NFPA 85 : #PURGE CREDIT FOR COMBUSTION TURBINE & HRSG
We have SGT 700 gas turbine followed by HRSG. HRSG is capable to run 100% firing mode also.
As per customer requirement while gas turbine trips, the HRSG (which is normally in un-fired mode) need to change over in fired mode of operation with duct burner within a short span of time. The main problem here is for purge cycle indicated in NFPA 85. However, it also defines Purge Credit, but validity of same is only for 8 days. Can some one explain what does the validity means, shall we have to trip the unit & purge to re-establish the purge credit.