About Oil Skimming
Industrial applications of oil skimmers
How to choose an appropriate oil skimmer machine/equipment?
Specifying an oil separation system
What is an oil skimmer?
Skimming is the act of collecting floating oil from a liquid surface. An oil skimmer is a machine that removes floating oil, grease, or fats from any liquid surface. The floating oil sticks to skimming media, such as a belt, tube, rope, mop, or disk.The oil skimmer machine/equipment scrapes off the collected oil from the media. Oil-water separators or coalescers use a floating device and a pump (instead of a media) to collect the surface oil. This oil is then separated using gravity or density difference.
Oil-Water physics
Oil and water do not mix; why this happens is governed by three physical properties:
Specific Gravity
Wikipedia defines specific gravity as- Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest (at 4 °C or 39.2 °F).
Most oils have a lower density than water. Hence their specific gravity is less than 1. Thus, without agitation, oil floats on the surface of water or any water-based solution.
Surface Tension
Wikipedia defines surface tension as Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension allows insects to float and slide on a water surface without becoming even partly submerged.
The cohesive forces of both water and oil drops will counteract each other and makes the oil form small droplets on the water surface.
Immiscibility
Chemistry says ‘like dissolves like’ (non-polar substance dissolve non-polar and polar dissolves polar). Water is polar, and oil is non-polar. Hence, there is no attraction between the molecules, leading to the formation of separate layers.
Oil Skimming
Although designs vary, all oil skimmers rely on specific gravity, surface tension, and a moving medium to remove floating oil from a fluid’s surface.
Floating oil and grease stick to skimming media more readily than water, as the media has more affinity towards oil than water. This allows skimming media in the shape of a belt, disk, drum, etc., to pass through a fluid surface to pick up floating oil and grease with very little water. The scraping mechanism removes this oily material from the media designed according to the type of oil skimming equipment.
Oil skimmers are simple, dependable, and practical tools for removing oil, grease, and other hydrocarbons from water and coolants. Often, an oil skimmer by itself can achieve the desired level of purity.
In more demanding situations, oil skimming is a cost-effective means of removing most of the oil before using more complicated and costly treatments such as membrane filters and chemical processes.
Industrial applications of oil skimmers
Machining Coolants or Cutting Fluids
Coolant is an emulsified solution of water and a particular oil mixed in a specific ratio. Coolant is used while cutting metals using any CNC machine. CNC machines employ various components such as bearings, slides, ball screws, and spindles that require lubrication to function efficiently. Over time, these lubricants find their way to the machine sump, where they mix with the coolant.
When machine coolants become contaminated with tramp oils, four things usually occur:
✔ Coolant life reduction
✔ The quality of machined components is affected
✔ Excessive smoke generation during machining
✔ Foul smell
✔ Skin irritation (Dermatitis) whoever comes in contact
Oil skimmer machines that remove tramp oils solve these problems and typically pay for themselves within a few months.
Degreasing Solution – Component washing
The process of removing grease, dirt, or oil sticking to the component surface either before or after machining is called degreasing. Removing this oil and grease is usually done in a component washing machine that uses a solution of alkaline chemical (kind of soap/detergent) with water. The removed oil/grease then starts floating on the alkaline solution degrading its cleaning properties over time.
Removed quench oils from heat-treated parts by washing can be captured for reuse or disposal. The results are lower quench oil costs, prolonged wash water life, and lower disposal costs.
Coalescer Oil-water separators are most effective for this application.
Degreasing Solution- Surface Pre-treatment for coating
Like component washing, degreasing is the first step in any painting or surface coating process. During this, component that is to be painted or powder coated is thoroughly cleaned by dipping in or spraying the heated degrease solution. Surface pre-treatment removes the grease or oil present on the component surface, making it ready for surface coating.
Innovation Filter System’s Super or Mega Coalescer is a preferred choice for this application.
Steel Mills/Scale Pits
Most steel mills have scale pits in which grease and heavy oils accumulate. To avoid pollution control board fines and expensive sand bed filters, steel mills must limit the amount of fat in wastewater. Reclaimed grease and oil can be reused as furnace fuel, avoiding disposal costs.
Effluent Treatment Plants
Manufacturers need to follow a particular procedure to dispose of all the process fluids after their use. With the pollution norms getting stricter by the day, manufacturers cannot just throw away their oily effluents in the open environment. First it must be treated in an effluent treatment plant or ETP in which the harmful chemicals, agents, oils, grease, etc are removed and better-quality water is then allowed to flow back to the environment.
Innovation Filter System’s tube skimmers are most suitable for this application
How to choose an appropriate oil skimmer machine/equipment?
