PNEUMATIC BARRIER FOR OIL SPILL CONTAINMENT

PNEUMATIC BARRIER FOR OIL SPILL CONTAINMENT
Term Project by Brett M. Durham

INTRODUCTION

Increasing environmental awareness and several marine disasters have made governmental regulations standard on marine transfer operations. Many states have adopted laws requiring that oil spill containment devices be deployed during all ship off loadings. With mandatory containment laws many oil companies are researching different containment systems to replace the labor intensive containment boom commonly used. The method some are turning to is the pneumatic barrier. The pneumatic barrier offers significant advantages over traditional boom for spill containment because of its ease of operation, effective containment, and oxygenation of the local waterbody. Over the past five decades the rapid economic development of many countries has greatly increased the need for the marine transportation of crude and refined oils. Also during this time companies were starting to look to the sea to satisfy the increased need for fossil fuels. The use of offshore drilling and offshore transportation has led to many ecological disasters over this period of time. The first of these disasters, the 1967 grounding of the "Torrey Canyon" spilling 117,000 tons of oil and the 1969 blow-out of the drilling platform "Santa Barbara" spilling 13,600 tons of oil, caused many national and international laws attempting to control and contain major oil spills (Doerffer, 1992).

As our scientific knowledge broadened we gained a better understanding of the ecological consequences of oil spills. After the spill of the "Exxon Valdez' in the spring of 1989 the nation was subjected to the environmental horrors of oil related disasters. The media presented the public with pictures of oil soaked animals that were doomed to die a slow and painful death. This event raised the social consciousness related to the potential hazards of marine fossil fuels transportation. It was events like the "Exxon Valdez' spill and other recent spills that prompted the State of Connecticut to enact a bill requiring off-loading vessels to be surrounded by containment boom. This bill was passed on January 1, 1992 and many other states followed Connecticut's lead (Santa, J 1993). Until a safer type of fuel is developed dangerous oil spills are bound to occur and the law passed by the State of Connecticut and other states is an attempt to limit the destructive affects of petroleum spills on the marine environment. This report will analyze the pneumatic barrier as the most effective means of containing these dangerous oil spills at marine vessel transshipment operations

METHODS OF OIL SPILL CONTAINMENT

The scope of this report will concentrate on the most effective method of oil spill containment at vessel transfer operations (i.e. barge off-loadings). Presently, the most popular method of containment is the traditional boom, a floating apparatus consisting of an underwater "skirt" to contain oil. Another method increasing in popularity is the pneumatic barrier which forces air through a pipe located beneath the surface of the water to cause a surface current entraining the oil. Other methods include a hydraulic jet which lies on the surface of the water and projects high velocity jets of water to capture the oil. Lastly, the surface acting air jet acts above the waters surface and entrains the oil with high pressure air (Doerffer, 1992).

TRADITIONAL BOOM

COMPONENTS

A traditional floating containment boom consists of four primary elements:
1) A method of flotation. The boom must be equipped with some way to stay afloat. Common materials used for flotation include plastics, natural cork or wood, or gases such as air or carbon dioxide.
2) The skirt. The skirt is the part of the boom which lies beneath the surface and contains most of the oil. Many different materials are used for the skirts but common types include a strong fabric coated with nylon or fiberglass.
3) The freeboard. The freeboard is attached to the top of the boom and prevents waves from carrying oil over the top. Because of the considerable windage caused by the freeboard it must not be built too high.
4) A tension member. This member must be incorporated into the entire length of the boom to carry the load caused by wind, waves, and current. The tension members are located at or slightly below the waterline and are constructed generally of cable (Doerffer, 1992).

There are many types of boom available today. Different booms are designed for different uses and sea states. When several booms are to be joined together to form a containment barrier the ends must be able to form a tight joint to keep oil from leaking through.

