JP7484351B2 - Fuel Cell Systems - Google Patents

Description

The present invention relates to a fuel cell system.

Conventionally, this type of fuel cell system includes a reformer that reforms raw fuel gas with steam, a fuel cell (solid oxide fuel cell) that generates electricity through an electrochemical reaction between the reformed fuel gas reformed in the reformer and air (oxidant), and a blower means that supplies air to the fuel cell, and the blower means is controlled so that the operating temperature of the fuel cell does not exceed a limit temperature (see, for example, Patent Document 1). In this system, by preventing the operating temperature of the fuel cell from exceeding the limit temperature, it is possible to suppress the progression of deterioration of the fuel cell and extend the life of the fuel cell.

Also, a fuel cell system has been proposed that includes a reformer that steam-reforms raw fuel gas, a condenser that recovers water (condensed water) from the steam in the exhaust gas of the fuel cell, and a water tank that stores the condensed water, and reuses the water in the water tank as steam for reforming. When the water level in the water tank is lower than a predetermined set water level, the amount of air supplied to the cathode of the fuel cell is reduced, and when the water level in the water tank is higher than the set water level, the amount of air supplied to the cathode is increased (see, for example, Patent Document 2). In this system, when the water level in the water tank falls below the set water level, the amount of air supplied is reduced below a specified value, thereby increasing the air utilization rate and reducing the amount of exhaust gas from the fuel cell. This increases the amount of water recovered in the water tank, raising the water level in the water tank, and it is said that operation without replenishing water from the outside (water-independent operation) can be stably continued.

JP 2010-114000 A JP 2008-234869 A

In the fuel cell system described in Patent Document 1, when the amount of air supplied to the fuel cell is increased to lower the temperature of the fuel cell, the amount of exhaust gas from the fuel cell increases, which reduces the amount of water collected in the water tank and may make it impossible to continue water-independent operation. On the other hand, in the fuel cell system described in Patent Document 2, when the water level in the water tank is lower than the set water level, the amount of air supplied to the fuel cell (cathode) is reduced, which increases the amount of water collected in the water tank and allows water-independent operation to continue, but this causes the temperature of the fuel cell to rise, which may accelerate the deterioration of the fuel cell.

The main objective of the fuel cell system of the present invention is to provide a fuel cell system that can continue to operate independently of water while suppressing deterioration due to high temperatures of the fuel cell.

The fuel cell system of the present invention employs the following means to achieve the above-mentioned main objective.

The first fuel cell system of the present invention comprises:
a fuel cell that generates electricity using a fuel gas and an oxidant gas;
a reforming unit that reforms a raw fuel gas using steam to generate the fuel gas;
an evaporation section that evaporates reforming water to generate the water vapor;
a reforming water supply device that supplies reforming water stored in a water tank to the evaporator;
an oxidant gas supply device for supplying the oxidant gas to the fuel cell;
a condensation unit that condenses moisture from exhaust gas generated in conjunction with power generation of the fuel cell to generate condensed water and supplies the generated condensed water to the water tank;
a control device that controls the oxidant gas supply device and the reforming water supply device so that, when the temperature of the fuel cell is equal to or higher than a first predetermined temperature and the amount of reforming water stored in the water tank is less than a predetermined amount, the power generation output of the fuel cell is reduced, the amount of the oxidant gas supply is increased until the amount of the oxidant gas supply becomes equal to or higher than a predetermined amount, and when the amount of the oxidant gas supply becomes equal to or higher than the predetermined amount, the amount of the reforming water supply is increased;
The gist of the project is to provide the following:

In the first fuel cell system of the present invention, when the temperature of the fuel cell is equal to or higher than a first predetermined temperature and the amount of reforming water stored in the water tank is less than a predetermined amount, the power generation output of the fuel cell is reduced, and the amount of oxidant gas supplied is increased until the amount of oxidant gas supplied reaches a predetermined amount or more, and when the amount of oxidant gas supplied reaches the predetermined amount or more, the amount of reforming water supplied is increased by controlling the oxidant gas supply device and the reforming water supply device. That is, first, the amount of oxidant gas supplied is increased (supply of excess oxidant gas that does not contribute to power generation) to suppress the temperature rise of the fuel cell, and when the amount of oxidant gas supplied reaches the predetermined amount or more and it becomes difficult to continue water-independent operation, the amount of reforming water supplied is increased, and the latent heat of vaporization when the reforming water evaporates in the evaporation section suppresses the temperature rise of the fuel cell. As a result, a fuel cell system can be obtained that can suppress deterioration due to high temperatures of the fuel cell while continuing water-independent operation.

In the first fuel cell system of the present invention, the control device may control the reforming water supply device to increase the amount of the reforming water supplied when the amount of the oxidant gas supplied becomes equal to or greater than the predetermined amount, until the temperature of the evaporator becomes less than a second predetermined temperature or the steam-to-carbon ratio in the reformer becomes greater than a predetermined ratio. In this way, the amount of the reforming water supplied can be increased within a range in which steam is properly generated in the evaporator. In other words, it is possible to prevent a situation in which the amount of heat required to evaporate the reforming water in the evaporator is insufficient to generate sufficient steam, preventing steam reforming from being performed properly, or a situation in which excessive steam is generated, causing the partial pressure of the steam to become excessive, thereby deteriorating the fuel cell.

