JP2019121466A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the efficiency of power generation of a fuel cell in a fuel cell system. A control device 15 of a fuel cell system 1 includes a fuel flow rate setting unit 15a that sets a flow rate of a fuel gas supplied to the fuel cell 34 to a first flow rate based on power generated by a fuel cell 34, and a fuel flow rate setting unit 15a. A power determination unit 15c that determines whether the power generated by the battery 34 is within a predetermined power range, and whether the first combustion unit temperature of the first combustion unit 36 in which the fuel off gas is burned is within a predetermined temperature range. The temperature determination unit 15d that determines whether or not the power generation unit 15c determines that the generated power is within the predetermined power range, and the temperature determination unit 15d determines that the first combustion unit temperature is within the predetermined temperature range. And a fuel flow rate changing unit 15f that changes the flow rate of the fuel gas set by the fuel flow rate setting unit 15a so as to decrease stepwise from the first flow rate each time the above state continues for the first predetermined time T1. There is. [Selection diagram]

Description

  The present invention relates to a fuel cell system.

  As one type of fuel cell system, one disclosed in Patent Document 1 is known. As shown in FIG. 1 of Patent Document 1, a fuel cell system generates a fuel cell using power of a reformed gas as a fuel gas, a reformer that generates a reformed gas obtained by reforming a raw material (reforming (reforming) And a combustion unit that heats the reformer by burning a fuel off gas not used for power generation of the fuel cell, and a temperature detection unit that detects the temperature of the reforming unit or the combustion unit.

  The fuel cell system is configured such that the temperature of the reforming unit or the temperature of the combustion unit becomes the temperature suitable for the reforming of the raw material in the reforming unit based on the temperature detected by the temperature detection unit. The flow rate of the supplied raw material and hence the flow rate of the fuel gas supplied to the fuel cell are controlled. Thereby, the power generation efficiency of the fuel cell can be improved while maintaining the reforming efficiency. The power generation efficiency of the fuel cell is higher as the flow rate of the fuel gas supplied to the fuel cell is smaller than the power generated by the fuel cell.

International Publication No. 2010/010699

  In the fuel cell system of Patent Document 1 described above, since the temperature of the reforming unit or the temperature of the combustion unit is controlled while maintaining the reforming efficiency, it is necessary to maintain a sufficiently stable combustion state in the combustion unit. There is. For this reason, the flow rate of the fuel off gas that burns the combustion unit, that is, the flow rate of the fuel gas becomes a flow rate having a margin relative to the flow rate of the minimum fuel gas required to burn the fuel off gas in the combustion unit. On the other hand, there is a demand to further improve the power generation efficiency of the fuel cell.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the efficiency of power generation of a fuel cell in a fuel cell system.

  In order to solve the above problems, a fuel cell system according to claim 1 comprises a fuel cell generating electricity from a fuel gas and an oxidant gas, a fuel supply unit for supplying the fuel gas to the fuel cell, and an oxidant for the fuel cell. An oxidant gas supply unit for supplying gas, a combustion unit for burning a fuel off gas and an oxidant off gas derived from a fuel cell, a power detection device for detecting generated power generated by the fuel cell, and a combustion unit A fuel cell system comprising a temperature sensor for detecting a temperature of a combustion unit and a control device for at least controlling a fuel cell, wherein the control device is based on generated power detected by the power detection device. Whether the fuel flow rate setting unit sets the flow rate of the fuel gas supplied by the fuel supply unit to the first flow rate, and whether the generated power detected by the power detection device is within a predetermined power range The generated power is determined to be within the predetermined power range by the power determination unit to be determined, the temperature determination unit to determine whether the combustion unit temperature detected by the temperature sensor is within the predetermined temperature range, and the power determination unit Also, each time the temperature determination unit determines that the combustion unit temperature is within the predetermined temperature range continues for the first predetermined time, the flow rate of the fuel gas set by the fuel flow rate setting unit is stepped from the first flow rate And a fuel flow rate changing unit which changes to decrease the pressure.

  According to this, whenever the state where the generated power generated by the fuel cell is within the predetermined power range and the temperature of the combustion unit is within the predetermined temperature range continues for the first predetermined time, the flow rate of the fuel gas is increased. Decrease gradually. That is, the flow rate of the fuel gas can be reduced stepwise while the generated power is stable and the combustion state of the combustion unit is stable. Therefore, it is possible to reduce the flow rate of the fuel gas to the minimum required flow rate of the fuel gas for burning the fuel off gas in the combustion unit while confirming the combustion state of the combustion unit. Therefore, in the fuel cell system, high efficiency of power generation of the fuel cell can be achieved.

FIG. 1 is a schematic view of a fuel cell system according to an embodiment of the present invention. It is a block diagram of a fuel cell system shown in FIG. It is a flowchart which the control apparatus shown in FIG. 1 performs. It is a flowchart which the control apparatus shown in FIG. 1 performs. It is a time chart which shows operation of a fuel cell system when a flow chart shown in Drawing 3A and Drawing 3B is performed, and it is a fuel utilization factor, a flow rate of fuel gas, an air utilization factor, a flow rate of air, power generation The power, the first combustion unit temperature and the second combustion unit temperature are shown.

  Hereinafter, an embodiment of a fuel cell system according to the present invention will be described. As shown in FIG. 1, the fuel cell system 1 includes a power generation unit 10 and a hot water storage tank 21.

  The power generation unit 10 includes a housing 10 a, a fuel cell module 11, a heat exchanger 12, a power converter 13, a water tank 14, and a controller 15. The fuel cell module 11 includes at least a fuel cell 34 as described later.

  The heat exchanger 12 is a heat exchanger to which the combustion exhaust gas exhausted from the exhaust port 31a of the fuel cell module 11 is supplied and the stored hot water from the hot water storage tank 21 is supplied, and the combustion exhaust gas and the stored hot water exchange heat. is there. The heat exchanger 12 is connected (penetrated) to an exhaust pipe 11d connected to the exhaust port 31a. The heat exchanger 12 is connected to a condensed water supply pipe 12 a connected to the water tank 14.

