Directing against the problems resulted from mixedly burning brown coal in a 670 t/h bituminous coal fired boiler

such as exploision in the coal-pulverizing system

low output capacity of the said system

low capability of the unit to take load

plugging in the coal chute

and unsafety in the pulverized coal sending system

etc.

a scheme of retrofitting the composition of drying medium in the coal pulverizing system from originally designed mode of "hot air + recirculation"to a mode of "hot flue gas + hot air + recirculation"

has been put forward

and the pulverized coal sending mode being retrofitted from originally designed"by using hot air" to a mode "by using warm air".The said retrofit scheme is realistic and feasible.After implementation

the safety and economic efficiency of said equipment have been enhanced during the time of mixedly burning larger proportion of brown coal.