The second fuel cell system of the present invention comprises:
a fuel cell that generates electricity using a fuel gas and an oxidant gas;
a reforming unit that reforms a raw fuel gas using steam to generate the fuel gas;
an evaporation section that evaporates reforming water to generate the water vapor;
a reforming water supply device that supplies reforming water stored in a water tank to the evaporator;
an oxidant gas supply device for supplying the oxidant gas to the fuel cell;
a condensation unit that condenses moisture from exhaust gas generated in conjunction with power generation of the fuel cell to generate condensed water and supplies the generated condensed water to the water tank;
a control device which controls the reforming water supply device and the oxidant gas supply device so as to reduce the power output of the fuel cell when the temperature of the fuel cell is equal to or higher than a first predetermined temperature and the amount of reforming water stored in the water tank is less than a predetermined amount, increase the amount of the reforming water supplied until the temperature of the evaporation section becomes less than a second predetermined temperature or the steam-to-carbon ratio in the reforming section becomes greater than a predetermined ratio, and increase the amount of the oxidant gas supplied when the temperature of the evaporation section becomes less than the second predetermined temperature or the steam-to-carbon ratio becomes greater than the predetermined ratio;
The gist of the project is to provide the following:

In the second fuel cell system of the present invention, when the temperature of the fuel cell is equal to or higher than a first predetermined temperature and the amount of reforming water stored in the water tank is less than a predetermined amount, the power output of the fuel cell is reduced, and the amount of reforming water supplied is increased until the temperature of the evaporator falls below a second predetermined temperature or the steam-to-carbon ratio in the reformer exceeds a predetermined ratio. When the temperature of the evaporator falls below the second predetermined temperature or the steam-to-carbon ratio exceeds a predetermined ratio, the amount of oxidant gas supplied is increased by controlling the reforming water supply device and the oxidant gas supply device. That is, first, the amount of reforming water supplied is increased within a range in which water vapor is appropriately generated in the evaporator to suppress the temperature rise of the fuel cell, and when it becomes difficult to supply reforming water within the appropriate range, the amount of oxidant gas supplied is increased (supply of surplus oxidant gas that does not contribute to power generation) to suppress the temperature rise of the fuel cell. As a result, a fuel cell system can be obtained that can suppress deterioration due to high temperatures of the fuel cell while continuing water-independent operation.

In the first or second fuel cell system of the present invention, the control device may increase the amount of reforming water supplied to the evaporation section by a predetermined amount at each predetermined time. In this way, the amount of reforming water can be increased taking into account the response delay until the temperature of the fuel cell drops due to the increase in the amount of reforming water.

1 is a diagram showing an outline of the configuration of a fuel cell system according to an embodiment of the present invention; 5 is a flowchart showing an example of a battery temperature control routine. 5 is a flowchart illustrating an example of a supply switching process according to the first embodiment. 13 is a flowchart illustrating an example of a supply switching process according to a second embodiment. 13 is a flowchart illustrating an example of a supply switching process according to a third embodiment.

The embodiment of the present invention will be described with reference to the drawings.

1 is a schematic diagram of a fuel cell system. As shown in FIG. 1, the fuel cell system 10 of this embodiment includes a power generation module 20 including a fuel cell stack 21 that generates power by an electrochemical reaction between hydrogen in an anode gas (fuel gas) and oxygen in a cathode gas (oxidant gas), a raw fuel gas supply device 30 that supplies raw fuel gas (e.g., natural gas or LP gas) that is a raw material for the anode gas to the power generation module 20, a reforming water supply device 40 that supplies reforming water required for steam reforming of the raw fuel gas into the anode gas to the power generation module 20, an air supply device 50 that supplies air as a cathode gas to the power generation module 20 (fuel cell stack 21), an exhaust heat recovery device 60 for recovering exhaust heat generated in the power generation module 20, and a power conditioner 70 that is connected to the output terminal of the fuel cell stack 21 and is connected to the power line 3 from the power system 2 to the load 4 via a relay. These are housed in a housing 12. The housing 12 is formed with an intake port 12a and an exhaust port 12b, and a ventilation fan 14 is installed near the intake port 12a to take in outside air and ventilate the inside of the housing 12.

The power generation module 20 includes a fuel cell stack 21, a vaporizer 22, and two reformers 23, which are housed in a module case 29 serving as a fuel cell case in this embodiment. In this embodiment, the power generation module 20 has two fuel cell stacks 21, which are installed on a manifold 24 arranged in the module case 29 so as to face each other with a gap between them.

Each fuel cell stack 21 has an electrolyte such as zirconium oxide, an anode electrode and a cathode electrode that sandwich the electrolyte, and has multiple solid oxide type single cells arranged in the left-right direction (horizontal direction) in FIG. 1. An anode gas passage (not shown) is formed in the anode electrode of each single cell so as to extend in a direction perpendicular to the arrangement direction of the single cells, i.e., in the vertical direction. In addition, a cathode gas passage (not shown) for circulating cathode gas is formed around the cathode electrode of each single cell so as to extend in a direction perpendicular to the arrangement direction of the single cells, i.e., in the vertical direction. The anode gas passage of each single cell is connected to the manifold 24, and the cathode gas passage of each single cell is connected to the air passage in the module case 29. Furthermore, a temperature sensor 94 is installed between (near) the two fuel cell stacks 21 so that the distance between them is the same. The temperature sensor 94 detects a temperature T4 that correlates with the temperature of each fuel cell stack 21.

