JP2013134920A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the CO concentration of a hydrogen-containing gas being supplied to a fuel cell, while suppressing thermal runaway of temperature at a selective oxidation unit.SOLUTION: The fuel cell system comprises a hydrogen generation device 1 including a modification unit 14 which is supplied with a material and water and produces a hydrogen-containing gas by modification reaction, a selective oxidation unit 17 which is supplied with air and reduces the CO concentration in the hydrogen-containing gas produced by the modification unit by selective oxidation reaction, an air supply unit 16 which supplies air to the selective oxidation unit, and a selective oxidation temperature detection unit 20 for detecting the temperature of the selective oxidation unit, a fuel cell 2 which is supplied with the hydrogen-containing gas the CO concentration of which is reduced by the selective oxidation unit and an oxygen-containing gas and generates power, and a control unit 12 which outputs a power generation output command to the fuel cell and an air flow rate command value to the selective oxidation unit on the basis of the temperature detected by the selective oxidation temperature detection unit and the power generation output command value to the fuel cell.

Description

  The present invention relates to a fuel cell system.

  Development of a fuel cell system using a fuel cell stack (hereinafter simply referred to as “fuel cell”) that enables small-sized and highly efficient power generation as a distributed energy supply source is underway. A fuel cell system supplies a hydrogen-containing gas and an oxygen-containing gas to a fuel cell, which is the main body of a power generation unit, and proceeds with an electrochemical reaction between hydrogen and oxygen to generate chemical energy. This is a system that generates electricity by taking it out as natural energy.

  In general, hydrogen-containing gas is not supplied from the infrastructure. Therefore, the conventional fuel cell system uses a city gas supplied from an existing infrastructure or LPG as a raw material, and undergoes a reforming reaction with water vapor at a temperature of 600 to 700 ° C. using a Ru catalyst or a Ni catalyst. A hydrogen generation apparatus including a reforming unit is provided. Note that the hydrogen-containing gas obtained by the reforming reaction usually contains carbon monoxide derived from the raw material, and if the concentration is high, the power generation characteristics of the fuel cell are degraded.

  Therefore, the hydrogen generator is provided with a shift unit and a reaction unit in addition to the reforming unit. The shift unit includes a Cu—Zn-based catalyst or a noble metal-based catalyst that reduces the carbon monoxide by advancing a shift reaction between carbon monoxide and water vapor at a temperature of 200 ° C. to 350 ° C. The reaction unit adds air as an oxidant, selectively oxidizes carbon monoxide at a temperature of 100 ° C. to 200 ° C., and further reduces the carbon monoxide. Is provided. The selective oxidation reaction is represented by the formula (1).

CO + 1 / 2O2 → CO2 (1)
The selective oxidation reaction is an exothermic reaction, and when the air (oxygen) flow rate is increased, the exothermic reaction proceeds and the temperature of the selective oxidation unit increases. On the other hand, when the air (oxygen) flow rate is lowered, the exothermic reaction is suppressed and the temperature of the selective oxidation unit is lowered. In order to reduce carbon monoxide derived from the raw material contained in the hydrogen-containing gas, generally, the air flow rate supplied to the selective oxidation unit is determined according to the raw material flow rate supplied to the reforming unit.

  By the way, in the long-term operation of the fuel cell system or the like, when the mixing of the air supplied to the selective oxidation unit and the hydrogen-containing gas becomes uneven, or the air supplied to the selective oxidation unit and the hydrogen-containing gas In the case where a mixed gas flow is unevenly distributed, a portion where the ratio of the air (oxygen) flow rate to the carbon monoxide flow rate is locally high in the selective oxidation unit, the carbon monoxide flow rate, and the air (oxygen) flow rate. In this part, the selective oxidation reaction (exothermic reaction) is accelerated, the temperature of a part of the selective oxidation part rises excessively, and is dragged by it. There was a fear of rising.

  Further, in the selective oxidation part, when the temperature of the selective oxidation part rises to around 190 ° C. to 200 ° C., in addition to the selective oxidation reaction, hydrogen and carbon monoxide contained in the hydrogen-containing gas, and methane by hydrogen and carbon dioxide Methanation begins to occur. The methanation reaction is represented by formulas (2) and (3).

CO + 3H2 → CH4 + H2O (2)
CO2 + 4H2 → CH4 + 2H2O (3)
The methanation reaction is an exothermic reaction similar to the selective oxidation reaction, and when the methanation reaction starts to occur, the exothermic reaction is accelerated, the temperature of the selective oxidation portion is increased, and the methanation reaction is further accelerated. As a result, the temperature of a part of the selective oxidation unit rises excessively, and the temperature of the entire selective oxidation unit is likely to be thermally runaway.

  Therefore, for example, Patent Document 1 discloses that when the temperature of the catalyst layer of the selective oxidation unit exceeds the upper limit temperature for the purpose of preventing the temperature of the selective oxidation unit from excessively rising, A technique for reducing the supply amount per unit time (corresponding to the air flow rate of the present invention) is disclosed.

