Electrolytic system

Abstract

This ensures the necessary cooling for hydrogen absorption by the hydrogen carrier while reducing energy losses associated with hydrogen absorption. [Solution] The electrolytic system comprises a solid oxide electrolytic cell that electrolyzes water vapor supplied to a hydrogen electrode; a hydrogen absorption and release unit that cools a hydrogen carrier to absorb hydrogen and heats the hydrogen carrier to release hydrogen; a water vapor supply line that supplies water vapor to the hydrogen electrode; a recovery line that recovers hydrogen contained in the exhaust gas discharged from the hydrogen electrode to the hydrogen absorption and release unit; a gas-liquid separation unit provided in the recovery line that cools the exhaust gas by heat exchange with a coolant to separate the gas and liquid; a coolant supply line that supplies coolant to the gas-liquid separation unit and then to the hydrogen absorption and release unit; and a first cooling heat exchange unit provided in the hydrogen absorption and release unit that cools the hydrogen carrier by heat exchange with the coolant supplied from the coolant supply line.

Description

Technical Field

[0001] This specification discloses an electrolysis system.

Background Art

[0002] Conventionally, an electrochemical device has been proposed that includes a solid oxide electrolysis cell that electrolyzes H2O to produce H2, a hydrogen storage material that stores the H2 produced by the solid oxide electrolysis cell, and a heat transport means that transports heat from the hydrogen storage material to the solid oxide electrolysis cell (see, for example, Patent Document 1). This device includes, as the heat transport means, a heat exchanger that exchanges heat between a pipe that supplies H2O to the solid oxide electrolysis cell and the hydrogen storage material. This heat exchanger transfers heat from the hydrogen storage material to the H2O so as to vaporize the H2O to be supplied to the solid oxide electrolysis cell. Thereby, it is said that the endothermic of the solid oxide electrolysis cell and the exothermic of the hydrogen storage material can be offset, and the energy efficiency can be improved. In addition, for a pipe that transports only H2 from a gas containing H2 and H2O discharged from the solid oxide electrolysis cell to the hydrogen storage material, a heat exchanger that cools the gas by heat exchange with cooling water and a pipe for removing drain water after cooling the gas are provided.

[0003] In addition, those that store and transport hydrogen based on the bicarbonate-formic acid cycle have also been proposed (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the electrochemical apparatus described above, the cold energy of H2O supplied to the solid oxide electrolytic cell is used to absorb hydrogen into the hydrogen storage material. However, the amount of H2O supplied to the solid oxide electrolytic cell is limited by the target amount of hydrogen to be produced, which can result in insufficient cold energy being secured for hydrogen absorption. This problem can also occur when using liquid organic hydrogen carriers (LOHCs) such as bicarbonate / formic acid instead of hydrogen storage materials as the hydrogen carrier.

[0006] The primary objective of this disclosure is to provide an electrolysis system that can secure the necessary cooling for hydrogen absorption into a hydrogen carrier and reduce energy loss associated with hydrogen absorption. [Means for solving the problem]

[0007] This disclosure employs the following means to achieve the primary objectives described above.

[0008] The electrolytic system of this disclosure comprises: a solid oxide electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to a hydrogen electrode; a hydrogen absorption and release unit that cools a hydrogen carrier to absorb hydrogen and heats the hydrogen carrier to release hydrogen; a water vapor supply line that supplies water vapor to the hydrogen electrode; a recovery line that recovers hydrogen contained in the exhaust gas discharged from the hydrogen electrode to the hydrogen absorption and release unit; a gas-liquid separation unit provided in the recovery line that cools the exhaust gas by heat exchange with a coolant to separate the gas and liquid; a coolant supply line that 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 provided in the hydrogen absorption and release unit that cools the hydrogen carrier by heat exchange with the coolant supplied from the coolant supply line.

[0009] The electrolytic system of this disclosure includes a gas-liquid separation unit that separates the exhaust gas from the hydrogen electrode of a solid oxide electrolytic cell into gas and liquid, and a coolant supply line that sequentially supplies coolant to the hydrogen carrier. By using the coolant used in the gas-liquid separation unit to cool the hydrogen carrier as well, it is possible to secure the cooling energy necessary for hydrogen absorption by the hydrogen carrier and reduce energy loss associated with hydrogen absorption. As a result, the overall energy efficiency of the system can be further improved. Examples of hydrogen carriers include hydrogen storage materials and liquid organic hydrogen carriers. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the electrolysis system according to the first embodiment. [Figure 2] This is an explanatory diagram showing the flow of raw water, cooling water, and unused waste heat during hydrogen production. [Figure 3] This is an explanatory diagram showing the flow of unused waste heat during hydrogen release. [Figure 4] This is a schematic diagram of the electrolysis system according to the second embodiment. [Figure 5] This is an explanatory diagram showing the flow of raw water, cooling water, and unused waste heat during hydrogen production. [Figure 6] This is an explanatory diagram showing the flow of unused waste heat during hydrogen release. [Modes for carrying out the invention]

[0011] Next, the forms for implementing this disclosure will be described with reference to the drawings.

