Simulation and technical, economic, and environmental analyses of natural gas liquefaction cycle using different configurations

This paper aims to improve the performance of the simple C3MR natural gas liquefaction cycle from the thermodynamic, economic, and environmental aspects. Four processes are proposed where the first system uses heat recovery with the ORC cycle and boil-off gas cooling, and the second proposed plant uses the first plant with a distillation tower added for the separation of ethane plus and simultaneous production of NGL/LNG. The third scenario adds a Proton Exchange Membrane, gas turbine cycle, steam turbine, and electrolyzer to the second scenario. And the fourth scenario is in which a Rankine ammonia cycle is added to the structure of the second scenario to recover more wasted heat. Regarding exergy analysis, the third scenario represents 64.32% exergetic efficiency, while the base, 1st, 2nd, and 4th scenarios have 35.4, 47.35, 12.64%, and 17.1% exergetic efficiency, respectively. The LNG production requires 260.76, 941, 469, and 893 kWh/ tonLNG energy for the 1st, 2nd, 3rd, and 4th scenarios. According to the economic analysis, the first scenario with 0.0034 $/kg total cost rate of products has the best economic performance compared to 0.0037, 0.042, 0.059 $/kg, and 0.055 total cost rate of products for the base, 2nd, 3rd, and 4th scenarios, respectively. The environmental assessment results reveal that the first scenario with 72,567 kgCO2/h has the minimum CO2 emission. The overall results indicate that the first scenario is the best, but considering the trigeneration, the third scenario is a proper system.