Design of the compressor-assisted LNG fuel gas supply systems

Abstract

This study proposes an LNG fuel gas supply system, it is called the Compressor-Assisted Fuel Gas Supply System (CA-FGSS) which utilizes compressors for multi-purpose. In the CA-FGSS, the compressors are used not only to manage boil-off gas (BOG) in the LNG fuel tank but also to provide a pressure differential for drawing LNG from the tank. The operation sequence of the CA-FGSS is defined and the feasibility of the sequence is verified by dynamic process simulations. The CA-FGSS is applied to 2-stroke dual-fuel engines which require medium or high fuel gas injection pressure (16 or 300 bar). Availability analysis shows that the CA-FGSS had 99% system availability with the lesser number of redundant equipment than conventional pump-based FGSS (PB-FGSS) because CA-FGSS is free of components with high failure frequency and long maintenance time such as in-tank pumps installed in the LNG fuel tank. This result affects economic feasibility of the CA-FGSS, so the capital expenditure (CAPEX) of the CA-FGSS is 10% lower than that of the PB-FGSS. A sensitivity analysis for the entire propulsion system shows that the propulsion systems which adopt the CA-FGSS are more economical than the pump-based propulsion systems at the same pressure. On the other hand, high-pressure propulsion systems are more economical than the medium-pressure systems when the LNG fuel price is high.