Influence Of Burner Vertical Tilt Angle On Combustion Processes Of A 700MWe Tangentially Fired Boiler

The tangentially fired pulverized coal boiler equipped with vertically tilting burner is very common in power generation industry, and the tilt angle of burner has obvious impact on combustion characteristics of the furnace during operation. The primary objective of this paper is to analysis the low-NOx modification and the impact of burner tilt angle on combustion, heat transfer, turbulence-chemical interaction and flue gas deviation characteristics of the boiler. A 700 MWe tangentially fired pulverized coal boiler is taken as the object of study, the numerical simulating method and in-site measurements are utilized.Firstly, based on strictly validated models and mesh system, the characteristics of flow,combustion, heat transfer and NO formation after and before low-NOx combustion modification are numerically simulated. After low-NOx modification the O2 concentration in main burning zone decreases and CO concentration rise up considerably, forming considerable reductive atmosphere. It is conducive to inhabit the NO formation and enhance the NO reduction. The NOx emission is reduced from 364mg/m3 to 112mg/m3. The combustion characteristics of low-NOx strategies on condition of different loads and oxygen contents are also simulated, it is proved that the operation for different loads and oxygen contents is fine.Secondly, the adopted numerical methodology is used to simulate the main processes with furnace with different burner tilt angle. The high temperature flame center gets closer to platen zone as tilt angle increasing from 0° to 22°. The high heat flux area of water-cooled wall moves upward and the uniformity of heat flux distribution decreases as the increasing of burner tilt angle. CO and volatile concentration in PCZ and above AA zone are reduced. The CO emissions drop from 1219 ppm to 287 ppm and the burnout rate slightly increases firstly and then drops when burner tilt angle reaches 22°. NOx emission level is obviously increased from 112mg/m3 to 187 mg/m3 as increasing of burner tilt angle.Finally, the model is further used to investigate the forming mechanism of re-heat steam temperature deviation as well as the influence of burner tilt angle on it. It is foundthat tilting the burner upward can effectively reduce the intensity of residual flow as well as the flue gas deviation degree. The +11° tilt angle of burner is relatively optimum considering the flue gas deviation and final re-heater overheating potential. When the tilt angle of additional air(AA) is bias set, the flow field of upper furnace is changed.Consequently, the residual swirl flow intensity and the flue gas deviation are reduced considerably. Operation parameters indicate that the combination of tilting burner upward for +11° and setting the bias of AA tilt angle for 10° can further reduce the re-heat steam temperature deviation to 4?.