JP2008247735A - Fuel reforming system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce CO concentration while operating stably for a long term. <P>SOLUTION: The fuel reforming system comprises providing at least a reforming reactor 1 and a CO selective oxidation reactor 2, wherein the reactor produces a reformed gas by reacting a raw fuel gas with steam and/or air under the coexistence of a reforming catalyst and the reactor produces a hydrogen rich gas converting into CO<SB>2</SB>by selectively oxidizing CO in the reformed gas produced in the reforming reactor 1 under the coexistence of a CO selective oxidation catalyst. A steam condensing separation means 3 which condenses and separates steam contained in the reformed gas before feeding into the CO selective oxidation reactor 2 is provided between the reforming reactor 1 and the CO selective oxidation reactor 2. Steam is condensed and separated from the reforming gas which feeds into the CO selective oxidation reactor 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention, for example, is a fuel reformer that produces a hydrogen-rich gas with an extremely reduced CO concentration in a reformed gas, using hydrocarbons or the like as a raw fuel, which is used for supplying fuel to a polymer electrolyte fuel cell. Quality system.

BACKGROUND ART A fuel reforming system used for supplying fuel to a polymer electrolyte fuel cell (PEFC) generates a reformed gas by reacting raw fuel with steam and / or air in the presence of a reforming catalyst. In order to reduce the CO concentration in the reformed gas from the reforming reactor to 10 ppm or less, a CO selective oxidation reactor is provided. In such a CO selective oxidation reactor, in the presence of a CO selective oxidation catalyst, air or the like is added to the reformed gas to selectively oxidize CO with oxygen to convert it into CO ₂ .

  Depending on the fuel used, a desulfurizer may be installed in front of the reforming reactor, or a CO converter may be installed between the reforming reactor and the CO selective oxidation reactor. In particular, in a fuel reforming system that supplies PEFC fuel, it is desirable that water vapor of a constant partial pressure is finally contained in the fuel gas for humidification of the PEFC membrane, and the fuel gas is 60 to 80 Since it is desirable to supply at 0 ° C., the water vapor in the reformed gas is not condensed and separated during the reforming process.

  On the other hand, the CO selective oxidation reaction, which is the final stage of the reforming process, is a reaction that selectively oxidizes CO in hydrogen-rich gas with oxygen. Since this reaction is basically a combustion reaction, it generates a large amount of heat. Accompanied by. However, when the temperature rises, the CO oxidation selectivity decreases, and the CO purification performance may deteriorate, or side reactions such as methanation may occur in a chain and the operation cannot be continued.

  In order to prevent this, measures are taken to suppress the temperature rise by providing a heat exchanger for cooling so that heat can be removed from the CO selective oxidation reactor, or the amount of heat generated in the CO selective oxidation reactor is reduced. In order to suppress this, a method of dividing the CO selective oxidation reactor into several stages and injecting air at each stage has been widely studied.

  However, in the CO selective oxidation reaction in the conventional fuel reforming system, the temperature range (ΔT) in which CO can be reduced is only about 40 to 50 ° C., and it is difficult to strictly control the temperature, and the temperature is too high. There is a problem that runaway due to side reactions such as methanation occurs and if the temperature is too low, water vapor condenses in the CO selective oxidation reactor and accelerates the deterioration of the catalyst.

  Further, when the temperature condition is not appropriate, there is a problem of promoting the deterioration of the CO selective oxidation catalyst. In addition, when the CO selective oxidation reactor is multistage, the system is complicated and leads to cost increase. From the viewpoint of the CO selective oxidation reactor in the final stage, the CO concentration at the entrance due to load fluctuation and catalyst deterioration However, the reaction conditions have changed significantly, and it has been extremely difficult to maintain stable performance for a long time.

The present invention has been made in view of such circumstances, and the invention according to claim 1 aims to be able to stably reduce the CO concentration to 10 ppm or less stably over a long period of time. An object of the present invention is to enable the CO concentration to be satisfactorily reduced even when reforming at a high temperature, and the invention according to claim 3 is to enable continuous processing with a simple configuration. The invention according to claim 4 aims to avoid a decrease in activity and condensation of water in the CO selective oxidation reactor, and the invention according to claim 5 recovers exhaust heat from the system. The purpose is to improve the thermal efficiency of the system.
The invention according to claim 6 aims at recovering exhaust heat while stably performing condensation, and the invention according to claim 7 aims at increasing CO conversion rate stably. The invention according to item 8 aims to avoid runaway due to side reactions such as methanation, and the invention according to claim 9 makes it possible to operate the CO selective oxidation reactor in a small size and stably. The invention according to claim 10 aims to make it possible to use the exhaust heat from the system, and the invention according to claim 11 avoids deterioration of the catalyst and simplifies the control to reduce CO 2. An object of the present invention is to allow the heat of reaction of the selective oxidation reactor to be removed by cooling.

  As a result of intensive studies, the present inventors have found that the temperature range in which CO can be reduced can be expanded by lowering the dew point of the reformed gas to be used in the CO selective oxidation reaction, and is further necessary for the CO selective oxidation reaction. It has been found that poisoning of the CO selective oxidation catalyst with iron can be prevented by adding oxygen and maintaining the reformed gas and the tube wall temperature up to the catalyst layer at 100 ° C. or lower. Also, the present invention was completed by finding that these conditions can be easily achieved by condensing and separating the water vapor in the reformed gas before subjecting it to the CO selective oxidation reaction, and that the CO concentration can be reduced stably over a long period of time. I let you.

That is, as shown in the flowchart corresponding to claim 1 of FIG.
A reforming reactor 1 for generating a reformed gas by reacting raw fuel with steam and / or air in the presence of a reforming catalyst;
Wherein selectively one of the CO-selective for producing a hydrogen-rich gas is converted to CO ₂ by oxidizing CO in the reformed reformed gas generated in the reactor 1 with oxygen in the presence of CO selective oxidation catalyst In a fuel reforming system comprising at least an oxidation reactor 2,
A steam condensing / separating means 3 for condensing and separating water vapor contained in the reformed gas before being supplied to the CO selective oxidation reactor 2 is provided.

  The raw fuel used in the present invention is not particularly limited as long as it is a raw fuel that generates hydrogen-rich gas by reacting with water vapor and / or air, but natural gas, propane gas, butane gas, naphtha, gasoline, kerosene. And hydrocarbon fuels such as methanol and alcohol fuels such as methanol are included.

