Properties and influencing factors of spray drying products

1 The influence of operating parameters of spray dryer on the properties of the product The influence of operation parameters on the properties of the product (mainly referred to the size and loose density) of the product is as follows (1) Under constant atomization and drying conditions, the particle size and bulk density of dried products increase with the increase of feeding rate (2) When the solid content of the material increases, the particle size of the dried product also increases At a constant drying temperature and feeding rate, the evaporation load will be reduced due to the increase of solid content in the feed liquid, so the product with lower wet content can be obtained Due to the rapid evaporation of water, it is easy to generate dry hollow particles and products with low bulk density (3) If the viscosity needs to be reduced in order to facilitate the transportation and atomization of the feed liquid, increasing the feed temperature has a certain impact on the properties of the dry products Increasing the feed temperature will reduce the total heat needed for droplet evaporation However, it is still very small to continue to increase the heat content of feed liquid compared with the heat required for vaporization (4) The influence of surface tension on the properties of dried products depends on the mechanism of drying and atomization When the proportion of micro droplets in the droplets is increased, the droplet distribution is wider The droplets produced by the feed solution with low surface tension are smaller However, when the surface tension is high, larger droplets are produced, and the size distribution is relatively large (5) The influence of the inlet temperature of dry air on the inlet temperature of dry air depends on the drying characteristics of the product For the expanded droplets during drying, increasing the drying temperature will produce large particles with low bulk density However, if the temperature is increased to make the evaporation rate slow down and increase, so as to make the droplets expand, break or split, then dense fragments will be formed and loose dense dust will be formed (6) With the increase of the contact speed between the droplets and the air, the mixing degree and the heat and mass transfer rate will be increased With the increase of contact speed, the evaporation time becomes shorter, and the dried product particles show irregular shape Due to different products, the bulk density has also changed, but no general conclusion has been reached 2 The formation principle of hollow particles the tendency of droplet expansion and the formation of hollow particles play an important role in the final loose density of dry products Hollow particles can be formed by four mechanisms ① A semi permeable surface layer is formed on the droplet surface With the increase of the humidity of the droplet, the droplet expands and ejects the vapor generated inside ② The rate of water evaporation is faster than the rate of solid diffusion returning to the inside of the droplet When evaporation is completed, there are many pores, especially in the case of crystalline products ③ As a result of the capillary action, when dry, the liquid in it moves to the drop surface through the micro pores between the solid particles The liquid leaves the center of the droplet to form a void This mechanism is suitable for clay paste ④ The air brought into the feed liquid helps to form an air space inside the drop Spray dryer