Towards comprehensive computational fluid dynamics modeling of pyrolysis furnaces with next generation low-NO x burners using finite-rate chemistry

Abstract

This paper reviews a CFD-based reacting flow code designed to simulate the complex physics associated with low/ultra-low-NO x burners in process heaters/furnaces. The computational tool couples together the effects of turbulent fluid mechanics, gas-phase combustion chemistry, and conductive, convective, and radiative heat transfer within the radiant firebox. The code uses adaptive mesh refinement to capture near-burner mixing. It includes two turbulent combustion models—an Eddy Dissipation Concept model and a joint scalar Probability Density Function model. These models allow for finite-rate chemistry, which is represented by reduced mechanisms based on quasi-steady state assumption in this work. An in-situ Adaptive Tabulation algorithm is used to speed-up the computation of reaction source terms. The radiative heat transfer is calculated using a discrete-ordinates method. Multiple simulations were performed in a single burner test furnace to demonstrate the capability of the modeling tool using two reduced mechanisms and the two turbulent combustion models. The results are compared to measured data to assess the impacts of these models on the accuracy and efficiency of the CFD code. Among the simulations, the case combining the PDF model and a 19-species reduced mechanism achieved the best results in CO and NO predictions. Although its run-time was significantly longer than the other cases, the future of this approach in industrial applications is still very encouraging considering the limited computational resource used in this study.