JP5090656B2 - Solid oxide fuel cell system - Google Patents

Description

  The present invention relates to a solid oxide fuel cell system that generates power by oxidation and reduction of a reformed gas and an oxidizing material obtained by reforming raw fuel gas.

Conventionally, a solid oxide fuel cell is known as a fuel cell. This solid oxide fuel cell is attracting attention as a promising power generation technology because it has higher power generation efficiency than other fuel cell systems and gas engines.

A solid oxide fuel cell includes a solid electrolyte that conducts oxygen ions, a fuel electrode having a function of oxidizing fuel gas is provided on one side of the solid electrolyte, and an oxygen having a function of reducing an oxidant on the other side An electrode is provided (see, for example, Patent Document 1 and Patent Document 2). Generally, zirconia doped with yttria is used as the solid electrolyte. In this solid oxide fuel cell, a fuel gas, for example, a gas containing hydrogen, carbon monoxide and hydrocarbons is supplied to the fuel electrode side, and an oxidizing material, for example, air is supplied to the oxygen electrode side. Electricity is generated by an electrochemical reaction with the material.

In this fuel cell system using a solid oxide fuel cell, for example, a hydrocarbon (for example, natural gas) is used as a raw fuel gas, and when a hydrocarbon is used, a reformer that reforms the raw fuel is provided. Installed. Hydrocarbon gas (for example, natural gas) is reformed by this reformer into a gas containing hydrogen and carbon monoxide, and the reformed fuel gas is supplied to the fuel electrode side of the solid oxide fuel cell.

JP 2002-289244 A JP 2005-285340 A

  This type of solid oxide fuel cell system is classified into a business use and industrial use of several tens of kW class or more, and a 1 kW class small use and home use. A small and household fuel cell system with a rated power output of 1 kW class has a usage characteristic that the power load for supplying generated power fluctuates greatly with time. For this reason, when the fuel cell system is partially loaded, It is required to exhibit high characteristics even when power is loaded.

In this type of solid oxide fuel cell, the reformer is disposed in the combustion chamber adjacent to the fuel cell stack, and reacts with the reaction fuel gas (which contains residual fuel gas) discharged from the fuel cell stack and the oxidation. A material (for example, air) is mixed and combusted, and the reformer is heated using the combustion exhaust gas, and a reforming reaction which is an endothermic reaction is performed in the reformer using such heat (Patent Document) 1).

  However, in this solid oxide fuel cell, when the generated power is suddenly increased, the supply amount of the raw fuel gas is also increased accordingly. The amount of heat absorbed due to the reforming reaction in the reactor increases, and the heat from the combustion exhaust gas due to combustion in the combustion chamber becomes insufficient. When the heat in the reformer is insufficient, the unreformed component in the reformed gas supplied to the fuel cell stack increases, and this unreformed component is reformed in the fuel cell stack. As a result, the temperature at the fuel side inlet of the fuel cell decreases, and it becomes difficult to increase the generated current in the fuel cell stack.

  In order to solve such a problem, the residual fuel component in the reaction fuel gas should be increased to increase the amount of heat of the combustion exhaust gas. However, if the residual fuel component is increased, the outlet temperature of the reformer increases. It becomes easy. When the outlet temperature of the reformer rises, the concentration of carbon monoxide in the reformed gas increases, and carbon deposits due to the decomposition reaction of carbon monoxide in the downstream fuel cell stack, causing failure of the fuel cell stack. It tends to occur.

An object of the present invention is to provide a solid oxide fuel cell system capable of reducing the temperature change in the reformer and suppressing an increase in unreformed gas that is likely to be generated when the power generation output of the fuel cell stack is rapidly increased. It is to be.

A solid oxide fuel cell system according to claim 1 of the present invention includes a reformer for reforming raw fuel, and oxidation and reduction of reformed fuel gas and oxidant reformed by the reformer. A solid oxide fuel cell system comprising a solid oxide fuel cell that generates electric power by:
In connection with the reformer, there is provided latent heat storage means for storing latent heat by melting, the latent heat storage means comprising a latent heat storage material having a melting point of 600 to 750 ° C., and the reformer or its surroundings When the temperature becomes a predetermined temperature suitable for the reforming reaction of the reformer or a temperature slightly higher than the predetermined temperature , the latent heat storage material is prevented from melting and storing heat to excessively increase the temperature. At the same time, when the temperature is lowered , the latent heat storage material is solidified to dissipate the stored heat to suppress the temperature drop.

