WO2012128369A1

WO2012128369A1 - Fuel-cell system

Info

Publication number: WO2012128369A1
Application number: PCT/JP2012/057628
Authority: WO
Inventors: 修平咲間; 俊幸海野
Original assignee: Ｊｘ日鉱日石エネルギー株式会社
Priority date: 2011-03-24
Filing date: 2012-03-23
Publication date: 2012-09-27
Also published as: JPWO2012128369A1

Abstract

A fuel-cell module provided with: a reformer that uses a hydrogen-containing fuel to generate a reformed gas; a cell stack that uses said reformed gas to generate electricity; a desulfurizer that desulfurizes the hydrogen-containing fuel supplied to the reformer; a hydrogen-containing-fuel supply channel for supplying the hydrogen-containing fuel to the desulfurizer; a feed pump, for providing the hydrogen-containing fuel to the desulfurizer, that is provided upstream of the desulfurizer in the hydrogen-containing-fuel supply channel; a circulation channel for returning part of the reformed gas, which is supplied to the cell stack by the reformer, to upstream of the feed pump in the hydrogen-containing-fuel supply channel; and a first pressure-reduction part that is provided in the hydrogen-containing-fuel supply channel, upstream of the junction between said channel and the circulation channel, and that reduces the pressure of the hydrogen-containing gas supplied to the feed pump such that the suction pressure of the feed pump is less than the pressure of the reformed gas supplied to the cell stack by the reformer.

Description

Fuel cell system

The present invention relates to a fuel cell system.

Conventionally, as a fuel cell system, a reformer that generates reformed gas using a hydrogen-containing fuel, a cell stack that generates power using the reformed gas, and desulfurization of hydrogen-containing fuel supplied to the reformer The thing which comprises the desulfurizer which performs this is known. Such a fuel cell system includes, for example, a supply flow path for supplying a hydrogen-containing fuel to a desulfurizer, and a feed pump (raw fuel compressor) provided in the supply flow path, as described in Patent Document 1. A circulation channel (recycling line) that circulates part of the reformed gas supplied from the reformer to the cell stack to the supply channel.

JP 2008-277308 A

However, in the fuel cell system as described above, for example, when the pressure of the reformed gas supplied from the reformer to the cell stack is not sufficiently high, the reformed gas is circulated to the supply channel by the circulation channel. May become difficult. In this respect, there is a case where a feed pump or the like is provided in the circulation flow path, and the reformed gas is actively circulated through the circulation flow path. However, in this case, a feed pump is required, which increases costs and is not preferable.

Therefore, an object of the present invention is to provide a fuel cell system that can reliably circulate the reformed gas at a low cost.

In order to solve the above problems, a fuel cell system according to one aspect of the present invention includes a reformer that generates a reformed gas using a hydrogen-containing fuel, a cell stack that generates power using the reformed gas, A desulfurizer that performs desulfurization of the hydrogen-containing fuel supplied to the catalyst, a hydrogen-containing fuel supply passage for supplying the hydrogen-containing fuel to the desulfurizer, and a hydrogen-containing fuel that is provided upstream or downstream of the desulfurizer. A feed pump for pumping fuel, and a circulation flow path for circulating a part of the reformed gas supplied from the reformer to the cell stack to the upstream side of the desulfurizer and feed pump of the hydrogen-containing fuel supply flow path. The hydrogen-containing fuel supply flow path is provided upstream of the junction with the circulation flow path so that the suction pressure of the feed pump is lower than the pressure of the reformed gas supplied from the reformer to the cell stack. Supplied to the feed pump A first pressure drop section to reduce the pressure of that the hydrogen-containing fuel, and a.

