M. Falcitelli

Modelling practical combustion systems and predicting NOx emissions with an integrated CFD based approach

Abstract An integrated methodology for the simulation of practical combustion systems and NOx prediction is presented. It is based on 3D CFD simulation coupled to a postprocessor which yields reactor networks, extracted from 3D fields, as ‘equivalent’ simplified flow models for which it is possible to use a detailed reaction kinetics. The study of two glass melting furnaces is presented to illustrate the methodology. The furnaces were experimentally characterised, then CFD simulations were performed, setting the suitable boundary conditions for the radiative heat exchange and the sub-model for the chemistry. From each CFD simulation, a chemical reactor network was extracted to perform the computation of the secondary product combustion species by means of a complex kinetics mechanism. An evaluation of the models was given comparing the measurements with the temperature of the CFD field and the NOx prediction. Finally, an estimate of the effect of some NOx reducing techniques was given.

An algorithm for extracting chemical reactor network models from cfd simulation of industrial combustion systems

Chemical engineering models significantly reduce the amount of computational time for detailed chemical kinetics with respect to the direct implementation of a three-dimensional CFD code, but to be of real aid in dealing with industrial problems, they should be generated from CFD outputs in an automatic and objective way that does not depend on the specific case to be modeled. In the present study, the features of an algorithm developed and encoded for this purpose are shown: The criteria and logical steps adopted in generating chemical reactor networks (CRNs) from CFD simulation of industrial combustion devices are presented, and a method for evaluating the accuracy of the simplification is discussed. The assessment of the algorithm focuses on its performance in yielding CRNs capable of reproducing the concentration of main species calculated by CFD. This is a necessary condition for the subsequent use of comprehensive and detailed reaction schemes for the prediction of pollutant and harmful species involved in combustion.

NOx emission prediction from 3-D complete modelling to reactor network analysis

Abstract This paper describes the activities carried out for the development and the use of CRFD codes and related procedures for the design of industrial furnaces. The objective is to predict the emission of pollutants, such as nitrogen oxides, in combustion flue gases. This prediction may be correctly accomplished using a detailed kinetic mechanism, which cannot be directly implemented on CRFD codes due to actual computational limits (both in terms of memory and CPU time consumption). A new approach has been developed: analysing the 3D CRFD flow fields, an “equivalent” chemical reactors network model is extracted with corresponding residence time distributions and overall reactor properties, and the detailed kinetic calculation is performed on this simpler scheme. The approach has been successfully applied to different scale of furnaces such as pilot plants and industrial boilers, low- NOx burners and glass furnaces. In the papers a description of the CRFD codes is given, and the methodology to extract a chemical ideal reactor network from CFRD fields is presented. Finally, an application of the procedure on the Monfalcone #3 steam generator is discussed.

Simulation of NOx formation in glass melting furnaces by an integrated computational approach: CFD+Reactor network analysis

A procedure, called Reactor Network Analysis, has been developed for the prediction of NOx emissions by practical combustion systems. It is a postprocessor of a CFD simulation which allows to extract from CFD 3D fields an “equivalent” network of reactors, for which it is possible to use a detailed reaction kinetics. The study of two glass melting furnaces, drawn from the experience of the authors, are presented to illustrate the methodology. The furnaces were experimentally characterised, then CFD simulations were performed, setting carefully the boundary conditions for the radiative heat exchange, and adopting a simplified reaction kinetic scheme with 9 species and 10 reactions, for the chemistry. Then, from each CFD simulation, a chemical reactor network was extracted, as simplified flow model, to perform the computation of the secondary product combustion species by means of a complex kinetics mechanism. An evaluation of the models was given comparing the measurements with of both the temperature CFD field and the NOx prediction by Reactor Network Analysis. Finally, an estimate of the effect of some NOx reducing techniques was given, changing some key parameter of the reactors model.