KR20220042014A - Ammonia-based reversible fuel cell system - Google Patents

Abstract

The present invention relates to a fuel cell system including: a fuel cell that includes a fuel electrode, an air electrode, and an electrolyte interposed therebetween and can operate in a fuel cell mode; a gas storage unit for storing a gas containing nitrogen and hydrogen; and a heat exchanger for heating ammonia supplied to the fuel electrode of the fuel cell with an exhaust gas discharged from the fuel cell, wherein the exhaust gas passing through the heat exchanger is stored in the gas storage unit.

Description

Ammonia-based reversible fuel cell system

The present invention relates to a fuel cell system, and more particularly, to an ammonia-based bidirectional fuel cell system that can be operated in a fuel cell mode, a water electrolysis mode, or a fuel cell and a water electrolysis mode using ammonia as a fuel for a fuel cell. it's about

Recently, research on power generation systems using renewable energy such as solar power or wind power is being conducted. In particular, when excess power is generated from renewable energy power generation facilities beyond the power demand, hydrogen is produced and stored using a water electrolysis device, and the amount of power generation is low. A regenerative (bidirectional) fuel cell system capable of producing and supplying electric power from a fuel cell using stored hydrogen is being researched.

Conventional general bidirectional fuel cell systems generate electricity using hydrogen or generate and store hydrogen. Although hydrogen has a very high energy density to weight ratio, since it has a low energy storage density to volume ratio, it is necessary to store it in an appropriate way to increase the energy density to volume ratio.

For this reason, recently, a fuel cell system using ammonia instead of hydrogen has been studied. Ammonia can be easily liquefied, providing an economical method for storing and supplying hydrogen. However, when driving a fuel cell using ammonia as a fuel, nitrogen is contained in the fuel cell exhaust gas, and if this exhaust gas is recirculated and put into the fuel cell, the fuel cell operation is not smooth and the exhaust gas recirculation is not easy. Due to several problems, an efficient ammonia-based fuel cell system has not yet been proposed.

Patent Document 1: Republic of Korea Patent Registration No. 10-1340492 (December 11, 2013 Announcement)

An object of the present invention is to solve the above problems, and to provide an ammonia-based fuel cell system in at least one of a fuel cell mode and a water electrolysis mode using ammonia as a fuel.

According to one embodiment of the present invention, there is provided a fuel cell system, comprising: a fuel cell comprising an anode, an air electrode, and an electrolyte interposed therebetween and operable in a fuel cell mode; a gas storage unit for storing a gas containing nitrogen and hydrogen; and a heat exchanger for heating ammonia supplied to the anode of the fuel cell with exhaust gas discharged from the anode, wherein the exhaust gas passing through the heat exchanger is stored in the gas storage unit. .

According to an embodiment of the present invention, there is provided a fuel cell system, comprising: a fuel cell comprising an anode, an air electrode, and an electrolyte interposed therebetween and operable in a water electrolysis mode; a gas storage unit for storing a gas containing nitrogen and hydrogen; and an ammonia synthesizing device for generating ammonia using hydrogen in exhaust gas discharged from the anode of the fuel cell and nitrogen and hydrogen supplied from the gas storage unit.

According to an embodiment of the present invention, it is possible to provide an ammonia-based fuel cell system that uses ammonia as a fuel and is operable in at least one of a fuel cell mode and a water electrolysis mode. The fuel cell system of the present invention can be used as a bidirectional fuel cell system, and in the fuel cell mode, ammonia is used as a fuel to produce electricity, and in the water electrolysis mode, ammonia can be regenerated and stored in the ammonia storage unit. It can operate continuously in solution mode.

In addition, the fuel cell system of the present invention stores hydrogen and nitrogen of the anode exhaust gas in the gas storage unit during the fuel cell mode operation, extracts hydrogen from the anode exhaust gas during the water electrolysis mode operation, and mixes it with the gas of the gas storage unit for ammonia synthesis Therefore, efficient system operation is possible by reusing the anode exhaust gas without discarding it, even if it operates in any of the fuel cell mode and the water electrolysis mode.

