Study On The Oil Mixing Characteristics And Leakage Estimation Method During Batch Transportation Process In A Multi-product Pipeline

Tracking the mixed oil and handling leakage during the operation of the product pipelines have a great impact on economics and safety management.Proper prediction of mixed oil concentration distribution in the pipeline is an important part of concentration-cutting in stations.The existing classic models cannot explain the phenomenon of oil mixing and tailing that occur during the transportation process.At the same time,the leakage of the refined oil may cause serious results,not only the loss of oil and the adverse impact on normal operation of the pipeline,but also the second accident.However,due to the complicated boundary conditions involved in the normal delivery and leakage process of the product pipelines,it is difficult to calculate the amount of mixed oil during normal pipeline transportation and the amount of leaked oil after the leakage occurs.Firstly,this thesis introduces the experimental study on the single-pipe batch transport of different viscosity liquids.The oil-mixing tailing is found and quantitatively analyzed by conducting a series of experiments.The dimensionless oil mixing length,axial tailing length,and radial concentration difference are proposed to reveal the tailing-phenomenon characteristics of the concentration distribution.Secondly,based on the Fick's diffusion law and considering the adsorption effect of the rough wall on the oil,a new model for calculating the diffusion coefficient of the material and the concentration distribution of the mixed oil is proposed.The analysis,based on the results,reveals the influence of physical properties of concentration before and after the oil interface,turbulence effects,and adsorption effects on the distribution of mixed oil concentration and tailing phenomenon.Thirdly,the heat and mass transfer process of the single-phase incompressible multi-component fluid is numerically simulated by considering the coupling of heat conductivity and exchange inside and outside the pipe and coupling of oil flow-heat transfer-mixing process in the pipeline.The variation regularity of the dimensionless numbers within the oil mixing section is analyzed,and the flow field and concentration distribution in the oil mixing section are obtained.Furthermore,the sensitivity analysis is carried out on the key factors affecting the amount of mixed oil and the length of its tail.On the other hand,the hydraulic characteristics of the process of leaking or punching and stealing oil are studied and a method of measuring the amount of leakage or the amount of stolen oil is proposed.The instantaneous leakage and the cumulative leakage volume at the leak point or punched hole are calculated,and the leak hole size can be predicted.Finally,the non-steady-state pipe flow regularity after leakage,the outflow regularity at the small hole and the seepage diffusion regularity in the external environment are combined to achieve the coupling calculation of ?pipe flow-leakage-seepage?.Moreover,the seepage and diffusion regularity of the leaked oil in the porous soil medium is analyzed.The results proved that the proposed model can describe tailing effect of mixed oil,which reveals the nature of oil mixing.It is observed that tailing exists in the center of pipelines and wall adjacent area based on concentration distribution from the experiments.The length of the tail is 7% to 22% longer than the head for the mixed portion.This is never presented in existing numerical and empirical studies.The dimensionless length of the mixture is much larger than that of the tail,where both of them decrease with increasing Reynolds number.In the numerical investigation,it is found that batch transportation is having high Prandtl number and Peclet number,where Richardson number remains less than 1.There are hardly effects of temperature and gravity on the formation of oil mixture.Tailing is affected positively by convection and negatively by diffusion,where convection dominates in the axial direction and diffusion dominates in the radial direction.The diffusion coefficient at the center of the pipelines is larger than that near the wall.Differences from oil physical properties are the main reason for the interface formation,where it affects the axial diffusion coefficient as well.The radial diffusion coefficient is mainly affected by turbulence.Adsorption affects though indirectly on the diffusion coefficient,directly on the axial concentration distribution.The diffusion coefficient is affected together by the above three factors,further affecting the concentration distribution and tailing.Mixing quantity and tail length are positively correlated with pipe diameter and negatively correlated with flow rate,temperature and diffusion coefficient.On the other hand,on-site leaking tests are carried out by small hole draining and delivery,which approves the accuracy and robustness of the model.The model delivers higher accuracy in the situation of low flow rate,large leakage rate,and high-pressure fluctuation.The effect of leaking hole size on accuracy is greater than the pressure drop,flow rate,and temperature at the leak point.The "pipe flow-leakage-seepage" coupling model of the oil leakage process has a higher accuracy of calculating the leakage amount,and can simultaneously give the evolution regularity of the seepage diffusion range of the leaked oil in the soil.To sum up,this research can provide theoretical guidance for the process of on-site mixed oil prediction and cutting,and provide the important basis and technical support for pipeline accident handling.