Detection And Localization Of CO₂ Leakage Based On Acoustic Emission

Global warming has become a growing concern around the world.The main reason of global warming is the emission of large amount of CO2 gas which comes from the combustion of fossil fuels,such as coal,petroleum and natural gas.Limitted by energy structure and exploitation technology,fossil fuels are going to dominate the energy consumption domain of the world for a long period of time.So it has become a porpular research subject how to reduce the emission of CO2 gas without limitting the use of fossil fuels.CCS(Carbon Capture and Stroage)technology is specialized in solving this problem by capturing and storing CO2 for long time in order to reduce the emission of CO2.It has the great potential to slow down the speed of global warming.However,there are many challenges still in the research phase in the process of CCS.CCS technology includes three key steps,carbon capture,carbon transportation and carbon storage.It is a commom phenomenon that CO2 will leak into the atmosphere in the process of transportation.Unfortunately,measurement of CO2 leakages is challenging for the following reasons.Firstly,leak signal is usually weak and has a low signal-to-noise ration because the size of the leak hole or crack is small.Data acquisition is not easy and the signal has no obvious characteristic.Secondly,leakage is unstable because there is a phase chage(liquid to gas or solid to gas)in the leak process.Thirdly,most of the previous studies were conducted under the condition that there was only a single leak source in the area of interest.Multiple leak sources in a large vessel are common,especially if the vessel has been in use for a long period of time.To date there have been very limited studies of localization of multiple leak sources.In this thesis,advantages and disadvantages of previous methods are reviewed.Detection and localization algorithm based on acoustic emission methods have been explained taking consideration of the feature of transportation equipments.Performance of the proposed method was evaluated through experimental tests and signal analysis in order to assure technical process of CCS.Main work in this thesis includes the following.(1)Research on the characterictics of leak signals.It is important to detect a leakage accident and to accurately assess the severity when a leakage has occurred.In this study,a 304 style stainless steel plate with leak holes from small to large was used to simulate a leaking area of a large CO2 pressure vessel.Besides,a continuous leak was simulated by a CO2 gas cylinder which was linked to the leak hole.The leak signal was analyzed in time and frequency domains.Energy distribution of different frequency bands was calculated to identity the size of a leak hole.(2)Research on the localization of multiple leak sources.The case that multiple leak sources occur m a large pressure vessel is complicated than that of a single one.Multiple leak holes in a stainless steel plate were used to simulate multiple leak sources in industry.Characteristic frequency band was chosen through analysis of the PSD(Power Spectrum Density)of the leak signal.Wavelet packet was used to decompose the frequency and to extract the characteristic band.MUSIC algorithm was applied to construct a space spectrum function to calculate the directions of the signals.Localization was realized based on the results of different positions of the sensor array.Besides,AE leak signals corresponding to different leak pressures were obtained.The effects of this method was demonstrated under different leak pressures.