KR102500283B1 - Reversible fuel cell system for preventing negative pressure by using hydrogen generated from fuel cell - Google Patents

Abstract

According to one embodiment, a discharge passage for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit; a high-temperature hydrogen pump installed in the discharge passage to electrochemically separate hydrogen from the fluid discharged from the hydrogen electrode; and a buffer tank storing hydrogen separated from the high-temperature hydrogen pump. A water electrolysis system is disclosed, wherein a portion of the hydrogen stored in the buffer tank is provided to the discharge passage when the pressure of the discharge passage is equal to or less than a reference pressure.

Description

Reversible fuel cell system for preventing negative pressure by using hydrogen generated from fuel cell}

The present invention relates to a bidirectional water electrolysis system and an operating method thereof for preventing generation of negative pressure using hydrogen generated from a fuel cell.

Recently, research on a power generation system using renewable energy such as solar light or wind power is being conducted. In the case of a power generation system using renewable energy, since the electrical output varies according to the natural environment, it is necessary to study how to store and use it when surplus power exceeds the amount of power demanded. For example, if surplus power is generated from a renewable energy power generation facility, hydrogen is produced and stored using a water electrolysis device, and when the amount of power generation is small, a system that can produce and supply power from a fuel cell using the stored hydrogen has been researched. It is becoming.

The reversible (two-way) water electrolysis system based on high-temperature water electrolysis and fuel cell technology requires an operating environment of 700 ° C or higher and a heat source to generate high-temperature water vapor. Therefore, it is necessary to improve system efficiency by maintaining the operating environment of the water electrolysis system at a high temperature and effectively utilizing exhaust heat discharged from the water electrolysis system.

In addition, a number of devices, including a compressor, are used to store hydrogen produced in the electrolysis mode. These devices are complex and difficult to control, and the risk of explosion due to air inflow during compression prevents water electrolysis. It is difficult to control and needs to be addressed.

Patent Document 1: Republic of Korea Patent Registration No. 10-0776353 (Announced on November 07, 2007) Patent Document 2: Republic of Korea Patent Registration No. 10-1340492 (Announced on December 11, 2013)

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a bidirectional water electrolysis system and an operating method thereof for preventing generation of negative pressure using hydrogen generated from a fuel cell.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a bidirectional water electrolysis system capable of improving system efficiency and increasing capacity by efficiently utilizing thermal energy of the bidirectional water electrolysis system.

According to one embodiment of the present invention, a discharge passage for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit; a high-temperature hydrogen pump installed in the discharge passage to electrochemically separate hydrogen from the fluid discharged from the hydrogen electrode; and a buffer tank storing hydrogen separated from the high-temperature hydrogen pump. A water electrolysis system is disclosed, wherein a portion of the hydrogen stored in the buffer tank is provided to the discharge passage when the pressure of the discharge passage is equal to or less than a reference pressure.

According to another embodiment of the present invention, a heat exchanger installed in the discharge passage for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit; and a compressor installed downstream of the heat exchanger. and when the pressure of the discharge passage is equal to or less than the reference pressure, a part of the exhaust gas discharged from the compressor is provided to the discharge passage.

According to another embodiment of the present invention, as a method of operating a water electrolysis system,

In the water electrolysis mode, monitoring the pressure of the discharge passage for discharging the fluid from the hydrogen electrode of the water electrolysis unit; compressing the fluid discharged from the discharge passage; and providing a fluid for pressure control when the pressure in the discharge passage is equal to or less than the reference pressure, wherein the step of providing the fluid for pressure control includes compressing a portion of the fluid compressed in the compressing step. Disclosed is a method of operating a water electrolysis system, which is provided as the discharge passage before being compressed by.

According to one or more embodiments of the present invention, when hydrogen is compressed in the water electrolysis mode, the risk of explosion due to air inflow according to the negative pressure of the suction line and the pressure of the water electrolysis stack due to the fluctuation of the suction pressure of the compressor are easily controlled effect was achieved.

According to one or more embodiments of the present invention, in the water electrolysis mode, some of the exhaust gas discharged from the hydrogen electrode of the fuel cell is configured to be re-supplied to the hydrogen electrode, and in the fuel cell mode, some of the exhaust gas is recycled to the hydrogen electrode. By configuring to supply, the effect of improving system efficiency was achieved.

According to one or more embodiments of the present invention, electricity can be generated using ammonia as fuel in the fuel cell mode, and ammonia can be regenerated and stored in the ammonia storage unit in the water electrolysis mode, so that the fuel cell mode and the water electrolysis mode can be continuously operated. It can work.

According to one or more embodiments of the present invention, hydrogen and nitrogen of the anode exhaust gas are stored in the gas storage unit during the fuel cell mode operation, and hydrogen from the anode exhaust gas is extracted and mixed with the gas of the gas storage unit during the water electrolysis mode operation to ammonia. Since it is used for synthesis, it is possible to operate the system efficiently by reusing the exhaust gas from the anode without discarding it, regardless of whether it operates in either the fuel cell mode or the water electrolysis mode.

1 is a diagram for explaining a bi-directional water electrolysis system according to a first embodiment of the present invention.
Fig. 2 is a diagram for explaining the water electrolysis mode of the first embodiment.
3 is a diagram for explaining a bi-directional water electrolysis system according to a second embodiment.
4 is a diagram for explaining a bi-directional water electrolysis system according to a third embodiment of the present invention.
Fig. 5 is a diagram for explaining the fuel cell mode of the third embodiment.
Fig. 6 is a diagram for explaining the water electrolysis mode of the third embodiment.
7 is a diagram for explaining an operating method in a water electrolysis system according to an embodiment of the present invention.

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 content will be thorough and complete and the spirit of the present invention will be sufficiently conveyed to those skilled in the art.

Definition of Terms

In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. The terms 'comprise' and/or 'comprising' used in the specification do not exclude the presence or addition of one or more other elements.

In the present specification, when a certain element (hereinafter referred to as 'component A') is located 'upstream' of any other element (hereinafter referred to as 'component B'), gas or liquid It means that component A and component B are located on the flow path through which the fluid flows, and component A is arranged to receive the fluid first before component B.

In the present specification, when a component is installed or connected to a flow path, it means that the component is operatively coupled to the flow path to affect the flow of fluid flowing in the flow path. For example, components operatively coupled to a flow path may include steam generators, ejectors, water electrolyzers, heaters, other flow paths, heat exchangers, valves, blowers, and pumps; Elements, for example, block the flow of a fluid, allow the flow of a fluid or change the pressure of a fluid, divert or filter a portion of a fluid, physically or chemically change a fluid, or temporarily store a fluid. Alternatively, it may be thermally coupled with the fluid, or coupled with the flow path to operate to join the fluid from the outside.

Hereinafter, the present invention will be described in detail with reference to the drawings. In describing specific embodiments below, a number of specific details have been prepared to more specifically describe the invention and aid understanding. However, readers who have knowledge in this field to the extent that they can understand the present invention can recognize that it can be used without these various specific details. In some cases, it is mentioned in advance that parts that are commonly known in describing the invention and are not greatly related to the invention are not described to prevent confusion in describing the present invention.