The vaporizer 22 and reformer 23 of the power generation module 20 are disposed above the two fuel cell stacks 21 in the module case 29 at a distance from each other. In this embodiment, the vaporizer 22 and one reformer 23 are disposed above one fuel cell stack 21, and the other reformer 23 is disposed above the other fuel cell stack 21. Furthermore, between the one fuel cell stack 21 and the vaporizer 22 and one reformer 23, and between the other fuel cell stack 21 and the other reformer 23, combustion sections 25 are defined to generate heat required for the operation of the fuel cell stack 21 and the reactions in the vaporizer 22 and reformer 23. An ignition heater 26 is installed in each combustion section 25.

The vaporizer 22 heats the raw fuel gas from the raw fuel gas supply device 30 and the reforming water from the reforming water supply device 40 using heat from the combustion section 25, preheating the raw fuel gas and evaporating the reforming water to generate steam. The raw fuel gas preheated by the vaporizer 22 is mixed with steam, and the mixed gas flows from the vaporizer 22 into the reformer 23. The reformer 23 is also provided with a temperature sensor 91 that detects the temperature T1 of the mixed gas flowing into the reformer 23.

The reformer 23 has a Ru-based or Ni-based reforming catalyst filled therein, and generates hydrogen gas and carbon monoxide by a reaction (steam reforming reaction) of the mixed gas from the vaporizer 22 with the reforming catalyst in the presence of heat from the combustion section 25. Furthermore, the reformer 23 generates hydrogen gas and carbon dioxide by a reaction (carbon monoxide shift reaction) between the carbon monoxide generated in the steam reforming reaction and steam. As a result, the reformer 23 generates anode gas containing hydrogen, carbon monoxide, carbon dioxide, steam, unreformed raw fuel gas, etc. The anode gas generated by the reformer 23 flows into the anode gas passage of each single cell via the piping and manifold 24 and is supplied to the anode electrode.

Air is supplied as a cathode gas to the cathode electrode of each unit cell of the fuel cell stack 21 through an air passage formed in the module case 29. Oxide ions ( _O2- ) are generated at the cathode electrode of each unit cell, and the oxide ions pass through the electrolyte and react with hydrogen and carbon monoxide at the anode electrode to generate electric energy. The anode gas (hereinafter referred to as "anode off-gas ^" ) and cathode gas (hereinafter referred to as "cathode off-gas") that are not used in the electrochemical reaction (power generation) in each unit cell flow out from the anode gas passage and cathode gas passage of each unit cell to the combustion section 25 above.

The anode offgas that flows into the combustion section 25 from each unit cell is a combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the cathode offgas that contains oxygen that flows into the combustion section 25 from each unit cell. Hereinafter, the mixed gas of the anode offgas and the cathode offgas is referred to as "offgas". When the offgas (anode offgas) is ignited by the ignition heater 26 in the combustion section 25, the combustion of the offgas generates heat required for the operation of the fuel cell stack 21, preheating the raw fuel gas in the vaporizer 22, generating steam, and the steam reforming reaction in the reformer 23. In addition, in the combustion section 25, a combustion exhaust gas containing unburned fuel and steam is generated, and the combustion exhaust gas is supplied to the heat exchanger 62 via the combustion catalyst 27. The combustion catalyst 27 is an oxidation catalyst for reburning the unburned fuel in the combustion exhaust gas. Furthermore, in the gas passage in which the combustion catalyst 27 is provided, a catalyst heater 28 for warming up the combustion catalyst 27 and a temperature sensor 98 for detecting the temperature T8 of the combustion exhaust gas are installed.

The raw fuel gas supply device 30 has a raw fuel gas supply pipe 31 that connects the raw fuel supply source 1 that supplies the raw fuel gas to the vaporizer 22, and on-off valves (two valves) 32, 33, an orifice 34, a gas pump 35, and a desulfurizer 36 built into the raw fuel gas supply pipe 31. By operating the gas pump 35, the raw fuel gas is pumped (supplied) from the raw fuel supply source 1 to the vaporizer 22 via the desulfurizer 36. The desulfurizer 36 is configured as, for example, a room temperature desulfurization type desulfurizer, and is installed so as to be in contact with the module case 29. In addition, between the on-off valve 33 and the orifice 34 of the raw fuel gas supply pipe 31, a pressure sensor 37 that detects the pressure inside the raw fuel gas supply pipe 31 and a flow rate sensor 38 that detects the flow rate per unit time of the raw fuel gas flowing through the raw fuel gas supply pipe 31 (gas flow rate Qg) are installed.

