Oil Skimming Facts Tutorial Handbook
New Updated Edition!
It is the industry's most complete handbook on how to select and
size an oil skimmer for your application. This handbook contains
information on all aspects of oil skimmer application.
The relationship between oil and water in a mixture is well-known and governed by two physical properties:
Specific Gravity: Most hydrocarbons have a lower specific gravity than water. Without agitation, oil separates from the water and floats to the surface. These oils are known as LNAPL's, Light Non-Aqueous Phase Liquid. Oils (and other compounds) that sink in water have a higher specific gravity and are known as DNAPL's, Dense Non-Aqueous Phase Liquid.
Surface Tension and Affinity: Normally, oil bonds more tightly to itself and other materials than to water. This affinity, and differences in surface tension between oil and water, cause oils to adhere to a skimming medium.
Floating oil and grease cling to skimming media more readily than water, and water has little affinity for the media. 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. This oily material is subsequently removed from the media with wiper blades or pinch rollers.
Oil skimmers are simple, dependable and effective tools for removing oil, grease and other hydrocarbons from water and coolants. Often, an oil skimmer by itself can achieve the desired level of water 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 coalescers, membrane filters and chemical processes.
Grease skimming involves higher viscosity hydrocarbons. Oil skimmers must be equipped with heaters powerful enough to keep grease fluid for discharge. The patented Abanaki Grease Grabber® is fitted with heating elements to handle these applications.
If the floating grease has formed into solid clumps or mats, a spray bar, aerator or mechanical apparatus can be used to break up grease mats and facilitate removal.
|Typical Applications for Industrial Oil Skimmers|
Coolants and Cutting Fluids
Food Processing Facilities
Steel Mills/Scale Pits
Parking Lots, Garages and Service Facilities
Outdoor Ponds, Lakes, Basins, Etc.
|Choosing an Appropriate Skimmer|
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. First, define the application in terms of the following characteristics:
All oil skimmers have a moving medium, and possibly other parts, immersed in the liquid. The performance and life of the pick-up medium, wiper blades, pulleys, etc. are affected by different conditions. These conditions include temperatures in and out of the liquid, pH of the solution, and the presence of solvents or other reactive chemicals.
Applications involving flammable materials or explosive vapors require the use of explosion proof or air driven motors and controls.
All oil skimmers require floating oil to be in a liquid, free-flowing state. If the oil congeals or solidifies at ambient temperatures, the tank and/or oil skimmer will require heaters to maintain fluid flow. This is especially true at temperatures low enough to freeze water. A heater option is a must if an oil skimmer is to be used outdoors in freezing temperatures.
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). When specifying removal capacity, it is better to err on the high side to allow for peaks in the oil influx.
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 they are 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.
Tank or Sump Characteristics
The location, shape, and capacity of a tank or water impoundment are major factors in choosing the right oil skimmer. Also consider fluctuations in water level, turbulence and possible emulsions. Although oil skimmers do not cause emulsions, they can have trouble removing certain types.
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 accumulate 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. Does skimmed oil need tom 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? Cheap oil skimming systems quickly lose appeal when costs for additional components, increased maintenance and expensive tank modifications are involved.
|Industrial Oil Skimmers||Special Purpose Skimmers|
|Small Applications||Medium Applications||Large Applications||Monitoring Wells up to 10"||Large Pits||Harsh Environments|
|Light Duty||Medium Duty||Light Heavy Duty||Medium Heavy Duty||Heavy Heavy Duty||Groundwater Remediation||Heavy Oil or Grease||316 SS Construction|
|Reach of Skimmer||Up to 2'||Up to 5'||Up to 100'||Up to 100'||Up to 100'||Up to 100'||Up to 100'||N/A|
Removal rates based on SAE 30 motor oil.
Grease Grabber removal based on Plexelene 750™.
Size of application must be taken into consideration for optimal recovery rates.
= Appropriate sizing.
= Capacity well above desired level.
|Different Types of Oil Skimmers|
For industrial oil skimming, there are six basic designs commonly used:
These oil skimmers rotate a disk shaped medium through the liquid. Oil is wiped off and discharged into a collection container in a manner similar to belt oil skimmers. It is important to consider reach, the portion of the disk that actually gets immersed, when looking at a disk oil skimmer. Less disk in the fluid means less oil removed. Obviously, fluctuating fluids can be a real problem for disk oil skimmers.
These are similar to the disk type, but use a rotating drum shaped medium. Compared to disk types, they are usually more rugged and have higher removal capacity. Depending on the design, these units can also be rendered ineffective by fluctuating fluid levels. Also, water pickup with this type of oil skimmer can be high.
These oil skimmers use an endless medium shaped like a rope and having mop-like tendrils that pick up the oil. As the medium leaves the liquid and enters the drive unit, it is pressed and wrung out with pinch rollers. For higher viscosity oils, the medium tends to mat down and lose effectiveness. A decant system is a must for these units, as water pickup can be very high. Also, replacement oil mops can be very expensive, so check prices on replacements before purchasing.
Large Tube Skimmers:
Mini Tube Skimmers:
Floating Suction Skimmers:
|Specifying an Abanaki Skimmer for Your Application|
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.
Abanaki Oil Skimmer Models
Oil Skimmer Belt and Tube Length:
Removal capacity is not affected by length. Choose a length that: assures contact with the liquid at its lowest level; allows easy mounting of the oil skimmer where oil discharge is convenient; and has good access for routine service. Abanaki's ability to supply oil skimmers with long belts, and lift skimmed oil well over 100 feet with no loss in capacity or efficiency, is important to many users.
The disk must always be touching the fluid. Size the diameter accordingly.
Abanaki offers 4 wiper blade materials for a variety of operating environments. The standard is Nitrile (also known as Buna-N), which is appropriate for about 80% of all applications. Optional materials are designed for applications with harsh operating conditions. The materials include: CRV (very high chemical resistance), ceramic hybrid (excellent lubricity and moderate chemical resistance), and stainless steel wipers.
All Abanaki oil skimmers are designed with standard, industrially rated, continuous duty motors and fully enclosed speed reducing drives. Most of these oil skimmers can be specified with the following motor options:
Contact Abanaki regarding availability of special motors, controls and drive components to satisfy unusual requirements.
Choosing the Right Belt Material for your Abanaki Belt Skimmer
Abanaki offers 5 different belt materials. The chart indicates which material is most suitable for common situations. However, belt performance and durability depends on the nature of the liquid, its chemical composition, temperature, etc. For instance, high temperature increases a belt's sensitivity to pH levels. To make sure the belt oil skimmer performs satisfactorily in your application, Abanaki offers free samples of belt material for test purposes.
|pH Range 2-13*||Yes||Yes||Yes||Yes||Yes|
|Operates in the presence
of grit fines and other
|Removes certain DNAPL's
and some emulsified oils
|Effective for every light oils||No||No||No||No||Yes|
*At ambient temperatures.
Abanaki accessories make it easy to customize your oil skimming system for quick installation and optimal performance. Listed below are the most commonly requested items. More specialized accessories are available on request.
Solar Oil Skimming System:
Transfer Package and Underground Oil Skimming System:
Concentrators: Abanaki Oil Concentrators® provide a secondary separation step after oil skimming to virtually eliminate water from skimmed product. Units are available for easy installation on most Abanaki oil skimmers.