Equipment for preparing carbon nano tube

Abstract

A device for preparing a carbon nano tube belongs to the technical field of preparation of carbon nano materials and comprises a direct-current arc plasma generating mechanism, the direct-current arc plasma generating mechanism is communicated with a radio-frequency plasma generating mechanism, the lower portion of the direct-current arc plasma generating mechanism is provided with a reducing structure which is folded firstly and then expanded, and the diameter of the reducing structure is larger than that of the radio-frequency plasma generating mechanism. The inner diameter of the waisted part of the reducing structure is D1, the inner diameter of the direct current plasma cavity is D2, the inner diameter of the radio frequency plasma cavity is D3, and the inner diameter is D1 lt; d2lt; d3, adopting a dual-discharge mode integrated structure to generate a high-temperature heat source for preparing the carbon nanomaterial, and combining the characteristics of high arc column center temperature of direct-current arc plasma and high edge temperature and low flow velocity of radio-frequency plasma; the problem of insufficient cracking caused by high gas flow speed or uneven temperature distribution in a single discharge mode can be effectively solved, so that the process flow of hydrocarbon gas cracking is greatly shortened, and the cracking efficiency and the yield and productivity of the target carbon nanomaterial are improved.

Description

Technical Field

[0001] The utility model relates to the technical field of carbon nano material preparation, in particular to a device for preparing carbon nano tubes. Background Art

[0002] Carbon nanomaterials (such as high thermal conductivity carbon black, carbon nanotubes and graphene) have excellent mechanical, mechanical, thermal and modulatable electrical properties, which makes them have significant application prospects in many fields such as new energy power batteries, electrochemical energy storage, biomedicine, electrochemical analysis and nanoelectronic devices. With the rapid development of the new energy industry, the method of preparing carbon nanomaterials by high-temperature cracking of hydrocarbon gases has also become the forefront of carbon material research.

[0003] At present, the preparation methods of carbon nanomaterials mainly include arc method, catalytic cracking CVD method, etc. The quality of carbon nanomaterials synthesized by arc method is good, but there are problems of low yield and high cost; the reaction process of preparing carbon nanomaterials by catalytic cracking CVD method is easy to control, but most of the products are easy to bend and deform, which seriously limits its large-scale application. At present, in order to improve the production quality and production efficiency of carbon nanomaterials, there are existing documents that disclose the technical solution of using plasma generated by gas discharge as a high-temperature heat source (such as publication number CN114710870A).

[0004] Most of the existing gas discharge methods are single gas discharge (such as DC arc discharge, etc.), and the method of generating high-temperature heat source is arc discharge. In order to avoid excessive arc temperature, a large amount of gas is used to purge the arc. This will cause the problem of insufficient raw material cracking reaction time due to the fast arc flow rate, resulting in low raw material conversion rate and low graphitization degree. In order to improve the conversion rate of the raw material, the prior art generally chooses to return the initially cracked raw material to the cracking furnace for multiple cracking. However, this method reduces the output of the equipment on the one hand, and wastes more energy on the other hand, ultimately resulting in high production costs and limiting its application.

[0005] In addition, the existing contact method between the cathode and the raw material is mostly direct impact, which seriously reduces the life of the cathode. Finally, the components are mostly cooled in series, the cooling of the components interferes with each other, and the temperature control distribution is uneven, which can easily affect the quality and production efficiency of the product. Utility Model Content

[0006] In order to solve the technical problem in the above background technology that a fast gas flow velocity or uneven temperature distribution in a single gas discharge mode easily leads to insufficient cracking, the utility model provides a device for preparing carbon nanotubes.

[0007] The technical solution of this utility model is as follows:

[0008] The utility model provides a device for preparing carbon nanotubes, comprising: a direct-current arc plasma generating mechanism, which is connected to a radio-frequency plasma generating mechanism. The lower part of the direct-current arc plasma generating mechanism is provided with a variable-diameter structure that first converges and then expands. The inner diameter of the converging part of the variable-diameter structure is D1, the inner diameter of the direct-current plasma chamber is D2, and the inner diameter of the radio-frequency plasma chamber is D3, where D1 < D2 < D3. An integrated structure with a dual-discharge mode is adopted to generate a high-temperature heat source for the preparation of carbon nanomaterials. Combining the characteristics of a high central temperature of the direct-current arc plasma column, a high edge temperature and a low flow rate of the radio-frequency plasma, it can effectively solve the problem of insufficient cracking caused by a relatively fast gas flow rate or uneven temperature distribution in a single-discharge mode. Thus, the technological process of cracking hydrocarbon gas is greatly shortened, the cracking efficiency, the yield and the production capacity of the target carbon nanomaterials are improved. It can be used to prepare carbon materials with a fixed arrangement such as carbon nanotubes. When preparing carbon nanotubes, especially single-walled carbon nanotubes, the primary conversion rate of the carbon source can reach more than 90%, without the need for carbon source recycling cracking, which can greatly reduce energy consumption and improve production efficiency.