JP 2010-262747 A

  However, the conventional technique has a problem that when the carbon monoxide concentration (hereinafter referred to as “CO”) increases, the selective oxidation portion of the fuel cell system cannot sufficiently reduce the CO concentration. When the concentration of CO contained in the hydrogen-containing gas supplied to the fuel cell increases, there is a risk that the power generation output decreases due to CO poisoning of the fuel cell, or the life of the fuel cell decreases.

  The present invention solves the above-described conventional problem, and can sufficiently reduce the CO concentration of the hydrogen-containing gas supplied to the fuel cell while sufficiently suppressing thermal runaway of the temperature of the selective oxidation unit. An object is to provide a battery system.

  Further, in the conventional technique, it is sometimes necessary to excessively reduce the flow rate of air supplied to the selective oxidation unit in order to sufficiently lower the temperature of the selective oxidation unit. In this case, it has been found that there is a problem that the air flow rate necessary for oxidizing the CO in the selective oxidation unit is insufficient, and the CO concentration cannot be sufficiently reduced in the selective oxidation unit. If the CO concentration cannot be sufficiently reduced in the selective oxidation part, the noble metal catalyst of the fuel cell may be poisoned and the catalytic activity may be lowered.

  FIG. 7 is a graph showing an example of the relationship between the CO concentration contained in the hydrogen-containing gas and the temperature of the selective oxidation unit. When the air flow rate command value is lowered from the reference value (for example, the air flow rate command value corresponding to O2 / CO = 2.0 is reduced to the air flow rate command value corresponding to O2 / CO = 1.7), the selective oxidation temperature is reduced. There was a tendency for the CO concentration to increase.

  For example, when the allowable CO concentration for preventing CO poisoning of the fuel cell is set to 20 ppm, in order to make the CO concentration less than 20 ppm, the air flow rate command value based on O2 / CO = 2.0 is used. In this case, an air flow rate command value equivalent to O2 / CO = 1.8 or more is required.

  However, with the air flow rate command value corresponding to O2 / CO = 1.8, the temperature of the selective oxidation unit can be lowered only to the lower limit of the temperature range in which the temperature of the selective oxidation unit reaches thermal runaway. There was a risk that the temperature of the heat could not be sufficiently prevented from reaching a thermal runaway. In order to lower the temperature of the selective oxidation section to the upper limit of the temperature range suitable for the selective oxidation reaction, it is necessary to lower the air flow rate command value from O2 / CO = 2.0 equivalent to 1.6 equivalent.

That is, when the air flow rate command value is lowered from the reference value, if the air flow rate is lowered excessively, the CO concentration contained in the hydrogen-containing gas may increase. On the other hand, if the CO concentration is to be sufficiently reduced, the temperature of the selective oxidation portion cannot be sufficiently reduced, and thermal runaway may not be sufficiently suppressed.

  In order to solve the problems of the conventional technique, the fuel cell system of the present invention is configured to generate power output to the fuel cell based on the temperature detected by the selective oxidation temperature detector and the power generation output command value to the fuel cell. A control unit that outputs a command value and an air flow rate command value to the selective oxidation unit, the selective oxidation temperature detected by the selective oxidation temperature detection unit exceeds a threshold value T1, and a power generation output command value to the fuel cell is When the threshold value W is exceeded, the power generation output command value to the fuel cell is lowered to the threshold value W, and the air flow rate command value to the selective oxidation unit is lowered to the predetermined value P1.

  First, the selective oxidation temperature exceeds a threshold value (for example, the temperature at which the selective oxidation unit does not cause thermal runaway or its upper limit), and the power generation output command value is a threshold value (for example, the air flow rate command value is O2 / CO = 2.0). When the temperature of the selective oxidation unit exceeds the power generation output that does not lead to thermal runaway or its upper limit), the flow rate of the hydrogen-containing gas generated by the hydrogen generator is reduced by lowering the power generation output command value to the threshold value. Therefore, the reference value of the air flow rate command value determined according to the raw material flow rate supplied to the reforming unit and the raw material flow rate supplied to the selective oxidation unit is lowered.

  Next, by lowering the air flow rate command value supplied to the selective oxidation unit from the reference value (for example, the air flow rate command value at which the CO concentration is less than 20 ppm or its lower limit), the air command value is further lowered.

  As a result, the command value of the flow rate of air supplied to the selective oxidation unit is greatly reduced and the selective oxidation reaction (exothermic reaction) is greatly reduced, so that the temperature of the selective oxidation unit is lowered to a temperature range suitable for the selective oxidation reaction. Moreover, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm.

  The fuel cell system of the present invention can sufficiently reduce the CO concentration of the hydrogen-containing gas supplied to the fuel cell while suppressing thermal runaway of the temperature of the selective oxidation unit.

