The variation of drying time in flash dryer can be divided into four stages

1. Flash dryer raw material acceleration and drying stage

In the heat transfer medium, particles are at a higher temperature and the air humidity is below 100%. In a short period of time, the surface is heated to the dry material humidity, and the rate of water evaporation increases rapidly. After a certain period of time, the heat generated by the digestion and absorption of particles is the same as the heat generated by the evaporation of water, achieving equilibrium. This stage is very short in time, and the discharged water flow rate is not large, and then it enters the constant velocity stage.

2. The stage of uniform drying of raw materials in the flash dryer

At some stages, the water evaporated from the surface of the particles continues to fill from the inside to the surface of the particles, and the surface remains moist throughout. At this point, the drying speed will not change, and the surface temperature of the particles will not change. The evaporation rate is related to the difference in water vapor concentration and temperature of the particle surface and surrounding substances, and the larger the difference, the faster the drying rate. In addition, the drying rate is also related to the gas velocity on the particle surface. There is always a gas film on the particle surface that is not easy to flow, and the reduction of gas film search is beneficial for the evaporation of water and heat exchanger. Therefore, expanding the rate of surface cyclones on particles can enhance the drying speed. After a certain period of drying, the external diffusion rate of water inside the particles begins to be lower than the surface evaporation rate. The moisture in the particles cannot completely wet the surface to maintain surface evaporation, and then the next drying stage begins.

3. Temperature reduction and drying stage of raw materials in flash dryer

When the evaporation reaches a certain level, the moisture inside the particles cannot make the surface completely wet, the wet surface slowly decreases, and the drying speed slowly decreases. At this stage, the evaporation and heat consumption obviously decrease, the particle surface temperature is higher than the material humidity and slowly increases, and the temperature difference with the medium slowly decreases until it is close to or the same.

4. Material balance stage in flash dryer
The moisture absorption and evaporation on the particle surface are balanced. The drying speed is zero. The moisture in the particles is dry and restless, generally not less than the equilibrium moisture during storage. After the rotating flash dryer dries, the raw material particles are small, and the waiting time in the dryer is very short, usually 1-3 seconds. Therefore, during the uniform drying stage of particles, their surface temperature is the humidity of the drying substance. The rotating flash dryer is selected, and the particle size distribution of raw materials is uniform, which is beneficial to ensuring the product quality.