JP5105701B2 - Power generator - Google Patents

Description

  The present invention relates to a power generation device, and more particularly to a power generation device with high power generation efficiency capable of operating a fuel cell without discharging flammable and toxic gases such as carbon monoxide and hydrogen, which are harmful components, to the outside air. is there.

  In recent years, various fuel cells in which a stack of fuel cells is housed in a housing have been proposed as next-generation energy.

  In conventional polymer fuel cells, hydrocarbon fuels such as city gas and propane gas are reformed by a reformer, and poisoning components of polymer fuel cells contained in the reformed fuel gas In order to remove carbon monoxide, fuel is supplied to the fuel cell via a carbon monoxide remover such as a carbon monoxide transformer or a selective oxidizer. Excess fuel gas and oxygen-containing gas supplied to the fuel cell are discharged to the outside air via the purification device (see, for example, Patent Document 1).

The reforming of hydrocarbon fuels is often an endothermic reaction, and as a heat source in the reformer, surplus fuel gas that has not been used in the fuel cells is burned in a purifier and the exothermic energy is used. ing. In that case, the surplus gas alone is insufficient as a heat source, and a separate heat source can be installed, for example, hydrocarbon fuel can be burned to advance the reforming reaction and purify the exhaust gas (see, for example, Patent Document 2). .
JP 2002-79058 A JP-T-2004-513487

Fuel in the solid oxide fuel cell is reformed by the reformer hydrocarbon fuels such as city gas and propane gas, also the carbon monoxide contained in the reformed gas unlike polymer fuel cell Since it can be used as a fuel like hydrogen gas, a carbon monoxide remover is not required. Since these reformed fuels are used to operate at a temperature of 800 ° C. to 1000 ° C., surplus fuel gas discharged from the fuel cells is burned, for example, carbon monoxide is carbon dioxide and hydrogen is water. to become a purification apparatus for solid oxide fuel cells has been considered to be unnecessary.

However, in the solid oxide fuel cell, in particular the operation of a high state of the fuel utilization rate, and by operating in a state of increased air utilization, to achieve a high overall efficiency in excess of polymer fuel cell In such a case, the amount of fuel gas that is not used for power generation is extremely reduced, and the oxygen concentration in the air is reduced. In such a state, even when the power generation temperature is as high as 800 to 1000 ° C., the combustion of the exhausted gas becomes incomplete and there is a fear of misfire. As a result, there is a risk of releasing harmful components such as carbon monoxide to the outside.

The present invention, in a case of operating a solid oxide fuel cell with high efficiency, and to provide a power generator capable of detoxifying the gas is discharged to the outside.

The power generation device of the present invention includes a plurality of solid oxide fuel cells configured to burn excess fuel gas not used for power generation in a housing, and disposed above the solid oxide fuel cells. And a reformer for generating fuel gas to be supplied to the solid oxide fuel cell, and disposed above the reformer to purify combustion exhaust gas generated by combustion of the surplus fuel gas And a purification device.

In the combustion exhaust gas of solid oxide fuel cells, carbon monoxide is caused by unburned fuel gas, incomplete combustion or misfire especially at high efficiency power generation, that is, at high fuel utilization rate, high air utilization rate. In the present invention, the present invention has a purification device that purifies the fuel exhaust gas discharged from the solid oxide fuel cell, so that the combustion exhaust gas can be made harmless and clean. It can be discharged as exhaust gas.

Furthermore, the power generator of the present invention has a heat exchanger in the housing, and the combustion exhaust gas enters the purification device before entering the heat exchanger. In such a power generation device, the purification device is present in the vicinity of the fuel cell, so that the reaction heat of the fuel cell and the heat from the high-temperature combustion exhaust gas can be used as a heat source of the purification device, and once the purification device. , And is discharged to the outside through the heat exchanger, so that it can be efficiently purified without losing all the combustion exhaust gas.

Moreover, the power generator of the present invention is characterized in that combustion exhaust gas is burned and purified in the purification device. In such a power generation device, purification using the heat source generated by the power generation of the fuel cell and the heat source when the gas from the fuel cell burns can be effectively performed without using a special catalyst.