In this fuel cell system, the pressure of the hydrogen-containing fuel is reduced at the upstream side of the junction with the circulation passage in the supply passage by the first pressure reduction portion, and the suction pressure of the feed pump is changed from the reformer to the cell stack. The pressure is lower than the pressure of the reformed gas supplied. Therefore, a pressure difference is generated between the pressure on the inlet side and the pressure on the outlet side in the circulation channel so that the reformed gas circulates, and the reformed gas is supplied to the supply channel without providing a feed pump or the like in the circulation channel. Thus, it is reliably circulated to the upstream side of the feed pump by self-pressure. Therefore, the reformed gas can be reliably circulated at a low cost.

1 is a schematic block diagram showing a fuel cell system according to a first embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 2nd Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 3rd Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 4th Embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is a schematic block diagram showing a fuel cell system according to the first embodiment. As shown in FIG. 1, the fuel cell system 1 includes a desulfurizer 2, a reformer 3, and a cell stack 4. The fuel cell system 1 generates power in the cell stack 4 using a hydrogen-containing fuel and an oxidant. The type of the cell stack 4 in the fuel cell system 1 is not particularly limited, and examples thereof include a polymer electrolyte fuel cell (PEFC), a solid oxide fuel cell (SOFC), and phosphoric acid. Fuel cell (PAFC: PhosphoricAcid)
Fuel Cell), Molten Carbonate Fuel Cell (MCFC), and other types can be employed.

As the hydrogen-containing fuel, for example, a hydrocarbon fuel is used. As the hydrocarbon fuel, a compound containing carbon and hydrogen in the molecule (may contain other elements such as oxygen) or a mixture thereof is used. Examples of hydrocarbon fuels include hydrocarbons, alcohols, ethers, and biofuels. These hydrocarbon fuels are derived from conventional fossil fuels such as petroleum and coal, and synthetic systems such as synthesis gas. Those derived from fuel and those derived from biomass can be used as appropriate. Specific examples of hydrocarbons include methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, town gas, gasoline, naphtha, kerosene, and light oil.

In addition, methanol and ethanol are mentioned as alcohols. Examples of ethers include dimethyl ether. Examples of biofuels include biogas, bioethanol, biodiesel, and biojet. As the oxidizing agent, for example, air, pure oxygen gas (which may contain impurities that are difficult to remove by a normal removal method), or oxygen-enriched air is used.

The desulfurizer 2 desulfurizes the hydrogen-containing fuel supplied to the reformer 3. The desulfurizer 2 has a desulfurization catalyst for removing sulfur compounds contained in the hydrogen-containing fuel. The desulfurizer 2 employs a hydrodesulfurization method in which a sulfur compound is removed by reacting with hydrogen. In addition to the hydrodesulfurization system, as another desulfurization system of the desulfurizer 2, for example, an adsorptive desulfurization system that adsorbs and removes sulfur compounds may be used in combination. The desulfurizer 2 supplies the desulfurized hydrogen-containing fuel to the reformer 3.

The reformer 3 generates a reformed gas as a hydrogen-rich gas (hydrogen-containing gas) from the supplied hydrogen-containing fuel. The reformer 3 reforms the hydrogen-containing fuel and generates a reformed gas by a reforming reaction using a reforming catalyst. The reforming method in the reformer 3 is not particularly limited, and for example, steam reforming, partial oxidation reforming, autothermal reforming, and other reforming methods can be employed. The reformer 3 may have a configuration for adjusting the properties in addition to the reformer reformed by the reforming catalyst depending on the properties of the hydrogen-rich gas required for the cell stack 4. For example, when the type of the cell stack 4 is a polymer electrolyte fuel cell (PEFC) or a phosphoric acid fuel cell (PAFC), the reformer 3 is configured to remove carbon monoxide in the hydrogen-rich gas. (For example, a shift reaction part and a selective oxidation reaction part). The reformer 3 supplies the reformed gas to the cell stack 4.

The cell stack 4 generates power using the reformed gas and oxidant from the reformer 3. The cell stack 4 supplies a reformed gas and an oxidant that have not been used for power generation as off-gas to a subsequent combustion section (not shown).

