A method for producing hydrogen by microwave plasma decomposition of ammonia

Abstract

This invention provides a method for producing hydrogen from ammonia via microwave plasma decomposition, belonging to the field of new energy technology. This method is based on a hydrogen production system. First, ammonia is introduced into the microwave plasma discharge center and afterglow region for decomposition to obtain hydrogen. Heat loss is reduced by arranging an insulation layer on the outer wall of the reaction buffer chamber, or by placing it inside a thermocatalytic reactor. The heat from the carrier gas is used for co-heating the reactor through heat conduction from the metal cavity wall of the reaction buffer chamber. Simultaneously, a gas heat exchange system is used to preheat the ammonia to be decomposed, further reducing system heat loss. Finally, the hydrogen is separated and collected. This invention introduces ammonia into the microwave plasma discharge center and afterglow region, which can fully ensure discharge stability and effectively improve hydrogen yield and microwave energy utilization. Furthermore, it can reduce the cost of plasma hydrogen production and effectively alleviate the problems of thermocatalytic decomposition hydrogen production not being able to achieve "instant production" and high energy loss. Experiments have shown that this invention can be scaled up to actual industrial applications.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology and relates to a plasma hydrogen production method, specifically a method for producing hydrogen by microwave plasma decomposition of ammonia. Background Technology

[0002] Currently, hydrogen energy, as one of the most promising secondary energy sources in the 21st century, plays a crucial role in addressing the energy crisis. However, the commercial application of hydrogen in the energy sector is severely limited by storage and transportation. Adhering to the principle of "on-demand production," supplying hydrogen through the decomposition of liquid hydrogen carriers at distributed hydrogen refueling stations or in mobile vehicles can effectively reduce the cost and risk of hydrogen storage. Ammonia, as a highly efficient hydrogen carrier, can be stored in the liquid phase at room temperature and medium pressure, possessing high hydrogen storage capacity (17.7 wt.%) and high energy density (3000 Wh / kg). Furthermore, ammonia, as a renewable energy source, can be produced on a large scale industrially using the Haber process at low cost. The ammonia decomposition process requires relatively low heat, with an enthalpy change of only 91.2 kJ / mol, and produces only hydrogen and nitrogen, achieving 100% "zero-carbon" hydrogen production. However, due to its very high activation energy barrier, the reaction rate is slow and requires temperatures above 400°C. Therefore, developing an effective ammonia decomposition hydrogen production technology is of great significance.

[0003] In recent years, many researchers both domestically and internationally have studied methods for hydrogen production through ammonia decomposition. Examples include the thermocatalytic method reported in patents CN116924327A, CN 116899584 A, and CN 219751920 U; the electrolytic method reported in CN110273161B and CN 218115612 U; and the plasma method reported in CN 116850915 A, CN116854033A, and CN 115684423 A. Among these, the plasma method offers advantages such as small equipment size, low cost, instantaneous start-up and shutdown, and no need for additional heating. Plasma contains high molecular energy, intense thermal motion, and a large number of active species and high-energy particles. Therefore, it can break the chemical bonds of ammonia molecules through energy transfer via collisions, enabling physicochemical reactions that are impossible in traditional processes. This alters the chemical equilibrium and increases the conversion rate of ammonia.