Furthermore, the power generation device of the present invention is characterized in that combustion exhaust gas is burned with an oxidation catalyst in the purification device and purified. As a result, it is possible to efficiently purify the combustion exhaust gas even in a low oxygen concentration environment after power generation, and to suppress the generation of trace components such as NOx and SOx.

Further, the power generation device of the present invention is characterized in that an oxygen-containing gas is introduced into the purification device. Since oxygen is consumed in power generation, the oxygen concentration in the combustion exhaust gas after power generation decreases, and in the combustion reaction, oxygen may be deficient and incomplete combustion may occur, so oxygen-containing gas such as outside air is introduced into the purification device. By doing so, the combustion reaction can be promoted and the purification function can be enhanced.

Furthermore, the power generation device of the present invention is characterized in that a harmful component separation concentrator is provided upstream of the purification device. In such a power generator, harmful components can be separated and concentrated, and the concentrated harmful components can be purified efficiently. For example, when using an oxidation catalyst or a catalyst such as adsorption, contact between the harmful component and the catalyst is prevented. Therefore, effective purification can be achieved, and the required minimum amount of catalyst can be obtained.

Furthermore, the power generator of the present invention is characterized by having a harmful component concentration detector for detecting the concentration of harmful components in the combustion exhaust gas discharged from the purification device. Further, the power generation device of the present invention, when a predetermined amount or more harmful components is detected in harmful component concentration detector, characterized Rukoto by circulating flue gas into purifying apparatus again. Further, the power generation device of the present invention, when Ru is circulated flue gas to purifying apparatus again, characterized by circulating to the cleaning device by separating and concentrating the harmful components.

  In such a power generation device, it is possible to detect the concentration of harmful components discharged into the outside air and determine whether to repurify as necessary. That is, it can be surely rendered harmless until harmful components can be reduced below a predetermined amount. Further, the concentration of harmful components in the circulated combustion exhaust gas can be increased, that is, the concentration of combustible gas such as carbon monoxide and hydrogen can be increased. For example, an oxidation catalyst or a catalyst such as adsorption is used. Even in this case, the contact between the harmful component and the catalyst can be increased, and effective purification becomes possible.

In the power generation apparatus of the present invention, unburned hydrogen contained in the combustion exhaust gas after power generation of the solid oxide fuel cell, the carbon monoxide, using a high temperature heat source within the housing combustion, catalytic combustion, Also, the passage to the outside of the housing, catalytic combustion using a medium temperature heat source of several hundred degrees C or less inside the waste heat recovery section, adsorption removal of harmful components in the low temperature combustion exhaust gas just before being released to the outside air, etc. By using it, the combustion exhaust gas discharged to the outside air can be rendered harmless without requiring a separate heating source and without causing a decrease in power generation efficiency.

Figure 1 shows an example of a power generation apparatus, reference numeral 1 indicates a housing having a heat insulating structure. Inside the housing 1, a plurality of cell stacks 3 in which a plurality of solid oxide fuel cells 2 are arranged in a tandem arrangement, a combustion region 4 existing above the cell stack 3, and the combustion region 4 are provided. An oxygen-containing gas supply pipe 5 disposed between the cell stacks 3, a reformer 6 provided above the combustion region 4, and an upper part of the reformer provided above the reformer 6 It has the area | region 20 and the heat exchanger 7, and is comprised. A waste heat recovery unit 22 is connected to the upper portion of the housing 1 through an exhaust gas passage 21, and the final exhaust gas is discharged to the outside air through the exhaust port 23. The oxygen-containing gas supply pipe 5 is indicated by a broken line for easy understanding.

  The housing 1 includes a frame body 1a made of a heat-resistant metal and a heat insulating material 1b provided on the inner surface of the frame body 1a.

  For example, as shown in FIG. 2, the cell stack 3 is configured by arranging a plurality of fuel cells 2, and the three cell stacks 3 are arranged in three rows, and the two outermost cell stacks 3 arranged adjacent to each other. The fuel cells 2 are connected to each other by a conductive member 42, whereby a plurality of fuel cells 2 arranged in three rows are electrically connected in series. Each cell stack 3 has a fuel gas tank 11.

