SOEC-SOFC-HBR Hybrid System for Green Ammonia Production

Abstract

Provided is a SOFC-SOEC-HBR hybrid system for green ammonia production. 【Solution means】Basically, an electric solid oxide electrolysis cell (SOEC) is driven by electricity produced from renewable energy such as wind power and solar power, but the intermittency of renewable energy is complemented by a solid oxide fuel cell (SOFC). Hydrogen produced by the water electrolysis cell (SOEC) and nitrogen discharged by the fuel cell (SOFC) are input into a Haber-Bosch reactor (Habor-Bosch Reactor), and heat from the SOFC and the Haber-Bosch reactor is recovered to provide a SOFC-SOEC-HBR hybrid system that efficiently and continuously produces green ammonia.

Description

Technical Field

[0001] The present invention relates to a SOFC - SOEC - HBR hybrid system for green ammonia production, which basically drives a solid oxide electrolysis cell (SOEC) with electricity produced from renewable energy such as wind power and sunlight. However, the intermittency of renewable energy is complemented by a solid oxide fuel cell (SOFC). Hydrogen produced by the electrolysis cell (SOEC) and nitrogen discharged by the fuel cell (SOFC) are input into a Haber - Bosch reactor (Habor - Bosch Reactor), and by recovering the heat of the SOFC and the Haber - Bosch reactor, the present invention relates to a SOFC - SOEC - HBR hybrid system for efficiently and continuously producing green ammonia.

Background Art

[0002] Green ammonia is produced by reacting green hydrogen generated by electrolyzing renewable energy electricity with nitrogen collected during standby. Since it does not contain carbon, its net emissions are close to zero from the perspective of life cycle assessment.

[0003] Green ammonia sometimes means a synthetic fuel convertible into electricity and thermal energy. Recently, however, its role as an energy carrier for storing and transporting green hydrogen produced by electrolyzing renewable energy in liquid form has been more focused. In particular, an emerging industry is producing ammonia, which is advantageous for storage and transportation, without carbon generation in regions rich in renewable energy, synthesizing green ammonia by the Haber - Bosch reaction, and then exporting it to regions such as Northeast Asia, North America, and Europe with high energy demand.

[0004] For the production of green ammonia, a hybrid technology that links renewable energy such as wind power and sunlight, an electrolysis cell (SOEC), and a Haber - Bosch reactor (HBR) has been proposed.

[0005] However, the hybrid systems proposed conventionally have the following problems.

[0006] First, since the power generation amount of renewable energy is not constant due to the intermittent power generation characteristics, it is difficult to stably start the solid oxide electrolysis cell (SOEC). Therefore, an energy storage system (ESS) may be added to complement the unstable power generation amount of renewable energy, but a huge cost must be incurred.

[0007] Second, although solid oxide electrolysis cells (SOECs) vary by type, low-temperature electrolysis cells require a driving temperature of 20 to 200°C, and high-temperature electrolysis cells require a driving temperature of 500 to 1000°C. Therefore, a separate heat source and heat exchanger are required for driving the solid oxide electrolysis cell (SOEC). However, if fossil fuels are used for heat production, the goal of carbon neutrality will inevitably fail.

[0008] Third, in order to produce ammonia in a Haber-Bosch reactor (HBR), in addition to the hydrogen provided by the solid oxide electrolysis cell (SOEC), nitrogen is further required. Therefore, another facility such as an air separation unit (ASU) must be added for nitrogen supply. However, a large amount of nitrous oxide (N2O) is generated during the operation of the air separation unit, which goes against the goal of producing green ammonia.

[0009] Fourth, in addition to hydrogen, oxygen is further discharged by the operation of the solid oxide electrolysis cell (SOEC). In order to utilize such by-product oxygen, a precise collection facility is required, which is a further factor increasing the system construction cost.

[0010] For reference, Korean Registered Patent No. 10-2186440 (prior art) relates to an electrochemical ammonia synthesis method and discloses a technology for synthesizing green ammonia by an electrochemical method without using fossil fuels.

