Solid oxide electrolysis cell hydrogen production system and method using waste heat

Abstract

The present invention relates to a solid oxide electrolysis cell (SOEC) system and, more specifically, to a system capable of improving the energy efficiency of an SOEC system and reducing hydrogen production costs by effectively using waste heat generated during an industrial process. According to the present invention, a SOEC hydrogen production system using waste heat can be provided, the system comprising: an external heat source; a waste heat distribution system, which classifies, according to the temperature, waste heat supplied from the external heat source, so as to supply the classified heat to each heat exchanger; a blower for supplying air; a pump for supplying water; a vaporizer for generating steam by vaporizing the water supplied from the pump; a first heat exchanger group including an air-preheating first heat exchanger for preheating the air supplied from the blower and a steam-preheating first heat exchanger for preheating the steam supplied from the vaporizer; a second heat exchanger group including a steam-generating second heat exchanger, which heats the vaporizer so as to generate the steam from the water, and a steam temperature-maintaining second heat exchanger, which maintains the temperature of the steam; a plurality of high-temperature heat exchangers including an air-heating high-temperature heat exchanger for increasing the temperature of the preheated air and a steam-heating high-temperature heat exchanger for increasing the temperature of the preheated steam; and an SOEC stack to which the high-temperature air and steam that have passed through the high-temperature heat exchangers are supplied to produce hydrogen.

Description

High-temperature water electrolysis hydrogen production system and method utilizing waste heat

[0001] The present invention relates to the field of solid oxide electrolysis cells (SOEC), and more specifically, to a system and method capable of improving the energy efficiency of a solid oxide electrolysis system and reducing hydrogen production costs by effectively utilizing waste heat generated in industrial processes.

[0002] The importance of hydrogen as a next-generation clean energy source is growing day by day, and it is receiving particular attention as a key energy source for achieving carbon neutrality. Among the commercially used hydrogen production methods currently available, water electrolysis is known as an eco-friendly approach that produces hydrogen by electrolyzing water.

[0003] Among water electrolysis technologies, the Solid Oxide Electrolysis Cell (SOEC) method has the advantage of efficiently producing hydrogen with low electrical energy due to its high-temperature operation. However, additional energy is consumed to supply the thermal energy required for high-temperature operation, which is a major cause of rising hydrogen production costs.

[0004] Meanwhile, significant amounts of waste heat are generated at industrial sites such as steel mills, cement plants, glass factories, and incinerators; however, the reality is that most of this waste heat is released into the atmosphere without being utilized. It is expected that if this unused waste heat can be effectively applied to high-temperature water electrolysis systems, the energy efficiency of the systems can be significantly improved.

[0005] Most conventional high-temperature water electrolysis systems supplied the necessary heat using electric heaters or separate heating devices. This approach faced difficulties in ensuring the economic viability of hydrogen due to high power consumption and operating costs. Furthermore, significant temperature fluctuations within the system posed challenges in securing thermal stability.

[0006] Therefore, there is a need for the development of technology that can effectively utilize waste heat generated at industrial sites in high-temperature water electrolysis systems. In particular, there is a need for technology that can maximize energy efficiency by utilizing waste heat in appropriate processes within the system according to its temperature range, while simultaneously ensuring the thermal stability of the system.

[0007] By providing one aspect of the present invention, we aim to provide a system and method that can effectively utilize waste heat generated at industrial sites in a high-temperature water electrolysis system to improve energy efficiency required for hydrogen production and reduce production costs.

[0008] By providing another aspect of the present invention, the utilization of waste heat is maximized by classifying waste heat into low, medium, and high temperatures according to its temperature range and configuring a heat exchange system suitable for each temperature range.

[0009] By providing another aspect of the present invention, we aim to provide a system and method capable of stably maintaining the operating temperature of a high-temperature water electrolysis stack while ensuring the thermal stability of the entire system.

[0010] By providing another aspect of the present invention, we aim to realize an eco-friendly hydrogen production process by utilizing unused waste heat generated in steel mills, cement plants, glass plants, incinerators, etc., as a renewable heat source.

[0011] According to one aspect of the present invention, a high-temperature water electrolysis hydrogen production system utilizing waste heat comprises: an external heat source; a waste heat distribution system that classifies waste heat supplied from the external heat source according to temperature and supplies the classified heat to respective heat exchangers; a blower that supplies air; a pump that supplies water; a vaporizer that vaporizes water supplied from the pump to generate steam; a first heat exchanger group comprising a first heat exchanger for preheating air supplied from the blower and a first heat exchanger for preheating steam supplied from the vaporizer; a second heat exchanger group comprising a second heat exchanger for generating steam from water by heating the vaporizer and a second heat exchanger for maintaining the temperature of the steam; a plurality of high-temperature heat exchangers comprising a high-temperature heat exchanger for heating air that raises the temperature of preheated air and a high-temperature heat exchanger for heating steam that raises the temperature of preheated steam; and a high-temperature water electrolysis stack to which high-temperature air and steam that have passed through the high-temperature heat exchangers are supplied to produce hydrogen. A high-temperature water electrolysis hydrogen production system including can be provided.

[0012] For example, a high-temperature water electrolysis hydrogen production system may be provided, wherein the waste heat distribution system classifies waste heat supplied from an external heat source into low-temperature waste heat of less than 150°C, medium-temperature waste heat of 150 to 300°C, and high-temperature waste heat of more than 300°C.

