JP2018010763A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically regulate a fuel gas flow rate so as to generate power at a rated output even if a fuel gas different in composition is supplied thereto in a fuel cell system 1 which is arranged so that an air flow rate required for a fuel battery 2 to generate power at the rated output is previously set, and which generates power at the rated output by inputting a fuel gas having a predetermined composition corresponding to the air flow rate.SOLUTION: A fuel cell system comprises: an oxygen concentration detector 41 operable to detect an oxygen concentration included in an exhaust gas exhausted from a combustor 4 operable to burn an off-gas exhausted from a fuel battery 2; and a fuel gas flow rate control part 51 operable to control a fuel gas flow rate-regulating valve 222 so that a concentration value detected by the oxygen concentration detector 41 becomes a previously set target concentration value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system.

  The fuel cell system generates power by supplying hydrogen-containing fuel (anode gas) to the anode side and air (cathode gas) to the cathode side in the fuel cell and reacting hydrogen and oxygen inside the cell. . The anode gas is generally generated by reacting hydrocarbon fuel and water (steam) supplied to the reformer from the outside on the catalyst of the reformer (see Patent Document 1).

  In order for the fuel cell to operate at a predetermined battery output, an appropriate amount of anode gas needs to be provided from the reformer to the fuel cell. When an appropriate amount of anode gas is not provided to the fuel cell, for example, the balance between the cell output of the fuel cell and the supply amount of the anode gas may be lost, and the anode may be oxidized due to an insufficient amount of hydrogen. The oxidation of the anode can lead to cell damage and loss of the power generation capability of the fuel cell.

JP 2008-243555 A

  Normally, in a fuel cell, an air flow rate necessary for operating at a predetermined battery output is set in advance. Then, a fuel gas having a predetermined composition set in advance (hereinafter referred to as “designated fuel gas”) is supplied at a predetermined flow rate corresponding to the air flow rate, so that the rated output is achieved. In such a fuel cell, if a fuel gas having a composition different from that of the designated fuel gas is supplied at the same flow rate as that of the designated fuel gas, there is a possibility that the fuel heat amount fluctuates.

Continuing power generation with fluctuations in the amount of fuel heat may lead to a decrease in the power generation efficiency of the fuel cell system and the battery output of the fuel cell in the short term, and will have a major impact on the life of the cell stack in the long term. May affect. Specifically, if the amount of fuel heat is too large, the amount of fuel heat that is not used for power generation increases, and the actual power generation efficiency of the fuel cell system decreases. In addition, if the amount of heat of fuel is too large, the cell stack body and the surroundings become hot, so that sintering of the anode and the like easily proceeds. In addition, since the exhaust gas temperature is extremely high, heat recovery from the exhaust gas cannot be sufficiently performed, the thermal efficiency of the fuel cell system is reduced, or condensate cannot be recovered from the exhaust gas and water independence cannot be established. To do.
On the other hand, if the amount of heat of fuel is too small, oxidative deterioration of the anode tends to proceed due to lack of hydrogen. In addition, if the amount of heat of fuel is too small, the heat balance between heat generation and heat dissipation is lost, and the operating temperature at which the fuel cell system is thermally independent cannot be maintained.

  In the present invention, an air flow rate necessary for generating power at a rated output is set in advance, and fuel gas having a predetermined composition corresponding to the air flow rate is supplied at a predetermined flow rate so that power is generated at a rated output. Provided is a fuel cell system capable of automatically adjusting the flow rate of a fuel gas so that power is generated at a rated output even when fuel gases having different compositions are supplied. For the purpose.

  The present invention relates to a fuel cell, an air supply line that supplies a preset air flow rate to the fuel cell, a reformer that generates hydrogen from fuel gas and water, and supplies the generated hydrogen to the fuel cell. A fuel gas supply line that supplies the fuel gas to the reformer; a fuel gas flow rate adjustment unit that is provided in the fuel gas supply line and that adjusts the flow rate of the fuel gas supplied to the reformer; A water supply line for supplying water to the reformer, a combustor for burning off-gas discharged from the fuel cell, and an oxygen concentration detector for detecting an oxygen concentration contained in the exhaust gas discharged from the combustor; A fuel gas flow rate control unit that controls the fuel gas flow rate adjustment unit, and the fuel gas flow rate control unit is configured so that the detected concentration value of the oxygen concentration detector becomes a preset target concentration value. Fuel gas Controlling the amount adjuster, a fuel cell system.

  The air flow control unit includes an air flow rate adjusting unit that is provided in the air supply line and adjusts an air flow rate supplied to the fuel cell, and an air flow rate control unit that controls the air flow rate adjusting unit. Controlling the air flow rate adjusting unit so that a battery output of the fuel cell according to the power generation output of the fuel cell system is obtained, and the fuel gas flow rate control unit controls the fuel according to the power generation output of the fuel cell system. It is preferable to control the fuel gas flow rate adjusting unit so that the battery output of the battery can be obtained.