[0011] At first glance, the prior art seems to be an environmentally friendly technology in that it produces ammonia using an electrochemical cell in which an oxidation electrode part and a reduction electrode part are partitioned by a cation conductive membrane. However, since it does not clarify by what source the nitrogen to be supplied to the electrochemical cell for ammonia synthesis or the electricity for driving the electrochemical cell is provided, the sources of nitrogen and the driving power source may induce carbon generation and still have the aforementioned conventional problems.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] One problem to be solved by the present invention is to present a solution for stably supplying power to a solid oxide electrolysis cell (SOEC) in a hybrid system of a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR) for green ammonia production.

[0014] Another problem to be solved by the present invention is to present a solution for generating and supplying the heat required for driving a solid oxide electrolysis cell (SOEC) in a hybrid system of a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR) in an environmentally friendly manner.

[0015] Yet another problem to be solved by the present invention is to provide a solution for generating and supplying nitrogen required for a Haber-Bosch reactor (HBR) in a hybrid system of a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR) in an environmentally friendly manner.

[0016] Yet another problem to be solved by the present invention is to provide a solution for recycling oxygen generated during the operation of a solid oxide electrolysis cell (SOEC) within the system.

Means for Solving the Problems

[0017] The present invention proposes an SOEC-SOFC-HBR hybrid system for green ammonia production, which includes a solid oxide fuel cell (SOFC), a power compensator that uses a renewable energy source and the solid oxide fuel cell to regulate the supplied power to be constant, a solid oxide electrolysis cell (SOEC) that produces hydrogen using the supplied power regulated by the power compensator, and a Haber-Bosch reactor that produces ammonia using the hydrogen produced by the solid oxide electrolysis cell and the nitrogen provided by the solid oxide fuel cell.

[0018] In one embodiment, the solid oxide electrolysis cell can also vaporize feed water using heat provided from at least one of the Haber-Bosch reactor and the solid oxide fuel cell.

[0019] In one embodiment, at least a part of the oxygen input to the air electrode of the solid oxide fuel cell may be supplied from the solid oxide electrolysis cell.

[0020] In one embodiment, the solid oxide fuel cell uses ammonia as a raw material, and at least a part of the ammonia produced by the Haber-Bosch reactor may be reused as fuel for the solid oxide fuel cell.

[0021] In one embodiment, a controller may be further included to adjust the ammonia production amount of the Haber-Bosch reactor by controlling the output of the solid oxide fuel cell.

Advantages of the Invention

[0022] According to an embodiment of the present invention, a stable and constant power source can be supplied to the solid oxide electrolysis cell (SOEC) even when renewable energy is used to drive a green ammonia production system based on a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR).

[0023] According to an embodiment of the present invention, heat required to drive the solid oxide electrolysis cell (SOEC) in a green ammonia production system based on a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR) can be generated and supplied in an environmentally friendly manner.

[0024] According to an embodiment of the present invention, nitrogen required for the Haber-Bosch reactor (HBR) in a green ammonia production system based on a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR) can be generated and supplied in an environmentally friendly manner.

[0025] According to an embodiment of the present invention, oxygen generated during the operation of a green ammonia production system based on a solid oxide electrolysis cell (SOEC)-Haber-Bosch reactor (HBR) can be reused within the system.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0027] Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. However, this is not intended to limit the present invention to a specific embodiment, and all transformations, equivalents, and substitutions including the technical idea of the present invention should be understood to be included within the scope of the present invention.

[0028] In this specification, a singular expression includes a plural expression unless otherwise specified in the context.

[0029] In this specification, when a certain configuration is described as "having" or "comprising" a certain sub - configuration, it means that, unless otherwise specified, other configurations are not excluded, and other configurations may be further included.

[0030] In this specification, the terms "... Unit", "... Module", and "Component" mean a unit that processes at least one function or operation, and may be implemented by hardware, software, or a combination of hardware and software.

[0031] In this specification, the description of "connected" may mean that two components are directly connected, but is not necessarily limited thereto, and may mean that they are connected with one or more other components arranged therebetween interposed.

[0032] <Example 1> FIG. 1 is a configuration diagram of the SOEC - SOFC - HBR hybrid system according to Example 1 of the present invention.

