Research On Cascaded Packed Bed Cryogenic Storage Method Based Supercritical Air Energy Storage System

Supercritical compressed air energy storage is one of the most promising largescale energy storage technologies.In the supercritical compressed air energy storage system,the loss of cold energy from the cold storage subsystem greatly affects the system efficiency.In order to reduce the loss of cold energy and improve the energy transfer efficiency between supercritical compressed air and indirect heat exchange medium during charging and discharging process,a cascaded packed bed cryogenic storage model was innovatively proposed.The cascaded packed bed cryogenic storage subsystem adopts a multi-channel plate-fin heat exchanger to exchange heat between supercritical air and multi-stage low-pressure circulating nitrogen.The high grade packed bed charge/discharge cryogenic energy from low temperature to ambient temperature and the low grade packed bed charge/discharge cryogenic energy from low temperature to a middle temperature which is between low temperature and ambient temperature.The cascaded packed bed cryogenic storage system has the characteristics of high efficiency,low cost and high safety.In order to explore the effects of the charge/discharge cold cycles on the properties of rock cryogenic energy storage materials,an experimental bench of automatic charge/discharge was designed and constructed.The effects of 1,000 charge/discharge cold cycles on the thermophysical properties and strengths of four types of rocks including marble,granite,limestone and basalt are studied.The results show that the appearance of marble,basalt,and limestone is basically unchanged before and after the charge/discharge cold cycles,while granite shows a few cracks and peelings.One thousand charge/discharge cold cycles have no significant effect on the density,thermal conductivity and specific heat of the rocks.The compressive strengths of marble and basalt are basically unchanged,while the compressive strengths of granite and limestone are significantly improved.Based on the experimental results,The relationships between thermal conductivity and specific heat of four rock materials and temperature in the cryogenic interval from cryogenic to ambient temperature was obtained.This article details the design process of the cascaded packed bed cryogenic storage supercritical compressed air energy storage system,and designs the steady-state heat exchanger and packed bed.On the basis of appropriate simplification,a onedimensional non-steady-state numerical calculation model is established.The changes of unsteady temperature,temperature distribution,exergy storage capacity and system exergy efficiency under continuous circulation conditions are studied.The effects of different sensible heat storage materials,heat exchanger lengths and packed bed volumes on the effects of cold storage were also explored.The results show that after multiple charge/discharge process,the performance of the cascaded packed bed cryogenic storage system is stable and the system efficiency is about 87.4%.A comparative analysis of the influence of marble,granite,limestone and basalt on the cold storage effect of the cascaded packed bed cryogenic storage system shows that the use of limestone has the best cold storage density and efficiency.The increase in the heat exchange area of the heat exchanger and the volume of the packed bed will improve the performance of the cold storage system.The research can provide new theoretical and experimental data supports for the development of supercritical compressed air energy storage system performance and provide reference for other research in the field of cold storage.