JP5002025B2 - Fuel reforming system and control method of fuel reforming system - Google Patents

Description

  The present invention relates to a fuel reforming system and a control method for the fuel reforming system.

  Hydrogen consumed in a fuel cell or the like is generated, for example, in a fuel reforming system. In a fuel reforming system, hydrogen is generated by a steam reforming reaction between reformed fuel such as hydrocarbon and reformed water in a reformer. Since the steam reforming reaction is a chemical reaction process, if the amount of reforming water supplied to the reformer becomes unstable, the amount of generated hydrogen becomes unstable. Therefore, in the technique of Patent Document 1, a steam flow meter is provided to control the reforming water supply amount.

JP-A-4-331896

  However, since the steam flow meter is very expensive, the cost increases.

  The present invention has been made in view of the above problems, and a fuel reforming system and a fuel capable of optimizing and controlling the supply amount of reforming water without using a detector such as a flow meter for detecting a water vapor flow rate It aims at providing the control method of a reforming system.

A fuel reforming system according to the present invention includes a reformer that reforms reformed fuel by a steam reforming reaction using reformed water to generate a fuel gas containing hydrogen, and reformed water to the reformer. A supply amount adjusting means for adjusting the supply amount of the gas, a pressure detecting means for detecting the gas pressure in the reformer, and a standard deviation of the gas pressure detected by the pressure detecting means , And a correction unit that corrects the supply amount of the reforming water by the supply amount adjustment unit so that the fluctuation range falls within a range in which the S / C ratio in a predetermined range is realized . In the fuel reforming system according to the present invention, the reforming water supply amount is corrected based on the variation amount of the gas pressure. Therefore, the supply amount of the reforming water can be optimized and controlled without using an expensive detector such as a flow meter for detecting the water vapor flow rate.

  The correction means may perform correction to reduce the supply amount of the reforming water when the standard deviation of the gas pressure exceeds a predetermined value. The correction means may perform correction to increase the supply amount of the reforming water when the standard deviation of the gas pressure is below a predetermined value. In this case, the reforming water supply amount is corrected so that the standard deviation of the gas pressure falls within a predetermined range. Therefore, the S / C ratio can be controlled to a preferable value.

  The correction means may not correct the amount of reforming water supplied by the supply amount adjusting means when the amount of change in the reforming amount of the reformer exceeds a predetermined value. In this case, erroneous correction in a transient state in which the amount of change in the reforming amount in the reformer is large is avoided.

  Setting means for setting the supply amount of reformed fuel to the reformer is provided, and the correction means is detected by the reforming water supply amount derived based on the supply amount set by the setting means and the pressure detection means. When the difference from the reforming water supply amount derived based on the gas pressure exceeds a predetermined value, it is not necessary to correct the reforming water supply amount by the supply amount adjusting means. In this case, it is possible to avoid erroneous correction in the gas pressure fluctuation amount small region due to excessive supply of reforming water. The correction range of the reforming water supply amount corrected by the correcting unit may be changed according to the reforming amount of the reformer.

A control method for a fuel reforming system according to the present invention includes the supply of reformed water to a reformer that reforms the reformed fuel by a steam reforming reaction using the reformed water to generate a fuel gas containing hydrogen. A supply amount adjusting step for adjusting the amount, a pressure detecting step for detecting the gas pressure in the reformer, and a fluctuation range of the pressure in the reformer based on the standard deviation of the gas pressure detected in the pressure detecting step. Includes a correction step of correcting the supply amount of the reforming water in the supply amount adjustment step so as to fall within a range in which a predetermined S / C ratio is realized . In the control method for the fuel reforming system according to the present invention, the reforming water supply amount is corrected based on the variation amount of the gas pressure. Therefore, the supply amount of the reforming water can be optimized and controlled without using an expensive detector such as a flow meter for detecting the water vapor flow rate.

  The correction step may be a step of performing correction to reduce the supply amount of the reforming water when the standard deviation of the gas pressure exceeds a predetermined value. The correction step may be a step of performing correction to increase the supply amount of the reforming water when the standard deviation of the gas pressure is below a predetermined value. In this case, the reforming water supply amount is corrected so that the standard deviation of the gas pressure falls within a predetermined range. Therefore, the S / C ratio can be controlled to a preferable value.

  In the correction step, the supply amount of the reforming water may not be corrected when the amount of change in the reforming amount of the reformer exceeds a predetermined value. In this case, erroneous correction in a transient state in which the amount of change in the reforming amount in the reformer is large is avoided.

