The grain growth mechanism of nano-CaO regenerated by nano-CaCO3 in calcium looping

Abstract

The grain growth mechanism of nano-CaO-based CO₂ adsorbents in calcium looping (CaL) process was studied to figure out the main factors affecting sorption durability. First, the thermal growth characteristics of nano-CaCO₃ grains and nano-CaO grains at 750–850 °C was measured to fit the grain growth kinetic models. The activation energy data of grain growth of nano-CaCO₃ and nano-CaO were obtained as 104.8 kJ mol⁻¹ and 212.8 kJ mol⁻¹ respectively, which indicated that the grain growth of nano-CaCO₃ was easier than that of nano-CaO. Then, the grain sizes of regenerated nano-CaO undergoing 10 CaL cycles were compared with those derived from nano-CaCO₃ suffering high temperature heat-treatment under the same looping temperature and time. It was found that CaCO₃–CaO chemical conversion could accelerate the grain growth of regenerated nano-CaO. Based on these results, the grain growth mechanism of regenerated nano-CaO grain in CaL process was proposed. The thermal growth of nano-CaCO₃ grain was the key issue to influence the grain growth of regenerated nano-CaO. Therefore, shortening the high temperature residence time as well as preventing the interface contact of nano-CaCO₃ grains were good for limiting the grain growth of regenerated nano-CaO.