FUEL CELL SYSTEM AND METHOD FOR CONTROLLING SAME

The purpose of the present invention is to provide fuel cell system capable of stably executing differential pressure control and having a simplified configuration, and method for controlling the same. Fuel cell system equipped with fuel cell, a turbocharger, exhaust fuel gas line, exhaust oxidizing gas line, combustion gas supply line for supplying combustion gas discharged from a combustor to a turbine, oxidizing gas supply line for supplying oxidizing gas compressed by a compressor to cathode, a regulator valve provided to the exhaust fuel gas line, and a control unit for controlling the differential pressure between the pressure of the cathode of the fuel cell and the pressure of the anode thereof by controlling the regulator valve, wherein the exhaust oxidizing gas line is not provided with venting system for discharging exhaust oxidizing gas outside the system.

TECHNICAL FIELD

The present disclosure relates to fuel cell system and control method therefor.

BACKGROUND ART

Fuel cell that generates power by chemically reacting fuel gas with oxidizing gas has characteristics such as excellent power generation efficiency and environmental friendliness. Among fuel cells, solid oxide fuel cell (hereinafter, referred to as SOFC) generates power by using ceramics such as zirconia ceramics as an electrolyte, supplying hydrogen, town gas, natural gas, petroleum, methanol, and gas such as gasified gas produced from carbonaceous raw materials by a gasification facility, as fuel gas, and reacting in high temperature atmosphere of approximately 700° C. to 1000° C. (For example, PTL 1, PTL 2, PTL 3, and PTL 4)

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

SOFC can improve power generation efficiency by combining with an internal combustion engine, and some are combined with, for example, a gas turbine (for example, a micro gas turbine). The SOFC needs to properly keep differential pressure between anode (fuel electrode) and cathode (air electrode) stable. However, in case where power generation system combining the SOFC and the micro gas turbine causes trip for some reason, a generator of the micro gas turbine becomes unloaded, and there is possibility that protection measures for the micro gas turbine are required. Therefore, in preparation for the occurrence of trip, it is necessary to provide discharge system, a shutoff valve, and the like that release exhaust oxidizing gas discharged from the cathode of the SOFC to the atmosphere (outside the system). However, the shutoff valve is an expensive device and needs to control the differential pressure between the cathode and the anode within predetermined value. Therefore, in system including the SOFC, it is desired to simplify the configuration while maintaining stable operating state.

The present disclosure has been made in view of such circumstances, and the object of the present disclosure is to provide fuel cell system capable of stably performing differential pressure control and control method therefor.

Solution to Problem

According to first aspect of the present disclosure, there is provided fuel cell system including: fuel cell having cathode (air electrode) and anode (fuel electrode); a turbocharger having a turbine and a compressor; exhaust fuel gas line for supplying exhaust fuel gas discharged from the fuel cell to a combustor; exhaust oxidizing gas line for supplying exhaust oxidizing gas discharged from the fuel cell to the combustor; combustion gas supply line for supplying combustion gas discharged from the combustor to the turbine; oxidizing gas supply line for supplying oxidizing gas compressed by the compressor to the cathode by rotationally driven by the turbine; a regulating valve provided on the exhaust fuel gas line; and a control unit that controls the regulating valve to control differential pressure between pressure of the cathode and pressure of the anode in the fuel cell, in which vent system that releases the exhaust oxidizing gas to outside of the system is not provided on the exhaust oxidizing gas line.

According to second aspect of the present disclosure, there is provided method for controlling fuel cell system including fuel cell having cathode and anode, a turbocharger having a turbine and a compressor, exhaust fuel gas line for supplying exhaust fuel gas discharged from the fuel cell to a combustor, exhaust oxidizing gas line for supplying exhaust oxidizing gas discharged from the fuel cell to the combustor, combustion gas supply line for supplying combustion gas discharged from the combustor to the turbine, oxidizing gas supply line for supplying oxidizing gas compressed by the compressor to the cathode by rotationally driven by the turbine, and a regulating valve provided on the exhaust fuel gas line, in which vent system that releases the exhaust oxidizing gas to outside of the system is not provided on the exhaust oxidizing gas line, the method including: controlling the regulating valve to control differential pressure between pressure of the cathode and pressure of the anode in the fuel cell.

Advantageous Effects of Invention

According to the present disclosure, it is possible to stably perform the differential pressure control and to simplify the configuration.

DESCRIPTION OF EMBODIMENTS

Hereinafter, one embodiment of the fuel cell system and the method for controlling the same according to the present disclosure will be described with reference to the drawings.

In the following, for convenience of description, the positional relationship between each of the configuration elements described using the expressions “up” and “down” on the paper surface indicates perpendicularly upper side and perpendicularly lower side, respectively, and perpendicular direction is not exact and includes uncertainty. In the present embodiment, regarding up-down direction and horizontal direction which can obtain the same effect, for example, the up-down direction on the paper surface is not necessarily limited to the perpendicularly up-down direction, and the direction may correspond to the horizontal direction orthogonal to the perpendicular direction.

Hereinafter, although a cylindrical (tubular) cell stack will be described as an example of a cell stack of solid oxide fuel cell (SOFC), the cell stack is not necessarily limited thereto, and may be, for example, a flat cell stack. The fuel cell is formed on a substrate, but electrode (anode (fuel electrode)109or cathode (air electrode)113) may be formed thick without the substrate, and may also serve as the support part.

First, a cylindrical cell stack using a substrate tube will be described as example according to the present embodiment with reference toFIG.1. When the substrate tube is not used, for example, the anode109may be formed thick and may also be used as the substrate tube, and the use of the substrate tube is not limited. The substrate tube in the present embodiment will be described using cylindrical shape, but the substrate tube may be tubular, and the cross section thereof is not necessarily limited to circular shape, and may be, for example, elliptical shape. A cell stack having flat tubular shape or the like in which peripheral side surface of the cylinder is vertically transposed may be used. Here,FIG.1illustrates the aspect of the cell stack according to the present embodiment. A cell stack101includes, for example, a cylindrical substrate tube103, a plurality of fuel cells105formed on an outer peripheral surface of the substrate tube103, and an interconnector107formed between the fuel cells105adjacent to each other. The fuel cell105is formed by laminating anode109, solid electrolyte film111, and cathode113. The cell stack101includes lead film115electrically connected via the interconnector107to the cathode113of the fuel cell105formed at one end at the endmost part of the substrate tube103in axial direction, and lead film115electrically connected to the anode109of the fuel cell105formed at the other end at the endmost part, in the plurality of fuel cells105formed on the outer peripheral surface of the substrate tube103.

The substrate tube103is made of porous material, for example, CaO stabilized ZrO2(CSZ), a mixture of CSZ and nickel oxide (NiO), Y2O3stabilized ZrO2(YSZ), MgAl2O4, or the like as main components. The substrate tube103supports the fuel cell105, the interconnector107, and the lead film115, and diffuses the fuel gas supplied to the inner peripheral surface of the substrate tube103to the anode109formed on the outer peripheral surface of the substrate tube103through pores of the substrate tube103.

The anode109is made of an oxide of composite material of Ni and zirconia-based electrolyte material, and, for example, Ni/YSZ is used. The thickness of the anode109is 50 μm to 250 μm, and the anode109may be formed by screen-printing slurry. In this case, the anode109has Ni which is a component of the anode109and which has a catalytic reaction on the fuel gas. The catalytic reaction is performed for the fuel gas, for example, mixed gas of methane (CH4) and steam, supplied through the substrate tube103, and reformed to hydrogen (H2) and carbon monoxide (CO). The anode109electrochemically reacts reformed gas which obtains hydrogen (H2) and carbon monoxide (CO) with oxygen ions (O2−) supplied through the solid electrolyte film111, in the vicinity of interface with the solid electrolyte film111, and generates water (H2O) and carbon dioxide (CO2). At this time, the fuel cell105generates power via electrons released from oxygen ions.

