Import Dependence in Oily Wastewater: What a Domestic Cyclone Flotation Unit Actually Changes

For years the core equipment used on the hardest oily wastewater streams - oilfield produced water at ultra-high water cut, refinery electro-desalting cut water - came from abroad. Technical barriers were high, service response was slow, and operation and maintenance cost more than plants had budgeted for. That combination turned imported flotation equipment into a bottleneck on the sector's green transition rather than a way out of one.

The CDFU cyclone dissolved-air flotation device developed independently by SINOKLE Technology broke that monopoly. It now serves domestic majors including CNPC, Sinopec and CNOOC, and has reached overseas markets in Africa and the Middle East.

Why Substitution Became Unavoidable

Imported equipment was never designed for Chinese oilfield conditions. High emulsification, high polymer content and large water-quality swings are routine here, and the adaptability and shock resistance of imported units were visibly insufficient against them. Maintenance cycles ran long and spare parts were expensive, producing the familiar situation of equipment that is affordable to buy but not affordable to run or repair.

The chemical route had its own problem. The traditional chemical demulsification and sedimentation path depends on large doses of demulsifiers and flocculants. That pushes up operating cost and generates large volumes of oily chemical sludge, which is classified as hazardous waste. For a million-tonne-scale refining enterprise, annual disposal cost for that sludge alone can reach several million yuan.

Then there is the space question. Older stations rarely have room to expand. Gravity sedimentation tanks and large flotation pools occupy huge areas and need hydraulic retention time of tens of minutes or even hours, which rules out retrofitting while production continues. The industry needed something autonomously controllable, compact, efficient and green.

Three Mechanisms Working in One Shell

SINOKLE CDFU (Compact Cyclone Dissolved-air Flotation) is a direct answer to that call. It integrates cyclone centrifugal separation, ultra-fine bubble generation and coalescence demulsification, and through independently developed flow-field design and manufacturing achieves a step change in oily wastewater treatment efficiency.

Ultra-fine bubbles

Using patented dissolved-air release technology, CDFU generates ultra-fine bubbles with a diameter of only 5-30 μm. Conventional flotation works with bubbles in the hundreds of micrometres to millimetre range. The finer bubbles carry a much larger specific surface area and stay in suspension longer, so capture efficiency for tiny emulsified oil droplets - including the stubborn fraction at a particle size of 2 μm or below - multiplies. That is what breaks the traditional flotation bottleneck on fine oil.

Cyclone field enhancement

Unlike the static separation of a conventional flotation tank, the CDFU influent enters tangentially and forms a high-speed rotating flow field. Heavy suspended solids are thrown to the periphery and settle quickly. More importantly, the collision probability between oil droplets and micro-bubbles rises sharply inside the cyclone field, forming a stable oil-gas-solid composite that floats rapidly. The synergy cuts hydraulic retention time from the traditional 15-40 minutes down to 1-5 minutes and lifts treatment efficiency by 3-8 times.

Purely physical demulsification

The strong shear generated by the cyclone field, combined with interfacial adsorption by the micro-bubbles, achieves demulsification without chemistry. No demulsifier and no flocculant are added at any point, so oily chemical sludge is never produced in the first place.

What the Field Record Shows

At a CNPC petrochemical electro-desalting wastewater treatment project, the core process adopted a two-stage CDFU arrangement at a treatment scale of 2400 m3/d. Electro-desalting cut water carries high oil content and strong emulsification; the two-stage CDFU train ran stably under purely physical, chemical-free conditions, with effluent oil content meeting design requirements consistently. It also removed a downstream shock problem that had troubled the site's sewage plant for years, and delivered a synergistic removal effect on harmful gases such as hydrogen sulfide.

High-Tech, High-Efficiency, High-Quality

Measured against the new quality productive forces yardstick that now defines industrial upgrading, the technology reads as follows:

• High-tech: interdisciplinary innovation across fluid mechanics, interface science and materials science, forming a core technology group with independent intellectual property.
• High-efficiency: hydraulic retention time shortened to 1/8-1/3 of traditional processes, footprint reduced by more than 70 percent, unit treatment energy consumption down significantly.
• High-quality: single-stage oil removal efficiency above 90 percent, suspended solids removal above 85 percent, and effluent oil content held stably at <10 mg/L, in some cases <5 mg/L, meeting high-standard reinjection or discharge requirements.
• Green and low-carbon: the zero-agent process eliminates chemical sludge entirely, and fully enclosed operation means no waste gas leakage.

Where This Leaves the Sector

From reliance on imports to independent innovation, from technology follower to industry leader, the trajectory of SINOKLE CDFU mirrors a broader shift in manufacturing. It demonstrates that domestic equipment can replace imports outright and, on complex working conditions and environmental performance, go further than what it replaced.

The next step is application breadth rather than performance. Using CDFU as the core technology platform, the work now extends into refining, oilfields, coal chemical industry and landfill leachate, with the aim of serving global customers and keeping the environmental side of energy production honest.