[0012] Figure 1 is a schematic diagram of the electrolytic system 10 of the first embodiment. As shown in Figure 1, the electrolytic system 10 of the first embodiment includes an electrolytic module 20 containing an electrolytic cell stack 21 that generates hydrogen by steam electrolysis, a steam supply system 30 that supplies steam to the electrolytic module 20, a hydrogen supply system 40 that supplies hydrogen to the electrolytic module 20, an air supply system 50 that supplies air as a sweep gas to the electrolytic module 20, and a hydrogen recovery system 60 that recovers the generated hydrogen produced in the electrolytic module 20 by adsorbing it onto a hydrogen storage alloy 71.

[0013] The electrolytic module 20 includes an electrolytic cell stack 21, a combustor 22, and a heat exchanger (not shown), all of which are housed in an insulated module case 24.

[0014] The electrolytic cell stack 21 comprises a plurality of solid oxide electrolytic cells (SOECs), each containing a solid electrolyte, a hydrogen electrode positioned on one side of the solid electrolyte, and an oxygen electrode positioned on the other side of the solid electrolyte. The electrolytic operation 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 generated when the water vapor is decomposed into oxygen ions and hydrogen. At the oxygen electrode, oxygen is generated when the decomposed oxygen ions permeate the solid electrolyte and combine with electrons. The power supply unit 26 can be a grid power supply, a renewable energy device (e.g., a solar power generation device), a storage battery, etc.

[0015] Since the electrolytic cell stack 21 operates in a high-temperature environment, for example, 650-800°C, the solid electrolyte, hydrogen electrode, and oxygen electrode are made of ceramic material. Furthermore, because the catalyst decomposes water vapor into oxygen ions and hydrogen, a cermet made of a catalytic metal such as nickel and ceramic is used for the hydrogen electrode. In order to maintain good catalytic activity of the hydrogen electrode, it is necessary to keep the hydrogen electrode in a reducing atmosphere and prevent oxidation of the metal. For this reason, in this embodiment, hydrogen for oxidation prevention is mixed into the water vapor supplied to the hydrogen electrode.

[0016] One end of the hydrogen electrode inlet pipe 21a is connected to the hydrogen electrode inlet of the electrolytic cell stack 21, and the other end of the hydrogen electrode inlet pipe 21a is connected to the steam supply system 30 and the hydrogen supply system 40. One end of the oxygen electrode inlet pipe 21b is connected to the oxygen electrode inlet of the electrolytic cell stack 21, and the other end of the oxygen electrode inlet pipe 21b is connected to the air supply system 50. One end of the hydrogen electrode outlet pipe 21c is connected to the hydrogen electrode outlet of the electrolytic cell stack 21, and the other end of the hydrogen electrode outlet pipe 21c is connected to the hydrogen recovery system 60. One end of the oxygen electrode outlet pipe 21d is connected to the oxygen electrode outlet of the electrolytic cell stack 21, and the other end of the oxygen electrode outlet pipe 21d is connected to the combustor 22. A hydrogen supply pipe 43 for combustion is connected to the combustor 22.

[0017] The steam supply system 30 includes a water tank 31 for storing raw water (pure water) supplied via 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 in the water supply pipe 33 for 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 generates steam using unused waste heat (e.g., 50-60°C) discharged from a factory or the like and supplied via the waste heat supply pipe 81 as a heat source. An example of a steam generator 32 is a steam heat pump that includes a heat recovery heat exchanger (evaporator), a compressor, a steam generation heat exchanger (condenser), an expansion valve, and circulation piping connecting these so that the refrigerant circulates. After heat exchange between unused waste heat and the refrigerant in the heat recovery heat exchanger, the compressed and heated refrigerant is heat-exchanged with raw water in the steam generation heat exchanger to generate steam (saturated steam). Note that the steam generator 32 can be any type that uses unused waste heat as at least one heat source to heat the raw water and generate steam. The steam introduced from the steam supply system 30 to the hydrogen electrode inlet piping 21a is heated by heat exchange with combustion exhaust gas, etc., in a heat exchange section (not shown) installed in the hydrogen electrode inlet piping 21a, and then supplied to the hydrogen electrode of the electrolytic cell stack 21.