The reforming water supply device 40 has a reforming water tank 42 that stores reforming water, a reforming water supply pipe 41 that connects the reforming water tank 42 and the vaporizer 22, and a reforming water pump 43 built into the reforming water supply pipe 41. The reforming water in the reforming water tank 42 is pumped (supplied) to the vaporizer 22 by the reforming water pump 43 by operating the reforming water pump 43. A water purifier (not shown) that purifies the stored reforming water is installed in the reforming water tank 42. In addition, a water level sensor 44 (e.g., a float switch) is installed in the reforming water tank 42 to detect the water level of the stored reforming water.

The air supply device 50 has an air supply pipe 51 connected to an air passage formed in the module case 29, an air filter 52 provided at the inlet of the air supply pipe 51, and an air pump 53 built into the air supply pipe 51. By operating the air pump 53, air as cathode gas is sucked into the air supply pipe 51 through the air filter 52, and is pressure-fed (supplied) to each fuel cell stack 21 via the air passage in the module case 29.

The exhaust heat recovery device 60 has a hot water tank 63 for storing hot water, a heat exchanger 62 for exchanging heat between the hot water and the combustion exhaust gas generated in the combustion section 25 of the power generation module 20, a circulation pipe 61 for connecting the hot water tank 63 and the heat exchanger 62, and a circulation pump 64 incorporated in the circulation pipe 61. The hot water stored in the hot water tank 63 is introduced into the heat exchanger 62 by operating the circulation pump 64, and is heated by heat exchange with the combustion exhaust gas in the heat exchanger 62, and then returned to the hot water tank 63. In addition, although not shown, the exhaust heat recovery device 60 also has a radiator incorporated in the circulation pipe 61, a radiator fan (electric fan) that sends air to the radiator, an electric heater (e.g., a ceramic heater) that consumes surplus electricity from the power generation module 30 to heat the hot water in the circulation pipe 61, and a thermistor (temperature sensor) that detects the temperature of the hot water heated by the electric heater.

The heat exchanger 62 of the exhaust heat recovery device 60 is connected to the reforming water tank 42 via a pipe 66, and the condensed water obtained by condensing the water vapor in the combustion exhaust gas through heat exchange with hot water is introduced into the reforming water tank 42 via the pipe 66. Furthermore, the combustion exhaust gas passage of the heat exchanger 62 is connected to a combustion exhaust gas exhaust pipe 67. As a result, the exhaust gas discharged from the combustion section 25 of the power generation module 20 and from which moisture has been removed by the heat exchanger 62 is discharged into the atmosphere via the combustion exhaust gas exhaust pipe 67.

The power conditioner 70 has a DC/DC converter that converts the DC voltage output from the fuel cell stack 21 to a predetermined voltage (e.g., DC 250V to 300V), and an inverter that converts the converted DC voltage to an AC voltage (e.g., AC 200V) that can be connected to the power grid 2. A current sensor (not shown) that detects the current I output from the fuel cell stack 21 is provided at the output terminal of the fuel cell stack 21, and a voltage sensor (not shown) that detects the terminal-to-terminal voltage of the fuel cell stack 21 is provided between the output terminals of the fuel cell stack 21. The power conditioner 70 controls the switching of switching elements provided in the DC/DC converter and inverter so that a current corresponding to the required power generation required for the system is output from the fuel cell stack 21.

A power supply board 72 is connected to the power line branched off from the power conditioner 70. The power supply board 72 converts the DC voltage from the fuel cell stack 21 and the AC voltage from the power system 2 into a DC voltage suitable for the operation of the auxiliary equipment and supplies it to the auxiliary equipment. In the embodiment, examples of the auxiliary equipment include the ventilation fan 14, the on-off valves 32 and 33, the gas pump 35, the reforming water pump 43, the air pump 53, and the circulation pump 64.

The control device 80 is configured as a microprocessor centered on a CPU 81, and in addition to the CPU 81, includes a ROM 82 for storing processing programs, a RAM 83 for temporarily storing data, a timer 84 for measuring time, and an input/output port (not shown). Various detection signals from the pressure sensor 37, flow sensor 38, water level sensor 44, temperature sensors 91, 94, 98, etc. are input to the control device 80 via the input port. In addition, the control device 80 outputs various control signals to the fan motor of the ventilation fan 14, the solenoids of the on-off valves 32 and 33, the pump motor of the gas pump 35, the pump motor of the reformed water pump 43, the pump motor of the air pump 53, the pump motor of the circulation pump 64, the DC/DC converter and inverter of the power conditioner 70, the power supply board 72, the ignition heater 26, the catalytic heater 28, etc. via the output port.

Next, the operation of the fuel cell system 10 of the present embodiment thus configured will be described. In this embodiment, the supply amounts of raw fuel gas, reforming water, and air are controlled so that the target current Itag corresponding to the required power generation output required for the system is output from the fuel cell stack 21. The supply amount of raw fuel gas is controlled by setting a target gas flow rate Qgtag in which the gas flow rate corresponding to the target current Itag is corrected to the increasing side based on the fuel utilization rate Uf, and controlling the gas pump 35 so that the gas flow rate Qg detected by the flow sensor 38 matches the set target gas flow rate Qgtag. The supply amount of reforming water is controlled by setting a target reforming water flow rate Qwtag so that the steam carbon ratio SC (the molar ratio of carbon contained in the hydrocarbons in the raw fuel gas and the steam added for steam reforming) in the reformer 23 matches a predetermined target ratio SCtag, and controlling the reforming water pump 43 so that reforming water at the set target reforming water flow rate Qwtag is supplied. The amount of air supplied is controlled by setting a target air flow rate Qtag through feedback control so that the temperature T4 detected by the temperature sensor 94 coincides with a predetermined target temperature T4tag, and by controlling the air pump 53 so that air is supplied at the set target air flow rate Qtag.

