JP5485555B2 - Solid oxide fuel cell system - Google Patents

Description

  The present invention relates to a control technique for a fuel cell, particularly a solid oxide fuel cell system used at a high temperature.

  Solid oxide fuel cells generate electricity by taking out hydrogen by reforming various hydrocarbon raw materials with steam. Since the steam used for reforming is generated by vaporizing the reforming water with a vaporizer, the vaporizer is at a high temperature, and the reformer is also required to operate at a high temperature.

  For this reason, the vaporizer and reformer are often heated separately from the solid oxide fuel cell main body (fuel cell stack) and connected in series to the fuel line of the solid oxide fuel cell. Is done.

  This connection is a factor, and the flow rate of the fuel gas is greatly influenced by the pressure change when water is vaporized and the pressure decrease due to the endothermic reaction of vaporization. Therefore, the control of the fuel gas flow rate becomes unstable.

  This reformed water is sent by a pump, but in a solid oxide fuel cell for distributed installation, there are two methods for supplying stable reformed water because the flow rate of water is small. One is a method of controlling by the number of steps of the stepping motor, and the second is a method of controlling the total amount of water with electric power by a combination of a control pump, a needle valve and a high-precision flow meter.

  In the former case, although the amount of water supply is stable, water is supplied according to the rotation period of the stepping motor, so that the pressure change during vaporization is large, and in the latter case, water is continuously supplied. However, since the flow rate is not stable and feedback from the flow meter, reforming water may be insufficient. Moreover, there is a problem that the system becomes complicated, which is not realistic.

  In order to suppress the pressure change using a stepping motor, it is possible to install a buffer tank, which is a conventional technology, to absorb the pressure change. However, it is necessary to install the buffer tank in the stack. As a result, the amount of heat radiation increases, leading to a decrease in efficiency.

  Furthermore, there is a method of suppressing a change in the pressure of the supplied fuel gas by inserting a check valve into the fuel gas line and utilizing the crack pressure of the check valve. That is, if a check valve is inserted into the fuel gas line and a required resistance is given to the fuel gas line by the crack pressure of the check valve, the pressure change of the supplied fuel gas can be suppressed. Therefore, the pressure change can be controlled by controlling the crack pressure of the check valve (see, for example, Patent Document 1).

JP 2006-216283 A

  However, in the method of inserting a check valve in the fuel gas line and controlling the crack pressure, the pressure exceeding the cracking pressure is always maintained in the fuel gas line, so the pump load at a low flow rate always increases. There is a problem that the overall efficiency is lowered and the practicality is low.

  The present invention has been made in view of these problems, and an object of the present invention is to provide an efficient solid oxide fuel cell system that suppresses a pressure change in a fuel gas line with a simple configuration.

Solid oxide fuel cell system made to solve such a problem (1: In this column, in order to facilitate understanding of the invention, in the column “Best Mode for Carrying Out the Invention” as necessary, The reference numerals used are attached, but the reference is not meant to be limited by the reference numerals).
The fuel cell stack (10), the reforming means (20), the vaporization means (30), the fuel supply means (50), the water supply means (60), the estimation means (70), and the control means (70) are provided.

  The fuel cell stack (10) is formed by connecting a plurality of fuel cells each formed with a fuel electrode and an air electrode across an electrolyte layer, and the reforming means (20) supplies the fuel cell stack (10). Before being done, the fuel gas is reformed with water vapor, and the vaporization means (30) vaporizes water to form water vapor used in the reforming means (20).

  The fuel supply means (50) supplies the reformed fuel gas to the reforming means (20), the water supply means (60) periodically supplies water to the vaporization means (30), and the estimation means ( 70) estimates the vaporization timing at which the water supplied by the water supply means (60) is vaporized by the vaporization means (30).

  The control means (70) controls the supply pressure of the fuel gas supplied from the fuel supply means (50) to the fuel cell stack (10) based on the water vaporization timing estimated by the estimation means (70).

  In such a solid oxide fuel cell system (1), water is periodically supplied to the vaporization means (30) by the water supply means (60), and the supplied water is vaporized by the vaporization means (30). The reforming means (20) is used for the reforming reaction. The reforming means (20) is supplied with fuel gas from the fuel supply means (50).

