JP5215527B2 - Operation method of fuel cell - Google Patents

Description

  The present invention relates to an operation method for preventing instability of output and carbon deposition due to a sudden change in heat balance during operation in a high-temperature fuel cell power generation system, particularly in a solid oxide fuel cell power generation system.

A solid oxide fuel cell (SOFC), which is a typical high-temperature fuel cell, is configured by accommodating a fuel cell stack composed of a plurality of solid electrolyte fuel cells in a storage container, and has a temperature of about 700 to 1000 ° C. Operated at temperature. In a conventional SOFC, for example, a hydrogen-containing gas serving as a power generation fuel is produced by reacting a hydrocarbon gas (CH ₄ or the like) and steam on a catalyst (steam reforming reaction) in a reformer. The steam reforming reaction of hydrocarbon gas is an endothermic reaction that proceeds at 500 ° C. to 800 ° C., but conventionally, a sufficient heat source for the reformer is provided by power generation reaction in fuel cells and radiant heat generated by Joule heat. Therefore, it is common not to provide a heating source dedicated to the reformer. As a result, high-efficiency power generation was possible with high-temperature fuel cells.

  Conventional high-temperature fuel cells are said to be suitable for large-scale power output of several hundred to several thousand kW, and constant power generation. However, due to recent progress in research and development, lower operating temperature and lower output New knowledge such as realization of thermal self-sustained operation and good load followability has been obtained, and it is expected to be used in various applications such as small distributed power generation.

  However, with the progress of such technology, new problems that did not exist in the conventional SOFC have emerged, and there is an urgent need to solve these problems. Specifically, the amount of heat is further reduced due to the lack of heat associated with lower operating temperatures, the low load operation associated with load following operation, and the heat balance inside the power generation system changes abruptly depending on the required load. In addition, the output becomes unstable, and at the same time, the amount of heat for generating the steam for the reforming reaction is insufficient, which may cause carbon deposition. Therefore, a situation has arisen where the reforming reaction can be difficult only by a heat supply method that relies solely on the power generation reaction as a heat source for reforming as in the prior art.

Various methods have been studied to deal with such problems. For example, in the case of a polymer electrolyte fuel cell (PEFC) that requires load follow-up like SOFC, reforming the high-temperature combustion exhaust gas generated by catalytic combustion of part of the fuel gas or exhaust gas containing hydrogen A method of supplying heat to the outer periphery of the vessel to cover the amount of heat necessary for reforming has been proposed. (Patent Document 1)
JP 2003-123819 A

  The PEFC of Patent Document 1 is a low temperature fuel cell, and requires a fuel and a combustion chamber as separate heating sources for heating the reformer. Generally, in order to perform reforming in a low-temperature fuel cell, it is essential to attach a dedicated heating source such as a burner to the reformer, but this reduces power generation efficiency.

  In the case of a high-temperature fuel cell as well, if a separate heating source dedicated to the reformer is provided, it is relatively easy to adjust the amount of heat to optimize the heat balance of the reformer, but there is no heating source dedicated to the reformer. This negates the merits of high-temperature fuel cells that can generate high-efficiency power.

  In view of the above situation, the present invention provides a rapid change in the heat balance during operation in a high-temperature fuel cell power generation system, particularly in a solid oxide fuel cell system, without providing a separate heating source to optimize the heat balance in reforming. It is an object of the present invention to provide an operation method that avoids instability of output by quickly responding to the above and prevents carbon deposition due to insufficient amount of heat of vaporization.

In order to achieve the above object, the present invention provides the following configurations.
(1) The method of operating a fuel cell according to claim 1, and a mixing unit for mixing plural kinds of reforming gas containing hydrocarbon gas, a plurality of kinds of modifying gases are mixed in the mixing unit a reforming unit for reforming the hydrogen-containing gas by the reforming catalyst, the use of hydrogen-containing gas obtained by the reforming unit have a power generating unit for solid electrolyte fuel cells to generate electricity, the mixing unit An operation method of a fuel cell provided with a temperature sensor for measuring each temperature of the reforming unit and the power generation unit , wherein in the step of stopping power generation of the fuel cell, the mixing unit , the reforming parts and to monitor the respective temperatures of the power generation section, the mixing section, between the both of the reforming portion and the temperature of the power generation unit is a temperature above a preset respectively, water vapor in the mixing portion after mixing with the hydrocarbon gas, steam reforming in the reformer unit Was performed, and the mixing unit, one of the reforming section and the temperature of the power generation unit, after a preset temperature below respectively, wherein the carbonizing an oxygen-containing gas in the mixing unit After mixing with hydrogen gas, partial oxidation reforming is performed in the reforming section .