Next, the operation for maintaining (adjusting) the temperature of the fuel cell stack 21 within the appropriate range will be described. FIG. 2 is a flowchart showing an example of a battery temperature control routine executed by the CPU 81 of the control device 80. This routine is executed repeatedly at predetermined time intervals.

When the battery temperature control routine is executed, the CPU 81 of the control device 80 first inputs data necessary for control, such as the water temperature T4 from the temperature sensor 94 and the water level Lw from the water level sensor 44 (step S100). Next, it is determined whether the execution flag F is 0 (step S110). Here, the execution flag F indicates whether the supply switching process described later is being executed, and if it is 0, it indicates that the supply switching process is not being executed, and if it is 1, it indicates that the supply switching process is being executed. If it is determined that the execution flag F is 0, it is determined whether the temperature T4 is equal to or higher than a predetermined temperature Tref (e.g., a temperature slightly higher than the target temperature T4tag) (step S120), and whether the water level Lw is less than a predetermined water level Lref (e.g., a water level slightly lower than the upper limit water level of the reforming water tank 42) (step S130). That is, it is determined whether the temperature of the fuel cell stack 21 has risen and the amount of reforming water in the reforming water tank 42 has decreased. If it is determined that the temperature T4 is not equal to or higher than the predetermined temperature Tref, the battery temperature control routine is terminated. If it is determined that the temperature T4 is equal to or higher than the predetermined temperature Tref and the water level Lw is not less than the predetermined water level Lref, the amount of air supplied to the fuel cell stack 21 is increased so that the temperature rise of the fuel cell stack 21 is suppressed by air (step S140), and the battery temperature control routine is terminated. In this embodiment, the amount of air supplied is controlled by setting the target air flow rate Qtag by feedback control so that the temperature T4 detected by the temperature sensor 94 coincides with the target temperature T4tag. Therefore, when the temperature T4 is equal to or higher than the predetermined temperature Tref, the feedback control acts to increase the amount of air supplied.

On the other hand, if it is determined that the temperature T4 is equal to or higher than the predetermined temperature Terf and the water level Lw is lower than the predetermined water level Lref, the power generation output of the fuel cell stack 21 is reduced to reduce the amount of heat generated by the fuel cell stack 21 (step S150), the execution flag F is set to a value of 1 (step S160), and a supply switching process is executed to switch between the supply of reforming water and the supply of air so as to suppress a rise in the temperature of the fuel cell stack 21 while maintaining water-independent operation in which water is not replenished from the outside to the reforming water tank 42 (step S170), and the battery temperature control routine is terminated.

Here, when the amount of air supplied to the fuel cell stack 21 is increased, the amount of fuel exhaust gas generated in the combustion section 25 also increases, and the amount of water carried away into the atmosphere as exhaust gas (gas with 100% humidity) increases, so that the amount of water carried away into the atmosphere is greater than the amount of reforming water input, and the amount of reforming water in the reforming water tank 42 decreases. Therefore, if the amount of air supplied is increased for a long period of time to keep the temperature of the fuel cell stack 21 below the predetermined temperature Tref, there is a risk that the reforming water in the reforming water tank 42 will be insufficient and water self-sustaining operation will not be able to continue. Therefore, in this embodiment, when the temperature T4 is equal to or higher than the predetermined temperature Terf and the water level Lw is less than the predetermined water level Lref, the power generation output of the fuel cell stack 21 is reduced to reduce the amount of heat generated, and if the temperature of the fuel cell stack 21 still rises, a supply switching process is executed to suppress the temperature rise of the fuel cell stack 21 while continuing water self-sustaining operation. Details of the supply switching process will be described later.

After the supply switching process is executed, when the battery temperature control routine is executed in the next control cycle, it is determined in step S110 that the execution flag F is set to a value of 1, and it is then determined whether the temperature T4 is less than the predetermined temperature Tref (step S180) and whether the water level Lw is equal to or greater than the predetermined water level Lref (step S190). In other words, it is determined whether the temperature of the fuel cell stack 21 has dropped and the amount of reforming water in the reforming water tank 42 has recovered. The predetermined temperature used in step S180 may be set to a temperature lower than the predetermined temperature used in step S120. If it is determined that the temperature T4 is not less than the predetermined temperature Tref or that the water level Lw is not equal to or greater than the predetermined water level Lref, the supply switching process is continued (step S170) and the battery temperature control routine is terminated. On the other hand, if it is determined that the temperature T4 is less than the predetermined temperature Tref and the water level Lw is equal to or greater than the predetermined water level Lref, the timer 84 determines whether or not this state has continued for a predetermined time (step S210). If it has not continued for the predetermined time, the supply switching process continues (step S170) and the battery temperature control routine ends. If it is determined that the state has continued for the predetermined time, the power generation output of the fuel cell stack 21 is restored (step S210), the execution flag F is set to 0 (step S220), and the battery temperature control routine ends.

