Spray drying is a method of systematic technology applied to material drying. What are the various forms?
Spray drying is a method of systematic technology applied to material drying. After atomization of the dilute material in the drying room, the moisture rapidly vaporizes upon contact with hot air, resulting in the dried product. This method can directly dry solutions and emulsions into powder or granular products, eliminating processes such as evaporation and crushing.
By mechanical action, the material to be dried is dispersed into very fine mist like particles (increasing the evaporation area of water and accelerating the drying process), which come into contact with hot air to instantly remove most of the water and dry the solid matter in the material into powder.
Mechanism of action
(1) Pressure spray drying method:
① Principle: Using a high-pressure pump, the material is passed through an atomizer (spray gun) at a pressure of 70-200 atmospheres, and polymerized into 10-200 mist like particles that come into direct contact with hot air for heat exchange, completing drying in a short period of time.
② Pressure spray granulation device: M-type and S-type, with a guide groove that can make the liquid flow rotate. The axis of the M-type guide groove is perpendicular to the axis of the nozzle and does not intersect with it; The axis of the S-shaped guide ditch is at a certain angle to the horizontal. The purpose is to try to increase the turbulence of solution during spray.
(2) Centrifugal spray drying method:
① Principle: Using a horizontally rotating disk at high speed to apply centrifugal force to a solution, it is thrown out at high speed, forming a thin film, filament, or droplet. Due to the friction, obstruction, and tearing of air, the tangential acceleration generated by the rotation of the disk and the radial acceleration generated by centrifugal force result in a combined speed moving on the disk, with a spiral trajectory. After the liquid is thrown out of the disk along this spiral line, it disperses into very small droplets that move along the radial direction of the disk at an average speed. At the same time, the droplets fall due to the gravity of the earth, and the particles sprayed are of different sizes. Therefore, their flight distances are also different, and particles falling at different distances form a cylinder symmetrical about the axis of rotation.
② Requirements for obtaining more uniform droplets: a. Reduce vibration during disc rotation b. Maintain a constant amount of liquid entering the disc per unit time c. Smooth and flat disc surface d. The circular velocity of the disc should not be too small, rmin=60m/s, If the milk (100-160m/s) is less than 60m/s, the spray droplets are uneven, and the spray distance seems to be mainly composed of a group of droplets and a group of fine droplets sinking near the disk, and decreases with the rotation speed.
③ Structure of centrifugal spray: requirements: the wetting perimeter is long, the solution can reach high rotation speed, the spray is uniform, the structure is solid, light, simple, no dead corner, easy to disassemble and wash, and the productivity is high.
(3) Airflow spray drying method:
① Principle: Wet materials enter the dryer simultaneously with heated natural air through the conveyor, and the two are fully mixed. Due to the large heat and mass exchange area, the purpose of evaporation drying can be achieved in a very short time. The dried finished product is discharged from the cyclone separator, and a small portion of the fly ash is recycled by the cyclone dust collector or bag filter. The Q-type airflow dryer operates under negative pressure, and the material does not pass through the fan; QG type airflow drying is a positive pressure operation, and the material is crushed by a fan; FG type airflow dryer is a tail gas circulation type; JG type airflow drying is an enhanced airflow dryer that integrates flash evaporation drying and airflow drying. It is a new type of drying equipment designed by our factory according to user requirements.
structural components
According to the direction of movement between hot air and dry particles in the drying chamber, they are classified as parallel flow, countercurrent flow, and mixed flow. Parallel flow is often used in milk. Parallel flow can be dried using a higher inlet air temperature without affecting the quality of the product.
a. Horizontal parallel flow pattern
b. Vertical descent and flow pattern
c. Vertical descending mixed flow type.
d. Vertical upward flow pattern