  The hot water storage tank 21 stores hot water storage, and is connected to a hot water circulation line 22 through which the hot water circulates (circulates in the direction of the arrow in the figure). The hot water circulating pump 22 a and the heat exchanger 12 are disposed on the hot water circulating line 22 in order from the lower end to the upper end.

  In the heat exchanger 12, the combustion exhaust gas from the fuel cell module 11 is introduced into the heat exchanger 12 through the exhaust pipe 11d, and heat exchange is performed with the stored hot water to be cooled and the combustion exhaust gas Water vapor contained therein is condensed. The flue gas after cooling is discharged to the outside through the exhaust pipe 11d. Further, the condensed condensed water is supplied to the water tank 14 through the condensed water supply pipe 12a. The water tank 14 purifies the condensed water with the ion exchange resin and stores it as reformed water.

  An exhaust heat recovery system 20 is configured from the heat exchanger 12, the hot water storage tank 21 and the hot water storage water circulation line 22 described above. The exhaust heat recovery system 20 recovers and stores exhaust heat of the fuel cell module 11 in stored hot water.

  Furthermore, the power conversion device 13 receives the DC voltage output from the fuel cell 34, converts it into a predetermined AC voltage, and connects the AC system power supply 16a and the external power load 16c (for example, an electric appliance) to a power supply. Output to line 16b.

  In addition, the power conversion device 13 receives an AC voltage from the system power supply 16a via the power supply line 16b, converts it into a predetermined DC voltage, and controls auxiliary equipment (each pump 11a1, 11b1, blower 11c1, etc.) and control described later. Output to the device 15.

  The control device 15 controls at least the fuel cell 34. The controller 15 drives the accessory to control the operation of the fuel cell system 1. The control device 15 controls the generated power of the fuel cell 34 to be the power consumption of the external power load 16c during the power generation operation of the fuel cell system 1 (load following operation).

Next, the fuel cell module will be described in detail.
The fuel cell module 30 includes a casing 31, an evaporation unit 32, a reforming unit 33, and a fuel cell 34. The casing 31 is formed of a heat insulating material in a box shape, and an exhaust port 31a is provided.

  In the fuel cell module 30, one end of the fuel cell module 30 is connected to the supply source Gs, and the other end of the reforming material supply pipe 11a to which the reforming material is supplied is connected. The supply source Gs is, for example, a gas supply pipe of city gas, a gas cylinder of LP gas. The raw material supply pipe 11a for reforming is provided with a raw material pump 11a1. The raw material pump 11a1 is a pump for feeding the raw material for reforming. As the raw material pump 11a1 sends the reforming raw material, the fuel gas is supplied to the fuel cell 34 as described later. The raw material pump 11a1 corresponds to the fuel supply unit of the present invention.

  Further, one end (lower end) of the evaporating section 32 is connected to the water tank 14, and the other end of the reforming water supply pipe 11b to which the reforming water is supplied is connected. The reforming water supply pipe 11b is provided with a reforming water pump 11b1 for feeding reforming water.

  Further, in the fuel cell module 30, one end is connected to the cathode air blower 11c1, and the other end of the cathode air supply pipe 11c is connected to the cathode 31 in which cathode air (air) as oxidant gas is supplied to the fuel cell in the casing 31 ing. The cathode air blower 11c1 is a pump for feeding cathode air. The cathode air blower 11c1 supplies cathode air to the fuel cell 34 as described later. The cathode air blower 11c1 corresponds to the oxidant gas supply unit of the present invention.

  The evaporation unit 32 generates steam from the reforming water. Specifically, the evaporation unit 32 is heated by a combustion gas described later, and evaporates the reforming water supplied from the water tank 14 to generate steam. Further, the evaporation unit 32 preheats the reforming raw material supplied from the supply source Gs.

  The evaporation unit 32 mixes the water vapor thus generated and the preheated reforming raw material, and supplies the resulting mixture to the reforming unit 33. As the reforming raw material, there are a gas fuel for reforming such as natural gas and LP gas, a liquid fuel for reforming such as kerosene, gasoline, and methanol, and the present embodiment will be described using a natural gas.

  The reforming unit 33 generates a reformed gas from the reforming material from the supply source Gs and the water vapor from the evaporation unit 32 and supplies the reformed gas to the fuel cell 34. Specifically, the reforming unit 33 is a mixture gas (raw material for reforming, steam supplied from the evaporating unit 32 by being heated by a combustion gas described later and supplied with heat necessary for the steam reforming reaction. ) To generate and derive a reformed gas.

  The reforming unit 33 is filled with a catalyst (for example, Ru or Ni-based catalyst), and the mixed gas is reacted by the catalyst to be reformed, and a reformed gas containing hydrogen gas, carbon monoxide, etc. It is being produced (so-called steam reforming reaction). The reformed gas includes hydrogen, carbon monoxide, carbon dioxide, steam, natural gas not reformed (methane gas), reformed water not used for reforming (steam). The steam reforming reaction is an endothermic reaction.

  The fuel cell 34 generates electricity from the fuel gas and the oxidant gas. The fuel gas is a reformed gas. The fuel cell 34 is configured by stacking a plurality of cells 34 a composed of a fuel electrode, an air electrode (oxidizer electrode), and an electrolyte interposed between the two electrodes. The fuel cell 34 of the present embodiment is a solid oxide fuel cell, and uses zirconium oxide, which is a type of solid oxide, as an electrolyte.

  A reformed gas (hydrogen, carbon monoxide, methane gas or the like) is supplied to the fuel electrode of the fuel cell 34 as a fuel. On the fuel electrode side of the cell 34a, a fuel flow passage 34b through which a fuel gas (reformed gas) flows is formed. On the air electrode side of the cell 34a, an air flow path 34c through which air (cathode air), which is an oxidant gas, flows is formed. The fuel cell 34 generates power at a relatively high operating temperature.

  The fuel cell 34 is provided on the manifold 35. The reformed gas from the reforming unit 33 is supplied to the manifold 35 via the reformed gas supply pipe 39. The lower end (one end) of the fuel flow passage 34b is connected to the fuel outlet (not shown) of the manifold 35, and the reformed gas led out from the fuel outlet is introduced from the lower end and derived from the upper end It has become.

