Session: 10-08-01: Multiphase Flows and Applications

Paper Number: 144303

144303 - A Numerical Study on Effect of Inlet Fluid Conditions on Performance of Horizontal Separator for Three-Phase Mixture With Viscous Oil 

With the increasing importance of securing natural resources, unconventional oil reserves have gained significant attention worldwide. As the production fluid in an unconventional oil well is a multiphase fluid containing highly viscous oil, an effective equipment to separate the production fluid from the oil well into each phase of fluid is crucial to provide appropriate fluids to individual downstream processes.

The horizontal gravity separator has been commonly used for the last several decades. It utilizes gravity and buoyancy to separate fluid phases based on their density differences. As fluid phases flow downstream, they naturally separate. The separation becomes more effective as the length of the separator increases. However, increasing the length of the separator also raises costs, such as manufacturing, maintenance, and shipping. Therefore, it is crucial to determine the optimal size of the separator that balances effective separation performance and lower costs.

Various previous studies have suggested design methods based on the movement of liquid droplets and gas bubbles. For liquid droplets, the route can begin at the upper side of the separator at the inlet and ends at the normal interface level at the outlet of the water phase. During this route, the water droplets must fall through the gas phase and penetrate the oil phase above the water phase. In contrast, the route for gas bubbles starts at the lowest side of the separator at the inlet due to the plunge of the mixture inlet flow. Gas bubbles then rise through the water and oil phases and merge into the gas continuous phase at the gas outlet. The terminal velocity of the rising or falling dispersed phase in the shape of a sphere can be obtained by balancing gravity, buoyancy, and drag forces acting on the dispersed phase. By considering both the route and terminal velocity of dispersed phases, the size of the separator can be derived. However, due to the nonlinear behavior of multi-phase flow, determining the size of the separator based on the assumed route of either bubble rise or droplet fall can lead to less optimized designs.

The primary objective of this study is to examine the performance of the three-phase horizontal separator under different flow condition and thermophysical properties of working fluids. This study conducts a computational fluid dynamics (CFD) to investigate the performance of a three-phase horizontal separator for air-water-oil mixture with high-viscosity oil. The multiphase flow within the separator is calculated through three-dimension simulations utilizing ANSYS Fluent, a commercial CFD program. Multiphase fluid models that are commonly used include Volume-Of-Fluid (VOF) and Eulerian models. However, the availability of multiphase fluid model differs depending on the simulated condition. Therefore, the employed numerical analysis technique is validated through a comparison of numerical result with experimental results.

This study evaluates the performance of the separator for different inlet flow rates and thermophysical properties of working fluids. The levels between gas and liquid phases, as well as between water and oil in the separator, and the phase fractions at the gas, water, and oil outlets are specifically monitored. The levels of each phase are highly associated with the separation of fluids by the interior construction of the separator. Fractions of each fluid indicate the separation performance. The separation efficiencies of separator for water and oil are calculated by comparing the volumetric flow rate of water and oil at the inlet and outlets. In particular, the study investigates multiphase fluid behaviors such as interfacial instability, liquid aeration, and liquid droplet entrainment to characterize separator performance comprehensively. Interfacial instability is induced by the velocity difference between phases and hinders the stratification of working fluids by buoyancy. Also, it generates interfacial waves that can result in flooding of oil to the water section. Liquid aeration refers to the small gas bubbles entrapped in liquid phase. The higher the oil viscosity, the more difficult it is for entrapped gas bubbles to be emitted to the upper bulk gas flow. In the separator, any impact overcoming the retaining force of surface tension can generate liquid droplets into gas bulk flow. Once the liquid droplet is departed from the bulk liquid flow, it splits into smaller sizes due to the gas shear. In conclusion, this study suggests several ideas to enhance the performance of the separator to cope with various inlet flow conditions and the thermophysical properties of working fluids.

Presenting Author: Hong-Cheol Shin KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY

Presenting Author Biography: Hong-Cheol Shin received Ph.D. degree from Sungkyunkwan University in South Korea in 2023. The title of dissertation is "An Experimental Study on Gas-Oil Mixture Flow in Horizontal Pipes with Two Synthetic Oils." He has conducted studies concerning multi-phase flow, single-phase and phase-change heat transfer from macro-scale to micro-scale. His research interests include fluid equipment and thermal management systems based on multi-phase fluid engineering.

Authors:

Hong-Cheol Shin KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY
Hyeon-Seok Seo KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY
In-Ju Hwang KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY