Alumina powder preparation system and method based on plasma heating and chlorination process

Abstract

The invention discloses an aluminum oxide (Al2O3) powder preparation system and method based on a plasma heating and chlorination method, and solves the problems of insufficient reaction temperature, dependence on an external heat source, scabbing and agglomeration and the like in a traditional method. The system comprises an AlCl3 preheating sublimation device, a plasma torch, a Laval nozzle, a negative pressure chamber, a Venturi nozzle reactor, a cooling separation device and a tail gas treatment device. Through the synergistic effect of plasma heating and supersonic airflow, efficient oxidation of AlCl3 is realized, scabbing is inhibited, and aluminum oxide powder with high purity and narrow particle size distribution is continuously produced. The innovation points are that plasma-supersonic speed cooperation improves the product quality and efficiency, negative pressure material guiding reduces the blocking risk, the crystal form is controllable, and the cooling design reduces the production cost. The nano alpha-Al2O3 and submicron gamma-Al2O3 powder meeting the requirements in the fields of electronics, ceramics, catalysts and the like is successfully prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature chemical engineering and nanomaterial preparation, and particularly relates to a production system for alumina (Al2O3) nano- and sub-micron powders based on plasma heating technology. This system realizes the efficient continuous production of high-purity alumina powders with a narrow particle size distribution by integrating plasma heating and supersonic gas flow technology. Background Art

[0002] Due to their excellent physical and chemical properties, Al2O3 nano- or sub-micron powders have broad application prospects in fields such as electronics, ceramics, and catalysts. However, traditional methods for preparing alumina powders by chlorination (such as the high-temperature oxidation method of AlCl3) have the following problems:

[0003] (1) Insufficient reaction temperature: Conventional heating is difficult to quickly reach the temperature required for the complete oxidation of AlCl3 (≥1200 °C), resulting in uneven crystal forms of the product (such as a mixture of γ-Al2O3 and α-Al2O3).

[0004] (2) Dependence on external heat sources: Continuous heat supply (such as hydrogen combustion) is required, resulting in high production costs and involving the use of flammable and explosive raw materials, posing a significant risk to process safety.

[0005] (3) Scaling and agglomeration: The temperature gradient in the reaction zone is large, and gaseous products are prone to depositing and scaling on the pipe wall during cooling, and nanoparticles sinter due to excessive residence time. Summary of the Invention

[0006] Oxidation Furnace Reactor System

[0007] The present invention provides an oxidation furnace reactor and method that integrates plasma heating and supersonic gas flow, realizes the efficient oxidation of AlCl3, inhibits scaling, and continuously produces high-purity Al2O3 nano / sub-micron powders.

[0008] An alumina powder preparation system based on plasma heating and chlorination method, characterized by comprising:

[0009] 1) An AlCl3 gas preheating and sublimation device for heating and sublimating solid AlCl3 into gas, with a preheating temperature of 200 - 300 °C, and a check valve is provided at the outlet;

[0010] 2) A high-pressure oxygen source for providing the oxygen required for the reaction;

[0011] 3) A plasma torch for providing a high-temperature environment to heat oxygen, using arc plasma, with a power of 50 - 200 kW, capable of heating oxygen to 800 - 1200 °C;

[0012] 4) A Laval nozzle, used to accelerate the heated oxygen to form a high-temperature supersonic gas flow, with a throat diameter of 1 - 3 mm and an exit Mach number ≥ 2.0;

[0013] 5) A negative pressure chamber, introducing AlCl3 gas through the negative pressure area near the exit of the Laval nozzle, with a relative vacuum degree ≥ 0.3 bar;

[0014] 6) A Venturi nozzle reactor, serving as the place where AlCl3 reacts with oxygen to generate Al2O3, and the reaction temperature can reach 1200 °C;

[0015] 7) A cooling and separation device, including an induced draft fan, a cyclone separator, and an electrostatic precipitator, used to cool the reaction products and separate out nano or sub-micron Al2O3 powder;

[0016] 8) An exhaust gas treatment device, including an alkaline solution absorption tower, used to treat the exhaust gas Cl2;

[0017] 9) A temperature measurement sensor, located at the front end of the inlet contraction section of the Laval nozzle and inside the jacket of the Venturi tube wall, used to monitor the oxygen and reaction temperature in real time and feedback to adjust the power of the plasma torch.

