Ammonia in your amine unit?
July 9, 2007
What seems like an insignificant amount of ammonia in the sour feed gas to an amine unit can be detrimental to the sweetening process. Ammonia in an amine sweetening system can cause reduced absorption of acid gas, as well as greatly increased stripper condenser and reboiler duties due to build up of NH3 in the system. Corrosion in the stripper condenser loop is also a significant problem. We recently looked at a refinery DEA unit which had only a small amount of NH3 in the feed to one absorber (0.7%), and with no water wash ProMax was calculating a duty 3 times the actual. Finally we discovered that a water wash was being used on the feed containing ammonia to remove as much NH3 as possible from the feed. When the water wash was simulated, the reboiler duty predicted by ProMax matched the plant operating data. A good source of information concerning ammonia may be found in a BR&E Technical Paper at the following location on the BR&E website:
Influence of Ammonia on Gas Sweetening Units Using Amine Soluti.pdf
This paper describes operating problems due to ammonia in amine unit feed. Although an ammonia stripper is the solution used in this paper to solve the problems caused by ammonia, sometimes just a purge stream from the stripper reflux is sufficient to stop the buildup of ammonia in the system and to allow the unit to operate more efficiently. The paper mentions 0.5% ammonia as being the maximum amount of ammonia that can be present in the amine unit feed. If the ammonia content of the feed is above this amount, the gas would have to be pre-treated to remove the ammonia before being sent to the amine sweetening unit.
Authored by Lili Lyddon (BR&E Technical Support and Help Author)