Some 75% of chemical manufacturing processes
involve small solid particles (fine particles)
at some point. Proper design and handling of these fine particles
often makes the difference between success and failure.
Careful attention to particle characteristics during the design
and operation of a facility can significantly improve
environmental performance and increase profitability
by improving product yield and reducing waste.
In the early stages of product and process R&D, as the
process is scaled up from from bench-top glassware
to several-gallon, then hundred-gallon, and finally
production scale, technologists should explicitly consider
how the particulate material in the system
will behave in the sequence of unit operations and in the
equipment for processing, storage, and transport.
For each particulate material -- raw material,
intermediate, final product, or co-product
consider the following:
- SAMPLING AND ANALYSIS:
To characterize the particles, you need
a good sampling protocol, sound analytical procedures,
and photographs that allow you to monitor the particles
continuously on-line (best case) or through grab samples
taken while trying to resolve a problem.
- SIZE DISTRIBUTION:
The particle size distribution should be
carefully-controlled and consistent from batch to batch,
or over time (in continuous reactors). It should be optimized
to give the least trouble during processing and the best product
characteristics.
- SHAPE, STATE OF AGGREGATION, AREA:
The particle shape, state of aggregation, and
surface area per gram should be characterized after
each key processing stage. Understanding and controlling
the conditions which produce the particles can help you
to optimize them for their intended use.
- FLOW, SEDIMENTATION, BED DENSITY:
Flow characteristics (powder or slurry), sedimentation rates
(in liquid or gas), and bed density (sifted, settled, or packed)
significantly affect processing, so you
should characterize them and understand how changes in these
parameters will affect the process.
- ATTRITION:
Attrition resistance (resistance to breakage)
should be known, well-controlled and optimum for the task.
Keep in mind that particle breakdown during processing can
destroy carefully developed characteristics.
- STATE OF DISPERSION (IN LIQUIDS):
Particles suspended in liquid may flocculate,
agglomerate, float, fail to wet-in, foul the walls, or
stabilize foam.
- STATE OF DISPERSION (IN GASES):
Particles suspended in gas may pick up
a charge, explode, form agglomerates, or coat the walls.
- SAFETY, HEALTH, AND ENVIRONMENT:
It is prudent (and generally required) that you evaluate
and minimize hazards related to
explosion or fire (of a dust cloud or fluidized bed or
pneumatic conveying line or dust buildup on equipment
or walls)
inhalation or contact with dusts or mists from the process
discharge to the environment of dust particles or sprays
The study of particle technology has many interesting technical
facets and many rewarding economic aspects. Failure to consider
the particle science involved in a process can result in very
expensive or unpleasant consequences.
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