2011 IR&D Annual Report

High-Pressure Entrainment Measurement/Modeling, 18-R8156

Principal Investigator
Flavia Viana

Inclusive Dates:  06/07/10 – Current

Background — Wet gas scenarios are encountered during natural gas production, transmission and processing. The amount and distribution of liquid in the gas stream plays an important role in the selection and operation of flow measurement devices, the design of transmission lines, the design of gas processing and separation equipment, and corrosion occurrence and mitigation inside the pipe. In this last scenario, the distribution of the gas and liquid phases is very important, as it affects the contact of corrosion inhibitors with the pipe wall.

Several experimental projects have been conducted to investigate and characterize wet gas flows in pipes. Most of these studies are based on experimental data collected at low pressures (less than 100 psig). However, the pressure has a significant effect on the distribution and behavior of two-phase flow mixtures. In a mixture of natural gas and hydrocarbon liquid, the gas will dissolve in the liquid phase as the pressure is increased. The density of the gas increases with the pressure, which affects the separation of the gas and liquid phases as a consequence of a decreased density gradient. One of the motivations for this project is to fill the gap in the understanding of wet gas and rate of liquid droplet entrainment at high pressures.

Approach — The general approach of this project is to develop modeling and experimental tools for characterizing multiphase and wet gas flows in high-pressure environments. The main components of the project are tool development, high-pressure testing and modeling.

The goal of tool development is to design and fabricate two devices to be used in test programs at SwRI's Multiphase Flow Facility (MFF) to investigate and characterize multiphase flows. Given that the design pressure of the MFF is 3,600 psig, the design pressure of the two devices was selected to match that of the MFF, which imposes a significant challenge in the mechanical design of the tools. The first device consists of a non-intrusive, high-pressure optical system that would allow visualizing the structure of the multiphase flow stream through a pipe. The second device would be used to measure the amount of liquid entrained in the gas.

Figure 1.  Cutout View of Iso-kinetic Sampling System Designed for Measuring Liquid Entrainment at High Pressure
Figure 1. Cutout view of iso-kinetic sampling system designed for measuring liquid entrainment at high pressure.

The purpose of the experimental project is to develop the experimental technique for undisturbed flow visualization and liquid entrainment measurement using the devices developed on the project, and to generate non-existing data on liquid entrainment at high pressure. Tests will be conducted at the MFF under various superficial gas velocities, liquid volume fractions and pressures. Methane gas and a hydrocarbon liquid will be used as the test fluids to simulate field-like conditions.

Modeling for this project involves reviewing existing models and correlations for predicting liquid entrainment in gas, developing new or improved models or correlations that take into account the pressure of the system and validating the modeling tools using experimental data generated during the experimental program.

Accomplishments

  • An extensive review of potential methods for measuring liquid entrainment at high pressure was conducted. Optical, light diffraction and mechanical methods were considered and the readiness level of existing technology was evaluated. A sampling method was selected for development as the most feasible option.

  • An iso-kinetic sampling system was designed and is being fabricated for the testing. The sampling system can be used at pressures up to 3,600 psig and in pipe sizes up to six inches in diameter. Figure 1 shows a cutout view of the liquid entrainment measurement device.

  • A high-pressure, flow-visualization device was designed and fabricated by a contractor. This device will allow visualizing the flow through a 3-inch pipe without introducing any perturbation on the flow and without affecting the flow pattern. The unit has already been received and is undergoing some preliminary testing to develop a flow visualization technique to be used during the high-pressure experiments.

  • A customized test section has been designed for the experimental project. The setup to be installed at the MFF includes the injection of the liquid phase into a gas phase stream, a 60-foot-long flow development section to allow a fully developed flow pattern, a liquid entrainment measurement section using the isokinetic sampling system and a flow visualization section.

  • A review of existing models and correlation for predicting liquid entrainment fraction has been completed, and the various models are being evaluated and compared with existing data.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.
04/15/14