Fuel cell system

Abstract

In a fuel cell system according to the present invention, when starting up the system, an oxidant gas is supplied, and a fuel pre-injection step is executed in which a fuel gas is supplied at a supply flow rate of the fuel gas such that fuel concentration in a combustion section is a lower explosion limit or less with respect to a supply flow rate of the oxidant gas, until oxygen concentration remaining in a fuel line from the fuel supply system to the combustion section is a prescribed concentration or less, after which an ignition step is executed to ignite the combustion section.

Description

Technical Field

[0001] This specification discloses a fuel cell system.

Background Art

[0002] Conventionally, as this type of fuel cell system, there has been proposed a fuel cell system including a reformer, a solid oxide fuel cell, a fuel collection unit where gases passing through the solid oxide fuel cell gather, a combustion unit that burns the gas blown out from the fuel collection unit, and an igniter used for ignition of the combustion unit (see, for example, Patent Document 1). In this system, at startup, after performing a purge to discharge various gases remaining in the system to the outside of the system by supplying power generation air and reforming air, the supply of fuel is started to replace the air remaining in the fuel collection unit with a high-concentration fuel exceeding the upper limit value of the flammable range of the fuel. Then, the supply of reforming air is started to ignite the gas blown from the fuel collection unit to the combustion unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described fuel cell system, if the fuel concentration deviates from the target concentration due to tolerances of auxiliary equipment or control, etc., there is a risk of backfire from the combustion unit to the fuel line. Although it is conceivable to apply a backfire prevention device, it causes an increase in cost. Further, in a fuel cell system in which a plurality of power generation modules each including one or more fuel cell stacks are connected, when supplying fuel gas at system startup and igniting it in a combustor, if the fuel gas is uniformly supplied to each power generation module, there is a risk of causing backfire due to insufficient fuel gas in some of the power generation modules. Although it is conceivable to apply a backfire prevention device, it will cause an increase in cost.

[0005] The primary objective of the fuel cell system disclosed herein is to ignite the combustion section at a low cost and more safely during system startup. [Means for solving the problem]

[0006] The fuel cell system of this disclosure employs the following means to achieve the primary objective described above.

[0007] The fuel cell system disclosed herein is The gist of the system is that it comprises a fuel cell stack that generates electricity by the reaction of a fuel gas and an oxidizer gas, a combustion section that burns a mixture of residual fuel gas and residual oxidizer gas from the fuel cell stack, an igniter used to ignite the combustion section, a case having thermal insulation properties that houses the fuel cell, the combustion section, and the igniter, a fuel supply system that supplies fuel gas to the fuel cell stack, an oxidizer gas supply system that supplies oxidizer gas to the fuel cell stack, and a control unit that, when starting the system, supplies the oxidizer gas and performs a fuel pre-feed step in which it supplies the fuel gas at a fuel gas supply flow rate such that the fuel concentration in the combustion section is below the lower explosive limit relative to the supply flow rate of the oxidizer gas until the oxygen concentration remaining in the fuel line from the fuel supply system to the combustion section is below a predetermined concentration, and then performs an ignition step in which it ignites the combustion section.

[0008] In the fuel cell system of this disclosure, when starting the system, a fuel pre-feeding process is performed in which fuel gas is supplied at a flow rate that ensures the fuel concentration in the combustion chamber is below the lower explosive limit, until the oxygen concentration remaining in the fuel line from the fuel supply system to the combustion chamber falls below a predetermined concentration. This prevents the flame from flashing back into the fuel line when the combustion chamber is ignited, allowing for safe ignition of the combustor. Furthermore, there is no need to install dedicated devices such as flashback prevention devices, which can reduce costs. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the fuel cell system of this embodiment. [Figure 2] This is a schematic diagram of the configuration of multiple power generation units, each including a power generation module and auxiliary equipment. [Figure 3] This is a schematic diagram of the power generation module. [Figure 4] This is a flowchart showing an example of the startup process. [Figure 5] This flowchart shows an example of a hydrogen pre-injection process. [Figure 6] Figures 6A and 6B are explanatory diagrams showing an example of the required replacement amount, hydrogen injection time, air flow rate, and hydrogen flow rate for each power generation module during the hydrogen pre-injection process at the initial startup. [Figure 7] This is an explanatory diagram showing the time-dependent changes in hydrogen flow rate and integrated hydrogen flow rate for each power generation module during the hydrogen pre-injection process. [Figure 8] This is an explanatory diagram showing an example of a map used to obtain the required replacement amount during system restart. [Figure 9] This is an explanatory diagram showing an example of the required replacement amount, hydrogen injection time, air flow rate, and hydrogen flow rate for each power generation module during the hydrogen pre-injection process when restarting. [Figure 10] The flowchart shows the hydrogen pre-injection process according to another embodiment. [Figure 11] This is an explanatory diagram showing the time changes in hydrogen flow rate and integrated hydrogen flow rate for each power generation module in the hydrogen pre-injection process according to another embodiment. [Figure 12] The flowchart shows the hydrogen pre-injection process according to another embodiment. [Figure 13] This is a flowchart showing an example of the first ignition process. [Figure 14] This is a flowchart showing an example of the second ignition process. [Figure 15] This is a schematic diagram of a fuel cell system according to another embodiment. [Figure 16] This is a schematic diagram of a power generation module according to another embodiment.

Embodiments for Carrying Out the Invention

[0010] Embodiments for carrying out the present disclosure will be described with reference to the drawings.

[0011] FIG. 1 is a schematic configuration diagram of a fuel cell system 10 according to this embodiment, FIG. 2 is a schematic configuration diagram of a plurality of power generation units 11 each including a power generation module 20 and auxiliary equipment 30, and FIG. 3 is a schematic configuration diagram of the power generation module 20.

[0012] As shown in FIG. 1, the fuel cell system 10 of the embodiment includes a plurality of power generation units 11 and an integrated control device 100 that manages the plurality of power generation units 11.

[0013] As shown in FIGS. 1 and 2, each of the plurality of power generation units 11 includes a power generation module 20 including a fuel cell stack 21 and various auxiliary equipment 30 necessary for the operation of the fuel cell stack 21, and a module control device 90 that controls the various auxiliary equipment 30.

[0014] As shown in FIG. 3, in addition to the fuel cell stack 21, the power generation module 20 includes a combustor 22 and heat exchangers 23 and 24, and these are housed in a module case 29 having heat insulation properties. The various auxiliary equipment 30 includes a fuel supply system 40, an air supply system 50, a circulation system 60, a waste heat recovery system 70, etc. (see FIG. 2).

[0015] The fuel cell stack 21 includes a plurality of solid oxide type single cells each including an electrolyte made of stabilized zirconia (for example, YSZ), a fuel electrode made of a composite of a catalytic metal such as Ni and stabilized zirconia or the like disposed on one surface side of the electrolyte, and an air electrode such as LSCF disposed on the other surface side of the electrolyte. Each fuel cell stack 21 generates electricity by the reaction of hydrogen contained in the fuel gas and oxygen contained in the oxidant gas (air). A temperature sensor 25 is installed near the fuel cell stack 21. The temperature sensor 25 detects a temperature (stack temperature Tst) correlated with the temperature of the fuel cell stack 21.

[0016] As shown in Figure 3, one end of a fuel gas supply pipe 21a is connected to the fuel electrode inlet of the fuel cell stack 21, and the other end of the fuel gas supply pipe 21a is connected to a fuel supply system 40. A heat exchanger 23 is installed in the fuel gas supply pipe 21a to exchange heat between the fuel gas flowing through the fuel gas supply pipe 21a from the fuel supply system 40 and the fuel electrode off-gas discharged from the fuel electrode outlet of the fuel cell stack 21. One end of an oxidizer gas supply pipe 21b is connected to the air electrode inlet of the fuel cell stack 21, and the other end of the oxidizer gas supply pipe 21b is connected to an air supply system 50. A heat exchanger 24 is installed in the oxidizer gas supply pipe 21b to exchange heat between the oxidizer gas flowing through the oxidizer gas supply pipe 21b from the air supply system 50 and the combustion exhaust gas discharged from the combustor 22.