  Further, the fuel gas flow rate adjustment unit includes a main adjustment valve and a sub adjustment valve, and the fuel gas flow rate control unit is configured to obtain a battery output of the fuel cell according to a power generation output of the fuel cell system. Furthermore, it is preferable that the main adjustment valve is controlled so that the sub adjustment valve is controlled so that the detected concentration value of the oxygen concentration detector becomes the target concentration value.

  According to the present invention, an air flow rate necessary for generating power at a rated output is set in advance, and fuel gas having a predetermined composition corresponding to the air flow rate is supplied at a predetermined flow rate, thereby generating power at a rated output. In the fuel cell system configured as described above, a fuel cell system capable of automatically adjusting the flow rate of the fuel gas so as to generate power at a rated output even when fuel gas having a different composition is supplied. Can be provided.

1 is a schematic diagram showing a fuel cell system 1 according to an embodiment of the present invention. It is the schematic which shows an example of the fuel gas flow volume adjustment part 22 in embodiment of this invention.

First, common items in the first embodiment and the second embodiment will be described.
The fuel cell system according to the present invention includes a fuel cell (cell stack) and various auxiliary devices as main components. The power generation output of the fuel cell system is the power (unit: W) that can be supplied from the fuel cell system to the load (lights, electrical equipment, etc.) connected to the system. This is the power obtained by subtracting (the power necessary to operate the auxiliary machine) and adjusting the voltage and synchronizing with the power conditioner. A part of the battery output is used for the auxiliary machine loss that occurs during the power generation operation of the fuel cell system, but the “net battery output” of the fuel cell excluding the auxiliary machine loss is the power output of the fuel cell system. Match. In the present application, each embodiment will be described assuming that “power generation output of the fuel cell system” and “cell output of the fuel cell” are equivalent power.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a fuel cell system 1 according to an embodiment of the present invention.
As shown in FIG. 1, the fuel cell system 1 according to the embodiment of the present invention includes a fuel cell 2, a reformer 3, a combustor 4, and a system control unit 5.

  The fuel cell system 1 includes an air supply line L1, a fuel gas supply line L2, a water supply line L3, and a combustion exhaust gas line L4. “Line” is a general term for a flow path, a path, a pipe line, and the like.

[Fuel cell 2]
As the fuel cell 2, for example, a high-temperature solid oxide fuel cell (SOFC) is used. The fuel cell 2 has a cell stack structure in which a plurality of cells are stacked. A general cell stack is roughly divided into a flat plate structure and a cylindrical structure. In either case, a single cell made of ceramics consisting of an anode (fuel electrode), a cathode (air electrode), and an electrolyte is connected via an interconnector. It is a linked structure.
The fuel cell 2 supplies hydrogen-containing fuel (anode gas) from the reformer 3 to the anode side of the cell, and air (cathode gas) from the air supply line L1 to the cathode side of the cell. It is possible to generate electric power by reacting with. The operating temperature of the fuel cell 2 during power generation is a high temperature of about 700 ° C to 1000 ° C. The DC power generated by the fuel cell 2 is sent to a power conditioner 6 (described later) and converted into AC power.
The fuel cell 2 exhausts the anode off-gas containing unreacted hydrogen discharged from the anode side to the combustor 4 and the cathode off-gas containing unreacted oxygen discharged from the cathode side to the combustor 4. And exhaust.

[Reformer 3]
The reformer 3 generates anode gas from fuel gas and water. Specifically, fuel gas (for example, city gas mainly composed of methane gas) supplied via the fuel gas supply line L2 is supplied to the reformer 3 after the sulfur compound is removed by the desulfurizer 21. Is done. On the other hand, water required for the steam reforming reaction or the like is vaporized through the water supply line L3 and supplied to the reformer 3.
At this time, in the reformer 3, the fuel gas is heated to a high temperature (for example, about 700 ° C.), and an anode gas is generated by causing a steam reforming reaction or the like with a catalyst filled therein. This heating is performed by radiant heat from the combustor 4 and the cell stack. The anode gas generated by the reformer 3 is supplied to the fuel cell 2.

[Combustor 4]
The combustor 4 burns by mixing a high-temperature anode off-gas containing unreacted hydrogen discharged from the anode side of the fuel cell 2 and a high-temperature cathode off-gas containing unreacted oxygen discharged from the cathode side. To process. Since the anode off gas contains combustible hydrogen, it is necessary to exhaust the anode off gas to the outside in the state of an inert gas combusted by the combustor 4.
Exhaust gas generated by burning the anode off-gas and cathode off-gas in the combustor 4 is discharged to the outside through an exhaust gas line L4 connected to the downstream side of the combustor 4.
In addition, when the fuel cell system 1 is configured to perform water self-supporting, condensed water is generated by cooling the exhaust gas, and the condensed water is recirculated to the water supply line L3.

[Air supply line L1]
The air supply line L <b> 1 is connected to the fuel cell 2 and supplies air as a cathode gas to the cathode of the fuel cell 2. A filter 11 and an air flow rate adjusting unit 12 are disposed upstream of the air supply line L1. The filter 11 removes foreign matters in the air and causes clean air to flow through the air flow rate adjustment unit 12.

