JP2012140524A - Desulfurization system, hydrogen production system, fuel cell system, fuel-desulfurization method, and method for producing hydrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desulfurization system capable of desulfurizing a raw fuel with satisfactory desulfurization performance without reducing the water content of the raw fuel to <0.2 vol.%, a hydrogen production system producing hydrogen from a raw fuel desulfurized with the desulfurization system, and a fuel cell system provided with the desulfurization system and the hydrogen production system.SOLUTION: The desulfurization system is provided with: a fuel supply unit that supplies a hydrocarbon fuel containing water and a sulfur compound to the subsequent unit; and a desulfurization unit that uses a catalyst comprising silver supported by zeolite X, to desulfurize the hydrocarbon fuel supplied by the fuel supply unit. The water constitutes 0.2-0.4 vol.% of the total volume of the hydrocarbon fuel supplied by the fuel supply unit.

Description

  The present invention relates to a desulfurization system, a hydrogen production system, a fuel cell system, a fuel desulfurization method, and a hydrogen production method.

  As a conventional fuel cell system, a reformer that generates a reformed gas containing hydrogen using raw fuel, a fuel cell that generates power using the reformed gas generated by the reformer, and a reformer A device including a desulfurizer that performs desulfurization of raw fuel on the upstream side is known (see, for example, Patent Document 1).

JP 2010-27579 A

  In the fuel cell system as described above, if the raw fuel supplied to the desulfurizer contains water, the desulfurization catalyst accommodated in the desulfurizer may be deactivated, and the desulfurization performance may be significantly reduced. is there. Therefore, in the conventional fuel cell system, it is required to sufficiently remove water from the raw fuel (for example, the water content is less than 0.2% by volume). However, in order to remove water from the raw fuel until the moisture content is less than 0.2% by volume, a large-scale dehumidifying means may be required.

  Therefore, the present invention provides a desulfurization system capable of desulfurizing with sufficient desulfurization performance without reducing the moisture content of the raw fuel to less than 0.2% by volume, and hydrogen from raw fuel desulfurized by the desulfurization system. It is an object of the present invention to provide a hydrogen production system for producing a fuel cell system and a fuel cell system including the desulfurization system and the hydrogen production system. The present invention also provides a fuel desulfurization method capable of desulfurization with sufficient desulfurization performance without reducing the moisture content of the raw fuel to less than 0.2% by volume, and the raw fuel desulfurized by the desulfurization method. It is an object of the present invention to provide a method for producing hydrogen from which hydrogen is produced.

  The desulfurization system according to the present invention includes a fuel supply unit that supplies a hydrocarbon-based fuel containing water and a sulfur compound to a subsequent stage, the hydrocarbon-based fuel supplied from the fuel supply unit, and silver in an X-type zeolite. A desulfurization unit that desulfurizes using a supported catalyst, and the water content in the hydrocarbon fuel supplied by the fuel supply unit is 0.2 to about the total amount of the hydrocarbon fuel. It is characterized by 0.4% by volume.

  The water content in the hydrocarbon-based fuel referred to in this specification is a value obtained from a saturated water vapor pressure calculated from a dew point temperature measured with a dew point meter.

  According to such a desulfurization system, the hydrocarbon fuel supplied from the fuel supply unit contains 0.2 to 0.4% by volume of water by providing the desulfurization unit using a specific catalyst. However, the fuel can be desulfurized with sufficient desulfurization performance.

  In the desulfurization system of the present invention, the hydrocarbon fuel preferably includes a hydrocarbon compound having 4 or less carbon atoms.

  The hydrogen production system of the present invention includes the desulfurization system of the present invention and a hydrogen generation unit that generates hydrogen from the hydrocarbon fuel desulfurized in the desulfurization unit.

  In such a hydrogen production system, the hydrocarbon fuel is desulfurized with sufficient desulfurization performance by the desulfurization system, so that a decrease in hydrogen generation efficiency due to sulfur compounds in the hydrogen generation part is sufficiently suppressed. Therefore, according to the hydrogen production system of the present invention, hydrogen can be efficiently produced from a hydrocarbon-based fuel containing 0.2 to 0.4% by volume of water.

  The fuel cell system of the present invention includes the hydrogen production system of the present invention.

  According to such a fuel cell system, since hydrogen is efficiently produced by the hydrogen production system, good power generation efficiency is achieved using a hydrocarbon-based fuel containing 0.2 to 0.4% by volume of water. Can be realized.

