Multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system and control method

Abstract

The application discloses a kind of multistage negative pressure ammonia decomposition fluidized bed hydrogen production system and control method, belong to hydrogen production technical field.System includes ammonia supply unit, first fluidized bed reactor, second fluidized bed reactor and vacuum supply unit.Ammonia enters first fluidized bed reactor from bottom, and forms fluidized state with catalyst under negative pressure environment and carries out decomposition reaction;Hydrogen-nitrogen mixed gas is generated and enters second fluidized bed reactor, and further reacts under higher vacuum degree, realizes ammonia deep conversion.The application combines the advantages of high-efficiency heat transfer of fluidized bed and multistage negative pressure step-by-step driving reaction balance, with high heat transfer efficiency, uniform and controllable temperature, low reaction temperature, high conversion rate, suitable for large-scale continuous production and other characteristics, can realize ammonia efficient hydrogen production under mild conditions.

Description

Technical Field

[0001] This invention relates to the field of ammonia decomposition hydrogen production equipment technology, specifically to a multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system and its control method. Background Technology

[0002] The ammonia decomposition reaction (2NH3 ⇌ N2 + 3H2) is a typical reversible reaction involving an increase in gas volume. According to Le Chatelier's principle, reducing the reaction pressure favors shifting the equilibrium towards the direction of increasing molecular number, thus promoting the decomposition of ammonia. Under vacuum conditions, the absolute pressure of the reaction system is much lower than atmospheric pressure, resulting in extremely low partial pressures of the products nitrogen and hydrogen, thereby forcibly pushing the equilibrium point to the right. Even under medium to low temperature conditions, vacuum operation can achieve much higher equilibrium conversion rates than at atmospheric pressure. Under atmospheric or pressurized conditions, to obtain higher ammonia decomposition conversion rates, it is usually necessary to heat the reactor to very high temperatures, which not only consumes a lot of energy but also places high demands on the temperature level of the heat source. Furthermore, in a closed system at atmospheric pressure, as ammonia decomposition proceeds, the product concentration gradually increases, and the rate of the reverse reaction (i.e., ammonia synthesis) increases accordingly, limiting the continuation of the forward reaction.

[0003] Currently, most ammonia decomposition processes utilize fixed-bed reactors, where catalyst particles are stacked into a stationary bed of a certain height, and the fluid reacts through this bed. However, fixed-bed reactors present several problems in practical applications, including: 1) poor heat transfer performance, with hot spots easily forming in the bed, requiring complex internal heat exchange structures for strongly endothermic reactions; 2) uneven radial and axial temperature distribution within the bed, making isothermal operation difficult; 3) significant pressure drop of gas passing through the stationary catalyst bed, especially when using small-particle catalysts; 4) high diffusion resistance within the catalyst, limiting its utilization rate; 5) inconvenient catalyst regeneration and replacement, requiring shutdown operations, which is detrimental to continuous production; and 6) poor process reproducibility during the transition from pilot-scale to intermediate-scale or industrial-scale production due to nonlinear changes in heat transfer and flow behavior. Summary of the Invention

[0004] To address the shortcomings of existing technologies, such as high energy consumption in ammonia decomposition processes under normal or pressurized conditions, poor thermal conductivity of existing fixed-bed reactors, and large temperature distribution and internal diffusion resistance affecting ammonia decomposition efficiency and hydrogen production costs, this paper proposes a multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system and control method that provides a uniform, efficient, stable, and repeatable ammonia decomposition process.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: A multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system, comprising an ammonia supply unit; a first fluidized bed reactor, a second fluidized bed reactor, and a vacuum supply unit; the ammonia supply unit is connected to the gas distribution zone at the bottom of the first fluidized bed reactor and is used to supply ammonia to the first fluidized bed reactor; the first fluidization device includes a first gas distribution zone, a first reaction heat exchange zone, and a first settling zone; the first gas distribution zone is located at the bottom of the first fluidization device; the first reaction heat exchange zone is located above the first gas distribution zone and communicates with the first gas distribution zone; the first reaction heat exchange zone is filled with a catalyst; the bulk density of the catalyst is 0.8–1.1 g / cm³. 3 The particle density of the catalyst is 2.0–2.5 g / cm³. 3 The flow rate of the gas entering the first reaction heat exchange zone from the first gas distribution zone is greater than the minimum fluidization velocity of the gas; the other end of the first reaction heat exchange zone is connected to the first settling zone; the cross-sectional area of ​​the first settling zone is larger than the cross-sectional area of ​​the first reaction heat exchange zone and is used to separate the gas from the catalyst; the first settling zone is connected to the bottom of the second fluidizing device; the second fluidizing device includes a second gas distribution zone, a second reaction heat exchange zone, and a second settling zone; the second gas distribution zone is located at the bottom of the second fluidizing device; the second reaction heat exchange zone is located above the second gas distribution zone and communicates with the second gas distribution zone; the interior of the second reaction heat exchange zone is filled with a catalyst; the flow rate of the gas entering the second reaction heat exchange zone from the second gas distribution zone is greater than the minimum fluidization velocity of the gas; the other end of the second reaction heat exchange zone is used to discharge the hydrogen-nitrogen mixture and is connected to the vacuum supply unit; the vacuum supply unit is used to evacuate the gas from the first fluidizing device and the second fluidizing device and to create a negative pressure environment in the first fluidizing device and the second fluidizing device, respectively.

[0006] Furthermore, the ammonia supply unit includes an ammonia tank, a first heat exchanger, an ammonia flow meter, an ammonia control valve, and an ammonia heater; the ammonia tank is connected to the first heat exchanger; the first heat exchanger is connected in sequence to the ammonia flow meter, the ammonia control valve, and the ammonia heater; the ammonia heater is connected to the first gas distribution zone; the temperature of the ammonia after being heated by the ammonia heater is 350-400℃.

[0007] Furthermore, the cross-sectional shape of the first gas distribution zone is trapezoidal; the cross-sectional area of ​​the end of the first gas distribution zone connected to the ammonia heater is smaller than the cross-sectional area of ​​the end of the first gas distribution zone connected to the first reaction heat exchange zone; a first gas distributor is horizontally fixed within the first gas distribution zone; the first gas distributor has through holes; the cross-sectional shape of the second gas distribution zone is trapezoidal; the cross-sectional area of ​​the end of the second gas distribution zone connected to the first fluidization device is smaller than the cross-sectional area of ​​the end of the second gas distribution zone connected to the second reaction heat exchange zone; a second gas distributor is horizontally fixed within the second gas distribution zone; the second gas distributor has through holes; a first gas distribution plate is horizontally arranged at the end of the first reaction heat exchange zone that communicates with the first gas distribution zone; a second gas distribution plate is horizontally arranged at the end of the second reaction heat exchange zone that communicates with the second gas distribution zone; the particle size range of the catalyst is 50–100 μm; a pressure measuring point is set below the first gas distribution plate; a pressure measuring point is set below the second gas distribution plate.

