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

Abstract

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 O2/N2 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.