(183c) Development of LNG Heel Stock Estimation Technology for Ballast Voyage

In the Asia Pacific region, LNG is transported by LNG vessels with cryogenic tanks intended for long distance transportation. A significant fraction of the cargo LNG volume evaporates during voyage as Boil-off Gas (BOG) including spraying operation. It is difficult to utilize generated BOG for LNG vessel operation efficiently, and especially to minimize (optimize) the LNG heel stock for ballast voyage.

The authors developed a dynamic simulation system to estimate LNG heel stock in LNG cargo tanks of MOSS cargo containment system, in order to decide the minimum LNG heel stock for ballast voyage. The dynamic simulation is performed in a commercial process simulator.

The LNG heel stock dynamic simulator will be a part of a Ship Information Management System (SIMS) with the aim of precisely understanding the fuel consumption and propulsion performance conditions of oceangoing vessels.

The dynamic simulator will be combined with SIMS on LNG vessels, in order to save fuel energy, the more efficient Gas Management System (GMS) operation cam be executed by utilizing the dynamic simulator (as online system), based on the actual vessel operation (vessel speed and fuel consumption, predicted weather condition).

In this paper, we describe the rigorous and realistic dynamic simulation of boil-off gas, considering cargo tank spray operation and vessel energy requirement.

The simulation model considers the effect of several process factors such as LNG compositions, ambient temperature, pressure, sloshing factor (ship motion), spray operation schedule, and LNG vessel voyage plan. Based on the dynamic simulation, the optimum LNG heel sock can be decided for long LNG transportation.