The prediction of pulverized greek lignite combustion in axisymmetric furnaces

Abstract

A general numerical method for calculating pulverized coal combustion in axisymmetric geometries is utilized, aiming at the optimization of combustion model constants for Greek lignite. The two-equation, “ k-ϵ” turbulence model is used for the gas phase, whereas a stochastic approach, based on the lagrangian technique, is used for the particulate phase. The method employs a “constant devolatilization rate” model for both the volatiles and the moisture of the fuel, a char combustion model, a relation of the “eddy-dissipation” family for the reaction rate of the gaseous mixture, and the “nonequilibrium diffusion” radiation model. The maximum permissible rate of devolatilization and the preexponential factor of the char oxidation reaction rate are optimized in order to match available experimental data for Greek lignite; these parameters were found to influence considerably, albeit in a different fashion, the combustion process in cylindrical furnaces operating on pulverized lignite. Finally, the liftoff characteristics of the lignite flame were also predicted using a temperature criterions, as well as a flame stability model.