A new approach to the kinetic modeling of the reaction of gaseous HCl with solid lime at low temperatures

Abstract

The chemical reaction between gaseous HCl and solid Ca(OH) 2 has several applications, namely in the dry scrubbing of acid gases. The behavior of this reacting system in a laboratory-scale tubular reactor was simulated using the ‘grain model’ for the solid phase and a cascade of CSTRs for the gaseous phase. This model was applied to experimental data obtained in a previous study, at low temperatures (50–130°C) and high humidity level. The results show that the diffusion of the gaseous reactant through the product solid layer is the rate-limiting step for this reaction. In the first reacting moments, when no solid product has yet been formed, the reaction is limited by the total consumption of the gaseous reactant, indicating a very fast chemical reaction (k s>10 −3 ms −1) . These results were compared with those obtained by two other models used to describe the behavior of the gaseous phase: the ‘differential reactor model’ and the ‘average concentration model’. We show that the differential reactor model, which has been largely applied in published works about this and other similar reacting systems, is not adequate for modeling the reaction process, particularly in its initial phase.