[0033] The SOEC-SOFC-HBR hybrid system of Example 1 includes a solid oxide electrolysis cell 110, a Haber-Bosch reactor 120, a solid oxide fuel cell 130, and a power compensator 140.

[0034] In FIG. 1, a renewable power source 10 is a general term for power generation means that obtains power from natural forces such as wind, sunlight, river water, ocean currents, solar heat, etc. It is environmentally friendly because the amount of carbon generated during the power production process is very small. However, it has the disadvantage that it is difficult to maintain constancy in the power production amount because the supply of natural forces is not constant.

[0035] In this example, in order to complement such disadvantages, the solid oxide fuel cell 130 is used as an auxiliary means for a stable supply of power. Specifically, when the supply power of the renewable power source 10 does not reach a predetermined reference amount required by the hybrid system of this example, the shortage is supplemented by the supply power of the solid oxide fuel cell 130, so that a constant power is always supplied to the solid oxide electrolysis cell 110 or the hybrid system of this example including the same.

[0036] Hereinafter, each element constituting the SOEC-SOFC-HBR hybrid system of Example 1 will be described in detail.

[0037] A solid oxide electrolysis cell (SOEC) 110 is a ceramic cell that uses a solid oxide that can permeate oxygen ions as an electrolyte, and electrolyzes water to produce hydrogen and oxygen. Energy for electrolysis is supplied to the solid oxide electrolysis cell 110 from at least one of the renewable power source 10 and the solid oxide fuel cell 130.

[0038] The solid oxide electrolysis cell 110 may be embodied as a high-temperature type electrolysis cell that requires heat of 500°C to 1000°C among electrolysis cells.

[0039] The high-temperature steam electrolysis method used by high-temperature water electrolysis cells utilizes the phenomenon that the electrical energy required for water decomposition becomes lower as the temperature increases. The high-temperature steam electrolysis method enables highly efficient water decomposition with less electrical energy. Since its structure and principle are the same as those of solid oxide fuel cells, bidirectional operation is possible with a single solid oxide fuel cell or solid oxide water electrolysis cell. Also, by using a solid electrolyte, it has excellent durability against corrosion and does not require replenishment of the electrolyte, making maintenance easy. However, a large amount of heat is required to heat steam to 700 °C or higher.

[0040] Therefore, the solid oxide water electrolysis cell 110 of Example 1 basically receives the heat required for water vaporization from the Haber-Bosch reactor 120, and the insufficient amount of heat is further supplied from the exhaust gas of the solid oxide fuel cell 130. Alternatively, the solid oxide water electrolysis cell 110 of Example 1 may basically receive the heat required for water vaporization from the exhaust gas of the solid oxide fuel cell 130, and the insufficient amount of heat may be further supplied from the Haber-Bosch reactor 120.

[0041] The Haber-Bosch reactor (HBR) 120 produces ammonia using the hydrogen produced by the solid oxide water electrolysis cell 110 and the nitrogen provided by the solid oxide fuel cell 130.

[0042] The Haber-Bosch reactor 120 is a device that produces ammonia using the Haber-Bosch process. The Haber-Bosch process is a chemical reaction in which nitrogen gas (N2) in the air is reacted with hydrogen gas (H2) extracted from natural gas or other sources to synthesize ammonia (NH3).

[0043] For chemical reactions, in addition to a small amount of other accelerators, a catalyst such as iron or iron oxide is required, and the chemical reaction occurs at high temperature (>400 °C) and high pressure (>200 Bar). Since the Haber-Bosch reaction is an exothermic reaction, at least a part of the high-temperature heat generated in the Haber-Bosch reactor 120 can be recovered by a heat exchanger (not shown) and supplied to the solid oxide electrolysis cell 110 or utilized for other purposes.

[0044] The formula for the Haber-Bosch process is as follows. (Chemical formula 1) N2(g) + 3H2(g) ⇌ 2NH3(g) (Formula 1)

[0045] This process releases heat by an exothermic reaction, and the reaction proceeds in the direction of ammonia synthesis while the temperature decreases.

