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Oil Spill Equipment and Products
Oil spills happen to behave differently from case to case. Even during one spill response operation, the conditions change from area to area and also over time. Therefore you cannot count on – for instance in a marine spill - one specific type of boom, or one type of skimmer, for the collection and recovery of the oil. Mainly for marine spills, but also for land spills, you must have at your disposal a selection of equipment and products which combined will meet the demands for a well prepared contingency.Therefore this chapter of the Response Handbook will describe the most common types of oil spill equipment , -tools , and -products, such as the most relevant types of booms, skimmers, pumps, dispersants, absorbents, storage facilities, vessels, etc.
The displayed equipment photos and sketches do not express oil-spill-web’s preferences, but they have been selected because they best describe the principle or function in question.
Booms Skimmers Pumps Storage Dispersants and Spray Systems Response Vessels Absorbents Other Spill Response Equipment
Booms
Booms In General
Booms (or Oil Containment Booms) are floating devices which may have one or more of the following functions in connection with oil spill response on water:
- Deflecting oil to prevent that the oil slick hits sensitive areas
- Containment of oil (for instance for later recovery by a skimmer)
- Containment and concentration of oil (for instant recovery by a skimmer)
Booms are manufactured in many sizes, materials, and designs in order to meet the various combat environments and the requirements from the market. But they all follow the same basic principle, having a flotation member at the top, a skirt below, a tension member, and a ballast member at the bottom.
Ro-Boom with Oil
Vikoma Beach Boom
NOFI Vee Sweep
LORI circulation system
The flotation member may be
- an inflatable chamber
- a self inflatable air chamber (springs inside the chamber automatically force the air into the chamber as the boom is deployed)
- an air chamber which automatically fills with air, which is permanently encapsulated within a two-layer light weight boom design.
- foam filled buoyancy chamber
- buoyancy chamber made of absorbent material (absorbent boom)
The skirt may consist of one or two layers of the boom fabric. Some special designs have water permeable skirts.A tension member is any longitudinal part of the boom (boom fabric, ballast chain or wire), and combined they take up the forces of wind, waves, current, and the forces when the boom is dragged through the water in a sweep.
The ballast member may be made of steel or lead, or even water.
A typical boom for off-shore use have a heavy steel chain which can function as both a ballast member and a tension member.
Smaller and more simple multi-purpose booms may have a steel wire which can function as both a ballast member and a tension member.
Booms, which have been specially designed to be able to seal the beach/water interface, so-called beach booms, have one or two water filled ballast chambers at the bottom of the boom.
Sections of booms may be interconnected using standardized connectors, thus creating any practical length necessary.
A tow bar at the end of a boom can transfer the drag forces from a vessel to the boom, or it may be the transmitter of forces from an anchor line, as is the case for a deflection boom in a river or at the water intake of a desalination plant. (Back)
Boom/Water Speed
(of a boom when used in a sweep formation OR of the water when the boom is used stationary, for instance in a river):The ability of containment booms to collect floating oil is subject to limitations described by fundamental physical laws (the speed of the boom moving through the water, or the speed of the water passing under the boom skirt)
The maximum sweeping speed (the speed of the water passing perpendicular to the boom) using a conventional inflatable or foam filled containment boom is 0.7 knots, if you don’t want to loose oil, escaping under the boom. The maximum speed perpendicular to the boom is 0.7 knots, no matter how much draught the boom has.
There are, however, minimal variations, dependent on for instance the specific gravity of the oil.
Certain boom sweep formations and boom designs, such as the NOFI Vee Sweep and Oil Stop, Inc.’s Fast Sweep System - having a fine meshed net to make a water permeable bottom between the lower parts of the skirts at the apex of the "V-shaped" boom sweep formation - can create a strainer bag effect where the water escapes easier than the oil through the net. These specially designed boom sweep apex formations may reach an effective sweep speed of approx. 1.5 knots before a significant amount of oil is lost under the boom.
