When there are measurable chlorides in the Coker fractionator overhead accumulator water, there is a risk of ammonium chloride salts. The Coker generates ammonia as one of the decomposition products from the nitrogen in the feed. Keeping the main fractionator overhead temperature over 250 F (121 C) is a way to prevent the formation of salts in the fractionator.
Ammonium chloride salts can be very corrosive. There have been many examples of poor desalter performance resulting in high chlorides in the Coker overhead system that has deposited salts within the fractionator that has resulted in severe corrosion. Lowering the chlorides and increasing the overhead temperature are the two actions that can prevent the salt deposition. Operating with a tower top temperature at 25 F (15 C) higher than the calculated salt point temperature should prevent the deposition of salts within the fractionator. If this provides a Coker naphtha with a distillation that is too heavy, then focus on removing chlorides from the feed to the unit.