International Journal of Refrigeration 156 (2023) 186–197 Available online 10 October 2023 0140-7007/© 2023 Elsevier Ltd and IIR. All rights reserved. Optimization and exergy analysis of a cascade organic Rankine cycle integrated with liquefed natural gas regasifcation process Optimisation et analyse exerg´ etique d’un cycle organique de Rankine en cascade int ´ egrant un processus de regaz´ eifcation du gaz naturel liqu´ ef´ e Mohsen Fakharzadeh a , Nassim Tahouni a, * , Mojgan Abbasi b , M.Hassan Panjeshahi a a School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran b Institute of Petroleum Engineering, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran A R T I C L E INFO Keywords: Organic Rankine cycle Liquefed natural gas Genetic algorithm Heat Integration Optimization Exergy analysis Mots cl´ es: Cycle organique de Rankine Gaz naturel liqu´ ef´ e Algorithme g´ en´ etique Int´ egration de chaleur Optimisation Analyse exerg´ etique ABSTRACT One of the most effcient methods of exergy recovery during the regasifcation process is integrating the LNG stream with an Organic Rankine Cycle (ORC) to generate electricity. This study employs a cascade structure of ORC consisting of two double-stage condensations operating at 6 bar regasifcation pressure. To obtain an optimal ORC system integrated with an LNG, three optimization levels for a specifc heat source are addressed, including process variables, working fuids, and structure. Ten process variables and two working fuid variables for the top and bottom cycle among 13 candidates of refrigerants were optimized to provide the maximum power output. The results determined that refrigerants of R41 and R1150 have the best performance in the optimized process conditions for the top and bottom cycles, respectively. For the regasifcation of 36 tonnes per hour of an LNG stream, the produced net power and the exergy effciency are achieved by 2116.76 kW and 0.29, respec- tively. The exergy analysis revealed that employing the double-stage condenser ORC is not a good choice. Accordingly, a cascade-parallel structure is proposed for further studies. 1. Introduction Natural gas is a clean energy source with lower CO 2 and SOx emis- sions than other fossil fuels. It is probably the only fossil fuel to retain its share of the energy carrier in the coming decades (Sun et al., 2018). Liquefaction is an effective way to transport and store natural gas. The whole chain of exploitation and use of natural gas includes four stages exploration and production, liquefaction, transfer, and regasifcation (Bao et al., 2018b). Regasifcation means transferring Liquefed Natural Gas (LNG) from liquid to a gaseous state at ambient temperature and atmospheric pressure. LNG volume is about 625 times less than the volume of natural gas in the standard condition (20 ◦ C and atmospheric pressure). Its temperature is 162 ◦ C, and it usually transports at at- mospheric pressure. The power consumption for liquefaction and pro- duction of one ton of LNG is about 850 kWh. When LNG is regasifed, a large amount of cold energy is released, about 830 kJ/kgLNG (Ma et al., 2018). Conventional regasifcation systems release this cold energy into seawater or ambient air to be wasted, consume power in pump/blower drivers, and negatively affect the environment around import terminals. In contrast, cold energy can be used by different conventional and innovative methods for electricity generation, air separation, ice pro- duction, CO 2 capture and liquefaction, seawater desalination and refrigeration chambers (Sung and Kim, 2017). If this energy absorbed by the LNG can be converted to electrical energy at 100 % effciency, the electricity generated by the LNG cold energy will be approximately 240 kWh per ton (Mehrpooya et al., 2018). The Conventional technologies utilizing LNG regasifcation cold energy to generate electricity are direct expansion expanders, systems consisting of the Stirling engines, Rankine cycles, Kalina cycles, Brayton cycles, Allam cycles and fuel cells (Nasir et al., 2023). Yang et al. (2023) proposed a hydrogen liquefaction process inte- grated with an LNG regasifcation process. Three situations for hydrogen pre-cooling were investigated in their research including (a) LNG direct * Corresponding author at: School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran. E-mail address: ntahuni@ut.ac.ir (N. Tahouni). Contents lists available at ScienceDirect International Journal of Refrigeration journal homepage: www.elsevier.com/locate/ijrefrig https://doi.org/10.1016/j.ijrefrig.2023.10.004