From 20000 ppm to 150 ppm: How Cyclonic Flotation Handles Oil That Refuses to Separate
Oil in wastewater is never just one thing. In petroleum refining, oilfield produced water, tank-farm draw-off water and heavy-fuel-oil depot drainage, the same stream usually carries floating oil, dispersed oil, emulsified oil and oil adsorbed on the surface of suspended solids simultaneously. Floating oil has a larger particle size and can be partly removed by gravity settling or a simple oil separator. Dispersed oil and emulsified oil are small, strongly stable, and bound more tightly to the water phase, which is exactly where traditional oil-separator tanks, settling tanks and ordinary flotation start producing unstable results.
Four Mechanisms, One Vessel
SINOKLE's CDFU cyclonic dissolved-air flotation technology was built for that residual fraction. Rather than relying on a single separation mechanism, it integrates cyclonic separation, dissolved-air flotation, micro-nano bubble capture and coalescence into one, improving oil-water separation efficiency through the synergy of several physical actions at once.
1. Cyclonic Flow Field
After wastewater enters the equipment, a rotating flow forms under the action of a specific structure. Because oil droplets, the aqueous phase and solid particles differ in density, the oil droplets gradually migrate toward favourable separation positions under centrifugal force, buoyancy and flow shear. Compared with traditional static settling, the cyclonic flow field shortens the migration path and raises separation speed significantly, achieving rapid three-phase separation of oil, water and solids.
2. Dissolved-Air Flotation
Fine bubbles released by the system collide with and adhere to fine oil droplets and suspended particles, reducing their apparent density so they float and separate more easily. For fine oil droplets, gravity flotation alone is extremely slow; once bubbles attach, flotation capability is significantly enhanced and capture efficiency for dispersed oil and emulsified oil improves.
3. Coalescence Enhancement
Under cyclonic disturbance, bubble collision and the equipment internal structure, fine oil droplets collide, adhere, coalesce and grow. Once droplet size increases, flotation speed accelerates and subsequent separation becomes easier. For wastewater with a high degree of emulsification and small oil-droplet sizes, this step is doing a large share of the work.
Two Cases, Two Different Problems
A petrochemical electric-desalting and tank-farm black-water treatment project in Xinjiang faced high oil content, large water-quality fluctuation and complex oil forms. The installed route was a high-efficiency coalescing deoiler followed by two-stage CDFU, with a treatment capacity of 150 m3/h. Influent oil content ran at <=20000 ppm, treated effluent oil content came out at <=150 ppm, and oil water content <=30%. The front-end coalescer took the bulk; CDFU then removed the fine droplets and emulsified oil the coalescer could not reach, delivering stable oil reduction on high-oil refining wastewater.
The Bangladesh fuel-power-station project treated heavy-fuel-oil depot wastewater, a harder feed containing heavy oil, dispersed oil and more suspended impurity than a light-oil stream, where oil-water separation is more difficult than for ordinary light-oil wastewater. It adopted two-stage CDFU + KFM filter, taking influent oil from <=2000 ppm to <=10 ppm at a treatment capacity of 120 m3/d. The point of that case is that multi-stage flotation combined with terminal filtration is a workable answer for heavy-fuel-oil depot wastewater, not only for lighter streams.
Reading the Two Cases Together
What separates them is not technology but feed character. The Xinjiang stream was defined by absolute oil concentration and variability; the Bangladesh stream by oil type and solids load. In both, the same logic applied: remove the separable fraction cheaply first, then let the fine-treatment stage work on a feed it can actually handle. Neither project would have met its limit with a single separation principle, and neither relied on escalating chemical dosing to close the gap.
Where the Technology Sits in a Flow Sheet
CDFU can be widely used for petroleum-refining electric-desalting draw-off water, crude-oil tank-farm draw-off water, oil-depot oily wastewater, oilfield produced water, fracturing flowback fluid and other oily and suspended-solid wastewaters. For water with high oil content, high emulsification and high fluctuation it serves as the front-end core oil-removal unit. For projects with higher effluent requirements it combines with KFM filtration, KHC coalescing deoiling or a CDOF advanced-oxidation unit to form a more complete system solution.
How to Judge Whether You Need It
A useful first test is to look at what the existing separator or settling tank is already achieving. If it removes floating oil reliably and the effluent still fails on total oil, the shortfall is almost certainly dispersed and emulsified oil, and that is the fraction a cyclonic field plus microbubbles is built to attack. If the existing unit struggles even with floating oil, the problem is hydraulic sizing rather than separation mechanism, and additional flotation stages will not fix it. The second test is variability: streams whose oil concentration swings widely punish any process that depends on a fixed chemical dose, which is where a purely physical front end tends to pay back fastest.
What It Is Not
This is not an incremental upgrade of ordinary flotation equipment. It is a compact separation device integrating cyclonic rapid separation, microbubble capture and coalescence demulsification, and its technical value shows up in three measurable places: improved removal capacity for fine oil droplets and emulsified oil, simultaneous reduction of suspended-solids content, and better stability of downstream treatment systems because the front-end load is cut quickly.
The objective was never simply floating-oil removal. Multi-form oil in complex oily wastewater needs several physical actions working together inside a short retention time, so that oxidation, filtration, biochemical or reuse treatment downstream sees influent conditions it was actually designed for.