SPRAY DRAYER

 

Principle:

ü The feed solution consisting of dispersed core in coating solution is sprayed through an atomizer (produces fine droplets) from the top of the spray chamber.

ü As the liquid feed moves downward, it interacts with circulating hot air.

ü Thus solvent present in droplets gets evaporated, as a result of which dry microcapsules are formed.

ü Drying is achieved in a very short time i.e., even before the droplets, reach the bottom of the drying chamber (usually 2-3 seconds).

ü Spraying the droplets of sufficient smaller size and subsequent interaction with hot air is the important step in whole process.

 

Construction:

ü Spray dryer consists of a spray chamber and a separating chamber (cyclone separator).

ü They are interconnected by means of a narrow pipe.

ü An atomizer is fitted at the top of the spray chamber which sprays the feed as droplets.

ü An inlet for hot air (or gas) is present at the top.

ü The entire equipment is made up of stainless steel.

ü The cyclone separator is provided with two outlets one at the top and another at the bottom, below which a product receiver is placed.

ü The internal lining of the spray chamber is smooth. The diameter and height of the spray chamber vary depending upon the type of operation.

 

Working:

ü Feed solution consisting of dispersed core is passed into the atomizer from where it is sprayed as small droplets.

ü The nozzle delivers these droplets radially into the spray chamber.

ü The size of the droplets must be as small as possible in order to facilitate rapid drying.

ü When hot air is introduced into the spray chamber, the liquid interacts with the hot air and get dried.

ü As a result, solid particles are formed which then follow helical path and reach the bottom of the spray chamber.

ü The temperature of the hot air must be sufficiently high (usually in between 300 to 1500° F), so as to make the drying process effective.

ü Coarse and fine solid particles obtained travel along with air into the cyclone separator, where the air is removed and particles are collected in the product receiver.