[0004] Currently, the plasma discharge modes applied to ammonia decomposition are mainly dielectric barrier discharge (DBD) and sliding arc discharge (SAD). For example, patent publication CN 116850915 A discloses a method for producing hydrogen from ammonia by using a dielectric barrier discharge plasma in conjunction with a catalyst. By employing a supported catalyst with active metal components, the ambient temperature required for ammonia decomposition can be reduced, thus decreasing the system's energy consumption. Patent publication CN 116854033 A provides a device for producing hydrogen from ammonia using a coaxial dielectric barrier discharge plasma in conjunction with a proton exchange membrane. By combining packed bed DBD plasma, ammonia decomposition, and membrane separation, the efficiency of ammonia-to-hydrogen production can be improved, and hydrogen can be effectively separated. In addition, a sliding arc discharge plasma decomposition system for producing hydrogen from ammonia, reported in the journal article Energy Technol. (2021) 9, 2100677, achieves an ammonia conversion rate of up to 70% at an ammonia flow rate of 0.15 SLM. However, in these reports, the hydrogen production per unit time is very low due to the limitation of ammonia feed rate caused by its discharge characteristics, making it difficult to meet the actual demand for hydrogen energy supply. It is worth noting that patent CN207070436U discloses a dual-cavity excited atmospheric pressure microwave plasma torch, demonstrating that the plasma torch (MPT) has advantages such as no need for driving electrodes, high energy density, a large number of active species, and a large working gas flow rate, enabling the scaling up of plasma hydrogen production technology to practical industrial applications. Currently, MPT has been developed for producing hydrogen from various hydrogen carriers. For example, publication CN114852962B reports a system for producing hydrogen by injecting liquid ethanol into the afterglow zone of an MPT using a nozzle; publication CN113401868B provides an apparatus for producing hydrogen by decomposing industrial byproducts (H2S) using an MPT combined with a cooling reaction buffer chamber; and publication KR 102588840B1 develops an apparatus and method for producing hydrogen using an MPT to reform plastic waste. Therefore, MPT is a very promising practical hydrogen production device. However, as an emerging technology, there are currently no reports on the MPT ammonia decomposition hydrogen production method.

[0005] Based on the above hydrogen production technologies and implementation plans, the following main problems exist in the current ammonia decomposition hydrogen production methods: (1) Traditional thermocatalytic methods have practical problems such as long preheating time and high energy consumption; (2) The current plasma method cannot meet the actual industrial demand for hydrogen production per unit time; (3) Microwave plasma decomposition of ammonia is a promising method, but as an emerging technology, there are currently no relevant reports. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, a method for producing hydrogen by microwave plasma decomposition of ammonia is provided.

[0007] The technical solution adopted in this invention is:

[0008] A method for producing hydrogen from ammonia by microwave plasma decomposition is disclosed. The method is based on a hydrogen production system, which includes a microwave plasma system 1, a reactor 2, a gas delivery system 3, a gas flow control system 4, a heat exchange system 5, a gas separation system 6, and a gas storage system 7. The method involves introducing ammonia into the microwave plasma discharge center and afterglow region for decomposition to obtain hydrogen. During the decomposition process, heat loss is reduced by arranging an insulation layer on the outer wall of the reaction buffer chamber, or by placing it inside a thermocatalytic reactor, where the heat from the carrier gas is used for heat conduction through the metal cavity wall of the reaction buffer chamber to synergistically heat the reactor. Simultaneously, a gas heat exchange system is used to preheat the ammonia to be decomposed, further reducing system heat loss. Finally, the hydrogen is separated and collected. This combination of methods, with their complementary advantages, effectively improves hydrogen production and microwave energy utilization, and alleviates the practical problems of long preheating times and high energy consumption associated with thermocatalytic methods. It also maintains the characteristics of rapid system reaction and quick start-up and shutdown, making it well-suited for use with renewable energy power generation systems such as solar and wind power.

[0009] A method for producing hydrogen by microwave plasma decomposition of ammonia, comprising the following specific steps:

[0010] Step 1: Turn on the gas delivery system 3, and introduce the working carrier gas into the discharge tube 12 of the microwave plasma system 1 in a vortex flow manner through the gas flow control system 4. Control the ignition device 11 to provide seed electrons, and turn on the microwave power. Under the excitation of microwave power, the working carrier gas forms a microwave plasma torch in the discharge tube 12 and extends sequentially into the mixing chamber 14 and the reaction buffer chamber 16. Preferably, the working carrier gas is selected from at least one of nitrogen and argon or a mixture of both, the gas flow rate is selected from 5 to 200 SLM, and the microwave discharge power of the microwave plasma system 1 is selected from 1 to 10 kW.

