Effect of different air excess ratios on energy efficiency, emissions, environmental impact, and enviroeconomic performance of an LNG-fueled rotary burner for cement pre-calcination

The cement industry is one of the most energy-intensive sectors and is responsible for a considerable share of industrial emissions. In cement production, the pre-calcination stage plays a critical role in fuel consumption and pollutant formation. Therefore, replacing coal with cleaner fuels such as liquefied natural gas (LNG) and optimizing combustion conditions are important for improving energy performance and reducing environmental impacts. This study investigates the effects of different LNG flow rates and excess air ratios on the energy efficiency, emission characteristics, environmental impact, and enviroeconomic performance of an LNG-fueled rotary burner used for cement pre-calcination. Experiments were conducted at LNG flow rates ranging from 5 to 30 L/min under different air excess ratio conditions. The results showed that increasing the LNG flow rate reduced both energy efficiency and environmental sustainability. The highest overall energy efficiency of 95.66% was achieved at λ = 1.15 with an LNG flow rate of 5 L/min, while the efficiency generally showed a decreasing trend at higher flow rates. Increasing lambda to 1.15 decreased CO, HC, and soot emissions by approximately 60%, 38%, and 60%, respectively. However, CO2 and NOx emissions increased by 6% and 29%, respectively. Due to the dominant contribution of CO2 and NOx, their combined share in the total environmental impact and enviroeconomic cost reached 99%. Overall, within the investigated operating range, the 5 L/min LNG condition provided the most favourable thermo-environmental performance due to its higher energy efficiency, lower heat-transfer losses, and lower absolute environmental and enviroeconomic burdens, whereas higher LNG flow rates increased the environmental and economic loads.