[0008] Furthermore, the ratio of the height to the diameter of the first reaction heat exchange zone is 2–4; the expansion ratio of the first fluidizing device is 1–3; the orifice ratio of the first gas distributor is 0.5–2.5%; differential pressure sensors are respectively installed at the upper and lower ends of the first reaction heat exchange zone; temperature detection points are provided at the bottom and middle of the first fluidizing device; the temperature of the first reaction heat exchange zone is 400–450℃; multiple thermocouples are arranged at different heights and at different radial positions at the same height in the first reaction heat exchange zone; the ratio of the height to the diameter of the second reaction heat exchange zone is 2–4; the expansion ratio of the second fluidizing device is 1–3; the orifice ratio of the second gas distributor is 0.5–2.5%; differential pressure sensors are respectively installed at the upper and lower ends of the second reaction heat exchange zone; temperature detection points are provided at the bottom and middle of the second fluidizing device; the temperature of the second reaction heat exchange zone is 400–450℃; multiple thermocouples are arranged at different heights and at different radial positions at the same height in the second reaction heat exchange zone.

[0009] Furthermore, multiple guide tubes are vertically arranged inside the first reaction heat exchange zone; the guide tubes are vertically structured and penetrate the first reaction heat exchange zone; the multiple guide tubes simultaneously circulate with the first heat transfer system; the first heat transfer system is located outside the first fluidizing device; a heat transfer source circulates in the first heat transfer system; a heat transfer control valve is installed between the first heat transfer system and the guide tubes; multiple guide tubes are vertically arranged inside the second reaction heat exchange zone; the guide tubes are vertically structured and penetrate the second reaction heat exchange zone; the multiple guide tubes simultaneously circulate with the second heat transfer system; the second heat transfer system is located outside the second fluidizing device; a heat transfer source circulates in the second heat transfer system; a heat transfer control valve is installed between the second heat transfer system and the guide tubes.

[0010] Furthermore, the cross-sectional area of ​​the first settling zone is larger than that of the first reaction heat exchange zone; the first settling zone is provided with a first feed inlet, a first filter, and a first guide pipe; the first feed inlet is located on the side wall of the first settling zone; the first filter is located near the top of the first settling zone; the first filter has a mesh structure; the first guide pipe is located at the top of the first settling zone; the first guide pipe is connected to a first gas-solid separator located outside the first settling zone; the bottom of the first gas-solid separator is connected to a first connecting pipe; the first connecting pipe is then connected to the bottom of the first reaction heat exchange zone; the cross-sectional area of ​​the second settling zone is larger than that of the second reaction heat exchange zone; the second settling zone is provided with a second feed inlet, a second filter, and a second guide pipe; the second feed inlet is located on the side wall of the second settling zone; the second filter is located near the top of the second settling zone; the second filter has a mesh structure; the second guide pipe is located at the top of the first settling zone; the second guide pipe is connected to a second gas-solid separator located outside the second settling zone; the bottom of the second gas-solid separator is connected to a second connecting pipe; the second connecting pipe is then connected to the bottom of the first reaction heat exchange zone.

[0011] Furthermore, a cooler is installed at the outlet of the second fluidization unit; the cooler is connected to the second settling zone and the ammonia supply unit; the vacuum supply unit includes a vacuum pump and a vacuum regulating valve; the vacuum pump is connected to the second fluidization unit through the vacuum regulating valve; a cooling medium flows through the cooler, and the temperature of the cooler is 50 to 80°C; the operating pressure range of the vacuum pump is -0.09 to -0.05 MPa.

[0012] A control method for a multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system includes the following steps: Step 1: Ammonia gas is introduced into the first gas distribution zone at the bottom of the first fluidizing device through an ammonia supply unit; when the ammonia gas flow rate in the first gas distribution zone reaches the critical fluidization velocity; the ammonia gas in the first gas distribution zone is then introduced into the first reaction heat exchange zone; Step 2: The ammonia gas drives the catalyst in the first reaction heat exchange zone to move and enter a fluidized state, heating the first reaction heat exchange zone; in the first reaction heat exchange zone, the ammonia gas decomposes into a hydrogen-nitrogen mixture; Step 3: The second fluidizing device is directly drawn in through a vacuum supply unit, causing the connected first fluidizing device to form a negative pressure environment in both the first and second fluidizing devices; in the first reaction heat exchange zone... The hydrogen-nitrogen mixture enters the first settling zone and then enters the second gas distribution zone at the bottom of the second fluidization device. Step four: When the hydrogen-nitrogen mixture in the second gas distribution zone reaches the critical fluidization velocity, it is introduced into the second reaction heat exchange zone. The hydrogen-nitrogen mixture drives the catalyst in the second reaction heat exchange zone to move and enter the fluidization state. Step five: The second reaction heat exchange zone is heated, and the ammonia in the hydrogen-nitrogen mixture in the second reaction heat exchange zone decomposes into hydrogen-nitrogen mixture. Step six: The hydrogen-nitrogen mixture in the second reaction heat exchange zone is introduced into the second settling zone. After passing through the second settling zone, the hydrogen-nitrogen mixture exchanges heat with the ammonia introduced through the ammonia supply unit. After heat exchange, the hydrogen-nitrogen mixture is collected or used.

[0013] Furthermore, in steps one through three, ammonia gas is preheated to 400°C and then enters the first gas distribution zone; the first fluidizing device maintains an operating vacuum of -0.05 to -0.06 MPa, the temperature of the first reaction heat exchange zone is controlled at 400 to 450°C, and the minimum conversion rate of ammonia gas in the first reaction heat exchange zone is 95%; the heat load occupied by the first fluidizing device is 60 to 70% of the total heat load.

[0014] Furthermore, in steps four to six; the vacuum degree in the second fluidization device is maintained at -0.08 to -0.09 MPa, the temperature in the second reaction heat exchange zone is controlled at 350 to 400°C, and the minimum conversion rate of ammonia in the second reaction heat exchange zone is 99%.

[0015] The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system and control method described in this invention have the following advantages: 1. Extremely high heat transfer efficiency and uniform, controllable temperature: The fluidized bed uses fine-particle catalysts that are in a state of vigorous motion under the action of airflow, resulting in extremely high heat transfer efficiency and uniform temperature distribution within the bed. Heat can be rapidly transferred to the catalyst particles, effectively avoiding the "cold spots" or localized overheating problems common in fixed beds, ensuring that the catalyst is always within its optimal activity temperature range, thereby improving reaction efficiency. The heat transfer coefficient between the bed and the internal heat exchange surface can reach 200–400 W / (m²·K), exhibiting excellent thermal stability. The fluidized bed itself has excellent heat transfer performance, and the staged structure further enhances the precision of temperature control. The heat transfer coefficients between catalyst particles, between the bed and the vessel wall, and between the bed and the heat-conducting cylinder wall are large, resulting in a fast heat transfer rate, a small required heat exchange area, and a uniform temperature distribution within the bed. The catalyst bed can be stably controlled within the optimal reaction range of approximately 400℃, avoiding localized overcooling that leads to a decrease in reaction rate or localized overheating that causes catalyst deactivation, significantly improving energy utilization efficiency.

[0016] 2. Effective suppression of side reactions and improved selectivity: Due to the thorough mixing of particles throughout the entire bed, the temperature and concentration distribution within the bed are highly uniform. The intense gas-solid contact and rapid heat transfer within the fluidized bed can avoid side reactions caused by localized temperature and concentration unevenness, which is beneficial for improving the decomposition efficiency and reaction selectivity of the target product, ammonia.