[0017] Furthermore, a fuel electrode off-gas pipe 62 is connected to the fuel electrode outlet of the fuel cell stack 21. The fuel electrode off-gas pipe 62 is routed to pass through the heat exchanger 34. The combustor 22 is connected to the oxidizer gas electrode outlet of the fuel cell stack 21 via the oxidizer gas electrode off-gas pipe.

[0018] The combustor 22 is equipped with an igniter 27, which burns a mixed gas of fuel electrode off-gas and oxidizer gas electrode off-gas introduced into the combustor 22. The combustion exhaust gas generated by the combustion of the mixed gas in the combustor 22 is discharged outside the module case 29 through the heat exchanger 24. The combustor 22 is equipped with a temperature sensor 26 for detecting the temperature of the combustion region within the combustor 22 (combustor temperature Tf).

[0019] Hydrogen gas supplied by the fuel supply system 40 is introduced as fuel gas to the fuel electrode of the fuel cell stack 21 via the fuel gas supply pipe 21a, and air supplied by the air supply system 50 is introduced as oxidant gas to the air electrode of the fuel cell stack 21 via the oxidant gas supply pipe 21b. At the air electrode, oxide ions (O 2-) is generated, and these oxide ions permeate the electrolyte and react with hydrogen at the fuel electrode to obtain electrical energy. Fuel electrode off-gas that is not used in the electrochemical reaction (power generation) at the fuel electrode of each single cell is heat-exchanged with fuel gas (hydrogen gas) supplied to the fuel electrode from the fuel supply system 40 in the heat exchanger 23 and then discharged outside the module case 29. The fuel electrode off-gas is then supplied to the circulation system 60 through the fuel electrode off-gas piping 62, where it is cooled by the condenser 61 provided in the circulation system 60 to remove water vapor contained in the fuel electrode off-gas, and then supplied to the combustor 22 through the fuel electrode off-gas piping 63. In addition, air electrode off-gas that is not used in the electrochemical reaction (power generation) at the air electrode of each single cell is supplied directly to the combustor 22. The fuel electrode off-gas introduced into the combustor 22 is a combustible gas containing hydrogen, and is mixed with the air electrode off-gas containing oxygen introduced into the combustor 22. The combustion of the mixed gas in the combustor 22 maintains the fuel cell stack 21 at an appropriate temperature due to the heat of combustion. Furthermore, combustion exhaust gas is generated in the combustor 22. This combustion exhaust gas exchanges heat with air supplied from the air supply system 50 to the air electrode in the heat exchanger 24, and is then supplied to the exhaust heat recovery system 70 through the combustion exhaust gas piping 72. After the exhaust heat is recovered in the exhaust heat recovery system 70, the combustion exhaust gas is discharged into the outside air.

[0020] The fuel supply system 40 includes a hydrogen supply pipe 31 with one end connected to a hydrogen supply source such as a hydrogen tank, branch pipes 41 branching from the other end of the hydrogen supply pipe 31 to each power generation module 20, and hydrogen blowers 42 installed in each branch pipe 41. By operating the hydrogen blowers 42, hydrogen gas in the hydrogen tank 2 is pressurized and supplied to the power generation modules 20. Since hydrogen blowers 42 are installed in each branch pipe 41, the amount of hydrogen gas supplied to each power generation module 20 can be controlled by individually controlling each hydrogen blower 42. In addition, the hydrogen supply pipe 31 is equipped with an on / off valve 32 (double valve) and a negative pressure prevention valve (not shown), and each branch pipe 41 is equipped with a zero governor 43 (pressure equalizing valve) and a flow sensor 44 in addition to the hydrogen blower 42. The flow sensor 44 detects the flow rate (fuel flow rate Fg) of hydrogen gas (fuel gas) flowing through the branch pipe 41 per unit time. The hydrogen gas introduced into the power generation module 20 is heated in the heat exchanger 23 through heat exchange with the fuel electrode off-gas, and then supplied to the fuel electrode of the fuel cell stack 21.

[0021] The air supply system 50 includes an air supply pipe 51 connected to each power generation module 20, a filter 52 provided at the inlet of each air supply pipe 51, and an air blower 53 installed on each air supply pipe 51. By operating the air blower 53, air is drawn in from the filter 52 and the drawn-in air is pressurized and supplied to the power generation module 20. Since an air blower 53 is installed on each air supply pipe 51, the amount of air supplied to each power generation module 20 can be controlled by individually controlling each air blower 53. In addition, a flow sensor 54 is installed on each air supply pipe 51. The flow sensor 54 detects the flow rate (air flow rate Fa) of the air flowing through the air supply pipe 51 per unit time. The air introduced into the power generation module 20 is heated by heat exchange with combustion exhaust gas in the heat exchanger 24 and then supplied to the air electrode of the fuel cell stack 21.

[0022] The circulation system 60 includes a condenser 61 having a separate heat exchange channel for each power generation module 20, a fuel electrode off-gas pipe 62 with one end connected to each power generation module 20 (fuel electrode side of the fuel cell stack 21) and the other end connected to the inlet of each heat exchange channel of the condenser 61, a fuel electrode off-gas pipe 63 with one end connected to the outlet of each heat exchange channel of the condenser 61 and the other end connected to each power generation module 20 (combustor 22 side), a circulation pipe 64 connecting the condenser 61 to heat utilization equipment, and a circulation pump 65 installed in the circulation pipe 64. The fuel electrode off-gas discharged from the fuel electrode side of the fuel cell stack 21 is supplied to the combustor 22 after the water vapor contained in the fuel electrode off-gas is removed in the condenser 61 by heat exchange with a heat exchange medium circulating in the circulation pipe 64 by operating the circulation pump 65.

[0023] Furthermore, the circulation system 60 includes a recirculation pipe 66 that branches off from the fuel electrode off-gas pipe 63 downstream of the condenser 61 and is connected between the hydrogen blower 42 and the zero governor 43 in the branch pipe 41 of the fuel supply system 40, and a control valve 67 (solenoid valve) installed in the recirculation pipe 66. By opening the control valve 67, a portion of the fuel electrode off-gas that has passed through the condenser 61 can be recirculated and supplied from the fuel supply system 40 to the power generation module 20. Alternatively, an orifice may be provided in the recirculation pipe 66 instead of the control valve 67.

[0024] The waste heat recovery system 70 includes a heat exchanger 71 connected to each combustion exhaust gas pipe 72, a heat storage tank 73, a circulation pipe 74 connecting the heat exchanger 71 and the heat storage tank 73, and a circulation pump 75 installed in the circulation pipe 74. By operating the circulation pump 75, the combustion exhaust gas supplied to the heat exchanger 71 is heat-exchanged with the heat exchange fluid in the heat storage tank 73, and the waste heat from the combustion exhaust gas is recovered in the heat storage tank 73. The waste heat recovery system 70 also includes a circulation pipe 76 connecting the heat storage tank 73 to heat utilization equipment installed in factories, etc., and a circulation pump 77 installed in the circulation pipe 76. By operating the circulation pump 77, the heat recovered in the heat storage tank 73 can be supplied to the heat utilization equipment.

[0025] Each of the multiple power generation units 11 has a fuel cell stack 21, which is connected in series to a single power conditioner 15. The DC power generated in each fuel cell stack 21 is converted by the power conditioner 15 and supplied to the load L. A voltage sensor 91 is installed between the output terminals of the fuel cell stack 21 of each power generation module 20 to detect the output voltage of the fuel cell stack 21. In addition, a voltage sensor 92 is installed between one terminal (fuel electrode terminal) of the fuel cell stack 21 located at one end of the series-connected fuel cell stack 21 and the other terminal (air electrode terminal) of the fuel cell stack 21 located at the other end to detect the total voltage (total voltage Vt) of each fuel cell stack 21. Furthermore, a current sensor 93 is installed in the power line connecting each fuel cell stack 21 in series to detect the current flowing through the power line.

