ABSTRACT 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 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. 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. This topic describes the development of the OS with typical working model.
TABLE OF CONTENTS CHAPTER NO.
TITLE
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ABSTRACT LIST OF TABLE LIST OF FIGURES LIST OF SYMBOLS 1. 1.1. 1.2. 1.3. 2. 2.1. 2.2. 2.3. 2.4. 2.5. 2.5.1. 2.5.2. 3. 4. 4.1. 4.2. 4.3. 4.4. 4.5. 4.6. 5. 6. 7.
INTRODUCTION OIL OIL SKIMMER SKIMMER TECHNOLOGIES TYPES OF SKIMMERS DISC ROPE MOP DRUM BRUSH BELT NON OLEOPHILIC SUCTION WEIR OIL SKIMMER WORKING PRINCIPLE DESIGN CALCULATIONS OIL RISING VELOCITY CORRESPONDED-FEASIBLE SEPARATOR SIZE TORQUE & TENSION IN BELT DC MOTOR STEEL SELECTION AND PROPERTIES BELT SELECTION LIST OF COMPONENTS PROTOTYPING CONCLUSIONS AND PROPOSAL REFERENCES
LIST OF TABLES
LIST OF FIGURES
LIST OF SYMBOLS, ABBREVIATIONS AND NOMENCLATURE
INTRODUCTION
Oils Oil can be defined as: “A viscous liquid derived from petroleum, especially for use as a fuel or lubricant” or “Any of various viscous liquids which are insoluble in water but soluble in organic solvents and are obtained from animals or plants” (Oxford Dictionaries, 2012). Oils are, based on these definitions, divided into two categories with different chemical composition; mineral oils (also called crude oils) and organic oils (also called fats) in which essential oils are included.
Oil Skimming Overview Oil skimming is a low-tech but reliable and efficient technique. An oil skimmer is defined as: “Any mechanical device specifically designed for the removal of oil (or oil-water mixture) from the surface of water without altering the water’s physical and/or chemical characteristics”. (NOAA, 2010) The skimming principle, upon which the technique relies, is dependent on three physical properties of oils, namely specific gravity, surface tension and affinity. Most oils have a lower specific gravity than water, which allows it to separate from water and float to the surface unless agitated. These oils are possible to collect using an oil skimmer. Other oils do the opposite and, if not agitated, sink to the bottom of the water and must be collected by other means than skimming. (Abanaki, 2011) The light oils, which can be skimmed off the water surface, are possible to collect due to the surface tension and affinity of the oil. Most oils have little or no affinity for water, which prevents mixing of oil and water. As the skimming medium enters the water, the oil wets the surface preventing water from doing the same. Any water on the surface is pushed away as more oil attaches to the surface because of the surface tension of the oil. However, it is important that the skimming medium is not submerged too deep into the water, as it may cause the oil to be washed off the skimming medium and thereby lowering the efficiency. (Persson K. , 2013) A number of factors are to be taken into account when selecting skimmers but the most important aspects to consider are the viscosity and the adhesive properties of the oil intended to be skimmed. In open sea spills, other important factors are sea state, currents, and level of debris. In relatively predictable situations such as
at fixed facilities, for instance industry processes, marine terminals and refineries, the type of oil handled may be known and hence the type of skimmer to be used can be selected accordingly. Subsequently, a versatile skimmer able to handle different kinds of oil and various situations may be preferable in some cases, but is to be kept in mind that no single skimmer can cope with all potential situations that may arise. A combination of skimmers is hence desirable, particularly as the oil weathers. (ITOPF, 2012) The second most important factor to assess is the skimmer’s intended use and expected operational conditions. Depending on if the skimmer is to form an integral part of a vesselmounted, offshore recovery system or if it is to be deployed manually in a port or fixed in a cooling water reservoir the selected type of skimmer will differ and aspects such as size, robustness and ease of operation, handling, and maintenance can then be evaluated. (ITOPF, 2012)
Skimming Technologies
The mechanisms through which oil is removed from the water surface can be divided into oleophilic techniques, which rely on the adhesion of oil to a moving surface, and nonoleophilic techniques. Non-oleophilic techniques include weir skimmers relying on gravity, suction systems, and mechanical skimmers, which physically lift the oil with scoops, or grabs. (ITOPF, 2012) Oleophilic Skimmers Oleophilic skimmers recover oil based on the properties of specific materials, which have greater affinity for oil than for water. There exist numerous types of oleophilic skimmers and they are therefore divided into subgroups such as disc skimmers, drum skimmers, rope mop skimmers, belt skimmers, and brush skimmers. Regardless of the type of skimmer, the principle behind the technique used is the same for all oleophilic skimmers. The skimming head, i.e. the part with the oleophilic surface, is rotated or pulled through the oil slick and the oil is then scraped or squeezed off and the oil removed into a sump to be pumped or sucked away. (NOAA, 2010) (ITOPF, 2012) Oleophilic skimmers usually achieve