JP2001085039A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce external heating quantity and CO quantity, and to effectively use the heat by providing a catalyst for presenting activity to partial oxidation reaction of original fuel and a steam supply means for supplying steam required to perform water gas shift reaction on CO generated by the partial oxidation reaction in a fuel reformer. SOLUTION: Fuel is heated by a burner 19 with air and spray water after desulfurization, and is supplied to a catalyst part of a fuel reformer 5 together with steam generated by heating. Partial oxidation reaction of the fuel is caused on a catalyst of the fuel reformer 5 to generate hydrogen and CO, and at the same time, water gas shift reaction is caused by existing steam to generate hydrogen and carbon dioxide to reduce the CO concentration. The catalyst fore presenting activity to the partial oxidation reaction is filled in the fuel reformer 5, and sprayed water from a water tank 17 is heated by the burner 19 to be formed as steam to be supplied. The partial oxidation reaction and the water gas shift reaction are exothermic reaction so that a heating quantity from an external part is reduced, in its turn, can be obviated after starting the reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a fuel cell system.

[0002]

2. Description of the Related Art A fuel cell is generally known as a power generator in which hydrogen supplied to a negative electrode is used as fuel, and oxygen supplied to a positive electrode is used as an oxidant, and these are reacted through an electrolyte. Hydrogen used in this fuel cell can be produced by reforming hydrocarbon or methanol.

[0003] Japanese Patent Publication No. 58-57361 discloses that a hydrocarbon is allowed to react with air, air and oxygen, or air and steam in the presence of a rhodium catalyst, and hydrogen and CO (carbon monoxide) are produced by a partial oxidation method. Is described. The reaction temperature is 690-900C. Air and oxygen are used as oxidizing agents for hydrocarbons, and steam is used for the purpose of generating hydrogen by steam reforming reaction from fuel remaining unoxidized by the oxidation reaction. Therefore, the reactions that occur on a rhodium catalyst when air and water vapor act on hydrocarbons are a partial oxidation reaction and a water vapor reforming reaction.

Japanese Patent Application Laid-Open No. 54-76602 discloses 81
A method is described in which a gas containing free oxygen is allowed to act on hydrocarbons under conditions of 5 to 1930 ° C. and 1 to 250 absolute pressure to generate hydrogen and CO by partial oxidation. Moderators are described for the addition of hydrocarbon fuels for preheating, dispersion and transfer.

[0005] JP-A-6-92603 discloses that hydrocarbon, oxygen-containing gas and water vapor are mixed in the presence of a catalyst in the range of 2 to 1%.
00 bar, 750-1200 ° C. (preferably 1
It is described that hydrogen and CO are generated by performing a partial oxidation reaction at a temperature of 000 to 1200 ° C.).

[0006] Japanese Patent Application Laid-Open No. 7-57756 discloses a method in which steam is allowed to act on hydrocarbons in the presence of a catalyst, and the hydrocarbons are introduced into a fuel reformer that generates hydrogen and CO by a steam reforming reaction. Describes a fuel cell power generation system in which a partial oxidation reaction is caused to occur simultaneously. In this method, since the steam reforming reaction is an endothermic reaction, the heat required for the steam reforming reaction is supplemented by utilizing an exothermic partial oxidation reaction.

[0007] JP-A-10-308230 discloses a fuel reformer for reforming hydrocarbons into hydrogen by a partial oxidation reaction in the presence of a catalyst, and a process for converting CO generated during the reforming by a water gas shift reaction. A fuel cell power generator including a CO converter to be oxidized and a selective oxidizer to selectively oxidize remaining CO is described. The fuel reformer is filled with a catalyst exhibiting activity for the steam reforming reaction of hydrocarbons in addition to the catalyst exhibiting activity for the partial oxidation reaction. It also describes that by supplying steam and steam, hydrogen is generated by a partial oxidation reaction of hydrocarbons and a steam reforming reaction.

[0008]

As described above, in reforming hydrocarbons into hydrogen by a partial oxidation reaction, it is known that oxygen and water vapor act on hydrocarbons in the presence of a catalyst. Steam is added to obtain a steam reforming reaction, which is an endothermic reaction, or to control temperature. In this case, it is necessary to provide the fuel reformer with external heating means having a large heat transfer area in order to maintain the reforming reaction, and the CO generated by the partial oxidation reaction of hydrocarbons or the steam reforming reaction causes In order to avoid poisoning of the catalyst electrode, a large transformer for oxidizing and removing this CO is required.

