Alternative fuels exhibit different features respect to traditional fuels and require an experimental characterization in conditions similar to those of practical applications (high temperature, high heating rate, low residence time). In this work, a lab-scale drop tube reactor is characterized and an experimental procedure is developed to test a bituminous coal and a biomass fuel at high heating rate in oxidative conditions. Thermogravimetric, size and SEM analyses are used to determine the conversion degree, the reactivity and the morphological variations (swelling, fragmentation, agglomeration) of solid residues in different operating conditions. Furthermore, a model is developed in order to simulate the fluidynamics, the energy balance and the mass transfer during the partial oxidation of fuel particles. The application of this model allows the residence time and the thermal history of the particle inside the drop tube to be estimated. The experimental and model results are in agreement, considering both configurations, namely, constant diameter and density models. (c) 2005 Elsevier Ltd. All rights reserved.