LOW LOAD TURNDOWN FOR COMBINED CYCLE POWER PLANTS

摘要

A combined cycle power unit (10) including a gas turbine (16), a heat recovery steam generator (HRSG) (34) to generate steam from an exhaust flow (24) of the gas turbine (16), and a steam turbine (64) driven by the steam generated from the HRSG (34). Steam generated in an evaporator (50) in the HRSG (34) is conveyed through an upstream superheater stage (46a) and a downstream superheater stage (46b) in the HRSG (34). The steam is then conveyed from the downstream superheater stage (46b) to the steam turbine (64). Between the upstream and downstream superheater stages (46a, 46b), the steam flow from the upstream superheater stage (46a) is throttled to a lower pressure to form a reduced pressure steam flow prior to entering the downstream superheater stage (46b) where the steam is reheated to an elevated temperature at the reduced pressure.