JP2008277308A - Solid polymer electrolyte fuel cell power generating system and solid polymer electrolyte fuel cell power generating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, highly efficient and maintenance-free PEFC power generating system, realizing stable and highly-developed desulfurization with a small quantity of desulfurizing agent, which can afford a repeated start and stop with short starting time, and a PEFC (polymer electrolyte fuel cell) power generating method. <P>SOLUTION: The PEFC power generating system comprises the PEFC, and a fuel reforming system generating hydrogen-rich gas from raw fuel, of which, the fuel reforming system comprises at least a desulfurizer, a reforming reaction device, and a selective CO oxidizing reactor. The PEFC power generating system also comprises a vapor condensing and separating means condensing and separating vapor from at least a part of the reformed gas before being supplied to the selective CO oxidizing reactor, and a system of adding the gas with the vapor condensed, separated and removed by the vapor condensing and separating means to the raw fuel by recycling. A hydrogenation adsorptive desulfurizing agent, containing at least Cu, Zn and Ni or/and Fe, is used, as a desulfurizing agent of the desulfurizer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte fuel cell (PEFC) power generation system and a PEFC power generation method. More specifically, the present invention relates to a PEFC power generation system and a PEFC power generation method including a fuel reforming system that reforms a raw fuel containing a sulfur compound and supplies it as fuel for a fuel cell.

  A PEFC power generation system that uses hydrocarbons, alcohol, or the like as a raw fuel includes a fuel reforming system. In a fuel reforming system, hydrogen-rich gas containing a large amount of hydrogen that is fuel for a fuel cell is produced from raw fuel. As a method for efficiently producing a hydrogen-rich gas from raw fuel, a steam reforming method in which reformed gas is obtained by reacting steam and raw fuel in the presence of a catalyst has been widely put into practical use. Generally used in stationary fuel cell power generation systems. Since steam reforming catalysts are vulnerable to sulfur poisoning, when using raw fuels containing sulfur compounds (for example, hydrocarbon fuels such as city gas, LPG, naphtha, etc.), the raw fuel must be desulfurized before steam. Used for reforming.

  On the other hand, in the case of PEFC, if the concentration of CO in the hydrogen-rich gas used as fuel is high, the electrode catalyst of the battery is poisoned and the power generation performance decreases, so the CO concentration in the hydrogen-rich gas is usually 10 ppm. Must be less than or equal to

However, the reformed gas obtained by steam reforming hydrocarbons, alcohols, etc. usually contains 0.1% or more of CO. Therefore, in order to reduce the CO concentration to about 10 ppm or less, the reformed gas contains oxygen. (Air) is added, and a CO selective oxidation process is provided in which CO is selectively oxidized and converted to CO ₂ in the presence of a catalyst.

That is, a general fuel reforming system for a PEFC power generation system includes a desulfurizer filled with a desulfurizing agent that removes sulfur compounds from raw fuel, and the desulfurized raw fuel reacts with steam in the presence of a steam reforming catalyst. Reforming reactor that generates reformed gas and CO selective oxidation reactor that selectively oxidizes CO contained in reformed gas with oxygen in the air in the presence of a CO selective oxidation catalyst and converts it to CO ₂ And are included.

In addition, when using raw fuel that reduces efficiency due to constraints such as equilibrium when reformed at low temperatures such as hydrocarbons, in order to reduce the CO concentration in the reformed gas to about 0.1 to 1%, in general, A CO converter that converts CO in the reformed gas into CO ₂ by reacting with steam in the presence of a catalyst is provided prior to the CO selective oxidation reactor.

  In such a fuel reforming system in the PEFC power generation system, the flow of the process gas is unidirectional, and the reformed gas is not mixed with the raw fuel.

  In the desulfurizer, an adsorptive desulfurizing agent is used, and an ordinary temperature desulfurizing agent that performs adsorptive desulfurization at ordinary temperature is often used.

  However, the room temperature desulfurization agent not only has a small catch amount of sulfur compounds, but also does not have a high adsorption selectivity, and therefore adsorbs some hydrocarbons as well as sulfur compounds. For this reason, the amount of sulfur catch-up varies depending on the composition and temperature of the raw fuel. Furthermore, since the adsorbed hydrocarbons are desorbed due to changes in operating conditions and reach the reforming reactor at a high concentration, there is a problem of causing carbon deposition on the reforming catalyst.

  As a desulfurizing agent that can solve these problems, Japanese Patent Laid-Open Nos. 1-123627 and 1-123628 disclose copper-zinc-based desulfurizing agents and copper-zinc-aluminum-based desulfurizing agents. When these desulfurization agents are used, sulfur in the raw fuel can be stably desulfurized to 1 ppb or less.

  However, even when these desulfurizing agents are used, the amount of the desulfurizing agent must be increased in order to maintain a high desulfurization level.

  On the other hand, in general, a hydrodesulfurization process is employed in order to perform stable desulfurization by reducing the amount of desulfurizing agent used. Hydrodesulfurization uses sulfurized Ni-Mo and Co-Mo-based catalysts, converts organic sulfur to hydrogen sulfide in the presence of hydrogen in the presence of hydrogen at 250 to 350 ° C, and reacts this hydrogen sulfide with ZnO, an adsorptive desulfurization agent And desulfurized as ZnS. As a hydrogen source for hydrogenation, hydrogen obtained by reforming is usually recycled and mixed with raw fuel.

  However, in this method, the desulfurization level is usually about 0.1 ppm, and a small amount of sulfur slips into the reforming process. Therefore, sulfur poisoning shortens the life of the reforming catalyst, and S in the steam reforming process. Economical operation with low / C (steam / carbon ratio in raw fuel) is not possible.

  Moreover, since raw fuel cannot be input unless the temperature exceeds 250 ° C., it takes a long time to start, and is not suitable for applications such as fuel cells. Actually, in an on-site phosphoric acid fuel cell employing such a hydrodesulfurization process, it takes about 3 hours from starting operation to generating power.

  Furthermore, since there is no hydrogen for hydrogenation at startup, it is necessary to prepare hydrogen separately to avoid catalyst poisoning, but PEFC is expected to be applied as a small power generation system for home use. Preparation of hydrogen is difficult to consider because of cost and maintainability. In addition, since start-up and stop-off are frequently performed for household use, omission of hydrogenation for hydrogenation during start-up immediately leads to deterioration of the reforming catalyst.

