LNG transport costs can be reduced by improving the thermal performance of containment systems
For the last decade, French membrane containment engineering company GTT has been concentrating on ways to improve the thermal performance of an LNG carrier’s containment system to help reduce transport costs. Since 2010, it has reduced its boil-off rate (BOR) from 0.15% of volume per day in the Mark III containment system to 0.07% in the Mark III Flex+.
“The thermal performance of LNG cargo containment systems is one of the chief concerns in the LNG sector,” says GTT technical director Karim Chapot. “It has a direct impact on transport costs and CO2 emissions. Technological advances have made it possible to continuously improve this performance over recent years, halving LNGC emissions in the space of a decade. Furthermore, there is a strong correlation between thermal performance, vessel power usage, emissions and the efficiency of the containment system.”
Mr Chapot explains that the design BOR corresponds to the amount of heat transferred to the tank under IGC code design temperature conditions (ambient air temperature = +45°C, sea water temperature = +32°C) with its insulation under a thermal steady state. Consequently, the guaranteed BOR depends only on the performance of the cargo containment system’s thermal characteristics.
Unlike boil-off gas (BOG), BOR does not take into account cargo loaded, actual environmental conditions, tank and insulation cooling, the propulsion system and the way the vessel is generally operated.
In September last year, GTT won an approval in principle from class society Bureau Veritas for the development of one of its latest cargo containment systems, NO96 Flex. Much like its NO96 membrane technology, the NO96 Flex cargo containment system has insulating panels that are mechanically anchored to the inner hull and the double metallic barrier concept remains, with an unchanged secondary Invar membrane. One key change made by GTT is that the primary membrane is corrugated, waffled stainless steel, instead of Invar, a 36% nickel-steel alloy.
NO96 Flex also contains the refinements first initiated with NO96 L-03 technology. It integrates the insulating foam panels within the NO96 system, leveraging the continuous improvement in thermal performance of the polyurethane foam (PUF) material. The use of PUF at the primary and secondary levels reduces the BOR to 0.07% of volume per day, according to GTT.
GTT expects to begin a mock-up phase of the NO96 Flex containment system in Q1 2020.
“The thermal performance of LNG cargo containment systems is one of the chief concerns in the LNG sector [having] a direct impact on transport costs and CO2 emissions”
At about the same time it launched the NO96 Flex, GTT unveiled the Mark III Flex+, a variant of its Mark III Flex solution, which had obtained general approval from classification societies ABS, BV, DNV GL and LR at the end of 2017. Mark III Flex+ reduces the guaranteed BOR, reaching a performance of 0.07% volume per day as compared with the 0.085% volume per day guaranteed by Mark III Flex. The reduced BOR is possible thanks to an increased insulation thickness and a reinforced arrangement of the secondary barrier.
The Mark III Flex+ containment systems have been licenced by Samsung Heavy Industries (SHI) for two 180,000m3 LNGCs for Monaco-based Gaslog Ltd. Those ships, set for delivery in Q2 and Q3 2021, respectively, will each go on a seven-year time charter with a wholly owned subsidiary of US-based Cheniere Energy, Inc.
Earlier this year, GTT received an order from South Korea’s Daewoo Shipbuilding & Marine Engineering (DSME) to supply its NO96 GW membrane containment system for two 174,000m3 LNGCs for delivery in Q1 2021.
GTT's NO96 GW membrane containment system uses a cryogenic liner directly supported by the ship’s inner hull. The primary and secondary layers of the liner are both made from Invar, 0.7-mm thick, and two independent insulation layers consisting of a load-bearing system made of prefabricated plywood boxes filled with expanded perlite – a form of volcanic glass.
GTT is also implementing digital tools to study the relationship between BOR and cargo sloshing that can occur due to wave action or navigation while the ship is underway. Working with Paris-based Cryovision, GTT installed a sloshing monitoring system in the 155,000m3 LNGC GasLog Singapore that provides real-time information to the crew. GasLog and GTT are co-operating in the project, which aims to demonstrate the performance of the sloshing monitoring system, SloShield. Using data provided by Gaslog, GTT’s teams will study the relationship between sloshing and the BOR in the tanks. The relationship between these two phenomena has been a key topic of discussion among shipowners but has not been investigated in an in-depth study based on actual data.
“The installation”, said GasLog general manager of newbuildings and projects Theodoros Katemidis, would “further optimise the operations of our vessels and lead to improved efficiencies for GasLog and our customers.”
In February, GTT launched its Digital Hub of Excellence, designed to help shipping companies reduce costs, mitigate risks and improve operational efficiency. GTT says the solution also helps those companies implement compliance and sustainability programmes and encourages data-driven collaboration.
Small-scale LNGCs get containment systems
Two small-scale 7,500m3 LNG carriers being built for Korea Line at SHI will be fitted with KC-1 containment systems and chartered to state-owned utility Korea Gas Corp for domestic coastal trades.
The two small-scale carriers are only the third and fourth ships to use KC-1 containment systems. The others are the SK Spica and SK Serenity, 174,000m3 sister ships delivered by SHI to South Korea’s SK Shipping last year. Korea Gas Corp (Kogas) has chartered both vessels for 20 years to carry LNG cargoes from Cheniere Energy’s export terminal at Sabine Pass in Louisiana.
The SK Spica is one of two 174,000m3 KNGCs with a KC-1 cargo containment system
Working with South Korea’s leading shipbuilders, SHI, Hyundai Heavy Industries and DSME, Kogas established KC LNG Tech in 2016 to develop the KC-1 cargo containment system as a domestic alternative to GTT containment systems, which are built under licence from GTT by the shipyards.
Last year, shipyards worldwide paid GTT €232M (US$259M) in royalty fees based on a record number of newbuild orders for 48 LNGCs, two floating storage and regasification units, and one onshore storage facility.
Lessons learnt during the construction of the SK Serenity and SK Spica are being applied in the construction of the two small-scale LNGCs, according to KC LNG Tech. It said the delay in delivery of the SK ships was due to “insufficient” preparations for the mass production of membrane panels, rather than an issue with the KC-1 cargo containment system itself. The SK Shipping pair were delivered about six months late.
Both the primary and secondary barriers of the KC-1 system are of 1.5 mm thick stainless-steel plate and have corrugations to accommodate thermal expansion and contraction. The barriers are positioned close to each other and are backed by a single layer of PUF insulation, supplied as panel pieces.
Inter-barrier spacers are placed between the primary and secondary membranes to maintain equidistant spacing between the two, thus ensuring that any damage to the primary barrier does not impact on the secondary barrier.
Under a 20-year contract with Kogas, the two small-scale LNGCs will transport cargo to a new LNG terminal being built on the Korean island of Jeju. KC-1 membranes will also be used as the containment systems for two 45,000 m3 storage tanks under construction at the new Jeju terminal.
The first vessel will deliver small-scale shipments of LNG and the second will supply LNG as marine fuel. The first vessel will be delivered this May, followed by the second in December 2019.
Approved by various major classification societies, the KC-1 cargo containment system was awarded concept approval certification by the US Coast Guard in December 2017 for KC-1 LNG ships of up to 174,000 m3 in capacity.