  The cathode air delivered by the cathode air blower 11c1 is supplied via the cathode air supply pipe 11c, introduced from the lower end of the air flow path 34c and drawn out from the upper end.

  Further, a first combustion unit 36 (corresponding to the combustion unit of the present invention) is provided between the fuel cell 34 and the evaporation unit 32 and the reforming unit 33. The first combustion unit 36 burns the fuel off gas and the oxidant off gas which are derived from the fuel cell 34. That is, the first combustion unit 36 is a space where the fuel off gas burns. The fuel off gas is a fuel gas (reformed gas) that has not been used for power generation. The oxidant off gas is oxidant gas (cathode air (air)) that was not used for power generation. The first combustion unit 36 is provided with a pair of ignition heaters 36 a for igniting the fuel off gas.

  In the first combustion unit 36, the fuel off gas is burned to generate a combustion gas (flame 37). The combustion gas heats the evaporating unit 32 and the reforming unit 33. Further, the first combustion unit 36 brings the temperature in the fuel cell module 30 to the operating temperature of the fuel cell 34. Furthermore, in the first combustion unit 36, the fuel off gas is burned to generate relatively high temperature flue gas. The relatively high temperature flue gas is led to the heat exchanger 12 through the exhaust port 31a and the exhaust pipe 11d.

  In addition, a second combustion unit 38 is provided in the exhaust port 31a. The second combustion unit 38 introduces, as combustible gas (non-combustible combustible gas), the fuel off gas not burned in the first combustion unit 36 among the combustion exhaust gas, and burns it out. The unburned combustible gas is, for example, hydrogen, methane gas, carbon monoxide and the like. The second combustion unit 38 is composed of a combustion catalyst (for example, a ceramic honeycomb or a metal honeycomb and a catalyst of a noble metal) which is a catalyst for burning a flammable gas.

  The second combustion unit 38 is provided with a combustion catalyst heater 38 a. The combustion catalyst heater 38a heats the combustion catalyst that burns the unburned combustible gas. The combustion catalyst heater 38a heats the combustion catalyst to the activation temperature of the catalyst.

  The fuel cell system 1 further includes a current sensor 40a, a voltage sensor 40b, a first temperature sensor 41 (corresponding to the temperature sensor of the present invention), and a second temperature sensor 42.

  The current sensor 40 a detects the current generated by the fuel cell 34. The voltage sensor 40 b detects a generated voltage of the fuel cell 34. The current sensor 40 a and the voltage sensor 40 b are disposed in the power converter 13. The detection result of the current sensor 40 a and the detection result of the voltage sensor 40 b are output to the control device 15.

  The first temperature sensor 41 detects a first combustion unit temperature (corresponding to the combustion unit temperature of the present invention) which is the temperature of the first combustion unit 36. The first temperature sensor 41 is disposed at a portion where the flame 37 does not directly contact in the first combustion unit 36, and detects the temperature of the disposed position. The detection result of the first temperature sensor 41 is output to the control device 15.

  The second temperature sensor 42 detects a second combustion unit temperature which is the temperature of the second combustion unit 38. The second temperature sensor 42 detects the temperature of the position disposed in the second combustion unit 38. The detection result of the second temperature sensor 42 is output to the control device 15.

  Next, the control device 15 will be described in detail. As shown in FIG. 2, the control device 15 includes a power calculation unit 150, a fuel flow rate setting unit 15a, a pump drive unit 15b, a power determination unit 15c, a temperature determination unit 15d, a first state determination unit 15e, and a fuel flow rate change unit 15f. Air flow setting unit 15g (corresponding to the oxidant gas flow setting unit of the present invention), blower drive unit 15h, air flow changing unit 15i (corresponding to the oxidant gas flow changing unit of the present invention), second state determination unit 15j The blow-off determination unit 15k, the lower limit flow rate setting unit 15m, and the ignition control unit 15n are provided.

  The power calculation unit 150 calculates the generated power of the fuel cell 34 using the detection result of the current sensor 40 a and the detection result of the voltage sensor 40 b. As described above, the current sensor 40 a, the voltage sensor 40 b, and the power calculation unit 150 correspond to the power detection device 40 that detects the generated power generated by the fuel cell 34. In the power detection device 40, instead of the current sensor 40a and the voltage sensor 40b, a power sensor that detects the generated power of the fuel cell 34 may be used. In this case, the power calculation unit 150 is a power acquisition unit that acquires the detection result of the power sensor.

  The fuel flow rate setting unit 15a sets the flow rate (flow rate per unit time) of the fuel gas supplied by the raw material pump 11a1 to the first flow rate based on the generated power calculated by the power calculation unit 150. The fuel flow rate setting unit 15a uses the first map (not shown) indicating the correlation between the generated power of the fuel cell 34 and the first flow rate, and generates the first flow rate from the generated power calculated by the power calculation unit 150. To derive. The first map is stored in a storage unit (not shown) of the control device 15.

  The pump drive unit 15b controls the drive amount of the raw material pump 11a1 such that the flow rate of the reforming raw material delivered by the raw material pump 11a1 and thus the fuel gas flow becomes the first flow rate set by the fuel flow rate setting unit 15a. It is. Since the raw material pump 11a1 is controlled by PWM (Pulse Width Modulation), the control command value to the raw material pump 11a1 is calculated by the duty ratio.

  The power determination unit 15 c determines whether the generated power calculated by the power calculation unit 150 is within a predetermined power range. The predetermined power range is, for example, a range in which the upper limit is the maximum output value of the fuel cell 34 and the lower limit is 90% of the maximum output value of the fuel cell 34.

  The temperature determination unit 15 d determines whether the first combustion unit temperature detected by the first temperature sensor 41 is within a predetermined temperature range. The predetermined temperature range is based on the temperature of the position where the first temperature sensor 41 is disposed when the first combustion unit 36 is in the combustion state and the fuel cell 34 is operating within the predetermined power range. Is set. The predetermined temperature range is measured and derived in advance by experiments and the like.

  In the first state determination unit 15e, a state where the power determination unit 15c determines that the generated power is within the predetermined power range, and the temperature determination unit 15d determines that the first combustion unit temperature is within the predetermined temperature range It is determined whether (hereinafter referred to as a first state) continues the first predetermined time T1. The first predetermined time T1 is, for example, 2 minutes.

