Fungsi objektif dari penelitian ini adalah total konsumsi energi dari sistem pencairan, dengan variabel keputusan berupa tekanan gas bumi pascakompresi, tekanan nitrogen pascakompresi, suhu nitrogen preekspansi, suhu pendinginan refrigeran precooling, dan jenis refrigeran precooling. Refrigeran yang digunakan sebagai precooling adalah beberapa senyawa hidrokarbon seperti propana, siklopropana, isobutana, nbutana, dan neopentana. Proses simulasi, regresi, dan optimisasi secara berurutan dilakukan dengan perangkat lunak UNISIM, Microsoft Excel, dan GAMS. Solver yang digunakan dalam penelitian ini adalah COUENNE. Hasil penelitian ini menunjukan bahwa penambahan sistem precooling pada nitrogen expander dapat menurunkan total konsumsi energi hingga 25,24%, tergantung refrigeran yang digunakan. Lebih lanjut, berdasarkan hasil optimisasi yang dilakukan, propana merupakan refrigeran precooling yang paling optimal dalam menurunkan total konsumsi energi jika dibandingkan dengan refrigeran precooling lainnya.

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Nitrogen expander is the liquefaction process which suitable for SSLNG production plant because its characteristic. However, the major issue of this technology is it has relatively low energy efficiency. In this study, optimization of small-scale natural gas liquefaction through nitrogen expander was will be conducted with attaching precooled cycle to the liquefaction process.

Unit consumption energy is chosen to be objective function, while decision variables of this study are natural gas pressure after compression, the nitrogen pressure after compression, the inlet temperature of the high-pressure expander, the evaporation temperature in precooling cycle, and type of precooling refrigerant.

The refrigerant which used for precooling cycle are propane, cyclopropane, isobutane, nbutane, and neopentane. Simulation, regression, and optimization process sequentially will be supported by UNISIM, Microsoft Excel, and GAMS software. Moreover, the solver which used for this study is COUENNE.

This study shows that adding precooling cycle to the nitrogen expander system can reduce total consumption energy up to 25,24%, depends on the refrigerant which used. Furthermore, based on optimization result, propane is the most effective precooling refrigerant to reduce total consumption energy if compared with others precooling refrigerant.