A numerical code calculating the burnout time of a single biomass particle in a fluidized bed reactor was developed. Combustion modelling was performed by numerical calculation of energy and mass balances on the particle. Kinetic data for pyrolysis and char combustion stages, as determined by thermogravimetric analysis, were used. The results showed that the time needed for the completion of each partial combustion stage is less for biomass rather than brown coal. In particular, the fast heating of the biomass particle is attributed to its lower thermal volumetric capacity and is maintained at the same level throughout the whole combustion process. The faster and more prolific volatiles release, as well as the increased char reactivity when using biomass, further accelerates fuel conversion and results in great changes on the total conversion compared to brown coal. The same remarks hold for all biomass species studied, while the predictions of the simulation model were in agreement with the results of other researchersí efforts. The effect of uncertain parameters on model predictions was investigated and it was proved that the particle diameter, moisture content, oxygen concentration and especially the gas temperature have the greater influence on the calculated results. Combined use of the developed combustion model with thermogravimetric studies provides a comprehensive view of biomass combustion behaviour and this methodology can be incorporated in advanced computational tools for the design and operation of large scale fluidised bed combustion installations.
Keywords: burnout time, volatiles, char combustion, kinetics, residues.