  Including a setting step for setting the supply amount of reformed fuel to the reformer, and in the correction step, the reforming water supply amount derived based on the supply amount set by the setting step and the pressure detection step When the difference between the reforming water supply amount derived based on the gas pressure and the reforming water supply amount exceeds a predetermined value, the reforming water supply amount may not be corrected. In this case, it is possible to avoid erroneous correction in the gas pressure fluctuation amount small region due to excessive supply of reforming water. The correction range of the reforming water supply amount that is corrected in the correction step may be changed according to the reforming amount of the reformer.

  According to the present invention, there are provided a fuel reforming system and a control method for the fuel reforming system capable of optimizing the supply amount of reforming water without using a detector such as a flow meter for detecting a water vapor flow rate. be able to.

1 is an explanatory diagram schematically showing a configuration of a fuel cell system to which a fuel reforming system according to Embodiment 1 is applied. FIG. It is a fragmentary perspective view containing the cross section of the fuel cell which comprises a fuel cell stack. It is a perspective view for demonstrating a fuel cell stack. It is a perspective view which extracts and shows a fuel cell stack, a combustion part, and a reformer. It is a perspective view for demonstrating the detail of a reformer. It is a figure which shows the relationship between saturated water vapor pressure and water vapor temperature. It is a figure which shows the correlation of the amount of reforming water supply and gas pressure in the power generation experiment from the light load of a fuel cell stack to a rated load. It is a figure which shows transition of the gas pressure at the time of making the reforming water supply amount increase gradually. It is a figure which shows transition of the gas pressure after a reformed water supply start. It is a flowchart showing the reforming water supply amount optimization routine when the reforming water flow rate control program is executed. It is a figure which shows the map and table which are used with the flowchart of FIG.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is an explanatory diagram schematically showing the configuration of a fuel cell system 1000 to which a fuel reforming system according to Embodiment 1 of the present invention is applied. The fuel cell system 1000 includes a fuel cell stack 100, a combustion unit 200, a heat exchanger 300, a reformer 400, a control unit 600, and the like.

  The fuel cell stack 100 obtains an electromotive force by causing an electrochemical reaction between hydrogen as a fuel gas and oxygen in the air as an oxidant gas at each electrode. In this embodiment, the fuel cell stack 100 is a solid oxide fuel cell (SOFC) having a reaction temperature of about 600 ° C. to 1000 ° C. Exhaust gas discharged from the anode side of the fuel cell stack 100 (hereinafter also referred to as anode exhaust gas) is supplied to the combustion unit 200 via the anode exhaust gas passage 108.

  The air supply system that supplies air as an oxidant gas to the fuel cell stack 100 includes an air supply path 114 and an air pump 116 provided on the air supply path 114. The air pump 116 supplies air taken from the outside through the air cleaner as an oxidant gas to the cathode of the fuel cell stack 100 through the air supply path 114. Exhaust gas discharged from the cathode side of the fuel cell stack 100 (hereinafter also referred to as cathode exhaust gas) is supplied to the combustion unit 200 via the cathode exhaust gas path 118.

  The combustion unit 200 includes a glow ignition mechanism, and applies a predetermined voltage to the glow ignition mechanism, thereby utilizing oxygen in the cathode exhaust gas supplied via the cathode exhaust gas channel 118 and passing through the anode exhaust gas channel 108. The anode exhaust gas supplied is burned. The combustion unit 200 is provided with a combustion exhaust gas passage 202, and combustion exhaust gas including the gas after combustion in the combustion unit 200 and unburned gas is released into the atmosphere through the combustion exhaust gas passage 202.

  The heat exchanger 300 is provided with a tap water introduction path 302 and a hot water discharge path 304. In the heat exchanger 300, the tap water introduced through the tap water introduction path 302 is warmed by the combustion heat accompanying combustion in the combustion unit 200 to make warm water. The hot water discharge path 304 is connected to a water storage tank. The hot water warmed by the heat exchanger 300 is stored in the water storage tank via the hot water discharge path 304. The water storage tank is connected to, for example, a user's home bath or shower, and hot water stored in the water storage tank is supplied to the user in response to a request from the user. The hot water in the water storage tank may be reintroduced into the heat exchanger 300 and reheated. For example, it is suitable when the temperature of the hot water in the water storage tank decreases, or when the temperature of the hot water in the water storage tank is lower than the temperature required by the user.

