JP2005190995A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of maintaining a stable operation over a longer period of time, by eliminating impurities in the air supplied. <P>SOLUTION: This fuel cell system comprises a reforming portion 1, for producing hydrogen rich gas, a shift reaction portion 2 for producing hydrogen and carbon dioxide from carbon monoxide and water in the hydrogen rich gas, a hydrogen production device 20, having a carbon monoxide eliminating portion 3 for further reducing carbon monoxide in the hydrogen rich gas which has not been eliminated in the shift reaction portion 2; a fuel cell 4 for generating electric power with the hydrogen rich gas and oxidant gas supplied from the hydrogen production device 20, an air supplying portion 6 and 9 for supplying air to (1) the upstream of the reforming portion 1 with reference to the circulation direction of the fuel gas or (2) a least one part between the carbon monoxide eliminating portion 3 and the fuel cell 4, and dopant eliminating means 12 and 13 for eliminating the dopant gas contained in the air. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system. More specifically, in a fuel cell system having a hydrogen generator that generates a hydrogen-rich gas containing carbon monoxide by flowing fuel and water containing hydrocarbons through a catalyst, the fuel is distributed to the reforming section or anode in the hydrogen generator. The present invention relates to a fuel cell system from which impurity gas contained in air is removed.

Various types of fuel cell systems that generate power using hydrogen and oxygen in the air have been developed, and fuel cell systems used in homes and the like are generally configured as follows.
First, methane, ethane, propane, butane, city gas, LP gas, and other hydrocarbon gases (including a mixed gas of two or more types of hydrocarbons) are reformed in a reformer to generate a hydrogen rich gas.

  Examples of the reforming method include a steam reforming method in which reforming is performed using steam, a partial oxidation method in which reforming is performed using oxygen in the air, or an autothermal method in which both are combined.

  In the hydrogen-rich gas obtained by these reforming methods, carbon monoxide (hereinafter referred to as CO in the present specification) as a side reaction product is usually 8 to 15 depending on the performance of the reformer. % (Concentration based on volume, the same applies hereinafter). For example, when this CO is supplied to a polymer electrolyte fuel cell (hereinafter referred to as PEFC in this specification), the CO content in the hydrogen-rich gas supplied to the PEFC is limited to about 50 ppm. If exceeded, the battery performance will be significantly deteriorated. Therefore, it is necessary to remove CO as much as possible before introducing it into PEFC.

  For this reason, the hydrogen-rich gas obtained by the reforming method is introduced into the shift reaction section in order to remove this by-product CO. In the shift reaction part, CO is changed to carbon dioxide and hydrogen by a shift reaction (see the following formula (1)). Also for the hydrogen-rich gas obtained through the shift reaction part, CO is not completely removed, and a trace amount of CO is contained. For this reason, an oxidant gas such as air is added, and CO is reduced to 50 ppm or less, preferably 10 ppm or less by a CO selective oxidation reaction (see the following formula (2)) in the CO selective oxidation unit. The hydrogen-rich gas thus produced is supplied to the PEFC anode.

  However, in order to prepare for a case where the CO concentration increases, such as when the load changes, air breathing is often performed to further supply air to the anode and suppress CO poisoning of the anode electrode catalyst.

CO + H ₂ O → CO ₂ + H ₂ (1)
CO + 1 / 2O ₂ → CO ₂ (2)
Moreover, in a domestic fuel cell, in order to improve efficiency, it is desirable to stop the device when the amount of power consumption is small. At the time of such a stop, there is a safety problem if a flammable residual gas such as a hydrogen rich gas remains in the fuel cell system. Therefore, it is necessary to purge the residual gas with a nonflammable gas. However, since it is difficult to permanently install an N ₂ cylinder or the like in a household fuel cell, after purging residual gas with water vapor in the hydrogen generator and the anode flow path, air is used in a temperature range where water vapor does not condense. A method of purging water vapor has been proposed.

  As described above, in the fuel cell system, there are various places for supplying air into the fuel cell system. Among them, when impurities such as an organic solvent are contained in the air sent to the cathode of the PEFC, Since the organic solvent is not decomposed by the cathode electrode catalyst, the ability to adsorb oxygen to the cathode electrode is hindered, and there is a problem in that the battery characteristics and lifetime are reduced. In order to solve this problem, a catalytic combustor that removes an organic solvent such as kerosene before supplying air to the cathode has been proposed (for example, see Patent Document 1).

Further, as described above, air as an oxidant gas is supplied to the CO selective oxidation reaction unit. Organic substances such as HCHO contained in the air, or NOx and SOx poison the CO selective oxidation catalyst, and CO selection is performed. In order to solve the problem that the anode is poisoned by CO due to the deterioration of the characteristics of the oxidation catalyst, a CO remover for removing impurities in the air for CO selective oxidation reaction and a fuel cell system using the same are proposed. (For example, refer to Patent Document 2).
JP 2000-277139 A JP 2000-327305 A

However, in addition to the fuel cell system described in the above patent document, impurities contained in the air supplied into the fuel cell system may cause a problem for the fuel cell system. For example, the air for anode air breathing is mentioned.

  The supply amount of the anode air breathing air is small compared to the air supplied to the cathode of the fuel cell. For example, in the case of a 1 kW fuel cell, the cathode air amount is 65 Nl / min (hereinafter referred to as 0 ° C., 0.1 MPa equivalent value). In contrast, anode air breathing air is in the order of 0.3 Nl / min.

  Examples of impurities contained in the air include inorganic gases such as sulfur oxides, hydrogen sulfide, nitrogen oxides, and ammonia, and organic gases such as amines, fatty acids, aromatic compounds, and aldehydes. The concentration of gas in the atmosphere is extremely small, from several tens of ppm to several ppb.

  However, when there is a material that irreversibly deteriorates the catalyst, such as a sulfur compound among the impurities contained in the air, that is, a so-called permanent poisonous substance, for example, the air supply amount is small and the concentration contained in the air is extremely high. Even if it is small, when it is exposed to a long period of time such as tens of thousands of hours, the active site of the catalyst is covered and finally the catalytic properties are deteriorated.

