Experimental Investigation ofCaMnO3−δBased Oxygen Carriers Used in Continuous Chemical-Looping Combustion

Abstract

Three materials of perovskite structure,CaMn1−xMxO3−δ(M = Mg or Mg and Ti), have been examined as oxygen carriers in continuous operation of chemical-looping combustion (CLC) in a circulating fluidized bed system with the designed fuel power 300 W. Natural gas was used as fuel. All three materials were capable of completely converting the fuel to carbon dioxide and water at 900°C. All materials also showed the ability to release gas phase oxygen when fluidized by inert gas at elevated temperature (700–950°C); that is, they were suitable for chemical looping with oxygen uncoupling (CLOU). Both fuel conversion and oxygen release improved with temperature. All three materials also showed good mechanical integrity, as the fraction of fines collected during experiments was small. These results indicate that the materials are promising oxygen carriers for chemical-looping combustion.

Ca1−A MnO3 (A = Sr and Ba) perovskite based oxygen carriers for chemical looping with oxygen uncoupling (CLOU)

“…Up to 8.8% decrease in initial decomposition temperature was reported for perovskite supported mixed metal oxides. As a standalone oxygen carrier, perovskites of the CaMnO 3 family are extensively studied for CLOU and CLC applications [20,[29][30][31][32][33][34][35][36][37][38][39]49,[57][58][59][60][61]. While its oxygen uncoupling capacity is smaller than copper oxides, CaMnO 3 , which can be synthesized from abundantly available manganese ores and Ca precursors [29,60], has been reported to be active for solid fuel conversions [29,31,34,36].…”

“…The authors noted CaMn 2 O 4 spinel formation after testing the oxygen carrier's CLOU properties in three cycles and activity for methane conversion in a single cycle. Hallberg et al also investigated the addition of both Ti and Mg in a 300 W fluidized bed system using natural gas as the fuel [61]. The designed oxygen carriers showed higher conversion of the fuel than Ni oxides while showing little attrition, however, it was determined that the spent particles contained a noticeable amount of the spinel CaMn 2 O 4 phase.…”

Determining CLOU Reaction Kinetics for Combined Oxygen Carriers—Discussing the Experimental Methods

“…The perovskite particles, C28, were manufactured by VITO (Flemish Institute for Technological Research, Belgium) using the spray‐drying method. The particles were sintered at 1375 °C for 4 h . The manganese ore, LU, used in the experiments is a natural mineral.…”

“…Manganese oxides such as manganese–silica oxides (Mn y Si 1− y )O x are cheap and readily available, they have CLOU properties, and are not expected to react with sulfur at relevant temperatures . Manganese‐based perovskites, such as CaMn 1− x − y Mg x Ti y O 3− δ , have been tested in continuous operation with good results and, due to the oxygen deficiency in the perovskite phase, can release at least 0.90 wt % as gas‐phase O 2 . Manganese ores are of interest especially for ash‐rich fuels because they are a low‐cost material that can be replaced fairly often if the carriers should be deactivated by ash .…”

“…In this work, experiments are done on three oxygen carriers, that is, a perovskite (C28), a manganese ore (LU) and a manganese silica oxide (M75S) (the notations are taken from the original articles). The experiments were carried out by TGA.…”