JP2016119151A - Fuel cell system and operation method of fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing deterioration of a cell stack.SOLUTION: A fuel cell system 1 includes: a desulfurization unit 2 for desulfurizing a hydrogen-contained fuel; a modification unit 4 for generating hydrogen-enriched gas by modifying the hydrogen-contained fuel desulfurized by the desulfurization unit 2; a cell stack 5 for performing power generation by using the hydrogen-enriched gas generated in the modification unit 4; a recycle gas line R for recycling a part of the hydrogen-enriched gas to the upstream side of the desulfurization unit 2; a valve 35 for adjusting a circulation amount of the hydrogen-enriched gas in the recycle gas line R; and a control unit 11 for controlling the valve 35. The control unit 11, when the voltage of the cell stack 5 is a predetermined voltage F1 or more, performs first control for controlling the valve 35 so as to start circulation of the hydrogen-enriched gas or second control for controlling the valve 35 so as to increase the circulation amount of the hydrogen-enriched gas.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell system and a method for operating the fuel cell system.

Patent Document 1 describes a fuel cell system including a fuel reforming system and a fuel cell. The fuel reforming system includes a desulfurizer, a reforming reactor, and a CO selective oxidation reactor that are sequentially arranged from the upstream side. The desulfurizer removes sulfur compounds from raw fuel using a hydrogenated adsorption desulfurizing agent. The reforming reactor reacts the desulfurized raw fuel with steam to generate a reformed gas. The CO selective oxidation reactor selectively oxidizes CO contained in the reformed gas and converts it into CO ₂ . The fuel cell system has a recycle line for adding a part of the reformed gas (recycle gas) before being supplied to the CO selective oxidation reactor to the raw fuel. The recycle gas added to the raw fuel is used for desulfurization of the raw fuel in the desulfurizer.

Japanese Patent No. 4931865

  In the fuel cell system described in Patent Document 1, when the reforming reaction is sufficiently performed in the reforming reactor and the reformed gas is not generated, desulfurization using a part of the recycled gas is performed. Desulfurization in the reactor becomes insufficient, and undesulfurized gas may be supplied to the reforming reactor to cause deterioration of the reforming catalyst. In this case, as a result of supplying unreformed gas to the fuel cell, the fuel cell may be deteriorated.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a fuel cell system capable of suppressing deterioration of a cell stack and an operation method of the fuel cell system.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a desulfurization unit that desulfurizes a hydrogen-containing fuel, and a reformer that generates hydrogen-enriched gas by reforming the hydrogen-containing fuel desulfurized in the desulfurization unit. And a cell stack that generates power using the hydrogen-enriched gas generated in the reforming unit, a circulation path for circulating part of the hydrogen-enriched gas upstream of the desulfurization unit, and hydrogen enrichment in the circulation path A flow rate adjusting unit for adjusting the flow rate of gas, and a control unit for controlling at least the flow rate adjusting unit, and the control unit is rich in hydrogen when the voltage of the cell stack is equal to or higher than a predetermined voltage. Performing a first control for controlling the flow rate adjusting unit so as to start the circulation of the chemical gas, or a second control for controlling the flow rate adjusting unit so as to increase the flow rate of the hydrogen-enriched gas. .

  Further, in order to solve the above-described problems, a method of operating a fuel cell system according to the present invention includes a desulfurization unit that desulfurizes a hydrogen-containing fuel, and a hydrogen-rich fuel that is desulfurized in the desulfurization unit by reforming the hydrogen-containing fuel. A reforming section for generating gas, a cell stack for generating power using the hydrogen-enriched gas generated in the reforming section, a circulation path for circulating a part of the hydrogen-enriched gas upstream of the desulfurization section, and a circulation And a flow rate adjusting unit for adjusting a flow rate of hydrogen-enriched gas in the road, and determining whether or not the voltage of the cell stack is equal to or higher than a predetermined voltage A first control that controls the flow rate adjusting unit so as to start circulation of the hydrogen-enriched gas when the voltage is equal to or higher than a predetermined voltage as a result of the determination of the first step and the first step, or hydrogen enrichment Control the flow rate adjustment unit to increase the gas flow rate A second step of performing a second control that, characterized in that it comprises a.

  In these fuel cell systems and fuel cell system operation methods, the first control for controlling the flow rate adjusting unit to start the circulation of the hydrogen-enriched gas to the desulfurization unit, or the hydrogen enrichment to the desulfurization unit Second control is performed to control the flow rate adjusting unit so as to increase the gas flow rate. Thereby, in the desulfurization part, desulfurization of the hydrogen containing fuel using hydrogen enriched gas is performed. In particular, in these fuel cell systems and fuel cell system operation methods, the fact that the voltage of the cell stack is equal to or higher than a predetermined voltage is used as a trigger for the first control and the second control. That the voltage of the cell stack is equal to or higher than a predetermined voltage indicates that the reforming reaction is sufficiently performed in the reforming unit to generate the hydrogen-enriched gas and is supplied to the cell stack. Therefore, in the desulfurization section, it is possible to sufficiently desulfurize the hydrogen-containing fuel by using a part of the hydrogen-enriched gas. As a result, supply of undesulfurized hydrogen-containing fuel to the reforming unit is suppressed. As a result, deterioration of the reforming part is suppressed, and consequently deterioration of the cell stack is suppressed.

  In the fuel cell system according to the present invention, the control unit may further perform the first control or the second control when the temperature of the cell stack is equal to or higher than a predetermined first temperature. In this case, the first control or the second control is performed in a state in which the reforming reaction is sufficiently performed in the reforming unit and the hydrogen-containing gas is reliably generated. For this reason, as a result of reliably suppressing the undesulfurized hydrogen-containing fuel from being supplied to the reforming section, deterioration of the reforming section and the cell stack is reliably suppressed.

  Here, when an insufficiently reformed gas is circulated and supplied to the desulfurization section through the circulation path, hydrogen-containing fuel of the indicated value or more is supplied to the desulfurization section. In this case, there is a risk that coking will occur with respect to the desulfurization catalyst, and as a result, the desulfurization performance of the desulfurization part may be reduced. Further, when hydrogen-containing fuel exceeding the indicated value is supplied to the reforming section through the desulfurization section, the steam / carbon ratio in the reforming section is lowered to cause coking, and the reforming section outlet has insufficient reforming. There is a possibility that a further increase in the proportion of gas (and hence deterioration of the cell stack) may occur.