The present invention can be applied to various types of water electrolysis systems. For example, a water electrolysis system such as an alkaline water electrolysis system, a polymer electrolyte membrane (PEM) water electrolysis system, a solid oxide water electrolysis system, or an anion exchange membrane (AEM) water electrolysis system. The present invention can be applied to. In addition, the present invention can be applied to a bidirectional water electrolysis system having both a water electrolysis mode and a fuel cell mode. That is, the present invention is applied to various types of water electrolysis systems by injecting and supplying hydrogen to a hydrogen low-pressure line generated and moved by water electrolysis, so that explosions due to air inflow or the like according to the negative pressure of the suction line during hydrogen compression It is possible to easily control the pressure of the water electrolysis stack due to the risk or the suction pressure fluctuation of the compressor. Therefore, in the present specification, the term 'water electrolysis system' refers to an alkaline water electrolysis system, a polymer electrolyte membrane (PEM) water electrolysis system, a solid oxide water electrolysis system, or an anion exchange membrane (AEM) water electrolysis system. ) It will be used in the sense of including both the water electrolysis system and the bidirectional water electrolysis system.

Hereinafter, the present invention has been mainly described in embodiments in which the present invention is applied to a bidirectional water electrolysis system, but these are exemplary. It can also be applied to various water electrolysis systems such as a solid oxide water electrolysis system or an anion exchange membrane (AEM) water electrolysis system.

1 is a diagram for explaining a bi-directional water electrolysis system according to a first embodiment of the present invention.

Referring to the drawings, the water electrolysis system of the first embodiment includes components such as a steam generator 10, an ejector 20, a water electrolysis unit 30, heaters 61 and 62, and a high-temperature hydrogen pump 80. It may include a plurality of flow passages connecting components, and a plurality of heat exchangers, valves, blowers, and pumps disposed in the passages.

According to the first embodiment, the water electrolysis unit 30 is a bidirectional water electrolysis fuel cell capable of operating in a water electrolysis mode and a fuel cell mode, and when the water electrolysis unit 30 operates in the water electrolysis mode, the 'water electrolysis unit ( 30)', and when operating in the fuel cell mode, it will be referred to as 'the fuel cell 30'. This is the same in other embodiments as well.

The operation of components included in the first embodiment may be controlled by a controller (not shown). For example, the control unit (not shown) includes the steam generator 10, the water electrolysis unit 30, the heaters 61 and 62, the high-temperature hydrogen pump 80, heat exchangers, valves, blowers, and pumps. You can control the action. Among the plurality of valves described above, a pressure control valve 18 for regulating the pressure of the water electrolysis stack is included in order to prevent the risk of explosion due to air flowing into the discharge passage L41 under negative pressure during hydrogen compression. there is. The pressure control valve 18 may be opened or closed by a control unit (not shown).

The water electrolysis unit 30 is a water electrolysis mode in which hydrogen and oxygen are generated by steam and electricity supplied from the outside and a fuel cell mode in which electricity and water are generated by a chemical reaction between hydrogen and oxygen supplied from the outside. mode can work.

In one embodiment, the water electrolysis unit 30 may be implemented with any fuel cell, such as, for example, a solid oxide fuel cell (SOFC) or a molten carbonate fuel cell (MCFC). For convenience of explanation, in this specification, it is assumed that the water electrolysis unit 30 is implemented as a solid oxide fuel cell (SOFC).

In one embodiment, the water electrolysis unit 30 may be composed of a hydrogen electrode 31, an air electrode 32, and an electrolyte interposed therebetween. In the water electrolysis mode (hereinafter also referred to as “SOEC mode”), the hydrogen electrode 31 receives steam (H 2 O) from the outside and produces hydrogen (H 2 ) therefrom. That is, the hydrogen electrode 31 generates hydrogen (H2) by receiving steam (H2O) from the flow path (L21 and/or L31), and the generated hydrogen (H2) and the steam (H2O) not converted to hydrogen are included. The resulting gas is discharged as the first exhaust gas through the flow path L41. In the water electrolysis mode, the air electrode 32 receives oxygen (O2) from the hydrogen electrode 31, and transports the oxygen (O2) received from the outside through the flow path L53 using air supplied from the outside. The cathode 32 discharges gas containing oxygen and air as the second exhaust gas through the flow path L61.

In the fuel cell mode, the hydrogen electrode 31 generates water (steam) by a chemical reaction between hydrogen supplied from the flow path L11 and oxygen transferred from the air electrode 32, and is not converted into steam and steam. A gas containing hydrogen may be discharged as an exhaust gas through the flow path L41. The air electrode 32 receives air through the flow path L53, transfers oxygen to the hydrogen electrode 31 through the electrolyte, and discharges nitrogen (N2) and air through the flow path L61 as the second exhaust gas. there is.

Theoretically, water (steam) and electricity are supplied to the fuel cell 30 in the water electrolysis mode, and hydrogen and oxygen are supplied to the fuel cell 30 in the fuel cell mode. It is preferable to supply a mixed gas of hydrogen and steam to the fuel cell 30 in each mode of the mode and the fuel cell mode. However, since steam is mainly required in the water electrolysis mode, a mixed gas of steam and hydrogen is supplied to the fuel cell 30 at a mass ratio of, for example, 80:1 (volume ratio of approximately 8.9:1), and hydrogen in the fuel cell mode. Since hydrogen and steam are mainly required, for example, hydrogen and steam may be mixed at a mass ratio of 3.6:1 (approximately a volume ratio of 32:1) and supplied to the fuel cell 30 . In this case, of course, the mixing ratio of hydrogen and steam in each of the water electrolysis mode and the fuel economy mode may vary depending on the specific embodiment. In addition, in order to adjust and supply the mixing ratio of hydrogen and steam differently according to each mode, for example, a blower and a pump in at least one of the hydrogen supply passage L11 and the steam supply passage L21, L22, and L31, although not shown in the drawing. , and / or a flow control valve may be installed to adjust the supply amount of hydrogen and / or steam.

In the illustrated embodiment, hydrogen is supplied to the fuel cell 30 through the hydrogen supply passage L11. The hydrogen supply passage L11 may be connected to, for example, a hydrogen storage tank (not shown). Hydrogen introduced into the hydrogen supply passage L11 may be heated in the first heat exchanger 41 . The first heat exchanger 41 is configured to exchange heat between hydrogen gas supplied to the hydrogen electrode 31 of the fuel cell 30 and exhaust gas discharged from the hydrogen electrode 31 . In one embodiment, the hydrogen supplied to the hydrogen electrode 31 may be room temperature or 35 to 45 degrees Celsius, and the exhaust gas discharged from the hydrogen electrode 31 may be 700 to 750 degrees Celsius, in which case the hydrogen electrode Hydrogen supplied to (31) may be heated to, for example, 650 degrees Celsius or more in the first heat exchanger (41).

In the illustrated embodiment, steam is supplied to the fuel cell 30 through the first steam supply passage L21 and the second steam supply passage L31. The steam generator 10 connected to the first steam supply passage L21 may include, for example, a pump 11 and a boiler 12, and heats water supplied to the boiler 12 by the pump 11. create steam In one embodiment, the boiler 12 may be implemented as an existing combustion device or incinerator, such as a waste solid fuel boiler system, a combined heat and power system, a combined power generation system, and a waste incineration system.

The first steam supply passage L21 includes a branch passage L22. As shown, the branch flow path L22 is configured to diverge from the first steam supply flow path L21 and join the flow path L121 again. An on/off valve 13 may be installed in the branched flow path L22, and although not shown in the drawing, an on/off valve may also be installed on the first steam flow path L121, and steam is supplied to the first steam supply flow path by control of the valve. (L21) and branch flow path (L22) can be controlled to flow. Alternatively, steam flow may be controlled by installing a three-way valve at a branching point where the branched flow path L22 diverges.

In one embodiment, the bidirectional water electrolysis system includes an ejector 20 disposed in the first steam supply passage L21. The ejector 20 is a device for mixing fluids using a Venturi effect, and the diameter of the pipe In general, the input end of the ejector 20 is a motive nozzle, the output end is a diffuser nozzle, and an inlet for inputting the fluid to be mixed is used. Referred to as a suction port, in the illustrated embodiment, the drive nozzle of the ejector 20 is connected to the upstream side of the first steam supply passage L21 and the injection nozzle is the downstream side of the first steam supply passage L21 and the inlet is connected to the feedback passage L47, which is a passage diverging from the discharge passage L41 through which the exhaust gas of the hydrogen electrode 31 flows.

