Abstract
The carbonation reaction between carbon dioxide and calcium oxide based solid sorbents is the basis of a promising CCS (Carbon Capture and Storage) technology. The kinetics of the carbonation reaction is characterized by several peculiarities, including incomplete conversion, a first fast stage followed by a product- layer diffusion controlled slow stage, an abrupt transition between the two stages, pore reduction and modification of the reactive/pore surfaces. Even though several kinetic models (grain models, random pore models) have been proposed to simulate the carbonation kinetics, the identification of a kinetic model capable to accurately predict the whole conversion vs time curves, particularly at short times, has been a challenging task.
In this work a random pore model accounting for a continuous sorbent pore size distribution was developed and applied to the carbonation reaction, including the reaction rate dependence on the equilibrium carbon dioxide partial pressure and the reaction order switch (from zeroth to first order). Such model is predictive once the intrinsic rate constant, the product-layer diffusivity and the initial pore size distribution are known.
The simulation results include the conversion versus time curves, as well as the evolution of the pore size distribution and of the pore and reaction surfaces over time, and are compared with experimental data of conversion over time, obtained through a high-pressure thermo-gravimetric analyzer, at a carbon dioxide pressure of 5 bar. The simulation results show that the presented model is capable to predict accurately the whole conversion-time curves, particularly at short times, both in the fast and in the product-layer diffusion regimes, and to represent the abrupt transition due to the pore closure.