[0018] The hydrogen supply system 40 includes a hydrogen supply pipe 41 for antioxidant connected at one end to the hydrogen electrode inlet pipe 21a, a hydrogen blower 42 installed in the hydrogen supply pipe 41 for antioxidant, a hydrogen supply pipe 43 for combustion connected at one end to the combustor 22, and a hydrogen blower 44 installed in the hydrogen supply pipe 43 for combustion. By driving the hydrogen blower 42, hydrogen is introduced into the hydrogen supply pipe 41 for antioxidant, and the introduced hydrogen is supplied as antioxidant hydrogen to the hydrogen electrode of the electrolytic cell stack 21. Also, by driving the hydrogen blower 44, hydrogen is introduced into the hydrogen supply pipe 43 for combustion, and the introduced hydrogen is supplied as combustion hydrogen to the combustor 22. Note that flow meters (not shown) are installed in the hydrogen supply pipe 41 for antioxidant and the hydrogen supply pipe 43 for combustion, respectively.

[0019] 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 in the air supply pipe 51. By driving the air blower 52, the air inhaled into the air supply pipe 51 is introduced into the oxygen electrode inlet pipe 21b, and after being heated by heat exchange with combustion exhaust gas, hydrogen electrode off-gas, etc. in a heat exchange section (not shown) installed in the oxygen electrode inlet pipe 21b, it is supplied to the oxygen electrode of the electrolytic cell stack 21.

[0020] The hydrogen recovery system 60 recovers generated hydrogen from the hydrogen electrode off-gas containing generated hydrogen and unreacted water vapor discharged from the hydrogen electrode outlet. The hydrogen recovery system 60 includes a hydrogen storage device 70, a hydrogen recovery pipe 61 connecting the hydrogen electrode outlet pipe 21c and the inlet of the hydrogen storage device 70, a condenser 62 installed in the hydrogen recovery pipe 61, and a cooling water supply pipe 63 that supplies cooling water to the condenser 62 and the hydrogen storage device 70 in this order. The condenser 62 condenses the water vapor contained in the hydrogen electrode off-gas flowing through the hydrogen recovery pipe 61 by heat exchange with the cooling water flowing through the cooling water supply pipe 63, and separates the hydrogen electrode off-gas into generated hydrogen and condensed water. The condensed water separated by the condenser 62 is stored in the water tank 31 through the condensed water pipe 64. The condensed water stored in the water tank 31 is used as raw water for generating electrolytic water vapor.

[0021] The hydrogen storage device 70 includes a hydrogen storage alloy 71 that stores hydrogen by cooling and releases hydrogen by heating, a first cooling heat exchanger 72 and a second cooling heat exchanger 73 for cooling the hydrogen storage alloy 71, and a heating heat exchanger 74 for heating the hydrogen storage alloy 71.

[0022] The hydrogen storage alloy 71 is a powdery or granular member that is an alloy of two or more metals including, for example, magnesium, titanium, vanadium, lanthanum, etc. It has the property of storing hydrogen at about 30 - 40°C and releasing the stored hydrogen at about 50 - 60°C.

[0023] The first cooling heat exchanger 72 is connected to the cooling water supply pipe 63 on the downstream side of the condenser 62 and cools the hydrogen storage alloy 71 by heat exchange with the cooling water (for example, 35 - 40°C) that has passed through the condenser 62. The second cooling heat exchanger 73 is connected to the water supply pipe 33 on the downstream side of the water tank 31 and upstream of the steam generator 32, and cools the hydrogen storage alloy 71 by heat exchange with the raw water (for example, 20 - 30°C) from the water tank 31. The raw water heated by heat exchange with the hydrogen storage alloy 71 is supplied to the steam generator 32. In this embodiment, the first cooling heat exchanger 72 and the second cooling heat exchanger 73 are arranged such that the first cooling heat exchanger 72 is on the upstream side of the second cooling heat exchanger 73 with respect to the flow of the generated hydrogen so as to exchange heat with the generated hydrogen introduced into the hydrogen storage device 70 in the order of cooling water, raw water (from the higher water temperature). A large amount of cooling water is supplied to the condenser 62 for heat exchange with the hydrogen electrode off - gas. Since the heat capacity is large, the cooling water that has passed through the condenser 62 can ensure the cooling heat required for the hydrogen storage of the hydrogen storage alloy 71. On the other hand, although the water temperature of the raw water is lower than the cooling water that has passed through the condenser 62, the supply amount of the raw water is restricted according to the target hydrogen production amount. Therefore, sufficient cooling heat cannot be ensured only by the supply of the raw water. In this embodiment, since the supply of the raw water is used in combination with the supply of the cooling water, the cooling of the hydrogen storage alloy 71 can be promoted, the performance of the hydrogen storage alloy 71 can be exerted, and a sufficient amount of hydrogen can be stored.

[0024] The heating heat exchanger 74 is connected to the exhaust 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 exhaust heat supply pipe 81.

