Closed-loop circulation system and method based on green ammonia hydrogen cracking and resynthesis

Abstract

The invention relates to a closed-loop circulation system and method based on green ammonia hydrogen cracking and resynthesis, in particular to the technical field of clean energy. The invention discloses a closed-loop circulation system based on green ammonia cracking hydrogen production and resynthesis. The closed-loop circulation system comprises the following collaborative components: an ammonia cracking reactor, a hydrogen separation device, a nitrogen recovery device, a gas mixer, an electrochemical synthesis reactor, a thermal coupling module and a control unit. The invention discloses a closed-loop circulation method of a closed-loop circulation system based on green ammonia cracking hydrogen production and resynthesis. The closed-loop circulation method comprises the steps of molten salt flow rate control, catalyst activity maintenance and membrane separator regeneration. According to the method, efficient catalysis, long-life and high-purity separation and circulation are achieved, the raw material cost is effectively reduced, waste discharge is reduced, and the sustainable development requirement is met. Intelligent regulation and stable operation are highly matched with wind and light intermittency, and the utilization efficiency of renewable energy sources and the practical application flexibility of the system are improved. The production automation level is improved, and the economic feasibility and competitiveness of the system in industrial application are enhanced.

Description

Technical Field

[0001] The present invention belongs to the field of clean energy chemical industry, specifically relating to a closed-loop circulation system and method based on the cracking and resynthesis of hydrogen from green ammonia. More specifically, the invention relates to a closed-loop circulation system and method that utilizes green ammonia (ammonia synthesized from renewable energy) as a hydrogen carrier, through cracking to produce hydrogen, hydrogen utilization, nitrogen recovery, and ammonia resynthesis, thereby achieving efficient storage, transportation, and regeneration of hydrogen energy. Background Art

[0002] Against the backdrop of the global push for energy transition, the development and utilization of clean energy has become a key initiative in addressing environmental challenges and energy crises. Hydrogen, with its significant advantages of cleanliness, efficiency, and sustainability, holds a crucial position in the future energy landscape. However, challenges in hydrogen storage and transportation severely hinder its large-scale application. In this context, green ammonia, a highly promising hydrogen energy carrier, offers an innovative solution for large-scale hydrogen storage and transportation through a closed-loop system that produces hydrogen through cracking and then resynthesizes it. However, this technology currently faces numerous challenges that need to be overcome.

[0003] Component performance bottlenecks limit system efficiency: Existing closed-loop systems based on green ammonia cracking and hydrogen resynthesis exhibit significant performance shortcomings in various components. The ammonia conversion rate and energy efficiency of ammonia cracking reactors urgently need to be improved. The nickel-based catalysts used in most conventional reactors exhibit poor activity and stability, making it difficult to achieve ammonia conversion rates exceeding 90%. Maintaining the reaction requires high temperatures, which consumes significant energy. Furthermore, poor insulation design leads to significant heat loss, further reducing energy efficiency. For example, some reactors using simple insulation materials experience heat loss rates as high as 20%-30%. The separation efficiency and stability of hydrogen separation units are also unsatisfactory. The cryogenic condenser has low condensation and recovery efficiency for uncracked ammonia, and the palladium alloy membrane separator is susceptible to contamination by impurities, resulting in reduced hydrogen recovery rate and purity. Furthermore, the membrane's lifespan is short, increasing maintenance costs and downtime. Nitrogen recovery units typically struggle to achieve a nitrogen recovery rate exceeding 90%. The carbon molecular sieve adsorption tower and cryogenic distillation tower operate inefficiently, the adsorption tower regeneration consumes high energy, and the distillation tower is significantly affected by operating conditions. The purity of the nitrogen at the top of the tower and the liquid ammonia content in the bottom of the tower are unstable. Gas mixers struggle to achieve rapid and uniform mixing of hydrogen and nitrogen, and the control accuracy of the H2 / N2 molar ratio is insufficient, impacting ammonia synthesis reaction efficiency and product quality. The temperature and pressure fields within the electrochemical synthesis reactor are unevenly distributed, and catalyst performance needs to be optimized, resulting in reduced ammonia synthesis efficiency and selectivity.

[0004] Poor collaborative operation and inefficient thermal management: The lack of a collaborative operation mechanism between components has greatly affected the overall operating efficiency of the system. When the flow rate and composition of the cracked gas produced by the ammonia cracking reactor fluctuate, the subsequent hydrogen separation, nitrogen recovery and electrochemical synthesis reactors cannot respond and adjust in time, resulting in material waste and reduced production efficiency. The operating parameters of each component have not been optimized and matched, and the synergistic effect of the system cannot be fully utilized. For example, the working pressure of the electrochemical synthesis reactor does not match the pressure of the ammonia cracking reactor, which hinders the smooth flow of gas and increases energy consumption and operating costs. In addition, the system's thermal management has serious defects. The large amount of waste heat generated by ammonia cracking has not been effectively recovered and reasonably distributed to hydrogen separation, nitrogen recovery and ammonia storage tank insulation, resulting in prominent energy waste. The existing thermal coupling module makes it difficult to achieve accurate distribution and efficient utilization of waste heat in different temperature ranges, resulting in low overall energy efficiency of the system.

[0005] Control strategy lags lead to stability issues: The current system's control strategy is mostly based on simple feedback control. Faced with large fluctuations in the input power of renewable energy sources such as wind and solar power generation, it is difficult to quickly and accurately adjust key parameters such as the cracking temperature of the ammonia cracking reactor, the synthesis pressure and circulation flow of the electrochemical synthesis reactor. This results in poor system operation stability and large fluctuations in product quality. For example, when the wind and solar power generation power drops sharply, the traditional control strategy cannot quickly maintain the minimum operating temperature of the ammonia cracking reactor, which in turn affects the stability of the entire system. At the same time, the existing control strategy does not fully consider the mutual influence and synergy between the various components. The independent control of a single component can easily disrupt the material and energy balance of the system, resulting in unstable operation.

