JP7396176B2 - fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

Conventionally, this type of fuel cell system includes a fuel cell that generates electricity using reformed gas containing hydrogen and air, a reforming section that generates reformed gas by steam reforming raw material for reforming, and a reforming section that generates reformed gas by steam reforming the reforming raw material. A desulfurizer that removes the sulfur component contained in the gas with hydrogen and supplies it to the reforming section, a raw material pump installed in the reforming raw material supply pipe that supplies the reforming raw material to the desulfurizer, and a reforming raw material The supply pipe is connected to the reformed gas supply pipe that supplies reformed gas from the reformer to the fuel cell, and a part of the reformed gas is returned to the desulfurizer as recycled fuel via the recycled gas pipe and the air supply pipe. A system has been proposed that includes an air blower that supplies air to the fuel cell using a fuel cell, and a combustion section that heats a reforming section by burning off gas from the fuel cell (for example, see Patent Document 1).

JP2017-62973A

In a fuel cell system that recirculates (recycles) a portion of the fuel that flows out of the reforming section, there is a risk that the condition of the fuel cell or combustion section may deteriorate if the amount of fuel supplied to the desulfurizer is changed. . For example, when starting the system, the supply of fuel to the desulfurizer is started according to a predetermined supply amount so that the air and fuel in the combustion section have an air-fuel ratio (target value) suitable for ignition (the amount of fuel supplied is (increased), part of the supplied fuel is recirculated, so the fuel flow rate flowing to the combustion section becomes temporarily smaller than the supplied fuel flow rate. In this case, the air-fuel ratio in the combustion section becomes larger than the target value, resulting in poor combustibility (ignitability).

The fuel cell system of the present invention recirculates a portion of the fuel that has flowed out from the reforming section, and even when changing the amount of fuel supplied to the reforming section, it maintains the condition of the fuel cell and the combustion section in good condition. The main objective is to provide a fuel cell system that can.

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

The fuel cell system of the present invention includes:
A fuel cell that generates electricity using fuel gas containing hydrogen and air;
a reforming unit that reforms raw fuel gas to generate the fuel gas and supplies the generated fuel gas to the fuel cell;
a desulfurizer that desulfurizes sulfur components contained in the raw fuel gas using hydrogen and supplies it to the reforming section;
a raw fuel gas supply device that supplies the raw fuel gas to the desulfurizer;
an air supply device that supplies the air to the fuel cell;
a combustion section that burns off gas from the fuel cell;
A portion of the fuel flowing out from the reforming section by connecting a raw fuel gas flow path through which the raw fuel gas flows to the desulfurizer and a fuel gas supply path through which the fuel gas flows from the reforming section to the fuel cell. a reflux path for refluxing the water to the desulfurizer;
When the reflux amount, which is the flow rate of reflux gas returned from the reforming section to the desulfurizer via the reflux path, changes, the air-fuel ratio in the fuel cell or the combustion section does not deviate from the appropriate range. a control device that corrects the supply amount of the raw fuel gas or the air;
The main point is to have the following.

In the fuel cell system of the present invention, when the reflux amount, which is the flow rate of reflux gas returned from the reforming section to the desulfurizer via the reflux path, changes, the air-fuel ratio in the fuel cell or the combustion section deviates from the appropriate range. Correct the supply amount of raw fuel gas or oxidizer gas so that it does not come off. Thereby, even if the amount of fuel supplied to the reforming section is changed, the air-fuel ratio in the fuel cell or the combustion section can be made appropriate, and the conditions of the fuel cell or the combustion section can be improved.

In such a fuel cell system of the present invention, when setting the flow rate correction value for correcting the supply amount, the control device may increase the flow rate correction value as the amount of change in the recirculation amount increases. . In this way, the air-fuel ratio in the fuel cell and the combustion section can be brought to a more appropriate state, and the conditions of the fuel cell and the combustion section can be maintained in a good state.

Further, in the fuel cell system of the present invention, when setting the flow rate correction value for correcting the supply amount, the control device sets an initial value to the flow rate correction value when the recirculation amount changes. The flow rate correction value may be gradually decreased toward a value of 0 with the passage of time. In this way, the flow rate correction value can be set to zero with the convergence of the change in the reflux amount through simple processing.

Furthermore, the fuel cell system of the present invention includes a temperature sensor that detects the temperature of the reflux gas flowing through the reflux path, and the control device controls the temperature detected by the temperature sensor when the reflux amount changes. The amount of supply may be corrected when the amount of change in is equal to or greater than a predetermined amount. In this way, it is possible to determine whether or not the amount of recirculation of fuel gas has changed without using a flow meter.

