Ship borne oil containment system and method

Abstract: When a section of a tanker vessel (10) is damaged, it is imperative that the liquid cargo (22) be transferred from the ruptured tank (B) to an undamaged tank on the vessel as quickly as possible. By doing so, the contents of the damaged tank are less likely to escape in a sufficiently voluminous quantity to seriously befoul the environment. To that end, a normally-empty emergency holding tank (122) is provided on the vessel with a pump means (106) to provide for emergency transfer of the liquid cargo from the damaged section into the emergency holding tank. At the same time, the ruptured tank is enshrouded by a flexible barrier curtain (12) to entrap a liquid cargo that may have leaked from the ruptured tank.

Description: This invention is concerned with the containment and removal of marine pollution at or near the immediate source, such as a stricken tanker, to prevent further dispersal of the pollution into the environment. Major spills of pollution material such as crude oil occur infrequently at sea but when they do happen, the results can be catastrophic. The disastrous effects stem not so much from the actual localized flow of the pollution from a point source, but from the uncontrolled widespread dispersal of the material over the water surface and beaches due to wave, wind and current action. If the flow of pollution can be substantially contained and/or shut off at or near the source, the environmental impact of the spill is minimal. Although the environmental effects of an oil spill are of concern, the economic loss of the natural resource is also important. Once the spill has spread over a large area, even if the thin layer of the scum can be recovered, it becomes so badly emulsified by the water that the scum cannot be economically processed. It is wasted. Recovery of the crude at the source, before it becomes seriously water-contaminated, is essential. For example, the PEMEX oil spill in the Gulf of Mexico several years back, reportedly lost more than 900,000 cubic meters of oil. Another problem in handling oil spills is the absence of proper and effective equipment to handle the accident. Historically, it has required days or even weeks to mobilize personnel and equipment and to put them into place. By that time it is often too late. Most of the presently-known control equipment is directed to merely skimming the already-dispersed pollution from the water surface and pumping the scum into holding tanks or pits. The equipment typically consists of buoyant plastic or rubber booms. A typical oil-spill boom made by Hurum Marine Inc. of Longueil, Quebec, is their FLEXY 3 oil boom. The curtain has a draft of 0.6 meters and a freeboard of 0.3 meters. The boom is made in 15 m. sections, any one of which allegedly may be coupled together as required. The boom is handled by small tugs. That sort of boom is of limited use in harbors or relatively protected waters but it is ineffective on the high seas where wave heights of 2 to 5 meters are not uncommon. The waves of the open ocean wash the floating oil scum over the 0.3 meter freeboard of the boom, rendering the boom completely useless, if indeed, the boom itself survives the vicious pounding of the waves. Even in calm water, heavy crude forms large globs of congealed oil. Because of their shallow draft, the curtains slide over the globs rather than raking them in. In the presence of a moderate current, the oil slick washes beneath the containment boom and escapes capture. Other types of cleanup devices include rope mops, botters, weir skimmers, oil sorbents, microbial agents and chemical oil dispersants such as supplied, for example, by Abasco,Inc. of Houston, Texas. Those techniques may be helpful in cleaning up dispersed pollution in quiet water but are of little use in containing the spill at the source ab initio. US Patent 4,412,501 teaches a ship-borne oil dispersant procedure and apparatus. The tanker ship carries a leak detector. If a leak is detected, a dispersant is released into the leaking oil, presumably rendering the oil harmless to the environment. Such dispersants are known to be effective for relatively small leaks but have proved to be useless in the case of a massive spill, as was clearly demonstrated during the recent Alaskan oil spill. In fact, some States such as Louisiana do not allow use of chemical dispersants. It would seem prudent to carry aboard a tanker a self-contained means for immediately containing and recovering its own leaking liquid cargo. All ships carry emergency fire-fighting equipment, emergency communication equipment and life boats; they should also be required to carry emergency spillage containment and recovery systems. U.S. patent 4,389,959 teaches an improved tanker ship that includes a redundant liquid cargo charging and discharging system, coupled to the cargo compartments which includes a longitudinal pipe and transversely-disposed branch lines coupled to the longitudinal pipe. The branch lines each include a suction opening disposed in and opening into a corresponding one of the compartments at a distance above the hull bottom and just beneath the external