Research On Wax Deposition Characteristics Of Unheated Crude Oil Pipeline

In this paper,we select Jienuo crude oil from Linyi-Puyang pipeline as an example to study the wax deposition characteristics of unheated crude oil pipeline.The basic physical properties such as the basic composition,density,pour point,density,specific heat,wax release characteristics and viscosity curve were measured by experiments.Using the Couette rotating waxing device and Flunt software which can get the internal temperature field of the device,the inner wax deposition law of Jeinuo oil was obtained.When the temperature difference between the oil sample and the wax wall is the same and the rotational speed of the sample cylinder is the same,the wax deposition rate is basically the same as the change trend of the wax solubility coefficient.When the temperature of the sample cylinder and the wall temperature of the wax barrel were changed,the wax deposition rate increased with the increase of the temperature gradient at the wall.When the temperature of the oil sample,the wax wall temperature is constant,the wax deposition rate decreases as the sample cylinder speed increases.The radial temperature difference of the unheated crude oil pipeline leads to the diffusion of the wax molecules to the tube wall.Therefore,the wax deposition model chosen in this paper is the universal wax model based on the Fick's diffusion law-the Huang Qiyu model.Based on the experimental data of Jienuo oil wax deposition in the room,a wax deposition model suitable for Jienuo oil was established.Based on it,a calculation program is designed to calculate wax deposition rate,pipeline running cost and the optimized pigging frequencies in different working conditions of unheated crude oil pipeline The accuracy of the program is verified by comparing with the amount of wax which was pigged in the running pipeline during a certain period.The effects of wax solubility coefficient,temperature gradient,viscosity and shear stress on the wax deposition rate and the optimized pigging frequencies of the Linyi-Puyang pipeline are studied and analyzed.The results show that in winter,spring and autumn,with the decreasing of the outlet temperature,the wax deposition rate of Jienuo oil gradually decrease,and the change of wax deposition rate in summer is complicated,and the location where exists the most serious wax deposition is moving toward the station exit.With the increase of throughput,the wax deposition rate of the pipeline gradually decreases at first,and then gradually increases.The wax deposition rate decreases with the increase of soil temperature.The effect of the four wax deposition factors on the wax deposition of the pipe was summarized.The wax solubility coefficient works the most significant in the higher temperature of the pipeline.The influence of the shear stress and viscosity work normally.The temperature gradient will seriously largely slow down the wax deposition rate at a minimal value.In the study of the optimized pigging frequencies,the results show that the decrease of the outlet temperature in winter,spring and autumn will reduce the slope of daily average operating cost,and the pigging frequency will be prolonged.In summer,with the decrease of outlet temperature,the pigging frequency will first decrease and then increase.The average daily costs of pipeline operation will increase while the pigging frequency will be shortened with the throughput rising,and the average daily costs of pipeline operation will decrease first and then increase while the pigging frequency will be extended with the soil temperature increasing.In actual operations,avoiding the too low outlet temperature and the appropriate increase in throughput,can effectively avoid frequent pigging.Changing the outlet temperature,ground temperature and wax thickness,we find that the station friction and throughput are in a single increase between Linyi-Zhaozhaizi pipeline.It is not easy to enter the unstable work area.The interactions between oil/wax surfaces and wax/wax surfaces were calculated using molecular simulation.The influence of temperature on the adsorption energy of oil/wax surface and wax/wax surface was studied by changing the temperature,and the mechanism of the temperature on the delamination property of wax layer was discussed.