Six Figures of Oil Going In and Under 100mg/L Coming Out: A Coking Sour Water Line

Anyone who has worked on refinery wastewater knows that coking sour water is not to be trifled with. While a coking unit produces petroleum coke, it also generates a stream of highly concentrated oily wastewater with three properties that give engineers headaches.

What Makes This Stream So Awkward

First, the oil content is extremely high - routinely well over a hundred thousand milligrams per litre. The inlet oil specification at Sinopec Luoyang Petrochemical is ≤150000mg/L. What that means in practice: close to half a bottle of that water would be oil. Second, emulsification is severe - the oil and water are churned together as stubbornly as sesame paste. Third, water quality swings widely: adjust the unit's operating conditions and the incoming water changes character. Environmental professionals in the petrochemical sector privately agree that coking sour water is the hardest category to handle in the whole spectrum of refinery wastewater.

Why the Conventional Train Runs Out of Road

The usual answer is essentially gravity settling tanks plus dissolved-air flotation, then filtration. That works well enough on wastewater carrying 30,000-50,000 mg/L of oil. Faced with coking sour water in the hundred-thousand class, nothing settles, nothing floats, and cartridges blind at speed. Many plants fall back on large basins and long quiescent periods - a big footprint, low efficiency, and outright failure under shock loads. Worse, effluent oil content often sits at several hundred or even over a thousand mg/L, leaving the downstream biological system smothered in oil and barely functioning.

Four Gates, Each Taking a Cut

Rather than taking the single-unit breakthrough route, SINOKLE designed a multi-stage combination process tailored to the characteristics of coking sour water. The core logic is simple: let each step do what it does best and strip the oil out stage by stage. The chain runs coarse filter, CDFU high-efficiency compact cyclonic flotation, fine filter, then KHC high-efficiency coalescing oil-water separator. Four gates, each taking its cut, and final effluent oil content comes out at <100mg/L.

The coarse filter leads the charge

Large-particle impurities, lumps of oily sludge and silt in the incoming water are stopped here first. This step looks unremarkable, but it is essentially taking the bullet for the precision equipment downstream. Without this barrier, the cyclonic flotation unit and the fine filter behind it simply could not cope.

CDFU carries the load

Conventional dissolved-air flotation basins routinely take up tens of square metres. The CDFU fuses cyclonic separation with dissolved-air flotation instead, for a small footprint and high treatment efficiency. Water arriving with more than a hundred thousand mg/L of oil enters the CDFU, where the cyclonic force field first throws out most of the free oil, and microbubbles then lift the remaining dispersed and emulsified oil to the surface. One unit does the work of two, pulling oil content straight from six figures down to four or even three.

The fine filter fills the gap

Water leaving the CDFU is already far lower in oil, but small amounts of suspended solids and very fine droplets remain, and the fine filter intercepts them with high-precision cartridges. The key is getting cartridge rating and material right: too fine and it blinds easily, too coarse and it does not catch enough. SINOKLE's selection criteria and operating parameters here distil years of project experience.

KHC closes the sequence

Coalescing separation works by merging micron-scale droplets into large droplets and then separating them on the density difference. The KHC coalescing packing is SINOKLE's own development, an order of magnitude more efficient at separation than conventional corrugated plates. The stubborn holdouts left in the water after flotation and fine filtration are essentially cleaned up by the time they reach the KHC, and effluent oil content settles firmly below 100mg/L.

Stringing four units together is not simply 1+1+1+1. The selection and parameters of every step are matched specifically to the oil characteristics, degree of emulsification and flow variability of coking sour water. That is exactly what pure equipment vendors cannot do - you have to have spent real time on petrochemical sites and made the mistakes yourself to know how to break that cream-like emulsion layer in sour water.

What Luoyang Petrochemical Actually Measured

The client is Sinopec Luoyang Petrochemical Company, with a treatment capacity of 15m³/h; the plant was delivered and entered operation. Inlet oil content is specified at 15 0,000 mg/L, outlet oil content <100mg/L, and oil removal efficiency runs above 99.9%. These are figures you can state with confidence in the field of coking sour water treatment: from 150,000 mg/L down to below 100 mg/L, an absolute drop of three orders of magnitude. And these are not laboratory bench numbers - they are the real performance of more than three years of continuous industrial operation.

Luoyang Petrochemical is a major refining base in central China and has always held a tight line on environmental indicators. That this unit passed the client's acceptance and has run steadily ever since is more persuasive than any parameter in a brochure.

Why the Project Matters

For Luoyang Petrochemical, coking sour water stopped being the bottleneck dragging environmental compliance down. Treated water meets standards consistently, the biological system runs more reliably, and the operations crew has one less nerve-wracking monitoring point on night shift.

For SINOKLE the project carries more weight. First, it validated the technical feasibility of the combined process on coking sour water - the ceiling of difficulty among petrochemical wastewaters - closing the full loop from equipment design to process parameters to on-site commissioning. Second, the benchmark effect within the Sinopec system speaks for itself: in later conversations with sister plants such as Jiujiang Petrochemical, Anqing Petrochemical and Wuhan Petrochemical, there is no need to labour the question of whether the technology is up to it. You simply say the Luoyang project was ours, and that is enough. Third, 15m³/h is neither large nor small - exactly the size for a replicable modular solution. Scale up by running multiple modules in parallel to reach 30m³/h or 45m³/h, or scale down to 5-10m³/h to meet the needs of smaller refineries. That flexible granularity is a genuine plus for market expansion.