(74b) The Effects of Caustic Tower Operations and Spent Caustic Handling on the Wet Air Oxidation (WAO) of Ethylene Spent Caustic

Ethylene spent caustic is frequently treated using a Spent Caustic Oxidation Unit (SCOU). Commonly, this is a medium pressure (~400 psig) Wet Air Oxidation (WAO) system. There is spent caustic storage for feeding the system. Events that cause excessive downtime in the WAO unit are not acceptable because the spent caustic storage capacity is limited. The hazardous and malodorous nature of the spent caustic makes large inventory unappealing; and ad-hoc storage difficult.

WAO system operations are affected by the composition of the spent caustic. Off-spec feed can cause disruptions or even damage to the WAO system. The design and operations of the caustic tower, gasoline wash, and spent caustic storage affect the spent caustic composition, which ultimately affects WAO operations. While such disruptions are rare, when they do occur the most common cause is excessive organic contamination (red oil) in the spent caustic.

This paper describes the WAO system and the spent caustic parameters that affect WAO operations. Red oil in particular affects WAO operations and the upstream handling and techniques to best manage this material are discussed.