JP4993346B2 - Fuel cell equipment - Google Patents

Description

  The present invention relates to a fuel cell facility, and more particularly to a fuel cell facility that uses a solid oxide fuel cell or the like as a battery body.

  One typical fuel cell is a solid oxide fuel cell (SOFC). In this fuel cell, normally, a fuel electrode layer is formed on one surface of a thin and brittle solid electrolyte layer made of a sintered body such as yttria stabilized zirconia (YSZ), and an air electrode layer is formed on the other surface. A laminated body having a structure is used as a single battery cell. Then, power is generated by flowing fuel gas on the fuel electrode side and oxidizing gas such as air on the air electrode side from the central part to the periphery with the unit cell sandwiched therebetween.

  Ni and YSZ cermet are used as the fuel electrode, and lanthanum strontium manganite (LSM) is used as the air electrode. Both are porous sintered bodies.

  Since this single battery cell has an electromotive force as low as 1 V or less, it is usually used by stacking a plurality of sheets in the thickness direction and connecting them in series. More specifically, the cell stack is configured by stacking interconnectors in the thickness direction while sandwiching the unit cells so that reaction spaces are formed on both sides of the unit cells. The cell stack is housed in a furnace and operated at a high temperature of 800-1000 ° C.

  The interconnector is a conductive plate that electrically connects battery cells in series and is a separator plate that separates fuel gas and oxidizing gas, and is required to have excellent electrical conductivity and heat resistance. From these viewpoints, Fe-Cr alloy, especially ferritic stainless steel with high heat resistance and comparatively low thermal expansion coefficient, is often used as the material of the interconnector, and both surfaces are adjacent to adjacent battery cells. A gas distribution groove for forming a reaction space is formed.

  In the operation of the fuel cell, after preheating the inside of the furnace to the operating temperature with a burner, hydrogen-rich fuel gas and oxidizing gas such as air are supplied to the center of the cell stack in the furnace. The fuel gas supplied into the cell stack circulates from the central portion to the periphery through a reaction space on the fuel electrode side formed on one surface side of the unit cell. Further, the oxidizing gas flows from the central part to the surroundings in the reaction space on the air electrode side formed on the other surface side of the single battery cell. As described above, power is generated in each single battery cell when both gases circulate from the central portion to the surroundings with each single battery cell interposed therebetween. The operating temperature is 800 to 1000 ° C. as described above.

  As the fuel gas, a hydrocarbon gas mainly composed of methane such as city gas is reformed to be hydrogen rich with water vapor, or the hydrocarbon gas is reformed to hydrogen rich by partial oxidation using air. Something is used. For this reason, regardless of which raw material gas is used, a reformer for reforming the hydrocarbon-based gas to be rich in hydrogen is provided on the gas inflow side of the cell stack. The reforming requires a high temperature of 700 ° C., for example, when using steam. For this, the reformer is equipped with a dedicated heating burner or is thermally combined with the cell stack.

  On the other hand, moisture-containing air such as air is usually used as the oxidizing gas. This air is also preheated to a temperature close to the operating temperature and supplied to the cell stack. For this preheating, a heat exchanger for preheating air with the exhaust gas from the cell stack is provided on the gas inflow side of the cell stack. Since an oxidizing gas supply system including a heat exchanger is required to have high high-temperature strength and high-temperature oxidation resistance, an Fe—Cr alloy represented by stainless steel such as SUS310S or SUS316L, or Ni—such as Inconel. It is composed of a Cr alloy.

  One of the serious problems in such a solid oxide fuel cell is chromium poisoning. This problem is a phenomenon of deterioration of battery performance over time due to chromium vapor generated on the air electrode side of the battery cell, and is caused by an interconnector in the cell stack. This problem will be described in detail below.

As described above, the interconnector of the cell stack is made of an Fe—Cr alloy such as ferritic stainless steel. In this case, since high-temperature air flows through the reaction space on the air electrode side of the battery cell, an oxide scale [mainly chromia (Cr ₂ O ₃ )] is formed on the surface of the interconnector on the air electrode side. This oxide scale has excellent heat resistance, protects the interconnector from high temperatures, has a relatively high electrical conductivity, and does not hinder the electrical connection of the battery cells. The high electrical conductivity of the oxide scale is one of the major reasons why Fe—Cr alloys are used for interconnectors.