  The fuel flow rate changing unit 15f sets the flow rate of the fuel gas set by the fuel flow rate setting unit 15a from the first flow rate every time when the first state determination unit 15e determines that the first state continues for the first predetermined time T1. It is changed to decrease gradually (details will be described later).

  For example, the fuel flow rate changing unit 15 f decreases the flow rate of the fuel gas by a first predetermined flow rate. The first predetermined flow rate is set to, for example, approximately 2% of the maximum flow rate of the fuel gas (corresponding to the flow rate of the fuel gas at the maximum output of the fuel cell 34).

  Further, the fuel flow rate changing unit 15 f changes the flow rate of the fuel gas to decrease so that the fuel utilization rate of the fuel cell 34 becomes high. The fuel utilization rate of the fuel cell 34 is the ratio of the flow rate of the fuel gas used for power generation of the fuel cell 34 to the flow rate of the fuel gas supplied to the fuel cell 34 (fuel utilization rate = (used for power generation of the fuel cell 34 Fuel gas flow rate) / (flow rate of fuel gas supplied to the fuel cell 34)). Specifically, the fuel flow rate changing unit 15 f does not change the flow rate of the fuel gas used for power generation, and reduces the flow rate of the fuel off gas that is derived from the fuel cell 34 without being used for power generation. Reduce the fuel gas flow rate.

  In addition, the fuel flow rate changing unit 15 f is equal to or less than the first flow rate and the lower limit flow rate setting unit when the first combustion unit 36 is in the combustion state after it is determined by the blowout determination unit 15k that blowoff has occurred. The flow rate of the fuel gas is changed stepwise from the first flow rate within the range of the flow rate of the fuel gas equal to or more than the lower limit fuel flow rate set by 15 m (details will be described later).

  The air flow rate setting unit 15g sets the flow rate of air supplied by the cathode air blower 11c1 (flow rate per unit time) to the second flow rate based on the generated power calculated by the power calculation unit 150. The air flow rate setting unit 15 g uses the second map (not shown) indicating the correlation between the power generated by the fuel cell 34 and the second flow rate, and generates the second flow rate from the generated power calculated by the power calculation unit 150. To derive. The second map is stored in the storage unit of the control device 15.

  The blower drive unit 15 h controls the drive amount of the cathode air blower 11 c 1 so that the flow rate of the air delivered by the cathode air blower 11 c 1 becomes the second flow rate set by the air flow rate setting unit 15 g. Since the cathode air blower 11c1 is PWM controlled, the control command value to the cathode air blower 11c1 is calculated by the duty ratio.

  The air flow rate changing unit 15i changes the flow rate of air from the second flow rate set by the air flow rate setting unit 15g when the flow rate of the fuel gas is changed by the fuel flow rate changing unit 15f. The air flow rate changing unit 15i increases the air utilization rate when reducing the flow rate of air.

  The air utilization rate is a ratio of the flow rate of air used for power generation of the fuel cell 34 to the flow rate of air supplied to the fuel cell 34 (air utilization rate = (flow rate of air used for power generation of the fuel cell 34) / (Flow rate of air supplied to the fuel cell 34)). Specifically, the air flow rate change unit 15i reduces the flow rate of air (oxidant off gas) that is derived from the fuel cell 34 without being used for power generation without changing the flow rate of air used for power generation. So, reduce the air flow rate.

  Further, the air flow rate changing unit 15i changes the flow rate of air from the second flow rate so that the ratio of the flow rate of the oxidant off gas to the flow rate of the fuel off gas is equal to or more than a predetermined ratio. The predetermined ratio is set to a value larger than one.

  Specifically, the air flow rate changing unit 15i changes the flow rate of air from the second flow rate by a second predetermined flow rate before the flow rate of the fuel gas is actually changed by the fuel flow rate changing unit 15f. (Details will be described later). The second predetermined flow rate is set such that the ratio of the flow rate of the oxidant off gas to the flow rate of the fuel off gas is equal to or more than the predetermined rate even when the flow rate of the fuel gas is changed from the first flow rate or the first flow rate There is.

  When the air flow rate is changed by the air flow rate change unit 15i, the second state determination unit 15j determines that the temperature of the first combustion unit is determined to be within the predetermined temperature range by the temperature determination unit 15d (hereinafter referred to as second State is determined to be continued for the second predetermined time T2.

  If it is determined by the second state determination unit 15j that the second state has continued for the second time, the flow rate of the fuel gas set by the fuel flow rate setting unit 15a is changed by the fuel flow rate change unit 15f (details will be described later) ). In the present embodiment, the second predetermined time T2 is set to a time (for example, one minute) shorter than the first predetermined time T1.

  The blow-off determination unit 15k determines, from the second combustion unit temperature detected by the second temperature sensor 42, whether or not blow-out in which the combustion state of the first combustion unit 36 is canceled has occurred. . Blow-off of the first combustion portion 36 means that the combustion state of at least a part of the first combustion portion 36 is eliminated (completed). Blow-off of the first combustion portion 36 is caused by a change in concentration or flow rate of an unintended fuel gas.

  When at least a part of the first combustion unit 36 blows off when the first combustion unit 36 is in the combustion state during the power generation operation of the fuel cell system 1, the above-described unburned combustion is performed by the second combustion unit 38 Since the flow rate of the flammable gas is increased, the temperature of the second combustion unit 38 is increased. Thus, when the temperature detected by the second temperature sensor 42 becomes equal to or higher than the first determination temperature, the blow-off determination unit 15k determines that the blow-off of the first combustion unit 36 has occurred. The first determination temperature is measured and derived in advance by experiments and the like.

  The lower limit flow rate setting unit 15m has a flow rate of the fuel gas changed by the fuel flow rate changing unit 15f, and if it is determined by the blowout determination unit 15k that blowout has occurred, it is smaller than the first flow rate and blowoff The flow rate larger than the flow rate of the fuel gas at the time when it is determined by the determination unit 15k that blow-off has occurred is set to the lower limit fuel flow rate which is the lower limit value of the flow rate of the fuel gas.

