Boil-off gas is not waste: Why LNG compression strategy matters more than ever

Every LNG storage tank, carrier, and terminal produces boil-off gas. The question is no longer whether to manage it, but how to get the most value from it. This article is Part 1 of a 2-part series on boil-off gas compression in LNG applications. 

As global LNG infrastructure continues to expand, boil-off gas (BOG) management has become one of the most important operational considerations across the value chain. Whether at a liquefaction plant, onboard an LNG carrier, or at a receiving terminal, BOG forms naturally whenever heat enters cryogenic storage. Left unmanaged, it leads to over-pressurization, lost product, and unnecessary emissions. But with the right compression strategy, this cryogenic vapor becomes a genuine asset. 

From flaring to fuel: How the industry’s approach has evolved. In earlier generations of LNG infrastructure, BOG was typically vented or flared. That approach controlled tank pressure, but it came with the cost of lost product and increased emissions. As environmental regulations tightened and energy efficiency became a financial priority, operators began investing in systems to capture and reuse BOG productively. 

Today, BOG is routinely put to work in three ways across the LNG value chain. 

Fuel gas for onsite power. At liquefaction and regasification terminals, BOG is compressed and routed to gas turbines or reciprocating engines. This offsets the use of pipeline natural gas and improves overall energy efficiency. 

Re-liquefaction. In facilities equipped with re-liquefaction units, BOG is recompressed, cooled, and returned to cryogenic storage as liquid, recovering product that would otherwise be lost. 

Pipeline export. High-pressure BOG can be compressed and injected into natural gas pipelines for distribution or blending with send-out gas, maximizing product recovery and minimizing flaring. 

Each of these approaches transforms BOG from an operational nuisance into a strategic energy resource, improving plant economics and reducing emissions intensity. 

Two compression jobs, two different challenges. Since LNG is stored at relatively low pressure, any vapor that forms is also at low pressure (near atmospheric). From there, BOG compressors fall into two main categories based on how much pressure boost is required. 

Low-pressure BOG compression. Low-pressure BOG compressors typically operate at 2 to 4 bara outlet pressure. Their primary function is to capture vapor displaced from storage tanks, ship loading and unloading operations, or natural heat leak. In most facilities, they compress the vapor to a level suitable for fuel gas systems or re-liquefaction loops. 

The design priorities for these machines include cryogenic gas handling (BOG can arrive near −160°C at suction), oil-free operation to avoid contamination, high reliability with wide turndown to handle fluctuating flow rates, and low maintenance . 

Due to the moderate pressure ratios involved, single-stage integrally geared compressors are a common and effective choice for low-pressure BOG service. They offer a compact, efficient, and simple configuration that’s well suited to these duties. 

Beyond tank boil-off, integrally geared compressors are also commonly used for end flash gas compression. This flash gas, generated during the final expansion of feed gas in the liquefaction process, is typically nitrogen-rich and must be captured to avoid venting or flaring. Compressing it allows routing to fuel gas systems or nitrogen rejection units, improving overall plant efficiency. 

High-pressure BOG compression. High-pressure BOG compressors operate in a different league, typically targeting 40 to 60 bara outlet pressure. Their job is to take vaporized LNG and boost it to pipeline or gas turbine supply pressure. 

Key roles include supplying fuel gas to high-pressure engines or gas turbines at liquefaction plants and compressing BOG to match pipeline delivery pressure for injection into the gas export stream. 

These machines handle significantly higher pressure ratios and must be engineered for multistage compression, often within tight footprints. And it’s in this high-pressure space where the choice of compressor architecture becomes especially consequential. 

The high-pressure question. For decades, the default solution for high-pressure BOG compression has been the traditional inline (barrel-type) compressor. These machines are well proven and widely installed across the LNG industry. But as projects evolve toward more compact, modular, and offshore configurations, the limitations of inline designs are becoming more apparent. 

In the next post in this series, we’ll take a closer look at how integrally geared compressor technology is stepping into high-pressure BOG service, why it can deliver the same (or better) performance in fewer stages and a smaller footprint, and what the industry’s shift toward modular LNG and FLNG means for compressor selection going forward. 

To learn more about BOG compression solutions for LNG applications, contact Atlas Copco Gas and Process. 

NOTE

This post is adapted from an article originally published in LNG Industry, September 2025. 

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