Comprehensive evaluation of energy consumption in LNG liquefaction plants and investigation of energy saving optimization

Small-scale LNG plants play a crucial role in energy conversion but encounter challenges such as unclear energy consumption levels, rising operating costs, and environmental impacts. Despite the accumulation of substantial production data in existing plants, the lack of sophisticated analysis tools hinders the development of a systematic energy consumption evaluation strategy, thereby limiting the effectiveness of optimization measures. Based on a case study of the GY LNG plant with a design capacity of 1 × 10⁶ Nm³/d and actual operational data from 2020 to 2022, this study introduces an intelligent comprehensive evaluation method for the first time, establishing an energy consumption evaluation index system comprising 37 three-level indexes. Through field implementation, the energy consumption indexes are quantitatively assessed using rough set theory and fuzzy subordinate function to determine the energy efficiency level and optimization direction of each process system. The analysis reveals that the unit energy consumption of the plant was initially 0.6173 kW·h/kg, significantly higher than industry benchmarks. Furthermore, a steady-state simulation numerical model of the plant is developed to analyze the impact of key factors on energy consumption and identify energy consumption weaknesses through an analysis method. The study employs a genetic algorithm for parameter optimization, leading to a significant reduction in unit energy consumption and offering a viable pathway and production guidance for energy saving and consumption reduction in similar small-scale LNG plants. The optimization results demonstrate a 9.51 % reduction in unit energy consumption to 0.5586 kW·h/kg, translating to annual operational cost savings of approximately $580,000 with a payback period of 1.6 years. This research systematically evaluates the energy consumption of LNG plants and demonstrates that the implementation of energy consumption optimization measures not only reduces operating costs but also decreases greenhouse gas emissions by approximately 4,800 tonnes annually, thereby promoting the green transformation of small-scale LNG plants.