1 is a schematic configuration diagram of a fuel cell system. It is a flowchart which shows an example of a flow rate correction process. FIG. 3 is an explanatory diagram showing an example of a map for setting an air flow rate correction value. FIG. 7 is an explanatory diagram showing how the temperature THT10, target air flow rate Qatag, air flow rate correction value δa, and target gas flow rate Qgtag change over time at the time of system startup. It is a flow chart which shows an example of flow rate correction processing concerning other embodiments. It is an explanatory view showing an example of a map for setting a gas flow rate correction value. FIG. 7 is an explanatory diagram showing how the temperature THT10, target air flow rate Qatag, target gas flow rate Qgtag, and gas flow rate correction value δg change over time at the time of system startup.

Embodiments for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a fuel cell system. As shown in FIG. 1, the fuel cell system 10 of this embodiment includes a fuel cell stack 21 that generates electricity through an electrochemical reaction between hydrogen in an anode gas (fuel gas) and oxygen in a cathode gas (oxidant gas). a power generation module 20 including a power generation module 20; a raw fuel gas supply device 30 that supplies raw fuel gas (for example, natural gas or LP gas) that is a raw material for anode gas to the power generation module 20; The reformed water supply device 40 supplies reformed water necessary for steam reforming, the air supply device 50 supplies air as cathode gas to the power generation module 20 (fuel cell stack 21), and the power generation module 20 An exhaust heat recovery device 60 for recovering exhaust heat, and a power conditioner 70 connected to the output terminal of the fuel cell stack 21 and connected to the power line 3 from the power system 2 to the load 4 via a relay. , is provided. 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 that serves as the fuel cell case of this embodiment. In this embodiment, the power generation module 20 has two fuel cell stacks 21, and the two fuel cell stacks 21 are installed on a manifold 24 arranged in a module case 29 so as to face each other with a gap between them. be done.

Each fuel cell stack 21 includes an electrolyte such as zirconium oxide, an anode electrode and a cathode electrode that sandwich the electrolyte, and a plurality of solid oxide monomers arranged in the left-right direction (horizontal direction) in FIG. It has a cell. An anode gas passage (not shown) is formed in the anode electrode of each unit cell so as to extend in a direction perpendicular to the arrangement direction of the unit cells, that is, in a vertical direction. Further, around the cathode electrode of each unit cell, a cathode gas passage (not shown) through which cathode gas flows is formed so as to extend in a direction perpendicular to the arrangement direction of the unit cells, that is, in a 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 an air passage within the module case 29. Further, a temperature sensor 94 is installed between (near) the two fuel cell stacks 21 so that the distance therebetween is the same. Temperature sensor 94 detects 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 arranged above the two fuel cell stacks 21 in the module case 29 with a space therebetween. In this embodiment, a vaporizer 22 and one reformer 23 are arranged above one fuel cell stack 21, and the other reformer 23 is arranged above the other fuel cell stack 21. Further, between the fuel cell stack 21 on one side and the vaporizer 22 and the reformer 23 on the other hand, and between the other fuel cell stack 21 and the other reformer 23, there are , a combustion section 25 that generates the heat necessary for the reaction in the vaporizer 22 and reformer 23 is defined. 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 reformed water from the reformed water supply device 40 using heat from the combustion section 25, preheats the raw fuel gas, and converts the reformed water into evaporates to produce water vapor. The raw fuel gas preheated by the vaporizer 22 is mixed with water vapor, and the mixed gas flows from the vaporizer 22 into the reformer 23 . Furthermore, a temperature sensor 91 is installed in the reformer 23 to detect the temperature T1 of the mixed gas flowing into the reformer 23.

The reformer 23 has, for example, a Ru-based or Ni-based reforming catalyst filled therein, and in the presence of heat from the combustion section 25, the reforming catalyst reacts the mixed gas from the vaporizer 22. Hydrogen gas and carbon monoxide are generated by (steam reforming reaction). Furthermore, the reformer 23 generates hydrogen gas and carbon dioxide by a reaction between carbon monoxide generated in the steam reforming reaction and steam (carbon monoxide shift reaction). As a result, the reformer 23 generates an anode gas containing hydrogen, carbon monoxide, carbon dioxide, water vapor, unreformed raw fuel gas, and the like. The anode gas generated by the reformer 23 flows into the manifold 24 through a pipe 23p connecting the reformer 23 and the manifold 24, and is distributed from the manifold 24 to the anode gas passage of each unit cell. , is supplied to the anode electrode of each single cell.

Furthermore, air as a cathode gas is supplied to the cathode electrode of each single cell of the fuel cell stack 21 through an air passage formed in the module case 29 . Oxide ions (O ₂ ⁻ ) 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, thereby obtaining electrical 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 for electrochemical reactions (power generation) in each single cell are stored in the anode gas passage and cathode gas of each single cell. It flows out from the passage to the combustion section 25 above.

