Experimental Investigation on Oil-Water Displacement Process of a Vertical Oil Storage System in Offshore Floating Platform

Based on the oil-water displacement principle, Wang and Luo (2016) developed a new type of offshore oil storage system. This storage system can be applied to a conventional Spar platform or any other platforms. However, there is the potential for the hydrocarbon contamination of the discharged ballast water, for the formation of oil/water emulsion and for heat transfers between the hot oil and the cold water in the wet storage system. When wet storage system is applied to a floating platform, the sloshing of oil-water interface in the storage tank may exacerbate above-mentioned potential problems. Extensive tests, using crude oil and seawater, were performed in a 1:40 scale model of the wet storage system developed by Wang and Luo (2016). The objective of the experiment is to test and prove the feasibility of oil-water displacement principle in floating platforms, to demonstrate the superiority of the present wet storage system, and, finally, to investigate the mechanism of oil-water heat transfer in the vertical cylindrical storage tank. The model is mounted on a sloshing test rig, which could simulate the motion of the floating platform in the practical sea conditions. Movement speed of oil-water interface in the model was to simulate the anticipated movement speed in the proposed storage system and the repeated cycling of all operations. Operating temperature of the incoming crude oil and incoming seawater are 60 °C and 10 °C, respectively. In addition, in order to investigate the effect of liquid sloshing on the process of oil-water displacement, two different cases were done at static condition and at sloshing condition, respectively. In each case the interface was recycled up and down forty times to far exceed any anticipated recycling in the actual storage tank in one year. The important observations of the present work are listed below: The displaced water can be discharged to the sea directly without any treatment; There is no chance for emulsion to form at the oil-water interface; The effect of stratified liquid sloshing on the process of oil-water displacement is negligible; The heat of hot oil is mainly transferred to the exterior of the storage tank.