Further, in the solid oxide fuel cell system according to claim 2 of the present invention, the latent heat storage material is accommodated in a storage container, and the storage container is in contact with or adjacent to the reformer. It is characterized by being provided.

Further, in the solid oxide fuel cell system according to claim 3 of the present invention, the solid oxide fuel cell includes a fuel cell stack for performing power generation by oxidation and reduction of the reformed fuel gas and the oxidizing material The heat shield wall defining a high temperature space for accommodating the fuel cell stack is provided, and the reformer and the latent heat storage means are disposed in the heat shield wall.

Furthermore, in the solid oxide fuel cell system according to claim 4 of the present invention, the latent heat storage material is formed of aluminum or an aluminum alloy containing aluminum as a main component.

According to the solid oxide fuel cell system of claim 1 of the present invention, there is provided a latent heat storage means for storing latent heat by melting in association with the reformer, and the latent heat storage means is 600 to 750 ° C. Since the latent heat storage material having a melting point is provided, the temperature of the reformer or its surroundings exceeds the melting point (in other words, a predetermined temperature suitable for the reforming reaction in the reformer or a temperature slightly higher than the predetermined temperature). When the temperature rises, the latent heat storage material melts and absorbs ambient heat, and the temperature rise of the reformer is suppressed. When the temperature of the reformer rises, the concentration of carbon monoxide in the reformed gas increases, and carbon tends to precipitate due to the decomposition reaction of carbon monoxide in the downstream fuel cell stack, but this latent heat storage material melts. Thus, excessive temperature rise of the reformer can be suppressed, and carbon deposition in the fuel cell stack can be suppressed. As the latent heat storage material, a material having a melting point of a predetermined temperature suitable for the reforming reaction in the reformer or a temperature somewhat higher than the predetermined temperature is selected from the temperature range of 600 to 750 ° C.

Further, when the temperature of the reformer or its surroundings is decreased, the latent heat storage material is solidified to dissipate the absorbed heat, and the temperature decrease of the reformer is suppressed. When the reformer is decreased temperature, the number of unreformed component in the reformed gas, but increases the generated current in the fuel cell stack temperature of the fuel-side inlet of the fuel cell stack is reduced becomes difficult, the latent heat The heat is dissipated by the solidification of the heat storage material , whereby the temperature drop of the reformer is suppressed, and the decrease in the generated current in the fuel cell stack can be suppressed. The heat stored in the latent heat storage material can also be used to raise the temperature of the reformer when starting the solid oxide fuel cell system.

  In this solid oxide fuel cell system, the temperature variation of the reformer is suppressed with a simple configuration using the melting and solidification of the latent heat storage means and the provision of the latent heat storage means, thereby improving the reliability of the fuel cell system. Can be extended to extend its lifespan.

In addition, according to the solid oxide fuel cell system of the second aspect of the present invention, the storage container storing the latent heat storage material is provided inside or in contact with or adjacent to the reformer. When the temperature of the reformer or the vicinity thereof exceeds the melting point, heat is absorbed by melting of the latent heat storage material, while when the temperature falls below this melting point, heat dissipation is performed by solidification of the heat storage material . Temperature fluctuation of the reformer can be suppressed .

  According to the solid oxide fuel cell system of claim 3 of the present invention, the reformer and the fuel cell stack of the solid oxide fuel cell are disposed in a high temperature space defined by the heat shield wall. Therefore, the reformer and the fuel cell stack can be kept at a high temperature.

Furthermore, according to the solid oxide fuel cell system according to claim 4 of the present invention, a material formed from aluminum or an aluminum alloy containing aluminum as a main component can be advantageously used as the latent heat storage material.

DETAILED DESCRIPTION Hereinafter, a preferred embodiment of a solid oxide fuel cell system according to the present invention will be described with reference to the accompanying drawings.
First Embodiment First, a first embodiment of a solid oxide fuel cell system according to the present invention will be described with reference to FIG. FIG. 1 is a simplified diagram schematically illustrating the solid oxide fuel cell system according to the first embodiment.