The anode off-gas that has flowed into the combustion section 25 from each single cell is a flammable gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the cathode off-gas containing oxygen that has flowed into the combustion section 25 from each single cell. . Hereinafter, the mixed gas of anode offgas and cathode offgas will be referred to as "offgas." Then, when the off-gas (anode off-gas) is ignited by the ignition heater 26 and ignited in the combustion section 25, the combustion of the off-gas causes the operation of the fuel cell stack 21, the preheating of raw fuel gas in the vaporizer 22, and the generation of water vapor. Heat necessary for generation, steam reforming reaction in the reformer 23, etc. will be generated. Further, in the combustion section 25 , combustion exhaust gas containing unburned fuel and water vapor 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 unburned fuel in the combustion exhaust gas. Further, in the gas passage where 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 includes a raw fuel gas supply pipe 31 that connects the raw fuel supply source 1 that supplies raw fuel gas and the vaporizer 22, and an on-off valve (2) built into the raw fuel gas supply pipe 31. (connection valves) 32, 33, an orifice 34, a gas pump 35, and a desulfurizer 36. The raw fuel gas is pumped (supplied) from the raw fuel supply source 1 to the vaporizer 22 via the desulfurizer 36 by operating the gas pump 35 . Further, between the on-off valve 33 and the orifice 34 of the raw fuel gas supply pipe 31, there is a pressure sensor 37a that detects the pressure inside the raw fuel gas supply pipe 31, and a unit of raw fuel gas flowing through the raw fuel gas supply pipe 31. A flow rate sensor 37b is installed to detect the flow rate per hour (gas flow rate Qg).

In this embodiment, the desulfurizer 36 is configured to be filled with a hydrodesulfurization agent, reacts a sulfur compound with hydrogen to convert it into hydrogen sulfide, and removes the converted hydrogen sulfide by adsorption. . Hydrogen required for the desulfurization reaction is provided by recycling (refluxing) the fuel gas generated in the reformer 23 to the desulfurizer 36 via the recycle gas pipe 38. That is, the recycled gas pipe 38 branches from the pipe 23p connecting the reformer 23 and the manifold 24, and is installed so as to be connected between the orifice 34 of the raw fuel gas supply pipe 31 and the gas pump 35, A part of the fuel that has flowed out of the reformer 23 is sucked into the gas pump 35 via the recycle gas pipe 38 as recycle gas (reflux gas), and is pressure-fed (supplied) to the desulfurizer 36 by the gas pump 35 . An orifice 39 is incorporated into the recycle gas pipe 38. Furthermore, a temperature sensor 99 is installed near the entrance of the recycle gas pipe 38 to detect the temperature THT10 of the recycle gas within the recycle gas pipe 38.

The reformed water supply device 40 is assembled into a reformed water tank 42 that stores reformed water, a reformed water supply pipe 41 that connects the reformed water tank 42 and the vaporizer 22, and the reformed water supply pipe 41. and a reforming water pump 43. The reformed water in the reformed water tank 42 is pumped (supplied) to the vaporizer 22 by the reformed water pump 43 by operating the reformed water pump 43 .

The air supply device 50 includes an air supply pipe 51 connected to an air passage formed in the module case 29, an air filter 52 provided at the entrance of the air supply pipe 51, and an air pump incorporated in the air supply pipe 51. 53. By operating the air pump 53, air as a cathode gas is sucked into the air supply pipe 51 via the air filter 52, and is forcefully sent (supplied) to each fuel cell stack 21 through the air passage in the module case 29. Ru.

The exhaust heat recovery device 60 includes a hot water storage tank 63 that stores hot water, a heat exchanger 62 that exchanges heat between the combustion exhaust gas generated in the combustion section 25 of the power generation module 20 and the hot water, and the hot water storage tank 63 and the heat exchanger 62. and a circulation pump 64 built into the circulation pipe 61. The hot water stored in the hot water storage tank 63 is introduced into the heat exchanger 62 by operating the circulation pump 64, and after being raised in temperature by heat exchange with combustion exhaust gas in the heat exchanger 62, the hot water is stored in the hot water storage tank 63. It is returned to tank 63. Water vapor in the combustion exhaust gas is condensed by heat exchange with hot water in the heat exchanger 62, thereby obtaining condensed water.

Further, the heat exchanger 62 of the exhaust heat recovery device 60 is connected to the reformed water tank 42 via a pipe 66, and the condensed water obtained by condensing water vapor in the combustion exhaust gas is The reformed water is introduced into the reformed water tank 42 via. Further, 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 discharge pipe 67.

The power conditioner 70 includes a DC/DC converter that converts the DC voltage output from the fuel cell stack 21 into a predetermined voltage (for example, DC 250V to 300V), and an AC converter that can connect the converted DC voltage to the power system 2. It has an inverter that converts the voltage (for example, AC 200V). The output terminal of the fuel cell stack 21 is provided with a current sensor (not shown) that detects the current I output from the fuel cell stack 21. A voltage sensor (not shown) is provided to detect voltage. The power conditioner 70 performs switching control on switching elements included in the DC/DC converter and the inverter so that the fuel cell stack 21 outputs a current corresponding to the required generated power required by the system.