  On the other hand, with regard to hydrogen recycling, large-scale hydrogen production plants recycle product hydrogen and add it to raw fuel. However, the fuel reforming system included in the fuel cell power generation system does not purify hydrogen, so it is improved. Quality gas and anode off-gas are recycled. In the 200kW class phosphoric acid fuel cell power generation system, the flow rate of the recycle gas is large and the battery operating temperature is as high as about 180-200 ° C, so that water vapor does not condense in the recycle gas. In the case of a small kW class PEFC power generation system, the operating temperature of the battery is as low as about 80 ° C or less, and the flow rate is extremely low, so the moisture contained in the recycle gas condenses in the recycle line, causing a blockage problem. There is a case.

  Furthermore, in the case of a PEFC power generation system, since air is added in a CO selective oxidation reactor, there is a problem that nitrogen is supplied to the reforming reactor and ammonia that adversely affects PEFC is generated. And anode off-gas could not be recycled.

  The present invention realizes stable advanced desulfurization with a small amount of desulfurization agent by enabling the recycling of reformed gas, which is a problem especially when applied to small PEFC systems, and ensuring desulfurization performance at startup. Another object of the present invention is to provide a PEFC power generation system and a PEFC power generation method that are small in size, highly efficient, maintenance-free, and capable of increasing the frequency of start and stop with a short start time.

  As a result of intensive studies in view of the above problems, the present inventors branch the recycle gas from the upstream side of the CO selective oxidation reactor to condense and separate moisture from the gas. As a result, it has been found that stable operation is possible even with a small size without generating ammonia and without causing trouble due to moisture condensation in the recycle line.

  In addition, when a specific hydrogenated adsorptive desulfurization agent is used, it has hydrogenation activity, and even under conditions in which hydrogen does not coexist, if it is not continuous for a long period of time, 1 ppb of organic sulfur compounds in the raw fuel can be obtained by adsorptive desulfurization. We found that it can be removed to the following levels.

  Furthermore, sulfur compounds can be adsorbed even at room temperature for a short time, and sulfur compounds in raw fuel can be removed to a level of 1 ppb or less, and the adsorbed sulfur compounds are desulfurizing agents up to about 250 ° C. which is a preferred operating temperature. After being heated, it is decomposed and sulfur is absorbed into the bulk. Therefore, even if the raw fuel is added when the desulfurizing agent is not sufficiently heated during startup, the catalyst will not slip into the reforming process. I found nothing.

That is, the present invention relates to the following polymer electrolyte fuel cell power generation system and polymer electrolyte fuel electronic power generation method.
1. A solid polymer comprising at least a fuel reforming system that reforms raw fuel to generate a hydrogen-rich gas, and a fuel cell that generates electricity by electrochemically reacting the hydrogen-rich gas and oxygen via a solid polymer electrolyte Type fuel cell power generation system, wherein the fuel reforming system reacts with steam in the presence of a desulfurizer filled with a desulfurizing agent that removes sulfur compounds from the raw fuel and a steam reforming catalyst. Reforming reactor that generates reformed gas and CO selective oxidation reactor that selectively oxidizes CO contained in reformed gas with oxygen in the air in the presence of a CO selective oxidation catalyst and converts it to CO ₂ A water vapor condensing / separating means for condensing and separating water vapor from at least a part of the reformed gas before being supplied to the CO selective oxidation reactor, and the water vapor condensing / separating means. Steamed There the system is provided to add by recycling condensed separated and removed gas to a raw fuel,
A solid polymer fuel cell power generation system characterized in that desulfurization is performed using a hydrogenated adsorption desulfurization agent containing at least Cu, Zn, Ni, and / or Fe as a desulfurization agent of the desulfurizer.
2. A CO reformer, in which the fuel reforming system, converts between the reforming reactor and the CO selective oxidation reactor to CO ₂ by reacting most of the CO in the reformed gas with steam in the presence of the CO shift catalyst 2. The polymer electrolyte fuel cell power generation system according to 1 above, which is installed.
3. The fuel reforming system includes a raw fuel compressor that compresses and supplies gaseous raw fuel upstream of the desulfurizer, and a part of the reformed gas before being supplied to the CO selective oxidation reactor is provided. 3. The polymer electrolyte fuel cell power generation system according to the above 1 or 2, wherein means for adding to the raw fuel is provided by supplying water vapor to the suction side of the raw fuel compressor after being condensed and separated.
4). The hydrogenated adsorptive desulfurizing agent is a hydrogenated adsorptive desulfurizing agent obtained by hydrogen reduction of a composition obtained by impregnating and supporting Ni and / or Fe in a mixture containing at least Cu and Zn oxides obtained by a coprecipitation method. 4. The polymer electrolyte fuel cell power generation system as described in 1 to 3 above.
5. A means for condensing and separating water vapor in the reformed gas is provided immediately before being supplied to the CO selective oxidation reactor, and all the reformed gas is supplied to the water vapor condensing and separating means, and after steam separation, for CO selective oxidation. 5. The polymer electrolyte fuel cell power generation system according to any one of 1 to 4, wherein means for recycling a part of the reformed gas before adding the air is added to the raw fuel.
6). A solid polymer comprising at least a fuel reforming process for reforming raw fuel to generate a hydrogen-rich gas, and a fuel cell that generates electricity by electrochemically reacting the hydrogen-rich gas and oxygen via a solid polymer electrolyte Type fuel cell power generation method, a desulfurization process in which sulfur compounds are removed from raw fuel with a desulfurization agent, and reforming in which desulfurized raw fuel is reacted with steam in the presence of a steam reforming catalyst to generate reformed gas During normal operation in a fuel reforming process including at least a CO selective oxidation process that selectively oxidizes CO contained in reformed gas with oxygen in the air in the presence of a CO selective oxidation catalyst and converts it to CO ₂ , At least a part of the reformed gas before being subjected to the CO selective oxidation process is condensed and separated by a steam condensation separation process, and the steam is separated by the steam condensation separation process. Recycled gas that has been condensed and removed, added to the raw fuel, and in the above desulfurization process, desulfurization using a hydrogenated desulfurization agent containing at least Cu, Zn, Ni and / or Fe Polymer fuel cell power generation method.
7). After the fuel reforming process, the presence of most of the CO shift catalyst in CO in the reformed gas leaving the reforming process, and subjected to CO conversion process of converting the CO ₂ is reacted with steam, during normal operation 7. The polymer electrolyte fuel cell power generation method according to 6 above, which is a fuel reforming process in which at least a part of the reformed gas before being subjected to the CO selective oxidation process is subjected to a steam condensation separation process.
8). The hydrogenated adsorptive desulfurizing agent is a hydrogenated adsorptive desulfurizing agent obtained by hydrogen reduction of a composition obtained by impregnating and supporting Ni and / or Fe in a mixture containing at least Cu and Zn oxides obtained by a coprecipitation method. 8. The polymer electrolyte fuel cell power generation method according to 6 or 7 above.
9. 9. The polymer electrolyte fuel cell power generation method according to 6 to 8, wherein the raw fuel is a gaseous hydrocarbon mainly composed of alkane having 4 or less carbon atoms.
10. 10. The polymer electrolyte fuel cell power generation method according to 9 above, wherein S / C (steam / carbon molar ratio in raw fuel) in the steam reforming process is 2 to 3.
11. 11. The polymer electrolyte fuel cell power generation method according to 9 or 10 above, wherein the volume ratio of the flow rate of the gas used for recycling to the raw fuel gas flow rate is 0.001 to 0.05.
12 11. The polymer electrolyte fuel cell power generation method according to any one of 6 to 10 above, wherein when the reformed gas cannot be recycled, such as at the time of start-up, the reformed gas is temporarily suspended and the desulfurization process is performed, and then the recycling is started.