[0011] Step 2: A portion of the ammonia gas is introduced into the discharge tube 12 via the airflow control system 4 in a vortex airflow manner, while the other portion of the ammonia gas is introduced into the plasma afterglow region through the inlet of the mixing chamber 14. Preferably, the total ammonia gas flow rate is selected as 10-100 SLM, and the ammonia gas introduced into the discharge tube 12 is selected as 0-50 SLM. Preferably, the number of inlets in the mixing chamber 14 is selected as 2-4, and the inclination angle θ between the central axis of each inlet and the side wall of the mixing chamber 14 is selected as 30°-150°.

[0012] Step 3: Install a heat insulation layer on the outer wall of the reaction buffer chamber 16, or place the outer wall of the reaction buffer chamber 16 inside the reaction chamber 21 of the thermocatalytic ammonia decomposition reactor 2. Turn on the reactor 2, and introduce ammonia gas into the first inlet 51 of the heat exchange system 5 via the airflow control system 4. The outlet gas of the reaction buffer chamber 16 is introduced into the second inlet 54 of the heat exchange system 5. After heat exchange in the heat exchange system 5, the gas entering through the first inlet 51 and the second inlet 54 is introduced into the gas separation system 6 and the reactor 2 through the first outlet 52 and the second outlet 53, respectively. The outlet gas of the reactor 2 is introduced into the second inlet 54 of the heat exchange system 5. Preferably, the heat insulation layer is selected as vacuum insulation or wrapped with high-temperature resistant quartz wool. Preferably, the reactor 2 is a high-temperature tubular furnace, and the internal catalyst is selected as Ni / Al2O3.

[0013] Step 4: Open the gas separation system 6 to separate the hydrogen, nitrogen, argon and undecomposed ammonia in the mixed gas and collect them through the gas storage system 7.

[0014] The hydrogen production system is as follows:

[0015] In step one, the microwave plasma system 1 includes an ignition device 11, a discharge tube 12, a gradient-section waveguide 13, a mixing chamber 14, a first flange 15, a reaction buffer chamber 16, and a second flange 17. The ignition device 11 is located at the bottom of the discharge tube 12 and can insert a tungsten filament electrode deep into the discharge tube 12 to provide seed electrons. The first flange 15 is embedded at one end of the surface of the gradient-section waveguide 13. The discharge tube 12 extends vertically into the slot of the first flange 15 and passes through the gradient-section waveguide 13. One end of the discharge tube 12 extends into the mixing chamber 14, and the other end is connected to the airflow control system 4. The length of the discharge tube 12 can be adjusted according to the required plasma torch shape and the structure of the mixing chamber 14. One end of the mixing chamber 14 is connected to the gradient-section waveguide 13 via the first flange 15, and the other end is connected to the reaction buffer chamber 16 via the second flange 17. The other end of the reaction buffer chamber 16 is connected to the second air inlet 54 of the heat exchange system 5. The mixing chamber 14 has multiple air inlets distributed on its sidewalls, allowing for thorough mixing of the introduced gas with the plasma afterglow region. The air inlets on the sidewalls of the mixing chamber 14 are connected to the airflow control system 4. The outer wall of the reaction buffer chamber 16 is reinforced with an insulation layer, or the reaction buffer chamber 16 is placed inside the reactor 2. Preferably, the inclination angle θ between the central axis of the air inlets on the sidewalls of the mixing chamber 14 and the sidewall is selected as 30°–150°, and the number of air inlets is selected as 2–4. Preferably, the reaction buffer chamber 16 has a cylindrical structure with an outer diameter of 20–200 mm, a height of 100–2000 mm, and a wall thickness of less than 30 mm. Preferably, the mixing chamber 14 can be dismantled as needed, and after dismantling, the reaction buffer chamber 16 is directly connected to the cross-section tapered waveguide 13 via the first flange 15.

[0016] In step two, the input end of the airflow control system 4 is connected to the airflow delivery system 3. The airflow control system 4 has three output ends: the first output end is connected to the discharge tube 12, which can adjust the working gas flow rate and send nitrogen, argon, and ammonia into the discharge tube 12 in a vortex airflow manner; the second output end is connected to the air inlet of the mixing chamber 14, which can adjust the working gas flow rate and send ammonia into the mixing chamber 14; the third output end is connected to the first air inlet 51 of the heat exchange system 5, which can adjust the working gas flow rate and send ammonia into the heat exchange system 5.