[0006] Insufficient stability restricts industrial application: The above-mentioned problems in component performance, coordinated operation and control strategy have resulted in poor stability in the closed-loop circulation system of green ammonia cracking to produce hydrogen and resynthesis. In actual operation, product output and quality fluctuate frequently, and the equipment failure rate remains high, which seriously limits the large-scale industrial application of this technology. For example, due to the unstable power of wind and solar power generation, the system operating parameters fluctuate greatly, which directly affects product quality and output. Unstable component performance and poor coordination increase the risk of equipment failure. For example, the membrane components of the hydrogen separation device are frequently damaged due to impurity contamination, and the nitrogen recovery device frequently fails due to unreasonable operating parameters. These problems pose severe challenges to the stable operation of the system.

[0007] In summary, it is urgent to develop an efficient, stable and renewable energy-efficient green ammonia cracking hydrogen production and resynthesis closed-loop circulation system to break through the existing technological bottleneck and promote the large-scale application of green ammonia in the hydrogen energy field. Summary of the Invention

[0008] In order to overcome the deficiencies of the prior art, the present invention aims to provide a closed-loop circulation system and method for hydrogen production and resynthesis by cracking green ammonia.

[0009] In order to achieve the above object, the present invention provides the following technical solutions: A closed-loop circulation system based on green ammonia cracking and hydrogen production and resynthesis, including the following collaborative components and connections: Ammonia cracking reactor: It has a liquid green ammonia inlet and a cracked gas outlet. The liquid green ammonia inlet is connected to the discharge port of the ammonia energy storage tank through a pipeline, and the cracked gas outlet is connected to the hydrogen separation device and the high-temperature section heat exchanger of the thermal coupling module through pipelines respectively; The hydrogen separation device comprises a low-temperature condenser and a palladium alloy membrane separator. The low-temperature condenser adopts a corrugated fin tube structure with a fin spacing of 1.5 mm. The membrane surface of the palladium alloy membrane separator is modified with anatase phase TiO2 nanowires with a wire diameter of 75 nm and an anatase phase content of ≥94%. The outlet of the low-temperature condenser is connected in series with the inlet of the palladium alloy membrane separator. Nitrogen recovery device: It consists of a carbon molecular sieve adsorption tower and a cryogenic distillation tower in parallel. The regeneration heat source inlet of the carbon molecular sieve adsorption tower is connected to the outlet of the medium temperature section heat exchanger of the thermal coupling module. Gas mixer: It is a Venturi tube structure with an ultrasonic atomizing nozzle at the throat. The nozzle atomizing particle size is ≤10μm, the atomizing frequency is 20-50kHz, and the ratio of throat diameter to inlet diameter is 1:3; Electrochemical synthesis reactor: Its discharge port is connected to the ammonia energy storage tank through a pipeline. The reactor is filled with Fe2O3-K2O / Al2O3 catalyst, with an Fe2O3 content of 10-15wt% and a K2O content of 3-5wt%. The catalyst carrier is cordierite ceramic with a porosity of 45%; Thermal coupling module: High-temperature heat exchanger: adopts counter-flow fin tube structure, fin height 8mm, spacing 2mm; medium-temperature heat exchanger: adopts plate heat exchanger, plate corrugation angle 60°, corrugation depth 3mm; low-temperature heat exchanger: adopts shell-and-tube heat exchanger, inner tube is copper-nickel alloy, wall thickness 1.5mm, outer tube is stainless steel, wall thickness 2mm; Control unit: includes a dynamic hysteresis control module, which is based on the real-time wind and solar power generation power P (t) With the average power P avg The ratio of P (t) / P avg When the pressure is ≥1.2, the synthetic mode is activated, the hysteresis range is [0.75,1.25], and the three-stage pressure relief valve is triggered when the pressure fluctuation exceeds ±15%. The pressure relief response time is ≤20ms.

[0010] This system architecture and connection relationship realizes a closed-loop cycle process for green ammonia, from cracking hydrogen production to resynthesis. The components have clear division of labor and work together to ensure the orderly flow of materials within the system, providing an infrastructure guarantee for efficient hydrogen production and ammonia synthesis. For example, the ammonia cracking reactor provides cracking gas for subsequent processes, the hydrogen separation device and nitrogen recovery device respectively separate and recover hydrogen and nitrogen in the cracking gas, the gas mixer precisely mixes hydrogen and nitrogen, the electrochemical synthesis reactor completes the synthesis of ammonia, the thermal coupling module realizes waste heat recovery and utilization, and the control unit dynamically adjusts the system operation according to factors such as wind and solar power generation, improving the system's stability and adaptability.

[0011] Furthermore, the ammonia cracking reactor is filled with a nickel-based catalyst bed with a nickel loading of 15-25wt% and a particle size of 20-50nm. The catalyst bed temperature is regulated by a molten salt circulation channel. The molten salt is a NaNO3-KNO3 mixed salt with a mixed salt molar ratio of 1:1 and a flow rate of v (t) =0.5+0.7×(1-e -t / 300 ) m / s; the surface of the nickel-based catalyst is coated with a graphene layer with a thickness of 1.0 nm, the Pd-Ag alloy membrane thickness of the palladium alloy membrane separator is 20-30 μm, and the membrane support is a porous α-Al2O3 ceramic with an average pore size of 0.5 μm.

[0012] Furthermore, the flow rate control function v of the molten salt circulation channel is (t) In the system, an exponential decay term with a time constant of 300s is used to smooth fluctuations in wind and solar power generation, with a flow rate error range of ≤±5%. The pressure relief rate of the three-stage pressure relief valve is 120% of the system's maximum flow rate. Using an exponential decay term with a time constant of 300s to smooth fluctuations in wind and solar power generation allows the molten salt flow rate to be adaptively adjusted based on power fluctuations, thereby stabilizing the temperature within the ammonia cracking reactor, ensuring the stable progress of the ammonia cracking reaction, and improving the system's adaptability to fluctuations in wind and solar power generation. The three-stage pressure relief valve's rapid pressure relief response and high pressure relief rate (pressure relief response time ≤20ms and a high pressure relief rate of 120% of the system's maximum flow rate) enable rapid pressure relief in the event of abnormal system pressure, ensuring safe system operation and preventing damage to equipment caused by excessive pressure.

