CFD simulations of a cylindrical bubble column with an external loop were carried out. The effects of average bubble size, bubble size distribution, axial liquid velocity, and the two-inlets configuration were evaluated and compared with experimental and simulation data. The drag force was modelled with the Ishii-Zuber model and the turbulence of the continuous phase with the k-epsilon model. For breakup the Luo and Svendsen model was chosen and for the coalescence effects the Prince and Blanch model was used. Results show that the external loop influences gas holdup near the entrance and at high gas superficial velocities a radial symmetry is obtained in the fully developed region.