water line of the vessel. In the event of a rupture, the cargo is transferred from the ruptured tank into others of the cargo compartments should any space exist therein. According to a first aspect of the invention there is provided a method of minimising water pollution caused by rupture of any tank of a set of liquid containing cargo tanks carried by a vessel, the method comprising sailing with all the tanks of the set charged with liquid, with a first pumping system by which the set of tanks can be substantially fully discharged when required, and with a second, emergency, pumping system having provision for a suction intake to enter each tank of the set via an access port of the tank with the suction intake extending down to a level at or just below the external water level of the vessel, the second pumping system comprising at least one pump dedicated solely to emergency use so that a water seal can be formed in a ruptured tank by pumping out a portion of the liquid so as to water-flood the ruptured tank to at least a level above the topmost edge of the rupture, characterised in that the method comprises sailing with additional, emergency, tank means positioned in a protected location and dedicated solely to emergency use and into which the second pumping system will discharge in order to transfer liquid cargo through the suction intake of a ruptured tank. According to a second aspect of the invention there is provided a vessel arranged to carry out the method of the above first aspect and comprising a set of cargo tanks, a first pumping system by which the set of tanks can be substantially fully discharged, a second, emergency, pumping system having a suction intake passing into each tank of the set through an access port to be at a level at or just below the external water level of the vessel, the second pumping system comprising at least one pump, dedicated solely to emergency use, and characterised in that there are additional, emergency, tank means into which the second pumping system can discharge and in that the emergency tank means is arranged so that in use it is separated from the water by a tank of said set. It will be seen that certain embodiments of the invention can be designed so as to provide a self-contained emergency oil containment system for a vessel, such as an il tanker, that may be available for immediate emergency sue in the event of a ruptured liquid cargo tank. The system may include means for preventing dispersal of leaking oil, or the like, over the water. In one embodiment of this invention, said at least one pump of the second pumping system is a self-powered, high-volume, pre-primed pump. Each liquid cargo tank may be provided with a valved port through which the pump can be coupled to corresponding ones of the suction intakes so that any one of the tanks may be selectively emptied of its contents in event of a rupture. In another embodiment of the invention, the vessel is provided with means for enshrouding a ruptured tank, outboard of the vessel, with an impermeable barrier curtain. The bottom of the curtain is arranged to extend beneath the lowermost edge of the rupture in the tank. The leaking liquid cargo is entrapped in the sump formed between the barrier curtain and the hull of the vessel, whence the entrapped pollutant can be pumped into an emergency storage container. For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: FIGURE 1 is a plan view of a tanker ship showing the arrangement of the emergency pumps and plumbing for waterflooding a ruptured liquid cargo tank; FIGURE 2 is a cross section along line 2-2' showing a ruptured cargo tank prior to waterflooding; FIGURE 3 is a cross section along line 2-2' showing how waterflooding of the tank cuts off further leakage; FIGURE 4 is a cross section along line 4-4' of Figure 2; FIGURE 5 is a cross section along line 5-5' of Figure 3; FIGURE 6 is a plan view of the tanker showing only the equipment for handling the barrier curtains; FIGURE 7 is an end view of the oil containment barrier unfurled to entrap leaking oil; FIGURE 8 is a plan view of FIGURE 7; and FIGURE 9 is a side view of FIGURE 7. Preferred embodiments will now be described in which it is intended to minimize leakage from a ruptured cargo tank of a ship such as a tanker. To be truly effective, such a system should be installed aboard the ship itself, ready for immediate emergency use by trained damage-control personnel in event of an accident. The system comprises two aspects: First, means for emptying the contents of a damaged tank into an emergency temporary-holding container; Second, containment means for preventing widespread dispersal of the leakage over the water. Figures 1-5 illustrate a first embodiment; Figures 6-9 illustrate a second embodiment. Figure 1 is a perspective of a tanker ship 10. The ship includes a plurality of liquid cargo tanks such as A, B, C, D, as outlined by the dashed lines. Conventional piping and pumps normally used for loading and offloading liquid cargo are generally shown schematically by 100. It is to be understood that the conventional plumbing forms no part of this invention and, in fact, I do not even to try to use it for