Taking a 660 MW wall-tangentially fired boiler as the research object

the effects of air distribution ratio on the characteristics of in-furnace coal combustion and heat transfer processes and NOx transformation were numerically investigated. Results show that under the fixed SOFA ratio

the increase of primary air ratio makes the overall boiler performance changes in V type that deteriorates evidently at first and then gets improved somewhat.The increased in primary air ratio leads to the generation of more fuel-NOx at the initial combustion stage

which thus increases the final NOx emission at the furnace exit. SOFA ratio does not change the variation trend of combustion performance along with the primary air ratio

but its increase leads to the decrease of the critical primary air ratio at which coal combustion performance deteriorates significantly. The variation of primary and secondary airflow momentums caused by the air distribution ratio is the main factor affecting the overall boiler performance

and coal combustion performance deteriorates significantly when their momentums are too close. Based on this

the large increase in the primary air ratio should be avoided during the practical boiler operation process. If it is inevitable

the SOFA ratio should be decreased to alleviate the deterioration of boiler performance caused by the increased primary air ratio.