Reliability and durability from large HRSGs

摘要

Experience with heat recovery steam generators (HRSGs) designed for larger heat input and higher steam conditions highlights limitations in sone features of traditional designs extrapolated from smaller HRSGs that operated predominantly continously. Many combined-cycle units may be sujbected to periods of regular overnight shutdown much earlier than expected and unless anticipated during the initial design, there will be s ignificant adverse impact on reliability and durability. Very premature problems already experienced on large HRSG designs in combined-cycle/cogeneration applications give early warning that more widespread problems will arise as HRSGs are subjected to more thermal cycling. Problems that arise when inadequate attention is given to transient conditions over the full range of operation of the combined cycle gas tubine (CCGT) unit, including at part loads, during shutdowns and restarts from diverse prestart conditions, are hightighted. The paper gives examples how the damage to HRSGs duriing shutdown and starts can be mitigated by minor modifications and sympathetic operating procedures and suggests how 0rudent purchasers can enhance reliability and lower lifetime costs at a small premium in installed ocst by specification of appropriate design features. Other weaknesses which cause problems for operation and manintenance are discussed.