  According to the present invention, troubles due to water condensation and ammonia generation during recycling of reformed gas, which are problems when applied to a small PEFC system, can be avoided. The present invention can be suitably used particularly for a polymer electrolyte fuel cell power generation system including a small PEFC of about 5 kW or less (more preferably about 0.5 to 2 kW).

  In the present invention, the desulfurization performance can be ensured not only at the steady state but also at the start-up when the hydrogenation hydrogen is not supplied. As a result, even when only a small amount of the desulfurizing agent is used, stable and high-quality desulfurization can be realized.

  According to the present invention, it is possible to obtain a PEFC power generation system that is small, highly efficient, maintenance-free, and has a short start-up time and a high start-stop frequency.

  The PEFC power generation system according to the present invention includes a fuel reforming system that reforms raw fuel to generate a hydrogen-rich gas, and generates electricity by electrochemically reacting the hydrogen-rich gas and oxygen via a solid polymer electrolyte. And at least a fuel cell.

  The fuel cell used in the present invention is not particularly limited as long as it is a fuel cell that generates electricity by electrochemically reacting a hydrogen-rich gas and oxygen or oxygen in the air via a solid polymer electrolyte. Also, the PEFC power generation method according to the present invention is not particularly limited with respect to the fuel cell operation method. The effect of the present invention is enhanced when a so-called PEFC that operates the fuel cell at about 100 ° C. or less is used.

As illustrated in FIG. 1, the fuel reforming system used in the present invention includes a desulfurizer 1 filled with a desulfurizing agent that removes sulfur compounds from raw fuel 6 and the desulfurized raw fuel in the presence of a steam reforming catalyst. Reforming reactor 2 that reacts with water vapor 7 to generate reformed gas, and CO contained in the reformed gas is selectively oxidized with oxygen in air 8 in the presence of a CO selective oxidation catalyst and converted to CO ₂ . At least one of the reformed gases before being supplied to the CO selective oxidation reactor, which is positioned in the order of the desulfurizer, the reforming reactor, and the CO selective oxidation reactor from the upstream side. There is provided means for condensing and separating the water vapor contained in the reformed gas and recycling it to the raw fuel.

  Hereinafter, a part of the reformed gas after the water vapor is condensed and separated, and the gas added to the raw fuel is referred to as a recycle gas. A line through which recycled gas flows is called a recycling line.

  The hydrogen-rich gas exiting the CO selective oxidation reactor is supplied to the PEFC as fuel, but if necessary, a shut-off valve, check valve, flow control valve, purge branch line, A humidifier or the like may be provided.

In order to reduce the CO concentration in the reformed gas entering the CO selective oxidation reactor, most of the CO in the reformed gas is placed between the reformer reactor 2 and the CO selective oxidation reactor 3 as shown in FIG. A CO converter 11 may be installed which reacts with water vapor in the presence of a CO conversion catalyst to convert to CO ₂ . In this case, the recycle line 5 may be structured to branch the gas between the CO converter 11 and the CO selective oxidizer 3. At this time, before adding the CO selective oxidation air to the reformed gas, it is necessary to branch the reformed gas into a recycle line and a line to the CO selective oxidation reactor.

  The desulfurizer used in the present invention is filled with a hydrogenated desulfurization agent containing at least Cu, Zn, Ni and / or Fe, and the reformed gas before being supplied to the raw fuel and the CO selective oxidation reactor. A mixed gas with a recycle gas obtained by condensing and separating water vapor contained in the reformed gas from a part is supplied.

  When the pressure of the raw fuel supplied to the desulfurizer is insufficient, a raw fuel compressor 12 for boosting the raw fuel may be installed upstream of the desulfurizer as shown in FIG. Further, a structure may be adopted in which the recycle gas is supplied to the intake side of the raw fuel compressor. In this case, there is an advantage that a recycle gas blower for mixing the recycle gas with the raw fuel may be omitted.

  The reforming reactor used in the present invention may be a commonly used steam reforming reactor, which is filled with a steam reforming catalyst such as Ni-based or Ru-based, and usually has a means for supplying steam 7 and is necessary for the reaction. Means for supplying heat are provided. Moreover, you may provide the water vapor generator which evaporates water and generate | occur | produces the water vapor | steam for reforming.

  The CO selective oxidation reactor used in the present invention may be a commonly used CO selective oxidation reactor, which is filled with a CO selective oxidation catalyst such as Pt-based or Ru-based, and is provided with means for supplying normal air 8. However, in the present invention, the recycle line must be branched from the reformed gas before the air is mixed.