As described in JP-A-7-57756 and JP-A-10-308230, the endothermic component due to the steam reforming reaction is supplemented by the heat generated by the partial oxidation reaction, so that the external heating means is provided. Although there is an idea that the heat of steam reforming reaction is about 205 kJ / mol (endothermic) in the case of methane,
The heat of reaction of the partial oxidation reaction is about 36 kJ / mol, and the difference in calorific value is large. Therefore, it is actually difficult to eliminate the external heating means in view of adding steam mainly for causing a steam reforming reaction.

That is, one of the objects of the present invention is to reduce the amount of external heating required to maintain the above-mentioned fuel reforming reaction, and to reduce the amount of external heating to zero.

Another object of the present invention is to reduce the amount of CO generated by fuel reforming as much as possible, and thereby to reduce the burden on the CO converter.

Another object of the present invention is to achieve effective use of heat as a whole fuel cell system and to simplify the system configuration.

[0013]

In order to solve the above-mentioned problems, the present invention is to make the partial oxidation reaction and the water gas shift reaction proceed sequentially.

That is, the present invention provides a fuel reformer (5) for reforming a hydrocarbon-based raw fuel to produce hydrogen,
In a fuel cell system comprising: a fuel cell that generates electricity using hydrogen generated by the fuel reformer (5) as a fuel, the fuel reformer (5) has an activity against a partial oxidation reaction of the raw fuel. A catalyst (27) exhibiting
In the fuel reformer (5), steam supply means (35, 40) for supplying steam to the reformer (5) so as to generate a water gas shift reaction using CO generated by the partial oxidation reaction as a reactant. It is characterized by having.

The above sequential reaction can be represented by the following formula.

CnHm + (n / 2) O ₂ → nCO + (m / 2) H ₂ (1) CO + H ₂ O → CO ₂ + H ₂ (2) The equation (1) is a partial oxidation reaction. The desired hydrogen is obtained by the reaction, and simultaneously generated CO is oxidized by the water gas shift reaction of the formula (2), thereby generating hydrogen. The addition of water vapor to the raw material gas does not significantly affect the fuel conversion rate in the partial oxidation reaction of (1), but the addition facilitates the water gas shift reaction of (2) (equilibrium is inclined to the generation side). Therefore, the yield of hydrogen increases.

The partial oxidation reaction (1) is an exothermic reaction,
ΔH = −36 when the raw fuel CnHm is methane (CH ₄ ).
07 kJ / mol. The water gas shift reaction of (2) is also an exothermic reaction, and ΔH = −41.12 kJ / mol.
It is. Therefore, although it is necessary to heat the fuel reformer (5) or the raw material gas (raw fuel, oxygen or air, and steam) to a predetermined temperature in order to start the reforming reaction, after the reaction starts, the reaction starts. Is required by the reaction heat, the amount of external heating can be reduced, and external heating can be eliminated.

Further, since the CO generated by the partial oxidation reaction of (1) is oxidized by the water gas shift reaction of (2), the CO of the reformed gas sent from the fuel reformer (5) to the fuel cell is changed. The concentration will be lower. Therefore, CO converter (CO is oxidized by water gas shift reaction)
Even if a CO or CO selective oxidation reactor is provided, the burden on them is reduced, and their size can be reduced.

CO in the outlet gas of the fuel reformer (5)
By adjusting the water gas shift reaction so that the CO ₂ / CO ratio, which is the ratio of CO ₂ to CO ₂ , becomes 0.2 or more, the yield of hydrogen can be increased and the load on the subsequent CO converter can be reduced. .

This point will be further clarified in the examples described later. The fact that the CO ₂ / CO ratio is high means that the water gas shift reaction is in progress, thereby generating hydrogen. .

The increase in the CO ₂ / CO ratio, that is, the progress of the water gas shift reaction depends on the supply ratio of the raw fuel and steam to the fuel reformer (5). Ratio of the number of moles of water vapor to H ₂ O It is preferable that / C be 0.5 or more.

In the present invention, water vapor is added for the water gas shift reaction, and H ₂ O The higher the / C ratio, the better the water gas shift reaction proceeds. If the ratio is less than 0.5, the water gas shift reaction is not sufficiently promoted, and the CO concentration of the obtained gas increases, so that the size of the CO converter cannot be reduced. Also,
The hydrogen yield also does not improve.

Further, as described above, the H ₂ O / C ratio to 0.
By setting it to 5 or more, the CO concentration of the reformed gas is surely reduced by the water gas shift reaction, so that it is possible to prevent the CO converter from being overheated. That is, when the CO concentration in the reformed gas is high, the temperature of the converter is excessively increased by the water gas shift reaction there (for example, the temperature is 100 K or more higher than the temperature of the gas at the inlet of the reformer), and the sintering of the catalyst is performed. Or may lead to early deterioration,
This is prevented.

