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Prediction of thickener performance with aggregate densification

Zhang, Yi and Martin, Alastair and Grassia, Paul (2013) Prediction of thickener performance with aggregate densification. Chemical Engineering Science, 101. pp. 346-358. ISSN 0009-2509

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Abstract

This paper aims at investigating the effects of densification of aggregates within a suspension on thickener dewatering performance. The comparisons of the maximum permitted underflow solids flux calculated from both an initial undensified thickener and a densified thickener were achieved. Large underflow solids fluxes were attained in densified thickeners. The effects of densification on the bed heights and on the solids residence times required to achieve a given underflow solids flux and a given underflow solids volume fraction were also computed and compared. Substantial reductions in the bed heights and the solids residence times are possible in densified cases. Previous studies have assumed the functional form of the compressive yield stress in the suspension so as to give an exceedingly weak gel in the neighbourhood of the solids volume fraction at the top of the bed. The implications of considering a different gel rheology with a rather stronger gel were considered. The effects of this new rheology lead to a slightly less sharp spatial gradient in the solids volume fraction near the top of the bed. In addition, the effect of varying the underflow solids volume fraction was considered. The observations of substantial increases in underflow solids fluxes and substantial reductions in bed heights and solids residence times were only achieved when the underflow solids volume fraction was less than or comparable with the solids volume fraction within the aggregates. However, if the underflow solids volume fraction was considerably larger, aggregates were considered to be overlapping and interpenetrating. As a result, the improvements in thickener performance due to densification were insignificant.