KR20220042015A - Ammonia-based fuel cell system with continuous operation - 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; and a first heat exchanger for heating ammonia that is fuel of the fuel cell with a first exhaust gas discharged from the fuel electrode of the fuel cell, wherein hydrogen in the first exhaust gas passed through the first heat exchanger is re-supplied to the fuel electrode.

Description

Ammonia-based fuel cell system with continuous operation

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 provide an ammonia-based fuel cell system that uses ammonia as a fuel and is capable of continuous operation in at least one of a fuel cell mode and a water electrolysis mode.

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; and a first heat exchanger configured to heat ammonia, which is a fuel of the fuel cell, with the first exhaust gas discharged from the anode of the fuel cell, wherein hydrogen in the first exhaust gas that has passed through the first heat exchanger is recycled to the anode. A fuel cell system configured to supply is provided.

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 first heat exchanger for heating ammonia, which is a fuel of the fuel cell, with a first exhaust gas discharged from the anode of the fuel cell; and an ammonia synthesizing device for generating ammonia using hydrogen in the first exhaust gas that has passed through the first heat exchanger and nitrogen supplied from the outside; provides a fuel cell system including a.

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 extracts hydrogen from the anode exhaust gas during fuel cell mode operation and supplies it back to the fuel cell, and during water electrolysis mode operation, extracts hydrogen from the anode exhaust gas and uses it for ammonia synthesis. Efficient system operation is possible by reusing hydrogen in exhaust gas without throwing away even if it operates in any mode of the solution 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 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 is 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, the fuel cell system according to an embodiment includes an ammonia storage unit 10 , a fuel cell 20 , a plurality of heat exchangers 31 to 35 , a water discharge unit 40 , and an ammonia synthesis device 60 . , the turbine 70 , the gas extraction unit 80 , and a plurality of flow paths connecting these components, a blower, a pump, and the like.

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

The fuel cell 20 includes an anode, an air electrode, 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 20 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 20 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 20 may be a unidirectional fuel cell rather than a bidirectional fuel cell. In this case, the fuel cell 20 may operate only in the fuel cell mode or only in the water electrolysis mode.

In the illustrated embodiment, ammonia is supplied from the ammonia storage unit 10 to the fuel cell 20 through the supply passage L1. Ammonia supplied to the fuel cell 20 may be vaporized in the first heat exchanger 31 and supplied to the anode 21 of the fuel cell 20 . The first heat exchanger 31 is configured to exchange heat between the exhaust gas discharged from the anode 21 of the fuel cell 20 and ammonia supplied to the anode 21 of the fuel cell 20 .

In an alternative embodiment, the fuel cell system may further include a second heat exchanger 32 . The second heat exchangers 32 and 32 ′ are disposed on the upstream side of the first heat exchanger 31 on the supply path L1 for supplying ammonia to the fuel cell 20 and convert ammonia to the anode exhaust gas of the fuel cell. can be vaporized. Although it is shown in the drawing as if there are two second heat exchangers 32 and 32', this is for a simplified representation of the drawing, and the second heat exchangers 32 and 32' are disposed between the anode exhaust gas and ammonia in the supply flow path L1. It will be understood that it can be implemented as a single component that conducts heat exchange of

In an alternative embodiment, the fuel cell system may further include a turbine 70 . The turbine 70 may be disposed between the first heat exchanger 31 and the second heat exchanger 32 on the supply path L1, and converts the energy of the high-pressure ammonia gas vaporized in the second heat exchanger 32. can be used to generate mechanical work in the turbine 70 .

Steam is supplied to the fuel cell 20 through the supply passages L4 and L5. 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 20 through the supply passages L5 and L1 . At this time, an ammonia synthesizing device 60 is used as in the illustrated embodiment to vaporize water. That is, water can be vaporized by using high-temperature thermal energy generated in the ammonia synthesis device 60 . In an alternative embodiment, the fuel cell system 20 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 one embodiment, the fuel cell system receives additional supply of water or steam supplied from outside the system in addition to the supply passages L4 and L5. It may include more Euros. In the case of the illustrated embodiment, the fuel cell system further includes first to third additional supply passages L11, L12, and L13, and if necessary, at least one of the first to third additional supply passages L11, L12, and L13. Steam may be additionally supplied to the fuel cell 20 by using it.

