CO2 Carrying Capacities of Cement Raw Meals in Calcium Looping Systems

Calcium looping, CaL, is an emerging CO2 capture technology that is of special interest for use in cement plants, as it offers the possibility of exploiting several energy and material synergies. In this work, the CO2 carrying capacity of calcined raw meal materials for cement plants has been investigated with thermogravimetric equipment in a wide range of testing conditions. When calcination was carried out at high temperatures and over long times, some raw meals display a sharp decrease in their subsequent CO2 capture capacity compared to their limestone counterparts, while others perform as expected from their CaO content. XRD observations of calcined samples confirmed the formation of Ca2SiO4, i.e., belite, as the main deactivation agent, since belite formation removes active CaO for CO2 capture during the carbonation stage. The extent of belite formation was found to be greatly influenced by the nature of the raw meal (in particular by the level of aggregation of Ca and Si atoms in the material), by the calcination temperature, by reaction atmosphere, and by the duration of the calcination stage. The screening of conditions to minimize belite formation indicates that calcination time should be below 1 min, at the typically high calcination temperatures required in CaL systems (i.e., slightly over 900 °C), thus ensuring that the CO2 carrying capacity of these raw meals is kept at a level as close as possible to the value in equivalent materials with the same CaCO3 content.