Experimental Study On Risk Of CO₂ Leakage From High Pressure Pipeline

Pipeline transportation is characterized by its safety,economy and high efficiency as an important intermediate link for CO2 capture,storage and utilization.Due to a variety of complex reasons,CO2 pipelines are at risk of leakage and fracture.The existing research has a deep understanding of the inside pipeline flow characteristics,thermohydrodynamics,near-field concentration,etc.during the leakage process.But the systematic research on the disaster risks such as low temperature,strong noise,and far field high concentration caused by pipeline leakage is relatively less,especially the lack of research results obtained from industrial-scale experimental devices.Moreover,most of the existing researches focus on above-ground pipelines,and there are fewer studies on the risks of buried pipelines.Based on these,this paper carried out the above-ground horizontal leakage experimental device and buried leakage experimental device of high-pressure CO2 release from the industrial-scale pipeline.And characteristics of the low temperature,sound level and far-field concentration disasters in the leakage process and the soil morphology and dry ice accumulation in buried areas was researched systematically.The details are as follows:(1)The industrial scale high-pressure CO2 pipeline horizontal leakage experimental device was improved.And realized the measurement of temperature,near and far field noise and concentration in the leakage area.Four leakage orifices,including 15 mm,50 mm,100 mm and 233 mm,were selected to conduct horizontal leakage experiments of gas phase,dense phase and supercritical phase.An experimental device for leakage of high-pressure CO2 buried pipeline was designed and built,and experiments were carried out under different leakage orifices and directions.(2)The temperature variation of horizontal leakage zone under different leakage orifices was measured and analyzed.The results showed that when the pipeline leaks,the severity of the low temperature effect is dense phase,supercritical and gas phase.Based on the standard diagnosis of occupational frostbite,the limit of frostbite was 10 ?,the axial hazard distance of gas phase,supercritical and dense phase are 7 m,12 m and 25 m,respectively.(3)The variation rule of sound level in horizontal leakage zone under different leakage orifices was measured and analyzed.The results showed that the sound level is only related to the distance and has nothing to do with the orientation.Due to the high jet velocity,the degree of danger under the supercritical leakage is higher than that of in the dense phase.When the size of leakage orifice was 50 mm,100 mm and 233 mm,the dangerous distance of supercritical CO2 at 50 mm,100 mm and 233 mm was 100 m,140 m and 150 m by linear extrapolation respectively,and the dangerous distance of dense CO2 at 50 mm and 100 mm was 80 m and 120 m.(4)The variation rule of horizontal leakage zone concentration in different leakage orifices was measured and analyzed.It is found that jet expansion and media diffusion lead to an increase in CO2 concentration near leakage zone.Leakage orifice,distance to the leak and phase have an effect on the concentration distribution.Under full-bore leakage,the axial danger distance is 45 m for gas phase leakage,140 m for supercritical phase and 120 m for dense phase.(5)The leakage risk rules of buried pipelines with different leakage orifice were measured and analyzed.The results showed that in the process of leakage,there is an "ellipsoidal" frozen soil ball in the soil.The frozen soil ball consists of three parts: frozen soil layer,dry ice layer and cavity layer.The minimum temperature reached by the outer wall of the pipe is-78 °C.Dry ice accumulation occurs around the pipeline,and the accumulation amount is the largest along the leakage direction.The distance of dry ice accumulation with the leakage time show a logarithm function relationship.For distributed temperature sensing fiber detection technology,it is recommended to lay two fibers in the process of actually laying the fiber,and the axial angle of the fiber is 180°.It can be considered to be placed 300-500 mm parallel to the top of the pipe or the bottom of the pipe.