[0013] Furthermore, the preparation method of anatase phase TiO2 nanowires includes hydrothermal synthesis and hydrogen annealing; wherein the hydrothermal synthesis reaction temperature is 180°C, the reaction time is 24h, the hydrogen annealing temperature is 450°C, the time is 2h, and the coverage density of the nanowires on the surface of the palladium alloy film is 10 6 -10 7roots / cm². A specific preparation method enables the anatase-phase TiO2 nanowires to develop a favorable growth morphology and coverage density on the surface of the palladium alloy membrane, effectively improving the performance of the palladium alloy membrane. The nanowire modification enhances the membrane's hydrophilicity and anti-fouling properties, while also increasing hydrogen permeation selectivity. This further improves the hydrogen recovery rate and purity of the hydrogen separation device, while also extending the life of the palladium alloy membrane and reducing equipment maintenance costs.

[0014] Furthermore, the ratio of the space velocity (SV2) of the Fe2O3-K2O / Al2O3 catalyst to the space velocity (SV1) of the nickel-based catalyst is dynamically adjusted using the following formula: SV2 / SV1 = 0.35 + 0.05 × sin(2πt / T); where T is a parameter set by the control unit based on the periodicity of the ammonia storage tank level change, and T = 120-300s. This dynamic adjustment of the catalyst space velocity ratio optimizes the reaction conditions of the ammonia cracking reactor and the electrochemical synthesis reactor in real time based on the system material conditions reflected by the ammonia storage tank level changes. This ensures that the reaction processes in the two reactors are mutually compatible, improving overall reaction efficiency, thereby enhancing the system's ammonia synthesis efficiency and product quality, and ensuring stable and efficient operation under various operating conditions.

[0015] Furthermore, the gas mixer's ultrasonic atomizing nozzle and ratio sensor have a feedback delay of ≤50ms, and the H2 / N2 molar ratio adjustment response time is 3-5s. This extremely short feedback delay and rapid molar ratio adjustment response time enable the gas mixer to quickly and accurately adjust the H2 / N2 molar ratio based on real-time system requirements, ensuring that the feed gas ratio entering the electrochemical synthesis reactor is always optimal. This helps improve the efficiency and selectivity of the ammonia synthesis reaction, reduces unnecessary feedstock waste, and enhances overall system performance.

[0016] Furthermore, the thermal coupling module's waste heat distribution ratio is 5:3:2 for high-temperature section: medium-temperature section: low-temperature section, with the total heat transfer coefficients of each heat exchanger section being 120-150 W / (m²·K), 80-100 W / (m²·K), and 50-70 W / (m²·K), respectively. This rational waste heat distribution ratio and the appropriate total heat transfer coefficients of each heat exchanger section enable the thermal coupling module to efficiently recover and distribute waste heat generated by the ammonia cracking reactor based on the heat requirements of different components. The high-temperature section provides preheating for the hydrogen separation unit, the medium-temperature section provides a regenerative heat source for the nitrogen recovery unit, and the low-temperature section maintains the temperature of the ammonia storage tank. This achieves cascaded energy utilization, significantly improving the system's overall energy efficiency and reducing its reliance on external energy sources.

[0017] Furthermore, the multi-layer insulation structure of the ammonia cracking reactor includes: Outer layer: ceramic fiber insulation layer, thickness 30-50mm, density 160kg / m³, thermal conductivity ≤0.1W / (m·K); Middle layer: microporous calcium silicate board, thickness 20mm, porosity 60%; Inner layer: high temperature resistant alloy lining, Inconel 600, thickness 5mm.

[0018] This meticulously designed multi-layer insulation structure, from the outer ceramic fiber insulation layer that effectively blocks external heat transfer and reduces internal heat loss, to the middle layer of microporous calcium silicate board that leverages its high porosity for further insulation, and the inner high-temperature alloy lining that ensures the stability and corrosion resistance of the reactor's internal structure, significantly reduces heat loss from the ammonia cracking reactor, improving energy efficiency, reducing energy consumption, and extending the reactor's service life.

[0019] Furthermore, the energy efficiency optimization algorithm of the control unit includes: When the instantaneous power fluctuation ΔP=±30%, by adjusting the molten salt flow rate v (t) The exponential term coefficient of the system energy efficiency η satisfies: η=87.2-0.5|ΔP|, and the hydrogen production fluctuation control equation is: δ H =5%×e -0.1t , where t is the duration of the fluctuation, in minutes. ΔP = instantaneous power P (t) -Average power P avg The energy efficiency optimization algorithm enables the system to dynamically adjust the molten salt flow rate based on instantaneous power fluctuations, thereby optimizing the system's energy distribution and utilization efficiency. During power fluctuations, the system's energy efficiency is maintained at a high level, reducing energy losses caused by power fluctuations. At the same time, the hydrogen production fluctuation rate control equation can effectively control the stability of hydrogen production. Even in the case of power fluctuations, the hydrogen production fluctuation rate can be controlled at a low level, ensuring the stability of the system's product quality.

[0020] A closed-loop control method for a closed-loop circulation system based on green ammonia cracking to produce hydrogen and resynthesis: Molten salt flow rate control: According to the wind and solar power generation power fluctuation frequency f of 0.1Hz-1Hz, adjust v (t) The time constant τ in the function satisfies τ=1 / (2πf); the fluctuation frequency f is collected in real time according to the wind and solar power generation power sensor; Catalyst activity maintenance: inject a nitrogen mixture containing 0.5-1.0 vol% hydrogen into the ammonia cracking reactor every 24 hours for 10-15 minutes; Membrane separator regeneration: When the hydrogen permeation rate of the palladium alloy membrane drops by 10%, introduce 400°C nitrogen for 30 minutes at a nitrogen flow rate of 2-3 L / min.