The above H ₂ O The / C ratio is preferably 3 or less. Increasing this ratio, that is, increasing the amount of water vapor is advantageous in promoting the water gas shift reaction, but increasing the amount of water vapor requires a correspondingly large amount of heat, and as a whole the system Energy efficiency is reduced. Therefore, the ratio is set to 3 or less.

The outlet gas temperature of the fuel reformer (5) is 8
The temperature is preferably not higher than 00 ° C. As described above, since the partial oxidation reaction and the water gas shift reaction are exothermic reactions, unlike the case of the steam reforming reaction which is an endothermic reaction, if the reaction temperature is too high, it is disadvantageous for the progress of the reaction. . The lower limit of the outlet gas temperature is preferably about 450 ° C. If the temperature is lower than this, the partial oxidation reaction and the water gas shift reaction become difficult to proceed.

[0026] O in the fuel feed rate and for the original fuel and oxygen reformer (5), the ratio of moles of oxygen to the number of moles of carbon of the raw fuel O ₂ / C is the partial oxidation reaction ₂
It is preferable that the ratio be 0.9 times or more of the / C stoichiometric ratio.

Here, in the partial oxidation reaction, O ₂ /
Since the C stoichiometric ratio is 0.5 as is apparent from the above equation (1), the O ₂ / C ratio is 0.45 or more. Thereby, even when the flow velocity (space velocity) of the raw material gas supplied to the fuel reformer (5) is high, the fuel conversion rate (reformation rate) can be increased.

If the lower limit of the ratio is lower than the above stoichiometric ratio, a part of the raw fuel may cause a steam reforming reaction, but the ratio is small and the main reaction is a partial oxidation reaction. The thermal effect (temperature drop) on the surface does not matter.

In order to minimize the occurrence of the steam reforming reaction, the ratio should be larger than the above stoichiometric ratio, that is, larger than 0.5. However, if the ratio is too large, a complete oxidation reaction is likely to occur and the yield of hydrogen is reduced. Therefore, the upper limit of the ratio is 1.5 times the O ₂ / C stoichiometric ratio, that is, 0. It is preferred to be about 75.

As the hydrocarbon-based raw fuel, besides the methane, propane, natural gas (including LNG), naphtha, kerosene, liquefied petroleum gas (LPG), city gas, and the like can be used.

Rhodium and ruthenium are preferred as the catalyst metal of the catalyst (27) exhibiting activity against the partial oxidation reaction. These catalyst metals may be supported on a support in the form of a simple metal, an alloy, or a compound, for example, an oxide. Further, the catalyst may be one in which two or more types of catalyst metals (for example, two types of rhodium and ruthenium) are supported on the same carrier, or a mixture of two or more types of catalyst metals each supported on separate carriers. Good.

As the carrier, an inorganic porous material having a large specific surface area is preferable, for example, alumina is preferable.

The catalyst (27) obtained by supporting the catalyst metal on the carrier can be filled in the fuel reformer (5) in the form of pellets, and can be supported on a monolithic carrier, for example, a honeycomb-shaped material by a binder. You can make it.

Of the raw material gases, oxygen (or air) and water vapor can be supplied to the fuel reformer (5) by separately providing their respective sources, and the exhaust gas of the fuel cell is used for them. You can also. That is, the gas discharged from the oxygen electrode of the fuel cell contains oxygen not used in the cell reaction and water vapor generated by the cell reaction. Therefore, if an exhaust gas supply means for supplying the exhaust gas from the oxygen electrode to the fuel reformer (5) is provided, the oxygen (or air) supply source, the steam supply source and their supply pipes are omitted. And the configuration of the fuel cell system is simplified. However, oxygen (or air) or steam replenishing means may be separately provided to replenish the exhaust gas from the oxygen electrode.

Further, if output current adjusting means for adjusting the output current of the fuel cell is provided, the oxygen concentration and the water vapor concentration of the exhaust gas supplied to the fuel reformer (5) are set within a predetermined range. Can be adjusted.

That is, the fuel (hydrogen) in the fuel cell
The utilization rate and the oxygen (air) utilization rate vary depending on the load (electric power consumption) of the fuel cell. That is, when the fuel inflow amount and the oxygen inflow amount into the fuel cell are kept constant, if the output current value of the cell is changed, the amounts of hydrogen and oxygen consumed by the cell reaction change, and the amount of hydrogen and oxygen is generated accordingly. The amount of water vapor also changes. Therefore, by adjusting this output current value, it is possible to supply exhaust gas having a predetermined oxygen concentration and water vapor concentration suitable for fuel reforming to the fuel reformer (5).