Examples of the fuel gas that can be supplied to the anode109of the solid oxide fuel cell and used, include gasified gas produced by gasification facility from carbonaceous raw material such as petroleum, methanol, and coal, in addition to hydrogen (H2), carbon monoxide (CO), and hydrocarbon gas such as methane (CH4), town gas, and natural gas.

As the solid electrolyte film111, YSZ having airtightness that makes it difficult for gas to pass and high oxygen ionic conductivity at high temperature is mainly used. The solid electrolyte film111transfers oxygen ions (O2−) generated at the cathode113to the anode109. The film thickness of the solid electrolyte film111positioned on the surface of the anode109is 10 μm to 100 μm, and the solid electrolyte film111may be formed by screen-printing slurry.

The cathode113is made of, for example, a LaSrMnO3-based oxide or a LaCoO3-based oxide, and the cathode113is coated with slurry by screen-printing or using a dispenser. The cathode113dissociates oxygen in the oxidizing gas such as air to be supplied in the vicinity of the interface with the solid electrolyte film111and generates oxygen ions (O2−).

The cathode113can also have a two-layer configuration. In this case, the cathode layer (cathode intermediate layer) on the solid electrolyte film111side is made of material having high ionic conductivity and excellent catalytic activity. The cathode layer (cathode conductive layer) on the cathode intermediate layer may be made of a perovskite type oxide represented by Sr and Ca-doped LaMnO3. In this way, it is possible to further improve the power generation performance.

The oxidizing gas is gas containing approximately 15% to 30% oxygen, and representatively, air is suitable. However, in addition to air, mixed gas of combustion exhaust gas and air, mixed gas of oxygen and air, and the like can be used.

The interconnector107is made of a conductive perovskite type oxide represented by M1-xLxTiO3(M is alkaline earth metal element and L is lanthanoid element) such as SrTiO3, and is formed by screen-printing slurry. The interconnector107is dense film such that the fuel gas and the oxidizing gas do not mix with each other. The interconnector107has stable durability and electric conductivity under both oxidizing atmosphere and reducing atmosphere. The interconnector107electrically connects the cathode113of one fuel cell105and the anode109of the other fuel cell105in the fuel cells105adjacent to each other, and connects the fuel cells105adjacent to each other in series.

Since the lead film115needs to have electron conductivity and to have a similar thermal expansion coefficient to that of other materials constituting the cell stack101, the lead film115is made of composite material of Ni and zirconia-based electrolyte material such as Ni/YSZ or M1-xLxTiO3(M is alkaline earth metal element and L is lanthanoid element) such as SrTiO3. The lead film115conducts DC power generated by the plurality of fuel cells105connected to each other in series by the interconnector107, to the vicinity of end portion of the cell stack101.

The substrate tube103on which the slurry film of the anode109, the solid electrolyte film111, and the interconnector107is formed is co-sintered in the atmosphere. The sintering temperature is specifically set at 1350° C. to 1450° C.

Next, the substrate tube103on which the slurry film of the cathode113is formed is sintered in the atmosphere on the co-sintered substrate tube103. The sintering temperature is specifically set at 1100° C. to 1250° C. The sintering temperature here is lower than the co-sintering temperature after forming the substrate tube103to the interconnector107.

Next, an SOFC module and an SOFC cartridge according to the present embodiment will be described with reference toFIGS.2and3. Here,FIG.2illustrates aspect of the SOFC module according to the present embodiment.FIG.3illustrates a sectional view of aspect of the SOFC cartridge according to the present embodiment.

As illustrated inFIG.2, an SOFC module (fuel cell module)201includes, for example, a plurality of SOFC cartridges203(fuel cell cartridges) and a pressure vessel205that stores the plurality of SOFC cartridges203therein. Although a cylindrical SOFC cell stack101is described as example inFIG.2, the cell stack is not limited thereto, and may be, for example, a flat cell stack. The SOFC module201includes a fuel gas supply pipe207, a plurality of fuel gas supply branch pipes207a,a fuel gas discharge pipe209, and a plurality of fuel gas discharge branch pipes209a.The SOFC module201includes an oxidizing gas supply pipe (not illustrated), an oxidizing gas supply branch pipe (not illustrated), an oxidizing gas discharge pipe (not illustrated), and a plurality of oxidizing gas discharge branch pipes (not illustrated).

The fuel gas supply pipe207is provided on the outside of the pressure vessel205, connected to a fuel gas supply unit for supplying fuel gas having a predetermined gas composition and predetermined flow rate in accordance with the power generation amount of the SOFC module201, and connected to the plurality of fuel gas supply branch pipes207a.The fuel gas supply pipe207branches the predetermined flow rate of fuel gas supplied from the above-described fuel gas supply unit to the plurality of fuel gas supply branch pipes207a,and guides the fuel gas. The fuel gas supply branch pipe207ais connected to the fuel gas supply pipe207and is connected to the plurality of SOFC cartridges203. The fuel gas supply branch pipe207aguides the fuel gas supplied from the fuel gas supply pipe207to the plurality of SOFC cartridges203at substantially uniform flow rate, and makes the power generation performance of the plurality of SOFC cartridges203substantially uniform.

The fuel gas discharge branch pipe209ais connected to the plurality of SOFC cartridges203and to the fuel gas discharge pipe209. The fuel gas discharge branch pipe209aguides the exhaust fuel gas discharged from the SOFC cartridge203to the fuel gas discharge pipe209. The fuel gas discharge pipe209is connected to the plurality of fuel gas discharge branch pipes209a,and a part thereof is disposed on the outside of the pressure vessel205. The fuel gas discharge pipe209guides the exhaust fuel gas derived from the fuel gas discharge branch pipe209aat substantially equal flow rate to the outside of the pressure vessel205.

Since the pressure vessel205is operated at internal pressure of 0.1 MPa to approximately 3 MPa and at internal temperature of the atmospheric temperature to approximately 550° C., material that maintains pressure tolerance and corrosion resistance with respect to oxygen containing gas, such as oxygen contained in the oxidizing gas, is used. For example, stainless steel material such as SUS304 is suitable.

Here, in the present embodiment, aspect in which the plurality of SOFC cartridges203are assembled and stored in the pressure vessel205is described, but the present invention is not limited thereto, and aspect in which the SOFC cartridges203are not assembled and stored in the pressure vessel205can also be employed.

As illustrated inFIG.3, the SOFC cartridge203includes a plurality of cell stacks101, a power generation chamber215, a fuel gas supply header217, a fuel gas discharge header219, an oxidizing gas (air) supply header221, and an oxidizing gas discharge header223. The SOFC cartridge203includes an upper tube plate225a,a lower tube plate225b,an upper thermal insulation227a,and a lower thermal insulation227b.In the present embodiment, the SOFC cartridge203has a structure in which the fuel gas supply header217, the fuel gas discharge header219, the oxidizing gas supply header221, and the oxidizing gas discharge header223are arranged as illustrated inFIG.3such that the fuel gas and the oxidizing gas flow while facing the inner side and the outer side of the cell stack101, but this structure is not necessary, and, for example, the gas may flow while being parallel to the inner side and the outer side of the cell stack101, and the oxidizing gas may flow in a cross flow to an axial direction of the cell stack101.

