JP6582572B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system including a fuel cell stack and a hydrodesulfurizer that removes sulfur components contained in raw fuel.

  In general, a sulfur compound is added as an odorant to a hydrocarbon-based fuel (raw fuel) such as LNG or LPG used as a fuel for the fuel cell system. This sulfur compound needs to be removed to poison the reformer and the fuel cell stack catalyst mounted on the fuel cell system.

  For example, in Patent Document 1, in a fuel cell system using a solid oxide fuel cell (SOFC), a sulfur component contained in raw fuel is reduced to generate hydrogen sulfide, and the generated hydrogen sulfide is adsorbed. The structure provided with the hydrodesulfurizer which removes a sulfur component is disclosed. Such a hydrodesulfurizer needs to maintain a temperature state of about 300 ° C. for its stable operation. Therefore, in the configuration of Patent Document 1, the anode off-gas is combusted and the combustion heat is used as a heat source for the hydrodesulfurizer.

International Publication No. 2014/115502

  The configuration of Patent Document 1 requires that a combustor for burning the anode off-gas be disposed between the fuel cell stack and the hydrodesulfurizer, which increases the number of parts, complicates the system configuration, and reduces the manufacturing cost. Increase.

  The present invention has been made in consideration of the above-described conventional problems, and an object of the present invention is to provide a fuel cell system that can simplify the system configuration and reduce the manufacturing cost.

  A fuel cell system according to the present invention generates electricity using a hydrodesulfurizer that removes sulfur components contained in raw fuel, and fuel and air that are raw fuels from which sulfur components have been removed by the hydrodesulfurizer. A fuel cell system comprising a fuel cell stack, wherein an anode off gas, which is a fuel containing unreacted hydrogen discharged from the fuel cell stack, is used as a heat source for the hydrodesulfurizer, and a heating unit of the hydrodesulfurizer And an off-gas supply path for supplying the gas.

  According to such a configuration, the anode off-gas from the fuel cell stack is supplied to the heating unit of the hydrodesulfurizer and used as a heat source, thereby eliminating the need for a combustor for heating the hydrodesulfurizer and system configuration. It can be simplified and the manufacturing cost can be reduced.

  The hydrodesulfurizer includes a reducing unit that introduces raw fuel together with hydrogen from a hydrogen source, reduces a sulfur component contained in the raw fuel, and an adsorption unit that adsorbs the sulfur component reduced by the reducing unit. A part of the anode off-gas that branches off from the off-gas supply path connected to the heating unit of the hydrodesulfurizer and flows through the off-gas supply path is supplied to the reduction unit of the hydro-desulfurizer as a hydrogen source. It is good also as a structure provided with the branch path | route and the fuel supply path which joins the anode off gas which came out of the said heating part with the fuel which left the said reduction | restoration part and the said adsorption part, and supplies it to the said fuel cell stack. Then, the anode off gas used as a heat source of the hydrodesulfurizer can be merged with the fuel again and introduced into the fuel cell stack by the heating unit. As a result, unreacted hydrogen contained in the anode off-gas can be effectively utilized, the utilization rate of hydrogen as a whole system can be improved, and the concentration of hydrogen introduced into the fuel cell stack can be increased.

  The hydrodesulfurizer has a multi-tube structure, and the heating unit is formed on at least one of an outer periphery and an inner periphery of the reducing unit and the adsorbing unit through which a mixed gas of raw fuel and anode off-gas from the branch path flows. Route may be used. If it does so, the raw fuel which flows through a reduction | restoration part and an adsorption | suction part can be efficiently heated with the anode off gas which flows through a heating part, and a hydrodesulfurizer can be stably maintained in the operating temperature range.

  You may provide the water | moisture-content removal apparatus which removes the water | moisture content contained in the anode off gas introduce | transduced into the said hydrodesulfurizer from the said branch path. If it does so, since the water | moisture content in anode off gas can be removed, it can prevent that a water | moisture content is introduce | transduced into a reduction | restoration part and an adsorption | suction part.