[0025] One end of a hydrogen supply pipe 75 is connected to the outlet of the hydrogen storage unit 70, and the other end of the hydrogen supply pipe 75 is connected to the other end of an oxidation-preventing hydrogen supply pipe 41 and the other end of a combustion hydrogen supply pipe 43. An on-off valve 76 is installed in the hydrogen supply pipe 75. The hydrogen stored in the hydrogen storage alloy 71 of the hydrogen storage unit 70 is released when the hydrogen storage alloy 71 is heated by the heating heat exchanger 74. The released hydrogen is then drawn into the oxidation-preventing hydrogen supply pipe 41 by driving the hydrogen blower 42 with the on-off valve 76 open, and supplied from the oxidation-preventing hydrogen supply pipe 41 to the hydrogen electrode of the electrolytic cell stack 21. The released hydrogen is also drawn into the combustion hydrogen supply pipe 43 by driving the hydrogen blower 44 with the on-off valve 76 open, and supplied from the combustion hydrogen supply pipe 43 to the combustor 22.

[0026] The recirculation pipe 65 branches off from the downstream side of the condenser 62 and the upstream side of the hydrogen storage unit 70 in the hydrogen recovery pipe 61 and connects to the other end of the oxidation prevention hydrogen supply pipe 41 and the other end of the combustion hydrogen supply pipe 43. The generated hydrogen flowing through the hydrogen recovery pipe 61 is drawn from the recirculation pipe 65 to the oxidation prevention hydrogen supply pipe 41 by driving the hydrogen blower 42 with the on-off valve 76 closed, and supplied from the oxidation prevention hydrogen supply pipe 41 to the hydrogen electrode of the electrolytic cell stack 21. In addition, the generated hydrogen flowing through the hydrogen recovery pipe 61 is drawn from the recirculation pipe 65 to the combustion hydrogen supply pipe 43 by driving the hydrogen blower 44 with the on-off valve 76 closed, and supplied from the combustion hydrogen supply pipe 43 to the combustor 22.

[0027] The waste heat supply system 80 includes a waste heat supply pipe 81 that branches off from a pipe connected to a source of unused waste heat and is connected to the steam generator 32 and the hydrogen storage unit 70, and a switching valve 82 installed at the branching point of the waste heat supply pipe 81 to switch the destination of the unused waste heat. The waste heat supply system 80 may also include a heat storage tank for storing unused waste heat, and the unused waste heat stored in the heat storage tank may be supplied to the steam generator 32 and the hydrogen storage unit 70 (heating heat exchanger 74) via the waste heat supply pipe 81.

[0028] The control device 90 is configured as a microprocessor centered around a CPU, and in addition to the CPU, it is equipped with ROM, RAM, input / output ports, etc. Detection signals from temperature sensors installed near the electrolytic cell stack 21, temperature sensors installed in the combustor 22, flow meters installed in the oxidation prevention hydrogen supply pipe 41, flow meters installed in the combustion hydrogen supply pipe 43, and flow meters installed in the hydrogen recovery piping 61 are input to the control device 90 via its input ports. Control signals to the steam generator 32, water pump 34, hydrogen blowers 42, 44, air blower 52, on-off valve 76, switching valve 82, etc. are output from the control device 90 via its output ports.

[0029] Next, the operation of the electrolytic system 10 configured in this way will be described. In particular, the operation when the generated hydrogen produced during electrolysis is absorbed into the hydrogen storage unit 70, and the operation when the hydrogen absorbed into the hydrogen storage unit 70 is released during electrolysis stoppage and startup will be described. Figure 2 is an explanatory diagram showing the fluid flow of raw water, cooling water, unused waste heat, etc., during hydrogen production. In the figure, dotted lines indicate the absence of fluid flow.

[0030] During electrolysis operation, the control device 90 controls the steam generator 32 and water pump 34 so that steam is supplied to the hydrogen electrode of the electrolytic cell stack 21, and controls the switching valve 82 so that unused waste heat is supplied to the steam generator 32 (heat recovery heat exchanger), and controls the air blower 52 so that air is supplied to the oxygen electrode of the electrolytic cell stack 21. Subsequently, the control device 90 supplies power from the power supply unit 26 to the terminals of the electrolytic cell stack 21 to perform electrolysis. Then, the control device 90 controls the hydrogen blowers 42 and 44 so that the hydrogen generated by the electrolysis operation is supplied to the hydrogen electrode of the electrolytic cell stack 21 as antioxidant hydrogen via the reflux pipe 65 and also supplied to the combustor 22 as combustion hydrogen.

