In upstream round ducts of medium speed mills in a 1 000 MW UNIT coal-fired boiler

the measurements of the flow rate of primary air are usually not accurate and thus automatic control systems cannot work.To solve this problem

a cold-hot air flow mixing and equalizing device which is suitable for the circular primary air duct in front of the coal mill is designed

by numerical simulations.Moreover

the performance of this device is verified through the pilot-scale cold state experiment of physical models.The numerical simulation and cold state physical model test results indicate that

the combined layout of the uniform distribution device of cold air

deflector

grilling and perforated plate can solve the torsion problem of flow stream in the circular primary air duct in front of the medium speed coal mill

make the incoming gas velocity's direction(in measurement section of the primary air)be vertical to the detecting device.The combination layout makes the relative standard deviation(RSD)of the air velocity and temperature at the recommend traverse drop to 6% and 2%

respectively.Simultaneously

the corresponding increases of the pressure losses of cold and hot primary air are less than 400 Pa.The uniform distribution of the cold primary air at the confluence of cold and hot air is realized.