  Therefore, in the fuel cell system according to the present invention, the control unit may further perform the first control or the second control when the temperature of the reforming unit is equal to or higher than a predetermined second temperature. . In this case, the first control or the second control is performed in a state where the reforming reaction is sufficiently performed in the reforming unit. For this reason, the insufficiently reformed gas is reliably suppressed from being circulated and supplied to the desulfurization section. Therefore, coking in the desulfurization part and the reforming part is avoided, and deterioration of the cell stack is reliably suppressed.

  In the fuel cell system according to the present invention, the control unit may further perform the first control or the second control when the temperature of the desulfurization unit is equal to or higher than a predetermined third temperature. Generally, a desulfurization catalyst adsorbs a hydrogen-containing fuel. As the desulfurization catalyst is heated, the adsorbed hydrogen-containing fuel is desorbed. Further, when the temperature exceeds a certain temperature, the desorption is almost eliminated, and a certain amount of hydrogen-containing fuel remains adsorbed on the desulfurization catalyst. Therefore, as in this case, if the temperature of the desulfurization section is triggered by the first control or the second control, the influence of the hydrogen-containing fuel on the reforming section due to desorption from the desulfurization catalyst (steam / carbon) (Decrease in the ratio) can be reduced.

  In the fuel cell system according to the present invention, the control unit may perform the first control or the second control before the cell stack starts power generation. In this case, it is possible to suppress in advance that the fuel utilization rate rises due to the change in the flow rate of the hydrogen-enriched gas during power generation, and the deterioration of the cell stack is reliably suppressed.

  Here, “before the cell stack starts power generation” means before the start of current drawing from the cell stack. In this case, the cell stack voltage is the open circuit voltage of the cell stack. On the other hand, the state in which current is being drawn from the cell stack may be referred to as “power generation in the cell stack”.

  Here, when the hydrogen-enriched gas is circulated and supplied to the desulfurization section, the hydrogen-containing fuel adsorbed by the desulfurization catalyst of the desulfurization section is desorbed as described above, so that the reforming section exceeds the indicated value. Of hydrogen-containing fuel may be supplied. In that case, as a result of the steam / carbon ratio in the reforming portion being temporarily lowered, an insufficiently reformed gas is supplied to the cell stack, and the cell stack may be deteriorated.

  In view of this, a fuel cell system according to the present invention includes a reforming water supply path that supplies reforming water to the reforming section, and a supply amount of reforming water from the reforming water supply path to the reforming section. A reforming unit including a steam reforming catalyst, and the control unit increases the steam / carbon ratio in the reforming unit in advance before the first control or the second control. Alternatively, the supply amount adjusting unit may be controlled. In this case, the steam / carbon ratio in the reforming unit is increased in advance before the first control or the second control. For this reason, even if the steam / carbon ratio in the reforming section temporarily decreases, the steam / carbon ratio does not decrease to the extent that an insufficiently reformed gas is generated, Deterioration of the cell stack is suppressed.

  In the fuel cell system according to the present invention, the control unit is configured to control the flow rate adjusting unit so as to stop the circulation of the hydrogen-enriched gas, or the flow rate so as to reduce the flow rate of the hydrogen-enriched gas. The power generation of the cell stack may be stopped before the fourth control that controls the adjustment unit. In this case, by performing the third control or the fourth control after the power generation is stopped, an increase in the fuel utilization rate during power generation due to a change in the flow rate of the hydrogen-enriched gas is suppressed, and the cell stack is reliably deteriorated. It is suppressed.

  In the fuel cell system according to the present invention, the control unit controls the flow rate adjustment unit to stop the circulation of the hydrogen-enriched gas during the power generation of the cell stack, or the flow of the hydrogen-enriched gas. When performing the fourth control for controlling the flow rate adjusting unit so as to decrease the amount, the fuel utilization rate of the cell stack may be decreased in advance before the third control or the fourth control. In this case, even if the fuel utilization rate in the cell stack temporarily increases due to the execution of the third control or the fourth control, the fuel utilization rate does not increase to the extent that the cell stack deteriorates, Deterioration of the stack is suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the operating method of a fuel cell system which can suppress deterioration of a cell stack, and a fuel cell system can be provided.

It is a block diagram which shows the fuel cell system which concerns on this embodiment. It is the schematic which shows the structure of the fuel cell system shown by FIG. 2 is a flowchart showing an example of a method for operating the fuel cell system shown in FIG. 1. 2 is a flowchart showing an example of a method for operating the fuel cell system shown in FIG. 1.

  Hereinafter, an embodiment of a fuel cell system and a fuel cell system operation method according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements or corresponding elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a block diagram showing a fuel cell system according to this embodiment. As shown in FIG. 1, a fuel cell system 1 according to this embodiment includes a desulfurization unit 2, a water vaporization unit 3, a reforming unit 4, a cell stack 5, an off-gas combustion unit (combustion unit) 6, and a hydrogen-containing fuel supply. Unit 7, water supply unit 8, oxidant supply unit 9, power conditioner 10, and control unit 11. The fuel cell system 1 generates power in the cell stack 5 using a hydrogen-containing fuel and an oxidant. As the cell stack 5, for example, a solid oxide fuel cell (SOFC) is employed.

  However, the cell stack 5 is not limited to a solid oxide fuel cell. Examples of the cell stack 5 include a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), and a molten carbonate fuel cell (MCFM). ) And others can be employed. Further, the components shown in FIG. 1 may be appropriately omitted or changed according to the type of the cell stack 5, the type of the hydrogen-containing fuel, the reforming method, and the like.

  As the hydrogen-containing fuel, for example, a hydrocarbon fuel is used. As the hydrocarbon fuel, a compound containing carbon and hydrogen in a molecule (may contain other elements such as oxygen) or a mixture thereof is used. Examples of the hydrocarbon fuel include hydrocarbons, alcohols, ethers, and biofuels. As hydrocarbon fuels, those derived from conventional fossil fuels such as petroleum and coal, those derived from synthetic fuels such as synthesis gas, and those derived from biomass can be used as appropriate.

  More specifically, examples of the hydrocarbons include methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, town gas, gasoline, naphtha, kerosene, and light oil. Examples of alcohols include methanol and ethanol. Examples of ethers include dimethyl ether. Examples of the biofuel include biogas, bioethanol, biodiesel, and biojet. As the oxidizing agent, for example, air, pure oxygen gas (which may contain impurities that are difficult to remove by a normal removing means), oxygen-enriched air, or the like is used.