The air flow rate adjustment unit 12 adjusts the flow rate of the air that has passed through the filter 11. In the air flow rate adjusting unit 12, the air flow rate is adjusted to supply an appropriate flow rate of air to the fuel cell 2.
Specifically, for setting the required air flow rate, for example, the value of the required air flow rate when the battery output of the fuel cell 2 is changed is stored in a table in the storage unit in advance. When the power generation output of the battery system 1 is designated, a necessary air flow rate can be set based on the table.
Further, the relationship between the air flow rate and the operation amount of the air flow rate adjustment unit 12 is stored in advance in a table in the storage unit, so that the air flow rate adjustment unit for supplying the necessary air flow rate based on the table. Twelve operation amounts may be set.
In the present embodiment, the air flow rate adjustment unit 12 is adjusted in advance so that the fuel cell system 1 operates at a predetermined power generation output (rated output) and supplies a predetermined constant air flow rate.

Here, the flow rate of air required when the fuel cell system 1 operates at the rated output is set as a standard flow rate (unit: normal liter / min) in the reference state (temperature 0 ° C., atmospheric pressure 1013 hPa). Since the air that has passed through the filter 11 is not normally in the reference state, the density of the air is smaller than that in the reference state, and oxygen shortage occurs at the cathode. Therefore, the system control unit 5 (described later) corrects the standard flow rate based on, for example, the outlet temperature and outlet pressure of the air blower 121 (described later), and calculates the necessary air flow rate.
Moreover, it is convenient to use a differential pressure type flow meter for the measurement and confirmation of the air flow rate. For example, an orifice is provided on the outlet side of the air blower 121, and a differential pressure generated at the orifice is detected. At the same time, the air temperature at the outlet side of the air blower 121 is detected to determine the specific weight of the air. And if Bernoulli's theorem is applied to the differential pressure and the specific weight, the actual air flow rate can be calculated.

  The air flow rate adjusting unit 12 can be configured to include, for example, an air blower 121 and an inverter (frequency converter or circuit: not shown). Thereby, the air which passed the filter 11 by the drive of the air blower 121 distribute | circulates to the air supply line L1. Moreover, the air flow rate can be controlled by designating the drive frequency output from the inverter and driving at a rotational speed corresponding to the input drive frequency.

  Further, the air flow rate adjusting unit 12 may include an air blower 121 and a damper (not shown). The damper can adjust the opening degree and can control the flow rate of air supplied to the fuel cell 2. For example, when a damper is applied to the air flow rate adjusting unit 12, the air flow rate supplied to the fuel cell 2 can be adjusted by controlling the motor that drives the damper and adjusting the rotation stop position of the damper.

  Further, instead of the damper, an air flow rate adjustment valve 122 capable of adjusting the valve opening degree may be used. For example, the air flow rate adjustment valve 122 may be a proportional control valve capable of adjusting the valve opening degree.

  The air flow rate adjusting unit 12 is electrically connected to the system control unit 5 and controlled based on a control signal output from the system control unit 5.

[Fuel gas supply line L2]
The fuel gas supply line L2 is connected to a fuel gas supply source (not shown) on the upstream side, and connected to the reformer 3 on the downstream side, and supplies the fuel gas to the reformer 3. A desulfurizer 21 and a fuel gas flow rate adjustment unit 22 are disposed in the fuel gas supply line L2.

  The desulfurizer 21 removes sulfur compounds contained in the fuel gas by adsorbing them on an adsorbent such as zeolite. The fuel gas from which the sulfur compound has been removed by the desulfurizer 21 is supplied to the fuel gas flow rate adjusting unit 22.

The fuel gas flow rate adjusting unit 22 adjusts the flow rate of the fuel gas from which the sulfur compound has been removed by the desulfurizer 21. In the fuel gas flow rate adjusting unit 22, an appropriate flow rate of fuel gas can be supplied to the reformer 3.
Specifically, for example, the relationship between the fuel gas flow rate of the designated fuel gas and the operation amount of the fuel gas flow rate adjusting unit 22 is stored in advance in a table in the storage unit, so that the designated fuel gas is based on the table. The operation amount of the fuel gas flow rate adjusting unit 22 for supplying the required fuel gas flow rate may be set.
By doing so, in the first embodiment, it is assumed that the fuel gas flow rate adjustment unit 22 is adjusted so as to supply a preset fuel gas flow rate to the reformer 3.

  The fuel gas flow rate adjusting unit 22 can be configured to include, for example, a fuel booster (booster) 221 and an inverter (frequency converter or circuit: not shown). As a result, the fuel gas from which the sulfur compound has been removed by the desulfurizer 21 by the drive of the fuel booster 221 flows through the fuel gas supply line L2. Also, the fuel gas flow rate can be controlled by designating the drive frequency output from the inverter and driving at a rotational speed corresponding to the input drive frequency.

