Throttling Process And Decompression Property For Pipeline Transportation Of Anthropogenic CO₂ In Different Phase

Pipeline transportation has been certified as the main choice for large-scale and long-distance onshore transportation of carbon dioxide?CO₂?.Transportation in supercritical way is one of the efficient and feasible choices in different phases.The phase property of supercritical CO₂ is special.The safety issue under high pressure has been concerned in operating process.The researches of CO₂ phase property near the critical point and decompression are still in the primary state.The study on safety control technology of transported CO₂ in pipeline includes phase property of supercritical CO₂,throttling process of different phase CO₂,decompression property of pipeline leakage,and impurity influence.It is very significant to improve the theory of CO₂ pipeline transportation and practical application.For the researches of phase property of transported CO₂ in pipeline and sensitivity of impurity influence,the Peng-Robinson equation of state selected by comparing is the calculation model for phase equilibrium and physical parameters of CO₂.The variation of main parameters such as density,viscosity,and heat capacity relating to pipeline transportation of CO₂ will be presented.The region between dense phase and supercritical phase where the physical parameters have sharp discontinuities is the quasi-critical region.The quasi-critical region defined by the mass density is based on the quasi-critical temperature line,which consists of temperatures at which the mass density has the sharpest discontinuity at each pressure.The function for the quasi-critical temperature and pressure of the transported pure CO₂ in the pipeline is given.The parameters in pipeline should be avoided approaching the quasi-critical region under the operation and shutdown conditions.According to the influence of impurities on phase equilibrium,physical parameters and quasi-critical property based on molecular polarity,the nonpolar impurities and weak polarity shift the corresponding quasi-critical lines to lower temperatures.Conversely,the polar impurities shift the lines to higher temperatures compared to pure CO₂.For CO₂ with impurity transportation in high pressure dense phase,the N2 content is recommended to be below 10mol% and the H2 content is recommended to be below 4mol%.An inlet pressure at or above 14 MPa is acceptable because the density variation range can be ignored above 14 MPa.For the research of parameter variation of CO₂ throttling process in different phases,the experimental device is designed and built based on the throttling effect and thermodynamics laws.The experimental results demonstrate the variation of main parameters in the blowdown process of CO₂ by throttling in different cases and make up the shortage of relevant research.The observed variation of ambient cloud has been illustrated a detailed description.According to the experimental results,outlet temperature of different stage throttling will change with the variation of inlet temperature.The temperature will increase to the temperature in main pipe and decrease.The temperature drop in throttling process of liquid CO₂ and CO₂ with nonpolar impurity is larger.The experimental outlet temperature of CO₂ with nonpolar impurity is lower than that of pure CO₂ throttling.Impurity will change the variation rate of parameters in main pipe larger than that of pure CO₂ experiment.The higher inlet pressure and the lower inlet temperature will produce lower throttling outlet temperature.The recommendation is presented that the throttling inlet temperature will be increased to deal with the temperature drop in blowdown process by throttling of CO₂ in pipeline.The calculation model and algorithm on the parameters variations in throttling pipe and main pipeline is given under the blowdown process of CO₂ pipeline.For analysis to throttling property of CO₂ in different phase,the model has a good prediction on throttling process of supercritical CO₂ and gaseous CO₂.According to the calculation results,the variation and fitting function are given that the parameters and throttling coefficient of CO₂ in throttling pipe in the whole throttling process.For the research of throttling property of supercritical CO₂,the throttling coefficient of supercritical CO₂ is represented by weight factor.The line at which the gaseous phase property is equal to the liquid phase property of supercritical CO₂ is defined quasi-equilibrium line.The supercritical phase region of CO₂ is redefined.In the whole system of pipeline transportation including main pipeline and processing station,supercritical CO₂ shows the low viscosity liquid property under the hydraulic process in main pipeline with simple flow,whereas it shows the high density gaseous property under the thermodynamic process in processing station with complicated flow.According to the analysis on the influence of impurities,the nonpolar impurities will change the CO₂ throttling coefficient larger and change the outlet temperature lower.The polar impurities will change the CO₂ throttling coefficient smaller and change the outlet temperature higher.The more the amount of impurity is,the larger the deviation of throttling coefficient from that of pure CO₂ is.For the research of the variation property of CO₂ parameters in pipe under leakage condition,the parameters along the pipeline are illustrated by experiments in leakage process and decompression wave speed is calculated.Based on the experimental results,the final temperature in pipe under the leakage condition is higher than that under the throttling process.The decompression wave speed is represented by the function of density and temperature.The variation of parameters along the pipeline is calculated by method of characteristics under the leakage condition.Considering decompression wave model,the variation and propagation of decompression wave speed are given under the leakage condition.Under different cases,the decompression wave initial speed of CO₂ is defined by parameters of initial state.In the leakage process of liquid CO₂,the phase change will produce with the infinitesimal unit and propagate in pipe with the radial section.The phase section will produce the pressure platform in the change process of decompression wave speed of liquid CO₂.Calculation model of CO₂ elasticity coefficient in different phases is given.The supercritical CO₂ elasticity coefficient is between that of liquid CO₂ and that of gaseous CO₂.Based on the analysis on the influence of decompression wave propagation,the conclusion on variation of pressure along the pipeline and flowrate at the orifice may be given under the case of supercritical CO₂ pipeline leakage.The main choices of safety control include limiting the initial wave speed,keeping CO₂ purity in pipeline,and emphasizing the environmental protection without ambient cloud.