Feedwater system of combined cycle power plant

A feedwater system of a combined cycle power plant including:

• a gas turbine plant, a heat recovery steam generator which generates steam by using heat of exhaust of the gas turbine plant;
• and a steam turbine plant which is driven by the steam generated by the heat recovery steam generator, the feedwater system comprising:
• a feed pump which supplies feedwater to the heat recovery steam generator, the feed pump having a flow path for the feedwater, the flow path having an outlet;
• a first pipe which extracts part of the feedwater from the flow path of the feed pump upstream of the outlet;
• a first boiler which is in the heat recovery steam generator and supplied with the feedwater led into the first pipe and subjected to a first water treatment;
• a second pipe where the feedwater discharged discharges from the outlet of the follow flow path of the feed pump;
• a second boiler which is in the heat recovery steam generator and supplied with the feedwater led into the second pipe and subjected to a second water treatment being different from the first water treatment;
• a water-treating substance supply device which supplies a water-treating substance for the second water treatment to the flow path of the feedwater in the feed pump at a position of the flow path of the feed pump downstream of the first pipe and upstream of the outlet;
• a third pipe which connects the second pipe and the feed pump and leads part of the feedwater flowing in the second pipe to the feed pump;
• and
• a supply pressure adjusting device which is in the third pipe and adjusts a supply pressure of a mixed solution of the water-treating substance and the feedwater which are to be supplied to the feed pump from the third pipe, wherein:
• the water-treating substance supply device is provided to the third pipe;
• and
• P1<P4<P3<P2 is satisfied, where P1 is a first discharge pressure of the feedwater extracted from the feed pump to the first pipe, P2 is a second discharge pressure of the feedwater discharged from the feed pump to the second pipe, P3 is the supply pressure of the mixed solution of the water-treating substance and the feedwater which are supplied to the feed pump from the third pipe, and P4 is a water pressure of the feedwater in the feed pump at a connection position of the third pipe and the feed pump.