the highest ratio of recovered oil in relation to entrained water, also referred to as the recovery efficiency, compared to other skimmer types. Oleophilic skimmers reach their highest efficiency when handling medium viscosity oils (between 100 – 2000 cSt). Diesel, kerosene and other low viscosity oil products generally do not adhere to the oleophilic surface in sufficiently thick layers to attain high recovery rates. Higher viscosity oils such as heavy bunker oil on the other hand, can prove to be difficult to remove due to its tendency to form large clumps in the water, which are too heavy and compact to be skimmed. Comparatively, oil-water emulsions can be almost impossible to recover with oleophilic skimmers, due to the fact that emulsions are nearly non-adhesive. (ITOPF, 2012) Oleophilic materials are often made of some form of polymer even though metal surfaces have shown to be effective. Furthermore, studies show that discs and drums with grooved surfaces result in higher recovery rates than smooth surfaces. (ITOPF, 2012) (Broje & Keller, 2006)
TYPES OF SKIMMERS
Disc Skimmers Disc skimmers work best with lighter types of oil (medium viscosity) and cannot handle emulsified oil. However, disc skimmers can be used for open sea operations and are controlled by crane operators. The volume and weight of the disc skimmers are quite large due to the size and number of rotating discs (NOAA, 2010).
Rope Mop Skimmers Rope mop skimmers use ropes floating on the surface of the water to retrieve the oil. Rope mop skimmers are large units and require the use of a crane during the entire operation for launching from either a vessel or shore. The oil is recovered by the ropes, which are then wrung releasing the oil into a collection tank either on board the vessel or on the shore. This skimmer type is not sensitive to waves but is normally only used for single sweep operations. Vertical rope mop skimmers are most suited for lighter oil types as very little water is collected during recovery. Debris or ice will not affect the skimming operation (NOAA, 2010). Rope mop skimmers are ideal for shallow water conditions, as the rope requires minimal water to float. Furthermore, Rope mops are ideal in trash-laden environments since the trash falls off the ropes as they come up to the wringer unit. (Cleanup Oil, 2003)
Drum Skimmers Drum skimmers are driven by air or hydraulics and are therefore often considered for use in hazardous areas and environments. Drum skimmers are versatile skimmers and can handle 26 various types of oils ranging from light oils such as diesel to heavier oils such as crude oil. (Cleanup Oil, 2003)
Brush Skimmers
Brush skimmers can be packaged in a wide range of configurations from stand-alone units to modules mounted on a barge (self-floating unit) or on a specially constructed recovery vessel. Depending on the stiffness and density of the bristles used and the comb configuration, different types of oil can be recovered. In general, light oil is better recovered by finer, softer bristles while stiffer and wider spaced bristles are better suited for heavy oils. (Cleanup Oil, 2003)
Belt Skimmers Belt skimmers are large and are therefore often mounted on a barge or on a specially constructed vessel. These skimmers have a high recovery efficiency and good recovery rate, but are specialised products and can be complicated to operate, which requires heavy equipment and specially trained personnel (NOAA, 2010). However, a fixed position mounted belt skimmer requires an initial tuning but can then operate independently. (Nilsson, 2013)
Non-Oleophilic Skimmers
Suction Skimmers Suction skimmers such as vacuum skimmers represent the simplest skimmer design in terms of operational theory, whereby oil is recovered by air suction systems directly from the water surface (ITOPF, 2012). The simplest type of vacuum skimmer uses a hose directly connected to a vacuum truck, which can easily be employed in harbours or rivers. Due to the sensitivity to waves, vacuum skimmers are often restricted to use in harbours and calm waters. (NOAA, 2010) Furthermore, suction skimmers are ideally suited for recovery of oil on or near the shoreline due to the widespread availability of vacuum systems. Nonetheless, the undifferentiating nature of the suction device may result in high proportions of water also being collected. (ITOPF, 2012)
Weir Skimmers
Weir skimmers refer to skimming devices using gravitational force to drain oil from the water surface. Weir skimmers are floating units where the edge of the weir is positioned just below the upper slick surface or at the interface between the floating oil and water, hence allowing oil to flow over the weir edge into a collecting sump. The oil is then pumped to storage tanks. Weir skimmers are normally launched from vessels using a crane and the weir can either be remote controlled by compressed air or self-adjusting. Weir skimmers are one of the most commonly used skimmer type due to its simple construction. (NOAA, 2010) (ITOPF, 2012) Weir skimmers are however prone to be jammed or clogged due to floating debris, and although swell alone does not interfere with skimming operation, weir skimmers are very sensitive to steep waves (ITOPF, 2012). In table 2, an overview over different skimming technologies and their properties are briefly presented.
