The spray dryer is a drying equipment widely used in the food industry,According to the capacity, it can be divided into large scale spray dryer and small scale spray dryer.
Spray drying is a drying method that uses an atomizer to disperse the raw material liquid into droplets, and use hot gas (air, nitrogen or superheated steam) to dry the droplets to obtain a product.The raw material liquid can be a solution, an emulsion, or a suspension.
The liquefied atomizer disperses the material liquid into droplets, increasing the heat and mass transfer rate of the drying process.Atomizer is one of the key components of spray drying. There are currently three commonly used ones, namely, pressure atomizer, centrifugal atomizer, and airflow atomizer.
The atomized liquid has a large contact surface area with the hot air flow, and it quickly conducts heat and mass transfer as soon as it comes into contact with the higher temperature air flow.After the droplet moisture absorbs heat, it quickly evaporates into water vapor, and the air acts as both a heat carrier and a moisture carrier.In the initial stage of drying, the droplets are very small, and the drying resistance caused by the diffusion and transmission of the moisture content in the material is almost equal to zero. The temperature of the material has been at the surface temperature of the material, which is a constant-speed drying stage.When there is insufficient moisture on the surface of the material, the material begins to heat up and form a temperature gradient inside, which is the slow-down drying stage.If the temperature gradient is large and the vapor pressure inside the material is greater than the cohesive force on the surface of the material particles, the particles will explode, instantly increasing the mass transfer evaporation surface.
Advantages of spray drying:
1. The drying process is very fast;
2. It can be directly dried into powder;
3. Easy to change drying conditions and adjust product quality standards;
4. Due to instantaneous evaporation, the equipment material selection requirements are not strict;
5. There is a certain negative pressure in the drying room, which ensures the sanitary conditions during production, prevents dust from flying in the workshop, and improves the purity of the product;
6. High production efficiency and few operators.
Spray drying is often the last step in the manufacturing process, which is to change the substance from liquid to powder through continuous spraying, mixing and drying.Among the many technologies for storing food, spray drying has its unique advantages.Because the temperature used by this technology is not very high, it can effectively retain the taste, color and nutrition of the food while removing microbial contamination.