A break-bulk breakthrough

Gediminas Jotauta, Eimutis Gandramavičius, and Martynas Tamošaitis, AB Klaipėdos nafta, Lithuania, discuss the lessons learned regarding FSRU breakbulking and the preparation required to introduce this service into terminal operations.

Over the past several years, the LNG industry has seen a steady growth of FSRU-based LNG import terminals unlocking new markets. The primary regasification demand comes in various forms – ensuring security of gas supply, meeting the demand for gas to power, increasing market competition, or replacing depleting gas fields. Soon after commissioning an additional phenomenon is being witnessed. After a year or two of operations, operators begin to investigate the scope of expansion and seek to introduce an additional service – LNG break-bulking into smaller cargoes. This was first pioneered in 2017 at Klaipeda LNG terminal and later replicated in other FSRU-based LNG terminals across the globe. Even though at first glance this service might seem like a simple cargo reload operation, on the contrary it has many different layers and aspects which must be taken into account from commercial and technical standpoints, so that it can be seamlessly integrated into overall terminal operations. In this article, AB Klaipėdos nafta will take a closer look and touch on a few specific aspects that must be considered before introducing such a service into terminal operations.

Safety first

Upon the introduction of a new service into the terminal, the following safety related tasks should be addressed: environmental impact assessment (EIA) including quantitative risk assessment (QRA), and corrections in spatial planning procedure. Also, a safety report (according to Seveso directive and/or other applicable requirements) including an emergency response plan with its scenarios should be updated.

Small scale LNG vessel mooring to the FSRU

Considering the size difference between the small scale LNG vessels and conventional FSRUs, there are at least several important aspects which should be accounted for when assessing the mooring system effectiveness between these two ships moored side-by-side. Firstly, it should be evaluated that freeboard of the small scale LNG vessel is sufficient to be used with available ship-to-ship (STS) fenders deployed on the FSRU as well as whether these fenders can be rearranged to fit with the flat body surface of the small scale LNG vessel. This might require new smaller fenders, otherwise it may result in the incompatibility of the two vessels and in the worst case, the possible rollover of the fender or a similar related incident during the operation. Secondly, due to the height differences between the fairleads of the two vessels, the vertical angle of the mooring lines might exceed industry recommendations, and there may be challenges to place the gangway, transfer the equipment, or connect cargo hoses. Last but not least, operational and permanence limits for small scale LNG vessels are likely to differ from those applicable for operations of large scale LNG carriers. Therefore, prior to commencing the LNG break-bulk operations, a prudent operator should run several distinct scenarios for dynamic mooring analyses for main sizes of the small scale LNG vessels which are expected to call at the terminal. This is especially important for ports which are susceptible to adverse metocean conditions or extreme weather phenomena.

Figure 1. The first LNG break-bulking operation at the Klaipeda LNG terminal.

Small scale LNG vessel manifold height vs flexible hose length

Size differences between the two vessels as well as the cargo transfer rate – which can be as much as 10 times lower compared to an STS operation between an FSRU and a conventional LNG carrier – requires an evaluation of cargo transfer equipment suitability.

For FSRUs that are equipped with MLAs for STS transfer, it is very likely that using the existing MLAs for LNG breakbulk operations will be limited by the operational envelope of the arms. The manifold height of small scale LNG vessels varies and is usually significantly lower than the standard FSRU manifold, thus the safe connection between the two is often unachievable. FSRUs that are equipped with flexible composite hoses for STS transfer might face a similar issue, although in this case the main limiting factor may be the length of the hose – being either too short or too long may lead to incompatibility between the FSRU and small scale LNG vessel. Also, when evaluating the suitability of cargo transfer equipment and choosing the best option, it must be acknowledged that there are more aspects to be evaluated. This includes which specific small scale LNG vessels are most likely to arrive for a cargo transfer and what their manifold arrangements, reception flow, and pressure design parameters are, whether the minimum bending radius will be maintained at times of connection, and whether both vessels are equipped with the required reducers.

After taking those variables into account there is a clearer picture about the potential solution – a new LNG hose which is either universal for large scale and small scale LNG operations or a new LNG hose that will be dedicated solely for the small scale operations. If the latter option is selected, then the hoses need to be swapped each time in between the receipt of cargo delivered by conventional LNG carriers and the arrival of a small scale LNG vessel for break-bulk operations. This may require additional manning on the FSRU for handling and bolting the hoses, as the minimum time required between two STS operations is likely to increase and there is a higher risk of the crane damaging the hose while manipulating it between the storage location and FSRU manifold.

From an operational perspective, having a single hose suitable for both large and small scale operations is more convenient, however the potential implications of a longer hose for large scale transfers should also be evaluated. For instance, upon emergency disconnection, a longer hose risks falling into the water which may lead to a number of safety and integrity issues. Furthermore, having a set-up with a longer hose may lead to lower transfer rates, resulting in extended laytime for standard STS operations due to exacerbated pressure losses within the LNG transfer system.

FSRU ESD C&E matrix

Before commencing a cargo reload operation to a small scale LNG vessel, the existing set-up of an FSRU emergency shutdown system must be assessed with regards to compatibility for simultaneous operations of LNG reload and regasification. In some cases, a few minor adjustments on the FSRU’s integrated automation system may be required in order to allow safe and reliable simultaneous operations.

