CN113247881A - Device and method for preparing nano carbon by methane plasma cracking - Google Patents
Device and method for preparing nano carbon by methane plasma cracking Download PDFInfo
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- CN113247881A CN113247881A CN202110536295.4A CN202110536295A CN113247881A CN 113247881 A CN113247881 A CN 113247881A CN 202110536295 A CN202110536295 A CN 202110536295A CN 113247881 A CN113247881 A CN 113247881A
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Abstract
A device and a method for preparing nano carbon by methane plasma cracking belong to the technical field of nano carbon preparation. The device comprises a raw material gas inlet pipe, a mixed pipe type heat exchanger, a plasma reactor, a high-temperature pipe type heat exchanger, a particle trap and a combustion chamber which are sequentially connected through pipelines. Methane and background gas are mixed and heated in a mixed tube type heat exchanger, then the mixed gas is introduced into a plasma reactor and ionized to form high-temperature plasma jet, at the moment, the methane component is dehydrogenated at high temperature to form nano carbon particles, and the waste gas is subjected to heat exchange and temperature reduction to obtain nano carbon through an electrostatic particle catcher and a bag type catcher. And finally, the waste gas after removing the particles enters a combustion chamber for full combustion, and the combustion flue gas is introduced into a mixed tube type heat exchanger to utilize the heat of the combustion flue gas. The two-stage heat exchanger in the reactor is arranged for fully utilizing heat, so that the energy utilization efficiency is improved, and the energy consumption is reduced. Can avoid the emission of harmful gas and has the advantages of high yield of nano-carbon, high decomposition efficiency and the like.
Description
Technical Field
The invention relates to the technical field of nano-carbon preparation, in particular to a device and a method for preparing nano-carbon by methane plasma cracking.
Background
At present, methods for preparing a nanocarbon material by using a carbon source include a chemical vapor deposition method, an arc plasma method, a laser ablation method, and the like. Among them, the plasma method is considered as one of the effective methods for producing the nanocarbon material because of the advantages of energy saving, high conversion rate of raw materials, no pollution, simple process, etc. in preparing the nanocarbon. The method uses organic compounds which have more active chemical properties and contain unsaturated chemical bonds, such as ethylene, acetylene, styrene, benzene, toluene, methane, and the like as carbon sources; a gas having stability such as argon, helium, nitrogen, or hydrogen is used as a carrier gas. High-energy electrons and high temperature are generated through arc discharge between the two electrodes, so that gas in the reaction chamber is changed into a plasma state, the carbon source gas is cracked into gas atoms through electron collision and pyrolysis, and then the gas atoms are cooled to re-nucleate to grow the required nano particles.
In the existing method for preparing nano-carbon by using plasma organic compounds, there are problems (1) that carbon deposition in a reactor is serious, for example, since the flow rate of a carbon source is set to be large and a reaction occurs rapidly because a mixed gas passes through a plasma reaction zone, target nano-carbon may be directly deposited in the reactor and on an electrode. (2) The problem of low yield of nano carbon particles is that in a collecting mode of preparing nano carbon by using plasma organic matters, a cyclone separator, an ash bucket, a bag-type dust remover and the like are arranged, and the method is usually incomplete in carbon nano capture. (3) The end discharge gas has a low utilization rate, and the gas by-product is directly discharged to the atmosphere, thereby not utilizing the value and polluting the environment. Therefore, the design of a system for preparing nano carbon by plasma cracking, which can improve the utilization rate of raw materials and the yield of products and reduce the emission of harmful gases, is urgent.
Disclosure of Invention
The technical problem to be solved is as follows: aiming at the technical problems, the invention provides a device and a method for preparing nano-carbon by methane plasma cracking, which can avoid the emission of harmful gas and have the advantages of high yield of nano-carbon, high decomposition efficiency, low energy consumption and the like.