  More specifically, the fuel cell 2 has a flat shape, and a plurality of fuel gas passage holes 8 are formed through the fuel cell 2 in the axial direction. This fuel battery cell 2 has an oxygen-side electrode 2d made of a fuel-side electrode (inner electrode) 2b, a dense solid electrolyte 2c, and porous conductive ceramics on the outer surface of an elliptical columnar (flat) electrode support 2a. Are sequentially laminated, and an interconnector 2e is formed on the outer surface of the electrode support 2a opposite to the oxygen side electrode 2d.

  A current collecting member 9 is interposed between one fuel battery cell 2 and the other fuel battery cell 2, and an electrode support 2a of one fuel battery cell 2 is connected to the electrode connector 2a. The cell stack 3 is configured by being electrically connected to the oxygen side electrode 2d of the other fuel cell 2 through the current collecting member 9e. The current collecting member 9 has a plate shape and / or a felt shape made of a metal and / or a conductive inorganic material.

  The fuel cell 2 will be described in more detail. The electrode support 2a is a plate-like piece that is elongated in the vertical direction, and has both flat surfaces and both sides of a semicircular shape. A plurality of (six in FIG. 2) fuel gas passage holes 8 are formed in the electrode support 2a so as to penetrate the electrode support 2a in the vertical direction.

  The interconnector 2e is disposed on one surface of the electrode support 2a. The fuel side electrode 2b is disposed on the other surface and both side surfaces of the electrode support 2a, and both ends thereof are joined to both ends of the interconnector 2e. The solid electrolyte 2c is disposed so as to cover the entire fuel side electrode 2b, and both ends thereof are joined to both ends of the interconnector 2e. The oxygen-side electrode 2d is disposed on the main part of the solid electrolyte 2c, that is, on the portion covering the other surface of the electrode support 2a, and is positioned to face the interconnector 2e with the electrode support 2a interposed therebetween.

  A current collecting member 9 is disposed between adjacent cells 2 in the cell stack 3 to connect the interconnector 2e of one cell 2 and the oxygen side electrode 2d of the other cell 2. Current collecting members 42 are also arranged at both ends of the cell stack 3, that is, one side and the other side of the cell 2 located at the upper end and the lower end in FIG. Electric power extraction means (not shown) is connected to the current collecting members 42 located at both ends of the cell stack 3.

  More specifically about the cell 2, the electrode support 2a is gas permeable to allow the fuel gas to permeate to the fuel side electrode 2b, and is also conductive to collect current via the interconnector 2e. Can be formed from a porous conductive ceramic (or cermet) that satisfies such requirements.

  In order to produce the electrode support 2a by co-firing with the fuel side electrode 2b and / or the solid electrolyte 2c, it is preferable to form the electrode support 2a from an iron group metal component and a specific rare earth oxide. In order to provide the required gas permeability, it is preferable that the open porosity is in the range of 30% or more, in particular 35 to 50%, and the conductivity is also 300 S / cm or more, in particular 440 C / cm or more. Is preferred.

  In particular, the electrode support 2a is composed mainly of a rare earth element oxide composed of one or more selected from Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm and Pr, and Ni and / or NiO. Is desirable. By setting it as such a composition, it can approximate the thermal expansion coefficient of a solid electrolyte.

The fuel side electrode 2b can be formed of a porous conductive ceramic, for example, ZrO ₂ (referred to as stabilized zirconia) in which a rare earth element is dissolved and Ni and / or NiO.

The solid electrolyte 2c has a function as an electrolyte for bridging electrons between electrodes, and at the same time needs to have a gas barrier property in order to prevent leakage between the fuel gas and the oxygen-containing gas. Usually, it is formed from ZrO ₂ in which ₃ to 15 mol% of a rare earth element is dissolved.

The oxygen side electrode 2d can be formed of a conductive ceramic made of a so-called ABO ₃ type perovskite oxide. The oxygen side electrode 2d is required to have gas permeability, and the open porosity is preferably 20% or more, particularly preferably in the range of 30 to 50%.