In general, the volume ratio of steam and hydrogen injected into the hydrogen electrode 31 in the water electrolysis mode is about 9:1, and since the exhaust gas discharged from the hydrogen electrode 31 has a high hydrogen content, If some of the exhaust gas is recycled, there is no need to separately supply hydrogen through the hydrogen supply passage L11. At this time, the amount of exhaust gas recirculated through the feedback passage L47 can be adjusted by adjusting the pressure or flow rate of steam supplied to the drive nozzle of the ejector 20 (that is, transferred to the passage L121).

After the branch passage L22 joins the first steam supply passage L21, the first steam supply passage L21 joins the hydrogen supply passage L11, and the mixed gas of hydrogen and steam flows into the mixed gas supply passage L12. ) is supplied to the hydrogen electrode 31 of the fuel cell 30. At this time, the junction of the first steam supply passage L21 and the hydrogen supply passage L11 is located on the downstream side of the first heat exchanger 41, that is, between the first heat exchanger 41 and the hydrogen electrode 31. Therefore, the high-temperature exhaust gas discharged from the hydrogen electrode 31 only needs to heat hydrogen in the first heat exchanger 41 without the need to reheat steam already heated to a high temperature, compared to heating a mixed gas of hydrogen and steam. Hydrogen can be heated to higher temperatures.

The water electrolysis system of the present invention may further include a second steam supply passage L31. One or more pumps 15 and the second heat exchanger 42 are installed in the second steam supply passage L31. The pump 15 supplies water (hereinafter referred to as "external supply water") from the outside of the system by the pump 15 to the second heat exchanger 42, and the second heat exchanger 42 heats the external supply water. .

In one embodiment, the second heat exchanger 42 is configured to exchange heat between the externally supplied water and the exhaust gas discharged from the hydrogen electrode 31, and when viewed from the flow of the exhaust gas, the first heat exchanger 41 ) is placed on the downstream side of In one embodiment, the externally supplied water may be room temperature or 35 to 45 degrees Celsius, and the exhaust gas supplied to the second heat exchanger 42 may be 700 to 750 degrees Celsius, in which case the second heat exchanger 42 The steam (externally supplied water vaporized) discharged from ) can be heated to, for example, 600 degrees Celsius or more.

The second steam supply passage 31 is configured to join the first steam supply passage L21 at the front end of the ejector 20 . Accordingly, the steam discharged from the second heat exchanger 42 is mixed with the steam in the first steam supply passage L21 and then injected into the drive nozzle side of the ejector 20 .

The first heater 61 is disposed on the mixed gas supply passage L12 adjacent to the inlet side of the hydrogen electrode 31 . The first heater 61 may heat the temperature of the mixed gas of hydrogen and steam within a predetermined temperature range so that the fuel cell 30 can operate in the water electrolysis mode and the fuel cell mode with optimum efficiency. In one embodiment, the first heater 61 may heat the mixed gas of hydrogen and steam to a temperature in the range of 650 degrees Celsius to 750 degrees Celsius. In addition, although not shown in the drawings, one or more temperature sensors are installed inside or at the front or rear of the first heater 61 to measure the temperature of the mixed gas and heat the mixed gas based on this.

According to this embodiment, an air supply passage L53 for supplying air from the outside to the cathode 32 and an air-exhaust gas heat exchanger 53 disposed in the passage L53 are included. The heat exchanger 53 exchanges heat between air transferred to the cathode 32 through the air supply passage 53 and exhaust gas discharged from the cathode 32 and transferred to the discharge passage L61.

A second heater 62 may be installed in the air supply passage 53 . The second heater 62 may be disposed on the air supply passage L53 adjacent to the air electrode 32 to heat air to a predetermined temperature range so that the fuel cell 30 operates with optimum efficiency. In one embodiment, the heat exchanger 53 heats room temperature air to about 650 to 700 degrees Celsius, and then the second heater 62 heats the air to about 700 to 750 degrees Celsius and supplies it to the cathode 32. can

In the illustrated embodiment, a first branch passage L51 and a second branch passage L52 arranged in parallel with each other are connected upstream of the air supply passage L53, and each branch passage L51 and L52 has a first branch passage L51 and L52. A blower 51 and a second blower 52 are installed. The second branch passage L52 is configured to transport a larger amount of air than the first branch passage L51. For example, the pipe of the second branch passage (L52) has a larger diameter than the pipe of the first branch passage (L51) so that the second blower (52) can supply more air than the first blower (51). It consists of In one embodiment, the second blower 52 has an air supply 5 to 15 times larger than the first blower 51 .

Water electrolysis mode requires a lot of water (steam) and electricity, and a relatively small amount of air, and fuel cell mode requires a lot of hydrogen and oxygen (air), so the air supply must be large. Therefore, in one embodiment, only the first blower 51 is driven in the water electrolysis mode, the second blower 52 is not driven, and only the second blower 52 is driven and the first blower 51 is driven in the fuel cell mode. I never do that. In an alternative embodiment, both the first and second blowers 51 and 52 may be driven in fuel cell mode.

Meanwhile, the exhaust gas discharged from the hydrogen electrode 31 of the fuel cell 30 is discharged to the outside along the exhaust flow path L41. In one embodiment, the first heat exchanger 41 and the second heat exchanger 42 are sequentially installed along the discharge passage L41. In the first heat exchanger 41, the exhaust gas transfers heat energy to hydrogen supplied to the hydrogen electrode 31 through the hydrogen supply passage L11 to heat the hydrogen. In the second heat exchanger 42, the exhaust gas vaporizes and heats externally supplied water supplied through the second steam supply passage L31.

In the illustrated embodiment, the water discharge unit includes a high-temperature hydrogen pump 80, a heat exchanger 82, a buffer tank 83, and a gas-liquid separator 84.

The high-temperature hydrogen pump 80 may electrochemically separate hydrogen from exhaust gas. The high-temperature hydrogen pump 80 receives the exhaust gas in a gaseous state, separates the hydrogen, and discharges the remainder in a gaseous state.

The buffer tank 83 may receive and temporarily store hydrogen discharged from the high-temperature hydrogen pump 80 . A part of the hydrogen stored in the buffer tank 83 may be supplied to the discharge passage L41, and the rest may be moved to a hydrogen storage device (not shown) and stored.

The high-temperature hydrogen pump 80 may include an anode, a cathode, and a cell having a high-temperature and low-hydration exchange membrane. Here, the exchange membrane may be a polymer electrolyte membrane (PEM). Hydrogen diffuses through the polymer electrolyte membrane by the potential difference between the anode and cathode located on either side of the electrolyte. The high-temperature hydrogen pump 80 may be disclosed in, for example, US Patent Application No. 10/360,583 (Publication No. 2003/0196893) and US Patent Application No. 11/730,255. Meanwhile, all contents contained in these patent applications are combined as part of the present specification.

Hydrogen is separated in the high-temperature hydrogen pump 80, and the remaining gas passes through the heat exchanger 82 and flows into the gas-liquid separator 84. Water and gas are separated in the gas-liquid separator 84, and the separated water and gas may be discharged to the outside. Meanwhile, although not shown in the drawing, a portion of hydrogen stored in the buffer tank 83 may be supplied to the recirculation passage L44. That is, in the water electrolysis mode, a part of the hydrogen stored in the buffer tank 83 is provided to the pressure control flow path L81 when a predetermined standard is satisfied, and a part of the hydrogen stored in the buffer tank 83 is provided to the recirculation flow path ( L44) can be supplied. As such, the hydrogen stored in the buffer tank 83 is supplied to the pressure control passage L81 and the recirculation passage L44, and the remaining hydrogen is stored in a hydrogen storage device (not shown). This configuration is equally applied to the embodiment of FIG. 3 .