The technical scheme is as follows: a device for preparing nano carbon by methane plasma cracking comprises a raw material gas inlet pipe, a mixed pipe type heat exchanger, a plasma reactor, a high-temperature pipe type heat exchanger, a particle catcher and a combustion chamber which are sequentially connected through pipelines, wherein the raw material gas is a mixture of methane and background gas, and the raw material gas inlet pipe comprises a methane inlet pipe and a background gas inlet pipe which are communicated;
the mixed tube type heat exchanger comprises a static mixer and a tube type heat exchanger connected with the static mixer in series, wherein a feed gas is connected with a gas inlet pipeline of the static mixer, a gas outlet of the static mixer is connected with a cold feed gas inlet of the tube type heat exchanger, a cold feed gas outlet of the tube type heat exchanger is connected with a gas inlet pipeline of the plasma reactor, a hot flue gas inlet of the tube type heat exchanger is connected with a gas outlet pipeline of a combustion chamber, flue gas at a hot flue gas outlet of the tube type heat exchanger is discharged into a chimney, hot flue gas at about 800 ℃ from the combustion chamber is introduced into a heat exchange tube of the tube type heat exchanger, and the feed gas at normal temperature is arranged outside the heat exchange tube and is heated to 500-550 ℃ through heat exchange;
the plasma reactor comprises a heat preservation heating layer, a shell, two groups of spray pipe type electrode groups and a gas outlet, wherein the shell is a hollow cylindrical closed cavity, the heat preservation heating layer is arranged on the outer surface of the shell, the two groups of spray pipe type electrode groups are axially symmetrical and extend into the shell from the outside, the two groups of spray pipe type electrode groups are not contacted with each other and have the same distance, each group of spray pipe type electrode group comprises a plurality of parallel hollow stainless steel pipes (spray pipes), one ends of the plurality of parallel hollow stainless steel pipes, which are arranged outside the shell, are communicated through a stainless steel main pipe, one ends of the plurality of parallel hollow stainless steel pipes extend into the shell are opened, a feed gas is introduced into the stainless steel main pipe, which is communicated from the outside of the shell, one group of the two groups of spray pipe type electrode groups is grounded, the other group of spray pipe type electrode groups is connected with a high voltage, the gas outlet is arranged on one side, which is vertical to the direction of the stainless steel pipes, and the feed gas is evenly distributed, the discharge jet flow is sprayed out of each spray pipe to form discharge jet flow with certain intensity;
the gas outlet of the plasma reactor is connected with the hot reaction gas inlet pipeline of the high-temperature tubular heat exchanger, the hot reaction gas outlet of the high-temperature tubular heat exchanger is connected with the gas inlet pipeline of the particle trap, the cold gas inlet of the high-temperature tubular heat exchanger is connected with the air, the cold gas outlet of the high-temperature tubular heat exchanger is connected with the gas inlet pipeline of the combustion chamber, normal-temperature air is introduced from the outside, hot reaction gas is led out from the plasma reactor, enters the particle trap after exchanging heat with cold air for combustion, the temperature of the reactor entering the particle trap is controlled to be 150-200 ℃, finally waste gas enters the small combustion chamber for combustion, and non-decomposed CH (CH) is obtained4、H2And other small molecular organic matters are fully combusted in the combustion chamber;
the gas outlet of the particle catcher is connected with the gas inlet pipeline of the combustion chamber, and the particle catcher comprises an electrocoagulation-static catching device and a cloth bag catcher which are sequentially connected in series.
Preferably, the electrocoagulation and electrostatic trapping device comprises two reaction electrodes, an electrostatic trapping cavity, a dust collecting plate and a sampling chamber, wherein the electrostatic trapping cavity is a hollow cavity, two holes are formed in the top end of the wall of the electrostatic trapping cavity, the two reaction electrodes are symmetrically inserted into the cavity wall holes in a parallel and sealed mode and extend into the wall of the cavity, the two reaction electrodes are positive and negative, the positive and negative reaction electrodes are arranged on the upstream and are connected with high voltage of 30 kV-50 kV, the dust collecting plate is arranged at the bottom end of the inner part of the electrostatic trapping cavity and corresponds to the cavity wall holes and is used for collecting carbon nanoparticles, and the sampling chamber is arranged below the dust collecting plate and is used for storing the carbon nanoparticles on the surface of the dust collecting plate.
