The relevance of comminution phenomena in the fluidized bed combustion of a biomass (Robinia Pseudoacacia)

Combustion of a biomass, namely Robinia Pseudoacacia, has been investigated in a bench scale bubbling fluidized bed combustor operated in a batch mode. The study has focused on the characterization of the relative importance of combustion and comminution phenomena (primary fragmentation, attrition, char fragmentation) in determining the fraction of carbon leaving the combustor as elutriated particles and that of carbon burning in the bed. Experiments showed that the comminution scenario recently proposed to describe the fate of fixed carbon during fluidized bed combustion of waste-derived fuels, applies also in the case of the biomass under consideration. In particular carbon conversion occurs to a large extent via the generation of carbon fines and, in turn, through the competitive processes of fines elutriation and post-combustion. Analysis of gaseous products in the flue gases, focused on the determination of the CO/CO2 ratio, has been directed to characterize the relative contributions to overall carbon conversion of coarse and fine particles combustion.