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For the first startup of crude distillation unit, since we did not have any startup gas oil for flushing procedure (cold and hot circulation), we used the crude as flushing stream. According to operating manual, after establishing of gasoil we should store it into relevant storage tank and then stop the process. After that we should flush the system with existed gas oil, again. I want to know, when we are producing gas oil why should we stop the process and go back to flushing mode?
 
Answers
07/12/2015 A: Jayaraj Jayam, Chennai Petroleum Corporation Limited, njayaraj@gmail.com
It looks odd. Once you start to produce gas oil, it is fine to store in relevant tank but need not stop the process just for the sake of flushing.
May be the tank is exclusively used for supplying flushing oil and in subsequent shut down or start up flushing oil from the designated tank may be used.
'Stopping the process and do flushing' may not be the intended communication in your manual.
06/12/2015 A: Satyalal Chakravorty, Sr Consultant, satya1354@yahoo.co.in
Once you have flushed with crude oil, it is not required once again to flush with gas oil provided crude oil used was not very heavy crude (low API). It is essential that during the flushing, water needs to be removed/displaced to prevent water shots in columns & systems by following safe procedure. Moreover, it is required that even during hot circulation; the Furnace tube skin temperature for each pass is monitored to prevent tube overheating.
06/12/2015 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
I would consider it unnecessary.
05/12/2015 A: Satyalal Chakravorty, Sr Consultant, satya1354@yahoo.co.in
Once you have taken crude oil for initial flushing , it is not required to again flush with gas oil if you did not take any heavy crude oil (low API) at the start up. Only thing, it is essential to remove water from the systems including main column to prevent water shots by following the safe procedure. Secondly ,please monitor furnace pass flows & tube skin temperatures for each pass even during hot circulation to prevent tube overheating.