1 is a schematic configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. The flowchart which shows typically 1 cycle of characteristic operation | movement of the fuel cell system in Embodiment 1 of this invention. The flowchart which shows typically 1 cycle of the characteristic operation | movement of the fuel cell system in Embodiment 2 of this invention. Graph showing the selective oxidation temperature behavior when the selective oxidation part reaches thermal runaway 1 is a graph schematically showing the behavior of one cycle of characteristic operations of the fuel cell system according to Embodiment 1 of the present invention. The graph which shows typically the behavior of 1 cycle of the characteristic operation | movement of the fuel cell system in Embodiment 2 of this invention. A graph schematically showing the relationship of CO concentration to selective oxidation temperature

The first invention includes a reforming unit that supplies a raw material and water to generate a hydrogen-containing gas by a reforming reaction, and the hydrogen-containing gas that is supplied by air and generated by the reforming unit by a selective oxidation reaction A hydrogen generator comprising: a selective oxidation unit that further reduces the CO concentration in the gas; an air supply unit that supplies air to the selective oxidation unit; and a selective oxidation temperature detection unit that detects a temperature of the selective oxidation unit; A fuel cell that generates power by supplying the hydrogen-containing gas and the oxygen-containing gas whose CO concentration is reduced in the selective oxidation unit, and a temperature detected by the selective oxidation temperature detection unit and a power generation output to the fuel cell. And a control unit that updates a power generation output command value to the fuel cell based on the command value and outputs an air flow rate command value to the selective oxidation unit. With this configuration, the temperature of the selective oxidation unit is lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit can be sufficiently prevented. In addition, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, and it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell or a decrease in the life of the fuel cell.

  In a second aspect of the invention, particularly in the first aspect of the invention, the control unit has a selective oxidation temperature detected by the selective oxidation temperature detection unit exceeding a threshold value T1, and a power generation output command value to the fuel cell has a threshold value W. When exceeded, the power generation output command value to the fuel cell is lowered to a threshold value W, and the air flow rate command value to the selective oxidation unit is lowered to a predetermined value P1. As a result, the command value of the air flow rate supplied to the selective oxidation unit is greatly reduced without significantly reducing O2 / CO, and the selective oxidation reaction (exothermic reaction) is greatly reduced, so the temperature of the selective oxidation unit is selected. The temperature falls to a temperature range suitable for the oxidation reaction, and thermal runaway at the temperature of the selective oxidation portion can be sufficiently prevented. In addition, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, and it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell or a decrease in the life of the fuel cell.

  According to a third aspect of the invention, particularly in the second aspect of the invention, the control unit is configured such that the selective oxidation temperature detected by the selective oxidation temperature detection unit exceeds the threshold value T1, and the power generation output command value to the fuel cell is equal to or less than the threshold value W. At this time, the air flow rate command value to the selective oxidation unit is lowered to a predetermined value P2. As a result, the command value of the low air flow rate supplied to the selective oxidation unit is further reduced without significantly reducing O2 / CO, and the selective oxidation reaction (exothermic reaction) is reduced. Therefore, the thermal runaway of the temperature of the selective oxidation portion can be sufficiently prevented. In addition, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, and it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell or a decrease in the life of the fuel cell.

  According to a fourth aspect of the invention, particularly in the second or third aspect of the invention, the control unit is configured such that the selective oxidation temperature detected by the selective oxidation temperature detection unit is equal to or lower than a threshold value T2, and the power generation output command value to the fuel cell is a threshold value. When W, the power generation output command value to the fuel cell is set to the power generation output required by the fuel cell, and the air flow rate command value to the selective oxidation unit is increased to a predetermined value P3. Thereby, the power generation output required by the fuel cell can be generated. In addition, since O2 / CO increases, the CO concentration in the hydrogen-containing gas is less than 20 ppm and further decreases, preventing a decrease in power generation output due to fuel cell CO poisoning or a decrease in fuel cell life. can do.

  According to a fifth aspect of the invention, particularly in the second to fourth aspects of the invention, the control unit is configured such that the selective oxidation temperature detected by the selective oxidation temperature detection unit is equal to or lower than a threshold value T2, and the power generation output command value to the fuel cell is a threshold value. When it is less than W, the air flow rate command value to the selective oxidation unit is increased to a predetermined value P4. As a result, O2 / CO increases, so that the CO concentration contained in the hydrogen-containing gas is less than 20 ppm and decreases further, resulting in a decrease in power generation output due to CO poisoning of the fuel cell, or a decrease in the life of the fuel cell. Can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
The configuration of the fuel cell system of the present invention will be described. FIG. 1 is a schematic configuration diagram of a fuel cell system 100 using a hydrogen generator 1 and a fuel cell 2 according to Embodiment 1 of the present invention.

The fuel cell system 100 includes a hydrogen generator 1 that generates a hydrogen-containing gas, a fuel cell 2 that generates power using the hydrogen-containing gas supplied from the hydrogen generator 1, and a switch from the hydrogen generator 1 to the fuel cell 2. A hydrogen gas supply path 4 for supplying hydrogen gas via the valve 3a, and a fuel supply path 6 for supplying the fuel discharged from the fuel cell 2 to the burner unit 5 of the hydrogen generator 1 via the switching valve 3b. A fuel cell bypass path 7 that connects the valve 3a and the switching valve 3b, and a control unit 12 that controls the operation of the hydrogen generator 1 and the fuel cell 2 in accordance with a load 26 used in a general household, etc. It has. In addition, since it is a structure equivalent to the general polymer electrolyte fuel cell system 100, detailed description of another structure is abbreviate | omitted.