A power supply board 72 is connected to a power line branched 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 the DC voltage to the auxiliary equipment. In the embodiment, examples of auxiliary equipment include the ventilation fan 14, the on-off valves 32 and 33, the gas pump 35, the reformed water pump 43, the air pump 53, and the circulation pump 64.

The control device 80 is configured as a microprocessor centered around a CPU 81, and includes, in addition to the CPU 81, a ROM 82 for storing processing programs, a RAM 83 for temporarily storing data, a timer 84 for measuring time, and a non-volatile memory (not shown). It includes a digital memory and an input/output port (not shown). Various detection signals from the pressure sensor 37a, flow rate sensor 37b, temperature sensors 91, 94, 98, 99, etc. are input to the control device 80 via input ports. The control device 80 also controls 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, and the pump motor of the circulation pump 64. , various control signals to the DC/DC converter and inverter of the power conditioner 70, the power supply board 72, the ignition heater 26, the catalyst heater 28, etc. are outputted via the output port.

Next, the operation of the fuel cell system 10 of this embodiment configured in this manner will be described. When system startup is requested, the CPU 81 of the control device 80 performs a fuel adsorption process to adsorb fuel components to the desulfurizer 36, a purge process to purge the inside of the combustion section 25 by supplying air, and a process to supply fuel and air to the combustion section 25. and a steam reforming process in which raw fuel gas and reformed water are supplied to the vaporizer 22 and a steam reforming reaction is caused in the reformer 23. Boot the system. Here, the ignition process is performed by controlling the gas pump 35 and the air pump 53 by setting the target gas flow rate Qgtag and the target air flow rate Qatag so that the air-fuel ratio of the mixed gas in the combustion section 25 becomes a predetermined target ratio. This is done by controlling the ignition heater 26 to ignite the mixed gas in the section 25. The target ratio in the ignition process is set to an air-fuel ratio smaller than the stoichiometric air-fuel ratio in the initial stage of ignition in order to improve ignitability, and after ignition is gradually increased so as to approach the stoichiometric air-fuel ratio as time passes.

When the system startup is completed, the CPU 81 controls the supply amount of raw fuel gas, reformed water, and air so that the target current Itag corresponding to the required power generation output required by the system is output from the fuel cell stack 21. and start generating electricity. The supply amount of the raw fuel gas is controlled by setting a target gas flow rate Qgtag, which is the gas flow rate corresponding to the target current Itag corrected to the increasing side based on the fuel utilization rate Uf, so that the gas flow rate Qg detected by the flow rate sensor 37b is This is done by controlling the gas pump 35 to match the set target gas flow rate Qgtag. The supply amount of reformed water is controlled by predetermining the steam carbon ratio SC (molar ratio of carbon contained in hydrocarbons in raw fuel gas to steam added for steam reforming) in the reformer 23. The target reforming water flow rate Qwtag is set based on the target gas flow rate Qgtag so as to match the target ratio SCtag, and the reforming water pump 43 is controlled so that the reformed water of the set target reforming water flow rate Qwtag is supplied. It is done by doing. To control the air supply amount, a target air flow rate Qatag is set by feedback control so that the temperature T4 detected by the temperature sensor 94 matches a predetermined target temperature T4tag, and air of the set target air flow rate Qatag is supplied. This is done by controlling the air pump 53 so that the

When a system stop is requested during power generation, the CPU 81 determines the extent to which the fuel cell stack 21 (electrodes) will not deteriorate due to oxidation in a high temperature atmosphere until the temperature T4 detected by the temperature sensor 94 becomes equal to or lower than the stop permission temperature. The gas pump 35 is controlled by setting the flow rate (constant flow rate) as the target gas flow rate Qgtag, and the air pump 53 is controlled by setting the flow rate (constant flow rate) necessary for cooling the fuel cell stack 21 as the target air flow rate Qatag. do. Then, when the temperature T4 becomes lower than the stop permission temperature, the gas pump 35 and the air pump 53 are stopped to stop the system.

Next, the operation when the flow rate of combustion gas flowing through the recycle gas pipe 38 changes will be explained. FIG. 2 is a flowchart illustrating an example of a flow rate correction process executed by the CPU 81 of the control device 80. This process is repeatedly executed at predetermined time intervals, for example, when the system is started (ignited), when power is generated, and when the system is stopped.

When the flow rate correction process is executed, the CPU 81 of the control device 80 first inputs the temperature THT10 (the temperature of the recycle gas flowing through the recycle gas pipe 38) from the temperature sensor 99 (step S100). Subsequently, the temperature change amount ΔTHT10 is calculated by subtracting the previously input temperature (previous THT10) from the currently input temperature THT10 (step S110).

