JP5126582B2 - Fuel cell system and operation method thereof - Google Patents

Description

  The present invention relates to a fuel cell system having a structure in which a solid electrolyte fuel cell stack is accommodated in a heat insulating container, and an operation method thereof.

  A conventional fuel cell system includes a fuel cell stack formed by stacking solid oxide fuel cell units, and a heat insulating container that hermetically accommodates the fuel cell stack. Some have an oxidizing gas supply path for supplying (air), a fuel gas supply path for supplying fuel gas, and a gas discharge path for exhaust gas.

  The fuel cell system described above generates power by supplying an oxidant gas and a fuel gas to the fuel cell stack, but at the time of start-up, the introduction air is heated by the heat of the burner provided in the gas exhaust path and the start-up is promptly performed. To be done. In steady operation, the flow rate of the oxidizing gas or fuel gas is increased or decreased according to the temperature of the fuel cell stack, or the temperature of the fuel cell stack is maintained within a suitable range by adjusting or stopping the heat of the burner. Control.

The temperature control of this type of fuel cell system is not an example of a solid electrolyte type, but the wall portion of the heat insulating container that houses the fuel cell is made to have a double structure, and the degree of vacuum in the space inside the wall portion is adjusted. There is one in which the heat dissipation amount of the heat insulating container is controlled to keep the temperature of the fuel cell at a specified value (Patent Document 1).
Japanese Patent No. 2612653

  However, the conventional fuel cell system as described above has the following problems.

  At startup, the temperature rise of the fuel cell stack depends on the temperature rise by power generation and the temperature rise by heating of the introduced air, so that it is difficult to start up and raise the temperature in a short time.

  During steady operation, if the temperature of the fuel cell stack exceeds the specified value, cooling is performed by reducing the flow rate of the fuel gas or increasing the flow rate of the oxidizing gas. In addition, making the reforming reaction instability unstable, and increasing the flow rate of the oxidizing gas may cause a temperature difference between the inside and outside of the fuel cell stack, which may cause thermal strain in the stack.

  Furthermore, during steady operation, if the temperature of the fuel cell stack falls below the specified value, heating is performed by increasing the combustion heat of the burner, but fuel gas is supplied in excess of the amount required for power generation. As a result, power generation efficiency was reduced.

  In addition to the above temperature control, for example, if the wall portion of the heat insulating container is made to have a double structure and control for adjusting the degree of vacuum of the space in the wall portion is added, although a slight improvement in operating efficiency can be expected, sufficient It was hard to say that the effect was obtained.

  For this reason, conventionally, in a solid electrolyte fuel cell system, improvement has been desired in order to realize further startup and temperature rise and further improvement in operation efficiency in a short time.

  The present invention has been made in view of the above-described conventional situation, and in a solid electrolyte fuel cell system, the start, steady operation, and stop can be stably performed, and improvement in operation efficiency is realized. It is an object of the present invention to provide a fuel cell system that can be used and a method for operating the fuel cell system.

The fuel cell system according to the present invention is a fuel cell system having a structure in which a solid oxide fuel cell stack is accommodated in a heat insulating container, and an air supply in the container for supplying exhaust gas from the fuel cell stack to the internal space of the heat insulating container. Means and an in-container exhaust means for exhausting the inner space of the heat insulating container, and the in-container exhaust means includes an exhaust pump for forcibly exhausting the inner space of the container, As a means for supplying air, a gas control unit that adjusts the supply amount, temperature, and humidity of the exhaust gas is provided in the path from the fuel cell stack to the space in the container . And as the operation method, by adjusting the supply amount of exhaust gas supplied to the inner space of the heat insulating container, the temperature and humidity of the exhaust gas, the heat transfer amount and the heat capacity of the inner space of the container are changed, and the fuel cell stack To control the temperature.

  According to the fuel cell system and the operation method thereof of the present invention, in the solid oxide fuel cell system, the start, steady operation, and stop can be stably performed by appropriately controlling the temperature of the fuel cell stack. It is possible to improve the driving efficiency.

