This work proposes a simplified model to simulate the incineration of a single particle of wastewater sludge under fluidized bed conditions. The wet particle is burned in a first completely stirred reactor (CSTR1) containing gas and sand and operating under the usual conditions of a fluidized bed emulsion. The gas generated by the sludge decomposition reacts into CSTR1 according to different homogeneous and heterogeneous mechanisms, then it enters a second completely stirred reactor (CSTR2), which simulates the post-combustion zone. In this reactor only homogeneous reactions occur, and the composition of the gas at the outlet may approach the one of a real process. The analysis of the simulation results indicates that the homogeneous reactions occurring in CSTR1 have little effect on the distribution of the nitrogen compounds within the gas at the outlet of the reactor. At the opposite, the heterogeneous reactions have a significant effect on the production of nitrogen oxides from char combustion. The homogeneous reactions occurring in CSTR2 enable the conversion of the main nitrogenous volatile compounds, such as HCN and NH3 in N2, NO and N2O. An increase in the volume of this second reactor (post-combustion zone) enables a reduction in the emissions of HCN, NH3 and N2O at the outlet of the system. The NO content is essentially related to the amount of nitrogenous volatiles (notably NH3), whereas the N2O depends widely on the amount of nitrogen within the char. The effect of some simulation parameters (percentage of NH3 and HCN into the volatiles, the fraction of nitrogen in the char, the volume of the post-combustion zone) on the emission of oxide nitrogen compounds is also investigated.