  In FIG. 1, the illustrated solid oxide fuel cell system includes a solid oxide fuel cell 2, a reformer 4 for reforming raw fuel, and an air preheater for preheating air as an oxidizing material. 6 is provided. The solid oxide fuel cell 2 includes a substantially cuboid fuel cell main body 10 and a fuel cell stack 12 for generating power by an electrochemical reaction. The fuel cell body 10 is formed by a heat shield wall 14, a high temperature space 8 is defined by the heat shield wall 14, and a heat insulating member (not shown) is provided so as to cover the fuel cell body 10.

  The fuel cell stack 12 includes a solid electrolyte 16 that conducts oxygen ions. For example, zirconia doped with yttria is used as the solid electrolyte 16. A fuel electrode (not shown) is provided on one side (right side in FIG. 1) of the solid electrolyte 16 of the fuel cell stack 12, oxidation is performed on the fuel electrode side 15 (right side in FIG. 1), and the other side ( An oxygen electrode (not shown) is provided on the left side in FIG. 1, and a reduction action is performed on the oxygen electrode side 17.

  A reformed fuel gas obtained by reforming a raw fuel gas (for example, natural gas) as a raw fuel is supplied to the fuel electrode side 15 of the fuel cell stack 12. In this embodiment, the introduction side of the fuel electrode side 15 of the fuel cell stack 12 is connected to the reformer 4 via the reformed fuel gas supply line 18, and the reformer 4 is connected to the raw fuel gas supply line 20. And connected to a raw fuel gas supply source 22 (for example, buried pipe, storage tank). A steam supply line 24 is connected to the raw fuel supply line 20, and a steam supply source 26 for supplying steam is connected to the steam supply line 24.

  The introduction side of the oxygen electrode side 17 of the fuel cell stack 12 is connected to the air preheater 6 via an air supply line 28, and the air preheater 6 supplies outside air via an air supply line 30. 32.

  Further, combustion chambers 34 are provided on the discharge side of the oxygen electrode side 15 and the oxygen electrode side 17 of the fuel cell stack 12, and the reaction fuel gas (including residual fuel gas) discharged from the fuel electrode side 15 of the fuel cell stack 12 is provided. The air (containing oxygen) discharged from the oxygen electrode side 17 is supplied to the combustion chamber 34 and burned. The combustion chamber 34 is connected to the air preheater 6 via a combustion exhaust gas supply line 36, and the air preheater 6 is opened to the atmosphere via a combustion exhaust gas discharge line 38.

The reformer 4 is known per se in which a reforming catalyst is filled in a reforming housing, and a mixture of raw fuel gas (natural gas) and steam contains hydrogen and carbon monoxide by a reforming reaction. Reformed fuel gas is reformed. This reforming reaction is an endothermic reaction, and the reforming reaction is accelerated by the action of the reforming catalyst at a high temperature of about 650 ° C.

  The air preheater 6 exchanges heat between the air supplied through the air supply line 30 and the combustion exhaust gas flowing through the combustion exhaust gas supply line 36, and the oxygen in the fuel cell stack 12 through the air supply line 28. Air supplied to the electrode side 17 is heated.

The operation of this solid oxide fuel cell system is as follows. The raw fuel gas from the raw fuel gas supply source 28 is supplied through the raw fuel gas supply line 20 and is sent to the reformer 4 together with the steam supplied from the steam supply source 26 through the steam supply line 24. In the reformer 4, the raw fuel gas is reformed by the reforming reaction, and the reformed reformed gas is sent to the fuel electrode side 15 of the fuel cell stack 12 through the reformed fuel gas supply line 18. Be paid.

  In addition, air from the blower 32 is supplied to the air preheater 6 through the air supply line 30, heat is exchanged with the combustion exhaust gas in the air preheater 6 and heated, and then the air supply line 28. To the oxygen electrode side 17 of the fuel cell stack 12.

  In the fuel cell stack 12, an electrochemical reaction is performed by the reformed fuel gas and oxygen in the air, and power generation is performed by this electrochemical reaction. The electrochemical reaction in the solid oxide fuel cell 2 is performed at a high temperature of 700 to 1000 ° C., and the upper limit of the operating temperature, that is, the set upper limit temperature is, for example, in consideration of the power generation efficiency of the fuel cell stack 12 and the lifetime thereof. It is set to about 800 ° C.

