Spray drying is a method that can complete the drying and granulation together. It can directly dry the solution, emulsion and suspension into powder or granular products without evaporation and destruction.

Now, spray drying is widely used in the rapid drying of liquid materials, which is suitable for medicine and other fields. According to relevant technical personnel, there are three main spray drying methods: pressure type, centrifugal type and air flow type.

Pressure spray drying

The principle of the pressure spray drying method is to use the high-pressure pump to gather the materials through the atomizer (spray gun) to form fog like particles, which are in direct contact with the hot air for heat exchange and complete the drying in a short time.

The pressure spray micronization equipment has two kinds of guide grooves to make the liquid rotate, in order to try to increase the turbulence of the solution during spray. One of the guide groove axes is perpendicular to the nozzle axis and does not intersect with it; The other is that the axis of the guide ditch is at a certain angle to the horizontal.

Centrifugal spray drying

The principle of the centrifugal spray drying method is that the disc rotating at high speed in the horizontal direction is used to give centrifugal force to the solution, so that it can be thrown out at high speed to form films, filaments or droplets. Due to the conflict, prevention and tearing of air, the tangential acceleration with the disc rotation and the radial acceleration with the centrifugal force result in the disc moving at a combined speed, and its orbit is a spiral, After the liquid is thrown from the disk along this spiral line, it will be dispersed into very small droplets, which will move along the tangential direction of the disk at an average speed. One droplet will fall again by gravity. Because the size of the sprayed particles is different, their flight distance will be different. Therefore, the particles falling at different distances form a cylinder symmetrical around the center of the rotating axis.

Technicians said that the method of obtaining more uniform droplets by using centrifugal spray drying method is to reduce the sensation when the disc rotates; When the amount of liquid entering the disc remains constant in unit time, the disc surface shall be flat and lubricated. In addition, the circular velocity of the disc should not be too small.

Centrifugal spray dryer is a kind of drying equipment suitable for drying emulsion, suspension, paste, solution and other liquids. The equipment has fast drying speed, is suitable for drying heat sensitive materials, can adhere to the color, aroma and taste of materials, and is easy to operate and control. It is suitable for continuous control and production. The product has good laxity, fluidity and solubility. Now it is widely used in medicine and other fields.

Air spray drying

The operating principle of the air flow spray drying method is that the wet materials enter the dryer together with the heated natural air through the conveyor, and the two are fully mixed. Because the heat and mass exchange area is large, the purpose of evaporation drying can be achieved in a very short time.

It is reported that the air flow spray dryer mainly has four ways. One is that the air flow dryer is operated under negative pressure, and the materials do not pass through the fan; The second is air drying, which is a positive pressure operation, and the materials have a destructive effect through the fan; The third air flow dryer is the exhaust gas circulation type; The fourth type of airflow drying is the enhanced airflow dryer.