[0018] A method for preparing alumina powder using the system as described above, characterized in that the production method includes the following steps:

[0019] 1) Oxygen supply and heating: Oxygen from a high-pressure storage tank enters the plasma torch through a regulating valve and is heated;

[0020] 2) Gas flow acceleration: The heated oxygen is ejected through the Laval nozzle to form a high-temperature supersonic gas flow, enters the Venturi nozzle, and forms a negative pressure area near the entrance of the Venturi nozzle;

[0021] 3) Introduction and mixing of AlCl3 gas: The preheated and sublimated AlCl3 gas is introduced into the negative pressure chamber under negative pressure, mixed with the supersonic and high-temperature oxygen gas flow, and then enters the Venturi nozzle;

[0022] 4) Reaction and separation: Inside the Venturi nozzle, AlCl3 reacts with oxygen to generate Al2O3 particles and Cl2 gas, and the reacted mixed products are introduced into the cyclone separator and electrostatic precipitator for separation;

[0023] 5) Exhaust gas treatment: The exhaust gas Cl2 is discharged after being treated by the alkaline solution absorption tower.

[0024] Furthermore, the angle of the inlet contraction section of the Laval nozzle is 25 - 45°, the throat diameter is 1 - 3 mm, and the angle of the exit expansion section is 25 - 45°.

[0025] Furthermore, the total length of the Venturi nozzle reactor is 50 - 100 mm, the throat length is 2 - 5 mm, the angles of the two end expansion sections are 25 - 45°, and the inner wall is sprayed with a silicon carbide coating.

[0026] Furthermore, in the cooling and separation device, the cyclone separator is used to separate powders with a particle size greater than 100 nm, and the electrostatic precipitator is used to separate powders with a particle size less than 100 nm.

[0027] Furthermore, by adjusting the oxygen temperature in the range of 800 - 1200 °C, the crystal form of Al2O3 is controlled to be the α-phase or γ-phase.

[0028] Furthermore, an induced draft fan is used to replace the traditional cooler, and the air intake volume is adjusted through the cold air intake valve. Innovation points

[0029] (1) Plasma-supersonic synergy: The plasma provides instantaneous high temperature, and the Laval nozzle accelerates oxygen to form a supersonic airflow. The chemical reaction takes place in a high-temperature and high-speed turbulent flow, and the reaction time is < 0.1 second, effectively avoiding the scarring of nano or submicron powder, and improving the product quality and production efficiency.

[0030] (2) Negative pressure feeding: The Venturi effect automatically sucks in AlCl3 gas without mechanical transportation, reducing the risk of blockage. At the same time, a check valve is provided before the AlCl3 gas is introduced into the negative pressure area to prevent air flow back or backfire, improving the safety and stability of the equipment.

[0031] (3) Controllable crystal form: A temperature measurement sensor is provided at the inlet contraction section of the Laval nozzle to measure the oxygen temperature. By adjusting the oxygen temperature (800 - 1200 °C), the crystal form of Al2O3 (α-phase or γ-phase) is controlled.

[0032] (4) Cooling design: Cooling air is used to replace the traditional cooler, and the air intake volume is adjusted through the cold air intake valve, saving the use of cooling water and reducing the production cost. Description of the drawings

[0033] Figure 1 It is a process flow schematic diagram, including: oxygen storage tank 1; plasma torch 2; Laval nozzle 3; negative pressure chamber 4; Venturi nozzle reactor 5; AlCl3 sublimator 6; induced draft fan 7; cyclone separator 8; electrostatic precipitator 9; alkali liquor absorption tower 10; oxygen regulating valve 11; temperature sensor 12; check valve 13; temperature sensor 14; air intake valve 15.