  Specifically, the lower limit flow rate setting unit 15m sets the lower limit fuel flow rate to that of the fuel gas immediately before being changed by the fuel flow rate change unit 15f with respect to the flow rate of the fuel gas when it is determined that blowout has occurred. Set to flow rate. That is, the lower limit fuel flow rate is set to a flow rate of fuel gas that is increased by a first predetermined flow rate from the flow rate of fuel gas when it is determined that blow-off has occurred.

  The ignition control unit 15n executes ignition control for igniting the first combustion unit 36 when the blowout determination unit 15k determines that blowout has occurred. The ignition control unit 15 n turns on the ignition heater to start ignition control. The ignition control unit 15 n ends the ignition control when the first combustion unit temperature detected by the first temperature sensor 41 becomes equal to or higher than the second determination temperature. The second determination temperature is derived and set in advance by experiments and the like.

  When the first combustion unit 36 is not ignited even when a third predetermined time (for example, 30 seconds) has elapsed from the time when the ignition control is started, the ignition control unit 15 n may, for example, May not be supplied. In this case, the ignition control unit 15 n shuts down the fuel cell system 1.

  Next, the high efficiency power generation operation performed by the fuel cell system 1 described above will be described using the flowcharts shown in FIGS. 3A and 3B. The high efficiency power generation operation is an operation to improve the power generation efficiency of the fuel cell 34 during the power generation operation of the fuel cell system 1. The initial value of the lower limit fuel flow rate is set to zero.

  When the high efficiency power generation operation is not performed during the power generation operation of the fuel cell system 1, the normal power generation operation is performed. The normal power generation operation is the load following operation described above, and the flow rate of the fuel gas is set to the first flow rate (the fuel flow rate setting unit 15a) according to the generated power of the fuel cell 34 (the fuel flow rate setting unit 15a). Is set (the air flow rate setting unit 15g), and the fuel cell 34 generates power.

  When the normal power generation operation is being performed, the control device 15 determines whether blow-off has occurred or not in step S102 (blowing-off determination unit 15k). For example, when the concentration of the fuel off gas fluctuates due to the fluctuation of the concentration of the reforming raw material and blowout of the first combustion unit 36 occurs, the temperature of the second combustion unit 38 rises as described above. Accordingly, when the second combustion unit temperature detected by the second temperature sensor 42 becomes equal to or higher than the first determination temperature, the control device 15 determines “YES” in step S102, and performs the ignition control in step S104. Is executed (ignition control unit 15n).

  Since the first combustion unit 36 is ignited by eliminating the fluctuation of the concentration of the reforming raw material and turning on the ignition heater 36a, the first combustion unit temperature detected by the first temperature sensor 41 is the second When the temperature exceeds the determination temperature, the ignition control ends. Subsequently, the control device 15 returns the program to step S102 and continues the normal power generation operation.

  On the other hand, when the combustion state of the first combustion unit 36 is stable and blow-off does not occur in the first combustion unit 36, the control device 15 determines “NO” in step S102, and step S106. To determine whether the first state (the state where the generated power is within the predetermined power range and the first combustion unit temperature is within the predetermined temperature range) continues for the first predetermined time T1 (electric power Determination unit 15c, temperature determination unit 15d, and first state determination unit 15e).

  For example, the generated power deviates from the predetermined power range due to fluctuations in the power consumption of the external power load 16c and hence the generated power, or the combustion state of the first combustion portion 36 becomes unstable and the first combustion portion temperature becomes a predetermined temperature If the first state is canceled before the first predetermined time T1 elapses due to being out of the range, the control device 15 determines “NO” in step S106. Then, the control device 15 returns the program to step S102, and repeatedly executes steps S102 and S106 while the combustion state of the first combustion unit 36 continues.

  On the other hand, when the variation of the power consumption of the external power load 16c is relatively small, and the combustion state of the first combustion unit 36 is stable, the control device 15 operates when the first state continues for the first predetermined time T1. In step S106, the determination is "YES", and the flow rate of air is changed in step S108 (air flow rate change unit 15i).

  Subsequently, as in step S102, the control device 15 determines whether or not blowout has occurred in step S110 (blowndown determination unit 15k). The blow-off occurs, for example, when the flow rate of air is changed and the combustion state of the first combustion unit 36 becomes unstable.

  When the second combustion unit temperature becomes equal to or higher than the first determination temperature because the flow rate of air is changed in step S108 described above and blowout of the first combustion unit 36 occurs, the control device 15 performs step At S110, the determination is "YES", and at step S112, the flow rate of air is returned to the second flow rate. Furthermore, the control device 15 executes the ignition control in step S104 (ignition control unit 15n). Then, as described above, when the ignition control is finished, the program is returned to step S102, and the normal power generation operation is continued.

  On the other hand, even when the air flow rate is changed in step S108, if blow-off has not occurred in first combustion unit 36, control device 15 determines “NO” in step S110, and step At S114, it is determined whether the second state (the state where the first combustion unit temperature is within the predetermined temperature range) continues for the second predetermined time T2 (second state determination unit 15j).

  For example, in a state where the fuel cell 34 is deteriorated due to use for a relatively long time, when the flow rate of air is changed, the temperature of the first combustion portion rises. Thus, when the second state is canceled before the second predetermined time T2 elapses because the first combustion unit temperature is out of the predetermined temperature range, the control device 15 determines “NO” in step S114. Do. And while the combustion state of the 1st combustion part 36 is continuing, step S110, S114 is repeatedly performed.

  As described above, when the flow rate of the fuel gas is changed to increase the fuel utilization rate by the high-efficiency power generation operation described later when the fuel cell 34 is deteriorated, the deterioration of the fuel cell 34 is further promoted. Is considered. That is, before the high efficiency power generation operation is performed, it is possible to confirm whether the high efficiency power generation operation may actually be performed by changing the flow rate of air.

  On the other hand, even if the flow rate of air is changed, if the combustion state of the first combustion unit 36 is stable and the second state continues for the second predetermined time T2, the control device 15 determines “YES” in step S114. It judges and starts high efficiency operation at Step S116.