  Here, when considering permanent poisoning to the noble metal catalyst, it is said that if the permanent poisoning substance covers about 1 to ½ of several tenths of the exposed surface of the noble metal, the poisoning is remarkable. In a 1 kW class fuel cell, the precious metals of Pt and Ru used in the anode catalyst of the fuel cell are about 0.02 mol each, and when air containing 0.5 ppm hydrogen sulfide is sent as air breathing at 0.3 Nl / min, It is thought that the amount of poisonous substances that affect the catalyst accumulates in thousands to tens of thousands of hours.

  Here, the poisoning mechanism of the electrode catalyst of the anode of the fuel cell will be described.

For example, sulfur oxide and hydrogen sulfide among sulfur compounds are at the following standard potential (vs. SHE (Standard Hydrogen Electrode)), and hydrogen sulfide is considered to be adsorbed on metal as S ²⁻ and poisoned.

Since the anode potential is 0 V, SO ₂ becomes SO ₄ ^{2− at the} anode, but the influence is small because the polymer electrolyte is a sulfonate. However, in the case of H ₂ S, since it is stable at 0 V, the oxidation characteristics of hydrogen are deteriorated.

In the case of anodic hydrogen sulfide as described above has a greater effect on catalyst activity reduction than SO ₂ , but sulfur oxides are easily hydrogen sulfide in a reducing atmosphere where hydrogen is present on the noble metal catalyst. Therefore, depending on the catalyst type and gas atmosphere, the influence of sulfur oxides may be equal to that of hydrogen sulfide. By the way, because the Japanese environmental standard for sulfur oxide concentration is 0.04 ppm, in the long-term, fuel cells installed near roads with heavy traffic may affect the catalyst characteristics due to sulfur oxides. There is sex.

  In addition to hydrogen sulfide, among substances contained in the air breathing air, formaldehyde is cited as a substance that poisons the anode of the fuel cell. As shown below, since the standard potential is different in the anode, it is presumed that formaldehyde is less oxidized and more likely to be a catalyst poison compared to CO.

  In addition, since aldehydes other than formaldehyde are more stable than formaldehyde, they are less likely to be oxidized.

  Furthermore, the CO selective oxidation catalyst is relatively easy to increase the amount of the catalyst, but the anode catalyst increases the amount of the catalyst, so that the diffusibility of the gas in the fuel cell decreases and flooding easily occurs. Another problem is that it is difficult to mitigate the effects of catalyst poisoning by increasing the amount of catalyst.

  In addition to the above-mentioned hydrogen sulfide and formaldehyde, flame retardant and volatile organic compounds may be mentioned as substances that poison the anode of the fuel cell. Depending on the location where the fuel cell system is installed, there are many cases where such a flame-retardant and volatile organic compound is present in the air. Toluene or the like, which is a volatile organic substance contained in paints, is flame retardant and hardly oxidatively decomposes at 200 ° C. or less even when a noble metal catalyst is used. Therefore, at a temperature (70 to 80 ° C.) at which the anode electrode catalyst operates. It remains on the catalyst and acts as a poison. The regulation standard of toluene in Japan's Odor Control Law is 10 ppm in Type 1 areas, and the effect is great in places where the odor of paint is always floating. Therefore, in an environment where flame retardant organic substances (including fatty acids) are always present, the organic substances cause catalyst poisoning.

  In addition to the above impurities, examples of substances that poison the anode of the fuel cell include basic compounds such as ammonia and amines. This is because the basic compound neutralizes the polymer electric reforming membrane and the cell performance of the fuel cell is lowered.

  Next, residual gas purge air or autothermal reaction air can be cited as an air supply that may cause problems in the fuel cell system. These are air supplied to the reformer that generates the reformed gas. These air also contain the above impurities, and the supply amount is 100 Nl / times, 8 Nl / min, which is larger than the anode air breathing air. Therefore, it goes without saying that the impurities contained in a minute amount in the air cause deterioration of the reforming catalyst during long-term operation. The deterioration mechanism due to the air supplied to the reforming catalyst will be described below.

  When air is sent from the inlet of the reformer, the Ru catalyst that is the reforming catalyst is most significantly affected. That is, when the reforming reaction is performed in a state where a sulfur compound is present at the active site of the catalyst, the deposition of carbon in the fuel is accelerated on the catalyst, and the conversion rate of the fuel into hydrogen is reduced.

In addition, since noble metal catalysts such as Pt / CeZrO _x and Pt / TiO ₂ are often used downstream of the reformer, in the shift reaction section and in the CO selective oxidation section, sulfidation that has passed through the reformer. Hydrogen poisons CeZrO _x and TiO ₂ which are noble metal catalyst supports in the shift reaction section and the CO selective oxidizer, lowers the water activation ability, and deteriorates the catalyst characteristics.

  Specifically, when 300 g of a 2 wt% Ru / alumina catalyst is used as the reforming catalyst, the Ru amount is 0.06 mol, and 100 Nl of air containing 0.5 ppm of hydrogen sulfide is sent in one purge operation. It is considered that an amount of poisonous substances that affect the catalyst characteristics is accumulated by purging operations of several hundred to several thousand times. If the activation is stopped every day, the activation is stopped 3650 times in 10 years, so this effect cannot be ignored for long-term use.

Further, when 300 g of 1 wt% Pt-1 wt% Rh / ZrO ₂ catalyst is used as the reforming catalyst, when air containing 0.5 ppm of hydrogen sulfide is sent from the reformer at 8 Nl / min, several hundred to several It is thought that an amount of poisoning substance that affects the catalytic characteristics of the reforming catalyst accumulates in 1000 hours. That is, in the case of autothermal reaction air, the amount of supplied air is large, and even a very small amount of impurities is likely to be affected in a short period due to accumulation.

