Ca-looping process using wastes of marble powders and limestones for CO2 capture from real flue gas in the cement industry

Abstract

The potential of CaO-based sorbents using waste and natural geological materials (two wastes of marble powders and four limestones) for CO2 capture through the Calcium-looping process was assessed using two distinct carbonation gas atmospheres: a real industrial flue gas from a cement plant, and a synthetic gas mixture. The sorbents’ CO2 capture capacity was evaluated on a Fluidized Bed Reactor laboratory scale unit, through ten carbonation-calcination cycles (calcination: 930 °C, 70 % CO2 in air; carbonation: 700 °C, 15 % CO2 in air/real industrial flue gas). The sorbents carbonated with the real industrial flue gas showed a better performance and stability for CO2 capture than with the synthetic gas, which can be explained by presence of moisture in the former. The textural and mineralogical properties of spent sorbents, were characterized by N2 sorption and XRD techniques. The results show that the moisture (below 0.3 %) present in the real flue gas hinders the growth of the CaO crystallite size and leads to an increase of the surface area and total pores volume after 10 cycles. Also, better CO2 capture capacity results were associated with fresh CaO compositions above 52.0 wt. % while for values bellow 46.0 wt. % the performance decreased significantly. The sorbents with high CaO content have an interesting potential to be used in the Ca-looping process under a real carbonation atmosphere, namely the wastes of marble, that appear as a possible economically attractive option, which can contribute to minimize the adverse environmental impacts of the high volume of Portuguese industrial wastes.