A voyage optimization model of LNG carriers considering boil-off gas

A voyage optimization model is proposed to minimize the operating costs of LNGC (Liquefied Natural Gas Carrier). The model is utilized to suggest the RPM and route plan of the vessel based on the amount of boil-off gas generated. Voyage optimization of LNGC is different from that of general cargo ships because of the natural characteristics of its product, LNG. LNG is vaporized by heat ingress in the cargo containment system. Releasing it into the atmosphere becomes an economic loss since this boil-off gas is a commodity to be transported despite a phase transition. Therefore, LNGC uses it as fuel or reliquefies and reloads it in cargo tanks. A voyage planning problem to minimize the total consumption of fuel and cargo is formulated as an optimization model. For this study, LNGC with a dual-fuel engine is considered. The daily amount of BOG (Boil-Off Gas) is predicted based on forecasts of seawater temperature and atmospheric temperature on the route. Ship's speed and the total amount of fuel consumption in-service condition is estimated considering marine weather forecast. The proposed model is applied to various voyage planning problems of the actual route of LNGC. The results obtained from the case studies show that the total cost of operation can be reduced compared to sailing the shortest route.