Modeling of turbulent burning flow and performance evaluation of municipal solid incinerator

Finite-element simulations are presented to advance the knowledge of flow structures, species distributions, and mixing behaviors of turbulent burning flows in municipal solid incinerators under various operating conditions. The modified kappa-epsilon turbulence model together with wall functions was adopted. Devolatilization of solid wastes were simulated by gaseous methane (CH4) nonuniformly distributed along the inclined grate. The combustion process was considered as a two-step reaction when primary underfire air entered and mixed with methane gas in the first combustion chamber. A mixing-controlled eddy-dissipation model was used for predicting the reaction rates of CH4, O-2, CO2, and CO. Results show that the grate is covered by cone-shaped flames that are bent and aligned with the how directions. Postflame oxidation is done in the second combustion chamber and can be improved by provision of more excess air or by the injection of secondary overfire air. Combustion efficiency up to 99.98% and an exit temperature around 1,000 degrees C can be achieved at 100-200% excess air. Reasonable agreements are achieved between numerical predictions and available in-situ measurements.