High-Pressure Entrainment Measurement/Modeling, 18-R8156
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 wall of the pipe. Several experimental programs 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 (<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 testing 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. 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. The testing will be conducted at the MFF under various superficial gas velocities, liquid volume fractions, and various pressures. Methane gas and a hydrocarbon liquid will be used as the test fluids to simulate field-like conditions. The modeling on the 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 — The accomplishments to date are:
- 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 built for measuring the fraction of liquid entrained in the form of droplets in a high-pressure gas stream. The sampling system can be used at pressures up to 3,600 psig and in pipe sizes up to 6 inches in diameter. Figure 1 shows a picture of the liquid entrainment measurement device developed on this project.
- A high-pressure flow visualization device was designed and fabricated. This device allows visualizing the flow through a 3-inch pipe without introducing any perturbation on the flow and without affecting the flow pattern. A photograph of the flow visualization device is shown in Figure 2.
- A customized test section was designed and installed at the MFF for conducting high-pressure entrainment testing. The test section included the injection of the liquid phase into a gas phase stream, a 60-ft long flow development section to allow a fully-developed flow pattern, the liquid entrainment measurement section using the iso-kinetic sampling system (Figure 1), and the high-pressure flow visualization device (Figure 2).
- Testing at high pressure was conducted using hydrocarbon fluids at various gas and liquid rates and various pressures. The data collected during the experimental program are being compared against predictions obtained from existing models and correlations and will be used to validate an improved model for estimating the liquid entrainment in high-pressure systems.
- Modeling efforts have concentrated evaluating existing models and correlations found in the literature and incorporating the high-pressure effect on the entrainment prediction models.