US class society ABS and Piraeus-based GasLog LNG Services have joined forces to develop a new approach to evaluating LNG boil-off rate (BOR).
Rates of LNG boil-off gas, the vapour phase of LNG carried in a cargo tank, vary between different LNG carrier designs, ship sizes and sailing speeds. Older-generation, steam turbine LNG carriers that are less efficient can lose some US$30,000 worth of cargo as boil-off gas.
ABS and GasLog launched the project because it is critical to accurately assess the rate of LNG boil-off gas generation when designing cargo tanks and boil-off gas processing systems.
They developed a robust computational fluid dynamics (CFD) analysis procedure, modelling the physics of heat transfer, boiling, phase change and vapour flow. They then ran simulations on a representative LNG carrier, measuring BOR to demonstrate that the analysis results were accurate.
“By expanding the application of CFD analysis to simulate the LNG BOR in cargo tanks, owners are able to better predict boil-off gas and account for it in future designs and operations of LNG carriers,” says ABS chief technology officer Howard Fireman. “As a technology leader, we are committed to working with industry to drive safer and more efficient operations.”
GasLog floating storage and regasification unit project engineer Vassilis Millas says that predicting BOR in varied operating conditions will help the shipowner to build efficiencies into future ship designs.
“By taking a collaborative approach with ABS on this project, we were able to demonstrate and prove the viability of CFD analysis to determine LNG BOR,” he said.