Three-dimensional combustion modeling in municipal solid-waste incinerator

Three-dimensional flame structures and mixing behaviors of turbulent burning hows in a municipal solid-waste incinerator are investigated by finite-element simulation. The modified kappa-epsilon turbulence model together with wall functions was adopted. Devolatilization of solid wastes was simulated by gaseous methane (CH4) nonuniformly distributed along the inclined grate. The combustion process was considered as two-step stoichiometric reactions when primary underfire air entered and mixed with methane gas in the first combustion chamber. The mixing-controlled eddy-dissipation model was employed 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 flow directions. Additional mixing in the second combustion chamber can enhance the oxidation and can be improved by provision of more excess air or by the injection of secondary overfire air. Combustion efficiency up to 99.97% and an exit temperature around 1,100-1,300 K can be achieved at 100-150% excess air. Reasonable agreements are achieved between numerical predictions and available in-situ measurements.