Hydrogen-fused salt energy storage coupled industrial waste heat recovery hydrogen production system and method

Abstract

The invention belongs to the technical field of industrial waste heat resource utilization, and provides a hydrogen-fused salt energy storage coupled industrial waste heat recovery hydrogen production system and method, a fused salt energy storage subsystem comprises an energy storage module and a waste heat heat exchange module which are connected with each other, and a thermochemical circulation subsystem adopts a reactor; the reactor adopts a horizontal fixed bed reactor, and CaO-Ca (OH) 2 particles are filled in the reactor; a heat absorption stage: the high-temperature molten salt flows through a reactor jacket, a bed layer is heated to a first preset temperature, Ca (OH) 2 is subjected to a decomposition reaction, and nitrogen is introduced in the reaction process; a heat release stage: introducing water vapor into the reactor, carrying out hydration reaction on the water vapor and CaO, heating the fused salt to a second preset temperature by virtue of reaction heat release, and providing a heat source for the electrolytic hydrogen production subsystem; through coupling of a fused salt energy storage system and CaO-Ca (OH) 2 thermochemical circulation, efficient recovery and utilization of low-grade waste heat at the temperature of 300-500 DEG C are achieved, an electrolytic bath is driven to produce hydrogen at low cost, the heat efficiency of the system is improved to 75% or above, and green hydrogen self-supply in the high-energy-consumption industry is promoted.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste heat resource utilization technology, and particularly relates to an industrial waste heat recovery and hydrogen production system and method coupled with hydrogen-molten salt energy storage. Background Technology

[0002] In the production processes of heavy industries such as steel, cement, and chemicals, a large amount of energy is emitted as waste heat. Industrial waste heat resources account for a high proportion of total energy consumption, with medium- and low-temperature waste heat of 300-500℃ accounting for more than 60%. Due to its wide temperature range and low grade, this type of waste heat is difficult to utilize efficiently using traditional recovery technologies (such as waste heat boilers and heat exchangers), resulting in a large amount of energy waste.

[0003] Currently, the mainstream hydrogen production methods include fossil fuel reforming and water electrolysis. Fossil fuel reforming (such as methane steam reforming) has high carbon emissions (per unit of production...). Hydrogen emissions are approximately 9-12 Problems include reliance on fossil resources; while alkaline water electrolysis for hydrogen production is a mature technology, it has high energy consumption (typically requiring 4.5-5.5 kWh). Electricity costs account for 70% of production costs. The above makes it difficult to achieve economic viability. While utilizing industrial waste heat to drive hydrogen production can significantly reduce energy consumption, existing technologies suffer from the following problems: Low matching degree between waste heat and hydrogen production process: The temperature of medium- and low-temperature waste heat (300-500℃) is mismatched with that of traditional electrolyzers (such as alkaline electrolyzers operating at 80-90℃, and PEM electrolyzers at 60-80℃), requiring multi-stage heat exchange for cooling, resulting in significant heat loss and a system efficiency of only 40%-50%. Lack of energy storage: Industrial waste heat is intermittent (such as the periodic operation of blast furnaces in steel plants), and the lack of efficient energy storage devices leads to instability in the hydrogen production process and low equipment utilization. Insufficient thermochemical cycle efficiency: Traditional... The high mass transfer resistance and slow reaction rate of the circulating system, requiring a decomposition temperature of 550-600℃, and insufficient heat recovery limit the application of low-temperature waste heat. Furthermore, some waste heat recovery hydrogen production systems use heat transfer oil as the heat transfer medium, but its upper operating temperature limit is only 350℃, failing to fully utilize the 500℃ waste heat. Additionally, the heat transfer oil is prone to oxidation and deterioration, resulting in high maintenance costs. Another approach utilizes molten salt to store waste heat to drive SOEC electrolyzers, but SOEC requires an operating temperature of 600-800℃, which is incompatible with the 300-500℃ waste heat, and the compatibility issues between the molten salt and reactor materials remain unresolved. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes an industrial waste heat recovery and hydrogen production system and method coupled with hydrogen-molten salt energy storage. By coupling the molten salt energy storage system with the CaO-Ca(OH)2 thermochemical cycle, the system achieves efficient recovery and utilization of low-grade waste heat at 300-500℃, drives low-cost hydrogen production in electrolyzers, improves the system's thermal efficiency to over 75%, and promotes green hydrogen self-sufficiency in energy-intensive industries.

