During the cold state start-up of gas-steam combined cycle unit

the metal temperature of steam turbine is low

in order to avoid the thermal stress generated during the rotation process affecting the unit safety

the steam turbine needs medium-speed heater to increase the metal temperature

which greatly limits the ability of the unit to quickly respond to peak regulation of the power grid. Therefore

steam turbine preheating system is applied in the gas-steam combined cycle unit for the first time

and the twice cold state start-up processes of the unit before and after the steam turbine preheating system is put into operation are compared. The results show that

the preheating system can make the steam turbine reach the warm state start-up requirements before the whole cold state start-up

which greatly shortens the start-up time of the unit under the cold state start-up and improves the economy of the unit. In addition

through optimization for cold-state preheating process of the unit

the phenomenon of rapid decline of the unit speed caused by insufficient steam source pressure is effectively avoided. This experience can be referred for the relevant combined cycle units.