However, chromium vapor composed of chromium compounds such as CrO ₃ and CrO ₂ (OH) ₂ is generated from chromia (Cr ₂ O ₃ ), which is the main component of the oxide scale. These chromium vapors [CrO ₃ (g), CrO ₂ (OH) ₂ (g)] are deposited as high-resistance SrCrO ₄ on the air electrode layer side, or chromia (at the interface between the electrolyte and the air electrode). By changing to Cr ₂ O ₃ ) and reducing the reaction field, the battery characteristics are gradually deteriorated. This deterioration in battery performance due to chromium vapor is chromium poisoning, which is one of the problems that must be solved when an Fe—Cr alloy is used for the interconnector.

  In order to solve this problem, coating various compounds on the surface of an interconnector made of an Fe—Cr alloy such as ferritic stainless steel is widely performed. If a dense coating layer is formed on the surface of the Fe—Cr alloy base material, generation of chromium vapor from the base material can be effectively suppressed.

As one of the coating techniques, for example, Patent Document 1 discloses that a dense layer of a perovskite complex oxide is formed on the surface of an Fe—Cr alloy base material. In addition, an Fe—Cr alloy (such as SUS430) that forms a coating layer of a spinel type complex oxide such as (Mn, Cr) ₃ O ₄ on the surface in an operating environment has also been developed. Furthermore, a countermeasure for coating the surface of the Fe—Cr alloy base material with a spinel type complex oxide not containing Cr such as (Mn, Co) ₃ O ₄ is also known. Furthermore, a measure for completely eliminating Cr from the interconnector has been developed in advance by the present applicant.

JP 2004-281105 A

  These measures prevent chromium poisoning caused by the interconnector. In particular, if Cr is completely eliminated from the interconnector, the interconnector should not cause chrome poisoning. However, in actual fuel cell operation, the phenomenon of chromium poisoning is not completely eliminated. In other words, it is a fact that the decrease in battery performance is suppressed by taking measures against chrome poisoning to the interconnector compared to the case where it is not applied, but the decrease is not completely prevented. is there.

  An object of the present invention is to provide a fuel cell facility that can suppress chromium poisoning in a solid oxide fuel cell as much as possible.

  In order to achieve the above object, it is considered to use pure Ni or Ni-based alloy containing no Cr as an interconnector material in a solid oxide fuel cell. In practice, however, these Ni-based metals are not used in interconnectors. This is because the oxide scale formed on the surface of the Ni base material has low electrical conductivity and lacks basic performance as an interconnector (cell voltage does not reach the rating). This oxide scale is mainly nickel oxide (NiO).

To solve this problem, the present applicant applied a specific spinel type complex oxide coating, more specifically, Co, Cu, Mn as metal elements on the base metal surface of the interconnector made of Ni-based metal not containing Cr. This was solved by forming a spinel complex oxide containing at least one of the above and Ni as a coating layer. According to this measure, since the base material does not contain Cr, there is no generation of chromia (Cr ₂ O ₃ ), and there is no danger of chromium poisoning. Moreover, unlike the perovskite complex oxide, the spinel complex oxide is not accompanied by a decrease in electrical conductivity.

  However, it has been found that even in a fuel cell facility using such an interconnector for a cell stack, if the operation is continued for a long time, the battery performance is likely to be deteriorated with time due to chromium poisoning. Therefore, the present inventor has sought the cause of chromium poisoning in addition to the interconnector, and has studied it from various angles. As a result, it has been found that an oxidizing gas supply system that supplies an oxidizing gas to the cell stack can also cause chromium poisoning.

That is, the oxidizing gas supply system supplies high-temperature water-containing air to the reaction space on the air electrode side of the battery cell in the cell stack. For preheating, a preheater for exchanging heat with the exhaust gas from the cell stack is provided in the middle of the system path. As described above, the oxidizing gas supply system including the preheater is composed of an Fe—Cr alloy or an Ni—Cr alloy in order to require high high temperature strength and high temperature oxidation resistance. For this reason, chromia (Cr ₂ O ₃ ) is formed in the downstream side of the preheater of the oxidizing gas supply system, particularly in the preheater, and chromium vapor generated from this reaches the reaction space on the air electrode side of the battery cell. By gradually depositing as high-resistance SrCrO ₄ or the like on the side of the air electrode layer, or by changing to chromia (Cr ₂ O ₃ ) at the interface between the electrolyte and the air electrode, the reaction field is gradually reduced. The characteristics will be reduced.

