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OPENING TIME HYDROGEN • IT IS NOW WIDELY EXPECTED THAT HYDROGEN WILL PLAY AN IMPORTANT ROLE IN THE PATH TO DECARBONISATION. CLASSNK EXPLAINS HOW TO MOVE IT SAFELY BY SEA AS A ZERO-EMISSION fuel that is easily available around the world, hydrogen has the potential to transform modern society during the transition to a carbon-neutral fuel. Hydrogen can be used in fuel cells to power mobility, households and industry, as well as fuelling gas turbines, but considerable work remains before a ‘hydrogen society’ can be supported on an industrial scale. One key component will be the ability for ships to carry large amounts of hydrogen worldwide. From the viewpoint of transport efficiency, practical options include the carriage of liquefied hydrogen in bulk, the organic chemical hydride method and deriving hydrogen from transported ammonia. In the latter two cases, transport is possible using conventional chemical tankers or liquefied gas carriers.
considered to be the most efficient method. As liquefied hydrogen must be kept at temperatures below -253°C to maintain its liquid state under atmospheric pressure, however, it presents an even tougher handling and storage challenge at sea than LNG. ClassNK responded to the expectations for liquefied hydrogen transport in 2017, publishing a comprehensive set of Guidelines for Liquefied Hydrogen Carriers. The guidelines took into account the provisions of the International Maritime Organisation’s (IMO) Interim Recommendations for Carriage of Liquefied Hydrogen in Bulk, adopted by the Maritime Safety Committee (MSC) in 2016, and prescribed each item as a more specific requirement based on scenarios for possible accidents to ensure the safety of liquefied
The existing statutory framework has also been under development to cover the carriage of liquefied hydrogen, which is
hydrogen in bulk during maritime transport.
KHI EXPECTS TO DELIVER THE WORLD’S FIRST DEDICATED HYDROGEN CARRIER SHORTLY
HCB MONTHLY | DECEMBER 2020
WHAT ARE THE RISKS? The IMO Interim Recommendation was developed primarily based on a comparison of the physical properties of methane (the main component of LNG) and liquefied hydrogen.
Both are cryogenic and non-toxic, and both generate flammable high-pressure gas. On the basis of that comparison, liquefied hydrogen – when compared to LNG – has a low ignition energy (0.017 mJ vs 0.274 mJ); a wider flammability range (4.0 to 75.0 per cent, vs 5.3 to 17.0 per cent); low flame visibility during fires; high burning velocity (3.15 m/s vs 0.385 m/s), which may lead to detonations; high permeability; and low viscosity. Additional hazards involve the condensation (liquefaction) and coagulation (solidification) of gas, which may lead to the formation of a low-temperature atmosphere with a high concentration of oxygen, which can present a greater combustion and explosion hazard and also lead to the clogging of pipes. Further, being carried at such a low temperature, liquefied hydrogen presents risks of embrittlement in tanks, piping, process equipment and welds. In view of those hazards, the guidelines developed by ClassNK include special requirements for 19 items: -M aterials, welding of cargo tanks, cargo process piping, pressure vessels and equipment -T hermal insulation of cargo tanks, piping, pressure vessels and equipment -V acuum insulation for cargo containment systems -V acuum insulation for cargo process piping, pressure vessels and equipment -D esign, construction and testing of cargo tanks -D esign and arrangement of cargo process piping, pressure vessels and equipment -C onstruction and testing of cargo process piping, pressure vessels and equipment -P ressure relief valves for cargo tanks -V ent systems for cargo containment -C argo pressure and temperature control -A tmosphere control - Ventilation -T emperature and gas concentration measurement and hydrogen gas and fire detection -M easures against hydrogen fires -P ersonnel protection -F illing limits for cargo tanks -O perational procedures and manuals -R isk assessment - I n-service survey plans.
