Abstract
To realize the safe and economic operation of a waxy crude oil pipeline, a thermal–hydraulic model in an unsteady state was established for the restart process of waxy crude oil. The model is based on the thermodynamic and hydraulic characteristics of crude oil within a pipeline intercoupling with media outside the pipeline during the restart process of the crude oil pipeline. The characteristics of waxy crude oil are considered, and the model includes the continuity equation, momentum conservation equation, and energy conservation equation. This article suggests a method for developing the model based on shockwave theory combined with the characteristic line method, numerically simulates the restart process of a certain buried oil pipe in summer and winter, and analyzes how the oil temperature at the beginning and terminal of the pipeline and the pressure at the beginning of the pipeline change during restart. In addition, this article confirms the safe duration of shutdown in two seasons for a waxy oil pipe, which are 37 h in summer and 33 h in winter.
Highlights
Most of the crude oil produced in China is waxy crude oil with a high viscosity
The high freezing point of waxy crude oil generates a condensed oil layer once the oil temperature decreases below the freezing point, which increases the possibility of a condensed pipe and the difficulty of restarting the pipe
It is known by calculations that during the restart process after a shutdown of 10, 20, and 30 h in summer, the times when the thrusting liquid reaches the terminal of the pipe are 10.3, 10.7, and 11.2, respectively
Summary
Most of the crude oil produced in China is waxy crude oil with a high viscosity. The waxy crystals precipitate as the temperature decreases and become condensed during piping. To further understand the restart characteristics during the restart process, we simulate how the inbound and outbound temperatures, pressures, and flows change with time during the restart process of a certain pipe in Daqing as an example after different shutdown durations in the summer and winter ð49Þ
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