However, changing the oxidizing gas supply system including the preheater to a Ni-based metal not containing Cr is difficult to implement mainly from an economical viewpoint. Therefore, the present inventor considered that it is effective to separate and trap chromium vapor in the oxidizing gas at the most downstream side of the oxidizing gas supply system, and studied the method from various angles. As a result, chromium vapors such as CrO ₃ (g) and CrO ₂ (OH) ₂ (g), which are generated from chromia (Cr ₂ O ₃ ) and cause chromium poisoning, are negative by trapping electrons. It has been found that the polarity can be easily shown and trapping is possible by applying an electric field.

The production process of chromium vapor is shown in Chemical Formula 1. It is considered that the generation of CrO ₂ (OH) ₂ (g) is the main and the generation of CrO ₃ (g) is the subordinate.

  FIG. 6 shows one of confirmation experiments that these chromium vapors easily show negative polarity. An insulating plate 2 made of mica is sandwiched between insulating electrodes 3 between electrodes 1 and 1 made of austenitic stainless steel (SUS310S), and a high voltage is applied by a power source 4 at a high temperature corresponding to the operating temperature of the fuel cell. . Then, a yellow deposit 5 is generated on the negative electrode facing surface of the insulating plate 2 only when the spacer 3 exists on the negative electrode side of the insulating plate 2. This deposit 5 has been confirmed to be hexavalent chromium, and the chromium vapor generated from the electrode 1 on the negative electrode side has a negative polarity. Therefore, it is considered that the deposit 5 adhered to the negative electrode facing surface of the insulating plate 2. The reason why chromium vapor has a negative polarity is that thermoelectrons are generated at a high temperature such as 800 ° C. corresponding to the operating temperature of the fuel cell, and this is considered to be negatively ionized by adhering to the chromium vapor molecules. is there.

  The fuel cell equipment of the present invention has been completed on the basis of such knowledge, and is composed of a cell stack formed by stacking interconnectors with the fuel cell sandwiched therebetween, and a raw material gas and an oxidizing gas in the cell stack, respectively. Two types of gas supply systems to supply, a preheater provided in the oxidation gas supply system to preheat the oxidation gas by exchanging heat with the exhaust gas from the cell stack, and capture chromium vapor contained in the oxidation gas after preheating Therefore, it comprises a chromium trap provided in the oxidizing gas supply system downstream of the preheater.

  In the fuel cell facility of the present invention, the chromium vapor in the exhaust gas is captured at the downstream side of the preheater, preferably the most downstream, so that the vapor is prevented from flowing into the cell stack. By combining with the chromium poisoning countermeasure in the interconnector in the cell stack, it becomes possible to completely prevent the chromium poisoning which is a problem on the air electrode side of the battery cell.

The fuel cell includes a solid electrolyte type and a carbonated molten salt type. As the chromium trap, an electric field application type in which an oxidizing gas is circulated between a positive electrode and a negative electrode arranged to face each other is preferable. This is because chromium vapors such as CrO ₃ (g) and CrO ₂ (OH) ₂ (g) generated from chromia (Cr ₂ O ₃ ) tend to exhibit a negative polarity by trapping electrons. This is because when an oxidizing gas is circulated between the negative electrodes, it is attracted to and captured by the positive electrode side. It is possible to promote the negative polarity of chromium vapor by using a material that easily generates thermoelectrons for the negative electrode or by generating a corona discharge by applying a high voltage pulse voltage. Further, the means for attaching electrons and the means for capturing chromium vapor that has been made negative by the attachment of electrons can be configured separately. Furthermore, by making the positive electrode side gas-permeable to the back side, the chromium vapor trapped on the positive electrode side can be discharged from the gap to the outside to prevent the deposition of chromium vapor on the pole surface. it can.

  Electric field applied type chrome traps that make use of the fact that these chrome vapors tend to exhibit a negative polarity are simple in structure, effective, and very efficient. It can also be incorporated into the cell stack so as to be effective against the oxidizing gas flowing through the gas.

