Three-phase bubble column reactors, despite their broad diffusion in chemical process, are often difficult to describe given the intricate mutual phase interactions. Moreover, validation of computational models is likewise complex, since it is considerably challenging to obtain exhaustive and precise experimental data from these systems. The aim of this work is to predict reliably the effect of disperse solid particles on the overall fluid dynamics of a bubble column by computational fluid dynamics.
The small size of particles allowed us to approximate the solid-liquid mixture as a single pseudo-homogeneous phase in the Euler-Euler framework. The simulation settings were tuned on two-phase gas-liquid systems and then extended to the three-phase gas-solid-liquid columns. Experimental data from different setups and correlations for the global gas hold-up in slurry systems were used to validate the model. In particular, what emerges from experiments is that the presence of the solid reduces gas hold-up, as a consequence of the higher density of the slurry in comparison to the pure liquid and the increased coalescence of the bubbles.
Results show that this model is able to predict the reduction of the hold-up with a solid volumetric loading up to 20%, achieving good agreement with experimental data. Moreover, what stands out from the simulations is that the addition of the solid also changes the shape of the flow map curve (global hold-up as a function of the gas superficial velocity), switching to a smoother transition between the behavior at low and high gas superficial velocity.