Meanwhile, in the fuel cell mode, at least a portion of the gas separated in the gas-liquid separator 84 is recirculated to the recirculation passage L44 and re-supplied to the hydrogen electrode 31, and in the water electrolysis mode, the recirculation passage L44 is closed. can do.

In the illustrated embodiment, the third heat exchanger 43 and the blower 45 may be installed in the recirculation passage L44. Preferably, the third heat exchanger 43 and the blower 45 are sequentially installed from the upstream to the downstream of the recirculation passage L44.

The third heat exchanger 43 increases the temperature of the recirculated gas by exchanging heat between the exhaust gas of the discharge passage L41 and the recirculation gas of the recirculation passage L44. In one embodiment, the third heat exchanger 43 is a small heat exchanger that raises the temperature of the recycle gas to prevent condensation from occurring in the recycle gas. The recirculation gas branched into the recirculation passage L44 is a gas in a saturated state, and if even a little condensation occurs depending on the environment of the recirculation passage L44, devices such as the blower 45 at the rear end may be damaged. In addition, durability of the blower 45 may become a problem even when the recycle gas is heated to an excessively high temperature in the third heat exchanger 43 . Therefore, in a preferred embodiment of the present invention, a small heat exchanger 43 is installed at the front end (upstream side) of the blower 45 to slightly increase the temperature of the recycle gas and then transfer it to the blower 45. In one embodiment, the temperature of the recycle gas is increased by the third heat exchanger 43 in the range of 5 degrees to 25 degrees.

As such, the recycle gas passing through the third heat exchanger 43 and the blower 45 joins the hydrogen supply passage L11 and is heated together with the hydrogen gas to a high temperature in the first heat exchanger 41, and then the fuel cell 30 ) can be supplied to the hydrogen electrode 31.

In one embodiment of the present invention, part of the hydrogen stored in the buffer tank 83 is branched through the flow path L81 (hereinafter referred to as 'pressure control flow path'). According to this embodiment, a portion of the hydrogen stored in the buffer tank 83 is supplied to the discharge passage L41 through the pressure control passage L81 only when a predetermined criterion is satisfied. To this end, a pressure control valve 18 for allowing or blocking the flow of fluid is installed in the pressure control passage L81. The pressure control valve 18 may be opened to allow hydrogen to flow into the pressure control flow path L81 according to a predetermined criterion, or may be closed so that hydrogen does not flow and is blocked.

The predetermined criterion may be, for example, a pressure determined so that negative pressure (negative pressure) is not applied to the water electrolysis unit 30 .

In detail, the pressure control flow path L81 is connected to the discharge flow path L41, and thus, the hydrogen stored in the buffer tank 83 can be supplied to the discharge flow path L41 through the pressure control flow path L81.

According to one embodiment, the pressure control valve 18 is opened when the applied pressure of the fluid flowing in the discharge passage L41 (hereinafter, 'pressure of the discharge passage L41') is less than or equal to the reference pressure, and if it is greater than the reference pressure, the pressure The control valve 18 is closed.

Although not shown in FIG. 1, a pressure sensor (not shown) for measuring the pressure applied to the discharge passage L41 is installed in the discharge passage L41.

The control unit (not shown) controls the opening or closing operation of the valve 18 for pressure control based on the detection result. In the water electrolysis mode, the pressure control valve 18 is opened when the pressure in the discharge passage L41 is less than the reference pressure, and the pressure control valve 18 is closed when the pressure in the discharge passage L41 is greater than the reference pressure.

In this embodiment, the location where the pressure control passage L81 is connected to the discharge passage L41 can be modified in various ways.

For example, the flow path L81 for pressure control is connected upstream of the heat exchanger 41, is connected between the heat exchanger 41 and the heat exchanger 42, or is connected between the heat exchanger 42 and the heat exchanger 43. can be connected between

Fuel cell (SOFC) mode

Referring now to FIG. 1, the operation of the fuel cell (SOFC) mode of the electrolytic system of the first embodiment will be described in more detail. In the fuel cell mode, hydrogen is supplied through the hydrogen supply passage L11 and a small amount of steam is supplied through the first steam supply passage L21. Hydrogen is heated by exchanging heat with the discharge gas of the discharge passage L41 in the first heat exchanger 41 and then supplied to the hydrogen electrode 31 . Steam is transported by bypassing the ejector 20 along the branch passage L22, and then joined with hydrogen and supplied to the hydrogen electrode 31 of the fuel cell 30 through the passage L12. In the fuel cell mode, since a relatively large amount of air is required, the second blower 52 operates and the first blower 51 does not operate to supply air to the cathode 32 . In an alternative embodiment, both the first and second blowers 51 and 52 may operate.

As the chemical reaction between hydrogen and oxygen occurs in the fuel cell 30, the first exhaust gas composed of steam and hydrogen is discharged from the hydrogen electrode 31 through the discharge passage L41 and flows into nitrogen and air from the cathode 32. The formed second exhaust gas is discharged through the discharge passage (L61).

The first exhaust gas heats hydrogen while passing through the first heat exchanger 41 . Since external supply water is not supplied in the fuel cell mode, the first exhaust gas passes through the second heat exchanger 42 without heat exchange and heats the recycle gas by exchanging heat with the recycle gas in the third heat exchanger 43. The first exhaust gas is then conveyed to the water outlet.

Water electrolysis (SOEC) mode

Now, with reference to FIG. 2, the water electrolysis mode operation of the water electrolysis system of the first embodiment will be described.

Fig. 2 shows the operating state of the water electrolysis (SOEC) mode of the water electrolysis system of the first embodiment. A flow path indicated by a thick line in the drawing is a flow path used in the water electrolysis mode.

Referring to the drawings, in the water electrolysis mode, steam is supplied through the first steam supply passage (L21), and externally supplied water is supplied through the second steam supply passage (L31) to convert the second heat exchanger (42) into steam. It is vaporized and joins the first steam supply passage (L21). The mixed steam is supplied to the hydrogen electrode 31 of the water electrolysis unit 30 through the flow path L12. In the water electrolysis mode, since a relatively small amount of air is required, the first blower 51 operates and the second blower 52 does not operate to supply air to the cathode 32 of the water electrolysis unit 30 .

As the water electrolysis reaction occurs in the water electrolysis unit 30, the first exhaust gas composed of hydrogen and steam is discharged from the hydrogen electrode 31 through the discharge passage L41, and the second exhaust gas composed of oxygen and air is discharged from the cathode 32. Exhaust gas is discharged through the discharge passage (L61).

A portion of the first exhaust gas discharged to the discharge passage L41 is branched from the feedback passage L47 and supplied to the inlet of the ejector 20, mixed with steam transported through the steam supply passage L121, and mixed with the hydrogen electrode ( 31) is supplied again. The remaining first exhaust gas that is not branched into the feedback passage 47 passes through the first heat exchanger 41 without heat exchange, and exchanges heat with externally supplied water in the second heat exchanger 42 to vaporize and heat the externally supplied water. . In the illustrated embodiment, the recirculation passage L44 is closed in the water electrolysis mode (that is, the valve 14 is closed), and therefore the first exhaust gas of the discharge passage L41 passes through the third heat exchanger 43 without heat exchange. and transferred to the water outlet. In the water discharge unit, hydrogen and water are separated, and hydrogen may be temporarily stored in the buffer tank 83 and then moved to a separate hydrogen storage device (not shown) for storage.

