The fluid dynamics of a new reaction system composed of a slurry transport reactor-hydrocyclon were studied using two column diameters at different gas and liquid linear velocities. The cold models used a gas collector in the top that allowed measurement of the gas disengaged by radial zones and a conductimetric probe that measured the frequency of the bubbles exiting from the top of the reactor. Gas and liquid hold-ups were determined. Liquid and solid tracers were also employed to determine the resident time distribution (RTD), global residence time, and the recycle of slurry near the wall. The results show the effect of sparger and disengaging design, as well as the effect of gas and liquid flow rate on the radial and axial gas hold-up profiles and on the recycle of slurry by the wall. This recycle is similar to those observed with a draft tube. No significant effect of column diameter was observed. A smooth circulation of slurry and solid was achieved through a mechanical optimization of the inlet and outlet of the reactor. It was demonstrated that the RTD of the system can be simulated using a set of continuous stirred tank reactors and plug flow reactor in a recycle (three parameters). Empirical equations are proposed for predicting the hold-up and the three parameters needed by the model. The similarity to a spouted bed reactor is discussed. (c) 2008 Elsevier Ltd. All rights reserved.