Spray drying is a process widely used in liquid process forming and drying industry. Zui is suitable for generating powder, granular or block solid products from solutions, lotion, suspended lotion and pumpable paste liquid materials. Therefore, spray drying is a very ambitious process when it is necessary to meet the standards of particle size distribution, residual moisture content, bulk density and new particle installation of products.

With this drying method, the gas-solid two-phase touch surface area in the spray dryer is large, and the drying time is short, generally 5~30s, which is suitable for drying heat sensitive materials. The product obtained through dry processing has outstanding functions and can obtain particles of 30-50mm. The product has good fluidity and solubility. The defect is that the volume of the dryer is large, the heat transfer coefficient is low, resulting in low thermal efficiency and high power consumption.

There are many ways to classify spray dryers, which can be divided into parallel flow type, counter flow type and mixed flow type according to the flow direction of gas and liquid; According to the installation method of the atomizer, it can be divided into upper spray and lower spray, and lower spray and upper spray; According to the structure of the atomizer, it can be divided into centrifugal, pressure, and airflow types; According to whether the heating gas is circulating, it can be divided into open type, partial circulation type, and closed type.

The wall sticking phenomenon is a prominent problem that hinders the normal operation of the spray dryer, especially the spray drying process of solid preparations (especially traditional Chinese medicine). Material sticking to the wall is not only detrimental to collection operations, but over time, sensitive sticking materials can also transform into unqualified materials. From a process perspective, treatment methods include selecting suitable solvents, adding auxiliary materials, and modifying process parameters. However, these methods are not very adaptable, so it is necessary to seek fundamental treatment solutions from the perspective of equipment. Domestic and foreign experts have discussed the problems of wall sticking and agglomeration in the dry process, and believe that the primary cause of wall sticking is wall temperature.

The wall sticking of spray dryer generally has the following three conditions:

1. Semi wet material sticking to the wall: The reason is that the sprayed droplets have already touched the wall before reaching the dry surface, so they stick to the wall. The direction of the wall sticking is generally on the plane of the trajectory of the droplets sprayed by the atomizer, which is related to the structure of the atomizer and the movement of the hot air inside the tower;

2. Hot melt adhesion of low melting point materials: The reason is that the material reaches its melting point at a certain temperature and begins to melt and become sticky, adhering to the wall of the vessel;

3. The surface adhesion of dry powder: When dry powder moves in a limited space, there will always be some contact with the wall, which cannot be avoided. However, such adhesion is generally not thick and can be shaken off by air blowing or quietly striking. The simplest solution is to polish the inner wall, which can to some extent solve this problem.

Here are five ways to avoid wall sticking:

1. Choose a wall clamped dry tower, which is cooled with air to maintain the wall temperature below 50 ℃;

2. Introduce the secondary air cooling tower wall tangentially through the tower wall rotating air sheet;

3. Install an air broom consisting of a row of nozzles near the tower wall and slowly roll it along the tower wall;

4. Add an air hammer to the tower wall, and through the impact of the air hammer, force the sticky material to detach;

5. Adding processing precision to the equipment and polishing the inner wall of the tower can also reduce wall sticking.