  The catalyst poisoning with hydrogen sulfide has been described above. In the case of hydrogen sulfide, the concentration in the air can be 0.05 to 10 ppm in a volcanic area or a hot spring area. In addition, since the concentration can be high near the septic tank, it is assumed that the deterioration of the catalyst is further accelerated.

  In view of the above conventional problems, an object of the present invention is to provide a fuel cell system capable of maintaining stable operation for a longer period of time by removing impurities in the supplied air. .

  In order to achieve the above object, the first aspect of the present invention provides a reforming unit that generates a hydrogen-rich gas containing carbon monoxide from a fuel containing hydrocarbon and water, and carbon monoxide and water in the hydrogen-rich gas. A hydrogen generator having a shift reaction unit for generating hydrogen and carbon dioxide from the carbon, and a carbon monoxide removal unit for further reducing carbon monoxide in the hydrogen-rich gas that has not been removed in the shift reaction unit; A fuel cell that generates power using the hydrogen-rich gas and oxidant gas supplied from the hydrogen generator, and (1) upstream of the reforming unit, or (2) the monoxide, based on the flow direction of the fuel A fuel cell system, comprising: an air supply unit that supplies air to at least one location between a carbon removal unit and the fuel cell; and an impurity removal unit that removes impurity gas contained in the air. .

  In addition, the second aspect of the present invention includes an air supply unit that supplies air upstream of the reforming unit, and an impurity removal unit that removes sulfur compounds from the air, based on the flow direction of the fuel. The fuel cell system of the first invention.

  In addition, the third aspect of the present invention includes an air supply unit that supplies air between the carbon monoxide removal unit and the fuel cell, and ammonia, amine, fatty acid, hydrogen sulfide, and aldehyde, based on the flow direction of the fuel. And a means for removing impurities from the air.

  According to a fourth aspect of the present invention, the reforming section is a reforming section that generates a hydrogen-rich gas containing carbon monoxide from a fuel containing hydrocarbon, water, and air. It is.

  The fifth aspect of the present invention is the fuel cell system according to the first aspect of the present invention, wherein the impurity removing means has a hydrogen sulfide adsorbent or absorbent.

  The sixth aspect of the present invention is the fuel cell system according to the first aspect of the present invention, wherein the impurity removing means has a sulfur oxide adsorbent or absorbent.

  The seventh aspect of the present invention is the fuel cell system according to the first aspect of the present invention, wherein the impurity removing means has a catalytic combustion section.

  According to an eighth aspect of the present invention, based on the air flow direction, the impurity removing means further includes a catalytic combustion section upstream of the sulfur oxide adsorbent or absorbent. This is a fuel cell system.

  According to a ninth aspect of the present invention, the catalytic combustion section is disposed at a position where heat can be exchanged with the hydrogen generator, or at a position where heat can be exchanged with the combustion exhaust gas used for heating the hydrogen generator. It is the fuel cell system of 7th this invention.

  Further, the tenth aspect of the present invention is that the sulfur oxide adsorbent or absorbent can exchange heat with the hydrogen generator, or with the combustion exhaust gas used to heat the hydrogen generator. It is a fuel cell system of the 6th present invention arranged at a position.

  In an eleventh aspect of the present invention, the catalytic combustion section also serves as an adsorbent or absorbent for the sulfur oxide, and has a catalyst containing a noble metal and an alkaline earth metal. It is the fuel cell system of the 8th aspect of this invention arrange | positioned in the position which can be exchanged, or the position which can be heat-exchanged with the combustion exhaust gas used for the heating of the said hydrogen generator.

  According to the present invention, it is possible to provide a fuel cell system capable of maintaining stable operation for a longer period of time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. As shown in FIG. 1, the fuel cell system according to Embodiment 1 includes a hydrogen generator 20 that generates a hydrogen-rich gas. The hydrogen generator 20 includes a reforming unit 1 filled with a Ru / alumina catalyst that generates a hydrogen-rich gas containing carbon monoxide from a fuel containing hydrocarbon and water. The hydrogen generator 20 is provided with a shift reaction section 2 filled with a Pt / CeZrOx catalyst, which is an oxidation-resistant shift reaction catalyst, on the downstream side of the reforming section 1 with reference to the fuel flow direction. In the shift reaction unit 2, CO generated as a by-product in the reforming unit 1 is reduced. Further, the hydrogen generator 20 includes a CO selective oxidation reaction unit (carbon monoxide removal unit) 3 filled with a Ru / alumina catalyst that is a selective oxidation reaction catalyst on the downstream side of the shift reaction unit 2. The CO selective oxidation reaction unit 3 further reduces CO that could not be removed by the shift reaction unit 2.

  Further, a PEFC (solid polymer fuel cell) 4 which is an example of the fuel cell of the present invention is installed on the downstream side of the CO selective oxidation reaction unit 3 to generate power using a hydrogen rich gas with reduced CO as an anode gas. ing. Examples of the fuel cell anode catalyst include a Pt—Ru / C catalyst. In addition, the fuel cell system of the first embodiment includes a cathode air supply unit 10 for supplying air from which impurities have been removed to the cathode side of the PEFC 4.

  Further, in the gas flow path from the reforming unit 1 to the PEFC 4, upstream of the reforming unit 1 is air for purging residual gas in the fuel cell system when the fuel cell system is stopped, or the fuel cell system A reforming air supply unit 6 is provided for supplying air for performing an autothermal reaction during operation. A CO selective oxidation air supply unit 8 for supplying air to the CO selective oxidation reaction unit 3 is connected to a gas flow path between the shift reaction unit 2 and the CO selective oxidation reaction unit 3. An anode air breathing air supply unit 9 is connected to the gas flow path between the CO selective oxidation reaction unit 3 and the PEFC 4.

