There are many classification methods for experimental spray dryers. They can be divided into parallel flow, counter flow and mixed flow according to the flow direction of gas and liquid. According to the installation method of atomizer, it can be divided into upper spray type and lower spray type; The structure of the device can be divided into centrifugal type, pressure type and air flow type; according to whether the heating gas is circulated, it can be divided into open type, partial circulation type and closed type.
The sticking phenomenon is a prominent problem that hinders the normal operation of the spray dryer, and the spray drying process of the solid preparation (especially the traditional Chinese medicine) is particularly obvious. The sticky wall of the material is not only unfavorable for the collection operation, but the sensitive sticky wall material will deteriorate into unqualified materials over time. From a process point of view, the solution includes selecting the right solvent, adding excipients, and changing the process parameters. However, there is not much room for adjustment of these methods, so a fundamental solution must be sought from the perspective of the equipment. Experts at home and abroad have studied the problem of sticking and agglomeration in the drying process. It is believed that the main cause of sticking is the wall temperature.
Spray dryer sticking walls generally have the following three conditions:
1. Hot-melt sticky wall of low-melting material: The reason is that the material reaches the melting point at a certain temperature and begins to melt and become sticky and adhere to the wall;
2. The semi-wet material sticks to the wall: the reason is that the sprayed droplets are in contact with the wall before they reach the surface drying, so they stick to the wall, and the position of the sticky wall is generally the droplets sprayed against the atomizer. On the plane of the motion trajectory, and the structure of the atomizer, the hot air is related to the motion state in the tower;
3, the surface adhesion of dry powder: dry powder in the limited space will always have some touch on the wall, this is unavoidable, but such a sticky wall is generally not thick, as long as the air is blown or gently tapped Can be shaken, the simplest solution is to polish the inner wall, which can solve this problem to some extent.
Use the following five methods to solve the problem of sticking walls
1. Increase the processing precision of the equipment, and the inner wall polishing of the tower can also reduce the sticking wall.
2. The air hammer is added to the tower wall, and the sticking material is forcibly removed by the hammering of the air hammer;
3. Install an air broom consisting of a row of nozzles near the wall of the tower and slowly rotate it along the tower wall;
4. Introducing a secondary air cooling tower wall through the tangential direction of the tower wall cyclone;
5, using a wall drying tower, with air cooling between them, so that the wall temperature is kept below 50 ° C;
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