  In step S118, the controller 15 determines whether the flow rate of the changed fuel gas is equal to or more than the lower limit fuel flow rate. When the lower limit fuel flow rate is the initial value (zero), the first flow rate, which is the current flow rate of the fuel gas, is equal to or higher than the lower limit fuel flow rate even when it is changed to decrease by the first predetermined flow rate. The device 15 determines “YES” in step S118, and changes the flow rate of the fuel gas in step S120 (fuel flow rate change unit 15f).

  Subsequently, as in step S102, the control device 15 determines whether blow-off has occurred or not in step S122 (blown-out determination unit 15k). If blow-off of the first combustion unit 36 does not occur even if the flow rate of the fuel gas is changed, the control device 15 determines “NO” in step S122, and in step S124 as in step S106, It is determined whether the first state continues for a first predetermined time T1 (power determination unit 15c, temperature determination unit 15d, first state determination unit 15e).

  Since the use of the external power load 16c and hence the fluctuation of the power consumption are relatively small, and the combustion state of the first combustion unit 36 is stable even if the flow rate of the fuel gas is changed, the first state is a first predetermined time When T1 continues, the control device 15 determines “YES” in step S124, and returns the program to step S118.

  Thus, in the case where the blowout of the first combustion unit 36 does not occur and the flow rate of the changed fuel gas is equal to or more than the lower limit fuel flow rate and the first state continues, the above-described step S118 S124 is repeatedly executed. Thereby, the flow rate of the fuel gas is changed so as to decrease stepwise by the first predetermined flow rate every first predetermined time T1.

  On the other hand, after the lower limit fuel flow rate is set to a flow rate greater than zero as described later, if the above-described steps S118 to S124 are repeatedly executed, the flow rate of the changed fuel gas becomes smaller than the lower limit fuel flow rate The controller 15 determines “NO” in step S118, and returns to step S118 after performing steps S122 and S124 without changing the flow rate of the fuel gas. That is, in this case, the high efficiency power generation operation is continued without changing the flow rate of the fuel gas.

  Moreover, when blow-off has generate | occur | produced in the 1st combustion part 36, when step S118 to S124 mentioned above is repeatedly performed, the control apparatus 15 determines with "YES" in step S122. In this case, the control device 15 sets the lower limit fuel flow rate in step S126 (the lower limit flow rate setting unit 15m), and ends the high efficiency power generation operation in step S128. Thus, the normal power generation operation is performed again. Further, in step S130, the control device 15 executes the ignition control as in step S104 (ignition control unit 15n), and returns the program to step S102.

  Furthermore, in the case where steps S118 to S124 described above are repeatedly executed, the external power load 16c fluctuates and the generated power deviates from the predetermined power range, or the flow rate of the fuel gas decreases and the first combustion unit 36 When the first state is canceled before the first predetermined time T1 elapses because the first combustion unit temperature deviates from the predetermined temperature range due to the unstable combustion state, the control device 15 performs step S124. It is judged as "NO" at. Subsequently, the control device 15 ends the high efficiency power generation in step S132, and returns the program to step S102.

  Next, the operation of the fuel cell system 1 when the above-described flowchart is executed will be described using the time chart of FIG. A point in time when normal power generation operation is started in a state where the generated power is within the predetermined power range, the first combustion unit temperature is within the predetermined temperature range, and the lower limit fuel flow rate is the initial value (zero) (time t1 I will explain from.

  From the time when the normal power generation operation is started (time t1), blow-off does not occur, and the first state (the generated power is within the predetermined power range and the first combustion unit temperature is within the predetermined temperature range When the first predetermined time T1 has elapsed (time t2), the controller 15 changes the flow rate of air to decrease from the second flow rate by the second predetermined flow rate so that the air utilization rate increases ((t2) Step S108).

  From the time when the air flow rate is changed (time t2), blow-off does not occur, and the second state (state in which the temperature of the first combustion unit 36 is within the predetermined temperature range) is the second predetermined time T2 When the time has passed (time t3), the high efficiency power generation operation is started (step S116), and the fuel gas flow rate is decreased from the first flow rate by the first predetermined flow rate so that the fuel utilization rate is increased. Three flow rates are changed (step S120). In this case, since the flow rate of the fuel off gas decreases, the temperature of the first combustion portion slightly decreases.

  Since blow-off does not occur from the time (time t3) at which the flow rate of the fuel gas is changed to the third flow rate, and the first state continues, the first predetermined time is elapsed each time the first predetermined time T1 passes. When the time T1 has elapsed (time t4, t5), the flow rate of the fuel gas is changed in order of the fourth flow rate and the fifth flow rate so as to decrease by the first predetermined flow rate (step S120).

  Then, before the first predetermined time T1 elapses from the time when the flow rate of the fuel gas is changed to the fifth flow rate (time t5), the flow rate of the fuel gas decreases and the flow rate of the fuel off gas runs short. As the disappearance occurs (time t6), the temperature of the first combustion portion gradually decreases and the temperature of the second combustion portion rises.

  Then, the lower limit fuel flow rate is set at a time (time t7) when the second combustion portion temperature becomes equal to or higher than the first determination temperature (step S126). In this case, since it is determined that blow-off has occurred when the flow rate of the fuel gas is the fifth flow rate, the fourth flow rate immediately before being changed to the fifth flow rate is set to the lower limit fuel flow rate.

  Furthermore, in order to return to the normal power generation operation after the high efficiency power generation operation ends (step S128), the flow rate of the fuel gas is set to the first flow rate, and the flow rate of air is set to the second flow rate. Subsequently, the ignition control is started (step S130). As a result, the first combustion unit 36 is ignited, the first combustion unit temperature rises, and the ignition control is ended when the first combustion unit temperature reaches the second determination temperature (time t8).

  From the time when the ignition control is finished (time t8), the blow-off does not occur, and the flow rate of air is changed (time t9) when the first state is the first predetermined time T1 (time t9) (step S108). Furthermore, the high efficiency power generation operation is started (step S116) when blow-off does not occur and when the second state has passed the second predetermined time T2 (time t10).

  Then, the blow-off does not occur, and while the first state continues, the flow rate of the fuel gas is the third flow rate at the time when the first predetermined time T1 passes each time the first predetermined time T1 passes. The order of the fourth flow rate is changed (time t10, t11). As described above, since the lower limit fuel flow rate is set to the fourth flow rate, even when the first predetermined time T1 has elapsed from the time (the time t11) at which the flow rate of the fuel gas is set to the fourth flow rate (time t12) The fuel gas flow rate is not changed.

