Due to the change of coal quality

the pulverizing system of fan mill in a power plant is to be reformed via extracting low temperature flue gas for the requirement of operation safety. Five retrofit schemes are put forward and compared by thermodynamic calculation of pulverizing system

boiler efficiency test

boiler thermodynamic calculation and aerodynamic calculation of pulverizing system. The results show that

after the reform using scheme 2(drying the pulverizing system with extracted high temperature flue gas

low temperature flue gas and hot air)

the oxygen content at outlet of the mill separator can be controlled within 9%

but the boiler exhaust temperature will be about 28 ℃ higher than that before the reform

affecting the boiler operation economy. After the reform using scheme 4(drying the pulverizing system with extracted medium temperature flue gas)

the oxygen content at outlet of the mill separator can also be controlled within 12%

and the boiler exhaust temperature rise will reach about 10 ℃. However

the temperature regulation effect will be poor and will cause ash accumulation and blockage in the furnace flue gas transmission pipeline. Compared with scheme 4

in scheme 5 the addition of a flue gas fan can effectively avoid the problem of ash accumulation and blockage in flue duct in scheme 4

and improve the reliability and flexibility of operation. After comparative analysis

scheme 5 is selected as the final recommendation retrofit scheme.