[0013] For example, a high-temperature water electrolysis hydrogen production system may be provided in which the first heat exchanger group receives low-temperature waste heat of less than 150°C through a heat medium from a waste heat distribution system.

[0014] For example, a high-temperature water electrolysis hydrogen production system may be provided in which the second heat exchanger group receives medium-temperature waste heat of 200 to 300°C through a heat medium from a waste heat distribution system.

[0015] For example, a high-temperature water electrolysis hydrogen production system may be provided in which a plurality of high-temperature heat exchangers receive high-temperature waste heat of 400°C or higher through a heat medium from a waste heat distribution system.

[0016] According to another aspect of the present invention, a high-temperature water electrolysis hydrogen production system may be provided, further comprising: a condenser for cooling a gas discharged from a high-temperature water electrolysis stack; a compressor connected to the condenser for compressing the cooled gas; an evaporator connected to the compressor for vaporizing the compressed gas; and a separator connected to the evaporator for separating hydrogen from the vaporized gas.

[0017] For example, a high-temperature water electrolysis hydrogen production system may be provided in which the operating temperature of the high-temperature water electrolysis stack is 600 to 800°C.

[0018] For example, a high-temperature water electrolysis hydrogen production system may be provided in which the temperature of the air passing through the high-temperature heat exchanger is 600 to 700°C and the temperature of the steam passing through the high-temperature heat exchanger is 650 to 750°C.

[0019] For example, a high-temperature water electrolysis hydrogen production system may be provided in which the waste heat is supplied from any one of a steel mill, a cement plant, a glass plant, and an incinerator.

[0020] For example, a high-temperature water electrolysis hydrogen production system may be provided in which the heat medium is any one fluid selected from the group consisting of heat medium oil, molten salt, and water.

[0021] According to another aspect of the present invention, a post-treatment system may be provided comprising: a condenser for cooling a gas discharged from a high-temperature water electrolysis stack; a compressor connected to the condenser for compressing the cooled gas; an evaporator connected to the compressor for vaporizing the compressed gas; a separator connected to the evaporator for separating hydrogen from the vaporized gas; and a control valve for controlling the flow rate of the system.

[0022] According to another aspect of the present invention, a method for producing hydrogen by high-temperature water electrolysis utilizing waste heat comprises: a step of receiving waste heat from an external heat source; a step of classifying the received waste heat according to temperature and supplying it to each heat exchanger; a step of supplying air through a blower, wherein the supplied air is preheated through a first heat exchanger for air preheating; a step of supplying water through a pump and vaporizing the supplied water in a vaporizer to generate steam, wherein the generated steam is preheated through a first heat exchanger for steam preheating, the vaporizer is heated through a second heat exchanger for steam generation to generate steam from the supplied water, and the temperature of the generated steam is maintained through a second heat exchanger for steam temperature maintenance; a step of raising the temperature of the preheated air through a high-temperature heat exchanger for air heating and raising the temperature of the preheated steam through a high-temperature heat exchanger for steam heating; A method for producing hydrogen by high-temperature water electrolysis may be provided, characterized by including a step of producing hydrogen using high-temperature air and steam that have passed through a high-temperature heat exchanger in a high-temperature water electrolysis stack.

[0023] According to one aspect of the present invention, a hydrogen production system and method can be provided in which energy efficiency required for hydrogen production is improved and production costs are reduced by effectively utilizing waste heat from an industrial site in a high-temperature water electrolysis system.

[0024] According to another aspect of the present invention, a hydrogen production system and method in which the utilization of waste heat is maximized can be provided by classifying waste heat by temperature range and configuring a heat exchange system suitable for each temperature range.

[0025] According to another aspect of the present invention, a hydrogen production system and method can be provided in which the operating temperature of the high-temperature water electrolysis stack is stably maintained while the thermal stability of the entire system is ensured.

[0026] According to another aspect of the present invention, a system and method capable of producing hydrogen in an eco-friendly and economical manner can be provided by utilizing unused waste heat generated in steel mills, cement plants, glass plants, incinerators, etc., as a renewable heat source.

[0027] FIG. 1 is a schematic diagram showing the configuration of a high-temperature water electrolysis hydrogen production system utilizing waste heat according to one embodiment of the present invention.

[0028] FIG. 2 is a flowchart schematically illustrating a method for producing high-temperature water electrolysis hydrogen using waste heat according to one embodiment of the present invention.

[0029] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0030] According to one aspect of the present invention, a high-temperature water electrolysis hydrogen production system (100) utilizing waste heat comprises: an external heat source (110); a waste heat distribution system (120) that classifies waste heat supplied from the external heat source (110) according to temperature and supplies the classified heat to each heat exchanger; a blower (130) that supplies air; a pump (140) that supplies water; a vaporizer that vaporizes water supplied from the pump (140) to generate steam; a first heat exchanger group comprising a first heat exchanger (210) for preheating air supplied from the blower (130) and a first heat exchanger (220) for preheating steam supplied from the vaporizer; and a second heat exchanger group comprising a second heat exchanger (310) for generating steam from water by heating the vaporizer and a second heat exchanger (320) for maintaining the temperature of the steam. A high-temperature water electrolysis hydrogen production system (100) may be provided, comprising: a plurality of high-temperature heat exchangers including a high-temperature heat exchanger (410) for heating air that raises the temperature of preheated air and a high-temperature heat exchanger (420) for heating steam that raises the temperature of preheated steam; and a high-temperature water electrolysis stack (500) that produces hydrogen by supplying high-temperature air and steam that have passed through the high-temperature heat exchangers.