The fuel cell has an oxygen utilization rate of 0.4
It is preferable to adjust the output current so as to be 0.75 (40 to 75% of the supplied oxygen amount). Thereby, the H ₂ O / C ratio of the raw material gas of the fuel reformer (5) is set to 0.67 to
It can be adjusted to about 3.0.

That is, in a fuel cell, the oxygen consumption
Because twice the amount of water vapor is generated (O_Two+ 2H_Two→ 2H
_TwoO), when the oxygen utilization rate is 0.4, double that 0.8
A considerable amount of water vapor is generated, and the amount of residual oxygen becomes 0.6 equivalent.
You. Therefore, the H _TwoO / O_TwoThe ratio is (0.8 /
0.6). The exhaust gas is supplied to the fuel reformer (5).
Supply amount of raw gas O_Two/ C ratio is a stoichiometric ratio of 0.5
If it is adjusted so that_TwoO / C ratio
Is as follows.

H ₂ O / C ratio = 0.5 × (0.8 / 0.
6) = approximately 0.67 Similarly, the calculation for the case of the oxygen utilization rate of 0.75 is as follows.

H ₂ O / C ratio = 0.5 × (1.5 / 0.25) = 3 According to the fuel reformer as described above, a reformed gas having a low CO concentration can be obtained. In order to further reduce the CO concentration, at least one of a high-temperature CO converter, a low-temperature CO converter, and a partial CO oxidation reactor may be provided and passed through the fuel cell.

[0041]

As described above, according to the present invention, in a fuel cell system including a fuel reformer (5) and a fuel cell, the fuel reformer (5) includes a partial oxidation of a raw hydrocarbon fuel. A catalyst (27) exhibiting activity with respect to the reaction is provided, and the reformer (5) is formed in the fuel reformer (5) so as to generate a water gas shift reaction using CO generated by the partial oxidation reaction as a reactant. ) Is equipped with steam supply means for supplying steam, so that the hydrogen yield can be increased by the partial oxidation reaction and the water gas shift reaction, and the external heating means for maintaining the fuel reforming reaction is reduced in size. Alternatively, the external heating means can be omitted, and the CO concentration in the reformed gas is reduced, so that the size of the post-processing device for reducing the CO concentration can be reduced.

Further, if the water gas shift reaction is adjusted so that the CO ₂ / CO ratio in the outlet gas of the fuel reformer (5) becomes 0.2 or more, it is advantageous in increasing the yield of hydrogen. And H ₂ O supplied to the fuel reformer (5) / C
When the ratio is set to 0.5 or more, it is advantageous in that a water gas shift reaction is caused to increase the hydrogen yield.

Further, if the outlet gas temperature of the fuel reformer (5) is set to 800 ° C. or lower, it is advantageous in efficiently proceeding the partial oxidation reaction and the water gas shift reaction.

If the O ₂ / C ratio of the raw material gas supplied to the fuel reformer (5) is set to be at least 0.9 times the O ₂ / C stoichiometric ratio in the partial oxidation reaction, the fuel conversion This is advantageous in increasing the rate (reformation rate).

The above H ₂ O When the upper limit of the / C ratio is set to 3.0, energy loss can be reduced. When the O ₂ / C ratio is set to 1.5 times or less of the O ₂ / C stoichiometric ratio, the raw fuel can be reduced. This is advantageous in preventing complete combustion and maintaining high fuel reforming efficiency.

The use of a catalyst containing rhodium or ruthenium as the catalyst (27) of the fuel reformer (5) is advantageous in promoting the partial oxidation reaction.

If the exhaust gas from the oxygen electrode of the fuel cell is supplied as a reforming gas to the fuel reformer (5), the supply source of oxygen (or air), the supply source of steam, and the supply pipes thereof are omitted. This is advantageous in simplifying the configuration of the fuel cell system. In this case, if output current adjusting means for adjusting the output current of the fuel cell is provided, the oxygen concentration and the water vapor concentration of the exhaust gas supplied to the fuel reformer (5) fall within predetermined ranges suitable for fuel reforming. Adjustment becomes easier.

[0048]

Embodiments of the present invention will be described below with reference to the drawings.

<Overall Description of Fuel Cell System> In the fuel cell system configuration shown in FIG. 1, reference numeral 1 denotes a solid fuel cell having an oxygen electrode (cathode) 2 as a catalyst electrode and a hydrogen electrode (anode) 3 as a catalyst electrode. This is a fuel cell of a molecular electrolyte type. An air compressor 4 is connected to an oxygen electrode 2 by an air supply pipe 10.
, And a fuel reformer 5 is connected to the hydrogen electrode 3 by a reformed gas supply pipe 20. A first heat exchanger 6, a high-temperature CO converter 7, a second heat exchanger 8, a low-temperature CO converter 9, a third heat exchanger 11,
The selective oxidation reactor 12 and the fourth heat exchanger 13 are provided in order toward the fuel cell 1.