(2) The method of operating a fuel cell according to claim 2, a mixing unit for mixing plural kinds of reforming gas containing hydrocarbon gas, a plurality of kinds of modifying gases are mixed in the mixing unit a reforming portion for reforming to the hydrogen-containing gas by the reforming catalyst, the use of hydrogen-containing gas obtained by the reforming unit have a power generating unit for solid electrolyte fuel cells to generate electricity, the mixing unit An operation method of a fuel cell provided with a temperature sensor for measuring each temperature of the reforming unit and the power generation unit , wherein in the step of stopping power generation of the fuel cell, the mixing unit , the reforming parts and to monitor the respective temperatures of the power generation section, the mixing section, between the both of the reforming portion and the temperature of the power generation unit is a temperature above a preset respectively, water vapor in the mixing portion after mixing with the hydrocarbon gas, steam reforming in the reformer unit Was performed, and the mixing unit, one of the reforming section and the temperature of the power generation unit, after a preset temperature below respectively, the water vapor and oxygen-containing gas in the mixing unit After the mixing with the hydrocarbon gas, the reforming unit performs the combined reforming.

(3) In the fuel cell operating method according to claim 3, in the case where the steam reforming is performed in claim 1 or 2, the steam is obtained by supplying water in the mixing section and vaporizing. It is characterized by that.

The method of operating a fuel cell according to claim 1 is to monitor each temperature of the mixing unit, the reforming unit, and the power generation unit in the step of stopping the power generation of the fuel cell, and The steam reforming is performed while each of the temperatures of the sections is equal to or higher than a preset temperature, and any of the temperatures of the mixing section, the reforming section, and the power generation section is preset. After the temperature is lowered , partial oxidation reforming is performed . The optimum state of heat balance refers to a state in which the thermal equilibrium state in the fuel cell is maintained and a stable power generation output is obtained without causing carbon deposition in the reforming section . The case where the heat balance changes from the optimum state is, for example, when the temperature inside the fuel cell is lowered. If a separate heating source for controlling the reforming reaction is not provided, in the conventional operation method in which only steam reforming is performed, steam is insufficient due to insufficient amount of heat of vaporization when the temperature is lowered, and carbon deposition occurs. In the present invention, when the heat balance changes from the optimum state, the reforming can be performed without steam by switching from steam reforming to partial oxidation reforming, and carbon deposition can be prevented. Since the partial oxidation reforming is an exothermic reaction, the lowered temperature can be raised again, contributing to the recovery of the optimum heat balance. Therefore, when the heat balance does not satisfy the optimum state due to various factors during the operation of the fuel cell and the heat quantity for the reforming part is insufficient, the lack of heat quantity is compensated and adjusted by switching to partial oxidation reforming. Can do. Further, by switching the reforming method, it is possible to prevent a large fluctuation in the heat balance, and to solve the unstable output of the fuel cell power generation.
The operation method of the present invention can be particularly suitably used for a fuel cell of 1 kW or less used for home use, and can be suitably used for a fuel cell that generates electric power following a load.

-In Claim 2, after any of each temperature of a mixing part, the said modification | reformation part, and the said electric power generation part becomes less than preset temperature, respectively , steam reforming and partial oxidation reforming were used together Perform combination reforming. In this case, instead of completely switching to partial oxidation reforming, only a shortage of steam is compensated by partial oxidation reforming. Thereby, carbon deposition due to water vapor shortage can be prevented and the same effect as in the first aspect can be obtained. In addition, since the balance with the heat generated by partial oxidation reforming can be adjusted by the large endotherm accompanying water vaporization, the heat balance can be controlled while preventing pulsation. Moreover, since steam reforming with high reforming efficiency is utilized as much as possible, higher reforming efficiency can be obtained.

