Heat Recovery Steam Generators forlarge combined cycle plants (250 MweGT output): experiences with differentdesign options and promisingimprovements by once-throughtechnology development

摘要

Ansaldo Caldaie has gained extensive experience in designing, manufacturing and installingrnHRSGs for gas turbine sizes ranging from 40 Mwe to 250 Mwe. The purpose of this paper isrnto focus on large size HRSG units suitable for Siemens GT V94.3A or GE 9FA with 250rnMwe output. These HRSG units are designed under our proprietary technology based on tworndesign options: horizontal gas flow with natural circulation and vertical gas flow withrnassisted circulation. Most of the units have been successfully tested and entered intorncommercial operation during the last five years. The most relevant projects of these types ofrnunits are herein presented and described along with their distinguishing features; specifically,rnthe vertical HRSG design suitable for insertion into the existing steel structure of old firedrnboilers in re-powered power stations is described. A comparison between the horizontal andrnvertical design options is provided on the basis of functional, constructive and operating datarncollected from a combined cycle power plant where two units with the same operatingrncharacteristics and output, but with different configuration (horizontal and vertical), havernbeen delivered.rnFollowing a market trend towards extensive cycling operation and combined cycles ofrnincreasing size with gas turbines of improved technology having higher exhaust gasrntemperatures and flowrates, a new design option has become interesting in the recent yearsrnand has been taken into account as a possible advancement for the HRSG technology: once-throughrnmode in the high pressure levels of the unit. For this design option, we, - as Siemensrnlicensee for Benson Once Through HRSG technology – have developed our own standardrnproject. This paper describes the main features of this project and highlights the most relevantrnadvantages that HRSG units based on this concept offer compared to Drum Type units.