Combustion in a coke oven battery: Numerical modeling and testing with focus on NOx emission

In the present study numerical simulations are exploited to give insight on a heating flue combustion chamber, typical unit of a coke oven battery heating wall, employing fuels from steelmaking process. The main purpose is to develop an accurate modeling approach for NOx emission assessment, suitable for the combustion optimization during the design stage. Such goal is pursued by CFD simulations based on a novel approach: a detailed model of combustion allows to directly estimate the radicals involved in the formation of NOx estimated by thermal, prompt and reburn mechanism, the last leading to “depletion” of nitrogen oxides in fuel-rich zones. A 24 species with 134 reactions mechanism and the Eddy Dissipation Concept (EDC) for turbulence-chemistry interaction are employed. The proposed modeling approach is validated by comparison against data from plant testing in two different operating conditions, proving its suitability and accuracy. Moreover, it is shown that reburn mechanism is essential to properly evaluate the emission levels in this application. Furthermore, sensitivity analyses are carried out assessing the influence on combustion performance, namely emission, of the main operating parameters like fuel thermal input, inlet air temperature and excess air fed, which can also represent the main source of uncertainty when setting the boundary conditions for CFD simulations. The present work sheds light on the combustion characteristics and the balance between the different NOx formation mechanisms inside a heating flue combustion chamber, also providing a complete, accurate and validated modeling approach, alternative to others already available in the literature.