A dynamic optimization procedure for non-catalytic nitric oxide reduction in waste incineration plants

Reduced chemical kinetic models are often used to simulate the kinetics of full-scale DeNOxDeNOx systems because of the computational expense of combining a detailed description of fluid dynamics and a complete mechanism of reaction. In particular, these simplified models might be useful when complete combustion minimizes the influence of CO and hydrocarbon fuels on the kinetic mechanism of thermal DeNOxDeNOx, such as that occur in large-scale systems for non-catalytic nitrogen oxides reduction installed in hazardous waste incineration plants. In this work, a lumped mechanism is involved in a dynamic optimization procedure to reach a maximum efficiency of NO abatement in such devices, by handling the inlet ratio of H2H2 or CH4CH4 to inlet NH3NH3. As a consequence, a simplified chemical kinetic model reported in the literature was modified to reproduce the influence of hydrogen and methane addition on the selective non-catalytic reduction of nitric oxide with ammonia. The consistency of the lumped mechanism, which involves only two global reactions to describe the NO/NH3/O2NO/NH3/O2 and H2H2 or CH4CH4 gas phase reaction system, was verified by using a large set of experimental results obtained at stationary conditions in tubular reactors. The dynamic optimization procedure aims to compensate the effect of the main kinetic disturbances on nitrogen oxides reduction, as variation in the flue-gas temperature in NH3NH3 injection zones and in the flue-gas residence time, which are typically found in incinerators due to the heterogeneity of the waste composition. Calculated results of NO abatement by assuming typical fluctuations in the kinetic characteristics of exhausts in incineration plants evidence an increase of nitric oxide abatement from 5% to approximately 40–50% when involving the suggested dynamic optimization strategy.