Numerical Simulation And Experimental Study On The Process Of Heavy Oil Transportation By Core Annular Flow

Core-annular flow transport is a high viscosity oil transport technology,which can be used to transport high viscosity crude oil and heavy oil.Compared with the traditional conveying technology of high viscosity oil,core-annular flow transportation has its unique advantages: without adding emulsifying agent,will not cause secondary pollution,transport procession requires no extra heating or costly sound insulation pipeline;don't need to build high pressure pump station to provide energy;post-processing process is simple.Liquid ring conveying technology can not only be widely applied to all aspects of oil field development,crude oil transportation,sea pipe transportation and other gathering systems,but also can be applied to chemical industry,and is suitable for mass transportation of various high viscosity fluids.Therefore,the numerical and Experimental Research on Water membrane of core-annular flow transport is of great significance to the development of oil transportation technology.Based on the research status of core-annular flow transport at home and abroad,the numerical model of core-annular flow and the indoor experimental loop were established.The formation process of core-annular flow and the effect of pipeline structure on the stability characteristics of core-annular flow were studied.The main contents of this paper include:(1)The structure optimization of the core-annular flow generator was studied.The drag reduction mechanism of heavy oil transported by core-annular flow is analyzed,and the numerical study of the structure optimization of the core-annular flow generator is carried out.The VOF model was used to simulate the numerical simulation of core-annular flow and the model verification was completed.The influence of different gap thickness on the stability of core-annular flow generator was studied and the structure optimization was carried out.It is found that there is an optimal interval for the thickness of the gap.Too small is not conducive to the formation and stability of the core-annular flow.When the outlet is too large,the velocity of the core oil flow is higher than that of the water layer,which is not conducive to the formation of the core-annular flow.After adding the spiral blade on the basis of the original generator,it is 2.3 times higher than that before the optimization.(2)Study on the regularity of the stability of core-annular flow in the elbow.Based on the numerical model of core-annular flow,the change rule of volume fraction and velocity field of core-annular flow in elbow is studied,and the influence of surface tension,velocity of inlet,oil-water density ratio and oil to water viscosity ratio on the stable characteristics of core-annular flow is also analyzed.It is found that with the increase of surface tension,the tendency of the core oil flow in the elbow to migrate to the pipe wall weakened.As the flow rate increases,the core oil flow increases to the outside of the pipe.The deviation of the inner core oil flow to the outside of the pipe wall increases with the decrease of the oil-water density ratio,and the smaller the oil density,the more the core oil flow is offset to the upper side of the pipe wall.No significant effect on stability and drag reduction characteristics.(3)The structure design of core-annular flow maintenance device and its effect on the reformation of core-annular flow are studied.The numerical simulation of core-annular flow maintenance device with rotating blade structure is carried out.The effect of tangential velocity on the internal flow field and ring forming performance of the core-annular flow maintenance device is studied by changing the rotational speed of the high speed rotary cylinder.It is found that the maximum tangential velocity becomes larger as the rotating speed of high-speed rotating drum increases,and the tendency of core oil flowing toward the center of the pipeline also increases.When the rotating speed of high-speed rotating drum is 4500 r/min and above,core-annular flow formed in the pipeline.As the inlet flow rate increases,the diameter of the core oil flow increases or even becomes unstable.Under simulated conditions,the core-annular flow maintenance device should be added at a pipe flow rate of 0.6 m/s.(4)The core-annular flow generator indoor loop experiment was carried out,and the structure and design adopted in the previous simulation were used.The results show that the core-annular flow generated in the indoor loop can achieve the effect of drag reduction.Keeping other conditions constant,changing the gap size and inlet flow rate of the generator found that the optimum size of the generator gap was 0.9 mm to 1.4 mm under the experimental conditions when using a 19 mm inner diameter of the pipe for core-annular flow conveying high viscosity oil.Under the simulation conditions,the gap width of 0.8 ~ 1.2 mm transport best,can make the core-annular flow to maintain a long period of time.By the above simulation results and experimental studies,it can be concluded: When using a 19 mm inner diameter of the pipe for high-viscosity core-annular folw delivery,the optimum size of the generator gap is 0.9 mm to 1.2 mm.