Abstract The present paper deals with the combustion of liquid fuels in bubbling fluidized bed. The focus is on micro-explosions that were experimentally observed when burning a commercial bio-diesel in the intermediate temperature range 873–1023 K. The measured micro-explosions frequency fell in the range 2.4–3.8 Hz. A simplified model for the combustion of a rising fuel-bubble was purposely developed. It applies to a single non-premixed bubble that can undergo coalescence with other bed bubbles. A mechanistic approach is also included in the model in order to relate the frequency of micro explosions to the frequency by which relatively well-premixed bubbles approach the bed surface. The number of coalescences experienced by the endogenous bubble during its residence time is less than one, as predicted by the model with reference to the experimental conditions reported in the paper. Even with large simplifications, the model is able to explain the temperature dependence of the micro-explosive behavior. The accordance between the experimental frequency of micro-explosions and the predicted frequency of coalescence-free bubbles reaching the bed surface is rather good.