JP2004284875A - Hydrogen production system, and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable and high efficiency hydrogen production system even in the case where decomposition residual components are present in a reformed gas, and to provide a fuel cell system. <P>SOLUTION: The hydrogen production system is provided with: a reformer where hydrocarbon fuel is reformed to obtain a reformed gas comprising hydrogen; a CO transformer where the concentration of CO in the reformed gas is reduced by shift reaction; and a CO selective oxidizer where the concentration of CO in the gas reduced by the CO transformer is further reduced by selective oxidation reaction. In the downstream of the reformer, there is equipped with an adsorber provided with an adsorbent adsorbing decomposition residual components. The fuel cell system is provided with the hydrogen production system and a fuel cell. In the downstream of the reformer, which is also the upstream of the fuel electrode of the fuel cell, there is equipped with the adsorber adsorbing the decomposition residual components. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen production system that reforms a hydrocarbon fuel such as kerosene to produce a reformed gas containing hydrogen. More specifically, the present invention relates to a hydrogen production system including a reformer and a CO shift converter and a CO selective oxidizer to produce a reformed gas having a low CO concentration.
[0002]
The present invention also relates to a fuel cell system using a reformed gas obtained from such a hydrogen production system as a fuel.
[0003]
[Prior art]
Fuel cells are being actively developed as power generation systems with high energy use efficiency. Since a fuel cell is a system that generates power by an electrochemical reaction between hydrogen and oxygen, it is essential to establish a hydrogen supply means. As one of the methods, there is a method of reforming a hydrocarbon fuel to extract hydrogen, which is more advantageous than a method of using pure hydrogen in that a hydrocarbon fuel supply system has already been socially prepared.
[0004]
Hydrocarbon fuels include city gas, gasoline, kerosene, and light oil. Among them, liquid fuels such as gasoline, kerosene, and light oil are easy to handle, store and transport, and are inexpensive. Has attracted attention as a fuel for fuel cells. In order to use these hydrocarbon fuels in a fuel cell, it is necessary to extract hydrogen from the hydrocarbon fuels. For this reason, usually, the hydrocarbons are reacted with water in a reformer to produce mainly carbon monoxide. Decompose into hydrogen, then convert most of the carbon monoxide with water in a CO converter to convert it to hydrogen and carbon dioxide, and finally react a small amount of residual carbon monoxide with oxygen in a CO selective oxidizer to convert carbon dioxide. Is done.
[0005]
As a technique related to such reforming, Patent Literature 1 discloses a technique relating to an adsorption tower of a pressure fluctuation adsorption apparatus for hydrogen production, and Patent Literature 2 discloses a technique relating to removal of an acid gas in a vaporization power unit by generation of hydrogen. Patent Document 3 discloses a technique related to a steam separator for a fuel cell.
[0006]
[Patent Document 1]
JP 2001-300244 A
[Patent Document 2]
JP 2001-505615 A
[Patent Document 3]
JP-A-11-3722
[0007]
[Problems to be solved by the invention]
However, when a hydrocarbon fuel such as gasoline, kerosene, or light oil is decomposed by a reforming reaction, some residual components may be present. When this flows into, for example, a polymer electrolyte fuel cell, there is an adverse effect such as a decrease in power generation efficiency. Furthermore, the catalyst is poisoned by the decomposition residual components flowing into the CO conversion catalyst or the selective oxidation catalyst, which is the subsequent catalyst. In particular, low-temperature CO shift catalysts are susceptible to this effect.
[0008]
As one of the decomposition residual components, there is a residual hydrocarbon fuel in which the hydrocarbon fuel supplied to the reformer passes as it is without reacting in the reformer and remains in the reformed gas. Further, there are also by-products generated by the hydrocarbon fuel undergoing a side reaction in the reformer, that is, substances other than the original reforming reaction products such as hydrogen and carbon monoxide. Examples of the by-products include ammonia, oxygen-containing compounds such as formic acid and aldehyde.
[0009]
Methods for increasing the amount of the reforming catalyst or performing the reforming treatment at a high temperature of 700 ° C. or more to reduce the decomposition residual components are considered.
[0010]
However, when the amount of the reforming catalyst is increased, the capacity of the reformer is increased, which causes a reduction in the compactness of the hydrogen production system or the fuel cell system. Further, maintaining the reformer temperature at a high temperature promotes deterioration of the apparatus and the reforming catalyst, and requires a large amount of heat supply. Furthermore, even if these measures are taken, a decomposition residual component may be generated due to the deterioration of the reforming catalyst over time.
[0011]
An object of the present invention is to provide a hydrogen production system and a fuel cell system that can prevent performance degradation of a device for removing CO and a fuel cell main body even if decomposition residual components are generated from a reformer. Another object of the present invention is to suppress the influence of the residual components without increasing the amount of the reforming catalyst and without maintaining the reformer temperature at a high temperature, and to achieve a stable and highly efficient operation. It is to provide a hydrogen production system and a fuel cell system that can perform the above.