  The fuel cell facility of the present invention is a oxidant gas supply system for supplying an oxidant gas to a cell stack. A chrome trap is provided downstream of a preheater that preheats the oxidant gas by exchanging heat with exhaust gas from the cell stack. The chromium vapor contained in the oxidizing gas after preheating is trapped, and the flow into the cell stack is prevented. By preventing the inflow of chromium vapor from the oxidizing gas supply system to the cell stack, which has not been omitted in the past, chromium poisoning in the cell stack due to the chromium vapor can be prevented. A decrease in battery performance due to poisoning can be stably prevented over a long period of time.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a fuel cell facility showing an embodiment of the present invention, FIG. 2 is a block diagram of a cell stack used in the fuel cell facility, and FIG. 3 is a chromium trap used in the fuel cell facility. It is a block diagram of a container.

  As shown in FIG. 1, a fuel cell facility of the present invention includes a cell stack 10 that is a main body of a solid oxide fuel cell, and a reformer 20 provided in a source gas supply system that supplies a source gas to the cell stack 10. And a preheater 30 provided in the oxidizing gas supply system for supplying the oxidizing gas to the cell stack 10, and a chromium trap 40 provided in the oxidizing gas supply system together with the preheater 30.

  As shown in FIG. 2, the cell stack 10 is configured by laminating disk-like interconnectors 12 in the thickness direction while sandwiching disk-like single battery cells 11 therebetween. The unit cell 11 is a thin disk having a three-layer structure in which a fuel electrode layer 11b is stacked on one surface of a solid electrolyte layer 11a and an air electrode layer 11c is stacked on the other surface.

  The solid electrolyte layer 11a of the single battery cell 11 is made of, for example, YSZ and has a thickness of 5 to 30 μm. The fuel electrode layer 11b is made of, for example, cermet of Ni and YSZ, and has a thickness of 0.5 to 2 mm. The air electrode layer 11c is made of, for example, LSM and has a thickness of 20 to 50 μm.

  Two types of through-holes are provided in the center of the unit cell 11 in order to allow the fuel gas and the oxidizing gas to pass therethrough.

  The interconnector 12 is a metal disk having the same outer diameter as that of the single battery cell 11 and is made of Ni-based alloy or Fe—Ni alloy not containing pure Ni and Cr. At the center of the interconnector 12, fuel gas and oxidant gas through holes corresponding to the through holes of the unit cells 11 are provided. The thickness of the interconnector 12 is preferably 0.5 to 2.5 mm, particularly preferably 1.0 to 2.0 mm. If it is too thin, a temperature gradient is generated due to a decrease in thermal conductivity in the radial direction, and cell cracking due to thermal distortion or thermal stress of the interconnector occurs. On the other hand, if it is too thick, the material cost increases and the stack capacity increases.

  The interconnector 12 is used to electrically connect a plurality of stacked unit battery cells 11 in series and to form reaction spaces on both sides of the unit battery cell 11. It is the same structure except for things.

  The interconnector 12 except the ones at both ends, that is, the interconnector 12 sandwiched between the two unit cells 11, 11 penetrates the fuel gas through the center of the unit cell 11 on the surface facing the surface on the fuel electrode side. It has a gas distribution groove 12a for fuel gas that flows while being diffused from the hole to the outer periphery. Further, a gas distribution groove 12b for oxidizing gas is provided on the surface of the single battery cell 11 opposite to the surface on the air electrode side for allowing the oxidizing gas such as air to flow while diffusing from the central through hole to the outer peripheral portion. ing.

  One of the interconnectors 12 and 12 at both ends is in contact with the surface of the unit cell 11 on the fuel electrode side, on which the fuel gas is circulated while being diffused from the central through hole to the outer periphery. Gas distribution groove 12a is provided. The other is in contact with the surface of the unit cell 12 on the air electrode side, and the surface is provided with a gas distribution groove 12b for oxidizing gas through which the oxidizing gas flows while diffusing from the through hole in the central portion to the outer peripheral portion. Yes.

On both surfaces of each interconnector 12, a spinel-type composite oxide coating layer 12c represented by (Co, Ni) ₃ O ₄ , (Mn, Ni) ₃ O ₄ , (Cu, Ni) ₃ O _4, or the like is provided. Is formed. The coating layer 12c is formed by electrolytically or electrolessly plating Co, Mn, Cu or the like on the surface of the Ni-based metal that is the base material of the interconnector 12, and then holding the base material in a high-temperature oxidizing atmosphere. Is formed. The thickness of the coating layer 12c is 50 μm or less.

  In the interconnector 12 arranged between two adjacent unit cells 11, 11, the coating layer 12 c is necessary on both surfaces because it is necessary to electrically connect the unit cells 11, 11. In the interconnectors 12 and 12 at both ends where only one surface is opposed to the unit cell 11, it is only necessary to provide it on the opposing surfaces where the gas distribution grooves 12 a and 12 b are provided, and it is not always necessary to provide them on both surfaces.