OPERATION

The deployment of the boom around a barge during transshipment is a lengthy, costly, and potentially dangerous project. When the barge is moored one or two people in a small boat must physically place the boom around the vessel and anchor it properly. These same people must remain on call for the eight to ten hours the barge is off-loading. When the barge is ready to leave they must go back out in the small boat and retrieve the boom (Applicability of an Air Barrier, 1992). In daylight and mild conditions deploying the boom is not much of a problem, but barges frequently arrive at night during the middle of winter. This increases the risk of hypothermia or even death for the people deploying the boom if they fall in the water.

PNEUMATIC BARRIER

The pneumatic barrier is a containment method that offers significant advantages over the traditional boom in transfer operations. This barrier produces a current with sufficient velocity to stop oil from over running it or becoming entrained below it. The current is produced by air flowing through a perforated manifold laid on the bed of the water body. The air is supplied from a compressor that is located ashore.

COMPONENTS

The pneumatic barrier is composed of two parts, a compressor and a perforated pipe. Together these act to create the surface current entraining the spilled oil. The compressor must be sized to create sufficient air flow to overcome hydrostatic pressure, frictional losses, and expel water from the pipe (Applicability of an Air Barrier, 1992). On page 15 there is a chart relating the total air flow required to the power required from the compressor. The pipe may be constructed from steel, aluminum, rubber, PVC, or polyethylene. Each of these materials have properties making them suitable to be used as the manifold. However, polyethylene or rubber can withstand the water pressure, are flexible, and resist corrosion in the sea. For these reasons they are more highly recommended. The holes to expel the air can easily be drilled into any of these materials (Applicability of an Air Barrier, 1992). Water currents and frequent barge traffic over the pipe make it necessary to anchor it to the bottom. Anchoring methods may be simple or complex depending on the anticipated currents and overhead traffic. In many instances cinder blocks or other weights are suitable for anchoring the manifold. These weights should be easy to remove if dredging operations make it necessary to remove the manifold from the water.

OPERATION

The pneumatic barrier uses a physical flow mechanism to produce the desired surface current. This is done when the air bubbles are released from the manifold under pressure. The bubbles rise and expand as the hydraulic pressure decreases. The rising air column causes an upward water flow. As the vertical flowing water reaches the surface it is diverted into the horizontal direction causing a surface current extending in both directions away from the vertical stream of bubbles. This generated surface current effectively entrains the spilled oil (Doerffer, 1992). A diagram of the pneumatic barrier in operation is found on page 16. The pneumatically generated current will achieve its maximum speed at a distance of 0.3 to 0.6 times the water depth from centerline of the system. The formula for determining the maximum induced current speed is: Umax = K(gQ) ^ 0.33 Umax = maximum surface current generated pneumatically K= experimental constant, approximately equal to 1.46 g= force of gravitational acceleration Q= air flow rate at depth of pipe With this formula, and a knowledge of the required induced current, one can determine the flow rate Q and therefore know the proper sized compressor (Applicability of an Air Barrier, 1992). The proper sized compressor to deliver the air required to form a barrier is related to the following three factors: 1) The maximum surface current required to overcome wind forces and natural tidal currents. 2) The amount of air to overcome loss through the pipes orifices. 3) The amount of air to overcome frictional loss (Applicability of an Air Barrier, 1992).

OTHER TYPES OF CONTAINMENT METHODS

Though the traditional boom and pneumatic barrier are the most popular types of containment during transshipment there are two other types available. These types are the hydraulic jet and the surface acting jet. The hydraulic jet contains oil by spraying a high pressure stream of water along the water surface. This stream creates a surface current entraining oil. The surface acting jet uses air blown from a manifold slightly above the water surface to contain the oil. (Doerffer, 1992) The surface acting jet and the hydraulic jet will not be considered in this report because they are not commonly used during transshipment operations.