[0005] To achieve the above objectives, in a first aspect, the present invention provides an industrial waste heat recovery and hydrogen production system coupled with hydrogen-molten salt energy storage, employing the following technical solution: A hydrogen-molten salt energy storage coupled industrial waste heat recovery hydrogen production system includes a molten salt energy storage subsystem, a thermochemical cycle subsystem, and an electrolytic hydrogen production subsystem; the molten salt energy storage subsystem includes an energy storage module and a waste heat exchange module connected to each other; the thermochemical cycle subsystem adopts a reactor, which is connected to the waste heat exchange module and the electrolytic hydrogen production subsystem. The reactor is a horizontal fixed-bed reactor, which is filled with CaO-Ca(OH)2 particles. In the endothermic stage, high-temperature molten salt flows through the reactor jacket, heating the bed to a first preset temperature, and Ca(OH)2 undergoes a decomposition reaction. Nitrogen gas is introduced during the reaction. In the exothermic stage, water vapor is introduced into the reactor, which reacts with CaO to undergo a hydration reaction. The reaction releases heat and heats the molten salt to a second preset temperature, providing a heat source for the electrolytic hydrogen production subsystem.

[0006] Furthermore, the molten salt medium in the molten salt energy storage subsystem is a LiNO3-KNO3 eutectic molten salt with a mass ratio of 60:40, a melting point of 142℃, and an operating temperature range of 150-550℃.

[0007] Furthermore, the energy storage module includes a high-temperature molten salt storage tank and a low-temperature molten salt storage tank. The waste heat exchange module adopts a spiral tube heat exchanger. One input and output end of the spiral tube heat exchanger are connected to an industrial flue gas pipeline and an exhaust gas pipeline, respectively. The other input and output end of the spiral tube heat exchanger are connected to the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, respectively, through pipelines. A molten salt pump is installed between the low-temperature molten salt storage tank and the spiral tube heat exchanger.

[0008] Furthermore, the electrolytic hydrogen production subsystem includes an electrolytic cell, a gas-liquid separator, and a hydrogen compressor that are connected to each other in sequence via pipelines; the molten salt outlet of the electrolytic cell is connected to the cryogenic molten salt tank via a pipeline.

[0009] Furthermore, the output ends of both the high-temperature molten salt storage tank and the low-temperature molten salt storage tank are connected to the reactor via pipelines; a molten salt pump is installed between the high-temperature molten salt storage tank and the thermochemical reactor; the output end of the reactor is connected to the low-temperature molten salt storage tank and the electrolytic cell respectively; a molten salt pump is installed between the reactor and the electrolytic cell; and the thermochemical reactor is also equipped with an inert gas inlet and a water vapor inlet.

[0010] To achieve the above objectives, in a second aspect, the present invention also provides a method for hydrogen production through industrial waste heat recovery coupled with hydrogen-molten salt energy storage, employing the following technical solution: A hydrogen-molten salt energy storage coupled industrial waste heat recovery hydrogen production system and method are disclosed. The system uses the hydrogen-molten salt energy storage coupled industrial waste heat recovery hydrogen production system as described in the first aspect, including: an endothermic stage: high-temperature molten salt flows through the reactor jacket, heating the bed to a first preset temperature, Ca(OH)2 undergoes a decomposition reaction, and nitrogen gas is introduced during the reaction; an exothermic stage: water vapor is introduced into the reactor, which undergoes a hydration reaction with CaO, and the reaction releases heat to heat the molten salt to a second preset temperature, providing a heat source for the electrolytic hydrogen production subsystem.

[0011] Furthermore, during the endothermic stage, Ca(OH)2 undergoes a decomposition reaction: Ca(OH)2(s) → CaO(s) + H2O(g) - 109 kJ / mol; during the exothermic stage, steam is introduced into the reactor and reacts with CaO to undergo a hydration reaction: CaO(s) + H2O(g) → Ca(OH)2(s) + 65 kJ / mol.

[0012] Furthermore, during the exothermic phase, the heated molten salt flows through the external coil of the electrolytic cell, preheating the electrolyte to the third preset temperature, while the molten salt cools down to the fourth preset temperature and returns to the cryogenic storage tank.