[0031] Referring to FIG. 1, a high-temperature water electrolysis hydrogen production system (100) utilizing waste heat according to one embodiment of the present invention includes an external heat source (110), a waste heat distribution system (120), a blower (130), a pump (140), a vaporizer (150), a first heat exchanger group, a second heat exchanger group, a plurality of high-temperature heat exchangers, and a high-temperature water electrolysis stack (500). Waste heat supplied from the external heat source (110) is transferred to the waste heat distribution system (120). The waste heat distribution system (120) classifies the supplied waste heat into low-temperature waste heat of less than 150°C, medium-temperature waste heat of 150 to 300°C, and high-temperature waste heat of more than 300°C, and distributes it to each heat exchanger group. The blower (130) supplies air, and the supplied air is preheated as it passes through the first heat exchanger (210) for air preheating of the first heat exchanger group. A pump (140) supplies water, and the supplied water is converted into steam in a vaporizer (150). The generated steam is preheated as it passes through a first heat exchanger (220) for steam preheating in a first heat exchanger group (200). A second heat exchanger group includes a second heat exchanger (310) for generating steam and a second heat exchanger (320) for maintaining the steam temperature. The second heat exchanger (310) for generating steam heats the vaporizer (150) to promote a phase change from water to steam, and the second heat exchanger (320) for maintaining the steam temperature stably maintains the temperature of the generated steam. A plurality of high-temperature heat exchangers include a high-temperature heat exchanger (410) for heating air and a high-temperature heat exchanger (420) for heating steam. A high-temperature heat exchanger (410) for heating air raises the temperature of preheated air to 600 to 700°C, and a high-temperature heat exchanger (420) for heating steam heats the temperature of preheated steam to 650 to 750°C. Finally, a high-temperature water electrolysis stack (500) receives high-temperature air and steam and produces hydrogen through electrolysis. The operating temperature of the stack is maintained in the range of 600 to 800°C, which is essential for optimizing the efficiency of the electrochemical reaction and minimizing overpotential at the electrodes.

[0032] The system (100) may also optionally include a post-treatment system. The post-treatment system consists of a condenser (610), a compressor (620), an evaporator (630), a separator (640), and a control valve (650) and is responsible for purifying and separating the produced hydrogen. Each component is connected sequentially through piping, enabling a continuous hydrogen purification process.

[0033] In the system of the present invention, the external heat source (110) is a heat source capable of supplying waste heat of various temperature ranges generated in an industrial process, and the waste heat distribution system (120) connected thereto analyzes the temperature characteristics of the supplied waste heat and can distribute optimal thermal energy according to the requirements of each heat exchanger.

[0034] In the fluid supply section, the blower (130) can supply air containing oxygen, the pump (140) can supply water, and the vaporizer can efficiently receive and utilize thermal energy in the process of converting the supplied water into steam.

[0035] Depending on the application, the pump (140) may be selectively applied as a reciprocating pump, a multi-stage centrifugal pump, a gear pump, etc., and the blower (130) may be a turbo blower, a Roots blower, a screw blower, etc. In particular, the pump (140) and the blower (130) may be capable of continuous flow rate control in the range of 0-100% through an inverter control method. To improve heat transfer efficiency, various structures such as microchannel type, plate fin type, and bare fin type may be applied to the vaporizer, and the material may be selectively used as stainless steel (SUS304, SUS316L), duplex steel, Inconel, etc. In particular, baffles (vertical type, horizontal type, disc-donut type) or vortex generators (twist tape, spiral coil) for flow stabilization may be installed inside the vaporizer.

[0036] In the first heat exchanger group, the air preheating heat exchanger (210) can reduce the load of the downstream heat exchanger by primarily heating the ambient air supplied from the blower (130), and the steam preheating heat exchanger (220) can stably raise the temperature of the steam generated in the vaporizer. In the second heat exchanger group, the steam generating heat exchanger (310) can effectively supply the latent heat required for the phase change from water to steam, and the steam temperature maintaining heat exchanger (320) can compensate for heat loss by maintaining the temperature of the generated steam at a constant level.

[0037] In the first and second heat exchanger groups, various joining methods such as gasket type, brazing type, and welding type may be applied, and various patterns such as chevron, waffle, and dimple may be used for the shape of the heat transfer plates. In the high-temperature heat exchanger group, various ceramic materials such as silicon carbide, silicon nitride, and alumina may be applied, and structurally, tubular, plate, and printed types may be selectively used.

[0038] In the high-temperature heat exchanger group, the air heating heat exchanger can raise the temperature of the preheated air to the operating temperature of the high-temperature water electrolysis stack (500), and the steam heating heat exchanger can heat the preheated steam to a temperature optimized for the electrolytic reaction. Finally, the high-temperature water electrolysis stack (500) can efficiently produce hydrogen using the high-temperature air and steam prepared through this multi-stage heat exchange process.

[0039] In order to improve temperature uniformity, multiple temperature control zones such as a preheating zone, an isothermal zone, and a postheating zone may be installed in the gas supply line to the high-temperature water electrolysis stack (500), and each zone may include various types of auxiliary heating devices such as ceramic heaters, Kanthal heaters, and SiC heaters. In addition, various insulating materials such as vacuum insulation, ceramic fibers, and calcium silicate may be applied to the piping.

[0040] Additionally, the waste heat distribution system (120) of the present invention may include a temperature sensing unit and a flow rate control unit, the temperature sensing unit may include various temperature sensors such as thermocouples (Type B, Type R, Type S), optical pyrometers, etc., and the flow rate control unit may include various types of control valves such as butterfly valves, globe valves, ball valves, etc.

