Screening of different manganese ores for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)

Oxygen carriers based on manganese oxides have recently shown great promise for use in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). In this work, eleven different manganese ores have been investigated for application in CLC and CLOU. The reactivity towards methane and synthesis gas (50% CO in H2) and the oxygen uncoupling behaviour at 900, 950 and 1000 °C have been investigated. The mechanical stability and integrity of the ores were also evaluated in a jet-cup attrition rig. It was found that some of the ores could convert approximately 70-80% of the added methane to carbon dioxide, and most of them provided almost complete conversion of synthesis gas. In these experiments the bed mass was 15 g for experiments with methane and 2 g for experiments with syngas, corresponding to a specific solids inventory of 57 and 25 kg/MW, respectively. All of the oxygen carrier materials released small amounts of gas phase oxygen via CLOU, between 0.01 and 0.03 mass% of the oxygen carrier during the inert period. Some of the investigated ores also exhibited low rates of attrition. The combination of high reactivity with different fuel gases, relatively low attrition rates and low cost make some of these manganese ores highly interesting for a CLC process based on interconnected fluidized beds.