CDFU in Numbers: Bubble Size, Retention Time and Chemical-Free Oil Removal Against Mainstream CFU Units

Cyclonic dissolved-air flotation is what happens when cyclonic centrifugal separation and dissolved-air flotation (DAF) stop being two unit operations and become one. Designed with CFD-optimized flow paths, the CDFU from SINOKLE is a compact oil-water separator built around that fusion, and it is easier to evaluate on parameters than on adjectives.

What the Unit Actually Is

CDFU (Compact Cyclonic Dissolved Gas Flotation) is a proprietary patented product of SINOKLE. It combines cyclonic centrifugal separation and dissolved-air flotation (DAF) through CFD optimized design into a single high-efficiency oil-water separator. After the wastewater mixes with the dissolved-air water it enters the CDFU, where cyclonic centrifugal force causes micro-bubbles (5-30 um) to rapidly collide with and adhere to oil droplets, forming floating oil that can be skimmed.

Two things distinguish this from a conventional compact flotation unit at first glance. There is no chemical injection point, because the separation is entirely physical, and the vessel is sealed, because the dissolved-air circuit runs pressurised rather than atmospheric. Both choices carry consequences that only show up after commissioning: no dosing budget to manage, and no open surface for odour or vapour release.

The Four Steps Inside the Shell

The process reads simply on a flowsheet and depends entirely on execution:

• Dissolved-air mixing — wastewater and micro-nano bubbles (5-30 um, D50 about 25 um) are mixed at high shear in the multi-stage dissolved-air pump.
• Cyclonic separation — the mixed liquid enters the flotation tank tangentially, forming a stable swirl field; centrifugal force causes bubbles and oil droplets to collide and aggregate.
• Oil-water separation — floating oil rises into the oil-collection cylinder for discharge; clear water leaves from the bottom, with part recirculated for dissolved-air circulation.
• Core advantages — pure physical oil removal requiring no chemicals, cyclonic action enhancing flotation efficiency, and a skid-mounted structure that holds up under 10%-120% flow fluctuations.

Against Conventional DAF

The comparison is unflattering to the conventional unit on every line that matters:

• Retention time: 15~40min for traditional DAF, <5min for CDFU.
• Oil removal efficiency: 60~85% versus >90%.
• Removal particle size: >10um versus <2um.
• Bubble diameter: non-uniform versus 5~30um.
• Operation mode: manual and open versus fully automatic and enclosed.

The retention time figure is the one that changes plant layout. A five-fold reduction in residence requirement turns a concrete basin into a skid.

Against Mainstream CFU Units on the Market

Measured against SBL, VEOLIA and SIEMENS compact flotation units, the pattern is consistent:

• Bubble diameter: >500um, 100~500um, 5~75um, and 5~30um for CDFU — TOP.
• Retention time: 0.5~1min, 1~2min, 3~5min, and 1~3min for CDFU — TOP.
• Free-oil removal rate: 80~90%, >90%, >=96%, and >=99% for CDFU — TOP.
• Emulsified-oil removal: almost ineffective, poor effect, 50~70%, and 80~90% for CDFU — TOP.
• Chemical reagents: required, required, less, and not required for CDFU — OK.
• Oil recovery: not possible, not possible, most, and complete for CDFU — OK.
• Stability: low, low, high, and extremely high for CDFU — TOP.
• Control precision: low, low, low, and +/-5mm for CDFU — TOP.

Two rows deserve comment. Emulsified-oil removal is where mechanical flotation usually concedes defeat, and a unit that recovers 80~90% of it without demulsifier changes the chemical budget outright. Control precision at +/-5mm liquid level is what makes automatic operation credible rather than nominal.

The particle size row deserves a second look. Moving the cut from above 10um to below 2um shifts the unit from polishing duty into primary treatment for many refinery streams, and it follows directly from bubble size rather than from any change in water chemistry.

Structural Choices Behind the Numbers

Three physical features produce most of the above. Dual tangential inlets increase swirl velocity and centrifugal acceleration through a dual-tangential-angle design, improving flotation efficiency and shortening retention time. A central cylinder divides inner and outer flotation zones, generating stronger centrifugal force and higher space utilisation. And a conical bottom provides cyclonic desanding, flinging particles toward the inner wall so sand does not accumulate. CFD fine-grained flow-field simulation underpins all three and keeps the swirl stable across the operating range.

Energy, Footprint and Maintenance

Energy consumption is only 10% of IGF, with air consumption at 1~3%. No reagents are required, no sludge is generated, and the oil is recoverable. Footprint is 1/3 of a conventional installation, and the unit is not prone to scaling. The air consumption figure deserves a note of its own: drawing only 1~3% of the treated flow as air keeps the dissolved-air circuit, the recycle pump and the parasitic load all small.

The conclusion the data supports is narrow but useful: using a multi-stage dissolved-air pump to generate ultra-fine bubbles (D50 about 25 um), combined with dual-tangential-water-inlet and dual-flotation-zone designs and zero chemicals, CDFU achieves removal of free oil >=99% and emulsified oil 80~90%, with the lowest cost and simplest maintenance in its class. For oilfield-produced water and refinery oily streams, that is the shortlist, not the long one.