The isothermal decomposition of ozone has been implemented in the CFD code FLOTRACS-MP-3D. The code is a three dimensional (3D) multiphase computational fluid dynamics code with an Eulerian description of both gas and particle phase. The turbulent motion of the particulate phase is modeled using the kinetic theory for granular flow, and the gas phase turbulence is modeled using a sub-grid-scale model, cf. Ibsen et al. (Ind. Eng. Chem. Res. 40 (2001) 5081). The decomposition reaction is studied in a 3D representation of a 0.254m i.d. riser, which has been studied experimentally by Ouyang et al. (Powder Technol. 75 (1993) 73). The authors obtained profiles of ozone concentration in the 10.85-m high riser by the use of a UV detector system. Furthermore, a pressure drop profile was reported. Comparison between measured and simulated time-averaged ozone concentration at different elevations in the riser shows good agreement. The 3D representation of the reactor geometry gives better predictions of the radial variation in concentration than in a similar 2D simulation, Samuelsberg and Hjertager (Adv. Multiphase Flow (1995) 679). A parameter study is performed to investigate improvements in the predicted pressure drop profile. (C) 2004 Elsevier Ltd. All rights reserved.