Study On The Propagation Model Of Pressure Pulse Wave And The Blockage Detection Method In Natural Gas Pipeline

With the proportion of natural gas in Chinese energy consumption increasing year by year,the mileage of natural gas transmission pipeline is increasing.The length of the natural gas pipelines in China has exceeded 104,000 km in 2020 and will reach 200,000 km by 2030.Various types of blockages such as hydrate,paraffin,ice,and water are often generated due to various reasons in the transportation process of natural gas,which seriously threaten the safety of natural gas pipeline production.Early warning and positioning of pipeline blockage in time is necessary to prevent pipeline blockage and ensure pipeline production safety.Pressure wave-based blockage detection technology is considered as one of the promising methods because of its advantages of a short response time,low costs,antiinterference capabilities and high precision.However,most of the existing studies are based on numerical simulation and lack of experimental and theoretical research,including the propagation and attenuation characteristics of finite amplitude pressure wave in pipeline,the reflection and response rules with complex pipeline structure and different types of blockages,and the wave signal analysis and processing technology in complex background environment.In view of the above problems,this paper established the propagation attenuation model of finite amplitude pressure pulse wave in pipeline,proposed the blockage position,length and severity calculation theory based on the pressure pulse wave method,and developed the software and hardware system for pressure wave signal processing under complex environment and pipeline structure,which provides theoretical and experimental support for the engineering application of pressure wave pipeline blockage detection technology.The research contents and main achievements are as follows:(1)Established the propagation attenuation model of finite amplitude pressure pulse wave in pipeline.The waveform distortion process of finite amplitude pulse pressure wave caused by nonlinear effect in the propagation process is analyzed,and the calculation formulas of local sound velocity and waveform of pulse pressure wave in the propagation process are deduced according to the nonlinear acoustic theory.Furthermore,the attenuation model of pulse pressure wave is deduced,the periodic attenuation law of pressure wave propagation is obtained According to the law of mass conservation.The model is verified by related experiments: the pressure wave propagation experiment results show that the average prediction error of the attenuation of the pulse pressure wave is 4.92%,the blockage detection experiment results show that the pressure wave attenuation model makes the average detection error of blockage severity has been reduced from-9.0% to-4.2%.(2)Proposed the blockage position,length and severity calculation theory based on the pressure pulse wave method.The pulse pressure wave signal analysis method and prediction theory of the blockage position,length and severity was developed according to the pulse pressure wave attenuation model and the propagation,reflection,and transmission law of the pressure wave in the pipeline.A series of detection experiments have been conducted: for continuous partial blockages,the average errors of blockage position,length,and severity are0.16%,0.55%,and 1.10% respectively;for single-point blockage,the length of the blockage is hard to detect and the predicted error of the blockage severity increases significantly;For multi-point partial blockage,the time-domain information of the reflected signals will not interfere with each other,the detection result is correct when the distance between the blockages is greater than the wavelength of the pressure wave;when the blockage material is solid,different materials will not affect and reflection characteristics and the reflectivity of the pressure wave obviously,and different cross-sectional shapes will have a significant impact on the pressure wave reflectivity;when the blocking material is water,the reflected wave waveform of the blockage section is clearly visible but irregular,the blockage position prediction error is 0.78 %,the prediction error of the blockage length and severity are obviously higher.(3)Developed the software and hardware system for pressure wave signal processing under complex environment and pipeline structure.The blockage detection experiments on the large-diameter and long-distance pipeline and the pipeline with complex network structure under the complex field environment were conducted,the pressure wave signal response law under the long-distance,large pipe diameter and complex pipe network conditions in the complex environment was explored,and the interaction mechanism between different frequency components of pressure wave and different pipeline structures was investigated.The combination of fast Fourier transforms and FFT filtering is used to process the complex pressure wave signal to improve the detection accuracy,the low-pass,band-pass and highpass filters with appropriate frequency are selected to eliminate the interference of irrelevant frequency components.For the long-distance pipeline with large diameter detection experiment,the position prediction error of the blockage point is 1.41% in average,the maximum error is 2.39%,and the minimum error is 0.61%;for the pipeline with complex structure and numerous branch pipes detection experiment,the position prediction error of the abnormal point is is 0.97% in average,the maximum error is 3.43%,and the minimum error is 0.03%.