JP2010027283A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology to prevent a situation that a mixed gas in the middle of adjusting air-fuel ratio is heated by a fuel cell. <P>SOLUTION: The fuel cell system 1 is equipped with a mixing part 3 to mix a fuel gas and an oxidizer gas, a fuel cell 2 to generate electric power by an electrochemical reaction with the fuel gas and the oxidizer gas in the mixed gas when the mixed gas mixed into the mixing part 3 is supplied, and an adiabatic means 8 to prevent that reaction heat of the fuel cell 2 is transferred to the mixing part 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

Fuel cells are attracting attention as a power source that excels in operating efficiency and environmental performance. A fuel cell generates electricity by an electrochemical reaction between a fuel and an oxidant. In recent years, in order to simplify the device configuration, a fuel cell that generates power using a mixed gas obtained by mixing a fuel gas with air containing an oxidant has been developed (for example, see Patent Document 1).
JP 2006-114373 A

  A fuel cell is heated to high temperatures by reaction heat accompanying an electrochemical reaction. For this reason, the mixed gas supplied to the fuel cell needs to be sufficiently adjusted in the mixing ratio of the fuel gas before being heated by the reaction heat. This invention is made | formed in view of such a subject, and makes it a subject to provide the technique which prevents that the mixed gas in the middle of adjusting a mixing ratio is heated with a fuel cell.

  In order to solve the above problems, the present invention prevents the reaction heat of the fuel cell from being transmitted to the mixing section.

  Specifically, in the fuel cell system, when a mixing unit that mixes a fuel gas and an oxidant gas and a mixed gas mixed by the mixing unit are supplied, the fuel gas in the mixed gas and the oxidizing agent are supplied. A fuel cell that generates electric power by an electrochemical reaction with the agent gas; and heat insulation means for preventing reaction heat of the fuel cell from being transmitted to the mixing unit.

  The fuel cell system generates electric power by causing an electrochemical reaction with a mixed gas in which a fuel gas and an oxidant gas are mixed. The mixed gas supplied to the fuel cell realizes an electrochemical reaction in the fuel cell by selectively reacting the fuel gas at the anode electrode catalyst and the oxidant gas at the cathode electrode catalyst.

  Here, when the fuel gas and the oxidant gas are mixed, the gas concentration inevitably varies until the gas concentration becomes uniform. In the fuel cell system, since the gas is mixed in the mixing unit, the concentration of the mixed gas varies in the mixing unit. Therefore, the fuel cell system according to the present invention includes heat insulating means for preventing the reaction heat of the fuel cell from being transmitted to the mixing section. By being configured so that the reaction heat of the fuel cell is not transmitted to the heat insulating means, it is possible to prevent the mixed gas whose mixing ratio is being adjusted from being heated by the reaction heat of the fuel cell.

  The heat insulating means prevents the heat of reaction from being transmitted from the fuel cell to the mixing section so that the temperature of the fuel gas in the mixing section reaches a predetermined temperature at which the fuel gas does not ignite. Also good. According to the fuel cell system configured as described above, the fuel gas does not react with the oxidant gas in the mixing section. The predetermined temperature is a temperature at which the fuel gas does not self-ignite, for example, a temperature lower than the ignition point temperature of the fuel gas.

The mixing unit mixes the fuel gas and the oxidant gas so that a predetermined mixing ratio is obtained in which combustion due to a reaction between the fuel gas and the oxidant gas in the mixed gas does not occur. There may be. According to the fuel cell system configured as described above, the fuel gas in the mixed gas supplied to the fuel cell does not react with the oxidant gas and burn. The predetermined mixing ratio is a mixing ratio at which combustion does not occur even if an ignition source is present in the mixed gas. In general, the term “combustion” may include a phenomenon such as an electrochemical reaction in a fuel cell in a broad sense, but in the present application, the combustion due to such an electrochemical reaction is excluded.

  The predetermined mixing ratio is a mixing ratio at which combustion due to a reaction between the fuel gas and the oxidant gas in the mixed gas does not occur due to a high ratio of the fuel gas to the oxidant gas, The mixing unit may mix unreacted fuel gas separated from the off-gas of the fuel cell with the oxidant gas.

  When the ratio of the fuel gas to the oxidant gas is high, the off-gas exhausted from the fuel cell contains a large amount of fuel gas. This is because the oxidant gas that can completely consume the fuel gas by the electrochemical reaction is not originally contained in the mixed gas supplied to the fuel cell. When combustion is prevented from occurring even if an ignition source is present in the mixed gas by increasing the ratio of the fuel gas, a large amount of the fuel gas contained in the off-gas of the fuel cell is exhausted. In the system, the unreacted fuel gas contained in the off-gas is mixed again by the mixing unit with the oxidant gas. Thereby, the effective use of fuel gas is achieved.