[0013] Furthermore, the industrial waste heat medium enters the shell side of the spiral tube heat exchanger through one inlet and exchanges heat in the opposite direction with the low-temperature molten salt in the tube side; after heat exchange, the waste gas temperature decreases and is discharged, while the molten salt temperature rises to the first preset temperature and enters the high-temperature storage tank.

[0014] Furthermore, during the exothermic phase, the heated molten salt flows through the external coil of the electrolytic cell, preheating the electrolyte, while the molten salt cools down and returns to the cryogenic storage tank; the energy consumption of the electrolytic cell is reduced to 3.8. It reduces costs by more than 15% compared to traditional room temperature electrolytic cells.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention comprises a molten salt energy storage subsystem, a thermochemical cycle subsystem, and an electrolytic hydrogen production subsystem. The molten salt energy storage subsystem includes interconnected energy storage modules and waste heat exchange modules. The thermochemical cycle subsystem employs a reactor; the reactor is a horizontal fixed-bed reactor filled with CaO-Ca(OH)2 particles. In the endothermic stage, high-temperature molten salt flows through the reactor jacket, heating the bed to a first preset temperature, causing Ca(OH)2 to decompose. Nitrogen gas is introduced during the reaction. In the exothermic stage, steam is introduced into the reactor, reacting with CaO to undergo a hydration reaction. The exothermic reaction heats the molten salt to a second preset temperature, providing a heat source for the electrolytic hydrogen production subsystem. Through the coupling of the molten salt energy storage system and the CaO-Ca(OH)2 thermochemical cycle, efficient recovery and utilization of low-grade waste heat at 300-500℃ are achieved, driving low-cost hydrogen production in the electrolyzer, increasing the system thermal efficiency to over 75%, and promoting green hydrogen self-sufficiency in energy-intensive industries. Attached Figure Description

[0016] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0017] Figure 1 This is a schematic diagram of the system structure of Embodiment 1 of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0020] Example 1: like Figure 1 As shown, in view of the problems of low utilization rate of industrial waste heat and high energy consumption of hydrogen production in the prior art, this embodiment provides an industrial waste heat recovery and hydrogen production system coupled with hydrogen-molten salt energy storage, including a molten salt energy storage subsystem, a thermochemical cycle subsystem, an electrolysis hydrogen production subsystem, and an intelligent control subsystem, etc.; each subsystem is connected through pipelines, valves and sensors to form a complete waste heat recovery and hydrogen production process.

[0021] The molten salt energy storage subsystem includes an energy storage module and a waste heat exchange module. The molten salt medium is a LiNO3-KNO3 eutectic molten salt (mass ratio 60:40), with a melting point of 142℃ and an operating temperature range of 150-550℃, possessing a high thermal conductivity (1.2). ), large specific heat capacity (1.5) It has advantages such as good chemical stability. Optionally, when preparing molten salt medium, the raw materials are weighed according to the ratio of LiNO3:KNO3=60:40 (mass ratio), heated to 200℃ under an inert atmosphere (nitrogen), stirred until completely melted, filtered to remove impurities, and then injected into a storage tank.

[0022] The energy storage module includes a high-temperature molten salt storage tank (operating temperature 500-550℃) and a low-temperature molten salt storage tank (operating temperature 150-200℃). The tank body adopts a double-layer stainless steel structure (inner layer 316L, outer layer Q235B), with a nano-aerogel insulation layer in between (thermal conductivity... The volume is designed based on the industrial waste heat emission, with a single tank capacity of 50-500. .

[0023] The waste heat exchange module employs a spiral tube heat exchanger. The shell side is circulated with industrial waste heat medium (such as cooling exhaust gas from sintered ore in steel plants or tail gas from rotary kilns in cement plants, with a temperature of 300-500℃), while the tube side flows through low-temperature molten salt. The heat exchange tubes are made of nickel-based alloy (Inconel 625), with a wall thickness of 3mm, a spiral diameter of 1.2m, and a pitch of 0.3m. The heat exchange area is calculated based on the waste heat flow rate to ensure that the molten salt outlet temperature reaches 500℃±10℃.

