The LNG carriers are undergoing a period of rapid and profound change, with much larger size ships and novel propulsion systems emerging for fulfilling the market trends of LNG shipping industry. There are various proposed propulsion solutions for LNG carriers, ranging from the conventional steam turbine and dual fuel diesel electric propulsion, until more innovative ideas such as slow speed dual fuel diesel engine, combined gas turbine electric & steam system, and hybrid propulsion based on steam turbine and gas engine. Since propulsion system significantly influenced the ship's capital, emission regulation compliance and navigation safety, the selection of a proper propulsion option with technical feasibility and economic viability for LNG carriers is currently a major concern from the shipping industry and thus must be comprehensively assessed. In this context, this chapter investigated the main characteristics of these propulsion options in terms of BOG treatment, fuel consumption, emission standards compliance, and plant reliability. Furthermore, comparisons among different propulsion system were also carried out and related evaluation was presented.
Ship-source air pollutants, especially sulphur oxides (SOx), have a major impact on human health, the marine environment and the natural resources. Therefore, control of SOx emissions has become a main concern in the maritime industry. The International Maritime Organization (IMO) has set a global limit on sulphur content of 0.50% m/m (mass by mass) in marine fuels which has entered into effect on 1 January 2020.To comply with the sulphur limits, ship owners are facing the need to select suitable abatement solutions. The choice of a suitable solution is a compromise among many issues, but the economic performance offers the basis for which ones are attractive to ship owners. Currently, there are three technologically feasible SOx abatement solutions that could be used by ships, namely, liquified natural gas (LNG) as a fuel (Solution A), scrubbers (Solution B) and low-sulphur fuel oil (LSFO) (Solution C). To compare the economic performances of the mentioned three solutions for a newbuilding very large crude carrier (VLCC), this paper proposes a voyage expenses-based method (VEM). It was found that, within the initial target payback period of 6 years, Solution A and C are more expensive than Solution B, while Solution C is more competitive than Solution A. Five scenarios of target payback years were assumed to compare the trends of the three proposed solutions. The results show that Solution B maintains its comparative advantage. As the assumed target payback years becomes longer, the economy of Solution A gradually improves and the economics of Solution B and C gradually decline. A comparison between Solution A and C shows 6.5 years is a turning point. The advantage of Solution A is prominent after this payback period. In addition, the performance of a certain solution in terms of adaptability to the IMO greenhouse gas (GHG) emissions regulations is also a factor that ship owner need to consider when making decisions. In conclusion, when the IMO air pollutant regulations and GHG regulations are considered simultaneously, the advantages of using LNG are obvious.
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