U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060Unless very heavy with large pieces, floating debris does not usually hinder belt skimmers. Themoving belt will carry debris to the top of the plane and onto gratings installed above the oil sumpwhere it is removed easily. Wire mesh or netting placed before the belt prevents trash and debrisfrom entering the recovery mechanisms. Since the debris is usually oil-soaked, it should be kepton board for eventual disposal. This will require manual intervention and may require frequentremoval if there is little storage space on the skimming vessel.5-2.1.2 Rope Mops. Rope mops, shown in Figure 5-2, consist of an endless loop or loops of oleophilicmaterial that is continuously drawn across the water surface between a collection deviceand pulleys held by moorings. Collected oil is squeezed out of the oil into a reservoir by rollers inthe collection device. Rope length can be adjusted to suit the location. Rope mops usually passthrough debris with little fouling and can be used in very shallow water. The collection device canbe mounted on shore or on a vessel. Some systems are designed to be suspended above the sea bya crane with multiple mops hanging into the water from the collection device. Rope mops havehigh recovery efficiency and are relatively easy to deploy and maintain.Figure 5-2. Rope Mop-Type Skimmer System.5-2.1.3 Oleophilic Drum, Disk, Bristle and Brush Skimmers. The oleophilic property of thepolymer, aluminum or stainless steel components of drum, disk, bristle and brush skimmersattract oil in the same manner as the oleophilic materials in the belt or rope skimmers. Oil adheresto the oleophilic material as it rotates through the oil-water interface. The oil is removed from thesmooth disk or drum surfaces with scrapers and diverted to a sump.Likewise, rotating drums or belts with brushes or bristles attached attract oil as the oleophilicmaterial passes through it. The oil collects at the ends of the brushes and bristles where removal iseasy. Bar- or comb-type scrapers remove the oil before the oleophilic material enters the oil again.Figure 5-3 shows various oleophilic disk, drum and brush devices and how they operate. Becauseof the large vertical dimension of the disks, disk skimmers are relatively effective in waves. Theyare, however, easily clogged by debris. Disk skimmers do not work well with very viscous oil andare ineffective on mousse. Some disk skimmers incorporate intermeshing toothed disks toimprove performance in viscous oils. Efficiency and applicability of drum systems is generallysimilar to that of belt skimmers.5-4