-In Claim 3, since vaporization is performed immediately before mixing of water vapor and hydrocarbon gas, the amount of heat for vaporization can be utilized without waste. Both the equipment and the process can be simplified as compared with the case where the steam is supplied.

Mixing unit in the OPERATION, heat balance condition is the temperature of the reforming section or the power generation unit as a parameter. The temperature (including the temperature change) is a parameter that directly indicates the heat balance. This makes it possible to quickly respond to an abrupt change in the heat balance and perform a stable operation.

During operation stop gradually there is a possibility that the amount of heat for moisture reduction for the low temperature is carbon deposition insufficient, but to prevent this by partial modification or combination modification. As a result, the temperature can be safely lowered without using an inert gas and without damage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First referential embodiment of the fuel cell operation method, reforming a mixing step of mixing a plurality of types of reforming gas containing hydrocarbon gas, a plurality of types of reforming gas is mixed in the mixing step A reforming step for reforming into a hydrogen-containing gas by a catalyst, and a power generation step in which the solid oxide fuel cell generates power using the hydrogen-containing gas obtained in the reforming step, and a mixing step thereof. Monitors whether the reforming process or the power generation process is performed under preset heat balance conditions, and if it is performed under preset heat balance conditions, steam is mixed with hydrocarbon gas in the mixing process After performing steam reforming in the reforming step and mixing the oxygen-containing gas with the hydrocarbon gas in the mixing step when not performed under preset heat balance conditions, the reforming step In this method, partial oxidation reforming is performed.

  During the operation of the fuel cell, the amount of gas and the amount of water change greatly depending on the operating state. Therefore, as with the power generation step of generating power by the fuel cell, a mixing step of mixing the reforming gas (preferably supplying water) The heat balance of the reforming process in which the water vaporization is performed) and the reforming reaction is easily changed. If the heat balance changes abruptly, the amount of heat required for water vaporization is not supplied uniformly, and sudden boiling of water is likely to occur, causing pulsation in the gas supply and unstable output, or conversely, the amount of heat for water vaporization is insufficient There is a risk of carbon deposition. In order to prevent these problems, if it is detected that the mixing process, the reforming process, or the power generation process is not performed under a preset heat balance condition, water that causes output instability and / or carbon deposition may occur. The reforming method is switched from the steam reforming method using NO to the partial oxidation reforming method not using water. As a result, stable operation can be maintained even in a state where the heat balance has suddenly changed.

Second referential embodiment of the method for operating the fuel cell, reforming a mixing step of mixing a plurality of types of reforming gas, a plurality of types of reforming gas is mixed in the mixing step including a hydrocarbon gas A reforming process for reforming to a hydrogen-containing gas by a solid catalyst, and a power generation process for generating power by the solid oxide fuel cell using the hydrogen-containing gas obtained in the reforming process. Monitoring whether the quality process or power generation process is performed under preset heat balance conditions, and when the process is performed under preset heat balance conditions, steam is mixed with hydrocarbon gas in the mixing process Then, steam reforming is performed in the reforming process, and when not performed under preset heat balance conditions, steam and oxygen-containing gas are mixed with hydrocarbon gas in the mixing process, and reforming is performed. This is a method of performing the combined reforming in the process.

The difference between the second reference form and the first reference form is that a predetermined amount of water vapor is further added to the mixed gas of hydrocarbon gas and oxygen-containing gas when the heat balance condition is not set in advance. The combined reforming method is a combination of the steam reforming method and the partial oxidation reforming method. By doing this, since the oxygen source used for reforming increases, the risk of carbon deposition accompanying the reforming can be further suppressed, and also by the endothermic effect of steam reforming (and when water vaporization is performed, Since the balance with the heat generated by the partial oxidation reforming can be adjusted (by the large heat absorption associated with the conversion), the heat balance can be controlled while preventing pulsation. The ratio of water vapor and oxygen-containing gas is controlled so as not to cause carbon deposition.

