In the operation of the spray dryer, it is very important to determine the temperature of the hot air entering the tower (hot air temperature) and the outlet temperature (exhaust air temperature) for drying. The exhaust air temperature is related to the moisture content of the product and should be determined according to the moisture allowed by the product. The higher the hot air temperature, the higher the thermal efficiency and the better the economy. But too high hot air temperature will cause product quality to deteriorate, so the hot air temperature must be properly increased on the premise of ensuring product quality.
The hot air temperature of the spray dryer will have a significant impact on the bulk density of the product. High-temperature hot air tends to produce low bulk density. This is due to the rapid drying effect of hot air, which hardens the surface of the particles and expands the residual moisture, which promotes the formation of balloon-shaped hollow particles. If high bulk density (low specific volume) is required, or solid particles are required, high-temperature hot air should not be used to contact newly formed droplets during design. In the drying of chemicals, the temperature of the hot air is as high as 538°C, and the product particles are large. It can be found that the residual steam has enough pressure to blow the outer surface into a cavity. In food spray drying, the hot air temperature generally does not exceed 177°C, so the initial diameter of the hollow particles is not as large as that of chemicals.
The hot air inlet temperature of the spray dryer will directly affect the evaporation intensity of the drying chamber. For non-heat-sensitive materials, high-temperature hot air should be used as much as possible in order to increase the evaporation intensity.
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