CO2 looping cycles with CaO-based sorbent pretreated in CO2 at high temperature

In this study, pretreatment of CaO-based sorbent in a CO2 atmosphere at high temperature is investigated for its effect on CO2 capture. Three limestones from three widely different geographical locations are used for the tests: Kelly Rock (Canada), La Blanca (Spain), and Katowice (Poland). The particle sizes used are typically as employed in fluidized bed conversion systems. Pretreatment was done in a tube furnace at different temperatures and for different durations. The pretreated samples are characterized by nitrogen physisorption tests, scanning electron microscopy (SEM), and carbonation/calcination conversion measurements in a thermogravimetric analyzer (TGA). The results obtained showed significant decrease of sorbent surface area after pretreatment and the presence of smooth CaO grains was typical of the sorbent particle surface morphology. The pore surface area of pretreated sorbent samples increased after CO2 cycling, with a peak in pore volume distributions at 50 nm, and SEM images showed the reappearance of smaller CaO grains. In the case of Kelly Rock and Katowice samples, this led to an increase in CO2 capture activity, up to 45% after 20 cycles. After that, conversions decreased but still remained 5-10% above those for the original (no pretreatment) samples. This beneficial effect means that particles of larger size, typical of fluidized bed combustion (FBC) systems, can be suitably pretreated for use in longer series of CO2 capture cycles. An additional expected advantage of pretreating sorbent in this manner is reduced elutriation at any given FBC condition. Attempts to pretreat La Blanca failed, as they did when using N2, and it is believed that this is explained by the high Na content of this limestone. Crown Copyrigh