In view of the features of blast furnace gas

i.e. low heat value and high flow rate

in Xiangtan Iron And Steel Corp

a 75t/h pulverized coal fired boiler proper and its system at the co-generation power plant had been retrofitted in three aspects: （1） adopting large tangential circle corner combustion with burners having slotted blunt body; （2） increasing the heat surface of slag-cooling tubes and economizer

to fully use the heat capacity of flue gas

effectively reduce the flue gas temperature

and ensure the superheater not to be overheated; （3） retrofitting the flue gas duct in the heat recovery section

to decrease the draft resistance

and ensure the output capacity of induced draft fan. The after-retrofit test shows that the boiler output can reach 78t/h

the overall thermal efficiency of the said boiler be higher than 80%

the exhaust flue gas temperature be lower than 180℃

the superheated steam temperature be in the expected range

and the output of induced draft fan meet requirements under condition of burning solely blast furnace gas. And the boiler capacity can reach 88t/h under condition of buring mixed fuel of pulverized coal and blast furnace gas.