Another way to increase the effective sweep speed is the patented LORI circulation system, where the collected oil via a side sweep on a vessel is forced away from the critical zone at the apex of the boom and via a side door in the hull into to an internal recovery area inside the vessel. Any oil which is not recovered immediately by the skimmer inside the hull is then forced back to the collection area via another side door in the hull. The LORI system may likewise reach about 1.5 knots effective sweep speed without significant losses. (Back)
Boom Configurations for the Containment, Concentration, and Recovery of Oil:
U Configuration
U+V Configuration
J Configuration
V Sweep
J+V Sweep
Single Vessel Sweep
Double Sweep
Open U + Single Vessel V
Booms, moored and used for deflection of spilt oil, for instance in a river, must be placed in an angle to the current which ensures that the speed component of water - projected into a direction perpendicular to any section of the boom - does not exceed 0.7 knots.
All static containment of spilt oil must obey the same rule which is that the velocity of the component of water which flows perpendicular to the boom configuration must be less than 0.7 knots.
Dynamic containment and concentration of oil may be performed using several types of boom configurations:
"U" Configuration
Concentrating capability: Poor
Maneuverability: PoorThis is the most commonly used, and unfortunately also the most inefficient way of sweeping oil for recovery by a skimmer. The "U" sweep will "concentrate" the oil in a large area inside its huge apex, and therefore it will only build up a thin layer of oil, thus making efficient skimming difficult. The U-shape will normally require two vessels towing the boom, and one vessel operating the skimmer. A three vessel operation is extremely difficult to maintain for the masters of the vessels.
"U+V" Configuration
Concentrating capability: Good
Maneuverability: Poor.This adds a "V" shaped pocket to the apex of the "U", thus enabling an efficient concentration of the oil, which will support a high recovery efficiency of the skimmer. But still very difficult to navigate.
"J" Configuration
Concentrating capability: Poor to Medium
Maneuverability: MediumIn this concept, the vessel towing the shorter end of the "J" sweep will also operate the skimming unit. This facilitates navigation, but the oil is still not concentrated very well and therefore only in a thin layer, thus making efficient skimming difficult.
"V" Configuration or V-Sweep
Concentrating capability: Medium
Maneuverability: GoodA large scale V-shaped sweep is not possible. It will eventually end up as a U. But for smaller sweeps, mounted at one side of the recovery vessel, this is an extremely efficient way of tracing the "windrows". The limited sweeping width limits the overall concentrating capability, but the efficient concentration of the oil which is caught by the sweep, supports a high recovery efficiency of the skimmer. The use of a bottom net design - incorporated into the V-apex of the sweep - may result in increased recovery speed and efficiency.
"J+V" Configuration
Concentrating capability: Good
Maneuverability: MediumIn this concept, a "V" pocket has been attached to the apex of the "J", and the vessel next to the "V" will also operate the skimming unit. Two vessels facilitate navigation when compared to three vessels, as needed for a "U", and the efficient concentration of the oil entering the V part of the sweep supports a high recovery efficiency of the skimmer
Side Fitted Single Vessel Sweep
Concentrating capability: Poor to medium
Maneuverability: GoodThis configuration is very common, and is recommended due to an excellent maneuverability. The vessel is equipped with a side fitted outrigger arm (jib) which holds the boom in either a U shape (poor oil concentration ability), see sketch to the right, or a V shaped formation, see V Sweep sketch above. The V shape has the ability to concentrate the oil and therefore build up a thick oil layer for high skimming efficiency. The sweeping width is, however, limited.
Side Fitted Single Vessel Double Sweep
Concentrating capability: Medium to good
Maneuverability: GoodTwo side fitted sweeps are used, one jib arm on each side of the hull hold the sweeps. The sweeping width will be increased, and still the maneuverability of this configuration is good.
"U" Configuration with an open apex, followed by a Side Fitted Single Vessel Sweep
Concentrating capability: Very good
Maneuverability: MediumCompared to the "U" with two towing vessels and one recovery vessel operating a skimmer at the apex of the boom, this concept combines the advantage of a large sweeping width, with the efficiency of an independent recovery vessel mounted with a single or double side fitted sweep. The oil which is concentrated by the large "U" will be guided into a narrow stripe behind the U-sweep, and may immediately be contained and recovered by the Side Fitted Single Vessel Sweep following right after the U. (Back)
Skimmers
Skimmers in General:
An oil skimmer is a device which can be used to recover floating oil from (or near) the surface of water.The Skimmer is only one out of several links in the recovery chain, which for instance at sea may consist of the recovery vessel, tug boats, containment booms, skimmers, transfer pumps, and temporary storage. No chain is stronger than the weakest link, and where this is in the recovery chain, depend very much on weather and sea conditions, size of oil spill and type of oil, presence of debris, seamanship, vessel capability, boom configuration/performance, skimmer type, type and capacity of transfer pump, and finally the storage capability.
