In this study a prismatic spouted bed was characterized experimentally and modelled by means of 3D CFD-DEM simulations. The main focus was on the investigation of the influence of the gas flow rate on the bed dynamics and spouting stability. Pressure drop time series obtained at different gas velocities were used for the identification of flow regimes by means of the frequency domain and of chaotic properties such as the correlation dimension and Kolmogorov entropy. The gas and particle dynamics were investigated through simulations of different operational regimes: the spouting onset, as well as stable and instable regimes. A 3-D bed behaviour, typical for slot-rectangular beds, was found. A good agreement between simulations and experiments in the particle flow patterns, bed expansion and dynamics of characteristic gas pressure fluctuations was achieved. The particle dynamics as a function of the gas velocity was investigated for the entire bed. For one of the stable regimes, the bed regions showing different particle dynamics (spout, fountain and annulus) were characterized in detail. A regime map showing the stable operational window in dependence on an inlet-to-bed size ratio and gas velocity is also provided.