[0026] The power conditioner 15 has a DC / DC converter and an inverter, and converts the DC power from each fuel cell stack 21 into AC power at a voltage (e.g., AC200V) that can be connected to the grid power supply and outputs it. A power supply board (not shown) is connected to the power conditioner 15. The power supply board converts the power from each fuel cell stack 21 into DC power suitable for driving various auxiliary equipment 30, module control device 90, and integrated control device 100, and supplies them to each. In addition, the auxiliary equipment room where the power conditioner 15 and power supply board are located is equipped with a cooling fan (not shown) and a ventilation fan for cooling the power conditioner 15 and power supply board.

[0027] Each module control device 90, though not shown in the diagram, is configured as a microprocessor centered around a CPU. In addition to the CPU, it includes a ROM for storing processing programs, a RAM for temporarily storing data, input / output ports, and communication ports. Each module control device 90 receives input via its input ports, including the stack temperature Tst from a temperature sensor 25 installed near the fuel cell stack 21 of the corresponding power generation module 20, the combustor temperature Tf from a temperature sensor 26 installed on the combustor 22, the voltage V from a voltage sensor 91 installed between the output terminals of the fuel cell stack 21, the fuel flow rate Qg from a flow sensor 44 installed on the corresponding branch pipe 41 of the fuel supply system 40, and the air flow rate Qa from a flow sensor 54 installed on the corresponding air supply pipe 51 of the air supply system 50. Furthermore, each module control device 90 outputs control signals to the corresponding hydrogen blower 42 of the fuel supply system 40, the corresponding air blower 53 of the air supply system 50, and the corresponding control valve 67 of the circulation system 60 via its output ports.

[0028] The integrated control unit 100 is configured as a microprocessor centered around a CPU 101. In addition to the CPU 101, it includes a ROM 102 for storing processing programs, a RAM 103 for temporarily storing data, an EEPROM 104 as non-volatile memory, a timer (not shown), input / output ports, and communication ports (not shown). The integrated control unit 100 receives inputs such as the total voltage Vt detected by the voltage sensor 92 and the current I from the current sensor 93 via its input ports. The integrated control unit 100 also outputs control signals to the on / off valve 32, the circulation pump 65 of the circulation system 60, and the circulation pumps 75 and 77 of the heat recovery system 70 via its output ports. Furthermore, the integrated control unit 100 is connected to each module control unit 90 via a communication bus 12, and they exchange control signals and data with each other.

[0029] Next, the operation of the fuel cell system 10 of this embodiment, as configured in this way, will be described.

[0030] When a higher-level system requests that the fuel cell system 10 be started, the integrated control unit 100 sends a start instruction to each module control unit 90 to perform the start process. The start process includes an air purge process, a hydrogen pre-injection process, an ignition process (first ignition process, second ignition process), and a warm-up process, and each module control unit 90 executes each process in order according to the instructions from the integrated control unit 100. When the warm-up of each fuel cell stack 21 is complete and it is ready to generate power, the integrated control unit 100 sends a power generation instruction to each module control unit 90.

[0031] In the power generation process, each module control device 90 receives the target fuel flow rate Fgtag and target air flow rate Fatag set by the integrated control device 100 based on the power requirements of the system, and controls the corresponding hydrogen blower 42 and air blower 53 based on the input target values. Specifically, each module control device 90 drives the hydrogen blower 42 by feedback control based on the difference between the target fuel flow rate Fgtag and the fuel flow rate Fg detected by the flow sensor 44, and drives the air blower 53 by feedback control based on the difference between the target air flow rate Fatag and the air flow rate Fa detected by the flow sensor 54.

[0032] When a system shutdown is requested, each module control device 90 performs a shutdown process according to instructions from the integrated control device 100. During the shutdown process, each module control device 90 controls the hydrogen blower 42 so that hydrogen gas is supplied at a flow rate that does not cause oxidative degradation of the electrodes of the fuel cell stack 21, and controls the air blower 53 so that air is supplied at a flow rate necessary for cooling the fuel cell stack 21. When the stack temperature Tst from the temperature sensor 94 drops below a predetermined temperature, each module control device 90 stops the supply of fuel gas and air. Once the system shutdown is complete, the integrated control device 100 starts measuring the elapsed time (system shutdown time). The system shutdown time is used in the hydrogen pre-injection process described later.

[0033] Furthermore, the details of the startup process will be explained. Figure 4 is a flowchart showing an example of the startup process performed by the integrated control device 100. This process is executed when a request to start the fuel cell system 10 is received from a higher-level system.

[0034] In the startup process, the integrated control device 100 confirms that each power generation module 20 is in an operational state (step S100), then opens the on-off valve 32 (step S102), and sends various instructions to the module control devices 90 of each power generation module 20 to perform the startup process.

[0035] The integrated control unit 100 first instructs each module control unit 90 to perform an air purge process, which involves supplying air to purge the inside of the combustor 22 (step S104). Upon receiving the instruction, each module control unit 90 executes the air purge process by controlling the corresponding air blower 53 with a predetermined air flow rate. The air purge process is performed until the combustor temperature Tf from the temperature sensor 26 is below a predetermined temperature α (e.g., 200°C) and this condition continues for a predetermined period of time. Once the air purge process is completed, the integrated control unit 100 instructs each module control unit 90 to perform the hydrogen pre-injection process, unless the hydrogen pre-injection process has already been performed (NO in step S106) (step S108). Here, the hydrogen pre-injection process is a process to replace the oxygen (air) remaining in the fuel gas line (branch pipe 41, fuel gas supply pipe 21a, and fuel electrode off-gas pipes 62, 63) from the hydrogen supply system 40 to the combustor 22 of each power generation module 20 with hydrogen introduced from the hydrogen supply system 40 until the hydrogen concentration in the fuel gas line reaches or exceeds the upper explosive limit (75%). This hydrogen pre-injection process is performed to prevent the flame from flashing back into the fuel gas line when the igniter 27 is turned on and the combustor 22 is ignited in the subsequent ignition process (first ignition process). Details of the hydrogen pre-injection process will be described later.

[0036] When the hydrogen pre-injection process is completed, the integrated control unit 100 instructs each module control unit 90 to perform the first ignition process (step S110). Each module control unit 90 controls the hydrogen blower 42 and the air blower 53 so that hydrogen gas and air are supplied to the combustion region of the combustor 22 at a predetermined hydrogen concentration (for example, a concentration near the lower combustion limit of hydrogen), and then performs the first ignition process by turning on the igniter 27 to ignite the fuel gas and perform partial combustion. Each module control unit 90 also monitors the temperature change of the combustor temperature Tf to determine whether the first ignition process was successful or not, and transmits the determination result to the integrated control unit 100. Based on the determination result received from each module control unit 90, the integrated control unit 100 decides whether or not to re-execute the first ignition process (step S112). This determination is made based on whether or not a determination result indicating failure of the first ignition process has been received from any of the module control units 90. When the integrated control unit 100 determines that the first ignition process should be re-executed, it instructs the module control unit 90 of the corresponding power generation module 20 to execute the air purge process (step S104). Since the hydrogen pre-injection process has already been performed (YES in step S106), the integrated control unit 100 skips the hydrogen pre-injection process and instructs the module control unit 90 of the corresponding power generation module 20 to re-execute the first ignition process (step S110). Note that the re-execution of the first ignition process may be performed only for power generation modules 20 that have failed to perform the first ignition process, or it may be performed for all power generation modules 20.

