Electrolysis system

Abstract

The present invention provides an electrolysis system that ensures refrigeration required for a hydrogen storage carrier to absorb hydrogen and reduces energy loss associated with the absorption of hydrogen. The present invention is provided with: a solid oxide electrolysis cell for electrolyzing water vapor supplied to a hydrogen electrode; the hydrogen absorbing and releasing part is used for cooling the hydrogen storage carrier to absorb hydrogen and heating the hydrogen storage carrier to release hydrogen; a water vapor supply line for supplying water vapor to the hydrogen electrode; a recovery line for recovering the hydrogen gas contained in the exhaust gas discharged from the hydrogen gas electrode to the hydrogen gas absorption / release unit; a gas-liquid separation unit which is provided in the recovery line and performs gas-liquid separation by cooling the exhaust gas by means of heat exchange with the cooling liquid; the cooling liquid supply pipeline is used for supplying the cooling liquid to the gas-liquid separation part and then supplying the cooling liquid to the hydrogen absorption and release part; and a first heat exchange unit for cooling, which is provided in the hydrogen gas absorption / release unit, and which cools the hydrogen storage carrier by exchanging heat with the coolant supplied from the coolant supply line.

Description

Technical Field

[0001] This specification discloses an electrolysis system. Background Technology

[0002] Conventionally, an electrochemical device has been proposed comprising: a solid oxide electrolytic cell for electrolyzing H2O to generate H2, a hydrogen storage material for absorbing the H2 generated by the solid oxide electrolytic cell, and a heat transfer unit for transferring heat from the hydrogen storage material to the solid oxide electrolytic cell (for example, see Patent Document 1). This device includes a heat exchanger that exchanges heat between the piping supplying H2O to the solid oxide electrolytic cell and the hydrogen storage material, and serves as the heat transfer unit. The heat exchanger moves heat from the hydrogen storage material to the H2O in a manner that vaporizes the H2O to be supplied to the solid oxide electrolytic cell. This allows the heat absorption of the solid oxide electrolytic cell to offset the heat generation of the hydrogen storage material, thereby improving energy efficiency. Furthermore, a heat exchanger is provided on the piping for transferring only H2 from a gas containing H2 and H2O discharged from the solid oxide electrolytic cell to the hydrogen storage material, to cool the gas through heat exchange with cooling water, and a piping for removing water after cooling the gas.

[0003] In addition, a technology for storing and transporting hydrogen based on the bicarbonate-formic acid cycle has been proposed (for example, see Patent Document 2).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-199675

[0005] Patent Document 2: Japanese Patent Publication No. 2017-500272

[0006] In the aforementioned electrochemical device, hydrogen storage material absorbs hydrogen gas, and cooling is achieved using H2O supplied to the solid oxide electrolyzer. However, since the amount of H2O supplied to the solid oxide electrolyzer is limited by the target amount of hydrogen produced, insufficient cooling to ensure adequate hydrogen absorption occurs. The same problem arises when using a liquid organic hydrogen carrier (LOHC) such as bicarbonate-formic acid instead of the hydrogen storage material. Summary of the Invention

[0007] The purpose of this disclosure is to provide an electrolysis system that can ensure the refrigeration required for hydrogen storage carrier to absorb hydrogen and reduce energy losses associated with hydrogen absorption.

[0008] The following means are employed in this disclosure to achieve the aforementioned main objective.

[0009] The main feature of the electrolysis system disclosed herein is that it comprises: a solid oxide electrolytic cell for electrolyzing water vapor supplied to a hydrogen electrode to generate hydrogen; a hydrogen absorption and release section for cooling a hydrogen storage carrier to absorb hydrogen and heating the hydrogen storage carrier to release hydrogen; a water vapor supply line for supplying water vapor to the hydrogen electrode; a recovery line for recovering hydrogen contained in the exhaust gas discharged from the hydrogen electrode to the hydrogen absorption and release section; a gas-liquid separation section provided in the recovery line for cooling the exhaust gas through heat exchange with a coolant to perform gas-liquid separation; a coolant supply line for supplying the coolant to the gas-liquid separation section and then to the hydrogen absorption and release section; and a first cooling heat exchange section provided in the hydrogen absorption and release section for cooling the hydrogen storage carrier through heat exchange with the coolant supplied from the coolant supply line.

[0010] The electrolysis system disclosed herein includes a gas-liquid separation unit that sequentially separates the exhaust gas from the hydrogen electrode of a solid oxide electrolyzer into a gas-liquid mixture, and a coolant supply line that supplies coolant to the hydrogen storage carrier. By using the coolant from the gas-liquid separation unit also for cooling the hydrogen storage carrier, the refrigeration required for hydrogen absorption by the hydrogen storage carrier is ensured, and energy losses related to hydrogen absorption are reduced. As a result, the overall energy efficiency of the system can be further improved. Here, hydrogen storage materials and liquid organic hydrogen storage carriers can be cited as examples of hydrogen storage carriers. Attached Figure Description

[0011] Figure 1 This is a schematic structural diagram of the electrolysis system according to the first embodiment.

[0012] Figure 2 This is an explanatory diagram showing the flow patterns of raw water, cooling water, and unused waste heat during hydrogen generation.

