The Numerical Simulation Study On Vacuum Transfer Line

The vacuum transfer line is an important pipeline in refining atmospheric and vacuum distillation unit. Well-designed transfer line not only can improve decompression pull out rate and reduce energy consumption, but also can improve the quality of oil, increase oil stability and avoid pyrolysis. The oil flows in the vacuum transfer line, which belongs to gas-liquid two-phase process with temperature changing. The pressure decreases gradually and the liquid evaporates gradually with the oil flowing along the transfer line, temperature, flow velocity, vaporization rate, viscosity, density and other physical properties of oil change continually.In this paper, it is the first time to make use of computational fluid dynamics to investigate the single-phase flow and gas-liquid two-phase flow in the vacuum transfer line, The law of temperature distribution, pressure distribution, velocity distribution and vaporization rate distribution can be obtained.In this paper, the vacuum transfer line is studied, structural size and physical property data of six the vacuum transfer are collected, a single-phase flow model is established, the gas flow of the six vacuum transfer line is simulated and analysed, and the structure of vacuum transfer has been optimized according to the simulation results. The gas-liquid two-phase flow mathematical model for transfer line is also developed according to two-phase flow characteristics of complex hydrocarbon mixture, the structure characteristic of the different vacuum transfer line and gas-liquid two-phase flow pattern are simulated and analysed. In this model, the discrete and continuous phase are solved couple and the heat, mass and momentum transfer between the discrete and continuous phase are consider, the evaporation of oil-drop is also consider.The simulation and study show that: temperature drop and the pressure drop of the vacuum transfer line mainly concentrate in the transition, elbow, height difference, pipeline confluence, variable diameter and other structure in the vacuum transfer line have great influence on pressure drop, temperature drop and flow rate; it is beneficial to reduce the pressure drop and temperature drop of the transfer line by using the form of pants-tee. Simulation results of two-phase flow is closer to the actual working conditions than that of single-phase flow.Simulation studies for the vacuum transfer line through CFD can guide the engineering design of vacuum transfer line, which has great significance on realising vacuum deep distillation and improving economic benefits of refining atmospheric and vacuum distillation unit.