Mechanical Modification Of Limestone For High Temperature CO₂ Capture

Calcium looping process?CLP? has been considered as a promising solution to the greenhouse effect and global warming. But CaO-based sorbents suffers the problem of lossin-capacity during a long series of carbonation/calcination cycles, which is attributed to the sintering of the sorbent.A mechanical modification method was used to enhance the performance of natural limestone, which is more economical for its simple operation and easy-to-batch production compared with the traditional way that researchers used to prepare sintering-resisting sorbents.Performance enhanced CaO-based sorbents were prepared by mechanical milling of raw limestone with different content of Bayer aluminum hydroxide. Part of the sorbents were pelletized via a novel extrusion-spheronization method.The cyclic carbonation-calcination performance of the sorbents was investigated. It was found that the ball-milled limestone exhibit an improved performance for capturing CO₂. In particular, the mechanical-modified sorbents with Bayer aluminum hydroxide?Bah? adding into shows a better carbonation conversion. Ball-milled sorbent with 5wt% Bah into limestone?CA5-B? displays a highest conversion of 56.5% in the 25 th cycle. We believe that Ca3Al3O6, produced during calcination, acts as the inert matrix to hinder the CaO/CaCO3 sintering during carbonation-calcination cycles. The performance of the ball-milling treated sorbents could be improved when prolonging the milling time properly. For example, a high conversion of about 56.5% were obtained after 25 carbonation-calcination cycles for CA10-B4h?sorbent with 10wt% Bah after 4h of ball-milling treatment?. The pelletization via extrusion-spheronization method results in an inferior CO₂ sorption performance. But the mechanical milling process could enhance the mechanical strength of the pellets.The superior performance of modified sorbent was also found when tested under the oxyfuel atmosphere of calcination stage. In O₂/CO₂ condition, CC-B?limestone after 2h of ballmilling treatment? shows a worse performance after being pelletized, however CA10-B4 h and its pellets display almost the same cyclic CO₂ sorption capacity. But, CA10-B4 h decreases more serious than raw limestone for capturing CO₂ with the SO₂-presence carbonation.Our research shows that mechanical modification, could enhance CO₂ capture performance of natural limestone effectively, is hence a promising preparation method for CaO-based sorbents.