[0012]
[Means for Solving the Problems]
According to the present invention, a reformer for reforming a hydrocarbon fuel to obtain a reformed gas containing hydrogen, a CO converter for reducing the CO concentration in the reformed gas by a shift reaction, and a CO concentration in the CO converter In a hydrogen production system including a CO selective oxidizer that further reduces the CO concentration in the reduced gas by a selective oxidation reaction,
A hydrogen production system comprising an adsorber provided with an adsorbent for adsorbing residual decomposition components is provided downstream of the reformer.
[0013]
A hydrogen production system has a plurality of the adsorbers, and a flow path switching unit that shuts off the flow of the reformed gas for each of the adsorbers and flows the gas for desorption regeneration is provided.
The reformed gas flows into some of the adsorbers to perform adsorption, during which desorption regeneration is performed in the remaining adsorbers, and the adsorber that performs adsorption and desorption regeneration is sequentially switched to sequentially perform adsorption and desorption. It is preferable to provide a control device for enabling efficient hydrogen production.
[0014]
The adsorbent is preferably at least one selected from activated carbon and zeolite.
[0015]
The reformer may be a steam reformer, an autothermal reformer or a partial oxidation reformer.
[0016]
According to the present invention, a reformer for reforming a hydrocarbon fuel to obtain a reformed gas containing hydrogen, a CO converter for reducing the CO concentration in the reformed gas by a shift reaction, and a CO concentration in the CO converter A hydrogen production system including a CO selective oxidizer that further reduces the CO concentration in the gas with reduced CO by a selective oxidation reaction, and a fuel cell that uses a reformed gas whose CO concentration is reduced by the CO selective oxidizer as a fuel. In a fuel cell system comprising:
There is provided a fuel cell system comprising an adsorber provided with an adsorbent for adsorbing residual decomposition components downstream of the reformer and upstream of the fuel electrode of the fuel cell.
[0017]
A fuel cell system includes a plurality of the adsorbers, and a flow path switching unit that shuts off the flow of the reformed gas for each of the adsorbers and flows the gas for desorption regeneration is provided.
The reformed gas flows into some of the adsorbers to perform adsorption, during which desorption regeneration is performed in the remaining adsorbers, and the adsorber that performs adsorption and desorption regeneration is sequentially switched to sequentially perform adsorption and desorption. It is preferable to provide a control device that enables efficient hydrogen production.
[0018]
It is preferable that the gas for desorption regeneration is a fuel cell anode off-gas.
[0019]
It is preferable that the reformer includes a combustion means, and a fuel cell system having a line for leading the fuel cell anode off-gas used for the desorption regeneration to the combustion means.
[0020]
A fuel having a heat exchanger downstream of the fuel cell anode and upstream of the adsorber, which heats the fuel cell anode off-gas to a temperature equal to or higher than the desorption regeneration temperature of the adsorber by heat exchange with other gases in the fuel cell system. Battery systems are preferred.
[0021]
The effect of the present invention is particularly remarkable when the fuel cell is a polymer electrolyte fuel cell.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
The hydrogen production system of the present invention comprises a reformer for reforming a hydrocarbon fuel to obtain a reformed gas containing hydrogen, a CO converter for reducing the CO concentration in the reformed gas by a shift reaction, and a CO converter. It has a CO selective oxidizer that further reduces the CO concentration in the gas whose CO concentration has been reduced by a selective oxidation reaction. Further, a desulfurizer described later may be provided.
[0023]
Further, a fuel cell system of the present invention has at least the hydrogen production system and a fuel cell.
[0024]
Further, known components of the hydrogen production system or the fuel cell system can be appropriately provided as necessary. Specific examples include means for supplying an oxygen-containing gas such as air to the cathode of a fuel cell, a steam generator for generating water vapor for humidifying the gas supplied to the fuel cell, and cooling of various devices such as a fuel cell. Pressure control means such as a cooling system, a pump for pressurizing various fluids, a compressor, a blower, etc., and a flow control means such as a valve for adjusting the flow rate of the fluid or for shutting off / switching the flow of the fluid. Heat blocking / switching means, heat exchanger for heat exchange / heat recovery, vaporizer for vaporizing liquid, condenser for condensing gas, heating / heating means for externally heating various devices with steam, etc. They include storage means, air and electric systems for instrumentation, signal systems for control, control devices, and electric systems for output and power.
[0025]
(Reformer)
This is a device that reacts hydrocarbon fuel with water. In this device, hydrocarbon fuel is mainly decomposed into carbon monoxide and hydrogen. Usually, carbon dioxide and methane are also contained in the cracked gas. For example, examples of the reformer include a steam reformer that performs a steam reforming reaction as a decomposition reaction, an autothermal reformer that performs an autothermal reforming reaction, and a partial oxidation reformer that performs a partial oxidation reaction. it can.
