Study On Numerical Calculation Of Wax Deposition In Waxy Crude Oil Pipeline

Most of the crude oil produced in China is waxy crude oil.When the waxy crude oil is transported,the oil temperature gradually decreases.When the oil temperature at the pipeline wall is lower than the wax appearance temperature of the crude oil,wax deposition will occur on the pipeline wall.Although it has been researched for many years at domestic and international,and instructive progress has been made in many aspects,considering the complex and variable wax deposition phenomenon,it is still necessary to conduct more in-depth research in order to ensure the safe operation of pipelines and improve the profits of enterprises.In this paper,wax deposition of the waxy crude oil pipelines is studied from the aspects of numerical calculation and algorithm optimization.First,the MRF method of FLUENT software was used to simulate the space flow field and temperature field of wax deposition in four kinds of oil in Structure drawing of rotary facility of the wax deposition.The simulation results show that viscosity and wax crystal solubility coefficient,temperature gradient and sheer stress at the wall plays a major role in the internal mechanism under different operating conditions,respectively.Secondly,the parameters of two typical wax deposition rate models are optimized based on optimization algorithm combined by Levenberg-Marquardt(L-M)and Universal Global Optimization and the model prediction results is compared.The results show that the accuracy of the mathematical model obtained by the optimization algorithm is much better than that of the model fitted by the least square method.The maximum error is reduced from 30% to 10%,and the average error is reduced from 10.3% to 2.42%.The mathematical model established by this optimization algorithm is also better than that established by L-M alone.The maximum error is reduced from 13.62% to 11%,and the average error is reduced from 6.46% to 4.77%,which is because the optimization algorithm avoids the premature phenomenon caused by using L-M alone to a certain extent.In addition,based on the 1st Opt software,the optimization algorithm does not require suitable initial values,prior knowledge and programming,easy to use,and has important use value.Finally,based on optimization algorithm combined by L-M and Universal Global Optimization and the data obtained by the simulation,Four representative models were fitted for the four crude oils studied in this paper,respecttively,and the model prediction errors are compared.Through the error comparison results,it is suggested that: if the use of wax deposition dynamic model is involved,it is suggested to choose the huang qiyu model or thehuang qiyu improved model which is convenient and has high precision for modeling.The results of this paper are of great practical significance for the inhibition of wax deposition in pipelines,the accurate prediction of wax deposition rate and the formulation of the optimal pigging cycle.