Dual fuel consumption and efficiency of marine steam generators for the propulsion of LNG carrier

The steam generator is an essential component of marine steam propulsion plant. Nowadays steam propulsion is a relatively rare occurrence, but still dominant in the LNG carriers. LNG carrier analyzed in this study is equipped with two identical, mirror-oriented steam generators. In exploitation, steam generator burners use two types of fuel: heavy fuel oil and natural gas. Measurements were performed for various steam generator operating parameters in ship exploitation at different loads. Data values from conducted measurements were used in the equations for calculating energy and exergy efficiencies and losses of analyzed steam generators at various loads. Also, measured fuel consumption data from exploitation were compared with the manufacturer's test data. Analyzed steam generator's energy and exergy efficiencies and losses were compared with the efficiencies and losses of steam generators from land based power plants. As the primary function of the marine steam generators is the production of steam at required pressure and temperature for the main propulsion turbine operation, several operating regimes of the main propulsion turbine, based on the measured data from exploitation, are presented. Finally, the paper presents calculated CO2 emissions for three different steam generator operating modes: from exploitation using both fuels, then when a steam generators use only natural gas and when a steam generators use only heavy fuel oil. The highest cumulative CO2 emissions were obtained at the higher steam generator loads, while at the same loads, specific CO2 emissions per kWh of total produced power on the main turbine are the lowest.