Refinery Circulating Water Oil Leaks: Sizing a Pressure-Type Coalescing Separator

To address the pain points of refining enterprises' circulating cooling water systems, namely oil pollution caused by heat exchanger leakage and the easy clogging and frequent backwashing of traditional filtration equipment, SINOKLE Technology has launched the pressure-type coalescing oil separator. The technology uses the physical coalescence principle to achieve efficient oil-water separation without adding chemical agents, providing a green, low-consumption solution for refinery circulating water systems.

Why the circulating water loop keeps getting dirty

Refinery circulating water systems mostly adopt closed or open designs. Although the closed system theoretically loses little water, it still faces multiple pollution risks in actual operation.

Oil intrusion is the headline one: leakage of heat exchangers, maintenance errors and similar causes let oil such as crude oil and diesel mix into the circulating water, with concentrations reaching above 2000 mg/L, forming multi-phase pollutants such as dissolved oil and emulsified oil. Microbial growth follows, with anaerobic bacteria such as sulfate-reducing bacteria multiplying in dead corners and producing corrosive substances such as hydrogen sulfide, accelerating pipeline corrosion. Suspended solids accumulation adds to it, with corrosion products such as iron oxide and sediment depositing, reducing water flow velocity and increasing energy consumption.

These pollutants act synergistically, leading to decreased system efficiency and rising maintenance costs. In particular, oil pollutants easily adhere to equipment surfaces, forming an insulation layer that reduces the heat transfer coefficient of heat exchangers by more than 30%. That heat-transfer penalty is usually what finally gets a project funded, not the discharge permit.

What the separator actually does

The pressure-type coalescing oil separator is a high-efficiency device integrating cyclone centrifugation, coalescence by coarse-grained media, and shallow-pool separation, with core technology based on Stokes' law and fluid dynamics optimization. Three mechanisms carry the work.

Coalescence effect: using patented fillers with a specific surface area of at least 350 m2/m3, the surface energy difference promotes the collision and coalescence of micron-scale oil droplets, increasing the particle size from <30 um to the millimeter level, accelerating flotation separation.

Shallow-pool separation principle: optimize the flow channel design, extend the residence time of oil droplets, and achieve rapid oil-water stratification under gravity.

CFD flow field optimization: through computational fluid dynamics simulation, eliminate short-circuit flow and eddies, ensure laminar flow, and improve separation efficiency by more than 20%.

The equipment structure includes an inlet cyclone device, a coalescing filler zone, an oil collection package, and a backwash system. The inlet cyclone unit pre-separates large oil droplets through centrifugal force, reducing the downstream load; the coalescing filler is made of 316L stainless steel, which is corrosion-resistant and has a service life of more than 5 years; the oil collection package is equipped with an interface meter to realize automatic discharge of waste oil. This design enables the equipment to stably reduce the effluent oil concentration to 100 mg/L or less when the influent oil concentration is 2000 mg/L or less, with a removal rate exceeding 95%.

Four stages, fully enclosed

Aiming at the characteristics of refinery circulating water, the pressure-type coalescing oil separation system adopts a four-stage treatment unit to achieve fully enclosed automated operation throughout.

Influent pre-treatment: the circulating water enters the oil separator under pressure, and the inlet cyclone device preliminarily separates more than 50% of the dispersed oil. Coalescing separation: the water flows through the high-efficiency filler layer, the oil droplets coalesce and float up to the oil collection package, and the design flow velocity of the filler zone is 10 m/h or less, ensuring sufficient contact time. Waste oil recovery: the waste oil in the oil collection package, with water content of 10% or less, is automatically discharged to the collection tank through interface meter control, and sent out for treatment by a lift pump. Backwash mechanism: a backwash is initiated once a month using the system's own circulating water, without external water source, and the backwash wastewater is self-pressurized and discharged into the sewage system.

The system integrates PLC control, monitoring pressure, flow, oil-water interface and other parameters in real time, with automatic alarm for abnormal conditions.

Advantages against sand filtration and flotation

Compared with traditional quartz sand filter or flotation processes, the pressure-type coalescing oil separator has significant advantages. High efficiency and energy saving: a single unit can treat up to 500 m3/h, with fewer moving equipment and supporting facilities, saving 30% electricity compared with traditional technology. Compact footprint: modular skid-mounted design, suitable for refineries with limited space. Long-period operation: filler life above 5 years, backwash cycle extended to 30 days, reducing maintenance costs. Full automation: one-click start and stop through the DCS or PLC system, no manual intervention required, reducing operational risks.

The innovation lies in the integration of cyclone pre-separation and coalescence amplification technology, overcoming the difficulty of emulsified oil treatment. The equipment adopts a bidirectional flow design internally, and the oil droplet removal rate is insensitive to the particle size distribution, with a removal effect of more than 90% even for emulsified oil of <10 um. Insensitivity to droplet size distribution is the property that matters most in a refinery, because a leak does not deliver a steady droplet spectrum.

With increasingly stringent environmental regulations, refining enterprises have put forward higher requirements for the greening and resource utilization of circulating water treatment. The pressure-type coalescing oil separator, with its purely physical oil removal, no chemical addition, and long-period operation features, not only solves the safety hazards of the cooling system but also reduces the full-life-cycle operation and maintenance costs for enterprises.