[en] Amendments to strict anti-pollution maritime regulations have given rise to the shipping industry having to undertake costly technological investments in propulsion systems aboard LNG (Liquefied Natural Gas) vessels. The flexible fuel consumption of DF (Dual Fuel) engines have resulted in them becoming the main choice as the prime propulsion system, providing great versatility to the ship. However, particular attention should be given to gas management systems on those LNG vessels without a reliquefaction plant, as the excess BOG (Boil Off Gas) produced is burned in the GCU (Gas Combustion Unit) without any energy input, thereby determining a clear need to improve the system. To this end, this thesis focuses on the study of the use of excess BOG generated on LNG vessels, with the aim of improving plant efficiency. Thus, the different propulsion systems on board LNG ships are reviewed and the gas management process is analysed to determine the available energy of the BOG, as well as the amount that can be recovered. Such analysis is aimed at proposing a new gas management plant configuration to exploit the excess BOG produced and hence increase the performance of the plant. The proposed plant is thermodynamically modelled and analysed using EES (Engineering Equation Solver) software to perform a parametric analysis and optimisation thereof in terms of efficiency. The plant concerned is based on the use of excess BOG in a steam reforming system in order to obtain hydrogen, a clean fuel that allows vessels to navigate without limitations in areas with strict anti-pollution regulations.

[gl] Debido a evolución das estritas normativas anticontaminación, os sistemas de propulsión a bordo dos buques GNL (Gas Natural Licuado) están nunha época de cambios tecnolóxicos e económicos. Os motores DF (Dual Fuel) establecéronse como o sistema de propulsión mais empregado debido a posibilidade que ofrecen de consumir diferentes combustibles, proporcionando unha gran versatilidade ao buque. Pero se debese prestar especial atención ao sistema de xestión de gas nos buques GNL sen planta de relicuefacción, debido a que o exceso de BOG (Boil Off Gas) xerado é queimado na GCU (Gas Combustion Unit) sen ningún aporte enerxético, polo que é evidente a necesidade de mellorar o sistema. Esta tese centrase no estudio do aproveitamento do exceso de BOG xerado en buques GNL, para mellorar a eficiencia das plantas. Revísanse os diferentes sistemas de propulsión a bordo dos buques GNL e analízase o proceso de xestión de gas, para determinar a enerxía dispoñible do BOG e a que se pode recuperar. O anterior ten como obxectivo propoñer unha nova configuración da planta de xestión de gas para aproveitar o exceso de BOG xerado e aumentar o rendemento da planta. A planta proposta é modelizada termodinámicamente e analizada con software EES (Engineering Equation Solver) para realizar un análises paramétrico e optimizala baixo o punto de vista da eficiencia. A planta tratada baséase no aproveitamento do exceso de BOG nun sistema de reformado con vapor para a obtención do hidróxeno, un combustible limpo o que nos permite navegar sen limitacións en zonas con estritas normativas anticontaminación.