A model for the simulation of a fluidized bed combustion reactor was developed using sequential modular approach in which two submodels for describing physical and chemical phenomena were integrated simultaneously. The adopted submodels were hydrodynamic and kinetic submodels, respectively. Dynamic two-phase model was used as the hydrodynamic submodel, and the latter submodel was extracted from literatures. The combustion reactor was divided into two regions, namely dense bed and freeboard. The dense bed was divided into several sections, determined by a newly introduced dimensionless number, in which gaseous phase was considered as a plug flow through the bubble phase, and a mixed flow through the emulsion phase. Moreover, energy balance and the effect of bubble growth were taken into account, and a new correlation for obtaining the critical temperature of natural gas combustion was proposed. Various sets of experimental data were derived from the literature and used to validate the proposed model, and a close agreement was observed between them. The sequential modular approach, which is developed in this research, can be used for the simulation of nonideal fluidized bed combustors inside the industrial process simulators such as Aspen Plus and Aspen HYSYS.