Next, it is determined whether the execution flag F is 0 (step S120). The execution flag F is a flag indicating whether or not air flow rate correction, which will be described later, is being executed; a value of 0 indicates that it is not being executed, and a value of 1 indicates that it is being executed. If it is determined that the execution flag F is 0, it is determined whether the temperature change amount ΔTHT10 is greater than or equal to the predetermined change amount ΔTref (step S130). The predetermined amount of change ΔTref is a threshold value for determining whether the flow rate of the recycle gas flowing through the recycle gas pipe 38 has changed to the increase side. In this embodiment, the reformer 23 is heated by heat generated by combustion of off-gas in the combustion section 25, and high-temperature gas (recycle gas) from the reformer 23 flows into the recycle gas pipe 38, so that the reformer 23 is recycled. There is a correlation between gas temperature and flow rate (recycle amount). Therefore, it is possible to determine whether the flow rate of the recycle gas has changed to the increase side based on the amount of change in the temperature THT10 (amount of temperature change ΔTHT10) detected by the temperature sensor 99 installed in the recycle gas pipe 38. .

If it is determined in step S130 that the temperature change amount ΔTHT10 is not equal to or greater than the predetermined change amount ΔTref, it is determined that flow rate correction is not necessary, and the flow rate correction process is ended. On the other hand, if it is determined that the temperature change amount ΔTHT10 is greater than or equal to the predetermined change amount ΔTref, the execution flag F is set to a value of 1 (step S140). Then, the air flow rate correction value δa is set based on the temperature change amount ΔTHT10 (step S150), and the target air flow rate Qatag is corrected by subtracting the set air flow rate correction value δa from the target air flow rate Qatag (step S150). S160), the flow rate correction process ends.

In this embodiment, the air flow rate correction value δa is set by determining the relationship between the temperature change amount ΔTHT10 and the air flow rate correction value δa in advance and storing it in the ROM 82 as a map for setting the air flow rate correction value. When the amount of change ΔTHT10 is given, this is done by deriving the corresponding air flow rate correction value δa from the map. An example of the air flow rate correction value setting map is shown in FIG. As shown in the figure, the air flow rate correction value δa is set to increase as the temperature change amount ΔTHT10 increases. That is, the target air flow rate Qatag is corrected so that the larger the temperature change amount ΔTHT10 is (the larger the change amount in the recycle gas flow rate is toward the increase side), the larger the target air flow rate Qatag is reduced.

As mentioned above, the recycle gas pipe 38 branches from the pipe 23p connecting the reformer 23 and the manifold 24 and is connected to the raw fuel gas supply pipe 31, and is used to collect the fuel that has flowed out from the reformer 23. The ratio r [%] of the flow rate (recycled amount) of fuel recycled via the recycle gas pipe 38 in the flow rate is determined by the pressure drop difference between the pipe 23p and the recycle gas pipe 38. In such a system, when the amount of fuel supplied to the power generation module 20 (vaporizer 22) is increased by a predetermined amount a, the recycled amount increases by an amount (a×r/100) according to the above-mentioned ratio r. The flow rate of fuel from the fuel cell stack 21 toward the fuel cell stack 21 momentarily increases by only a×(1−r/100) with respect to the increased amount a of fuel supplied to the power generation module 20. Therefore, even if the amount of fuel supplied to the power generation module 20 is controlled so that the air-fuel ratio in the combustion section 25 reaches the target value at the time of system startup (at the time of ignition), the amount of fuel supplied increases (the amount of fuel supplied (starting), the air-fuel ratio deviates from the target value, resulting in poor combustibility (ignitability). Furthermore, during power generation, in addition to the air-fuel ratio in the combustion section 25 deviating from the target value, the fuel utilization rate in the fuel cell stack 21 changes, and the voltage output from the fuel cell stack 21 (stack voltage) decreases. There is also a possibility that In this embodiment, when the recycle amount changes to the increase side, the occurrence of the above-described problem can be suppressed by setting the target air flow rate Qatag corrected to the decrease side so that the air-fuel ratio does not deviate from the appropriate range.

When the flow rate correction process is executed after setting the execution flag F to the value 1, a negative determination ("NO") is made in step S120. A new air flow rate correction value δa is set by subtracting a predetermined value α from the flow rate correction value δa (step S170), and it is determined whether the set air flow rate correction value δa is larger than the value 0 (step S180). ). If it is determined that the air flow rate correction value δa is larger than the value 0, the process proceeds to step S160, where the target air flow rate Qatag is corrected by subtracting the air flow rate correction value δa from the target air flow rate Qatag, and the flow rate correction process is ended. . In this embodiment, since the flow rate correction process is repeatedly executed at predetermined time intervals, the air flow rate correction value δa is gradually decreased by the predetermined value α toward the value 0. The recycle gas recycled to the raw fuel gas supply pipe 31 via the recycle gas pipe 38 is again pressure-fed (supplied) to the desulfurizer 36 by the gas pump 35, so the increased amount of recycling increases the fuel cell stack 21 and the combustion section. The shortage of fuel flow rate that occurs at 25 is temporary and will subside over time. The reason why the air flow rate correction value δa is gradually decreased toward the value 0 is to adjust the air flow rate in accordance with the end of the fuel flow shortage. As a result of gradually decreasing the air flow rate correction value δa by the predetermined value α in this way, when the air flow rate correction value δa becomes 0 or less in step S180, the execution flag F is set to 0 in order to end the execution of the flow rate correction. (Step S190), the flow rate correction process ends.

