxidant gas supplied by the first oxidant supply pump 34 is also heated in the second heat exchanger 78 and flows into the fuel cell stack 90 . This oxidant gas also contributes to the temperature rise of the fuel cell stack 90 . The temperature of the raw fuel supplied to the partial oxidation reformer 70 is also raised by the first heat exchanger 76 .

The control device 60 estimates the temperature of the catalyst of the steam reformer 72 based on the obtained reformer temperature. When the temperature of the catalyst of the steam reformer 72 reaches the temperature required for steam reforming, the controller 60 stops reforming by the partial oxidation reformer 70 and starts reforming by the steam reformer 72. . Note that there may be a period in which the reforming by the partial oxidation reformer 70 and the reforming by the steam reformer 72 are used together. The controller 60 controls the second oxidant supply pump 36 to stop the supply of the oxidant gas to the partial oxidation reformer 70 . The controller 60 controls the water supply pump 32 to start supplying water to the steam reformer 72 .

As a result, raw fuel and water are supplied to the first heat exchanger 76 . The water is changed to steam by the first heat exchanger 76 . A mixed gas containing raw fuel and steam is supplied to a steam reformer 72 through a partial oxidation reformer 70 . The steam reformer 72 produces reformed gas by reforming hydrocarbons with steam. The reformed gas flows into the fuel cell stack 90 .

Shortly before the stack temperature of the fuel cell stack 90 reaches a predetermined temperature, a part of the reformed gas and the oxidant gas that respectively flowed in through the fuel gas inlet 120 and the oxidant gas inlet 122 are used to generate electricity in each fuel cell 110 . A chemical reaction begins. Therefore, the electric power generated by the fuel cell stack 90 can be obtained by the amount of the electrochemical reaction.

Fuel exhaust gas containing water (water vapor) generated at the anode electrode 112 by the electrochemical reaction, carbon dioxide, and the reformed gas remaining without the electrochemical reaction passes through the fuel gas outlet 124 to the combustor 74. Head. The oxidant gas remaining without electrochemical reaction passes through the oxidant gas outlet 126 and is directed to the combustor 74 as oxidant exhaust gas. When the stack temperature reaches a predetermined temperature, normal power generation by the fuel cell stack 90 continues stably.

FIG. 2 is a functional block diagram of the control device 60. As shown in FIG. The control device 60 has a processing circuit and a memory that stores programs and the like. The processing circuit includes a processor such as a CPU.

By the processing circuit of the control device 60 executing the program, the control device 60 operates the state determination unit 200, the current value determination unit 202, the fuel supply amount determination unit 204, the total amount determination unit 206, the first calculation unit 208, the second It functions as a calculation unit 210 , a third calculation unit 212 , a fourth calculation unit 214 , a ratio determination unit 216 , a target value determination unit 218 , a pump control unit 220 and a valve control unit 222 . At least some of these units may be implemented by ASICs, FPGAs, or other integrated circuits.

The memory of the control device 60 includes volatile memory such as RAM and non-volatile memory such as ROM and flash memory. A map, which will be described later, is stored in the storage unit 250, which is one of the memories.

The state determination unit 200 determines the system state of the solid oxide fuel cell system 10 . The system state is a first stage in which the solid oxide fuel cell system 10 starts up, a second stage in which the solid oxide fuel cell system 10 performs normal power generation processing, and a third stage in which the solid oxide fuel cell system 10 stops. indicates which stage it is in.

Current value determination unit 202 determines the current value (output current value) of the current output from fuel cell stack 90 based on the system state and the stack temperature. A fuel supply amount determination unit 204 determines the fuel supply amount based on the system state, stack temperature or reformer temperature, and output current value. The fuel supply amount is the amount of raw fuel and water supplied to the fuel cell stack 90 by the raw fuel supply pump 30 and the water supply pump 32 .

The total amount determining unit 206 determines the total amount of oxidant gas supplied to the fuel cell stack 90 based on the stack temperature, system state, output current value, fuel supply amount, catalyst temperature, and reformer temperature. is determined as a theoretical value. When the system state is in the first stage, the total amount determination unit 206 determines the total amount of oxidant supplied from the first oxidant supply pump 34 and the second oxidant supply pump 36 based on the determined total amount (theoretical value of the total oxidant supply amount). Determine the target value for the total amount of agent supplied.

The first calculator 208 calculates the supply amount for power generation based on the system state and the output current value. The power generation supply amount indicates the amount of oxidant gas supplied from the first oxidant supply pump 34 and the second oxidant supply pump 36 for power generation by the fuel cell stack 90 .

The second calculator 210 calculates the supply amount for combustion based on the system state and the fuel supply amount. The combustion supply amount indicates the amount of oxidant gas supplied from the first oxidant supply pump 34 and the second oxidant supply pump 36 for combustion of the fuel exhaust gas discharged from the fuel cell stack 90 .

The third calculator 212 calculates the supply amount for dilution based on the system state and the fuel supply amount. The supply amount for dilution indicates the amount of oxidant gas supplied from the first oxidant supply pump 34 and the second oxidant supply pump 36 for diluting the fuel exhaust gas discharged from the fuel cell stack 90 .

The fourth calculator 214 calculates the supply amount for temperature control based on the system state, catalyst temperature, stack temperature and reformer temperature. The supply amount for temperature adjustment indicates the amount of oxidant gas supplied from the first oxidant supply pump 34 and the second oxidant supply pump 36 to adjust the catalyst temperature, stack temperature and reformer temperature. .

When the stack temperature exceeds a predetermined temperature, the ratio determining unit 216 determines the ratio of the oxidant gas supplied from the first oxidant supply pump 34 to the total amount of oxidant gas supplied to the fuel cell stack 90 (theoretical value of the total oxidant supply amount). The gas oxidant supply rate is determined as a function of the stack temperature. Note that the ratio determination unit 216 may determine the ratio of the oxidant supply amount of the oxidant gas from the second oxidant supply pump 36 to the total amount of the oxidant gas.

The target value determination unit 218 determines the amount of oxidant supplied from the first oxidant supply pump 34 (second Determine the theoretical value and the first target value of 1 supply amount). The target value determining unit 218 determines the oxidant supply amount (second supply amount) from the second oxidant supply pump 36 based on the first target value and the total amount of oxidant gas (theoretical value of the total oxidant supply amount). Determine a second target value. Specifically, the second target value is determined by subtracting the first target value from the theoretical value of the total oxidant supply amount. Note that the target value determining unit 218 may first determine the second target value, and then determine the first target value by subtracting the second target value from the theoretical value of the total oxidant supply amount. .