  The reforming reactor used in the present invention may be a known reforming reactor for reforming by adding steam and / or air to the raw fuel, and when using a steam reforming reaction that is reformed exclusively by steam. And an autothermal type that has a means for adding steam to the raw fuel upstream of the reforming reactor and a heat exchange means for supplying heat necessary for the reaction from the outside, and reacts in the presence of air and steam. When using the partial combustion type, a reforming reactor having means for adding air in addition to means for supplying water vapor is used. The reforming reactor may have both a heat exchanger that preheats and cools process gas and the like as necessary, and a steam generator that generates steam for reforming from water. When the raw fuel contains a sulfur compound, a desulfurizer for desulfurizing the raw fuel before supplying it to the reforming reactor may be provided in order to avoid sulfur poisoning of the reforming catalyst.

In addition, as a CO selective oxidation reactor, a known CO selective oxidation reaction that selectively converts CO in the reformed gas into CO ₂ by adding air or oxygen to the reformed gas in the presence of a CO selective oxidation catalyst. The catalyst used may be a known CO selective oxidation catalyst.

Except when the raw fuel is methanol, etc., and can be reformed at a low temperature of about 300 ° C, if the CO concentration in the reformed gas leaving the reforming reactor is as high as 1% by volume or more on a dry basis, It is preferable to configure like the invention according to item 2.
That is, as shown in the flowchart corresponding to claim 2 of FIG.
The fuel reforming system according to claim 1, wherein
A CO converter 4 is provided between the reforming reactor 1 and the CO selective oxidation reactor ₂ to convert most of the CO in the reformed gas into steam by reacting with steam in the presence of a CO conversion catalyst. The water vapor condensing / separating means 3 is configured to condense and separate water vapor from the reformed gas after being treated by the CO converter 4.
The CO converter may be a known CO converter that causes CO conversion reaction using CO remaining in the reformed gas and / or steam added from the outside. You may provide the heat exchange function which removes heat and cools a CO converter.

  In the fuel reforming system according to the first and second aspects of the present invention, before the reformed gas exiting the reforming reactor or the CO shift reactor is supplied to the CO selective oxidation reactor, In order to condense and separate the water vapor, it is supplied to the water vapor condensing and separating means.

  The steam condensing / separating means in claims 1 and 2 is capable of continuously condensing and separating water vapor from the reformed gas supplied to the CO selective oxidation reactor, and in other words, the temperature of the reformed gas at the outlet, that is, CO selective There is no particular limitation as long as it has a mechanism that allows the temperature of the reformed gas supplied to the oxidation reactor to be 100 ° C or lower.

As the water vapor condensing and separating means, those having the structure of the invention according to claim 3 can be used.
That is, as shown in the flowchart corresponding to claim 3 of FIG.
The fuel reforming system according to claim 1 or 2,
The steam condensing / separating means 3 is composed of a heat exchanging section 5 for cooling the reformed gas and condensing the steam in the reformed gas, and a steam / water separating section 6 for separating the condensed water and the reformed gas. .
The invention according to claim 4
The fuel reforming system according to any one of claims 1, 2, and 3,
The steam condensing / separating means is configured to condense and separate the water vapor contained in the reformed gas so that the dew point of the reformed gas after condensation separation is 60 ° C. or less.
As the degree of water vapor separation to be achieved by the water vapor condensation and separation means in the inventions according to claims 1, 2, and 3, preferably, the dew point of the reformed gas obtained by condensing and separating water vapor is 60 ° C. or less, more preferably 40 ° C. It is desirable to design so that it is below ℃. If the temperature exceeds 60 ° C., the activity in the CO selective oxidation reactor decreases, and there is a possibility that water may be condensed.

  For example, in a fuel cell cogeneration system constructed using a hydrogen-rich gas produced by the fuel reforming system according to the first, second, third, and fourth aspects of the invention, the fuel cell cogeneration system can be obtained along with cooling in the heat exchange section. Since the heat from the reformed gas also becomes a valuable heat source, it is desirable to recover this heat. As a method for recovering this heat most efficiently, it is conceivable to use room temperature tap water for generating hot water as a low-temperature heat medium in the heat exchange section.

Furthermore, in polymer electrolyte fuel cell (PEFC) cogeneration systems, etc., high power generation efficiency is required, so heat from the reformed gas obtained with cooling in the heat exchange section is generated as steam for reforming. The efficiency of the fuel reforming system can also be improved by using it for preheating or evaporating raw water. However, in this case, since the dew point of the reformed gas at the heat exchange section outlet cannot be controlled by the flow rate of the raw water, it may be difficult to obtain a sufficient cooling effect of the reformed gas. In order to solve this problem, the invention according to claim 5 is configured as follows.
That is, the invention according to claim 5 is a flowchart corresponding to claim 5 of FIG.
The fuel reforming system according to claim 3 or 4,
A water-cooled cooler 7 for cooling the reformed gas entering the CO selective oxidation reactor 2;
Supplying the reformed gas after cooling with the water-cooled cooler 7 to the heat exchanging unit 5;
The raw water for generating the reforming steam necessary for the reforming is used as a low-temperature heat medium of the water-cooled cooler 7, and the raw water is preheated by the reformed gas.

In order to more suitably apply to the fuel cell cogeneration system, the invention according to claim 6 is configured as follows.
That is, the invention according to claim 6
The fuel reforming system according to any one of claims 3, 4, and 5,
A fuel reforming system for supplying fuel to a fuel cell in a fuel cell cogeneration system, wherein hot water obtained by exhaust heat recovery from the fuel cell cogeneration system is stored in a state of forming a temperature stratification Equipped with hot water storage tanks,
It is configured to supply low-temperature water before exhaust heat recovery, which is taken out from the low-temperature part of the stratified hot water tank and recovers exhaust heat and then returned to the high-temperature part of the stratified hot water tank, to the heat exchange part.
A heat exchanger for recovering exhaust heat generated from other parts of the fuel cell cogeneration system may be provided on the water line circulated from the low temperature part to the high temperature part of the stratified hot water tank, These heat exchangers and heat exchange units may be attached in series or in parallel, but in order to reliably perform the condensation and separation of the water vapor in the reformed gas, the heat exchange unit that cools the reformed gas Is preferably provided in a relatively low temperature portion of the circulating water line.

As described above, the catalyst used in the CO selective oxidation reactor may be a known CO selective oxidation catalyst. However, since the reformed gas is cooled, the following configuration is preferable.
That is, the invention according to claim 7
The fuel reforming system according to any one of claims 1, 2, 3, 4, 5, and 6.
The CO selective oxidation catalyst is composed of a Ru-containing catalyst.

