Improving the oxygen demand in biomass CLC using manganese ores

Negative Emission Technologies (NETs) should be implemented to reach the objectives set by the Paris Agreement to limit the average temperature increment to 2 degrees C. One of the options is the development of bioenergy with Carbon Capture and Storage (BECCS) technologies. In this sense, Chemical Looping Combustion (CLC) is one of the most efficient CO2 Capture technologies both from economical and energy points of view. In CLC, a solid oxygen carrier is used to transfer the oxygen from air to the fuel. In this work two manganese-based ores were used as oxygen carriers to burn three different types of biomass (pine sawdust and two Spanish agricultural residues) in a 0.5 kWth CLC continuous unit. Operational conditions were varied to evaluate their effect on the CO2 capture efficiency and the total oxygen demand of the process. Almost 100% of CO2 capture efficiency was reached working with pine sawdust as well as with almond shells. However, high values of total oxygen demand (10-20%) were found, which led to consider further technological solutions to increase the combustion efficiency. In this respect, fuel reactor outlet recycling was evaluated as an operational solution to reduce the oxygen demand with good results (about 30% reduction in the total oxygen demand value). NOx and tar formation from the CLC system were also evaluated. There were no NOx emissions during the experimental campaign and low tar content in the fuel reactor outlet gas was reached (0.3-3.2 g/Nm(3)), being naphthalene the major tar compound.