In our December 2025 issue of LNG Industry, Daniel Patrick, Market Segment Manager – LNG & Hydrogen, Atlas Copco Gas and Process, highlights the various challenges that boil-off gas compressors face in LNG operations and explores how integrally geared compressors help to tackle them.
As LNG infrastructure expands to meet global energy demands, managing boil-off gas (BOG) remains a critical operational requirement across the value chain. Whether in liquefaction plants, LNG carriers, or receiving terminals, BOG forms naturally due to heat ingress during storage and handling.
Left unmanaged, BOG can lead to over-pressurisation, product loss, and emissions. However, with the right compression strategy, this cryogenic vapour can be changed from a liability to a valuable resource. This article explores two main applications of centrifugal BOG compressors – low pressure and high pressure – and highlights how integrally geared compressors (IGCs), like those engineered by Atlas Copco Gas and Process, can offer performance and space-saving benefits.
From waste to value: Productive use of BOG
In earlier generations of LNG infrastructure, BOG was often vented or flared. While this controlled tank pressure, it came at the cost of lost product and added emissions. As environmental regulations tightened and energy efficiency became a financial driver, plant operators began investing in systems to capture and reuse BOG productively.
As shown in Figure 1, BOG is routinely used or recycled in three primary ways across the LNG value chain:
- Fuel gas for onsite power: In liquefaction and regasification terminals, BOG is compressed and routed to gas turbines or reciprocating engines. This process offsets the use of pipeline natural gas and enhances energy efficiency.
- Reliquefaction: In facilities equipped with reliquefaction units, BOG is recompressed, cooled, and reliquefied to be returned to the cryogenic storage tanks.
- Pipeline export: High-pressure BOG can be compressed and injected into natural gas pipelines for distribution or blending with send-out gas, reducing the need for flaring and maximising product recovery.
These approaches transform BOG from an operational nuisance into a strategic energy asset, improving plant economics and reducing emissions intensity.
Inline vs integrally geared compressors
In high-pressure BOG applications, two compressor architectures dominate: traditional inline (barrel-type) compressors and IGCs. While both can be engineered to meet pressure and flow requirements, they differ significantly in design philosophy and performance as summarised in Table 1.
Multi-stage IGCs can be configured to efficiently meet the higher-pressure ratios required for high-pressure BOG service. In this arrangement, each impeller is mounted on its own pinion shaft, with multiple pinions driven by a central bull gear. This design allows each stage to operate at its optimal speed, enabling maximum aerodynamic efficiency while maintaining a compact overall footprint. In addition, the modular design of IGCs allows for easier customisation across projects with different gas compositions, pressures, and flow rates, yielding more attractive CAPEX for EPCs and end-users compared to inline machines.
Offshore considerations: IGCs in floating LNG and space-constrained projects
IGCs can offer advantages in certain offshore LNG applications, such as floating LNG (FLNG) facilities and FSRUs. In these environments, space and weight are important design factors and optimising equipment layout can help reduce structural steel requirements, buoyancy needs, and installation complexity.
Potential benefits of IGCs in these settings include:
- Compact footprint and lower weight: The radial arrangement of impellers can allow for a more compact layout compared to some inline designs.
- Modular skids: Compressor trains can be pre-assembled and tested onshore, supporting streamlined installation and commissioning.
- Efficient operation: The ability to run each stage at an optimised speed can help improve overall energy efficiency, which is even more important where electrical power is limited, such as in offshore settings.
- Serviceability: Individual stage access can simplify maintenance activities, which is valuable when maintenance windows are limited.
While equipment selection depends on project-specific requirements, IGCs can be a strong option for offshore projects where compact design, maintainability, and energy efficiency are important considerations.
Conclusion
As LNG plays an expanded role in the global energy mix, the need for reliable, efficient BOG handling is more important than ever. Whether at a large onshore terminal, a floating production vessel, or a bunkering station, BOG can no longer be seen as waste. Instead, BOG is an asset that, when properly managed, contributes to plant efficiency, emissions reduction, and operational resilience.
Low-pressure BOG compressors ensure safe tank management and support fuel gas or re-liquefaction loops. High-pressure BOG compressors enable LNG to serve power generation or pipeline export. When it comes to delivering efficient, compact, and maintainable compression, IGCs can offer clear advantages over traditional designs.
As projects grow in complexity and global LNG trade continues to diversify, investing in the right compression technology can deliver long-term performance, flexibility, and peace of mind.
Read the rest of this abridged article in the full issue here!