  Here, when water is vaporized in the vaporization means (30), the water vapor pressure in the vaporization means (30) increases, so the water vapor pressure in the reforming means (20) also increases. On the other hand, since the vaporization means (30) is also communicated with the fuel supply means (50) via the reforming means (20), the pressure in the fuel supply means (50) (the sum of the fuel gas pressure and the water vapor pressure). ) Will also rise. In other words, the water vapor pressure is transmitted to the fuel gas line through the mixing portion (reforming means), and causes a shortage of the fuel gas flow rate by pressing the fuel gas pressure.

  On the other hand, the solid oxide fuel cell system (1) of the present invention estimated and estimated the vaporization timing at which water was vaporized in the vaporization means (30) by using the estimation means (70). If the fuel supply pressure of the fuel supply means (50) is controlled to increase the fuel supply pressure in accordance with the vaporization timing based on the water vaporization timing, for example, the fuel gas can be operated with the necessary and sufficient fuel gas at all times. Thus, an efficient solid oxide fuel cell system (1) can be obtained.

  Moreover, since the output change by the pulsation of fuel gas can be suppressed, the output of a solid oxide fuel cell system (1) is stabilized. In addition, since the necessary and sufficient fuel gas is always supplied, it is possible to suppress the fuel gas from being exhausted during power generation, and the deterioration of the reforming catalyst, the fuel electrode, and the air electrode due to the fuel gas exhaustion is eliminated. The durability of the system (1) is improved.

  By the way, in the vaporization means (30), it is only necessary to generate in advance an amount of water vapor (including surplus) necessary for the reforming action in the reforming means (20). There is no need to vaporize. Therefore, the water supply means (60) may be configured to periodically supply water to the vaporization means (30) as in the present invention.

  If it does in this way, since it is not necessary to always supply water with a water supply means (60), it can be set as a simple structure, such as making the water supply means (60) into a pump using a stepping motor, for example.

  Moreover, since water is periodically supplied to the vaporizing means (30), the water is periodically vaporized. Therefore, it is easy to estimate the water vaporization timing in the estimation means (70).

  By the way, various methods for estimating the vaporization timing of water by the estimating means (70) are conceivable, but it is preferable to estimate based on the pressure of the mixed gas containing fuel gas and water vapor. That is, as in the present invention, pressure measuring means (80) for measuring the pressure of the mixed gas containing the supplied fuel gas and water vapor is provided, and the estimating means (70) is mixed gas pressure via the pressure measuring means (80). Then, the change in the water vapor pressure is obtained from the change in the mixed gas pressure, and the vaporization timing of the water in the vaporization means (30) is estimated based on the change in the water vapor pressure.

  If it does in this way, the vaporization timing in a vaporization means (30) can be estimated based on the pressure of the mixed gas containing the supply fuel gas and water vapor | steam acquired from a pressure measurement means (80). That is, if the water vapor pressure changes, the pressure of the mixed gas containing the supplied fuel gas and water vapor also changes. For example, if the water vapor pressure increases, the pressure of the mixed gas also increases, and if the water vapor pressure decreases, the pressure of the mixed gas also decreases. Therefore, the vaporization timing in the vaporization means (30) based on the pressure of the mixed gas. Can be estimated accurately.

  Further, when the fuel gas is supplied from the fuel supply means (50) to the reforming means (20), generally, the fuel gas flow rate changes as the upstream pressure of the fuel gas changes. For example, if the upstream pressure rises rapidly, the fuel gas flow rate temporarily decreases. Accordingly, as in the present invention, the flow rate measuring means (82) for measuring the flow rate of the fuel gas supplied by the fuel supply means (50) is provided, and the estimating means (70) Even if the flow rate is acquired and the vaporization timing of water in the vaporization means (30) is estimated based on the obtained change in the fuel gas flow rate, the vaporization timing of water in the vaporization means (30) can be estimated.

  Further, as described above, with the vaporization of water in the vaporization means (30), the upstream pressure of the fuel gas increases and the supplied fuel gas temporarily decreases. Then, the fuel supply means (50) tries to increase the fuel gas flow rate so as to compensate for the decreased fuel gas flow rate, so that the energy consumption in the fuel supply means (50) changes.

  Therefore, as in the present invention, the fuel supply means (50) includes the energy consumption measuring means (54) for measuring the energy consumption when the fuel gas is supplied, and the estimation means (70) is the energy consumption measuring means ( The vaporization timing can also be estimated by acquiring the energy consumption amount from 54) and estimating the vaporization timing of water in the vaporization means (30) based on the obtained change in the energy consumption amount.