[0037] Next, the integrated control unit 100 instructs each module control unit 90 to perform the second ignition process (step S114). Each module control unit 90 executes the second ignition process by controlling the hydrogen blower 42 and the air blower 53 so that hydrogen gas and air are supplied to the combustion region of the combustor 22 at a predetermined hydrogen concentration (a hydrogen concentration equal to or greater than the hydrogen concentration during the first ignition process), thereby completely burning the fuel gas. Each module control unit 90 also monitors the temperature change of the combustor temperature Tf to determine whether the second ignition process was successful and transmits the determination result to the integrated control unit 100. Based on the determination result received from each module control unit 90, the integrated control unit 100 determines whether or not to re-execute the second ignition process (step S116). This determination is made based on whether or not a determination result indicating failure of the second ignition process has been received from any of the module control units 90. When the integrated control device 100 determines that the second ignition process should be re-executed, it instructs the module control device 90 of the corresponding power generation module 20 to re-execute the second ignition process (step S114).

[0038] The integrated control unit 100 then instructs each module control unit 90 to perform a warm-up process (step S118). Each module control unit 90 executes the warm-up process by setting a target fuel flow rate Fgtag and a target air flow rate Fatag, and controlling the hydrogen blower 42 and air blower 53 so that the fuel cell stack 21 reaches a state where it can generate power. Each module control unit 90 also monitors the stack temperature Tst from the temperature sensor 25, and when the stack temperature Tst reaches a predetermined warm-up completion temperature, it sends a notification to the integrated control unit 100 indicating that the warm-up is complete. When the integrated control unit 100 determines that it has received notifications from all module control units 90 indicating that the warm-up is complete (YES in step S120), it controls the power conditioner 15 to start current sweeping and instructs each power generation module 20 to start power generation operation (step S122), and ends the startup process.

[0039] Next, we will describe the details of the hydrogen pre-injection process performed in step S108. Figure 5 is a flowchart of an example of the hydrogen pre-injection process. The hydrogen pre-injection process will be described below with reference to Figures 6A and 6B, using the example of a fuel cell system 10 having five power generation modules HM1 to HM5 as the power generation module 20.

[0040] In the hydrogen pre-injection process, the integrated control device 100 determines whether this is the first system startup (step S200). If the integrated control device 100 determines that this is the first system startup, it obtains the required replacement amount, which is the amount of hydrogen needed to replace the oxygen (air) remaining in the fuel gas line from the hydrogen supply system 40 to the combustor 22 for each power generation module 20 until the hydrogen concentration in the fuel gas line reaches or exceeds the upper combustion limit (75%) (step S202). The required replacement amount is determined according to the piping length of the fuel gas line for each power generation module 20. In this embodiment, the piping length from the branching point of the branch pipe 41 to the hydrogen blower 42 (primary side piping length) differs for each power generation module 20, while the piping length from the hydrogen blower 42 to the combustor 22 (secondary side piping length) is the same for all power generation modules 20. The required replacement amount is stored in the ROM 102 in advance for each power generation module 20 according to the piping length for each power generation module 20. The integrated control device 100 obtains the required replacement amount by reading the required replacement amount for the corresponding power generation module 20 from the ROM 102.

[0041] When the integrated control device 100 obtains the required replacement amount for each power generation module 20, it calculates the hydrogen injection time required to replace the required amount for each power generation module 20, assuming that the hydrogen injection flow rate is set to a predetermined value for the air injection flow rate such that the hydrogen concentration in the fuel area of ​​the combustor 22 is equal to the lower combustion limit of hydrogen (4%) multiplied by a predetermined safety factor (step S204). For example, if the air injection flow rate is 20 [NLM] and the safety factor is 0.5, the hydrogen injection flow rate becomes 0.4 [NLM], and the hydrogen injection time for power generation module HM1, which requires a replacement amount of 6.0 [L], is 15.0 [min], as shown in Figure 6A. Similarly, the hydrogen input time for power generation module HM1, which requires a replacement amount of 6.2[L], is 15.5[min], for power generation module HM3, which requires a replacement amount of 5.8[L], is 14.5[min], for power generation module HM4, which requires a replacement amount of 6.1[L], is 15.25[min], and for power generation module HM5, which requires a replacement amount of 7.0[L], is 17.5[min].

[0042] Next, the integrated control device 100 sets the calculated maximum hydrogen input time as the common effective hydrogen input time for all power generation modules 20 (step S206). As shown in Figure 6B, the maximum hydrogen input time for each power generation module HM1 to HM5 is 17.5 [min], so the common effective hydrogen input time for all power generation modules MH1 to MH5 is set to 17.5 [min]. Then, the integrated control device 100 calculates the effective hydrogen input amount for each power generation module 20 by dividing the required replacement amount for each power generation module 20 by the common effective hydrogen input time (step S208). As shown in Figure 6B, since the effective hydrogen input time is set to 17.5 [min], the effective hydrogen input flow rate for power generation module HM1, which requires a replacement amount of 6.0 [L], is set to 0.3429 [NLM]. Similarly, the effective hydrogen input flow rate for power generation module HM1, which requires a replacement amount of 6.2[L], is set to 0.3543[NLM]; the effective hydrogen input flow rate for power generation module HM3, which requires a replacement amount of 5.8[L], is set to 0.3314[NLM]; the effective hydrogen input flow rate for power generation module HM4, which requires a replacement amount of 6.1[L], is set to 0.3486[NLM]; and the effective hydrogen input flow rate for power generation module HM5, which requires a replacement amount of 7.0[L], is set to 0.4[NLM].

[0043] Once a common execution hydrogen injection time and execution hydrogen injection flow rate for each power generation module 20 are set, the integrated control device 100 transmits a hydrogen pre-injection instruction, including the execution hydrogen injection time and execution hydrogen injection flow rate, to the corresponding module control device 90 (step S210), thereby ending the hydrogen pre-injection process. Upon receiving the hydrogen pre-injection instruction, each module control device 90 sets the execution hydrogen injection flow rate to the target fuel flow rate Fgtag and controls the hydrogen blower 42 by feedback control so that the fuel flow rate Fg from the flow sensor 44 matches the target fuel flow rate Fftag until the execution hydrogen injection time has elapsed. This allows the air in the fuel gas line from the fuel supply system 40 to the combustor 22 of each power generation module 20 to be replaced with hydrogen, preventing the flame from flashing back into the fuel gas line when the combustor 22 ignites in the next ignition process (first ignition process). Furthermore, since the required replacement amount is obtained for each power generation module 20 and the execution hydrogen injection flow rate and execution hydrogen injection time are set according to the obtained required replacement amount, unnecessary fuel consumption can be suppressed. As described above, the actual hydrogen injection time is the same for all power generation modules 20, so as shown in Figure 7, the hydrogen pre-injection process is completed at the same time for all power generation modules 20. Therefore, the timing of ignition of the combustor 22 by the first ignition process, which is performed after the hydrogen pre-injection process, can be synchronized for each power generation module 20, thereby more reliably preventing flashback.

[0044] If the integrated control device 100 determines that this is a restart and not the first time the system is started, it obtains the elapsed time since the system was last shut down (system downtime) (step S212). Next, the integrated control device 100 estimates the required replacement amount common to all power generation modules 20 based on the acquired system downtime (step S214). Immediately after the system is shut down, the fuel gas line from the fuel supply system 40 to the combustor 22 is filled with hydrogen gas. Over time, the hydrogen gas in the fuel gas line is gradually replaced by air introduced from the combustion exhaust gas line, etc. Therefore, when the system is restarted, the integrated control device 100 estimates the required replacement amount needed to replace the air that has replaced the hydrogen with hydrogen again, based on the system downtime. In this embodiment, the required replacement amount is estimated by experimentally determining the relationship between the system downtime and the required replacement amount in advance and storing it as a required replacement amount map in the ROM 102, and then deriving the corresponding required replacement amount from the map when the system downtime is given. Figure 8 shows an example of the required replacement amount map. In this embodiment, the piping downstream of the hydrogen blower 42 (secondary piping) in the fuel gas line is the same length for all power generation modules 20. Therefore, the amount of air replaced by hydrogen in the fuel gas line per unit time is considered to be approximately the same for all power generation modules 20. Accordingly, when the system is restarted, the integrated control device 100 estimates the required replacement amount common to all power generation modules 20.