The fuel reformer 5 has a raw fuel source (city gas) 1
4 are connected by a source gas supply pipe 30. The raw material gas supply pipe 30 has a gas compressor 15 and a desulfurizer 16.
Are sequentially provided toward the fuel reformer 5. Also,
The fuel reformer 5 is connected to a pipe branched from the air supply pipe 10 so as to supply air for the partial oxidation reaction from the air compressor 4 and is used to obtain water vapor for the water gas shift reaction. The water tank 17 is connected by a supply pipe 40 to spray and supply the water. The water supply pipe 40 is provided with a pump 18.

The raw fuel from the raw fuel source 14 and the air compressor 4
Air from the tank and steam from the water tank 17 are
, And can be supplied to the fuel reformer 5. Further, a pipe branched from the water supply pipe 40 is connected to an upstream portion of the first heat exchanger 6 of the reformed gas supply pipe 20 so as to spray and supply water for obtaining water vapor for the water gas shift reaction. . A pipe branched from the air supply pipe 10 to supply air for the selective oxidation reactor 12 is connected to a portion of the reformed gas supply pipe 20 upstream of the third heat exchanger 11.

The exhaust gas from the oxygen electrode 2 and the exhaust gas from the hydrogen electrode 3 of the fuel cell 1 are passed through the steam separators 21 and 22 and then combined to be sent to the combustor 19 through the gas pipe 50 as a combustion gas. Have been. The exhaust gas from the oxygen electrode 2 is
Can be discharged to the atmosphere as appropriate. The gas pipe 50 is connected to the fourth heat exchanger 13 and the third heat exchanger 1.
The pipe is arranged so as to pass through the first and second heat exchangers 8 in order, and the exhaust gas is heated by heat exchange with the reformed gas in each heat exchanger and supplied to the combustor 19. Accordingly, the reformed gas is cooled by each heat exchanger and sent to the fuel cell 1. Another cooling water pipe 24 is passed through the first heat exchanger 6, and the reformed gas is cooled by heat exchange with the cooling water.

The fuel reformer 5 is filled with a catalyst (catalyst in which Ru or Rh is supported on Al ₂ O ₃ ) exhibiting an activity in the partial oxidation reaction.
A catalyst (Fe ₂ O ₃ , Cr ₂ O ₃ ) exhibiting an activity in the water gas shift reaction at about 0 ° C.)
Is filled with a catalyst (CuO, ZnO) exhibiting an activity in a water gas shift reaction at a low temperature (around 180 ° C.), and a catalyst (Ru or Pt) exhibiting an activity in a selective oxidation reaction of CO is filled in a CO selective oxidation reactor 12. (A catalyst supported on Al ₂ O ₃ or zeolite), and the combustor 19 is filled with a combustion catalyst. Further, the fuel reformer 5 is provided with an electric heater for preheating.

FIG. 2 shows a reactor 25 in which the fuel reformer 5 and the combustor 19 are integrated. In the reactor 25 shown in the figure, an electric heater 26 is incorporated between the upper fuel reformer 5 and the lower combustor 19. A portion of the fuel reformer 5 is loaded with a honeycomb catalyst 27 in which a catalyst is supported on a honeycomb monolith carrier. A portion of the combustor 19 is filled with a combustion catalyst 28, and a raw material gas passage 29 extends from a raw material gas inlet 31 at a lower end to a portion where the electric heater is provided so as to penetrate the catalyst filled portion of the combustor 19. . In the same figure, 32 is an outlet for reformed gas, 33 is an inlet for exhaust gas from the fuel cell 1, and 34 is an outlet for combustion exhaust gas.

In the above fuel cell system, when the fuel reformer 5 is started, the temperature of the fuel reformer 5 is low, so that the electric heater is operated to heat the catalyst to a temperature at which the catalyst becomes active, for example, to about 460 ° C. After startup, the electric heater is stopped, and the raw material gas (mixed gas of raw fuel, air and water vapor) is only preheated in the combustor 19. The source gas is H ₂ O O ₂ / C so that the / C ratio is 0.5 to 3
The supply amounts of the raw fuel, air and steam are adjusted so that the ratio becomes 0.45 to 0.75, and the outlet gas temperature of the fuel reformer 5 is separately adjusted so as not to rise to 800 ° C. or more. You. The most preferred operating conditions are the above H ₂ O A C / C ratio of 1.0, an O ₂ / C ratio of 0.52 to 0.60 (preferably 0.56), an outlet gas temperature of the fuel reformer 5 of 720 ° C.,
The CO ₂ / CO ratio of the outlet gas of the fuel reformer 5 is 0.4.

