The crusher selected in the production process requires the particle size distribution of the products to be within a certain range. In fact, the particle size distribution of the products produced by the crusher is wider than the required particle size range, and most of them are difficult to meet the requirements. Therefore, in the grinding process, classification is one of the most important links to improve the ultrafine grinding efficiency and produce fine powder products that meet the fineness and grading requirements. The so-called classification is the operation process of sorting the crushed products according to a certain particle size or different types of particles according to the requirements of the production process.
There are two ways of classification: screening with a sieve and classification in a fluid. The representative products of screen screening mainly include linear screen, circular vibrating screen and other screening machines. Representative products of air flow screening include gravity classifier, coarse classifier, centrifugal classifier (also known as centrifugal powder concentrator), cyclone classifier, O-SEPA classifier, jet vortex classifier and forced vortex classifier.
The airflow classifier is mainly composed of secondary air, tertiary air, impeller, transmission system, etc. When the production line works, the materials enter through the feed pipe of the classifier under the action of the gravity of the induced draft fan. The air and materials inside the classifier are fully mixed, and the gas-solid two-phase flow is fully dispersed under the action of the tertiary air of the lower cylinder of the classifier and the dispersion cone.
When the gas-solid two-phase flow rises to the classification area, each individual particle is subjected to both the centrifugal force generated by the rotation of the classification wheel and the centripetal force generated by the gravity of the induced draft fan. When the centrifugal force on the particles is greater than the centripetal force, the coarse particles above the grading diameter are thrown to the inner wall of the cylinder, and then fall along the inner wall of the cylinder to the secondary air elutriation area after stalling. Under the attraction of the induced draft fan, the air enters the scouring area through the secondary air inlet evenly distributed on the cone, and performs air screen scouring on the coarse and fine mixed powder. In this way, the fine particles mixed or adhered to the coarse material are separated and returned to the classification area, and the coarse particles are discharged from the classifier by the unloading device. Fine particles meeting the particle size requirements enter the cyclone collector and pulse dust collector with the air flow and are collected, and the purified gas is discharged into the atmosphere through the exhaust outlet of induced draft fan
How to solve the defects of air flow classifier in accuracy and energy consumption:
First, increase the secondary air inlet at the coarse powder outlet. In this way, the waste caused by the direct settlement of unseparated particles in the traditional classification method is solved. After grading, the secondary air inlet device shall be compared to make the coarse powder discharge effectively.
Secondly, we talked about the coarse powder outlet just now. In fact, secondary induced draft should also be carried out at the subdivision outlet. The purpose of such action is to exert a force on the fine powder and let the fine powder discharge smoothly. This also allows the air flow classifier to save unnecessary energy waste.
Third, the application of secondary air inlet to the import of raw materials will also save energy. However, this law has advantages and disadvantages. It is better to use it carefully according to the actual situation.