Figure 3 is a flowchart showing an example of the supply switching process of the first embodiment. In the supply switching process of the first embodiment, the CPU 81 first inputs the flow rate of air supplied from the air pump 53 (air flow rate Qa) (step S300). In the fuel cell system 10 of this embodiment, the air supply device 50 does not have a flow rate sensor that detects the flow rate of air flowing through the air supply pipe 51, so the process of step S300 is performed by inputting the target air flow rate Qtag of the air pump 53 as the air flow rate Qa. Of course, if the air supply device 50 is equipped with a flow rate sensor, the flow rate detected by the flow rate sensor may be input as the air flow rate Qa.

Next, it is determined whether the input air flow rate Qa is equal to or greater than a predetermined flow rate Qaref (step S310). Here, the predetermined flow rate Qaref is a threshold value for determining whether the amount of water carried away into the atmosphere as exhaust gas is equal to or greater than the amount of reforming water input, and a flow rate determined in advance through experiments is set. Therefore, the determination in step S310 can be said to be a determination as to whether or not it will be difficult to continue water-independent operation if the state in which the amount of air supply is increased further is continued. If it is determined that the air flow rate Qa is not equal to or greater than the predetermined flow rate Qaerf, the amount of air supply is increased (step S320) and the supply switching process is terminated. Note that the increase in the amount of air supply is due to the action of feedback control for matching the temperature T4 detected by the temperature sensor 94 to the target temperature T4tag, as in step S140 of the battery temperature control routine described above. When the supply switching process is terminated, the process returns to the battery temperature control routine and the battery temperature control routine is terminated.

On the other hand, if it is determined that the air flow rate Qa is equal to or greater than the predetermined flow rate Qaref, it is determined whether the increase in the amount of reforming water supply is the first time (in step S310 of the previously executed supply switching process, it was determined that the air flow rate Qa is not equal to or greater than the predetermined flow rate Qaref) (step S330), and if it is the first time, the amount of reforming water supply is increased by a predetermined amount (step S350), and the supply switching process is terminated. The increase in the amount of reforming water supply is performed by setting a new target reforming water flow rate Qwtag by adding a predetermined amount ΔQw to the previous target reforming water flow rate Qwtag, and controlling the reforming water pump 43 with the set new target reforming water flow rate Qwtag. As a result, the temperature rise of the fuel cell stack 21 is suppressed by the latent heat of vaporization when the reforming water is vaporized in the vaporizer 22. When the supply switching process is terminated, the process returns to the battery temperature control routine, and the battery temperature control routine is terminated. Then, when the supply switching process is continued in the battery temperature control routine executed in the next control cycle, it is determined in step S330 that it is not the first time, and then the timer 84 determines whether or not a predetermined time has passed since the previous increase (step S340). If it is determined that the predetermined time has not passed since the previous increase, the supply switching process is terminated as is, and if it is determined that the predetermined time has passed since the previous increase, the flow rate of the reforming water is increased by a predetermined amount again (step S350), and the supply switching process is terminated. That is, in the first embodiment, when the air flow rate Qa is equal to or greater than the predetermined flow rate Qaref, the supply rate of the reforming water is increased by a predetermined amount each time a predetermined time has passed. This is done in consideration of the relatively long response delay that occurs between the increase in the supply rate of the reforming water and the temperature of the fuel cell stack 21 decreasing after this response delay time has been taken into consideration.

In this way, in the first embodiment, when the temperature T4 is equal to or higher than the predetermined temperature Terf and the water level Lw is lower than the predetermined water level Lref, the power generation output of the fuel cell stack 21 is lowered, and the amount of air supply is increased until the air flow rate Qa is equal to or higher than the predetermined flow rate Qaref, and after the air flow rate Qa is equal to or higher than the predetermined flow rate Qaref, the amount of reforming water supply is increased. This makes it possible to suppress the temperature rise of the fuel cell stack 21 while continuing water-independent operation by switching between the supply of air and the supply of reforming water. In addition, by managing the water level in the reforming water tank 42 so that water-independent operation can be continued, the radiator and radiator fan for promoting condensation of water vapor in the combustion exhaust gas in the heat exchanger 62 can be made smaller.