Further, the fuel cell system 1 includes a hydrogen-containing fuel supply channel R1, a reformed gas supply channel R2, a reformed water supply channel R3, and a circulation channel R4.

The hydrogen-containing fuel supply flow path R <b> 1 is a hydrogen-containing fuel supply line for supplying at least a hydrogen-containing fuel to the desulfurizer 2, and is connected to the desulfurizer 2. The hydrogen-containing fuel supply flow path R1 is provided with a feed pump P as pressure feeding means. The feed pump P is provided upstream of a later-described branch portion G1, and adjusts the flow rate of fuel supplied to the cell stack 4.

The reformed gas supply flow path R2 is a reformed gas supply line for supplying reformed gas from the reformer 3 to the cell stack 4, and is connected to the reformer 3 and the cell stack 4. The reforming water supply flow path R <b> 3 is a reforming water line for supplying the reforming water as steam to the reformer 3, and is connected to the reformer 3.

The circulation flow path R4 is a recycle line for circulating a part of the reformed gas supplied from the reformer 3 to the cell stack 4 to the upstream side of the feed pump P of the hydrogen-containing fuel supply flow path R1. The circulation channel R4 is connected to the reformed gas supply channel R2 and the hydrogen-containing fuel supply channel R1 upstream of the feed pump P. Here, the circulation flow path R4 is branched from the middle of the reformed gas supply flow path R2 (hereinafter, the branched portion is referred to as a branch portion G1), and upstream of the feed pump P of the hydrogen-containing fuel supply flow path R1. (Hereinafter, the joined part is referred to as a joining part G2). Note that the reformed gas circulated in the circulation flow path R4 is used, for example, for hydrodesulfurization or for catalyst regeneration of the desulfurizer 2.

The heat exchanger 6 for transferring heat from the reformed gas to the reformed water is provided in the reformed water supply channel R3 and the circulation channel R4. Thereby, the retained water of the reformed gas is utilized to heat the reformed water. Further, a drainage drain 7 for collecting and draining water (condensed water) generated from the reformed gas flowing through the circulation channel R4 is provided downstream of the heat exchanger 6 in the circulation channel R4. Thereby, it is possible to prevent the condensed water from flowing into the feed pump P together with the reformed gas flowing through the circulation flow path R4.

In addition, a first pressure reduction unit 8 such as a capillary that is a capillary for generating a differential pressure is provided on the upstream side of the merging portion G (merging portion G2) with the circulation channel R4 in the hydrogen-containing fuel supply channel R1. It has been. The first pressure reduction unit 8 reduces the pressure of the hydrogen-containing fuel so that the suction pressure of the feed pump P is lower than the pressure of the reformed gas supplied from the reformer 3 to the cell stack 4. The first pressure reduction unit 8 is not limited. For example, as the first pressure reduction unit 8, a first pressure reduction unit that reduces a predetermined amount of pressure from the inlet pressure of the first pressure reduction unit 8 itself. The amount of pressure that can be reduced from the inlet pressure of the lowering portion 8 itself can be adjusted in multiple stages, and the outlet pressure of the lowering portion 8 can be adjusted in advance regardless of the inlet pressure of the first pressure lowering portion 8 itself. What reduces to a certain fixed pressure value etc. can be selected suitably. For example, in addition to the capillary, an orifice, a check valve, a proportional valve, a pressure reducing valve, a zero governor, or the like can be used.

In the circulation channel R4, a second pressure reduction unit 9 such as a capillary that is a capillary for generating a differential pressure is provided between the drainage recovery drain 7 and the junction G (junction G2). The second pressure reduction unit 9 reduces the pressure of the reformed gas circulating to the hydrogen-containing fuel supply channel R1 so that the flow rate of the reformed gas becomes a predetermined flow rate. If the pressure drop amount in the circulation flow path R4 is sufficient, the second pressure drop unit 9 can be omitted. However, by providing the second pressure drop unit 9, for example, fluctuations in the power generation amount of the fuel cell system 1 can be achieved. Based on this, even if the discharge pressure of the feed pump P fluctuates, the reformed gas can be circulated more stably. For example, as the second pressure reduction unit 9, similarly to the first pressure reduction unit 8, an orifice, a check valve, a proportional valve, a pressure reducing valve, a zero governor, and the like can be used in addition to the capillary.