Preferably, the reaction electrode is a stainless steel needle electrode with the length of 8-10 mm and the diameter of 0.5 mm, the two reaction electrodes are symmetrically inserted into the cavity wall hole in parallel and are inserted into the wall hole in a sealing mode and stretch into the wall hole by 1-2 mm, the dust collecting plate is arranged at the position 15mm away from the lowest end of the reaction electrode, the distance between the two reactor wall holes is 20-30 mm, and after the nano carbon particles are collected by the dust collecting plate, the nano carbon particles are manually or manually conveyed into the sampling chamber through a scraper. When a high voltage is applied between two parallel needle electrodes, a curved electric field is generated and expands the space between the two electrodes outwards, and thenTwo ion winds are induced, the two ion winds have equal but opposite charges, and the nanocarbon flow passes through the channel under the action of double ion winds with opposite charges generated by the electrodes arranged in parallel. Are charged by the electric field as they pass through the channel. Under interaction with the ion wind at the upstream positive electrode, the aerodynamic and electrostatic forces of the ion wind move the charged particles toward a dust collection plate mounted on the opposite side of the electrode. The dust collecting plate is made of stainless steel. On the way to the dust collection plate, the charged nanocarbon particles move downstream due to their initial airflow momentum and the curved electric field and continue to interact with the negative ion wind from the downstream electrode. The negative ion wind further pushes the particles towards the other side of the channel and neutralizes their charge. In the process, nanoparticles with positive and negative charges are mutually attracted and coagulated to form larger particles, which is beneficial to electrostatic trapping and cloth bag filtration trapping. The trapping rate of the device to the nano carbon can reach as high as 90 percent; the bag catcher is connected behind the electrostatic catcher and is used for collecting products entering the combustion chamber from the electrostatic catcher, filtered waste gas enters the combustion chamber to be combusted, and undecomposed CH is removed4、H2And other small molecular organic matters are fully combusted in the combustion chamber.
Preferably, the internal unit of the static mixer is a corrugated sheet.
Preferably, in the two groups of spray pipe type electrode groups, each group of spray pipe type electrode group comprises 3-5 parallel stainless steel pipes, the vertical distance between every two steel pipes is 8-10 mm, the outer diameter of each stainless steel pipe is 2-3 mm, the wall thickness is 0.2-0.3 mm, and the horizontal distance between two opposite stainless steel pipe openings is 10-20 mm.
Preferably, the two groups of nozzle type electrode groups are horizontally arranged or vertically arranged.
Preferably, the device for preparing nanocarbon by methane plasma cracking further comprises two flow regulating valves, two gas flow meters and two thermometers, wherein one flow regulating valve and one gas flow meter are arranged on a methane inlet pipe, the other flow meter and the other flow regulating valve are arranged on an inlet pipe of background gas, the thermometers are respectively arranged on a cold gas reaction gas outlet pipeline of the mixed tube type heat exchanger and a hot air outlet pipeline of the tube type heat exchanger, the flow regulating valve is used for regulating the flow of gas, the gas flow meters are used for detecting the flow of gas, and the thermometers are used for detecting the temperature of the cold gas reaction gas outlet of the mixed tube type heat exchanger and the hot air outlet of the tube type heat exchanger.
The method for preparing the nano carbon by methane plasma cracking based on the device comprises the following steps:
step one, CH4Mixed with background gas to form feed gas, CH4The volume concentration of the feed gas is controlled to be 5-10%, and the flow of the feed gas is controlled to be 3-5L/min;
feeding the mixed raw material gas into a mixing tube type heat exchanger, exchanging heat with combustion flue gas, heating cold raw material gas to 500-550 ℃, feeding the cold raw material gas into a plasma reactor for reaction, feeding the heated raw material gas into two groups of nozzle type electrode groups respectively in two paths, simultaneously starting a high-voltage power supply of 30 kV-50 kV, forming jet spark discharge near the openings of the nozzle type electrodes at two sides, and ionizing methane to form nano carbon particles;
step three, enabling the reaction product to enter a high-temperature tubular heat exchanger, exchanging heat with cold air for combustion, and then entering a particle catcher, wherein the temperature of the reaction product after heat exchange is 150-200 ℃;
carrying out electrocoagulation and electrostatic capture and cloth bag capture by using a particle trap, and collecting carbon nanoparticles in multiple stages to realize the capture efficiency of more than 90% of the carbon nanoparticles;
step five, after the carbon particles are collected and removed, the waste gas enters a combustion chamber for combustion, and the undecomposed CH is burnt out4、H2And other micromolecular organic matters, hot flue gas generated by combustion flows back to the mixing tube type heat exchanger for heat recovery, and the flue gas after heat recovery is finally discharged in the high altitude through a chimney with the length of 15-25 m.