Figure 4 is a flowchart showing an example of the supply switching process of the second embodiment. In the supply switching process of the second embodiment, the CPU 81 first inputs the temperature T1 (temperature of the vaporizer 22) detected by the temperature sensor 91 (step S400), and determines whether the input temperature T1 is equal to or higher than a predetermined temperature T1ref (step S410), and whether the current steam-carbon ratio SC (target ratio SCtag) is equal to or lower than the predetermined ratio SCref (step S420). Here, the predetermined temperature T1ref is set near the lower limit temperature in the temperature range in which the vaporizer 22 can properly vaporize the reforming water. In addition, the predetermined ratio SCref is set near the upper limit ratio in the range of steam-carbon ratios in which the reformer 23 can properly perform steam reforming. When it is determined that the temperature T1 is equal to or higher than the predetermined temperature T1ref and the current steam-carbon ratio SC is equal to or lower than the predetermined ratio SCref, it is determined whether the increase in the amount of reforming water is the first time (step S430). If it is the first time, the supply amount of reforming water is increased by a predetermined amount (step S450), and the supply switching process is terminated. On the other hand, if it is not the first time, it is determined whether a predetermined time has elapsed since the previous increase (step S440). If it is determined that the predetermined time has not elapsed, the supply switching process is terminated as it is, and if it is determined that the predetermined time has elapsed, the supply amount of reforming water is increased by a predetermined amount again (step S450), and the supply switching process is terminated. That is, in the second embodiment, when the temperature T1 is equal to or higher than the predetermined temperature T1ref and the steam-carbon ratio SC is equal to or lower than the predetermined ratio SCref, the supply amount of reforming water is increased by a predetermined amount each time a predetermined time has elapsed.

On the other hand, if the temperature T1 is not equal to or higher than the predetermined temperature T1ref, the reforming water cannot be properly vaporized in the vaporizer 22 if the reforming water is further increased. If the current steam-carbon ratio SC is not equal to or lower than the predetermined ratio SCref, it is determined that if the reforming water is further increased, excessive water vapor will be generated in the vaporizer 22, causing the water vapor partial pressure to become excessive, which may cause deterioration of the fuel cell stack 21. The amount of air supplied is increased so that the temperature rise of the fuel cell stack 21 is suppressed by supplying air instead of the supply of reforming water (step S460), and the supply switching process is terminated. The increase in the amount of air supplied is due to the action of feedback control to make the temperature T4 detected by the temperature sensor 94 coincide with the target temperature T4tag, as in step S140 of the battery temperature control routine described above.

In this way, in the second embodiment, when the temperature T4 is equal to or higher than the predetermined temperature Terf and the water level Lw is less than the predetermined water level Lref, the power generation output of the fuel cell stack 21 is lowered and the amount of reforming water supplied is increased until the temperature T1 becomes less than the predetermined temperature T1ref or the steam carbon ratio SC (target ratio SCtag) becomes greater than the predetermined ratio SCref, and after the temperature T1 becomes less than the predetermined temperature T1ref or the steam carbon ratio SC (target ratio SCtag) becomes greater than the predetermined ratio SCref, the amount of air supplied is increased. This makes it possible to suppress the temperature rise of the fuel cell stack 21 while continuing water-independent operation by switching between the supply of air and the supply of reforming water.

Figure 5 is a flowchart showing an example of the supply switching process of the third embodiment. In the supply switching process of the third embodiment, the CPU 81 first inputs the flow rate of air supplied from the air pump 53 (air flow rate Qa) and the temperature T1 detected by the temperature sensor 91 (step S500). Next, it is determined whether the input air flow rate Qa is equal to or greater than the predetermined flow rate Qaref (step S510). The predetermined flow rate Qaref has been described above. If it is determined that the air flow rate Qa is not equal to or greater than the predetermined flow rate Qaerf, the amount of air supplied is increased (step S520) and the supply switching process is terminated. The increase in the amount of air supplied is due to the action of feedback control for matching the temperature T4 detected by the temperature sensor 94 with the target temperature T4tag, as in step S140 of the battery temperature control routine described above. When the supply switching process is terminated, the process returns to the battery temperature control routine and the battery temperature control routine is terminated.

On the other hand, if it is determined that the air flow rate Qa is equal to or greater than the predetermined flow rate Qaref, it is determined whether the input temperature T1 is equal to or greater than the predetermined temperature T1ref (step S530), and whether the current steam carbon ratio SC (target ratio SCtag) is equal to or less than the predetermined ratio SCref (step S540). The predetermined temperature T1ref and the predetermined ratio SCref have been described above. If it is determined that the temperature T1 is equal to or greater than the predetermined temperature T1ref and that the current steam carbon ratio SC is equal to or less than the predetermined ratio SCref, it is determined whether the increase in the amount of reforming water is the first time (step S550). If it is the first time, the supply amount of reforming water is increased by a predetermined amount (step S570), and the supply switching process is terminated. On the other hand, if it is not the first time, it is determined whether a predetermined time has passed since the previous increase (step S560). If it is determined that the predetermined time has not passed, the supply switching process is terminated as it is, and if it is determined that the predetermined time has passed, the supply amount of reforming water is increased by a predetermined amount again (step S570), and the supply switching process is terminated.

In this way, in the third embodiment, when the temperature T4 is equal to or higher than the predetermined temperature Terf and the water level Lw is lower than the predetermined water level Lref, the power generation output of the fuel cell stack 21 is lowered and the amount of air supply is increased until the air flow rate Qa is equal to or higher than the predetermined flow rate Qaref, and after the air flow rate Qa is equal to or higher than the predetermined flow rate Qaref, the amount of reforming water supply is increased until the temperature T1 is lower than the predetermined temperature T1ref or the steam-carbon ratio SC (target ratio SCtag) is greater than the predetermined ratio SCref. In this way, by switching between the supply of air and the supply of reforming water, it is possible to suppress the temperature rise of the fuel cell stack 21 while continuing water-independent operation.

