Desalting Wastewater at 100,000 mg/L of Oil: A Purely Physical Route That Holds Up
Before crude oil can be distilled, it must be washed. Electric desalting equipment strips out the salts - chlorides such as sodium chloride, magnesium chloride and calcium chloride - along with the water dissolved or emulsified in the crude, and the wastewater that process generates is desalting wastewater. It arrives loaded: oil content runs high, with the oil phase volume fraction exceeding 10% in severe cases, droplets are fine, and a large load of fine suspended solids rides along with the oil. Organic concentration is elevated, carrying volatile phenols and petroleum substances, and salinity measured as chloride ions typically falls between 2,000-5,000 mg/L.
Why the stream keeps getting worse
Crude quality has been sliding heavier and more inferior for years, and refiners compensate by injecting more water and more agent to keep recovery and transportation efficiency acceptable. Every increase in injection widens the volume and complexity of the desalting wastewater stream. Composition that was once merely difficult is now genuinely variable: emulsion stability shifts with the crude, solids loading spikes with the slate, and a treatment design tuned for last year's feed can find itself out of range this quarter.
The salt problem behind the oil problem
Oil gets the attention, but the chlorides explain why desalting wastewater cannot simply be recycled back into ordinary water systems. Sodium, magnesium and calcium chlorides at thousands of milligrams per litre corrode equipment, poison biological treatment and upset downstream water balances. The desalter exists precisely to move these salts out of the crude, which means the wastewater it produces is their unavoidable destination. Any treatment route must therefore tolerate saline feed without fouling, corroding or losing efficiency - a constraint that quietly eliminates many surface-treatment-based technologies and favors robust physical separation in pressure vessels built for refinery service.
The treatment route SINOKLE built for it
Shenzhen SINOKLE Technology Co., Ltd. answers this stream with an integrated scheme combining a coalescing separator with CDFU technology, purpose-built for desalting oily wastewater. The design premise is purely physical separation, and everything else follows from it.
Oil removal runs above 95%, achieved without any chemical addition: demulsification and oil separation happen through physics, not reagents. Because no chemicals are involved, the recovered oil retains good quality and can be directed straight back into refining - converting the worst stream in the plant into a small feed contribution. No oily sludge is produced either, which removes the hazardous-waste handling burden at the source and relieves environmental pressure while creating economic value.
The hardware side matches the process logic. The flow sheet is short, equipment structure compact, and the footprint small; the unit is skid-mounted and highly automated, straightforward to operate and maintain, with a short construction and installation period. Shock resistance is built in, so the system runs smoothly through the feed fluctuations that define desalting service.
Where this stream fits in the refinery water map
Context helps when planning an installation. Desalting wastewater usually arrives together with other refinery sour streams, and its extreme oil loading makes it the stream that sets the design point for upstream de-oiling. Sizing the first physical separation stage for desalting duty, then routing the remaining waters through the same train, is the pattern the verified projects above follow: one robust stage absorbs the worst feed the plant can produce, and everything downstream runs easier as a result. Refineries planning crude slate changes or capacity increases should treat this stream as the anchor case for their water system upgrades, since a route proven at 100,000 mg/L of inlet oil will view every other refinery wastewater as light duty.
Verified under real feed conditions
Laboratory claims mean little against a stream this aggressive, so the decisive evidence comes from operating plants. At a petrochemical enterprise desalting wastewater treatment project, actual operation verified that the process removes more than 95% of oil and suspended solids from refinery sour water entering the system.
The verified envelope deserves attention. When influent oil runs as high as 100,000 mg/L - a concentration at which the stream is more emulsion than water - and suspended solids reach 2,000 mg/L, effluent oil and suspended solids both hold below 150 mg/L. Holding that boundary across such an extreme inlet range is what qualifies the route for desalting duty, where feed conditions are set by the crude market rather than by the water plant.
What refiners gain operationally
- Compliance without reagents. Chemical-free operation removes dosing control from the list of variables that can push effluent out of spec.
- Oil back into the process. Recovered crude of good quality returns directly to refining, a small but continuous credit against operating cost.
- No sludge contract. With no oily sludge generated, disposal liabilities and their paperwork disappear.
- Fast installation. Skid-mounted, automated equipment with a short construction period fits into live refineries without extended shutdown.
The wider significance
Desalting wastewater concentrates every difficulty a refinery water system faces - extreme oil loading, fine emulsions, high salinity and variable composition - into one stream. A treatment route that masters it on purely physical principles has essentially passed the hardest test oily water treatment offers. For refineries processing heavier crude slates, the combination of a coalescing separator with CDFU provides a stable, verifiable answer that keeps both the discharge compliant and the recovered oil productive.