  The present invention also includes a step of desulfurizing a hydrocarbon fuel containing a sulfur compound and 0.2 to 0.4% by volume of water using a catalyst in which silver is supported on an X-type zeolite. A desulfurization method is provided.

  According to such a fuel desulfurization method, the content of water in the hydrocarbon fuel is in a specific range, and a specific catalyst is used so that the water in the hydrocarbon fuel is not completely removed. Desulfurization performance can be realized.

  In the fuel desulfurization method of the present invention, the hydrocarbon fuel preferably contains a hydrocarbon compound having 4 or less carbon atoms.

  The present invention further provides a method for producing hydrogen, comprising the step of reforming the hydrocarbon fuel desulfurized by the fuel desulfurization method according to the present invention to obtain hydrogen.

  According to such a method for producing hydrogen, since the hydrocarbon-based fuel is desulfurized with sufficient desulfurization performance by the desulfurization method, a reduction in reforming efficiency due to a sulfur compound is sufficiently suppressed, and hydrogen is efficiently consumed. Can be manufactured.

  According to the present invention, a desulfurization system capable of desulfurizing with sufficient desulfurization performance without reducing the moisture content of the raw fuel to less than 0.2% by volume, and hydrogen from the raw fuel desulfurized by the desulfurization system. , A fuel cell system including the desulfurization system and the hydrogen production system are provided. Further, according to the present invention, a fuel desulfurization method capable of desulfurization with sufficient desulfurization performance without reducing the moisture content of the raw fuel to less than 0.2% by volume, and desulfurization by the desulfurization method. A method for producing hydrogen is provided that produces hydrogen from raw fuel.

It is a conceptual diagram which shows an example of the fuel cell system which concerns on embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual diagram showing an example of a fuel cell system according to an embodiment of the present invention. The fuel cell system 1 includes a fuel supply unit 2, a desulfurization unit 3, a hydrogen generation unit 4, a cell stack 5, an off-gas combustion unit 6, a water supply unit 7, a water vaporization unit 8, and an oxidant supply unit. 9, a power conditioner 10, and a control unit 11, and each part is connected by piping in the flow shown in FIG. 1.

  The fuel supply unit 2 constitutes a desulfurization system 20 together with the desulfurization unit 3, and supplies hydrocarbon fuel to the desulfurization unit 3. Here, as the hydrocarbon fuel, a compound containing carbon atoms and hydrogen atoms in the molecule (may contain other elements such as oxygen) or a mixture thereof can be used. Examples of hydrocarbon fuels include hydrocarbons, alcohols, ethers, and biofuels. These hydrocarbon fuels include those derived from conventional fossil fuels such as petroleum and coal, synthesis gas, and the like. Those derived from synthetic fuels and those derived from biomass can be used as appropriate.

  Examples of hydrocarbons include hydrocarbon compounds such as methane, ethane, propane, and butane methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, town gas, gasoline, naphtha, kerosene, Light oil is mentioned. Examples of alcohols include methanol and ethanol. Examples of ethers include dimethyl ether. Examples of the biofuel include biogas, bioethanol, biodiesel, and biojet. The hydrocarbon fuel may contain alcohols such as methanol and ethanol, and ethers such as dimethyl ether. In the present embodiment, a gas containing methane as a main component (for example, city gas, town gas, natural gas, biogas, etc.) or LPG supplied through a pipeline is suitable. Can be used for

  The hydrocarbon fuel preferably contains a hydrocarbon compound having 4 or less carbon atoms. Specific examples of the hydrocarbon compound having 4 or less carbon atoms include saturated aliphatic hydrocarbons such as methane, ethane, propane, and butane, and unsaturated aliphatic hydrocarbons such as ethylene, propylene, and butene. The hydrocarbon-based fuel is preferably a gas containing a hydrocarbon compound having 4 or less carbon atoms, that is, a gas containing one or more of methane, ethane, ethylene, propane, propylene, butane and butene. Moreover, as gas containing a C4 or less hydrocarbon compound, the gas containing 80 volume% or more of methane is preferable, and the gas containing 85 volume% or more of methane is more preferable.

  The hydrocarbon fuel supplied from the fuel supply unit 2 contains water and a sulfur compound. Here, the water contained in the hydrocarbon-based fuel is, for example, the one mixed during the production of the hydrocarbon-based fuel, the one mixed in due to damage to the pipeline, or the like until the hydrocarbon-based fuel is supplied to the desulfurization unit 3. The thing mixed in the distribution channel etc. are mentioned. The content of water in the hydrocarbon fuel is 0.2 to 0.4% by volume based on the total amount of the hydrocarbon fuel. When the water content exceeds the above range, the desulfurization performance is lowered. Moreover, in order to make water content less than the said range, a large-scale dehumidification means etc. may be needed and productivity falls.