OIL SKIMMER WORKING PRINCIPLE
As the BELT rotates, oil adheres to the belt surface separating it from the water. Oil is wiped from the belt surface and drained into the collection trough. In a full size skimmer the oil would be pumped or sucked out to a remote containment location. 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.Design of the proposed skimmer
DESIGN CALCULATIONS
Defining oil rising velocity Stokes’ Law (Equation 1) defines the rising velocity of oil droplet from the bottom of a separator to the surface of water. From this equation, the most important variables are the viscosity of the continuous liquid, specific gravity difference between the continuous liquid, and the oil droplet size. After these are known, the rising velocity and therefore the size of separator required may be calculated
Where,
Determining a corresponded-feasible separator size
Determining Torque & Tension in Belt = πNTP *60/2 Where, N = Motor Speed T = Torque transmitted by Motor
Dc motor Motor Spec (Model# 25GA370D12, i = 1:25.5) 1. Voltage: 12.0VDC 2. Output Speed: 200 +/- 10% RPM 3. No-Load output current: =< 50 mA 4. Rotation Output: CW / CCW 5. Noise: No Gear Noise 6. Stall output: : Slip Gear, Broken Gear is no allowed 7. Output shaft of the axial clearance: =< 0.1 ~ 0.3mm, Horizontal clearance requirement =< 0.05 Electrical Spec 1. No-Load Speed: 5700 RPM 2. No-Load Current: =< 30mA 3. Rotation: CW 4. Motor#: 370
Steel Selection and Properties
Sheet Bending process The equation for estimating the maximum bending force is,
, where k is a factor taking into account several parameters including friction. T is the ultimate tensile strength of the metal. L and t are the length and thickness of the sheet metal, respectively. The variable W is the open width of a V-die or wiping die.
Belt Selection and properties 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 skimmer operating costs. First, define the application in terms of the following characteristics: Operating Conditions All 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. 1) Hazardous Materials: Applications involving flammable materials or explosive vapors require the use of explosion proof (or air driven) motors and controls. 2) Temperature/Viscosity: All skimmers require floating oil to be in a liquid, freeflowing state. If the oil congeals or solidifies at ambient temperatures, the tank and/or 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 a skimmer is to be used outdoors in freezing temperatures.
Removal Capacity Rating Skimmers usually have an oil removal rate expressed in gallons per hour. The rate varies with oil viscosity and most manufacturer’s rate skimmers using SAE 30 weight motor oil at 65°F (18°C). If a manufacturer doesn’t specify the test oil for its rating, or your application involves a much different viscosity, it is wise to ask for additional test data. When specifying removal capacity, it is better to err on the high side to allow for peaks in the oil influx.
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 pick-up media. An Oil Concentrator® or decanter installed at the skimmer discharge port provides secondary oil/water separation that can reduce water content to nearly zero.
Residual Oil A skimmer continues to remove oils as long as they are present. Depending on oil influx rate and the 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 Skimmer portability is a plus in some applications. For example, in plants, mobile equipment service shops, and at remediation sites, a portable 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 skimmer. Also consider fluctuations in water level, turbulence and possible emulsions. Although skimmers do not cause emulsions, they can have trouble removing certain types. Size/Design: 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. Shape: Tanks without nooks and crannies for oil to accumulate in are best. If you have an irregular shape, put the skimmer where the largest amount of oil accumulates. Consider a means of directing oil towards the skimmer such as a floating boom or baffle plate. Location/Installation: The physical location and characteristics of the tank and collection container are important. Does skimmed material need to be pumped from the skimmer to the container? Will skimmer access for periodic maintenance be a problem? How much mounting space is available? Are tank or container modifications required? Cheap systems quickly lose appeal when costs for additional components, increased maintenance and expensive tank modifications are involved.