The anode exhaust gas discharged from the anode 21 of the fuel cell 20 is transported along the discharge flow path L2 to the first heat exchanger 31 , the second heat exchanger 32 , and the third heat exchanger 33 . pass through sequentially. The exhaust gas from the first heat exchanger 31 transfers thermal energy to ammonia supplied to the anode 21 through the supply passage L1 to heat or vaporize the ammonia. Also in the second heat exchanger 32 , the anode exhaust gas may heat or vaporize ammonia. In the third heat exchanger 33 , the anode exhaust gas may heat water by transferring thermal energy to water supplied from the outside through the second additional supply passage L12 .

In an embodiment, the fuel cell system may further include a recirculation flow path L10 and a blower 93 installed therein, and some of the anode exhaust gas passing through the first to third heat exchangers 31 , 31 , 33 is It is re-supplied to the anode 21 through the recirculation passage L10. For example, when operating in the water electrolysis mode, hydrogen and water (steam) are discharged as an anode exhaust gas from the anode 21, and a part of this exhaust gas is branched into the recirculation flow path L10 to convert hydrogen in the exhaust gas to the anode 21 ) can be resupplied.

The anode exhaust gas cooled while passing through the first to third heat exchangers 31 , 32 , and 33 is transferred to the water discharge unit 40 . The water discharge unit 40 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. The anode exhaust gas passing through the water discharge unit 40 may be transferred along the discharge passage L2 and sequentially supplied to the compressor 50 and the ammonia synthesis device 60 . The compressor 50 compresses the anode exhaust gas to a pressure of, for example, 10 bar to 20 bar, and supplies the compressed exhaust gas to the ammonia synthesis device 60 . However, the numerical value of the pressure is exemplary, and the pressure may vary according to a specific embodiment of the present invention.

The ammonia synthesizing device 60 may generate ammonia by using the anode exhaust gas, and the ammonia generated in the ammonia synthesizing device 60 is transferred to and stored in the ammonia storage unit 10 along the flow path L3 . In an embodiment, the ammonia synthesis apparatus 60 may be a Haber-Bosch reactor that receives hydrogen (H2) and nitrogen (N2) and generates ammonia (NH3) therefrom, but is not limited thereto, and the anode electrode It may be any synthesizer capable of synthesizing ammonia using the exhaust gas.

Meanwhile, the anode exhaust gas discharged from the water discharge unit 40 is configured to communicate with the gas extraction unit 80 through the flow path L6 . The gas extraction unit 80 may extract nitrogen from the supplied gas, and may be implemented as, for example, a pressure shift adsorber (PSA). In the fuel cell mode, the gas extractor 80 receives the anode exhaust gas through the flow path L6 and separates it into nitrogen and hydrogen, and may re-supply the separated hydrogen to the anode 21 through the flow path L7 . In the water electrolysis mode, the gas extractor 80 may receive air, separate nitrogen, and supply the separated nitrogen to the anode discharge passage L2 through the passage L6.

In one embodiment, one gas extractor 80 may operate in the fuel cell mode and the water electrolysis mode as described above. In an alternative embodiment, the gas extraction unit 80 may be composed of a plurality of PSA devices of different types, and any one PSA device may operate according to each mode. For example, the gas extraction unit 80 is composed of a PSA device for hydrogen extraction, a PSA device for nitrogen extraction, and a valve for switching a flow path between the two, and the PSA device for hydrogen extraction and the PSA device for nitrogen extraction are alternately configured according to mode conversion It can also be configured to work.

In one embodiment, the fuel cell system includes an air supply passage L9 for supplying external air to the cathode 22 of the fuel cell, and at least one blower 92 and a fourth heat exchanger 34 installed in this passage. . The cathode exhaust gas discharged from the cathode 22 of the fuel cell 20 passes through the fourth heat exchanger 34 and is discharged to the outside through the discharge passage L8, in which case the fourth heat exchanger 34 is air Heat is exchanged between the air transferred to the cathode 22 along the supply passage L9 and the cathode exhaust gas discharged from the cathode 22 and transferred along the discharge passage L8 .