[0024] Specifically, industrial waste heat media (e.g., temperature 450℃, flow rate 10000) The sintered ore cooling exhaust gas enters the shell side of the spiral tube heat exchanger from one inlet, where it reacts with the low-temperature molten salt (150°C, flow rate 500 liters / kg / tumbler) in the tube side. Reverse heat exchange; after heat exchange, the temperature of the exhaust gas drops to below 200°C and is discharged from the exhaust gas outlet, while the temperature of the molten salt rises to 500°C and enters the high-temperature storage tank.

[0025] Optionally, one input and output end of the spiral tube heat exchanger are connected to an industrial flue gas pipeline and an exhaust gas outlet pipeline (exhaust gas outlet), respectively; the other input and output end of the spiral tube heat exchanger are connected to the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, respectively, via pipelines. A molten salt pump is installed between the low-temperature molten salt storage tank and the spiral tube heat exchanger.

[0026] The thermochemical cycle subsystem employs a thermochemical reactor, which can be a horizontal fixed-bed reactor with an inner diameter of 1.5m and a length of 8m, filled with CaO-Ca(OH)2 particles (particle size 2-5mm, specific surface area 50-80). The inner wall of the reactor is coated with an Al2O3 ceramic coating (0.5 mm thick) to improve its resistance to high-temperature corrosion.

[0027] The output ends of both the high-temperature molten salt storage tank and the low-temperature molten salt storage tank are connected to the thermochemical reactor via pipelines; a molten salt pump is installed between the high-temperature molten salt storage tank and the thermochemical reactor; the output end of the thermochemical reactor is connected to the low-temperature molten salt storage tank and the electrolytic cell (high-temperature alkaline electrolytic cell) respectively; a molten salt pump is installed between the thermochemical reactor and the electrolytic cell; the thermochemical reactor is also equipped with an inert gas inlet and a water vapor inlet.

[0028] Specifically, in the endothermic stage (residual heat storage): high-temperature molten salt (500℃) flows through the reactor jacket, heating the bed to 500℃, causing Ca(OH)₂ to decompose: Ca(OH)₂(s) → CaO(s) + H₂O(g) - 10⁹ kJ / mol. A small amount of nitrogen gas (flow rate 0.5-1.0) is introduced during the reaction. The bed layer carries away water vapor, maintaining the forward reaction and achieving a decomposition rate of over 90%. Specifically, in the endothermic stage (residual heat storage): the molten salt pump between the reactor and the high-temperature molten salt tank is started to transport the high-temperature molten salt (500℃) to the jacket of the thermochemical reactor, where the bed layer is heated to 500℃ via heat transfer oil. The inert gas inlet is opened, and nitrogen gas (flow rate 50) is introduced. Meanwhile, the gas is evenly distributed from the bottom of the reactor. Ca(OH)2 particles decompose at 500℃, and the generated water vapor is discharged from the top of the reactor with nitrogen and enters the condensation device to recover the moisture (the condensate can be recycled for the electrolytic cell). The decomposition reaction lasts for 60 minutes until the Ca(OH)2 conversion rate reaches 90%, and the molten salt temperature drops to 450℃ and is returned to the low temperature storage tank.

[0029] Exothermic Stage (Heat Release): When industrial waste heat is insufficient, steam (temperature 180-200℃, pressure 0.5-1.0MPa) is introduced into the reactor to react with CaO in a hydration reaction: CaO(s) + H2O(g) → Ca(OH)2(s) + 65kJ / mol. The exothermic reaction heats the molten salt to 300℃, providing a heat source for the electrolytic cell. Specifically, in the exothermic stage (heat release): when the liquid level in the high-temperature molten salt storage tank is lower than the set value (e.g., 30%), an exothermic reaction is triggered. Steam at 180℃ and 0.8MPa (flow rate 300kg / h) is introduced from the steam inlet, enters the bed through the gas distributor, and reacts with CaO in a hydration reaction. The exothermic reaction raises the temperature of the molten salt to 300℃, and is pumped to the external coil of the electrolytic cell to preheat the electrolyte. The hydration reaction continues for 40 minutes until the CaO conversion rate reaches 85%, and the generated Ca(OH)2 is decomposed again in the next endothermic stage.