  As a means for condensing and separating water vapor from the reformed gas used in the present invention, there is no particular limitation on the structure or the like as long as the water vapor is not condensed in the line on the downstream side of the means. For example, a water-cooled condenser and a gas-liquid separator can be combined and the drain can be extracted.

  Further, the means for condensing and separating the water vapor may be mounted on the recycle line as shown in FIGS. 1 to 3, and as shown in FIG. 4, the water can be condensed and separated by allowing the entire reformed gas to pass therethrough. You may attach to. In the latter case, after the water vapor is condensed and separated, the recycle line may be branched before adding air in the CO selective oxidation reactor. In this case, since the reformed gas entering the CO selective oxidation reactor is separated from water vapor, the operating temperature range of the CO selective oxidation reactor is widened and operation at a low temperature is possible. Therefore, there is an advantage that the controllability and stability of the CO selective oxidation reactor, which is a problem in the operation of the fuel reforming system of the PEFC power generation system, is improved. In the flow shown in FIG. 4, if necessary, means for condensing and separating water vapor may be further provided on the recycle line.

  Although not shown in the figure, the recycle line used in the present invention may be provided with a shut-off valve, a control valve, a check valve, a blower, a metering pump, etc., if necessary. However, when the hydrogenated adsorptive desulfurization agent according to the present invention is used, it is not always necessary to strictly control the amount of the recycle gas according to the flow rate of the raw fuel. In addition, CO is selected for a system that uses low-pressure city gas in Japan with a gauge pressure of about 2 kPa as raw fuel, compresses raw fuel using a raw fuel compressor, and adds recycle gas to the intake side of the raw fuel compressor. Since the back pressure of the process gas after the oxidation reactor is usually much higher than 2 kPa, there is no back flow even if a check valve is not provided on the recycle line.

  The hydrogenated desulfurization agent containing at least Cu, Zn, Ni and / or Fe used in the present invention is not particularly limited, but in order to be usable under a wide range of conditions, Cu obtained by a coprecipitation method is used. Further, it is desirable to be a hydrogenated adsorptive desulfurization agent obtained by hydrogen reduction of a composition obtained by impregnating and supporting Ni and / or Fe on an oxide of Zn.

  The hydrogenated adsorptive desulfurization agent is not particularly limited as long as it is obtained by hydrogen reduction of a composition obtained by impregnating and supporting Ni and / or Fe on Cu and Zn oxides obtained by a coprecipitation method. It can be manufactured by the following manufacturing method.

  First, an aqueous solution that dissolves a water-soluble copper compound such as copper nitrate and copper acetate, and a water-soluble zinc compound such as zinc nitrate and zinc acetate, and an alkaline aqueous solution such as sodium carbonate are mixed and stirred to cause precipitation. The produced precipitate is washed with water, filtered and dried, then calcined in an oxidizing atmosphere such as air at about 270 to 400 ° C., further added with water to form a slurry, filtered, molded and dried to obtain copper oxide- A mixed molded body of zinc oxide is obtained. In addition, you may improve heat resistance by containing Al at the time of coprecipitation, and setting it as the mixed molded object of a copper oxide-zinc oxide-aluminum oxide.

  The ratio of copper and zinc in the copper oxide-zinc oxide mixed molded body is not particularly limited, but the atomic ratio is about 1: 0.3 to 10, preferably about 1: 0.5 to 3, more preferably 1 : 1 to 2.3. The size of the mixed molded body is not particularly limited, but if it is too small, the pressure loss of the process becomes large, and if it is too large, the amount of sulfur catch-up may be reduced. Therefore, a size of about 2 to 6 mm is usually preferable.

  Next, the copper oxide-zinc oxide mixed molded body obtained as described above is immersed in an aqueous solution in which water-soluble salts such as nitrates and acetates of Ni and / or Fe are dissolved, and Ni and / or Fe is added. After impregnating and drying, firing is usually performed at about 270 to 400 ° C. in an oxidizing atmosphere such as air to obtain a hydrogenated adsorptive desulfurizing agent precursor. At this time, the content of Ni and / or Fe in the precursor is preferably adjusted to be about 1 to 10% by weight.

  Next, the precursor obtained above is reduced at about 150 to 350 ° C. in the presence of a mixed gas of hydrogen and inert gas containing about 6% by volume or less, preferably about 0.5 to 4% by volume of hydrogen. By processing, a desired hydrogenated adsorptive desulfurization agent can be obtained.

  Examples of the raw fuel supplied to the PEFC power generation system of the present invention include hydrocarbons and alcohols. In the case of a synthetic fuel that does not contain any sulfur compounds, the system according to the invention can be used but is not very effective. Examples of raw fuels containing sulfur compounds include LPG such as natural gas, propane gas, and butane gas supplied as city gas, naphtha, and the like. Gaseous hydrocarbons mainly composed of alkanes having 4 or less carbon atoms such as natural gas and LPG are more preferred. When such a gaseous hydrocarbon containing alkane as a main component is used, the effects of the present invention can be obtained more stably and under a wide range of operating conditions.

  In the PEFC power generation method according to the present invention, the raw fuel is first desulfurized by a desulfurization process. In normal operation, recycle gas obtained by condensing and separating water vapor from reformed gas before being subjected to the CO selective oxidation process is mixed with raw fuel before desulfurization, and this is mixed with Cu, Zn, Ni and / or Fe. It desulfurizes by contacting with the hydrogenated adsorption desulfurizing agent contained at least. The temperature of the desulfurizing agent at this time is preferably about 100 to 400 ° C, more preferably about 200 to 300 ° C.

  The flow rate of the recycle gas to be added can be appropriately set according to the type and concentration of the sulfur compound in the raw fuel, the composition of the recycle gas and the raw fuel, and the like. For example, as long as the sulfur content is on the order of ppm and the alkene that is easily hydrogenated is not contained in the raw fuel, it is sufficient that the hydrogen is about 0.0005 or more by volume with respect to the raw fuel, More preferably, it is about 0.005 or more. Since the recycle gas in the present invention usually has a hydrogen concentration of about 50% or more, the flow rate of the recycle gas is about 0.001 or more, more preferably about 0.01 or more by volume ratio to the raw fuel.