  A heat exchanger for lowering the temperature of the anode offgas supplied to the hydrodesulfurizer may be provided at a position between the fuel cell stack and the hydrodesulfurizer in the offgas supply path. If it does so, the high temperature anode off gas discharged | emitted from a fuel cell stack can be reduced to the operating temperature range of a hydrodesulfurizer, and the more stable operation | movement of a hydrodesulfurizer will be attained.

  In this case, when the heat exchanger is configured to exchange heat between the fuel that has exited the hydrodesulfurizer and the anode offgas flowing through the offgas supply path, the fuel immediately before being introduced into the fuel cell stack is anode offgas. Can be preheated.

  Further branching off from the off-gas supply path connected to the heating unit of the hydrodesulfurizer, a part of the anode off-gas flowing through the off-gas supply path is joined to the fuel supply path by bypassing the hydrodesulfurizer. The structure provided with a bypass path | route may be sufficient. Then, all of the high-temperature anode off-gas is introduced into the hydrodesulfurizer, and the hydrodesulfurizer can be prevented from becoming higher than the appropriate temperature.

  According to the present invention, the anode off gas from the fuel cell stack is supplied to the heating unit of the hydrodesulfurizer as a heat source, thereby eliminating the need for a combustor for heating the hydrodesulfurizer and simplifying the system configuration. The manufacturing cost can be reduced.

FIG. 1 is a block diagram schematically showing the configuration of a fuel cell system according to an embodiment of the present invention. FIG. 2 is an explanatory view schematically showing the configuration of the hydrodesulfurizer. FIG. 3 is an explanatory diagram schematically showing the configuration of a hydrodesulfurizer provided with a bypass path. FIG. 4 is a plan view schematically showing the configuration of the hydrodesulfurizer according to the modification. FIG. 5 is a plan view schematically showing the configuration of a hydrodesulfurizer according to another modification.

  Preferred embodiments of the fuel cell system according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram schematically showing the configuration of a fuel cell system 10 according to an embodiment of the present invention. As shown in FIG. 1, the fuel cell system 10 includes a fuel cell stack 12, a hydrodesulfurizer 14, a fuel preheater 16, a reformer 18, and an air preheater 20.

  The fuel cell stack 12 reacts the fuel (fuel gas) supplied from the fuel supply path LF1 via the fuel preheater 16 and the reformer 18 and the air supplied from the air supply path LA1 via the air preheater 20. This is a cell stack in which a plurality of power generation cells for generating power are provided. The fuel exhaust gas (anode off gas) containing unreacted hydrogen discharged from the fuel cell stack 12 is circulated to the off gas supply path LF2, and the air exhaust gas (cathode off gas) containing unreacted oxygen is discharged to the air discharge path LA2. .

  The fuel cell stack 12 may employ a known configuration such as a configuration in which a plurality of cylindrical power generation cells are bundled or a configuration in which a plurality of rectangular flat power generation cells are stacked. The fuel cell stack 12 of this embodiment uses a solid oxide fuel cell (SOFC) in which an ion conductive ceramic is interposed as an electrolyte between a fuel electrode (anode) and an air electrode (cathode). The fuel cell stack 12 is housed in a heat insulating housing (not shown) (high temperature chamber) together with the reformer 18, for example.

  In the hydrodesulfurizer 14, raw fuel gas (for example, hydrocarbon fuel such as natural gas, LPG or city gas) sent from an external supply source via the fuel blower 22 through the raw fuel supply path LF3, An anode off gas sent from the off gas supply path LF2 via the circulation blower 23 is introduced. The hydrodesulfurizer 14 removes sulfur compounds (sulfur components) contained in the raw fuel using hydrogen contained in the anode off gas as a hydrogen source, and the detailed configuration thereof will be described later.

  A fuel supply path LF1 from the hydrodesulfurizer 14 and an off-gas supply path LF2 from the fuel cell stack 12 are connected to the fuel preheater 16. The fuel preheater 16 is a heat exchanger that preheats the fuel introduced into the fuel cell stack 12 from the fuel supply path LF1 using the heat of the anode offgas discharged from the fuel cell stack 12. In other words, the fuel preheater 16 can lower the temperature of the anode offgas by the fuel before being introduced into the fuel cell stack 12.