The reformer 400 includes a mixing unit and a reforming unit. A reformed fuel supplied from a reformed fuel tank 402 described later and water supplied from a reformed water tank 500 described later (hereinafter also referred to as reformed water) are mixed in a mixing unit. The reforming water is vaporized in the mixing part. Hereinafter, the gas mixed and vaporized in the mixing section is referred to as “mixed gas”. The reforming unit includes a reforming catalyst that promotes the reforming reaction. When the mixed gas generated in the mixing section is introduced into the reforming section, the reforming reaction proceeds by the reforming catalyst, and a fuel gas containing hydrogen is generated. Since this reforming reaction is an endothermic reaction, heat input is required. In this embodiment, the heat generated by the combustion reaction in the combustion unit 200 is used. The reforming catalyst is appropriately determined according to the reformed fuel used for the reforming reaction. The fuel gas generated in the reformer 400 and supplied to the fuel cell stack 100 includes carbon monoxide (CO), carbon dioxide (CO ₂ ), unreacted reformed fuel, and the like in addition to hydrogen. It is.

  A reformed fuel supply system for supplying reformed fuel to the reformer 400 includes a reformed fuel tank 402, a reformed fuel supply path 404, and a flow rate adjustment valve 406 provided on the reformed fuel supply path 404. Prepare. The reformed fuel supply system is provided with a pressure sensor 410 that detects a gas pressure in the reformer 400 (hereinafter also referred to as an anode pressure). The pressure sensor 410 may be provided at any location on the piping from the flow rate adjustment valve 406 to the anode of the fuel cell stack 100.

  The reformed fuel tank 402 stores hydrocarbons as reformed fuel. The reformed fuel is not limited to hydrocarbons, and ammonia or the like may be used. Note that a supply pipe for city gas or the like may be used as the reformed fuel supply means without using the reformed fuel tank 402. The hydrocarbon stored in the reformed fuel tank 402 is adjusted to a predetermined flow rate by the flow rate control valve 406 and supplied to the reformer 400 via the reformed fuel supply path 404. The fuel gas containing hydrogen, carbon monoxide, carbon dioxide, unreacted reformed fuel and the like generated in the reformer 400 is supplied to the anode of the fuel cell stack 100 via the fuel supply path 408.

  A reforming water supply system for supplying reforming water to the reformer 400 includes a condenser 504, a reflux pump 505, a condensing water path 506, a reforming water tank 500, a reforming water supply path 508, A reforming water pump 510 and a reforming water metering solenoid valve 512 are provided. The condenser 504 is provided on the exhaust gas discharge path 206 and condenses water vapor contained in the combustion exhaust gas cooled in the heat exchanger 300. A condenser water channel 506 is connected to the condenser 504. The reflux pump 505 introduces the liquid water condensed in the condenser 504 (hereinafter also referred to as “condensed water”) into the reformed water tank 500 via the condensed water path 506. Condensed water (reformed water) stored in the reformed water tank 500 is introduced into the reformed fuel supply path 404 via the reformed water supply path 508 by the reformed water pump 510. The reformed water metering solenoid valve 512 adjusts the amount of reformed water introduced into the reformed fuel supply path 404. In this way, both the hydrocarbon as reformed fuel and the reformed water are supplied to the reformer 400.

  The control unit 600 is configured as a logic circuit centered on a microcomputer. The control unit 600 includes a CPU 610 that executes predetermined calculations, a memory 620 that stores a reforming water flow rate control program 621, a map 622, a map 623, a map 624, and the like, and an input / output port that inputs and outputs various signals. 630. The CPU 610 executes predetermined calculations and the like according to the reforming water flow rate control program 621.

  The control unit 600 acquires the detection signal of the pressure sensor 410 described above, information related to the power generation request for the fuel cell stack 100, and the like. The control unit 600 calculates an appropriate flow rate of the reforming water supplied to the reformer 400 based on the acquired information, and outputs a drive signal to the reforming water metering electromagnetic valve 512. In addition, the control unit 600 outputs a drive signal to each unit related to power generation of the fuel cell stack 100 such as the flow rate adjustment valve 406 and the air pump 116.

  Next, details of the fuel cell stack 100, the combustion unit 200, and the reformer 400 will be described. FIG. 2 is an excerpt of the fuel cell 10 constituting the fuel cell stack 100, and is a partial perspective view including a cross section of the fuel cell 10. As shown in FIG. 2, the fuel battery cell 10 has a flat plate-like overall shape. A plurality of fuel gas passages 12 penetrating along the axial direction are formed in the conductive support 11 having gas permeability. On one plane, the anode 13, the solid electrolyte 14, and the cathode 15 are laminated in order. On the other plane of the outer peripheral surface of the conductive support 11, an interconnector 17 is provided via a bonding layer 16, and a P-type semiconductor layer 18 for reducing contact resistance is provided thereon. Thereby, the anode 13 and the interconnector 17 are disposed so as to face each other with the conductive support 11 interposed therebetween.