  The hydrogen generator 1 includes a water supply unit 8 that supplies water to the hydrogen generator 1 and a desulfurization unit 9 that allows a hydrocarbon-based raw material containing a sulfur component to pass therethrough and adsorbs and removes the sulfur component contained in the raw material. And a reformer 10 that generates a hydrogen-containing gas using the raw material after passing through the desulfurization unit 9 and the water supplied from the water supply unit 8, and the flow rate of the raw material supplied to the desulfurization unit 9 is controlled. And a raw material supply unit 11.

  The reformer 10 evaporates the water supplied from the water supply unit 8 and preheats the mixed gas of the raw material and water vapor, and the reforming unit 14 advances the reforming reaction between the raw material and water vapor. The reforming unit 15 includes a modification unit 15 that performs a modification reaction of CO and water vapor in the hydrogen-containing gas generated in the reforming unit 14 to reduce the CO concentration of the hydrogen-containing gas. Further, CO remaining in the hydrogen-containing gas after passing through the shift unit 15 is mainly oxidized using air supplied from the air supply unit 16 to the hydrogen-containing gas after passing through the shift unit 15. A selective oxidation unit 17 to be removed is provided. The reforming section 14 is provided with a Ru-based reforming catalyst, the shift section 15 is provided with a Cu—Zn-based shift catalyst, and the selective oxidation section 17 is provided with a Ru-based selective oxidation catalyst.

  Further, the reforming unit 14, the conversion unit 15, and the selective oxidation unit 17 are provided with a reforming temperature detection unit 18, a conversion temperature detection unit 19, and a selective oxidation temperature detection unit 20 for detecting respective temperatures.

  The reformer 10 includes a burner unit 5 for supplying heat necessary for each reaction in the reforming unit 14, the shift unit 15, and the selective oxidation unit 17. The burner unit 5 is provided with a fuel supply path 6 for supplying fuel and a combustion fan 21 for supplying air. The fuel is supplied from the hydrogen gas supply path 4 to the burner unit 5 via the fuel cell bypass path 7 or from the fuel supply path 6 via the fuel cell 2.

  The reforming unit 14 and the evaporation unit 13 are configured to be supplied with heat from the combustion exhaust gas generated in the burner unit 5 through the wall surface of the inner cylinder 22. In the configuration of the reforming unit 14, the transformation unit 15, and the selective oxidation unit 17, illustration and detailed description of the same components as the general configuration are omitted.

  The hydrocarbon-based raw material supplied to the desulfurization section 9 may be a raw material containing an organic compound composed of at least carbon such as hydrocarbon and hydrogen element, for example, city gas mainly composed of methane, Natural gas, LPG, etc. Here, a city gas gas infrastructure line 23 is used as a raw material supply source, and the desulfurization section 9 is connected to the gas infrastructure line 23. The desulfurization part 9 has a shape that can be attached to and detached from the desulfurization connection part 24 arranged on the upstream side and the downstream side, and when the adsorption amount for the sulfur component of the desulfurization part 9 is saturated and the adsorption characteristics are reduced, The new desulfurization unit 9 can be replaced. The desulfurization section 9 is filled with a zeolite-based adsorption / removal agent that adsorbs sulfur compounds, which are odorous components in city gas. Moreover, the desulfurization connection part 24 also has a valve function which controls the distribution | circulation of a raw material, for example, an electromagnetic valve is provided in a structure. In addition, the desulfurization part 9 is good also as a structure using hydrodesulfurization.

The water supply unit 8 has a pump having a flow rate adjusting function. The raw material supply unit 11 is disposed in a raw material supply path 25 that connects the desulfurization unit 9 and the reformer 10, and controls the flow rate of the raw material supplied to the reformer 10, thereby desulfurizing unit 9 from the gas infrastructure line 23. The flow rate of the raw material supplied to is controlled. In addition, the raw material supply part 11 should just be able to control the raw material flow volume supplied to the desulfurization part 9, and may be arrange | positioned in the downstream of the raw material supply part 11. FIG. The raw material supply unit 11 has a booster pump, and has a function of adjusting the flow rate of the raw material supplied to the desulfurization unit 9 by controlling, for example, input current pulses, input power, and the like.

  The control unit 12 stores the operation information such as the operation sequence of the reformer 10, the raw material integrated flow rate, and the like by using a semiconductor memory, a CPU, and the like, calculates an appropriate operation condition according to the situation, and the fuel cell 2, The operating conditions necessary for operation, such as the water supply unit 8, the raw material supply unit 11, the air supply unit 16, and the switching valves 3a and 3b of the hydrogen generator 1, are commanded.

  The operation of the fuel cell system of the present invention will be described. The operation (starting, power generation, stopping) of the fuel cell system 100 configured as described above will be described below centering on the operation of the hydrogen generator 1.

  First, when the hydrogen generator 1 is started from a stopped state, the raw material is supplied from the raw material supply unit 11 to the reformer 10 through the raw material supply path 25 according to a command from the control unit 12. The raw material that has passed through the evaporation unit 13, the reforming unit 14, the conversion unit 15, and the selective oxidation unit 17 is supplied from the fuel supply path 6 to the burner unit 5 via the hydrogen gas supply path 4 and the fuel cell bypass path 7, and is a combustion fan. The reformer 10 starts to be heated by being ignited by the burner unit 5 supplied with the combustion air by 21.