  The reformer 18 reforms the fuel desulfurized by the hydrodesulfurizer 14 to generate reformed fuel containing hydrogen and carbon monoxide, and various reforming catalysts are provided inside. . In the case where the fuel cell stack 12 has a structure in which fuel reforming is performed, the reformer 18 can be omitted.

  An air discharge path LA2 from the fuel cell stack 12 and an air supply path LA1 are connected to the air preheater 20. The air preheater 20 is preheated using cathode off-gas discharged from the fuel cell stack 12, which is sent from the external supply source via the air blower 24 through the air supply path LA <b> 1 and introduced into the fuel cell stack 12. Heat exchanger.

  The cathode off gas that has exited the air preheater 20 is sent to the combustor 26 from the air discharge path LA2. Anode offgas from the fuel discharge path LF4 branched from the offgas supply path LF2 by the three-way valve 28 is introduced into the combustor 26 together with the cathode offgas. The three-way valve 28 is a branch pipe that circulates a part of the anode off-gas flowing through the off-gas supply path LF2, for example, about 20% to the fuel discharge path LF4 and supplies the remaining 80% to the hydrodesulfurizer 14. . That is, the combustor 26 uses the oxygen contained in the cathode offgas for the surplus part supplied from the fuel discharge path LF4 among the anode offgas circulated to the fuel cell stack 12 again through the hydrodesulfurizer 14. It is burned and exhausted to the outside. The combustor 26 may be provided with a heat exchanger for producing hot water (not shown). Then, the fuel cell system 10 can be configured as a cogeneration system that can generate hot water and water vapor simultaneously with power generation.

  FIG. 2 is an explanatory view schematically showing the configuration of the hydrodesulfurizer 14.

  As shown in FIG. 2, the hydrodesulfurizer 14 has a double pipe structure formed of a metal pipe such as stainless steel, and has a cylindrical inner pipe path 14a provided inside and an outer periphery of the inner pipe path 14a. And an annular outer tube path 14b provided on the side. The hydrodesulfurizer 14 may have a rectangular tube shape.

  In the inner pipe path 14a, the branch path LF5 branched from the off-gas supply path LF2 via the three-way valve 32 is connected to the inlet port 30a, and the fuel supply path LF1 is connected to the outlet port 30b. Between the inlet port 30a and the outlet port 30b in the inner pipe path 14a, a reducing unit 34 and an adsorbing unit 35 are provided in order along the gas flow direction. The three-way valve 32 is a branch pipe that circulates, for example, about 1% of the anode off gas flowing through the off gas supply path LF2 to the branch path LF5 and supplies the remaining 99% to the outer pipe path 14b. The three-way valve 32 may have a structure capable of adjusting an inflow ratio of the anode off gas to the branch path LF5. After the anode off gas flowing into the branch path LF5 is mixed with the raw fuel from the raw fuel supply path LF3 and introduced into the inner pipe path 14a from the inlet port 30a, the sulfur component is removed by the reducing unit 34 and the adsorbing unit 35. , Flows into the fuel supply path LF1 from the outlet port 30b.

  The reducing unit 34 generates hydrogen sulfide by reducing the sulfur component contained in the raw fuel by introducing the raw fuel together with hydrogen from the hydrogen source. For example, a nickel-based or cobalt-based catalyst is used. . The adsorbing part 35 adsorbs hydrogen sulfide, which is a sulfur component reduced by the reducing part 34, and an adsorbing material such as zinc oxide is used, for example.

  The branch path LF5 may be provided with a moisture remover 36 for removing moisture contained in the anode off gas. The moisture remover 36 is, for example, an air-cooled heat exchanger, and can prevent moisture from being introduced into the reduction unit 34 and the adsorption unit 35 by removing moisture in the anode off gas.

  In the outer pipe path 14b, an off-gas supply path LF2 through the three-way valve 32 is connected to the inlet port 38a, and a merging path LF6 that joins the fuel supply path LF1 is connected to the outlet port 38b. The anode off gas introduced into the outer pipe path 14b from the inlet port 38a flows while contacting the outer peripheral surface of the inner pipe path 14a to heat the inside of the inner pipe path 14a, and then flows from the outlet port 38b through the merging path LF6. Into the fuel supply path LF1. That is, the outer pipe path 14b functions as a heating part 40 for stably maintaining the removal reaction of the sulfur component in the reduction part 34 and the adsorption part 35 by heating the inner pipe path 14a.