In the aftermath of the Exxon Valdez incident and the OPA 90, high skimmer/pump capacity has been of higher priority. It is, however, from a practical standpoint necessary to mention, that VERY rarely the skimmer’s name plate recovery rate sets the limitation for a successful response operation (the type of skimmer and transfer pump being used is more important). Even the best sweep configurations can rarely concentrate more oil than what a 50-100 cbm/hour skimmer can recover simultaneously. Skimmers with 200 or even 400 cbm/hour capacity must be considered more political than relevant. If the very seldom situation should occur where real high capacity is required, it is much more likely that the best efficiency and match with the other links in the recovery chain is obtained by throwing in several smaller sweeps and skimmers.
Several dozens of skimmers have been designed and manufactured over the years, and many have also found their way to a permanent position on the market for equipment which especially is suitable for sheltered and quiescent water. But for open sea response, only a few types and brands form the backbone of the World’s preparedness as a whole.
This is due to the circumstances in this special field: When oil spills at sea happen, and response operations are initiated, very few equipment designers will ever be involved. The parties behind a response operation do not wish to let in curious persons, not directly involved in the clean-up. Therefore most of the design work have been based on theoretic studies or second or third hand knowledge to the realities of an oil spill. Several ingenious designs have been created, but most of them will only work under calm, laboratory like conditions on a spill with nice, liquid oil without debris.
It is important to realize how oil behaves when spilt on water. It is important to know how weather and especially wave action influence the movements and thereby the performance of a skimmer. Low inertia mass and small dimensions are musts if a skimmer shall maintain its operating position relative to the sea surface.
An evaluation and comparison of the different skimmer principles is possible. But what actually is more relevant is to compare the overall performance of the combined skimmer and transfer pump. Therefore the following presentation should be read with the "PUMP" section in mind.
A skimmer may be
free floating
side mounted on a vessel
built into a vessel
built into the apex of a containment boom
held by a crane
held by handSkimmer designs are based on the following principles (in alphabetic order):
adhesion/oleophilic
air conveying
belt
filter
inclined plane/hydrodynamic
mechanical feeder
vortex
weir
and combinations of these principlesNOTE: How buoyancy is provided to the different principles will not be discussed, but will appear from the various photos and illustrations (coming soon!).
Skimmers may be static or dynamic. However, these terms have caused some confusion over the years. Therefore it is specified for this presentation that a static skimmer is a recovery device which is not being moved through the water and no water and oil is moving past it. A dynamic skimmer is a unit which is is moved through the water, for instance in conjunction with a boom sweep and a vessel. Or it may be fixed in a river where the water and oil is moving by. Most skimmers are meant to be dynamic.
Skimmer Principles and their Performance
- Adhesion/Oleophilic Skimmers
- Air Conveying Skimmers
- Belt Skimmers
- Filter Skimmers
- Inclined Plane Skimmers
- Mechanical Feeder Skimmers
- Vortex Skimmers
- Weir Skimmers
Adhesion/Oleophilic Skimmers
This principle uses the oil’s ability to stick to certain materials. Polypropylene, PVC and aluminium are – among others - good adhesion materials. The aim is to let the floating oil stick to a moving surface and then – once out of the water - scrape or squeeze it off into a sump or a pump. This may be a rotating disc, drum, or brush. Or it may be an endless band, mop rope or bristles. Bristles and teethed discs combine adhesion and mechanical feeding.Viscosity range: Pure adhesion will work up to a maximum of 10,000 cSt, although optimum is 100-1000 cSt and above 5,000 cSt, efficiency is very low.
Water content: Is low at low disc-, band-, drum-, mop-, and bristle speed and at low viscosity. Higher speed and viscosity will increase the water content significantly.