Has the advantages that: the device and the method for preparing the nano carbon by the plasma system have the following advantages that:
1. the raw material gas is introduced from the spray pipe type tubular electrode, so that the decomposition efficiency is greatly improved, the deposition of target nano carbon is avoided, and the yield is improved by designing a plurality of electrodes;
2. a two-stage heat exchanger is designed, the heat of the system is fully utilized, and the energy consumption is reduced;
3. the invention can efficiently collect the nano-carbon through the electric coagulation and electrostatic trapping device and the cloth bag trap, and the trapping rate of the nano-carbon can reach as high as 90 percent;
4. the invention avoids the discharge of harmful gas, does not produce waste water and realizes clean production. The invention can provide technical support for incremental utilization of methane-rich gas and upgrading of nano carbon preparation technology in China.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus for preparing nanocarbon by methane plasma cracking according to the present invention;
fig. 2 is a schematic structural diagram of the plasma reactor, wherein (a) is a structural diagram when two groups of nozzle type electrode sets are horizontally arranged, and (b) is a structural diagram when two groups of nozzle type electrode sets are vertically arranged;
FIG. 3 is a schematic structural diagram of the mixed tube heat exchanger;
fig. 4 is a schematic view of the particle catcher.
The numerical designations in the drawings represent the following: 1. a mixed tube heat exchanger; 2. a plasma reactor; 3. a high temperature tubular heat exchanger; 4. a particle trap; 5. a combustion chamber; 6. a flow regulating valve; 7. a flow meter; 8. a thermometer; 9. a housing; 10. a heat preservation heating layer; 11. and a nozzle type electrode group.
Detailed Description
The invention is further described below with reference to the accompanying drawings and specific embodiments.
The device and the method for preparing the nano-carbon by cracking the methane plasma are characterized in that methane and background gas are mixed and heated in a mixed tube type heat exchanger, then the mixed gas is introduced into a plasma reactor and is electrolyzed to form high-temperature plasma jet, the methane component is dehydrogenated at high temperature to form nano-carbon particles, and the waste gas after heat exchange and temperature reduction passes through an electrostatic particle catcher and a bag type catcher to obtain the nano-carbon. And finally, the waste gas after removing the particles enters a combustion chamber for full combustion, and the combustion flue gas is introduced into a mixed tube type heat exchanger to utilize the heat of the combustion flue gas. The two-stage heat exchanger in the reactor is arranged for fully utilizing heat, so that the energy utilization efficiency is improved, and the energy consumption is reduced.
Example 1
The utility model provides a device of methane plasma schizolysis preparation nanometer carbon, refers to fig. 1-4, including feed gas intake pipe, mixed tubular heat exchanger 1, plasma reactor 2, high temperature tubular heat exchanger 3, particle trap 4 and the combustion chamber 5 of pipe connection in proper order, the feed gas is the mixture of methane and background gas, and the feed gas intake pipe is including the methane intake pipe and the background gas intake pipe of intercommunication.
The raw material gas enters the mixing tube type heat exchanger 1 to be mixed and heated. The mixed tube type heat exchanger 1 comprises a static mixer and a tube type heat exchanger connected with the static mixer in series, a feed gas is connected with a gas inlet pipeline of the static mixer, a gas outlet of the static mixer is connected with a cold feed gas inlet of the tube type heat exchanger, a cold feed gas outlet of the tube type heat exchanger is connected with a gas inlet pipeline of the plasma reactor 2, a hot flue gas inlet of the tube type heat exchanger is connected with a gas outlet pipeline of the combustion chamber 5, flue gas at a hot flue gas outlet of the tube type heat exchanger is discharged into a chimney, hot flue gas at about 800 ℃ from the combustion chamber 5 is introduced into a heat exchange tube of the tube type heat exchanger, the feed gas at normal temperature is arranged outside the heat exchange tube, and the feed gas is heated to 500-550 ℃ through heat exchange. The static gas mixer is vertically arranged in front of the heat exchanger, and the state of gas in the pipe is changed by utilizing an internal unit body fixed in the pipe. The tubular heat exchanger is connected behind the static gas mixer, hot flue gas at about 800 ℃ from the combustion chamber 5 is introduced into the heat exchange tube of the tubular heat exchanger, the raw material gas at normal temperature is arranged outside the heat exchange tube, the raw material gas is heated to more than 500 ℃ through heat exchange of the hot flue gas, and the heat is supplied to the plasma reactor 2 for utilization. Because the hot flue gas is combusted, the hot flue gas is directly discharged without pollution.