  Further, the fuel gas flow rate adjusting unit 22 may include a fuel booster 221 and a fuel gas flow rate adjusting valve 222. The fuel gas flow rate adjusting valve 222 is openable and closable, and can control the flow rate of the fuel gas supplied to the reformer 3. The fuel gas flow rate adjustment valve 222 may be a proportional control valve capable of adjusting the valve opening degree.

  The fuel gas flow rate adjusting unit 22 is electrically connected to the system control unit 5 and controlled based on a control signal output from the system control unit 5.

[Water supply line L3]
The water supply line L3 is connected to a water supply unit (not shown) on the upstream side, is connected to the reformer 3 on the downstream side, and supplies water to the reformer 3. An impurity removal unit 31, a pump 32, and an evaporator 33 are disposed in the water supply line L3.

The impurity removing unit 31 removes impurities contained in the water supplied from the water supply unit.
The pump 32 is driven to circulate water from the water supply unit to the water supply line L3.
The evaporator 33 evaporates the water supplied from the water supply line L2. The water (evaporated water) evaporated by the evaporator 33 is supplied to the reformer 3. Note that the reformer 3 may include the evaporator 33.

[Exhaust gas line L4]
The exhaust gas line L4 discharges the exhaust gas generated by burning the anode off-gas and the cathode off-gas in the combustor 4 to the outside.
An oxygen concentration detector 41 is disposed in the exhaust gas line L4.

The oxygen concentration detector 41 detects the oxygen concentration contained in the exhaust gas discharged from the combustor 4. As the oxygen concentration detector 41, for example, a zirconia type or electrochemical type sensor can be used.
The oxygen concentration detector 41 is electrically connected to the system control unit 5. The detected concentration value of the oxygen concentration detector 41 is output to the system control unit 5 as a detection signal.

Here, the relationship between the power generation output of the fuel cell system 1 (cell output of the fuel cell 2) and the oxygen concentration contained in the exhaust gas discharged from the combustor 4 will be described.
First, in the fuel cell system 1, a required air flow rate supplied to the cathode of the fuel cell 2 is set according to the power generation output (for example, rated output) of the fuel cell system 1. Specifically, in the first embodiment, it is assumed that the air flow rate adjustment unit 12 is adjusted in advance so that a preset air flow rate is supplied to the fuel cell 2.

  In the fuel cell system 1, the fuel gas flow rate of the designated fuel gas supplied to the reformer 3 is set based on the air flow rate supplied to the cathode of the fuel cell 2. In the first embodiment, it is assumed that the fuel gas flow rate adjusting unit 22 is adjusted so as to supply a preset fuel gas flow rate to the reformer 3.

  The amount of hydrogen obtained by the reformer 3 and the amount of fuel heat of the fuel gas are in a proportional relationship. Therefore, in order to operate the fuel cell system 1 at the rated output regardless of the composition of the fuel gas, when the flow rate of air supplied to the cathode of the fuel cell 2 is set to a constant value, fuels having different compositions It is necessary to adjust the gas flow rate so as to output the same amount of fuel heat as when the designated fuel gas is supplied at a predetermined flow rate. By doing so, the fuel cell system 1 can be operated at the rated output, similarly to the designated fuel gas.

  On the other hand, when the designated fuel gas and the fuel gas having a different composition output the same amount of fuel heat, the oxygen concentration contained in the exhaust gas discharged from the combustor 4 becomes the same value.

As described above, when the flow rate of air supplied to the cathode of the fuel cell 2 is set to a constant value, when the fuel gas having a composition different from that of the designated fuel gas is applied, the detected concentration value of the oxygen concentration detector 41 is designated. What is necessary is just to adjust the flow volume of fuel gas so that it may become the detection density | concentration value (henceforth "target density | concentration value") at the time of applying fuel gas. The target concentration value of the oxygen concentration contained in the exhaust gas is appropriately set according to the fuel utilization rate (U _f ) and air utilization rate (U _a ) of the fuel cell system 1.

[Power conditioner 6]
The power conditioner 6 is a device that adjusts the battery output of the fuel cell 2. The power conditioner 6 has a DC / DC converter (boost circuit: not shown) that boosts the DC voltage output from the fuel cell 2, and the DC voltage boosted by the DC / DC converter can be synchronized with the system power supply. It has a grid interconnection inverter (voltage conversion circuit: not shown) for converting into AC voltage, and an output current control unit (output control circuit: not shown) for controlling the output current of the fuel cell 2. A DC / DC converter is electrically connected to the fuel cell 2, and a grid interconnection inverter is electrically connected to the DC / DC converter.

  A distribution board (not shown) of a commercial power system is electrically connected to the grid interconnection inverter. The grid interconnection inverter and distribution board can be switched between parallel and disconnected via a grid interconnection switch. A grid power supply (not shown) and a plurality of loads (not shown) are electrically connected to the distribution board. Further, an electrical measuring device (not shown) is arranged between the distribution board and the system power supply so that the power supplied from the system power supply to the load can be detected. The detailed connection among the fuel cell 2, the power conditioner 6, the distribution board, the system power supply, the auxiliary machine, and the like is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-103931 by the present applicant.