[0045] The integrated control device 100 estimates the required replacement amount common to all power generation modules 20, and sets the hydrogen input flow rate common to all power generation modules 20 to a predetermined air input flow rate such that the hydrogen concentration in the fuel region of the combustor 22 is equal to the lower combustion limit of hydrogen (4%) multiplied by a predetermined safety factor (step S216). Then, the integrated control device 100 calculates the common effective hydrogen input time common to all power generation modules 20 by dividing the required replacement amount common to all power generation modules 20 by the set effective hydrogen input flow rate (step S218). For example, if the air input flow rate is 20 [NLM] and the safety factor is 0.5, the effective hydrogen input flow rate will be 0.4 [NLM] as shown in Figure 9. Also, since the required replacement amount is common to all power generation modules HM1 to HM5, if the required replacement amount is 1.57 [L], the effective hydrogen input time for all power generation modules HM1 to HM5 will be 3.925 [min].

[0046] Once a common effective hydrogen injection time and effective hydrogen injection flow rate for each power generation module 20 are set, the integrated control device 100 transmits a hydrogen pre-injection instruction, including hydrogen, to the corresponding module control device 90 (step S210), thereby ending the hydrogen pre-injection process. As a result, when the system is restarted, the required replacement amount is estimated according to the system downtime and the effective hydrogen injection flow rate and effective hydrogen injection time are set accordingly, thereby suppressing unnecessary fuel consumption and preventing flashback during ignition of the combustor 22 by pre-injecting hydrogen.

[0047] In the embodiment described above, at the initial startup of the system, the integrated control device 100 sets the effective hydrogen input flow rate for each power generation module 20 and the effective hydrogen input time common to all power generation modules 20 based on the required replacement amount for each power generation module 20. However, the integrated control device 100 may set the effective hydrogen input amount common to all power generation modules 20 and set the effective hydrogen input time for each power generation module 20. Figure 10 is a flowchart of the hydrogen pre-injection process according to another embodiment. Note that for each process in the hydrogen pre-injection process in Figure 10 that is the same as in Figure 5, the same step number is used, and the explanation is omitted as it would be redundant.

[0048] In the hydrogen pre-injection process shown in Figure 10, the integrated control device 100 determines in step S200 that this is the first system startup, and then in the following step S202, it obtains the required replacement amount for each power generation module 20. It then sets the hydrogen injection flow rate to a common effective hydrogen injection flow rate for all power generation modules 20 such that the hydrogen concentration in the fuel area of ​​the combustor 22 is obtained by multiplying the lower combustion limit of hydrogen (4%) by a predetermined safety factor (step S300). The integrated control device 100 then calculates the effective hydrogen injection time for each power generation module 20 by dividing the required replacement amount for each power generation module 20 by the common effective hydrogen injection flow rate (step S302). For example, if the air injection flow rate is set to 20 [NLM] and the safety factor to 0.5, as shown in Figure 6A, the effective hydrogen injection flow rate will be 0.4 [NLM], and the hydrogen injection times for each power generation module HM1, HM2, HM3, HM4, and HM5 will be 15.0 [min], 15.5 [min], 14.5 [min], 15.25 [min], and 17.5 [min], respectively. This allows the air in the fuel gas line from the fuel supply system 40 to the combustor 22 of each power generation module 20 to be replaced with hydrogen, preventing the flame from flashing back into the fuel gas line when the combustor 22 is ignited in the next ignition process (first ignition process). Furthermore, since the effective hydrogen injection flow rate and effective hydrogen injection time are set according to the required replacement amount, unnecessary fuel consumption can be suppressed. Note that in the hydrogen pre-injection process according to other embodiments, the effective hydrogen injection time differs for each power generation module 20. Therefore, as shown in Figure 11, the module control devices 90 of power generation modules HM1 to HM4, which do not have the longest effective hydrogen input time among the power generation modules HM1 to HM5, will set the target fuel flow rate Fgtag to 0 and stop supplying hydrogen once their respective effective hydrogen input times have elapsed, and will wait until the effective hydrogen input time of power generation module MH5, which has the longest effective hydrogen input time, has elapsed.

[0049] In the embodiment described above, the length of the piping (secondary piping) from the hydrogen blower 42 to the combustor 22 was standardized across all power generation modules 20. However, the length of the secondary piping may differ in some power generation modules 20. In this case, the hydrogen pre-injection process shown in Figure 12 is performed instead of Figure 5. Note that for each step in the hydrogen pre-injection process in Figure 12 that is the same as the step in Figure 5, the same step number is used, and the explanation is omitted to avoid duplication.

[0050] In the hydrogen pre-injection process shown in Figure 12, the integrated control device 100 determines in step S200 that this is not the first system startup, and then in the following step S212, it obtains the system downtime and estimates the required replacement amount for each power generation module 20 based on the obtained system downtime (step S400). The integrated control device 100 estimates the required replacement amount using a required replacement amount map, similar to this embodiment. However, since the length of the secondary piping differs for each power generation module 20, the required replacement amount map is prepared for each power generation module 20 by conducting experiments in advance. Subsequently, the integrated control device 100, similar to step S204, calculates the hydrogen injection time required to replace the required amount for each power generation module 20, assuming that the hydrogen injection flow rate is set so that the hydrogen concentration in the fuel area of ​​the combustor 22 is equal to the lower combustion limit of hydrogen (4%) multiplied by a predetermined safety factor (step S402). Next, the integrated control device 100 sets the calculated maximum hydrogen input time to the common execution hydrogen input time for all power generation modules 20, similar to step S206 (step S404). Then, similar to step S208, the integrated control device 100 calculates the execution hydrogen input amount for each power generation module 20 by dividing the required replacement amount for each power generation module 20 by the common execution hydrogen input time (step S406). This makes it possible to replace the air in the secondary piping with hydrogen while reducing wasted fuel consumption in the hydrogen pre-injection process when the system is restarted, even if the piping length of the secondary piping differs for each power generation module 20.

[0051] In the embodiment described above, the integrated control device 100 sets the effective hydrogen input time and effective hydrogen input flow rate for the fuel supply system 40 of each power generation module 20. However, each module control device 90 may set the effective hydrogen input time and effective hydrogen input flow rate for the corresponding fuel supply system 40.

[0052] Next, the first ignition process performed in step S110 and the second ignition process performed in step S114 will be described in more detail. Figure 13 is a flowchart of an example of the first ignition process. The first ignition process is performed by each module control device 90 according to instructions from the integrated control device 100.

[0053] In the first ignition process, each module control device 90 determines whether the first ignition process to be executed is a re-execution (ignition retry) (step S1200). If each module control device 90 determines that it is not an ignition retry, it determines whether this is the first system startup (step S1202). If each module control device 90 determines that this is the first system startup, it sets the increase value ΔFg1 to 0 (step S1204), and then sets the target fuel flow rate Fgtag to the initial value Fini1 plus the increase value ΔFg1 (step S1206). In this embodiment, the initial value Fini1 is a hydrogen flow rate determined such that the hydrogen concentration in the combustor 22 is less than the lower explosion limit (4%) with respect to the air flow rate supplied from the air supply system 50 in step S1208, which will be described later. For example, it is set to a flow rate equivalent to 2% or 3% in terms of hydrogen concentration. Since we are considering the case where this is the first system startup, the increase value ΔFg1 is set to 0, and the target fuel flow rate Fgtag is set to the initial value Fini1. Next, each module control device 90 controls the air blower 53 with a predetermined air flow rate to start supplying air (step S1208), and controls the hydrogen blower 42 with the target fuel flow rate Fgtag to start supplying hydrogen (step S1210). Then, each module control device 90 turns on the igniter 27 to ignite the hydrogen and air mixture introduced into the combustor 22 (step S1212).