[0026]
The steam reforming reaction is a reaction between steam and a hydrocarbon fuel. However, the steam reforming reaction involves a large heat absorption and usually requires external heating. Usually, the reaction is carried out in the presence of a metal catalyst represented by a Group VIII metal such as nickel, cobalt, iron, ruthenium, rhodium, iridium and platinum. The reaction can be carried out at a temperature of 450 ° C to 900 ° C, preferably 500 ° C to 850 ° C, more preferably 550 ° C to 800 ° C. The amount of steam introduced into the reaction system is defined as the ratio of the number of moles of water molecules to the number of moles of carbon atoms contained in the raw hydrocarbon fuel (steam / carbon ratio). Preferably it is 1-7, more preferably 2-5. The liquid hourly space velocity (LHSV) at this time can be represented by A / B when the flow velocity of the hydrocarbon fuel in the liquid state is A (L / h) and the volume of the catalyst layer is B (L). Preferably 0.05 to 20 h ^-1 , More preferably 0.1 to 10 h ^-1 , More preferably 0.2 to 5 hours ^-1 Is set in the range.
[0027]
The autothermal reforming reaction is a method in which a part of the hydrocarbon fuel is oxidized, and the steam generated by the heat generated at this time is allowed to proceed to reform the steam while balancing the reaction heat. In recent years, it has attracted attention as a method for producing hydrogen for fuel cells because of a short start-up time and easy control. Also in this case, the reaction is usually performed in the presence of a metal catalyst represented by a Group VIII metal such as nickel, cobalt, iron, ruthenium, rhodium, iridium, and platinum. The amount of steam introduced into the reaction system is preferably 0.3 to 10, more preferably 0.5 to 5, and still more preferably 1 to 3 as a steam / carbon ratio.
[0028]
In autothermal reforming, oxygen is added to the raw material in addition to steam. Pure oxygen may be used as the oxygen source, but air is often used. Usually, oxygen is added to such an extent that it can generate an amount of heat that can balance the endothermic reaction accompanying the steam reforming reaction, but the amount of addition is appropriately determined in relation to heat loss and external heating provided as necessary. The amount thereof is preferably 0.05 to 1, more preferably 0.1 to 0.75, more preferably 0.1 to 0.75, as the ratio of the number of moles of oxygen to the number of moles of carbon contained in the raw hydrocarbon fuel (oxygen / carbon ratio). Is set to 0.2 to 0.6. The reaction temperature of the autothermal reforming reaction is set in the range of 450 ° C to 900 ° C, preferably 500 ° C to 850 ° C, and more preferably 550 ° C to 800 ° C, as in the case of the steam reforming reaction. The liquid hourly space velocity (LHSV) at this time is selected in the range of preferably 0.1 to 30, more preferably 0.5 to 20, and still more preferably 1 to 10.
[0029]
The partial oxidation reforming reaction is a method of obtaining a reformed gas containing hydrogen as a main component by partially oxidizing a hydrocarbon fuel without completely burning it. Also in this case, the reaction is usually performed in the presence of a noble metal catalyst such as ruthenium, rhodium, iridium, rhenium, and platinum. Introducing steam is also preferably performed to suppress soot formation, in which case the steam / carbon ratio is preferably 0.3 to 10, more preferably 0.5 to 5, and still more preferably 1 to 3.
[0030]
In partial oxidation reforming, oxygen is added to the raw material. Pure oxygen may be used as the oxygen source, but air is often used. Usually, oxygen is added to such an extent that it can generate an amount of heat that can balance the endothermic reaction accompanying the steam reforming reaction, but the amount of addition is appropriately determined in relation to heat loss and external heating provided as necessary. The amount is preferably 0.1 to 1, more preferably 0.2 to 0.8 as a ratio of the number of moles of oxygen molecules to the number of moles of carbon atoms contained in the raw hydrocarbon fuel (oxygen / carbon ratio). . The reaction temperature of the partial oxidation reforming reaction is preferably set in a range from 600 ° C to 1000 ° C, more preferably from 700 ° C to 900 ° C. The liquid hourly space velocity (LHSV) at this time is selected in the range of preferably 0.1 to 30, more preferably 0.5 to 20, and still more preferably 1 to 10.
[0031]
[CO transformer]
The gas generated in the reformer contains substances other than hydrogen, such as carbon monoxide, carbon dioxide, methane, and steam. When air is used as the oxygen source in the autothermal reforming, nitrogen is also contained. Of these, the CO converter performs a shift reaction of reacting carbon monoxide with water to convert it to hydrogen and carbon dioxide. Usually, the reaction proceeds in the presence of a catalyst, and a mixed oxide of Fe-Cr, a mixed oxide of Zn-Cu, a catalyst containing a noble metal such as platinum, ruthenium, and iridium is used. Mol%) is reduced to preferably 2% or less, more preferably 1% or less, and still more preferably 0.5% or less. From the viewpoint of more effectively lowering the CO concentration, the shift reaction is preferably performed in two stages. In this case, a high-temperature CO converter and a low-temperature CO converter are used.
