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Double drum crude fractionator has frequent leaks in the crude/overhead heat exchanger. The water used is recycled water from the second drum boot containing H2S in high concentration. The purge-out is only to the quantity to the steam added to the fractionator. Is this water, rich in H2S, being used for washing the main cause of the leak? Will stripped water make up in good quantities help? If yes, how much stripped water should be used? The vapor entry in the condenser is side entry instead of the usual top entry. Could this change in configuration also be the reason?
 
Answers
02/01/2008 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
HCl is normally the cause of corrosion in crude unit overheads. H2S in the recycled water is not likely to be a problem. Side entry of vapor is likely a major contributor to the problems. With side entry the wash water may not be well distributed in the top of the bundle, leading to a low pH at the secondary water dew point in the top of the bundle.
The design of water wash injection system, the amount of water wash, the design of chemical injection system, and the overhead neutralizer chemistry being used all could potentially be contributing to the problems as well. You should try to engage the technical experts from your unit's chemical supplier to help troubleshoot your problems.
27/12/2007 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
I do not have too much experience with corrosion handling in crude tower, but generally speaking the water from the CDU is not very high in H2S. The CDU does not produce very much H2S and crude tends not to contain too much H2S. It would therefore be helpful if you could quantify the quantity of H2S in the water.
In other processing units (HDS/hydrocracking), water containing more than 2-4% H2S + NH3 is considered to be corrosive. This is very seldom the case on a CDU.
My experience relates to handling sour water in refineries from various places (amine unit, HDS, Hydrocracker etc.)