[Electric power supply to auxiliary equipment]
Various peripheral devices necessary for the power generation operation and output adjustment of the fuel cell 2 such as the air blower 121, the fuel booster 221, the pump 32, the reformer 3, the combustor 4, and the power conditioner 6 described above are “auxiliaries”. That's it. Among these auxiliary machines, those that require electricity for driving are driven by electricity generated by the fuel cell 2 or electricity supplied from a system power supply. Therefore, in the auxiliary machine, the DC voltage output from the fuel cell 2 is converted by a DC / DC converter (not shown), or the AC voltage supplied from the system power supply is AC / DC converter (not shown). ), Or any one of the DC voltages converted in (1) is input. During the power generation operation of the fuel cell 2 (including power supply standby in the disconnected state), electricity generated by the fuel cell 2 is supplied to the auxiliary machine, and supplied from the system power source when the fuel cell 2 is started up. The supplied electricity is supplied to the auxiliary machine. Of the battery output obtained during the power generation operation of the fuel cell 2, the power consumed by the auxiliary machine is called auxiliary machine loss.

[System control unit 5]
In the fuel cell system 1 in which the flow rate of air supplied to the cathode is set in advance so that power is generated at a preset constant power generation output (rated output), a fuel gas having a composition different from that of the designated fuel gas is supplied. Even in such a case, in order to automatically adjust the flow rate of the fuel gas so that an appropriate fuel gas flow rate is supplied to the reformer 3 and power is generated with a constant power generation output, the system control unit 5 A flow control unit 51 is provided.

The fuel gas flow rate control unit 51 feedback-controls the fuel gas flow rate so that the detection concentration value of the oxygen concentration detector 41 becomes a preset target concentration value.
Specifically, the fuel gas flow rate control unit 51 controls the operation amount of the fuel gas flow rate adjustment unit 22 so that the detected concentration value of the oxygen concentration detector 41 becomes a preset target concentration value.
For example, when the fuel booster 221 includes an inverter, the fuel gas flow rate control unit 51 drives the fuel booster 221 at a rotational speed corresponding to the input drive frequency by specifying the drive frequency output by the inverter. You may control to.
The fuel gas flow rate control unit 51 may control the fuel gas flow rate according to the valve opening degree by adjusting the valve opening degree of the fuel gas flow rate adjusting valve 222.

[Effect of this embodiment]
According to the fuel cell system 1 of the first embodiment, the following effects can be obtained.
The fuel cell system 1 includes a fuel gas flow rate adjusting unit 22 so that the oxygen concentration contained in the exhaust gas discharged from the combustor 4 (the detected concentration value of the oxygen concentration detector 41) becomes a preset target concentration value. A fuel gas flow rate control unit 51 for controlling the operation amount is provided.
Accordingly, when the air flow rate is set so that the fuel cell system 1 generates power at a predetermined power generation output (rated output), for example, when fuel gas having a different composition is supplied (the heat amount of the fuel gas is Even in the case of a change), an appropriate amount of fuel gas without excess or deficiency can be supplied to the reformer 3, and the fuel cell system 1 can be automatically adjusted to generate power at the rated output.
By doing so, the optimum power generation efficiency can be maintained and the life of the fuel cell 2 can be maintained. Furthermore, since the fuel gas flow rate adjusting unit 22 can be configured with an inexpensive valve, it is possible to cope with the addition of fuel gas having a different composition without incurring additional costs.
Further, a flow meter for measuring the flow rate of the fuel gas is not necessary, and the flow rate can be adjusted at a low cost.

[Second Embodiment]
In the first embodiment, in order for the fuel cell system 1 to generate power at a power generation output (rated output) specified in advance, the air flow rate supplied to the fuel cell 2 is set in advance, and the air flow rate adjustment unit 12 is set based on the flow rate. It has been adjusted in advance. In the first embodiment, when the designated fuel gas is used, the fuel gas flow rate of the designated fuel gas supplied to the reformer 3 is set based on the air flow rate supplied to the cathode of the fuel cell 2.
On the other hand, 2nd Embodiment demonstrates the case where the electric power generation output of the fuel cell system 1 is changed from a rated output. In the description of the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the fuel cell system 1 according to the second embodiment, the system control unit 5 further includes an air flow rate control unit 52 in order to adjust the air flow rate according to the power generation output of the fuel cell system 1.

The air flow rate control unit 52 controls the air flow rate adjustment unit 12 so that the battery output of the fuel cell 2 corresponding to the power generation output of the fuel cell system 1 is obtained. Specifically, the air flow rate control unit 52 sets a necessary air flow rate to be supplied to the cathode of the fuel cell 2 based on the power generation output after the output adjustment by the power conditioner 6. On the other hand, the fuel gas flow rate control unit 51 controls the fuel gas flow rate adjustment unit 22 so that the battery output of the fuel cell 2 corresponding to the power generation output of the fuel cell system 1 is obtained. Specifically, the fuel gas flow rate control unit 51 needs to be supplied to the reformer 3 on the assumption that the fuel gas is the designated fuel gas based on the power generation output after the output adjustment by the power conditioner 6. Set the correct fuel gas flow rate.
For setting the required air flow rate and the required fuel gas flow rate, for example, the values of the required air flow rate and the fuel gas flow rate when the battery output of the fuel cell 2 is varied are stored in advance in the storage unit. In this table, when the power generation output of the fuel cell system 1 is designated, the necessary air flow rate and the necessary fuel gas flow rate may be set based on the table.