The hydrocarbon fuel generally contains a sulfur compound. Examples of the sulfur compound include a sulfur compound originally mixed in hydrocarbons and the like and a compound contained in an odorant for detecting gas leakage. Examples of sulfur compounds originally mixed in hydrocarbons include hydrogen sulfide (H ₂ S), carbonyl sulfide (COS), carbon disulfide (CS ₂ ), and the like. As the odorant, alkyl sulfide, mercaptan alone or a mixture thereof is used. For example, diethyl sulfide (DES), dimethyl sulfide (DMS), ethyl methyl sulfide (EMS), tetrahydrothiophene (THT), tert-butyl mercaptan ( TBM), isopropyl mercaptan, dimethyl disulfide (DMDS), diethyl disulfide (DEDS) and the like are used. The sulfur compound is usually contained in an amount of about 0.1 to 10 mass ppm in terms of sulfur atom based on the total amount of hydrocarbon fuel.

  The hydrocarbon-based fuel may contain components other than those described above within a range that does not adversely affect the characteristics of the fuel cell system.

  The hydrocarbon fuel supplied from the fuel supply unit 2 is desulfurized in the desulfurization unit 3. The sulfur compound contained in the hydrocarbon-based fuel is removed by the desulfurization catalyst in the desulfurization unit 3 in order to poison the reforming catalyst in the hydrogen generation unit 4 and the electrode catalyst in the cell stack 5. As the desulfurization catalyst, a catalyst in which silver is supported on X-type zeolite is used.

As the X-type zeolite, for example, one having a SiO ₂ / Al ₂ O ₃ ratio of 2 to 3, preferably 2.2 to 3, more preferably 2.3 to 3 can be used. When the ratio is smaller than 2, the life of the resulting catalyst as a desulfurization catalyst tends to be reduced. When the ratio is larger than 3, the silver necessary for obtaining sufficient desulfurization performance is supported. Can be difficult.

  The range of the supported amount of silver is preferably 10 to 30% by mass, and more preferably 15 to 25% by mass, based on the total amount of zeolite and silver, from the viewpoint that the desulfurization performance is further improved. When the supported amount is less than 10% by mass, the desulfurization performance may not be sufficient, and when it is more than 30% by mass, the desulfurization performance corresponding to the added amount of silver may not be exhibited. In addition, X type zeolite can carry more silver compared with Y type zeolite, for example.

  As a method for supporting silver, an ion exchange method is preferably used. Examples of the zeolite used in the ion exchange method include various types such as sodium type, ammonium type, and proton type, and among these, sodium type is preferably used. On the other hand, silver is usually prepared as a cation dissolved in water. Specific examples thereof include an aqueous solution of silver nitrate and silver perchlorate, an aqueous solution of silver ammine complex ion, and the like, and an aqueous silver nitrate solution is most preferably used. The density | concentration of the aqueous solution containing silver ion is 0.5-10 mass% normally as a density | concentration of silver, Preferably it is the range of 1-5 mass%.

  The method of ion exchange is not particularly limited, but usually the above-mentioned zeolite is added to the above solution containing cationic silver, and it is usually 0 to 90 ° C., preferably 20 to 70 ° C. for 1 hour to The ion exchange treatment is performed for several hours, preferably with stirring. Next, the solid matter is separated by means such as filtration and washed with water, and then dried at a temperature of 50 to 200 ° C., preferably 80 to 150 ° C. This ion exchange treatment can be repeated. Next, if necessary, it may be fired at 200 to 600 ° C., preferably 250 to 400 ° C. for about several hours. By such a method, the target silver ion exchange zeolite (silver supported zeolite) can be obtained.

  Zeolite carrying silver produced by the above method is alumina, silica, clay mineral, etc., using these precursors such as boehmite as an appropriate binder, extrusion molding, tableting molding, rolling granulation, It can be molded and used by a normal method such as spray drying and firing as necessary.

  In the desulfurization unit 3, the hydrocarbon fuel is desulfurized by bringing the hydrocarbon fuel into contact with the desulfurization catalyst. The temperature at the time of desulfurization is, for example, −50 to 100 ° C., more preferably −20 to 80 ° C., and still more preferably 0 to 60 ° C.

