Experiments for low liquid loading in two- and three-phase flows have been conducted at the SINTEF Multiphase Flow Laboratory in the Large Scale Loop. Low liquid loading means that the superficial liquid velocity is small compared to the superficial gas velocity; but the liquid holdup fraction can become significant if the superficial gas velocity is reduced. Two diameters (8" and 12") were investigated, covering three inclination angles (1°, 2.5° and 5°). The experiments were carried out with nitrogen as the gas phase and four different types of liquids (naphtha, Exxsol D40, water and a glycerol-water mixture).
The main objective in this project was to investigate the existence of multiple solutions in flows with low liquid loading. Specifically, maps were generated showing the critical flow rates for which the flow changes from the low-holdup solution to the high-holdup solution. Such maps were created for various pipe diameters, pipe angles, liquid densities, gas densities and liquid viscosities. In addition, the effect of the oil flow rate in three-phase flows was measured. This paper provides an overview of the experimental test campaign and gives some examples of the key results.
This paper presents an experimental study of low liquid loading in two- and three-phase flows in inclined pipes. Low liquid loading means that the superficial liquid velocity is small compared to the superficial gas velocity; but the liquid holdup fraction can become significant if the superficial gas velocity is reduced. The focus of this study was to determine the onset of liquid accumulation, i.e. the flow rate where the liquid holdup jumps from a low to a high holdup solution and where the flow becomes gravity dominated. From an industrial perspective, the accurate prediction of the onset of liquid accumulation is critical for long wet-gas transport lines. In such systems, the drop in pressure and temperature along the line leads to (retrograde) condensation (of condensate and water), potentially leading to increased liquid flow rates. Here, the local liquid flow rate will typically increase along the flow path. If the gas rate is sufficiently low, the condensed liquid can start to accumulate in the inclined parts of the pipeline. This can then lead to an increased pressure drop and to unstable flow, with liquid surges/slugs propagating through the flow line, creating upset conditions in the receiving facilities. Liquid accumulation is therefore undesirable, and must either be prevented or at least managed in a controlled way. In order to effectively prevent or manage liquid accumulation in such wet-gas systems, accurate multiphase models are needed to predict when and where this will happen. Such models will thus enable to obtain a correct design of the pipeline (e.g. diameter) and of the receiving facilities, minimizing the pressure loss and ensuring operability of the multiphase transport system through its entire lifetime.