| Natural gas resources are often located in mountainous and hilly aeras, resulting in pipe undulation. Affected by gravity, the liquid flow out from wells would gather in the low-lying sections and plug the pipe. Pigging operation is taken regularly to enssure efficient gas transportation. To make pigging analysis, the volumn and distribution of liquid in the pipe must be calculated, so are the pressure variation, the volumn of liquid in slug body and the time of pigging operation. Based on the Theory of Gas-Liquid Flow and Numerical Simulation, methods for holdup calculation and pigging model is studied in detail. The specific research achievements are as follows:(1) The results of holdup calculation is closely related to the methods of flow pattern judgement and pressure acquisition. To get a appropriate flow pattern judgement method for fluctuation pipeline, experiments data is collected for 6 angles (-21°,-11°,0°,15°,30°,60°) and 4 IDs (14.8mm,25mm,26mm,40mm), which would act as criterias of the evaluation of Mukherjee-Brill method, Barnea method and Xiao-Brill method. A flow pattern judgement method is established with the evaluation results, as well as characteristics of horizontal pipes, upward pipes and downward pipes:Mukherjee-Brill method is proposed in horizontal pipes and downward pipes, while Barnea method is proposed in upward pipes. The deviation of various holdup correlations is evaluated with experimental data, which is used to build a holdup calculation model:G.H.Abdul-Majeed correlation is used when the pipe is horizontal and BBE correlation is used in other cases. The Mukherjee-Brill correlations for pressure drop is chosen for pressure calculation, and the stratified flow pressure correlation is modified. Double Circle Model and FLAT model is used for geometry calculation for different holdup range. The result of research carried out by Ullmann and Brauner is introduced for shear stress calculation. Based on the achievements got above, a steady state model for gas-liquid flow is established and the solution of it is introduced.(2) McDonald-Baker pigging model and Minami pigging model are briefly analyzed; The model built here is divided into four sections:the gas liquid flow zone being re-established, the gas flow zone, the slug zone and the downstream gas liquid flow zone. Four mathematic models have been established for each section. Two different forms of the slug body were analyzed, and each of them is modeled. Based on conclusions above, a quasi-steady state pigging model is established.(3) A pigging simulation program is written with achievements in (1) and (2), which could make out the pressure variation, the position of pig and the volumn of slug body.(4) The law of pigging time and holdup variation in fluctuated pipeline is researched by the program, it is found that the holdup in pipe with angle between -30° and 30° is significantly affected by the angle. A law that the holdup in upward pipes is more sensitive with the change of liquid flow than holdup in downward pipes is also observed. The pigging time is affected by the length of pipe, as well as the angle of upward pipe, while the angle of downward pipe has little effect on the time of pigging. The pigging operation of a natrual gas gathering line is simulated in detail:First, the holdup along the pipeline is simulated by the program; Then the pressure variation of inlet, the position of pig and the volume of slug are all calculated. By this way, the model built here is validated to be able to support the design and maintenance of natural gas pipeline. |
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