International Journal of Hydrogen Energy, Vol.44, No.29, 15056-15071, 2019
Analysis and assessment of partial re-liquefaction system for liquefied hydrogen tankers using liquefied natural gas (LNG) and H-2 hybrid propulsion
Boil-off gas (BOG) is inevitable on board liquefied hydrogen tankers and must be managed effectively, by using it as fuel, re-liquefying it or burning it, to avoid cargo tank pressure issues. This study aims to develop a BOG re-liquefaction system optimized for 160,000 m(3) liquefied hydrogen tankers with an LNG and hydrogen hybrid propulsion system. The proposed system comprises hydrogen compression and helium refrigerant sections with 2 J -Brayton cascade cycles. Cold energy recovery from the fuels and feed BOG exiting the cargo tanks was used. The system exhibits a coefficient of performance (COP) of 0.07, a specific energy consumption (SEC) of 3.30 kWh/kg(LH2), and exergy efficiency of 74.9%, with the hydrogen BOG entering the re-liquefaction system at a feed temperature of -220 degrees C. The theoretical COP and SEC values at ideal conditions were 0.09 and 2.47 kWh/kg(L)(H2), respectively. The effects of varying the hydrogen compression pressure, inlet temperature of the hydrogen expander, feed hydrogen temperature and helium compression pressure were investigated. Additionally, the LNG-to-hydrogen fuel ratio was adjusted to satisfy the Energy Efficiency Design Index (EEDI) Phase 2 and 3 emission requirements. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.