Clinker based on calcium looped meals from the Cleanker Project

The Cleanker (CLEAN clinKER production by Calcium Looping process) project, financed in the framework of Horizon 2020 EU funding program, has demonstrated the feasibility of the integrated CaL concept at industrial scale in a new demo system realised in the Buzzi Unicem cement plant in Vernasca (IT). The Calcium Looping (CaL) CO2 capture process exploits the reversible reaction of limestone calcination/carbonation (CaCO3 ↔ CaO + CO2). The Cleanker pilot plant consists of the coupling of a carbonator and an oxyfuel calciner. When the flue gases from kiln (containing CO2) flow through the carbonator together with calcined meal, which acts as a CO2 sorbent, carbonation takes place and CO2 is fixed in calcium carbonate. CaO is then regenerated in the calciner, where the opposite reaction takes place, and the captured CO2 is released. When the lime/limestone looping is carried out through a carbonator and a calciner operated in oxyfuel, a concentrated CO2 stream is obtained that can be efficiently addressed towards CCS or CCUS processes. In the Cleanker Project, the possibility to use raw meal for clinker production has been exploited and the meals sampled at the outlet of the oxyfuel calciner have been characterised and used for producing clinker at a lab scale. Calcium looped (CaL) meals collected at different sampling point during the operation of the CaL plant were characterised by means of X-ray fluorescence spectroscopy, X-ray diffraction and particle size distribution. Electron scanning microscopy revealed significant differences in the surface of particles of the looped meals with respect to the original one, resulting from the loading and unloading of CO2 during the looping cycles. The meals were burnt in a laboratory furnace and the obtained clinkers have been characterised on a chemical, mineralogical and microscopical point of view, revealing the good burnability of all the meals and attesting the possibility to reintegrate the materials in the clinker production process. A lower alite/belite ratio in the clinker produced from the looped meals was observed: actually, the depletion of calcium during the recirculation of the meal in the calciner/carbonator system led to a reduction of the lime saturation factor influencing the mineralogical composition of the product.

Preparation of Cement Clinker from Geopolymer-Based Wastes

In order to avoid potential environmental pollution from geopolymer-based material wastes, this work investigated the feasibility of using these materials as alternative raw materials in the preparation of cement clinker. The geopolymer binders and mortars were used as substitutes for natural mineral clays since they are rich in silica and alumina. Simulated geopolymer wastes were prepared by the activation of metakaolin or fly ash by an alkaline silicate solution. The cement-clinkers fired at 1450 °C for 1h were characterized by XRD, XRF, SEM-EDS, and a free lime (CaO_f) content test. The anhydrous clinker mineral phases C₃S (Ca₃SiO₅), C₂S (Ca₂SiO₄), C₃A (Ca₃Al₂O₆), and C₄AF (Ca₄Al₂Fe₂O₁₀) were well-crystallized in all investigated formulations. The free lime was lower than 1.3 wt% in all elaborated clinkers, which indicates a high degree of clinkerization. The results demonstrate that geopolymer binder and mortar materials are suitable substitutes for natural mineral clay incement clinker preparation.