The plasma reactor 2 comprises a heat preservation heating layer 10, a shell 9, two groups of spray pipe type electrode groups 11 and an air outlet, wherein the shell 9 is a hollow cylindrical closed cavity, the heat preservation heating layer 10 is arranged on the outer surface of the shell 9, the two groups of spray pipe type electrode groups 11 are axially symmetrical and extend into the shell 9 from the outside, the length extending into the shell 9 is adjustable, the two groups of spray pipe type electrode groups 11 are not in contact with each other and have the same interval, in order to improve the electrolysis efficiency, each group of spray pipe type electrode groups comprises a plurality of parallel hollow stainless steel pipes, one ends of the plurality of parallel hollow stainless steel pipes arranged outside the shell 9 are communicated through a stainless steel main pipe, one end of each spray pipe type electrode group extending into the shell 9 is opened, raw material gas is introduced into a stainless steel main pipe communicated from the outside of the shell 9, one group of spray pipe type electrode groups in the two groups of spray pipe type electrode groups 11 is grounded, the other group of spray pipe type electrode groups is connected at a high voltage, spark discharge is formed under the action of high voltage. The gas outlet is arranged on one side of the inner wall of the shell 9, which is vertical to the direction of the stainless steel pipe, and the raw gas is sprayed out of each spray pipe after being uniformly distributed to form discharge jet flow with certain strength. The plasma reactor 2 is made of quartz glass. The nozzle type electrode is provided to prevent clogging due to carbon deposition. The heat preservation heating layer 10 is made of rubber.
The gas outlet of the plasma reactor 2 is connected with the hot reaction gas inlet pipeline of the high-temperature tubular heat exchanger 3, the hot reaction gas outlet of the high-temperature tubular heat exchanger 3 is connected with the gas inlet pipeline of the particle trap 4, the cold gas inlet of the high-temperature tubular heat exchanger 3 is connected with the air, the cold gas outlet is connected with the gas inlet pipeline of the combustion chamber 5, the normal temperature air is introduced from the outside in the high-temperature tubular heat exchanger 3, the hot reaction gas is led out from the plasma reactor 2, the hot reaction gas enters the particle trap 4 after exchanging heat with the cold air for combustion, the temperature of the reactor entering the particle trap 4 is controlled to be 150-200 ℃, finally the waste gas enters the small combustion chamber 5 for combustion, and the undecomposed CH4、H2And other small molecular organic matters are fully combusted in the combustion chamber 5. The high temperature tubular heat exchanger 3 is provided to make full use of the system heat.
The air outlet of the particle catcher 4 is connected with the air inlet pipeline of the combustion chamber 5, and the particle catcher 4 comprises an electrocoagulation electrostatic catching device and a cloth bag catcher which are sequentially connected in series.
The method for preparing the nano carbon by methane plasma cracking based on the device comprises the following steps:
step one, CH4Mixed with background gas to form feed gas, CH4The volume concentration of the feed gas is controlled to be 5-10%, and the flow of the feed gas is controlled to be 3-5L/min;
secondly, the mixed raw material gas enters a mixing tube type heat exchanger 1 to exchange heat with combustion flue gas, cold raw material gas is heated to 500-550 ℃ and then enters a plasma reactor 2 to react, the heated raw material gas is divided into two paths and respectively enters two groups of spray tube type electrode groups 11, a high-voltage power supply is turned on simultaneously, spark discharge is formed near the openings of the spray tubes at two sides, and methane is ionized to form nano carbon particles;
step three, enabling the reaction product to enter a high-temperature tubular heat exchanger 3, exchanging heat with cold air for combustion, and then entering a particle catcher 4, wherein the temperature of the reaction product after heat exchange is 150-200 ℃;
carrying out electrocoagulation and electrostatic capture and cloth bag capture by using a particle trap 4, and collecting carbon nanoparticles in multiple stages to realize the capture efficiency of the carbon nanoparticles of more than 90%;
step five, after the carbon particles are collected and removed, the waste gas enters a combustion chamber 5 for combustion, and the undecomposed CH is burnt out4、H2And other micromolecular organic matters, hot flue gas generated by combustion flows back to the mixing tube type heat exchanger 1 for heat recovery, and the flue gas after heat recovery is finally discharged in the high altitude through a chimney with the length of 15-25 m.