  The reaction fuel gas from the fuel electrode side 15 of the fuel cell stack 12 and the air from the oxygen electrode side 17 are supplied to the combustion chamber 34, and the reaction combustion gas is combusted using oxygen in the air. The reformer 4 is disposed above the combustion chamber 34, and the reformer 4 is heated using the heat of the combustion exhaust gas in the combustion chamber 34. The combustion exhaust gas from the combustion chamber 34 is supplied to the air preheater 6 through the exhaust gas supply line 36, and is used for heat exchange with the air in the air preheater 6 and discharged to the atmosphere through the combustion exhaust gas discharge line 38.

  This solid oxide fuel cell system is further configured as follows. That is, the fuel cell stack 12, the reformer 4, and the air preheater 6 are accommodated in the high temperature space 8 defined by the heat shield wall 14, and these are brought into a high temperature state using the heat of the combustion exhaust gas in the combustion chamber 34. It is configured to be kept.

A latent heat storage means 40 is provided in association with the reformer 4. The latent heat storage means 40 includes a storage container 42 and a latent heat storage material (not shown) filled in the storage container 42, and the storage container 42 is provided in contact with or adjacent to the reformer 4. The storage container 42 is made of, for example, stainless steel, and the latent heat storage material may be in an appropriate form such as a granular shape, a chip shape, a block shape, or a rod shape, and the latent heat storage material is sealed in the storage container 42, The latent heat storage means 40 is also disposed in the high temperature space 8.

  As the latent heat storage material, a material having a melting point of 600 to 750 ° C. is used. In this embodiment, a predetermined temperature suitable for the reforming reaction performed in the reformer 4 or a temperature slightly higher than the predetermined temperature, for example, What has melting | fusing point in 650-660 degreeC is used. As such a latent heat storage material, aluminum having a melting point of 660 ° C. can be conveniently used, and an aluminum alloy mainly composed of aluminum may be used.

In the solid oxide fuel cell system provided with such latent heat storage means 40, when the temperature of the reformer 4 rises and exceeds the melting point of the latent heat storage material, the latent heat storage material melts and absorbs heat, Thus, the temperature rise of the reformer 4 can be suppressed. On the other hand, for example, when the power generation output of the solid oxide fuel cell 2 suddenly increases and the temperature of the reformer 4 decreases, the latent heat storage material solidifies and the stored heat is dissipated, and this heat dissipation reforms. The temperature drop of the vessel 4 is suppressed. In this way, heat absorption and heat release are performed by melting and solidifying the latent heat storage material, and the amount of heat absorption and heat release due to melting and solidification also increases, so that the latent heat storage means 40 is provided and the reformer 4 has a simple configuration. The variation of the reforming temperature can be suppressed, and as a result, the reforming of the raw fuel gas can be performed stably. In this embodiment, the latent heat storage means 40 is provided in contact with or adjacent to the reformer 4. However, the latent heat storage means 40 may be disposed inside the reformer 4.

Second Embodiment Next, a second embodiment of the solid oxide fuel cell according to the present invention will be described with reference to FIG. FIG. 2 is a simplified diagram schematically illustrating the solid oxide fuel cell system according to the second embodiment. In the second embodiment, substantially the same members as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted.

In FIG. 2 , in the solid oxide fuel cell system of the second embodiment, the latent heat storage means 40A is on the lower side of the air preheater 6, that is, on the fuel cell stack 12 side. Line 36 is provided adjacent to it. The latent heat storage means 40A may be substantially the same as that in the first embodiment, and the storage container 42A is filled with a latent heat storage material (not shown) made of, for example, aluminum . By disposing the latent heat storage means 40A in such a part, when the operating temperature of the fuel cell stack 12 reaches the set upper limit temperature, the latent heat storage material of the latent heat storage means 40A reaches the melting point and melting occurs. It becomes like this. Other configurations in the second embodiment are substantially the same as those in the first embodiment described above.

