To unveil the ultra-low load operating characteristics and performance optimization method of large-scale units burning high moisture lignite

the influences of burners operating scheme under 33%BMCR condition on the coal combustion

heat transfer and NO_x transformation characteristics of a 660 MW unit utility boiler were investigated

based on an established and validated simulation model of coal-fired boiler. The results show that

well-organized flow and combustion field can still be formed inside the furnace under ultra-low load condition

but the overall boiler performance deteriorates evidently

such as obvious decreases in combustion temperature and heat transfer intensity

and increase in NO_x emission at outlet of the furnace. When 4 layers of burners are in-service

continuous lower-middle groups or middle-upper groups of burners should be put into operation

to prevent the significant deteriorations of combustion and heat transfer processes and the significant increase in NO_x emissions. The number of in-service burners layers significantly affects the overall boiler performance. When there are only two layers of burners in-service

the intense coal combustion area is too concentrated

which is not conducive to maintaining a high combustion temperature and heat transfer intensity

and NO_x emissions at the furnace outlet increase at the same time. These findings reveal the influences of burner operating scheme under ultra-low load condition on the overall performance of a 660 MW lignite boiler

which can provide guidance for deep peak shaving operation adjustment and optimization of coal-fired units in the context of large-scale renewable energy power grid connection in the future.