Method for the shutdown and restarting of combined power plant

A method for a shutdown and restarting of a combined plant comprising in combination a gas turbine, a waste heat recovery boiler heated by a heat of exhausts from said gas turbine to generate steam, and a steam turbine driven by the steam generated by said waste heat recovery boiler, said method comprising the steps, which are followed when the plant is restarted following temporary shutdown, of:

• (1) shutting down the steam turbine while the gas turbine is still operating at high load by reducing a load applied to the steam turbine before reducing the load applied to the gas turbine, when the load applied to the entire plant is to be reduced;
• (2) allowing excess main steam produced by the load reduction and shutdown of the steam turbine to flow through a bypass system to a condenser without causing the excess main steam to flow through the steam turbine;
• (3) maintaining metal of the steam turbine at a temperature level substantially equal to a temperature at which the metal is maintained during operation of the steam turbine by supplying steam, as gland sealing steam, of a temperature level substantially equal to a temperature level of the metal of the steam turbine in operation at the time of load reduction and shutdown of the steam turbine;
• (4) shutting down the gas turbine after further reducing the gas turbine load to a level lower than a level attained in said steam turbine shutting down step;
• (5) starting the gas turbine first to increase the load applied to the plant when the plant is to be restarted;
• (6) maintaining the metal of the steam turbine at a temperature level substantially equal to the temperature level of the metal of the steam turbine attained during operation of the latter, by supplying steam of a temperature level substantially equal to a temperature level of the metal of the steam turbine attained during operation of the latter as gland sealing steam for the steam turbine;
• and
• (7) starting the steam turbine by the steam generated by the waste heat recovery boiler to increase the plant load.