Holdup predictions for wet-gas pipelines compared

Abstract

In several predictive methods commonly used for wet-gas pipeline holdup, the magnitude of errors varies greatly. Comparison of these methods and their errors, given in this article, indicate that correlation-based methods should not be used for holdup prediction. Mechanistic models, on the other hand, yield better predictions of liquid holdup for hilly terrain pipelines. Test data from the Sintef Multiphase Flow Laboratory, Trondheim, Norway, however, indicate that even the best methods can give errors on the order of 40% for certain ranges of rates. For wet-gas systems, liquid holdup is a function of gas velocity and angle of inclination. At low rates, the liquid holdup may increase by a factor of 100 or more as the inclination angle changes a fraction of a degree. To illustrate the magnitude of errors in holdup prediction, the predictions of five methods sere compared to data from the Sintef laboratory for conditions similar to those found in wet gas lines through hilly terrain. Good prediction of the liquid holdup for wet-gas pipelines is critical in the design of pipeline slug catchers. For hilly terrain pipelines, the liquid holdup also has a significant influence on the pressure-drop predictions at low rates.