Spray dryer is to spray the material into fog droplets dispersed in the hot air, the material and hot air parallel flow, counterflow or mixed flow of mutual contact, make the water quickly evaporation, achieve the purpose of drying.The spray drying method can eliminate the unit operation such as concentration, filtration and crushing, and the drying time is short, the product liquidity and the instant solubility is good, so it is widely used in the pharmaceutical industry.
Sticking to the wall is a prominent problem that hinders the normal operation of spray dryer.Sticky wall material is not only not conducive to collection operation, but also with the extension of time, sensitive sticky wall material will deteriorate into unqualified material.
The wall sticking phenomenon of spray dryer generally has the following three conditions:
The semi-wet material sticks to the wall.The reason is that the spray droplets have been in contact with the vessel wall before reaching the surface drying, so they stick to the wall. The position of the stick wall is generally on the plane of the movement track of the spray droplets emitted by the atomizer, which is related to the structure of the atomizer and the motion state of hot air in the tower.
Wall adhesion of low melting point materials.The reason is that the material reaches the melting point at a certain temperature and begins to melt, which makes it sticky and sticks to the wall.
The surface adhesion of dry powder.Dry powder movement in a limited space there will always be some encounter on the wall, this is not to be avoided, but such sticky wall is generally not thick, as long as through the air blowing or gently hit can shake off, the simple solution is the inner wall polishing, can solve this problem to a certain extent.
After finding out the reason of sticking the wall, the insiders listed five ways to prevent sticking the wall:
1. A clip-wall drying tower is adopted, during which air is used for cooling, so that the wall temperature is kept below 50℃
2. Introduce secondary air cooling tower wall through tangential direction of column wall rotor;
3. Install an air broom composed of a row of nozzles near the wall of the tower, and make it rotate slowly along the wall of the tower;
4. Add an air hammer to the wall of the tower to force the material sticking to the wall to be separated by hitting with an air hammer;
5, increase the processing accuracy of the equipment, the tower wall polishing can also reduce the sticky wall