LNG a clean fuel – the underlying potential to improve thermal efficiency

Abstract

The presence of sulphur in marine fuel oil relates to health and environmental concerns, as the respective combustion generates sulphur dioxide (SO2). The only method to control this SO2 generation is to limit the quantity of sulphur in the fuel. Shipping activities, although not the main source, contribute around 13% of the total anthropogenic SO2 IMO-3GHG [2015. Third IMO Greenhouse Gas Study, 3rd ed. London: International Maritime Organisation]; on a positive note, this is expected to reduce after the worldwide implementation of 0.5% sulphur regulation for marine fuel. One of the accepted methods to comply with the regulatory criteria is the use of alternate fuel, i.e. liquefied natural gas (LNG). The analysis in hand discusses the potential benefits of LNG as a marine fuel. The technical limitation associated with the formation of sulphuric acid (H2SO4) is directly related to its Dew point, as it condenses below 160°C and causes acidic corrosion of machinery components. The prevalent combustion-based systems are maintaining a safe and economical exhaust gas range between 150°C and 170°C. If the exhaust gas temperature is higher than 170°C excessive heat is lost, which makes the plant inefficient; in contrast, if the temperature drops below 150°C there is the possibility of corrosion damage to the equipment. Considering that LNG is absolutely free from sulphur contamination, it can be used to overcome this technical limitation and add to the overall thermal efficiency due to the availability of increased operating range.