  Therefore, in the fuel cell system 10 configured as described above, the raw fuel supplied from the external supply source via the raw fuel supply path LF3 is contained in the hydrodesulfurizer 14 together with the anode off-gas from the branch path LF5. The reduction part 34 and the adsorption part 35 provided in the pipe path 14a are circulated in order. At the same time, the fuel and heat introduced into the fuel cell stack 12 by the fuel preheater 16 after being discharged from the fuel cell stack 12 at about 500 ° C., for example, into the heating unit 40 that is the outer pipe path 14 b of the hydrodesulfurizer 14. The anode off-gas which has been exchanged and is about 300 ° C. suitable for the catalytic reaction in the hydrodesulfurizer 14 is introduced from the off-gas supply path LF2.

As a result, in the hydrodesulfurizer 14, the hydrogen contained in the anode offgas introduced from the branch path LF5 is used as a hydrogen source, and the heat of the anode offgas flowing through the heating unit 40 is used as a heat source in the reducing unit 34 and the adsorbing unit 35. Such a sulfur component removal reaction is performed. That is, a hydrogenation reaction that reduces the sulfur compound to hydrogen sulfide is performed in the reducing unit 34 as shown in the following formula (1), and an adsorption reaction that adsorbs hydrogen sulfide in the adsorption unit 35 as shown in the following formula (2) is performed. As a result, sulfur components in the raw fuel are removed.
Formula (1): CnHnS + H ₂ → H ₂ S + CnHn
Formula (2): ZnO + H ₂ S → ZnS + H ₂ O

  The fuel that is the raw fuel from which the sulfur component has been removed by the hydrodesulfurizer 14 is preheated by absorbing the heat of the anode offgas flowing through the offgas supply path LF2 by the fuel preheater 16 and reformed by the reformer 18. After that, it is introduced into the fuel electrode of the fuel cell stack 12 and reacts with the air introduced into the air electrode from the air supply path LA1 to generate power. At this time, in the fuel cell system 10, since the sulfur component in the fuel is removed by the hydrodesulfurizer 14, the poisoning of the catalyst in the reformer 18 and the fuel cell stack 12 is prevented.

  Then, the anode offgas containing hydrogen that has not been used for the power generation reaction in the fuel cell stack 12 flows again through the offgas supply path LF2, and a part thereof is sent from the three-way valve 28 to the combustor 26, while the remaining part is again hydrogenated. It is introduced into the desulfurizer 14 and used here as a hydrogen source and a heat source.

  As described above, in the fuel cell system 10 according to this embodiment, the anode degas which is a fuel containing unreacted hydrogen discharged from the fuel cell stack 12 is used as a heat source for the hydrodesulfurizer 14. 14 is provided with an off-gas supply path LF2 for supplying to the 14 heating units 40. Therefore, by supplying the anode off gas from the fuel cell stack 12 directly to the heating unit 40 of the hydrodesulfurizer 14 as a heat source, a combustor for heating the hydrodesulfurizer 14 becomes unnecessary, and the system configuration The manufacturing cost can be reduced.

  In the fuel cell system 10, the hydrogen desulfurizer 14 is branched from the offgas supply path LF 2 connected to the heating unit 40 of the hydrodesulfurizer 14 and a part of the anode offgas flowing through the offgas supply path LF 2 is used as a hydrogen source. A branch path LF5 for supplying to the reduction unit 34 and a fuel supply path LF1 for introducing the anode off gas from the heating unit 40 with the fuel from the reduction unit 34 and the adsorption unit 35 and introducing the fuel into the fuel cell stack 12 are provided. . As a result, the anode off gas used as the heat source of the hydrodesulfurizer 14 by the heating unit 40 can be merged with the fuel again and introduced into the fuel cell stack 12. As a result, unreacted hydrogen contained in the anode off-gas can be effectively utilized, the utilization rate of hydrogen as a whole system can be improved, and the concentration of hydrogen introduced into the fuel cell stack 12 can be increased.

