Numerical simulation of low nitrogen oxides emissions through cement precalciner structure and parameter optimization

Abstract

To reduce nitrogen oxides (NOx) emissions in the combustion process, the structure and parameters of a 4500 t d^-1 precalciner were optimized. The precalciner model was established using ANSYS FLUENT software (version 14.5). The effects of raw material angle, tertiary air velocity, and tertiary air temperature on NO concentration were studied. A Box-Behnken design (BBD) with three factors was employed to establish a two-order response model based on response surface methodology. The results showed that the simulated total NO concentration at outlet was 526 ppm. Compared to the monitoring data of 496 ppm, the error was within an acceptable range. The raw material angle primarily affected the generated location and rate of NO. The NO concentration at the precalciner outlet increased from 124 ppm to 220 ppm, when the tertiary air velocity increased from 22 m s^-1 to 38 m s^-1. When the temperature was 1123 K, the NO concentration rose to the highest value of 211 ppm. The interaction between the tertiary air velocity and tertiary air temperature was insignificant, while the other interactions were significant (P < 0.05). Finally, a new response surface model was obtained through optimization, which can accurately predict NO concentration. The optimum conditions for low NOx combustion were a raw material angle of 70°, tertiary air velocity of 26 m s^-1, and tertiary air temperature of 1280 K.

Keywords: Cement; Nitrogen oxides; Numerical simulation; Optimization; Precalciner; Response surface model.