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I'm working in ExxonMobil licensed FlexiCracking unit. After emergency shutdown in unit, Slurry PA, HCO PA, LCO PA flows are disturbing. Slurry PA flow is establishing after 2 - 3 trials. Whereas LCO PA & HCO PA were unable to maintain even after opening cutter to both the circuits. Immediately after unit trip, we are closing stripping steam to LCO, HCO strippers, LCO PA, HCO PA pumps are drained thoroughly before placing it in service. LCO PA, HCO PA are slowly dropping to zero. that time main fractionator top temp increasing too high to >170 C. How can I maintain steady LCO PA, HCO PA flows during unit startup, while maintaining main column top temp at 140 C. Please help me how can i maintain steady PA flows during startup so that MF temp profile is steady.
 
Answers
21/11/2017 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
Perhaps one of your slurry/steam generators has a tube leak and boiler feedwater leaked into the fractionator while the slurry pumparound was inoperative? In this case the water would flash on contact with hot oil on restart and could blow out the HCO and LCO pumparound drawoff trays. Have you checked pressure trends for the fractionator flash zone?
20/11/2017 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
What is causing the flows to drop to zero... the pumps or lack of liquid on the draw offs?..... maximize your top reflux (without flooding the top of the tower) PA's are for energy efficiency not fractionation efficiency.... they actual reduce fractionation efficiency.... Do a dead head test on your pumps to see if it is a pump problem (which I doubt) check your results against the manufacturers pump curve....then do a three point test on the pump comparing your results against the curve if you flushed the circuits as you said I suspect you will find the 3 point test will show the suction lines are restricted...(If the dead head test is on the curve but the subsequent tests fall below the curve)... Did you flush back to the fractionator from the pumps?