  The desulfurization unit 2 performs desulfurization of the hydrogen-containing fuel supplied to the reforming unit 4. The desulfurization part 2 has a desulfurization catalyst for removing sulfur compounds contained in the hydrogen-containing fuel. As the desulfurization method of the desulfurization unit 2, for example, a hydrodesulfurization method in which a sulfur compound is removed by reacting with hydrogen is employed. As the desulfurization catalyst of the desulfurization part 2, for example, a combination of a NiMo catalyst and a ZnO catalyst, a combination of a CoMo catalyst and a ZnO catalyst, a Cu—ZnO—Ni catalyst, or the like is used.

  The water vaporization part 3 produces | generates water vapor | steam by heating and vaporizing water. Heating of water in the water vaporization unit 3 uses heat from the off-gas combustion unit 6. In addition, for the heating of the water in the water vaporization part 3, the heat | fever generate | occur | produced in the fuel cell system 1, such as the heat | fever of waste gas, may be utilized, for example, and other heat sources, such as a heater and a burner, may be used separately. . The water vaporization unit 3 supplies the generated water vapor to the reforming unit 4.

  The reforming unit 4 reforms the hydrogen-containing fuel to generate a hydrogen-enriched gas. The reforming unit 4 supplies the generated hydrogen-enriched gas to the anode 12 of the cell stack 5. The recycle gas line (circulation path) R circulates a part of the hydrogen-enriched gas generated in the reforming unit 4 as a recycle gas upstream of the desulfurization unit 2. The water vaporization unit 3 and the reforming unit 4 are included in the hydrogen generation unit 20. That is, the fuel cell system 1 includes a hydrogen generation unit 20 that reforms the hydrogen-containing fuel desulfurized by the desulfurization unit 2 to generate a hydrogen-enriched gas. Further, as described above, the fuel cell system 1 includes the recycle gas line R that circulates a part of the reformed gas generated in the hydrogen generation unit 20 to the upstream side of the desulfurization unit 2.

  As the reforming method in the reforming unit 4, for example, steam reforming, partial oxidation reforming, autothermal reforming, and other reforming methods can be adopted. Here, the case where the reforming method of the reforming unit 4 is steam reforming (when the reforming unit 4 includes a steam reforming catalyst) will be described as an example. In this case, the reforming unit 4 is supplied with the hydrogen-containing fuel from the desulfurization unit 2 and with the steam from the water vaporization unit 3 as described above. The heat used for generating the reformed gas in the reforming unit 4 is the heat of the off-gas combustion unit 6. However, the heat used for generating the reformed gas in the reforming unit 4 may use, for example, heat generated in the fuel cell system 1 such as heat of exhaust gas, or other heat source such as a heater or a burner. May be used.

  The hydrogen generation unit 20 may have other configurations instead of or in addition to the reforming unit 4. For example, when the cell stack 5 is a polymer electrolyte fuel cell (PEFC) or a phosphoric acid fuel cell (PAFC), the hydrogen generation unit 20 uses carbon monoxide in the gas discharged from the reforming unit 4. A removal part (for example, a shift reaction part, a selective oxidation reaction part, etc.) can be provided.

  The cell stack 5 generates power using the hydrogen-enriched gas from the hydrogen generation unit 20 and the oxidant from the oxidant supply unit 9. The cell stack 5 includes an anode 12 to which a hydrogen-enriched gas is supplied, a cathode 13 to which an oxidant is supplied, and an electrolyte 14 disposed between the anode 12 and the cathode 13. The cell stack 5 supplies power to the outside via the power conditioner 10. The cell stack 5 supplies the hydrogen-enriched gas and oxidant that have not been used for power generation to the off-gas combustion unit 6 as off-gas.

  The off gas combustion unit 6 burns off gas supplied from the cell stack 5. The off-gas combustion unit 6 is formed on the cell stack 5. The heat generated by the off-gas combustion unit 6 is supplied to the water vaporization unit 3 to be used for generating water vapor, and is also supplied to the reforming unit 4 to be used for generating reformed gas.

  The hydrogen-containing fuel supply unit 7 supplies the hydrogen-containing fuel to the desulfurization unit 2. The water supply unit 8 is provided in the reformed water supply line (reformed water supply path) 40 for supplying the reformed water (water) to the hydrogen generating unit 20 and the reformed water supply line 40, and the reformed water supply line And a valve (supply amount adjusting unit) 41 for adjusting the amount of water supplied from 40 to the hydrogen generating unit 20 (see FIG. 2), and based on a control signal from the control unit 11. Driven. The oxidant supply unit 9 supplies an oxidant to the cathode 13 of the cell stack 5. The hydrogen-containing fuel supply unit 7 and the oxidant supply unit 9 are configured by a pump, for example, and are driven based on a control signal from the control unit 11.

  The power conditioner 10 adjusts the power from the cell stack 5 according to the external power usage state. The power conditioner 10 performs, for example, a process for converting a voltage, a process for converting DC power into AC power, and the like.

  The control unit 11 is configured as a computer including a CPU, a ROM, a RAM, an input / output interface, and the like, for example. For example, the control unit 11 performs overall control of the fuel cell system 1 including control described below by executing a predetermined program in the computer. More specifically, the control unit 11 includes elements such as the hydrogen-containing fuel supply unit 7, the water supply unit 8, the oxidant supply unit 9, and the power conditioner 10, and other elements that will be described later and sensors (not shown). And are electrically connected to elements such as auxiliary machines. The control unit 11 acquires various signals generated in the fuel cell system 1 and outputs a control signal to each element of the fuel cell system 1. Thereby, the control part 11 controls each element mentioned above.

  FIG. 2 is a schematic diagram showing the configuration of the fuel cell system shown in FIG. As shown in FIG. 2, in the fuel cell system 1, the hydrogen generation unit 20 is heated by the off-gas combustion unit 6 and is disposed at a position where it can receive the combustion heat generated by the off-gas combustion unit 6. ing. Here, the hydrogen generation unit 20 is disposed above the off-gas combustion unit 6 so as to face the cell stack 5. The off-gas combustion unit 6 is defined between the hydrogen generation unit 20 and the cell stack 5 by, for example, opening the anode outlet of the cell stack 5 to the hydrogen generation unit 20 side. Exhaust gas from the off-gas combustion unit 6 is exhausted to the outside through, for example, an exhaust catalyst.