FIG. 4 is an explanatory diagram showing how the temperature THT10, the target air flow rate Qatag, the air flow rate correction value δa, and the target gas flow rate Qgtag change over time at the time of system startup (at the time of ignition). At the time of ignition, the gas pump 35 and the air pump 53 are controlled by setting the target gas flow rate Qgtag and the target air flow rate Qatag to predetermined constant amounts, respectively, so that the air-fuel ratio in the combustion section 25 reaches a target value. When the supply of fuel (raw fuel gas) is started at the target gas flow rate Qgtag (fixed amount) (time t11), a part of the fuel flowing out from the reformer 23 is recycled (refluxed) to the raw fuel gas supply pipe 31. Therefore, the amount of recycling increases and the temperature THT10 rises. At this time, an air flow rate correction value δa is set according to the amount of change in temperature THT10 (temperature change amount ΔTHT10), and the target air flow rate Qatag is reduced by the air flow rate correction value δa (time t12). Thereby, the air-fuel ratio in the combustion section 25 is maintained at the target value. Thereafter, as the increase in the recycle amount converges, the air flow rate correction value δa gradually decreases toward the value 0, and the target air flow rate Qatag is returned to the original target air flow rate Qatag (time t13). Note that in the figure, the value of the target air flow rate Qatag after convergence is larger than the initial value because, as mentioned above, in the ignition process, the air-fuel ratio at the initial stage of ignition is kept relatively small in order to improve ignition performance. This is to gradually bring the air-fuel ratio closer to the stoichiometric air-fuel ratio in order to suppress the generation of carbon monoxide as ignition progresses.

In the fuel cell system 10 of this embodiment described above, the desulfurizer 36 desulfurizes the sulfur component contained in the raw fuel gas using hydrogen and supplies it to the reformer 23, and the raw fuel gas flows to the desulfurizer 36. A recycle gas pipe 38 connects the raw fuel gas supply pipe 31 and a pipe 23p through which fuel gas flows from the reformer 23 to the fuel cell stack 21 and recirculates a part of the combustion from the reformer 23 to the desulfurizer 36. , when the flow rate (recycled amount) of fuel returned from the reformer 23 to the desulfurizer 36 via the recycled gas pipe 38 changes, the air-fuel ratio in the fuel cell stack 21 or the combustion section 25 changes. The target air flow rate Qatag is corrected by setting the air flow rate correction value δa so as not to deviate from the appropriate range. As a result, even if the amount of fuel supplied to the reformer 23 is changed, the air-fuel ratio in the fuel cell stack 21 and the combustion section 25 is made appropriate, and the conditions of the fuel cell stack 21 and the combustion section 25 are improved. be able to.

Furthermore, in the fuel cell system 10 of this embodiment, when the recycle amount changes, the initial value of the air flow rate correction value δa is set based on the amount of change in the recycle amount, and the air flow rate correction value δa is adjusted as time passes. Gradually decrease toward the value 0. As a result, the air flow rate correction value δa can be set to 0 with a simple process as the change in the recycle amount converges.

Furthermore, in the fuel cell system 10 of the present embodiment, when the amount of change in the temperature THT10 (amount of temperature change ΔTHT10) detected by the temperature sensor 99 installed in the recycled gas pipe 38 exceeds the predetermined amount of change ΔTref, the target Correct the air flow rate Qatag. Thereby, it is not necessary to install a highly accurate flow meter in the recycled gas pipe 38, and it is possible to reduce costs.

In the embodiment described above, the amount of air supplied to the fuel cell stack 21 (target air flow rate Qatag) is corrected when the recycling amount changes, but the amount of raw fuel gas supplied (target gas flow rate Qgtag) is corrected. It may be corrected. FIG. 5 is a flowchart illustrating an example of flow rate correction processing according to another embodiment. Note that among the flow rate correction processing in FIG. 5, the same steps as those in FIG. 2 are given the same step numbers, and the explanation thereof will be omitted since it is redundant. In the flow rate correction process according to this other embodiment, when it is determined in step S120 that the execution flag F is 0, and in the subsequent step S130 it is determined that the temperature change amount ΔTHT10 is greater than or equal to the predetermined change amount ΔTref, in step S140 After setting the execution flag F to a value of 1, the gas flow rate correction value δg is set based on the temperature change amount ΔTHT10 (step S200), and the target gas flow rate correction value δg is added to the target gas flow rate Qgtag. The gas flow rate Qgtag is corrected (step S210). Further, a target reforming water flow rate Qwtag is set based on the target gas flow rate Qgtag corrected so that the steam carbon ratio SC in the reformer 23 becomes the target ratio SCtag (step S220), and the flow rate correction process is ended.

