A simple mixing approach for use in reactive systems is considered. This mixing approach has so far been applied to reburning and selective non-catalytic reduction (SNCR) processes, two well-known techniques to reduce NOx emissions. Detailed kinetic models together with the mixing approaches, based on the work of Zwietering, are used to simulate both the chemistry and mixing of the reactants. Two different configurations for the mixing approach have been considered: the so-called direct and reverse approach. The study includes a comparison between different experimental results obtained in pilot installations and theoretical results calculated with the present approach.