As described above, when a Ru-containing catalyst is used, it is excellent in low-temperature activity, but at high temperatures, side reactions such as CO ₂ methanation occur, and the reaction is accelerated by the reaction heat in an autocatalytic manner. Therefore, the CO selective oxidation reactor to be used is preferably configured as follows.
That is, the invention according to claim 8
The fuel reforming system according to claim 7, wherein
The CO selective oxidation reactor is configured to include heat exchange means for setting the maximum temperature of the catalyst layer to 180 ° C. or less.

In such a fuel reforming system, since the dew point of the reformed gas supplied to the CO selective oxidation reactor is lowered, the lower limit temperature at which sufficient catalyst performance can be obtained is lowered as compared with the conventional method. Depending on the cooling conditions of the gas, the catalyst bed temperature of the CO selective oxidation reactor may be too low to start the CO selective oxidation reaction.
In order to avoid such a situation, the invention according to claim 9 is preferably configured as follows.
That is, as shown in the longitudinal sectional view of the main part of FIG.
The fuel reforming system according to claim 8, wherein
The CO selective oxidation reactor 2 is configured to include a heating means 9 for heating the reformed gas inlet side catalyst 8a and a cooling means 10 for cooling the outlet side catalyst 8b.
In such a CO selective oxidation reactor, since the CO selective oxidation catalyst layer is heated at the inlet, the temperature of the reformed gas is not too low to start the reaction, and at the outlet, Since the CO selective oxidation catalyst layer is cooled, no runaway occurs due to side reactions such as methanation.

  The method for heating and cooling the CO selective oxidation catalyst layer is not particularly limited in the case of a Ru-based catalyst as long as the maximum temperature of the catalyst layer is maintained at 180 ° C. or lower, but more preferably, the maximum temperature of the catalyst layer is 130. It is preferable to adopt a method in which the temperature is maintained at from ℃ to 180 ℃. If the temperature is lower than 130 ° C, the catalyst may be poisoned by iron. If the temperature is higher than 180 ° C, the CO conversion rate may decrease due to the reverse reaction of CO conversion, and side reactions such as methanation may occur. It is.

Further, regarding the heating means for the CO selective oxidation catalyst layer, if an electric heater or the like is used, the thermal efficiency of the fuel reforming system is lowered.
In order to avoid this decrease in thermal efficiency, the invention according to claim 10 is preferably configured as follows.
That is, the invention according to claim 10 is
The fuel reforming system according to claim 9, wherein
The heat source of the heating means for the catalyst of the CO selective oxidation reactor is configured to be obtained by heat exchange with a portion of the fuel reforming system having a temperature higher than that of the CO selective oxidation reactor.
As the temperature higher than the CO selective oxidation reactor, the sensible heat of the reformed gas from the reforming reactor, the exhaust heat of the combustion exhaust gas from the external heating furnace, the reaction heat generated from the CO converter or the like is used. As long as the maximum temperature of the catalyst layer can maintain the above-described preferable range (130 ° C. to 180 ° C.), it is not necessary to be able to actively control the heating amount.

In addition, regarding the cooling means for the CO selective oxidation catalyst layer, the amount of heat removal can be actively controlled so that the temperature of the catalyst layer does not extremely decrease or increase depending on conditions such as start-up and load fluctuation. The invention according to claim 11 is preferably configured as follows.
That is, the invention according to claim 11 is
The fuel reforming system according to claim 9 or 10,
The cooling means for the catalyst of the CO selective oxidation reactor is constituted by an air-cooled fan capable of controlling the shutdown.

In the present invention, the gas composition supplied to the CO selective oxidation reactor is not particularly limited, but it is desirable to reduce the calorific value in the CO selective oxidation reactor as much as possible, so the CO concentration in the reformed gas is preferably It is preferable that the upstream reforming reactor or CO converter is designed so that is 1 vol% or less, more preferably 0.5 vol% or less. On the other hand, the amount of air added to the reformed gas is such that the molar ratio of CO concentration in the reformed gas to oxygen in the air, that is, O ₂ / CO, is preferably 3 or less, more preferably 2 or less, most preferably. It is preferable to limit the air flow rate so as to be 1.5 or less. This is because if O ₂ / CO exceeds 3, the temperature rises and the CO conversion rate decreases. The amount of catalyst required in the preferred temperature range, preferred CO concentration range, and preferred O ₂ / CO range varies depending on the type of catalyst, etc., but in the case of a Ru-based catalyst, GHSV is preferably 500 to 50000, more preferably 1000. It should be set to be ~ 30000.

[Action / Effect]
According to the configuration of the fuel reforming system of the invention according to claim 1, the water vapor contained in the reformed gas is condensed and separated by the steam condensing and separating means before being supplied to one CO selective oxidation reactor, The CO selective oxidation reaction can be performed stably for a long period of time.

Further, according to the configuration of the fuel reforming system of the invention according to claim 2, the CO converter converts most of the CO in the reformed gas to steam in the presence of the CO conversion catalyst to convert to CO ₂ . Then, the water vapor is condensed and separated by the water vapor condensing / separating means before being supplied to the CO selective oxidation reactor, so that the CO selective oxidation reaction can be stably performed even when the CO in the reformed gas has a high concentration. it can.

According to the configuration of the fuel reforming system of the invention according to claim 3, the reformed gas is cooled in the heat exchange unit to condense the water vapor, and the condensed water and the reformed gas are separated in the steam / water separation unit. Thus, the reformed gas can be cooled and the water vapor can be separated at the same time.
According to the configuration of the fuel reforming system of the invention according to claim 4, the steam is separated so that the dew point of the reformed gas obtained by condensing and separating the steam is 60 ° C. or less.

  Further, according to the configuration of the fuel reforming system of the invention according to claim 5, the reformed gas before entering the CO selective oxidation reactor is cooled by the water-cooled cooler and supplied to the CO selective oxidation reactor. It is possible to reduce the temperature of the gas and use raw water for generating reforming steam necessary for reforming as a low-temperature heat medium for the water-cooled cooler, and preheat the raw water with the reformed gas. it can.

  According to the structure of the fuel reforming system of the invention according to claim 6, the stratified hot water tank used in the fuel cell cogeneration system is used, and the low temperature water taken out from the low temperature part of the stratified hot water tank is used. The reformed gas can be condensed and the heat of the reformed gas can be recovered in the low-temperature water.