[0021] By adjusting the time constant of the molten salt flow rate in real time based on the frequency of wind and solar power fluctuations, the system's adaptability to power fluctuations is further enhanced, ensuring stable operation of the ammonia cracking reactor. Regular injection of a nitrogen-hydrogen mixture maintains catalyst activity, effectively extending the life of the nickel-based catalyst and ensuring efficient ammonia cracking. Regenerating the palladium alloy membrane when the hydrogen permeation rate decreases helps maintain stable performance of the hydrogen separation unit, ensuring long-term stable operation and improving system reliability and cost-effectiveness.

[0022] Beneficial effects of the present invention 1. Component performance is significantly improved.

[0023] Ammonia cracking reactor: By optimizing nickel-based catalyst parameters and adopting precise temperature control and a multi-layer insulation structure, the ammonia conversion rate is ≥92%, significantly reducing energy consumption and hydrogen production costs, and improving energy utilization efficiency.

[0024] Hydrogen separation device: The unique structure of the low-temperature condenser improves the condensation efficiency by ≥90%, and the palladium alloy membrane modification improves the hydrogen recovery rate by ≥98.5% and the purity by ≥99.9%, reducing raw material waste and providing high-purity hydrogen.

[0025] Nitrogen recovery device: The carbon molecular sieve adsorption tower and the cryogenic distillation tower work together to achieve a nitrogen recovery rate of ≥90%. The waste heat of the thermal coupling module is used to reduce energy consumption and ensure the quality of recovered nitrogen.

[0026] Gas mixer: The special structure and nozzle design achieve rapid and uniform mixing of H2 / N2, with a mixing uniformity of ≥95%. It can also accurately and quickly adjust the molar ratio, improving the efficiency and selectivity of ammonia synthesis.

[0027] Electrochemical synthesis reactor: precise control of catalyst composition and carrier, combined with dynamic adjustment of space velocity, ammonia selectivity ≥ 95%, ensuring efficient ammonia synthesis reaction.

[0028] Thermal coupling module: The heat exchanger structure designed for different temperature ranges, combined with a reasonable waste heat distribution ratio and heat transfer coefficient, efficiently recovers and distributes waste heat, improving the overall energy utilization efficiency of the system.

[0029] 2. Component synergy is enhanced.

[0030] Material coordination: All components are tightly and reasonably connected, allowing materials to flow smoothly and be efficiently utilized within the system, thus avoiding waste and backlogs and improving production efficiency.

[0031] Parameter coordination: The pressure and catalyst space velocity of the electrochemical synthesis reactor and the ammonia cracking reactor meet specific ratios and are dynamically adjusted to optimize the overall system performance and improve product yield and quality.

[0032] 3. Efficient energy management.

[0033] Waste heat recovery and utilization: The thermal coupling module efficiently recovers the waste heat from ammonia cracking and accurately distributes it according to different temperature ranges to provide energy for each component, realizing cascaded energy utilization and improving overall energy efficiency.

[0034] Energy efficiency optimization algorithm: The control unit dynamically adjusts system parameters through algorithms based on real-time power fluctuations, optimizes energy distribution, reduces dependence on external energy, and improves energy efficiency.

[0035] 4. Precise system control Real-time monitoring and dynamic control: The control unit monitors the power ratio in real time, accurately activates the synthesis mode, and quickly responds to pressure fluctuations to ensure safe and stable system operation.

[0036] Closed-loop control accuracy: Closed-loop control methods precisely control key parameters such as raw material supply, molar ratio adjustment and product circulation, maintain material balance, and improve system stability and product quality.

[0037] 5. Good stability and adaptability.

[0038] Responding to power fluctuations: Facing ±30% input power fluctuations, the system coordinates parameter adjustments to ensure stable hydrogen production, with a hydrogen production fluctuation rate of ≤±5%, and operates reliably under complex energy inputs.

[0039] Environmental adaptability: The design of each component and the selection of parameters enable the system to adapt to different environmental conditions and ensure stable system performance.

[0040] 6. Operation and maintenance costs are reduced.

[0041] Long-life component design: For example, palladium alloy membrane separators extend membrane service life through surface modification, reduce replacement frequency, and lower maintenance costs.

[0042] Efficient energy utilization: Reducing energy consumption not only reduces energy costs, but also reduces equipment failure rate and maintenance costs due to improved system stability, thereby improving the economic efficiency of system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the overall structure of the closed-loop circulation system based on green ammonia cracking hydrogen and resynthesis.

[0044] In the figure, 1. Ammonia cracking reactor, 1a. Nickel-based catalyst bed, 1b. Molten salt circulation channel; 2. Hydrogen separation device, 2a. Low-temperature condenser, 2b. Palladium alloy membrane separator; 3. Nitrogen recovery device, 3a. Carbon molecular sieve adsorption tower, 3b. Low-temperature distillation tower; 4. Electrochemical synthesis reactor, 4a. Fe2O3-K2O / Al2O3 catalyst; 5. Thermal coupling module, 5a. High-temperature section heat exchanger, 5b. Medium-temperature section heat exchanger, 5c. Low-temperature section heat exchanger; 6. Control unit, 6a. Dynamic hysteresis control module, 6b. Three-stage pressure relief valve; 7. Ammonia energy storage tank; 8. Gas mixer, 8a. Ultrasonic atomizing nozzle, 8b. Proportional sensor.

[0045] Figure 2 It is a dynamic control logic flow chart.

[0046] Figure 3 Schematic diagram comparing hydrogen production rate (kg / h) and system efficiency η (%) between the embodiment and the comparative example.

[0047] Figure 4 Schematic diagram of the internal structure of the ammonia cracking reactor 1, including a nickel-based catalyst bed 1a and a molten salt circulation channel 1b.

[0048] Figure 5 Schematic diagram of the internal structure of the nickel-based catalyst bed 1a.

