Circulating Air Classification of Manufactured Sand

Due to environmental concerns, the supply and use of natural gravel has been limited by the Swedishgovernment. The Swedish concrete industry is therefore examining manufactured sand as analternative that has equal or better product quality, and which the Swedish quarry industry alreadyhas the ability to deliver. However, in order to comply with the specifi cations set by the concreteindustry, a better means of classifi cation is needed, as the proportion of fi ne particles (fi ller) smallerthan 63 - 125 μm in size must be reduced. One classifi cation technology that meets the requirementsmay be air classifi cation. This paper examines the process of circulating air classifi cation, which isnot yet commonly used in the Swedish quarry industry; suggesting that a better understanding of theprocess is needed.The circulating air classifi er in this study has two internal machine parameters that can affect theseparation point; namely, the speeds of the circulating fan and the separator fan. We study theireffect on the separation point as well as the interaction between these parameters.Full-scale parameter tests are also conducted, in which size distribution is measured before andafter the circulating air classifi cation. This study shows how the different parameters affect theseparation point and that it is possible to produce manufactured sand according to specifi cations.Computational fl uid dynamics (CFD, Fluent) is used to study the internal fl ow of the air circulatingwithin the classifi er. A single-phase study of the fl ow fi eld is conducted to support and explain thefi ndings from the full-scale tests