Hydrogen is supplied to the anode 13 by supplying the fuel gas containing hydrogen to the fuel gas passage 12. On the other hand, oxygen is supplied to the cathode 15 by supplying an oxidant gas containing oxygen around the fuel cell 10. As a result, the following electrode reaction occurs at the cathode 15 and the anode 13 to generate power. The power generation reaction is performed at 600 ° C. to 1000 ° C., for example.
Cathode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte)
Anode: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻

The cathode 15 has oxidation resistance and is porous so that gas phase oxygen can reach the interface with the solid electrolyte 14. The solid electrolyte 14 has a function of moving oxygen ions O ²⁻ from the cathode 15 to the anode 13. The solid electrolyte 14 is composed of an oxygen ion conductive oxide. Further, since the solid electrolyte 14 physically separates the fuel gas and the oxidant gas, the solid electrolyte 14 is stable and dense in the oxidizing / reducing atmosphere. The anode 13 is made of a material that is stable in a reducing atmosphere and has an affinity for hydrogen, and is porous. The interconnector 17 is provided to connect the fuel cells 10 in series, and is dense so as to physically separate the fuel gas and the oxidant gas.

For example, the cathode 15 is formed of a lanthanum manganate-based perovskite complex oxide having high conductivity of both electrons and ions. The solid electrolyte 14 is formed of ZrO ₂ (YSZ) containing Y ₂ O ₃ having high ion conductivity. The anode 13 is formed by a mixture of Ni having high electronic conductivity and ZrO ₂ (YSZ) containing Y ₂ O ₃ . The interconnector 17 is made of LaCrO ₃ or the like that has a high electronic conductivity and in which an alkaline earth oxide is dissolved. These materials are preferably close in thermal expansion coefficient.

  FIG. 3 is a perspective view for explaining the fuel cell stack 100. As shown in FIG. 3, in the fuel cell stack 100, a plurality of fuel cells 10 are stacked on each other via current collecting members. In this case, each fuel cell 10 is laminated so that the anode 13 side and the cathode 15 side face each other. In FIG. 3, arrows indicate the flow of fuel gas, and thick arrows indicate the flow of oxidant gas.

  FIG. 4 is a perspective view showing the fuel cell stack 100, the combustion unit 200, and the reformer 400 extracted. As shown in FIG. 4, two fuel cell stacks 100 are disposed on the manifold 40, and the reformer 400 is disposed above the fuel cell stack 100.

  The two fuel cell stacks 100 are arranged in parallel so that the stacking directions of the fuel cells 10 constituting each fuel cell stack 100 are substantially parallel. The reformer 30 extends above one fuel cell stack 100 along the stacking direction of the fuel cells 10, and extends above the other fuel cell stack 100 into a U shape along the stacking direction of the fuel cells 10. Wrap. The outlet of the reformer 400 and the inlet of the anode manifold 40 are connected by a fuel gas pipe 50.

  The lower end of the fuel cell stack 100 is fixed to the manifold 40. The manifold 40 has a hole communicating with the fuel gas passage 12 of each fuel cell 10. As a result, a fuel gas passage communicating from the reformer 30 to the fuel gas pipe 50, the manifold 40 and the fuel gas passage 12 is formed.

  FIG. 5 is a perspective view for explaining the details of the reformer 400. As shown in FIG. 5, the reformer 400 has a structure in which the vaporization unit 31, the heating unit 32, and the reforming unit 33 are sequentially connected from the inlet side. The vaporizer 31 is a space that vaporizes the reformed water using the combustion heat of the anode exhaust gas.

  The heating unit 32 is a space that heats the reformed water and the reformed fuel by the combustion heat of the anode exhaust gas. For example, a ceramic ball is enclosed in the heating unit 32. The reforming part 33 is a space part for causing a steam reforming reaction between reformed water and reformed fuel. For example, a ceramic ball such as alumina carrying a catalyst metal such as Ni or Ru is enclosed in the reforming unit 33.

  As described with reference to FIG. 4, the fuel gas is supplied from the manifold 40 to the fuel gas passage 12 of each fuel cell 10. The oxidant gas is supplied around each fuel cell 10 after moving downward between the fuel cell stacks 100. Thereby, power generation is performed in each fuel cell 10.

