To improve the unit economy

the effects of using over fire air(OFA)technology on NOxformation

furnace combustion and denitrification costs were investigated.Taking a 300 MW unit boiler as the research object

the support vector machine(SVM)theory was applied to establish a mathematic model.In this model

the input variables are unit load

the primary and secondary air volume

the opening degree of the secondary air damper in each layer and the OFA damper opening degree.The output variables are the NOxformation

coal consumption and denitrification efficiency.The change rules between the OFA damper opening degree and the costs of combustion and denitrification were studied

on the premise of a constant total air volume.Moreover

the calculation results were verified by the actual operation data.The results show that

in the 87%to 100%load stage and 50% to 75%load stage

the NOxformation decreased and the coal consumption increased with the increasing OFA damper opening degree

and the combustion and denitrification costs increased a little.In the 75%to 87%load stage

the NOxformation decreased while the coal consumption tended to be stable with the increasing OFA damper opening degree

and the combustion and denitrification costs decreased slightly.