Design of the compressor-assisted LNG fuel gas supply system

This paper proposes an LNG fuel gas supply system in which the compressors are used for multiple purposes. Referred to as the compressor-assisted fuel gas supply system (CA-FGSS), the proposed system uses its compressors to both manage the boil-off gas (BOG) in the LNG fuel tank and generate a pressure differential for drawing LNG from the tank. The feasibility of the defined operation sequence of the CA-FGSS was verified by dynamic process simulations in which the system was applied to two-stroke dual-fuel engines that required medium and high fuel gas injection pressures (16 and 300 bar), respectively. An availability analysis revealed 99% system availability of the CA-FGSS, which has a lower number of redundant equipment compared to a conventional pump-based fuel gas supply system (PB-FGSS). This is because the CA-FGSS does not use components with high failure rates and long maintenance times, such as in-tank pumps in the LNG fuel tank. These findings demonstrate the economic feasibility of the CA-FGSS, which also has a 10% lower capital expenditure compared to a PB-FGSS. A sensitivity analysis of the entire propulsion system of the CA-FGSS further showed that it was operationally more economical than a PB-FGSS for the same gas supply pressure. Moreover, a high-pressure propulsion system that utilizes the CA-FGSS was found to be more economical than a medium-pressure propulsion system for a high LNG price.