Daewoo looks at gas for gas

Korean yard Daewoo Shipbuilding & Marine Engineering has presented an extensive study, in partnership with the influential Gaztransport & Technigaz of France, which concludes that gas turbine propulsion systems for LNG carriers have an advantage over steam turbine based systems in terms of increased cargo volume, which leads to “a favourable economic evaluation”.

The study, presented in a paper at last month?s Gastech conference in Doha, Qatar, evaluates gas turbines in various configurations – direct gas turbine propulsion; gas turbine electric propulsion with motors; gas turbine electric propulsion with pod; and combined cycle gas turbine electric propulsion (with one and two gas turbines). It weighs these options up against steam turbine propulsion.

JungHan Lee, principal research engineer and currently leader of the ship/plant R&D team at Daewoo, and Pierre Michalski, development manager at Gaz Transport, say that gas turbine propulsion systems can be a feasible alternative to steam propulsion systems for LNG carriers, essentially because of their inherent lightweight, flexible machinery arrangement, efficiency, low emissions and the availability onboard of a high quality fuel (boil-off gas or vaporised LNG).

Of the configurations studied Lee and Michalski observe that the economic case for combined cycle electric propulsion systems is stronger than for direct gas turbine propulsion or gas turbine electric propulsion with motors or pods.

Their research finds that the initial cost of an LNG carrier does not play a major role in the overall evaluation of gas turbine propulsion when set in the context of fuel cost advantages and revenue increase by cargo volume, except in the case of gas turbine electric propulsion with pods. It also finds that operating costs can be lower in relation to steam turbine propulsion if the LNG price is within a “reasonable range” and that combined cycle gas turbine electric propulsion with a single gas turbine can offer “very significant” fuel cost savings even if the LNG prices are high compared to fuel oil due to the high efficiency of the system.

Lee and Michalski hope the research will give shipowners a better understanding of gas turbine propulsion systems in LNG carriers and that it can be used as a basis for further evaluation. Such evaluation needs to cover operation in comparison with other alternative propulsion systems as well as system reliability and redundancy.