Chemical Engineering November 2013 - 54

Solids Processing
As a check of the population-balance
model analysis, the cumulative breakage
data points were plotted along with
the computed cumulative breakage
functions from the population-balance
model (Figure 17). This plot indicates a
good agreement between the breakage
data and the values computed from the
population-balance analysis.
Summary
Mills can be qualitatively ranked based
on their tendency to induce fracture, fatigue,
abrasion or shear by examining
the milling action. Mills where classification
is part of the milling operation
can induce fatigue events. Mills where
References
1. Epstein, B., Logarithmico - Normal Distribution
in Breakage of Solids, Ind. Eng. Chem.
Vol 40, pp. 2,281-1,191, 1948.
2. Sedlatschek, K. and Bass, L., Contribution
to the Theory of Milling Processes, Powder
Metal. Bull., 6: 148-153., 1953
3. Kapur, P.C. and Agrawal P.K., Approximate
glancing blows of particles against
surfaces are dominant cause abrasion
events. Mills where impacts or stress
application are more direct result in induced-fracture
events. Particles or materials
where toughness is much larger
than resilience require mills with a lot
of shear to induce particle breakage. The
population-balance model can be used
with mill tests to deduce the dominant
breakage mechanisms for a given material.
The optimal mill is then selected
by matching the dominant mechanisms
with qualitative ranks based on the tendency
to induce fracture, fatigue, abrasion
or shear. This simple analysis can
aid engineers in selecting the right mill
Solutions to the Discretized Batch Grinding
Equation, Chem. Eng. Science, Volume 25,
Issue 6, pp. 1,111-1,113, 1970.
4. Bilgili, E. and Scarlett, B., Nonlinear Effects
in Particulate Processes, Nonlinear Analysis,
Volume 63, Issues 5-7, pp. e1,131-e1,141,
Nov. 30-Dec. 15, 2005.
5. Broadbent, S. and Calcott, T., J., Inst. Fuel,
Vol 30, pp. 13-15, 1957.
for the job the first time. These criteria
for mill selection can be combined with
other information about the bulk material,
such as adhesive tendencies and
particle size, to help select a mill that is
free from troublesome operation.
■
Author
Kerry Johanson is chief
operations officer for Material
Flow Solutions, Inc. (7010
NW 23 Way, Suite A, Gainesville,
Fla., 32653; Phone: 352379-8879;
Cell 352-303-9123;
Email: matflowsol@bellsouth.
net), the consulting firm he
founded in 2001. He also
spends time researching at
the University of Florida Particle
Engineering Research
Center. He began his career as a laboratory technician
with Jenike & Johanson, before moving
to JR Johanson, Inc. in 1985, where he became
chief technical officer for the company. He has
authored over 40 technical papers, which have
been published in numerous technical journals
internationally and has presented at many industry
seminars. He has also developed a graduate
course on powder flow and technology at
the University of Florida. Johanson holds a PE
license and has a Ph.D. in chemical engineering
from Brigham Young University.
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