In this embodiment, the gas flow rate correction value δg is set by determining the relationship between the temperature change amount ΔTHT10 and the gas flow rate correction value δg in advance and storing it in the ROM 82 as a map for setting the gas flow rate correction value. When the amount of change ΔTHT10 is given, this is done by deriving the corresponding gas flow rate correction value δg from the map. An example of the gas flow rate correction value setting map is shown in FIG. As shown in the figure, the gas flow rate correction value δg is set to increase as the temperature change amount ΔTHT10 increases. That is, the target gas flow rate Qgtag is corrected so that the larger the temperature change amount ΔTHT10 is, the larger the target gas flow rate Qgtag is increased. In this way, when the recycled amount increases, setting the corrected target gas flow rate Qgtag to the increasing side so that the air-fuel ratio does not go out of the appropriate range reduces the deterioration of combustibility in the combustion section 25 and the fuel cell stack 21. Fluctuations in usage rates can be suppressed.

When the flow rate correction process is executed after setting the execution flag F to the value 1, a negative determination ("NO") is made in step S120, so next, the gas set in the previous flow rate correction process is The value obtained by subtracting the predetermined value β from the flow rate correction value δg is set as a new gas flow rate correction value δg (step S230), and it is determined whether the set gas flow rate correction value δg is larger than the value 0 (step S240). ). If it is determined that the gas flow rate correction value δg is larger than the value 0, the process proceeds to step S210, where the target gas flow rate Qgtag is corrected by adding the gas flow rate correction value δg to the target gas flow rate Qgtag, and the steam carbon ratio SC is set to the target ratio. The target reforming water flow rate Qwtag is set based on the target gas flow rate Qgtag corrected to be SCtag (steps S210, S220), and the flow rate correction process is ended. Since the flow rate correction process is repeatedly executed at predetermined time intervals, the gas flow rate correction value δg is gradually decreased by the predetermined value β toward the value 0. As a result of gradually decreasing the gas flow rate correction value δg by the predetermined value β in this way, when the gas flow rate correction value δg becomes less than or equal to 0 in step S240, the execution flag F is set to 0 in order to end the execution of the flow rate correction. (Step S190), the flow rate correction process ends.

FIG. 7 is an explanatory diagram showing how the temperature THT10, target air flow rate Qatag, target gas flow rate Qgtag, and gas flow rate correction value δg change over time at the time of system startup. At the time of ignition, the gas pump 35 and the air pump 53 are controlled by setting the target gas flow rate Qgtag and the target air flow rate Qatag to predetermined constant amounts, respectively, so that the air-fuel ratio in the combustion section 25 reaches a target value. When the supply of fuel (raw fuel gas) is started at the target gas flow rate Qgtag (fixed amount) (time t21), a part of the fuel flowing out from the reformer 23 is recycled (refluxed) to the raw fuel gas supply pipe 31. Therefore, the amount of recycling increases and the temperature THT10 rises. At this time, a gas flow rate correction value δg is set according to the amount of change in temperature THT10 (temperature change amount ΔTHT10), and the target gas flow rate Qgtag is increased by the gas flow rate correction value δg (time t22). Thereby, the air-fuel ratio in the combustion section 25 is maintained at the target value. Thereafter, as the increase in the recycle amount converges, the gas flow rate correction value δg gradually decreases toward the value 0, and the target gas flow rate Qgtag is returned to the original target gas flow rate Qgtag (time t23).

In the embodiment described above, the target air flow rate Qatag and the target gas flow rate Qgtag are corrected when the recycle amount changes to the increase side. However, the target air flow rate Qatag and the target gas flow rate Qgtag may be corrected even when the recycle amount changes to the reduction side. When correcting the target air flow rate Qatag, the air flow rate correction value δa is set so as to increase as the amount of change in the recycle amount increases toward the reduction side (the more the temperature change amount ΔTHT10 is less than the value 0 and is larger as an absolute value). A new target air flow rate Qatag may be set by adding the air flow rate correction value δa to the target air flow rate Qatag. In addition, when correcting the target gas flow rate Qgtag, the gas flow rate correction value δg is set so that it becomes larger as the amount of change in the recycle amount increases toward the reduction side (the more the temperature change amount ΔTHT10 is less than the value 0 and is larger as an absolute value). At the same time, a new target gas flow rate Qgtag may be set by subtracting the gas flow rate correction value δg from the target gas flow rate Qgtag.