[0009] The direct-current arc plasma generating mechanism includes an anode assembly. The converging part is the anode of the anode assembly. The lower part of the anode has a flared opening to form a transition zone communicating with the radio-frequency plasma generating mechanism. The converging part can increase the gas flow rate and effectively reduce the temperature of the gas around the direct-current arc plasma. The expanding part forms a transition zone communicating with the radio-frequency plasma generating mechanism, which can reduce the flow rate of the raw material gas and increase the residence time of the raw material gas in the high-temperature zone of the radio-frequency plasma generating mechanism.

[0010] The anode assembly further includes an anode water-cooling jacket. The anode is fixedly installed in the anode water-cooling jacket. An anode cooling space is formed between the outer periphery of the anode and the inner periphery of the anode water-cooling jacket for the independent cooling of the anode to accelerate the cooling rate of the anode.

[0011] The direct-current arc plasma generating mechanism includes a cathode assembly. The cathode assembly includes a cathode and an intermediate layer sleeve. At least one spiral air duct is provided on the side of the intermediate layer sleeve close to the cathode. The raw material gas enters the high-temperature zone after spiral winding. The spiral winding changes the contact mode of the raw material gas with the cathode from direct impact to circumferential winding around the surface. When the plasma reaches the cathode surface, there will be a deceleration, causing the arc spot near the cathode to rotate, reducing cathode ablation and effectively extending the service life of the cathode.

[0012] The direct-current arc plasma generating mechanism further includes a plurality of intermediate electrodes. Insulating parts and / or heat-insulating parts are provided between adjacent intermediate electrodes. The intermediate electrodes do not interfere with each other, facilitating uniform temperature control and ensuring the production quality and production efficiency of the product.

[0013] The DC arc plasma generating mechanism also includes a trigger electrode. The cathode assembly, the trigger electrode and the intermediate electrode are all provided with independent coolant inlets and outlets. The components do not interfere with each other, which facilitates uniform temperature control.

[0014] The components of the intermediate electrode, cathode assembly and anode assembly are coaxially arranged.

[0015] A cathode bushing is arranged between the cathode assembly and the trigger electrode, and the cathode bushing is made of high-temperature resistant ceramic material.

[0016] D1:D2=1:(1.1-3), preferably, D1:D2=1:(1.3-2).

[0017] D1:D3=1:(3-10), preferably, D1:D3=1:(5-8).

[0018] It can be seen from the above technical solutions that the advantages of the utility model are:

[0019] 1. The dual discharge mode integrated structure is used to generate a high-temperature heat source for the preparation of carbon nanomaterials. Combined with the characteristics of high temperature at the center of the DC arc plasma column and high temperature and low flow rate at the edge of the RF plasma, the problem of insufficient cracking caused by fast air flow velocity or uneven temperature distribution in a single discharge mode can be effectively solved, thereby greatly shortening the process flow of hydrocarbon gas cracking, improving the cracking efficiency and the yield and production capacity of the target carbon nanomaterials. It can be used to prepare carbon materials with fixed arrangement such as carbon nanotubes. When preparing carbon nanotubes, especially single-walled carbon nanotubes, the one-time conversion rate of the carbon source can reach more than 90%, and there is no need for carbon source circulation cracking, which can greatly reduce energy consumption and improve production efficiency.

[0020] 2. The lower part of the anode is expanded to form a transition zone connected to the RF plasma generating mechanism. The contraction part can increase the flow rate of the gas and effectively reduce the temperature of the gas around the DC arc plasma. The expansion part forms a transition zone connected to the RF plasma generating mechanism, which can reduce the flow rate of the raw gas and increase the residence time of the raw gas in the high temperature zone of the RF plasma generating mechanism.

[0021] 3. At least one spiral air channel is provided on the side of the intermediate layer casing close to the cathode. The raw gas enters the high-temperature zone after being spirally wound. The spiral winding changes the contact mode between the raw gas and the cathode from direct impact to winding around the surface. The plasma will be decelerated when reaching the cathode surface, causing the arc spot near the cathode to rotate, reducing cathode ablation and effectively extending the service life of the cathode.

