Abstract: Continuous upflow filters can combine the nutrient
(nitrogen and phosphate) and suspended solid removal in one unit
process. The contaminant removal could be achieved chemically or
biologically; in both processes the filter removal efficiency depends
on the interaction between the packed filter media and the influent. In
this paper a residence time distribution (RTD) study was carried out
to understand and compare the transfer behaviour of contaminants
through a selected filter media packed in a laboratory-scale
continuous up flow filter; the selected filter media are limestone and
white dolomite. The experimental work was conducted by injecting a
tracer (red drain dye tracer –RDD) into the filtration system and then
measuring the tracer concentration at the outflow as a function of
time; the tracer injection was applied at hydraulic loading rates
(HLRs) (3.8 to 15.2 m h-1). The results were analysed according to
the cumulative distribution function F(t) to estimate the residence
time of the tracer molecules inside the filter media. The mean
residence time (MRT) and variance σ2 are two moments of RTD that
were calculated to compare the RTD characteristics of limestone with
white dolomite. The results showed that the exit-age distribution of
the tracer looks better at HLRs (3.8 to 7.6 m h-1) and (3.8 m h-1) for
limestone and white dolomite respectively. At these HLRs the
cumulative distribution function F(t) revealed that the residence time
of the tracer inside the limestone was longer than in the white
dolomite; whereas all the tracer took 8 minutes to leave the white
dolomite at 3.8 m h-1. On the other hand, the same amount of the
tracer took 10 minutes to leave the limestone at the same HLR. In
conclusion, the determination of the optimal level of hydraulic
loading rate, which achieved the better influent distribution over the
filtration system, helps to identify the applicability of the material as
filter media. Further work will be applied to examine the efficiency
of the limestone and white dolomite for phosphate removal by
pumping a phosphate solution into the filter at HLRs (3.8 to 7.6 m h-1).
Abstract: This paper presents the prediction of air flow,
humidity and temperature patterns in a co-current pilot plant spray
dryer fitted with a pressure nozzle using a three dimensional model.
The modelling was done with a Computational Fluid Dynamic
package (Fluent 6.3), in which the gas phase is modelled as
continuum using the Euler approach and the droplet/ particle phase is
modelled by the Discrete Phase model (Lagrange approach).Good
agreement was obtained with published experimental data where the
CFD simulation correctly predicts a fast downward central flowing
core and slow recirculation zones near the walls. In this work, the
effects of the air flow pattern on droplets trajectories, residence time
distribution of droplets and deposition of the droplets on the wall also
were investigated where atomizing of maltodextrin solution was
used.