  In the hydrodesulfurizer 14, the outer pipe path 14 b formed on the outer periphery of the inner pipe path 14 a having the reducing section 34 and the adsorbing section 35 through which the mixed gas of raw fuel and anode off gas flows is configured as the heating section 40. As a result, the raw fuel flowing through the reducing unit 34 and the adsorbing unit 35 can be efficiently heated by the anode off gas flowing through the heating unit 40, and the hydrodesulfurizer 14 can be stably maintained at about 300 ° C., which is the operating temperature zone. can do.

  The fuel cell system 10 is a heat exchanger that lowers the temperature of the anode offgas supplied to the hydrodesulfurizer 14 at a position between the fuel cell stack 12 and the hydrodesulfurizer 14 in the offgas supply path LF2. A fuel preheater 16 is provided. As a result, the temperature of the anode offgas discharged from the fuel cell stack 12 at, for example, about 500 ° C. can be lowered to about 300 ° C., which is the operating temperature range of the hydrodesulfurizer 14, and the hydrodesulfurizer 14 is further layered. Stable operation is possible. Moreover, since the fuel preheater 16 is configured to exchange heat between the fuel that has exited the hydrodesulfurizer 14 and the anode offgas flowing through the offgas supply path LF2, the fuel immediately before being introduced into the reformer 18 and the fuel cell stack 12 is used. There is also an advantage that can be preheated using an anode off gas.

  By the way, in the above, part of the anode off-gas introduced into the hydrodesulfurizer 14 from the off-gas supply path LF2 via the three-way valve 28 flows into the branch path LF5 from the three-way valve 32 as a hydrogen source for reduction, and the remainder Is made to flow into the heating unit 40 as a heat source of the hydrodesulfurizer 14. However, the temperature of the anode off-gas introduced into the hydrodesulfurizer 14 may vary depending on the type and specification of the fuel cell stack 12, the capacity of the fuel preheater 16, and the like. The heating amount becomes excessive, and it may be difficult to maintain the hydrodesulfurizer 14 at about 300 ° C., which is an appropriate operating temperature range.

  Therefore, as shown in FIG. 3, the off-gas supply path LF2 connected to the heating unit 40 on the downstream side of the three-way valve 32 is further branched by the three-way valve 42, and a part of the anode off-gas flowing through the off-gas supply path LF2 in this portion. May be provided with a bypass path LF7 that bypasses the hydrodesulfurizer 14 to join the fuel supply path LF1 (merging path LF6). By providing this bypass path LF7, all of the high-temperature anode off-gas is introduced into the hydrodesulfurizer 14, and the hydrodesulfurizer 14 can be prevented from becoming higher than the appropriate temperature. In other words, by providing the bypass path LF7, a part of the anode off-gas is allowed to bypass the hydrodesulfurizer 14 and merge with the fuel in the fuel supply path LF1 before being introduced into the fuel cell stack 12. Since the fuel preheater 16 can be omitted, the system configuration can be further simplified. Of course, the bypass path LF7 may be provided in a system configuration including the fuel preheater 16.

  In the above description, the hydrodesulfurizer 14 has a double pipe structure, the reducing unit 34 and the adsorption unit 35 are provided in the inner inner pipe path 14a, and the heating unit 40 is provided in the outer outer pipe path 14b. For example, as shown in FIG. 4, a hydrodesulfurizer 50 may be configured in which a heating unit 40 is provided in the inner inner pipe path 14 a and a reducing unit 34 and an adsorbing part 35 are provided in the outer outer pipe path 14 b.

  Moreover, as shown in FIG. 5, you may comprise as the hydrodesulfurizer 52 of a triple pipe structure. In the hydrodesulfurizer 52, an intermediate path 14c is provided between the inner inner pipe path 14a and the outer outer pipe path 14b, and the inner pipe path 14a and the outer pipe path 14b serve as the heating unit 40, and the intermediate path 14c therebetween. In addition, a reducing unit 34 and an adsorbing unit 35 are provided. Thereby, the raw fuel flowing through the reducing unit 34 and the adsorbing unit 35 can be more efficiently heated by the anode off gas flowing through the heating unit 40 inside and outside. Of course, the hydrodesulfurizer may have a structure of four or more pipes, and the arrangement of the reduction unit 34, the adsorption unit 35, and the heating unit 40 may be set as appropriate.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be freely changed without departing from the gist of the present invention.