[0013] Figure 3 This is an illustration of the flow pattern of unused waste heat during hydrogen release.

[0014] Figure 4 This is a schematic structural diagram of the electrolysis system according to the second embodiment.

[0015] Figure 5 This is an explanatory diagram showing the flow patterns of raw water, cooling water, and unused waste heat during hydrogen generation.

[0016] Figure 6 This is an illustration of the flow pattern of unused waste heat during hydrogen release.

[0017] Explanation of reference numerals in the attached figures

[0018] 10, 110… Electrolysis system, 21… Electrolytic cell stack (solid oxide electrolytic cell), 32… Steam generator (evaporation section), 33… Water supply pipe (raw water supply pipeline), 35… Steam supply pipe (steam supply pipeline), 61… Hydrogen recovery piping (recovery pipeline), 62… Condenser (gas-liquid separation section), 63… Cooling water supply pipe (cooling water supply pipeline), 70… Hydrogen storage tank (hydrogen absorption and release section), 71… Hydrogen storage alloy, 72… First cooling heat exchange section, 73… Second cooling heat exchange section 74…Heat exchange section, 81…Waste heat supply pipe (external heat supply pipeline), 170…Hydrogen absorption and release system (hydrogen absorption and release section), 171…Bicarbonate tank (first tank), 172…Absorption reactor (absorption reaction section), 172b…First cooling heat exchange section, 172c…Second cooling heat exchange section, 173…Formate tank (second tank), 174…Release reactor (release reaction section), 174a…Heat exchange section, 175…Circulation piping (circulation path). Detailed Implementation

[0019] The manner in which this disclosure is implemented will now be described with reference to the accompanying drawings.

[0020] Figure 1 This is a schematic structural diagram of the electrolysis system 10 according to the first embodiment. For example... Figure 1 As shown, the electrolysis system 10 of the first embodiment includes: an electrolysis module 20, including an electrolysis cell stack 21 for generating hydrogen by electrolysis of steam; a steam supply system 30 for supplying steam to the electrolysis module 20; a hydrogen supply system 40 for supplying hydrogen to the electrolysis module 20; an air supply system 50 for supplying air to the electrolysis module 20 as scavenging air; and a hydrogen recovery system 60 for causing a hydrogen storage alloy 71 to absorb and recover the generated hydrogen from the electrolysis module 20.

[0021] In addition to the electrolytic cell stack 21, the electrolysis module 20 also includes a burner 22 and a heat exchange section (not shown), which are housed in a heat-insulated module housing 25.

[0022] The electrolytic cell stack 21 comprises multiple solid oxide electrolytic cells (SOECs), each including a solid electrolyte, a hydrogen electrode disposed on one surface of the solid electrolyte, and an oxygen electrode disposed on the other surface of the solid electrolyte. Electrolysis of the electrolytic cell stack 21 is performed by supplying water vapor to the hydrogen electrode and power from the power supply unit 26. At the hydrogen electrode, hydrogen is produced by decomposing water vapor into oxygen ions and hydrogen gas. At the oxygen electrode, oxygen is produced by allowing the decomposed oxygen ions to permeate through the solid electrolyte and combine with electrons. Furthermore, the power supply unit 26 can utilize system power, renewable energy devices (such as solar power generation devices), batteries, etc.

[0023] The electrolytic cell stack 21 operates in a high-temperature environment, for example, 650–800°C, so the solid electrolyte, hydrogen electrode, and oxygen electrode are made of ceramic materials. Furthermore, since water vapor is decomposed into oxygen ions and hydrogen gas by a catalyst, the hydrogen electrode uses a cermet material, combining a metal such as nickel (which has catalytic activity) with ceramic. To maintain the catalytic activity of the hydrogen electrode, it is necessary to keep it in a reducing atmosphere to prevent metal oxidation. Therefore, in this embodiment, anti-oxidation hydrogen is mixed into the water vapor supplied to the hydrogen electrode.

[0024] A hydrogen inlet pipe 21a is connected to the hydrogen electrode inlet of the electrolytic cell stack 21. A steam supply system 30 and a hydrogen supply system 40 are connected to the other end of the hydrogen inlet pipe 21a. An oxygen inlet pipe 21b is connected to the oxygen electrode inlet of the electrolytic cell stack 21. An air supply system 50 is connected to the other end of the oxygen inlet pipe 21b. A hydrogen electrode outlet pipe 21c is connected to the hydrogen electrode outlet of the electrolytic cell stack 21. A hydrogen recovery system 60 is connected to the other end of the hydrogen electrode outlet pipe 21c. An oxygen electrode outlet pipe 21d is connected to the oxygen electrode outlet of the electrolytic cell stack 21. A burner 22 is connected to the other end of the oxygen electrode outlet pipe 21d. A combustion hydrogen supply pipe 43 is connected to the burner 22.