  The desulfurization unit 2 is provided so as to come into contact with the housing 15 that houses the hydrogen generation unit 20 and the cell stack 5. Thereby, the heat | fever in the said housing | casing 15 (namely, heat dissipation from the electric power generation module containing the cell stack 5) is transmitted to the desulfurization part 2, and the temperature of the desulfurization part 2 is hold | maintained to high temperature (or it heats up). ). The desulfurization section 2 is filled with a desulfurization catalyst as described above. A heat insulating material (not shown) is appropriately provided around the desulfurization unit 2, the cell stack 5, and the hydrogen generation unit 20.

  The recycle gas line R is for circulating a part of the hydrogen-enriched gas as a recycle gas to the desulfurization section 2. One end (upstream side) of the recycle gas line R is connected to the downstream side of the hydrogen generation unit 20, and the other end (downstream side) is provided with the hydrogen-containing fuel supply unit 7 provided in the feed line 16 that supplies hydrogen-containing fuel. And a pressure adjusting unit 31 such as a check valve. The desulfurization unit 2 can perform hydrodesulfurization of the hydrogen-containing fuel using the recycle gas introduced through the recycle gas line R.

  In the recycle gas line R, there are a drainer (moisture removal unit) 32 for removing water, a pressure adjusting unit 34 such as a check valve, and a valve (flow rate adjusting unit) 35 in a direction from the upstream side to the downstream side of the recycled gas. They are provided in this order. The recycle gas line R may be further provided with a pump or the like. A valve 36 is provided on the upstream side of the pressure adjusting unit 31 in the feed line 16.

  The carbon monoxide removal unit described above may be provided in the recycle gas line R. Thereby, the hydrogen concentration of the recycle gas introduced into the desulfurization part 2 via the recycle gas line R can be improved, and the hydrodesulfurization reaction can be promoted. In particular, when a carbon monoxide removal unit that uses a shift reaction is provided, the amount of water in the recycle gas flowing through the recycle gas line R decreases due to the shift reaction. Therefore, the blockage of the recycle gas line R due to condensation of moisture contained in the recycle gas can be suppressed.

  Subsequently, an example of the control of the control unit 11 will be described. The control unit 11 inputs a signal indicating the voltage of the cell stack 5. Based on the signal, the control unit 11 determines whether or not the voltage of the cell stack 5 is equal to or higher than a predetermined voltage F1 (V). As a result of the determination, when the voltage of the cell stack 5 is equal to or higher than the predetermined voltage F1 (V), the control unit 11 performs the following first control or second control.

  The first control is to control the valve 35 of the recycle gas line R so as to start the circulation of the recycle gas (open the valve 35). Therefore, the control unit 11 transmits a signal for opening the valve 35 to the valve 35. The second control is to control the valve 35 (increase the opening degree of the valve 35) so as to increase the circulation amount of the recycle gas in the recycle gas line R in a state where the valve 35 is opened in advance. is there. Therefore, the control unit 11 transmits a signal for increasing the opening degree of the valve 35 to the valve 35. The circulation amount of the recycle gas in the recycle gas line R is the supply amount of the recycle gas to the desulfurization unit 2.

  The predetermined voltage F1 (V) is an open circuit voltage of the cell stack 5 before the cell stack 5 starts generating power, and is about 140 (V) as an example. Here, “before the cell stack 5 starts power generation” means that before current insertion from the cell stack 5 is started. On the other hand, the predetermined voltage F1 (V) is about 100 (V) as an example when the cell stack 5 is generating power. Here, “cell stack 5 is generating power” means a state in which current is being drawn from cell stack 5.

  The voltage of the cell stack 5 can be equal to or higher than the above-described predetermined voltage F1 (V) due to the reaction between hydrogen in the hydrogen-enriched gas and oxygen in the oxidant in the cell stack 5. That is, the voltage of the cell stack 5 being equal to or higher than the predetermined voltage F1 (V) indicates that the hydrogen-enriched gas is generated by sufficiently performing the reforming reaction in the hydrogen generator 20. Accordingly, if the fact that the voltage of the cell stack 5 is equal to or higher than the predetermined voltage F1 (V) is used as an opportunity for the first control and the second control, a part of the hydrogen-enriched gas generated in the hydrogen generation unit 20 is used. The desulfurization unit 2 can be supplied as a recycle gas via the recycle gas line R.

  Further, the control unit 11 inputs a signal indicating the temperature of the cell stack 5. And the control part 11 determines whether the temperature of the cell stack 5 is more than predetermined 1st temperature T1 (degreeC) based on the signal. As a result of the determination, when the temperature of the cell stack 5 is equal to or higher than the first temperature T1 (° C.), the control unit 11 performs the first control or the second control. The first temperature T1 (° C.) is, for example, about 500 ° C. when the cell stack 5 is a solid oxide fuel cell (SOFC), and when the cell stack 5 is a fixed polymer fuel cell (PEFC). It is about 60 ° C.

  The fact that the temperature of the cell stack 5 is equal to or higher than the first temperature T1 (° C.) described above means that, similarly to the voltage, the hydrogen generation part 20 is sufficiently reformed to generate hydrogen-enriched gas. Indicates. Therefore, if the fact that the temperature of the cell stack 5 is equal to or higher than the first temperature T1 (° C.) is further used as an opportunity for the first control and the second control, the hydrogen-enriched gas is reliably supplied to the desulfurization unit 2 as the recycled gas. Can be supplied. As an example, the temperature of the cell stack 5 can be a temperature measured near the center of the cell stack 5. However, the temperature of the cell stack 5 should just be used as a reference | standard that hydrogen-enriched gas is fully produced | generated in the hydrogen generation part 20, The measurement location is not limited.

  Further, the control unit 11 inputs a signal indicating the temperature of the reforming unit 4. Then, the control unit 11 determines whether or not the temperature of the reforming unit 4 is equal to or higher than a predetermined second temperature T2 (° C.) based on the signal. As a result of the determination, when the temperature of the reforming unit 4 is equal to or higher than the second temperature T2 (° C.), the control unit 11 performs the first control or the second control. The second temperature T2 (° C.) is a temperature at which the reforming reaction is sufficiently performed in the reforming unit 4, and is about 600 (° C.) as an example.