The power generation chamber215is a region formed between the upper thermal insulation227aand the lower thermal insulation227b.The power generation chamber215is a region where the fuel cells105of the cell stack101are arranged, and is a region where power is generated by electrochemically reacting the fuel gas and the oxidizing gas. The temperature in the vicinity of center portion of the power generation chamber215in the longitudinal direction of the cell stack101is monitored by a temperature measurement unit (temperature sensor, thermocouple, or the like), and high temperature atmosphere of approximately 700° C. to 1000° C. is achieved during the steady operation of the SOFC module201.

The fuel gas supply header217is a region surrounded by an upper casing229aand an upper tube plate225aof the SOFC cartridge203, and is connected to the fuel gas supply branch pipe207athrough a fuel gas supply hole231aprovided in upper portion of the upper casing229a.The plurality of cell stacks101are joined to the upper tube plate225aby a seal member237a,and the fuel gas supply header217guides the fuel gas supplied from the fuel gas supply branch pipe207athrough the fuel gas supply hole231aat substantially uniform flow rate on the inside of the substrate tube103of the plurality of cell stacks101, and makes the power generation performance of the plurality of cell stacks101substantially uniform.

The fuel gas discharge header219is a region surrounded by a lower casing229band the lower tube plate225bof the SOFC cartridge203, and is connected to the fuel gas discharge branch pipe209a(not illustrated) through a fuel gas discharging hole231bprovided in the lower casing229b.The plurality of cell stacks101are joined to the lower tube plate225bby a seal member237b,and the fuel gas discharge header219collects the exhaust fuel gas that passes through the inside of the substrate tube103of the plurality of cell stacks101and that is supplied to the fuel gas discharge header219, and guides the exhaust fuel gas to the fuel gas discharge branch pipe209athrough the fuel gas discharging hole231b.

Oxidizing gas having predetermined gas composition and predetermined flow rate is branched into the oxidizing gas supply branch pipe in accordance with the power generation amount of the SOFC module201and is supplied to a plurality of SOFC cartridges203. The oxidizing gas supply header221is a region surrounded by the lower casing229b,the lower tube plate225b,and the lower thermal insulation227bof the SOFC cartridge203, and is connected to the oxidizing gas supply branch pipe (not illustrated) through an oxidizing gas supply hole233aprovided on side surface of the lower casing229b.The oxidizing gas supply header221guides predetermined flow rate of oxidizing gas supplied from the oxidizing gas supply branch pipe (not illustrated) through the oxidizing gas supply hole233a,to the power generation chamber215through an oxidizing gas supply gap235awhich will be described later.

The oxidizing gas discharge header223is a region surrounded by the upper casing229a,the upper tube plate225a,and the upper thermal insulation227aof the SOFC cartridge203, and is connected to an oxidizing gas discharge branch pipe (not illustrated) through an oxidizing gas discharging hole233bprovided on the side surface of the upper casing229a.The oxidizing gas discharge header223guides the exhaust oxidizing gas supplied from the power generation chamber215to the oxidizing gas discharge header223through an oxidizing gas discharge gap235bwhich will be described later, to the oxidizing gas discharge branch pipe (not illustrated) through the oxidizing gas discharging hole233b.

The upper tube plate225ais fixed to the side plate of the upper casing229asuch that the upper tube plate225a,the top plate of the upper casing229a,and the upper thermal insulation227aare substantially parallel to each other, between the top plate of the upper casing229aand the upper thermal insulation227a.The upper tube plate225ahas a plurality of holes corresponding to the number of cell stacks101provided in the SOFC cartridge203, and the cell stacks101are respectively inserted into the holes. The upper tube plate225aairtightly supports one end portion of the plurality of cell stacks101via one or both of the seal member237aand an adhesive member, and further isolates the fuel gas supply header217and the oxidizing gas discharge header223from each other.

The upper thermal insulation227ais disposed at lower end portion of the upper casing229asuch that the upper thermal insulation227a,the top plate of the upper casing229a,and the upper tube plate225aare substantially parallel to each other, and is fixed to the side plate of the upper casing229a.The upper thermal insulation227ahas a plurality of holes corresponding to the number of cell stacks101provided in the SOFC cartridge203. The diameter of the hole is set to be higher than the outer diameter of the cell stack101. The upper thermal insulation227aincludes an oxidizing gas discharge gap235bformed between the inner surface of the hole and the outer surface of the cell stack101inserted into the upper thermal insulation227a.

The upper thermal insulation227aseparates the power generation chamber215and the oxidizing gas discharge header223from each other, the temperature increase of the atmosphere around the upper tube plate225a,which causes the strength deterioration or increase in corrosion due to the oxygen containing gas contained in the oxidizing gas, is suppressed. The upper tube plate225aand the like are made of high temperature durable metallic material such as Inconel to prevent thermal deformation since the upper tube plate225aand the like are exposed to the high temperature in the power generation chamber215, and the temperature difference in the upper tube plate225aand the like increases. The upper thermal insulation227aguides the exhaust oxidizing gas that has passed through the power generation chamber215and that has been exposed to the high temperature, to the oxidizing gas discharge header223through the oxidizing gas discharge gap235b.

According to the present embodiment, due to the structure of the above-described SOFC cartridge203, the fuel gas and the oxidizing gas flow while facing the inner side and the outer side of the cell stack101. Accordingly, the exhaust oxidizing gas exchanges heat with the fuel gas supplied to the power generation chamber215through the inside of the substrate tube103, is cooled to temperature at which deformation such as buckling of the upper tube plate225aand the like made of metallic material does not occur, and is supplied to the oxidizing gas discharge header223. The temperature of the fuel gas increases via the heat exchange with the exhaust oxidizing gas discharged from the power generation chamber215, and the fuel gas is supplied to the power generation chamber215. As a result, it is possible to supply the fuel gas preheated to temperature suitable for power generation without using a heater or the like, to the power generation chamber215.

The lower tube plate225bis fixed to the side plate of the lower casing229bsuch that the lower tube plate225b,the bottom plate of the lower casing229b,and the lower thermal insulation227bare substantially parallel to each other, between the bottom plate of the lower casing229band the lower thermal insulation227b.The lower tube plate225bhas a plurality of holes corresponding to the number of cell stacks101provided in the SOFC cartridge203, and the cell stacks101are respectively inserted into the holes. The lower tube plate225bairtightly supports the other end portion of the plurality of cell stacks101via one or both of the seal member237band an adhesive member, and further isolates the fuel gas discharge header219and the oxidizing gas supply header221from each other.

The lower thermal insulation227bis disposed at upper end portion of the lower casing229bsuch that the lower thermal insulation227b,the bottom plate of the lower casing229b,and the lower tube plate225bare substantially parallel to each other, and is fixed to the side plate of the lower casing229b.The lower thermal insulation227bhas a plurality of holes corresponding to the number of cell stacks101provided in the SOFC cartridge203. The diameter of the hole is set to be higher than the outer diameter of the cell stack101. The lower thermal insulation227bincludes the oxidizing gas supply gap235aformed between the inner surface of the hole and the outer surface of the cell stack101inserted into the lower thermal insulation227b.

The lower thermal insulation227bseparates the power generation chamber215and the oxidizing gas supply header221from each other, the temperature of the atmosphere around the lower tube plate225bincreases, and the strength deterioration or increase in corrosion due to the oxygen containing gas contained in the oxidizing gas is suppressed. The lower tube plate225band the like are made of high temperature durable metallic material such as Inconel, but thermal deformation is prevented since the lower tube plate225band the like are exposed to the high temperature, and the temperature difference in the lower tube plate225band the like increases. The lower thermal insulation227bguides the oxidizing gas supplied to the oxidizing gas supply header221to the power generation chamber215through the oxidizing gas supply gap235a.

