analysis of a pilot-scale anaerobic baffled reactor treating domestic ...

spacing on flow patterns in a single liquid phase was modelled, and an upflow-to-downflow area ratio
(Figure 3.2) was selected to achieve uniform low upflow velocities without large dead volumes.
Figure 3.2: Velocity vector profiles obtained for a 20 h HRT using CFD software FLUENT
for hanging baffle positioning. Profiles for 1:1 (left) and 2:1 (right) upflow-todownflow
area ratios are shown. (Dama et al., 2001)
(a) (b)
(c)
Figure 3.3: Longitudinal section through an ABR compartment illustrating the CFD velocity
contours for the two different baffle configurations: (a) angled baffle, (b)
straight baffle. Darker colours represent low flow rates. (c) Laboratory scale
verification of CFD results using a dye tracer (Foxon et al., 2006) in a single ABR
compartment constructed of perspex. The image shows a dye pulse moving
around the bottom of an angled hanging baffle. Photographs of the progress of
the dye pulse were similar to dye pulse trajectories simulated in FLUENT.
The velocity vector profiles along a transverse plane for the two baffle positions are presented in
Figure 3.2. The magnitude of the velocity is indicated by the length of the velocity vector i.e., the
longer the arrow, the greater the velocity. An upflow-to-downflow area ratio of 2:1 resulted in a fairly
uniform distribution of flow relative to a ratio of 1:1. Increasing the upflow area resulted in a further
increase in channelling and dead-space in the upflow region. These results are valid for a single liquid
phase without gas or solids effects, and were not expected to be the same as in a reactor with all three
phases present.
A CFD model showing the effect of angling the bottom of the hanging baffle was attempted. Figure
3.3 shows the flow contours around an angled and straight baffle. It was found that the angled baffle
52
Feed Down-flow side
Dye
pulse
up-flow
side