Example 2
With embodiment 1, the difference lies in, electricity congeals and static entrapment device includes two reaction electrode, static entrapment chamber, dust collection plate and sampling chamber, the static entrapment chamber is inside hollow cavity, and open on static entrapment cavity wall top has two holes, two reaction electrode parallel symmetry seal insert cavity wall hole to stretch into the chamber wall, two reaction electrode one are positive one burden, and positive reaction electrode locates the upper reaches, inserts 30kV ~50 kV's high-tension electricity, the dust collection plate is located static entrapment intracavity portion bottom and is corresponded with the chamber wall pore for collect carbon nanoparticle, the sampling chamber is located the below of dust collection plate for the carbon nanoparticle on storage dust collection plate surface.
The reaction electrode is 8 mm long, diameter 0.5 mm's stainless steel needle electrode, and two reaction electrode parallel symmetry seal insert chamber wall hole to stretch into wall hole 2mm, the dust collecting plate is located apart from reaction electrode least significant 15mm department, and the distance between two reactor wall holes is 20~30 mm. When a high voltage is applied between two parallel needle electrodes, a bent electricity is generatedThe nano carbon flow passes through the channel under the action of double ion wind with opposite charges generated by the electrodes arranged in parallel. Are charged by the electric field as they pass through the passageway. Under interaction with the ion wind at the upstream positive electrode, the aerodynamic and electrostatic forces of the ion wind move the charged particles toward a dust collection plate mounted on the opposite side of the electrode. On the way to the dust collection plate, the charged nanocarbon particles move downstream due to their initial airflow momentum and the curved electric field and continue to interact with the negative ion wind from the downstream electrode. The negative ion wind further pushes the particles towards the other side of the channel and neutralizes their charge. The trapping rate of the device to the nano carbon can reach as high as 90 percent; the bag catcher is connected behind the electrostatic catcher and is used for collecting products entering the combustion chamber 5 from the electrostatic catcher, filtered waste gas enters the combustion chamber 5 to be combusted, and undecomposed CH is removed4、H2And other small molecular organic matters are fully combusted in the combustion chamber 5.
The internal unit of the static mixer is a corrugated sheet. The device adopts a thin steel plate or a steel strip to roll into corrugated sheets, and a plurality of groups of corrugated sheets are combined into a cylindrical unit, so that methane and background gas are well dispersed and completely mixed after passing through the cylindrical unit. The material can be selected from stainless steel, carbon steel, PVC plastic, polytetrafluoroethylene and the like.
In two sets of spout tubular electrode group 11, every group spout tubular electrode group includes 3~5 parallel nonrust steel pipes, and the vertical distance between every steel pipe is 8~10 mm, and nonrust steel pipe external diameter is 2~3 mm, and wall thickness 0.2~0.3 mm, horizontal distance 10~20 mm between two relative nonrust steel pipes.
The two groups of nozzle type electrode groups 11 are horizontally arranged or vertically arranged.
The device of methane plasma schizolysis preparation nanometer carbon still includes two flow control valves 6, two gas flowmeter 7 and two thermometers 8, a flow control valve and a gas flowmeter locate on the methane intake pipe, another flowmeter and another flow control valve locate with the intake pipe of background gas on, the thermometer is located respectively on 1 air conditioning reaction gas pipeline of hybrid tube heat exchanger and the tubular heat exchanger hot air pipeline of giving vent to anger, the flow adjustment valve is used for adjusting gaseous flow, gas flowmeter is used for detecting gaseous flow, the thermometer is used for detecting the temperature that 1 air conditioning reaction gas of hybrid tube heat exchanger is given vent to anger and tubular heat exchanger hot air is given vent to anger.