According to the present embodiment, due to the structure of the above-described SOFC cartridge203, the fuel gas and the oxidizing gas flow while facing the inner side and the outer side of the cell stack101. Accordingly, the exhaust fuel gas that has passed through the power generation chamber215exchanges heat with the oxidizing gas supplied to the power generation chamber215through the inside of the substrate tube103, is cooled to temperature at which deformation such as buckling of the lower tube plate225band the like made of metallic material does not occur, and is supplied to the fuel gas discharge header219. The temperature of the oxidizing gas increases via the heat exchange with the exhaust fuel gas, and the fuel gas is supplied to the power generation chamber215. As a result, it is possible to supply the oxidizing gas of which the temperature has increased to temperature necessary for power generation without using a heater or the like, to the power generation chamber215.

After the DC power generated in the power generation chamber215is conducted to the vicinity of the end portion of the cell stack101by the lead film115made of Ni/YSZ or the like provided in the plurality of fuel cells105, the DC power is collected on a current collecting rod (not illustrated) of the SOFC cartridge203through a current collecting plate (not illustrated), and is taken out to the outside of each of the SOFC cartridges203. The DC power conducted to the outside of the SOFC cartridge203by the current collecting rod connects the generated power of each SOFC cartridge203to predetermined serial number and parallel number, is conducted to the outside of the SOFC module201, converted to predetermined AC power via a power conversion device (such as an inverter), a power conditioner and the like (not illustrated), and is supplied to a power consumer (for example, electric load equipment or a power grid).

A schematic configuration of fuel cell system310according to embodiment of the present disclosure will be described.

FIG.4shows a schematic configuration of the fuel cell system310according to the embodiment of the present disclosure. As illustrated inFIG.4, the fuel cell system310includes a turbocharger411and SOFC313. The SOFC313is configured by combining one or a plurality of SOFC modules (not illustrated), and is hereinafter simply referred to as “SOFC”. The fuel cell system310uses the SOFC313to generate power. The fuel cell system310is controlled by the control unit20.

The turbocharger411includes a compressor421and a turbine423, and the compressor421and the turbine423are connected to each other by a rotary shaft424so as to be integrally rotatable. The compressor421is rotationally driven by rotation of the turbine423which will be described later. The present embodiment is example in which air is used as the oxidizing gas, and the compressor421compresses air A taken in from air intake line325.

The air A is taken into the compressor421that configures the turbocharger411and is compressed, and the compressed air A is supplied as oxidizing gas A2to the cathode113of the SOFC. Exhaust oxidizing gas A3after being used in the chemical reaction for power generation in the SOFC is sent to a catalytic combustor (combustor)422via exhaust oxidizing gas line333, exhaust fuel gas L3used in the chemical reaction for power generation in the SOFC is boosted by a recycling blower348, and a part of the exhaust fuel gas L3is recycled and supplied to fuel gas line341via fuel gas recycling line349, and the other part is sent to the catalytic combustor422via exhaust fuel gas line343.

In this manner, a part of the exhaust fuel gas L3and the exhaust oxidizing gas A3is supplied to the catalytic combustor422, and stably performs combustion even at relatively low temperature using a combustion catalyst in a catalytic combustion unit461(described below) to produce combustion gas G. At this time, the catalytic combustor422is provided with a pressure equalizing unit (hereinafter, referred to as “pressure equalizing space”)462as illustrated inFIG.5. The pressure equalizing space462is a region for equalizing the pressure of the exhaust oxidizing gas A3and of the exhaust fuel gas in a common space, and is also a region for mixing the gases. In other words, in the pressure equalizing space462, the pressures of the exhaust oxidizing gas A3supplied to the catalytic combustor422and of the exhaust fuel gas become the same, and the pressure is equalized. In other words, the outlet pressures of the exhaust oxidizing gas line333and of the exhaust fuel gas line343are equalized. When the pressure can be equalized, the pressure equalizing space462is not limited to be located adjacent to the catalytic combustor422.

The catalytic combustor422mixes the exhaust fuel gas L3, the exhaust oxidizing gas A3, and fuel gas L1if necessary, and combusts the mixed gas in the catalytic combustion unit461to produce the combustion gas G. The catalytic combustion unit461is filled with a combustion catalyst containing, for example, platinum or palladium as a main catalytic component, and stable combustion is possible at relatively low temperature and at a low oxygen concentration. The exhaust fuel gas L3, the exhaust oxidizing gas A3, and, when necessary, the fuel gas L1are mixed in the pressure equalizing space462. The combustion gas G is supplied to the turbine423through combustion gas supply line328. The turbine423is rotationally driven by the adiabatic expansion of the combustion gas G, and the combustion gas G is discharged from combustion exhaust gas line329.

The fuel gas L1is supplied to the catalytic combustor422by controlling the flow rate with a control valve352. The fuel gas L1is combustible gas, and, for example, gas obtained by vaporizing liquefied natural gas (LNG) or natural gas, town gas, hydrogen (H2), carbon monoxide (CO), hydrocarbon gases such as methane (CH4), and gas produced by a gasification facility from carbonaceous raw materials (petroleum, coal, and the like) are used. The fuel gas means fuel gas of which calorific value has been regulated to be substantially constant in advance.

The combustion gas G of which the temperature has been raised by combustion in the catalytic combustor422is sent to the turbine423that configures the turbocharger411through the combustion gas supply line328, and the turbine423is rotationally driven to generate rotational power. By driving the compressor421with this rotational power, the air A taken in from the air intake line325is compressed to generate compressed air. Since the power of the rotating device that compresses and blows the oxidizing gas (air) can be produced by the turbocharger411, the required additional power can be reduced, and the power generation efficiency of the power generation system can be improved.

A heat exchanger (regenerative heat exchanger)430exchanges heat between the exhaust gas discharged from the turbine423and the oxidizing gas A2supplied from the compressor421. The exhaust gas is cooled by heat exchange with the oxidizing gas A2, and then released to the outside through a chimney (not illustrated), for example, through waste heat recovery equipment442.

The SOFC313generates power by reacting at predetermined operating temperature by supplying the fuel gas L1as reducing agent and the oxidizing gas A2as oxygen containing gas.

The SOFC313is constituted of an SOFC module (not illustrated) and accommodates an aggregate of the plurality of cell stacks provided in the pressure vessel of the SOFC module, and the anode109, the cathode113, and the solid electrolyte film111are provided in the cell stack (not illustrated).

The SOFC313generates power by supplying the oxidizing gas A2to the cathode113and supplying the fuel gas L1to the anode109, converts the power to predetermined power via a power conversion device (such as an inverter) such as a power conditioner (not illustrated), and supplies the converted power to a power consumer.

The SOFC313is connected to oxidizing gas supply line331for supplying the oxidizing gas A2compressed by the compressor421to the cathode113. The oxidizing gas A2is supplied to an oxidizing gas introduction unit (not illustrated) of the cathode113through the oxidizing gas supply line331. The oxidizing gas supply line331is provided with a control valve335for regulating the flow rate of the oxidizing gas A2to be supplied. In the heat exchanger430, the oxidizing gas A2exchanges heat with the combustion gas discharged from the combustion exhaust gas line329, and the temperature thereof increases. Furthermore, heat exchanger bypass line332that bypasses the heat transfer part of the heat exchanger430is provided in the oxidizing gas supply line331. A control valve336is provided in the heat exchanger bypass line332such that the bypass flow rate of the oxidizing gas can be regulated. By controlling the opening of the control valve335and the control valve336, the flow ratio of the oxidizing gas passing through the heat exchanger430and the oxidizing gas bypassing the heat exchanger430is regulated, and the temperature of the oxidizing gas A2to be supplied to the SOFC313is regulated. The temperature of the oxidizing gas A2supplied to the SOFC313maintains temperature at which the fuel gas of the SOFC313and the oxidizing gas are electrochemically reacted to generate power, and the upper limit of temperature is limited so as not to damage the materials of each component on the inside of the SOFC module (not illustrated) that configures the SOFC313.