[0017] In step three, the reactor 2 includes a reaction chamber 21, a feed channel 22, and a discharge channel 23. The reaction chamber 21 is coaxially connected to the reaction buffer chamber 16, and the space between the outer walls of the reaction chamber 21 and the reaction buffer chamber 16 is filled with an ammonia decomposition catalyst. The feed channel 22 and the discharge channel 23 are respectively connected to both ends of the reaction chamber 21. The other end of the feed channel 22 is connected to the second air outlet 53 of the heat exchange system 5. The other end of the discharge channel 23 is connected to the second air inlet 54 of the heat exchange system 5.

[0018] In step four, one end of the gas separation system 6 is connected to the first outlet 52 of the heat exchange system 5, and the other end is connected to the gas storage system 7. The gas separation system 6 can separate nitrogen, hydrogen, argon and ammonia, and send them to nitrogen cylinder 71, hydrogen cylinder 72, argon cylinder 73 and ammonia cylinder 74 in the gas storage system 7 for storage.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention provides a method for hydrogen production by microwave plasma decomposition of ammonia. By introducing ammonia gas into the microwave plasma discharge center and afterglow region, discharge stability is fully guaranteed, effectively improving hydrogen yield and microwave energy utilization. Furthermore, by implementing an insulation layer on the outer wall of the reaction buffer chamber or placing it inside a thermocatalytic reactor to effectively utilize the Joule heat in the gas, the cost of plasma hydrogen production can be reduced, and the problems of "instantaneous production" and high energy loss in thermocatalytic decomposition hydrogen production can be effectively alleviated. Experiments have demonstrated that this invention can be scaled up to actual industrial applications, achieving an effective combination of economic benefits and meeting practical needs. Attached Figure Description

[0021] Figure 1 This is a block diagram of a system for producing hydrogen by decomposing ammonia using microwave plasma.

[0022] Figure 2 This is a schematic diagram of the distribution of the microwave plasma system and the reactor.

[0023] In the diagram: 1. Microwave plasma system, 2. Reactor, 3. Gas delivery system, 4. Gas flow control system, 5. Heat exchange system, 6. Gas separation system, 7. Gas storage system.

[0024] 11 Ignition device, 12 Discharge tube, 13 Gradual cross-section waveguide, 14 Mixing chamber, 15 First flange, 16 Reaction buffer chamber, 17 Second flange.

[0025] 21 Reaction chamber, 22 Feeding channel, 23 Discharge channel.

[0026] 31 Nitrogen storage container, 32 Argon storage container, 33 Ammonia storage container.

[0027] 51 First air inlet, 52 First air outlet, 53 Second air outlet, 54 Second air inlet.

[0028] 71 Hydrogen storage container, 72 Nitrogen storage container, 73 Argon storage container, 74 Ammonia storage container.

[0029] Figure 3 The accompanying drawings are for Application Embodiment 1.

[0030] Figure 4 The accompanying drawings are for Application Embodiment 2.

[0031] Figure 5 The accompanying drawings are for application embodiment three. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] This invention discloses a method for producing hydrogen through microwave plasma decomposition of ammonia, based on a hydrogen production system. The hydrogen production system mainly includes: a microwave plasma system 1, a reactor 2, a gas delivery system 3, a gas flow control system 4, a heat exchange system 5, a gas separation system 6, and a gas storage system 7. The specific steps of the hydrogen production method are as follows:

[0034] Step 1: Turn on the gas delivery system 3, and introduce the working carrier gas into the discharge tube 12 of the microwave plasma system 1 in a vortex flow manner through the gas flow control system 4. Control the ignition device 11 to provide seed electrons, and turn on the microwave power. Under the excitation of microwave power, the working carrier gas forms a microwave plasma torch in the discharge tube 12 and extends sequentially into the mixing chamber 14 and the reaction buffer chamber 16. Preferably, the working carrier gas is selected from at least one of nitrogen and argon or a mixture of both, the gas flow rate is selected from 5 to 200 SLM, and the microwave discharge power of the microwave plasma system 1 is selected from 1 to 10 kW.