The pump control unit 220 controls the first oxidant supply pump 34 and the second oxidant supply pump 36 to supply the oxidant gas to the fuel cell stack 90 . When the system state is in the first stage, the pump control unit 220 controls the first oxidant supply pump 34 and the second oxidant supply pump 36 based on the target value of the total oxidant supply amount.

When the system state is in the second stage or the third stage, the pump control section 220 controls the first oxidant supply pump 34 based on the first target value. The pump controller 220 controls the second oxidant supply pump 36 based on the second target value. The pump control unit 220 controls the raw fuel supply pump 30 and the water supply pump 32 to adjust the power generated by the fuel cell stack 90 .

The valve control unit 222 controls the first valve 44 to supply the oxidant gas from the second oxidant supply pump 36 to the partial oxidation reformer 70 . The valve control unit 222 controls the second valve 46 to supply the oxidant gas from the second oxidant supply pump 36 to the fuel cell stack 90 .

The valve control unit 222 controls the first valve 44 and the second valve 46 before the stack temperature reaches a predetermined temperature and during the period in which the raw fuel is reformed by the partial oxidation reformer 70, The first valve 44 is opened and the second valve 46 is closed. Since the first valve 44 is open, the oxidant gas from the second oxidant supply pump 36 can be supplied to the partial oxidation reformer 70 .

When the stack temperature exceeds a predetermined temperature, the valve control section 222 controls the first valve 44 and the second valve 46 so that the first valve 44 is closed and the second valve 46 is opened. Since the second valve 46 is open, the oxidant gas from the second oxidant supply pump 36 can be supplied to the fuel cell stack 90 .

FIG. 3A is a diagram schematically showing how the stack temperature CB and the reformer temperature CR change as time T elapses. The system state until time T=T1 is in the first stage. From time T=T1 to time T=T2 the system state is in the second phase. After time T=T2, the system state is in the third stage.

In the first stage, when the partial oxidation reaction by the partial oxidation reformer 70 starts, the reformer temperature CR rises. Since the temperature of the fuel cell stack 90 is raised by the hot reformed gas generated thereby, the stack temperature CB starts to rise. At time T1, when stack temperature CB reaches predetermined temperature C1, normal power generation by fuel cell stack 90 is performed. In the second stage, it is preferable to maintain the stack temperature CB at the predetermined temperature C1 so as not to accelerate deterioration of the fuel cell stack 90 .

FIG. 3B is a diagram schematically showing how the current IC of the fuel cell stack 90 changes as time T elapses. In the first stage, when the stack temperature CB rises, the fuel cell stack 90 starts power generation for startup in order to further raise the stack temperature CB to the predetermined temperature C1. When the fuel cell stack 90 starts power generation for start-up, the current IC increases. In the second stage, normal power generation by the fuel cell stack 90 continues stably, and the current IC becomes substantially constant during this period. In the third stage, power generation by the fuel cell stack 90 is stopped, so the current IC decreases step by step.

FIG. 3C is a diagram schematically showing how the raw fuel supply amount AF changes as time T elapses. In the first stage, after the temperature of the exhaust catalyst 80 is raised, the supply amount AF of the raw fuel starts to increase from the time point when the partial oxidation reformer 70 starts to generate the reformed gas. In the second stage, while normal power generation by the fuel cell stack 90 continues stably, the raw fuel supply amount AF becomes substantially constant. In the third stage, the supply amount AF of the raw fuel is reduced step by step so that the power generation by the fuel cell stack 90 can be stopped.

FIG. 3D is a diagram schematically showing how the total amount XT of oxidant gas changes as time T elapses. The total amount of oxidant gas XT is the sum of the amount of oxidant supplied from the first oxidant supply pump 34 and the amount of oxidant supplied from the second oxidant supply pump 36 . Oxidant gas is supplied in any of the first, second and third stages. A specific type of supply amount of the oxidant gas will be described with reference to FIG.

FIG. 4 is a diagram showing types of oxidant gas supply amounts calculated for each system state of the solid oxide fuel cell system 10. In FIG. The system states, which are divided into the first, second, and third stages, are subdivided into the following 11 types of detailed states (1) to (11). The types of oxidant gas supply amount calculated in each state will be described.

(1) State in which exhaust catalyst 80 is being heated At the beginning of the first stage, in order to raise the temperature of exhaust catalyst 80 , a supply amount of oxidant gas for temperature control is supplied into power unit 20 . The supply amount for temperature adjustment is calculated by the fourth calculator 214 based on the catalyst temperature. A supply amount of the oxidant gas for temperature control is supplied from the first oxidant supply pump 34 . The total amount XT of oxidant gas is determined based on the supply amount for temperature control.

(2) State of Starting Partial Oxidation Reforming Oxidant gas is supplied to start partial oxidation reforming by the partial oxidation reformer 70 . The valve control unit 222 controls the first valve 44 to supply the oxidant gas from the second oxidant supply pump 36 to the partial oxidation reformer 70 . In order to start partial oxidation reforming by the partial oxidation reformer 70, the temperature of the catalyst of the partial oxidation reformer 70 must be raised.

The high temperature flue gas output from the combustor 74 raises the temperature of the partial oxidation reformer 70 . The combustion exhaust gas is generated when the combustor 74 burns the fuel exhaust gas and the oxidant exhaust gas output from the fuel cell stack 90 . Since power generation by the fuel cell stack 90 has not started, substantially the reformed gas generated using the raw fuel from the raw fuel supply pump 30 is substantially the same as the oxidant gas in the amount supplied for combustion. Burned.

A combustion supply of oxidant gas is supplied into the power unit 20 . The amount of oxidant gas supplied for combustion is calculated by the second calculator 210 based on the fuel supply amount of the raw fuel. A supply of oxidant gas for combustion is supplied from a first oxidant supply pump 34 and a second oxidant supply pump 36 . The oxidant gas from the second oxidant supply pump 36 is used to generate reformed gas. The reformed gas is combusted by combustor 74 using oxidant gas from first oxidant supply pump 34 . The total amount of oxidant gas XT is determined based on the combustion supply.

(3) State during Partial Oxidation Reforming In order to start steam reforming by the steam reformer 72 during partial oxidation reforming, it is necessary to raise the temperature of the catalyst of the steam reformer 72 . The reformed gas produced by the partial oxidation reaction in the partial oxidation reformer 70 raises the temperature of the steam reformer 72 . The fourth calculator 214 calculates the supply amount for temperature adjustment, which indicates the supply amount of the oxidizing gas required to raise the temperature of the steam reformer 72, based on the reformer temperature CR. The calculated supply amount of the oxidant gas for temperature control is supplied into the power unit 20 . A supply amount of oxidant gas for temperature control is supplied from the second oxidant supply pump 36 .

