With the increase of tanker transport of oil by sea and exploration and production of oil offshore, particularly in areas with especially hazardous marine conditions such as those near the North Slope of Alaska and in the Arctic Ocean, the potential for oil spillage at sea has increased. Much attention has been given recently to preventing and reducing pollution from such oil spillage.
Spilled oil at sea tends to float in slicks on the surface of the sea water. Near shorelines, wave action can cause oil on the water's surface to mix with sand on the shore. Some such oil may remain deposited on the beach. Other oil mixed with sand may be taken by wave action back to sea. Back at sea, such oil coated sand may sink to the subtidal sea floor near the shoreline. Removing floating, deposited or submerged oil is generally considered the most desirable way of combating pollution by the oil.
Many mechanical devices, generally known as skimmers, for such removal or collection of oil floating on the surface of water have been proposed. Relatively few, however, have been found to be commercially practicable. Of those skimmers available, most are limited to operation in one type situation only, for example, removing only less viscous oils on calm seas.
A number of factors are known to affect the effectiveness of skimmers in collecting oil. Such factors include viscosity of oil spilled, the location and thickness of the oil slick, and water conditions, including wave height and the presence of debris or ice in the water.
Commonly available skimmers that are generally known as weirs, centrifugal devices, and suction devices employing vacuum pumps require calm waters and relatively thick oil slicks for efficient removal of oil from the surface of water. Otherwise, they collect substantially more water than oil. Weirs and suction devices employing vacuum pumps are also susceptible to clogging with debris or ice.
Sorbent surface skimmers are not as sensitive to wave height and water currents as are weirs, centrifugal devices and suction devices. Thus, sorbent surface skimmers are generally preferred for use in removing oil slicks at sea.
There are a number of basic kinds of sorbent surface skimmers known--drum, disc, belt, and rope--all of which generally operate by absorption or adhesion of oil on a surface, usually oleophilic, which is then cleaned off, usually by squeezing or scraping. Of the sorbent surface skimmers commonly available, none are general purpose that can operate on water, a sea floor or riverbed, and a shoreline or beach.
Drum type skimmers generally do not have sufficient surface area to collect oil efficiently. Disc and rope type skimmers have more surface area than drum type skimmers, but they can leave narrow streaks of oil where their surfaces do not touch or overlap, particularly if the oil is viscous, as in the Arctic. The squeezing and scraping means of removing oil from the devices are also generally too slow for efficient use of the devices with viscous oil such as that encountered in oil spills in the Arctic. With very viscous oil, the sorbent surfaces or the squeezing or scraping means may even become gummed. Drum, disc and belt type skimmers are also very susceptible to damage by debris or ice floating in the water.
No available skimmer seems ideally suited for the conditions of the Arctic, where the sea waters may contain ice and be less than calm, and the oil slick may be very viscous. There is a substantial need for a skimmer that can be effectively used in the Arctic. There is also a need for versatile skimmers or devices capable of removing various types of oils under various types of conditions, whether the oil is floating on water or deposited on a seafloor or riverbed, shoreline or beach.
A number of mechanical devices are known for removal of oil from a shoreline or beach. The operation of such devices available, however, is limited by the beach topography. For example, some sandy beaches may not be hard enough to support construction equipment commonly used for beach cleaning. Pebbly beaches are particularly difficult to clean because oil gets into crevices between the pebbles, and graders or scrapers commonly used for beach cleaning are unstable on such a surface. Front-end loaders or bulldozers that may be used on a pebbly surface must remove substantial amounts of the beach surface to clean up oil on the beach. Such removal of much of the surface can disrupt normal beach processes. To prevent erosion, the removed surface has to be replaced. There is a need for versatile beach cleaners that can remove various types of oils deposited on various types of beach surfaces while minimizing removal of the sand or pebbles naturally comprising the beach.
There is no device generally available commercially that is satisfactory for removing submerged oil from a subtidal sea floor or riverbed.