How a Coalescing Oil Separator Works: The Core Logic of Industrial Oil-Water Separation
The coalescing pressure deoiler is a special device for purifying oil-containing liquids. Its core function is to efficiently separate suspended oil and fine solid impurities from liquids. With stable treatment performance and strong adaptability, it is widely used in liquid transmission and wastewater treatment systems in many industries such as petrochemicals, metallurgy and power, textile and dyeing, and food processing. Breaking through the limitations of traditional oil removal technology, the device combines the coalescence (coarse-graining) principle and the shallow-tank principle, and uses CFD simulation technology to optimize the tank structure and internal flow field design, so that the oil-water mixture can complete rapid coalescence and separation under pressure, ultimately achieving liquid purification. The core logic of its working principle is to increase the oil droplet size, shorten the separation path, and enhance the collision and coalescence probability through multiple technical means, thereby completing oil-water separation efficiently.
Coalescing Pressure Deoiler Project Site Built by SINOKLE for a Petrochemical Enterprise
The tank structure of the coalescing pressure deoiler is precisely optimized. The interior is mainly divided into three functional zones—the inlet pre-separation zone, the primary separation zone, and the main separation zone—forming a progressive separation process. The inlet pre-separation zone is equipped with a specially designed cyclonic separation device, which first performs preliminary treatment of the oil-containing liquid, separating out larger oil droplets and solid impurities and reducing the treatment load of subsequent separation units. The primary separation zone and the main separation zone are filled with coalescing packing of different specifications to targetedly treat fine oil droplets of different particle sizes. An oil collecting sump is provided at the top of the tank to collect the separated oil and discharge it in a centralized manner. The bottom is equipped with an efficient sand-flushing and desilting device, which can timely remove deposited solid impurities, avoid equipment blockage, and ensure long-term stable operation.
I. Core Working Principles
1. Coarse-graining (coalescence) principle: the basis for small oil droplets to "cluster"
Coarse-graining is the core prerequisite for the coalescing pressure deoiler to achieve oil-water separation. Its principle is based on the significant difference in affinity between the oil and water phases for the coalescing material. When oily wastewater flows through the bed filled with coalescing material, because the affinity of the coalescing material for the oil phase is much greater than that for the water phase, fine oil droplets will be captured by the material surface and retained in the pores and on the surface of the material. As the number of captured oil droplets keeps increasing, adjacent oil droplets will deform in shape and then merge and coalesce with each other into larger oil droplets.
According to Stokes' law, the floating velocity of an oil particle in water is proportional to the square of its diameter. For a specific oily wastewater at constant temperature, its dynamic viscosity, the densities of water and oil, and the gravitational acceleration are all fixed values, so the floating velocity can be simplified as a function only related to the oil droplet diameter. This means that the floating velocity of coalesced large oil droplets will increase geometrically, greatly reducing the difficulty of subsequent separation and laying the foundation for efficient oil removal. The core object of coarse-graining treatment is the dispersed oil in water, and the whole process is an organic combination of coarse-graining capture and subsequent settling separation.
2. Shallow-tank principle: the "key" to improving separation efficiency
The shallow-tank theory proposed by Hazen in the 20th century provides key theoretical support for the structural optimization of the coalescing pressure deoiler. The theory points out that, under ideal conditions, the ratio of tank length L to tank depth H of a sedimentation tank equals the ratio of the horizontal flow velocity v to the particle settling velocity μ0, i.e., L/H = v/μ0. It can be inferred that when the tank length L and the flow velocity v remain constant, the smaller the tank depth H, the smaller the particle size of suspended particles (or oil droplets) that can be removed. If horizontal baffles are used to divide the tank depth H into n layers, with the particle settling velocity μ0 and the flow velocity v unchanged, only 1/n of the original tank length is needed to remove particles of the same size, and the total volume can be reduced to 1/n of the original; if the tank length remains unchanged, after the depth is reduced, the flow velocity can be increased n times, and the treatment capacity increases n times accordingly.
Specifically for the oil droplet removal efficiency, its calculation formula shows that the removal efficiency is only related to the oil droplet diameter, the physical properties of oil and water, the treatment capacity, and the floating area, and is independent of the floating height—this is exactly the core connotation of the shallow-tank principle. By virtue of this principle, the coalescing pressure deoiler shortens the oil droplet floating height through a multi-layer separation structure, significantly improving the oil droplet removal efficiency, while greatly increasing the treatment capacity of the equipment at the same volume.
3. Enhanced coalescence by the coalescing packing
On the basis of the coarse-graining principle and the shallow-tank principle, the coalescing pressure deoiler adopts multi-layer corrugated plates (or inclined plates) as the coalescing packing. The design of this packing can not only shorten the oil droplet floating height, but also enhance the collision and coalescence of oil droplets through the special flow channel structure. When the oil-water mixture flows in the plate pack, the corrugated flow channels make the flow cross-section change constantly, so that the fluid velocity alternates between high and low and the flow direction changes frequently. This unstable flow state greatly increases the collision probability between small oil droplets, prompting them to continuously coalesce and grow.
Meanwhile, based on the affinity of the coalescing material for the oil phase, oil droplets will form an oil film on the lower surface of the corrugated plates through wetting, adsorption, and other actions. Driven by gravity and fluid thrust, the oil film moves and converges along the plate surface, and finally detaches to form larger oil masses; the water phase settles under gravity and flows to the upper surface of the lower-layer corrugated plates to continue separation. Through this process, the oil and water phases achieve rapid and efficient separation, further improving the purification effect of the equipment.
II. Evidence from Practical Applications
In a refinery wastewater treatment project of a coastal petrochemical enterprise, a combined treatment process with the coalescing pressure deoiler as the core was adopted for the oily wastewater discharged from the units (inlet oil content 3%~8%, treatment capacity 200 m³/h). The project was put into operation in March 2024. Using the above working principles, the coalescing pressure deoiler first coalesces and separates most of the oil, followed by deep treatment units. The final effluent oil content is stably reduced to below 100 ppm, meeting the national industrial wastewater discharge standard and ensuring the stable operation of subsequent production processes and the safety of the surrounding water environment.
In summary, the coalescing pressure deoiler achieves the preliminary coalescence of small oil droplets through the coarse-graining principle, optimizes the separation structure to improve efficiency relying on the shallow-tank principle, enhances collision coalescence with special coalescing packing, and is complemented by a scientific tank zoning design, forming an efficient and stable oil-water separation system. The systematic and synergistic nature of its working principle makes it play an irreplaceable role in the treatment of oil-containing liquids in various industries, providing important technical support for green industrial production.