  The cell stack 10 is configured by stacking a predetermined number of interconnectors 12, 12,... With the single battery cells 11 sandwiched therebetween, and fixing with a connecting rod or the like (not shown). The constructed cell stack 10 is accommodated in a furnace (not shown) and is equipped with a burner for preheating below.

  The reformer 20 mixes city gas, which is a raw material gas for fuel, with water vapor to form a hydrogen-rich raw material gas. The reformer 20 is equipped with a burner (not shown) for preheating. The reformer 20 is composed of an Fe—Cr alloy such as austenitic stainless steel (SUS310S) excellent in heat resistance, or a Ni—Cr alloy such as Inconel, together with a raw material gas supply system (gas pipe).

  The preheater 30 is a heat exchanger that heats the oxidizing gas, such as air, by exchanging heat with the high-temperature exhaust gas from the cell stack 10. The preheater 30 is made of an oxidation gas supply system (gas pipe) and an Fe—Cr alloy such as austenitic stainless steel (SUS310S) excellent in heat resistance, or an Ni—Cr alloy such as Inconel.

  The chromium trap 40 is provided on the downstream side of the preheater 30, particularly in the most downstream portion of the oxidizing gas supply system (immediately near the oxidizing gas inlet of the cell stack 10). As shown in FIG. 3, the chromium trap 40 includes a pair of electrode plates 41 and 42 arranged to face each other at a predetermined interval, a DC power source 43 that applies a high voltage to the electrode plates 41 and 42, a positive electrode And an insulating plate 44 disposed between the electrode plates 41 and 42 in contact with the surface of the electrode plate 41 on the side, and an oxidizing gas is interposed between the insulating plate 44 on the positive electrode side and the electrode plate 42 on the negative electrode side. It is configured to pass in one direction.

  The electrode plates 41 and 42 are made of, for example, a Ni-based alloy, a Fe alloy, or pure Ni that does not contain Cr. As a material of the insulating plate 44, ceramics such as alumina and magnesia are suitable.

  The function of the fuel cell facility configured as described above is as follows.

  The cell stack 10 and the reformer 20 are preheated by a burner while a predetermined amount of fuel gas and air as an oxidizing gas are passed through the cell stack 10. As the cell stack 10 is preheated, the preheated gas is sent to the preheater 30 to preheat the air. When the cell stack 10 and the reformer 20 reach a predetermined temperature, the power generation operation is started.

  In the power generation operation, the hydrogen-rich fuel gas obtained by the reformer 20 and the air preheated by the preheater 30 are supplied to the cell stack 10. In the cell stack 10, a hydrogen-rich fuel gas flows from the central part to the outer peripheral part between the fuel electrode 11 a of the single battery cell 11 and the interconnector 12 on the fuel electrode side, and the air electrode of the single battery cell 11. Air flows between the central part 11b and the outer electrode part between the air electrode side interconnector 12b. As a result, power is generated in each single battery cell 11. Each single battery cell 11 is connected in series by an interconnector 12.

  The operating temperature in the cell stack 10 is 800 ° C., for example. Therefore, in the preheater 30, air is preheated to a high temperature, for example, near 800 ° C., and supplied to the cell stack 10 through the oxidizing gas pipe.

Here, the interconnectors 12, 12... In the cell stack 10 are made of pure Ni, Ni-based alloy not containing Cr, or Fe—Ni alloy. Since these metals are excellent in heat resistance and have high electrical conductivity, they function as gas separators and electrical connection members between adjacent unit cells 11 and 11. In particular, each interconnector 12 has (Co, Ni) ₃ O ₄ , (Mn, Ni) ₃ O ₄ , (Cu, Ni) ₃ on the surface of the unit cell 11 on the fuel electrode side and on the air electrode side. A spinel-type composite oxide coating layer 12c containing at least one of Co, Cu, Mn, and Ni as a metal element, such as O ₄ , and preferably not containing Cr is formed.

  The characteristics of the coating layer 12c made of a spinel complex oxide containing at least one of Co, Cu, and Mn and Ni are as follows. First, for example, the surface of the base material can be easily formed by coating a metal composed of at least one of Co, Cu, and Mn by electrolytic plating, electroless plating, or the like, and heat-treating in an oxidizing atmosphere. . Secondly, according to electrolytic plating or electroless plating of metal, the layer thickness can be easily increased, and durability can be enhanced.

