Preparation and characterization of fly ash hydrated lime sorbents for SO2 removal

Coal combustion fly ash and its mixtures with lime and hydrated lime are being widely studied for use as sorbents in desulfurization processes. In this work, coal fly ash has been slurried with hydrated lime in a Parr pressure reactor. In order to study the preparation process of the solids, the influence of the operation variables (temperature, time, fly ash/Ca(OH)(2) ratio, pressure and water/solids ratio) on the structural properties of the final sorbent, the BET-nitrogen specific surface area and the pore volume distribution are studied using a factorial design for the experiments. Results of the specific surface area were correlated by a linear expression of the Ay ash/Ca(OH), ratio and hydration time, the variables which exhibit the main influence on the generation of specific surface area in the studied range of variables. The influence of the hydration time was studied for solids prepared at atmospheric pressure and under pressure. No influence of the studied variables on the total pore volume distribution was detected in the researched range of variables. X-ray diffraction analysis was also used for solids characterization, showing that the hydration reaction resulted in the formation of CaCO3, mullite and calcium aluminium silicate hydroxide. SEM analysis showed the macrostructural changes with the hydration reaction. (C) 1997 Elsevier Science S.A.