  After the heating by the burner unit 5 is started, the water supply unit 8 is operated to supply water to the reformer 10 to start the reforming reaction between water and the raw material. In the present embodiment, city gas (13A) containing methane as a main component is used as a raw material. The water supply flow rate from the water supply unit 8 is controlled so that water vapor is about 3 moles per mole of carbon molecular weight in the average molecular formula of the city gas (S / C = about 3).

  Further, the air supply unit 16 is operated to supply air to the reformer 10. The air supply flow rate from the air supply unit 16 is controlled such that the oxygen flow rate is twice the number of moles (O2 / CO = 2) of the CO flow rate contained in the hydrogen-containing gas. In the reformer 10, a steam reforming reaction is performed in the reforming unit 14, a reforming reaction is performed in the shift unit 15, and a selective oxidation reaction of CO is performed in the selective oxidation unit 17. At this time, the combustion of the burner unit 5 is controlled so that the reforming unit 14, the conversion unit 15, and the selective oxidation unit 17 have temperatures suitable for each reaction.

  After the CO concentration is reduced to a predetermined concentration (for example, less than 20 ppm on a dry gas basis), the switching valves 3a and 3b are operated, and hydrogen-containing gas is supplied to the fuel cell 2 through the hydrogen gas supply path 4, thereby A power generation operation is performed in the battery 2. Further, the fuel discharged from the fuel cell 2 passes through the fuel supply path 6 and is supplied to the burner unit 5.

  During the power generation operation, the control unit 12 outputs the power generation output command value Wa to the fuel cell 2 and the power generation output to the hydrogen generator 1 in accordance with the power generation output Wb required by the load 26 for the fuel cell system 100. A hydrogen-containing gas corresponding to the command value Wa is generated, and the raw material flow rate and the reforming water corresponding to the raw material flow rate are set so that the reforming unit 14, the shift unit 15, and the selective oxidation unit 17 have temperatures suitable for each reaction. And the air flow rate and the combustion flow rate of the burner unit 5 (λ (air ratio to fuel) = about 1.7) are controlled.

When stopping the operation of the fuel cell system 100, the switching valve 3 a, 3 b is operated according to a command from the control unit 12, and the hydrogen-containing gas supplied to the fuel cell 2 is passed through the fuel cell bypass path 7 to the burner unit. 5 is supplied. Thereafter, the operations of the water supply unit 8, the raw material supply unit 11, and the air supply unit 16 are stopped, the supply of water, the raw material, and the air is stopped, and the operation of the hydrogen generator 1 is stopped.

  The hydrogen generator 1 is stopped when the switching valves 3a and 3b are operated to seal the reformer 10, and the amount of raw material corresponding to the amount of the reformer 10 that cools and decreases its volume. It is preferable to perform an operation for preventing the outside air from being mixed in the reformer 10 such as an operation for supplying the air.

  Next, the operation of the fuel cell system 100 according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 2 is a flowchart schematically showing one cycle of the characteristic operation of the fuel cell system 100 according to Embodiment 1 of the present invention. In practice, during the power generation operation of the fuel cell system 100, the operation of one cycle shown in FIG. 2 is continuously performed without being intermittent.

  First, the control unit 12 included in the fuel cell system 100 includes a selective oxidation temperature Ta detected by the selective oxidation temperature detection unit 20, a power generation output Wb required for the fuel cell 2, and a power generation output required for the fuel cell 2. A power generation output command value Wa commanded to the fuel cell 2 to follow Wb is acquired (step S1).

  And the control part 12 determines whether the selective oxidation temperature Ta exceeds the selective oxidation temperature threshold value T1 preset in the memory | storage part of the control part 12 (step S2). Note that the selective oxidation temperature threshold T1 may be set to a temperature at which the selective oxidation unit 17 does not cause thermal runaway, or an upper limit thereof.

  Here, when the control unit 12 determines that the selective oxidation temperature Ta exceeds the selective oxidation temperature threshold T1 (YES in step S2), the control unit 12 sets the power generation output command value Wa in the storage unit of the control unit 12 in advance. It is determined whether or not the generated power output command value threshold W is exceeded (step S3). The power generation output command value threshold W may be set to a power generation output at which the selective oxidation unit 17 does not cause thermal runaway or an upper limit thereof when the air flow rate command value is equivalent to O2 / CO = 2.0.

  Here, when the control unit 12 determines that the power generation output command value Wa exceeds the power generation output command value threshold W (YES in step S3), the power generation output command value Wa is lowered to W, and the air flow rate command value is set. Lower to P1 (step S4). Note that the air flow rate command value P1 may be set to an air flow rate command value at which the CO concentration is less than 20 ppm, or a lower limit thereof.

  That is, when the selective oxidation temperature exceeds the threshold value T1 and the power generation output command value exceeds the threshold value W, by reducing the power generation output command value to the threshold value W, the flow rate of hydrogen-containing gas generated in the hydrogen generator 1 decreases. The reference value of the command value of the air flow rate determined according to the raw material flow rate supplied to the reforming unit 14 and the raw material flow rate supplied to the selective oxidation unit 17 can be lowered. Further, the air command value can be lowered by lowering the air flow rate command value supplied to the selective oxidation unit 17 from the reference value.