[0041] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided, wherein the waste heat distribution system (120) classifies waste heat supplied from an external heat source (110) into low-temperature waste heat of less than 150°C, medium-temperature waste heat of 150 to 300°C, and high-temperature waste heat of more than 300°C.

[0042] Although low-temperature waste heat is difficult to utilize directly in high-temperature processes, utilizing it in preheating processes can improve the overall energy efficiency of the system. For example, the lower limit of low-temperature waste heat may be 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, and the upper limit of low-temperature waste heat may be 150°C, 140°C, 130°C, 120°C, or 110°C. Such low-temperature waste heat can be recovered in exhaust gas heat exchangers, cooling water heat exchangers, condensate recovery systems, etc.

[0043] Waste heat in the medium temperature range is at a temperature sufficiently higher than the vaporization point of water and can stably supply the thermal energy required for the generation and maintenance of steam. Waste heat in this temperature range can prevent rapid temperature changes while maintaining the superheat of the steam appropriately, thereby contributing to securing the thermal stability of the system. For example, the lower limit of medium temperature waste heat may be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or 210°C, and the upper limit of medium temperature waste heat may be 300°C, 290°C, 280°C, 270°C, 260°C, or 250°C, and this can be collected from boiler blowdown, medium pressure steam piping, drying processes, etc.

[0044] High-temperature waste heat is at a temperature close to the operating temperature range of the high-temperature water electrolysis stack (500) and can be utilized in the final heating stage. Utilizing this high-temperature waste heat can significantly reduce the additional heating load of the system, thereby reducing energy costs and maximizing the thermal efficiency of the entire system. In addition, by selecting and using a heat medium optimized for each temperature range, the recovery rate of waste heat energy can be further improved. For example, the lower limit of high-temperature waste heat may be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 500°C, 600°C, 700°C, 800°C, or 900°C, and the upper limit of high-temperature waste heat may be 1500°C, 1400°C, 1300°C, 1200°C, 1100°C, or 1000°C, which can be obtained from incinerator exhaust, melting furnace exhaust, calcination furnace exhaust, etc.

[0045] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided in which the first heat exchanger group receives low-temperature waste heat of less than 150°C through a heat medium from a waste heat distribution system (120).

[0046] In the first heat exchanger, the first heat exchanger (210) for preheating air can distribute the load of the downstream heat exchangers by gradually heating the air at room temperature. This can mitigate thermal shock of the entire system and prevent device damage caused by thermal stress.

[0047] The first heat exchanger (220) for preheating steam can serve to stably raise the initial temperature of the steam generated in the vaporizer. In this process, it may be important to prevent condensation of the steam and maintain an appropriate superheat, and the use of low-temperature waste heat can economically satisfy these conditions. In particular, an indirect heat exchange method using a heat medium can enable efficient heat transfer while protecting the system from contaminants that may be contained in the waste heat.

[0048] The utilization of low-temperature waste heat in the first heat exchanger can be achieved through various heat exchanger structures, such as fin-tube, spiral plate, and double-tube types. In particular, for air preheating, expanded heat transfer surfaces made of various materials, such as aluminum fins, copper fins, and stainless steel fins, can be applied, while for steam preheating, materials with excellent corrosion resistance, such as titanium, Inconel, and Hastelloy, can be selectively used.

[0049] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided in which a second heat exchanger group receives medium-temperature waste heat of 200 to 300°C through a heat medium from a waste heat distribution system (120).

[0050] The configuration of the second heat exchanger group can be designed to effectively perform two key functions: steam generation and temperature maintenance. The second heat exchanger (310) for steam generation can stably supply the high latent heat required during the phase change process of water. In this process, the utilization of medium-temperature waste heat can enable efficient heat transfer by maintaining an appropriate temperature difference between the heat source and the water, thereby ensuring both stability and efficiency of the steam generation process.

[0051] The second heat exchanger (320) for maintaining the steam temperature can perform the role of maintaining the temperature of the generated steam at a level suitable for the next process. This may be essential for compensating for heat loss that may occur in piping, preventing condensation of the steam, and supplying steam in a stable state to the downstream high-temperature heat exchanger. This dual heat exchange structure can improve the thermal stability of the system while maximizing the utilization of medium-temperature waste heat.

[0052] In the second heat exchanger group, heat exchangers for steam generation can be manufactured in various structures, such as vertical shell-and-tube, horizontal shell-and-tube, and U-tube types, and segmental baffles, helical baffles, and rod baffles can be installed internally to improve heat transfer efficiency. Heat exchangers for maintaining steam temperature can utilize structures such as double-tube, multi-tube, and plate types, and internal flow paths can be designed in various forms, such as straight, spiral, or zigzag shapes.

[0053] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided in which a plurality of high-temperature heat exchangers receive high-temperature waste heat of 400°C or higher through a heat medium from a waste heat distribution system (120).

[0054] The high-temperature heat exchanger group can perform the role of finally raising the temperature of air and steam to a temperature suitable for the operation of the high-temperature water electrolysis stack (500). The high-temperature heat exchanger (410) for air heating raises the temperature of the preheated air to the stack operating temperature range, and in this process, the utilization of high-temperature waste heat can significantly reduce the additional electric heating load. In addition, it can provide optimal heat transfer conditions to minimize thermal stress that may occur during the process of raising the temperature of the air.

