Chemical Engineering July 2022 - 42

Solids Processing
Conveyor Selection for Bulk Solids Processes
Use this guide to aid the selection of conveying technologies for applications in
powder and bulk solids handling
Josh Marion
Jenike & Johanson Inc.
M
any sectors of the chemical
process
industries
batteries,
(CPI) - including chemicals,
plastics,
mining, power generation, plastics,
food, agriculture, pharmaceuticals
and others - handle a wide range
of bulk solids and powders in manufacturing.
Research has shown that
more than 70% of all products contain
ingredients that are handled in
bulk solid or powder form at some
point during the production chain.
Each bulk solid tends to have its
own unique characteristics, behaviors
and requirements for getting it
(and keeping it) flowing and moving
through solids handling equipment.
Solids-handling
equipment,
such
as bins, silos, hoppers, feeders and
chutes have their own set of difficulties
and challenges for getting material
flowing [1-3], and conveyors are
no different.
There are dozens of different conveying
technologies, many of which
may be marketed as a " one-size-fitsall "
solution for moving bulk solids
around. However, there can be significant
consequences if you don't
get conveying " right. " Depending on
your material, application, and conveying
technology, you may experiJenike
& Johanson
ence production bottlenecks, flow
stoppages and plugging, poor or
inefficient transport, product degradation
or particle breakage, as well
as rapid abrasive wear, segregation
and product variability, spillage, dust
release, excessive maintenance requirements,
or a number of other issues.
So when selecting the " best "
conveying technology for an application
from the start, it becomes
essential to cut through some of the
vendor claims to mitigate risk of experiencing
these handling issues.
This article outlines important factors
to consider for conveyor selection,
and discusses the pros and
cons and appropriate use cases for
common conveying technologies.
FIGURE 1. Several examples of conveying equipment
are shown in this solids-handling facility
42
Conveyor types and functions
For the purposes of this article, conveyors
are technology or equipment,
other than gravity, for moving dry
bulk solids through a process. This
includes moving solids horizontally,
diagonally or vertically, and may involve
multiple pickup or discharge
points. Unlike bulk solids feeders,
conveyors are not choke-fed from a
hopper, and they operate only partially
full (typically at only 30-50%
capacity or less). In addition, they
do not meter or control the solidsthroughput
rate, and generally operate
at constant speeds. Feeders
tend to be quite short, while conveyors
often move materials over
significantly longer distances. In fact,
there are some belt conveyors used
to transport heavy ores several miles
overland, with the world's longest
belt conveyor system carrying phosphate
ore more than 60 miles (97
km) from a mine in the Sahara desert
to a shipping port [4].
Proper design and selection of
bulk-solids feeders, as well as attending
to details of how feeders interface
with conveying systems are
also extremely important for ensuring
reliable process operation and
avoiding bottlenecks, but are beyond
the scope of this article.
Conveying technologies come in
a wide number of shapes, sizes and
configurations. Some of the most
common types include the following:
* Pneumatic conveyors
* Screw conveyors
* Belt conveyors
* Bucket elevators
* Vibratory conveyors
* Drag chain and cable conveyors
* Fluidizing conveyors (for example,
airslides)
A typical industrial process with
a number of these technologies is
shown in Figure 1. The list above
is only a partial listing of conveying
technologies, and there is significant
variety and specialized conveyors
with unique features within each of
these categories. Regardless of what
type of conveyor you use to move
your material, all conveyors should
meet the following requirements:
* Reliable transfer of the material
from the pickup point(s) to the delivery
point(s), at the required flowrate,
with no pluggage or material buildup
within the system
* Minimal product degradation or
particle breakage, if required
* Minimal abrasive wear
* Reasonable energy consumption
* Safe operation with minimal spillage
and dust release
* Sensible maintenance intervals,
with minimal operator intervention
required between intervals
* Sufficient flexibility to fit within the
available space
Conveyor selection criteria
When selecting what type of conveyor
to use in a given application,
it is important to ask some of these
critical questions:
Material properties. Is the solid
material free-flowing?
Cohesive
and sticky? Frictional? Fine, dusty
and aeratable? Friable/breakable?
Abrasive? Corrosive or reactive?
What's the bulk density? What is
the particle-size distribution, including
the largest clump or lump size?
Could the material's characteristics
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