Left: Figure 3. Two arms agitator built in one single piece, achieving efficient mixing
by differential velocities.
Above: Figure 4. Lab scale filter dryer vessel in stainless steel or glass for simulation
studies prior to scaling-up.
directly heating the product and usually only accounts for 5% of the heat
transfer. Other units have direct base heating, where the filter media sits
directly on a woven mesh that sits directly on the heated base, and can
supply up to 25% of the heat transfer [see Figure 2]. This leaves the sidewalls that are in direct contact with the cake to make up for the other 25
to 40% of the heat transfer. In order to eliminate any condensation of the
evaporated solvent from dripping back into the product during drying,
the rest of the vessel wall and dished-top need to be heated.
Drying in any equipment can cause problems of product caking
and product balling. To avoid product drying too quickly on the
filter media or sidewalls and caking up, it is important have a dryer
as a wet cake, as a reslurry, and as a dissolved product, which are very
useful especially if the product is an intermediate. The heat transfer
area of the dryer is one of the most important factors in product drying.
The heat transfer area can be divided into 3 basic parts: the filter base,
the vessel sidewall and dished-top, and the heated agitator. The heat
transfer media is usually applied to the base, sidewall and dished-top
either through a half pipe or a jacket. The jacket with internal baffling is
the best overall distribution of the heating media. The agitator is, by far,
the most active heat transfer surface of the dryer, accounting for more
than 50% of the heat used for drying. The second most depends on the
type of dryer. Some filters have a few centimeter gap of air between the
heated base and the filter media. This air gap will isolate the heat from
Figure 5. Full range of ANFD for each product development stage for optimum technology transfer.