Optimization of natural gas combustion characteristics and motion characteristics in an industrial-scale alumina roaster

The alumina roaster plays a crucial role in industries such as aluminum production, with natural gas serving as the primary fuel. However, the irregular motion of alumina particles and their complex gas-solid reactions with natural gas under high-temperature conditions often lead to unstable combustion and excessive NOx emissions, limiting the optimization of the roasting process. Based on industrial experiments, this study develops a natural gas combustion model for the alumina roaster to detail the motion trajectories of alumina particles and their combustion states. By combining simulations and experiments, the effects of air preheating temperature (Tair) and excess air coefficient (α) on flame structure, flue gas velocity, radical distribution, and pollutant emissions (CO and NO) are investigated. The results show that the Mech2.11 reaction mechanism yields the smallest prediction error, with a deviation of less than 10 % between the experimental and simulated temperatures. When Tair increases from 600 °C to 800 °C, the NO concentration increases by 33.7 %; when α increases from 1.2 to 1.4, the NO concentration rises from 305 ppm to 450 ppm. At α = 1.3, the maximum effective temperature volume is between 268.536 m3 and 274.064 m3, with the highest chemical flame filling degree of 42.17 %. The optimal ranges for α and Tair are 1.3 and 600 °C–650 °C, respectively. The predicted NO concentration is 325 ppm, and simulations show that within these optimal parameters, the furnace temperature can reach the required roasting temperature for alumina (1000 °C–1200 °C). This study provides valuable insights for improving combustion efficiency and reducing environmental impact in industrial processes.