  The fuel cell system of Embodiment 1 removes hydrogen sulfide contained in the air supplied to the reforming air supply unit 6, the CO selective oxidation air supply unit 8, and the anode air breathing air supply unit 9. The hydrogen sulfide absorption part 5 for carrying out is provided. On the downstream side of the hydrogen sulfide absorption unit 5, a heat exchange unit 11 for heating the air is installed in contact with the CO selective oxidation reaction unit 3 so as to be able to exchange heat with the air flow direction as a reference. A catalytic combustion section 12 having a Pt / alumina catalyst is disposed downstream of the heat exchange section 11 so as to be in contact with the shift reaction section 2 so as to be able to exchange heat. Further, on the downstream side of the catalytic combustion unit 12, a sulfur oxide absorption unit 13 having calcium oxide is installed so as to be able to exchange heat with the shift reaction unit 2. Air is supplied from the sulfur oxide absorbing unit 13 to the reforming air supply unit 6, the CO selective oxidation air supply unit 8, and the anode air breathing air supply unit 9. Further, a valve 7 is installed between the reforming air supply unit 6 and the sulfur oxide absorption unit 13.

  The operation method of the fuel cell system in the first embodiment having the above configuration (the first operation method of the fuel cell system of the present invention) will be described below.

  In FIG. 1, fuel that has passed through an adsorbent that adsorbs and removes sulfur components in the fuel is mixed with water, heated, and introduced into the reforming unit 1. The temperature of the steam reforming catalyst also depends on the type of fuel. When the fuel is city gas, the temperature immediately after the steam reforming catalyst outlet is maintained at about 650 ° C. The hydrogen-rich gas generated in the reforming unit 1 passes through the shift reaction unit 2 and the CO selective oxidation reaction unit 3. Thereby, CO byproduced in the reforming unit 1 is reduced. This hydrogen rich gas is supplied to PEFC 4 as an anode gas. City gas is natural gas mainly composed of methane.

  On the other hand, the air passes through the hydrogen sulfide absorption part 5 and is then heated by the heat exchange part 11 in contact with the CO selective oxidation reaction part 3.

  Next, after passing through the catalytic combustion section 12 maintained at 250 ° C. during steady operation, it passes through the sulfur oxide absorbing section 13 maintained at 300 ° C. The catalytic combustion unit 12 and the sulfur oxide absorption unit 13 are in contact with the shift reaction unit 2 and are heated. Even without the hydrogen sulfide absorbing portion 5, hydrogen sulfide is oxidized to sulfur oxide on the Pt / alumina catalyst and absorbed by the sulfur oxide absorbing portion 13. However, since some of the hydrogen sulfide remains on the Pt / alumina, it is desirable to remove it in advance by the hydrogen sulfide absorber 5.

  Next, the air that has passed through the sulfur oxide absorbing section 13 is sent to the CO selective oxidation reaction section 3 and the anode electrode of the PEFC 4 through the CO selective oxidation air supply section 8 and the anode air breathing air supply section 9, respectively. For example, the supply amounts here are 0.5 Nl / min and 0.3 Nl / min, respectively. The air that has passed through the sulfur oxide absorbing unit 13 may be supplied to the cathode air supply unit 10 and used as cathode air.

  Further, since it is dangerous if flammable gas such as hydrogen or city gas remains in the system when the fuel cell is stopped, the inside of the system needs to be purged with air. In the first embodiment, the valve 7 is opened after the apparatus is cooled to a temperature at which Ru of the steam reforming catalyst does not oxidize when stopped.

  The air that has passed through the sulfur oxide absorbing section 13 is supplied to the reforming section 1 through the reforming air supply section 6, and is sequentially replaced with air to the shift reaction section 2, the CO selective oxidation reaction section 3, and the PEFC 4. . The amount of air to be replaced here is, for example, 10 Nl / min for 10 minutes.

  As the sulfur oxide adsorbent and absorbent of the sulfur oxide absorber 13 described above, alkaline earth metal oxides, transition metal oxides such as Mn, Co, Fe, Cu and Zr, and rare earth metal oxides such as Ce It is desirable to use a product. Depending on the absorbent, it is desirable to use it by heating. For example, in the case of CaO, sulfur oxides are absorbed by the mechanism represented by the following formulas (3) and (4) at 300-600 ° C.

2SO ₂ + CaO → 2CaSO ₃ (3)
2CaSO ₃ + SO ₂ → 2CaSO ₄ + 1 / 2S ₂ (4)
Further, as the sulfur oxide absorbent, alkaline component-impregnated activated carbon, zeolite, or the like may be used.

  Moreover, as a hydrogen sulfide adsorbent of the hydrogen sulfide absorption part 5 mentioned above, zeolite, such as MS4A, an alkaline component impregnated activated carbon, etc. are mentioned.

  Further, examples of the catalyst for burning the organic compound in the catalyst combustion unit 12 include Pt / alumina. Furthermore, it is desirable to use a Pt—Rh catalyst having sulfur poisoning resistance. By using the combustion catalyst having sulfur poisoning resistance and high oxidation activity, hydrogen sulfide can be converted into sulfur oxide, so that the hydrogen sulfide absorbing portion 5 can be omitted. In addition, from the viewpoint of maintenance-free, it is desirable to burn the organic compound by catalytic combustion, but it may be adsorbed and removed by an activated carbon filter or the like.

The second operation method is an operation method in which hydrogen is generated by a so-called autothermal reaction during the operation of the fuel cell system according to the first embodiment. Note that a Pt—Rh / ZrO ₂ catalyst is used as the catalyst of the reforming unit 1.

  During the operation of the fuel cell system according to the first embodiment, air is supplied from the reforming air supply unit 6. As a result, the hydrocarbon fuel undergoes an oxidation reaction. Since the hydrocarbon oxidation reaction becomes an exothermic reaction, it becomes a so-called autothermal reaction, and the steam reforming reaction, which is an endothermic reaction, is promoted. Here, the supply amount of air is, for example, 8 Nl / min. Note that the second operation method is effective when performed when the fuel cell system is started, because the startup time of the fuel cell system is shortened.

