Chemical Engineering October 2014 - 69

ditional gas flow can be generated
either by temporarily using a spare
compressor or blower, or by sucking
in additional air from the environment
using a Venturi. If the conveying
gas is taken from the plant air
supply, then the gas-management
system has to allow for a purging
cycle with a higher gas flowrate,
provided that the plant air supply
has sufficient capacity. The use of
pressure reservoirs only helps for
smaller systems, since most of these
purge tanks have a relatively small
volume that is insufficient to clean
long and large conveying lines.
Closing thoughts
Reliable operation of pneumatic
conveying systems requires knowledge
of the state diagram and desirable
operating windows. This is
based on conveying characteristics
that are either measured in a test
facility or generated while operating
a similar industrial system.
Velocity is the key control variable
for dilute-phase systems. The velocity
control (or airflow control) can
be accomplished in many ways depending
of the type of air mover.
A more-sophisticated control system
is required for dense-phase
conveying where the stable operatAuthors
Harald
Wilms is a senior
bulk-solids-handling expert
with Zeppelin Systems GmbH
(Graf-Zeppelin-Platz
1,
88045 Friedrichshafen, Germany,
Email: harald.wilms@
zeppelin.com; Phone: +49171-364-6447).
He received
his diploma in mechanical
engineering and process technology
from the TU Braunschweig
and his Ph.D. from
the same university. For 30 years, Wilms has
been working in various positions with the Zeppelin
Group. He was the first CEO of Zeppelin
Systems in Houston (1998 to 2001). Wilms has
presented many papers and lectures on bulksolids
technology, especially on issues related to
silos, pneumatic conveying, polymer logistics and
plant design. He is a member of international
bulk-solids-handling committees, and is a lecturer
at the TU Braunschweig.
Shrikant V. Dhodapkar is a
Fellow in the Dow Performance
Plastics Group at The Dow
Chemical Co. (Freeport, TX
77541; Phone: 979-238-7940;
Email: sdhodapkar@dow.com)
and adjunct professor in chemical
engineering at the University
of Pittsburgh. He received
his B. Tech. in chemical engineering
from I.I.T-Delhi (India)
and his M.S.Ch.E. and Ph.D.
from the University of Pittsburgh. During the
past 28 years, he has published numerous papers
on particle technology and contributed chapters
to several handbooks. He has extensive industrial
experience in powder characterization, fluidization,
pneumatic conveying, silo design, gas-solid
separation, mixing, coating, drying, feeding and
dosing, computer modeling and the design of solids
processing plants. He is a past chair of AIChE's
Particle Technology Forum.
ing zone, line forces, system stability,
startup and shutdown must be
taken into account. Today, suppliers
of dense-phase conveying systems
have developed expertise that is
incorporated into specialized hardware
and software to appropriately
manage these variables.
■
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