  FIG. 1 is a diagram illustrating an embodiment of a fuel cell system of the present invention. The illustrated fuel cell system includes a fuel cell stack S formed by stacking solid oxide fuel cell units, and a heat insulating container C that hermetically accommodates the fuel cell stack S. And an oxidizing gas supply path L1 for supplying oxidizing gas (air), a fuel gas supplying path L2 for supplying fuel gas, and a gas discharging path L3 for exhaust gas.

  The oxidizing gas supply path L <b> 1 includes a blower 1 for gas pressure feeding, a flow rate regulator 2, and a heat exchanger 3. The fuel gas supply path L2 includes a flow rate regulator 4 and a reformer 5 for taking out hydrogen from, for example, hydrocarbon fuel.

  The gas discharge path L3 includes a burner 6 that mixes fuel exhaust gas in which the fuel component remains and oxidant exhaust gas in which the oxidant component remains. In the heat exchanger 3, heat is generated between the introduced air and the combustion gas. Exchange is performed and the introduced air is heated.

  The fuel cell system includes an in-container exhaust means L4 that exhausts the internal space of the heat insulating container C and an in-container air supply means L5 that supplies exhaust gas from the fuel cell stack S to the internal space of the container.

  The in-container exhaust means L4 includes an exhaust pump 7 that forcibly exhausts the internal space of the container. The exhaust pump 7 is provided downstream of the heat exchanger 3 in the gas discharge path L3. The in-container exhaust means L4 of this embodiment includes a first exhaust path L41 that directly reaches the exhaust pump 7 from the internal space and a second exhaust path L42 that directly reaches the burner 6 from the internal space.

  The in-container air supply means L5 forms an exhaust gas path from the fuel cell stack S to the internal space of the container once through the outside of the container, and a first air supply path L51 for the fuel exhaust gas and an oxidized exhaust gas (air exhaust Gas) for the second air supply path L52. In the first and second air supply paths L51 and L52, the fuel exhaust gas and the oxidized exhaust to the inner space of the container are provided outside the container as means for sucking the exhaust gas from the fuel cell stack S into the heat insulating container C. Gas control units C51 and C52 for adjusting the gas supply amount, temperature, and humidity are provided.

  Further, in the fuel cell system, a large number of non-contact fins F (only some of them are shown) F are provided on the inner surface of the heat insulating container C, and the heat transfer amount and heat capacity of the space in the container are provided by the fins F. As a result, the heat dissipation and heat insulation of the heat insulation container C itself are further improved. Note that the fins Fh can be provided on a part or almost the entire inner surface of the heat insulating container C.

  Further, although not shown, the fuel cell system includes sensors for measuring the temperature of the fuel cell stack S, the temperature of the exhaust gas (fuel exhaust gas, oxidized exhaust gas) from the fuel cell stack S, and the like. Each functional unit can be controlled based on these measured values.

  Next, a method for operating the fuel cell system having the above-described configuration will be described using the flowchart shown in FIG.

  When the fuel cell system is started, air is introduced into the oxidizing gas supply path L1 through the blower 1, the flow rate regulator 2 and the heat exchanger 3, and the introduced air is supplied as an oxidizing gas to the fuel cell stack S. To do. On the other hand, in the fuel gas supply path L2, hydrocarbon fuel is supplied to the reformer 5 via the flow rate regulator 4, and hydrogen is taken out from the hydrocarbon fuel in the reformer 5, and this hydrogen is used as fuel gas for fuel. The battery stack S is supplied.

  At this time, the fuel cell system drives the exhaust pump 7 of the in-container exhaust means L4 in step S1 of FIG. 2, and the inside of the heat insulating container C via the first exhaust path L41 or the second exhaust path L42. Start exhausting (degassing) the space. Further, the exhaust gas from the fuel cell stack S, that is, the fuel exhaust gas in which the fuel component remains and the oxidized exhaust gas in which the oxidant component remains are mixed and burned by the burner 6, and in the heat exchanger 3, the heat of the combustion gas and the introduced air The introduced air is heated (preheated) by exchanging heat between the two.

  The fuel cell system starts power generation by supplying oxidizing gas and fuel gas to the fuel cell stack S as described above, and the temperature of the fuel cell stack S is increased by heat from its own power generation reaction and heat from preheated air. The oxidation exhaust gas and the fuel exhaust gas, which are exhaust gases, also start to rise in temperature.

