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LNG Bunkering in Action
Gianpaolo Benedetti spoke to LNG Industry Magazine about current LNG bunkering practices with an eye on the future.
“LNG is becoming increasingly viable as a marine fuel. It is already available across Northern Europe and Scandinavia with Norway leading the way. Interest in the US is growing steadily as its economic and environmental benefits become clearer. This has led to an established set of bunkering and transfer procedures, however there is still a way to go to standardise them with codes and guidance still evolving.
Houlder has built a strong in-house understanding of bunkering operations through the development of new vessels and transfer equipment. The following outlines this knowledge, shares the company’s conclusions and showcases some of the resulting engineering.
LNG Bunkering Standards and Codes
Today, the supply of LNG is governed by the IMO / IGC Code. This Code provides an international standard for the safe carriage, by sea in bulk, of liquefied gases and similar substances. Through consideration of the products carried, it prescribes the design and construction standards of the ships involved and the equipment they should carry to minimise risks.
Standards for bunkering and receiving operations are less well defined. ISO has recently published the ISO-TS 18683 2015 – Guidelines for Systems and Installation for Supply of LNG as Fuel to Ship, while the Society for Gas as a Marine Fuel (SGMF) has issued “Gas as a Marine Fuel Safety Guidelines for Bunkering” and “Gas as a Marine Fuel – An Introductory Guide.”
Useful as these guidelines are, they are caveated by only providing guidance supplemental to the requirements of local legislation.
The draft IGF Code of Safety for Ships using Gases or other Low flashpoint Fuels makes some general statements regarding bunkering. LNG bunkering systems shall have an arrangement for purging; not discharge gas to the atmosphere, with the exception of safety relief valve; be fitted with a manually operated stop valve and a remote operated shutdown valve; be possible to operate the remote valve from a control location and be fitted with ship-shore link (or equivalent) for automatic and manual Emergency Shutdown (ESD).
The industry will have to wait until 2017 for this to become mandatory. Bunkering and transfer operations, especially ship to ship, risk remaining grey areas for a while yet.
This lack of clarity has thus far not been overly problematic. The transfer of LNG is widely viewed as a success with an enviable safety record. Houlder is very aware of commonalities at work across industries and the following outlines current good practices.
Safety is the key priority of bunkering and success is dependent on everyone’s full understanding of the systems at work. Hazard, safety and security zones need to be defined, as do the appropriateness of mooring arrangements, connection to the receiving manifold and Emergency Shutdown (ESD) systems. Given the potential for variance in equipment and methodology, it is vital roles and responsibilities are clear to all parties. The supply vessel Master and Cargo Room controller are typically key personnel. The Master, Engine Room Controller and Manifold Watch on the receiving vessel are equally vital. Given the number and variety of people involved, it is essential to nominate an overall Person in Charge (PIC) for LNG Bunkering and Transfer operations covering both supply and delivery. The PIC can ensure that all involved are aware of the operational procedures; permissions required; communication systems and Safety Management. This is typically achieved through a pre-bunkering meeting or briefing actioned well in advance of operations.
LNG Bunkering Checklists
To help with the above, the International Association of Ports & Harbours (IAPH) has issued LNG Bunkering Checklists as part of its World Ports Climate Initiative (WPCI). The lists cover shore-to-ship and truck-to-ship as well as ship-to-ship transfers. Aware of the potential for confusion, the WPCI’s published goal is to harmonise approaches to known scenarios. They are confident that, given checks and advice that reflect the additional requirements LNG makes of ports, a high level of quality and responsibility can be obtained. The receiving vessel also ought to check its water curtain, station ventilation, gas detection system and tank pressures and temperatures, for example.
Connection requires the deployment of a gas system compatible with the receiving manifold and operating within its allowable forces. This should take into account vessel motions including the impact of wind, current, tide, swell, passing ships, trim, list and fendering. The IGF code specifies the receiving manifold should be located on open deck, or semi-enclosed in special circumstances.
