The basic idea of spray drying
Basic principles of spray drying
The definition of spray drying: the solution, the emulsion, suspension and other forms of slurry in the hot air spray into small droplets, in its fall process, the water is evaporated into a powder or particles of the product.
In the top of the drying tower into the hot air, while the material pump will be sent to the top of the slurry, spray through the atomizer spray droplets, droplets group surface area increases, and high temperature hot air contact after the rapid evaporation of water, In a very short period of time will become a dry product, discharged from the bottom of the tower. Among them, the hot air and droplets in contact with the rapid decline in temperature caused by increased humidity, as the hot and humid exhaust gas from the exhaust fan, the exhaust gas was fine powder with a separation device recovery.
The whole drying is divided into two stages of constant speed and deceleration. At the same speed stage, the evaporation of water occurs on the surface of the droplet. The evaporation rate is controlled by the diffusion rate of the vapor through the surrounding air film. The power is the temperature difference between the hot air and the droplet. The faster the temperature difference is, the faster the water is The rate of diffusion through the particles is greater than the evaporation rate. Then, when the diffusion rate is reduced and the saturation of the particle surface can no longer be maintained, the evaporation rate starts to slow down and the drying starts to enter the deceleration stage. During the deceleration phase, the particle temperature begins to rise and the drying is completed, where the temperature of the material is close to the ambient air temperature.
 
1.2 Features of spray drying
1.2.1 The temperature of the droplets during drying is not high and the product is of good quality
Spray drying used in a wide temperature range, even with high temperature hot air, the exhaust temperature is still not high. In the early drying, the material temperature does not exceed the ambient hot air wet bulb temperature, the dry product quality is better. It is in the pharmaceutical industry application significance is: not prone to protein egg changes, loss of vitamins or oxidation and other defects, the quality of heat-sensitive drugs are basically close to the standard vacuum drying.
1.2.2 After drying, the product has good dispersibility, fluidity and solubility
As the drying process is done in clean air, the product is basically able to keep the ball similar to the droplet.
1.2.3 drying speed is very fast
After the liquid spray, the surface area increases, in the role of high temperature airflow, can instantaneously evaporate 95% to 98% of the water, the drying time is generally only 10 ~ 40s (relative to 1l material liquid).
1.2.4 The process is simple, easy to control and for continuous scale production
Spray drying is often used in moisture content of 40% to 60% of the material, special materials can be up to 90%, without concentration can also be a dry powder. Spray dry after most of the products do not need to crush or screening process, so that the entire production process is simplified. At the same time, in a certain range can change the operating conditions to control the product size, bulk density and moisture and other performance indicators. In addition, due to dry products can be continuous discharge, so spray drying can be applied to continuous scale production.
1.2.5 The entire operation of the closed, suitable for clean production areas
As the spray drying operation in the closed tower to avoid cross-contamination and dust flying, suitable for the pharmaceutical industry in the production of bulk drugs, especially the production of sterile bulk drugs.
1.2.6 Spray dry imperfections
Spray drying is not perfect: First, when the hot air temperature is lower than 150 ℃, the heat capacity coefficient is low (the corresponding evaporation intensity is low), so the tower's volume will become larger; Second, about 15% of the exhaust gas entrainment powder to be efficient Separation collection device.
 
1.3 Spray drying in the pharmaceutical industry applications
Spray drying can be widely used in the production of bulk drugs, the applicable varieties are: amoxicillin, ampicillin, acetaminine, dihydro streptomycin, kanamycin, ampicillin, penicillins, tetracycline, streptomycin , Chloramphenicol, sulfamethoxazole, vitamin A, vitamin E, vitamin B12, aluminum hydroxide, aluminum sulfate glycol, amylase, barium sulfate, calcium lactate, calcium pantothenate, hormones, l-lysine, nicotinic acid , Protease, rutin derivatives, liver and so on.