Innovative Electro-Desalting Wastewater Purification for Refineries: Superior Oil Removal, Reliable Discharge
Electro-desalting is a key step in petroleum refining. However, as domestic oilfields continue to be developed and imported crude volumes grow, refineries source crude through increasingly diverse channels with more complex compositions. Meanwhile, as production progresses, crude quality declines and the share of heavy and poor-quality crude keeps rising. To adapt, most refineries blend recovered heavy slop oil back into crude after pretreatment. This improves crude utilization but also intensifies emulsification, posing a significant challenge to electro-desalting.
In actual operation, electro-desalting units often suffer from unsatisfactory demulsification and unstable oil-water interface control due to long-term equipment service, overload operation and non-standard maintenance and operation. As a result, oil content in the discharged water substantially exceeds standards, placing a strong load shock on the downstream wastewater treatment system and wasting large amounts of valuable crude oil.
Electro-desalting oily wastewater currently has several distinctive features: a high proportion of heavy oil whose density is close to that of the wastewater, making separation especially difficult. Oil concentration is extremely high, peaking above 20%, and droplets are fine and severely emulsified, further increasing separation difficulty. There is also a large amount of fine suspended solids, which not only aggravate emulsification but also cause equipment corrosion and clogging. High salinity and high mineralization accelerate corrosion and scaling and also produce harmful gases such as sulphides and volatile phenols, posing potential risks to worker health and the surrounding environment.
Conventional approaches are no longer adequate for electro-desalting oily wastewater. Existing technologies rely mainly on gravity settling and cyclonic centrifugation, yet both have limitations in treatment efficiency, energy consumption and chemical dosing. Gravity settling is simple to operate but its performance fluctuates; cyclonic centrifugation offers higher separation efficiency but consumes more energy and often requires chemical agents.
Oil content in refinery electro-desalting wastewater is high and fluctuates widely, placing extremely high demands on equipment shock resistance. Because emulsification is severe, demulsification is the core step in the treatment flow. Chemical demulsification has limited reliability and does not apply to all cases, making physical demulsification a key direction. Since oil and water densities are similar, separation based on density difference alone cannot meet targets, and more efficient oil-water separation technology is required. In addition, the wastewater is highly corrosive, prone to scaling and carries large amounts of sediment, so equipment must have excellent anti-clogging and sediment removal capability.
To solve these problems, SINOKLE Technology Co., Ltd. has developed an innovative, high-efficiency new electro-desalting wastewater treatment solution through long-term R&D and field testing. The process first cools the oily wastewater cut from electro-desalting through heat exchange, then feeds it to a high-efficiency oil-water separator for primary separation. Inside the separator, free oil, dispersed oil and part of the emulsified oil gather rapidly into larger oil agglomerates, which separate from the wastewater and are discharged through the oil collection chamber. The wastewater after primary separation still contains much emulsified oil, so it is then sent to a high-efficiency cyclonic dissolved gas flotation unit for advanced treatment. There, emulsified oil is adsorbed by fine bubbles and, under cyclonic action, continuously aggregates, merges and demulsifies into oil agglomerates that finally separate from the water. The treated wastewater can then be discharged to the wastewater treatment plant network for further processing.
Schematic of the new electro-desalting wastewater treatment process
The core advantage of this new process is that it breaks away from the traditional mode of separation relying only on the oil-water density difference and instead relies on gas-water and oil-gas-water density differences, so oil removal is essentially unaffected by slop oil density and separation efficiency improves markedly. The solution also uses advanced equipment such as high-efficiency coalescing/corrugated plate pressure oil separators and high-efficiency compact dissolved gas flotation units, featuring high separation efficiency, strong shock resistance, low clogging tendency and low energy consumption.
Electro-desalting wastewater treatment performance (effluent on the left, influent on the right)
The complete process offers high oil removal efficiency, low required working pressure (below 0.15 MPa), low energy consumption and stable, reliable operation. Even when oil content in electro-desalting wastewater fluctuates sharply, the effluent consistently and stably meets the requirements for entry into the wastewater treatment plant (oil content below 100 mg/L).
In addition, the new process enables automatic control with a high level of automation and fully enclosed operation. This not only reduces labour for operation and maintenance but also prevents the escape of harmful gases, minimizing impacts on operators and the surrounding environment. The equipment is reasonably priced with outstanding cost-effectiveness, bringing significant economic and social benefits to enterprises.
