Session: 12-07-01 Blue Economy VII: Floating Offshore Wind and Green Shipping Technologies

Submission Number: 181545

Reducing Boil-Off Gas (Bog) Emissions of Lng-Fueled Ships - Phase 1: Conceptual Design 

This study presents the conceptual design and proposal for reducing boil-off gas (BOG) emissions from LNG-fueled ships as the first phase of a comprehensive project. As the global shipping industry accelerates its transition toward carbon neutrality, LNG has emerged as one of the most practical alternative fuels. However, the inherent phenomenon of LNG evaporation during storage and operation generates BOG, which, if not properly managed, results in both economic losses and significant greenhouse gas (GHG) emissions due to methane’s high global warming potential. When LNG-fueled ships remain at berth for extended periods after bunkering, continuous heat ingress from the surrounding environment leads to a gradual rise in tank pressure accompanied by BOG generation. Although certain amounts of BOG can be consumed by onboard consumers such as gas generators, boilers, and compressors, complete tank pressure control is impossible when propulsion demand is absent. Consequently, BOG venting to the atmosphere may become unavoidable to maintain the safety and integrity of the storage system.

The present study focuses on identifying the mechanisms of BOG generation and release during both ship construction and operational phases, followed by the proposal of practical BOG handling solutions that minimize venting and energy losses. During ship construction, particularly when LNG-fueled vessels are berthed alongside the quay for commissioning or testing, noticeable BOG emissions occur due to LNG evaporation inside the tanks. Similarly, ships already in service may face unintended methane releases under port alternative maritime power (AMP) regulations when main engine operation is restricted. To quantify and analyze this phenomenon, a monitoring campaign was conducted on large-scale LNG-fueled containerships (CNTR) and product carriers (PC) under construction. Variations in tank temperature, internal pressure, and pressure holding time were recorded and analyzed throughout the construction process to estimate total BOG emission volumes and identify time-dependent patterns. Based on these observations, conceptual designs for feasible BOG treatment methods were developed. Due to the unsuitable application of traditional approaches such as onboard reliquefaction, this study proposes a more practical solution leveraging the compositional similarity between BOG and city gas. The concept involves supplying unavoidable BOG to onshore energy systems as city gas, thereby converting potential methane emissions into usable energy. Two system configurations were considered: (1) construction of a dedicated shore-based facility near the berth, and (2) integration of an additional interface within the ship’s existing fuel gas supply system (FGSS) to enable direct BOG transfer to the onshore gas network. Conceptual process flow diagrams for both configurations were developed to evaluate safety, operational feasibility, and regulatory compliance.

The proposed concept not only reduces atmospheric venting but also promotes circular energy utilization by integrating marine and onshore infrastructures. Since multiple stakeholders including shipbuilders, shipowners, classification societies, and port authorities need to be involved in implementing BOG-to-city-gas systems, industry-wide collaboration is crucial to establish standardized procedures. Currently, a joint development program is being conducted by major global shipbuilding groups, equipment suppliers, classification societies, and national gas authorities to validate the proposed configurations. The detailed system development and performance results of these full-scale demonstrations will be introduced in Phase 2 of this project, focusing on real-world applications to LNG-fueled ships.

Presenting Author: Sung-In Park HD Korea Shipbuilding & Offshore Engineering Co., Ltd.

Presenting Author Biography: Responsible for risk assessment & safety design of alternative fueled ships
- Ph.D. Naval Architect and Ocean Engineering

Authors:

Jaeseung Roh HD Korea Shipbuilding & Offshore Engineering Co., Ltd.
Sung-In Park HD Korea Shipbuilding & Offshore Engineering Co., Ltd.