[0017] 3. Suitable for large-scale production with relatively low scale-up risk: Fluidized beds can use fine-particle catalysts, which are in full contact with the fluid in a suspended state, resulting in a huge gas-solid contact area, reaching 3280–16400 m² / m³, significantly improving the efficiency of heterogeneous reactions and the utilization rate of the active catalyst components. Higher reaction rates can be achieved with the same catalyst loading. The catalyst can be continuously removed and replenished, facilitating the construction of a continuous reaction-regeneration system. The bed pressure drop is relatively stable and typically lower than that of a fixed bed. The reactor structure is simple, with high processing capacity, making it suitable for large-scale and continuous production.

[0018] 4. Promoting Chemical Equilibrium and Suppressing Reverse Reactions: Under negative pressure operation, the absolute pressure of the reaction system is much lower than atmospheric pressure, resulting in extremely low partial pressures of the products nitrogen and hydrogen, forcibly pushing the reaction equilibrium towards decomposition. Even at moderate temperatures, a much higher equilibrium conversion rate than at atmospheric pressure can be achieved. Simultaneously, due to continuous suction in the reaction system, the product gases are rapidly removed from the reaction zone, maintaining a low product concentration environment on the catalyst surface, effectively suppressing the reverse reaction (ammonia synthesis) and ensuring the continuous and efficient advancement of the ammonia decomposition process. Through a staged depressurization design, each stage of the reaction zone constructs a thermodynamic environment favorable to that stage's reaction, effectively avoiding reaction stagnation caused by product accumulation in a single-stage reactor, thereby pushing the overall conversion rate close to the thermodynamic equilibrium limit. The reaction proceeds under negative pressure, and with continuous suction from the vacuum pump group, the hydrogen and nitrogen mixture obtained from the decomposition can be directly kept under low or negative pressure, reducing the pressure for subsequent processing. The produced hydrogen can be stored in a gas collection tank or buffer tank. If the purity is high, it can be directly used in processes with high gas quality requirements, such as fuel cells and hydrogenation reactions. If the purity is limited, it can also be used as fuel gas in boilers for hydrogen blending and combustion or in flare systems for combustion and power generation. In addition, in specific application scenarios such as use as protective gas or fuel gas, this device avoids the operational risks of high-pressure gases, improving system safety and operational flexibility. 5. Enhanced mass transfer and reduced reaction temperature: The vacuum environment reduces the collision frequency between gas molecules, increases the mean free path, and improves the diffusion coefficient, which facilitates the penetration of ammonia molecules into the catalyst's internal pores. Simultaneously, it promotes the desorption and rapid diffusion of product molecules from the catalyst surface, reducing the time active sites are occupied by products, thereby improving catalyst utilization efficiency and overall reaction rate. Furthermore, the vacuum condition reduces the thermodynamic limitations of the reaction, allowing it to proceed at milder temperatures, which is practically significant for reducing energy consumption, simplifying heating systems, and adapting to low-temperature heat sources. The fluidized bed structure itself is suitable for large-scale continuous production, and the multi-stage series design combines the high-efficiency heat transfer characteristics of the fluidized bed with the flow advantages of near-plug flow, ensuring both processing capacity and conversion depth. The catalyst particles and fluid are in a state of vigorous agitation, with continuous renewal of the gas-solid interface, significantly improving the mass transfer coefficient. In addition, the use of fine-particle catalysts results in a large specific surface area per unit volume, further accelerating the mass transfer rate. Efficient capture and return of entrained catalyst through filters, combined with optimized design of the fluidization velocities at each stage, ensures good fluidization while minimizing mechanical breakage and escape losses of the catalyst. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to the present invention. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1 As shown, the multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system of the present invention includes an ammonia supply unit 1; a first fluidized bed reactor 2; a second fluidized bed reactor 4; and a vacuum supply unit 8. The ammonia supply unit 1 is connected to the gas distribution zone 21 at the bottom of the first fluidized bed reactor 2 and is used to supply ammonia to the first fluidized bed reactor 2; The first fluidizing device 2 includes a first gas distribution zone 21, a first reaction heat exchange zone 22, and a first settling zone 23; the first gas distribution zone 21 is located at the bottom of the first fluidizing device 2; the first reaction heat exchange zone 22 is located above the first gas distribution zone 21 and communicates with the first gas distribution zone 21; the first reaction heat exchange zone 22 is filled with a catalyst; the bulk density of the catalyst is 0.8–1.1 g / cm³. 3 The catalyst has a particle density of 2.0–2.5 g / cm³. 3； The flow rate of the gas entering the first reaction heat exchange zone 22 from the first gas distribution zone 21 is greater than the minimum fluidization velocity of the gas. The other end of the first reaction heat exchange zone 22 is connected to the first settling zone 23; the cross-sectional area of ​​the first settling zone 23 is larger than the cross-sectional area of ​​the first reaction heat exchange zone 22 and is used to separate the gas from the catalyst; the first settling zone 23 is connected to the bottom of the second fluidization device 4. The second fluidizing device 4 includes a second gas distribution zone 41, a second reaction heat exchange zone 42, and a second settling zone 43. The second gas distribution zone 41 is located at the bottom of the second fluidizing device 4. The second reaction heat exchange zone 42 is located above and communicates with the second gas distribution zone 41. The second reaction heat exchange zone 42 is filled with a catalyst. The bulk density of the catalyst is 0.8–1.1 g / cm³. 3 The catalyst has a particle density of 2.0–2.5 g / cm³. 3； The flow rate of the gas entering the second reaction heat exchange zone 42 from the second gas distribution zone 41 is greater than the minimum fluidization velocity of the gas; the other end of the second reaction heat exchange zone 42 is used to discharge the hydrogen-nitrogen mixture and is connected to the vacuum supply unit 8; the vacuum supply unit 8 is used to draw gas from the first fluidizing device 2 and the second fluidizing device 4 and form a negative pressure environment in the first fluidizing device 2 and the second fluidizing device 4 respectively.

[0023] exist Figure 1 In this system, the ammonia supply unit 1 includes an ammonia tank, a first heat exchanger 10, an ammonia flow meter 11, an ammonia control valve 12, and an ammonia heater 13. The ammonia tank is connected to the first heat exchanger 10. The first heat exchanger 10 is sequentially connected to the ammonia flow meter 11, the ammonia control valve 12, and the ammonia heater 13. Ammonia gas discharged from the ammonia tank is heated by the first heat exchanger 10 and then flows through the ammonia flow meter 11 and the ammonia control valve 12. The ammonia flow meter 11 and the ammonia control valve 12 are used to measure and control the flow rate of ammonia gas entering the first fluidization device 2, respectively, to achieve accurate control of the ammonia gas flow rate. The ammonia gas is then further heated by the ammonia heater 13 before entering the first gas distribution zone 21 of the first fluidization device 2. Specifically, the temperature of the ammonia gas after being heated by the ammonia heater 13 is 350–400°C.

