An estimate of the axial dispersion during flow through a compressible wood-chip bed

• Published in: Canadian journal of chemical engineering 2012-12, Vol.90 (6), p.1602-1611
• Main Authors: Alaqqad, M., Bennington, C. P. J., Martinez, D. M.
• Format: Article
• Language: English
• Subjects: chip digester; dispersion; electrical resistance tomography; packed beds; wood chips
• ISSN: 0008-4034; 1939-019X
• DOI: 10.1002/cjce.20637

In this work, we present a methodology to characterise the axial dispersion of a solute during steady‐flow through a compressible bed of wood chips under mechanical load. We use a non‐invasive imaging technique, namely electrical resistance tomography (ERT), to visualise the uniaxial displacement of a salt solution. Here we demonstrate that under two limiting cases the porosity of the porous bed varies slowly in the flow‐direction and to the lowest order can be considered a constant. This simplified the optimisation routine we used to match the experimental data to the numerical results of the advection–diffusion equation. Using this, a methodology to estimate the axial dispersion is given by a minimisation scheme. In the experimental portion of the work we measure the axial dispersion of a bed of hemlock wood chips at three different kappa numbers κ, and compacted to three different compaction pressures pc. We find that the dispersion De in the axial direction varies as a function of the porosity ε, according to $D_{{\rm e}} = a\varepsilon {}^{b} $, where a = 7.2 × 10−4 m2/s and b = −3.8 for hemlock wood chips. © 2011 Canadian Society for Chemical Engineering