Debris: Adhesion skimmers are not very debris sensitive as long as the debris does not restrict the flow of oil to the skimmer. Smaller debris may nevertheless clog the suction- or pump inlet. Big debris will not be dragged into the skimmer.
Operating conditions: Disc, band, and drum skimmers: Relatively calm water, as the wave action may push the oil away from the adhesion surfaces. Mop ropes and bristles are less wave sensitive. Mops and bristles have demonstrated good performance in water with broken ice. Small disc and mop skimmers (5-15 cbm/h) are the most commonly used skimmers World wide, for in-shore, harbour, and lake spills. Mop skimmers are used in many static applications, for instance in API separators. (Back)
Air Conveying Skimmers
Vacuum trucks or smaller vacuum units are often used as skimmers with or without a skimmer head mounted at the end of the suction hose. But only for very light oil is vacuum the effective player. With a maximum of 0.8-0.9 bar(12 PSI) of suction, the vacuum will be inefficient on higher viscosities due to friction losses in the suction hose (Please see the "Pump" section of the Response Handbook). But how can it be that they are used anyway?The secret behind the vacuum unit’s ability to recover oil is the high speed movement of the air at the end of- and inside the suction hose. You could talk about an air conveyor belt. The high speed air merely lifts off the oil from the surface of the water and transports it to the reception tank. With viscous oil this is only possible if a lot of air is dragged into the hose "parallel" with the oil. Vacuum (and no air flow) will not do it.
Air conveying has been refined in portable units with small reception tanks, but with powerful air conveying capability.
Viscosity range: Air conveying will handle even solid oil, provided it is in lumps small enough to enter the intake. Range: up to about 1 million cSt.
Water content: Low in calm water conditions, but high in waves.
Debris: As long as the size is small enough to enter the inlet, there is no problem, but bigger debris will clog the intake and seize operation until cleared away.
Operating conditions: Preferably calm water. Autonomous self floating units will due to weight and size get out of phase with waves, thus loosing efficiency. If only the intake head is floating, the wave performance may be somewhat better.
(Back)
Belt Skimmers
As belts are used in several ways, covering "adhesion","mechanical feeder", "inclined plane", and "filter", and combinations thereof, it is relevant to describe the belt type as a separate principle, although it is not one.The filterbelt combines filtration with adhesion and mechanical feeding . The belt is moved through the water/oil, and a pump behind the belt may increase the flow to and through the belt. The filter effect separates oil and debris, letting the water pass through the filterbelt. The adhesion effect lifts the oil and oily debris out of the water, conveyed by the belt’s movement. At the top of the belt the oil is scraped off into a sump or a pump, while the biggest debris is guided to a separate storage.
The non-adhesion belt is used to convey the floating oil below the water surface and feed it into a collection and recovery tank, where the oil again will float up to the surface. The belt’s movement will offers almost zero relative velocity to the oil, thus facilitating separation and re-floating. As the layer builds up, a built in weir skimmer recovers the oil, and a pump will transfer it to a reception tank. This principle combines mechanical feeding and inclined plane, and is called the submerged belt or Dynamic Inclined Plane, DIP.
The conveying belt is used to lift - by means of cups or scrapers - the oil (and in some cases also some water) out of the water and dump it into a sump or a pump. This principle is actually mechanical feeding. When cups are mounted on the belt, some water will be be recovered together with the oil. However, this may be decanted from the recovery sump prior to transferring the oil.
Viscosity range: The above water belt type skimmers may recover even very viscous oil. The expected maximum is 50-100,000 cSt. The cup belts may have a problem getting high viscosity oil out of the cups. The submerged belt skimmers will only recover what the pump or skimmer in the reception tank will handle.
Water content: The conveying belt with cups will always recover a lot of water with the oil. The other types will have a low water content in calm water, however, increasing with increased wave action, belt speed, and viscosity.
Debris: The belt skimmers are very good at handling debris. Normally it is the transfer pump which sets the limitation.