In the desulfurization part 3, it is preferable to set various conditions other than the desulfurization temperature as follows. That is, when using a hydrocarbon-based fuel that is gaseous at normal temperature (for example, 25 ° C.) and normal pressure (for example, gauge pressure of 0 MPa) such as city gas, GHSV is 10 to 20000 h ⁻¹ , preferably 10 to 7000 h ⁻¹ . It is preferable to select between. When GHSV is lower than 10 h ⁻¹ , desulfurization performance is improved, but since a large amount of desulfurization catalyst is used, it is necessary to use an excessive desulfurizer as the desulfurization section 3. Moreover, the desulfurization performance of the desulfurization part 3 further improves by making GHSV into 20000 h- ¹ or less. In addition, liquid fuel can also be used as a hydrocarbon fuel, and in that case, it is preferable to select LHSV between 0.01 and 100 h- ¹ .

  The working pressure is usually selected in the range of normal pressure to 1 MPa (gauge pressure, the same shall apply hereinafter), preferably normal pressure to 0.5 MPa, more preferably normal pressure to 0.2 MPa. Most preferably, it can be implemented.

  Here, usually, when a fuel containing 0.2% by volume or more of water is brought into contact with the desulfurization catalyst, the desulfurization performance of the desulfurization catalyst is significantly reduced. On the other hand, when the specific desulfurization catalyst (catalyst formed by supporting silver on X-type zeolite) is used, the water content in the fuel is in the range of 0.2 to 0.4% by volume. By doing, the fall of desulfurization performance is suppressed. Specifically, for example, when the water content is in the above range, the relative desulfurization performance is improved by about 1.4 times compared to the case where the water content is 0.5% by volume. Further, when the water content is in the above range, the relative desulfurization performance is reduced only about 0.1 times compared to the case where the water content is 0.1% by volume, and sufficient desulfurization performance is obtained. Is obtained.

  The fuel supply unit 2 dehumidifies the hydrocarbon fuel having a water content exceeding 0.4% by volume, and the water content in the hydrocarbon fuel is within the range of 0.2 to 0.4% by volume. There may be provided a dehumidifying means. Examples of the dehumidifying means include a dehumidifying means that uses a dehumidifying agent such as a molecular sieve to adjust the water content in the hydrocarbon fuel to 0.2 to 0.4% by volume.

  The hydrocarbon-based fuel from which the sulfur compound has been removed by the desulfurization unit 3 is supplied to the hydrogen generation unit 4. The hydrogen generator 4 and the desulfurization system 20 constitute a hydrogen production system 30. The hydrogen generator 4 includes a reformer that reforms the hydrocarbon-based fuel after desulfurization using a reforming catalyst, and generates a hydrogen-rich gas. The reforming method in the hydrogen generating unit 4 is not particularly limited, and for example, steam reforming, partial oxidation reforming, autothermal reforming, and other reforming methods can be employed. The reforming temperature is usually 200 to 800 ° C, preferably 300 to 700 ° C. The hydrogen generator 4 may have a configuration for adjusting the properties in addition to the reformer reformed by the reforming catalyst depending on the properties of the hydrogen rich gas required by the cell stack 5. For example, when the type of the cell stack 5 is a polymer electrolyte fuel cell (PEFC) or a phosphoric acid fuel cell (PAFC), the hydrogen generation unit 4 is configured to remove carbon monoxide in the hydrogen-rich gas. (For example, a shift reaction part and a selective oxidation reaction part). The hydrogen generation unit 4 supplies a hydrogen rich gas to the anode 12 of the cell stack 5.

  Examples of the reforming catalyst include cerium oxide or a catalyst carrier containing a rare earth element oxide mainly composed of cerium oxide and an active metal supported on the carrier.

  The reforming catalyst preferably uses Ru or Rh as the active metal. As the loading amount of Ru or Rh, the atomic ratio of cerium to Ru or Rh (Ce / Ru or Ce / Rh) is 1 to 250, preferably 2 to 100, more preferably 3 to 50. When the atomic ratio is out of the above range, sufficient catalytic activity may not be obtained, which is not preferable. The amount of Ru or Rh supported is 0.1 to 3.0% by mass, preferably 0.5 to 3.0% by weight, based on the catalyst weight (total weight of catalyst support and active metal), with Ru or Rh as the metal equivalent. 2.5% by mass.

