Refinery Sour Water: Cutting Stripper Fouling by Removing Emulsified Oil and Coke Fines Physically
In refining and petrochemicals, the sour water produced by units such as delayed coking and vacuum distillation carries sulfur, ammonia and phenol — and, increasingly, the combination that actually shuts plants down: emulsified oil plus coke fines. Desulfurisation and deammoniation get most of the engineering attention, but a growing number of field cases show that the oil and the fine suspended solids are what paralyse the system. Together they scale and block strippers, threatening the safe, stable, long-term, full-capacity operation every refiner is measured on.
How oil and coke fines disable a stripper
Under surfactants and process conditions, oil forms in the water an extremely small particle-size oil-in-water emulsion, typically 0.1-10 um, that is stable enough to defeat traditional gravity settling and even ordinary flotation. Coke fines from the coker are tiny, and they readily wrap around and adsorb onto those emulsified droplets, producing a more complex oil-solid composite pollutant. Whatever survives pretreatment then reaches the stripper, where in the high-temperature environment it deposits and carbonises on tray surfaces, packing and reboiler tube bundles. Heat-transfer efficiency falls sharply, differential pressure climbs and energy consumption soars. Finer coke fines and polymerised oil sludge plug tray sieve holes and packing gaps, causing flooding and lost capacity and eventually forcing unplanned shutdowns, with losses that dwarf the cost of the pretreatment itself. High-oil, high-suspended-solids influent also disrupts vapour-liquid balance and desulfurisation and deammoniation efficiency, so purified water goes off-spec and the cycle reinforces itself.
Why chemical pretreatment runs out of road
The industry answer has long been a pretreatment mode built on large doses of demulsifier and flocculant. It works partially and creates its own problems. Chemical cost is a continuous operating expense, and the dosage needs frequent adjustment as water quality moves. Hazardous waste is generated: the oily chemical sludge produced is expensive to dispose of and carries real environmental risk. Oil quality deteriorates too — waste oil recovered by chemical demulsification has high water and impurity content, is hard to re-refine and has low resource value. And the system is fragile: it adapts poorly to changes in emulsification degree and cannot give the downstream stripper the stable, high-quality influent it needs. SINOKLE took a different path, using CDFU swirl dissolved-air flotation ahead of KHC high-precision coalescing separation with no chemical demulsification at all.
First line: CDFU swirl dissolved-air flotation
The CDFU unit integrates swirl centrifugal separation with ultra-fine-bubble dissolved-air flotation. Feed enters tangentially and forms a strong swirl field; under centrifugal force, heavy coke fines and large particles are flung to the wall while oil droplets are enriched at the swirl centre. The system then generates large numbers of bubbles of 5-30 um diameter, D50 about 25 um, which efficiently collide with and adhere to the enriched oil droplets and fine particles. Once the bubble-oil droplet complex forms it floats rapidly to the liquid surface and is skimmed, with hydraulic retention time as short as 1-5 minutes. Single-stage removal runs at 99% or better for free oil, 80-90% for emulsified oil and above 85% for suspended solids, with zero chemical addition and strong tolerance of influent swings.
Second line: KHC high-precision coalescing separation
After CDFU treatment, a small amount of extremely stubborn fine emulsified oil at <10 um may remain, and that is precisely where the KHC high-precision coalescing separator comes in. It uses coalescing filter elements made of special fibre material, working on a coalescence-and-growth principle. Fine oil droplets passing through are captured by the super-oleophilic and hydrophobic fibre; captured droplets then accumulate and merge on the filter surface, gradually growing into droplets large enough to overcome the shear force of the water flow. Those large droplets finally detach and float free by density difference. Removal precision can reach 0.1 um, and with effluent oil content held stably below 10 ppm and free of dissolved oil, the KHC closes the gap that flotation alone cannot. A single element processes 10 m3/h and lasts two to five times as long as a traditional coalescing element, with chemical compatibility good enough that surfactants do not cause failure.
What the combination buys
Pairing the two is a designed sequence, not a stack of equipment. Stable low-oil-content, low-suspended-solids influent down to the 10 ppm level removes the material source of stripper scaling and blockage and extends run length between cleanings. Oil recovered by physical separation is high purity, low in water and impurities, and can go back to the crude oil tank farm for re-refining — resource value rather than disposal cost. Expensive demulsifier and flocculant purchases disappear along with hazardous sludge disposal, and high automation keeps O&M labour low. The whole process runs enclosed and pressurised with no waste-gas escape, and being purely physical it adds no new chemical pollution.
Field position
The synergistic process has been applied successfully at several petrochemical enterprises. For refineries handling highly emulsified coking or atmospheric and vacuum overhead sour water, the real problem is breaking the stable emulsified oil and coke fines system, and doing it without generating a hazardous sludge stream. SINOKLE's CDFU swirl dissolved-air flotation and KHC high-precision coalescing separator provide a purely physical route that is technically sound and reliably effective, and through source reduction and resource recovery it converts environmental investment into economic return.