Some items are indispensable to obtain a complete view of ours dryers.
High drying air flow rate leads to a fast dislocation of product in the chamber, with increase of residual humidity.
Low drying air flow rate leads to a long permanence of product in the chamber, which results in a very dry powder.
High air speed leads to a good separation of product in the cyclone.
High speed of atomizer disk results in smaller particles of product.
High concentration of product results in larger particles of product.
Low concentration of product and high speed of atomizer disk result in very small particles of product, making it more difficult to obtain a good cyclonic separation.
With very small and fine particles, the extraction has to be done with manga type filters.
When the air flow rate of the Feed Pump increases and the inletl temperature remains constant, the outlet temperature decreases.
Inlet temperature is equal to air temperature that enters in the drying chamber, which is introduced through the air disperser, by a ventilator/exhaust, and encounters the pulverized product, making the vaporization. The final product (solid) is not submitted to the inlet temperature.The temperature of drying air mixed with the solvent vapors and the dry material, before entering in the cyclone, is denominated outlet temperature. This temperature is not necessarily the temperature of the dry material, which goes relatively cold, according to the residence time in the equipment. Therefore, outlet temperature can be considered the highest temperature that the final product could reach with a slow process of recovery. While the inlet temperature is controlled only by the burner, the outlet temperature is controlled by the following parameters:
- Inlet temperature- Air flow rate.- Air flow rate of Feed Pump.- Concentration of product to dry.
One of the most important points to consider in drying by atomization is the optimum difference At between the inlet temperature and the outlet temperature, which is called .
Increasing the difference At of temperature by raising the amount of product entering in the chamber and keeping the inlet temperature constant, the residual humidity of the final product will raise.
A necessary point which has to be determined to obtain a specific product is the type of air heating utilized. They are called direct and indirect air heating.
Dryer with indirect air heating utilizes the same gases of combustion, of liquid or gas fuels, to heat the drying air. This mixture contacts the product directly.
Dryer with indirect air heating can utilize any thermal source to heat the drying air. In indirect air heating can only enter atmospheric hot air and or previously filtered air.
For a correct performance of drying by spray, the dosage of product has to be uniform (not pulsing) and controlled by microprocessor constantly. The correct gradual variation of dosage makes the equipment to work in continuous periods, without eventual interruptions.