Construction And Performance Research Of Liquid Carbon Dioxide Energy Storage System With Low Pressure Storage

Since the industrial revolution,the excessive consumption of fossil energy has brought serious climate change,energy shortage and environmental pollution problems.The further development of economy and society is seriously hindered.All countries in the world are vigorously developing renewable energy to lift this restriction.They accelerate the transformation of energy structure and actively move towards the goal of carbon peak and carbon neutrality.The unstable characteristics of renewable energy have led to problems such as wind and electricity abandonment and grid connection safety of renewable energy power generation.The further promotion and application of renewable energy is greatly limited.The combination of energy storage technology and renewable energy power generation could smooth the power output of renewable energy and solve the grid connection problem of renewable energy power generation.It can also achieve peak shaving and valley filling in the power grid and maintain a balance between power supply and demand.Compressed gas energy storage technology has been widely concerned by scholars all over the world in recent years because it has huge potential and can be applied on a large scale.As an important development direction of compressed gas energy storage,liquid carbon dioxide energy storage technology has developed rapidly in recent years.It uses carbon dioxide with superior thermophysical properties as the working medium and has the advantages of high energy storage density and no geographical constraints.The storage pressure of carbon dioxide is usually relatively large in existing liquid carbon dioxide energy storage systems.The carbon dioxide storage tanks have been put forward high material and technical requirements and the storage cost is greatly increased.In this paper,a liquid carbon dioxide energy storage system with low pressure storage is proposed to solve above problems.Its thermodynamic performance and technical economy are studied.The main work and conclusions are as follows:A liquid carbon dioxide energy storage system with low pressure storage is proposed.The energy analysis model and exergy analysis model are established.The performance of the system under design condition is analyzed.The parameter analysis is conducted to explore the impact of key parameters.The analysis indicates that the round-trip efficiency and energy density of the system can reach 54.50%and 20.69k Wh/m~3 respectively under design condition.Low-pressure compressor,cold recuperator and high-pressure compressor are ranked in the top three places in terms of exergy destruction and should be prioritized for improvement.There is a suitable mass flow ratio of stream 12 to stream 9,mass flow ratio of stream 21 to stream 18,energy release pressure and cooling temperature of low-pressure cooler to maximize the round-trip efficiency of the system within the scope of study.Compared to the cooling temperature of the low-pressure cooler,the round-trip efficiency of the system is more sensitive to changes in the cooling temperature of the high-pressure cooler.The thermal energy storage module in the system is optimized and improved based on the fact that the physical properties of supercritical carbon dioxide change drastically.The purpose is to reduce the exergy destruction during the heat transfer process between supercritical carbon dioxide and heat storage media and improve the overall performance of the system.The performance comparison between the improved system and the baseline system proves the superiority of the improved system.The thermodynamic performance of the improved system is explored.The analysis indicates that the exergy destruction of the high-pressure cooler and heater in the improved system has decreased by 47.17%and 43.86%respectively.The round-trip efficiency and energy density have increased by 3.24%and 1.66 k Wh/m~3 respectively.The optimal operating range of energy storage pressure and energy release pressure is 19 MPa and 18-19 MPa respectively in the improved system.Both carbon dioxide mass flow separation ratios should be set to 0.5 to achieve maximum round-trip efficiency for the system.The techno-economic model of the 1 MW improved system is established.Levelized cost of energy,net present value and dynamic payback period are used as the evaluation indexes of system economic performance.The variation trend of system economy with key thermodynamic parameters are investigated.The analysis indicates that the economic benefit of the power station is 1.566×10~7 yuan over its 30-year life cycle.The capital recovery of the power station project can be completed in 10.22 years.Reducing the pinch point temperature difference of heat exchange equipment and improving the efficiency of compressors and turbines are beneficial to improve the economic performance of the system.A power supply system integrating wind power,photovoltaic and liquid carbon dioxide storage power stations is designed.The optimal scheduling strategy of using liquid carbon dioxide energy storage power station as energy buffer and dispatching hub is explored.The performance of the system in different application scenarios is compared and analyzed.The analysis indicates that in three application scenarios where the power in the system is provided by wind farms,photovoltaic panels,and both of them,the start time of energy storage scheduling should be set at 12 o’clock,3 o’clock,and 17 o’clock,respectively.This can minimize the capacity and investment of the power station and maximize the profitability of the system.Based on the combination of wind farms and photovoltaic panels,the introduction of power grid can significantly reduce the capacity and investment of the power station and improve the system profit.