JP7226129B2 - Fuel cell system and its control method - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a fuel cell system including a fuel cell stack including a plurality of single cells that generate power through an electrochemical reaction between an anode gas and a cathode gas, and a method of controlling the fuel cell system.

Conventionally, this type of fuel cell system includes a fuel pump for supplying raw fuel gas for anode gas, a water pump for supplying reforming water, and a reformer for steam reforming the raw fuel gas. , a fuel cell stack that generates electricity by oxidation and reduction of a reformed fuel gas and a cathode gas (oxidant), and a controller for controlling a fuel pump and a water pump (see, for example, Patent Document 1). When the operating state of the fuel cell system is the partial load operating state, the controller of the fuel cell system sets the partial load normal fuel utilization rate corresponding to the partial load operating state to the fuel utilization rate, and sets the partial load operating state to the partial load normal fuel utilization rate. When the generated current is maintained in a static state at , the partial load high fuel utilization rate is set as the fuel utilization rate in order to increase the power generation efficiency. Furthermore, when the partial load normal fuel utilization rate is set, the controller steams the normal S/C based on the relationship between the generated current of the fuel cell stack and the steam carbon ratio (S/C) in the reformer. When the carbon ratio is set and the partial load high fuel utilization rate is set, a low S/C smaller than the normal S/C is set as the steam carbon ratio. As a result, the amount of steam (water vapor) contained in the reformed fuel gas is reduced by setting the low S/C, thereby suppressing the temperature drop of the fuel cell stack due to the increased fuel utilization rate.

JP 2018-110079 A

Since it is difficult to directly measure the temperature of the fuel cell stack in the fuel cell system as described above, a temperature sensor placed near the fuel cell stack detects a temperature correlated with the temperature of the fuel cell stack. be done. In order to keep the temperature of the fuel cell stack within an appropriate range and ensure good performance and durability of the fuel cell stack, various controls of the fuel cell system are performed so that the detected value of the temperature sensor reaches the target temperature. parameters are set. However, as described above, when the steam carbon ratio in the reformer is changed according to the state of the fuel cell stack, even if the fuel cell system is controlled so that the detected value of the temperature sensor becomes the target temperature, the fuel It may become impossible to maintain the temperature of the battery stack properly.

Therefore, the main object of the present disclosure is to improve the efficiency of a fuel cell system and maintain the temperature of the fuel cell stack appropriately to ensure good performance and durability of the fuel cell stack.

The fuel cell system of the present disclosure includes a fuel cell stack including a plurality of single cells that generate power through an electrochemical reaction between an anode gas and a cathode gas, and a reformer that steam reforms raw fuel gas to generate the anode gas. a temperature sensor for detecting a temperature correlated with the temperature of the fuel cell stack; and steam in the reformer when a first condition is satisfied during rated operation of the fuel cell stack. Adjusting the amount of steam supplied to the reformer so that the target ratio of the carbon ratio is smaller than a predetermined reference ratio so that the steam carbon ratio matches the target ratio, and the temperature sensor detects the target ratio. a control device for adjusting the supply amount of the cathode gas to the fuel cell stack so that the temperature obtained coincides with the target temperature corrected based on the target ratio of the steam carbon ratio.

In the fuel cell system of the present disclosure, when the first condition is satisfied during rated operation of the fuel cell stack, the target ratio of the steam carbon ratio in the reformer is set smaller than the predetermined reference ratio, and the steam The amount of steam supplied to the reformer is adjusted so that the carbon ratio matches the target ratio. As a result, the energy required for reforming the raw fuel gas can be reduced, and the amount of water vapor in the anode gas can be reduced, thereby improving the efficiency of the fuel cell system. Here, according to the research of the present inventors, when the steam carbon ratio is reduced in accordance with the establishment of the first condition during rated operation, the correlation between the temperature of the fuel cell stack and the detected value of the temperature sensor is It has been found that there is a misalignment which makes it impossible to properly maintain the temperature of the fuel cell stack. Based on this, in the fuel cell system of the present disclosure, when the target ratio of the steam carbon ratio is set smaller than the reference ratio, the target temperature is corrected based on the target ratio and the temperature detected by the temperature sensor is corrected. is adjusted to match the target temperature. As a result, even if the correlation between the temperature of the fuel cell stack and the detected value of the temperature sensor deviates due to the reduced steam carbon ratio, the temperature of the fuel cell stack can be properly maintained. As a result, while improving the efficiency of the fuel cell system, it is possible to properly maintain the temperature of the fuel cell stack and ensure good performance and durability of the fuel cell stack.

Further, when the first condition is satisfied during the rated operation, the control device sets the target ratio of the steam carbon ratio to be smaller as the amount of the cathode gas supplied to the fuel cell stack is smaller. In addition to setting, the target temperature may be corrected to be higher based on the target ratio. As a result, even if the correlation between the temperature of the fuel cell stack and the detected value of the temperature sensor deviates due to the reduced steam carbon ratio, it is possible to satisfactorily suppress the decrease in the temperature of the fuel cell stack. .

Furthermore, the first condition may be satisfied when at least the temperature of the mixed gas of the raw fuel gas and the steam supplied to the reformer is within a predetermined range. As a result, it is possible to satisfactorily suppress the occurrence of failures in the reformer due to the reduction in the amount of steam supplied in order to reduce the steam carbon ratio.