1 is a view for explaining a fuel cell system according to an embodiment of the present invention;
2 is a view for explaining a fuel cell mode of a fuel cell system according to an embodiment;
3 is a view for explaining a water electrolysis mode of a fuel cell system according to an embodiment.

The above objects, other objects, features and advantages of the present invention will be easily understood through the following preferred embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed subject matter may be thorough and complete, and that the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, the expressions “comprises”, “consists of”, and/or “consists of” do not exclude the presence or addition of one or more other components other than those recited in the expression. .

Hereinafter, the present invention will be described in detail with reference to the drawings. In describing the specific embodiments below, various specific contents have been prepared to more specifically explain and help the understanding of the invention. However, readers with enough knowledge in this field to understand the present invention It can be recognized that it can be used without specific content. In some cases, it should be mentioned in advance that parts which are commonly known in describing the invention and which are not largely related to the invention are not described in order to avoid confusion in describing the present invention.

1 is a view for explaining a fuel cell system according to an embodiment of the present invention.

Referring to the drawings, a fuel cell system according to an embodiment includes a fuel cell 10 , an ammonia storage unit 20 , a gas storage unit 30 , a water discharge unit 70 , an ammonia synthesis device 80 , and the It may be composed of a plurality of flow paths connecting between the components, a blower, a pump, and the like.

The fuel cell 10 includes an anode, a cathode, and an electrolyte interposed therebetween, and may operate in at least one of a fuel cell mode and a water electrolysis mode. The fuel cell 10 may generate electricity and water by a chemical reaction between ammonia and oxygen in the fuel cell mode, and may generate hydrogen and oxygen by steam and electricity in the water electrolysis mode. In one embodiment, the fuel cell 10 is a bidirectional water electrolysis fuel cell operable in both the fuel cell mode and the water electrolysis mode. In an alternative embodiment, the fuel cell 10 may be a unidirectional fuel cell rather than a bidirectional fuel cell, in which case the fuel cell 10 may operate only in the fuel cell mode or only in the water electrolysis mode.

The ammonia storage unit 20 stores ammonia (NH3), which is a fuel of the fuel cell 10 . In one embodiment, the storage unit 20 may store ammonia in a liquid state, for example, may store ammonia liquid in a high pressure state of 10 bar or more.

In the illustrated embodiment, the ammonia storage unit 20 supplies ammonia to the fuel cell 10 through the supply passage L1. Ammonia supplied to the fuel cell 10 may be heated and vaporized in the first heat exchanger 61 to be supplied to the anode 11 of the fuel cell 10 . The first heat exchanger 61 allows heat exchange between the exhaust gas discharged from the anode 11 of the fuel cell 10 to the discharge passage L2 and ammonia supplied to the anode 11 of the fuel cell 10 to occur. is composed

In an alternative embodiment, the fuel cell system may further include a second heat exchanger 62 . The second heat exchanger 62 is disposed on the upstream side of the first heat exchanger 61 on the supply path L1 for supplying ammonia to the fuel cell 10 and is a first branch flow path branched from the discharge flow path L2 ( Ammonia can be heated with the anode exhaust gas transferred to L3).

In an alternative embodiment, the fuel cell system may further include a turbine 40 . The turbine 40 may be disposed between the first heat exchanger 61 and the second heat exchanger 62 on the supply path L1 , and converts the energy of the high-pressure ammonia gas vaporized in the second heat exchanger 62 . It can be used to generate mechanical energy in the turbine 40 .

In the water electrolysis mode, the fuel cell system may supply steam to the fuel cell 10 through the water supply passage L7 . For example, water may be supplied from the outside by the pump 91 , the water may be heated to generate steam, and then steam may be supplied to the fuel cell 10 through the supply passages L7 and L1 . In the illustrated embodiment, heat generated in the ammonia synthesizer 80 may be used to heat and vaporize water. That is, water transferred through the water supply passage (L7) is vaporized using high-temperature thermal energy generated during the operation of the ammonia synthesis device 80, and then steam is supplied to the anode 11 through the supply passage (L1). there is. In an alternative embodiment, the fuel cell system 10 may use other heat sources in the system to vaporize water into steam.