[0030] The electrolytic hydrogen production subsystem includes an electrolytic cell, a gas-liquid separator, and a hydrogen compressor, which are connected in sequence via pipelines. The molten salt outlet of the electrolytic cell is connected to the cryogenic molten salt tank via a pipeline.

[0031] The electrolyzer can be a high-temperature alkaline electrolyzer (operating temperature 200℃, operating pressure 3.0MPa), with Ni-Mo alloy (anode) and Ni-Fe alloy (cathode) as electrode materials, and an asbestos-reinforced KOH electrolyte membrane (concentration 30wt%). The rated power of a single cell is 500kW, and the hydrogen production capacity is 100... .

[0032] Specifically, the electrolyte (30wt% KOH solution) preheated to 200℃ is introduced into a high-temperature alkaline electrolytic cell, and electrolysis is performed under a pressure of 3.0 MPa. Anode reaction: 4 -4e⁻→O₂↑+2H₂O, cathode reaction: 4H₂O+4e⁻→2H₂↑+4 Electrolytic cell input current 2000 Voltage 1.8 3600 power Hydrogen production 90 After the hydrogen gas passes through a gas-liquid separator to remove the entrained electrolyte, it enters the compressor and is pressurized to 20 °C. Oxygen is stored and discharged through the vent. Heat recovery: Waste heat generated during electrolytic cell operation (approximately 200...) The water vapor is recovered through a cooling water jacket and used to preheat the water vapor entering the reactor, thereby improving the overall thermal efficiency of the system.

[0033] Heat coupling: During the exothermic phase, the molten salt (300℃) flows through the external coil of the electrolyzer, preheating the electrolyte to 200℃, while the molten salt cools to 150℃ and returns to the cryogenic storage tank. The electrolyzer's energy consumption is reduced to 3.8. It reduces costs by more than 15% compared to traditional room temperature electrolytic cells.

[0034] Hydrogen processing: The hydrogen produced by electrolysis (99.9% purity) passes through a gas-liquid separator, a cooler (cooled to 40°C), and a compressor (pressurized to 20°C). After storage, the oxygen can be recycled or discharged after drying.

[0035] The intelligent control subsystem includes sensor arrays, PLC hardware configuration, SCADA system, communication link, and control system.

[0036] The sensor group includes a molten salt temperature sensor (accuracy ±1℃, model PT1000), a reactor pressure sensor (accuracy ±0.5%FS, model EJA110A), an electrolytic cell current sensor (accuracy ±0.2%, model LEM LTS25-NP), etc., to collect system operating parameters in real time.

[0037] The PLC hardware configuration can use an S7-1500 series PLC or other series PLCs, equipped with 16 analog input modules, 8 analog output modules and 16 digital input / output modules, responsible for low-level real-time control.

[0038] The SCADA system functions can be built using WinCC configuration software, including a real-time monitoring interface (displaying 32 key parameters such as molten salt temperature, reactor pressure, and electrolytic cell current), a historical data storage module, an alarm module, and a report generation module.

[0039] The communication link is implemented as follows: the PLC communicates with the sensor / actuator via PROFINET bus, and the PLC is connected to the SCADA host computer via industrial Ethernet, ensuring that the data transmission delay is ≤50ms.

[0040] The control system can adopt a PLC+SCADA architecture, based on a fuzzy PID algorithm, to automatically adjust the molten salt flow rate, reactor gas inlet volume, and electrolytic cell operating current according to industrial waste heat fluctuations. When waste heat is sufficient, the thermochemical cycle is driven first to store heat; when waste heat is insufficient, the exothermic reaction is started to maintain stable operation of the electrolytic cell, ensuring that the system thermal efficiency remains stable at 75%±2%.

[0041] The core logic of the fuzzy PID algorithm is as follows: Input selection: The three inputs for the fuzzy PID controller are "industrial waste heat temperature fluctuation (ΔT, unit °C)," "high-temperature molten salt storage tank level deviation (ΔH, unit %)," and "electrolytic cell operating temperature deviation (ΔTe, unit °C)." Among them: ΔT = measured waste heat temperature - set temperature (400℃), with the universe of discourse being [-100, 100]; ΔH = measured liquid level - target liquid level (60%), with the universe of discourse being [-30, 30]. ΔTe = measured electrolytic cell temperature - set temperature (200℃), with the universe of discourse being [-10, 10].

