Fueling sites that store liquefied natural gas (LNG) can manage boil-off gas (BOG) by using it as fuel, compressing it for gas delivery or storage, reliquefying it, or routing it to an approved disposal system when recovery is not practical. The best option depends on the site’s BOG rate, operating schedule, pressure requirements, nearby equipment, and local safety and emissions rules. We recommend measuring expected vapor generation and matching the control system to normal operation as well as shutdown and upset conditions. In most projects, a combination of recovery and pressure control is more practical than relying on a single method.
Boil-off gas is vapor produced as LNG absorbs heat or experiences changes in pressure during storage and handling. LNG is kept at cryogenic temperatures; methane’s normal boiling point is approximately -161.5°C at 101.325 kPa absolute. Actual LNG properties vary with composition, and operating conditions depend on the storage vessel and system design.
BOG may arise during tank storage, vehicle or trailer loading, unloading, and periods when fueling demand is low. A site needs to control tank pressure while keeping equipment within its specified operating envelope. The amount generated is not a fixed percentage that applies to every facility, so project decisions should rely on site-specific calculations, equipment data, and operating patterns.
A site may route suitable gas to an on-site consumer, such as a compatible heater, boiler, or other gas-fired equipment. This option can make use of vapor that would otherwise need to be recovered or disposed of. It depends on having a steady enough demand, matching gas pressure and quality, and a safe control arrangement that does not interfere with the consumer’s normal operation.
Fuel use is less attractive when the consumer is unavailable for long periods or when its demand is lower than the BOG supply. The design should define what happens when the consumer shuts down, including how pressure is controlled and where excess vapor is routed. We advise buyers to confirm operating compatibility with both the LNG system designer and the equipment manufacturer.
BOG can be compressed for delivery to a compatible gas network, a site fuel system, or a suitable gas storage arrangement. Compression allows vapor to be handled at a pressure required by downstream equipment, but it adds machinery, controls, maintenance, and power demand. The compressor must be selected for the expected gas conditions and operating range, not simply for a nominal flow rate.
Before choosing this route, confirm that a receiving system exists and can accept gas when the site produces it. Check pressure limits, gas quality requirements, connection arrangements, and the consequences of downstream unavailability. If the site is isolated from a suitable network or consumer, compression alone does not provide a complete BOG management solution.
A reliquefaction system cools BOG so it can return to liquid service or be incorporated into an appropriate LNG process. This can reduce routine gas loss where the site has enough continuous vapor flow and a suitable process configuration. The decision involves more than equipment purchase: buyers should assess energy use, operating complexity, maintenance access, and the system’s turndown capability.
Reliquefaction may be difficult to justify at a small or intermittently operated fueling site. Low or highly variable BOG flow can make equipment sizing and efficient operation challenging. Request a project-specific assessment rather than assuming that every LNG station benefits from a dedicated reliquefaction unit.
During some LNG transfer arrangements, vapor can be returned to the supplying vehicle, trailer, or process system through a designed vapor-return connection. This can help manage vapor displacement during transfer, provided the receiving equipment is configured to accept it. The connection, operating sequence, pressure limits, and responsibilities of each party should be established before commissioning.
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Vapor return is not a substitute for managing BOG generated during long storage periods or when no transfer vehicle is present. It works best as part of a broader system that includes storage pressure control and a plan for periods without an available return path. Buyers should confirm interface details with the LNG supplier and the equipment providers involved.
Venting and flaring are not interchangeable, and neither should be treated as a routine substitute for evaluating recovery options. Their use may be constrained by local codes, permits, environmental requirements, and the facility’s hazard analysis. Relief devices and emergency arrangements must be engineered for their intended safety function and should not be repurposed as normal operating controls.
Ask the project engineer to define the approved response to abnormal conditions, including loss of power, equipment trips, and unavailable gas consumers. The design should identify where gas may be routed, which devices operate automatically, and how the system is inspected and maintained. Applicable regulations and authority requirements take precedence over general guidance.
Start with the LNG tank configuration, expected inventory, operating pressure range, delivery frequency, and hours of fueling demand. Estimate or measure BOG generation under normal storage, transfer, idle, and upset conditions, and express flow consistently, such as in kg/h or standard m³/h. A useful illustrative calculation is that a hypothetical peak generation rate of 10 kg/h sustained for 8 hours represents 80 kg of gas; this is only an arithmetic example, not a typical site value or equipment recommendation.
Also establish the required pressure at each potential gas consumer or destination. Record whether the site has an available gas network, a suitable fuel user, a vapor-return arrangement, or space and utilities for additional equipment. These facts help determine whether the project needs one recovery method or a layered approach.
| Option | Best considered when | Main checks |
|---|---|---|
| On-site fuel use | A compatible gas consumer is available regularly | Demand, gas quality, pressure, backup route |
| Compression and delivery | A receiving network or storage system is accessible | Pressure, capacity, connection terms, power and maintenance |
| Reliquefaction | Vapor flow and project economics support added process equipment | Flow range, energy use, turndown and service requirements |
| Vapor return | Transfer equipment can accept returned vapor | Interface design, operating sequence and availability |
Use the comparison as a screening tool, then have qualified engineers verify the design against the applicable codes and site conditions. Consider both capital and operating costs, including electricity, maintenance, downtime, permitting, and any receiving-system charges. For example, a 20°C ambient condition and LNG near -162°C represent an approximate 182°C temperature difference; this illustrates the severe thermal environment, but does not by itself determine a site’s BOG rate.
When procuring LNG storage or related equipment, share the project design basis rather than requesting a tank or component in isolation. Provide required storage capacity, design and operating pressures, expected LNG composition where available, site conditions, transfer method, and the intended BOG destination. Ask suppliers to identify what is included in their scope and what must be coordinated with compressors, controls, piping, or downstream users.
Dongzhao supports B2B buyers evaluating natural gas and LNG equipment requirements, including cryogenic storage tank needs and project-specific interfaces. We encourage customers to confirm the operating envelope, documentation requirements, customization scope, and delivery schedule during technical review. Clear scope definition helps buyers compare proposals on a consistent basis and identify gaps before procurement.
The suitable BOG management option for a fueling site depends on how much vapor the facility produces, when it is produced, and whether a reliable consumer or recovery destination is available. Fuel use, compression, reliquefaction, and vapor return can each be appropriate under different conditions; venting or flaring should be addressed only within the applicable safety and regulatory framework. No single option should be selected without checking the complete operating and upset-case design.
As a next step, document the site’s expected BOG flow and pressure range, operating schedule, transfer interfaces, and available gas consumers. Use that information to request a project-specific technical review and compare lifecycle requirements, not just equipment price. Dongzhao can work with your team to clarify LNG storage and equipment interfaces for a fueling-site project.
For more information, please visit Boil-Off Gas Management Options for Fueling Sites.