  The “preliminarily set heat balance condition” is set to a condition in which an optimum state of heat balance is obtained in the fuel cell, particularly in the steps of mixing and reforming. Here, the optimum state of heat balance refers to a state in which a thermal equilibrium state inside the fuel cell is maintained and a stable power generation output is obtained without causing carbon deposition in the reforming process. The case where the heat balance changes from the optimum state is when, for example, the temperature inside the fuel cell falls below the normal operating temperature. The “heat balance condition” is set by a parameter indicating whether the heat balance is in an optimum state. The parameters include, for example, the temperature (including temperature change) of the portion where the mixing process, reforming process and / or power generation process are performed inside the fuel cell, the amount of power generated from the fuel cell (including power generation change), the fuel cell It is a signal or the like indicating a specific driving operation time. Accordingly, the “preset heat balance condition” is a condition in which the heat balance is in an optimum state, and is indicated by a predetermined parameter being within a preset value or range. For example, in the case of temperature, a temperature range in which a sufficient amount of steam for steam reforming is obtained and suitable for the reforming reaction is set.

FIG. 1 is a schematic configuration diagram of an example of a fuel cell system capable of implementing the solid oxide fuel cell operating method of the first or second reference embodiment. In the figure, black arrows indicate the flow of gas (or water), and white arrows indicate the flow of control. The main components of the fuel cell system 1 are an operation control unit 10, a fuel cell 20, a power generation amount detection unit 30, and an operation operation unit 40. In the fuel cell 20, a mixing unit 21 that mixes a plurality of types of reforming gases including hydrocarbon gas, and a reforming unit that reforms the mixed types of reforming gases into a hydrogen-containing gas using a reforming catalyst. A mass part 22 and a power generation part 23 for generating power by the solid oxide fuel cell using the obtained hydrogen-containing gas are provided.

  In any reforming method, the mixing unit 21 is supplied with a hydrocarbon gas as a reformed gas. Then, water or steam is supplied when performing steam reforming, oxygen-containing gas is supplied when performing partial oxidation reforming, and water or steam and oxygen-containing gas (for example, air) when performing combined reforming. And are supplied. In addition, when supplying water, it vaporizes in the vaporization part 21b provided in the mixing part 21, and is set as water vapor | steam. The mixing unit 21, the reforming unit 22, and the power generation unit 23 are arranged in one storage container.

  The fuel cell 20 is configured to use heat generated by the power generation unit 23 and Joule heat as the heat for vaporizing water in the vaporization unit 21b and the heat for performing the reforming reaction in the reforming unit 22. ing. For example, radiant heat from the fuel battery cell, off-gas as surplus fuel after power generation, combustion heat due to combustion of off-gas, and heat recovered from the exhaust gas. Therefore, a heating source for exclusively heating the vaporizing unit 21b and the reforming unit 22 is not provided.

  In the fuel cell system 1, basically, steam reforming is performed, and an operation method for switching between steam reforming and partial oxidation reforming according to a change in the heat balance in the fuel cell 20, or steam reforming and combined reforming. The optimal state of heat balance is maintained by the operation method of switching between. That is, in the fuel cell system 1, optimal heat balance control in the mixing step and the reforming step is realized without separately providing a heating source in the mixing portion 21 and the reforming portion 22.

Incidentally, the reaction formula of the steam reforming reaction when the hydrocarbon gas is methane is as follows.
CH ₄ + H ₂ O → 3H ₂ + CO (endothermic reaction)
Moreover, the reaction formula of the partial reforming reaction when the hydrocarbon gas is methane is as follows.
CH ₄ + 1 / 2O ₂ → CO + 2H ₂ (exothermic reaction)

  Switching between steam reforming and partial oxidation reforming, or switching between steam reforming and combined reforming is performed by the operation control unit 10 in FIG. The operation control unit 10 includes control units 11a, 12a, and 13a that output signals for controlling the supply amounts of hydrocarbon gas, water / water vapor, and oxygen-containing gas supplied to the mixing unit 21 of the fuel cell 20, respectively. A control signal from each control unit is sent to each flow control valve 11b, 12b and 13b provided in each gas or water supply pipe to adjust the supply amount of each gas or water or stop the supply. .