  At this time, since the fuel cell system exhausts (degass) the inner space of the heat insulating container C in the process of raising the temperature of the fuel cell stack S, the thermal conductivity of the inner space of the container decreases, and the fuel cell stack S This makes it difficult to release the heat to the surroundings, the heat capacity of the space in the container is reduced, the heat insulation is improved, and the temperature of the fuel cell stack S can be raised in a short time. That is, it is possible to shorten the activation time.

  Next, when the temperature of the oxidized exhaust gas fuel exhaust gas reaches the specified value (T1) in step S2 of FIG. 2, the fuel cell system, in step S3, the second air supply path of the in-vessel air supply means L5. By L52, supply of the oxidizing exhaust gas to the space in the container is started. In this way, the fuel cell stack S is heated from the outside by supplying the heated oxidizing exhaust gas to the inner space of the container. Thereby, the temperature rising time of the fuel cell stack S is further shortened.

  Thereafter, in the fuel cell system, the power generation reaction further proceeds, and after the exhaust gas temperature reaches the specified value (T2) in step S4 in FIG. 2, in order to prevent excessive temperature rise in step S5, The exhaust amount (deaeration amount) of the inner space of the container is reduced or the exhaust is stopped, and further, the supply amount of the oxidizing exhaust gas to the inner space of the container is reduced or the supply is stopped.

  As described above, when the exhaust amount of the inner space of the heat insulating container C is decreased, the thermal conductivity of the inner space of the container is increased (the heat insulating property is lowered), and the heat of the fuel cell stack S is easily released to the surroundings. . Moreover, heating is suppressed even if the supply amount of the oxidizing exhaust gas to the space in the container is decreased. The specified value T2 of the exhaust gas is a temperature immediately before the steady operation temperature of the fuel cell system.

  In the above-described fuel cell system, during steady operation, the exhaust gas temperature is lower than the specified value T3 in step S6 of FIG. 2, and the exhaust gas temperature is lower than the specified value T3 in step S8 of FIG. When the temperature rises, control of heating and cooling is performed.

  That is, when the temperature of the exhaust gas falls below the specified value T3, basically the second supply path L2 of the in-vessel supply means L5 in step S7 of FIG. Thus, the oxidizing exhaust gas from the fuel cell stack S is supplied to the space in the container, and at this time, the supply amount, temperature and humidity of the oxidizing exhaust gas are adjusted in the gas control unit C52, and the exhaust in the container is made as necessary. The space in the container is exhausted (degassed) by means L4. Thereby, the fuel cell stack S is heated.

  That is, in order to increase the temperature of the fuel cell stack S, it is effective to reduce the thermal conductivity of the space in the heat insulating container C or to increase the temperature of the space in the container. The specific means is deaeration of the inner space of the container and supply of oxidized exhaust gas to the inner space of the container. If the space in the container is degassed, the thermal conductivity is lowered and the heat insulation is improved. Further, the oxidized exhaust gas is heated by reaction heat generated by power generation and does not contain moisture, so that the thermal conductivity is low and the heat capacity is small.

  Therefore, deaeration of the inner space of the heat insulating container C is to insulate the fuel cell stack S, and supply of oxidizing exhaust gas to the inner space of the container has a low thermal conductivity and a heat capacity. The fuel cell stack S is accommodated in a small high-temperature space, and the temperature of the fuel cell stack can be raised.

  Next, when the temperature of the exhaust gas rises above the specified value T3, the fuel exhaust gas from the fuel cell stack S is transmitted through the first air supply path L51 of the in-container air supply means L5 in step S9 of FIG. In this case, the supply amount, temperature and humidity of the fuel exhaust gas are adjusted in the gas control unit C51, and in particular, the fuel exhaust gas is cooled in the gas control unit C51. The fuel exhaust gas supplied to the inner space of the container contributes to the cooling of the fuel cell stack S and is then discharged to the outside by the in-vessel exhaust means L4 and the like.

  As a result, the fuel cell stack S is housed in a space having a lower temperature than that of the stack, a high thermal conductivity, and a large heat capacity, and is cooled.

