Comparative study and optimization of a solar combined power and natural gas liquefaction cycle equipped with various ejector refrigeration loops

This research develops and analyzes three combinations of a solar driven cascade organic Rankine cycle (CORC) with ejector refrigeration loop (ERL) to produce power and liquefied natural gas (LNG) using exergy, exergoeconomic and exergoenvironmental concepts. In Case I, the extracted streams from turbines are used as ejectors primary fluids, in Case II, the ejector in high temperature (HT) loop is inserted after turbine and in Case III both ejectors are installed before the turbines. A comparative study is conducted to evaluate the performances of the proposed layouts. The simulation results demonstrate that Case III gives the lowest total product cost rate of 78.372 $/h and Case II causes the maximum energy and exergy efficiencies of 14.3% and 7.101%, respectively. Moreover, in this layout, the cost and environmental impact (EI) per exergy unit of LNG are improved by about 0.003 $/GJ and 17 mPts/GJ, respectively in relation to Case I. Finally, the ultimate solution of Case II as the best layout is ascertained and compared with Case I by applying Non-dominated Sorting Genetic Algorithm II (NSGA-II) and three decision makers, namely LINMAP, TOPSIS and Shannon Entropy. According to the optimization results, the maximum improvements in product cost rates are achieved within 1.2% and 2.2% for cases I and II, respectively and the maximum reduction in EI rate for Case I is obtained within 1.05% through LINMAP method.