Numerical Calculation Of Hot Oil Pipeline Temperature Drop Process After Shutdown

It is important to research the temperature drop process of hot oil pipeline for guiding the fixing of safely shutdown time, proposing restart scheme and making maintenance plan. A more easy method for solving temperature drop problem of hot oil pipeline was found in this paper by doing numerical calculation with the FLUENT software. During the calculating process, increase the viscosity of crude oil whose temperature was lower than the critical temperature (lower than anomalistic point temperature by 3℃) to enough, and change some correlated software settings when the temperature of upper peak inside pipe wall is equal to the critical temperature. This method does not need to follow the moving of phase interface in the wax precipitation process and invert the latent heat to heat absorption capacity additive. Based on this, temperature drop processes in winter of different laying conditions pipelines in Hua Dong area were calculated. The results shows that, for underwater pipeline, increasing the pipe diameter is more valid to prolong temperature drop time than raising initial oil temperature while other conditions are the same; for overhead pipeline, as the heat exchange factor is small, the temperature drop velocity of this pipeline is nearly equal to that of underwater pipeline, and the diurnal variation of air temperature can be ignored when calculated; for buried pipeline, the oil temperature drop velocity is slow down obviously because of the increase of temperature drop influence zone with the prolong of shutdown time, and the initial oil temperature has no effect on the size of influence zone if the soil properties are well-proportioned. In addition, decreasing the soil rectangle solving area properly can reduce the calculated amount while ensure the results exactitude. The oil temperature distribution during shutdown process was studied, and found that, with the prolong of shutdown time, high temperature area which lies upper inside the pipe as the result of natural convection after shutdown would move adown gradually, and at last to the pipe center for underwater and overhead pipe, but the lower part inside pipe for buried pipeline.