There are several types of industrial oil skimmers. Choosing one best suited for your application will maximize oil removal while minimizing capital outlay and oil skimmer operating costs. Considerations for selecting an appropriate oil skimmer machine.
Operating Conditions
All oil skimmers have a moving medium and possibly other parts immersed in the liquid. Conditions affecting the performance and life of the skimmer medium, wiper blades, pulleys-
✔ Temperature- ambient as well as of the liquid
✔ The pH of the solution
✔ Presence of solvents or other reactive chemicals
Hazardous Materials
Applications involving flammable materials or explosive vapors require explosion-proof or pneumatic equipment.
Removal Capacity
Oil removal rating
Oil skimmers are designed based on their oil removal rating defined in terms of ‘lit/hr’ of oil removal for skimmers and ‘lit/min’ of oil suction for coalescer type oil-water separators. It is always advisable to consider the highest possible oil addition rate level while designing an oil skimming system.
Allowable water content
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 skimming media.
Oil presence tolerance
An oil skimmer continues to remove oils as long as they are present. Depending on the oil addition 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.
Portability vs. fixed installation
Having a portable oil skimming system is advantageous in some applications like removing tramp oil from machining coolants. A single mobile oil skimming system can cater to the entire shop-floor. However, for specific applications where the oil addition rate is high, it is always advisable to have a dedicated oil skimmer installed on the tank.
Tank Design
The location, shape, and capacity of a tank are significant factors in choosing the right oil skimmer. Water level fluctuations, turbulence also need to be considered while selecting appropriate oil skimming equipment.
Tank size
The primary design parameter to be considered while designing an oil skimmer system is tank size. An oil skimmer designed as per tank size will skim or remove oil even from the tank’s remotest corners with low residual oil accumulation chances.
Turbulence
Oil and water can emulsify when subjected to turbulence and other mechanical agitation. Oil-free water must return to the tank below the liquid surface at as low a velocity as practical to avoid emulsification. Ensure your tank or sump provides quiet areas, weirs, and sufficient volume to allow adequate time for oil/water separation.
Shape
Tanks without nooks and crannies for oil to accumulate are best. If you have an irregular shape, install the oil skimmer where the most considerable amount of oil collects. Consider a means of directing oil towards the oil skimmer, such as a baffle plate.
Location/Installation
The physical location and characteristics of the tank and collection container are essential. Is pumping required to remove skimmed oil? Will periodic maintenance be a problem? How much is mounting space available? Are tank or container modifications needed? Cheap oil skimming systems quickly lose appeal when costs for additional components, increased maintenance, and expensive tank modifications are involved.
Specifying an oil separation system
Innovation filter system provides customized oil separation systems for various applications; we base our designs on the following inputs.
Medium to be removed
✔ Oil addition rate (gm/hr)
✔ Number of shifts
✔ Number of hours/shift
We base our skimmer capacity on the maximum amount of oil removal within the shortest available time. For instance, the total oil addition rate may be 200 gms in a 24-hour period, which averages about 8.3 gm/hour. But if most of it comes during a single eight-hour shift, the oil removal rate needed is three times as high.
Medium to be cleaned
✔Cooling Water
✔Waste (sewage) water
✔Washing / Degrease solution
✔Emulsion
✔Other
In case of other pH-
Max. Temperature-
✔Oil level tolerated in final process fluid (gm)
Installation
✔ The volume of the process tank
Length (mm)
Width (mm)
Total tank height (mm)
✔ Vertical distance
The vertical distance between tank top and the lowest level of fluid
in the tank (mm)
The approximate fluctuation of level in the tank (mm)
Oil skimming is a cruel practice that sees many animals killed by an oil spill. At the end of each oil spill in Texas, volunteers are sent across the country to clean up the remaining mess
Hi innovationfilter.com owner, Thanks for the well-structured and well-presented post!
Most Welcome
I find it interesting when you said that the oil skimmer will depend on the size of the tank that it has to work on, since it will reach even the remotest corners of it. I can imagine how this type of equipment would be needed for oil tank removal services as well to remove the contents before they actual container is tackled. The companies offering such services might probably have various available tools to be able to cater to every client they might have, big or small properties.
To the innovationfilter.com administrator, Your posts are always well-supported and evidence-based.
Thank you
This article provided an excellent overview of oil skimmers. I appreciated how it explained the different types of skimmers and their applications. The content was well-researched and easy to understand, making it accessible to both professionals and beginners. I feel confident now in using oil skimmers to remove oil and other contaminants from my industrial processes.
Thank you very much for your appreciation.