Two Stages, No Chemicals: An Equipment Level Breakdown of a 105 m3/h Desalter Effluent Deoiling Package
Why this project is interesting at all
In a deoiling project for desalter effluent from the atmospheric/vacuum unit at a PetroChina refinery in Southwest China, Shenzhen SINOKLE delivered a combined skid-mounted package built around a coalescing pressure oil separator followed by CDFU cyclonic dissolved-air flotation (CDAF).
The interesting thing is not the scale. At 105 m³/h this is not a large installation by petrochemical standards. What makes it worth an equipment-level teardown is the logic behind three words: the pure-physical-method approach. There is no dosing point anywhere in the line.
The route, in two stages
The package adopts a two-stage series structure.
- Stage 1: coalescing pressure oil separator, handling coarse separation of large free oil and dispersed oil.
- Stage 2: CDFU cyclonic dissolved-air flotation, handling fine separation of emulsified oil and fine droplets.
No dosing point sits between the two stages. The whole process is purely physically driven, which is unusual at this duty and is why the operating cost profile looks different from a conventional chemical-dosed train.
Stage 1: letting droplets grow by themselves
Coalescence is not complicated in principle. Oily wastewater passes through a bed packed with specific material; tiny droplets are captured by the surface and held, then collide and merge with later droplets as they travel the tortuous channels, finally growing large enough to detach and rise under gravity or buoyancy. The engineering difficulties sit in three places.
First, selection of coalescing media. Different material surfaces are oleophilic or oleophobic to different degrees, and coalescing efficiency for specific oils varies markedly, so SINOKLE customizes the coalescing medium based on petrochemical oil characteristics. Second, balancing flow velocity against residence time: too fast and droplets cannot collide and merge in time, too slow and capacity suffers. Making the coalescer work effectively at the total treatment capacity of 105 m³/h is the core hydraulic-design challenge. Third, the requirements for the pressure vessel, since the coalescer runs under pressure and the sealing and strength design directly determine safety.
Stage 2: four technologies in one cavity
CDFU, full name Cyclonic Dissolved Gas Flotation Unit, is a cyclonic dissolved-air flotation unit, a patented SINOKLE product and China's first enclosed pressurized flotation technology. Rather than adding a cyclone onto a conventional flotation tank, it redesigns the separation chamber from the fluid-dynamics level. Four coupled technologies sit inside it.
3.1 Cyclonic centrifugal separation
Oily wastewater enters the CDFU cavity tangentially, forming a high-speed swirl in the cylindrical separation zone. By the centrifugal variant of Stokes' law, oil droplets, being less dense than water, migrate toward the axis in the centrifugal field. Separation efficiency is proportional to the square of swirl intensity, which is the physical basis for CDFU reaching higher efficiency than conventional gravity flotation.
3.2 Ultra-fine bubble generation
This is the core technical barrier distinguishing CDFU from conventional flotation. SINOKLE uses proprietary dissolved-air release technology: pressurized dissolved-air water is instantaneously depressurized through a special releaser, generating large numbers of micron-scale bubbles. Bubble size is critical for three reasons at once. The smaller the bubble, the larger its specific surface area and the higher the collision probability with oil droplets. A single bubble also rises more slowly under Stokes' law, so its sweeping time in the water is longer. And the total interfacial area available for attachment rises with the number of bubbles. Conventional flotation bubbles are usually millimeter-scale, so micron-scale bubbles are equivalent to raising the capture net's mesh density by orders of magnitude.
3.3 Dissolved-air flotation
After micro-bubbles collide with oil droplets, a stable attachment forms at the oil–water–gas interface. The bubble lowers the droplet's overall effective density, letting the droplet-bubble aggregate float quickly to the surface. The enclosed pressurized design matters here: it ensures the whole flotation proceeds in a stable pressure field, avoiding the bubble escape and scum-layer destruction that surface fluctuation causes in conventional open flotation tanks.
3.4 Coalescent demulsification
CDFU internally integrates a coalescing unit so that tiny droplets not captured by the previous three mechanisms collide and merge while passing the coalescing media. Put plainly: the cyclone throws out what it can fling out, the bubbles stick to what they can stick to, and the coalescer grows what neither can fling out nor stick to, then sends it back to the first two mechanisms.
Coupling, not series
The core value of this combination lies not in any single technology but in the synergy. Conventional process logic is series: gravity separation, then flotation, then filtration, each independent and each managing its own segment. The SINOKLE logic is fusion: in one cavity the cyclone creates a centrifugal-force gradient, the bubbles create a buoyant-force gradient, and coalescence creates a size gradient, and the three gradient fields superimpose to capture oil droplets of different sizes simultaneously.
The result is that processing efficiency rises while equipment volume is greatly compressed. That is the physical premise behind skid-mounting 105 m³/h, whereas conventional schemes need ponds of hundreds of square meters to match it.
What the delivered project shows
SINOKLE has not disclosed detailed equipment design parameters, but several key indicators can be extracted from the delivered project results.
- Treatment capacity: 105 m³/h
- Effluent oil content: <150 mg/L, meeting the discharge standard
- Operation mode: no dosing throughout, pure-physical method
- Oily-waste recovery: separated oil can be re-refined
- Waste: no oily sludge generated
The commercial logic follows directly from that list. Removing dosing cuts the recurring chemical-cost line; producing no oily sludge cuts the hazardous-waste-disposal compliance-cost line; and skid-mounting compresses the construction period from half a year to months. For refinery operators it is a win on three fronts at once, and a reason to evaluate a purely physical route before reaching for a chemical programme.