TRI-CON CRYOGENIC

SERIES FOR LNG AND H2 APPLICATIONS

LNG quality measurement

Accurately determining LNG quality at the time of LNG transfer is a key element for a successful commercial transaction. Quality measurement principles during a break-bulk operation may differ from a standard STS operation at an FSRU import terminal. Conventional cargoes frequently arrive from a single source and the quality of the liquid is normally consistent across all of the carrier’s tanks. In comparison, LNG in FSRU cargo tanks ages differently depending on the cargo management and regasification profile, the time since last STS operation, etc.

The most reliable option to determine the quality of reloaded cargo is an ISO 8943 compliant LNG quality measurement system with online gas chromatograph and sample constant pressure floating piston (CP/FP) cylinders. An online chromatograph enables quality measurement in real-time while usually three cylinders of gas are taken during a cargo transfer as back-up gas samples for each concerned party and can be used later for a laboratory analysis. However, before using this system for LNG breakbulk operations, it is important to confirm that it can be used with flow direction from an FSRU to an LNG carrier. In addition, it is also important to confirm that the pressure and flow parameters at the sampling point are achievable and stable during the whole cargo reload operation.

If a sampling system onboard an FSRU is unavailable, then the quality of reloaded bulk can be estimated by the third-party surveyor using an LNG ageing model, the latest regasified gas composition measured onboard the FSRU, or by a shore gas chromatograph. In case the latter option is exercised, it should be noted that running the recondenser onboard will normally increase the methane content within the send-out compared to actual bulk composition within the tanks and consequently, representative quality data will not be acquired.

Cargo transfer

One operational issue to consider is the pressure in the FSRU cargo tanks before the cargo transfer operation. The type of incoming small scale LNG vessel has to be taken into account, however it is a common requirement that the FSRU should have a specific lower pressure at its tanks before cargo operations. It is a good practice to consider and define pressures in cargo tanks of both the FSRU and small scale LNG vessel upon its arrival as well as maximum allowable operating pressure during the transfer operation – this is normally undertaken during the compatibility study.

Sometimes small scale LNG vessels arrive with warm cargo tanks and only small amounts of LNG remaining in the tanks, or even without any LNG cargo remaining. In such cases, an important aspect is that the BOG that they return is warm and at the same time accepting that such BOG to the FSRU tanks might compromise the temperature of the LNG in its tanks. Even if this is acceptable to the terminal user which requested the LNG break-bulking operation, this could also influence the temperature and composition of shared inventory when there is more than one user using the terminal.

An LNG terminal operator must therefore discuss with the FSRU operator and decide what amounts of BOG can be returned to the FSRU tanks and whether BOG should mostly be managed in the small scale LNG vessel.

Fuel consumption and BOG

A TCP with an FSRU owner will usually include a contractual obligation for an FSRU to stay within a specific limit of fuel consumption and boil-off (LNG, BOG, and diesel) during terminal operations.

It is important to consider whether these limits shall remain in place when LNG break-bulk operations are added to the usual regasification service provision. It is also worth considering whether these limits are still applicable in cases where the FSRU has stopped send-out completely but is still performing LNG break-bulking operations. Such aspects should be explicitly defined in the TCP in order to have a full visibility of all costs and clear limits of responsibilities during the LNG break-bulk operation. There can be an additional layer of complexity when an LNG terminal is simultaneously used by multiple terminal users and the operator of the terminal must assign amounts of fuel consumed and boil-off between multiple terminal users. It is an interesting challenge to design methodology to determine which part of fuel consumption was used for regasification purposes and which part was used to break-bulk LNG.

The specific allocation algorithm at each terminal must provide tools for the operator to fairly assign fuel consumption and boil-off to the terminal users which are using different types of services.

Scheduling of LNG break-bulk operations

When an LNG break-bulking service is added to the overall offering for the terminal users, the operator will have to devise a priority system and scheduling rules for LNG cargo arrivals and LNG break-bulking operations. Typically, LNG break-bulking is considered only as an ancillary service and therefore the arrival windows for small scale LNG vessels would have lower priority than the LNG cargo delivery windows.

Frequency of operations and crew rest

FSRU crew rest requirements are an operational aspect which might have some contractual consequences. It is important to cover this aspect within the TCP/OSA so that the FSRU crew has no restriction to perform frequent reload/load operations.

Due to FSRU regasification limitations there will typically be at least several days between LNG cargo arrivals at the terminal. However, when LNG break-bulking operations are added as a service of the LNG terminal, the terminal users might want to book LNG break-bulk operations with little or no time before/after LNG cargo arrival. Therefore, the FSRU might need more crew to be able to perform operations with little time in between. Timely identification and management of complex technical and commercial challenges as well as mitigation of risks arising from the introduction of an LNG break-bulking service at an FSRU-based LNG terminal is the key to success in achieving maximum value. Early involvement of an experienced terminal operator when devising LNG break-bulking services is a reliable way to ensure safe and seamless integration into an overall terminal service offering.

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