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Power and automation technology group, ABB, has revealed details of a comprehensive study by DNV-GL R&D which concludes that optimized dual-fuel diesel-electric (DFDE) propulsion can be the most energy-efficient technology for liquefied natural gas (LNG) carriers.

ABB instructed DNV-GL R&D to undertake an analysis of DFDE propulsion under realistic operating conditions for LNG carriers, instead of calculations using design specifications. The study's calculations are based on realistic operating conditions, with data provided by ABB or taken from publicly available literature.

The study used three representative operating profiles based on the distance-specific trade route for a typical 174k twin-skeg LNG carrier, including laden/ballast sailing modes and non-sailing modes, while considering propulsion power and electricity, as well as steam demand.

According to the study, it is possible to improve overall vessel efficiency - and thus asset competitiveness - in certain vessel and configuration cases. It also says that an optimized DFDE LNG carrier can be a highly fuel-efficient solution for the specific case and boundaries of the study.

The research claims that duel-fuel electric propulsion excels when considering the total fuel consumption of handling cargo and travelling at variable speeds.

When taking into consideration the round trip data, operating profiles and fuel costs, the study indicates that 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, ABB says that annual fuel savings "can be considerable".

ABB also points out that DFDE enables flexibility in location of equipment, therefore optimizing both space and ship design; and uses the same power plant for propulsion, hotel load, cargo handling and steam production. In the event of failure, the LNG carrier is said to be able to maintain between 70-90 percent of full speed, with the possibility of maintenance during normal operation.

Dual-fuel electric propulsion is compatible with the efficient Azipod thrusters, and new technology such as fuel cells can be easily integrated into existing power distribution cells in the future, ABB says.

"This study is very important because it reflects the complexity of an LNG carrier and includes realistic operating profiles rather than hypotheticals," commented Heikki Soljama, ABB's 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."

ABB propulsion technology was first employed on an LNG carrier in 2003, and has since been installed in 180 vessels. "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," concluded Soljama.