Enhancement of Ca-Based Sorbent Multicyclic Behavior in Ca Looping Process for CO2 Separation

The Ca-based sorbent looping cycle represents an innovative way Of CO2 capture for power plants. However, the CO2 capture capacity of the Ca-based sorbent decays sharply with calcination/carbonation cycle number increasing. In order to improve the CO2 capture capacity of the sorbent in the Ca looping cycle, limestone was modified with acetic acid solution. The cyclic carbonation behaviors of the modified and original limestones were investigated in a twin fixed-bed reactor system. The modified limestone possesses better cyclic carbonation kinetics than the original limestone at each cycle. The modified limestone carbonated at 640-660 degrees C achieves the optimum carbonation conversion. The acetic acid modification improves the long-term performance of limestone, resulting in directly measured conversion as high as 0.4 after 100 cycles, while the original limestone remains at a conversion of less than 0.1 at the same reaction conditions. Both the pore volume and pore area distributions of the calcines derived from the modified limestone are better than those derived from the original limestone. The CO2 partial pressure for carbonation has greater effect on conversion of the original limestone than on that of the modified sorbent because of the difference in their pore structure characteristics. The carbonation conversion of the original limestone decreases with the increase in particle size, while the change in particle size of the modified sorbent has no clear effect on cyclic carbonation behavior.