Since a large amount of water (steam) is required when the fuel cell system operates in the water electrolysis mode, in an exemplary embodiment, the fuel cell system has an additional supply passage through which water or steam is supplied from outside the system in addition to the water supply passage L7. may further include. In the case of the illustrated embodiment, the fuel cell system further includes first and second additional supply passages L8 and L9 and, if necessary, uses at least one of the first and second additional supply passages L8 and L9 to generate steam. It may be additionally supplied to the fuel cell 10 .

The anode exhaust gas discharged from the anode 11 of the fuel cell 10 is transferred along the discharge passage L2 and passes through the first heat exchanger 61 , and the anode exhaust gas is supplied from the first heat exchanger 61 . Heat energy is transferred to ammonia supplied to the anode 11 through the flow path L1 to heat or vaporize the ammonia. In one embodiment, when the additional supply passage L8 for supplying water is installed, the third heat exchanger 63 may be installed in the discharge passage L2 , and the anode exhaust gas is additionally supplied from the third heat exchanger 63 . The water in the flow path L8 can be heated.

In an embodiment, the fuel cell system may further include a recirculation passage L21 connecting between the supply passage L1 and the exhaust passage L2 and a blower 93 installed therein. In the illustrated embodiment, some of the anode exhaust gas that has passed through the first heat exchanger 61 and the third heat exchanger 63 may be re-supplied to the anode 11 through the recirculation passage L21. For example, when the fuel cell system operates in the water electrolysis mode, hydrogen and water (steam) are discharged from the anode 11 as an anode exhaust gas, and a part of the exhaust gas is branched into the recirculation flow path L21, so that hydrogen in the exhaust gas may be re-supplied to the anode 11 .

The anode exhaust gas cooled while passing through the first and third heat exchangers 61 and 63 is transferred to the water discharge unit 70 . The water discharge unit 70 is a device that separates and discharges water in the exhaust gas, and may include, for example, a condenser, a drain, and a pump, a cooling device, etc. installed on the circulation path of the refrigerant circulating through the condenser. Since the specific configuration of the water discharge unit is known technology, a description thereof will be omitted.

On the downstream side of the water discharge part 70 , the discharge flow path L2 branches into a first branch flow path L3 and a second branch flow path L4 . When the fuel cell system of the present invention is a bidirectional system, the anode exhaust gas may be transferred to either one of the first branch flow path L3 and the second branch flow path L4 according to the fuel cell mode and the water electrolysis mode. For this branching operation, although not shown in the drawings, for example, one or more on-off valves or three-way valves may be installed on the branch point or the first and second branch flow paths L3 and L4.

In an embodiment, when the fuel cell system operates in the fuel cell mode, the second branch passage L4 is closed and the anode exhaust gas is transferred through the first branch passage L3 . A second heat exchanger 62 may be installed in the first branch flow path L3 , and the anode exhaust gas in the second heat exchanger 62 may be vaporized by heating ammonia transferred from the ammonia storage unit 20 . .

The anode exhaust gas passing through the second heat exchanger 62 may be supplied to the first compressor 51 . The first compressor 51 compresses the anode exhaust gas to a pressure of, for example, 5 bar. In an embodiment, when the fuel cell system includes the turbine 40 , mechanical energy generated by the turbine 40 may be used to drive the first compressor 51 . In an alternative embodiment, the mechanical energy generated by the turbine 40 may produce electrical energy, and the generated electricity may drive a peripheral auxiliary device (BOP) of the fuel cell system or supply electricity to the outside of the fuel cell system. .

The exhaust gas compressed by the first compressor 51 is supplied to and stored in the gas storage unit 30 . In the fuel cell mode, the anode exhaust gas transferred to the first branch flow path L3 is a gas containing nitrogen (N2) and hydrogen (H2) as main components, and thus the gas storage unit 30 stores a mixed gas of nitrogen and hydrogen. can

In one embodiment, when the fuel cell system operates in the water electrolysis mode, the first branch passage L3 is closed and the anode exhaust gas passes through the second branch passage L4 to the second compressor 52 and the ammonia synthesis device ( 80) sequentially. The second compressor 52 may compress the anode exhaust gas to a pressure required by the ammonia synthesis device 80 . For example, the ammonia synthesis device 80 may be a device operating between 10 bar and 180 bar, and the second compressor 52 may compress the anode exhaust gas to a pressure required for ammonia synthesis.