  That is, when it is desired to lower the temperature of the fuel cell stack S, it is effective to increase the heat transfer coefficient of the space in the container of the heat insulating container D or increase the heat capacity of the space in the container. The specific means is to supply the fuel exhaust gas containing the cooled water to the inner space of the container. Since the fuel exhaust gas contains a large amount of water generated by power generation, its heat conductivity is high, and the heat transfer coefficient of the space can be increased by supplying it to the space in the container. Further, since the fuel exhaust gas contains moisture, it has a large heat capacity and can increase the heat capacity of the space in the container.

  Therefore, supplying the fuel exhaust gas to the inner space of the heat insulating container C means that the fuel cell stack S is accommodated in a low-temperature space having high heat conduction and large heat capacity, and heat dissipation from the fuel cell stack is performed. The temperature of the fuel cell stack S can be lowered.

  When the fuel cell system is stopped, the supply of the oxidizing gas and the fuel gas through the oxidizing gas supply path L1 and the fuel gas supply path L2 is stopped. At this time, in step S10 of FIG. The first air supply path L51 supplies the dehumidified fuel exhaust gas to the inner space of the heat insulating container C to seal the space.

  In step S11 of FIG. 2, when the temperature of the residual exhaust gas becomes equal to or lower than the specified value (T4), the filled fuel exhaust gas is discharged in step S12 of FIG. The dehumidified fuel exhaust gas is a reducing gas, and the oxidation of the fuel cell stack S composed of metal members is prevented by preventing the temperature of the fuel cell stack S from rapidly decreasing when the fuel exhaust gas is stopped. Can do.

  As described above, the fuel cell system particularly has an exhaust amount (deaeration amount) in the inner space of the heat insulating container C according to the increase or decrease in the temperature of the fuel cell stack S or the temperature of the exhaust gas, during the steady operation. By adjusting the supply amount, temperature, and humidity of the exhaust gas (oxidized exhaust gas, fuel exhaust gas) to the inner space, the temperature of the fuel cell stack S is controlled to be within an appropriate range. And as a whole, starting, steady operation, and stopping can be performed stably, and improvement in operating efficiency can be realized.

  Here, FIG. 3A is a graph showing a change in fuel exhaust gas temperature at startup, and FIG. 3B is a graph showing a change in fuel exhaust gas temperature during steady operation. In each graph, data of the fuel cell system according to the present invention having the configuration shown in FIG. 1 is shown by a solid line, and data of a fuel cell system of a comparative example without these means is shown by a broken line.

  At start-up, the temperature of the fuel exhaust gas rises from room temperature to about 750 ° C., which is a steady operation temperature (T3). As is clear from FIG. 3A, in the present invention, the time required to reach the steady operating temperature was 20 minutes, and in the comparative example, the time required to reach the steady operating temperature was 40 minutes.

  That is, the configuration shown in FIG. 1, that is, the in-container exhaust means L4 and the in-container air supply means L5 are provided. In particular, the in-container exhaust means L4 includes the exhaust pump 7 for forcibly exhausting the internal space of the container and When the gas means L5 is a fuel cell system including the gas control units C51 and C52, the startup time can be shortened by 20 minutes compared to the comparative example.

  Further, during steady operation, as is apparent from FIG. 3B, the width of the temperature change of the fuel exhaust gas is smaller in the present invention than in the comparative example. That is, when the temperature range with respect to the appropriate temperature is expressed by ± X ° C., X = 20 in the present invention and X = 50 in the comparative example.

  That is, the configuration shown in FIG. 1, that is, the in-container exhaust means L4 and the in-container air supply means L5 are provided. In particular, the in-container exhaust means L4 includes the exhaust pump 7 for forcibly exhausting the internal space of the container and When the gas means L5 is a fuel cell system including the gas control units C51 and C52, the temperature controllability can be compressed by about 30 ° C. compared to the comparative example.

  FIG. 4 is a diagram for explaining another embodiment of the fuel cell system of the present invention. Note that the same components as those of the previous embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the fuel cell system of the illustrated embodiment, the configuration different from that of the previous embodiment (FIG. 1) is that the in-container exhaust means L4 is not provided with an exhaust pump that performs forced exhaust. One exhaust path L41 has a structure that directly reaches the heat exchanger 3 from the inner space of the heat insulating container C.

  The fuel cell system described above is started, normally operated, and stopped according to steps S21 to S32 shown in FIG. 5. At this time, the difference from the previous embodiment (FIG. 1) is that forced exhaust by an exhaust pump is performed. This is where natural exhaust through the heat exchanger 3 is performed.

