Task 1

Selection and Characterisation of Portuguese CaCO₃-based Wastes and Natural Resources for Ca-Looping Thermochemical Energy Storage

🕒 24 months

Objectives | Assess the suitability of CaO-based sorbents from national wastes, e.g. waste marble powder (WMP) and water treatment sludge, as well as natural sorbents like limestone and dolomite, to be used as thermochemical energy storage (TCES) materials. Improve the CaO-based materials reactivity performance after carbonation-calcination cycles considering the operational conditions (e.g. temperature) recommended for thermochemical storage.

Task Description | The first step is the analysis of the chemical composition (Ca, Mg, Al, Fe, etc.) of TCES material to identify the maximum theoretical CO₂ carrying capacity and quantify the amount of other elements than CaO, attending the integration of deactivated (spent) material in cement industry as raw material to produce clinker. The CaCO₃ is the common clinker raw matter, but until 20% of impurities such as aluminosilicates are acceptable and, additionally, the incorporation of MgCO₃ could significantly reduce the CO₂ footprint of cement production.
Routine methods, where CATHPRO group has wide experience will be used:
i) N2 sorption to provide information on specific surface area, total pore volume, average pore size diameter and pores size distribution which influence the reactivity of TCES material;
(ii) Powder X-ray diffraction (PXRD) to infer about mineralogical composition;
(iii) SEM for detailed microscopy images of the particle morphology and surface changes during the experiments.
As a first approach of deactivation evaluation along the Cal process, successive cycles followed by thermogravimetric analysis (TGA) will be performed. Factorial experimental designs will be applied to optimize operating conditions, namely calcination and carbonation temperatures as well as different CO₂, N₂ and air ratio. The in-situ XRD technique, using a reaction chamber with controlled temperature and N₂, CO₂ and air atmospheres, will be used to study the TCES material deactivation and mineralogical changes during the carbonation-calcination cycles. The Rietveld refinement method (Topas 4.2 software from Bruker) will be applied to fit experimental XRD patterns and perform quantitative analysis: determination of CaO conversion, changes in the mineralogical composition, calculation of oxides average crystallite size by Debye-Scherrer formula, etc.

Results | Understand the mechanisms associated to the TCES materials deactivation, optimize and define experimental conditions for task 2 (i.e, reduce the TCES material deactivation) and obtain experimental data for parameters estimation and models validation in tasks 4 and 5.