Spray drying is a method in which drying and granulation can be completed at the same time, and the solution, the emulsion, and the suspension can be directly dried into a powdery or granular product, and the steps of evaporation and pulverization are omitted. By mechanical action, the material to be dried can be dispersed into fine particles, and most of the moisture is removed, so that the solid matter in the material is dried into a powder.
At present, spray drying is widely used in the rapid drying of liquid materials, and is suitable for use in medicine and other fields. According to the relevant technical personnel, the current spray drying methods mainly include pressure type, centrifugal type and air flow type.
Pressure spray drying
The principle of the pressure spray drying method is to use a high-pressure pump to pass the material through an atomizer (spray gun), and to form a mist-like particle to directly contact with hot air for heat exchange and complete drying in a short time.
The pressure spray micronization device has two guide grooves for rotating the liquid in order to increase the turbulence of the solution during spraying. One of the guide groove axes is perpendicular to the nozzle axis and does not intersect with it; the other is that the guide groove axis is at an angle to the horizontal.
Centrifugal spray drying
The principle of the centrifugal spray drying method is to use a disk rotating at a high speed in the horizontal direction to give a solution to centrifugal force to cause it to be ejected at a high speed to form a film, a filament or a droplet, which is caused by friction, obstruction and tear of air. The tangential acceleration generated by the rotation of the disc and the radial acceleration generated by the centrifugal force, the result is moving on the disc at a combined speed, the trajectory is a spiral shape, and the liquid is thrown from the disc along the spiral line. The droplets that are dispersed into very small droplets move at an average speed along the tangential direction of the disc, and the droplets are again sucked by the centripetal suction. Because of the different sizes of the sprayed particles, their flight distances are different, so they are different. The falling particles form a cylinder that is symmetrical about the center of the shaft.
The skilled person stated that the method of obtaining a more uniform droplet by using the centrifugal spray drying method is to reduce the vibration when the disc is rotated; when the amount of liquid entering the disc is kept constant per unit time, the surface of the disc is kept smooth and smooth. In addition, the circumferential speed of the disc should not be too small.
The centrifugal spray dryer is a drying device suitable for drying liquids such as emulsions, suspensions, pastes, and solutions. The device has a fast drying speed, is suitable for the drying of heat-sensitive materials, can maintain the color, fragrance and taste of the material, and has convenient operation and control, is suitable for continuous control of production, and has good dispersibility, fluidity and solubility, and is currently widely used in medicine and other fields. .
Airflow spray drying
The working principle of the airflow spray drying method is that the wet material enters the dryer through the conveyor and the heated natural air at the same time, and the two are fully mixed, and the evaporation and drying are achieved in a short time due to the large heat and mass exchange area. . The dried product is discharged from the cyclone, and a small portion of the fly powder is recycled by a cyclone or bag filter.
It is reported that the airflow spray dryer mainly has four forms, one is that the airflow dryer is operated under negative pressure, the material does not pass through the fan; the second is that the airflow drying is a positive pressure operation, and the material passes through the fan with a pulverizing effect; The airflow dryer is a tail gas circulation type; the fourth airflow drying is a reinforced airflow dryer, which combines flash drying and airflow drying. This type of spray dryer is a new type of spray drying designed by our factory according to the needs of users. device.
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