Although the interconnector 2e can be formed from a conductive ceramic, it needs to have reduction resistance and oxidation resistance because it comes in contact with a fuel gas that may be hydrogen gas and an oxygen-containing gas that may be air. In addition, a lanthanum chromite perovskite oxide (LaCrO ₃ oxide) is preferably used. Interconnect motor 2e must be dense to prevent leakage of the oxygen-containing gas flowing outside of the fuel gas and the electrode support 2a through the fuel gas passage holes 8 formed in the electrode support 2a, It is desired to have a relative density of 93% or more, particularly 95% or more.

  The current collecting member 9 can be composed of a member having an appropriate shape formed from an elastic metal, alloy, or conductive ceramic, or a member obtained by adding a required surface treatment to a felt composed of metal fiber or alloy fiber. .

  And the lower end part of the some fuel cell 2 is being fixed to the fuel gas tank 11 as shown in FIG. The fuel gas tank 11 is connected to a fuel gas supply pipe 17 for supplying fuel gas into the fuel battery cell 2, and the fuel gas supply pipe 17 is connected to the reformer 6. The to-be-reformed gas supply pipe 19 for supplying the to-be-reformed gas is connected, and the to-be-reformed gas is supplied to the reformer 6 from the outside through the to-be-reformed gas supply pipe 19. The fuel gas is reformed by the reformer 6, and the fuel gas is supplied to the fuel gas tank 11 through the fuel gas supply pipe 17.

  Further, as shown in FIG. 1, the oxygen-containing gas supply pipe 5 inserted through the combustion region 4 has a tip portion located below the power generation region and located between the cell stacks 3. Excess oxygen-containing gas that has not been used for power generation is configured to naturally flow into the combustion region 4.

  The heat exchanger 7 is composed of an exhaust gas passage for deriving the combustion exhaust gas burned above the fuel battery cell 2 and an oxygen-containing gas passage provided along the exhaust gas passage, and is disposed so as to face each other. , Heat is exchanged in this part.

  In the fuel cell configured as described above, the oxygen-containing gas (for example, air) from the outside passes through the oxygen-containing gas passage of the heat exchanger 7 and passes through the oxygen-containing gas supply pipe 5 to the cell stack 3 of the power generation chamber. The gas to be reformed is supplied into the reformer 6 through the gas to be reformed gas supply pipe 19 and is reformed by the reformer 6. Then, a fuel gas (for example, hydrogen) is supplied into the fuel gas passage hole 8 of the fuel cell 2 through the fuel gas supply pipe 17 and the fuel gas tank 11 to generate power in the cell 2 in the power generation region.

  Excess fuel gas that has not been used for power generation is ejected into the combustion region 4 from the upper end of the fuel gas passage hole 8, and excess oxygen-containing gas that has not been used for power generation is introduced into the combustion region 4, The fuel gas is burned to generate combustion exhaust gas. This combustion exhaust gas is led out to the exhaust gas passage of the heat exchanger 7 through the combustion exhaust gas inlet 24 and is discharged from the upper end of the heat exchanger 7.

  Further, the combustion exhaust gas discharged from the housing 1 passes through the exhaust gas passage 21 and is introduced into the waste heat recovery unit 22 at the subsequent stage, and is used for, for example, production of hot water, desiccant type waste heat recovery, and the like. Is discharged from the discharge port 23 of the exhaust gas passage 21 to the outside air.

In the power generation device shown in FIG. 1, a purification device 51 is provided in the reformer upper region 20 in the housing 1. Thereby, the harmful component of the combustion exhaust gas discharged from the discharge port 23 to the outside air can be removed and purified. In the case of using direct combustion, it is considered that a temperature sufficient for combustion can be obtained in consideration of the temperature at the time of power generation. The purification device 51 includes a nichrome wire, a Pt heater, a ceramic heater, an igniter in the container. Combustion and removal of toxic carbon monoxide, flammable hydrogen, etc. by reacting surplus fuel gas with surplus oxygen-containing gas and burning again it can.

  The installation position is preferably in the combustion region 4 or the reformer upper region 20 in the vicinity of the reformer that is in the high temperature region and can transfer heat to the reforming unit that is endothermic. In particular, when installed in the combustion region 4, the temperature is high because it is close to the combustion section, and in the case of direct combustion, the installation position is more suitable. Sharing as a source is possible. Furthermore, since the purification device 51 as an ignition source is separated from the combustion region 4 and the reformer 6 in the reforming unit upper region 20, it is less likely to be exposed to the flame due to combustion in the upper part of the cell. Durability is improved.

