Combined with BFA and OFA technology

and adopting fluid calculation software FLUENT 6.3

selecting proper mathematic model

a numerical simulation of flow

heat transfer

and combustion in the furnace of a tangential firing 420 t/h boiler has been carried out.The said simulation adopts three-dimensional steady-state calculation and SIMPLEC algorithm

the turbulent model uses the double-equation realizable k-ε model

and the formation of NOx is calculated by using post-processing method.The results of calculation show that the temperature at center of the furnace decreases after retrofit

the NOx emission at exit of the furnace reduces about 30%

the concentration of CO at exit of the furnace is near to zero.However

owing to direct disturbance of the secondary air from BFA at the bottom

making the diameter of tangential circle to be enlarged

this phenomenon may result in slagging in the furnace.Therefore

in the process of retrofitting

the designed diameter of tangential circle at lower cross-section of the primary air has to be properly reduced.