[0046] As seen in Formula 1, nitrogen is required for the chemical reaction in the Haber-Bosch process. Conventionally, it was necessary to equip a separate air separation unit (ASU) to supply nitrogen to the Haber-Bosch reactor. However, in Example 1, since nitrogen contained in the exhaust gas of the solid oxide fuel cell 130 can be supplied to the Haber-Bosch reactor 120, no separate air separation device is required for nitrogen supply, or ammonia synthesis can be achieved by equipping only a minimum-capacity air separation device. By omitting the air separation device, the construction cost of the equipment can be reduced, and the power used for driving the air separation device can also be saved.

[0047] The ammonia synthesized in the Haber-Bosch reactor 120 is stored in the storage 150, but at least a part of it is fed back to the solid oxide fuel cell 130 and used as fuel, and another part is sold through the distribution route.

[0048] For reference, hydrogen can be liquefied and transported by itself without synthesizing it into ammonia. However, the liquefaction condition of hydrogen is -253°C under atmospheric pressure, while the liquefaction condition of ammonia is -33°C. Therefore, less energy is required for the liquefaction of ammonia compared to hydrogen. Thus, liquefying ammonia is more advantageous than liquefying hydrogen and is advantageous in terms of efficiently storing and transporting large-capacity green energy.

[0049] The solid oxide fuel cell 130 (Solid Oxide Fuel Cell, SOFC) is a fuel cell that uses an ion-conductive ceramic as an electrolyte and includes an oxygen ion-conductive electrolyte, an air electrode (cathode), and a fuel electrode (anode) located on both sides thereof.

[0050] If air and hydrogen are supplied to the air electrode and the fuel electrode, respectively, a reduction reaction of oxygen occurs at the air electrode to generate oxygen ions. The oxygen ions that have moved through the electrolyte to the fuel electrode further react with the hydrogen supplied to the fuel electrode to generate water. At this time, electrons are generated at the fuel electrode and consumed at the air electrode. Therefore, electricity is produced based on the principle that current flows when both electrodes are connected to each other.

[0051] The solid oxide fuel cell 130 can use pure hydrogen as fuel, can also use hydrogen obtained by reforming hydrocarbon fuels such as liquefied natural gas (LNG), liquefied propane gas (LPG), and methane gas as fuel, and can also use ammonia as fuel.

[0052] In an embodiment of using ammonia as fuel, the solid oxide fuel cell 130 thermally decomposes the supplied ammonia to generate nitrogen and hydrogen. Then, the generated hydrogen is used for electricity production, and the nitrogen contained in the exhaust gas is supplied to the Haber-Bosch reactor 120. A part of the ammonia generated in the Haber-Bosch reactor 120 may be supplied as fuel to the solid oxide fuel cell 130, or ammonia may be supplied through another route other than the Haber-Bosch reactor 120.

[0053]

[0053] In one embodiment where pure hydrogen or hydrogen produced by reforming is used as fuel, since nitrogen contained in the external air is contained as it is without participating in the chemical reaction of the stack in the exhaust gas of the solid oxide fuel cell 130, the nitrogen contained in the exhaust gas of the solid oxide fuel cell 130 is supplied to the Haber-Bosch reactor 120.

[0054] The solid oxide fuel cell 130 supplies at least a part of the high-temperature heat contained in the exhaust gas of the stack to the solid oxide water electrolysis cell 110 through a heat exchanger (not shown).

[0055] Oxygen may be supplied to the air electrode of the stack included in the solid oxide fuel cell 130 from the external air (AIR), or at least a part of the oxygen obtained by electrolyzing water in the solid oxide water electrolysis cell 110 may be supplied.

[0056] In one embodiment, the air electrode of the solid oxide fuel cell 130 preferentially receives oxygen supply from the solid oxide water electrolysis cell 110, but the insufficient oxygen may be replenished from the external air. Alternatively, in another embodiment, the air electrode of the solid oxide fuel cell 130 preferentially receives oxygen supply from the external air, but the insufficient oxygen may be replenished from the solid oxide water electrolysis cell 110.

[0057] The electric power produced by the solid oxide fuel cell 130 may be supplied or sold externally, or may be utilized as the in-plant power of the green ammonia hybrid plant.