Further, the control device increases a target fuel utilization rate of the fuel cell stack higher than a predetermined reference utilization rate when a second condition is satisfied during the rated operation of the fuel cell stack. to adjust the supply amount of the raw fuel gas to the reformer so that the fuel utilization rate coincides with the target utilization rate, and the temperature detected by the temperature sensor determines the target fuel utilization rate. The amount of the cathode gas supplied to the fuel cell stack may be adjusted so as to match the target temperature corrected based on the utilization rate. That is, according to the research of the present inventors, even when the fuel utilization rate is increased according to the establishment of the second condition during rated operation, the correlation between the temperature of the fuel cell stack and the detected value of the temperature sensor It has been found that the temperature of the fuel cell stack cannot be maintained properly. Based on this, in the fuel cell system of this aspect, when the target utilization rate of the fuel utilization rate is set higher than the reference utilization rate, the target temperature is corrected based on the target utilization rate and detected by the temperature sensor. The amount of cathode gas supplied to the fuel cell stack is adjusted so that the temperature to be supplied matches the target temperature. As a result, even if the correlation between the temperature of the fuel cell stack and the detected value of the temperature sensor deviates due to the increase in the fuel utilization rate, the temperature of the fuel cell stack can be properly maintained. In such a fuel cell system, by simultaneously changing the fuel utilization rate and the steam carbon ratio during rated operation, the fuel utilization rate is increased and the power generation efficiency is improved, while the steam carbon ratio is increased. can be reduced to improve the energy efficiency, and the decrease in the temperature of the fuel cell stack due to the increase in the fuel utilization rate can be suppressed satisfactorily.

Further, the control device gradually increases the target utilization rate of the fuel utilization rate from the reference utilization rate to a predetermined upper limit value according to the establishment of the second condition during the rated operation, The target temperature may be corrected higher based on the target utilization rate. As a result, it becomes possible to increase the fuel utilization rate while satisfactorily suppressing a decrease in the temperature of the fuel cell stack.

Further, the second condition may be satisfied at least when the temperature of the exhaust gas discharged from the fuel cell stack is within a predetermined range. As a result, it is possible to suppress deterioration of the power generation efficiency by increasing the fuel utilization rate in a state where the combustibility of the fuel component in the anode gas is deteriorated.

A control method for a fuel cell system according to the present disclosure includes a fuel cell stack including a plurality of single cells each generating power through an electrochemical reaction between an anode gas and a cathode gas, and steam reforming raw fuel gas to generate the anode gas. and a temperature sensor for detecting a temperature correlated with the temperature of the fuel cell stack, wherein when a first condition is satisfied during rated operation of the fuel cell stack and adjusting the steam supply amount to the reformer so that the target ratio of the steam carbon ratio in the reformer is smaller than a predetermined reference ratio and the steam carbon ratio matches the target ratio. and adjusting the supply amount of the cathode gas to the fuel cell stack so that the temperature detected by the temperature sensor coincides with the target temperature corrected based on the target ratio of the steam carbon ratio. is.

According to such a method, it is possible to improve the efficiency of the fuel cell system, maintain the temperature of the fuel cell stack appropriately, and ensure good performance and durability of the fuel cell stack.

1 is a schematic configuration diagram showing a fuel cell system of the present disclosure; FIG. 4 is a flow chart showing an example of a fuel utilization adjustment routine executed in the fuel cell system of the present disclosure; FIG. 3 is a time chart exemplifying the time change of the target fuel utilization rate when the routine of FIG. 2 is executed; FIG. 4 is a flow chart showing an example of a steam carbon ratio adjustment routine executed in the fuel cell system of the present disclosure; FIG. 4 is an explanatory diagram illustrating a target steam carbon ratio setting map used in the fuel cell system of the present disclosure; 4 is a flow chart showing an example of an air supply amount control routine executed in the fuel cell system of the present disclosure; FIG. 4 is an explanatory diagram illustrating a first corrected temperature setting map used in the fuel cell system of the present disclosure; FIG. FIG. 4 is an explanatory diagram illustrating a second corrected temperature setting map used in the fuel cell system of the present disclosure;

Next, embodiments for carrying out the invention of the present disclosure will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a fuel cell system 10 of the present disclosure. The fuel cell system 10 shown in the figure includes a power generation unit 20 having a fuel cell stack FCS that generates power through an electrochemical reaction between hydrogen in the anode gas (fuel gas) and oxygen in the air that is the cathode gas (oxidant gas). , a hot water supply unit 100 having a hot water storage tank 101 for storing hot water, and a control device 80 for controlling the entire system. The power generation unit 20 includes a power generation module 30 including two fuel cell stacks FCS, a box-shaped module case 31 made of a heat-insulating material, a vaporizer (evaporator) 33, two reformers 34, and the like; A raw fuel gas supply system 40 for supplying a raw fuel gas (raw fuel) such as natural gas or LP gas to the vaporizer 33 of the module 30, and air as a cathode gas is supplied to the fuel cell stack FCS of the power generation module 30. a reformed water supply system 55 for supplying reformed water to the vaporizer 33 of the power generation module 30; and an exhaust heat recovery system for recovering exhaust heat generated in the power generation module 30. 60, a power conditioner 71 connected to the output terminal of the fuel cell stack FCS, and a housing 22 that accommodates them.

