KHC Coalescing Oil-Water Separator: Reading the Numbers Behind Compact Deoiling

Refining and coal chemical sites treat oily wastewater as a compliance obligation and a cost centre at the same time. As discharge limits tighten and old plant areas run out of room, the equipment that was specified twenty years ago stops being adequate. SINOKLE approached that gap from the separation side rather than the chemistry side, and the result is the KHC coalescing oil-water separator, a unit that resolves the bottleneck through physical means alone.

Four Ways Conventional Oily Water Equipment Falls Short

Gravity settling tanks, horizontal oil separation pools and standard flotation cells share a set of limitations that show up whenever the feed gets harder than the design case.

• Separation precision. They capture free oil above roughly 50 microns and are essentially blind to emulsified and fine droplets below 10 microns. Effluent quality then fluctuates with whatever the upstream process did that day.
• Footprint. Long residence times, measured in hours, make the vessels large and the civil works expensive, which is precisely the wrong shape for a capacity upgrade inside an existing boundary.
• O&M costs. Internal structures foul, so the unit needs frequent shutdowns for cleaning or media replacement. Add the reagents most designs rely on and you also inherit a chemical sludge stream that has to be handled as waste.
• Shock resistance. Feed surges such as refinery electric desalting dump water push the process outside its tuned range, and performance collapses until conditions settle again.

Inside the KHC: Three Steps, No Reagents

The KHC is not a tweak of an existing separator. It is a system built around coalescence theory, shallow-pool principles and CFD flow-field simulation, and its operation divides into three consecutive steps.

Flow distribution and pre-separation

Water enters through a purpose-designed dual tangential inlet. Swirl force dissipates the incoming energy and spreads the flow evenly across the section, while the largest droplets and heavy sand drop out early. This step exists mainly to make the next one predictable.

Coalescence

This is the heart of the design. Flow crosses a separation zone filled with SINOKLE's patented modified coalescing media. The material is super-oleophilic and hydrophobic, so it behaves almost like a magnet for fine droplets: they wet the fibre surface, spread, and merge, growing from micron scale to millimetre scale. Demulsification precision reaches 0.1 micron, which is well beyond what gravity or plain flotation can touch.

Shallow-pool separation and oil recovery

Because the pool is shallow, coalesced globules need only a short upward path to reach the top oil-collection package, where an automatic discharge system removes them. A dedicated sand-flushing system at the base sweeps the bottom clean so no dead corners accumulate sludge, which is what solves the clogging problem that plagues conventional internals.

Across the whole sequence, no chemical agent is introduced. Separation is carried out by the physical properties of the media and the flow field, and the recovered oil leaves the unit as a usable stream.

Two Projects, in Numbers

Design arguments are cheap; operating records are not. Two installations illustrate what the unit delivers under load.

At a back-pressure thermal power cogeneration construction project in Shaanxi, the plant generated oily wastewater with an oil content as high as 500,000 ppm, roughly 50 percent oil. It is about as hostile a feed as a separator will ever see. A combination of pre-filtration and the KHC coalescing oil-water separator brought effluent oil content down below 5 ppm, a removal rate above 99 percent and far inside discharge requirements.

The second case is a coking acidic wastewater project at a refinery in Henan, commissioned in 2020 at a treatment scale of 15 cubic meters per hour. The core equipment was the CDFU cyclonic dissolved-air flotation unit working with the KHC separator, again with no chemistry. Influent oil content, which reached 15,000 mg/L, came out below 98 mg/L, while suspended solids fell from 500 mg/L to 8.2 mg/L. The equipment footprint is only 12 m by 3 m, it is skid-mounted and automated, and O&M is straightforward enough that the construction period stayed short.

Where the Numbers Come From

Two figures explain most of the gap between these results and a conventional train. Coalescence grows droplets by orders of magnitude before they ever need to rise, which turns a slow separation problem into a fast one. And the shallow pool shortens the distance those droplets travel, so the vessel can be small without sacrificing throughput.

What the Numbers Do Not Show

Two things are easy to underestimate when separator options are compared side by side. The first is the cost of the sludge a chemical route generates, which never appears in the capital quotation but keeps arriving as a disposal invoice. The second is the value of a stable process, because an operator who is not constantly re-tuning dosage is an operator who can attend to the rest of the plant. Both advantages come from removing chemistry rather than from adding equipment.

For a plant looking at a retrofit, the practical consequence is that capacity and effluent quality can both improve without a large civil works programme, and the recovered oil offsets part of the operating bill. That combination is what makes a physical separator worth the specification effort.