The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem will be explained. In the embodiment, the fuel cell stack 21 corresponds to the "fuel cell", the reformer 23 corresponds to the "reforming section", the vaporizer 22 corresponds to the "evaporation section", the reforming water supply device 40 corresponds to the "reforming water supply device", the air supply device 50 corresponds to the "oxidizer gas supply device", the heat exchanger 62 corresponds to the "condensation section", and the control device 80 corresponds to the "control device".

The correspondence between the main elements of the embodiment and the main elements of the invention described in the Means for Solving the Problem column does not limit the elements of the invention described in the Means for Solving the Problem column, since the embodiment is an example for specifically explaining the form for implementing the invention described in the Means for Solving the Problem column. In other words, the interpretation of the invention described in the Means for Solving the Problem column should be based on the description in that column, and the embodiment is merely a specific example of the invention described in the Means for Solving the Problem column.

The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment in any way, and it goes without saying that the present invention can be carried out in various forms without departing from the spirit of the present invention.

The present invention can be used in the fuel cell system manufacturing industry, etc.

1 raw fuel supply source, 2 power system, 3 power line, 4 load, 10 fuel cell system, 12 housing, 12a intake port, 12b exhaust port, 14 ventilation fan, 20 power generation module, 21 fuel cell stack, 22 vaporizer, 23 reformer, 24 manifold, 25 combustion section, 26 ignition heater, 27 combustion catalyst, 28 catalytic heater, 29 module case, 30 raw fuel gas supply device, 31 raw fuel gas supply pipe, 32, 33 opening and closing valve, 34 orifice, 35 gas pump, 36 desulfurizer, 37 pressure sensor, 38 flow sensor, 40 reforming water supply device, 41 reforming water supply pipe, 42 reforming water tank, 43 reforming water pump, 50 air supply device, 51 air supply pipe, 52 air filter, 53 air pump, 60 exhaust heat recovery device, 61 Circulation piping, 62 heat exchanger, 63 hot water tank, 64 circulation pump, 66 piping, 67 combustion exhaust gas exhaust pipe, 70 power conditioner, 72 power supply board, 80 control device, 81 CPU, 82 ROM, 83 RAM, 84 timer, 91, 94, 98 temperature sensor.

Claims (4)

a fuel cell that generates electricity using a fuel gas and an oxidant gas;
a reforming unit that reforms a raw fuel gas using steam to generate the fuel gas;
an evaporation section that evaporates reforming water to generate the water vapor;
a reforming water supply device that supplies reforming water stored in a water tank to the evaporator;
an oxidant gas supply device for supplying the oxidant gas to the fuel cell;
a condensation unit that condenses moisture from exhaust gas generated in conjunction with power generation of the fuel cell to generate condensed water and supplies the generated condensed water to the water tank;
a control device that controls the oxidant gas supply device and the reforming water supply device so that, when the temperature of the fuel cell is equal to or higher than a first predetermined temperature and the amount of reforming water stored in the water tank is less than a predetermined amount, the power generation output of the fuel cell is reduced, the amount of the oxidant gas supply is increased until the amount of the oxidant gas supply becomes equal to or higher than a predetermined amount, and when the amount of the oxidant gas supply becomes equal to or higher than the predetermined amount, the amount of the reforming water supply is increased;
Equipped with
The control device increases the amount of reforming water supplied to the evaporation section by a predetermined amount at every predetermined time . 2. The fuel cell system according to claim 1,
when the supply amount of the oxidant gas becomes equal to or greater than the predetermined amount, the control device controls the reforming water supply device to increase the supply amount of the reforming water until the temperature of the evaporator section becomes lower than a second predetermined temperature or the steam-to-carbon ratio in the reforming section becomes greater than a predetermined ratio.
Fuel cell system. a fuel cell that generates electricity using a fuel gas and an oxidant gas;
a reforming unit that reforms a raw fuel gas using steam to generate the fuel gas;
an evaporation section that evaporates reforming water to generate the water vapor;
a reforming water supply device that supplies reforming water stored in a water tank to the evaporator;
an oxidant gas supply device for supplying the oxidant gas to the fuel cell;
a condensation unit that condenses moisture from exhaust gas generated in conjunction with power generation of the fuel cell to generate condensed water and supplies the generated condensed water to the water tank;
a control device which controls the reforming water supply device and the oxidant gas supply device so as to reduce the power output of the fuel cell when the temperature of the fuel cell is equal to or higher than a first predetermined temperature and the amount of reforming water stored in the water tank is less than a predetermined amount, increase the amount of the reforming water supplied until the temperature of the evaporation section becomes less than a second predetermined temperature or the steam-to-carbon ratio in the reforming section becomes greater than a predetermined ratio, and increase the amount of the oxidant gas supplied when the temperature of the evaporation section becomes less than the second predetermined temperature or the steam-to-carbon ratio becomes greater than the predetermined ratio;
A fuel cell system comprising: 4. The fuel cell system according to claim 3 ,
When increasing the amount of reforming water supplied to the evaporation section, the control device increases the amount by a predetermined amount at every predetermined time.
Fuel cell system.

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