The ammonia synthesizing device 80 generates ammonia by using the anode exhaust gas. In one embodiment, the ammonia synthesis apparatus 80 is a Haber-Bosch reactor that receives hydrogen (H2) and nitrogen (N2) and generates ammonia (NH3) therefrom. However, the ammonia synthesizing device 80 is not limited to such a Haber-Bosch reactor and may be any synthesizing device capable of synthesizing ammonia using the anode exhaust gas. Ammonia generated in the ammonia synthesizing device 80 is transferred to and stored in the ammonia storage unit 20 along the second branch flow path L4.

Hydrogen and nitrogen are required to synthesize ammonia in the ammonia synthesizing device 80. In the water electrolysis mode, the anode exhaust gas transported through the discharge flow path L2 and the second branch flow path L4 does not contain nitrogen. In an embodiment of the present invention, a mixed gas of nitrogen and hydrogen stored in the gas storage unit 30 may be additionally supplied to the ammonia synthesis device 80 . That is, as shown in the drawing, the gas storage unit 30 and the second branch passage L4 are connected to the gas supply passage L10 to transfer a mixed gas of nitrogen and hydrogen to the second branch passage L4. At this time, the third compressor 53 may be installed on the gas supply passage L10 and the nitrogen and hydrogen mixed gas may be compressed to a pressure required for ammonia synthesis in the third compressor 53 .

In one embodiment, the fuel cell system includes an air supply passage L5 for supplying external air to the cathode 12 of the fuel cell, and at least one blower 92 and a fourth heat exchanger 64 installed in this passage. . The cathode exhaust gas discharged from the cathode 12 of the fuel cell 10 passes through the fourth heat exchanger 64 and is discharged to the outside through the discharge passage L6, in which case the fourth heat exchanger 64 is air Heat exchanges between the air transferred to the cathode 12 along the supply passage L5 and the cathode exhaust gas discharged from the cathode 12 and transferred along the discharge passage L6 .

In an embodiment, a fifth heat exchanger 65 may be further installed on the downstream side of the fourth heat exchanger 64 on the discharge flow path L6 , and the cathode exhaust gas in the fifth heat exchanger 65 is a second addition Water supplied along the supply passage L9 may be heated and vaporized. In addition, in an alternative embodiment, the heat of the cathode exhaust gas that has passed through the fourth heat exchanger 64 may be additionally used. For example, the cathode exhaust gas that has passed through the fourth heat exchanger 64 vaporizes fuel or water in the fuel supply passage L1 or the water supply passage L7 through the fifth heat exchanger 65 or another additional heat exchanger. can be used additionally.

Now, an operation in the fuel cell mode and the water electrolysis mode of the fuel cell system according to an embodiment of the present invention will be described with reference to FIGS. 2 and 3 , respectively.

2 shows an operation state in a fuel cell mode of a fuel cell system according to an exemplary embodiment. In FIG. 2, a flow path used in the fuel cell mode is indicated by a thick line.

Referring to the drawings, ammonia gas is supplied to the fuel cell 10 through the fuel supply passage L1 in the fuel cell mode. For example, liquid ammonia stored in the ammonia storage unit 20 at approximately 11 bar is transferred along the supply passage L1 and sequentially passes through the second heat exchanger 62 and the first heat exchanger 61 to be vaporized. . At this time, the high-pressure ammonia gas heated or vaporized in the second heat exchanger 62 may be used to generate a predetermined mechanical energy in the turbine 40, and the ammonia gas passing through the turbine 40 is transferred to the first heat exchanger ( 61 ), and then it may be supplied to the anode 11 of the fuel cell 10 . In an alternative embodiment, the turbine 40 and the second heat exchanger 62 may be omitted, in which case the liquid ammonia is vaporized in the first heat exchanger 61 and then supplied to the fuel cell 10 .

