Global cost optimization of a mini-scale liquefied natural gas plant

Cryogenic natural gas liquefaction plant has huge capital and operating expenses corresponding to operating equipment and energy utilization. Considering ever-increasing energy price, therefore, minimization of energy consumption rate for a better profit is highly required. However, any un-engineered energy cut off would result in larger surface area of heat-exchanger and hence bigger capital cost. Here, the net profit of establishing a mini 50 ton/day liquefied natural gas facility, operating for 25 years, is optimized via Genetic Algorithm technique. Poly Refrigerant Integrated Cycle Operations (PRICO) process is simulated in HYSYS environment and linked to MATLAB software for subsequent maximization. The simulation resulted in total consumed power, heat exchanger area and total profit by 2745.33 kW, 3285.58 m2 and 1266.64 million$, respectively. In order to determine unit efficiency and plant irreversibility rate, exergy analysis is performed on individual equipment. Basically, thirteen independent variables are considered for optimization of objective function. Sensitivity analysis for objective function is considered by altering each variable. Final results indicate 9.26% rise in total profit (1383.95 million$) by 59% reduction in energy utilization (1127.68 kW) and 37.50% in heat-exchanger size (2053.7 m2). Meanwhile, the total and heat-exchanger exergy losses are decreased by 65.8% and 80.7%, respectively.