  Therefore, the command value of the air flow rate supplied to the selective oxidation unit 17 can be greatly reduced without greatly reducing O2 / CO, and the selective oxidation reaction (exothermic reaction) can be greatly reduced. Further, the temperature of the selective oxidation unit 17 can be lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit 17 can be sufficiently prevented. Further, since the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell 2 or a decrease in the life of the fuel cell 2.

  On the other hand, when the control unit 12 determines that the power generation output command value Wa does not exceed the power generation output command value threshold W (NO in step S3), the air flow rate command value is lowered to P2 (step S5). As a result, the flow rate of the hydrogen-containing gas generated by the hydrogen generator 1 decreases, and the flow rate of the raw material supplied to the reforming unit 14 decreases.

  As a result, the command value for the low air flow rate supplied to the selective oxidation unit 17 can be further lowered without significantly reducing O2 / CO, and the selective oxidation reaction (exothermic reaction) can be lowered. Further, the temperature of the selective oxidation unit 17 can be lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit 17 can be sufficiently prevented. Further, since the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell 2 or a decrease in the life of the fuel cell 2.

  On the other hand, when the control unit 12 determines that the selective oxidation temperature Ta does not exceed the selective oxidation temperature threshold T1 (NO in step S2), the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T1, and the power generation operation is normally performed. Is done. In this case, no control operation is performed and the process proceeds to END.

  Next, characteristic operations of the fuel cell system 100 and the hydrogen generator 1 according to Embodiment 1 of the present invention will be described with reference to FIGS. 4 and 5.

  First, in FIG. 4, the power generation output required by the fuel cell 2, the power generation output command value commanded to the fuel cell 2 to follow the power generation output required by the fuel cell 2, and the air supply unit 16 are commanded. The graph showing the time change between the air flow rate command value and the selective oxidation temperature detected by the selective oxidation temperature detection unit 20 shows the selective oxidation temperature behavior when the selective oxidation unit 17 reaches thermal runaway.

  While the selective oxidation temperature is stable when normal, the selective oxidation temperature rises excessively when abnormal, and in addition to the selective oxidation reaction, the methanation reaction begins, and the temperature of the selective oxidation unit 17 becomes a thermal runaway. (Sudden rise).

  As one of the causes of the abnormality, there is a case where the mixture of the air and the hydrogen-containing gas supplied to the selective oxidation unit 17 becomes uneven due to the long-term operation of the fuel cell system 100 or the like. Another cause is that some change occurs in the hydrogen generator 1 such as a drift in the flow of the mixed gas of the air and the hydrogen-containing gas supplied to the selective oxidation unit 17, and the local oxidation is performed locally in the selective oxidation unit 17. A portion having a high ratio of the air flow rate to the CO flow rate and a portion having a high CO flow rate and a high absolute flow rate of the air flow rate are formed. In this portion, the selective oxidation reaction (exothermic reaction) is accelerated, and the selective oxidation unit 17 is accelerated. It is conceivable that a part of the temperature of the selective oxidation portion 17 rises excessively and is dragged to increase the temperature of the selective oxidation unit 17 as a whole.

  Next, FIG. 5 shows a selective oxidation temperature behavior by the operations of steps S1 to S4, which is a characteristic operation of the present invention.

  First, when the time is t1, in step S1, the control unit 12 included in the fuel cell system 100 selects the selective oxidation temperature detected by the selective oxidation temperature detection unit 20, the power generation output required by the fuel cell 2, the fuel The power generation output command value commanded to the fuel cell 2 to follow the power generation output required by the battery 2 is acquired.

  Next, in step S <b> 2, the control unit 12 determines that the selective oxidation temperature exceeds the selective oxidation temperature threshold set in advance in the storage unit of the control unit 12. The selective oxidation temperature threshold is set as a temperature at which the selective oxidation unit 17 does not cause thermal runaway.

  Next, in step S <b> 3, the control unit 12 determines that the power generation output command value exceeds a power generation output command value threshold set in advance in the storage unit of the control unit 12. The power generation output command value threshold is set as a power generation output at which the selective oxidation unit 17 does not cause thermal runaway when the air flow rate command value is equivalent to O2 / CO = 2.

  In step S4, the power generation output command value is lowered, and the air flow rate command value at the lowered power generation output command value is lowered from the reference value. Since the minimum of O2 / CO at which the CO concentration is less than 20 ppm is 1.8, the air flow rate command value is set to be equivalent to O2 / CO1.8.

  By reducing the power generation output command value, the flow rate of the hydrogen-containing gas produced by the hydrogen generator 1 is lowered, so that the reference value of the air flow rate command value determined according to the raw material flow rate supplied to the selective oxidation unit 17 can be lowered. In addition, the air command value can be further lowered from the reference value by lowering the air flow rate command value supplied to the selective oxidation unit 17 from O2 / CO = 2.0 to 1.8.

  Therefore, the command value of the flow rate of air supplied to the selective oxidation unit 17 can be lowered and the selective oxidation reaction (exothermic reaction) can be greatly reduced without significantly reducing O2 / CO. Thereby, the temperature of the selective oxidation unit 17 can be lowered to the upper limit of the temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit 17 can be sufficiently prevented. Further, since the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell 2 or a decrease in the life of the fuel cell 2.

