Analysis Of Phase Transition Characteristics Of Liquid Carbon Dioxide Pipeline Transport

Pipeline transportation is an important way to transport CO₂ in large scale and long distance.Due to various complex factors,CO₂ has a phase change during pipeline transportation,which affects the transportation safety and efficiency.Existing studies have not yet understood the characteristics of phase transitions when the pipeline transport liquid CO₂.In this paper,the liquid CO₂ injection pipeline experiment and the pipeline transport experiment are carried out.The characteristics of pressure,temperature and phase change in liquid CO₂ injection and transport process were studied.The specific research contents are as follows:?1?In this paper,the CO₂ phase transition test system of high pressure pipeline is established,and the parameters such as temperature,pressure and injection flow are collected.?2?The pressure response and phase change of liquid CO₂ injection end closed pipe were studied experimentally.The results showed that the liquid CO₂ injected by the pipeline rapidly changed into a gas phase,and the pressure rapidly increased.When the liquid CO₂ is completely vaporized as a gas,the pressure in the pipe no longer increases and is in a pressure-retaining state.The liquid CO₂ phase changes and absorbs a lot of heat,which causes the temperature of the inlet end of the high pressure pipe to drop rapidly,while the gaseous CO₂ at the end of the pipe is adiabatic compression,which makes the temperature of the end of pipe rise.Under the same initial conditions,the time needed to complete phase transition is shorter as the external temperature increases.The smaller the initial pressure in the pipeline,the shorter the time required for complete phase transition.?3?The release process characteristics of CO₂ were studied experimentally.The results show that the temperature of the pipe drops sharply after the release,and then rises gradually after reaching the lowest temperature.Moreover,the closer to the outlet,the lower the temperature.?4?The pressure response and phase change in liquid CO₂ continuous transportation were studied.The results show that the pressure drop is easy to cause CO₂ gasification,and the abrupt change of pressure can lead to dry ice formation in the tube.Constant pressure transport can effectively prevent the formation of dry ice due to pressure drop.In the early stage of conveying liquid CO₂,the first stage pressure increases rapidly,the temperature drops rapidly,and the corresponding phase state process changes from the gasification process to the gas-liquid two-phase transport process.In the second stage,the pressure and temperature change smoothly,and the corresponding phase transition process is changed from the gas-liquid two-phase dynamic process to the superheated liquid transport process.In the initial stage of injection,the supercharging is affected by the transient flow,and the average flow size has no direct effect on it.?5?With the increase of pipe temperature,the maximum pressure increase in the pipe and the average pressure increase rate also increase.The increase in injection volume causes the increase in pressure in the pipeline to take longer.The maximum pressure increases linearly with the increase of injection volume.