In the fuel cell system 1 configured as described above, first, in the hydrogen-containing fuel supply flow path R1, for example, the pressure of the hydrogen-containing fuel flowing at a pressure of 2.5 kPa is reduced by the first

pressure reducing unit

8, 1 The outlet pressure of the pressure drop unit 8 is a negative pressure (for example, −5 kPa). Subsequently, the hydrogen-containing fuel is merged with the reformed gas from the circulation flow path R4 via the merging portion G (merging portion G2), and the hydrogen-containing fuel and the reformed gas are downstream at a discharge pressure of, for example, 5 kPa by the feed pump P. Pumped to the side. Thereafter, these hydrogen-containing fuel and reformed gas are supplied to the desulfurizer 2. In addition, the numerical value of the pressure illustrated in the above is a gauge pressure (hereinafter the same).

Subsequently, after the hydrogen-containing fuel is desulfurized by the desulfurizer 2, the hydrogen-containing fuel is reformed by the reformer 3 to generate a reformed gas. Further, the pressure of the reformed gas decreases (for example, 0.4 kPa) due to pressure loss in the desulfurizer 2 and the reformer 3. Subsequently, the reformed gas having a pressure of 0.4 kPa, for example, is supplied to the cell stack 4 in the reformed gas supply channel R2. Then, an off gas having a pressure of, for example, 0.1 kPa is generated from the cell stack 4.

On the other hand, in the reformed gas supply flow path R2, a part of the reformed gas supplied from the reformer 3 to the cell stack 4 (here, the reformed gas supplied from the reformer 3 to the cell stack 4). About 5%) flows from the branch part G1 into the circulation channel R4. In the circulation channel R4, the reformed gas heats the reformed water in the reformed water supply channel R3 via the heat exchanger 6, and then the water in the reformed gas is recovered by the drainage recovery drain 7. The reformed gas is reduced in pressure by the second pressure reduction unit 9 so that the flow rate becomes a predetermined flow rate, and then, as described above, the hydrogen-containing fuel supply flow path R1 contains hydrogen through the junction G. Joined with fuel.

Here, in the present embodiment, as described above, the pressure of the hydrogen-containing fuel supplied to the feed pump P in the hydrogen-containing fuel supply flow path R1 is reduced by the first pressure reduction unit 8, and the feed pump P The suction pressure is set to a negative pressure (−5 kPa) lower than the pressure (0.4 kPa) of the reformed gas supplied from the reformer 3. Specifically, the suction pressure of the feed pump P is set to a value smaller than a value obtained by subtracting the pressure drop amount in the entire circulation flow path R4 from the pressure of the reformed gas supplied from the reformer 3 to the cell stack 4. . Therefore, in the circulation flow path R4, a pressure difference is generated between the pressure on the inlet side and the pressure on the outlet side, and the reformed gas can be circulated at its own pressure so as to be sucked from the inlet side to the outlet side. As a result, the reformed gas is reliably and stably circulated to the hydrogen-containing fuel supply flow path R1 without separately providing a pressure feeding means such as a feed pump in the circulation flow path R4.

That is, in the present embodiment, the first pressure drop unit 8 is arranged in the suction line (upstream) of the feed pump P, and the reformed gas can be supplied to the cell stack 4 after the suction pressure of the feed pump P is set to a negative pressure. The pressure difference between the pressure of the reformed gas from the reformer 3 and the suction pressure of the hydrogen-containing fuel and the reformed gas by the feed pump P is artificially generated by pumping the hydrogen-containing fuel at a feed pump discharge pressure. To produce. As a result, the reformed gas can be circulated through the circulation flow path R4 at its own pressure. Therefore, according to the present embodiment, it is possible to reliably circulate the reformed gas at a low cost.