The SOFC313is connected to the exhaust oxidizing gas line333for supplying the exhaust oxidizing gas A3discharged after being used by the cathode113to the turbine423via the catalytic combustor422. The exhaust oxidizing gas line333is provided with an exhaust air cooler351. Specifically, in the exhaust oxidizing gas line333, the exhaust air cooler351is provided on the upstream side of an orifice441described later, and the exhaust oxidizing gas A3is cooled by heat exchange with the oxidizing gas A2flowing through the oxidizing gas supply line331.

The exhaust oxidizing gas line333is provided with a pressure loss unit. In the present embodiment, the orifice441is provided as a pressure loss unit. The orifice441adds pressure loss to the exhaust oxidizing gas A3that flows through the exhaust oxidizing gas line333. The pressure loss unit is not limited to the orifice441, and a throttle such as a Venturi tube may be provided, and any means capable of adding pressure loss to the exhaust oxidizing gas A3can be used. As the pressure loss unit, for example, an additional burner may be provided. The additional burner causes pressure loss in the exhaust oxidizing gas, and the additional fuel can be combusted when combustion exceeding the combustion capacity of the catalytic combustor422is required. Therefore, a sufficient amount of heat can be supplied to the exhaust oxidizing gas. In the fuel cell system310, the pressure difference between the cathode113side and the anode109side is controlled by a regulating valve347provided in the exhaust fuel gas line343so as to be within predetermined range, and thus, by adding pressure loss to the exhaust oxidizing gas line333that merges with the exhaust fuel gas line343, it is possible to ensure the operating differential pressure required for stable control of the regulating valve347provided in the exhaust fuel gas line343.

The exhaust oxidizing gas line333is not provided with vent system and a vent valve for releasing the exhaust oxidizing gas A3to the atmosphere (outside the system). For example, in case of power generation system that combines the SOFC and the gas turbine (for example, a micro gas turbine) that combusts the exhaust oxidizing gas A3discharged from the cathode113and the exhaust fuel gas L3discharged from the anode109, there is case where the pressure state of the oxidizing gas supplied to the cathode113changes according to the change in the state of the micro gas turbine at the time of start-up or stop, and further, there is possibility that the differential pressure control between the anode109and the cathode113becomes unsuccessful because of sudden fluctuations in pressure. Therefore, in case where a trip occurs for some reason, the generator of the micro gas turbine becomes unloaded, and protection measures for the micro gas turbine are required. Therefore, vent system and a vent valve that release the exhaust oxidizing gas A3to the outside of the system such as to the atmosphere are required. However, in the present embodiment, the turbocharger411is used, there is no generator communicating with the rotary shaft, and the load is not applied. Therefore, since there is no case where the load disappears during the trip, over-rotation occurs, and the pressure increases sharply, the differential pressure state can be stably controlled by the regulating valve347, and thus, a mechanism (bent system and vent valve) for releasing the exhaust oxidizing gas A3to the atmosphere can be omitted.

The SOFC313is further connected to the fuel gas line341for supplying the fuel gas L1to a fuel gas introduction unit (not illustrated) of the anode109, and to the exhaust fuel gas line343for supplying the exhaust fuel gas L3, which is discharged after being used for the reaction in the anode109, to the turbine423via the catalytic combustor422. The fuel gas line341is provided with a control valve342for regulating the flow rate of the fuel gas L1supplied to the anode109.

As illustrated inFIG.4, the fuel cell system310includes a differential pressure sensor370that measures the differential pressure between the anode109and the cathode113. The information on the differential pressure value between the anode109and the cathode113measured by the differential pressure sensor370is sent to the control unit20. A pressure sensor may be provided in each line of the cathode113and the anode109, and each of the pressure of the cathode113and the pressure of the anode109with the differential pressure calculated by those measured values, may be acceptable. The pressure measurement positions inFIG.4are schematically illustrated, and each pressure measurement position is not limited to the positions inFIG.4.

The recycling blower348is provided in the exhaust fuel gas line343. The exhaust fuel gas line343is provided with the regulating valve347for regulating the flow rate of a part of the exhaust fuel gas L3supplied to the catalytic combustor422. In other words, the regulating valve347regulates the pressure state of the exhaust fuel gas L3. Therefore, as will be described later, the differential pressure between the anode109and the cathode113can be regulated by controlling the regulating valve347with the control unit20.

Exhaust fuel gas release line350that releases the exhaust fuel gas L3to the atmosphere (outside the system) is connected to the exhaust fuel gas line343on the downstream side of the recycling blower348. A shutoff valve (fuel vent valve)346is provided on the exhaust fuel gas release line350. In other words, by opening the shutoff valve346, a part of the exhaust fuel gas L3of the exhaust fuel gas line343can be released from the exhaust fuel gas release line350. By discharging the exhaust fuel gas L3to the outside of the system, the excess pressure can be quickly regulated. In the exhaust fuel gas line343, the fuel gas recycling line349for recycling the exhaust fuel gas L3to the fuel gas introduction unit of the anode109of the SOFC313is connected to the fuel gas line341.

Furthermore, the fuel gas recycling line349is provided with purified water supply line361for supplying purified water for reforming the fuel gas L1at the anode109. The purified water supply line361is provided with a pump362. By controlling the discharge flow rate of the pump362, the amount of purified water supplied to the anode109is regulated. Since water vapor is generated at the anode during power generation, the exhaust fuel gas L3of the exhaust fuel gas line343contains water vapor. Therefore, the water vapor is recycled and supplied by the fuel gas recycling line349, and accordingly, the flow rate of purified water supplied by the purified water supply line361can be decreased or cut off.

Next, a configuration for releasing the oxidizing gas discharged from the compressor421will be described. Specifically, in the oxidizing gas supply line331on the downstream side of the compressor421, oxidizing gas blow line444is provided such that the oxidizing gas can flow so as to bypass the heat exchanger430and be released. One end of the oxidizing gas blow line444is connected to the upstream side of the heat exchanger430of the oxidizing gas supply line331, and the other end is connected to the downstream side of the heat exchanger430of the combustion exhaust gas line329which is the downstream side of the turbine423. A release valve (air extraction blow valve)445is provided on the oxidizing gas blow line444. In other words, by opening the release valve445, a part of the oxidizing gas discharged from the compressor421is released to the atmosphere outside the system through the chimney (not illustrated) via the oxidizing gas blow line444.

Next, the configuration used for starting the fuel cell system310will be described. The oxidizing gas supply line331is provided with a control valve451on the downstream side of the connection point with the oxidizing gas blow line444, and the downstream side (upstream side of the heat exchanger430) of the control valve451is connected to start-up air supply line454having a blower452for supplying the start-up air and a control valve453. When performing the start-up of the fuel cell system310, while the blower452supplies the start-up air to the oxidizing gas supply line331, the control valve451and the control valve453switch to the oxidizing gas from the compressor421. In the oxidizing gas supply line331, start-up air heating line455is connected to the downstream side (upstream side of the control valve335) of the heat exchanger430, is connected to the exhaust oxidizing gas line333on the downstream side of the exhaust air cooler351via the control valve456, and is connected to the oxidizing gas supply line331(inlet side of the cathode113) via a control valve457. The start-up air heating line455is provided with a start-up heater458, and the fuel gas L1is supplied via a control valve459to heat the oxidizing gas flowing through the start-up air heating line455.

The control valve457regulates the flow rate of the oxidizing gas supplied to the start-up heater458, and controls the temperature of the oxidizing gas supplied to the SOFC313.

