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CN-117065689-B - Microwave plasma CO for product circulation separation2Cracking device and method

CN117065689BCN 117065689 BCN117065689 BCN 117065689BCN-117065689-B

Abstract

The invention discloses a microwave plasma CO 2 cracking device and method for product circulation separation, comprising a microwave plasma power supply unit, a gas supply and reactor unit, a post-treatment and circulation unit and a signal acquisition control unit 4, wherein a solid power supply generates microwaves through a magnetron, microwave plasmas are formed in the reactor through a waveguide to crack CO 2 into CO and O 2 , a shrinkage-expansion nozzle forms vortex and more reasonable temperature distribution in the microwave reactor to realize higher CO 2 conversion rate, a constant temperature cavity and a carbon bed provide O 2 in the product to remove so as to improve the concentration of CO, a pressure swing adsorption device separates and collects CO, and unreacted raw material gas is circulated through a vacuum pump to realize thorough cracking of CO 2 . The invention has novel function integration, can realize high-efficiency cracking conversion of CO 2 , can expand the conversion process of gaseous products which is mainly used for other microwave plasma technologies, and is easy for industrial conversion.

Inventors

  • GAO YUAN
  • SHAO TAO
  • XU YUXUAN
  • DOU LIGUANG
  • HUANG BANGDOU

Assignees

  • 中国科学院电工研究所

Dates

Publication Date
20260505
Application Date
20230904

Claims (10)