Operating conditions: From calm sheltered water and near shore up to 8 m/sec wind speed, 1.5 m significant wave height. Higher waves will push the oil away from or under the skimmer. Belt skimmers have been used with good results for many years, although they - due to price and size - have only been distributed moderately. (Back)
Filter Skimmers:
The filter belt has already been mentioned above under belt skimmers. Filter skimming also takes place in the net-drum skimmer, which consists of a horizontally oriented drum made of stretch metal, which rotates around a circular tube with a built in hopper. The diameter of the net-drum varies from maximum at the opening or inlet, to minimum at the horizontal tube and hopper, thus creating a concentrating capability by rotation. The hopper is well above the water surface, so the concentrated oil will be scraped into the hopper with no or minimum water content. Inside the hopper an Archimedes’ screw feeds the recovered oil into the transfer pump. The net-drum combines filter and mechanical feeding, and to some extent adhesion.Net bags, or so called oil trawls, which can be attached to the apex of a sweep, in order to recover tar balls and high gravity oil and bitumen(floating in or under the water surface), must in principle be considered as a filter skimmer. The forward movement of the sweep will force both oil and water into the oil trawl. The water will escape through the masks, which, however, will hold back the oil, due to the oil’s higher viscosity and inner tension (shear rate).
Viscosity range: Net drums and net bags will recover oil well over 100,000 cSt.
Water content: The net drum will increase the water content with increasing RPM of the drum and with the increase of viscosity. But in general both the net drum and the net bag will - under moderate working conditions - recover very little water.
Debris: Once debris, which is too big for the feeding screw and the transfer pump to handle, gets into the net drum, it is very difficult to remove, and it may seize the operation for a long time. But smaller debris is no problem. The net bag will recover whatever debris can get into the bag.
Operating conditions: The net drum and the net bag are not very sensitive to wave action as long as oil is constantly moved to the unit. The expected maximum significant wave height is about 2m for the net drum, while the net bag will work as long as the containment booms can hold the oil. The filter or net principle is not as widely distributed World wide as it deserves. (Back)
Inclined Plane Skimmers:
The belt combination was mentioned above, under belt skimmers. The inclined plane skimmer (without belt) works in a similar way. But here it is solely the forward movement of the skimmer through oil and water which forces the oil under the plane and into the collection and recovery area, where the oil will re-float. As the layer builds up, a built in weir skimmer recovers the oil, and a pump will transfer it to a reception tank.Viscosity range: It should not be expected that the inclined plane skimmers will be efficient above 20,000 cSt, as oil of higher viscosity will tend to be pushed in front of the skimmer, and will also have difficulties in following the flow to the surface of the collection chamber. This principle will further be limited to recover what the pump or skimmer in the reception tank will take.
Water content: For moderate weather and moderate viscosity (less than 10,000 cSt) the build up of a thick oil layer in the collection chamber will result in a low water content with the recovered oil. Higher speed, bigger waves and high viscosity will increase water percentage significantly.
Debris: Larger debris may enter the collection chamber, but may not be handled by the built in weir skimmer or transfer pump. This situation will require personnel ready to manually remove debris.
Operating conditions: The principle of re-floating submerged oil limits how much bumping the skimmer can take before the oil is lost under the skimmer. A significant wave height of about 1.5 m will be the upper limit for a reasonable performance. The principle is intended for higher speed than the normal 0.5 to 1 knots. But the higher speed, the smaller waves can it take. The principle is not widely spread outside the USA. (Back)
Mechanical Feeder Skimmers:
This principle is always used in combination with one or more of the other skimmer principles. One exception could be the conveyor belt cup skimmer, which is best described as a mechanical feeder.Combination examples:
A disc skimmer with teeth at the perimeter of the discs combines adhesion with the teeth’s ability to feed.
Rotating (or endless ropes of) bristles or brushes, mounted on a weir skimmer, combine adhesion to the bristles, and feeding capability provided by the stiffness of the bristles, with the simplicity and low inertia mass of the weir skimmer.
The net drum skimmer, combines filtration and adhesion with the feeding and concentrating geometry of the stretch metal drum.
The filterbelt combines filtration with adhesion and mechanical feeding.