The fuel gas L1is also supplied to the cathode113via a control valve460. The control valve460controls, for example, the flow rate of the fuel gas L1supplied to the cathode113when the fuel gas L1is supplied to the cathode113from the downstream side of the control valve457in the start-up air heating line455when the SOFC313is started, and the temperature of the power generation chamber is raised by catalytic combustion.

The control unit20performs control in the fuel cell system310. In particular, the differential pressure control for the SOFC is performed.

FIG.6shows example of a hardware configuration of the control unit20according to the present embodiment.

As illustrated inFIG.6, the control unit20is computer system (computing system), and includes, for example, a CPU11, a read only memory (ROM)12for storing a program or the like executed by the CPU11, a random access memory (RAM)13that functions as a work region at the time of executing each program, a hard disk drive (HDD)14as a large-capacity storage device, and a communication unit15for connecting to a network or the like. As the large-capacity storage device, a solid state drive (SSD) may be used. Each of these parts is connected via a bus18.

The control unit20may include an input unit including a keyboard, a mouse, and the like; and a display unit including a liquid crystal display device for displaying data.

The storage medium for storing the program or the like executed by the CPU11is not limited to the ROM12. For example, the storage medium may be another auxiliary storage device such as a magnetic disk, a magneto-optical disk, or a semiconductor memory.

A series of processes for realizing various functions (will be described later) is stored in the hard disk drive14or the like in the form of a program, the CPU11reads the program into the RAM13or the like and executes information processing and arithmetic processing, and accordingly, various functions are realized. The program may be installed in advance in the ROM12or other storage medium, provided in state of being stored in a computer-readable storage medium, or delivered via wired or wireless communication means. The computer-readable storage medium is a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

The control unit20controls the regulating valve347to control the differential pressure between the pressure of the cathode113and the pressure of the anode109in the fuel cell. In the fuel cell, differential pressure state is preferable in which the pressure of the anode109is larger than the pressure of the cathode113by predetermined differential pressure (for example, 0.1 kPa or more and 1 kPa or less) during normal operation. Therefore, in the control unit20, the regulating valve347controls the pressure on the anode109side to regulate the differential pressure between the pressure of the cathode113and the pressure of the anode109. The pressure of the cathode113is the pressure of the oxidizing gas or of the exhaust oxidizing gas A3flowing through the cathode line, for example, the pressure of the oxidizing gas in the SOFC module201.

The pressure of the anode109is the pressure of the fuel gas L1or of the exhaust fuel gas L3flowing through the anode line, for example, the pressure of the fuel gas L1in the SOFC module201.

In the present embodiment, the exhaust fuel gas line343and the exhaust oxidizing gas line333are connected to the pressure equalizing space462of the catalytic combustor422. In other words, the gas containing the fuel component discharged from the exhaust fuel gas line343and the gas containing the oxidizing gas component discharged from the exhaust oxidizing gas line333are connected to common space called the pressure equalizing space462and the pressure thereof is equalized, and the gases are mixed together. In other words, the pressure state of the exhaust fuel gas line343and of the exhaust oxidizing gas line333on the outlet side (pressure equalizing space462side) is equalized. Furthermore, since the orifice441is provided in the exhaust oxidizing gas line333, constant pressure loss according to the flow rate of the exhaust oxidizing gas A3flowing inside is added in the exhaust oxidizing gas line333. Therefore, the pressure loss of the orifice441is added based on the pressure of the pressure equalizing space462, and the pressure loss of the pipe to the outlet of the cathode113, such as the exhaust oxidizing gas line333, is added, and the pressure state on the cathode113side is determined. Meanwhile, the anode109is connected to the pressure equalizing space462via the regulating valve347in the exhaust fuel gas line343. Therefore, based on the pressure in the pressure equalizing space462, pressure loss due to the regulation of the opening of the regulating valve347is added, and further, pressure loss of the pipe to the outlet of the anode109, such as the exhaust fuel gas line343, is added, and the pressure state on the anode109side is determined. In other words, the pressure on the anode109side can be regulated by regulating the pressure loss accompanying the regulation of the opening of the regulating valve347. In this manner, by using the pressure equalizing space462and the orifice441, the pressure loss of the orifice441is added to the exhaust oxidizing gas based on the pressure in the pressure equalizing space462, and accordingly, pressure difference sufficient to enable effective and stable control of pressure regulation by the regulating valve347provided in the exhaust fuel gas line343can be obtained.

In the present embodiment, case where the differential pressure can be effectively controlled by the regulating valve347using the regulating valve347, the pressure equalizing space462, and the orifice441will be described, but either one of the pressure equalizing space462and the orifice441can control the differential pressure by the regulating valve347. When the operating differential pressure for pressure regulation by the regulating valve347of the exhaust fuel gas line343can be ensured without installing the orifice (pressure loss unit)441, only the regulating valve347can be provided to control the differential pressure.

The control unit20acquires the pressure on the cathode113side and the pressure on the anode109side. Then, the difference between the pressure of the cathode113and the pressure of the anode109is used as the differential pressure, and the opening of the regulating valve347is controlled such that the differential pressure becomes predetermined differential pressure. The pressure of the cathode113and the pressure of the anode109may be acquired individually, or the differential pressure may be acquired by using the differential pressure sensor370. In the present embodiment, the differential pressure is value obtained by subtracting the pressure of the cathode113from the pressure of the anode109. In other words, in case where the pressure is higher on the anode109side, the differential pressure is positive value, and in case where the pressure is higher on the cathode113side, the differential pressure is negative value. For example, in case where the pressure of the anode109is higher than the predetermined differential pressure with respect to the pressure of the cathode113, control is performed in the direction of opening the opening of the regulating valve347such that the pressure of the anode109decreases.

In this manner, the differential pressure state is effectively regulated by controlling the regulating valve347.

In case where an abnormality occurs in the differential pressure state, the control unit20performs abnormality response control. The abnormal state is case where the pressure difference of the anode109against the cathode113is higher than the predetermined value. The predetermined value is set as lower limit value that is assumed to be in abnormal state in case where the anode109is higher than the cathode113. In the present embodiment, for example, predetermined value is set in range of differential pressure of 1 kPa or more and 50 kPa or less.

Specifically, in case where the pressure difference of the anode109against the cathode113becomes higher than the predetermined value, the control unit20opens the shutoff valve346provided in the exhaust fuel gas release line350. Accordingly, a part of the exhaust fuel gas discharged from the anode109can be released to the atmosphere to quickly decrease the pressure on the anode109side. Therefore, it is possible to prevent the case where the differential pressure state becomes abnormal state and continues, and to return to the stable state.

The abnormal state may be case where the cathode113is higher than a predetermined value with respect to the anode109. In such case, the predetermined value is set as lower limit value that is assumed to be abnormal state in case where the cathode113is higher than the anode109. In the present embodiment, for example, predetermined value is set in range of differential pressure of −50 kPa or more and −1 kPa or less.

Specifically, in case where the pressure of the cathode113against the pressure of the anode109becomes higher than a predetermined value, the control unit20opens the release valve445provided in the oxidizing gas blow line444. Accordingly, the amount of oxidizing gas supplied to the cathode113can be reduced, and the pressure of the cathode113can be quickly lowered. Therefore, it is possible to prevent case where the differential pressure state becomes abnormal state and continues, and to return to the stable state.

Next, example of differential pressure control by the above-described control unit20will be described with reference toFIG.7.FIG.7is a flowchart illustrating example of procedure of the differential pressure control according to the present embodiment. The flow illustrated inFIG.7is repeatedly executed, for example, at predetermined control cycle.

First, the pressure of the cathode113and the pressure of the anode109are acquired, and the differential pressure is confirmed. Otherwise, the differential pressure between the anode109and the cathode113may be acquired (S101).

