Noncalcined Manganese Ores as Oxygen Carriers for Chemical Looping Combustion with Oxygen Uncoupling in a Circulating Fluidized Bed Reactor System

As chemical looping combustion (CLC) technology advances from pilot operations to industrial applications, the importance of finding robust and economically feasible oxygen carriers becomes increasingly evident. Natural manganese ores are appealing due to their abundance and oxygen release property. In this study, the performance of four different noncalcined manganese ores were investigated during CLC operations. The phase compositions and elemental distribution of the ores before and after CLC operation were determined. Here, Mn, Fe, Si, and Ca were of primary importance. Despite these common elements, the phase compositions and element distributions varied significantly among the four manganese ores. It was observed that Si in the Mn oxide phase (braunite) can be displaced by Fe during CLC operations, forming Mn–Fe oxide phases such as bixbyite and hausmannite. The content of Fe in manganese ores plays a crucial role in their O₂ release properties. A sufficiently high content of Ca facilitates the formation of perovskite calcium manganite, which enhances both the O₂ release and reactivity properties, albeit with a higher potential for attrition. CLC operations with noncalcined manganese ores proceed as smoothly as with calcined ones, suggesting a high potential to bypass the energy-intensive precalcination step for oxygen carriers in large-scale applications.