Comparison of inorganic constituents in bottom and fly residues from pelletised wood pyro-gasification

Wood biomass is a source of renewable energy and now recognized as a potential alternative for sustainable energy production. During the pyro-gasification process, the species of the mineral component of the biomass accumulate under the grate of the pyro-gasifier (bottom residue) or become volatile and are deposited as fly residue in the cyclone filters. This work analyses the constituents of the two residues produced by a pilot scale downdraft pellet fuelled system. The residues are characterised by a high carbon content and ash content of 7 % (bottom residue) and 38 % (fly residue). The Ca, Mg, Na, S, P, Si and Cu contents in the two residues are more or less comparable. Fe, Al, Cr, Zn, Ni, Pb, Cd, Mn and B are concentrated in the fly residue. Potassium is a case apart and is present in a lower concentration in the fly residue. Mass balance has revealed that certain elements succeed in passing the first filtration phase (cyclones) and are entrained in the gas which must be cleaned. Therefore, knowledge of the composition of the biomass (macro and microelements) and of the behaviour of their transformation products is important for plant design and functioning and equally important for disposal or utilisation of process by-products, e.g. as actived carbons or as fuels.