Study On Numerical Simulation Of Shutdown And Restart Of Thermal Insulation Crude Oil Pipeline

During the operation of the insulated crude oil pipeline,it is affected by force majeure or planned maintenance,and the oil pipeline needs to be shut down.Due to the influence of the rheological properties of the crude oil pipeline,the rheological properties of the crude oil in the pipeline are gradually deteriorating with the increase of the shutdown time.In severe cases,the "condensation tube" accident is caused.In order to avoid such accidents,it is necessary to study the temperature field around the insulated crude oil pipeline and analyze the thermal and hydraulic conditions.Accurately grasp the situation of steady-state operation and unsteady operation of the pipeline,reduce the energy loss.The safe and economic operation management of the insulated crude oil pipeline has far-reaching significance.This paper aims at Tieling-Faku section of Qing-ji thermal insulation crude oil pipeline,a method combining finite element analysis.The main aspects of the study are as follows:(1)In the calculation of parameters related to crude oil transportation,the influence of latent heat of wax deposition is fully considered.Different sections of the oil pipeline are divided,and relevant mathematical models are established in the calculation of thermal and hydraulic forces to accurately solve the temperature drop and pressure drop of the insulated crude oil pipeline at different axial positions.(2)According to the temperature field of different operation conditions,this paper uses Gambit,ANSYS and other software to set up three seasonal states in winter,spring,autumn and summer respectively,and simulates the temperature field of the insulated crude oil pipeline and its surrounding media under steady operation conditions,shutdown for 5 h,10 h,15 h and 20 h.(3)In view of the influence of temperature field on wax deposition and oil properties after shutdown,the temperature gradient at the pipe wall under different working conditions and different distance is calculated in this paper based on the relevant data of numerical simulation.Based on Fick's law,the effects of different temperature gradients on wax deposition rate were summarized,and the effects of pipeline temperature drop on oil viscosity and shear stress were obtained by combining the constitutive equation of different oil flow forms.(4)Aiming at the pressure of shutdown and restart,the thermal and hydraulic analysis is carried out under the condition of restart,and the peak values of start-up pressure and two pressure peaks along the shutdown and restart of thermal insulated crude oil pipeline are obtained.