  The fuel gas (anode exhaust gas) that has not been used for power generation in the fuel cell 10 and the oxidant gas (cathode exhaust gas) that has not been used for power generation merge at the upper end of each fuel cell 10. In this embodiment, the portion where the anode exhaust gas burns between the upper end of the fuel cell 10 and the reformer 30 functions as the combustion unit 200.

  Subsequently, the behavior of the reformed water will be described with reference to FIGS. Among the raw materials supplied to the reformer 400, it is the reformed water that changes from the liquid phase to the gas phase. FIG. 6 is a diagram showing the relationship between saturated water vapor pressure and water vapor temperature. In FIG. 6, the horizontal axis indicates the water vapor temperature, and the vertical axis indicates the saturated water vapor pressure. As shown in FIG. 6, the saturated water vapor pressure increases rapidly as the water vapor temperature increases. Since the reformer 400 is heated by the combustion unit 200, the reformed water is easily vaporized under a high saturated steam pressure. Therefore, under a volume that can be regarded as a closed space such as the fuel supply path 408, assuming that the water vapor temperature is constant, the reforming water flow rate dominates the anode pressure.

  FIG. 7 is a diagram showing a correlation between the reforming water supply amount and the anode pressure in a power generation experiment from a light load to a rated load of the fuel cell stack 100. In FIG. 7, the horizontal axis represents the amount of reforming water supplied to the reformer 400, and the vertical axis represents the anode pressure. As shown in FIG. 7, there is a positive correlation between the reforming water supply amount and the anode pressure. According to the result of FIG. 7, the anode pressure is dominated by the pressure generated by the vaporization of the reforming water. Therefore, it is possible to estimate the reforming water flow rate based on the anode pressure.

  When the reforming water is vaporized, a bumping phenomenon occurs. The bumping phenomenon is a phenomenon in which a gas dissolved in a liquid expands instantaneously. In the present embodiment, when the reforming water bumps, the anode pressure rapidly increases. In a state where the amount of heat for vaporizing reformed water is controlled to be substantially constant as in the case of steady power generation of the fuel cell stack 100, the water vapor temperature can be considered to be substantially constant. Therefore, if the amount of heat that causes bumping when the reforming water is supplied at a predetermined flow rate is set in advance, the amount of reforming water supplied is appropriate by detecting the fluctuation range of the anode pressure. It is possible to detect whether or not.

  FIG. 8 is a diagram showing the transition of the anode pressure when the reforming water supply amount is gradually increased. In FIG. 8, the horizontal axis indicates the elapsed time, and the vertical axis indicates the S / C ratio, the anode pressure, the anode pressure fluctuation index, and the combustion part heat quantity. In addition, the value of S / C ratio is shown on the right vertical axis. “S” in the S / C ratio indicates the number of moles of reforming water supplied to the reformer 400, and “C” indicates the number of moles of carbon in the reformed fuel supplied to the reformer 400. Therefore, when the S / C ratio is high, the amount of reforming water supplied to the reformer 400 is large, and when the S / C ratio is low, the amount of reforming water supplied to the reformer 400 is small. The equivalent of the S / C ratio of the steam reforming reaction is “1”. However, in consideration of control variation, reformed fuel flow rate distribution variation, and the like, the control target value of the S / C ratio is preferably about 2 to 3. The anode pressure fluctuation index is a standard deviation of the difference between the anode pressure measured last time and the anode pressure measured this time (in FIG. 8, the number of samples n = 50). The combustion part heat quantity is the combustion heat in the combustion part 200.

  As shown in FIG. 8, when the S / C ratio is small, the anode pressure fluctuation index is also small. When the S / C ratio is larger than a predetermined value, the anode pressure fluctuation index becomes equal to or greater than the predetermined value. When the C ratio becomes larger than a predetermined value, the anode pressure fluctuation index rapidly decreases. Therefore, it can be seen that bump boiling occurs when the S / C ratio is in the predetermined value range (the reforming water supply amount is in the predetermined range). On the other hand, when the S / C ratio is smaller than the predetermined value (reformed water supply amount is small) and when the S / C ratio is larger than the predetermined value (reformed water supply amount is excessive), bumping occurs. You can see that it is not. From the above, bumping does not occur even if the heating amount per unit reforming water is too small or too large. Therefore, if the pressure fluctuation of the anode pressure is within a predetermined range, the water vapor temperature can be controlled to be substantially constant.

