Numerical comparison of pulverized coal combustion characteristics in cement rotary kiln between O2/CO2 atmosphere and O2/N2 atmosphere

Carbon dioxide (CO2) emissions in the cement production approximately make up 7% of worldwide anthropogenic greenhouse gas emissions. Currently, reducing the CO2 emissions of cement industry has become an urgent problem. Oxy-fuel combustion technology possesses significant application prospects, which increases the CO2 concentration in flue gas remarkably, and simplifies the capture process. However, current research primarily focuses on the thermal transfer characteristics of pulverized coal, with limited systematic studies addressing combustion behavior, flow field, species field, and the mechanisms of pollutant formation. This study conducts a comparative analysis of the heat transfer and combustion characteristics of pulverized coal using the computational fluid dynamics (CFD) methods, thoroughly investigates flow, temperature, species, and NOx distribution in cement rotary kiln under the 21%O2/79%N2 and 21%O2/79%CO2 atmospheres, thereby addressing the current gap in multi-physics field coupling research. Results show that the transformation of combustion atmosphere from 21%O2/79%N2 atmosphere to 21%O2/79%CO2 atmosphere does not significantly alter the flow field structure, although it reduces gas velocity. Meanwhile, notable changes occur in temperature field, species field, and NOx distribution. Specifically, it has a great impact on temperature, species, and NOx. The ignition of pulverized coal delays, the flame length becomes shorter, CO2 concentration at the kiln outlet increases significantly, and NOx emissions are markedly reduced. Consequently, adjusting the combustion environment to 21%O2/79%CO2 facilitates the efficient recovery and utilization of exhaust gas from the kiln outlet. This strategy not only effectively lowers the cost of carbon capture but also significantly reduces pollutant emissions, thereby contributing to the green and sustainable development of the cement industry.