On modelling the roles played by diffusive and convective transport in limestone dissolution for wet flue gas desulphurisation

Limestone dissolution has been widely studied because of its importance in different fields, a common assumption has been to consider that the roles of mass transport and chemical reaction change as a function of pH. Furthermore, a commonly accepted model for the kinetics has not been presented thus far for a wide pH range. A model which considers only diffusion based on Fick ́s second law and chemical reaction was derived in the present work and compared to the two-step model that takes into account both diffusion and convection with reaction. The comparison was done in terms of the Peclet (Pe) number, and the newly introduced Peclet number for the just suspended condition (Pe*) which can be used to estimate the distribution of solids in the system. This approach allowed for a quantification of the differences between the assumption of only diffusion limitation and both convective and diffusive transport done in terms of the hydrodynamic factors affecting the mass transport process rather than the pH as has been widely applied in literature.