A novel approach to estimate the size of stagnant regions in large-scale fluidized beds by means of experimental data obtained from images recorded on the bed surface was presented. For this purpose, the internal structure of an induced maldistributed pseudo-2D fluidized bed was first studied. Half of the total distributor area was covered to generate an induced stagnant region. The size and shape of this area was studied for several relative gas velocities and bed aspect ratios. The defluidized area was found to be almost independent of the bed aspect ratio, however, it was found to decrease for higher relative gas velocities. A solids recirculation zone was also found above the defluidized zone. The size of this zone increases with relative gas velocity, suggesting that it is strongly related to bubble motion. A correlation was developed to relate the visible bubble flow to the size of the defluidized zone. The results obtained in the 2D bed were extrapolated to a 3D cylindrical fluidized bed with a half-covered distributor plate to estimate the volume of the defluidized zone. The visible bubble flow in the 3D facility was estimated. Using the proposed correlation for the defluidized volume in the 2D bed was used to estimate the defluidized volume in the 3D bed. Finally, the calculated values of the defluidized volume were compared with the experimental values in the 3D facility, obtaining a maximum relative error of 20% in the estimations. (C) 2015 Elsevier B.V. All rights reserved.