Sewage Sludge Fluidized Bed Combustion For CLC Oxygen Carriers Production

Chemical looping combustion (CLC) is a promising strategy to produce energy from fossil fuel coupling the CO2 sequestration. This process is typically realized adopting two interconnected fluidized beds with a solid, the oxygen carrier, circulating between them. The oxygen carriers should have high reactivity with gaseous fuels and oxygen and oxygen transport capacity, low fragmentation, attrition and agglomeration tendency and high stability to a large number of redox cycles. However, the choice of the proper oxygen carrier is still open and it deserves further investigations. Usually the oxygen carrier is made of a metal oxide. Among transition metals, Fe-based oxygen carriers are considered an attractive option for the chemical looping combustion owing to their low cost, abundance and environmental compatibility. In particular it is also reported that the use of coal, also needs to develop low-cost oxygen carriers, because the ash removal/separation process can cause consistent bed material losses. In this paper CLC oxygen carriers produced by sewage sludge fluidized bed combustion are proposed as low-cost materials. In particular, the metals (Fe, Ca, Mn) present in sewage sludge ash have been deposited on high surface ?-alumina with high mechanical resistance used as bed materials during sewage sludge fluidized bed combustion. The produced oxygen carriers have been characterized using ICP-MS, X-ray diffraction (XRD) analysis. The redox behaviour of the oxygen carrier has been investigated using H2 reduction experiment. Reduction/oxidation cycles have been performed to assess the carrier stability. The reactivity of the carriers and their oxygen transport capacity have been also evaluated under repeated cycles of methane combustion/air regeneration carried out in a fluidized bed reactor