[0022] 4. The cathode assembly, trigger electrode and intermediate electrode of the DC arc plasma generating mechanism are all equipped with independent coolant inlets and outlets, which do not interfere with each other, facilitate uniform temperature control, and ensure product quality and production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solution of the utility model, the drawings required for use in the description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1A It is a schematic diagram of the overall cross-sectional structure of a device for preparing carbon nanotubes according to one or more embodiments of the present invention;

[0025] Figure 1B A schematic diagram of the inner diameter relationship of a carbon nanotube preparation device according to one or more embodiments of the present invention;

[0026] Figure 2 It is a cross-sectional structural schematic diagram of a DC arc plasma generating mechanism according to one or more embodiments of the present invention;

[0027] Figure 3 is a schematic cross-sectional structure diagram of a cathode assembly according to one or more embodiments of the present invention;

[0028] Figure 4 It is a schematic structural diagram of a cathode water cooling jacket according to one or more embodiments of the utility model;

[0029] Figure 5 This is a schematic structural diagram of an intermediate layer casing according to one or more embodiments of the present invention;

[0030] Figure 6 is a schematic diagram of a three-dimensional cross-sectional structure of an intermediate electrode according to one or more embodiments of the present invention;

[0031] Figure 7 A schematic diagram of the flow direction of the medium inside the cathode water cooling jacket according to one or more embodiments of the utility model;

[0032] Figure 8 is a schematic cross-sectional structure diagram of a trigger electrode according to one or more embodiments of the present invention;

[0033] Fig. 9 is a schematic cross-sectional structure diagram of an intermediate electrode according to one or more embodiments of the present invention;

[0034] Fig.10 is a schematic cross-sectional structure diagram of an anode assembly according to one or more embodiments of the present invention;

[0035] Fig.11A schematic diagram of the cross-sectional structure of an anode according to one or more embodiments of the present invention;

[0036] Fig.12 It is a schematic cross-sectional structure diagram of a radio frequency plasma generating mechanism according to one or more embodiments of the present invention;

[0037] The components represented by the reference numerals in the figure are:

[0038] 1. DC arc plasma generating mechanism;

[0039] 11. cathode assembly; 111. cathode; 112. cathode fixing ring; 113. cathode insulating sleeve; 114. tightening nut; 115. fixing flange; 116. cathode water cooling jacket; 117. first cooling water inlet; 118. first cooling water outlet; 119. air inlet; 1110. spiral airway;

[0040] 12. Cathode bushing; 121. Variable diameter structure;

[0041] 13. trigger electrode; 131. second cooling water inlet; 132. second cooling water outlet; 133. first cooling space;

[0042] 14. middle electrode; 141. third cooling water inlet; 142. third cooling water outlet; 143. second cooling space;

[0043] 15. Insulation gasket; 16. Heat insulation pad;

[0044] 17, anode assembly; 171, anode water cooling jacket; 172, anode; 173, pressing ring; 174, fourth cooling water inlet; 175, fourth cooling water outlet;

[0045] 2. RF plasma generating mechanism; 21. upper connecting flange; 22. RF restraining tube; 23. RF induction coil; 24. lower connecting flange; 25. fixing screw; 26. insulating sleeve;

[0046] 3. Connecting screw; 4. Insulating sleeve; 5. Connecting boss; 6. Raw gas channel. DETAILED DESCRIPTION

[0047] In order to make the purpose, features and advantages of the utility model more obvious and easy to understand, the technical scheme of the utility model will be clearly and completely described below in combination with the drawings in the specific embodiment. Obviously, the embodiments described below are only part of the embodiments of the utility model, not all of them. Based on the embodiments in this patent, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this patent.