In addition, as one of operation controls of the fuel cell system 1, a control mode is known in which the amount of power generation is changed in accordance with a change in power demand. In this case, the required hydrogen-containing fuel increases and decreases according to the increase and decrease of the power generation amount. That is, the fuel discharge amount per unit time of the feed pump P increases and decreases, and the reformed gas pressure supplied to the cell stack 4 also varies. In such a case, there may be a delay in response to control of the feed pump P or pressure change. However, by providing the second pressure drop unit in the circulation flow path R4, it is possible to reduce the transient pressure fluctuation and stably circulate the reformed gas flowing in the circulation flow path R4.

Note that the pressure difference between the suction pressure of the feed pump P and the pressure of the reformed gas from the reformer 3 is smaller in the case of the SOFC cell stack 4 than in the case of the PEFC because the pressure loss of the cell stack 4 is small. This embodiment is particularly effective in the case of the SOFC cell stack 4 because the reformed gas is not easily circulated by the self-pressure.

In this embodiment, as described above, the heat exchanger 6 is provided in the reforming water supply channel R3 and the circulation channel R4, and heat is transferred from the reformed gas to the reforming water. This makes it possible to recover the retained heat of the reformed gas circulated in the circulation channel R4 with the reformed water.

[Second Embodiment]
FIG. 2 is a schematic block diagram showing a fuel cell system according to the second embodiment. As shown in FIG. 2, the fuel cell system 200 of the second embodiment is mainly different from the first embodiment (see FIG. 1) in that the feed pump P is provided on the downstream side of the desulfurizer 2. The heat exchange unit 6 cools the reformed gas with a heat medium. Here, the heat exchanging unit 6 is provided in the circulation flow path R4, and water, air, oil, and the like are circulated as a heat medium. The heat recovered by the heat medium is stored in, for example, a hot water tank and can be used as hot water. The feed pump P is provided between the desulfurizer 2 and the reformer 3. However, if the feed pump P is provided downstream of the merging portion G2 and between the branch portions G1, the feed pump P is used to circulate the reformed gas. This is because a necessary pressure difference can be generated.

In addition, this embodiment can be suitably implemented in a fuel cell system in which the supply pressure to the cell stack 4 is relatively high. If the pressure of the branch part G1 is high, the reformed gas can be circulated without excessively reducing the pressure of the merge part G2, so that even if the feed pump P is provided downstream of the desulfurizer 2, good desulfurization conditions are maintained. Because it can.

[Third Embodiment]
FIG. 3 is a schematic block diagram showing a fuel cell system according to the third embodiment. As shown in FIG. 3, the fuel cell system 300 according to the third embodiment is provided between the second pressure drop portion 9 and the merging portion G2 of the circulation flow path R4 in addition to the first embodiment (see FIG. 1). The condensate water removed by the drainage drain 7 is reused as reforming water.

In the present embodiment, the pressure of the hydrogen-containing fuel supplied to the feed pump P by the first pressure reduction unit 8 is set so that the pressure of the reformed gas supplied to the cell stack 4 becomes larger than the suction pressure of the feed pump P. For example, in the case where city gas is used as the hydrogen-containing fuel, for example, when the supply pressure of the hydrogen-containing fuel to the fuel cell system 300 fluctuates, the pressure at the junction G2 changes to the pressure at the branch G1. May be more transiently high. In this case, hydrogen-containing fuel that has not been subjected to fuel treatment such as desulfurization or reforming is supplied to the cell stack 4. When the hydrogen-containing fuel that is insufficiently processed is supplied to the cell stack 4 as described above, the life of the cell stack 4 is reduced. Therefore, the circulation flow path R <b> 4 includes the backflow prevention unit 11, whereby supply of untreated hydrogen-containing fuel to the cell stack 4 can be suppressed.

