The cause of high exhaust gas temperature of an HG-1900/25.4-HM2boiler was analyzed from design and operation aspects.The results showed that:(1)because of the increase of flue gas volume and specific heat capacity and other factors

the design value of exhaust temperature of boilers firing lignite coal was about 20℃higher than that firing bituminous coal;(2)a decrease in total heat transfer efficiency of tail heating surface caused by over small opening degree of the reheater damper

the gas temperature at air preheater inlet was higher than the design value which caused by serious fouling on the tail heating surface

drop of the air volume and theoretical air volume ratio(β″)at the air preheater outlet

and the gas temperature at air preheater inlet was higher than the design value were the main reasons for high exhaust temperature.Thus

measures such as increasing the air temperature set value at coal mill outlet

optimizing the soot blowing and enlarging opening degree of the reheater gas damper were adopted.After the improvement

the exhaust temperature decreased by 15℃to 20℃

returning to normal.