Furthermore, the high-temperature flue gas output from the combustor 74 raises the temperature of the steam reformer 72 . The second calculator 210 calculates a supply amount for combustion, which indicates the supply amount of the oxidant gas necessary for generating combustion exhaust gas. The supply amount for combustion is calculated based on the fuel supply amount of the raw fuel. The calculated supply amount of oxidant gas for combustion is supplied into the power unit 20 . A supply of oxidant gas for combustion is supplied from a first oxidant supply pump 34 . The total amount of oxidant gas XT is determined based on the temperature control feed rate and the combustion feed rate.

(4) State in which the partial oxidation reformer 70 and the steam reformer 72 are being used together The steam reforming performed by the steam reformer 72 is an endothermic reaction. Therefore, it is necessary to continuously adjust the temperature of the steam reformer 72 using the high-temperature flue gas. A supply amount of oxidant gas for temperature regulation and a supply amount of oxidant gas for combustion are supplied into the power unit 20 .

The supply amount for temperature control is calculated by the fourth calculator 214 based on the reformer temperature CR. The fuel supply amount for combustion is calculated by the second calculator 210 based on the fuel supply amount of the raw fuel and water. The temperature control supply and the combustion supply of oxidant gas are supplied from the second oxidant supply pump 36 and the first oxidant supply pump 34, respectively. The total amount of oxidant gas XT is determined based on the temperature control feed rate and the combustion feed rate.

(5) State during steam reforming As described above, steam reforming is an endothermic reaction. Therefore, even after the reformed gas transitions from being generated by the partial oxidation reformer 70 to being generated by the steam reformer 72, steam reforming using the high-temperature flue gas continues. Temperature control of the qualityr 72 is required.

Therefore, the supply amount of the oxidant gas for temperature regulation and the supply amount of the oxidant gas for combustion are supplied into the power unit 20 . The supply amount for temperature control is calculated by the fourth calculator 214 based on the reformer temperature CR. The fuel supply amount for combustion is calculated by the second calculator 210 based on the fuel supply amount of the raw fuel and water.

The oxidant gas for temperature control supply and combustion supply is supplied from a first oxidant supply pump 34 . The total amount of oxidant gas XT is determined based on the temperature control feed rate and the combustion feed rate. The partial oxidation reforming in the partial oxidation reformer 70 is stopped. The valve control unit 222 controls the first valve 44 to stop the supply of the oxidant gas from the second oxidant supply pump 36 to the partial oxidation reformer 70 .

(6) State during start-up power generation The reformed gas and the oxidant gas flowing into the fuel cell stack 90 are heated by the high-temperature flue gas output from the combustor 74 before flowing into the fuel cell stack 90. be. Therefore, the reformed gas and the oxidant gas raise the temperature of the fuel cell stack 90 . When the stack temperature CB of the fuel cell stack 90 rises, the fuel cell stack 90 starts the start-up power generation just before the stack temperature CB reaches the predetermined temperature C1. A power generation supply amount of oxidant gas is supplied into the power unit 20 . The power generation supply amount is calculated by the first calculator 208 based on the output current value of the fuel cell stack 90 . The power generation supply amount of oxidant gas is supplied from the first oxidant supply pump 34 .

Power generation for startup of the fuel cell stack 90 contributes to temperature rise of the fuel cell stack 90 itself. A supply amount of the oxidant gas for temperature regulation is supplied into the power unit 20 until the stack temperature CB reaches the predetermined temperature C1. The supply amount for temperature control is calculated by the fourth calculator 214 based on the reformer temperature CR. A supply amount of the oxidant gas for temperature control is supplied from the first oxidant supply pump 34 . The total amount XT of the oxidant gas is determined based on the supply amount for power generation and the supply amount for temperature control.

(7) State during normal power generation When the stack temperature CB reaches the predetermined temperature C1, the system state enters the second stage. The fuel cell stack 90 stably performs normal power generation. A power generation supply amount of oxidant gas is supplied into the power unit 20 . The supply amount for power generation is calculated by the first calculator 208 based on the output current value. The power generation supply amount of oxidant gas is supplied from the first oxidant supply pump 34 .

Electric power generation by the fuel cell stack 90 contributes to an increase in the temperature of the fuel cell stack 90 itself. Therefore, the stack temperature CB may exceed the predetermined temperature C1 and further increase. If the stack temperature CB rises, the fuel cell stack 90 may deteriorate. When the fuel cell stack 90 deteriorates, power generation output may decrease. The stack temperature CB may rise as a result of an increase in the amount of fuel supplied so that the power output of the fuel cell stack 90 is maintained. When the stack temperature CB rises, it is necessary to lower the stack temperature CB so as to approach the predetermined temperature C1 by adjusting the stack temperature CB.

A supply amount of the oxidant gas for temperature regulation is supplied into the power unit 20 until the stack temperature CB reaches the predetermined temperature C1. The supply amount for temperature adjustment is calculated by the fourth calculator 214 based on the stack temperature CB. The supply amount of oxidant gas for temperature control is supplied from at least one of the first oxidant supply pump 34 and the second oxidant supply pump 36 . The total amount XT of the oxidant gas is determined based on the supply amount for power generation and the supply amount for temperature control. The oxidant supply amount (first supply amount) from the first oxidant supply pump 34 is determined by multiplying the total amount XT of the oxidant gas by a ratio. The oxidant supply amount (second supply amount) from the second oxidant supply pump 36 is determined by subtracting the first supply amount from the total amount XT of the oxidant gas.

When the temperature control supply amount of oxidant gas is supplied from the second oxidant supply pump 36 , the valve control unit 222 controls the second valve 46 so that the oxidant gas from the second oxidant supply pump 36 is is supplied to the fuel cell stack 90 . When the supply of the oxidant gas from the second oxidant supply pump 36 is stopped, the valve control unit 222 controls the second valve 46 so that the oxidation from the second oxidant supply pump 36 to the fuel cell stack 90 is stopped. Stop the agent gas supply.

(8) State during cooling while reducing generated power When an instruction to stop power generation by the fuel cell stack 90 is given, the system state enters the third stage. Power unit 20 is cooled due to the weakening of power generation. A power generation supply amount of oxidant gas is supplied into the power unit 20 . The supply amount for power generation is calculated by the first calculator 208 based on the output current value. The amount of oxidant gas supplied for power generation is supplied from at least one of the first oxidant supply pump 34 and the second oxidant supply pump 36 . The total amount XT of oxidant gas is determined based on the power generation supply amount. The oxidant supply amount (first supply amount) from the first oxidant supply pump 34 is determined by multiplying the total amount XT of the oxidant gas by a ratio. The oxidant supply amount (second supply amount) from the second oxidant supply pump 36 is determined by subtracting the first supply amount from the total amount XT of the oxidant gas.