[0049] Figure 6 Schematic diagram of the internal structure of the low-temperature condenser 2a.

[0050] Figure 7 Schematic diagram of the internal structure of palladium alloy membrane separator 2b.

[0051] Figure 8 It is a schematic structural diagram of the thermal coupling module 5, which includes a high-temperature section heat exchanger 5a, a medium-temperature section heat exchanger 5b, and a low-temperature section heat exchanger 5c.

[0052] Figure 9 The gas mixer 8 includes an ultrasonic atomizing nozzle 8a and a proportional sensor 8b. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0054] Example 1 A closed-loop circulation system based on green ammonia cracking and hydrogen production and resynthesis ( Figure 1 ).

[0055] 1. System construction and initialization: Ammonia cracking reactor 1: Ammonia cracking reactor 1 ( Figure 4 ) is made of high-strength and pressure-resistant materials. The nickel-based catalyst bed 1a ( Figure 5 ) has the following characteristics: nickel loading is controlled at 20wt%, particle size is 30nm, and a 1.0nm thick graphene layer is evenly coated on its surface. This design significantly enhances the activity and stability of the catalyst, providing an efficient catalytic environment for the ammonia cracking reaction. The molten salt channel 1b uses a NaNO3-KNO3 mixed salt with a molar ratio of 1:1 as the heat transfer medium, and its flow rate is calculated according to v(t)=0.5+0.7×(1-e ⁻ᵗ / 300 ) m / s. In this way, the catalyst bed temperature can be precisely controlled to ensure that the ammonia cracking reaction proceeds efficiently under appropriate temperature conditions.

[0056] To effectively minimize heat loss and lower energy consumption, ammonia cracking reactor 1 utilizes a multi-layer insulation structure. The outermost layer is a 40mm-thick ceramic fiber layer with a thermal conductivity of ≤0.1W / (m·K), effectively blocking external heat transfer and reducing internal heat loss. The middle layer is a 20mm-thick microporous calcium silicate board with a porosity of up to 60%, further enhancing the thermal insulation effect. The inner layer is a 5mm-thick Inconel 600 alloy lining, which not only ensures the stability of the reactor's internal structure but also provides excellent high-temperature resistance.

[0057] Hydrogen separation device 2: Hydrogen separation device 2 is composed of low temperature condenser 2a and palladium alloy membrane separator 2b. The specific parameters of each part are as follows: Low temperature condenser 2a ( Figure 6 ): It adopts a corrugated fin tube structure with a fin spacing of 1.5mm. This structure greatly increases the heat exchange area and significantly improves the condensation efficiency, ensuring efficient condensation and recovery of uncracked ammonia and other impurities in the cracked gas. Palladium alloy membrane separator 2b ( Figure 7 ): The surface of the membrane is modified with anatase TiO2 nanowires with a diameter of 75nm, anatase content ≥94%, and a coverage density of 10 6 Roots / cm². These nanowires effectively improve the membrane's surface properties and enhance hydrogen permeation selectivity. These anatase TiO2 nanowires are obtained through a specific preparation process: a hydrothermal synthesis reaction at 180°C for 24 hours, followed by a hydrogen annealing treatment at 450°C for 2 hours. The Pd-Ag alloy membrane is 25μm thick, supported by a porous α-Al2O3 ceramic with an average pore size of 0.5μm. This combination ensures the membrane's mechanical strength and separation performance, enabling efficient hydrogen separation and purification.

[0058] Nitrogen Recovery Unit 3: Nitrogen Recovery Unit 3 consists of a carbon molecular sieve adsorption tower 3a and a cryogenic distillation tower 3b connected in parallel. The regenerative heat source of the carbon molecular sieve adsorption tower 3a is connected to the outlet of the medium-temperature heat exchanger 5b of the thermal coupling module 5. This design effectively utilizes waste heat from the system and reduces energy consumption during the nitrogen recovery process. The synergistic operation of these two systems enables efficient recovery of nitrogen from the cracked gas.

[0059] Gas mixer 8: Gas mixer 8 ( Figure 9 ) utilizes a Venturi tube structure with a throat-to-inlet diameter ratio of 1:3. An ultrasonic atomizing nozzle 8a is installed at the throat, featuring atomized particle size ≤8μm and an atomization frequency of 35kHz. This ensures rapid gas dispersion during mixing, achieving efficient mixing. The accompanying ratio sensor 8b has a feedback delay of ≤50ms and an H2 / N2 molar ratio adjustment response time of 3-5s. This enables the gas mixer to quickly and accurately adjust the H2 / N2 molar ratio based on real-time system requirements, providing the optimal ratio of feed gas for the subsequent ammonia synthesis reaction.

[0060] Electrochemical synthesis reactor 4: Electrochemical synthesis reactor 4 is filled with Fe2O3-K2O / Al2O3 catalyst 4a, with an Fe2O3 content of 12wt% and a K2O content of 4wt%. The catalyst support is cordierite ceramic with a porosity of 45%. This catalyst and support combination provides excellent catalytic activity and selectivity for the ammonia synthesis reaction.

[0061] Furthermore, the reactor's space velocity is dynamically controlled, adjusting according to SV2 / SV1 = 0.35 + 0.05 × sin(2πt / T). T is determined by the liquid level cycle of the ammonia storage tank 7, ranging from 120 to 300 seconds. This dynamic adjustment allows the reaction processes of the ammonia cracking reactor and the electrochemical synthesis reactor to be aligned, further improving the overall reaction efficiency of the system.

