Making headway in hydrogen shipping

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. The existing statutory framework has also been under development to cover the carriage of liquefied hydrogen, which is 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 hydrogen in bulk during maritime transport.

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: - Materials, welding of cargo tanks, cargo process piping, pressure vessels and equipment - Thermal insulation of cargo tanks, piping, pressure vessels and equipment - Vacuum insulation for cargo containment systems - Vacuum insulation for cargo process piping, pressure vessels and equipment - Design, construction and testing of cargo tanks - Design and arrangement of cargo process piping, pressure vessels and equipment - Construction and testing of cargo process piping, pressure vessels and equipment - Pressure relief valves for cargo tanks - Vent systems for cargo containment - Cargo pressure and temperature control - Atmosphere control - Ventilation - Temperature and gas concentration measurement and hydrogen gas and fire detection - Measures against hydrogen fires - Personnel protection - Filling limits for cargo tanks - Operational procedures and manuals - Risk assessment - In-service survey plans.

KHI EXPECTS TO DELIVER THE WORLD’S FIRST DEDICATED

For a risk assessment to be conducted in an exhaustive manner for the design specifications of an individual ship carrying liquefied hydrogen cargo, it must consider risks to persons on board, the environment and the structural strength/integrity of the ship, with adequate counter-measures proposed. Key items, such as possible vent release scenarios, vent fires, gas diffusion analysis, boiling liquid expanding vapour explosion (BLEVE), the possibility of explosions and detonations in enclosed compartments, and the loss of a single vacuum compartment in a vacuum insulation system, must be specified in detail.

IN THE REAL WORLD The guidelines developed by ClassNK to support the development of liquefied hydrogen transport have already been applied in an actual project: the world’s first liquefied hydrogen carrier, built by Kawasaki Heavy Industries (KHI) for the CO²-free Hydrogen Energy Supply-chain Technology Research Association (HySTRA).

HySTRA is a consortium “established primarily to achieve technologies and carry out demonstration of everything from production of hydrogen via effective use of brown coal through to transportation and storage of said hydrogen, aimed at the cultivation of a CO²-free hydrogen supply chain and its commercialisation”.

Named Suiso Frontier, the resulting vessel has a length overall of 116 m, a cargo tank capacity of approximately 1,250 m³ and was launched in December 2019. Its construction is expected to be completed by late 2020, according to Kawasaki Heavy Industries..

ClassNK received the application for classification survey during construction and carried out the verification and validation in line with its guidelines and applicable rules. In the meantime, ClassNK is updating the guidelines based on experience and knowledge acquired through the ship’s design and construction and, as the new ship approaches its operational phase, in its role of ensuring safety in the transport of liquefied hydrogen by sea. www.classnk.com