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CaBr 2 HYDROLYSIS FOR HBr PRODUCTION USING A DIRECT SPARGING CONTACTOR
will be formed, go into solution, and be drawn into the wake of the spherical cap bubble at an
essentially isothermal condition. A parameter sweep of bubble size is shown in Figure 1. The analysis
indicates that good conversion of steam to HBr can be obtained over a broad range of kinetic rate
constant, near that determined from published experimental data.
Figure 1: Left: Laminar flow field around a 400-μm diameter spherical steam
bubble rising at 0.06 m/s. Right: Mean flow around a 4-mm equivalent sphere
diameter spherical-cap steam bubble rising at 20 cm/s in molten CaBr 2 at 1 013 K.
Based on these modelling results it appeared that laboratory experiments involving the reaction
of steam with molten calcium bromide in a sparging reactor would be successful, producing appreciable
conversion. In fact, preliminary experiments at Argonne have produced reactions rates up to an order
of magnitude higher than previous experiments using solid calcium bromide either as a matrix or as
crystals. Of special importance, model results also showed low temperature steam would reach melt
temperatures within a few milliseconds thus simplifying system design.
The models developed in this paper, combined with further experiments to determine the reaction
rate will help to size the bubble column reactor and identify the optimum operating range for bubble
size to maximise conversion of steam to HBr in the reactor. The reaction might produce eutectic and/or
solid calcium oxide products which would be convected away from the bubble surface reaction front.
Some of these reaction products may end up in the wakes of bubbles, and the effects on the reaction
rate at the trailing edge of the bubble surface need investigation. The bubble models will couple internal
circulation, mixing and diffusion of steam and HBr to and from the reaction front at the surface.
Results of this modelling will aid in reactor design. Additional modelling may be required to aid in
sparger tube or bubble distributor design. Bubble scale modelling will also be extended to model the
effects of bubbles riding in the wakes of other bubbles. Based on results of bubble scale modelling,
sub-models will be developed to characterise reaction progress and interfacial heat, mass, momentum
transfer between bubbles and the surrounding molten CaBr 2 pool. These sub-models can then be
incorporated into larger reactor scale models.
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