Study On The Leakage And Diffusion Behavior Of Supercritical Pressure CO₂ From Pipelines

In order to mitigate the global warming,Carbon Caputure and Storage（CCS）is being extensively studied as a promising technology.In the process of CCS,the carbon dioxide is mainly transported in pipelines.Accidental leakage of CO₂ transportation pipelines poses potential risk to people and environment,while we don’t have good knowlegde of the phenomenon and rules lying in the leakage processs.As a result,this study on the leakage and diffusion behavior of supercritical pressure CO₂ from transportation pipelines has been done.In this study,both experimental research and numerical simulation has been carried out.In experiments,paramenters measurement,visualization of flow in pipe,jet visualization outside the leakage hole by schlieren system are presented;In numerical simulation,we suppose that the CO₂ is ideal gas,and the work is carried out by code of FLUENT13.0.The main results of this study are as followings:（1）In the process of leakage,the pressure drop along pipe is very small.When the CO₂ is in dense phase or liquid phase before leakage,the pressure in the pipe drop through 3 stages:liquid phase（dense phase）stage,pressure decrease quickly;saturation stage,pressure decrease sloly;gas phase stage,pressure decrease slower than liquid stage but quicker than gas stage.The depressurization speed in the pipe can be described by the parameter（?p/?ρ）T ,（?p/?ρ）T explains well all the rules related with depressurization speed.The enthalpy of CO₂ before leakage can predict accurately the pressure value when the CO₂ change from liquid to saturation phase.Based on the conservation of energy,the enery equation of the time-varing temperature of CO₂ in the bottle has been derived,and an isoenthalpy model for the space-varing temperature of CO₂ in the pipe.By comparing with the experimental data,it’s proved that this two theoretical model works well.（2）When the CO₂ is in dense phase or liquid phase before leakage,the preocess of phase transition goes through 3 stages: :liquid phase（dense phase）stage,saturation phase stage,gas phase stage.On the basis of experiment data and theoretical analysis,it’s concluded that dry ice will not present in pipe during the process of CO₂ leakage.As CO₂ flow along pipe following isoenthalp rule,a critical value of enthalpy tells weather phase transition will happen inside and outside pipe,and this theory is well proven by experiments.Thermodynamic unequilibrium phenomenon is discovered when it starts to change phase from liquid to vapour in the pipe.Visualization of flow in the pipe revealed variation of the flow condition in the leakage process,and the phenomenon happened in pipe after the discharge valve is shut down.（3）An leakgage rate model based on isoentropy blocking flow is carried out to predict CO₂ leakage rate,it’s proven worked accurately by comparison with both my experiments and BP Company’s experiments.The temperature around the mach disk outside the leakage hole is nearly aound-80℃。（4）Two kind of typical highly underexpanded jet structure has been revealed by schlieren system.And a lot of data of temperature and CO₂ concentration in the air outside the leakage hole,it will be used as benchmark data for numerical simulation work carried out later.（5）The numerical simulation work based on ideal gas assumption divides near-field jet and far-field dispersion into two calculation area.And it captured the shock structure outside the leakage hole successfully.