KR102232001B1 - Reversible solid oxide electrolysis system having heat recovery function using ejector and method for operating the same reversible solid oxide electrolysis system - Google Patents

Abstract

The present invention relates to a two-way water electrolysis system, according to an embodiment, consisting of a hydrogen electrode, an air electrode, and an electrolyte interposed therebetween, and is capable of operating in any one of a water electrolysis mode and a fuel cell mode. battery; A first heat exchanger for exchanging the hydrogen supplied to the hydrogen electrode with the first exhaust gas discharged from the hydrogen electrode; A steam supply passage for supplying steam to the hydrogen electrode and a branch passage formed in the supply passage; And an ejector disposed in the steam supply passage.

Description

Two-way water electrolysis system having heat recovery function using ejector and method for operating the same reversible solid oxide electrolysis system}

The present invention relates to a two-way water electrolysis system, and more particularly, to a two-way water electrolysis system capable of improving system efficiency by recovering heat energy of exhaust gas discharged from a fuel cell using an ejector.

Recently, research on a power generation system using renewable energy such as solar or wind power has been conducted. In the case of a power generation system using renewable energy, the electrical output varies depending on the natural environment, so when excess power exceeding the amount of power demand occurs, a study on a method of storing and using it is required. For example, when excess power is generated from the renewable energy generation facility, hydrogen is produced and stored using a water electrolysis device, and when the amount of power generated is low, a system capable of producing and supplying power from a fuel cell using the stored hydrogen is studied. Has become.

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

Patent Document 1: Korean Patent Registration No. 10-0776353 (announced on November 7, 2007)

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

According to an embodiment of the present invention, there is provided a two-way water electrolysis system, comprising: a two-way water electrolysis fuel cell comprising a hydrogen electrode, an air electrode, and an electrolyte interposed therebetween and operable in any one of a water electrolysis mode and a fuel cell mode; A first heat exchanger for exchanging the hydrogen supplied to the hydrogen electrode with the first exhaust gas discharged from the hydrogen electrode; A steam supply passage for supplying steam to the hydrogen electrode and a branch passage formed in the supply passage; And an ejector disposed in the steam supply passage, wherein a driving nozzle of the ejector is connected to an upstream side of the steam supply passage, and an injection nozzle of the ejector is connected to a downstream side of the steam supply passage, and the ejector It provides a two-way water electrolysis system, characterized in that the inlet of is connected to a feedback flow path branched from the discharge flow path of the first exhaust gas.

According to an embodiment of the present invention, a method of operating a bidirectional water electrolysis system operable in a water electrolysis mode and a fuel cell mode, wherein the bidirectional water electrolysis system comprises a hydrogen electrode, an air electrode, and an electrolyte interposed therebetween, A bidirectional electrolysis fuel cell operable in any one of a water electrolysis mode and a fuel cell mode; And a steam supply passage for supplying steam to the hydrogen electrode and a branch passage formed in the supply passage. And an ejector disposed in the steam supply passage, wherein the driving method of the bidirectional water electrolysis system includes supplying steam to the hydrogen electrode through the steam supply passage in the water electrolysis mode and bypassing the ejector in the fuel cell mode. Supplying steam to the hydrogen electrode through a branch passage; And resupplying at least a part of the exhaust gas discharged from the hydrogen electrode to the hydrogen electrode through the ejector in the water electrolysis mode.

According to an embodiment of the present invention, some of the exhaust gas discharged from the hydrogen electrode of the fuel cell in the water electrolysis mode is configured to be resupplied to the hydrogen electrode through an ejector, and a part of the exhaust gas is recycled to the hydrogen electrode in the fuel cell mode. By configuring to re-supply to the system, the effect of improving the system efficiency was achieved.

1 is a view for explaining a two-way electrolysis system according to a first embodiment of the present invention;
2 is a diagram for explaining a water electrolysis (SOEC) mode of the bidirectional water electrolysis system of the first embodiment;
3 is a view for explaining a fuel cell (SOFC) mode of the bi-directional water electrolysis system of the first embodiment;
4 is a view for explaining a two-way electrolysis system according to a second embodiment;
5 is a diagram for explaining a two-way electrolysis system according to a third embodiment.