  In the solid oxide fuel cell system having such latent heat storage means 40A, when the operating temperature of the fuel cell stack 12 exceeds a set upper limit temperature (for example, set to about 800 ° C.), the latent heat storage means 40A The latent heat storage material melts and absorbs heat, and this heat absorption suppresses an increase in the operating temperature of the fuel cell stack 12 and prevents operation in a temperature range exceeding the set upper limit temperature. On the other hand, for example, when the power generation output of the solid oxide fuel cell 2 decreases and the operating temperature of the fuel cell stack 12 decreases, the latent heat storage material solidifies and the stored heat is dissipated, and this heat dissipation dissipates the fuel cell stack. The decrease in the operating temperature of 12 is suppressed. In this way, heat absorption and heat dissipation are performed by melting and solidifying the latent heat storage material, and the heat absorption and heat dissipation due to melting and solidification are also increased. Therefore, with the simple configuration of providing the latent heat storage means 40A, the fuel cell stack 12 The operation exceeding the set upper limit temperature is prevented, and fluctuations in the operating temperature can be suppressed. As a result, the operation of the solid oxide fuel cell 2 can be stabilized and the power generation efficiency can be increased.

  In this embodiment, the latent heat storage means 40A is provided adjacent to the combustion exhaust gas supply line 36 or adjacent thereto, but is not limited to such a configuration, and is appropriately disposed in the high-temperature space 8 defined by the heat shield wall 14. (The portion where the latent heat storage material reaches the melting point when the operating temperature of the fuel cell stack 12 reaches the set upper limit temperature).

  In this embodiment, the latent heat storage material is melted when the operating temperature of the fuel cell stack 12 reaches the set upper limit temperature. However, the present invention is not limited to this, and is somewhat lower than the set upper limit temperature. It can also be configured such that the latent heat storage material is melted when it reaches a temperature (for example, a temperature lower by 5 to 10 ° C.).

  As mentioned above, although embodiment of the solid oxide fuel cell system according to this invention was described, this invention is not limited to this embodiment, A various change thru | or correction | amendment are possible without deviating from the scope of the present invention.

  For example, in the first embodiment, the latent heat storage means 40 is provided in relation to the reformer 4, and in the second embodiment, the latent heat storage means is related to the solid oxide fuel cell 2, that is, the fuel cell stack 2. Although 40A is provided, one latent heat storage means may be provided in association with both the reformer 4 and the solid oxide fuel cell 2.

Examples and Comparative Examples In order to confirm the effects of the above-described invention, experiments related to the reformer were performed as follows. As Example 1, a solid oxide fuel cell system having the form shown in FIG. 1 was used, and natural gas mainly composed of methane was used as a raw fuel gas. The rated output of the solid oxide fuel cell of this system was 1 kW. In addition, as a latent heat storage means, a cylindrical container made of stainless steel filled with a latent heat storage material made of aluminum was used, and this container was provided so as to contact the reformer. The melting point of the latent heat storage material was 660 ° C., and the filling amount was 1.0 kg.

  The fuel cell system of Example 1 was operated by following the power load, and power was generated so that the power generation output was as shown in FIG. Then, the temperature at the outlet portion of the reformer when operated in this way was measured, and the measurement result was as shown by the solid line A in FIG.

As Comparative Example 1, the solid oxide fuel cell system of Example 1 in which the latent heat storage means was omitted was used. Also in this comparative example 1, the fuel cell system was operated by following the electric power load, and the power generation output was generated as shown in FIG. And the temperature in the exit site | part of the reformer when it operate | moves in this way was measured, and the measurement result was as having shown with the broken line in FIG.3 (b).

  As is apparent from the measurement results in FIG. 3A, in Example 1, the temperature at the outlet of the reformer is maintained at around 660 ° C., whereas in Comparative Example 1, the outlet temperature of the reformer is 600. It fluctuates greatly from around ℃ to about 750 ℃. From this, by providing latent heat storage means in connection with the reformer, it is possible to prevent overheating of the reformer and to maintain the reforming temperature optimum for reforming the raw fuel gas. Was confirmed.

Next, an experiment on a solid oxide fuel cell was performed as follows. As Example 2, a solid oxide fuel cell system having the form shown in FIG. 2 was used, and natural gas mainly composed of methane was used as a raw fuel gas. The rated output of the solid oxide fuel cell of this system was 1 kW. In addition, as in the first embodiment, as the latent heat storage means, a stainless steel storage container filled with a latent heat storage material made of aluminum as a latent heat storage material is used, and this storage container is placed under the air preheater (fuel Attached in contact with the battery stack side). The melting point of the latent heat storage material was 660 ° C., and the filling amount was 1.0 kg.