(9) Cooling State with Combustor 74 Stopped When an instruction to stop combustion by the combustor 74 is given, the combustor 74 is stopped. Power unit 20 is cooled by the loss of heat generated by combustion. Since the power generation by the fuel cell stack 90 has not completely stopped, the power generation supply amount of the oxidant gas is supplied into the power unit 20 . The supply amount for power generation is calculated by the first calculator 208 based on the output current value. The power generation supply amount of oxidant gas is supplied from the first oxidant supply pump 34 .

The fuel exhaust gas output from the fuel cell stack 90 may contain reformed gas or raw fuel remaining without being electrochemically reacted with the oxidant gas. The reformed gas contains carbon monoxide. The raw fuel contains hydrocarbons. Since combustor 74 is stopped, carbon monoxide or hydrocarbons may be discharged to the outside of power unit 20 without being burned.

In order to prevent this, fuel exhaust gas containing carbon monoxide or hydrocarbons must be diluted with oxidant gas before being discharged. Therefore, the oxidant gas necessary for diluting the fuel exhaust gas is supplied into the power unit 20 . The supply amount for dilution is calculated by the third calculator 212 based on the fuel supply amounts of the raw fuel and water.

A supply of oxidant gas for dilution is supplied from at least one of the first oxidant supply pump 34 and the second oxidant supply pump 36 . The total amount XT of oxidant gas is determined based on the power generation supply amount and the dilution supply amount. The oxidant supply amount (first supply amount) from the first oxidant supply pump 34 is determined by multiplying the total amount XT of the oxidant gas by a ratio. The oxidant supply amount (second supply amount) from the second oxidant supply pump 36 is determined by subtracting the first supply amount from the total amount XT of the oxidant gas.

(10) Power Generation Stopped and Cooling State During the period from the stop of power generation by the fuel cell stack 90 to the stop of supply of the raw fuel and water, carbon monoxide or carbonized carbon monoxide generated from the raw fuel and water vapor Fuel exhaust gases containing hydrogen may be emitted. Therefore, the oxidant gas necessary for diluting the fuel exhaust gas is supplied into the power unit 20 .

The supply amount for dilution is calculated by the third calculator 212 based on the fuel supply amounts of the raw fuel and water. A supply of oxidant gas for dilution is supplied from at least one of the first oxidant supply pump 34 and the second oxidant supply pump 36 . The total amount XT of oxidant gas is determined based on the diluent supply amount. The oxidant supply amount (first supply amount) from the first oxidant supply pump 34 is determined by multiplying the total amount XT of the oxidant gas by a ratio. The oxidant supply amount (second supply amount) from the second oxidant supply pump 36 is determined by subtracting the first supply amount from the total amount XT of the oxidant gas.

(11) Cooling State with Stopped Fuel Supply When the supply of the raw fuel and water is stopped, the power unit 20 is cooled by supplying the temperature control supply amount of the oxidant gas into the power unit 20. . The temperature control supply amount is calculated by the fourth calculator 214 based on the stack temperature CB and the reformer temperature CR. The supply amount of oxidant gas for temperature control is supplied from at least one of the first oxidant supply pump 34 and the second oxidant supply pump 36 . The total amount XT of oxidant gas is determined based on the supply amount for temperature control. Based on the total amount of oxidant gas XT, the oxidant supply amount (first supply amount) from the first oxidant supply pump 34 and the oxidant supply amount (second supply amount) from the second oxidant supply pump 36 are determined. It is determined. For example, the second supply amount may be zero.

FIG. 5 is a diagram showing the basis for calculating the supply amount of the oxidant gas for each type. Of the oxidant gas supply amount, the power generation supply amount is calculated based on the system state of the solid oxide fuel cell system 10 and the output current value of the fuel cell stack 90 . Of the oxidant gas supply amount, the combustion supply amount is determined based on the system state of the solid oxide fuel cell system 10 and the fuel supply amount of the raw fuel and water (fuel) supplied to the fuel cell stack 90. Calculated.

Of the oxidant gas supply amount, the supply amount for dilution is determined based on the system state of the solid oxide fuel cell system 10 and the fuel supply amount of the raw fuel and water (fuel) supplied to the fuel cell stack 90. Calculated. Of the oxidant gas supply amount, the supply amount for temperature control depends on the system state of the solid oxide fuel cell system 10, the catalyst temperature of the exhaust catalyst 80, the stack temperature CB of the fuel cell stack 90, and the partial oxidation reforming It is calculated based on the reformer temperature CR of the reactor 70 and the steam reformer 72 .

FIG. 6 is a flow chart showing a processing procedure for determining the target value of the supply amount of the oxidant gas. This processing procedure is performed, for example, by the processing circuit of the control device 60 executing a program. When this processing procedure is started, the state determination unit 200 determines the system state of the solid oxide fuel cell system 10 in step S400. In step S402, the state determination unit 200 determines whether the system state is in the first stage.

If YES in step S402, the process proceeds to step S404. If NO in step S402, the process proceeds to step S440. In step S<b>404 , the fourth calculator 214 acquires the catalyst temperature of the exhaust catalyst 80 from the catalyst temperature detector 140 . In step S<b>406 , the fourth calculator 214 acquires the reformer temperatures CR of the partial oxidation reformer 70 and the steam reformer 72 from the reformer temperature detector 150 .

In step S<b>408 , the fourth calculator 214 acquires the stack temperature CB of the fuel cell stack 90 from the stack temperature detector 130 . In step S410, the current value determination unit 202 determines the output current value of the fuel cell stack 90 based on the system state and the stack temperature CB. In step S412, the fuel supply amount determination unit 204 determines the fuel supply amounts of raw fuel and water based on the system state, stack temperature CB or reformer temperature CR, and output current value.

In step S414, the first calculator 208 calculates the supply amount for power generation based on the system state and the output current value. In step S416, the second calculator 210 calculates the supply amount for combustion based on the system state and the fuel supply amount. In step S418, the fourth calculator 214 calculates the supply amount for temperature adjustment based on the system state, the catalyst temperature and the reformer temperature CR.

In step S<b>420 , the total amount determining unit 206 determines the total amount XT of oxidant gas supplied to the fuel cell stack 90 . The total amount of oxidant gas (theoretical value of the total oxidant supply amount) XT is determined based on the type of oxidant gas supply amount calculated for each subdivided detailed system state shown in FIG. . In step S422, the total amount determination unit 206 determines the target value of the total amount of oxidant to be supplied. Details of the processing performed in step S422 will be described later using FIG. When the processing of step S422 is completed, this processing procedure ends.