[0024] The first fluidizing device 2 has a three-dimensional tubular structure; from bottom to top, the first fluidizing device 2 consists of a first gas distribution zone 21, a first reaction heat exchange zone 22, and a first settling zone 23; the first gas distribution zone 21 is connected to the first reaction heat exchange zone 22; the other end of the first reaction heat exchange zone 22 is connected to the first settling zone 23; the cross-sectional shape of the first gas distribution zone 21 is conical; the cross-sectional area of ​​the end of the first gas distribution zone 21 connected to the ammonia heater 13 is smaller than the cross-sectional area of ​​the end of the first gas distribution zone 21 connected to the first reaction heat exchange zone 22, so that the gas enters... Within the first gas distribution zone 21, the gas can be buffered and adjusted; this promotes uniform distribution of gas entering the first reaction heat exchange zone 22 and allows the gas flow rate in the first gas distribution zone 21 to reach the critical fluidization velocity more quickly; preferably, a first gas distributor is laterally fixed within the first gas distribution zone 21; the first gas distributor has through holes; the through holes on the first gas distributor are opened in different directions according to the shape of the first gas distribution zone 21; this allows the heated ammonia gas to be evenly and fully distributed into the first gas distribution zone 21 after passing through the first gas distributor.

[0025] A first gas distribution plate is horizontally arranged at one end of the first reaction heat exchange zone 22 that communicates with the first gas distribution zone 21. The first gas distribution plate is used to control the volume of ammonia gas entering the first reaction heat exchange zone 22, so that the ammonia gas entering from the first gas distribution zone 21 can enter the first reaction heat exchange zone 22 uniformly. The first gas distribution plate is covered with a catalyst. The catalyst is an ammonia decomposition catalyst, such as a ruthenium-based catalyst or a nickel-based catalyst. The catalyst has a powdered particulate structure with a particle size range of 50-100 μm, for example, 75 μm. The bulk density of the catalyst is 0.8-1.1 g / cm3, and the particle density of the catalyst is 2.0-2.5 g / cm3. By using particulate, small-volume catalysts and controlling the bulk density of the catalyst, it is beneficial for ammonia gas to reach the critical fluidization velocity more quickly and promotes the loosening of catalyst particles. This allows the bed to enter a stable fluidization state more quickly, thus improving the contact between ammonia gas and the catalyst. And the heat transfer between them; ammonia gas is fed in from below the first gas distribution plate. When the ammonia gas velocity reaches the critical fluidization velocity, the catalyst particles begin to loosen; as the ammonia gas velocity further increases, the interior of the first reaction heat exchange zone 22 enters a stable fluidization state; as the ammonia gas continuously contacts and impacts the catalyst particles, the heat of the ammonia gas itself is evenly distributed, and under the promoting effect of the catalyst, it decomposes into a mixture of hydrogen and nitrogen gas; specifically; the ratio between the height and diameter of the first reaction heat exchange zone 22 is 2 to 4; the expansion ratio of the first fluidization device is 1 to 3; the opening ratio of the first gas distributor is 0.5 to 2.5%; differential pressure sensors are respectively set at the upper and lower ends of the first reaction heat exchange zone 22 for real-time monitoring of the catalyst content; temperature detection points are set at the bottom and middle of the first fluidization device 2, and the highest temperature point signal is interlocked with the flow rate of the heat transfer medium system for adjusting the fluidized bed reaction temperature; the temperature of the first reaction heat exchange zone 22 is controlled at 400 to 450°C.

[0026] Multiple thermocouples are arranged at different heights (e.g., upper, middle, and lower) and at different radial positions (e.g., from the center to the sidewall) within the first reaction heat exchange zone 22. The average value of each measuring point is taken as the control parameter representing the bed temperature. For the strongly endothermic reaction of ammonia decomposition, this temperature measurement value will be used to adjust the flow rate of the heating medium or the electric heating power in the built-in heat-conducting cylinder to ensure that the bed temperature is stable within the optimal reaction range. A pressure measuring point is set below the first gas distribution plate. Pressure fluctuations at this location are a key indicator for judging fluidization quality. By analyzing the fluctuation amplitude, abnormal bubble behavior or changes in particle size distribution can be inferred. At the same time, multiple pressure measuring ports are opened at different heights on the sidewall of the first reaction heat exchange zone. By calculating the pressure difference between each measuring point, changes in bed height and catalyst content can be indirectly monitored, providing real-time basis for preventing catalyst loss. This design, through an integrated structure and refined control strategy, significantly improves the reaction efficiency, energy utilization, and operational stability of the ammonia decomposition process.

[0027] To better catalyze the ammonia decomposition process, provide heat for the ammonia decomposition process, and promote uniform mixing of ammonia gas, specifically, multiple guide tubes are vertically arranged inside the first reaction heat exchange zone 22. These guide tubes are vertical and penetrate the first reaction heat exchange zone 22. Multiple guide tubes simultaneously circulate with the first heat carrier system 6. The first heat carrier system 6 is located outside the first fluidization device 2. A heat transfer source, such as oil or molten salt, circulates in the first heat carrier system 6. The first heat carrier system 6 is used to simultaneously introduce the heat transfer source to the bottom of the multiple guide tubes. After entering the multiple guide tubes, the heat source can flow inside the multiple guide tubes; and is discharged through the top of the guide tubes and flows back to the first heat carrier system 6; realizing the circulation of the heat source within the multiple guide tubes, relative to the stationary heating heat source; the circulating heat source can improve the heat exchange effect with the ammonia and catalyst flowing in the first reaction heat exchange zone 22; thereby promoting the efficient heat absorption of ammonia and catalyst and the decomposition of ammonia; preferably; a heat carrier control valve is provided between the first heat carrier system 6 and the guide tubes; used to control the flow rate of the heat source entering the guide tubes; thereby controlling the heating effect on ammonia.

[0028] One end of the first reaction heat exchange zone 22 relative to the first gas distribution zone 21 is connected to the first settling zone 23; the cross-sectional area of ​​the first settling zone 23 is larger than the cross-sectional area of ​​the first reaction heat exchange zone 22; the first settling zone 23 is provided with a first feed port, a first filter 24, and a first guide pipe 25; wherein the first feed port is located on the side wall of the first settling zone 23; a catalyst is introduced into the first settling zone 23 through the first feed port, thereby improving the catalytic effect and fluidization state of ammonia, and achieving control and adjustment of ammonia catalysis and gas fluidization state; wherein, the hydrogen-nitrogen mixture obtained by the endothermic decomposition of ammonia, discharged from the first reaction heat exchange zone 22, carries the catalyst particles into the top-expanded first settling zone 23, and the hydrogen-nitrogen mixture is discharged from the first settling zone 23 after separation from the catalyst, while the catalyst slowly descends along the annular gap region under the action of gravity; during the descent, the catalyst undergoes efficient heat exchange with the built-in guide pipe (through which a heat source, such as oil or molten salt, is introduced), and is reheated to the reaction heat exchange zone 23. After reaching the required temperature, the gas circulates back to the bottom and re-enters the first reaction heat exchange zone 22 to participate in the ammonia decomposition catalytic reaction. This design organically couples the reaction, catalyst heating, and circulation flow within the same device, resulting in a compact structure and extremely high thermal efficiency. The first filter 24 is located near the top of the first settling zone 23. The first filter 24 has a mesh structure and separates the mixed gas from the trapped catalyst particles through filtration. The separated hydrogen-nitrogen mixed gas is discharged through the first filter 24 and then through the first guide pipe 25 located at the top of the first settling zone 23. The separated catalyst falls to the first filter 24 under the obstruction of the first filter 24 and enters the first reaction heat exchange zone 22, which is connected to the bottom of the first filter 24. It then enters the cavity of the first reaction heat exchanger 22 and continues to form a fluidized state in the first reaction heat exchange zone 22 under the action of ammonia introduced through the first gas distribution zone 21.

