To reduce the low-temperature corrosion of a low-pressure economizer by regulating the flow rate of feed water at a low-pressure economizer outlet to be re-circulated to a low-pressure economizer so that the feed water temperature at the low-pressure economizer inlet is kept at and above the temperature sufficient for evaporating the condensate for the prescribed time or over when a boiler is started.
A temperature/flow rate controller 18 set the inlet feed water temperature of a low-pressure economizer 8 to two kinds of temperature, i.e., the temperature on the relatively high temperature side and the temperature on the relatively low temperature side depending on the magnitude of the load. The feed water temperature at an inlet of the low-pressure economizer 8 is once raised to 80°C by increasing the re-circulation volume of feed water to the low-pressure economizer 8 through opening regulation of a flow rate regulation valve 16 since an exhaust heat recovery boiler is started, the temperature is kept for at least 0.15 hour to complete evaporation of the condensate at 80°C, and then, the control is returned so that the feed water temperature at the inlet of the low-pressure economizer 8 is kept at 50°C.
KUSAKA IWAO
ISODA KAETSU
YOSHIZAKI HIROSHI
TOYOSHIMA KOICHI
KAWAHARA ATSUO