The raw fuel is heated by an electric heater or a combustor 19 together with air and spray water after being desulfurized and supplied to the catalyst of the fuel reformer 5. This heating turns the spray water into steam. A partial oxidation reaction of the raw fuel occurs on the catalyst of the fuel reformer 5 to generate hydrogen and CO ((1)
See formula). Since water vapor is present in the fuel reformer 5, a water gas shift reaction occurs at the same time to generate hydrogen and carbon dioxide, and the CO concentration decreases (see equation (2)).

The reformed gas that has exited the fuel reformer 5 is cooled to about 400 ° C. by the first heat exchanger 6 and sent to the CO high-temperature converter 7, where the water gas shift reaction occurs on the catalyst. Further, the CO concentration decreases. The reformed gas exiting the CO high-temperature shifter 7 is supplied to the second heat exchanger 8 to
The temperature is lowered to about 0 ° C. and sent to the CO low-temperature shift converter 9, where the water gas shift reaction occurring on the catalyst further lowers the CO concentration. The reformed gas exiting the CO low-temperature shifter 9 is cooled down to about 140 ° C. by the third heat exchanger 11 and sent to the CO selective oxidation reactor 12, where CO is oxidized by the selective oxidation reaction of CO generated on the catalyst. The concentration is further reduced. The reformed gas exiting the CO selective oxidation reactor 12 is cooled down to about 80 ° C. by the fourth heat exchanger 13 and enters the hydrogen electrode 3 of the fuel cell 1.

In the fuel cell 1, 2H is applied on the electrode surface of the hydrogen electrode 3.
₂ → 4H ⁺ + 4e ⁻ , O ₂ + 4H ⁺ + on the electrode surface of oxygen electrode 2
4e ^- → cause a cell reaction of 2H ₂ O. Therefore, oxygen electrode 2
The exhaust gas contains excess air not used for the battery reaction and water vapor generated by the battery reaction. On the other hand, the exhaust gas from the hydrogen electrode 3 contains hydrogen not used in the battery reaction, unreformed raw fuel, air and water vapor.

The exhaust gases from the oxygen electrode 2 and the hydrogen electrode 3 join through the steam separators 21 and 22 and are exchanged by the fourth heat exchanger 13, the third heat exchanger 11 and the second heat exchanger 8. And is sent to the combustor 19. Hydrogen and oxygen contained in this exhaust gas react by the action of a combustion catalyst in the combustor 19, and the reaction heat serves as a preheating source for the raw material gas. Also burns at the same time and becomes a preheat source.

<H_TwoO / C ratio and CO_Two/ CO ratio and hydrogen yield
Relationship with Ratio> FIG. 3 shows the raw material gas introduced into the fuel reformer 5.
H_TwoO / C ratio (water vapor relative to moles of carbon in raw fuel)
Of the reformed gas flowing out of the fuel reformer 5
CO _Two/ CO ratio (CO to CO in reformer outlet gas
_TwoRatio) and the hydrogen yield ratio (H_TwoO
/ C ratio is 0.5 when the hydrogen yield is 1) and
The relationship is shown. The operating conditions of the fuel reformer 5 are as follows.
Gas temperature of 460 ° C, O_Two/ C ratio (carbon of raw fuel
Ratio of the number of moles of oxygen to the number of moles of
The pressure is 150 kPa.

According to the figure, the CO ₂ / CO ratio increases as the H ₂ O / C ratio increases. The large CO ₂ / CO ratio means that CO in the fuel reformer 5 is CO ₂
It is changing to. The cause of this change is considered to be a complete oxidation reaction of the raw fuel and a water gas shift reaction of CO, but an increase in the H ₂ O / C ratio, that is,
Since it is not considered that the complete oxidation reaction easily proceeds with an increase in the amount of water vapor, it can be seen that the water gas shift reaction in the fuel reformer 5 was efficiently advanced by the addition of water vapor.

Then, from the figure, the H ₂ O / C ratio was set to 0.
If it is set to 5 or more, the hydrogen yield increases, and in order to increase the hydrogen yield, the water gas shift reaction in the fuel reformer 5 is adjusted so that the CO ₂ / CO ratio becomes 0.2 or more. It is understood that what is necessary is just to adjust the composition of the source gas, the reaction temperature and the like.

