Crude Oil Organic Chlorides Origin

[MaNaTMoS]

Hello, Eng-Tips

Does anyone know origin of organic chlorides in crude oil? What is the average organic/anorganic chlorides ratio in crude (REB, for example), and is there any relation between crude origin and organic chlorides content? Which chemical compounds/species of chlorine are mostly present?

Use of chlorinated solvents in cleaning purposes (upstream of refinery plants)is one possible cause. Please share your views and experiences.

Regards,
;o)

 

[25362]

I was thinking of some -internally used- spent lubes added as slops, as a potential source of additives containing chlorinated hydrocarbons.

 

[MaNaTMoS]

Thanks, 25362.

Since it is impossible to remove them through desalting of crude oil, what further actions should we take? Corrosion and fouling problems become drastically bigger, due to salt decomposition to form HCl.
What percentage of total chlorides content goes on organic chlorides in raw crude (oil fields/platforms, i.e. before contamination)?

 

[orenda1168]

MaNaTMos:

Though it's been some 25 years since my direct involvement with crude desalting, as I recall organic chlorides are almost always at a very low level and rarely present a downstream issue of excessive hydrogen chloride evolution in and of themselves. The greater problem is adequately and consistently removing the inorganic chlorides to minimize HCl generation and downstream corrosion.

Regards,

Orenda

 

[MaNaTMoS]

Hi, Orenda

Desalted crude has less than 20ppm of chlorides (average). Drastic difference between desalter waste water and CDU overhead sour water chlorides content comes from, in my opinion, organic chlorides. The problem is impossibility of desalter to remove organic chlorides due to their very low solubility in aqueous phase; all of them are being converted to HCl in downstream preheat train and CDU furnace. NHT/Platformer units are also adversely affected with org. chlorides, which create severe corrosion problems in feed/effluent heat exchanger.

Changing/mixing the crude unit feed and monitoring org. chlorides content in crude (ASTM D4929) is the best idea I've got so far.

MaNaTMoS

 

[25362]

Staged desalting (check NATCO, Petrolite, etc.) has succeeded in many cases in bringing down the chlorides content originally at, say, 100 ptb, to below 1 ptb, while single stage desalting barely succeeds to reduce it below 4 ptb (~16 ppm) which is above the 10 ppm generally considered a maximum limit to minimize downstream corrosion.

This brings one to think that the remaining salt isn't just of organic origin but may still be basically inorganic. One way to check that would be to measure salt and the amount of Na, Ca and Mg, before and after desalting. Any comments ?

 

[Yordif]

Every instance of "organic chlorides" in a cdu system I have ever run into could be traced back to either the slop oil system and a cleaning event or the purchase of a "Dumb bell" crude where the crude had been contaminated with some oil for disposal.

Other than knowing your feed sources there isn't much you can do. The organics break down in the cdu furnace so you get the HCl in the overhead system. Consistent monitoring of the overhead system water for pH spikes and the appropriate change in injection rate of the neutralizing amines.