A Study On The Shutdown And Restart Problem Of Oil Pipeline In Nanyi Oil Depot

The buried heating method is used in the pipeline of Nanyi oil depot.During the actual operation of the pipeline,the shutdown process of oil pipeline unavoidable occurred because of pipeline maintenance,insufficient oil,accident conditions,natural disasters and other reasons.If the shutdown time is too long,it will significantly increase the possibility of pipeline condensation accident and cause huge economic losses.Therefore,in order to ensure the safe operation of Nanyi oil depot pipeline,it is necessary to study the process of pipeline shutdown and restart.Specific research contents are as follows:Firstly,the density,freezing point,specific heat capacity,viscosity-temperature relationship,yield stress,thixotropy and wax precipitation characteristics of crude oil transported from Nanyi Oil Depot are tested.According to the test results,thixotropic model and the calculation models suitable for characterizing the density,specific heat capacity,viscosity and temperature of the crude oil are obtained.On this basis,according to the actual operation conditions,the total heat transfer coefficient of pipeline in different months is obtained by inverse algorithm,so that the average relative error of the oil temperature at the end of pipeline is 4.6%.Based on the least square method and the optimal fitting technology,a modified model for calculating hydraulic friction coefficient of pipeline is established,which makes the average error of calculating pipeline pressure drop reach 4.73%.Secondly,the hydraulic and thermal models and the corresponding numerical solution method of shutdown and restart process of Nanyi oil depot pipeline are established.Fifteen groups of actual operation conditions are selected for numerical simulation,and the oil temperature distribution and variation law along the pipeline during shutdown are obtained.During restart process,under the same conditions,the distribution and variation law of temperature and pressure along the pipeline are analyzed.On this basis,the constraint condition is that the maximum pressure of the pipeline does not exceed the pressure-bearing capacity of the pipeline and the pressure provided by the pump.And the safe shutdown time under 27 working conditions is calculated by constant flow starting mode.The influence of oil transportation temperature,volume and ambient temperature on safe shutdown time of pipeline is also analyzed.Finally,the oil transportation temperature,volume and ambient temperature are taken as the key factors affecting the working characteristics and safety during shutdown and restart process.Based on the grey relational theory,the influence degree of each factor on safe shutdown time,cooling rate during shutdown process,peak restart pressure,terminal oil temperature recovery time and heating rate of pipeline is identified,which provides a theoretical basis for the formulation of safe shutdown and restart scheme of Nanyi oil depot pipeline.