In step S440, state determination unit 200 determines whether the system state is in the second stage. If YES in step S440, the process proceeds to step S442. If NO in step S440, it is determined that the system state is in the third stage, and the process proceeds to step S472. In step S<b>442 , the fourth calculator 214 acquires the stack temperature CB of the fuel cell stack 90 from the stack temperature detector 130 .

At step S444, the current value determination unit 202 determines the output current value of the fuel cell stack 90 based on the system state and the stack temperature CB. In step S446, the first calculator 208 calculates the supply amount for power generation based on the system state and the output current value. In step S448, the fourth calculator 214 calculates the supply amount for temperature adjustment based on the system state and the stack temperature CB.

In step S<b>450 , the total amount determination unit 206 determines the total amount XT of oxidant gas supplied to the fuel cell stack 90 . The total amount of oxidant gas (theoretical value of the total amount of oxidant supplied) XT is determined based on the type of oxidant gas supply amount shown in FIG. In step S452, the ratio determination unit 216 determines the ratio of the oxidant supply amount (first supply amount) from the first oxidant supply pump 34 to the theoretical value of the total oxidant supply amount.

In step S<b>454 , the target value determination unit 218 determines the first target value of the oxidant supply amount (first supply amount) from the first oxidant supply pump 34 and the oxidant supply amount from the second oxidant supply pump 36 . A second target value of (second supply amount) is determined. Details of the processing performed in step S454 will be described later using FIG. When the processing of step S454 is completed, this processing procedure ends.

In step S<b>472 , the fourth calculator 214 acquires the reformer temperature CR of the steam reformer 72 from the reformer temperature detector 150 . In step S<b>474 , the fourth calculator 214 acquires the stack temperature CB of the fuel cell stack 90 from the stack temperature detector 130 .

At step S476, the current value determination unit 202 determines the output current value of the fuel cell stack 90 based on the system state and the stack temperature CB. In step S478, the fuel supply amount determination unit 204 determines the fuel supply amount of raw fuel and water based on the system state, stack temperature CB or reformer temperature CR, and output current value. In step S480, the first calculator 208 calculates the supply amount for power generation based on the system state and the output current value.

In step S482, the third calculator 212 calculates the supply amount for dilution based on the system state and the fuel supply amount. In step S484, the fourth calculator 214 calculates the supply amount for temperature adjustment based on the system state, stack temperature CB and reformer temperature CR.

In step S<b>486 , total amount determination unit 206 determines the total amount XT of oxidant gas supplied to fuel cell stack 90 . The total amount of oxidant gas (theoretical value of the total oxidant supply amount) XT is determined based on the type of oxidant gas supply amount calculated for each subdivided detailed system state shown in FIG. . When the processing of step S486 is completed, the processing procedure advances to the processing of step S452 described above. When the processing of steps S452 and S454 is completed, this processing procedure ends.

FIG. 7 is a flowchart showing a processing procedure for determining the target value of the total amount XT of oxidant gas. FIG. 7 shows the detailed processing contents of step S422 shown in FIG.

In step S600, the total amount determination unit 206 determines whether the theoretical value of the total oxidant supply amount determined in step S420 of FIG. 6 is smaller than the current target value of the total oxidant supply amount. If YES in step S600, the process proceeds to step S602. If NO in step S600, the process proceeds to step S620. The initial value of the target value of the total oxidant supply amount is the lower limit value of the total oxidant supply amount. The lower limit value of the total oxidant supply amount is predetermined according to the control stability of the first oxidant supply pump 34 and the second oxidant supply pump 36 .

In step S602, the total amount determining unit 206 updates the target value to a value obtained by subtracting the predetermined value for subtraction from the current target value of the total oxidant supply amount. In step S604, the total amount determination unit 206 determines whether or not the updated target value is smaller than the above-described lower limit value of the total oxidant supply amount. If YES in step S604, the process proceeds to step S606. If NO in step S604, this processing procedure ends. In step S606, the total amount determining unit 206 re-updates the target value to the lower limit value. When the processing of step S606 is completed, this processing procedure ends.

In step S620, the total amount determination unit 206 updates the target value to a value obtained by adding the predetermined value for addition to the current target value of the total oxidant supply amount. In step S622, the total amount determination unit 206 determines whether or not the updated target value is greater than the upper limit value of the total oxidant supply amount. The upper limit value of the total oxidant supply amount is predetermined according to the design specifications of the first oxidant supply pump 34 and the second oxidant supply pump 36 .

If YES in step S622, the process proceeds to step S624. If NO in step S622, this processing procedure ends. In step S624, the total amount determination unit 206 re-updates the target value to the upper limit value. When the processing of step S624 is completed, this processing procedure ends.

The processing of step S454 shown in FIG. 6 is performed when the system state is in the second stage or the third stage. The processing of step S454 will be described using the case where the system state is in the second stage as an example, but the processing of step S454 is the same even when the system state is in the third stage. FIG. 8A is a diagram schematically showing how the generated power P of the fuel cell stack 90 remains constant regardless of the passage of time T. As shown in FIG. Since the system state is in the second stage, the generated power P is constant.

FIG. 8B is a diagram schematically showing how the stack temperature CB changes as time T elapses. As described above, in the second stage, it is preferable to maintain the stack temperature CB at the predetermined temperature C1 so as not to accelerate deterioration of the fuel cell stack 90 . In the example shown in FIG. 8B, the stack temperature CB is a temperature C0 higher than the predetermined temperature C1. It is necessary to lower the stack temperature CB from the current temperature C0 so as to approach the predetermined temperature C1.

For power generation by the fuel cell stack 90 , a power generation supply of oxidant gas is supplied from at least one of the first oxidant supply pump 34 and the second oxidant supply pump 36 . The oxidant gas supplied from the first oxidant supply pump 34 is heated in the second heat exchanger 78 . When the oxidant gas from the second oxidant supply pump 36 is supplied to the fuel cell stack 90 by opening the second valve 46, the temperature of the oxidant gas is not raised.

Therefore, it is preferable to decrease the ratio of the oxidant supply amount (first supply amount) from the first oxidant supply pump 34 as the stack temperature CB becomes higher than the predetermined temperature C1. As a result, the amount of oxidant supplied from the second oxidant supply pump 36 (second supply amount) increases. Since the oxidant gas from the second oxidant supply pump 36 has a lower temperature than the oxidant gas from the first oxidant supply pump 34, the effect of lowering the stack temperature CB is enhanced.

The ratio of the oxidant supply amount (first supply amount) from the first oxidant supply pump 34 decreases while the total amount XT of the oxidant gas remains unchanged. As a result, the effect of lowering the stack temperature CB can be obtained without increasing the drive power of the first oxidant supply pump 34 and the second oxidant supply pump 36 .

