Abstract: Liquefied natural gas (LNG) is regarded as one of the cleanest fossil fuel and has experienced significant developments in recent years. The liquefaction process of natural gas is energy-intensive, while the regasification of LNG gives out a huge amount of waste energy since plenty of high grade cold energy (-160℃) from LNG is released to sea water directly in most cases, and also sometimes LNG is burned for regasification. On the other hand, liquid air energy storage (LAES) is an emerging energy storage technology for applications such as peak load shifting of power grids, which generates 30%-40% of compression heat (~200℃). Such heat could lead to energy waste if not recovered and used. The recovery of the compression heat is technically feasible but requires additional capital investment, which may not always be economically attractive. Therefore, we propose a power plant for recovering the waste cryogenic energy from LNG regasification and compression heat from the LAES. The challenge for such a power plant is the wide working temperature range between the low-temperature exergy source (-160℃) and heat source (~200℃). Nitrogen and argon are proposed as the working fluids to address the challenge. Thermodynamic analyses are carried out and the results show that the power plant could achieve a thermal efficiency of 27% and 19% and an exergy efficiency of 40% and 28% for nitrogen and argon, respectively. Here, with the nitrogen as working fluid undergoes a complete Brayton Cycle, while the argon based power plant goes through a combined Brayton and Rankine Cycle. Besides, the economic analysis shows that the payback period of this proposed system is only 2.2 years, utilizing the excess heat from a 5 MW/40MWh LAES system. The findings suggest that the waste energy based power plant could be co-located with the LNG terminal and LAES plant, providing additional power output and reducing energy waste.

Key words: Waste energy recovery, Power plant, Liquid air energy storage, Liquefied natural gas, Integration

摘要： Liquefied natural gas (LNG) is regarded as one of the cleanest fossil fuel and has experienced significant developments in recent years. The liquefaction process of natural gas is energy-intensive, while the regasification of LNG gives out a huge amount of waste energy since plenty of high grade cold energy (-160℃) from LNG is released to sea water directly in most cases, and also sometimes LNG is burned for regasification. On the other hand, liquid air energy storage (LAES) is an emerging energy storage technology for applications such as peak load shifting of power grids, which generates 30%-40% of compression heat (~200℃). Such heat could lead to energy waste if not recovered and used. The recovery of the compression heat is technically feasible but requires additional capital investment, which may not always be economically attractive. Therefore, we propose a power plant for recovering the waste cryogenic energy from LNG regasification and compression heat from the LAES. The challenge for such a power plant is the wide working temperature range between the low-temperature exergy source (-160℃) and heat source (~200℃). Nitrogen and argon are proposed as the working fluids to address the challenge. Thermodynamic analyses are carried out and the results show that the power plant could achieve a thermal efficiency of 27% and 19% and an exergy efficiency of 40% and 28% for nitrogen and argon, respectively. Here, with the nitrogen as working fluid undergoes a complete Brayton Cycle, while the argon based power plant goes through a combined Brayton and Rankine Cycle. Besides, the economic analysis shows that the payback period of this proposed system is only 2.2 years, utilizing the excess heat from a 5 MW/40MWh LAES system. The findings suggest that the waste energy based power plant could be co-located with the LNG terminal and LAES plant, providing additional power output and reducing energy waste.

关键词: Waste energy recovery, Power plant, Liquid air energy storage, Liquefied natural gas, Integration