Oil skimmer

Last updated

An oil skimmer is a device that is designed to remove oil floating on a liquid surface. They are commonly used to recover oil from oil spills in water, or in Industrial situations where waters are contaminated with oil. Oil skimmers are designed to remove free floating oil and are not water treatment devices.

Contents

The effectiveness of a skimmer deployed in open water or oil spill recovery is highly dependent on the roughness of the surrounding water that it is working on: the more choppy the surrounding wake and water, the more water the oil skimmer will take in along with the oil, rather than take in oil alone. Oil spill Skimmers can be self-propelled, used from shore, or operated from vessels, with the best choice being dependent on the specifics for the job at hand. [1]

Oil skimmers were used to great effect to assist in the remediation of the Exxon Valdez oil spill in 1989.

Oil Skimmers are also used in a large number applications other than oil spills. Examples include as a part of oil removal in vehicle wash water, fuel storage sites and workshops. Industries that extensivly use oil skimmers include Manufacturing, Mining, Oil and Gas, Refining, Petrochemical, Solvent Extraction and Food Industries. Selecting the correct type to use depends on the nature of the intended application and the nature of the oil and water. Oil skimmers are frequently one component of oily water treatment systems.

Oil skimmers are different from swimming pool sanitation skimmers, which are designed for a similar but unrelated purpose.

Limitation and design factors

There are many different types of oil skimmer. Each type has different design features and therefore results in different applications and use. It is important to understand the design features and fluid properties before employing a particular skimmer type.

Some factors to consider are:

Applications

The use of skimmers in industrial applications is often required to remove oils, grease and fats prior to further treatment for environmental discharge compliance. By removing the top layer of oils, water stagnation, smell and unsightly surface scum can be reduced. Placed before an oily water treatment system an oil skimmer may give greater overall oil separation efficiency for improved discharge wastewater quality. All oil skimmers will pick up a percentage of water with the oil which will need to be decanted to obtain concentrated oil.

Types

There are three types of oil skimmers: [2] Weir, Oleophilic and Suction. Oleophilic skimmers include disc, belt, tube, brush, mop, brush, grooved disc, smooth drum, and grooved drum. The material chosen for an oleophilic skimmer affects the collection rate based on the material's affinity for the particular type of oil that is skimmed.

Industrial weir type oil skimmer Self adjusting weir type oil skimmer, Ultraspin.jpg
Industrial weir type oil skimmer

Oleophilic

Oleophilic skimmers function by using an element such as a drum, disc, belt, rope or mop to which the oil adheres as the element is moved through the oil/water surface. Adhesion is the tendency of dissimilar particles or surfaces to cling to one another (cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). Any adhering oil is then wiped or scraped from the oleophilic surface and collected in a tank. As the oil adheres to the collection surface the amount of water collected is limited. When there is no oil left, some water will be collecte. The amount collected depends on the material properties of the oleophilic element and its affinity to water. Oilophilic skimmers can remove many kinds of oil; including machine oil, kerosene, diesel oil, lubricating oil, plant oil and other liquids with specific gravity less than water.

Small Oleophilic oil skimmers can be reliable and economical. Larger Oleophilic skimmers require larger drive motors with moving mechanical parts and require maintenance. Oleophilic skimmers are not effected by the oil layer thickness.

Recovery rates are lower than other types of skimmer. Recovery rates depend on the surface area of the oleophilic material, the surface speed and the material's affinity to oil as well as other factors such as temperature, specific oil makes-up, debris in the water and other chemicals that maybe present. Surfactants such as detergents, cleaners, caustics and fine suspended solids can impare the ability of oil to adhere to the Oleophilic material. Simple tests are available to determine the impairment cause by these chemicals.

Belt

Belt oil skimmers use a continuous loop belt that enters and exits the oil/water surface. As the belts exits the liquid surface oil clings to both sides. Wiper blades remove the oil from the rotating belt depositing it into a collection trough where it is moved to a storage location either via gravity or a pumping system. Belts are generally wide, thin and flexible.

Drum

Smooth drum type oil skimmer Drumskimmer 004.jpg
Smooth drum type oil skimmer

Drum skimmers operate by using one or more drums made from oleophilic material. As the drums rotate oil adheres to the surface, separating it from the water. Wiper blades remove the oil from the drums depositing it into the collection trough where it is pumped to a storage location. Drum skimmers are lightweight and may have a high oil recovery rate depending on the size and number of drums used. The drums can be either smooth or grooved. These types of skimmers are generally used in oil spill response and various industrial operations.

Disc

Disc skimmers are oleophilic skimmers that use a disc constructed from PVC, steel or aluminum and can be either smooth or grooved. They are capable of recovering high volumes of oil with little water. They can be equipped with either a single or multiple discs. The discs can be driven by hydraulic, electric, diesel or air motors. DISCOIL technology patented by OCS in the year 1970, is able to recover most of the hydrocarbons on the surface of water: 98% of oil with the only 2% water. It is hydraulic type and able to operate also in classified areas, as ATEX Zone 0, 1 and 2.