The air flow rate control unit 52 adjusts the air flow rate adjustment unit 12 in order to supply a necessary air flow rate to the cathode of the fuel cell 2. Specifically, for example, the relationship between the air flow rate and the operation amount of the air flow rate adjustment unit 12 is stored in advance in a table in the storage unit, thereby supplying a necessary air flow rate based on the table. The operation amount of the air flow rate adjustment unit 12 may be set.
By doing so, the air flow rate control unit 52 controls the air flow rate adjustment unit 12 so as to obtain a necessary air flow rate.
For example, when the air blower 121 includes an inverter, the air flow rate control unit 52 controls the air blower 121 to be driven at a rotational speed corresponding to the input driving frequency by specifying the driving frequency output by the inverter. May be.
Further, the air flow rate control unit 52 may control the air flow rate according to the opening degree by adjusting the opening degree of the air flow rate adjustment valve 122.

Similarly, the air flow rate control unit 52 adjusts the fuel gas flow rate adjusting unit 22 in order to supply the required fuel gas flow rate (of designated fuel gas) to the reformer 3. Specifically, for example, the relationship between the fuel gas flow rate and the operation amount of the fuel gas flow rate adjustment unit 22 is stored in advance in a table in the storage unit, so that the necessary fuel gas flow rate is supplied based on the table. The amount of operation of the fuel gas flow rate adjustment unit 22 for doing so may be set.
By doing so, the air flow rate control unit 52 can control the operation amount of the fuel gas flow rate adjustment unit 22 so that the required fuel gas flow rate is obtained.
For example, when the fuel booster 221 includes an inverter, the air flow rate control unit 52 drives the fuel booster 221 at a rotation speed corresponding to the input drive frequency by specifying the drive frequency output by the inverter. You may control.
Further, the output control unit 52 may control the fuel gas flow rate according to the opening degree by adjusting the opening degree of the fuel gas flow rate adjusting valve 222.

  The system control unit 5 in the second embodiment has an output adjustment function of the power conditioner 6 and adjusts the power generation output of the fuel cell system 1 according to the power supplied from the system power supply to the load. Specifically, the electric power supplied from the system power source to the load is detected by an electric measuring device arranged between the distribution board and the system power source, and the power generation output of the fuel cell system 1 follows the increase and decrease of the power. Increase or decrease. That is, when the power supplied to the load increases, the system control unit 5 performs control to increase the power generation output of the fuel cell system 1 (cell output of the fuel cell 2). Conversely, when the power supplied to the load decreases, Control is performed to reduce the power generation output of the fuel cell system 1 (cell output of the fuel cell 2).

  In the power generation output control of the fuel cell system 1, the order of the output adjustment of the fuel cell 2 and the output adjustment of the power conditioner 6, and the order of the control of the fuel gas flow rate and the control of the air flow rate during the output adjustment of the fuel cell 2 are as follows. It is preferable to be as follows.

When the power generation output of the fuel cell system 1 is increased, the output adjustment of the power conditioner 6 is performed after the output adjustment of the fuel cell 2 is performed. In the output adjustment of the fuel cell 2 preceding the output adjustment of the power conditioner 6, the fuel gas flow rate is increased after the air flow rate is increased.
On the other hand, when the power generation output of the fuel cell system 1 is lowered, the output adjustment of the fuel cell 2 is performed after the output adjustment of the power conditioner 6 is performed. In the output adjustment of the fuel cell 2 subsequent to the output adjustment of the power conditioner 6, the air flow rate is reduced after the fuel gas flow rate is reduced.
By operating in the order as described above, the power generation output of the fuel cell system 1 can be changed to a desired value without causing an unstable output state in the fuel cell 2.

In the output adjustment for increasing the power generation output of the fuel cell system 1, a specific operation procedure is as follows.
(1) The air flow rate control unit 52 calculates an air flow rate that can obtain the battery output of the fuel cell 2 according to the power generation output after the output adjustment, and supplies the air flow rate to the fuel cell 2 so that the air flow rate is supplied to the fuel cell 2. The adjustment unit 12 is controlled. Thereby, the air flow rate supplied to the fuel cell 2 is increased.
(2) When the air flow rate is increased, the fuel gas flow rate control unit 51 calculates the fuel gas flow rate when using the designated fuel gas that can obtain the battery output of the fuel cell 2 according to the power generation output after the output adjustment. Then, the fuel gas flow rate adjusting unit 22 is controlled to supply this fuel gas flow rate to the reformer 3. As a result, the flow rate of the fuel gas supplied to the fuel cell 2 is increased.
(3) When the fuel gas flow rate is increased, the system control unit 5 adjusts the output of the power conditioner 6 to increase the power generation output of the fuel cell system 1. Thereby, the power generation output of the fuel cell system 1 is shifted to a higher output state (for example, shift from 50% output to rated 100% output).
(4) After adjusting the output of the fuel cell system 1, the fuel gas flow rate control unit 51 sets the detected concentration value of the oxygen concentration detector 41 in advance while the air flow rate control unit 52 keeps the air flow rate constant. The fuel gas flow rate is feedback controlled so as to achieve the target concentration value. As a result, even when a fuel gas having a composition different from that of the designated fuel gas is used, the fuel gas flow rate is corrected, and the amount of fuel heat input to the reformer 3 is kept constant.

