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Comparison of Decarbonisation Solutions for Shipping: Hydrogen, Ammonia and Batteries

Recent regulations are targeting the carbon footprint of ships and the International Maritime Organisation (IMO) has set a target to reduce the GHG emissions by 50% until 2050, compared to the 2008 levels. Therefore, attention has been placed on the variety of available fuels and technologies that can be potential pathways for decarbonisation and special focus has been given to developing practical design options for the new generation ships. Shipping applications of batteries, hydrogen and ammonia powered fuel cells have a critical role to meet the IMO requirements by 2050. Hydrogen and batteries are emerging technologies that can be effective solutions, especially for short shipping routes. On the other hand, ammonia is also an attractive alternative option and with further development, it can potentially be utilised for ocean-going vessels. However, safety and risk assessments must be performed to support the endorsement of any new marine system design. Therefore, this work aims to guide safe and practical design solutions that can comply with the decarbonising regulatory framework. Therefore, a qualitative Hazard Identification (HAZID) approach was conducted for potential solutions with hydrogen, battery and ammonia and guidance for potential safe designs were proposed. Considering the lack of past accident statistics due to the novelty of applications, the HAZID results were discussed with experts. Hydrogen is usually stored in liquefied form in double-walled super-insulated tanks to reduce the risk of large accumulations of gas in the air, in case of potential leakage, which can induce fire (4-75% gas concentrations in the air) or explosion risks (18-59% gas concentrations in the air). Fuel cells, which produce the electricity required, should be placed within gastight enclosures in a well-ventilated space with redundant hydrogen or ammonia detection systems. Batteries use stored energy to produce electric energy, however, their use is associated with high fire risk. They are placed in battery holds/compartments in which fire doors and effective firefighting systems are mandatory to prevent the escalation of fire in adjacent places and reduce the fire duration respectively. Leakage in the fuel cell room due to pipe damage and fire in the battery room was considered the most severe hazards for hydrogen and battery version respectively. On the other hand, ammonia is considered as a low reactive gas and explosion should be a concern of only enclosed spaces at concentrations close to the stoichiometry. However, ammonia is a highly toxic gas and in high concentration, it can even be even fatal. Therefore, one of the main hazards for ammonia is the ammonia leakage from different parts of the system that can lead to injuries or fatalities to the crew due to the high toxicity of ammonia. This can be prevented with various measures, among which are sufficient ventilation and identification of hazardous zones. Overall, all the designs seem feasible in terms of safety provided that proper safety measures are considered.  Redundancy of equipment and proper arrangement of safety valves, ventilation and detection systems as well as firefighting protection are amongst the most effective risk control options to mitigate the hazards.