Comparison and analysis of two processes for BOG re-liquefaction in LNG carrier with normal-temperature compressor
Abstract Two processes for boil-off gas (BOG) re-liquefaction of liquefied natural gas (LNG) carrier with normal-temperature compressor are proposed and compared: (1) the re-liquefaction system with the single mixed refrigerant process (SMRP), (2) the re-liquefaction system with the dual mixed refrigerant process (DMRP). The main thermodynamic parameters to be compared are specific energy consumption, exergy efficiency, coefficient of performance, heat transfer curves and exergy losses of main equipment in optimized case and base case. The result shows that the performance of the DMRP is better than that of the SMRP and the specific energy consumption of DMRP is 0.5635 kWh/kgLNG. In addition, by comparing the thermodynamic parameters of the re-liquefaction system with the normal-temperature compressor and the cryogenic compressor, it can be found that not only the cooling capacity of BOG is used effectively, but also the energy consumption is reduced and the efficiency is improved for the normal-temperature compressor system. Therefore, for the two mixed refrigerant re-liquefaction systems, the performance of the normal-temperature compression system is better than that of the low-temperature compression system.