The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments related to 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 may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

In this specification, the singular form also includes the plural form unless specifically stated in the phrase. As used in the specification, "comprise" and/or "comprising" does not exclude the presence or addition of one or more other components.

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

1 is a diagram for explaining a two-way electrolysis system according to a first embodiment of the present invention.

Referring to the drawings, the two-way water electrolysis system of the first embodiment includes components such as a steam generator 10, an ejector 20, a two-way water electrolysis fuel cell 30, and heaters 61 and 62. It may be composed of a plurality of flow paths connecting therebetween and a plurality of heat exchangers, blowers, and pumps disposed in the flow path.

The bi-directional water electrolysis fuel cell 30 is one of a water electrolysis mode that generates hydrogen and oxygen by steam and electricity supplied from the outside, and a fuel cell mode that generates electricity and water by a chemical reaction of hydrogen and oxygen supplied from the outside. It can operate in either mode.

In one embodiment, the bi-directional water electrolysis fuel cell 30 may be implemented as an arbitrary fuel cell such as a solid oxide fuel cell (SOFC) or a molten carbonate fuel cell (MCFC). For convenience of explanation, in the present specification, a description will be made on the premise that the bi-directional water electrolysis fuel cell 30 is implemented as a solid oxide fuel cell (SOFC).

In one embodiment, the bi-directional water electrolysis fuel cell 30 may be composed of a hydrogen electrode 31, an air electrode 32, and an electrolyte interposed therebetween. In the water electrolysis mode (hereinafter referred to as "SOEC mode"), the hydrogen electrode 31 receives steam (H2O) from the outside and produces hydrogen (H2) therefrom. That is, the hydrogen electrode 31 generates hydrogen (H2) by receiving steam (H2O) from the flow path (L21 and/or L31), and includes the generated hydrogen (H2) and steam (H2O) that cannot be converted to hydrogen. The generated 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 transfers the oxygen (O2) received in this way by using air supplied from the outside through the flow path L53. The cathode 32 discharges the gas containing oxygen and air as the second exhaust gas through the flow path L61.

In the fuel cell mode (hereinafter referred to as “SOFC mode”), the hydrogen electrode 31 generates water (steam) by a chemical reaction of hydrogen supplied from the flow path L11 and oxygen delivered from the air electrode 32. , The steam generated in this way and the gas containing hydrogen that has not been converted into steam may be discharged as exhaust gas through the flow path L41. The air electrode 32 receives air through the flow path L53 and transfers oxygen to the hydrogen electrode 31 through an electrolyte, and discharges nitrogen (N2) and air as a second exhaust gas through the flow path L61. have.

In theory, 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, the mixed gas of steam and hydrogen is supplied to the fuel cell 30 in a mass ratio of 80:1 (approximately 8.9:1 by volume) of steam and hydrogen, and hydrogen in the fuel cell mode. Since is mainly required, hydrogen and steam may be mixed at a mass ratio of 3.6:1 (approximately 32:1 by volume) and supplied to the fuel cell 30. In this case, it goes without saying that the mixing ratio of hydrogen and steam in each of the water electrolysis mode and the fuel consumption mode may vary according to the specific embodiment. In addition, in order to supply by adjusting the mixing ratio of hydrogen and steam differently according to each mode, although not shown in the drawing, for example, a blower or pump is placed in at least one of the hydrogen supply flow path L11 and the steam supply flow path L21, L22, L31. , And/or a flow control valve may be installed to control 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 cause heat exchange between the hydrogen gas supplied to the hydrogen electrode 31 of the fuel cell 30 and the exhaust gas discharged from the hydrogen electrode 31. In one embodiment, the hydrogen supplied to the hydrogen electrode 31 may be at 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 this case, the hydrogen electrode Hydrogen supplied to (31) may be heated in the first heat exchanger (41), for example, 650 degrees Celsius or higher.

