Enhanced performance of manganese ore as oxygen carrier for chemical-looping with oxygen uncoupling (CLOU) by combination with Ca(OH)2 through spray-drying

Abstract

Chemical-looping with oxygen uncoupling (CLOU) is an innovative combustion technology with inherent capture of the CO2 and potential to drastically reduce the cost of capture. The process requires two interconnected reactors, between which the oxygen carrier particles are circulated while carrying oxygen from the combustion air to the fuel. In this work, the reactivity and mechanical stability of five materials were studied; three natural ores and two materials which were combinations of an ore and Ca(OH)2. The overall aim was to investigate the feasibility of making a reactive and mechanically stable material using cheap raw materials and an industrially relevant particle manufacturing process.The two combined materials behaved differently from their natural counterparts. The Brazilian ore+Ca(OH)2 showed a decrease in reactivity towards methane, but higher reactivity towards syngas in comparison to the pure ore. The South African ore+Ca(OH)2 showed a major improvement in reactivity towards both syngas and methane, which could be attributed to formation of a perovskite-structure material with significant CLOU properties. A comparison between the pure ores and the combined materials show that the addition of Ca(OH)2 had generally a beneficial impact on the mechanical stability of the oxygen carriers. As a significant change in the particle size distribution was seen for all oxygen carrier materials after repeated redox cycles with long reduction periods, the particle disintegration was likely caused by the chemical phase transformations occurring inside the particles, rather than by mechanical forces.