  1. 1. The microwave plasma CO 2 cracking device for circularly separating products is characterized by comprising a microwave plasma power supply unit, a gas supply and reactor unit, a post-treatment and circulation unit and a signal acquisition control unit; The microwave plasma power supply unit comprises a solid-state power supply, a high-voltage transmission line, a magnetron, a rectangular waveguide, a conical waveguide, a tungsten rod electrode, a circulating water machine and a circulating water pipeline, wherein the solid-state power supply is connected with the magnetron through the high-voltage transmission line to generate microwaves, and forms standing waves after multiple reflections in cavities of the rectangular waveguide and the conical waveguide to generate stable microwave field intensity, and the electrode tip breaks down gas discharge to trigger microwave plasma; the gas supply and reactor unit comprises a high-pressure steel cylinder, a stainless steel pipeline, an electromagnetic valve, a flowmeter, an insulating pipeline, a cylindrical quartz tube, a connector clamping sleeve and an arc quartz tube, wherein the high-pressure steel cylinder, the electromagnetic valve and the flowmeter are connected through the stainless steel pipeline; The post-treatment and circulation unit comprises a constant temperature cavity, a resistance heating system, a flange connector, a shrinkage-expansion nozzle, a ventilation plate, a carbon bed, a feed tank, a conical tube, a pressure swing adsorption instrument, a gas storage and transportation tank, a vacuum pump and a barometer, wherein the constant temperature cavity is heated and maintained in temperature through the resistance heating system, an inlet of the constant temperature cavity is connected with the arc quartz tube, an air inlet of the shrinkage-expansion nozzle is connected with the arc quartz tube through the flange connector, an air outlet of the shrinkage-expansion nozzle is connected with the carbon bed, an air inlet of the carbon bed is separated from the shrinkage-expansion nozzle through the ventilation plate, an air outlet of the carbon bed is separated from the conical tube through the ventilation plate, the air inlet of the conical tube is connected with the air outlet of the carbon bed, the air outlet of the carbon bed is connected with the constant temperature cavity, the pressure swing adsorption instrument is connected with the air outlet of the conical tube, CO in a mixed gas product is separated and injected into the gas storage and transportation tank through a stainless steel pipeline, the internal gas pressure is monitored in real time through the barometer, and the air inlet of the vacuum pump is connected with the pressure swing adsorption instrument, and the air outlet is connected with the cylindrical quartz tube, so that gas circulation under the condition of less than 1 standard atmospheric pressure is realized; The signal acquisition control unit comprises a thermocouple, an upper computer and a signal transmission line, wherein the thermocouple penetrates through the constant temperature cavity and is inserted into the carbon bed, and is connected with the upper computer through the signal transmission line, and the upper computer is in communication connection with a solid-state power supply, an electromagnetic valve, the thermocouple, a resistance heating system and a barometer.
  2. 2. The apparatus of claim 1, wherein the solid state power supply is configured to drive the magnetron to generate uniform microwaves in the waveguide at a frequency of 915, MHz or 2.45, GHz.
  3. 3. The microwave plasma CO 2 cracking device for product cycle separation according to claim 1, wherein the rectangular waveguide and the conical waveguide are hollow structures, the inner side of the rectangular waveguide and the conical waveguide is made of metal material, the metal material is one of copper and aluminum, the outer side of the rectangular waveguide and the conical waveguide is made of insulating material, and the insulating material is polytetrafluoroethylene.
  4. 4. The microwave plasma CO 2 cracking device for product cycle separation according to claim 1 is characterized in that the tip of the tungsten rod electrode is positioned at the center of the conical waveguide and is fixed with the air inlet of the cylindrical quartz tube, the air outlet of the cylindrical quartz tube is connected with the arc quartz tube through a connector cutting sleeve, and the connector cutting sleeve is made of polytetrafluoroethylene.
  5. 5. The device for circularly separating microwave plasma CO 2 from products according to claim 1, wherein the constant temperature cavity has 4 openings, namely an opening connected with the arc quartz tube, an opening connected with the feed chute, an opening connected with the conical tube and an opening connected with the thermocouple, and each opening is sealed with the constant temperature cavity by high-temperature glue.
  6. 6. The apparatus of claim 1, wherein the middle of the convergent-divergent nozzle has a smaller diameter than the two sides, so that the flow velocity of the gas stream changes to form a vortex, and the material is stainless steel.
  7. 7. The microwave plasma CO 2 cracking device for product cycle separation according to claim 1, wherein the carbon bed is a hollow cuboid, an upper opening is connected with a feed chute, carbon particles are filled in the upper opening, the diameter of the carbon particles is 0.1-2 mm, and the feed chute is kept sealed in the reaction process.
  8. 8. The microwave plasma CO 2 cracking device for product circulation separation according to claim 1 is characterized in that a water inlet and a water outlet of the magnetron are connected with a circulating water machine through a circulating water pipeline, circulating water is tap water with the flow rate of 5-15L/min, an air inlet of the vacuum pump is connected with an air outlet of a pressure swing adsorption instrument, and an air outlet of the vacuum pump is connected with a cylindrical quartz tube through a flowmeter.
  9. 9. The microwave plasma CO 2 cracking device for product cycle separation according to claim 1, wherein the probe of the thermocouple extends into the carbon bed to measure the temperature in real time, and is communicated with an upper computer through a signal transmission line, and the upper computer controls a resistance heating system to regulate the temperature of the constant temperature cavity through the signal transmission line according to temperature information.
  10. 10. A process for the conversion by pyrolysis of a microwave plasma CO 2 pyrolysis unit for the cyclical separation of products according to any one of claims 1 to 9, comprising the steps of: The method comprises the following steps that (1) a solid-state power supply drives a magnetron to generate microwaves, standing waves are formed in a rectangular waveguide and a conical waveguide, and microwave plasmas are generated by discharging at a tungsten rod electrode; Step (2), raw gas in the high-pressure steel cylinder sequentially passes through the electromagnetic valve and the flowmeter and then enters the cylindrical quartz tube at a set fixed flow rate, and meanwhile, the vacuum pump is started to form the circulating flow of the gas; Step (3), the raw material gas passes through a cylindrical quartz tube, then enters a constant temperature cavity from an arc quartz tube, and enters a carbon bed after passing through a shrinkage-expansion nozzle; Step (4), the thermocouple monitors the temperature inside the carbon bed in real time and sends the temperature to the upper computer, and the upper computer controls the resistance heating system to adjust the temperature of the constant temperature cavity according to the temperature, so that the temperature of the carbon bed is suitable for the reaction between O 2 in the product and carbon to be converted into CO; Step (5), extracting CO in the mixed product through a pressure swing adsorption instrument, injecting the CO into a gas storage tank, and re-entering the residual gas into a gas inlet of a cylindrical quartz tube through a vacuum pump; Step (6), when the value of the barometer reaches the set maximum pressure value of the gas storage and transportation tank or the carbon bed needs to be replaced with carbon particles, the upper computer controls the solid-state power supply and the electromagnetic valve to be closed through the signal transmission line, and further sends out signals to control the resistance heating system, the vacuum pump and the pressure swing adsorption instrument to stop running; and (7) after the gas in the gas storage and transportation tank is exhausted or carbon particles are replaced, transmitting data to an upper computer by a barometer, controlling an electromagnetic valve, a vacuum pump and a resistance heating system to be started, further controlling a solid-state power supply and a pressure swing adsorption instrument to operate after exhausting air for a period of time, and circulating the steps (1) to (7) to realize all-weather unattended operation.

