During low load operation of coal-fired power plants

the flue gas temperature at the economizer outlet is always too low to satisfy the requirements for temperature by the selective catalytic reduction(SCR)catalyst

thus the desulfurization efficiency is low.To solve this problem

this paper takes a supercritical 600 MW coal-fired unit as the research object to carry out transformations on feedwater bypass of the economizer

flue gas bypass of the economizer and staged arrangement of the economizer.The boiler thermal calculation results show that

under 50% THA condition

by the method of economizer classification

when the heating surface of Economizer 1reached 83% of the total heating surface area

and the that of Economizer 2is 17%

the temperature at the SCR reactor inlet reached 320 ℃

which satisfied the catalyst operation requirement.Moreover

the boiler thermal efficiency kept at 94.69%

indicating the transformation effect is the optimum.