Reactivity of a spray-dried NiO/NiAl2O4 oxygen carrier for chemical-looping combustion

Kinetic data of a promising oxygen carrier of NiO/NiAl2O4 have been established from experiments in a small fluidized bed batch reactor using methane. The particles were prepared by spray-drying using commercially available raw material and selected as the best candidates from an earlier screening study. The particles clearly showed high reactivity, with a maximum gas yield between 86% and 93% in the temperature interval 750 °C to 950 °C when using a bed mass and a gas flow corresponding to only 6 kg/MWfuel. A comparison of the reactivity with data from TGA experiments showed that the reactivity generally was faster in the batch fluidized bed in the investigated temperature interval. A simple reactor model using kinetic data from the batch fluidized bed reactor and the TGA predicted a minimum mass of 9–24 kg/MWfuel of oxygen carrier particles for full gas yield of methane to carbon dioxide in the fuel reactor. Comparison with experiments performed in a 10 and 120 kW CLC reactor with the same type of oxygen carrier showed that even when employing 13 to 50 times the amount of oxygen carrier theoretically needed for complete gas conversion, full gas yield was not obtained in the circulating systems. Hence it is of great importance to consider the fluid dynamics and gas-solid contact when modeling the fuel reactor of a chemical-looping combustor.

► Chemical-looping combustion with oxygen carriers of NiO/NiAl2O4.
► Preparation of Ni-based oxygen carrier with spray-drying using commercial powders.
► Reactivity investigation of oxygen carriers using batch fluidized bed reactor.
► Reactivity of particles is high, meaning low theoretical solids inventories for complete gas yield to carbon dioxide, something which was not found in larger continuous CLC units.
► There was a high discrepancy between rate data obtained in a TGA and the batch fluidized bed.