Next, it is determined whether or not the differential pressure is predetermined differential pressure (S102). In S102, the target differential pressure may be set as predetermined differential pressure range (including predetermined differential pressure), and it may be determined whether or not the differential pressure is within the predetermined differential pressure range.

In case where the differential pressure is predetermined differential pressure (YES determination in S102), the process ends.

In case where the differential pressure is not predetermined differential pressure (NO determination in S102), the opening of the regulating valve347is controlled to execute the differential pressure regulation control (S103).

In this manner, the differential pressure state between the anode109and the cathode113is maintained at appropriate value.

Next, example of an abnormality process by the above-described control unit20will be described with reference toFIG.8.FIG.8shows example of a flowchart of procedure to deal with the abnormal process according to the present embodiment. The flow illustrated inFIG.8is repeatedly executed, for example, at predetermined control cycle.

First, the pressure of the cathode113and the pressure of the anode109are acquired (S201). Otherwise, the differential pressure between the anode109and the cathode113may be acquired.

It is determined whether or not the pressure on the anode109side is higher than predetermined value with respect to the cathode113(S202).

In case where the pressure on the anode109side is not higher than predetermined value with respect to the cathode113(NO determination in S202), the process ends.

In case where the pressure on the anode109side is higher than the predetermined value with respect to the cathode113(YES determination in S202), the shutoff valve (fuel vent valve)346provided in the exhaust fuel gas release line350is opened (S203). In this manner, immediate atmospheric release control of the fuel gas is performed.

In case where the pressure on the anode109side is less than predetermined value with respect to the cathode113, the shutoff valve (fuel vent valve)346is closed (S204).

Next, example of the abnormality process by the above-described control unit20will be described with reference toFIG.9.FIG.9shows example of flowchart of procedure of the abnormality process according to the present embodiment. The flow illustrated inFIG.9is repeatedly executed, for example, at predetermined control cycle.

First, the pressure of the cathode113and the pressure of the anode109are acquired (S301). Otherwise, the differential pressure between the anode109and the cathode113may be acquired.

It is determined whether or not the pressure on the cathode113side is higher than predetermined value with respect to the anode109(S302).

In case where the pressure on the cathode113side is not higher than predetermined value with respect to the anode109(NO determination in S302), the process ends.

In case where the pressure on the cathode113side is higher than predetermined value with respect to the anode109(YES determination in S302), the release valve (air extraction blow valve)445provided in the oxidizing gas blow line444is opened (S303). In this manner, the immediate atmospheric release control of the oxidizing gas is performed.

In case where the pressure on the cathode113side is less than predetermined value with respect to the anode109, the release valve (air extraction blow valve)445is closed (S304).

As described above, according to the fuel cell system and the control method therefor according to the present embodiment, in case where the exhaust fuel gas discharged from the fuel cell and the oxidizing gas discharged from the fuel cell are supplied to the turbocharger411, by controlling the regulating valve347provided in the exhaust fuel gas line343to control the differential pressure between the pressure of the cathode113and the pressure of the anode109in the fuel cell, the pressure difference between the cathode113and the anode109in the fuel cell can be properly regulated.

In case of applying the present disclosure to power generation system that combines the fuel cell and the gas turbine (for example, a micro gas turbine), the pressure state of the oxidizing gas supplied to the cathode113changes according to the change in the state of the micro gas turbine at the time of start-up or stop, and thus, there is possibility that the differential pressure control between the anode109and the cathode113becomes unsuccessful because of sudden fluctuations in pressure. Therefore, in case where trip occurs for some reason, the generator of the micro gas turbine becomes unloaded, and protection measures for the micro gas turbine are required. Therefore, it is necessary to provide vent system and a vent valve for releasing the oxidizing gas to the atmosphere (outside the system) through the exhaust oxidizing gas line333, but when the turbocharger411is applied to the fuel cell and the differential pressure is regulated by the regulating valve347, it becomes possible to eliminate the need for the vent system and the vent valve that releases the oxidizing gas to the atmosphere. Therefore, it is possible to simplify the configuration and to decrease the cost.

By providing the pressure equalizing space462which is connected to the exhaust fuel gas line343and to the exhaust oxidizing gas line333and which mixes the exhaust fuel gas and the oxidizing gas to equalize the pressure, the pressure state of the outlet of the exhaust oxidizing gas line333and of the outlet of the exhaust fuel gas line343can be easily equalized. Therefore, the pressure difference between the anode109and the cathode113can be controlled more efficiently by the regulating valve347.

The exhaust fuel gas release line350that releases the exhaust fuel gas to the atmosphere is provided on the exhaust fuel gas line343, the shutoff valve346is provided in the exhaust fuel gas release line350, and accordingly, even in case of abnormal state where the pressure of the exhaust fuel gas in the exhaust fuel gas line343is higher than predetermined value, the exhaust fuel gas can be released to the atmosphere by the shutoff valve346. In case where the pressure of the anode109against the pressure of the cathode113becomes higher than predetermined value, by opening the shutoff valve346, the pressure of the anode109can be regulated by the shutoff valve346, and the abnormal state can be suppressed.

In case where the oxidizing gas supply line331is provided with the oxidizing gas blow line444through which the oxidizing gas flows and the oxidizing gas blow line444is provided with the release valve445, by opening the release valve445in case where the pressure of the cathode113against the pressure of the anode109becomes higher than predetermined value, it is possible to suppress abnormal state where the pressure of the cathode113against the pressure of the anode109becomes higher than the predetermined value.

The present disclosure is not limited to the above-described embodiments, and can be appropriately modified without departing from the gist of the present invention.

The fuel cell system and the control method therefor described in each of the above-described embodiments are understood as follows, for example.

Fuel cell system (310) according to the present disclosure includes fuel cell (313) having cathode (113) and anode (109); a turbocharger (411) having a turbine (423) and a compressor (421); exhaust fuel gas line (343) for supplying exhaust fuel gas (L3) discharged from the fuel cell (313) to a combustor (422); exhaust oxidizing gas line (333) for supplying exhaust oxidizing gas (A3) discharged from the fuel cell (313) to the combustor (422); combustion gas supply line (328) for supplying combustion gas (G) discharged from the combustor (422) to the turbine (423); oxidizing gas supply line (331) for supplying oxidizing gas (A2) compressed by the compressor (421) to the cathode (113) by rotationally driven by the turbine; a regulating valve (347) provided on the exhaust fuel gas line (343); and a control unit (20) that controls the regulating valve (347) to control differential pressure between pressure of the cathode (113) and pressure of the anode (109) in the fuel cell (313), in which vent system that releases the exhaust oxidizing gas (A3) to outside of the system is not provided on the exhaust oxidizing gas line (333).

According to the fuel cell system (310) relating to the present disclosure, in case where the exhaust fuel gas (L3) discharged from the fuel cell (313) and the oxidizing gas discharged from the fuel cell (313) are supplied to the turbocharger (411), by controlling the regulating valve (347) provided in the exhaust fuel gas line (343) to control the differential pressure between the pressure of the cathode (113) and the pressure of the anode (109) in the fuel cell (313), the pressure difference between the anode (109) and the cathode (113) in the fuel cell (313) can be properly regulated.