[0034] Oxygen path: High-pressure storage tank → regulating valve → plasma torch → Laval nozzle (accelerated to supersonic speed) → Venturi nozzle (forming negative pressure).

[0035] AlCl3 Path: Preheat sublimation device (200 - 300 °C) → Check valve → Negative pressure chamber → Mix with oxygen.

[0036] Reaction, cooling, separation: The mixed gas reacts in the Venturi nozzle → Induced draft fan (quenched to <200 °C) → Separation device (cyclone separator and electrostatic precipitator, collect powder by classification).

[0037] Tail gas treatment: Cl2 gas → Alkali liquor absorption tower (generate NaCl / NaClO).

[0038] Figure 2 It is a schematic structural diagram of a plasma torch, including: electrode 2-1, electrode 2-2, gas inlet 2-3, heating chamber 2-4, etc. Axially symmetric structure, the cathode material is tungsten, and the anode material is copper. It is used to generate plasma, the gas inlet is used to introduce oxygen, and the heating chamber is used to heat oxygen to a high temperature.

[0039] Figure 3 It is a schematic structural diagram of a Laval nozzle, including: inlet contraction section 3-1, throat 3-1, expansion section 3-3 and extension section 3-4. The contraction angle is 25 - 45°, the throat diameter is 1 - 3 mm, and the outlet expansion angle is 25 - 45°. The shape design of the nozzle enables it to accelerate high-pressure oxygen to supersonic speed and form a negative pressure area near the outlet.

[0040] Figure 4 It is a schematic structural diagram of a Venturi nozzle reactor, including: mixing section 4-1, reaction section 4-2 and diffusion section 4-3. The total length is 50 - 100 mm, the throat length is 2 - 5 mm, the expansion angles at both ends are 25 - 45°, and the inner wall is sprayed with a silicon carbide (SiC) coating. The mixing section is used for the mixing of AlCl3 gas and high-temperature oxygen, the reaction section is the main place for the generation of Al2O3 particles, and the diffusion section is used to disperse the reacted gas flow to form a turbulent flow field and prevent material scaling.

[0041] Figure 5 It is a schematic structural diagram of a negative pressure chamber, including: AlCl3 gas inlet 5-1, AlCl3 check valve 5-2, Venturi nozzle interface 5-3 and channel 5-4 connecting the Laval nozzle. The check valve is used to prevent air flow from flowing back or backfiring and ensure the stable introduction of AlCl3 gas.

[0042] Figure 6 It is a schematic structural diagram of a cyclone separator, including: air inlet 6-1, separation chamber 6-2, air outlet 6-3 and powder collection port 6-4. The Al2O3 powder is separated from the mixed gas flow by the action of centrifugal force.

[0043] Figure 7Schematic diagram of the induced draft fan, including: reaction product inlet 7-1, cold air inlet 7-2, air flow control valve 7-3, and air outlet 7-4. An air flow control valve is provided at the cold air inlet to adjust the cold air flow rate and achieve cooling of the reaction product gas flow. Made of stainless steel, with a wind speed of 3 m / s.

[0044] Figure 8 Schematic diagram of the tail gas treatment device, including: caustic scrubber 8-1, tail gas inlet 8-2, caustic liquid pump circulation system 8-3, and tail gas outlet 8-4. The caustic scrubber is used to absorb HCl gas in the tail gas and prevent environmental pollution. Specific implementation method

[0045] (1) Equipment installation and commissioning

[0046] 1) According to the process flow diagram and equipment design drawing, install each equipment in place to ensure that all connecting pipes are well sealed and there is no leakage.

[0047] 2) Commission key equipment such as plasma torches, Laval nozzles, and induced draft fans to ensure that their performance meets the design requirements.