[0025] The steam supply system 30 includes: a water tank 31 storing raw water (pure water) supplied by a pure water device (not shown); a steam generator 32 for heating the raw water to generate steam; a water supply pipe 33 connected to the water tank 31 and the steam generator 32; a water pump 34 installed on the water supply pipe 33 and pressurizing the raw water in the water tank 31 to the steam generator 32; and a steam supply pipe 35 for supplying the steam generated by the steam generator 32 to the hydrogen electrode inlet pipe 21a of the electrolysis module 20. The steam generator 32 is connected to a waste heat supply pipe 81 and uses unused waste heat (e.g., 50-60°C) discharged from a factory or the like and supplied through the waste heat supply pipe 81 as a heat source to generate steam. As a steam generator 32, a steam heat pump can be cited as an example. This steam heat pump includes: a heat recovery heat exchanger (evaporator), a compressor, a steam generation heat exchanger (condenser), an expansion valve, and circulation piping connecting them and circulating the refrigerant. Water vapor (saturated steam) is generated by exchanging heat between unused waste heat and the refrigerant using the heat recovery heat exchanger, followed by heat exchange between the compressed and heated refrigerant and the feed water using the steam generation heat exchanger. Furthermore, the steam generator 32 can be of any structure as long as it uses at least one of the unused waste heat sources to heat the feed water and generate water vapor. The water vapor introduced from the steam supply system 30 to the hydrogen electrode inlet piping 21a is heated by heat exchange between the water vapor and combustion exhaust gases, etc., at the heat exchange section (not shown) provided at the hydrogen electrode inlet piping 21a, and then supplied to the hydrogen electrode of the electrolytic cell stack 21.

[0026] The hydrogen supply system 40 includes: an oxidation-preventing hydrogen supply pipe 41 connected at one end to the hydrogen electrode inlet pipe 21a; a hydrogen blower 42 mounted on the oxidation-preventing hydrogen supply pipe 41; a combustion hydrogen supply pipe 43 connected at one end to the burner 22; and a hydrogen blower 44 mounted on the combustion hydrogen supply pipe 43. Hydrogen is introduced into the oxidation-preventing hydrogen supply pipe 41 by driving the hydrogen blower 42, and the introduced hydrogen is supplied as oxidation-preventing hydrogen to the hydrogen electrode of the electrolytic cell stack 21. Additionally, hydrogen is introduced into the combustion hydrogen supply pipe 43 by driving the hydrogen blower 44, and the introduced hydrogen is supplied as combustion hydrogen to the burner 22. Furthermore, flow meters (not shown) are respectively installed on the oxidation-preventing hydrogen supply pipe 41 and the combustion hydrogen supply pipe 43.

[0027] The air supply system 50 includes an air supply pipe 51 connected to the oxygen electrode inlet pipe 21b and an air blower 52 installed on the air supply pipe 51. By driving the air blower 52, the air drawn into the air supply pipe 51 is introduced into the oxygen electrode inlet pipe 21b. After the air is heated by heat exchange between the air and combustion exhaust gas, hydrogen electrode exhaust gas, etc., by the heat exchange section (not shown) installed at the oxygen electrode inlet pipe 21b, the air is supplied to the oxygen electrode of the electrolytic cell stack 21.

[0028] The hydrogen recovery system 60 recovers generated hydrogen from the hydrogen electrode exhaust gas, which contains generated hydrogen and unreacted water vapor discharged from the hydrogen electrode outlet. The hydrogen recovery system 60 includes: a hydrogen storage tank 70; a hydrogen recovery pipe 61 connecting the hydrogen electrode outlet pipe 21c to the inlet of the hydrogen storage tank 70; a condenser 62 installed on the hydrogen recovery pipe 61; and a cooling water supply pipe 63 that sequentially supplies cooling water to the condenser 62 and the hydrogen storage tank 70. The condenser 62 condenses the hydrogen electrode exhaust gas by exchanging heat between the water vapor contained in the hydrogen electrode exhaust gas flowing in the hydrogen recovery pipe 61 and the cooling water flowing in the cooling water supply pipe 63, separating the hydrogen electrode exhaust gas into generated hydrogen and condensate. The condensate separated by the condenser 62 is collected in a water tank 31 by a condensate pipe 64. The condensate collected in the water tank 31 is used as feed water for generating water vapor for electrolysis.

[0029] The hydrogen storage device 70 includes: a hydrogen storage alloy 71 that absorbs hydrogen when cooled and releases hydrogen when heated; a first cooling heat exchange unit 72 and a second cooling heat exchange unit 73 for cooling the hydrogen storage alloy 71; and a heating heat exchange unit 74 for heating the hydrogen storage alloy 71.

[0030] Hydrogen storage alloy 71 is a powder or granular component of an alloy containing two or more metals, such as magnesium, titanium, vanadium, and lanthanum, and has the characteristic of absorbing hydrogen at around 30 to 40°C and releasing the absorbed hydrogen at around 50 to 60°C.

