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Dr. Kathrin Rübberdt
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e-Mail: presse@dechema.de
Trendreport No. 7: Bulk Solids Technology
February 2015
The Character is Key- Challenges for Bulk Solids
Technology

Characterization of bulk solids facilitates smooth production
flows

Nanoparticles pose a special challenge

Bulk solids expertise needed for urban mining
Roughly 50% or more of substances used in the chemical industry
are solids which need to be processed, handled and transported, so
it is hardly surprising that exhibitors and visitors at ACHEMA have
an interest in bulk solids technology. A learning curve is associated
with the handling of powder and granulate.
Bulk solids are found in all sectors of industry including food, cosmetics,
chemicals, automobile production, biomass processing and waste
management. Particles with special property profiles are often the secret
to success in new product development. Composite materials, fuel cells
and catalysts are a few examples. In addition, special surface properties,
particle size and particle distribution can be manipulated to create new
active ingredients for cosmetics and pharmaceuticals.
The widespread use of pods and capsules for household coffee makers
would be inconceivable without particle technology expertise. The same is
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DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e.V.
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true of powdered soup and prepared mixes. The trick is to prevent the
ingredients from separating after packaging. The dried product has a
longer shelf life and is easier to transport than canned soup.
The basic principles behind many bulk solids processing techniques
including screening, mixing and comminution have not changed for the
past hundred years. That does not mean, however, that no further
innovation is possible. Mechanical processing on display in Halls 5 and 6
at ACHEMA is currently undergoing a renaissance. Bulk solid property
profiles are becoming increasingly complex and the quality standards are
more and more demanding. Particle size, for example, continues to
decrease. 20 years ago the micrometer range tended to be the norm but
nanotechnology has now become mainstream. This has created the need
for finer distributions.
Bulk solids – a challenge for equipment operators
The properties of fluids are now well understood, but surprising things can
happen during handling of powder, dust and granulate. This is something
which equipment and plant operators are well aware of. What makes bulk
solids handling so difficult? One bulk solid can be easily filled, but bridging
can be a problem with a second product and a third substance rushes
through the pipes like a liquid. There are products that constantly exhibit
different behavior in identical filling trials or, even worse, stagnant zones
form in the fourth trial (but not before), negating all of the previous results.
Upstream handling of bulk solids can also have an influence. Particle
compaction during conveying and filling is a factor that may need to be
considered.
The ideal particle rarely exists. In most cases, minor variations in size and
surface characteristics make it difficult to accurately predict filling and
dosing behavior. Knowledge about properties such as bulk solid density,
particle size, particle shape, moisture, etc. makes things easier. Precise
characterization of the flow properties is also important. Getting that
wrong can lead to disruption in the process flow. Most equipment
manufacturers have a test and development center where they can run
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DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e.V.
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trials and investigations. The engineering teams identify industry-specific
characteristics. Gentle handling is very important in the plastics industry to
avoid problems like angel hair (hair-like strands caused by friction during
material handling). Explosion protection is often mandatory at chemical
plants. Hygienic material handling is the top priority in the food and
pharmaceutical industries.
Nanoparticles: a lot to learn?
Nanoparticles create special challenges for equipment operators and bulk
solids experts. These products are already being used on an industrial
basis in cosmetics and detergents. High hopes are placed on them in the
medical sector for drug delivery and even to release drugs only when they
reach cancer cells in order to avoid therapeutic side effects.
The size, shape and surface properties of nanoparticles have a direct
influence on product characteristics in items such as semiconductors and
solar cells. Classification of particles < 20 nm is difficult using current
techniques. Electrostatic forces and molecular interaction are the
predominant factors rather than mass or density. A lot of research is still
needed on nanoparticle characterization, properties, processing and
classification. Scientists borrow knowledge from other disciplines which
already have in-depth experience in handling large molecules and small
particles. Chromatographic techniques used in protein purification are
being applied to nanoparticles with promising results.