(Embodiment 2)
Next, characteristic operations of the fuel cell system 100 according to Embodiment 2 of the present invention will be described with reference to FIG. Note that the description of the same operation as that of Embodiment 1 is omitted.

  FIG. 3 is a flowchart schematically showing one cycle of characteristic operations of the fuel cell system 100 according to Embodiment 2 of the present invention. Actually, during the power generation operation of the fuel cell system 100, the operation of one cycle shown in FIG. 3 is continuously performed without being intermittent.

  First, when it is determined that the selective oxidation temperature Ta does not exceed the selective oxidation temperature threshold T1 (NO in step S2), the control unit 12 determines whether the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T2 (step S2). S6). The selective oxidation temperature threshold T2 may be set to a temperature at which the selective oxidation unit 17 is suitable for the selective oxidation reaction, or an upper limit thereof.

  Here, when the control unit 12 determines that the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T2 (YES in step S6), “the power generation output command value Wa is lowered to W and the air flow rate command value is set to P1. It is determined whether or not the air flow rate command value has been lowered to P2 (step S7).

  Here, when the control unit 12 determines that “the power generation output command value Wa is lowered to W and the air flow rate command value is lowered to P1 or the air flow rate command value is lowered to P2” (step S7). The control unit 12 further determines whether or not the power generation output command value Wa is equal to the power generation output command value threshold W (step S8).

  Here, when the control unit 12 determines that the power generation output command value Wa is equal to the power generation output command value threshold W (YES in step S8), the power generation output command value Wa is set to the power generation output Wb required by the fuel cell. And the air flow rate command value is increased to P3 (step S9). Note that the air flow rate command value P3 may be set to the air flow rate command value at which the CO concentration is less than 20 ppm, or the lower limit thereof.

That is, when the selective oxidation temperature becomes equal to or lower than the threshold value T2, there is no fear that the temperature of the selective oxidation unit 17 will cause thermal runaway. Therefore, the power generation output command value Wa set to the threshold value W of the power generation output command value is set to the fuel cell 2.
Can be returned to the required power generation output Wb, and the air flow rate command value supplied to the selective oxidation unit 17 can be increased to a predetermined value.

  Therefore, the power generation output required by the fuel cell 2 can be generated. In addition, since the O2 / CO increases, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm and can be further reduced, and the power generation output decreases due to CO poisoning of the fuel cell 2 or the fuel cell 2 It is possible to prevent a decrease in the service life.

  On the other hand, when the control unit 12 determines that the power generation output command value Wa is not equal to the power generation output command value threshold W (NO in step S8), in other words, the power generation output command value Wa is equal to the power generation output command value threshold W. If it is determined that the air flow rate is lower, the air flow rate command value is increased to P4. The air flow rate command value P4 may be set to a magnification at which the CO concentration is less than 20 ppm or the lower limit thereof.

  That is, when the selective oxidation temperature becomes equal to or lower than the threshold value T2, the temperature of the selective oxidation unit 17 is not likely to cause thermal runaway, so the air flow rate command value supplied to the selective oxidation unit 17 can be increased to a predetermined value. . Since the power generation output command value is lower than the threshold value W, the power generation output command value and the power generation output required by the fuel cell 2 are equal, and here, the operation for changing the power generation output command value is not performed.

  Therefore, since O 2 / CO increases, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm and can be further reduced, and the power generation output decreases due to CO poisoning of the fuel cell 2 or the fuel cell 2 It is possible to prevent a decrease in the service life.

  On the other hand, when the control unit 12 determines that the selective oxidation temperature Ta is not equal to or lower than the selective oxidation temperature threshold T2 (NO in step S6), the selective oxidation temperature Ta is equal to the selective oxidation temperature threshold T1 and the selective oxidation temperature threshold T2. (T1 ≧ Ta> T2), and the power generation operation is normally performed. In this case, no control operation is performed and the process proceeds to END.

  Further, when it is determined that the operation of “reducing the power generation output command value Wa to W and lowering the air flow rate command value to P1 or lowering the air flow rate command value to P2” is not performed (step S7). NO), the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T2, and the power generation operation is normally performed. Therefore, no operation is performed and the process proceeds to END.

  Next, characteristic operations of the fuel cell system 100 and the hydrogen generator 1 according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 6 shows the selective oxidation temperature behavior when the operations of steps S6 to S9, which are characteristic operations of the present invention, are added to the operations of steps S1 to S4 described in FIG. Here, for the sake of convenience, the description of the operations in steps S1 to S4 described in FIG. 5 is omitted.

  First, at time t2, in step S1, the control unit 12 included in the fuel cell system 100 selects the selective oxidation temperature detected by the selective oxidation temperature detection unit 20, the power generation output required by the fuel cell 2, and the power generation output. Get command value.

  Next, in step S <b> 2, the control unit 12 determines that the selective oxidation temperature does not exceed the selective oxidation temperature threshold set in advance in the storage unit of the control unit 12. The selective oxidation temperature threshold is set as a temperature at which the selective oxidation unit 17 does not cause thermal runaway.