[0029] After separation, the hydrogen-nitrogen mixture is discharged from the first guide pipe 25 at the top of the first settling zone 23 and then enters the first gas-solid separator 26 connected to the first guide pipe 25 for gas-solid separation to remove small amounts of catalyst particles that have not been fully filtered from the gas, thereby further improving the purity of the discharged hydrogen-nitrogen mixture. The separated catalyst is discharged from the bottom of the first gas-solid separator 26 and enters the first connecting pipe 27 connected to the bottom of the first reaction heat exchange zone 22. The end of the first connecting pipe 27 connected to the first gas-solid separator 26 has a U-shaped bend structure. Through the U-shaped bend structure at the end of the first connecting pipe 27, the gas-solid separation process is maintained in this part. A certain amount of separated and recovered catalyst is retained to prevent gas backflow and improve catalyst recovery. The separated catalyst enters the bottom of the first reaction heat exchange zone 22 through the first connecting pipe 27. It continues to react with the ammonia introduced from the first gas distribution zone 21 and promotes its decomposition, improving the fluidization effect inside the first reaction heat exchange zone 22 and also realizing the recycling of the catalyst. This improves the system's energy utilization rate. The end of the first gas-solid separator 26 used for discharging gas is connected to the mixed gas heater 3. The mixed gas heater 3 is used to further increase the gas temperature of the hydrogen-nitrogen mixture and promote the further decomposition of the undecomposed ammonia in the second fluidization device 4.

[0030] The structure of the second fluidizing device 4 is the same as that of the first fluidizing device 2; the second fluidizing device 4 is a three-dimensional tubular structure; from bottom to top, the second fluidizing device 4 consists of a second gas distribution zone 41, a second reaction heat exchange zone 42, and a second settling zone 43; the second gas distribution zone 41 is connected to the second reaction heat exchange zone 42; the other end of the second reaction heat exchange zone 42 is connected to the second settling zone 43; the cross-sectional shape of the second gas distribution zone 41 is conical; the cross-sectional area of ​​the end of the second gas distribution zone 41 connected to the first fluidizing device 2 is smaller than the cross-sectional area of ​​the end of the second gas distribution zone 41 connected to the second reaction heat exchange zone 42. The surface area allows for buffering and adjustment of the gas as it enters the second gas distribution zone 41, promoting uniform gas distribution in the second reaction heat exchange zone 42 and enabling the gas flow rate in the second gas distribution zone 41 to reach the critical fluidization velocity more quickly. Preferably, a second gas distributor is laterally fixed within the second gas distribution zone 41. The second gas distributor has through holes of uniform size. The through holes on the second gas distributor are oriented in different positions in accordance with the shape of the second gas distribution zone 41, ensuring that the heated ammonia gas is evenly and fully distributed into the second gas distribution zone 41 after passing through the second gas distributor.

[0031] A second gas distribution plate is horizontally arranged at one end of the second reaction heat exchange zone 42 that communicates with the second gas distribution zone 41. The second gas distribution plate is used to control the volume of ammonia gas entering the second reaction heat exchange zone 42, so that the ammonia gas entering from the second gas distribution zone 41 can enter the second reaction heat exchange zone 42 uniformly. The second gas distribution plate is covered with a catalyst. The catalyst is an ammonia decomposition catalyst, such as a ruthenium-based catalyst or a nickel-based catalyst. The catalyst has a powdered particulate structure with a particle size range of 50-100 μm, for example, 75 μm. The bulk density of the catalyst is 0.8-1.1 g / cm³. 3 The particle density of the catalyst is 2.0–2.5 g / cm³. 3 By using granular, small-volume catalysts and controlling their packing density, ammonia gas reaches the critical fluidization velocity more quickly, promoting the loosening of catalyst particles. This allows the bed to enter a stable fluidization state more rapidly, thus improving the contact between ammonia gas and the catalyst, as well as the heat transfer between them. Ammonia gas is introduced from below the second gas distribution plate. When the ammonia gas velocity reaches the critical fluidization velocity, the catalyst particles begin to loosen. As the ammonia gas velocity further increases, the interior of the second reaction heat exchange zone 42 enters a stable fluidization state. With the continuous contact and impact mixing of ammonia gas with the catalyst particles, the heat of ammonia gas itself is evenly distributed, and under the promoting effect of the catalyst, it decomposes into a mixture of hydrogen and nitrogen gas. Specifically; the ratio between the height and diameter of the second reaction heat exchange zone 42 is 2 to 4; the expansion ratio of the second fluidizing device is 1 to 3; the opening ratio of the second gas distributor is 0.5 to 2.5%; differential pressure sensors are respectively installed in the upper and lower sections of the second reaction heat exchange zone 42 for real-time monitoring of catalyst storage; temperature detection points are provided at the bottom and middle of the second fluidizing device 4, and the highest temperature signal is used to interlock with the flow rate of the heat transfer medium system to adjust the fluidized bed reaction temperature; the temperature of the second reaction heat exchange zone 42 is controlled at 350 to 400°C.

[0032] Multiple thermocouples are arranged at different heights (e.g., upper, middle, and lower) and at different radial positions (e.g., from the center to the sidewall) within the second reaction heat exchange zone 22. The average value of each measuring point is taken as the control parameter representing the bed temperature. For the strongly endothermic reaction of ammonia decomposition, this temperature measurement value will be used to adjust the flow rate of the heating medium or the electric heating power in the built-in heat-conducting cylinder to ensure that the bed temperature remains stable within the optimal reaction range. A pressure measuring point is set below the second gas distribution plate. Pressure fluctuations at this location are a key indicator for judging fluidization quality. By analyzing the fluctuation amplitude, abnormal bubble behavior or changes in particle size distribution can be inferred. Simultaneously, multiple pressure measuring ports are opened at different heights on the sidewall of the second reaction heat exchange zone. By calculating the pressure difference between each measuring point, changes in bed height and catalyst content can be indirectly monitored, providing real-time data for preventing catalyst loss. This design, through its integrated structure and refined control strategy, significantly improves the reaction efficiency, energy utilization, and operational stability of the ammonia decomposition process.

[0033] To better catalyze the ammonia decomposition process, provide heat for the ammonia decomposition process, and promote uniform mixing of ammonia gas, specifically, multiple guide tubes are vertically arranged inside the second reaction heat exchange zone 42. These guide tubes are vertical and penetrate the second reaction heat exchange zone 42. Multiple guide tubes simultaneously circulate with the second heat transfer system 7. The second heat transfer system 6 is located outside the second fluidization device 4. A heat transfer source, such as oil or molten salt, circulates in the second heat transfer system 7. The second heat transfer system 7 is used to simultaneously introduce the heat transfer source to the bottom of the multiple guide tubes. After entering the multiple guide tubes, the heat source can flow inside the multiple guide tubes; and is discharged through the top of the guide tubes and returned to the second heat carrier system 7; realizing the circulation of the heat source within the multiple guide tubes, relative to the stationary heating heat source; the circulating heat source can improve the heat exchange effect with the ammonia and catalyst flowing in the second reaction heat exchange zone 42; thereby promoting the efficient heat absorption of ammonia and catalyst and the decomposition of ammonia; preferably; a heat carrier control valve is provided between the second heat carrier system 7 and the guide tubes; used to control the flow rate of the heat source entering the guide tubes; thereby controlling the heating effect on ammonia.