[0042] Fuzzification processing: A triangular membership function is used to divide the input quantity into 7 fuzzy subsets: "Negative Large (NB), Negative Medium (NM), Negative Small (NS), Zero (Z), Positive Small (PS), Positive Medium (PM), and Positive Large (PB)". For example, when ΔT = +50℃, it belongs to the "PM" subset (membership degree 0.8) and the "PB" subset (membership degree 0.2).

[0043] Fuzzy rule base: Contains 49 core rules (based on 7×7×7 combinations of 3 inputs), some key rules are as follows: If ΔT=PB (residual heat temperature is much higher than the set value), ΔH=NS (liquid level is slightly lower than the target), and ΔTe=Z (temperature is normal), then output "molten salt flow rate increment = PB, reactor nitrogen inlet flow rate = PS, electrolytic cell current = PM"; If ΔT=NB (residual heat temperature is much lower than the set value), ΔH=NB (liquid level is much lower than the target), and ΔTe=NB (temperature is too low), then output "molten salt flow rate increment = Z, reactor steam inlet flow rate = PB, electrolytic cell current = NS".

[0044] Fuzzy logic de-fuzzing and PID parameter tuning: The centroid method is used to convert fuzzy output quantities into precise values ​​(such as molten salt flow adjustment, intake valve opening, and current correction value), and the proportional coefficient (Kp), integral time (Ti), and derivative time (Td) of the PID controller are corrected in real time. The correction formula is as follows: Kp = Kp0 + ΔKp (ΔKp is the proportional correction amount for fuzzy output); Ti = Ti0 + ΔTi (ΔTi is the integral correction amount of the fuzzy output); Td = Td0 + ΔTd (ΔTd is the differential correction amount of the fuzzy output).

[0045] Optional, data acquisition: Temperature sensors monitor the reactor temperature in real time, pressure sensors monitor the reactor pressure, and the PLC system collects data every 5 seconds and transmits it to the SCADA host computer. Based on the above data, the dynamic adjustment process under industrial waste heat fluctuations is as follows: During the stage with sufficient residual heat (blast furnace tapping period, residual heat temperature 450-500℃): The sensor detected The PLC outputs the following using a fuzzy PID algorithm: Molten salt flow rate from 50 Increased to 60 (By adjusting the frequency of the molten salt pump, the frequency was increased from 50Hz to 60Hz). The nitrogen inlet flow rate to the reactor is increased from 50 Increased to 60 (Open the intake valve from 50% to 60%) to accelerate the decomposition of Ca(OH)2; The electrolytic cell current is maintained at 2000A (full load), and the SCADA interface displays the "excess waste heat - energy storage priority" mode in real time. The liquid level in the high-temperature molten salt storage tank rises at a rate of 0.5% / min.

[0046] Waste heat intermittent stage (blast furnace shutdown period, waste heat temperature drops to 200-300℃): The sensor detects ΔT = NM (-100 to -50℃), and the PLC triggers the heat dissipation mode. Molten salt flow rate reduced to 30 (Pump frequency 30Hz) Prioritize ensuring the heat source for the electrolytic cell; Increasing the steam inlet flow rate of the reactor from 300 kg / h to 400 kg / h (with the steam valve opening from 60% to 80%) increased the exothermic rate of the CaO hydration reaction by 20%. The electrolyzer current was reduced from 2000A to 1600A (voltage maintained at 1.8V), and the hydrogen production decreased from 90... Dropped to 72 SCADA automatically records the "insufficient residual heat - stable production priority" status, and the temperature fluctuation of the electrolytic cell is controlled within ±3℃.

[0047] Control Strategy: When the waste heat temperature exceeds 500℃, the waste heat bypass valve automatically opens to prevent molten salt overheating. When the high-temperature molten salt storage tank level exceeds 80% and the electrolytic cell is operating at full load, a portion of the molten salt is automatically switched to a low-temperature storage tank. The molten salt flow rate and reactor air intake are dynamically adjusted using a fuzzy PID algorithm to ensure the electrolytic cell operating temperature remains stable at 200℃±5℃ and current fluctuations do not exceed ±2%. To ensure safe and stable system operation, the following linkage protection mechanisms are implemented: Over-temperature protection: When the outlet molten salt temperature of the spiral tube heat exchanger is >510℃ (exceeding the set value by 10℃), the PLC immediately opens the waste heat bypass valve (opening degree 50%), and at the same time reduces the frequency of the molten salt pump to 30Hz. Within 10 seconds, the molten salt temperature is controlled at 500±5℃, and SCADA triggers "high temperature warning" and records the fault time point.

