Energy integration of LNG light hydrocarbon recovery and air separation: Process design and technic-economic analysis

Liquefied natural gas (LNG) regasification process releases much cold energy, and LNG contains light hydrocarbon with high added value. The utilization of LNG cold energy and recovery of light hydrocarbon has been a research hotspot. In this paper, an energy integrated process of air separation and light hydrocarbon recovery driven by LNG cold energy is proposed. HYSYS is used to model and simulate the energy integrated process. For technical and economic analysis, cold energy utilization ratio (CUR), ethane recovery ratio (ERR) and partial annualized cost (PAC) are selected as the optimization objectives. Sensitivity analysis is conducted to investigate the influence trend of nine process parameters on optimization objectives. Next, a multi-objective model is introduced, and a genetic algorithm is used in multi-objective optimization. Finally, a compromised optimization scenario is determined based on three optimization objectives. The optimal key process conditions are determined: the temperature of stream L₂ (outlet stream of air separation unit) is −129.6 °C, the temperature of stream L₃ (outlet stream of demethanizer condenser) is −106.8 °C, and the vapor fraction of stream L₄ (feed stream of demethanizer) is 0.6430. Results show that the CUR reaches 67.05%, ERR is 99.76%, and PAC is 3.144 × 10⁷ USD/year.