When Influent Oil Swings from 500 mg/L to 5000 mg/L: A Field Case for Cyclonic Flotation

Oil and gas extraction, petrochemical refining, machinery processing and metallurgy all generate oily wastewater, and all of them eventually hit the same wall: streams where the oil-water density difference is very small, emulsification runs deep, and the suspended-solids composition is complex. Gravity settling, ordinary flotation and chemical demulsification have been the default answers for decades. On this class of water they produce low treatment efficiency, a large footprint, a heavy chemical bill, and a sludge problem that is arguably worse than the original one.

Where Conventional Flotation Runs Out of Road

Oil in industrial wastewater shows up in three states: floating oil, dispersed oil and emulsified oil. Floating oil is easy and settles out by gravity alone. Dispersed oil can still be addressed by conventional flotation. The real hard bone is emulsified oil and the fine suspended solids (SS) that travel with it.

Traditional flotation technologies such as DAF dissolved-air flotation and IGF induced-gas flotation fail in predictable ways here:

• Bubbles too large and unevenly distributed. Conventional equipment mostly produces bubbles above 50-100 microns that disperse poorly. Catching micron-scale droplets with those is like using a large net to catch small fish.
• Weak impact-load resistance. Water quality and quantity fluctuate in industrial production. Once oil content spikes, a traditional flotation tank loses oil and effluent quality collapses instantly.
• Large footprint, long retention. To compensate for low capture efficiency, plants exchange space for time, building huge tanks and holding water for tens of minutes or hours.
• Heavy chemical dependence. Demulsifiers and coagulants are dosed continuously to force emulsion breaking, which keeps operating cost high and generates difficult-to-treat chemical sludge.

The industry has lived with ineffective flotation for a long time. What was missing was a separation technology that is faster, more efficient and smaller at the same time.

The Mechanism Behind CDFU

SINOKLE (CLEAR) captured this pain point and, after years of R&D and iteration, launched CDFU, the Cyclonic Dissolved Gas Flotation Unit, or cyclonic dissolved-air flotation. The core is the physical coupling of micro-bubble flotation with a centrifugal cyclone field, which is not a simple superposition of two technologies but a genuine change in the fluid mechanics at micro level.

Microbubbles in the 5-20 Micron Range

The system carries SINOKLE's patented micro-nano dissolved-air release technology. Through a specific flow-channel design and sudden pressure drop, it releases a very large population of microbubbles in the 5-20 micron range. They have an extremely large specific surface area and look milky white in the water. Like countless miniature salvage ships, they penetrate the whole water body and even reach the interior of emulsified oil droplets and fine suspended solids, adsorbing firmly through surface tension.

The Centrifugal Multiplier

In a traditional flotation tank, a bubble with oil attached drifts upward on natural buoyancy alone, which is gravity-field separation. CDFU's difference is a high-speed rotating centrifugal flow field built inside the separation vessel. Mixed fluid carrying microbubbles enters tangentially, and centrifugal force takes over immediately. Per Stokes' law, separation speed in a centrifugal field reaches tens or even hundreds of times that in a gravity field. Heavy clean water is flung outward and discharged downward; the light microbubble-oil-droplet polymer is squeezed toward the central axis, forming a low-pressure gas core that runs top to bottom, and is scraped off at the top at high speed.

Collision Probability

The high-speed swirl also raises the collision frequency between microbubbles and oil droplets or suspended solids under turbulent conditions. Intense fluid shear and vortex mixing mean even the tiniest emulsified oil cannot escape the dragnet.

What That Translates to on Site

• Second-level separation. Hydraulic retention time compresses to roughly 15-60 seconds against 30-60 minutes for traditional flotation, so equipment volume lands at about 1/10 to 1/5 of a conventional tank. Offshore drilling platforms, space-limited refineries and old-plant renovations are the obvious beneficiaries of a compact skid-mounted unit.
• Shock tolerance. Even for extreme slug flow where upstream influent oil content soars from 500 mg/L to 5000 mg/L, the powerful centrifugal flow field maintains structural stability without oil loss or collapse. Effluent oil content (TOG) and suspended solids (TSS) drop to below 10 mg/L, and often below 5 mg/L, meeting stringent discharge or oilfield reinjection standards directly.
• Lower chemical demand. Physical capture probability plus swirl-enhanced coalescence cut demulsifier and flocculant dosing by more than 30%-50%, with a matching reduction in downstream chemical sludge.
• Enclosed operation. Traditional open flotation tanks are the hardest-hit areas for unorganized VOC and odour emissions. The fully enclosed pressurized-vessel design carries wastewater from inlet to outlet and gas from dissolution to release entirely inside the closed system, fundamentally preventing harmful gas escape.

Where It Has Been Deployed

CNPC, Sinopec and CNOOC have put CDFU into engineering service, along with many large chemical parks, coal-chemical enterprises and metallurgical steel plants. On an offshore platform in Bohai Bay the deciding factors were the extremely small footprint and resistance to wave surge. At a million-ton-scale refinery in Northwest China it became the gatekeeper for deep treatment of electric-desalting wastewater and oily wastewater, enabling ultimate reuse of water resources. At fracturing flowback fluid sites for unconventional oil and gas it handles high-suspension, high-viscosity water that conventional units cannot.

Where This Leaves the Technology

Enterprise demand has shifted from simple compliance to low-carbon, low-consumption, high-efficiency and intelligent operation, and emission targets have tightened alongside already strict environmental regulation. Relying on more than ten years of deep cultivation in cyclonic separation and micro-nano bubbles, SINOKLE (CLEAR)'s CDFU represents a credible evolution route for physical separation of oily wastewater. It is one of the few routes where high efficiency and environmental protection, compactness and stability are not traded against each other. As new materials, fluid-mechanics simulation and intelligent control are integrated further, the oil-water boundary will keep moving.