Influence of turbulence–chemical interaction on CFD pulverized coal MILD combustion modeling

Abstract

MILD (Moderate and Intensive Low oxygen Dilution) combustion is a novel approach to reducing NOx emissions and improving combustion efficiency in fossil fuels power plants. It is characterized by elevated temperature and high dilution of reactants and strong recirculation inside the combustion chamber which produce a low temperature increase, thus reducing NOx formation. The main differences with conventional combustion concern the chemical reactions that take place in almost the entire volume of the combustion chamber and the uniformity of both temperature and the chemical species concentration. For this reason advanced turbulence-chemistry interaction models with detailed kinetic mechanisms are required to accurately simulate MILD by means of CFD calculations.The main aim of this work is to deepen the influence of turbulence-chemistry interaction on pulverized coal MILD combustion and to understand which models are more accurate and suitable to reproduce the process. In particular, two turbulence-chemistry interaction models are analyzed. On one hand, a conventional model based on infinitely fast chemistry Eddy Dissipation Model with a two-step global kinetic mechanism is considered. On the other hand, an advanced model based on finite rate chemistry Eddy Dissipation Concept is considered and used with both a global and detailed kinetic mechanisms. The results are finally compared with an experimental test-case.From the comparison, advanced turbulence-chemistry models used with complex kinetic mechanisms give, as expected, the best agreement with numerical results, despite the higher computational resources required.