[0048] 3) Check the accuracy of instrument equipment such as temperature measurement sensors, pressure sensors, and flow control valves to ensure that they can work normally.

[0049] 4) Conduct a trial run of the entire system to check the coordinated operation of each equipment and eliminate possible problems.

[0050] (2) Production operation steps

[0051] 1) Oxygen supply and heating

[0052] Open the oxygen outlet valve of the high-pressure storage tank and adjust the regulating valve to allow oxygen to enter the plasma torch at an appropriate flow rate.

[0053] Start the plasma torch, generate plasma through the electrode, and heat the oxygen to a high temperature (for example, 800 °C to 1200 °C).

[0054] The heated oxygen is ejected through the Laval nozzle to form a high-temperature supersonic gas flow, enters the Venturi nozzle, and a negative pressure area is formed near the nozzle outlet.

[0055] 2) Preheating sublimation and introduction of AlCl3 gas

[0056] Start the AlCl3 gas preheating sublimation device and preheat the AlCl3 gas to the temperature required for sublimation (for example, 200 °C to 300 °C).

[0057] Open the check valve, and introduce the preheated and sublimated AlCl3 gas into the negative pressure chamber through negative pressure. Then, it is mixed with the supersonic and high-temperature oxygen flow near the outlet of the Laval nozzle and enters the Venturi nozzle.

[0058] 3) Reaction and separation

[0059] Inside the Venturi nozzle, AlCl3 reacts chemically with high-temperature oxygen to produce Al2O3 particles and Cl2 gas.

[0060] The reacted mixture is introduced into the cyclone separator and electrostatic precipitator by the induced draft fan, and nano or sub-micron Al2O3 powder is separated by centrifugal force.

[0061] The separated Al2O3 powder is discharged from the powder collection ports of the cyclone separator and electrostatic precipitator and collected into the powder collection device.

[0062] 4) Tail gas treatment

[0063] The separated tail gas (mainly composed of Cl2 gas) enters the alkaline solution absorption tower of the tail gas treatment device, reacts chemically with the alkaline solution, absorbs the Cl2 gas, and produces harmless by-products (such as sodium chloride, sodium hypochlorite, etc.).

[0064] (3) Cooling and temperature control

[0065] The cooling air enters the system through the cold air inlet of the induced draft fan, mixes with the reaction product gas flow, replaces the traditional cooler, and cools the reaction product gas flow.

[0066] Measure the oxygen temperature through the temperature measurement sensor at the contraction section of the Laval nozzle inlet, and adjust the power of the plasma torch or the oxygen flow rate as needed to control the oxygen temperature within a suitable range, thereby adjusting the crystal form of the product Al2O3 particles.

[0067] Adjust the cold air flow rate through the air flow control valve of the induced draft fan to ensure that the reaction product gas flow can be effectively cooled and prevent the powder from scaling on the cooler wall again.

[0068] The treated tail gas is discharged from the tail gas outlet, meeting the environmental protection emission standards.

[0069] (4) Examples

[0070] Example 1 (Preparation of nano α-Al2O3)

[0071] Parameter settings:

[0072] 1) Plasma power: 150 kW, oxygen flow rate 25 L / min;

[0073] 2) AlCl3 feeding rate: 4 kg / h;

[0074] 3) Oxygen temperature: 1200 °C (regulated by feedback of temperature sensor);

[0075] 4) Cooling rate: 600 °C / s.

[0076] Product characteristics:

[0077] 1) Average particle size: 80 nm (detected by SEM);

[0078] 2) Crystal form: pure α-Al2O3 (verified by XRD);

[0079] 3) Specific surface area: 130 m 2 / g.

[0080] Example 2 (preparation of submicron γ-Al2O3)

[0081] 1) Adjust the oxygen temperature to 800 °C and extend the residence time to 0.2 s;

[0082] 2) The product is γ-Al2O3, with a particle size of 500 nm and a specific surface area of 180 m 2 / g.

