Tank-Bottom Water Without Chemicals: Coalescing Separation Paired With CDFU Cyclonic Flotation
Among the daily headaches of oilfields and refining enterprises, tank-farm draw-off water, usually called tank-bottom water, is one that never goes away. It is discharged intermittently, it carries high oil content, it fluctuates severely and its composition is complicated. The traditional answer, chemical demulsification followed by settling, is now showing its age under the combined pressure of stricter environmental supervision and cost reduction. A purely physical process built around SINOKLE's CDFU cyclonic dissolved air flotation is changing that picture.
What the chemical route actually costs
Dosing demulsifiers and flocculants, then separating in separator tanks, flotation tanks or settling tanks, has been the mainstream method for a long time. In service it exposes a familiar list of problems.
Chemical dosing produces large amounts of oily chemical scum or sludge, which counts as hazardous waste, with disposal costs and environmental risk attached. Shock resistance is weak: the quality and quantity of tank-farm draw-off water fluctuate drastically, traditional processes adjust slowly, and when incoming oil spikes the effluent exceeds its limit and the downstream wastewater treatment system takes the hit. Operating cost is high, because continuous chemical purchase, hazardous-waste disposal fees and the maintenance burden of corrosion and scaling all accumulate. Recovered-oil quality suffers too, since chemicals contaminate the recovered foul oil and produce aged oil of degraded quality and low re-refining value, which can even disturb the main process.
A different premise: strengthen the physics
Rather than refine the chemistry, SINOKLE dropped chemical dependence and pursued efficient oil-water separation through multi-stage strengthened physical mechanisms. The core route is a high-efficiency coalescing oil remover followed by CDFU cyclonic dissolved air flotation.
The first stage is coalescence. Wastewater enters the high-efficiency coalescing oil remover, where a specially formulated coalescing material makes the tiny oil droplets collide and merge rapidly into large oil beads. Once the droplets have grown, everything downstream gets easier, and this is the step that quietly determines how well the flotation stage performs.
The CDFU then does the separation. It fuses cyclonic centrifugal separation with micro-fine bubble flotation. A patented dissolved-air release system generates microbubbles of only 5 to 30 μm in diameter; their specific surface area is enormous, and their capture ability and adsorption efficiency for oil droplets far exceed what traditional large bubbles achieve. At the same time the water forms a strong swirl inside the tank, and the centrifugal force not only strengthens oil-water separation but greatly increases the collision probability between oil droplets and microbubbles. Under that synergy oil droplets are removed rapidly and the effluent runs clear, with no chemical dosing anywhere in the process.
Six ways the comparison comes out
Set against traditional chemical demulsification plus settling or DAF, the physical route differs on every dimension an operator cares about. The mechanism changes from relying on chemicals to alter interfacial properties, which transfers the pollutant, to purely physical coalescence and separation, which removes it. Secondary pollution disappears, because there is no chemical addition and therefore no chemical sludge and no hazardous waste to consign. Recovered oil is clean rather than aged, with low water content, and can go straight back into a crude tank where it has real economic value. Shock resistance is strong, so severe oil fluctuation is absorbed instead of exported as an exceedance. Operating cost collapses to a little electricity, and O&M cost falls with it. Footprint shrinks from settling tanks and DAF tanks to a compact skid that is a fraction of the traditional size.
Evidence from a working project
The process has been applied at several large petrochemical enterprises with operating results certified by authoritative bodies. At the electric-desalting wastewater treatment project of Sinopec Cangzhou Refining, the core process uses a coalescing pressure oil remover plus CDFU cyclonic dissolved air flotation. After purely physical treatment the effluent oil content sits stably at 35 mg/L, comfortably better than the design standard, and the process adds no chemicals at all, achieving efficient oil removal and sludge reduction together.
One practical note on specification. Because draw-off water is discharged intermittently, the plant is often sized on an average that the tank farm never actually delivers, and the units then see short, violent loads instead of a steady feed. Sizing for the draw-down event rather than the monthly mean is the single change that most improves how these installations behave, and it costs far less than upsizing equipment later.
Where it fits and where it does not
Tank-bottom water suits this route because the pollutant is oil in a form that physics can reach. Streams dominated by dissolved organics or by ammonia will still need biological treatment, and mixing them into the draw-off line only dilutes the advantage. But for the intermittent, high-oil, wildly variable stream that tank farms actually produce, the case is straightforward.
Treating tank-farm draw-off water no longer has to mean treating pollution with pollution. With CDFU cyclonic dissolved air flotation as its core patented technology, SINOKLE is pushing the industry toward zero chemicals, zero hazardous waste and high oil recovery. That is a response to environmental regulation, and it is also the sensible economic choice.