  As described above, if the fact that the temperature of the reforming unit 4 is equal to or higher than the second temperature T2 (° C.) is further used as an opportunity for the first control and the second control, the hydrogen-enriched gas can be more reliably used as the recycle gas. The desulfurization unit 2 can be supplied. The temperature of the reforming unit 4 is, for example, the reforming catalyst temperature in the reforming unit 4 or the hydrogen-enriched gas temperature discharged from the reforming unit 4. The temperature of the reforming unit 4 can be measured at the outlet of the reforming unit 4 as an example, but may be performed anywhere as long as the temperature of the reforming unit 4 can be estimated.

  Further, the control unit 11 inputs a signal indicating the temperature of the desulfurization unit 2. And the control part 11 determines whether the temperature of the desulfurization part 2 is more than predetermined 3rd temperature T3 (degreeC) based on the signal. As a result of the determination, when the temperature of the desulfurization unit 2 is equal to or higher than the third temperature T3 (° C.), the control unit 11 performs the first control or the second control. The third temperature T3 (° C.) is equal to or higher than the operation start temperature of the desulfurization catalyst in the desulfurization section 2 (hereinafter referred to as “operation start temperature”), and the gas adsorption amount in the desulfurization catalyst is reduced to a negligible level. It is a temperature that satisfies both the temperature (hereinafter referred to as “gas adsorption amount decrease temperature”) and higher.

  For example, when the operation start temperature <the gas adsorption amount decrease temperature, the third temperature T3 (° C.) may be equal to or higher than the gas adsorption amount decrease temperature. On the other hand, when the operation start temperature> the gas adsorption amount decrease temperature, the third temperature T3 (° C.) may be equal to or higher than the operation start temperature. As an example in this case, when the operation start temperature is 250 (° C.) and the gas adsorption amount decrease temperature is 150 (° C.), the third temperature T3 (° C.) may be 250 ° C. or more.

  Moreover, the temperature of the desulfurization part 2 is the temperature of the desulfurization catalyst of the desulfurization part 2, or a desulfurization fuel temperature. The measurement of the temperature of the desulfurization part 2 can be performed in the exit of the desulfurization part 2 as an example. The temperature of the desulfurization unit 2 can be measured at the outlet of each layer when a plurality of desulfurization catalysts are stacked in the desulfurization unit 2.

  As described above, the control unit 11 sets the voltage of the cell stack 5, the temperature of the cell stack 5, the temperature of the reforming unit 4, and the temperature of the desulfurization unit 2 as an opportunity to execute the first control or the second control. Can be used. However, in the control unit 11, at least the voltage of the cell stack 5 may be used as an opportunity for executing the first control or the second control, and the temperature of the cell stack 5, the temperature of the reforming unit 4, and the desulfurization unit As for the temperature of 2, one or more may be selected as necessary and used in combination with the voltage of the cell stack 5. In addition, the control unit 11 can perform the first control or the second control particularly before the cell stack 5 starts power generation.

  Here, in addition to the first control or the second control described above, the control unit 11 can further perform the following control. In other words, the control unit 11 increases the steam / carbon ratio (hereinafter referred to as “S / C”) in the reforming unit 4 before performing the first control or the second control. The valve 41 is controlled. At this time, the control unit 11 increases the supply amount of water to the reforming unit 4 (water vaporization unit 3) by transmitting a signal for increasing the opening degree of the valve 41 to the valve 41, and the reforming unit 4 The S / C at can be increased. In this case, after the S / C increase in the reforming unit 4 and the first control or the second control, the control unit 11 in the reforming unit 4 after a predetermined time (a predetermined time F3 (min) described later) has elapsed. Restore S / C.

  Moreover, the control part 11 can perform the following 3rd control or 4th control. The third control and the fourth control are controls performed in a state where the valve 35 is opened and the recycle gas is flowing through the recycle gas line R. More specifically, the third control is to control the valve 35 of the recycle gas line R so as to stop the circulation of the recycle gas (the valve 35 is closed). Therefore, the control unit 11 transmits a signal for closing the valve 35 to the valve 35. In the fourth control, the valve 35 is controlled (the opening degree of the valve 35 is reduced) so as to reduce the circulation amount of the recycle gas in the recycle gas line R. Therefore, the control unit 11 transmits a signal for reducing the opening degree of the valve 35 to the valve 35.

  In particular, the control unit 11 can stop the power generation of the cell stack 5 before the third control or the fourth control. Alternatively, when performing the third control or the fourth control during the power generation of the cell stack 5 (that is, without stopping the power generation of the cell stack 5), the control unit 11 performs the third control or the fourth control. Before this, the fuel utilization rate in the cell stack 5 can be reduced. In this case, the control unit 11 controls the hydrogen-containing fuel supply unit 7 so as to increase the supply amount of the hydrogen-containing fuel from the hydrogen-containing fuel supply unit 7 to the desulfurization unit 2, so that the fuel utilization rate in the cell stack 5 is increased. Can be reduced. Alternatively, the fuel utilization rate in the cell stack 5 can be reduced by reducing the power generation amount of the cell stack 5. In this case, the control unit 11 reduces the fuel utilization rate in the cell stack 5 and uses the fuel in the cell stack 5 after a predetermined time (a predetermined time F6 (min) described later) elapses after the third control or the fourth control. Restore the rate.

  Subsequently, an example of an operation method of the fuel cell system 1 under the control of the control unit 11 described above will be described. FIG. 3 is a flowchart showing an example of an operation method of the fuel cell system shown in FIG. In the example shown in FIG. 3, first, the control unit 11 determines whether or not the cell stack 5 is generating power (step S101).

  If the cell stack 5 is not generating power as a result of the determination in step S101, the control unit 11 determines whether or not the temperature of the cell stack 5 is equal to or higher than the first temperature T1 (° C.) as described above (step). S102: First step). As a result of this determination, when the temperature of the cell stack 5 is equal to or higher than the first temperature T1 (° C.), the control unit 11 determines whether or not the voltage of the cell stack 5 is equal to or higher than the predetermined voltage F1 (V) as described above. Is determined (step S103).

  As a result of the determination in step S103, when the voltage of the cell stack 5 is equal to or higher than the predetermined voltage F1 (V), the control unit 11 increases the S / C in the reforming unit 4 (step S104). Here, the control unit 11 increases the amount of water supplied to the reforming unit 4 (water vaporization unit 3) by transmitting a signal for increasing the opening degree of the valve 41 to the valve 41, so that the reforming unit 4 S / C at is F2 + α. F2 is a preset value of S / C, and α is an increment that is increased in step S104.

