| Energy storage technology can decouple the electrical energy in time and space,improving the economy of the power system and the utilization rate of the renewable energy.With the rapid development of renewable clean energy in China,the demand for energy storage is increasing.As one of the preferred choices for large-scale energy storage projects,compressed air energy storage(CAES)in salt cavern has great development potential and is becoming a hot spot in China.Compared with crude oil and natural gas storage in salt cavern,the operation of CAES in salt cavern requires daily cyclic injection and withdrawal.Thus,the short-term and long-term mechanical properties of surrounding rock under high-frequency cyclic loading conditions will directly affect the safety and stability of the operation of a CAES plant,which is worth studying.Based on salt cavern CAES project,this dissertation adopts a combination of theoretical analysis,laboratory experiment and numerical simulation to analyze the stress of surrounding rock under high-frequency cyclic loading,short-term unloading failure,long-term fatigue deformation properties,characterization model of salt rock under cycling loading,the comparison of fatigue and creep behavior,and the stability simulation of Jintan salt cavern CAES.The research results are significant for optimizing the operation pressure for the salt cavern CAES plant in China.The main research contents of the thesis are as follows:1.The system composition and operation process of the CAES project are introduced in detail,and the relevant geological and operating parameters of the two commercial CAES plants are summarized.Also,based on the injection parameters of Huntorf CAES plant,the dissertation analyzes the temperature and pressure changes in the cavern and the stress of surrounding rock caused by a cycle injection and withdrawal,and concludes that the stress state of the waist surrounding rock during withdrawal period is more dangerous.Based on this conclusion,a triaxial unloading confining pressure test is used to simulate the stress change of the waist surrounding rock during the air withdrawal.The failure strength,deformation and failure modes of the salt rock under different unloading rates are also analyzed and compared in this part.Finally,the unloading damage under real working conditions is discussed and predicted.2.According to the mechanical properties of surrounding rock under different operation schemes,step cyclic loading tests are carried out in this dissertation.the influences of the maximum stress,minimum stress,mean stress,half-amplitude,and frequency(period)changes of sinusoidal cyclic loading on the deformation properties of the salt rock are analyzed and compared.The waveform and holding stress under unconventional cyclic conditions are also studied in this dissertation.Thus,the deformation response law of salt rock to different cyclic conditions are obtained.3.Based on the similarity between creep and cyclic deformation,the Burgers creep model is used to derive the cyclic deformation characterization equation under sinusoidal cyclic loading.Comparing the deformation under different cyclic parameters are obtained by this equation with the cyclic deformation under different cyclic loading in tests,it is found that there is a big difference between the two results.The dissertation establishes a stiffness scaling factor that varies with the cycle parameters through the fitting analysis of the test results.Furthermore,this factor is incorporated into the conventional Burgers creep model,and an improved Burgers model is obtained.The improved Burgers model is highly consistent with the test results with a good characterization ability for the deformation under different cyclic parameters.4.Scanning electron microscope test(SEM)tests are carried out in the dissertation on salt rock under uniaxial,creep and cyclic three loading modes,the macroscopic fracture degree and microscopic deformation mechanism under the three modes are analyzed.Based on the step creep and step cyclic failure tests,the long-term creep strength and fatigue strength are obtained by isochronous stress-strain curves and steady strain rate curves respectively,and the values of the two strength are compared in detail.Through alternating creep and cyclic tests,the equivalent creep stress of cyclic loading is obtained,which helps to simplify the prediction of cyclic deformation.5.Based on the relevant geology parameters of Jintan salt cavern,the common exponential creep model and Burgers model are used to simulate by FLAC3 D software,and then the plastic zone,dilatancy damage and volume shrinkage of surrounding rock under cyclic loading are analyzed and compared.The shortcomings of the two traditional creep models in predicting the deformation law under different cyclic loading conditions are pointed out.Furthermore,the improved Burgers model is used to predict the mechanical behavior of surrounding rock under various cyclic conditions,and suggestions are provided for adjusting the operation scheme of CAES plant. |
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