FIG. 8C shows that the oxidant supply amount (first supply amount) XM from the first oxidant supply pump 34 and the oxidant supply amount (second supply amount) XS from the second oxidant supply pump 36 are FIG. 4 is a diagram schematically showing how the total amount XT of the oxidizing gas changes over time and how the total amount XT of the oxidant gas remains constant regardless of the passage of time T;

When the stack temperature CB is a temperature C0 higher than the predetermined temperature C1, the second supply amount XS is greater than the first supply amount XM. Therefore, as the stack temperature CB decreases as the time T elapses, the second supply amount XS decreases and the first supply amount XM increases. When the stack temperature CB drops to a temperature substantially equal to the predetermined temperature C1, the ratio of the first supply amount XM to the total amount XT of the oxidant gas becomes one. At this time, the second supply amount XS is substantially zero, and the first supply amount XM is substantially equal to the total amount XT of the oxidant gas.

As shown in FIG. 8C, the total amount XT of the oxidant gas remains constant regardless of the passage of time T, so the total driving power of the first oxidant supply pump 34 and the second oxidant supply pump 36 increases. to be deterred.

FIG. 9 is a map 300 that defines the correspondence relationship between the ratio RM of the oxidant supply amount (first supply amount) XM from the first oxidant supply pump 34 to the total amount XT of the oxidant gas and the stack temperature CB. It is a figure which illustrates. For reference, FIG. 9 also shows the ratio RS of the oxidant supply amount (second supply amount) XS from the second oxidant supply pump 36 to the total amount XT of the oxidant gas. The sum of the ratio RM and the ratio RS is always 1 regardless of the value of the stack temperature CB.

When the stack temperature CB is equal to the predetermined temperature C1, the ratio RM of the first supply amount XM to the total amount XT of the oxidant gas is one. As the stack temperature CB becomes higher than the predetermined temperature C1, the ratio RM decreases. When the stack temperature CB is equal to or higher than the temperature C2 which is higher than the predetermined temperature C1, the ratio RM is zero. In this case, since the ratio RS is 1, the effect of lowering the stack temperature CB is high.

A map 300 shown in FIG. 9 is stored in the storage unit 250 . When the stack temperature CB exceeds the predetermined temperature C1, the ratio determining unit 216 determines the ratio RM based on the corresponding relationship between the ratio RM defined in the map 300 and the stack temperature CB.

FIG. 10 shows the first target value of the oxidant supply amount (first supply amount) XM from the first oxidant supply pump 34 and the oxidant supply amount (second supply amount) from the second oxidant supply pump 36. 7 is a flow chart showing a processing procedure for determining a second target value of XS; FIG. 10 shows the detailed processing contents of step S454 shown in FIG.

In step S800, the target value determining unit 218 determines the amount of the oxidizing agent supplied from the first oxidizing agent supply pump 34 based on the ratio RM determined by the ratio determining unit 216 and the total amount of oxidizing gas (theoretical value of the total oxidizing agent supply amount) XT. A theoretical value of the oxidant supply amount (first supply amount) XM is determined.

In step S802, the target value determining unit 218 determines whether or not the theoretical value of the first supply amount XM is smaller than the current first target value of the first supply amount XM. If YES in step S802, the process proceeds to step S804. If NO in step S802, the process proceeds to step S820. Note that the initial value of the first target value is the lower limit value of the first supply amount XM. The lower limit value of the first supply amount XM is predetermined according to the control stability of the first oxidant supply pump 34 .

In step S804, the target value determining unit 218 updates the first target value to a value obtained by subtracting the first predetermined value from the current first target value. In step S806, the target value determining unit 218 determines whether or not the updated first target value is smaller than the lower limit value of the first supply amount XM described above. If YES in step S806, the process proceeds to step S808. If NO in step S806, the process proceeds to step S810.

At step S808, the target value determination unit 218 re-updates the first target value to the lower limit value. In step S810, the target value determination unit 218 subtracts the first target value from the theoretical value of the total oxidant supply amount to obtain the oxidant supply amount (second supply amount) XS from the second oxidant supply pump 36. Determine a second target value. When the processing of step S810 is completed, this processing procedure ends.

In step S820, the target value determining unit 218 updates the first target value to a value obtained by adding the second predetermined value to the current first target value. In step S822, the target value determination unit 218 determines whether or not the updated first target value is greater than the upper limit value of the first supply amount XM. The upper limit value of the first supply amount XM is determined in advance according to the design specifications of the first oxidant supply pump 34 .

If YES in step S822, the process proceeds to step S824. If NO in step S822, the process proceeds to step S810. In step S824, the target value determination unit 218 re-updates the first target value to the upper limit value. When the processing of step S824 is completed, the processing procedure advances to the processing of step S810 described above. When the processing of step S810 is completed, this processing procedure ends.

The present invention is not limited to the above-described embodiments, and can take various configurations without departing from the gist of the present invention.

[Invention obtained from the embodiment]
Inventions that can be understood from the above embodiments and modifications will be described below.

(1) A solid oxide fuel cell system (10) comprises a fuel cell stack (90) that generates electricity through an electrochemical reaction between a fuel and an oxidant gas, and a fuel exhaust gas and an oxidant exhaust gas discharged from the fuel cell stack. A combustor (74) that burns and outputs combustion exhaust gas, a stack temperature detector (130) that detects a stack temperature (CB) of the fuel cell stack, and supplies the oxidant gas to the fuel cell stack. a first oxidant supply pump (34); a second oxidant supply pump (36) different from the first oxidant supply pump for supplying the oxidant gas to the fuel cell stack; a heat exchanger (78) for raising the temperature of the oxidant gas supplied by the oxidant supply pump using the combustion exhaust gas before being supplied to the fuel cell stack; When it exceeds the stack temperature, the ratio (RM) of the oxidant supply amount of the oxidant gas from the first oxidant supply pump to the total amount of the oxidant gas (XT) supplied to the fuel cell stack is adjusted to the stack temperature. a first target value of the oxidant supply amount from the first oxidant supply pump and a first target value of the oxidant supply amount from the first oxidant supply pump based on the ratio and the total amount; a target value determination unit (218) for determining a second target value of the oxidant supply amount of the second target value; a pump control unit (220) for controlling the second oxidant supply pump based on the above to supply the oxidant gas from the first oxidant supply pump and the second oxidant supply pump to the fuel cell stack; Prepare. As a result, the effect of lowering the stack temperature can be obtained without increasing the drive power of the first oxidant supply pump and the second oxidant supply pump.