[0035] Step 2: A portion of the ammonia gas is introduced into the discharge tube 12 via the airflow control system 4 in a vortex airflow manner, while the other portion of the ammonia gas is introduced into the plasma afterglow region through the inlet of the mixing chamber 14. Preferably, the total ammonia gas flow rate is selected as 10-100 SLM, and the ammonia gas introduced into the discharge tube 12 is selected as 0-50 SLM. Preferably, the number of inlets in the mixing chamber 14 is selected as 2-4, and the inclination angle θ between the central axis of each inlet and the side wall of the mixing chamber 14 is selected as 30°-150°.

[0036] Step 3: Install a heat insulation layer on the outer wall of the reaction buffer chamber 16, or place the outer wall of the reaction buffer chamber 16 inside the reaction chamber 21 of the thermocatalytic ammonia decomposition reactor 2. Turn on the reactor 2, and introduce ammonia gas into the first inlet 51 of the heat exchange system 5 via the airflow control system 4. The outlet gas of the reaction buffer chamber 16 is introduced into the second inlet 54 of the heat exchange system 5. After heat exchange in the heat exchange system 5, the gas entering through the first inlet 51 and the second inlet 54 is introduced into the gas separation system 6 and the reactor 2 through the first outlet 52 and the second outlet 53, respectively. The outlet gas of the reactor 2 is introduced into the second inlet 54 of the heat exchange system 5. Preferably, the heat insulation layer is selected as vacuum insulation or wrapped with high-temperature resistant quartz wool. Preferably, the reactor 2 is a high-temperature tubular furnace, and the internal catalyst is selected as Ni / Al2O3.

[0037] Step 4: Open the gas separation system 6 to separate the hydrogen, nitrogen, argon and undecomposed ammonia in the mixed gas and collect them through the gas storage system 7.

[0038] The hydrogen production system is as follows:

[0039] In step one, the microwave plasma system 1 includes an ignition device 11, a discharge tube 12, a gradient-section waveguide 13, a mixing chamber 14, a first flange 15, a reaction buffer chamber 16, and a second flange 17. The ignition device 11 is located at the bottom of the discharge tube 12 and can insert a tungsten filament electrode deep into the discharge tube 12 to provide seed electrons. The first flange 15 is embedded at one end of the surface of the gradient-section waveguide 13. The discharge tube 12 extends vertically into the slot of the first flange 15 and passes through the gradient-section waveguide 13. One end of the discharge tube 12 extends into the mixing chamber 14, and the other end is connected to the airflow control system 4. The length of the discharge tube 12 can be adjusted according to the required plasma torch shape and the structure of the mixing chamber 14. One end of the mixing chamber 14 is connected to the gradient-section waveguide 13 via the first flange 15, and the other end is connected to the reaction buffer chamber 16 via the second flange 17. The other end of the reaction buffer chamber 16 is connected to the second air inlet 54 of the heat exchange system 5. The mixing chamber 14 has multiple air inlets distributed on its sidewalls, allowing for thorough mixing of the introduced gas with the plasma afterglow region. The air inlets on the sidewalls of the mixing chamber 14 are connected to the airflow control system 4. The outer wall of the reaction buffer chamber 16 is reinforced with an insulation layer, or the reaction buffer chamber 16 is placed inside the reactor 2. Preferably, the inclination angle θ between the central axis of the air inlets on the sidewalls of the mixing chamber 14 and the sidewall is selected as 30°–150°, and the number of air inlets is selected as 2–4. Preferably, the reaction buffer chamber 16 has a cylindrical structure with an outer diameter of 20–200 mm, a height of 100–2000 mm, and a wall thickness of less than 30 mm. Preferably, the mixing chamber 14 can be dismantled as needed, and after dismantling, the reaction buffer chamber 16 is directly connected to the cross-section tapered waveguide 13 via the first flange 15.

