Flow patterns in the mixing of sludge simulant with jet recirculation system

Low, S, Eshtiaghi, N, Shu, L and Parthasarathy, R 2017, 'Flow patterns in the mixing of sludge simulant with jet recirculation system', Process Safety and Environmental Protection, vol. 112, pp. 209-221.


Document type: Journal Article
Collection: Journal Articles

Title Flow patterns in the mixing of sludge simulant with jet recirculation system
Author(s) Low, S
Eshtiaghi, N
Shu, L
Parthasarathy, R
Year 2017
Journal name Process Safety and Environmental Protection
Volume number 112
Start page 209
End page 221
Total pages 13
Publisher Elsevier
Abstract In this study, we examined the efficiency of mixing due to liquid jets in a model anaerobic digester. Xanthan Gum Keltrol T (XGKT) solution which is transparent and has similar rheological characteristics to those of digested sludge was selected as the model liquid. Experiments were carried out using 0.15 and 0.4. wt% XGKT solutions. Four different liquid jet orientations were used in a cylindrical vessel, namely vertical-downward, vertical-upward, tangential 45° upward and tangential 45° downward. A decolourisation method involving an acid-base reaction was used for flow visualisation. A fluorescent dye was used as the tracer to observe the mixing patterns in the vessel. Video images of flow visualisation experiments were analysed to investigate the changes in the volume of well-mixed regions as a function of mixing time. The results from flow visualization were compared with those from both computational flow dynamics (CFD) simulations and electrical resistance tomography (ERT). Results showed that well mixed region volume decreases with increasing liquid apparent viscosity. Complete mixing was achieved in 0.15. wt% XGKT solution, which has rheology similar to that of digested sludge with 2.3% solids, with all four different jet arrangements. For 0.4. wt% XGKT solution, which has rheology similar to that of digested sludge with 5% solids, mixing efficiency with jet arrangement changes in the following order: upward. > . 45° upward. > . 45° downward. > . downward jet arrangement. The results suggested that we can use transparent materials to study rheological behaviours of sludge and visualize the dynamics of mixing. Results from both ERT and CFD agreed well with those from flow visualization experiments.
Subject Wastewater Treatment Processes
Keyword(s) Anaerobic digesters
CFD modeling
ERT
Flow visualization
Hydraulic mixing
Inactive volume
Jet recirculation
Sludge simulant
DOI - identifier 10.1016/j.psep.2017.08.016
Copyright notice © 2017 Institution of Chemical Engineers
ISSN 0957-5820
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