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 flow path L21 may include, for example, a pump 11 and a boiler 12, and heats water supplied to the boiler 12 by the pump 11 It generates steam. In one embodiment, the boiler 12 may be implemented as a conventional combustion device or incineration device such as a waste solid fuel boiler system, a cogeneration 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 then join the flow path L21 again. An on-off valve 13 may be installed in the branch passage L22, and although not shown in the drawing, an on-off valve may be installed in the first steam passage L21 as well, and steam is supplied to the first steam supply passage by the control of the valve. It can be controlled to flow in one of the L21 and the branch flow path L22. Alternatively, the steam flow may be controlled by installing a three-way valve at the branch point where the branch flow path L22 is branched.

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 that mixes fluids using a Venturi effect, and injects a fluid to be mixed into a venturi tube whose diameter gradually decreases and then expands. In general, the input end of the ejector 20 is referred to as a driving nozzle, the output end is a diffuser nozzle, and the injection port for inputting the fluid to be mixed is referred to as a suction port. The driving nozzle of) is connected to the upstream side of the first steam supply flow path L21, the injection nozzle is connected to the downstream side of the first steam supply flow path L21, and the suction port is connected to the feedback flow path L47. The feedback flow path L47 is a flow path branched from the discharge flow path L41 through which the exhaust gas of the hydrogen electrode 31 flows.

In general, in the water electrolysis mode, the volume ratio of steam and hydrogen injected into the hydrogen electrode 31 is approximately 9:1, but the exhaust gas discharged from the hydrogen electrode 31 has a large hydrogen content, so the feedback flow path L47 is used. When some of the exhaust gas is recycled, there is no need to separately supply hydrogen through the hydrogen supply flow path L11. At this time, by adjusting the pressure or flow rate of the steam supplied to the drive nozzle of the ejector 20 (that is, transferred to the flow path L21), the amount of exhaust gas recirculated to the feedback flow path L47 can be adjusted.

After the branch passage L22 joins the first steam supply passage L21, the first steam supply passage L21 merges with the hydrogen supply passage L11, and the mixed gas of hydrogen and steam is a 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 flow path L21 and the hydrogen supply flow path L11 is located downstream 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 be heated in the first heat exchanger 41 without the need to reheat the steam already heated to the high temperature, compared to heating a mixed gas of hydrogen and steam. Hydrogen can be heated to a higher temperature.

The bidirectional water electrolysis system of the present invention may further include a second steam supply passage L31. At least one pump 15 and a second heat exchanger 42 are installed in the second steam supply passage L31. In the pump 15, water (hereinafter referred to as "external supply water") is supplied to the second heat exchanger 42 from the outside of the system by the pump 15, and the second heat exchanger 42 heats the external supply water. .

In one embodiment, the second heat exchanger 42 is configured to cause heat exchange 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 It is placed on the downstream side of ). In one embodiment, the externally supplied water may be at 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 this case, the second heat exchanger 42 ) Discharged from (the external supply is vaporized) can be heated to, for example, 600 degrees Celsius or higher.

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 of the ejector 20.

In one embodiment, the bidirectional water electrolysis system may further include a first heater 61. The first heater 61 is disposed on the mixed gas supply flow path 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 to a predetermined temperature range so that the fuel cell 30 can operate in the electrolysis mode and the fuel cell mode with optimum efficiency. In an embodiment, the first heater 61 may heat the temperature of the mixture gas of hydrogen and steam in a range of 650 degrees Celsius to 750 degrees Celsius. In addition, although not shown in the drawing, for this temperature control, one or more temperature sensors are installed inside or at the front or rear end of the first heater 61 to measure the temperature of the mixed gas and heat the mixed gas based thereon.

In one embodiment, the bidirectional water electrolysis system includes an air supply flow path L53 for supplying air from the outside to the cathode 32 and an air-exhaust gas heat exchanger 53 disposed in the flow path L53. The heat exchanger 53 exchanges heat between the air transferred to the cathode 32 through the air supply channel 53 and the exhaust gas discharged from the cathode 32 and transferred to the exhaust channel L61.

