Investigations on Kinetics and Mechanisms of CaCO<sub>3</sub> Calcination in Calcium Looping
Zeya Li, Xiaojin Guo, Xiaoyong Xue, Xiang Xu, Bo Wang
Abstract
Calcium looping-based CO 2 capture is generally considered more efficient than conventional postcombustion CO 2 capture. Calcium carriers’ calcination in the regenerator is crucial because proper operating parameters can provide regenerated carriers suitable for the gasifier and prevent sintering. This work focuses on the calcination behavior of CaCO 3 in calcium looping systems. In this study, the calcination kinetic parameters under various conditions were investigated using a model-free isoconversional method based on nonisothermal thermogravimetric analysis in a macroscope, in combination with X-ray diffraction tests of the samples in a microscope. Results in the macroscope showed that the apparent activation energy ranges from 121.8 to 163.0 kJ/mol under a conversion range of 0.3–0.9, and the CaCO 3 calcination mechanism involves transient nucleation and two-dimensional growth. Results observed from the microscope demonstrated that CaCO 3 tends to be calcined on a plane, consistent with the macroscope model with two-dimensional nucleation. Since the microscopic mechanism is reflected, the kinetic model can be widely adopted, and calcium-based carrier modification strategies can also be proposed to prevent sintering of the carrier perpendicular to the (1̅04) plane.