LIST OF COMPONENTS
Belt – polyurethane Pulley – length - 120mm, dia – 33mm Shaft – L - 140mm – 12mm dia Bearing – ID – 10mm – OD – 16mm Structure – 1 inch square rod Base – 1mm sheet metal Motor – 12v dc motor – 300 rpm Coupler – 15mm dia Reservoir – 140mm x 150mm Wiper – 100mm width – 150 mm length
PROTOTYPING
A scale model of the oil skimmer is prototyped in this project. The minimum scale must be 1:40 because under this ratio, the surface tension or electro-chemical forces have an effect that impedes the inertial forces (pers. comm. Dr. Viaja Raghavan, 2011). For the testing of the dimension based on Stokes's Law , 1:10 is a reasonable scale for the testing purposes. The real dimensions are 6 meters x 1 meter x 0.75 meter, therefore the scale model will be 60cm x 10cm x 7.5cm. The stoke number is the dimensionless measure useful for having a ratio of raising particles between the prototype and the real scale model.
The corresponding images are shown below. ____________________ PLEASE ATTACH YOUR PROJECT PHOTOS HERE.
CONCLUSION AND PROPOSAL In this project, we enforced to highlight the function of oil skimmer, its various design aspects and performance. All the results of experimental studies indicate that slight design improvement of typical oil skimmers towards to include additional belt shaft and use of belt with steel material instead of rope; significantly improve the oil recovery efficiency and also its structure became simpler. As practical overview of different oil spillage cleanup method. This Project has illustrated several limitations of these methods and current oil spill technology. Further extensive research & testing can improve the existing techniques and equipment to have better control for oil recovery exercise.
Typical Applications for Industrial Oil Skimmers
Wastewater Sumps Most manufacturing or processing facilities have circulating water systems. This water collects in a central tank or sump. Removing floating hydrocarbon contamination with little water content can reduce the cost of disposal and lower the contingent liabilities of wastewater discharge. Coolants and Cutting Fluids When machine coolants become contaminated with tramp oils, four things usually occur: 1. coolant life is reduced 2. quality of machined parts is reduced 3. in many cases, a smoke will begin to appear in the shop, causing irritation to the workers on the job 4. the fluid takes on a “rotten egg” odor. Skimmers that remove tramp oils solve these problems and typically pay for themselves within a few months. Heat Treating Quench oils that must be removed from heat treated parts can be captured for re-use or disposal. The results are lower quench oil costs, prolonged wash water life and lower disposal costs. Parts Washers
Floating oils re-contaminate parts as they are removed from a wash tank. Oil skimmers can remove this oil. The benefits of using an oil skimmer are oil-free parts and extended fluid life. Food Processing Facilities Removal of vegetable oils, greases, and animal fats from a plant’s wastewater stream reduces the costs of processing and disposal. Parking Lots, Garages and Service Facilities Waste oil from leaks, spills and other sources must be retrieved from sumps before water can be discharged to storm or sanitary sewers. Outdoor Ponds, Lakes, Basins, Etc. Where floating oils are present, skimmers provide inexpensive and effective removal, solving a serious environmental problem.
Recovery/Monitoring Wells Removing oil, fuel and other hydrocarbon liquid from wells can be more cost-effective using a belt skimmer instead of a down well pump. Skimmers don’t have nearly the maintenance issues and can reach depths of 100 feet or more, removing product despite fluctuating water tables. Skimmers can handle very thick fluids effortlessly and some (like the Abanaki PetroXtractor®) can separate some DNAPL’s such as coal tar and creosote from water.
REFERENCES
[1] ‘Victoria Broje’ and ‘Arturo A. Keller’, “ Improvedrecovery of oil spills from water surfaces using tailoredsurfaces in Oleophilic skimmers, Donald Bren School of Environmental Science & Management, University of California, Santa Barbara.
[2] ‘ASTM.2007.ASTM F726-06’, “Standard test methods for sorbent performance of adsorbents”, American society of testing and materials, West Conshohocken.P.A.
[3] R.S. Khurmi and J.K.Gupta, Machine Design-І, S chand
[4] K Subhramanya, Fluid Mechanics and Hydraulic Machines, Tata McGraw Hill (2012)
[5] ‘S.H. Schwartz’, “Performance tests of four selected oil spill skimmers, in: Proceedings of the International Oil Spill Conference”, American Petroleum Institute, Washington, DC, USA, 1979, pp. 493–496.
[6] ‘S.D. Gill, W. Ryan’, “Assessment of the ACW-400 oil skimmer by the Canadian Coast Guard for oil spill countermeasure operations, in: Proceedings of the International Oil Spill Conference”, American Petroleum Institute, Washington, DC, USA, 1979, pp. 279–282.