[0040] In step two, the input end of the airflow control system 4 is connected to the airflow delivery system 3. The airflow control system 4 has three output ends: the first output end is connected to the discharge tube 12, which can adjust the working gas flow rate and send nitrogen, argon, and ammonia into the discharge tube 12 in a vortex airflow manner; the second output end is connected to the air inlet of the mixing chamber 14, which can adjust the working gas flow rate and send ammonia into the mixing chamber 14; the third output end is connected to the first air inlet 51 of the heat exchange system 5, which can adjust the working gas flow rate and send ammonia into the heat exchange system 5.

[0041] In step three, the reactor 2 includes a reaction chamber 21, a feed channel 22, and a discharge channel 23. The reaction chamber 21 is coaxially connected to the reaction buffer chamber 16, and the space between the outer walls of the reaction chamber 21 and the reaction buffer chamber 16 is filled with an ammonia decomposition catalyst. The feed channel 22 and the discharge channel 23 are respectively connected to both ends of the reaction chamber 21. The other end of the feed channel 22 is connected to the second air outlet 53 of the heat exchange system 5. The other end of the discharge channel 23 is connected to the second air inlet 54 of the heat exchange system 5.

[0042] In step four, one end of the gas separation system 6 is connected to the first outlet 52 of the heat exchange system 5, and the other end is connected to the gas storage system 7. The gas separation system 6 can separate nitrogen, hydrogen, argon and ammonia, and send them to nitrogen cylinder 71, hydrogen cylinder 72, argon cylinder 73 and ammonia cylinder 74 in the gas storage system 7 for storage.

[0043] Application Example 1 (without mixing chamber 14):

[0044] This application provides a method for producing hydrogen by decomposing ammonia using microwave plasma, with reference to... Figure 3 The method includes the following steps:

[0045] The microwave plasma system 1 is connected to the reaction buffer chamber 16 via a flange. The reactor 2 is a high-temperature tubular furnace. The reaction buffer chamber 16 is placed inside the tubular furnace for thermocatalytic ammonia decomposition. The outer wall of the reaction buffer chamber 16 is filled with ammonia decomposition catalyst Ni / Al2O3 between it and the inner wall of the tubular furnace. The reaction buffer chamber 16 has a cylindrical structure with an outer diameter of 50 mm, a height of 400 mm, and a wall thickness of 10 mm. The discharge tube 12 is 90 mm long and extends 15 mm into the reaction buffer chamber 16. The plasma generator discharges at a microwave power of 1500 W, a working gas nitrogen flow rate of 5 SLM, and an argon flow rate of 5 SLM. Subsequently, 20 SLM of ammonia gas is introduced into the discharge tube 12 for decomposition. The decomposition products are sent from the outlet of the reaction buffer chamber 16 to the heat exchange system 5 to preheat the ammonia gas introduced into the tubular furnace. The decomposition products from the tubular furnace and the products from the reaction buffer chamber 16 are sent together to the heat exchange system 5, and then to the gas separation system 6. Hydrogen, nitrogen, argon and ammonia are extracted by gas separation system 7 and collected in gas storage cylinders.

[0046] Application Example 2 (with mixing chamber 14):

[0047] This application provides a method for producing hydrogen by decomposing ammonia using microwave plasma, with reference to... Figure 4 The method includes the following steps:

[0048] The microwave plasma system 1 is connected sequentially to the mixing chamber 14 and the reaction buffer chamber 16 via flanges. The discharge tube 12 is 80 mm long and extends 5 mm into the reaction buffer chamber 16. The mixing chamber 14 has four inlets, with two inlets positioned 10 mm from the waveguide axis and the other two positioned 30 mm from the waveguide axis. The mixing chamber 14 has four inlets, and the angle θ between the central axis of each inlet and the side wall of the reaction buffer chamber 16 is 45°. The reaction buffer chamber 16 has a cylindrical structure with an outer diameter of 40 mm, a height of 1000 mm, and a wall thickness of 10 mm. A vacuum insulation layer is added to the outer wall of the reaction buffer chamber 16. The plasma generator discharges at a microwave power of 8 kW and a working gas nitrogen flow rate of 50 SLM. Subsequently, 15 SLM of ammonia gas is introduced into the discharge tube 12, and 3 SLM of ammonia gas is introduced into each of the four inlets of the mixing chamber 14 for decomposition. The outlet gas from reaction buffer chamber 16 enters gas separation system 6. Hydrogen, nitrogen, and ammonia are extracted by gas separation system 6 and collected in gas storage cylinders.