  FIG. 9 is a diagram showing the transition of the anode pressure after the start of the supply of reforming water. In FIG. 9, the horizontal axis indicates the elapsed time, and the vertical axis indicates the reforming water supply amount, the anode pressure, and the anode pressure fluctuation index. As shown in FIG. 9, when the anode pressure does not vary greatly, the anode pressure variation index is also small. On the other hand, when the anode pressure suddenly changes with time, the anode pressure fluctuation index increases. According to the result of FIG. 9, it can be estimated that the main factor of the fluctuation of the anode pressure is bumping.

  Here, the behavior of the reforming water described in FIGS. First, the reforming water is vaporized in the reformer 400. Accordingly, the anode pressure varies. This anode pressure depends on the supply amount of reforming water. The fluctuation of the anode pressure is caused by bumping of the reforming water. Therefore, the supply amount of the reforming water can be optimized by detecting the bumping of the reforming water from the anode pressure.

  Depending on the installation environment of the fuel cell stack 100, the range of S / C ratio = 2 to 3 overlaps with the range in which bumping occurs. Therefore, if the S / C ratio is to be controlled within a preferable range, the reforming water supply amount can be corrected to an appropriate value by correcting the reforming water supply amount so that bumping occurs. In the present embodiment, optimal control of the supply amount of reforming water using the pressure sensor 410 that detects the anode pressure will be described.

  FIG. 10 is a flowchart illustrating a reforming water supply amount optimization routine when the reforming water flow rate control program 621 is executed in the CPU 610 of the control unit 600. This routine is executed at a predetermined cycle (for example, every second) after the fuel cell system 1000 is started.

  As shown in FIG. 10, the CPU 610 obtains a generated power request P_req to the fuel cell stack 100 (step S1). Next, the CPU 610 determines a pump drive command value VF_and for the flow rate adjustment valve 406 based on the generated power request P_req acquired in step S1 (step S2). The pump drive command value VF_and is a voltage value applied to the flow rate adjustment valve 406 and corresponds to the target value of the reformed fuel amount supplied to the reformer 400.

  FIG. 11A is a diagram showing a map in which the relationship between the generated power request P_req and the pump drive command value VF_and is stored. The map in FIG. 11A is a map 622 stored in the memory 620 in FIG. Since the amount of hydrogen required for power generation increases as the required amount of generated power increases, the pump drive command value VF_and increases in proportion to the generated power request P_req, as shown in FIG. The reason why the pump drive command value VF_and is not zero even when the generated power request P_req is zero is that reformed fuel is required to maintain the temperature of the fuel cell stack 100.

  Next, the CPU 610 derives the reforming water supply amount QW_f to the reformer 400 based on the pump drive command value VF_and determined in step S2 (step S3). The reforming water supply amount QW_f can be derived from the pump drive command value VF_and and the control target value of the S / C ratio. FIG. 11B is a diagram showing a map in which the relationship between the pump drive command value VF_and and the reforming water supply amount QW_f when the S / C ratio is 2.5 is stored. The map in FIG. 11B is a map 623 stored in the memory 620 in FIG.

  Next, the CPU 610 acquires the anode pressure PRS_and from the pressure sensor 410 (step S4). Next, the CPU 610 derives the reforming water supply amount QW_p based on the anode pressure PRS_and acquired in step S4 (step S5). Since the anode pressure is governed by the vaporization of the reforming water, the reforming water supply amount QW_p increases in proportion to the anode pressure PRS_and as shown in FIG. The map of FIG. 11C is a map 624 stored in the memory 620 of FIG.

  Next, the CPU 610 determines whether or not a value obtained by subtracting the reforming water supply amount QW_f from the reforming water supply amount QW_f is smaller than a threshold value QW_ref (for example, 0.8 cc / min) (step S6). . When it is determined “No” in step S6, the CPU 610 ends the execution of the flowchart. Accordingly, it is possible to avoid erroneous correction in the anode pressure fluctuation amount small region due to excessive supply of reforming water.

  When it is determined as “Yes” in Step S6, the CPU 610 calculates a standard deviation σVF_and of the pump drive command value VF_and (Step S7). The standard deviation σVF_and can be calculated from about 50 samples, for example. Next, the CPU 610 determines whether or not the standard deviation σVF_and is smaller than a threshold σVF_and_ref (for example, 0.01V) (step S8).

