This paper describes a modification to a standard reheat HRSG (Heat Recovery Steam Generator) enabling it startup faster. It also allows the plant to operate the gas turbine in simple cycle and to operate the HRSG as a stand-alone auxiliary boiler. An external fan, pre-heater and burner are connected to the diffuser of the HRSG. When the gas turbine is out of service, the fan and burner are actuated, providing enough flue gas to allow the HRSG to operate as a small auxiliary boiler. Steam produced during this operation pressurizes the drum, heats the steam lines provides sealing steam for the steam turbine, and allows a vacuum to be maintained in the condenser. The system is designed to produce enough steam to synchronize a steam turbine. When the HRSG, condenser, circulating water system or steam turbine is removed from service, the HRSG is drained and the fan turned on without the burner, mixing tempering air to the exhaust of the gas turbine operating in a simple cycle mode. The tempering air lowers the flue gas temperature enough to allow the operation of the SCR system while preventing damage to the carbon steel tubes of the HRSG.

Volume Subject Area:
Simple and Combined Cycles
Topics:
Heat recovery steam generators, Steam, Gas turbines, Steam turbines, Boilers, Condensers (steam plant), Cycles, Flue gases, Carbon steel, Damage, Diffusers, Exhaust systems, Sealing (Process), Temperature, Vacuum, Water
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