Caustic to control chlorides on top of crude destillation column

[0707]

On crude units, normally to control chlorides on top of the destillation column, we inject downstream of the dessalters, less than 12 ppm of caustic OHNa, This injection limit is to avoid caustic embrittlement on downstream equipment. My question is: in what extend this caustic injection can contribute to coke promotion on heaters? The charge to the visbreak unit comes from the bottom residuum of the vacuum unit, as the caustic precipitates on bottom cuts we have on the feed that goes to the visbreak unit about 45 ppm of sodium and we have experienced heavy cokefication on visbreak heater tubes. Does anyone from the forum know something about this subject?
Thanks for your concern
Luis Marques

 

[Sandeep1970]

Two things (1) keep the temperature high enough in the visbreaker heater to avoid any king of coke formation.
(2) steam purge in the heater cross over can also avoid coking in the heater. You need to keep the appropriate velocity inside the heater and the feed piping.

Impact of caustic to cause coking is not significant for the reasons of chemistry of NaOH and the coking.

For the details you can reply on the email with the details of your plants operating conditions.

Is the bottoms piping is insulated.