The sulfation reaction rate of CaO particles in three reactors comprising a post-combustion calcium looping system is discussed: a combustion chamber generating flue gases, a carbonator reactor to capture CO2 and SO2, and an oxy-fired calciner to regenerate the CO2 sorbent. Due to its strong impact on the pore size distribution of CaO particles, the number of carbonation/calcination cycles arises as a new important variable to understand sulfation phenomena. Sulfation patterns change as a result of particle cycling, becoming more homogeneous with higher number of cycles. Experimental results from thermogravimetric tests demonstrate that high sulfation rates can be measured under all conditions tested, indicating that the calcium looping systems will be extremely efficient in SO2 capture.