On the other hand, in the desulfurization process according to the present invention, even if hydrogen is present in excess, the desulfurization performance is not substantially affected. However, as the proportion of recycled gas added increases, there is a risk that the temperature rise will increase if a side reaction occurs in which CO ₂ or CO and hydrogen contained in the recycled gas react on the desulfurization agent to produce methane. is there. Therefore, unless the raw fuel has a particularly high sulfur concentration and alkenes that are easily hydrogenated are not significantly contained, the recycle gas flow rate should be about 0.05 or less by volume with respect to the raw fuel. Is preferred. Even when the recycle gas is completely methanated, the temperature rise in the desulfurization process is only tens of degrees Celsius, so that no substantial problem occurs as long as the operation is performed in a more preferable temperature range. Therefore, even when the flow rate of the raw fuel is changed in accordance with the power generation amount, when the volume ratio of the recycle gas is about 0.001 to 0.05 which is a preferable range in the entire flow rate range of the raw fuel, In particular, it is not necessary to control the flow rate of the recycled gas.

  The pressure in the desulfurization process is more preferably around normal pressure, but if a hydrogenated desulfurization agent obtained by the production method described above is used, the pressure can be increased to about 1 MPa with a gauge pressure.

The GHSV (space velocity per gas hour) of the desulfurization process is designed as appropriate depending on the type and concentration of sulfur compounds in the raw fuel, operating time, etc., but the sulfur content is on the order of ppm and is easily hydrogenated. Unless alkene is contained in the raw fuel, GHSV may be determined to be about 100 to 5000 h ⁻¹ , preferably about 200 to 2000 h ⁻¹ .

  When the desulfurization process is operated under such operating conditions, the sulfur concentration in the raw fuel can be easily reduced to 1 ppb level or less.

  On the other hand, in an operating state where the reformed gas cannot be recycled, such as at the time of startup, the raw fuel may be directly desulfurized by contacting the hydrogenated adsorbent desulfurizing agent without recycling the reformed gas. Cases where the reformed gas cannot be recycled, such as when starting, include when the hydrogen concentration of the recycled gas is too low (usually around 50% or less), or when the CO concentration of the recycled gas is too high (usually around 2% or more) Is the case.

  The time during which sufficient desulfurization performance can be obtained without recycling is dependent on the composition of the raw fuel, the type and concentration of sulfur compounds, the elapsed time of use of the desulfurizing agent, etc. As long as the content is on the order of ppm, alkene that is easily hydrogenated is not contained in the raw fuel, and is operated with a properly designed GHSV in the preferred temperature range, about 10 to 100 hours Desulfurization performance can be maintained continuously. Thereafter, if the reformed gas is recycled, fresh hydrogen is supplied to the desulfurization agent. Therefore, even if the recycle is stopped again, the desulfurization performance can be maintained continuously for about 10 to 100 hours.

  Further, at the time of start-up, when the desulfurizing agent has not reached the preferred temperature range, it is possible to desulfurize the raw fuel by directly contacting the hydrogenated adsorbing desulfurizing agent without adding the recycle gas. The time during which sufficient desulfurization performance is obtained in this state depends on the composition of raw fuel, the type and concentration of sulfur compounds, the elapsed time of use of the desulfurization agent, etc., but the sulfur content is on the order of ppm, and hydrogen As long as the alkene to be converted is not contained in the raw fuel and is operated at the preferred GHSV, the desulfurization performance can be maintained continuously for about 1 to 3 hours. Then, if the temperature of the desulfurizing agent is raised and the reformed gas is recycled, the organic sulfur adsorbed on the desulfurizing agent is decomposed and fresh hydrogen is supplied. Therefore, the recycling is stopped again, and the temperature is lower than the preferred temperature. Even so, the desulfurization performance can be maintained continuously for about 1 to 3 hours.

  In addition, when the sulfur concentration in the raw fuel is high, the raw fuel is brought into contact with a known adsorbing desulfurizing agent such as ZnO to greatly reduce the amount of hydrogenated adsorbing desulfurizing agent used. After removing, it may be brought into contact with a hydrogenated adsorption desulfurizing agent.

  Furthermore, if the raw fuel contains a highly decomposable organic sulfur compound at a high concentration, or if the alkene that is easily hydrogenated is noticeably contained, first add a recycle gas to the raw fuel, then add Ni- Hydrogenate organic sulfur and alkenes by contacting with known hydrodesulfurization catalysts such as Mo-based and Co-Mo-based, then contact with the above-mentioned adsorptive desulfurizing agent to adsorb and remove most of the sulfur, and then hydrogenated adsorptive desulfurization. You may make it contact an agent. In this case, the volume ratio of the recycle gas needs to be set to be larger than that in the case of desulfurization only with the hydrogen adsorption desulfurization agent in accordance with the use conditions of the known hydrodesulfurization catalyst. It is desirable to use an adsorbed desulfurizing agent.

  The raw fuel desulfurized by the desulfurization process is mixed with steam and used for the steam reforming process. In the PEFC power generation system, since the operating temperature of the PEFC is low, it is not possible to generate steam for reforming using the exhaust heat of the PEFC, and it is necessary to consume excess fuel to generate steam. In order to increase the thermal efficiency of the quality system and improve the power generation efficiency of the PEFC power generation system, it is only necessary to operate at a low S / C ratio (steam / carbon ratio in raw fuel). In the present invention, the steam reforming catalyst used in the steam reforming process and the reaction conditions may be known methods, but with the PEFC power generation method according to the present invention, the sulfur in the raw fuel is stable and below 1 ppb level. Therefore, low S / C operation with S / C <3 is possible. When natural gas, LPG, or the like is used as the raw fuel, it is preferable to operate at S / C of about 2 to 3, preferably about 2.2 to 2.8, at which power generation efficiency is maximized.

  When the CO concentration in the reformed gas produced by the steam reforming process is as high as about 1% or more, the reformed gas is preferably subjected to a CO shift process. In the present invention, the CO conversion catalyst used in the CO conversion process may be a known CO conversion catalyst such as a Cu-Zn-based catalyst, and the reaction conditions may be known conditions, but the CO reduction performance and durability in the CO selective oxidation process. It is preferable to reduce the CO concentration as much as possible in the CO conversion process, and the CO concentration in the reformed gas at the CO conversion outlet is preferably 1 on a dry basis. It is desirable to select the reaction conditions for the CO shift process so that it is about% or less, more preferably about 0.5% or less.