[0034] One end of the second reaction heat exchange zone 42 relative to the second gas distribution zone 41 is connected to the second settling zone 43; the cross-sectional area of ​​the second settling zone 43 is larger than that of the second reaction heat exchange zone 42; the second settling zone 43 is provided with a second feed port, a second filter 44, and a second guide pipe 45; wherein the second feed port is located on the side wall of the second settling zone 43; the catalyst is introduced into the second settling zone 43 through the second feed port, thereby improving the catalytic effect and fluidization state of ammonia, and achieving control and adjustment of ammonia catalysis and gas fluidization state; wherein, the hydrogen-nitrogen mixture obtained by the endothermic decomposition of ammonia, discharged from the second reaction heat exchange zone 42, carries the catalyst particles into the top-expanded second settling zone 43, and the hydrogen-nitrogen mixture is discharged from the second settling zone 43 after separation from the catalyst, while the catalyst slowly descends along the annular gap region under the action of gravity; during the descent, the catalyst undergoes efficient heat exchange with the built-in guide pipe (through which a heat source, such as oil or molten salt, is introduced), and is reheated to the reaction heat exchange zone 43. After reaching the required temperature, the gas circulates back to the bottom and re-enters the second reaction heat exchange zone 42 to participate in the ammonia decomposition catalytic reaction. This design organically couples the reaction, catalyst heating, and circulation flow within the same device, resulting in a compact structure and extremely high thermal efficiency. The second filter 44 is located near the top of the second settling zone 43. The second filter 44 has a mesh structure and separates the mixed gas from the trapped catalyst particles through filtration. The separated hydrogen-nitrogen mixed gas is discharged through the second filter 44 and then discharged from the second settling zone 43 through the second guide pipe 45 located at the top of the second settling zone 43. The separated catalyst falls to the second filter 44 under the obstruction of the second filter 44 and enters the second reaction heat exchange zone 42, which is connected to the bottom of the second filter 44. It then enters the cavity of the second reaction heat exchanger 42 and continues to form a fluidized state in the second reaction heat exchange zone 42 under the action of ammonia introduced through the second gas distribution zone 41.

[0035] After separation, the hydrogen-nitrogen mixture is discharged from the second guide pipe 45 at the top of the second settling zone 43 and then enters the second gas-solid separator 46 connected to the second guide pipe 45 for gas-solid separation to remove small amounts of catalyst particles that have not been fully filtered from the gas, thereby further improving the purity of the discharged hydrogen-nitrogen mixture. The separated catalyst is discharged from the bottom of the second gas-solid separator 46 and enters the second connecting pipe 47 connected to the bottom of the second reaction heat exchange zone 42. The end of the second connecting pipe 47 connected to the second gas-solid separator 46 has a U-shaped bend structure. Through the U-shaped bend structure at the end of the second connecting pipe 47, a certain amount of separated catalyst is maintained in this part during the gas-solid separation process. The recovered catalyst prevents gas backflow and improves catalyst recovery. The separated catalyst enters the bottom of the second reaction heat exchange zone 42 through the second connecting pipe 47. It continues to react with the ammonia gas introduced from the second gas distribution zone 41 and promotes its decomposition, improving the fluidization effect inside the second reaction heat exchange zone 42 and also realizing the recycling of the catalyst. This improves the system energy utilization rate. The end of the second gas-solid separator 46 used for gas discharge is connected to the first heat exchanger 10. The hydrogen-nitrogen mixture discharged from the second gas-solid separator 46 serves as the heat source in the first heat exchanger 10. It exchanges heat with the introduced ammonia gas, thereby heating the introduced ammonia gas while reducing the temperature of the gas from the second gas distribution zone 41. The temperature of the hydrogen-nitrogen mixture discharged from the gas-solid separator 46; after heat exchange, the hydrogen-nitrogen mixture is discharged from the first heat exchanger 10 and directly enters the vacuum supply unit 8; the vacuum supply unit 8 includes a vacuum pump 81 and a vacuum regulating valve 82; the vacuum pump 81 is connected to the gas outlet of the second gas-solid separator 46 through the vacuum regulating valve 82; the vacuum pump 81 performs unified evacuation of the second fluidizing device 4 and the first fluidizing device 2 connected in series; negative pressure is formed in the second fluidizing device 4 and the first fluidizing device 2 respectively, thereby forming a vacuum structure respectively; by adjusting the relative pressure between the second fluidizing device 4 and the first fluidizing device 2 and the vacuum pump 81... Distance; combined with the unified evacuation of the first fluidizing device 2 and the second fluidizing device 4 by the vacuum pump 81; different degrees of vacuum are formed inside the first fluidizing device 2 and the second fluidizing device 4; combined with the catalyst loading amount and ammonia flow rate inside different devices, the ammonia decomposition effect inside each device is adjusted and controlled; thereby achieving comprehensive regulation of catalyst loading amount, gas flow rate and gas pressure; to control the overall ammonia decomposition effect, the hydrogen-nitrogen mixture discharged from the second gas-solid separator 46 enters the vacuum pump 81; that is, by uniformly evacuating the hydrogen-nitrogen mixture, the negative pressure effect of different fluidizing devices is achieved; the hydrogen-nitrogen mixture extracted and discharged from the vacuum pump 81 is finally discharged from the vacuum pump 81 and used for subsequent applications.Specifically, the outlet of the second fluidization device 4 is equipped with a cooler, which is connected to the second gas-solid separator 46; the cooling medium is water or other refrigerant, and the cooling temperature is controlled at 50-80℃; the vacuum pump is a liquid ring vacuum pump or a dry oil-free vacuum pump, and the operating pressure is controlled at -0.09 to -0.05 MPa according to the system control pressure selection, and the pressure control is achieved through frequency conversion regulation.

[0036] The system consists of two independently configured fluidized bed units connected in series. Ammonia gas sequentially passes through each fluidized bed's reaction zones, including a gas distribution zone, a reaction heat exchange zone, and a settling zone. By connecting pipes at the bottom of the settling and reaction heat exchange zones, combined with the separation function of a gas-solid separator, controllable catalyst flow and bed height maintenance between stages are achieved. An enlarged settling section is designed at the top of the reactor. By reducing the gas velocity, entrained catalyst particles initially settle under gravity and return to the bed, thus achieving a near-plug flow material distribution overall, effectively overcoming the severe backmixing problem of single-stage fluidized beds. The system uses an oil-free dry vacuum pump to avoid corrosion and fluctuations caused by ammonia dissolving in the working fluid, improving the system's stability and reliability. A unified vacuum supply unit provides uniform adsorption for the series-connected fluidized bed units, achieving a step-by-step reduction in fluidization at each stage. This ensures the reaction is always in an optimized negative pressure environment. A gas distribution plate at the bottom of each reactor stage is used to break up bubbles and regulate the gas flow, ensuring uniform and stable gas-solid contact over a wide pressure range. The fluidized bed is internally arranged with guide pipes (through which high-temperature heat transfer oil or molten salt is introduced) to provide the necessary heat for the strongly endothermic reaction while maintaining a uniform bed temperature. Furthermore, internal components within each fluidized bed optimize the gas-solid contact path, extending the residence time of the gas in the reaction zone and ensuring complete ammonia decomposition. Each reactor stage is equipped with a filter at the top, such as a high-efficiency cyclone separator, to capture fine catalyst particles entrained by the gas and return them to the bed via connecting pipes, significantly reducing catalyst loss and protecting downstream vacuum equipment. The backmixing process of the high-temperature catalyst particles also preheats the newly introduced ammonia, enabling cascade utilization of the reaction heat and further improving energy efficiency and overall conversion rate; more specifically, the product conversion rate of the first fluidized bed 2 is >95%, and the product conversion rate of the second fluidized bed 4 is >99%.

