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Power and automation technology group, ABB, has disclosed details of a study from DNV-GL R&D examining the potential for efficiency improvements of dual-fuel diesel-electric (DFDE) propulsion. The outcome of the study concludes that it is possible to improve overall vessel efficiency, and thus asset competitiveness, in certain vessel and configuration cases. Furthermore, it says that an optimized DFDE liquefied natural gas (LNG) carrier can be a highly fuel efficient solution for the specific case and boundaries of the study.

ABB requested DNV-GL R&D to undertake an analysis of DFDE propulsion under realistic operating conditions for LNG carriers, rather than relying on calculations using design specifications. LNG carrier machinery systems are highly complex, featuring tightly integrated sub-systems and components. Using DNV GL's analytical tools, the study made calculations based on realistic operating conditions. Data for the study was either provided by ABB or taken from publicly available literature.

DNV GL R&D used three representative operating profiles based on distance specific trade route for a typical 174k twin skeg LNG carrier, including laden/ballast sailing modes and non-sailing modes, while considering not only propulsion power and electricity but also steam demand.

"This study is very important because it reflects the complexity of an LNG carrier and includes realistic operating profiles rather than hypotheticals," said Heikki Soljama, Managing Director of Marine and Ports. "It shows that DFDE configurations have the potential to be a fuel efficient solution. Combine this with its proven track record, flexibility in operation and adaptability to energy storage, it can be a competitive business case for ship owners."

Fuel savings 'can be considerable'

When taking into consideration the round trip data, operating profiles and fuel costs, the study indicated DFDE can potentially be a more fuel-efficient solution among the alternatives considered when combined with energy recovery technologies and optimally operated. Depending on the specific speed profile and fuel costs, annual fuel savings "can be considerable", according to ABB.

First ordered for an LNG carrier in 2003 and established on 180 vessels, DFDE comes with an established record of reliability. Its compatibility to future technologies is also key, as Soljama points out: "It's better capacity for integration with fuel cells and advanced energy storage mean that, after over a decade of proven operational performance, DFDE remains a technology of the future."