[0054] Next, each module control device 90 receives the combustor temperature Tf from the temperature sensor 25 (step S1214), and calculates the temperature change ΔTf (=Tf-previousTf) by subtracting the previously input combustor temperature (previousTf) from the combustor temperature Tf input this time (step S1216). Then, each module control device 90 determines whether the calculated temperature change ΔTf is greater than or equal to a predetermined amount α1 (step S1218), and whether that state continued for a predetermined time β1 (step S1220). Here, the predetermined amount α1 and the predetermined time β1 are thresholds for determining the occurrence of partial combustion, in which a portion of the hydrogen gas introduced into the combustor 22 burns, and are determined by experimentally obtained values. Each module control device 90 determines whether a predetermined determination time has elapsed if it determines that the temperature change amount ΔTf is less than a predetermined amount α1, or if it determines that even if the temperature change amount ΔTf is greater than or equal to the predetermined amount α1, that state has not continued for a predetermined time β1 (step S1222). If each module control device 90 determines that the determination time has not elapsed, it returns to step S1214 and repeats the processing in steps S1214 to S1222. If each module control device 90 determines that the temperature change amount ΔTf is greater than or equal to the predetermined amount α1 and that state has continued for a predetermined time β1 before the determination time has elapsed, it determines that the first ignition process (partial combustion) was successful (step S1224). Then, each module control device 90 records the current increment value ΔTg1 (value 0 in this case) in the EEPROM 104 (step S1226) and terminates the first ignition process.

[0055] In the process of repeating steps S1214 to S1222, each module control device 90 determines that the first ignition process has failed if it determines in step S1222 that the determination time has elapsed (step S1228). Next, each module control device 90 counts up the increase value ΔFg1 of the hydrogen flow rate supplied from the hydrogen supply system 40 when the first ignition process is re-executed (ignition retry) (step S1230). The increase value ΔFg1 is counted up in such an increment as to increase by 1%, for example, in terms of the hydrogen concentration in the combustor 22. Then, each module control device 90 determines whether the value obtained by adding the increase value ΔFg1 to the initial value Fini1 exceeds the upper limit value Fmax1 (step S1232). The process in step S1232 determines whether the hydrogen concentration in the combustor 22 exceeds a predetermined upper limit concentration (for example, 4%, which is the lower explosive limit of hydrogen) when an ignition retry is performed with a target fuel flow rate Fgtag, which is the sum of the increment value ΔFg1 that has been counted up. When each module control device 90 determines that the value obtained by adding the increment value ΔFg1 to the initial value Fini1 is less than or equal to the upper limit value Fmax1, it determines to perform an ignition retry (step S1234) and terminates the first ignition process. In this case, as described above, the first ignition process is re-executed after the air purge process is performed during the startup process.

[0056] When the first ignition process is re-executed, each module control device 90 determines in step S1200 that the first ignition process to be executed this time is a re-execution (ignition retry). Therefore, in step S1230, it adds the increment value ΔFg1 that has been counted up to the initial value Fini1 and sets the value obtained by this addition to the target fuel flow rate Fgtag (step S1206). Then, through the processing in steps S1208 to S1222, it re-executes the first ignition process and determines whether the first ignition process is successful or not. If the first ignition process is successful (step S1224), each module control device 90 records the current increment value ΔTg1 (in this case, the incremented value) to the EEPROM 104 (step S1226) and terminates the first ignition process. Meanwhile, if the first ignition process fails (step S1228), each module control device 90 repeats the process of re-executing the first ignition process (ignition retry) by further counting up the increase value ΔTg1 until the first ignition process succeeds or the value obtained by adding the increase value ΔFg1 to the initial value Fini1 exceeds the upper limit value Fmax1. In the process of repeating the process, if each module control device 90 determines in step S1232 that the value obtained by adding the increase value ΔFg1 to the initial value Fini1 exceeds the upper limit value Fmax1, it determines that some kind of abnormality has occurred in the fuel cell system 10, stops the fuel cell system 10 (step S1236), resets the increase value ΔFg1 recorded in the EEPROM 104 to a value of 0 (step S1238), and terminates the first ignition process. In this way, if the first ignition process fails, the first ignition process can be repeated while gradually increasing the amount of hydrogen supplied to the combustor 22, thereby ensuring safe and reliable ignition of the combustor 22. Furthermore, if the first ignition process fails even after repeated attempts, the fuel cell system 10 is shut down, allowing for appropriate response to any malfunctions in the fuel cell system 10.

[0057] If the first ignition process is successful after a re-execution, the EEPROM 104 records the increment value ΔFg1 that was counted up during the re-execution of the first ignition process. When each module control device 90 starts the system again, in step S1202 it determines that this is not the first system startup, reads the increment value ΔFg1 recorded in the EEPROM 104 (step S1240), adds the read increment value ΔFg1 to the initial value Fini1 to set the target fuel flow rate Fgtag, and executes the first ignition process. As a result, as the system restarts are repeated, the optimal increment value ΔFg1 is set, making it possible to execute the first ignition process more reliably on the first attempt.

[0058] Next, the second ignition process will be described. Figure 14 is a flowchart showing an example of the second ignition process. The second ignition process is executed by each module control device 90 based on instructions from the integrated control device 100. Note that for each process in the second ignition process that is the same as that in the first ignition process, the same step number is used, and detailed explanations are omitted to avoid duplication.

[0059] In the second ignition process, if each module control device 90 determines in steps S1200 and S1202 that the second ignition process to be executed this time is not a re-execution (ignition retry) but rather the first system startup, it sets the increase value ΔFg2 to 0 (step S1204B), and then sets the target fuel flow rate Fgtag to the initial value Fini2 plus the increase value ΔFg2 (step S1206B). The initial value Fini2 is a larger value than the initial value Fini1 used in the first ignition process, and is set to a hydrogen flow rate such that the hydrogen concentration in the combustion section 22 reaches the lower explosive limit (4%) relative to the air flow rate. Subsequently, each module control device 90 supplies air at a predetermined air flow rate (step S1208) and supplies hydrogen at the target fuel flow rate Fgtag (step S1210).

[0060] Next, each module control device 90 inputs the combustor temperature Tf and calculates the temperature change amount ΔTf (steps S1214, S1216). It then determines whether the temperature change amount ΔTf is greater than or equal to a predetermined amount α2 (step S1218B) and whether that state has continued for a predetermined time β2 (step S1220B). Here, the predetermined amount α2 and the predetermined time β2 are thresholds for determining whether the combustor 22 has transitioned from partial combustion to complete combustion, and are determined by experimentally obtained values. If each module control device 90 determines that the temperature change amount ΔTf is less than the predetermined amount α2, or if it determines that the temperature change amount ΔTf is greater than or equal to the predetermined amount α2 but that state has not continued for a predetermined time β2, it determines whether a predetermined determination time has elapsed (step S1222). If each module control device 90 determines that the determination time has not elapsed, it returns to step S1214 and repeats the processing of steps S1214 to S1222. Each module control device 90 determines that the second ignition process (complete combustion) was successful if, before the judgment time has elapsed, the temperature change amount ΔTf is equal to or greater than a predetermined amount α2 and that this state has continued for a predetermined time β2 (step S1224B). Then, each module control device 90 records the current increase value ΔTg2 (value 0 in this case) in the EEPROM 104 (step S1226B) and terminates the second ignition process.