  The method for supporting Ru or Rh on the catalyst carrier is not particularly limited, and can be easily performed by applying a known method. For example, an impregnation method, a deposition method, a coprecipitation method, a kneading method, an ion exchange method, a pore filling method and the like can be mentioned, and the impregnation method is particularly desirable. The starting material for Ru or Rh used in the production of the catalyst varies depending on the above-mentioned supporting method and can be appropriately selected. Usually, a Ru or Rh chloride or a Ru or Rh nitrate is used. For example, when an impregnation method is applied, a method of preparing a solution of Ru or Rh salt (usually an aqueous solution), impregnating the above carrier, drying, and firing as necessary can be exemplified. Firing is usually performed in air or a nitrogen atmosphere, and the temperature is not particularly limited as long as it is equal to or higher than the decomposition temperature of the salt, but is usually 200 to 800 ° C, preferably 300 to 800 ° C, more preferably 500. About ~ 800 ° C is desirable. In the present invention, it is usually possible to prepare a catalyst by supporting Ru or Rh on a catalyst carrier and then performing a reduction treatment at 400 to 1000 ° C., preferably 500 to 700 ° C. in a reducing atmosphere (usually a hydrogen atmosphere). Preferably employed. The above reforming catalyst may be in a form in which other noble metals (platinum, iridium, palladium, etc.) are further supported.

  The catalyst support for the reforming catalyst is preferably a support containing cerium oxide or a rare earth element oxide containing cerium oxide as a main component in an amount of 5 to 40% by mass and aluminum oxide in an amount of 60 to 95% by mass.

The cerium oxide is not particularly limited, but second cerium oxide (commonly called ceria) is preferable. The method for preparing cerium oxide is not particularly limited, and for example, cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O, Ce (NO ₃ ) _4, etc.), cerium chloride (CeCl ₃ .nH ₂ O) ), Cerium hydroxide (CeOH ₃ , CeOH ₄ .H ₂ O, etc.), cerium carbonate (Ce ₂ (CO ₃ ) ₃ .8 H ₂ O, Ce ₂ (CO ₃ ) ₃ .5H ₂ O etc.), cerium oxalate , Cerium (IV) ammonium oxalate, cerium chloride and the like as starting materials, and can be prepared by a known method, for example, firing in air.

  The rare earth element oxide mainly composed of cerium oxide can be prepared from a salt of a mixed rare earth element mainly composed of cerium. In the rare earth element oxide mainly composed of cerium oxide, the content of cerium oxide is usually 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more. As rare earth element oxides other than cerium oxide, scandium, yttrium, lanthanum, protheodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, etc. Is mentioned. Of these, oxides of each element of yttrium, lanthanum, and neodymium are preferable, and oxides of lanthanum are particularly preferable. Of course, the crystal form is not particularly limited, and any crystal form may be used.

  In addition to alumina, aluminum oxide also includes double oxides of aluminum and other elements such as silicon, copper, iron, and titanium. Typical examples of double oxides include silica alumina. As the aluminum oxide of the present invention, alumina is particularly desirable, and the alumina is not particularly limited, and any crystal form such as α, β, γ, η, θ, κ, χ, etc. can be used. Is preferred. Alumina hydrates such as boehmite, bayerite, and gibbsite can also be used. Silica alumina is not particularly limited, and any crystal form can be used. Of course, the aluminum oxide used in the present invention can be used without any problem even if it contains a small amount of impurities.

  The composition ratio of the cerium oxide and the rare earth element oxide mainly composed of cerium oxide in the catalyst carrier used in the present invention is 5 to 40% by mass, preferably 10 to 35% by mass. When the rare earth element oxide containing cerium oxide and cerium oxide as a main component is less than 5% by mass, the carbon precipitation suppressing effect, the activity promoting effect, and the heat resistance improving effect in the presence of oxygen are insufficient, which is not preferable. On the other hand, when the amount is more than 40% by mass, the surface area of the support is decreased, and sufficient catalytic activity may not be obtained.

  The composition ratio of the aluminum oxide in the catalyst support of the reforming catalyst is 60 to 95% by mass, preferably 65 to 90% by mass. When the composition ratio of the aluminum oxide is less than 60% by mass, the surface area of the support is decreased, so that sufficient catalytic activity may not be obtained. This is not preferable because the effect and the effect of improving heat resistance in the presence of oxygen are insufficient.

  The method for producing the catalyst carrier of the reforming catalyst is not particularly limited, and can be easily produced by a known method. For example, it can be produced by impregnating aluminum oxide with an aqueous solution of cerium or a rare earth element salt containing cerium as a main component, followed by drying and baking. The salt used at this time is preferably a water-soluble salt. Specific examples of the salt include nitrates, chlorides, sulfates, acetates, and the like. Nitrate or organic acid salt is preferable. Firing is usually performed in air or an oxygen atmosphere, and the temperature is not particularly limited as long as it is equal to or higher than the decomposition temperature of the salt, but it is usually about 500 to 1400 ° C, preferably about 700 to 1200 ° C. As another method for preparing the carrier, it can also be prepared by a coprecipitation method, a gel kneading method, or a sol-gel method.