[0048] In a typical embodiment of the present utility model, as shown in 1A, Figure 1B a composite high-temperature heat source generator is proposed, which includes a DC arc plasma generating mechanism 1 and a radio frequency plasma generating mechanism 2. Generally, in order to make the gas flow more smoothly in the generator, the DC plasma generating mechanism 1 is located above the radio frequency plasma generating mechanism 2, so that the high temperature generated by the DC plasma can be fully utilized to crack a part of the raw material gas first, such as cracking more than 45%. Of course, the DC plasma generating mechanism 1 can also be located below the radio frequency plasma generating mechanism 2, and the gas flow is first cracked by the radio frequency plasma. The primary cracking rate of the gas flow in this scheme is relatively low, generally about 40%. The raw material gas with 40% cracking is introduced into the DC plasma generating mechanism 1. Due to the short residence time of the raw material gas, the final conversion rate of the raw materials in this scheme is about 80%. In this embodiment, the DC arc plasma generating mechanism 1 and the radio frequency plasma generating mechanism 2 are coaxially arranged up and down, the DC arc plasma generating mechanism 1 is located above the radio frequency plasma generating mechanism 2, and the DC arc plasma generating mechanism 1 and the radio frequency plasma generating mechanism 2 are connected by a connecting screw 3. An insulating sleeve 4 is sleeved outside the connecting screw 3 to ensure electrical insulation. The present utility model adopts an integrated structure design of a dual discharge mode to generate a high-temperature heat source for the preparation of carbon nanomaterials, effectively controls the residence time of the raw material gas in different high-temperature zones, and greatly improves the output of carbon nanomaterials. Combining the characteristics of the high temperature at the center of the DC arc plasma column, the high temperature at the edge of the radio frequency plasma, and the low flow rate, it can effectively suppress the problem of insufficient cracking caused by the relatively fast gas flow rate or uneven temperature distribution in a single gas discharge mode, thereby greatly shortening the process flow of cracking hydrocarbon gases and improving the cracking efficiency, the yield and production capacity of the target carbon nanomaterials.

[0049] As Figure 1B shown, it is a schematic diagram of the composite high-temperature heat source generator provided by the present utility model. The lower part of the DC arc plasma generating mechanism 1 is designed with a variable diameter structure 121 that first converges and then expands. The inner diameter of the waist part of the variable diameter structure 121 is D1, the inner diameter of the DC plasma cavity is D2, and the inner diameter of the radio frequency plasma cavity is D3, where D1 < D2 < D3. Preferably, D1 = 8 - 10 mm, such as 8.5 mm, 9 mm, 9.5 mm, etc., D2 = 9 - 20 mm, such as 10 mm, 11 mm, 18 mm, 19 mm, etc., more preferably 12 - 17 mm, such as 13 mm, 14 mm, 15 mm, 16 mm, etc.; D3 = 30 - 80 mm, such as 35 mm, 40 mm, 70 mm, 75 mm, etc., preferably 45 - 65 mm, such as 50 mm, 52 mm, 55 mm, 58 mm, 60 mm, 62 mm, 64 mm, etc.

[0050] It should be noted that the specific numerical values ​​in this embodiment are only for illustrating the approximate relationship between the diameters of the various parts. The composite high-temperature heat source generator provided by the utility model can be proportionally enlarged or reduced according to the needs of production capacity.

[0051] like Figure 2 As shown, the DC arc plasma generating mechanism 1 includes a cathode assembly 11 and an anode assembly 17. After power is applied, an arc is generated between the cathode assembly 11 and the anode assembly 17 to ionize the gas. In order to facilitate installation and avoid dead angles inside the device during use, the components are coaxially arranged in sequence.

[0052] In order to improve the cracking rate of the raw gas in the DC plasma generating mechanism 1, the DC arc plasma generating mechanism 1 can also be provided with at least one intermediate electrode 14, and the intermediate electrode 14 is located between the cathode assembly 11 and the anode assembly 17. According to the Joule's law formula Q=I2Rt, by extending the cracking length and increasing the resistance value of R, more Joule heat can be generated in the same time under the condition of constant current. Therefore, the setting of the intermediate electrode 14 can, on the one hand, increase the heat in the DC plasma generating mechanism 1, and on the other hand, can also effectively extend the length of the high-temperature zone inside the DC plasma generating mechanism 1, extend the contact time between carbon source gas such as methane and heat (high-temperature plasma), and improve the cracking efficiency of the raw gas.

[0053] In other preferred embodiments, a hole is provided in the middle of the intermediate electrode 14 for the raw material gas and / or the carrier gas to pass through, so that the gas flow passes through the middle of the intermediate electrode 14 .

[0054] In addition, the middle electrode 14 has the function of stabilizing the arc, because the plasma generated by the arc is inherently unstable and will affect the ionization stability of the airflow due to jitter. Adding the middle electrode 14 can redistribute the direction of the middle electric field and have a suppressive effect on the electric field that generates the plasma, so the range of the plasma "flame" will be significantly narrowed, improving the stability of the system.

[0055] In other embodiments, the number of the intermediate electrodes 14 can be multiple, and the design of multiple intermediate electrodes 14 can effectively increase the length of the electric field and improve the stability of the electric field. This is because the electric field of a single electrode is generally concentrated at both ends of the electrode, and splitting the intermediate electrode 14 into multiple electrodes can effectively improve the uniformity of the electric field distribution and move the effective electric field position downward.