In addition, in this embodiment, although the backflow prevention part 11 was arrange | positioned between the 2nd pressure fall part 9 and the confluence | merging part G2, as long as it is on the circulation flow path R4, it may arrange | position anywhere. For example, as shown in FIG. 3, in the system in which the circulation flow path R4 includes the drainage recovery drain 7 and the removed condensed water is reused as reformed water, the backflow prevention unit 11 is provided downstream of the drainage recovery drain 7. It is preferable. Thereby, it can suppress that the condensed water containing a sulfur compound touches an untreated hydrogen-containing fuel and mixes in reformed water, and that sulfur compound is supplied to the cell stack 4 via the reformer 3 by extension. It is possible to suppress a decrease in the life of the cell stack 4 due to the above.

Incidentally, in the embodiment shown in FIG. 3, the second pressure drop unit 9 can be omitted. In addition, when a check valve is used as the second pressure drop unit 9 or the backflow prevention unit 11, any pressure difference can be generated by adjusting the cracking pressure. Can also serve as the backflow prevention unit 11 or the second pressure reduction unit 9.

[Fourth Embodiment]
FIG. 4 is a schematic block diagram showing a fuel cell system according to the fourth embodiment. In addition to the first embodiment (see FIG. 1), the fuel cell system 400 of the fourth embodiment includes a pressure measurement unit 12 that measures the feed pump suction pressure, and a control unit 13 that operates the first pressure reduction unit. And a reforming water tank 14 for storing the reforming water. In addition, a proportional valve 8a is used as the first pressure drop unit 8.

The control unit 13 measures the suction pressure of the feed pump P by the pressure measurement unit 12. The control unit 13 compares whether or not the measured suction pressure of the feed pump P is within a predetermined reference suction pressure range of the feed pump P. When the suction pressure is smaller than the suction reference pressure range, the control unit 13 controls the proportional valve 8a so as to increase the opening degree of the proportional valve 8a to reduce the pressure drop amount. On the other hand, when the suction pressure is larger than the suction reference pressure range, the control unit 13 controls the proportional valve 8a so as to increase the pressure drop amount by decreasing the opening degree of the proportional valve 8a. Thereby, since the suction pressure of the feed pump P can be stably maintained within a predetermined suction pressure range, a part of the reformed gas can be circulated stably. The reforming tank 14 stores the introduced reforming water and the reforming water recovered by the drainage recovery drain 7 and supplies the reforming water to the heat exchanger 6.

In the embodiment shown in FIG. 4, the example in which the pressure decrease amount of the first pressure decrease unit 8 is increased or decreased according to the suction pressure of the feed pump P is shown, but the pressure decrease amount of the second pressure decrease unit 9 is changed. It may be increased or decreased. For example, when the circulated reformed gas is used for catalyst regeneration in the desulfurizer 2, the reformed gas can be circulated with a circulation amount suitable for regeneration.

The preferred embodiments have been described above. However, the present invention is not limited to the above-described embodiments, and may be modified without changing the gist described in each claim or applied to other embodiments. Also good.

For example, in the above-described embodiment, it is preferable that the pressure of the hydrogen-containing fuel supplied to the feed pump P is reduced to the negative pressure by the first pressure reduction unit 8, but the reformer 3 does not have to be reduced to the negative pressure. The suction pressure of the feed pump P may be lowered to be lower than the pressure of the reformed gas supplied to the cell stack 4.

