For LNG bunkering to remain safe and efficient, it is vital that shipowners give full and proper consideration to the ESD systems they use, writes Trelleborg marine and infrastructure operation managing director David Pendleton
With the implementation of the IMO 0.50% sulphur cap, shipowners only have a few options to comply with the stricter regulations; either operate on low sulphur fuel oil, burn HFO with exhaust gas cleaning systems or use a lower carbon intensive alternative fuel such as LNG. LNG has emerged as the front running sustainable fuel alternative in the maritime industry, producing 15% fewer greenhouse gases than HFO; 95% less NOx, 99% fewer particulates and virtually no SOx.
As the most clean-burning fossil fuel, LNG and natural gas are being more widely adopted for industrial power, power generation and road vehicle applications as part of the clean energy transition. Global demand for LNG grew by 12.5% to 359M tonnes in 2019, and longer term, is expected to double to 700M tonnes by 2040, according to the Shell LNG Outlook 2020 report.
Not only is LNG sustainable, but it is also safe and has been securely transported across oceans for the last 50 years. The industry has firmly set the standard in terms of safety for the containment, transport and transfer of product from ship to shore.
Considering the increased LNG uptake, various regulations exist to support the industry and ensure that LNG remains one of the safest and most efficient marine fuels. This includes the International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF code) issued by the IMO in 2015, which provides mandatory criteria for the arrangement and installation of machinery, equipment and systems for appropriate vessels, minimising the risk to ships, their crews and the environment. In the same year, The Society for Gas as a Marine Fuel (SGMF) issued LNG bunkering safety guidelines, and in 2017, International Organisation for Standardisation (ISO) issued ISO 20519 – a specification for bunkering LNG-fuelled vessels.
Although not enough on its own to fulfil the ambitious IMO 2050 greenhouse gas (GHG) reduction targets, LNG is the most suitable fuel currently available. Used along with other GHG reduction techniques to meet the target, and as part of the ultimate decarbonisation of shipping, LNG is considered the bridging fuel required to see shipping through until future technologies become available for truly carbon-free shipping.
Safe transfer of LNG
To assist with the safe control of the LNG transfer process, the transfer of hazardous liquids in a marine environment necessitates the use of linked emergency shutdown (ESD) systems. The primary purpose of the system is the safe, timely and mutual shutdown of both the ship and shore transfer processes; in order to do this, these two processes must be interlinked.
For large-scale operations, ESD systems are typically linked via an electrical analogue fibre optic or pneumatic system. During these operations, associated umbilical cable ship-shore link systems typically monitor and carry ESD signals, as well as telecoms and mooring load data. With the development of the floating storage and regasification unit, digital fibre optic systems were upgraded to also allow the transfer of process data.
For LNG bunkering, while ESD-only electric and pneumatic links are satisfactory for many users, others want the digital fibre optic link to carry telecommunications and process data to inform operators on both ship and shore sides of the status of the bunkering operation.
When using an electric or pneumatic connection, only an ESD signal can be received and all other data must be communicated by other means, such as radio. However, when the optical fibre is connected, both systems automatically share the process data for the LNG tanks as well as telecommunications, CCTV and other services. This means that one person can control and monitor the whole process across both vessels, reducing the need for constant radio communication, the effectiveness of which can vary depending where the system is on the ship. Details of links, now generically called bunkering safety links, are included in the latest SGMF recommendations for linked ESD arrangements for LNG bunkering.
The silent transfer
One of the first LNG bunkering operations was put in place by US-based Harvey Gulf International Marine (HGIM), a leading offshore marine transportation company. It commissioned the construction of a fleet of six LNG-powered platform supply vessels (PSVs) – five of which are in operation – and built its own bunkering infrastructure at Port Fourchon, Louisiana on the US Gulf Coast.
By utilising the ISO 20519-compliant Trelleborg Universal Safety Link (USL), not only is HGIM integrating the emergency shutdown systems of the facility and vessels, but it also has a full overview of the process parameters on both sides of the link. Feedback from the operation is positive with the overriding sentiment that, thanks to the USL, the bunkering process is now a ‘silent transfer’.
Prior to the completion of HGIM’s onshore storage facilities, the LNG-fuelled PSVs were bunkered directly from road tankers. In this arrangement, the pneumatic shutdown link that formed part of the USL linked the ESD valve on the truck to the onboard bunkering shutdown system. This ensured a minimum safety level was met, but this method relied on constant radio communication between the truck operator, facility and vessel staff, to ensure the transfer was carried out to defined operational requirements.
As bunkering quantities could exceed the volume contained in a single road truck, multiple trucks were essential to provide required volumes, further complicating the arrangement. Lessons were learnt in these early transfers. Although the pneumatic shutdown link is well defined in the original SIGTTO publication, ‘ESD Arrangements and Linked Ship/Shore Systems for Liquefied Gas Carriers’, and the subsequent SGMF equivalent publication, the pneumatic pressure levels required by the truck to keep the ESD valve open were in the higher range of the vessel systems’ capabilities and required optimising.
As the facility began commissioning its storage capacity, there were then two separate stages of LNG transfers. In the first stage, the storage tanks at the facility were loaded by several road trucks. In the second stage, the LNG-fuelled PSVs were bunkered directly from its storage tanks. The trucks utilised the pneumatic shutdown during the loading of the storage tanks. However, with the option to now use the terminal’s enhanced capabilities of the USL fibre optic system and the 155M bps digital synchronous optical networking data link, the connection between the terminal facility and the vessels is one of the most comprehensive in use at any LNG transfer facility.
Full visibility essential
LNG is undoubtedly starting to play its part as a sustainable marine fuel and its increased uptake will aid the industry in reducing its negative contribution towards climate change. However, for the transfer of LNG to remain safe and efficient, it is vital that shipowners give full and proper consideration to the ESD systems they use. Emergency situations are unplanned, so full visibility of the bunkering process is critical, along with a system that functions reliably and effectively, so that ship operators can maintain control and safety, while making a contribution to a greener world.
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