Sequential modular simulation (SMS), as a new modelling approach, was developed to simulate the photocatalytic oxidation (PCO) of gaseous pollutants in fluidized bed reactors. In the experimental part, the PCO of gaseous acetone was studied in a fluidized bed photo-reactor (FBPR) and the influence of operating conditions (inlet concentration, relative humidity (RH) and superficial gas velocity) on both acetone conversion and mineralization was investigated. It was found that the RH, as a key factor in PCO reactions, had a contradictory effect on the conversion and mineralization of acetone. In the modelling part, the bed was divided into several sections in which the bubble and emulsion phases were considered as a plug flow and a completely mixed flow reactor, respectively. Dynamic two-phase model was adopted as the hydrodynamic sub-model and the Langmuir-Hinshelwood (LH) mechanism as the kinetic sub-model. Kinetic constants of the latter sub-model were estimated using experimental data from the literature. A new dimensionless number (HA number) was introduced to determine the optimum number of sections, as the most important factor in model predictions. The performance of the proposed model was compared with the experimental data obtained in this study and several sets of experimental data from the literature. The results showed that the simple and easy-to-achieve approach, which has the capability of integrating into the industrial process simulators such as Aspen Plus((c)) and Aspen HYSYS (c), can be used to simulate the behaviour of non-ideal FBPRs in PCO processes.