High-Temperature Thermochemical Heat Storage Performance of CaO Honeycombs During CaO/CaCO3 Cycles

Thermochemical heat storage based on calcium looping is a promising technology for high-temperature solar thermal applications. CaO-based materials suffer from severe fragmentation and attrition in multiple heat storage cycles, which can accelerate the elutriation of some fine particles from the reactor. It is necessary to mold CaO-based materials to enhance mechanical strength. In this work, CaO honeycombs prepared by extrusion molding were selected as the molding materials for heat storage. The thermochemical heat storage and mechanical performances of the CaO honeycomb during CaO/CaCO3 cycles were studied. The effects of carbonation conditions, calcination conditions, and addition amounts of the binder were investigated. As the carbonation pressure increases from 0.1 to 0.2 MPa, the heat storage capacity of the CaO honeycomb is improved significantly, while it decreases rapidly with increasing the carbonation pressure from 0.2 to 1.0 MPa further. The CaO honeycomb carbonated at 0.2 MPa achieves the highest heat storage capacity. The effective conversion and heat storage density of the CaO honeycomb carbonated at 0.2 MPa are 0.45 and 1431 kJ/kg after 25 cycles, respectively, which are both 2.3 times as large as those of the CaO honeycomb carbonated at 0.1 MPa. Polyvinylpyrrolidone (PVP) is an appropriate binder to enhance the heat storage capacity of CaO honeycombs. The CaO honeycomb with 3 wt % PVP exhibits a higher heat storage capacity. Furthermore, the obvious cracks and structural deformation do not appear on the surface of the CaO honeycomb after 20 cycles. The CaO honeycomb carbonated under 0.2 MPa after 20 cycles shows a high crushing strength of 0.663 MPa. This indicates that CaO honeycombs have good thermal shock resistance and mechanical properties. Therefore, CaO honeycombs appear attractive for the calcium looping heat storage.