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How Spray Dryer Uses Hot Air to Achieve Drying of Mist Produ Time:2018.03.21
     Holves spray dryer is the use of hot air to achieve the drying of the mist-like products. The drying hot air enters the drying tower through the tower mouth. After the drying work is completed, the exhaust gas is exhausted by the induced draft fan. In the process of spray dryer operation, the control of the temperature (hot air temperature) and the exit temperature (exhaust air temperature) when the drying hot air enters the tower is very important. It determines the quality of the product and the dry bulk density and other factors, must be strictly control.
In the spray dryer operation, the exhaust air temperature is related to the moisture content of the product and should be determined according to the allowable moisture of the product. The higher the hot air temperature, the higher the thermal efficiency and the better the economy. However, excessive hot air temperature will cause deterioration of product quality. Therefore, the hot air temperature must be properly increased under the premise of ensuring product quality.
    Spray dryer hot air temperature will have a significant effect on the bulk of the product. High-temperature hot air tends to produce a low bulk density because the hot air has a rapid drying effect, hardens the surface of the particles and expands residual moisture, and promotes the formation of balloon-like hollow particles. If high bulk density (low specific volume) is required or solid particles are required, high temperature hot air should not be used in the design to make contact with newly formed droplets. In the drying of chemicals, the hot air temperature 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 hollow. In food spray drying, the hot air temperature generally does not exceed 177[deg.] C., and thus the starting diameter of the hollow particles formed is not as large as that of chemicals.
    The dry density of the spray dryer is also called bulk density, which plays a decisive role in the drying effect of the product. Therefore, determining the dry bulk density is an important task. Generally, when designing a spray dryer, the dry bulk density should be set. Only in this way can the product achieve a better drying effect. The dryness of the spray dryer is not determined casually, and a number of factors must be taken into consideration when determining, as follows:
 
(1) Equipment type
If a co-current spray dryer is used, a product with a high bulk density can be obtained, so it is necessary to select according to actual needs.
(2) Effects of additives
If you want to obtain products with low bulk, such as instant coffee, instant tea, certain paint powders, etc., you can add nitrogen or carbon dioxide into the dry material. However, if inorganic salts, such as sodium chloride, are added, the bulkiness will be increased. Therefore, care should be taken to add it. It cannot be added wrong, because it may be counterproductive.
(3) Feed concentration
The feed concentration is directly proportional to the bulk density. When the feed concentration is small, the bulk density is small, and the productivity is also reduced accordingly.
(4) Hot air and exhaust air temperature
If the temperature difference between the hot air and the exhaust air temperature is large, the bulk density of the product is lower; when the temperature difference is small, the bulk density is high. However, the temperature difference should not be too small, because the small temperature difference will require a large amount of air, which will increase the required power and thermal energy, and will have adverse effects, so it cannot be too small.


 
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