  Incidentally, the control means (70) controls the fuel gas pressure supplied by the fuel supply means (50) based on the vaporization timing estimated by the estimation means (70). When the gas flow rate changes, the fuel gas pressure also changes.

  Therefore, the fuel gas pressure of the fuel supply means (50) can be controlled by controlling the fuel gas flow rate of the fuel supply means (50) as in the present invention.

  Further, in the vaporization timing estimation means (70), the estimation method described above, that is, the estimation method based on the pressure change of the mixed gas containing the supplied fuel gas and water vapor, the estimation method based on the fuel gas flow rate change, and the fuel supply means (50) The vaporization timing may be estimated by combining estimation methods based on changes in energy consumption.

1 is a block diagram showing a schematic configuration of a solid oxide fuel cell system 1. FIG. It is a flowchart which shows the flow of an estimation control process. It is a flowchart which shows the flow of an estimation control process. FIG. 3 is a diagram showing the pressure and flow rate of the fuel line 52 and the power consumption of the fuel pump 50 in the solid oxide fuel cell system 1. 1 is a block diagram showing a schematic configuration of a solid oxide fuel cell system 2. FIG.

  Embodiments to which the present invention is applied will be described below with reference to the drawings. The embodiment of the present invention is not limited to the following embodiment, and can take various forms as long as they belong to the technical scope of the present invention.

[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration of a solid oxide fuel cell system 1 to which the present invention is applied. As shown in FIG. 1, the solid oxide fuel cell system 1 includes a fuel cell stack 10, a reformer 20, a vaporizer 30, a heat insulating container 40, a fuel pump 50, a water pump 60, a pressure sensor 80, and a control device 70. It has.

  The fuel cell stack 10 is a device that generates power by receiving supply of a fuel gas (specifically, hydrogen in the fuel gas) and an oxidant gas (specifically, oxygen in the air). A plurality of fuel cells each having the shape is connected to each other.

  The solid electrolyte is for taking out electric power by moving oxygen ions. YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samaria-added ceria), GDC (gadolinium-added ceria), Various known oxygen ion conductive materials such as perovskite oxide can be used.

  In addition, perovskite oxide, various precious metals, cermets of precious metals and ceramics can be used as the air electrode, and various precious metals, base metals such as Ni, cermets of these metals and ceramics, etc. can be used as the fuel electrodes. Can be used.

  The solid electrolyte moves as a part of one of the fuel gas (combustible gas) introduced into the fuel electrode during operation of the fuel cell or the oxidant gas (combustion gas) introduced into the air electrode. It has ionic conductivity. Examples of the ions include oxygen ions and hydrogen ions.

  Further, the fuel electrode comes into contact with the fuel gas serving as a reducing agent and functions as a negative electrode in the fuel battery cell. The air electrode is in contact with an oxidant gas serving as an oxidant and functions as a positive electrode in the fuel cell.

  The reformer 20 reforms the fuel gas with water vapor. For example, the reformer 20 reforms the fuel gas such as city gas using a catalyst such as nickel or platinum to produce hydrogen gas that reacts with oxygen. It is a device to generate.

  The vaporizer 30 vaporizes water used for steam reforming in the reformer 20 into water vapor, and water that supplies water (pure water) to the front stage of the vaporizer 30 via a water line 62. A pump 60 is provided.

  The water pump 60 includes a stepping motor and a disk-shaped rotor attached to the rotating shaft of the stepping motor. The rotor is provided with a notch, and water is supplied to the water line 62 from the notch (supplied from one notch at a time).

  Accordingly, by rotating the stepping motor, water is supplied to the vaporizer 30 via the water line 62 periodically (at regular time intervals).

  The heat insulating container 40 is a heat insulating container having a heat insulating function for housing the fuel cell stack 10, the reformer 20, and the vaporizer 30.

  The fuel pump 50 is a pump for supplying fuel gas to the reformer 20 via the fuel line 52, and the pressure sensor 80 is a fuel gas supply pressure (fuel gas supply pressure of the fuel pump 50) in the fuel line 52. It is a sensor for measuring (equal to).

