Abstract
In this study, oxygen release/consumption behavior of calcium manganese-based oxides (CaMn1–xBxO3, where B: Cu, Fe, Mg and x = 0.1 or 0.2) used in a chemical looping oxygen uncoupling (CLOU) application was investigated. The effect of B-site dopants such as Fe, Mg, and Cu on the oxygen release behavior was also investigated with the aim to use these materials in thermal energy storage (TES). Previous literature studies about CLOU performance of doped calcium manganites were taken into consideration for dopants selection. Calcium manganite-based oxides have been used in chemical looping oxygen uncoupling (CLOU) applications owing to their oxygen release behavior to the gas phase. Studies have revealed that calcium manganite-based oxides show a promising nonstoichiometry over a range of temperatures and oxygen partial pressures, which makes them useful for thermochemical energy storage applications. However, the related literature studies have been mainly focused on their nonstoichiometric characteristics related to temperature and oxygen partial pressure and thermodynamic properties. In this work, thermal analysis and fluidized bed tests were carried out as complementary techniques. CaMn0.8Cu0.2O3 showed the highest oxygen release performance in fluidized bed tests, while CaMn0.9Mg0.1O3 had the best cyclic stability overall among the samples used in the study.
Highlights
Thermal energy storage (TES) is a necessary tool to reach the sustainable energy goals via green and sustainable energy resources.[1]
As the other studies suggested that CaMnO3 may be reduced via reaction 3, where pO2 is lower than 0.18 atm,[17,39] our study revealed that reaction 1 can occur, where pO2 is above 0.21 atm
From this point of view, promising doped CaMnO3-based oxygen carriers used in chemical looping oxygen uncoupling (CLOU) applications were tested for potential thermochemical energy storage (TCES)
Summary
Thermal energy storage (TES) is a necessary tool to reach the sustainable energy goals via green and sustainable energy resources.[1]. Among the energy storage techniques, thermochemical energy storage (TCES) exhibits a significantly good performance regarding energy storage density (0.5−1 kWh/kg),[3] theoretically unlimited storage period or storage within a large temperature range (25−1000 °C).[4] Besides, there is no need to use specific and complex storage procedures as the heat is stored in the form of chemical energy in TCES.[5] To store a high amount of energy, redox reactions of metal oxides can be useful since their operational temperatures are relatively high.[6]. Mn2O3 is very promising since it is less expensive, more abundant, more cyclically stable, and environmentally friendly.[8,9] Since the reoxidation rates of pure Mn3O4 to Mn2O3 are slightly slow, the combination of the Mn oxides was tested in some studies to increase the performance of the Mn oxides for thermochemical energy storage applications.[4,10−15] Especially, Cu/Mn combined oxides showed a lower redox temperature than the pure Cu or Mn oxides.[4,16] In addition, Fe/Mn combined oxides showed much faster reoxidation rates compared to pure Mn oxides.[10,13,16]
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