  In any reforming method, a plurality of types of reforming gases including hydrocarbon gas are mixed in the mixing unit 21 (mixing step), and the reforming reaction is performed by the reforming catalyst in the reforming unit 22. (Reforming step), a hydrogen-containing gas that is a reformed gas is supplied to the power generation unit 23. The power generation unit 23 is provided with fuel cells. In the fuel cell, a power generation reaction is performed by a hydrogen-containing gas and an oxygen-containing gas (for example, air, which is controlled separately from the oxygen-containing gas for partial oxidation reforming shown in FIG. 1) supplied separately (power generation). Step), electric power is taken out and supplied to the load. The exhaust gas after the power generation reaction is exhausted to the outside.

  The mixing unit 21, the reforming unit 22, and the power generation unit 23 are provided with temperature sensors 21 a, 22 a, and 23 a such as thermocouples, and temperature data of each unit during operation is sent to the operation control unit 10. These temperature data are used as parameters of the heat balance condition. For example, steam reforming is performed if the temperature in any of the mixing unit 21, the reforming unit 22, or the power generation unit 23 is equal to or higher than a preset value, and when the temperature falls below a preset value, partial oxidation modification is performed. Switch to quality or combined reform.

  The power generation amount detection unit 30 detects the power generation amount in the power generation unit 23. For example, the output value of voltage and / or current is measured. The detected value of the power generation amount is sent from the power generation amount detection unit 30 to the operation control unit 10. The detected value of the power generation amount is used as a parameter for the heat balance condition. Recent research and development has enabled high-temperature fuel cells to be applied to small distributed power generation of several hundred watts to tens of kW, and load follow-up characteristics with a large fluctuation range can be obtained. If the state continues for a long time, the temperature of the portion where high temperature is required, such as the fuel cell and the reforming portion, is lowered, and it becomes difficult to sufficiently exhibit the performance. In addition, it cannot quickly respond to a sudden increase in required load. There is also a risk of carbon deposition due to lack of water vapor. Therefore, when the power generation amount is less than a preset value and continues for a preset time or longer, the temperature inside the fuel cell is increased by switching from steam reforming to partial oxidation reforming or combined reforming. , Restore the optimal balance of heat. This makes it possible to respond quickly to sudden load requests. In particular, it can be suitably used in a small fuel cell for home use of 1 kW or less.

  Furthermore, the driving operation unit 40 includes an activation unit 41 and a stop unit 42 that perform basic operations such as activation and deactivation of the fuel cell system 1 manually or automatically. When the fuel cell system 1 enters a start operation or a stop operation (for example, when a start switch or a stop switch is pressed) from the start unit 41 and the stop unit 42, a signal notifying that is respectively displayed on the operation control unit. 10 is sent. These start notification signals or stop notification signals are also used as parameters of the heat balance condition.

  For example, when the activation notification signal is received, the operation activation operation time from when the activation operation is started until the normal operation state is reached is determined as “when not performed under a preset heat balance condition”, and partial oxidation is performed. Reform or combination reform is performed. The operation start operation time may be set, for example, after a predetermined time has elapsed after receiving the start notification signal, or reached a certain temperature (for example, 600 ° C. to 750 ° C.) by any temperature sensor inside the fuel cell. It may be up to the time when it is determined. By using partial oxidation reforming or combined reforming at the start of operation, not only the large amount of heat required for water vaporization is required, but also the amount of heat generated by the exothermic reaction is reduced to the fuel cell, mixing unit and reforming unit Since it can be used to raise the temperature, it becomes possible to start up quickly. At the same time, carbon deposition due to poor water vaporization can be prevented.

  On the other hand, for example, when the stop notification signal is received, the operation stop operation time until the stop operation is started and the system is completely stopped is determined as “when not performed under a preset heat balance condition”, Partial oxidation reforming or combined reforming is performed. The operation stop operation time may be set, for example, from the time when it is determined that the temperature has decreased to a certain temperature by any temperature sensor inside the fuel cell after receiving the stop notification signal. Since it is necessary to cool the fuel cell safely without any damage when the operation is stopped, the temperature was conventionally lowered using an inert gas. However, it is not possible to install an inert gas supply facility for small distributed applications. Have difficulty. Therefore, in the conventional small dispersion type application, a reducing atmosphere is created by steam reforming in the same manner as during operation to protect the fuel cell and the catalyst. However, as the temperature drops, the amount of heat necessary for water vaporization gradually decreases, which may cause carbon deposition. In the present invention, by using partial oxidation reforming or combined reforming during the shutdown operation time, the concern of poor water vaporization is eliminated, and, for example, a small distributed fuel cell for home use of 1 kW or less is not damaged. The temperature can be lowered safely.

