Components and stages of an oil water separator

During the process of generating compressed air, condensate (water vapor) is produced. This moisture contains traces of oil and other contaminants. To protect the environment and your equipment, condensate must be treated. After the oil is filtered out, it needs to be separated before it can be safely disposed of.

As you might expect, this is where the oil water separator comes in. This equipment separates water and oil within condensate to prevent oil from ending up in the environment.

In this article, we will discuss how separators work and why they are essential for legal compliance and environmental protection. When it comes to oil water separation, the more condensate that's purified before it reaches groundwater, the better for the planet.

While the experiment mentioned above demonstrates that oil and water don't mix, it doesn't mean oil can be skimmed off the top. This is why oil-water separation in compressed air systems is necessary for meeting legal regulations and minimizing environmental impact.

The good news is separators can eliminate approximately 99.5% of oil found in compressed air water vapor. Now let’s take a closer look at how an oil-water separator works.

As you might imagine, there are differences between oil water separator brands and types. However, most involve multi-stage filtration and the principle of adsorption. Adsorption is a surface phenomenon where oil simply settles on the surface due to its lower density than water.

To treat condensate, separators often use two or three stages of filtration which rely on different filtration media. Let’s go over each stage to better understand how a compressor’s condensate is treated.

The oil containing condensate from a compressor flows under pressure into the separator. It moves through a first-stage filter, which is usually a pre-filter. A pressure relief vent typically helps reduce the pressure and avoid turbulence in the separator tank. This allows the gravitational separation of free oils.

First-stage filters typically consist of polypropylene fibers that adsorb the oil, but not the water. This means oil droplets will stick to the surface of the propylene fibers. Due to their oil-attracting characteristics, these are known as "oleophilic" fibers. This type of filtration media usually floats on the surface of the water. However, as it gets heavier, it adsorbs oil droplets, sinking deeper near the end of its service life.

After the first-stage filtration, the condensate flows through the main filters. These include second-stage and sometimes third-stage filters. They often rely on activated carbon (or organoclay for stronger emulsions) to purify and "polish" the condensate. Essentially, depending on the type and size of the separator, condensate will undergo one or two consecutive stages of filtration with activated carbon/organoclay.

At the end of this process, the remaining oil residues in the condensate are collected. At an ambient temperature of 20 ℃ containing 1-2 g/m3 of oil after the first stage, there is around 2-3 mg/m3 of oil after separation.

The remaining water is sufficiently free from contaminants and can be safely discharged into the sewer system. The oil water separator has done its job. In the end, everybody benefits. The company has followed regulations, avoiding fines while protecting the environment.