[0058] The power compensator 140 adjusts the power supply of the renewable energy source 10 or the solid oxide fuel cell 130 so that the solid oxide water electrolysis cell 110 can perform electrolysis smoothly. In one embodiment, the power compensator 140 preferentially uses the renewable energy source 10 as the power source, but controls the output of the solid oxide fuel cell 130 so that the power supplied to the solid oxide water electrolysis cell 110 becomes constant.

[0059] As an example of specific operations, the power compensator 140 senses the amount of power of the renewable energy source 10 supplied to the solid oxide electrolysis cell 110, and when the supply amount of the renewable energy source 10 is less than the amount of power required by the solid oxide electrolysis cell 110, the solid oxide fuel cell 130 is controlled to supplement the insufficient amount of power with the electricity generated by the solid oxide fuel cell 130. In this sense, the power compensator 140 may be regarded as a controller (not shown) of the solid oxide fuel cell 130.

[0060] Therefore, the hybrid system according to Embodiment 1 enables stable operation by the complementary power supply of the renewable energy source and the solid oxide fuel cell, so that another energy storage system (Electric power Storage System, ESS) for complementing the intermittency of the renewable energy is not required, or a minimum-capacity energy storage system is sufficient, and the construction cost of the system can be significantly reduced.

[0061] <Example 2> Example 2 relates to the case where the heat required for the evaporation of water in the solid oxide electrolysis cell is supplied only from the Haber Bosch reactor as compared with Example 1.

[0062] FIG. 2 is a configuration diagram of the SOEC-SOFC-HBR hybrid system according to Example 2 of the present invention.

[0063] The SOEC-SOFC-HBR hybrid system of Example 2 includes a solid oxide electrolysis cell 210, a Haber Bosch reactor 220, a solid oxide fuel cell 230, and a power compensator 240.

[0064] In Example 2, since the solid oxide electrolysis cell 210, the Haber Bosch reactor 220, and the power compensator 240 have the same technical configuration as the solid oxide electrolysis cell 110, the Haber Bosch reactor 120, and the power compensator 140 of Example 1, duplicate explanations are omitted.

[0065] The solid oxide fuel cell 230 differs only in that the heat generated in the stack is not sent to the solid oxide electrolysis cell 210 compared to the solid oxide fuel cell 130 of Example 1, and all other technical configurations are the same.

[0066] When the heat supplied from the Haber-Bosch reactor 220 is sufficient for the generation of steam in the solid oxide electrolysis cell 210, the heat discharged from the solid oxide fuel cell 230 may be utilized for other uses required in the system.

[0067] <Example 3> Example 3 relates to the case where the oxygen required for the air electrode of the solid oxide fuel cell is supplied only from external air (Air) compared to Example 1.

[0068] FIG. 3 is a configuration diagram of the SOEC-SOFC-HBR hybrid system according to Example 3 of the present invention.

[0069] The SOEC-SOFC-HBR hybrid system of Example 3 includes a solid oxide electrolysis cell 310, a Haber-Bosch reactor 320, a solid oxide fuel cell 330, and a power compensator 340.

[0070] In Example 3, since the Haber-Bosch reactor 320 and the power compensator 340 have the same technical configuration as the Haber-Bosch reactor 120 and the power compensator 140 of Example 1, duplicate explanations are omitted.

[0071] The solid oxide electrolysis cell 310 differs only in that the oxygen produced by electrolysis is not sent to the solid oxide fuel cell 330 compared to the solid oxide electrolysis cell 110 of Example 1, and all other technical configurations are the same.

[0072] Also, the solid oxide fuel cell 330 differs only in that the oxygen required for the air electrode is supplied only from external air (Air), and all other technical configurations are the same as those of the solid oxide fuel cell 130 of Example 1.

[0073] The solid oxide electrolysis cell 310 can supply the produced oxygen to a burner (not shown) of the system, can store it in an external storage tank, or can utilize it for other necessary applications.

[0074] <Example 4> Example 4 uses hydrogen as the fuel of the solid oxide fuel cell compared with Example 1, and relates to the case where the ammonia synthesized in the Haber - Bosch reactor is used for other applications such as full - scale sales.