  In the first embodiment, the air supplied to the reforming air supply unit 6 is configured to pass through the hydrogen sulfide absorption unit 5, the catalytic combustion unit 12, and the sulfur oxide absorption unit 13. However, the air supplied to the reforming air supply unit 6 may be configured to pass through the hydrogen sulfide absorption unit 5 and the sulfur oxide absorption unit 13 without passing through the catalyst combustion unit 12. Thereby, the sulfur compound can be removed from the air supplied to the reforming unit 1.

(Embodiment 2)
FIG. 2 is an explanatory diagram showing a schematic configuration of the fuel cell system according to Embodiment 2 of the present invention. As shown in FIG. 2, the fuel cell system according to the second embodiment is the same as the first embodiment except that the catalytic combustion unit 14 has a sulfur oxide absorption function. Therefore, in FIG. 2, the same or corresponding parts as in FIG. 1 are denoted by the same reference numerals, detailed description is omitted, and different points will be mainly described.

  The catalyst combustion unit 14 of the fuel cell system of Embodiment 2 is a pellet catalyst in which barium oxide and platinum are supported on alumina. The catalytic combustion unit 14 corresponds to the catalytic combustion unit 12 and the sulfur oxide absorption unit 13 in the first embodiment. On the heated noble metal, sulfur dioxide and hydrogen sulfide are oxidized to sulfur trioxide and absorbed by barium oxide existing in the vicinity of the noble metal. Here, barium oxide is taken as an example, but other alkaline earth metal oxides such as calcium oxide may be used.

  Further, the noble metal catalyst can combust organic substances such as toluene and sulfur compounds at a relatively low temperature. Thus, the organic compound, sulfur oxide, and hydrogen sulfide can be effectively removed.

  The carbon monoxide removal unit of the present invention corresponds to the CO selective oxidation reaction unit 3 in the first and second embodiments. However, carbon monoxide may be removed by a methanation reaction instead of a CO selective oxidation reaction. Further, CO may be reduced by using a methanation reaction and a CO selective oxidation reaction together. In short, it is only necessary to further reduce carbon monoxide in the hydrogen-rich gas supplied from the shift reaction section. When only the methanation reaction is used as the carbon monoxide removal unit, it is not necessary to provide the CO selective oxidation air supply unit.

  Further, the impurity removal unit of the present invention corresponds to the hydrogen sulfide absorption unit 5, the heat exchange unit 11, the catalytic combustion unit 12, and the sulfur oxide absorption unit 13 in the first embodiment, and absorbs hydrogen sulfide in the second embodiment. Although it corresponds to the part 5, the heat exchange part 11, and the catalyst combustion part 14, not only this structure but the hydrogen sulfide absorption part 5 does not need to be installed as mentioned above. However, since some of the hydrogen sulfide remains on the Pt / alumina of the catalytic combustion unit 12, it is desirable to remove in advance by the hydrogen sulfide absorption unit 5.

  The air supply unit provided upstream of the reforming unit of the present invention corresponds to the reforming air supply unit 6 of the first and second embodiments. The air supply unit provided between the carbon monoxide removal unit and the fuel cell of the present invention corresponds to the air supply unit 9 for anode air breathing according to the first and second embodiments. In the first embodiment, impurities of all air supplied from the reforming air supply unit 6 and the anode air breathing air supply unit 9 are removed, but the air supplied from any one place is removed. Impurities may be removed. However, in order to perform a stable operation for a longer time, it is more preferable to remove all impurities from the supplied air.

  Further, the catalytic combustion unit 12 and the sulfur oxide absorption unit 13 of the first embodiment are installed in contact with the shift reaction unit 2 so as to be capable of exchanging heat. It may be arranged so as to be able to exchange heat with the combustion exhaust gas used for heating, and may be placed in contact with the CO selective oxidation reaction unit 3 as well as the shift reaction unit 2. It is only necessary to heat the sulfur oxide absorption part to a temperature suitable for combustion and to a temperature suitable for absorbing or adsorbing sulfur oxide. The same applies to the catalytic combustion unit 14 of the second embodiment.

  Hereinafter, the fuel cell system and the operation method thereof according to the present invention will be described more specifically based on examples.

(Example 1)
In Example 1, a catalyst layer electrolyte assembly (hereinafter referred to as MEA) was prepared, and gas and air were circulated through this MEA to test the influence of impurities in the air.

  First, an MEA creation method will be described below.

Water and a perfluorosulfonic acid ionomer ethanol solution (Flemion: 9 wt% perfluorosulfonic acid ionomer) manufactured by Asahi Glass were added to the Pt / C catalyst to prepare a catalyst ink. In addition, it prepared so that the weight ratio of Flemion and carbon black might be set to 1. This catalyst ink was applied to carbon paper by a doctor blade method so as to be Pt 0.3 mg / cm ^2, and dried at 60 ° C. to prepare a cathode side gas diffusion electrode layer.

On the other hand, the anode side gas diffusion electrode layer was prepared by the same method so that Pt was 0.3 mg / cm ² with 30 wt% Pt-24 wt% Ru / C.

  A Nafion 112 membrane (registered trademark, manufactured by Dupont) was sandwiched between the two gas diffusion electrode layers thus prepared, and hot-pressed at 130 ° C. to prepare a catalyst layer electrolyte assembly (MEA).

The produced MEA was operated using air and hydrogen at an oxygen utilization rate of 40%, a hydrogen utilization rate of 70%, a cell temperature of 75 ° C., a cathode dew point of 65 ° C. and an anode dew point of 70 ° C. with an output current of 0.2 A / cm ^2. It was. At this time, a simulated gas of 50 ppm CO-20% CO ₂ / H ₂ and 0.0013 Nl / min air containing 20 ppm of hydrogen sulfide were mixed and circulated through the anode. The output voltage of the MEA was 0.715 V at the beginning of power generation, but dropped to 0.642 V after 1000 hours.

  On the other hand, an experiment in which air containing 20 ppm of hydrogen sulfide was circulated to the MEA through a hydrogen sulfide absorbent filled with zeolite (MS4A) pellets was similarly performed. As a result, the same voltage after 1000 hours was 0.707 V, and the voltage drop was suppressed.