<Effect of Type of Catalyst in Fuel Reformer on Reformed Gas Composition> Inlet of fuel reformer 5 when fuel reforming is performed by changing the type of catalyst used in fuel reformer 5 Gas composition (raw gas composition) and outlet gas composition (reformed gas composition)
Is shown in Table 1. The type of catalyst is Ni-Al ₂ O ₃
(A catalyst in which Ni is supported on Al ₂ O ₃ ), Rh-Al
₂ O ₃ (a catalyst comprising Rh supported on Al ₂ O ₃ ) and Ru
—Al ₂ O ₃ (a catalyst in which Ru is supported on Al ₂ O ₃ ).

[0064]

[Table 1]

According to the table, the Rh—Al ₂ O ₃ catalyst and the R
Although a high conversion to hydrogen of methane in u-Al ₂ O ₃ catalyst, a Ni-Al ₂ O ₃ catalyst is its low conversion. From this, the Rh-Al ₂ O ₃ catalyst or Ru-A
It turns out that it is preferable to use the l ₂ O ₃ catalyst.

<H ₂ O / C in Rh-Al ₂ O ₃ catalyst
Effect of Ratio on Reformed Gas Composition>
An inlet gas composition (raw material gas composition) and an outlet gas composition (reformed gas composition) of the fuel reformer 5 when an Al ₂ O ₃ catalyst is employed and the H ₂ O / C ratio is changed to perform fuel reforming. Is shown in Table 2.

[0067]

[Table 2]

According to the table, as the H ₂ O / C ratio increases, the CO ₂ / CO ratio increases, and the hydrogen yield increases. This is consistent with the results shown in FIG.

<Another Embodiment of Fuel Cell System> FIG.
Shows another embodiment of the fuel cell system.
The difference from the previous system is that instead of introducing the air of the air compressor 4 and the water of the water tank 17 to the fuel reformer 5, the exhaust gas of the oxygen electrode 2 is supplied by a supply pipe 35, The fuel cell 1 and another power supply 37 are connected in parallel to the electric load 36, and a power controller 38 for adjusting the output current value of the fuel cell 1 is provided. The flow control valve 39 is connected to the branch pipe extending toward
Is provided to constitute the air supply means.

That is, since the exhaust gas of the oxygen electrode 2 contains water vapor and unused air as described above, this exhaust gas is used in the fuel reformer 5 as a raw fuel reforming gas.
In order to make the composition of the exhaust gas suitable for fuel reforming, a power controller 38 is provided. By adjusting the output current value of the fuel cell 1 by the power regulator 38, the utilization rates of hydrogen and air of the fuel cell 1 change, and the oxygen concentration and the water vapor concentration of the exhaust gas at the oxygen electrode 2 change. The power shortage caused by this adjustment will be supplemented by another power supply 37.

The amount of hydrogen used in the fuel cell 1 is 1 L /
Assuming that the utilization is 100% at min. (0 ° C., 1 atm), the output current value A at that time is theoretically as follows.

A = 2 nF = 143 (ampere) (A; C (coulomb) / sec, n: mol / sec, F: Faraday constant) Therefore, if the output current value is reduced below the theoretical value, the hydrogen utilization rate (fuel Utilization) and air utilization will be reduced. In this case, the air utilization rate is adjusted, for example, in the range of 0.4 to 0.75.

When the air utilization rate is increased, the shortage of air is compensated by introducing the air from the air compressor 4 through the flow control valve 39.

<Relationship Between Fuel Utilization Rate and Fuel Conversion Rate> FIG.
In the fuel cell system using the unreformed raw fuel and unused hydrogen among the raw fuel supplied from the raw fuel source 14 for preheating the fuel gas, the fuel efficiency of the fuel cell 1 is maximized. 4 is a graph showing the relationship between the rate and the fuel conversion rate of the fuel reformer 5.

For example, when the fuel conversion rate is 0.94, the fuel utilization rate with the highest energy efficiency is 0.98.
In this example, the remaining 6% of the unreformed raw fuel and the remaining 2% of the hydrogen not used for the cell reaction in the reformed gas are used for preheating the raw material gas. Become.

In each of the above embodiments, the combustor 19 is provided so that the exhaust gas of the fuel cell 1 is used for preheating the raw material gas. However, the combustor 19 is omitted and the exhaust gas is burned by the catalyst. Other heat sources. Since both the partial oxidation reaction and the water gas shift reaction occurring in the fuel reformer 5 are exothermic reactions, after the fuel reformer 5 is heated to the reaction temperature by the electric heater at the time of starting, the reaction temperature is increased by the reaction heat. Because it is maintained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a fuel cell system according to an embodiment of the present invention.

FIG. 2 is a sectional view showing the structure of a fuel reformer and a combustor of the system.

