Investigation On Liquid Carrying Capacity Of Gas Flowing In A Pipeline Dip With Liquid Accumulation

Liquid accumulation may occur in the wet gas pipeline dip due to different reasons,such as low gas production,pipeline shutdown,erroneous operation and upstream pigging liquid drained to downstream of pipeline.The liquid accumulation problem may also take place in the natural gas transmission pipeline due to incomplete dewatering and drying techniques or faulty gas treatment plant.The accumulated liquid may be completely or partially carried away,or be spread over the upwardly-inclined pipe segment when the upstream gas flows through the pipeline dip.Liquid carrying by gas flowing in the upwardly-inclined pipe segment is simplied as gas-liquid two phase flow with zero net liquid flow.Based on zero net liquid flow,the gas-liquid two phase flow models are established to predict the gas-liquid flow characteristics and liquid carrying capacity of gas flowing through accumulated liquid.Furthermore,the applicability of the new models was evaluated by experimental data on low liquid loading two-phase flow.The flow patterns in the process of liquid carrying by gas flowing in the upwardly inclined section are mainly intermittent flow and stratified flow.A prediction model for the transition from intermittent to stratified flow is established based on the stratified flow.The liquid holdup for combined gas-liquid momentum equation is searched,and the condition for no liquid holdup solution is taken as the criterion for the flow pattern transition between intermittent and stratified flow.The predictions of the new model with different gas-liquid interfacial shapes and closure relationships are compared with the experiments from Wood and Amaravadi.The critical gas velocities for flow pattern transition predicted by the new model with the flat gas-liquid interface show the best agreements with experiments.The new model predictions demonstrate that the critical velocity for flow pattern transition increases with the increase of the pipe inclination angle and the decrease of the operating pressure,which is consistent with the experiment.Based on the slug flow unit cell model and the structural stability of slug model,a new mechanistic model to predict the stable volume of liquid retained in the upwardly inclined pipe segment is developed with introducing the closure relationships for intermittent flow.The new model predictions are compared with the experiments and mechanistic models of Wood and Amaravadi,and show a fair precision.The new predictions manifest that as the superficial gas velocity increases,the steadily retained liquid volume decreases and the decreasing rate becomes slow,which is consistent with the experiment.Based on the low liquid loading gas-liquid pipe flow experiments from Fan,Rodrigues and Alsaadi,the predictions of the critical gas velocities for flow pattern transition and the stable volumes of liquid retained at different gas rates are fairly consistent with the corresponding experimental data.