[0031] The first cooling heat exchange unit 72 is connected to the cooling water supply pipe 63 downstream of the condenser 62, and cools the hydrogen storage alloy 71 by heat exchange with the cooling water (e.g., 35-40°C) passing through the condenser 62. The second cooling heat exchange unit 73 is connected to the water supply pipe 33 downstream of the water tank 31 and upstream of the steam generator 32, and cools the hydrogen storage alloy 71 by heat exchange with the feed water (e.g., 20-30°C) from the water tank 31. The feed water, heated by the heat exchange with the hydrogen storage alloy 71, is supplied to the steam generator 32. In this embodiment, the first cooling heat exchange unit 72 and the second cooling heat exchange unit 73 are configured such that, relative to the flow of generated hydrogen, the first cooling heat exchange unit 72 is upstream of the second cooling heat exchange unit 73, so that heat exchange is performed with the generated hydrogen introduced into the hydrogen storage tank 70 in the order of cooling water and feed water (in order of water temperature from high to low). A large amount of cooling water is supplied to the condenser 62 for heat exchange with the hydrogen electrode exhaust. Due to its large heat capacity, the cooling water passing through the condenser 62 can be used to ensure the necessary cooling for hydrogen absorption in the hydrogen storage alloy 71. On the other hand, although the temperature of the feed water is lower than that of the cooling water passing through the condenser 62, the supply of feed water is limited by the target amount of hydrogen generated, so the supply of feed water alone cannot ensure sufficient cooling. In this embodiment, since the feed water is supplied in conjunction with the cooling water supply, the cooling of the hydrogen storage alloy 71 can be promoted, the performance of the hydrogen storage alloy 71 can be maximized, and a sufficient amount of hydrogen can be absorbed.

[0032] The heating heat exchange unit 74 is connected to the waste heat supply pipe 81 and heats the hydrogen storage alloy 71 by heat exchange with unused waste heat (e.g., 50-60°C) supplied through the waste heat supply pipe 81.

[0033] One end of a hydrogen supply pipe 75 is connected to the outlet of the hydrogen storage tank 70, and the other end of an anti-oxidation hydrogen supply pipe 41 and a combustion hydrogen supply pipe 43 are connected to the other end of the hydrogen supply pipe 75. An on / off valve 76 is provided on the hydrogen supply pipe 75. The hydrogen stored in the hydrogen storage alloy 71 of the hydrogen storage tank 70 is released by heating the hydrogen storage alloy 71 by the heating heat exchange unit 74. Furthermore, by driving the hydrogen blower 42 with the on / off valve 76 open, the released hydrogen is introduced into the anti-oxidation hydrogen supply pipe 41 and supplied from the anti-oxidation hydrogen supply pipe 41 to the hydrogen electrode of the electrolytic cell stack 21. In addition, by driving the hydrogen blower 44 with the on / off valve 76 open, the released hydrogen is introduced into the combustion hydrogen supply pipe 43 and supplied from the combustion hydrogen supply pipe 43 to the burner 22.

[0034] The circulating pipe 65 branches off from the downstream side of the condenser 62 and the upstream side of the hydrogen storage tank 70 in the hydrogen recovery pipe 61, and connects to the other end of the anti-oxidation hydrogen supply pipe 41 and the other end of the combustion hydrogen supply pipe 43. By driving the hydrogen blower 42 with the on / off valve 76 closed, the generated hydrogen flowing in the hydrogen recovery pipe 61 is introduced from the circulating pipe 65 into the anti-oxidation hydrogen supply pipe 41, and then supplied from the anti-oxidation hydrogen supply pipe 41 to the hydrogen electrode of the electrolyzer stack 21. Additionally, by driving the hydrogen blower 44 with the on / off valve 76 closed, the generated hydrogen flowing in the hydrogen recovery pipe 61 is introduced from the circulating pipe 65 into the combustion hydrogen supply pipe 43, and then supplied from the combustion hydrogen supply pipe 43 to the burner 22.

[0035] The waste heat supply system 80 includes: a waste heat supply pipe 81 branching off from a piping connected to a source of unused waste heat and connected to a steam generator 32 and a hydrogen storage tank 70; and a reversing valve 82 located at the branch point of the waste heat supply pipe 81 and switching the destination of the unused waste heat supply. Furthermore, the waste heat supply system 80 may also include a heat storage tank for accumulating unused waste heat, and supply the unused waste heat accumulated in the heat storage tank to the steam generator 32 and the hydrogen storage tank 70 (heat exchange unit 74) via the waste heat supply pipe 81.

[0036] The control device 90 is configured as a CPU-centric microprocessor, and in addition to the CPU, it also includes ROM, RAM, input / output ports, etc. Detection signals from temperature sensors located near the electrolytic cell stack 21, temperature sensors located at the burner 22, flow meters located at the anti-oxidation hydrogen supply pipe 41, flow meters located at the combustion hydrogen supply pipe 43, and flow meters located at the hydrogen recovery pipe 61 are input to the control device 90 via the input ports. Furthermore, control signals for the steam generator 32, water pump 34, hydrogen blowers 42 and 44, air blower 52, on / off valve 76, and reversing valve 82 are output from the control device 90 via the output ports.

[0037] Next, the operation of the electrolysis system 10 configured as described will be explained. In particular, the operation when the generated hydrogen is stored in the hydrogen storage tank 70 during electrolysis operation, and the operation when the hydrogen stored in the hydrogen storage tank 70 is released during electrolysis shutdown or startup will be explained. Figure 2 This is an explanatory diagram showing the flow patterns of fluids such as feedstock water, cooling water, and unused waste heat during hydrogen generation. Additionally, dashed lines in the diagram indicate areas without fluid flow.