  According to the configuration of the fuel reforming system of the invention according to claim 7, the CO selective oxidation catalyst is configured with a catalyst containing Ru having a high activity at a low temperature, and the CO concentration can be easily lowered. it can.

  According to the fuel reforming system of the invention according to claim 8, stable CO selective oxidation reaction can be performed by setting the maximum temperature of the catalyst layer of the CO selective oxidation reactor to 180 ° C. or less. .

  Further, according to the configuration of the fuel reforming system of the invention according to claim 9, on the reformed gas inlet side of the CO selective oxidation reactor, the reformed gas having a low temperature due to the condensation of water vapor is heated, By cooling on the outlet side, a stable CO selective oxidation reaction can be performed.

  Further, according to the configuration of the fuel reforming system of the invention according to claim 10, the heat source of the heating means of the catalyst of the CO selective oxidation reactor can be obtained by utilizing the exhaust heat.

  In the fuel reforming system according to the eleventh aspect of the invention, the temperature of the reactor can be easily controlled by cooling the catalyst of the CO selective oxidation reactor with the air-cooled fan.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

First, a reference example will be described.
Reference Example 1 (Preparation of Ru catalyst)
A spherical γ-alumina carrier having a diameter of 2 to 4 mm is immersed in an aqueous ruthenium trichloride solution, supported by ruthenium by an impregnation method, dried, then immersed in an aqueous sodium carbonate solution to fix ruthenium, washed with water, and dried to be a precursor. Got. The obtained precursor was immersed in an aqueous hydrazine solution to reduce ruthenium, washed with water, then immersed again in an aqueous hydrazine solution to complete the reduction, washed again with water, and dried at 105 ° C. to obtain a Ru catalyst.
In the obtained Ru catalyst, the Ru concentration was 0.98% by weight, and the average pore diameter was 7.4 nm. In the following reference examples, comparative examples, and examples, as the pretreatment, the obtained Ru catalyst was maintained at 200 ° C. for 1 hour in a mixed gas stream of hydrogen and nitrogen containing 5% by volume of hydrogen. .

Reference example 2
In a SUS reaction tube (inner diameter: 21.2 mm) filled with 8 cc of the Ru catalyst prepared in Reference Example 1, CO = 0.5%, CH ₄ = 0.5%, CO ₂ = 21%, O _A reaction simulation gas of 1 Nl / min in which ₂ = 0.75%, N ₂ = 3% and the balance being H ₂ was passed at normal pressure, the temperature of the catalyst layer was changed, and the CO concentration at the outlet was measured. Next, water vapor is added to the reaction simulation gas having the same composition and flow rate so that the water vapor concentration in the wet gas is 5% (equivalent to a dew point of 33 ° C) and 20% (equivalent to a dew point of 61 ° C). The CO concentration at the outlet was measured by changing the temperature of the catalyst layer.

  A result is shown in the graph which showed the relationship between the temperature dependence of CO selective oxidation reaction of the Ru type | system | group CO selective oxidation catalyst of FIG. 6, and the water vapor | steam density | concentration in inlet gas. When the reaction temperature (the maximum temperature of the catalyst layer) is changed, the CO concentration at the outlet will be 10 ppm or less at any water vapor concentration in the temperature range of 110-180 ° C. It can be seen that it spreads significantly on the low temperature side.

Reference example 3
The Ru catalyst prepared in Reference Example 1 was forcibly degraded to a corresponding activity after about 20,000 hours of use by firing it at 450 ° C. for 945 hours in a mixed gas having a composition of H ₂ 80% -CO ₂ 20%. Measure the CO concentration at the outlet of the reaction tube when the water vapor concentration is 5% (equivalent to a dew point of 33 ° C) and 20% (equivalent to a dew point of 61 ° C), except that a catalyst (forced deterioration catalyst) is used. did.

  The results are shown in the graph of FIG. 12 showing the relationship between the temperature dependence of the CO selective oxidation activity of the accelerated Ru-based CO selective oxidation catalyst and the water vapor concentration in the inlet gas. Compared to the new catalyst data in FIG. 6, it can be seen that the outlet CO concentration is generally increased and deteriorated. However, even after deterioration, when the water vapor concentration is 5%, the temperature is 100 to 190 ° C. It can be seen that the CO concentration is 10 ppm or less, whereas when the water vapor concentration is 20%, the CO concentration exceeds 10 ppm at 100 ° C. and 190 ° C., and there is no temperature range in which the CO concentration is 1 ppm or less. . From this, it can be seen that, even after deterioration, the lower the water vapor concentration, the wider the active temperature range of CO selective oxidation can be secured.

Reference example 4
The water vapor concentration was 5% (corresponding to a dew point of 33 ° C.) in the same manner as in Reference Example 3 except that the forced deterioration catalyst obtained in Reference Example 3 was used, the temperature was maintained at 123 ° C., and the reaction was continued under steady conditions for a long time. The CO concentration at the outlet of the reaction tube at 20% (corresponding to a dew point of 61 ° C.) was measured.

The results are shown in a graph showing the relationship between the change over time in the CO selective oxidation activity of the Ru-based CO selective oxidation catalyst in FIG. 13 and the water vapor concentration in the inlet gas. The initial value (outlet CO concentration at 0 hour) has the same result as in FIG. 12, but when the water vapor concentration is 20%, the outlet CO concentration increases with time, and 20 ppm after 12 hours. The experiment was interrupted. On the other hand, when the water vapor concentration was 5%, the outlet CO concentration could be kept below 1 ppm for 60 hours.
The reason why the CO concentration increased with time when the water vapor concentration was 20% was thought to be because it took time for the active sites of the catalyst to reach a coverage ratio that was in equilibrium with the water vapor pressure. Activity means that the water vapor concentration is greatly different between 5% and 20%.
From this, it can be seen that the water vapor concentration greatly affects the activity of the CO selective oxidation catalyst after deterioration, and the lower the water vapor concentration, the higher the CO selective oxidation activity.

Reference Example 5
Reaction simulation in which CO = 0.5%, CO ₂ = 20%, O ₂ = 1%, N ₂ = 4%, and the balance is H ₂ in a reaction tube filled with a Ru catalyst obtained in the same manner as in Reference Example 1. Water vapor was added to the gas so that the water vapor concentration in the wet gas was 20%, and the mixture was circulated so that GHSV = 7,500 on a dry gas basis, and reacted at 120 ° C. for 17,500 hours. The CO concentration at the outlet of the reaction tube at the end was about 5 ppm.
Subsequently, the GHSV = 3,750 and 7,500, the water vapor concentration was 20% and 5%, and the temperature of the catalyst layer was changed to measure the CO concentration at the outlet of the reaction tube.

