"Chlorides control of crude unit destillation column with caustic soda"

Question:

"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."

Answer:

We are aware that caustic can contribute to coking and foaming in crude distillation units. However, we do not have personal experience with what maximum levels of sodium to maintain to avoid excessive coke formation.

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