In the water electrolysis mode, the pressure control valve 18 is opened when the pressure in the discharge passage L41 is less than or equal to the reference pressure, and is closed when the pressure is greater than the reference pressure. When the valve 18 for pressure control is opened, part of the hydrogen stored in the buffer tank 83 is moved to the discharge passage L41.

By this operation, it is possible to prevent the risk of explosion due to air inflow or the like according to the negative pressure of the discharge passage L41 during hydrogen compression.

As described above, according to the first embodiment, an appropriate mixed gas of hydrogen and steam can be supplied to the fuel cell 30 according to each operation mode of the water electrolysis system. For example, since only a small amount of hydrogen is required in the water electrolysis mode, there is no need to supply hydrogen from the outside through the hydrogen supply passage L11 by using the hydrogen contained in the exhaust gas fed back through the feedback passage L47. Since a relatively small amount of air is required, only the first blower 51, which is a small blower, is driven to supply air. In the fuel cell mode, the exhaust gas is re-supplied through the recirculation passage L44 instead of the feedback passage L47, thereby minimizing hydrogen that is discarded without being reacted in the fuel cell 30. In addition, at this time, by bypassing the ejector 20 and supplying steam, it is possible to prevent the ejector 20 from interfering with the flow of steam, and a third heat exchanger is installed upstream of the blower 45 of the recirculation passage L44. By providing (43), damage to the blower (45) can be prevented.

Meanwhile, in the above-described first embodiment, the water electrolysis unit 30 is a bi-directional water electrolysis fuel cell capable of operating in a water electrolysis mode and a fuel cell mode, but this is an exemplary case and the present invention is a water electrolysis unit 30 It can also be applied to the case where is operated only in the water electrolysis mode, not in both directions. This is the same for the second embodiment as well as the first embodiment.

Now, with reference to FIG. 3, each bidirectional water electrolysis system according to the second embodiment will be described.

3 shows a bidirectional water electrolysis system according to a second embodiment. Referring to the drawings, the bidirectional water electrolysis system of the second embodiment includes a steam generator 10, an ejector 20, a water electrolysis unit 30, heaters 61 and 62, a high-temperature hydrogen pump 80, and a buffer tank ( 83) and the like, a plurality of flow passages connecting the components, and a plurality of heat exchangers, valves, blowers, and pumps disposed in the flow passages. Referring to Figure 3, the operation of the components included in the second embodiment can be controlled by a controller (not shown). For example, the control unit (not shown) includes the steam generator 10, the water electrolysis unit 30, the heaters 61 and 62, the high-temperature hydrogen pump 80, heat exchangers, valves, blowers, and pumps. You can control the action. For example, the control unit may control the opening or closing operation of the valves. According to the second embodiment, among the plurality of valves described above, a pressure control valve for adjusting the pressure of the water electrolysis stack in order to prevent the risk of explosion due to air inflow according to the negative pressure applied to the flow path L41 during hydrogen compression. (18) is included. The pressure control valve 18 may be opened or closed by a control unit (not shown).

Since the above-described components included in the second embodiment have the same or similar operations and configurations as those of the first embodiment, descriptions thereof are omitted.

Compared with the first embodiment of FIG. 1, the system of the second embodiment differs only in that it further includes a fourth heat exchanger 44 installed in the recirculation passage L44. The fourth heat exchanger 44 serves to heat the recycle gas by exchanging heat between the recycle gas and the first exhaust gas. From the point of view of the recirculation passage L44, the fourth heat exchanger 44 is located on the downstream side of the blower 45, and from the perspective of the discharge passage L41, the fourth heat exchanger 44 is the second heat exchanger. (42) and the third heat exchanger (43).

In the second embodiment, the third heat exchanger 43 is a small heat exchanger and can raise the temperature of the recycle gas by 5 to 20 degrees Celsius, and the fourth heat exchanger 44 can heat the recycle gas by at least 200 degrees Celsius. . For example, when the recycle gas branched to the recirculation flow path L44 is 30 to 40 degrees Celsius, the third heat exchanger 43 heats the recycle gas to 40 to 60 degrees Celsius to prevent condensation of the recycle gas, and the fourth The heat exchanger 44 can heat the recycle gas to between 250 and 300 degrees Celsius.

According to this embodiment, since the heat energy of the exhaust gas discharged from the first heat exchanger 41 is used once more in the fourth heat exchanger 44 to heat the recycle gas, waste heat recovery is possible. In addition, since the recycle gas heated once in the fourth heat exchanger 44 is mixed with hydrogen and then heated again in the first heat exchanger 41, the temperature of the mixed gas flowing through the mixed gas passage L12 is higher than that of the first embodiment. There is an advantage to further increase.

4 is a diagram for explaining a bi-directional water electrolysis system according to a third embodiment of the present invention, FIG. 5 is a diagram for explaining a fuel cell mode of the third embodiment, and FIG. 6 is a water electrolysis mode of the third embodiment. It is a drawing for explaining. The third embodiment has a configuration in which a fluid for pressure control is supplied to the discharge passage L102 in a bidirectional water electrolysis system in which ammonia is used as a fuel. Hereinafter, the third embodiment will be described in detail with reference to these drawings.

4 is a diagram for explaining a bi-directional water electrolysis system according to a third embodiment of the present invention.

Referring to the drawings, the bidirectional water electrolysis system according to the third embodiment includes a fuel cell 110, an ammonia storage unit 120, a gas storage unit 130, a water discharge unit 170, an ammonia synthesis device 180, And it may be composed of a plurality of flow passages, blowers, and pumps connecting between these components.

The fuel cell 110 is composed of 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 110 may generate electricity and water by a chemical reaction between ammonia and oxygen in a fuel cell mode and generate hydrogen and oxygen by steam and electricity in a water electrolysis mode. In one embodiment, the fuel cell 110 is a bidirectional water electrolysis fuel cell capable of operating in both a fuel cell mode and a water electrolysis mode. In an alternative embodiment, the fuel cell 110 may be a unidirectional fuel cell rather than a bidirectional fuel cell, in which case the fuel cell 110 may operate only in a fuel cell mode or in a water electrolysis mode.

The ammonia storage unit 120 stores ammonia (NH 3 ), which is a fuel of the fuel cell 110 . In one embodiment, the storage unit 120 may store ammonia in a liquid state, and may store ammonia liquid at a high pressure of 10 bar or more, for example.

In the illustrated embodiment, the ammonia storage unit 120 supplies ammonia to the fuel cell 110 through the supply passage L101. Ammonia supplied to the fuel cell 110 may be heated and vaporized in the first heat exchanger 161 and supplied to the fuel electrode 111 of the fuel cell 110 . The first heat exchanger 161 causes heat exchange between the exhaust gas discharged from the anode 111 of the fuel cell 110 to the discharge passage L102 and ammonia supplied to the anode 111 of the fuel cell 110. It consists of

In an alternative embodiment, the bi-directional water electrolysis system may further include a second heat exchanger 162. The second heat exchanger 162 is disposed upstream of the first heat exchanger 161 on the supply path L101 for supplying ammonia to the fuel cell 110 and is branched from the discharge path L102 to the first branch flow path ( Ammonia can be heated by the anode exhaust gas transported to L103).

In an alternative embodiment, the bi-directional water electrolysis system may further include a turbine 140. The turbine 140 may be disposed between the first heat exchanger 161 and the second heat exchanger 162 on the supply path L101, and the energy of the high-pressure ammonia gas vaporized in the second heat exchanger 162 It is possible to generate mechanical energy in the turbine 140 by using.