(2) The solid oxide fuel cell system includes a first reformer (70) that reforms the fuel through an oxidation reaction between the fuel and the oxidant gas, and A first valve (44) for switching whether or not to supply the oxidant gas to the first reformer, and to supply the oxidant gas from the second oxidant supply pump to the fuel cell stack. and a valve control section (222) for controlling the first valve and the second valve, wherein the valve control section controls the stack temperature to reach the predetermined temperature and before the fuel is reformed by the first reformer, the first valve and the second valve are controlled so that the oxidation from the second oxidant supply pump is When the oxidant gas is supplied to the first reformer and the stack temperature exceeds the predetermined temperature, the first valve and the second valve are controlled to supply the oxidant from the second oxidant supply pump. Gas may be supplied to the fuel cell stack. As a result, the second oxidant supply pump, which is used for reforming the fuel before power generation by the fuel cell stack starts, can be used to lower the stack temperature after power generation starts. No additional oxidant pump is required to reduce the stack temperature.

(3) The ratio may decrease as the stack temperature rises above the predetermined temperature. This enhances the effect of lowering the stack temperature CB.

(4) The solid oxide fuel cell system further includes a map (300) defining a correspondence relationship between the stack temperature and the ratio, and the ratio determination unit determines the correspondence defined in the map (300). The ratio may be determined based on the relationship. This makes it possible to easily determine the ratio.

(5) When the theoretical value of the oxidant supply amount determined from the ratio and the total amount from the first oxidant supply pump is smaller than the current value of the first target value, the target value determination unit updates the first target value to a value obtained by subtracting a first predetermined value from the current value, and if the theoretical value is greater than the current value, adds a second predetermined value to the current value The first target value may be updated to a value obtained by As a result, the supply of the oxidant gas from the first oxidant supply pump is increased or decreased stepwise, so the fuel cell stack can be protected.

(6) When the theoretical value is smaller than the current value, the target value determination unit determines that the value obtained by subtracting the first predetermined value from the current value is a predetermined lower limit value. if smaller, update the first target value to the lower limit; if the theoretical value is greater than the current value, and the value obtained by adding the second predetermined value to the current value is greater than a predetermined upper limit, the first target value may be updated to the upper limit. This makes it possible to determine the supply amount of the oxidant gas in consideration of the specifications of the first oxidant supply pump.

(7) When updating the first target value, the target value determination unit may update the second target value to a value obtained by subtracting the first target value from the total amount. This makes it possible to easily calculate the amount of oxidant gas supplied by the second oxidant supply pump.

(8) The solid oxide fuel cell system includes a second reformer (72) that reforms the fuel with water vapor, and the fuel through the first reformer and the second reformer. A fuel pump (30, 32) that supplies fuel to the fuel cell stack, an exhaust catalyst (80) that removes impurities from exhaust gas discharged from the fuel cell stack by the electrochemical reaction, and a catalyst temperature of the exhaust catalyst is detected. a catalyst temperature detection unit (140), a reformer temperature detection unit (150) for detecting the reformer temperature (CR) of the first reformer and the second reformer, and the solid oxide fuel At any one of a first stage in which the battery system starts up, a second stage in which the solid oxide fuel cell system performs normal power generation processing, and a third stage in which the solid oxide fuel cell system goes to shutdown. a state determination unit (200) that determines the system state, and a current value determination unit that determines the current value of the current (IC) output from the fuel cell stack based on the system state and the stack temperature. (202) determining a fuel supply amount of the fuel to be supplied to the fuel cell stack by the fuel pump based on the system state, the stack temperature or the reformer temperature, and the current value; A fuel supply amount determination unit (204) determines the total amount based on the stack temperature, the system state, the current value, the fuel supply amount, the catalyst temperature, and the reformer temperature. and a total amount determination unit (206) for determining the total amount. As a result, the total amount of oxidant gas to be supplied can be appropriately determined according to the system state.

(9) The solid oxide fuel cell system is configured to generate power indicating the supply amount of the oxidant gas supplied from the first oxidant supply pump and the second oxidant supply pump for power generation by the fuel cell stack. a first calculator (208) for calculating the amount of fuel supplied based on the system state and the current value; the first oxidant supply pump and the a second calculation unit (210) for calculating a supply amount for combustion indicating the supply amount of the oxidant gas supplied from the second oxidant supply pump based on the system state and the fuel supply amount; The dilution supply amount indicating the supply amount of the oxidant gas supplied from the first oxidant supply pump and the second oxidant supply pump for diluting the fuel exhaust gas discharged from the cell stack is calculated by the system. a third calculator (212) for calculating based on the state and the fuel supply amount; A fourth calculation unit ( 214), wherein the total amount determination unit determines the total amount based on the system state, the supply amount for power generation, the supply amount for combustion, the supply amount for dilution, and the supply amount for temperature control. may As a result, the total amount of oxidant gas to be supplied can be appropriately determined according to the purpose of supply of the oxidant gas.

(10) When the solid oxide fuel cell system is in the first stage, the total amount determining unit determines the total amount based on the supply amount for power generation, the supply amount for combustion, and the supply amount for temperature control. and when the solid oxide fuel cell system is in the second stage, the total amount determining unit determines the total amount based on the power generation supply amount and the temperature control supply amount, and determines the solid oxide fuel When the battery system is in the third stage, the total amount determining unit may determine the total amount based on the power generation supply amount, the dilution supply amount, and the temperature control supply amount. As a result, the total amount of oxidant gas to be supplied can be appropriately determined according to the system state and the application of oxidant gas supply.

DESCRIPTION OF SYMBOLS 10... Solid oxide fuel cell system 20... Power unit 30... Raw fuel supply pump 32... Water supply pump 34... First oxidant supply pump 36... Second oxidant supply pump 40... First flow path 42... Second flow path 44... First valve 46... Second valve 50... Power conditioner system 60... Control device 70... Partial oxidation reformer 72... Steam reformer 74... Combustor 76... First heat exchanger 78... Second heat exchanger 80 Exhaust catalyst 90 Fuel cell stack 100 Ignition device 110 Fuel cell 112 Anode electrode 114 Cathode electrode 116 Electrolyte membrane 120 Fuel gas inlet 122 Oxidant gas inlet 124 Fuel gas outlet 126 Oxidant gas Exit 130 Stack temperature detection unit 140 Catalyst temperature detection unit 150 Reformer temperature detection unit 200 State determination unit 202 Current value determination unit 204 Fuel supply amount determination unit 206 Total amount determination unit 208 First calculation unit DESCRIPTION OF SYMBOLS 210... 2nd calculation part 212... 3rd calculation part 214... 4th calculation part 216... Ratio determination part 218... Target value determination part 220... Pump control part 222... Valve control part 250... Storage part 300... Map