[0056] In other preferred embodiments, an insulating member and / or a heat insulating member may be provided between two adjacent intermediate electrodes 14. The insulating member and / or the heat insulating member may be an insulating sealing pad 15 and a heat insulating pad 16, respectively. Preferably, the insulating sealing pad 15 and the heat insulating pad 16 are circular plate-shaped structures to improve the insulation and heat insulation between the adjacent intermediate electrodes 14. In addition, the insulating sealing pad 15 and the heat insulating pad 16 also play the role of separating the adjacent intermediate electrodes 14, promoting the redistribution of the electric field, and improving the uniformity of the electric field distribution.

[0057] In other preferred embodiments, a cathode bushing 12 is further provided at the bottom of the cathode assembly 11. The cathode bushing 12 is generally made of high temperature resistant ceramic material, such as boron nitride, etc., in order to prevent the high temperature generated by the plasma from damaging the insulating material on the outside. This is because if the insulating material is damaged, the insulation performance between the electrodes is affected, affecting the normal discharge or the success rate of the next start-up of the device.

[0058] In other preferred embodiments, the DC arc plasma generating mechanism 1 may also be provided with a trigger electrode 13, which is used to trigger the DC arc plasma generating mechanism 1. After the DC arc plasma generating mechanism 1 is started, the trigger electrode 13 is powered off, and DC current is passed between the cathode assembly 11 and the anode assembly 13 to form an arc in the air therebetween.

[0059] In a preferred embodiment of the present invention, the intermediate electrode 14, cathode assembly 11, anode assembly 13 and other components are independently cooled, insulated and heat-insulated, so that the temperature of each section of the furnace body can be independently controlled without being affected by the temperature of other furnace bodies, thereby improving the temperature control accuracy of the equipment.

[0060] In other preferred embodiments, the intermediate electrode 14, the cathode assembly 11, the anode assembly 13 and other components are coaxially arranged. The coaxial arrangement is convenient for installation between the components. The positions of the components are generally determined by connecting the holes, such as Figure 2 As shown, the cathode assembly 11 is located directly above the trigger electrode 13, the cathode bushing 12 is located between the cathode assembly 11 and the trigger electrode 13, a plurality of intermediate electrodes 14 are provided, and the plurality of intermediate electrodes 14 are stacked up and down in sequence, and all the intermediate electrodes 14 are coaxially arranged, and a plurality of intermediate electrodes 14 are located directly below the trigger electrode 13.

[0061] In other preferred embodiments, Figure 3As shown, the cathode assembly 11 includes a cathode 111, a cathode fixing ring 112, a cathode insulating sleeve 113, a tightening nut 114, a fixing flange 115 and a cathode water cooling sleeve 116. Preferably, the cathode 111 is a cerium tungsten cathode head. In order to improve the stability of the cathode 111, the cathode 111 is embedded in the cathode seat by interference fit. In order to improve the high temperature resistance of the cathode seat, the cathode seat is preferably a copper cathode seat. The copper cathode seat is connected to the bottom end of the cathode water cooling sleeve 116 by threaded connection and sealed by an O-ring. The cathode water cooling sleeve 116 is used to cool the copper cathode seat. The cathode water cooling sleeve 116 is a three-layer sandwich gap structure, such as Figure 7 As shown, from the inside to the outside, there are the inner casing, the middle casing and the outer casing, the top of the inner casing is processed with a first cooling water inlet 117; the outer circumferential surface of the top of the middle casing is processed with a first cooling water outlet 118, the first cooling water inlet 117 is connected with the gap between the inner casing and the middle casing, the first cooling water outlet 118 is connected with the inside of the inner casing, the circumference of the bottom end of the middle casing is protruding outward, and a plurality of spiral air channels 1110 are uniformly processed along the circumferential surface of the protruding outward, the raw gas and / or the carrier gas (the raw gas in this patent can be a mixture of raw gas and carrier gas) enters the high temperature zone after spiral winding, and the spiral winding changes the contact mode between the raw gas and the cathode 111 from Direct impact is changed to circling around the surface, and the plasma will be decelerated when reaching the surface of the cathode 111, so that the arc spot near the cathode 111 rotates, reducing the ablation of the cathode 111 and extending the life of the cathode 111; the outer circumferential surface at the upper and middle position of the outer casing is processed with an air inlet 119 for the entry of raw gas and carrier gas; the gap between the inner casing, the middle casing and the cathode 111 of the cathode water-cooling jacket 116 jointly forms a cathode cooling water channel; the gap between the outer casing and the middle casing of the cathode water-cooling jacket 116 constitutes a gas channel for the raw gas and the carrier gas, and the gas channel is connected to the spiral gas channel 1110, and the raw gas and the carrier gas spirally enter the interior of the DC arc plasma generating mechanism 1 through the spiral gas channel 1110.

