Commissioning Numbers That Matter: A KHC Coalescing Skid on High-Oil Sour Water

Emulsified sour water with recoverable light oil sitting in it is both an operating risk and wasted money. A recent chemical-project commissioning shows how a coalescing oil-removal skid turns that double loss into a single win — with sample data to back it.

The Problem Arrives Before the Skid Does

Petroleum and its derivatives normally carry sulfur and nitrogen compounds. Through atmospheric and vacuum distillation, catalytic cracking, delayed coking and hydrotreating, these become hydrogen sulfide and ammonia nitrogen in high-temperature cracking, catalytic conversion and hydrocracking, riding into the product stream. Cool the stream, dewater or water-wash it, and sour water — sulfur- and ammonia-rich — is what collects.

At this project the sour wastewater was high in oil and severely emulsified. Downstream, that meant operating risk for the stripper and sulfur recovery unit — packing plugging, temperature excursions — plus an upset wastewater treatment plant and threatened final discharge compliance. Upstream, large volumes of high-quality light oil with real recovery value were simply not being collected. Both the hazard and the economics pointed to the same fix.

The KHC-Based Scheme

SINOKLE formulated a scheme matched to the water quality and successfully applied its independently developed KHC coalescing oil-removal skid. Driven by its own pressure, the sour wastewater first passes through a filter to remove impurities, then enters the KHC high-efficiency coalescing separator. Inside, 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.

The Commissioning Data

Site sampling covered three points — unit inlet, KHC separator oil outlet and water outlet — analysed for oil and water content across five sample sets. Treated effluent oil content held stable between 15 mg/L and 35 mg/L, with removal efficiency as high as 99%, comfortably inside the requirement of oil content at 50 mg/L or less. Representative rows: Sample 1 measured 4122.77 mg/L at the inlet; Sample 2 read 19.26 mg/L with 99.53% removal; Sample 3 read 7.91 mg/L with 99.81% removal. With phenolic interference excluded, the actual oil content of the treated sour wastewater was only 7.91 mg/L — far below the 50 mg/L discharge limit and below 10 mg/L in the interference-corrected reading.

The recovered oil mattered as much as the water. Water content in the oil drawn off the KHC coalescing separator measured 1.42% and 0.54% in two samples — good-quality recovered oil with very low water content, ready to reclaim the recovery value the project had been losing.

Why Coalescing Suits This Stream

The physics is unforgiving but well understood. Emulsified droplets carry surface films that keep them dispersed indefinitely; gravity separation waits forever. A coalescing separator works the problem from the other end — the packing and cartridge surfaces strip those films and merge droplets until buoyancy does the rest. Because nothing chemical is injected, the recovered oil keeps its value, the water carries no additive burden into the stripper, and the unit cannot be knocked out of spec by a dosing error. The trade-offs are equally clear: inlet solids should be screened first (hence the upstream filter), and the oil draw-off needs monitoring to keep the collected phase dry — which the 1.42% and 0.54% water-content readings confirm is happening in practice.

Operating Notes for Similar Projects

Reading the Removal Curve

The progression from 4122.77 mg/L at the inlet to double digits at the outlet is worth unpacking, because no single mechanism achieves it. Bulk free oil separates almost immediately on entry; the emulsified fraction falls as the packing strips surface films and droplets merge; and the final polish comes from buoyancy doing the last metre of work in the collection zone. Removal rates above 99% therefore reflect the whole geometry, not a single magic packing material. It also explains why the outlet numbers cluster so tightly between 15 mg/L and 35 mg/L across five sample sets — once the emulsion breaks, the process has no remaining sensitivity to inlet swings, which is exactly the stability an upstream stripper wants.

• Sample all three points — inlet, oil outlet, water outlet — before judging performance; single-point data hides both the removal rate and the recovery quality.
• Watch phenolic interference in oil analysis; the raw instrument reading overstated oil content, and the corrected 7.91 mg/L tells the true story.
• Size the skid for the emulsified fraction, not the free oil; free oil is easy, and oversizing on it wastes footprint.

On-site effluent data demonstrate that the KHC coalescing oil-removal unit developed by SINOKLE delivers outstanding demulsification and oil removal on sour wastewater: effluent below 50 mg/L, below 10 mg/L after excluding phenolic interference, and a recovered oil phase with low water content and high quality. Effluent quality is safeguarded, the load on downstream stripping and sulfur recovery is cut, discharge compliance stops being a daily negotiation, and the light oil recovery adds an income line that conventional routes surrender to the sewer.