[0031] As shown in Figure 2, the raw water in the water tank 31 is heated by heat exchange with the hydrogen storage alloy 71 through the second cooling heat exchange section 73 when the water pump 34 is driven, and then supplied to the steam generator 32 (heat exchanger for steam generation) to become steam. This steam is then heated by heat exchange with combustion exhaust gas etc. through the hydrogen electrode inlet pipe 21a, and then supplied to the hydrogen electrode of the electrolytic cell stack 21 to be electrolyzed. The generated hydrogen produced at the hydrogen electrode by electrolysis is discharged to the hydrogen recovery pipe 61 via the hydrogen electrode outlet pipe 21c along with the unreacted steam. The exhaust gas (hydrogen electrode off-gas) containing the generated hydrogen and steam is then supplied to the hydrogen storage unit 70 after the steam in the hydrogen electrode off-gas is condensed through heat exchange with the cooling water in the condenser 62. The generated hydrogen supplied to the hydrogen storage unit 70 is cooled by sequential heat exchange with the cooling water that has passed through the condenser 62 and the raw water from the water tank 31, and then absorbed by the hydrogen storage alloy 71. Furthermore, a portion of the generated hydrogen is refluxed through the reflux piping 65 and supplied to the hydrogen electrode of the electrolytic cell stack 21 as antioxidant hydrogen, and also supplied to the combustor 22 as fuel hydrogen.

[0032] In this way, since the cooling water and the cold energy of the raw water are used to cool the hydrogen storage alloy 71, the cold energy necessary for hydrogen storage in the hydrogen storage alloy 71 can be secured, and the energy loss associated with hydrogen storage can be reduced. Furthermore, since the raw water is preheated in the hydrogen storage alloy 71 (second cooling heat exchange section 73) and unused waste heat is used as a heat source to generate steam from the raw water in the steam generator 32, the energy required for steam generation can be reduced. As a result, the energy efficiency of the electrolysis system 10 can be further improved.

[0033] Next, the operation of releasing hydrogen stored in the hydrogen storage unit 70 will be described. Figure 3 is an explanatory diagram showing the flow of unused waste heat during hydrogen release. Hydrogen is released when the electrolysis system 10 is stopped or started. Hydrogen released during electrolysis stoppage is used to maintain the temperature inside the electrolysis module 20 by burning combustion hydrogen in the combustor 22 in order to quickly start up again, or it is supplied outside the system for other purposes. Hydrogen released during startup is used to warm up the electrolysis module 20 by burning combustion hydrogen in the combustor 22.

[0034] The control device 90 controls the switching valve 82 so that unused waste heat is supplied to the heating heat exchange unit 74. As a result, as shown in Figure 3, the hydrogen storage alloy 71 of the hydrogen storage unit 70 is heated by the unused waste heat, and the hydrogen stored in the hydrogen storage alloy 71 is released. In this way, unused waste heat is used to heat the hydrogen storage alloy 71, so that the energy loss required for hydrogen release can also be reduced. Furthermore, when starting the electrolysis system 10 or when maintaining the temperature inside the electrolysis module 20 while electrolysis is stopped, the control device 90 opens the on-off valve 76 so that the outlet of the hydrogen storage unit 70 is connected to the hydrogen supply pipe 41 for oxidation prevention and the hydrogen supply pipe 43 for combustion.The control device 90 then controls the hydrogen blowers 42, 44 and the air blower 52 so that hydrogen for oxidation prevention is supplied to the hydrogen electrode of the electrolytic cell stack 21, and hydrogen for combustion and air are supplied to the combustor 22. As a result, the released hydrogen is supplied to the hydrogen electrode of the electrolytic cell stack 21 via the hydrogen supply pipe 41 for oxidation prevention, and also supplied to the combustor 22 via the hydrogen supply pipe 43 for combustion.

[0035] In the first embodiment described above, the hydrogen storage unit 70 is provided with a first cooling heat exchange section 72 that is cooled by cooling water and a second cooling heat exchange section 73 that is cooled by raw water, as a cooling heat exchanger for cooling the hydrogen storage alloy 71 and storing hydrogen. However, depending on the amount of cooling required, the second cooling heat exchange section 73 may be omitted.

[0036] In the first embodiment described above, the hydrogen storage unit 70 is equipped with a heating heat exchanger 74 that heats using unused waste heat to heat the hydrogen storage alloy 71 and release hydrogen, but hydrogen may be released using other heat sources.

[0037] In the first embodiment described above, hydrogen absorption and release are performed using a hydrogen storage alloy 71, but hydrogen absorption and release may also be performed using a liquid organic hydrogen carrier (LOHC). Figure 4 is a schematic diagram of the electrolytic system 110 of the second embodiment. As shown in the figure, the electrolytic system 110 of the second embodiment includes a hydrogen absorption and release system 170 instead of a hydrogen storage unit 70.