[0032]
[High-temperature CO transformer]
For the high-temperature CO shift converter, a high-temperature shift catalyst that is a catalyst having a shift reaction activity at 300 to 500 ° C. can be used.
[0033]
The high-temperature shift catalyst preferably contains at least one metal selected from iron, chromium, and copper, in addition to sulfur, from the viewpoint of shift reaction activity at 300 to 500 ° C. For example, the mass composition of the high-temperature shift catalyst on an oxide basis is preferably one containing sulfur and containing 60 to 95% of iron, 1 to 30% of chromium, and 0.1 to 10% of copper. The shape is preferably spherical, cylindrical, massive, ring-shaped, honeycomb-shaped, or monolith-shaped, and any molding method may be used, but tablet molding and extrusion molding are preferred.
[0034]
In the high-temperature CO conversion process, GHSV is 200 to 10000 hours ^-1 (GHSV represents a gas hourly space velocity in terms of 0.101 MPa at 15 ° C .; the same applies hereinafter). 200hr ^-1 By doing so, the gas processing capacity and economic efficiency can be improved, and 10,000 hours ^-1 If it is below, it is excellent in the CO concentration reducing ability.
[0035]
[Low-temperature CO transformer]
For the low-temperature CO shift converter, a low-temperature shift catalyst that is a catalyst having a shift reaction activity at 160 to 300 ° C. can be used.
[0036]
As the low-temperature shift catalyst, those containing at least one metal selected from copper, zinc, nickel, iron, manganese, platinum, gold, ruthenium, rhodium and rhenium are preferable from the viewpoint of shift reaction activity. The total metal content is preferably from 5 to 90% by mass on an oxide basis, and the shape is preferably spherical, cylindrical, massive, ring-shaped, honeycomb-shaped, or monolithic, and the molding method may be any method. However, tablet molding and extrusion molding are preferred. The method for preparing the catalyst is not particularly limited, but a coprecipitation method, a gel kneading method and an impregnation method are preferred.
[0037]
The gas supplied to the low-temperature CO shift converter has a CO concentration (dry base mol%) of 0.5% or more from the viewpoint of preventing the load on the high-temperature CO shift catalyst from increasing and preventing deterioration. Preferably, the CO concentration is preferably 20% or less from the viewpoint of preventing the load on the low-temperature CO conversion catalyst from increasing and preventing catalyst deterioration. Therefore, in a high-temperature CO converter, it is preferable to reduce the CO concentration to this range.
[0038]
As for the gas supplied to the low-temperature conversion CO converter, GHSV is 200 to 50,000 hr. ^-1 It is preferable that 200hr ^-1 By doing so, the gas processing capacity and economic efficiency can be improved, and 50,000 hours ^-1 If it is below, it is excellent in the CO concentration reducing ability.
[0039]
[CO selective oxidizer]
In order to produce a reformed gas that can be suitably used in a device having low resistance to CO, such as a polymer electrolyte fuel cell, the concentration of carbon monoxide in the gas processed in the CO converter is further reduced. For this purpose, the outlet gas of the CO converter (or the low-temperature CO converter if there is a high-temperature CO converter and a low-temperature CO converter) is treated by a selective oxidation reaction. In this step, a catalyst containing iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, silver, gold, or the like is used, and preferably 0.5 to The carbon monoxide concentration is preferably changed by selectively converting carbon monoxide to carbon dioxide by adding 10 times, more preferably 0.7 to 5 times, even more preferably 1 to 3 times of oxygen. Is reduced to 10 ppm (mole on a dry basis) or less. In this case, the concentration of carbon monoxide can be reduced by reacting carbon monoxide with coexisting hydrogen at the same time as oxidation to produce methane. GHSV is preferably 1,000 to 30,000, more preferably 5,000 to 20,000 on a dry basis.
[0040]
〔Fuel cell〕
As the fuel cell, a fuel cell of a type in which hydrogen is a reactant of an electrode reaction at a fuel electrode can be appropriately used. For example, a polymer electrolyte fuel cell, a phosphoric acid fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell can be employed. Among them, solid polymer fuel cells have low resistance to CO and low resistance to hydrocarbon fuel remaining in the reformed gas, so that the effects of the present invention are remarkably exhibited. The configuration of the fuel cell will be described.
[0041]
The fuel cell electrode has an anode (fuel electrode) and a cathode (air electrode) and a solid polymer electrolyte sandwiched between them. On the anode side, the reformed gas containing hydrogen obtained by the reformer described above is used as a cathode. On the side, an oxygen-containing gas such as air is introduced after performing appropriate humidification treatment if necessary.
[0042]
At this time, a reaction in which hydrogen gas becomes protons and emits electrons proceeds at the anode, and a reaction at which oxygen gas obtains electrons and protons to become water proceeds at the cathode. In order to promote these reactions, platinum black and activated carbon-supported Pt catalyst or Pt-Ru alloy catalyst are used for the anode, and platinum black and activated carbon-supported Pt catalyst are used for the cathode. Normally, both the anode and cathode catalysts are formed into a porous catalyst layer together with Teflon, a low molecular weight polymer electrolyte membrane material, activated carbon and the like, if necessary.
