The German environmental association Naturschutzbund Deutschland (NABU) commissioned the Dutch research institute CE Delft a study to assess whether natural gas-powered ships liquefied containers, and in particular container ships, are suitable for be powered through the shore power grid when they are stopped in ports, turning off the on-board engines and connecting to the cold ironing systems installed on the docks, connection which in the European Union will become mandatory for many types of of ships from 2030 in order to reduce emissions pollutants in port cities.

The study recalls that an increasing number of types of ships, In addition to LNG carriers, it uses liquefied natural gas for the propulsion or to meet other energy needs on board and whereas, in order to reduce the space on board ships occupied by tanks, Natural gas must be stored in a liquid state. For reach the liquid state, the gas must be cooled to about -162 ° C, to prevent regasification, are used special LNG tanks. The study specifies that, given that the evaporation of the liquefied gas inside the tanks on board of ships cannot be completely avoided, in the tanks boil-off gas (BOG) is formed. A depending on the type of tank and the operating profile of the ship, the BOG management is necessary to avoid overpressures in tanks and to comply with international regulations aimed at prevent emergency venting. The study explains that a strategy is to use the BOG on board the energy vessels and notes that, however, during the stopover in ports, when the demand for energy is relatively low level, there would be a risk of inefficient use of the BOG or that the possibility of an emergency vent increases, especially in cases where ships receive electricity from land during mooring through Onshore Power's facilities Supply (OPS).

The study finds that if LNG-powered containerships equipped with type B or membrane tanks generally have a enough capacity to consume BOG during a normal stop in a port using auxiliary engines; however, when are connected to an OPS system to receive electricity from ground these motors must be turned off, resulting in a limitation of the ability to consume BOG on board. The document explains that the container ships considered for the generally do not have systems for reliquefaction, subcooling systems, combustion units nor the ability to accumulate large volumes of BOG in the tank. As a result, mixed-combustion boilers are often the only on-board systems available to burn BOG and check the tank pressure during a port stop where the OPS system is used. The study specifies that Generally, ships' boilers operate independently from the ship's electrical network, and therefore cannot be powered by an OPS connection, and specifies that, given the possibility of using the BOG in double boilers during a port stop with the use of OPS, the risk of emergency venting is considered relatively low, even if - the study also specifies - it was not It is possible to confirm the installation of a gas or double boiler fuel for all the ships examined by the research. In addition, the study specifies that the speed at which the BOG should be consumed by the boiler generally exceeds the actual steam demand of the ship, resulting in BOG combustion unused. This, the study notes, implies waste of energy and related emissions that can be avoided in the absence of further BOG management measures.

The study also notes that, with regard to container ships LNG, an increasing share is being with tanks with a higher pressure tolerance and this characteristic reduces the probability of that tank pressure reaches dangerous levels or that it waste of energy during the ship's stay in the ports with the use of OPS, while for the current fleet of container ship with type B and membrane LNG tanks The modernization of the tanks could be extremely expensive. According to the study, for container ships ordered before there was a clear perspective on the obligations of the connection OPS facilities in ports could be justified by rules from the point of view of energy efficiency and emissions if the ship has no other means to safely manage the BOG. It should be noted that, under current rules, these ships They should be confronted with two options from an economic point of view: connect to the OPS and bear the costs for the OPS and for the waste of BOG, or not to connect or connect for a short time to the OPS and pay the relevant penalty according to the European FuelEU regulation Maritime thus avoiding the costs for the OPS and for the waste of BOG.

If the study presents different perspectives on the modalities LNG container ships could comply with the obligation of the use of OPS in ports, Sönke Diesener, an expert in NABU's maritime transport, seems to have no doubts: "the - he commented - clearly show that LNG is not a viable bridging technology for maritime transport. Many LNG ships can adapt to mandatory energy use only to a limited extent. This is due to the so-called boiling gas, which is produced during LNG storage and must be constantly vented. If this gas is not used by ship engines during port stopover, may cause additional methane emissions or safety concerns due to to the increase in pressure in the tanks. This means - it has stressed Diesener - that LNG threatens to undermine the main emission reduction measures in ports'. "The maritime energy transition - he continued - requires Long-term solutions compatible with neutrality climatic climate. Investments in LNG could lead to the Maintaining fossil fuel infrastructure to decades and stifle innovation. On the other hand, the political guidelines must be constantly turned towards propulsion systems climate-neutral, such as ammonia green or methanol. At the same time - concluded Diesener - it is essential to better integrate technical standards, infrastructure and regulatory requirements so that the reduction of emissions in ports actually take place".