Purpose - The purpose of this paper is to optimize the performance of an incinerator plant in terms of NO emissions and temperature of particles 2 s after the last air injection, which must be above 850 degrees C as established from the Directive 2000/76/EC of the European Parliament and of the Council - December 4, 2000 on dioxins formation in waste incineration plants. Design/methodology/approach - Investigation is made by coupling proper models developed within three commercial software environments: FLUENT, to reproduce the thermodynamic field inside the combustion chamber of the incinerator plant taken into account, MATLAB, to evaluate the position and temperatures of the particles 2 s after the last air injection, MODEFRONTIER, to change both the secondary air mass flow rate and the equivalent heat transfer coefficient of the refractory walls to fulfill the conflicting objectives of reducing the NO formation and increasing the mean gases temperature as required by the Directive. Findings - The investigations suggest that it is possible to create the conditions allowing the reduction of NO emissions and the fulfilment of the European limits. In particular, the obtained results suggest that increasing the overall mass flow rate of the secondary air and using a different refractory material on the walls, the environmental performance of the incinerator plant can be improved. Research limitations/implications - Many other parameters could be optimized and, at the same time, more detailed models could be used for the Computational Fluid Dynamics simulations. Moreover, also the energy generated at the plant would need a better investigation in order to understand if optimal conditions can be really achieved. Originality/value - The work covers new aspects of Waste-to-Energy (WtE) systems, since it deals with an optimization study of plant design and operating parameters. This kind of investigation allows not only to improve already existing technologies for WtE systems, but also to develop new ones.