As described above, it has been found that the presence of hydrogen sulfide as an impurity in the air of the anode air breathing causes a voltage drop, and the voltage drop can be suppressed by an impurity remover excluding hydrogen sulfide.
Next, instead of hydrogen sulfide, air containing 20 ppm of trimethylamine was mixed with the simulated gas and passed through the anode. The output voltage of the MEA was 0.720 V at the beginning of power generation, but dropped to about 0.5 V after 1000 hours. As described above, the voltage drop of MEA occurred due to the basic compound.

(Example 2)
Methane gas humidified to S / C (steam / carbon ratio) = 3 with respect to 1.3 cc of 2 wt% Ru / alumina catalyst pellets as a reforming catalyst, GHSV (Gas Highest Space Velocity) = 3200 h ⁻¹ , 640 ° C. When the methane gas was steam reformed through circulation, the conversion rate of methane to hydrogen was 86%. Thereafter, the catalyst pellets were cooled to room temperature, and then air containing 20 ppm of hydrogen sulfide was circulated at 0.25 Nl / min for 20 h. Thereafter, the steam reforming reaction was performed again under the same conditions and measured in the same manner. As a result, the conversion rate was reduced to 70%.

  On the other hand, in a similar test, air containing 20 ppm of hydrogen sulfide was passed through the catalyst through a hydrogen sulfide absorbent packed with zeolite (MS4A) pellets. When the characteristics of the steam reforming catalyst were measured after 20 hours of circulation, the conversion rate was 85%.

  As described above, when hydrogen sulfide is present as an impurity in the purge air of the steam reforming catalyst, the steam reforming catalyst deteriorates in several tens of hours, and the catalyst removal can be suppressed by the impurity remover excluding hydrogen sulfide. It was.

(Example 3)
A mixed gas of methane: water: air = 1: 1.5: 3 (molar ratio) with respect to 3 cc of catalyst pellets of 1 wt% Pt-1 wt% Rh / ZrO ₂ which is an autothermal reaction catalyst is GHSV = 10000 h ^{− 1} circulated at 750 ° C. to perform a steam reforming reaction. The air contained 20 ppm of hydrogen sulfide. As a result, immediately after the start of the experiment, the conversion rate from methane to hydrogen was 94.6%, but after 400 hours, the conversion rate was reduced to 84.7%.

  On the other hand, air containing 20 ppm of hydrogen sulfide is passed through a hydrogen sulfide absorber filled with a hydrogen sulfide absorbent pellet made of zeolite (MS4A) and then circulated through the catalyst pellet. A reaction test was performed. The same conversion rate after passing through 400 hours was 94.2%.

  As described above, it has been verified from Example 3 that, when air is sent to the reforming unit 1 to cause an autothermal reaction, the catalytic characteristics of the reforming unit 1 deteriorate if hydrogen sulfide is contained as an impurity in the air. It was. Moreover, it was verified that such a catalyst characteristic deterioration can be suppressed by an impurity remover excluding hydrogen sulfide.

Example 4
In the autothermal reaction, the sulfur compound eventually becomes hydrogen sulfide, and part of it is supplied to the downstream catalyst, so the influence of hydrogen sulfide on the shift reaction catalyst and selective oxidation reaction catalyst was investigated.

A test gas of 11% CO-12% CO ₂ / H ₂ was supplied to 4 cc of the shift reaction catalyst in the form of 2 wt% Pt / CeZrOx pellets. The test gas was fed through a bubbler with a dew point of 57 ° C. The GHSV was set at 3000h- ¹ . Further, a gas having a composition of 500 ppmH ₂ S / N ₂ was mixed so that the hydrogen sulfide concentration of the test gas was 20 ppm on a dry basis. The shift reaction catalyst was maintained at 230 ° C. and the test gas was passed over the shift reaction catalyst for 1000 hours. The CO concentration on the outlet side of the shift reaction catalyst immediately after the start of distribution was 0.41% on a dry basis, but increased to 0.48% after 1000 hours.

Further, a honeycomb having a diameter of 2 cm and a thickness of 1 cm carrying Ru equivalent to 1.5 g / l was used as a CO selective oxidation reaction catalyst, and 0.5% CO-20% CO ₂ / H ₂ was used as the CO selective oxidation reaction catalyst. Test gas was supplied. In the same manner as the shift reaction catalyst test, the test gas was supplied with hydrogen sulfide mixed so that the dew point was 70 ° C. and the hydrogen sulfide concentration of the test gas was 20 ppm on a dry basis. The test gas was mixed with air so that O ₂ /CO=1.5. The GHSV was set at 9300 h ⁻¹ . The test gas was passed through the CO selective oxidation reaction catalyst at a catalyst temperature of 150 ° C. for 10 hours. The CO concentration on the outlet side of the CO selective oxidation reaction catalyst immediately after the start of distribution was 112 ppm, but increased to 322 ppm after 10 hours.

  As described above, it has been found that when a small amount of hydrogen sulfide is supplied to the shift reaction catalyst and the CO selective oxidation reaction catalyst, the characteristics deteriorate.

(Example 5)
FIG. 3 is a schematic configuration diagram of a fuel cell system according to the fifth embodiment. The basic configuration of the fuel cell system of the fifth embodiment is the same as that of the fuel cell system of the first embodiment, but the hydrogen sulfide absorbing portion 5 is not installed in the fifth embodiment, and the first embodiment It shows in more detail. Therefore, the description will focus on points not shown in the first embodiment.

  As shown in FIG. 3, the fuel cell system according to the fifth embodiment includes a fuel supply unit 15 that supplies city gas. A zeolite-based adsorptive desulfurization unit 16 is installed on the downstream side of the fuel supply unit 15, and a water supply unit 17 is connected to a gas flow path downstream of the zeolite-based adsorptive desulfurization unit 16. A water evaporation unit 18 is installed downstream of the water supply unit 17. The reforming unit 1 has a cylindrical shape, and a water evaporation unit 18 is installed on the outer periphery of the cylindrical reforming unit 1 so that the waste heat of the steam reforming reaction can be used. A steam reforming reaction heating unit 19 having an off-gas burner for heating the reforming unit 1 is installed at the center of the reforming unit 1. The steam reforming reaction heating unit 19 heats the reforming unit 1 by burning the anode off gas from the fuel cell 4. A Ru catalyst is arranged around the arranged off-gas burner. The Ru catalyst is configured to be supplied with city gas containing water vapor from above to below.

