Ammonium Metatungstate Spray Dryer Wall Sticking Reasons and Solutions
Spray drying tower is a wide applied process in liquid process shaping and drying industry. It can be used to transform solution, emulsion, suspension and paste liquid into powder and granular solids. When the finished particle size distribution, residual moisture content, density and particle shape must meet with precise standards, spray drying becomes an ideal method.
The types and reasons for ammonium metatungstate (AMT) wall sticking during spray drying were analyzed. There are three types of wall sticking: half wet materials, materials with low melting point, dry powder. The wall sticking of half wet materials is concerned to the structure, fixing and operation of spray drying tower and sprayer, the motion of hot air in tower. The melting sticking occurred when the melting point of materials is lower than the drying temperature. The wall sticking of dry powder is concerned to geometric figure of cyclone chamber, roughness of wall, velocity of air and static charge. 
Ammonium metatungstate spray dryer wall sticking solutions include improve the structure and texture of drying tower, use the proper atomizer, proper installation of atomizer, proper operation process, etc.
1. Improve the structure and texture of drying tower. If the design of diameter of dry tower is smaller than the atomizer cone, it will cause a mass amount of wall sticking. In order to prevent wall sticking, the diameter of dry tower should be larger, thus the liquid material will fall down directly without making contact with wall of tower. But the diameter can not be too large because it will increase cost of equipment and occupied area, it also affects flow speed of hot air in the tower and drying quality.
2. Use the proper atomizer. Atomizer is also called nozzle, it is the key part of spray dryer. Its different structure affect the distribution of misty liquid, also diameter and property of micro grains.
3. Installation of atomizer. If there is only one atomizer in the dry tower, the axis of atomizer should be on the center line of tower. If there is more than one atomizer, then the nozzle of atomizers should not be face to face.
4. Proper operation process. For the pheumatic spray drying tower, the process parameter often refers to drying temperature, feeding velocity and pressure of nozzle. Drying temperature includes inlet air temperature and outlet air temperature. Increase inlet air temperature can promote liquid evaporation, which will solidify the liquid before it contacts the wall which will reduce the wall sticking waste rate and increase yield of product. Besides that, temperature also affects the diameter of grains. When the temperature is low, the grain size is bigger which will prolong the drying process. When the inlet air temperature stay the same, raise the outlet air temperature can reduce the temperature differences to fasten drying efficiency.
5. The movement of hot air in the dry tower. The movement of hot air in the dry tower affects wall sticking directly. When the total amount of inlet air stay the same, the proportion of the air for protection atmosphere and air for drying will affects the drying result. If the air is insufficient for drying, then the liquid will stick on the wall before getting dried.
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