[0037] This application also discloses a control method for a multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system, including the following steps: Step 1: Introduce ammonia into the first gas distribution zone at the bottom of the first fluidization device through the ammonia supply unit; when the ammonia flow rate in the first gas distribution zone reaches the critical fluidization rate; introduce the ammonia in the first gas distribution zone into the first reaction heat exchange zone; Step 2: Ammonia gas drives the catalyst in the first reaction heat exchange zone to move and enter the fluidized state, heating the first reaction heat exchange zone; in the first reaction heat exchange zone, ammonia gas decomposes into a hydrogen-nitrogen mixture; Step 3: The second fluidizing device is directly drawn in through the vacuum supply unit, which drives the connected first fluidizing device to form a negative pressure environment in both the first and second fluidizing devices; the hydrogen-nitrogen mixture in the first reaction heat exchange zone enters the first settling zone; and enters the second gas distribution zone at the bottom of the second fluidizing device through the first settling zone. Step 4: When the hydrogen-nitrogen mixture in the second gas distribution zone reaches the critical fluidization velocity, the hydrogen-nitrogen mixture in the second gas distribution zone is introduced into the second reaction heat exchange zone; the hydrogen-nitrogen mixture drives the catalyst in the second reaction heat exchange zone to move and enter the fluidization state; Step 5: Heat the second reaction heat exchange zone, where ammonia in the hydrogen-nitrogen mixture decomposes into a hydrogen-nitrogen mixture; Step 6: Introduce the hydrogen-nitrogen mixture in the second reaction heat exchange zone into the second settling zone; after passing through the second settling zone, the hydrogen-nitrogen mixture exchanges heat with the ammonia introduced through the ammonia supply unit; after heat exchange, the hydrogen-nitrogen mixture is collected or used.

[0038] In steps one through three, ammonia gas is preheated to 400°C before entering the first gas distribution zone. The first fluidizing device maintains a relatively low operating vacuum (e.g., -0.05 to -0.06 MPa), and the bed temperature is controlled within a high-temperature range of 400 to 450°C to ensure a total ammonia conversion rate of over 95%. Ammonia gas comes into intense contact with the fluidized catalyst, achieving initial decomposition. Under a high-concentration ammonia atmosphere, the reaction is rapidly initiated using high-temperature conditions, effectively reducing the ammonia partial pressure. As the initial reactor for ammonia decomposition, the first fluidizing device undertakes most of the cracking task, loaded with a highly active and high-strength catalyst to ensure overall reaction efficiency. The first fluidizing device is mainly heated by heat transfer oil, molten salt, or electric heating. The heat load occupied by the first fluidizing device accounts for 60-70% of the total heat load. The outlet of the first fluidizing device is connected to the second fluidizing device, and the connecting pipe is equipped with insulation and heat tracing structures. The inlet of the second fluidizing device is equipped with an intermediate heater for supplemental heating to maintain the reaction temperature.

[0039] In steps four through six, unreacted ammonia gas from the outlet of the first fluidizing unit, along with some products, enters the second fluidizing unit. In the second fluidizing unit, the vacuum level is further increased (e.g., -0.08 to -0.09 MPa), and the bed temperature is controlled at a medium-high level (350–400°C). Since the inlet ammonia concentration has been significantly reduced, the partial pressures of the product hydrogen and nitrogen are relatively high. By increasing the vacuum level, the thermodynamic equilibrium of this stage is forcibly broken, driving the reaction continuously towards decomposition. The ammonia partial pressure is pulled to an extremely low level, ensuring that the total ammonia conversion rate reaches over 99%. The second fluidizing unit, as a refining reactor, focuses on "deep purification," specifically treating residual ammonia gas to achieve the final high-efficiency conversion.

[0040] The high-temperature hydrogen-rich gas from the final stage outlet enters a filter and a gas-solid separator. After gas-solid separation, the purified hydrogen / nitrogen mixture enters the subsequent heat exchanger and vacuum unit. The vacuum unit continuously extracts the product gas and delivers it to the hydrogen-using unit or storage unit, completing the entire process.

[0041] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system, comprising an ammonia supply unit; a first fluidized bed reactor, a second fluidized bed reactor, and a vacuum supply unit; characterized in that: The ammonia supply unit is connected to the gas distribution area at the bottom of the first fluidized bed reactor and is used to supply ammonia to the first fluidized bed reactor; The first fluidizing device includes a first gas distribution zone, a first reaction heat exchange zone, and a first settling zone; the first gas distribution zone is located at the bottom of the first fluidizing device; the first reaction heat exchange zone is located above and communicates with the first gas distribution zone; the first reaction heat exchange zone is filled with a catalyst; the bulk density of the catalyst is 0.8–1.1 g / cm³. 3 The catalyst has a particle density of 2.0–2.5 g / cm³. 3； The flow rate of the gas entering the first reaction heat exchange zone from the first gas distribution zone is greater than the minimum fluidization velocity of the gas; the other end of the first reaction heat exchange zone is connected to the first settling zone; the cross-sectional area of ​​the first settling zone is greater than the cross-sectional area of ​​the first reaction heat exchange zone and is used to separate the gas from the catalyst; the first settling zone is connected to the bottom of the second fluidization device. The second fluidizing device includes a second gas distribution zone, a second reaction heat exchange zone, and a second settling zone; the second gas distribution zone is located at the bottom of the second fluidizing device; the second reaction heat exchange zone is located above the second gas distribution zone and communicates with it; the catalyst is filled inside the second reaction heat exchange zone; the flow rate of the gas entering the second reaction heat exchange zone from the second gas distribution zone is greater than the minimum fluidization velocity of the gas; the other end of the second reaction heat exchange zone is used to discharge the hydrogen-nitrogen mixture and is connected to the vacuum supply unit; the vacuum supply unit is used to evacuate the gas from the first fluidizing device and the second fluidizing device and to create a negative pressure environment in the first fluidizing device and the second fluidizing device, respectively.

2. The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to claim 1, characterized in that: The ammonia supply unit includes an ammonia tank, a first heat exchanger, an ammonia flow meter, an ammonia control valve, and an ammonia heater; the ammonia tank is connected to the first heat exchanger; the first heat exchanger is connected in sequence to the ammonia flow meter, the ammonia control valve, and the ammonia heater; the ammonia heater is connected to the first gas distribution zone; the ammonia temperature after being heated by the ammonia heater is 350-400℃.

