KR102536133B1 - Reversible fuel cell system capable of efficiently separating and storing hydrogen - Google Patents

Abstract

According to one embodiment, a discharge passage (L41) for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit 30; and a high-temperature hydrogen pump 80 installed in the discharge passage l41 to separate hydrogen from the fluid discharged from the hydrogen electrode. There is provided a water electrolysis system, which separates hydrogen into.

Description

Reversible fuel cell system capable of efficiently separating and storing hydrogen}

The present invention relates to a bidirectional water electrolysis system capable of efficiently separating and storing hydrogen and an operating method thereof.

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)

The present invention has been made to solve the above problems, and an object of the present invention is to provide a bi-directional water electrolysis system capable of efficiently separating and storing hydrogen and an operating method thereof.

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 (L41) for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit (30); and a high-temperature hydrogen pump 80 installed in the discharge passage l41 to separate hydrogen from the fluid discharged from the hydrogen electrode. There is provided a water electrolysis system, which separates hydrogen into.

According to another embodiment of the present invention, discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit 30 through the discharge passage L41; and electrochemically separating hydrogen contained in the fluid discharged from the discharge passage L41.

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 through an ejector, and in the fuel cell mode, some of the exhaust gas is recycled to supply water. By configuring to re-supply to the negative electrode, the effect of improving system efficiency was achieved.

1 is a diagram for explaining a bi-directional water electrolysis system according to a first embodiment of the present invention.
2 is a diagram for explaining the water electrolysis (SOEC) 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 an operating method in a bidirectional 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 passage L22 is configured to diverge from the first steam supply passage L21 and join the passage L21 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 L21, 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 bi-directional 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 the Venturi effect, and injects the fluid to be mixed into a Venturi pipe whose diameter gradually decreases and then expands. In general, the input end of the ejector 20 is called a motive nozzle, the output end is called a diffuser nozzle, and the inlet for inputting the fluid to be mixed is called a suction port. In the illustrated embodiment, the ejector 20 The driving nozzle of ) is connected to the upstream side of the first steam supply passage L21, the injection nozzle is connected to the downstream side of the first steam supply passage L21, and the suction port is connected to the feedback passage L47. The feedback passage L47 is a passage branching 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, by adjusting the pressure or flow rate of steam supplied to the drive nozzle of the ejector 20 (that is, transferred to the flow path L21), the amount of exhaust gas recirculated through the feedback path L47 can be adjusted.

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, 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 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 may be discharged to the outside.

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, some of the steam transported to the flow path L21 is branched through the flow path L62 (hereinafter referred to as 'pressure control flow path'). According to this embodiment, the flow path for pressure control (L62) is branched from the flow path (L21) so that a part of the steam flowing through the flow path (L21) can be provided to the discharge flow path (L41) only when a predetermined standard is satisfied. It is configured to be connected to the discharge passage (L41). To this end, a pressure control valve 18 is installed in the pressure control flow path L62 to allow or block fluid flow. The pressure control valve 18 may be opened so that steam flows into the pressure control passage L62 according to a predetermined standard or 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 30 .

In detail, the pressure control passage L62 is connected to the discharge passage L41, and thus steam branched through the pressure control passage L62 can be supplied to the discharge passage L41.

According to one embodiment, the pressure control valve 18 is opened when the pressure applied to the fluid flowing in the discharge passage L41 (hereinafter referred to as 'the pressure of the discharge passage L41') is less than or equal to the reference pressure, and the pressure is greater than the reference 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, various modifications are possible such as the branching position of the pressure control passage L62 from the steam supply passage L21 and the connection of the pressure control passage L62 to the discharge passage L41.

For example, the pressure control passage L62 is branched upstream of the ejector 20 (for example, between the heat exchanger 12 and the ejector 20), or upstream of the heater 61 (eg, between the heat exchanger 12 and the ejector 20). For example, between the ejector 20 and the heater 61) may be branched.

For example, the connection location L62 for pressure control is connected upstream of the heat exchanger 41, connected between the heat exchanger 41 and the heat exchanger 42, or between the heat exchanger 42 and the heat exchanger. (43) can be connected.

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. Then, the first exhaust gas is transferred 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 transferred through the steam supply passage L21, 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 outlet, hydrogen and water are separated, and hydrogen is separately stored.

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 pressure control valve 18 is opened, part of the steam moving along the flow path L21 is transferred to the discharge flow path 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 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. and a plurality of flow passages connecting between 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 an operating method of a water electrolysis system according to an embodiment of the present invention.

Referring to FIG. 4 , 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.

The pressure control fluid providing step (S105) is a step of providing a pressure control fluid to the discharge passage (L41) when the pressure of the discharge passage (L41) is less than the reference pressure. Here, the fluid for pressure control may be steam.

For example, the pressure control fluid supply step (S105) may be a step of providing some of the steam flowing in the steam supply line (L21) 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, a portion of the steam upstream of the ejector 20 installed in the steam supply line (L21) is transferred to the discharge passage ( It may be a step of providing L41).

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, a part of the steam upstream of the heater 21 installed in the steam supply line (L21) is used as the discharge passage. It may be a step of providing in (L41).

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 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.

Meanwhile, the method of operation in a water electrolysis system according to an embodiment of the present invention described with reference to FIG. 4 can be applied not only to a water electrolysis mode in a bidirectional water electrolysis system but also to a general non-bidirectional water electrolysis system. way. For example, an 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

Claims (10)

a discharge passage (L41) for discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit (30);
a high-temperature hydrogen pump 80 installed in the discharge passage 141 to separate hydrogen from the fluid discharged from the hydrogen electrode;
a steam supply line L21 for supplying steam to the hydrogen electrode of the water electrolysis unit 30; and
A pressure control passage (L62) branched from the steam supply line (L21) and connected to the discharge passage (L41);
The high-temperature hydrogen pump 80 electrochemically separates hydrogen from the fluid discharged from the hydrogen electrode,
A pressure control valve 18 is installed in the pressure control passage L62, and the pressure control valve 18 is opened when the pressure in the discharge passage L41 is equal to or less than the reference pressure. delete According to claim 1,
An ejector 20 installed in the steam supply line L21; and
The water electrolysis system, wherein the flow path (L62) for pressure control is branched upstream of the ejector (20). delete delete As a method of operating a water electrolysis system,
discharging the fluid discharged from the hydrogen electrode of the water electrolysis unit 30 through the discharge passage L41;
electrochemically separating hydrogen contained in the fluid discharged from the discharge passage (L41);
monitoring the pressure of the discharge passage (L41);
When the pressure of the discharge passage (L41) is less than the reference pressure, providing a pressure control fluid to the discharge passage (L41); and
Including; supplying steam by the steam supply line L21 to the hydrogen electrode of the water electrolysis unit 30,
The step of providing the pressure control fluid,
A method of operating a water electrolysis system, wherein a part of the steam flowing through the steam supply line (L21) is provided to the discharge passage (L41) when the pressure of the discharge passage (L41) is equal to or less than the reference pressure. delete delete According to claim 6,
An ejector 20 is installed in the steam supply line L21,
The step of providing the pressure control fluid,
A method of operating a water electrolysis system comprising providing a part of steam upstream of the ejector 20 to the discharge passage L41 when the pressure of the discharge passage L41 is equal to or less than the reference pressure. delete

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