[0062] In the composite high-temperature heat source generator provided by the utility model, according to the different temperatures of the arc generated between the cathode and the anode in the DC arc plasma generating mechanism 1, two ionization principles can be formed to improve the conversion rate of the raw gas. One is that when the arc temperature is 7000-8000°C, the high temperature generated by the arc ionizes the carrier gas, such as argon, nitrogen, helium, etc., and the high temperature generated by the ionization of the carrier gas causes the raw gas, such as methane, to crack under the action of the catalyst to form high-temperature steam, and then to prepare carbon nanomaterials, such as single-walled carbon nanotubes, etc. through rapid cooling. The second is that when the arc temperature is (1.2-1.5)x104°C, the high temperature generated by the arc directly ionizes the raw gas to form C+ ions, and finally forms single-walled carbon nanotubes, etc.

[0063] The cathode insulating sleeve 113 is coaxially sleeved and connected to the outside of the lower end of the cathode water-cooling sleeve 116 by means of a threaded connection. A convex surface is machined on the outer circumferential surface of the cathode insulating sleeve 113, and is fixedly connected to the tightening nut 114 and the fixing flange 115 by bolts / screws. A concave surface is machined on the inner circumferential surface of the end of the cathode insulating sleeve 113 close to the cathode 111 (i.e., the bottom end of the cathode insulating sleeve 113), and a certain gap is left between the fixing flange 115 for installing and fixing the cathode sleeve 12.

[0064] The trigger electrode 13 and the intermediate electrode 14 are copper ring plate structures (high temperature resistant), such as Figure 8 , Fig. 9 As shown, the trigger electrode 13 and the middle electrode 14 are provided with a raw gas channel 6 in the middle to allow the raw gas and / or carrier gas to pass through; the trigger electrode 13 and the middle electrode 14 are both provided with cooling spaces for accommodating cooling water. Specifically, the trigger electrode 13 is provided with a first cooling space 133, and the trigger electrode 13 is provided with a second cooling water inlet 131 and a second cooling water inlet 132 at two symmetrical ends, and the second cooling water inlet 131 and the second cooling water inlet 132 are both connected to the first cooling space 133; the middle electrode 14 is provided with a second cooling space 143, and the middle electrode 14 is provided with a third cooling water inlet 141 and a third cooling water outlet 142 at two symmetrical ends, and the third The cooling water inlet 141 and the third cooling water outlet 142 are both connected to the second cooling space 143, and the outer circumferential surfaces of the trigger electrode 13 and the intermediate electrode 14 are provided with a plurality of connecting bosses 5 extending outward along the circumferential direction thereof, and each connecting boss 5 is provided with a screw through hole for installing the connecting bolt 3; the inner circumferential surface of the top of the trigger electrode 13 is processed into a conical surface, and the angle between the taper and the conical surface of the cathode 111 is 15 to 25°. The number of the plurality of intermediate electrodes 14 can be determined according to the actual power usage requirements, generally 3 to 10, and as a preferred embodiment, the number of the intermediate electrodes 14 is 3. The function of the intermediate electrode 14 is to extend the length of the high temperature zone and improve the stability of the arc spark.

[0065] like Fig.10 , Fig.11As shown, it is an embodiment of the composite high-temperature heat source generator provided by the utility model, the anode assembly 17 includes an anode water cooling jacket 171, an anode 172 and a pressure ring 173, the anode water cooling jacket 171 is a 304 stainless steel ring plate structure, and a fourth cooling water inlet 174 and a fourth cooling water outlet 175 are provided on the upper and lower sides of the symmetrical outer circumferential surface of the anode water cooling jacket 171, the fourth cooling water inlet 174 is located below the fourth cooling water outlet 175, an annular sealing groove is machined on the inner side of the bottom end of the anode water cooling jacket 171, and a concave table with a threaded hole is machined on the top end face to fix the anode 172, the anode 172 is fixedly installed in the anode water cooling jacket 171, the anode 172 is a hollow structure, and the outer periphery of the anode 172 and the inner periphery of the anode water cooling jacket 171 form a cooling space for the anode 172. The interior of the anode 172 is connected to the raw gas channel 6 at the middle position of the intermediate electrode 14, and the anode water cooling jacket 171 is provided with a screw mounting threaded hole in the same vertical plane as the trigger electrode 13 and the connecting bosses 5 on the plurality of intermediate electrodes 14, so as to be connected to the cathode assembly 11 through the connecting screw 3; the anode 172 is a red copper Laval nozzle structure, and a table is extended outward from the outer circumference of the top of the anode 172 to fix the anode 172, and a sealing groove is provided on one end face of the table. The interior of the anode 172 is a convergent-divergent variable diameter structure from top to bottom, and the lower part of the anode 172 is expanded to form a transition zone connected to the radio frequency plasma generating mechanism 2, which can reduce the flow rate of the raw gas and increase the residence time of the raw gas in the high temperature zone. The anode 172 is pressed tightly on the concave table of the anode water cooling jacket 171 by bolts / screws through a pressing ring 173.

