A hydrodynamic and kinetic model was developed and applied to simulate the experimental data from a three-stage fluidized bed pilot plant with downcomers. This was used to study the activated carbon production from a Spanish bituminous coal by steam gasification. The steam gasification kinetics, considering the influence of inhibitors, were also determined in a thermobalance. With the kinetic equation and the experimental solids residence time distribution of the pilot plant, the model simulates the overall process that takes place in the reactor. The proposed model is able to reproduce the experimental results satisfactorily.