In this embodiment, the two fuel cell stacks FCS of the power generation module 30 are installed on the manifold 32 arranged inside the module case 31 so as to face each other with a space therebetween. Each fuel cell stack FCS has an electrolyte such as zirconium oxide, an anode electrode and a cathode electrode sandwiching the electrolyte, and a plurality of solid oxide type single cells arranged in the left-right direction (horizontal direction) in FIG. Contains cell C. An anode gas passage (not shown) is formed in the anode electrode of each unit cell C so as to extend in a direction perpendicular to the arrangement direction of the unit cells C, that is, in the vertical direction. Around the cathode electrode of each unit cell C, an air passage (not shown) for circulating air (cathode gas) is formed so as to extend in a direction perpendicular to the direction in which the unit cells C are arranged, that is, in the vertical direction. . The anode gas passage of each single cell C is connected to the anode gas passage formed in the manifold 32 , and the air passage of each single cell C is connected to the air passage inside the module case 31 . Further, a temperature sensor 94 is installed between (near) the two fuel cell stacks FCS so that the distance between them is the same. A temperature sensor 94 detects a temperature T4 that correlates with the temperature of each fuel cell stack FCS.

The vaporizer 33 and the reformer 34 of the power generation module 30 are arranged above the two fuel cell stacks FCS in the module case 31 with a space therebetween. In this embodiment, the vaporizer 33 and one reformer 34 are arranged above one fuel cell stack FCS, and the other reformer 34 is arranged above the other fuel cell stack FCS. Further, between one fuel cell stack FCS and the vaporizer 33 and one reformer 34 and between the other fuel cell stack FCS and the other reformer 34 in the vertical direction, fuel cell stack FCS and the heat required for the reaction in the vaporizer 33 and the reformer 34 are defined. Each combustion section 35 is provided with an ignition heater 36 .

The vaporizer 33 heats the raw fuel gas from the raw fuel gas supply system 40 and the reforming water from the reforming water supply system 55 with the heat from the combustion unit 35, preheats the raw fuel gas, and heats the reforming water. evaporate to form water vapor. The raw fuel gas preheated by the vaporizer 33 is mixed with water vapor, and the mixed gas of the preheated raw fuel gas and water vapor flows from the vaporizer 33 into the two reformers 34 through the gas passage. . A temperature sensor 91 for detecting the temperature T1 of the mixed gas is installed in the gas passage connecting the vaporizer 33 and each reformer 34 so as to be close to the two reformers 34 .

The reformer 34 has, for example, a Ru-based or Ni-based reforming catalyst filled therein, and in the presence of heat from the combustion section 35, the mixed gas from the vaporizer 33 reacts with the reforming catalyst. A (steam reforming reaction) produces hydrogen gas and carbon monoxide. Furthermore, the reformer 34 produces hydrogen gas and carbon dioxide through a reaction (carbon monoxide shift reaction) between carbon monoxide produced in the steam reforming reaction and steam. As a result, the reformer 34 generates anode gas containing hydrogen, carbon monoxide, carbon dioxide, water vapor, unreformed raw fuel gas, and the like. The anode gas generated by the reformer 34 is supplied to the anode electrode of each single cell C via a pipe (not shown) or the anode gas passage of the manifold 32 .

Also, air as a cathode gas containing oxygen is supplied to the cathode electrode of each unit cell C of the fuel cell stack FCS through the air passage in the module case 31 . Oxide ions (O ₂ ⁻ ) are generated at the cathode electrode of each single cell C, and the oxide ions permeate the electrolyte and react with hydrogen and carbon monoxide at the anode electrode to obtain electrical energy. The anode gas (hereinafter referred to as "anode off-gas") and air (hereinafter referred to as "cathode off-gas") that have not been used for the electrochemical reaction (power generation) in each single cell C are removed from the anode gas passage of each single cell C and the air. It flows out of the passage to the upper combustion section 35 .

The anode off-gas that has flowed into the combustion section 35 from each single cell C is a combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the oxygen-containing cathode off-gas that has flowed into the combustion section 35 from each single cell C. Fit. A mixed gas of the anode off-gas and the cathode off-gas is hereinafter referred to as "off-gas". When offgas (anode offgas) is ignited by the ignition heater 36 and ignited in the combustion unit 35, the combustion of the offgas activates the fuel cell stack FCS, preheats the raw fuel gas in the vaporizer 33, and produces water vapor. Heat necessary for production, steam reforming reaction in the reformer 34, etc. is generated. In addition, combustion exhaust gas containing unburned fuel and water vapor is generated in the combustion unit 35 , and the combustion exhaust gas is supplied to the heat exchanger 62 via the combustion catalyst 37 . The combustion catalyst 37 is an oxidation catalyst for re-burning unburned fuel in the combustion exhaust gas. Furthermore, a temperature sensor 98 is installed in the gas passage between the combustion catalyst 37 and the heat exchanger 62 to detect the temperature T8 of the combustion exhaust gas flowing out from the combustion catalyst 37 .

As shown in FIG. 1 , a raw fuel gas supply system 40 includes a raw fuel gas supply pipe 41 connecting a raw fuel supply source 1 that supplies natural gas or LP gas and a vaporizer 33 , and a raw fuel gas supply pipe 41 A raw fuel gas supply valve (electromagnetic on-off valve) 42 and a raw fuel pump 44 incorporated in the raw fuel gas supply pipe 41 so as to be positioned between the vaporizer 33 and the raw fuel pump 44, for example, at room temperature A desulfurization type desulfurizer 45 is included. Further, the raw fuel gas supply pipe 41 is provided with a pressure sensor 48 for detecting the pressure of the raw fuel gas in the raw fuel gas supply pipe 41, A flow rate sensor 49 is installed to detect the flow rate.