The results are shown in the graph of FIG. 14 showing the relationship between the temperature dependence of the CO selective oxidation activity of the deteriorated Ru-based CO selective oxidation catalyst, the water vapor concentration in the inlet gas, and the space velocity. When the water vapor concentration is 20% and GHSV = 7,500, there is no region where the concentration is 1 ppm or less. However, when the water vapor concentration is 5%, the outlet CO concentration is in the range of 100 to 120 ° C. even when GHSV = 7,500. It can be seen that at 1 GH or less, GHSV = 3,750, the outlet CO concentration is below 1 ppm in almost all temperature ranges tested. On the other hand, when the water vapor concentration is 20%, at 90 ° C. or less, even when GHSV = 3,750, the outlet CO concentration greatly exceeds 10 ppm, and the water vapor concentration greatly affects the activity of the CO selective oxidation catalyst. .
A tendency similar to that shown in FIG. 12 is also observed in the deteriorated catalyst after actually operating for a long time, and it can be seen that the CO selective oxidation catalyst can be stably operated for a long time as the water vapor concentration is lower under the actual use conditions.

Next, a comparative example will be described.
Comparative Example 1
A fuel reforming system having the same configuration as that shown in FIG. 2 was produced except that a gas-gas heat exchanger was disposed instead of the steam condenser and a desulfurizer was disposed upstream of the reforming reactor. As the reforming reaction, a steam reforming reaction was adopted, an external heating type reforming reactor was used, and a heat exchange type CO converter was used. A commercially available catalyst was used in addition to the CO selective oxidation catalyst, but the CO selective oxidation reactor was charged with the Ru catalyst obtained in Reference Example 1 and cooled by blowing air on the outer wall with an air-cooled fan. Was provided.

Using this fuel reforming system, city gas 13A (natural gas: 88% methane, 6% ethane, 3% propane, 3% butane) 4.2 Nl / min S / C = 3.0 (steam / carbon molar ratio in feed) ) Steam reforming and CO conversion with the remaining steam, after the reformed gas temperature was set to 80 ° C. with a gas-gas heat exchanger, air 0.8Nl / min was added and supplied to the CO selective oxidation reactor .
At this time, the CO concentration in the reformed gas before adding air was 0.35%, and the dew point was 61 ° C.
In addition, the air-cooled fan of the CO selective oxidation reactor was operated intermittently to keep the maximum temperature of the CO selective oxidation catalyst layer from exceeding 180 ° C.

  The CO concentration in the CO selective oxidation reactor outlet gas was about 8 ppm for a while after the start of operation, but the temperature of the CO selective oxidation reactor became unstable and the CO concentration began to rise in about 30 minutes. Stopped driving. When the inside of the CO selective oxidation reactor was observed, a large amount of drain was accumulated and the catalyst was immersed in water.

Comparative Example 2
Using the same fuel reforming system manufactured in Comparative Example 1 and reforming the city gas 13A in the same manner as in Comparative Example 1, except that the gas temperature supplied to the CO selective oxidation reactor is 120 ° C. It was.
The temperature of the CO selective oxidation catalyst layer begins to rise immediately after the start of operation. Even if the air-cooled fan is continuously operated, it cannot be kept below 180 ° C, and the temperature suddenly increases and reaches 250 ° C. Canceled.
Analysis of the CO selective oxidation reactor outlet gas immediately before the operation was stopped. The CO concentration exceeded 500 ppm, and the methane concentration was clearly increased from the inlet, resulting in a runaway methanation reaction. I think that the.

FIG. 7 is a longitudinal sectional view of a steam condensing separator 3 as a steam condensing / separating means used in the first embodiment of the fuel reforming system according to the present invention. The exchanger (heat transfer area 250 cm ² ) 21 and the steam separator 22 are combined.

  In the heat exchanger 21, the inner tube 23 is filled with steel wool 24 for promoting heat transfer, and a cooling medium flow is caused to flow a cooling medium between the inner peripheral surface of the inner tube 23 and the inner peripheral surface of the outer tube 25. A space 26 is formed, and the reformed gas flowing downward in the inner pipe 23 is cooled to condense the water vapor.

  The steam separator 22 receives the drain condensed in the heat exchanger 21 in the container 27 and supplies the reformed gas from which the water vapor has been separated to the CO selective oxidation reactor via the gas pipe 28. ing. In the figure, reference numeral 29 denotes a drain pipe. An open / close valve 30 is provided on the drain pipe 29, and the drain can be appropriately discharged by opening the open / close valve 30 as a predetermined amount of drained water vapor is accumulated.

A fuel reforming system having the same configuration as that of Comparative Example 1 was manufactured except that the steam condenser / separator 3 having the above configuration was incorporated in place of the gas-gas heat exchanger.
Using this system, the city gas 13A was reformed in the same manner as in Comparative Example 1 except that tap water was supplied to the outer periphery of the heat exchanger and the reformed gas was cooled to about 40 ° C. At this time, the dew point of the reformed gas before adding air was 39 ° C.
The CO concentration in the CO selective oxidation reactor outlet gas was stably maintained at about 8 ppm or less after the start of operation, and the concentration was maintained after 7 hours.

  FIG. 8 is a longitudinal sectional view showing Embodiment 2 of the fuel reforming system according to the present invention, which includes a desulfurizer 41, a reforming reactor 42, a CO converter 43, and a CO selective oxidation catalyst layer 44. A CO selective oxidation reactor 45 is connected via piping so as to flow the processing gas in that order, and feeds raw fuel to the desulfurizer 41, and performs desulfurization → reformation → CO conversion → CO selective oxidation to obtain CO concentration. Is configured to produce a low hydrogen-rich reformed gas.

  A pipe 46 connecting the CO converter 43 and the CO selective oxidation reactor 45 is connected to a heat exchanger 47 (corresponding to a heat exchange part of claim 5) and a steam / water separator 48 (to the steam / water separation part of claim 5). A water vapor condensing / separating device 49 as a water vapor condensing / separating means is configured to condense and separate water vapor in the reformed gas before supplying it to the CO selective oxidation reactor 45. . As the water vapor condensing and separating means, the same one as in Example 1 was used.

  The CO selective oxidation reactor 45 is in contact with a part of the CO converter 43 with the hollow plate type element 50 interposed therebetween, and during operation, heat generated by the CO conversion reaction is generated by the outer wall and the cavity of the plate type element 50. Is transmitted to the CO selective oxidation catalyst layer 44 of the CO selective oxidation reactor 45 through the air present in the gas.