Once connected, the chosen transfer system should be subject to a safety visual inspection and leak test. Houlder is confident high flow rates of liquid and vapour can be achieved depending on means of transfer including couplers and hoses. Transfer requires careful monitoring of pressure and temperature with cooling down and topping up of tanks required to maintain efficiency.
Once transfer is complete and pumping has been stopped, LNG needs to be drained from the system and vapour needs purging from the lines. This inerting reduces the risk of ignition.
Typical triggers for emergency shutdown during transfer include electrical failure, a drop in hydraulic oil pressure, exceeding safe cargo capacity, a drop in gas blower pressure, low pneumatic pressure in connections and low control air pressure. An electronic signal from the receiving ship, activated should the safe working envelope be exceeded, and a manual switch can both also trigger a shutdown event.
Systems should be equipped with a hydraulically powered Emergency Release System (ERS) that allows full control in case of a shutdown event. Disconnection can be activated by Quick Connect/Disconnect Coupling (QCDC) or Dry-Coupling or in case of emergency by Emergency Release Couplings (ERC) or Breakaway Couplings. Nitrogen purging for the receiving vessel manifold and an Emergency shutdown link are also key safety features.
Given the challenges outlined above, it is clear LNG bunkering is an area in which innovation and ingenuity will be rewarded. As requirements become clearer, vessel owners and operators will turn to equipment suppliers like Houlder for a wide range of systems and components. Example of Houlder’s work are included in the following.
Deployable Transfer Manifold (DTM)
Houlder engineers have developed an innovative LNG transfer manifold that can be deployed and manoeuvred by the port or supplying vessel crane. The deployable manifold consists of a twin-line gas system allowing for concurrent handling of liquid and vapour. It is designed to connect securely to a wide range of receiving vessel manifold arrangements while eliminating the load transmitted and mitigating the risk of spillage at the connection point. The design accommodates for bunker stations located either on an open deck or inside a side shell door. Active emergency release valves, dry-couplers, and a nitrogen umbilical are integrated parts of the system.
Tensioner & Compensating System (TCS)
The TCS is a hydraulically operated system that provides multiple functions in support of transfer. These including vessel movement compensation, vessel drift monitoring and ESD limit alarms. Based on proven offshore tensioner system technology, it offers a robust, highly reliable and innovative solution to deploy and control transfer lines during bunkering operations.
The complete TRAV&L System is an articulated marine crane structure that deploys, recovers and controls the Transfer Manifold and Tensioner & Compensating systems for LNG bunker operations. The geometry of the hoses is governed to allow compensation for relative vessel movements induced by wave motions and/or changes in vessel draft. The TRAV&L is capable of handling the concurrent transfer of liquid and vapour when necessary. It offers full control in the event of an emergency effecting shutdown by activation of a powered Emergency Release System (ERS). It is also compliant with the draft ‘Guidelines for systems and installations for supply of LNG as fuel to Ships,’ (ISO-TS 18683 2015).
The design philosophy behind Houlder’s LNG bunkering equipment is based on the industry’s broadening list of requirements. Flexibility is key to success given the range of LNG-fuelled vessels currently in development. Any system will need to allow for a range of receiving manifold configurations and positions. Any additional rigging of hoses and equipment needs to be minimised to save time between transfers as operations become more time and cost sensitive. The ability to safely manage emergency release is a critical requirement. Any system also needs to eliminate load transmitted to the receiving vessel manifolds and dry-coupler to ensure safe operations. Ease of manoeuvrability and operation is key to success. Similarly, the industry requires a solution that is easy to maintain. There is a general consensus to move away from cryogenic swivel joints and towards more easy replaceable hoses.
As well as marine equipment, Houlder’s naval architects have used their LNG knowledge and experience to develop the concept design for a 110m 5000m3 capacity bunkering vessel. This has been created to fulfil likely future requirements in major European LNG bunkering ports.
The news that standardising bunkering operations is on the agenda should be welcomed. A complex and challenging set of requirements will force the supply chain to innovate as LNG fuelling grows as an industry. Houlder is looking forward to a bright, if challenging, future.”