  Subsequently, the control unit 11 opens the valve 35 of the recycle gas line R (step S105: second step). More specifically, here, the control unit 11 opens the valve 35 by transmitting a signal to the valve 35, and starts circulation of the recycled gas via the recycled gas line R. That is, in this step S105, the control unit 11 performs the first control described above. Thereby, supply of the recycle gas to the desulfurization part 2 via the recycle gas line R is started.

  Subsequently, the control unit 11 performs a predetermined time F3 (min) from the time when the valve 35 is opened by the first control in step S105 (that is, from the time when the supply of the recycle gas to the desulfurization unit 2 is started). The count of the timer set to is started (step S106).

  And the control part 11 determines whether the count of the said timer was complete | finished (that is, whether it counted up only for predetermined time F3 (min)) (process S107). This determination is made as to whether or not a predetermined time F3 (min) has elapsed since the valve 35 of the recycle gas line R was opened in step S105 (that is, since the supply of the recycle gas to the desulfurization unit 2 started). Corresponds to judgment.

  As a result of the determination in step S107, when the count of the timer is completed (that is, when the count is increased by a predetermined time F3 (min)), the control unit 11 decreases the S / C in the reforming unit 4 (step S108). ). Here, the control unit 11 decreases the amount of water supplied to the reforming unit 4 (water vaporization unit 3) by transmitting a signal for decreasing the opening degree of the valve 41 to the reforming unit 4. S / C at is F2. In other words, here, the control unit 11 restores the S / C of the reforming unit 4 that has been raised by α in step S104 as F2.

  Thereafter, the control unit 11 sets the target power generation amount in the cell stack 5 to F4 (W), starts power generation in the cell stack 5 (step S109), and ends the process.

  On the other hand, as a result of the determination in step S102, if the temperature of the cell stack 5 is not equal to or higher than the first temperature T1 (° C.), the determination in step S102 is repeated at predetermined time intervals. If the voltage of the cell stack 5 is not equal to or higher than the predetermined voltage F1 (V) as a result of the determination in step S103, the determination in step S103 is repeated at a predetermined time interval. Furthermore, if the result of the determination in step S107 is that the timer has not finished counting (that is, if the timer has not been counted up for a predetermined time F3 (min)), the determination in step S107 is repeated at predetermined time intervals.

  On the other hand, if the cell stack 5 is generating power as a result of the determination in step S101, the control unit 11 increases the S / C in the reforming unit 4 as in step S104 (step S110). Subsequently, the control unit 11 opens the valve 35 of the recycle gas line R in the same manner as in step S105 (step S111). Subsequently, the control unit 11 starts counting the timer set at the predetermined time F3 (min), similarly to step S106 (step S112).

  Subsequently, as in step S107, the control unit 11 determines whether or not the timer has finished counting (that is, whether or not the timer has been counted up for a predetermined time F3 (min)) (step S113). As a result of the determination in step S113, when the count of the timer is completed (that is, when the count is incremented by a predetermined time F3 (min)), the control unit 11 performs S / C in the reforming unit 4 as in step S108. Is reduced (the amount of increase is restored) (step S114), and the process is terminated.

  Subsequently, another example of the operation method of the fuel cell system 1 under the control of the control unit 11 will be described. FIG. 4 is a flowchart showing an example of an operation method of the fuel cell system shown in FIG. The operation method of the fuel cell system 1 shown in FIG. 4 is performed in a state where the valve 35 of the recycle gas line R is opened by the controller 11 performing the first control or the second control, for example. Is called.

  As shown in FIG. 4, here, first, the control unit 11 determines whether or not the cell stack 5 is generating power (step S201).

  As a result of the determination in step S201, when the cell stack 5 is generating power, the control unit 11 decreases the fuel utilization rate (Uf) in the cell stack 5 (step S202). Here, for example, the control unit 11 controls the hydrogen-containing fuel supply unit 7 so as to increase the supply amount of the hydrogen-containing fuel from the hydrogen-containing fuel supply unit 7 to the desulfurization unit 2, thereby fuel in the cell stack 5. The utilization rate is F5-β. F5 is a value of the fuel utilization rate set in advance, and β is a decrease in the fuel utilization rate that is decreased in step S202.

  Subsequently, the control unit 11 closes the valve 35 of the recycle gas line R (step S203). More specifically, here, the control unit 11 transmits a signal to the valve 35 to close the valve 35 and stops the circulation of the recycle gas via the recycle gas line R. That is, in this process S203, the control part 11 performs the 3rd control mentioned above. Thereby, supply of the recycle gas to the desulfurization part 2 via the recycle gas line R is stopped.

  Subsequently, the control unit 11 performs a predetermined time F6 (min) from the time when the valve 35 is closed by the third control in step S203 (that is, from the time when supply of the recycle gas to the desulfurization unit 2 is stopped). The count of the timer set to is started (step S204).

  Then, the control unit 11 determines whether or not the timer has finished counting (that is, whether or not the timer has been counted up for a predetermined time F6 (min)) (step S205). This determination is made in step S203 whether or not a predetermined time F6 (min) has elapsed since the valve 35 of the recycle gas line R was closed (that is, after the supply of the recycle gas to the desulfurization unit 2 was stopped). This corresponds to the determination.

  As a result of the determination in step S205, when the count of the timer is completed (that is, when the timer counts up for a predetermined time F6 (min)), the control unit 11 increases the fuel utilization rate (Uf) in the cell stack 5 ( Step S206). Here, for example, the control unit 11 controls the hydrogen-containing fuel supply unit 7 so as to decrease the supply amount of the hydrogen-containing fuel from the hydrogen-containing fuel supply unit 7 to the desulfurization unit 2, so that only β is obtained in step S <b> 202. The fuel utilization rate in the cell stack 5 that has been lowered is restored to F5. Thereafter, the process ends.

  Note that, as a result of the determination in step S201, when the cell stack 5 is not generating power, the control unit 11 closes the valve 35 of the recycle gas line R (that is, performs the third control) and ends the process. To do.

  As described above, in the fuel cell system 1 and the operation method thereof in the present embodiment, the first control for controlling the valve 35 of the recycle gas line R so as to start the circulation of the recycle gas to the desulfurization unit 2; Or the 2nd control which controls valve | bulb 35 so that the distribution | circulation amount of the recycle gas to the desulfurization part 2 may be performed is performed. Thereby, in the desulfurization part 2, desulfurization of the hydrogen-containing fuel using recycle gas is performed.