In the water electrolysis mode, the bidirectional water electrolysis system may supply steam to the fuel cell 110 through the water supply passage L107. For example, after water is supplied from the outside by the pump 191 and steam is generated by heating the water, the steam may be supplied to the fuel cell 110 through the supply passages L7 and L1. In the illustrated embodiment, heat generated in the ammonia synthesizer 180 may be used to heat and vaporize water. That is, water transported through the water supply passage L107 is vaporized using high-temperature thermal energy generated during the operation of the ammonia synthesizer 180, and then steam can be supplied to the fuel electrode 111 through the supply passage L101. there is. In an alternative embodiment, the fuel cell system 110 may vaporize water into steam using another heat source in the system.

Since the bidirectional water electrolysis system requires a large amount of water (steam) when operated in the water electrolysis mode, in one embodiment, the bidirectional water electrolysis system includes an additional water supply channel (L107) supplied with water or steam from the outside of the system. A supply passage may be further included. In the case of the illustrated embodiment, the bidirectional water electrolysis system further includes first and second additional supply passages L108 and L109, and steam using at least one of the first and second additional supply passages L108 and L109 as necessary. may be additionally supplied to the fuel cell 110.

The anode exhaust gas discharged from the anode 111 of the fuel cell 110 is transported along the discharge passage L102 and passes through the first heat exchanger 161, and the anode exhaust gas is supplied from the first heat exchanger 161. Thermal energy is transferred to ammonia supplied to the fuel electrode 111 through the flow path L101 to heat or vaporize the ammonia. In one embodiment, when the additional supply passage L108 for supplying water is installed, the third heat exchanger 163 may be installed in the discharge passage L102, and the anode exhaust gas is additionally supplied from the third heat exchanger 163. Water in the flow path L108 can be heated.

In one embodiment, the bidirectional water electrolysis system may further include a recirculation passage L121 connecting between the supply passage L101 and the discharge passage L102 and a blower 193 installed therein. In the illustrated embodiment, some of the anode exhaust gas passing through the first heat exchanger 161 and the third heat exchanger 163 may be re-supplied to the anode 111 through the recirculation passage L121. For example, when the bi-directional water electrolysis system operates in the water electrolysis mode, hydrogen and water (steam) are discharged from the fuel electrode 111 as fuel electrode exhaust gas, and some of the exhaust gas is branched into the recirculation passage L121, thereby reducing the amount of exhaust gas. Hydrogen may be re-supplied to the fuel electrode 111 .

The anode exhaust gas cooled while passing through the first and third heat exchangers 161 and 163 is transported to the water discharge unit 170 . The water discharge unit 170 is a device that separates and discharges water from exhaust gas, and may include, for example, a condenser, a drain, and a pump installed on a circulation path of a refrigerant that circulates through the condenser, a cooling device, and the like. Since the specific configuration of the water discharge unit is a well-known technology, description thereof will be omitted.

On the downstream side of the water discharge unit 170, the discharge passage L102 is branched into a first branch passage L103 and a second branch passage L104. In the bidirectional water electrolysis system of the present invention, the anode exhaust gas may be transported to one of the first branch passage L103 and the second branch passage L104 according to the fuel cell mode and the water electrolysis mode. For this branching operation, although not shown in the drawing, for example, one or more on-off valves or three-way valves may be installed on the branching points or the first and second branching passages L103 and L104.

In one embodiment, when the bidirectional water electrolysis system operates in the fuel cell mode, the second branch passage L104 is closed and the anode exhaust gas is transported through the first branch passage L103. A second heat exchanger 162 may be installed in the first branch flow passage L103, and in the second heat exchanger 162, the ammonia discharged from the anode may heat and vaporize ammonia transported from the ammonia storage unit 120. .

The anode exhaust gas passing through the second heat exchanger 162 may be supplied to the first compressor 151 . The first compressor 151 compresses the anode exhaust gas to a pressure of, for example, 5 bar. In one embodiment, when the fuel cell system includes the turbine 140 , mechanical energy generated by the turbine 140 may be used to drive the first compressor 151 .

The exhaust gas compressed by the first compressor 151 is supplied to and stored in the gas storage unit 130 . In the fuel cell mode, the anode exhaust gas transported to the first branch passage L103 is a gas containing nitrogen (N2) and hydrogen (H2) as main components, and thus the gas storage unit 130 stores a mixed gas of nitrogen and hydrogen. can

In one embodiment, when the bidirectional system operates in the water electrolysis mode, the first branch passage L103 is closed and the anode exhaust gas passes through the second branch passage L104 to the second compressor 152 and the ammonia synthesizer 180. ) are sequentially supplied. The second compressor 152 may compress the anode exhaust gas to a pressure required by the ammonia synthesizer 180 . For example, the ammonia synthesizer 180 may operate between 10 bar and 180 bar, and the second compressor 152 may compress the anode exhaust gas to a pressure required for ammonia synthesis.

In one embodiment, some of the exhaust gas transferred to the second branch flow path L104 is branched through the flow path L81 (hereinafter, referred to as 'pressure control flow path'). According to this embodiment, the flow path for pressure control (L181) is configured so that only when a predetermined standard is satisfied, a part of the exhaust gas flowing through the second branch flow path (L104) can be provided to the discharge flow path (L102) again. there is. To this end, a pressure control valve 118 for allowing or blocking the flow of fluid is installed in the pressure control flow path L181. The pressure control valve 118 may be opened so that steam flows into the pressure control passage L181 according to a predetermined standard, or may be closed so that steam does not flow and is blocked.

The predetermined criterion may be, for example, a pressure determined so that negative pressure (negative pressure) is not applied to the water electrolysis unit 110 .

In detail, the pressure control flow path L181 is connected to the discharge flow path L102, and thus the exhaust gas diverged through the pressure control flow path L181 can be supplied to the discharge flow path L102.

According to one embodiment, the pressure control valve 118 is opened when the applied pressure of the fluid flowing in the discharge passage L102 (hereinafter referred to as 'the pressure of the discharge passage L102') is less than or equal to the reference pressure, and the pressure is greater than the reference pressure. The control valve 118 is closed.

Although not shown in FIG. 4, a pressure sensor (not shown) for measuring the pressure applied to the discharge passage L102 is installed in the discharge passage L102.

The control unit (not shown) controls the opening or closing operation of the valve 118 for pressure control based on the detection result. In the water electrolysis mode, the pressure control valve 118 is opened when the pressure in the discharge passage L102 is equal to or less than the reference pressure, and the pressure control valve 118 is closed when the pressure in the discharge passage L102 is greater than the reference pressure.

In this embodiment, the location where the pressure control passage L181 is connected to the discharge passage L102 can be variously modified. For example, the flow path L181 for pressure control may be connected upstream of the heat exchanger 161, connected between the heat exchanger 161 and the heat exchanger 163, or connected downstream of the heat exchanger 163.

The ammonia synthesizer 180 generates ammonia using the anode exhaust gas. In one embodiment, the ammonia synthesizer 180 is a Haber-Bosch reactor that receives hydrogen (H2) and nitrogen (N2) and generates ammonia (NH3) therefrom. However, the ammonia synthesizer 180 is not limited to the Haber-Bosch reactor and may be any synthesizer capable of synthesizing ammonia using an anode exhaust gas. Ammonia generated in the ammonia synthesizer 180 is transported to the ammonia storage unit 120 along the second branch passage L104 and stored therein.