Example 3
The difference from example 2 is that each set of nozzle type electrode set in the plasma reactor 2 includes 3 sets of parallel stainless steel nozzles, the outer diameter of each set of stainless steel tubes is 2mm, the thickness is 0.2mm, the vertical distance between each steel tube is 9 mm, the horizontal distance between two sets of stainless steel nozzle openings is 15mm, the flow rate of methane and argon is 3L/min, the concentration of methane is 10%, and the discharge voltage of a positive reaction electrode is 40 kV. The conversion of methane then reached 15%, H2The selectivity of (A) is up to 40%.
Comparative example 1
On the basis of example 3, the stainless steel lance was changed to a solid tube, and methane and argon were flowed through additional openings in the reactor. The conversion of methane is then only 6%, H2The selectivity of (A) is only 15%.
Comparative example 2
On the basis of example 3, the horizontal distance between two opposing sets of stainless steel nozzle orifices was reduced to 5 mm. The conversion of methane at this point was 8%, H2The selectivity of (3) was 26%.
Comparative example 3
On the basis of example 3, the horizontal distance between two opposing sets of stainless steel nozzle orifices was increased to 25 mm. The conversion of methane is then only 7%, H2The selectivity of (a) is only 20%.
Comparative example 4
On the basis of example 3, the vertical distance between the stainless steel lances was reduced to 5 mm. The conversion of methane is then only 5%, H2The selectivity of (A) is only 15%.
Claims (10)
1. The device for preparing the nano-carbon by cracking the methane plasma is characterized by comprising a raw material gas inlet pipe, a mixed tube type heat exchanger (1), a plasma reactor (2), a high-temperature tube type heat exchanger (3), a particle catcher (4) and a combustion chamber (5) which are sequentially connected through pipelines, wherein the raw material gas is a mixture of methane and background gas, and the raw material gas inlet pipe comprises a methane inlet pipe and a background gas inlet pipe which are communicated with each other;
the mixing tube type heat exchanger (1) comprises a static mixer and a tube type heat exchanger connected in series with the static mixer, a feed gas is connected with a gas inlet pipeline of the static mixer, a gas outlet of the static mixer is connected with a cold feed gas inlet of the tube type heat exchanger, a gas outlet of the cold feed gas of the tube type heat exchanger is connected with a gas inlet pipeline of the plasma reactor (2), a hot flue gas inlet of the tube type heat exchanger is connected with a gas outlet pipeline of the combustion chamber (5), and flue gas at a hot flue gas outlet of the tube type heat exchanger is discharged into a chimney;
the plasma reactor (2) comprises a heat preservation heating layer (10), a shell (9), two groups of spray pipe type electrode groups (11) and a gas outlet, the shell (9) is a hollow cylindrical closed cavity, the heat preservation heating layer (10) is arranged on the outer surface of the shell (9), the two groups of spray pipe type electrode groups are axially symmetrical (11) and extend into the shell (9) from the outside, the two groups of spray pipe type electrode groups (11) are not in contact with each other and have the same distance, each group of spray pipe type electrode groups comprises a plurality of parallel hollow stainless steel pipes, one ends of the plurality of parallel hollow stainless steel pipes arranged outside the shell (9) are communicated through a stainless steel main pipe and extend into an opening at one end inside the shell (9), raw material gas is introduced into the stainless steel main pipe which is communicated from the outside of the shell (9), one group of spray pipe type electrode groups in the two groups of spray pipe type electrode groups (11), the air outlet is arranged on one side of the inner wall of the shell (9) which is vertical to the direction of the stainless steel pipe;
an air outlet of the plasma reactor (2) is connected with a hot reaction gas inlet pipeline of the high-temperature tubular heat exchanger (3), an air outlet of the hot reaction gas of the high-temperature tubular heat exchanger (3) is connected with an air inlet pipeline of the particle trap (4), a cold air inlet of the high-temperature tubular heat exchanger (3) is connected with air, and a cold air outlet is connected with an air inlet pipeline of the combustion chamber (5);
the air outlet of the particle catcher (4) is connected with the air inlet pipeline of the combustion chamber (5), and the particle catcher (4) comprises an electrocoagulation-static catching device and a cloth bag catcher which are sequentially connected in series.