[0048] Liquid level interlock: When the liquid level in the high-temperature molten salt storage tank is >90% (risk of full tank), even if there is sufficient residual heat, the PLC will automatically shut down the residual heat exchange module, switch the molten salt flow to the low-temperature storage tank (switching via a three-way valve, response time <2s), and reduce the electrolytic cell current to 1500A to prevent molten salt from overflowing.

[0049] Electrolytic cell abnormality handling: If the electrolytic cell temperature is <190℃ (10℃ deviation from the set value), the PLC will simultaneously increase the steam intake of the reactor (increase the intake by 5kg / h for every 1℃ decrease) and extend the residence time of the molten salt in the external coil of the electrolytic cell (by adjusting the valve opening to reduce the flow rate from 2m / s to 1.5m / s) to ensure that the temperature is restored to above 195℃ within 1 minute.

[0050] Example 2: This embodiment provides an industrial waste heat recovery hydrogen production system and method coupled with hydrogen-molten salt energy storage. It uses the industrial waste heat recovery hydrogen production system coupled with hydrogen-molten salt energy storage as described in Embodiment 1, including: an endothermic stage: high-temperature molten salt flows through the reactor jacket, heating the bed to a first preset temperature, Ca(OH)2 undergoes a decomposition reaction, and nitrogen gas is introduced during the reaction; an exothermic stage: water vapor is introduced into the reactor, which undergoes a hydration reaction with CaO, and the reaction releases heat to heat the molten salt to a second preset temperature, providing a heat source for the electrolytic hydrogen production subsystem.

[0051] Optionally, during the endothermic stage, Ca(OH)2 undergoes a decomposition reaction: Ca(OH)2(s) → CaO(s) + H2O(g) - 109 kJ / mol; during the exothermic stage, steam is introduced into the reactor to react with CaO and undergo a hydration reaction: CaO(s) + H2O(g) → Ca(OH)2(s) + 65 kJ / mol.

[0052] During the exothermic phase, the heated molten salt flows through the external coil of the electrolytic cell, preheating the electrolyte to the third preset temperature. At the same time, the molten salt cools down to the fourth preset temperature and returns to the cryogenic storage tank.

[0053] Industrial waste heat medium enters the shell side of the spiral tube heat exchanger through one inlet and exchanges heat in the opposite direction with the low-temperature molten salt in the tube side. After heat exchange, the waste gas temperature decreases and is discharged, while the molten salt temperature rises to the first preset temperature and enters the high-temperature storage tank.

[0054] During the exothermic phase, the heated molten salt flows through the external coil of the electrolytic cell, preheating the electrolyte, while the molten salt cools and returns to the cryogenic storage tank. The energy consumption of the electrolytic cell is reduced to 3.8. It reduces costs by more than 15% compared to traditional room temperature electrolytic cells.

[0055] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A hydrogen-molten salt energy storage coupled industrial waste heat recovery and hydrogen production system, characterized in that, It includes a molten salt energy storage subsystem, a thermochemical cycle subsystem, and an electrolytic hydrogen production subsystem; the molten salt energy storage subsystem includes interconnected energy storage modules and waste heat exchange modules; the thermochemical cycle subsystem uses a reactor, which is connected to the waste heat exchange module and the electrolytic hydrogen production subsystem. The reactor is a horizontal fixed-bed reactor, which is filled with CaO-Ca(OH)2 particles. In the endothermic stage, high-temperature molten salt flows through the reactor jacket, heating the bed to a first preset temperature, and Ca(OH)2 undergoes a decomposition reaction. Nitrogen gas is introduced during the reaction. In the exothermic stage, water vapor is introduced into the reactor, which reacts with CaO to undergo a hydration reaction. The reaction releases heat and heats the molten salt to a second preset temperature, providing a heat source for the electrolytic hydrogen production subsystem.