[0043]
Examples of solid polymer electrolytes include Nafion (Nafion, manufactured by Dupont), Gore (Gore, manufactured by Gore), Flemion (Flemion, manufactured by Asahi Glass Co., Ltd.), and Aciplex (Aciplex, manufactured by Asahi Kasei Corporation). A molecular electrolyte membrane is usually used, and the porous catalyst layers are laminated on both sides to form a MEA (Membrane Electrode Assembly). Furthermore, the fuel cell is assembled by sandwiching the MEA with a separator having a gas supply function made of a metal material, graphite, carbon composite, or the like, a current collection function, and particularly a drainage function that is important for the cathode. The electric load is electrically connected to the anode and the cathode.
[0044]
(Hydrocarbon fuel)
If the hydrocarbon compound contained in the hydrocarbon fuel is a so-called heavy component, the adverse effect of the decomposition residual component tends to increase. According to the present invention, since the adverse effect of the decomposition residual component can be suppressed, the present invention can be particularly suitably applied when the hydrocarbon fuel contains a hydrocarbon compound having a boiling point of a pure substance of 160 ° C. or higher. When the hydrocarbon fuel contains a hydrocarbon compound of 180 ° C. or higher, and more preferably 200 ° C. or higher, the effect of the present invention becomes more remarkable. From the same viewpoint, the present invention can be suitably applied when the hydrocarbon fuel contains a hydrocarbon compound having 8 or more carbon atoms. When the hydrocarbon fuel contains a hydrocarbon compound having preferably 10 or more carbon atoms, more preferably 12 or more and 40 or less, the effects of the present invention become more remarkable.
[0045]
Specific examples of the hydrocarbon compound include saturated hydrocarbons such as decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane and eicosane;
Xylene, ethylbenzene, trimethylbenzene, cumene, propylbenzene, or butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, octylbenzene, nonylbenzene, decylbenzene, naphthalene, methylnaphthalene, dimethylnaphthalene, ethylnaphthalene, propylnaphthalene, biphenyl, Substituted or unsubstituted aromatic compounds such as methylbiphenyl, ethylbiphenyl and propylbiphenyl;
Aromatic or non-aromatic compounds having a saturated ring, such as tetralin and decalin
However, it is needless to say that these are only some examples of a very large number of target compounds.
[0046]
The pure substance can be used alone as a hydrocarbon fuel containing the hydrocarbon compound, but usually, the hydrocarbon fuel contains a plurality of types of hydrocarbon compounds as a mixture. Examples thereof include petroleum-based fuels such as naphtha, gasoline, kerosene, light oil, and the like, and GTL (gas to liquid, liquid fuels produced from gases such as natural gas).
[0047]
(Desulfurization)
Since the sulfur in the hydrocarbon fuel has the effect of inactivating the reforming catalyst, it is desirable that the concentration be as low as possible, preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less. Thus, the fuel can be desulfurized in advance if necessary. There is no particular limitation on the sulfur concentration in the raw material supplied to the desulfurization step, and any one can be used as long as it can be converted to the above sulfur concentration in the desulfurization step.
[0048]
Although there is no particular limitation on the desulfurization method, a method in which hydrodesulfurization is performed in the presence of an appropriate catalyst and hydrogen and the generated hydrogen sulfide is absorbed by zinc oxide or the like can be given as an example. In this case, examples of the catalyst that can be used include a catalyst containing nickel-molybdenum, cobalt-molybdenum, or the like as a component. On the other hand, if necessary, in the presence of a suitable sorbent, a method of sorbing sulfur in the presence of hydrogen can also be adopted. In this case, as a sorbent that can be used, a sorbent containing copper-zinc as a main component or a sorbent containing nickel-zinc as a main component as described in Japanese Patent No. 2654515, Japanese Patent No. An adhesive can be exemplified.
[0049]
(Gas composition)
When the steam reforming reaction is used in the reformer, the composition of the gas passed through the reformer, the CO shift converter and the CO selective oxidizer (mole% on a dry basis) is usually, for example, 65 to 75% of hydrogen, 0.1% of methane. 1-5%, carbon dioxide 20-30%, nitrogen 1-10%. On the other hand, when the autothermal reforming reaction or the partial oxidation reforming reaction is used, the composition (mol% on a dry basis) is usually, for example, 25 to 40% hydrogen, 0.1 to 5% methane, and 20 to 40 carbon dioxide. %, Nitrogen 30 to 60%.
[0050]
In addition, when the steam reforming reaction is used in the reformer, the composition of the gas (mol% or mol ppm on a dry basis) that has passed through the reformer and the CO shift converter is usually, for example, 65 to 75% of hydrogen and 0.1 to 0.9% of methane. 1-5%, carbon dioxide 20-30%, carbon monoxide 1000 ppm-10000 ppm. On the other hand, when the autothermal reforming reaction or the partial oxidation reforming reaction is used, the composition (mol% or mol ppm on a dry basis) is usually, for example, 25 to 40% hydrogen, 0.1 to 5% methane, and carbon dioxide. 20-40%, carbon monoxide 1000 ppm-10000 ppm, nitrogen 30-60%.
