Exhibition & Conference

13-16 September 2021

Singapore EXPO, Singapore

Technical Programme

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Ravindu Atapattu

R&D Product Manager

Keppel Gas Technology Development


14:00 - 14:30

Wednesday, 18 September 2019

T2.5 An Innovative Approach to Re-Liquefy Bog Through Cold Energy Recovery

In recent years, demand for the LNG fueled vessels and investments for bunkering infrastructures have been increased significantly due to the emission control regulations imposed by various regulatory bodies; which makes LNG fuel as a captivating alternative to meet the global 0.5% sulphur cap limits by 1st Jan 2020.

LNG bunkering is a fast growing market with forecasted Compound Annual Growth Rate (CAGR) of 62.5% during the period of 2017-2023 and is expected to reach USD 24 Billion by 2023. It is also expected double the number of LNG bunkering fleets in the next five (5) years and nearly thirty (30) LNG bunker vessels would be operating worldwide.

It is well known to LNG vessel operators that on-board Boil-off gas (BOG) management and cargo tank pressure control is always adding operational complexities and challenges. Regulations prohibit venting of excess BOG to atmosphere, marine class societies and IMO has mandated to have shipboard BOG management systems, which can be re-liquefaction, thermal oxidation, pressure accumulation or gas fuel cooling. Thermal oxidation (Gas Combustion Unit-GCU), could be a commercially appealing solution over conventional BOG Re-liquefaction systems, but thermal oxidation adding excess greenhouse gases into the atmosphere and eventually defeat the purpose of using LNG as a marine fuel to cut greenhouse gas emissions.  

Despite the fact of technological superiority of Re-Liquefaction over thermal oxidation to manage on-board BOG, most of the ship owners are reluctant to adopt Re-liquefaction as a solution for these relatively small BOG capacities mainly because either CAPEX is not appealing or available systems are thermally inefficient (Higher OPEX). Unless someone solve these problems, thermal oxidation will continue and it will fuel the ongoing debate on whether the LNG is an alternative fuel to curb greenhouse gas emissions.

To address above concerns, Keppel GTD has developed an innovative technological solution to bring down the CAPEX/OPEX associated with conventional BOG Re-Liquefaction Systems. In this new approach, waste cold energy is utilizing to minimize the power demand by half and the system is comprising limited number of equipment namely cold energy recovery exchanger and gas compressor to make the Keppel Re-Liquefaction system (KRL) attractive commercially. It’s also worth to highlight that, this new approach is not just focusing on Re-liquefaction, but also complement the vessel fuel gas system by producing gas for onboard power generation. Since, KRL does not use any external refrigerant to Re-liquefy BOG, the use of standard and proven equipment preserve the simplicity and safety of the system.

This paper covers the simulation results of KRL system performance and reliquefaction capacity envelop for various operating scenarios including vessel navigation, maneuvering and Harbour idle/bunkering, alongside with general comparison against existing technologies.