Simulation and optimization of Rankine power generation cycle purposing the efficiency of liquefied natural gas cold exergy

Liquefied natural gas (LNG) is obtained by cooling the natural gas to −162℃ at the atmospheric pressure. Methane is the major chemical component of LNG which varies between 87.0–99.8% for different sources. The cryogenic power generation cycle using LNG as its heat sink is known to be one of the considerable ways for the LNG exergy recovery. A double-stage Rankine power generation cycle using the single component working fluid in each stage for liquefied natural gas (LNG) cold exergy recovery is used as a base case in the present study. To improve the recovery of LNG cold exergy, a three-stage Rankine power generation cycle has been proposed using mixture working fluid. Optimization is done using the particle swarm algorithm. The performance of three-stage Rankine power generation cycle is studied regrading to the effects of thermal efficiencies, exergy efficiencies, overall heat transfer coefficient of condensers and natural gas distribution pressure. Specific power production of the cycle is 100.45 , thermal efficiency is 12.76%, exergy efficiency is 27.92%. By decreasing the total coefficient of heat transfer, the condensers of different stages of the cycle reduce the maximum output power of the cycle with different trends. The results show that by decreasing the distribution pressure of natural gas, specific power production, thermal efficiency and exergy efficiency increases. So that their optimal values at 6 bar are 290.87 , 25.63% and 39.12%, respectively.