As spray drying
is the most widely used industrial process involving particle formation and
drying, it is natural that the GEA Niro Test
Center has the widest range of test plants available for testing the complete
range of spray drying techniques.
All pumpable products, both heat or
non-heat sensitive, can be processed via GEA Niro’s versatile spray dryers and
are able to meet the requirements for small- or large-scale production. GEA
Niro’s spray dryers are designed to produce precise properties such as particle
size, bulk density, moisture content, solubility, dispersibility etc. to the
exact requirements as defined by the plant operator.
Before selecting
the design of a spray dryer and the type of atomizer, several properties of the
source feed and final product have to be evaluated, hence the need for testing.
Factors to be taken into consideration may include the actual liquid to be
dried, particle size, distribution and powder quality. This might mean testing
with more than one type of technique – thus the opportunities within GEA Niro’s
Test
Center, where parallel testing can be arranged, are unmatched.
Overview of spray drying techniques
Co-current Mode:
Rotary Atomizer
Atomization is achieved by
feeding a liquid solution or suspension onto a high speed spinning wheel. The
rotary atomizer is placed in the ceiling air disperser and operates with a
vaned atomizer wheel for non-abrasive feeds, or with a carbide bushing wheel
for abrasive feeds. Other wheel designs are available for special applications.
The particle size of the powder produced is controlled through change of wheel
speed.
Two-fluid
Nozzle
Atomization is
achieved by using a compressed gas to atomize the liquid feed. The nozzle is
placed close to the outlet of the ceiling air disperser. This arrangement is
ideal for heat sensitive feeds and has the added advantage of being able to
handle both low and high viscosity liquids. The particle size is controlled by
varying the nozzle flow ratio between compressed gas and feed.
Pressure
Nozzle
Atomization
is achieved by pressing a liquid solution or suspension through an orifice in
the nozzle by means of a high pressure piston pump or a mono pump. Pressure
nozzles are typically used to form coarser powders. Particle size of the
product is controlled by the pressure given by the pump.
Fountain Mode
Two-fluid Nozzle or Pressure Nozzle. The nozzle is
placed in the conical section of the drying chamber, spraying upwards into hot
air entering the drying chamber through the ceiling air disperser. The fountain
mode has the advantage of spray drying higher solid feeds and producing coarser
powders. Selection of nozzle type depends on the feed properties and powder
specification.