[0038] The hydrogen absorption and release system 170 uses bicarbonate / formate as a liquid organic hydrogen carrier to absorb and release hydrogen through a chemical reaction. This hydrogen absorption and release system 170 comprises a bicarbonate tank 171 for storing an aqueous bicarbonate solution, an absorption reactor 172 that uses cold heat (e.g., 30-40°C) to react the aqueous bicarbonate solution with hydrogen to produce an aqueous formate solution, a formate tank 173 for storing the aqueous formate solution, an release reactor 174 that uses warm heat (e.g., 50-60°C) to decompose the aqueous formate solution to produce bicarbonate and hydrogen, and a circulation pipe 175 that connects these in a ring shape.

[0039] The absorption reactor 172 includes a mixing tank 172a for mixing a bicarbonate solution and hydrogen, and a first cooling heat exchanger 172b and a second cooling heat exchanger 172c for supplying the necessary cooling energy for the reaction between the bicarbonate solution and hydrogen. 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 in the circulation pipe 175. The bicarbonate solution in the bicarbonate tank 171 is supplied to the mixing tank 172a by the operation of the pump 176. In addition, a hydrogen recovery pipe 61 is connected to the mixing tank 172a, and the generated hydrogen separated into gas and liquid form in the condenser 62 is introduced into it. The bicarbonate aqueous solution supplied to the mixing tank 172a passes through the first cooling heat exchange section 172b and the second cooling heat exchange section 172c in that order, and is cooled by heat exchange with cold energy in each section, reacting with the mixed hydrogen to produce a formate aqueous solution. As a result, the generated hydrogen can be stored as a formate aqueous solution (liquid).

[0040] The first cooling heat exchanger 172b is connected to the downstream side of the condenser 62 in the cooling water supply pipe 63 and cools the bicarbonate solution by heat exchange with the cooling water (e.g., 35-40°C) that has passed through the condenser 62. The second cooling heat exchanger 172c is connected to the downstream side of the water tank 31 and the upstream side of the steam generator 32 in the water supply pipe 33 and cools the bicarbonate solution by heat exchange with the raw water (e.g., 20-30°C) from the water tank 31. The raw water, which has been heated by heat exchange with the bicarbonate solution, is supplied to the steam generator 32. The first cooling heat exchanger 172b and the second cooling heat exchanger 172c are positioned upstream of the second cooling heat exchanger 172c relative to the flow of the bicarbonate solution so that heat exchange with the bicarbonate solution is performed in the order of cooling water and then raw water (from the water with the highest temperature). A large amount of cooling water is supplied to the condenser 62 for heat exchange with the hydrogen electrode off-gas, and because of its large heat capacity, the cooling water that passes through the condenser 62 can secure the necessary cooling for the reaction between the bicarbonate solution and hydrogen. On the other hand, although the temperature of the raw water is lower than the cooling water that passes through the condenser 62, the amount of raw water supplied is constrained according to the target amount of hydrogen produced, so sufficient cooling cannot be secured by supplying raw water alone. By supplying raw water in addition to cooling water, the cooling of the bicarbonate solution is promoted, the reaction with hydrogen is promoted, and a sufficient amount of hydrogen can be absorbed.

[0041] The discharge reactor 174 includes a heating heat exchanger 174a that supplies the heat necessary for the decomposition of the formate solution, and a separation tank 274b that separates the bicarbonate and hydrogen produced by the decomposition of the formate solution. The 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 in the circulation pipe 175. Driven by the pump 177, the formate solution in the formate tank 173 is supplied to the heating heat exchanger 174a. The formate solution supplied to the heating heat exchanger 174a is heated by heat exchange with the heat, causing it to decompose into bicarbonate and hydrogen. The bicarbonate and hydrogen are separated in the separation tank 174b, the bicarbonate is stored in the bicarbonate tank 171, and the hydrogen is released.

[0042] The heating heat exchange section 174a is connected to the exhaust 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 exhaust heat supply pipe 81.

[0043] 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 produced during electrolysis is absorbed into the liquid organic hydrogen carrier, and the operation when the hydrogen absorbed into the liquid organic hydrogen carrier is released during electrolysis stoppage and startup will be described. Figure 5 is an explanatory diagram showing the flow of fluids such as raw water, cooling water, and unused waste heat during hydrogen production. In the figure, dotted lines indicate the absence of fluid flow.

[0044] In the electrolytic system 110 of the second embodiment during electrolytic operation, the control device 90 controls the switching valve 82 to supply unused waste heat to the steam generator 32 so that steam is supplied to the hydrogen electrode of the electrolytic cell stack 21, similar to the electrolytic system 10 of the first embodiment described above, and also drives the water pump 34 to supply raw water from the water tank 31 to the steam generator 32. The control device 90 also controls the air blower 52 to supply air to the oxygen electrode of the electrolytic cell stack 21 and supplies power to the electrolytic cell stack 21 from the power supply unit 26.