In an embodiment, a fifth heat exchanger 35 may be further installed on the downstream side of the fourth heat exchanger 34 on the discharge flow path L8, and the cathode exhaust gas in the fifth heat exchanger 35 is added to the first Water supplied along the supply passage L11 may be heated and vaporized. In addition, in an alternative embodiment, the heat discharged from the fifth heat exchanger 35 may be additionally used. For example, the cathode exhaust gas heated by the air in the fourth heat exchanger 34 is supplied with fuel or water in the fuel supply passage L1 or the water supply passage L4 through the fifth heat exchanger 35 or another additional heat exchanger. It can be used in addition to vaporizing.

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 20 through the fuel supply passage L1 in the fuel cell mode. For example, liquid ammonia stored in the storage unit 10 in a state of about 11 bar liquid may be transferred along the supply passage L1 and vaporized in the second heat exchanger 32 . The vaporized high-pressure ammonia gas may be used to generate predetermined mechanical energy in the turbine 70 , and the ammonia gas passing through the turbine 70 is further heated in the first heat exchanger 31 and then the fuel cell 20 . may be supplied to the anode 21 of In an alternative embodiment, the turbine 70 and the second heat exchanger 32 may be omitted, in which case the liquid ammonia is vaporized in the first heat exchanger 31 and then supplied to the fuel cell 20 .

Meanwhile, the blower 92 of the air supply passage L9 operates to supply external air to the cathode 22 of the fuel cell 20 . The air transferred to the air supply passage L9 may be heated in the fourth heat exchanger 34 and then injected into the cathode 22 .

In the fuel cell mode, the anode 21 of the fuel cell 20 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 22 discharges nitrogen and unreacted air as cathode exhaust gas through the discharge passage L8.

The anode exhaust gas discharged from the anode 21 sequentially passes through the first and second heat exchangers 31 and 32 to heat and vaporize ammonia in the supply passage L1. Thereafter, water is removed from the water discharge unit 40, and accordingly, hydrogen and nitrogen are the main components of the anode exhaust gas. The anode exhaust gas is supplied to the gas extraction unit 80 along the flow path L6, and the gas extraction unit 80 separates hydrogen and nitrogen. The separated nitrogen may be discharged to the outside, and the separated hydrogen may join the ammonia supply flow path L1 through the flow path L7, and accordingly, is re-supplied to the anode 21. Therefore, according to the embodiment of the present invention, hydrogen from the anode exhaust gas can be extracted and re-supplied to the fuel cell 20 in the fuel cell mode, so that unreacted and discharged hydrogen from the fuel cell 20 can be minimized.

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, in the water electrolysis mode, water is transferred into the system through the water supply passage L4 and the transferred water is vaporized into steam using the heat of the ammonia synthesis device 60 . The vaporized steam joins the supply flow path L1 along the flow path L5 and is then supplied to the anode 21 of the fuel cell 20 . At this time, since the ammonia storage unit 10 and the supply passage L1 are closed by means such as a valve, only steam can be supplied to the anode 21 . Since a lot of steam is required in the water electrolysis mode, steam may be received through the first to third additional supply passages L11, L12, and L13 according to circumstances. In addition, air is supplied to the cathode 22 through the air supply passage L9.

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 21 through the discharge passage L2 , and the cathode exhaust gas is also discharged from the cathode 22 through the discharge passage L8 . ) is released through

The anode exhaust gas discharged to the discharge passage L2 sequentially passes through the first heat exchanger 31 and the third heat exchanger 33 to heat water or steam to be supplied to the fuel cell, and then to the water discharge unit 40 ) is transferred to A portion of the anode exhaust gas is branched into the recirculation passage L10 before being transferred to the water discharge unit 40 . Even in the water electrolysis mode, it is necessary to supply a small amount of hydrogen to the anode 21. Since hydrogen in the exhaust gas can be supplied to the anode 21 by branching and recirculating some of the exhaust gas through the recirculation passage L10, separate hydrogen The advantage is that there is no need to supply.

