Validation of the oxygen buffering ability of bed materials used for OCAC in a large scale CFB boiler

Abstract

Oxygen carrier aided combustion (OCAC) is a novel concept where the inert bed material is fully or partly replaced by an oxygen carrying metal oxide to increase the oxygen distribution in fluidized bed combustors. In this work, the basic claim that metal oxides provide oxygen buffering and oxygen transporting properties is investigated further. The study includes initial experiments where an oxygen carrier has been used exclusively in large scale for combustion purposes. In the experiments, conducted in Chalmers 12MWth CFB-boiler, distinct fuel pulses were introduced to the combustor as the boiler was operated at the same conditions, first with 100% silica sand and later during operation with 100% iron-titanium based metal oxide. The results from the experimental progression were explored further by creating a dynamic pulse response, in which the experimental data was used to derive the empirical coefficients. The results from the experiments and the subsequent evaluation of the dynamic response provide proof of the claim that the oxygen carrying bed material enhances the utilization of the oxygen provided to a boiler by distributing it in space and time.