  The reforming section 1 was filled with 0.3 L of Ru catalyst, the shift reaction section 2 with 2 L of Pt / CeZrOx catalyst, and the CO selective oxidation reaction section 3 with 0.2 L of Ru catalyst. As the packed catalyst, a honeycomb-shaped catalyst body was used as the CO selective oxidation catalyst, and a pellet-shaped catalyst body was used as the other catalyst.

  The following experiment was conducted using the fuel cell system of Example 5 configured as described above.

  The city gas of 4 Nl / min from the fuel supply unit 15 and the reformed water adjusted to have S / C of 3 were supplied from the water supply unit 17 to the reforming unit 1. Further, the combustion amount of the steam reforming reaction heating unit 19 was adjusted so that the Ru catalyst in the reforming unit 1 was 650 ° C. In the fuel cell power generation unit, power was generated so that the direct current power was 1.2 kW. Separately from the cathode air, 20 ppm toluene and 20 ppm hydrogen sulfide were added to air used for anode air breathing, CO selective oxidation air, and purge air. This air is passed through the heat exchanging section 11 around the CO selective oxidation reaction section 3 and heated, and then is placed in contact with the shift reaction section 2 and is supplied to the catalytic combustor 12 made of Pt / alumina catalyst maintained at 250 ° C. Then, it was passed through the sulfur oxide absorbing part 13 containing CaO which was installed in contact with the shift reaction part 2 and kept at 300 ° C. Air through the sulfur oxide absorption unit 13 was supplied to the CO selective oxidation reaction unit 3 and the anode catalyst at 0.5 Nl / min and 0.3 Nl / min, respectively. This was designated as fuel cell system A.

  This fuel cell system A is stopped after 12 hours of operation, and when the steam reforming catalyst is lowered to 200 ° C. at the time of stoppage, the air containing 20 ppm of toluene and 20 ppm of hydrogen sulfide is converted into the catalytic combustion section 12 and the sulfur oxide absorption section. 13 was passed through the reforming air supply unit 10 at 10 Nl / min for 10 minutes, and the residual gas was purged and cooled. When the DSS (Daily Start-Stop Operation) operation was performed after 12 hours of operation and stopped after 12 hours of operation, stable operation was possible even after 3000 hours of operation.

  On the other hand, in the fuel cell system A, a fuel cell system in which the order of the catalyst combustion unit 12 and the sulfur oxide absorption unit 13 was reversed was created. Similarly, when the DSS operation was performed, the stability of the fuel cell system was lowered as compared with the above.

  Further, in the fuel cell system A, a fuel cell system in which a hydrogen sulfide absorption unit filled with a hydrogen sulfide absorbent pellet made of zeolite (MS4A) is installed after the catalyst combustion unit 12 instead of the sulfur oxide absorption unit 13. Created. The air was cooled to several tens of degrees and then passed through zeolite (MS4A). When DSS operation was performed in the same manner, the stability of the fuel cell system was similarly reduced.

  Furthermore, in the fuel cell system A, the catalyst combustion unit 12 and the sulfur oxide absorption unit 13 were eliminated, and a fuel cell system in which air was circulated as it was was created. As the air used, air added with 20 ppm of toluene was used for anode air breathing, CO selective oxidation, and purge air. When the DSS operation was performed in the same manner, when the operation was performed for 280 hours, the battery voltage decreased and it became difficult to generate power.

  As described above, the catalyst combustion section 12 and the air used for the anode air breathing air, the CO selective oxidation air, and the purge air, that is, the air mixed with the raw material or the hydrogen-rich gas generated from the raw material, In addition, the sulfur oxide absorption part 13 having a sulfur oxide adsorbent or absorbent is disposed downstream of the catalyst combustion part 12, so that the catalyst combustion part 12 contains a flame-retardant and volatile organic compound. It functions as an impurity removing means for removing. Moreover, the catalyst combustion part 12 and the sulfur oxide absorption part 13 function as an impurity removal means for removing the sulfur compound exemplified by hydrogen sulfide and sulfur oxide. Thus, the present invention can be applied even when a flame-retardant and volatile organic compound and a sulfur compound are contained in the atmosphere, which is a supply source of air mixed with the raw material or the hydrogen-rich gas generated from the raw material. The fuel cell system was able to perform particularly stable operation.

(Example 6)
In the fuel cell system A in Example 5, 0.3 l of 1 wt% Pt-1 wt% Rh / ZrO ₂ catalyst was used as the reforming reaction catalyst, and the fuel cell system A was operated from the reforming air supply unit 6 during operation. A second operation method in which an autothermal reaction for supplying air was performed was performed. Autothermal air was supplied at 8 Nl / min during rated operation. A DSS test was performed in the same manner as in Example 5. However, even if air containing 20 ppm of toluene and 20 ppm of hydrogen sulfide was added, PEFC4 could be stably operated even if the operation was continued for 3000 hours.

  However, when a fuel cell system in which the catalyst combustion unit 12 and the sulfur oxide absorption unit 13 are omitted from the fuel cell system A is configured and the same operation test is performed, the hydrogen generator 20 is downstream after 203 hours of operation. The hydrogen concentration of the hydrogen-rich gas was reduced, that is, the conversion rate of methane to hydrogen in the hydrogen generator 20 was reduced, and power generation became difficult.