The air supply system 50 includes an air supply pipe 51 connected to the air passage in the module case 31, an air filter 52 installed at the gas inlet of the air supply pipe 51, and a blower 53 incorporated in the air supply pipe 51. including. By operating the blower 53, the air as the cathode gas sucked through the air filter 52 is pressure-fed (supplied) by the blower 53 through the air passage to each fuel cell stack FCS. Further, the air supply pipe 51 is provided with a flow rate sensor 54 for detecting the flow rate of the air flowing through the air supply pipe 51 per unit time.

The reforming water supply system 55 includes a reforming water supply pipe 56 connected to the vaporizer 33, a reforming water tank 57 connected to the reforming water supply pipe 56 and storing reforming water, and reforming water. It includes a reforming water pump 58 incorporated in the supply pipe 56 and a flow sensor (not shown) installed in the reforming water supply pipe 56 . By operating the reformed water pump 58 , the reformed water in the reformed water tank 57 is pumped (supplied) to the vaporizer 33 by the reformed water pump 58 . A water purifier (not shown) for purifying the stored reformed water is installed in the reformed water tank 57 .

The exhaust heat recovery system 60 is a circulation pipe 61 connected to the hot water storage tank 101 of the hot water supply unit 100, and a heat exchanger that exchanges heat between hot water flowing through the circulation pipe 61 and combustion exhaust gas from the combustion unit 35 of the power generation module 30. 62 and a circulation pump 63 incorporated in the circulation pipe 61 . By operating the circulation pump 63, the hot water stored in the hot water storage tank 101 is introduced into the heat exchanger 62 by the circulation pump 63, and the heat exchanger 62 removes heat from the combustion exhaust gas to heat the hot water. It can be returned to the hot water storage tank 101 . Furthermore, the exhaust heat recovery system 60 heats the hot water in the circulation pipe 61 by consuming electric power from the radiator incorporated in the circulation pipe 61, a radiator fan (electric fan) that sends air to the radiator, and the power generation module 30. and a thermistor (temperature sensor) for detecting the temperature of hot water heated by the electric heater (not shown).

In addition, the heat exchanger 62 (the gas passage of the combustion exhaust gas) of the exhaust heat recovery system 60 is connected to the reforming water tank 57 via a pipe so that the water vapor in the combustion exhaust gas mixes with the hot water from the hot water storage tank 101. The condensed water obtained by condensing by heat exchange is introduced into the reforming water tank 57 through the pipe. Furthermore, the gas passage of the combustion exhaust gas of the heat exchanger 62 is connected to an exhaust pipe 68 . As a result, the exhaust gas discharged from the combustion section 35 of the power generation module 30 and from which moisture has been removed by the heat exchanger 62 is discharged into the atmosphere through the exhaust pipe 68 .

The power conditioner 71 includes a DC/DC converter that boosts the DC power from each fuel cell stack FCS, an inverter that converts the DC power from the DC/DC converter into AC power, and the like (not shown). An output terminal of the power conditioner 71 (inverter) is connected to the power line 3 connected to the system power supply 2 . This makes it possible to convert the DC power from each fuel cell stack FCS into AC power and supply it to the load 4 such as a home appliance. Furthermore, the fuel cell system 10 includes a power board 72 connected to the power conditioner 71 . The power supply board 72 converts the DC power from each fuel cell stack FCS and the AC power from the system power supply 2 into low-voltage DC power, and supplies the raw fuel gas supply valve 42, the raw fuel pump 44, the blower 53, and the reforming water pump. 58, circulating pump 63, accessories such as a radiator fan, sensors such as temperature sensors 91, 94, and 98, controller 80, and the like. In addition, a cooling fan (not shown) for cooling the power conditioner 71, the power supply board 72, etc., and a ventilation fan 24 are arranged in the auxiliary equipment room in which the power conditioner 71, the power supply board 72, etc. are arranged. It is A cooling fan (not shown) sends air to the heat-generating portions of the power conditioner 71 and the power supply substrate 72 , and the air heated by cooling the heat-generating portions is discharged into the atmosphere by the ventilation fan 24 .

The control device 80 is a computer including a CPU 81, a ROM 82 that stores various programs, a RAM 83 that temporarily stores data, an input port, an output port, and the like (all not shown). The control device 80 includes a current sensor (not shown) that detects a current I (stack current) output from the two fuel cell stacks FCS, and a current sensor (not shown) that detects a voltage V (stack voltage) output from the two fuel cell stacks FCS. Detected values from the voltage sensor, temperature sensors 91, 94, 98, pressure sensor 48, flow rate sensor 49, thermistor of the exhaust heat recovery system 60, signals from the flow rate sensor 54, etc. are inputted. Further, the control device 80 controls the raw fuel gas supply valve 42, the raw fuel pump 44, the blower 53, the reforming water pump 58, the ignition heater 36, the ventilation fan 24, the circulation pump 63, and the like based on the signals from these sensors. , radiator fan, electric heater, power conditioner 71 (DC/DC converter and inverter), power supply board 72, display panel (not shown), etc., to control these devices. Furthermore, a remote controller (not shown) is connected to the control device 80 via a wireless or wired communication line. The control device 80 executes various controls based on signals from the remote controller operated by the user of the fuel cell system 10 .