[0075] FIG. 4 is a configuration diagram of the SOEC - SOFC - HBR hybrid system according to Example 4 of the present invention.

[0076] The SOEC - SOFC - HBR hybrid system of Example 4 includes a solid oxide electrolysis cell 410, a Haber - Bosch reactor 420, a solid oxide fuel cell 430, and a power compensator 440.

[0077] In Example 4, since the solid oxide electrolysis cell 410, the Haber - Bosch reactor 420, and the power compensator 440 have the same technical configuration as the solid oxide electrolysis cell 110, the Haber - Bosch reactor 120, and the power compensator 140 of Example 1, the repeated description is omitted.

[0078] The solid oxide fuel cell 430 uses hydrogen as the fuel, but pure hydrogen may be used, or hydrogen reformed with carbonaceous gas may be used. Therefore, all other technical configurations are the same as those of the solid oxide fuel cell 130 in Example 1.

[0079] In Examples 1 to 4 described above, modified examples for adjusting the ammonia production amount of the hybrid system may be presented.

[0080] That is, in order to adjust the ammonia synthesis amount in the Haber - Bosch reactors 120, 220, 320, 420, it is necessary to adjust the hydrogen supply amount of the solid oxide water electrolysis cells 110, 210, 310, 410 or adjust the nitrogen supply amount of the solid oxide fuel cells 130, 230, 330, 430.

[0081] As an example for this, in addition to the function of maintaining a constant amount of electric power supplied to the solid oxide water electrolysis cells 110, 210, 310, 410, the power compensators 140, 240, 340, 440 can further have the function of adjusting the amount of electric power itself. By adjusting the electric power supplied to the solid oxide water electrolysis cells 110, 210, 310, 410, the hydrogen generation amount of the water electrolysis cells can be decreased or increased.

[0082] As another example, the controller of the solid oxide fuel cells 130, 230, 330, 430 can decrease or increase the nitrogen supplied to the solid oxide water electrolysis cells 110, 210, 310, 410 by adjusting the power generation amount of the fuel cells.

[0083] As described above with reference to some embodiments of the present invention, those having ordinary knowledge in the technical field can understand that the present invention can be variously modified and changed within the scope not departing from the idea and scope of the present invention described in the following claims.

Explanation of Reference Numerals

[0084] 10: Renewable energy source 110, 210, 310, 410: Solid oxide water electrolysis cell 120, 220, 320, 420: Haber - Bosch reactor 130, 230, 330, 430: Solid oxide fuel cell 140, 240, 340, 440: Power compensator

Claims

1. A solid oxide fuel cell (SOFC), a renewable energy source, and a power compensator that regulates the supplied power to be constant using the solid oxide fuel cell, a solid oxide electrolysis cell (SOEC) that produces hydrogen using the supplied power regulated by the power compensator, and a Haber-Bosch reactor that produces ammonia using the hydrogen produced by the solid oxide electrolysis cell and the nitrogen provided by the solid oxide fuel cell. An SOEC-SOFC-HBR hybrid system for green ammonia production, comprising the above components.

2. The solid oxide electrolysis cell is characterized in that it vaporizes feed water using heat provided from at least one of the Haber-Bosch reactor and the solid oxide fuel cell. The SOEC-SOFC-HBR hybrid system for green ammonia production according to Claim 1.

3. At least a part of the oxygen input to the air electrode of the solid oxide fuel cell is supplied from the solid oxide electrolysis cell. The SOEC-SOFC-HBR hybrid system for green ammonia production according to Claim 1.

4. The solid oxide fuel cell uses ammonia as a raw material, and at least a part of the ammonia produced by the Haber-Bosch reactor is reused as fuel for the solid oxide fuel cell. The SOEC-SOFC-HBR hybrid system for green ammonia production according to Claim 1.

5. The SOEC-SOFC-HBR hybrid system for green ammonia production according to any one of Claims 1 to 4, further comprising a controller that regulates the ammonia production amount of the Haber-Bosch reactor by controlling the output of the solid oxide fuel cell.

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