  Next, in step S <b> 6, the control unit 12 determines that the selective oxidation temperature is equal to or lower than the selective oxidation temperature threshold set in advance in the storage unit of the control unit 12. The selective oxidation temperature threshold is set as the temperature of the selective oxidation unit 17 suitable for the selective oxidation reaction.

  Next, in step S7, the control unit 12 determines that the power generation output command value is lowered and the lowered air flow rate command value is further lowered in the previous step S4.

  Next, in step S8, the control unit 12 determines that the power generation output command value is equal to the power generation output command value threshold.

  In step S9, the control unit 12 sets the power generation output command value to the power generation output required by the fuel cell 2, and increases the air flow rate command value from O2 / CO = 1.8 equivalent to 2.0 equivalent. Note that the air flow rate command value is set to be 2.0 equivalent to the value before being lowered to O2 / CO = 1.8 equivalent in step S4.

  Therefore, the power generation output required by the fuel cell 2 can be generated. Further, since O2 / CO = 1.8 increases to 2.0, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm and can be further reduced, and the power generation output due to CO poisoning of the fuel cell 2 Or a reduction in the life of the fuel cell 2 can be prevented.

  The air flow rate command value P3 is equivalent to O2 / CO = 2.0, but O2 / CO = 2.0 equivalent> P3> P1, or O2 / CO = 2.0 equivalent> P3> P2. Also good. In this case, the air flow rate command value is lower than O2 / CO = 2.0, the selective oxidation reaction becomes low, and the temperature rise rate of the selective oxidation unit 17 becomes slow, so that the temperature of the selective oxidation unit 17 causes thermal runaway. It can be suppressed more. In addition, P3> O2 / CO = 2.0 may be sufficient.

  Further, although the air flow rate command value corresponding to O2 / CO = 2.0 is used as a reference, it goes without saying that the present invention is not limited to this.

  As described above, the fuel cell system of the present invention can sufficiently prevent thermal runaway at the temperature of the selective oxidation unit. Furthermore, it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell, a stoppage of power generation, or a decrease in the life of the fuel cell. Furthermore, the present invention can be applied to uses that combine a solar power generation system, a storage battery, and the like.

DESCRIPTION OF SYMBOLS 1 Hydrogen generator 2 Fuel cell 3a Switching valve 3b Switching valve 4 Hydrogen gas supply path 5 Burner unit 6 Fuel supply path 7 Fuel cell bypass path 8 Water supply part 9 Desulfurization part 10 Reformer 11 Raw material supply part 12 Control part 13 Evaporation Unit 14 Reforming unit 15 Transformation unit 16 Air supply unit 17 Selective oxidation unit 18 Reforming temperature detection unit 19 Transformation temperature detection unit 20 Selective oxidation temperature detection unit 21 Combustion fan 22 Inner cylinder 23 Gas infrastructure line 24 Desulfurization connection unit 25 Raw material supply Path 26 Load 100 Fuel cell system

Claims (5)

A reforming unit that supplies a raw material and water and generates a hydrogen-containing gas by a reforming reaction; and a CO concentration in the hydrogen-containing gas that is supplied by air and is generated by the reforming unit by a selective oxidation reaction. A hydrogen generator comprising: a selective oxidation unit that further reduces; an air supply unit that supplies air to the selective oxidation unit; and a selective oxidation temperature detection unit that detects a temperature of the selective oxidation unit;
A fuel cell that generates power by being supplied with the hydrogen-containing gas and the oxygen-containing gas with a reduced CO concentration in the selective oxidation unit;
Based on the temperature detected by the selective oxidation temperature detection unit and the power generation output command value to the fuel cell, the power generation output command value to the fuel cell is updated, and the air flow rate command value to the selective oxidation unit is changed. A control unit for outputting;
A fuel cell system comprising:   When the selective oxidation temperature detected by the selective oxidation temperature detection unit exceeds a threshold T1, and the power generation output command value to the fuel cell exceeds a threshold W, the control unit generates a power generation output command to the fuel cell. 2. The fuel cell system according to claim 1, wherein the value is lowered to a threshold value W, and the air flow rate command value to the selective oxidation unit is lowered to a predetermined value P <b> 1.   When the selective oxidation temperature detected by the selective oxidation temperature detection unit exceeds a threshold value T1 and the power generation output command value to the fuel cell is equal to or less than the threshold value W, the control unit controls the air flow rate to the selective oxidation unit. The fuel cell system according to claim 2, wherein the command value is lowered to a predetermined value P2.   The control unit generates a power generation output command value to the fuel cell when the selective oxidation temperature detected by the selective oxidation temperature detection unit is a threshold value T2 or less and the power generation output command value to the fuel cell is a threshold value W. The fuel cell system according to claim 2 or 3, wherein the power generation output required by the fuel cell is set, and the air flow rate command value to the selective oxidation unit is increased to a predetermined value P3.   When the selective oxidation temperature detected by the selective oxidation temperature detection unit is less than or equal to a threshold T2 and the power generation output command value to the fuel cell is less than the threshold W, the control unit is configured to supply an air flow rate to the selective oxidation unit. The fuel cell system according to any one of claims 2 to 4, wherein the command value is increased to a predetermined value P4.