Non-oleophilic

Smooth industrial disc oil skimmer Oil Skimmer for StingRay Parts Washer.jpg
Smooth industrial disc oil skimmer

Non-oleophilic skimmers are distinguished by the component used to collect the oil. A metal disc, belt or drum is used in applications where an polymeric material is inappropriate, such as in a hot alkaline aqueous parts washer. [3] The skimmer is generally turned off whenever there is no oil to skim thus minimizing the amount of water collected. Metal skimming elements are nearly as efficient as oleophilic skimmers when oil is present.

Weir

Weir skimmers function by allowing the oil floating on the surface of the water to flow over a weir. There are two main types of weir skimmer, those that require the weir height to be manually adjusted and those where the weir height is automatic or self-adjusting. Whilst manually adjusted weir skimmer types can have a lower initial cost, the requirement for regular manual adjustment makes self-adjusting weir types more popular in most applications.

Weir skimmers will collect some water if operating when oil is no longer present. To overcome this limitation most weir type skimmers contain an automatic water drain on the oil collection tank. Large debris 20mm plus must be prevented from entering a Weir skimmer. This is usually done with simple screens added to the skimmer or in the case of pit operation, screening debris at the entrance to collection pits.

Weir skimmers can remove oil at a greater rate than other types of skimmer. Oil removal rates of over 25 m3/hr are available. They can also pull in oil from a greater radius on a surface than other skimmers. This makes Weir skimmers popular if high oil recovery rates rates and large coverage areas are required.

Weir type skimmers do not rely on oil adherance or coalecance and therefore are not affected by detergants, chemicals and other surfactants in the water. Equelly they are not affected by fine suspended solids in the water which can impeed adherance and thefore the operation of other types of skimmer.

See also

Related Research Articles

A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

<span class="mw-page-title-main">Drum brake</span> Type of vehicle brake

A drum brake is a brake that uses friction caused by a set of shoes or pads that press outward against a rotating bowl-shaped part called a brake drum.

<span class="mw-page-title-main">Surfactant</span> Substance that lowers the surface tension between a liquid and another material

Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word "surfactant" is a blend of surface-active agent, coined c. 1950. As they consist of a water-repellent and a water-attracting part, they enable water and oil to mix; they can form foam and facilitate the detachment of dirt.

<span class="mw-page-title-main">Cutting fluid</span> Coolants and lubricants used in metalworking

Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases. Cutting fluids are made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant.

<span class="mw-page-title-main">Sandpaper</span> Abrasive material used for smoothing softer materials

Sandpaper, also known as glasspaper or as coated abrasive, is a type of material that consists of sheets of paper or cloth with an abrasive substance glued to one face. In the modern manufacture of these products, sand and glass have been replaced by other abrasives such as aluminium oxide or silicon carbide. It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide paper", or "silicon carbide paper".

<span class="mw-page-title-main">Protein skimmer</span> Water treatment technology

A protein skimmer or foam fractionator is a device used to remove organic compounds such as food and waste particles from water. It is most commonly used in commercial applications like municipal water treatment facilities, public aquariums, and aquaculture facilities. Smaller protein skimmers are also used for filtration of home saltwater aquariums and even freshwater aquariums and ponds.

<span class="mw-page-title-main">Pressure washing</span> Use of high-pressure water jet for cleaning hard surfaces

Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure washer is expressed in gallons or liters per minute, often designed into the pump and not variable. The pressure, expressed in pounds per square inch, pascals, or bar, is designed into the pump but can be varied by adjusting the unloader valve or using specialized nozzle tips. Machines that produce pressures from 750 to 30,000 psi or more are available.

Dissolved air flotation (DAF) is a water treatment process that clarifies wastewaters by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank basin. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.

<span class="mw-page-title-main">Sand cleaning machine</span> Machine, usually pulled by a Tractor, for cleaning sand on a beach

A sand cleaning machine, beach cleaner, or (colloquially) sandboni is a vehicle that drags a raking or sifting device over beach sand to remove rubbish and other foreign matter. They are manually self-pulled vehicles on tracks or wheels or pulled by quad-bike or tractor. Seaside cities use beach cleaning machines to combat the problems of litter left by beach patrons and other pollution washed up on their shores. A chief task in beach cleaning strategies is finding the best way to handle waste matter on the beaches, taking into consideration beach erosion and changing terrain. Beach cleaning machines work by collecting sand by way of a scoop or drag mechanism and then raking or sifting anything large enough to be considered foreign matter, including sticks, stones, litter and other items.

