Chemical Engineering August 2023 - 34

FIGURE 9. The material shown here is fine wheat that is exhibiting
caking behavior
could create dust fires, deflagrations
and explosions. Combustibledust
testing is critical in evaluating
whether a material can form a combustible
dust at the necessary concentration,
and if so, how severe the
explosion could be. Further, toxicity
hazards should be established in
this phase.
Once the material is properly characterized,
comminution and screening
equipment should be evaluated.
Going back once again to the earlier
cement-industry example, consider
a very wet, cohesive limestone. Recall
from that example that gyratory
crushers are often used in primary
crushing. This is highly effective
at
reducing large
limestone
rock,
and could lead to 6:1 size reduction
within the rock. However, if the
limestone has a significant clay concentration,
plugging of the gyratory
crusher can occur, severely limiting
throughput. Perhaps in this application,
it makes more sense to utilize a
shear crusher, which is better suited
at handling sticky, cohesive materials.
Likewise, the transfer chute
following the crusher must be designed
to prevent buildup, plugging
and dusting of fine limestone particles.
The same concept applies to
all equipment downstream, including
screeners, silos, dust collectors
and feeders. Conducting a proper
" flowability " review of the entire system
before it goes online can reduce
downtime, improve product quality,
and result in significant operating
cost savings.
Once equipment is selected and
process flow diagrams begin to take
shape, the most important step takes
place. Designing safe processes is
paramount, and final safety assess34
ments
should be performed
before commissioning any
comminution or screening
equipment. In fact, the Occupational
Safety and Health
Administration (OSHA; Washington,
D.C.; www.osha.gov)
recommends beginning with
a process hazards analysis
(PHA) to identify, evaluate
and develop control schemes
for highly hazardous materials
[4]. Likewise, a dust hazards
analysis (DHA) should
be performed to evaluate potential
fire, deflagration and explosion hazards,
before the equipment goes
online. In fact, the National Fire Protection
Association (NFPA) requires
DHAs for many industries, including
chemicals, food processing and
woodworking [5]. PHAs and DHAs
should be performed by qualified
professionals who have knowledge
in industrial safety and specific hazards
associated with the materials
being handled.
Concluding remarks
In most industries that handle solids,
comminution and screening operations
are crucial. There are various
methods and technologies available
for comminution and choosing the
appropriate one can significantly affect
the efficiency of energy usage,
product quality, and the equipment
lifespan. Similarly, screening methods
can also have many of the same
significant impacts. Both operations
may lead to unintended consequences
that can increase the risk
of flow disruptions, downtime and
safety hazards. However, by assessing
the physical, chemical and flow
properties of the materials, conducting
a thorough flow processing
review, and performing PHAs and
DHAs when necessary, it is possible
to mitigate these risks before implementing
comminution and screening
processes and before purchasing
equipment. Following these steps
will ensure that new operations will
function correctly and safely right
from the start.
n
Edited by Scott Jenkins
Editor's note: all photos and diagrams in this article
appear courtesy of Jenike & Johanson
References
1. Maynard, Eric. Fundamentals of Crusher Selection. World Cement,
March 2010.
2. Maynard, E. (Presenter), and Cronin, K. (Moderator). Break it
Down! How to Effectively Choose Size Reduction Equipment
[Webinar]. Powder & Bulk Solids by Informa Markets, February
15, 2023.
3. Combustible dust safety. Chemical Safety Board (CSB). www.
csb.gov/recommendations/mostwanted/combustibledust/
4. Occupational Safety and Health Administration. Process safety
management: Hazards. Retrieved May 3, 2023, from www.
osha.gov/process-safety-management/hazards
5. NFPA 652, " Standard for the Fundamentals of Combustible
Dust " , 2016 ed.
Authors
Eric Maynard is a vice president
for Jenike & Johanson (400 Business
Park Drive, Tyngsboro, MA
01879; Email: epmaynard@jenike.com;
Phone: Website: www.
jenike.com),
a world-renowned
engineering consulting firm specializing
in the storage, flow and
processing of powder and bulk
solids. During his 27 years at Jenike
& Johanson, he has designed handling systems for
bulk solids including iron ore, cement, coal, limestone,
plastic powder, fertilizers, food products, and pharmaceuticals.
He has gained valuable hands-on experience
from working on over 750 solids handling and pneumatic
conveying projects, and specializes in the cement
and mining industries helping clients to reliably handle
challenging bulk solids that are sticky, abrasive, and
prone to segregate. Maynard has specialized knowledge
in the areas of dust explosions, static electricity
generation, and crushing
technologies.
Maynard's
working knowledge of the National Fire Protection Association
(NFPA) standards for safe handling of combustible
dusts helps him provide valuable advice to his
clients to ensure safe handling of materials prone to
explosions or fires. He sits on NFPA committees for
standards 660, 652, 654, 655, and 91. His expertise
also includes designing new pneumatic conveying systems
and troubleshooting systems that are poorly operating
and experiencing costly problems with abrasive
wear, line blockages, throughput limitations, and particle
attrition. Maynard has authored over 50 technical
articles and is the company's principal instructor for
training on the storage, flow and pneumatic conveying
of bulk solids presented through the American Society
of Mechanical Engineers (ASME) and the American Institute
of Chemical Engineers (AIChE). Additional subject
areas of expertise include stockpile and feeder design,
mixing/blending, particle segregation, sampling,
and caking/agglomeration of bulk materials. Maynard
frequently presents customized courses at individual
companies and numerous conferences. Maynard received
a bachelor of science degree in mechanical engineering
from Villanova University and a master of
science degree in mechanical engineering from
Worcester Polytechnic Institute.
McKinnon Ray is a project engineer
with Jenike & Johanson
(same address; Email: mray@jenike.com)
specializing in the design
of storage bins, stockpiles, transfer
chutes, and conveying equipment
for tricky powders and bulk solids.
During his four years with the firm,
has has worked on projects across
several industries including cement,
mining, food & beverage, agriculture, chemicals,
and more. In addition to design work, he has experience
with flow property and pneumatic conveying characteristics
testing. Before Jenike & Johanson, Ray worked at
Anheuser-Busch in the operations and logistics departments.
McKinnon has a chemical engineering degree
from Mississippi State University.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
AUGUST 2023
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Chemical Engineering August 2023

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