[0051]
Further, when the steam reforming reaction is used in the reformer, the composition of the gas passed through the reformer (mol% on a dry basis) is usually, for example, 63 to 73% of hydrogen, 0.1 to 5% of methane, and carbon dioxide. 5-20%, carbon monoxide 5-20%. On the other hand, when the autothermal reforming reaction or the partial oxidation reforming reaction is used, the composition (mol% on a dry basis) is usually, for example, 23 to 37% of hydrogen, 0.1 to 5% of methane, 5 to 25% of carbon dioxide. %, 5 to 25% of carbon monoxide, and 30 to 60% of nitrogen.
[0052]
In addition, in any of the reforming methods, depending on the operating conditions of the reformer, a trace amount of decomposition residual component mainly composed of hydrocarbon fuel as a raw material may be detected. This amount tends to be detected more as the space velocity of the reformer is higher and the reaction temperature is lower. Further, the same tendency is observed even when the catalyst of the reformer is deteriorated.
[0053]
The amount of the detected residual decomposition component depends on the operating conditions, but depending on the case, may be 10,000 ppm by volume or less, 5000 ppm by volume or less, or 1000 ppm by volume or less. The presence of these decomposition residual components may cause an increase in polarization of the polymer electrolyte fuel cell.
[0054]
(Adsorber)
Therefore, in the present invention, an adsorber is provided downstream of the reformer. The adsorber is provided with an adsorbent for adsorbing hydrocarbon fuel remaining in the reformed gas. By the adsorber, it is also possible to remove the by-products of the reforming reaction at the same time as the removal of the remaining hydrocarbons, the amount of the decomposition remaining components including these both preferably 100 ppm by volume or less, more preferably It can be reduced to 50 vol ppm or less, more preferably 1 vol ppm or less. This ensures, for example, a stable and highly efficient operation of the polymer electrolyte fuel cell.
[0055]
As the adsorbent, for example, a porous substance having a high surface area such as activated carbon and zeolite can be used, but activated carbon and zeolite are preferably used from the viewpoint of increasing the pore volume in order to increase the amount of adsorption. . These can be used in combination. The structure of the adsorber may be a known one, and the adsorbent can be put in a cylindrical or cylindrical container to form the adsorber. The container can also be provided with suitable temperature control means. As the temperature adjusting means, for example, an electric heater for heating can be used, and heating can be performed using a high-temperature gas in the system as a heat medium, or cooling can be performed using water or air as a heat medium. A tube through which the heat medium flows can be provided in the container or on the container wall.
[0056]
When activated carbon and zeolite are used as the adsorbent, the adsorption is performed at a temperature of the activated carbon of preferably 50 to 500C, preferably 60C to 400C, and more preferably 100C to 300C. By setting the temperature to 500 ° C. or lower, it is possible to favorably prevent the adsorbing ability of activated carbon from being lowered, and to satisfactorily remove residual hydrocarbons and by-products. By setting the temperature at 50 ° C. or higher, it is possible to favorably prevent the phenomenon that the adsorption capacity is reduced due to the aggregation of the moisture in the reformed gas.
[0057]
From the viewpoint of suppressing the volume of the adsorbent while satisfactorily removing residual hydrocarbons and by-products, the gas space velocity GHSV (water Excluding), preferably 1 to 100000 h ^-1 , More preferably 10 to 50,000 h ^-1 , More preferably 100 to 10000h ^-1 Is set to be
[0058]
The particle size of the activated carbon and zeolite used is not particularly limited, but is preferably 0.1 mm or more from the viewpoint of suppressing the pressure loss of the activated carbon layer, and is preferably 5 mm or less from the viewpoint of adsorption ability. More preferably 0.5 mm to 4 mm, even more preferably 1 mm to 3 mm is used.
[0059]
The adsorber is located downstream of the reformer in order to adsorb decomposition residual components discharged from the reformer. It may be downstream of the CO selective oxidizer in the hydrogen production system. In the fuel cell system, the fuel cell system is located upstream of the fuel cell unit in order to prevent the deterioration of the fuel cell due to the decomposition residual components. That is, the fuel gas is supplied upstream of the fuel electrode of the fuel cell to which the reformed gas is supplied. From the viewpoint of preventing deterioration of the CO shift catalyst, the upstream of the CO shift converter is preferable. When the CO converter is composed of two stages, a high-temperature CO converter and a low-temperature CO converter, the downstream of the high-temperature CO converter and the upstream of the low-temperature CO converter are preferable from the viewpoint of the gas temperature and the performance of the adsorbent. .