[0049] Application Example 3 (without mixing chamber 14):

[0050] This application provides a method for producing hydrogen by decomposing ammonia using microwave plasma, with reference to... Figure 5 The method includes the following steps:

[0051] The microwave plasma system 1 is connected to the reaction buffer chamber 16 via a flange. The outer wall of the reaction buffer chamber 16 is wrapped with insulating quartz wool. The reaction buffer chamber 16 has a cylindrical structure with an outer diameter of 40 mm, a height of 1000 mm, and a wall thickness of 10 mm. The discharge tube 12 is 90 mm long and extends 15 mm into the reaction buffer chamber 16. The plasma generator discharges under the conditions of a microwave power of 5 kW, a working gas nitrogen flow rate of 30 SLM, and an argon flow rate of 10 SLM. Subsequently, 20 SLM of ammonia gas is introduced into the discharge tube 12 for decomposition. The outlet gas of the reaction buffer chamber 16 enters the gas separation system 6. Hydrogen, nitrogen, argon, and ammonia are extracted by the gas separation system 6 and collected in a gas storage cylinder.

[0052] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for producing hydrogen by microwave plasma decomposition of ammonia, characterized in that, The method described is based on a hydrogen production system, which includes a microwave plasma system (1), a reactor (2), a gas delivery system (3), a gas flow control system (4), a heat exchange system (5), a gas separation system (6), and a gas storage system (7). The method first involves introducing ammonia into the microwave plasma discharge center and afterglow region for decomposition to obtain hydrogen. Heat loss is reduced by arranging an insulation layer on the outer wall of the reaction buffer chamber, or by placing it inside a thermal catalytic reactor, where the heat from the carrier gas is conducted through the metal cavity wall of the reaction buffer chamber to heat the reactor. Simultaneously, a gas heat exchange system is used to preheat the ammonia to be decomposed, reducing system heat loss. Finally, the hydrogen is separated and collected. The specific steps of the method are as follows: Step 1: Open the air delivery system (3), and introduce the working carrier gas into the discharge tube (12) of the microwave plasma system (1) in the form of vortex airflow through the airflow control system (4). Control the ignition device (11) to provide seed electrons, turn on the microwave power supply, and the working carrier gas forms a microwave plasma torch in the discharge tube (12) under the excitation of microwave power and extends into the mixing chamber (14) and the reaction buffer chamber (16) in sequence. Step 2: A portion of ammonia gas is introduced into the discharge tube (12) via the airflow control system (4) in the form of vortex airflow, and another portion of ammonia gas is introduced into the plasma afterglow region through the air inlet of the mixing chamber (14). Step 3: Install an insulation layer on the outer wall of the reaction buffer chamber (16), or place the outer wall of the reaction buffer chamber (16) inside the reaction chamber (21) of the thermocatalytic ammonia decomposition reactor (2); turn on the reactor (2), and introduce ammonia gas into the first inlet (51) of the heat exchange system (5) through the airflow control system (4); the outlet gas of the reaction buffer chamber (16) is introduced into the second inlet (54) of the heat exchange system (5); the gas entering through the first inlet (51) and the second inlet (54) is heated in the heat exchange system (5) and then introduced into the gas separation system (6) and the reactor (2) through the first outlet (52) and the second outlet (53) respectively; the outlet gas of the reactor (2) is introduced into the second inlet (54) of the heat exchange system (5); Step 4: Open the gas separation system (6) to separate the hydrogen, nitrogen, argon and undecomposed ammonia in the mixed gas and collect them through the gas storage system (7).

2. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 1, characterized in that, In the first step, the working carrier gas is selected from at least one of nitrogen and argon or a mixture of both, and the gas flow rate is selected from 5 to 200 SLM.

3. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 1, characterized in that, In the first step, the microwave discharge power of the microwave plasma system (1) is selected to be 1 ~ 10 kW.

4. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 1, characterized in that, In the second step, the total ammonia flow rate is selected as 10 ~ 100 SLM, and the ammonia flow rate introduced into the discharge tube (12) is selected as 0 ~ 50 SLM.

5. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 1, characterized in that, In the third step, the insulation layer is selected as vacuum insulation or wrapped with high-temperature resistant quartz wool.

6. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 1, characterized in that, In the hydrogen production system described above: The microwave plasma system (1) includes an ignition device (11), a discharge tube (12), a gradient waveguide (13), a mixing chamber (14), a first flange (15), a reaction buffer chamber (16), and a second flange (17). The ignition device (11) is located at the bottom of the discharge tube (12) and can insert a tungsten wire electrode into the discharge tube (12) to provide seed electrons. The first flange (15) is embedded at one end of the surface of the gradient waveguide (13). The discharge tube (12) extends vertically into the slot of the first flange (15) and passes through the gradient waveguide (13). One end of the discharge tube (12) extends into the mixing chamber (14), and the other end is connected to the airflow control system (4). The length of the discharge tube (12) is adjusted according to the required plasma torch shape and the structure of the mixing chamber (14). 14) One end is connected to the cross-section tapered waveguide (13) through the first flange (15), and the other end is connected to the reaction buffer chamber (16) through the second flange (17); the other end of the reaction buffer chamber (16) is connected to the second air inlet (54) of the heat exchange system (5); the mixing chamber (14) has multiple air inlets distributed on the side wall of the mixing chamber (14), which can make the introduced gas fully mixed with the plasma afterglow region; the air inlets on the side wall of the mixing chamber (14) are connected to the airflow control system (4); the outer wall of the reaction buffer chamber (16) is added with a heat insulation layer, or the reaction buffer chamber (16) is placed in the reactor (2); the mixing chamber (14) can be removed as needed, and after removal, the reaction buffer chamber (16) is directly connected to the cross-section tapered waveguide (13) through the first flange (15); The input end of the airflow control system (4) is connected to the airflow delivery system (3); the airflow control system (4) has three output ends: the first output end is connected to the discharge tube (12), which can adjust the working gas flow rate and send nitrogen, argon and ammonia into the discharge tube (12) in the form of vortex airflow; the second output end is connected to the air inlet of the mixing chamber (14), which can adjust the working gas flow rate and send ammonia into the mixing chamber (14); the third output end is connected to the first air inlet (51) of the heat exchange system (5), which can adjust the working gas flow rate and send ammonia into the heat exchange system (5); The reactor (2) includes a reaction chamber (21), a feed channel (22), and a discharge channel (23); the reaction chamber (21) is coaxially connected to the reaction buffer chamber (16), and the space between the inner wall of the reaction chamber (21) and the outer wall of the reaction buffer chamber (16) is filled with an ammonia decomposition catalyst; the feed channel (22) and the discharge channel (23) are respectively connected to both ends of the reaction chamber (21); the other end of the feed channel (22) is connected to the second air outlet (53) of the heat exchange system (5); the other end of the discharge channel (23) is connected to the second air inlet (54) of the heat exchange system (5); The gas separation system (6) is connected at one end to the first outlet (52) of the heat exchange system (5) and at the other end to the gas storage system (7). The gas separation system can separate nitrogen, hydrogen, argon and ammonia and send them to the hydrogen storage container (71), nitrogen storage container (72), argon storage container (73) and ammonia storage container (74) in the gas storage system (7) for storage.

7. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 6, characterized in that, The mixing chamber (14) has 2 to 4 air inlets, and the inclination angle θ between the central axis of each air inlet on the side wall of the mixing chamber (14) and the side wall is selected as 30° to 150°.

8. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 6, characterized in that, The reactor (2) is a high-temperature tube furnace, and the internal catalyst is selected to be a single / bimetallic or carbon / nitride solid catalyst.

9. The method for producing hydrogen by microwave plasma decomposition of ammonia according to claim 6, characterized in that, The reaction buffer chamber (16) is selected as a cylindrical structure, with an outer diameter of 20 to 200 mm, a height of 100 to 2000 mm, and a wall thickness of less than 30 mm.

Images