Description

Microwave plasma CO 2 cracking device and method for product circulation separation Technical Field The invention belongs to the technical field of greenhouse gas conversion, and particularly relates to a microwave plasma CO 2 cracking device and method for product circulation separation. Background The capture, utilization and sequestration of greenhouse gases mainly comprising CO 2 are one of the key technical means. Among these, cracking of CO 2 to produce CO and O 2, and further conversion of CO to high value chemicals by a Fischer-Tropsch process, is a widely interesting route of use. However, as CO 2 molecules have very high chemical bond energy (803 kJ/mol), the traditional thermochemical CO 2 pyrolysis has the problems of high energy consumption, low activity, further improvement of selectivity and stability and the like, and the plasma technology can utilize high-energy electrons and active species generated by high-voltage discharge to activate energy micromolecules, so that the breaking of inert chemical bonds is realized, the catalytic reaction energy barrier is reduced, the reaction energy consumption is reduced, and a new thought is provided for CO 2 emission reduction and high-value utilization. Among the different types of plasma sources, microwave (MW) plasma has high CO 2 dissociation energy efficiency due to the effective vibration excitation (dissociation effective channel) process, and the relatively high temperature of heavy particles in the plasma promotes the thermal cracking of CO 2, and the conversion rate of CO 2 generated by using a microwave plasma reactor to realize the dissociation of CO can reach the thermodynamic limit of 50% (Chemical Society Reviews,2017, 46:5805-63). However, the microwave plasma core gas temperature may reach 5000K or even higher, and the surrounding region temperature may also reach 3000K or higher. Excessive temperature can lead to reverse recombination reaction of CO and O, and the risk of explosion exists after the concentration of CO and O 2 in the product reaches a certain range. Therefore, the key to achieving efficient microwave plasma CO 2 cracking beyond thermodynamic limitations is the control of the internal temperature distribution of the reactor and the removal of O 2 components from the product gas mixture. The improvement of the reactor system to accommodate the above requirements is the basis for the trend toward industrial large-scale applications of microwave plasma pyrolysis CO 2. Chinese patent application CN201910449663.4 discloses a device for producing hydrogen by microwave plasma pyrolysis, which comprises a microwave energy supply unit, a plasma torch supply unit and a pyrolysis cavity, which are sequentially connected, so that the effects of low loss, high pyrolysis efficiency, safety and reliability are achieved. Aiming at the problems that the technology for preparing pure hydrogen with low cost and high efficiency in the prior art is not mature, an electrode for generating plasma through arc discharge is easy to wear, the service life is short, fuel cracking is insufficient and the like, the invention provides a device for preparing hydrogen by microwave plasma cracking, which has low wear, high cracking efficiency, safety and reliability, solves the problem of insufficient fuel cracking combustion in the hydrogen preparation process, however, the device does not process reaction products correspondingly, and the problem of product separation is faced. Chinese patent application No. cn200580022852.X discloses a microwave plasma nozzle with higher plume stability and heating efficiency, providing various systems and methods for generating relatively cold microwave plasmas using atmospheric pressure. These systems have lower unit costs and operate at atmospheric pressure with lower operating costs, lower energy consumption and shorter sterilization cycle times. A relatively cool microwave plasma is generated by a nozzle that operates at atmospheric pressure with greater operating efficiency, unlike existing plasma generation systems. However, the addition of nozzles limits the temperature of the reactor and there is still a lack of a matching design for the corresponding post-treatment process. In summary, the traditional thermal catalytic CO 2 pyrolysis conversion often needs high temperature and high pressure and is matched with a proper catalyst to realize the large-scale utilization, and the microwave plasma technology provides a sustainable and energy-saving application scheme for the rapid and efficient pyrolysis conversion of CO 2. However, there is no design search for a post-treatment device for controlling the temperature distribution of a microwave plasma reactor. Disclosure of Invention In order to solve the technical problems, the invention provides a microwave plasma CO 2 cracking device and method for circularly separating products, which can realize reasonable distribution of the internal temperature of a react