[0060]
The hydrocarbon fuel adsorbed on the adsorbent can be desorbed by increasing the temperature. For example, the adsorber can be desorbed and regenerated by flowing a high-temperature gas through the adsorber. The desorption regeneration temperature is desirably equal to or higher than the adsorption temperature. It is preferable that the gas for desorption regeneration does not contain oxygen.
[0061]
It is preferable to use a fuel cell anode off-gas discharged from the anode of the fuel cell as the gas for desorption regeneration, from the viewpoint that efficiency is not reduced by introducing gas from outside the system without containing oxygen. The anode off-gas, if necessary, is heated to a temperature higher than the desorption regeneration temperature of the adsorber by heat exchange with a gas having a higher temperature than the anode off-gas present in the fuel cell system, for example, a reformed gas immediately downstream of the reformer. This allows the adsorbent to be brought to the desorption regeneration temperature. For this purpose, a heat exchanger for heating the anode off-gas with a high-temperature gas by heat exchange can be provided downstream of the anode and upstream of the adsorber. In practice, for example, the temperature of the anode off-gas at the outlet of the heat exchanger can be determined so that the adsorbent reaches the desorption regeneration temperature in consideration of the temperature effect due to heat loss from the heat exchanger to the adsorbent.
[0062]
In addition to the method of raising the temperature of the anode off-gas by heat exchange, desorption regeneration can be performed by flowing the anode off-gas while directly heating the adsorber with a high-temperature gas or an electric heater.
[0063]
As a reformer, there is an externally heated or externally heated reformer that heats a reaction tube containing a reforming catalyst from outside to supply heat required for a reforming reaction occurring inside the reaction tube. . For this external heating, combustion means such as burners and catalytic combustors are used. Such a reformer is typical of a steam reformer, but when performing autothermal reforming, such a combustion means is provided as necessary. When such a reformer is used, the anode offgas used for the desorption regeneration can be burned as fuel for the combustion means provided in the reformer.
[0064]
One adsorber may be used. In this case, when the desorption regeneration of the adsorber is performed or the adsorbent is replaced, the hydrogen production system is stopped, or if the operation of the hydrogen production system is to be continued, the gas passing through the adsorber is bypassed (accordingly, the adsorption is performed). Do not do).
[0065]
A plurality of adsorbers are provided, and the reformed gas flows into some of the adsorbers to perform adsorption. During this time, the remaining adsorber performs desorption regeneration, and the adsorption adsorber and the adsorption desorption regeneration It is preferable to switch the vessels sequentially. This is because hydrogen production with continuous adsorption can be performed in this manner. The hydrogen production system can include a flow path switching unit for this switching. That is, each adsorber is provided with a flow path switching means for blocking the inflow of the reformed gas and flowing the gas for desorption regeneration, and when performing the adsorption, the reformed gas is caused to flow into the adsorber to perform the hydrogen production. A line is established, and during desorption regeneration, the adsorber is separated from the hydrogen production line, gas for desorption regeneration flows in, and a desorption regeneration line is created.These hydrogen production line and desorption regeneration line are separated. It can be switched alternately. If at least one adsorber always forms a hydrogen production line by shifting the line switching timing for a plurality of adsorbers, hydrogen production with continuous adsorption can be performed.
[0066]
Examples of the flow path switching unit include a valve such as a stop valve or a three-way valve. In addition, it is also possible to automatically switch the flow path. At this time, it is preferable that the valve be an automatic valve and a control device for automatically performing the switching be provided. As the automatic valve, a known automatic valve driven by air or electricity can be used.
[0067]
FIG. 1 schematically shows an example of the switching timing. FIG. 1A shows a case in which adsorption and desorption regeneration are performed by alternately switching two adsorbers at approximately equal intervals, and FIG. 1B shows a case where the two adsorbers are alternately switched but the time required for desorption regeneration is short. In the case (c), three adsorbers are provided, and adsorption and desorption regeneration are sequentially switched.
[0068]
As the control device, a known control device such as a sequencer or a computer that can emit a signal at predetermined time intervals may be used for the automatic switching as described above, and an automatic valve that opens and closes according to the signal may be used. It can be installed in the system to switch the flow path in the system. Instrumentation piping, instrumentation wiring, etc. can also be provided as appropriate.
[0069]
【Example】
Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[0070]
FIG. 1 shows an embodiment of the fuel cell system of the present invention. Here, two adsorbers are used. Kerosene is supplied as a raw material to the desulfurizer 1 and is desulfurized. The reformed gas obtained from the reformer is cooled by the anode off-gas of the fuel cell in the heat exchanger 8 and supplied to the high-temperature CO converter 3. The reformed gas whose CO concentration has been reduced by the high-temperature CO converter is supplied to the first adsorber 4a via the valve 11a, the remaining decomposition component is removed, and supplied to the low-temperature CO converter 5 via the valve 12a. You. The reformed gas whose CO concentration has been reduced by the low-temperature CO shift converter is further supplied to the anode 7 a of the fuel cell 7 after the CO concentration is further reduced by the CO selective oxidizer 6. The anode off-gas discharged from the anode 7a is heated by heat exchange with the reformed gas in the heat exchanger 8, and is supplied to the second adsorber 4b through the valve 13b. In the adsorber 4b, desorption regeneration is performed by the anode off-gas, and the gas discharged from the adsorber 4b is supplied as a fuel for combustion to the burner 2a of the reformer through the valve 14b. It is exhausted outside. Further, air is supplied to the cathode 7c of the fuel cell, and the cathode off-gas discharged from the cathode is recovered as necessary, and then discharged outside the system. Each adsorber is filled with activated carbon.
