The market for LNG as a marine fuel will grow significantly over the next few years. Fuelling will have to be completed within tight time frames to meet ship sailing schedules and to take into account simultaneous operations, such as loading containers, vehicles or passengers. There is simply no margin for error if the operation is to be completed safely each and every time.
Fortunately, LNG bunkering companies can build upon the excellent standards set by bulk LNG shipping, which has one of the most impressive safety records in any marine transportation sector. The 50 year history of LNG cargo trade has undoubtedly proved that LNG can be transferred safely and efficiently. This outstanding record was achieved by using well-trained crews and highly effective safety technology. In particular, the bulk LNG sector makes extensive use of linked ship-shore shutdown systems, in accordance with the Society of International Gas Tanker and Terminal Operators (SIGTTO) recommendations. Effective communication between the parties involved in LNG bunkering is critical to ensuring safety. All those involved require a common understanding of the entire process arrangement.
Background to ship-shore links
The linking of emergency shutdown (ESD) systems during LNG transfers has been common place since the earliest of LNG marine transfers. In 2006, the latest fibre optic digital ship-shore link was developed and has since been used in the vast majority of floating storage and regasification unit (FSRU) and floating storage unit (FSU) applications when a jetty connection has been required. The digital link supports the primary ESD and secondary telecoms that have become standard.
However, in the more complex process arrangements of these floating installations, further integration of the terminals and vessels has been required. This includes the provision of additional ESD signals in relation to the gas send out or other plant requirements. The key advancement of these systems has been the ability to transfer bulk quantities of data such as process data communication, CCTV, internet and other Ethernet type signals. The link itself is based around Synchronous Optical Networking (SONET) communication protocols, which make it both sustainable in the future, expandable and open for others to interface with.
Solutions to bunkering links
Unfortunately, the majority of large scale LNG link systems utilise a great deal of legacy technology and connectors. These add substantial cost to systems, something that cannot be borne by the LNG fuelling vessels.
The process of bunkering LNG is generally performed on one side by a well-trained operator; these handle LNG either at a shore facility or a bunker vessel with routine LNG transfers taking place at regular intervals, either during bulk loading or during bunkering offtakes; and, on the other side, the receiving vessels crew, who are suitably trained but may not have the experience of handling LNG or cryogenic liquids. To ensure a safe, efficient and cost-effective transfer, it is vital that the process is transparent and the bunker provider is able to control the transfer with real-time information.
To meet this requirement, the digital fibre optic link was found to not only offer the basic ESD requirement, it could also be utilised for telecommunications as well as process data transfer and other future data transfer requirements. For the first time in link technology, the system would be future-proof to allow additional functionality as required.
With a fibre optic primary, the SIGTTO electric link can be utilised as an ESD only backup, as the SIGTTO link system is referenced by SIGTTO, the Oil Companies International Marine Forum (OCIMF) and the Chemical Distribution Institute (CDI) guidelines. Additionally, while its functionality is currently fixed to just ESD, there may be future options to expand the system to utilise some spare connector cores for a limited system upgrade. This however would require agreement of all stake-holding parties.
In ship-to-ship (STS) operations, the SIGTTO electric link base systems are the same on both sides of the transfer. However, the interposing relay interface is typically only installed in shore systems and has historically been carried out by specific hazardous area relay modules, which were not only expensive, but also not freely available in the market. The solution for bunkering therefore was to redesign the output of the link circuit around the rest of the circuitry, so that it formed part of a single system. This, therefore, allowed the relay interfaces to be switched in or out of circuit depending on the mode of operation – master (shore or supplier type), or slave (ship or receiver type).
Pneumatic links have been identified as a solution, but only for lower volume transfer (ISO20519). However, there are inherent issues in the pneumatics around calibrating system volumes, operating at common pressure settings both in healthy conditions and at defining a mutual trip pressure. The pneumatic link is a very simple system comprising a hose linking the two ESD systems. Each side will monitor the hose pressure via a pressure switch or transmitter to detect an ESD initiated by the connected system and will have control of a solenoid valve to allow the pressure to be released in the case of an ESD generated on the local system.
All of these link options, together with the original large scale solutions, can be packaged in numerous ways to suit a vessel’s intended trading or bunkering pattern.
Bunker vessel considerations
When specifying LNG bunker vessels, further in-depth analysis of current and future potential trading patterns is required to ensure that the vessel is not only capable of physically berthing at the terminals it may trade with, but also to ensure it has the correct linked ESD interface to be able to connect to the bunkering vessels and large scale terminals it may be required to load from. The number of LNG bunker vessels is increasing rapidly, and these considerations need addressing.
The SIGTTO ESD guidelines clearly state that the SIGTTO electric link system has not been adopted by any major international LNG projects. What this points to is bunker vessels either having to install low cost equipment purely for bunkering (which limits loading to a few specialist facilities), or to install a variety of systems to enable trouble-free connection compatibility. The bunker vessel is the equivalent of a small scale LNG carrier, it just so happens to also provide bunkering services.
To accommodate these cross-over type installations, in 2017, Trelleborg launched the GEN3 SmartPort enabled ship-shore link, which allows all known link types to be available via a single cabinet. The use of a new common electronics infrastructure means separate complete system modules are no longer required. These have been reduced to single circuit boards per system, expandable to suit the vessel’s operation, simplifying the installations required in the more complex arrangements.
In 2017, it was announced that Q-LNG would build a 4000 m³ articulated tug and barge (ATB) at VT Halter Marine construction yard to provide LNG distribution and bunkering services around Florida and the Caribbean. As the project scope expanded, so too did the configuration of the required links. Originally, the concept included options for loading at a dedicated refuelling facility. The link was defined as a digital fibre optic Universal Safety Link (USL) onboard the barge to allow it to load from this dedicated facility and discharge to vessels requiring an LNG bunker.
However, it became clear that the charterer’s requirements for the barge were that it should be able to load LNG from any of the existing LNG facilities around the Gulf and by extension, any international LNG terminal. As well as the barge now having to install a second raised manifold arrangement to facilitate berthing at the large scale terminals, the link options were re-addressed to cater for the project requirements.
Additionally, as this would be an ATB construction with the barge operated via the tug, the main control station would have to be within the push tug wheel house. As networking of other systems was already specified within the barge-tug interface, the GEN3 ship-shore link system could utilise its network extension capabilities to allow the operator full control of the ship-shore link system, from the tug control station via a third-party hardware interface. This functionality was not even an option on other ship-shore link implementations.
The LNG bunkering market is not standing still, there are already custom built bunker vessels, converted small LNG carrier bunker vessels, bunker barges either pushed, towed or self-propelled being put into operation worldwide. It is vital that this industry does not settle on a lowest common safety factor, but continues to push for the safest solutions; not only in emergency protection via ESD, but in looking at processes that can be integrated in the future to enable more oversight, more automation and enhanced safety within the LNG transfer application space.
Read the article online at: https://www.lngindustry.com/special-reports/15012019/lng-bunkering-today-and-tomorrow/
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