[0066] The cathode assembly 11, the trigger electrode 13, the plurality of intermediate electrodes 14 and the anode assembly 17 are coaxially arranged in sequence from top to bottom. The cathode assembly 11, the trigger electrode 13 and the plurality of intermediate electrodes 14 are fixed on the top end surface of the anode water cooling jacket 171 by a plurality of connecting screws 3 uniformly distributed along the circumferential direction. A polytetrafluoroethylene insulating sleeve 4 is sleeved on the outer periphery of each connecting screw 3 for the purpose of electrical insulation. A plurality of annular insulating sealing pads 15 and thermal insulation pads 16 are arranged between the cathode assembly 11, the trigger electrode 13, the plurality of intermediate electrodes 14 and the anode assembly 17. The cathode bushing 12 and the thermal insulation pad 16 are made of high-temperature resistant ceramic materials and are coaxially sleeved on the inner side. The cathode insulating sleeve 113 and the insulating sealing pad 15 are made of polytetrafluoroethylene. The sealing between each component and the insulating sealing pad 15 adopts knife-edge sealing, and the sealing performance between the polytetrafluoroethylene material itself and the knife-edge is used to prevent the generated high-temperature arc plasma from overflowing.

[0067] like Fig.12As shown, the RF plasma generating mechanism 2 includes an upper connecting flange 21, a RF confinement tube 22, a RF induction coil 23 with equal turn spacing, a lower connecting flange 24, a fixed screw 25 and an insulating sleeve 26. The upper connecting flange 21, the RF confinement tube 22 and the lower connecting flange 24 are coaxially arranged from top to bottom. The RF induction coil 23 is sleeved on the outer wall of the RF confinement tube 22, and the RF induction coil 23 is fixedly connected to the RF induction power supply; the upper connecting flange 21 and the lower connecting flange 24 are connected and pressed by the fixed screw 25, and the RF confinement tube 22 is formed together with the RF induction coil 23 to form the RF plasma generating mechanism 2. The outer periphery of the fixed screw 25 is sleeved with an insulating sleeve 26, the purpose of which is to insulate the electromagnetic induction electric field. The RF has an eddy current effect. When the raw gas is CH4, the CH4 molecules stay longer in the cavity of the RF confinement tube 22, and can be cracked more thoroughly, and the CH4 conversion rate can reach more than 90%.

[0068] The upper connecting flange 21 is a stainless steel ring plate structure with a cooling air inlet on the outer circumferential surface, and a cooling water inlet and a cooling water outlet are arranged on the upper and lower sides of the symmetrical outer circumferential surface. The inner side of the upper connecting flange 21 is upwardly provided with a concave table with an annular sealing groove on the wall surface to fix the RF constraint tube 22. The concave surface of the concave table is evenly distributed with a plurality of exhaust holes along the inner wall of the RF constraint tube. The exhaust holes are connected to the cooling air inlet to cool the RF constraint tube 22. The RF induction coil 23 is wound by a hollow copper tube with equal turn spacing, and the number of turns is 4 to 6. The RF constraint tube 2 2 is made of a material that can pass electromagnetic waves, such as quartz glass, and has a thickness of 3-5 mm; the lower connecting flange 24 is a stainless steel ring plate structure with symmetrical cooling water inlets and cooling water outlets on the outer circumferential surface, a plurality of threaded connection holes are arranged on the outer table surface of the lower connecting flange 24, and a fixed table surface with an annular sealing groove on the wall is arranged on the inner side, the upper end of the RF constraint tube 22 is connected with the interior of the upper connecting flange 21, the anode assembly 17, the intermediate electrode 14, and the trigger electrode 13 in sequence, and the lower end of the RF constraint tube 23 is connected with the interior of the lower connecting flange 24.

