MODELING HYDROCARBON OXIDATION AND POLLUTANT FORMATION IN FBC OF LIQUID FUELS

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 NOxformation and destruction reactions. The model calculates the axial profile of the nitrogen species in the endogenous bubble and predicts, under certain simplifying hypotheses, NOxemissions. 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 ndodecane. 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, CO2and NOxin the splash zone were used.