Abstract: A fast HRSG starting method and apparatus for combined cycles requiring frequent cycling, baseload and backup power; preventing grid failure from variables of wind and solar power. A once-through HRSG, eliminating all except two hot thick wall components: the high pressure superheater and reheater headers. The method fills the high pressure superheater with boilerwater; whereby steam is generated in starting as thick header's and tube's ramp-up together at saturation temperatures as the gas turbine attains synchronous speed No-Load; reducing conventional thermal stress failures loss of availability and costly repairs. At gas turbine full power dry steam is generated by the high pressure superheater at low allowable temperature start and load the steam turbine and protect the reheater.

Abstract: Apparatus and method to wet start the HRSG and combined cycle in the fastest time with minimum thermal stress. This wet start provides the earliest possible cooling steam during acceleration, reducing stress in the superheater, reheater and steam turbine. The gas turbine is started and loaded to full power in the fastest possible time without holds. A once-through HRSG filled with saturated boilerwater including the superheater generates dry steam during acceleration. Start apparatus positions the dryout zone in each superheater tube, controls surge swell, ensures uniform pressure rise, and controls the steam temperature. The superheater generates temperature controlled steam to cool the tubes while heating headers. Superheater and reheater tubes and headers start at saturation and increase to operating with minimum differential temperatures. The superheater evaporating boilerwater supplies constant low temperature dry steam to start the steam turbine without the use of attemporators.

Abstract: A once-through high pressure steam generator and reheater configured to eliminate the majority of components limiting cyclical life of fast start conventional HRSGs. Two remaining problematic components in conventional designs the final superheater and reheater tubes overheat while their headers remain colder in fast starts. In this inventive HRSG the critical components are arranged and started by a method that limits these damaging temperature differentials. At ignition when exhaust gas surges into a wet superheater steam flow starts minutes before conventional systems. This early steam flow cools the tubes while heating the headers, thereby reducing life damaging stresses. Steam temperature is controlled through the start and warms the rest of the plant earlier without attemperators with their problematic thermal stress history. Faster starts than conventional result without damaging fatigue life depletion with this low cost innovation.