Claims

1. An alumina powder preparation system based on plasma heating and chlorination method, characterized in that Including: 1) An AlCl3 gas preheating and sublimation device, which is used to heat and sublime solid AlCl3 into gas. The preheating temperature is 200 - 300 °C, and a check valve is provided at the outlet; 2) A high-pressure oxygen source, which provides the oxygen required for the reaction; 3) A plasma torch, which is used to provide a high-temperature environment to heat the oxygen. An arc plasma is adopted, and the power is 50 - 200 kW, which can heat the oxygen to 800 - 1200 °C; 4) A Laval nozzle, which is used to accelerate the heated oxygen to form a high-temperature supersonic gas flow. The throat diameter is 1 - 3 mm, and the outlet Mach number ≥ 2.0; 5) A negative pressure chamber, which introduces AlCl3 gas through the negative pressure area near the outlet of the Laval nozzle, and the relative vacuum degree ≥ 0.3 bar; 6) A Venturi nozzle reactor, which serves as the place where AlCl3 reacts with oxygen to generate Al2O3, and the reaction temperature can reach 1200 °C; 7) A cooling and separation device, including an induced draft fan, a cyclone separator, and an electrostatic precipitator, which is used to cool the reaction products and separate nano or sub-micron Al2O3 powder; 8) An exhaust gas treatment device, including an alkali liquor absorption tower, which is used to treat the exhaust gas Cl2; 9) Temperature measurement sensors, which are located at the front end of the inlet contraction section of the Laval nozzle and inside the jacket of the Venturi tube wall, and are used to monitor the oxygen and reaction temperature in real time and feedback to adjust the power of the plasma torch.

2. A method for preparing alumina powder using the system according to claim 1, characterized in that, The production method includes the following steps: 1) Oxygen supply and heating: Oxygen from a high-pressure storage tank enters the plasma torch through a regulating valve and is heated; 2) Gas flow acceleration: The heated oxygen is ejected through the Laval nozzle to form a high-temperature supersonic gas flow, enters the Venturi nozzle, and forms a negative pressure area near the inlet of the Venturi nozzle; 3) Introduction and mixing of AlCl3 gas: The preheated and sublimated AlCl3 gas is introduced into the negative pressure chamber under negative pressure, mixed with the supersonic and high-temperature oxygen gas flow, and then enters the Venturi nozzle; 4) Reaction and separation: In the Venturi nozzle, AlCl3 reacts with oxygen to generate Al2O3 particles and Cl2 gas. The reaction mixture is introduced into the cyclone separator and the electrostatic precipitator for separation; 5) Exhaust gas treatment: The exhaust gas Cl2 is discharged after being treated by the alkali liquor absorption tower.

3. The alumina powder preparation system based on plasma heating and chlorination method according to claim 1, characterized in that The angle of the inlet contraction section of the Laval nozzle is 25 - 45°, the throat diameter is 1 - 3 mm, and the outlet expansion angle is 25 - 45°.

4. The alumina powder preparation system based on plasma heating and chlorination method according to claim 1, characterized in that, The total length of the Venturi nozzle reactor is 50 - 100 mm, the throat length is 2 - 5 mm, the angles of the two ends of the expansion section are 25 - 45°, and the inner wall is sprayed with a silicon carbide coating.

5. A preparation system for alumina powder based on plasma heating and chlorination method according to claim 1, characterized in that, In the cooling and separation device, the cyclone separator is used to separate powders with a particle size greater than 100 nm, and the electrostatic precipitator is used to separate powders with a particle size less than 100 nm.

6. The alumina powder preparation system based on plasma heating and chlorination method according to claim 1, characterized in that, By adjusting the oxygen temperature in the range of 800 - 1200 °C, the crystal form of Al2O3 is controlled to be α-phase or γ-phase.

7. The alumina powder preparation system based on plasma heating and chlorination method according to claim 1, characterized in that, An induced draft fan is used to replace the traditional cooler, and the air intake volume is adjusted through a cold air intake valve.

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