  Here, although the pressure sensor 80 is provided in the fuel line 52, the vaporizer 30 communicates with the fuel pump 50 via the reformer 20, so that the water vapor vaporized by the vaporizer 30 also enters the fuel line 52. coming and going. Therefore, the pressure of the fuel line 52 is the sum of the fuel gas pressure and the water vapor pressure (the pressure of the mixed gas).

  That is, since the space communicating in the system has an equal pressure (mixed gas), the pressure sensor 80 measures the pressure change of the mixed gas. On the other hand, since the pressure change of the fuel gas is extremely small compared with the change of the water vapor pressure, the pressure change of the mixed gas can be used as the pressure change of the water vapor.

  The fuel flow sensor 82 is a sensor for measuring the flow rate of the fuel gas supplied by the fuel pump 50 and feedback-controlling the flow rate of the fuel gas, and is an electric flow sensor such as an electromagnetic flow meter or an ultrasonic flow meter, or a turbine. A mechanical flow sensor such as a flow meter can be used.

  The control device 70 includes a CPU, a ROM, a RAM, a first counter, a second counter, and an I / O (not shown). The control device 70 continuously acquires the fuel gas pressure from the pressure sensor 80, and determines the acquired fuel gas pressure. Based on the change, the vaporization timing of water in the vaporizer 30 is estimated. Then, the fuel gas supply pressure of the fuel pump 50 is controlled by controlling the fuel gas flow rate of the fuel pump 50 based on the estimated water vaporization timing.

  The estimation of the water vaporization timing executed by the control device 70 and the control process of the fuel gas supply pressure based on the estimated vaporization timing are collectively referred to as “estimated control processing”, and the details thereof will be described below.

(Estimated control processing)
Next, the estimation control process executed by the control device 70 will be described with reference to FIGS. 2 and 3 are flowcharts showing the flow of the estimation control process.

  In the estimation control process, first, initial setting is performed in S100. In the initial setting, the “pressure value”, “previous pressure”, “vaporization interval”, “previous vaporization interval”, “timer (1)”, and “timer (2)” in the RAM are set to 0, and there is a pressure change. A “pressure change flag” which is a flag indicating whether or not is set to OFF.

  Here, “the pressure flag is on” means that the pressure flag in the RAM is set to “1”, and “the pressure flag is off” means that the pressure flag in the RAM is “0”. It means the set state.

  In the subsequent S105, the required flow rate of the fuel gas supplied by the fuel pump 50 is calculated. In the subsequent S110, the fuel gas pressure is acquired from the pressure sensor 80, and the acquired fuel gas pressure is stored in the RAM as a “pressure value”. The

  In subsequent S115, it is determined whether or not the pressure value has changed. That is, the previous pressure stored in the RAM in the previous processing loop (the process of repeating S105 to S195) is subtracted from the pressure value stored in the RAM in S110, and whether or not the subtracted value is greater than the threshold value. Determined.

  If it is determined that the subtracted value is greater than the threshold value (S115: Yes), that is, if it is determined that the pressure value has changed, the process proceeds to S120, and the subtracted value is equal to or less than the threshold value. If it is determined (S115: No), that is, if it is determined that the pressure value has not changed, the process proceeds to S165 (see FIG. 3).

  In S120, it is determined whether or not the pressure change flag is turned on, that is, whether or not there has been a pressure change in the previous processing loop, and when it is determined that the pressure change flag is turned on (S120: Yes). ) That is, if it is determined that there has been a pressure change in the previous processing loop, that is, if there has been a second or subsequent pressure fluctuation, the process proceeds to S125 and it is determined that the pressure change flag is not turned on. If (S120: No), that is, if it is determined that there was no pressure change in the previous processing loop, the process proceeds to S145.

  In S125, the “vaporization interval” is replaced with the value of timer (1), and in subsequent S130, the values of timer (1) and timer (2) are set to zero.

  In subsequent S135, whether or not the absolute value of the difference between the vaporization interval and the previous interval replaced with the value of the timer (1) in the previous processing loop is larger than the threshold value, that is, the pressure change interval is a predetermined interval (threshold value). ) Is determined. And when it determines with the absolute value of a difference being larger than a threshold value (S135: Yes), ie, when it determines with the space | interval of a pressure change not having generate | occur | produced with the predetermined space | interval, a process is transferred to S140, and pressure After the change flag is turned off (that is, when the cycle is changed), the process proceeds to S165. On the other hand, when it is determined that the difference threshold is equal to or less than the threshold (S135: No), that is, when it is determined that the pressure change interval occurs at a predetermined interval, the process proceeds to S165 (see FIG. 3). Is done.