  The CO selective oxidation reactor 45 is located at the end, and the inlet side of the outer surface thereof is covered with a heat insulating material 51, while the outlet side is exposed, and air cooling is performed so that cooling air is blown to the exposed portion. A fan 52 is provided.

  A temperature sensor 53 that measures the temperature of the CO selective oxidation catalyst layer 44 is provided at a predetermined position on the outer surface of the CO selective oxidation reactor 45 that is substantially in the middle of the layer length of the CO selective oxidation catalyst layer 44. Is connected to the controller 54, and the fan motor 55 of the air-cooled fan 52 is connected to the controller 54.

The controller 54 operates the air-cooled fan 52 based on the temperature of the CO selective oxidation catalyst layer 44 measured by the temperature sensor 53 so that the measured temperature does not exceed a certain temperature (for example, 160 ° C.). Stop control is provided.
As the CO selective oxidation catalyst, the catalyst obtained in Reference Example 1 was used, and for the other catalysts, known catalysts were used.

  Using this fuel reforming system, city gas 13A was reformed in the same manner as in Example 1. At this time, the dew point of the reformed gas at the outlet of the steam condensing separator 49 was 32 ° C., and the CO concentration in the product gas was stably 3 ppm or less for about 7 hours during the experiment. An example of examining the temperature distribution of the catalyst layer of the CO selective oxidation reactor 45 during operation is shown in FIG. The reformed gas reaches the CO selective oxidation catalyst layer 44 at about 70 ° C., but the temperature rises rapidly as it advances in the catalyst layer length direction due to the inflow of heat from the CO converter 43, thereby causing the oxidation reaction to self It accelerates catalytically and reaches the temperature range favorable for the CO selective oxidation reaction in the first half of the catalyst layer. After that, the cooling effect at the outlet reaches the first half due to heat transfer, so the catalyst layer temperature has a maximum slightly upstream from the middle of the catalyst layer, but the maximum temperature is a suitable temperature of 150 ° C. It is kept in.

FIG. 10 is a longitudinal sectional view showing a third embodiment of the fuel reforming system according to the present invention. The differences from the second embodiment are as follows.
That is, a water-cooled cooler 61 that cools the reformed gas after being treated by the CO converter 43 is interposed in the upstream portion of the heat exchanger 47 that constitutes the water vapor condensing separator 49, and the water-cooled cooler 61 The reformed gas after being cooled in step 1 is supplied to the heat exchanger 47.

  A raw water supply pipe 63 that supplies raw water to a steam generator 62 that generates reforming steam necessary for reforming is introduced into the water-cooled cooler 61 so that heat can be transferred. Is used as a low-temperature heat medium for the water-cooled cooler 61, and the raw water is preheated by the sensible heat of the reformed gas after being treated by the CO converter 43. Other configurations are the same as those of the second embodiment, and the same reference numerals are given and description thereof is omitted.

The city gas 13A was reformed in the same manner as in Example 2 except that the fuel reforming system of Example 3 was used and the raw water flow rate supplied to the water-cooled cooler 61 was 12 ml / min.
The dew point of the reformed gas at the outlet of the steam condensing separator 49 was 16 ° C., and the CO concentration in the product gas was always less than 1 ppm.
Although the temperature of the raw water was 15 ° C., the temperature of the raw water rose to about 85 ° C. by passing through the water-cooled cooler 61. This means that the exhaust heat of the reformed gas that can be recovered by the water-cooled cooler 61 is about 60 W, and if the fuel can be reduced by that amount, the thermal efficiency of the reformer is improved compared to the case where the water-cooled cooler 61 is not attached. This can be increased by about 2 points, which leads to an increase of about 1 point in terms of power generation efficiency.
Furthermore, although the operation was continued for 7000 hours, the temperature of the CO selective oxidation reactor 45 was stable, and the CO concentration in the product gas was always less than 1 ppm. It can be seen that long-term stability of the oxidation reaction has been realized.

FIG. 11 is a longitudinal sectional view showing Embodiment 4 of the fuel reforming system according to the present invention. The difference from Embodiment 3 is as follows.
That is, a fuel cell cogeneration system is constructed by the fuel cell stack 71 and the stratified hot water tank 72 using the fuel reforming system according to the present invention.

  A circulation pipe 73 for exhaust heat recovery connected across the fuel cell stack 71 and the stratified hot water tank 72 is introduced into the heat exchanger 47, and low temperature water with little temperature change taken out from the low temperature part of the stratified hot water tank 72 is supplied. The reformed gas is cooled and condensed by using it, and the heat of the reformed gas can be recovered in the low-temperature water. Other configurations are the same as those of the third embodiment, and the same reference numerals are given and description thereof is omitted.

The city gas 13A was reformed in the same manner as in Example 3 except that the fuel reforming system of Example 4 was used and the flow rate of circulating water in the stratified hot water tank 72 was set to 0.3 l / min. The dew point of the reformed gas at the outlet of the steam condenser / separator 49 was 21 ° C., and the CO concentration in the product gas was always less than 1 ppm. PEFC also achieved stable power generation performance.
On the other hand, the temperature of the inlet of the low-temperature heat medium of the heat exchanger 47 for cooling the reformed gas was 12 ° C., and the outlet was 19 ° C. This means that about 140 W of exhaust heat was recovered, and the 1 kW class PEFC cogeneration system recovers exhaust heat recovery efficiency by recovering the exhaust heat from the heat exchanger for cooling the reformed gas. In addition, there is an effect of improving the overall efficiency by about 4 points.

Using the fuel reforming system shown in FIG. 10, changing the temperature of the CO converter 43 to change the CO concentration of the reformed gas at the inlet of the CO selective oxidation reactor 45, and the inlet of the CO selective oxidation reactor 45 The city gas 13A was reformed in the same manner as in Example 3 except that the dew point of the reformed gas was changed.
First, the heat exchange unit 47 of the water vapor condensing separator 49 was operated through cooling water. At this time, the temperature and dew point of the reformed gas at the outlet were about 25 to 30 ° C.
Subsequently, the cooling water was not supplied to the heat exchanging portion 47 of the water vapor condensing separator 49, and the operation was performed. At this time, the temperature and dew point of the reformed gas at the outlet were about 58 ° C.