[0061] Each module control device 90, in the process of repeating steps S1214 to S1222, determines in step S1222 that the determination time has elapsed, and determines that the second ignition process has failed (step S1228B). Next, each module control device 90 counts up the increase value ΔFg2 of the hydrogen flow rate supplied from the hydrogen supply system 40 when the second ignition process is re-executed (ignition retry) (step S1230B). The increase value ΔFg2 is counted up in such a way that it increases by, for example, 1% in terms of the hydrogen concentration in the combustor 22. Then, each module control device 90 determines whether the value obtained by adding the increase value ΔFg2 to the initial value Fini2 exceeds the upper limit value Fmax2 (step S1232B). The process in step S1232B determines whether the hydrogen concentration in the combustor 22 exceeds a predetermined upper limit concentration when an ignition retry is performed with the target fuel flow rate Fgtag which includes the counted increase value ΔFg2. This upper limit concentration can be, for example, a concentration (e.g., 9%) obtained by multiplying the detonation lower limit (18%) by a predetermined safety factor (e.g., 0.5). When each module control device 90 determines that the value obtained by adding the increment value ΔFg2 to the initial value Fini2 is less than or equal to the upper limit value Fmax2, it determines to perform an ignition retry (step S1234) and returns to step S1200. Since a positive determination is made in step S1200, each module control device 90 sets the value obtained by adding the increment value ΔFg2, which is counted up to the initial value Fini2, to the target fuel flow rate Fgtag (step S1206B), and repeats the processing in steps S1208 to S1222 to re-execute the second ignition process.

[0062] Then, if the second ignition process is successful (step S1224B), each module control device 90 records the current increment value ΔTg2 (in this case, the counted-up value) in the EEPROM 104 (step S1226B) and terminates the second ignition process. On the other hand, if the second ignition process fails (step S1228B), each module control device 90 repeats the process of re-executing the second ignition process (ignition retry) by counting up the increment value ΔTg2 by a predetermined value until the second ignition process is successful or the value obtained by adding the increment value ΔFg2 to the initial value Fini2 exceeds the upper limit value Fmax2. In the process of repeating the process, if each module control device 90 determines in step S1232B that the sum of the initial value Fini2 and the increase value ΔFg2 exceeds the upper limit value Fmax2, it determines that some kind of abnormality has occurred in the fuel cell system 10, stops the fuel cell system 10 (step S1236), resets the increase value ΔFg2 recorded in the EEPROM 104 to 0 (step S1238B), and terminates the second ignition process. In this way, if the second ignition process fails, the second ignition process is repeated while gradually increasing the amount of hydrogen supplied to the combustor 22, thereby more reliably preventing detonation and deflagration and successfully completing the ignition of the combustor 22. Furthermore, if the second ignition process fails even after repeated re-execution, the fuel cell system 10 is stopped, allowing for appropriate response to abnormalities in the fuel cell system 10.

[0063] If the second ignition process is successful after a re-execution, the EEPROM 104 records the increased fuel value ΔFg2 that was counted up during the re-execution of the second ignition process. When each module control device 90 starts the system again, in step S202 it determines that this is not the first system startup, reads the increased fuel value ΔFg2 recorded in the EEPROM 104 (step S1240B), adds the read increased fuel value ΔFg2 to the initial value Fini2, sets the target fuel flow rate Fgtag, and executes the second ignition process. As a result, as the system restarts are repeated, the optimal increased fuel value ΔFg2 is set, making it possible to execute the second ignition process more reliably on the first attempt.

[0064] Thus, in this embodiment, by sequentially executing a first ignition step (partial combustion) and a second ignition step (complete combustion) as the ignition process, even if there is a slight deviation in the fuel concentration in the combustor 22 due to tolerances in the auxiliary equipment 30 or control, the occurrence of detonation and deflagration can be prevented. As a result, the hydrogen-air mixture in the combustor 22 can be ignited more safely and reliably.

[0065] In the embodiments described above, each fuel cell stack 21 performs a power generation operation by reacting hydrogen with oxygen contained in the air. However, the fuel cell stack 21 may be a reversible solid oxide cell stack and may include an FC mode in which power generation is performed, and an EC mode in which hydrogen is produced by high-temperature steam electrolysis while power is supplied from a power source. As a power source, grid power, renewable energy such as solar power generation equipment, or storage batteries can be used.

[0066] Figure 15 is a schematic diagram of a fuel cell system 10B according to another embodiment, and Figure 16 is a schematic diagram of its power generation module 20. In the fuel cell system 10B according to the other embodiment, the power generation module 20 includes a fuel cell stack 21, a combustor 22, heat exchangers 23 and 24, as well as an evaporator 25, etc., which are housed in a module case 29 with thermal insulation properties. The evaporator 25 may be equipped with a heater to supplement the heat that is insufficient in the evaporator 25. Various auxiliary equipment 30 include a fuel supply system 40, an air supply system 50, a circulation system 60, a waste heat recovery system 70, as well as a water supply system 80, etc.

[0067] The water supply system 80 includes a water tank 81 for storing water (raw water), a water supply pipe 82 with one end connected to the water tank 81, branch pipes 83 branching from the other end of the water supply pipe 82 to each power generation module 20, and water pumps 84 installed in each branch pipe 83. By operating the water pumps 84, the raw water in the water tank 81 is pressurized and supplied to the power generation modules 20. Since each branch pipe 83 has a water pump 84, the amount of raw water supplied to each power generation module 20 can be controlled by individually controlling each water pump 84. An evaporator 25 is connected between the branch pipe 83 of the water supply system 80 and the fuel gas supply pipe 21a. The raw water is evaporated in the evaporator 25 and converted into water vapor.

[0068] In EC mode, water vapor supplied by the water supply system 80 and the fuel supply system 40, along with a small amount of hydrogen gas, is introduced to the fuel electrode of the fuel cell stack 21 via the fuel gas supply pipe 21a as fuel gas, and air supplied by the air supply system 50 as sweep gas is introduced to the air electrode of the fuel cell stack 21 via the oxidizer gas supply pipe 21b. When a predetermined voltage of power is supplied between the terminals of the fuel cell stack 21 (reversible solid oxide cell stack) by the power supply, the water vapor introduced to the fuel electrode is electrolyzed at the fuel electrode to produce hydrogen and oxygen ions (O). 2-) is decomposed into and and the oxygen ions permeate the electrolyte, generating oxygen at the air electrode. In this embodiment, a small amount of hydrogen gas is also supplied to the fuel electrode along with water vapor, so that the fuel electrode is kept in a reducing atmosphere and oxidation degradation of the fuel electrode can be suppressed. The hydrogen gas generated at the fuel electrode is discharged as fuel electrode off-gas along with unreacted water vapor, and after heat exchange with water vapor supplied to the fuel electrode from the water supply system 80 in the heat exchanger 23, it is discharged outside the module case 29. The fuel electrode off-gas, which contains hydrogen gas and water vapor, is supplied to the circulation system 60 through the fuel electrode off-gas piping 62, cooled by the condenser 61 provided in the circulation system 60 to remove water vapor, and then stored in the hydrogen tank 2 via the manifold 3 and on-off valve 4. The on-off valve 4 is closed in FC mode and opened in EC mode. In addition, a portion of the fuel electrode off-gas (hydrogen gas) that has passed through the condenser 61 is supplied to the combustor 22 through the fuel electrode off-gas piping 63. Meanwhile, the oxygen gas generated at the air electrode is supplied directly to the combustor 22 as air electrode off-gas along with the air passing through the air electrode. The heat of combustion generated by the combustion of the mixed gas of fuel electrode off-gas and air electrode off-gas in the combustor 22 is transferred to the evaporator 25. The evaporator 25 evaporates water (raw water) supplied from the water supply system 80 to generate steam and also raises the temperature of the generated steam. In addition, combustion exhaust gas is generated in the combustor 22, and the generated combustion exhaust gas exchanges heat with the air supplied to the air electrode from the air supply system 50 in the heat exchanger 24, before passing through the combustion exhaust gas piping 72 and being discharged to the outside air via the exhaust heat recovery system 70.

