PREDICTION OF AEROSOL IN A BIOMASS-FIRED FURNACE

The use of biomass for energy production requires more attention to emissions of fine (submicron) particles. Aerosol from biomass combustion contains large amounts of sulphates and chlorides of alkali metals (K, Na) as well as heavy metals (Pb); the composition depends on both fuel properties and combustion process. These elements and their compounds have typically relatively low melting temperatures so they generate deposits. Hence predicting inorganic aerosol formation in biomass-fired power generation systems could be appealing to control fouling and corrosion. During biomass combustion, some mineral matter compounds, i.e. Na, K, S, Cl, Ca and Mg, vaporize and subsequently undergo a series of gas-phase chemical reactions leading to the formation of the main aerosol precursors, KCl (g) and K2SO4 (g). When the gases are cooled down in the heat exchange section of boiler, these chlorides and sulphates, condense to form aerosol by either homogeneous nucleation or heterogeneous condensation on existing particles entrained in the flue gas. The present work is aimed at defining a possible methodology to estimate inorganic aerosol formation from biomass-fired systems. The target is challenging, as it requires the prediction of aerosol forming compounds in the gas phase as well as the gas-to-particle conversion. The determination of aerosol precursors involves complex kinetics, so the application of Computational Fluid Dynamics modelling is not feasible because of the large number of cells that are needed to discretize the burner and the furnace. The work is in the framework of the EU project OnCord “Online Corrosion Diagnostics”. The chosen system is the pilot-scale KVSA vertical furnace belonging to the University of Stuttgart.