Dual-Scale Flamelet/Progress Variable Approach for Prediction of Polycyclic Aromatic Hydrocarbons Formation under the Condition of Coal Combustion

Abstract

A dual-scale flamelet/progress variable (DS-FPV) approach is developed to predict polycyclic aromatic hydrocarbon (PAH) formation in the environment of coal combustion. An additional progress variable C PAHs is newly defined in this approach to describe the evolution of PAHs, and the major species and temperature are still described by the traditional progress variable defined in the original FPV approach. Detailed chemistry simulations of a counterflow flame fueled with volatile matter and char off-gas are performed, and the solutions are regarded as references to evaluate the developed DS-FPV approach. It is found that the position of PAHs formation is located at the region that is close to the flame center in the fuel-rich side, and PAHs are mainly produced at the stage of volatile combustion. The original FPV approach can correctly predict the major species and temperature, but significant discrepancies appear for the species of PAHs that has a very weak correlation with the traditional progress variable. This issue is successfully addressed by the DS-FPV approach. Both the a priori and a posteriori analyses demonstrate that the developed DS-FPV approach can accurately and efficiently predict not only the distribution of major species and temperature but also the distribution of PAHs, although the peak values of mass fractions of PAHs are slightly underpredicted. The extension of this approach to turbulent pulverized coal combustion needs further efforts in the future.

Direct Numerical Simulation and Flamelet Modeling of Coal/Ammonia Cofiring Flame

“…The flamelet/progress variable (FPV) model allows for the consideration of detailed mechanisms at an acceptable computational expense and incorporates turbulent-chemistry interactions through a preassumed probability density function (PDF) approach . The FPV model for pulverized coal combustion was originally developed by Watanabe and Yamamoto , and has been further extended to consider multiple fuel streams, − heat losses, − reacting stages, NO formation, − polycyclic aromatic hydrocarbon formation, and soot formation − in recent years, and reasonable agreements with the experimental data or detailed chemistry predictions can be achieved. However, as for the coal and ammonia co-firing flame, there have only been three flamelet LES works reported for combustion modeling of coal and ammonia co-firing. − In the study by Meller et al, they first validated the performance of their flamelet models on the CRIEPI coal flame and then conducted a parametric study to evaluate the ammonia co-firing on flame behavior.…”