What are the recommended dosages of caustic in the crude unit for controlling overhead boot water chlorides? What is the desired limit of sodium in VR? Do anyone has experience of dosing organic neutralizer in crude?
Answers
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14/05/2016
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
A survey found that 50% of refiners worldwide inject caustic. Caustic or neutralizing amines are used to maintain water boot pH of 5.5 to 6.5. Quantities are site and crude specific.
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12/05/2016
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Mohamed Banjar, SA &PRC, banjarms@yahoo.com
to avoid the fouling risk and risk of caustic stress corrosion cracking increase we inject the caustic after mixing with crude oil stream just after heat train and before charge heaters
slip stream of crude oil is mixing with caustic and injected
control caustic at 3PTB and 5Be
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12/05/2016
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NS Murthy, Suez, murthy.ns.ext@suez.com
Ideally one shall avoid any addition of caustic in desalted crude. The limit of Na in vac residue when fed to Coker is 10 ppm max. However, if vac residue is sent to Visbreaker unit, the Na limit can be relaxed to 40ppm. Addition of organic neutralizer in pace of caustic is not a good practice as it lead to deposition of organic chloride salts in the OH trays of CDU column leading to heavy fouling and corrosion. The solution lies selection of good demulsifier, operating crude unit within compatibility window and choosing right chemistry to take care of OH system from HCl corrosion. talk to nearest GE representative to offer a holistic solution including optimization of additives.
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12/05/2016
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karthik ramesh, indian oil corporation, rameshkarthik810@gmail.com
normally desalter outlet crude salt content to be maintained at less than 0.5 ptb for two stage desalter. The same is equivalent to 1.5 ppm of chloride. since caustic and crude neutralization is not 100% we dose @ 2.5 ppm . this will land in RCO and equvivalent sodium in RCO is 5ppm. and in VR is 10 ppm .
10 ppm sodium is the limit in most of the cokers.
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11/05/2016
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Eric Hennings, Technip Stone & Webster, EHennings@technip.com
Caustic injection of 1 PTB is reasonable for bottoms going to a coker. If the long resid is going to a resid FCC, the increased sodium will be problematic to catalyst.
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11/05/2016
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Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
You typically want to keep caustic at 1 PTB (pound per thousand barrels) or less if possible (~3ppm), although I have seen some units go as high as 3-5 PTB. As the amount of caustic increases the fouling risk and risk of caustic stress corrosion cracking increase. Many refiners set a limit of 20 ppm of Na in vac resid. I would be concerned about thermal breakdown of the organic chlorides in a downstream coker if an organic compound is used to control chlorides instead of caustic. This would just transfer the chloride problem from the crude unit to the coker.
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