In the output adjustment for reducing the power generation output of the fuel cell system 1, the specific operation procedure is as follows.
(1) The system control unit 5 adjusts the output of the power conditioner 6 to lower the power generation output of the fuel cell system 1. Thereby, the power generation output of the fuel cell system 1 is shifted to a lower output state (for example, the rated 100% output is shifted to 50% output).
(2) When the output of the power conditioner 6 is adjusted, the fuel gas flow rate control unit 51 uses the designated fuel gas that can obtain the battery output of the fuel cell 2 according to the power generation output after the output adjustment. The gas flow rate is calculated, and the fuel gas flow rate adjusting unit 22 is controlled to supply this fuel gas flow rate to the reformer 3. As a result, the flow rate of the fuel gas supplied to the fuel cell 2 is reduced.
(3) When the fuel gas flow rate is decreased, the air flow rate control unit 52 calculates an air flow rate at which the battery output of the fuel cell 2 can be obtained according to the power generation output after the output adjustment, and this air flow rate is used as the fuel. The air flow rate adjusting unit 12 is controlled so as to be supplied to the battery 2. Thereby, the air flow rate supplied to the fuel cell 2 is reduced.
(4) After adjusting the output of the fuel cell system 1, the fuel gas flow rate control unit 51 sets the detected concentration value of the oxygen concentration detector 41 in advance while the air flow rate control unit 52 keeps the air flow rate constant. The fuel gas flow rate is feedback controlled so as to achieve the target concentration value. As a result, even when a fuel gas having a composition different from that of the designated fuel gas is used, the fuel gas flow rate is corrected, and the amount of fuel heat input to the reformer 3 is kept constant.

[Modification]
Here, the fuel gas flow rate adjustment unit 22 may be configured to include, for example, a main adjustment valve 2221 and a sub adjustment valve 2222.
Specifically, the fuel gas flow rate control unit 51 controls the main regulating valve 2221 so that the battery output of the fuel cell 2 corresponding to the power generation output of the fuel cell system 1 is obtained, and the oxygen concentration detector 41 The sub adjustment valve 2222 may be controlled so that the detected density value becomes the target density value.
By doing so, in a normal state (a state where electric power is generated using the designated fuel gas), an optimal fuel gas flow rate can be realized by adjusting the opening of the main adjustment valve 2221. When the composition of the fuel gas slightly changes due to a change or the like, the reformer 3 can be adjusted to the composition variation of the fuel gas by finely adjusting the sub-regulating valve 2222 while keeping the opening degree of the main regulating valve 2221 as it is. The fuel gas flow rate can be optimized so that the amount of fuel heat input to is kept constant. Thereby, while being able to maintain suitable power generation efficiency, the lifetime of the fuel cell 2 can be maintained.

[Configuration of Main Adjustment Valve 2221 and Sub Adjustment Valve 2222]
In the fine adjustment of the sub adjustment valve 2222, fine adjustment to increase the fuel gas flow rate by the sub adjustment valve 2222 or fine adjustment to decrease the fuel gas flow rate is required with respect to the fuel gas flow rate by the main adjustment valve 2221.

  When the main adjustment valve 2221 and the sub adjustment valve 2222 are arranged in series, the sub adjustment valve 2222 is preferably arranged on the downstream side of the main adjustment valve 2221. By doing so, the flow rate of the fuel gas adjusted by the main adjustment valve 2221 can be finely adjusted by the sub adjustment valve 2222 so as to decrease.

  When the main adjustment valve 2221 and the sub adjustment valve 2222 are arranged in parallel, the flow rate of the fuel gas by adjusting the opening of the sub adjustment valve 2222 is adjusted to the flow rate of the fuel gas adjusted by the main adjustment valve 2221. Added. By doing so, the flow rate of the fuel gas by the sub-regulation valve 2222 is added to the flow rate of the fuel gas adjusted by the main adjustment valve 2221, thereby finely adjusting the flow rate of the fuel gas to be increased. be able to.

