In this study, an experiment was carried out to investigate the mixing and segregation of fluidizing materials and char particles in a fluidized bed reactor. Specifically, the shape of the fluidized bed column was changed and the effect of the bed column shape on the segregation characteristics of the materials was investigated by varying the superficial gas velocity. The mixing and segregation behavior of the materials was analyzed in terms of char mass fraction and mixing index. For the three different column shapes considered, the mixing index reached a minimum value at U/U-mf = 1.14. In the segregation regime, the circular bed column yielded the lowest mixing index. However, with increasing superficial gas velocity, the flow regime changed from the particle segregation regime to the mixing, and the rectangular-shaped column had the lowest mixing index. In addition, the transition from segregation to mixing was investigated by comparing the pressure drop characteristics across the bed. (C) 2013 Elsevier B.V. All rights reserved.