reasons to be explained below with respect to Figures 2-5. On deck of the ship, I provide at least one and preferably two, self-powered, pre-primed, high-volume pumps 104 and 106. The pumps preferably have a capacity of 38 to 57 cubic meters per minute and may be driven by suitable diesel engines (not shown). Pumps 104 and 106 are dedicated solely to emergency use. Each of the liquid cargo tanks is provided with an access port 110 that is equipped with a valve, such as 112, for receiving a suction intake to be described in connection with Figures 2-5. All of the tanks are similarly equipped. A large-diameter pipe line 114, serving as a manifold, interconnects all of the liquid cargo tanks on the port side of the ship with a pump 104 having a discharge line 108'. Pipe line 116 similarly interconnects the starboard-side tanks to pump 106 with its discharge line 108. A cross-tie line 118, provided with a valve 120, interconnects pipe lines 114 and 116 so that either or both pumps 104 and 106 may be fluidly coupled selectively to either or both pipe lines. I provide one or more relatively large, normally-empty emergency temporary-holding tanks, 122 and 124, in the ship, either at or below-deck and near the center of the vessel in a protected location. Alternatively an empty ballast tank, if available, could be pressed into service. The sole function of such tanks is to provide an emergency temporary-holding container for receiving the contents of a ruptured liquid cargo tank. In the Figures, the holding tanks 122 and 124 are shown as open vat-like receptacles by way of example only. They could be located in any convenient location and arranged in any preferred configuration. Refer now to Figures 2 and 3 which are cross-sectional views of ship 10 along line 2-2', showing ruptured liquid cargo tank B, intact cargo tank D and emergency temporary-holding tanks 122 and 124. Also refer to Figures 4 and 5 which are cross sections along 4-4' and 5-5' of Figures 2 and 3 respectively. Suction intakes 126 and 128 are fluidly coupled to valves 112, 112' in ports 110, 110' which they are interconnected with pumps 104 and 106 through pipe lines 114 and 116. Suction intakes 126 and 128 are located at or just below the water line as measured externally of the ship. If desired, the immersion depth of the suction intakes may be adjustable. The pump discharge lines 108, 108' terminate inside normally empty holding tanks 122 and 124. In the Figures, a hole 20 has been ripped into the side of tank B. The liquid cargo such as oil 22 pours out of hole 20 into the sea water 15 where it is contained by a barrier curtain 12, hung from supports 14, that enshrouds the hole (to be described in detail in connection with Figures 6-9 infra). Pump 106 is immediately activated to empty cargo tank B from the top by transferring its contents into temporary-holding tank 122. As the cargo is pumped out, sea water 15, being heavier than oil 22, invades tank B, through hole 20, to waterflood the tank to a level at least above the topmost edge 21 of the rupture 20. At that point, the effluent flowing from the leaking tank is cut off by reason of the water seal as shown in Figure 3. As holding tank 122 fills up while ruptured cargo tank B is being emptied, valve 120 may be opened so that the discharge out of cargo tank B may be diverted into holding tank 124 through cross tie line 118 as shown in Figure 3. It should now be clear why it is desirable not to use the conventional plumbing 100 to empty a ruptured tank. In a normal offloading operation of liquid cargo from an undamaged cargo tank, the entire tank must be emptied clear to the bottom. To that end, the suction intake coupled to the conventional cargo-discharge pumps must reach to the very bottom of a cargo tank. If the tank in question had been stove-in because of grounding, the cargo-discharge pump would simply pump out, through the suction intake, whatever sea water that had accumulated in the bottom of the tank through the gash, but without necessarily pumping out any of the oil. The tank should be emptied from the top to take advantage of the differential hydrostatic pressure between water and oil thereby to force the oil continuously upwards to create the required water seal inside the tank above the topmost edge of the gash. Figures 6-9, now to be discussed, show a method for preventing widespread dispersal of the leakage from a ruptured liquid cargo tank. For clarity, the details shown in Figures 1-5 are not duplicated in Figures 6-9 although common reference numbers are used where appropriate. Figure 6 is a cross section of a ship 10 having a furled-up emergency oil containment curtain or barrier 12 suspended from a support 14 of any desired type. Support 14 may for example, be a suitably modified version of a life boat davit of any well known variety. Barrier 12 is suspended from a cable 16 that may be connected to a winch 18 that may be either hand-operated or electrically or hydraulically powered. The barrier may conveniently be made in segments, each 30 meters long, in sufficient number to completely surround the ship if need be. A plurality of supports are needed, perhaps one every 5 meters. In