API oil–water separator

API oil–water separator is a device designed to separate gross amounts of oil and suspended solids from the water in industrial and environmental applications. The API separator is one of the oldest and most common types of oil-water separators used globally. It utilizes the difference in density between oil and water to facilitate the separation process. The name "API" refers to the American Petroleum Institute, which first published the design specifications for these separators.

Design and Operation

The design of an API oil-water separator is relatively simple and is based on Stokes' Law, which predicts the rise velocity of oil droplets based on their density and size, the density and viscosity of the water, and the force of gravity. The separators are typically large rectangular tanks that allow for the slow flow of oily water through the tank. As the water flows, oil droplets rise to the surface due to their lower density compared to water. A series of baffles or weirs may be used to collect and remove the accumulated oil from the surface of the water.

The effectiveness of an API separator depends on several factors, including the size of the oil droplets, the temperature of the incoming water (which affects oil viscosity and water density), and the presence of other substances that may stabilize the oil droplets in suspension. Generally, API separators are designed to remove oil droplets larger than 150 micrometers in diameter.

Applications

API oil-water separators are widely used in a variety of industries, including:

• Petroleum refining
• Petrochemical and chemical plants
• Natural gas processing plants
• Power generation facilities

They are particularly suited for treating large volumes of water containing relatively low concentrations of oil. API separators are often used as a preliminary treatment step, reducing the oil load on more sophisticated downstream treatment processes such as dissolved air flotation (DAF), biological treatment, and filtration.

Maintenance and Limitations

Regular maintenance is crucial for the efficient operation of an API separator. This includes the removal of accumulated oil and sludge from the separator to prevent the reduction of the effective volume of the tank and to maintain the designed flow path of the water. Limitations of API separators include their inability to effectively remove small oil droplets and emulsified oils without the addition of chemical flocculants or coagulants to increase droplet size.

Environmental Impact

The use of API oil-water separators plays a significant role in preventing oil pollution in water bodies. By removing oil from wastewater before it is discharged, these separators help protect aquatic ecosystems and comply with environmental regulations. However, the separated oil and sludge require proper disposal or further treatment to minimize environmental impact.

Regulations

In many countries, the discharge of oil-contaminated water is regulated by environmental agencies. The efficiency of oil-water separation, as well as the quality of the effluent, must meet specific standards. For example, in the United States, the Environmental Protection Agency (EPA) sets limits on the amount of oil and grease that can be discharged into navigable waters or onto adjoining shorelines.

Conclusion

The API oil-water separator is a crucial component in managing oil-contaminated wastewater in various industrial processes. Its simple design and operation make it an effective solution for preliminary oil removal. However, to meet stringent environmental standards and achieve higher levels of purification, API separators are often used in conjunction with other treatment technologies.

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