[0062] Thermal coupling module 5: Thermal coupling module 5 ( Figure 8The system's waste heat is efficiently recovered and rationally distributed based on a 5:3:2 waste heat distribution ratio. Each heat exchanger section has the following parameters: High-temperature section 5a: Utilizes a counterflow finned tube structure with fins of 8mm height, 2mm pitch, and a heat transfer coefficient of 130W / (m²·K). This structure efficiently recovers the high-temperature waste heat generated by the ammonia cracking reactor, which is used to preheat the feed gas for the hydrogen separation unit, improving system energy efficiency. Medium-temperature section 5b: Utilizes a plate heat exchanger with a 60° corrugation angle and 3mm depth, achieving a heat transfer coefficient of 90W / (m²·K). This section is primarily responsible for further utilizing waste heat from the high-temperature section, providing a regenerative heat source for the carbon molecular sieve adsorption tower in the nitrogen recovery unit. Low-temperature section 5c: Utilizes a tube-in-tube structure with a 1.5mm thick inner tube made of Cu-Ni alloy and a 2mm thick outer tube made of stainless steel. The heat transfer coefficient is 60W / (m²·K). The residual heat is used to maintain the temperature of the ammonia storage tank 7 stable, ensuring that the storage conditions of ammonia are suitable.

[0063] Control unit 6: Control unit 6 integrates a variety of advanced control strategies and functional modules ( Figure 2 ), as follows: Dynamic hysteresis control module 6a: Set the hysteresis interval to [0.75, 1.25], and monitor the real-time wind and solar power generation power P in real time. (t) With the average power P avg The ratio of P (t) / P avg When ≥1.2, the synthesis mode is precisely activated to ensure that the system operates efficiently according to the energy supply situation.

[0064] Energy Efficiency Optimization Algorithm: When the system's instantaneous power fluctuation ΔP = ±30%, the molten salt flow rate coefficient is adjusted to ensure that the system's energy efficiency η satisfies η = 87.2 - 0.5|ΔP|. This algorithm dynamically optimizes system energy distribution based on power fluctuations, ensuring high energy efficiency across all operating conditions.

[0065] The hydrogen production fluctuation rate follows the control equation δH=5%×e⁻ 0.1t (t is the duration of fluctuation, in minutes), effectively controlling fluctuations in the hydrogen production process and ensuring the stability of product quality.

[0066] Three-stage pressure relief valve 6b: Features fast response time of ≤15ms and a pressure relief rate of 120% of the system's maximum flow rate. When system pressure fluctuations exceed the set range, it can quickly initiate pressure relief, ensuring safe and stable system operation.

[0067] 2. Implementation of closed-loop control method Molten salt flow rate control: According to the wind power generation fluctuation frequency f = 0.0053Hz, the time constant τ = 300s is accurately adjusted to make it consistent with v (t)Function matching. In this way, the molten salt flow rate can be adjusted in real time according to the fluctuations in wind and solar power generation, stabilizing the temperature in the ammonia cracking reactor and ensuring the efficient and stable progress of the ammonia cracking reaction.

[0068] Maintaining Catalyst Activity: A N2 mixture containing 0.8 vol% H2 is injected into the ammonia cracking reactor 1 for 10-15 minutes every 24 hours. This effectively maintains the activity of the nickel-based catalyst, ensuring that the ammonia cracking reaction maintains a high reaction rate and conversion rate.

[0069] Membrane separator regeneration: When the hydrogen permeation rate of the palladium alloy membrane drops by 10%, nitrogen gas at 400°C is immediately introduced at a flow rate of 2.5 L / min for 30 minutes. This operation effectively removes impurities from the surface of the palladium alloy membrane, restores the membrane's separation performance, and ensures the continued stable operation of the hydrogen separation device.

[0070] 3. Performance After actual operation verification, the system has demonstrated excellent performance: during 1000 hours of continuous and stable operation, the hydrogen production rate reached 12.5 kg / h, and the system efficiency η was 87.2%, fully demonstrating the high efficiency and stability of the system.

[0071] The hydrogen purity reached 99.999%, providing high-quality hydrogen raw material for subsequent industrial applications. Pressure fluctuations were controlled within ±8%, effectively ensuring the safe operation of the system equipment. The response time was 3.5 seconds, demonstrating the system's ability to quickly respond to external changes and exhibiting excellent dynamic performance.

[0072] The hydrogen fluctuation rate δH is strictly in accordance with δH=5%×e -0.1t The regular decay is in line with the design expectations, further verifying the effectiveness and stability of the system control strategy.

[0073] Example 2 1. System improvement and adjustment: Based on Example 1, the thermal coupling module 5 is optimized.

[0074] Thermal Coupling Module 5: The overall heat transfer coefficient of the high-temperature heat exchanger 5a is increased to 150 W / (m²·K) to enhance waste heat recovery efficiency in the high-temperature section. A reinforced casing design is adopted for the low-temperature heat exchanger 5c, reducing the inner tube wall thickness to 1.2 mm to optimize heat transfer performance in the low-temperature section. Furthermore, the waste heat distribution ratio is adjusted to 6:2:2, making heat distribution more efficient and further improving the overall energy efficiency of the system. Furthermore, by optimizing the molten salt flow rate control system, the molten salt flow rate error is reduced to ≤±3%, improving flow rate control accuracy.

[0075] Control Unit 6: The pressure relief response system of Control Unit 6 was optimized, shortening the pressure relief response time to 10ms, improving the system's response to pressure fluctuations. Furthermore, the catalyst space velocity ratio was adjusted to SV2 / SV1 = 0.35 + 0.05sin(2πt / 200s), further aligning the reaction processes of ammonia cracking reactor 1 and electrochemical synthesis reactor 4, and further improving system performance.

[0076] 2. Performance Improvement Analysis: After the above optimizations, the system demonstrated improved performance during operation. Hydrogen production increased to 13.2 kg / h, system efficiency η increased to 88.5%, and pressure fluctuations were further reduced to ±5%. While maintaining H2 purity at 99.999%, the overall system stability and energy efficiency were significantly improved.

[0077] Example 3 1. System optimization and upgrade: optimize the dynamic response performance of the system.