In addition, in the fuel cell system 10 of the present embodiment, when the operation state of the power generation module 30 shifts from the partial load operation state to the rated operation state, the target utilization rate Uftag (target Uf) of the fuel utilization rate Uf in each fuel cell stack FCS is set to a predetermined reference utilization rate Ufref (for example, a value around 80%). Further, when the operating state of the power generation module 30 shifts to the rated operating state, the steam carbon ratio SC in each reformer 34 (the ratio of carbon contained in hydrocarbons in the raw fuel gas and steam added for steam reforming ) is set to a predetermined reference ratio SCref (for example, a value of about 2.5 to 2.7). Then, when the operating state shifts to the rated operating state, the power generation module 30 is operated at the rated operation with an air-fuel ratio within a predetermined range, and the fuel utilization rate Uf in each fuel cell stack FCS becomes the reference utilization rate Ufref. In addition, the supply amounts of raw fuel gas, air and reforming water are controlled so that the steam carbon ratio SC in each reformer 34 becomes the target ratio SCtag.

Next, a control procedure of the fuel cell system 10 when the power generation module 30 is operated at rated operation will be described with reference to FIGS. 2 to 7. FIG.

FIG. 2 is a flowchart showing an example of a fuel utilization rate adjustment routine that is executed by the control device 80 at predetermined time intervals while the power generation module 30 is in rated operation. At the start of the routine of FIG. 2, the control device 80 (CPU 81) controls the current I from the two fuel cell stacks FCS detected by the current sensors and the current I from the two fuel cell stacks FCS detected by the voltage sensors. Data necessary for control such as voltage V and temperatures T4 and T8 detected by temperature sensors 94 and 98 are acquired (step S100). Next, control device 80 determines whether or not current I, voltage V and temperature T4 are each within a predetermined output stabilization range (step S110). If it is determined in step S110 that at least one of current I, voltage V, and temperature T4 is not within the corresponding output stabilization range (step S110: NO), control device 80 controls power generation module 30, that is, It is assumed that the output of each fuel cell stack FCS is not stable, and the routine of FIG. 2 is terminated at that time.

On the other hand, if it is determined in step S110 that current I, voltage V, and temperature T4 are within their corresponding output stabilization ranges (step S110: YES), controller 80 causes temperature sensor 98 to detect It is determined whether or not the temperature T8 of the combustion exhaust gas obtained is within a predetermined allowable range (for example, a predetermined temperature or lower) (step S120). When it is determined in step S120 that the temperature T8 is not within the permissible range (step S120: NO), the control device 80 determines that the amount of unburned fuel burning in the combustion catalyst 37 is relatively large, and fuel utilization It is assumed that the rate Uf cannot be increased, and the routine of FIG. 2 is terminated at that time.

On the other hand, after it is determined in step S110 that current I, voltage V, and temperature T4 are within their corresponding output stabilization ranges, temperature T8 is within the allowable range in step S120. (steps S110 and S120: YES), the control device 80 sets the target utilization rate Uftag set at that time (previous Uftag, the first execution of step S130 after shifting to the rated operation, A value obtained by adding a predetermined value ΔUf (for example, a positive value of about 0.2 to 0.3%) to Uftag (=reference utilization rate Ufref) is set as a new target utilization rate Uftag (step S130).

After the process of step S130, the control device 80 sets the target supply rate (flow rate per unit time) of the raw fuel gas according to the operating state of the power generation module 30 in step S130. ), the raw fuel pump 44 is feedback-controlled so that the flow rate detected by the flow rate sensor 49 becomes the target supply rate (step S140). Further, the control device 80 determines whether or not a predetermined time (for example, about 5 minutes) has passed since the process of step S130 was started (step S150). The process of step S140 is repeatedly executed at predetermined time intervals.

When it is determined in step S150 that the predetermined time has passed (step S150: YES), the control device 80 sets the target utilization rate Uftag to an upper limit value Ufmax (for example, the reference utilization rate Ufref+value of about 1%) is determined (step S160). If it is determined in step S160 that the target utilization rate Uftag has not reached the upper limit value Ufmax (step S160: NO), the control device 80 sets a new target utilization rate Uftag in step S130 and The process of step S140 is repeatedly executed until it is determined that has elapsed. When the control device 80 determines in step S160 that the target utilization rate Uftag has reached the upper limit value Ufmax (step S160: YES), the fuel utilization rate adjustment routine of FIG. 2 is once ended at that time.

As a result of executing this fuel utilization rate adjustment routine, when the output of each fuel cell stack FCS is stabilized during the rated operation of the power generation module 30 and the temperature T8 of the combustion exhaust gas is within the allowable range (the second condition is established), as shown in FIG. 3, the target utilization rate Uftag of the fuel utilization rate Uf is set to increase stepwise from the reference utilization rate Ufref to a predetermined upper limit value Ufmax over time. The raw fuel gas flowing out of the raw fuel pump 44 is reduced so that Uf matches the target utilization Uftag. This makes it possible to gradually increase the fuel utilization rate Uf during the rated operation of the power generation module 30 to increase the power generation efficiency in each fuel cell stack FCS.

FIG. 4 is a flow chart showing an example of a steam carbon ratio adjustment routine that is executed by the controller 80 at predetermined intervals in parallel with the fuel utilization rate adjustment routine of FIG. 2 when the power generation module 30 is in rated operation. be. At the start of the routine of FIG. 4, the control device 80 (CPU 81) controls the current I detected by the current sensor, the voltage V detected by the voltage sensor, and the temperatures T1 and T4 detected by the temperature sensors 91 and 94. acquires data necessary for (step S200). Next, control device 80 determines whether or not current I, voltage V, and temperature T4 are each within a predetermined output stabilization range (each of which is the same as that used in step S110 of FIG. 2). is determined (step S210). If it is determined in step S210 that at least one of the current I, voltage V, and temperature T4 is not within the corresponding output stabilization range (step S210: NO), the control device 80 controls the power generation module 30 to It is assumed that the output is not stable, and the routine of FIG. 4 is terminated at that point.