  When the standard deviation σVF_and is smaller than the threshold value σVF_and, it can be determined that the power generation amount of the fuel cell stack 100 is in a steady operation state. On the other hand, when the standard deviation σVF_and is greater than or equal to the threshold value σVF_and, it can be determined that the fuel cell stack 100 is in a transient operation state in which the amount of generated power changes.

  Therefore, when it is determined “No” in step S8, the CPU 610 ends the execution of the flowchart. Thereby, erroneous correction in the transient operation state can be avoided. When it is determined as “Yes” in Step S8, the CPU 610 calculates the standard deviation σPRS_and of the anode pressure PRS_and (Step S9). The standard deviation σPRS_and can be calculated from, for example, about 50 samples.

Next, the CPU 610 determines whether or not the standard deviation σPRS_and is smaller than a threshold σPRS_and_lwr (for example, 0.04 kPa) (step S10). When it is determined as “Yes” in step S10, the CPU 610 calculates the reforming water flow rate correction value QW_fb according to the following equation (1) (step S11). In addition, dfb of following formula (1) can be set to 1 / 10000cc / min, for example.
QW_fb = QW_fb + dfb (1)

Next, the CPU 610 corrects the target supply amount QW of the reforming water adjustment electromagnetic valve 512 according to the following equation (2) (step S12). Note that map (VF_and) in the following equation (2) is a reforming water supply amount determined according to the pump drive command value VF_and. Thereafter, the CPU 610 ends the execution of the flowchart.
QW = map (VF_and) + QW_fb (2)

When it is determined as “No” in Step S10, the CPU 610 determines whether or not the standard deviation σPRS_and is smaller than the threshold σPRS_and_upr (Step S13). The threshold value σPRS_and_upr is larger than the threshold value σPRS_and_lwr, and is, for example, 0.16 kPa. When it determines with "Yes" in step S13, CPU610 calculates | requires the reforming water flow volume correction value QW_fb according to following formula (3) (step S14). In addition, dfb of following formula (3) can be set to 1 / 10000cc / min, for example.
QW_fb = QW_fb−dfb (3)

  Thereafter, the CPU 610 executes Step S12 and ends the execution of the flowchart. If it is determined “No” in step S13, the CPU 610 ends the execution of the flowchart. Thereby, the current target supply amount QW of the reforming water metering electromagnetic valve 512 is maintained as an appropriate value.

  According to the present embodiment, the reforming water supply amount can be corrected based on the anode pressure fluctuation amount. Thereby, the supply amount of reforming water can be optimized and controlled without using an expensive detector such as a flow meter for detecting the water vapor flow rate. Further, since the reforming water supply amount is corrected based on the standard deviation of the anode pressure, the detection accuracy of the anode pressure fluctuation amount is improved. Furthermore, since the reforming water supply amount is corrected so that the standard deviation of the anode pressure falls within a predetermined range, the S / C ratio can be controlled to a preferable value.

  Further, when the difference between the reforming water supply amount derived from the pump drive command value to the flow control valve 406 and the reforming water supply amount derived from the anode pressure is large, the reforming water supply amount is not corrected. Therefore, it is possible to avoid erroneous correction in the small anode pressure fluctuation amount region caused by excessive supply of reforming water. Furthermore, when the fluctuation amount of the pump drive command value to the flow rate control valve 406 is large, the reforming water supply amount is not corrected, and therefore, the transient state (the fuel cell stack 100 where the fluctuation amount of the reforming amount in the reformer 400 is large. Erroneous correction in a transient operation state in which the amount of fluctuation in power generation is large).

  In the flowchart of FIG. 11, the pump drive command value VF_and is used to determine the amount of change in the reforming amount in the reformer 400 (the amount of power generation fluctuation in the fuel cell stack 100), but is not limited thereto. For example, detection results such as generated power, generated current, and generated voltage of the fuel cell stack 100 may be used. Based on the control value of the reformed fuel supply amount or the reformed water supply amount, the detection result, or the detection result. Information obtained may be used.

  In the flowchart of FIG. 11, the reforming water flow rate correction value QW_fb is one type, but is not limited thereto. For example, as shown in FIG. 12 (d), a table for holding different reforming water flow rate correction values QW_fb may be prepared according to the classification of the pump drive command value VF_and. In addition to the pump drive command value VF_and, a control value or a detected value (generated power, generated current of the fuel cell stack 100, generated current or A table for holding different reforming water flow rate correction values QW_fb may be prepared according to the classification of the power generation voltage or the reformed fuel supply amount or the reformed water supply amount control value or detection value). Further, a threshold σPRS_and_upr and a threshold σPRS_and_lwr may be prepared for each section. In this case, fine control according to the amount of heat received by the reformer can be performed.