  As described above, autothermal air is also mixed with anode air breathing air, CO selective oxidation air, purge air, that is, raw material or hydrogen-rich gas generated from the raw material, as in Example 5 above. The catalyst combustion section 12 is disposed in the air supply flow path, and the sulfur oxide absorption section 13 having a sulfur oxide adsorbent or absorbent downstream of the catalyst combustion section 12, thereby the catalyst combustion section. 12 functions as an impurity removing means for removing a flame-retardant and volatile organic compound. Moreover, the catalyst combustion part 12 and the sulfur oxide absorption part 13 function as an impurity removal means for removing the sulfur compound exemplified by hydrogen sulfide and sulfur oxide. Thus, the present invention can be applied even when a flame-retardant and volatile organic compound and a sulfur compound are contained in the atmosphere, which is a supply source of air mixed with the raw material or the hydrogen-rich gas generated from the raw material. The fuel cell system was able to perform particularly stable operation.

(Example 7)
FIG. 4 is a schematic configuration diagram of a fuel cell system according to the seventh embodiment. The fuel cell system of Example 7 has the sulfur oxide absorption function shown in Embodiment 2 instead of the catalytic combustion unit 12 and the sulfur oxide absorption unit 13 of the fuel cell system of Example 5. A catalytic combustion unit 14 is provided. This is a fuel cell system A in which a Pt / BaO—Al ₂ O ₃ catalyst is disposed in the catalytic combustion part, and the sulfur oxide absorbing part 13 is further eliminated.

  As air used for anode air breathing air, CO selective oxidation air, and purge air, air containing 20 ppm toluene and 20 ppm hydrogen sulfide was used. The catalytic combustion section 14 was kept at 250 ° C. When the DSS operation was performed after 12 hours and stopped after 12 hours, stable operation was possible even after 3000 hours.

  As described above, by using a combustion catalyst containing a noble metal and an alkaline earth metal oxide, the catalyst combustion unit 14 can remove impurity impurities for removing volatile organic compounds and hydrogen sulfide and sulfur oxides. It functions as an impurity removing means for removing sulfur compounds. Thus, the present invention can be applied even when a flame-retardant and volatile organic compound and a sulfur compound are contained in the atmosphere, which is a supply source of air mixed with the raw material or the hydrogen-rich gas generated from the raw material. The fuel cell system was able to perform particularly stable operation.

  The fuel cell system of the present invention has an effect capable of maintaining stable operation for a longer period of time, and is useful as, for example, a household cogeneration fuel cell system.

1 is a schematic diagram of a fuel cell system according to a first embodiment of the present invention. Schematic diagram of a fuel cell system according to a second embodiment of the present invention. Schematic of the fuel cell system in Example 5 according to the present invention. Schematic of the fuel cell system in Example 7 according to the present invention.

Explanation of symbols

1 reforming unit 2 shift reaction unit 3 CO selective oxidation reaction unit 4 polymer electrolyte fuel cell (PEFC)
DESCRIPTION OF SYMBOLS 5 Hydrogen sulfide absorption part 6 Reforming air supply part 7 Valve 8 CO selective oxidation air supply part 9 Anode air breathing air supply part 10 Cathode air supply part 11 Heat exchange part 12 Catalytic combustion part 13 Sulfur oxide Absorption section 14 Catalytic combustion section 15 Fuel supply section 16 Zeolite adsorption desulfurization section 17 Water supply section 18 Water evaporation section 19 Steam reforming reaction heating section 20 Hydrogen generator

Claims (11)

A reforming unit that generates a hydrogen-rich gas containing carbon monoxide from a fuel containing hydrocarbon and water, a shift reaction unit that generates hydrogen and carbon dioxide from carbon monoxide and water in the hydrogen-rich gas, and the shift reaction A hydrogen generator having a carbon monoxide removal unit for further reducing carbon monoxide in the hydrogen-rich gas that has not been removed,
A fuel cell that generates power using the hydrogen-rich gas and the oxidant gas supplied from the hydrogen generator;
On the basis of the flow direction of the fuel, (1) upstream of the reforming unit, or (2) an air supply unit that supplies air to at least one place between the carbon monoxide removal unit and the fuel cell;
A fuel cell system comprising impurity removal means for removing impurity gas contained in the air. An air supply unit that supplies air upstream of the reforming unit, based on the flow direction of the fuel;
The fuel cell system according to claim 1, further comprising an impurity removing unit that removes a sulfur compound from the air. An air supply unit that supplies air between the carbon monoxide removal unit and the fuel cell, based on the flow direction of the fuel;
2. The fuel cell system according to claim 1, further comprising an impurity removing unit that removes ammonia, amine, fatty acid, hydrogen sulfide, and aldehyde from the air. The fuel cell system according to claim 1, wherein the reforming unit is a reforming unit that generates a hydrogen-rich gas containing carbon monoxide from a fuel containing hydrocarbon, water, and air.   The fuel cell system according to claim 1, wherein the impurity removing means has an adsorbent or absorbent of hydrogen sulfide.   The fuel cell system according to claim 1 or 2, wherein the impurity removing means has a sulfur oxide adsorbent or absorbent.   The fuel cell system according to claim 1, wherein the impurity removing unit includes a catalytic combustion unit. Based on the air flow direction,
The fuel cell system according to claim 6, wherein the impurity removing unit further includes a catalytic combustion section upstream of the sulfur oxide adsorbent or absorbent.   The fuel cell system according to claim 7, wherein the catalytic combustion unit is disposed at a position where heat exchange can be performed with the hydrogen generator, or at a position where heat exchange can be performed with combustion exhaust gas used for heating the hydrogen generator. .   The adsorbent or absorbent of the sulfur oxide is disposed at a position where heat exchange can be performed with the hydrogen generator, or at a position where heat exchange can be performed with the flue gas used to heat the hydrogen generator. The fuel cell system described in 1.   The catalytic combustion section also serves as an adsorbent or absorbent for the sulfur oxide, has a catalyst containing a noble metal and an alkaline earth metal, and is capable of heat exchange with the hydrogen generator, or the hydrogen generation 9. The fuel cell system according to claim 8, wherein the fuel cell system is disposed at a position where heat exchange with the combustion exhaust gas used for heating the vessel is possible.

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