[0078] Gas mixer 8: The gas mixer 8 is improved by adopting more advanced control technology. The feedback delay time between the ultrasonic atomizing nozzle 8a and the proportional sensor 8b is compressed to 30ms. At the same time, the H2 / N2 molar ratio adjustment response time is shortened to 3s. This enables the gas mixer to respond to system requirements more quickly and accurately, adjust the H2 / N2 molar ratio, and provide higher-quality raw gas for the electrochemical synthesis reactor 4.

[0079] Hydrogen separation device 2: Optimize the palladium alloy membrane separator 2b and increase the coverage density of anatase TiO2 nanowires to 10 7 roots / cm², further enhancing the membrane's separation performance. At the same time, the palladium alloy membrane thickness is reduced to 20μm, increasing the hydrogen permeation rate while ensuring the strength and stability of the membrane.

[0080] Control Unit 6: Adjust the energy efficiency optimization algorithm of Control Unit 6 to the formula η = 87.2 - 0.45|ΔP|. This allows the system to more effectively optimize energy distribution and improve energy utilization during power fluctuations. Furthermore, the pressure relief rate of the third-stage pressure relief valve 6b was increased to 130% of the system's maximum flow rate, further enhancing the system's ability to cope with pressure anomalies.

[0081] 2. Performance Advantages: The optimized system demonstrated excellent performance in actual operation. The hydrogen yield was further increased to 14.0 kg / h, the system efficiency η reached 89.0%, pressure fluctuations were controlled within ±4%, H2 purity remained at 99.999%, and the response time was shortened to 2.8 seconds, significantly improving the system's dynamic response performance and overall efficiency.

[0082] Comparative Example 1 1. Differences in system settings: In this comparative example, the palladium alloy membrane separator 2b is not modified with TiO2 nanowires, and the remaining components and parameter settings are exactly the same as those in Example 1.

[0083] 2. Performance Degradation Analysis: Because the palladium alloy membrane surface was not modified with TiO2 nanowires, its hydrophilicity and anti-fouling properties decreased, leading to a decrease in hydrogen permeation rate. To maintain a certain hydrogen yield, the operating temperature needed to be increased by 30°C, which not only increased energy consumption but also adversely affected the membrane's service life. Ultimately, the hydrogen yield dropped to 9.8 kg / h, and the H2 purity dropped to 99.95%, significantly inferior to that of Example 1.

[0084] Comparative Example 2 1. System changes: In this comparative example, the exponential decay term of the molten salt flow rate is cancelled, and the molten salt flow rate is fixed at v(t) = 1.2 m / s. Other components and parameter settings are consistent with those in Example 1.

[0085] 2. Performance Impact Assessment: After fixing the molten salt flow rate, the system was unable to smoothly adjust the temperature within the ammonia cracking reactor (1) in response to fluctuations in wind and solar power generation. When power fluctuated, the temperature fluctuations within the reactor increased, causing the pressure fluctuation rate to increase to ±25%, affecting the stability of the ammonia cracking reaction. At the same time, the system efficiency η decreased to 80.5%, and the hydrogen yield dropped to 10.1 kg / h, fully demonstrating the importance of dynamic molten salt flow rate control to system stability and efficiency.

[0086] Comparative Example 3 1. System adjustment: In this comparative example, the gas mixer 8 adopts a mechanical atomizing nozzle with a particle size of 50 μm, and the ultrasonic device is eliminated. Other components and parameter settings are the same as those in Example 1.

[0087] 2. Performance Comparison Results: Due to the use of traditional mechanical atomizing nozzles, H2 / N2 mixing uniformity decreased, resulting in uneven mixing of the feed gases entering electrochemical synthesis reactor 4, affecting the efficiency of the ammonia synthesis reaction. The hydrogen yield dropped to 8.7 kg / h, and the system efficiency η dropped to 78.9%. Compared with Example 1, this performance was significantly reduced, highlighting the key role of ultrasonic atomization in improving mixing efficiency and system performance.

[0088] Table 1, performance comparison table

[0089] 1. TiO2 nanowire modification (Example 1 vs. Comparative Example 1): The hydrogen yield increased by 27.6%, and the purity reached 5N level, indicating that TiO2 nanowire modification can significantly improve the separation performance of the palladium alloy membrane, thereby improving the hydrogen yield and purity of the system.

[0090] 2. Dynamic molten salt control (Example 1 vs. Comparative Example 2): System efficiency increased by 8.3%, and pressure fluctuations decreased by 68%. This demonstrates that dynamic molten salt flow rate control plays a key role in system stability and energy efficiency, and can effectively address the impact of wind and solar power generation power fluctuations on the system.

[0091] 3. Ultrasonic atomization (Example 1 vs. Comparative Example 3): Mixing uniformity was improved, and hydrogen yield increased by 43.7%, highlighting the importance of ultrasonic atomization in the gas mixing process. It can achieve rapid and uniform mixing of hydrogen and nitrogen, providing high-quality feed gas for the ammonia synthesis reaction, thereby improving the hydrogen yield of the system.

[0092] The comparison of hydrogen production rate (kg / h) and system efficiency η (%) between the embodiment and the comparative example is shown in Figure 3 .

[0093] Matters not covered by the present invention are known technologies.

