Large heat recovery steam generators (HRSGs) are increasingly
required to be designed for cyclic operation and also required to meet faster startup
times. The ability of horizontal HRSGs cyclic operation has been discussed and
widely reported in literatures and studies. However, the operation and design life of
HRSGs become more important when the system is operated with fast startup
times.This paper deals with the effect of fast startups on evaporator design and looks at the impact to the overall design and operation of the HRSG. The paper provides a comparison to traditional startups, explains the need to verify the design of evaporators for fast startups, and analyzes design issues.