USES OF THE PNEUMATIC BARRIER

Presently the pneumatic barrier is being used by relatively few terminal operators to contain oil spills. This report will concentrate on two relevant trials of the pneumatic barrier for spill containment. The first example is the City of Buffalo's use of a pneumatic barrier in the Buffalo River to prevent the pollution of Lake Erie. Second, is Inland Fuel Terminals Inc. use of the pneumatic barrier for spill containment in response to the State of Connecticut law requiring all off-loading vessels to be surrounded by containment boom.

THE PNEUMATIC BARRIER ON THE BUFFALO RIVER

The Buffalo River has been troubled by pollution for numerous years. This pollution, a combination of continuous discharge, accidental spillage, and illegal disposal, has contaminated the waters of the Buffalo Harbor and Niagara River and has also threatened Lake Erie. In May 1968 the City of Buffalo applied for and received a grant from the Federal Water Pollution Control Administration for preventing oil pollution on the Buffalo River. With the grant Buffalo hired the Cornell Aeronautical Laboratory (CAL) to conduct research and development for the program (Frank, 1970). The Buffalo River required an upper and lower river containment system. The upper river system used a traditional boom to contain spills. This could not be done in the lower river due to the fact that it is open to navigation and using a traditional boom would not allow ships to pass without removing the boom. For this reason the pneumatic barrier was proposed by CAL (Frank, 1970). This was not the first application of the pneumatic barrier. They had been used in the past as breakwaters and also as oil containment devices. However, very little quantitative data on their effectiveness of containment devices was available. CAL, therefore, had to develop the air barrier with many extensive laboratory studies (Grace, Sowyrda, 1970). The results of these laboratory and river tests have been invaluable to the development of the pneumatic barrier.

LABORATORY TESTS

Lacking any substantial information on pneumatic barriers CAL used water tank testing to study the surface currents produced by buoyant plumes. Through this study variations of the system, mainly, orifice diameter, orifice spacing, air supply pressure, plume form and surface velocities were noted. The test materials consisted of a 4 foot long and 3 inch diameter steel pipe, with multiple sized orifices of 1,2, and 3 mm, which served as the manifold. The air was supplied through a rubber tube from a 27.5 cfm (cubic feet per minute) compressor. The tank was 60 feet long, 15 feet wide, and 15 feet deep (Grace, Sowyrda, 1970). The manifold was submerged at various depths in the tank and the compressor was operated. Surface currents generated by this system were then measured by a propeller type current meter and recorded. The laboratory tests indicated that the most effective type of manifold would be either 1 mm orifice at 1 foot spacing, 2 mm orifice at 1 foot spacing, or 2 mm orifice at 2 foot spacing. These nozzle and spacing combinations provided the greatest surface current and these types would be tested in the Buffalo River (Grace, Sowyrda, 1970).

BUFFALO RIVER TESTS

The pneumatic barrier was installed in the Buffalo River and connected to two 600 cfm, 150 horsepower compressors. The compressors could be used alone or together and for most of the testing only one compressor was used. Much was learned from the testing and the strengths and weaknesses of the system were evaluated . The modes of failure of the pneumatic barrier were discovered. The first type of failure occurred when the supply pressure was only slightly greater than the hydrostatic pressure. When there was a river current the system was unable to generate a curtain of air bubbles because the bubbles were swept away by the current. This could be remedied by increasing the supplied air. The other possible failure occurred when the surface current was greater than 1.5 fps (feet per second). When this occurred the oil became closer to the plume of air and could overrun the barrier. This was a serious mode of barrier failure and was referred to as barrier breakdown (Grace, Sowyrda, 1970)

THE PNEUMATIC BARRIER AT INLAND FUEL TERMINALS INC.