The fuel cell system of Example 2 was operated by following the power load, and power was generated so that the power generation output was as shown in FIG. The upper limit of the operating temperature of the solid oxide fuel cell is set to 800 ° C., and when the temperature of the fuel cell stack exceeds 800 ° C., the air utilization rate is lowered (in other words, the amount of air supplied through the air supply line is reduced). (Increased) The temperature rise was controlled. And the operating temperature of the fuel cell stack when operated in this way was measured, and the measurement result was as shown by the solid line A in FIG.

As Comparative Example 2, the solid oxide fuel cell system of Example 2 in which the latent heat storage means was omitted was used. Also in this comparative example 2, the fuel cell system was operated by following the power load, and the power generation output was generated as shown in FIG. And the operating temperature of the fuel cell stack when operated in this way was measured, and the measurement result was as shown by the broken line in FIG.

  As is apparent from the measurement results of FIG. 4A, in Example 2, the operating temperature of the fuel cell stack becomes gentle from a point before the set upper limit temperature of 800 ° C., and when the output of the solid oxide fuel cell decreases. In contrast, in Example 2, the temperature rise to the set upper limit temperature is abrupt, and the temperature drop at the time of output reduction of the solid oxide fuel cell is suddenly and large. From this, by providing the latent heat storage means in connection with the solid oxide fuel cell, in particular, the fuel cell stack, the temperature rise and temperature drop near the set upper limit temperature of the operating temperature of this fuel cell stack becomes moderate, As a result, the time that can be maintained in the vicinity of the set upper limit temperature becomes longer, and as a result, it was confirmed that the power generation efficiency of the solid oxide fuel cell can be increased. Further, when comparing the power generation efficiency at this time, the power generation efficiency in the section T of FIG. 4 was 1.3 points higher than that of Comparative Example 2 of Example 2. As described above, in the present invention, it was confirmed that high power generation efficiency can be brought out while suppressing the operating temperature of the solid oxide fuel cell and suppressing its deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified diagram illustrating a solid oxide fuel cell system according to a first embodiment. The simplification figure which shows the solid oxide fuel cell system of 2nd Embodiment simply. In Example 1 and Comparative Example 1, the figure which shows the temperature change of the reformer when the electric power generation output is fluctuate | varied. The figure which shows the change of the operating temperature of a fuel cell stack when Example 2 and the comparative example 2 fluctuate | varied electric power generation output.

Explanation of symbols

2 Solid oxide fuel cell 4 Reformer 6 Air preheater 8 High temperature space 10 Fuel cell body 12 Fuel cell stack 14 Heat shield wall 16 Solid electrolyte 34 Combustion chamber 40, 40A Latent heat storage means 42, 42A Storage container

Claims (4)

A solid oxide type comprising a reformer for reforming raw fuel, and a solid oxide fuel cell that generates power by oxidation and reduction of the reformed fuel gas and the oxidizing material reformed by the reformer A fuel cell system,
In connection with the reformer, there is provided latent heat storage means for storing latent heat by melting, the latent heat storage means comprising a latent heat storage material having a melting point of 600 to 750 ° C., and the reformer or its surroundings When the temperature becomes a predetermined temperature suitable for the reforming reaction of the reformer or a temperature somewhat higher than the predetermined temperature , the latent heat storage material melts and stores heat to suppress an excessive increase in temperature. The solid oxide fuel cell system is characterized in that, when the temperature is lowered , the latent heat storage material is solidified to dissipate the heat stored to suppress the temperature drop. 2. The solid oxide according to claim 1, wherein the latent heat storage material is stored in a storage container, and the storage container is provided inside or in contact with or adjacent to the reformer. Type fuel cell system. The solid oxide fuel cell includes a fuel cell stack for generating power by oxidation and reduction of a reformed fuel gas and an oxidizing material, and a heat shield wall that defines a high-temperature space for housing the fuel cell stack. The solid oxide fuel cell system according to claim 1, wherein the reformer and the latent heat storage unit are disposed in the heat shield wall. The solid oxide fuel cell system according to any one of claims 1 to 3, wherein the latent heat storage material is made of aluminum or an aluminum alloy mainly composed of aluminum.

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