Flotation Selection Guide: From DAF Fundamentals to CDFU Operating Data

How Flotation Separates Oil from Water

Flotation (Dissolved Air Flotation, DAF) is a solid-liquid and liquid-liquid separation technique that uses fine bubbles as carriers. Bubbles attach to suspended particles, oil droplets and colloids and form bubble-particle complexes whose density is lower than water, so they rise quickly and build a scum layer that a scraper removes mechanically. For oily wastewater, high-turbidity water and hard-to-degrade streams it remains one of the core processes, because treatment efficiency is high, the footprint is small and operation is flexible.

Four Bubble-Generation Routes, Four Different Fits

Flotation units are usually classified by how the bubbles are produced, and the choice is dictated by water quality rather than by preference. Dissolved gas systems suit fine and emulsified contaminants because the bubbles are small and numerous. Induced air systems tolerate higher solids loads. Electrolytic systems avoid gas supply infrastructure altogether. Hybrid swirl-plus-dissolved-gas designs exist specifically for stable emulsions where one mechanism is not enough. Getting that classification right at the sizing stage saves a retrofit later.

Where Flotation Is Applied

Industrial oily wastewater is the primary field. In oilfield water treatment the duties are produced water, fracturing flowback fluid and offshore platform wastewater, where flotation acts as a core process rather than a polishing step. Refining brings electric desalting wastewater, tank farm black water and sour water, all of them high-oil and highly emulsified. Outside oil and gas, flotation serves food processing, papermaking, electroplating heavy-metal wastewater and landfill leachate.

Development Trends Worth Tracking

Ultra-fine bubble generation has pushed bubble size down to 5-30μm, which raises collision and adhesion efficiency against emulsified oil droplets and lifts single-stage oil removal above 90%. Materials have moved to duplex stainless steel and titanium alloy for high-salt and highly corrosive duties such as offshore platforms and high-salinity oilfield water. Process integration now merges cyclonic centrifugal separation with dissolved gas flotation, achieving physical demulsification and efficient separation in the same vessel. On control, AI algorithms adjust dissolved gas pressure and reflux ratio in real time, cutting energy consumption by 22% or more and enabling unattended remote operation.

Where CFU Designs Stop Being Enough

Conventional CFU technology is a mature baseline, but it carries known pain points on difficult oily wastewater: emulsified oil is hard to remove, energy consumption is high, the footprint is large and corrosion resistance is limited. SINOKLE CDFU (cyclonic dissolved gas flotation unit) is a deliberate iteration on that baseline, built around deep integration of cyclonic centrifugal separation and dissolved gas flotation.

Bubble size is controlled at 5-30μm with a median of about 25μm, which matches 1-10μm emulsified oil droplets well and improves collision and adhesion efficiency by 3 times. Single-stage oil removal exceeds 90% and suspended solids removal exceeds 85%. The cyclonic unit handles preliminary oil-water separation using a CFD optimised flow field, while the dissolved gas stage removes the residual emulsified fraction, giving two physical barriers in series rather than one.

Demulsification is purely physical throughout. No chemical agent is added, so no oily sludge is generated at source, and the separated waste oil can be recovered and reused. Hazardous waste disposal cost falls by 30% or more. The design is predominantly static equipment with no mechanical slag-scraping device, which extends the maintenance cycle to 6 months and cuts manual maintenance cost by 50%. The compact skid reduces equipment volume by 50% or more against conventional flotation and shortens the deployment period by 40%, which matters on offshore platforms where deck space is the real constraint. Key components in duplex stainless steel and titanium alloy tolerate high-salt, highly corrosive and high-temperature (below 80℃) service.

An IoT control system supports remote monitoring, parameter adjustment and fault early warning, so O&M can be unattended. Shock load resistance reaches 110%, which means compliance holds while influent quality moves. Effluent oil content is controllable at ≤10mg/L and suspended solids at ≤20mg/L, meeting stringent domestic and international standards including IMO discharge requirements.

Operating Data from Three Projects

At an oilfield produced water project in Africa, treatment scale is 5000m³/d on a feed with large oil-content swings and severe emulsification. Effluent oil content holds below <10mg/L, operation has been stable and maintenance cost fell 60%. At a tank farm black water project for a petrochemical enterprise in Xinjiang, capacity is 3600m³/d with CDFU as a single stage. Shock load resistance of 110% was confirmed, operating energy consumption fell 40%, and effluent oil content held below <15mg/L against refining discharge standards. At a PetroChina petrochemical electric desalting wastewater project, capacity is 2400m³/d on a two-stage CDFU combined process, delivering effluent oil content of ≤10mg/L and suspended solids of ≤5mg/L with wastewater reuse and compliant discharge.

Matching the Unit to the Scenario

The configurations that pay back fastest share a common feature: space is scarce, salinity is high, or the emulsion is stubborn. Offshore oilfield platforms combine all three, which is where the skid and the corrosion-resistant materials matter most. Highly emulsified streams such as refining sour water and fracturing flowback fluid reward purely physical demulsification. High-salinity reinjection water and saline wastewater justify duplex steel and titanium alloy on service-life grounds. Old plant retrofits benefit most from the modular quick-install design, because capacity can be added without pouring new concrete. In bid work, the cyclone-plus-flotation configuration, the physical nature of the process and the intelligent O&M capability are the three points that carry technical competitiveness, and they are also what determines whether the plant still performs in year five.