  In particular, in the fuel cell system 1 and the operation method thereof according to the present embodiment, the fact that the voltage of the cell stack 5 is equal to or higher than the predetermined voltage F1 (V) is used as an opportunity for the first control and the second control. Yes. The voltage of the cell stack 5 being equal to or higher than the predetermined voltage F1 (V) means that a reforming reaction is sufficiently performed in the reforming unit 4 to generate a hydrogen-enriched gas and supplied to the cell stack 5. Indicates. Therefore, in the desulfurization section 2, it is possible to sufficiently desulfurize the hydrogen-containing fuel by using the recycle gas that is a part of the hydrogen-enriched gas. Thereby, supply of undesulfurized hydrogen-containing fuel to the reforming unit 4 is suppressed. As a result, deterioration of the reforming unit 4 is suppressed, and consequently deterioration of the cell stack 5 is suppressed.

  In the fuel cell system and the operation method thereof according to the present embodiment, the control unit 11 further performs the first control when the temperature of the cell stack 5 is equal to or higher than a predetermined first temperature T1 (° C.). Alternatively, the second control is performed. In this case, the first control or the second control is performed in a state where the reforming reaction is sufficiently performed in the reforming unit 4 and the hydrogen-enriched gas is reliably generated. For this reason, as a result of reliably suppressing the non-desulfurized hydrogen-containing fuel from being supplied to the reforming unit 4, the deterioration of the reforming unit 4 and the cell stack 5 is reliably suppressed.

  Here, when the insufficiently reformed gas is circulated and supplied to the desulfurization unit 2 through the recycle gas line R, hydrogen-containing fuel of the indicated value or more is supplied to the desulfurization unit 2. In this case, there is a risk that coking will occur with respect to the desulfurization catalyst, and as a result, the desulfurization performance of the desulfurization section 2 may be reduced. Further, when hydrogen-containing fuel exceeding the indicated value is supplied to the reforming unit 4 through the desulfurization unit 2, the S / C in the reforming unit 4 is lowered to cause coking, and reforming is performed at the outlet of the reforming unit 4. There is a possibility that a further increase in the proportion of the insufficient gas (and hence deterioration of the cell stack 5) may occur.

  Therefore, in the fuel cell system 1 according to the present embodiment, the control unit 11 further performs the first control or the second control when the temperature of the reforming unit 4 is equal to or higher than a predetermined second temperature T2 (° C.). Control can be performed. In this case, the first control or the second control is performed in a state where the reforming reaction is sufficiently performed in the reforming unit 4. For this reason, the insufficiently reformed gas is reliably suppressed from being circulated and supplied to the desulfurization section 2. Therefore, coking in the desulfurization unit 2 and the reforming unit 4 is avoided, and deterioration of the cell stack 5 is reliably suppressed.

  In the fuel cell system 1 according to the present embodiment, the control unit 11 further performs the first control or the second control when the temperature of the desulfurization unit 2 is equal to or higher than a predetermined third temperature T3 (° C.). May be performed. Generally, a desulfurization catalyst adsorbs a hydrogen-containing fuel. As the desulfurization catalyst is heated, the adsorbed hydrogen-containing fuel is desorbed. Further, when the temperature exceeds a certain temperature (for example, the gas adsorption amount decreasing temperature described above), the desorption is almost eliminated, and a certain amount of hydrogen-containing fuel remains adsorbed on the desulfurization catalyst. Therefore, if the temperature of the desulfurization section 2 is triggered by the first control or the second control, the influence (deterioration of S / C) of the hydrogen-containing fuel on the reforming section 4 due to desorption from the desulfurization catalyst is reduced. It can be reduced.

  In the fuel cell system 1 according to the present embodiment, the control unit 11 can perform the first control or the second control before the cell stack 5 starts power generation. In this case, it is possible to suppress in advance that the fuel utilization rate rises due to the change in the flow rate of the hydrogen-enriched gas during power generation, and the deterioration of the cell stack is reliably suppressed.

  Here, when the hydrogen-enriched gas is circulated and supplied to the desulfurization section 2 as a recycle gas, the hydrogen-containing fuel adsorbed by the desulfurization catalyst of the desulfurization section 2 is desorbed as described above, thereby the reforming section 4. In some cases, hydrogen-containing fuel exceeding the indicated value is supplied. In that case, as a result of the S / C in the reforming unit 4 temporarily lowering, the insufficiently reformed gas is supplied to the cell stack 5 and the cell stack 5 may be deteriorated.

  Therefore, in the fuel cell system 1 and the operation method thereof according to the present embodiment, the control unit 11 reforms so as to increase the S / C in the reforming unit 4 before the first control or the second control. The valve 41 of the water supply line 40 can be controlled. In this case, the S / C in the reforming unit 4 is raised in advance before the first control or the second control. For this reason, even if the S / C in the reforming unit 4 temporarily decreases, the S / C does not decrease to the extent that an insufficiently reformed gas is generated. Supply of poor quality gas to the cell stack 5 is suppressed. Therefore, deterioration of the cell stack 5 is suppressed.

  Further, in the fuel cell system 1 according to the present embodiment, the control unit 11 controls the third control for controlling the valve 35 of the recycle gas line R so as to stop the circulation of the recycle gas, or the circulation amount of the recycle gas. The power generation of the cell stack 5 can be stopped before the fourth control for controlling the valve 35 to decrease. In this case, by performing the third control or the fourth control after the power generation is stopped, an increase in the fuel utilization rate due to the change in the flow rate of the hydrogen-enriched gas can be suppressed during power generation, and the cell stack 5 is more deteriorated. Suppressed reliably.

  Further, in the fuel cell system 1 and the operation method thereof according to the present embodiment, the control unit 11 performs the third control or the fourth control when performing the third control or the fourth control during the power generation of the cell stack 5. Before the control, the fuel utilization rate of the cell stack 5 can be reduced in advance. In this case, even if the fuel usage rate in the cell stack 5 temporarily increases due to the execution of the third control or the fourth control, the fuel usage rate does not increase to the extent that the cell stack 5 deteriorates. The cell stack 5 is suppressed from deteriorating.

  The above embodiment describes one embodiment of the fuel cell system and the operation method of the fuel cell system according to the present invention. Therefore, the fuel cell system and the operation method of the fuel cell system according to the present invention are not limited to the above-described fuel cell system 1 and the operation method thereof. The fuel cell system and the operation method of the fuel cell system according to the present invention are those in which the above-described fuel cell system 1 and the operation method thereof are arbitrarily changed without changing the gist of each claim. Can do.