2. The device for preparing nano-carbon through methane plasma cracking according to claim 1, wherein the electrocoagulation-static trapping device comprises two reaction electrodes, a static trapping cavity, a dust collecting plate and a sampling chamber, the static trapping cavity is a hollow cavity, two holes are formed in the top end of the wall of the static trapping cavity, the two reaction electrodes are symmetrically inserted into the hole of the wall in a parallel manner and are extended into the wall, one positive reaction electrode and one negative reaction electrode are arranged on the upstream, the high voltage of 30-50 kV is applied, the dust collecting plate is arranged at the bottom end of the inner part of the static trapping cavity and corresponds to the hole of the wall, and is used for collecting carbon nano-particles, and the sampling chamber is arranged below the dust collecting plate and is used for storing the carbon nano-particles on the surface of the dust collecting plate.
3. The device for preparing nano-carbon by methane plasma cracking according to claim 2, wherein the reaction electrode is a stainless steel needle electrode with a length of 8-10 mm and a diameter of 0.5 mm, the two reaction electrodes are symmetrically inserted into the cavity wall hole in parallel and hermetically and extend into the wall hole by 1-2 mm, the dust collecting plate is arranged at a position 15mm away from the lowest end of the reaction electrodes, and the distance between the two reactor wall holes is 20-30 mm.
4. The apparatus for preparing nano-carbon by methane plasma cracking according to claim 1, wherein the internal unit of the static mixer is a corrugated sheet.
5. The device for preparing nano-carbon by methane plasma cracking according to claim 1, wherein each group of the two groups of the nozzle type electrode groups (11) comprises 3-5 parallel stainless steel pipes, the vertical distance between each two stainless steel pipes is 8-10 mm, the outer diameter of each stainless steel pipe is 2-3 mm, the wall thickness is 0.2-0.3 mm, and the horizontal distance between two opposite stainless steel pipe openings is 10-20 mm.
6. The device for preparing nano-carbon by methane plasma cracking according to claim 1, wherein the two groups of nozzle type electrode sets (11) are horizontally arranged or vertically arranged.
7. The apparatus for preparing nano-carbon by methane plasma cracking according to claim 1, wherein the apparatus for preparing nano-carbon by methane plasma cracking further comprises two flow regulating valves (6), two gas flow meters (7) and two thermometers (8), one flow regulating valve and one gas flow meter are arranged on a methane inlet pipe, the other flow meter and the other flow regulating valve are arranged on a background gas inlet pipe, and the thermometers are respectively arranged on a cold air reaction gas outlet pipeline and a hot air outlet pipeline of the tubular heat exchanger of the mixed tubular heat exchanger (1).
8. The method for preparing nano-carbon by methane plasma cracking based on the device of any one of claims 1 to 7 is characterized by comprising the following steps:
step one, CH4Mixed with background gas to form feed gas, CH4The volume concentration of the feed gas is controlled to be 5-10%, and the flow of the feed gas is controlled to be 3-5L/min;
secondly, the mixed raw material gas enters a mixed tube type heat exchanger (1) to exchange heat with combustion flue gas, cold raw material gas is heated to 500-550 ℃ and then enters a plasma reactor (2) to react, the heated raw material gas is divided into two paths to enter two groups of nozzle type electrode groups (11) respectively, a high-voltage power supply of 30 kV-50 kV is started simultaneously, jet flow spark discharge is formed near the openings of the nozzle type electrodes on the two sides, and methane is ionized to form nano carbon particles;
step three, enabling the product after reaction to enter a high-temperature tubular heat exchanger (3), exchanging heat with cold air for combustion, and then entering a particle catcher (4), wherein the temperature of reaction gas after heat exchange is 150-200 ℃;
carrying out electrocoagulation and electrostatic trapping and cloth bag trapping through a particle trap (4), and collecting carbon nanoparticles in multiple stages to realize the trapping efficiency of the carbon nanoparticles of more than 90%;
step five, after the carbon particles are collected, the waste gas enters a combustion chamber (5) for combustion, and the undecomposed CH is burnt out4、H2And other micromolecular organic matters, hot flue gas generated by combustion flows back to the mixing tube type heat exchanger (1) for heat recovery, and the flue gas after heat recovery is finally discharged in the high air through a chimney with the height of 15-25 m.
9. The method for preparing nano-carbon by methane plasma cracking according to claim 8, wherein the background gas is at least one of argon, helium and nitrogen.
10. The method for preparing nano-carbon by methane plasma cracking according to claim 8, wherein the temperature of the combustion flue gas in the second step is 800 ℃.
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