[0094] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A closed-loop circulation system based on green ammonia cracking and hydrogen production and resynthesis, characterized in that: Includes the following collaborative components and connection relationships: An ammonia cracking reactor (1) has a liquid green ammonia inlet and a cracking gas outlet, wherein the liquid green ammonia inlet is connected to the discharge port of the ammonia energy storage tank (7) through a pipeline, and the cracking gas outlet is connected to the hydrogen separation device (2) and the high-temperature section heat exchanger (5a) of the thermal coupling module (5) through pipelines. A hydrogen separation device (2) comprising a low-temperature condenser (2a) and a palladium alloy membrane separator (2b), wherein the low-temperature condenser (2a) adopts a corrugated fin tube structure with a fin spacing of 1.5 mm, and the membrane surface of the palladium alloy membrane separator (2b) is modified with anatase phase TiO2 nanowires with a wire diameter of 75 nm and anatase phase content of ≥94%; the outlet of the low-temperature condenser (2a) is connected in series with the inlet of the palladium alloy membrane separator (2b); Nitrogen recovery device (3): composed of a carbon molecular sieve adsorption tower (3a) and a cryogenic distillation tower (3b) connected in parallel, wherein the regeneration heat source inlet of the carbon molecular sieve adsorption tower (3a) is connected to the outlet of the medium temperature section heat exchanger (5b) of the thermal coupling module (5); Gas mixer (8): a venturi tube structure, with an ultrasonic atomizing nozzle (8a) at the throat, the nozzle atomizing particle size ≤ 10 μm, the atomizing frequency 20-50 kHz, and a ratio of the throat diameter to the inlet diameter of 1:3; Electrochemical synthesis reactor (4): its discharge port is connected to an ammonia energy storage tank (7) through a pipeline, and the reactor is filled with a Fe2O3-K2O / Al2O3 catalyst (4a), with a Fe2O3 content of 10-15wt% and a K2O content of 3-5wt%. The catalyst carrier is cordierite ceramic with a porosity of 45%; Thermal coupling module (5): high temperature section heat exchanger (5a): adopts counter-flow fin tube structure, fin height 8mm, spacing 2mm; medium temperature section heat exchanger (5b): adopts plate heat exchanger, plate corrugation angle 60°, corrugation depth 3mm; low temperature section heat exchanger (5c): adopts shell-and-tube heat exchanger, inner tube is copper-nickel alloy, wall thickness 1.5mm, outer tube is stainless steel, wall thickness 2mm; Control unit (6): includes a dynamic hysteresis control module (6a), which is configured to control the real-time wind and solar power generation power P (t) With the average power P avg The ratio of P (t) / P avg When the pressure is ≥1.2, the synthetic mode is activated, the hysteresis range is [0.75,1.25], and the three-stage pressure relief valve (6b) is triggered when the pressure fluctuation exceeds ±15%, and the pressure relief response time is ≤20ms.

2. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The ammonia cracking reactor (1) is filled with a nickel-based catalyst bed (1a), with a nickel loading of 15-25 wt% and a particle size of 20-50 nm. The catalyst bed temperature is regulated by a molten salt circulation channel (1b). The molten salt is a NaNO3-KNO3 mixed salt with a mixed salt molar ratio of 1:1 and a flow rate v (t) =0.5+0.7×(1-e -t / 300 ) m / s; the surface of the nickel-based catalyst (1a) is coated with a graphene layer with a thickness of 1.0 nm, the Pd-Ag alloy membrane of the palladium alloy membrane separator (2b) has a thickness of 20-30 μm, and the membrane support is a porous α-Al2O3 ceramic with an average pore size of 0.5 μm.

3. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The flow rate control function v of the molten salt circulation channel (1b) (t) In the embodiment, an exponential decay term with a time constant of 300s is used to smooth the fluctuation of wind and solar power generation, and the flow rate error range is ≤±5%; the pressure relief rate of the three-stage pressure relief valve (6b) is 120% of the maximum flow of the system.

4. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The preparation method of anatase phase TiO2 nanowires includes hydrothermal synthesis and hydrogen annealing; wherein the hydrothermal synthesis reaction temperature is 180°C, the reaction time is 24h, the hydrogen annealing temperature is 450°C, the time is 2h, and the coverage density of the nanowires on the surface of the palladium alloy film is 10 6 -10 7 roots / cm².

5. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The ratio of the space velocity SV2 of the Fe2O3-K2O / Al2O3 catalyst (4a) to the space velocity SV1 of the nickel-based catalyst (1a) is dynamically adjusted by the following formula: SV2 / SV1=0.35+0.05×sin(2πt / T); wherein T is a parameter set by the control unit (6) according to the liquid level change cycle of the ammonia energy storage tank (7), and T=120-300s.

6. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The feedback delay time between the ultrasonic atomizing nozzle (8a) and the ratio sensor (8b) of the gas mixer (8) is ≤50ms, and the H2 / N2 molar ratio adjustment response time is 3-5s.

7. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The waste heat distribution ratio of the thermal coupling module (5) is high temperature section: medium temperature section: low temperature section = 5:3:2, and the total heat transfer coefficients of the heat exchangers in each section are 120-150 W / (m²·K), 80-100 W / (m²·K), and 50-70 W / (m²·K), respectively.

8. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The multi-layer insulation structure of the ammonia cracking reactor (1) comprises: Outer layer: ceramic fiber insulation layer, thickness 30-50mm, density 160kg / m³, thermal conductivity ≤0.1W / (m·K); Middle layer: microporous calcium silicate board, thickness 20mm, porosity 60%; Inner layer: high temperature resistant alloy lining, Inconel 600, thickness 5mm.

9. The closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to claim 1, characterized in that: The energy efficiency optimization algorithm of the control unit (6) includes: When the instantaneous power fluctuation ΔP=±30%, by adjusting the molten salt flow rate v (t) The exponential term coefficient of the system energy efficiency η satisfies: η=87.2-0.5|ΔP|, and the hydrogen production fluctuation control equation is: δ H =5%×e -0.1t , where t is the duration of the fluctuation, in minutes.

10. A closed-loop control method for a closed-loop circulation system for hydrogen production and resynthesis based on green ammonia cracking according to any one of claims 1 to 9, characterized in that include: Molten salt flow rate control: According to the wind and solar power generation power fluctuation frequency f of 0.1Hz-1Hz, adjust v (t) The time constant τ in the function satisfies τ=1 / (2πf); the fluctuation frequency f is collected in real time according to the wind and solar power generation power sensor; Catalyst activity maintenance: inject a nitrogen mixture containing 0.5-1.0 vol% hydrogen into the ammonia cracking reactor (1) every 24 hours for 10-15 minutes; Membrane separator regeneration: When the hydrogen permeation rate of the palladium alloy membrane (2b) drops by 10%, introduce nitrogen at 400°C for 30 minutes at a nitrogen flow rate of 2-3 L / min.

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