Common for the addition of mechanical feeding to the various skimmer principles is that it results in significantly increased performance regarding high viscosity, debris capability, and to some extent, low water content. However, this puts further stress on the importance of the transfer pump’s performance. But there is no doubt that "above water" feeding combinations are good choices in difficult oil spill operations with weathered and debris laden water-in-oil emulsion. (Back)
Vortex Skimmers:
This principle creates a vortex in the central zone of the skimmer, by rotating and evacuating water through the bottom of the recovery chamber, using a large diameter propeller pump or paddle wheel. Thereby water and oil is "dragged" towards the skimmer, and simultaneously a centrifuge function is created, which tends to allow for the build up of an increased oil layer in the center of the vortex. The oil is sucked by a pump or recovered via a simple weir at the center. A different way of creating the vortex is to let a forward movement force oil and water tangentially into a circular chamber. The water escapes through the bottom, and the oil is sucked away from the increased oil layer at the center of the vortex.Viscosity range: Up to a maximum of about 5000 cSt this principle may work as intended. But increased viscosity will disable the circulating water’s ability to bring the oil along.
Water content: Relatively low, provided absolutely calm conditions.
Debris: The vortex may be severely disturbed by the presence of debris. The vortex inducing propeller pump or paddle wheel will very soon be jammed up with debris.
Operating conditions: Absolutely calm and clean conditions. More like a laboratory situation… But for such condition the paddle wheel vortex principle may be the only skimmer which will have any effect in static mode. The principle was popular in the earlier years of oil spill response history. (Back)
Weir Skimmers:
This is the most simple of all the principles. Actually, all it does is the same as when the cook skims the fat off the soup, using a table spoon. The weir lip may be adjusted vertically up/down hydraulically, or the entire skimmer may be air ballasted up/down by dragging water out of - or into - one of the floats. A few have manual adjustment. However, the most common adjustment is by means of a self adjusting weir lip, which floats higher or lower depending on the pumping rate.Weir skimmers may be free floating skimmers, mounted on a crane, hand held, or built into combination skimmers as described above. A special combination is the weir boom, where a weir, a hopper, and a transfer pump is integrated in the apex section of a boom. There are also designs with two or more weirs built into the boom.
Combinations where the weir skimmer is the basis for attachments of different cassettes with disc sections, bristles, or other feeders are also available, offering a versatile concept.
A weir skimmer may have an internal transfer pump mounted in or under the weir hopper. Or transfer of recovered oil may be handled by an external suction pump or a vacuum unit.
Viscosity range: As a free floating dynamic weir skimmer, preferably placed in the apex of a V sweep, efficient skimming will seize at about 30-40,000 cSt, dependent on the design of the weir lip. Additional mechanical feeding may expand the viscosity range up to 50-100,000 cSt. Free floating lumps of almost solid oil may also be recovered, provided they can pass the weir lip and enter the intake of an appropriate transfer pump.
Water content: Weir skimmers will – especially at open sea - recover more water than most other skimmers, but over a longer term their simplicity and reliability still make them recover more oil than other skimmers.
Debris: Big debris may obstruct the oil’s flow to the weir or may clog the transfer pump or suction intake. Depending on the type of transfer pump, medium and smaller size debris will not affect the skimmer.
Operating conditions: Due to small size and weight, when compared to recovery capacity, this principle will allow skimming in up to 12 m/sec wind speed and a significant wave height of 2 to 2.5m. In general you can say that an open sea weir skimmer will work as long as the containment boom can hold the oil. Weir skimmers are the most widely distributed skimmers for open sea and near shore skimming, and over the last few years they have become quite common in land spill clean-up operations and in waste oil pit-cleaning, as it is convenient that responders may push or shovel oil sludge directly into the hopper. (Back)
Pumps:
Please check the most advanced pump transfer techniques available for spills of heavy oil:
Positive Displacement Archimedes’ Screw Pumps and Flow Enhancing Techniques. Essential Tools in Response to Spills of Heavy Oil and Bitumen. flemingCo presentation at the AMOP 2003 seminar in Victoria, Canada.
[DOWNLOAD paper 1.1 Mb PDF]
Storage:
Coming soon
Dispersants and Spray Systems:
Coming soon, but in the meantime get the information as provided by ITOPF: http://www.itopf.com/dispersa.html
Response Vessels:
Coming soon
Absorbents:
Coming soon
Other Spill Response Equipment:
Coming soon
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