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A product's intended use often dictates what type of agglomeration equipment should be used. Presented here is a discussion of the main types of equipment and methods for forming agglomerates
Agglomeration is the process of converting fine powder particles into larger ones through the introduction of external forces. Agglomeration offers numerous benefits for bulk solids processors, including significant dust reduction, improved handling, more complete utilization of raw materials and densification. Agglomeration can be accomplished by a variety of means, including mixing with a liquid, applying pressure and heating.
This article describes various technologies available for particle size enlargement. The technologies fall into three general categories: (1) tumble-growth agglomeration, (2) pressure agglomeration, and (3) agglomeration by heating or sintering. Tumble-growth agglomeration includes both wet and dry methods. Stresses developed in pressure agglomeration equipment can range from moderate to extreme. For some materials, agglomeration by heating or sintering can be accomplished at relatively moderate temperatures. An end product's intended use often dictates what type of agglomeration equipment should be used.
General principles
Tumble-growth agglomeration equipment tends to have lower capital costs than the other methods, but costs may be higher if drying is required. Agglomerates produced by tumble-growth technologies tend to have a lower bulk density and a wider particle size distribution as compared to other agglomeration methods. Binders frequently must be added to ensure that "green" (that is, wet) or dry agglomerates have sufficient strength.
Pressure agglomeration equipment, as well as equipment that agglomerate particles by heat or sintering, tend to have higher capital costs, but lower operating costs. The agglomerates formed by these methods have a higher bulk density, but they may be prone to attrition if the pellets that are produced have sharp edges.
Particles are held together by a number of mechanisms. Solid bridges between particles can be the result of sintering, partial melting and recrystallization during drying. Binders that readily adhere to solid particles are effective agglomerating aids. Liquid bridges in spaces between individual particles can form strong agglomerates as a result of capillary forces that develop when the voids are completely filled with the liquid. Attractive forces, such as van der Waals interactions, valence forces and hydrogen bridges can also hold solid particles together. If adjacent particles have shapes that...