  The operation control unit 10 determines whether or not each parameter indicating the heat balance condition is a preset value or range, and generates a control signal from each control unit 11a, 12a, and 13a based on the determination result. To do. When performing steam reforming and combined reforming, water / steam is supplied and the flow rate is controlled. When performing partial oxidation reforming, an oxygen-containing gas is supplied and the flow rate is controlled. Further, when each reforming method is performed, the flow rate of the hydrocarbon gas is controlled so as to have an optimal ratio with the flow rate of the water / water vapor or oxygen-containing gas.

  As described above, according to the operation method of the present invention, the control for optimizing the heat balance can be sufficiently performed without having a dedicated heating source for water vaporization and reforming in the mixing unit and the reforming unit. Can do. In particular, in high-temperature fuel cells where the heat balance is likely to change greatly depending on the operating conditions of the fuel cell, it is possible to combine not only the steam reforming method but also the partial oxidation reforming method or the combined reforming method as the reforming method. It is effective for optimizing the system and performing stable operation.

1 is a schematic configuration diagram of a fuel cell system to which a solid oxide fuel cell operating method according to the present invention is applied. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 10 Operation control part 21 Mixing part 21a, 22a, 22b Temperature sensor 21b Vaporization part 22 Reforming part 23 Power generation part 30 Power generation amount detection part

Claims (3)

A mixing unit for mixing plural kinds of reforming gas containing hydrocarbon gas, a reforming section for reforming a plurality of kinds of modifying gases are mixed in the mixing portion to the hydrogen-containing gas by a reforming catalyst , using said hydrogen-containing gas obtained by the reforming unit have a power generating unit for solid electrolyte fuel cells to generate electricity, the mixing unit, measuring each temperature of the reforming section and the power generating unit a temperature sensor to a method of operating a fuel cell comprising each for,
In the step of stopping the power generation of the fuel cell,
Monitor each temperature of the mixing unit , the reforming unit and the power generation unit ,
While each temperature of the mixing unit, the reforming unit, and the power generation unit is equal to or higher than a preset temperature, steam is mixed with the hydrocarbon gas in the mixing unit , and then the reforming is performed. Steam reforming is performed in the mass part , and
After each of the temperatures of the mixing unit, the reforming unit, and the power generation unit is less than a preset temperature, after the oxygen-containing gas is mixed with the hydrocarbon gas in the mixing unit A method of operating a fuel cell, wherein partial reforming reforming is performed in the reforming unit . A mixing unit for mixing plural kinds of reforming gas containing hydrocarbon gas, a reforming section for reforming a plurality of kinds of modifying gases are mixed in the mixing unit into a hydrogen-containing gas by a reforming catalyst , using said hydrogen-containing gas obtained by the reforming unit have a power generating unit for solid electrolyte fuel cells to generate electricity, the mixing unit, measuring each temperature of the reforming section and the power generating unit a temperature sensor to a method of operating a fuel cell comprising each for,
In the step of stopping the power generation of the fuel cell,
Monitor each temperature of the mixing unit , the reforming unit and the power generation unit ,
While each temperature of the mixing unit, the reforming unit, and the power generation unit is equal to or higher than a preset temperature, steam is mixed with the hydrocarbon gas in the mixing unit , and then the reforming is performed. Steam reforming is performed in the mass part , and
The mixing unit, one of the reforming section and the temperature of the power generation unit, after a preset temperature below respectively, mixing the water vapor and oxygen-containing gas and the hydrocarbon gas in said mixing unit Then, the reforming unit performs the combined reforming, and the fuel cell operating method. 3. The method of operating a fuel cell according to claim 1, wherein, when the steam reforming is performed, the steam is obtained by supplying water in the mixing section and vaporizing the steam. 4.

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