2. The industrial waste heat recovery and hydrogen production system with hydrogen-molten salt energy storage coupling as described in claim 1, characterized in that, The molten salt medium in the molten salt energy storage subsystem is a LiNO3-KNO3 eutectic molten salt with a mass ratio of 60:40, a melting point of 142℃, and an operating temperature range of 150-550℃.

3. The industrial waste heat recovery and hydrogen production system with hydrogen-molten salt energy storage coupling as described in claim 1, characterized in that, The energy storage module includes a high-temperature molten salt storage tank and a low-temperature molten salt storage tank. The waste heat exchange module adopts a spiral tube heat exchanger. One input and output end of the spiral tube heat exchanger are connected to an industrial flue gas pipeline and an exhaust gas pipeline, respectively. The other input and output end of the spiral tube heat exchanger are connected to the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, respectively, through pipelines. A molten salt pump is installed between the low-temperature molten salt storage tank and the spiral tube heat exchanger.

4. The industrial waste heat recovery and hydrogen production system with hydrogen-molten salt energy storage coupling as described in claim 3, characterized in that, The electrolytic hydrogen production subsystem includes an electrolytic cell, a gas-liquid separator, and a hydrogen compressor connected in sequence via pipelines; the outlet of the electrolytically produced molten salt is connected to the cryogenic molten salt tank via a pipeline.

5. The industrial waste heat recovery and hydrogen production system with hydrogen-molten salt energy storage coupling as described in claim 4, characterized in that, The output ends of both the high-temperature molten salt storage tank and the low-temperature molten salt storage tank are connected to the reactor via pipelines; a molten salt pump is installed between the high-temperature molten salt storage tank and the thermochemical reactor; the output end of the reactor is connected to the low-temperature molten salt storage tank and the electrolytic cell respectively; a molten salt pump is installed between the reactor and the electrolytic cell; the thermochemical reactor is also equipped with an inert gas inlet and a water vapor inlet.

6. A hydrogen-molten salt energy storage coupled industrial waste heat recovery hydrogen production system and method, characterized in that, An industrial waste heat recovery hydrogen production system using hydrogen-molten salt energy storage coupling as described in any one of claims 1-5 includes: an endothermic stage: high-temperature molten salt flows through the reactor jacket, heating the bed to a first preset temperature, Ca(OH)2 undergoes a decomposition reaction, and nitrogen gas is introduced during the reaction; an exothermic stage: water vapor is introduced into the reactor, which undergoes a hydration reaction with CaO, and the reaction releases heat to heat the molten salt to a second preset temperature, providing a heat source for the electrolytic hydrogen production subsystem.

7. The industrial waste heat recovery hydrogen production system and method with hydrogen-molten salt energy storage coupling as described in claim 6, characterized in that, During the endothermic stage, Ca(OH)2 undergoes a decomposition reaction: Ca(OH)2(s)→CaO(s)+H2(g)-109kJ / mol; during the exothermic stage, steam is introduced into the reactor and reacts with CaO to undergo a hydration reaction: CaO(s)+H2O(g)→Ca(OH)2(s)+65kJ / mol.

8. The industrial waste heat recovery hydrogen production system and method with hydrogen-molten salt energy storage coupling as described in claim 6, characterized in that, During the exothermic phase, the heated molten salt flows through the external coil of the electrolytic cell, preheating the electrolyte to the third preset temperature. At the same time, the molten salt cools down to the fourth preset temperature and returns to the cryogenic storage tank.

9. The industrial waste heat recovery hydrogen production system and method with hydrogen-molten salt energy storage coupling as described in claim 6, characterized in that, Industrial waste heat medium enters the shell side of the spiral tube heat exchanger through one inlet and exchanges heat in the opposite direction with the low-temperature molten salt in the tube side. After heat exchange, the waste gas temperature decreases and is discharged, while the molten salt temperature rises to the first preset temperature and enters the high-temperature storage tank.

10. The industrial waste heat recovery hydrogen production system and method with hydrogen-molten salt energy storage coupling as described in claim 6, characterized in that, During the exothermic phase, the heated molten salt flows through the external coil of the electrolytic cell, preheating the electrolyte, while the molten salt cools down and returns to the cryogenic storage tank; the energy consumption of the electrolytic cell is reduced to 3.

8. It reduces costs by more than 15% compared to traditional room temperature electrolytic cells.

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