Dolomite-derived composites doped with binary ions for direct solar thermal conversion and stabilized thermochemical energy storage

Abstract

Thermochemical energy storage (TCES) via the calcium looping (CaL) process is an emerging technology applied in third-generation concentrated solar power plants. A range of CaO-based composites was developed via binary Fe and Mn ions doping of low-cost dolomite for direct solar absorption. The doping ratio of Fe and Mn ions was investigated and optimized aiming to produce the highly efficient Fe/Mn-doped, acid-modified dolomite composites. After comprehensively considering the spectral absorptance and energy storage density, the composite with a molar ratio of Ca/Mg:Mn:Fe=100:2:4 is optimal. It possesses a relatively high spectral absorptance of 63.7% due to the generated, dark Ca-Mn-Fe oxides, which is up to ∼2.1 times higher than that of raw dolomite. Moreover, the composite exhibits excellent cycling stability (a gravimetric energy storage density loss of ∼6.6% after 30 cycles) resulting from uniformly distributed, intrinsic MgO grains. Additionally, dolomite-derived composite pellets were prepared using extrusion-spheronization, and their volumetric energy density is remarkably superior to that of the powder, ∼2.37 GJ/m3 after 30 cycles. The fresh pellets (7.25± 0.64 MPa) and calcined pellets (3.19 ± 0.29 MPa) both possess desirable ability to resist mechanical stress and thermal shock. Therefore, Fe/Mn-doped, dolomite-derived composite pellets are potential candidates for direct solar absorption when applied in CaL-based TCES systems due to their simultaneously desirable spectral absorbance and cycling stability.