  For example, in the above-described embodiment, a configuration using a solid oxide fuel cell (SOFC) as the fuel cell stack 12 has been exemplified. However, the present invention is applied to a fuel cell having another structure, for example, a molten carbonate fuel cell (MCFC). Is also applicable.

  Further, the hydrodesulfurizer 14 together with the anode offgas from the offgas supply path LF2 is used for the cathode offgas discharged from the fuel cell stack 12 to the air discharge path LA2 using a path (not shown) branched from the air discharge path LA2. You may introduce into heating parts 40, such as. However, in the case of this configuration, it is necessary to discharge the mixed gas of the anode off-gas and the cathode off-gas that has exited the heating unit 40 to the outside via, for example, the combustor 26.

DESCRIPTION OF SYMBOLS 10 Fuel cell system 12 Fuel cell stack 14, 50, 52 Hydrodesulfurizer 14a Inner pipe path 14b Outer pipe path 14c Intermediate path 16 Fuel preheater 18 Reformer 20 Air preheater 28, 32, 42 Three-way valve 30a, 38a Inlet port 30b, 38b Outlet port 34 Reducing part 35 Adsorbing part 36 Moisture remover 40 Heating part LA1 Air supply path LA2 Air discharge path LF1 Fuel supply path LF2 Off-gas supply path LF3 Raw fuel supply path LF4 Fuel discharge path LF5 Branch path LF6 Joint flow Route LF7 Bypass route

Claims (6)

A fuel cell system comprising a hydrodesulfurizer that removes sulfur components contained in raw fuel, and a fuel cell stack that generates power using air and fuel that is the raw fuel from which sulfur components have been removed by the hydrodesulfurizer Because
An off-gas supply path for supplying an anode off-gas, which is a fuel containing unreacted hydrogen discharged from the fuel cell stack, to a heating unit of the hydro-desulfurizer as a heat source of the hydro-desulfurizer ;
The hydrodesulfurizer includes a reducing unit that introduces raw fuel together with hydrogen from a hydrogen source, reduces a sulfur component contained in the raw fuel, and an adsorption unit that adsorbs the sulfur component reduced by the reducing unit. Have
Further, a branch branched from the off-gas supply path connected to the heating unit of the hydrodesulfurizer, and a part of the anode off-gas flowing through the off-gas supply path is supplied to the reducing unit of the hydrodesulfurizer as a hydrogen source. Route,
A fuel supply path for supplying the anode off-gas exiting the heating unit with the fuel exiting the reduction unit and the adsorption unit and supplying the fuel to the fuel cell stack;
The fuel cell system according to claim Rukoto equipped with. The fuel cell system according to claim 1 , wherein
The hydrodesulfurizer has a multi-tube structure,
The heating section is a path formed in at least one of the outer circumference and the inner circumference of the reducing section and the adsorbing section through which a mixed gas of raw fuel and anode off gas from the branch path flows. . The fuel cell system according to claim 1 or 2 ,
A fuel cell system comprising a moisture remover that removes moisture contained in an anode offgas introduced into the hydrodesulfurizer from the branch path. The fuel cell system according to any one of claims 1 to 3 ,
A fuel having a heat exchanger for lowering the temperature of the anode offgas supplied to the hydrodesulfurizer at a position between the fuel cell stack and the hydrodesulfurizer in the offgas supply path. Battery system. The fuel cell system according to claim 4 , wherein
The said heat exchanger is a fuel cell system characterized by exchanging heat with the fuel which left the said hydrodesulfurizer, and the anode offgas which flows through the said offgas supply path. The fuel cell system according to any one of claims 1 to 5,
Further branching off from the off-gas supply path connected to the heating unit of the hydrodesulfurizer, a part of the anode off-gas flowing through the off-gas supply path is joined to the fuel supply path by bypassing the hydrodesulfurizer. A fuel cell system comprising a bypass path.

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