The causes leading to somewhat higher carbon content in fly ash of boilers have been analysed from several aspects

namely fuel

primary air

tertiary air

and oxigen rate etc.. Through retrofit of the fine pulverized coal separator and adjustment of coal sorts

primary air velocity and air temperature

as well as burning admixture of other fuel

the carbon content in fly ash during the time of burning single coal has been decreased from an original value of 8% to about 2.4%

and during the time of burning simutanuously admixture of blast-furnace gas

the carbon content in fly ash can be controlled to below 8%

enhancing the boiler efficiency from 89.4% in 1998 to 92.4% in 2002.