As one of the types of continuous atmospheric dryer, it can complete drying and granulation simultaneously. According to its technological requirements, the pressure, flow and the size of the nozzle of the feed pump can be regulated to obtain the required spherical particles according to a certain size proportion. In terms of methods of liquid spraying, there are mainly three types of spray dryers, including centrifugal-type spray dryers, nozzle-type spray dryers, and pneumatic-type spray dryers. It is especially suitable for heat-sensitive materials.
Working Principle of a Spray Dryer
A spray dryer belongs to a kind of hot air direct drying equipment. When working, the atomizer (nozzle) decomposes the raw liquid material into droplets and sprays them into the hot air with the temperature of 120 ~ 300℃. It can dry materials rapidly within a few seconds to a dozen seconds by utilizing the velocity difference between droplets moving and hot air. The raw materials can be solution, emulsion, suspension, melt or paste liquid. The dry products can be made into powder, granule, pellet or even hollow ball according to the technological requirements. The spray drying technology can be divided into pressure spray drying, centrifugal spray drying, air flow spray drying.
Parts of a Spray Dryer
A spray dryer is mainly composed of a drying tower, atomizer, cyclone separator, receiving bottle, waste material receiving bottle, air compressor, draught fan, dryer body and integrated control circuit.
The main component of a spray dryer is atomizer, which is regarded as the heart of a spray dryer. It is directly related to product quality and economic indicators. The higher the dispersity of a spray dryer is, the higher the drying efficiency is. The more uniform the atomization is, the less the moisture content of the product changes. Therefore, the atomizer should not only ensure the dispersion of the feed liquid, but also keep the particle size change to a minimum.
What is the Difference Between Spray Drying and Freeze Drying?
Generally, spray drying varies from freeze drying. For example, the spray drying can make moisture vaporize rapidly, having a pretty good drying effect. At the same time, the spray drying speed is fast, and the particles are more uniform with a good dispersion. But high temperature spray will damage the organizational structure of products. For freeze drying, it happens at low temperature with a small sample handling capacity and long time.