Modeling the gas absorption in a spray scrubber with dissolving reactive particles

Abstract

The absorption of a gaseous species into a spherical slurry droplet with internal circulation that contains reactive, sparingly soluble microparticles is studied. The droplet recirculation is assumed to be similar to Hill's vortex flow, and the chemical reaction is assumed to be either instantaneous or of second order. Reactive gas species diffusion, chemical reaction and particle dissolution are numerically modeled using droplet recirculation streamlines as a coordinate. Parametric calculations are performed, and are utilized to assess the adequacy of the widely used film theory, and to examine the effect of particle size variation on the absorption rate. A transient model is also developed that utilizes the aforementioned quasi-steady droplet mass transfer and reaction models and calculates the time variation of the average solid particle size in the droplet. Parametric calculations are presented that confirm the importance of particle size and its variation as a result of dissolution. Transient parametric calculations show a declining total absorption rate with time as a result of the shrinkage of the average particle size. The results are everywhere sensitive to droplet internal circulation, however. Partial suppression of droplet internal circulation leads to significant reduction in absorption rate, even with a high concentration of particles. The calculation results thus demonstrate that several parameters should be considered for optimal design of a slurry spray scrubber.