[0055] A high-temperature heat exchanger (420) for heating steam can perform the function of heating preheated steam to a temperature optimized for the electrolytic reaction. In this process, by utilizing high-temperature waste heat, the degree of superheating of the steam can be appropriately controlled, and temperature conditions that can maximize the efficiency of the electrolytic reaction can be secured. In particular, the structure and material of the heat exchanger can be specially designed to optimize heat transfer efficiency in the high-temperature region, thereby ensuring both the durability and stability of the system.

[0056] For high-temperature heat exchangers, various ceramic materials such as alumina, zirconia, and silicon carbide may be used for durability at high temperatures, and structurally, monolithic, honeycomb, and tubular types may be applied. In particular, high-temperature heat exchangers (420) for heating air / steam may adopt various fluid flow methods such as counterflow, crossflow, and mixedflow, and various heat transfer promoters such as turbators, dimples, and grooves may be installed inside.

[0057] According to another aspect of the present invention, a high-temperature water electrolysis hydrogen production system (100) may be provided, further comprising: a condenser for cooling a gas discharged from a high-temperature water electrolysis stack (500); a compressor connected to the condenser for compressing the cooled gas; an evaporator connected to the compressor for vaporizing the compressed gas; and a separator connected to the evaporator for separating hydrogen from the vaporized gas.

[0058] The configuration of the post-treatment system may include a series of processes for purifying and separating hydrogen produced in the high-temperature water electrolysis stack (500). The condenser can improve the thermal efficiency of the entire system by recovering heat from the high-temperature exhaust gas and condensing unreacted water vapor. The thermal energy recovered in this process can be recycled in other parts of the system, and the condensed water can also be reused.

[0059] The compressor can increase the pressure of the cooled gas to provide conditions suitable for the downstream separation process. In this process, by optimizing the compression ratio and compression speed, conditions can be established for efficient gas separation while minimizing energy consumption. The evaporator can regulate the state of the compressed gas to conditions optimized for gas separation, which can play a crucial role in improving hydrogen separation efficiency.

[0060] The separator is a key device for separating high-purity hydrogen from a gas mixture and can be designed to maximize separation efficiency while minimizing energy consumption. Additionally, a recirculation system for unseparated gases can improve the hydrogen recovery rate and enhance the overall efficiency of the system.

[0061] The condenser of the post-treatment system can be manufactured in various structures, such as vertical tubular, horizontal tubular, and plate types, and the compressor can be selectively applied in screw, centrifugal, or piston types. Various types of evaporators, such as flash, spray, and thin-film types, can be used, and various separation technologies, such as Pressure Swing Adsorption (PSA), membrane, and cryogenics, can be applied to the separator.

[0062] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided, wherein the operating temperature of the high-temperature water electrolysis stack (500) is 600 to 800°C. In this operating temperature range, the electrochemical reaction efficiency can be maximized, and at the same time, the overvoltage at the electrode can be minimized, and it can contribute to improving the overall energy efficiency of the system.

[0063] The operating temperature of the high-temperature water electrolysis stack (500) can be optimized in various ranges depending on the type of electrolyte, fuel electrode, and air electrode. The optimal operating temperature of the electrolyte may be 600 to 700°C, 650 to 750°C, or 700 to 800°C. The optimal operating temperature of the fuel electrode may be 600 to 750°C, 650 to 775°C, or 700 to 800°C. The optimal operating temperature of the air electrode may be 600 to 725°C, 650 to 775°C, or 700 to 800°C.

[0064] YSZ, ScSZ, LSGM, etc., can be used as electrolyte materials, and Ni-YSZ, Ni-ScSZ, Ni-GDC, etc., can be applied as fuel electrode materials. LSM, LSCF, LSC, etc., can be used as air electrode materials. Various temperature measuring devices such as thermocouples, optical sensors, and ultrasonic sensors can be installed to control the temperature inside the stack, and various control algorithms such as PID control, fuzzy control, and model predictive control can be applied.

[0065] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided, wherein the temperature of the air passing through the high-temperature heat exchanger is 600 to 700°C and the temperature of the steam passing through the high-temperature heat exchanger is 650 to 750°C.

[0066] Temperature control of the air and steam passing through the high-temperature heat exchanger can have a direct effect on the performance and stability of the high-temperature water electrolysis stack (500). The temperature of the air can be set to be optimized for the conduction and reduction reactions of oxygen ions, which may be important for maintaining the oxygen partial pressure at the electrodes appropriately and securing the driving force for the electrochemical reaction. At the same time, electrode degradation can be suppressed by preventing an excessive temperature rise at the air electrode.

[0067] The temperature of the steam can be a key factor in determining the efficiency of the steam decomposition reaction for hydrogen production. By supplying steam within an appropriate temperature range, the reaction rate at the electrolyte interface can be optimized, and the hydrogen production efficiency can be maximized. In addition, by maintaining the superheat of the steam appropriately, localized condensation at the electrode can be prevented, thereby preventing degradation of the electrode's performance.

[0068] At the outlet of the high-temperature heat exchanger, the temperature of the air can be controlled in the range of 600 to 650°C, 625 to 675°C, or 650 to 700°C. The temperature of the water vapor can be maintained in the range of 650 to 700°C, 675 to 725°C, or 700 to 750°C.

[0069] For measuring such temperatures, flow meters such as differential pressure, thermal, and vortex types may be used, and thermometers such as thermocouples, RTDs, and optical pyrometers may be applied. Pressure gauges such as diaphragm, Bourdon tube, and electronic types may be utilized. For temperature control, various control elements such as electric valves, pneumatic valves, and solenoid valves may be used.