FIG. 3 H ₂ O / C ratio of raw material gas and CO ₂ / C of reformed gas
FIG. 4 is a graph showing a relationship between an O ratio and a hydrogen yield ratio.

FIG. 4 is a configuration diagram of a fuel cell system according to another embodiment of the present invention.

FIG. 5 is a graph showing a relationship between a fuel utilization rate and a fuel conversion rate at which the energy efficiency of the fuel cell system is highest.

[Description of Signs] 1 fuel cell 2 oxygen electrode 3 hydrogen electrode 4 air compressor (air source) 5 fuel reformer 7 CO high-temperature transformer 14 water tank (steam source) 27 catalyst 35 exhaust gas supply pipe (exhaust gas supply means) 38 power controller (output current control means) 39 flow control valve (air supply means) 40 water supply pipe (steam supply means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunori Okamoto 1304 Kanaokacho, Sakai City, Osaka Daikin Industries Inside Kanaoka Plant of Sakai Seisakusho Co., Ltd. (72) Inventor Kazuo Yonemoto 1304 Kanaokacho, Sakai City, Osaka Daikin 4G040 EA02 EA03 EA06 EB03 EB16 EB32 EB43 EC03 5H027 AA06 BA01 BA05 BA09 BA10 BA16 BA17 MM01 MM26

Claims (14)

[Claims] 1. A fuel reformer (5) for reforming a hydrocarbon-based raw fuel to produce hydrogen, and a fuel for generating electricity using the hydrogen produced by the fuel reformer (5) as a fuel In the fuel cell system including the battery (1), the fuel reformer (5) is provided with a catalyst (27) exhibiting an activity with respect to the partial oxidation reaction of the raw fuel; In 5), there is provided steam supply means (35, 40) for supplying steam to the reformer (5) so as to generate a water gas shift reaction by using CO generated by the partial oxidation reaction as a reactant. And fuel cell system. 2. The fuel cell system according to claim 1, wherein CO in the outlet gas of the fuel reformer (5) is smaller than CO in the outlet gas.
_2. The fuel cell system according to claim 1, wherein the water gas shift reaction is adjusted so that the CO ₂ / CO ratio, which is a ratio of ₂ , is 0.2 or more. 3. The fuel cell system according to claim 1, wherein a supply ratio of the raw fuel and the steam to the fuel reformer (5) is a ratio of the steam to the mole number of carbon of the raw fuel. H ₂ O / C is set to 0.5 or more. 4. The fuel cell system according to claim 3, wherein said H ₂ O A fuel cell system having a / C ratio of 3 or less. 5. The fuel cell system according to claim 1, wherein an outlet gas temperature of the fuel reformer (5) is 800 ° C. or less. Battery system. 6. The fuel cell system according to claim 1, wherein the supply ratio of the raw fuel and oxygen to the fuel reformer (5) is determined based on the amount of carbon of the raw fuel. A fuel cell system wherein the ratio O ₂ / C of the number of moles of oxygen to the number of moles is set to be 0.9 times or more the O ₂ / C stoichiometric ratio in the partial oxidation reaction. 7. The fuel cell system according to claim 1, wherein the supply ratio of the raw fuel and oxygen to the fuel reformer (5) is determined based on the amount of carbon of the raw fuel. A fuel cell system characterized in that the ratio O ₂ / C of the number of moles of oxygen to the number of moles is set to be larger than the O ₂ / C stoichiometric ratio in the partial oxidation reaction. 8. The fuel cell system according to claim 6, wherein the O ₂ / C ratio is 1.5 times or less of the O ₂ / C stoichiometric ratio. Fuel cell system. 9. The fuel cell system according to claim 1, wherein an active site of the catalyst (27) is formed by at least one of rhodium and ruthenium. Fuel cell system. 10. The fuel cell system according to claim 9, wherein the catalyst (27) is supported on a honeycomb-shaped monolithic carrier. 11. The fuel cell system according to any one of claims 1 to 10, wherein a gas discharged from an oxygen electrode of the fuel cell is used as the steam supply means. 5) A fuel cell system comprising exhaust gas supply means (35) for supplying the exhaust gas to the fuel cell system. 12. The fuel cell system according to claim 11, wherein the output current of the fuel cell is adjusted so that the oxygen concentration and the water vapor concentration of the exhaust gas supplied to the fuel reformer (5) fall within predetermined ranges. A fuel cell system comprising an output current adjusting means (38) for adjusting the pressure. 13. The fuel cell system according to claim 11, wherein an output current of the fuel cell is adjusted so that an oxygen utilization rate of the fuel cell becomes 0.4 to 0.75. A fuel cell system comprising: 14. The fuel cell system according to claim 11, further comprising air supply means (39) for supplying air to said fuel reformer (5).