Spent limestone sorbent from calcium looping cycle as a raw material for the cement industry

It has been found that a spent limestone sorbent, coming from a pilot-scale calcium looping fluidized bed (CaL-FB) plant and purged after 60 cycles of calcination and carbonation, can be successfully employed in the Portland cement clinker manufacture in place of natural limestone. Laboratory measurements showed that the burnability index for a clinker-generating raw mixture consisting of commercial clay and the exhausted sorbent was better than that of a reference mixture containing the same clay and fresh limestone. The results of the burnability test were confirmed by (i) the mineralogical composition data on the synthetic clinkers obtained from both raw mixtures at 1500 °C and (ii) the hydration rate of the related Portland cements, evaluated by means of X-ray diffraction analysis and simultaneous differential thermal-thermogravimetric analysis, respectively. Preliminary and novel results reported in this communication show that the utilization of the spent limestone sorbent as a raw material for making cement can have a very favorable effect not only on the economics of the CaL-FB process, but also on the cement manufacture in terms of (i) reduced generation of carbon dioxide and pollutants, (ii) saving of raw materials and fuel, (iii) decreased flow rate of gaseous emissions.