Optimization of energy consumption in LNG regasification through waste heat recovered from thermal discharge

To address the critical industry challenge of sharply reduced heat transfer efficiency and increased energy consumption of Open Rack Vaporizers (ORV) in Liquefied Natural Gas receiving terminals under low-temperature seawater conditions, this paper proposes an optimized co-operational strategy for ORV and Intermediate Fluid Vaporizers (IFV) based on the utilization of waste heat from warm water discharge. Focusing on a domestic LNG terminal equipped with ORVs, Submerged Combustion Vaporizers (SCV), and IFVs, a process and mathematical model for the combined ORV-IFV operation was developed using simulation software. The study specifically investigates the influence mechanism of introducing warm water discharge from an adjacent power plant on the energy efficiency of the system. The research reveals the direct impact of seawater temperature on the energy consumption of the combined system: low seawater inlet temperatures severely constrain the heat exchange efficiency of ORVs, preventing them from reaching their rated design capacity. The integration of warm water discharge fundamentally improves heat transfer efficiency by increasing the temperature differential within the vaporizers. Furthermore, the study quantifies the coupled relationships between the system's minimum theoretical energy consumption and key operational parameters—including thermal discharge input volume, seawater inlet temperature difference, and LNG processing capacity—under both winter and summer conditions. This study reveals that low seawater temperatures (5 °C) severely constrain ORV performance, limiting its throughput to only 57% of rated capacity at 10 MPa. The integration of warm water discharge fundamentally overcomes this limitation. Quantitative analysis demonstrates that the proposed ORV-IFV co-operation strategy, utilizing waste heat, reduces total system energy consumption by approximately 20% in winter and up to 45% in summer. A subsequent economic analysis, based on actual industrial data, reveals annual cost savings of approximately 152 million CNY with a simple payback period of 2.0 years. The results demonstrate that the warm water integration strategy significantly reduces the total energy consumption of the combined system and effectively compensates for the performance deficiency of ORVs at low temperatures, achieving efficient cascade utilization of industrial waste heat. This innovative approach not only provides a feasible pathway to enhance the full-condition energy efficiency and economic viability of LNG receiving terminals but also offers a theoretical foundation and reference for energy-saving retrofitting projects utilizing low-grade heat sources in similar terminals.