The rapid growth of world's population and the distinctive development of industrial technologies have recently accelerated marine pollutions. This led to stringent regulations on the marine pollutions. Among the marine pollutions, especially oil-caused pollution has become a severe issue with direct damage such as the demolition of marine ecosystem. Petroleum hydrocarbon, however, is widely applied in large volume, which increases continuously.
Waste oils are one of the sources of marine oil pollution generated from ships. It was currently difficult to treat them the whole quantity within a ship so that they are transferred to a shore treating facility after being collected inside the ship's sludge tank mostly. However, shore transferring method causes cost generation in the economic standpoint, consumes much time, and entails the risk of oil pollution. Accordingly, a fundamental measure in the light of prevention of marine oil pollution would be self treatment in respective ships.
Ultrasonic vibrator is an equipment which atomizes and homogenization the oils by breaking the oil particles with ultrasonic vibration cavity, and would improve the properties. But it has not been yet applied to treat waste oil.
This study intended to investigate a method, as a fundamental preventive measure against oil pollution from ships, to self treat sludge and waste oils unavoidably generated in operating ships. For this, the matrix structures of fuel oil, lubricating oil and sludge oil, which are marine oils, were investigated. These oil solutions from various environments were irradiated with ultrasonic vibration and then observed the aspects of the change of oil particles. From these, the recycling feasibility of sludge oil for usable oil to be burnt was determined.
And, in order to analyze erosion aspect on transducer horn tip, which is a principle part of ultrasonic vibrator, the erosion damage was investigated on weight loss and weight loss rate mainly using SS41, as horn tip material. Also, the erosion damage of metallic material and the homogenization of oil caused by cavitation in the sludge oil environment were identified by investigating the aspect of the erosion of SS41 specimen caused by the impact pressure generated from the demolition of the cavity of ultrasonic vibrator horn.
The important findings from this study are as follows.
1) Waste oils go through homogenization of oil particle by cavitation from ultrasonic vibration, and the effects are good according to the oil temperature increased and the experimental time takes long.
2) Viscosity, pH value, and specific gravity of marine oil decrease by repetition of cavity flow fluctuation. The decrement is larger in the oil with fuel oil property than in the oil with lubricant oil property.
3) The ratio of erosion damage at amplitude 50㎛ was larger over 2 times than that of 24㎛, and the value of rate was larger in fuel oil sludge than in lub. oil sludge.
4) The erosion damage to the increase of oil temperature was decreased in lub. oil sludge but increased in fuel oil sludge to the contrary. Therefore, the demolition pressure of cavity is lower to the increase of oil temperature in lub. oil sludge environment.
5) It was the largest effect of cavity at immersion depth 3mm of transducer horn at oil temperature 30℃ in sludge oil environment. But in case of oil temperature 50℃, 70℃ and 90℃, the effect of cavity was the largest at immersion depth 6mm.
6) As the space of between transducer horn and specimen decreased, the erosion damage and the effect of demolition pressure of cavity were increased.
7) The effect of cavity fluid fluctuation on the homogenization of sludge oil and erosion of SS41 acted larger in the oil environment with fuel oil property than the lubricant oil property.
As these experimental results, it was found that the possibility on the development of ultrasonic breaking systems to recycle waste oils from ships. Also, the optimum conditions were ascertained to obtain the best efficiency according to the environment of oil properties. In addition, it would help investigate the aspect of cavitation erosion damages in varieties of equipment, metallic materials of different operating environment and material characteristics, and also would help establish the countermeasures of cavitation erosion damages.