Chemical Engineering August 2015 - 61

Solids Processing
A Pragmatic Approach to Powder Processing
Modern powder-testing methods can offer valuable insights into bulk material
behavior and lead to efficient powder-processing solutions
Jamie Clayton
Freeman Technology
P
rocess simulation is a powerful
tool for engineers in
the chemical process industries
(CPI) and one that
plays an important role in commercializing
new manufacturing routes
and supporting process optimization.
While it might be costly to
construct a robust process model,
once such a model is in place, it will
deliver value throughout the lifetime
of the process. For powder processors,
however, comprehensive
simulation is not yet an industrially
practical option, largely because
the mathematical modelling of powder
behavior cannot yet be reliably
achieved. Establishing a successful
manufacturing solution by applying
experimentation and process simulation
in combination is therefore not
viable, so alternative methods must
be considered.
Traditionally, companies that handle
and manufacture powders have
relied heavily on processing experience,
supported by basic forms of
powder testing. However, this approach
is more difficult to sustain
within the lean-manufacturing environments
that now prevail across
all industrial sectors. Developing a
knowledge base to extend powder
processing expertise is seen as increasingly
important, whether in the
development of continuous processes
for pharmaceutical products
or in advancing the application of
additive manufacturing (AM).
This article provides a review of the
challenges associated with powder
processing and characterization, and
demonstrates how modern powdertesting
methods provide increased
insight to support efficient process
development and optimization. An
example case, describing work carried
out by a leading global powder
processor, illustrates the potential
Powders
Solids
Liquids
Gases
FIgure 1. Powders are bulk assemblies consisting of solids, liquids and gases. Interactions between all
three of these phases determine the bulk powder behavior
benefits of adopting a pragmatic approach
to powder handling that is
based on measuring and applying
powder properties that are directly
relevant to a specific process.
Powder behavior
Powders are ubiquitous throughout
the CPI. As raw materials and
intermediates, they are used in the
production of goods, ranging from
processed foods and pharmaceuticals
to paints, coatings and metal
components for automotive and
aerospace applications. Learning
how to control powder behavior to
meet advancing manufacturing requirements
is critical, especially as
markets become more competitive,
and as the use of new production
techniques, such as additive manufacturing,
grows.
Powders are bulk assemblies
(Figure 1) comprising solids, in the
form of particles, gases (normally in
the form of air), and liquid, (usually
present in the form of moisture on
the surface of the particle or within
its structure). A network of complex
interactions between these constituent
elements dictates the bulk properties
of powders, such as flowability,
compressibility, permeability and the
ability to aerate, which give powders
their industrial versatility.
The behavior of a powder is a
function of the physical properties of
the particles, as well as other external
variables. For example, physical
properties include particle size, morChemiCal
engineering www.Chemengonline.Com august 2015
phology and surface texture. Variables
associated with the bulk assembly
include the extent of air and
the level of moisture content in the
bulk. The complex, numerous and
varied interactions complicate efforts
toward process modeling and also
make the measurement and control
of a bulk powder challenging.
Modeling and powder testing
Considering modeling first, there
have been many attempts to mathematically
model powder behavior,
and this area remains one of
continuing study, particularly as
computing power increases. The
starting point for the mathematical
modeling of powders tends to involve
uniformly sized, spherical particles
- typically microscopic glass
beads - and interesting, important
progress has been made. However,
powder modeling is still a predominantly
academic activity and not yet
a practical tool for industrial processors.
Progressing from the modeling
of " ideal " particles, to a situation
that more accurately represents the
types of materials in routine industrial
use, increases the complexity of the
modeling significantly. The reality is
that all of the particle properties and
environmental conditions that influence
powder behavior cannot yet be
reliably replicated and there is still a
lack of robust correlations between
the physical properties of solid particles
and bulk powder behavior.
These acknowledged limitations
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Chemical Engineering August 2015

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