Overhead Sour Water Treatment Technology for Greener Refining

Overhead sour water from the atmospheric and vacuum distillation unit is a difficult refinery wastewater: complex in composition, high in pollutant concentration and hard to treat. It contains large amounts of hydrogen sulphide, ammonia nitrogen and volatile phenols, and the oil is heavily emulsified, so conventional processes rarely achieve stable compliance.

Technical bottlenecks of conventional processes

The industry generally uses gravity settling for overhead sour water, relying on natural oil-water separation with settling times of 50-70 hours, and its separation effect on heavily emulsified oily wastewater is limited. Conventional equipment is usually open or semi-enclosed, so acidic gases such as hydrogen sulphide easily escape, creating safety and environmental risks. Conventional processes also have a large footprint, high investment and depend entirely on manual operation, with heavy cleaning and maintenance work.

Some companies have tried cyclonic de-oiling. Although better than gravity settling, it still performs poorly because emulsified oil droplets are small and close to water in density. The process has weak shock resistance and unstable operation, and cyclones plug easily, pushing up maintenance costs.

Innovative technical solution

Developed by SINOKLE, the CDFU cyclonic dissolved-air flotation + high-efficiency coalescing oil removal combination provides a completely new solution for overhead sour water. The technology organically integrates centrifugal separation, dissolved-air flotation and coalescing oil removal into an efficient multi-stage treatment system.

Schematic of SINOKLE's overhead sour wastewater treatment process

Core technical features:

· CDFU unit uses cyclonic pre-separation together with microbubble flotation, with bubble diameter controlled at 5-30 microns, greatly improving contact efficiency with oil droplets

· The high-efficiency coalescing oil remover uses special media to coalesce droplets rapidly, removing particles down to 2µm

· Purely physical demulsification with no chemical dosing, avoiding secondary pollution

· Fully enclosed pressurised operation prevents acidic gas leakage and ensures safety

Field performance verification

In practice the combination shows excellent performance. In 2021, a Luoyang petrochemical company treated sour wastewater with the CDFU cyclonic dissolved-air flotation + high-efficiency coalescing oil removal process at 15m3/h. With average influent oil content of 15%, effluent oil stayed below 50mg/L, an oil removal efficiency of 99.96%.

Sour water treatment unit at a Luoyang petrochemical company

The technology uses a skid-mounted design with a high degree of automatic control. The system is equipped with intelligent monitoring that adjusts operating parameters in real time to cope with water quality fluctuations, greatly reducing manual work. Compared with conventional processes, operating costs fall by about 30%, and the recovered oil is of high quality and can be returned directly to the production process.

Technical advantages and economic benefits

Treatment efficiency: residence time of only 1-5 minutes and a footprint only 10% of conventional processes, far faster than conventional equipment. Single-stage oil removal exceeds 90% and suspended solids removal exceeds 85%, with effluent oil kept consistently low.

Operating cost: purely physical demulsification means no chemicals and few moving parts, so maintenance costs are relatively low. The intelligent control system supports remote monitoring and unattended operation, further cutting labour costs.

Safety and environment: the fully enclosed design eliminates gas leakage and produces no oily sludge, achieving genuinely green treatment. The equipment has strong shock resistance and handles 10%-120% flow fluctuation while keeping effluent stable.

Application prospects

With environmental requirements tightening, overhead sour water treatment has become an unavoidable issue for refiners. SINOKLE's CDFU cyclonic dissolved-air flotation + high-efficiency coalescing oil removal technology, with its efficiency, stability and environmental performance, provides the industry with a reliable solution. It has already been applied successfully at Sinopec, PetroChina and other major companies, with results proven in practice.