University of Oulu

Petri Tervasmäki, Jari Tiihonen, Heikki Ojamo, Comparison of solids suspension criteria based on electrical impedance tomography and visual measurements, In Chemical Engineering Science, Volume 116, 2014, Pages 128-135, ISSN 0009-2509,

Comparison of solids suspension criteria based on electrical impedance tomography and visual measurements

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Author: Tervasmäki, Petri1; Tiihonen, Jari2; Ojamo, Heikki3
Organizations: 1University of Oulu, Faculty of Technology, Chemical process engineering, Finland
2Outotec Oyj, Finland
3Aalto University, Department of Biotechnology and Chemical Technology, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 0.7 MB)
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Language: English
Published: Elsevier, 2014
Publish Date: 2017-10-31


Different approaches have been adopted to quantify the performance of stirred vessels in suspending sinking solids into liquid phase. In this study we used electrical impedance tomography (EIT) to estimate the solids distribution in a lab-scale stirred vessel with a diameter of 362 mm. Also visual measurements were performed to determine the cloud height and just suspended impeller speed. Quartz sand with a density of 2650 kg/m³ was employed as the solid phase with different particle size fractions from 50 to 180 µm and solids volume fractions of 7.5% and 15%. The effect of impeller type was studied by using two axial flow impellers, a pitched blade turbine and a hydrofoil impeller.

Two different states—partial and homogeneous suspensions—were defined from the EIT data in addition to visual measurement of complete off-bottom suspension and cloud height. Partial suspension was determined from the EIT data, and it was reached at relatively low agitation rates. Visual measurements and data from the literature also support this observation, and EIT was proved to be a suitable method to quantify a repeatable partial suspension criterion. Complete off-bottom suspension was measured visually by determining the agitation rate at which there were no stationary solid particles at the vessel bottom for longer than 2 s. However, the applicability of this widely used criterion was questioned in the case of dense suspensions of small particles. Homogeneous suspension was estimated from the EIT data, and it was reached by approximately doubling the impeller revolution rate from the partial suspension criterion. The hydrofoil impeller reached all states of suspension with lower power consumption compared to the pitched blade turbine.

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Series: Chemical engineering science
ISSN: 0009-2509
ISSN-E: 1873-4405
ISSN-L: 0009-2509
Volume: 116
Pages: 128 - 135
DOI: 10.1016/j.ces.2014.05.003
Type of Publication: A1 Journal article – refereed
Field of Science: 215 Chemical engineering
Copyright information: © 2014. This manuscript version is made available under the CC-BY-NC-ND 4.0 license