THE USE OF THE PENETRATION MODEL FOR THE DISSOLUTION OF LIMESTONE IN THE CO2-WATER SYSTEM

The penetration model was implemented for the dissolution of limestone in the CO2-water system. The model includes the acid-base reactions of the carbonate species as well as the autoprotolysis of water. It was also assumed that there is no surface resistance to the dissolution of the solid. This assumption restricts the use of the model to those conditions where the dissolution rate is limited by the rate of mass transfer. When using the model, only the hydrodynamics of the water solution need to be experimentally determined and put in terms of the model’s hydrodynamic parameter. All other model inputs are either physical constants or known bulk concentrations. Dissolution experiments, performed on a rotating cylinder system, were used to test the ability of the model to predict the dissolution rate of limestone in an aqueous solution. Of special significance was the ability of the model to predict the dissolution rate at different pH-values, CO2 partial pressures, temperatures and hydrodynamic conditions. An explicit finite differences method was used to deal with the system of non-linear partial differential and algebraic equations, which arose from the implementation of the penetration model. This investigation has shown that the limestone dissolution process in the mass transfer controlled region, can be modelled and described by the penetration model. The penetration model accurately describes the effects of all parameters investigated, including the enhancement effect from CO2(up to a factor of 10 compared with dissolution in a CO2-free atmosphere) and temperature. The penetration model has also been compared with the film theory model. The comparison of the two models shows that the penetration model yields a better correlation to the experimental data in a CO2 atmosphere. In a CO2-free atmosphere the models are almost identical. However, the penetration model is computationally more difficult. A numerical procedure for solving the penetration model has been designed. This procedure includes a method of dealing with the unusual boundary conditions at the surface. © 1990, Taylor & Francis Group, LLC. All rights reserved.