Sensitivity Analysis of a Single Mixed Refrigerant Liquefaction Process of Natural Gas

Abstract

The demand for greater efficiency and large capacity for liquefaction process is inevitable for optimization. This study presents the sensitivity analysis of the factors that affects liquefaction processes of natural gas. Some of these factors are the natural gas pressure, temperature and composition on the single mixed refrigerant liquefaction process was simulated using ASPEN HYSYS 8.6 software. The effects of these parameters on specific power, power consumption and refrigerant flow rate of the process were simulations and examined. At constant pressure, temperature decreased from 15 to 5°C resulted in a 15% decrease in specific power and an increase from 15 to 25 °C resulted to 40% increase. At constant temperature, a decrease in natural gas pressure from 60 to 30bar and increase in specific power from 0.387 to 0.452 kWh/kg-LNG was observed which amounts to a 16.80% increase and when increased from 60 to 90bar specific power decreases from 0.387 to 0.348kWh/kg-LNG about 10.08 % decrease. Thus, when natural gas is supplied at a given pressure and temperature, a decrease in supply pressure will increase power consumption and an increase in supply pressure will decrease power consumption. The useful exergy for the system was about 26% of the total energy (46.42MW) available, indicating that about 74% of energy supplied by the compressor ended up as losses in different components in the process liquefaction cycle. However, the largest loss occurred in LNG heat exchanger and cooler which were to 25 and 24% respectively. The simulation results showed that, natural gas supplied at 150MMScf, 60bar and 15°C gave rise to LNG production of about 0.95MTPA.