[0045] As shown in Figure 5, the water pump 34 drives the raw water in the water tank 31, which passes through the second cooling heat exchange section 172c of the absorption reactor 172, where it is heated by heat exchange with the bicarbonate solution before being supplied to the steam generator 32 (heat exchanger for steam generation) where it becomes steam. This steam is then heated by heat exchange with combustion exhaust gas, etc., through the hydrogen electrode inlet pipe 21a, and then supplied to the hydrogen electrode of the electrolytic cell stack 21 for electrolysis. The hydrogen produced at the hydrogen electrode by electrolysis, along with the unreacted steam, is discharged to the hydrogen recovery pipe 61 via the hydrogen electrode outlet pipe 21c. The exhaust gas (hydrogen electrode off-gas) containing the produced hydrogen and steam is then supplied to the mixing tank 172a of the absorption reactor 172 after the steam in the hydrogen electrode off-gas is condensed by heat exchange with cooling water in the condenser 62. The generated hydrogen supplied to the mixing tank 172a is mixed with the bicarbonate solution supplied from the bicarbonate tank 171 to the mixing tank 172a by the drive of the pump 176. The bicarbonate solution, now mixed with the generated hydrogen, is then cooled by sequential heat exchange with the cooling water that has passed through the condenser 62 and the raw water from the water tank 31, and reacts with the generated hydrogen. This produces a formate solution, which is then stored in the formate tank 173.

[0046] Thus, since the absorption reactor 172 uses the cooling energy of both the cooling water and the raw material water to cool the bicarbonate solution, it is possible to secure the cooling energy necessary for the reaction with hydrogen while reducing the energy loss associated with hydrogen absorption. Furthermore, since the raw material water is preheated in the second cooling heat exchange section 172c of the absorption reactor 172 and unused waste heat is used as a heat source to generate steam from the raw material water in the steam generator 32, the energy required for steam generation can be reduced. As a result, the energy efficiency of the electrolysis system 110 can be further improved.

[0047] Next, the operation of releasing hydrogen stored as a formate aqueous solution will be explained. Figure 6 is an explanatory diagram showing the flow of unused waste heat during hydrogen release. Hydrogen is released when the electrolysis system 110 is stopped or started. Hydrogen released during electrolysis stoppage is used to maintain the temperature inside the electrolysis module 20 by burning combustion hydrogen in the combustor 22 in order to quickly start up the next time, or it is supplied outside the system for other purposes. Hydrogen released during startup is used to warm up the electrolysis module 20 by burning combustion hydrogen in the combustor 22.

[0048] The control device 90 controls the switching valve 82 to drive the pump 177 so that unused waste heat is supplied to the heating heat exchange section 174a of the discharge reactor 174. As a result, as shown in Figure 6, the formate aqueous solution passing through the heating heat exchange section 174a is heated by heat exchange with the unused waste heat and decomposed into bicarbonate and hydrogen, and the hydrogen separated in the separation tank 174b is released. In this way, unused waste heat is used to heat the formate aqueous solution, so that the energy loss required for hydrogen release can also be reduced. Furthermore, when starting the electrolysis system 110 or when maintaining the temperature inside the electrolysis module 20 while electrolysis is stopped, the control device 90 opens the on-off valve 76 so that the separation tank 174b of the discharge reactor 174 is connected to the oxidation prevention hydrogen supply pipe 41 and the combustion hydrogen supply pipe 43. The control device 90 then controls the hydrogen blowers 42, 44 and the air blower 52 so that antioxidant hydrogen is supplied to the hydrogen electrodes of the electrolytic cell stack 21, and combustion hydrogen and air are supplied to the combustor 22. As a result, the released hydrogen is supplied to the hydrogen electrodes of the electrolytic cell stack 21 via the antioxidant hydrogen supply pipe 41 and to the combustor 22 via the combustion hydrogen supply pipe 43.

[0049] In the second embodiment described above, the hydrogen absorption and release system 170 is equipped with a heating heat exchanger 174a that is heated by unused waste heat to heat a liquid organic hydrogen carrier (aqueous formate solution) and release hydrogen. However, hydrogen may be released using other heat sources.

[0050] In the first and second embodiments described above, the electrolysis systems 10 and 110 are equipped with an electrolytic cell stack 21 that generates hydrogen by steam electrolysis. However, the electrolysis system 10 may also be configured to use the electrolytic cell stack 21 as a reversible solid oxide cell stack, allowing it to switch between an electrolysis mode that generates hydrogen by steam electrolysis and a power generation mode that generates electricity through the reaction of hydrogen as a fuel gas with oxygen contained in the air. When the reversible solid oxide cell stack is operated in power generation mode, for example, unused waste heat may 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 may be supplied to the hydrogen electrode of the reversible solid oxide cell stack by a hydrogen blower 42.

