Numerical simulation of oxy-coal combustion in a rotary cement kiln

In this paper, a comprehensive computational fluid dynamics (CFD) methodology was adopted to investigate the characteristics of oxy-coal combustion in a cement kiln with a specially designed burner. The simulation was conducted under five oxidant stream conditions with different O-2/N-2 volume ratios: 21/79, 24/76, 27/73, 30/70, and 33/67. The results revealed that there is strong entrainment from the primary air to the secondary air, resulting in an inner recirculation zone and outside recirculation zone. The oxygen-enriched combustion increases the maximum temperature and improves the combustion efficiency; however, the uniformity of the temperature field becomes worse. The temperature rises sharply as the oxygen content increases; however, the enhancement is slight when the oxygen content exceeds 30%. At a lower oxygen content (<27%), the NOx emissions increase slowly as the oxygen content increases, whereas NOx increases sharply when the oxygen content exceeds 27% in volume. This suggests that the optimal oxygen content is no more than 27% for pulverized coal combustion in a cement kiln. The simulation results reasonably agree with the measured data. The findings of this work will help save fuel consumption and decrease production cost (C) 2016 Elsevier Ltd. All rights reserved.