In the above description, the outlet pressure of the first pressure drop unit 8, the pressure of the junction G2 of the circulation flow path R4, and the suction pressure of the feed pump P are regarded as the same pressure for the sake of convenience. In addition, the outlet pressure of the reformer 3, the supply pressure of the reformed gas supplied to the cell stack 4, and the pressure of the branching portion of the circulation flow path R4 are assumed to be pressures in another region. However, there may be a pressure gradient that can be implemented between them. In the above description, the value of the suction pressure of the feed pump P is the value of the outlet pressure of the first pressure drop unit 8 or the junction of the circulation flow path R4 from the viewpoint of convenience or practical (handling). The pressure value of G2 can also be used.

According to the present invention, the reformed gas can be reliably circulated at a low cost.

DESCRIPTION OF SYMBOLS 1,200,300,400 ... Fuel cell system, 2 ... Desulfurizer, 3 ... Reformer, 4 ... Cell stack, 6 ... Heat exchanger, 8 ... 1st pressure reduction part, 8a ... Proportional valve (1st pressure 9) 2nd pressure drop part, R1 ... Hydrogen-containing fuel supply flow path, R3 ... Reformed water supply flow path, R4 ... Circulation flow path, P ... Feed pump, G1 ... Circulation flow path branching part, G2 ... circulation channel junction.

Claims

A reformer that generates reformed gas using hydrogen-containing fuel;
A cell stack for generating power using the reformed gas;
A desulfurizer for desulfurizing the hydrogen-containing fuel supplied to the reformer;
A hydrogen-containing fuel supply channel for supplying the hydrogen-containing fuel to the desulfurizer;
A feed pump that is provided upstream or downstream of the desulfurizer and pumps the hydrogen-containing fuel;
A circulation flow path for circulating a part of the reformed gas supplied from the reformer to the cell stack to the upstream side of the desulfurizer and the feed pump of the hydrogen-containing fuel supply flow path;
The hydrogen-containing fuel supply flow path is provided upstream of the junction with the circulation flow path, and the suction pressure of the feed pump is higher than the pressure of the reformed gas supplied from the reformer to the cell stack. A fuel cell system comprising: a first pressure reduction unit that reduces the pressure of the hydrogen-containing fuel supplied to the feed pump so as to be low.
The desulfurizer branches a part of the reformed gas from a reformed gas supply channel for supplying the reformed gas from the reformer to the cell stack downstream from the junction and from the reformer gas to the circulation channel. The fuel cell system according to claim 1, wherein the fuel cell system is upstream of the branching section.
The fuel cell system according to claim 1 or 2, wherein the feed pump is provided upstream of the desulfurizer in the hydrogen-containing fuel supply flow path, and supplies the hydrogen-containing fuel to the desulfurizer.
4. The suction pressure of the feed pump is smaller than a value obtained by subtracting the pressure drop amount of the circulation flow path from the pressure of the reformed gas supplied from the reformer to the cell stack. The fuel cell system according to one item.
The circulation channel is provided with a second pressure reduction unit that reduces the pressure of the reformed gas so that the flow rate of the reformed gas circulating to the hydrogen-containing fuel supply channel becomes a predetermined flow rate. Item 5. The fuel cell system according to any one of Items 1 to 4.
6. The fuel cell system according to claim 5, wherein at least one of the first and second pressure drop portions has a variable pressure drop amount.
A pressure measuring unit for measuring the suction pressure of the feed pump;
The fuel cell system according to claim 6, wherein a pressure drop amount in at least one of the first and second pressure drop portions is changed according to a suction pressure of the feed pump.
The fuel cell system according to any one of claims 1 to 7, wherein the circulation flow path further includes a backflow prevention unit.
A reforming water supply channel for supplying reforming water as steam to the reformer;
The fuel according to any one of claims 1 to 8, wherein a heat exchanger for transferring heat from the reformed gas to the reformed water is provided in the circulation channel and the reformed water supply channel. Battery system.
The fuel cell system according to any one of claims 1 to 9, wherein the circulation channel further includes a waste water recovery drain for removing condensed water generated from the reformed gas that circulates to the hydrogen-containing fuel supply channel. .