Modeling NOx emission of coke combustion in iron ore sintering process and its experimental validation

Abstract

NOx emission of coke combustion in iron ore sintering was modeled by overall reaction rate equations of NOx formation and reduction. Incorporating into a previous sintering heat treatment model, overall NOx emission can be predicted and the simulated results were well agreed with four sinter pot tests under varying conditions which are similar to actual production. In sintering, NOx emission is significantly related to fuel combustion. Due to heat input by ignition and smaller airflow in the initial stage of sintering, the predicted NOx emission has a higher value of about 350ppm first then it decreases a little and keeps at a relatively constant level of about 300ppm until the burn-through point, and decreases rapidly as a result of the accomplishment of coke combustion. Simulation results indicate that fuel NOx is the main NOx emission in sintering while thermal NOx is rarely produced since the bed temperature is much lower than 1800K. The generated NOx could be reduced not only on the surface and in the pores of coke but also by CO around coke particles, about 50% and 10% of the generated NOx could be reduced by char and CO, respectively. Increasing coke rate and decreasing coke size promote NOx generation by accelerating the coke combustion. The reduction extent by char is greatly influenced by contact between NOx and char while the reduction extent by CO is mainly determined by the combustion atmosphere.