Sour Water Stripping (SWS)

Sour water stripping is used to remove ammonia (NH3) and hydrogen sulfide (H2S) from sour water streams coming from many unit operations to condition it for discharge or reuse within the refinery. In a complex refinery, most of the sour water comes from distillation, fluid catalytic cracking, catalytic reforming, coker and acid gas removal units, with many other operations contributing to the balance. The different streams are collected in a surge tank for centralized processing via a heat exchanger and a single stripper column, or two in series.

A combination of pH control and heat, from direct injection steam or reboiler drives off the ammonia and hydrogen sulfide. The presence of solids and hydrocarbons (‘oils’) are major contaminants that cause heat exchanger, stripper column, and reboiler fouling. The impact is loss of SWS capacity that may bottleneck refinery production rates, drive the need for unscheduled SWS shutdowns and cleanouts leading to additional production losses, high maintenance costs and increased worker safety issues from exposure to the highly volatile H2S in the sour water system.

Oil contamination of the stripper also leads to a range of problems downstream. One is oil carryover in the acid gas stream heading to the sulfur plant, leading to sulfur plant reliability issues and increased risk of fires from oil coking of the reactor beds. Another is excess oil in the stripped water to the water treatment plant creating an overload condition resulting in environmental risk and/or the need to reduce refinery capacity.