MODELING HYDROCARBON OXIDATION AND POLLUTANT FORMATION IN FBC OF LIQUID FUELS

摘要

This paper utilizes a mathematical model of homogeneous combustion in a bubbling fluidized bed (FBC) whose distinctive feature is the sub-model of the heat-up, chemical conversion and mass transfer of the "endogenous" bubble, i.e., a fuel-rich bubble formed after liquid fuel injection and vaporization. A unit fed with a under-bed liquid fuel and fired in a temperature range lower than the classical values for conventional systems (e.g., 1200°C) and solid fuel FBC (i.e., 850°C) is examined. This paper uses a detailed chemical kinetics scheme extended also to homogeneous NO_X formation and destruction reactions. The model calculates the axial profile of the nitrogen species in the endogenous bubble and predicts, under certain simplifying hypotheses, NO_X emissions. The most crucial characteristics influencing the endogenous bubble behavior - such as the initial size and the stoichiometric ratio -are treated as parameters. The actual liquid fuel is represented very simply by n-dodecane. A qualitative model validation is carried out on experiments that were performed on a pre-pilot, bubbling fluidized combustor with under-bed injection of a diesel fuel. Experimentally measured radial profiles of CO, CO_2 and NO_X in the splash zone were used.