| Energy storage technology can realizes the on-demand supply of renewable energy and helps to shave and shift the peak load of power demand for the stability of the power grid.Pumped hydro energy storage（PHS）is limited by the scarcity of geographical conditions of upper and lower reservoirs,while underground caverns needed by compressed air energy storage system（CAES）are relatively abundant.Compressed air energy storage technology,as a large-scale and environment-friendly energy storage technology,can solve the problems of randomness,intermittence and fluctuation of renewable energy through energy conversion at different times（peak and valley）.It is an important way to realize the large-scale utilization of renewable energy.The existing compressed air energy storage system mainly adopts multi-stage compression,intermediate cooling,multi-stage expansion and intermediate heating,of which the process is complicated and the equipment cost is expensive.It is difficult to make profit by using the normal peak-valley electricity price difference.Aiming at the problems that the process of the existing compressed air energy storage technology needs to be simplified and the economy needs to be improved,the isobaric compressed air energy storage system based on dual-usage compressor-expander was proposed and studied,which has the advantages of simplified process,higher efficiency and lower cost.The REFPROP was used to calculate the thermodynamic property of the working medium,and the effects of some key parameters on the performances of the system were performed by MATLAB.The main research contents and achievements of this paper are as follows:Firstly,the isobaric adiabatic compressed air energy storage system based on a single stage dual-usage compressor-expander was discussed,which mainly includes compression and expansion equipment,heat storage subsystem and gas storage subsystem.The single-stage multi-cylinder rotating with rotor（Q type）dual-usage compressor-expander is adopted;Water assisted nylon cloth pipes are used to store gas at constant pressure to ensure that the operation pressure of either compressor or expander is stable at design point;The helical channel oil storage tank is introduced to replace two sets of cold and hot tanks,and the shared equipment of thermal oil energy storage/release system with road-return scheme is adopted.Taking the energy storage efficiency and theoretical energy storage density as evaluation indexes,the numerical simulation solution was carried out by using MATLAB,and the effects of compression outlet pressure/temperature,ambient temperature,pinch temperature difference of heat exchanger and compression/expansion isentropic efficiencies on the system were explored.The results show that the compression/expansion isentropic efficiency has the most significant effect on the indexes of system energy storage efficiency and theoretical energy storage density,followed by the pinch temperature difference,the compressor outlet gas pressure and temperature,while the ambient temperature has little effect.Under the conditions that the air mass flow rate is 9 kg·s-1,the compression outlet parameters is 10 MPa/320°C,the ambient temperature is 25°C,the pinch temperature difference is 10°C and the compression/expansion isentropic efficiency is 0.86,the energy storage efficiency and theoretical energy storage density are 67.83%and 16.67 k Wh·m-3respectively,which is 7.51%and 11.73%higher than that of the three-stage isobaric adiabatic compressed air energy storage system.A reasonable evaluation system was established to analyze the economy of the energy storage system proposed in this paper.The economic indexes including Levelized Cost of Energy（LCOE）,Investment Cost per Total Output Energy（ICPE）,Cost of Energy（COE）,capital payback period（SPB）and Net Present Value（NPV）were emphatically analyzed,which are affected by compressor outlet air pressure/temperature,ambient temperature,the pinch temperature difference and compression/expansion isentropic efficiency.The economic performance of the system is sensitive to the compressor outlet air pressure,pinch temperature difference and the isentropic efficiency of compression/expansion.Under the abovementioned conditions,the LCOE of the isobaric adiabatic compressed air system based on the dual-usage compressor-expander is 4.24%lower than that of three-stage isobaric adiabatic compressed air energy storage system;The ICPE is 18.82%lower than that of three-stage isobaric adiabatic compressed air energy storage system;The COE is 10.62%higher than that of three-stage isobaric adiabatic compressed air energy storage system;The SPB is 8.68 years,which is 6.26 years less than the three-stage isobaric advanced adiabatic compressed air energy storage system.The proposed new scheme has the advantages of simplified process,higher efficiency and lower cost,which provides reference and theoretical support for the improvement and optimization of the compressed air energy storage system,and provides an economical and feasible way for the development of large-scale and popular energy storage technology. |
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