  The reformed gas generated by the steam reforming process or the reformed gas in which CO has been reduced by the CO conversion process is subjected to a CO selective oxidation process after adding air for oxidation. In the present invention, the CO selective oxidation catalyst and reaction conditions used in the CO selective oxidation process may be known methods, but the reformed gas before adding the oxidation air is branched for recycling.

  The process of condensing and separating water vapor from the reformed gas to be recycled may be performed after the recycle gas is branched and mixed into the raw fuel, or after the water vapor is condensed and separated from the entire reformed gas, the recycle gas is removed. It may be branched and added to the raw fuel.

  When condensing and separating water vapor from reformed gas, it is not always necessary to completely condense and separate water vapor, and conditions, methods, etc. so that water vapor does not condense before the recycle gas is added to the raw fuel from the recycle line. May be set as appropriate. For example, it is possible to exemplify a method in which water at normal temperature (about 10 to 25 ° C.) is circulated through a water-cooled water vapor condenser to condense the water vapor and extract the drain with a steam-water separator.

  The hydrogen-rich gas exiting the CO selective oxidation reactor is supplied to the PEFC and generates electric power through an electrochemical reaction with oxygen or air. A method for generating electricity with PEFC using the hydrogen-rich gas as a fuel is not particularly limited, and a method for generating electricity with PEFC using a known hydrogen-rich gas as a fuel can be applied.

  In addition, when the composition of the hydrogen-rich gas is not suitable for power generation by PEFC, such as at the time of startup, it may be processed by burning it as it is without supplying it to PEFC.

  When the system is shut down, there is no particular limitation as long as measures are taken to prevent air from entering the fuel reforming system. Since the raw fuel can be input within a short time (about 1 to 3 hours as the rated gas flow rate) after the recycling is stopped, if the raw fuel is a gas, the fuel reforming system is purged with the raw fuel. You can also. The PEFC stop operation may be performed according to a conventional method.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using a reference example, an Example, and a comparative example, this invention is not limited to an Example.

Reference example 1
A mixed aqueous solution containing copper nitrate, zinc nitrate and aluminum hydroxide in a molar ratio of 1: 1: 0.3 was added dropwise to an aqueous sodium carbonate solution maintained at about 60 ° C. with stirring to cause precipitation. The resulting precipitate was washed with water, filtered and dried, then tableted into a 1/8 inch diameter x 1/8 inch length and fired at about 300 ° C. to form a copper oxide-zinc oxide-aluminum oxide mixture molded body. Obtained.

  Subsequently, the obtained mixture molded body was immersed in an aqueous nickel nitrate solution so as to be impregnated with nickel, dried, and then fired at about 300 ° C. to obtain a desulfurizing agent precursor. The nickel concentration in the obtained desulfurizing agent precursor was 5% by weight.

  By reducing the desulfurization agent precursor obtained above at about 200 ° C. in a hydrogen-nitrogen mixed gas stream containing 2% by volume of hydrogen, a Cu—Zn—Al—Ni hydrogenated adsorption desulfurization agent was obtained. Obtained.

Reference example 2
To the SUS reaction tube (catalyst layer length 30 cm) filled with the Cu—Zn—Al—Ni hydrogenated adsorption desulfurization agent obtained in Reference Example 1, the city gas (13A gas) having the composition shown in Table 1 was added. Desulfurization was performed under the conditions of GHSV = 2000 h ⁻¹ , hydrogen / city gas = 0.01 (molar ratio), pressure 0.02 kg / cm ² -G, temperature 250 ° C. The sulfur content in the gas after desulfurization was 0.1 ppb or less over 5000 hours.

Table 1
Methane 88%
Ethane 6%
Propane 3%
Butane 3%
Dimethyl sulfide 3mg-S / Nm ³
t-Butyl mercaptan 2mg-S / Nm ³
Reference example 3
The city gas was desulfurized in the same manner as in Reference Example 2 except that the Cu—Zn—Al—Ni hydrogenated adsorption desulfurization agent obtained in Reference Example 1 was used and hydrogen was not added. The sulfur content in the gas after desulfurization was 0.1 ppb or less over 200 hours.

Reference example 4
The city gas was desulfurized in the same manner as in Reference Example 2 except that the Cu—Zn—Al—Ni-based hydrogenated adsorptive desulfurization agent obtained in Reference Example 1 was used and the temperature was set to room temperature (about 25 ° C.). The sulfur content in the gas after desulfurization was 0.1 ppb or less over 20 hours.

Example 1
The basic flow constituted the PEFC power generation system shown in FIG. In other words, the SUS desulfurizer 1 filled with 100 ml of the Cu-Zn-Al-Ni hydrogenated adsorptive desulfurization agent obtained in Reference Example 1 and the external heating steam reforming reaction filled with 200 ml of the Ru-based steam reforming catalyst. , A heat exchange type CO converter 11 charged with 800 ml of a Cu-Zn-based CO shift catalyst, a CO selective oxidation reactor 3 charged with 200 ml of a Ru-based CO selective oxidation catalyst, and a 1 kW-class atmospheric pressure PEFC The stacks 9 were combined according to the flow shown in FIG. In addition, a part of the reformed gas at the outlet of the CO converter was branched and introduced into a steam condenser consisting of a water-cooled condenser and a steam / water separator. .

