Electric Desalting Wastewater as a Profit Point: A Purely Physical Separation Route

The Cost Centre Nobody Questions

In the refining and petrochemical industry, the treatment of drained water from electric desalting units has long been a recognized difficult problem. This wastewater is severely emulsified, its oil content fluctuates sharply, and it is rich in various refractory pollutants. Every one of those three characteristics works against a conventional process, and they arrive together rather than in turn.

Traditional processes relying on gravity settling or chemical demulsification not only have limited separation performance and unstable effluent quality, but also produce high-water-content waste oil, large amounts of hazardous waste (oily sludge), and continuous chemical consumption, all of which ultimately translate into high long-term operating costs and environmental pressure for the enterprise. The pattern is familiar across the industry: the treatment step is treated as an unavoidable cost, budgeted annually, and never examined for whether it could be operated differently.

The Reframing That Changes the Design

Faced with this industry pain point, SINOKLE, drawing on deep industry insight and continuous technological innovation, has proposed a disruptive solution: centering on pure-physical separation technology and turning wastewater treatment from a cost center into a profit growth point.

That reframing is not marketing language. It follows directly from a technical property of the physical route. Chemical demulsification degrades the oil it recovers, because flocculant and demulsifier remain mixed into the oil phase. A physical route does not, so the recovered oil can be returned to the refinery slate. Once the recovered stream has value, the economics of the treatment step change category — the largest recurring cost becomes a partial offset rather than a pure expense.

The Technological Cornerstone

The core of the electric desalting wastewater treatment solution developed by SINOKLE lies in adopting a pure-physical process route that combines "high-efficiency coalescing de-oiling" and "CDFU swirl dissolved air flotation". The technology eliminates the addition of chemical agents and, through the precise synergy of multiple physical effects such as coalescence, swirl centrifugation, and micro-bubble flotation, achieves efficient separation.

Why the Swirl Stage Protects the Flotation Stage

Sequence matters more here than it does in most combined processes. If flotation ran first, it would be asked to lift droplets of a size that flotation handles poorly, and the air demand would rise until the saturator became the limiting unit. Running coalescence and swirl concentration ahead of it means the flotation stage receives an oil phase that is already enlarged and already concentrated toward the vessel axis. The same flotation performance is then achieved with a smaller recycle flow and a lower saturator pressure. That is the mechanism behind the energy saving the route claims — it comes from resequencing the duties, not from any single high-efficiency component.

The three effects are sequenced deliberately rather than run in parallel.

• Coalescence comes first. Fine droplets meet on an oleophilic surface, the interfacial film is disrupted by contact, and droplets merge into a size that buoyancy can act on.
• Swirl centrifugation concentrates the enlarged oil phase toward the axis of the vessel, so the flotation stage receives a feed already enriched in oil rather than a dilute dispersion.
• Micro-bubble flotation finishes the job, attaching gas to the remaining droplets and lifting them clear of the water phase.

What the Refinery Gets Back

Four differences show up in operation. No chemical procurement line appears in the budget. No oily sludge leaves the site as regulated hazardous waste. The recovered oil has value rather than a disposal cost. And effluent quality becomes consistent, because the process no longer depends on how accurately an operator judged the dose required for an unpredictable feed.

What the Route Delivers in Numbers

The case rests on specific figures. Inlet oil content from an electric desalting unit can reach 2,000 ppm and, during heavy desalting campaigns, 10 ppm in the treated stream is the level the refinery expects to sustain, while a severely emulsified batch may carry 20,000 ppm before treatment. A train sized for 100 m3/h covers the drained-water load of a large single-train desalting unit without a parallel standby.

The absence of reagents is what keeps O&M demand low. No chemical storage, no dosing pumps, no prepared solution line, and no reagent procurement contract. Maintenance is limited to periodic inspection of the coalescing internals and the dissolved-gas circuit. For a plant where the treatment step has historically generated a hazardous waste stream, that combination removes both the largest recurring cost and the largest recurring compliance risk in one change.

What to Measure When Evaluating the Route

Four figures tell the whole story on an operating desalting unit. The mass of chemical reagent consumed per cubic metre treated. The tonnage of oily sludge leaving site each year and what disposal costs per tonne. The volume and quality of recovered oil returned to the slate. And the variability of effluent oil content rather than its average. The first two fall to near zero on a physical route, the third becomes a positive figure, and the fourth narrows because the process no longer depends on an operator's judgement. Comparing those four numbers between the existing arrangement and a proposed change is a more reliable basis for a decision than any comparison of installed equipment lists.

Applicability and Design Cautions

The route is strongest where emulsification is severe and where the desalting unit is large enough that recovered oil volume is material. It is less compelling on small, lightly loaded streams where the capital cost of additional separation stages cannot be amortised. Two design points deserve early attention: coalescing internals need protection from gross solids carry-over, and the swirl stage requires a pressure profile that the existing pump set can actually supply. Where those are resolved at the design stage, the operating case is unusually clean — a treatment step that meets its environmental obligation while contributing recoverable product instead of regulated waste.