cpp – Process technology for the chemical industry 02.2020

The mixing helix of the cylindro conical dryer CCD ensures short drying
times
The vapour filter is jet-cleaned to rule out product deposits on the filter
elements
The vessel including the dished cover is
heated by a jacket, half-pipe coils or pillow
plates using heat carriers such as hot water,
(saturated) steam or thermal oil, which can
be heated to temperatures of up to 400 °C.
By heating the complete dryer, the
formation of cold spots is prevented. In addition,
an insulating jacket keeps the heat
inside the dryer and at the same time offers
operator protection against injury.
A ball segment valve with an inflatable,
sanitary lip seal is normally used as an emptying
device at the cone’s central outlet,
guaranteeing maximum tightness in vacuum
or pressure operation. It allows the lowest
helix segment to be adapted exactly to
the ball segment’s geometry, thus minimising
unmixed zones and product residues.
The cylindro conical dryer is often used as a
vacuum contact dryer for increased
throughput as well as gentle product drying
at low temperatures. A vacuum pump provides
the required vacuum, producing an
operating vacuum in the dryer in the range
from 5 to 100 mbar absolute. As a result,
moisture evaporates at lower temperatures,
throughput is higher and energy losses are
reduced. The lower process temperatures
have a positive effect on the quality of the
end and intermediate products, particularly
when handling temperature-sensitive substances
such as enzymes.
For easy and hygienic cleaning, the Bolz cylindro
conical dryer features WIP or CIP
nozzles. At the end of the drying process
and before the next drying batch starts,
cleaning liquid can be sprayed into the interior
of the dryer under (high) pressure
while the agitator is rotating. After the
cleaning liquid has been completely discharged,
the dryer is heated and the remaining
moisture evaporates.
Vapour filter
Like every Bolz dryer, the cylindro conical
dryer CCD also has a vapour filter to prevent
product particles from escaping into the environment
or the connected vacuum pipeline
during charging or discharging. The
filter surface, filtration efficiency and material
are always adjusted to the dryer size,
the operating parameters and the product.
To avoid condensation of the vapours and
thus sticking and blocking of the filter elements,
the vapour filter is heated and insulated.
The vapour filter is jet-cleaned to rule
out product deposits on the filter elements.
Wide range of applications
The Bolz cylindro conical dryer is not only
used as a vacuum contact dryer. It demonstrates
its flexibility and versatility in the
production of cocoa, for example. First, the
fermented cocoa beans, broken into cocoa
nibs, are heated in the central shaft dryer by
the addition of steam. An alkaline solution is
then also added by means of overpressure
and temperature, reducing the bitter flavouring
components, raising the pH to approximately
7, washing out unwanted bitter
substances and adjusting the cocoa’s colour.
This process includes operation under vacuum,
use as an overpressure reactor, homogeneous
mixing and sterilisation of the
broken cocoa nibs. The Bolz cylindro conical
dryer is moreover ideal for sterilising spices
by adding superheated steam as well as for
evaporating liquid or pasty products, which
are difficult or impossible to filter due to
their low solids content, meaning that no
mechanical solid-liquid separation can be
installed upstream.
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AUTHOR:
FRANK BESSNER
Product Manager,
Bolz Process Technology
cpp 02-2020 13