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

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

In the water electrolysis mode, a lot of water (steam) and electricity are required, and a relatively small amount of air is required, and in the fuel cell mode, a large amount of hydrogen and oxygen (air) is required, so the amount of air supplied must be large. Therefore, in one embodiment, only the first blower 51 is driven in the water electrolysis mode and the second blower 52 is not driven. In the fuel cell mode, only the second blower 52 is driven and the first blower 51 is driven. I never do that. In an alternative embodiment, both the first and second blowers 51 and 52 may be driven in the 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 discharge 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. The exhaust gas from the first heat exchanger 41 transfers thermal energy to hydrogen supplied to the hydrogen electrode 31 through the hydrogen supply passage L11 to heat the hydrogen. The exhaust gas from the second heat exchanger 42 vaporizes and heats externally supplied water supplied through the second steam supply passage L31.

The exhaust gas conveyed along the exhaust flow path L41 is conveyed to the water discharging unit. The water discharge unit is a device for separating and discharging water in the exhaust gas, and in the illustrated embodiment, a pump installed on the circulation passage L70 of the refrigerant circulating through the condenser 71 and the drain 72 and the condenser 71 , A cooling device, and the like. The water of the exhaust gas is condensed in the condenser 71, and the condensed water is discharged from the drain 72 to the outside through the water discharge passages L42 and L43. The remaining uncondensed gas components (i.e., hydrogen and uncondensed steam) are transferred along the flow path L45 and separated into hydrogen and steam through a blower 73, a compressor 74, a hydrogen separator 75, etc. Each can be processed. The water discharging unit shown in the drawings shows an exemplary configuration of a known technology, and according to an embodiment of the present invention, the method of separating and discharging water from the exhaust gas and extracting hydrogen may vary, as well as a specific device configuration. to be.

In one embodiment of the present invention, at least a portion of the gas that passes through the drain 72 and is transferred to the flow path L45 is branched through the recirculation flow path L44. The recirculation flow path L44 is connected to the hydrogen supply path L11, and thus, the gas branched through the recirculation flow path L44 may be resupplied to the hydrogen electrode 31 as a recycle gas.

For example, in the fuel cell mode, at least a part of the gas in the flow path L45 is recirculated to the recirculation flow path L44 to be resupplied to the hydrogen electrode 31, and in the water electrolysis mode, the recirculation flow path L44 may be closed. have. To this end, for example, a three-way valve may be installed at a branch point of the recirculation passage L44 or an opening/closing valve may be installed at an arbitrary point on the recirculation passage L44 for control.

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

The third heat exchanger 43 exchanges heat between the exhaust gas of the exhaust flow path L41 and the recycle gas of the recycle flow path L44 to increase the temperature of the recycle gas. In one embodiment, the third heat exchanger 43 is a small heat exchanger that increases the temperature of the recycle gas so that condensation does not occur in the recycle gas. The recirculation gas branched into the recirculation flow path L44 is a gas in a saturated state, and if even a little condensation occurs according to the environment of the recirculation flow path L44, devices such as the blower 45 at the rear stage may be damaged. In addition, even when the recycle gas is heated to an excessively high temperature in the third heat exchanger 43, durability of the blower 45 may be a problem. 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 recirculation gas and then transfer to the blower 45. In one embodiment, the temperature of the recycle gas is increased in a range between 5 degrees and 25 degrees by the third heat exchanger 43.

As described above, the recycle gas that has passed through the third heat exchanger 43 and the blower 45 joins the hydrogen supply flow path L11 and is heated to a high temperature in the first heat exchanger 41 together with the hydrogen gas, and then the fuel cell 30 ) Can be supplied to the hydrogen electrode 31.

Now with reference to Figs. 2 and 3, the operation of the electrolysis mode and the fuel cell mode of the bidirectional electrolysis system of the first embodiment will be described, respectively.

