Calcium Looping Energy Storage Characteristics of Mn-Impregnated Limestone in Fluidization under Direct Solar Irradiation

Abstract

The directly irradiated reactor is suitable for the solar calciner in calcium looping energy storage technology. However, the low optical absorption performance of CaCO 3 is disadvantageous for its decomposition under direct irradiation. In this work, a directly irradiated fluidized-bed reactor was designed for calcium looping energy storage. The top of the fluidized-bed reactor can receive the simulated solar irradiation from the xenon lamp with a maximum irradiation intensity of 260 kW/m 2 . The energy storage characteristics of CaCO 3 under fluidization and static conditions were compared. The effect of the irradiation intensity on the solar−thermal conversion efficiency was investigated. Furthermore, the energy storage characteristics of Mn-impregnated CaCO 3 were also studied. The results indicate that direct irradiation leads to a high temperature difference in the bed. The temperature difference in the fluidization state is 30% lower than that under the static condition. Increasing the irradiation intensity enhances the decomposition efficiency of CaCO 3 . However, a high radiation efficiency exacerbates irradiation reflection, reducing the solar−thermal conversion efficiency. Mn impregnation enhanced the optical absorption performance of CaCO 3 . The optical absorbance of Mn-impregnated CaCO 3 with a CaCO 3 /Mn mass ratio of 100:3 is 0.83, which is 6 times higher than that of CaCO 3 . The solar−thermal conversion efficiency of Mnimpregnated CaCO 3 increases by 25% compared with CaCO 3 at 200 kW/m 2 . This work further promotes the application of directly irradiated fluidized-bed reactors in calcium loop energy storage.