<span class="mw-page-title-main">API oil–water separator</span>

An API oil–water separator is a device designed to separate gross amounts of oil and suspended solids from industrial wastewater produced at oil refineries, petrochemical plants, chemical plants, natural gas processing plants and other industrial oily water sources. The API separator is a gravity separation device designed by using Stokes Law to define the rise velocity of oil droplets based on their density and size. The design is based on the specific gravity difference between the oil and the wastewater because that difference is much smaller than the specific gravity difference between the suspended solids and water. The suspended solids settles to the bottom of the separator as a sediment layer, the oil rises to top of the separator and the cleansed wastewater is the middle layer between the oil layer and the solids.

A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid to improve the separation of the particles and to prevent their settling or clumping.

<span class="mw-page-title-main">Cleaning agent</span> Substance used to remove dirt or other contaminants

Cleaning agents or hard-surface cleaners are substances used to remove dirt, including dust, stains, foul odors, and clutter on surfaces. Purposes of cleaning agents include health, beauty, removing offensive odor, and avoiding the spread of dirt and contaminants to oneself and others. Some cleaning agents can kill bacteria and clean at the same time. Others, called degreasers, contain organic solvents to help dissolve oils and fats.

Foam fractionation is a chemical process in which hydrophobic molecules are preferentially separated from a liquid solution using rising columns of foam. It is commonly used, albeit on a small scale, for the removal of organic waste from aquariums; these units are known as "protein skimmers". However it has much broader application in the chemical process industry and can be used for the removal of surface active contaminants from waste water streams in addition to the enrichment of bio-products.

Induced gas flotation (IGF) is a water treatment process that clarifies wastewaters by the removal of suspended matter such as oil or solids. The removal is achieved by injecting gas bubbles into the water or wastewater in a flotation tank or basin. The small bubbles adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.

Groundwater remediation is the process that is used to treat polluted groundwater by removing the pollutants or converting them into harmless products. Groundwater is water present below the ground surface that saturates the pore space in the subsurface. Globally, between 25 per cent and 40 per cent of the world's drinking water is drawn from boreholes and dug wells. Groundwater is also used by farmers to irrigate crops and by industries to produce everyday goods. Most groundwater is clean, but groundwater can become polluted, or contaminated as a result of human activities or as a result of natural conditions.

<span class="mw-page-title-main">Defoamer</span> Chemical additive that reduces and hinders the formation of foam in liquids

A defoamer or an anti-foaming agent is a chemical additive that reduces and hinders the formation of foam in industrial process liquids. The terms anti-foam agent and defoamer are often used interchangeably. Strictly speaking, defoamers eliminate existing foam and anti-foamers prevent the formation of further foam. Commonly used agents are insoluble oils, polydimethylsiloxanes and other silicones, certain alcohols, stearates and glycols. The additive is used to prevent formation of foam or is added to break a foam already formed.

Continuous foam separation is a chemical process closely related to foam fractionation in which foam is used to separate components of a solution when they differ in surface activity. In any solution, surface active components tend to adsorb to gas-liquid interfaces while surface inactive components stay within the bulk solution. When a solution is foamed, the most surface active components collect in the foam and the foam can be easily extracted. This process is commonly used in large-scale projects such as water waste treatment due to a continuous gas flow in the solution.

<span class="mw-page-title-main">Boiler blowdown</span> Wastewater removal of impurities from boilers

Boiler blowdown is water intentionally wasted from a boiler to avoid concentration of impurities during continuing evaporation of steam. The water is blown out of the boiler with some force by steam pressure within the boiler. Bottom blowdown used with early boilers caused abrupt downward adjustment of boiler water level and was customarily expelled downward to avoid the safety hazard of showering hot water on nearby individuals.

An oil water separator (OWS) is a piece of equipment used to separate oil and water mixtures into their separate components. There are many different types of oil-water separator. Each has different oil separation capability and are used in different industries. Oil water separators are designed and selected after consideration of oil separation performance parameters and life cycle cost considerations. "Oil" can be taken to mean mineral, vegetable and animal oils, and the many different hydrocarbons.

<span class="mw-page-title-main">Pool skimmer</span>

A skimmer or surface separator is an essential accessory for the maintenance and cleaning of the water in a swimming pool. It is used to remove all the surface dirt floating on the water surface, such as leaves, tanning oil and human secretions. These impurities remain suspended on the surface, affect the appearance of the water and are not always removed by the conventional vacuuming process. The skimmer is installed directly in the surface water suction system and also has the function of controlling the water level to prevent accidental overflows. In the United States and Portugal, the use of skimmers in the construction of swimming pools is mandatory, regulated and standardized by competent bodies.

References

  1. US EPA, OLEM (2013-07-30). "Skimmers". www.epa.gov. Retrieved 2021-10-16.
  2. "EPA Emergency Response skimmers". US Environmental Protection Agency. Retrieved 1 May 2023.
  3. non-oleophilic parts washer skimmer