Meanwhile, the blower 92 of the air supply passage L5 operates to supply external air to the cathode 12 of the fuel cell 10 . The air transferred to the air supply passage L5 may be heated in the fourth heat exchanger 64 and then injected into the cathode 12 .

In the fuel cell mode, the anode 11 of the fuel cell 10 generates hydrogen, nitrogen, and water (steam) by a chemical reaction between ammonia gas and air (oxygen), and the anode exhaust gas through the exhaust passage L2 The cathode 12 discharges nitrogen and unreacted air as cathode exhaust gas through the discharge passage L6.

The anode exhaust gas discharged from the anode 11 along the discharge passage L2 passes through the first heat exchanger 61 to heat and vaporize ammonia in the supply passage L1, and then in the water discharge unit 70 As water is removed, the anode exhaust gas is mainly composed of hydrogen and nitrogen. The anode exhaust gas is supplied to the second heat exchanger 62 along the first branch flow path L3 , and the second heat exchanger 62 heats or vaporizes ammonia. Thereafter, the anode exhaust gas may be compressed by the first compressor 51 to a high pressure and then transferred to and stored in the gas storage unit 30 .

3 shows an operation state of a water electrolysis mode of a fuel cell system according to an exemplary embodiment. The flow path used in the water electrolysis mode is indicated by a thick line in FIG. 3 .

Referring to the drawings, water is transferred into the system through the water supply passage L7 in the water electrolysis mode. The transferred water is vaporized into steam using high-temperature heat generated during the operation of the ammonia synthesis device 80 . The vaporized steam joins the supply passage L1 along the water supply passage L7 and is then supplied to the anode 11 of the fuel cell 10 . At this time, since the ammonia storage unit 20 and the supply passage L1 are closed by means such as a valve, only steam can be supplied to the anode 11 . Since a lot of steam is required in the water electrolysis mode, steam may be received through the first and second additional supply passages L8 and L9 depending on circumstances. In addition, air is supplied to the cathode 12 through the air supply passage L5.

As the water electrolysis reaction occurs in the fuel cell 20 , the anode exhaust gas composed of hydrogen and steam is discharged from the anode 11 through the discharge passage L2 , and the cathode exhaust gas is also discharged from the cathode 12 through the discharge passage L6 . ) is released through

The anode exhaust gas discharged to the discharge passage L2 sequentially passes through the first heat exchanger 61 and the third heat exchanger 63 to heat water or steam to be supplied to the fuel cell, and then to the water discharge unit 70 ) is transferred to A portion of the anode exhaust gas may be branched into the recirculation passage L21 before being transferred to the water discharge unit 70 . Even in the water electrolysis mode, it is necessary to supply a small amount of hydrogen to the anode 11. Since hydrogen in the exhaust gas can be supplied to the anode 11 by branching and recirculating some of the exhaust gas through the recirculation passage L21, separate hydrogen The advantage is that there is no need to supply. In an embodiment, the recirculation passage L21 may be connected between the first heat exchanger 61 and the third heat exchanger 63 or may be connected to the downstream side of the water discharge unit 70 .

In the water electrolysis mode, since the main components of the anode exhaust gas are hydrogen and steam, when the steam is condensed and removed in the water discharge unit 70, the anode exhaust gas becomes a hydrogen-based gas, and then is discharged along the second branch flow path L4. 2 is supplied to the compressor (52). Meanwhile, the mixed gas of nitrogen and hydrogen stored in the gas storage unit 30 may be compressed in the third compressor 53 and then supplied to the second branch passage L4 through the gas supply passage L10, and thus hydrogen and nitrogen A high-pressure mixed gas containing as a main component may be supplied to the ammonia synthesis device 80 through the second branch passage L4.

The ammonia synthesizing device 80 generates ammonia using the supplied high-pressure hydrogen and nitrogen mixed gas, and the generated ammonia is supplied to and stored in the ammonia storage unit 20 along the second branch flow path L4.

As described above, in the water electrolysis mode of the fuel cell system according to the present invention, hydrogen can be supplied to the fuel cell by recirculating some of the anode exhaust gas discharged from the fuel cell 10, so that there is no need to provide a separate path for hydrogen supply. There is an advantage, and after mixing nitrogen and hydrogen gas in the gas storage unit 30 with hydrogen extracted from the anode exhaust gas, ammonia may be generated in the ammonia synthesis device 80 and stored in the ammonia storage unit 20 .