Hydrogen and nitrogen are required to synthesize ammonia in the ammonia synthesizer 180, but the anode exhaust gas transported through the discharge passage L102 and the second branch passage L104 in the water electrolysis mode does not contain nitrogen. In one embodiment of the invention, the mixed gas of nitrogen and hydrogen stored in the gas storage unit 130 may be additionally supplied to the ammonia synthesizer 180. That is, as shown in the drawing, the gas storage unit 130 and the second branch passage L104 are connected to the gas supply passage L10 to transfer the mixed gas of nitrogen and hydrogen to the second branch passage L104. At this time, a third compressor 153 may be installed on the gas supply passage L10 and the third compressor 153 may compress the nitrogen and hydrogen mixed gas to a pressure necessary for synthesizing ammonia.

In one embodiment, the bidirectional water electrolysis system includes an air supply passage L105 for supplying external air to the cathode 112 of the fuel cell, one or more blowers 192 installed in the passage, and a fourth heat exchanger 164. do. The cathode exhaust gas discharged from the cathode 12 of the fuel cell 110 passes through the fourth heat exchanger 164 and is discharged to the outside through the discharge passage L106. At this time, the fourth heat exchanger 164 passes through the air Heat is exchanged between air transported to the cathode 112 along the supply passage L105 and cathode exhaust gas discharged from the cathode 112 and transported along the discharge passage L106.

In one embodiment, a fifth heat exchanger 165 may be further installed downstream of the fourth heat exchanger 164 on the discharge passage L106, and the cathode exhaust gas from the fifth heat exchanger 165 may be supplied with a second additional heat exchanger. Water supplied along the supply passage L109 may be vaporized by heating. In addition, in an alternative embodiment, heat of the cathode exhaust gas passing through the fourth heat exchanger 164 may be additionally used. For example, the cathode exhaust gas passing through the fourth heat exchanger 164 vaporizes fuel or water in the fuel supply passage L101 or water supply passage L107 through the fifth heat exchanger 165 or another additional heat exchanger. can be used additionally.

Now, with reference to FIGS. 5 and 6 , operations of the bidirectional water electrolysis system according to an embodiment of the present invention in a fuel cell mode and a water electrolysis mode will be described respectively.

5 shows an operating state of a fuel cell mode of a bidirectional water electrolysis system according to an embodiment. In FIG. 5, 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 110 through the fuel supply passage L101 in the fuel cell mode. For example, liquid ammonia stored in the ammonia storage unit 120 at about 11 bar may be transported along the supply flow path L101 and vaporized while passing through the second heat exchanger 162 and the first heat exchanger 161 in sequence. . At this time, the high-pressure ammonia gas heated or vaporized in the second heat exchanger 162 can be used to generate a predetermined mechanical energy in the turbine 140, and the ammonia gas passing through the turbine 140 is transferred to the first heat exchanger ( After being additionally heated in 161, it can be supplied to the fuel electrode 111 of the fuel cell 110. In an alternative embodiment, the turbine 140 and the second heat exchanger 162 may be omitted, in which case the liquid ammonia is vaporized in the first heat exchanger 161 and then supplied to the fuel cell 110 .

Meanwhile, the blower 192 of the air supply passage L105 operates to supply external air to the cathode 112 of the fuel cell 110 . The air transported through the air supply passage L105 may be heated in the fourth heat exchanger 164 and then injected into the cathode 112 .

In the fuel cell mode, the anode 111 of the fuel cell 110 generates hydrogen, nitrogen, and water (steam) by a chemical reaction between ammonia gas and air (oxygen), and passes the anode exhaust gas through the discharge passage L102. In the cathode 112, nitrogen and unreacted air are discharged as cathode exhaust gas through the discharge passage L106.

The anode exhaust gas discharged from the anode 111 along the discharge passage L102 passes through the first heat exchanger 161, heats and vaporizes ammonia in the supply passage L101, and then passes through the water outlet 170. Water is removed, and accordingly, the anode exhaust gas becomes hydrogen and nitrogen as main components. The anode exhaust gas is supplied to the second heat exchanger 162 along the first branch flow path L103, and ammonia is heated or vaporized in the second heat exchanger 162. Thereafter, the anode exhaust gas may be compressed to a high pressure in the first compressor 151 and transferred to the gas storage unit 130 to be stored.

6 shows an operating state of the water electrolysis mode of the bidirectional water electrolysis system according to an embodiment. A flow path used in the water electrolysis mode is indicated by a thick line in FIG. 3 .

Referring to the drawing, in the water electrolysis mode, water is transported into the system through the water supply passage L107. The transported water is vaporized into steam using high-temperature heat generated during the operation of the ammonia synthesizer 180. The vaporized steam is supplied to the anode 111 of the fuel cell 110 after joining the supply passage L101 along the water supply passage L107. At this time, since the space between the ammonia storage unit 120 and the supply passage L101 is closed by means such as a valve, only steam can be supplied to the anode 111 . Since a lot of steam is required in the water electrolysis mode, steam may be received through the first and second additional supply channels L108 and L109 depending on circumstances. In addition, air is supplied to the cathode 112 through the air supply passage L105.

As the water electrolysis reaction occurs in the water electrolysis unit 110, the anode exhaust gas composed of hydrogen and steam is discharged from the anode 111 through the discharge passage L102, and the cathode exhaust gas is also discharged from the air cathode 112 through the discharge passage L106. ) is released through

The anode exhaust gas discharged through the discharge passage L102 sequentially passes through the first heat exchanger 161 and the third heat exchanger 163, heats water or steam to be supplied to the fuel cell, and then the water discharge unit 170 ) is transferred to A portion of the exhaust gas from the anode before being transferred to the water discharge unit 170 may branch into the recirculation passage L121. Even in the water electrolysis mode, it is necessary to supply a small amount of hydrogen to the anode 111. By diverting and recirculating some of the exhaust gas through the recirculation passage L121, hydrogen in the exhaust gas can be supplied to the anode 111, so that separate hydrogen It has the advantage of not having to supply it. In one embodiment, the recirculation passage L121 may be connected between the first heat exchanger 161 and the third heat exchanger 163 or may be connected to the downstream side of the water outlet 170.

In the water electrolysis mode, the pressure control valve 118 is opened when the pressure in the discharge passage L102 is less than or equal to the reference pressure, and is closed when the pressure is greater than the reference pressure. When the valve 118 for pressure control is opened, a part of the exhaust gas moving along the branch flow path L104 is moved to the discharge flow path L102. By this operation, it is possible to prevent the risk of explosion due to air inflow or the like according to the negative pressure of the discharge passage L102 during hydrogen compression.

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 170, the anode exhaust gas becomes a gas mainly composed of hydrogen, and then is removed along the second branch passage L104. 2 is supplied to compressor 152. Meanwhile, after compressing the mixed gas of nitrogen and hydrogen stored in the gas storage unit 130 in the third compressor 153, it can be supplied to the second branch passage L104 through the gas supply passage L110, and thus hydrogen and nitrogen. A high-pressure mixed gas containing as a main component may be supplied to the ammonia synthesizer 180 through the second branch passage L104.

The ammonia synthesizer 180 generates ammonia using the supplied high pressure mixed gas of hydrogen and nitrogen, and the generated ammonia is supplied to the ammonia storage unit 120 along the second branch passage L104 and stored therein.

As described above, in the water electrolysis mode of the present invention, hydrogen can be supplied to the fuel cell by recirculating some of the anode exhaust gas discharged from the fuel cell 110, which has the advantage of not having to prepare a separate path for supplying hydrogen and discharging the anode. After mixing nitrogen and hydrogen gas in the gas storage unit 130 with hydrogen extracted from the gas, ammonia may be generated in the ammonia synthesizer 180 and stored in the ammonia storage unit 120 .

