GTT is a French engineering company based in Saint Rémy-Lès-Chevreuse near Paris, specialising in the design of liquefied natural gas (LNG) containment systems for over 50 years. More than two thirds of the existing LNG carrier fleet uses GTT containment systems for the transport of LNG cargoes, while around 90 percent of LNG carriers on order or under construction today will be fitted with the GTT membrane insulation system. GTT also designs LNG tanks for onshore storage for small, medium and large storage capacities. In the current context of the progressive adoption of LNG as a fuel for commercial ships, GTT positions itself as a solution provider capitalising on its long experience in LNG containment and the mobilising of highly skilled engineers. For the last few years, GTT has developed innovative solutions covering LNG fuel tanks and associated systems on board commercial vessels, as well as LNG handling and storage infrastructure for the whole supply chain from delivery to the end user. This article focuses on the advantages provided by low pressure LNG fuel storage for bunkering infrastructure integrated into port facilities. In the particular example developed here, the tank is integrated into a jetty used as a berth for large passenger ferries. However, this principle could easily be applied to other configurations.
LNG storage solution
In view of the constraints of operating passenger ships on a regular line and the relative impossibility of carrying out bunker operations separately from commercial operations (embarking/ disembarking passengers and cars) due to timetable restrictions, safety issues other risks; GTT proposes the use of its membrane technology for LNG storage. The tank is a rectangular/prismatic shaped membrane containment system of Mark III, Mark III Flex, NO96 etc. integrated into a gravity-based concrete caisson similar to the other caissons at the jetty. The capacity of such tanks has no limit from a technical point of view. It could be as small as 1,000 m3 and as big as 10,000 m3. The membrane tank is a low pressure containment system meaning that the vapour pressure inside the tank cannot exceed 500 mbarg. The tank is used for LNG fuel storage as part of a bunkering station dedicated to the ships berthing alongside. The jetty storage system (see Figure 1) is regularly refilled by a small LNG carrier sourcing cold LNG from the main import LNG terminals in the area. This kind of service could be shared with other ports as a ‘milk run’ service and this LNG carrier would then deliver partial cargoes to each of its port clients. In Figure 2, the small LNG carrier is approaching the jetty where it will be moored before connecting to the two loading arms on the quay side which are connected to the jetty storage system. Once connected, the loading operation will follow standard procedures including safety checks, inerting and cooling down of lines etc. One arm is used for liquid transfer from the LNG carrier to the jetty storage and the other arm for returning vapour from the jetty tank to the LNG carrier. Typical connections and transfer line diameters would be six or eight inches depending on the required flow rates. Once the jetty tank is full, the transfer lines are inerted, disconnected etc. and the LNG carrier can sail safely away to its next port of call.
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