Pigging Study Of Large Diameter And High Pressure Natural Gas Transportation Pipeline

The pigging of high pressure of wet natural gas pipeline is very important to the pipeline operation and management. Tracking monitoring the velocity, pressure distribution, liquid holdup, can provide theoretical foundation for multiphase transmission pipelines.This paper, on the basis of analyzing the pigging physical model, divided the pipeline into three parts, established gas-liquid pigging model and transient two-phase model, and simplified the complicated flow problems to different mathematical models. The used Minami pigging model ignores temperature change. In the front of pig is the liquid slug section, in this section continuation equations and momentum equations are applied to the slug zone. Transient model uses two-phase model (TFM). Continuation equations and momentum equations are separately established to gas-phase and liquid-phase. Two-phase interaction can not be ignored. In order to solve the model, method of characteristics is applied. Because the liquid includes gas phase and liquid phase, we use the BWRS equation, which is a thermodynamic model based on state equation.To the whole pipeline, pigging model and transient two-phase model must be coupled, then the change-rule graphs of flow parameters could be drawed. The key is to track these positions of pig front and slug front at each timestep. Two-phase model is used twice to determine the pig front position and slug front position, and the two parts are called upstream transient two-phase flow section and downstream transient two-phase flow section. In downstream transient two-phase flow section, boundary conditions are: pressure at outlet, the gas and liquid volume flow at slug front. In downstream transient two-phase flow section, boundary conditions are: pressure at pig front, the gas and liquid volume flow at inlet. Then, the data of pressure, velocity and liquid holdup can be obtained. Paper using the data from calculation programs drawed pictures. We can track pig in the pipeline by the way of numerical simulation.