  Third, the spinel complex oxide exhibits the characteristics of a p-type semiconductor, and in particular, it becomes a spinel complex oxide of a transition metal having a plurality of valences. Therefore, the spinel complex oxide exhibits high electrical conductivity by a hopping conduction mechanism, and perovskite. Although it is difficult for ions to diffuse as compared with the type complex oxide, it exhibits much higher electrical conductivity than NiO.

  Fourth, since the spinel type complex oxide has a close-packed structure of oxygen and an extremely dense crystal structure in terms of density, the oxide ion (oxygen ion) compared to the perovskite type complex oxide. Ni ions and Co ions are difficult to diffuse. For this reason, the reactivity with a base material is low, and the production | generation of the Ni-type oxide scale in an interface is suppressed. In addition, since the oxide scale formed at this interface is a spinel oxide showing the characteristics of a p-type semiconductor, the electrical conductivity is better than that of NiO. For these reasons, the spinel complex oxide is applied to the coating layer of the interconnector and does not hinder the electrical connection of the single battery cell.

Fifth, the heat resistance of the coating layer is excellent, and the base material is protected from the harsh operating environment of the fuel cell. Sixth, since the base material does not contain Cr, chromia (Cr ₂ O ₃ ) is not generated at the interface between the base material and the coating layer on the air electrode side of the single battery cell, resulting in chromium poisoning. There is no danger.

  That is, when a spinel-type composite oxide coating layer is formed on the surface of the Fe—Cr alloy, the oxide scale formed at the interface causes problems such as chromium poisoning. On the other hand, when a spinel-type composite oxide coating layer is formed on the surface of pure Ni or Cr-free Ni-based alloy or Fe-Ni alloy, problems due to oxide scale formed at the interface (chromium poisoning, electrical No decrease in conductivity occurs.

  The Ni content in the Ni-based alloy is preferably 60% by weight or more. This is to ensure the heat resistance and corrosion resistance necessary for the fuel cell. Suitable elements other than Ni include Mo, Fe, Co, and Cu. A typical Ni-based alloy is permalloy. It should be noted that these base metals can contain a trace amount of Cr that does not cause chromium poisoning. Specifically, it is 1% by weight or less.

On the other hand, the air preheated to a high temperature by the preheater 30 is supplied to the cell stack 10 through the oxidizing gas pipe. Both the preheater 30 and the oxidizing gas pipe are made of austenitic stainless steel (SUS310S), and chromia (Cr ₂ O ₃ ) is generated on the inner surface, and chromium vapor such as CrO ₃ (g) and CrO ₂ (OH) ₂ (g) Arise. This chromium vapor captures thermoelectrons at a high temperature and exhibits a negative polarity. For this reason, when it passes between the electrode plates 41 and 42 in the downstream chromium capturer 40, it is pulled to the positive electrode plate 41 side and adheres to the surface of the insulating plate 44 provided in contact with the surface. . For this reason, chromium vapor in the air supplied to the cell stack 10 is removed in advance, and on the air electrode side of the single battery cell 11, not only chromium in the interconnector but also chromium caused by chromium vapor in the air. Poisoning is also prevented.

  Thus, the cell stack 10 avoids a decrease in battery performance over time and maintains stable battery performance for a long period of time.

  FIG. 5 is a graph showing the cell performance of the fuel cell facility of the present invention in comparison with other cell facilities.

  The vertical axis in FIG. 5 is the unit cell voltage in the cell stack, and the horizontal axis is the operation time. The relationship between the two is taken as a countermeasure against chromium poisoning in the interconnector in the cell stack and in the oxidizing gas supply system. Example 1 of the present invention provided with a chrome catcher, Conventional example 1 in which only a countermeasure against chromium poisoning in an interconnector is taken, Conventional example 2 in which neither a chromium poisoning countermeasure in an oxidizing gas supply system nor a chromium poisoning countermeasure in an interconnector is taken Show.

As a countermeasure against chromium poisoning in the interconnector, a coating layer of 5 μm thick made of (Co, Ni) ₃ O _{4 is} formed on both surfaces of a disk-shaped base material made of pure Ni having a thickness of 1.5 mm and a diameter of 120 mm. Formed. This coating layer is obtained by coating Co on both surfaces of a disk-shaped base material made of pure Ni by electroless plating and holding the disk-shaped base material in an oxidizing heating atmosphere at 800 ° C. for 48 hours. Formed. The interconnector that does not take measures against chromium poisoning was made of ferritic stainless steel (SUS430).