Inland Fuel Terminals Inc. (Inland) is a medium sized petroleum terminal based in Bridgeport Connecticut. The law passed by the State of Connecticut requiring off-loading barges to have containment boom surrounding them at all times prompted Inland to look for a more effective and safe method of spill containment. The system that Inland researched and chose was the pneumatic barrier. I interviewed Norman K. Santa, Vice-president of Inland, with regards to the events leading to the choice of the pneumatic barrier over the traditional containment boom. Inland is located on Cedar Creek, an estuary of Long Island Sound, and primarily receives their petroleum from the sea. Cedar Creek is 180 feet wide at Inland's off-loading dock and terminates approximately one quarter mile beyond the dock. Because of the shape of the creek, Inland petitioned the State of Connecticut to allow them to place their containment boom across the creek rather than around the barge. This arrangement would trap the oil between the containment boom and the end of the creek allowing no oil to escape. The State of Connecticut granted this request. This set-up made the boom much easier to deploy (personal interview, Santa, N 1993). Even with the easier deployment the cost of setting the boom was still $500 - $700 per barge. With Inland receiving oil between 60 - 70 barges per year the costs added up. Deployment costs of up to $ 49,000 per year caused Inland to look for a more cost effective barrier (personal interview, Santa, N 1993). Inland contacted Stan White, of Ocean and Coastal Consultants Inc. (OCC) with the possibility of a more cost effective barrier. OCC recommended the consideration of the Air-Guard system, a pneumatic barrier. This system, according to White would be more cost effective and easier to deploy than the traditional boom, while aerating the local waterbody (personal interview, Santa, N 1993). The State of Connecticut and the US Coast Guard approved this type of barrier for use in spill containment with a few requirements. The requirements were that studies were to be made about the effect of the barrier on the sediment on the bottom of the creek, and that the traditional type boom should be on hand to be deployed in case of the pneumatic barriers failure.

COST ANALYSIS OF PNEUMATIC BARRIER

The system proposed by OCC consists of a compressor, 180 feet of three inch diameter pipe with 1/16 inch diameter orifices every foot, and concrete anchoring devices. The compressor proposed is a 100 horsepower delivering an air flow of 479 cfm (cubic feet per minute). The costs of the system are as follows: (Applicability of an Air Barrier, 1992) Capital cost - $ 25000 Operating cost - $ 5000-6000 (per year) Maintenance cost - $ 800-1000 (per year) The system Inland chose to use consisted of all the same equipment proposed by OCC with the exception of a used diesel powered compressor in place of the electric. The diesel compressor uses approximately 50 gallons for each barge off-loading. At a price of $ 1 per gallon makes operating of the compressor $ 3500 per year (assuming 70 off-loadings). Maintenance in the compressor is done in-house for a cost of $ 2000 per year (personal interview, Santa, N 1993). The capital costs and operating and maintenance costs are considered below for both the traditional boom and the pneumatic barrier.
(Table 1 ) Traditional Boom Pneumatic Barrier Capital cost - $ 5000 Capital cost - $ 30000 O/M cost (deployment) - $ 49000* O/M cost - $ 5500* O/M costs assume an eight hour transshipment time and 70 barges per year. The cost to deploy traditional boom is assumed to be $ 700 per deployment. As these tables show even with the much greater capital cost of the pneumatic barrier the traditional booms deployment costs allow the pneumatic barrier to pay for itself within the first year of operation. It was these very significant cost benefits that led Inland to choose the pneumatic barrier.