Therefore, in the fuel cell mode, ammonia of the ammonia storage unit 120 is used as fuel to generate electricity, a mixed gas of hydrogen and nitrogen is stored in the gas storage unit 130, and in the water electrolysis mode, the gas storage unit 130 Since ammonia can be generated using gas and stored in the ammonia storage unit 10, a bidirectional water electrolysis system capable of continuously operating by alternating between a fuel cell mode and a water electrolysis mode can be implemented.

In addition, from the point of view of hydrogen recirculation, in the fuel cell mode operation, hydrogen from the anode exhaust gas is extracted and stored in the gas storage unit 130, and in the water electrolysis mode operation, hydrogen from the anode exhaust gas is extracted and used for ammonia synthesis. Efficient system operation can be performed by reusing the hydrogen in the exhaust gas without discarding it even if it is operated in any mode of the electrolysis mode and the water electrolysis mode.

7 is a diagram for explaining an operating method of a water electrolysis system according to an embodiment of the present invention.

Referring to FIG. 7 , a method of operating a water electrolysis system according to an embodiment of the present invention (hereinafter referred to as 'this operating method') includes a discharge step (S100), a separation step (S102), a storage step (S104), and pressure monitoring. It may include step S101, determination step S103, pressure control fluid supply step S105, and pressure control fluid non-provision step S107.

In the discharge step S100, the discharge passage L41 discharges the fluid from the hydrogen electrode of the water electrolysis unit 30.

The separation step (S102) is a step in which the high-temperature hydrogen pump electrochemically separates hydrogen contained in the fluid discharged from the discharge passage (L41).

The pressure monitoring step (S101) is a step of monitoring the pressure of the discharge passage (L41).

The determination step (S103) is a step of determining whether the pressure of the discharge passage (L41) is equal to or less than the reference pressure.

In the pressure control fluid providing step (S105), when the pressure of the discharge passage L41 is equal to or less than the reference pressure, the pressure control fluid is supplied to the discharge passage L41. Here, the fluid for pressure control may be hydrogen.

For example, the pressure control fluid supply step (S105) may be a step of providing some of the hydrogen generated in the separation step (S102) to the discharge passage (L41) when the pressure of the discharge passage (L41) is less than the reference pressure. there is.

For another example, in the pressure control fluid supply step (S105), when the pressure of the discharge passage (L41) is less than the reference pressure, it may be installed upstream of the heat exchangers installed in the discharge passage (L41) or between the heat exchangers. can Referring to the drawings of the above-described embodiments, the pressure control fluid supply step (S105) is provided upstream of the heat exchanger (L41), or provided between the heat exchanger (L41) and the heat exchanger (L42), or It may be provided between the heat exchanger L42 and the heat exchanger L44.

In the pressure control fluid non-supply step (S107), when the pressure of the discharge passage L41 is greater than the reference pressure, the pressure control fluid is not supplied to the discharge passage L41. For example, if the pressure in the discharge passage L41 is greater than the reference pressure while the step S105 is being executed, the pressure control fluid is no longer supplied to the discharge passage L41.

According to another embodiment of the present invention, a method of operating a water electrolysis system includes monitoring the pressure of a discharge passage (L102) for discharging fluid from a hydrogen electrode of a water electrolysis unit in a water electrolysis mode, the discharge passage (L102) It may include compressing the fluid discharged from the fluid, and providing a fluid for pressure control when the pressure of the discharge passage (L102) is less than the reference pressure. Here, the step of providing the fluid for pressure control may be providing a part of the compressed fluid in the compression step to the discharge passage L102 before being compressed by the step of compressing.

The above-described step of providing the fluid for pressure control may be performed when the pressure of the discharge passage L102 before the step of compressing the fluid is performed is equal to or less than the reference pressure.

The heat exchanger 161 is installed in the discharge passage L102, and the step of providing the fluid for pressure control may include providing the fluid for pressure control between the heat exchanger 161 and the hydrogen electrode.

The water electrolysis system in the present method may generate electricity and water by a chemical reaction of ammonia and oxygen in a fuel cell mode, and generate hydrogen and oxygen by steam and electricity in a water electrolysis mode.

According to the operating method described above, hydrogen can be safely separated while preventing the risk of explosion due to air inflow according to the negative pressure of the discharge passage L41 during hydrogen compression.

On the other hand, the method of operation in a water electrolysis system according to an embodiment of the present invention described with reference to FIG. 7 can be applied not only to the water electrolysis mode in a bidirectional water electrolysis system, but also to a general non-bidirectional water electrolysis system. way. For example, the operation method in a water electrolysis system according to an embodiment of the present invention may include an alkaline water electrolysis system, a polymer electrolyte membrane (PEM) water electrolysis system, a solid oxide water electrolysis system, or It can also be applied to a water electrolysis system such as an anion exchange membrane (AEM) water electrolysis system.

As described above, those skilled 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 not be defined, but should be defined by not only the claims to be described later, but also those equivalent to these claims.

10: steam generating unit 20: ejector
30: bidirectional water electrolysis fuel cell 41, 42, 43, 44, 53: heat exchanger
61,62: heater
80: high-temperature hydrogen pump
83: buffer tank

Claims (10)

a discharge passage for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit;
a high-temperature hydrogen pump installed in the discharge passage to electrochemically separate hydrogen from the fluid discharged from the hydrogen electrode;
a buffer tank for storing hydrogen separated from the high-temperature hydrogen pump; and
A pressure control passage connected from the buffer tank to the discharge passage; and
When the pressure of the discharge passage is less than the reference pressure, a part of the hydrogen stored in the buffer tank is supplied to the discharge passage,
A pressure control valve is installed in the pressure control passage, and the pressure control valve is opened when the pressure in the discharge passage is less than the reference pressure,
The water electrolysis system, wherein the reference pressure is a pressure determined so that negative pressure is not applied to the water electrolysis unit. delete According to claim 1,
Further comprising a first heat exchanger installed in the discharge passage,
The water electrolysis system, wherein the flow path for pressure control is connected upstream of the first heat exchanger from the buffer tank. A heat exchanger installed in the discharge passage for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit;
A compressor installed downstream of the heat exchanger; and
A flow path for controlling pressure branched downstream of the compressor and connected to the discharge flow path; and
When the pressure of the discharge passage is less than the reference pressure, a part of the discharge gas discharged from the compressor is provided to the discharge passage,
A pressure control valve is installed in the pressure control passage, and the pressure control valve is opened when the pressure in the discharge passage is equal to or less than the reference pressure.
The water electrolysis system, wherein the reference pressure is a pressure determined so that negative pressure is not applied to the water electrolysis unit. delete According to claim 4,
The water electrolysis system generates electricity and water by a chemical reaction of ammonia and oxygen in a fuel cell mode and generates hydrogen and oxygen by steam and electricity in a water electrolysis mode. As a method of operating a water electrolysis system,
In the water electrolysis mode, monitoring the pressure of the discharge passage for discharging the fluid from the hydrogen electrode of the water electrolysis unit;
compressing the fluid discharged from the discharge passage; and
Including; providing a pressure control fluid when the pressure of the discharge passage is less than the reference pressure;
In the step of providing the fluid for pressure control, a part of the fluid compressed in the compressing step is provided to the discharge passage before being compressed by the compressing step,
The step of providing the pressure control fluid,
It is performed when the pressure of the discharge passage before the step of compressing the fluid is performed is less than the reference pressure,
A heat exchanger is installed in the discharge passage,
The step of providing the pressure control fluid provides a pressure control fluid between the heat exchanger and the hydrogen electrode,
The reference pressure is a pressure determined so that negative pressure is not applied to the water electrolysis unit. delete delete According to claim 7,
The water electrolysis system generates electricity and water by a chemical reaction of ammonia and oxygen in a fuel cell mode and generates hydrogen and oxygen by steam and electricity in a water electrolysis mode.

Images