Under the respective conditions, when the reaction was stabilized, the CO concentration at the inlet of the CO selective oxidation reactor 45 and the CO concentration in the product gas were appropriately measured. FIG. 15 shows the result of calculating O ₂ / CO from the molar ratio with the flow rate of the air 56 added in front of the CO selective oxidation reactor 45 and plotting the CO concentration in the product gas at that time against O ₂ / CO. Shown in When the dew point is 25 to 30 ° C., the CO concentration in the product gas is 2 ppm or less in the entire region of O ₂ /CO=0.8 to 3.7, whereas when the dew point is 58 ° C., the O _The CO concentration exceeds 2 ppm when ₂ / CO is 1.2 or less, and greatly exceeds 10 ppm when 0.8.

  From this, when the CO conversion catalyst activity decreases and the CO concentration at the inlet of the CO selective oxidation reactor 45 increases, the steam in the reformed gas is condensed and separated in front of the CO selective oxidation reactor 45. However, it can be seen that CO can be stably reduced even when the CO concentration at the inlet of the CO selective oxidation reactor 45 is higher with a smaller amount of added air.

The fuel reforming system shown in FIG. 10 is installed in a closed space where the ambient temperature can be changed, and the ambient temperature is changed, and the dew point of the reformed gas at the inlet of the CO selective oxidation reactor 45 is changed. The city gas 13A was reformed in the same manner as in Example 3 except that.
First, the heat exchange unit 47 of the water vapor condensing separator 49 was operated through cooling water. At this time, the temperature and dew point of the reformed gas at the outlet were about 25 to 30 ° C.
Under these conditions, the ambient temperature was increased by 5 ° C. When the ambient temperature is 50 ° C. or lower, ON / OFF control of the air cooling fan is recognized, the temperature of the CO selective oxidation reactor 45 is normally controlled, and the CO concentration in the product gas is less than 1 ppm. It was. When the atmospheric temperature was raised to 55 ° C., the CO concentration in the product gas was less than 1 ppm, but the air-cooled fan was in a continuous operation state, and the cooling ability was insufficient, making it impossible to control the temperature.

Subsequently, the cooling water was not supplied to the heat exchanging portion 47 of the water vapor condensing separator 49, and the operation was performed. At this time, the temperature and dew point of the reformed gas at the outlet were about 58 ° C.
Under these conditions, the ambient temperature was similarly raised. When the ambient temperature is 45 ° C or lower, ON / OFF control of the air cooling fan is recognized, the temperature of the CO selective oxidation reactor 45 is normally controlled, and the CO concentration in the product gas is about 1 ppm. It was. When the ambient temperature was increased to 50 ° C, the CO concentration in the product gas was less than 1 ppm, but the air-cooled fan was in a continuous operation state, and the cooling capacity was insufficient, making temperature control impossible. In the case of not condensing and separating water vapor, the activity of the CO selective oxidation catalyst becomes low, so the part that reacts mainly shifts to the second half, and the heat generation in the second half increases, so the cooling capacity of the air cooling fan is insufficient, It is considered that the upper limit of the usable atmospheric temperature is lowered.
From this, it is understood that the CO concentration can be surely reduced even at a higher atmospheric temperature by performing condensation separation of water vapor.

  As is clear from the above description, according to the fuel reforming system of the invention according to claim 1, the water vapor contained in the reformed gas is condensed and separated before being supplied to one CO selective oxidation reactor. The temperature range where CO can be reduced can be expanded by lowering the dew point of the reformed gas supplied to the CO selective oxidation reaction, and further, the reformed gas from the addition of oxygen necessary for the CO selective oxidation reaction to the catalyst layer In addition, the tube wall temperature can be kept at 100 ° C. or less, poisoning of the CO selective oxidation catalyst with iron can be prevented, and the CO concentration can be reduced while performing stable operation for a long period of time.

Further, according to the fuel reforming system of the invention according to claim 2, the CO converter converts most of CO in the reformed gas into steam in the presence of the CO conversion catalyst to convert to CO ₂ , Since the water vapor contained in the reformed gas after being processed by the CO converter is condensed and separated before being supplied to the CO selective oxidation reactor, the CO concentration is improved even when reforming at a high temperature at which the CO concentration increases. Can be reduced.

Further, according to the fuel reforming system of the invention according to claim 3, since the reformed gas is cooled in the heat exchange unit to condense the water vapor, and the condensed water and the reformed gas are separated in the steam / water separation unit. For example, when removing water vapor with a desiccant, the water vapor removal performance deteriorates over time, so it is necessary to replace it. In addition, the temperature of the reformed gas supplied to the CO selective oxidation reactor can be stably maintained below a predetermined temperature.
According to the fuel reforming system of the invention according to claim 4, since the dew point of the reformed gas obtained by condensing and separating water vapor is 60 ° C. or less, it is possible to avoid a decrease in activity in the CO selective oxidation reactor. At the same time, water condensation can be avoided.

  According to the fuel reforming system of the invention according to claim 5, the reforming necessary for reforming is used as a low-temperature heat medium of a water-cooled cooler that lowers the temperature of the reformed gas supplied to the CO selective oxidation reactor. If raw water is used to generate steam for the use, the raw water can be preheated by the reformed gas, the exhaust heat from the system can be recovered, and the exhaust heat recovery efficiency can be improved. , Power generation efficiency can be improved.

  Further, according to the fuel reforming system of the invention according to claim 6, since the reformed gas is condensed using the low temperature water from the low temperature part of the stratified hot water tank used in the fuel cell cogeneration system, the condensation is stabilized. In addition, since the heat of the reformed gas is recovered in the low-temperature water, the exhaust heat can be recovered to improve the overall efficiency.

  Further, according to the fuel reforming system of the invention according to claim 7, by using a catalyst containing Ru having a high activity at a low temperature as the CO selective oxidation catalyst and condensing and separating water vapor from the reformed gas. Since high activity is maintained, CO conversion can be increased.

  Further, according to the configuration of the fuel reforming system of the invention according to claim 8, since the maximum temperature of the catalyst layer of the CO selective oxidation reactor is 180 ° C. or less, runaway due to side reactions such as methanation can be avoided. Stable operation can be performed.

  Further, according to the fuel reforming system of the invention according to claim 9, since the reformed gas having a low temperature due to the condensation of water vapor is heated at the reformed gas inlet side of the CO selective oxidation reactor, The start of the CO selective oxidation reaction in the reactor can be promoted. On the other hand, since the reaction is suppressed by cooling at the outlet side, runaway due to side reactions such as methanation can be avoided and stable operation can be performed.

