The Computational Method Research On Shutdown And Restart-up Of Buried Hot-oil Pipeline

During the operation process of buried hot-oil pipeline, it is inevitability that hot-oil pipeline be in shutdown sometime, such as natural disasters, power-off, pipeline's repair and maintenance and so on. After sometime when the pipeline is shutdown, the structure strength of crude oil will be larger than the pump's start-up pressure or itself which can't endurance the pressure, at this time, solidification pipeline accident is occurred. Rising out-station oil temperature can decrease the risk of solidification pipeline accident, but the transportation cost of corporation will be increased largely. How can insure the hot-oil pipeline that keeps economically and safely during the operation process, it is need to has a good master of the temperature drop change on the shut-down pipeline and the technological parameters change on the process of restart-up . The following aspects are mainly discussed in this paper:①Wax deposit of crude oil, the effect of friction, the effect of temperature change on the physical properties of oil are also considered. And thermodynamic & hydraulics are constructed for the buried hot-oil pipeline during steady operating condition. The temperature and pressure of the pipeline's arbitrary cross section can be solved;②Based on the characteristics of thermal& hydraulic coupling of Crude oil in the pipeline, an integrated double-coupling mathematic model was presented which was adopted to solve the thermodynamic and hydraulics parameters of crude oil.③The energy equation was expressed by a form of enthalpy to reflect the temperature change of crude oil which during the process of hot-oil pipeline be shutdown. And the approach to calculate the enthalpy equation by finite element method was given and the max safe shutdown time was calculated;.④The control equation of crude oil in the buried hot-oil pipeline during the process of restart-up after shutdown was established. Control-volume methods are applied to discrete the partial differential equations. Anticipation-revise method was adopted to express the relation of oil temperature and outflow along the pipeline between restart-up times.⑤As the GingTie oil pipeline for an instance, a computer program has been programmed which can simulate and analyze the each station's the minimum out-station oil temperature, in-station oil temperature, out-station pressure, the max safe shutdown time, and the pump pressure, fluid volume, the relation of oil temperature along the pipeline between restart-up time in each season of the whole year.