| With the increasing consumption of non-renewable energy sources,such as coal,oil and natural gas,the environmental pollution and energy shortage have become prominent increasingly.People have gradually realized the crisis of survival and accelerated the transformation of the energy structure.Renewable energy,such as solar energy and wind energy,are developing rapidly under the driven by the goal of global low-carbon energy development.As a big country in energy production and energy consumption,it is imperative for China to improve energy utilization and optimize energy structure.In the future,China’s renewable energy and innovative energy technologies will further achieve leapfrog development under the encouragement of the goal of "carbon peaking and carbon neutrality".However,renewable energy have the technical characteristics of intermittent power generation and power fluctuation,and their large-scale grid connection will affect the stability of the power system.Therefore,the phenomenon of "abandoning wind","abandoning solar" and "abandoning water" occurs frequently.Energy storage technology can effectively solve the "difficulties" of grid connection of renewable energy.During offpeak period of power consumption,the energy storage system stores surplus electric energy,and releases the electric energy for "peak load and frequency regulation" and "peak shaving and valley filling" during peak period of power consumption.At present,various energy storage technologies are developing rapidly.Liquid air energy storage(LAES)technology converts electric energy into the internal energy of liquid air for electrical energy storage.It not only has many advantages of compressed air energy storage technology,but also gets rid of the restrictions on the construction site selection of underground caves,salt caves and other geographical conditions.Therefore,LAES technology can be applied to all aspects of power system generation,transmission,distribution and use.During energy storage process,the air in the LAES system cannot be completely liquefied,and the compression heat cannot be fully utilized during the energy release process,which is an important factor affecting the energy efficiency of the energy storage system.In order to make full use of the surplus heat energy and improve the comprehensive utilization rate of energy in the LAES system,a novel multi-generation LAES(M-LAES)system is proposed in this paper.The M-LAES system uses the surplus high-temperature heat conduction oil as the driving heat source of absorption refrigerator to generate cold energy for cooling.The heat exchangers are used to collect waste heat of heat conduction oil and exhaust air for heating.The exhaust air for supply fresh air.The M-LAES system not only solves the problem of low energy efficiency of the LAES system,but also meets various energy supply requirements and improves the economy of the system.The main work and research results of this paper are as follows:(1)The thermodynamic model of the M-LAES system and its main components are established,and the effects of the main parameters such as unit series,mass air flow,energy storage pressure,energy release pressure and adiabatic efficiency on the thermodynamic characteristics of system are studied.The results show that the energy efficiency of MLAES system can be effectively improved by increasing the pressure in front of throttle valve,reducing the temperature in front of throttle valve,increasing the energy release pressure,reducing the energy storage pressure,increasing the energy release temperature,reducing the heat exchange end difference and improving the adiabatic efficiency.Compared with the LAES system that only performs electricity-to-electricity conversion,the energy efficiency of the M-LAES system is 75.40%,relatively increased by 33.50%.In addition to meeting the demand for 1.5MW of electrical power,the M-LAES system can also provide 325.02kW of thermal energy,177.43kW of cold energy and 3.01m3/s of fresh air.(2)The exergy analysis model of the M-LAES system and its main components are established,the exergy loss and exergy efficiency of each main component in the system were calculated,and the effects of adiabatic efficiency and heat transfer end difference on exergy loss and exergy efficiency of the system are studied.The results show that the compressor unit,the expander unit,the throttle valve and the heat regenerator are the four components with the largest exergy loss in the M-LAES system,and the sum of the exergy loss accounting for 89.49%of the total exergy loss of the system.The exergy efficiency of the M-LAES system can be effectively improved by increasing the adiabatic efficiency of the mechanical equipment and reducing the heat exchange end difference of the heat exchange equipment.(3)Three working modes of priority cooling,priority heating and balanced energy supply for the M-LAES system are proposed,and thermodynamic analysis is carried out.The results show that the energy utilization rate of the M-LAES system is the highest in the balanced energy supply mode,and the exergy efficiency reaches 59.13%,which is relatively increased by 4.69%comparing with LAES system.(4)The dynamic model of energy release process of the M-LAES system is established.The dynamic characteristics of no-load startup,load operation,load fluctuation and load rejection are studied.The results show that the fluctuation range of the main parameters during the energy release process of the M-LAES system will be effectively reduced by shortening the valve closing time,reducing the rotor rising rate,reducing power change rate and reducing load fluctuation range.During no-load startup,the control method of variable rising rate can greatly shorten the startup time and reduce the fluctuation range of main parameters.During the load rejection,when the valve closing time is shortened from 2s to 0s,the overspeed ratio of the rotor speed of the expander is reduced from 130.67%to 102.90%.(5)The life cycle economic calculation model of the M-LAES system is established.The economy of the M-LAES system in four typical regions of China are calculated,and the sensitivity analysis of the economic evaluation index and the prediction of energy storage subsidies are also carried out.The results show that the M-LAES system has the best economic profits in Beijing,the rate of return on investment is 23.56%,the internal rate of return is 84%,the static payback period is 2.19 years,and the dynamic payback period is 2.31 years.Compared with the LAES system that only supply electricity,the rate of return on investment is increased by 2.83%,the internal rate of return is increased by 13%,the static payback period is reduced by 0.23 years,and the dynamic payback period is reduced by 0.27 years.Sensitivity analysis results show that the economic benefits of the M-LAES system can be effectively improved by reducing low valley electricity prices,increasing peak electricity prices,increasing annual operating hours,extending loan periods,increasing system capacity and reducing initial investment costs.In addition,when the energy storage subsidy higher than (?)0.18/kWh in Guangzhou and higher than(?)0.15/kWh in Qinghai,the M-LAES system will reach the benchmark return rate of 8%. |
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