Heat inflow to a cargo of liquefied natural gas (LNG) from the surroundings causes generation of vapours called boil-off gas (BOG) and thus an increase of a vapour pressure in cargo tanks. The paper discusses selected issues related to handling of boil-off gas on LNG carriers. Presented are general conditions permitting vapour pressure increase during the voyage, conditions enabling its venting and burning in gas combustion units (GCU, thermal oxidizers). Particular attention is given to BOG utilization as a fuel in steam or gas turbines or reciprocating engines. Presented are general comments on selection criteria for choosing a solution of LNG carrier propulsion system. Attention is drawn to an increase of possibilities of heat recovery from exhaust gas from Diesel engines and gas turbines. This is due to a lowering of exhaust gas dew point temperature thus deeper cooling of the exhaust gas in exhaust gas boilers is possible. This enables production of larger quantities of steam which can be directed to auxiliary steam turbine and as a result increasing the efficiency of the ship’s energy system. The paper also addresses the specifics of fuel installation operation on ships utilizing LNG vapours as a fuel.
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