  FIG. 2 is a schematic diagram illustrating an example of the fuel gas flow rate adjusting unit 22 according to the embodiment of the present invention. As shown in FIG. 2, the fuel gas flow rate adjustment valve 222 of the present embodiment includes a sub adjustment valve 2222 </ b> S arranged in series with the main adjustment valve 2221 and a sub adjustment valve arranged in parallel with the main adjustment valve 2221. The adjustment valve 2222P is preferably provided. By doing so, if the composition of the fuel gas slightly changes due to a change in the fuel gas supply source or the like, the fuel gas flow control unit 51 performs rough adjustment at the main adjustment valve 2221 and the fuel gas flow control unit. The fuel gas flow rate to the reformer 3 can be adjusted to an appropriate range by the combination with the fine adjustment by the sub adjustment valve (2222S and 2222P) by 51.

As described above, according to the fuel cell system 1 of the second embodiment, the following effects can be obtained in addition to the effects exhibited by the first embodiment.
The fuel cell system 1 includes an air flow rate adjustment unit 12 that is provided in the air supply line L1 and adjusts the air flow rate supplied to the fuel cell 2, and an air flow rate control unit 53 that controls the air flow rate adjustment unit 12. The air flow rate control unit 52 controls the air flow rate adjustment unit 52 so that the battery output of the fuel cell 2 corresponding to the power generation output of the fuel cell system 1 can be obtained, and the fuel gas flow rate control unit 52 controls the fuel cell system 1. The fuel gas flow rate adjusting unit 22 is controlled so that the battery output of the fuel cell 2 corresponding to the generated power output is obtained. Thereby, the electric power generation output of the fuel cell system 1 can be adjusted according to the electric power supplied from the system power supply to the load.

The fuel gas flow rate adjustment unit 22 includes a main adjustment valve 2221 and a sub adjustment valve 2222, and the fuel gas flow rate control unit 51 has a battery output of the fuel cell 2 corresponding to the power generation output of the fuel cell system 1. As can be obtained, the main adjustment valve 2221 is controlled, and the sub adjustment valve 2222 is controlled so that the detected concentration value of the oxygen concentration detector 41 becomes the target concentration value.
Thereby, in a normal state (a state in which power generation is performed using a fuel gas having a predetermined composition set in advance), an optimal fuel gas flow rate can be realized by adjusting the opening of the main adjustment valve 2221. When the composition of the fuel gas changes slightly due to a change in the gas supply source or the like, the amount of fuel heat input to the reformer 3 with respect to the composition variation of the fuel gas can be finely adjusted by adjusting the sub-regulating valve 2222. The fuel gas flow rate can be optimized so that is kept constant.

  The present invention is not limited to the above-described embodiments, and can be modified within the technical scope described in the claims. The configuration of the fuel cell system 1 is not limited to the system configuration in the present embodiment.

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell 3 Reformer 4 Combustor L1 Air supply line 11 Filter 12 Air flow rate adjustment part 121 Air blower 122 Air flow rate adjustment valve (a damper is included)
L2 Fuel gas supply line 21 Desulfurizer 22 Fuel gas flow rate adjustment unit 221 Fuel booster 222 Fuel gas flow rate adjustment valve 2221 Main adjustment valve 2222, 2222S, 2222P Sub-regulation valve L3 Water supply line 31 Impurity removal unit 32 Pump 33 Evaporator L4 Combustion exhaust gas line 41 Oxygen concentration detector 5 System control unit 51 Fuel gas flow rate control unit 52 Air flow rate control unit 6 Power conditioner

Claims (3)

A fuel cell;
An air supply line for supplying a preset air flow rate to the fuel cell;
A reformer that generates hydrogen from fuel gas and water, and supplies the generated hydrogen to the fuel cell;
A fuel gas supply line for supplying the fuel gas to the reformer;
A fuel gas flow rate adjusting unit that is provided in the fuel gas supply line and adjusts the flow rate of the fuel gas supplied to the reformer;
A water supply line for supplying water to the reformer;
A combustor for burning off-gas discharged from the fuel cell;
An oxygen concentration detector for detecting the oxygen concentration contained in the exhaust gas discharged from the combustor;
A fuel gas flow rate control unit for controlling the fuel gas flow rate adjustment unit,
The fuel gas flow rate control unit controls the fuel gas flow rate adjustment unit so that a detected concentration value of the oxygen concentration detector becomes a preset target concentration value. An air flow rate adjusting unit that is provided in the air supply line and adjusts an air flow rate supplied to the fuel cell;
An air flow rate control unit for controlling the air flow rate adjustment unit,
The air flow rate control unit controls the air flow rate adjustment unit so as to obtain a battery output of the fuel cell according to a power generation output of the fuel cell system;
The fuel gas flow rate control unit controls the fuel gas flow rate adjustment unit so as to obtain a battery output of the fuel cell according to a power generation output of a fuel cell system;
The fuel cell system according to claim 1. The fuel gas flow rate adjusting unit is
A main regulating valve;
A sub-regulator valve,
The fuel gas flow rate control unit controls the main adjustment valve so as to obtain a battery output of the fuel cell according to a power generation output of a fuel cell system, and a detected concentration value of the oxygen concentration detector is set to the target concentration. Controlling the sub-regulator valve so as to become a value,
The fuel cell system according to claim 2.

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