  Although the catalyst carrier can be obtained in this way, it is preferable to calcinate the catalyst carrier in the atmosphere of air or oxygen before supporting Ru or Rh. As a calcination temperature at this time, it is 500-1400 degreeC normally, Preferably it is 700-1200 degreeC. Further, for the purpose of increasing the mechanical strength of the catalyst carrier, a small amount of a binder such as silica or cement can be added to the catalyst carrier. The shape of the catalyst carrier of the reforming catalyst is not particularly limited, and can be appropriately selected depending on the form in which the catalyst is used. For example, an arbitrary shape such as a pellet shape, a granule shape, a honeycomb shape, or a sponge shape is adopted.

  Moreover, in the hydrogen generation part 4, it is preferable that water vapor | steam is supplied from the water vaporization part 8 in order to modify | reform hydrocarbon fuel. The water vapor is preferably generated by heating the water supplied from the water supply unit 7 in the water vaporization unit 8 and vaporizing it. Heating of the water in the water vaporization unit 8 may use heat generated in the fuel cell system 1 such as recovering heat of the hydrogen generation unit 4, heat of the off-gas combustion unit 6, or exhaust gas. Moreover, you may heat water using other heat sources, such as a heater and a burner separately. In FIG. 1, only heat supplied from the off-gas combustion unit 6 to the hydrogen generation unit 4 is described as an example, but the present invention is not limited to this.

  Hydrogen rich gas is supplied from the hydrogen production system 30 to the fuel cell system 1 through a pipe (not shown) connecting the hydrogen production system 30 and the cell stack 5. Electric power is generated in the cell stack 5 using this hydrogen-rich gas and an oxidizing agent. The type of the cell stack 5 in the fuel cell system 1 is not particularly limited, and examples thereof include a polymer electrolyte fuel cell (PEFC), a solid oxide fuel cell (SOFC), and phosphoric acid. A fuel cell fuel cell (PAFC), a molten carbonate fuel cell (MCFC), and other types can be employed. It should be noted that the components shown in FIG. 1 may be omitted as appropriate according to the type of cell stack 5, the reforming method, and the like.

  The oxidant is supplied from the oxidant supply unit 9 through a pipe connecting the oxidant supply unit 9 and the fuel cell system 1. As the oxidizing agent, for example, air, pure oxygen gas (which may contain impurities that are difficult to remove by a normal removal method), or oxygen-enriched air is used.

  The cell stack 5 generates power using the hydrogen rich gas from the hydrogen generation unit 4 and the oxidant from the oxidant supply unit 9. The cell stack 5 includes an anode 12 to which a hydrogen-rich gas is supplied, a cathode 13 to which an oxidant is supplied, and an electrolyte 14 disposed between the anode 12 and the cathode 13. The cell stack 5 supplies power to the outside via the power conditioner 10. The cell stack 5 supplies the hydrogen rich gas and the oxidant, which have not been used for power generation, to the off gas combustion unit 6 as off gas. Note that a combustion section (for example, a combustor that heats the reformer) provided in the hydrogen generation section 4 may be shared with the off-gas combustion section 6.

  The off gas combustion unit 6 burns off gas supplied from the cell stack 5. The heat generated by the off-gas combustion unit 6 is supplied to the hydrogen generation unit 4 and used for generation of a hydrogen rich gas in the hydrogen generation unit 4. The fuel supply unit 2, the water supply unit 7, and the oxidant supply unit 9 are configured by, for example, a pump and are driven based on a control signal from the control unit 11.

  The power conditioner 10 adjusts the power from the cell stack 5 according to the external power usage state. For example, the power conditioner 10 performs a process of converting a voltage and a process of converting DC power into AC power.

  The control unit 11 performs control processing for the entire fuel cell system 1. The control unit 11 includes, for example, a device including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output interface. The control unit 11 is electrically connected to the fuel supply unit 2, the water supply unit 7, the oxidant supply unit 9, the power conditioner 10, and other sensors and auxiliary equipment not shown. The control unit 11 acquires various signals generated in the fuel cell system 1 and outputs a control signal to each device in the fuel cell system 1.

  As described above, according to the desulfurization system, the hydrogen production system, and the fuel cell system of the present invention, a sufficiently desulfurized hydrocarbon fuel can be obtained by setting the raw fuel water in the range of 0.2 to 0.4% by volume. Stable supply is possible.