  Moreover, it is preferable that the purification device is formed of a hollow container from the viewpoint of protecting the purification device 51 from a combustion flame at the upper part of the cell and a high temperature state during power generation. Inside the container, there are provided an exhaust gas introduction port, an exhaust port, a nichrome wire for an ignition source for direct combustion, a Pt heater, a ceramic heater, and the like.

  In addition, the ignition source for direct combustion may be in a state where the ignition source is always energized, but from the viewpoint of efficiency, at least at the time of high fuel utilization rate during high-efficiency power generation, high air utilization rate It is preferable to be in a state of being energized at times.

On the other hand, in catalytic combustion using an oxidation catalyst , an oxidation catalyst formed in the shape of a honeycomb or monolith is installed inside the container, or is filled with an oxidation catalyst in a shape such as a spherical shape or a pellet shape. Excess fuel gas and excess oxygen-containing gas can be burned again by a catalytic reaction to burn and remove toxic carbon monoxide, combustible hydrogen, and the like. The installation position is preferably in the combustion region 4 or the reformer upper region 20 in the vicinity of the reformer that is in the high temperature region and can transfer heat to the reformer that is endothermic. In particular, when it is installed in the combustion region 4, it is close to the combustion region, so that it can transfer thermal energy as a heat source at the start of the catalytic reaction.

  Further, in the reformer upper region 20, the purification device 51 is separated from the combustion region via the reformer, so that it is less exposed to the flame caused by the combustion in the upper portion of the cell, thereby improving the durability of the oxidation catalyst. To do. As the catalyst itself, a composite oxide catalyst in which a mixture of heavy metal oxides is molded or supported, a noble metal catalyst in which a noble metal is supported, or the like is used. Furthermore, the purification device 51 can also be provided at the combustion exhaust gas inlet 24 to the heat exchanger 7.

  By providing the purification device 51 in the housing 1 in this manner, the reaction heat of the fuel cell 2 and the heat from the high-temperature combustion exhaust gas can be used as a heat source for the purification device 51. In particular, in the case of FIG. 1 or when provided at the combustion exhaust gas inlet 24, since it once enters the purification device 51 and is discharged to the outside through the heat exchanger 7, the efficiency is improved without missing all the combustion exhaust gas. Can be well purified.

Further, a purification device can be provided in the exhaust gas passage inside the heat exchanger 7. Since all the combustion exhaust gas passes through this exhaust gas passage, it is possible to efficiently purify the combustion exhaust gas by providing a purification device in the exhaust gas passage, and use the sensible heat because the combustion exhaust gas is relatively hot. Direct combustion and combustion using a catalyst are possible.

  For example, in the case of direct combustion, it is configured by installing nichrome wires for ignition sources, Pt heaters, ceramic heaters, etc. in part or multiple places of the exhaust gas passage. The catalyst component may be supported directly inside the passage, but the passage may be filled with, for example, spherical catalyst particles. From the viewpoint of reducing pressure loss, a honeycomb or monolith-shaped catalyst is installed. May be. As the catalyst itself, a composite oxide catalyst or a catalyst supporting a noble metal is used.

Further , a purification device is installed in the combustion exhaust gas passage 21 or the waste heat recovery unit 22 when introducing the medium-temperature combustion exhaust gas of several hundred degrees or less after heat exchange in the heat exchanger 7 to the waste heat recovery unit 22 in the subsequent stage. Can be provided. In the purification at this site, all the combustion exhaust gas is aggregated (all the combustion exhaust gas passes), and since it is a combustion exhaust gas in the middle temperature range of several hundred degrees or less, direct combustion is not possible Although difficult, a combustion catalyst system using a catalyst is effective. In the combustion catalyst system, the catalyst component may be directly supported inside the passage, but the passage may be filled with, for example, spherical catalyst particles. From the viewpoint of reducing the pressure loss, the honeycomb or monolith shape may be used. The catalyst may be installed. As the catalyst itself, an oxide-based catalyst or a catalyst supporting a noble metal is used.

