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The effect of off-wall clearance of a side-entering impeller on the mixing of pulp suspensions in a cylindrical stock chest

Authors

  • Manish R. Bhole,

    Corresponding author
    1. Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3
    • Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3.
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  • Leo K. Hui,

    1. Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3
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  • Clara Gomez,

    1. Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3
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  • Chad P. J. Bennington,

    1. Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3
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    • Posthumous.

  • Guy A. Dumont

    1. Department of Electrical and Computer Engineering, The University of British Columbia, 2332 Main Mall, Vancouver, BC, Canada V6T 1Z4
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Abstract

For a side-entering impeller of diameter D, the clearance from the off-wall (E) is characterised by E/D and it affects the mixing quality attained in a pulp stock chest. For agitation of pulp suspensions, mixing can be characterised by the size of cavern produced by the impeller. In this work, we have investigated cavern size as a function of the impeller off-wall clearance in a laboratory-scale cylindrical stock chest. Hardwood pulp suspensions of Cm = 2%, 3%, and 4% (fibre mass concentration) were agitated using an axial flow impeller with E/D varied from 0.14 to 0.68. Cavern size was measured using electrical resistance tomography (ERT) in batch operation and dynamic mixing tests in continuous operation, with cavern size increasing with increasing E/D. At E/D = 0.14, throttling of the impeller suction occurred which reduced cavern size. Computational fluid dynamic (CFD) simulations for steady state operation under-predicted the cavern size, but correctly captured the trend in cavern size variation with E/D. The measured cavern volumes compared well with predictions of an axial force model that accounted for interaction between the cavern and the vessel walls only when impeller throttling was absent.

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