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

Referring to the drawings, in the water electrolysis mode, steam is supplied through the first steam supply flow path L21, and externally supplied water is supplied through the second steam supply flow path L31 to form steam from the second heat exchanger 42. It vaporizes and joins the first steam supply flow path L21. The mixed steam is supplied to the hydrogen electrode 31 of the fuel cell 30 through the flow path L12. In the 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 fuel cell 30.

As the water electrolysis reaction takes place in the fuel cell 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 air electrode 32. The exhaust gas is discharged through the discharge passage L61.

Part of the first exhaust gas discharged to the discharge flow path L41 is branched from the feedback flow path L47 and supplied to the inlet of the ejector 20, and mixed with the steam transferred through the steam supply flow path L21, and the hydrogen electrode ( 31). The remaining first exhaust gas that is not branched into the feedback flow path 47 passes through the first heat exchanger 41 without heat exchange, and exchanges heat with the external supply water in the second heat exchanger 42 to vaporize and heat the external supply water. . In the illustrated embodiment, the recirculation passage L44 is closed in the water electrolysis mode, and thus the first exhaust gas of the discharge passage L41 passes through the third heat exchanger 43 without heat exchange and is transferred to the water discharge portion. Steam is condensed in the water discharge unit and discharged to the outside along the water discharge passage L43, and hydrogen and uncondensed steam are transported along the passage L45 to be treated separately.

Fig. 3 shows the operating state of the fuel cell (SOFC) mode of the bidirectional water electrolysis system of the first embodiment. The flow path indicated by the thick line in the drawing is the flow path used in the fuel cell mode.

Referring to the drawings, in the fuel cell mode, hydrogen is supplied through the hydrogen supply flow path L11 and a small amount of steam is supplied through the first steam supply flow path L21. Hydrogen is heated by heat exchange with the exhaust gas of the exhaust flow path L41 in the first heat exchanger 41 and then supplied to the hydrogen electrode 31. Steam is transferred along the branch flow path L22, bypassing the ejector 20, and then merges with hydrogen and is supplied to the hydrogen electrode 31 of the fuel cell 30 through the flow path 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 a 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 flow path L41, and is converted 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. In the fuel cell mode, since externally supplied water is not supplied, the first exhaust gas passes through the second heat exchanger 42 without heat exchange and heats the recycle gas by heat exchange with the recycle gas in the third heat exchanger 43. After that, the first exhaust gas is transferred to the water discharge unit, and the steam is condensed and discharged to the outside along the water discharge channel L43, and hydrogen and uncondensed steam are recycled gas as the hydrogen electrode 31 along the recycle channel L44. Is resupplied.

As described above, according to the first embodiment, there is an advantage in that an appropriate mixed gas of hydrogen and steam can be supplied to the fuel cell 30 according to each operation mode of the bidirectional water electrolysis system. For example, since only a small amount of hydrogen is required in the water electrolysis mode, it is necessary to supply hydrogen from the outside through the hydrogen supply channel L11 by configuring to use hydrogen contained in the exhaust gas fed back through the feedback channel L47. It was configured to supply air by driving only the first blower 51, which is a small blower, because a relatively small amount of air is required. In the fuel cell mode, the exhaust gas is resupplied through the recirculation passage L44 instead of the feedback passage L47, thereby minimizing hydrogen discarded without being reacted in the fuel cell 30. In addition, at this time, by bypassing the ejector 20 to supply steam, it is possible to prevent the ejector 20 from interfering with the flow of steam, and a third heat exchanger on the upstream side of the blower 45 of the recirculation flow path L44. By installing the device 43, damage to the blower 45 can be prevented.

Now, a bidirectional electrolysis system according to the second and third embodiments will be described with reference to FIGS. 4 and 5, respectively.