3. The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to claim 1, characterized in that: The first gas distribution zone has a trapezoidal cross-sectional shape; the cross-sectional area of ​​the end of the first gas distribution zone connected to the ammonia heater is smaller than the cross-sectional area of ​​the end of the first gas distribution zone connected to the first reaction heat exchange zone; a first gas distributor is fixed laterally within the first gas distribution zone; and a through hole is provided on the first gas distributor. The cross-sectional shape of the second gas distribution zone is trapezoidal; the cross-sectional area of ​​the end of the second gas distribution zone connected to the first fluidizing device is smaller than the cross-sectional area of ​​the end of the second gas distribution zone connected to the second reaction heat exchange zone; a second gas distributor is fixed laterally within the second gas distribution zone; and a through hole is provided on the second gas distributor. A first gas distribution plate is horizontally arranged at one end of the first reaction heat exchange zone that communicates with the first gas distribution zone; a second gas distribution plate is horizontally arranged at one end of the second reaction heat exchange zone that communicates with the second gas distribution zone; the particle size range of the catalyst is 50-100 μm; a pressure measuring point is arranged below the first gas distribution plate; a pressure measuring point is arranged below the second gas distribution plate.

4. The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to claim 1, characterized in that: The ratio of the height to the diameter of the first reaction heat exchange zone is 2 to 4; the expansion ratio of the first fluidizing device is 1 to 3; the orifice ratio of the first gas distributor is 0.5 to 2.5%; differential pressure sensors are respectively installed at the upper and lower ends of the first reaction heat exchange zone; temperature detection points are provided at the bottom and middle of the first fluidizing device; the temperature of the first reaction heat exchange zone is 400 to 450°C; multiple thermocouples are arranged at different heights and at different radial positions at the same height in the first reaction heat exchange zone. The ratio between the height and diameter of the second reaction heat exchange zone is 2 to 4; the expansion ratio of the second fluidizing device is 1 to 3; the orifice ratio of the second gas distributor is 0.5 to 2.5%; differential pressure sensors are respectively installed at the upper and lower ends of the second reaction heat exchange zone; temperature detection points are provided at the bottom and middle of the second fluidizing device; the temperature of the second reaction heat exchange zone is 400 to 450°C; and multiple thermocouples are arranged at different heights and at different radial positions at the same height in the second reaction heat exchange zone.

5. The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to claim 1, characterized in that: Multiple guide tubes are vertically arranged inside the first reaction heat exchange zone; the guide tubes are vertical structures and penetrate through the first reaction heat exchange zone; the multiple guide tubes simultaneously circulate with the first heat carrier system; the first heat carrier system is located outside the first fluidization device; a heat transfer source circulates in the first heat carrier system; a heat transfer control valve is provided between the first heat carrier system and the guide tubes. Multiple guide tubes are vertically arranged inside the second reaction heat exchange zone; the guide tubes are vertical structures and penetrate through the second reaction heat exchange zone; the multiple guide tubes are simultaneously circulated with the second heat transfer system; the second heat transfer system is located outside the second fluidization device; a heat transfer heat source circulates in the second heat transfer system; a heat transfer control valve is provided between the second heat transfer system and the guide tubes.

6. The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to claim 1, characterized in that: The cross-sectional area of ​​the first settling zone is larger than that of the first reaction heat exchange zone; the first settling zone is provided with a first feed inlet, a first filter, and a first guide pipe; the first feed inlet is located on the side wall of the first settling zone; the first filter is located near the top of the first settling zone; the first filter has a mesh structure; the first guide pipe is located at the top of the first settling zone; the first guide pipe is connected to a first gas-solid separator located outside the first settling zone; the bottom of the first gas-solid separator is connected to a first connecting pipe; the first connecting pipe is then connected to the bottom of the first reaction heat exchange zone. The cross-sectional area of ​​the second settling zone is larger than that of the second reaction heat exchange zone; the second settling zone is provided with a second feed inlet, a second filter, and a second guide pipe; the second feed inlet is located on the side wall of the second settling zone; the second filter is located near the top of the second settling zone; the second filter has a mesh structure; the second guide pipe is located at the top of the first settling zone; the second guide pipe is connected to a second gas-solid separator located outside the second settling zone; the bottom of the second gas-solid separator is connected to a second connecting pipe; the second connecting pipe is then connected to the bottom of the first reaction heat exchange zone.

7. The multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to claim 1, characterized in that: The outlet of the second fluidizing device is equipped with a cooler; the cooler is connected to the second settling zone and the ammonia supply unit; the vacuum supply unit includes a vacuum pump and a vacuum regulating valve; the vacuum pump is connected to the second fluidizing device through the vacuum regulating valve; a cooling medium flows through the cooler, and the temperature of the cooler is 50 to 80°C; the operating pressure range of the vacuum pump is -0.09 to -0.05 MPa.

8. A control method for a multi-stage negative pressure ammonia decomposition fluidized bed hydrogen production system according to any one of claims 1 to 7, comprising the following steps: Step 1: Introduce ammonia into the first gas distribution zone at the bottom of the first fluidization device through the ammonia supply unit; when the ammonia flow rate in the first gas distribution zone reaches the critical fluidization rate; introduce the ammonia in the first gas distribution zone into the first reaction heat exchange zone; Step 2: Ammonia gas drives the catalyst in the first reaction heat exchange zone to move and enter the fluidized state, heating the first reaction heat exchange zone; in the first reaction heat exchange zone, ammonia gas decomposes into a hydrogen-nitrogen mixture; Step 3: The second fluidizing device is directly drawn in through the vacuum supply unit, which drives the first fluidizing device connected to it to form a negative pressure environment in both the first and second fluidizing devices; the hydrogen-nitrogen mixture in the first reaction heat exchange zone enters the first settling zone; and enters the second gas distribution zone at the bottom of the second fluidizing device through the first settling zone. Step 4: When the hydrogen-nitrogen mixture in the second gas distribution zone reaches the critical fluidization velocity, the hydrogen-nitrogen mixture in the second gas distribution zone is introduced into the second reaction heat exchange zone; the hydrogen-nitrogen mixture drives the catalyst in the second reaction heat exchange zone to move and enter the fluidization state; Step 5: Heat the second reaction heat exchange zone, where the ammonia in the hydrogen-nitrogen mixture decomposes into a hydrogen-nitrogen mixture; Step 6: Introduce the hydrogen-nitrogen mixture in the second reaction heat exchange zone into the second settling zone; after passing through the second settling zone, the hydrogen-nitrogen mixture exchanges heat with the ammonia introduced through the ammonia supply unit; after heat exchange, the hydrogen-nitrogen mixture is collected or used.

9. The control method according to claim 8, characterized in that: In steps one through three, ammonia gas is preheated to 400°C and then enters the first gas distribution zone; the first fluidizing device maintains an operating vacuum of -0.05 to -0.06 MPa, the temperature of the first reaction heat exchange zone is controlled at 400 to 450°C, and the minimum conversion rate of ammonia gas in the first reaction heat exchange zone is 95%; the heat load occupied by the first fluidizing device is 60 to 70% of the total heat load.

10. The control method according to claim 8, characterized in that: In steps four to six, the vacuum level in the second fluidization device is maintained at -0.08 to -0.09 MPa, the temperature in the second reaction heat exchange zone is controlled at 350 to 400°C, and the minimum ammonia conversion rate in the second reaction heat exchange zone is 99%.

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