Operational Impact of a Turbo-Brayton LN G Subcooler Retrofiton a DFDE LNG Carrier: An Empirical Case Study
Keywords:
Liquefied natural gas (LNG), Natural boil- off gas (NBOG), LNG carrier, Turbo- Brayton subcooler, Dual fuel diesel electric (DFDE), Cargo thermal management, Gas combustion unit (GCU), Boil- off rate (BOR), Voyage- based case study, LNG cargo preservation, Sustainable shippingAbstract
Natural gas is currently recognized as a primary transitional fuel in maritime transport due to its lower carbon intensity compared to conventional marine fuels. In response to increasingly stringent maritime environmental regulations and growing concerns regarding methane emissions, efficient boil-off gas (BOG) management has become an important operational and environmental challenge for liquefied natural gas (LNG) carriers.
This study evaluates the operational impact of retrofitting a dual fuel diesel electric (DFDE) LNG carrier with a Turbo-Brayton subcooler using actual shipboard operational data collected from two comparable voyages conducted before and after retrofit. The study focuses on cargo thermal behavior, gas consumption, and operational gas management.
The post-retrofit voyage exhibited a mean daily boil-off rate (BOR) of 0.122%/day compared to 0.134%/day pre-retrofit. Actual gas combustion unit (GCU) consumption reduced by 11.0%. Cargo temperature remained more stable after retrofit, suggesting improved thermal stability of the LNG cargo. The observed gross difference in NBOG generation was approximately 205 m³; after accounting for the estimated energetic penalty of the subcooling system, the estimated netequivalent retained volume was approximately 186 m³ LNG.
Although limited to a single- vessel case study, the findings indicate that the Turbo-Brayton subcooling system may reduce excess gas combustion in the GCU and improve operational control of LNG cargo under comparable voyage conditions thus contributing to maritime decarbonization and more sustainable shipping.
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Copyright (c) 2026 Aleksandar Vorkapić, Radoslav Radonja, Josip Dujmović, Mario Stipanov
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