Single shaft combined cycle plant and operating thereof

A single shaft combined cycle plant, comprising:

• a gas turbine;
• an exhaust heat recovery boiler for generating steam using exhaust heat discharged from the gas turbine;
• and
• a steam turbine driven by steam generated from the exhaust heat recovery boiler,
• rotors of the gas turbine and rotors of the steam turbine being coupled, and the steam turbine comprising:
• a first turbine being driven by steam generated at a superheater of the exhaust heat recovery boiler supplied via a first steam path, and a second turbine supplied with and driven by steam that passes through the first turbine, and then through a second steam path back to the exhaust heat recovery boiler where it is reheated by a reheater of the exhaust heat recovery boiler, with the reheated steam then passing through a third steam path,
• wherein there exists a fourth steam path providing communication between the second steam path and the third steam path, and
• cooling steam is supplied to the first turbine from the exhaust heat recovery boiler, the cooling steam discharged from the first turbine is made to bypass the reheater by the fourth steam path and is introduced to the third steam path leading to the second turbine, during a period from starting up of the gas turbine until ventilation of the steam turbine.

A method of activating a single shaft combined cycle plant, comprising a gas turbine, an exhaust heat recovery boiler for generating steam using exhaust heat discharged from the gas turbine and a steam turbine driven by steam generated from the exhaust heat recovery boiler, rotors of the gas turbine and rotors of the steam turbine being coupled, and the steam turbine comprising:

• a high pressure turbine being supplied with and driven by high pressure steam generated at a superheater of the exhaust heat recovery boiler, and a reheating turbine supplied with and driven by steam that passes through the high pressure turbine, and back to the exhaust heat recovery boiler where it is reheated by a reheater of the exhaust heat recovery boiler, said activating method comprising:
• a first step of activating the gas turbine and causing rotor speed thereof to rise;
• a second step of supplying gas turbine exhaust gas to the exhaust heat recovery boiler and causing steam to be generated at the exhaust heat recovery boiler;
• a third step of supplying cooling steam generated at the exhaust heat recovery boiler to the high pressure turbine rotating with the gas turbine during a period from starting up of the gas turbine until ventilation of the steam turbine, and supplying cooling steam that has passed through this high pressure turbine to the reheating turbine via a bypass path connecting a path leading the cooling steam outputted from the high pressure turbine to the reheater and a path leading to the reheating turbine from the reheater;
• a fourth step of supplying steam generated by the superheater to the reheating turbine via the reheater after desired conditions for the steam generated from the exhaust heat recovery boiler are reached;
• and
• a fifth step of obtaining an output from the steam turbine.