Powders - Spray drying

From Liquid Feeds

Spray Drying (One-Stage)

Powder

Spray Dryer

One of the most important continuous drying techniques for converting solutions, emulsions, and slurries into powders. The liquid feed is atomized into droplets which are directed into a controlled flow of hot air. Particles are formed as moisture evaporates from each droplet. The final shape and structure of the particles depend upon the air temperature and humidity conditions, and the drying characteristics of the feed material. Single stage spray drying produces powders consisting of mainly individual particles. Some partial agglomeration occurs due to self-adhesion surface effects. The free flowability of powders improves with increase in particle size. The spray drying chamber and atomizer are selected according to the desired particle size of the powder, i.e.

From Semi-Solid Feeds

Swirl Fluidizer™

Vortex Disintegrator Drying

The Swirl Fluidizer™ is a continuous drying system specially designed to produce powders of small particle size (<50 microns mean) from filter cakes, pastes and sludge-like feeds. The fee is discharged into a drying chamber containing a high speed comminutor which disintegrates and disperses the solids into hot air. The resulting powder is collected in a bag filter.

From Moist Powders

Fluid Bed and Flash Drying

Fluid Bed Dryer

Fluid bed and flash drying systems are selected according to feed properties and during the drying process the granulometry of the moist particulates does not change to any degree.

Fluid bed dryers involve the passing of air upwards through a bed of particulates so a state of fluidization occurs. Different types of fluid bed designs are available. Stationary designs are used for particulates that are fluidizable, either in their moist state or after initial drying in the presence of fluidizing material.

Vibrating designs are used for non-fluidizable particulates due to their particle distribution and shape, or when a most lenient treatment is required. The design of the air distributor plate is crucial to all fluid bed operations.

Flash dryers involve the dispersion of moist particulates into high velocity air streams. Flash drying is ideal for fine and course particulates where drying can be completed within a few seconds (surface moisture evaporation only). It can also act as a pre-drying stage prior to fluid bed processing.

Microwave Vacuum Dryer

Microwave Vaccum Drying

Drying under the vacuum with microwave heating is applicable for aqueous and organic solvent wet powders, particularly those involving heat sensitive, active, high value, and toxic materials. Microwave energy overcomes the heat transfer limitations of conventional vacuum drying without the need for elevated temperatures. Energy is transferred by a high frequency electromagnetic field which causes heating due to the rapid vibration of polar molecules.

From Melts

Spray Congealer

Spray Congealing

Liquid melts are sprayed into a cooling chamber in a plant design that resembles a spray dryer operating with cold air. Use of cold air causes the melt droplets to congeal into individual spherical particles that give a highly free flowing powder.

Different sizes of congealed particles can be produced through control of the atomizer operation (upper mean size limit=2 mm).