[0038] In the electrolysis system 10 during electrolysis operation, the control device 90 controls the steam generator 32 and the water pump 34 to supply steam to the hydrogen electrode of the electrolysis cell stack 21, and controls the reversing valve 82 to supply unused waste heat to the steam generator 32 (heat recovery heat exchanger), and controls the air blower 52 to supply air to the oxygen electrode of the electrolysis cell stack 21. Next, the control device 90 supplies power from the power supply device 26 to the terminals of the electrolysis cell stack 21 to perform electrolysis operation. Furthermore, the control device 90 controls the hydrogen blowers 42 and 44 to supply the generated hydrogen from the electrolysis operation via the circulating piping 65 as anti-oxidation hydrogen to the hydrogen electrode of the electrolysis cell stack 21, and as combustion hydrogen to the burner 22.

[0039] like Figure 2 As shown, driven by the water pump 34, the raw water in the water tank 31 passes through the second cooling heat exchange section 73. After being heated by heat exchange with the hydrogen storage alloy 71, it is supplied to the steam generator 32 (steam generation heat exchanger) and becomes water vapor. Then, the water vapor passes through the hydrogen electrode inlet pipe 21a, and after being heated by heat exchange with combustion exhaust gas, it is supplied to the hydrogen electrode of the electrolytic cell stack 21 and electrolyzed. The generated hydrogen gas produced at the hydrogen electrode due to electrolysis is discharged together with the unreacted water vapor through the hydrogen electrode outlet pipe 21c to the hydrogen recovery pipe 61. Moreover, the exhaust gas containing generated hydrogen and water vapor (hydrogen electrode exhaust gas) is condensed in the condenser 62 by heat exchange with the cooling water, and then supplied to the hydrogen storage tank 70. The generated hydrogen supplied to the hydrogen storage tank 70 is cooled by heat exchange with the cooling water passing through the condenser 62 and the raw water from the water tank 31, and is then absorbed by the hydrogen storage alloy 71. In addition, a portion of the generated hydrogen is returned via the circulation piping 65 and supplied as anti-oxidation hydrogen to the hydrogen electrode of the electrolyzer stack 21, and is also supplied as fuel hydrogen to the burner 22.

[0040] In this way, since the cooling of the hydrogen storage alloy 71 utilizes both cooling water and feed water, the cooling required for hydrogen absorption into the hydrogen storage alloy 71 can be ensured, and energy losses related to hydrogen storage can be reduced. Furthermore, by preheating the feed water using the hydrogen storage alloy 71 (second cooling heat exchange section 73) and using unused waste heat as a heat source to generate steam from the feed water at the steam generator 32, the energy required for steam generation can be reduced. These structural features result in a further improvement in the energy efficiency of the electrolysis system 10.

[0041] Next, the operation of releasing the hydrogen stored in the hydrogen storage unit 70 will be explained. Figure 3This is an explanatory diagram illustrating the flow pattern of unused waste heat during hydrogen release. Hydrogen is released during the electrolysis shutdown or startup of the electrolysis system 10. Regarding the hydrogen released during electrolysis shutdown, it is either used to preheat the electrolysis module 20 by combustion of combustion hydrogen in the burner 22 for rapid startup, or it is supplied outside the system for other purposes. In the case where the hydrogen released during startup is used to preheat the electrolysis module 20 by combustion of combustion hydrogen in the burner 22...

[0042] The control device 90 controls the reversing valve 82 to supply unused waste heat to the heating heat exchange unit 74. Thus, as... Figure 3 As shown, the hydrogen storage alloy 71 of the hydrogen storage tank 70 is heated using unused waste heat, causing the hydrogen stored in the hydrogen storage alloy 71 to be released. In this way, since unused waste heat is used in the heating of the hydrogen storage alloy 71, energy loss related to hydrogen release can also be reduced. Furthermore, when the electrolysis system 10 is started, and during the maintenance of the electrolysis module 20 during electrolysis shutdown, the control device 90 opens the on / off valve 76, connecting the outlet of the hydrogen storage tank 70 to the anti-oxidation hydrogen supply pipe 41 and the combustion hydrogen supply pipe 43. Moreover, the control device 90 controls the hydrogen blowers 42 and 44 and the air blower 52 to supply anti-oxidation hydrogen to the hydrogen electrode of the electrolysis cell stack 21, and to supply combustion hydrogen and air to the burner 22. Thus, the released hydrogen is supplied to the hydrogen electrode of the electrolysis cell stack 21 via the anti-oxidation hydrogen supply pipe 41, and to the burner 22 via the combustion hydrogen supply pipe 43.

[0043] In the first embodiment described above, the hydrogen storage unit 70 includes a first cooling heat exchange unit 72 cooled by cooling water and a second cooling heat exchange unit 73 cooled by raw material water, and serves as a cooling heat exchanger for cooling the hydrogen storage alloy 71 to store hydrogen. However, depending on the required amount of cooling, the second cooling heat exchange unit 73 may be omitted.

[0044] In the first embodiment described above, the hydrogen storage unit 70 includes a heating heat exchanger 74 that is heated by unused waste heat. This heat exchanger is used to heat the hydrogen storage alloy 71 to release hydrogen, but other heat sources can also be used to release hydrogen.