Figure 8, two supports are shown by way of example, but many more may be provided. All ships have a draft that is commensurate with the configuration of the ship in accordance with well known naval-architectural principles. Typically, the draft of large tankers may be 12 to 18 meters: Each barrier segment such as 12 must have a draft that is substantially equal to the draft of the ship. The material may be PVC or Neoprene and weighs about 22 kg per running meter for a 15 meter draft or about 660 kg for a 30 meter long segment. Rather than having a plurality of segments, it would be possible to provide fewer, portable segments that would be available for local disposition around the ship as needed. The segments could be handled by small cranes mounted on tracks disposed along the gunwales of the ship, mounted perhaps, just outside the handrails. Regardless of the arrangement, it is essential that the curtains be instantly deployable in an emergency. In Figure 7, I show the supports swung outboard with the barrier unfurled into the water 15 opposite the gash 20 in ship 10 from which oil 22 is exuding (see also, Figures 2 and 3). Barrier curtain 12 is spaced apart from the hull by spacer bars such as 24 that may be 1.5 to 3 meters long, thereby to provide a sump for the accumulated oil between the barrier and the ship's hull. A plurality of weights such as 26 are provided on the bottom of barrier curtain 12 to hold it down in the water. Barrier curtain 12 is attached to cable 16 by a plurality of rings such as 17 through which cable 16 is threaded in the manner of a sail unfurled from a yardarm. Support 14, curtain 12, cable 16 and spacer bar 24 collectively form means for enshrouding the ruptured tank outboard of the ship with a flexible impermeable barrier. I furnish one or more high-volume pumps such as 28 aboard the ship. Such pumps may be especially-assigned pumps or one of pumps 104 or 106 of Figure 1 may be substituted. A suction pipe such as 30 reaches from pump 28 into the sump region between the barrier curtain and the hull for pumping out the effluent 22. If the discharge from pump 28 cannot be transferred into the temporary-holding tank previously described or into an empty ballast tank, inflatable buoyant oil storage bags such as 31 may be used. Commercially available bags of ·10 m³ capacity or more are available from Abasco Inc. of Houston, TX. Such bags, when collapsed, take little space and may be carried aboard a tanker in large numbers for emergency use. If used, as each bag such as 31 is filled with effluent from discharge pipe 32 through bag fluid-inlet 34, it may be sealed and left to float in the water behind the ship, tethered thereto by lines 44 and 46 as shown at 48 and 50, Figure 8. Figure 8 is a plan view of Figure 7. Here, two supports 14 and 14' and two line handling winches 18 and 18' are shown but many more may be used. Barrier curtain 12 has laterally disposed ends 36 and 38 that may be mechanically sealed to intact portions of the ship's hull such as be electromagnetic devices 40 and 42 which may be coupled to a source of electric power aboard the ship. Figure 9 is a side view of Figure 7 showing barrier curtain 12 enclosing the leaking oil. In addition to the elements previously shown in the Figures, barrier curtain 12 may be provided with quick disconnect fittings 52 and 54. When a relief ship arrives to assist the stricken tanker, the pumps of the relief vessel can be coupled to the fittings 52 and 54 to continue salvage of the spillage without disturbing the integrity of the seal of barrier 12. In operation, upon discovery of a ruptured liquid cargo tank, the emergency transfer pumps 104 and 106 are immediately started and interconnected with the damaged cargo tank through the pipelines 114 and 116. A valve, such as 112, in a port such as 110, appropriate to the damaged tank or tanks is opened. The appropriate suction intake such as 126 is positioned below the level of the water surface 13 as measured externally of the ship 10. The content of the damaged tank is emptied into one or both emergency temporary-holding tanks 122 and 124 to allow formation of a water seal above the topmost edge 21 of the gash 20 by waterflooding the ruptured cargo tank as quickly as possible. Concurrently, the barrier curtains 12 are deployed to enshroud the damaged tank outboard of the ship to entrap whatever portion of the liquid cargo 22 that may have leaked into water 15. The entrapped spillage is transferred into temporary storage means to prevent further dispersal over the water. Although this invention is primarily applicable to oil tankers by way of example, it may also be applied to any ship carrying liquid cargo that is potentially capable of contaminating the environment. In this disclosure, emphasis was placed upon containing oil leakage from tank damage due to a ship running aground on rocks or reefs or to a collision with another ship or with icebergs. This system would also be useful in protecting against any sort of cargo-tank leakage or to drippings from fill-discharge pipes and hose fittings that might occur when taking on or offloading liquid cargo at a terminal or between ships at sea.