4 shows a two-way electrolysis system according to a second embodiment. Referring to the drawings, the two-way water electrolysis system of the second embodiment includes components such as a steam generator 10, an ejector 20, a two-way water electrolysis fuel cell 30, and heaters 61 and 62. It consists of a plurality of flow paths connecting therebetween, and a plurality of heat exchangers, blowers, and pumps arranged in the flow path, and these components are the same as or similar to each of the components of the first embodiment, and thus a description thereof will be omitted.

Compared with the first embodiment of Fig. 1, the system of the second embodiment is different only in that it further includes a fourth heat exchanger 44 installed in the recirculation flow path 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 viewpoint of the recirculation flow path L44, the fourth heat exchanger 44 is located on the downstream side of the blower 45, and the fourth heat exchanger 44 is the second heat exchanger from the viewpoint of the discharge flow path L41. It is located between (42) and the third heat exchanger (43).

In the second embodiment, the third heat exchanger 43 is a small heat exchanger that increases the temperature of the recycle gas by 5 to 20 degrees Celsius, and the fourth heat exchanger 44 can heat the recycle gas at least 200 degrees Celsius or more. . 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 heat exchanger 44 may heat the recycle gas between 250 degrees Celsius 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 flow path L12 compared to the first embodiment. There is an advantage that can be further increased.

5 shows a two-way electrolysis system according to a third embodiment. Referring to the drawings, the two-way water electrolysis system of the third embodiment includes components such as a steam generator 10, an ejector 20, a two-way water electrolysis fuel cell 30, and heaters 61 and 62, and these components. It is composed of a plurality of flow paths that connect therebetween, and a plurality of heat exchangers, blowers, and pumps arranged in the flow path, and these components are the same or similar to each of the components of the first embodiment, and thus descriptions thereof will be omitted.

Compared with the first embodiment of Fig. 1, the system of the third embodiment is different in that it further includes a pump 77 installed in the water discharge passage L43. The pump 77 forcibly pumps water discharged from the drain 72 along the flow path L42 and discharges it to the outside.

According to this third embodiment, first, the pressure difference between the inlet of the hydrogen electrode 31 and the inlet of the air electrode 32 of the fuel cell 30 may be eliminated or reduced to a predetermined range to be maintained. The smaller the pressure difference between the inlet side of the hydrogen electrode 31 and the air electrode 32 of the fuel cell 30, the more stable the fuel cell system can be operated and the higher the efficiency. In comparison, since a plurality of flow paths and devices such as a heat exchanger are installed on the inlet side and the outlet side of the hydrogen electrode 31, the pressure of the hydrogen electrode 31 is in a higher state. However, when the pump 77 of the present invention is driven, the suction force of the pump 77 acts on the hydrogen electrode 31 along the discharge flow path L41 of the hydrogen electrode 31, thereby reducing the inlet pressure of the hydrogen electrode 31. Can be lowered. Therefore, by controlling the operation of the pump 77, the pressure on the inlet side of the hydrogen electrode 31 and the air electrode 32 can be kept the same or almost the same within a predetermined range, so that the system can be operated stably and the efficiency is improved. You can increase it.

In addition, as the inlet pressure of the hydrogen electrode 31 decreases, the capacity of a pump or blower (not shown) for transferring hydrogen along the hydrogen supply flow path L11 to the hydrogen electrode 31 may be reduced, and the discharge flow path L41 ) Even when the internal pressure is lowered than the atmospheric pressure as a whole, since water is forcibly discharged by the pump 77, it is possible to prevent water from flowing back into the discharge passage L41.

According to the embodiments of the present invention described above, an appropriate mixture of hydrogen and steam is supplied to the fuel cell according to each operation mode of the two-way water electrolysis system and the fuel cell mode, and the exhaust gas discharged from the fuel cell is reduced. There is an advantage of improving system efficiency by properly utilizing and reusing waste heat.

In general, in a two-way electrolysis system, the system efficiency in the electrolysis mode can be defined as follows.