On the other hand, if it is determined in step S210 that current I, voltage V, and temperature T4 are within their corresponding output stabilization ranges (step S210: YES), controller 80 causes temperature sensor 91 to detect It is determined whether or not the temperature T1 of the mixed gas obtained is within a predetermined allowable range (for example, a predetermined temperature or less) (step S220). When it is determined in step S220 that the temperature T1 is not within the allowable range (step S220: NO), the controller 80 reduces the steam carbon ratio SC because the temperature T1 of the mixed gas is relatively high. is not possible, and the routine of FIG. 4 is terminated at that point. On the other hand, after it is determined in step S210 that current I, voltage V, and temperature T4 are within their corresponding output stabilization ranges, temperature T1 is within the allowable range in step S220. (steps S210 and S220: YES), the controller 80 acquires the flow rate of air detected by the flow sensor 54, that is, the air supply amount A (step S230). to set the target ratio SCtag of the steam carbon ratio SC (step S240).

At step S240, the control device 80 derives a target ratio SCtag corresponding to the air supply amount A acquired at step S230 from the target steam carbon ratio setting map illustrated in FIG. In this embodiment, the target steam carbon ratio setting map sets the target ratio SCtag to a lower limit value SCmin (for example, 0.2 value), the target ratio SCtag is increased (closer to the reference ratio SCref) as the air supply amount A increases, and the air supply amount A approaches the maximum air supply amount Amax determined by the performance of the blower 53, etc. and the target ratio SCtag to the reference ratio SCref, and are stored in the ROM 82 of the controller 80 .

After setting the target ratio SCtag in step S240, the control device 80 controls the reforming water supplied from the reforming water pump 58 to the vaporizer 33 ( A flow rate correction value for decreasing the flow rate of steam supplied to each reformer 34 is set (step S250), and the routine of FIG. 4 is temporarily terminated. When the reforming water flow rate correction value is set in step S250, the reforming water pump 58 is feedback-controlled so that the reforming water supply amount to the vaporizer 33 is decreased by the flow rate correction value.

That is, in the fuel cell system 10, when the output of each fuel cell stack FCS is stabilized during the rated operation of the power generation module 30 and the mixed gas temperature T1 is within the allowable range (when the first condition is satisfied). In addition, the target ratio SCtag of the steam carbon ratio SC is set so as to decrease as the air supply amount A to each fuel cell stack FCS decreases, and each reformer 34 is adjusted so that the steam carbon ratio SC coincides with the target ratio SCtag. is reduced. As a result, the energy required for reforming the raw fuel gas is reduced, the amount of water vapor in the anode gas is reduced, and the efficiency of the fuel cell system 10 is improved. It is possible to satisfactorily suppress the temperature drop of

Here, in the fuel cell system 10 of the present embodiment, the power generation module 30 (each fuel cell stack FCS) is operated in a state where the fuel utilization rate Uf is the reference utilization rate Ufref and the steam carbon ratio SC is the reference rate SCref. The temperature sensor 94 and the control device 80 are configured (adapted) so that the temperature sensor 94 outputs a temperature T4 that accurately reflects the temperature of each fuel cell stack FCS when the fuel cell stack FCS is in rated operation. However, according to research by the present inventors, the target utilization rate Uftag of the fuel utilization rate Uf is set to a large value depending on the determination results (satisfaction of the second condition) in steps S110 and S120 of FIG. 2 during rated operation. , the target ratio SCtag of the steam carbon ratio SC is set to a small value according to the determination result (the first condition is satisfied) in steps S210 and S220 of FIG. It has been found that the temperature T4 of each fuel cell stack FCS cannot be properly maintained due to a deviation in the correlation between the temperature T4 and the temperature T4. Based on this, in the fuel cell system 10 of the present disclosure, the temperature of each fuel cell stack FCS can be detected even if there is a deviation in the correlation between the temperature of each fuel cell stack FCS and the temperature T4 detected by the temperature sensor 94. In order to properly maintain the air supply amount, the control device 80 executes an air supply amount control routine shown in FIG.

At the start of the routine of FIG. 6, the control device 80 (CPU 81) acquires the separately set target utilization Uftag of the fuel utilization Uf and the target ratio SCtag of the steam carbon ratio SC (step S300). A corrected temperature ΔT _Uf corresponding to Uftag and a corrected temperature ΔT _SC corresponding to the target ratio SCtag are set (step S310). In step S310, the control device 80 derives the correction temperature ΔT _Uf corresponding to the target utilization rate Uftag acquired in step S300 from the first correction temperature setting map illustrated in FIG. A correction temperature ΔT _SC corresponding to the target ratio SCtag obtained in step S300 is derived from the correction temperature setting map.

In this embodiment, as shown in FIG. 7, the first correction temperature setting map sets the correction temperature ΔT _Uf to zero when the target utilization rate Uftag is the reference utilization rate Ufref, and the target utilization rate Uftag is set to the upper limit value. It is prepared (adapted) in advance so that the corrected temperature ΔT _Uf increases as it increases toward Ufmax, and is stored in the ROM 82 of the controller 80 . In this embodiment, the corrected temperature ΔT _Uf when the target utilization rate Uftag is the upper limit value Ufmax is, for example, about 1 to 2°C. Further, as shown in FIG. 8, the second correction temperature setting map sets the correction temperature ΔT _SC to zero when the target ratio SCtag is the reference ratio SCref, and the target ratio SCtag decreases toward the lower limit value SCmin. It is prepared (adapted) in advance so that the correction temperature ΔT _SC increases as the temperature increases, and is stored in the ROM 82 of the control device 80 . In this embodiment, the correction temperature ΔT _SC when the target ratio SCtag is the lower limit value SCmin is, for example, about 3 to 5°C.