FIELD TESTS

After installation of the Air-Guard system Ocean and Coastal Consultants Inc. (OCC) performed two field tests, on March 9, 1992 and August 31, 1992. The purpose of these field tests was to analyze any positive or negative environmental effects the Air-Guard system had. Specifically the tests recorded the following information:
  • Any change in turbidity
  • Any increase of the dissolved oxygen content within the waterbody
  • Inspect the pipe to see if operation of the pneumatic barrier resuspended sediment in the water (White, 1992) The findings of these field inspections were very positive. In both reports the divers inspecting the pipe found it to be relatively free of sediment and when the barrier was operated there was no significant suspension of sediment. Additionally the reports show that there was no increase in turbidity. (White, 1992). The lack of resuspension of any sediment and any increase in turbidity was vital in showing that the Air-Guard system was not causing any negative environmental effects. In the contrary, the tests performed on the dissolved oxygen concentration proved that there was an increase of dissolved oxygen in Cedar Creek. The dissolved oxygen tests were performed by Stephen Edwards of Environmental Services. In the analyses of the water quality two stations were set-up, one at the barrier and one 700 feet downstream. Ambient water samples were taken and then the Air-Guard system was operated for one hour and forty-five minutes and additional water samples were taken. The samples were taken at the surface, mid-depth, and one foot from the bottom. The results of this report are shown in the table below.
    (Table 2) Station Depth Dissolved oxygen (mg/1 ) ambient samples: barrier surface 9.9 mid-depth 6.4 bottom 2.4 700 ft. from surface 10.0 barrier mid-depth 6.6 bottom 0.0 samples after 1.75 hours of Air-Guard operation: barrier surface 7.9 mid-depth 5.3 bottom 2.9 700 ft. from surface 13.6 barrier mid-depth 10.9 bottom 2.4 These results show the improved water quality due to the pneumatic barrier. Two significant points are that 700 feet from the barrier the dissolved oxygen concentration is noticeably improved. This is due to the strong upwelling current caused by the Air-Guard system. This current not only transfers the dissolved oxygen along the river but also brings the bottom water to the surface This is advantageous when dissolved oxygen is exceptionally low in the bottom depths. The improved water quality on the bottom of the waterbody will have positive impacts on any biological organisms inhabiting the lower regions of Cedar Creek (White, 1992).

    ANALYSIS OF THE PNEUMATIC BARRIER

    As has been stated earlier in the report the pneumatic barrier offers significant advantages over the traditional boom in spill containment during transfer operations. The past section on the uses of the pneumatic barrier is useful to show that both municipalities, with the case of Buffalo, as well as moderate sized businesses, with the case of Inland, can benefit from the pneumatic barrier. I will refer back to these examples in my analysis of the pneumatic barrier.

    ADVANTAGES

    The benefits of the pneumatic barrier are many. They are easier to operate, cost effective, and environmentally beneficial. The ease of operation is due to the relatively labor free deployment. The cost effectiveness is a result of the high costs of boom deployment. And lastly, the increased dissolved oxygen can help restore life to the lower depths of heavily polluted waterbodies.

    EASE OF OPERATION

    The traditional boom's deployment was briefly described in the METHODS OF OIL SPILL CONTAINMENT section. The boom must be physically strung around a barge and anchored in place by one or two people in a small boat. This method of deployment causes several problems. The first and most serious problem is the risk of hypothermia or death for someone deploying boom in adverse weather conditions. The pneumatic barrier's operation is virtually risk free and does not require anyone to be physically on the water for deployment (White, 1992).

    Another disadvantage of the traditional boom is in particularly severe weather. In states were containment booms are required for all transfer operations one may not be able to deploy the boom due to weather and notify the State. The transshipment operation is allowed to continue even without the precautionary boom deployed (personal interview, Santa, N 1993). The pneumatic barrier operation is not weather dependent and if a spill occurred during severe weather one could contain it. The operation of the pneumatic barrier is virtually "push-button". The compressor must be activated and then the surface current will form entraining any spilled oil. This can all be done in very short time with only one person and is a significant advantage over the time and labor intensive traditional boom.

