The basic principle of spray drying is that the materials are transported to the atomizer at the top of the spray dryer by the pump through the filter, and the liquid materials are dispersed into droplets by the atomizer. Because the radius of the droplets is small, the specific surface area and surface free energy are large, and they are highly dispersed, the vapor pressure of the moisture on the surface of the droplets is greater than that of the liquid moisture on the plane under the same conditions, so the moisture volatilizes extremely quickly, and the product is dried quickly. Dai Minghe et al. deduced a one-dimensional and bidirectional static mathematical model of spray drying process based on the conservation of mass, energy and Newton's second law, and theoretically studied the thermal drying mechanism of spray drying, which is of great significance to improve the technical level of spray drying.

The spray granulation dryer is a new one-step granulation equipment that organically combines the spray drying technology with the fluidized bed granulation technology. It uses the negative pressure suction of the induced draft fan to dry the fog droplets and gather them into particles, and can adjust the particle size according to requirements, which is more powerful than the general equipment in terms of function.

In the working process of the spray granulating dryer, a certain amount of powder materials are put into the fluidized bed as crystal seeds, and the liquid materials are pumped to the nozzle atomizer. First, with the spray, some water is removed instantaneously with high temperature air, and the residual water is dried at the bottom of the fluidized bed at low temperature and granulated at the same time.

Firstly, the material solution (solution, suspension, extract, paste) is uniformly sprayed onto the inert particles in a fluidized state through an atomizer. The inert particles are located above the distribution plate and are fluidized by the impact of hot air passing through the distribution plate. Hot air not only fluidizes inert particles, but also transfers heat to the particles. When the liquid is sprayed onto the surface of particles, it receives the heat from the particles (from the inside out) and the heat from the hot air (from the outside in) to quickly evaporate the water, forming a thin shell on the surface of the particles. The material changes from elastic shrinkage to elastic brittleness. Due to the violent movement of particles, collisions and friction occur, causing the dried material to detach from the surface of the particles and be ground into fine powder, which is dispersed and collected by the gas-solid separation device along with the exhaust gas. The working process can be roughly divided into three stages, namely, the material liquid is coated on the surface of inert particles, the moisture is heated and vaporized to dry the material, and the dry material falls off.