Further, a purification device can be provided at the outlet 23 at the rear stage of the waste heat recovery unit 22. At the discharge port 23, waste heat is also collected, and the temperature thereof is sufficiently lowered. Therefore, for example, a method using adsorption is effective. As the catalyst used for the adsorption, a physical adsorption such as activated carbon or zeolite, a chemical adsorption, or the like is used.

Furthermore, methods for direct combustion, catalytic combustion method, it is possible to clean of any one of the combustion exhaust gas in the use of the adsorption method, utilized by various combination of three schemes for more reliable purification It is desirable. For example, it is desirable to provide a purification device in the housing and to provide a purification device outside the housing, for example, in the combustion exhaust gas passage 21.

  Furthermore, in the present invention, as shown in FIG. 3 (a), by providing a separation concentrator for separating and concentrating harmful components upstream of the purification device, the concentration of harmful components is once increased and then sent to the purification device. Can be effectively purified, and at the same time, even when the concentration of harmful components is very low, the concentration of harmful components can be increased to make it more combustible (because harmful components are flammable gases). Since it is difficult to burn in a low concentration state, it is better to burn it at a higher concentration), and the necessary catalyst and ignition source of combustion can be reduced to the minimum necessary. As the separation concentrator, a known one such as a polymer or inorganic separation membrane or a PSA (pressure fluctuation adsorption) method can be used.

Also, in the operation at a high air utilization or high fuel utilization rate, as shown in FIG. 3 (b), since the state of lack of oxygen and fuel in such burned there, cause incomplete combustion There can be easy situations. Therefore, overall efficiency can be improved by installing an oxygen-containing gas introduction pipe containing oxygen such as air on the upstream side of the purification device.

  Further, in the present invention, as shown in FIG. 3 (c), a gas detector for detecting the concentration of harmful components can be provided on the downstream side of the purification device. Further, as shown in FIG. 3 (d), When harmful components are detected in a predetermined amount or more, it is possible to reliably purify the gas released into the outside air by providing a mechanism for circulating the combustion exhaust gas again upstream of the purification device.

  In the present invention, as shown in FIG. 3 (e), when circulating exhaust gas, the harmful components are separated and concentrated to reduce the load on the purification device and increase the concentration of the harmful components. Purification in the state becomes possible.

Cross-sectional view showing an example of the implementation form of power generation equipment. The top view which shows the cell stack of FIG. The figure which shows the various forms at the time of providing the purification apparatus outside a housing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Housing 2: Fuel cell 6: Reformer 7: Heat exchanger 21: Combustion exhaust gas passage 22: Waste heat recovery part 51 ... Purification device

Claims (9)

A plurality of solid oxide fuel cells configured to burn surplus fuel gas that has not been used for power generation is disposed in the housing, and the solid oxide fuel cells are disposed above the solid oxide fuel cells. a reformer for generating a fuel gas supplied to the fuel cell is disposed above the reformer, accommodating, and apparatus for removing the combustion exhaust gas produced by combustion of the excess fuel gas Rukoto a Te power generator according to claim. Has a heat exchanger in said housing, power generating apparatus according to claim 1, combustion exhaust gas, characterized that you enters the purifier before entering into the heat exchanger. The power generation apparatus according to claim 1 or 2, wherein the exhaust gas is purified by burning the combustion exhaust gas in the purification apparatus. The power generation apparatus according to claim 3, wherein combustion exhaust gas is burned with an oxidation catalyst in the purification apparatus and purified. The power generation device according to claim 3 or 4, wherein an oxygen-containing gas is introduced into the purification device. The power generator according to any one of claims 1 to 5, wherein a separation and concentrator for harmful components is provided upstream of the purification device. The power generator according to any one of claims 1 to 6, further comprising a harmful component concentration detector for detecting a concentration of harmful components in the combustion exhaust gas discharged from the purification device. The power generator according to claim 7, wherein when the harmful component concentration detector detects a harmful component of a predetermined amount or more, the flue gas is circulated through the purification device again. 9. The power generator according to claim 8, wherein when exhaust gas is circulated through the purification device again, harmful components are separated and concentrated and circulated to the purification device.

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