  In S145, the pressure change flag is turned on, and in subsequent S150, the timer (1) and the timer (2) start counting up. In subsequent S155, the fuel gas flow rate (actual flow rate value) supplied by the fuel pump 50 is acquired from the fuel flow rate sensor 82.

  In subsequent S160, the value obtained by subtracting the actual flow rate value acquired in S155 from the command flow rate is set as a correction value, and then the process proceeds to S165 (see FIG. 3).

  In S165, it is determined whether or not the value obtained by subtracting the vaporization interval set in S125 from the timer (2) is greater than the response delay time of the fuel pump 50. If it is determined that the response time is greater than the response time (S165: Yes), the process proceeds to S170. If it is determined that the response time is equal to or less (S165: No), the process proceeds to S180.

  In S170, the timer (2) is set to 0, and in the subsequent S175, the correction value is added to the required flow rate to obtain the indicated flow rate. Here, the correction value is a preset flow rate value required to compensate for the response delay time of the fuel pump 50.

  On the other hand, in S180, after the necessary flow rate is set as the instruction flow rate as it is, the process proceeds to S185.

  In S185, the supply pressure of the fuel gas in the fuel line 52 is acquired from the pressure sensor 80, and in S190, the value of the supply pressure is set as the previous pressure. In S195, the vaporization interval set in S125 is the previous interval. Then, the process returns to S105, and the estimation control process is repeated.

(Characteristics of solid oxide fuel cell system 1)
Next, the characteristics of the solid oxide fuel cell system 1 as described above will be described with reference to FIG. FIG. 4 is a diagram illustrating changes in the fuel line 52 (water vapor) pressure, the flow rate of the fuel gas, and the power consumption of the fuel pump 50 over time in the solid oxide fuel cell system 1. In FIG. 4, the solid line indicates the (water vapor) pressure in the fuel line 52, the broken line indicates the power consumption of the fuel pump 50, and the alternate long and short dash line indicates the flow rate of the fuel gas in the fuel line 52.

  In the solid oxide fuel cell system 1, water is periodically vaporized in the vaporizer 30 because the water pump 60 rotates the rotor with notches at equal intervals by the stepping motor to supply water to the vaporizer 30. To do.

  When water is vaporized periodically in the vaporizer 30, the pressure in the vaporizer 30 rises, so that the pressure in the reformer 20 also changes periodically. When the pressure of the reformer 20 changes periodically, the pressure (steam) in the fuel line 52 that supplies fuel gas to the reformer 20 also changes periodically as shown by a solid line in FIG. A pressure peak occurs. When a pressure peak occurs periodically, the flow rate of the fuel gas changes (decreases) with a response delay, as shown by a one-dot chain line in FIG.

  At this time, the pressure (80) of the fuel line 52 is continuously measured by the pressure sensor 80, the timing at which the next pressure peak occurs from the pressure peak is estimated, and the fuel pump 50 is matched with the estimated vaporization timing. Is increased (the power consumption of the fuel pump 50 in FIG. 4 is increasing).

  When the fuel gas flow rate is increased, the fuel gas pressure in the fuel line 52 increases. That is, the pressure change (decrease in fuel gas flow rate) in the fuel line 52 can be suppressed at the estimated vaporization timing. Therefore, since it is possible to always operate with the necessary and sufficient fuel gas, the efficient solid oxide fuel cell system 1 can be obtained without wasting the fuel gas or the like.

  Moreover, since the output change by the pulsation of fuel gas can be suppressed, the output of the solid oxide fuel cell system 1 is stabilized. In addition, since the necessary and sufficient fuel gas is always supplied, it is possible to suppress the fuel gas from being exhausted during power generation, and the deterioration of the reforming catalyst, the fuel electrode, and the air electrode due to the fuel gas exhaustion is eliminated. The durability of the system 1 is improved.

  Furthermore, the fuel pump 50 rotates the rotor with a notch every 90 degrees to supply water, but by doing so, it is not necessary to always supply water by the water pump 60. Therefore, the water pump 60 can have a simple configuration such as a pump using a stepping motor.

