Clinker based on calcium looped meals from the Cleanker Project

Abstract

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.

Keywords: CO2 reduction; SEM; alternative raw materials; calcium looping technology; characterisation; low CO2 clinker; optical microscopy.