Refinery Circulating Water De-Oiled at 17,000 m3/d: Coalescing Oil Removal at Scale

Refinery circulating water systems sit at an awkward intersection of the plant: the same water cools and washes across the refinery, and every leak, every process-media carryover and every upstream upset deposits oil into the loop. What returns to the coolers is therefore oily wastewater with high emulsification, complex pollutant composition and strongly fluctuating quality - exactly the combination conventional treatment handles worst. Letting the oil circulate is not an option either, since films on heat-exchange surfaces cut thermal performance and oil carryover accelerates fouling throughout the loop.

Where oil in the loop actually comes from

Understanding the sources explains why one-off cleanups never fix circulating water. Cooler bundle leaks push process hydrocarbons straight into the cooling circuit. Seal failures on pumps, over-speed of wash water, and carryover from adjacent process units all contribute their share, and none of them announce themselves - the oil simply appears at the sampling point days later. Because the inputs are continuous and varied, the removal step must also be continuous and tolerant: batch hand-cleaning of basins or periodic blowdown merely resets the clock while the oil tax keeps accruing on heat-transfer surfaces. A duty of this character calls for equipment that rides through fluctuation automatically, which is precisely the design brief the coalescing oil remover was built around.

The separation principle, step by step

The coalescing oil remover separates oil from water through specially designed coalescing media and the coalescence principle rather than chemicals. Oily water passes through a special polyester fibre material where fine droplets are captured and adsorbed on the fibre surfaces. Under the driving flow, captured droplets migrate along the fibres to the crossing points, coalesce into larger drops on collision, and finally separate once they are big enough for the vessel's internals to catch them.

Two design refinements keep the process honest. Bidirectional flow arrangement and CFD-optimised flow fields maintain stable internal hydraulics, preventing the short-circuiting and internal recirculation that quietly ruin separation in poorly designed vessels. Uniform flow is not glamorous, but it is why measured performance matches design performance.

Engineered details that matter in service

A high-efficiency coalescing inclined-plate section enlarges droplet size and shortens droplet residence time, so efficient separation happens inside a more compact vessel rather than a sprawling tank. Ahead of the media, a specially designed inlet cyclone applies centrifugal force to strip dispersed oil quickly, cutting the load on the coalescing media and preventing the plugging that ends most media-based systems prematurely.

The media itself carries super-hydrophilic modification, applied through atomic layer deposition for molecular-level surface treatment. The result is high density and shape retention in the packing, which translates into removal of droplets of 20 um and above, strong fouling resistance and stable long-term operation on feed that swings.

Three deployments, three different duties

Scale comes first: at an Uzbek refinery circulating water de-oiling project, a unit processes 17,000 m3/d. Handling that throughput continuously and steadily, with effluent meeting design requirements, demonstrates large-scale capacity rather than pilot-scale promise - circulating water systems of this size underpin entire refinery cooling operations, and any de-oiling step inserted into them must run without becoming the bottleneck.

Adaptability comes second. At CNOOC Huizhou Refining, a coalescing oil remover paired with CDFU treats oily sludge washing wastewater at 720 m3/d. Sludge washing water is a nastier feed than circulating water - high oil, variable solids - and the combined process handled it successfully, showing the technology tolerates complex water conditions beyond its nominal duty.

Third, a Zhejiang petrochemical desalter wastewater project applies the same coalescing oil remover plus CDFU combination at 900 m3/d, extending the record into chemical-industry service and confirming that the pairing scales across feed types and sites.

Operational features that keep it running

• Fully automatic control. Operation stays smooth and reliable without dedicated operator attention, an important property for a utility duty inside a large plant.
• Enclosed pressure de-oiling. The pressurized, closed design adapts to complex site conditions and contains the process completely.
• Special sand-flushing system. Deposits are flushed out in time, preventing the gradual plugging that degrades most media systems.

Why circulating water deserves better treatment

Circulating water is easy to neglect because it is a utility, not a product. Yet the oil that circulates silently taxes the whole refinery: fouled exchangers raise energy consumption, off-spec cooling water complicates blowdown handling, and every upset propagates through the loop. A coalescing oil remover sized for the duty, with proven references from 720 m3/d to 17,000 m3/d, turns that quiet tax into controlled removal at modest cost - and does so continuously, without the batch interventions that reset the problem every few weeks. As environmental rules tighten across the petrochemical sector, this combination of innovative technology and stable performance is becoming the practical route for circulating water de-oiling - and a small investment relative to the efficiency it protects.