Two CDFU Stages Plus KFM Filtration: Sizing a Reuse-Grade Oily Water Train

Oily wastewater sits at the intersection of environmental obligation and operating cost in oil and gas chemicals and oilfield service work. What operators need is not a single clever unit but a train that behaves predictably as feed quality swings. SINOKLE has built that train around two of its own core technologies, the CDFU cyclonic dissolved-air flotation unit and the KFM active filter-media filter, and the configuration is worth examining stage by stage because the sequencing is the point.

The Configuration in One Paragraph

The process runs as two stages of cyclonic dissolved-air flotation followed by active filter-media filtration. Water enters the first CDFU, where most floating oil, dispersed oil and suspended solids are removed. It then passes to a second CDFU that targets emulsified oil and finer impurities. Finally it crosses the KFM media filter for deep purification, so that what leaves the train meets reuse or downstream process requirements. Separate oil is collected centrally and the tail gas is routed to a dedicated system, which keeps the whole path under environmental control.

Why Two Flotation Stages Instead of One

The CDFU is the patented core of the offering. It couples cyclonic centrifugal separation, ultra-fine nano-bubble generation and dissolved-air flotation in a single vessel. Feed enters tangentially and forms a high-speed vortex, which pre-separates heavy particles under centrifugal force and enriches oil droplets toward the axis. At the same time the system releases a dense cloud of ultra-microbubbles in the 5-30 micron band. Those bubbles have a large specific surface and strong adsorption, so they collide and attach with emulsified droplets, forming bubble-pollutant composites that rise into a central collection zone and are continuously skimmed away.

Against traditional flotation, the unit needs no chemical dosing. Single-stage oil removal exceeds 90 percent, and a skid-mounted layout needs only about one third of the footprint, which suits space-constrained projects and allows fast deployment.

One stage is rarely enough on a difficult feed, however, because the droplet population reaching the first stage covers a wide size range. Running two CDFU stages in series lets the first pass take the bulk load and the second work on the harder emulsified fraction. Together the two stages remove more than 99 percent of the floating oil, dispersed oil and most of the emulsified oil, which is what makes the following filtration step reliable rather than overloaded.

KFM Media: Charge Adsorption on Top of Interception

As the last line of defence, the KFM active filter-media filter uses silicon-based media modified by atomic deposition, and it purifies in two ways at once: physical interception and charge adsorption.

• The media surface is super-hydrophilically modified into a nano-scale pore structure with a specific surface area 300 times that of quartz sand.
• Filtration precision reaches 1 micron, with suspended-solids interception above 95 percent.
• The surface carries a permanent negative charge, so charged colloids, fine oil droplets and some dissolved pollutants are captured by electrostatic attraction as well.
• Wear rate is only 0.07 per mille and the breakage rate 0.08 percent, giving a theoretical service life of up to 15 years, well beyond anthracite or corundum beds.

That combination addresses the two chronic complaints about conventional filtration: media that clogs too early, and media that has to be replaced too often.

Numbers, Costs and Range of Application

On performance, the two-stage flotation plus media filtration train brings oil content in oily wastewater below 5 mg/L and suspended solids below 1 mg/L, which is what oilfield reinjection and industrial reuse standards ask for.

On cost, three factors work in the same direction. No demulsifier or flocculant has to be purchased or dosed, so chemical consumption disappears. Integration and automation are high, so labour demand is low. And long-life media reduces consumable replacement, which is where filtration trains often quietly lose money.

On application range, the modular design accepts oilfield produced water, refining wastewater, tank farm cut water and power plant oily water, and can be recombined to match different treatment scales. Nitrogen protection throughout the process prevents escape of volatile organic compounds (VOCs), with tail gas collected and treated centrally and oily waste recovered, so the train closes the loop rather than merely relocating the problem.

Operating the Train Day to Day

The practical appeal of this configuration shows up in the operating routine rather than in the design case. There is no dosing loop to calibrate, no reagent inventory to hold, and no jar test to run when the feed changes character. Operators watch pressure differential across the media bed and turbidity at the outlet, and the flotation stages largely look after themselves. The result is a shorter training burden, fewer ways for a shift to set the process wrong, and a maintenance schedule driven by differential pressure rather than by chemistry.

Because the media is long-lived, planned maintenance is also predictable in a way that consumable-heavy filtration never is, which makes budgeting for the train straightforward from the first operating year.

For a project that has to produce reuse-grade water without a chemistry budget, that sequence is a reasonable starting specification.