In the above formula, η1 is the efficiency defined as the energy produced compared to the input energy, and the denominator represents the amount of heat of waste supplied to the boiler 12 and the electric energy supplied to the fuel cell 30 by renewable energy, and the numerator is As the heat quantity of hydrogen generated in the fuel cell 30, it indicates how much hydrogen is generated. η2 is the denominator of η1 minus the amount of waste heat. η3 is exergy efficiency, which reflects the quantity and quality of energy at the same time.

Similar to the above equations, the efficiency in the fuel cell mode of the bidirectional electrolysis system can be defined as follows.

As a result of calculating the exergy efficiency (η3) in the water electrolysis mode of the first to third embodiments of the present invention according to the above equation, the first embodiment is 83.87%, the second embodiment is 83.84%, and the third embodiment. Showed an efficiency of 83.78%. Considering that the exergy efficiency of the conventional general electrolysis mode is 70 to 75%, it can be seen that the system efficiency is improved when the bidirectional electrolysis system is configured as in the present invention.

As described above, those of ordinary skill in the field 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 is limited to the described embodiments and should not be defined, and should be defined by the claims to be described later, as well as those equivalent to the claims.

10: steam generator
20: ejector
30: two-way electrolysis fuel cell
41, 42, 43, 44, 53: heat exchanger
61,62: heater

Claims (17)

