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

S0300-A6-MAN-060• Inclined plane• Multiple weir• Hydroclone5-2.3.1 Inclined Plane Skimmers. Inclined plane skimmers operate by forcing oil downwardwith an adjustable inclined plane under the skimmer well, where the oil rises into a sump and thewater is allowed to escape. The oil is drawn from the top of the sump for transfer to a holdingtank. The gravity separation of oil from water in the sump may be enhanced by flow across underflowweirs as shown in Figure 5-5. Flow across the weirs may be induced by a pump suction orvessel motion.Figure 5-5. Inclined Plane Skimmer.Flow down the inclined plane is created by the rotating movement of the belt and/or the forwardmotion of the vessel driving through the water. Because the belt drive direction is opposite of thevessel’s movement, relative motion between the belt and the oil is low and little turbulence is generatedas the liquids come into contact with the belt. Lack of turbulence reduces mixing of oil andwater. Most inclined plane belt speeds and angles are adjustable to change oil pickup rates to fitthe situation. The aspect of the belt as it moves through the water is the opposite of belt-drivenoleophilic systems discussed in Paragraph 5-2.1.1. Induction pumps can also create additionalflow down the inclined plane as the skimmer operates.There is usually an oil-water interface within the tank or sump. Most systems have electronicinterface and quantity indicators. As the interface level drops as the oil rises in the decanting tank,pumps transfer the oil to holding tanks. The transfer pumping induces a flow within the sump thatassists oil entry.5-2.3.2 Multiple Weir Systems. Weir systems are either underflow or overflow design. Overflowweir float systems operate on the shear principle discussed in Paragraph 5-2. Weir heightcan be fixed or adjustable. Adjustable weirs allow vertical movement that causes shearing at the5-7