Numerical investigation of flue gas recirculation impacts on coal combustion and raw meal decomposition in an oxy-fuel cement precalciner

Oxy-fuel combustion technology has attracted significant attention due to its potential for reducing emissions in the cement industry. In this study, a detailed numerical simulation of a swirl-type precalciner was conducted to systematically investigate the effects of flue gas recirculation (FGR) ratio on the airflow field, temperature distribution, coal combustion mechanism, and raw meal decomposition under oxy-fuel conditions. The results demonstrate that the FGR ratio has a pronounced effect on both the flow and temperature fields. As the FGR ratio increases, the average velocity and temperature rise progressively, the temperature distribution becomes more uniform, and local high-temperature zones are alleviated. When the FGR ratio reaches 60 %, the flow field closely resembles that under air combustion conditions. For all FGR ratios studied, the proportion of char gasification remains below 10 %, with specific values influenced by local temperatures and the concentrations of CO2 and H2O. Higher gasification proportion lead to shorter burnout distances for coal particles. Moreover, the decomposition degree of calcium carbonate increases approximately linearly with the FGR ratio. At 60 % FGR, the decomposition degree reaches around 95 %, which is comparable to that under air combustion conditions. Simultaneously, the CO2 concentration at the outlet rises to 91.4 %, significantly enhancing carbon capture efficiency, with a potential capture capacity of up to 5320 t/d. These findings contribute to the optimization of oxy-fuel combustion in precalciner systems and offer insights that are applicable to a wider range of industrial configurations.