[0045] In the first embodiment described above, hydrogen storage alloy 71 is used for hydrogen absorption and release, but alternatively, a liquid organic hydrogen storage carrier (LOHC) can be used for hydrogen absorption and release. Figure 4 This is a schematic structural diagram of the electrolysis system 110 according to the second embodiment. As shown, the electrolysis system 110 of the second embodiment includes a hydrogen absorption and release system 170 instead of a hydrogen storage tank 70.

[0046] The hydrogen absorption and release system 170 uses bicarbonate-formate as a liquid organic hydrogen storage carrier and absorbs and releases hydrogen through a chemical reaction. The hydrogen absorption and release system 170 comprises: a bicarbonate tank 171 for storing an aqueous bicarbonate solution; an absorption reactor 172 that uses refrigeration (e.g., 30–40°C) to react the aqueous bicarbonate solution with hydrogen to generate an aqueous formate solution; a formate tank 173 for storing the aqueous formate solution; a release reactor 174 that uses heat (e.g., 50–60°C) to decompose the aqueous formate solution to generate bicarbonate and hydrogen; and a circulation piping 175 that connects these components in a ring.

[0047] The absorption reactor 172 includes a mixing tank 172a for mixing an aqueous bicarbonate solution and hydrogen gas, and a first cooling heat exchange unit 172b and a second cooling heat exchange unit 172c for supplying the aqueous bicarbonate solution with the cooling required for the reaction with hydrogen gas. A bicarbonate tank 171 is connected to the mixing tank 172a via a circulation pipe 175, and a pump 176 is installed between the mixing tank 172a and the bicarbonate tank 171 on the circulation pipe 175. Driven by the pump 176, the aqueous bicarbonate solution in the bicarbonate tank 171 is supplied to the mixing tank 172a. In addition, a hydrogen recovery pipe 61 is connected to the mixing tank 172a, and the mixed tank 172a is introduced with the generated hydrogen gas separated by the gas-liquid separation of the condenser 62. The bicarbonate aqueous solution supplied to the mixing tank 172a passes sequentially through the first cooling heat exchange section 172b and the second cooling heat exchange section 172c, where it is cooled by heat exchange formed between the cooling operation and the bicarbonate aqueous solution. As a result, the bicarbonate aqueous solution reacts with the mixed hydrogen gas to generate a formate aqueous solution. The generated hydrogen gas is then stored as a formate aqueous solution (liquid).

[0048] The first cooling heat exchange unit 172b is connected downstream of the condenser 62 in the cooling water supply pipe 63, and cools the bicarbonate aqueous solution through heat exchange with the cooling water (e.g., 35-40°C) that has passed through the condenser 62. The second cooling heat exchange unit 172c is connected downstream of the water tank 31 and upstream of the steam generator 32 in the water supply pipe 33, and cools the bicarbonate aqueous solution through heat exchange with the raw water (e.g., 20-30°C) from the water tank 31. The raw water, heated by the heat exchange with the bicarbonate aqueous solution, is supplied to the steam generator 32. The first cooling heat exchange unit 172b and the second cooling heat exchange unit 172c are configured such that, relative to the flow of the bicarbonate aqueous solution, the first cooling heat exchange unit 172b is upstream of the second cooling heat exchange unit 172c, so that heat exchange occurs with the bicarbonate aqueous solution in the order of cooling water and raw water (from high to low temperature). Because a large amount of cooling water is supplied to condenser 62 for heat exchange with the hydrogen exhaust gas, and the cooling water has a large heat capacity, the cooling water passing through condenser 62 can be used to ensure the refrigeration required for the reaction between the bicarbonate aqueous solution and hydrogen. On the other hand, although the temperature of the feed water is lower than that of the cooling water passing through condenser 62, the supply of feed water is limited by the amount of hydrogen produced, so sufficient refrigeration cannot be ensured by supplying feed water alone. Since the feed water is also used in the supply of cooling water, the cooling of the bicarbonate aqueous solution can be promoted, the reaction between it and hydrogen can be promoted, and a sufficient amount of hydrogen can be absorbed.

[0049] The release reactor 174 includes a heating heat exchanger 174a for supplying the temperature required for the decomposition of the formate aqueous solution, and a separation tank 174b for separating the bicarbonate and hydrogen generated from the decomposition of the formate aqueous solution. A formate tank 173 is connected to the heating heat exchanger 174a via a circulation pipe 175, and a pump 177 is installed between the heating heat exchanger 174a and the formate tank 173 on the circulation pipe 175. Driven by the pump 177, the formate aqueous solution in the formate tank 173 is supplied to the heating heat exchanger 174a. The formate aqueous solution supplied to the heating heat exchanger 174a is heated by heat exchange with the heat source, and decomposed into bicarbonate and hydrogen. The bicarbonate and hydrogen are separated in the separation tank 174b, the bicarbonate is accumulated in the bicarbonate tank 171, and the hydrogen is released.

[0050] The heating heat exchange unit 174a is connected to the waste heat supply pipe 81, and heats the formate aqueous solution by heat exchange with unused waste heat (e.g., 50-60°C) supplied through the waste heat supply pipe 81.

