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Korean scientists have designed a liquid air energy storage (LAES) technology that purportedly overcomes the main limitation of LAES systems: their relatively low round-trip efficiency. The novel system improves efficiency by increasing output power through thermal energy generation using natural gas as an external fuel during energy release.
Researchers at South Korea’s Dongguk University have designed a self-contained liquid air energy storage (LAES) system that reportedly demonstrates significant improvements in both energy efficiency and cost performance compared to conventional LAES.
“LAES systems have attracted a great deal of interest in the energy storage sector due to their high energy density and geographic independence,” Jinwoo Park, lead author of the research, explains to pv magazine . “However, a major limitation of these systems is their relatively low round-trip efficiency compared to other energy storage systems, such as pumped hydro storage (PHS) and compressed air energy storage (CAES).”
According to Park, although previous studies have explored improving the round-trip efficiency of LAES systems by integrating external thermal systems or using external fuels, several critical challenges remain.
“First, integration of LAES with external thermal systems requires adjacent thermal power plants or industrial facilities,” he added. “This requirement limits the inherent advantage of LAES systems, which is their ability to be installed and operated independently. Second, integration with cryogenic and high-temperature thermal systems, essential to maximizing the efficiency of LAES systems, can restrict the ability to reuse heat for other applications, as these systems often rely on waste heat to improve their efficiency. Finally, the use of external fuels is associated with CO2 emissions, even though it can improve the efficiency of LAES systems. Many studies overlook these associated emissions, which can cause environmental problems and pose a major obstacle to the development of sustainable energy systems.”
In the article “ Liquid air energy storage system with oxy-fuel combustion for clean energy supply: Comprehensive energy solutions for power, heating, cooling, and carbon capture” published in Applied Energy , Park and colleagues explain that the proposed system improves efficiency by increasing power output by generating thermal energy using natural gas as an external fuel during energy release. The oxy-fuel method is employed to generate thermal energy, and a cryogenic air separation unit (ASU) separates a portion of the stored liquid air into nitrogen and oxygen. The separated oxygen is then used as an oxidizing agent in the combustion reaction. In addition, economic benefits can be obtained by selling the produced nitrogen as a by-product.
“The flue gases generated in the oxy-fuel combustion process are dehumidified to facilitate efficient CO2 capture,” Park explains. “In addition, the heat generated during the air compression process is stored in a thermal fluid and subsequently used for direct heating and cooling using the absorption refrigeration cycle (ARC).”
The research group performed an energy and economic analysis of the system and compared its performance with that of a conventional LAES system; both systems were designed to store 100 MW of power. During discharge mode, the conventional system generated 51.41 MW, while the proposed system can produce 118.19 MW, which represents a 129.9% improvement over the conventional system. In addition, the proposed system can supply 38.64 MW for heating and 81.07 MW for cooling. Although the exergy efficiency of the proposed system is 1.32% lower than that of the conventional system, this decrease is offset by a significant improvement in its round-trip efficiency, which is 56.7% higher.
“The overall performance of the proposed system is superior, especially due to its higher power and round-trip efficiency,” Park said. “These improvements highlight that the proposed system has potential for more efficient energy storage and utilization, making it a promising solution for future energy needs.”
The research team also found that the total cost of the conventional system is $553.65 million, while the total energy sales are $245.08 million, resulting in a negative cost balance. In addition, the net present value (NPV) is negative at $258.34 million, indicating that the system is not economically viable. According to the scientists, this is mainly due to the low efficiency of the system, which causes operating costs to exceed sales due to insufficient energy production relative to consumption. In contrast, the proposed system has a total cost of $832.20 million and total sales of $1,708.38 million, resulting in a positive cost balance.
“The proposed system demonstrates an economically viable NPV of $636.51 million and an internal rate of return (IRR) of 25.67%,” Park added. “The total costs of the proposed system increased by 47.58% compared to the conventional system. Specifically, capital costs increased significantly by 71.55% due to several factors: the increased turbine output, modifications to the heat exchange system to improve efficiency, and the installation of additional equipment. Operating costs also increased by 37.01% due to the additional use of natural gas as an external fuel. Despite these cost increases, electricity sales more than doubled due to significant improvements in system efficiency. In addition, additional revenue from nitrogen sales as well as cooling and heating supplies contributed to a remarkable 597.07% increase in total sales.”
According to the research group, the novel system effectively addresses limitations identified in previous studies, such as challenges in integrating other thermal systems and using external fuels. Specifically, it overcomes the limitations of existing thermal integration methods, which rely on specific thermal power plants or industrial facilities, and addresses the CO2 emissions associated with the use of external fuels.
“In conclusion, the proposed LAES system represents a promising technology for future sustainable energy supply and is expected to provide valuable insights for developing efficient energy systems to achieve a carbon-neutral society,” Park said. |