  It is possible to prevent the mixed gas in the middle of adjusting the mixing ratio from being heated by the fuel cell.

  Hereinafter, embodiments of the present invention will be exemplarily described. Each embodiment shown below is an illustration and this invention is not limited to these.

<First embodiment>
FIG. 1 is a configuration diagram of a fuel cell system 1 according to the present embodiment. As shown in FIG. 1, a fuel cell system 1 includes a fuel cell stack 2 (corresponding to a fuel cell in the present invention), and a mixer 3 for supplying a mixed gas to the fuel cell stack 2 (in the present invention). , Corresponding to the mixing section). The mixer 3 mixes a mixed gas in which air and fuel gas (hydrogen) are mixed through the valve 4 so that the concentration is uniform, and supplies the mixed gas to the fuel cell stack 2. The valve 4 mixes the hydrogen supplied from the hydrogen storage tank 6 that stores hydrogen into the air exhausted from the air compressor 5. The air contains oxygen gas that acts as an oxidant gas in the electrochemical reaction of the fuel cell stack 2.

  In the fuel cell system 1 configured in this way, an electrochemical reaction occurs when a mixed gas in which hydrogen and air are mixed is supplied to the fuel cell stack 2 to generate electric power. FIG. 2 is a schematic structural diagram showing the internal structure of the fuel cell stack 2. As shown in FIG. 2, the fuel cell stack 2 includes a ceramic solid electrolyte that can withstand the reaction heat of an electrochemical reaction that reaches about 800 ° C., and a fuel electrode and an air electrode that are disposed on the ceramic solid electrolyte. Composed. The fuel electrode and the air electrode are electrodes carrying a catalyst. When the mixed gas passes through the surface of the electrolyte where the fuel electrode and the air electrode are arranged, the following reaction occurs.

  That is, when the mixed gas passes through the surface of the electrolyte, an anion is generated from oxygen contained in the mixed gas by a catalytic action at the air electrode. The anion generated at the air electrode is supplied to the fuel electrode via the electrolyte. Further, at the fuel electrode, hydrogen contained in the mixed gas reacts with anions provided from the air electrode via the electrolyte due to catalytic action. As a result, electrons flow in a circuit between the fuel electrode and the air electrode that are electrically connected via the load, and power is supplied to the load. The single-chamber fuel cell stack 2 configured as described above does not require a gas seal or separator for shutting off the gas, unlike the one that shuts off the gas passing through the fuel electrode and the gas passing through the air electrode. Therefore, it is very advantageous for miniaturization and integration.

  The fuel cell system 1 has a separation membrane module 7 as shown in FIG. The separation membrane module 7 is a device that separates hydrogen from an unreacted mixed gas exhausted from the fuel cell stack 2. The separation membrane module 7 returns unreacted hydrogen to the fuel cell stack 2 by flowing hydrogen separated from the mixed gas to the valve 4. Since the mixing ratio of air and hydrogen required for the electrochemical reaction is 7: 3, if the hydrogen concentration in the mixed gas supplied to the fuel cell stack 2 is reduced to about 30% or less, the hydrogen in the mixed gas is converted into the fuel cell It is possible to consume all the hydrogen in the mixed gas by performing an electrochemical reaction in the stack 2. Accordingly, in this case, such a separation membrane module 7 is useless, but as will be described later, the present fuel cell system 1 has a hydrogen concentration in the mixed gas supplied from the mixer 3 to the fuel cell stack 2. It exceeds 75 vol%. Therefore, even if the capacity of the fuel cell stack 2 is extremely large, it is impossible to completely consume hydrogen in the mixed gas supplied from the mixer 3. The separation membrane module 7 collects unreacted hydrogen inevitably contained in the off-gas of the fuel cell stack 2.

  The fuel cell system 1 also includes a heat insulating material 8 (corresponding to heat insulating means in the present invention) that prevents the heat of the fuel cell stack 2 from being transferred to the mixer 3. Details of the heat insulating material 8 will be described later.

  The fuel cell system 1 configured as described above generates power by operating as follows. That is, in the fuel cell system 1, when the operating power of the system is supplied, an electronic control device (not shown) starts the air compressor 5 and causes hydrogen in the hydrogen storage tank 6 to flow. As a result, a mixed gas of hydrogen and air flows through the fuel cell stack 2, and power generation is performed by an electrochemical reaction between hydrogen and oxygen. The fuel cell stack 2 that generates electricity through an electrochemical reaction generally has the following performance, although it varies depending on the constituent materials.

