Application of jet pulverization equipment in the production of titanium dioxide
1. Titanium dioxide requirements for crushing
Titanium dioxide used as a pigment has excellent optical properties and stable chemical properties. Titanium dioxide has very high requirements on particle size, particle size distribution and purity. Generally, the particle size of titanium dioxide is based on the wavelength range of visible light, that is, 0.15m ~ 0.35m. And as a white basic pigment, it is very sensitive to the increase of impurities, especially iron impurities, and the increase is required to be less than 5 ppm when pulverized. In addition, titanium dioxide is also required to have good dispersibility in different coating systems. Therefore, the general mechanical crushing equipment is difficult to meet the requirements, so the final crushing of titanium dioxide (finished product crushing), at present, jet mills are used at home and abroad.
2. The choice of jet mill for titanium dioxide production
According to the crushing requirements of titanium dioxide: narrow particle size distribution, less increase in inclusions, good dispersibility, etc., and the material characteristics of titanium dioxide: high viscosity, poor fluidity, fine particle size and easy wall attachment, etc. The flat type (also known as horizontal disc type) jet mill with high-level function is used as the final crushing equipment for titanium dioxide;
And use superheated steam as the crushing medium. Because the steam is easy to get and cheap, the pressure of the steam working medium is much higher than that of the compressed air and it is also easy to increase, so the kinetic energy of the steam is larger than that of the compressed air. At the same time, the cleanliness of superheated steam is higher than that of compressed air, with low viscosity and no static electricity. Moreover, while crushing, it can eliminate the static electricity generated by material collision and friction, and reduce the secondary cohesion of powdered materials. In addition, crushing at high temperature can improve the application dispersibility of titanium dioxide and increase the fluidity of titanium dioxide. The energy consumption of superheated steam is low, which is only 30% to 65% of that of compressed air.
In addition, using a flat jet mill, organic additives can be added while pulverizing to organically modify the surface of titanium dioxide to increase the dispersibility of titanium dioxide in different application systems.
3. Factors affecting jet milling equipment
(1) Jet mill: As the most important equipment for jet milling, the quality of the jet mill directly determines the quality of the product. The gas powder machine is required to be reasonably designed, well-made, with high impact kinetic energy, good classification effect, wear resistance and high temperature resistance. Therefore, it is very important to choose a gas powder machine.
(2) Steam quality: The crushing medium of jet milling is superheated steam. If the steam quality does not meet the crushing requirements, it will seriously affect the quality of gas powder. Generally, the requirements for the steam of the gas powder machine are: the pressure is 1.6-2.0 MPa, and the temperature is between 290 ° C and 310 ° C. If the temperature and pressure are lower than the requirements, the impact kinetic energy will be low, the crushing force will be reduced, the heat of the system will not be enough, the material will be easily affected by moisture and many other unfavorable factors, which will affect the crushing effect, block the system, and make it unable to operate normally; if the temperature and pressure are too high, it will damage the damage to equipment within the system.
(3) Process control: Jet milling requires stable and continuous operation, and the fluctuation of steam and feed amount should be controlled within a certain range. The adjustment must be adjusted slowly, and it is strictly forbidden to be suddenly large or small. In addition, once the air-powder system is normal, it should keep running continuously, and avoid frequent driving and parking. Furthermore, the operating procedures should be strictly followed when driving and parking.
(4) System monitoring: In order to ensure the normal operation of the system, necessary monitoring equipment must be installed in a reasonable position of the system, so that timely adjustments can be made according to changes in the situation.