Spray drying is a method of systematic technology applied to material drying. After atomizing the diluent in the drying room, the moisture rapidly vaporizes in contact with hot air, resulting in a dry product. This method can directly dry solutions and emulsions into powder or granular products, eliminating the need for evaporation, crushing, and other processes.
Through mechanical action, the material that needs 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 and instantly remove most of the water, drying the solid substances in the material into powder.
Mechanism of action
(1) Pressure spray drying method:
① Principle: Using a high-pressure pump, the material is atomized into 10-200 mist like particles through a atomizer (spray gun) at a pressure of 70-200 atmospheres, which are directly in contact with hot air for heat exchange and complete drying in a short time.
② Pressure spray micronization device: M type and S type, with a guide channel to rotate the liquid flow, The M-shaped guide groove axis is perpendicular to the nozzle axis 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: A high-speed rotating disk in the horizontal direction is used to apply centrifugal force to the solution, causing it to be thrown out at high speed, forming thin films, fine threads, or liquid droplets. Due to the friction, obstruction, and tearing of air, the tangential acceleration generated by the disk rotation and the radial acceleration generated by centrifugal force move at a combined speed on the disk, with a trajectory of a spiral shape. After the liquid is thrown out of the disk along this spiral line, it is dispersed into very small liquid droplets that move along the tangential direction of the disk at an average speed. At the same time, the liquid droplets are also attracted by the gravity and fall, due to the different sizes of particles sprayed out. Therefore, their flying distances are also different, and the particles falling at different distances form a cylinder symmetrical around the axis of rotation.
② Requirements for obtaining more uniform liquid droplets: a. Reduce vibration during disk rotation b. Maintain a constant amount of liquid entering the disk per unit time c. The surface of the disk is flat and smooth d. The circumferential velocity of the disk 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 evaporative drying is achieved in a short time. The dried finished product is discharged from the cyclone separator, and a small portion of the flying powder is recycled and reused by the cyclone or bag filter. The Q-type airflow dryer is operated under negative pressure, and the material does not pass through the fan; QG type air flow drying is a positive pressure operation, and the material is crushed by a fan; The FG type airflow dryer is a tail gas circulation type; JG type airflow drying is an enhanced airflow dryer that integrates flash 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 drying particles in the drying room, they are classified as co flow, counter flow, and mixed flow. Parallel flow is commonly used in milk. The parallel flow pattern can be dried at a higher inlet temperature without affecting the quality of the product.
a. Horizontal parallel flow pattern
b. Vertical descent and flow pattern
c. Vertical descent mixed flow type.
d. Vertical rising and parallel flow pattern