After setting the correction temperatures ΔT _Uf and ΔT _SC in step S310, the control device 80 calculates the sum of a predetermined base temperature T4base (for example, a constant value of about 650°) and the correction temperatures ΔT _Uf and ΔT _SC . The target temperature T4tag of the temperature T4 detected by the temperature sensor 94 is set (step S320). Further, the control device 80 controls each fuel cell stack FCS so that the power generation module 30 is operated at rated operation with an air-fuel ratio within a predetermined range, and the temperature T4 detected by the temperature sensor 94 reaches the target temperature T4tag. A target air supply amount is set (step S330). Then, the controller 80 feedback-controls the blower 53 so that the flow rate detected by the flow rate sensor 54 becomes the target air supply rate (step S340), and terminates the routine of FIG.

As described above, in the fuel cell system 10 of the present disclosure, when the output of each fuel cell stack FCS is stabilized during rated operation of the power generation module 30 and the temperature T8 of the combustion exhaust gas is within the allowable range (second When the condition is established), the target utilization rate Uftag of the fuel utilization rate Uf in each fuel cell stack FCS is set to be greater than the predetermined reference utilization rate Ufref, and the fuel utilization rate Uf matches the target utilization rate Uftag. The amount of raw fuel gas supplied to each reformer 34 is adjusted so as to do so (FIG. 2). This makes it possible to increase the fuel utilization rate Uf in each fuel cell stack FCS and improve the power generation efficiency.

Further, when the output of each fuel cell stack FCS is stabilized during rated operation of the power generation module 30 and the temperature T1 of the mixed gas supplied to each reformer 34 is within the allowable range (when the first condition is satisfied). , the target ratio SCtag of the steam carbon ratio SC in each reformer 34 is set to be smaller than a predetermined reference ratio SCref, and each reformer 34 is adjusted so that the steam carbon ratio SC matches the target ratio SCtag. is regulated (Fig. 4). As a result, the energy required for reforming the raw fuel gas can be reduced, the amount of water vapor in the anode gas can be reduced, and the efficiency of the fuel cell system 10 can be improved.

Furthermore, in the fuel cell system 10, if the target utilization rate Uftag of the fuel utilization rate Uf is set higher than the reference utilization rate Ufref, or the target ratio SCtag of the steam carbon ratio SC is set lower than the reference rate SCref, the target The target temperature T4tag of the temperature T4 detected by the temperature sensor 94 is corrected based on at least one of the utilization rate Uftag and the target ratio SCtag, and each fuel cell stack FCS is adjusted so that the temperature T4 matches the target temperature T4tag. The air supply to is adjusted (Fig. 6). As a result, even if the correlation between the temperature of each fuel cell stack FCS and the detected value of the temperature sensor 94 deviates by increasing the fuel utilization rate Uf or decreasing the steam carbon ratio SC, the fuel It becomes possible to properly maintain the temperature of the battery stack FCS.

By simultaneously changing the fuel utilization rate Uf and changing the steam carbon ratio SC during the rated operation of the power generation module 30, the fuel utilization rate Uf is increased to improve the power generation efficiency, and the steam carbon It is possible to satisfactorily suppress a decrease in the temperature of each fuel cell stack FCS caused by increasing the fuel utilization rate Uf while increasing the energy efficiency by decreasing the ratio SC. As a result, in the fuel cell system 10, it is possible to maintain the temperature of each fuel cell stack FCS appropriately while improving the efficiency, thereby ensuring good performance and durability of the fuel cell stack FCS.

Further, in the fuel cell system 10, the target utilization rate Uftag of the fuel utilization rate Uf is changed from the reference utilization rate Ufref to the predetermined upper limit value Ufmax in response to the affirmative determinations in steps S110 and S120 of FIG. (steps S140-S160 in FIG. 2), and the target temperature T4tag of the temperature T4 is corrected higher based on the target utilization rate Uftag (steps S300-S320 in FIG. 6). As a result, it becomes possible to increase the fuel utilization rate Uf while satisfactorily suppressing a decrease in the temperature of each fuel cell stack FCS. In addition, in the fuel cell system 10, the target utilization rate Uftag is set large on the condition that the temperature T8 of the flue gas discharged from each fuel cell stack FCS is within a predetermined allowable range (Fig. 2 steps S120-S160). As a result, it is possible to prevent deterioration of the power generation efficiency by increasing the fuel utilization factor Uf when the combustibility of the fuel component in the anode gas is deteriorated.

Furthermore, in the fuel cell system 10, if the determinations in steps S210 and S220 in FIG. (steps S230-S240 in FIG. 4), and the target temperature T4tag of the temperature T4 is corrected to be higher based on the target ratio SCtag (steps S300-S320 in FIG. 6). As a result, even if the correlation between the temperature of each fuel cell stack FCS and the value detected by the temperature sensor 94 deviates due to the reduction of the steam carbon ratio SC, the temperature drop of each fuel cell stack FCS can be suppressed satisfactorily. It becomes possible to In the fuel cell system 10, the target ratio SCtag is set small on the condition that the temperature T1 of the mixed gas of the raw fuel gas and steam supplied to each reformer 34 is within a predetermined allowable range. (steps S220-S240 in FIG. 4). As a result, it is possible to satisfactorily suppress the occurrence of failures in the reformers 34 due to the reduction in the amount of steam supplied in order to reduce the steam carbon ratio SC when the temperatures of the reformers 34 are high. .