  For example, in the example of the operation method of the fuel cell system 1 shown in FIG. 3, the control unit 11 performs the first control in steps S105 and S111. However, when the valve 35 is opened in advance and the recycle gas is flowing through the recycle gas line R, the second control can be performed in steps S105 and S111.

  In the example of the operation method of the fuel cell system 1 shown in FIG. 4, the control unit 11 performs the third control in step S203. However, the control unit 11 may perform the fourth control in step S203.

  In the operation method of the fuel cell system 1 shown in FIG. 3, the determination of the temperature of the cell stack 5 (step S102) and the determination of the voltage of the cell stack 5 (step S103) are triggered by the first control in step S105. Was used. However, at least the determination of the voltage of the cell stack 5 (step S103) may be used as the trigger for the first control in step S105. Alternatively, as an opportunity of the first control in step S105, one or more of the determination of the temperature of the cell stack 5, the determination of the temperature of the reforming unit 4, and the determination of the temperature of the desulfurization unit 2 are selected as necessary, It can be used in combination with the determination of the voltage of the cell stack 5.

  Further, in the fuel cell system 1 and the operation method thereof, the control unit 11 improves after the elapse of a predetermined time F3 (min) after the S / C increase in the reforming unit 4 and the first control or the second control. The S / C in the quality part 4 was restored. On the other hand, as an opportunity to restore the S / C in the reforming unit 4, the temperature of the off-gas combustion unit 6 has entered the range of the specified value instead of the lapse of the predetermined time F3 (min). May be used. Alternatively, both of the fact that the predetermined time F3 (min) has passed and the temperature of the off-gas combustion unit 6 being within a specified range may be used. Furthermore, either one is given priority over the other. You may use it higher.

  Further, in the fuel cell system 1 and the operation method thereof, the control unit 11 performs the cell stack after a predetermined time F6 (min) has elapsed after the fuel utilization rate in the cell stack 5 decreases and the third control or the fourth control. The fuel utilization rate in 5 was restored. On the other hand, as an opportunity to restore the fuel utilization rate in the cell stack 5, the fact that the temperature of the off-gas combustion unit 6 is within a specified range is used instead of the elapse of the predetermined time F6 (min). May be. Alternatively, both the fact that the predetermined time F6 (min) has elapsed and the temperature of the off-gas combustion unit 6 being within a specified range may be used, and furthermore, either one is given priority over the other. You may use it higher.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Desulfurization part, 4 ... Reformation part, 5 ... Cell stack, 20 ... Hydrogen generation part, 35 ... Valve (flow-rate adjustment part), 40 ... Reformation water supply line (reformation water supply path) ), 41... Valve (supply amount adjusting unit), R... Recycle gas line (circulation path).

Claims (9)

A desulfurization section for desulfurizing a hydrogen-containing fuel;
A reforming section for reforming the hydrogen-containing fuel desulfurized in the desulfurization section to generate a hydrogen-enriched gas;
A cell stack that generates power using the hydrogen-enriched gas generated in the reforming section;
A circulation path for circulating a part of the hydrogen-enriched gas upstream of the desulfurization section;
A flow rate adjusting unit for adjusting the flow rate of the hydrogen-enriched gas in the circulation path;
A control unit for controlling at least the flow rate adjustment unit;
With
The control unit is configured to control the flow rate adjusting unit to start circulation of the hydrogen-enriched gas when the voltage of the cell stack is equal to or higher than a predetermined voltage, or the hydrogen-rich Performing a second control for controlling the flow rate adjusting unit to increase the flow rate of the gasified gas,
A fuel cell system. The control unit further performs the first control or the second control when the temperature of the cell stack is equal to or higher than a predetermined first temperature.
The fuel cell system according to claim 1. The control unit further performs the first control or the second control when the temperature of the reforming unit is equal to or higher than a predetermined second temperature.
The fuel cell system according to claim 1 or 2, wherein The control unit further performs the first control or the second control when the temperature of the desulfurization unit is equal to or higher than a predetermined third temperature.
The fuel cell system according to any one of claims 1 to 3, wherein: The control unit performs the first control or the second control before the cell stack starts power generation.
The fuel cell system according to any one of claims 1 to 4, wherein A reforming water supply path for supplying reforming water to the reforming section;
A supply amount adjusting unit for adjusting the supply amount of the reforming water from the reforming water supply path to the reforming unit,
The reforming unit includes a steam reforming catalyst,
The control unit controls the supply amount adjusting unit so as to increase a steam / carbon ratio in the reforming unit before the first control or the second control.
The fuel cell system according to any one of claims 1 to 5, wherein: The control unit controls the flow rate adjusting unit to reduce the flow rate of the hydrogen-enriched gas, or the third control for controlling the flow rate adjusting unit to stop the circulation of the hydrogen-enriched gas. Before the fourth control, power generation of the cell stack is stopped.
The fuel cell system according to any one of claims 1 to 6, wherein: The control unit may be configured to control the flow rate adjusting unit so as to stop the circulation of the hydrogen-enriched gas during power generation of the cell stack, or to reduce the flow rate of the hydrogen-enriched gas. When performing the fourth control for controlling the flow rate adjusting unit, the fuel utilization rate of the cell stack is reduced before the third control or the fourth control.
The fuel cell system according to any one of claims 1 to 6, wherein: A desulfurization section for desulfurizing a hydrogen-containing fuel;
A reforming section for reforming the hydrogen-containing fuel desulfurized in the desulfurization section to generate a hydrogen-enriched gas;
A cell stack that generates power using the hydrogen-enriched gas generated in the reforming section;
A circulation path for circulating a part of the hydrogen-enriched gas upstream of the desulfurization section;
A flow rate adjusting unit for adjusting the flow rate of the hydrogen-enriched gas in the circulation path;
A method for operating a fuel cell system comprising:
A first step of determining whether the voltage of the cell stack is equal to or higher than a predetermined voltage;
As a result of the determination in the first step, when the voltage is equal to or higher than the predetermined voltage, a first control for controlling the flow rate adjusting unit to start circulation of the hydrogen-enriched gas, or the hydrogen-enrichment A second step of performing a second control for controlling the flow rate adjusting unit so as to increase a gas flow rate;
A method for operating a fuel cell system, comprising:

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