Spray Drying Technology.pdf - National University of Singapore

In a process analogous to spray drying, spray cooler, Poh et al. [76]
showed how the CFD technique can be used to assist in the modification of
an existing unit. In the industrial spray cooler investigated, collision between
the hot molten fatty acid particle with the wall causes the production capacity
to decrease. CFD simulations were then used to modifications to the inlet
geometry to provide more swirl in the chamber which minimized the particle
accumulation on the chamber wall. Other illustrations on the application of
the CFD technique to better understand and manipulate the airflow patterns
includes studying the effect of chamber size and air inlet turbulence or design
[5][23][29] .
Operating parameters such as atomization can also be evaluated using
CFD simulations. Straatsma et al. [11] and Langrish and Zbicinski [30] also
used CFD simulations to assess the effect of cone spray angle on the
deposition problem. Although it is relatively established that a wider spray
angle results into more propensity for the particles to reach the wall,
visualization from the CFD simulations allows clearer evidence for decision
making.
The CFD technique can also be used as an overall optimization tool for
the process. Lo [48] used the CFD technique to determine the optimal
operating condition of their spray tower to use minimal air flow rate in
achieving the desired product quality in dairy products. Optimization was
undertaken by looking at the yield, particle outlet moisture and particle outlet
temperature as predicted by the CFD model.
5.2 Exploring new ideas
Using the advantage of CFD which enables the non-linearity of the
process to be captured, Huang et al. [77] assessed and visualized the
efficiency different chamber configurations. Some of the different
configurations are the lantern type chamber and the inverted type spray dryer,
in which standard design correlations might not be applicable. Along that line,
Huang et al. [78] also evaluated the horizontal spray drying process,
incorporating a bottom fluidized bed, using the CFD visualization technique.
In a recent paper, Huang and Mujumdar [79] also proposed and evaluated a
method of using low humidity conditions in a spray dryer to cater for drying of
heat sensitive materials. It was found that such operation conditions are
advantageous for heat sensitive materials. Therefore, the CFD can be a cost
effective method to explore and design new spray drying chambers. New
ideas can be evaluated without the need for expensive pilot scale construction
in the preliminary stage, particularly as a scale up tool as noted by Oakley [80] .
As mentioned earlier, Niro has already reported the use of CFD in their
commercial design of spray dryers. CFD could also be used in future for online
control of spray dryers.
Woo, Huang, Mujumdar, Daud – CFD modeling of spray dryers 29