  Then, since the external power load 16c fluctuates and the generated power decreases, the high power generation operation is ended at the time when the first state is canceled (time t13) due to being out of the predetermined power range and the normal power generation operation Is executed again (steps S124 and S132). Furthermore, since the external power load 16c fluctuates and the generated power increases, blowout does not occur from the time when the generated power falls within the predetermined power range (time t14), and the first state is the first predetermined time At the time when T1 is continued (time t15), the flow rate of air is changed (step S108). Thereafter, blow-off does not occur, and as long as the first state continues, high-efficiency power generation operation is continued with the fourth flow rate as the lower limit value of the flow rate of the fuel gas.

  According to the present embodiment, the fuel cell system 1 includes the fuel cell 34 generating electric power from the fuel gas and the oxidant gas, the raw material pump 11a1 for supplying the fuel gas to the fuel cell 34, and the oxidant gas to the fuel cell 34. A cathode air blower 11c1 to be supplied, a first combustion unit 36 for burning the fuel off gas and the oxidant off gas derived from the fuel cell 34, and a power detection device 40 for detecting generated power generated by the fuel cell 34; A first temperature sensor 41 that detects a temperature of the first combustion unit 36, which is the temperature of the first combustion unit 36, and a controller 15 that controls at least the fuel cell 34 are provided. The control device 15 detects the flow rate of the fuel gas supplied by the raw material pump 11a1 as the first flow rate based on the generated power detected by the power detection device 40 and the power detection device 40 by the power detection device 40 Power determination unit 15c that determines whether the generated power is within the predetermined power range, and determines whether the first combustion unit temperature detected by the first temperature sensor 41 is within the predetermined temperature range A state in which the temperature determination unit 15 d and the power determination unit 15 c determine that the generated power is within the predetermined power range, and the temperature determination unit 15 d determines that the first combustion unit temperature is within the predetermined temperature range The fuel is changed so that the flow rate of the fuel gas set by the fuel flow rate setting unit 15a is gradually decreased from the first flow rate every time the one state) continues for the first predetermined time T1. It includes the amount changing section 15f, a.

  According to this, every time the first state continues for the first predetermined time T1, the flow rate of the fuel gas decreases stepwise. That is, the flow rate of the fuel gas can be reduced stepwise in the state where the generated power is stable and the combustion state of the first combustion unit 36 is stable. Therefore, it is possible to reduce the flow rate of the fuel gas to the minimum required flow rate of the fuel gas for burning the fuel off gas in the first combustion portion 36 while confirming the combustion state of the first combustion portion 36. Therefore, in the fuel cell system 1, the efficiency of power generation of the fuel cell 34 can be enhanced.

Further, the fuel flow rate changing unit 15 f changes the flow rate of the fuel gas so as to increase the fuel utilization rate of the fuel cell 34.
According to this, it is possible to achieve high efficiency of power generation of the fuel cell 34 while maintaining the generated power of the fuel cell 34.

  In addition, the control device 15 sets an air flow rate of the air supplied by the cathode air blower 11c1 to a second flow rate based on the generated power detected by the power detection device 40, and a fuel flow rate changing portion When the flow rate of the fuel gas is changed by 15f, the flow rate of the air is set to the second flow rate set by the air flow rate setting unit 15g such that the ratio of the flow rate of the oxidant off gas to the flow rate of the fuel off gas becomes a predetermined ratio or more. And an air flow rate change unit 15i to be changed.

  According to this, when the flow rate of the fuel gas is changed, the flow rate of the air is changed such that the ratio of the flow rate of the oxidant off gas to the flow rate of the fuel off gas is equal to or more than a predetermined ratio. Therefore, the efficiency of power generation of the fuel cell 34 can be enhanced while the combustion state of the first combustion unit 36 is more stable.

  Moreover, the control device 15 changes the flow rate of the fuel gas by the blow-off determination unit 15k, which determines whether blow-off that cancels the combustion state of the first combustion unit 36 is occurring, and the fuel flow rate change unit 15f. After that, if it is determined that blow-off has occurred by the blow-off determination unit 15k, the flow rate of the fuel gas is smaller than the first flow rate, and the flow rate of fuel gas at the time when it is determined that blow-off occurs by the blow-off determination unit 15k And a lower limit flow rate setting unit 15m configured to set a larger flow rate to a lower limit fuel flow rate which is a lower limit value of the flow rate of the fuel gas. If the first combustion unit 36 is in a combustion state after the blowout determination unit 15k determines that the blowout has occurred, the fuel flow rate change unit 15f does not exceed the first flow rate and the lower limit flow rate setting unit 15m The flow rate of the fuel gas is changed so as to gradually decrease from the first flow rate in the range of the flow rate of the fuel gas equal to or more than the set lower limit fuel flow rate.

  According to this, after the flow rate of the fuel gas decreases and blow-off of the first combustion unit 36 occurs, the first combustion unit 36 is put into the combustion state again, and reduction of the flow rate of the fuel gas is executed again. The lower limit value of the flow rate of the fuel gas is set to a flow rate greater than the flow rate of the fuel gas at the time of blowout. Therefore, the flow rate of the fuel gas is decreased again at a flow rate greater than the flow rate of the fuel gas at the time of the blow-off. Therefore, the generation efficiency of the power generation of the fuel cell 34 can be enhanced while suppressing the occurrence of blowout of the first combustion portion 36.

  In the embodiment described above, an example of the fuel cell system is shown, but the present invention is not limited to this, and other configurations can be adopted. For example, the lower limit flow rate setting unit 15m sets the lower limit fuel flow rate to the flow rate of the fuel gas immediately before being changed by the fuel flow rate changing unit 15f with respect to the flow rate of the fuel gas at the time when it is determined that blowout has occurred. However, the flow rate may be set higher than the flow rate of the fuel gas immediately before being changed by the fuel flow rate changing unit 15f.