[0070] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided, wherein the waste heat is waste heat supplied from any one of a steel mill, a cement plant, a glass plant and an incinerator.

[0071] The selection and utilization of waste heat sources can be important factors in determining the economic feasibility and stability of the system of the present invention. In the case of steel mills, high-temperature waste heat generated during the ironmaking and steelmaking processes can be continuously supplied, making it suitable for large-scale hydrogen production. In such a continuous process, the temperature and flow rate of the waste heat can be maintained relatively constant, enabling stable operation of the system.

[0072] In the case of cement and glass factories, the waste heat generated from the kiln process and melting furnace, respectively, can exist across various temperature ranges and serve as a suitable heat source for the multi-stage heat exchange system of the present invention. In particular, since these processes are characterized by stable operation throughout the year, continuous hydrogen production is possible.

[0073] In the case of incinerators, environmental value can be further enhanced by utilizing waste heat generated during the waste treatment process. Due to their geographically dispersed nature, incinerators can be utilized as a heat source for small-scale, decentralized hydrogen production facilities. This enables the optimization of hydrogen production and supply at the local level.

[0074] As a waste heat source, waste heat can be recovered from coke ovens, sintering furnaces, electric furnaces, etc. in steel mills; from preheaters, kilns, coolers, etc. in cement plants; from melting furnaces, slow cooling furnaces, heat treatment furnaces, etc. in glass plants; and from primary combustion chambers, secondary combustion chambers, boilers, etc. in incinerators. Various dust collection equipment and heat exchangers, such as cyclones, bag filters, and electrostatic precipitators, can be installed for each source.

[0075] For example, a high-temperature water electrolysis hydrogen production system (100) may be provided, wherein the heat medium is any one fluid selected from the group consisting of heat medium oil, molten salt, and water.

[0076] The selection of a heat transfer medium can be a critical factor in determining heat transfer efficiency and system stability across various temperature ranges. In the case of heat transfer fluids, they can maintain stable properties over a wide temperature range, allowing them to be applied to heat exchange processes at various temperatures. In particular, their low temperature dependence on viscosity can reduce pumping power, and their excellent heat transfer coefficient allows for the optimization of heat exchanger sizes.

[0077] Molten salts exhibit excellent thermal stability at high temperatures, making them suitable heat transfer media for high-temperature heat exchangers. Their high heat capacity enables efficient storage and transfer of thermal energy, while their low vapor pressure facilitates pressure management in the system even at high temperatures. Furthermore, their superior chemical stability allows for long-term use.

[0078] Using water as a heat transfer medium offers advantages such as ease of handling and low cost. Particularly in low-temperature regions, efficient heat exchange is possible based on its excellent heat transfer characteristics. Furthermore, it is environmentally friendly and ensures safety even in the event of a leak, making system maintenance easier.

[0079] The heat transfer oils used as the heat medium may include mineral oil-based, synthetic hydrocarbon-based, and silicone-based types, while the molten salts may include nitrate-based, chloride-based, and fluoride-based types. When water is used as the heat medium, various water qualities such as soft water, pure water, and ultrapure water may be applied, and various water treatment agents such as corrosion inhibitors, scale inhibitors, and pH regulators may be added.

[0080] According to another aspect of the present invention, a post-treatment system may be provided comprising: a condenser for cooling a gas discharged from a high-temperature water electrolysis stack (500); a compressor connected to the condenser for compressing the cooled gas; an evaporator connected to the compressor for vaporizing the compressed gas; a separator connected to the evaporator for separating hydrogen from the vaporized gas; and a control valve for controlling the flow rate of the system.

[0081] The post-treatment system includes a series of devices for purifying the hydrogen mixed gas produced from the high-temperature water electrolysis stack (500) to obtain high-purity hydrogen. The condenser (610) performs the function of cooling the high-temperature mixed gas to condense unreacted water vapor. To maximize heat exchange efficiency, the condenser (610) can be manufactured in various structures such as shell-and-tube type, plate type, or fin-tube type, and the material can be optionally stainless steel, titanium, copper, etc.

[0082] The compressor (620) increases the pressure of the cooling gas passing through the condenser (610) to provide conditions suitable for the subsequent separation process. Various types of compressors (620), such as screw type, centrifugal type, and piston type, can be applied, and the compression ratio can be continuously adjusted through inverter control. In particular, when selecting the compressor (620), a sealing system and a lubrication system suitable for hydrogen handling must be considered.

[0083] The evaporator (630) controls the state of the compressed gas to conditions optimized for gas separation, and various types such as flash type, spray type, and thin film type can be used. The control valve (650) controls the flow of fluid within the system, and globe valves, butterfly valves, ball valves, etc., can be used.

[0084] The separator (640) is a core device for separating high-purity hydrogen from a gas mixture, and various separation technologies such as Pressure Swing Adsorption (PSA), membranes, and cryogenic separation can be applied. In the case of the PSA method, various adsorbents such as zeolite, activated carbon, and carbon molecular sieves can be used, and in the case of the membrane method, various separation membrane materials such as polyimide and palladium can be applied.