[0051] Next, the operation of the electrolysis system 110 of the second embodiment configured in this way will be described. In particular, the operation when the generated hydrogen gas produced during electrolysis is absorbed into the liquid organic hydrogen storage carrier, and the operation when the hydrogen gas absorbed by the liquid organic hydrogen storage carrier is released during electrolysis shutdown or startup will be described. Figure 5 This is an explanatory diagram showing the flow of fluids such as feedstock water, cooling water, and unused waste heat during hydrogen generation. Additionally, dashed lines in the diagram indicate areas without fluid flow.

[0052] In the second embodiment of the electrolysis system 110 during electrolysis operation, similar to the first embodiment of the electrolysis system 10 described above, the control device 90 controls the reversing valve 82 to supply unused waste heat to the steam generator 32, and drives the water pump 34 to supply the raw material water in the water tank 31 to the steam generator 32, thereby supplying steam to the hydrogen electrode of the electrolysis cell stack 21. Furthermore, the control device 90 controls the air blower 52 to supply air to the oxygen electrode of the electrolysis cell stack 21, and supplies power to the electrolysis cell stack 21 from the power supply device 26.

[0053] like Figure 5 As shown, driven by water pump 34, the raw water in water tank 31 passes through the second cooling heat exchange section 172c of absorption reactor 172. After being heated by heat exchange with the bicarbonate aqueous solution, it is supplied to steam generator 32 (steam generating heat exchanger) and becomes water vapor. Furthermore, this water vapor passes through hydrogen electrode inlet pipe 21a, and after being heated by heat exchange with combustion exhaust gas, it is supplied to the hydrogen electrode of electrolytic cell stack 21 for electrolysis. The generated hydrogen gas produced by electrolysis at the hydrogen electrode is discharged along with unreacted water vapor through hydrogen electrode outlet pipe 21c to hydrogen recovery pipe 61. Then, the exhaust gas containing generated hydrogen and water vapor (hydrogen electrode exhaust gas) is condensed at condenser 62 by heat exchange with cooling water, and then supplied to mixing tank 172a of absorption reactor 172. The generated hydrogen gas supplied to mixing tank 172a is mixed with the aqueous bicarbonate solution supplied from bicarbonate tank 171 to mixing tank 172a by pump 176. Furthermore, the aqueous bicarbonate solution mixed with the generated hydrogen gas is cooled by heat exchange with cooling water passing through condenser 62 and raw material water from water tank 31, and reacts with the generated hydrogen gas. This produces an aqueous formate solution, which is stored in formate tank 173.

[0054] Thus, by using cooling water and feed water for cooling the bicarbonate aqueous solution at the absorption reactor 172, the cooling required for the reaction with hydrogen can be ensured, and energy losses associated with hydrogen absorption can be reduced. Furthermore, by preheating the feed water using the second cooling heat exchange section 172c of the absorption reactor 172 and using unused waste heat as a heat source to generate water vapor from the feed water using the steam generator 32, the energy required for water vapor generation can be reduced. These results further improve the energy efficiency of the electrolysis system 110.

[0055] Next, the procedure for releasing the hydrogen gas accumulated in the form of an aqueous formate solution will be explained. Figure 6 This is an explanatory diagram illustrating the flow pattern of unused waste heat during hydrogen release. Hydrogen release occurs during the electrolysis shutdown or startup of the electrolysis system 110. During electrolysis shutdown, the released hydrogen is either used to maintain the temperature inside the electrolysis module 20 by combustion of combustion hydrogen at burner 22 for rapid startup, or it is supplied outside the system for other purposes. During startup, the released hydrogen is used to preheat the electrolysis module 20 by combustion of combustion hydrogen at burner 22.

[0056] Control device 90 controls reversing valve 82 and drives pump 177 to supply unused waste heat to the heating heat exchange section 174a of release reactor 174. Thus, as... Figure 6 As shown, the formate aqueous solution passing through the heating heat exchange section 174a is heated and decomposed into bicarbonate and hydrogen through heat exchange with unused waste heat, thereby releasing the hydrogen separated in the separation tank 174b. In this way, since unused waste heat is used in the heating of the formate aqueous solution, energy loss related to hydrogen release can also be reduced. Furthermore, when the electrolysis system 110 is started, during electrolysis shutdown, or when the electrolysis module 20 is kept warm, the control device 90 opens the on / off valve 76, connecting the separation tank 174b of the release reactor 174 to the anti-oxidation hydrogen supply pipe 41 and the combustion hydrogen supply pipe 43. Moreover, the control device 90 controls the hydrogen blowers 42 and 44 and the air blower 52 to supply anti-oxidation hydrogen to the hydrogen electrode of the electrolysis cell stack 21 and to supply combustion hydrogen and air to the burner 22. The released hydrogen is then supplied to the hydrogen electrode of the electrolytic cell stack 21 via the anti-oxidation hydrogen supply pipe 41, and to the burner 22 via the combustion hydrogen supply pipe 43.

