Mathematical modelling of batch sedimentation subject to slow aggregate densification

• Published in: Chemical engineering science Vol. 128; pp. 54 - 63
• Main Authors: Zhang, Yi, Grassia, Paul, Martin, Alastair, Usher, Shane P., Scales, Peter J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 25.05.2015
• Subjects: Compressive yield stress; Gels; Mathematical modelling; Rheology; Sedimentation; Suspension; Suspension; Mathematical modelling; Gels; Rheology; Sedimentation; Compressive yield stress
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2015.01.066

This paper considers an initially networked suspension in a batch settler subjected to very slow aggregate densification. The so-called pseudo-steady state aggregate densification theory developed by van Deventer (2012) has been extended to the case of initially networked suspensions. The solids behaviour and the evolutions of the suspension height and the consolidated bed height in the batch settler have been predicted using the extended pseudo-steady state theory. Different formulae for the weight-bearing strength of the consolidated bed (so-called weak gel and strong gel formulae, which differ near the top of the bed) are considered. The suspension height approaches the consolidated bed height far more quickly when using the weak gel formula than when using the strong gel one. This paper also investigates how the initial feed solids volume fraction and the initial suspension height affect the evolutions of the heights of the suspension and the consolidated bed, as well as the determinations of the solids volume fractions obtained at the bottom of the batch settler. When the initial feed solids fraction is sufficiently large and/or the initial suspension is sufficiently tall, the densification process has little effect on the solids fraction observed at the bottom of the settler. [Display omitted] •Model presented for suspension batch settling subject to aggregate densification.•Suspension is assumed to be gelled even before it starts settling/consolidating.•Unconsolidated/consolidated material boundary readily located for slow densification.•No unconsolidated material remains once gel point reaches initial solids fraction.•For weak gels, unconsolidated column height tends to collapse even earlier than this.