Claims: A method of minimising water pollution caused by rupture of any tank of a set of liquid containing cargo tanks (A to D) carried by a vessel (10), the method comprising sailing with all the tanks of the set charged with liquid (22), with a first pumping system by which the set of tanks can be substantially fully discharged when required, and with a second, emergency, pumping system having provision for a suction intake (126, 128) to enter each tank of the set via an access port (110) of the tank with the suction intake extending down to a level at or Just below the external water level (13) of the vessel, the second pumping system comprising at least one pump (104, 106) dedicated solely to emergency use so that a water seal can be formed in a ruptured tank by pumping out a portion of the liquid so as to water-flood the ruptured tank to at least a level above the topmost edge of the rupture, characterised in that the method comprises sailing with additional, emergency, tank means (122, 124) positioned in a protected location and dedicated solely to emergency use and into which the second pumping system will discharge in order to transfer liquid cargo through the suction intake of a ruptured tank. A method according to claim 1, comprising the steps of concurrently enshrouding a ruptured tank, outboard of the vessel (10), with a flexible impermeable barrier curtain (12), the bottom of said curtain extending at least beneath the lowermost edge of the rupture, thereby to create a sump between said curtain and the hull of said vessel for entrapping liquid cargo (22) leaking from said ruptured tank into the surrounding water, and transferring the entrapped liquid cargo into an emergency storage container (31). A vessel arranged to carry out the method of claim 1 or 2 and comprising a set of cargo tanks (A to D), a first pumping system by which the set of tanks can be substantially fully discharged, a second, emergency, pumping system having a suction intake passing into each tank of the set through an access port (110) to be at a level at or just below the external water level (13) of the vessel, the second pumping system comprising at least one pump (104, 106), dedicated solely to emergency use, and characterised in that there are additional, emergency, tank means (122, 124) into which the second pumping system can discharge and in that the emergency tank means is arranged so that in use it is separated from the water by a tank of said set. A method according to claim 1 or 2 or a vessel according to claim 3, wherein the second pumping system is arranged to transfer liquid from tanks of the set of cargo tanks only to the emergency tank means but not to any other tank of the set. A method according to claim 1, 2 or 4 or a vessel according to claim 3 or 4, wherein said at least one pump is a self-powered, preprimed, high volume pump unit. A method according to claim 1, 2, 4 or 5 or a vessel according to any one of claims 3 to 5, wherein the access ports (110) for the suction intakes to enter respective ones of the tanks of said set are on-deck (110) access ports. A method according to claim 1 or 2 or any one of 4 to 6 or a vessel according to any one of claims 3 to 6, wherein the emergency tank means is located in a central region of the ship. A method according to claim 1 or 2 or any one of 4 to 7 or a vessel according to any one of claims 3 to 7, wherein the emergency tank means is located on the upper deck.

Inventors: STRANGE BOOTH B, STRANGE, BOOTH B.
Applicants: MARINE SAFETY SYSTEMS INC, MARINE SAFETY SYSTEMS INC.
Application year: 1990
Main classification: B63B25
IPC codes: E02B15, B63B25