Design and optimization of large-scale natural gas liquefaction process based on triple refrigeration cycles

In large-scale natural gas liquefaction, minimizing specific energy consumption has consistently been a primary objective. This study aims to develop a large-scale natural gas liquefaction process that balances energy efficiency and cost-effectiveness, presenting a viable option for industrial production. By employing a refrigerant strategy of “propane + mixed refrigerant + mixed refrigerant”, a novel large-scale natural gas liquefaction process based on triple refrigeration cycles (TRC) is proposed. To address the challenge of boil-off gas (BOG) re-liquefaction, the TRC process is further refined to integrate BOG re-liquefaction (TRC-BR). Thermodynamic models are built for the proposed TRC and TRC-BR processes, as well as the propane pre-cooled mixed refrigerant (C3MR) and AP-X processes as baseline cases. Global optimization is conducted using the Particle Swarm Optimization (PSO) algorithm, with the specific power consumption (SPC) serves as the objective function. The results reveal that the SPC of the TRC and TRC-BR processes are 0.2726 and 0.2704 kWh/kg-LNG respectively. Compared with the C3MR and AP-X processes, the SPC of the TRC decrease by 1.54% and 4.84%, respectively. The total investments for the TRC and TRC-BR processes are estimated at a similar level compared to the baseline cases, demonstrating their significant potential for industrial application. •A new LNG process based on Triple Refrigeration Cycle (TRC) is proposed.•The three cycles use propane, mixed refrigerant and mixed refrigerant respectively.•TRC-BR process is further proposed to meet the need for BOG re-liquefaction.•Optimization using the PSO algorithm is conducted by integrating HYSYS with MATLAB.•The new processes show superior performance compared to the C3MR and AP-X processes.