[0057] In the second embodiment described above, the hydrogen absorption and release system 170 includes a heating heat exchanger 174a that is heated by unused waste heat, which serves as a heating heat exchanger for releasing hydrogen by heating a liquid organic hydrogen storage carrier (formate aqueous solution), but other heat sources may also be used to release hydrogen.

[0058] In the first and second embodiments described above, the electrolysis systems 10 and 110 include an electrolytic cell stack 21 for generating hydrogen through steam electrolysis. However, the electrolysis system 10 can also switch between an electrolysis mode that generates hydrogen through steam electrolysis and a power generation mode that generates electricity by reacting hydrogen, which is a fuel gas, with oxygen contained in the air, by using the electrolytic cell stack 21 as a reversible solid oxide type stack. When the reversible solid oxide type stack is operated in power generation mode, for example, unused waste heat can be supplied to the heating heat exchange section 74 of the hydrogen storage unit 70 to release hydrogen from the hydrogen storage unit 70, and the released hydrogen can be supplied to the hydrogen electrode of the reversible solid oxide type stack via a hydrogen blower 42.

[0059] While the embodiments described above illustrate the methods for implementing this disclosure, the present invention is not limited in any way to such embodiments, and can of course be implemented in various ways without departing from the spirit of this disclosure.

[0060] Furthermore, this specification also discloses the technical concept obtained by changing "the electrolysis system described in claim 1" in the current claim 4 to "the electrolysis system described in any one of claims 1 to 3".

[0061] [Potential for industrial applications]

[0062] This disclosure can be applied to industries such as the manufacturing of electrolysis systems.

Claims

1. An electrolysis system comprising: A solid oxide electrolytic cell generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode; The hydrogen absorption and release unit cools the hydrogen storage carrier to absorb hydrogen and heats the hydrogen storage carrier to release hydrogen. A steam supply pipeline supplies steam to the aforementioned hydrogen electrode. The recovery pipeline recovers the hydrogen contained in the exhaust gas discharged from the hydrogen electrode to the hydrogen absorption and release section. A gas-liquid separation unit is installed in the above-mentioned recovery pipeline, and the above-mentioned exhaust gas is cooled by heat exchange with the coolant in order to perform gas-liquid separation. The coolant supply line supplies the coolant to the gas-liquid separation unit and then to the hydrogen absorption and release unit; and A first cooling heat exchange unit is provided in the hydrogen absorption and release unit, and cools the hydrogen storage carrier by heat exchange with the coolant supplied from the coolant supply pipeline.

2. The electrolysis system according to claim 1, wherein, have: The raw water supply pipeline, after supplying raw water to the aforementioned hydrogen absorption and release unit, supplies raw water to the aforementioned steam supply pipeline; and The second cooling heat exchange unit is provided in the hydrogen absorption and release unit, and cools the hydrogen storage carrier by heat exchange with the raw water supplied from the raw water supply pipeline.

3. The electrolysis system according to claim 2, wherein, The first cooling heat exchange unit and the second cooling heat exchange unit are configured to cool the hydrogen from the recovery pipeline or the hydrogen storage carrier in the order of the first cooling heat exchange unit and the second cooling heat exchange unit.

4. The electrolysis system according to claim 1, wherein, have: The evaporation section is connected to the aforementioned steam supply pipeline and uses external heat to generate steam. A heating heat exchange unit is provided in the hydrogen absorption and release unit, and heats the hydrogen storage carrier by heat exchange with external heat. An external heat supply pipeline selectively supplies the aforementioned external heat to the aforementioned evaporation section and the aforementioned hydrogen absorption and release section.

5. An electrolysis system comprising: A solid oxide electrolytic cell generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode; The hydrogen absorption and release unit cools the hydrogen storage carrier to absorb hydrogen and heats the hydrogen storage carrier to release hydrogen. A steam supply pipeline supplies steam to the aforementioned hydrogen electrode. The evaporation section is connected to the aforementioned steam supply pipeline and uses external heat to generate steam. A heat exchange unit for heating is provided in the aforementioned hydrogen absorption and release unit, and heats the aforementioned hydrogen storage carrier through heat exchange with external heat; and An external heat supply pipeline selectively supplies the aforementioned external heat to the aforementioned evaporation section and the aforementioned hydrogen absorption and release section.

6. The electrolysis system according to any one of claims 1 to 5, wherein, The aforementioned hydrogen absorption and release section has a hydrogen storage material as the hydrogen storage carrier.

7. The electrolysis system according to any one of claims 1 to 5, wherein, The aforementioned hydrogen absorption and release section has a liquid organic hydrogen storage carrier as the hydrogen storage carrier.

8. The electrolysis system according to claim 7, wherein, The hydrogen absorption and release unit comprises: a first tank for storing the liquid organic hydrogen storage carrier; an absorption reaction unit for cooling the liquid organic hydrogen storage carrier and reacting it with hydrogen; a second tank for storing the reacted liquid organic hydrogen storage carrier; a release reaction unit for heating the reacted liquid organic hydrogen storage carrier to release hydrogen; and a circulation path that connects the first tank, the absorption reaction unit, the second tank, and the release reaction unit in a ring. The aforementioned first cooling heat exchange unit is provided in the aforementioned absorption reaction unit.

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