Research On Pigging Process Based On Bypass State

In recent years,natural gas condensate pipelines have long been faced with problems such as increased liquid accumulation and increased friction,which have seriously affected the transportation of oil and gas.Regular pigging operations are an important guarantee for pipeline transportation.On medium-and short-distance pipelines,due to the high impurity content of the conveying medium,serious corrosion and aging and other bad factors,the traditional pigs cause serious wear of the soft sealing disc of the pigs and the formation of a bypass gap between the inner wall of the pipeline.Will be stuck in the pipeline due to lack of power.Due to the existence of the jet hole,the bypass jet pig can effectively reduce the accumulation of liquid plugs,so it is mainly used in long-distance pipelines.However,the existence of the deflector will make the flow of gas and the change of the flow field elusive,and the problem of fluid migration will also increase a lot of uncertainty.In view of the limitations of unclear mechanism,unclear motion law and insufficient theoretical framework of engineering application of the two types of pigs in the current engineering under their respective working conditions,this paper combines theoretical research,numerical simulation and experimental analysis to analyze the two types of pigs respectively.Extensive and in-depth research has been carried out on the motion law and fluid migration of the pipe under their respective working conditions.In this study,the working principle of the two pigs was first described,and the simulation model of the pig was established after simplifying the physical model.The model applies the nested mesh technology and integrates the dynamic control equations into Fluent through the UDF program interface to control the operation of the pig.Using this model,parameters such as the running speed and flow field of the pig can be obtained.Secondly,it analyzes and studies the fluid migration pattern and distribution in the "bypass" state of traditional pigs.The effects of the operating speed of the pig,the size of the gap,and the inlet velocity on the liquid phase volume fraction of the liquid plug section and the liquid plug velocity were mainly explored,and the influencing factors of the liquid volume at the terminal outlet were analyzed.The results show that when there is a gap,the front and rear of the pig are gas-liquid two-phase flow.The decrease of the clearance amount and the increase of the pig speed will cause the liquid phase volume fraction of the slug segment to increase.And the liquid phase distribution depends on the balance between the liquid-carrying effect of the gas and the pushing effect of the pig.The results of the liquid phase distribution at the outlet of the terminal show that when the gap increases,the total volume of the effusion at the outlet decreases.But the change in clearance volume does not affect the time when the liquid reaches the terminal,pig speed is still the main factor.Thirdly,the jet dissipation mechanism of the diversion disk bypass cleaner is explored,the influence of the bypass rate size and the diversion regulating hole opening on the flow characteristics around the cleaner is analyzed,and the influence of multiple parameters on the overall model pressure loss coefficient is studied.Finally,the whole liquid removal process is simulated.The simulation results show that the existence of the diversion disk will make the passing gas produce high-speed jet at the edge of the regulating hole,and produce the recirculation area downstream of the pipeline.The axial bypass rate and the reduction of the regulating hole angle will lead to the maximum flow rate in the flow field.The pressure loss lines of the overall scavenger model is summarized and the CFD simulation results verify the accuracy of the model.When an effusion is present in the pipe,the jet effect causes the gas to blow out the accumulated liquid phase,distributing it downstream of the longer pipe.The overall liquid phase volume fraction of the downstream liquid plug section in front of the baffle decreases with the axial bypass rate of the cleaner.Finally,a visual indoor pipeline experiment system is established,and the pigging experiments are simulated under the conditions of single gas phase and gas-liquid two-phase,respectively.The running speed of the pig and the variation law of the outflow characteristics of the terminal effusion are analyzed.The experimental results show that the increase of the clearance of the traditional pig makes the driving gas volume increase,and under the same driving gas speed conditions,the increase of the clearance volume reduces the average speed of the pig.At the same time,the increase in the amount of clearance will result in a longer time for the front liquid plug to reach the terminal.For the bypass pig with a deflector,there is a certain linear relationship between the running speed and the rear driving gas speed.Under the gas-liquid two-phase operating conditions,the increase of the bypass rate and the adjustment hole angle will cause the reduction of the driving force,which will lead to the slow movement of the liquid plug and prolong the flow time to the terminal.