(159ak) Coalescence of Emulsified Hydrocarbons from Refinery Sour Water

A recent case study on removal of hydrocarbons from refinery sour water provided some valuable direction on design and selection of a liquid/liquid coalescing system. In refineries, sour water is a mixture of wastewater streams gathered from various units. It must be treated in the sour water stripper (SWS) to remove toxic gases including H₂S, NH₃ and other contaminants before it can be reused or sent to the wastewater treatment plant. The feed sour water has significant amounts of hydrocarbon contaminants in free, emulsified and dissolved form accumulated or entrained from various upstream processes. Presence of these hydrocarbons leads to various problems such as reduced stripper efficiency, corrosion, fouling, and environmental challenges. The pH of the sour water, presence of various types of hydrocarbons and surfactants, chemical reactions, and temperature variations taking place in upstream units can stabilize the emulsions or reduce the droplet sizes to sub-micron levels. The stable emulsions and reduced droplet sizes makes coalescence and separation of hydrocarbons challenging. Typical hydrocarbon separation equipment such as three phase separators and feed sour water storage tanks can separate free hydrocarbons but are ineffective in separation of emulsified hydrocarbons. The generic cartridge coalescing technologies specified for applications where surface energy and density difference between liquids are favorable do not work well in applications like sour water. Therefore, there is a continuing need for development of effective coalescing technologies for applications like sour water. This paper discusses a case study and field experience in evaluating coalescing technologies for removal of hydrocarbons from refinery sour water. This paper also provides coalescer vessel design guidelines supported by analytical results.