  Next, the fuel desulfurization method and the hydrogen production method of the present invention will be described. The fuel desulfurization method of the present invention includes a step of desulfurizing a hydrocarbon-based fuel containing a sulfur compound and 0.2 to 0.4% by volume of water using a catalyst in which silver is supported on an X-type zeolite. Prepare.

  Examples of the hydrocarbon fuel containing a sulfur compound and 0.2 to 0.4% by volume of water include the hydrocarbon fuels described above.

  Specific means for bringing the hydrocarbon fuel into contact with a catalyst (desulfurization catalyst) formed by supporting silver on X-type zeolite includes the fuel supply unit 2 and the desulfurization unit 3 described above. That is, the hydrocarbon fuel is supplied to the desulfurization unit 3 by the fuel supply unit 2, and the supplied hydrocarbon fuel is brought into contact with the desulfurization catalyst in the desulfurization unit 3.

  It is preferable that the desulfurization conditions are usually conditions in which the fuel is vaporized. The desulfurization temperature is preferably −50 to 100 ° C., more preferably −20 to 80 ° C., and further preferably 0 to 60 ° C.

Various conditions other than the desulfurization temperature are preferably set as follows. That is, when using a hydrocarbon-based fuel that is gaseous at normal temperature (for example, 25 ° C.) and normal pressure (for example, gauge pressure of 0 MPa) such as city gas, GHSV is 10 to 20000 h ⁻¹ , preferably 10 to 7000 h ⁻¹ . It is preferable to select between. When GHSV is lower than 10 h ⁻¹ , the desulfurization performance is improved, but an excessive amount of desulfurizer is required because a large amount of desulfurization agent is used. Moreover, desulfurization performance improves further by making GHSV into 20000h- ¹ or less. In addition, liquid fuel can also be used as a hydrocarbon fuel, and in that case, it is preferable to select LHSV between 0.01 and 100 h- ¹ .

  The working pressure is usually selected in the range of normal pressure to 1 MPa (gauge pressure, the same shall apply hereinafter), preferably normal pressure to 0.5 MPa, more preferably normal pressure to 0.2 MPa. Most preferably, it can be implemented.

  The method for producing hydrogen according to the present invention reforms the hydrocarbon fuel desulfurized by the desulfurization method to generate hydrogen (hydrogen-rich gas). The reforming method is not particularly limited as described above, and for example, steam reforming, partial oxidation reforming, autothermal reforming, and other reforming methods can be employed. The reforming temperature is usually 200 to 800 ° C, preferably 300 to 700 ° C.

  As described above, the reforming catalyst preferably uses Ru or Rh as the active metal, and the catalyst carrier is cerium oxide or a rare earth element oxide containing cerium oxide as a main component, and an aluminum oxide. A carrier containing 60 to 95% by mass is preferable.

  In reforming, it is preferable that steam is supplied from the water vaporization section 8 to the hydrogen generation section 4 because steam is necessary to reform the fuel in some cases. The water vapor is preferably generated by heating the water supplied from the water supply unit 7 in the water vaporization unit 8 and vaporizing it.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to an Example.

<Preparation of desulfurization catalyst A>
An aqueous silver nitrate solution was prepared by adding 600 ml of distilled water to 30 g of silver nitrate. Next, the mixture was mixed with 50 g of commercially available NaX-type zeolite powder with SiO ₂ / Al ₂ O ₃ (molar ratio) = 2.5 with stirring, and ion exchange was performed. Then, it was washed with distilled water so as not to leave nitrate radicals. After washing, it was dried overnight at 180 ° C. in air. 5 g of an alumina binder was mixed with 30 g of the powdered silver-exchanged zeolite after drying, and extrusion molding was performed at 1 mmφ to obtain a desulfurization catalyst A (shown as “Ag / X” in Table 1). The amount of silver supported in the desulfurization catalyst A was 24% by mass on the basis of zeolite.

<Preparation of desulfurization catalyst B>
To 40 g of copper sulfate pentahydrate, 600 ml of distilled water was added to prepare an aqueous copper sulfate solution. Next, the mixture was mixed with 50 g of commercially available NaY-type zeolite powder with SiO ₂ / Al ₂ O ₃ (molar ratio) = 4.5 while stirring, and ion exchange was performed. Then, it washed with distilled water so that a sulfate radical might not remain. After washing, it was dried overnight at 180 ° C. in an air stream. 5 g of an alumina binder was mixed with 30 g of the powdered copper-exchanged zeolite after drying, and extrusion molding was performed at 1 mmφ to obtain a desulfurization catalyst B (shown as “Cu / Y” in Table 1). The amount of copper supported in the desulfurization catalyst B was 15% by mass based on the zeolite.

