Coking Sour Wastewater at 15% Oil: A Fully Physical Train of CDFU, Filtration and KHC

Coking is one of the harshest duties in a refinery, and the wastewater it produces inherits that character. The sour water leaving the coking unit is highly emulsified, strongly acidic, complex in composition and extremely high in concentration — a combination that makes it a persistent treatment problem rather than an occasional one.

Four properties define it. It is rich in fine coke particles of small particle size. It carries high oil content in a fine, tightly emulsified state, so the droplets are too small for gravity separation to catch. It holds high concentrations of sulphur, ammonia nitrogen and phenols. And its composition varies, with content fluctuating enough that a process tuned to yesterday average may not handle today load.

What Happens if It Goes Straight to the Stripper

The stripping unit is designed to transfer volatiles from liquid to gas, and it does that well when the liquid is clean. Fed with this water, it does not. Fine coke particles and emulsified oil cause equipment blockage, stripping efficiency falls, and the quality of the liquid ammonia product drops with it. In the worst case the unit trips, and an unplanned shutdown in a coking complex is a serious economic loss rather than an inconvenience.

The consequence reaches beyond the coking unit. Sour water quality constrains the whole downstream chain, so purifying it effectively is not a water treatment nicety — it is the condition for stable operation of the units that follow.

Why Chemical Treatment Lost Favour

Historically this water was treated with chemicals, and the approach had a predictable set of drawbacks: high reagent consumption, increased production of scum and oily sludge, treatment results that fluctuated with the feed, and a standing risk of secondary pollution. Each of those is a cost, and together they turn a treatment step into an ongoing negotiation between the operations team and the environmental team.

Breaking through that required a different premise. Through continuous R&D and practice, SINOKLE developed a coking sour wastewater treatment system built on purely physical demulsification and separation — no chemical dosing anywhere in the process.

Four Stages, One Physical Logic

The system takes CDFU swirl dissolved air flotation, precision filtration equipment and a KHC high-efficiency oil coalescing separator as its core, with coarse filtration ahead of them.

Coarse filtration comes first and does the least glamorous job: intercepting larger particle impurities so that nothing downstream has to deal with them. The water then enters the CDFU swirl dissolved air flotation unit, where swirl and dissolved air action separate suspended solids and emulsified oil. From there a precision filtration system removes fine solid particles and the residual emulsified oil that survived flotation. Finally the KHC high-efficiency oil-water separator performs deep purification, removing trace oil droplets and suspended matter to leave effluent that is clear and transparent.

The order is not arbitrary. Flotation handles the bulk load cheaply; precision filtration catches what flotation could not lift; coalescence polishes the last few milligrams per litre, which is the range where coalescing media outperform every other mechanism. Reversing any two of those stages would either blind the filter with oil or overload the coalescer with solids.

What the Physical Route Changes

No chemical dosing means no massive reagent consumption and no scum or oil residue generation, which fundamentally eliminates the possibility of secondary pollution — the phrase is accurate here, because there is no reagent whose fate has to be tracked.

A purely physical process is also stable and reliable in a way that chemically assisted processes are not, with demulsification results that hold up on a feed whose oil content moves. The recovered oil is of good quality with low water content and can be returned to the furnace for reuse, which converts a waste stream into a fuel stream and improves both resource utilisation and the project economics at the same time.

The system runs fully automated in enclosed, pressurised mode, so operation is safe and reliable with no environmental risk from fugitive emissions. The footprint is compact and the operation and maintenance costs are low — the two characteristics that decide whether a system keeps running as designed in year five.

The Luoyang Project

The reference case is a coking sour wastewater treatment system that SINOKLE designed for a petrochemical company in Luoyang and which has since gone into stable operation. The influent oil content is as high as 15%, that is 150,000 ppm. After treatment, effluent oil content is steadily controlled below 50 ppm, with an average oil removal efficiency above 99%.

Those three numbers describe a duty that most physical separation trains would refuse. An inlet at 150,000 ppm is not oily wastewater in the ordinary sense; it is oil with water in it. Getting from there to below 50 ppm without a single chemical dose is what makes the case worth citing, and the fact that it has stayed stable in operation is what makes it a reference rather than a demonstration.

Why the Case Matters Beyond Coking

The Luoyang installation solved a long-standing sour water problem for that company, but its wider value is as evidence about a class of streams. Highly emulsified, high-concentration, solids-laden wastewater appears in many industries, and the usual answer is more chemistry. A physical train that holds up at 150,000 ppm suggests that the chemical answer is often a substitute for good hydraulic design rather than a necessity.

For China coking wastewater treatment as a whole, the project marks a step forward that can be replicated. That is the more durable contribution: not one plant performing, but a configuration that other plants can copy with confidence.