In case of applying the present disclosure to power generation system that combines the fuel cell (313) and the gas turbine (411) (for example, a micro gas turbine (411)), the pressure state of the oxidizing gas supplied to the cathode (113) changes according to the change in the state of the micro gas turbine at the time of start-up or stop of the micro gas turbine (411), and thus, there is possibility that the differential pressure control between the anode109and of the cathode113becomes unsuccessful because of sudden fluctuations in pressure. Therefore, in case where trip occurs for some reason, the generator of the micro gas turbine becomes unloaded, and protection measures for the micro gas turbine are required. Therefore, it is necessary to provide a vent valve on the vent line for releasing the oxidizing gas to the atmosphere through the exhaust oxidizing gas line (333), but when the turbocharger (411) is applied to the fuel cell (313) and the differential pressure is regulated by the regulating valve (347), it becomes possible to eliminate the need for the vent valve of the vent system that releases the oxidizing gas to the atmosphere. Therefore, it is possible to simplify the configuration and to decrease the cost. The vent system releases the exhaust oxidizing gas to the outside of the system during operation.

The fuel cell system (310) according to the present disclosure may further include a pressure equalizing unit (462) that is connected to the exhaust fuel gas line (343) and to the exhaust oxidizing gas line (333), and that equalizes the pressures of the exhaust fuel gas (L3) and of the exhaust oxidizing gas (A3).

According to the fuel cell system (310) of the present disclosure, the exhaust fuel gas line (343) and the exhaust oxidizing gas line (333) are connected to common space portion, the pressure equalizing unit (462) that equalizes the pressures of the exhaust fuel gas (L3) and of the exhaust oxidizing gas is formed, and accordingly, the pressure state of the outlet of the exhaust fuel gas line (343) and of the outlet of the exhaust oxidizing gas line (333) can be easily equalized. Therefore, the pressure difference between the cathode (113) and the anode (109) can be controlled more efficiently by the regulating valve (347). Since the exhaust fuel gas (L3) and the exhaust oxidizing gas can also be mixed in the pressure equalizing unit (462), the fuel cell system is suitable for combustion.

In the fuel cell system (310) according to the present disclosure, the pressure equalizing unit (462) may be provided as common space to which the exhaust fuel gas and the exhaust oxidizing gas are supplied in the combustor (422).

According to the fuel cell system (310) according to the present disclosure, by providing a pressure equalizing unit as common space to which the exhaust fuel gas and the exhaust oxidizing gas are supplied in the combustor (422), the pressure of the exhaust fuel gas (L3) and of the oxidizing gas can be equalized, and the gases can be mixed with each other. Specifically, as the combustor, a catalytic combustor can be used.

In the fuel cell system (310) according to the present disclosure, the combustor (422) may mix the exhaust fuel gas (L3) and the exhaust oxidizing gas (A3) at the pressure equalizing unit (462) and combust the mixed gas at a catalytic combustion unit (461) using a combustion catalyst.

According to the fuel cell system (310) relating to the present disclosure, pressure equalization and catalytic combustion can be performed in the combustor.

In the fuel cell system (310) according to the present disclosure, a pressure loss unit (441) that is provided in the exhaust oxidizing gas line (333) and that adds pressure loss to the exhaust oxidizing gas (A3) may further be provided.

According to the fuel cell system (310) relating to the present disclosure, by providing a pressure loss unit (for example, an orifice) that adds pressure loss to the oxidizing gas in the exhaust oxidizing gas line (333), it is possible to perform differential pressure control more efficiently via the regulating valve (347).

In the fuel cell system (310) according to the present disclosure, exhaust fuel gas release line (350) that is connected to the exhaust fuel gas line (343) and that releases the exhaust fuel gas (L3) to the atmosphere; and a shutoff valve (346) provided on the exhaust fuel gas release line (350), may further be provided.

According to the fuel cell system (310) relating to the present disclosure, the exhaust fuel gas release line (350) that releases the fuel gas to the atmosphere is provided on the exhaust fuel gas line (343), the shutoff valve (346) is provided in the exhaust fuel gas release line (350), and accordingly, even in case of abnormal state where the pressure of the fuel gas in the exhaust fuel gas line (343) is higher than predetermined value, the exhaust fuel gas can be released to the atmosphere by the shutoff valve (346).

In the fuel cell system (310) according to the present disclosure, the control unit (20) may open the shutoff valve (346) in case where the pressure of the anode (109) against the pressure of the cathode (113) becomes higher than predetermined value.

According to the fuel cell system (310) relating to the present disclosure, in case where the pressure of the anode (109) against the pressure of the cathode (113) becomes higher than predetermined value, by opening the shutoff valve (346), the pressure of the anode (109) can be regulated by the shutoff valve (346), and the abnormal state can be suppressed.

In the fuel cell system (310) according to the present disclosure, blow line (444) connected to the oxidizing gas supply line (331) and through which the oxidizing gas (A2) flows; and a release valve (445) provided on the blow line (444), may further be provided, and the control unit (20) may open the release valve (445) in case where the pressure of the cathode (113) against the pressure of the anode (109) becomes higher than predetermined value.

According to the fuel cell system (310) relating to the present disclosure, in case where the oxidizing gas supply line (331) is provided with the oxidizing gas blow line (444) through which the oxidizing gas flows and the oxidizing gas blow line (444) is provided with the release valve (445), by opening the release valve (445) in case where the pressure of the cathode (113) against the pressure of the anode (109) becomes higher than predetermined value, it is possible to suppress abnormal state where the pressure of the cathode (113) against the pressure of the anode (109) becomes higher than the predetermined value.

Method for controlling fuel cell system (310) according to the present disclosure is method for controlling fuel cell system (310) including fuel cell (313) having cathode (113) and anode (109), a turbocharger (411) having a turbine (423) and a compressor (421), exhaust fuel gas line (343) for supplying exhaust fuel gas (L3) discharged from the fuel cell (313) to a combustor (422), exhaust oxidizing gas line (333) for supplying exhaust oxidizing gas (A3) discharged from the fuel cell (313) to the combustor (422), combustion gas supply line (328) for supplying combustion gas (G) discharged from the combustor (422) to the turbine (423), oxidizing gas supply line (331) for supplying oxidizing gas (A2) compressed by the compressor (421) to the cathode (113) by rotationally driven by the turbine, and a regulating valve (347) provided on the exhaust fuel gas line (343), in which vent system that releases the exhaust oxidizing gas (A3) to outside of the system is not provided on the exhaust oxidizing gas line (333), the method including: controlling the regulating valve (347) to control differential pressure between pressure of the cathode (113) and pressure of the anode (109) in the fuel cell (313).

REFERENCE SIGNS LIST

14: hard disk drive

15: communication unit

20: control unit

101: cell stack

105: fuel cell

111: solid electrolyte film

115: lead film

205: pressure vessel

207: fuel gas supply pipe

207a:fuel gas supply branch pipe

209: fuel gas discharge pipe

209a:fuel gas discharge branch pipe

215: power generation chamber

217: fuel gas supply header

219: fuel gas discharge header

221: oxidizing gas supply header

223: oxidizing gas discharge header

225a:upper tube plate

225b:lower tube plate

231a:fuel gas supply hole

231b:fuel gas discharging hole

233a:oxidizing gas supply hole

233b:oxidizing gas discharging hole

235a:oxidizing gas supply gap

235b:oxidizing gas discharge gap

310: fuel cell system

325: air intake line

328: combustion gas supply line

329: combustion exhaust gas line

331: oxidizing gas supply line

332: heat exchanger bypass line

333: exhaust oxidizing gas line

335: control valve

336: control valve

341: fuel gas line

342: control valve

343: exhaust fuel gas line

349: fuel gas recycling line

350: exhaust fuel gas release line

351: exhaust air cooler

352: control valve

361: purified water supply line

370: differential pressure sensor

442: waste heat recovery equipment

443: control valve

444: oxidizing gas blow line

451: control valve

453: control valve

454: start-up air supply line

455: start-up air heating line

456: control valve

457: control valve

459: control valve

460: control valve

461: catalytic combustion unit