  Further, since water is supplied to the vaporizer 30 at predetermined intervals, the water is vaporized periodically. Therefore, estimation of the water vaporization timing in the control device 70 is facilitated.

  Thus, the fuel gas pressure is continuously acquired from the pressure sensor 80 installed in the fuel line 52, and the vaporization timing of water in the vaporizer 30 is estimated based on the timing at which the peak of the acquired fuel gas pressure occurs. Yes.

  Here, the fuel line 52 includes a mixed gas containing the supplied fuel gas and water vapor, but if the water vapor pressure changes, the pressure of the mixed gas containing the supplied fuel gas and water vapor also changes. For example, if the water vapor pressure increases, the pressure of the mixed gas also increases, and if the water vapor pressure decreases, the pressure of the mixed gas also decreases. Therefore, the vaporization timing in the vaporization means (30) based on the pressure of the mixed gas. Can be estimated accurately.

[Second Embodiment]
Next, instead of the first embodiment in which the water vaporization timing is estimated based on the change in the fuel gas pressure, a second embodiment in which the vaporization timing is estimated based on the change in the fuel gas flow rate will be described.

  That is, in the first embodiment, the vaporization timing of water in the vaporizer 30 is estimated based on the change in the fuel gas pressure acquired from the pressure sensor 80 installed in the fuel line 52, but in the second embodiment, the fuel line is estimated. The vaporization timing of water in the vaporizer 30 is estimated based on the change in the fuel gas flow rate acquired from the fuel flow rate sensor 82 installed for feedback control of the fuel gas supply amount installed in 52.

  Specifically, in S110 of FIG. 2, instead of acquiring the fuel gas pressure from the pressure sensor 80, the fuel gas flow rate is acquired from the fuel flow rate sensor 82. Then, the fuel gas flow rate is converted into the fuel gas pressure from the pressure versus flow rate characteristics of the fuel pump 50 and stored in the RAM as a “pressure value”.

  Thereafter, in S115 to S180, the process is performed in the same manner as in the first embodiment. In S185, instead of acquiring the fuel gas pressure from the pressure sensor 80 in the same manner as in S115, the fuel gas flow rate is obtained from the fuel flow rate sensor 82. Is acquired. Then, the fuel gas flow rate is converted into the fuel gas pressure from the pressure-flow rate characteristic of the fuel pump 50. Thereafter, in S190 and S195, the same processing as in the first embodiment is executed.

  In general, since the fuel gas flow rate changes as the fuel gas supply pressure changes, the solid oxide fuel cell system 1 in the second embodiment based on the change in the fuel gas flow rate instead of the pressure. The vaporization timing of water in the vaporizer 30 can be estimated.

[Third Embodiment]
Next, the solid oxide fuel cell system 2 that estimates the vaporization timing based on the change in the power consumption of the fuel pump 50 instead of the first embodiment that estimates the vaporization timing of water based on the change in the fuel gas pressure. explain.

  That is, in the first embodiment, the vaporization timing of water in the vaporizer 30 is estimated based on the change in the fuel gas pressure acquired from the pressure sensor 80 installed in the fuel line 52. In the third embodiment, FIG. As shown, the ammeter 54 is installed in the fuel pump 50, and the vaporization timing of water in the vaporizer 30 is estimated based on the change in the power consumption of the fuel pump 50 acquired from the ammeter 54.

  Specifically, in S110 of FIG. 2, the power consumption of the fuel pump 50 is acquired from the ammeter 54 instead of acquiring the fuel gas pressure from the pressure sensor 80. Then, the power consumption is converted into the fuel gas pressure from the pressure versus power consumption characteristic of the fuel pump 50 and stored in the RAM as a “pressure value”.

  Thereafter, in S115 to S180, the process is performed in the same manner as in the first embodiment. In S185, instead of acquiring the fuel gas pressure from the pressure sensor 80 in the same manner as in S115, the ammeter 54 calculates the fuel pump 50. Power consumption is acquired. Then, the power consumption is converted into the fuel gas pressure from the pressure versus power consumption characteristic of the fuel pump 50. Thereafter, in S190 and S195, the same processing as in the first embodiment is executed.

  As the water in the vaporizer 30 evaporates, the pressure in the fuel line 52 increases and the supplied fuel gas temporarily decreases. Then, since the fuel pump 50 tries to increase the fuel gas flow rate so as to compensate for the decreased fuel gas flow rate, the energy consumption in the fuel pump 50 changes.

