Proposal and assessment of a new integrated liquefied natural gas generation process with auto - Cascade refrigeration (exergy and economic analyses)

The main objective of this study is to propose a novel Liquefied Natural Gas (LNG) production process using the auto - cascade refrigeration as the pre-cooling system. This auto - cascade system operates as stand-alone (without external electricity), and can supply the refrigeration temperature of -54.62 degrees C, which can decrease the total electricity consumption of the process. The Aspen HYSYS V11 software is employed for simulation of this hybrid process. Based on the energy analysis, this integrated process can produce 31.71 kg/s LNG by consuming the specific power of 0.189 kWh/kg LNG. In order to evaluate the system technically, the exergy analysis is implemented for each subunit and the whole process. The outcomes of exergy evaluation depicted that the overall exergy efficiency and overall destroyed exergy rate are 91.68% and 67688 kW, respectively. Also, about 77.3% of the overall irreversibility occurred in the heat exchangers. The economic aspect of this process is evaluated by the Annualized Cost of System (ACS) method. Based on the outcomes of economic assessment, the annualized cost and prime cost of product are accounted for 182.6 MMUS$/year and 0.1959 US$/kg LNG, respectively. In continue, the technical and economic outputs of the proposed configuration are compared to the previous investigations. It was found that by utilizing the auto - cascade refrigeration system as the precooling system of LNG production, the required power and primary costs for producing LNG are considerably reduced. Finally, in order to specify the effects of economic factors on the electricity price, the sensitivity analysis is implemented. Furthermore, the influence of turbine inlet pressure on the efficiency of the hybrid process is investigated.