    COST EFFECTIVENESS

    The cost effectiveness of the pneumatic barrier over the traditional boom is clearly seen on page 9 in the Inland example. In this case the operating and maintenance costs are remarkable in favor of the pneumatic barrier. An annual savings of $ 43,500 is possible. With these tremendous differences in O/M costs the pneumatic barrier will not only pay for itself in one year but will save Inland $ 18,500. While savings of this magnitude is seen at the medium size level a savings can also be realized on a large level. Ocean and Coastal Consultants Inc. is currently working on an Air-Guard system for Citgo in New Jersey. The system Citgo requires is a tanker containment system that uses 1100 feet of manifold and two 1200 cubic foot per minute compressors. The complete capital cost of this system is not yet known but the compressors alone will be $ 80,000 a piece. Citgo has determined the Air Guard system to be more cost effective (personal interview, White, 1993). The importance of the Citgo and Inland examples are that they show the feasibility of a pneumatic barrier for entirely different levels of use. Where as Citgo is a global distributor of many petroleum products, Inland is a local distributor of generally heating and industrial oils. The pneumatic barrier has proven itself cost effective at both of those levels.

    ENVIRONMENTAL BENEFITS

    The tests done in by Steve Edwards of Environmental Services at Inland show the positive effects of the pneumatic barrier. There was initial fear by the State of Connecticut that the pneumatic barrier would cause sediment resuspension, increased turbidity, and increased temperature. These problems would have had an undesirable effect on the biological organisms and were not at all evidenced in the Inland field tests. What Mr. Edwards discovered however, was increased dissolved oxygen concentrations and a more favorable distribution of dissolved oxygen allowing life to return to the bottom of Cedar Creek. See table-2. The possibility of oxygenating the lower depths of our polluted water is a very exciting prospect. The pneumatic barrier will generally be installed in highly industrialized and therefore polluted harbors. The oxygenating effects of the pneumatic barrier could prove very beneficial to the marine environment.

    MODES OF FAILURE OF THE PNEUMATIC BARRIER

    The pneumatic barrier has one serious mode of failure that must be considered in a serious analysis and that is in tidal current. When the tidal current exceeds 1.5 fps (feet per second) the oil slick will get to close to the plume of air and become entrained below it. Though this is a drawback of the pneumatic barrier the traditional boom will also fail in tidal current at .98 fps (Doerffer, 1992). Until a more efficient containment method is available for transfer operations it will be difficult to entrain spills when the current exceeds 1.5 fps. Another possible failure is compressor failure. This mode of failure can be virtually eliminated if the compressor is properly maintained or if back-up compressors were kept on hand.

    CONCLUSION

    This report has shown in theoretical tests and practical real life examples the advantages offered by the pneumatic barrier. The Buffalo River tests proved that the pneumatic barrier could work as a containment device. And the Inland example shows the advantages offered over the traditional boom for moderate sized terminal operators. Together these examples prove that not only is the pneumatic barrier a viable substitute for traditional boom, but also offers numerous advantages over the traditional boom. pneumatic barrier a viable substitute for traditional boom, but also offers numerous advantages over the traditional boom. The advantages of the pneumatic barrier over the traditional boom are the ease of operation, cost effectiveness and environmental benefits. These three factors make the pneumatic barrier the choice of the future in oil spill containment at transshipment operations.

    ACKNOWLEDGMENTS

    I would like to thank Norman Santa, of Inland Fuel Terminals, Inc. and Stan White, of Ocean and Coastal Consultants, Inc., for their time and information.

    REFERENCES

    "Applicability of an Air Barrier For Containment Within a Waterbody" Ocean and Coastal Consultants, Inc. l992 Doerffer, J W, l 992 OIL SPILL RESPONSE IN THE MARINE ENVIRONMENT New York Pergamon Press
    Frank, Ronald, l970 "Oil Pollution Control on the Buffalo River" PROCEEDINGS - Joint Conference on Prevention and Control of Oil Spills
    Grace, J and Sowyrda, A, l 970 " The Development and Evaluation of a Pneumatic Barrier for Restraining Surface Oils in a River" Water Pollution Control Federation
    Santa, John, 1993 - Personal Interview
    Santa, Norman, 1993 - Personal Interview
    White, Stan, 1993- Personal Interview
    White, Stan 1992 "Field Inspection of Manifold and Environmental Issues Summary Report" unpublished