In step S320 _{of FIG. 6, only the larger one of the correction temperature ΔT Uf corresponding to the target utilization rate Uftag and the correction temperature ΔT SC corresponding} to the target ratio SCtag may be added to the base temperature T4base. Further, in the fuel cell system 10, execution of the routine of FIG. 2, that is, adjustment of the fuel utilization rate Uf may be omitted. Furthermore, the fuel cell system 10 may include a single fuel cell stack FCS, or may include three or more fuel cell stacks FCS.

It goes without saying that the invention of the present disclosure is not limited to the above-described embodiments, and various modifications can be made within the scope of the present disclosure. Furthermore, the above-described embodiment is merely one specific form of the invention described in the Summary of the Invention column, and does not limit the elements of the invention described in the Summary of the Invention column.

INDUSTRIAL APPLICABILITY The invention of the present disclosure can be used in the manufacturing industry of fuel cell systems and the like.

1 raw fuel supply source, 2 system power supply, 3 power line, 4 load, 10 fuel cell system, 20 power generation unit, 22 housing, 24 ventilation fan, 30 power generation module, 31 module case, 32 manifold, 33 vaporizer, 34 reformer, 35 combustion unit, 36 ignition heater, 37 combustion catalyst, 40 raw fuel gas supply system, 41 raw fuel gas supply pipe, 42 raw fuel gas supply valve, 44 raw fuel pump, 45 desulfurizer, 48 pressure sensor, 49 flow sensor, 50 air supply system, 51 air supply pipe, 52 air filter, 53 blower, 54 flow sensor, 55 reformed water supply system, 56 reformed water supply pipe, 57 reformed water tank, 58 reformed water pump , 60 exhaust heat recovery system, 61 circulation pipe, 62 heat exchanger, 63 circulation pump, 68 exhaust pipe, 71 power conditioner, 72 power supply board, 80 control device, 81 CPU, 82 ROM, 83 RAM, 91, 94, 98 temperature sensor, 100 hot water supply unit, 101 hot water storage tank, C single cell, FCS fuel cell stack.

Claims (7)

In a fuel cell system including a fuel cell stack including a plurality of single cells each generating power through an electrochemical reaction between an anode gas and a cathode gas, and a reformer steam reforming raw fuel gas to generate the anode gas ,
a temperature sensor that detects a temperature correlated with the temperature of the fuel cell stack;
When a first condition is established during rated operation of the fuel cell stack, the target ratio of the steam carbon ratio in the reformer is made smaller than a predetermined reference ratio so that the steam carbon ratio reaches the target ratio. The amount of steam supplied to the reformer is adjusted so that the temperature detected by the temperature sensor matches the target temperature corrected based on the target ratio of the steam carbon ratio. and a controller that adjusts the supply amount of the cathode gas to the fuel cell stack. In the fuel cell system according to claim 1,
The control device sets the target ratio of the steam carbon ratio so as to decrease as the amount of the cathode gas supplied to the fuel cell stack decreases when the first condition is satisfied during the rated operation. and a fuel cell system that corrects the target temperature to be higher based on the target ratio. 3. In the fuel cell system according to claim 1,
In the fuel cell system, the first condition is satisfied when at least the temperature of the mixed gas of the raw fuel gas and the steam supplied to the reformer is within a predetermined range. In the fuel cell system according to any one of claims 1 to 3,
When a second condition is satisfied during the rated operation of the fuel cell stack, the control device increases a target fuel utilization rate of the fuel cell stack above a predetermined reference utilization rate to increase the fuel utilization rate. The amount of the raw fuel gas supplied to the reformer is adjusted so that the fuel utilization rate matches the target utilization rate, and the temperature detected by the temperature sensor determines the target utilization rate of the fuel utilization rate. a fuel cell system that adjusts the supply amount of the cathode gas to the fuel cell stack so as to match the target temperature corrected based on the above. 5. The fuel processing system of claim 4, wherein
The control device gradually increases the target utilization rate of the fuel utilization rate from the reference utilization rate to a predetermined upper limit value in accordance with the establishment of the second condition during the rated operation, and the target A fuel cell system that corrects the temperature to be higher based on the target utilization rate. In the fuel cell system according to claim 4 or 5,
A fuel cell system in which the second condition is satisfied when at least the temperature of the exhaust gas discharged from the fuel cell stack is within a predetermined range. a fuel cell stack including a plurality of single cells each generating power through an electrochemical reaction between an anode gas and a cathode gas; a reformer for steam reforming raw fuel gas to generate the anode gas; A control method for a fuel cell system including a temperature sensor that detects a temperature correlated with the temperature,
When a first condition is established during rated operation of the fuel cell stack, the target ratio of the steam carbon ratio in the reformer is made smaller than a predetermined reference ratio so that the steam carbon ratio reaches the target ratio. The amount of steam supplied to the reformer is adjusted so that the temperature detected by the temperature sensor matches the target temperature corrected based on the target ratio of the steam carbon ratio. A fuel cell system control method for adjusting the supply amount of the cathode gas to the fuel cell stack.

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