GTT’s NO96 Super+ CCS has a lower boil-off rate to match the efficiency of two-stroke, slow-speed, dual-fuel engine technology
French cryogenic engineering firm GTT has released a refinement of its popular NO96 LNG cargo containment system (CCS) that promises to further reduce cargo boil-off rates, matching the consumption needs of new generation two-stroke, dual-fuel engine technology.
GTT commercial vice president David Colson explains that the introduction of highly efficient, two-stroke, slow-speed dual-fuel engine technology from MAN Energy Solutions and WinGD in 2010 and 2011 provided the impetus for the development of the NO96 Super+, an evolution of its popular NO96 system.
“We had to match our systems’ natural boil-off rate – which we guarantee – with the consumption of the engines,” Mr Colson tells LNG Shipping & Terminals. This meant GTT had to reduce the standard boil-off rate (BOR) of 0.15% volume per day from its systems.
GTT released the Mark III Flex with a guaranteed BOR of 0.085% in 2011, but “we didn’t have a solution for NO96 better than 0.1%. NO96 Super+ is now the equivalent of the Mark III Flex in terms of guaranteed BOR,” he says.
Building on the success of NO96 technology, NO96 Super+ technology integrates insulating reinforced polyurethane foam panels instead of plywood boxes, used for both the primary and secondary insulation spaces, to reduce the heat ingress inside the tank. Glass wool flat joints are inserted between adjacent foam panels to optimise the behaviour of the system and ensure it has the best thermal performance.
As in NO96, NO96 Super+ uses the principle of double Invar metallic membranes and the mechanical anchors fixing the insulating panels to the inner hull.
With NO96 Super+, GTT can offer a guaranteed BOR of 0.085%V/d for the current standard size design of LNG carrier of 174,000 m3. For larger capacity vessels, such as 200,000 m3, depending on tank configuration, the guaranteed rate may be reduced further.
NO96 Super+ received an approval in principle (AiP) from class society Bureau Veritas in April.
This will allow shipyard licensees China’s Hudong-Zhonghua Shipbuilding and South Korea’s Daewoo Shipbuilding & Marine Engineering to propose NO96 Super+ CCS in their responses to tenders that have equivalent boil-off performance as those made by Hudong-Zhonghua, Samsung and Hyundai in their proposals using Mark III Flex technology. “Now they can be equivalent without having to add any supplementary boil-off handling equipment like reliquefaction,” says Mr Colson.
“Hydrogen is a different beast”
While classification societies have already approved the system, they will have to approve the construction process to ensure that there are no difficulties, says Mr Colson. As this is an evolution and not a radical new technology, he says the construction approach is almost identical to the previous systems, with one or two slight modifications. “But the methodology and the processes and the way the system was put together is very similar,” he says.
A mock-up using NO96 Super+ technology was erected in February 2021 and validated the satisfactory assembly of the CCS.
He expects the first LNG newbuild proposal containing the NO96 Super+ technology by June 2021.
Tackling future fuels
In looking at GTT’s development roadmap, Mr Colson points out that candidate future fuels – ammonia and hydrogen – pose their own unique shipboard cargo containment challenges. As it incorporates an Invar metallic barrier – containing 36% nickel – NO96 Super+ is not compatible for use with ammonia. “Nickel doesn’t like ammonia,” says Mr Colson. “Our Mark III system, with a stainless steel barrier and low nickel content, however, is compatible with ammonia.” In February, GTT received an AiP from BV regarding the use of Mark III technology, which was an ‘NH3 Ready’ notation, meaning Mark III could be used for ammonia fuel-tank containment. Shipped at -34°C, ammonia has a higher density and about half the energy content as LNG, which must be maintained at minus 162°C.
“Ammonia could be a solution going forward because there’s no carbon molecule,” says Mr Colson, but it depends on how ammonia is produced. “It’s not green today and it’s also a very inefficient fuel and highly toxic”, he points out.
He said that GTT is not a believer in ethanol or methanol as shipping fuel solutions. “The next step as far as we’re concerned is hydrogen.”
He describes hydrogen as “a different beast.” It is the smallest molecule in the periodic table – which means it can migrate through materials – and needs to be kept at -253°C, “so you have a significant challenge for the installation itself. You need to be able to control the liquid and keep it liquid. Our current systems haven’t got the performance to do that, so we’re looking at other solutions,” he says.
Still, Mr Colson says, hydrogen as a global energy solution is some years off. He also notes that a recent report by the World Bank, which touted hydrogen and was unflattering to LNG as a marine fuel, fell far short of providing the full story, failing to properly discuss advances made in reducing methane emissions, methane slip and use of bioLNG. “I think LNG has a definite future. It’s important that people understand LNG is definitely part of the mix,” he says.
JIP explores LNG carrier designs with Type A CCS
Elsewhere, Qatar Petroleum (QP) joined with a subsidiary of China State Shipbuilding, ABS and LNT Marine in a joint industry project in March to develop new medium- and large-sized LNG carrier designs based on LNT A-Box cargo containment systems. Other signatories to the agreement were Qatargas and affiliates of ConocoPhillips, ExxonMobil, Shell and Total.
The LNT A-Box system is based on an independent IMO Type A tank as the primary barrier and a full secondary barrier. The tank is flexible in shape and geometry, catering for excellent volume utilisation, while the internal structure mitigates sloshing and eliminates any loading limitations.
The tank itself is not insulated, but is installed in an insulated cargo space. This means that the insulation is attached to the interior surface of the hold, while a liquid-tight barrier is fitted on the inner surface of the insulation, acting as the secondary barrier. In between the tank and the secondary barrier is a cold inter-barrier space, which offers direct access for visual inspections and maintenance of both barriers, as well as the tank supports.
The first LNG carrier fitted with the new CCS was the 45,000-m3 Saga Dawn, which entered service in Q2 2020.