Tank testing of skimmers with waxy and viscous oils

A series of tests of four offshore skimmers (Framo ACW-400, GT-185, Walosep W2, Heavy Oil Skimmer) was conducted in a 120-by-60-meter wave basin. Each skimmer was tested with each of 3 oils: a conventional crude, a waxy crude, and a bunker oil. Each test involved 4-6 h of skimming, partly conducted in waves having a period of 4 s and heights of 0.4-0.8 m. Near the end of selected tests, the additive Elastol was applied to the oil and its effect on recovery parameters evaluated. All the optimum results were obtained in calm conditions. In general, waves had no effect on the performance of the Walosep W2, had little effect on the performance of the GT-185, and greatly reduced the performance of the Framo. The experimental Heavy Oil Skimmer failed to recover oil at significant rates without addition of Elastol to the oils. The fluid recovery rate less the water entrainment rate generally declined as oil viscosity increased. For a waxy oil, recovery rates under conditions typical of the Grand Banks in summer would be 30-40% less than for a conventional crude with the Framo skimmer and about the same as the recovery rates for conventional crude with the Walosep and GT-185 skimmers. The Walosep, unlike the other skimmers, did not entrain more water when skimming waxy oil compared to conventional oil. Adding Elastol to the oils improved the corrected recovery rates of the Walosep by ca 15% and had no effect on its water entrainment rate. For the Framo, Elastol addition had no effect on the recovery rate but increased its water entrainment rate. Elastol reduced the GT-185's recovery rate by 25-35% and increased its water entrainment rate. Adding Elastol had several negative effects on subsequent downstream operations. 11 refs., 55 figs., 14 tabs