Study On Thermodynamic Characteristics Of Industrial-scale CO₂ Pipeline Leakage Process

As an important link in the technology of CO₂ capture,utilization and storage,the safety of long-distance pipeline has always been concerned because of the inevitable leakage risk.Existing research focuses on inner medium pressure and temperature change rule,pipe jet diffusion research,but for the leakage of pipeline system of medium pressure and temperature in the process of change rule and phase behavior change law and fluid heat variation is relatively small,especially through the industrial scale experiment data,few and far between.Based on this,this paper carried out an industrial-scale CO₂ pipeline leakage experiment to study the variation rules of medium pressure,temperature,density,enthalpy and Prandtl number in the pipeline during the leakage process,as well as the variation rules of medium phase state and fluid heat transfer.The details are as follows:?1?An industrial-scale CO₂ level leakage experimental device was established and perfected.The data of medium pressure and temperature changes in the pipe during the leakage process were obtained by changing the size of the leakage orifice?50mm,100mm and 233mm?and the initial phase state?supercritical phase and dense phase?.The device is mainly divided into five parts:injection device,heating device,emptying device,leakage control device and data acquisition device.?2?According to the data of pressure and temperature in the pipe during the leakage process,the variation rules are summarized.The results showed that the pressure drop and rebound phenomenon occurred in the high-pressure medium in the pipeline during the leakage process,and the pressure drop and rebound phenomenon did not exist in the full diameter.The number of reduced pressure wave produced by leakage decreases with the increase of caliber,and the number of reduced pressure wave propagated by dense phase is less than that of supercritical phase.In the process of rapid descent,the pressure-drop and the rebound decrease with the distance from the leakage hole.Due to the joule Thomson effect of CO₂ itself,the larger the leakage caliber is,the temperature drop at the bottom of the pipe at the same position is larger than that at the top of the pipe,and the temperature drop rate when the measuring point at the bottom of the pipe reaches the lowest temperature is larger than that at the top of the pipe,which increases with the distance from the leakage hole.?3?According to the data of pressure and temperature in the leakage process,the change rule of phase state is summarized.The results show that the supercritical phase?gas-liquid phase?gas phase in the leakage process.Dense phase?gas-liquid two-phase?gas-liquid-solid three-phase.The phase state of CO₂ is transformed from the position of the pipe leakage hole to the end of the pipe in sequence.The phase change occurs at the top of the pipe before the bottom of the pipe at the same section,and the phase state changes more frequently the farther away from the pipe leakage hole.?4?Calculate the density according to the pressure and temperature data and explore the variation rule of density with temperature.The results show that the medium density depends on the pressure drop before the phase state changes during the leakage process.When the medium in the pipeline is completely changed into gas phase,the density depends on the temperature drop in the pipeline.The initial density of dense phase was larger than that of supercritical phase,and the density drop was larger than that of supercritical phase.?5?Calculate the enthalpy value according to the pressure and temperature data and explore the change rule of the enthalpy value with the pressure.The results show that the pressure enthalpy diagram can describe the phase change of the medium more clearly than the pressure temperature diagram.Phase change of medium in the pipeline results in change of enthalpy value.When the enthalpy value is greater than437.06kJ/kg,phase change does not occur in CO₂,but vice versa.?6?According to the pressure and temperature data,calculate the Prandtl number and explore its variation rules.The results showed that during the leakage process,the Prandtl number changed suddenly at the critical point of phase transition of CO₂,and the heat transfer effect of the medium in the pipeline reached the highest.The larger the leakage caliber,the greater the Prandtl number in the medium and the greater the Prandtl number mutation range,and the fluid heat transfer degree moves from the bottom of the pipe to the top of the pipe.