[0051] The above describes the forms for implementing this disclosure using embodiments, but this disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of this disclosure.

[0052] Furthermore, this specification also discloses a technical concept in which the "electrolytic system described in claim 1" in claim 4 of the original application was changed to "electrolytic system described in any one of claims 1 to 3". [Industrial applicability]

[0053] This disclosure can be used in industries such as the manufacturing of electrolytic systems. [Explanation of Symbols]

[0054] 10,110 Electrolysis system, 21 Electrolytic cell stack (solid oxide type electrolytic cell), 32 Steam generator (evaporator), 33 Water supply pipe (raw water supply line), 35 Steam supply pipe (steam supply line), 61 Hydrogen recovery piping (recovery line), 62 Condenser (gas-liquid separation section), 63 Cooling water supply pipe (cooling water supply line), 70 Hydrogen storage unit (hydrogen absorption / release section), 71 Hydrogen storage alloy, 72 First cooling heat exchange section, 73 Second cooling heat exchange section, 74 Heating heat exchange section, 81 Exhaust heat supply pipe (external heat supply line), 170 Hydrogen absorption / release system (hydrogen absorption / 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 Discharge reactor (discharge reaction section), 174a Heat exchange section for heating, 175 Circulation piping (circulation path).

Claims

1. A solid oxide type electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode, A hydrogen absorption and release unit that cools a hydrogen carrier to absorb hydrogen and heats the hydrogen carrier to release hydrogen, A steam supply line that supplies steam to the hydrogen electrode, A recovery line for recovering hydrogen contained in the exhaust gas discharged from the hydrogen electrode into the hydrogen absorption / discharge section, A gas-liquid separation unit is provided in the aforementioned recovery line, which cools the exhaust gas by heat exchange with a coolant to separate the gas and liquid, A coolant supply line that supplies the coolant to the gas-liquid separation unit and then to the hydrogen absorption / release unit, A first cooling heat exchange unit is provided in the hydrogen absorption and release unit and cools the hydrogen carrier by heat exchange with the coolant supplied from the coolant supply line, An electrolytic system equipped with the following features.

2. The electrolytic system according to claim 1, A raw water supply line that supplies raw water to the hydrogen absorption and release section and then supplies it to the steam supply line, A second cooling heat exchange unit is provided in the hydrogen absorption and release unit and cools the hydrogen carrier by heat exchange with the raw water supplied from the raw water supply line, An electrolytic system equipped with the following features.

3. The electrolytic system according to claim 2, The first cooling heat exchange section and the second cooling heat exchange section are arranged to cool the hydrogen or hydrogen carrier from the recovery line in the order of the first cooling heat exchange section and the second cooling heat exchange section. Electrolytic system.

4. The electrolytic system according to claim 1, An evaporation unit connected to the aforementioned steam supply line, which generates steam using external heat, A heating heat exchange unit is provided in the hydrogen absorption and release unit and heats the hydrogen carrier by heat exchange with external heat, An external heat supply line that selectively supplies the external heat to the evaporation section and the hydrogen absorption / release section, An electrolytic system equipped with the following features.

5. A solid oxide type electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode, A hydrogen absorption and release unit that cools a hydrogen carrier to absorb hydrogen and heats the hydrogen carrier to release hydrogen, A steam supply line that supplies steam to the hydrogen electrode, An evaporation unit connected to the aforementioned steam supply line, which generates steam using external heat, A heating heat exchange unit is provided in the hydrogen absorption and release unit and heats the hydrogen carrier by heat exchange with external heat, An external heat supply line that selectively supplies the external heat to the evaporation section and the hydrogen absorption / release section, An electrolytic system equipped with the following features.

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

7. An electrolytic system according to any one of claims 1 to 5, The hydrogen absorption and release section has a liquid organic hydrogen carrier as the hydrogen carrier. Electrolytic system.

8. The electrolytic system according to claim 7, The hydrogen absorption and release unit comprises a first tank for storing the liquid organic hydrogen carrier, an absorption reaction unit for cooling the liquid organic hydrogen carrier and reacting it with hydrogen, a second tank for storing the liquid organic hydrogen carrier after the reaction, a release reaction unit for heating the liquid organic hydrogen carrier after the reaction to release hydrogen, and a circulation path connecting the first tank, the absorption reaction unit, the second tank, and the release reaction unit in a ring shape. The first cooling heat exchange section is provided in the absorption reaction section, Electrolytic system.

Images