LNG arriving at an FSRU is cryogenic, pure methane with trace components. Natural gas in a national pipeline network is warm, at a specific pressure, and often blended with other gases (nitrogen, ethane, or biogas). The floating gas terminal market is responsible for the critical transition: turning shipboard LNG into pipeline-quality gas.

Gas Quality Requirements

Each pipeline network has a gas quality specification: heating value (calorific value), Wobbe index (a measure of interchangeability), and limits on impurities (water, CO2, H2S, mercaptans). LNG typically meets these specifications because the liquefaction process removes most impurities. However, LNG from different sources may have different compositions. The floating storage unit market includes gas chromatographs (online analyzers) that continuously monitor gas composition. If the gas does not meet pipeline specifications, the FSRU may need to blend it with other gases or reject the cargo.

Heating Value Adjustment

LNG heating value varies with source. Some pipelines have a narrow heating value range; gas that is too "rich" (high heating value) can cause combustion issues in end-use equipment. The floating gas terminal market adjusts heating value by blending the regasified LNG with nitrogen (inert gas) or air (but air contains oxygen, which is generally not allowed in pipelines). Nitrogen blending is common: liquid nitrogen is stored on the FSRU or delivered by barge, vaporized, and injected into the gas stream. The nitrogen reduces heating value to the required level.

Pressure Control and Boosting

The FSRU's vaporizers output gas at low pressure (typically 5-15 bar). The onshore pipeline may require much higher pressure (up to 100 bar). The floating gas terminal market installs gas compressors (centrifugal or reciprocating) on the FSRU or onshore to boost pressure. Compressors are energy-intensive and require significant power; this power is typically generated on the FSRU using gas generators (burning some of the regasified LNG). The compressor station is a major topsides component, adding weight and complexity.

Odorization for Leak Detection

Natural gas is odorless. For safety, a mercaptan odorant is added to gas before it enters distribution networks, giving it the characteristic "gas smell." The floating storage unit market includes odorant injection systems on FSRUs (or at the onshore connection point). Odorant is stored in tanks and injected at a controlled rate. The system must ensure consistent odorant concentration even as gas flow varies. Over-odorization causes complaints; under-odorization creates safety risks.

Metering and Custody Transfer

The gas delivered to the pipeline is measured for quantity (volume or energy) and quality. The floating gas terminal market includes custody transfer metering systems with redundancy (multiple meter runs) and online verification. Ultrasonic flow meters are common; they measure gas velocity using sound waves. Heating value is measured by gas chromatograph. The metering system is calibrated regularly and is subject to audit by the pipeline operator. Measurement disputes are resolved using the metering data.

Subsea Pipeline Connection

The pipeline from the FSRU to shore is typically a flexible or rigid subsea pipe. The floating storage unit market specifies the pipeline based on water depth, seabed conditions, and distance to shore. The pipeline must be able to accommodate FSRU motion (if connected via a flexible riser) or be isolated from motion (if connected via a jetty). The pipeline includes pigging facilities (for cleaning and inspection) and emergency shutdown valves (ESVs) at both ends. Pipeline installation is a specialized operation using pipelay vessels.

Onshore Receiving Facility

The onshore end of the subsea pipeline connects to a receiving facility: a block valve station, filter separators (to remove any liquids or solids), a pressure reduction station (if the pipeline pressure is higher than the distribution network), and the odorization system. The floating gas terminal market often provides this onshore facility as part of the overall project. The receiving facility also includes the gas chromatograph and custody transfer metering if not located on the FSRU.

Gas Heating After Regasification

LNG leaves the vaporizers at very low temperatures (just above freezing). Cold gas can cause brittle fracture in carbon steel pipelines and can damage meters and regulators. The floating storage unit market includes gas heaters (using seawater, electric heat, or gas-fired heaters) to raise the gas temperature to acceptable levels (typically above 0°C). In cold climates, additional heating may be needed to prevent hydrate formation (ice-like crystals that block pipelines). Gas heating adds energy consumption.

Hydrate Prevention

Hydrates are solid ice-like structures that form when water (even trace amounts) combines with natural gas at low temperatures and high pressure. Hydrates can block pipelines and valves. The floating gas terminal market prevents hydrates by: (1) Drying the gas (removing water vapor) before cooling, (2) Adding hydrate inhibitors (methanol or glycol), and (3) Maintaining gas temperature above the hydrate formation point. On an FSRU, the gas is typically warm enough from the vaporizer that hydrates are not an issue, but if the pipeline is long and deep (cold seabed), heating may be required.

Interface with Renewable Gases

As Europe introduces biogas, hydrogen, and synthetic methane into its gas networks, the floating storage unit market may need to adapt. FSRUs could receive liquid biogas (LBG) or liquid hydrogen (LH2) in the future, requiring modified storage and regasification systems. Some new-built FSRUs are being designed as "hydrogen-ready," with materials compatible with hydrogen embrittlement. The floating gas terminal market is monitoring this trend; the FSRU of the future may be a multi-purpose floating terminal for various renewable gases. The floating gas terminal market is the critical link between global LNG trade and local gas distribution. And the floating storage unit market continues to refine gas handling, ensuring that what arrives as a cryogenic liquid leaves as pipeline-ready natural gas.

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