Spray Dryer in milk industry
The spray dryer is an automatic equipment, easy to operate, with intelligent program settings, shutdown protection, safe and reliable to use, and can also be used in the production of milk powder and coffee.
Among various drying methods, one of the most widely used technologies is spray drying, which can directly dry liquid into powder, effectively improve the drying speed and quality of milk emulsion, and improve the production efficiency of milk liquid into finished products. Spray drying The method has the following advantages: 1. It has a wide range of drying, especially for heat-sensitive liquids; 2. The drying process is continuous and easy to control, and can be automated, which greatly improves work efficiency; 3. As long as the drying conditions remain unchanged, the basic properties of the dried milk powder will not undergo any abnormality. With the development and improvement of technology, the milk powder produced will no longer be limited to one type, and other products including skimmed, full-fat, high-fat milk powder, whey powder, protein concentrate, etc. can be produced. With ultrafiltration and enzymatic methods The development of hydrolysis will also produce more diverse products.
Spray drying includes heat exchange of concentrated emulsion droplets, evaporation of surface water, diffusion of water droplets from inside to outside, and heat exchange of dry materials. The drying process has the following three processes:
1. Warm-up process. The moment the mist of the concentrated emulsion comes into contact with the hot air, the drying process begins, and the moisture on the surface of the mist starts to evaporate. If the outside temperature of the fog drop is lower than the wet bulb temperature of the hot air, the heat provided by the hot air makes the outside of the fog drop quickly reach the wet bulb temperature; if the outside temperature of the fog drop is higher than the wet bulb temperature of the hot air, due to the moisture evaporation zone Taking a lot of heat leads to a sharp drop in the outside temperature of the droplets. When the heat balance is reached, it means the process is over and the drying enters the next stage.
2. Constant speed drying process. In the constant-speed drying process, the moisture in the droplets continuously penetrates to the outside, and the external moisture is continuously vaporized and evaporated. The partial pressure of water vapor is consistent with the saturated vapor pressure of the water. The external temperature of the droplets and the temperature of the hot air reach equilibrium, and no longer proceed. Heat exchange. Various indicators of hot air directly affect the drying speed. The more the droplets are dispersed and the larger the contact area, the faster the drying speed. At the same time, if the temperature difference between the droplets and the hot air is greater, the heat exchange is more intense, and the drying will also be accelerated. The time of this stage is generally very short, depending on the equipment and technology will also cause time differences.
3. Deceleration drying process. When the moisture penetration rate in the droplet drops slower than the outside evaporation rate, the constant-rate drying process is declared complete, and the reduced-rate drying process begins. During the deceleration drying process, the emulsion droplet temperature will gradually be higher than the wet bulb temperature of the hot air, and will gradually be the same as the temperature of the hot air, and the moisture content of the dry material will be similar or equal to the equilibrium moisture of the hot air. The drying time of this process is longer than the constant-rate drying process, which is 10~30s or longer.
The working principle of the spray dryer is that the emulsion is dispersed into mist droplets through the nozzle at the top of the drying tower, and is in contact with the hot air from below. Because the temperature of the two is very different, heat exchange will occur, and the moisture in the mist droplets will evaporate by heating. Therefore, the moisture in it is quickly lost, so as to achieve the purpose of drying.