Example 2
A power generation test was conducted using the PEFC power generation system of Example 1. As raw fuel, city gas 4.2 l / min (standard state) shown in Table 1 was used. Recycled gas 50 ml / min (standard state) with a dew point of 20 ° C. or less by condensing and separating water vapor was added thereto, and the mixed fuel gas was preheated to 250 ° C. and desulfurized with a desulfurizer. Steam was added to the desulfurized raw fuel so that S / C = 2.5, and the raw fuel was supplied to an external heat steam reforming reactor maintained at an inlet of about 450 ° C. and an outlet of about 650 ° C. to obtain a reformed gas. The resulting reformed gas is cooled to about 250 ° C and supplied to a CO converter, so that most of the CO is removed with the remaining steam.
Converted to CO ₂ . A part of this gas was branched, and water vapor was condensed and separated into a recycled gas. For the remaining reformed gas, 0.8 l / min (standard condition) of air was added to a CO selective oxidation reactor whose temperature was controlled so that the inlet temperature was maintained at 90 ° C and the temperature of the catalyst layer did not exceed 180 ° C. CO was reduced to 10ppm or less. Using the hydrogen-rich gas thus obtained as fuel and air as an oxidant, the PEFC stack generated electricity at a constant current at a hydrogen utilization rate of approximately 70%, and a DC power of approximately 1.1 kW was obtained.

  At this time, the sulfur concentration in the raw fuel after desulfurization was 0.1 ppb or less. The methane concentration in the hydrogen-rich gas supplied to PEFC was 1.8%, and the CO concentration was less than 1 ppm. On the other hand, the hydrogen concentration in the recycled gas was about 75%.

  Furthermore, when the operation was continued for about 1000 hours, the DC power of about 1.1 kW was continuously obtained although the PEFC voltage dropped slightly. At this time, the sulfur concentration in the raw fuel gas after desulfurization was 0.1 ppb or less. The methane concentration in the hydrogen-rich gas supplied to PEFC was 1.8%, and the CO concentration was less than 1 ppm.

Comparative Example 1
Electricity was generated in the same manner as in Example 2 except that a part of the CO selective oxidation reactor outlet gas was used as the recycle gas. In the very beginning, DC power of about 1.1 kW was obtained, but then the voltage gradually decreased, and after about 300 hours, the generated power was cut below 1 kW. Furthermore, after about 200 hours, the voltage dropped sharply and power generation was stopped.

  When the CO selective oxidation reactor outlet gas was analyzed, about 0.1 ppm of ammonia was detected.

Example 3
The heat exchanger excluding each reactor and the heat exchanger for steam condensation separation is composed of plate-shaped elements with the same shape, and the fuel reforming system with the flow shown in Fig. 5 is manufactured by stacking and integrating these plate-shaped elements. did. The basic flow of the apparatus of FIG. 5 is the same as that of FIG. 4 except for the built-in steam generator except for the PEFC cell stack. The hydrogen-rich gas exiting the CO selective oxidation reactor was connected to be supplied as fuel to the PEFC stack, and a PEFC power generation system was configured.

  The gas exiting the CO converter is introduced into the water-cooled water vapor condensing separator to condense and separate the water vapor, and part of it is added as recycled gas to the intake side of the raw fuel compressor. It used for the selective oxidation reaction.

Here, the fuel gas is compressed by adding 50 ml / min (standard state) of the recycle gas with dew point of 20 ℃ or less to the city gas of 4.2 l / min (standard state) with the composition shown in Table 1. The pressure was increased to about 0.2 kg / cm ² with a heat exchanger, and after heat exchange, desulfurization was performed at about 250 ° C. with a desulfurizer filled with 100 ml of the Cu—Zn—Al—Ni hydrogen adsorption desulfurization agent obtained in Reference Example 1. . The raw fuel after desulfurization was steam reformed at S / C = 2.5, and then CO conversion was performed. After condensing and separating the steam, 0.8 l / min (standard state) of air was added and subjected to CO selective oxidation reaction. At this time, the reforming gas outlet reformed gas temperature is controlled to about 620 ° C, the CO converter outlet is about 150 ° C, the CO selective oxidation reactor inlet is about 25 ° C, and the catalyst layer of the CO selective oxidation reactor is The temperature was controlled so as not to exceed 160 ° C.

  At this time, the hydrogen concentration in the recycled gas was about 75%, the methane concentration in the obtained hydrogen-rich gas was 2.5%, the CO concentration was less than 3 ppm, and about 1.1 kW of electric power was obtained from PEFC.

  Furthermore, the system was continuously operated for 1000 hours, but the methane concentration and CO concentration in the obtained hydrogen-rich gas remained unchanged, and approximately 1.1 kW of electric power was continuously obtained from PEFC.

Comparative Example 2
Example except that the recycle of reformed gas was interrupted, and a room temperature desulfurizer filled with 100 ml of commercially available manganese oxide-based room temperature desulfurization agent was placed between the raw fuel compressor and the desulfurizer, and the desulfurizer was made hollow. The PEFC power generation system was configured in the same way as in Section 3.

  A power generation test was conducted in the same manner as in Example 3 except that desulfurization was performed at room temperature using a room temperature desulfurizer. As a result, in the initial stage, the methane concentration in the obtained hydrogen-rich gas was 2.5%, the CO concentration was less than 3 ppm, and about 1.1 kW of power was obtained from PEFC.

  Furthermore, when the operation was continued, the PEFC voltage began to drop significantly after about 600 hours. Furthermore, the operation was continued for about 100 hours, but the operation was stopped because the battery voltage finally dropped to a dangerous area.

  At this time, the methane concentration in the hydrogen-rich gas was 8.2%, and the CO concentration was less than 1 ppm. This is thought to be because the reforming catalyst was deteriorated by sulfur poisoning, the reforming performance was lowered, the flow rate of hydrogen was lowered, and the hydrogen utilization rate in PEFC was increased.

Example 4
A system similar to the PEFC power generation system used in Example 3 was used except that 400 ml of the hydrogenated adsorptive desulfurization agent was charged, and power generation was performed under the same conditions as in Example 3.

  The methane concentration and CO concentration in the hydrogen-rich gas obtained after 1000 hours did not change, and the PEFC output was maintained at about 1.1 kW.

  Subsequently, the fuel reforming system alone was operated while giving the following load fluctuations. First, run for 1 hour at 50% load, then run for 1 hour at 100% load as one cycle, and load fluctuations totaling 2900 cycles (running time including condition change time: 6100 hours) Gave. As operating conditions corresponding to 50% load, city gas 2.52 l / min (standard state) shown in Table 1 was used as raw fuel, and 30 ml / min (standard state) of recycle gas was added thereto. The operating conditions corresponding to 100% load are the same as the operating conditions in Example 3.

