Hydrodynamic Problems in Oil Spill Control and Removal

ABSTRACT The theoretical performance of oil spill control equipments in calm and rough water is considered. It is concluded that the scale up of disc-type skimmers is limited by oil layer instabilities: Other skimmer types are also treated. Increases in wave steepness within containment booms are shown to promote the formation of water-in-oil emulsions or enhanced oil dispersion. An operational cut-off is also suggested for oil spill control operations as a function of oil type and environmental conditions. An analysis is also given that explains observed thickening of oil in the crests of waves. INTRODUCTION Oil spills involve a bewildering number of hydrodynamic problems. The oil-water system is so complex, particularly when substantial wave motion is involved, that it has been difficult even to identify the essential problems in a useful way. The purpose of this paper is to discuss some fluid mechanical problems that have, or might be expected to have, important effects on oil spill control and removal. Mathematical models for oil volume collection rates in calm water of several generic types of skimmers are presented. By "calm" water we mean situations which admit a frame of reference in which events are steady in time. Each class of skimmer is considered in a general way, and results are applicable (when suitably adapted) to individual designs in the class. Specifically treated are (a) weir skimmers, with and without pumps for maintaining an inflow water current, (b) rotating disc skimmers, and (c) endless oleophilic belt skimmers. Attention is directed to the role of oil layer instabilities as a cause of performance failure in some skimmers. Detailed theoretical performance curves may be calculated from the models presented (or from the more complete ones from which the present material is abstracted), but this is not our object here. The intention 'throughout the paper is to reduce effects and to seek parametric trends. Oil spill removal and control in open water is seldom conducted in "calm" conditions, sothe effects of waves and turbulence on the performance of oil spill equipment must be faced. These effects, some of which will be enumerated, are readily apparent but difficult to model theoretically. In those cases where performance trends depend strongly on a critical water velocity, such as entrainment failurein booms, "calm water" results may be generalized to include wave orbital speeds. Such quasi-steady adaptations of calm water results are potentially of realistic value only if the acceleration effects associated with the waves are relatively unimportant. In addition to wave orbital speed and acceleration effects on skimming action other effects of waves and water turbulence.