CO2 capture and fluidity performance of CaO-based sorbents: Effect of Zr, Al and Ce additives in tri-, bi- and mono-metallic configurations

Abstract

The Calcium-looping (CaL) technology is based on the reversible carbonation reaction of CaO with CO2 and has been developing rapidly as a potential low cost process for post-combustion CO2 capture. One of the main challenges of CaL process, is the identification of CaO-based sorbents that can maintain their activity in multiple cycles and have proper fluidization. The present study focusses on the influence of Zr, Al and Ce additives in mono-, bi- (Zr/Ce, Zr/Al and Al/Ce) and tri-metallic (Zr/Al/Ce) configurations on the performance of synthetic CaO-based sorbents. The developed sorbents presented a substantially improved performance over multiple cycles compared to limestone-derived CaO, due to the formation of stable, mixed Ca-inert phases. Incorporation of Al, Al/Ce and Zr/Al/Ce in CaO structure led to the development of sorbents with small crystallites and porous morphology, resulting in improved stability with less than 25 % deactivation after 50 cycles. The enhanced stability of the Zr/Al/Ce-promoted sorbent was attributed to the formation of CaZrO3 and Ca3Al2O6 mixed phases in the CaO matrix, providing a porous and stable structure. The fluidizability of the most promising sorbents was also investigated. SiO2 nanoparticles were mechanically mixed with the sorbents in different fractions to improve their fluidization performance. A minimum amount of 15 wt% SiO2 was required in order to achieve a completely smooth and homogeneous fluidization without gas channeling, bubbles or even fine agglomerates. The highest bed expansion, accompanied by a high Richardson-Zaki index n (5.9) and low Umf (2.2 cm/s) were obtained with a Ca/Zr/Al/Ce +15 wt% SiO2.