5 Answers You Need to Know When Sizing an Oil Skimmer
Choosing an oil skimmer best suited for your application will maximize oil removal while minimizing initial outlay and oil skimming operation costs.
Capacity should be based on the maximum amount of oil to be removed within the shortest available time. For instance, total oil influx may be 200 gallons in a 24-hour period, which averages about 8.3 gallons per hour. But if most of it comes during a single eight-hour plant shift, you will probably need a removal rate that is three times as high, especially if you are trying to prevent an unwanted discharge of contaminated water to a sewer system. As a rule-of-thumb, specify approximately twice the maximum capacity you anticipate needing for normal conditions.
Oil skimmers usually have an oil removal rate expressed in gallons per hour. The rate varies with oil viscosity, so Abanaki rates skimmers using SAE 30 weight motor oil at 65°F (18°C). It is very important to ask the manufacturer what they are basing their capacities on and get an exact SAE weight or viscosity. Beware of generalities like “a medium weight oil”.
All oil skimmers pick up some water with the oil they remove. Some designs, particularly suction skimmers, pick up more water than others. High water content increases oil recycling and disposal costs. Generally, the ratio of water-to-oil decreases with thicker films of floating oil and slower moving pick-up media. An Oil Concentrator® or decanter installed at the oil skimmer discharge port provides secondary oil/ water separation that can reduce water content to nearly zero.
An oil skimmer continues to remove oils as long as there are oils present. Depending on oil influx rate and the oil skimmer's removal rate, residual oil in the water may be as low as a few parts per million. When residual oil reaches this level and further reduction is required, it may be more practical to use a secondary removal method following skimming, such as membrane filtration.
Oil skimmer portability is a plus in some applications. For example, in plants, mobile equipment service shops, and at remediation sites, a portable oil skimmer can sometimes service multiple machines, sumps, or wells. Portable units usually have a lower removal capacity than stationary units. Also, when you move an oil skimmer it can be dripping water or oil when you remove it, so having a few rags on hand is a good idea.
3 Tank Characteristics to consider in Choosing Oil Skimmers
Choosing an oil skimmer best suited for your application will maximize oil removal while minimizing capital and operational costs. The impoundment capacity, shape, and location of a tank and water impoundment are major factors in choosing the right oil skimmer to lower your costs.
It is critical that oil in the water is given the opportunity to separate. Oil and water can emulsify when subjected to turbulence and other mechanical agitation. Avoid this by having water return to the tank below the liquid surface at as low a velocity as practical. Make sure your tank or sump provides quiet areas, weirs, and sufficient volume to allow adequate time for oil/water separation.
Tanks without nooks and crannies for oil to get stuck in are best. If you have an irregular shape, put the oil skimmer where the largest amount of oil accumulates. Consider a means of directing oil towards the oil skimmer such as a floating boom or baffle plate.
The physical location and characteristics of the tank and collection container are important and it is vital to ask the right questions such as:
- Does skimmed oil need to be pumped from the oil skimmer to the container?
- Will oil skimmer access for periodic maintenance be a problem?
- How much mounting space is available?
- Are tank or container modifications required?
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