Experimental And Simulation Study On NO_x Emission Under Oxy-fuel Combustion

NOx from coal combustion significantly threatens the natural ecological environment and people's health, so it is imperative to control NOx emissions from coal combustion. The research about NOx emission and control has become an important field of the topics of coal combustion. However, most techniques of pollutions control are basically single and have some disadvantages. The combustion technology which can simultaneously curb CO₂, SO₂, and NOx as well as other pollutant will be the most competitive and promising. Oxy-fuel combustion is a new technology which can achieve integrative control of pollutants emissions. O₂ and recycled flue gases (mainly CO₂) were used as medium to replace air under combustion process in this technology. The study about NOx emission in this technology is still not enough, and more researches need to be further studied.In this study, experiments and simulations have been done to investigate the behavior of NOx emissions in oxy-fuel combustion summarized on the basis of research progress and NOx emission in the technology.First, the pyrolysis experiments were done on the integrated thermal gravimetric analyzer under different atmosphere, also NH₃ and HCN release characteristics were studied under the atmosphere of different mediums and CO₂ concentrations using horizontal tube furnace and portable infrared analyzer.The results showed that DTG had a bimodal structure under high concentrations of CO₂ atmosphere because of the gasification of char, and with CO₂ concentration increased, the release of NH₃ increased, however the release of NH₃ decreased; Then, static and dynamic pulverized coal combustion experiments were respectively done on the tube furnace and the drop tube furnace focusing on analysis of the effect of different medium,oxygen concentration and CO₂ concentration. Results showed that with CO₂ concentration increased, NOx emission peak was reduced, but the temperature corresponding to the peak point changed little on static combustion conditions, while NOx emissions decreased on dynamic combustion conditions. With increasing concentration of O₂, NOx emission peak changed little under static combustion, but significantly ahead of the peak point, while NOx emission increased under dynamic combustion. Finally, from the perspective of the use of chemical kinetics of reactions CHEMKIN software system C-H-O-N, NH₃, HCN and NO reaction were analyzed, and N transforming characteristics were investigated in the CH₄ Flame compared with the experimental results. Also fluent software was used to simulate and analyze the characteristic of combustion associated and NOx emissions on the different atmosphere in coal combustion process; The results showed that the initial CO₂ concentration was not conducive to the enhancement of the of NO degradation in the reductive atmosphere, however, with CO₂ concentration increased, the conversion of NH₃ and HCN to NO reduced, while NO degradation rate increased in the oxidizing atmosphere.The above research results have provided theoretical basis of further studies on the control and management of NOx under oxy-fuel combustion.