Generation of H <sub>2</sub> on Board Lng Vessels for Consumption in the Propulsion System
Ignacio Arias-Fernández, Manuel Romero Gómez, Javier Romero, Luis M. López-González
Abstract
Abstract At present, LNG vessels without reliquefaction plants consume the BOG (boil-off gas) in their engines and the excess is burned in the gas combustion unit without recovering any of its energy content. Excess BOG energy could be captured to produce H 2 , a fuel with high energy density and zero emissions, through the installation of a reforming plant. Such H 2 production would, in turn, require on-board storage for its subsequent consumption in the propulsion plant when navigating in areas with stringent anti-pollution regulations, thus reducing CO 2 and SO X emissions. This paper presents a review of the different H 2 storage systems and the methods of burning it in propulsion engines, to demonstrate the energetic viability thereof on board LNG vessels. Following the analysis, it is identified that a pressurised and cooled H 2 storage system is the best suited to an LNG vessel due to its simplicity and the fact that it does not pose a safety hazard. There are a number of methods for consuming the H 2 generated in the DF engines that comprise the propulsion plant, but the use of a mixture of 70% CH 4 -30% H 2 is the most suitable as it does not require any modifications to the injection system. Installation of an on-board reforming plant and H 2 storage system generates sufficient H 2 to allow for almost 3 days’ autonomy with a mixture of 70%CH 4 -30%H 2 . This reduces the engine consumption of CH 4 by 11.38%, thus demonstrating that the system is not only energy-efficient, but lends greater versatility to the vessel.