Open-circuit voltage: 0.9V (between a pair of fuel electrode / air electrode)
IV performance: 0.7 W / cm ² (IV: current voltage)
Power generation temperature: about 800 ° C
By the way, it is generally known that hydrogen mixed with air becomes combustible in combination with oxygen in the air when the hydrogen concentration in the air is 4 to 75 vol%. Since the ignition point temperature at which hydrogen self-ignites is 572 ° C. (less than 572 ° C. corresponds to the predetermined temperature in the present invention), in the fuel cell system 2, the hydrogen concentration of the mixed gas passing through the fuel cell stack 2 Is over 75 vol%, the mixing ratio of air and hydrogen joined by the valve 4 is adjusted. Further, since the concentration distribution of the mixed gas passing through the fuel cell stack 2 varies, the gas mixed by the valve 4 is prevented from generating in the mixed gas a region where the hydrogen concentration is locally 75 vol% or less. Is sufficiently mixed by the mixer 3. With this configuration, the fuel cell system 1 prevents combustion of the mixed gas, and realizes an electrochemical reaction of the mixed gas while simplifying the configuration of the fuel cell stack 2. In addition, the mixing ratio of hydrogen and air when the hydrogen concentration in the mixed gas is 0 vol% or more and less than 4 vol%, and is higher than 75 vol% and equal to or lower than 100 vol% corresponds to the predetermined mixing ratio in the present invention.

  By the way, the mixed gas mixed by the valve 4 reaches the mixer 3 and is stirred. Thereby, the region where the hydrogen concentration is 4 vol% or more and 75 vol% or less is not generated in the mixed gas supplied to the fuel cell stack 2. However, in the mixed gas flowing between the valve 4 and the mixer 3, there may be a region where the hydrogen concentration is 75 vol% or less. Therefore, in the fuel cell system 1 according to the present embodiment, the mixed gas between the valve 4 and the mixer 3 does not exceed the ignition point temperature at which hydrogen self-ignites due to the heat of the fuel cell stack 2. The heat of the fuel cell stack 2 is blocked. The fuel cell system 1 according to the present embodiment is configured in this way, thereby facilitating mixing of hydrogen and air in the mixer 3.

<Second embodiment>
Hereinafter, a second embodiment of the present invention will be described. FIG. 3 is a configuration diagram of the fuel cell system 11 according to the present embodiment. The difference between the fuel cell system 11 according to the present embodiment and the fuel cell system 1 according to the first embodiment described above is the presence or absence of the separation membrane module 7. That is, in the first embodiment described above, since the hydrogen concentration in the mixed gas supplied to the fuel cell stack 2 is adjusted to exceed 75 vol%, unreacted hydrogen contained in the off-gas of the fuel cell stack 2 However, in this embodiment, the separation membrane module 7 is adjusted by adjusting the hydrogen concentration in the mixed gas supplied to the fuel cell stack 2 to be less than 4 vol%. Is omitted. Hereinafter, the fuel cell system 11 according to the present embodiment will be described. In addition, the same code | symbol is attached | subjected about the component similar to the fuel cell system 1 which concerns on 1st embodiment mentioned above, and the detailed description is abbreviate | omitted.

  As shown in FIG. 3, the fuel cell system 11 includes a fuel cell stack 2, a mixer 3, an air compressor 5, and a hydrogen storage tank 6, similar to the fuel cell system 1 according to the first embodiment. Unlike the valve 4 according to the first embodiment, the valve 14 for mixing the air exhausted from the air compressor 5 and the hydrogen supplied from the hydrogen storage tank 6 is a mixed gas supplied to the fuel cell stack 2. The mixing ratio of air and hydrogen is adjusted so that the hydrogen concentration in the mixture is less than 4 vol%.

  As described in the description of the first embodiment, since the mixing ratio of air and hydrogen necessary for the electrochemical reaction is 7: 3, the hydrogen concentration in the mixed gas supplied to the fuel cell stack 2 is about 30% or less. By doing so, all the hydrogen in the mixed gas can be consumed by electrochemically reacting the hydrogen in the mixed gas in the fuel cell stack 2. Therefore, the fuel cell system 11 according to the present embodiment is adopted by adopting the valve 14 that adjusts the mixing ratio of air and hydrogen so that the hydrogen concentration in the mixed gas supplied to the fuel cell stack 2 is less than 4 vol%. However, the separation membrane module 7 is omitted.

  In the fuel cell system 11 configured as described above, the mixing ratio of air and hydrogen joined by the valve 14 is adjusted so that the hydrogen concentration of the mixed gas passing through the fuel cell stack 2 is less than 4 vol%. The In addition, since the concentration distribution of the mixed gas passing through the fuel cell stack 2 varies, the gas mixed by the valve 14 is prevented from generating in the mixed gas a region where the hydrogen concentration is locally 4 vol% or more. Is sufficiently mixed by the mixer 3. Therefore, even if the mixed gas passes through the fuel cell stack 2 that reaches about 800 ° C. due to the heat of the electrochemical reaction, combustion of the mixed gas is prevented.