As a two-way electrolysis system,
A two-way electrolysis fuel cell 30 composed of a hydrogen electrode, an air electrode, and an electrolyte interposed therebetween and operable in either a water electrolysis mode or a fuel cell mode;
A first heat exchanger (41) for exchanging the hydrogen supplied to the hydrogen electrode and the first exhaust gas discharged from the hydrogen electrode;
A steam supply passage L21 for supplying steam to the hydrogen electrode and a branch passage L22 formed in the supply passage; And
Includes; an ejector 20 disposed in the steam supply passage L21,
The drive nozzle of the ejector is connected to the upstream side of the steam supply flow path, the injection nozzle of the ejector is connected to the downstream side of the steam supply flow path, and the inlet of the ejector branched from the discharge flow path of the first exhaust gas. It is connected to the feedback flow path (L47),
In the water electrolysis mode, steam is supplied to the hydrogen electrode through the steam supply passage (L21), and in the fuel cell mode, steam is supplied to the hydrogen electrode through the branch passage (L22). The method of claim 1,
A two-way water electrolysis system, characterized in that a junction of the steam supply flow path L21 and the hydrogen supply flow path L11 for supplying hydrogen to the hydrogen electrode is located between the first heat exchanger 41 and the hydrogen electrode. The method of claim 2,
A two-way water electrolysis system further comprising an additional steam supply flow path L31 for supplying externally supplied water supplied from the outside to the steam supply flow path L21 side in a water electrolysis mode. The method of claim 2,
A second heat exchanger 42 for exchanging heat exchange between the externally supplied water supplied from the outside and the first exhaust gas; further comprising,
Bi-directional water electrolysis system, characterized in that configured to supply externally supplied water vaporized as steam in the second heat exchanger (42) to the drive nozzle side of the ejector. The method of claim 4,
A water discharge unit disposed downstream of the second heat exchanger 42 and configured to remove water from the first exhaust gas;
A recirculation passage (L44) for resupplying at least a portion of the gas passing through the water discharge unit as recirculation gas to the hydrogen electrode;
And a third heat exchanger (43) installed in the recirculation passage and exchanging heat between the recirculation gas and the first exhaust gas. The method of claim 5,
The two-way water electrolysis system, characterized in that the recirculation passage (L44) is closed in a water electrolysis mode and opened in a fuel cell mode. The method of claim 6,
Bi-directional water electrolysis system, characterized in that the temperature of the recycle gas is raised by 5 to 20 degrees by the third heat exchanger (43). The method of claim 6,
A fourth heat exchanger (44) installed between the second heat exchanger (42) and the third heat exchanger (43) and configured to exchange heat between the recycle gas and the first exhaust gas; Sea system. The method of claim 6,
Further comprising a pump 77 installed in the water discharge passage (L43) of the water discharge unit to pump water,
Bi-directional water electrolysis, characterized in that the pressure difference between the inlet of the hydrogen electrode and the inlet of the air electrode is maintained within a predetermined range by controlling the pressure of hydrogen supplied through the hydrogen supply channel L11 and the operation of the pump 77 system. The method of claim 8,
A first blower 51 and a second blower 52 connected in parallel to an air supply passage L53 supplying air to the cathode; And
A fifth heat exchanger (53) for exchanging heat between the air supplied to the cathode through the air supply passage (L53) and the second exhaust gas discharged from the cathode; further comprising,
Two-way water electrolysis system, characterized in that the air supply amount of the second blower is 5 to 15 times larger than the air supply amount of the first blower. The method of claim 10,
And driving the first blower in a water electrolysis mode among the first and second blowers and driving the second blower in a fuel cell mode. As an operation method of a two-way electrolysis system capable of operating in a water electrolysis mode and a fuel cell mode,
The bi-directional water electrolysis system,
A two-way electrolysis fuel cell 30 composed of a hydrogen electrode, an air electrode, and an electrolyte interposed therebetween and operable in any one of a water electrolysis mode and a fuel cell mode; And
A steam supply passage L21 for supplying steam to the hydrogen electrode and a branch passage L22 formed in the supply passage; And
Includes; an ejector 20 disposed in the steam supply passage L21,
The driving method of the bidirectional water electrolysis system,
Supplying steam to the hydrogen electrode through the steam supply passage L21 in the water electrolysis mode and bypassing the ejector in the fuel cell mode to supply steam to the hydrogen electrode through the branch passage L22; And
In the water electrolysis mode, the step of resupplying at least a part of the exhaust gas discharged from the hydrogen electrode to the hydrogen electrode through the ejector; The method of operating a two-way water electrolysis system comprising a. The method of claim 12,
In the fuel cell mode, the step of heating the hydrogen supplied to the hydrogen electrode in the first heat exchanger 41 for exchanging the hydrogen supplied to the hydrogen electrode and the exhaust gas discharged from the hydrogen electrode,
At this time, the confluence of the steam supply flow path L21 and the hydrogen supply flow path L11 for supplying hydrogen to the hydrogen electrode is located between the first heat exchanger 41 and the hydrogen electrode. How it works. The method of claim 13, wherein in the hydroelectrolysis mode,
Vaporizing the externally supplied water into steam in a second heat exchanger (42) that heat-exchanges the externally supplied water and the exhaust gas supplied from the outside; And
Supplying externally supplied water vaporized as steam in the second heat exchanger (42) to the drive nozzle of the ejector. The method of claim 14,
Removing water in the exhaust gas from a water outlet installed at a rear end of the first heat exchanger (41); And
In the fuel cell mode, the step of resupplying at least a portion of the gas that has passed through the water discharge unit as a recycle gas to the hydrogen electrode; the method of operating a two-way water electrolysis system further comprising a. The method of claim 15,
The bi-directional water electrolysis system is a third heat exchanger 43, a blower 45, and a fourth heat exchanger that are sequentially installed from an upstream side to a downstream side in a recycling flow path L44 for resupplying the recycle gas to the hydrogen electrode. 44) and
The third heat exchanger 43 heats the recycle gas by heat exchange between the recycle gas and the exhaust gas to heat the recycle gas to 5 to 20 degrees Celsius, and the fourth heat exchanger 44 exchanges heat between the recycle gas and the exhaust gas. Method of operating a two-way electrolysis system, characterized in that configured to heat at least 200 degrees Celsius or more. The method of claim 15,
The bidirectional water electrolysis system further includes a pump 77 installed in the water discharge passage L43 of the water discharge unit to pump water to the outside,
The method further includes controlling the pressure of hydrogen supplied through the hydrogen supply passage L11 and the operation of the pump 77 to maintain a pressure difference between the inlet of the hydrogen electrode and the inlet of the air electrode within a predetermined range. Method of operating a two-way electrolysis system comprising a.

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