Therefore, in such a solid oxide fuel cell system 2 in the third embodiment, the vaporization timing of water in the vaporizer 30 can be estimated based on the change in the power consumption of the fuel pump 50 instead of the fuel gas pressure. .
[Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this embodiment, A various aspect can be taken.

  (1) In the said 1st Embodiment, the vaporization timing of the water in the vaporizer 30 was estimated based on the water vapor pressure change, and in the 2nd Embodiment, the vaporization timing was estimated based on the flow volume change of fuel gas, The vaporization timing may be estimated in combination. By estimating the vaporization timing from the pressure change and the flow rate change, a more accurate pressure fluctuation cycle can be estimated, and the control accuracy is improved.

  (2) The vaporization timing may be estimated based on a combination of a change in the flow rate of the fuel gas and a change in the power consumption of the fuel pump 50. By estimating the vaporization timing from the flow rate change and the power consumption change, a more accurate pressure fluctuation cycle can be estimated, and the control accuracy is improved.

  (3) Further, the vaporization timing may be estimated by combining any two or all of a change in water vapor pressure, a change in fuel gas flow rate, or a change in power consumption of the fuel pump. Similarly to the above (1) and (2), the error in estimation timing of vaporization is reduced, so that the estimation accuracy of control timing is improved.

  (4) In the third embodiment, the power consumption of the fuel pump 50 is measured by the ammeter 54, but may be measured by a wattmeter.

  (5) When water vapor is generated in the vaporizer 30, it may be generated by vaporizing water using waste heat generated from the solid oxide fuel cell.

  DESCRIPTION OF SYMBOLS 1, 2 ... Solid oxide fuel cell system, 10 ... Fuel cell stack, 20 ... Reformer, 30 ... Vaporizer, 40 ... Thermal insulation container, 50 ... Fuel pump, 52 ... Fuel line, 54 ... Ammeter, 60 ... Water pump, 62 ... Water line, 70 ... Control device, 80 ... Pressure sensor, 82 ... Fuel flow sensor.

Claims (3)

A fuel cell stack formed by connecting a plurality of fuel cells each formed with a fuel electrode and an air electrode across an electrolyte layer; and
Reforming means for reforming the fuel gas with water vapor before being supplied to the fuel cell stack;
Vaporizing means for vaporizing water to form water vapor used in the reforming means;
Fuel supply means for supplying the reformed fuel gas to the reforming means;
Water supply means for periodically supplying water to the vaporization means;
Estimating means for estimating a vaporization timing at which water supplied by the water supply means is vaporized by the vaporizing means;
Control means for controlling the supply pressure of the fuel gas supplied from the fuel supply means to the fuel cell stack based on the water vaporization timing estimated by the estimation means;
Flow rate measuring means for measuring the flow rate of the fuel gas supplied by the fuel supply means;
With
The estimation means includes
A solid oxide fuel cell system characterized in that a flow rate of fuel gas is obtained from the flow rate measuring means, and a vaporization timing of water in the vaporization means is estimated based on a change in the obtained fuel gas flow rate. A fuel cell stack formed by connecting a plurality of fuel cells each formed with a fuel electrode and an air electrode across an electrolyte layer; and
Reforming means for reforming the fuel gas with water vapor before being supplied to the fuel cell stack;
Vaporizing means for vaporizing water to form water vapor used in the reforming means;
  Fuel supply means for supplying the reformed fuel gas to the reforming means;
Water supply means for periodically supplying water to the vaporization means;
Estimating means for estimating a vaporization timing at which water supplied by the water supply means is vaporized by the vaporizing means;
Control means for controlling the supply pressure of the fuel gas supplied from the fuel supply means to the fuel cell stack based on the water vaporization timing estimated by the estimation means;
Energy consumption measuring means for measuring energy consumption when fuel gas is supplied by the fuel supply means;
With
The estimation means includes
A solid oxide fuel cell system characterized in that an energy consumption amount is acquired from the energy consumption measuring means, and a vaporization timing of water in the vaporization means is estimated based on a change in the acquired energy consumption amount. The control means includes
By controlling the fuel gas flow rate of the fuel supply means, the solid oxide fuel cell system according to claim 1 or claim 2, characterized in that controlling the fuel gas pressure supplied by the fuel supply means.