Overview of sour water

Petroleum and its derivatives normally contain sulfur and nitrogen compounds. Through atmospheric and vacuum distillation, catalytic cracking, delayed coking and hydrotreating, these compounds form hydrogen sulfide and ammonia nitrogen in high-temperature cracking, catalytic conversion and hydrocracking reactions and pass into the product stream. When the product stream is cooled and dewatered or water-washed, wastewater containing sulfur and ammonia is formed, commonly called sour water or sulfur-bearing wastewater.

In a chemical project, the sour wastewater was high in oil and severely emulsified. This not only created operating risks for the downstream stripper and sulfur recovery unit — for example packing plugging and temperature excursions — but also upset the downstream wastewater treatment plant and threatened final discharge compliance. In addition, large amounts of high-quality light oil with recovery value were not effectively collected, causing an economic loss. The wastewater therefore had to be treated effectively to remove production and environmental hazards and to recover light oil, delivering both environmental and economic benefits.

SINOKLE sour water treatment solution

In view of the water quality at this project, SINOKLE formulated a well-founded sour wastewater treatment scheme and successfully applied its independently developed KHC coalescing oil-removal skid. Test results showed excellent demulsification and oil removal, with oil content in the treated water below 50 mg/L — below 10 mg/L in practice after excluding phenolic interference. The separated oil phase also had low water content and good quality.

Process flow diagram

SINOKLE sour water treatment process

Driven by its own pressure, the sour wastewater first passes through a filter to remove impurities and then enters the KHC high-efficiency coalescing separator. There the emulsified fine oil droplets are rapidly demulsified and coalesced into large droplets by the combined action of the coalescing packing and coalescing cartridge; they float up into the oil collection zone and are drawn off, while the separated clean water leaves from the bottom of the unit.

At the site, water samples were taken from the unit inlet, the KHC separator oil outlet and the water outlet and analysed for oil and water content. Data from five sample sets showed that after treatment by our coalescing oil-removal unit the oil content of the effluent was stable between 15 mg/L and 35 mg/L, with removal efficiency as high as 99% — a marked effect that fully meets the requirement of oil content ≤ 50 mg/L.

Further testing confirmed that, with phenolic interference excluded, the actual oil content of the sour wastewater treated by our coalescing oil-removal equipment was only 7.91 mg/L, far below the 50 mg/L discharge limit.

Oil draw-off from the KHC coalescing separator

In addition, the water content of the oil recovered by the coalescing unit was measured at 1.42% and 0.54% respectively, indicating good-quality recovered oil with very low water content.

On-site effluent data fully demonstrate that the KHC coalescing oil-removal unit developed by SINOKLE delivers outstanding demulsification and oil removal on sour wastewater. Effluent oil content is below 50 mg/L, below 10 mg/L after excluding phenolic interference, and the recovered oil phase has low water content and high quality.

SINOKLE’s coalescing demulsification and oil-removal process, with KHC at its core, effectively handles sour wastewater that is highly emulsified and high in oil, reducing its adverse impact on downstream stripping and sulfur recovery and on product quality. While safeguarding effluent quality, cutting the load on downstream treatment and improving discharge compliance, the scheme achieves efficient recovery of light oil with clear economic and environmental benefits.