Chemical Engineering August 2019 - 53

Solids Processing
Controlling Dust through Pelletizing
Tumble-growth agglomeration can reduce dust in solids-handling processes. Here's
how it works
FEECO
Chris Kozicki, Ron Eichhorn and
Carrie Carlson
FEECO International
H
andling and processing
bulk solids appears in
nearly every industrial sector,
from energy to agriculture.
Dust is a ubiquitous and challenging
issue when working with
bulk solids, because it can create
hazardous or unsanitary work environments,
transportation problems
and financial waste in the form of
lost product.
It is not surprising then, that each
year, companies go to great expense
to control and mitigate dust.
One of the most effective ways to
manage dust is through pelletizing
- a form of tumble-growth agglomeration
(particle size enlargement)
that produces rounded or
spherical granules. Pelletizing can
be an invaluable tool in managing
dusty bulk solids that opens opportunities
in beneficial reuse applications,
creates marketable products
and mitigates the handling and
processing challenges associated
with dust.
The term " pelletizing " is often
used to refer to various types of agglomeration.
This article references
the term as a form of tumble-growth
agglomeration carried out on a disc
pelletizer.
Dust reduction with pelletizing
Pelletizing significantly reduces dust.
Apart from collecting dust into small
masses of material, the pelletizing
process produces a rounded or
spherical granular product (Figure
1). Pelletizing is distinguished from
pressure agglomeration, which produce
granules with jagged edges
that can rub together and degrade
into fines. With rounded granules,
there are no edges to rub together
and break down, allowing pellets to
remain intact throughout handling
FIGURE 1. Pelletizing solid materials can reduce dust in solids-handling processes by forming rounded
granules (left) from the initial powders (right)
and storage.
Dust may be the byproduct of a
process or a recovered residue, a
material prone to degradation, or
simply a material that is inherently
dusty in its natural state. A material
in the form of dust presents an array
of issues that complicate the handling
and use of the material.
Pelletizing alleviates these issues,
and as a result, has become a popular
technique for solving a variety of
different material-handling problems.
Several dust-related aspects in
which pelletizing can realize benefits
are summarized here.
Recovering value. When dust is
produced as a process byproduct
or residue, it is often made up of, or
contains, a valuable material. The
recovery of the target component
is made difficult by the dusty nature
of the material. In cases like these,
pelletizing is used as an intermediate
step in a larger process to allow
for easier recovery of the valuable
component. An example of this is in
the pelletizing of electric-arc furnace
(EAF) dust.
EAF dust is a byproduct of steel
production and is rich in metals -
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
AUGUST 2019
particularly iron, lead and zinc. To
recover these metals, EAF dust is
roasted in a kiln. Roasting is made
especially complicated when the
material to be processed is in the
form of a dust. Pelletizing allows
roasting to be carried out efficiently
and economically, offering the following
advantages:
* Pellets eliminate the risk of entrainment
that dust presents (fines becoming
swept up into the airflow
and exit through the exhaust gas
system)
* Pellets can be produced to a desired
size to allow for both better
heat movement around the pellets
in the material bed and increased
heat-transfer efficiency
through each pellet for improved
metal recovery
* Overall process efficiency
is
increased,
because a higher gas velocity
can be used when entrainment
is not a concern
In addition to dust containing a
valuable component, dust generated
from product degradation
during handling, transportation or
processing generally represents a
loss in product. This dust can be
51

http://WWW.CHEMENGONLINE.COM

Chemical Engineering August 2019

Table of Contents for the Digital Edition of Chemical Engineering August 2019