Modeling of Nitrogen Pollutants in Turbulent Pulverized-Coal Flames. Final Report, July 1, 1980-June 30, 1983

摘要

This volume summarizes a three-year theoretical study of pollutant formation in pulverized-coal systems, with an emphasis on nitrogen pollutants. A NO pollutant model has been formulated to be consistent with the assumptions made in current comprehensive models for fuel-rich turbulent pulverized-coal flames. The model accounts for the effects of turbulent fluctuations on the pollutant formation process. The pollutant species equations are decoupled from the overall velocity, temperature and major species field equations. The fuel nitrogen is assumed to evolve from the coal at a rate proportional to coal weight loss, and to react quickly to HCN in the gas phase. The homogeneous rate of decay of HCN to NO or N sub 2 includes the effects of turbulent fluctuations to obtain a time-mean reaction rate. Heterogeneous reduction of the NO is modeled by a slow (non-fluctuating) rate. Thermal and prompt NO are considered to be insignificant in these fuel-rich coal flames, and only fuel nitrogen formation is considered. The time-mean reaction rates are obtained by assuming that the species mass fractions are linear functions of stoichiometry, and then integrating the resulting kinetic expression over the probability density functions for the appropriate mixture fractions. Computations are presented to demonstrate the applicability of the theory to practical coal combustion chambers. An analysis of the NO model was performed to determine the effect of various physical and inlet parameters on model predictions. Model evaluation has consisted of detailed local comparisons of model predictions with experimental data, and comparison of predicted and observed trends related to pollutant formation in coal systems. Additional applications of the NO model were also illustrated. 116 references, 57 figures, 12 tables. (ERA citation 09:000113)