  According to the configuration of the fuel reforming system of the invention according to claim 10, since the heat source of the heating means of the catalyst of the CO selective oxidation reactor is obtained by utilizing the exhaust heat from the system, the thermal efficiency of the system is improved. It can be improved.

According to the configuration of the fuel reforming system of the invention according to claim 11, since the catalyst of the CO selective oxidation reactor is cooled by the air-cooled fan, the water vapor is condensed in the reactor as in the case of the water-cooled type. It is possible to avoid the deterioration of the catalyst.
Moreover, since it can be controlled by operation and stop, reaction heat of the CO selective oxidation reactor can be cooled and removed with simple control.

It is a flowchart corresponding to the fuel reforming system of the invention according to claim 1. It is a flowchart corresponding to the fuel reforming system of the invention according to claim 2. It is a flowchart corresponding to the fuel reforming system of the invention according to claim 3. It is a flowchart corresponding to the fuel reforming system of the invention concerning Claim 5. It is a longitudinal cross-sectional view of the principal part of the CO selective oxidation reactor in the fuel reforming system of the invention according to claim 9. It is the graph which showed the relationship between the temperature dependence of CO selective oxidation activity of a Ru type | system | group CO selective oxidation catalyst, and the water vapor | steam density | concentration in inlet gas. It is a longitudinal cross-sectional view of the water vapor | steam condensation separation means used for Example 1 of the fuel reforming system which concerns on this invention. It is a longitudinal cross-sectional view which shows Example 2 of the fuel reforming system which concerns on this invention. It is a graph which shows the temperature distribution in the catalyst layer length direction in the CO selective oxidation reactor in Example 2 of the fuel reforming system which concerns on this invention. It is a longitudinal cross-sectional view which shows Example 3 of the fuel reforming system which concerns on this invention. It is a longitudinal cross-sectional view which shows Example 4 of the fuel reforming system which concerns on this invention. It is the graph which showed the relationship between the temperature dependence of CO selective oxidation activity of the Ru type | system | group CO selective oxidation catalyst made to accelerate deterioration, and the water vapor | steam density | concentration in inlet gas. It is the graph which showed the relationship between the time-dependent change of CO selective oxidation activity of the Ru type | system | group CO selective oxidation catalyst accelerated, and the water vapor | steam density | concentration in inlet gas. It is the graph which showed the relationship between the temperature dependence of CO selective oxidation activity of the deteriorated Ru type | system | group CO selective oxidation catalyst, the water vapor | steam density | concentration in an inlet gas, and space velocity. It is a graph showing the relationship between the O ₂ / CO dependence and concentration of water vapor in the inlet gas of CO concentration in the product gas in Example 5 of the fuel reforming system according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Reforming reactor 2 ... CO selective oxidation reactor 3 ... Steam condensing separation means 4 ... CO converter 5 ... Heat exchange part 6 ... Air-water separation part 7 ... Water-cooled cooler 42 ... Reforming reactor 43 ... CO Transformer 44 ... CO selective oxidation catalyst layer 45 ... CO selective oxidation reactor 47 ... Heat exchange section 48 ... Steam-water separation section 49 ... Steam condensing separator 56 ... Selective oxidation air 61 ... Water-cooled cooler 72 ... Stratified hot water storage Tank

Claims (11)

A reforming reactor for reacting raw fuel with steam and / or air in the presence of a reforming catalyst to generate reformed gas;
1 CO selective oxidation to produce a hydrogen-rich gas is converted to CO ₂ by selectively oxidizing CO in the reforming reformed gas generated in the reactor with oxygen in the presence of CO selective oxidation catalyst A fuel reforming system comprising at least a reactor,
A fuel reforming system comprising a steam condensing / separating means for condensing and separating steam contained in the reformed gas before being supplied to the CO selective oxidation reactor. The fuel reforming system according to claim 1, wherein
Between the reforming reactor and the CO selective oxidation reactor, a CO converter that converts most of the CO in the reformed gas to steam in the presence of a CO converting catalyst is converted to CO ₂ by steam condensation. A fuel reforming system, wherein the separation means condenses and separates water vapor from the reformed gas after being processed by the CO converter. The fuel reforming system according to claim 1 or 2,
A fuel reforming system in which the steam condensing / separating means comprises a heat exchanging unit for cooling the reformed gas and a steam / water separating unit for separating the condensed water and the reformed gas. The fuel reforming system according to any one of claims 1, 2, and 3,
A fuel reforming system in which the water vapor condensing and separating means condenses and separates the water vapor contained in the reformed gas so that the dew point of the reformed gas after the condensation and separation is 60 ° C. or less. The fuel reforming system according to claim 3 or 4,
A water-cooled cooler for cooling the reformed gas before entering the CO selective oxidation reactor;
Supply the reformed gas after cooling with the water-cooled cooler to the heat exchange unit,
A fuel reforming system that uses raw water for generating reforming steam necessary for reforming as a low-temperature heat medium for the water-cooled cooler and preheats the raw water with a reformed gas. The fuel reforming system according to any one of claims 3, 4, and 5,
A fuel reforming system for supplying fuel to a fuel cell in a fuel cell cogeneration system, wherein hot water obtained by exhaust heat recovery from the fuel cell cogeneration system is stored in a state of forming a temperature stratification Equipped with hot water storage tanks,
A fuel reforming system for supplying low-temperature water before exhaust heat recovery to the heat exchanging section after recovering exhaust heat from the low-temperature section of the stratified hot water tank and returning it to the high temperature section of the stratified hot water tank. The fuel reforming system according to any one of claims 1, 2, 3, 4, 5, and 6.
A fuel reforming system in which the CO selective oxidation catalyst is a catalyst containing Ru. The fuel reforming system according to claim 7, wherein
A fuel reforming system comprising a CO selective oxidation reactor provided with heat exchange means for setting the maximum temperature of the catalyst layer to 180 ° C. or less. The fuel reforming system according to claim 8, wherein
A fuel reforming system comprising a CO selective oxidation reactor comprising means for heating a catalyst on the inlet side of reformed gas and means for cooling the catalyst on the outlet side. The fuel reforming system according to claim 9, wherein
A fuel reforming system configured to obtain a heat source of a catalyst heating means of a CO selective oxidation reactor by heat exchange with a portion of the fuel reforming system having a temperature higher than that of the CO selective oxidation reactor. The fuel reforming system according to claim 9 or 10,
A fuel reforming system in which the cooling means for the catalyst of the CO selective oxidation reactor is an air-cooled fan capable of controlling the shutdown.

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