Leak Detection And Localization Of CO₂ Transportation And Storage Units Based On Acoustic Emission

With the deterioration of the global warming,CO₂ emission has caused great attention of many countries.Carbon capture and storage?CCS?is a major emerging technology to reduce CO₂ emission.CCS is of great significance for our country to address climate change and promote low carbon development.CO₂ transportation is the middle part in CCS technology linking the capture part and storage part.Once industrial scale CO₂ leakage happens and cannot control timely,it will cause serious harm for the ecological environment and human health.Therefore,accurate and reliable leak detection technology is indispensable.CCS is a developing technology and there are not mature and perfect methods for leak detection and localization at present.Although leak detection has accumulated some experience in the oil,gas and water industries,many problems need to be solved.Firstly,leak detection in other industries is imperfect and news of leakage and explosion can be seen frequently;Secondly,CO₂ has special properties and many phase states including gas,liquid and supercritical fluid may exist in the transport process;Thirdly,leak detection methods nowadays mainly focus on the pipe,however,there are few leakage research for the storage devices;Fourthly,CO₂ transportation and storage units have complex structures,covered with thermal insulating layer,buried underground,so leak detection methods should avoid digging and destroying much soil and insulating layer.Therefore,leak detection and localization for the CO₂ transportation and storage units are very challenging.In order to satisfy the security of the whole CO 2 transportation part,an effective leak detection and localization method is crucial.This thesis summarizes and compares the advantages,disadvantages and applicable conditions of the existing methods of leak detection.According to the characteristics of the CO₂ transportation units,leak detection and localization methods based on acoustic emission are proposed.Theoretical analysis,numerical simulation and experimental validation are conducted to research the key problems including the characteristics of the leak source and the acoustic wave propagation,arrangement of the sensor array,signal filtration and decomposition,leak localization.Accurate leak detection and localization,especially the recognition of multiple leak sources,for CO₂ transportation and storage units are achieved.These methods fill the domestic blank of CO₂ leak detection in transportation process.The detailed research contents and in this study includes the folling aspects:?1?Acoustic emission and signal characteristics from the leak sourceAcoustic emission phenomenon caused by CO₂ leakage is studied in combination with the theoretical analysis and experimental verification.Characteristics of the leakage signal from holes with different sizes,different shapes and multiple sources are compared.?2?Leak signal filtration and multi-scale decompositionNoise,dispersion and distortion are difficult problems of the acoustic study.Signal filtration,decomposition and feature extraction are researched in this thesis.According to the different CO₂ transportation and storage units,empirical mode decomposition,ensemble empirical mode decomposition and wavelet packet decomposition are proposed and applied to decompose the leak signal.?3?Leak localization of the CO₂ transportation pipeAccording to the geometric features of the CO₂ transportation pipe,the localization model is simplified into one-dimensional model.The propagation mode and attenuation law of the leak signals are analyzed.On this foundation,the rules of sensor selection and feasible localization algorithm is investigated.A T DOA leak localization method based on the correlation coefficient fusion and a n improved localization algorithm without wave speed are achieved in order to increase the accuracy.?4?Leak localization of the CO₂ storage unitsAccording to the geometric features of the CO₂ storage units,the localization model is simplified into two-dimensional model.Leak localization algorithms based on near field beamforming,far field beamforming and hyperbolic curve are proposed.The influence of sensor array arrangements,sensors spacing and sensr amount on the localization performance is investigated.The advantages and shortcomings of the different topologies are appraised and discussed.?5?Recognition and Localization of multiple leak sourcesThe present leak localization algorithms are mainly focus on the precondition that only one leak source exists,however,these algorithms have low accuracy or even do not work when facing multiple leak sources at the same time.In order to solve the leak detection problem of multiple leak sources,a method based on MUSIC algorithm and multiple sensor arrays is proposed which can recognise and locate of the multiple leak sources.The performance of this method is validated by simulation and experiments.