Spray drying can be defined as the
transformation of feed from a fluid state into a dried state by spraying the
feed or the substance into a hot medium. The feed used in the process can be a
solution, paste or suspension which can easily be transformed into
agglomerates, powders, and granules. The form that the final or finished product
takes is dependent on various factors including the chemical and physical
properties of the substance as well as the operation and design of the spray
dryer.
The basic idea of the overall spray drying
process is the production of highly dispersed dried powders from a fluid or
liquid feed by evaporating the solvent. The finished product is achieved by
mixing a heated gas with a sprayed fluid of high mass to surface ratio
droplets, within a drying chamber or vessel. This causes the liquid solvent to
evaporate quickly and uniformly through direct contact.
Uses of the spray drying process
The process of spray drying can be used in a
wide variety of applications where the production of a free-flowing dried form
of powder is required. But, this method of drying has become the most preferred
in the following areas:
-
Tooth and bone amalgams
-
Pharmaceuticals
-
Egg and milk products
-
Textiles
-
Beverages
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Resins, plastics, and polymers
-
Detergents and soaps
-
Plant extracts, flavors and colorings and many more.
Spray drying is a very flexible process that
can easily meet the necessary product requirements of the above-given area's
products, offering an inexpensive solution to many drying problems. It can
solve drying problems concerning thermally sensitive materials including food
ingredients and flavors. The products which are spray dried retain their
nutritional value of the ingredients, while providing with a material that can
further be used directly in a final composition, and even can be readily mixed
or reconstituted.
Phases or methods of the spray drying process
The process of spray drying consists of the
following steps:
1.
Feed preparation
The feed used in the process can be a
homogenous and free from impurities suspension, paste or solution.
2.
Atomization
Atomization is the most important and
critical step in the entire process of spray drying. It is the method of
transforming the feed into small liquid droplets. The degree of atomization
controls the drying level of the feed as well as of the dryer size.
3.
Drying
This phase of the spray drying process
ensures that moisture evaporates quickly from the surface of the feed. This is
then followed by a failing rate period where the drying level is controlled by
diffusion of the liquid to the surface of the particle.
4.
Removal of powder from moist gas
The separation of powder from the gas needs
to be carried out in an economical medium as well as in a pollutant-free
manner. The particles are generally removed with bag filters, scrubbers,
precipitators or cyclones.
5.
Packaging and cooling
The last step in the spray drying process is
the cooling and packaging of the final product.
All these steps are very important to
undertake if you want to get perfect spray drying results. However, to ensure
that you get powder particles that are free from any impurities, you need to
have proper information on drying kinetics as well as a good collection of
solid ingredients. Keeping all these will surely provide you with the desired
results.