Example 1
A fixed bed flow type reaction tube was filled with 6 ml of desulfurization catalyst A, the water content (shown as “H ₂ O concentration” in Table 1) was 0.2% by volume, and DSM (dimethyl sulfide) was used as a sulfur compound. Methane gas containing 80 mass ppm in terms of sulfur atom equivalent was circulated at GHSV = 5000 h ⁻¹ at normal pressure and 30 ° C. In addition, content of the sulfur compound in methane gas is made into the density | concentration higher than usual for the purpose of an accelerated durability test. The sulfur concentration at the outlet of the reaction tube was measured by SCD (sulfur Chemiluminescence Detector) gas chromatography. After the start of the experiment, the gas flow was stopped when the sulfur atom equivalent concentration based on the total amount of hydrocarbon fuel of the sulfur compound in the exit gas was 0.05 ppm by volume or more, and desulfurization was performed between the start of the experiment and the end of the experiment. The amount of sulfur trapped in the catalyst A was calculated to determine the desulfurization performance.

(Examples 2 and 3)
Experiments were conducted in the same manner as in Example 1 except that the content of water in methane gas was 0.3% by volume (Example 2) and 0.4% by volume (Example 3), respectively. Asked.

(Comparative Examples 1 and 2)
Experiments were conducted in the same manner as in Example 1 except that the contents of water in methane gas were 0.5% by volume (Comparative Example 1) and 1.0% by volume (Comparative Example 2), respectively. Asked.

(Comparative Example 3)
Except for using 6 ml of desulfurization catalyst B instead of desulfurization catalyst A, an experiment was performed in the same manner as in Example 1 to obtain desulfurization performance.

(Comparative Example 4)
An experiment was performed in the same manner as in Comparative Example 3 except that the content of water in methane gas was 1.0% by volume, and desulfurization performance was obtained.

  The desulfurization performance obtained in each of Examples 1 to 3 and Comparative Examples 1 to 4 was evaluated by relative comparison with the performance of Comparative Example 1 as 1. The evaluation results are as shown in Table 1.

  As shown in Table 1, when the hydrocarbon fuel containing water is desulfurized using the desulfurization catalyst A (Ag / X), the water content in the hydrocarbon fuel is 0.2 to 0.4. By setting it within the range of volume%, the desulfurization performance could be improved as compared with the case where the water content was 0.5 volume% or more. On the other hand, when the desulfurization catalyst was changed to the desulfurization catalyst B (Cu / Y), the desulfurization performance was inferior. In the present invention, since the water content in the hydrocarbon-based fuel may be in the range of 0.2 to 0.4% by volume, a large-scale dehumidifying means or the like is unnecessary, and the practicality is high.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel supply part, 3 ... Desulfurization part, 4 ... Hydrogen generation part, 5 ... Cell stack, 20 ... Desulfurization system, 30 ... Hydrogen production system.

Claims (7)

A fuel supply unit for supplying a hydrocarbon-based fuel containing water and a sulfur compound to the subsequent stage;
A desulfurization unit that desulfurizes the hydrocarbon fuel supplied from the fuel supply unit using a catalyst in which silver is supported on X-type zeolite,
The desulfurization system, wherein a content of the water in the hydrocarbon fuel supplied by the fuel supply unit is 0.2 to 0.4% by volume based on the total amount of the hydrocarbon fuel.   The desulfurization system according to claim 1, wherein the hydrocarbon fuel includes a hydrocarbon compound having 4 or less carbon atoms.   A hydrogen production system comprising: the desulfurization system according to claim 1; and a hydrogen generation unit that generates hydrogen from the hydrocarbon fuel desulfurized in the desulfurization unit.   A fuel cell system comprising the hydrogen production system according to claim 3.   A fuel desulfurization method comprising a step of desulfurizing a hydrocarbon fuel containing a sulfur compound and 0.2 to 0.4% by volume of water using a catalyst in which silver is supported on an X-type zeolite.   The fuel desulfurization method according to claim 5, wherein the hydrocarbon fuel includes a hydrocarbon compound having 4 or less carbon atoms.   A method for producing hydrogen, comprising a step of reforming the hydrocarbon fuel desulfurized by the fuel desulfurization method according to claim 6 to obtain hydrogen.

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