New optical techniques or combinations of different measurement
methods make it possible to measure particle size and morphology online
during ongoing production.
A window on the process
A few years ago, the general consensus was that bulk solids are
unpredictable, but in the meantime this attitude has changed. With the
increased computing power available today, simulation using techniques
such as finite element analysis is an effective process optimization tool.
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www.dechema.de
The advantage of methodologies like CFD (computational fluid dynamics)
based simulation is that a good model enables engineering teams to
safely investigate many process details and parameters. Simulation
provides important information about local conditions in many different
parts of the equipment. Filling operations in a silo at high and low load
levels or flow conditions in a mixer can be optimized using the model. The
list of parameters can include the location of the filling point, the size of
the filter, the bulk solids involved and their temperature. Good solutions
can also be developed for complex geometries and mounting
configurations. This can reduce test and development costs.
Particle analysis also provides a detailed understanding of the process.
Visualization has enormous advantages. What takes place at the
interfaces and how that affects the process are now understood. As a
result, properties such as the size, crystal morphology and shape of the
particles can be controlled with greater precision. This is important for the
development of personalized medicine where the active ingredients are
tailored to the individual patient.
Understanding of bulk solids behavior increases equipment service
life
In bulk solids handling, the objective is often to maintain the material flow.
The choice of the right gate, a change in the direction of flow from
horizontal to vertical and detailed silo design keep the bulk solids moving.
A lot can be accomplished by modification of the particle size distribution
or the formation of agglomerate or micro-granulate. This includes the
removal of fines, changing the comminution process or coating the
surface with very fine-grained flow promoters.
A proper understanding of the product prevents early wear on the
equipment. Wear normally depends more on system design than on the
bulk solids. Design changes may not eliminate wear but they can reduce
the deterioration rate. Changing the angle or speed of impact can
increase equipment service life over the long term.
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DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e.V.
Theodor-Heuss-Allee 25  60486 Frankfurt am Main  Germany  T + 49(0)69 75 64-0  F +49(0)69 75 64-201  presse@dechema.de
www.dechema.de
Equipment manufacturers need in-depth expertise
Requirements in the pharmaceutical industry have become increasingly
demanding over the past 15 years. Dust-free transfer, for example from a
container to a mixer, is a major priority. That is important in order to avoid
cross-contamination, and factors such as increased handling of highpotency active ingredients have major employee safety implications. The
situation is similar in the food and chemical industries. It is important that
the environment is dust free to prevent cross-contamination with allergens
and avoid human safety hazards and dangerous situations caused by
airborne dust.
The proliferation of container types is a major headache for design teams.
Raw bulk solids, intermediates and finished products are handled and
transported in big bags, octabins, barrels, sacks, mobile containers and
much more. The varying heights of feed and discharge connections are
another problem. Equipment manufacturers may have to make special
modifications or design changes, which can be expensive. The answer is
to design versatility into the systems.
Precision, uniform dosing is often a built-in feature of transfer stations and
that functionality is essential for high-quality production of many products.
Selection of the right dosing method has to be a joint decision by users
and manufacturers, and the choice becomes more difficult as the volumes
being handled decrease. Minute amounts of vitamins have to be added
with very high precision in the food industry. Hygiene requirements or
major space constraints which often exist in the plastics industry are other
factors that can make dosing more difficult.
Safety is the top priority
Explosion protection is an issue which most bulk solids technologies must
address. In Germany alone, it is estimated that one dust explosion occurs
every day. The outcome of these events may not always be tragic but
they clearly show the need to take the issue seriously. The lower
explosion limit (LEL) for many types of dust is 20 - 125 g/m³. The bulk
density of the types of dust normally found in industrial environments is
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around 800 kg/m³. Given a dust layer of 1 mm and a room height of 3
meters, this would equate to 270 g/m³. Any air current which kicks up the
dust would be enough to create a potentially explosive dust/air mixture.
Effective explosion protection is mandatory in many applications.