  The methane concentration and CO concentration in the obtained hydrogen-rich gas were the same as before the load fluctuation was given.

  After the load change was applied, the fuel reforming system was connected again to the PEFC, and power was generated while applying a 100% load. The PEFC output was about 1.1kW.

  From the above, it is clear that desulfurization is performed without any problem even if the flow rate of the gas flowing into the desulfurizer changes due to load fluctuation.

Example 5
Using the PEFC power generation system used in Example 3, the fuel reforming system was purged with nitrogen during shutdown. When starting up again, process gas is not circulated and the reforming reactor fuel is sent to raise the temperature of the reforming reactor, and the starting heater is activated to raise the temperature of the steam generator, desulfurizer, and CO converter. When the temperature of all the reactors through which the steam generator and process gas pass exceeded 120 ° C, raw water was started to be supplied to the steam generator. The city gas supply was started with the recycle line closed. At this time, the temperature of the desulfurizer was about 180 ° C., and the process gas temperature at the reformer outlet was 450 ° C. After continuing the temperature increase for about 20 minutes, air for CO selective oxidation reaction was introduced and the recycle line was opened. After that, after holding for about 20 minutes until the temperature of each part was stabilized, hydrogen-rich gas was supplied to PEFC, and power generation was started.

  The operation for 1000 hours including 50 stop / start operations was performed, but the resulting hydrogen-rich gas had a methane concentration of 2.4% and a CO concentration of less than 3 ppm. Obtained continuously.

  Furthermore, the operation was continued until the total number of stop / start operations was 135 and the total operation time was 1100 hours. There was no change in the methane concentration in the obtained hydrogen-rich gas, and approximately 1.1 kW of electric power was continuously obtained from PEFC.

Comparative Example 3
A power generation test including start and stop was performed in the same manner as in Example 5 except that 50 ml of Ni-Mo hydrodesulfurization catalyst and 50 ml of ZnO adsorption desulfurization agent were charged in the desulfurizer and the flow rate of the recycle gas was 500 ml.

  On the way, the PEFC voltage gradually began to drop, and eventually dropped to 1kW. At this time, the methane concentration in the hydrogen-rich gas increased to 5.7%.

Comparative Example 4
Electric power was generated in the same manner as in Example 2 except that a part of the gas at the CO transformer outlet was recycled without condensing and separating water vapor.

  The voltage often decreased after 2 hours from the start of power generation, and operation became impossible after 3 hours. This is probably due to water mixing in the raw fuel line and the flow becoming unstable.

FIG. 1 is a flowchart showing one embodiment of a PEFC power generation system according to the present invention. FIG. 2 is a flowchart showing another embodiment of the PEFC power generation system according to the present invention. FIG. 3 is a flowchart showing a third embodiment of the PEFC power generation system according to the present invention. FIG. 4 is a flowchart showing a fourth embodiment of the PEFC power generation system according to the present invention. FIG. 5 is a diagram illustrating a configuration and a flow of the PEFC power generation system used in the example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Desulfurizer 2 ... Reforming reactor 3 ... CO selective oxidation reactor 4 ... Steam condensing separator 5 ... Recycle line 6 ... Raw fuel 7 ... Process steam 8 ... CO selective oxidation air 9 ... Solid polymer fuel cell DESCRIPTION OF SYMBOLS 10 ... Drain 11 ... CO converter 12 ... Raw fuel compressor 13 ... Steam generator 14 ... Reformed gas cooling heat exchanger 15 ... Steam separator 16 ... Startup heater 17 ... CO selective oxidation reactor cooling fan 18 ... Raw water for steam generation 19 ... Fuel for reforming furnace 20 ... Combustion air 21 ... Heat insulating material 22 ... Combustion exhaust gas

Claims (6)

A solid polymer comprising at least a fuel reforming process for reforming raw fuel to generate a hydrogen-rich gas, and a fuel cell that generates electricity by electrochemically reacting the hydrogen-rich gas and oxygen via a solid polymer electrolyte Type fuel cell power generation method, a desulfurization process in which sulfur compounds are removed from raw fuel with a desulfurization agent, and reforming in which desulfurized raw fuel is reacted with steam in the presence of a steam reforming catalyst to generate reformed gas During normal operation in a fuel reforming process including at least a CO selective oxidation process that selectively oxidizes CO contained in reformed gas with oxygen in the air in the presence of a CO selective oxidation catalyst and converts it to CO ₂ , Before being subjected to the CO selective oxidation process and before adding the CO selective oxidation air to the reformed gas, at least a part of the reformed gas is condensed with steam by a steam condensation separation process. A hydrogenated adsorbing desulfurization agent containing at least Cu, Zn, Ni and / or Fe in the desulfurization process, wherein the gas obtained by condensing and separating the water vapor by the water vapor condensation process is recycled and added to the raw fuel. If the reformed gas cannot be recycled at the time of start-up, etc., it is temporarily decommissioned and the desulfurization process is stopped, and then the recycling is started. Fuel cell power generation method. After the fuel reforming process, the presence of most of the CO shift catalyst in CO in the reformed gas leaving the reforming process, and subjected to CO conversion process of converting the CO ₂ is reacted with steam, during normal operation 2. The solid polymer fuel cell power generation method according to claim 1, wherein the method is a fuel reforming process in which at least a part of the reformed gas before being subjected to the CO selective oxidation process is subjected to a steam condensation separation process. The hydrogenated adsorptive desulfurizing agent is a hydrogenated adsorptive desulfurizing agent obtained by hydrogen reduction of a composition obtained by impregnating and supporting Ni and / or Fe in a mixture containing at least Cu and Zn oxides obtained by a coprecipitation method. The solid polymer fuel cell power generation method according to claim 1 or 2. The solid polymer fuel cell power generation method according to any one of claims 1 to 3, wherein the raw fuel is a gaseous hydrocarbon mainly composed of alkane having 4 or less carbon atoms. 5. The polymer electrolyte fuel cell power generation method according to claim 4, wherein S / C (steam / carbon molar ratio in raw fuel) in the steam reforming process is 2 to 3. 6. The polymer electrolyte fuel cell power generation method according to claim 4, wherein a volume ratio of a flow rate of a gas used for recycling to a raw fuel gas flow rate is 0.001 to 0.05.

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