Aplicação da modelagem termodinâmica da clinquerização para dosagem e coprocessamento de matérias-primas na produção de cimentos

Abstract

The valorisation of industrial residues or by-products in the production of Portland clinker is a promising alternative for developing sustainable cements. The complexity of chemical reactions during clinkering requires an appropriate dosing method that considers the effect of impurities in raw materials to maximise the potential substitution of natural resources with residues or by-products, while ensuring the reactivity requirements of clinker. This study investigated the effect of impurities from co-processed alternative raw materials on the production of ordinary and alternative Portland clinkers using thermodynamic modelling. In the first step, a dosing and optimisation method for raw meals was developed using thermodynamic modelling to facilitate the co-processing of alumina-rich residues and maximise the reactivity of Portland clinker. Then, this method was applied to co-process the spent fluid catalytic cracking catalyst (SFCC), focusing on experimentally evaluating the effect of its impurities on the clinker. In the third step, modelling was used to investigate the effect of some of the main impurities of SFCC (lanthanides) on clinker production. Subsequently, the study evaluated the effect of alkali metals on the manufacture of belite clinker using thermodynamic modelling validated with experimental data from the literature. Lastly, the influence of co-processed SFCC on high ferrite Portland clinker (HFPC) was investigated. The proposed dosing method optimised the composition of the raw meal, resulting in clinkers with higher amounts of tricalcium silicate (potentially more reactive) and limited tricalcium aluminate content. The dosed samples produced clinkers with more than 50% Ca5SiO3, even when 15% SFCC was co-processed in the raw meal. The optimised chemical combination of the impurities, the maximisation of cement reactivity, the reduction of natural limestone and clay consumption, and the proper disposal of SFCC are positive implications of the proposed method for clinker dosing. Thermodynamic modelling demonstrated that the co-processing of lanthanides promoted the formation of new compounds, mainly cubic perovskite containing Al and O. However, Ce2O3 remained in its pure crystalline forms. Increased lanthanide content generally stabilised calcium aluminoferrite, suggesting that these elements could be used to produce cements with high ferrite content (8~20%) and resistance to sulfate attack. Thermodynamic calculations simulated the formation reactions of belite clinker and confirmed the findings of previous experimental studies. In the presence of sodium (Na) doping, Ca3(Al,Fe)O6 was destabilised, resulting in orthorhombic tricalcium aluminate and minor phases. Potassium (K) doping increased Ca2(Al,Fe)O5 and potassium silicates as minor phases. The thermodynamic modelling of SFCC co-processing in HFPC differed from the experimental results for the CaO-Al2O3-Fe2O3 phases, mainly due to the simulation of new compounds containing dopants non-quantified by the experimental method. Thermodynamic modelling enhanced the understanding of phase evolution, the stabilisation of calcium aluminoferrite solutions, changes in the melt phase viscosity, and the volume of phases during the simulations. This technique proved to be an important tool for optimising industrial processes and environmentally safe production of clinkers containing residual raw materials.