Views: 7 Author: Site Editor Publish Time: 2021-02-22 Origin: Site
Spray dryer machines can generally be divided into three types, namely pressure spray drying machine, centrifugal spray drying machine, and airflow spray drying equipment. These three types of spray drying technique will be introduced in detail below.
Pressure Spray Drying Technology
Pressure spray dryer working principle
Using a high-pressure pump, the material is passed through an atomizer (spray gun) at a pressure of 70-200 atmospheres to polymerize into 10-200 atomized particles that directly contact the hot air for heat exchange and complete the spray drying process in a short time.
Pressure spray atomization device
M-type and S-type, with guide grooves that make the liquid flow rotate. The axis of the M-type guide groove is perpendicular to the nozzle axis and does not intersect with it. The axis of the S-shaped guide groove is at an angle to the horizontal. The purpose is to try to increase the turbulence of the solution when spraying.
Centrifugal Spray Dryer Technology
centrifugal spray dryer working principle
The centrifugal spray dryer uses a high-speed rotating disk in the horizontal direction to impart centrifugal force to the solution so that it is thrown out at a high speed to form a thin film, filament, or droplet. Due to the friction, hindrance, and tear of the air, the tangential acceleration generated by the rotation of the disk and the radial acceleration generated by the centrifugal force result in the movement on the disk at a combined speed, and its trajectory is a spiral. After the liquid is thrown from the disc along the spiral line, it is dispersed into tiny droplets that move along the tangential direction of the disc at an average speed, and the droplets fall under the suction of the earth. Because the spray dried powders are of different sizes, their flying distances are also different, so the particles falling at different distances form a cylinder symmetrical about the center of the axis of rotation.
Requirements for obtaining more uniform droplets:
a. Reduce the vibration when the disc rotates
b. The amount of liquid entering the disc remains constant per unit time
c. The surface of the disc is flat and smooth
d. The circumferential velocity of the disc should not be too small
rmin=60m/s, if the powder (100-160m/s) is less than 60m/s, the spray droplets will be uneven. The spray distance is mainly composed of a group of droplets and a group of fine droplets near the sinking plate and decreases with the increase of the rotation speed.
Structural requirements of centrifugal spray dryer
The wetting periphery is long, which can make the solution reach high speed, uniform spray, strong structure, lightweight, simple, no dead corners, easy to disassemble and wash, and high productivity.
Airflow Spray Drying Technology
Airflow spray drying working principle
The wet material enters the airflow spray dryer through the conveyor and the heated natural air at the same time. The two are fully mixed. Due to the large heat and mass exchange area, the purpose of evaporation and drying can be achieved in a short time. The dried product is discharged from the cyclone separator, and a small part of the fly spray dried powder is recycled by the cyclone dust collector or the bag filter