Abstract
The combustion process of one 1000-MW ultra-supercritical double-tangential-circle boiler was numerically studied and the three-dimensional full-size structure of the boiler was full considered. The influences of primary and over-fire air velocity as well as the jet structure on NOx generation characteristics were examined. In addition, the NOx generation characteristics of the improved burner structure were compared with those of the original one. Numerical results show that there exist two inverse elliptical flow fields and temperature fields. Moreover, the NOx generation and distribution characteristics are related to the temperature field to a certain extent. For different burner jet structures and arrangements, NOx distribution curves of the horizontal cross section are all W-shaped, but the NOx generation and distribution performance are correspondingly different, while the NOx emission changes are unobvious for different design schemes of the boiler burner. When we arrange one layer of auxiliary air from the burner undersurface, the flow area of the primary coal powder jet is enlarged by 100% and the coal feeding is increased by 20%. As a result, the temperature around the burner zone rises significantly. However, when two layers of auxiliary air are adopted, the combustion characteristic is promoted and NOx generation increases slightly. Based on the arrangement of the burner in the ultra-supercritical boiler, NOx generation does not vary obviously at different boiler loads. To achieve a better scheme, numerical and experimental studies are both performed in this study, and identical results are obtained. The current results may provide a theoretical basis for burner design improvement.
Highlights
Due to the promotion of steam pressure and temperature, the thermal efficiency of ultra-supercritical units is higher than that of the current units by nearly 10%, it has become the main development direction of thermal power units at home and abroad
The comparison of aerodynamic field, the temperature field, and NOx generation characteristics indicate that scheme 3 is the best burner structure, and the overall distribution on the scheme 3 NOx distribution in the furnace will be compared with the original structure
After comparison between the original and two improved structures, NOx generation characteristic distribution along the furnace height direction performs with the same regularity, the peak value of NOx generation is located at the middle or upper burner zone, which is consistent with results of other scholars.[18,19,20]
Summary
Due to the promotion of steam pressure and temperature, the thermal efficiency of ultra-supercritical units is higher than that of the current units by nearly 10%, it has become the main development direction of thermal power units at home and abroad. The simulation results show that in the original and improved burner structures conditions, the furnace horizontal cross-section velocity field and flow field perform as elliptical shapes, and the gas flows of both furnaces display certain regularity.
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