[0085] According to another aspect of the present invention, a method for producing hydrogen by high-temperature water electrolysis utilizing waste heat comprises: a step of receiving waste heat from an external heat source; a step of classifying the received waste heat according to temperature and supplying it to each heat exchanger; a step of supplying air through a blower, wherein the supplied air is preheated through a first heat exchanger for air preheating; a step of supplying water through a pump and vaporizing the supplied water in a vaporizer to generate steam, wherein the generated steam is preheated through a first heat exchanger for steam preheating, the vaporizer is heated through a second heat exchanger for steam generation to generate steam from the supplied water, and the temperature of the generated steam is maintained through a second heat exchanger for steam temperature maintenance; a step of raising the temperature of the preheated air through a high-temperature heat exchanger for air heating and raising the temperature of the preheated steam through a high-temperature heat exchanger for steam heating; A method for producing hydrogen by high-temperature water electrolysis may be provided, characterized by including a step of producing hydrogen using high-temperature air and steam that have passed through a high-temperature heat exchanger in a high-temperature water electrolysis stack.

[0086] According to another aspect of the present invention, a method for producing high-temperature water electrolysis hydrogen utilizing waste heat comprises: a step (S1) of receiving waste heat from an external heat source (110); a step (S2) of classifying the received waste heat according to temperature and supplying it to each heat exchanger; a step (S3) of supplying air through a blower (130), wherein the supplied air is preheated through a first heat exchanger (210) for air preheating; a step (S4) of supplying water through a pump (140) and vaporizing the supplied water in a vaporizer to generate steam, wherein the generated steam is preheated through a first heat exchanger (220) for steam preheating, the vaporizer is heated through a second heat exchanger (310) for steam generation to generate steam from the supplied water, and the temperature of the generated steam is maintained through a second heat exchanger (320) for steam temperature maintenance; A method for producing hydrogen by high-temperature water electrolysis may be provided, characterized by including the step (S5) of raising the temperature of preheated air through a high-temperature heat exchanger (410) for air heating and raising the temperature of preheated steam through a high-temperature heat exchanger (420) for steam heating; and the step (S6) of producing hydrogen using the high-temperature air and steam that have passed through the high-temperature heat exchangers (410, 420) in a high-temperature water electrolysis stack (500).

[0087] Referring to FIG. 2, the process flow of the high-temperature water electrolysis hydrogen production method utilizing waste heat according to the present invention can be observed. That is, the hydrogen production method of the present invention begins with a step (S1) of receiving waste heat from an external heat source. Next, a step (S2) of classifying the received waste heat according to temperature to supply it to each heat exchanger is performed. Next, a step (S3) of supplying air through a blower is carried out, followed by a step (S4) of vaporizing water supplied through a pump to generate steam. After that, a step (S5) of raising the temperature of the preheated air and preheated steam is performed, finally leading to a step (S6) of producing hydrogen in a high-temperature water electrolysis stack.

[0088] In the step (S3) of supplying air through the blower (130) during the process, the supplied air is preheated as it passes through the first heat exchanger (210) for air preheating, and in this process, some of the waste heat is utilized for air preheating, thereby improving the overall energy efficiency of the system. Subsequently, a step (S4) is performed in which water supplied through the pump (140) is vaporized in a vaporizer to generate steam, and the steam generated in this process is preheated through the first heat exchanger (220) for steam preheating. The vaporizer generates steam from the supplied water that has been heated through the second heat exchanger (310) for steam generation, and the temperature of the generated steam is maintained at a constant level through the second heat exchanger (320) for maintaining steam temperature.

[0089] Next, in the step (S5) of raising the temperature of the preheated air and preheated steam, the temperature of the preheated air is raised through a high-temperature heat exchanger (410) for air heating and the temperature of the preheated steam is raised through a high-temperature heat exchanger (420) for steam heating, in order to satisfy the appropriate temperature conditions required for high-temperature water electrolysis. Finally, in the high-temperature water electrolysis stack (500), the step (S6) of producing hydrogen using the high-temperature air and steam that have passed through the high-temperature heat exchangers (410, 420) is performed to efficiently produce hydrogen through electrolysis.

[0090] The present invention will be described in detail below using specific embodiments. It should be understood that the following embodiments are not intended to limit the scope of the invention, but are intended to illustrate the implementation of the invention.

[0091] Examples

[0092] To implement the high-temperature water electrolysis hydrogen production system (100) of the present invention, waste heat generated from a coke oven of a steel mill was used as an external heat source (110). The waste heat distribution system (120) used an S-type thermocouple with a measurement precision of 0.5°C and a butterfly valve with a response speed of 0.1 seconds to classify the waste heat into low-temperature waste heat of 100-150°C, medium-temperature waste heat of 200-300°C, and high-temperature waste heat of 400-800°C.

[0093] The blower (130) supplied 500 L of air per minute using a turbo blower with a control error of 0.05%. The pump (140) supplied 2 L of water per minute constantly using a multi-stage centrifugal pump with 0.02% precision. The vaporizer (150) has a heat transfer coefficient of 5000 W / m² 2 The microchannel type structure of K was adopted, and the twist tape type vortex generator installed inside maintained a Reynolds number of 10,000 or more.

[0094] In the first heat exchanger group (200), low-temperature waste heat in the range of 100-150°C was utilized, and water with a thermal conductivity of 0.6 W / mK was used as the heat medium. The first heat exchanger (210) for air preheating has a heat transfer surface area of ​​50 m² 2 Using an aluminum fin tube type, the air temperature was raised to 120°C, and the first heat exchanger (220) for steam preheating has a heat transfer area of ​​30m 2 The steam temperature was preheated to 140°C using a plate-shaped structure.

