Adopting the equivalent heat drop theory

the steam work-done loss resulted from two warming-up modes

namely positive warming-up and reverse warming-up

for feed-water pumps in one power plant has been quantitatively calculated

the characters of the two warming-up modes in aspects of economic efficiency and safety being compared.A retrofit scheme of the water-returning mode for positive warming-up has been put forward

the return water was originally entering into the condenser through a flash tank

being reconnected to the low-pressure heater no.4

making its heat to be fully utilized

and its economic efficiency to be enhanced by a big margin.