[0069] The anode water cooling jacket 171 of the DC arc plasma generating mechanism 1 and the upper connecting flange 21 of the RF plasma generating mechanism 2 are sealed and connected via a connecting screw 3 and a nut to form a composite high-temperature heat source generator.

[0070] The specific working principle is:

[0071] During operation, the working gas and cooling gas are respectively introduced into the composite high-temperature heat source generator, and the direct current (DC) power supply is started. The working gas generates spark discharge under the action of high-frequency pulse electricity, thereby forming a stable DC arc discharge; the generated high-temperature plasma flows downstream, and the radio frequency (RF) power supply is turned on at the same time to cause the working gas to be completely ionized and further heated; by adjusting the working gas flow rate and power, etc., a stable plasma flow field with different temperature field distributions can be obtained. The high-temperature flow field generated by the plasma is used to pass hydrocarbon gases (such as methane, acetylene, etc.) into the high-temperature area of ​​the DC arc plasma for cracking, and then the high-temperature steam is passed into the high-temperature area of ​​the RF plasma at the lower end to achieve secondary cracking, and then the completely cracked high-temperature carbon steam is quickly cooled and crystallized to form carbon nanomaterials. The production efficiency of carbon nanomaterials is controlled by adjusting the flow rate of hydrocarbon gas. Combined with the characteristics of high center temperature of the DC arc plasma arc column and high edge temperature and low flow rate of the RF plasma, the phenomenon of insufficient heating and cracking in a single gas discharge mode is effectively suppressed. At the same time, while ensuring sufficient cracking, the process flow of hydrocarbon gas cracking is greatly shortened, thereby improving the cracking efficiency and the yield and production capacity of the target carbon nanomaterials.

[0072] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for preparing carbon nanotubes, comprising: The DC arc plasma generating mechanism (1) is characterized in that the DC arc plasma generating mechanism (1) is connected to the radio frequency plasma generating mechanism (2), and the lower part of the DC arc plasma generating mechanism (1) is provided with a diameter-changing structure (121) which is first contracted and then expanded, the inner diameter of the waist portion of the diameter-changing structure (121) is D1, the inner diameter of the DC plasma cavity is D2, the inner diameter of the radio frequency plasma cavity is D3, and the inner diameter D1 <D2<D3。 2. The device for preparing carbon nanotubes according to claim 1, characterized in that: The DC arc plasma generating mechanism (1) comprises an anode assembly (17), the waist portion of which is an anode (172) of the anode assembly (17), and the lower portion of the anode (172) is expanded to form a transition zone connected to a radio frequency plasma generating mechanism (2).

3. The device for preparing carbon nanotubes according to claim 2, characterized in that: The anode assembly (17) further comprises an anode water cooling jacket (171), the anode (172) being fixedly mounted in the anode water cooling jacket (171), and the outer periphery of the anode (172) and the inner periphery of the anode water cooling jacket (171) forming a cooling space for the anode (172).

4. The device for preparing carbon nanotubes according to claim 1, characterized in that: The DC arc plasma generating mechanism (1) comprises a cathode assembly (11), wherein the cathode assembly (11) comprises a cathode (111) and an intermediate layer casing, wherein at least one spiral air channel (1110) is provided on a side of the intermediate layer casing close to the cathode (111).

5. The device for preparing carbon nanotubes according to claim 4, characterized in that: The DC arc plasma generating mechanism (1) further comprises a plurality of intermediate electrodes (14), and insulating members and / or heat insulating members are provided between adjacent intermediate electrodes (14).

6. The device for preparing carbon nanotubes according to claim 5, characterized in that: The DC arc plasma generating mechanism (1) also includes a trigger electrode (13), and the cathode assembly (11), the trigger electrode (13) and the intermediate electrode (14) are all provided with independent cooling liquid inlets and outlets.

7. The device for preparing carbon nanotubes according to claim 6, characterized in that: The components of the intermediate electrode (14), the cathode assembly (11) and the anode assembly (17) are coaxially arranged.

8. The device for preparing carbon nanotubes according to claim 6, characterized in that: A cathode bushing (12) is provided between the cathode assembly (11) and the trigger electrode (13), and the cathode bushing (12) is made of a high-temperature resistant ceramic material.

9. The device for preparing carbon nanotubes according to claim 1, characterized in that: D1:D2=1:(1.1-3).

10. The device for preparing carbon nanotubes according to claim 1, characterized in that: D1:D3=1:(3-10).

Images