LNG 벙커링용 비상차단밸브(ESD)의 제어에 관한 연구

Abstract

Recently, discussions have been active at sea to prevent climate change, an issue around the world. The International Maritime Organization has adopted an agreement to regulate air pollutants such as carbon dioxide and sulfur oxides and nitrogen oxides from ships. As a result, many countries have shown movements around their own waters as emission control areas. Domestic ports are also promoting marine pollution prevention and eco-friendly policies. This change has drawn attention from eco-friendly ships that use liquid natural gas as a ship fuel instead of the existing ship fuel oil such as heavy fuel oil and marine diesel oil. It is clean among the fuels currently available and emits a small amount of carbon dioxide and nitrogen oxide when burned in the engine and boiler. Since the compression ratio of liquefied natural gas is 1/600th that of natural gas, it is generally transferred in the form of a liquid at cryogenic temperature during the bunkering process. However, since liquefied natural gas is a flammable substance, leakage during the bunker can lead to a major accident. Therefore, in accordance with the relevant regulations, emergency shut-down valve shall be installed for transporting cargo remotely, and these emergency shut-down valve shall be called emergency shut-down valve. In this study, the controller for the displacement control of the emergency shut-off valve disk was designed. Before the controller design, the thermal analysis simulation model of the emergency shut-off valve by the cryogenic liquid was constructed using AMESim, a general purpose hydraulic numerical analysis tool, to reduce modeling error, and the temperature variation of the entire valve was also compared with the presence or absence of the stem present in the emergency shut-down valve. Because the emergency shut-down valve system uses long piping dues to the characteristics of the bunkering operation, the simulation model was constructed using a distributive pipe model to analyze the pressure loss and time delay occurring in the piping and the results were verified. Later, the control performance of the emergency shut-down valve was compared and analyzed by applying a PID controller designed using the variable structure system theory and Ziegler-Nichols the 2nd PID Tuning rule to the linear state space method derived by modeling the emergency shut-down valve. The performance of the controller in nonlinear system was analyzed using co-simulation through interoperate of AMESim and MATLAB simulink.