[0095] In the second heat exchanger group (300), medium-temperature waste heat in the range of 200-300°C was utilized, and a heat transfer oil with a melting point of 142°C was used as the heat medium. The second heat exchanger (310) for steam generation has a heat transfer surface area of ​​80m² 2 By applying a vertical shell-and-tube type, the temperature was heated to 250°C at a heating rate of 35°C per minute, and the second heat exchanger (320) for maintaining the steam temperature maintained the steam temperature at 280°C with a temperature fluctuation range of ±0.5°C.

[0096] In the high-temperature heat exchanger group (400), high-temperature waste heat in the range of 400-800°C was utilized, and molten salt was used as the heat medium. The high-temperature heat exchanger (410) for air heating, made of silicon carbide material with a thermal conductivity of 40 W / mK, reached 650°C within 2.5 minutes, and the high-temperature heat exchanger (420) for steam heating reached 700°C within 4 minutes. Both heat exchangers maintained a temperature deviation of ±1°C.

[0097] The high-temperature water electrolysis stack (500) used YSZ doped with 8 mol% Y2O3 as the electrolyte and achieved an ionic conductivity of 0.15 S / cm at 700°C. The fuel electrode was Ni-YSZ with a porosity of 35%, and the air electrode had a surface area of ​​3.5 m² 2 LSCF of / g was applied.

[0098] In the post-treatment system, a plate condenser (610) with a heat exchange efficiency of 95% and a screw compressor (620) capable of three-stage compression were used. A flash type evaporator (630) was applied, and a PSA separator (640) with a surface area of ​​1000 m² 2 Hydrogen purity of over 99.99% was achieved using zeolite adsorbent / g.

[0099] As a result of applying the system of the present invention, the overall energy efficiency of the system increased by 2~5%, and the hydrogen production cost was reduced by 400~800 won / kgH2.

[0100] Although various aspects of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention as described in the claims.

Claims

1. As a high-temperature water electrolysis hydrogen production system utilizing waste heat: External heat source; A waste heat distribution system that classifies waste heat supplied from the above external heat source according to temperature and supplies the classified heat to respective heat exchangers; A blower that supplies air; A pump that supplies water; A vaporizer that vaporizes water supplied from the above pump to generate water vapor; A first heat exchanger group comprising a first heat exchanger for preheating air supplied from the blower and a first heat exchanger for preheating steam supplied from the vaporizer; A second heat exchanger group comprising a second heat exchanger for generating steam from water by heating the vaporizer and a second heat exchanger for maintaining the temperature of the steam; A plurality of high-temperature heat exchangers including a high-temperature heat exchanger for air heating that raises the temperature of the preheated air and a high-temperature heat exchanger for steam heating that raises the temperature of the preheated steam; and A high-temperature water electrolysis stack that produces hydrogen by supplying high-temperature air and steam that have passed through the above-mentioned high-temperature heat exchanger; A high-temperature water electrolysis hydrogen production system comprising 2. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the waste heat distribution system classifies the waste heat supplied from the external heat source into low-temperature waste heat of less than 150°C, medium-temperature waste heat of 150 to 300°C, and high-temperature waste heat of more than 300°C.

3. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the first heat exchanger group receives low-temperature waste heat of less than 150°C through a heat medium from the waste heat distribution system.

4. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the second heat exchanger group receives medium-temperature waste heat of 200 to 300°C through a heat medium from the waste heat distribution system.

5. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the plurality of high-temperature heat exchangers receive high-temperature waste heat of 400°C or higher through a heat medium from the waste heat distribution system.

6. In Paragraph 1, A condenser for cooling the gas discharged from the above-mentioned high-temperature water electrolysis stack; A compressor connected to the above condenser to compress the cooled gas; An evaporator connected to the above compressor to vaporize the compressed gas; and A separator connected to the above evaporator to separate hydrogen from the vaporized gas; A high-temperature water electrolysis hydrogen production system that additionally includes 7. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the operating temperature of the high-temperature water electrolysis stack is 600 to 800°C.

8. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the temperature of the air passing through the high-temperature heat exchanger is 600 to 700°C and the temperature of the water vapor passing through the high-temperature heat exchanger is 650 to 750°C.

9. A high-temperature water electrolysis hydrogen production system according to claim 1, wherein the waste heat is waste heat supplied from any one of a steel mill, a cement plant, a glass plant, and an incinerator.

10. A high-temperature water electrolysis hydrogen production system according to paragraph 3, wherein the heat transfer medium is any one fluid selected from the group consisting of heat transfer oil, molten salt, and water.

11. As a method for producing hydrogen by high-temperature water electrolysis utilizing waste heat: A step of receiving waste heat from an external heat source; A step of classifying the supplied waste heat according to temperature and supplying it to each heat exchanger; A step of supplying air through a blower, wherein the supplied air is preheated through a first heat exchanger for air preheating; A step of supplying water through a pump and vaporizing the supplied water in a vaporizer to generate steam, wherein the generated steam is preheated through a first heat exchanger for steam preheating, the vaporizer is heated through a second heat exchanger for steam generation to generate steam from the supplied water, and the temperature of the generated steam is maintained through a second heat exchanger for steam temperature maintenance; A step of raising the temperature of the preheated air through a high-temperature heat exchanger for air heating and raising the temperature of the preheated steam through a high-temperature heat exchanger for steam heating; and A step of producing hydrogen in a high-temperature water electrolysis stack using high-temperature air and steam that have passed through the high-temperature heat exchanger. A method for producing high-temperature water electrolysis hydrogen characterized by including

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