Research On Erosion Wear Of Elbows In Natural Gas Gathering Pipelines

During the gas-gathering process, tiny solid particles and liquid water carried by natural gas often leads to erosion wear at the elbow and then causes failure of pipelines. Therefore, studying on the mechanism of erosion wear and the characteristic of wear distribution and then coming up with a control program to slow erosion wear effectively is the problem needs solving urgently in the process of designing and operating gas-gathering lines in all gas fields. The key point of the research of erosion wear at the elbow is to acquire relative data when particles collide at the wall of the elbow. Due to the complex flow field inside the elbow of gas-gathering lines, it becomes a typical gas-liquid-solid multiphase problem, bringing about great difficulties to solve the erosion wear problem at the elbow.Basing on computational fluid dynamics, the paper, aiming to solve the characteristic parameters of erosion wear at the elbow made use of FLUENT and custom function and studied on gas-liquid-solid multiphase flow field, operating parameters, impact of physical conditions on particles distribution and wear characteristics inside the elbow by numerical simulation. According to the basic theory of erosion wear, the paper compared the wear rate prediction equation based on wear mechanism with that based on experimental data through image comparison and correlation analysis and then came up with a two-equation model of wear rate using the attack angle as boundary conditions. Besides, the paper programmed a user-defined function in C language and connected it with the solver of FLUENT as a wear rate calculation part. The paper acquired physical data of natural gas through HYSYS, and judged gas-liquid two-phase flow pattern and set up simplified boundary conditions of the gas-liquid-solid multiphase inlet, using Goiver flow pattern map, Mandhane flow pattern map and OLGA. Finally, the paper set up models of erosion wear at the elbow of gas-gathering pipelines in the dry gas transmission condition and wet gas transmission condition respectively basing on the above physical data, boundary conditions and the two-equation model of wear rate. The paper set up a model of gas-liquid-solid multiphase flow inside the elbow of gas-gathering lines for characteristics of gas-liquid-solid multiphase flow inside the elbow. Gas-solid (liquid-solid) two-phase flow adopted the discrete model while gas-liquid two-phase flow adopted VOF model. The paper conducted the multiphase simulation after coupling the two models. The paper adopted finite volume method to disperse the fluid control equation and additional equations in space and time basing on the above erosion wear model in gas-gathering lines and the gas-liquid-solid multiphase flow model inside the elbow and used PISO algorithm to conduct coupling iterative calculation of pressure and speed of the flow field and then solved the model in consideration of actual operating data into consideration.Though the above research, the paper got the following important conclusions:under ninety-five percent of simulation conditions, the area where wear of the elbow was most serious was near to the outlet of the elbow; particles had relatively great influence on wall wear rate at the elbow inlet; with increase of the elbow diameter, the number of particles that didn't lead to erosion wear increased and could reached 45.4% of total number of particles at most; there were sorting rules of factors weighting influencing the biggest elbow wear rate; there were sorting rules of factors weighting of the central angle influencing the biggest elbow wear rate; the elbow wear rate of gas-gathering pipelines increased with increase of gas moisture content; erosion wear at the elbow can be slowed down by controlling velocity of flow. These conclusions provided significant basic data for conducting circle experiment study in the next step and important basis for designing geometry size of the elbow of gas-gathering pipelines.