Desalter Oily Wastewater Treatment Technology Explained

Treatment challenges

Extremely high oil concentration: in wastewater discharged from desalters, normal oil content ranges from 200 mg/L to 10,000 mg/L, and under abnormal conditions can exceed 10% or even reach 50%, posing a severe test for treatment systems.

Diverse crude oil sources and properties: crude oil is purchased from a wide range of domestic and international production areas, with many types and complex compositions — including light oil, condensate, heavy oil and various non-hydrocarbon compounds.

Pronounced emulsification: chemicals dosed during extraction, such as paraffin removers, paraffin inhibitors and demulsifiers, degrade oil quality and form stable emulsions that remain difficult to separate even after prolonged settling.

Innovative technical solution

High-efficiency coalescing pressure de-oiling unit: this equipment uses a bidirectional flow design and CFD-optimised flow field distribution to achieve efficient oil-water separation. The overall structure is compact, operation is simple, and safety and reliability are outstanding.

Cyclonic dissolved gas flotation system: this unit combines the principles of cyclonic centrifugal separation and dissolved gas flotation, offering excellent de-oiling performance, a small footprint and stable operation, and can effectively handle all kinds of difficult oily wastewater.

Practical applications

The technology has been successfully applied at Sinopec Cangzhou Petrochemical, PetroChina Sichuan Petrochemical and other enterprises, using the combined process of coalescing pressure de-oiling unit and cyclonic dissolved gas flotation to treat desalter wastewater. PetroChina Changqing Petrochemical and Dushanzi Petrochemical have also adopted the cyclonic dissolved gas flotation technology alone for similar units. Practice shows that the technology delivers remarkable treatment results, with effluent oil content stably below 150 mg/L and good resistance to load fluctuations.

The process flow is as follows:

Technical advantages

Outstanding removal performance: single-stage treatment efficiency exceeds 90%, the smallest separable oil droplet size is no less than 0.3 microns, and the hydraulic retention time is short — only 1 to 5 minutes;

Small space requirement: equipment volume and weight are significantly reduced, with a footprint only 1/8 to 1/3 that of conventional dissolved gas flotation systems;

Strong shock resistance: the dual tangential inlet design enhances rotational flow velocity and centrifugal force, giving the system higher adaptability;

Good operational stability: strong adaptability under varying influent loads, oil viscosity and oil content conditions;

Simple operation and maintenance: simple structural design, few moving parts, quick installation and low daily operating and maintenance costs;

Excellent treatment results: compact construction, high removal of emulsified oil and fine suspended solids, no chemical dosing required and low scum generation;

High degree of automation: fully enclosed pressurised operation with automatic control, pressure-driven oil and sludge discharge and no mechanical power requirement;

The technology is particularly suitable for treating high-oil-content wastewater generated by desalting units in refining and chemical enterprises.