Performance improvement of a three-pressure reheater HRSG using partial bypass for reheatsteam instead of using attemperator

In combined cycle power plants, Steam temperatureentering the steam turbine shall be controlled to avoidturbine damage and aging. HRSGs are typicallyequipped with attemperator (De-super heater) for steamtemperature control. Attemperator injects water into thesuper-heated steam and reduces its temperature byabsorbing evaporation latent heat. This is a routinesolution for most applications. Due to high thermal andmechanical shocks, attemperator is subjected todifferent failure mechanisms. In this study, acomplementary solution is proposed to control reheatedsteam temperature without spraying water during HRSGnormal operation. This method benefits from a by-passline which separates a portion of steam before enteringthe heat exchangers and mixes it with the main steam toreduce its temperature. Performance analysis of theHRSG using bypass line shows omitting sprayed water,increases the HP section heat absorption. Depending onthe steam turbine condition, higher generated steam canbe used for extra power generation, otherwise same HPsteam flow can be delivered to the steam turbineapplying less post combustion in the HRSG. In bothcases overall plant efficiency will be increased.