High-Efficiency Oil Removal Solution for Refinery Cooling Circulating Water

The refinery cooling circulating water system is a critical component in ensuring the stable operation of production units, with its water quality directly impacting heat exchange efficiency, equipment lifespan, and energy consumption levels. However, circulating water is prone to oil contamination during operation, primarily due to process material leakage, equipment corrosion, and microbial growth. Oil pollutants (including floating oil, dispersed oil, and emulsified oil) not only reduce heat exchange efficiency but can also form bio-slime, accelerating corrosion and leading to unplanned shutdowns. Traditional filtration technologies face challenges such as high backwash frequency and low efficiency, making it difficult to handle high-concentration oil contaminants. This paper, based on advanced water treatment technologies, focuses on the innovative application of pressure coalescing oil separators in refinery cooling water treatment. This technology employs coarse granulation and shallow pool separation principles to achieve efficient oil-water separation, providing reliable support for the long-term, stable operation of the circulating water system.

1. Refinery Cooling Water Pollution Challenges and Treatment Needs

Refinery cooling water systems are often designed as either closed-loop or open-loop systems. While closed-loop systems theoretically minimize water loss, they still face multiple pollution risks during actual operation:

· Oil Invasion: Leaks from heat exchangers, maintenance errors, etc., lead to the introduction of oils (e.g., crude oil, diesel) into the circulating water, with concentrations exceeding 2000 mg/L, forming multi-phase pollutants such as dissolved oil and emulsified oil.

· Microbial Growth: Anaerobic bacteria (e.g., sulfate-reducing bacteria) proliferate in dead zones, producing corrosive substances such as hydrogen sulfide, accelerating pipeline corrosion.

· Suspended Solids Accumulation: Corrosion products (e.g., iron oxide) and sediments accumulate, reducing water flow rates and increasing energy consumption.

These pollutants interact, leading to a decline in system efficiency and rising maintenance costs. Oil pollutants, in particular, tend to adhere to equipment surfaces, forming insulation layers that reduce the heat transfer coefficient of heat exchangers by over 30%. As a result, developing efficient and stable oil removal technologies becomes a core requirement for refinery water treatment. The High-Efficiency Coalescing Pressure Degreaser, using physical separation without chemical additives, offers deep oil removal in line with the principles of a green circular economy.

2. High-Efficiency Coalescing Pressure Degreaser: Technology Principles and Design Innovation

The High-Efficiency Coalescing Pressure Degreaser is a high-efficiency device integrating centrifugal vortex, coarse granulation coalescing, and shallow pool separation. Its core technology is based on Stokes' Law and fluid dynamics optimization:

· Coalescing Granulation Effect: The patented packing material (specific surface area ≥350 m²/m³) promotes the collision and coalescence of micron-sized oil droplets, increasing particle size from <30 μm to millimeter levels, thus accelerating flotation separation.

· Shallow Pool Separation Principle: The optimized flow channel design extends the oil droplet residence time, achieving rapid oil-water separation under gravity.

· CFD Flow Field Optimization: Computational fluid dynamics (CFD) simulation eliminates short-circuiting flow and eddies, ensuring laminar flow and improving separation efficiency by over 20%.

The equipment structure includes an inlet vortex device, coalescing packing area, oil collection tank, and backwash system. The inlet vortex unit pre-separates large oil droplets using centrifugal force, reducing downstream load. The coalescing packing is made of 316L stainless steel, corrosion-resistant and has a service life of more than 5 years. The oil collection tank is equipped with an interface device for automatic oil discharge. With this design, the effluent oil concentration can be stably reduced to ≤100 mg/L when the inlet oil concentration is ≤2000 mg/L, achieving an oil removal rate exceeding 95%.

3. Process Flow and System Integration

The High-Efficiency Coalescing Pressure Degreaser system adopts a four-stage treatment unit, ensuring fully enclosed, automated operation:

· Influent Pre-treatment: The circulating water enters the degreaser under pressure. The inlet vortex device initially separates >50% of the dispersed oil.

· Coalescing Separation: Water flows through the high-efficiency packing layer, where oil droplets coalesce and rise to the oil collection tank. The packing area is designed for a flow velocity ≤10 m/h, ensuring sufficient contact time.

· Oil Recovery: The oil collected in the tank (with water content ≤10%) is automatically discharged into a collection tank via the interface device, then sent for external treatment via a pump.

· Backwash Mechanism: Backwashing is initiated once a month using the system's circulating water, eliminating the need for external water sources. Backwash wastewater is self-pressed and discharged into the sewage system.

The system is PLC-controlled for real-time monitoring of pressure, flow, oil-water interface, and other parameters, with automatic alarm functions for abnormal conditions.

4. Technological Advantages and Innovations

Compared to traditional quartz sand filters or air flotation processes, the High-Efficiency Coalescing Pressure Degreaser offers significant advantages:

· High Efficiency and Energy Saving: The processing capacity of a single unit can reach 500 m³/h, while requiring fewer operating devices and supporting infrastructure, saving 30% more electricity compared to traditional technologies.

· Compact Footprint: The modular skid-mounted design is ideal for refineries with limited space.

· Long Operating Cycle: The packing material lasts for over 5 years, with the backwash cycle extended to 30 days, reducing maintenance costs. 

· Fully Automated: The system can be started and stopped with a single button via the DCS/PLC system, eliminating manual intervention and reducing operational risks.

The integration of vortex pre-separation and coalescing amplification technology overcomes challenges in treating emulsified oils. The internal "bidirectional flow" design makes the oil droplet removal rate less sensitive to particle size distribution, achieving over 90% removal efficiency even for emulsified oils with droplet sizes <10 μm.