Claims (10)

a fuel cell stack that generates electricity through an electrochemical reaction between a fuel and an oxidant gas;
a combustor that burns fuel exhaust gas and oxidant exhaust gas discharged from the fuel cell stack and outputs combustion exhaust gas;
a stack temperature detection unit that detects the stack temperature of the fuel cell stack;
a first oxidant supply pump that supplies the oxidant gas to the fuel cell stack;
a second oxidant supply pump different from the first oxidant supply pump, which supplies the oxidant gas to the fuel cell stack;
a heat exchanger that raises the temperature of the oxidant gas supplied by the first oxidant supply pump using the flue gas before being supplied to the fuel cell stack;
When the stack temperature exceeds a predetermined temperature, the ratio of the oxidant supply amount of the oxidant gas from the first oxidant supply pump to the total amount of the oxidant gas supplied to the fuel cell stack is set to the stack temperature. a ratio determination unit that determines according to
a first target value of the oxidant supply amount from the first oxidant supply pump and a second target value of the oxidant supply amount from the second oxidant supply pump, based on the ratio and the total amount; A target value determination unit that determines
The first oxidant supply pump is controlled based on the first target value, and the second oxidant supply pump is controlled based on the second target value to convert the oxidant gas into the first oxidant. a pump control unit for causing supply from the supply pump and the second oxidant supply pump to the fuel cell stack;
A solid oxide fuel cell system comprising: A solid oxide fuel cell system according to claim 1,
a first reformer that reforms the fuel by an oxidation reaction between the fuel and the oxidant gas;
a first valve for switching whether to supply the oxidant gas from the second oxidant supply pump to the first reformer;
a second valve for switching whether to supply the oxidant gas from the second oxidant supply pump to the fuel cell stack;
a valve control unit that controls the first valve and the second valve;
further comprising
The valve control unit is
Before the stack temperature reaches the predetermined temperature and during the period in which the fuel is reformed by the first reformer, the first valve and the second valve are controlled to perform the second oxidation process. supplying the oxidizing agent gas from the agent supply pump to the first reformer;
When the stack temperature exceeds the predetermined temperature, the solid oxidizer controls the first valve and the second valve to supply the oxidant gas from the second oxidant supply pump to the fuel cell stack. material fuel cell system. A solid oxide fuel cell system according to claim 2,
A solid oxide fuel cell system, wherein the ratio decreases as the stack temperature increases above the predetermined temperature. The solid oxide fuel cell system according to any one of claims 1 to 3,
a map that defines a correspondence relationship between the stack temperature and the ratio;
further comprising
The solid oxide fuel cell system, wherein the ratio determination unit determines the ratio based on the correspondence defined in the map. The solid oxide fuel cell system according to any one of claims 1 to 4,
The target value determination unit is
When the theoretical value of the oxidant supply amount determined from the ratio and the total amount from the first oxidant supply pump is smaller than the current value of the first target value, the current value is reduced to the first predetermined value updating the first target value to a value obtained by subtracting
if the theoretical value is greater than the current value, updating the first target value to a value obtained by adding a second predetermined value to the current value;
Solid oxide fuel cell system. A solid oxide fuel cell system according to claim 5,
The target value determination unit is
When the theoretical value is smaller than the current value and the value obtained by subtracting the first predetermined value from the current value is smaller than a predetermined lower limit, the lower limit Update the first target value,
When the theoretical value is greater than the current value and the value obtained by adding the second predetermined value to the current value is greater than a predetermined upper limit value, the upper limit value A solid oxide fuel cell system that updates a first target value. A solid oxide fuel cell system according to claim 5 or 6,
The solid oxide fuel cell system, wherein, when updating the first target value, the target value determination unit updates the second target value to a value obtained by subtracting the first target value from the total amount. A solid oxide fuel cell system according to claim 2,
a second reformer that reforms the fuel with steam;
a fuel pump that supplies the fuel to the fuel cell stack through the first reformer and the second reformer;
an exhaust catalyst that removes impurities from the exhaust gas discharged from the fuel cell stack by the electrochemical reaction;
a catalyst temperature detection unit that detects the catalyst temperature of the exhaust catalyst;
a reformer temperature detection unit that detects reformer temperatures of the first reformer and the second reformer;
A first stage in which the solid oxide fuel cell system starts up, a second stage in which the solid oxide fuel cell system performs normal power generation processing, and a third stage in which the solid oxide fuel cell system goes to shutdown. a state determination unit that determines the state of the system indicating which stage it is in;
a current value determination unit that determines a current value of the current output from the fuel cell stack based on the system state and the stack temperature;
A fuel supply amount determination unit that determines a fuel supply amount of the fuel supplied to the fuel cell stack by the fuel pump based on the system state, the stack temperature or the reformer temperature, and the current value. and,
a total amount determining unit that determines the total amount based on the stack temperature, the system state, the current value, the fuel supply amount, the catalyst temperature, and the reformer temperature;
A solid oxide fuel cell system, further comprising: A solid oxide fuel cell system according to claim 8,
The supply amount for power generation indicating the supply amount of the oxidant gas supplied from the first oxidant supply pump and the second oxidant supply pump for power generation by the fuel cell stack is determined by the system state and the current value. a first calculation unit that calculates based on
A combustion supply amount indicating a supply amount of the oxidant gas supplied from the first oxidant supply pump and the second oxidant supply pump for combustion of the fuel exhaust gas discharged from the fuel cell stack, a second calculator that calculates based on the system state and the fuel supply amount;
a supply amount for dilution indicating a supply amount of the oxidant gas supplied from the first oxidant supply pump and the second oxidant supply pump for diluting the fuel exhaust gas discharged from the fuel cell stack, a third calculator that calculates based on the system state and the fuel supply amount;
a temperature control supply indicating a supply amount of the oxidant gas supplied from the first oxidant supply pump and the second oxidant supply pump for regulating the catalyst temperature, the stack temperature and the reformer temperature; a fourth calculation unit that calculates an amount based on the system state, the catalyst temperature, the stack temperature, and the reformer temperature;
further comprising
The solid oxide fuel cell system, wherein the total amount determining unit determines the total amount based on the system state, the supply amount for power generation, the supply amount for combustion, the supply amount for dilution, and the supply amount for temperature control. A solid oxide fuel cell system according to claim 9,
When the solid oxide fuel cell system is in the first stage, the total amount determining unit determines the total amount based on the supply amount for power generation, the supply amount for combustion, and the supply amount for temperature control,
When the solid oxide fuel cell system is in the second stage, the total amount determining unit determines the total amount based on the power generation supply amount and the temperature control supply amount,
When the solid oxide fuel cell system is in the third stage, the total amount determining unit determines the total amount based on the power generation supply amount, the dilution supply amount, and the temperature control supply amount. Oxide fuel cell system.

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