Modelling and Operation of a Hybrid LNG Propulsion Tugboat

The need to reduce ship emissions and the increase in fuel oil prices has driven the interest in incorporating alternative energy solutions to traditional power systems in the maritime industry. In this paper, a hybrid energy system of liquified natural gas (LNG) and batteries for a tugboat is developed and studied. The flexibility of the load allocation is believed to reduce fuel consumption and emission as the tugboats with dynamic power profiles benefited from splitting the load among the multiple power sources. The hybrid system model is created in MATLAB/Simulink^®. In addition, fuel data recorded from an operational diesel propulsion tugboat is used where the generated operational data are replicated in the Simulink model before any further analysis and comparisons are conducted. The LNG-hybrid system is tested in three different configurations without the battery in both fixed speed and variable speed, and with a battery. The daily fuel cost, CO₂ emissions, energy efficiency operation indicator (EEOI) and CII ratings are then calculated for the different configurations in three different operation cases for comparison studies. The results demonstrate that an average reduction of CO₂ by 64.7% and a lowering average of daily fuel cost by 67.5% for an LNG battery hybrid tugboat are achieved as compared to a diesel system.