[0069] In the fuel cell system 10B according to this other embodiment, the system can switch between FC mode and EC mode depending on the demand for electricity. For example, the FC mode can be selected when load L is requesting electricity, and the EC mode can be selected when load L is not requesting electricity. Furthermore, in the fuel cell system 10B that has entered into a demand response contract, the FC mode can be selected when a downward DR (demand response) is requested to reduce the amount of electricity demand, and the EC mode can be selected when an upward DR (demand response) is requested to increase the amount of electricity demand.

[0070] In the embodiment described above, the integrated control device 100 sets the effective hydrogen input time and effective hydrogen input flow rate for the fuel supply system 40 of each power generation module 20. However, each module control device 90 may set the effective hydrogen input time and effective hydrogen input flow rate for the corresponding fuel supply system 40.

[0071] In the embodiment described above, each of the multiple power generation modules 20 in the fuel cell system 10 is equipped with one fuel cell stack 21. However, all or some of the multiple power generation modules 20 may be equipped with multiple fuel cell stacks 21 connected in series or in parallel.

[0072] In the embodiment described above, the fuel cell stacks 21 provided by each of the multiple power generation modules 20 are connected in series with each other, but they may also be connected in parallel with each other.

[0073] In the embodiment described above, the module control device 90 and the integrated control device 100 were configured with separate control units, but they may also be configured with a single control unit.

[0074] In the embodiment described above, the fuel cell system 10 comprises a plurality of power generation modules 20, each containing a fuel cell stack 21, but it may also comprise a single power generation module 20.

[0075] Although the embodiments for implementing this disclosure have been described above, this disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of this disclosure.

[0076] Furthermore, this specification also discloses a technical concept in which "the fuel cell system described in claim 1" has been changed to "the fuel cell system described in any one of claims 1 to 5" in claim 6 of the original application. [Industrial applicability]

[0077] This disclosure can be used in industries such as the manufacturing of fuel cell systems. [Explanation of Symbols]

[0078] 10,10B Fuel cell system, 20 Power generation module, 21 Fuel cell stack, 22 Combustor (combustion section), 26 Temperature sensor, 27 Ignitioner, 29 Module case (case), 30 Auxiliary equipment, 40 Fuel supply system, 50 Air supply system (oxidizer gas supply system), 90 Module control device (control unit, individual control unit), 100 Integrated control device (control unit, integrated control unit).

Claims

1. A fuel cell stack that generates electricity through the reaction of fuel gas and oxidizer gas, A combustion unit for burning a mixed gas of residual fuel gas and residual oxidizer gas from the fuel cell stack, An igniter used to ignite the combustion section, A case having thermal insulation properties, which houses the fuel cell, the combustion unit, and the igniter, A fuel supply system that supplies fuel gas to the aforementioned fuel cell stack, An oxidizer gas supply system that supplies oxidizer gas to the fuel cell stack, A control unit performs a fuel pre-feeding step when starting the system, which involves supplying the oxidizer gas and supplying the fuel gas at a rate that ensures the fuel concentration in the combustion section is below the lower explosive limit relative to the supply rate of the oxidizer gas, until the oxygen concentration remaining in the fuel line from the fuel supply system to the combustion section is below a predetermined concentration, and then performs an ignition step to ignite the combustion section. A fuel cell system equipped with the following features.

2. A fuel cell system according to claim 1, The control unit performs a first ignition step, which involves controlling the fuel supply system and the oxidizer gas supply system so that the fuel gas and oxidizer gas are supplied to the combustion section within a range where the fuel concentration in the combustion section is below the lower explosive limit, and controlling the igniter to ignite the mixed gas of the fuel gas and oxidizer gas in the combustion section. Subsequently, it performs a second ignition step, which involves controlling the fuel supply system and the oxidizer gas supply system so that the fuel concentration in the combustion section is above the fuel concentration at the time of the first ignition step and below the lower explosive limit. Fuel cell system.

3. A fuel cell system according to claim 2, The combustion section is equipped with a temperature sensor that detects the temperature of the combustion section, The control unit determines the success or failure of the first ignition step based on the temperature of the combustion section detected by the temperature sensor. If it determines that the first ignition step has failed, it repeats the process of purging the combustion section by supplying the oxidizer gas, increasing the flow rate of the fuel gas supplied to the combustion section, and re-executing the first ignition step until the first ignition step is successful. If the flow rate of the fuel gas after the increase exceeds a first upper limit without the first ignition step being successful, the fuel cell system is shut down. Fuel cell system.

4. A fuel cell system according to claim 2, The combustion section is equipped with a temperature sensor that detects the temperature of the combustion section, In the second ignition step, the control unit determines the success or failure of the second ignition step based on the temperature of the combustion section detected by the temperature sensor. If it determines that the second ignition step has failed, it repeatedly increases the flow rate of fuel gas supplied to the combustion section and re-executes the second ignition step until the second ignition step is successful. If the second ignition step is unsuccessful and the increased flow rate of fuel gas exceeds a second upper limit which is greater than the first upper limit and less than the lower detonation limit when converted to the fuel concentration of the combustor, the control unit shuts down the fuel cell system. Fuel cell system.

5. A fuel cell system according to claim 3 or 4, The system includes a storage unit that stores the increased amount of fuel gas supplied when the first ignition step or the second ignition step is re-executed, The control unit, after stopping the fuel cell system, starts the first ignition step or the second ignition step when it is started again, using a fuel gas supply flow rate increased by an increase value stored in the memory unit. Fuel cell system.

6. A fuel cell system according to claim 1, The system comprises a plurality of power generation modules, each including the fuel cell stack, the combustion section, the igniter, the case, the fuel supply system, and the oxidizer gas supply system. Each fuel cell stack is connected in series or in parallel among the multiple power generation modules. A plurality of individual control units that control the auxiliary equipment of the corresponding power generation module among the plurality of power generation modules based on instructions, When starting the fuel cell system, the integrated control unit instructs the plurality of individual control units to perform a fuel pre-feeding process, which involves supplying the oxidizer gas and supplying the fuel gas at a fuel flow rate such that the fuel concentration in the combustion section is below the lower explosive limit relative to the supply flow rate of the oxidizer gas, until the oxygen concentration remaining in the fuel line from the fuel supply system to the combustion section falls below a predetermined concentration, and then instructs the plurality of individual control units to ignite the combustion section. A fuel cell system that also features additional capabilities.

7. A fuel cell system according to claim 6, The integrated control unit or the individual control unit, in the fuel pre-feeding step, obtains for each power generation module the amount of fuel necessary to replace the oxygen remaining in the fuel line with the fuel gas until the fuel concentration in the fuel line of each power generation module exceeds the upper explosive limit, and sets the fuel gas supply flow rate and supply time for each power generation unit with respect to the oxidizer gas supply flow rate within a range where the fuel concentration in the combustion section is below the lower combustion limit. Fuel cell system.

8. A fuel cell system according to claim 7, The integrated control unit or the individual control unit sets the maximum value of the time obtained by dividing the required replacement amount for each power generation module by the fuel gas flow rate at which the fuel concentration in the combustion section is below the lower combustion limit relative to the supply flow rate of the oxidizer gas, as the common supply time for the multiple power generation modules, and sets the flow rate obtained by dividing the required replacement amount for each power generation module by the supply time as the supply flow rate for each power generation module. Fuel cell system.

9. A fuel cell system according to claim 7, The integrated control unit or the individual control unit sets the fuel gas flow rate common to the plurality of power generation modules so that the fuel concentration in the combustion section is below the lower combustion limit relative to the supply flow rate of the oxidizer gas, and sets the time obtained by dividing the required replacement amount for each power generation module by the supply flow rate as the supply time for each power generation module. Fuel cell system.

10. A fuel cell system according to any one of claims 7 to 9, The integrated control unit or the individual control unit measures the elapsed time since the fuel cell system stopped, and when starting the system again, it obtains the required replacement amount based on the elapsed time and sets the supply flow rate and the supply time based on the required replacement amount. Fuel cell system.

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