  Further, in the embodiment described above, the blowout determination unit 15k determines whether blowout of the first combustion unit 36 has occurred based on the second combustion unit temperature, but instead of this, The determination may be made based on the first combustion unit temperature. In this case, when the temperature of the first combustion unit becomes equal to or lower than the third determination temperature lower than the second determination temperature, it is determined that the blowout of the first combustion unit 36 has occurred.

  Further, in the above-described embodiment, the flow rate of air is changed before the flow rate of fuel gas is changed in the high efficiency power generation operation, but instead, the change of the flow rate of fuel gas is changed simultaneously, or After changing the flow rate of the fuel gas, the flow rate of the air may be changed. Furthermore, the change of the flow rate of air may be changed stepwise as the change of the flow rate of fuel gas. In addition, the flow rate of air may not be changed as it is the second flow rate.

  Further, in the above-described embodiment, the fuel flow rate changing unit 15 f changes the flow rate of the fuel gas so as to decrease the fixed amount of the first predetermined flow rate each time the first predetermined time T1 elapses. Alternatively, the flow rate may be changed so as to decrease each time the first predetermined time T1 elapses.

  In the above-described embodiment, the lower limit fuel flow rate is set by the fuel flow rate setting unit 15a and is set from the flow rate of the fuel gas changed by the fuel flow rate changing unit 15f. A flow rate sensor (not shown) for detecting the flow rate of the reforming raw material may be disposed in the supply pipe 11a, and the lower limit fuel flow rate may be set from the detection result of the flow rate sensor. In this case, since the lower limit fuel flow rate is set based on the actual flow rate of the fuel gas, not the control command value of the flow rate of the fuel gas, the lower limit fuel flow rate can be set with high accuracy.

  In the embodiment described above, the first state is determined by the power determination unit 15c that the generated power is within the predetermined power range, and the temperature determination unit 15d is within the predetermined temperature range of the first combustion unit temperature However, instead of this, it is determined that the generated power is the maximum generated power of the fuel cell 34, and the temperature determination unit 15d determines that the first combustion unit temperature is within the predetermined temperature range. It is good also as a state. In this case, the power determination unit 15 c determines whether the generated power is the maximum generated power of the fuel cell 34. Further, the fuel flow rate changing unit 15f is the first predetermined state where the generated power is the maximum generated power of the fuel cell 34 and the temperature determination unit 15d determines that the first combustion unit temperature is within the predetermined temperature range. Every time the time T1 is continued, the flow rate of the fuel gas is changed stepwise.

  DESCRIPTION OF SYMBOLS 1 fuel cell system 11 (30) fuel cell module 11a1 raw material pump (fuel supply part) 11c1 cathode air blower (oxidant gas supply part) 15 control device 15a fuel flow rate setting part 15c: power determination unit, 15d: temperature determination unit, 15e: first state determination unit, 15f: fuel flow rate change unit, 15g: air flow rate setting unit (oxidant gas flow rate setting unit), 15i: air flow rate change unit (oxidation Agent gas flow rate changing unit) 15j Second state judging unit 15k Blowing out judging unit 15m Lower limit flow setting unit 15n Ignition control unit 34 Fuel cell 36 First combustion unit (combustion unit) , 40: power detection device, 41: first temperature sensor, 42: second temperature sensor, T1: first predetermined time, T2: second predetermined time.

Claims (4)

A fuel cell that generates electricity from fuel gas and oxidant gas;
A fuel supply unit for supplying the fuel gas to the fuel cell;
An oxidant gas supply unit for supplying the oxidant gas to the fuel cell;
A combustion unit for burning the fuel off gas and the oxidant off gas derived from the fuel cell;
A power detection device for detecting generated power generated by the fuel cell;
A temperature sensor that detects a combustion unit temperature that is the temperature of the combustion unit;
A control device for at least controlling the fuel cell;
The controller is
A fuel flow rate setting unit configured to set a flow rate of the fuel gas supplied by the fuel supply unit to a first flow rate based on the generated power detected by the power detection device;
A power determination unit that determines whether the generated power detected by the power detection device is within a predetermined power range;
A temperature determination unit that determines whether the combustion unit temperature detected by the temperature sensor is within a predetermined temperature range;
The state in which the generated power is determined to be within the predetermined power range by the power determination unit, and the combustion unit temperature is determined to be within the predetermined temperature range by the temperature determination unit continues for a first predetermined time period A fuel flow rate changing unit for changing the flow rate of the fuel gas set by the fuel flow rate setting unit so as to decrease stepwise from the first flow rate each time the fuel cell system is installed.   The fuel cell system according to claim 1, wherein the fuel flow rate change unit changes the flow rate of the fuel gas to decrease so as to increase the fuel utilization rate of the fuel cell. The controller is
An oxidant gas flow rate setting unit that sets the flow rate of the oxidant gas supplied by the oxidant gas supply unit to a second flow rate based on the generated power detected by the power detection device;
When the flow rate of the fuel gas is changed by the fuel flow rate change unit, the flow rate of the oxidant gas is set to the oxidant so that the ratio of the flow rate of the oxidant off gas to the flow rate of the fuel off gas is equal to or greater than a predetermined ratio. The fuel cell system according to claim 1, further comprising: an oxidant gas flow rate change unit that changes the second flow rate set by the gas flow rate setting unit. The controller is
A blow-off determination unit that determines whether blow-off has occurred in which the combustion state of the combustion unit is canceled;
After the flow rate of the fuel gas is changed by the fuel flow rate changing unit, if the blow-off determination unit determines that the blow-off has occurred, the amount is smaller than the first flow rate and the blow-off determination unit A lower limit flow rate setting unit configured to set a flow rate larger than the flow rate of the fuel gas at the time when it is determined that the blowout has occurred, to a lower limit fuel flow rate which is a lower limit value of the flow rate of the fuel gas;
The fuel flow rate change unit is
When the combustion unit is in a combustion state after it is determined by the blowout determination unit that the blowout has occurred:
The flow rate of the fuel gas is decreased stepwise from the first flow rate within the range of the flow rate of the fuel gas which is less than the first flow rate and which is greater than the lower limit fuel flow rate set by the lower limit flow rate setting unit. The fuel cell system according to any one of claims 1 to 3, which is changed to

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