The flow patterns and transitions in a rectangular gas-liquid-solid three-phase bubble column were studied. The influence of solid volume fraction, particle size and particle density on the flow regime transitions of the three-phase bubble column was investigated experimentally. Experiments were carried out for solid volume fraction V-s = 0.03-0.3, average particle size d(p) = 48 mu m-270 mu m, particle density rho(p) = 2500 kg/m(3)-4800 kg/m(3), and superficial gas velocity U-g = 0.007 m/s-0.7 m/s in a rectangular bubble column measured 0.8 m tall, 0.1 m long and 0.01 m wide. Four distinct flow patterns and three transition points were observed in this experimental system, and the four flow regimes were discrete bubble regime, transition regime, bubble coalescence regime and strong turbulent regime, which were determined on the basis of criteria as well as schematic diagrams and typical flow pattern images obtained from a high-resolution digital charge couple device (CCD) camera. Typical flow patterns maps were plotted for illustrating flow regime transitions under different particle conditions. It was found out that particle volume fraction and particle density had an effect on the flow pattern transitions; when increasing the values of particle volume fraction and the particle density respectively, the values of the flow regime transition points all decreased. Particle size had a little effect on flow regime transition points when the particle size shifted in the range of 48 mu m to 150 mu m; when particle size was larger than 150 mu m and increased to 270 mu m, the operation ranges of the transition regime and the bubble coalescence regime decreased. (C) 2014 Elsevier B.V. All rights reserved.