Experimental evaluation and detailed characterisation of biomass reburning

Previous works demonstrate that biomass is a valid reburn fuel, displaying NOx reductions close to those obtained in natural gas reburning. However, available information on biomass reburning basically refers to parametric studies based on exhaust emissions, lacking a thorough description of the process. The present work is an attempt to provide a detailed experimental characterisation of biomass reburning, including parametric studies in propane and pulverised coal flames, as well as in-furnace spatial distributions of the relevant variables. The tests were performed in a semi-industrial-scale furnace. Both natural gas and sawdust were used as reburn fuels for a range of residence times (0.41–1.44 s) and stoichiometries (0.85–1.05) in the reburn zone. NOx and unburnt (CO and UHC) emissions were measured in all the tests. A detailed characterisation of the local temperatures and concentrations of CO, UHC, NOx, HCN and NH3 inside the reducing zone was accomplished for some selected cases.