Double Register Axial Swirl Burners Experiment And Optimization Study

Optimization of pulverized coal-fired burner is very important for large-scale boilers to achieve high efficiency combustion and low NOx emissions. The present thesis was aimed at Double Register Axial Swirl Burners applied in 4×330MW pulverized coal-fired boilers of Guodian Ningxia Shizuishan Electricity Generation Ltd. In order to solve the problems of the powder dropping and associated high unburrned carbon in slag, low combustion stability and low combustion adjustability, combustion tuning and optimization experiments, in-furnace aerodynamic experiments were performed to systematically study the structure, performance and aerodynamics of the burner.Combustion tuning and optimization experiments showed that the fundamental reason of the low flame stability and low combustion adjustability of the burner was the defect of the burner itself, which presented that the swirling intensity of inner secondary air could not obviously change the combustion performance and that the effect of combustion tuning was very limited. Meanwhile, the combustion tuning could not improve the unburned carbon in slag very much either. It was found in the cold-state in-laboratory experiments that the flame-stabling ring used in current burner lead to form a low velocity zone near the out wall of the primary air duct, which was the mean reason of the powder accumulation within the burner. Using flame-stabling teeth to replace the ring could uniform the velocity distribution, decrease the low velocity zone and enhance the turbulence near the out wall, which could not only solve the powder accumulation problem but also keep the advantages of the burner. Cold-state aerodynamic experiments indicated that the inner secondary air was important to re-circulation zone size. Increasing the swirling intensity increased the re-circulation zone size, which would be beneficial to enhance the ignition and stabilize the combustion, and vice versa. Increasing the flux of the inner secondary air had a relatively small effect. The main defects of the burner structure were found that the structure and flow dynamics in the inner secondary air duct was not good, which resulted in small re-circulation size, small spray extending angle and low adjustability. Furthermore, the CFD study indicated that the reason of the inner secondary air velocity and flux being not sufficient was too many blades and too big angle of the blades used, which lead to high flow resistance. High swirling intensity and relatively low axial...