Size Enlargement by Agglomeration-Wolfgang Pietsch, Sr. Consultant, Compactconsult, Inc

History, Fundamentals, Feed and Product Characteristics

Agglomeration is a natural phenomenon that exists since particulate solids first formed on earth. It is the sticking together of particles caused by the action of binding mechanisms which may be inherent, naturally present or enhanced, or produced by binders that themselves may be inherent or added. Later it was used by living beings and humans, was introduced in industry a few centuries ago, emerged as a unit operation of mechanical process technology, and, more recently as well as retroactively, has become a science with applications in all areas of powder and bulk solids processing and handling, life sciences, and nano-technology.  (History)

During the manufacturing of solid products from fine particulate components their size must be enlarged and/or their shape newly defined in most cases. Agglomeration is the technology that is used for that purpose. The distinguishing characteristic of Size Enlargement by Agglomeration is the formation of larger entities from particulate solids by sticking particles together with short range physical forces between the particles themselves or through binders, substances that adhere chemically or physically to the solid surfaces and form a material bridge between the particles. The components of an agglomerate are often widely disparate and, except if matrix binders are applied or after shrinkage during sintering, void spaces between the particles forming an agglomerate are present in the product. (Fundamentals)

Agglomerates may be made from many different raw materials and a multitude of additives, thus providing the opportunity to engineer new materials and products. (Feed and Product Characteristics)

Testing and Development, Unwanted Agglomeration and Methods to Lessen It

Bench-top testing, particularly, for example, to determine if and potentially what type of binder must be added and how much of it is required. After that, tests with actual equipment must be conducted to find process as well as capacity limitations and optimize product size, shape, and characteristics. Needs for peripheral equipment, post treatment as well as closed loop processing and recirculation must be also evaluated. (Testing and Development)

Agglomeration, the sticking together of particles, is a natural phenomenon which, under certain conditions, will cause lumping, build-up, caking, bridging, and other unfavorable situations that inhibit proper material handling and processing and cost the industry large sums for remediation. Methods to prevent the undesirable sticking, lumping, caking, and aggregation of particulate solids are presented and discussed. (Unwanted Agglomeration and Methods to Lessen It)

Methods of Size Enlargement by Agglomeration

Products are called Granules, Tablets, Briquettes, Extrudates, Pellets, Bricks, Compacts, as well as specific, brand related names. Their size, shape, structure, and properties (the latter mostly determined by their porosity [or density] and strength) are widely adjustable.
(Tumble/Growth Agglomeration: Pan and Drum, Mixer, Spray Drying, Fluid Bed, Vibration and Rolling, Immiscible Binder Agglomeration)
(Pressure Agglomeration: Low Pressure [Crumbling, Extrusion, Spheronizing], Medium Pressure [Extrusion, Pelleting], High Pressure [Extrusion, Punch-and-Die, Roller Presses])
(Agglomeration by Heat [Sintering])
(Other Technologies using the Binding Mechanisms of Agglomeration)

 

Size Enlargement in Industry-Wolfgang Pietsch, Sr. Consultant, Compactconsult, Inc.

Improvement of the properties of powders and bulk solids, Engineering criteria and plant design, Optimization of agglomeration equipment and systems, Troubleshooting

Fine particulate solids exhibit characteristics that limit their handling, storage, transportation and use in the process industry. These unfavorable qualities include bad flowability, large bulk volume, excessive dusting, segregation, and many more. Using binding mechanisms, size enlargement by agglomeration forms larger entities by sticking powder particles together. These products do no longer feature the disadvantages of fine particulate solids but retain most of their desirable properties, such as high surface area, solubility, and reactivity. On the other hand, for some applications, the technology may also be used to inertize powders. (Improvement of the properties of powders and bulk solids)

During the selection of an agglomeration system and its equipment for a new application utmost care must be employed by meticulously determining and defining all parameters during testing, development of the process, scale-up to industrial size, construction of the plant, training of the personnel, and start-up. (Engineering criteria and plant design)

Problems during the operation of an agglomeration system or plant can occur immediately or later. They are typically manifested by insufficient capacity, low process yield, and/or unacceptable product properties. In most cases, problems that develop immediately, during start-up or initial operation, can be resolved by modifications of the feed or of system components and/or the optimization of operating parameters. It is more difficult to understand and remedy problems that occur, often without warning, after long and successful operation of a plant. In such cases it is necessary to go back to the fundamentals, try to envision what happens mechanically, physically, and sometimes even chemically during agglomeration, understand the specifics of particle interaction, determine what, how, and why something has changed, develop corrective measures, and implement suitable modifications. An understanding of what commonly occurs and discusses means to overcome the problems will be provided. (Optimization of agglomeration equipment and systems, Troubleshooting)

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