Desalter Effluent Treatment Process

Desalter effluent treatment is a key environmental step in refineries, dealing with the high-oil, heavily emulsified wastewater discharged by the desalting unit. The main current technologies and trends are as follows:

1. Limitations of conventional processes

The conventional tank-in-tank gravity settling process relies on natural separation by oil-water density difference and has the following drawbacks:

• Low separation efficiency on heavily emulsified water, with effluent oil often exceeding limits (up to more than 5000mg/L)

• A semi-enclosed structure that readily allows hazardous gases such as hydrogen sulphide to leak

• A large footprint and high energy consumption, with manual tank cleaning required

2. Emerging treatment technologies

1. Cyclonic dissolved-air flotation (CDFU)

): combining cyclonic centrifugation with dissolved-air flotation, it uses microbubbles (5-30µm) that attach to oil droplets for efficient separation. Demulsification and de-oiling are purely physical with no chemicals, sludge volume is greatly reduced and the recovered oil can be reprocessed, delivering both environmental and economic benefits.

Typical case: after adoption at Sinopec Cangzhou Branch, effluent oil fell from ≤20000ppm to ≤100ppm

Advantages: strong shock resistance (handles 10%-120% flow fluctuation) and a compact skid-mounted footprint

2. Coalescing oil remover +CDFU combined process

A purely physical technology developed by SINOKLE, in which the coalescing pressure oil remover (capturing 0.1µm droplets) works together with cyclonic dissolved-air flotation

The PetroChina Sichuan Petrochemical project achieved 95% oil removal and recovers 864 tonnes of crude a year

A fully enclosed design eliminates waste gas leaks and no chemical demulsifier is needed

Desalter effluent treatment project of a Hebei petrochemical company

3. Technology comparison

4. Industry application trends

Sinopec and PetroChina are fully rolling out CDFU cyclonic dissolved-air flotation to replace conventional processes

EDI (continuous electrodeionisation) is beginning to be used for ultrapure water, but physical separation still dominates in refining

Future direction: integrated intelligent control systems and resource recovery of waste oil