In the embodiment described above, the air flow rate correction value δa and the gas flow rate correction value δg are assumed to be gradually decreased toward the value 0 with the passage of time after the initial values are set. The value may be set to vary from the initial value to the value 0 based on the value. That is, the air flow rate correction value δa and the gas flow rate correction value δg may be set so that, after the initial values are set, they approach the value 0 as the amount of change in the recycling amount approaches the value 0.

In the embodiment described above, the temperature THT10 detected by the temperature sensor 99 installed in the recycle gas pipe 38 was used as a parameter correlated to the amount of recycle, but the temperature THT10 is not limited to this. By installing a pressure sensor in 38, the pressure detected by the pressure sensor (recycle gas pressure) may be used, or the temperature of the recycle gas pipe 38 may be used. Of course, a flow rate sensor may be installed in the recycled gas pipe 38, and the recycled amount may be directly detected by the flow rate sensor.

The correspondence between the main elements of the embodiment and the main elements of the invention described in the section of means for solving the problems will be explained. In the embodiment, the fuel cell stack 21 corresponds to a "fuel cell," the reformer 23 corresponds to a "reforming section," the desulfurizer 36 corresponds to a "desulfurizer," and the raw fuel gas supply device 30 corresponds to a "reformer". It corresponds to a "raw fuel gas supply device", the air supply device 50 corresponds to an "air supply device", the combustion section 25 corresponds to a "combustion section", the recycled gas pipe 38 corresponds to a "reflux path", The control device 80 corresponds to a "control device." Further, the temperature sensor 99 corresponds to a "temperature sensor".

The correspondence relationship between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problem is that the embodiment implements the invention described in the column of means for solving the problem. Since this is an example for specifically explaining a form for solving the problem, it is not intended to limit the elements of the invention described in the column of means for solving the problems. In other words, the interpretation of the invention described in the column of means for solving the problem should be made based on the description in that column, and the embodiments should be based on the description of the invention described in the column of means for solving the problem. This is just one specific example.

Although the mode for implementing the present invention has been described above using the embodiments, the present invention is not limited to these embodiments in any way, and may be modified in various forms without departing from the gist of the present invention. Of course, it can be implemented.

INDUSTRIAL APPLICATION This invention can be utilized for the manufacturing industry of a fuel cell system, 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, 23p piping, 24 manifold, 25 combustion section, 26 ignition heater, 27 combustion catalyst, 28 catalyst heater, 29 module case, 30 raw fuel gas supply device, 31 raw fuel gas supply pipe, 32, 33 opening/closing Valve, 34 Orifice, 35 Gas pump, 36 Desulfurizer, 37a Pressure sensor, 37b Flow rate sensor, 38 Recycling gas pipe, 39 Orifice, 40 Reformed water supply device, 41 Reformed water supply pipe, 42 Reformed water tank, 43 Reform Quality 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 storage tank, 64 Circulation pump, 66 Piping, 67 Combustion exhaust gas Discharge 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 fuel gas containing hydrogen and air;
a reforming unit that reforms raw fuel gas to generate the fuel gas and supplies the generated fuel gas to the fuel cell;
a desulfurizer that desulfurizes sulfur components contained in the raw fuel gas using hydrogen and supplies it to the reforming section;
a raw fuel gas supply device that supplies the raw fuel gas to the desulfurizer;
an air supply device that supplies the air to the fuel cell;
a combustion section that burns off gas from the fuel cell;
A portion of the fuel flowing out from the reforming section by connecting a raw fuel gas flow path through which the raw fuel gas flows to the desulfurizer and a fuel gas supply path through which the fuel gas flows from the reforming section to the fuel cell. a reflux path for refluxing the water to the desulfurizer;
When the reflux amount, which is the flow rate of reflux gas returned from the reforming section to the desulfurizer via the reflux path, changes, the air-fuel ratio in the fuel cell or the combustion section does not deviate from the appropriate range. a control device that corrects the supply amount of the raw fuel gas or the air;
A fuel cell system equipped with The fuel cell system according to claim 1,
When setting the flow rate correction value for correcting the supply amount, the control device increases the flow rate correction value as the amount of change in the reflux amount increases;
fuel cell system. The fuel cell system according to claim 1 or 2,
When setting the flow rate correction value for correcting the supply amount, the control device sets an initial value to the flow rate correction value when the reflux amount changes, and adjusts the flow rate correction value as time passes. gradually decrease toward the value 0,
fuel cell system. The fuel cell system according to any one of claims 1 to 3,
comprising a temperature sensor that detects the temperature of the reflux gas flowing through the reflux path,
The control device corrects the supply amount when the amount of change in temperature detected by the temperature sensor is equal to or greater than a predetermined amount when the amount of recirculation changes.
fuel cell system.

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