The primary approach to explosion protection is to minimize or eliminate
one or more of the elements (ignition energy, oxygen and dust) in the
explosion triangle. It may be possible to find a non-combustible substitute
for a combustible material. Nitrogen inertization can reduce the oxygen
concentration. It is also important to eliminate ignition sources such as
welding operations, hot surfaces, electromagnetic waves and hot gas.
Once that has been done, the developers can look at ways of mitigating
the effects of an explosion. One possibility is to design equipment which
has explosion pressure relief, explosion suppression and limited explosion
volume so that it is able to withstand the explosion pressure.
Organizational measures are also part of an effective explosion protection
strategy. This can include simple rules such as a smoking ban, regular
cleaning to remove dust, periodic grounding checks and confirmation that
machines are still being used for the intended purpose. It is also important
to record all of these measures in an explosion protection document. A
documented explosion protection strategy provides sufficient evidence for
the authorities and ensures that the explosion protection program is
effective. User/supplier collaboration extends well beyond the supply of
individual components. Delivery is preceded by the provision of detailed
information on matters such as changes to applicable laws and
regulations. In recent years, experience has shown that strict separation
of fire protection and explosion protection during the storage of bulk solids
is not expedient. For one thing, it is not always possible to determine
whether it was the fire or the explosion that triggered an event. Moreover,
the two types of protection have been shown to complement each other.
Urban Mining
While minute quantities are commonly handled in the pharmaceutical and
cosmetics industries, material is handled on a totally different scale in
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metal recycling, at least at the start of the processing chain. The term
urban mining refers to the recovery of valuable materials from cars,
electrical appliances or even old waste disposal sites. One tonne of scrap
PC motherboards contain 30 times more gold than one tonne of gold ore.
250,000 tonnes of rare earth metals are thought to be present as slag at
German waste disposal sites. The recovery of re-usable material is an
elaborate process and it is very energy-intensive. If the motherboard is not
removed before the PC is put through the shredder, it is difficult or
impossible to get at the important trace elements. 75% of the gold would
be lost. Special comminution and sorting processes are needed to
improve the situation.
The process sequence starts with mechanical processing based on
conventional comminution and classification techniques which have a
crucial impact on the subsequent process steps and on the feasibility of
urban mining. A lot of research and development work lies ahead. One of
the items that need to be addressed is the processing of finely dispersed
polymetallic particle systems < 10 µm. Work remains to be done on
sorting techniques for ultrafine particle systems with very fine grains (< 50
µm, mainly in the 0.1 µm - 10 µm range) and on energy-efficient
comminution.
However even if a cost-effective process can be found, it is by no means
certain that there will be a payback over the long term. Fluctuations in
income generated from recycled materials tend to be in the double-digit
range. A system which is currently generating a good return could quickly
become a financial liability. In addition, a constant stream of new materials
and composites makes recovery increasingly difficult. The systems of the
future must have sufficient versatility to handle material streams which
have varying composition. It is also important to look over the edge of the
plate. Recycling always involves a long process chain which extends from
consumers to recycling and metallurgy companies. The economic
feasibility of the entire process depends on each individual link in the
chain.
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DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e.V.
Theodor-Heuss-Allee 25  60486 Frankfurt am Main  Germany  T + 49(0)69 75 64-0  F +49(0)69 75 64-201  presse@dechema.de
www.dechema.de
ACHEMA presents solutions
In order to design bulk solids handling systems and equipment which are
not susceptible to material flow interruptions and production stoppages,
developers need to have in-depth expertise and detailed knowledge of the
material properties. Very small particles down to the nano-scale and very
large volumes that need to be handled in urban mining call for new
approaches for engineers and bulk solid handlers. The ACHEMA
exhibition and congress will present solutions for both.
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DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e.V.
Theodor-Heuss-Allee 25  60486 Frankfurt am Main  Germany  T + 49(0)69 75 64-0  F +49(0)69 75 64-201  presse@dechema.de
www.dechema.de