[0071]
In this state, the valves 11a, 12a, 13b, and 14b are opened, the valves 11b, 12b, 13a, and 14a are closed, adsorption is performed by the first adsorber 4a, and desorption regeneration is performed by the second adsorber 4b. Has been done. To switch to perform adsorption by the second adsorber 4b and perform desorption regeneration by the first adsorber 4a, open the valves 11b, 12b, 13a, and 14a and close the valves 11a, 12a, 13b, and 14b. Just fine.
[0072]
A computer (not shown) is provided for automatically opening and closing the valve and automatically switching the flow path.
[0073]
【The invention's effect】
According to the present invention, a stable and highly efficient hydrogen production system and a fuel cell system are provided even when a decomposition residual component is present in a reformed gas.
[Brief description of the drawings]
FIG. 1 is a schematic timing chart showing an example of an operation pattern of a plurality of adsorbers.
FIG. 2 is a flowchart showing one embodiment of the fuel cell system of the present invention.
[Explanation of symbols]
1 desulfurizer
2 Reformer
2a Burner of reformer
3 High temperature CO transformer
4a First adsorber
4b Second adsorber
5 Low-temperature CO transformer
6 CO selective oxidizer
7 Fuel cell
7a anode
7c cathode
8 heat exchanger
11a, 11b, 12a, 12b, 13a, 13b, 14a, 14b Valve

Claims (10)

A reformer for reforming a hydrocarbon fuel to obtain a reformed gas containing hydrogen, a CO converter for reducing the CO concentration in the reformed gas by a shift reaction, and a CO concentration reduced in the CO converter In a hydrogen production system including a CO selective oxidizer that further reduces the CO concentration in the gas by a selective oxidation reaction,
A hydrogen production system comprising an adsorber provided downstream of the reformer and having an adsorbent for adsorbing residual decomposition components. A plurality of the adsorbers are provided, and a flow path switching unit for blocking the inflow of the reformed gas for each of the adsorbers and flowing the gas for desorption regeneration is provided,
The reformed gas flows into some of the adsorbers to perform adsorption, during which desorption regeneration is performed in the remaining adsorbers, and the adsorber that performs adsorption and desorption regeneration is sequentially switched to sequentially perform adsorption and desorption. The hydrogen production system according to claim 1, further comprising a control device for enabling efficient hydrogen production. 3. The hydrogen production system according to claim 1, wherein the adsorbent is at least one selected from activated carbon and zeolite. The hydrogen production system according to any one of claims 1 to 3, wherein the reformer is a steam reformer, an autothermal reformer, or a partial oxidation reformer. A reformer for reforming a hydrocarbon fuel to obtain a reformed gas containing hydrogen, a CO converter for reducing the CO concentration in the reformed gas by a shift reaction, and a CO concentration reduced in the CO converter A fuel cell including a hydrogen production system including a CO selective oxidizer for further reducing the CO concentration in a gas by a selective oxidation reaction, and a fuel cell using a reformed gas having a reduced CO concentration in the CO selective oxidizer as a fuel In the system,
A fuel cell system comprising: an adsorber provided with an adsorbent for adsorbing residual decomposition components, downstream of the reformer and upstream of the fuel electrode of the fuel cell. A plurality of the adsorbers are provided, and a flow path switching unit for blocking the inflow of the reformed gas for each of the adsorbers and flowing the gas for desorption regeneration is provided,
The reformed gas flows into some of the adsorbers to perform adsorption, during which desorption regeneration is performed in the remaining adsorbers, and the adsorber that performs adsorption and desorption regeneration is sequentially switched to sequentially perform adsorption and desorption. The fuel cell system according to claim 5, further comprising a control device capable of performing efficient hydrogen production. 7. The fuel cell system according to claim 6, wherein the gas for desorption regeneration is a fuel cell anode offgas. 8. The fuel cell system according to claim 7, wherein the reformer includes a combustion unit, and further includes a line for guiding the fuel cell anode off-gas used for the desorption regeneration to the combustion unit. A heat exchanger downstream of the fuel cell anode and upstream of the adsorber, wherein the heat exchanger heats the fuel cell anode off-gas above the desorption regeneration temperature of the adsorber by heat exchange with other gases in the fuel cell system. Item 10. The fuel cell system according to item 8. 10. The fuel cell system according to claim 5, wherein the fuel cell is a polymer electrolyte fuel cell.

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