12
11)
GENERAL ADVICE AND USEFUL HINTS
1)
Always start a trial with a low to medium inlet temperature (150-180
°
C), maximum air-flow, and
a slow pump rate. Observe the bottom of the main chamber for wetting and either reduce the
pumping rate or increase the temperature if the product is not completely drying. The
optimum pumping/temperature rates are achieved when no wet spotting of the product is
observed (this assumes water as the solvent).
2)
If the sample is a liquid with solids in suspension it may be necessary to keep it continually
agitated with a magnetic or overhead stirrer. Heavy suspensions are best pumped from the
sample container when it is positioned on the side shelf as this shelf, the pump and the jet are
all at a similar height. If the sample is pumped from the bench top the product may separate
as it is being pumped upwards in the silicone tube.
3)
Most spray drying processes lose fines in the exhaust. The amount lost usually depends on
air flow and particle weight. The air flow can be reduced using the screen controls. The
particle size/weight can often be increased by using a larger jet size.
4)
At the commencement of a run allow the main chamber a few minutes to heat up. The inlet
temperature may show the required setting but the glassware and main chamber will be quite
cool for a few minutes. (Wait until inlet temperature has stabilised).
5)
If the sprayed sample is light coloured it may be more easily observed by placing a dark card
behind the cyclone.
6)
The ideal flow path through the cyclone should be a continuous spiral. If product accumulates
on the cyclone wall try alterations to the air flow or the compressor jet pressure or the jet size.
7)
Only change one parameter at a time e.g. temperature, air flow etc.
8)
Some samples may require pre-heating before spraying.
9)
In rare instances the use of a suitably supported separating/dropping funnel positioned as
near as possible to the jet assembly has been found to be effective rather than using the
pump. This gravity feed method is effective where e.g. abrasive ceramics may cause the
pump tube to wear exceptionally quickly.
10)
Peristaltic pumping always creates a pulsing liquid flow. If this is a problem the pulsing effect
can be reduced by connecting a small glass expansion bulb in the tube between the pump and
the jet.
11)
Generally the most efficient drying is achieved using the highest temperatures compatible with
the product but temperatures as low as ambient may be used with e.g. non aqueous solvents.