  In addition, the effect of the fuel cell system 11 according to the present embodiment is the same as that of the fuel cell system 1 according to the first embodiment. For example, even if there is a region of 4 vol% or more and 75 vol% or less in the mixed gas flowing between the valve 14 and the mixer 3, the heat insulating material 8 does not exceed the ignition point temperature at which hydrogen self-ignites. Further, the heat of the fuel cell stack 2 is blocked. The fuel cell system 11 according to the present embodiment is configured in this manner, thereby facilitating mixing of hydrogen and air in the mixer 3.

<Modification 1>
Hereinafter, modifications of the first embodiment described above will be described. FIG. 4 is a configuration diagram of the fuel cell system 21 according to this modification. Hereinafter, although this modification is demonstrated as a modification of 1st embodiment, this modification is applicable also to 2nd embodiment.

The difference between this modification and the first embodiment is the presence or absence of the heat insulating material 8. That is, in the first embodiment described above, the heat from the fuel cell stack 2 transmitted to the mixer 3 is blocked by the heat insulating material 8. In this modification, heat is blocked by separating the fuel cell stack 2 and the mixer 3. Further, in order to prevent heat from being transmitted through a pipe connecting the mixer 3 and the fuel cell stack 2, a heat radiating portion 28 is provided in the pipe connecting the mixer 3 and the fuel cell stack 2. The heat dissipating unit 28 is formed by meandering a pipe connecting the mixer 3 and the fuel cell stack 2 and increasing the length of the pipe connecting the mixer 3 and the fuel cell stack 2. Heat transfer from the fuel cell stack 2 to the mixer 3 is prevented.

  The distance between the fuel cell stack 2 and the mixer 3 is appropriately adjusted so that the temperature of the mixed gas flowing between the valve 4 and the mixer 3 does not exceed the ignition point temperature of hydrogen. The same applies to the heat radiating portion 28.

  The effect of the fuel cell system 21 configured as described above is the same as that of the fuel cell system according to the first embodiment or the second embodiment. For example, even if there is a region of 4 vol% or more and 75 vol% or less in the mixed gas flowing between the valve 14 and the mixer 3, the temperature of the mixer 3 is self-ignited by the heat radiating unit 28 or the like. The heat of the fuel cell stack 2 is blocked so as not to exceed the ignition point temperature. The fuel cell system 11 according to the present embodiment is configured in this manner, thereby facilitating mixing of hydrogen and air in the mixer 3.

<Modification 2>
Further, each of the fuel cell systems may be modified as follows. For example, each fuel cell system may actively cool the mixer. As a means for cooling the mixer, it is possible to use cooling water used for cooling the fuel cell stack, air sucked by an air compressor, hydrogen supplied from a hydrogen storage tank, or the like. FIG. 5 shows an example in which the mixer is cooled by using the air sucked by the air compressor. For example, as shown in FIG. 5, each of the fuel cell systems described above cools the gas in the mixer 3 by allowing the air sucked into the air compressor to pass outside the mixer 3 and the valve 4. May be. According to this, even when the mixer 3 and the like cannot be sufficiently insulated with the heat insulating material, it is possible to suppress heating by the fuel cell stack 2 by cooling them.

1 is a configuration diagram of a fuel cell system according to a first embodiment. The block diagram of a fuel cell stack. The block diagram of the fuel cell system which concerns on 2nd embodiment. The block diagram of the fuel cell system which concerns on the modification 1. FIG. The block diagram of the fuel cell system which concerns on the modification 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11,21 .... Fuel cell system 2 ... Fuel cell stack 3 ... Mixer 5 ... Air compressor 8 ... Heat insulation material

Claims (4)

A mixing section for mixing fuel gas and oxidant gas;
A fuel cell that generates electricity by an electrochemical reaction between the fuel gas in the mixed gas and the oxidant gas when the mixed gas mixed by the mixing unit is supplied;
Heat insulation means for preventing reaction heat of the fuel cell from being transmitted to the mixing section,
Fuel cell system. The heat insulating means prevents reaction heat from being transmitted from the fuel cell to the mixing section so that the temperature of the fuel gas in the mixing section reaches a predetermined temperature at which the fuel gas does not ignite;
The fuel cell system according to claim 1. The mixing unit mixes the fuel gas and the oxidant gas so as to have a predetermined mixing ratio that does not cause combustion due to a reaction between the fuel gas and the oxidant gas in the mixed gas.
The fuel cell system according to claim 1 or 2. The predetermined mixing ratio is a mixing ratio at which combustion due to a reaction between the fuel gas and the oxidant gas in the mixed gas does not occur due to a high ratio of the fuel gas to the oxidant gas.
The mixing unit mixes the unreacted fuel gas separated from the off-gas of the fuel cell with the oxidant gas.
The fuel cell system according to claim 3.

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