Two-Column Sour Water Stripping without Sending Ammonia to The Sulfur Recovery Unit

Abstract

In conventional sour water stripping (SWS) in petroleum refineries, H2S and NH3 of the sour water are separated simultaneously at the top of a tray column by sending sour gases to the sulfur recovery unit (SRU). At SRU furnaces, ammonia is oxidized to NOx playing the role of a deactivator for downstream catalytic beds. From an industrial engineering viewpoint, it is proposed to strip ammonia and hydrogen sulfide separately using two stripper columns. The striped ammonia may be incinerated if it is allowed or traded as gaseous or aqueous ammonia. In this study, the two-column sour water stripping approach is implemented for the feed stream of an SWS unit currently working in Iran using a simulation model that was verified based on the design data of an industrial unit. It is concluded that the higher the pressure of the H2S stripper is, the higher the H2S recovery is, and the lower H2S impurity with ammonia stream is. Moreover, preheating of the feed stream and sending a lower portion of cold feed stream as a representative of liquid reflux resulted in increased utility consumption and also changed the amount of water sent with sour gas and ammonia stream. Finally, aqueous ammonia (less than 10% purity) or ammonia vapor stream (about 90% purity) can be traded as a value-added product for this unit.