Effects of air and oxy-fuel atmospheres on flamelet modeling of pollutant formation in laminar counterflow solid fuel flames

Abstract

In this work, effects of air and oxy-fuel atmospheres on flamelet modeling of NOx and SOx formation in two-dimensional laminar counterflow pulverized coal flames are investigated. The release and combustion of volatile-N, char-N and volatile-S are incorporated in the flamelet model, and a newly developed reaction mechanism for oxy-fuel combustion (129 species and 911 elementary reactions) is employed to describe the chemistry. Two different methods for prediction of pollutant species are evaluated using the flamelet model, in which the pollutant mass fractions are obtained by either extracting the flamelet library directly (“M1”) or solving the corresponding transport equations with the reaction source terms being taken from the flamelet library (“M2”). To evaluate the performance of proposed flamelet models, the flamelet predictions are compared to the reference results of the detailed chemistry solutions, in which the transport equations for the species mass fractions and total enthalpy are directly solved. At first, the atmosphere effects on the NOx and SOx formation are analyzed based on the detailed chemistry solutions, then the effects of atmosphere on flamelet modeling of pollutant formation are evaluated. The results show that M1 overall performs better than M2 at predicting the NOx and SOx species in both air and oxy-fuel atmospheres. The major pollutant species of NO and SO2 are over-predicted by M2 in certain regions for both atmospheres, and the reason for the incorrect prediction is explored by attributing to the interpolation error of the reaction source terms in the middle branch of the S-Shaped curve.