  In the above embodiment, the reforming water metering solenoid valve 512 functions as a supply amount adjusting unit that adjusts the supply amount of reforming water, and the pressure sensor 410 functions as a pressure detection unit that detects the gas pressure in the reformer. The control unit 600 functions as a correction unit that corrects the supply amount of reforming water and also functions as a setting unit that sets the supply amount of reformed fuel to the reformer.

  In addition, the said Example is applicable also to any other types of fuel cells, such as a solid polymer form, a solid oxide form, and a carbonated molten salt form.

DESCRIPTION OF SYMBOLS 10 Fuel cell 100 Fuel cell stack 400 Reformer 402 Reformed fuel tank 406 Flow control valve 410 Pressure sensor 500 Reformed water tank 512 Reformed water metering solenoid valve 600 Control unit 620 Memory 621 Reformed water flow control program 1000 Fuel cell system

Claims (12)

A reformer that reforms the reformed fuel by a steam reforming reaction using the reformed water to generate a fuel gas containing hydrogen; and
Supply amount adjusting means for adjusting the supply amount of the reforming water to the reformer;
Pressure detecting means for detecting gas pressure in the reformer;
Based on the standard deviation of the gas pressure detected by the pressure detecting means , the supply amount adjustment is performed so that the fluctuation range of the pressure in the reformer falls within a range in which a predetermined range of S / C ratio is realized. And a correction means for correcting the supply amount of the reformed water by the means. 2. The fuel reforming system according to claim 1 , wherein when the standard deviation of the gas pressure exceeds a predetermined value, the correction unit performs correction to reduce the supply amount of the reforming water. 2. The fuel reforming system according to claim 1 , wherein when the standard deviation of the gas pressure is less than a predetermined value, the correction unit performs correction to increase the supply amount of the reforming water. The said correction | amendment means does not correct | amend the supply_amount | feed_rate of the said reforming water by the said supply_amount | feed_rate adjustment means, when the fluctuation amount of the reforming amount of the said reformer exceeds a predetermined value . The fuel reforming system according to any one of claims. Comprising setting means for setting the amount of reformed fuel supplied to the reformer;
The correction means includes a reforming water supply amount derived based on a supply amount set by the setting means, a reforming water supply amount derived based on a gas pressure detected by the pressure detection means, The fuel reforming system according to any one of claims 1 to 3 , wherein the supply amount of the reforming water by the supply amount adjusting means is not corrected when the difference between the two exceeds a predetermined value. The fuel modification according to any one of claims 1 to 5 , wherein a correction range of the reforming water supply amount corrected by the correcting unit is changed in accordance with a reforming amount of the reformer. Quality system. A supply amount adjusting step of adjusting the supply amount of the reformed water to a reformer that reforms the reformed fuel by a steam reforming reaction using the reformed water to generate a fuel gas containing hydrogen; and
A pressure detecting step for detecting a gas pressure in the reformer;
Based on the standard deviation of the gas pressure detected in the pressure detection step, the supply amount adjustment step so that the fluctuation range of the pressure in the reformer falls within a range that realizes a predetermined S / C ratio. And a correction step of correcting the supply amount of the reforming water in the fuel reforming system. 8. The control of the fuel reforming system according to claim 7 , wherein the correction step is a step of performing correction to reduce the supply amount of the reforming water when a standard deviation of the gas pressure exceeds a predetermined value. Method. 8. The control of the fuel reforming system according to claim 7 , wherein the correcting step is a step of correcting the supply amount of the reforming water to be increased when a standard deviation of the gas pressure is less than a predetermined value. Method. In the correction step, wherein when the variation amount of the modifying amount of the reformer is above a predetermined value, according to any one of claims 7-9, characterized in that does not correct the supply amount of the reforming water Method for controlling the fuel reforming system. Including a setting step of setting a supply amount of reformed fuel to the reformer,
In the correction step, a reforming water supply amount derived based on the supply amount set by the setting step, and a reforming water supply amount derived based on the gas pressure detected by the pressure detection step, The method for controlling the fuel reforming system according to any one of claims 7 to 9 , wherein the supply amount of the reforming water is not corrected when the difference between the two exceeds a predetermined value. The fuel modification according to any one of claims 7 to 11 , wherein a correction range of the reforming water supply amount corrected in the correction step is changed according to a reforming amount of the reformer. Quality system control method.

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