Therefore, when the fuel cell system of the present invention is used as a bidirectional fuel cell system, in the fuel cell mode, ammonia in the ammonia storage unit 20 is used as a fuel to produce electricity and a mixed gas of hydrogen and nitrogen is used in the gas storage unit 30 . In the water electrolysis mode, ammonia can be generated using the gas of the gas storage unit 30 and stored in the ammonia storage unit 10, so bidirectional fuel that can continuously operate alternately between the fuel cell mode and the water electrolysis mode A battery system can be implemented.

In addition, from the viewpoint of hydrogen recirculation, when operating in the fuel cell mode, hydrogen from the anode exhaust gas is extracted and stored in the gas storage unit 30, and when operating in the water electrolysis mode, hydrogen from the anode exhaust gas is extracted and used for ammonia synthesis. Efficient system operation is possible by reusing the hydrogen in the exhaust gas without throwing away even if it operates in either mode or water electrolysis mode.

As described above, those of ordinary skill in the art to which the present invention pertains can understand that various modifications and variations are possible from the description of this specification. Therefore, the scope of the present invention should not be limited to the described embodiments and should be defined by the claims described below as well as the claims and equivalents.

10: fuel cell 20: ammonia storage unit
30: gas storage unit 40: turbine
51-53: compressor 61-65: heat exchanger
70: water discharge unit 80: ammonia synthesis device

Claims (11)

A fuel cell system comprising:
a fuel cell comprising an anode, a cathode, and an electrolyte interposed therebetween and capable of operating in a fuel cell mode;
a gas storage unit for storing a gas containing nitrogen and hydrogen; and
a heat exchanger for heating ammonia supplied to the anode of the fuel cell with exhaust gas discharged from the anode; and
and to store the exhaust gas passing through the heat exchanger in the gas storage unit. The method of claim 1,
Further comprising a water discharge unit for separating water from the exhaust gas that has passed through the heat exchanger,
The fuel cell system is configured to transfer the exhaust gas that has passed through the water discharge unit to the gas storage unit. 3. The method of claim 2,
Further comprising a compressor disposed between the water discharge unit and the gas storage unit,
The fuel cell system is configured to compress the exhaust gas in the compressor and then transfer it to a gas storage unit. 4. The method of claim 3,
Further comprising a turbine disposed on a supply passage for supplying ammonia to the anode to generate mechanical energy using ammonia,
and to drive the compressor with mechanical energy generated in the turbine or to produce electrical energy. A fuel cell system comprising:
a fuel cell comprising an anode, a cathode, and an electrolyte interposed therebetween and capable of operating in a water electrolysis mode;
a gas storage unit for storing a gas containing nitrogen and hydrogen; and
and an ammonia synthesizing device for generating ammonia using hydrogen in exhaust gas discharged from the anode of the fuel cell and nitrogen and hydrogen supplied from the gas storage unit. 6. The method of claim 5,
The fuel cell system, further comprising a heat exchanger for heating the water supplied to the anode of the fuel cell to exhaust gas discharged from the anode. 7. The method of claim 6,
The fuel cell system, further comprising a water discharge unit for separating water from the exhaust gas that has passed through the heat exchanger. 8. The method of claim 7,
Further comprising a compressor disposed between the water discharge unit and the ammonia synthesis device,
The fuel cell system is configured to compress the exhaust gas in the compressor and then transfer it to the ammonia synthesis device. 8. The method of claim 7,
The fuel cell system, further comprising an ammonia storage unit for storing the ammonia generated in the ammonia synthesis device. 10. The method of claim 9,
The fuel cell is configured to be operable even in a fuel cell mode,
The fuel cell system is configured to supply ammonia stored in the ammonia storage unit to the anode of the fuel cell when the fuel cell system operates in the fuel cell mode. 11. The method of claim 10,
and transferring the exhaust gas passing through the water discharge unit to the gas storage unit when the fuel cell system operates in the fuel cell mode.

Images