Since the anode exhaust gas is mainly composed of hydrogen and steam, when steam is condensed and removed in the water discharge unit 40 , the anode exhaust gas becomes a hydrogen-based gas and is then supplied to the compressor 50 . On the other hand, nitrogen can be extracted by supplying air to the gas extraction unit 80, and the extracted nitrogen joins the discharge path L2 on the downstream side of the water discharge unit 40 through the flow path L6, so that hydrogen and nitrogen A mixed gas containing as a main component is supplied to the compressor 50 . The compressor 50 compresses the mixed gas and then supplies it to the ammonia synthesizing device 60 , and the ammonia synthesizing device 60 generates ammonia using the supplied mixed gas of hydrogen and nitrogen.

Ammonia generated in the ammonia synthesizing device 60 is supplied to and stored in the ammonia storage unit 10 along the flow path L3, and also a water supply path using high-temperature heat generated during the operation of the ammonia synthesizing device 60. The water of (L4) can be heated to vaporize.

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 20, so that there is no need to provide a separate path for hydrogen supply. There is an advantage, and ammonia can be produced after nitrogen is mixed with hydrogen extracted from the anode exhaust gas.

Therefore, when the fuel cell system of the present invention is used as a bidirectional fuel cell system, electricity is generated by using ammonia as a fuel in the fuel cell mode, and ammonia can be regenerated and stored in the ammonia storage unit 10 in the water electrolysis mode. It is possible to implement a bidirectional fuel cell system that can continuously operate alternately between the cell mode and the water electrolysis mode.

In addition, from the perspective of hydrogen recirculation, when operating in fuel cell mode, hydrogen from anode exhaust gas is extracted and re-supplied to the fuel cell. During water electrolysis mode, hydrogen from anode exhaust gas is extracted and used for ammonia synthesis. Efficient system operation is possible by reusing hydrogen in exhaust gas without throwing away even if it operates in any of the modes.

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: ammonia storage unit 20: fuel cell
31 to 35: heat exchanger 40: water outlet
50: compressor 60: ammonia synthesis device
70: turbine 80: gas extraction unit

Claims (9)

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; and
a first heat exchanger configured to heat ammonia, which is a fuel of the fuel cell, by using ammonia supplied to the anode of the fuel cell as exhaust gas discharged from the anode; and
and re-supply hydrogen in the exhaust gas that has passed through the first heat exchanger to the anode. The method of claim 1,
a water discharge unit for separating water from the first exhaust gas that has passed through the first heat exchanger; and
The fuel cell system further comprising a; gas extraction unit for separating nitrogen and hydrogen from the exhaust gas. 3. The method of claim 2,
a second heat exchanger disposed upstream of the first heat exchanger in a supply path for supplying ammonia to the fuel cell and vaporizing ammonia as exhaust gas; and
The fuel cell system of claim 1 , further comprising a turbine disposed between the first heat exchanger and the second heat exchanger in the supply path. The method of claim 1,
The fuel cell system, further comprising a heat exchanger for heating the air to be supplied to the fuel cell with the exhaust gas discharged from the cathode of the fuel cell. 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 first heat exchanger for heating water supplied to the anode of the fuel cell with exhaust gas discharged from the anode; and
An ammonia synthesizing device for generating ammonia using hydrogen in the exhaust gas that has passed through the first heat exchanger and nitrogen supplied from the outside; the fuel cell system comprising a. 6. The method of claim 5,
The fuel cell system, further comprising a water discharge unit for separating water from the exhaust gas that has passed through the first heat exchanger. 7. The method of claim 6,
Further comprising a compressor disposed between the water discharge unit and the ammonia synthesis device,
The fuel cell system is configured to compress hydrogen and the nitrogen in the exhaust gas in the compressor and then supply it to the ammonia synthesis device. 6. The method of claim 5,
The fuel cell is configured to be operable even in a fuel cell mode,
and supplying ammonia generated in the ammonia synthesis device to the first heat exchanger side when the fuel cell system operates in the fuel cell mode. 9. The method of claim 8,
When the fuel cell system operates in the fuel cell mode, hydrogen in the exhaust gas that has passed through the first heat exchanger is supplied to the first heat exchanger and is not supplied to the ammonia synthesis device.

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