Structure characteristics and working principle of flash dryer

- Apr 09, 2019-

1 Structure of the flash dryer. Flash drying is a vertical fluidized bed dryer with a rotary pulverizing device that can simultaneously dry, pulverize, and classify materials. The main body of the device is a cylindrical drying chamber, which is composed of a pulverizing fluidized section at the bottom, a central drying section, and a top grading section. The bottom pulverizing section is equipped with a stirrer, and the stirrer speed is steplessly adjusted by an external motor. The agitator serves two purposes to drive the hot air entering the drying chamber from the distribution chamber to produce a high velocity rotating gas stream to form a fluidized bed. In addition, it has a strong stirring and pulverizing effect on the material, strengthens the mass transfer heat transfer, and accelerates the drying rate of the material. A volute air distribution chamber is arranged at the bottom of the dryer to allow the tangentially fed hot air to uniformly enter the drying chamber through the annular guide slit. A screw feeder is arranged in the drying section, the feeder is dragged by the speed regulating motor, the rotation speed is adjusted by the frequency converter, and the top classification section has a classification ring, and the corresponding classification ring diameter is replaced according to the granularity requirement of the product.

2 flash drying work principle. According to the structure of the flash dryer, the working process can be divided into four stages: crushing, gas-solid contact, drying, and grading. These four working processes are also not available at the same time.

3 broken. Since the flash dryer is mainly used for drying the paste material, the material is broken by the stirring blade and the high-speed air stream immediately after entering the dryer to maximize the dispersion of the material and the specific surface area of the wet material per unit volume.

4 gas-solid mixing and drying. The flash dryer generally uses wet air as the heat carrier, and whether the gas-solid mixing can be effectively achieved is the main factor affecting the drying rate. The stirring paddle of the flash dryer breaks up the material and produces a dispersion effect, and the air entering the dryer is also in a highly turbulent state, and the gas-solid mixing is quickly achieved. At the same time, the bulk material falls down under the action of gravity. Since the bottom of the dryer is an inverted cone structure, the velocity of the airflow is very high, up to 60m/s, which can ensure that the bulk material is in a good fluidized state and is heated by the air. Surrounded.

5 grading stage. The classifier is an annular baffle mounted on the top of the dryer. The material rises with the airflow. Due to the centrifugal force, the large and dry materials are subjected to centrifugal force and the radius of rotation increases. When the radius of rotation is larger than the radius of the step ring, it is blocked. Dry the room until the requirements are met before the dryer can be discharged through the classifier. When the material is added to the dryer, the material is in a fluidized state of rotation. After the mass is crushed, the diameter is rapidly reduced and the water is evaporated. The material is spirally raised under the entrainment of gas. The smaller the dry material is in the inner ring, the larger the damp material produces the centrifugal force larger than the outer layer close to the wall. However, the large particles of the outer layer are continuously pulverized and dried, and the centrifugal force is also reduced to move toward the inner ring. When the water meets the requirements, the gas is taken out, and the pressure in any section of the drying chamber changes.

6 structural characteristics of the flash dryer. The bottom of the drying chamber is provided with an inverted conical structure, so that the flow cross section of the hot air is continuously expanded from the bottom to the top, the bottom gas velocity is large, and the upper gas velocity is small, so that the lower large particles and the upper small particles can be in a good fluidization state. The inverted cone structure also reduces the length of the agitator shaft cantilever and increases the reliability of operation. The bearing is placed outside the machine to avoid long-term operation of the bearing in the high temperature zone and prolong the service life of the bearing.