  The specifications of the chromium trap that is a countermeasure against chromium poisoning in the oxidizing gas supply system are as follows. The structure is as shown in FIG. 3, and an insulating plate made of alumina is arranged in contact with the high voltage electrode plate between the high voltage electrode plate made of Ni and the low voltage electrode plate made of Ni, and the insulating plate and the low voltage electrode plate are interposed between them. Ventilation space is formed. The thickness of the insulating plate made of alumina is 1 mm. The spacer for forming the ventilation space is a mica plate having a thickness of 1 mm, and is disposed on both sides between the insulating plate and the low voltage electrode plate. The gap amount is 1 mm, the width is 50 mm, and the depth is 50 mm. A ventilation space was formed and 400 V was applied.

  As the fuel gas, hydrogen gas that does not require reforming was used for the experiment, and the flow rate was set to 0.2 L / min (N). As oxidizing gas, air at normal temperature and humidity was preheated to 800 ° C. with a preheater and supplied to the cell stack via the chromium trap. The flow rate was 2 L / min (N).

  The cell stack is configured by stacking 80 single battery cells, and the operating conditions are the same among the fuel cell facilities.

  As can be seen from FIG. 5, in the case of the conventional example 2 where no chrome poisoning measures are taken for the interconnector in the cell stack and no chrome poisoning measures are taken for the oxidizing gas supply system, the rated cell voltage (cell at the start of operation) Voltage) A voltage drop of about 0.2 V was generated after 5000 hours of operation with respect to 0.8 V. In the case of the conventional example 1 in which measures against chromium poisoning were taken only for the interconnector, this voltage drop was improved to a little less than 0.1V, but the drop in cell voltage that seems to be caused by chromium poisoning was completely prevented. Not. On the other hand, in the case of the present invention in which measures against chromium poisoning were taken for both, the cell voltage did not decrease with time, and the rated cell voltage was maintained during the operation for 5000 hours. Because of the large amount of hexavalent chromium adhering to the surface of the insulating plate in the chromium trap, the effectiveness of the chromium poisoning countermeasure in the oxidizing gas supply system was confirmed.

  FIG. 4 is a block diagram showing another example of the chromium trap. The chromium trap 40 has a structure in which an oxidizing gas flow passage is formed between the electrode plates 41 and 42 by interposing an insulating spacer 45 between a pair of electrode plates 41 and 42 arranged opposite to each other. It has become. Also by using this chromium trap 40, chromium vapor in the oxidizing gas flowing into the cell stack 10 is removed in advance by being adsorbed by the positive electrode plate 41 of the chromium trap 40, and the cell stack 10. Intrusion is prevented.

It is a block diagram of the fuel cell equipment which shows one Embodiment of this invention. It is a block diagram of the cell stack currently used for the fuel cell equipment. It is a block diagram of the chromium trap used for the fuel cell equipment. It is a block diagram of another chromium catcher which can be used for the fuel cell equipment. It is the graph which showed the battery performance in the fuel cell equipment of the present invention compared with other battery equipment. It is explanatory drawing of the confirmation experiment that chromium vapor | steam shows a negative polarity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cell stack 11 Single battery cell 12 Interconnector 20 Reformer 30 Preheater 40 Chromium trap 41,42 Electrode plate 43 DC power supply 44 Insulation plate

Claims (3)

  A cell stack constructed by stacking interconnectors with fuel cells sandwiched between them, two types of gas supply systems that supply raw gas and oxidizing gas to the cell stack, and oxidation by exchanging heat with the exhaust gas from the cell stack A preheater provided in the oxidizing gas supply system to preheat the gas, and a chromium trap provided in the oxidizing gas supply system downstream of the preheater to capture chromium vapor contained in the preheated oxidizing gas; A fuel cell facility comprising:   2. The fuel cell equipment according to claim 1, wherein the chromium trap is of an electric field application type in which an oxidizing gas is circulated between a positive electrode and a negative electrode that are arranged to face each other.   A chromium trap provided in an oxidant gas flow path for supplying an oxidant gas to a fuel cell and configured to circulate the oxidant gas between a positive electrode and a negative electrode.

Images