  6 (a) and 6 (b) are graphs showing changes in the temperature of the fuel exhaust gas during start-up and during steady operation. The fuel cell system data (solid line) shown in FIG. Data (broken line) is shown.

  At the time of start-up, as apparent from FIG. 6A, in the present invention, the time required to reach the steady operating temperature was 30 minutes, and in the comparative example, the time required to reach the steady operating temperature was 40 minutes. That is, by using the fuel cell system having the configuration shown in FIG. 4, the temperature controllability can be shortened by about 10 minutes compared to the comparative example.

  Further, during the steady operation, as is apparent from FIG. 6B, when the temperature range with respect to the appropriate temperature is expressed by ± X ° C., X = 20 in the present invention, and X = 50 in the comparative example. there were. That is, by using the fuel cell system having the configuration shown in FIG. 1, the temperature controllability can be compressed by about 30 ° C. as compared with the comparative example.

  Furthermore, according to the fuel cell system shown in FIG. 4, since the exhaust pump that performs forced exhaust is not used, the start-up time is slightly longer than when the exhaust pump is used, but the start-up time is longer than that of the comparative example. In addition, the system can be labor-saving as the exhaust pump is abolished.

  The configuration of the fuel cell system of the present invention is not limited to the above-described embodiments, and the details of the configuration can be changed without departing from the gist of the present invention.

It is a block diagram explaining one Embodiment of the fuel cell system of this invention. 2 is a flowchart illustrating an operation method of the fuel cell system shown in FIG. FIG. 5 is a graph (a) showing a change in fuel exhaust gas temperature at start-up and a graph (b) showing a change in fuel exhaust gas temperature during steady operation in the embodiment shown in FIG. It is a block diagram explaining other embodiment of the fuel cell system of this invention. 5 is a flowchart for explaining an operation method of the fuel cell system shown in FIG. FIG. 5 is a graph (a) showing a change in fuel exhaust gas temperature at startup and a graph (b) showing a change in fuel exhaust gas temperature during steady operation with respect to the embodiment shown in FIG. 4.

Explanation of symbols

C Insulated container F Fin C51 Gas control unit (fuel gas)
C52 Gas control unit (oxidizing gas)
L4 In-container exhaust means L41 First exhaust path L42 Second exhaust path L5 In-container air supply means L51 First air supply path L52 Second air supply path S Fuel cell stack 7 Exhaust pump

Claims (6)

In a fuel cell system having a structure in which a solid oxide fuel cell stack is accommodated in a heat insulating container, an in-container air supply means for supplying exhaust gas from the fuel cell stack to the internal space of the heat insulating container ;
Provided with an in-container exhaust means for exhausting the space in the container of the heat insulating container;
The container exhaust means includes an exhaust pump for forcibly exhausting the space in the container,
As a means for supplying the exhaust gas from the fuel cell stack into the container, a gas control unit for adjusting the supply amount, temperature and humidity of the exhaust gas is provided in the path from the fuel cell stack to the space in the container. A fuel cell system.   2. The fuel cell system according to claim 1, wherein a non-contact fin is provided on the inner surface of the heat insulating container to the fuel cell stack.   When operating the fuel cell system according to claim 1, the temperature of the fuel cell stack is controlled by adjusting the supply amount, temperature and humidity of the exhaust gas to the space in the container of the heat insulating container. How to operate the system. The temperature of the fuel cell stack is controlled by adjusting the exhaust amount from the space inside the container of the heat insulation container in addition to the supply amount, temperature and humidity of the exhaust gas to the space inside the heat insulation container. 4. A method for operating the fuel cell system according to 3.   5. The fuel according to claim 4, wherein at the time of startup, the space in the container of the heat insulating container is exhausted, and the exhaust gas is supplied to the space in the container after the temperature of the exhaust gas in the fuel cell stack reaches a specified value. Battery system operation method.   The exhaust gas of the fuel cell stack is supplied to the internal space of the container when the fuel cell stack is stopped, and the internal space of the container is exhausted after the temperature of the internal space of the heat insulating container drops below a specified value. Method of operating the fuel cell system.

Images